Significance
Climate variations are closely related to changes in ocean circulation, and this has important implications for the availability of oxygen in deep waters and the ocean’s CO2 sequestration capacity. Potentially anoxic conditions have previously been inferred for the deep waters of the Southern Ocean and the Pacific, and low oxygen has been proposed for the North Atlantic deep waters during glacial cycles. Here, we provide clear evidence that fully anoxic conditions occurred in the deep waters of the eastern South Atlantic during the last glacial interval. This is an important finding implying that the Atlantic Ocean circulation was more sluggish during the advanced stage of the last ice age than previously assumed.
Abstract
During the last glacial interval, marine sediments recorded reduced current ventilation within the ocean interior below water depths of approximately >1,500 m [B. A. Hoogakker et al., Nat. Geosci. 8, 40–43 (2015)]. The degree of the associated oxygen depletion in the different ocean basins, however, is still poorly constrained. Here, we present sedimentary records of redox-sensitive metals from the southwest African margin. These records show evidence of continuous bottom water anoxia in the eastern South Atlantic during the last glaciation that led to enhanced carbon burial over a prolonged period of time. Our geochemical data indicate that upwelling-related productivity and the associated oxygen minimum zone in the eastern South...
Read Full Story: https://www.pnas.org/content/118/49/e2107034118
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