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

Coccolithophore flux variations in sediment traps of the time-series statio n ESTOC (European Station for Time-series in the Ocean, Canary Islands), lo cated 60 nm north of Gran Canaria, were recorded from April 1993 to Decembe r 1996. The 20 cup particle traps were deployed at 1000 and 3000 m below se a 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 duri ng spring from March to April 1995 and from February to March 1996. Highest coccolith fluxes of 4538 x 10(6) coccoliths m(-2) d(-1) occurred at the be ginning of March 1996, whereas lowest values of 19.8 x 10(6) coccoliths m(- 2) d(-1) were recorded in June 1994. Total coccosphere fluxes were constant ly low during most of the investigated time interval and showed only high v alues during the main sedimentation phases from January to March 1995 (up t o 6.2 X 10(6) spheres m(-2) d(-1)) and in March 1996 (36.4 X 10(6) 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 a lso reached during spring time in February 1994 (8200 x 10(6) and 15.6 x 10 (6) m(-2) d(-1), respectively) and in March 1996 (8114 x 10(6) and 32.3 x 1 0(6) m(-2) d(-1), respectively). However, total coccolith flux peaks at 300 0 m were about 2-4 times higher compared ro the upper traps, probably due t o 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, Floris phaera profunda, and Gephyrocapsa ericsonii during the entire sampling peri od, whereas all other species together generally contributed less than 40% to the total assemblages. Variability of species compositions at either tra p depth was very low, indicating similar seasonal flux patterns of the diff erent species. (C) 2000 Elsevier Science B.V. All rights reserved.