The Ellrott grab: A small, lightweight sediment sampler for collecting undisturbed sandy sediments

Abstract

Sampling sandy surface sediments is an important first step in understanding biogeochemical processes in these dynamic environments. However, sampling such sediments poses several challenges, especially when undisturbed samples with porewater are required. Several grab samplers are commercially available, but they are either prone to sample loss, too heavy or bulky for use in small vessels, or those with spring-loaded mechanisms present safety issues. Here, we present the Ellrott grab, a lightweight sediment sampler designed for collecting undisturbed surface sediments including porewater and overlying bottom seawater. The sampler consists of a frame and a rotating bowl that can collect 370 cm² of surface sediments up to 10 cm deep (2.5 liters total volume). The instrument is 40 × 60 cm in size, has a basic weight of 10 kg, with up to 20 kg additional weights for stability in sandy sediments. Two persons can operate the grab and it can be used on small boats with a crane and winch system or a hand winch. The grab is now in routine use in the Wadden Sea and in Isfjorden, Svalbard. The samples obtained from the grab were suitable for various geochemical and microbial analyses. Using microelectrodes, we found that in situ oxygen profiles were similar to ex situ profiles in cores subsampled from the grab, confirming that the grab causes minimal disturbance to the sample. Although the grab was designed for collecting sandy sediments, it could also be applied to silty sediments, allowing straightforward and efficient sampling of various sediment types.