Articles | Volume 12, issue 3
Ocean Sci., 12, 771–780, 2016
Ocean Sci., 12, 771–780, 2016

Research article 02 Jun 2016

Research article | 02 Jun 2016

The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

Erwin Lambert, Dewi Le Bars, and Wilhelmus P. M. de Ruijter Erwin Lambert et al.
  • Institute of Marine and Atmospheric Sciences Utrecht, Utrecht University, Utrecht, the Netherlands

Abstract. East of Madagascar, the shallow “South Indian Ocean Counter Current (SICC)” flows from west to east across the Indian Ocean against the direction of the wind-driven circulation. The SICC impinges on west Australia and enhances the sea level slope, strengthening the alongshore coastal jet: the Leeuwin Current (LC), which flows poleward along Australia. An observed transport maximum of the LC around 22° S can likely be attributed to this impingement of the SICC. The LC is often described as a regional coastal current that is forced by an offshore meridional density gradient or sea surface slope. However, little is known about the controls of these open-ocean gradients. The regional circulation system is embedded in the subtropical “super gyre” that connects the Indo-Pacific via the Tasman Gateway and the Indonesian passages. The Indonesian Throughflow (ITF) circulates through the Indian Ocean back into the Pacific south of Australia. This return pathway appears to be partly trapped in the upper layer north of an outcrop line. It is redirected along this outcrop line and joins the eastward flow of the SICC. To study the connection of the basin-scale and the inter-ocean-scale dynamics, we apply both an ocean general circulation model and a conceptual two-layer model. Shutdown of the ITF in the models leads to a large decrease in Leeuwin Current transport. Most of the SICC was found to then reconnect to the internal gyre circulation in the Indian Ocean. ITF, SICC and LC thus appear to be dynamically connected.

Short summary
In the upper layers of the South Indian Ocean, three anomalous currents are observed: The South Indian Ocean Countercurrent, the Leeuwin Current and the Indonesian Throughflow. Using two models of different complexity, we show how these three currents can be dynamically connected, unravelling the large-scale connectivity. Further, we produce a conceptual theory of how this current system follows an idealized pattern of wind stress and buoyancy forcing.