ORCID Profile
0000-0001-5611-9498
Current Organisation
University of Tasmania
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Geodesy | Glaciology | Geophysics | Geodynamics | Seismology and Seismic Exploration | Geomatic Engineering | Oceanography | Physical Oceanography | Galactic Astronomy | Astronomical and Space Instrumentation | Climate Change Processes
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Earth Sciences | Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts) | Expanding Knowledge in the Environmental Sciences | Natural Hazards in Antarctic and Sub-Antarctic Environments | Climate and Climate Change not elsewhere classified | Expanding Knowledge in the Physical Sciences |
Related Links
Publications
Estimating ocean tide loading displacements with GPS and GLONASS
Publisher: Copernicus GmbH
Date: 14-10-2020
Abstract: Abstract. Ground displacements due to ocean tide loading have previously been successfully observed using Global Positioning System (GPS) data, and such estimates for the principal lunar M2 constituent have been used to infer the rheology and structure of the asthenosphere. The GPS orbital repeat period is close to that of several other major tidal constituents (K1, K2, S2) thus, GPS estimates of ground displacement at these frequencies are subject to GPS systematic errors. We assess the addition of GLONASS (GLObal NAvigation Satellite System) to increase the accuracy and reliability of eight major ocean tide loading constituents: four semi-diurnal (M2, S2, N2, K2) and four diurnal constituents (K1, O1, P1, Q1). We revisit a previous GPS study, focusing on 21 sites in the UK and western Europe, expanding it with an assessment of GLONASS and GPS+GLONASS estimates. In the region, both GPS and GLONASS data have been abundant since 2010.0. We therefore focus on the period 2010.0–2014.0, a span considered long enough to reliably estimate the major constituents. Data were processed with a kinematic precise point positioning (PPP) strategy to produce site coordinate time series for each of three different modes: GPS, GLONASS and GPS+GLONASS. The GPS solution with ambiguities resolved was used as a baseline for performance assessment of the additional modes. GPS+GLONASS shows very close agreement with ambiguity resolved GPS for lunar constituents (M2, N2, O1, Q1) but with substantial differences for solar-related constituents (S2, K2, K1, P1), with solutions including GLONASS being generally closer to model estimates. While no single constellation mode performs best for all constituents and components, we propose to use a combination of constellation modes to recover tidal parameters: GPS+GLONASS for most constituents, except for K2 and K1 where GLONASS (north and up) and GPS with ambiguities resolved (east) perform best.
Estimating Vertical Land Motion and Residual Altimeter Systematic Errors Using a Kalman‐Based Approach
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2020JC017106
Abstract: Vertical land motion (VLM) is the connection between absolute sea‐level (ASL) from a satellite altimeter (ALT) and relative sea‐level from a tide gauge (TG). VLM is often sparsely observed yet is required for understanding sea‐level rise. Many studies have sought to exploit ALT and TG data to infer VLM, yet regionally correlated systematic errors in altimetry have not been considered. We have developed a Kalman filtering and smoothing framework to simultaneously estimate location‐specific VLM and residual mission‐specific systematic errors in a geocentric reference frame. We used ALT minus TG, ALT crossovers and global positioning system (GPS) bedrock height observations in a multi‐stage solution approach that gradually separated time‐variable parameter estimates in an ill‐posed problem. We evaluated the performance of the method using the Jason‐series along‐track data in the Baltic Sea, where glacial isostatic adjustment is the dominant driver of VLM. We estimated local VLM variability at TGs of up to ∼4.5 mm/yr which is not evident in spatially interpolated GPS velocities. The estimated regional altimeter errors are significant and within the range of ∼±0.5–2.5 mm/yr. Our approach improves agreement between ASL estimates from ALT and TG records, provides a ∼20% decrease in root mean squared error of latitudinal ASL variability at TGs, and a reduction of the ASL rate from altimetry by ∼0.3 mm/yr across the region. This method advances the ALT‐TG approach to determining VLM at TG locations and systematic errors of altimetry, which is broadly applicable to other regional‐ and global‐scale studies.
J2: An evaluation of new estimates from GPS, GRACE, and load models compared to SLR
Publisher: American Geophysical Union (AGU)
Date: 11-2010
DOI: 10.1029/2010GL045229
Observations of enhanced thinning in the upper reaches of Svalbard glaciers
Publisher: Copernicus GmbH
Date: 20-11-2012
Abstract: Abstract. Changes in the volume and extent of land ice of the Svalbard archipelago have been the subject of considerable research since their sensitivity to changes in climate was first noted. However, the measurement of these changes is often necessarily based on point or profile measurements which may not be representative if extrapolated to a whole catchment or region. Combining high-resolution elevation data from contemporary laser-altimetry surveys and archived aerial photography makes it possible to measure historical changes across a glacier's surface without the need for extrapolation. Here we present a high spatial resolution time-series for six Arctic glaciers in the Svalbard archipelago spanning 1961 to 2005. We find high variability in thinning rates between sites with prevalent elevation changes at all sites averaging −0.59 ± 0.04 m a−1 between 1961–2005. Prior to 1990, ice surface elevation was changing at an average rate of −0.52 ± 0.09 m a−1 which decreased to −0.76 ± 0.10 m a−1 after 1990. Setting the elevation changes against the glaciers' altitude distribution reveals that significant increases in thinning rates are occurring most notably in the glaciers' upper reaches. We find that these changes are coincident with a decrease in winter precipitation at the Longyearbyen meteorological station and could reflect a decrease in albedo or dynamic response to lower accumulation. Further work is required to understand fully the causes of this increase in thinning rates in the glaciers' upper reaches. If on-going and occurring elsewhere in the archipelago, these changes will have a significant effect on the region's future mass balance. Our results highlight the importance of understanding the climatological context of geodetic mass balance measurements and demonstrate the difficulty of using index glaciers to represent regional changes in areas of strong climatological gradients.
Seasonal speedup of a Greenland marine-terminating outlet glacier forced by surface melt–induced changes in subglacial hydrology
Publisher: American Geophysical Union (AGU)
Date: 23-08-2011
DOI: 10.1029/2010JF001948
Assessment of Glacier Volume Change Using ASTER-Based Surface Matching of Historical Photography
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2009
Estimation of Glacial Isostatic Adjustment uplift rate in the Totten glacier's outlet from GPS and GRACE
Publisher: Copernicus GmbH
Date: 02-10-2020
DOI: 10.5194/GSTM2020-40
Abstract: & & Glacial Isostatic Adjustment (GIA) refers to the gradual response of the solid Earth to the deglaciation of historic ice sheets. & This ongoing rebound is contributing to the measurements of gravity change and land deformation, respectively, by Gravity Recovery And Climate Experiment (GRACE) and Global Positioning System (GPS). & When these space geodetic data are used to quantify the present-day ice mass change, the effect such as GIA must be accounted for. & In this study, we developed a method to estimate GIA and elastic deformation by the present-day ice mass change in the GPS time series with the ex le of Casey station in East Antarctica. & We determined a high-resolution, present-day ice mass change model on the outlet of Totten Glacier and calculated the elastic rebound over the area. & Our high-resolution model indicated a total mass loss of 15.7 & #177 0.5 Gt/yr on the outlet of Totten Glacier from 2002 to 2017 with the accelerated loss in the last half of the period. & We estimated the viscoelastic deformation attributed to GIA by removing the predicted elastic deformation from GPS measurements. & Four different GPS position solutions for the Casey station, the continuously operating GPS station near the area, were examined. & The estimated GIA signal appears to be within 0.3 & #8211 1.3 mm/yr which shows its contribution on the vertical deformation between 30 & #8211 60 % among different GPS solutions. & On the other hand, the vertical elastic deformation trend is predicted to be 0.7 mm/yr from the ice mass change model.& The GPS measured seasonal variation is explained equally by atmospheric-oceanic loading and degree-1 loading with a couple mm litude in vertical time series.& The elastic rebound from the present-day ice mass change also perturbed the horizontal displacement by 0.13 mm/yr in west and 0.21 mm/yr in north directions. & This is in the opposite to the plate motion of the East Antarctica around the Casey station and amounts approximately up to 10 % of the measured tectonic motion.& &
A new global GPS data set for testing and improving modelled GIA uplift rates
Publisher: Oxford University Press (OUP)
Date: 07-2018
DOI: 10.1093/GJI/GGY235
Rapid ice unloading in the Fleming Glacier region, southern Antarctic Peninsula, and its effect on bedrock uplift rates
Publisher: Elsevier BV
Date: 09-2017
Influence of ice-sheet geometry and supraglacial lakes on seasonal ice-flow variability
Publisher: Copernicus GmbH
Date: 26-07-2013
Abstract: Abstract. Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal meltwater to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on ice flow. We find large, spatially extensive speedups concurrent with times of lake drainage, showing that lakes play a key role in modulating regional ice flow. While surface meltwater is supplied to the bed via a geographically sparse network of moulins, the observed ice-flow enhancement suggests that this meltwater spreads widely over the ice-sheet bed. We also find that the complex spatial pattern of speedup is strongly determined by the combined influence of bed and surface topography on subglacial water flow. Thus, modeling of ice-sheet basal hydrology likely will require knowledge of bed topography resolved at scales (sub-kilometer) far finer than existing data (several km).
Estimating ocean tide loading displacements with GPS and GLONASS
Publisher: Copernicus GmbH
Date: 03-03-2020
DOI: 10.5194/SE-2020-22
Abstract: Abstract. Ground displacements due to ocean tide loading have previously been successfully observed using GPS data, and such estimates for the principal lunar M2 constituent have been used to infer the rheology and structure of the asthenosphere. The GPS orbital repeat period is close to several other major tidal constituents (K1, K2, S2) thus GPS-estimates of ground displacement at these frequencies is subject to GPS systematic errors. We assess the addition of GLONASS to increase the accuracy and reliability over eight major ocean tide loading constituents: four semi-diurnal (M2, S2, N2, K2) and four diurnal constituents (K1, O1, P1, Q1). We revisit a previous GPS study, focusing on 21 sites in the UK and Western Europe, expanding it with an assessment of GLONASS and GPS+GLONASS estimates. In the region, both GPS and GLONASS data are abundant since 2010.0. We therefore focus on the period 2010.0–2014.0 which is considered long enough to reliably estimate the major constituents. Data were processed with a kinematic PPP strategy to produce site coordinate time series for each of 3 different modes: GPS, GLONASS and GPS+GLONASS. The GPS solution with ambiguities resolved was used as a baseline for performance assessment of the additional modes. GPS+GLONASS shows very close agreement with ambiguity resolved GPS for lunar constituents (M2, N2, O1, Q1) but substantial differences for solar-related constituents (S2, K2, K1, P1). While no single constellation mode performs best for all constituents and components, we propose to use a combination of constellation modes to recover tidal parameters: GPS+GLONASS for most constituents except for K2 and K1 where GLONASS (north and up) and GPS with ambiguities resolved (east), perform best.
