Delimitation of domains in the external Río de la Plata estuary, involving phytoplanktonic and hydrographic variables

Abstract

Autumn and spring hydrological (temperature and salinity) and biological (chlorophyll, phaeopigments and phytoplankton species) variables were analysed. Phytoplankton biomass, expressed as chlorophyll a reach a maximum of 6.1 µg L-1in autumn and 22.8 µg L-1 during spring. Maxima were found in the frontal zone and marine adjacent area. Four domains were identified through multivariate analysis: Riverine, Estuarine, Frontal and Oceanic; mainly due to salinity and depth in autumn and due to salinity and chlorophyll in spring. The Riverine and Oceanic domains (West and East boundaries) matched in location in both seasons, while in spring an additional domain was discerned in the Canal Oriental (Channel domain). Salinity and chlorophyll concentration increased from the Riverine to the Frontal domain, being positively correlated for salinities 14, indicating that chlorophyll concentration was modulated mainly by the oceanic influence that improved light availability. While salinity maintains an increasing trend toward the Oceanic domain, phytoplankton biomass decreases. Though in this zone the chlorophyll concentration must be regulated by a combination of light availability and grazing, further investigation is needed.

The Imprint of the Geological Inheritance and Present Dynamics on Uruguayan Inner Shelf Sediments (South-Western Atlantic)

“…The strong vertical stratification observed is related to the influence of colder and diluted continental water from the RdlP on the surface, and warmer and saltier oceanic shelf waters at the bottom product of the still fall presence shelf waters advected by the BC during the austral warm season. This thermal inversion is typical of this region at de beginning of the cold austral season when halinestratification determines that the surface freshwater layer loses heat rapidly (Martínez and Ortega, 2015;Piola et al, 2018). However, this stratification may be favoured by the palaeovalley geomorphology.…”

Shelf Water Export at the Brazil-Malvinas Confluence Evidenced From Combined in situ and Satellite Observations

“…Surface chlorophyll-a was mostly positively correlated with the nutrient distribution, decreasing toward the deep ocean. Maximum values were measured near the coast immediately offshore from the turbidity front (10 < S A < 25 g kg −1 ), although they did not peak at station 1 in the RdlP waters, where nutrient values were maximum, due to the effect on light attenuation in muddy waters (e.g., Carreto et al, 2003;Kruk et al, 2015;Martínez and Ortega, 2015). High surface fluorescence and chlorophyll-a were also observed in the southernmost area of the Uruguayan EEZ, at stations 7 and 9 over the outer shelf and slope, over the Ewing Terrace and Rio de la Plata canyon under the influence of the MC retroflection at about 37 • S 54 • W. These stations showed the coldest surface waters and high concentration of nutrients (Figures 4D-F), and also the highest integrated fluorescence in the CTD profile (3.15 mg m −3 ) in the upper 50 m (Figure 4D), as these stations were occupied at the end of a chlorophyll bloom that took place 10-25 April according to satellite observations (Supplementary Video 1).…”

Weather, Hydrological and Oceanographic Conditions of the Northern Coast of the Río de la Plata Estuary during ENSO 2009–2010

“…In [28], phytoplankton Chl a usually displays a concentration peak by the end of summer and the beginning of autumn, showing a unimodal trend in the seasonal pattern. There are few studies of the RdlP regarding the seasonal patterns in total chlorophyll concentration; nevertheless, recent studies have demonstrated that salinity, depth, and light availability, which attain maximum values in spring, are the main variables controlling the biomass and composition of the phytoplankton community in the RdlP [43]. …”