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The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE

The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE
The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE
The accumulation of man-made chlorofluorocarbons (CFCs) in subsurface water masses is directly related to their formation rate, and the water mass formation rate can be calculated from its CFC inventory. CFC-11 inventories between 65°N and 10°S in the Atlantic Ocean have been calculated for Eighteen Degree Water (EDW) and the components of North Atlantic Deep Water (NADW) from data collected primarily between 1996 and 1998 as part of the World Ocean Circulation Experiment (WOCE). CFC-11 inventories for individual water masses are 5.4 million moles for EDW, 10.5 million moles for Upper Labrador Sea Water (ULSW) (4.6 million moles south of 42°N), 23.4 million moles for Classical Labrador Sea Water (CLSW), 10.4 million moles for Iceland-Scotland Overflow Water (ISOW), and 8.3 million moles for Denmark Strait Overflow Water (DSOW). The estimated error for these inventories is about ±10%. The sum of the NADW components (ULSW, CLSW, ISOW, DSOW) is 53.2 million moles which is about half of the total CFC-11 inventory, 103.8 million moles, in the North Atlantic Ocean. Maps of water column inventories illustrate the formation mechanisms and spreading pathways within these water masses. The inventories directly reflect the input of newly formed water in the North Atlantic over the time scale of the CFC transient, about 3 decades. The interior regions of the North Atlantic contain most (75–80%) of the CFC-11 inventory in NADW indicating strong recirculation and mixing of newly formed NADW from the DWBC into the interior with a time scale of 2–3 decades. Average water mass formation rates between 1970 and 1997 are: 3.3 Sv for EDW, 3.5 Sv for ULSW (2.0 Sv from the central Labrador Sea and 1.5 Sv from the southern Labrador Sea), 8.2 Sv for CLSW, 5.7 Sv for ISOW, and 2.2 Sv for DSOW. Estimated errors are ±20% for CLSW and ±16% for the other water masses. The total for NADW, which forms the deep limb of the North Atlantic Meridional Overturning Circulation, is 19.6 Sv. An extensive test of the effects of temporal variability on the average formation rate calculated from the CFC inventory indicates that the error introduced by the assumption of a constant water mass formation rate is no greater than 15% for CLSW and 10% for the other water masses.
North Atlantic Deep Water, Eighteen Degree Water, CFCs, Formation rate, Circulation
0967-0637
891-910
LeBel, Deborah A.
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Smethie, William M.
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Rhein, Monika
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Kieke, Dagmar
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Fine, Rana A.
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Bullister, John L.
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Min, Dong-Ha
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Roether, Wolfgang
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Weiss, Ray F.
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Andrié, Chantal
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Smythe-Wright, Denise
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Jones, E. Peter
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LeBel, Deborah A.
d333b919-fa6d-4159-8706-39273a8753c9
Smethie, William M.
8786b52a-eed7-49e4-8fcc-234b47e095b6
Rhein, Monika
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Kieke, Dagmar
bd180e52-7fe6-495e-b3bf-83028dd685bf
Fine, Rana A.
d2b1fef2-821e-41ec-b24a-2cb17381f167
Bullister, John L.
1f44626d-e17a-43c7-a5af-1ecdf6e5d39d
Min, Dong-Ha
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Roether, Wolfgang
a473e51f-6875-4ab2-8cf9-e0dbc8c115f6
Weiss, Ray F.
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Andrié, Chantal
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Smythe-Wright, Denise
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Jones, E. Peter
c88b4f89-f44f-40b5-8a00-c381cd31a0fb

LeBel, Deborah A., Smethie, William M., Rhein, Monika, Kieke, Dagmar, Fine, Rana A., Bullister, John L., Min, Dong-Ha, Roether, Wolfgang, Weiss, Ray F., Andrié, Chantal, Smythe-Wright, Denise and Jones, E. Peter (2008) The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE. Deep Sea Research Part I: Oceanographic Research Papers, 55 (8), 891-910. (doi:10.1016/j.dsr.2008.03.009).

Record type: Article

Abstract

The accumulation of man-made chlorofluorocarbons (CFCs) in subsurface water masses is directly related to their formation rate, and the water mass formation rate can be calculated from its CFC inventory. CFC-11 inventories between 65°N and 10°S in the Atlantic Ocean have been calculated for Eighteen Degree Water (EDW) and the components of North Atlantic Deep Water (NADW) from data collected primarily between 1996 and 1998 as part of the World Ocean Circulation Experiment (WOCE). CFC-11 inventories for individual water masses are 5.4 million moles for EDW, 10.5 million moles for Upper Labrador Sea Water (ULSW) (4.6 million moles south of 42°N), 23.4 million moles for Classical Labrador Sea Water (CLSW), 10.4 million moles for Iceland-Scotland Overflow Water (ISOW), and 8.3 million moles for Denmark Strait Overflow Water (DSOW). The estimated error for these inventories is about ±10%. The sum of the NADW components (ULSW, CLSW, ISOW, DSOW) is 53.2 million moles which is about half of the total CFC-11 inventory, 103.8 million moles, in the North Atlantic Ocean. Maps of water column inventories illustrate the formation mechanisms and spreading pathways within these water masses. The inventories directly reflect the input of newly formed water in the North Atlantic over the time scale of the CFC transient, about 3 decades. The interior regions of the North Atlantic contain most (75–80%) of the CFC-11 inventory in NADW indicating strong recirculation and mixing of newly formed NADW from the DWBC into the interior with a time scale of 2–3 decades. Average water mass formation rates between 1970 and 1997 are: 3.3 Sv for EDW, 3.5 Sv for ULSW (2.0 Sv from the central Labrador Sea and 1.5 Sv from the southern Labrador Sea), 8.2 Sv for CLSW, 5.7 Sv for ISOW, and 2.2 Sv for DSOW. Estimated errors are ±20% for CLSW and ±16% for the other water masses. The total for NADW, which forms the deep limb of the North Atlantic Meridional Overturning Circulation, is 19.6 Sv. An extensive test of the effects of temporal variability on the average formation rate calculated from the CFC inventory indicates that the error introduced by the assumption of a constant water mass formation rate is no greater than 15% for CLSW and 10% for the other water masses.

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Published date: August 2008
Keywords: North Atlantic Deep Water, Eighteen Degree Water, CFCs, Formation rate, Circulation

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Local EPrints ID: 63939
URI: http://eprints.soton.ac.uk/id/eprint/63939
ISSN: 0967-0637
PURE UUID: 6c780cb7-cad9-4202-9c46-056053f9662a

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Date deposited: 19 Nov 2008
Last modified: 15 Mar 2024 11:45

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Contributors

Author: Deborah A. LeBel
Author: William M. Smethie
Author: Monika Rhein
Author: Dagmar Kieke
Author: Rana A. Fine
Author: John L. Bullister
Author: Dong-Ha Min
Author: Wolfgang Roether
Author: Ray F. Weiss
Author: Chantal Andrié
Author: Denise Smythe-Wright
Author: E. Peter Jones

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