Delineating Marine Planktonic Habitats Through the Biogeochemical‐Argo Array Data

Abstract Phytoplankton play a crucial role in regulating marine biogeochemical pathways but studying their spatial and temporal dynamics often requires extensive and laborious oceanographic expeditions. Here, we report a novel use of Biogeochemical‐Argo data to delineate planktonic habitats in the Tropical North Atlantic Ocean (TNA). We then investigated the phytoplankton biomass via in situ measurement of the BGC‐Argo floats and phytoplankton community structure of each habitat using Phytoplankton Functional Types derived from satellite observations. Our habitat delineation approach provided a finer scale and dynamic overview of phytoplankton assemblages and their surrounding environment, complementary to the widely used and static biogeochemical provinces of Longhurst. While picophytoplankton remained dominant for most communities, we found elevated abundance of microphytoplankton, including diatoms and dinophytes, and nanophytoplankton, including haptophyte and green algae, following the seasonal displacement of the Intertropical Convergence Zone, and the Amazon and Orinoco River discharges into the Tropical Atlantic and Eastern Caribbean Sea. At midlatitude, our method was able to capture both the seasonal and spatial variations of the oligotrophic region of the North Atlantic subtropical gyre. These findings shed light on the seasonality of phytoplankton distribution driven by meteorological and oceanic forcings and demonstrated the potential of the BGC‐Argo in studying and monitoring marine ecosystem.