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Arndt J.E.,Alfred Wegener Institute for Polar and Marine Research | Schenke H.W.,Alfred Wegener Institute for Polar and Marine Research | Jakobsson M.,University of Stockholm | Nitsche F.O.,Lamont Doherty Earth Observatory | And 12 more authors.
Geophysical Research Letters | Year: 2013

The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60°S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). The IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single-beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 × 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at http://dx.doi.org/10.1594/PANGAEA.805736. Key Points The first regional bathymetric compilation covering the entire Southern Ocean A new keystone dataset for Antarctic research The southern equivalent to IBCAO is now released ©2013. American Geophysical Union. All Rights Reserved.


Campos P.C.,Grande Rio University | Moller Jr. O.O.,Grande Rio University | Piola A.R.,Servicio de Hidrografia Naval | Piola A.R.,University of Buenos Aires | And 3 more authors.
Journal of Geophysical Research: Oceans | Year: 2013

The Santa Marta Grande Cape (CSM) area, a relatively steep and narrow continental shelf off southeast Brazil, is under the influence of the Brazil Current and intense seasonal variations of the wind field that affect the composition of water masses and their circulation. Hydrographic data, satellite-derived wind stress, and numerical simulations are used to characterize the seasonal and shorter period variability of the oceanographic conditions off CSM, in the area between 27°S and 30°S. The study is focused on the upwelling episodes and the dynamical mechanisms associated with these events. Field data and numerical results indicate significant seasonal changes in the oceanographic structure, the water mass composition, and the dynamical balance. During fall and winter, when southwesterly winds prevail and the frequency of meteorological frontal systems increases, the region is characterized by waters of continental origin, the Plata Plume Water (PPW). During spring and summer, deeper waters reach the surface layer due to the action of northeasterly winds. Coastal upwelling events are revealed by surface temperature minima observed south of CSM. Synoptic data show that these events occur in pulses associated with changes in the wind direction. Analysis of the numerical results shows that this particular location of the upwelling band results from the synergy between shelf-break upwelling and the regional shelf circulation induced by the northeasterly winds, both of which are modulated by changes in the coastline orientation and shelf width. © 2013. American Geophysical Union. All Rights Reserved.


Saraceno M.,University of Buenos Aires | D'Onofrio E.E.,University of Buenos Aires | Fiore M.E.,University of Buenos Aires | Grismeyer W.H.,Servicio de Hidrografia Naval
Continental Shelf Research | Year: 2010

Sea surface height (SSH) as measured by satellites has become a powerful tool for oceanographic and climate related studies. Whereas in the open ocean good accuracy has been achieved, more energetic dynamics and a number of calibration problems have limited applications over continental shelves and near the coast. Tidal ranges in the Southwestern Atlantic (SWA) continental shelf are among the highest in the world ocean, reaching up to 12 m at specific locations. This fact highlights the relevance of the accuracy of the tidal correction that must be applied to the satellite data to be useful in the region. In this work, amplitudes and phases of tidal constituents are extracted from five global tide models and three regional models and compared to the corresponding harmonics estimated from coastal tide gauges (TGs) and satellite altimetry data. The Root Sum Square (RSS) of the misfit of the common set of the five tidal constituents solved by the models (M 2, N 2, S 2, K 1 and O 1) is higher than 18 cm close to the coast for two of the regional models and higher than 24.5 cm for the rest of the models considered. Both values are too high to provide an accurate estimation of geostrophic non-tidal currents from satellite altimetry in the coastal region. On the other hand, the global model with the highest spatial resolution has a RSS lower than 4.5 cm over the continental shelf even when the non-linear M 4 overtide is considered. Comparison with in-situ current measurements suggests that this model can be used to de-tide altimetry data to compute large-scale patterns of SSH and associated geostrophic velocities. It is suggested that a local tide model with very high resolution that assimilates in-situ and satellite data should meet the precision needed to estimate geostrophic velocities at a higher resolution both close to the coast and over the Patagonian shelf. © 2010 Elsevier Ltd.


Matano R.P.,Oregon State University | Palma E.D.,National University of the South | Palma E.D.,CONICET | Piola A.R.,Servicio de Hidrografia Naval | Piola A.R.,University of Buenos Aires
Ocean Science | Year: 2010

The oceanic circulation over the southwestern Atlantic shelf is influenced by large tidal amplitudes, substantial freshwater discharges, high wind speeds and - most importantly - by its proximity to two of the largest western boundary currents of the world ocean: the Brazil and Malvinas currents. This review article aims to discriminate the dynamical processes controlling the interaction between this extensive shelf region and the deep-ocean. The discussion is focused on two broad regions: the South Brazil Bight to the north, and Patagonia to the south. The exchanges between the Brazil Current and the South Brazil Bight are characterized by the intermittent development of eddies and meanders of the Brazil Current at the shelfbreak. However, it is argued that this is not the only - nor the most important - influence of the Brazil Current on the shelf. Numerical simulations show that the thermohaline structure of the South Brazil Bight can be entirely ascribed to steady state, bottom boundary layer interactions between the shelf and the Brazil Current. The Malvinas Current does not show the development of eddies and meanders, but its influence on the Patagonian shelf is not less important. Models and observations indicate that the Malvinas Current not only controls the shelfbreak dynamics and cross-shelf exchanges but also influences the circulation in the shelf's interior. © Author(s) 2010.


