6.3.1 Introduction
During the WOCE Hydrographic Programme
One-Time Survey, and as a major component of
International JGOFS (Joint Global Ocean Flux
Study), a Global Survey of CO 2 in the Oceans was
conducted in order to measure the global distribution of inorganic carbon in the oceans (Sabine
et al., 1997). The rationale for this large effort was
to improve characterization of the ocean’s past,
present and future role in removing Excess (or
Anthropogenic) CO 2 from the atmosphere. Prior
to the Global Survey, this could only be assessed
on the global scale using models, whereas an overall aim of the CO 2 Survey was to enable this to be
addressed from observations. The data would also
be used to assess and advance the state-of-the-art
in ocean carbon cycle modelling.
6.3.2 Background
6.3.2.1 Excess CO 2 : budgets, uncertainties,
definitions
Budget and uncertainties
During the 1980s, the ocean’s inventory of carbon
increased at a rate of ϳ2 PgC yr
91 (1 PgC is 10
15 g
of carbon; Siegenthaler and Sarmiento, 1993;
Schimel et al., 1996), thereby absorbing 36% of
the 5.5 PgC of fossil-fuel derived carbon released
annually to the atmosphere. In comparison, the
atmospheric inventory increased at a rate of
3.3 PgC yr
91
. This implies that net uptake or
release of carbon by the only other accessible carbon reservoir, the terrestrial biosphere, must have
been close to zero globally. Given that there are
known to be net CO 2 releases associated with
deforestation, there must therefore be additional,
poorly characterized, carbon sinks on land.
Of the major terms in the carbon budget, the
atmospheric increase is accurately determined from
measurements (uncertainty of 0.2 PgC yr
91
). This is
a consequence of the limited variability of the
atmospheric CO 2 concentration and the existence
of a high-quality, global measurement network
(Conway et al., 1994). The fossil-fuel term is the
next most accurately known term with an uncertainty of the order of 0.5 PgC yr
91
. The oceanic
uptake term is potentially the next most tractable in
terms of measurements, however present-day estimates are primarily based on models. Current estimates of the uncertainty of the ocean uptake term,
based largely on the level of agreement between
models, are 0.8 PgC yr
91 (Schimel et al., 1996).
Increasing insight concerning global-scale uptake is
now being provided by time-series measurements
of O 2 /N 2 in the atmosphere, but at present this
approach has similar levels of uncertainty (Keeling
et al., 1993, 1996; Bender et al., 1996; Langenfelds
et al., 1999; Battle et al., 2000). Whereas the
increase of carbon inventories in the ocean is not as
6.3
Storage and Transport of Excess CO 2
in the Oceans:The JGOFS/WOCE Global
CO 2 Survey
Douglas W. R.Wallace
489
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER
During the WOCE Hydrographic Programme
One-Time Survey, and as a major component of
International JGOFS (Joint Global Ocean Flux
Study), a Global Survey of CO 2 in the Oceans was
conducted in order to measure the global distribution of inorganic carbon in the oceans (Sabine
et al., 1997). The rationale for this large effort was
to improve characterization of the ocean’s past,
present and future role in removing Excess (or
Anthropogenic) CO 2 from the atmosphere. Prior
to the Global Survey, this could only be assessed
on the global scale using models, whereas an overall aim of the CO 2 Survey was to enable this to be
addressed from observations. The data would also
be used to assess and advance the state-of-the-art
in ocean carbon cycle modelling.
6.3.2 Background
6.3.2.1 Excess CO 2 : budgets, uncertainties,
definitions
Budget and uncertainties
During the 1980s, the ocean’s inventory of carbon
increased at a rate of ϳ2 PgC yr
91 (1 PgC is 10
15 g
of carbon; Siegenthaler and Sarmiento, 1993;
Schimel et al., 1996), thereby absorbing 36% of
the 5.5 PgC of fossil-fuel derived carbon released
annually to the atmosphere. In comparison, the
atmospheric inventory increased at a rate of
3.3 PgC yr
91
. This implies that net uptake or
release of carbon by the only other accessible carbon reservoir, the terrestrial biosphere, must have
been close to zero globally. Given that there are
known to be net CO 2 releases associated with
deforestation, there must therefore be additional,
poorly characterized, carbon sinks on land.
Of the major terms in the carbon budget, the
atmospheric increase is accurately determined from
measurements (uncertainty of 0.2 PgC yr
91
). This is
a consequence of the limited variability of the
atmospheric CO 2 concentration and the existence
of a high-quality, global measurement network
(Conway et al., 1994). The fossil-fuel term is the
next most accurately known term with an uncertainty of the order of 0.5 PgC yr
91
. The oceanic
uptake term is potentially the next most tractable in
terms of measurements, however present-day estimates are primarily based on models. Current estimates of the uncertainty of the ocean uptake term,
based largely on the level of agreement between
models, are 0.8 PgC yr
91 (Schimel et al., 1996).
Increasing insight concerning global-scale uptake is
now being provided by time-series measurements
of O 2 /N 2 in the atmosphere, but at present this
approach has similar levels of uncertainty (Keeling
et al., 1993, 1996; Bender et al., 1996; Langenfelds
et al., 1999; Battle et al., 2000). Whereas the
increase of carbon inventories in the ocean is not as
6.3
Storage and Transport of Excess CO 2
in the Oceans:The JGOFS/WOCE Global
CO 2 Survey
Douglas W. R.Wallace
489
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER