ALBERT

Description: In a widely‐held conception, the biological carbon pump (BCP) is equal to the export of organic matter out of the euphotic zone. Using global ocean‐atmosphere model experiments we show that the change in export production is a poor measure of the biological pump's feedback to the atmosphere. The change in global true oxygen utilization (TOU), an integrative measure of the imprint of the BCP on marine oxygen, however, is in good agreement with the net change in the biogenic air‐sea flux of oxygen. Since TOU correlates very well with apparent oxygen utilization (AOU) in our experiments, we propose to measure the change of AOU from data of global float programs to monitor the feedback of the BCP to the atmosphere. For the current ocean we estimate that BCP changes effect a CO2 uptake by the ocean in the range of 0.07 to 0.14 GtC/yr.

Description: Plain Language Summary: The biological carbon pump is an important element of marine carbon cycling and climate control on millennium timescales. In a widely‐held conception the export of organic carbon from the productive surface layer of the ocean is used as the essential measure of this carbon pump. Using numerical ocean modeling, we show here that the change in export production is, however, a poor measure of the biological carbon pump's feedback to the atmosphere on centennial timescales. In the contrary, we find that an oxygen‐based measure, the apparent oxygen utilization can be used to quantify the impact of biological pump changes on the atmosphere. Since the apparent oxygen utilization is easily accessible from an existing network of marine floats, our study suggests that the atmospheric impact of any future changes of the biological carbon pump can be monitored and quantified. For past decades our study proposes a negligible CO2 feedback to climate from biological carbon processing.

Description: Key Points: Apparent oxygen utilization is proposed to quantify the feedback of the biological carbon pump to the atmosphere in a warming ocean. Changes in export production are unrelated to changes in biotic oxygen air‐sea gas exchange. The CO2‐flux due to changes of the biological carbon pump over the recent decades is negligible compared to the total marine CO2 uptake.

Description: Deutsche Forschungsgemeinschat

Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Description: To monitor the success of carbon dioxide removal (CDR) or solar radiation management (SRM) that offset anthropogenic climate change, the forced response to any external forcing is required to be detectable against internal variability. Thus far, only the detectability of SRM has been examined using both a stationary and nonstationary detection and attribution method. Here, the spatiotemporal detectability of the forced response to artificial ocean alkalinization (AOA) and stratospheric aerosol injection (SAI) as exemplary methods for CDR and SRM, respectively, is compared in Max Planck Institute Earth System Model (MPI‐ESM) experiments using regularized optimal fingerprinting and single‐model estimates of internal variability, while working under a stationary or nonstationary null hypothesis. Although both experiments are forced by emissions according to the Representative Concentration Pathway 8.5 (RCP8.5) and target the climate of the RCP4.5 scenario using AOA or SAI, detection timescales reflect the fundamentally different forcing agents. Moreover, detectability timescales are sensitive to the choice of null hypothesis. Globally, changes in the CO2 system in seawater are detected earlier than the response in temperature to AOA but later in the case of SAI. Locally, the detection time scales depend on the physical, chemical, and radiative impacts of CDR and SRM forcing on the climate system, as well as patterns of internal variability, which is highlighted for oceanic heat and carbon storage.

Description: Key Points: Detectability is robust using regularized optimal fingerprinting and single‐model estimates of internal variability. Changes in the CO2 system in seawater are detected earlier than the thermodynamic response to AOA but later in the case of SAI. Local detectability depends on patterns of internal variability and physical, chemical, and radiative impacts of external forcing.

Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: Open access funding enabled and organized by Projekt DEAL.

Description: In soils and sediments, large amounts of total organic carbon (TOC) mark reducing conditions. As dark sediment colors are good predictors for high‐TOC zones, they indicate hot spots of biogeochemical turnover and microbial activity. Traditionally, obtaining the sediment color or TOC at depth requires costly core sampling, resulting in poor horizontal resolution and related uncertainty caused by interpolation. We suggest using a direct‐push tool for optical screening of the sediment color to acquire multiple high‐resolution vertical color profiles and demonstrate its applicability to a biogeochemical transition zone in floodplain sediments, dominated by tufa. We use Gaussian mixture models for a cluster analysis of 35 color logs in the International Commission on Illumination (CIE) L*a*b* color space to identify three colorfacies that differ in lithology and TOC content: a dark colorfacies that agrees well with peat layers, a gray colorfacies associated with clay, and a creamy‐brown facies made of autochthonous carbonate precipitates. We test different approaches either to infer the TOC content from color metrics, namely, the lightness and chroma, across all facies, or to identify TOC ranges for each colorfacies. Given the high variability in TOC due to organic carbon specks in the tufa, the latter approach appears more realistic. In our application we map the 3‐D distribution of organic matter in a floodplain in distinct facies over 20,000 m2 down to 12 m depth. While we relate the sediment color only to the TOC content, direct‐push color logging may also be used for in situ mapping of other biogeochemically relevant properties, such as the ferric‐iron content or sedimentary structure.

Description: Plain Language Summary: Geologists can say a lot about soils and loose materials in the ground by looking at their color. Dark materials normally contain dead plants, called organic carbon, which are food for bacteria and cause chemical reactions. To get the color of the soil, geologists normally need soil samples, but getting them from depth takes time and money. We test a method of pushing a camera into the ground and recording the color therein. From the recorded color we can say which type of geological material is at which depth and how much organic carbon is there without taking samples everywhere. This can be done very quickly, so that we can do it over a large area and down to the depth of the loose material in the ground, where most of the groundwater flows.

Description: Key Points: Direct‐push methods allow vertical in situ profiling of sediment color at high resolution. Cluster analysis reproducibly delineates colorfacies indicative of sedimentary units. Site‐specific relationships between color and TOC in sediments permit identifying biogeochemical hot spots.

Description: German Research Foundation (Deutsche Forschungsgemeinschaft, DFG)

Description: Organic micropollutants of anthropogenic origin in river waters may impair aquatic ecosystem health and drinking water quality. To evaluate micropollutant fate and turnover on a catchment scale, information on input source characteristics as well as spatial and temporal variability is required. The influence of tributaries from agricultural and urban areas and the input of wastewater were investigated by grab and Lagrangian sampling under base flow conditions within a 7.7‐km‐long stretch of the Ammer River (southwest Germany) using target screening for 83 organic micropollutants and 4 in vitro bioassays with environmentally relevant modes of action. In total, 9 pesticides and transformation products, 13 pharmaceuticals, and 6 industrial and household chemicals were detected. Further, aryl hydrocarbon receptor induction, peroxisome proliferator–activated receptor activity, estrogenicity, and oxidative stress response were measured in the river. The vast majority of the compounds and mixture effects were introduced by the effluent of a wastewater‐treatment plant, which contributed 50% of the total flow rate of the river on the sampling day. The tributaries contributed little to the overall load of organic micropollutants and mixture effects because of their relatively low discharge but showed a different chemical and toxicological pattern from the Ammer River, though a comparison to effect‐based trigger values pointed toward unacceptable surface water quality in the main stem and in some of the tributaries. Chemical analysis and in vitro bioassays covered different windows of analyte properties but reflected the same picture. Environ Toxicol Chem 2020;39:1382–1391. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: The combined algae test is a 96‐well plate‐based algal toxicity assay with the green algae Raphidocelis subcapitata that combines inhibition of 24‐h population growth rate with inhibition of photosynthesis detected after 2 and 24 h with pulse‐amplitude modulated (PAM) fluorometry using a Maxi‐Imaging PAM. The combined algae test has been in use for more than a decade but has had limitations due to incompatibilities of the measurements of the 2 biological endpoints on the same microtiter plates. These limitations could be overcome by increasing growth rates and doubling times on black, clear‐bottom 96‐well plates by application of dichromatic red/blue light‐emitting diode illumination. Different robotic dosing approaches and additional data evaluation methods helped to further expand the applicability domain of the assay. The combined algae test differentiates between nonspecifically acting compounds and photosynthesis inhibitors, such as photosystem II (PSII) herbicides. The PSII herbicides acted immediately on photosynthesis and showed growth rate inhibition at higher concentrations. If growth was a similar or more sensitive endpoint than photosynthesis inhibition, this was an indication that the tested chemical acted nonspecifically or that a mixture or a water sample was dominated by chemicals other than PSII herbicides acting on algal growth. We fingerprinted the effects of 45 chemicals on photosynthesis inhibition and growth rate and related the effects of the single compounds to designed mixtures of these chemicals detected in water samples and to the effects directly measured in water samples. Most of the observed effects in the water samples could be explained by known photosystem II inhibitors such as triazines and phenylurea herbicides. The improved setup of the combined algae test gave results consistent with those of the previous method but has lower costs, higher throughput, and higher precision. Environ Toxicol Chem 2020;39:2496–2508. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Description: The combined algae test (CAT) allows cost‐efficient high‐throughput monitoring of chemicals and water samples for their algae toxicity with a diagnostic component to differentiate between the mixture effects of photosynthesis inhibitors and other chemicals.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: A Jurassic negative carbon isotope excursion (CIE), co‐evolved with Toarcian Oceanic Anoxic Event (OAE) at ~183 Ma, is suggested to be linked to a global carbon‐cycle perturbation and is well documented for Toarcian terrestrial fossil woods and marine sediments around the globe. A theoretically coupled δ13Ccarb‐δ13Corg pattern due to such dubbed global carbon‐cycle event from the negative CIE in Dotternhausen Toarcian stratigraphic profile (southwest Germany) is unexpectedly disturbed by two‐step δ13Ccarb‐δ13Corg decoupling in which the last step, upper in the stratigraphic order, is of higher magnitude. However, the trigger(s) for these sudden decoupling disturbances are still poorly constrained. Here, connecting new carbon and oxygen isotope data with documentary lipid biomarkers shows that the global carbon cycle during the Toarcian OAE was disturbed by enhanced green sulfur bacteria (GSB) metabolisms and early diagenesis at local scales. The first step δ13Ccarb‐δ13Corg decoupling was induced in the initial stage of the GSB bloom. The second step of much larger δ13Ccarb‐δ13Corg decoupling arising from a GSB prosperity was, however, exaggerated by early diagenesis through the respiration of sulfate‐reducing bacteria (SRB). Paleo‐geographically distinct localities of the Tethys region show contrasting decoupled δ13Ccarb‐δ13Corg patterns, which implies that the second‐order carbon‐cycle perturbations have pervasively and independently impacted the global carbon event during the Toarcian OAE.

Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543

Description: Early marine diagenetic dolomite is a rather thermodynamically‐stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post‐depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ13C and δ18O isotopes, 87Sr/86Sr ratios, and U‐Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike‐slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric‐preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto‐Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high‐grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late‐stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years. Evidence for this preservation includes preserved Late Triassic seawater δ13CDIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically‐complex dolomite archives must be considered with caution.

Description: DFG http://dx.doi.org/10.13039/501100001659

Description: Amphistegina are common larger benthic foraminifer in coral reefs, with a nearly circumtropical distribution, and are major contributors to the CaCO3 budget of shallow marine environments. The family Amphisteginidae is dominant in Cenozoic carbonates. However, its potential as a proxy for paleoclimate reconstruction has not been completely explored. The intratest variability in trace elements of Amphistegina lessonii has been investigated using femtosecond‐laser ablation‐inductively coupled plasma‐mass spectrometry (fs‐LA‐ICP‐MS). We collected and analyzed adult specimens of A. lessonii in September 2003, November 2003, January 2004, and March 2004, from ∼2 m water depth in the coral reefs of Akajima, Okinawa, Japan. Tests of A. lessonii from these four collections were analyzed for Mg/Ca of the septa to observe Test Size‐Lifespan relationships. The lifespan of a specimen of A. lessonii of 1,200 µm in diameter is estimated at ∼3 and ∼2 months for specimens 900 µm in size. Over the estimated lifespans, Mg/Ca of individual specimens of A. lessonii is highly variable and displays co‐variation with temperature and tidal heights. Future projects may apply and further test this approach for the reconstruction of the tropical shallow marine paleoenvironments.