Simulated dynamic regrounding during marine ice sheet retreat
Publisher: Copernicus GmbH
Date: 25-07-2018
Abstract: Abstract. Marine-terminating ice sheets are of interest due to their potential instability, making them vulnerable to rapid retreat. Modelling the evolution of glaciers and ice streams in such regions is key to understanding their possible contribution to sea level rise. The friction caused by the sliding of ice over bedrock and the resultant shear stress are important factors in determining the velocity of sliding ice. Many models use simple power-law expressions for the relationship between the basal shear stress and ice velocity or introduce an effective-pressure dependence into the sliding relation in an ad hoc manner. Sliding relations based on water-filled subglacial cavities are more physically motivated, with the overburden pressure of the ice included. Here we show that using a cavitation-based sliding relation allows for the temporary regrounding of an ice shelf at a point downstream of the main grounding line of a marine ice sheet undergoing retreat across a retrograde bedrock slope. This suggests that the choice of sliding relation is especially important when modelling grounding line behaviour of regions where potential ice rises and pinning points are present and regrounding could occur.
Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations
Publisher: Springer Science and Business Media LLC
Date: 16-06-2010
Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier
Publisher: Springer Science and Business Media LLC
Date: 09-05-2010
DOI: 10.1038/NGEO863
Solid Earth change and the evolution of the Antarctic Ice Sheet
Publisher: Springer Science and Business Media LLC
Date: 30-01-2019
DOI: 10.1038/S41467-018-08068-Y
Abstract: Recent studies suggest that Antarctica has the potential to contribute up to ~15 m of sea-level rise over the next few centuries. The evolution of the Antarctic Ice Sheet is driven by a combination of climate forcing and non-climatic feedbacks. In this review we focus on feedbacks between the Antarctic Ice Sheet and the solid Earth, and the role of these feedbacks in shaping the response of the ice sheet to past and future climate changes. The growth and decay of the Antarctic Ice Sheet reshapes the solid Earth via isostasy and erosion. In turn, the shape of the bed exerts a fundamental control on ice dynamics as well as the position of the grounding line—the location where ice starts to float. A complicating issue is the fact that Antarctica is situated on a region of the Earth that displays large spatial variations in rheological properties. These properties affect the timescale and strength of feedbacks between ice-sheet change and solid Earth deformation, and hence must be accounted for when considering the future evolution of the ice sheet.
Tidally Controlled Stick-Slip Discharge of a West Antarctic Ice
Publisher: American Association for the Advancement of Science (AAAS)
Date: 22-08-2003
Abstract: A major West Antarctic ice stream discharges by sudden and brief periods of very rapid motion paced by oceanic tidal oscillations of about 1 meter. Acceleration to speeds greater than 1 meter per hour and deceleration back to a stationary state occur in minutes or less. Slip propagates at approximately 88 meters per second, suggestive of a shear wave traveling within the subglacial till. A model of an episodically slipping friction-locked fault reproduces the observed quasi-periodic event timing, demonstrating an ice stream's ability to change speed rapidly and its extreme sensitivity to subglacial conditions and variations in sea level.
Strong tidal variations in ice flow observed across the entire Ronne Ice Shelf and adjoining ice streams
Publisher: Copernicus GmbH
Date: 17-07-2017
DOI: 10.5194/ESSD-2017-70
Abstract: Abstract. We present a compilation of GPS time series, including those for previously unpublished sites, showing that flow across the entire Ronne Ice Shelf and its adjoining ice streams is strongly affected by ocean tides. Previous observations have shown strong diurnal and semidiurnal motion of the ice shelf and surface flow speeds of Rutford Ice Stream (RIS) are known to vary with a fortnightly (Msf) periodicity. Our new dataset shows that the Msf flow modulation, first observed on RIS, is also found on Evans, Talutis, Institute and Foundation Ice Streams, i.e. on all ice streams for which data are available. The litude of the Msf signal increases downstream of grounding lines, reaching up to 20 % of mean flow speeds where ice streams feed into the main shelf. Upstream of ice stream grounding lines, decay length scales are relatively uniform for all ice streams but the speed at which the Msf signal propagates upstream shows more variation. Observations and modelling of tidal variations in ice flow can help constrain crucial parameters that determine the rate and extent of potential ice mass loss from Antarctica. Given that the Msf modulation in ice flow is readily observed across the entire region, at distances of up to 80 km upstream of grounding lines, but is not completely reproduced in any existing numerical model, this new dataset suggests a pressing need to identify the missing processes responsible for its generation and propagation. The new GPS data set is publicly available through the UKPDC at 0.5285/4fe11286-0e53-4a03-854c-a79a44d1e356.
Choice of optimal averaging radii for temporal GRACE gravity solutions, a comparison with GPS and satellite altimetry
Publisher: Oxford University Press (OUP)
Date: 07-2006
“Antarctica just has this hero factor…”: Gendered barriers to Australian Antarctic research and remote fieldwork
Publisher: Public Library of Science (PLoS)
Date: 16-01-2019
Flow of the Ross Ice Shelf, Antarctica, is modulated by the ocean tide
Publisher: International Glaciological Society
Date: 2010
DOI: 10.3189/002214310791190875
Abstract: The ice streams feeding the Ross Ice Shelf, Antarctica, have large tidally modulated (sinusoidal and stick–slip) flow, but the interaction with the ice shelf is poorly understood. We show that the flow of the Ross Ice Shelf front, up to ∼650 km from the ice streams, exhibits smooth, sinusoidal motions corresponding to tidal modulation. These observations suggest a possible linking of the ice shelf with the ice streams to form a unified system that responds to small perturbations in stresses associated with ocean tides. If this is the case, the presence of the sinusoidal motion but the absence of stick–slip motion suggests there is d ing of very high-frequency signals. The dissimilar signatures of the motions observed in the ice streams and at the front of the ice shelf present challenges to model development aimed at understanding the dynamics of coupled ice-stream/ice-shelf flow and the movement of ice across grounding lines.
Basal mechanics of ice streams: Insights from the stick‐slip motion of Whillans Ice Stream, West Antarctica
Publisher: American Geophysical Union (AGU)
Date: 13-02-2009
DOI: 10.1029/2008JF001035
Climatic controls of decomposition drive the global biogeography of forest-tree symbioses
Publisher: Springer Science and Business Media LLC
Date: 05-2019
DOI: 10.1038/S41586-019-1128-0
Abstract: The identity of the dominant root-associated microbial symbionts in a forest determines the ability of trees to access limiting nutrients from atmospheric or soil pools
Strong tidal variations in ice flow observed across the entire Ronne Ice Shelf and adjoining ice streams
Publisher: Copernicus GmbH
Date: 20-11-2017
Abstract: Abstract. We present a compilation of GPS time series, including those for previously unpublished sites, showing that flow across the entire Ronne Ice Shelf and its adjoining ice streams is strongly affected by ocean tides. Previous observations have shown strong horizontal diurnal and semidiurnal motion of the ice shelf, and surface flow speeds of Rutford Ice Stream (RIS) are known to vary with a fortnightly (Msf) periodicity. Our new data set shows that the Msf flow modulation, first observed on RIS, is also found on Evans, Talutis, Institute, and Foundation ice streams, i.e. on all ice streams for which data are available. The litude of the Msf signal increases downstream of grounding lines, reaching up to 20 % of mean flow speeds where ice streams feed into the main ice shelf. Upstream of ice stream grounding lines, decay length scales are relatively uniform for all ice streams but the speed at which the Msf signal propagates upstream shows more variation. Observations and modelling of tidal variations in ice flow can help constrain crucial parameters that determine the rate and extent of potential ice mass loss from Antarctica. Given that the Msf modulation in ice flow is readily observed across the entire region at distances of up to 80 km upstream of grounding lines, but is not completely reproduced in any existing numerical model, this new data set suggests a pressing need to identify the missing processes responsible for its generation and propagation. The new GPS data set is publicly available through the UK Polar Data Centre at 0.5285/4fe11286-0e53-4a03-854c-a79a44d1e356.
Terminus dynamics at an advancing glacier: Taku Glacier, Alaska
Publisher: International Glaciological Society
Date: 2009
DOI: 10.3189/002214309790794887
Abstract: Taku Glacier, Alaska, USA, is currently in the advance stage of the tidewater glacier cycle. We investigated the near-terminus dynamics by measuring surface velocities, surface elevation changes, ice thickness and ablation. Velocities vary on sub-daily, diurnal, seasonal and interannual timescales. Flowline modeling shows that the modeled surface velocities are sensitive to changes in till yield strength and thus effective basal pressures. The glacier bed deepens in the up-glacier direction and this imposes a minimum subglacial water pressure necessary for water to drain along the bed. In a simple model we impose water-pressure gradients based on phreatic surfaces of constant slopes to simulate the winter–summer transitions. This proves sufficient to explain an observed early-season switch from compressional to block flow. Velocities also vary between years. Changing basal conditions can result in lower horizontal velocities, which decrease the ice supply to the terminus and result in temporary surface lowering. But a decrease in ice flux to the terminus must lead to ice storage further upstream, and that ice mass will eventually reach the terminus. This can explain the observed episodic nature of terminus advance.
Satellite gravity gradiometry: Secular gravity field change over polar regions
Publisher: Elsevier BV
Date: 05-2010
An assessment of forward and inverse GIA solutions for Antarctica
Publisher: American Geophysical Union (AGU)
Date: 09-2016
DOI: 10.1002/2016JB013154
A global,spherical,finite-element model for postseismic deformation using ABAQUS
Publisher: Copernicus GmbH
Date: 24-06-2020
DOI: 10.5194/GMD-2020-107
Abstract: Abstract. We present a finite-element model of postseismic solid Earth deformation built in the software package ABAQUS (version 2018). The model is global and spherical, and includes self-gravitation and is built for the purpose of calculating postseismic deformation in the far-field ( ~ 300 km) of major earthquakes. An earthquake is simulated by prescribing slip on a fault plane in the mesh and the model relaxes under the resulting change in stress. Both linear Maxwell and biviscous (Burgers) rheological models have been implemented and the model can be easily adapted to include different rheological models and lateral variations in Earth structure, a particular advantage over existing models. We benchmark the model against an analytical coseismic solution and an existing open-source postseismic model, demonstrating good agreement for all fault geometries tested. Due to the inclusion of self-gravity the model has the potential for predicting deformation in response to multiple sources of stress change, for ex le, changing ice thickness in tectonically active regions.
On the uncertainty associated with validating the global mean sea level climate record
Publisher: Elsevier BV
Date: 07-2021
Precipitable water vapor estimates from homogeneously reprocessed GPS data: An intertechnique comparison in Antarctica
Publisher: American Geophysical Union (AGU)
Date: 22-02-2011
DOI: 10.1029/2010JD013889
A new glacial isostatic adjustment model for Antarctica: calibrated and tested using observations of relative sea-level change and present-day uplift rates
Publisher: Oxford University Press (OUP)
Date: 27-06-2012
Basal friction of Fleming Glacier, Antarctica – Part 1: Sensitivity of inversion to temperature and bedrock uncertainty
Publisher: Copernicus GmbH
Date: 15-08-2018
Abstract: Abstract. Many glaciers in the Antarctic Peninsula are now rapidly losing mass. Understanding of the dynamics of these fast-flowing glaciers, and their potential future behaviour, can be improved through ice sheet modelling studies. Inverse methods are commonly used in ice sheet models to infer the spatial distribution of a basal friction coefficient, which has a large effect on the basal velocity and ice deformation. Here we use the full-Stokes Elmer/Ice model to simulate the Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula. With an inverse method, we infer the pattern of the basal friction coefficient from surface velocities observed in 2008. We propose a multi-cycle spin-up scheme to reduce the influence of the assumed initial englacial temperature field on the final inversion. This is particularly important for glaciers like the Fleming Glacier, which have areas of strongly temperature-dependent deformational flow in the fast-flowing regions. Sensitivity tests using various bed elevation datasets, ice front positions and boundary conditions demonstrate the importance of high-accuracy ice thickness/bed geometry data and precise location of the ice front boundary.
Plant functional trait change across a warming tundra biome
Publisher: Springer Science and Business Media LLC
Date: 26-09-2018
DOI: 10.1038/S41586-018-0563-7
Abstract: The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.
Functional susceptibility of tropical forests to climate change
Publisher: Springer Science and Business Media LLC
Date: 16-05-2022
DOI: 10.1038/S41559-022-01747-6
Abstract: Tropical forests are some of the most bio erse ecosystems in the world, yet their functioning is threatened by anthropogenic disturbances and climate change. Global actions to conserve tropical forests could be enhanced by having local knowledge on the forests' functional ersity and functional redundancy as proxies for their capacity to respond to global environmental change. Here we create estimates of plant functional ersity and redundancy across the tropics by combining a dataset of 16 morphological, chemical and photosynthetic plant traits s led from 2,461 in idual trees from 74 sites distributed across four continents together with local climate data for the past half century. Our findings suggest a strong link between climate and functional ersity and redundancy with the three trait groups responding similarly across the tropics and climate gradient. We show that drier tropical forests are overall less functionally erse than wetter forests and that functional redundancy declines with increasing soil water and vapour pressure deficits. Areas with high functional ersity and high functional redundancy tend to better maintain ecosystem functioning, such as aboveground biomass, after extreme weather events. Our predictions suggest that the lower functional ersity and lower functional redundancy of drier tropical forests, in comparison with wetter forests, may leave them more at risk of shifting towards alternative states in face of further declines in water availability across tropical regions.
Basal friction of Fleming Glacier, Antarctica – Part 2: Evolution from 2008 to 2015
Publisher: Copernicus GmbH
Date: 15-08-2018
Abstract: Abstract. The Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. Increases in the glacier velocity and dynamic thinning have been observed over the past two decades, especially after 2008 when only a small ice shelf remained at the Fleming Glacier front. It is important to know whether the substantial further speed-up and greater surface draw-down of the glacier since 2008 is a direct response to ocean forcing, or driven by feedbacks within the grounded marine-based glacier system, or both. Recent observational studies have suggested the 2008–2015 velocity change was due to the ungrounding of the Fleming Glacier front. To explore the mechanisms underlying the recent changes, we use a full-Stokes ice sheet model to simulate the basal shear stress distribution of the Fleming system in 2008 and 2015. This study is part of the first high resolution modelling c aign of this system. Comparison of inversions for basal shear stresses for 2008 and 2015 suggests the migration of the grounding line ∼9 km upstream by 2015 from the 2008 ice front/grounding line positions, which virtually coincided with the 1996 grounding line position. This migration is consistent with the change in floating area deduced from the calculated height above buoyancy in 2015. The retrograde submarine bed underneath the lowest part of the Fleming Glacier may have promoted retreat of the grounding line. Grounding line retreat may also be enhanced by a feedback mechanism upstream of the grounding line by which increased basal lubrication due to increasing frictional heating enhances sliding and thinning. Improved knowledge of bed topography near the grounding line and further transient simulations with oceanic forcing are required to accurately predict the future movement of the Fleming Glacier system grounding line and better understand its ice dynamics and future contribution to sea level.
Erratum: Corrigendum: Greenland supraglacial lake drainages triggered by hydrologically induced basal slip
Publisher: Springer Science and Business Media LLC
Date: 07-2015
DOI: 10.1038/NATURE14608
Late Holocene glacial advance and ice shelf growth in Barilari Bay, Graham Land, west Antarctic Peninsula
Publisher: Geological Society of America
Date: 16-09-2014
DOI: 10.1130/B31035.1
Tidal Modulation of Antarctic Ice Shelf Melting
Publisher: Copernicus GmbH
Date: 24-07-2020
DOI: 10.5194/TC-2020-169
Abstract: Abstract. Tides influence basal melting of in idual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt/yr (4 %), while decreasing continental shelf temperatures by 0.04 °C, indicating a slightly more efficient conversion of ocean heat into ice shelf melting. Regional variations can be larger, with melt rate modulations exceeding 500 % and temperatures changing by more than 0.5 °C, highlighting the importance of capturing tides for robust modelling of glacier systems and coastal oceans. Tide-induced changes around the Antarctic Peninsula have a dipolar distribution with decreased ocean temperatures and reduced melting towards the Bellingshausen Sea and warming along the continental shelf break on the Weddell Sea side. This warming extends under the Ronne Ice Shelf, which also features one of the highest increases in area-averaged basal melting (150 %) when tides are included. Further, by means of a singular spectrum analysis, we explore the processes that cause variations in melting and its drivers in the boundary layer over periods of up to one month. At most places friction velocity varies at tidal timescales (one day or faster), while thermal driving changes at slower rates (longer than one day). In some key regions under the large cold-water ice shelves, however, thermal driving varies faster than friction velocity and this can not be explained by tidal modulations in boundary layer exchange rates alone. Our results suggest that large scale ocean models aiming to predict accurate ice shelf melt rates will need to explicitly resolve tides.
GPS height time series: Short‐period origins of spurious long‐period signals
Publisher: American Geophysical Union (AGU)
Date: 02-2007
DOI: 10.1029/2005JB004047
Effects of azimuthal multipath asymmetry on long GPS coordinate time series
Publisher: Springer Science and Business Media LLC
Date: 24-05-2011
Variable deceleration of Whillans Ice Stream, West Antarctica
Publisher: American Geophysical Union (AGU)
Date: 02-2014
DOI: 10.1002/2013JF002958
Common mode error in Antarctic GPS coordinate time-series on its effect on bedrock-uplift estimates
Publisher: Oxford University Press (OUP)
Date: 29-05-2018
DOI: 10.1093/GJI/GGY217
Special section on observation and modeling of glacial isostatic adjustment
Publisher: Elsevier BV
Date: 11-2011
Brief communication: The global signature of post-1900 land ice wastage on vertical land motion
Publisher: Copernicus GmbH
Date: 06-06-2017
Abstract: Abstract. Melting glaciers, ice caps and ice sheets have made an important contribution to sea-level rise through the last century. Self-attraction and loading effects driven by shrinking ice masses cause a spatially varying redistribution of ocean waters that affects reconstructions of past sea level from sparse observations. We model the solid-earth response to ice mass changes and find significant vertical deformation signals over large continental areas. We show how deformation rates have been strongly varying through the last century, which implies that they should be properly modelled before interpreting and extrapolating recent observations of vertical land motion and sea-level change.
Strategies for High Precision Processing of GPS Measurements with Application to the Amery Ice Shelf, East Antarctica
Publisher: Springer Science and Business Media LLC
Date: 07-2000
DOI: 10.1007/PL00012824
Incomplete separability of Antarctic plate rotation from glacial isostatic adjustment deformation within geodetic observations
Publisher: Oxford University Press (OUP)
Date: 20-11-2015
DOI: 10.1093/GJI/GGV461
A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS
Publisher: Springer Science and Business Media LLC
Date: 26-11-2010
Supplementary material to "An iterative process for efficient optimisation of parameters in geoscientific models: a demonstration using the Parallel Ice Sheet Model (PISM) version 0.7.3"
Publisher: Copernicus GmbH
Date: 30-11-2020
Fracture Propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage
Publisher: American Association for the Advancement of Science (AAAS)
Date: 09-05-2008
Abstract: Surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change. The process whereby such a pathway is created through thick, cold ice has not, however, been previously observed. We describe the rapid ( hours) drainage of a large supraglacial lake down 980 meters through to the bed of the Greenland Ice Sheet initiated by water-driven fracture propagation evolving into moulin flow. Drainage coincided with increased seismicity, transient acceleration, ice-sheet uplift, and horizontal displacement. Subsidence and deceleration occurred over the subsequent 24 hours. The short-lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially. The integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup.
Mass change from GRACE: a simulated comparison of Level-1B analysis techniques
Publisher: Oxford University Press (OUP)
Date: 2014
DOI: 10.1093/GJI/GGU402
Lower satellite-gravimetry estimates of Antarctic sea-level contribution
Publisher: Springer Science and Business Media LLC
Date: 21-10-2012
DOI: 10.1038/NATURE11621
Abstract: Recent estimates of Antarctica's present-day rate of ice-mass contribution to changes in sea level range from 31 gigatonnes a year (Gt yr(-1) ref. 1) to 246 Gt yr(-1) (ref. 2), a range that cannot be reconciled within formal errors. Time-varying rates of mass loss contribute to this, but substantial technique-specific systematic errors also exist. In particular, estimates of secular ice-mass change derived from Gravity Recovery and Climate Experiment (GRACE) satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment (GIA). Here we adopt a new model of GIA, developed from geological constraints, which produces GIA rates systematically lower than those of previous models, and an improved fit to independent uplift data. After applying the model to 99 months (from August 2002 to December 2010) of GRACE data, we estimate a continent-wide ice-mass change of -69 ± 18 Gt yr(-1) (+0.19 ± 0.05 mm yr(-1) sea-level equivalent). This is about a third to a half of the most recently published GRACE estimates, which cover a similar time period but are based on older GIA models. Plausible GIA model uncertainties, and errors relating to removing longitudinal GRACE artefacts ('destriping'), confine our estimate to the range -126 Gt yr(-1) to -29 Gt yr(-1) (0.08-0.35 mm yr(-1) sea-level equivalent). We resolve 26 independent drainage basins and find that Antarctic mass loss, and its acceleration, is concentrated in basins along the Amundsen Sea coast. Outside this region, we find that West Antarctica is nearly in balance and that East Antarctica is gaining substantial mass.
