Abyssal upwelling in the Indian Ocean: Radiocarbon diagnostics

The GEOSECS Indian Ocean radiocarbon and carbonate chemistry data set are u sed to estimate the mean upwelling transport of bottom water in the Indian Ocean north of 30S. The study uses an "adjusted radiocarbon concentration" which is corrected for the effects of addition of particulate radiocarbon t o the deep ocean. The cross-basin uniformity in the vertical gradients of " adjusted radiocarbon" allows quantification of vertical transfer processes using horizontally averaged concentration and fluxes. The estimated total u pwelling flux, north of 30S, is 8.2 +/- 1.5 x 10(6) m(3) s(-1). The mean up welling velocity and the vertical diffusivity, in the 3000-4500 m depth ran ge, are estimated as 3 x 10(6) m s(-1) and 2.5 x 10(-4) m(2) s(-1), respect ively. The results also suggest faster upwelling in the western Indian Ocea n.