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X-Ray Diffraction (XRD) analysis of streambed sediments:\n\nWe investigated the mineral composition of the particle size fraction < 63 µm (silt and clay fraction) of streambed sediments collected within the Brøggerbreen, Midtre and Austre Lovénbreen catchments by X-Ray Diffraction (XRD) analysis. The samples were collected in July 2020, dried and sieved. The measurements were performed at the University of Bremen (Germany) using a Philips X’Pert Pro diffractometer equipped with a Cu‐tube and a monochromator following the method by Vogt (2009). We evaluated the data using the QUAX full-pattern analysis software (Vogt et al., 2002) for semiquantitative determination of the major mineral composition.\n\nRadiochemical analysis of sediment cores:\n\nSediment cores were collected at 4 sites PN, IA, F, and V in Kongsfjorden, Svalbard, July 28 – 30, 2021.  Gamma activities of 234Th, 7Be, 210Pb, 226Ra and 137Cs  in core sections were measured in the radiochemistry lab (Prof. J.K. Cochran; Director) at the School of Marine and Atmospheric Sciences, Stony Brook University. Samples from sectioned cores were dried at 75°C.  Gamma activities were measured using Canberra planar intrinsic germanium gamma detectors as follows: 234Th (63 keV) activities were counted shortly after collection and then recounted 6 months later to determine the supported activity (238U) or in some cases by using the average 234Th activity from multiple intervals at depth in the same core.    7Be (477 keV) activities were measured in the initially counted samples.  Corrections were made for self-absorption of gamma radiation by samples as a function of sample mass and counting geometry (Cochran et al., 1998).  It is possible that corrections for geometries may change slightly based on subsequent study so that reported activities are subject to possible updates. \n\nThese data are dicussed and cited in:\n\nLaura M. Wehrmann, Robert C. Aller, Sabine Kasten, Jack Dotzler  and Grit Steinhoefel.   Rapid forward and reverse weathering reactions drive cryptic silica and cation cycling in Arctic fjord sediments. Global Biogeochemical Cycles.  2025"]} 

In this study, pore-water and solid-phase samples were collected at four stations in the inner to mid Kongsfjorden, Svalbard, and analyzed in a multi-proxy geochemical approach, which included pore-water analyses, solid-phase operational reactive silica extractions, and lithium isotope analyses of pore-water. The goal of this study was to investigate possible forward and reverse weathering alteration in glacially influenced high-latitude systems by focusing on the early diagenetic processes occurring at several stations in Kongsfjorden, Svalbard, extending from the immediate vicinity of a marine-terminating glacier to a mid-fjord, bioturbated station. Our study focused on deciphering the pathways of the weathering reactions, and their relative roles in controlling reactive silica burial rates and benthic cation fluxes. This study is presented in a manuscript entitled "Rapid forward and reverse weathering reactions drive cryptic silica and cation cycling in Arctic fjord sediments" currently undergoing review."]} 

In this study, pore-water and solid-phase samples were collected at four stations in the inner to mid Kongsfjorden, Svalbard, and analyzed in a multi-proxy geochemical approach, which included pore-water analyses, solid-phase operational reactive silica extractions, and lithium isotope analyses of pore-water. The goal of this study was to investigate possible forward and reverse weathering alteration in glacially influenced high-latitude systems by focusing on the early diagenetic processes occurring at several stations in Kongsfjorden, Svalbard, extending from the immediate vicinity of a marine-terminating glacier to a mid-fjord, bioturbated station. Our study focused on deciphering the pathways of the weathering reactions, and their relative roles in controlling reactive silica burial rates and benthic cation fluxes. This study is presented in a manuscript entitled "Rapid forward and reverse weathering reactions drive cryptic silica and cation cycling in Arctic fjord sediments" currently undergoing review."]} 

Early diagenetic forward and reverse weathering reactions play a significant role in controlling alkalinity fluxes and silica, alkali metal and alkaline earth metal cycling in coastal systems. In Kongsfjorden, Svalbard, the inputs of autochthonous biogenic debris (diatomaceous silica) and allochthonous lithogenic material of varying reactivity (dominated by clays, especially illite and chlorite, and primary aluminosilicates, mostly plagioclase) drive complex balances of diagenetic silicate reactions in sediments. The rapid dissolution of reactive silica results in the release of dissolved silica (Si_d) into pore‐waters and sustains elevated benthic Si_dfluxes (−0.2 to −0.8 mmol m⁻² d⁻¹), which are on the upper end of values previously determined for Arctic environments. Increases with depth in pore‐water lithium (Li⁺), potassium, magnesium, and barium concentrations within the top centimeters provided evidence for forward weathering of clays quickly upon burial. Due to the prevalent occurrence of forward weathering, the benthic net Li⁺flux was associated with a light isotope signal. Decreases in pore‐water rubidium concentrations with depth at the near‐glacier station, elevated ratios of the authigenically altered silica to the biogenic silica pool at all sites, and small increases of pore‐water δ⁷Li values with depth showed that reverse weathering also takes place. Anoxic incubation of diatom frustule probes provided further evidence for the neoformation of cation‐rich clays. The superposition of reverse and forward weathering results in cryptic silica and cation cycling that muted net benthic fluxes. In deeper sediments, changes in pore‐water solute patterns indicated an interconnected occurrence of reverse and forward weathering, potentially driven by reactive silica‐limitation. 

