Abstract
The Abrolhos Bank is part of the so-called Eastern Brazilian Shelf and is an area of high ecological and economic importance. The bank supports the largest and richest coral reefs in the South Atlantic and the largest rhodolith bed in the world. The spatial and seasonal variation of phytoplankton concentration, however, and the dynamic processes controlling that variability have remained poorly known. The present study investigates the seasonal and spatial distributions of chlorophyll-a (Chl-a) and water conditions by analyzing nine years (2003–2011) of level-3 Moderate-resolution Imaging Spectroradiometer (MODIS) derived Chl-a, National Centers for Environmental Prediction (NCEP)/ETA model-derived winds, NCEP model-derived heat fluxes, thermohaline and velocity results from the Hybrid Circulation Ocean Model (HYCOM) 1/12o assimilated simulation. The results show that low/high concentrations occurred in austral spring-summer (wet season)/autumn-winter (dry season), with the highest values observed in the northern portion of the Abrolhos Bank. The typical meteorological and oceanographic conditions during austral summer favor the development of strong stratification. These conditions are 1) N-NE winds that favor an upwelling-type Ekman circulation; 2) coupling between the open ocean and the continental shelf through the western boundary current, which promotes cooler subsurface water to rise onto the shelf break; and 3) positive net heat flux. In contrast, the S-SE winds during autumn are in the opposite direction of the predominant current system over the Abrolhos Bank, thus reducing their speed and inducing an inverse shear. The warmer ocean and a somewhat cool and dry atmosphere promote the evaporative cooling of the surface layer. The above processes drive mixed layer cooling and deepening that reaches its maximum in winter. The blooming of phytoplankton in the Abrolhos Bank waters appears to be regulated by changes in the mixed layer depth, with Chl-a levels that start to increase during autumn and reach their peak in June-July.
Highlights
The Royal-Charlotte Bank (RCB) and the Abrolhos Bank (AB) are localized between 17°20’18°10’S and 38°35’-39°20’W (Fig. 1) and comprise an extension of the Eastern Brazilian Continental Shelf (EBS) [1]
The values ranged from 0.1 mg m-3 to 1.5 mg m-3, with lower values (< 0.3 mg m-3) at points PT2, PT4 and PT5 and relatively high concentrations (> 0.4 mg m-3) at the station located in the Abrolhos reef area (PT1)
The stratification was enhanced by typical northerly and northeasterly upwelling-favorable winds, the negative relative vorticity induced in the onshore portion of the Brazil Current (BC) and the interaction of eddies and meanders with the shelf break that resulted in raising colder subsurface water onto the shelf
Summary
The Royal-Charlotte Bank (RCB) and the Abrolhos Bank (AB) are localized between 17°20’18°10’S and 38°35’-39°20’W (Fig. 1) and comprise an extension of the Eastern Brazilian Continental Shelf (EBS) [1]. This region is an exception in an otherwise regular and narrow shelf. The Abrolhos Shelf harbors the largest continuous rhodolith bed in the world [3], which thrives in the outer and deeper parts of the Bank; the main reef-building corals, in contrast, are primarily restricted to the shallow areas (30–70 m depths). Mean Chl-a values of 1.22 mg m-3 (at the surface) and 0.86 mg m-3 (at the bottom) were reported by [9] for the inner reefs of Coroa doi:10.1371/journal.pone.0117082.g001
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
