Physical Drivers and Dominant Oceanographic Processes on the Uruguayan Margin (Southwestern Atlantic): A Review and a Conceptual Model

Abstract

The Uruguayan continental margin (UCM), located in the Southwestern Atlantic margin’s subtropical region, is positioned in a critical transitional region regarding the global ocean circulation (Río de la Plata (RdlP) outflow and Brazil-Malvinas Confluence), as also reflected in seafloor features (northernmost distribution of a large depositional contourite system and RdlP paleovalley). This complex oceanographic scenario occurring in a relatively small area highlights the advantage of considering the UCM as a natural laboratory for oceanographic research. The present work provides the first conceptual “control” model of the physical drivers (i.e., climate, geomorphology) and main oceanographic processes (i.e., hydrodynamics, sediment, and carbon dynamics) occurring along the UCM, reviewing and synthesizing available relevant information based on a functional integrated approach. Despite the conspicuous knowledge gaps on critical processes, a general picture of the system’s functioning is emerging for this complex biophysical setting. This includes conceptualizations of the actual controls, main processes, feedbacks, and interactions responsible for system dynamics. The structure adopted for developing our conceptual models allows permanent improvement by empirical testing of the working hypothesis and incorporating new information as scientific knowledge advances. These models can be used as a baseline for developing quantitative models and, as representations of relatively “pristine” conditions, for stressors models by identifying sources of stress and ecological responses of key system attributes under a transboundary approach.

Bioregionalization in a data-poor situation: Mapping of Uruguayan marine benthic regions

“…In the continental shelf, this characteristic is represented by the Subtropical Shelf Front (STSF), a shallow extension of the Brazil-Malvinas Confluence (BMC) that occurs in deep water off the shelf (Matano et al, 2010). Despite its small size compared to neighboring countries, the U-EEZ is considered one of the most productive areas of the southern hemisphere (Burone et al, 2021;de Mello et al, 2014), owing to regional oceanic circulation patterns and interactions with the RdlP freshwater discharge. Offshore, in the Brazil-Malvinas Confluence Zone, the southward-flowing subtropical Brazil Current (which transports: Tropical Water (TW) and South Atlantic Central Water (SACW)) meets the northward-flowing Malvinas/Falkland Current, displacing Subantarctic Water (SW) and Antarctic Intermediate Water (AAIW).…”

“…The lower slope and abyssal plain are dominated by mud deposits (Burone et al, 2021). This system must contribute to a high benthic species richness and emerging patterns of endemism at basin scales.…”

“…For the continental shelf, up to 50 m depth, and following Scarabino (2006), bathymetric categories from 0 m to 10 m and 10 m to 50 m were defined. From 50 m deep, were used those isobaths commonly used as reference in the scientific literature of the area (Rodriguez et al, 2014;Burone et al, 2021) (Figure 1). For salinity, average bottom salinity values were used, and three salinity categories were considered, from 27 to 31.5, from 31.5 to 33.5, and from 33.5 to 36, following Defeo et al (2009).…”

“…For dominant water masses, the McQuaid et al (In Press) model of the distribution of bottom water masses, which considered 8 water masses categories in the study area was used. These water masses categories were interpreted according to Burone et al (2021), based on Sverdrup et al (1942), Stramma & England (1999) and Peterson & Stramma (1991), from which surface (0 m-500 m) and intermediate (500 m-1200 m) water masses are reported, corresponding to Tropical Water (TW), South Atlantic Central Water (SACW), and Antarctic Intermediate Water (AAIW) respectively. From 1,200 m to 4,000m, the seafloor is under the influence of Upper Circumpolar Deep Water (UCDW), North Atlantic Deep Water (NADW), and Lower Circumpolar Deep Water (LCDW), in descending order.…”

Benthic invertebrates collected by the RV 'Walther Herwig I and II' in the Southwestern Atlantic Ocean (1966-1978): a review of the Zoological Museum of Hamburg invertebrates collection

“…In the confluence or transition zone (from 30° S to 46° S), a series of oceanographic phenomena (eddies, marine fronts, etc.) allows for high biological production (Franco-Fraguas et al 2014;Burone et al 2021).…”