Description: Plain Language Summary: Larger Benthic Foraminifera (LBF) have slow growth rates and can be used as a proxy to reconstruct seasonal variations in temperature. Amphistegina, a common genus of LBF found within the Cenozoic era including the past 55 million years, was sampled across four seasons from a modern coral reef of Okinawa, Japan. The trace element concentrations in nine specimens of A. lessonii were measured using femtosecond LA‐ICP‐MS. The intratest variation in Mg/Ca covaried with tidal heights and seawater temperature, assuming the ages of the specimens to be 2–3 months. We provide a temperature calibration equation for A. lessonii for reconstructing paleotemperatures of shallow marine environments of the Cenozoic.

Description: Key Points: Specimens of Amphistegina lessonii sampled across 4 months from Akajima are used for calibration for Mg/Ca temperature using femtosecond‐laser ablation‐inductively coupled plasma‐mass spectrometry. The Mg/Ca along the septa of A. lessonii covaries with seawater temperature and tidal heights while Na/Ca and Sr/Ca show no correlation. Intratest variations in Mg/Ca of A. lessonii are affected by light intensity attenuation by sediment re‐suspension caused by tidal currents.

Description: The magnitude of future emissions of greenhouse gases from the northern permafrost region depends crucially on the mineralization of soil organic carbon (SOC) that has accumulated over millennia in these perennially frozen soils. Many recent studies have used radiocarbon (14C) to quantify the release of this “old” SOC as CO2 or CH4 to the atmosphere or as dissolved and particulate organic carbon (DOC and POC) to surface waters. We compiled ~1,900 14C measurements from 51 sites in the northern permafrost region to assess the vulnerability of thawing SOC in tundra, forest, peatland, lake, and river ecosystems. We found that growing season soil 14C‐CO2 emissions generally had a modern (post‐1950s) signature, but that well‐drained, oxic soils had increased CO2 emissions derived from older sources following recent thaw. The age of CO2 and CH4 emitted from lakes depended primarily on the age and quantity of SOC in sediments and on the mode of emission, and indicated substantial losses of previously frozen SOC from actively expanding thermokarst lakes. Increased fluvial export of aged DOC and POC occurred from sites where permafrost thaw caused soil thermal erosion. There was limited evidence supporting release of previously frozen SOC as CO2, CH4, and DOC from thawing peatlands with anoxic soils. This synthesis thus suggests widespread but not universal release of permafrost SOC following thaw. We show that different definitions of “old” sources among studies hamper the comparison of vulnerability of permafrost SOC across ecosystems and disturbances. We also highlight opportunities for future 14C studies in the permafrost region.

Description: Key Points: We compiled ~1,900 14C measurements of CO2, CH4, DOC, and POC from the northern permafrost region. Old carbon release increases in thawed oxic soils (CO2), thermokarst lakes (CH4 and CO2), and headwaters with thermal erosion (DOC and POC). Simultaneous and year‐long 14C analyses of CO2, CH4, DOC, and POC are needed to assess the vulnerability of permafrost carbon across ecosystems.

Description: EC | H2020 | H2020 Priority Excellent Science | H2020 European Research Council (ERC) http://dx.doi.org/10.13039/100010663

Description: Gouvernement du Canada | Natural Sciences and Engineering Research Council of Canada (NSERC) http://dx.doi.org/10.13039/501100000038

Description: National Science Foundation (NSF) http://dx.doi.org/10.13039/100000001

Description: We compared stable isotopes of water in plant stem (xylem) water and soil collected over a complete growing season from five well‐known long‐term study sites in northern/cold regions. These spanned a decreasing temperature gradient from Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf Creek (northern Canada). Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. The degree to which potential soil water sources could explain the isotopic composition of xylem water was assessed quantitatively using overlapping polygons to enclose respective data sets when plotted in dual isotope space. At most sites isotopes in xylem water from angiosperms showed a strong overlap with soil water; this was not the case for gymnosperms. In most cases, xylem water composition on a given sampling day could be better explained if soil water composition was considered over longer antecedent periods spanning many months. Xylem water at most sites was usually most dissimilar to soil water in drier summer months, although sites differed in the sequence of change. Open questions remain on why a significant proportion of isotopically depleted water in plant xylem cannot be explained by soil water sources, particularly for gymnosperms. It is recommended that future research focuses on the potential for fractionation to affect water uptake at the soil‐root interface, both through effects of exchange between the vapour and liquid phases of soil water and the effects of mycorrhizal interactions. Additionally, in cold regions, evaporation and diffusion of xylem water in winter may be an important process.

Description: We compared stable isotopes of water in plant stem (xylem) water and soil collected over a complete growing season from five well‐known long‐term study sites in northern/cold regions. Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. At all sites except one, water sources of angiosperms could be associated with soil water, while the sources of water uptake by gymnosperms were much less easily explained.

Description: FP7 Ideas: European Research Council http://dx.doi.org/10.13039/100011199

Description: KAW Branch‐Point project

Description: SITES (VR)

Description: Boise State University http://dx.doi.org/10.13039/100007233

Description: US National Science Foundation

Description: Leverhulme Trust through the ISO‐LAND project

Description: This bibliographic review gives an outline of publications in 2019 focusing on reference materials (RMs) used in geochemistry and related fields, such as palaeoclimate and environmental research.

Description: Key Points: Literature review for 2019 of 6850 geoanalytical publications. Geochemical, environmental, palaeoclimatic and isotopic reference materials. 691 selected articles with summaries of target analytes, and relevant reference materials and producers. image

Description: Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca10(PO4)6(F,Cl,OH)2 solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for 37Cl/35Cl homogeneity using SIMS followed by δ37Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10% (1s) for the five samples with 〉 0.5% m/m Cl and ± 0.19% (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38% between the mean 37Cl/35Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ37ClSMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 103δ37ClSMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.

Description: Key Points: Six apatite reference materials having various Cl mass fractions were characterised for chlorine isotope ratios by SIMS and three GS‐IRMS laboratories. A small, but significant, crystal orientation effect was recorded by SIMS analyses. Correlation of instrumental mass fractionation factor with Cl mass fraction is visible along the apatite solid solution series.

Description: Narodowe Centrum Nauki

Description: Deutscher Akademischer Austauschdienst

Description: Helmholtz Recruiting Initiative

Description: Institute of Geological Sciences, Polish Academy of Sciences

Description: Primary productivity of forest ecosystems depends on the availability of plant‐essential mineral nutrients. Because nutrient demand of trees often exceeds nutrient supply from rock, tree nutrition is sustained by efficient reutilization of organic‐bound nutrients. These nutrients are continuously returned from trees to the forest floor in litterfall. However, over millennia nutrient limitation may develop in landscapes from which nutrients are permanently lost by drainage and erosion. Such a deficit is prevented if advection of unweathered bedrock toward the surface as driven by erosion continuously supplies fresh nutrients. Yet the mechanisms and the depth range over which this deep nutrient resource is accessed are poorly known. We show that in two montane temperate forest ecosystems in the Black Forest and Bavarian Forest the geogenic source of nutrients was found within a depth zone of several meters. This deep zone contains a large pool of biologically available nutrients. We applied isotope ratios as proxies for nutrient uptake depth, and we tracked the regolith depth at which the isotope ratios of 87Sr/86Sr and 10Be(meteoric)/9Be match the respective values in plant tissue. We mapped the depth distribution of the biologically available calcium‐bound form of the most plant‐essential mineral nutrient phosphorus and found that the depth of phosphorus availability is as deep or even deeper as the range defined by the isotope ratios. We conclude that nutrient supply from a regolith depth of several meters is critical for forest ecosystem function in landscapes of moderate hillslopes and rainfall that are affected by permanent nutrient loss.

Description: Key Points: Combined 87Sr(radiogenic)/86Sr and 10Be(cosmogenic)/9Be isotope ratios were applied as proxies for mineral nutrient uptake depth. These systems suggest mineral nutrient uptake by Picea abies and Fagus sylvatica of 2 to 〉10 m depth. Potentially biologically available calcium phosphate is not available at a depth shallower than 3 m. Loss of mineral nutrients from the nutrient‐rich forest floor is balanced by mineral nutrient uptake from the deep saprolite.

Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: Browning caused by colored dissolved organic matter is predicted to have large effects on aquatic ecosystems. However, there is limited experimental evidence about direct and indirect effects of browning on zooplankton in complex field settings. We used a combination of an ecosystem‐scale enclosure experiment and laboratory incubations to test how prolonged browning affects physiological and life‐history traits of the water flea Daphnia longispina, a key species in lake food webs, and whether any such effects are reversible. Daphnids and water were collected from enclosures in a deep clear‐water lake, where the natural plankton community had been exposed for 10 weeks to browning or to control conditions in clear water. Daphnid abundance was much lower in the brown than in the clear enclosure. Surprisingly, however, daphnids continuously kept in brown enclosure water in the laboratory showed increased metabolic performance and survival, and also produced more offspring than daphnids kept in clear enclosure water. This outcome was related to more and higher‐quality seston in brown compared to clear water. Moreover, daphnids transferred from clear to brown water or vice versa adjusted their nucleic acid and protein contents, as indicators of physiological state, to similar levels as individuals previously exposed to the respective recipient environment, indicating immediate and reversible browning effects on metabolic performance. These results demonstrate the importance of conducting experiments in settings that capture both indirect effects (i.e., emerging from species interactions in communities) and direct effects on individuals for assessing impacts of browning and other environmental changes on lakes.

Description: German Federal Ministry of Education and Research

Description: German Research Foundation http://dx.doi.org/10.13039/501100001659

Description: IGB's Frontiers in Freshwater Science program

Description: Effect‐based trigger (EBT) values for in vitro bioassays are important for surface water quality monitoring because they define the threshold between acceptable and poor water quality. They have been derived for highly specific bioassays, such as hormone‐receptor activation in reporter gene bioassays, by reading across from existing chemical guideline values. This read‐across method is not easily applicable to bioassays indicative of adaptive stress responses, which are triggered by many different chemicals, and activation of nuclear receptors for xenobiotic metabolism, to which many chemicals bind with rather low specificity. We propose an alternative approach to define the EBT from the distribution of specificity ratios of all active chemicals. The specificity ratio is the ratio between the predicted baseline toxicity of a chemical in a given bioassay and its measured specific endpoint. Unlike many previous read‐across methods to derive EBTs, the proposed method accounts for mixture effects and includes all chemicals, not only high‐potency chemicals. The EBTs were derived from a cytotoxicity EBT that was defined as equivalent to 1% of cytotoxicity in a native surface water sample. The cytotoxicity EBT was scaled by the median of the log‐normal distribution of specificity ratios to derive the EBT for effects specific for each bioassay. We illustrate the new approach using the example of the AREc32 assay, indicative of the oxidative stress response, and 2 nuclear receptor assays targeting the peroxisome proliferator–activated receptor gamma and the arylhydrocarbon receptor. The EBTs were less conservative than previously proposed but were able to differentiate untreated and insufficiently treated wastewater from wastewater treatment plant effluent with secondary or tertiary treatment and surface water. Environ Toxicol Chem 2021;40:487–499. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Description: New effect‐based triggers were derived for bioassays that are responsive to many different chemicals with relatively low potency accounting for their mixture effects. AhR = arylhydrocarbon receptor; BEQ = bioanalytical equivalent concentration; EBT = effect‐based trigger; PPARγ = peroxisome proliferator–activated receptor gamma; SR = specificity ratio; WWTP = wastewater‐treatment plant.

