Abstract: A multi-layer structure and mixing in the upper water column of Lake Biwa during summer time



Authors: H.Yamazaki, H.Honma,T.Nagai, M. Doubell, K.Amakasu and M.Kumagai

We have conducted a 24 hour station survey to observe mixing process in the upper water column of Lake Biwa during summer 2008.  We deployed a free fall microstructure profiler, TurboMAP-L, and a conventional CTD with oxygen sensor.  We also used a multi-frequency acoustic instrument TAPS that can map the distribution of zooplankton with several different scales.  The upper water column was strongly stratified below the surface mixed layer.  We found two mixing regimes: the surface mixing layer, ca 0-12m,  and the subsurface mixing layer, ca 20-30m.  These two layers were separated by a non-mixing layer, ca 12-20m, that consisted a multi-layer ecosystem structure: local oxygen maximum, local oxygen minimum, chlorophyll peak and highly abundant small zooplankton layer. We present how mixing is relating to these layers and discuss oxygen flux through this layer.