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Trace metal evidence for deglacial ventilation of the abyssal Pacific and Southern Oceans (2021)

Pavia, Frank ; Wang, Shouyi ; Middleton, Jennifer L. ; [et al.]

American Geophysical Union

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Publication Date: 2022-10-19

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 36(9), (2021): e2021PA004226, https://doi.org/10.1029/2021PA004226.

Description: The deep ocean has long been recognized as the reservoir that stores the carbon dioxide (CO2) removed from the atmosphere during Pleistocene glacial periods. The removal of glacial atmospheric CO2 into the ocean is likely modulated by an increase in the degree of utilization of macronutrients at the sea surface and enhanced storage of respired CO2 in the deep ocean, known as enhanced efficiency of the biological pump. Enhanced biological pump efficiency during glacial periods is most easily documented in the deep ocean using proxies for oxygen concentrations, which are directly linked to respiratory CO2 levels. We document the enhanced storage of respired CO2 during the Last Glacial Maximum (LGM) in the Pacific Southern Ocean and deepest Equatorial Pacific using records of deglacial authigenic manganese, which form as relict peaks during increases in bottom water oxygen (BWO) concentration. These peaks are found at depths and regions where other oxygenation histories have been ambiguous, due to diagenetic alteration of authigenic uranium, another proxy for BWO. Our results require that the entirety of the abyssal Pacific below approximately 1,000 m was enriched in respired CO2 and depleted in oxygen during the LGM. The presence of authigenic Mn enrichment in the deep Equatorial Pacific for each of the last five deglaciations suggests that the storage of respired CO2 in the deep ocean is a ubiquitous feature of late-Pleistocene ice ages.

Description: This work was performed with support from the National Science Foundation (NSF) over about 30 years. The TT013 and NBP9802 cores were collected during the U.S. JGOFS program. Their collection and analyses were supported by NSF OCE-9022301 and OPP-95303398 to R. F. Anderson, and NSF OCE 9301097 to R. W. Murray. Coring and radiocarbon analyses on NBP1702 were funded by NSF OPP-1542962. XRF analysis on NBP9802 and NBP1702 cores, as well as additional radiocarbon measurements, was funded by an LDEO Climate Center Grant to F. J. Pavia.

Description: 2022-02-17

Keywords: Manganese ; Southern Ocean ; Pacific Ocean ; Respired carbon ; Bottom water oxygen ; Deglaciations

Repository Name: Woods Hole Open Access Server

Type: Article

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Comparing glacial and Holocene opal fluxes in the Pacific sector of the Southern Ocean (2010)

Bradtmiller, Louisa I. ; Anderson, Robert F. ; Fleisher, Martin Q. ; [et al.]

American Geophysical Union

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Publication Date: 2022-05-26

Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 24 (2009): PA2214, doi:10.1029/2008PA001693.

Description: The silicic acid leakage hypothesis (SALH) predicts that during glacial periods excess silicic acid was transported from the Southern Ocean to lower latitudes, which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric CO2. Downcore records of 230Th-normalized opal (biogenic silica) fluxes from 31 cores in the Pacific sector of the Southern Ocean were used to compare diatom productivity during the last glacial period to that of the Holocene and to examine the evidence for increased glacial Si export to the tropics. Average glacial opal fluxes south of the modern Antarctic Polar Front (APF) were less than during the Holocene, while average glacial opal fluxes north of the APF were greater than during the Holocene. However, the magnitude of the increase north of the APF was not enough to offset decreased fluxes to the south, resulting in a decrease in opal burial in the Pacific sector of the Southern Ocean during the last glacial period, equivalent to approximately 15 Gt opal ka−1. This is consistent with the work of Chase et al. (2003a), and satisfies the primary requirement of the SALH, assuming that the upwelled supply of Si was approximately equivalent during the Holocene and the glacial period. However, previous results from the equatorial oceans are inconsistent with the other predictions of the SALH, namely that either the Corg:CaCO3 ratio or the rate of opal burial should have increased during glacial periods. We compare the magnitudes of changes in the Southern Ocean and the tropics and suggest that Si escaping the glacial Southern Ocean must have had an alternate destination, possibly the continental margins. There is currently insufficient data to test this hypothesis, but the existence of this sink and its potential impact on glacial pCO2 remain interesting topics for future study.

Description: Funding for this research was provided in part by the U.S. NSF (grant OPP02-30268). We thank the core repository at LDEO and the Antarctic Research Facility at FSU for providing samples.

Keywords: Southern Ocean ; Silica cycles ; Paleoceanography