Abstract
Seasonal abundance, volume, size distribution and carbon content of transparent ex- opolymeric particles (TEP) were examined in 2 hydrologically distinct sites in the NW Mediterranean (NWM) Sea: a coastal (Point B, Villefranche Bay) and an offshore (DYFAMED, France, JGOFS) site. TEP concentration varied from 0.2 to 2.2 × 10 5 particles ml -1 , and was higher offshore. The TEP pool was low during the winter mesotrophic period and increased after the spring bloom, remaining rela- tively high throughout summer at both sites. The increase in TEP abundance during the oligotrophic period was relatable to nitrate limitation and a decline in primary production. TEP formation in spring was associated to a nanoflagellate bloom, while the build-up of a large pool of TEP in summer oc- curred in the presence of a phytoplankton community dominated by picoplankters and during strong thermal stratification, limiting vertical sedimentation. In the NWM Sea, when the TEP carbon pool (TEP-C) is high, it may represent up to 22% of the total organic carbon, and reach down to 1% when it is low, suggesting that the particles play a significant role in the carbon cycle. In the NWM Sea, the trophic status of the system and the composition of primary producers control TEP formation. Hydrological processes appear to be of primary importance in governing seasonal TEP distribution.
Highlights
Transparent exopolymeric particles (TEP) are formed abiotically by spontaneous coagulation of the colloidal fraction of dissolved organic polysaccharides, substances exuded by phytoplankton and bacteria (Alldredge et al 1993, Passow & Alldredge 1994)
TEP were found in relatively high abundances (2 × to 2.2 × TEP ml–1) at every sampling occasion, both at coastal and offshore sites
We found TEP concentrations to be 1 to 3 orders of magnitude higher than those reported for a variety of systems
Summary
Transparent exopolymeric particles (TEP) are formed abiotically by spontaneous coagulation of the colloidal fraction of dissolved organic polysaccharides, substances exuded by phytoplankton and bacteria (Alldredge et al 1993, Passow & Alldredge 1994). TEP form the organic matrix of marine snow, enhancing vertical fluxes of organic matter (Smetacek 1985, Passow et al 2001) and carbon export from the surface ocean (Fowler & Knauer 1986, Engel 2002). Due to their high stickiness, these particles aggregate with each other and with detritus (Kiørboe & Hansen 1993), leading to flocculation and sedimentation of non-living matter. If TEP are consumed, they represent a direct transfer of energy from dissolved matter to higher trophic levels, shunting the microbial loop
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