Submersible‐operated porewater sampler for permeable sediments

Abstract

A sampler was developed to collect porewater from permeable (sandy) sediments during manned‐submersible operations. The sampler uses vacuum (or atmospheric‐pressure) reservoirs to draw porewater into a sediment probe and then into inline sample loops. The sampler is relatively inexpensive, easy to construct, and self‐contained, operating without an external power supply. The sample‐loop/reservoir system (without the probe) can also be used to sample wells or other apparatus installed in or on the seafloor, and would be comparatively easy to automate. In addition, the sampler should be adaptable to SCUBA diving operations (including rebreather or mixed‐gas diving). The sampler was used with Pisces submersibles to determine dissolved chemical profiles in sandy sediments inside and outside the extensive deepwater meadows of macroalgae offshore of the main Hawaiian Islands. The sampler collected porewater (to 25 cm sediment depth) from sites at 40‐200 m water depth. Porewater inorganic nutrient concentrations were comparable with those in nearshore permeable sediments, but showed distinct differences between a vegetated and an unvegetated site.