Southern Ocean pH Reconstructions over the Last Glacial Gycle and Implications for the Mechanism of Glacial CO2 Drawdown
Abstract
The rise and fall of atmospheric CO2 in pace with glacial-interglacial cycles over the past 800,000 years is thought to be largely linked to changes in deep ocean carbon storage. As the region which ventilates the majority of the global deep ocean today, the Southern Ocean has been invoked to play an important role in modulating this exchange, through changes in sea-ice cover, biological productivity, or ocean-atmosphere circulation. To date however, no records exist that uniquely trace the evolution of surface water CO2 over glacial cycles. Here, we present a sea-surface pH record over the last glacial cycle from the Weddell Sea - an important region for the production of Antarctic Bottom Water. We find that the onset of glacial conditions is associated with a pronounced increase in surface ocean pH, indicating a drop in surface water CO2. This pH shift occurs in tandem with the initial decrease in atmospheric CO2 and is consistent with the reduced ventilation of carbon-rich deep waters, signalling that circulation changes in this region played an important role early in the transition to a glacial state. We present a new model of glacial circulation based on our findings, where water mass reconfiguration increases biological pump efficiency in the Southern Ocean and carbon storage at deep to mid-depths in the ocean basins, promoting drawdown of atmospheric CO2.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP028..04C
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0429 Climate dynamics;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4273 Physical and biogeochemical interactions;
- OCEANOGRAPHY: GENERAL