Laminated deposits in Quaternary sediments of the Bay of Biscay as a recurrent phenomenon of glacial cycle terminations: the global perspective of a local seasonal deglacial pattern

High resolution paleoclimatic and paleoceanographic studies have shown that the orbital forcing may not have been the only control on ice sheet growth and decay (e.g. Heinrich events), then suggesting major feedback mechanisms implying both the atmosphere, the cryosphere, the oceans and the biosphere. Global climate modeling is one of the best methods of investigating these mechanisms and models of intermediate complexity have furnished a lot of robust hypothesis. Nevertheless, ice-sheets usually considered into these models are often classically resumed to massive polar ice-caps, following the pattern of those that were developed among large continental areas during glacial maxima. Until now, few simulations have tested the impact and the sensitivity of the response of small-sized and medium latitude ice-sheets. These ice-sheets, as for example, the British and Irish ice-sheets in western Europe, constitute however the more reactive part of the larger ice-caps, especially during periods of deglaciation while minor environmental changes could act drastically versus the global ice-sheet evolution. During Glacial Maxima of the four last climatic cycles, western European palaeoenvironments were characterized by low-stands of sea-level, then allowed the emersion of the Channel. The majority of the great north-western European merged into one unique drainage system, the "Channel River system". This palaeoriver would have been the convergence point of the melt-waters coming from the European glaciers (Alps), the British/Irish ice-sheet, and as well as, in part, from the Fennoscandian ice-sheet. Here we will present data from five hemipelagic cores retrieved on the Celtic margin which was directly connected to the Channel paleoriver during low-stands of sea-level. These cores all display a typical laminated sedimentological facies during at least one period of the four last glacial Terminations. Very high sedimentation rates, together with geochemical and micropaleontological evidences suggest massive local iceberg decay during the final step of the deglacial processes. Such a recurrent phenomenon, that furthermore seems to involve seasonal mechanisms, could help us to understand the modality and the timing of ice-sheet melting during these key periods that glacial/interglacial shifts are.