The Southwestern Atlantic Ocean (SWA), is considered one of the most productive areas of the world, with a high abundance of ecologically and economically important fish species. Yet, the biological responses of this complex region to climate variability are still uncertain. Here, using 24 years of satellite‐derived Chl‐a data, we classified the SWA into 9 spatially coherent regions based on the temporal variability of Chl‐a concentration, as revealed by SOM (Self‐Organizing Maps) analysis. These biogeographical regions were the basis of a regional trend analysis in phytoplankton biomass, phenological indices, and environmental forcing variations. A general positive trend in phytoplankton concentration was observed, especially in the highly productive areas of the northern shelf‐break, where phytoplankton biomass has increased at a rate of up to 0.42 ± 0.04 mg m⁻³ per decade. Significant positive trends in sea surface temperature were observed in 4 of the 9 regions (0.08–0.26 °C decade⁻¹) and shoaling of the mixing layer depth in 5 of the 9 regions (−1.50 to −3.36 m decade⁻¹). In addition to the generally positive trend in Chl‐a, the most conspicuous change in the phytoplankton temporal patterns in the SWA is a delay in the autumn bloom (between 15 ± 3 and 24 ± 6 days decade⁻¹, depending on the region). The observed variations in phytoplankton phenology could be attributed to climate‐induced ocean warming and extended stratification period. Our results provided further evidence of the impact of climate change on these highly productive waters.

Delgado, A.L.; Menéndez, M.C.; Piccolo, M.C., and Perillo, G.M.E., 2017. Hydrography of the inner continental shelf along the southwest Buenos Aires Province, Argentina: Influence of an estuarine plume on coastal waters. Estuarine plumes have a significant influence on the characteristics and biology of the adjacent inner shelf. In the sector occupied by the plume, several transformations occur to the sediment and nutrients exported from the continent to the oceans. The coastal zone of Pehuén Co (PC) and Monte Hermoso (MH) is located in a highly complex oceanographic and ecological regional system, which creates the basis of one of the most valuable Argentinean habitats for fishing of commercial species. In this work, the physical oceanographic characteristics of the inner shelf of the southwest Buenos Aires Province and the influence of the Bahia Blanca estuarine (BBE) waters are introduced. The in situ data obtained from oceanographic cruises included vertical profiles of water temperature, sal...

The aim of this study is to describe and understand the seasonal and inter-annual physical and biological dynamics of the inner and mid shelves of the Southwestern Buenos Aires Province (Argentina). We used chlorophyll-a (chl-a) concentrations and inherent optical properties (IOPs), derived from ocean color products between 2002 and 2010, as a proxy for the physical and biological parameters of interest. This study focuses on the absorption by phytoplankton, a_ph(443), particulate backscattering, b_bp(443), and absorption due to dissolved and particulate detrital matter, a_dg(443), and chl-a derived from a multiband quasi-analytical algorithm (QAA). A regionalization based on the coefficient of variation and the Census X-11 method were applied to define regions and to analyze the inter-annual and seasonal variability of the ocean color parameters, with regards to climate variability. The coastal zone presents the highest values of chl-a with two maxima in winter and autumn, while the mid-shelf shows a strong spring chl-a maximum. After 2009, all parameters under study shifted their seasonality and their magnitude changed over the entire area. In the coastal zone, mean values of a_ph(443) and b_bp(443) increased, while in the mid-shelf, chl-a and a_ph(443) decreased. The observed inter-annual and seasonal behavior of the parameters is tightly related to climate variability of the study area.

This work combines in situ measurements with a time series of satellite turbidity derived from Landsat 8-OLI images to provide a first synoptic overview of the main hydrometeorological drivers of turbidity in the Bahía Blanca Estuary (Argentina). An empirical relationship between turbidity and SPM concentrations was established for the study area (R² = 0.92; RMSE = 0.098 mg m⁻³; NMAE = 6.2%). Several atmospheric correction schemes and turbidity retrieval algorithms were tested and the combination of the SWIR-v and the retrieval algorithm by Dogliotti et al. (2015) were applied to 121 Landsat 8-OLI scenes (2013–2021). The effects of tides, winds, and rainfall on satellite turbidity were evaluated through Generalized Linear Models (GLM) built for three different sectors along Canal Principal, from the inner zone to its mouth. Regardless of the zone, cumulative rainfall had negligible effects on turbidity. Tides had a significant effect in the inner and middle zones. In the inner zone, higher turbidity values significantly associated with ebb tide conditions, which produce erosion. In the middle section tidal current speeds positively correlated with turbidity, suggesting sediment resuspension over shallow banks. Close to the mouth of the estuary, turbidity responded entirely to winds. Winds blowing from de NW, aligned with the azimuth of Canal Principal, would aid to the export of estuarine sediments to the shelf.

The water masses on the Northern Patagonian continental shelf (Figure 1) have sub-Antarctic origin, mixed with regional coastal inputs, and are influenced by the temperate thermal cycle and NW prevailing winds, making this region a complex oceanographic and ecological system (^{Lucas et al., 2005}). Its coastal zone presents temperate (15°C), high saline (35) and turbid waters (35 NTU) with pronounced seasonal variability (^{Delgado et al., 2017}). The Bahia Blanca Estuary is a tidally dominated, turbid and mixed system that is a main source of fine sediment to the inner shelf (^{Menendez et al., 2016}) towards the eastern coastline (^{Delgado et al., 2017}). Phytoplankton is mainly dominated by diatoms, comprising more than the 50 % of the cell abundances and biomass, followed by dinoflagellates (^{Guinder et al., 2018}) and coccolithophores, both also highly abundant (^{Guinder et al., 2018}; ^{Delgado et al., 2019}).

In this study, we characterized phytoplankton biomass variability in El Rincón, a shallow and biologically productive coastal region in the Patagonian Continental Shelf. We used as a proxy 7 years (2017–2024) of high-resolution Sentinel-3 OLCI satellite data to capture the fine scale spatio-temporal variability of Chl-a in this region. To obtain Chl-a concentration, we applied a regionally validated algorithm (MuRB&NDCI) which provides more accurate Chl-a estimates compared to traditional algorithms, particularly in optically complex waters. Self-organizing maps (SOM) neural network was applied to identify four distinct bio-geographical regions with unique bloom dynamics. The phenological estimates revealed that phytoplankton blooms typically initiate in fall (March), peak during winter (May–August), and are more pronounced near the Bahía Blanca Estuary (BBE), where nutrient and sediment inputs drive high productivity. The findings presented in this work highlight the utility of Optical Water Class–based algorithms for capturing the fine-scale spatiotemporal variability of Chl-a in coastal systems. This study advances our understanding of phytoplankton dynamics in El Rincón and underscores the importance of customized satellite-derived approaches for monitoring and managing productivity in shallow coastal environments.