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An improved method for detecting anthropogenic CO 2 in the oceans
Author(s) -
Gruber Nicolas,
Sarmiento Jorge L.,
Stocker Thomas F.
Publication year - 1996
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/96gb01608
Subject(s) - oceanography , environmental science , biogeochemistry , ocean current , disequilibrium , tracer , subtropics , north atlantic deep water , convergence zone , tropical atlantic , thermohaline circulation , atmosphere (unit) , biogeochemical cycle , geology , sea surface temperature , environmental chemistry , ecology , chemistry , geography , ophthalmology , medicine , physics , biology , meteorology , nuclear physics
An improved method has been developed for the separation of the anthropogenic CO 2 from the large natural background variability of dissolved inorganic carbon ( C ) in the ocean. This technique employs a new quasi‐conservative carbon tracer Δ C *, which reflects the uptake of anthropogenic CO 2 and the air‐sea disequilibrium when a water parcel loses contact with the atmosphere. The air‐sea disequilibrium component can be discriminated from the anthropogenic signal using either information about the water age or the distribution of Δ C * in regions not affected by the anthropogenic transient. This technique has been applied to data from the North Atlantic sampled during the Transient Tracers in the Ocean North Atlantic (TTO NAS) and Tropical Atlantic study (TTO TAS) cruises in 1981–1983. The highest anthropogenic CO 2 concentrations and specific inventories (inventory per square meter) are found in the subtropical convergence zone. In the North Atlantic, anthropogenic CO 2 has already invaded deeply into the interior of the ocean, north of 50°N it has even reached the bottom. Only waters below 3000 m and south of 30°N are not yet affected. We estimate an anthropogenic CO 2 inventory of 20 ± 4 Gt C in the North Atlantic between 10°N and 80°N. The 2.5‐dimensional ocean circulation model of Stocker et al. [1994] and the three‐dimensional ocean general circulation biogeochemistry model of Sarmiento et al. [1995] predict anthropogenic CO 2 inventories of 18.7 Gt C and 18.4 Gt C, respectively, in good agreement with the observed inventory. Important differences exist on a more regional scale, associated with known deficiencies of the models.