Increased ice loading in the Antarctic Peninsula since the 1850s and its effect on glacial isostatic adjustment
Publisher: American Geophysical Union (AGU)
Date: 12-09-2012
DOI: 10.1029/2012GL052559
Antarctic Surface Mass Balance: Natural Variability, Noise, and Detecting New Trends
Publisher: American Geophysical Union (AGU)
Date: 18-06-2020
DOI: 10.1029/2020GL087493
Abstract: The emergence of new, statistically robust trends in Antarctic surface mass balance (SMB) requires an understanding of the underlying SMB variability (noise). We show that simple white or AR[1] noise models do not adequately represent the variability of SMB in both the RACMO2.3p2 SMB model output (1979–2017) and composite ice core records (1800–2010), underestimating low‐frequency variability. By testing a range of noise models, we find that a Generalized Gauss Markov (GGM) model better approximates the noise around a linear trend. The general preference for GGM noise applies over spatial scales from the total ice sheet down to in idual drainage basins. Over the longest timescales considered, trend uncertainties are 1.3–2.3 times larger using a GGM model compared to using an AR1 model at the ice sheet scale. Overall, our results suggest that larger trends or longer periods are required before new SMB trends can be robustly separated from background noise.
A benchmark study for glacial isostatic adjustment codes
Publisher: Oxford University Press (OUP)
Date: 21-02-2011
An iterative process for efficient optimisation of parameters in geoscientific models: a demonstration using the Parallel Ice Sheet Model (PISM) version 0.7.3
Publisher: Copernicus GmbH
Date: 17-08-2021
Abstract: Abstract. Physical processes within geoscientific models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the uncertainty in model predictions therefore requires a systematic approach for s ling parameter space. In this study, we develop a simple and efficient approach to identify regions of multi-dimensional parameter space that are consistent with observations. Using the Parallel Ice Sheet Model to simulate the present-day state of the Antarctic Ice Sheet, we find that co-dependencies between parameters preclude any simple identification of a single optimal set of parameter values. Approaches such as large ensemble modelling are therefore required in order to generate model predictions that incorporate proper quantification of the uncertainty arising from the parameterisation of physical processes.
Revisiting GRACE Antarctic ice mass trends and accelerations considering autocorrelation
Publisher: Elsevier BV
Date: 2014
Pantropical modelling of canopy functional traits using Sentinel-2 remote sensing data
Publisher: Elsevier BV
Date: 2021
Ongoing postseismic vertical deformation of the Australian continent from far-field earthquakes
Publisher: Wiley
Date: 16-09-2020
Winter motion mediates dynamic response of the Greenland Ice Sheet to warmer summers
Publisher: American Geophysical Union (AGU)
Date: 06-08-2013
DOI: 10.1002/GRL.50764
Spatial and temporal Antarctic Ice Sheet mass trends, glacio-isostatic adjustment, and surface processes from a joint inversion of satellite altimeter, gravity, and GPS data
Publisher: American Geophysical Union (AGU)
Date: 02-2016
DOI: 10.1002/2015JF003550
A 4‐decade record of elevation change of the Amery Ice Shelf, East Antarctica
Publisher: American Geophysical Union (AGU)
Date: 30-01-2009
DOI: 10.1029/2008JF001094
Stability of direct GPS estimates of ocean tide loading
Publisher: American Geophysical Union (AGU)
Date: 08-2004
DOI: 10.1029/2004GL020588
Accuracy assessment of global barotropic ocean tide models
Publisher: American Geophysical Union (AGU)
Date: 07-08-2014
DOI: 10.1002/2014RG000450
Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change
Publisher: Copernicus GmbH
Date: 28-04-2014
Abstract: Abstract. This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating a firn densification model to account for firn compaction and surface processes as well as reprocessed data sets over a slightly longer period of time. A range of different Gravity Recovery and Climate Experiment (GRACE) gravity models were evaluated and a new Ice, Cloud, and Land Elevation Satellite (ICESat) surface height trend map computed using an overlapping footprint approach. When the GIA models created from the combination approach were compared to in situ GPS ground station displacements, the vertical rates estimated showed consistently better agreement than recent conventional GIA models. The new empirically derived GIA rates suggest the presence of strong uplift in the Amundsen Sea sector in West Antarctica (WA) and the Philippi/Denman sectors, as well as subsidence in large parts of East Antarctica (EA). The total GIA-related mass change estimates for the entire Antarctic ice sheet ranged from 53 to 103 Gt yr−1, depending on the GRACE solution used, with an estimated uncertainty of ±40 Gt yr−1. Over the time frame February 2003–October 2009, the corresponding ice mass change showed an average value of −100 ± 44 Gt yr−1 (EA: 5 ± 38, WA: −105 ± 22), consistent with other recent estimates in the literature, with regional mass loss mostly concentrated in WA. The refined approach presented in this study shows the contribution that such data combinations can make towards improving estimates of present-day GIA and ice mass change, particularly with respect to determining more reliable uncertainties.
Tidal Modulation of Antarctic Ice Shelf Melting
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-8431
Abstract: & & Tides influence basal melting of in idual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt/yr (4 %), while decreasing continental shelf temperatures by 0.04 & #176 C, indicating a slightly more efficient conversion of ocean heat into ice shelf melting. Regional variations can be larger, with melt rate modulations exceeding 500 % and temperatures changing by more than 0.5 & #176 C, highlighting the importance of capturing tides for robust modelling of glacier systems and coastal oceans. Tide-induced changes around the Antarctic Peninsula have a dipolar distribution with decreased ocean temperatures and reduced melting towards the Bellingshausen Sea and warming along the continental shelf break on the Weddell Sea side. This warming extends under the Ronne Ice Shelf, which also features one of the highest increases in area-averaged basal melting (128 %) when tides are included. Further, by means of a singular spectrum analysis, we explore the processes that cause variations in melting and its drivers in the boundary layer over periods of up to one month. At most places friction velocity varies at tidal timescales (one day or faster), while thermal driving changes at slower rates (longer than one day). In some key regions under the large cold-water ice shelves, however, thermal driving varies faster than friction velocity and this can not be explained by tidal modulations in boundary layer exchange rates alone. Our results suggest that large scale ocean models aiming to predict accurate ice shelf melt rates will need to explicitly resolve tides.& &
Unabated global mean sea-level rise over the satellite altimeter era
Publisher: Springer Science and Business Media LLC
Date: 11-05-2015
DOI: 10.1038/NCLIMATE2635
Uncertainty in geocenter estimates in the context of ITRF2014
Publisher: American Geophysical Union (AGU)
Date: 05-2017
DOI: 10.1002/2016JB013698
Analysis of ice shelf flexure and its InSAR representation in the grounding zone of the Southern McMurdo Ice Shelf
Publisher: Copernicus GmbH
Date: 23-02-2017
DOI: 10.5194/TC-2017-13
Abstract: Abstract. We examine tidal flexure in the grounding zone of the McMurdo Ice Shelf, Antarctica, using a combination of a TerraSAR-X repeat-pass radar interferometry, a precise digital elevation model, and GPS ground validation data. Satellite and field data were acquired in tandem between October and December 2014. Our GPS data show a horizontal modulation of up to 60 % of the vertical litude at tidal periods within a few km of the grounding line. We ascribe this to bending stresses and account for it using a simple elastic beam model. The horizontal surface strain is removed from nine differential interferograms to obtain precise vertical bending curves. This processing step allows us to identify a fixed (as opposed to tidally migrating) grounding line position and eliminates the possibility of significant upstream bending at this location. The change in apparent vertical motion due to horizontal strain can lead to a systematic mis-location of the interferometric grounding line by the order of up to one ice thickness, or several hundred metres. While our field site was selected in consideration of the simple boundary conditions and low background velocity the findings are relevant to other satellite-based grounding zone studies, particularly those looking at tidally-induced velocity changes or interpreting satellite-based flexure profiles.
Diurnal and semidiurnal tide‐induced lateral movement of Ronne Ice Shelf, Antarctica
Publisher: American Geophysical Union (AGU)
Date: 23-05-2012
DOI: 10.1029/2012GL051636
The increasing rate of global mean sea-level rise during 1993-2014
Publisher: Springer Science and Business Media LLC
Date: 26-06-2017
DOI: 10.1038/NCLIMATE3325
Validation of ocean tide models around Antarctica using onshore GPS and gravity data
Publisher: American Geophysical Union (AGU)
Date: 08-2005
DOI: 10.1029/2004JB003390
Basal drag of Fleming Glacier, Antarctica, Part B: implications of evolution from 2008 to 2015
Publisher: Copernicus GmbH
Date: 02-01-2018
DOI: 10.5194/TC-2017-242
Abstract: Abstract. The Wordie Ice Shelf-Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. Upstream glacier acceleration and dynamic thinning have been observed over the past two decades, especially after 2008 when only a little constraining ice shelf remained at the Fleming Glacier front. It is important to know whether the substantial speed up and surface draw-down of the glacier since 2008 is a direct response to increasing ocean forcing or driven by the feedback within an unstable marine-based glacier system or both. To explore the mechanism underlying the changes, we use a Stokes (full stress) model to simulate the basal shear stress of the Fleming system in 2008 and 2015. Recent observational studies have suggested the 2008–2015 velocity change was due to the ungrounding of the Fleming Glacier front. Our modelling shows that the fast flowing region of the Fleming Glacier shows a very low basal shear stress in 2008 but with a band of higher basal shear stress along the ice front. It indicates that the ungrounding process might have not started in 2008, which is consistent with the height above buoyancy calculation in 2008. Comparison of our inversions for basal shear stresses for 2008 and 2015 suggests the migration of the grounding line by ~ 9 km upstream from the grounding line position in 1996, a shift which is consistent with the change in floating area deduced from the height above buoyancy in 2015. The southern branch of the Fleming Glacier and the Prospect Glacier apparently have retreated by ~ 1–3 km from 2008 to 2015. The retrograde bed underneath the Fleming Glacier has promoted migration of the grounding line, which we suggest may be triggered by subglacial drainage as a response to the increased basal water supply through greater frictional heating at the ice-bedrock interface further upstream in the fast-flowing region. Improved knowledge of bed topography near the grounding line and further transient simulation is required to predict the future grounding line movement of the Fleming Glacier system precisely and subsequently understand better the ice dynamics and the its future contribution to sea level.
