Authigenic phases in lake sediments hold the potential to record changes in the isotope compositions of past lake water, potentially yielding valuable information on secular changes in continental weathering patterns and rates, including over past glacial cycles. Here, different leaching approaches are investigated with the aim of extracting Sr, Nd, Pb, and Be hosted in authigenic Fe-Mn (oxy)hydroxide sediment phases for precise isotope measurements. Elemental Al/Mn, Ca/Mn, and P/Mn ratios obtained via a mild reductive leach agree well with the composition of marine authigenic Fe-Mn phases. For core top sediments, leached Sr isotope compositions obtained with this leach agree well with the composition of lake water. The Be and Nd isotope compositions of core top leachates are consistent with the spatial variability observed in the water column. Due to high concentrations in Fe-Mn phases, leachate compositions are dominated by authigenic Be, Sr, Nd, and Pb, even in cases when as much as 40% of leached phases (by mass) are non-authigenic. These lines of evidence suggest that the mild reductive leach successfully extracts the modern lake isotope composition from modern sediments in terms of the isotope systems investigated. We further show that the leaching method is also reliable for older sediments (<340 ka): leached paleo-Sr isotope compositions are consistent between the current and previous interglacial periods, as well as for glacial periods. This suggests that reconstructed water isotope compositions are not affected by early diagenetic processes, instead reflecting environmental factors around the lake that determine the composition of weathering fluxes. Although more difficult to assess for Be, Nd, and Pb due to the heterogeneity of modern lake water, the data we present indicate the overall robustness of the leaching approach. These promising results open up lakes as archives for paleo-weathering reconstructions. Given that marine reconstructions face some important limitations (e.g., integration of basin-wide changes in weathering processes, long residence times for Sr, etc.Fe), lake records provide an avenue to improve our understanding of changes in regional weathering processes over glacial-interglacial timescales. The mild reductive leach used here may also be useful for meteoric Be studies in marine shelf settings, to prevent leaching of terrestrial sedimentary Fe-Mn oxy(hydroxide) phases.

Terrestrial enhanced rock weathering (ERW) is the application of pulverized silicate rock to soils for the purposes of carbon removal and improved soil health. Although a geochemical modeling framework for ERW in soils is emerging, there is a scarcity of experimental and field trial data exploring potential environmental impacts, risks, and monitoring strategies associated with this practice. This paper identifies potential negative consequences and positive cobenefits of ERW scale-up and suggests mitigation and monitoring strategies. To do so, we examined literature on not only ERW but also industry, agriculture, ecosystem science, water chemistry, and human health. From this work, we develop recommendations for future research, infrastructure, and policy needs. We also recommend target metrics, risk mitigation strategies, and best practices for monitoring that will permit early detection and prevention of negative environmental impacts.

Enhanced weathering (EW) of silicate rocks spread onto managed lands as agricultural amendments is a promising carbon dioxide removal (CDR) approach. However, there is an obvious need for the development of tools for Measurement, Reporting, and Verification (MRV) before EW can be brought to scale. Shifts in the concentration of mobile elements measured in the solid phase of soils after application of EW feedstocks can potentially be used to track weathering and provide an estimate of the initial carbon dioxide removal of the system. To measure feedstock dissolution accurately it is necessary to control for the amount of feedstock originally present in the sample being analyzed. This can be achieved by measuring the concentration of immobile detrital elements in soil samples after feedstock addition. However, the resolvability of a signal using a soil mass balance approach depends on analytical uncertainty, the ability to accurately sample soils, the amount of feedstock relative to the amount of initial soil in a sample, and on the fraction of feedstock that has dissolved. Here, we assess the viability of soil-based mass-balance approaches across different settings. Specifically, we define a metric for tracer-specific resolvability of feedstock mass addition (φ) and calculate the feedstock application rates (a) and dissolution fractions (b) required to resolve EW. Applying calculations of a, b, and φ to a gridded soil database from the contiguous USA in combination with known compositions of basalt and peridotite feedstocks demonstrates the importance of adequately capturing field heterogeneity in soil elemental concentrations. While EW signals should be resolvable after ~1–3 years of basalt feedstock addition at common application rates for most agricultural settings with adequate sampling protocols, resolving EW in the field is likely to be challenging if uncertainties in tracer concentrations derived from field-scale heterogeneity and analytical error exceed 10%. Building from this framework, we also present a simple tool for practitioners to use to assess the viability of carrying out soil-based EW MRV in a deployment-specific context.

