Core Sampler for Soft Bottom Sediments with Lower Closing Mechanism

Abstract

Summnry: A novel sediment core sampler is represented. It is suitable for liquid sediments a n d for nudisturbed sediment cores with a large core diameter from shallow and deep waters.For laboratory experiments on exchange processes between sediment and water, undisturbed sediment cores in which both microbial stratification and chemical stratification remain undisturbed are needed. A not too small core diameter offers the following advantages : a sufficiently large water volume which renders possible a n extensive water analysis and enough space for measuring apparatus (electrodes) in the experimental container (tube).Usually core samplers have an upper closing mechanism, so that the front end of the tube can entirely free penetrate into the sediment (AMBUHL; BLOMQVIST; ORZECHOWgm). With liquid sediment (Gyttja) and with great core diameters a lower closing mechanism appeared to be more reliable in operation. The novel lower closing mechanism described in this communication guarantees an easy penetration of the sampler and yields undisturbed cores. I t is particularly well-suited for sediments with a relatively high water content.The backing material of the sampler is a glass tube with a diameter of 80 mm (NW 80) from VEB Technisches Glas Ilmenau, GDR. So the lower closing mechanism was mounted on a detachable steel cap. The hinged cover is connected with two slewable angular arms, and a slight rotation of the arms is sufficient to draw the cover against the opening of the steel cap by two stretched tension springs (Fig. I).While lowering, the closing mechanism of the sampler is held open by a safety string connected with the suspension string. While lifting, another string turns the arms and the cover closes the sampling tube. The same string is used to draw the filled sampler to the surface.The particular advantage of the lower closing mechanism is its safety and the undisturbed and easy penetration into the sediment,. A disadvantage is the observation that freshly deposited material whirls up in the tube. The cause of t>his phenomenon is not yet cleared.For the sampling of several cores (e.g. for laboratory experiments) a plate is pushed into the slit of the steel cap, the closing mechanism is opened and the core is slowly pushed into the glass tube by means of a piston. Then the suspension and the steel cap are detached, the piston rod is separated from its top and the glass tube with the sediment core and the piston top is closed by a sealing plate. After that, the next, glass tube is prepared. The sampler is also suitable for vertical investigations of sediment cores.