In the framework of the Canaries-Iberian marine ecosystem Exchanges (CAIBEX) experiment, an interdisciplinary high-resolution survey was conducted in the NW African region of Cape Ghir (30838 0 N) during August 2009. The anatomy of a major filament is investigated on scales down to the submesoscale using in situ and remotely sensed data. The filament may be viewed as a system composed of three intimately connected structures: a small, shallow, and cold filament embedded within a larger, deeper, and cool filament and an intrathermocline anticyclonic eddy (ITE). The cold filament, which stretches 110 km offshore, is a shallow feature 60 m deep and 25 km wide, identified by minimal surface temperatures and rich in chlorophyll a. This structure comprises two asymmetrical submesoscale (18 km) fronts with jets flowing in opposite directions. The cold filament is embedded near the equatorward boundary of a much broader region of approximately 120 km width and 150 m depth that forms the cool filament and stretches at least 200 km offshore. This cool region, partly resulting from the influence of cold filament, is limited by two asymmetrical mesoscale (50 km) frontal boundaries. At the ITE, located north of the cold filament, we observe evidence of downwelling as indicated by a relatively high concentration of particles extending from the surface to more than 200 m depth. We hypothesize that this ITE may act as a sink of carbon and thus the filament system may serve dual roles of offshore carbon export and carbon sink.

The dynamics of the bottom boundary layer and their effects on the development of nepheloid layers (NLs) on a high-energy and upwelling-affected margin, the NW Iberian continental shelf, were studied by means of ADP currents, wave time series, and across-shelf hydrographic surveys covering an entire annual cycle. The bottom boundary layer hydrodynamics showed that high levels of bottom shear stress over the inner shelf occurred mainly during downwelling seasons, when there was a coupling between storm waves and intense currents. This wave-current coupling promotes strong resuspension events that favored the generation of bottom NLs (BNLs). BNLs were well developed on the inner continental shelf inshore of a thermohaline front generated by the interaction of the Iberian Poleward Current and the West Iberian Buoyant Plume. The existence of this front limited the extent of offshore export of resuspended particles during the downwelling season. In contrast, during the upwelling season, only thin BNLs were developed, and surface NLs, principally composed by biogenic particulate material, were advected offshore in the Ekman layer, often as part of the development of upwelling filaments. Our study confirmed that wave orbital velocity under stormy conditions, in combination with the hydrography, could explain the shoreward boundary of the Galician mud depocenter.Plain Language Summary This manuscript mainly focuses on hydrodynamics of the bottom boundary layer and the effect of wave-current bottom shear stress on the development and modulation of nepheloid layers on the NW Iberia continental shelf during more than 1 year. During this period, we analyze the role of hydrographic seasonality of this coastal upwelling system in the behavior of nepheloid layers and the possible offshore export pathways of particulate matter to the adjacent ocean. In addition, wave climate over the continental shelf was analyzed together with this hydrographic context in order to explain the surface sediment distribution.