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Franco-Fraguas P.,University of the Republic of Uruguay | Burone L.,University of the Republic of Uruguay | Mahiques M.,University of Sao Paulo | Ortega L.,Laboratorio Of Oceanografia | And 7 more authors.
Marine Geology | Year: 2014

The hydrology of the Southwestern Atlantic margin is dominated by the confluence of water masses with contrasting thermohaline properties, generating a frontal zone that extends from the Brazil-Malvinas Confluence zone (BMC) in the open ocean to the Subtropical Shelf Front (STSF) on the continental shelf. However, the hydrodynamics of the transition between these hydrographic features is still not fully understood. High-resolution morphological (multibeam) and hydrological (CTD) data were integrated with sedimentological data (textural and productivity proxies) in order to develop a sound framework to understand surface sedimentation of the slope extension of the STSF (subsurface, outer shelf and upper slope) and of the BMC (intermediate level, middle slope) on the Uruguayan continental margin (34° to 36°S). Since the detailed morphology of the study area is presented for the first time, related geological processes are briefly discussed. On the outer shelf and upper slope, and north of the STSF, the current direction of erosive mound scarps indicates the dominance of the southward-flowing Brazil Current (BC). This suggests a northernmost boundary for the distribution of the STSF. A strong flux of the BC favored by a steeper slope as well as by the occurrence of canyons incised on the upper slope is evidenced by the occurrence of coarser sediments and low values of productivity proxies, but also by the presence of deep sea coral reefs. Southwards, the effect of a less energetic Malvinas Current (MC) and the highly productive STSF is indicated by the deposition of fine sediments with high organic matter content, as well as by the absence of deep sea coral reefs. This depositional scenario is enhanced by a smooth slope and the occurrence of canyons incised deeper in the middle slope. Off-shelf sediment transport along the STSF is inferred by the similar texture registered between the outer shelf and shallow upper slope, the occurrence of biogenic shelly reworked sands and gravel, and by the observed decrease in grain size with depth. Glacial iceberg transport northwards and/or gravity processes are suggested by the occurrence of igneous/metamorphic gravel in lag deposits on the upper slope. On the middle slope, the northernmost influence of the erosive Antarctic Intermediate Water is evidenced by the vanishing of morphologic contouritic structures. This is also imprinted in a pronounced northward fining in grain size. This contribution increase our understanding of this highly dynamic and complex area, providing the first detailed analysis of the regional sediment patterns and oceanographic and morphological controls on surface sedimentation. © 2013 Elsevier B.V. Source


Riet-Sapriza F.G.,Proyecto Pinnipedos | Costa D.P.,University of California at Santa Cruz | Franco-Trecu V.,Proyecto Pinnipedos | Marin Y.,Laboratorio Of Tecnologia Pesquera | And 5 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

Resource competition between fisheries and marine mammal continue to raise concern worldwide. Understanding this complex conflict requires data on spatial and dietary overlap of marine mammal and fisheries. In Uruguay the South American sea lions population has been dramatically declining over the past decade. The reasons for this population decline are unknown but may include the following: (1) direct harvesting; (2) reduced prey availability and distribution as a consequence of environmental change; or (3) biological interaction with fisheries. This study aims to determine resource overlap and competition between South American sea lions (SASL, Otaria flavescens, n=10) and the artisanal fisheries (AF), and the coastal bottom trawl fisheries (CBTF). We integrated data on sea lions diet (scat analysis), spatial and annual consumption estimates; and foraging behavior-satellite-tracking data from lactating SASL with data on fishing effort areas and fisheries landings. We found that lactating SASL are benthic divers and forage in shallow water within the continental shelf. SASL's foraging areas overlapped with CBTF and AF fisheries operational areas. Dietary analysis indicated a high degree of overlap between the diet of SASL and the AF and CBTF fisheries catch. The results of our work show differing degrees of spatial resource overlap with AF and CBTF, highlighting that there are differences in potential impact from each fishery; and that different management/conservation approaches may need to be taken to solve the fisheries-SASL conflict. © 2012 Elsevier Ltd. Source

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