The Partitioning of Carbon Biomass among the Pico- and Nano-plankton Community in the South Brazilian Bight during a Strong Summer Intrusion of South Atlantic Central Water

Abstract

To investigate how pico-and nano-plankton respond to oceanographic conditions in the Southwestern Atlantic Ocean, we assessed the influence of a summer intrusion of the South Atlantic Central Water (SACW) on the spatial and vertical dynamics of planktonic abundance and carbon biomass across environmental gradients. Seawater samples were collected from six depths within the euphotic zone at nine oceanographic stations in a transect on the Brazilian continental shelf in January 2013. The abundance of pico-and nano-plankton populations was determined by flow cytometry, and carbon biomass was calculated based on conversion factors from the literature. The autotrophic Synechococcus spp., picoeukaryotes, and nanoeukaryotes were more abundant in the surface layers of the innermost stations influenced by Coastal Water (maximum of 1.19 × 10 5 , 1.5 × 10 4 , and 8.61 × 10 3 cell·mL −1 , respectively), whereas Prochlorococcus spp. dominated (max. of 6.57 × 10 4 cell·mL −1 ) at the outermost stations influenced by Tropical Water and in the uplifting layers of the SACW around a depth of 100 m. Numerically, heterotrophic bacterial populations were predominant, with maximum concentrations (2.11 × 10 6 cell·mL −1 ) recorded in the surface layers of the inner and mid shelves in Coastal Water and the upper limits of the SACW. Nutrient-rich (high silicate and phosphate) and relatively less saline waters enhanced the picoeukaryotic biomass, while Synechococcus and heterotrophic bacteria were linked to higher temperatures, lower salinities, and higher inputs of ammonia and dissolved organic carbon. The relative importance of each group to carbon biomass partitioning under upwelling conditions is led by heterotrophic bacteria, followed by picoeukaryotes, Synechococcus and Prochlorococcus, and when the SACW is not as influential, the relative contribution of each phytoplanktonic group is more evenly distributed. In addition to habitat preferences, the physical structure of oligotrophic waters has a large impact on the vertical and spatial distribution patterns of picoplankton, reflecting the strong effect of the SACW intrusion.

Hydrography-Driven Variability of Optically Active Constituents of Water in the South Brazilian Bight: Biogeochemical Implications

“…The SBB is a hydrographically dynamic environment with strong seasonality and the presence of mesoscale features as meanders and eddies (Castro, 2014). It sustains a diverse planktonic community encompassing a wide range of autoand heterotrophic organisms from picophytoplankton to microzooplankton (Brandini, 1990;Brandini et al, 2014;Detoni et al, 2016;Bergo et al, 2017;Gonçalves-Araujo et al, 2018a). During the Austral summer expedition CARBOM-3, we analyzed the hydrographic conditions and the OACs along a cross-shelf transect in the poorly sampled SBB.…”

“…Hydrographic results for the CARBOM-3 expedition have already been reported in a recent study focused on the planktonic component (Bergo et al, 2017) and, therefore, will be briefly presented in this paper. Here we present results based on hydrography profiles from the surface layer comprised between 0 and 500 m. Three water masses were observed, considering the thermohaline indices for the study region: CW, TW and SACW ( Figure 2).…”

“…Beneath the surface layer, the entire water column is characterized by the presence of the South Atlantic Central Water (SACW) (Castro, 2014). High phytoplankton biomass with great contribution of micro-planktonic organisms is observed in the inner-shelf, fueled by the nutrient input from continental runoff, whereas small organisms dominate within the oligotrophic TW (Brandini et al, 2007;Bergo et al, 2017;Gonçalves-Araujo et al, 2018a). During summer time, with the intense action of NE winds coupled to the Ekman transport, the shelf waters are pushed offshore, allowing for the intrusion of nutrient-rich SACW within the entire continental shelf (Castro, 2014).…”

“…During summer time, with the intense action of NE winds coupled to the Ekman transport, the shelf waters are pushed offshore, allowing for the intrusion of nutrient-rich SACW within the entire continental shelf (Castro, 2014). This promotes, in the euphotic zone, the fertilization of the shallower waters, triggers the phytoplankton development and, thus, stimulates the primary production within the region (Brandini et al, 2014;Bergo et al, 2017).…”

Prokaryotic picoplankton distribution within the oxygen minimum zone of the central Mexican Pacific across environmental gradients

“…Prochlorococcus and Synechococcus abundances were comparable with those found in other tropical areas, ranging from 0.17 to 30.37 X 10 4 cells mL -1 , and 0.9 to 30.97 X 10 4 cells mL -1 , respectively (Table 1). These numbers are similar to those found in another tropical zone, near the study area to the north (Gulf of California) (Hernández-Becerril and Pastén-Miranda, 2015) and to the south (Costa Rica Dome) (Gutiérrez-Rodríguez et al, 2014), and about exactly the same values (maxima densities ranging from 4.53 X 10 4 to 3.2 X 10 5 cells mL -1 for Prochlorococcus, and 1.19 X 10 5 to 3.8 X 10 5 cells mL -1 for Synechococcus) in tropical and subtropical zones such as East China (Guo et al, 2014), the Gulf of Mexico (Linacre et al, 2015), the Gulf of California (Hernández-Becerril & Pastén-Miranda, 2015), and the South Atlantic (Brazil) (Gérikas-Ribeiro et al, 2016;Bergo et al, 2017).…”