The distribution of benthic foraminifera in the Celtic Sea: The significance of seasonal stratification.

Seasonal stratification is an important phenomenon in tidally-stirred shelf seas, influencing biological productivity, sedimentation rates, the organic content of shelf sediments, and the climate of surrounding landmasses. Previous micropaleontological and stable isotopic investigation investigation of a Holocene sequence from the Celtic Sea suggests that benthic foraminiferal distributions are linked to the physical and biological oceanographic characteristics associated with stratification. We have tested this hypothesis by analyzing the living and dead foraminiferal faunas from surface samples collected during across-frontal cruises during the summers of 1995 and 1996. Foraminiferal and environmental data for 56 samples are presented. Live and dead foraminiferal data were analyzed by factor analysis and, along with the environmental data, canonical correspondence analysis (CCA). Four distinct assemblages were identified from factor analysis of the live data: (1) a frontal assemblage characterized by Stainforthia fusiformis, (2) a mixed water assemblage characterized by Cibicides lobatalus, Textularia bockii, Spiroplectammina wrightii, Ammonia batavus and Quinqueloculina seminulum, (3) a stratified assemblage characterized by Bulimina marginata, Hyalinea balthica, Adercotryma wrighti and Nonionella turgida, and (4) an eastern assemblage dominated by Bulimina gibba, Elphidium excavatum and Eggerelloides scaber. Factor analysis of the dead data reproduces all groupings except the frontal assemblage. These data therefore support interpretations based on earlier stratigraphic data, and highlight the significance of benthic foraminifera as faunal indicators of paleostratification in shelf seas. The distributions also support predicted cross-frontal transfer of nutrients and the existence of surface converging circulation cells. Statistical analyses indicate the significance of unmeasured ecological variables which we speculate might be food supply, and oxygen concentration of bottom and sediment pore waters.