The climatological freshwater input to the Sea of Okhotsk and the potential role of the Kamchatka Peninsula

Abstract:

The Sea of Okhotsk, which locates at the northwest of Pacific, produces Dense Shelf Water (DSW) by the high sea ice production. DSW plays as an important transporter of many materials to the North Pacific Ocean via the intermediate layer. Uehara et al. (2014) found that the variability of DSW salinity correlates the preceding precipitation around the Kamchatka Peninsula with anti-phase. Thus, the freshwater discharge from there might have a hidden contribution to the hydrological cycle in the Sea of Okhotsk. However, numerous small river basins with the lack of the direct observation hide the actual amount of total discharge. Such uncertainty also leads to unclarity of the estimation about total freshwater input in the Sea of Okhotsk.

In this study, we evaluated riverine discharge from the Kamchatka Peninsula by using the atmospheric model (WRF) with high horizontal resolution (5km). The riverine discharge derived by the precipitation and evaporation was compared with observed riverine discharge provided by Russian Hydromet. Additionally, the climatic freshwater input into the Sea of Okhotsk was evaluated by using several atmospheric reanalyses together with WRF. As a result, the total freshwater input reached about 1284 km³ /yr which consists of 49 % from the precipitation over the sea, 28 % from the Amur River, and 21 % from the northern coast of the sea and the Kamchatka Peninsula. Although the last region occupies about 14 % to the total catchment, the heavy precipitation in the narrow area contributes to increasing the discharge.

We also evaluated how the ocean salinity around the Kamchatka Peninsula is modified by the freshwater discharge. As a result, the salinity change expected by the seasonal amount of freshwater discharge can be comparable to the amount of observed seasonal tendency of salinity in the surface layer, especially for the summer season. This suggests that the climatic variation of halocline is largely dominated by the discharge of the Kamchatka Peninsula. Moreover, the variability of annual freshwater discharge relates to sea ice over the Sea of Okhotsk and sea surface temperature (SST). The significant lag relation preceding the discharge was found as negatively to the sea ice and positively to annual SST around Peninsula, which looks similar to the evidence found for the Amur River (Ogi et al.2001).