Planktonic drivers of carbon transformation during different stages of the spring bloom at the Patagonian Shelf-break front, Southwestern Atlantic Ocean

GILABERT, AZUL S.; LÓPEZ-ABBATE, CELESTE; FLOMBAUM, PEDRO; UNREIN, FERNANDO; ARBILLA, LISANDRO A.; GARZÓN-CARDONA, JOHN E.; MARTINEZ, ANA M.; IBARBALZ, FEDERICO M.; VINCENT, FLORA; SARACENO, MARTIN; RUIZ-ETCHEVERRY, LAURA A.; FERRONATO, CAROLA; GUINDER, VALERIA A.; SILVA, RICARDO; UIBRIG, ROMÁN A.; D?AGOSTINO, VALERIA; LOIZAGA, ROCÍO; LARA, RUBÉN J.

Biogeochemistry

Springer nature

Año: 2025 vol. 168

The processes involved in the carboncycle are essential for marine trophic networks andglobal climate regulation. Interactions within themicrobial loop play key roles in carbon transforma-tion and transport across the food web. The Argen-tine Patagonian Shelf in the Southwestern Atlantic Ocean is a hotspot for carbon sequestration. However,our understanding of microbial impacts on carboncycling in this area remains limited. This study exam-ines the microbial community structure and its rolein the carbon transformation during a progression ofthe spring bloom along the Patagonian shelf-breakand adjacent ocean. This progression was studiedin a latitudinal track where we observed a gradientof Dissolved Organic Matter (DOM) complexity. Inthe northern area, the bloom termination was char-acterised by low Chlorophyll-a concentrations, with smaller organisms (Synechococcus) dominating theautotrophic plankton biomass, and high viral concen-trations. DOM showed high humification and aroma-ticity, indicating an intensified microbial activity byheterotrophic bacteria that followed the production ofphytoplankton-derived DOM. In the southern area,high Chlorophyll-a was mainly attributed to large pro-tist plankton, accompanied by abundant heterotrophicbacteria and bioavailable DOM from recent phyto-plankton blooms. These results showed that duringbloom termination, bacterial production of refractorycompounds significantly immobilises carbon, sug-gesting a potential pathway for carbon sequestration.Additionally, data suggest high carbon retention onthe shelf side of the front by microbial transforma-tion and efficient trophic transfer within the microbialcommunity, while the side influenced by the Malvi-nas Current, presents high carbon export by advec-tion and a higher degree of unutilised carbon frombacterial origin. These findings highlight rapid shiftsin carbon dynamics driven by microbial successionsduring different bloom phases.