Abyssal circulation in the Indian Ocean from a 1/12∘1/12∘ resolution global hindcast

Abyssal pathways and volume transports in the Indian Ocean obtained from a 1/12∘1/12∘ global data assimilative hindcast for the years 2004–2006 are presented. The known features of bottom water circulation such as boundary currents and inter-basin exchanges are well represented in the hindcast solution. Further, the hindcast solution reveals a basin-wide, anti-cyclonic deep circulation pattern with the main inflow located in the east, in the Perth Basin, and outflow in the west along the African continent and Madagascar. Inter-basin westward transport at 10∘S10∘S across the Ninetyeast Ridge and along the Mascarene Plateau connect the inflow and outflow locations. The model develops a net bottom water inflow of 10±8Sv (mean±standard deviationmean±standard deviation) across 32∘S32∘S, below approximately 3500 m of which 4±7Sv are returned south across the same latitude in the deep layers between 2000 and 3500 m. Significant variability on intra-seasonal, semi-annual and annual time scales is present in the abyssal flow fields. The vertical mixing algorithm, based on resolved vertical shear, suggests enhanced diapycnal upwelling in the vicinity of the Central Indian Ridge.