Biogeochemical markers of organic matter along the Wight-Cherbourg transect (central English Channel)

Three cruises on the Wight-Cherbourg transect were undertaken during the Fl uxManche II Programme in order to study the origin, nature and behaviour of organic matter inputs to the waters of the English Channel. Suspended part iculate material (SPM) collected from surface and deep waters at each stati on was analysed at elemental level for Particulate Organic Carbon and Parti culate Organic Nitrogen (POC, PON), at molecular level for main classes of organic compounds using Pyrolysis-Gas Chromatography coupled with Mass Spec trometry (Py-GC-MS) and for phenolic compounds, particularly lignin-derived phenols, using High Performance Liquid Chromatography (HPLC). The SPM cont ent increases from the French (south) to the English coast (north) with the lowest values being observed in the central waters of the Channel. This di stribution is essentially linked to resuspension processes and the influenc e of terrigenous inputs from the Solent river inside English coastal waters . Py-GC-MS analyses show that organic material within French waters is usua lly marine in character and is more degraded than in English waters. Organi c material in the central waters always shows the highest state of degradat ion, probably due to its long transit time in the "central water mass" from the Atlantic to the English Channel. Autochthonous and allochthonous organ ic tracers were positively identified through the use of HPLC analyses. Sea sonal variations in the system lead to qualitative changes in terrigenous i nputs (lignin-derived phenols). To our knowledge, it is the first time that phenolic compounds of autochthonous origin have been recorded in central C hannel waters. Indeed, it is the study of the distribution and composition of hydroxybenzyl phenols which has allowed an estimate of the marine contri bution to the particulate organic matter to be made. These compounds may or iginate from phytoplankton and macroalgae tissues developing in the coastal environments of the Channel. (C) Elsevier, Paris / Ifremer / CNRS / IRD.