Abyssal currents during the formation and passage of a warm-core ring in the East Australian Current

Abstract

Measurements of currents and temperatures at abyssal depths in the Tasman Sea are compared with near-surface observations of the East Australian Current (EAC) System to ascertain the extent to which the deep and near-surface flows are related. The deep measurements come from three instruments which were moored at different locations on the Tasman Abyssal Plain from early December 1983 to late March 1984. They included an Anderaa current meter, recording velocity and temperature, a second temperature sensor, and an instrument which recorded fluctuations in temperature and the vertical component of the ambient electric field (from which zonal velocity is inferred). During this period a meander of the East Australian Current moved southwards and pinched off to form a warm-core ring. Both the current meter and the vertical electric field instrument recorded current surges to the east when the surface front first arrived at their positions. The maximum speed recorded by the current meter was 35 cm s-1 (when the flow was southward). Strong abyssal currents (over 10 cm s-1) were usually in the same approximate direction as the surface current at the EAC front and associated with the movement of the front before the ring pinched off. The abyssal temperature fluctuations increased in magnitude with the increase in water velocity as the front moved past, but the temperature records do not indicate that any thermal effect of the eddy extended to the sea floor. Show more