Séminaire
The itinerary of dense waters from the surface high latitudes to the ocean abyss and back to the air-sea interface determines in large part the ocean’s ability to store carbon and heat on time scales exceeding a century. In this talk, using water mass transformation scenarios and maps of the radiocarbon content of seawater, I will show that the depth distribution of seafloor north of 30ºS compels dense southern-origin waters to flow north below 4 km depth and to return south deeper than 2.5 km. In the absence of a northern surface source of deep water, as observed in the modern Pacific and Indian oceans, a shadow zone of relatively weak mean meridional flow consequently forms at mid-depths (about 1-2.5 km). The results highlight a fundamental relationship between basin and circulation geometries, helping to constrain the past and present structure of the abyssal circulation.
julien.brajard@upmc.fr