Seasonal Variability of Benthic Foraminiferal Faunas at 1000 M Depth in the Bay of Biscay

A 1000-meter-deep station in the Bay of Biscay (station A) was sampled 10 times between October 1997 and April 2001 for the purposes of studying the temporal variability of live foraminiferal faunas in the 63–150 mm and .150 mm size fractions. The results are compared with those obtained earlier for a 550-m-deep station nearby. The study area is marked by prolonged, two-month spring blooms and less clear autumn blooms that result in labile organic matter enrichment of the upper sediment layers. Episodic exportation of phytodetritus had a recognizable impact on early diagenetic processes only in April 2001. During the 2001 spring bloom, bottom-water oxygenation and the depth of the zero-oxygen boundary were minimum. Foraminiferal faunas respond to bloom events by increases in the abundance of opportunistic taxa. In the .150 mm size fraction, Uvigerina mediterranea and Uvigerina peregrina preferentially reproduced and thrived in shallow infaunal microhabitats that are seasonally enriched in phytodetritus. Although the seasonal changes in the 63–150 mm size fraction are less straightforward, Nuttallides pusillus and Uvigerina peregrina did show marked seasonal changes in abundance. The temporal changes in the foraminiferal faunas at the 1000m-deep station appear to be synchronous with those recorded at the 550-m-deep station.