GPS‐Observed Elastic Deformation Due to Surface Mass Balance Variability in the Southern Antarctic Peninsula
Publisher: American Geophysical Union (AGU)
Date: 17-02-2022
DOI: 10.1029/2021GL097109
Abstract: In Antarctica, Global Positioning System (GPS) vertical time series exhibit non‐linear signals over a wide range of temporal scales. To explain these non‐linearities, a number of hypotheses have been proposed, among them the short‐term rapid solid Earth response to contemporaneous ice mass change. Here we use GPS vertical time series to reveal the solid Earth response to variations in surface mass balance (SMB) in the Southern Antarctic Peninsula (SAP). At four locations in the SAP we show that interannual variations of SMB anomalies cause measurable elastic deformation. We use regional climate model SMB products to calculate the induced displacement assuming a perfectly elastic Earth. Our results show a reduction of the misfit when fitting a linear trend to GPS time series corrected for the elastic response to SMB variations. Our results imply that, for a better understanding of the glacial isostatic adjustment signal in Antarctica, SMB variability must be considered.
Velocity change of the Amery Ice Shelf, East Antarctica, during the period 1968–1999
Publisher: American Geophysical Union (AGU)
Date: 03-2007
DOI: 10.1029/2006JF000609
A global, spherical finite-element model for post-seismic deformation using <i>Abaqus</i>
Publisher: Copernicus GmbH
Date: 25-03-2022
Abstract: Abstract. We present a finite-element model of post-seismic solid Earth deformation built in the software package Abaqus (version 2018). The model is global and spherical, includes self-gravitation and is built for the purpose of calculating post-seismic deformation in the far field ( ∼300 km) of major earthquakes. An earthquake is simulated by prescribing slip on a fault plane in the mesh and the model relaxes under the resulting change in stress. Both linear Maxwell and biviscous (Burgers) rheological models have been implemented and the model can be easily adapted to include different rheological models and lateral variations in Earth structure, a particular advantage over existing models. We benchmark the model against an analytical coseismic solution and an existing open-source post-seismic model code, demonstrating good agreement for all fault geometries tested. Due to the inclusion of self-gravity, the model has the potential for predicting deformation in response to multiple sources of stress change, for ex le, changing ice thickness in tectonically active regions.
Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change
Publisher: Copernicus GmbH
Date: 16-07-2014
Abstract: Abstract. This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of time, and now include a firn densification model to account for firn compaction and surface processes. A range of different GRACE gravity models were evaluated, as well as a new ICESat surface height trend map computed using an overlapping footprint approach. When the GIA models created from the combination approach were compared to in-situ GPS ground station displacements, the vertical rates estimated showed consistently better agreement than existing GIA models. In addition, the new empirically derived GIA rates suggest the presence of strong uplift in the Amundsen Sea and Philippi/Denman sectors, as well as subsidence in large parts of East Antarctica. The total GIA mass change estimates for the entire Antarctic ice sheet ranged from 53 to 100 Gt yr−1, depending on the GRACE solution used, and with an estimated uncertainty of ±40 Gt yr−1. Over the time frame February 2003–October 2009, the corresponding ice mass change showed an average value of −100 ± 44 Gt yr−1 (EA: 5 ± 38, WA: −105 ± 22), consistent with other recent estimates in the literature, with the mass loss mostly concentrated in West Antarctica. The refined approach presented in this study shows the contribution that such data combinations can make towards improving estimates of present day GIA and ice mass change, particularly with respect to determining more reliable uncertainties.
Basal drag of Fleming Glacier, Antarctica, Part A: sensitivity of inversion to temperature and bedrock uncertainty
Publisher: Copernicus GmbH
Date: 02-01-2018
DOI: 10.5194/TC-2017-241
Abstract: Abstract. Many glaciers in West Antarctica and the Antarctic Peninsula are now rapidly losing ice mass. Understanding of the dynamics of these fast-flowing glaciers, and their potential future behavior, can be improved through ice sheet modeling studies. Inverse methods are commonly used in ice sheet models to infer the basal shear stress, which has a large effect on the basal velocity and internal ice deformation. Here we use the full-Stokes Elmer/Ice model to simulate the Wordie Ice Shelf-Fleming Glacier system in the southern Antarctic Peninsula. With a control inverse method, we model the basal drag from the surface velocities observed in 2008. We propose a three-cycle spin-up scheme to remove the influence of initial temperature field on the final inversion. This is particularly important for glaciers with significant temperature-dependent internal deformation. We find that the Fleming Glacier has strong, temperature-dependent, deformational flow in the fast-flowing regions. Sensitivity tests using various bed elevation datasets and ice front boundary conditions demonstrate the importance of high-accuracy ice thickness/bed geometry data and precise location of the ice front boundary.
Non-linear responses of Rutford Ice Stream, Antarctica, to semi-diurnal and diurnal tidal forcing
Publisher: International Glaciological Society
Date: 2010
DOI: 10.3189/002214310791190848
Abstract: Modulation of the flow of Rutford Ice Stream, Antarctica, has been reported previously at semi-diurnal, diurnal, fortnightly and semi-annual periods. A model that includes non-linear response to tidal forcing has been shown to fit closely observations at fortnightly frequencies. Here we examine that model further and test its fit at a larger set of observed frequencies, including the large semi-annual displacement. We show analytically that, when forced by major tidal terms, the model (using a basal shear stress exponent m = 3) predicts several discrete response periods from 4 hours to 0.5 years. We examine a 1.5 year GPS record from Rutford Ice Stream and find that the model, when forced by a numerical tide model, is able to reproduce the reported semi-annual signal. We confirm that about 5% of the mean flow is due solely to the ( m = 3) non-linear response to tidally varying basal shear stress. Our best-fitting set of model parameters is similar to those originally reported using a much shorter data record, although with noticeably improved fit, suggesting these parameters are robust. We find that m ≈ 3 fits the data well, but that m ≈ 2 does not. Furthermore, we find that a small variation in flow over the 18.6 year lunar node tide cycle is expected. Fits to semi-diurnal and diurnal terms remain relatively poor, possibly due to viscoelastic effects that are not included in the model and reduced GPS data quality at some discrete periods. For comparison, we predict the response of Bindschadler Ice Stream and Lambert Glacier and show, given identical model parameters, a similar response pattern but with ∼1–2 orders of magnitude smaller variability these may still be measurable and hence useful in testing the applicability of this model to other locations.
Ocean Stratification and Low Melt Rates at the Ross Ice Shelf Grounding Zone
Publisher: American Geophysical Union (AGU)
Date: 10-2018
DOI: 10.1029/2018JC013987
The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future
Publisher: American Geophysical Union (AGU)
Date: 11-11-2020
DOI: 10.1029/2019RG000663
Abstract: The Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic‐enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern observations by contrast suggest that the AIS has only just started to respond to climate change in recent decades. The maximum projected sea level contribution from Antarctica to 2100 has increased significantly since the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report, although estimates continue to evolve with new observational and theoretical advances. This review brings together recent literature highlighting the progress made on the known processes and feedbacks that influence the stability of the AIS. Reducing the uncertainty in the magnitude and timing of the future sea level response to AIS change requires a multidisciplinary approach that integrates knowledge of the interactions between the ice sheet, solid Earth, atmosphere, and ocean systems and across time scales of days to millennia. We start by reviewing the processes affecting AIS mass change, from atmospheric and oceanic processes acting on short time scales (days to decades), through to ice processes acting on intermediate time scales (decades to centuries) and the response to solid Earth interactions over longer time scales (decades to millennia). We then review the evidence of AIS changes from the Pliocene to the present and consider the projections of global sea level rise and their consequences. We highlight priority research areas required to improve our understanding of the processes and feedbacks governing AIS change.
Response of the East Antarctic Ice Sheet to past and future climate change
Publisher: Springer Science and Business Media LLC
Date: 10-08-2022
DOI: 10.1038/S41586-022-04946-0
Abstract: The East Antarctic Ice Sheet contains the vast majority of Earth's glacier ice (about 52 metres sea-level equivalent), but is often viewed as less vulnerable to global warming than the West Antarctic or Greenland ice sheets. However, some regions of the East Antarctic Ice Sheet have lost mass over recent decades, prompting the need to re-evaluate its sensitivity to climate change. Here we review the response of the East Antarctic Ice Sheet to past warm periods, synthesize current observations of change and evaluate future projections. Some marine-based catchments that underwent notable mass loss during past warm periods are losing mass at present but most projections indicate increased accumulation across the East Antarctic Ice Sheet over the twenty-first century, keeping the ice sheet broadly in balance. Beyond 2100, high-emissions scenarios generate increased ice discharge and potentially several metres of sea-level rise within just a few centuries, but substantial mass loss could be averted if the Paris Agreement to limit warming below 2 degrees Celsius is satisfied.
A model-based investigation of the recent rebound of shelf water salinity in the Ross Sea
Publisher: Authorea, Inc.
Date: 17-10-2023
Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance
Publisher: Elsevier BV
Date: 03-2015
Tidal observations on floating ice using a single GPS receiver
Publisher: American Geophysical Union (AGU)
Date: 02-2003
DOI: 10.1029/2002GL016182
Antarctic ice mass balance estimates from GRACE: Tidal aliasing effects
Publisher: American Geophysical Union (AGU)
Date: 10-04-2008
DOI: 10.1029/2007JF000871
Ocean tides in the Weddell Sea: New observations on the Filchner-Ronne and Larsen C ice shelves and model validation
Publisher: American Geophysical Union (AGU)
Date: 15-06-2011
DOI: 10.1029/2011JC006949
Limitations in one-dimensional (an)elastic Earth models for explaining GPS-observed M$_2$ Ocean Tide Loading displacements in New Zealand
Publisher: Wiley
Date: 03-2021
GPS Rates of Vertical Bedrock Motion Suggest Late Holocene Ice‐Sheet Readvance in a Critical Sector of East Antarctica
Publisher: American Geophysical Union (AGU)
Date: 23-02-2022
DOI: 10.1029/2021GL097232
Abstract: We investigate present‐day bedrock vertical motion using new Global Positioning System (GPS) timeseries from the Totten‐Denman glacier region of East Antarctica (∼77°–120°E) where models of glacial isostatic adjustment (GIA) disagree, glaciers are likely losing mass, and few data constraints on GIA exist. We show that varying surface mass balance loading (SMBL) is a dominant signal, contributing random‐walk‐like noise to GPS timeseries across Antarctica. In the study region, it induces site velocity biases of up to ∼+1 mm/yr over 2010–2020. After correcting for SMBL displacement and GPS common mode error, subsidence is evident at all sites aside from the Totten Glacier region where uplift is ∼1.5 mm/yr. Uplift near the Totten Glacier is consistent with late Holocene ice retreat while the widespread subsidence further west suggests possible late Holocene readvance of the region’s ice sheet, in broad agreement with limited glacial geological data and highlighting the need for s ling beneath the current ice sheet.
