Typology of hydrological structures modelled and observed over the Bay of Biscay shelf

Abstract

Collecting hydrological observations over the whole Bay of Biscay continental shelf can require several weeks. As a result, the observations are not truly synoptic and the interpretation of hydrological structures is corrupted by the time-lags between observations at distinct locations. We evaluated the effects of non-synoptic sampling during a spring cruise (17 April to 13 May 2000), using outputs from 3D hydrodynamic models as a substitute for true synoptic sampling. We developed a method for clustering hydrological regions based on the vertical structure of the water column and temporal changes in hydrography. In parallel, outputs from the 3D model were compared with field observations. The results show that in spring 2000 the Bay of Biscay continental shelf could be separated into six principal hydrological regions, one of them being characterised by vertical stability and low temporal variability. This region corresponds to an area where pelagic fish spawning activity is known to be persistently low.