Oceanic Suess effect of δ13C in subpolar region:: The North Pacific -: art. no. 2159

[1] We propose a simple approach for estimating the recent oceanic Suess effect of delta(13)C in the subpolar region of the North Pacific, an area which experiences a large seasonal variability of carbonate species, due to the biological activity and vertical water mixing. This approach is based simply on time-series data of delta(13)C from July 1997 to July 2001 and an equation of the Fourier sine expansion. Applying our approach to the fixed sampling location in the western North Pacific, station 'KNOT', we estimated values of -0.012parts per thousand-delta(13)C yr(-1) for the Suess effect of delta(13)C with an amplitude of 1.3parts per thousand-delta(13)C and 1.0 mumol-C kg(-1) yr(-1) for the increase rate of dissolved inorganic carbon with an amplitude of 134 mumol-C kg(-1) in surface water. The Suess effect of delta(13)C in this region was a similar value to that estimated in the Southern Ocean producing the deep water, while it was half as much as values estimated in the subtropical regions which experience a small seasonal variability. The ratio of Suess effect to the increase rate of dissolved inorganic carbon was -0.012parts per thousand (mumol kg(-1))(-1), which was different from the global mean values calculated by recent modeling study. Therefore, we conclude that the Suess effect of delta(13)C in the polar and subpolar regions is generally smaller than found in other regions, suggesting that it is necessary to reevaluate the uptake rate of anthropogenic carbon which has been based on the assumption that the ratio is uniform over the entire ocean.