Search

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]

Primary production is essential in shaping biogeochemical cycles and microbial and ecosystem dynamics. The distribution of chemosynthetic rates in pelagic zones and their participation in the carbon cycle, especially when compared to photosynthetic rates in the Southwestern Atlantic Ocean, are poorly constrained. This study aimed to measure pelagic photo- and chemosynthetic productivity and to analyze their spatial distribution and abiotic drivers. Samples for photosynthesis experiments collected at the surface and deep chlorophyll maximum (DCM) were incubated with 14C-bicarbonate at eight light levels, simulating in situ conditions. Samples for chemosynthesis experiments were collected throughout the water column, from the surface, DCM, 250 m, 900 m, 1,200 m, and 2,300 m, and were incubated in the dark. Rates were analyzed using statistical tests to verify spatial differences between groups of samples and generalized linear models to identify correlations with environmental variables (temperature, salinity, density, mixed layer depth, dissolved oxygen, nitrite, nitrate, silicate, phosphate, turbidity, CDOM, and phycoerythrin and chlorophyll-a concentrations). Moreover, both processes were integrated from the surface to the DCM and compared at the same stations to determine the relative contribution in the epipelagic zone. The photosynthetic and chemosynthetic rates were, on average, 3.00 ± 3.26 mg C m-3 h-1 and 0.97 ± 1.22 mg C m-3 h-1, respectively. In most stations, chemosynthesis represented an average of 10.2% of total primary productivity, but surpassed photosynthesis in three experiments (reaching 63.4 - 78.8%). Photosynthesis displayed a clear offshore-onshore gradient, along with correlated CDOM concentrations, indicating an autochthonous production of the latter. Chemosynthesis, on the other hand, exhibited high variability and lack of prediction by studied environmental variables, with isolated points of substantially higher activity. [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]

We investigated the influence of oceanic fronts on mesozooplankton distribution and grazing activity in the south-west Atlantic. Sampling was conducted during late spring 1993 along a north-south transect between subtropical waters off Brazil and Antarctic waters. Mesozooplankton abundance and biomass were ~10-fold higher in the Subtropical Confluence Zone (SCZ) and in the Antarctic Polar Front (APF) relative to subtropical and subantarctic waters beyond the influence of those frontal systems. Mesozooplankton was dominated by calanoid and cyclopoid copepods. Community ingestion rates ranged between 0.1 and 0.3 mg chlorophyll-a m-2 day-1 in interfrontal areas, increasing to 2.0 and 9.0 mg chlorophyll-a m-2 day-1 in the APF and SCZ respectively. Mesozooplankton grazing removed up to 40% of the total chlorophyll stock in the SCZ, and 22% in the APF, on a daily basis. These estimates suggest that mesozooplankton exert a significant grazing impact on phytoplankton over much of the frontal areas studied. Recent investigations have shown that the geographic position of oceanic fronts and plankton biomass maxima in the study area have remained basically the same from the time of our sampling effort to date, meaning that our results apply to present conditions. [ABSTRACT FROM AUTHOR]

Five oceanographic cruises were made between November 2005 and June 2006, sampling a cross-shelf transect off the South Brazilian Bight (SBB; 26°46′S) to follow the seasonal development of the South Atlantic Central Water (SACW) intrusion over the shelf and its influence on the assemblage of planktonic cnidarians. An onshore wind-driven bottom intrusion of the SACW was clearly perceptible, reaching the coast in January. From March onward, the SACW influence was gradually displaced seaward due to wind and tidal mixing. By late June the SACW influence was offshore and the inshore was dominated by low-salinity waters (<34.5). The abundance, distribution, and general taxonomic composition of both medusae and siphonophores were strongly influenced by the onshore intrusion of the SACW. An inshore–offshore gradient was clear. The Canonical Correspondence Analysis suggested that coastal species – dominated by Liriope tetraphylla , actinula larvae and Muggiaea kochi – were mostly related to food availability and a vertically mixed environment inshore, and their abundance and extent were reduced during intrusion periods. In contrast, species with offshore affinities tended to increase their abundance and distribution during intrusion periods, and were mostly related to the presence of thermal stratification and a deep chlorophyll maximum layer. Most of these offshore species, such as Aglaura hemistoma , Rhopalonema velatum and many calycophorans, are associated with the warm upper layer. However, high concentrations of large (>20 mm in diameter) Solmaris corona were observed exclusively in cold waters, suggesting this medusa is a SACW indicator. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Oceanography is the property of Instituto Oceanografico da Universidade de Sao Paulo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

Tintinnids were identified in 256 samples from 60 stations in the North Sea investigated by a German multidisciplinary [Zirkulation und Schadstoffumsatz in der Nordsee (ZISCH)] program, during late spring of 1986. Tbe distribution of the most frequently occurring species. Parafavella elegans, P.denticulatn, Acanthostomella norvegica, Helicostomella subulata, Prychocylis unurla, Stenosemella nivalis, Tintinnopsis beroidea and T.parvula, was described. Some species showed a similar horizontal distribution. However, a vertical division was evidenced after analyzing species abundances against temperature, salinity, depth and σ-t. Cellular carbon content for each species and the total weight of carbon per sample were estimated. The total weight of carbon in tintinnids in the North Sea was calculated to be 113 608 tons, with a depth-integrated average of 197.58 mg C m−2; the bulk of this biomass (44%) was concentrated in the euphotic zone (0–20 m). [ABSTRACT FROM PUBLISHER]

The spatial distribution of copepod populations on the eastern continental shelf off Rio de Janeiro State, Brazil, was analysed in relation to the hydrographic regime in December-January (summer 1991/92) and July (winter 1992). Advection of cold and nutrient-rich South Atlantic Central Water (SACW) onto the shelf was a prevailing circulation mechanism in both seasonal cruises. The SACW occupied a larger proportion of bottom layers in summer as compared to winter, but only in the latter a well-defined upwelling event was recorded off Cape Frio. Two calanoid copepods were representative of shelf areas influenced bySACW intrusions: Calanoides carinatus, which occurred mainly during summer and Ctenocalanus vanus, recorded at high densities in both periods. Paracalanus quasimodo was the dominant copepod at inner- and mid-shelf stations both in summer and winter, followed by Temora spp. and Oncaea spp. These coastal species peaked at the upwelling site. A highly diversified and comparatively less abundant copepod assemblage, dominated by Clausocalanus furcatus and Oithona plumifera, was recorded in outer-shelf stations occupied by the oligotrophic Tropical Waters of the Brazil Current. We conclude that regional and seasonal contrasts in copepod species composition and abundance are controlled to a great extent by the advection and upwelling of the SACW onto the shelf. [ABSTRACT FROM AUTHOR]