Reconstructing surface water carbonate ion concentration changes in the Eastern Equatorial Pacific over the past 25 kyr using δ13C and B/Ca in planktic foraminifera
Abstract
Although the eastern equatorial Pacific (EEP) is a source of CO2 to the atmosphere today, it is unknown how this may have varied in the past. This project is part of a larger goal to determine whether increased biological productivity stimulated by dust fertilization caused the EEP to switch and become a sink for atmospheric CO2 during Heinrich Event 1, as suggested by a recent study based on boron isotopes (Martínez-Botí et. al., 2015). We measured B/Ca ratios in the non-symbiotic planktic foraminifera Globigerina bulloides from core MV1014-17JC (00º10.83'S, 85º52.00'W; 2846 m water depth) as a proxy for changes in seawater carbonate ion concentration ([CO32-]) in the EEP over the last 25,000 years. In addition, we measured δ13C in the symbiotic planktic foraminifera Globigerinoides ruber and Trilobatus sacculifer because surface water [CO32-] affects the δ13C value of each species differently, allowing for the calculation of downcore Δ[CO32-] (Spero et al., 1999). Our B/Ca record suggests the Holocene had similar [CO32-] to the modern, with minimal variability across the deglaciation. During the LGM, B/Ca data suggest [CO32-] was 50 µmol/mol below modern values. In contrast, our calculated Δ[CO32-] record based on differences in δ13C values suggests the first part of the LGM (between 25 and 22 kyr) and the mid-deglaciation had higher than modern [CO32-]. Because G. bulloides prefer cooler, upwelling waters nearer the thermocline, while G. ruber and T. sacculifer prefer warmer waters in the upper mixed-layer, differences in depth habitat is a possible explanation for offsets between the two [CO32-] reconstructions. Nevertheless, both methods confine changes surface water [CO32-] in the EEP to less than 50 μmol/mol over the last 25 kyr.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP21D1633W
- Keywords:
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- 0419 Biomineralization;
- BIOGEOSCIENCES;
- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4994 Instruments and techniques;
- PALEOCEANOGRAPHY