Lake Baikal, the world's oldest and largest lake, has extensive and continuous sedimentary records dating back to the Miocene epoch 1 .Weathering fluxes in the catchment are representative of global processes in terms of the relative contribution of silicate weathering to dissolved fluxes 2 .The isotope composition of lake water is recorded in sediments through the precipitation of authigenic FeMn-(oxy)hydroxide phases 2 .Hence, Lake Baikal is a promising site to study paleo-weathering conditions.Focusing on the last 30 kyr, we apply radiogenic Sr, Nd, Pb, and meteoric Be isotopes to the sediment record of Lake Baikal to constrain past changes in in weathering sources, processes, and rates in the continental interior of Asia.All studied isotope systems indicate secular variability in detrital silicate fractions and paleo-water compositions.Authigenic Nd (~14.5 ε Nd units) and 208 Pb/ 204 Pb (by ~1.3 208 Pb/ 204 Pb) show large secular variability, with more radiogenic

The ratio of atmosphere-derived 10Be to continent-derived 9Be in marine sediments has been used to probe the long-term relationship between continental denudation and climate. However, its application is complicated by uncertainty in 9Be transfer through the land-ocean interface. The riverine dissolved load alone is insufficient to close the marine 9Be budget, largely due to substantial removal of riverine 9Be to continental margin sediments. We focus on the ultimate fate of this latter Be. We present sediment pore-water Be profiles from diverse continental margin environments to quantify the diagenetic Be release to the ocean. Our results suggest that pore-water Be cycling is mainly controlled by particulate supply and Mn-Fe cycling, leading to higher benthic fluxes on shelves. Benthic fluxes may help close the 9Be budget and are at least comparable to, or higher (~2-fold) than, the riverine dissolved input. These observations demand a revised model framework, which considers the potentially dominant benthic source, to robustly interpret marine Be isotopic records.

Lake Baikal is the oldest and most voluminous lake in the world, and has been suggested to be representative of global processes in terms of silicate weathering contribution to overall weathering fluxes 1 .On the other hand, the intermediate spatial scale of the catchment allows for a more straightforward assessment of elementary budgets, and results in shorter element residence times, compared to the oceans (i.e.~330 yrs for Sr 1 ).Authigenic Fe-Mn (oxyhydr)oxide phases formed in the lake record the isotope composition of lake water 1 and these sedimentary archives cover at least the last 12 Myr 2 .Hence, Lake Baikal offers a unique opportunity to study the evolution of chemical weathering rates in the past, including during the Quaternary glacial cycles.Here we present first records of past lake compositions in terms of radiogenic (Sr, Nd, Pb) and meteoric Be isotopes, specifically focusing on the last glacial interglacial transition.Today, the Selenga river, draining the majority of the southern part of the lake's catchment, is the major source of water and solutes to Lake Baikal 3 .Preliminary data on radiogenic Sr and Nd isotopes in authigenic sediment phases suggest that during the last glacial maximum, weathering fluxes originating in the northern parts of the catchment were more important to the overall lake budgets than today.This is consistent with U isotope based evidence indicating that riverine discharge of the Selenga was drastically reduced or even ceased during the last glacial period 4 .Preliminary data show more radiogenic Pb isotope compositions after the last glacial maximum (LGM), which most likely indicates the onset of chemical weathering after the LGM 5 .These data will be complemented by meteoric Be ratios and a record of past 10 Be deposition rates, shedding light on the evolution of chemical weathering rate through time and its relationship to radiogenic records.

