shelf-and river-derived elements to the central Arctic Ocean • The TPD is rich in dissolved organic matter (DOM), which facilitates long-range transport of trace metals that form complexes with DOM • Margin trace element fluxes may increase with future Arctic warming due to DOM release from permafrost thaw and increasing river discharge

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. 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.

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During the Polarstern (PS94) expedition, summer 2015, part of the international GEOTRACES program, sources and sinks of dissolved (D) Cd, Co, Cu, Fe, Mn, Ni, and Zn were studied in the central Arctic Ocean. In the Polar Surface Water in which the TransPolar Drift (TPD) is situated, salinity and δ18O derived fractions indicated a distinct riverine source for silicate DCo, DCu, DFe, DMn, and DNi. Linear relationships between DMn and the meteoric fraction depended on source distance, likely due to Mn‐precipitation during transport. In the upper 50 m of the Makarov Basin, outside the TPD core, DCo, DMn, DNi, DCd, and DCu were enriched by Pacific waters, whereas DFe seemed diluted. DCo, DFe, DMn, and DZn were relatively high in the Barents Sea and led to enrichment of Atlantic water flowing into the Nansen Basin. Deep concentrations of all metals were significantly lower in the Makarov Basin compared to the Nansen and Amundsen, the Eurasian, Basins. The Gakkel ridge hydrothermal input and higher continental slope convection are explanations for higher metal concentrations in the Eurasian Basins. Although scavenging rates are lower in the Makarov Basin compared to the Eurasian Basins, the residence time is longer and therefore scavenging can decrease the dissolved concentrations with time. This study provides a baseline to assess future change, and additionally identifies processes driving trace metal distributions. Our results underline the importance of fluvial input as well as shelf sources and internal cycling, notably scavenging, for the distribution of bio‐active metals in the Arctic Ocean.

Rare earth elements (REEs) are used as tracers for oceanic trace element cycling. However, the low (picomolar level) dissolved REE concentrations and time-consuming methods have so far hindered their extensive use in marine studies. This study reports the first application of the automated seaFAST-pico system (Elemental Scientific Inc.) in offline mode and using multi-element isotope dilution inductively coupled plasma-mass spectrometry (ID ICP-MS) for the robust and rapid pre-concentration, purification, and analysis of dissolved REEs from small volumes of seawater (11-12 mL). Accuracy of our new method is checked with replicates of GEOTRACES intercalibration seawater from BATS (Bermuda Atlantic Time Series, North Atlantic) at 15 m and 2000 m water depths. Our results show excellent agreement (within the analytical uncertainty, 2σ SD) with the published intercalibrated values from the GEOTRACES intercalibration study. Replicates of GEOTRACES intercalibration seawater from SAFe at 3000 m water depth (Sampling and Analysis of Iron, North Pacific) indicate a procedural long-term error of ≤3.9% 2σ RSD for all REEs, except for Ce and Gd. An international intercomparison from 4 labs using SAFe 3000 m seawater aliquots, 2 of which also use the seaFAST-pico system in offline mode, and different pre-concentration, purification, and analytical methods shows excellent agreement between REE concentrations