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

Overview

Over the last two decades 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 (Shepard et al. 2020). However, the relatively short time series of direct observations make it difficult to fully understand the interaction between the ice sheet and ocean. A better understanding of the nature and rate of response of the GIS to ocean forcing can be achieved by investigating the interplay between the oceans and the ice sheet over the last few centuries to millennia. This understanding is critical in testing and improving predictive models of future ice sheet response to ongoing ocean changes in the North Atlantic region.

This project seeks to address these issues by investigating the longer term interaction between the ocean and the northeast Greenland ice stream (NEGIS) using sedimentological, microfossil and geochemical 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). Indeed Zachariae Isstrom, one of the ice shelves buttressing NEGIS has started to disintegrate (Mouginot et al., 2015). The larger 79N ice shelf is still thought to be stable, however it is known to have undergone dramatic retreat during the Holocene Thermal Maximum (a period of increased air temperatures analogous to that predicted for 2100) (Larsen et al. 2018). Recent oceanographic observations have also potentially identified an increase in flux of relatively warm Atlantic Water into the cavity beneath the 79N ice shelf (Schaffer at al., 2020). The 79N ice shelf, therefore, has the potential to rapidly disintegrate in the near future with significant impact on ice discharge from NEGIS.

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, as well as changes in ocean forcing (temperature) using a series of sedimentological, geochemical and microfossil techniques.

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Image Captions

RV Polarstern collecting core material from in front of the NEGIS ice shelf (reproduced with permission from J. Lloyd)

Methodology

The student will work on a series of sediment gravity cores, box cores and modern surface samples 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. The student will use a multiproxy approach to examine key sections of selected cores that cover the time intervals of interest (Holocene Thermal Maximum and the last few millennia). Proxies to investigate will include sediment properties (MSCL logging, particle size), microfossils (planktic and benthic foraminifera) and geochemical/isotope foraminiferal composition (Mg/Ca, stable oxygen and carbon isotopes). These will provide information on sediment and meltwater flux from the ice margin and changes in ocean conditions, specifically the flux of Atlantic Water across the continental shelf. A critical aspect of this project will be the development and application of the Mg/Ca technique using planktic and benthic foraminifera. This technique has not previously been applied to the continental shelf of Greenland, but has the potential to provide quantitative estimates of ocean temperature back through time (cf. Moffa-Sanchez et al., 2014). This will provide, for the first time, quantitative estimates of changes in flux of Atlantic Water onto and across the northeast Greenland shelf up to and beneath the fringing ice shelves of NEGIS. In addition the student will develop a robust chronological framework for the cores studied based on 210Pb and 137Cs profiles and radiocarbon dating (14C).

Project Timeline

Year 1

Background reading followed by selection of suitable cores for detailed analysis. Faculty training programme. Initial laboratory work developing Mg/Ca technique based on modern samples from the Greenland margin. Submit samples for dating (through the NERC Radiocarbon Facility) to develop chronological framework for selected cores.

Year 2

Laboratory analyses: collect sedimentological data, preparation and analysis of foraminiferal samples for Mg/Ca and stable isotopes, produce 210Pb and 137Cs profiles to support core chronology. Initial data analysis. Preparation of preliminary review chapters. Present initial results at national postgraduate conference.

Year 3

Completion of laboratory work. Data analysis and interpretation with respect to  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 and analysis. In the laboratory the student will receive training in foraminiferal preparation, Mg/Ca measurements and stable isotope data collection techniques. Specific training in all aspects of work will be delivered at Durham University and Newcastle University with additional training through visits to NERC radiocarbon and stable isotope facilities. The student will also have the opportunity provided by a broad range of skills training provided in-house at Durham through the award-winning Career and Research Development (CAROD) group (thesis writing, writing for publication, presentation skills, enterprise skills etc.) and from the range of environmental science training provided as part of the IAPETUS2 Doctoral Training Partnership framework.

The student will be a member of the Sea Level, Ice and Climate Research Cluster in Geography at Durham (https://www.dur.ac.uk/geography/slic/) and a member of the Past Environments Research Theme at Newcastle. 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. The student will also attend and contribute to the programme of regular departmental seminars and discussion groups as well as National and International conferences to support their general development as a scientist. The student will be encouraged to write scientific papers for publication during their PhD. This will be a major benefit to their career and they will be well supported through this process by the experienced supervisory team

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., Levy, L., Carlson, A., Buizert, C., Olsen, J., Strunk, A., Bjork, A., Skov, D. 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.
Moffa-Sánchez, P., Hall, I., Barker, S., Thornalley, D., Yashayaev, I. 2014. Surface changes in the eastern Labrador Sea around the onset of the Little Ice Age. Paleoceanography 29, 160-175.
Mouginot, J., Rignot, E., Scheuchl, B., Fenty, I., Khazendar, A., Morlighem, M., Buzzi, A., Paden, J. 2015. Fast retreat of Zacharie Isstrom, northeast Greenland. Science 350, 1357-1361. DOI: 10.1126/science.aac7111.
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.
Schaffer, Janin; Kanzow, Torsten; von Appen, Wilken-Jon; von Albedyll, Luisa; Arndt, Jan Erik; Roberts, David H. 2020. Bathymetry constrains ocean heat supply to Greenland’s largest glacier tongue. Nature Geoscience, 13(3), 227-231.
Shepherd, A. & IMBIE Team. 2020. Mass balance of the Greenland Ice Sheet from 1992 to 2018. Nature 579, 233-239.
Straneo, F., Heimbach, P. 2013. North Atlantic warming and the retreat of Greenlandic 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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