[Abstracts] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]

Claudia Sprengel, Karl-Heinz Baumann, Jorijntje Henderiks, Rüdiger Henrich, Susanne Neuer:
Modern coccolithophore and carbonate sedimentation along a productivity gradient in the Canary Islands region: seasonal export production and surface accumulation rates
(Talk)

Coccolithophores, one of the main primary and carbonate producers in the surface-waters of the Canary Islands region, were investigated to quantify coccolith and coccolith-carbonate export fluxes and to determine possible trends in species composition related to different productivity conditions. Present day coccolith and coccolith-carbonate fluxes were compared to the long-term records of coccolith and carbonate accumulation in Holocene sediments underneath the mooring locations. Coccolithophore flux variations in sediment traps at three stations along an E-W transect, at approximately 29°N, from the upwelling influenced NW African shelf region to the open ocean were recorded from January to September, 1997. Four particle-traps were deployed at the oceanic sites LP (900m, 3700m) and ESTOC (750m, 3000m), and one at the near-coast site EBC (700m). All traps have been synchronised on a 14-day sampling interval.

Total coccolith fluxes along the studied transect were highly seasonal, with pronounced sedimentation events occurring in February (upper traps) and March (deep traps), related to the winter phytoplankton bloom in surface-waters. While total coccolith flux rates and fluxes of different species at the two oceanic sites, LP and ESTOC, were comparable (mean: 6.4 and 5.4x10⁸ coccoliths m^-2 d^-1), fluxes increased significantly towards the shallower site, EBC (mean: 13.7x10⁸ coccoliths m^-2 d^-1). This gradient points to increased productivity in surface-waters at the near-coast station, probably associated with nutrient-rich upwelling filaments detaching from the coast and/or upwelling effects along the easternmost islands. Additionally, a strong influence of lateral advected, coccolith-rich material was demonstrated for the deeper sediment traps at the two offshore sites, resulting in an increase of mean daily coccolith fluxes by a factor of three (LP) and by a factor of two (ESTOC), respectively. Estimated coccolith-carbonate fluxes along the transect were 2.8gm^-2 (EBC) and 1.2-1.3gm^-2 (ESTOC, LP) in the upper traps, representing 31-33% of the total annual carbonate flux. The coccolith-carbonate supply was higher in the deeper traps, with 63% at LP and 44% at ESTOC, respectively. Average Holocene coccolith and (coccolith-)carbonate accumulation rates derived from surface-samples at the mooring locations generally confirm the sediment trap results. Discrepancies mainly result from near-bottom and down-slope particle-transfer processes, which especially influence the site closer to the shelf. Dissolution processes are likely to affect primarily the deep sediments at the oligotrophic site, LP.

The highly diverse subtropical coccolithophore assemblages were quite similar in all sediment-trap samples from the three mooring sites, with three species (Emiliania huxleyi, Florisphaera profunda, Gephyrocapsa ericsonii) contributing significantly to the community. Despite the good correspondence between the assemblage compositions along the transect, some trends towards the upwelling-influenced site, EBC, could be observed. Whereas all Gephyrocapsa species (mainly G. ericsonii) respond positively to higher productivity conditions at the near-coast station, Calcidiscus leptoporus and the deep photic zone species, F. profunda, increased in mean relative abundances towards the two offshore sites, pointing to a preference for the more stable, oligotrophic conditions of the subtropical gyre.

[INA8] 

[Registration and Accomodation Form]
[First Circular and Pre-Registration]
[Second Circular]

 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

 [INA Europe]  

Copyright © 2000, most recent revision July 26, 2000