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In this work, we present, for the first time, the seawater carbonate system measurements of two coastal time-series in the NW Mediterranean Sea, L'Estartit Oceanographic Station (EOS; 42.05°N 3.2542°E) and the Blanes Bay Microbial Observatory (BBMO; 41.665°N 2.805°E). At these two time-series, measurements of total alkalinity (TA), pH, and associated variables, such as dissolved inorganic nutrients, temperature, and salinity, have been performed monthly since 2010 in surface seawater. Seasonality and seasonal amplitude are analogous in both time-series, with seasonality in pHT in situ (pH at in situ seawater conditions on the total hydrogen ion scale) primarily determined by seasonality in sea surface temperature. The evaluated pHT in situ trends at BBMO (-0.0021 ± 0.0003 yr-1) and EOS (-0.0028 ± 0.0005 yr-1) agree with those reported for coastal and open ocean surface waters in the Mediterranean Sea and open ocean surface waters of the global ocean, therefore indicating that these time-series are representative of global ocean acidification signals despite being coastal. The decreases in pHT in situ can be attributed to increases in total dissolved inorganic carbon (DIC; 1.5 ± 0.4 µmol kg-1 yr-1 at BBMO and 1.6 ± 0.6 µmolESkg-1 yr-1 at EOS) and sea surface temperature (0.08 ± 0.02℃ yr-1 at BBMOand 0.08 ± 0.04℃ yr-1 at EOS). The increases in carbon dioxide fugacity (fCO2; 2.4 ± 0.3 µmol kg-1 yr-1 at BBMO and 2.9 ± 0.6 µmol kg-1 yr-1 at EOS) follow the atmospheric CO2 forcing, thus indicating the observed DIC increase is related to anthropogenic CO2 uptake. The increasing trends in TA (1.2 ± 0.3 µmol kg-1 yr-1 at BBMO and 1.0 ± 0.5 µmol kg-1 yr-1 at EOS) buffered the acidification rates, counteracting 60% and 72% of the pHT in situ decrease caused by increasing DIC at EOS and BBMO, respectively. Once accounted for the neutralizing effect of TA increase, the rapid sea surface warming plays a larger role in the observed pH decreases (43% at EOS and 62% at BBMO) than the DIC increase (36% at EOS and 33% at BBMO). [ABSTRACT FROM AUTHOR]

Author(s): Fiz F. Perez (corresponding author) [1]; Marcos Fontela [1]; Maribel I. Garca-Ibez [1]; Herl Mercier [2]; Anton Velo [1]; Pascale Lherminier [2]; Patricia Zunino [2]; Mercedes de la Paz [...]

The meridional transport of anthropogenic CO2 (Cant) in the tropical North Atlantic (TNA) is investigated using data from transoceanic sections along 7.5°N and 24.5°N, carried out in the early 1990s and 2010s. The net Cant transport across both sections is northward. At 7.5°N, this transport increased from 315 ± 47 kmol s−1 in 1993 to 493 ± 51 kmol s−1 in 2010; similarly, across 24.5°N it grew from 530 ± 46 kmol s−1 in 1992 to 662 ± 49 kmol s−1 in 2011. These changes result from modifications in the intermediate and deep circulation patterns, as well as from Cant increase within the thermocline waters. In deep waters, lateral advection causes a net Cant input of 112 ± 60 kmol s−1 (234 ± 65 kmol s−1) in 1992-1993 (2010-2011); within these deep waters, the storage rate of Cant is not statistically different from the net Cant input, 139 ± 21 kmol s−1 (188 ± 21 kmol s−1) in 1992-1993 (2010-2011). The Cant increase in deep waters is due to the large injection of Cant across the 24.5°N by the Deep Western Boundary Current and the northward recirculation of North Atlantic Deep Water along 7.5°N. In contrast, a large net Cant output in the upper layer is caused by the Florida Current. Despite this net Cant output, the Cant accumulates at a rate of 215 ± 24 kmol s−1 (291 ± 24 kmol s−1) referenced to year 1993 (2010). From the two Cant budgets, we infer a Cant air-sea flux of 0.23 ± 0.02 Pg yr−1in the TNA, much larger than previous estimates. [ABSTRACT FROM AUTHOR]