Meetings: Documents

Salinification of the Atlantic Subtropical Central Water under the Expanding Tropics
[14-Dec-2018] Yu, L.
Presented at the 2018 AGU Fall Meeting
The subtropical underwater (STUW) salinity maximum is a component of the Central Waters formed by subduction of the subtropical sea-surface salinity maximum (SSS-max). In recent decades, the Atlantic Central Water is found to have become saltier, thicker, and deeper, meanwhile the SSS-max water has become saltier on the edge and fresher in the center. The pattern change at the surface seems to be different from the "dry-gets-drier-and-wet-gets-wetter" (DDWW) scenario that predicts the global water cycle intensifies under the global warming and the subtropical SSS-max should also intensify. In this study, we present observation evidence showing that the subtropical net evaporation zone has widened and weakened since 1979, and the pattern change in satellite-derived evaporation-minus-precipitation (E-P) flux is consistent with the SSS-max pattern change. We propose that the poleward movement of the subsiding branch of the Hadley Circulation shifted and expanded the ventilation zone, which acted as a main driver of the observed change of the Atlantic Central Water. The poleward and westward expansion of the ventilation zone increased the subduction rate and hence, the volume of the newly formed Central Water. We found that the ventilation zone (marked by the location of the 36.7 isohaline) in the North Atlantic has shifted northward by 1.2 ± 0.36° latitude since 1979. Change in the South Atlantic Central Water is also observed, albeit to a lesser extent. The study showed that the Atlantic surface and subsurface salinity maximum waters bear the imprint of the changing water cycle associated with the poleward expansion of the Hadley Cell. The role of ocean circulation in support of the relationship between SSS and E-P co-variability is also discussed.