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

Three cruises on the Wight-Cherbourg transect were undertaken during the FluxManche II Programme in order to study the origin, nature and behaviour of organic matter inputs to the waters of the English Channel. Suspended particulate material (SPM) collected from surface and deep waters at each station was analysed at elemental level for Particulate Organic Carbon and Particulate Organic Nitrogen (POC, PON), at molecular level for main classes of organic compounds using Pyrolysis-Gas Chromatography coupled with Mass Spectrometry (Py-GC-MS) and for phenolic compounds, particularly lignin-derived phenols, using High Performance Liquid Chromatography (HPLC). The SPM content increases from the French (south) to the English coast (north) with the lowest values being observed in the central waters of the Channel. This distribution is essentially linked to resuspension processes and the influence of terrigenous inputs from the Solent river inside English coastal waters. Py-GC-MS analyses show that organic material within French waters is usually marine in character and is more degraded than in English waters. Organic material in the central waters always shows the highest state of degradation, probably due to its long transit time in the “central water mass” from the Atlantic to the English Channel. Autochthonous and allochthonous organic tracers were positively identified through the use of HPLC analyses. Seasonal variations in the system lead to qualitative changes in terrigenous inputs (lignin-derived phenols). To our knowledge, it is the first time that phenolic compounds of autochthonous origin have been recorded in central Channel waters. Indeed, it is the study of the distribution and composition of hydroxybenzyl phenols which has allowed an estimate of the marine contribution to the particulate organic matter to be made. These compounds may originate from phytoplankton and macroalgae tissues developing in the coastal environments of the Channel.