The Structure of a Meander in the Sub-Antarctic Front

D. Randolph Watts, Univ. of Rhode Island, Kingston, Rhode Island
Che Sun, Univ. of Rhode Island, Kingston, Rhode Island
Douglas S. Luther, Univ. of Hawaii at Manoa, Honolulu, Hawaii
James G. Richman, Oregon State Univ., Corvallis, Oregon
Alan D. Chave, Woods Hole Oceanographic Institution, Woods Hole, Mass.
Stephen R. Rintoul, CSIRO Marine Laboratories, Hobart, Australia

Abstract:

Aboard R/V Melville in March 1995, to deploy moorings across the Sub-Antarctic Front (SAF) south of Tasmania, we conducted a CTD and SADCP (shipboard acoustic doppler current profiler) survey of a steep "S-shaped" meander. Because mooring operations had proceeded smoothly and we had not lost as many weather-days as anticipated, 3-4 days were available. Our aim was to determine the combined velocity, salinity, temperature, and path structure of this meander in the SAF. Meanders potentially generate cross-frontal exchange and subduction of waters along density surfaces.

Guided by a concurrent satellite IR image, we selected a region, centered near 51S 146E, exiting a steep meander trough and entering a steep crest. Four transects of 6--7 stations each, spaced 20--35 km apart, mapped a region 140 X 120 km. The CTDs were restricted to 1200 m depth to cover the region quickly. SADCP velocity profiles between stations and on station respectively extended to 250 m and 350 m depth.

The front width was about 70 km. The meander wavelength was about 300 km, spanning about 300 km from cyclonic trough to anticyclonic crest, with axes tilted NNE/ SSW. The current core speed was 0.85 m/s at depths from 48--200 m. The radius of curvature within both crest and trough was 60--120 km. The meander steepened and rotated slowly, but the portion which we surveyed was sufficiently stationary that we approximate the tendency terms associated with propagation and growth to be negligible. A few degrees of veering (and concomitant upwelling and warm advection) was observable from depth 48--88 m to 160--200 m. Quantification and implications of cross-frontal exchange will be discussed.