Enhanced weathering is a promising approach to remove carbon dioxide from the atmosphere. However, it may also pose environmental risks through the release of heavy metals, in particular nickel and chromium. In this perspective article I explore the potential role of plants in modulating these heavy metal fluxes. Agricultural basaltic soils may be valuable study sites in this context. However, the effect of biomass harvesting on the accumulation of heavy metals is currently not well studied. Mostly caused by different parent rock concentrations, there is a large variability of heavy metal concentrations in basaltic and ultramafic soils. Hence, to minimize environmental risks of enhanced weathering, basalts with low heavy metal concentrations should be favored. Existing phytoremediation strategies may be used to “phytoprevent” the accumulation of nickel and chromium released from enhanced weathering in soils. As a result, elevated nickel and chromium concentrations in rocks must not preclude enhanced weathering in all settings. In particular, hyperaccumulating plants could be used as part of a crop rotation to periodically remove heavy metals from soils. Enhanced weathering could also be employed on fields or forests of (non-hyper) accumulating plants that have a high primary production of biomass. Both approaches may have additional synergies with phytomining or bioenergy carbon capture and storage, increasing the total amount of carbon dioxide drawdown and at the same time preventing heavy metal accumulation in soils.

We present a detailed analysis of weathering fluxes at Lake Baikal, the largest lake in the world, using the major element, trace element and isotope geochemistry of major inflowing rivers, the lake itself, and its sediments. Our objective is to assess how lake records could be used to understand river-catchment-scale denudation and weathering processes. Total denudation rates at Lake Baikal, as obtained from meteoric Be-10/Be-9, are an order of magnitude lower than the global average, at 16-35 t km(-2) yr(-1). Chemical weathering rates obtained from the riverine dissolved load and discharge are, on the other hand, in the same range as global values, at 6-29 t km(-2) yr(-1). Chemical weathering rates are higher in the north of the catchment than in the south, consistent with higher runoff in the north. In contrast, Be-10/Be-9-derived denudation rates are higher in the south. We hypothesize that this pattern of variation may be due to the stabilizing effect of permafrost soils preventing erosion in the north. An inverse model shows that the Selenga River, Lake Baikal's major tributary, has a silicate weathering contribution to riverine dissolved cation fluxes of 42 mol%; this and other characteristics are representative of large rivers globally. Many trace elements have much lower concentrations in the lake than in inflowing rivers (Be (5%), Mn (3%), Fe (0.4%) and REE (1-2%)). We suggest, based on REE patterns and Mn, Fe-depth profiles in the lake, that this removal is the result of pH induced changes in dissolved-adsorbed partitioning at the river-lake interface, and the incorporation of trace elements into authigenic Fe-Mn (oxyhydr)oxide phases forming within the lake. Strontium is isotopically uniform within the lake, demonstrating that the whole lake mixes on a timescale shorter than its residence time (< 330 years). Neodymium and Be, in contrast, show isotopic variability between the basins. While the Sr isotope budget of the lake is largely consistent with observed riverine Sr fluxes, an unradiogenic Nd source is needed to explain lake Nd isotope compositions, especially in the Northern Basin. This source appears to derive from old crustal rocks in this part of the catchment and could be hydrothermal, or small rivers that were not sampled here. Similarly, elevated Be-10/Be-9 ratios in the lake basins relative to the river input imply variable but significant atmospheric inputs of Be-10 into the lake.Overall, this study demonstrates that records of the paleo-chemistry of lakes, and Lake Baikal in particular, hold promise for understanding denudation and weathering on the continents, in ways that are more directly relatable to the environmental conditions of the catchment than is possible with marine records. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Lake Baikal is the world’s largest (by volume), deepest, and oldest (30-40 Ma) lake. Climate varies from arid to semi-arid to arctic-boreal with extreme seasonal and spatial differences in temperature and precipitation 1 . The catchment has also been affected by periodic Quaternary glaciations 2 . Although the geology of the catchment is diverse, the most prominent lithologies are granitoids and gneisses 1 . Lake Baikal is therefore a promising site to study the effect of climate on silicate rock weathering. Here we present new insights into the modern weathering regime and, in anticipation of a paleo-weathering study, we evaluate how these weathering signals are transferred into the lake. Chemical weathering rates are higher in the northern part of the catchment, possibly due to the weathering of fine sediments produced during the last glaciation. Total denudation rates derived from dissolved riverine 10 Be/ 9 Be are, however, higher in the southern than in the northern river catchments, possibly due to more widespread permafrost 3 preventing soil erosion. For most rivers, Be-derived denudation rates exceed the summed estimates for chemical and physical erosion, pointing to the potential importance of sediment storage in floodplains. Preliminary results of an inverse model that apportions riverine dissolved loads to silicate, carbonate and evaporite weathering suggest that 74-94% of the Na flux and 19-42% of the total dissolved fluxes are derived from silicate weathering. From

