Open AccessA large increase of the CO 2 sink in the western tropical North Atlantic from 2002 to 2009
Author(s) -
Park GeunHa,
Wanninkhof Rik
Publication year - 2012
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jc007803
Subject(s) - sink (geography) , environmental science , fugacity , flux (metallurgy) , climatology , sea surface temperature , atmospheric sciences , salinity , carbon dioxide , mixed layer , atmosphere (unit) , oceanography , geology , meteorology , chemistry , geography , cartography , organic chemistry
Determining a robust trend of surface ocean carbon dioxide (CO 2 ) for a period shorter than a decade is challenging due to large seasonal variability and a sparsity of data. Here, we estimate the multiannual trend of surface CO 2 in the region of 19°N–20°N, 65°W–68°W for the period of 2002–2009. We used an unprecedented number of high‐quality underway data of the fugacity of CO 2 in surface seawater (fCO 2SW ) collected from 137 cruises using an automated system onboard the cruise ship Explorer of the Seas. The growth rate of fCO 2SW was estimated by two de‐seasonalization approaches that showed similar and significantly lower values than the atmospheric increases, leading to a large increase in the CO 2 sink. The seasonal difference in the trends was significant, with fCO 2SW values in winter showing no increase, while summer fCO 2SW values lagged only slightly with the atmosphere. We attribute the lack of an increase in winter fCO 2SW values to sea surface temperature changes, which are closely correlated with the El Niño‐Southern Oscillation cycle, and to changes in the mixed layer depth. The slower increase of fCO 2SW is also related to decreases in salinity. The 8‐year averaged annual net sea‐air CO 2 flux was −0.06 ± 0.18 mol m −2 yr −1 compared to a climatology that shows a flux out of the ocean of +0.11 mol m −2 yr −1 . The increasing flux differs from previous, mostly longer‐term results for regional studies and time series stations in the North Atlantic, which suggests a decrease or no change in oceanic CO 2 uptake.