Search Results (3)

This study aimed to describe the interannual variability of dense shelf water cascading and open ocean convection in the Gulf of Lions (NW Mediterranean) based on long-term temperature and current records and its impact on particle fluxes and associated metals. These observations highlight the predominant role of the rare intense events of dense shelf water cascading (1999/2000, 2005/2006, 2012/2013) in the basinward export of particles, which are mainly brought by rivers. Measurements of particulate trace metals in 2012 indicate that the monitored intense cascading event may be responsible for a significant fraction (~15%) of the annual input to the shelf. To this first process is added the effect of somehow more recurrent deep convection events (2005, 2009–2013) that remobilize the deep sediments, receptacle of coastal inputs, and disperse them rapidly at the scale of the northern Mediterranean basin, and gradually over the entire western basin. Coastal and oceanic dense water formations are key physical processes in the Mediterranean margins, whose reduction in intensity and recurrence has already been observed and also anticipate in climate scenarios that will likely change the dispersion pathways of chemical particles in this region. Full article

To understand the geomorphological contrast between the northern and southern parts of the Southeast Greenland margin with its marked differences in sedimentary regime, bathymetric and seismic reflection, data have been compiled and analysed. While previous studies focused on selected parts of this margin, the present study provides an intergraded overview of the entire margin from Cap Farewell to Denmark Strait. The prominent north–south contrast shows a wide northern shelf and a narrow southern shelf. The origin of this width disparity can be traced back to the initial formation stage of the Irminger Sea due to regional differences in uplift versus oceanic subsidence. This regional tectonic discrepancy also created a difference in sediment accommodation space that, in combination with a weak ocean circulation regime, favoured formation of Oligocene–Miocene turbidite fan complexes along the lower southern slope. These fan complexes became the core of sediment drift ridges that strike perpendicular to the slope. Strong bottom currents, which gradually increase in strength towards the south, were mainly prevalent during warmer climate stages. During glacial periods, downslope transport of glacigenic sediments and hyperpycnal meltwater flow further shaped the large drift ridges and formed several relatively narrow, V-shaped turbidite channels extending towards the deep Irminger Sea basin. These V-shaped channels are still active today when cascading dense winter water from the shelf flows downwards along the shelf to the Irminger Sea basin. Full article

Along the majority of Australian shallow coastal regions, summer evaporation increases the salinity of shallow waters, and subsequently in autumn/winter, the nearshore waters become cooler due to heat loss. This results in the formation of horizontal density gradients with density increasing toward the coast that generates gravity currents known as dense shelf water cascades (DSWCs) flowing offshore along the sea bed. DSWCs play important role in ecological and biogeochemical processes in Australian waters through the transport of dissolved and suspended materials offshore. In this study a numerical ocean circulation model of Rottnest continental shelf, validated using simultaneous ocean glider and mooring data, indicated that the passage of cold fronts associated with winter storms resulted in rapid heat loss through evaporative cooling. These conditions resulted in enhancement of the DSWCs due to modifications of the cross-shelf density gradient and wind effects. Specifically, onshore (offshore) directed winds resulted in an enhancement (inhibition) of DSWCs due to downwelling (vertical mixing). Consequently, the largest DSWC events occurred during the cold fronts when atmospheric temperatures reinforced density gradients and onshore winds promoted downwelling that enhanced DSWCs. Advection of DSWCs was also strongly influenced by the wind conditions, with significantly more transport occurring along-shelf compared to cross-shelf. Full article