Tasman leakage in a fine-resolution ocean model

Tasman leakage, the westward flow of thermocline waters south of Australia from the Pacific to the Indian Ocean, is one of the lesser-studied of the inter-ocean exchanges. Here, some of the properties of the Tasman leakage are inferred from Lagrangian particles integrated using the three-dimensional velocity fields of the 1/10 degree resolution OFES model. The mean Tasman leakage in this model is 4.2 Sv, with a standard deviation of 4.3 Sv. The heat flux associated with this leakage lies in the range 0.08 - 0.18 PW. There is large variability in the Tasman leakage on both sub-weekly and inter-annual scales, but no trend over the 1983-1997 period. Despite the large weekly variability, with peaks of more than 20 Sv, it appears that less than half of the Tasman leakage is carried within eddies.

Tasman leakage using Lagrangian particles. The particles are released in south of Tasmania in the fine-resolution OFES model and then advected both forward and backward in time. The influence of mesoscale eddies is clearly visible.

Figure 2: Overview of the Tasman leakage in the OFES simulation. (a) The transport through each 0.5° × 0.5° grid box for all Tasman leakage particles. (b) The transport by Tasman leakage particles on the release section at 146.4°E. (c) Time series of transport as the Tasman leakage particles cross the 146.4°E meridian. In (c) the thin lines denote transport on three-day resolution, and thick lines denote one-year running-mean transport. Due to ramp-up effects (it takes the particles typically 3 and 10 years to reach the Pacific and Indian Oceans, respectively), the time series before 1983 and after 1997 should not be regarded and is thus shown in grey. Between 1983 and 1996, the Tasman leakage varies on both sub-weekly and inter-annual time scales, with peaks of more than 20 Sv. The mean during this period is 4.2 Sv, with a standard deviation of 4.3 Sv.