Abstract.With an extension of > 40 km 2 the recently discovered Campeche cold-water coral province located at the northeastern rim of the Campeche Bank in the southern Gulf of Mexico belongs to the largest coherent cold-water coral areas discovered so far. The Campeche province consists of numerous 20-40 m-high elongated coral mounds that are developed in intermediate water depths of 500 to 600 m. The mounds are colonized by a vivid cold-water coral ecosystem that covers the upper flanks and summits. The rich coral community is dominated by the framework-building Scleractinia Enallopsammia profunda and Lophelia pertusa, while the associated benthic megafauna shows a rather scarce occurrence. The recent environmental setting is characterized by a high surface water production caused by a local upwelling center and a dynamic bottom-water regime comprising vigorous bottom currents, obvious temporal variability, and strong density contrasts, which all together provide optimal conditions for the growth of cold-water corals. This setting -potentially supported by the diel vertical migration of zooplankton in the Campeche area -controls the delivering of food particles to the corals. The Campeche cold-water coral province is, thus, an excellent example highlighting the importance of the oceanographic setting in securing the food supply for the development of large and vivid cold-water coral ecosystems.
This study presents new observations of fluid mud transport and of the interaction between mud‐induced stratification and the flow. Data collected in a hyperturbid estuarine tidal channel reveal details of the intratidal entrainment asymmetry, characterized by quasi‐instantaneous entrainment and upstream pumping of mud during flood, and a gradual reduction of layer thickness by shear dispersion during ebb. Rapid restratification early during the flood phase restores the predominant two‐layer structure and delimits the transport period, which is then significantly shorter than the overall flood duration. The hydraulic cross section is reduced, causing an increase of the salinity intrusion into the estuary at the end of the flood. The fluid mud layer occupies on average 40% of the water depth, and stratification exceeds that of highly stratified salt wedge estuaries. These data show how mud‐induced periodic stratification influences flow structure and sediment transport and thereby contribute to the understanding of the dynamics of hyperturbid estuaries.
Abstract. With an extension of >40 km2 the recently discovered Campeche cold-water coral province located at the northeastern rim of the Campeche Bank in the southern Gulf of Mexico belongs to the largest coherent cold-water coral areas discovered so far. The Campeche province consists of numerous 20 to 40 m high coral ridges that are developed in intermediate water depths of 500 to 600 m. The ridges are colonized by a vivid cold-water coral ecosystem that covers the upper flanks and summits. The rich coral community is dominated by the framework-building scleractinia Enallopsammia profunda and Lophelia pertusa while the associated benthic megafauna shows a rather scarce occurrence. The recent environmental setting is characterized by a high surface water production caused by a local upwelling center and a dynamic bottom water regime comprising vigorous bottom currents, internal waves and strong density contrasts, which all together provide optimal conditions for the growth of cold-water corals. The strong hydrodynamics – potentially supported by the diel vertical migration of zooplankton in the Campeche area – drive the delivering of food particles to the corals. The Campeche cold-water coral province is, thus, an excellent example highlighting the importance of the hydrographic setting in securing the food supply for the development of large and vivid cold-water coral ecosystems.
Large bedforms (dunes) are present in many shallow-water environments. Knowledge of their dimensions and dynamics is required for river and coastal management. In tidal rivers and estuaries, the interaction among hydrodynamics (which results from the action of river and tidal flows), sediment transport and bedform shape and size is complex. In the present study, the distribution and morphology of bedforms in the Weser Estuary, Germany, were investigated. Bedforms were identified in bathymetric data of monthly multibeam echosounder surveys along the navigation channel during the years 2009 to 2013. Their size and shape were characterized. Bedforms were present along most of the channel, except at the position of the estuarine turbidity maximum and where dredging is carried out. Average bedform length varied between 20 and 60 m and bedform height between 0.3 and 1.6 m. Bedform asymmetry varied spatially and temporally along the estuary. In times of high river discharge, bedforms were generally more ebb-asymmetric than in times of low discharge. The bedforms were predominantly two-dimensional low-angle dunes with their steepest slope situated near the bedform crest. A significant proportion of bedforms possessed a steep face (portion of the lee side steeper than 15 ). This implies that they are likely to create flow separation and a turbulent wake, with a strong potential to induce high bedform roughness. However, important variations in steep face area density were noted, both spatially along the estuary and temporally as a function of the tidal phase (ebb or flood) and the seasonal variation in river discharge. The results have wide implications in terms of understanding and modelling hydrodynamics and sediment transport in estuaries.
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