Description: Global Water Research Coalition (GWRC)

Description: Lake sediments are valuable natural archives to reconstruct paleoclimate and paleoenvironmental changes which consist of inorganic and organic sediment compounds of allochthonous origin from the catchment and of autochthonous production in the lake. However, for robust paleo‐reconstructions it is important to develop a better understanding about sedimentation processes, the origin of inorganic and organic sediment compounds and their distribution within the lake. In this context, modern process studies provide important insights, although environmental and anthropological changes can affect the spatial distribution of sediment compounds through time. Therefore, in this study the spatial distribution of grain size and geochemical proxies in 52 surface sediment samples from Lake Khar Nuur, a small high‐altitude lake in the Mongolian Altai with a small and anthropogenically used hydrological catchment, is investigated. The results show a distinct sediment focussing in the two deep basins of the lake, which therefore act as accumulation zones. In those accumulation zones, total organic carbon (TOC), total nitrogen (N) and their isotopic composition (δ13CTOC, δ15N) as well as n‐alkanes indicate that organic sediment compounds are a mixture of both allochthonous and autochthonous origin. While the recent catchment vegetation consists of grasses/herbs and the shrub Betula nana (L.) with distinct differences in their n‐alkane homologue patterns, those differences are not reflected in the sediment surface samples which rather indicates that grass‐derived n‐alkanes become preferentially incorporated in the lake. Extensive anthropogenic activity such as grazing and housing in the southern part of the catchment causes soil erosion which is well reflected by high TOC, N and sulphur (S) contents and 15N depleted δ15N values at the central southern shore, i.e. increased allochthonous sediment input by anthropogenically‐induced soil erosion. Overall, the surface sediments of Lake Khar Nuur origin from allochthonous and autochthonous sources and are focussed in the accumulation zones of the lake, while their distribution is both environmentally and anthropogenically driven.

Description: Surface sediments of lake Khar Nuur show highest transport energies at the shore lines and point to sediment accumulation of terrestrial and aquatic compounds in the deepest parts. Anthropogenic activity and soil erosion in the catchment are suggested by enhanced terrestrial input.

Description: Mercury (Hg) is a toxic metal that accumulates in organisms and biomagnifies along food webs; hence, long‐lived predators such as seabirds are at risk as a result of high Hg bioaccumulation. Seabirds have been widely used to monitor the contamination of marine ecosystems. In the present study, we investigated Hg concentrations in blood, muscle, and feathers of 7 procellariform seabirds breeding on the Chatham Islands, New Zealand. Using bulk and compound‐specific stable isotope ratios of carbon and nitrogen as a proxy of trophic position and distribution, we also tested whether Hg contamination is related to the species‐specific feeding ecology. Mercury exposure varied widely within the seabird community. The highest contaminated species, the Magenta petrel, had approximately 29 times more Hg in its blood than the broad‐billed prion, and approximately 35 times more Hg in its feathers than the grey‐backed storm petrel. Variations of Hg concentrations in blood and feathers were significantly and positively linked to feeding habitats and trophic position, highlighting the occurrence of efficient Hg biomagnification processes along the food web. Species and feeding habitats were the 2 main drivers of Hg exposure within the seabird community. The Pterodroma species had high blood and feather Hg concentrations, which can be caused by their specific physiology and/or because of their foraging behavior during the interbreeding period (i.e., from the Tasman Sea to the Humboldt Current system). These 2 threatened species are at risk of suffering detrimental effects from Hg contamination and further studies are required to investigate potential negative impacts, especially on their reproduction capability. Environ Toxicol Chem 2021;40:454–472. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: Nitrogen (N) fertilization is the major contributor to nitrous oxide (N2O) emissions from agricultural soil, especially in post‐harvest seasons. This study was carried out to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size. A microcosm experiment was conducted with soil planted with perennial ryegrass (Lolium perenne L.) and bare soil, each with four levels of N fertilizer (0, 5, 10 and 20 g N m−2; applied as calcium ammonium nitrate). The closed‐chamber approach was used to measure soil N2O fluxes. Real‐time PCR was used to estimate the biomass of bacteria and fungi and the abundance of genes involved in denitrification in soil. The results showed that the presence of ryegrass decreased the nitrate content in soil. Cumulative N2O emissions of soil with grass were lower than in bare soil at 5 and 10 g N m−2. Fertilization levels did not affect the abundance of soil bacteria and fungi. Soil with grass showed greater abundances of bacteria and fungi, as well as microorganisms carrying narG, napA, nirK, nirS and nosZ clade I genes. It is concluded that ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions in soils with moderate or high NO3− concentrations. This highlights the importance of cover crops for the reduction of N2O emissions from soil, particularly following N fertilization. Future research should explore the full potential of ryegrass to reduce soil N2O emissions under field conditions as well as in different soils. Highlights This study was to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size; Plant reduced soil N substrates on one side, but their root exudates stimulated denitrification on the other side; N2O emissions were lower in soil with grass than bare soil at medium fertilizer levels, and growing grass stimulated the proliferation of almost all the denitrifying bacteria except nosZ clade II; Ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions.

Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543

Description: The National Science Project for University of Anhui Province

Description: The paper presents oxygen and hydrogen isotopes of 284 precipitation event samples systematically collected in Irkutsk, in the Baikal region (southeast Siberia), between June 2011 and April 2017. This is the first high‐resolution dataset of stable isotopes of precipitation from this poorly studied region of continental Asia, which has a high potential for isotope‐based palaeoclimate research. The dataset revealed distinct seasonal variations: relatively high δ18O (up to −4‰) and δD (up to −40‰) values characterize summer air masses, and lighter isotope composition (−41‰ for δ18O and −322‰ for δD) is characteristic of winter precipitation. Our results show that air temperature mainly affects the isotope composition of precipitation, and no significant correlations were obtained for precipitation amount and relative humidity. A new temperature dependence was established for weighted mean monthly precipitation: +0.50‰/°C (r2 = 0.83; p 〈.01; n = 55) for δ18O and +3.8‰/°C (r2 = 0.83, p 〈 0.01; n = 55) for δD. Secondary fractionation processes (e.g., contribution of recycled moisture) were identified mainly in summer from low d excess. Backward trajectories assessed with the Hybrid Single‐Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that precipitation with the lowest mean δ18O and δD values reaches Irkutsk in winter related to moisture transport from the Arctic. Precipitation originating from the west/southwest with the heaviest mean isotope composition reaches Irkutsk in summer, thus representing moisture transport across Eurasia. Generally, moisture transport from the west, that is, the Atlantic Ocean predominates throughout the year. A comparison of our new isotope dataset with simulation results using the European Centre/Hamburg version 5 (ECHAM5)‐wiso climate model reveals a good agreement of variations in δ18O (r2 = 0.87; p 〈.01; n = 55) and air temperature (r2 = 0.99; p 〈.01; n = 71). However, the ECHAM5‐wiso model fails to capture observed variations in d excess (r2 = 0.14; p 〈 0.01; n = 55). This disagreement can be partly explained by a model deficit of capturing regional hydrological processes associated with secondary moisture supply in summer.

Description: A long‐term precipitation stable isotope dataset covering every month of the year at least 3 times has been obtained for Irkutsk in southeast Siberia. Distinct seasonal variations are mainly due to changes in air temperature. A new reliable and representative temperature dependency was established for weighted mean monthly precipitation: +0.50‰/°C for δ18O and +3.8‰/°C for δD.

Description: BMBF http://dx.doi.org/10.13039/501100002347

Description: SSHRC http://dx.doi.org/10.13039/501100000155

Description: Ministry of Education and Science of the Russian Federation http://dx.doi.org/10.13039/501100003443

Description: N‐acyl homoserine lactones (AHLs) are molecules produced by many Gram‐negative bacteria as mediators of cell‐cell signaling in a mechanism known as quorum sensing (QS). QS is widespread in marine bacteria regulating diverse processes, such as virulence or excretion of polymers that mediate biofilm formation. Associated eukaryotes, such as microalgae, respond to these cues as well, leading to an intricate signaling network. To date, only very few studies attempted to measure AHL concentrations in phototrophic microbial communities, which are hot spots for bacteria‐bacteria as well as microalgae‐bacteria interactions. AHL quantification in environmental samples is challenging and requires a robust and reproducible sampling strategy. However, knowing about AHL concentrations opens up multiple perspectives from answering fundamental ecological questions to deriving guidelines for manipulation and control of biofilms. Here, we present a method for sampling and AHL identification and quantification from marine intertidal sediments. The use of contact cores for sediment sampling ensures reproducible sample surface area and volume at each location. Flash‐freezing of the samples with liquid nitrogen prevents enzymatic AHL degradation between sampling and extraction. After solvent extraction, samples were analyzed with an ultra‐high performance liquid chromatography‐high resolution mass spectrometry (UHPLC‐HRMS) method that allows to baseline‐separate 16 different AHLs in less than 10 min. The sensitivity of the method is sufficient for detection and quantification of AHLs in environmental samples of less than 16 cm3.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: H2020 Marie Skłodowska‐Curie Actions

Description: Mercury accumulation in lake sediments is a widespread environmental problem due to the biomagnification of Hg in the aquatic food chain. Soil Hg concentrations, catchment vegetation, erosion, and lake productivity are major factors controlling the accumulation of Hg in lakes. However, their influence on the Hg mass balance in lakes with different catchment characteristics and trophic state is poorly understood. In this multilake study, we decipher the effects of catchment vegetation (coniferous vs. deciduous forest), soil Hg content, and trophic state on Hg sedimentation at six lakes in Germany. We investigated Hg concentrations in leaves, soils, and the lake's water phase. Soils under coniferous stands show slightly higher Hg concentrations than under deciduous forest. Hg concentrations in the water phase were higher in the oligotrophic brown water lakes (8.1 ± 5.6 ng L−1 vs. 3.0 ± 1.9 ng L−1). Lower Hg concentrations in sediment trap material indicate dilution by algae organic matter in the mesotrophic lakes (0.12–0.17 μg g−1 vs. 0.57–0.89 μg g−1). However, Hg accumulation rates in sediment traps were up to 14‐fold higher in the mesotrophic lakes (113–443 μg m−2 yr−1) than in the brown water lakes (32–144 μg m−2 yr−1), which could not be explained by higher Hg fluxes to the productive lakes. Hg mass balance calculation reveals that water phase Hg scavenging by algae is the major reason for the intense Hg export to the sediments of productive lakes which makes them significantly larger sedimentary sinks than oligotrophic brown water lakes.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: As reverse weathering has been shown to impact long‐term changes in atmospheric CO2 levels, it is crucial to develop quantitative tools to reconstruct marine authigenic clay formation. We explored the potential of the beryllium (Be) isotope ratio (10Be/9Be) recorded in marine clay‐sized sediment to track neoformation of authigenic clays. The power of such proxy relies on the orders‐of‐magnitude difference in 10Be/9Be ratios between continental Be and Be dissolved in seawater. On marine sediments collected along a Chilean margin transect we chemically extracted reactive phases and separated the clay‐sized fraction to compare the riverine and marine 10Be/9Be ratio of this fraction. 10Be/9Be ratios increase fourfold from riverine to marine sediment. We attribute this increase to the incorporation of Be high in 10Be/9Be from dissolved biogenic opal, which also serves as a Si‐source for the precipitation of marine authigenic clays. 10Be/9Be ratios thus sensitively track reverse‐weathering reactions forming marine authigenic clays.

Description: Plain Language Summary: Clay minerals can form on land by the chemical breakdown of rock‐forming minerals, but clays can also form in the ocean. When clay formation takes place in the ocean, CO2 is released. To date, there is no method that can easily measure the amount of clay minerals formed in the ocean. We used two isotopes of the same element, beryllium (Be), with the atomic mass of 9 and 10 to test whether this isotope system can be used to measure marine clay formation. The abundance of these isotopes differs majorly on land and in the ocean. We measured beryllium isotopes in river sediment and ocean‐bottom sediment offshore the Chile coast and compared the ratios of the isotopes (10Be/9Be). The ratio is four times higher in ocean sediment, when compared to river sediment. We interpret this increase to be due to the formation of clay minerals in the ocean, which include the high 10Be/9Be ratio during their formation. We conclude that the beryllium‐isotope system can be used to measure the formation of even very small amounts (less than 2%) of marine clay minerals. This is important, as the clay‐forming chemical reactions release CO2 which has a long‐term effect on global climate.

