A statistic of water mass intrusions in the south Indian Ocean between 100° E and 110° E

Abstract

The concept of water type richness wtr and inversion count inv is introduced and applied to high-resolution Argo float data in a meridional strip in the southern Indian Ocean as a test to evaluate the use of the concept for a global analysis of water mass intrusions in the upper 2 km of the ocean. It is found that wtr is a suitable parameter to identify regions of high-intrusion activity in the Antarctic Intermediate Water and below but is too much determined by the meridional sea surface temperature (SST) gradient in the upper 500 m to be of much use in that depth range. Inv, on the other hand, is derived from vertical gradients, which avoids the influence of the SST gradient, and is therefore a good indicator of inversion activity throughout the water column. The analysis finds large numbers of inversions in the upper 1 km of the ocean north of 22° S in the frontal region between the Australasian Mediterranean Water and the Indian Central Water, somewhat lower inversion frequency in the subtropical front south of 40° S, and very low inversion numbers in the region between. This region, however, displays numerous inversions in the depth range 600–1950 m, which contains only few inversions in the south and in the north.