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Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2

Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2
Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2
The effect of idealized wind-driven circulation changes in the Southern Ocean on atmospheric CO2 and the ocean carbon inventory is investigated using a suite of coarse-resolution, global coupled ocean circulation and biogeochemistry experiments with parameterized eddy activity and only modest changes in surface buoyancy forcing, each experiment integrated for 5,000 years. A positive correlation is obtained between the meridional overturning or residual circulation in the Southern Ocean and atmospheric CO2: stronger or northward-shifted westerly winds in the Southern Hemisphere result in increased residual circulation, greater upwelling of carbon-rich deep waters and oceanic outgassing, which increases atmospheric pCO2 by ?20 ?atm; weaker or southward-shifted winds lead to the opposing result. The ocean carbon inventory in our model varies through contrasting changes in the saturated, disequilibrium and biogenic (soft-tissue and carbonate) reservoirs, each varying by O(10–100) PgC, all of which contribute to the net anomaly in atmospheric CO2. Increased residual overturning deepens the global pycnocline, warming the upper ocean and decreasing the saturated carbon reservoir. Increased upwelling of carbon- and nutrient-rich deep waters and inefficient biological activity results in subduction of unutilized nutrients into the ocean interior, decreasing the biogenic carbon reservoir of intermediate and mode waters ventilating the Northern Hemisphere, and making the disequilibrium carbon reservoir more positive in the mode waters due to the reduced residence time at the surface. Wind-induced changes in the model carbon inventory are dominated by the response of the global pycnocline, although there is an additional abyssal response when the peak westerly winds change their latitude, altering their proximity to Drake Passage and changing the depth extent of the southward return flow of the overturning: a northward shift of the westerly winds isolates dense isopycnals, allowing biogenic carbon to accumulate in the deep ocean of the Southern Hemisphere, while a southward shift shoals dense isopycnals that outcrop in the Southern Ocean and reduces the biogenic carbon store in the deep ocean.
0930-7575
2145-2164
Lauderdale, Jonathan M.
b6794364-7060-4048-b2cc-d3ec8429353b
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Oliver, Kevin I.C.
588b11c6-4d0c-4c59-94e2-255688474987
Follows, Michael J.
12c723bc-f2f8-43f4-a309-bff6885b9c7c
Williams, Richard G.
2155309e-1c07-4365-b46a-04baeb2fb63c
Lauderdale, Jonathan M.
b6794364-7060-4048-b2cc-d3ec8429353b
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Oliver, Kevin I.C.
588b11c6-4d0c-4c59-94e2-255688474987
Follows, Michael J.
12c723bc-f2f8-43f4-a309-bff6885b9c7c
Williams, Richard G.
2155309e-1c07-4365-b46a-04baeb2fb63c

Lauderdale, Jonathan M., Naveira Garabato, Alberto C., Oliver, Kevin I.C., Follows, Michael J. and Williams, Richard G. (2013) Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2. Climate Dynamics, 41 (7-8), 2145-2164. (doi:10.1007/s00382-012-1650-3).

Record type: Article

Abstract

The effect of idealized wind-driven circulation changes in the Southern Ocean on atmospheric CO2 and the ocean carbon inventory is investigated using a suite of coarse-resolution, global coupled ocean circulation and biogeochemistry experiments with parameterized eddy activity and only modest changes in surface buoyancy forcing, each experiment integrated for 5,000 years. A positive correlation is obtained between the meridional overturning or residual circulation in the Southern Ocean and atmospheric CO2: stronger or northward-shifted westerly winds in the Southern Hemisphere result in increased residual circulation, greater upwelling of carbon-rich deep waters and oceanic outgassing, which increases atmospheric pCO2 by ?20 ?atm; weaker or southward-shifted winds lead to the opposing result. The ocean carbon inventory in our model varies through contrasting changes in the saturated, disequilibrium and biogenic (soft-tissue and carbonate) reservoirs, each varying by O(10–100) PgC, all of which contribute to the net anomaly in atmospheric CO2. Increased residual overturning deepens the global pycnocline, warming the upper ocean and decreasing the saturated carbon reservoir. Increased upwelling of carbon- and nutrient-rich deep waters and inefficient biological activity results in subduction of unutilized nutrients into the ocean interior, decreasing the biogenic carbon reservoir of intermediate and mode waters ventilating the Northern Hemisphere, and making the disequilibrium carbon reservoir more positive in the mode waters due to the reduced residence time at the surface. Wind-induced changes in the model carbon inventory are dominated by the response of the global pycnocline, although there is an additional abyssal response when the peak westerly winds change their latitude, altering their proximity to Drake Passage and changing the depth extent of the southward return flow of the overturning: a northward shift of the westerly winds isolates dense isopycnals, allowing biogenic carbon to accumulate in the deep ocean of the Southern Hemisphere, while a southward shift shoals dense isopycnals that outcrop in the Southern Ocean and reduces the biogenic carbon store in the deep ocean.

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Published date: October 2013
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 359566
URI: http://eprints.soton.ac.uk/id/eprint/359566
ISSN: 0930-7575
PURE UUID: 59ef6989-8a18-4d8b-b34a-6165681d7567
ORCID for Alberto C. Naveira Garabato: ORCID iD orcid.org/0000-0001-6071-605X

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Date deposited: 04 Nov 2013 14:22
Last modified: 15 Mar 2024 03:24

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Contributors

Author: Jonathan M. Lauderdale
Author: Michael J. Follows
Author: Richard G. Williams

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