PATTERNS AND TRENDS IN CHLOROPHYLL-A CONCENTRATION AND PHYTOPLANKTON PHENOLOGY IN THE BIOGEOGRAPHICAL REGIONS OF SOUTHWESTERN ATLANTIC OCEAN

DELGADO, ANA LAURA; HERNÁNDEZ?CARRASCO, ISMAEL; COMBES, VINCENT; FONT?MUÑOZ, JOAN; PRATOLONGO, PAULA D.; BASTERRETXEA, GOTZON

Palma de Mallorca

Congreso; ASLO Aquatic Sciences Meeting 2023; 2023

The Southwestern Atlantic Ocean (SAO), is considered as one of the most productive areas of the world, with high abundance of ecologically and economical 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 datasets, we classified the SAO into coherent regions based on homogeneous temporal variability of Chl-a concentration, as revealed by the Self-Organizing Maps analysis. These coherent biogeographical regions were the basis of our regional trend analysis in phytoplankton biomass, regional phenological indices, and environmental forcing variations. A generalized positive trend in phytoplankton concentration is observed, especially in the highly productive areas of the northern shelf-break, where phytoplankton biomass is increasing at an outstanding rate up to 0.42 ± 0.04 mg m-3 per decade associated with the SST warming (0.11 ± 0.02 °C decade-1) and the MLD shoaling (-3.36 ± 0.13 m decade-1). In addition to the generalized increase in Chl-a, in the northern inner shelf waters and the Patagonian temperate fronts, a significant positive trend in the start of the autumn bloom of 15 ± 3 and 24 ± 6 days decade-1, respectively, was observed, which might be explained by the significant warming trend of SST, which would sustain the water stratification for a longer period, thus delaying the secondary bloom initialization. Consistent with previous studies, our results provided further evidences of the impact of climate change in these highly productive waters.