The hydrographic structure in the Sea of Okhotsk is unique, especially regarding the existence of the Okhotsk Dichothermal Layer (ODTL), a near-freezing layer beneath a highly seasonal surface layer. The formation of this cold layer is linked to extensive sea-ice coverage in winter. Observations revealed strong signals of interannual variations of winter sea-ice extent in this marginal sea and indicated a likely linkage with observed changes in temperature and salinity fields. In this paper, a 1.5-dimensional coupled ocean-ice model is used to study the formation of the ODTL and to test how external forcing fields affect this process. The model, despite its simplicity, simulates well the temperature and the salinity profiles that resemble observations. It is found that the ODTL is replenished during winter convection. During warm seasons, meltwater creates a very stable surface layer that effectively prevents mixing between warm surface water and cold water in the ODTL. Thus the seasonal variation of sea ice plays a leading role in maintaining the ODTL structure. Although the minimum temperature feature of the ODTL is robust in the model, the hydrographic structure in the Sea of Okhotsk is sensitive to interbasin exchanges with the North Pacific Ocean and the Sea of Japan and to some other external forcing fields. More interestingly, an interannual oscillation arises from this model even though the model forcing excludes any interannual variation. We concluded that such oscillation is due to the model's subharmonic response to the annual cycle of the forcing fields. It suggests that the seemingly zero-net-gain annual cycle of winter freezing and spring melting is actually an effective process transporting salt from surface to deeper layers and thus the coupled ocean-ice's subharmonic response to this annual cycle is an important source for low-frequency variations. ¿ American Geophysical Union 1996