Geostrophic flow? Who cares?
In subtropics, see little precipitation & much evaporation, so surface waters have high salinity
Geostrophic flow causes surface waters to follow paths about centers of gyres
- Do not refresh surface waters by mixing low salinity water from continents
Strong pycnocline in subtropics results from well-developed thermocline (despite strong halocline)
- Do not refresh surface waters by upwelling lower salinity water from deep zone
Sea water in center of gyres is isolated from rest of ocean water - C14, tritium, Pb, GEOSECS, etc.