Abstract. We estimated monthly air–sea CO2 fluxes in the Arctic Ocean and
its adjacent seas north of 60∘ N from 1997 to 2014. This was done by
mapping partial pressure of CO2 in the surface water (pCO2w)
using a self-organizing map (SOM) technique incorporating chlorophyll a
concentration (Chl a), sea surface temperature, sea surface salinity, sea
ice concentration, atmospheric CO2 mixing ratio, and geographical
position. We applied new algorithms for extracting Chl a from satellite
remote sensing reflectance with close examination of uncertainty of the
obtained Chl a values. The overall relationship between pCO2w and
Chl a was negative, whereas the relationship varied among seasons and
regions. The addition of Chl a as a parameter in the SOM process enabled us
to improve the estimate of pCO2w, particularly via better
representation of its decline in spring, which resulted from biologically
mediated pCO2w reduction. As a result of the inclusion of Chl a, the
uncertainty in the CO2 flux estimate was reduced, with a net annual
Arctic Ocean CO2 uptake of 180 ± 130 Tg C yr−1. Seasonal to
interannual variation in the CO2 influx was also calculated.
[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.
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