Study on Water Exchange between Osaka Bay and Pacific Ocean

根据1995年夏季在Ki-i海峡进行的实地调查，结果表明，氮、磷等营养元素在土壤中的含量较高，研究结果表明，1998年以来，大坂湾的氮磷输入通量与1999年以来的入海通量基本一致，而1999年以来的入海通量与1999年以来的入海通量基本一致通过现场调查，进入大坂湾，并详细检查流结构的三维斜压流模式。(1)1997年8月23日在大坂湾进行了12小时的同步观测。在大坂湾沿着约20 m深的断面和友岛海峡进行了12小时的流速、温度和盐度的测量和水样采集。同时在明石海峡进行了STD和水样采集。在氮平衡方面，明石海峡一天的流入量为24吨，友岛海峡一天的流出量为35吨。在P. 68吨流入量和1吨流出量的情况下，这意味着大坂湾流出11吨N，流入67吨P。另一方面，16吨N和5吨P通过河口环流向湾头输送。(2)数值试验首先，在水平分辨率为1,000 m，垂直方向为10层的大尺度区域（包括大坂湾、Harimanada海和Ki-i海峡）计算了流场和密度结构，以获得Kitan海峡附近小尺度计算区域的边界条件。通过250 m的小尺度计算，阐明了海峡附近大尺度涡的产生机制、余流系统、水交换等。

According to the field survey conducted in Ki-i Channel in summer of 1995, its results indicated that lots of nutrients such as nitrogen (N) and phosphorus (P) of Pacific Ocean intrudes into Osaka Bay.Their volume surprisingly corresponds to total value discharged from coastal land area.One of objects of the present study is to verify the result of field survey.Other purpose is to clarify the inflow fluxes of N and P into Osaka Bay by field survey and to examine the flow structure in detail by a three-dimensional baroclinic flow model.(1) Field survey to clarify fluxes of N and PSimultaneous measurements in Osaka Bay were conducted on 23rd August in 1997.12 hours measurements of velocity, temperature and salinity, and water sampling were done in the sections across Osaka Bay along about 20 m depth and Tomogashima Channel.And, during the same time, STD and water sampling were done in Akashi Straits.As a result, in regard to the balance of N, 24 ton during one day inflows through Akashi Straits and 35 ton outflows thorough Tomogashima Channel.In the case of P.68 ton inflows and 1 ton outflows That means that 11 ton of N outflows from Osaka Bay and 67 ton of P inflows.On the other hand, 16 ton of N and 5 ton of P are transported toward the head of bay by estuarine circulation.(2) Numerical experimentAt first, the flow and density structures are computed in the large scale domain including Osaka Bay, Harimanada Sea and Ki-i Channel with 1,000 m horizontal resolution and 10 layers in vertical direction in order to obtain the boundary conditions for the small scale domain of computation near the Kitan Straits.Secondly, the small scale computation with 250 m clarifies the production mechanism of large scale eddy near the straits, residual current system, water exchange and so on.