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The Burdwood Bank (BB) is a subantarctic area, where two of the three Marine Protected Areas (MPA) of the Argentinean Exclusive Economic Zone are located: Namuncurá I, and Namuncurá II. The area is characterized by a high biodiversity of benthic invertebrates and teleost fishes; however, the available information on oviparous chondrichthyans is scarce. The aim of this study is to explore the potential reproductive use that oviparous chondrichthyans could make of the area based on the presence of egg-laying grounds. Additionally, we aim to provide an updated checklist of the species that inhabit the BB. Samples of specimens and egg capsules collected in four research cruises carried out between 2016 and 2018 were analyzed. Six skate species were found in both MPAs: Amblyraja doellojuradoi, Bathyraja albomaculata, B. brachyurops, B. macloviana,B. scaphiops, and Psammobatis rudis; whereas B. cousseauae, and B. magellanica were found exclusively in Namuncurá I, and B. multispinis in Namuncurá II. Here we report, for the first time, the presence of egg-laying grounds for five chondrichthyan species in the BB area: A. doellojuradoi, B. brachyurops, B. macloviana, B. scaphiops, and P. rudis. The results obtained highlighted the importance of the region for the conservation of oviparous chondrichthyans found in the southern Patagonian shelf. [ABSTRACT FROM AUTHOR]

The global overturning ocean circulation plays a key role in global climate by distributing heat around the Earth and by triggering or amplifying major climate changes. Neodymium (Nd) isotopes are widely used to trace present-day and past ocean circulation changes; however, their value as a circulation tracer has been increasingly challenged by studies that have focused on processes that can modify seawater Nd isotope ratios (for example, seawater interaction with particles, pore water fluxes from sediments). The Southwest Atlantic represents an excellent test bed for investigating the integrity of Nd isotopes as an ocean circulation tracer, as it includes the major Atlantic northern and southern hemisphere-sourced end-member water masses associated with the global overturning ocean circulation, Antarctic Intermediate Water, North Atlantic Deep Water, and Antarctic Bottom Water (AAIW, NADW, and AABW, respectively) and potential regional sources of Nd that could impact that integrity. This study reports Nd isotope data on the GEOTRACES GA02 Southwest Atlantic Meridional Transect, spanning the equator to ∼50°S. Below the pycnocline, substantial non-conservative behavior is observed only in samples dominated by AAIW in the northern portion of the transect (∼25°S to the equator); this appears to reflect addition of Nd from the cratons of South America or Africa from above the pycnocline. This effect is not observed at depths directly below dominated by NADW. Otherwise, Nd isotopes behave as a near-conservative water mass tracer along the transect, with 48% of samples within analytical error of the predicted value from water mass mixing, and 84% within 0.9 ε Nd -units (∼3 times the analytical error), thus confirming its potential at most depths and locations in the Southwest Atlantic to reconstruct past ocean circulation changes. • Ocean circulation plays a major role in climate, distributing heat around the Earth. • Nd isotopes are widely used to trace past ocean circulation in climate studies. • This study evaluates its utility to trace the major water masses in the SW Atlantic. • Nd isotopes are a near-conservative water mass tracer at most locations and depths. • Substantial non-conservative behavior is only seen at AAIW depths in the north. [ABSTRACT FROM AUTHOR]

Abstract: The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-14C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member. [Copyright &y& Elsevier]

