Affiliation:
1. Key Laboratory of Marine Geology and Metallogeny First Institute of Oceanography Ministry of Natural Resources Qingdao 266061 China mnr.gov.cn
2. Laboratory for Marine Geology Qingdao National Laboratory for Marine Science and Technology Qingdao 266237 China qnlm.ac
3. State Key Laboratory of Marine Geology Tongji University Shanghai 200092 China tongji.edu.cn
Abstract
Abstract
We present new geochemical evidence of changes in oxygenation of the deep Antarctic Pacific over the last 770 kyr. Our data are derived from redox-sensitive metals and export production proxies extracted from gravity core ANT34/A2-10 at 4217 m water depth. Our results show that oxygen levels in the deep Antarctic Zone (AZ) varied in line with the release of deeply sequestered remineralized carbon to the atmosphere during glacial–interglacial (G–IG) cycles, with lower oxygen concentrations and more carbon storage during glacial periods. Subsequent reductions in the amount of carbon stored at depth were closely associated with improved ventilation during glacial terminations. The systematic and repeated glacial-to-interglacial increases in export production in the AZ region indicate a robust pattern of enhanced Southern Ocean (SO) ventilation during interglacial periods. In addition to the decline in atmospheric CO2 caused by iron fertilization in the Subantarctic AZ (SAZ) during the latter half of the glacial progression, decreases in productivity in the central AZ suggest that the weakening of SO ventilation induced deep AZ carbon sequestration and that this might have made a continuous additional contribution to the CO2 decline from each interglacial peak to glacial maximum. Observed variations in the degree of deep oxygenation and “organic carbon pump” efficiency in the central AZ might be driven primarily by physical “ventilation” processes (i.e., overturning circulation, mixing, and/or air–sea gas exchange). Our records of abyssal oxygenation in the central AZ, which vary in concert with atmospheric CO2 levels over the last several G–IG cycles, provide strong evidence that SO ventilation plays a significant role in controlling variations in both the amount of respired carbon sequestered in the deep ocean and atmospheric CO2 concentrations on G–IG timescales. Specifically, we suggest that the “organic carbon pump” (OCP) in the SAZ and the physical ventilation processes in the AZ (the “carbon venting valve”) acted together synergistically, but dominated at different intervals over G–IG cycles, to repeatedly switch the SO between carbon sink and carbon source, thereby modulating the atmospheric CO2 over the last 770 kyr. These findings provide new insights into the role of the AZ in controlling deep SO carbon sequestration and atmospheric CO2 levels in G–IG cycles.
Funder
Taishan Scholars Project Funding
National Natural Science Foundation of China
Basic Scientific Fund for National Public Research Institutes of China
Impact and Response of Antarctic Seas to Climate Change
Cited by
3 articles.
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