The seasonal cycle of the South Indian Ocean subtropical gyre circulation as revealed by Argo and satellite data
The seasonal cycle in volume transport of the South Indian Ocean subtropical gyre is characterized for the first time. Only 3 complete hydrographic crossings of the gyre have been conducted over a 22 year period, from which a strengthening of the gyre is implied. However, some of this strengthening could result from aliasing of seasonal variability. We use data from Argo, satellite altimetry, and an Agulhas Current transport proxy at 34 S to quantify the seasonal variability of the upper 2000 m volume transport. A semi-annual cycle is revealed, with peak-to-peak amplitude of 6.4 +/- 5.1 Sv and dominated by anomalies in quadrature near the eastern and western boundaries. There is no evidence of seasonal aliasing between hydrographic crossings. The seasonal cycle of the gyre corresponds well with that predicted by mass balance of the Agulhas Current and the Indonesian Throughflow.