North Atlantic Deep Water Formation during the Deglacial Rise of Atmospheric C02



Glacial-interglacial cycles are the dominant feature of Earth’s climate over the past million years. These cycles were externally driven by orbitally induced changes in incoming solar radiation, but were amplified by feedbacks including: the growth and decay of large northern hemisphere ice sheets, changes in ocean circulation, and deep ocean storage and release of carbon dioxide. Investigating the mechanism(s) by which the Earth transitioned from peak glacial to interglacial conditions is of fundamental importance to understanding the sensitivity of the climate system.

The release to the atmosphere of CO2, previously stored in the deep ocean, was crucial in terminating glacial periods. Leading hypotheses regarding how this process occurred implicate an increase in the ventilation of the deep Southern Ocean. However, two new sets of observations – high-resolution atmospheric CO2 reconstructions and preliminary radiocarbon-based constraints on deep convection in the North Atlantic - draw attention to an additional process that may have played an important role in the deglacial release of CO2. We propose to test the hypothesis that abrupt increases in atmospheric CO2 during the last deglaciation coincided with the resumption of deep convection in the high latitude North Atlantic, building upon theory and modelling results that suggest transient flushing of the glacial Atlantic Ocean with well-ventilated North Atlantic Deep Water can cause a rapid release of oceanic CO2 to the atmosphere. We will achieve this through the production of three high resolution reconstructions of seawater radiocarbon concentration variability in the high latitude North Atlantic.

The proposed work thus aims to further our mechanistic understanding of how changes in ocean circulation can alter the partitioning of carbon between the deep ocean and atmosphere. This proxy dataset will form the basis for future targeted modelling studies. Moreover, in addition to testing the aforementioned hypothesis, the datasets produced will enable a broader investigation into the interplay between ocean circulation, abrupt climate change and the disintegration of high latitude ice-sheets. This work will also help form the basis for the PIs to develop a wider network of high resolution study sites that will greatly improve our understanding of centennial-scale ocean variability during the abrupt climate shifts of the deglacial.