Seasonal and interannual changes of planktic foraminiferal fluxes in the Gulf of Lions (NW Mediterranean) and their implications for paleoceanographic studies: Two 12-year sediment trap records

In order to investigate the seasonal and interannual variability of planktic foraminiferal fluxes in the NW Mediterranean, 266 samples from two 12-year-long sediment traps were analyzed. Two mooring lines were deployed at the east (Station Planier) and the west (Station Lacaze Duthiers) of the Gulf of Lions. The moorings were deployed at a water depth of around 1000m and were equipped with sediment traps at 500m above bottom (mab). In addition, an array of 13 core-tops recovered from different key areas of the Gulf of Lions is described. At Lacaze Duthiers, average foraminiferal fluxes were about double (411.8shellsm ^-2d ^-1) those found at the Planier sampling site (225.4shellsm ^-2d ^-1), probably due to the fertilizing effect of the Rhone river plume and the general oceanographic circulation. The annual total foraminiferal fluxes exhibited a unimodal trend, with maxima recorded during the winter-spring transition, i.e. the spring bloom, and minima during summer. Therefore, planktic foraminifers found in the sedimentary record in the Gulf of Lions may reflect the flux during the winter-spring period, rather than throughout the annual cycle. A total of eleven planktic foraminiferal species were identified in the sediment trap and core-top samples but only four species were dominant in the assemblages: Globigerina bulloides Neogloboquadrina pachyderma (dex.), Globorotalia inflata and Globorotalia truncatulinoides. The foraminiferal assemblages in the Gulf of Lions reflected the relatively cold conditions of the Northern Basin. No clear relationship between the NAO (North Atlantic Oscillation) and planktic foraminiferal fluxes was found in the sediment trap records. The low planktic foraminiferal fluxes recorded during the spring of 1998 were probably related to the anomalous environmental conditions triggered by the 1997-98 El Niño event. Furthermore, sediment trap samples were compared with surficial sediments recovered from different environmental and sedimentary settings of the Gulf of Lions and the application of these results in paleoceanographic reconstructions is discussed.