Low sea surface salinity in the East Sea during the last glacial maximum: review on freshwater supply

Abstract

Low sea surface salinity event in the East Sea during the LGM (last glacial maximum) has been critically and thoroughly reviewed based on previous studies, but freshwater source for this low paleosalinity still remains to a great extent questionable. This paper presents that the Korea Strait was partially open during the LGM, transporting the paleo-Water (0.5–2.1×1012 m3/yr) to the East Sea. The paleo-Water, presumably a mixture of high amount of freshwater and the paleo-Tsushima Current, might not be enough to explain the decrease of sea surface salinity (SSS) in the surface layer (79.75×1012 m3) of the LGM East Sea. Assuming that the paleo-Water is entire freshwater, it could only lower less than 1.1‰ of surface salinity. Moreover, differences in SSS (between 20‰ of the LGM and the present 34‰ in the East Sea) and planktonic foraminiferal σ18O (between the regional East Sea and the global Pacific Ocean during the LGM) are approximately 14‰ and 3.8–4.1‰, respectively. According to general trend that 1‰ salinity decrease correponds to about 0.5‰ lowering of σ18O (Broecker, 1989), 3.8–4.1‰ decrease in σ18O could lower 7.6–8.2‰ in salinity, resulting in 25.8–26.4‰ of the SSS in the LGM East Sea. This SSS (25.8–26.4‰) is still much saline than 20‰. Furthermore, about 5.8–6.4‰ of salinity difference needs to be explained, and further indicates freshwater dilution in the LGM East Sea. Therefore, these semi-quantitative calculations evidence additional freshwater supply to the East Sea, lowering sea surface salinity during the LGM. Potentially additional source for freshwater might have been the Amur River inflow into the East Sea.