Annual cycle of the Brazil‐Malvinas confluence region in the National Center for Atmospheric Research Climate System Model

Abstract

Abstract. The objective of this study is to compare the mean and seasonal variability of the circulation in the southwest Atlantic with observations. The results used in the comparison are fi'om the last 200 years of a 300 year control integration of the Climate System Model (CSM). The area of study includes the confluence region between the subtropical and subpolar waters represented by the Brazil and Malvinas Currents. The seasonal variation of transport and its relationship to changes in the wind stress forcing and in the sea surface temperature are examined and compared to available oceanographic observations. This study shows that a coarse resolution climate model, such as the CSM, can successfully reproduce major characteristics of the Brazil-Malvinas confluence seasonality, although the mesoscale features involving recirculation and meander dynamics are not resolved. The CSM transport values in the region of 38øS are consistent with hydrographically derived values. The transport of the CSM Brazil Current is higher during austral summer and smaller during austral winter. Conversely, the Malvinas Current transport is weaker during austral summer and stronger during austral winter. This is also consistent with observations. The CSM seasonal cycle in transport associated with both the Brazil and Malvinas Currents and its meridional displacement is closely linked to the seasonal variations in the local wind stress curl. However, the displacement is much smaller in the model than in observations. The CSM results show that the latitudinal displacement of the 24øC and 17øC at the South American coast beween austral summer and winter is 20 ø and 12 ø, respectively. This is very similar to the displacement seen in observations.

Foraging range and habitat associations of non‑breeding Tristan albatrosses: overlap with fisheries and implications for conservation

“…6), that result in eddies and vertical mixing that enhance local production. This area has consistently high productivity in summer and low productivity in winter (Wainer et al 2000), supporting the conclusion that its importance to seabirds is likely to vary seasonally. It is a key foraging area for other marine predators in summer, including black-browed albatrosses Thalassarche melanophris (Wakefield et al 2011) and white-chinned petrels Procellaria aequinoctialis (Phillips et al 2006) from South Georgia, southern elephant seals Mirounga leonina from Argentina (Campagna et al 2006), and migrant Cory's Calonectris diomedea (Dias et al 2011), sooty Puffinus griseus (Hedd et al 2012) and Manx P. puffinus (Guilford et al 2009) shearwaters.…”

“…6), that result in eddies and vertical mixing that enhance local production. This area has consistently high productivity in summer and low productivity in winter (Wainer et al 2000), supporting the conclusion that its importance to seabirds is likely to vary seasonally. It is a key foraging area for other marine predators in summer, including black-browed albatrosses Thalassarche melanophris (Wakefield et al 2011) and white-chinned petrels Despite the high productivity in summer, this area experiences relatively low pelagic longline fishing effort in this season, limiting the risk to Tristan albatrosses.…”

“…The areas they utilise off both South America and southern Africa are associated with eddies and mixing zones (Figs. 6 & 7), which are typically highly productive (Wainer et al 2000) There were clear seasonal pat- terns to their movements, with all tracked birds concentrating in the SW Atlantic during austral summer, but travelling eastward and dispersing more widely during austral winter, mostly to the SE Atlantic and SW Indian Ocean off South Africa. However, 2 birds moved to waters off northern Namibia and 2 to southern Australia.…”

The sea-level highstand correlated to marine isotope stage (MIS) 7 in the coastal plain of the state of Rio Grande do Sul, Brazil

“…The southwards influence of the BC and associated coastal water masses is controlled mostly by two seasonal processes: one is the shift of the intertropical convergence zone (ITCZ) to the south of the equator during austral summer (Emílsson 1960, Johns et al 1998, the other is the intensification of the ACC (and consequently northwards displacement of the MC) during austral winter (Matano et al 1993, Wainer et al 2000.…”

Frontal system changes in the Southeastern Atlantic Ocean

“…The latter can be regarded as the northernmost branch of the Antarctic Circumpolar Current (ACC). This is known as the Brazil-Malvinas Confluence, a region of high seasonal and interannual variability due to the strong interaction between the two current systems (Wainer et al, 2000;Piola and Matano, 2001;Goni and Wainer, 2001;Lumpkin and Garzoli, 2011). As the confluent currents flow eastward, they separate into two currents: the South Atlantic Current and the northern branch of the ACC, associated with the Subantarctic Front (SAF).…”