Atmosphere circulation patterns synchronize pan-Arctic glacier melt and permafrost thaw

The Arctic is changing rapidly due to the amplification of global temperature trends, causing profound impacts on the ice sheet in Greenland, glaciers, frozen ground, ecosystems, and societies. Here, we focus on impacts that atmospheric circulation causes in addition to the climate warming trends. We combine time series of glacier mass balance from temporal satellite gravimetry measurements (GRACE/GRACE-FO; 2002–2023), active layer thickness in permafrost areas from ESA’s Climate Change Initiative remote sensing and modelling product (2003–2019), and field measurements of the Circumpolar Active Layer Monitoring Network (2002–2023). Despite regional and system-related complexities, we identify robust covariations between these observations, which vary asynchronously between neighbouring regions and synchronously in regions antipodal to the North Pole. We reveal a close connection with dominant modes of atmosphere circulation, controlling about 75% of the common pan-Arctic impact variability (2002–2022), also affecting the Greenland Ice Sheet. We emphasize that it is necessary to consider such atmospheric driving patterns when projecting impacts, particularly caused by extremes, in an increasingly warmer Arctic

Matrix‐independent boron isotope analysis of silicate and carbonate reference materials by ultraviolet femtosecond laser ablation multi‐collector inductively coupled plasma mass spectrometry with application to the cold‐water coral Desmophyllum dianthus

Rationale: Boron isotopes are a powerful tool for pH reconstruction in marine carbonates and as a tracer for fluid–mineral interaction in geochemistry. Microanalytical approaches based on laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) often suffer from effects induced by the sample matrix. In this study, we investigate matrix-independent analyses of B isotopic ratios and apply this technique to cold-water corals. Methods: We employ a customized 193 nm femtosecond laser ablation system (Solstice, Spectra-Physics) coupled to a MC-ICP-MS system (Nu Plasma II, Nu Instruments) equipped with electron multipliers for in situ measurements of B isotopic ratios (11B/10B) at the micrometric scale. We analyzed various reference materials of silicate and carbonate matrices using non-matrix matched calibration without employing any correction. This approach was then applied to investigate defined increments in coral samples from a Chilean fjord. Results: We obtained accurate B isotopic ratios with a reproducibility of ±0.9‰ (2 SD) for various reference materials including silicate glasses (GOR132-G, StHs6/80-G, ATHO-G and NIST SRM 612), clay (IAEA-B-8) and carbonate (JCp-1) using the silicate glass NIST SRM 610 as calibration standard, which shows that neither laser-induced nor ICP-related matrix effects are detectable. The application to cold-water corals (Desmophyllum dianthus) reveals minor intra-skeleton variations in δ11B with average values between 23.01‰and 25.86‰. Conclusions: Our instrumental set-up provides accurate and precise B isotopic ratios independently of the sample matrix at the micrometric scale. This approach opens a wide field of application in geochemistry, including pH reconstruction in biogenic carbonates and deciphering processes related to fluid–mineral interaction

Lithium isotopic fractionation during weathering and erosion of shale

Clay weathering in shales is an important component of the global Li budget because Li is mobilized from Li-rich clay minerals and shale represents about one quarter of the exposed rocks on Earth. We investigate Li isotopes and concentrations to explore implications and mechanisms of Li isotopic fractionation in Shale Hills, a first-order catchment developed entirely on shale in a temperate climate in the Appalachian Mountains, northeastern USA. The Li isotopic compositions (δ7Li) of aqueous Li in stream water and groundwater vary between 14.5 and 40.0‰. This range is more than half that observed in rivers globally. The δ7Li of aqueous Li increases with increasing Li retention in secondary minerals, which is simulated using a box model that considers pore fluid advection to be the dominant transport process, silicate dissolution to be the source of Li to the pore fluid, and uptake of Li by kaolinite, Fe-oxides, and interlayer sites of clays to be the sinks. The simulations suggest that only those deep groundwaters with δ7Li values of ∼15‰ are explainable as steady state values; those fluids with δ7Li values > 18‰, especially near-surface waters, can only be explained as time-dependent, transient signals in an evolving system. Lithium is highly retained in the residual solid phase during chemical weathering; however, bulk soils (0.5 ± 1.2‰ (1 SD)) and stream sediments (0.3‰) have similar, or higher, δ7Li values compared to average bedrock (−2.0‰). This is attributed to preferential removal of clay particles from soils. Soil clays are isotopically depleted in 7Li (δ7Li values down to −5.2‰) compared to parental material, and δ7Li values correlate with soil Li concentration, soil pH, and availability of exchangeable sites for Li as a function of landscape position (valley floor versus ridge top). The strong depletion of Li and clay minerals in soils compared to bedrock is attributed at least partly to loss of Li through export of fine-grained clay particles in subsurface water flow. This process might be enhanced as the upper weathering zone of this catchment is highly fractured due to former periglacial conditions. The Li isotopic composition of vegetation is similar to soil clay and both are distinct from mobile catchment water (soil pore water, stream and groundwater). Extrapolating from this catchment means that subsurface particle loss from shales could be significant today and in the past, affecting isotopic signatures of soils and water. For example, clay transformations together with removal of clay particles before re-dissolution support weathering conditions that lead to a low aqueous Li flux but to high δ7Li values in water

