Davenport, Robert A.¹, Tim Freudenthal¹, Helge Meggers¹, Susanne Neuer², Octavio Llinas³ and Gerold Wefer¹

¹DFG Research Center Ocean Margins, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany, Tel: 0049-4212187759, Fax: 0049-4212183116, E-mail: davenport@uni-bremen.de, ²Arizona State University, Dep. of Biology, Tempe, AZ 85287, USA and ³Instituto Canario de Ciencias Marinas, 35200 Telde, Gran Canaria, Spain

Investigation of the productivity gradient off NW Africa using SeaWiFS imagery, sediment traps and analysis of surface sediments

The NW African upwelling productivity of surface waters has been investigated using Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll imagery and geochemical and micropaleontological parameters in trap material and sediments as proxies for surface water properties in the Canary Islands region. As part of JGOFS and the European Canary Islands Azores Gibraltar Observations (CANIGO) project, SeaWiFS chlorophyll data were used to investigate the near-surface productivity gradient over a 19-month period from September 1997 to March 1999 at 3 stations that fall along a quasi-zonal 29°N transect through the Canary Islands. These stations correspond to 3 fixed sediments traps positioned during the same period east of the island of Fuerteventura (Eastern Boundary Current, EBC) and north of the islands of Gran Canaria (European Station for Time-Series in the Ocean, Canary Islands, ESTOC) and La Palma (LP). The mean annual productivity during the 19-month period was observed to decrease steeply westwards along the transect, from 237 g C m^-2 yr^-1 at EBC to 164 and 145 g C m^-2 yr^-1 at ESTOC and LP, respectively. The high productivity at EBC indicates that this station is strongly influenced by the seasonal coastal upwelling off the adjacent Moroccan coast. Productivity indicating proxies on sediment trap material of the year 1997 (planktic foraminifera distribution, ¹⁵N, TOC) confirm the remote sensing results. The modern scenario is also mirrored within the surface sediment. E.g. the distribution of the upwelling indicating planktic foraminifera species Globigerina bulloides and the TOC concentration coincided well with the areas of strong filament production off Cape Ghir and Cape Yubi. The warm-water planktic foraminifera Globigerinoides ruber (white) and the ¹⁵N-values showed the opposite trend with high values in the open ocean. Data from ESTOC and from the sediment trap transect in the Canary Islands region may be found under http://www.pangaea.de/Projects/ESTOC.