Timing and impact of variable Arctic outflow on the Atlantic Meridional Overturning Circulation

The North Atlantic Deep Water (NADW) constitutes the major deep oceanic current of the Atlantic Overturning Meridional Circulation (AMOC), distributing heat throughout the globe and affecting nutrients distribution sustaining marine ecosystems and human fishing grounds, whilst variations in its intensity have been linked to changes in productivity, current strength, regional and global climate throughout the Cenozoic. The NADW is a mixture of deep currents originating from the Labrador Sea and the Arctic Ocean. Contribution from the latter component to NADW is largely influenced by the depth of the two gateways connecting the Nordic Sea to the North Atlantic basins on either side of Iceland. These gateways are shallower than 1500 m and the volume of Arctic overflow will vary directly in response to changes in the relative depth of the passages. Lower sea level during glaciations and periodic increased mantle activity under Iceland, effectively raising land and seafloor, will directly constrain the influx of cold and dense Arctic Water, weakening the NADW and overall AMOC on geological time scales.

This project will exploit the capacity of ferromanganese crusts to record the signature of oceanic currents in their stratigraphy to track past changes in the strength, source, and provenance of the NADW components. Using samples from two key localities in the North Atlantic, high-resolution isotope records will be produced to investigate how the NADW varied over the last 20-30 Ma in response to glaciations and mantle pulses. These records will be dated using a new method for time calibration based on astronomical parameters and their influence on the chemical signature of these samples. The information gained will be used to inform future climate models predicting the response of this major oceanic current to disturbances.