Controls of subsurface temperature variability in a western boundary upwelling system

Abstract

[1] The mechanisms controlling subsurface temperature variability on the outer shelf in a western boundary upwelling system are quantified using observations from a mooring deployed off Cabo Frio, Brazil. Results from a multiple linear regression analysis reveal that, in addition to low-frequency variations associated with the seasonal evolution of temperature, the dominant mechanisms controlling temperature variability are wind stress curldriven upwelling, cross-isobath transport, the proximity of the Brazil Current to the shelf break, and perhaps changes in the strength of tidal mixing associated with the springneap cycle. The influence of the proximity of the Brazil Current decreases strongly with depth, being restricted to the top 80 m. Regression coefficients indicate that the relative contributions from the different forcings are roughly similar and that no single process has a dominant role explaining temperature variability near the shelf break. These suggest that successful modeling efforts in the region must adequately represent each of those processes.Citation: Belem, A. L., R. M. Castelao, and A. L. Albuquerque (2013), Controls of subsurface temperature variability in a western boundary upwelling system, Geophys. Res. Lett., 40,

Particle Fluxes and Bulk Geochemical Characterization of the Cabo Frio Upwelling System in Southeastern Brazil: Sediment Trap Experiments between Spring 2010 and Summer 2012

“…This finding can basically be explained by differences in the sampling frequency between physical and geochemical data but also by the synergistic effect of multiple physical forcing factors. Similar results were found by Belem et al (2013) working only with physical variables. Under these conditions, statistical significance was useful as a tool to highlight potential causality between physical forcing and geochemical parameters.…”

“…Observed temperatures higher than 18°C may have been representative of tropical water (TW) and/ or coastal water (CW) or perhaps a mix of both. Isolated occurrences of warmer temperatures (T ≥ 24°C) were observed during autumn (March to June), and these temperatures likely represented the dominance of the internal front of the BC in the area (Belem et al 2013). …”

“…In addition, the balance between the BC poleward flow carrying warm and nutrient-poor water on the shelf edge and the cold and nutrient-rich water in subsurface layers is synergistically controlled by other mechanisms, including variations in the topographically induced flow around the cape (Rodrigues and Lorenzetti 2001); the instabilities of the Brazil Current, with its meanders sometimes invading the shelf area (Campos et al 2000); and the enhanced vertical transport driven by wind stress curl over the midshelf (Castelao andBarth 2006, Castelao 2012). Thus, the region off the coast of Cabo Frio represents a special oceanographic gradient from the classical coastal Ekman upwelling to a typical oligotrophic western boundary current (Belem et al 2013) and is considered a hot spot of productivity on the southeastern Brazilian shelf.…”

“…POC fluxes were also positively correlated with C/N ratios (r=0.34) and δ The variability of the thermal structure on the Cabo Frio shelf edge is not dominated by a single factor. Instead, it is related to the action of multiple factors, such as the influence of the BC front, cross-isobath transport and wind-stress-curl-driven upwelling (Belem et al 2013). Therefore, a number of different mechanisms combine to control the magnitude and timing of particulate sources and fluxes on the shelf edge.…”

“…Despite its location on a passive margin under the control of the nutrient-poor western boundary current, the sea surface temperature and chlorophyll concentrations in the CFUS area reveal a dynamic, complex oceanographic system controlled by interactions among instabilities of the southward trajectory of the oligotrophic Brazil Current (BC) , Belem et al 2013, wind-driven coastal Ekman transport (Valentin 1984, Carbonel 2003, Castelao and Barth 2006, mid-shelf eddy-induced cold-water intrusion of South Atlantic Central Water (SACW) to the photic zone (Brandini 1990, Campos et al 2000, Calado et al 2010) and mid-shelf thermal fronts (Castro et al 2008), leading to a heterogeneous pattern of primary productivity (Franchito et al 1998, Lopes et al 2006, recycling and transport of particulate material on the shelf. Understanding these synergic interactions among the physical and biogeochemical features in the CFUS is crucial to identifying particle sources and determining the extent of recycling or reworking as well as predicting whether the material will be deposited on the sea floor or exported to the deep ocean.…”