Dissolved inorganic nutrients and chlorophyll on the narrow continental shelf of Eastern Brazil

Abstract

The eastern Brazilian continental shelf is narrow and subject to the influence of a western boundary current system, presenting lower biological productivity than other regions. In this study, the distribution of water masses, dissolved inorganic nutrients, chlorophyll-a and total suspended solids (TSS) on the inner shelf (< 35 m depth), between Itacaré and Canavieiras, eastern Brazil, is presented. Sampling surveys were carried out in March and August 2006 and March 2007. Tropical water (TW) prevailed during March 2006 and August 2007 with the lower salinity waters (< 36) found in most samples taken in March 2007, reflecting the influence of continental outflow and rain in coastal waters. Low concentrations of dissolved inorganic nutrients and Chl-a found were typical of TW and results suggested that the inner shelf waters were depleted in dissolved inorganic nitrogen in August 2006 and March 2007, and in phosphate in March 2006, potentially affecting phytoplankton growth. Stratification of the water column was observed due to differences in dissolved nutrient concentrations, chlorophyll-a and TSS when comparing surface and bottom samples, possibly the result of a colder water intrusion and mixing on the bottom shelf and a deep chlorophyll maximum and/or sediment resuspension effect. Despite this stratification, oceanographic processes such as lateral mixing driven by the Brazil Current as well as a northward alongshore drift driven by winds and tides transporting Coastal Water can lead to an enhanced mixing of these waters promoting some heterogeneity in this oligotrophic environment.

SPATIAL AND TEMPORALVARIATION OF DISSOLVED INORGANIC NUTRIENTS, AND CHLOROPHYLL-α IN a TROPICAL ESTUARY IN NORTHEASTERN BRAZIL: DYNAMICS OF NUTRIENT REMOVAL

“…The coastal zone around the estuary of Rio Cachoeira is oligotrophic (Eça et al, 2014), with low concentrations of chlorophyll-a (< 1 µg/ L), phosphate (< 0.2 µM), dissolved silica (< 6 µM), nitrate and ammoniacal nitrogen (< 1 µM). Those authors reported a DIN:DIP ratio below 16:1 in two surveys, but up to 60:1 in March 2006.…”

Bio-optical properties of the Brazilian Abrolhos Bank’s shallow coral-reef waters

“…The presence of shallow banks and seamounts influences the BC flow pattern creating vortices, meanders, and upwelling in the shelf break and seamount flanks (Knoppers et al, 1999a;Ekau, 1999). The occurrence of vortices on the edge of the Abrolhos Bank, as well as the northward alongshore drift driven by winds and the tides transporting Coastal Water, can lead to enhanced mixing of these waters and contribute to local nutrient enrichment, influencing the plankton community structure and dynamics (Ekau, 1999;Eça et al, 2014).…”

“Shark is the man!”: ethnoknowledge of Brazil’s South Bahia fishermen regarding shark behaviors

“…So, most of the informers said that sharks “appear” in the summer because it is the time of year when the sea water is “warmer” (73.5%) and “cleaner” (78.1%). There is a deficiency of scientific oceanographic data for the study area and, only recently, Eça et al [ 89 ] published the first information on this subject for the coastal region. However, in this study, the authors did not include the temporal dimension of oceanographic variables throughout the year, which makes it impossible a deeper discussion of this seasonal distribution that fishermen perceive to sharks.Fishermen also stated that the females of some shark species “approach the shore” or “river mouths” in the summer to reproduce.…”