Description: Key Points: We explored the potential of the beryllium isotope ratio to track neoformation of marine authigenic clays. Beryllium isotope ratios increase fourfold from riverine to marine sediment due to the presence of marine Be incorporated in authigenic clay. Beryllium isotope ratios sensitively track reverse‐weathering reactions forming marine authigenic clays.

Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: IPGP multidisciplinary program PARI and by Paris‐IdF region SESAME Grant 12015903

Description: The sulfur cycle is an important, although understudied facet of today's modern oxygen minimum zones (OMZs). Sulfur cycling is most active in highly productive coastal OMZs where sulfide‐rich sediments interact with the overlying water column, forming a tightly coupled benthic‐pelagic sulfur cycle. In such productive coastal systems, highly eutrophic and anoxic conditions can result in the benthic release of sulfide leading to an intensification of OMZ‐shelf biogeochemistry. Active blooms involving a succession of sulfide‐oxidizing bacteria detoxify sulfide and reduce nitrate to N2, while generating nitrite and ammonium that augment anammox and nitrification. Furthermore, the abiotic interactions of sulfide with trace metals may have the potential to moderate nitrous oxide emissions. While sulfide/sulfur accumulation events were previously considered to be rare, new evidence indicates that events can develop in OMZ shelf waters over prolonged periods of anoxia. The prevalence of these events has ramifications for nitrogen loss and greenhouse gas emissions, including other linked cycles involving carbon and phosphorous. Sulfur‐based metabolisms and activity also extend into the offshore OMZ as a result of particle microniches and lateral transport processes. Moreover, OMZ waters ubiquitously host a community of organosulfur‐based heterotrophs that ostensibly moderate the turnover of organic sulfur, offering an exciting avenue for future research. Our synthesis highlights the widespread distribution and multifaceted nature of the sulfur cycle in oceanic OMZs.

Description: European Research Council http://dx.doi.org/10.13039/100010663

Description: Natural Sciences and Engineering Research Council of Canada http://dx.doi.org/10.13039/501100000038

Description: Villum Foundation http://dx.doi.org/10.13039/100008398

Description: The Apollo 16 sample 66095, named “Rusty Rock”, is enriched in volatile and moderately volatile elements. The impact melt breccia is characterized by abundant Fe‐rich sulfide and chloride alteration phases, including FeS, ZnS, and FeCl2. These phases have previously been interpreted to be the result of fumarolic alteration of the breccia. Here we present the results of two different experimental approaches, which aim to constrain the temperature conditions and the process under which the “Rusty Rock” alteration formed. The first experimental set‐up assumes that the metals Zn, Cu, and Fe were introduced into the rock by a C‐O‐S‐Cl gas phase, and that the Fe‐rich sulfides and chlorides were deposited from this gas phase. This “gas deposition” experiment suggests that the alteration assemblage formed over the temperature range of 538–638 ± 5°C. The second experimental set‐up simulates a scenario, where Fe metal particles in the lunar rock react with a Zn‐C‐O‐S‐Cl gas phase at six different temperatures between 396 ± 5°C and 1,005 ± 5°C. This latter “metal reaction” experiment resulted in the formation of sulfide and chloride coatings on the Fe metal chips. The “Rusty Rock” alteration phases FeCl2 and (Zn,Fe)S were abundantly present in the coating of the Fe metal chip reacted at 580 ± 10°C. Both experiments lead to results which are in agreement, providing a temperature of 580 ± 50°C for the fumarolic alteration on the Moon, as observed in the Apollo 16 “Rusty Rock”.

Description: Plain Language Summary: The Apollo 16 sample 66095, colloquially named “Rusty Rock”, is an unusual lunar rock which is enriched in volatile elements such as sulfur and chlorine. We investigate two processes by which sulfides and chlorides may form in a lunar fumarolic system, by conducting experiments in evacuated silica glass tubes at reducing conditions. First, we assume that metals and volatiles (Zn, Cu, Fe, S, and Cl) are all deposited from a gas phase (gas deposition experiments), and second, we assume that Fe metal is already present in the rock and that the Fe altered by the introduction of a Zn‐S‐Cl‐bearing gas phase (metal reaction experiment). In both experimental setups we observe the formation of “Rusty Rock” alteration phases FeCl2 and (Zn, Fe)S at 580 ± 50°C, constraining the temperature of fumarolic alteration recorded in the Apollo 16 sample 66095. Hence, our experiments confirm that the characteristic S‐ and Cl‐rich minerals found in the lunar “Rusty Rock” were formed by a lunar fumarole. More broadly, lunar metal deposits may be associated with ancient fumarolic processes.

Description: Key points: Experiments constrain the temperature of fumarolic Apollo 16 “Rusty Rock” alteration to 580 ± 50°C. The phase assemblage of FeCl2 and (Zn,Fe)S constrains the composition of the fumarolic gas at 600°C. Gas deposition and gas‐solid metal reaction experiments reproduce the “Rusty Rock” alteration phases FeCl2 and (Zn, Fe)S.

Description: Swiss National Science Foundation

Description: Deutsche Forschungsgemeinschaft

Description: We present dissolved and total dissolvable trace elements for spring and summer cruises in 2010 in the high‐latitude North Atlantic. Surface and full depth data are provided for Al, Cd, Co, Cu, Mn, Ni, Pb, and Zn in the Iceland and Irminger Basins, and consequences of biological uptake and inputs by the spring Eyjafjallajökull volcanic eruption are assessed. Ash from Eyjafjallajökull resulted in pronounced increases in Al, Mn, and Zn in surface waters in close proximity to Iceland during the eruption, while 3 months later during the summer cruise levels had returned to more typical values for the region. The apparent seasonal removal ratios of surface trace elements were consistent with biological export. Assessment of supply of trace elements to the surface mixed layer for the region, excluding volcanic inputs, indicated that deep winter mixing was the dominant source, with diffusive mixing being a minor source (between 13.5% [dissolved Cd, DCd] and −2.43% [DZn] of deep winter flux), and atmospheric inputs being an important source only for DAl and DZn (DAl up to 42% and DZn up to 4.2% of deep winter + diffusive fluxes) and typically less than 1% for the other elements. Elemental supply ratios to the surface mixed layer through convection were comparable to apparent removal ratios we calculated between spring and summer. Given that deep mixing dominated nutrient and trace element supply to surface waters, predicted increases in water column stratification in this region may reduce supply, with potential consequences for primary production and the biological carbon pump.

Description: Key Points: Bio‐essential element concentrations in surface waters decreased from spring to summer with removal ratios reflecting biological uptake. Effects of volcanic inputs from Eyjafjallajökull in spring 2010 were pronounced for Al, Mn, and Zn but returned to typical levels in summer. Deep winter convection dominated trace element supply to surface waters with minor contributions from atmospheric and diffusive mixing.

Description: GEOMAR Helmholtz Centre for Ocean Research Kiel http://dx.doi.org/10.13039/501100003153

Description: Natural Environment Research Council http://dx.doi.org/10.13039/501100000270

Description: We present new geochemical and isotopic data for rock samples from two island arc volcanoes, Erromango and Vulcan Seamount, and from a 500 m thick stratigraphic profile of lava flows exposed on the SW flank of Vate Trough back-arc rift of the New Hebrides Island Arc (NHIA). The basalts from the SW rift flank of Vate Trough have ages of ~0.5 Ma but are geochemically similar to those erupting along the active back-arc rift. The weak subduction component in the back-arc basalts implies formation by decompression melting during early rifting and rifting initiation by tectonic processes rather than by lithosphere weakening by arc magma. Melting beneath Vate Trough is probably caused by chemically heterogeneous and hot mantle that flows in from the North Fiji Basin in the east. The melting zone beneath Vate Trough back-arc is separate from that of the arc front, but a weak slab component suggests fluid transport from the slab. Immobile incompatible element ratios in South NHIA lavas overlap with those of the Vate Trough depleted back-arc basalts, suggesting that enriched mantle components are depleted by back-arc melting during mantle flow. The slab component varies from hydrous melts of subducted sediments in the Central NHIA to fluids from altered basalts in the South NHIA. The volcanism of Erromango shows constant compositions for 5 million years, that is, there is no sign for variable depletion of the mantle or for a change of slab components due to collision of the D'Entrecasteaux Ridge as in lava successions further north.

Description: Soil water stable isotopes are widely used across disciplines (e.g., hydrology, ecology, soil science, and biogeochemistry). However, the full potential of stables isotopes as a tool for characterizing the origin, flow path, transport processes and residence times of water in different eco-, hydro-, and geological compartments has not yet been exploited. This is mainly due to the large variety of different methods for pore water extraction. While recent work has shown that matric potential affects the equilibrium fractionation, little work has examined how different water retention characteristics might affect the sampled water isotopic composition. Here, we present a simple laboratory experiment with two well-studied standard soils differing in their physico-chemical properties (e.g., clayey loam and silty sand). Samples were sieved, oven-dried and spiked with water of known isotopic composition to full saturation. For investigating the effect of water retention characteristics on the extracted water isotopic composition, we used pressure extractors to sample isotopically labelled soil water along the pF curve. After pressure extraction, we further extracted the soil samples via cryogenic vacuum extraction. The null hypothesis guiding our work was that water held at different tensions shows the same isotopic composition. Our results showed that the sampled soil water differed isotopically from the introduced isotopic label over time and sequentially along the pF curve. Our and previous studies suggest caution in interpreting isotope results of extracted soil water and a need to better characterize processes that govern isotope fractionation with respect to soil water retention characteristics. In the future, knowledge about soil water retention characteristics with respect to soil water isotopic composition could be applied to predict soil water fractionation effects under natural and non-stationary conditions. In this regard, isotope retention characteristics as an analog to water retention characteristics have been proposed as a way forward since matric potential affects the equilibrium fractionation between the bound water and the water vapour.

Description: An extensive data set of biogenic silica (BSi) fluxes is presented for the Peruvian oxygen minimum zone (OMZ) at 11°S and 12°S. Each transect extends from the shelf to the upper slope (∼1,000 m) and dissects the permanently anoxic waters between ∼200 and 500 m water depth. BSi burial (2,100 mmol m−2 yr−1) and recycling fluxes (3,300 mmol m−2 yr−1) were highest on the shelf with mean preservation efficiencies (34% ± 15%) that exceed the global mean of 10%–20%. BSi preservation was highest on the inner shelf (up to 56%), decreasing to 7% and 12% under anoxic waters and below the OMZ, respectively. The data suggest that the main control on BSi preservation is the rate at which reactive BSi is transported away from undersaturated surface sediments by burial and bioturbation to the underlying saturated sediment layers where BSi dissolution is thermodynamically and/or kinetically inhibited. BSi burial across the entire Peruvian margin between 3°S to 15°S and down to 1,000 m water depth is estimated to be 0.1–0.2 Tmol yr−1; equivalent to 2%–7% of total burial on continental margins. Existing global data permit a simple relationship between BSi rain rate to the seafloor and the accumulation of unaltered BSi, giving the possibility to reconstruct rain rates and primary production from the sediment archive in addition to benthic Si turnover in global models.

