Observations of Open-Ocean Deep Convection in the Labrador Sea from Subsurface Floats*

Abstract

Abstract The occurrence and extent of deep convection in the Labrador Sea in winters 1996/97 and 1997/98 is investigated from measurements of over 200 neutrally buoyant subsurface Profiling Autonomous Lagrangian Circulation Explorer (PALACE) and Sounding Oceanographic Lagrangian Observer (SOLO) floats. In addition to providing drift velocity data and vertical profiles of temperature and salinity, 55 floats are equipped with vertical current meters (VCMs). Time series of vertical velocity (derived from measured pressure and vertical flow past the float) and temperature are obtained from the VCM floats. Mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997, but no deeper than 1000 m in 1998. Deep mixed layers were concentrated in the western basin, although a number of deep mixed layers were observed southwest of Cape Farewell and also north of 60°N. The highest variance in vertical velocity and the lowest mean temperatures were found in t...