Use of carbon isotopic composition of alkenone as a CO2 proxy in the East Sea/Japan Sea

The carbon isotopic composition of alkenones (δ13C37:2) can be used as a pCO2 proxy, although the applicability of this method is still controversial. In this study, the present oceanic pCO2 was reconstructed by analysing the δ13C37:2 of sinking particles collected by sediment traps in the East Sea/Japan Sea. The reconstructed pCO2 was compared with observed pCO2 to examine the applicability of this method. We applied the same method to marine sediments of core 05PC-21 to reconstruct the past pCO2 of the East Sea for the last 190 cal ka BP. The seasonal variation patterns of pCO2 which was reconstructed from the δ13C37:2 of sinking particles in the water column corresponded with those of observed oceanic pCO2. The pCO2 was relatively low in spring, and increased in summer. In consideration of the factors that can affect the seasonal variation of the pCO2, sea surface temperature seems to be a main factor. However, from January to March, there would be an influence of a deepening of the mixed layer depth and the vertical mixing of seawater. In April, the pCO2 decreased by a phytoplankton bloom. During the last 190 cal ka BP, oceanic pCO2 values and its variation pattern which were reconstructed by analysing the δ13C37:2 of marine sediment were similar to those of atmospheric pCO2 that were reconstructed from ice cores at high latitudes. These suggest that the carbon isotopic composition of alkenones (δ13C37:2) can be used as a proxy of long-term change in the partial pressure of atmospheric CO2.