The evolution of deep ocean chemistry and respired carbon in the Eastern Equatorial Pacific over the last deglaciation
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It has been shown that the deep Eastern Equatorial Pacific (EEP) region was poorly ventilated during the Last Glacial Maximum (LGM) relative to Holocene values. This finding suggests a more efficient biological pump, which indirectly supports the idea of increased carbon storage in the deep ocean contributing to lower atmospheric CO2 during the last glacial. However, proxies related to respired carbon are needed in order to directly test this proposition. Here we present Cibicides wuellerstorfi B/Ca ratios from Ocean Drilling Program Site 1240 measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) as a proxy for deep water carbonate saturation state (Δ[CO32−], and therefore [CO32−]), along with δ13C measurements. In addition, the U/Ca ratio in foraminiferal coatings has been analyzed as an indicator of oxygenation changes. Our results show lower [CO32−], δ13C, and [O2] values during the LGM, which would be consistent with higher respired carbon levels in the deep EEP driven, at least in part, by reduced deep water ventilation. However, the difference between LGM and Holocene [CO32−] observed at our site is relatively small, in accordance with other records from across the Pacific, suggesting that a “counteracting” mechanism, such as seafloor carbonate dissolution, also played a role. If so, this mechanism would have increased average ocean alkalinity, allowing even more atmospheric CO2 to be “sequestered” by the ocean. Therefore, the deep Pacific Ocean very likely stored a significant amount of atmospheric CO2 during the LGM, specifically due to a more efficient biological carbon pump and also an increase in average ocean alkalinity.
de la Fuente , M , Calvo , E , Skinner , L , Pelejero , C , Evans , D , Müller , W , Povea , P & Cacho , I 2017 , ' The evolution of deep ocean chemistry and respired carbon in the Eastern Equatorial Pacific over the last deglaciation ' , Paleoceanography and Paleoclimatology , vol. 32 , no. 12 , pp. 1371-1385 . https://doi.org/10.1002/2017PA003155
Paleoceanography and Paleoclimatology
© 2017. American Geophysical Union. All Rights Reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1002/2017PA003155
DescriptionThe authors acknowledge funding by the Spanish Ministry of Economy, Industry and Competitiveness through grants CTM2009-08849 (ACDC Project) and CTM2012-32017 (MANIFEST Project), by Generalitat de Catalunya through grant 2014SGR1029 (Marine Biogeochemistry and Global Change research group), and by NERC grant NE/L006421/1. Isabel Cacho thanks the ICREA Academia program from the Generalitat de Catalunya.
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