Ocean acidification from 1997 to 2011 in the subarctic western North Pacific Ocean

Abstract

Abstract. Rising atmospheric CO 2 contents have led to greater CO 2 uptake by the oceans, lowering both pH due to increasing hydrogen ions and CaCO 3 saturation states due to declining carbonate ion (CO 2− 3 ). Here we used previously compiled data sets and new data collected in 2010 and 2011 to investigate ocean acidification of the North Pacific western subarctic gyre. In winter, the western subarctic gyre is a source of CO 2 to the atmosphere because of convective mixing of deep waters rich in dissolved inorganic carbon (DIC). We calculated pH in winter mixed layer from DIC and total alkalinity (TA), and found that it decreased at the rate of −0.0011 ± 0.0004 yr −1 from 1997 to 2011. This decrease rate is slower than that expected under the condition of seawater/atmosphere equilibration, and it is also slower than the rate in the subtropical regions (−0.002 yr −1 ). The slow rate is caused by a reduction of CO 2 emission in winter due to an increase in TA. Below the mixed layer, the calcite saturation horizon (∼ 185 m depth) shoaled at the rate of 2.9 ± 0.9 m yr −1 as the result of the declining CO 2− 3 concentration (−0.03 ± 0.01 µmol kg −1 yr −1 ). Between 200 m and 300 m depth, pH decline during the study period (−0.0051 ± 0.0010 yr −1 ) was larger than ever reported in the open North Pacific. This enhanced acidification rate below the calcite saturation horizon reflected not only the uptake of anthropogenic CO 2 but also the increase in the decomposition of organic matter evaluated from the increase in AOU, which suggests that the dissolution of CaCO 3 particles increased.

Detecting the progression of ocean acidification from the saturation state of CaCO3 in the subtropical South Pacific

“…The results of the decomposition of ΔΩ arg were similar to those for ΔΩ cal (Figure 6, blue 47°N, 160°E), Wakita et al [2013] reported rates of À0.0055 a À1 to À0.0077 a À1 and À0.0035 a À1 to À0.0048 a À1 for Ω cal and Ω arg , respectively. Using repeat hydrography data, Murata and Saito [2012] found a maximum rate of Ω arg decrease of 0.034 a À1 at 200-300 dbar at 20°N along the 179°E meridian.…”

Calcium carbonate saturation and ocean acidification in Tokyo Bay, Japan

“…A detailed and long-term observation in the subtropical North Pacific off the southern coast of Japan showed that Ωar of surface water is ~3.5 during the summer, but decreases to lower than 3.0 during the winter (at 33°40′N-34°00′N; Ishii et al (2011)). In the western subarctic gyre further north, a similar seasonal pattern in surface Ωar was observed, but with a larger variation and lower values for both summer (~2.5) and winter (~1.3) (at ~45°N; Wakita et al 2013). From these observations, the Ωar of waters in Tokyo Bay would be ~3 with a maximum value in summer, if there is no alternation of water properties by processes within the bay.…”

“…Ishii et al 2011;Wakita et al 2013). The very high primary production and resulting remineralization of organic matter in this shallow and eutrophicated bay are the major causes of such large variations.…”

“…Variations are much larger than those in the open ocean (e.g.,Wakita et al 2013;Yasunaka et al 2013).…”

An updated synthesis of the observed and projected impacts of climate change on the chemical, physical and biological processes in the oceans

“…Calculated pH trends for the North Atlantic Gyre suggest a decrease of −0.0022 ± 0.0004 units yr −1 over the period 1981-2007(Lauvset and Gruber, 2014. In the North Pacific, a pH decrease of −0.0011 ± 0.0004 units yr −1 from 1997 to 2011 has been calculated ( Table 3; Wakita et al, 2013).…”