Circulation and haline structure of a microtidal bay in the Sea of Japan influenced by the winter monsoon and the Tsushima Warm Current

Abstract

Mooring and hydrographic surveys were conducted in Tango Bay, a microtidal region of freshwater influence (ROFI) in the Sea of Japan, in order to clarify the circulation pattern in the bay and its driving forces. Monthly mean velocity records at four stations revealed an inflow and outflow at the eastern and northern openings of the bay, respectively, indicating an anticyclonic circulation across the bay mouth. The circulation was significantly intensified in winter, in accordance with the prevailing NW wind component of the winter monsoon. The anticyclonic circulation at the bay mouth was connected to an estuarine circulation that was evident near the mouth of the Yura River at the bay head. Surface salinity just offshore of the river mouth was closely related to the Yura River discharge, whereas in lower layers the offshore water had a stronger influence on salinity. Prior to a seasonal increase in the Yura River discharge, summer salinity decreased markedly through the water column in Tango Bay, possibly reflecting intrusion of the Changjiang Diluted Water transported by the Tsushima Warm Current. In contrast with the traditional assumption that estuarine circulation is controlled mainly by river discharge and tidal forcing, the circulation in Tango Bay is strongly influenced by seasonal wind and the Tsushima Warm Current. The narrow shelf may be responsible for the strong influence of the Tsushima Warm Current on circulation and water exchange processes in Tango Bay.

Winter monsoon promotes the transport of Japanese temperate bass Lateolabrax japonicus eggs and larvae toward the innermost part of Tango Bay, the Sea of Japan

“…The density of planktonic eggs and larvae was correlated with the linear distance from the eastern opening of Tango Bay (Station 4), through which anticyclonic circulation flows into the bay (Itoh et al, ). Spearman's correlation of the density of eggs with the distance was always negative in January, being statistically significant in January 2013, 2016, and 2017 ( p < .05; Table ).…”

“…Although the correlation between winter winds and water flows was not statistically significant at Station 2, the clockwise turning of the water flows with respect to depth suggests the influence of Ekman current, which is south‐ to southwestward for northwesterly winds (Figure ). Combined with the geostrophically driven anticyclonic circulation (Itoh et al, ), this Ekman current likely transported planktonic larvae southwestward, while the combined flow may also have been modified by estuarine circulation. The southwestward transport of planktonic larvae by wind‐driven water movement was always discernible during the mooring observations with an exception of late January 2014, when planktonic larvae were uniformly distributed in the bay under exceptional conditions of wind forcing and water movement (Figures and ).…”

“…An anticyclonic circulation dominates around the mouth of Tango Bay, flowing from the eastern opening to the northern opening (Itoh et al, ). This circulation is intensified by northwesterly winds prevailing in winter, as Tango Peninsula likely weakens the southeastward wind stress close to the coast and the consequent negative stress curl accumulates water in Tango Bay.…”

“…To characterize atmospheric and oceanographic conditions at daily‐to‐yearly scales, we considered four key environmental parameters: wind velocity, air temperature, water temperature, and freshwater discharge (Itoh et al, ). Wind velocity data were obtained from the ERA‐Interim reanalysis of European Center for Medium‐Range Weather Forecasts (ECMWF), since observational data concerning wind velocities over Tango Bay were unavailable.…”

Spatial variations in zooplankton community structure along the Japanese coastline in the Japan Sea: influence of the coastal current

“…CC BY 4.0 License. Hirose et al, 2009;Onitsuka et al, 2010;Kodama et al, 2016;Kodama et al, 2015), and is the spawn and nursery field of important fisheries resources (Goto, 1998(Goto, , 2002Ohshimo et al, 2017;Kanaji et al, 2009) Zooplankton are transported by the TWC: the distributions of the giant jellyfish, Nemopilema nomurai, which originates from the Chinese coastal area of the East China Sea (Kitajima et al, 2015;Uye, 2008), and the giant salps, Thetys vagina (Iguchi and Kidokoro, 2006), depend on the TWC in the Japan Sea. However, studies of the relationship between the TWC and small 5 zooplankton such as copepods are very limited, especially concerning their spatial distribution.…”