Export of shelf waters from the western South Atlantic shelf

The western South Atlantic shelf is characterized by three distinct water masses of subantarctic, subtropical and continental runoff sources. These water masses and associated biota converge near 33ºS, creating a complex thermohaline structure which has a strong impact on the shelf ecosystem. Satellite and in-situ observations combined with numerical simulations suggest intense export events of shelf waters in this region. We use hydrographic data and direct velocity observations collected in October 2013 to describe the distribution of shelf waters as they are fluxed offshore. A high-resolution section across the Brazil/Malvinas Confluence displays cores of relatively cold (~12ºC), low-salinity (S<33.8) shelf waters embedded within the intense flow along the Confluence axis. Subantarctic Shelf Water, derived from the Patagonia continental shelf, occupies two well-defined subsurface cores observed along the 26 kg/m³ neutral density surface. The flow within these cores (~ 0.35 Sv) accounts for 100% of the cold variety shelf waters flowing southward over the shelf. An additional core of a warmer (15ºC) and lighter variety of low salinity waters is observed at the surface within the Confluence core. These waters include mixtures from the Rio de la Plata discharge and subtropical waters. Satellite salinity images detect the less dense variety of low salinity shelf waters beyond 1000 km from the shelf break. Export events of shelf waters to the deep ocean are likely to have a profound impact on the abundance of planktonic species.