Abstract: Hydrographic data collected during surveys carried out in austral winter 2003 and summer 2004 are used to analyze the distributions of temperature (T) and salinity (S) over the continental shelf and slope of eastern South America between 27°S and 39°S. The water mass structure and the characteristics of the transition between subantarctic and subtropical shelf water (STSW), referred to as the subtropical shelf front (STSF), as revealed by the vertical structure of temperature and salinity are discussed. During both surveys, the front intensifies downward and extends southwestward from the near coastal zone at 33°S to the shelf break at 36°S. In austral winter subantarctic shelf water (SASW), derived from the northern Patagonia shelf, forms a vertically coherent cold wedge of low salinity waters that locally separate the outer shelf STSW from the fresher inner shelf Plata Plume Water (PPW) derived from the Río de la Plata. Winter T–S diagrams and cross-shelf T and S distributions indicate that mixtures of PPW and tropical water only occur beyond the northernmost extent of pure SASW, and form STSW and an inverted thermocline characteristic of this region. In summer 2004, dilution of Tropical water (TW) occurs at two distinct levels: a warm near surface layer, associated to PPW–TW mixtures, similar to but significantly warmer than winter STSW, and a colder (T∼16°C) salinity minimum layer at 40–50m depth, created by SASW–STSW mixtures across the STSF. In winter, the salinity distribution controls the density structure creating a cross-shore density gradient, which prevents isopycnal mixing across the STSF. Temperature stratification in summer induces a sharp pycnocline providing cross-shelf isopycnal connections across the STSF. Cooling and freshening of the upper layer observed at stations collected along the western edge of the Brazil Current suggest offshore export of shelf waters. Low T and S filaments, evident along the shelf break in the winter data, suggest that submesoscale eddies may enhance the property exchange across the shelf break. These observations suggest that as the subsurface shelf waters converge at the STSF, they flow southward along the front and are expelled offshore, primarily along the front axis. [Copyright &y& Elsevier]

Abstract: The Río de la Plata waters form a low salinity tongue that affects the circulation, stratification and the distributions of nutrients and biological species over a wide extent of the adjacent continental shelf. The plume of coastal waters presents a seasonal meridional displacement reaching lower latitudes (28°S) during austral winter and 32°S during summer. Historical data suggests that the wind causes the alongshore shift, with southwesterly (SW) winds forcing the plume to lower latitudes in winter while summer dominant northeasterly (NE) winds force its southward retreat. To establish the connection between wind and outflow variations on the distribution of the coastal waters, we conducted two quasi-synoptic surveys in the region of Plata influence on the continental shelf and slope of southeastern South America, between Mar del Plata, Argentina and the northern coast of Santa Catarina, Brazil. We observed that: (A) SW winds dominating in winter force the northward spreading of the plume to low latitudes even during low river discharge periods; (B) NE winds displace the plume southward and spread the low salinity waters offshore over the entire width of the continental shelf east of the Plata estuary. The southward retreat of the plume in summer leads to a volume decrease of low salinity waters over the shelf. This volume is compensated by an increase of Tropical waters, which dominate the northern shelf. The subsurface transition between Subantarctic and Subtropical Shelf Waters, the Subtropical Shelf Front, and the subsurface water mass distribution, however, present minor seasonal variations. Along shore winds also influence the dynamics and water mass variations along the continental shelf area. In areas under the influence of river discharge, Subtropical Shelf Waters are kept away from the coastal region. When low salinity waters retreat southward, NE winds induce a coastal upwelling system near Santa Marta Cape. In summer, solar radiation promotes the establishment of a strong thermocline that increases buoyancy and further enhances the offshore displacement of low salinity waters under the action of NE winds. [Copyright &y& Elsevier]

The magnitude and causal mechanisms of a massive beach stranding of Tehuelche scallops that occurred in November 2017 in San José Gulf, Argentina, were investigated with the long-term goal of improving the assessment and management of the scallop fishery. The biomass of scallops washed ashore and deposited over a 10-km stretch of coast was estimated by quadrat sampling and compared with the results of a scallop stock assessment survey conducted three months prior to the stranding event. The resulting estimate of total biomass loss was in the order of 200 t, representing 10% of the estimated total scallop biomass in the San José gulf. The stranding coincided with persistent strong southerly winds (13 m/s) blowing for 24 h in San José Gulf, and large-scale windstorms that affected the southern tip of South America. Surface waves predicted under such windstorm conditions could generate strong bottom orbital velocities at shallow waters (<10 m depth), sufficient to drag and transport ashore scallops by Stokes drift (600-2000 m in 24 h). Analysis of local wind data recorded over a 6.8-year period indicated that such windstorm conditions occurred with an average frequency of 7.7 times per year, implying that beach strandings could have a significant impact on the scallop resource and its fishery. The actual impact of windstorms would depend on the location, depth and size composition of scallop beds, shallow beds (<10 m depth) being more susceptible to stranding risks. The use of spatial harvest control rules, instead of the global total allowable catch used at present, could reduce the risks of yield loss by directing the harvest to the more vulnerable scallop beds., (Copyright © 2022 Elsevier Ltd. All rights reserved.)