Abstract. The western tropical South
Pacific was sampled along a longitudinal 4000 km transect (OUTPACE cruise,
18 February, 3 April 2015) for the measurement of carbonate parameters (total
alkalinity and total inorganic carbon) between the Melanesian Archipelago
(MA) and the western part of the South Pacific gyre (WGY). This paper reports
this new dataset and derived properties: pH on the total scale
(pHT) and the CaCO3 saturation state with respect to
aragonite (Ωara). We also estimate anthropogenic carbon
(CANT) distribution in the water column using the TrOCA method
(Tracer combining Oxygen, inorganic Carbon and total Alkalinity). Along the
OUTPACE transect a deeper penetration of CANT in the intermediate
waters was observed in the MA, whereas highest CANT
concentrations were detected in the subsurface waters of the WGY. By
combining our OUTPACE dataset with data available in GLODAPv2 (1974–2009),
temporal changes in oceanic inorganic carbon were evaluated. An increase of
1.3 to 1.6 µmol kg−1 a−1 for total inorganic carbon in
the upper thermocline waters is estimated, whereas CANT increases
by 1.1 to 1.2 µmol kg−1 a−1. In the MA intermediate
waters (27 kg m−3 <σθ<27.2 kg m−3) an
increase of 0.4 µmol kg−1 a−1 CANT is
detected. Our results suggest a clear progression of ocean acidification in
the western tropical South Pacific with a decrease in the oceanic
pHT of up to −0.0027 a−1 and a shoaling of the saturation
depth for aragonite of up to 200 m since the pre-industrial period.
Achieving High Time-Resolution with a New Flow-through Type Analyzer for Total Inorganic Carbon in Seawater.