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

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 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]. The cores from the East Greenland margin 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 exceptional marine sediment cores. 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 past ocean conditions such as temperature and salinity.

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 currents.