HR: 14:55h
AN: PP43E-06 INVITED    [Abstracts]
TI: Effects of acidification on coccolithophore assemblages and on coccolith shapes
AU: * Beaufort, L
EM: beaufort@cerege.fr
AF: CNRS - Aix Marseille University, CEREGE Europole de l'Arbois BP80 - Cedex 04, Aix en Provence, 13545, France
AU: Probert, I
EM: probert@sb-roscoff.fr
AF: CNRS - Paris VI University, Place Georges Teissier BP74, Roscoff, 29682, France
AU: Buchet, N
EM: nbuchet@cerege.fr
AF: CNRS - Aix Marseille University, CEREGE Europole de l'Arbois BP80 - Cedex 04, Aix en Provence, 13545, France
AU: de Garidel Thoron, T
EM: garidel@cerege.fr
AF: CNRS - Aix Marseille University, CEREGE Europole de l'Arbois BP80 - Cedex 04, Aix en Provence, 13545, France
AB: The coccolithophores are not only an important group of oceanic primary producers, they are also one of the main carbonate producers in the ocean. Because the calcium carbonate plates (coccoliths) secreted by these unicellular algae are so small and light (a few picograms each) they cannot be directly weighed, with the result that very little is known about the effect of primary production and dissolution on the weight of coccoliths. Using a our new method that allows a rapid estimate of the weight of discrete coccoliths, we analysed the effect of dissolution on coccoliths. We performed four acidification experiments on, (1) a surface sediment sample, (2) a laboratory culture of E. huxleyi, (3) a filtered water sample combining several depths in photic zone, (4) a sample composed of a mixture of several cultured coccolithophores species. The results of the first two acidification experiments, using cultured and fossil coccoliths, indicate that acidification has very little effect on the shape of coccoliths. Based on these experiments, we identify four morphological parameters for identifying the effects of dissolution on a coccolith assemblage. These parameters were applied in samples from two sediment trap time-series taken at the same tropical Atlantic site (EUMELI), but separated by 2000m water depth. There was no evidence of increased dissolution with water depth with from 250 and to 2500m. This is indicative of the absence of dissolution of coccoliths between the photic zone and the lysocline and of dissolution in photic zone. We tested this hypothesis by comparing coccolithophores sampled in photic zone with coccoliths settling below at the same site. We compare those results with those of the third dissolution experiment made with the same suite of samples. The last dissolution experiment, on cultured artificial assemblages permitted to strengthen the results. With this suite of experiment we are able to modelize the dissolution of a coccolithophore assemblage from the photic zone to the sea floor.
DE: 0428 Carbon cycling (4806)
DE: 3022 Marine sediments: processes and transport
DE: 3030 Micropaleontology (0459, 4944)
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting