On the effect of the missing Indonesian throughflow in the Fine Resolution Antarctic Model (FRAM)

On the effect of the missing Indonesian throughflow in the Fine Resolution Antarctic Model (FRAM)

South of Tasmania, the Fine Resolution Antarctic Model (FRAM) shows a narrow band of westward flow in the surface layer. We argue that this is caused by the closure of the Indonesian passage in FRAM. This is supported by numerical experiments carried out by Hirst and Godfrey (1993) and by recent radiocarbon observations in the Great Australian Bight (Ribbe et al., 1996). The FRAM surface temperature and salinity distribution exhibits distinct anomalies in the southeast Indian Ocean, in good agreement with anomalies observed in the Hirst and Godfrey (1993) model. Indonesian Throughflow water advects heat into the Indian Ocean; its absence in FRAM results in a lack of thermal energy to warm the Indian Ocean in the model. The surface salinity anomaly is most likely caused by an over-estimated Ekman transport. The weakened heat and salinity transport in FRAM restricts surface convection in the mid-latitude region to approximately 350 m.

The effect of the Indonesian Throughflow closure in FRAM is even more dramatic for the circulation around Australia and Tasmania. Hirst and Godfrey's (1993) results suggest that in the case of an open Indonesian passage, the flow in the surface layer is eastward, ie from the Indian to the Pacific Ocean. Preliminary analysis of radiocarbon observations from the Great Australian Bight supports this, showing a better correlation with Indian Ocean data than Pacific Ocean data. FRAM shows westward flow, inconsistent with these observations.

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