Indian Ocean Subtropical Mode Water: its water characteristics and spatial distribution

Abstract

We have improved a basic description (water characteristics and spatial distribution) of the Indian Ocean Subtropical Mode Water (IOSTMW) using an isopycnally averaged three dimensional hydrographic dataset. Two mode waters and corresponding wintertime mixed layer depth maxima were observed north of the subtropical front (STF) in the South Indian Ocean: IOSTMW (within 25.8–26.2 ) in the region of 28–45 E and another subtropical mode water in the subtropical gyre (within 26.4–26.7 ) in the 60–80 E longitudinal band. Through careful examination of the spatial distribution and water characteristics of a core in the layer of minimum vertical temperature gradient (LMVTG), we identified that a mass of LMVTG corresponds to IOSTMW. The average water characteristics of the IOSTMW during approximately 1960–2004 were 16.54±0.49 C, 35.51±0.04 psu and 26.0±0.1 . The IOSTMW distribution area was estimated to be 25–50 E, 27–38 S. The formation region and approximate water characteristics of the second subtropical mode water were also estimated. Its probable formation region was 37–42 S, 60–80 E and north of the STF, with approximate water characteristics of 12.84±0.57 C, 35.17±0.11 psu and 26.57±0.04