HR: 11:35h
AN: PP52C-06    [Abstracts]
TI: Late Pleistocene Upwelling Variability on the Pacific Shelf of Baja California and in the Santa Barbara Basin
AU: * Beaufort, L
EM: beaufort@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Blanchet, C
EM: blanchet@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Buchet, N
EM: nbuchet@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Cuven, S
EM: phanie.cuven@infonie.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Grelaud, M
EM: grelaud@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Leduc, G
EM: leduc@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Licari, L
EM: licari@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Sylvestre, F
EM: sylevestre@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AU: Vidal, L
EM: vidal@cerege.fr
AF: CEREGE CNRS/Université Aix-Marseille III, Europole de l'arbois, Aix en Provence, 13545 C 04 France
AB: Two high resolution cores from Pacific shelf of Baja California (MD02-2508) and from Santa Barbara Basin (MD02-2503) retrieved during the IMAGES VIII cruise were studied in order to understand how primary production had varied in the upper Pleistocene/Holocene. The cores were taken in the present oxygen minimum zones. As a consequence of the limited bioturbation, the recent sediments are laminated in both cores. The oxygen content in those area had changed through time, and was considerably higher during global cold periods (Glacials and D/O stadials) allowing bioturbation (Behl and Kennett, 1996; Ortiz et al., 2004). The sediments are not laminated during these events and the organic carbon contents are reduced. The origin of these climatic related variations of oxygenation is strongly debated. These changes could results from local variations of primary production or from changes in the local path of the low oxygen intermediate water circulation. Few data exist on the variation in the diversity of the phytoplankton in this area, which have the potential to trace primary production variability. We studied past changes in the assemblages of calcareous nannoplankton (coccolithophirids) in the two cores in order to describe the plankton variability along the Western North Margin of the Pacific. The chronology of these cores is based on a mixture of C14 dates and correlation of the prominent D/O sedimentary features with the NGRIP deuterium record. Coccoliths have been counted by an automated microscope system trained to identify 14 coccoliths species. Five hundred to six thousand coccoliths have been counted per sample. The low productivity marker Florisphaera profunda is used to depict changes in primary production and therefore past strength of the upwelling. The records span the last 35 Kyr in the Santa Barbara Basin's core and the last 120 Kyr at the Baja California site. In the two cores the primary production varies very differently: The record in Santa Barbara is characterized by high (low) primary production in the Holocene (Glacial) and in the absence of D/O signature. The record in Baja California is marked by low (high) primary production in Holocene (Glacial) and a strong D/O signature. In this last core, the nannoplankton indicates lower primary production in levels of higher organic carbon preservation. In few, well marked D/O events we compare the nannoplankton record with other microfossils. The difference between Santa Barbara and Baja California primary production records indicates that the upwelling cells along the Northwestern margin of America do not vary in synchronism, although the two areas are strongly influenced by climate variations. We interpret the synchronous presence of laminations and high organic carbon in the sediment as the only result of the advection of low oxygen water along the margin between 400 and 900m. Behl, R.J. and Kennett, J.P., 1996. Brief interstadial events in the Santa Barbara Basin, NE Pacific, during the passt 60 kyr. Nature, 379: 243-246. Ortiz, J.D. et al., 2004. Enhanced marine productivity off western North America during warm climate intervals of the past 52 k.y. Geology, 32(6): 521-524.
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4944 Micropaleontology (0459, 3030)
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005