All material that exchanges between the sediment and seawater must pass through the benthic boundary layer – a decimeter- to meter-thick water layer above all sediments. We have little information about the temporal variability of physical, chemical and biological conditions in this layer, because it is difficult to sample with conventional water sampling methods such as CTD Rosette samplers. Yet, this layer is critical for regulating the benthic-pelagic coupling between sediment and seawater, because the conditions in this layer determine the habitat quality for benthic macro- and meiofauna and the chemical and biological exchange between sediment and overlying waters.

A particular focus of this pilot project is to explore small scale meter-scale depressions and the effect of steep contours at the sea floor for bottom boundary layer stratification and benthic pelagic exchange. The working hypothesis for this pilot investigation is that depressions and steep contours of the sea floor lead to the development of spatially and temporally semi-isolated areas of stratified bottom boundary layers with steep chemical gradients in oxygen, nutrients, and alkalinity. Small-scale bottom topography has to date not been considered as an important parameter shaping benthic communities.

We propose that the specific small-scale physicochemical conditions controlled by bottom topography shape benthic habitat and habitat diversity and that this needs to be accounted for as a regulator of benthic habitat quality.

For more information:
Volker Bruchert, Department of Geological Sciences, Stockholm University