Niels Munksgaard

Data Descriptor: Daily observations of stable isotope ratios of rainfall in the tropics

Publisher: Springer Science and Business Media LLC

Date: 08-10-2019

DOI: 10.1038/S41598-019-50973-9

Targeting both BDNF/TrkB pathway and delta-secretase for treating Alzheimer's disease

Publisher: Elsevier BV

Date: 10-2021

DOI: 10.1016/J.NEUROPHARM.2021.108737

Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

Publisher: Proceedings of the National Academy of Sciences

Date: 11-02-2020

DOI: 10.1073/PNAS.1902469117

Abstract: The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) (129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (∼2 m), ocean thermal expansion, and melting mountain glaciers (∼1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic meridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and environmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is underlain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet modeling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further lify warming.

Seasonal Shift From Biogenic to Geogenic Fluvial Carbon Caused by Changing Water Sources in the Wet‐Dry Tropics

Publisher: American Geophysical Union (AGU)

Date: 02-2020

DOI: 10.1029/2019JG005384

Automated calibration of laser spectrometer measurements of δ¹⁸O and δ²H values in water vapour using a Dew Point Generator

Publisher: Wiley

Date: 14-05-2018

DOI: 10.1002/RCM.8131

Abstract: Continuous measurement of stable O and H isotope compositions in water vapour requires automated calibration for remote field deployments. We developed a new low-cost device for calibration of both water vapour mole fraction and isotope composition. We coupled a commercially available dew point generator (DPG) to a laser spectrometer and developed hardware for water and air handling along with software for automated operation and data processing. We characterised isotopic fractionation in the DPG, conducted a field test and assessed the influence of critical parameters on the performance of the device. An analysis time of 1 hour was sufficient to achieve memory-free analysis of two water vapour standards and the δ The automated calibration system provides high accuracy and precision and is a robust, cost-effective option for long-term field measurements of water vapour isotopes. The necessary modifications to the DPG are minor and easily reversible.

Coupled Polymer-Membrane Equilibration and Cavity Ring-down Spectrometry for the Highly Sensitive Determination of Dissolved Methane in Environmental Waters

Publisher: Informa UK Limited

Date: 20-05-2020

DOI: 10.1080/00032719.2020.1767122

Partitioning of Microbially Respired CO₂ Between Indigenous and Exogenous Carbon Sources During Biochar Degradation Using Radiocarbon and Stable Carbon Isotopes

Publisher: Cambridge University Press (CUP)

Date: 05-11-2018

DOI: 10.1017/RDC.2018.128

Southern Ocean carbon sink enhanced by sea-ice feedbacks at the Antarctic Cold Reversal

Publisher: Springer Science and Business Media LLC

Date: 22-06-2020

DOI: 10.1038/S41561-020-0587-0

Coupled rainfall and water vapour stable isotope time series reveal tropical atmospheric processes on multiple timescales

Publisher: Wiley

Date: 12-09-2019

DOI: 10.1002/HYP.13576

Do ²H and ¹⁸O in leaf water reflect environmental drivers differently?

Publisher: Wiley

Date: 12-04-2022

DOI: 10.1111/NPH.18113

Abstract: We compiled hydrogen and oxygen stable isotope compositions (δ 2 H and δ 18 O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ 2 H was more closely correlated with δ 2 H of xylem water or atmospheric vapour, whereas leaf water δ 18 O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ 2 H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ 18 O. We next expressed leaf water as isotopic enrichment above xylem water (Δ 2 H and Δ 18 O) to remove the impact of xylem water isotopic variation. For Δ 2 H, leaf water still correlated with atmospheric vapour, whereas Δ 18 O showed no such correlation. This was explained by covariance between air relative humidity and the Δ 18 O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2 H and 18 O in leaf water do indeed reflect the balance of environmental drivers differently our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.

