Cross-Frontal Motion in 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


South of Australia near 51S 146E the R/V Melville surveyed a meander of the Subantarctic Front (SAF) in 3/95. Meanders may commonly generate cross-frontal exchange along sloping density surfaces, with downwelling (upwelling) entering a cyclonic trough (anticyclonic crest). AVHRR images tracked the path of the SAF. The meander wavelength and crest-to-trough displacement were each about 300km, producing a steep "S-shaped" path. In the survey-region, 140 X 120 km, the flow entered a crest. Four transects of 6--7 CTD profiles each to 1200m depth, spaced 20--35km apart, mapped the velocity, salinity, and temperature structure. ADCP velocity profiles extended to 250--350m depth along the ship track. Within the front of 60km width the current core speed reached 0.85m/s at depths from 50--200m. Vertical motions, w, were diagnosed for intermediate- depths via (a) the density equation and (b) the omega equation in Q-vector form, both methods revealing upwelling of O(0.05cm/s) in a mesoscale pattern. Additionally, salinity anomalies were traced moving cross-front, generally supporting these findings. Although each diagnosis of these data is not individually above doubt, all three diagnoses based upon different dynamics indicated generally consistent upwelling fluxes. The vertical flux crossing the 700m horizon in a single meander feature, with diameter = O(100km) and central w = O(0.05cm/s), is more than 1 Sv (10^6 m^3/s). This flux crosses the vertical plane of the front. Although much of the cross-frontal flux in meanders may be oscillatory, if in each steep meander a fraction of the water is expelled to either side, the effect along the circumglobal extent of the SAF could account for much of the meridional flux of intermediate waters.