Upwelling along the western barrier reef of New Caledonia

Abstract

Temperature decreases of up to 5°C at an automatic station at ~10 m depth at the outer reef of western New Caledonia signalled the occurrence of upwelling. The decreases are related to south-easterly wind events and they can take up to 5 days to develop. Successive wind events can depress the temperature for as much as 1 month. An upwelling shows in thermal satellite imagery as a band of cold water ~10 km wide and as long as several hundred kilometres just outside the reef. The cold water frequently spreads out to sea. The upwellings are more common in summer (October to March) than in winter. During lengthy periods of low wind speeds, the waters outside the reef appear to be overrun by warm water from farther north. The frequent occurrence of the warm water layer in the north may partly explain why upwellings are more common along the southern half of the reef. The entire lagoon cools in winter; most of the lagoon warms in summer, except at the southern end where the waters are cool, perhaps from tidal mixing.