An updated anthropogenic CO₂ inventory in the Atlantic Ocean

Abstract

This paper presents a comprehensive analysis of the basin‐wide inventory of anthropogenic CO2 in the Atlantic Ocean based on high‐quality inorganic carbon, alkalinity, chlorofluorocarbon, and nutrient data collected during the World Ocean Circulation Experiment (WOCE) Hydrographic Program, the Joint Global Ocean Flux Study (JGOFS), and the Ocean‐Atmosphere Carbon Exchange Study (OACES) surveys of the Atlantic Ocean between 1990 and 1998. Anthropogenic CO2 was separated from the large pool of dissolved inorganic carbon using an extended version of the ΔC* method originally developed by Gruber et al. [1996]. The extension of the method includes the use of an optimum multiparameter analysis to determine the relative contributions from various source water types to the sample on an isopycnal surface. Total inventories of anthropogenic CO2 in the Atlantic Ocean are highest in the subtropical regions at 20°–40°, whereas anthropogenic CO2 penetrates the deepest in high‐latitude regions (>40°N). The deeper penetration at high northern latitudes is largely due to the formation of deep water that feeds the Deep Western Boundary Current, which transports anthropogenic CO2 into the interior. In contrast, waters south of 50°S in the Southern Ocean contain little anthropogenic CO2. Analysis of the data collected during the 1990–1998 period yielded a total anthropogenic CO2 inventory of 28.4 ± 4.7 Pg C in the North Atlantic (equator‐70°N) and of 18.5 ± 3.9 Pg C in the South Atlantic (equator‐70°S). These estimated basin‐wide inventories of anthropogenic CO2 are in good agreement with previous estimates obtained by Gruber [1998], after accounting for the difference in observational periods. Our calculation of the anthropogenic CO2 inventory in the Atlantic Ocean, in conjunction with the inventories calculated previously for the Indian Ocean [Sabine et al., 1999] and for the Pacific Ocean [Sabine et al., 2002], yields a global anthropogenic CO2 inventory of 112 ± 17 Pg C that has accumulated in the world oceans during the industrial era. This global oceanic uptake accounts for approximately 29% of the total CO2 emissions from the burning of fossil fuels, land‐use changes, and cement production during the past 250 years.

The subsurface layer reference to calculate preformed alkalinity and air–sea CO2 disequilibrium in the Atlantic Ocean

“…The uncertainty of the A T º estimates obtained from equation (1) is ±4.6 mol kg -1 , which is lower than the ones reported in Gruber et al (1996) and in Lee et al (2003).…”

“…In the Equator (30ºS -30ºN), they assign all waters a constant A T º of 2291 mol kg -1 . The parameterizations from Gruber et al (1996) and Lee et al (2003) are very much alike consisting both of multiple linear regressions (MLR) of the form "A T º=  + ·S + ·Tr", where Tr=NO in the case of Lee et al (2003) and Tr=PO in Gruber et al (1996). Another difference between them is that Gruber et al"s can be applied globally, while Lee et al"s can only be applied south from 60ºN.…”

“…Among the several A T º parameterizations proposed in the past the ones from Gruber et al (1996), Millero et al (1998), and Lee et al (2003) have been widely used.…”

“…4b). On a general basis, the A T º parameterizations from Gruber et al (1996), Millero et al (1998), and Lee et al (2003) are significantly lower than the measured subsurface NPA T in the southern hemisphere and systematically higher in the North Atlantic.…”

The Oceanic Sink for Anthropogenic CO 2

“…The final data set consists of 9618 hydrographic stations collected on 95 cruises, which represents the most accurate and comprehensive view of the global ocean inorganic carbon distribution available (6). As individual basins were completed, the ocean tracer based C* method (7) was used to separate the anthropogenic CO 2 component from the measured DIC concentrations (8)(9)(10). Here we synthesize the individual ocean estimates to provide an ocean data-constrained global estimate of the cumulative oceanic sink for anthropogenic CO 2 for the period from ~1800 to 1994 (11).…”