Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age

• Published in: Nature (London) 2016-02, Vol.530 (7589), p.207-210
• Main Authors: Jaccard, Samuel L., Galbraith, Eric D., Martínez-García, Alfredo, Anderson, Robert F.
• Format: Article
• Language: English
• Subjects: 704/106/2738; 704/106/47; Antarctic Regions; Atmosphere - chemistry; Carbon Dioxide - analysis; Carbon Dioxide - history; Carbon Dioxide - metabolism; Carbon Sequestration; Cell Respiration; Climate; Dust; Geologic Sediments - chemistry; History, Ancient; Humanities and Social Sciences; Ice Cover; Iron - analysis; Iron - chemistry; letter; multidisciplinary; Oceans and Seas; Oxidation-Reduction; Oxygen - analysis; Oxygen - metabolism; Science; Seawater - chemistry; Temperature; Water Movements
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature16514

A reconstruction of changes in ocean oxygenation throughout the last glacial cycle shows that respired carbon was removed from the deep Southern Ocean during deglaciation and Antarctic warm events, consistent with a prominent role of reduced iron fertilization and enhanced ocean ventilation, modifying atmospheric carbon dioxide concentrations over the past 80,000 years. Glacial–interglacial CO 2 variation Carbon exchange between the deep Southern Ocean and the atmosphere is thought to play an important role in controlling glacial–interglacial variations in atmospheric carbon dioxide concentrations. This paper presents a reconstruction of changes in deep Southern Ocean oxygenation — reflecting changes in respired carbon storage — throughout the last glacial cycle. The record provides support for the idea that respired carbon was removed from the deep Southern Ocean during deglaciation as a result of reduced iron fertilization and enhanced ocean ventilation. In fact, the observed correlation between atmospheric carbon dioxide concentrations and deep Southern Ocean oxygenation was maintained during most of the past 80,000 years, suggesting that on millennial timescales, deep ocean circulation and iron fertilization in the Southern Ocean played a consistent role in controlling glacial–interglacial variations in atmospheric CO 2 concentrations. No single mechanism can account for the full amplitude of past atmospheric carbon dioxide (CO 2 ) concentration variability over glacial–interglacial cycles 1 . A build-up of carbon in the deep ocean has been shown to have occurred during the Last Glacial Maximum 2 , 3 . However, the mechanisms responsible for the release of the deeply sequestered carbon to the atmosphere at deglaciation, and the relative importance of deep ocean sequestration in regulating millennial-timescale variations in atmospheric CO 2 concentration before the Last Glacial Maximum, have remained unclear. Here we present sedimentary redox-sensitive trace-metal records from the Antarctic Zone of the Southern Ocean that provide a reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our data suggest that respired carbon was removed from the abyssal Southern Ocean during the Northern Hemisphere cold phases of the deglaciation, when atmospheric CO 2 concentration increased rapidly, reflecting—at least in part—a combination of dwindling iron fertilization by dust and en