On the Export of Subantarctic Shelf Waters from the Argentine Shelf Towards the Deep Ocean and its Impacts on the Fishery

VINCENT COMBES; MARCELO ACHA; BÁRBARA C. FRANCO; M. SARACENO; ELBIO D. PALMA

Portland

Congreso; 2018 Ocean Sciences Meeting; 2018

American Geophysical Union

It has been suggested that the Subtropical Shelf Front (STSF) could be a preferential site for the detrainment of Argentine shelf waters and related biological species onto the deep ocean. The offshore detrainment of commercially important planktonic larvae (squid, anchovy) might affect the development of fishing activities in Argentina, Uruguay and Southern Brazil. Therefore, a better understanding about the dynamics of the STSF isrequired to manage resources in this heavily exploited area, with potential effects on biodiversity in general. The STSF comprises a transition region between Subtropical Shelf Waters (STSW) from the north and Sub-Antarctic Shelf Waters (SASW) from the south. The front is located near the 50 m isobath at 32°S over the inner shelf off Rio Grande(Brazil) and it extends southwards towards the shelf break (200 m isobath) close to 36°S (Argentina). In this study, we characterize for the first time the 3-D structure of this subsurface thermohaline front and the main routes of offshore export of SASW from the Patagonian shelf during austral summer and winter by using numerical hydrodynamical model results and Lagrangian tracking simulations using neutrally buoyant floats. Our results show that the transport of SASW towards the open ocean is ~ 1 Sv (1 Sv = 10 m .s ) during summer and ~ 0.8 Sv during winter. SASW are exported offshore mainly near the Brazil?Malvinas Confluence (BMC) region while the STSF appears to act as an important retention mechanism for the plankton over the middle shelf during summer.