Anthropogenic CO2 changes in the Equatorial Atlantic Ocean

Abstract

a b s t r a c tMethods based on CO 2 and chlorofluorocarbon (CFC) data are used to describe and evaluate the anthropogenic CO 2 (C ant ) concentrations, C ant specific inventories, and C ant storage rates in the Equatorial Atlantic Ocean. The C ant variability in the water masses is evaluated from the comparison of two hydrographic sections along 7.5°N carried out in 1993 and 2010. During both cruises, high C ant concentrations are detected in the upper layers, with values decreasing progressively towards the deep layers. Overall, the C ant concentrations increase from 1993 to 2010, with a large increment in the upper North AtlanticDeep Water layer of about 0.18 ± 0.03 lmol kg À1 y À1 . In 2010, the C ant inventory along the whole section amounts to 58.9 ± 2.2 and 45.1 ± 2.0 mol m À2 using CO 2 and CFC based methods, respectively, with most C ant accumulating in the western basin. Considering the time elapsed between the two cruises, C ant storage rates of 1.01 ± 0.18 and 0.75 ± 0.17 mol m À2 y À1 (CO 2 and CFC based methods, respectively) are obtained. Below $1000 m, these rates follow the pace expected from a progressive increase of C ant at steady state; above $1000 m, C ant increases faster, mainly due to the retreat of the Antarctic Intermediate Waters.

Transports and budgets of anthropogenic CO2 in the tropical North Atlantic in 1992–1993 and 2010–2011

“…Fajar et al . [] estimated the C ant increase rates at 7.5°N as the difference in C ant concentration between 1993 and 2010 divided by the elapsed time and also provided uncertainty values. Guallart et al .…”

“…Recent studies by Fajar et al . [] and Guallart et al . [] have analyzed decadal C ant changes for different water masses and regions along 7.5°N and 24.5°N.…”

“…The changes along 7.5°N have been calculated between 1993 and 2010 by Fajar et al . []. An increase in C ant was detected at all depths, with maxima in the thermocline and intermediate waters.…”

“…Fajar et al . [] found that, along 7.5°N, the rate of C ant increase agrees with the TSS for deep waters, but it is larger than expected for the thermocline and intermediate waters. The changes along 24.5°N have been estimated between 1992 and 2011 by Guallart et al .…”

“…[] described the general circulation along 7.5°N and 24.5°N, for the same realizations studied by Fajar et al . [] and Guallart et al . [].…”