The multi-year development of long-lived convective chimneys in the Greenland Sea

The first convective chimney in the Greenland Sea to have its temperature and salinity structure fully mapped was discovered in March 2001 near 75degreesN 0degreesW [Wadhams et al., 2002]. Later cruises have shown that this remarkable feature has survived for a further 26 months, being remapped in summer 2001, winter 2002, summer 2002 and most recently in April-May 2003, making it the longest-lived chimney yet seen in the world ocean. The chimney has an anticyclonically rotating core and experiences an annual cycle in which it is uniform in properties from the surface to 2500 m in winter, but is capped by lower-density water in summer. The latest cruise also discovered a second chimney, 70 km NW of the first, during a thorough survey of 15,000 km(2) of the gyre centre which left the existence of further chimneys unlikely. We conclude that the 75degrees/0degrees chimney is not unique, but that Greenland Sea chimneys are rare and are probably rarer than in 1997, when several such features were discovered by a float survey. This has implications for deep water renewal and for the role of Greenland Sea convection in the North Atlantic circulation.