Abstract
There is evidence for greater carbon storage in the glacial deep Pacific, but it is uncertain whether it was caused by changes in ventilation, circulation, and biological productivity. The spatial εNd evolution in the deep Pacific provides information on the deepwater transit time. Seven new foraminiferal εNd records are presented to systematically constrain glacial to interglacial changes in deep Pacific overturning and two different εNd evolution regimes occur spatially in the Pacific with reduced meridional εNd gradients in glacials, suggesting a faster deep Pacific overturning circulation. This implies that greater glacial carbon storage due to sluggish circulation, that is believed to have occurred in the deep Atlantic, did not operate in a similar manner in the Pacific Ocean. Other mechanisms such as increased biological pump efficiency and poor high latitude air-sea exchange could be responsible for increased carbon storage in the glacial Pacific.
Highlights
There is evidence for greater carbon storage in the glacial deep Pacific, but it is uncertain whether it was caused by changes in ventilation, circulation, and biological productivity
Previous studies in the Atlantic Ocean have attributed the enhanced respired carbon storage at the Last Glacial Maximum (LGM) to an increase in the residence time of deep Atlantic waters[4,5], but few studies have focused on the past variability of Pacific deep ocean circulation and the results are still controversial[3,6,7,8,9,10,11]
These proxies are controlled by a combination of high latitude air-sea exchange, biological production, and ocean circulation, and have difficulty in distinguishing whether the increased CO2 storage in the glacial deep Pacific was the result of reduced air-sea exchange in the Southern Ocean or sluggish deepwater circulation
Summary
There is evidence for greater carbon storage in the glacial deep Pacific, but it is uncertain whether it was caused by changes in ventilation, circulation, and biological productivity. The partial dissolution of foraminifera calcite might complicate the reliable reconstruction of foraminifera-based geochemical proxies (such as δ18O, δ13C, Δ14C, Cd/Ca), which otherwise would provide valuable information about the past nutrient and ventilation states of the deep oceans These proxies are controlled by a combination of high latitude air-sea exchange, biological production, and ocean circulation, and have difficulty in distinguishing whether the increased CO2 storage in the glacial deep Pacific was the result of reduced air-sea exchange in the Southern Ocean or sluggish deepwater circulation. The strong linear relationships between seawater Nd isotope compositions and oxygen/ phosphate concentrations in the deep Pacific[12,15] support the dominant role of LCDW advection and the presence of an external (i.e. not from a particular water mass) radiogenic Nd source which is added to the deep ocean in a nearly spatially homogenous way similar to nutrients, but not a link with the biological processes per se[15]. These results will have important implications on how the strength of the overturning circulation is linked to carbon storage in the deep Pacific Ocean over G–I cycles
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