A Lagrangian numerical investigation of the origins and fates of
the Salinity Maximum Water in the Atlantic
Bruno BLANKE
Michel ARHAN
Laboratoire de Physique des Océans
CNRS-IFREMER-UBO, Brest, France
Alban LAZAR
Laboratoire d’Océanographie Dynamique et de Climatologie
CNRS-IRD-UPMC, Paris, France
Gwenaëlle PREVOST
Laboratoire de Physique des Océans
CNRS-IFREMER-UBO, Brest, France
In press for Journal of Geophysical Research
Abstract
The origins and fates of the Atlantic Salinity Maximum Water (SMW) formed
through excess evaporation in the subtropics of both hemispheres are studied
using monthly mean outputs of a numerical simulation of the world ocean climatological
circulation. After defining formation domains from the surface salinity field
and the vertical stratification, a Lagrangian technique is used to estimate
the formation rates and main pathways in each hemisphere, and the role of
this water in the framework of the warm water return flow of the meridional
overturning cell.
Formation rates around 9 Sv and 11 Sv are found in the Southern and Northern
Hemispheres, respectively. While the export of the southern SMW from its
formation area is realized by the western boundary currents, that of the
northern SMW mainly results from interior subduction. Equatorward of the
formation regions, a fraction of each SMW variety is entrained in the Shallow
Thermohaline Cells that connect the tropical and equatorial regions. Poleward
of them, both varieties are seen to feed the regions of Subtropical Mode
Water formation around 35º of latitude in both hemispheres. The bulk
of the transport associated with each variety eventually turns northward:
This amounts to ~ 6 Sv of southern SMW gathered in the North Brazil Undercurrent,
and ~ 10 Sv of northern SMW found in the Gulf Stream at 35°N, of which
8 Sv have gone through the Caribbean Sea. Of the 13.4 Sv northward transport
of the meridional overturning cell estimated by the model at 47°N, more
than 50% (6.9 Sv) is found to have transited through at least one of the
SMW regions. This gives an indication of the likely important role of SMW
formation in the observed North Atlantic salinity increase.