Subterranean estuaries are hidden connective zones between inland aquifers and the open sea where meteoric freshwater and circulating seawater mix and undergo major biogeochemical changes. Hence, they are considered powerful biogeochemical reactors affecting elemental net fluxes to the sea. DynaDeep is motivated by the fact that the functioning of subterranean estuaries below high-energy beaches is currently poorly understood, as field studies have mostly focussed on low- or moderate-energy sites. In particular the effect of hydro- and morphodynamics on subsurface flow and transport is unclear and related consequences on biogeochemical reactions and microbial habitat characteristics have not been investigated. We propose the existence of a so far unexplored biogeochemical reactor within the dynamic deep subsurface of high-energy beaches where dynamic boundary conditions propagate deep (tens of meters) into the subsurface leading to strong spatio-temporal variabilities of geochemical conditions. Subterranean estuaries below high-energy beaches may thus form a unique microbial habitat with an adapted microbial community unlike other typically more stable subsurface environments. DynaDeep studies groundwater flow patterns as a function of hydro- and morphodynamics. It delivers rates of redox processes and related abiotic transformations. Furthermore, it assesses speciation and transformation of trace metals and metal isotopes. Microbial interactions with organic matter as well as the diversity and metabolic functioning of microbial communities are investigated. Jointly, we carry out field campaigns, share sampling approaches and experimental work and use mathematical models in an integrative approach. Ultimately, DynaDeep will elucidate the global relevance of the dynamic deep subsurface of high-energy beaches for coastal ecosystems as well as for carbon, nutrient and trace element cycling.

uol.de/en/icbm/dynadeep

Dr. Rena Meyer (PI P7)

Dr. Stephan Seibert (PI P6)

Dr. Nele Grünenbaum (coordination)

Lejonina Herting

Johannes Ritter

Mohit Singh