Decadal increases of anthropogenic CO2 along 149°E in the western North Pacific

Abstract

Using high‐quality data for dissolved inorganic carbon and the related water properties obtained by two cruises over 12 years (1993–2005), we estimated increases in anthropogenic CO2 (ΔnCTCAL) along the 149°E meridian (WHP P10) from 4°S to 30°N. Significant ΔnCTCAL was found down to a maximum depth of about 800 m. In the upper thermocline (25.0–26.0σθ), ΔnCTCAL was mostly 10–13 μmol kg−1, close to the value expected from recent increases in atmospheric CO2. In the lower thermocline (26.1–27.5σθ), ΔnCTCAL was 3.5 ± 0.9 and 4.7 ± 1.7 μmol kg−1 in North Pacific Intermediate Water and Antarctic Intermediate Water, respectively. Water column inventories of ΔnCTCAL over the 12 years were calculated to be 3.8 ± 1.2 mol m−2 (minimum) and 7.3 ± 2.2 mol m−2 (maximum) at latitudes 0°–10°N and 24°N–30°N, respectively, showing a distribution pattern similar to that of the long‐term anthropogenic CO2 accumulation reported previously. The uptake rate of anthropogenic CO2 along the WHP P10 line over the time period was estimated to be 0.5 ± 0.1 mol m−2 a−1, which is half the rate in the South Pacific (1.0 ± 0.4 mol m−2 a−1), but equal to that in the South Atlantic (0.6 ± 0.1 mol m−2 a−1). We discuss the relationships between ΔnCTCAL and changes in apparent oxygen utilization from the standpoint of physical‐biological interactions.