THE FLOW OF ANTARCTIC BOTTOM WATER TO THE SOUTHWEST INDIAN-OCEAN ESTIMATED USING CFCS

Observations of chlorofluorocarbons (CFCs), carbon tetrachloride, temp erature, and salinity from five sections following the outflow path of Antarctic Bottom Water (AABW) into the southwest Indian Ocean are rep orted. The transient tracer data clearly show the plume of recently ve ntilated water whose hydrographic properties are progressively altered by mixing with the overlying waters. We use the CFC measurements to e stimate the mean speeds (or transit times) and mixing rates (or diluti ons) of the abyssal flow at each section using simple kinematic circul ation models. Given our assumptions, the CFC ventilation age equals th e transit time. The results suggest a transit time of 23 +/- 5 years ( outflow speed of 1.2 +/- 0.3 cm s(-1)) to the Crozet-Kerguelen Gap wit h a dilution of 8-15 from the surface waters of the Weddell Sea. The e stimated horizontal diffusivity is 30-70 m(2) s(-1), and the vertical diffusivity is 3-7 x 10(-4) m(2) s(-1). Combined with the estimate of R. R. Dickson (unpublished data, 1998) for the AABW transport at this point, we conclude that a volume flux of 0.8-1.6 Sv (10(6) m(3) s(-1)) is leaving the continental shelves of the Weddell Sea to eventually e nter the abyssal Indian Ocean past Crozet Island.