Description: Key Points: Biogenic silica (BSi) preservation is high on the shelf and low under predominantly anoxic bottom waters BSi burial across the Peruvian margin down to 1,000 m water depth accounts for up to 7% of the global burial on continental margins Existing global data permit a simple relationship between BSi accumulation and rain rate

Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: Radiogenic lead (Pb) and neodymium (Nd) isotope compositions extracted from authigenic phases in marine sediments are sensitive tracers to reconstruct past ocean circulation and water mass mixing. Chemical reductive leaching of hydrogenetic ferromanganese oxyhydroxides from bulk sediments is the most practical way to recover past seawater Pb and Nd isotope signatures in the Southern Ocean, due to the scarcity of alternative archives. However, the leached signal could be compromised if substantial quantities of Pb and Nd were released from non‐hydrogenetic sediment fractions during chemical extraction. Here we developed a very short 10‐s leaching method to extract reliable seawater Pb and Nd isotope signals from sediments in the Atlantic sector of Southern Ocean. The effect of a previously recommended MgCl2 pre‐wash, the role of chelate ligands in the leaching solution and length of leaching time were investigated. The results show that 10‐s exposure time of sediments to reductive leaching extracted sufficient and more reliable hydrogenetic Pb and Nd compared with the commonly used 30‐min leaching approaches. The robustness of our improved leaching method was validated via direct comparison of Pb and Nd isotope signatures with actual seawater, porewater, and corresponding sediment leachates from three stations in front of the Antarctic Filchner‐Rønne Ice Shelf. Our findings also indicate that in contrast previously studied sites on the West Antarctic continental shelf, the bottom seawater Nd concentration is less elevated through benthic fluxes in the area of the southern Weddell Sea shelf.

Description: Plain Language Summary: Individual modern ocean water masses can often be identified by the isotopic signature of dissolved trace metals lead (Pb) and neodymium (Nd) supplied from surrounding continents. By analyzing past seawater Pb and Nd isotope ratios preserved in the sedimentary archives, we can understand how the ocean circulation changed. In the Southern Ocean, archives preserving past seawater Pb and Nd isotope compositions are very scarce. Thus, the chemical extraction of Pb and Nd from seawater‐derived ferromanganese oxyhydroxides within deep marine sediments becomes the most practical way to recover past seawater signal. However, Southern Ocean sediments commonly contain substantial quantities of Antarctic continental fine‐grained sediment, which easily partially dissolve during extraction, thereby releasing Pb and Nd, which did not originate from past ambient seawater. Here we established a gentle and efficient extraction method to obtain reliable past Southern Ocean seawater signatures. In addition, via analysis of regional seawater‐derived Pb and Nd signatures in the Atlantic sector of Southern Ocean, we found that the sediments further away from Antarctica and volcanically active regions are better suited to preserve unaltered seawater Pb and Nd isotope signals, which strongly supports the unique possibility of tracing past water mass sourcing in the Southern Ocean with our analytical approach.

Description: Key Points: 10‐s reductive leaching is capable of reliably extracting seawater Pb and Nd isotope signals from Southern Ocean sediments. Natural porewater Pb isotopic compositions are analyzed for the first time in front of the Antarctic Filchner‐Rønne Ice Shelf. Identify potential sites for extracting seawater Pb and Nd isotopic signatures from bulk sediments in the Atlantic sector of Southern Ocean.

Description: China Scholarship Council (CSC)

Description: The precise determination of radium‐226 (226Ra) in environmental samples is challenging due to its low concentration. Seawater typically contains between 0.03 and 0.1 fg g−1 226Ra. Thus, this work addresses the need for an easy and precise methodology for 226Ra determination in seawater that may be applied routinely to a large number of samples. For this reason, a new analytical approach has been developed for the quantification of 226Ra in seawater via inductively coupled plasma mass spectrometry (ICP‐MS). Analysis by single collector sector‐field ICP‐MS was shown to be convenient and reliable for this purpose once potential molecular interferences were excluded by a combination of chemical separation and intermediate mass resolution analysis. The proposed method allows purification of Ra from the sample matrix based on preconcentration by MnO2 precipitation, followed by two‐column separation using a cation exchange resin and an extraction chromatographic resin. The method can be applied to acidified and unacidified seawater samples. The recovery efficiency for Ra ranged between 90% and 99.8%, with precision of 5%, accuracy of 95.7% to 99.9%, and a detection limit of 0.033 fg g−1 (referring to the original concentration of seawater). The method has been applied to measure 226Ra concentrations from the North Sea and validated by analyzing samples from the central Arctic (GEOTRACES GN04). Samples from a crossover station (from GEOTRACES GN04 and GEOTRACES GN01 research cruises) were analyzed using alternative methods, and our results are in good agreement with published values.

Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318

Description: Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re-homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe-rich basalt and the enrichment in LILE and U suggest a subduction-related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene-bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so-called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high-grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T-7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal-derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.

Description: Three synthetic reference glasses were prepared by directly fusing and stirring 3.8 kg of high-purity oxide powders to provide reference materials for microanalytical work. These glasses have andesitic major compositions and are doped with fifty-four trace elements in nearly identical abundance (500, 50, 5 µg g−1) using oxide powders or element solutions, and are named ARM-1, 2 and 3, respectively. We further document that sector-field (SF) ICP-MS (Element 2 or Element XR) is capable of sweeping seventy-seven isotopes (from 7Li to 238U, a total of sixty-eight elements) in 1 s and, thus, is able to quantify up to sixty-eight elements by laser sampling. Micro- and bulk analyses indicate that the glasses are homogeneous with respect to major and trace elements. This paper provides preliminary data for the ARM glasses using a variety of analytical techniques (EPMA, XRF, ICP-OES, ICP-MS, LA-Q-ICP-MS and LA-SF-ICP-MS) performed in ten laboratories. Discrepancies in the data of V, Cr, Ni and Tl exist, mainly caused by analytical limitations. Preliminary reference and information values for fifty-six elements were calculated with uncertainties [2 relative standard error (RSE)] estimated in the range of 1–20%.

Description: Basalts are ubiquitous in volcanic systems on several planetary bodies, including the Earth, Mars, Venus, and Jupiter's moon Io, and are commonly associated with sulfur dioxide (SO2) degassing. We present the results of an experimental study of reactions between SO2 and basaltic glasses. We examined Fe-free basalt, and Fe-bearing tholeiitic and alkali basalts with a range of Fe3+/Fetotal (0.05 to 0.79) that encompass the oxygen fugacities proposed for most terrestrial planetary bodies. Tholeiitic and alkali basalts were exposed to SO2 at 600, 700, and 800 °C for 1 hr and 24 hr. Surface coatings formed on the reacted basalts; these contain CaSO4, MgSO4, Na2SO4, Na2Ca(SO4)2, Fe2O3, Fe3O4, Fe-Ti-(Al)-oxides, and TiO2. Additionally, the SO2-basalt reaction drives nucleation of crystalline phases in the substrate to form pyroxenes and possible Fe-oxides. A silica-rich layer forms between the substrate and sulfate coatings. More oxidized basalts may readily react with SO2 to form coatings dominated by large Ca-sulfate and oxide grains. On less oxidized basalts (NNO−1.5 to NNO−5), reactions with SO2 will form thin, fine-grained aggregates of sulfates; such materials are less readily detected by spectroscopy and spectrometry techniques. In contrast, in very reduced basalts (lower than NNO−5), typical of the Moon and Mercury, SO2 is typically a negligible component in the magmatic gas, and sulfides are more likely.

Description: Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum (schorl 112566, dravite 108796 and elbaite 98144), which are already widely used for the calibration of in situ boron isotope measurements, are characterised here for their oxygen and lithium isotope compositions. Homogeneity tests by secondary ion mass spectrometry (SIMS) showed that at sub‐nanogram test portion masses, their 18O/16O and 7Li/6Li isotope ratios are constant within ± 0.27‰ and ± 2.2‰ (1s), respectively. The lithium mass fractions of the three materials vary over three orders of magnitude. SIMS homogeneity tests showed variations in 7Li/28Si between 8% and 14% (1s), which provides a measure of the heterogeneity of the Li contents in these three materials. Here, we provide recommended values for δ18O, Δ’17O and δ7Li for the three Harvard tourmaline reference materials based on results from bulk mineral analyses from multiple, independent laboratories using laser‐ and stepwise fluorination gas mass spectrometry (for O), and solution multi‐collector inductively coupled plasma‐mass spectroscopy (for Li). These bulk data also allow us to assess the degree of inter‐laboratory bias that might be present in such data sets. This work also re‐evaluates the major element chemical composition of the materials by electron probe microanalysis and investigates these presence of a chemical matrix effect on SIMS instrumental mass fractionation with regard to δ18O determinations, which was found to be 〈 1.6‰ between these three materials. The final table presented here provides a summary of the isotope ratio values that we have determined for these three materials. Depending on their starting mass, either 128 or 512 splits have been produced of each material, assuring their availability for many years into the future.

Description: Key Points: Three widely available tourmaline reference materials are characterized for δ7Li, δ17O and δ18O, while new EPMA and SIMS measurements refine their major element compositions. SIMS data document homogeneity for these isotope ratios. SIMS matrix effect causes bias of 1.9‰ between elbaite and schorl, whereas silicate glass shows even more severe bias.

Description: U.S. National Science Foundation

Description: Natural Environment Research Council http://dx.doi.org/10.13039/501100000270

Description: US Department of Energy http://dx.doi.org/10.13039/100000015

Description: The present study aims to estimate effective diahaline turbulent salinity fluxes and diffusivities in numerical model simulations of estuarine scenarios. The underlying method is based on a quantification of salinity mixing per salinity class, which is shown to be twice the turbulent salinity transport across the respective isohaline. Using this relation, the recently derived universal law of estuarine mixing, predicting that average mixing per salinity class is twice the respective salinity times the river run‐off, can be directly derived. The turbulent salinity transport is accurately decomposed into physical (due to the turbulence closure) and numerical (due to truncation errors of the salinity advection scheme) contributions. The effective diahaline diffusivity representative for a salinity class and an estuarine region results as the ratio of the diahaline turbulent salinity transport and the respective (negative) salinity gradient, both integrated over the isohaline area in that region and averaged over a specified period. With this approach, the physical (or numerical) diffusivities are calculated as half of the product of physical (or numerical) mixing and the isohaline volume, divided by the square of the isohaline area. The method for accurately calculating physical and numerical diahaline diffusivities is tested and demonstrated for a three‐dimensional idealized exponential estuary. As a major product of this study, maps of the spatial distribution of the effective diahaline diffusivities are shown for the model estuary.

Description: Plain Language Summary: Eddy diffusivity determines how intensively concentrations in a fluid are spreading due to turbulent motion. Here, we analyze the diffusivity that spreads salt concentration (i.e., salinity) across a surface of constant salinity (the isohalines), also called effective diahaline diffusivity. A new method is presented that calculates effective diahaline diffusivities based on the specific volume between two specified isohalines, on the salinity mixing within this volume as well as on the surface area of the isohalines. We define mixing as the rate of destruction of salinity variance per unit volume due to turbulent mixing processes. The method applies to computer models of ocean dynamics on scales ranging from coastal to global. In such models, the mixing is determined by statistical mathematical equations of turbulent processes, which is the so‐called physical mixing. In models, additional (numerical) mixing occurs due to numerical inaccuracies of algorithms that move around water masses passively with the currents, a process called advection. Using our method, the total effective diffusivity determined for each isohaline surface can be accurately separated into contributions from physical mixing and numerical mixing. We demonstrate the functioning of the new method for an idealized model simulation of an estuary.

Description: Key Points: Mixing and volume per salinity class determine effective diahaline diffusivity. Effective diahaline diffusivity is split into physical and numerical contributions. In an idealized estuary, largest effective diffusivities are found in the brackish waters of the navigational channel.

