Deglacial regional and global benthic δ13C stacks

Abstract:

Deglacial ventilation of respired carbon represents an important feedback in the climate system that impacts the carbon cycle, global temperatures, sea level, etc. Physical, chemical, and biological processes in the ocean change in step with glacial-interglacial cycles, influencing atmospheric pCO2 and benthic δ¹³C primarily through deep ocean carbon storage and ocean circulation changes. Therefore, reconstructing deglacial changes in benthic δ¹³C can improve estimates of changes in deep ocean carbon storage and the global carbon cycle.

One metric of interest is the deglacial mean δ¹³C change of the ocean, which provides an estimate of changes in terrestrial biosphere carbon storage. Here we estimate the mean change in ocean δ¹³C in 1-kyr time steps across the deglaciation by averaging seven regional δ¹³C stacks weighted by volume. Our regional δ¹³C stacks are composed of 116 benthic δ¹³C records that span 20-6 ka on regional age models (Stern and Lisiecki, 2014). We calculate regional δ¹³C stacks for the intermediate North Atlantic (INA) (0.5-2 km), mid-depth North Atlantic (MNA) (2-4 km), deep North Atlantic (>4 km), intermediate South Atlantic (0.5-2.5 km), deep South Atlantic (DSA) (>2.5 km), intermediate Indo-Pacific (0.5-2 km), and deep Indo-Pacific (>2 km).

We also use these regional stacks to perform mixing experiments that simulate MNA δ¹³C responses to different mixtures of the INA and DSA endmembers. Simulated INA, DSA, and MNA δ¹³C records are then analyzed with principal component analysis to determine which mixing scenario best fits the MNA δ¹³C observations. We conclude that the δ¹³C data are most consistent with a millennial-scale reduction in percent North Atlantic Deep Water (NADW) at 2-4 km in the North Atlantic during Heinrich Stadial 1.