Convective chimneys in the greenland sea: a review of recent observations

The nature and role of chimneys as a mode of open-ocean winter convection in the Greenland Sea are reviewed, beginning with a brief summary of Greenland Sea circulation and of observations of convection and of the resulting water structure. Then recent observations of long-lived chimneys in the Greenland Sea are described, setting them within the context of earlier observations and models. The longest-lived chimney yet seen in the world ocean was discovered in March 2001 at about 75°N 0°W, and subsequent observations have shown that it has survived for a further 26 months, having been remapped in summer 2001, winter 2002, summer 2002, and April-May 2003. The chimney has an anticyclonically rotating core with a uniform rotation rate of f/2 to a diameter of 9 km; it passes through an annual cycle in which it is uniform in properties from the surface to 2500 m in winter, while being capped by lower-density water in summer (primarily a 50-m-thick near-surface layer of low salinity and a 500-m-thick layer of higher salinity). The most recent cruise also discovered a second chimney some 70 km NW of the first, and accomplished a tightly gridded survey of 15,000 km 2 of the gyre centre, effectively excluding the possibility of further chimneys. The conclusion is that the 75°/0°chimney is not a unique feature, but that Greenland Sea chimneys are rare and are probably rarer than in 1997, when at least four rotating features were discovered by a float survey. This has important implications for ideas about chimney formation, for deepwater renewal in the Greenland Sea, and for the role of Greenland Sea convection in the North Atlantic circulation.