Different cold-water coral (CWC) species harbour distinct microbial communities and the community composition is thought to be linked to the ecological strategies of the host. Here we test whether diet shapes the composition of bacterial communities associated with CWC. We compared the microbiomes of two common CWC species in aquaria, Lophelia pertusa and Madrepora oculata, when they were either starved, or fed respectively with a carnivorous diet, two different herbivorous diets, or a mix of the 3. We targeted both the standing stock (16S rDNA) and the active fraction (16S rRNA) of the bacterial communities and showed that in both species, the corals' microbiome was specific to the given diet. A part of the microbiome remained, however, species-specific, which indicates that the microbiome's plasticity is framed by the identity of the host. In addition, the storage lipid content of the coral tissue showed that different diets had different effects on the corals' metabolisms. The combined results suggest that L. pertusa may be preying preferentially on zooplankton while M. oculata may in addition use phytoplankton and detritus. The results cast a new light on coral microbiomes as they indicate that a portion of the CWC's bacterial community could represent a food influenced microbiome.

Atmospheric deposition of trace metals of natural or anthropogenic origin is an important input of micronutrients to the surface ocean. However, understanding its direct impact on oceanic element cycles is challenging due to scarce data, coupled to diverse aerosol sources and variable solubilities. Here, we present a dataset that combines Ni, Zn and Pb isotopes for samples from the Moroccan and Senegalese coasts and in the high latitude North Atlantic Ocean. We combine the new with published data for other circum-North Atlantic sources to assess the processes that determine the isotope signatures in different types of aerosols. We then use open marine aerosol data to investigate the impact of these signatures in the open ocean. Isotope analyses were conducted on bulk aerosols (TSP), on their ultra-high-purity water leachates, and on rainwaters. Aerosols characterized by crustal elemental abundances have isotope compositions similar to Saharan mineral dust. Mixing with anthropogenic aerosols from Europe/North Africa results in lower Pb-206/Pb-207 and Pb-208/Pb-207 values for the Eastern North Atlantic region. Higher Pb-206/Pb-207 at a given Pb-208/Pb-207, observed near the Canadian margin and occasionally at the Senegalese coast, points to anthropogenic inputs from North America. Based on trends in the aerosol data (e.g., delta Zn-66(JMC-Lyon) versus Pb-206/Pb-207, delta Ni-60(SRM986) versus Ni/V), we identify several anthropogenic sources of Zn and Ni. The delta Zn-66(JMC-Lyon) of low-temperature pollution (e.g., non-exhaust traffic emission) appears to be around -0.1 parts per thousand to 0.2 parts per thousand, while leachate delta Zn-66(JMC-Lyon) as low as -0.21 parts per thousand indicates contributions from high-temperature combustion or smelting processes. Among aerosols with good correlations between Ni and V, delta Ni-60(SRM986) > 0.40 parts per thousand traces Ni contributions from oil combustion. Other Ni-enriched sources, possibly originating from laterite or sulfide, show relatively low delta Ni-60(SRM986) (as low as -0.85 parts per thousand) and low V/Ni. Generally, aerosol sources for Zn are consistent throughout the North Atlantic, while Ni can be highly heterogenous. Combining the new data with literature elemental data, ratios of soluble Zn/Pb in anthropogenic aerosols are 1-100 times surface ocean ratios, suggesting that the low delta Zn-66(JMC-Lyon) observed in anthropogenic aerosol can be key in controlling the upper ocean Zn isotope composition. These aerosols have, however, much less significance for surface ocean Ni.

