Submarine groundwater discharge and its effect on the methane cycle

Michael Schlüter, Ph.D.
Alfred-Wegener-Institut

Wednesday, October 2, 2002
3:00 p.m. – Pacific Forum

Fluid flow through sediments into coastal waters and the ocean is important for hydrological budgets, groundwater resource issues, and release of nutrients and trace gases from the seafloor. Submarine groundwater discharge was studied for regions of the Western Baltic Sea. Seepage of fresh water from sub-seafloor aquifers was observed by geochemical methods. The discharge occurs as dispersed flow and from well-defined morphological features, so-called pockmarks. The spatial distribution of pockmarks was studied by an AUV survey. The sub-seafloor aquifer was sampled directly through a submarine well system, allowing age dating of the groundwater. A budget for freshwater discharge was computed for the entire bay. The two-dimensional structure of flow within a pockmark was considered by pore water sampling and numerical modeling. This provides information about mechanisms controlling the release of methane from muddy sediments and allows a comparison between the 
CH₄ cycle at Pockmarks and Mud Volcanoes.