Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 49, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2107034118
Keywords
South Atlantic; deep water redox; last glacial; trace metal accumulation; carbon cycle
Categories
Funding
- Deutsche Forschungsgemeinschaft
- Emmy Noether Research Group ICONOX (Iron cycling in continental margin sediments and the nutrient and oxygen balance of the ocean) at GEOMAR
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Sedimentary records from the last glacial period in the eastern South Atlantic show evidence of continuous bottom water anoxia, leading to increased carbon burial. Geochemical data suggest that increased productivity and slowed deep water circulation were the main drivers of anoxic conditions in deep waters.
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 Atlantic shifted far seaward during the last glacial period and only slowly retreated during deglaciation times. While increased productivity during the last ice age may have contributed to oxygen depletion in bottom waters, especially on the upper slope, slow-down of the Late Quaternary deep water circulation pattern [Rutberg et al., Nature 405, 935-938 (2000)] appears to be the ultimate driver of anoxic conditions in deep waters.
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