Investigating past changes in Greenland melting and its impacts on ocean circulation as a key to the future.

Overview

The transformation of warm and salty surface waters in the North Atlantic into cold and dense deep waters, plays a key role in regional and global climate change. This process, referred to as the Atlantic Meridional Overturning Circulation (AMOC), is crucial for the re-distribution of heat, nutrients and gasses across the globe. For example, in the North Atlantic it contributes towards the northward transport of heat to higher latitudes, which helps maintain the relatively mild climate in NW Europe. This overturning is projected to weaken in the 21st century as a response to increased meltwater from polar regions and warming of the surface waters due to the increasing atmospheric CO2 levels [IPCC, 2019].

Over the last 60 years, melting of Greenland and Arctic ice has increased the flux of freshwater reaching the North Atlantic [Bamber et al., 2018]. Yet, the limited temporal span of oceanographic data (70 years) means that there are still large uncertainties surrounding the future AMOC’s sensitivity to freshwater forcing. The East Greenland Current is a key ocean current that acts as the main conduit of Arctic freshwater and sea-ice southward to the subpolar North Atlantic [Agaard and Carmack 1989] and can weaken the formation of deepwaters in the Labrador Sea with knock on consequences for the strength of the AMOC [Yang et al., 2016].
The aim of this PhD project is to address this crucial gap in the our knowledge by extending ocean measurements of the properties of the East Greenland Current System and its effects on deepwater formation across the current interglacial, the Holocene. To do this, exceptional sedimentary and biological archives will be used including marine sediment cores located along the East Greenland Coast [e.g. Dyke et al., 2017, Perner et al., 2015] and in the Eastern Labrador Sea [Moffa-Sanchez et al., 2014 and 2015, Moffa-Sanchez and Hall 2017], and shallow water calcifying algae collected from the Greenland continental shelf [e.g. Kamenos et al., 2012]. The cores from the East Greenland margin and the coralline algae will enable the reconstruction of meltwater run-off and iceberg fluxes in the EGC. The Eastern Labrador Sea core will be used to reconstruct surface and deep Subpolar North Atlantic responses to the freshwater input across the Holocene. This project will benefit from close collaboration with project partner Dr Camilla Andresen based at the Geological Survey of Denmark and Greenland (GEUS).

Methodology

The student will use a suite of sedimentary, chemical and biological proxies on marine sediment cores and coralline algae. Proxies such as trace metal (e.g. Mg/Ca) and stable isotope chemistry in foraminiferal calcite alongside foraminiferal assemblage counts will be used to reconstruct ocean conditions such as temperature and salinity. Chemical analysis of coralline chemistry will enable reconstruction of meltwater run-off from Greenland glaciers. Ice rafted debris composition and counts will give an indication of provenance and amount of land ice reaching the ocean. Bottom flow speed records of sortable silt mean grain size will be used to reconstruct the strength of the densest deep AMOC branch.

Project Timeline

Year 1

Review of existing literature relating to the AMOC and its response to freshwater forcing and the North Atlantic climate. Laboratory training for the sampling and processing of marine sediment cores for grain size analysis and training in the identification of foraminifera.

Year 2

Preparation and analysis of inorganic chemistry in foraminifera and calcifying algae including oxygen isotopes, and trace metals with particular focus on Mg/Ca in the foraminifera. Data analysis and interpretation of the datasets. Presentation of the results at national meetings/workshops and the European Geophysical Union Meeting (Vienna, April 2024). Production of paper 1

Year 3

Continued data analysis and interpretation. Production of paper II. Presentation of the results at eitherthe 15th International Conference in Paleoceanography (TBD, September 2025)

Year 3.5

Timeline – Year 3.5 (6 months only). Production of paper III. Writing and submission of thesis.

Training
& Skills

This project will provide the student with a wide range of skills in paleoceanographic reconstructions using geochemical, micropaleontological and physical proxies from different ocean archives such as marine sediment cores and coralline algae. The student will be trained in micropaleontological indentification, and geochemical analysis of marine sediments in the state-of-the-art laboratories of the Geography Department at Durham University. Training in coralline algae analysis will be provided during visits to Glasgow University (partner IAPETUS2 institution). Additional training will be provided through visits to NERC radiocarbon and stable isotope facilities, including training on core chronology development using different mathematical approaches.
The student will also benefit from close collaboration with the Marine Geology group of GEUS (Project Partner Andresen) and the project will involve an extended visit to Copenhagen to samples cores stored there and receive training in sediment core analysis. Participation on a research cruise will also be sought through project partners/collaborators and opportunities for data and climate model integration may be pursued.

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/). 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 IAPETUS Doctoral Training Partnership framework.

Through project collaborators/supervisors 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

-Aagaard, K., & Carmack, E. C. (1989). The role of sea ice and other fresh water in the Arctic circulation. Journal of Geophysical Research, 94(C10), 14,485– 14,498.
-Bamber, Tedstone, King, Howat, Enderlin, van den Broeke, and Noel (2018), Land Ice Freshwater Budget of the Arctic and North Atlantic Oceans: 1. Data, Methods, and Results, 123(3), 1827-1837.
-Dyke, L. M., Andresen, C. S., Seidenkrantz, M.-S., Hughes, A. L. C., Hiemstra, J. F., Murray, T., Bjørk, A. A., Sutherland, D. A., Vermassen, F. 2017. Minimal Holocene retreat of large tidewater glaciers in Køge Bugt, southeast Greenland. Scientific Reports 7(12330): 1–10.
-IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.
Kamenos, N. A., Hoey, T. B., Nienow, P., Fallick, A. E., & Claverie, T. (2012). Reconstructing Greenland ice sheet runoff using coralline algae. Geology, 40(12), 1095-1098.
-Moffa-Sanchez, Hall, Thornalley, Barker, and Stewart (2015), Changes in the strength of the Nordic Seas Overflows over the past 3000 years, Quaternary Science Reviews, 123, 134-143.
-Moffa-Sánchez, P., Hall, I.R. North Atlantic variability and its links to European climate over the last 3000 years. Nat Commun 8, 1726 (2017).
-Moffa-Sánchez, Hall, Barker, Thornalley, and Yashayaev (2014), Surface changes in the eastern Labrador Sea around the onset of the Little Ice Age, 29(3), 160-175.
-Perner, K., Moros, M., Lloyd, J.M., Jansen, E., Stein, R. 2015. Mid to Late Holocene strengthening of the East Greenland Current paralleled by increased Atlantic Intermediate Water outflow from the Arctic Ocean. Quaternary Science Reviews 129, 296-307
-Yang, Q., Dixon, T., Myers, P. et al. Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation. Nat Commun 7, 10525 (2016).

Further Information

For more information please contact paola.l.moffa-sanchez@durham.ac.uk

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