Seasonal and interannual variation of coccolithophore fluxes and species composition in sediment traps north of Gran Canaria (29°N 15°W)

Abstract

Coccolithophore flux variations in sediment traps of the time-series station ESTOC (European Station for Time-series in the Ocean, Canary Islands), located 60nm north of Gran Canaria, were recorded from April 1993 to December 1996. The 20 cup particle traps were deployed at 1000 and 3000m below sea surface, and sampling intervals ranged from eight days to three weeks.Coccolith and coccosphere fluxes at both trap depths were characterized by a strong seasonality. At 1000m, maximum coccolith fluxes were reached during spring from March to April 1995 and from February to March 1996. Highest coccolith fluxes of 4538×106 coccoliths m−2d−1 occurred at the beginning of March 1996, whereas lowest values of 19.8×106 coccoliths m−2d−1 were recorded in June 1994. Total coccosphere fluxes were constantly low during most of the investigated time interval and showed only high values during the main sedimentation phases from January to March 1995 (up to 6.2×106 spheres m−2d−1) and in March 1996 (36.4×106 spheres m−2d−1).At 3000m water depth, the sedimentation pattern was rather similar to the pattern observed at 1000m. Maximum coccolith and coccosphere fluxes were also reached during spring time in February 1994 (8200×106 and 15.6×106m−2d−1, respectively) and in March 1996 (8114×106 and 32.3×106m−2d−1, respectively). However, total coccolith flux peaks at 3000m were about 2–4 times higher compared to the upper traps, probably due to horizontal advection from phytoplankton material from north of the study site. This effect also influenced the coccolith–CaCO3 flux estimates. Mean calculated coccolith–CaCO3 fluxes ranged between 3.9mgm−2d−1 for the upper traps (1995/1996) and 9.9mgm−2d−1 for the lower traps (1996). Coccoliths contributed for about 8–78% of the measured total CaCO3 fluxes (<1mm fraction), with a mean contribution of 33.4% in the upper, and 41.4% in the lower traps.The coccolithophore assemblages were dominated by Emiliania huxleyi, Florisphaera profunda, and Gephyrocapsa ericsonii during the entire sampling period, whereas all other species together generally contributed less than 40% to the total assemblages. Variability of species compositions at either trap depth was very low, indicating similar seasonal flux patterns of the different species.