Multivariate analysis of surface water characteristics in the summer regime of the western Irish Sea

Abstract A part of the western Irish Sea is strongly stratified during the summer months, with the boundary of stratification marked by a front with horizontal temperature gradients. Continuous on-line analysis has been used to record the surface water variability of nine characteristics along a cruise path in this area. Multivariate analysis (principal component) indicates the presence of four distinct water types separated by thermal gradients. Two of these water types show land mass influence and two illustrated the effects of the mixed and stratified regimes. The stratified surface waters had a marked degree of homogeneity with respect to the measured characteristics, while the mixed surface waters exhibited greater variability. Marked micro-variations in chlorophyll a concentrations were observed in the latter water type. No consistent relationships were observed among the physical, chemical, and biological variables across the front because of the gradual change in the gross properties of the mixed surface water during its northward passage through the Irish Sea.