MARIA S. MERIAN MSM99/2

Cruise MSM99/2 aims to investigate the periodic formation of pockmarks north of Helgoland in the North Sea. It is generally assumed that the pockmarks form during the occurrence of large storms. The proposed mechanism is based on the fact that wave movements lead to pressure changes in the sedi-ment and thus free gas is formed in the upper sediment and can be stimulated to rise.

To test this hypothesis, sampling stations in two working areas are planned during the cruise. The first working area is located north of Helgoland. In this area pockmarks were described for the first time in 2015. The second working area is located south of Hel-goland in the so-called “Helgoland Mud Area”.

The planned investigations in both working areas include a high-resolution mapping of the study area as well as a targeted geo-chemical sampling of sediments and pore water. From the data obtained, we can de-duce how dissolved gases are distributed locally in the sediments and determine spatial changes. Together with land-based laborato-ry studies of permeability, we expect to gain insights into the formation and occurrence of wave-induced pockmarks in the North Sea.

These findings are essential to understand if and how often such pockmarks can be gen-erated and reactivated, thus allowing a better assessment of possible hazards for offshore structures.