Impacts of freshwater forcing on North Atlantic Circulation: Insights from the past

Changes in the strength of the deep-water formation in the North Atlantic, also known as the Atlantic Meridional Overturning Circulation (AMOC), play a key role in regional and global climate. Over the last 60 years melting of Greenland and Arctic ice has increased the flux of freshwater reaching the North Atlantic [Yang et al., 2016]. Controversy remains on whether this continued increase in freshwater fluxes will result in a future collapse or slowdown of the AMOC [Stouffer et al., 2006] although some studies suggest that an AMOC slowdown may already be underway [Thornalley et al., 2018]. Past climate events such as the outbursts of glacial lakes Agassiz and Ojibway around 8.2kyrs ago provide a perfect future analogue to study the North Atlantic’s response to freshwater forcing. This project aims to use unique decadally resolved marine sediment cores from the North Atlantic to reconstruct the response of the surface and deep ocean to the freshwater changes across the 8.2kyr event. In order to achieve this, the student will use a suite of paleoceanographic proxies including sediment chemical composition, foraminiferal geochemistry and ice rafted debris counts, and grain size analysis. 

Key references:

Stouffer, et al. (2006), Investigating the Causes of the Response of the Thermohaline Circulation to Past and Future Climate Changes, 19(8), 1365-1387.

Thornalley, et al. (2018), Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years, Nature, 556(7700), 227-230.

Yang, Dixon, Myers, Bonin, Chambers, van den Broeke, Ribergaard, and Mortensen (2016), Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation, Nature Communications, 7, 10525.