Southwestern Atlantic Ocean Fronts Detected from Satellite-Derived SST and Chlorophyll

The Southern Ocean front (SOF) is an important factor that affects the heat exchange and material transport of the Southern Ocean. In the past two decades, with the advancements in satellite remote-sensing technology, the study of the spatio-temporal variability of the Southern Ocean front has become a new hot topic. Nevertheless, the southwestern Atlantic, as an important part of the Southern Ocean, is poorly studied in this regard. Based on the 16-year (2004–2019) high-resolution satellite observations of sea surface temperature (SST) and 13-year (2007–2019) observations of chlorophyll (CHL), this study detected and analyzed the position and seasonal variation of the SOF in the southwestern Atlantic using a gradient-based frontal detection method. According to the experimental results, the thermal front (derived from the SST data) disappeared in winter due to the spatially uniform surface cooling, whereas the ocean color front (derived from the CHL data) existed without remarkable spatio-temporal changes. Furthermore, the exact position and seasonal variation of the SOF in the southwestern Atlantic are determined by comparing the paths of the two fronts. Since the formation of the Kuroshio front in the East China Sea (ECS) is similar to the SOF in the southwestern Atlantic, the seasonal distributions of the two fronts were compared. Apart from that, the Kuroshio thermal fronts were mostly distributed in winter and less in summer, while the Southern Ocean thermal fronts showed the opposite. These results indicated that the ocean current properties significantly influence the spatio-temporal variability of the front.

Effectiveness of Large-Scale Marine Protected Areas in the Atlantic Ocean for Reducing Fishing Activities

The implementation of large-scale marine protected areas (MPAs) depends upon scarce conservation resources, while their effects on biodiversity conservation are rarely assessed to date. Quantitative evaluations are necessary to assess the effectiveness of large-scale MPAs in enhancing ecosystem resilience, protecting biodiversity, and mitigating expanding threats. In this study, the effectiveness of large-scale MPAs, which are remotely managed and in offshore areas of the southwestern Atlantic Ocean (Brazil), was assessed concerning the occurrence of fishing activities within their boundaries before and after their implementation. Two sets of MPAs surrounding the São Pedro and São Paulo archipelago (SPSP) and the Trindade-Martin Vaz Islands (TMV) were established in early 2018, each comprising one no-take (i.e., fully-protected) and one multiple-use (i.e., partially-protected) area. For this assessment, I used satellite detections of Vessel Monitoring System transmission to quantify the fishing pressure (i.e., “likely fishing days”) from commercial fisheries spanning 5 years (2015–2019). I then derived three metrics – fishing area, intensity, and density – to compare fishing activity within each MPA and year. The results showed that the effectiveness of the multiple-use MPAs was variable and contrasting, with SPSP experiencing a reduction in the fishing intensity and area and TMV experiencing an increase in both measures. An inverted pattern was evident for the no-take MPAs: while the one in the SPSP region experienced an increase in the fishing density after its establishment following a squeeze factor, the no-take MPA in the TMV region observed a decrease in the fishing density when comparing years before and after MPA implementation. These outputs can support managers in planning the implementation of further conservation strategies, such as monitoring and enforcement plans, and the analyses here also contribute to enhancing our understanding on the implications and challenges of adopting large-scale MPAs in the offshore environment as a high-profile strategy of ocean conservation.

Temporal and Spatial Variability Scales of Salinity at a Large Microtidal Estuary

The Río de la Plata is a large fluvial–estuarine–sea system discharging into the southwestern Atlantic Ocean, which has relevant features such as high fluvial discharge, microtidal astronomical tidal scales, a relevant meteorological tide, and a strong atmospheric forcing effect, due to its large width. The objective of this study is to advance the understanding of the estuarine hydrodynamics and salt transport, as well as discussing the main characteristics of the spatiotemporal variability of the salinity field. To achieve this, the results of a 3D model of the Río de la Plata and its maritime front were used, simulating an extensive period of 10 years. In this study, the model was validated using vertical salinity profiles collected at different locations in the estuary. The temporal variability of the salinity stratification was characterised at different temporal scales: annual, monthly, and storm. At the same time, the influences of fluvial flow and winds were determined. The correlation analysis between fluvial flow and the salinity field showed that high annual fluvial flows generate an extension of the freshwater area, with larger longitudinal salinity gradients and a shift of the salinity front towards the ocean. The tendency at the monthly scale is not as clear as that observed at the annual scale. The results show that the effect of a storm coming from the northwest is quite similar to that of storms coming from the southwest, especially in the central and southern zones of the Río de la Plata, where mixing increases and stratification decreases, according to the intensity of the storm. The effect of south–southeasterly storms increases the mixing process and reduces stratification; the opposite effect was identified with respect to northeasterly storms, under the influence of which the stratified area increases. Synthesising the obtained results, a global zonification of the vertical salinity stratification for the Río de la Plata is proposed.