POSTER Session 1

Phenological patterns of coastal algal blooms in complex waters of El Rincón system (Southwestern Atlantic Ocean). A remote sensing approach

We evaluated phenology of coastal algal blooms in El Rincón. The performance of the Multiple Band Ratio algorithm (MuBR) was validated and used to derive Chl-a concentrations from all available L2 MODIS-Aqua (2003-2023) and Sentinel 3-OLCI (2017-2023). From MODIS-Aqua daily images we derived monthly Chl-a composites to perform an Empirical Orthogonal Function (EOF) analysis. Phytoplankton phenology was analyzed using 15-day composites derived from Sentinel3/OLCI. We used TIMESAT to obtain four indices: timing of bloom initiation, peak amplitude, timing of bloom termination and bloom duration. MODIS-Aqua exhibited a slight overestimation and higher scatter (RSME = 0.25 ug L-1, NMAE = 18%, bias = 0.13), compared to Sentinel3-OLCI (RSME = 0.13 ug L-1, NMAE = 8.2%, bias = 0.01). The first mode EOF-PC1 (ev=63%) had a significant 1-year period through the series. Deeper areas of El Rincon showed a stronger annual signal. The second mode EOF-PC2 (ev=22%) showed a 0.5-year period spatially correlated with estuarine channels. According to phenology indices, there was a main bloom in austral winter all over the region. In the estuarine area it showed higher amplitudes and shorter durations compared to the coastal zone. The main bloom in the inner and middle estuary lasted between 1.9 to 2.8 months, compared to 4 to 5 months in the coastal region, with amplitudes ranging between 1 to 2.5 ug L-1. The estuarine area presented a secondary peak, with lower amplitude and shorter duration. Finally, in deeper areas out of the coastal influence, the bloom has longer duration, minimum amplitude, and no secondary peak.

Paula Pratolongo, Centro de Recursos Naturales Renovables de la Zona Semiárida (CERZOS-CONICET- UNS), Argentina, https://orcid.org/0000-0001-8271-7942

Maximiliano Arena, Instituto Argentino de Oceanografía (IADO-CONICET-UNS), Argentina

Hubert Loisel, Laboratoire d’Océanologie et de Géosciences, Université du Littoral-Côte-d’Opale, Université Lille,

Duy Manh Tran, Laboratoire d’Océanologie et de Géosciences, Université du Littoral-Côte-d’Opale, Université Lille,

Daniel Jorge, Laboratoire d’Océanologie et de Géosciences, Université du Littoral-Côte-d’Opale, Université Lille,

Ana Laura Delgado, Institut Mediterrani d’Estudis Avançats (IMEDEA-CSIC-UIB), Spain, and Instituto Argentino de Oceanografía (IADO-CONICET-UNS), Argentina

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