A DEEP-TOWED ADCP-CTD INSTRUMENT PACKAGE DEVELOPED FOR ABYSSAL OVERFLOW MEASUREMENTS IN THE NORTHEASTERN CARIBBEAN SEA

A deep-towed instrument package has been developed to study the veloci ty and tracer signature of abyssal overflows in the northeastern Carib bean. Primary package components include a conductivity-temperature-de pth (CTD) instrument and an acoustic Doppler current profiler (ADCP), allowing for simultaneous measurement of density, watermass tracers, a nd absolute velocity. A description of package construction and operat ion is supplemented by examples from a set of 17 deployments during tw o oceanographic cruises in January 1991 and March 1992. A new method f or determining the three-dimensional position of the instrument packag e is described, bared on the ability of the ADCP to acquire reference velocities corresponding to its motion over the seafloor. Factors affe cting ADCP data quality are discussed, particularly those stemming fro m the low-scatterer environment at abyssal depths and the impact of la rge vertical accelerations due to surface wave-induced ship heave.