| Summary: | 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. © 2021. American Geophysical Union. Issue Online: 30 August 2021; Version of Record online: 30 August 2021; Accepted manuscript online: 17 August 2021; Manuscript accepted: 09 August 2021; Manuscript revised: 23 June 2021; Manuscript received: 18 January 2021. 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. ...
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