In Situ Sampling in the Benthic Boundary Layer

Abstract

Abstract The objective of most in situ benthic boundary layer (BBL) measurements is to quantify the transport of mass, either across or along the sediment-water interface, while also gaining knowledge of the roles played by specific processes in determining transfer rates. Studies can be separated into sediment transport investigations that focus on suspended sediment dynamics, and solute transport studies that focus on the workings of early diagenesis. A third and related category of study concerns the vertical structure of velocity in the boundary layer. Inasmuch as critical length and time scales, mechanisms of transport, and biological components vary greatly among different benthic environments, instrument packages and deployment vehicles of varying designs and degrees of complexity have been developed to make bottom boundary layer measurements. This chapter aims to (1) describe the general principles of several of the most common methodologies that are applied in situ to measure BBL mass transport and examples of instruments that implement these methodologies, (2) discuss a few specific limitations of these techniques and circumstances when these limits matter and when they do not, and (3) raise some unanswered questions concerning shallow and deep-sea BBLs that are revealed by new data sets collected with emerging in situ approaches.