Seawater chemistry and helium isotopes in the Tatar Strait, Far Eastern Federal District, Russia

Abstract:

Semi-enclosed basins in general have been particularly susceptible to climate change throughout the geologic past. Our research focuses on using chemical and isotopic tracers to determine the present distribution and circulation of waters in one such basin, the Tatar Strait. Seawater samples were collected using Niskin bottles at 16 sites along two major transects and were analyzed onboard the R/V Akademik M.A. Lavrentyev using gas chromatography in late May, 2019. Previous research in the area has focused on the presence of hydroacoustic plumes and on hydrocarbons dissolved in shallow sediments¹ . Two sites located near the gas plumes were also sampled for land-based determination of noble gas and stable isotopic composition. The primary input of cold waters into this shallow basin is assumed to be the Amur River to the north, which when coupled with seasonal ice melt, has generally resulted in circulation of cold less-saline surface waters spilling into the northern reaches of the Japan Sea. Deeper waters are more saline, and some of the ²⁰Ne/⁴He ratios seem to be influenced by ice melt while others have been influenced by bubble exclusion during the formation of ice. This is consistent with the stable oxygen isotopic composition as well. Although the noble gas sampling was done above active gas plumes, no appreciable affect of the plumes themselves was noticed. The deeper samples retain tritiogenic ³He similar to intermediate waters observed in the Japan Sea^2,3. Although our data is temporally limited to the springtime, it does give some indication of layers which undergo seasonal fluctuations as well as those the presence of more stable deeper water layers.

References: ¹Yatsuk et al., 2019, ²Postlethwaite et al., 2005,³Takahata et al., 2008.