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Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans

Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans
Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans
A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601–1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 ?atm y?1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 ?atm y?1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niño periods in the equatorial Pacific and those made in coastal zones are excluded from the database.

Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones.

The net air–sea CO2 flux is estimated using the sea–air pCO2 difference and the air–sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979–2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N–14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y?1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of ?0.70 Pg-C y?1 for the northern and ?1.05 Pg-C y?1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of ?2.5 tons-C month?1 km?2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°–62°S), the mean annual flux is small (?0.06 Pg-C y?1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be ?1.6±0.9 Pg-C y?1, which includes an undersampling correction to the direct estimate of ?1.4±0.7 Pg-C y?1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y?1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be ?2.0±1.0 Pg-C y?1 in 2000.
Carbon dioxide, Partial pressure, Surface ocean, Global ocean, Sea–air flux
0967-0645
554-577
Takahashi, Taro
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Sutherland, Stewart C.
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Wanninkhof, Rik
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Sweeney, Colm
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Feely, Richard A.
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Chipman, David W.
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Hales, Burke
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Friederich, Gernot
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Chavez, Francisco
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Sabine, Christopher
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Watson, Andrew
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Bakker, Dorothee C.E.
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Schuster, Ute
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Metzl, Nicolas
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Yoshikawa-Inoue, Hisayuki
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Ishii, Masao
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Midorikawa, Takashi
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Nojiri, Yukihiro
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Körtzinger, Arne
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Steinhoff, Tobias
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Hoppema, Mario
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Olafsson, Jon
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Arnarson, Thorarinn S.
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Tilbrook, Bronte
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Johannessen, Truls
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Olsen, Are
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Bellerby, Richard
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Wong, C.S.
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Delille, Bruno
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Bates, N.R.
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de Baar, Hein J.W.
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Takahashi, Taro
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Sutherland, Stewart C.
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Wanninkhof, Rik
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Sweeney, Colm
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Feely, Richard A.
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Chipman, David W.
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Hales, Burke
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Friederich, Gernot
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Chavez, Francisco
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Sabine, Christopher
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Watson, Andrew
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Bakker, Dorothee C.E.
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Schuster, Ute
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Metzl, Nicolas
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Yoshikawa-Inoue, Hisayuki
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Ishii, Masao
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Midorikawa, Takashi
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Nojiri, Yukihiro
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Körtzinger, Arne
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Steinhoff, Tobias
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Hoppema, Mario
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Olafsson, Jon
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Arnarson, Thorarinn S.
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Tilbrook, Bronte
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Johannessen, Truls
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Olsen, Are
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Bellerby, Richard
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Wong, C.S.
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Delille, Bruno
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Bates, N.R.
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de Baar, Hein J.W.
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Takahashi, Taro, Sutherland, Stewart C., Wanninkhof, Rik, Sweeney, Colm, Feely, Richard A., Chipman, David W., Hales, Burke, Friederich, Gernot, Chavez, Francisco, Sabine, Christopher, Watson, Andrew, Bakker, Dorothee C.E., Schuster, Ute, Metzl, Nicolas, Yoshikawa-Inoue, Hisayuki, Ishii, Masao, Midorikawa, Takashi, Nojiri, Yukihiro, Körtzinger, Arne, Steinhoff, Tobias, Hoppema, Mario, Olafsson, Jon, Arnarson, Thorarinn S., Tilbrook, Bronte, Johannessen, Truls, Olsen, Are, Bellerby, Richard, Wong, C.S., Delille, Bruno, Bates, N.R. and de Baar, Hein J.W. (2009) Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans. Deep Sea Research Part II: Topical Studies in Oceanography, 56 (8-10), 554-577. (doi:10.1016/j.dsr2.2008.12.009).

Record type: Article

Abstract

A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601–1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 ?atm y?1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 ?atm y?1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niño periods in the equatorial Pacific and those made in coastal zones are excluded from the database.

Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones.

The net air–sea CO2 flux is estimated using the sea–air pCO2 difference and the air–sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979–2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N–14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y?1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of ?0.70 Pg-C y?1 for the northern and ?1.05 Pg-C y?1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of ?2.5 tons-C month?1 km?2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°–62°S), the mean annual flux is small (?0.06 Pg-C y?1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be ?1.6±0.9 Pg-C y?1, which includes an undersampling correction to the direct estimate of ?1.4±0.7 Pg-C y?1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y?1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be ?2.0±1.0 Pg-C y?1 in 2000.

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More information

Published date: April 2009
Keywords: Carbon dioxide, Partial pressure, Surface ocean, Global ocean, Sea–air flux
Organisations: Ocean Biochemistry & Ecosystems

Identifiers

Local EPrints ID: 356955
URI: http://eprints.soton.ac.uk/id/eprint/356955
ISSN: 0967-0645
PURE UUID: c792a422-f515-4524-a2ad-f235ccd88d0e

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Date deposited: 17 Sep 2013 15:35
Last modified: 14 Mar 2024 14:54

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Contributors

Author: Taro Takahashi
Author: Stewart C. Sutherland
Author: Rik Wanninkhof
Author: Colm Sweeney
Author: Richard A. Feely
Author: David W. Chipman
Author: Burke Hales
Author: Gernot Friederich
Author: Francisco Chavez
Author: Christopher Sabine
Author: Andrew Watson
Author: Dorothee C.E. Bakker
Author: Ute Schuster
Author: Nicolas Metzl
Author: Hisayuki Yoshikawa-Inoue
Author: Masao Ishii
Author: Takashi Midorikawa
Author: Yukihiro Nojiri
Author: Arne Körtzinger
Author: Tobias Steinhoff
Author: Mario Hoppema
Author: Jon Olafsson
Author: Thorarinn S. Arnarson
Author: Bronte Tilbrook
Author: Truls Johannessen
Author: Are Olsen
Author: Richard Bellerby
Author: C.S. Wong
Author: Bruno Delille
Author: N.R. Bates
Author: Hein J.W. de Baar

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