Lantzsch H.,University of Bremen | Hanebuth T.J.J.,University of Bremen | Chiessi C.M.,University of Sao Paulo | Schwenk T.,University of Bremen | Violante R.A.,Servicio de Hidrografia Naval
Quaternary Research (United States) | Year: 2014

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. © 2014 University of Washington.


Preu B.,University of Bremen | Schwenk T.,University of Bremen | Hernandez-Molina F.J.,University of Vigo | Violante R.,Servicio de Hidrografia Naval | And 4 more authors.
Marine Geology | Year: 2012

Large sedimentary deposits consisting of several major contourite drifts were studied by means of high-resolution multichannel seismic data at the middle slope along the Northern Argentina Continental Margin to determine their evolutionary stages as well as to identify and assess the possible impact of Northern Source Deep Water (NSDW) on the slope architecture. The imaged contouritic sediments allow decoding on the regional paleo-oceanographic setting of the last 32. Ma. Earliest contouritic sedimentation can be observed close to the Eocene/Oligocene boundary based on an aggradational stacking pattern with a complex and wavy seismic facies, pointing toward a hydrodynamically turbulent flow pattern. This facies is most likely related to the opening of the Drake Passage associated with global cooling and a strengthening of surface, intermediate and deep ocean currents in the Southern Ocean. During the Middle Miocene plastered drift sequences with an aggradational reflection pattern were deposited. Their depositional style indicates weak, non-turbulent current conditions, which are interpreted to be related to a vertical shift of water mass interfaces caused by the first formation of NSDW during the Mid-Miocene climatic optimum. On top, the formation of plastered drift sequences led to the modern extent of the Ewing Terrace, which was probably controlled by the continuous strengthening and thickening of NSDW until the final closure of the Central American Seaway (CAS). During the Pliocene and Quaternary, after the complete closure of the CAS and under the influence of the full force of the NSDW, mounded plastered drift sequences are built upon the Ewing Terrace generating the modern slope morphology. Therefore, we suggest that deep-water production in the northern hemisphere plays a significant role by controlling the shape of the continental slopes in the southwestern South Atlantic since the Middle Miocene. © 2012 Elsevier B.V.


Boltovskoy D.,University of Buenos Aires | Boltovskoy D.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia | Correa N.,Servicio de Hidrografia Naval
Hydrobiologia | Year: 2014

We summarize current knowledge on the effects of the invasive Asian bivalve Limnoperna fortunei (introduced in South America around 1990) on local biota. Limnoperna modifies nutrient concentrations and decreases concentrations of particulate organic matter in the water column (including phytoplankton and zooplankton), thus enhancing light penetration and stimulating growth of periphyton and macrophytes. Selective grazing and modification of the N:P ratio are responsible for strong enhancements of toxic cyanobacterial blooms. Limnoperna beds significantly enhance the numbers, biomass, and diversity of practically all accompanying invertebrates. The mussel’s planktonic larvae represent an important food item for the larvae of 18 fish species, while juveniles and adults are consumed by at least 50 fish species. Limnoperna is the first and only abundant benthic filter-feeding animal in South American continental waters. The fact that it intercepts and retains in the freshwater lotic domain particulate organic matter that would otherwise be swept into the sea must represent an important energetic subsidy, but the ecosystem-wide consequences of this trophic shift have not yet been addressed. Comparison with the impacts of the zebra mussel in Europe and North America suggests important differences. © 2014, Springer International Publishing Switzerland.


Boltovskoy D.,University of Buenos Aires | Boltovskoy D.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia | Correa N.,Servicio de Hidrografia Naval | Bordet F.,Area Ecologia | And 4 more authors.
Freshwater Biology | Year: 2013