Lake Baikal is the world’s largest (by volume), deepest, and oldest (30-40 Ma) lake. In the catchment, climate varies from arid to semi-arid to arctic-boreal with extreme seasonal and spatial differences in temperature and precipitation1. Elevation ranges from 450-3000m, resulting in a large range of geomorphic settings. The catchment has also been affected by periodic Quaternary glaciations2. Although the geology of the catchment is diverse and contains igneous, metamorphic and sedimentary rocks of Archean to Cenozoic ages, the most prominent lithologies are granitoids and gneisses with only minor carbonate contributions1. Continuous lake sediment cores are available recording the Quaternary glacial cycles, and even dating back into the Miocene. Lake Baikal is therefore a promising site to study variation of silicate rock weathering in both space and time. In preparation for paleo-studies, we constrain the present-day budget of the lake with respect to radiogenic weathering tracers (Nd, Pb, and Sr) and meteoric 10Be/9Be isotope ratios. Nd, Sr, Pb, and their radiogenic isotope systems show different behaviors in Lake Baikal. Sr concentrations in the lake are similar to riverine inputs, reflecting conservative behavior of Sr and resulting in a uniform isotopic composition that is slightly higher than the average of riverine inputs (possibly due to loess inputs3). Pb concentrations are higher in the lake than in the major tributaries. The isotopic composition of both lake and rivers point to anthropogenic sources of Pb. In contrast, Nd concentrations in the lake are much lower than in the rivers. Nd isotopic compositions are similar in the central and southern basin but less radiogenic in the northern basin. Both 10Be and 9Be concentrations are much lower in Lake Baikal than in its tributaries, possibly indicating removal due to pH induced changes in dissolved-particulate partitioning4. This may also explain the contrast in Nd concentrations between rivers and the lake. 10Be/9Be ratios in the lake are slightly elevated compared to riverine inputs, suggesting a potential role for dust and/or precipitation as a source for 10Be5. We will also compare silicate weathering fluxes derived from meteoric Be isotope ratios with those derived from major element concentrations and riverine discharges. Taken together, these results highlight the importance of assessing modern processes at sediment core locations prior to interpreting variation in the past, and the benefits of using a suite of weathering proxies rather than relying on one: while Sr isotopes at any core location record changes to the chemistry of the whole lake (and the processes in its catchment), Be and Nd isotopes are likely biased to the inputs of the nearest rivers. 1. Zakharova et al. Chem. Geol. 214, 223–248 (2005). 2. Karabanov et al. Quat. Res. 50, 46–55 (1998). 3. Yokoo et al. Chem. Geol. 204, 45–62 (2004). 4. You et al. Chem. Geol. 77, 105–118 (1989). 5. Aldahan et al. Geophys. Res. Lett. 26, 2885–2888 (1999).

Removal of riverine trace elements from solution is well known for marine estuaries, resulting in dramatically lower concentration in seawater for elements like Fe, Mn, REEs, Al, and Be compared to rivers. Traditionally, this is often attributed to salinity induced coagulation and removal of colloidal matter and associated particle reactive elements1. Although Lake Baikal has a lower ionic strength than its tributaries, a similar drop in concentration from riverine values is observed for many of the same elements (like Fe, Mn, REEs, Al, Be, Cu, Y). Based on comparable Ce anomalies of lake surface waters and tributaries, the drop in concentration at the river-lake interface is mostly due to adsorption of solutes onto existing particulates. REE concentrations (as well as Fe, Mn, Be) in the lake also decrease with depth while Ce anomalies get more negative, indicating the ad-/absorption of REEs by newly formed authigenic FeMn phases2. The resulting short residence time of Nd in the lake leads to a non-uniform distribution of Nd isotopes. In contrast, Sr concentrations are similar in lake and rivers and Sr isotopes show a uniform distribution within the lake. The controlling parameter for the drop in concentrations of these trace elements across the river-lake interface appears to be pH, which is elevated in the lake (8.3-8.5 at the lake surface) compared to riverine values (7.8, flow weighted average). This finding is consistent with observed correlations between pH and the concentrations of some of these elements in river waters3. Together, these results call into question our understanding of the processes occurring in marine estuaries. Possibly, pH rather than salinity is also the dominant driver in the marine context.

