An instrument system for profiling suspended sediment, fluid, and flow conditions in shallow marine environments

Abstract

A new instrument system (sediment profiler) is described which is designed for making suspended sediment transport observations in shallow marine waters. The instrument system is capable of obtaining simultaneous profiles through the water column of suspended sediment concentration ( Cz), fluid properties (conductivity, temperature, depth) and flow conditions ( Uz, Vz), and of collecting water/suspended sediment samples at selected depths. Additionally it can be used in a calibration mode to intercompare multiple optical backscatter sensors (up to eight sensors). The sediment profiler is a relatively small aluminum tripod (91 cm high) that can be lowered through the water column in strong flows (∼2m s −1), measure suspended sediment concentrations between 5 mg l −1 and∼10g l −1, and can be lowered directly to the seabed (sensor elevations∼20cm). It contains internal battery power and on board digital logging capabilities and has no electrical connection with the vessel during operation. Since July 1989 the sediment profiler has been used extensively on a study of the Amazon shelf transport system (AmasSeds). Numerous profiles have been collected from hydrographic surveys off the northeast coast of Brazil to investigate spatial distributions of suspended sediment and to monitor net particle flux over 25 h anchor stations. The instrument system is rugged and reliable and has improved our ability to document the relationships between fluid properties, flow conditions, and suspended sediment characteristics in a complex shelf environment.