Observed low frequency variability of the Brazil Current front

Abstract

[1] The Brazil Current is a weak western boundary current, the southwest component of the South Atlantic subtropical gyre, which is the main conduit of upper ocean waters in the region. The objective of this work is to report on observed low frequency variability of the Brazil Current front using satellite-derived sea height anomaly and sea surface temperature observations during the 1993-2008 period. The variability of the front is studied in terms of the separation of the Brazil Current front from the continental shelf break. During the study period, estimates of this parameter vary 6 degrees in latitude, and the mean monthly estimates exhibit a shift to the south of approximately 1.5 degrees. Statistically significant changes are not observed in the geostrophic transport of the Brazil and Malvinas currents, suggesting that the low-frequency changes of the Brazil Current front are governed by different mechanisms than the seasonal variability of these surface currents. Surface drifter trajectories and simulations using synthetic drifters are consistent with the observed shift to the south of the Brazil Current front. Trends of eddy kinetic energy, sea height anomaly, sea surface temperature and wind stress curl are also in agreement with the variability reported here. Wavelet transform analysis revealed interesting changes in the periodicity of the latitude of separation of the Brazil Current front from the continental shelf break, with periods ranging from semiannual to biannual. Longer records, together with comprehensive numerical experiments, will ultimately be needed to determine the origin of these changes.

Variabilidade da Corrente do Brasil na região da Confluência Brasil-Malvinas através de simulações numéricas

“…Assim, a latitude em que essa isoterma cruza a isóbata de 1000 m corresponde a latitude de separação da CB da costa. A isóbata de 1000 m foi escolhida por marcar o limite da plataforma continental na região (Goni et al, 2011). A isoterma escolhida pode não corresponder extamente ao núcleo da CB, porém esta técnica segue as propriedades de uma determinada massa deágua na superfície.…”

“…Além disso, a latitude média obtida através dessa isoterma corrobora trabalhos recentes sobre a posição da confluência e separação da CB da costa (Goni et al, 2011;Lumpkin e Garzoli, 2011 Os três métodos utilizados para a marcação da separação da CB da costa são coerentes entre si e em relação aos dados de satélite. O método da isoterma de 18…”

“…A variabilidade encontrada para a separação da CB está em boa concordância com estudos recentes de Goni et al (2011) e Lumpkin e Garzoli (2011) no sinal das tendências encontradas em diferentes períodos.…”

Changes in the South Atlantic Subtropical Gyre circulation from the 20th into the 21st century

“…The SAC partially feeds the eastern boundary Benguela Current (BeC), recirculating within the subtropical gyre. The BeC then heads northwestward turning into the southern branch of the South Equatorial Current (sSEC), which is the one that forms the northern edge of the subtropical gyre (Stramma, 1991;Goni et al, 2011). The broad, westward flowing sSEC carries these subtropical waters towards the Brazilian shelf region, where it bifurcates around 15 o S, closing the subtropical gyre by flowing into the southward BC (Reid, 1994;Rodrigues et al, 2007;.…”

“…Moreover, in conjunction with a systematic change in winds over both hemispheres, it is found an accelerated surface ocean warming along the path of global subtropical western boundary currents (WBCs) in association with a synchronous poleward shift of their mid-latitude extensions and/or an intensification in their strength Confluence (BMC), which is documented to be drifting southwards (Goni et al, 2011;Lumpkin and Garzoli, 2011;Combes and Matano, 2014;Pontes et al, 2016).…”