Description: Corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production dominate Midwestern U.S. agriculture and impact the regional carbon and nitrogen cycles. Sustaining soil carbon is important for corn‐soybean production (CS); however, quantifying soil carbon changes requires long‐term field measurements and/or model simulations. In this study, changes in soil organic (SOC), inorganic (SIC), and total (TC) carbon; pH; total nitrogen (TN); and net ecosystem production (NEP) were measured in a conventional corn‐soybean rotation in central Iowa. Soil samples (n = 42; 0–120 cm depth) were collected from two adjacent fields in 2005 and 2016. Eddy‐flux stations set up in the fields continuously monitored NEP from 2005–2016, and net biome production (NBP) was calculated using yield records. The DayCENT model was used to simulate the effects of conventional management practices on soil carbon and calibrated with field‐measured NEP and SOC. Measured soil TC (0–120 cm) decreased by −14.19 ± 6.25 Mg ha−1, with highest reductions in SOC and SIC (p 〈 0.05) at 0–15 and 90–120 cm, respectively. Measured TN decreased by −0.7 ± 0.29 Mg ha−1 with N‐accumulation at 60–90 cm (p 〈 0.05). Eddy‐flux NBP decreased by −13.19 ± 0.05 Mg ha−1. Soil and eddy‐flux records show a carbon reduction by −1.14 ± 0.63 and −1.20 ± 0.06 Mg ha−1 yr−1, respectively. The validated DayCENT model suggests that all SOC pools declined. We postulate that conventional CS production has adverse effects on C and N dynamics in Midwestern United States.

Description: Key Points: Eddy covariance shows a decrease in ecosystem C after 11 yr of corn‐soybean production. Soil inorganic C decreased in 90–120 cm, and organic C decreased in 0–15 cm after 11 yr. DayCENT simulations suggest current conventional corn‐soybean rotations decrease all SOC pools in topsoil layer.

Description: ORISE http://dx.doi.org/10.13039/100006229

Description: Sustainable arable cropping relies on repeated liming. Yet, the associated increase in soil pH can reduce the availability of iron (Fe) to plants. We hypothesized that repeated liming, but not pedogenic processes such as lessivage (i.e., translocation of clay particles), alters the Fe cycle in Luvisol soil, thereby affecting Fe isotope composition in soils and crops. Hence, we analysed Fe concentrations and isotope compositions in soil profiles and winter rye from the long‐term agricultural experimental site in Berlin‐Dahlem, Germany, where a controlled liming trial with three field replicates per treatment has been conducted on Albic Luvisols since 1923. Heterogeneity in subsoil was observed at this site for Fe concentration but not for Fe isotope composition. Lessivage had not affected Fe isotope composition in the soil profiles. The results also showed that almost 100 years of liming lowered the concentration of the HCl‐extractable Fe that was potentially available for plant uptake in the surface soil (0–15 cm) from 1.03 (standard error (SE) 0.03) to 0.94 (SE 0.01) g kg−1. This HCl‐extractable Fe pool contained isotopically lighter Fe (δ56Fe = −0.05 to −0.29‰) than the bulk soil (δ56Fe = −0.08 to 0.08‰). However, its Fe isotope composition was not altered by the long‐term lime application. Liming resulted in relatively lower Fe concentrations in the roots of winter rye. In addition, liming led to a heavier Fe isotope composition of the whole plants compared with those grown in the non‐limed plots (δ56FeWholePlant_ + Lime = −0.12‰, SE 0.03 vs. δ56FeWholePlant_‐Lime = −0.21‰, SE 0.01). This suggests that the elevated soil pH (increased by one unit due to liming) promoted the Fe uptake strategy through complexation of Fe(III) from the rhizosphere, which favoured heavier Fe isotopes. Overall, the present study showed that liming and a related increase in pH did not affect the Fe isotope compositions of the soil, but may influence the Fe isotope composition of plants grown in the soil if they alter their Fe uptake strategy upon the change of Fe availability. Highlights Fe concentrations and stocks, but not Fe isotope compositions, were more heterogeneous in subsoil than in topsoil. Translocation of clay minerals did not result in Fe isotope fractionation in the soil profile of a Luvisol. Liming decreased Fe availability in topsoil, but did not affect its δ56Fe values. Uptake of heavier Fe isotopes by graminaceous crops was more pronounced at elevated pH.

Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Description: Spreading centers in the proximity of back‐rolling subduction zones constitute an ideal natural laboratory to investigate the interaction of magmatism and tectonism during the early evolution of back‐arc basins. Using 32 days of ocean bottom seismometer data, we located 697 micro‐earthquakes at the southern Fonualei Rift and Spreading Center (S‐FRSC). The majority of epicenters concentrate along the central region of the axial valley, marking the active ridge axis. Only odd events were associated with the prominent faults bounding the axial valley. About 450 events are spatially clustered around 17°42′S and their waveforms show a pronounced similarity. Most of these events are associated with a 138 h lasting earthquake swarm. The tectonic structure of the ridge axis in the S‐FRSC resembles a series of left‐stepping en echelon segments, expressed at the seafloor by numerous volcanic ridges. The recorded earthquake swarm is located at the stepover of two en echelon segments suggesting that the earthquake swarm is mainly tectonically driven. The events directly beneath our seismic network indicate a maximum depth of brittle faulting down to about 14 km below the seafloor. This is within the maximum depth range of brittle faulting at ultraslow mid‐ocean ridges. Since the thickness of the brittle lithosphere is mainly controlled by temperature, our results suggest a sub‐axial thermal structure similar to that of ultraslow mid‐ocean ridges of similar opening rates.

Description: Key Points: Microseismicity is focused in the axial valley along the spreading axis and coincides with volcanic ridges and lava flows. An earthquake swarm is located at the stepover of two en echelon segments. The swarm is mainly controlled by tectonism. The brittle axial lithosphere is about 14 km thick, which is in agreement with mid‐ocean ridges of similar spreading rates.

Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347

Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347

Description: GEOMAR Helmholtz‐Zentrum für Ozeanforschung Kiel http://dx.doi.org/10.13039/501100003153

Description: Serpentinization environments are key locations that support microbial communities by the abiogenic formation of reduced species associated with peridotite alteration. Here we studied partially serpentinized peridotites from the Chimaera seeps (Turkey), an active continental serpentinization system that vents highly methane‐rich fluids, to investigate the impact of water‐rock interaction on the sulfide and metal mineralogy and its implications on supporting microbial communities. Using high‐resolution scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy we found diverse pentlandite decomposition features with precipitation of secondary sulfides including millerite, heazlewoodite, as well as Cu‐bearing sulfides, native Cu, and awaruite (Ni3Fe). Awaruite forms dense veinlets to single crystal platelets tens of nanometers in size, which is formed by desulphurization of pentlandite. In addition, the nanometer‐sized awaruite platelets are intimately intergrown with serpentine suggesting its growth during peridotite alteration by a dissolution‐precipitation process, likely associated with the interaction of methane‐ and H2‐rich but highly sulfur‐undersaturated fluids. Based on sulfur isotope signatures we infer a mantle and mid‐ocean ridge origin of the sulfide minerals associated with the first stage of partial serpentinization and awaruite formation. Subsequent and ongoing continental fluid‐rock interaction causes significant sulfide decomposition resulting in the formation of porosity and the release of, amongst others, H2S and Fe. These species may likely provide a source of nutrients for active microbial communities in these comparatively nutrient‐starved, low‐temperature continental serpentinization environments.

Description: Key Points: High disequilibrium conditions induce skeletal awaruite growth during continental serpentinization. Pentlandite dissolution creates fluid pathways and nutrients for microbial life. Sulfur isotope compositions document ocean floor and subsequent continental serpentinization processes.

Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: European Research Council (ERC)

Description: The lunar meteorite Dhofar 1436 is dominated by solar wind type noble gases. Solar argon is equilibrated with “parentless” 40Ar commonly known as lunar orphan argon. Ar‐Ar isochron analyses determined the lunar trapped 40Ar/36Ar ratio to 2.51 ± 0.04, yielding a corrected plateau age of 4.1 ± 0.1 Ga, consistent with the lunar Late Heavy Bombardment period. Lunar trapped and radiogenic argon components are all released at high temperatures (1200–1400 °C). Surprisingly, solar noble gases and lunar trapped argon can largely be released by crushing. Initial crushing steps mainly release elementally fractionated solar wind gases, while in advanced crushing steps, cosmogenic components dominate. Cosmogenic noble gases indicate irradiation at the lunar surface; they are less fractionated than solar wind species. We favor a scenario in which both solar and a large fraction of cosmogenic gases were acquired before the 4.1 Ga event, which caused shock metamorphism and formation of the regolith breccia. Sintering and agglutination along grain boundaries resulted in mobilization of solar wind, reimplanted, radiogenic, and cosmogenic noble gases, and resulted in their partial homogenization, fractionation, and retrapping in voids and/or defects accessible by crushing. An alternative scenario would be complete reset of the K‐Ar system 4.1 Ga ago accompanied by loss of all previously accumulated solar and cosmogenic noble gases. Later, the precursor of Dhofar 1436 became lunar regolith and accumulated solar and cosmogenic noble gases and reimplanted 40Ar before its final formation of the polymict impact breccia. The C abundance of the step‐combusted Dhofar 1436 is 555.3 ppm, with δ13C of −28‰ to +11‰. Nitrogen contents released by crushing and combustion are 3.2 ppm and 20.8 ppm, respectively. The lightest nitrogen composition (δ15N = −79‰) is likely due to release from voids of shock metamorphic phases and is rather a result of the mobilization of nitrogen components that accumulated prior to the 4.1 Ga event.

Description: Klaus Tschira Stiftung http://dx.doi.org/10.13039/501100007316

Description: The in situ measurement of Sr isotopes in carbonates by MC-ICP-MS is limited by the availability of suitable microanalytical reference materials (RMs), which match the samples of interest. Whereas several well-characterised carbonate reference materials for Sr mass fractions 〉 1000 µg g−1 are available, there is a lack of well-characterised carbonate microanalytical RMs with lower Sr mass fractions. Here, we present a new synthetic carbonate nanopowder RM with a Sr mass fraction of ca. 500 µg g−1 suitable for microanalytical Sr isotope research (‘NanoSr’). NanoSr was analysed by both solution-based and in situ techniques. Element mass fractions were determined using EPMA (Ca mass fraction), as well as laser ablation and solution ICP-MS in different laboratories. The 87Sr/86Sr ratio was determined by well-established bulk methods for Sr isotope measurements and is 0.70756 ± 0.00003 (2s). The Sr isotope microhomogeneity of the material was determined by LA-MC-ICP-MS, which resulted in 87Sr/86Sr ratios of 0.70753 ± 0.00007 (2s) and 0.70757 ± 0.00006 (2s), respectively, in agreement with the solution data within uncertainties. Thus, this new reference material is well suited to monitor and correct microanalytical Sr isotope measurements of low-Sr, low-REE carbonate samples. NanoSr is available from the corresponding author.

Description: The continuous improvement of analytical procedures using multi-collector technologies in ICP-mass spectrometry has led to an increased demand for isotope standards with improved homogeneity and reduced measurement uncertainty. For magnesium, this has led to a variety of available standards with different quality levels ranging from artefact standards to isotope reference materials certified for absolute isotope ratios. This required an intercalibration of all standards and reference materials, which we present in this interlaboratory comparison study. The materials Cambridge1, DSM3, ERM-AE143, ERM-AE144, ERM-AE145, IRMM-009 and NIST SRM 980 were cross-calibrated with expanded measurement uncertainties (95% confidence level) of less than 0.030‰ for the δ25/24Mg values and less than 0.037‰ for the δ26/24Mg values. Thus, comparability of all magnesium isotope delta (δ) measurements based on these standards and reference materials is established. Further, ERM-AE143 anchors all magnesium δ-scales to absolute isotope ratios and therefore establishes SI traceability, here traceability to the SI base unit mole. This applies especially to the DSM3 scale, which is proposed to be maintained. With ERM-AE144 and ERM-AE145, which are product and educt of a sublimation–condensation process, for the first time a set of isotope reference materials is available with a published value for the apparent triple isotope fractionation exponent θapp, the fractionation relationship ln α(25/24Mg)/ln α(26/24Mg).

Description: In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01–0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95–99% local chemical loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozonesonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93% at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96% loss). The reason for the unprecedented chemical loss was an unusually strong, long-lasting, and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone-depleting substances on ozone depletion may be counteracted by low temperatures.

