Coastal El Niño triggers rapid marine silicate alteration on the seafloor.

Marine silicate alteration plays a key role in the global carbon and cation cycles, although the timeframe of this process in response to extreme weather events is poorly understood. Here we investigate surface sediments across the Peruvian margin before and after extreme rainfall and runoff (coastal El Niño) using Ge/Si ratios and laser-ablated solid and pore fluid Si isotopes (δ30Si). Pore fluids following the rainfall show elevated Ge/Si ratios (2.87 µmol mol-1) and δ30Si values (3.72‰), which we relate to rapid authigenic clay formation from reactive terrigenous minerals delivered by continental runoff. This study highlights the direct coupling of terrestrial erosion and associated marine sedimentary processes. We show that marine silicate alteration can be rapid and highly dynamic in response to local weather conditions, with a potential impact on marine alkalinity and CO2-cycling on short timescales of weeks to months, and thus element turnover on human time scales.

Interactions between temperature and energy supply drive microbial communities in hydrothermal sediment.

Temperature and bioavailable energy control the distribution of life on Earth, and interact with each other due to the dependency of biological energy requirements on temperature. Here we analyze how temperature-energy interactions structure sediment microbial communities in two hydrothermally active areas of Guaymas Basin. Sites from one area experience advective input of thermogenically produced electron donors by seepage from deeper layers, whereas sites from the other area are diffusion-dominated and electron donor-depleted. In both locations, Archaea dominate at temperatures >45 °C and Bacteria at temperatures <10 °C. Yet, at the phylum level and below, there are clear differences. Hot seep sites have high proportions of typical hydrothermal vent and hot spring taxa. By contrast, high-temperature sites without seepage harbor mainly novel taxa belonging to phyla that are widespread in cold subseafloor sediment. Our results suggest that in hydrothermal sediments temperature determines domain-level dominance, whereas temperature-energy interactions structure microbial communities at the phylum-level and below.

Serpentine alteration as source of high dissolved silicon and elevated δ30Si values to the marine Si cycle.

Serpentine alteration is recognized as an important process for element cycling, however, related silicon fluxes are unknown. Pore fluids from serpentinite seamounts sampled in the Mariana forearc region during IODP Expedition 366 were investigated for their Si, B, and Sr isotope signatures (δ30Si, δ11B, and 87Sr/86Sr, respectively) to study serpentinization in the mantle wedge and shallow serpentine alteration to authigenic clays by seawater. While serpentinization in the mantle wedge caused no significant Si isotope fractionation, implying closed system conditions, serpentine alteration by seawater led to the formation of authigenic phyllosilicates, causing the highest natural fluid δ30Si values measured to date (up to +5.2 ± 0.2‰). Here we show that seafloor alteration of serpentinites is a source of Si to the ocean with extremely high fluid δ30Si values, which can explain anomalies in the marine Si budget like in the Cascadia Basin and which has to be considered in future investigations of the global marine Si cycle.

Boron isotope variability related to boron speciation (change during uptake and transport) in bell pepper plants and SI traceable n(11 B)/n(10 B) ratios for plant reference materials.

RATIONALE: Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intra-plant fractionation mechanisms in response to the B concentration in the irrigation water spanning the range from B depletion to toxic levels. METHODS: A fully validated analytical procedure based on multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), sample decomposition and B matrix separation was applied to study B isotope fractionation. The validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8‰ for pure boric acid solutions and ≤1.5‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time. RESULTS: The B isotope compositions of irrigation water and bell pepper samples suggest passive diffusion of the heavy 11 B isotope into the roots during low to high B concentrations while uptake of the light 10 B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11 B isotope in higher located plant parts was observed (average Δ11 Bleaf-roots = 20.3 ± 2.8‰ (1 SD)), possibly by a facilitated transport of the heavy 11 B isotope to growing meristems by B transporters. CONCLUSIONS: The B isotopes can be used to identify plant metabolism in response to the B concentration in the irrigation water and during intra-plant B transfer. The large B isotope fractionation within the plants demonstrates the importance of biological B cycling for the global B cycle.