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The mesoscale activity of western boundary currents can induce changes in the oligotrophic conditions of the oceanic subtropical gyres. Off SE Brazil, recurrent meanders in the Brazil Current can modulate the pelagic ecosystem through eddy‐induced upwelling, as well as drive coastal upwelling and cross‐shelf exchanges. Despite their relevance, direct measurements of such meanders are scarce. At the end of the Spring of 2019, we acquired measurements of both physical and biogeochemical properties along a transect through one of these features, with 5–10 km spacing between stations. Displacements of the isopycnals at the meander edges arose from submesoscale filaments along the meander's rim, associated with the signature of shelf water masses. Chlorophyll distributions along the transect indicated phytoplankton responses to the different dynamic regimes in the meander: eddy stirring in the surface mixed layers versus eddy pumping in the subsurface waters, and mesoscale dynamics in the meander center versus submesoscale dynamics in its periphery. Subsurface phytoplankton biomass was enhanced in the meander center, likely due to eddy pumping raising the nutricline into the euphotic zone. Eddy pumping also appears to have contributed to a shift in the phytoplankton community composition to larger organisms. Our results indicate that the physical dynamics create different habitats across the meander, leading to spatial patchiness in the chlorophyll distributions, with different types of organisms in distinct parts of the meander. Plain Language Summary: Like rivers, ocean currents can meander along their paths. Off southeastern Brazil, the Brazil Current flows southward and meanders as it flows past capes in the region. These meanders are hundreds of kilometers wide (mesoscale) and can generate smaller features that are tens of kilometers wide (submesoscale). These multiscale processes impact the planktonic ecosystem by inducing nutrient inputs to the nutrient‐poor open ocean and consequently enhancing primary productivity. However, direct measurements of these features are scarce. We had the opportunity to survey one of these meanders in 2019, collecting physical and biogeochemical data along a single line through the meander from southwest to northeast. We found small‐scale distortions that indicated the presence of submesoscale features swirling around the meander's rim. Different parts of the meander showed distinct phytoplankton responses, with more phytoplankton in the center, below the surface, likely growing on nutrients pumped upward by the meander. This pumping process might have been correlated with a phytoplankton community shift from small to larger organisms. Overall, our study shows that mesoscale and submesoscale motions create a variety of habitats, leading to distinct chlorophyll distribution patterns in different parts of the meander. Key Points: We present the first physical‐biological measurements of a Brazil Current cyclonic meander drawing high chlorophyll shelf waters offshoreEddy pumping raised nutricline to the euphotic zone driving subsurface phytoplankton enhancement at eddy center and invisible to satellitesDistinct hydrodynamic regimes modulated the phytoplankton response in the center, rim, surface, and subsurface of the eddy [ABSTRACT FROM AUTHOR]

Coccolithophores are a key functional phytoplankton group and produce minute calcite plates (coccoliths) in the sunlit layer of the pelagic ocean. Coccoliths significantly contribute to the sediment record since the Triassic and their geometry have been subject to palaeoceanographic and biological studies to retrieve information on past environmental conditions. Here, we present a comprehensive analysis of coccolith, coccosphere and cell volume data of the Southern Ocean Emiliania huxleyi ecotype A, subject to gradients of temperature, irradiance, carbonate chemistry and macronutrient limitation. All tested environmental drivers significantly affect coccosphere, coccolith and cell volume with driver‐specific sensitivities. However, a highly significant correlation emerged between cell and coccolith volume with Vcoccolith = 0.012 ± 0.001 * Vcell + 0.234 ± 0.066 (n = 23, r2 =.85, p <.0001, σest = 0.127), indicating a primary control of coccolith volume by physiological modulated changes in cell volume. We discuss the possible application of fossil coccolith volume as an indicator for cell volume/size and growth rate and, additionally, illustrate that macronutrient limitation of phosphorus and nitrogen has the predominant influence on coccolith volume in respect to other environmental drivers. Our results provide a solid basis for the application of coccolith volume and geometry as a palaeo‐proxy and shed light on the underlying physiological reasons, offering a valuable tool to investigate the fossil record of the coccolithophore E. huxleyi. [ABSTRACT FROM AUTHOR]

The article refers to phytoplankton biomass. Phytoplankton biomass and photosynthesis were investigated in relation to physicochemical environmental conditions in Tokyo Bay from May 1979 through March 1981. Vertical and seasonal variations of "chlorophyll a," photosynthetic and respiratory activity, and environmental conditions were investigated in the inner part of the bay. It is found that "Chlorophyll a" concentrations were generally high when salinity was low, but no definite relationship was observed between photosynthesis and salinity. No clear relationship was observed between chlorophyll a and nutrient concentrations.