Description: Data from pore water (subterranean estuary) and seawater from Spiekeroog south (near ICBM time series station and campsite) and west beach ("Sturmeck"). South beach data were collected in August 2012, and west beach data were collected in November 2012. Pore water (event labels: DUNE, MIX, LTWL) sample collection was conducted at different sediment depths (50, 100, 150 cm below sediment surface). Stainless steel push-point lancets were insetred into the sediment, and pore water was withdrawn via vacuum (hand pumps) into nalgene polycarbonate bottles. Filtration was done using inline PES cartridge filters. The vacuum bottles were argon gas-flushed to avoid oxygen contamination. Sea water (event label SW) was collected with polycarbonate bottles and from LDPE seepage meter bags (event label SP) and filtered upon return to the laboratory (same day, PES filter cartridges). Sample collection was trace organic and metal clean (soaking and rinsing of bottles, tubing, and filters with diluted HNO3 and HCl suprapur), with sample materials consisting of polyethylene, polypropylene, and polycarbonate. Solid-phase extraction was done with BOND Elut PPL cartridges and elution with Methanol Optima grade. Measurements dissolved organic matter (DOM) were done with FT-ICR-MS. The crosstables describe the molecular composition of DOM and associated Fe and Cu. They contain characteristic properties and classifications of molecular sum formulas as well as FT-ICR-MS signal intensities of each sum formula for each sample (see event table of https://doi.pangaea.de/10.1594/PANGAEA.902704). File name description of “Spiekeroog beach STE_ESI_x_Crosstab_x": pos & neg = positive and negative ionization mode of electrospray ionization (ESI). BSA & NWA = basic/strong acidic and neutral/weak acidic DOM fraction (solid phase extracted)

Description: Data from pore water (subterranean estuary) and seawater from Spiekeroog south (near ICBM time series station and campsite, 53°45'13.5"N 7°40'22.5"E) and west beach ("Sturmeck", 53°46'10.0"N 7°40'26.2"E). South beach data were collected in August 2012, and west beach data were collected in November 2012. Sample abbreviations: SB=South Beach, WB=West Beach. DUNE=most landward station near dunes, MIX=mid-way station between dune base and low water line, LTWL=low tide water line. Pore water (DUNE, MIX, LTWL) sample collection was conducted at different sediment depths (50, 100, 150 cm below sediment surface). Stainless steel push-point lancets were insetred into the sediment, and pore water was withdrawn via vacuum (hand pumps) into nalgene polycarbonate bottles. Filtration was done using inline PES cartridge filters. The vacuum bottles were argon gas-flushed to avoid oxygen contamination. Sea water (SW) was collected with polycarbonate bottles and from LDPE seepage meter bags (SP) and filtered upon return to the laboratory (same day, PES filter cartridges). Sample collection was trace organic and metal clean (soaking and rinsing of bottles, tubing, and filters with diluted HNO3 and HCl suprapur), with sample materials consisting of polyethylene, polypropylene, and polycarbonate. Solid-phase extraction was done with BOND Elut PPL cartridges and elution with Methanol Optima grade. Measurements were done with VA Computrace 757 (Cu ligand concentrations and stability constants), HR-ICP-MS (Cu, Fe, and Mn concentrations), FT-ICR-MS (DOM), spectrophotometry (nutrients), and TOC analyzer (DOC and TDN). Trace metal concentrations (Fe, Cu, Mn) and speciation (oxidation state, size fractions, and organic association), as well as nitrogen species and concentrations: "Spiekeroog beach subterranean estuary environmental data". Concentrations (µM or nM) are denoted in the headers. CuL1=Cu-binding ligands concentrations (nM), logK1=Cu-binding ligand stability constant. Molecular composition of dissolved organic matter and associated Fe and Cu: "Spiekeroog beach STE_ESI_x_Crosstab_x". pos & neg = positive and negative ionization mode. BSA & NWA = basic/strong acidic and neutral/weak acidic, refer to the extracted DOM fraction. Processed figures and tables based on the original data are published here: https://doi.org/10.1016/j.gca.2019.06.004

Description: Data from pore water (subterranean estuary) and seawater from Spiekeroog south (near ICBM time series station and campsite) and west beach ("Sturmeck"). South beach data were collected in August 2012, and west beach data were collected in November 2012. Pore water (event labels: DUNE, MIX, LTWL) sample collection was conducted at different sediment depths (50, 100, 150 cm below sediment surface). Stainless steel push-point lancets were insetred into the sediment, and pore water was withdrawn via vacuum (hand pumps) into nalgene polycarbonate bottles. Filtration was done using inline PES cartridge filters. The vacuum bottles were argon gas-flushed to avoid oxygen contamination. Sea water (event label SW) was collected with polycarbonate bottles and from LDPE seepage meter bags (event label SP) and filtered upon return to the laboratory (same day, PES filter cartridges). Sample collection was trace organic and metal clean (soaking and rinsing of bottles, tubing, and filters with diluted HNO3 and HCl suprapur), with sample materials consisting of polyethylene, polypropylene, and polycarbonate. Solid-phase extraction was done with BOND Elut PPL cartridges and elution with Methanol Optima grade. Measurements were done with VA Computrace 757 (Cu ligand concentrations and stability constants), HR-ICP-MS (Cu, Fe, and Mn concentrations), spectrophotometry (nutrients), and TOC analyzer (DOC and TDN).

Description: This study addresses key processes in high-energy beach systems using an interdisciplinary approach. We assess spatial variations in subsurface pore water residence times, salinity, organic matter (OM) availability, and redox conditions and their effects on nutrient cycles as well as on microbial community patterns and microphytobenthos growth. At the study site on Spiekeroog Island, southern North Sea, beach hydrology is characterized by the classical zonation with an upper saline plume (USP), a saltwater wedge, and a freshwater discharge tube in between. Sediment and pore water samples were taken along a cross-shore transect from the dunes to the low water line reaching sediment depths down to 5 m below sediment surface. Spatial variations in pore water residence time, salinity, and organic matter availability lead to steep redox and nutrient gradients. Vertical and horizontal differences in the microbial community indicate the influence of these gradients and salinity on the community structure. Modeled seawater flux through the USP and freshwater flux through the tube are on average 2.8 and 0.75 m3 per day and meter of shoreline, respectively. Furthermore, ridge sediments at the lower beach discharge seawater at rates of 0.5 and 1.0 m3 per day and meter of shoreline towards the runnel and seaside, respectively. Applying seawater and freshwater fluxes and representative nutrient concentrations for the discharge zones, nutrient fluxes to adjacent nearshore waters are 117 mmol NH4+, 55 mmol PO43 − and 575 mmol Si(OH)4 per day and meter of shoreline. We propose that this nutrient efflux triggers growth of microphytobenthos on sediment surfaces of the discharge zone. A first comparison of nutrient discharge rates of the beach site with a nearby sandy backbarrier tidal flat margin indicates that the beach system might be of less importance in supplying recycled nutrients to nearshore waters than the backbarrier tidal flat area.

Description: Subterranean estuaries (STEs) are land-ocean interfaces where meteoric fresh groundwater mixes with intruding seawater in a coastal aquifer, before discharging into the adjacent water column. In contrast to surface estuaries, STEs have the potential to amplify concentrations of constituents such as copper (Cu) and iron (Fe) due to long residence times and reductive dissolution of mineral phases along the groundwater flowpaths. However, oxidative precipitation of Fe and Mn at the sediment-water interface may scavenge many constituents again before they reach the coastal water column. Hence, the geochemical impact of the suboxic to anoxic submarine groundwater discharge (SGD) on the oxygenated coastal ocean relies on the capability of constituents such as Cu and Fe to stay in solution across redox boundaries. Here, we propose that dissolved organic matter (DOM) in the STE plays a pivotal role in the speciation of Cu and Fe through (i) fueling reductive dissolution and (ii) providing ligands to form stable metal-DOM complexes, increasing their transfer from the STE into the coastal ocean. We investigated the concentrations and speciation of Cu and Fe, and DOM chemical characteristics, in two beach STEs of a barrier island. By combining well-established techniques with novel quantification and speciation approaches from both the inorganic and organic geochemical realm (size-fractionation filtration, ferrozine detection, voltammetry, sequential DOM extraction, and ultra-high resolution mass spectrometry) we characterized metal-DOM associations down to the molecular level. Overall, pore water from both STEs was enriched with Cu and Fe compared to seawater, which indicated transfer potential for both trace metals across the sediment-water interface. However, Fe gradients from pore water to surface were steeper than those for Cu, indicating a larger net transfer of the latter compared to the former. Our voltammetry data showed that Cu was exclusively organically bound in both STEs and the water column, mostly in soluble form (〈20 nm). The majority of 〉60 newly identified Cu-containing complexes had primarily aliphatic character and N and S in their molecular formulae resembling labile marine DOM, while two Cu-DOM complexes had polyphenol (“humic-like”) molecular formulae indicative of terrestrial vascular plant-derived material. In contrast to Cu, the Fe pool consisted of either reduced, soluble (〈20 nm), likely free Fe(II) in the anoxic STE, or of larger colloids (〈200 nm and 〉20 nm) in the fresh groundwater and seawater endmembers, likely as Fe(III)(hydr)oxides stabilized by DOM. Furthermore, while Fe and humic-like DOM seemed to share common sources, all directly identified mobile Fe-DOM complexes appeared to have marine origins. Therefore, organic forms of Fe in the STE may primarily consist of immobile humic-Fe coagulates, partially mobile Fe-nanocolloids, and mobile, N-containing, marine aliphatic Fe-complexes. Our study indicates that aliphatic, N-containing ligands may play an important role in the organic complexation and stabilization of Fe and particularly Cu in the STE, and enable them to cross redox boundaries at the sediment-water interface.