Ice sheet-ocean interactions in northeast Greenland: the role of ocean warming on ice stream stability

Overview

Over the last 15 years many of the major outlet glaciers of the Greenland Ice Sheet (GIS) have undergone a period of acceleration, thinning and retreat (Straneo and Heimbach, 2013). Changes in the flux of ice from the GIS to the ocean have important implications for sea-level change with recent research suggesting that the GIS is currently contributing to global sea-level rise (Pritchard et al. 2009). The presence of relatively warm Atlantic Water (AW) around the margins of the ice sheet and the penetration of this warm water into many Greenland fjords, as well as increased air temperatures and sea-ice loss have all been linked to rapid ice margin instability. However, the relatively short time series of direct observations make it difficult to fully understand the interaction between the ice sheet and ocean. This project seeks to address this by investigating the longer term interaction between the ocean and the northeast Greenland ice stream (NEGIS) using geochemical and stable isotope techniques.
NEGIS is important because it controls ice flux into the NE Atlantic (the circulation of which is sensitive to freshwater input) and it holds a potential sea-level equivalent of ~ 1.4 m. Recent studies have predicted that this sector of the ice sheet is vulnerable to future climatic change (Khan et al., 2014). It is also known to have undergone dramatic retreat during the Holocene Thermal Maximum (a period of increased air temperatures analogous to that predicted for 2100). In order to assess the longer term links between NEGIS and the ocean a series of sediment cores will be analysed covering the period immediately after the ice stream retreated across the continental shelf through to recent changes of the last few decades.
The PhD student will investigate the decadal to millennial history of meltwater, sediment and ice flux to the ocean using a series of geochemical and stable isotope techniques. These will include development and application of foraminiferal faunal analysis, Mg/Ca ratios and stable oxygen and carbon isotopes from planktic and benthic foraminifera.

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Image Captions

RV Polarstern collecting data from close to the Northeast Greenland Ice Stream, August 2016

Methodology

The student will work on a series of sediment cores collected during recent cruises to the NE Greenland margin. These cruises form part of a major NERC project (Greenland in a Warmer Climate) in collaboration with the Alfred Wegener Institute in Germany.
• Selection and sampling of gravity cores and box cores collected in 2016 and 2017.
• Processing and picking of planktic and benthic foraminifera.
• Processing and analysing foraminiferal Mg/Ca.
• Measurement of stable oxygen and carbon isotopes from foraminifera.
Mg/Ca measurements from foraminifera will provide quantitative estimates of surface and sub-surface water temperature (identifying changes in Atlantic Water flux to the Greenland margin). Oxygen and carbon stable isotope analyses will be used to investigate the variability in meltwater flux to the surface ocean and sea ice concentration (planktic foraminifera) and changes in sub-surface Atlantic Water flow to the ice margin (benthic foraminifera). Benthic foraminifera fauna will also provide information on water mass characteristics/environmental conditions more generally.

Project Timeline

Year 1

Background reading followed by selection of suitable cores for detailed analysis. Faculty training programme. Initial laboratory work in Durham to identify relative abundance of planktic and benthic foraminifera through cores to be analysed. Initial work developing Mg/Ca technique from new area in northeast Greenland. Visit to British Geological Survey (BGS) for laboratory work and to receive training in stable isotope techniques.

Year 2

Laboratory analyses: preparation and analysis of foraminiferal samples; visit BGS to analyse samples for planktic and benthic oxygen and carbon isotope signature; measurement of Mg/Ca for planktic and benthic foraminifera. Initial data analysis – assessment of geochemical and faunal techniques for palaeoenvironemtnal reconstruction. Preparation of preliminary review chapters. Present initial results at national postgraduate conference

Year 3

Completion of laboratory work. Data analysis and interpretation – investigating changes in glacial sediment and meltwater flux, and variability in Atlantic inflow. Preparation of major data and interpretation chapters of thesis.

Year 3.5

Preparation and completion of final thesis chapters. Submission of papers for publication. Presentation of research at international conference

Training
& Skills

The student will receive training in marine data collection techniques and in sediment core description. In the laboratory the student will receive training in foraminiferal preparation and identification and Mg/Ca sample preparation and measurement. The student will be primarily based at Durham University, though will also work with Prof Melanie Leng at the British Geological Survey and will receive training in oxygen and carbon isotope laboratory techniques during visits to BGS.
The student will be a member of the Ice Sheets and Sea Level Research Cluster in Geography (https://www.dur.ac.uk/geography/icesheetsandsealevel/). The student will also have the opportunity provided by a broad range of skills training provided in-house at Durham (e.g. thesis and paper writing, presentation skills etc.) and from the range of environmental science training provided as part of the IAPETUS Doctoral Training Partnership framework. As part of a broader research project the student will also have the opportunity to develop a network of national and international collaborators in the general study area.

References & further reading

Khan, S. et al. 2014. Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming. Nature Climate Change 4, 292-299.
Larsen, N. et al. 2018. Instability of the northeast Greenland Ice Stream over the last 45,000 years. Nature Communications 9, 1872. DOI: 10.1038/s41467-018-04312-7.
Pritchard, H., Arthern, R., Vaughan, D., Edwards, L. 2009. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets. Nature 461, 971-975.
Straneo, F., Heimbach, P. 2013. North Atlantic warming and the retreat of Greenland’s outlet glaciers. Nature 504, 36-43.

Further Information

Dr Jerry Lloyd, j.m.lloyd@durham.ac.uk
Tel: +44 (0)191 3341874

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