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Original Research Papers

Decreasing pH trend estimated from 25-yr time series of carbonate parameters in the western North Pacific

Authors:

Takashi Midorikawa ,

Geochemical Research Department, Meteorological Research Institute, Nagamine 1–1, Tsukuba 305–0052, JP
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Masao Ishii,

Geochemical Research Department, Meteorological Research Institute, Nagamine 1–1, Tsukuba 305–0052, JP
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Shu Saito,

Geochemical Research Department, Meteorological Research Institute, Nagamine 1–1, Tsukuba 305–0052; Institute of Observational Research for Global Change (IORGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima-chō 2–15, Yokosuka 237–0061, JP
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Daisuke Sasano,

Geochemical Research Department, Meteorological Research Institute, Nagamine 1–1, Tsukuba 305–0052, JP
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Naohiro Kosugi,

Geochemical Research Department, Meteorological Research Institute, Nagamine 1–1, Tsukuba 305–0052, JP
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Tatsuo Motoi,

Oceanographic Research Department, Meteorological Research Institute, Nagamine 1–1, Tsukuba 305–0052, JP
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Hitomi Kamiya,

Global Environment and Marine Department, Japan Meteorological Agency, Otemachi 1–3-4, Chiyoda-ku, Tokyo 100–8122, JP
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Akira Nakadate,

Global Environment and Marine Department, Japan Meteorological Agency, Otemachi 1–3-4, Chiyoda-ku, Tokyo 100–8122, JP
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Kazuhiro Nemoto,

Global Environment and Marine Department, Japan Meteorological Agency, Otemachi 1–3-4, Chiyoda-ku, Tokyo 100–8122, JP
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Hisayuki Y. Inoue

Graduate School of Environmental Earth Science, Hokkaido University, N10W5, Kita-ku, Sapporo 060–0810, JP
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Abstract

We estimated long-term trends of ocean acidification in surface waters in latitudinal zones from 3°N to 33°N along the repeat hydrographic line at 137°E in the western North Pacific Ocean. Estimates were based on the observational records of oceanic CO2 partial pressure and related surface properties over the last two decades. The computed pH time series both for 25 yr in winter (late January–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°N) in summer. We used the results from recent trends to evaluate future possible thermodynamic changes in the upper ocean carbonate system.

How to Cite: Midorikawa, T., Ishii, M., Saito, S., Sasano, D., Kosugi, N., Motoi, T., Kamiya, H., Nakadate, A., Nemoto, K. and Inoue, H.Y., 2010. Decreasing pH trend estimated from 25-yr time series of carbonate parameters in the western North Pacific. Tellus B: Chemical and Physical Meteorology, 62(5), pp.649–659. DOI: http://doi.org/10.1111/j.1600-0889.2010.00474.x
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  Published on 01 Jan 2010
 Accepted on 10 Jun 2010            Submitted on 23 Dec 2009

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