Benthic organisms in coastal sediments affect elemental cycling and control benthic-pelagic coupling through particle reworking and ventilation of their burrows. Bioirrigation and associated porewater advection create intermittently oxic regions within sediments. The spatio-temporal patterns of such biogenic redox oscillations likely respond to seasonal factors, but quantitative information on the seasonality of bioirrigator behaviors and associated redox dynamics is scarce. We examined bioirrigation by the maldanid polychaete Clymenella torquata and its impacts on sediment oxygenation patterns in permeable sediments using high-resolution planar optode oxygen imaging. In sediment mesocosms with reconstructed summer-collected sediment, the durations of pumping and resting varied inversely with temperature. The average durations of pumping and resting increased from 4 min/4 min at 21 °C, to 6 min/6 min at 12 °C, to 15 min/14 min at 5 °C. In intact cores collected in summer, irrigation patterns (3.5 min/3.5 min) were similar to those observed at 21 °C during the temperature ramp. Pumping and resting durations in intact cores collected in winter at 6 °C averaged 9 min/26 min, significantly different from patterns at comparable temperatures in the temperature ramp. Pumping patterns strongly affected the temporal patterns of redox dynamics in surrounding sediments. In addition, temperature strongly affected burrow irrigation depth (exclusively within the top ∼10 cm at 21 °C, and down to ∼20 cm at 5–6 °C with an apparent transition at ∼15 °C), indicating that the zone with dynamic redox conditions migrates vertically on a seasonal basis. The differences in pumping patterns between in- and out-of-season experiments and the effect of temperature on irrigation depth underscore the importance of conducting experiments with bioturbators in-season and at field temperatures. The observed seasonal differences in bioirrigation patterns and associated spatio-temporal redox dynamics suggest that rates and pathways of redox-sensitive diagenetic processes and benthic chemical fluxes in permeable sediments likely show considerable seasonal variation. 

Permeable sediments, which represent more than 50% of the continental shelves, have been largely neglected as a potential source of Fe in current global estimates of benthic dissolved iron Fed fluxes. There are open questions regarding the effects of a range of factors on Fed fluxes from these deposits, including seasonal dynamics and the role of bioirrigation. To address these gaps, we performed laboratory-based sediment incubation experiments with muddy sands during summer (21 °C) and winter (7 °C). We used bioirrigation mimics to inject overlying water into the permeable sediment with patterns resembling the bioirrigation activity of the prolific bioturbating polychaete,Clymenella torquata. Newly developed in-line Fe accumulators were used to estimate Fe fluxes with a recirculating set-up. We found high Fed fluxes from sandy sediments, especially in benthic chambers with simulated bioirrigation. In the winter fluxes reached 200 µmol Fed m-2 d-1 at the onset of irrigation and then decreased over the course of a 13-day experiment while in the summer fluxes from irrigated sediments reached 100 µmol Fed m-2 d-1 and remained high throughout a 7-day experiment. Despite different geochemical expressions of Fe-S cycling and resulting porewater Fed concentrations in winter and summer, large Fed fluxes were sustained during both seasons. Solid-phase and porewater concentration profiles showed that maximum concentrations of key constituents, including total solid-phase reactive Fe, and porewater Fed and ammonium, were located closer to the sediment water interface (SWI) in irrigated cores than in non-irrigated cores due to the upward advective transport of dissolved porewater constituents. This upward transport also facilitated Fed fluxes out of the sediments, especially during times of active pumping. Our study demonstrates the potential for large Fed fluxes from sandy sediments in both summer and winter, despite relatively low standing stocks of labile organic matter and porewater Fed. The primary driver of these high fluxes was advective porewater transport, in our study induced by the activity of infaunal organisms. These results suggest that permeable sediments, which dominate shelf regions, must be explicitly considered in global estimates of benthic Fed fluxes, and cannot be simply extrapolated from estimates based on muddy sediments.