Chemical and Nd isotope constraints on granitoid sources involved in the Caledonian Orogeny in Scotland

Major- and trace-element data and Nd isotope compositions for granitoid samples from the Grampian Highlands in Scotland show a systematic evolution in the composition of their sources in the course of the Caledonian Orogeny. Granitoids of 511-451 Ma, related to the collision of the Midland Valley island arc with the Grampian terrane, show S-type affinity and fractionated REE patterns with minor Eu anomalies and low initial epsilon(Nd) values of -14.1 to -11.2 suggesting melting of predominantly Dalradian metasediments. Subsequently formed granitoids of 425-406 Ma derived from an assumed Andean plate margin comprise a wide spectrum of rock types including I-type granite-granodiorite, and S-type granitoids, monzonites and alkali granites. The trace-element patterns of these rocks and the range of initial epsilon(Nd) values of -2.1 to -6.9 are consistent with melting of variably rejuvenated crust as found in continental margin settings. We conclude that the Grampian Highlands were affected by two major crust-modifying events during the Caledonian Orogeny: predominantly recycling of older crust during docking of the Midland Valley arc and addition of juvenile, mantle-derived material to the crust during the convergence of Avalonia with Laurentia.</p

Chemical and Nd isotope constraints on granitoid sources involved in the Caledonian Orogeny in Scotland

<p>Major- and trace-element data and Nd isotope compositions for granitoid samples from the Grampian Highlands in Scotland show a systematic evolution in the composition of their sources in the course of the Caledonian Orogeny. Granitoids of 511–451 Ma, related to the collision of the Midland Valley island arc with the Grampian terrane, show S-type affinity and fractionated REE patterns with minor Eu anomalies and low initial ϵ_Nd values of −14.1 to −11.2 suggesting melting of predominantly Dalradian metasediments. Subsequently formed granitoids of 425–406 Ma derived from an assumed Andean plate margin comprise a wide spectrum of rock types including I-type granite–granodiorite, and S-type granitoids, monzonites and alkali granites. The trace-element patterns of these rocks and the range of initial ϵ_Nd values of −2.1 to −6.9 are consistent with melting of variably rejuvenated crust as found in continental margin settings. We conclude that the Grampian Highlands were affected by two major crust-modifying events during the Caledonian Orogeny: predominantly recycling of older crust during docking of the Midland Valley arc and addition of juvenile, mantle-derived material to the crust during the convergence of Avalonia with Laurentia. </p

