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Multidecadal variations in Southern Hemisphere atmospheric 14C: Evidence against a Southern Ocean sink at the end of the Little Ice Age CO2 anomaly

Multidecadal variations in Southern Hemisphere atmospheric 14C: Evidence against a Southern Ocean sink at the end of the Little Ice Age CO2 anomaly
Multidecadal variations in Southern Hemisphere atmospheric 14C: Evidence against a Southern Ocean sink at the end of the Little Ice Age CO2 anomaly
Northern Hemisphere-wide cooling during the Little Ice Age (LIA; 1650-1775 Common Era, C.E.) was associated with a ~5 ppmv decrease in atmospheric carbon dioxide. Changes in terrestrial and ocean carbon reservoirs have been postulated as possible drivers of this relatively large shift in atmospheric CO2, potentially providing insights into the mechanisms and sensitivity of the global carbon cycle. Here we report decadally resolved radiocarbon (14C) levels in a network of tree-ring series spanning 1700-1950 C.E. located along the northern boundary of, and within, the Southern Ocean. We observe regional dilutions in atmospheric radiocarbon (relative to the Northern Hemisphere) associated with upwelling of 14CO2-depleted abyssal waters. We find the interhemispheric 14C offset approaches zero during increasing global atmospheric CO2 at the end of the LIA, with reduced ventilation in the Southern Ocean and a Northern Hemisphere source of old carbon (most probably originating from deep Arctic peat layers). The coincidence of the atmospheric CO2 increase and reduction in the interhemispheric 14C offset imply a common climate control. Possible mechanisms of synchronous change in the high latitudes of both hemispheres are discussed.
interhemispheric gradient (IHG), Little Ice Age (LIA), radiocarbon (C), Southern Hemisphere carbon dioxide (CO), Southern Ocean, tree rings
0886-6236
211-218
Turney, Chris S.M.
5149b57c-77c2-4375-97a2-a4f00aa74d97
Palmer, Jonathan
6b327a39-f234-4cdc-ae73-0c48340f05b3
Hogg, Alan
11978083-6632-42e2-ac46-4e0f9cd709c9
Fogwill, Christopher J.
3bad6ae9-5a6d-467e-b523-9d5ed0147455
Jones, Richard T.
f8b5db51-10c7-4b4e-81e3-e5c3833eb2ce
Bronk Ramsey, Christopher
58d46d3d-0731-46e9-b17b-a1552645d666
Fenwick, Pavla
8ce718a6-f147-4eac-9878-f8b67c491a70
Grierson, Pauline
95582c60-f007-4800-b6c2-b9d1228e8cdd
Wilmshurst, Janet
3738ab11-0f7b-4550-b8d3-f63198b3394e
O'Donnell, Alison
4d57334a-a12a-45aa-9712-3636d009b487
Thomas, Zoë A.
4b512d3a-3478-4270-9fdd-61256aa640d3
Lipson, Mathew
f599592a-28ae-4ede-9c7b-e484e3f94c62
et al.
Turney, Chris S.M.
5149b57c-77c2-4375-97a2-a4f00aa74d97
Palmer, Jonathan
6b327a39-f234-4cdc-ae73-0c48340f05b3
Hogg, Alan
11978083-6632-42e2-ac46-4e0f9cd709c9
Fogwill, Christopher J.
3bad6ae9-5a6d-467e-b523-9d5ed0147455
Jones, Richard T.
f8b5db51-10c7-4b4e-81e3-e5c3833eb2ce
Bronk Ramsey, Christopher
58d46d3d-0731-46e9-b17b-a1552645d666
Fenwick, Pavla
8ce718a6-f147-4eac-9878-f8b67c491a70
Grierson, Pauline
95582c60-f007-4800-b6c2-b9d1228e8cdd
Wilmshurst, Janet
3738ab11-0f7b-4550-b8d3-f63198b3394e
O'Donnell, Alison
4d57334a-a12a-45aa-9712-3636d009b487
Thomas, Zoë A.
4b512d3a-3478-4270-9fdd-61256aa640d3
Lipson, Mathew
f599592a-28ae-4ede-9c7b-e484e3f94c62

Turney, Chris S.M., Palmer, Jonathan, Hogg, Alan, Jones, Richard T. and Thomas, Zoë A. , et al. (2016) Multidecadal variations in Southern Hemisphere atmospheric 14C: Evidence against a Southern Ocean sink at the end of the Little Ice Age CO2 anomaly. Global Biogeochemical Cycles, 30 (2), 211-218. (doi:10.1002/2015GB005257).

Record type: Article

Abstract

Northern Hemisphere-wide cooling during the Little Ice Age (LIA; 1650-1775 Common Era, C.E.) was associated with a ~5 ppmv decrease in atmospheric carbon dioxide. Changes in terrestrial and ocean carbon reservoirs have been postulated as possible drivers of this relatively large shift in atmospheric CO2, potentially providing insights into the mechanisms and sensitivity of the global carbon cycle. Here we report decadally resolved radiocarbon (14C) levels in a network of tree-ring series spanning 1700-1950 C.E. located along the northern boundary of, and within, the Southern Ocean. We observe regional dilutions in atmospheric radiocarbon (relative to the Northern Hemisphere) associated with upwelling of 14CO2-depleted abyssal waters. We find the interhemispheric 14C offset approaches zero during increasing global atmospheric CO2 at the end of the LIA, with reduced ventilation in the Southern Ocean and a Northern Hemisphere source of old carbon (most probably originating from deep Arctic peat layers). The coincidence of the atmospheric CO2 increase and reduction in the interhemispheric 14C offset imply a common climate control. Possible mechanisms of synchronous change in the high latitudes of both hemispheres are discussed.

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More information

e-pub ahead of print date: 18 January 2016
Published date: February 2016
Additional Information: Funding Information: C.S.M.T., C.F., and P.G. acknowledge the support of the Australian Research Council (FL100100195, FT120100004, and DP130104156). Publisher Copyright: ©2016. American Geophysical Union. All Rights Reserved.
Keywords: interhemispheric gradient (IHG), Little Ice Age (LIA), radiocarbon (C), Southern Hemisphere carbon dioxide (CO), Southern Ocean, tree rings

Identifiers

Local EPrints ID: 476055
URI: http://eprints.soton.ac.uk/id/eprint/476055
ISSN: 0886-6236
PURE UUID: b2685bb6-2765-459b-b7b5-19ac8a8fcfaa
ORCID for Zoë A. Thomas: ORCID iD orcid.org/0000-0002-2323-4366

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Date deposited: 04 Apr 2023 17:06
Last modified: 06 Jun 2024 02:16

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Contributors

Author: Chris S.M. Turney
Author: Jonathan Palmer
Author: Alan Hogg
Author: Christopher J. Fogwill
Author: Richard T. Jones
Author: Christopher Bronk Ramsey
Author: Pavla Fenwick
Author: Pauline Grierson
Author: Janet Wilmshurst
Author: Alison O'Donnell
Author: Zoë A. Thomas ORCID iD
Author: Mathew Lipson
Corporate Author: et al.

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