Less remineralized carbon in the intermediate depth South Atlantic during Heinrich Stadial 1
Abstract
Matthew Lacerra1, David C. Lund1, Geoffrey Gebbie2, Delia W. Oppo3, Jimin Yu4, Andreas Schmittner5, and Natalie Umling3
The last deglaciation (~20-10 kyr BP) was characterized by a major shift in Earth's climate state, when the global mean surface temperature rose ~4°C and the concentration of atmospheric CO2 increased ~80 ppmv. Model simulations suggest that the initial 30 ppmv rise in atmospheric CO2 may have been driven by reduced efficiency of the biological pump or enhanced upwelling of carbon-rich waters from the abyssal ocean. Here we evaluate these hypotheses using benthic foraminiferal B/Ca (a proxy for deep-water [CO32-]) from a core collected at 1100 m water depth in the Southwest Atlantic. Our results imply that [CO32-] increased by 22 ± 2 μmol/kg early in Heinrich Stadial 1, or a decrease in ΣCO2 of approximately 40 μmol/kg, coeval with the initial rise in atmospheric CO2. Considering evidence that a reduced solubility pump would have been insufficient to drive the observed change in ΣCO2, we believe the most likely explanation is a reduction in remineralized carbon. The data imply that remineralized phosphate declined by approximately 0.3 μmol/kg, equivalent to 40% of the modern remineralized signal at this location. Given little observed change in Cd/Ca at the core site during HS1 (Umling et al., 2009), our results suggest that preformed phosphate increased, perhaps due to greater mixing with a more nutrient-rich water mass (Umling et al., 2019). Because remineralized phosphate at the core site reflects the integrated effect of export production in the sub-Antarctic, our results imply that biological productivity in the Atlantic sector of the Southern Ocean was reduced early in the deglaciation, possibly due to a reduction in iron fertilization, contributing to the initial rise in atmospheric CO2.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP13B1433L
- Keywords:
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- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1630 Impacts of global change;
- GLOBAL CHANGE;
- 1635 Oceans;
- GLOBAL CHANGE;
- 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHY