Trace elements and metal isotopes: Transformation and fractionation

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DynaDeep will unravel the functionality and relevance of marine-terrestrial interactions below high-energy beaches, where we propose the deep subsurface to act as a dynamic bioreactor and unique microbial habitat affecting elemental net fluxes to the sea. To reach this goal, six subprojects will cooperate in joint field campaigns, shared sampling approaches as well as experimental work and use mathematical models in an integrative approach. Subproject P4 will study trace element and metal isotope dynamics related to biogeochemical processes in the subterranean estuary (STE) on Spiekeroog Island. We hypothesise that overlapping redox zones, dynamic changes in microbial activity and spatially and temporally changing redox and salinity interfaces create distinct trace element and isotope records in high-energy beach systems. P4 will measure trace element concentrations (Fe, Mn, Co, Mo, Re, Tl, U, V, rare earth elements) and Fe and Mo isotope signatures in (pore)water and sediment samples. Regular field sampling will give insight into spatio-temporal variations of trace element and isotope patterns under varying boundary conditions. Laboratory incubation experiments will be used to determine trace element mobilisation, retention and isotope fractionation rates in order to understand the physico-chemical and microbial changes driving these reactions in the dynamic deep to shallow subsurface of the STE in detail. Trace element and supplementary major ion, nutrient and total alkalinity data will be provided for mathematical modelling (P1, P6), rate measurements (P2) and biogeochemical investigations carried out in P3 and P5 to collaboratively assess how trace element and metal isotope transformation and fractionation are interconnected with water source and age, redox conditions and organic matter and microbial community characteristics.