Limitations in one-dimensional (an)elastic Earth models for explaining GPS-observed M$_2$ Ocean Tide Loading displacements in New Zealand
Publisher: Wiley
Date: 29-09-2020
Higher-order ionospheric effects on the GPS reference frame and velocities
Publisher: American Geophysical Union (AGU)
Date: 24-03-2010
DOI: 10.1029/2009JB006677
Apparent stability of GPS monumentation from short‐baseline time series
Publisher: American Geophysical Union (AGU)
Date: 10-2009
DOI: 10.1029/2009JB006319
Analysis of ice shelf flexure and its InSAR representation in the grounding zone of the Southern McMurdo Ice Shelf
Publisher: Copernicus GmbH
Date: 03-11-2017
Abstract: Abstract. We examine tidal flexure in the grounding zone of the McMurdo Ice Shelf, Antarctica, using a combination of TerraSAR-X repeat-pass radar interferometry, a precise digital elevation model, and GPS ground validation data. Satellite and field data were acquired in tandem between October and December 2014. Our GPS data show a horizontal modulation of up to 60 % of the vertical displacement litude at tidal periods within a few kilometres of the grounding line. We ascribe the observed oscillatory horizontal motion to varying bending stresses and account for it using a simple elastic beam model. The horizontal surface strain is removed from nine differential interferograms to obtain precise bending curves. They reveal a fixed (as opposed to tidally migrating) grounding-line position and eliminate the possibility of significant upstream bending at this location. The consequence of apparent vertical motion due to uncorrected horizontal strain in interferometric data is a systematic mislocation of the interferometric grounding line by up to the order of one ice thickness, or several hundred metres. While our field site was selected due to its simple boundary conditions and low background velocity, our findings are relevant to other grounding zones studied by satellite interferometry, particularly studies looking at tidally induced velocity changes or interpreting satellite-based flexure profiles.
Climate variability a key driver of recent Antarctic ice-mass change
Publisher: Authorea, Inc.
Date: 19-10-2023
Climate variability as a major forcing of recent Antarctic ice-mass change
Publisher: Authorea, Inc.
Date: 17-01-2023
Empirical modelling of site-specific errors in continuous GPS data
Publisher: Springer Science and Business Media LLC
Date: 03-06-2014
Assessment of the Jason-1 and TOPEX/Poseidon Microwave Radiometer Performance Using GPS from Offshore Sites in the North Sea
Publisher: Informa UK Limited
Date: 07-2004
Limitations in One‐Dimensional (an)Elastic Earth Models for Explaining GPS‐Observed M2 Ocean Tide Loading Displacements in New Zealand
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2021JB021992
Abstract: GPS observations of ocean tide loading displacements can help infer the regional anelastic properties of the asthenosphere. We estimate M 2 ocean tide loading displacements at 170 GPS sites in New Zealand and compare these to modeled values using a range of numerical tide and radially symmetric (1D) elastic and anelastic Earth models. Regardless of the model combination, we are unable to reduce the strong spatial coherence of the M 2 residuals across the North Island where they reach 0.4 mm (2%). The best fit in the North Island is obtained when combining the FES2014b tide model with spatially variable ocean density and water compressibility, and the STW105 Earth model. The residuals exhibit a change of ∼0.3 mm in magnitude between the Taupo Volcanic Zone and the east coast (∼100 km), suggesting that this region's laterally varying, shallow rheological structure may need to be considered to explain these observations.
Brief Communication: The global signature of post-1900 land ice wastage on vertical land motion
Publisher: Copernicus GmbH
Date: 15-12-2016
DOI: 10.5194/TC-2016-274
Abstract: Abstract. Melting glaciers, ice caps and ice sheets have made an important contribution to sea-level rise through the last century. Self-attraction and loading effects driven by shrinking ice masses cause a spatially-varying redistribution of ocean waters that affects reconstructions of past sea level from sparse observations. We model the solid earth response to ice mass changes and find significant vertical deformation signals over large continental areas. We show how deformation rates have been strongly varying through the last century, which implies that they should be properly modelled before interpreting and extrapolating recent observations of vertical land motion and sea level change.
Exploring parameter uncertainty in a model of the Antarctic Ice Sheet
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-15304
Abstract: & & Physical processes within ice sheet models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the uncertainty in model predictions therefore requires a systematic approach for s ling parameter space. We demonstrate a simple and efficient approach to identify regions of multi-dimensional parameter space that are consistent with observations. Using the Parallel Ice Sheet Model to simulate the present-day state of the Antarctic Ice Sheet, we find that co-dependencies between parameters preclude the identification of a single optimal set of parameter values. Approaches such as large ensemble modelling are therefore required in order to generate model predictions, such as projections of future global sea level rise, that incorporate proper quantification of the uncertainty arising from the parameterisation of physical processes.& &
Detecting offsets in GPS time series: First results from the detection of offsets in GPS experiment
Publisher: American Geophysical Union (AGU)
Date: 05-2013
DOI: 10.1002/JGRB.50152
Tidal gravity variations revisited at Vostok Station, Antarctica
Publisher: Elsevier BV
Date: 06-2009
Ongoing Development of the Bass Strait GNSS/INS Buoy System for Altimetry Validation in Preparation for SWOT
Publisher: MDPI AG
Date: 03-01-2023
DOI: 10.3390/RS15010287
Abstract: GNSS equipped buoys remain an important tool in altimetry validation. Progressive advances in altimetry missions require associated development in such validation tools. In this paper, we enhanced an existing buoy approach and gained further understanding of the buoy dynamics based on in situ observations. First, we implemented the capability to separate the ambiguity fixing strategy for different constellations in the processing software TRACK. A comparison between GPS and GNSS solutions suggested up to 3 cm reduction in the root mean square of the buoy minus co-located mooring SSH residuals over the selected sidereal periods. Then, comparison between double differencing and precise point positioning solutions suggested a possible common mode error external to GNSS processing. To assess buoy performance in different ocean conditions and sea states, GNSS and INS observations were used during periods where external forcings (waves, current and wind) were not interacting substantially. For the deployments investigated, no significant relationship was found, noting the maximum significant wave height and current velocity was ~2.3 m and ~0.3 m/s, respectively. In the lead up to the validation required for the SWOT mission, these results place important bounds on the performance of the buoy design under real operating conditions.
Vertical deformation and residual altimeter systematic errors around continental Australia inferred from a Kalman-based approach
Publisher: Springer Science and Business Media LLC
Date: 12-2022
DOI: 10.1007/S00190-022-01680-3
Abstract: We further developed a space–time Kalman approach to investigate time-fixed and time-variable signals in vertical land motion (VLM) and residual altimeter systematic errors around the Australian coast, through combining multi-mission absolute sea-level (ASL), relative sea-level from tide gauges (TGs) and Global Positioning System (GPS) height time series. Our results confirmed coastal subsidence in broad agreement with GPS velocities and unexplained by glacial isostatic adjustment alone. VLM determined at in idual TGs differs from spatially interpolated GPS velocities by up to ~ 1.5 mm/year, yielding a ~ 40% reduction in RMSE of geographic ASL variability at TGs around Australia. Our mission-specific altimeter error estimates are small but significant (typically within ~ ± 0.5–1.0 mm/year), with negligible effect on the average ASL rate. Our circum-Australia ASL rate is higher than previous results, suggesting an acceleration in the ~ 27-year time series. Analysis of the time-variability of altimeter errors confirmed stability for most missions except for Jason-2 with an anomaly reaching ~ 2.8 mm/year in the first ~ 3.5 years of operation, supported by analysis from the Bass Strait altimeter validation facility. Data predominantly from the reference missions and located well off narrow shelf regions was shown to bias results by as much as ~ 0.5 mm/year and highlights that residual oceanographic signals remain a fundamental limitation. Incorporating non-reference-mission measurements well on the shelf helped to mitigate this effect. Comparing stacked nonlinear VLM estimates and altimeter systematic errors with the El Niño-Southern Oscillation shows weak correlation and suggests our approach improves the ability to explore nonlinear localized signals and is suitable for other regional- and global-scale studies.
The GPS Contribution to the Error Budget of Surface Elevations Derived From Airborne LIDAR
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2009
Migratory earthquake precursors are dominant on an ice stream fault
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-02-2021
Abstract: Migratory nucleation of earthquakes is dominant, and self-nucleation is rare over many repeats of a natural stick-slip cycle.
A Reconciled Estimate of Ice-Sheet Mass Balance
Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-11-2012
Abstract: Mass loss from the ice sheets of Greenland and Antarctica account for a large fraction of global sea-level rise. Part of this loss is because of the effects of warmer air temperatures, and another because of the rising ocean temperatures to which they are being exposed. Joughin et al. (p. 1172 ) review how ocean-ice interactions are impacting ice sheets and discuss the possible ways that exposure of floating ice shelves and grounded ice margins are subject to the influences of warming ocean currents. Estimates of the mass balance of the ice sheets of Greenland and Antarctica have differed greatly—in some cases, not even agreeing about whether there is a net loss or a net gain—making it more difficult to project accurately future sea-level change. Shepherd et al. (p. 1183 ) combined data sets produced by satellite altimetry, interferometry, and gravimetry to construct a more robust ice-sheet mass balance for the period between 1992 and 2011. All major regions of the two ice sheets appear to be losing mass, except for East Antarctica. All told, mass loss from the polar ice sheets is contributing about 0.6 millimeters per year (roughly 20% of the total) to the current rate of global sea-level rise.