Description: Micron-sized HNO3-containing particles in polar stratospheric clouds are known to denitrify the polar winter stratosphere and support chemical ozone loss. We show that populations of nitric acid trihydrate (NAT) particles with volume-equivalent median radii of 3–7 μm can be detected vortex-wide by means of infrared limb sounding. Key for detection are the applied optical characteristics of highly aspherical particles consisting of the β-NAT phase. Spectroscopic signatures and ambient conditions of detected populations show that these particles play a key role in denitrification of the Arctic winter stratosphere. Complementary gas-phase HNO3 observations indicate collocated highly efficient HNO3 sequestration within days and are consistent with measured spectral signals of populations of large NAT particles. High amounts of condensed gas-phase equivalent HNO3 exceeding 10 ppbv and long persistence of detected populations, despite expected gravitational settling, imply that our understanding of the particles is incomplete.

Description: The Global Carbon Budget 2018 (GCB2018) estimated by the atmospheric CO 2 growth rate, fossil fuel emissions, and modeled (bottom-up) land and ocean fluxes cannot be fully closed, leading to a “budget imbalance,” highlighting uncertainties in GCB components. However, no systematic analysis has been performed on which regions or processes contribute to this term. To obtain deeper insight on the sources of uncertainty in global and regional carbon budgets, we analyzed differences in Net Biome Productivity (NBP) for all possible combinations of bottom-up and top-down data sets in GCB2018: (i) 16 dynamic global vegetation models (DGVMs), and (ii) 5 atmospheric inversions that match the atmospheric CO 2 growth rate. We find that the global mismatch between the two ensembles matches well the GCB2018 budget imbalance, with Brazil, Southeast Asia, and Oceania as the largest contributors. Differences between DGVMs dominate global mismatches, while at regional scale differences between inversions contribute the most to uncertainty. At both global and regional scales, disagreement on NBP interannual variability between the two approaches explains a large fraction of differences. We attribute this mismatch to distinct responses to El Niño–Southern Oscillation variability between DGVMs and inversions and to uncertainties in land use change emissions, especially in South America and Southeast Asia. We identify key needs to reduce uncertainty in carbon budgets: reducing uncertainty in atmospheric inversions (e.g., through more observations in the tropics) and in land use change fluxes, including more land use processes and evaluating land use transitions (e.g., using high-resolution remote-sensing), and, finally, improving tropical hydroecological processes and fire representation within DGVMs.

Description: During seawater circulation in permeable intertidal sands, organic matter degradation alters the composition of percolating fluids and remineralization products discharge into surficial waters. Concurrently, coastal seawater nutrient and organic matter composition change seasonally due to variations in pelagic productivity. To assess seasonal changes in organic matter degradation in the intertidal zone of a high energy beach (Spiekeroog Island, southern North Sea, Germany), we analyzed shallow pore waters for major redox constituents (oxygen [O2], manganese [Mn], and iron [Fe]) and inorganic nitrogen species (nitrite [NO2−], nitrate [NO3−], and ammonium [NH4+]) in March, August, and October. Surface water samples from a local time series station were used to monitor seasonal changes in pelagic productivity. O2 and NO3− were the dominating pore water constituents in March and October. Dissolved Mn, Fe, and NH4+ were more widely distributed in August. Seasonal changes in seawater temperature as well as organic matter and nitrate supply by seawater were assumed to affect microbial rates and degradation pathways. Pore water and seawater variability led to seasonally changing constituent effluxes to surface waters. Mn, Fe, and NH4+ effluxes are minimal in March and reached their maximum in August. Furthermore, the intertidal sands switched from a net dissolved inorganic nitrogen sink in March to a net source in August. In conclusion, seasonal effects on intertidal pore water biogeochemistry affect constituent fluxes across the sediment-water interface. The seasonality of the beach bioreactor must be considered when fluxes are extrapolated to annual timescales.

Description: A geoarchaeological soil phosphorus (P) prospection is used to identify a gate within the prehistoric rampart of the Milseburg hillfort (Hesse, Germany). This study compares the application of a P fractionation scheme and P extraction with ammonium-oxalate. We hypothesized that oxalate-extractable P (P-ox) and the related degree of P saturation (DPS) could replace the more expensive and time-consuming fractionation schemes for geoarchaeological investigations. Comparing the results, the P fractionation helped to verify the existence of another section of the prehistoric ramparts and to identify the location of a gate within it. It also helped to discover the archaeologically relevant soil depths in the investigated area. This information could not be retrieved from the P-ox data alone. Soil P-ox contents and DPS values are relatively unspecific with regard to prehistoric land use. However, DPS at least indicates settled versus unsettled areas. Still, the results of the P fractionation more clearly delineate Iron Age land use areas including settlement, non-settlement, rampart, and rampart gap (probable gate). Thus, in geoarchaeological contexts, this method seems to be preferable to a singular P-ox extraction. However, for better results, P-ox determination could be integrated into a P fractionation scheme.

Description: Riparian zones are important buffer zones for streams as they are hotspots of nitrate transformation and removal in agricultural catchments. However, mixing of water from different sources and various transformation processes can complicate the quantification of nitrate turnover in riparian zones. In this study, we analyzed nitrate concentration and isotope data in riparian groundwater along a 2-km stream section in central Germany. We developed a mathematical model combining end-member mixing and isotope modeling to account for mixing of river water and groundwater and quantify nitrate transformation in riparian groundwater. This enabled us to explicitly determine the extent of denitrification (as process leading to permanent nitrate removal from riparian groundwater) and transient nitrate removal by additional processes associated with negligible isotope fractionation (e.g., plant uptake and microbial assimilation) and to perform an extensive uncertainty analysis. Based on the nitrogen isotope data of nitrate, the simulations suggest a mean removal of up to 27% by additional processes and only about 12% by denitrification. Nitrate removal from riparian groundwater by additional processes exceeded denitrification particularly in winter and at larger distance from the river, underlining the role of the river as organic carbon source. This highlights that nitrate consumption by additional processes predominates at the field site, implying that a substantial fraction of agricultural nitrogen input is not permanently removed but rather retained in the riparian zone. Overall, our model represents a useful tool to better compare nitrogen retention to permanent nitrogen removal in riparian zones at various temporal and spatial scales.

Description: Emissions of the potent greenhouse gas methane (CH4) from streams and rivers are a significant component of global freshwater methane emissions. The distribution of CH4 production and oxidation within stream sections and in vertical sediment profiles is not well understood, and the environmental controls on CH4 production and emission in such systems create a significant challenge for assessing larger-scale dynamics. Here we investigate factors driving the spatial variability of sediment potential methane production (PMP) and potential methane oxidation (PMO) in a temperate stream network in Germany. PMP was highly variable, ranging from 5 × 10−4 to 28.58 μg CH4 gDW−1 d−1 and PMO ranged from 0.43 μg CH4 gDW−1 d−1 to 14.41 μg CH4 gDW−1 d−1. Important drivers of spatial variability of PMP and PMO in the sediments of the stream main-stem were related to fine sediment fraction and organic carbon content. At smaller spatial scale, that is, in a sub-catchment stream section, the drivers were more complex and included sediment nitrogen and organic carbon content, as well as porewater dissolved organic carbon, dissolved organic matter quality, and metal concentrations. As with reservoirs and impounded rivers, fine sediment deposition and organic carbon content were found to be key controls on the spatial variability of CH4 production and oxidation. These findings enhance our understanding of CH4 dynamics, improve the potential for identifying CH4 production hotspots in small streams, and provide a potential means for upscaling emission rates in larger-scale assessments.

Description: Separate evaluation of methane (CH4) emission dynamics (e.g., oxidation, production, and transportation) at the soil-plant-atmosphere and soil-water-atmosphere interfaces has been limited in tropical rice paddies, but it is crucial for comprehending the entire CH4 cycles. We investigated CH4 oxidation, production, and transportation through plant and water pathways during the reproductive stage in a tropical Thailand rice paddy field using natural abundance carbon stable isotope ratios (δ13CH4 and δ13CO2). Mass balance equations using δ13CH4 and δ13CO2 in soil gases indicated that CH4 oxidation in the planted soil exceeded those in the interrow soil due to oxygen supply through rice roots. In addition, at 1–11 cm depth acetate fermentation was the dominant process in the planted soil, whereas in the interrow soil the dominant process was H2/CO2 reduction. The water pathway showed a significant negative correlation between CH4 flux and released δ13CH4 over 24 hr, driven by a diel change in episodic ebullition, steady ebullition, and diffusion, all due to diel changes in soil temperature and atmospheric pressure. In contrast, the plant pathway showed a significant positive relationship between CH4 flux and emitted δ13CH4 throughout one day. A comparison of the diel change in emitted δ13CH4 between the water and plant pathways showed that the rice plants transported CH4 in soil bubbles without any large isotopic fractionation. The diel change in the plant-mediated CH4 transportation was mainly controlled by diel changes in soil bubble expansion and CH4 diffusion through plants, which were probably regulated by diel changes in soil temperature and atmospheric pressure.

Description: Equilibrium passive sampling methods (EPSMs) allow quantification of freely dissolved contaminant concentrations (Cfree) in sediment porewater. Polydimethylsiloxane (PDMS) is a convenient sampling polymer that can be equilibrated in field (in situ) or laboratory (ex situ) sediments to determine Cfree, providing reliable compound‐specific PDMS–water partition coefficients (KPDMS‐water) are available. Polycyclic aromatic hydrocarbons (PAHs) are an important class of sediment contaminants comprised of parent and alkylated homologs. However, application of EPSM to alkylated PAHs is challenged by lack of KPDMS‐water measurements. Our first objective was to obtain KPDMS‐water for 9 alkylated PAHs and biphenyls using 3 different PDMS‐coated fibers. Quantitative relationships were then established to define KPDMS‐water for 18 parent and 16 alkyl PAHs included in the US Environmental Protection Agency's sediment quality benchmark method for benthic life protection based on additive toxic units. The second objective was to compare Cfree in porewater obtained using both in situ and ex situ EPSMs at 6 Baltic Sea locations. The results indicated that in situ and ex situ Cfree for alkyl PAHs generally agreed within a factor of 3. Further, all sites exhibited additive toxic units 〈1, indicating that PAHs pose a low risk to benthos. The results extend practical application of EPSMs for improved risk assessment and derivation of porewater‐based remediation goals for PAH‐contaminated sediments. Environ Toxicol Chem 2020;39:2169–2179. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Description: Bulk sediment δ15N records from the eastern tropical Pacific (ETP) extending back to the last ice age most often show low glacial δ15N, then a deglacial δ15N maximum, followed by a gradual decline to a late Holocene δ15N that is typically higher than that of the Last Glacial Maximum (LGM). The lower δ15N of the LGM has been interpreted to reflect an ice age reduction in water column denitrification. We report foraminifera shell‐bound nitrogen isotope (FB‐δ15N) measurements for the two species Neogloboquadrina dutertrei and Neogloboquadrina incompta over the last 35 ka in two sediment cores from the eastern equatorial Pacific (EEP), both of which have the typical LGM‐to‐Holocene increase in bulk sediment δ15N. FB‐δ15N contrasts with bulk sediment δ15N by not indicating a lower δ15N during the LGM. Instead, the FB‐δ15N records are dominated by a deglacial δ15N maximum, with comparable LGM and Holocene values. The lower LGM δ15N of the bulk sediment records may be an artifact, possibly related to greater exogenous N inputs and/or weaker sedimentary diagenesis during the LGM. The new data raise the possibility that the previously inferred glacial reduction in ETP water column denitrification was incorrect. A review of reconstructed ice age conditions and geochemical box model output provides mechanistic support for this possibility. However, equatorial ocean circulation and nitrate‐rich surface water overlying both core sites allow for other possible interpretations, calling for replication at non‐equatorial ETP sites.

