Short scale (6 h) temporal variation of sinking fluxes of planktonic and terrigeneous lipids at 200m in the NW Mediterranean Sea
Drifting sediment trap experiments were carried out at high temporal frequency in the northwestern Mediterranean in the course of the DYNAPROC2 campaign, every 6 h at 200m depth. Molecular biomarkers were analyzed in selected subsets of consecutive samples. Fluxes of n-alkanes, long-chain alkenones, sterols and steroid ketones show high variability between consecutive 6-hsamples, comparable in range to seasonnal variability. n-Alkane export ranges from 1.4 to 29.7 μgm-2 d-1, fluxes of C 37 alkenones varies from 0 to 14.2 μgm-2 d -1. Fluxes of sterols, steroid ketones and C30 alkane diol, respectively range from 31 to 377, 2.2 to 46 and 0.3 to 9.3 μgm -2 d-1. The Biomarker 10 composition is consistent with reworked algal and zooplanktonic organic matter with a remarkable refractory character. After a rain event ensuing the intrusion of coastal water at the study site, the relative signature of higher plant increases and corresponds to higher export fluxes of long-chain odd n-alkanes. Most phytoplanktonic biomarkers show concurrent variability in fluxes. Linear correlations between fluxes of distinct 15 biomarkers and between fluxes of biomarkers and flux of total carbon suggest that the short term temporal variability of export fluxes depends primarily on physical constrains exerted by carrier particle dynamics. Linear correlation of their carbon-normalized concentrations explained a lower part of the variance, indicating that short-term variability in particle composition is a secondary driver of flux timing. At the end of summer strat20 ification, export fluxes account for ca. 1% of the primary productivity. In this studied situation, biomarkers have a long residence time in the water column before they are exported at 200 m. Biomarkers exported at 200m may thus record processes averaged over a larger period than the sampling frequency. For instance, phytoplanktonic biomarker composition of sinking particles fails to reflect the community changes occur25 ring over the 4 weeks of study. At higher time resolution, the diel variability in primary productivity is not recorded by biomarker fluxes either. The coupling between primary productivity and biomarker export shows significant changes on time scales of days and even of 6 h. © Author(s) 2009.
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| Format: | artículo biblioteca |
| Published: |
European Geosciences Union
2009
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| Online Access: | http://hdl.handle.net/10261/217286 |
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