COCCOLITHOPHORE BIOGEOGRAPHY IN THE SOUTH AND WEST IBERIAN MARGIN: PRELIMINARY RESULTS FROM WATER AND MUDLINE SAMPLES (IODP EXPEDITION 339)

The Integrated Ocean Drilling Program (IODP), Expedition 339 (Mediterranean Outflow), was carried out in the Gulf of Cadiz and coastal areas off West Iberia (North East Atlantic) to explore the effects of Mediterranean Outflow Water (MOW) on North Atlantic circulation and climate. In order to interpret environmental signals from coccolith studies, it is necessary to understand the current coccolithophore distribution and to connect it to an adaptive response to surface water environmental change. Water and mudline samples were thus collected at each drilled site during the expedition, to compare the living and fossil (late Pleistocene and Holocene) coccolithophore communities. Preliminary results from the seven stations show the maximum coccosphere densities were recorded at 20 m water-depth (highest of 1.04 X 10⁵ cells/l). Coccolithophores show spatial variation and assemblages are dominated by E. huxleyi, G. small and G. oceanica. The living and fossil communities in sites 1390 and 1391 are quite different, where C. pelagicus, which is absent in all the water stations, is common, as well as reworked species (interpreted as influence of bottom-water). In contrast, the fossil record matches the water column assemblages at the other site locations (U1385, U1386, U1387 and U1389), suggesting more open sea conditions, where inorganic input and reworked species are less important. In site U1388, there were no coccoliths in the sediment, but abundant coccolithophores in the water column. This can indicate different sedimentary processes related to both superficial Atlantic Inflow and the MOW, (characterized here by higher velocity current up to 280 cm/s) that prevent the coccolith sedimentation at this site. However, loss of specimens during the drilling due to instrumental effects cannot be excluded. These preliminary results show a good correspondence between living species in the water column, the surface record and the flow of deep currents in the area. Further work will include the study of the benthic foraminifers and ostracods, as well as Mg/Ca, Sr/Ca ratios and the geochemical signal of the pore water. The integration of all these data will help improve our understanding of surface and deep-water dynamics of the Expedition 339 area for the last climatic cycles.

Co-authors: IODP Expedition 339 Scientists.