Developing boron isotopes to elucidate shale weathering in the critical zone

To further develop boron isotopes as a tool for understanding shale weathering, we explored patterns of boron concentrations and isotopes across the forested Susquehanna Shale Hills Critical Zone Observatory (CZO). We present boron measurements for all watershed components that provided a foundation for examining water-rock interactions in a shale dominated watershed, including water compartments (e.g., precipitation, stream water, groundwater) and solid compartments (e.g., soil, bedrock, stream sediments, suspended load, and leaf litter). Results show boron isotopes (δ11B) in the bedrock (− 4.6‰) and soil (− 5.9 to - 4.2‰) were very similar. All waters were enriched in 11B by comparison: precipitation (7.2 to 22.6‰), stream (10.3 to 15.5‰), and groundwater (2.2 to 17.4‰). Modeling revealed that isotopic fractionation observed in the surface water and groundwater could mainly be explained by water-rock interactions including clay mineral dissolution (e.g., chlorite) and coprecipitation/adsorption processes (e.g., coatings on illite particles), likely in the near surface soils (~2 m deep). We found that leaching, the loss of boron from vegetation to stream water, plays a secondary role. Specifically, such leaching likely contributes the equivalent of 10 to 26% of the B fluxes from the watershed outlet. Boron mass balance between bedrock and precipitation inputs and the exported flux of dissolved and solid pools identified a “missing” isotopically light solid flux (δ11B of −12.2 ± 5.3‰ at ~4.4 ± 3.8 mol/ha/y of B; uncertainty reported as 2 SD). We did not sample any pool with this isotopic signature. Here our data suggest the composition of this pool is more likely related to precipitation of secondary clays rather than adsorption or (co)precipitation on Fe oxides. We propose two hypotheses to explain the missing light B pool: 1) a significant portion of the particles carrying the missing 10B are not sampled because they enter groundwater at depth and are transported out of the catchment under the stream; and/or 2) the inputs and outputs of boron are not operating at steady state in the catchment today, suggesting that the missing boron particles were lost in the past in proportions higher than today. When this B budget is paired with studies of δ26Mg and δ56Fe from Shale Hills, both of which also show missing isotopic pools, the pattern indicates a fundamental gap in understanding of shale weathering. We concluded that light B particles, presumably generated in the upper soils, are likely transported deep beneath the surface in the groundwater system or episodically in the past through riverine fluxes

In-situ Iron isotope measurements and mineral compositions from ODP Hole 206-1256D and IODP Hole 335-U1256D

In-situ Fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the Fe isotopic composition of Fe-Ti-oxides and Fe-sulfides of the different lithologies of the drilled rocks from IODP Hole 1256D (eastern equatorial Pacific; 15 Ma crust formed at the East Pacific Rise). Most igneous rocks normally have a very restricted range in their 56Fe/54Fe ratio. In contrast, Fe isotope compositions of hot fluids (> 300 °C) from mid-ocean-ridge spreading centers define a narrow range that is shifted to lower delta 56Fe values by 0.2 per mil - 0.5 per mil as compared to igneous rocks. Therefore, it is expected that mineral phases that contain large amounts of Fe are especially affected by the interaction with a fluid that fractionates Fe isotopes during exsolution/precipitation of those minerals. We have used a femtosecond UV-Laser ablation system to determine mineral 56Fe/54Fe ratios of selected samples with a precision of < 0.1 per mil (2 sigma level) at micrometer-scale. We have found significant variations of the delta 56Fe (IRMM-014) values in the minerals between different samples as well as within samples and mineral grains. The overall observed scale of delta 56Fe (magnetite) in 1256D rocks ranges from - 0.12 to + 0.64 per mil, and of delta 56Fe (ilmenite) from - 0.77 to + 0.01 per mil. Pyrite in the lowermost sheeted dike section is clearly distinguishable from the other investigated lithological units, having positive delta 56Fe values between + 0.29 and + 0.56 per mil, whereas pyrite in the other samples has generally negative delta 56Fe values from - 1.10 to - 0.59 permil. One key observation is that the temperature dependent inter-mineral fractionations of Fe isotopes between magnetite and ilmenite are systematically shifted towards higher values when compared to theoretically expected values, while synthesized, well equilibrated magnetite-ilmenite pairs are compatible with the theoretical predictions. Theoretical considerations including beta-factors of different aqueous Fe-chlorides and Rayleigh-type fractionations in the presence of a hydrous, chlorine-bearing fluid can explain this observation. The disagreement between observed and theoretical equilibrium fractionation, the fact that magnetite, in contrast to ilmenite shows a slight downhole trend in the delta 56Fe values, and the observation of small scale heterogeneities within single mineral grains imply that a general re-equilibration of the magnetite-ilmenite pairs is overprinted by kinetic fractionation effects, caused by the interaction of magnetite/ilmenite with hydrothermal fluids penetrating the upper oceanic crust during cooling, or incomplete re-equilibration at low temperatures. Furthermore, the observation of significant small-scale variations in the 56Fe/54Fe ratios of single minerals in this study highlights the importance of high spatial-resolution-analyses of stable isotope ratios for further investigations