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Settling particle fluxes across the continental margin of the Gulf of Lion: the role of dense shelf water cascading

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Author(s): C. Pasqual | A. Sanchez-Vidal | D. Zúñiga | A. Calafat | M. Canals | X. Durrieu de Madron | P. Puig | S. Heussner | A. Palanques | N. Delsaut

Journal: Biogeosciences Discussions
ISSN 1810-6277

Volume: 6;
Issue: 4;
Start page: 7897;
Date: 2009;
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ABSTRACT
Settling particles were collected using sediment traps deployed along three transects in the Lacaze-Duthiers and Cap de Creus canyons and the adjacent southern open slope from October 2005 to October 2006. The settling material was analysed to obtain total mass fluxes and main constituent contents (organic matter, opal, calcium carbonate, and siliciclastics). Cascades of dense shelf water from the continental shelf edge to the lower continental slope occurred from January to March 2006. They were traced through strong negative near-bottom temperature anomalies and increased current speeds, and generated two intense pulses of mass fluxes in January and March 2006. This oceanographic phenomenon appeared as the major physical forcing of settling particles at almost all stations, and caused both high seasonal variability in mass fluxes and important qualitative changes in settling material. Fluxes during the dense shelf water cascading (DSWC) event ranged from 90.1 g m−2 d−1 at the 1000 m depth station in the Cap de Creus canyon to 3.2 g m−2 d−1 at the canyon mouth at 1900 m. Fractions of organic matter, opal and calcium carbonate components increased seaward, thus diminishing the siliciclastic fraction. Temporal variability of the major components was larger in the canyon mouth and open slope sites, due to the mixed impact of dense shelf water cascading processes and the pelagic biological production. Results indicate that the cascading event remobilized and homogenized large amounts of material down canyon and southwardly along the continental slope contributing to a better understanding of the internal dynamics of DSWC events. While the late winter/early spring bloom signature was diluted when DSWC occurred, the primary production dynamics were observable at all stations during the rest of the year and highlighted the biological community succession in surface waters.
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