open access

https://hdl.handle.net/2115/39027

Spatial variability and decadal trend of the oceanic CO2 in the western equatorial Pacific warm/fresh water

英語

Decadal trend

2009-04

Elsevier Ltd.

Deep Sea Research Part II : Topical Studies in Oceanography

56(8-10)

591-606

Data of the partial pressure of carbon dioxide in surface seawater (pCO2sw) collected in the western equatorial Pacific (144°E - 160°W, 5°S - 5°N) since the 1980's have been used to determine the spatial variability and decadal trends in pCO2sw. A total of 109 cruises since 1983, including 30 cruises since 1990 with total dissolved inorganic carbon (TCO2) measurements, are synthesized for this zone. The western equatorial Pacific warm/fresh surface water where T ≥ 29.0 ℃ and S ≤ 34.8 is nitrate-depleted and it is moderately supersaturated with CO2 (0 < ΔpCO2 (= pCO2sw - pCO2air) / μatm < 40). A slight CO2 undersaturation (-20 < ΔpCO2 / μatm < 0) was also observed on many cruises where thin, low density layers (σt < 21.4) capped barrier layers. The undersaturation may result from net biological uptake of CO2 due to nitrogen fixation. Excluding the data in such a extremely light waters, we determined changes in the linear growth rate of pCO2sw of +0.3 ± 1.3 μatm year^[-1] for 1985 - 1990, +2.2 ± 0.7 μatm year^[-1] for 1990 - 1999, and -0.2 ± 1.0 μatm year^[-1] for 1999 - 2004. The rate of increase was +1.5 ± 0.2 μatm year^[-1] for the entire period (1985 - 2004). The variation in the rate of increase of pCO2sw is fairly consistent with the change in the rate of increase of salinity-normalized TCO2 from +2.1 ± 0.4 μmol kg^[-1] year^[-1] during 1992 - 1999 to +0.4 ± 0.9 μmol kg^[-1] year^[-1] during 1999 - 2004. These changes are anti-correlated with the decadal variation in the geostrophic mass transport from subtropics of both hemispheres into the equatorial zone in the Pacific.

学術雑誌論文

Accepted Manuscript

0967-0645