Title: A study of Indian Ocean Subtropical Mode Water: subduction rate and water characteristics

Journal: Acta Oceanologica Sinica, 35(1): 38-5

Authors: MA J., J. Lan* and N. Zhang

Abstract:The annual subduction rate in the South Indian Ocean was calculated by analyzing Simple Ocean Data Assimilation (SODA) outputs in the period of 1950–2008. The subduction rate census for potential density classes showed a peak corresponding to Indian Ocean subtropical mode water (IOSTMW) in the southwestern part of the South Indian Ocean subtropical gyre. The deeper mixed layer depth, the sharper mixed-layer fronts and the associated relatively faster circulation in the present climatology resulted in a larger lateral induction, which primarily dominants the IOSTMW subduction rate, while with only minor contribution from vertical pumping.Without loss of generality, through careful analysis of the water characteristics in the layer of minimum vertical temperature gradient (LMVTG), the authors suggest that the IOSTMW was identified as a thermostad, with a lateral minimum of low potential vorticity(PV, less than 200×10^–12 m^–1·s^–1) and a low dT/dz(less than 1.5°C/(100m)). The IOSTMW within the South Indian Ocean subtropical gyre distributed in the region approximately from25° to 50° E and from 30° to 39°S. Additionally, the average characteristics (temperature, salinity, potential density) of the mode water were estimated about (16.38 ± 0.29)°C, (35.46 ± 0.04), (26.02 ± 0.04) σθ over the past 60 years.