Study on generation of wind-dirven current and behavior of the density interface between salt and fresh waters in Lake Abashiri

Abstract

In recent years, Lake Abashiri has been confronted with serious problems due to water accidents induced by aoshio and eutrophication. By using a fish detector and ADCP, we could make clear the spatial and temporal structure of density stratified flow, the short-term behaviors of salinocline(halocline) just after the occurrence of aoshio, and the overall characteristics of the flow in this lake. Based on the results of the observation, we carried out the numerical analysis regarding to the time-varying behaviors of the density interface and the wind-driven flow. Comparing the calculation results with field data, we could evaluate the influence of wind, the horizontal and vertical structure of the lake on the flow and the behaviors of salinocline.

Dynamic behaviours of anoxic saline water in Lake Abashiri, Hokkaido, Japan

“…This means that seawater moving upslope mixes with the upper fresh water in the lower Abashiri River. Ikenaga et al (1997) revealed by ®eld observation and numerical simulation that vertically constant salinity in the Abashiri River channel results from the breakage of a salt wedge by tidal currents. Figure 5 shows hourly records of wind vectors at sites W1 and W2 for the period of 5 June±23 August.…”

“…Winds at site W1 were then very weak over these periods. This suggests that the northward wind induced entrainment and consequent uplift of the lower cold saline water o Memanbetsu Bay by southward countercurrents in the bottom layer ( Figure 6; Ikenaga et al, 1997). Figure 10 shows time series of¯ow velocity and water temperature in the lower layer of site MD.…”

“…8 m s À1 occurred southwestward to northward during 0000±0700 h. Hence, by comparison with Figure 6, a northward wind rather than a southward wind is considered to have induced a relatively strong entrainment and advective diusion of the saline water, and a relatively large sediment resuspension in or o Memanbetsu Bay. The numerical simulation of Ikenaga et al (1997) with a multi-level model showed that a northward wind of 1±7 m s À1 makes southward countercurrents enforced in the bottom layer in or o Memanbetsu Bay (see Chikita et al, 1996Chikita et al, , 1999 for countercurrents). The countercurrents for compensation possibly initiated the entrainment of the lower saline water o Memanbetsu Bay, and subsequently produced its advective diusion into the bay.…”

“…The isoplethic patterns of 8±16 8C in temperature and 4±18% in salinity between 8000 m and 12 000 m in distance allow us to infer that the inverse strati®cation is connected to the upper entrainment and diusion of the saline water. Downwelling currents could be induced in the lower layer through vertical momentum transfer by wind-driven vertical circulation in the upper layer (see Ikenaga et al, 1997); the entrainment of the upper saline water was possibly initiated by the vertical shear from the downwelling currents, which coincide with countercurrents in the lower part of the upper layer to compensate for wind-driven currents in the surface layer. Hydrol.…”

“…The anoxic water was produced by deoxidization of intruded seawater during a long residence time ( probably more than several years (Mori, 1975)). Some researchers have investigated the upslope movement of seawater in the lower Abashiri River, the behaviours of intruded seawater and the lower saline water, and entrainment of the lower water in Lake Abashiri by ®eld observations and numerical simulation (Hirano et al, 1991;Yamada et al, 1996;Ikenaga et al, 1997Ikenaga et al, , 1998Shimizu et al, 1997). However, they did not systematically discuss how the intruded seawater, the lower saline water, and the upper freshwater in the lake interact.…”