A wide range of chemical, geological and microbiological processes take place in the sands beneath beaches, about which little is known to date. This dynamic underworld, in which saltwater and freshwater mix and which is termed the "subterranean estuary", is the focus of the research group DynaDeep ("The Dynamic Deep Subsurface of High Energy Beaches"). The German Research Foundation (DFG) is funding the project over four years with up to five million euros.

It is assumed that subterranean estuaries play an important role in the fluxes of nutrients from land to sea and that the dynamic mixing processes in beaches like at Spiekeroog can change this significantly. A better understanding of the subsurface processes in coastal regions therefore helps to advance the protection of our unique coastal ecosystems.

The researchers in DynaDeep hope to find answers to the following questions, among others:

• How much does the beach change due to individual tides or storm surges?
• What role do beaches play in the discharge of nutrients into coastal waters?
• Which microorganisms live in the beach at greater depths and what environmental conditions do they have to deal with?
• How much is the freshwater lens pushed inland by events such as storm surges?

In project phase 1, morphodynamics and related subsurface flow and solute transport were studied, delivering baseline information on the flow field, fluxes, mixing and salinity distribution to the biogeochemical working groups: They focused on metabolic rates under varying redox conditions, related abiotic transformations and microbial interactions with organic matter, transformation and fractionation of trace elements and metal isotopes as well as on diversity and metabolic functioning of microbial communities. Together, all cooperation partners conceptualized the dynamic deep bioreactor within the subsurface of high-energy beaches, whose integrated functioning was studied in reactive transport models. 

In phase 2, we will address new research questions regarding the role of reactive zones (‘hot spots’), events (‘hot moments’), and compounds (‘hot stuff’) for the overall turnover of the biogeochemical reactor that evolved during Phase 1 at our core field site Spiekeroog. We will further challenge the transferability and generalisability of our results by conducting research at additional high-energy field sites (De Panne, Belgium and Truc Vert, France) and with different global model approaches. Ultimately, DynaDeep will elucidate the global relevance of the dynamic deep subsurface of high-energy beaches for carbon, nutrient and trace element cycling.

There is a lot to be said for the green island of Spiekeroog as a project location. The natural conditions that characterize Spiekeroog make it a so-called "high-energy beach". This means that the energy of the sea in the form of wind and waves makes large and rapid changes to the beach. Those who have regularly visited Spiekeroog may have already noticed that the relief and location of the beach can change significantly from year to year. These are ideal conditions to study the influence of a changing coast on the subsurface processes in a short time. Furthermore, and very importantly, Spiekeroog offers excellent research infrastructure that has proven itself for many years and is what makes research work possible in the first place. 

In phase 2, we will further explore our research in De Panne (Belgium) and Truc-Vert (France). The rationale for these sites is that they are comparable to our core study site on Spiekeroog, i.e are characterized by thick sandy aquifers and high-energy conditions according to our definition, yet different amplitudes of mean tidal range and significant wave height. Additionally, both have previously been studied, providing a baseline for our in-depth investigations, yet open questions remain. At both sites, close scientific collaborations, local support and accessibility are ensured.

DynaDeep is supported and enabled by:
 

The DynaDeep project is divided into seven sub-projects. Researchers from different institutes carry out field studies and experimental work together in the sub-projects. Among other things, the knowledge gained is integrated into mathematical models that contribute to a better understanding of the processes in the beach subsurface. The DynaDeep team consists of researchers from the following research institutions:

• Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Bremerhaven
• Institute for Biology and Environmental Sciences, University of Oldenburg
• Institute for Chemistry and Biology of the Sea, University of Oldenburg
• Institute for Geosciences, University of Kiel
• LIAG-Institute for Applied Geophysics, Hanover
• ZMT, Bremen

The field work in Truc-Vert and De Panne are supported by the University of Bordeaux and the University of Ghent. 

• Information about the DynaDeep team and the project partners can be found here
• Information on the sub-projects in DynaDeep can be found here
• Information on the „Subterranean estuary observatory” can be found here
• Information about activities in DynaDeep can be found here
• Information about publications in DynaDeep can be found here

You are welcome to contact us during our investigations. We welcome questions and will try to give you an answer if possible.

Also note the announcements in the Spiekerooger event calendar . Our sampling campaigns are usually accompanied by a "walk on the beach" during which a researcher provides closer insights into and around the field investigations in DynaDeep.