Organic complexation and colloidal association of iron and copper in the subterranean estuary: Implications for trace metal mobility and bioavailability

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Submarine groundwater discharge (SGD), an advective underground water transport, has recently been identified as a large source of life-essential trace metals such as iron and copper to the ocean. It is hypothesized that this transport is facilitated by stabilization of the metals through complex for-mation and/or colloidal association with dissolved organic matter (DOM). This process may take place in the subterranean estuary (STE) at reactive interfaces of fresh groundwater and saline pore water, or upon entry into the coastal water column. Distribution patterns, advective fluxes, and chemical characteristics of metal-organic compounds will be investigated (i) descriptively and (ii) experimentally in a model STE on Spiekeroog Island, Germany and a submarine spring on Jeju Island, South Korea, where iron and copper concentrations are 1-2 orders of magnitude higher than in the adjacent coastal oceans. The analytical challenge of metal-DOM characterization will be addressed by combining well-established size fractionation and speciation (filtration, voltammetry) with state-of-the-art techniques: High-performance liquid chromatography/size-exclusion chromatography high resolution inductively-coupled-plasma mass-spectrometry (HPLC/HPSEC-HR-ICP-MS) and ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis of metal-DOM isolates, to reveal specific compound classes and molecular formulae. This novel analytical approach will provide powerful new tools with which to study metal-DOM complexes.