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

Coccolithophore flux variations in sediment traps of the time-series station ESTOC (European Station for Time-series in the Ocean, Canary Islands), located 60 nm north of Gran Canaria, were recorded from April 1993 to December 1996. The 20 cup particle traps were deployed at 1000 and 3000 m 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 1000 m, maximum coccolith fluxes were reached during spring from March to April 1995 and from February to March 1996. Highest coccolith fluxes of 4538 x 10⁶ coccoliths m^-2 d^-1 occurred at the beginning of March 1996, whereas lowest values of 19.8 x 10⁶ coccoliths m^-2 d^-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 x 10⁶ spheres m^-2 d^-1) and in March 1996 (36.4 x 10⁶ spheres m^-2 d^-1). At 3000 m water depth, the sedimentation pattern was rather similar to the pattern observed at 1000 m. Maximum coccolith and coccosphere fluxes were also reached during spring time in February 1994 (8200 x 10⁶ and 15.6 x 10⁶ m^-2 d^-1, respectively) and in March 1996 (8114 x 10⁶ and 32.3 x 10⁶ m^-2 d^-1, respectively). However, total coccolith flux peaks at 3000 m 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 3.9 mg m^-2 d^-1 for the upper traps (1995/1996) and 9.9 mg m^-2 d^-1 for the lower traps (1996). Coccoliths contributed for about 8-78% of the measured total CaCO₃ fluxes (< 1 mm 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. (C) 2000 Elsevier Science B.V.