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Lookup NU author(s): Dr Antoni Rosell-Mele,
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We report and discuss new data on alkenone fluxes from the North East Atlantic (48°N 21°W), in a site investigated by the Joint Global Ocean Flux Study and the North Atlantic Bloom Experiment from April 1989-March 1990. The investigated sediment trap station is situated within the North Atlantic Transition Zone in a region influenced by upwelling events induced by mesoscale eddy activity, for which branches of the North Atlantic Current act as major sources. The flux of alkenones in the NE Atlantic was consistent with the monthly evolution of particulate fluxes, rapidly increasing from April 1989 to June 1989 (peak bloom), and gradually declining until August 1989. The timing of the only bloom observed is not equivalent to the timing of alkenone flux maxima recorded elsewhere in the world's oceans. Hence, we further confirm that there is not a world-wide regular season of alkenone blooms. The annual alkenone flux profile in our trap resembled that of the coccospheres, but not so much that of coccoliths. This discrepancy may indicate that alkenones were mainly transported downwards to the sea-floor by coccospheres, as part of the intact structure of the dead coccolithophorid. The sedimentary concentration of alkenones, which is related to productivity and efficiency of preservation, may then be also partly dependent on the rate of disaggregation of coccospheres in the water column, and the factors that control them. Comparison of the ratios of amounts of alkenones per coccosphere and coccoliths, with those of amounts of alkenones per cell numbers from culture and field data, suggests that there could have been a contribution of alkenones to the traps by Coccolithus pelagicus, despite this species considered devoid of alkenones. We suggest, hence, that further laboratory tests of this species are carried out. U37(K)' in the sediment trap material showed a poor correlation with sea surface temperature during spring 1989. We propose that the anomalously low U37(K)' values reflects an input of alkenones from elsewhere to the trap, not from the overlying surface waters, associated to the presence of several eddies and phytoplanktonic material trapped within. The origin of the eddy-bound alkenones may be found in subpolar waters, as indicated by the presence of C. pelagicus tests in the trap, and also by the low U37(K)' values which are similar to the values found in surface sediments near the polar front. Our data, thus, further illustrates the challenge of using short-term studies of annual water-column alkenone fluxes to understand average sedimentation patterns of alkenones to the deep ocean. (C) 2000 Elsevier Science B.V.
Author(s): Rosell-Mele A, Comes P, Muller PJ, Ziveri P
Publication type: Article
Publication status: Published
Journal: Marine Chemistry
ISSN (print): 0304-4203
ISSN (electronic): 1872-7581
Publisher: Elsevier B.V.
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