The Deep Ocean's Carbon Exhaust

Type Article
Date 2022-07
Language English
Author(s) Chen HaidiORCID1, Haumann F. Alexander1, Talley Lynne D.2, Johnson Kenneth S.3, Sarmiento Jorge L.1
Affiliation(s) 1 : 1Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, NJ, USA
2 : 2Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
3 : 3Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA
Source Global Biogeochemical Cycles (0886-6236) (Amer Geophysical Union), 2022-07 , Vol. 36 , N. 7 , P. e2021GB007156 (21p.)
DOI 10.1029/2021GB007156
WOS© Times Cited 11
Note This article also appears in: Southern Ocean and Climate: Biogeochemical and Physical Fluxes and Processes
Keyword(s) carbon cycle, ocean circulation, Southern Ocean, biogeochemistry
Abstract

The deep ocean releases large amounts of old, pre-industrial carbon dioxide (CO2) to the atmosphere through upwelling in the Southern Ocean, which counters the marine carbon uptake occurring elsewhere. This Southern Ocean CO2 release is relevant to the global climate because its changes could alter atmospheric CO2 levels on long time scales, and also affects the present-day potential of the Southern Ocean to take up anthropogenic CO2. Here, year-round profiling float measurements show that this CO2 release arises from a zonal band of upwelling waters between the Subantarctic Front and wintertime sea-ice edge. This band of high CO2 subsurface water coincides with the outcropping of the 27.8 kg m(-3) isoneutral density surface that characterizes Indo-Pacific Deep Water (IPDW). It has a potential partial pressure of CO2 exceeding current atmospheric CO2 levels ( increment PCO2) by 175 +/- 32 mu atm. Ship-based measurements reveal that IPDW exhibits a distinct increment PCO2 maximum in the ocean, which is set by remineralization of organic carbon and originates from the northern Pacific and Indian Ocean basins. Below this IPDW layer, the carbon content increases downwards, whereas increment PCO2 decreases. Most of this vertical increment PCO2 decline results from decreasing temperatures and increasing alkalinity due to an increased fraction of calcium carbonate dissolution. These two factors limit the CO2 outgassing from the high-carbon content deep waters on more southerly surface outcrops. Our results imply that the response of Southern Ocean CO2 fluxes to possible future changes in upwelling are sensitive to the subsurface carbon chemistry set by the vertical remineralization and dissolution profiles.

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