One year of spectroscopic high-frequency measurements of atmospheric CO2, CH4, H2O and δ13C-CO2 at an Australian Savanna site

Publisher: Wiley

Date: 05-10-2022

DOI: 10.1002/GDJ3.180

Abstract: We provide a 1‐year dataset of atmospheric surface CO 2 , CH 4 and H 2 O concentrations and δ 13 C‐CO 2 values from an Australian savanna site. These semi‐arid ecosystems act as carbon sinks in wet years but the persistence of the sink in dry years is uncertain. The dataset can be used to constrain uncertainties in modelling of greenhouse gas budgets, improve algorithms for satellite measurements and characterize the role of vegetation and soil in modulating atmospheric CO 2 concentrations. We found pronounced seasonal variations in daily mean CO 2 concentrations with an increase (by 5–7 ppmv) after the first rainfall of the wet season in early December with peak concentrations maintained until late January. The CO 2 increase reflected the initiation of rapid microbial respiration from soil and vegetation sources upon initial wetting. As the wet season progressed, daily CO 2 concentrations were variable, but generally decreased back to dry season levels as CO 2 assimilation by photosynthesis increased. Mean daily concentrations of CH 4 increased in the wet season by up to 0.2 ppmv relative to dry season levels as the soil profile became waterlogged after heavy rainfall events. During the dry season there was regular cycling between maximum CO 2 /minimum δ 13 C‐CO 2 at night and minimum CO 2 /maximum δ 13 C‐CO 2 during the day. In the wet season diel patterns were less regular in response to variable cloud cover and rainfall. CO 2 isotope data showed that in the wet season, surface CO 2 was predominantly a two‐component mixture influenced by C 3 plant assimilation (day) and soil lant respiration (night), while regional background air from higher altitudes represented an additional CO 2 source in the dry season. Higher wind speeds during the dry season increased vertical mixing compared to the wet season. In addition, night‐time advection of high‐altitude air during low temperature conditions also promoted mixing in the dry season.

Revisiting Michael Bonell's work on humid tropical rainforest catchments: Isotope tracers reveal seasonal shifts in catchment hydrology

Publisher: Wiley

Date: 10-2022

DOI: 10.1002/HYP.14722

Abstract: It has been almost 50 years since the foundational work at the Babinda catchments in North Queensland kickstarted the field of tropical hydrology globally. To expand upon this work and build a more generalized hydrological understanding of steep rainforest catchments, we studied the seasonal evolution of hydrological response from two catchments with broadly similar characteristics to the Babinda catchments. Both hydrometric and water stable isotope data were collected at relatively high frequencies during one wet season (Thompson Creek) and a 3‐year period (Atika Creek). The longer dataset spans a wide range of environmental conditions experienced in the humid tropics, including events that cover the wetting‐up transitional period of the wet season and tropical cyclones (TC). Both catchments displayed a fast streamflow response to rainfall with the shallow upper soil profile responding quickly to rainfall at Atika Creek. New findings from this study include the importance of pre‐event water ( % using the two component hydrograph separation technique) for overall event flows, especially when the catchment was wet. Rainfall, surface runoff and groundwater isotope and specific electrical conductivity (SEC) compositions varied between rainfall events with the most complex bivariate mixing plots observed for multi‐peak events that occurred at the start of the wet season and after a dry period within the wet season. Two‐tracer, 3 component hydrograph separations did not provide satisfactory results in identifying source water contributions to streamflow. These results highlighted the time‐variant and non‐conservative behaviour of the rainfall, surface runoff and shallow groundwater source waters over the seasonal timescale, with soil water being an important unidentified source contributor. Our findings highlight the need for high frequency multi‐source s ling to accurately interpret catchment behaviour and the importance of soil water contributions to streamflow. We propose a framework to describe the seasonal evolution of streamflow response in steep tropical rainforest catchments experiencing seasonal rainfall activity.

Ghent University

Location: Belgium

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Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0560940

Start Date: 05-2005

End Date: 06-2006

Amount: $229,326.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP110100691

Start Date: 2011

End Date: 12-2015

Amount: $260,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0455703

Start Date: 04-2005

End Date: 12-2009

Amount: $70,668.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0669439

Start Date: 03-2007

End Date: 12-2010

Amount: $195,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0455496

Start Date: 2004

End Date: 07-2005

Amount: $70,668.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP120200110

Start Date: 07-2012

End Date: 12-2015

Amount: $252,000.00

Funder: Australian Research Council