Evolution of Physical and Biological Patterns Along the Tropical and South Atlantic Western Boundary: A Satellite Perspective

Abstract

We investigate the spatial and temporal patterns of satellite‐derived sea surface temperature, salinity and chlorophyll‐a concentration along the eastern South American coast. Two decade‐long time series (2002–2019; except for the salinity) allowed us to investigate changes from seasonal to interannual time scales on an array that stretches from the south (42°S) to the north (10°N) of the continent and from isobaths ranging from −50 to −1000 m away from the coast. The novelty of our approach is to assess comparatively the magnitude, variability, and spectrum of these variables following the same isobaths and using the same methodology. This allowed us to examine the influence of large scale ocean circulation patterns entangled with the local forcing systems such as river discharge and coastal currents, and to quantify to what extent these patterns are spatially and temporally consistent. The seasonal cycle of the temperature explains more variance than that of salinity and chlorophyll on average. Comparatively, salinity has a weak seasonal signal, except near major rivers. Significant long‐term trends were observed in specific regions in the salinity time series. Our study revealed distinct interannual changes at 2‐ and 4‐year period in the whole array with the largest spectral peaks near the La Plata and the Amazon Rivers. Within this period band, thermal signals propagate northward along the whole array. Statistical correlations between satellite‐derived variables and several climate indices suggest remote forcing.

Phytoplankton Responses to Mesoscale and Submesoscale Processes in a Tropical Meander

“…Pacheco et al. (2022) suggested that the change in the orientation of the Brazilian coastline at Cape Frio modifies the spectral composition of oceanographic properties, which show a cascade of energy toward higher frequencies, that is, mesoscale activity and eddy formation. Uchoa et al.…”

“…We will use "eddy" and "meander" interchangeably since a meander is just an eddy still connected to a geophysical jet, in this case, the Brazil Current, rather than an isolated ring. Pacheco et al (2022) suggested that the change in the orientation of the Brazilian coastline at Cape Frio modifies the spectral composition of oceanographic properties, which show a cascade of energy toward higher frequencies, that is, mesoscale activity and eddy formation. Uchoa et al (2023) also revealed high mesoscale activity downstream of Cape Frio and Cape São Tomé, suggesting the frequent formation of mesoscale eddies in the Brazil Current.…”

Testing macroecological hypotheses in sandy beach populations: the wedge clam Donax hanleyanus in South America

“…Between 20 and 40°S, the western South Atlantic shelf is influenced by seasonally reversing winds, strong western boundary currents interacting with outer shelf waters, and a significant discharge of freshwater from the RdlP and, to a lesser extent, the LdP (see Palma et al 2008, Matano et al 2010. The seasonal amplitude of SST is highest (> 7°C) in the outer RdlP (Rivas 2010), exceeds 6°C in the neighboring shelf, and decreases northward, reaching about 1.5°C near Cape Frío (23°S; Pacheco et al 2022). In contrast, sea surface salinity and chl a present the highest seasonal amplitudes (exceeding 3 and 8 mg m −3 , respectively) over the southern Brazil continental shelf, south of Cape Santa Marta Grande , Pacheco et al 2022.…”

“…The seasonal amplitude of SST is highest (> 7°C) in the outer RdlP (Rivas 2010), exceeds 6°C in the neighboring shelf, and decreases northward, reaching about 1.5°C near Cape Frío (23°S; Pacheco et al 2022). In contrast, sea surface salinity and chl a present the highest seasonal amplitudes (exceeding 3 and 8 mg m −3 , respectively) over the southern Brazil continental shelf, south of Cape Santa Marta Grande , Pacheco et al 2022. While salinity changes >10 may be observed along the coast in the outer RdlP estuary, particularly along the coast of Uruguay (Guerrero et al 1997).…”