CTD observations on the North Brazil shelf during a multidisciplinary Amazon Shelf Sediment Study, AMASSEDS, May-June 1990

Abstract

Hydrographic (CTD) and acoustic Doppler current profiler (ADCP) observations were made on the North Brazil shelf adjacent to the mouth of the Amazon River during R/V Iselin cruise I9004 May 23-June 13, 1990 as part of A Multidisciplinary Amazon Shelf SEDiment Study (AMASSEDS). These observations were obtained during a small-scale survey on Leg 1 in support of mooring deployment operations, during a large-scale survey on Leg 3 in support of geological and geochemical sampling, during a frontal zone survey on Leg 4 consisting of 12 and 24 hourly CTD casts at anchored stations, and during a bottom tripod recovery on Leg 5. The maximum sampling depth at each station was within two meters of the bottom. The primary objectives of the AMASSEDS hydrographic measurement program were (a) to observe and characterize the temperature, salinity, density, oxygen, fluorescence and light transmission fields and their spatial variabilty on the North Brazilian shelf directly influenced by the Amazon River discharge, (b) to resolve the seaward extend and vertical structure of the surface plume of low salinity Amazon River water during different stages of river discharge, (c) to describe the spatial structure of the turbidity and associate suspended sediment distributions across the shelf, (d) to characterize the properties of the Amazon shelf water beneath the surface plume and their seasonal variabilty, and (e) to describe the landward penetration of the North Brazil Current with respect to water properties and shelf currents. This report represents a summary in graphic and tabular form of the hydrographic observations made during the third AMASSEDS cruise (I9004) on the R/V Iselin.