Seasonal and interannual variability of the mixed layer properties and steric height at station KERFIX, southwest of Kerguelen

Monthly hydrographic data collected from May 1991 to December 1994 at stati on KERFIX (50 degrees 40'S, 68 degrees 25'E) were analysed to describe and understand the seasonal and interannual variability of the mixed layer prop erties and steric height for the first 500-m water column. The monthly mean mixed layer depth (determined from the density difference criterion of 0.0 2 sigma(theta)) varies from 60 m in January to 185 m in August, with corres ponding temperature and salinity varying within a Limited annual range of 2 .3 degrees C (around 4.1 degrees C in March and 1.8 degrees C in September) and 0.06 (around 33.825 in June and 33.886 in October). A noticeable inter annual change in mixed layer properties has been detected: warm and low-sal inity anomalies in 1992 and cold and high-salinity anomalies in 1994; the m ixed layer depth was significantly deeper in more recent years. A possible linkage of these low-frequency variations to the Pacific Fl Nino Southern O scillation (ENSO) is suspected. The 3 years' (1992-1994) mean monthly steri c height varies from +2.2 cm in March to -2.3 cm in September, with the app earance of a secondary maximum in July and a secondary minimum in June. Con sistent with the mixed layer properties, the steric sea level of the site r eveals an important interannual change, with a positive anomaly (+1.3 cm) i n 1992 and a negative anomaly (-1.3 cm) in 1994. Superimposed on this low-f requency drift are quasi-semiannual (5-6 months) variations, due to the hal ocline-layer salinity anomalies having the same periodicity. The commonly o bserved mesoscale eddy activity in the Kerguelen region seems to be the maj or cause. Finally, the monthly mixed layer salinity of the site is determin ed largely by the competing effects of evaporation-precipitation and horizo ntal advection. On an annual basis, however, the entrainment of saltier dee p water mostly compensates the eventual freshening of the mixed layer which might otherwise be caused by the excess of precipitation over evaporation in this region.