Ocean acidification off the south coast of Japan: A result from time series observations of CO₂parameters from 1994 to 2008

Abstract

[1] Ocean acidification resulting from increases in present and future atmospheric CO 2 levels could seriously affect diverse coastal and oceanic ecosystems. In this work, we determine that a significant trend in ocean acidification is superposed on the large seasonal and interannual variabilities of acidity in surface waters off the south coast of Honshu, Japan, based on our repeated observations of partial pressure of CO 2 ( pCO 2 ), total inorganic carbon (TCO 2 ), and pH. Multiple regression analysis of TCO 2 as a function of temperature, salinity, and timing of observations shows that TCO 2 increased at a rate of +1.23 ± 0.40 mmol kg −1 yr −1 for the period 1994-2008, while no long-term change has been determined for total alkalinity calculated from TCO 2 and pCO 2 in seawater. These results indicate that pH and the aragonite saturation state (W arag ) are decreasing at a rate of −0.020 ± 0.007 decade −1 and −0.12 ± 0.05 decade −1 , respectively. If future atmospheric CO 2 levels keep increasing as predicted by the Intergovernmental Panel on Climate Change emission scenario A1FI, which postulates intensive fossil fuel use associated with very rapid economic growth, a further reduction of −0.8 to −1.0 in W arag is likely in the next 50 years. Such a rapid reduction of W arag could have negative impacts on a variety of calcareous organisms.

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

“…The observed pH changes in the surface ocean are consistent with those predicted based on equilibration of atmospheric CO 2 with the seawater (about −0.002 yr −1 ) (Dore et al, 2009;Byrne et al, 2010;Midorikawa et al, 2010;Ishii et al, 2011). In subsurface water, pH decreases (-0.003 yr −1 at Station ALOHA (22.75 • N; 158 • W; Dore et al (2009) and 0.004 yr −1 in North Pacific Intermediate Water; Byrne et al (2010)) have been enhanced by the accumulation of anthropogenic CO 2 and by natural variability related to temporal changes in physical and biogeochemical processes such as ocean ventilation, and remineralization of organic matter related to apparent oxygen utilization (AOU).…”

“…Ocean acidification of surface and subsurface waters of the North Pacific Ocean has been clearly documented in time series and repeat hydrography data (direct basin-wide observations) over the past two decades (e.g., Dore et al, 2009;Byrne et al, 2010;Midorikawa et al, 2010, Ishii et al, 2011Feely et al, 2004;Feely et al, 2012;Murata and Saito, 2012). The observed pH changes in the surface ocean are consistent with those predicted based on equilibration of atmospheric CO 2 with the seawater (about −0.002 yr −1 ) (Dore et al, 2009;Byrne et al, 2010;Midorikawa et al, 2010;Ishii et al, 2011).…”

“…In the winter mixed layer, pH decreased at -0.0011 ± 0.0004 pH in situ T yr −1 from 1997 to 2011, whereas aragonite , calcite , and CO 2− 3 remained unchanged. This decreasing trend of pH was slower than that predicted based on equilibration of atmospheric CO 2 with the seawater (−0.002 pH in situ T yr −1 ) and slower than decrease rates in other regions (Dore et al, 2009;Midorikawa et al, 2010;Ishii et al, 2011;Byrne et al, 2010). We attribute this lower rate to a reduction of CO 2 emission in winter caused by increased TA win .…”

Ocean acidification in the subtropical North Pacific estimated from accumulated carbonate data

“…The uptake of anthropogenic CO 2 by the ocean and the subsequent increase in the partial pressure of CO 2 in surface seawater (pCO 2 sea ) are not constant, however, but exhibit substantial interannual to decadal variability (e.g., in the North Pacific; Brix et al, 2004;Midorikawa et al, 2006;Ishii et al, 2011). Furthermore, possible future ocean acidification and global warming could reduce the capacity of the ocean to take up additional CO 2 .…”

Variability and trends of carbon parameters at a time series in the eastern tropical Atlantic

“…AzetsuScott et al, 2010) and undersaturation of aragonite has already occurred in surface water in some regions of the Arctic, such as the south-eastern Hudson Bay (AzetsuScott et al, 2014) and the Canadian Arctic archipelago (Chierici and Fransson, 2009). A decrease of pH and aragonite saturation state was also observed off the south coast of Japan from a time series at 136Á1408E over the period 1998Á2004 (Ishii et al, 2011). In different regions of the world ocean, a decrease of pH has been reported, for example, in the Atlantic subtropical gyre such as the European Station for Time series in the Ocean at the Canary Islands (ESTOC) and the Bermuda Atlantic Time-series Study (BATS), for periods over 15 years (Bates et al, 2014), at a time series station in the North Pacific near Hawaii over 20 years (Dore et al, 2009).…”