%A"Midorikawa, Takashi" %A"Ishii, Masao" %A"Sasano, Daisuke" %A"Kosugi, Naohiro [Geochemical Research Dept., Meteorological Research Institute Tsukuba (Japan)]" %A"Saito, Shu [Geochemical Research Dept., Meteorological Research Institute, Tsukuba (Japan)]" %A"Institute of Observational Research for Global Change (IORGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka (Japan))" %A"Motoi, Tatsuo [Oceanographic Research Dept., Meteorological Research Institute, Tsukuba (Japan)]" %A"Kamiya, Hitomi" %A"Nakadate, Akira" %A"Nemoto, Kazuhiro [Global Environment and Marine Dept., Japan Meteorological Agency, Tokyo (Japan)]" %A"Inoue, Hisayuki Y [Graduate School of Environmental Earth Science, Hokkaido Univ., Sapporo (Japan)]" %D2010 %I; %2 %J[] %K54 ENVIRONMENTAL SCIENCES, PH VALUE, PACIFIC OCEAN, ACIDIFICATION, CARBON DIOXIDE, SEASONAL VARIATIONS %PMedium: X; Size: page(s) 649-659 %TDecreasing pH trend estimated from 25-yr time series of carbonate parameters in the western North Pacific %XWe estimated long-term trends of ocean acidification in surface waters in latitudinal zones from 3 deg N to 33 deg N along the repeat hydrographic line at 137 deg E in the western North Pacific Ocean. Estimates were based on the observational records of oceanic CO{sub 2} partial pressure and related surface properties over the last two decades. The computed pH time series both for 25 yr in winter (late January to early February) and for 21 yr in summer (June-July) exhibited significant decreasing trends in the extensive subtropical to equatorial zones, with interannual variations that were larger in summer. The calculated rates of pH decrease ranged from 0.0015 to 0.0021 yr-1 (average, 0.0018 +- 0.0002 yr-1) in winter and from 0.0008 to 0.0019 yr-1 (average, 0.0013 +- 0.0005 yr-1 ) in summer. The thermodynamic effects of rising sea surface temperature (SST) accounted for up to 44% (average, 15%) of the trend of pH decrease in the subtropical region in winter, whereas a trend of decreasing SST slowed the pH decrease in the northern subtropical region (around 25 deg N) in summer. We used the results from recent trends to evaluate future possible thermodynamic changes in the upper ocean carbonate system %0Journal Article %N;Journal ID: ISSN 0280-6509; TRN: SE1107066 %1 %CSweden %Rhttps://doi.org/10.1111/J.1600-0889.2010.00474.X Journal ID: ISSN 0280-6509; TRN: SE1107066 SWD %GEnglish