7 research outputs found
Abyssal upwelling in the Indian Ocean: Radiocarbon diagnostics
The GEOSECS Indian Ocean radiocarbon and carbonate chemistry data set are used 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 to 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 upwelling flux, north of 30S, is 8.2 ± 1.5 à 106 m3 s-1. The mean upwelling velocity and the vertical diffusivity, in the 3000-4500 m depth range, are estimated as 3 à 106 m s-1 and 2.5 à 10-4 m2 s-1, respectively. The results also suggest faster upwelling in the western Indian Ocean
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On the connection between the Mediterranean outflow and the Azores Current
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Abyssal upwelling in the Indian Ocean: Radiocarbon diagnostics
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Effects of lowâfrequency current variability on nearâinertial submesoscale vortices
From September 30 to October 14, 1993, and from May 18 to June 13, 1994, ocean surface currents along the inshore boundary of the Florida Current were measured using a landâbased ocean surface current radar (OSCR) deployed along the Florida Keys. A dualâstation OSCR mapped the current fields at 20âmin intervals with a horizontal resolution of 1.2 km over a 30Ă44 km domain using the highâfrequency (HF, 25.4 MHz) mode. An upward looking, narrowband acoustic Doppler current profiler (ADCP) was moored in 150 m of water seaward of the shelf break concurrently sampling the threeâdimensional current vector between 15 and 130 m at 30âmin intervals. Regression analyses between surface and subsurface currents at 15 m depth from the ADCP indicated biases of 3â12 cm sâ1 and slopes of O(0.8â1). Rootâmeanâsquare differences were about 18 cm sâ1 because of a 15âmâdepth separation between the two measurements, and bulk current shears were O(10â3 sâ1) in the Florida Current where maximum velocities exceeded 150 cm sâ1 between 40 and 70 m. Surface tidal currents were 2â10 cm sâ1 in the diurnal and semidiurnal bands and revealed fineâscale variability in the tidal ellipses due to topographical variations. Differences in the tidal current amplitudes between the surface and 15 m ranged from 1 to 3 cm sâ1 in these constituents and explained more of the current variance with depth. During the second experiment a submesoscale surface feature was detected along the shelf break and progressed eastward at a rate of about 30 cm sâ1. This feature was embedded in the nearâinertial wave band where the local inertial period was â29 hours that may have been forced by an abrupt change in the wind direction. This transient feature was trapped and advected along the inshore edge of the Florida Current where the anticyclonic vorticity of the subinertial flow shifted the frequency of the nearinertial motions by a few percent of f. These energetic nearâinertial currents of 15â20 cm sâ1 had horizontal and vertical wavelengths of 40 km and 50â100 m, respectively