Chemical weathering of silicate rock is one of the major long-term sinks of atmospheric CO2. While several radiogenic isotope systems (e.g. Nd, Pb, Os) in the authigenic component of marine sediments show temporal patterns that could be interpreted in terms of fluctuations in chemical weathering rate over glacial cycles, recent work using beryllium isotopes suggests little such variation. However, our knowledge of the sources of 9Be to the oceans is incomplete. Here, we address some of the gaps in knowledge with new data on Be in Croatian and Scottish rivers and estuaries, as well as with mixing experiments between Amazon tributaries and ocean water. The new data, combined with data from the literature, confirm that riverine Be is only marginally affected by carbonate weathering, which only accounts for 0.4–1.5% of dissolved riverine Be fluxes. The behavior of Be in estuaries is highly variable, with some estuaries showing removal and others addition. Based on the available data, about 55% of dissolved riverine Be is removed in estuaries, with complexation by both organic vs. inorganic ligands appearing to exert a strong control on the specific behavior in a given estuary. Beryllium complexation with organic material facilitates transport across estuaries, whereas the presence of inorganic complexants results in loss. Presence of both ligand types may lead to stronger non-conservative behavior than the presence of only one. Combining different approaches for estimating the dissolved riverine Be flux and estuarine removal, we calculate that 13–30% (4–48% error range) of the marine 9Be input is derived from riverine dissolved loads, and 70–87% (53–96% error range) from other sources like desorption from particulate matter and release from shelf sediments. It seems likely that this 13–30% of the marine Be input would respond quickly to changes in continental weathering rates, instantaneously impacting marine Be isotopes. However, the exact response of marine Be isotopes to changes in continental weathering rates also depends on the timescale of Be release from the riverine particulate pool stored in sediments on continental margins.

Ocean warming (OW), ocean acidification (OA) and their interaction with local drivers, e.g., copper pollution, may negatively affect macroalgae and their microscopic life stages. We evaluated meiospore development of the kelps Macrocystis pyrifera and Undaria pinnatifida exposed to a factorial combination of current and 2100-predicted temperature (12 and 16 °C, respectively), pH (8.16 and 7.65, respectively), and two copper levels (no-added-copper and species-specific germination Cu-EC50). Meiospore germination for both species declined by 5–18% under OA and ambient temperature/OA conditions, irrespective of copper exposure. Germling growth rate declined by >40%·day−1, and gametophyte development was inhibited under Cu-EC50 exposure, compared to the no-added-copper treatment, irrespective of pH and temperature. Following the removal of copper and 9-day recovery under respective pH and temperature treatments, germling growth rates increased by 8–18%·day−1. The exception was U. pinnatifida under OW/OA, where growth rate remained at 10%·day−1 before and after copper exposure. Copper-binding ligand concentrations were higher in copper-exposed cultures of both species, suggesting that ligands may act as a defence mechanism of kelp early life stages against copper toxicity. Our study demonstrated that copper pollution is more important than global climate drivers in controlling meiospore development in kelps as it disrupts the completion of their life cycle.

Four common consumer plastic samples (polyethylene, polystyrene, polyethylene terephthalate, polyvinylchloride) were studied to investigate the impact of physical parameters such as turbulence, salinity and UV irradiance on leaching behavior of selected plastic components. Polymers were exposed to two different salinities (i.e. 0 and 35 g/kg), UV radiation and turbulence. Additives (e.g. bisphenol A, phthalates, citrates, and Irgafos® 168 phosphate) and oligomers were detected in initial plastics and aqueous extracts. Identification and quantification was performed by GC-FID/MS. Bisphenol A and citrate based additives are leached easier compared to phthalates. The print highly contributed to the chemical burden of the analyzed polyethylene bag. The study underlines a positive relationship between turbulence and magnitude of leaching. Salinity had a minor impact that differs for each analyte. Global annual release of additives from assessed plastics into marine environments is estimated to be between 35 and 917 tons, of which most are derived from plasticized polyvinylchloride.