A tidal front in winter influenced by river discharge

Abstract

Water quality of Osaka Bay is greatly influenced by freshwater discharge from rivers, to the effect of salinity playing a major role in forming the stratification. The tidal front is expected to appear in such an area even in winter considering the theory of the formation of a tidal front. From the field observation, we recognized a tidal front in winter for the first time in Osaka Bay. The critical value of a parameter log(H/U 3 ) for generation of a tidal front is obtained as a function of river discharge and cooling effect through sea surface. Differences of nutrients (NH 4 -N, PO 4 -P) concentration across the front are not clear, probably because they are utilized by phytoplankton easily. But in (NO 2 -N)+(NO 3 -N), DIN, PP and T-P, there is a discontinuity structure across the front, even if the absolute value of concentration difference is small.

Nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter

“…In Fig. 1 K and O means the typical location of the thermohaline front in Kii Channel and tidal front in Osaka Bay, respectively (Yoshioka, 1988;Yanagi et al, 1988;Yuasa et al, 1992). The course of the ferry boat crosses these fronts.…”

“…In the central part of Osaka Bay, nitrogen and phosphorus exibit a sharp change across the Osaka Bay front in which temperature and salinity do so in all observations. This front is the tidal front in Osaka Bay (Yuasa and Ueshima, 1992).…”