Toxic cyanobacterial blooms and biological invasions are major threats to freshwater systems worldwide. While usually dealt with independently, the two threats can interact to produce synergistic or antagonistic outcomes. The aim of this survey is to analyse interactions between the cyanobacterium Microcystis spp. and the Asian invasive mussel Limnoperna fortunei. On the basis of 9 years of observational data in a large subtropical reservoir (Salto Grande, Argentina-Uruguay), we analyse causal relationships between recurring summer-early autumn blooms of Microcystis spp. and recruitment by L. fortunei. Reproduction of the mussel was interrupted during dry summers (January-April), coinciding with periods of peak Microcystis spp. growth and low water discharge (which favours build-up of algal biomass). On the other hand, wet summers with high discharge rates were characterised by low Microcystis spp. densities and high numbers of L. fortunei larvae in the water column. Of the seven South American waterbodies investigated, Salto Grande was the only one with very marked cyanobacterial blooms and where larval numbers decrease to near zero during January-April; in all others, reproduction peaks in January-April. The assumption that microcystin-producing algae are responsible for these troughs during periods when elsewhere larvae are very abundant was reinforced by experimental results indicating that microcystin-LR is highly toxic to the mussel's larvae, eliminating 58-100% of animals in 48 h at 10-20 μg L-1. Paradoxically, high concentrations of microcystin in water are probably partly due to L. fortunei's own activity, which enhances growth of Microcystis spp. through modification of nutrient concentrations, selective grazing of solitary Microcystis spp. cells over colonial ones and production of chemical cues that trigger the formation of colonies. These interactions have important implications for the management of biofouling of industrial raw cooling water facilities by the byssate mussels, as well as policies oriented at curtailing the spread of the invasive bivalve. © 2013 John Wiley & Sons Ltd.


Boltovskoy D.,University of Buenos Aires | Boltovskoy D.,CONICET | Boltovskoy D.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia | Almada P.,University of Buenos Aires | Correa N.,Servicio de Hidrografia Naval
Environmental Science and Policy | Year: 2011

Between July 2007 and December 2008 we surveyed 194 commercial vessels for compliance with ballast water (BW) regulations at five Argentine ports (four of them along the Patagonian coast). Our survey included the inspection of the BW reporting forms and collection of BW samples for salinity and biological (plankton) analyses from 261 BW tanks. Most (77%) ships had some type of BW form on board, but the information in these forms was often unclear, incomplete or inconsistent and did not allow tracking the origin of the BW. Salinity of the BW was often in conflict with the reported geographic location of BW exchange, and the reported volumes of BW discharged in the ports surveyed appeared to be fictitious. Most (80%) BW tanks contained identifiable organisms, usually in very good state of preservation, totaling 408 plant and animal taxa, but only three of these had not been previously recorded in Argentina (two diatoms and one copepod). In spite of the fact that compliance with national and international regulations and guidelines on BW management is poor in the area, the number of recorded marine aquatic nonindigenous species (ANS) in Argentina is comparatively low (ca. 40). Several factors seem to buffer the Argentine coastline from ANS: (1) the low activity of most Patagonian ports; (2) the fact that most (61%) incoming ship traffic originates from domestic ports or areas unlikely to supply ANS; (3) the harsh environmental conditions (cold and turbulent, with few sheltered areas); and (4) the scarcity of hard substrates. In order to maintain its waters relatively free of ANS, Argentina needs to significantly increase its efforts at enforcing existing international and national legislation, and to revise and update its standards on BW management. We anticipate that the problems encountered are also characteristic of many other developing countries, both in South America and elsewhere, where compliance with IMO's BW guidelines is still seldom tested or enforced. © 2011 Elsevier Ltd.


Cavallotto J.L.,Servicio de Hidrografia Naval | Violante R.A.,Servicio de Hidrografia Naval | Hernandez-Molina F.J.,University of Vigo
Biological Journal of the Linnean Society | Year: 2011

The Patagonian continental margin records some of the tectonic, sedimentary, climatic, and oceanographic events that participated in the evolution of the Patagonian and south-western Atlantic regions. Those records are essential for fully understanding the geology and biodiversity of Patagonia. Regional geotectonic and morphosedimentary features are characterized by different types of continental margins (passive, transcurrent, and transpressive). In each of them the constituent features (shelf, slope, and rise) acquire particular morphological and sedimentary configurations. Characteristics of the sedimentary sequences and the limiting discontinuities document the different evolutive stages of the margin and intervening major processes. The regional tectonic, palaeoclimatic, and palaeoceanographic events that occurred after the break-up of Gondwana until the Quaternary, which conditioned the morphosedimentary characteristics, are analysed and described here. It is concluded that the region evolved in three major stages, according to the predominance of different factors: (1) a stage dominated by endogene factors, which occurred in Mesozoic times, when the major processes at work were plate tectonics and oceanic opening; (2) a transitional stage, which occurred in the lower Tertiary, when the proto-Atlantic Ocean evolved towards an open sea, and climatic and oceanographic factors became at least as important as tectonic factors; and (3) a stage dominated by exogene factors, which occurred in post-Oligocene times, when the Atlantic Ocean was definitively installed and the circulation of oceanic currents influenced the characteristics of the sedimentary environments - this stage ended in the Quaternary when glacioeustatic fluctuations imprinted the present morphosedimentary configuration. © 2011 The Linnean Society of London.

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