Temporal Evolution and Spatial Transformation of Subsurface South Atlantic Overturning Waters between 30°S and 24°S

Mixing, upwelling and subduction in the South Atlantic allow it to play pivotal interconnected roles in the global overturning circulation, carbon cycle and climate system. At the largest scales, the characteristics of these water masses have been subject to detectable climate-related changes, but the complexity of the system leaves fundamental questions concerning the magnitude and the spatial versus temporal variation of properties, overturn, pathways and mixing in this unique basin unanswered. Our investigation combines an examination of decadal-scale property changes observed at 30°S and 24°S with Lagrangian particle simulations to improve our understanding of how both properties and property changes evolve with the subtropical South Atlantic. At 24°S, four repeat occupations of the A095 line cover the 1958-2018 timeframe. At 30°S, three repeat occupations cover the period 1992-2011 (a fourth repeat is expected in 2021). The 1/12° data assimilating HYCOM model provides the velocity fields for the particle tracking experiments and the recent analysis of 2003/2011 30°S transport field based on the hydrographic and L-ADCP measurements is used for validation.