ORCID Profile
0000-0002-5857-8361
Current Organisation
Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
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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.
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-11231
Abstract: & & Antarctic Bottom Water (AABW) forms around Antarctica, sinks to the ocean& #8217 s abyss and fills more than 30% of the ocean& #8217 s volume. The formation of AABW includes mixing of distinct water masses, such as High Salinity Shelf Water (HSSW), Ice Shelf Water (ISW) and Circumpolar Deep Water on the continental shelf. Despite its climatic importance, the mechanisms of AABW formation are poorly known due to the lack of observations and the inability of climate models to simulate those mechanisms. We applied the Water Mass Transformation (WMT) framework in density space to simulations from a circumpolar ocean-ice shelf model (WAOM, with horizontal resolution ranging from 10 to 2 km) to understand the role of surface fluxes and oceanic processes to water mass formation and mixing on the Antarctic continental shelf, including the ice shelf cavities. The salt budget dominates the water mass transformation rates, with only secondary contribution from the heat budget. The buoyancy gain at relatively light density classes (27.2 & & #963 & sub& & #920 & /sub& & 27.5 kg/m& sup& & /sup& ) is dominated by basal melting. At heavier densities (& #963 & sub& & #920 & /sub& & 27.5), salt input associated with sea-ice growth in coastal polynyas drives buoyancy loss. The formation of HSSW occurs via diffusion of the surface fluxes, but it is advected towards the cavities of large ice shelves (e.g., Ross, Ronne-Filchner), where it interacts with ice shelf through melting and refreezing and forms ISW. The sensibility of those mechanisms to the model horizontal resolution was evaluated. The basal melting and associated buoyancy gain rates largely decrease with increased resolution, while buoyancy loss associated with coastal polynyas are less sensible to resolution as surface fluxes are estimated from sea ice concentration observations. These results highlight the importance of high resolution to accurately simulate AABW formation, where mixing processes occurring below ice shelf cavities play an important role in WMT.& &
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.& &
Publisher: Copernicus GmbH
Date: 26-01-2022
Abstract: Abstract. The Regional Ocean Modeling System (ROMS), including an ice shelf component, has been applied on a circum-Antarctic domain to derive estimates of ice shelf basal melting. Significant improvements made compared to previous models of this scale are the inclusion of tides and a horizontal spatial resolution of 2 km, which is sufficient to resolve on-shelf heat transport by bathymetric troughs and eddy-scale circulation. We run the model with ocean–atmosphere–sea ice conditions from the year 2007 to represent nominal present-day climate. We force the ocean surface with buoyancy fluxes derived from sea ice concentration observations and wind stress from ERA-Interim atmospheric reanalysis. Boundary conditions are derived from the ECCO2 ocean state estimate tides are incorporated as sea surface height and barotropic currents at the open boundary. We evaluate model results using satellite-derived estimates of ice shelf melting and established compilations of ocean hydrography. The Whole Antarctic Ocean Model (WAOM v1.0) qualitatively captures the broad scale difference between warm and cold regimes as well as many of the known characteristics of regional ice–ocean interaction. We identify a cold bias for some warm-water ice shelves and a lack of high-salinity shelf water (HSSW) formation. We conclude that further calibration and development of our approach are justified. At its current state, the model is ideal for addressing specific, process-oriented questions, e.g. related to tide-driven ice shelf melting at large scales.
Publisher: Springer Science and Business Media LLC
Date: 19-12-2016
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.
Publisher: Copernicus GmbH
Date: 17-06-2020
DOI: 10.5194/GMD-2020-164
Abstract: Abstract. The Regional Ocean Modeling System (ROMS), including an ice shelf component, has been applied on a circum-Antarctic domain to derive estimates of ice shelf basal melting. Significant improvements made compared to previous models of this scale are the inclusion of tides and a horizontal spatial resolution of 2 km, which is sufficient to resolve onshelf heat transport by bathymetric troughs and eddy scale circulation. We run the model with ocean-atmosphere-sea ice conditions from the year 2007, to represent nominal present day climate. We force the ocean surface with buoyancy fluxes derived from sea ice concentration observations and wind stress from ERA-Interim atmospheric reanalysis. At the northern boundaries ocean conditions are derived from the ECCO2 reanalysis and tides are incorporated as sea surface height and barotropic currents. The accuracy of tidal height signals close to the coast is comparable to those simulated from widely-used barotropic tide models, while off-shelf hydrography agrees well with the Southern Ocean State Estimate (SOSE) model. On the shelf, most details of ice shelf-ocean interaction are consistent with results from regional modelling and observational studies, although a paucity of observational data (particularly taken during 2007) prohibits a full verification. We conclude that our improved model is well suited to derive a new estimate of present day Antarctic ice shelf melting at high resolution and is able to quantify its sensitivity to tides.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-15622
Abstract: Understanding the processes involved in basal melting of Antarctic ice shelves is important to quantify the rate at which Antarctica will lose mass. Current research of ice shelf-ocean interaction highlights deep warm water intrusions and melting along narrow grounding lines. The majority of the ice, however, lies in much shallower waters. Here we analyse the vertical structure of previously published Antarctic-wide estimates of ice shelf basal melting derived from satellites and ice shelf buttressing derived from ice sheet flow modelling. The results show that ice shelf regions with a draft shallower than 500 m account for more than 60 % of the total basal mass loss and more than 30 % of the total buttressing flux response. The oceanic processes that drive melting in shallow regions might be very different compared to the ones at depth and how well these are represented in large-scale models of Antarctic ice shelf-ocean interaction is not clear. This gap should be addressed for more accurate predictions of the Antarctic response to climate change.&
Location: Germany
No related grants have been discovered for Ole Richter.