Postseismic Deformation in the Northern Antarctic Peninsula Following the 2003 and 2013 Scotia Sea Earthquakes
Publisher: American Geophysical Union (AGU)
Date: 10-2023
DOI: 10.1029/2023JB026685
Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line
Publisher: American Geophysical Union (AGU)
Date: 30-03-2020
DOI: 10.1029/2019JC015562
Kinematic and static GPS techniques for estimating tidal displacements with application to Antarctica
Publisher: Elsevier BV
Date: 2006
Ice Sheets, Glaciers, and Sea Level
Publisher: Elsevier
Date: 2015
Seismicity on the western Greenland Ice Sheet: Surface fracture in the vicinity of active moulins
Publisher: American Geophysical Union (AGU)
Date: 06-2015
DOI: 10.1002/2014JF003398
Widespread low rates of Antarctic glacial isostatic adjustment revealed by GPS observations
Publisher: American Geophysical Union (AGU)
Date: 11-2011
DOI: 10.1029/2011GL049277
GPS in Glaciology, Applications
Publisher: Springer Netherlands
Date: 2011
Regional biases in absolute sea‐level estimates from tide gauge data due to residual unmodeled vertical land movement
Publisher: American Geophysical Union (AGU)
Date: 27-07-2012
DOI: 10.1029/2012GL052348
Nonlinear interaction between ocean tides and the Larsen C Ice Shelf system
Publisher: American Geophysical Union (AGU)
Date: 21-04-2011
DOI: 10.1029/2011GL046680
The impact of tides on Antarctic ice shelf melting
Publisher: Copernicus GmbH
Date: 21-04-2022
Abstract: Abstract. Tides influence basal melting of in idual Antarctic ice shelves, but their net impact on Antarctic-wide ice–ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas using a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt yr−1 (4 %) while decreasing continental shelf temperatures by 0.04 ∘C. The Ronne Ice Shelf features the highest increase in mass loss (44 Gt yr−1, 128 %), coinciding with strong residual currents and increasing temperatures on the adjacent continental shelf. In some large ice shelves tides strongly affect melting in regions where the ice thickness is of dynamic importance to grounded ice flow. Further, to explore the processes that cause variations in melting we apply dynamical–thermodynamical decomposition to the melt drivers in the boundary layer. In most regions, the impact of tidal currents on the turbulent exchange of heat and salt across the ice–ocean boundary layer has a strong contribution. In some regions, however, mechanisms driven by thermodynamic effects are equally or more important, including under the frontal parts of Ronne Ice Shelf. Our results support the importance of capturing tides for robust modelling of glacier systems and shelf seas, as well as motivate future studies to directly assess friction-based parameterizations for the pan-Antarctic domain.
An iterative process for efficient optimisation of parameters in geoscientific models: a demonstration using the Parallel Ice Sheet Model (PISM) version 0.7.3
Publisher: Copernicus GmbH
Date: 30-11-2020
DOI: 10.5194/GMD-2020-382
Abstract: Abstract. Physical processes within geoscientific models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the uncertainty in model predictions therefore requires a systematic approach for s ling parameter space. In this study, we develop a simple and efficient approach to identify regions of multi-dimensional parameter space that are consistent with observations. Using the Parallel Ice Sheet Model to simulate the present-day state of the Antarctic Ice Sheet, we find that co-dependencies between parameters preclude the identification of a single optimal set of parameter values. Approaches such as large ensemble modelling are therefore required in order to generate model predictions that incorporate proper quantification of the uncertainty arising from the parameterisation of physical processes.
Long GPS coordinate time series: Multipath and geometry effects
Publisher: American Geophysical Union (AGU)
Date: 03-04-2010
DOI: 10.1029/2009JB006543
Rapid bedrock uplift in the Antarctic Peninsula explained by viscoelastic response to recent ice unloading
Publisher: Elsevier BV
Date: 07-2014
Greenland supraglacial lake drainages triggered by hydrologically induced basal slip
Publisher: Springer Science and Business Media LLC
Date: 03-06-2015
DOI: 10.1038/NATURE14480
Abstract: Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet. These drainage events drive transient ice-sheet acceleration and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season. Although it is well established that cracks must remain water-filled to propagate to the bed, the precise mechanisms that initiate hydro-fracture events beneath lakes are unknown. Here we show that, for a lake on the western Greenland Ice Sheet, drainage events are preceded by a 6-12 hour period of ice-sheet uplift and/or enhanced basal slip. Our observations from a dense Global Positioning System (GPS) network allow us to determine the distribution of meltwater at the ice-sheet bed before, during, and after three rapid drainages in 2011-2013, each of which generates tensile stresses that promote hydro-fracture beneath the lake. We hypothesize that these precursors are associated with the introduction of meltwater to the bed through neighbouring moulin systems (vertical conduits connecting the surface and base of the ice sheet). Our results imply that as lakes form in less crevassed, interior regions of the ice sheet, where water at the bed is currently less pervasive, the creation of new surface-to-bed conduits caused by lake-draining hydro-fractures may be limited.
Spurious periodic horizontal signals in sub-daily GPS position estimates
Publisher: Springer Science and Business Media LLC
Date: 29-06-2003
Simulated dynamic regrounding during marine ice sheet retreat
Publisher: Copernicus GmbH
Date: 23-10-2018
DOI: 10.5194/TC-2017-217
Abstract: Abstract. Marine terminating ice sheets are of interest due to their potential instability, making them vulnerable to rapid retreat. Modelling the evolution of glaciers and ice streams in such regions is key to understanding their possible contribution to sea level rise. The friction caused by the sliding of ice over bedrock, and the resultant shear stress, are important factors in determining the velocity of sliding ice. Many models use simple power-law expressions for the relationship between the basal shear stress and ice velocity or introduce an effective pressure dependence into the sliding relation in an ad hoc. manner. Sliding relations based on water-filled sub-glacial cavities are more physically motivated, with the overburden pressure of the ice included. Here we show that using a cavitation based sliding relation allows for the temporary regrounding of an ice shelf at a point downstream of the main grounding line of a marine ice sheet undergoing retreat across a retrograde bedrock slope. This suggests that the choice of sliding relation is especially important when modelling grounding line behaviour of regions where potential ice rises and pinning points are present and regrounding could occur.
A new open-source viscoelastic solid earth deformation module implemented in Elmer (v8.4)
Publisher: Copernicus GmbH
Date: 12-03-2020
Abstract: Abstract. We present a new, open-source viscoelastic solid earth deformation model, Elmer/Earth. Using the multi-physics finite-element package Elmer, a model to compute viscoelastic material deformation has been implemented into the existing linear elasticity solver routine. Unlike approaches often implemented in engineering codes, our solver accounts for the restoring force of buoyancy within a system of layers with depth-varying density. It does this by directly integrating the solution of the system rather than by applying stress-jump conditions in the form of Winkler foundations on inter-layer boundaries, as is usually needed when solving the minimization problem given by the stress ergence in commercial codes. We benchmarked the new model with results from a commercial finite-element engineering package (ABAQUS, v2018) and another open-source code that uses viscoelastic normal mode theory, TABOO, using a flat-earth setup loaded by a cylindrical disc of 100 km in diameter and 100 m in height at the density of ice. Evaluating the differences in predicted surface deformation at the centre of the load and two distinctive distances (100 and 200 km), average deviations of 7 and 2.7 cm of Elmer/Earth results to ABAQUS and TABOO, respectively, were observed. In view of more than 100 cm maximum vertical deformation and the different numerical methods and parameters, these are very encouraging results. Elmer is set up as a highly scalable parallel code and distributed under the (L)GPL license, meaning that large-scale computations can be made without any licensing restrictions. Scaling figures presented in this paper show good parallel performance of the new model. Additionally, the high-fidelity ice-sheet code Elmer/Ice utilizes the same source base as Elmer and thereby the new model opens the way to undertaking high-resolution coupled ice-flow–solid-earth deformation simulations, which are required for robust projections of future sea-level rise and glacial isostatic adjustment.
Seasonal variations in Greenland Ice Sheet motion: Inland extent and behaviour at higher elevations
Publisher: Elsevier BV
Date: 07-2011
Reduced ice mass loss and three-dimensional viscoelastic deformation in northern Antarctic Peninsula inferred from GPS
Publisher: Oxford University Press (OUP)
Date: 11-05-2020
DOI: 10.1093/GJI/GGAA229
Abstract: We consider the viscoelastic rheology of the solid Earth under the Antarctic Peninsula due to ice mass loss that commenced after the breakup of the Larsen-B ice shelf. We extend the previous analysis of nearby continuous GPS time-series to include five additional years and the additional consideration of the horizontal components of deformation. They show strong uplift from ∼2002 to 2011 followed by reduced uplift rates to 2018. Modelling the GPS-derived uplift as a viscoelastic response to ongoing regional ice unloading from a new ice model confirms earlier estimates of low upper-mantle viscosities of ∼0.3–3 × 1018 Pa s in this region but allows a wide range of elastic lithosphere thickness. The observed and modelled north coordinate component shows little nonlinear variation due to the location of ice mass change to the east of the GPS sites. However, comparison of the observed and modelled east coordinate component constrains the upper-mantle viscosity to be less than ∼9 × 1018 Pa s, consistent with the viscosity range suggested by the uplift rates alone and providing important, largely independent, confirmation of that result. Our horizontal analysis showed only marginal sensitivity to modelled lithospheric thickness. The results for the horizontal components are sensitive to the adopted plate rotation model, with the estimate based on ITRF2014 suggesting that the sum of residual plate motion and pre-2002 glacial isostatic adjustment is likely less than ∼±0.5 mm yr−1 in the east component.
Greenland ice sheet motion coupled with daily melting in late summer
Publisher: American Geophysical Union (AGU)
Date: 2009
DOI: 10.1029/2008GL035758
Continued deceleration of Whillans Ice Stream, West Antarctica
Publisher: American Geophysical Union (AGU)
Date: 11-2005
DOI: 10.1029/2005GL024319
Accuracy assessment of ocean tide models around Antarctica
Publisher: American Geophysical Union (AGU)
Date: 12-2005
DOI: 10.1029/2005GL023901
Ocean Bottom Deformation Due To Present-Day Mass Redistribution and Its Impact on Sea Level Observations
Publisher: American Geophysical Union (AGU)
Date: 23-12-2017
DOI: 10.1002/2017GL075419
Greenland ice sheet motion insensitive to exceptional meltwater forcing
Publisher: Proceedings of the National Academy of Sciences
Date: 18-11-2013
Abstract: During summer, meltwater generated on the Greenland ice sheet surface accesses the ice sheet bed, lubricating basal motion and resulting in periods of faster ice flow. However, the net impact of varying meltwater volumes upon seasonal and annual ice flow, and thus sea level rise, remains unclear. In 2012, despite record ice sheet runoff, including two extreme melt events, ice at a land-terminating margin flowed more slowly than in the average melt year of 2009, due principally to slower winter flow following faster summer flow. Our findings suggest that annual motion of land-terminating margins of the ice sheet, and thus the projected dynamic contribution of these margins to sea level rise, is insensitive to melt volumes commensurate with temperature projections for 2100.
