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Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds
Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds
Tree ring ?14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric ?14C varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD 950 and 1830. The Northern and Southern Hemispheric ?14C records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of 14C in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of 14CO2 has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD 950–1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980–2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.
1814-9332
1123-1138
Rodgers, K.B.
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Mikaloff-Fletcher, S.E.
61b76d3a-2104-4319-8abc-5bbbbca8d894
Bianchi, D.
a8ad2342-66b4-4871-ae59-6efd945f321a
Beaulieu, C.
13ae2c11-ebfe-48d9-bda9-122cd013c021
Galbraith, E.D.
cc8cae0d-d549-4a66-bccc-2e5ba88e167f
Gnanadesikan, A.
58fdbed1-e584-436b-b801-421e9509b511
Hogg, A.G.
ec7a91a1-7b28-40ae-abdb-fbcb0c625bc1
Iudicone, D.
04300734-e5dc-460b-b207-934faed74572
Lintner, B.R.
d2bf08b0-d08d-4cd1-a8e8-589105d753da
Naegler, T.
00a252ec-96fc-48a9-8f84-e66596e39475
Reimer, P.J.
429388f9-0926-4214-9022-6c5b5cbadcf1
Sarmiento, J.L.
5887047e-92ac-47f7-a504-fb1699dd8d17
Slater, R.D.
02cdf450-d76f-468f-9eee-9afd70d9e05c
Rodgers, K.B.
6c395d25-c114-4ed4-8e65-b63c232680e8
Mikaloff-Fletcher, S.E.
61b76d3a-2104-4319-8abc-5bbbbca8d894
Bianchi, D.
a8ad2342-66b4-4871-ae59-6efd945f321a
Beaulieu, C.
13ae2c11-ebfe-48d9-bda9-122cd013c021
Galbraith, E.D.
cc8cae0d-d549-4a66-bccc-2e5ba88e167f
Gnanadesikan, A.
58fdbed1-e584-436b-b801-421e9509b511
Hogg, A.G.
ec7a91a1-7b28-40ae-abdb-fbcb0c625bc1
Iudicone, D.
04300734-e5dc-460b-b207-934faed74572
Lintner, B.R.
d2bf08b0-d08d-4cd1-a8e8-589105d753da
Naegler, T.
00a252ec-96fc-48a9-8f84-e66596e39475
Reimer, P.J.
429388f9-0926-4214-9022-6c5b5cbadcf1
Sarmiento, J.L.
5887047e-92ac-47f7-a504-fb1699dd8d17
Slater, R.D.
02cdf450-d76f-468f-9eee-9afd70d9e05c

Rodgers, K.B., Mikaloff-Fletcher, S.E., Bianchi, D., Beaulieu, C., Galbraith, E.D., Gnanadesikan, A., Hogg, A.G., Iudicone, D., Lintner, B.R., Naegler, T., Reimer, P.J., Sarmiento, J.L. and Slater, R.D. (2011) Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds. Climate of the Past, 7 (4), 1123-1138. (doi:10.5194/cp-7-1123-2011).

Record type: Article

Abstract

Tree ring ?14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric ?14C varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD 950 and 1830. The Northern and Southern Hemispheric ?14C records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of 14C in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of 14CO2 has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD 950–1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980–2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.

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Published date: 2011
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 352256
URI: https://eprints.soton.ac.uk/id/eprint/352256
ISSN: 1814-9332
PURE UUID: 39a924ba-eda0-455c-8153-75431a2b76df

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Date deposited: 08 May 2013 10:17
Last modified: 16 Jul 2019 21:34

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Contributors

Author: K.B. Rodgers
Author: S.E. Mikaloff-Fletcher
Author: D. Bianchi
Author: C. Beaulieu
Author: E.D. Galbraith
Author: A. Gnanadesikan
Author: A.G. Hogg
Author: D. Iudicone
Author: B.R. Lintner
Author: T. Naegler
Author: P.J. Reimer
Author: J.L. Sarmiento
Author: R.D. Slater

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