Low Sea Surface Salinity Event of the Japan Sea During the Last Glacial Maximum

Abnormal lightening of the oxygen isotope ratio (d(18)O) of planktonic foraminifera during the Last Glacial Maximum (LGM, similar to 21 kyr BP) suggests that the Japan Sea had experienced a low sea surface salinity event at that time. However, the exact value and timing of minimum salinity have been controversial so far. To address this issue, we adopt a simple box model and reconstruct the sea surface salinity in the Japan Sea (S-JP) over the past 35 kyr with a focus on the LGM period. In particular, as input data for the box model, the inflow transport through the Tsushima Strait (Q) is converted from sea level evolution using a newly defined relationship, in which Q reduces non-linearly with the sea level reduction through a dynamically-constrained realistic ocean model. Meanwhile, another input data of the box model, sea surface freshwater flux (precipitation minus evaporation (P-E) evolution), is obtained by averaging multi-paleoclimate models (PMIP3 and MIROC4m models) results. The reconstructed S-JP using the box model reached its minimum value (20.2) at 20 kyr BP with a high coefficient of determination (R-2) for d(18)O (0.81, p << 0.01). Further analysis demonstrates that the above non-linear relationship, determined by h(3/2) (h is the strait depth), promises a more reasonable reconstruction of the S-JP evolution. It is also concluded that both the value and timing of the minimum S-JP depend on the Q evolution, and the P-E evolution can modify the former. Therefore, the combination of Q and P-E determines the exact value and timing of minimum salinity.