GNSS/INS-Equipped Buoys for Altimetry Validation: Lessons Learnt and New Directions from the Bass Strait Validation Facility
Publisher: MDPI AG
Date: 15-09-2020
DOI: 10.3390/RS12183001
Abstract: Global Navigation Satellite System (GNSS)-equipped buoys have a fundamental role in the validation of satellite altimetry. Requirements to validate next generation altimeter missions are demanding and call for a greater understanding of the systematic errors associated with the buoy approach. In this paper, we assess the present-day buoy precision using archived data from the Bass Strait validation facility. We explore potential improvements in buoy precision by addressing two previously ignored issues: changes to buoyancy as a function of external forcing, and biases induced by platform dynamics. Our results indicate the precision of our buoy against in situ mooring data is ~15 mm, with a ~8.5 mm systematic noise floor. Investigation into the tether tension effect on buoyancy showed strong correlation between currents, wind stress and buoy-against-mooring residuals. Our initial empirical correction achieved a reduction of 5 mm in the standard deviation of the residuals, with a 51% decrease in variance over low frequency bands. Corrections associated with platform orientation from an Inertial Navigation System (INS) unit showed centimetre-level magnitude and are expected to be higher under rougher sea states. Finally, we conclude with further possible improvements to meet validation requirements for the future Surface Water Ocean Topography (SWOT) mission.
Supplementary material to "Estimating ocean tide loading displacements with GPS and GLONASS"
Publisher: Copernicus GmbH
Date: 03-03-2020
Seasonal Speedup Along the Western Flank of the Greenland Ice Sheet
Publisher: American Association for the Advancement of Science (AAAS)
Date: 09-05-2008
Abstract: It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller ( %). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow.
Present‐Day Vertical Land Motion of Australia From GPS Observations and Geophysical Models
Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019JB018034
Short‐term variability in Greenland Ice Sheet motion forced by time‐varying meltwater drainage: Implications for the relationship between subglacial drainage system behavior and ice velocity
Publisher: American Geophysical Union (AGU)
Date: 07-07-2012
DOI: 10.1029/2011JF002220
A comparison of GPS, VLBI and model estimates of ocean tide loading displacements
Publisher: Springer Science and Business Media LLC
Date: 12-2006
Sea-Level Trend Uncertainty With Pacific Climatic Variability and Temporally-Correlated Noise
Publisher: American Geophysical Union (AGU)
Date: 03-2018
DOI: 10.1002/2017JC013655
Geodetic vertical velocities affected by recent rapid changes in polar motion
Publisher: Oxford University Press (OUP)
Date: 18-09-2014
DOI: 10.1093/GJI/GGU325
Abstract: Secular motion of Earth's rotation pole results in large-scale secular deformation of Earth. Here, we investigate the magnitude of the deformation that has resulted from the rapid motion of the rotation pole to the east since ∼2005. We show that geodetic (GNSS, DORIS, VLBI and SLR) estimates of vertical velocity since ∼2005 have been biased by up to ±0.38 mm yr–1 relative to the longer-term deformation pattern. The largest signals occur within regions that include the U.S. Pacific Coast, Europe and South Pacific islands where geodetic measurements provide essential measurements of tide-gauge vertical movement and important constraints on models of glacial isostatic adjustment. Consequently, geodetic vertical velocities based on recent data should not be interpreted as being identical to centennial or longer term vertical land movement. Since 2010 the effect is further lified by the overprediction of the IERS polar motion model relative to the ongoing secular change in pole position—during this time geodetic vertical velocities based on the IERS pole tide model are not just biased relative to the long-term rates but also from actual post-2010 Earth deformation. For geophysical or reference frame studies seeking geodetic vertical velocities that are representative of decadal timescales, where interannual variation is considered noise, the correction for this non-linear effect is straightforward, requiring an elastic computation using a reference rate of polar motion that is linear over the timescales of interest.
Climate variability as a major forcing of recent Antarctic ice-mass change
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-9747
Abstract: Antarctica has been losing ice mass for decades, but its link to large-scale modes of climate forcing is not clear. Shorter-period variability has been partly associated with El Ni& #241 o Southern Oscillation (ENSO), but a clear connection with the dominant climate mode, the Southern Annular Mode (SAM), is yet to be found. We show that space gravimetric estimates of ice-mass variability over 2002-2021 may be substantially explained by a simple linear relation with detrended, time-integrated SAM and ENSO indices, from the whole ice sheet down to in idual drainage basins. Approximately 40% of the ice-mass trend over the GRACE period can be ascribed to increasingly persistent positive SAM forcing which, since the 1940s, is likely due to anthropogenic activity. Similar attribution over 2002-2021 could connect recent ice-sheet change to human activity.
A first look at the effects of ionospheric signal bending on a globally processed GPS network
Publisher: Springer Science and Business Media LLC
Date: 06-2010
Impact of tide‐topography interactions on basal melting of Larsen C Ice Shelf, Antarctica
Publisher: American Geophysical Union (AGU)
Date: 05-2012
DOI: 10.1029/2011JC007263
Simultaneous teleseismic and geodetic observations of the stick–slip motion of an Antarctic ice stream
Publisher: Springer Science and Business Media LLC
Date: 06-2008
DOI: 10.1038/NATURE06990
Abstract: Long-period seismic sources associated with glacier motion have been recently discovered, and an increase in ice flow over the past decade has been suggested on the basis of secular changes in such measurements. Their significance, however, remains uncertain, as a relationship to ice flow has not been confirmed by direct observation. Here we combine long-period surface-wave observations with simultaneous Global Positioning System measurements of ice displacement to study the tidally modulated stick-slip motion of the Whillans Ice Stream in West Antarctica. The seismic origin time corresponds to slip nucleation at a region of the bed of the Whillans Ice Stream that is likely stronger than in surrounding regions and, thus, acts like an 'asperity' in traditional fault models. In addition to the initial pulse, two seismic arrivals occurring 10-23 minutes later represent stopping phases as the slip terminates at the ice stream edge and the grounding line. Seismic litude and average rupture velocity are correlated with tidal litude for the different slip events during the spring-to-neap tidal cycle. Although the total seismic moment calculated from ice rigidity, slip displacement, and rupture area is equivalent to an earthquake of moment magnitude seven (M(w) 7), seismic litudes are modest (M(s) 3.6-4.2), owing to the source duration of 20-30 minutes. Seismic radiation from ice movement is proportional to the derivative of the moment rate function at periods of 25-100 seconds and very long-period radiation is not detected, owing to the source geometry. Long-period seismic waves are thus useful for detecting and studying sudden ice movements but are insensitive to the total amount of slip.
Location for direct access to subglacial Lake Ellsworth: An assessment of geophysical data and modeling
Publisher: American Geophysical Union (AGU)
Date: 06-2010
DOI: 10.1029/2010GL042884
Ongoing deformation of Antarctica following recent Great Earthquakes
Publisher: American Geophysical Union (AGU)
Date: 06-03-2016
DOI: 10.1002/2016GL067773
Subdaily signals in GPS observations and their effect at semiannual and annual periods
Publisher: American Geophysical Union (AGU)
Date: 02-2008
DOI: 10.1029/2007GL032252
Glacial isostatic adjustment in response to changing Late Holocene behaviour of ice streams on the Siple Coast, West Antarctica
Publisher: Oxford University Press (OUP)
Date: 05-02-2016
DOI: 10.1093/GJI/GGV532
Monument-antenna effects on GPS coordinate time series with application to vertical rates in Antarctica
Publisher: Springer Science and Business Media LLC
Date: 18-06-2011
Supplementary material to "Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change"
Publisher: Copernicus GmbH
Date: 16-07-2013
Ice flow modulated by tides at up to annual periods at Rutford Ice Stream, West Antarctica
Publisher: American Geophysical Union (AGU)
Date: 09-2007
DOI: 10.1029/2007GL031207
Upper Mantle Viscosity Underneath Northern Marguerite Bay, Antarctic Peninsula Constrained by Bedrock Uplift and Ice Mass Variability
Publisher: American Geophysical Union (AGU)
Date: 24-12-2021
DOI: 10.1029/2021GL097065
Abstract: We constrain viscoelastic Earth rheology and recent ice‐mass change in the northern Marguerite Bay region of the Antarctic Peninsula. Global Positioning System (GPS) time series from Rothera and San Martin stations show bedrock uplift range of ∼−0.8–1.8 mm/year over 1999–2005 and 2016–2020 but ∼3.5–6.0 mm/year over ∼2005–2016. Digital elevation models reveal substantial surface lowering, but at a lower rate since ∼2009. Using these data, we show that an elastic‐only model cannot explain the non‐linear uplift of the GPS sites but that a layered viscoelastic model can. We show close agreement between GPS uplift changes and viscoelastic models with effective elastic lithosphere thickness and upper‐mantle viscosity ∼10–95 km and ∼0.1−9 × 10 18 Pa s, respectively. Our viscosity estimate is consistent with a north‐south gradient in viscosity suggested by previous studies focused on specific regions within the Antarctic Peninsula and adds further evidence of the low viscosity upper mantle in the northern Antarctic Peninsula.
A new open-source visco-elastic Earth deformation module implemented in Elmer (v8.4)
Publisher: Copernicus GmbH
Date: 28-11-2019
DOI: 10.5194/GMD-2019-270
Abstract: Abstract. We present a new, open source visco-elastic Earth-deformation model, Elmer/Earth. Using the multi-physics Finite Element package Elmer, a model to compute visco-elastic material deformation has been implemented into the existing linear elasticity solver routine. Unlike approaches often implemented in engineering codes, our solver accounts for the restoring force of buoyancy within a system of layers with depth-varying density. It does this by directly integrating the solution of the system rather than by applying stress-jump conditions in the form of Winkler foundations on inter-layer boundaries, as is usually needed when solving the minimisation problem given by the stress- ergence in commercial codes. We benchmarked the new model with results from a commercial Finite Element engineering package (ABAQUS, v2018) and another open-source code that uses visco-elastic Normal Mode theory, TABOO, using a flat-earth setup loaded by a cylindrical disc of 100 km diameter and 100 m height of ice density. Evaluating the differences of predicted surface deformation at the centre of the load and two distinctive distances (100 km and 200 km), average deviations of 7 cm and 2.7 cm of Elmer/Earth results to ABAQUS and TABOO, respectively, were observed. In view of more than 100 cm maximum vertical deformation and the different numerical methods and parameters, these are very encouraging results. Elmer is set up as a highly scalable parallel code and distributed under the (L)GPL license, meaning that large scale computations can be made without any licensing restrictions. Scaling figures presented in this paper show good parallel performance of the new model. Additionally, the high fidelity ice sheet code Elmer/Ice utilises the same source-base of Elmer and thereby the new model opens the way to undertaking high-resolution coupled ice-flow - Earth deformation simulations, which are required for robust projections of future sea-level rise and glacial isostatic adjustment.
Related Organisations
Newcastle University
Location: United Kingdom of Great Britain and Northern Ireland
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