Journal of Oceanography, (revised)
Winter oceanographic conditions in the southwestern part of the
Okhotsk Sea and their relation to sea ice
K. I. Ohshima, G. Mizuta, M. Itoh, Y. Fukamachi, M. Wakatsuchi, T. Watanabe,
Y. Nabae, and K. Suehiro
In the southwestern part of the Okhotsk Sea we carried out oceanographic and sea-ice observations on board the icebreaker Soya, in February 1997. We first found that a mixed layer with temperatures uniformly near the freezing point extends down to a depth of ~ 300 m, which is much deeper than previously reported. It is suggested that this deep mixed layer originated from the north (off East Sakhalin), being advected along the shelf slope via the East Sakhalin Current, accompanied with the thick (average of 0.6 m) first-year ice. This vertically uniformed winter water, through mixing with the surrounding water, makes the surface water more saline (losing a characteristic of East Sakhalin Current Water) and the water in the 100-300 m depth zone less saline, colder, and oxygen-richer (a characteristic of the intermediate Okhotsk Sea water). The oceanographic structure and heat budget analysis suggest that new ice zone, which often appears at ice edges, can be formed through preconditioning of thick ice advection and subsequent cooling by the latent heat release due to its melting.