Transparent Exopolymer Particles (TEP) in the NE Aegean Sea frontal area: Seasonal dynamics under the influence of Black Sea water

Abstract

The abundance of Transparent Exopolymer Particles (TEP) was determined on a seasonal basis (autumn, spring and summer) along a north-south transect in the NE Aegean Sea and the vicinity of the Dardanelles Straits. Their distribution patterns were studied in respect to hydrographic conditions and water mass characteristics in the area, as well as particulate organic carbon (POC) concentrations, changes in standing stocks of chlorophyll-α and bacterial production. TEP concentrations ranged from 15.4 to 188µg GX eqL-1. Their spatial distribution patterns within the euphotic zone displayed significant seasonal variability, which appears to closely reflect the temporal variation of the water column structure, resulting from the encounter and interplay of the Black Sea and Levantine Water masses, and the associated biogeochemical processes. Minimum TEP concentrations during autumn could be likely attributed to a minor quantity of TEP and/or its dissolved precursors exuded by phytoplankton and their enhanced degradation due to their long residence time in the water column. During spring, high TEP production was mediated by actively growing phytoplankton, while during summer a positive link to the intense stratification of the water column and the enhanced bacterial growth within the Black Sea Water layer was observed. The results reported in this study highlight the fact that TEP carbon represents a significant fraction of the POC pool. Moreover, TEP production is critical in promoting particle coagulation rates, playing an important role in carbon cycling/transportation out of the euphotic zone.