Flows in the Tasman Front south of Norfolk Island

Abstract

The Tasman Front is a narrow band of eastward flowing subtropical water crossing the Tasman Sea from Australia to North Cape, New Zealand. It is the link between the two subtropical western boundary currents of the South Pacific, the East Australian Current (EAC) off eastern Australia, and the East Auckland Current (EAUC) off northeastern New Zealand. Here we report the first direct measurements of flow in the Tasman Front from a moored array deployed across gaps in the submarine ridges south of Norfolk Island and hydrographic and ADCP measurements during the deployment and recovery voyages. The mean flow through the array over July 2003 to August 2004 was found to be eastward only in the upper 800 m with a transport of ∼6 Sv. Below 800 m a weak westward mean flow (∼1.5 Sv) was measured, associated with Antarctic Intermediate Water (AAIW). Using sea surface height to account for additional transport south of the moored array results in a total mean eastward transport between Norfolk Island and North Cape, New Zealand of ∼8 Sv, varying between −4 and 18 Sv. The measurements show that the Tasman Front is much shallower than either the EAC or EAUC, both of which extend below 2000 m depth, has less transport than either the EAC or EAUC and has instances of flow reversal. Thus, the Tasman Front is a weaker connection between the EAC and EAUC than the paradigm of a contiguous South Pacific western boundary current system would suggest.