Description: Plain Language Summary: The 15N/14N ratio of sediments provides information on the past marine nitrogen (N) cycle through the production of N‐bearing organic matter in the surface ocean and its burial in the sediments. Previous measurements of the sedimentary 15N/14N ratio in the eastern equatorial Pacific (EEP) indicate lower values during the last ice age compared to the Holocene (the current warm period). This has been interpreted to reflect an ice age reduction in the oceanic N loss process known as “denitrification” that occurs between 200 and 500 m depth in this region of the ocean. However, the 15N/14N ratio measured on the whole sediment can be biased by biological and chemical processes in the sediments and by foreign N inputs. To avoid these complications, we measured the 15N/14N ratio of organic N embedded in the calcite shell of unicellular zooplankton (foraminifera) in two sediment cores from the EEP. We found similar foraminifera‐bound 15N/14N ratios during the last ice and the Holocene. This may argue against the long‐held interpretation of a reduction in denitrification during the last ice age. However, the oceanographic setting of these equatorial cores leaves open alternative interpretations, calling for further work at other eastern tropical Pacific sites.

Description: Key Points: Foraminifera‐bound δ15N was similar during the last ice age and the Holocene in the eastern equatorial Pacific, unlike bulk sedimentary δ15N. Bulk sediment δ15N is likely biased to lower ice age values by foreign N inputs and weaker sedimentary diagenesis. The foraminifera‐bound δ15N data may reflect that water column denitrification was not reduced during the last glacial period.

Description: Swiss National Science Foundation

Description: US National Science Foundation

Description: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung http://dx.doi.org/10.13039/501100001711

Description: National Science Foundation http://dx.doi.org/10.13039/100000001

Description: The oxidation of dimethyl sulfide (DMS) is key for the natural sulfate aerosol formation and its climate impact. Multiphase chemistry is an important oxidation pathway but neglected in current chemistry‐climate models. Here, the DMS chemistry in the aerosol‐chemistry‐climate model ECHAM‐HAMMOZ is extended to include multiphase methane sulfonic acid (MSA) formation in deliquesced aerosol particles, parameterized by reactive uptake. First simulations agree well with observed gas‐phase MSA concentrations. The implemented formation pathways are quantified to contribute up to 60% to the sulfate aerosol burden over the Southern Ocean and Arctic/Antarctic regions. While globally the impact on the aerosol radiative forcing almost levels off, a significantly more positive solar radiative forcing of up to +0.1 W m−2 is computed in the Arctic (〉60°N). The findings imply the need of both further laboratory and model studies on the atmospheric multiphase oxidation of DMS.

Description: Plain Language Summary: The emission of dimethyl sulfide (DMS) represents the largest natural reduced sulfur source into the atmosphere. There, DMS can be oxidized to sulfur dioxide, sulfuric acid, or methane sulfonic acid modifying the radiative properties of aerosol particles and clouds. DMS oxidation is represented in chemistry‐climate models by a limited number of very simplified reactions. Small changes in the parameter settings can have large effects, that's why these should be as accurate as possible. In this study, the DMS chemistry in ECHAM‐HAMMOZ was upgraded. Sensitivity simulations show variations in the natural aerosol radiative forcing due to the different schemes tested in this study. Further laboratory and process studies with models are therefore essential.

Description: Key Points: Dimethyl sulfide (DMS) chemistry in chemistry‐climate simulations extended by multiphase methane sulfonic acid (MSA) formation provides more realistic MSA gas‐phase concentrations. Formation of MSA is very sensitive toward reactive uptake on deliquesced aerosol particles. In the Arctic, the extended DMS chemistry leads to a significantly less negative effective radiative forcing of sulfate aerosol.

Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: The worldwide recognition of the Toarcian carbon isotope excursion (T‐CIE) in organic‐rich sedimentary rocks has been linked to an oceanic anoxic event (OAE) which implies the world's deep oceans were anoxic ∼183 Ma. The majority of independent redox observations used to build this argument were mainly obtained from T‐CIE organic‐rich sediments deposited on northern European epicontinental shelf. However, increasing evidence has shown that this shelf had limited connection with the open ocean, making it unsuitable for reconstructing the T‐CIE ocean redox structure. To unveil such controversy, we present integrated δ15Nbulk and δ15Nker from Dotternhausen profile, Germany, combined with literature data from other T‐CIE profiles. Both δ15Nbulk and δ15Nker values are predominantly between +0.3 and +2.5‰. These positive near‐zero δ15N values imply enhanced N2 fixation by cyanobacteria using molybdenum (Mo)‐based nitrogenase to compensate bioavailable N loss following quantitative denitrification and/or anammox in a strongly redox‐stratified marine setting. Such N isotope composition contradicts the typical sedimentary δ15N values (〉3‰) induced by partial water‐column denitrification and/or anammox in modern‐ocean oxygen minimum zones. We rather propose the existence of local oxygen‐deficient basins on northern European epicontinental shelf where dissolved N underwent extensive denitrification and/or anammox causing bioavailable N deficiency. Mo‐based diazotrophy thus played a critical role in discriminating N isotope compositions among multiple hydrographically restricted T‐CIE marginal basins. Restricted oxygen‐depleted environments on the northern European epicontinental shelf unlikely represent the open‐ocean redox landscape. The existence of the global OAE thus needs comprehensive redox investigations on Tethys and/or Panthalassa deep‐sea T‐CIE successions to validate.

Description: Key Points: Molybdenum‐based nitrogen fixation was prevalent in the northern European epicontinental shelf during the Toarcian carbon isotope excursion. Quantitative denitrification and/or anammox caused nitrogen famine in strongly redox‐stratified environments during the early Toarcian. Oxygen‐deficient basins on the northern European epicontinental shelf across the Toarcian carbon isotope excursion.

Description: China Scholarship Council (CSC) http://dx.doi.org/10.13039/501100004543

Description: German Research Foundation

Description: Organic carbon (OC) in inland waters is found in either dissolved or particulate states, each contributing differently to carbon cycling through state‐specific forms of transport, processing, and mineralization. Degradation of macroscopic organic material into solutes is the most common transition between these states, yet there is also the potential for dissolved organic carbon to aggregate and form particles. This latter process at the soil‐stream interface is subject of a new study by Einarsdóttir et al. (2020, https://doi.org/10.1029/2020JG005654) published in this issue. Their findings advance the understanding of the links between the dissolved and the particulate domain of OC with possible implication for long‐term OC burial and ecosystem functioning of inland waters.

Description: Plain Language Summary: Lakes and rivers are influenced by their surrounding landscape: Dead biomass releases water‐soluble, organic substances that can be washed into surface waters. There, the organic substances are either removed by microorganisms or sunlight, or transported to the oceans. Under some conditions, water‐soluble substances stick together and form particles. Particles are no longer transported and sink to the bottom of lakes and rivers, where they can remain for a long time. Recent research, some of it featured in this issue of Journal of Geophysical Research: Biogeosciences, describes how the organic particles are formed. The involved mechanisms influence the important role of lakes and rivers in the global cycle of carbon.

Description: Key Points: Dissolved organic carbon is the dominant form of biomass in inland waters but various processes trigger its aggregation to particles. The role of organic particles in the global carbon cycle is discussed in context of a recent manuscript published in Journal of Geophysical Research: Biogeosciences.

Description: Neodymium (Nd) isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance. To better constrain the controls of water mass provenance and nonconservative effects on the archived Nd isotope signal, we present a new depth transect of Nd isotope reconstructions from the Blake Bahama Outer Ridge along the North American continental margin covering the past 30 ka. We investigated five sediment cores that lie directly within the main flow path of the Deep Western Boundary Current, a major advection route of North Atlantic Deep Water. We found offsets between core tops and seawater Nd isotopic compositions that are observed elsewhere in the Northwest Atlantic. A possible explanation for this is the earlier suggested redistribution of sediment by nepheloid layers at intermediate as well as abyssal depths, transporting material downslope and along the continental margin. These processes potentially contributed to Nd isotope excursions recorded in Northwest Atlantic sediment cores during the Bølling-Allerød and early Holocene. An Atlantic-wide comparison of Nd isotope records shows that the early Holocene excursions had an additional contribution from conservative advection of unradiogenic dissolved Nd. Nevertheless, the trends of the Nd isotope records are in general agreement with previous reconstructions of water mass provenance from the entire Atlantic and also reveal millennial-scale changes during the last deglaciation in temporal high resolution, which have rarely been reported before. Further, the new records confirm that during cold periods the Northwest Atlantic was bathed by an increased contribution of southern sourced water.

Description: Methane (CH4) production in the ocean surface mixed layer is a widespread but still largely unexplained phenomenon. In this context marine algae have recently been described as a possible source of CH4 in surface waters. In the present study we investigated the effects of temperature and light intensity (including daylength) on CH4 formation from three widespread marine algal species Emiliania huxleyi, Phaeocystis globosa, and Chrysochromulina sp. Rates of E. huxleyi increased by 210% when temperature increased in a range from 10°C to 21.5°C, while a further increase in temperature (up to 23.8°C) showed reduction of CH4 production rates. Our results clearly showed that CH4 formation of E. huxleyi is controlled by light: When light intensity increased from 30 to 2,670 μmol m−2 s−1, CH4 emission rates increased continuously by almost 1 order of magnitude and was more than 1 order of magnitude higher when the daylength (light period) was extended from 6/18 hr light-dark cycle to continuous light. Furthermore, light intensity is also an important factor controlling CH4 emissions of Chrysochromulina sp. and P. globosa and could therefore be a species-independent regulator of phytoplankton CH4 production. Based on our results, we might conclude that extensive blooms of E. huxleyi could act as a main regional source of CH4 in surface water, since blooming of E. huxleyi is related to the seasonal increase in both light and temperature, which also stimulate CH4 production. Under typical global change scenarios, E. huxleyi will increase its CH4 production in the future.

Description: Zur Ermittlung von geochemischen "proximity indicators" für den erzhöffigen (oberen) Abschnitt des Alpinen Muschelkalks wurden 11 Probennahmeprofile aus den Nördlichen Kalkalpen sowie als Vergleich 2 Probennahmeprofile aus den Südlichen Kalkalpen bearbeitet. Die Probennahme erfolgte in annähernd homogenen Gesteinsserien systematisch, in inhomogenen oberen und mittleren Partien des Alpinen Muschelkalks auch (fazies-) differenziert. Aus insgesamt ca. 1750 Schichtmetern wurden 652 Proben zur geochemischen Analyse aufbereitet. Die Bestimmung des Mg- und der Spurenelementgehalte von Sr, Zn, Pb, Fe, Mn, Cu und Cr erfolgten mit einem Atom-Absorptionsspektrophotometer (AAS). Die Fluoranalyse geschah mit ionenselektiven Elektroden (potentiometrische Fluoridbestimmung). Der Anteil der unlöslichen Rückstände wurde gravimetrisch ermittelt und fallweise mit Hilfe eines Roentgendiffraktometers näher untersucht. Die Auswertung der ca. 10 600 Analysendaten erfolgte über EDV. Mit Hilfe von Rechenprogrammen wurden Ca-Gehalte, Korrelationskoeffizienten, geometrische Mittelwerte und Streuungen ermittelt. Ober die konventionelle Statistik der geochemischen Analysendaten mit Ermittlung r e g i o n a l e r Background- und Threshold-Daten hinaus wurden zusätzlich l o k a l e Background- und Threshold-Werte festgestel1t, um die l o k a l e n Anomalien der als regional repräsentativ angenommenen Profile herauszuarbeiten und vergleichbar zu machen. Die Obergrenze des Alpinen Muschelkalks mußte nach konventionellen lithologischen Gesichtspunkten angenommen werden. Eine genauere stratigraphische Korrelierung der Probennahmeprofile war jedoch durch Tuff-Lagen (Pietra verde) möglich, soweit diese aufgeschlossen waren. Korrelationsrechnungen gaben Hinweise auf die Bindung der einzelnen Elemente sowie ihre primäre und sekundäre Anreicherung im Sediment. Die Hauptelemente Ca und Mg stammen vorherrschend aus dem Calcit- und Dolomitanteil. Säureunlösliche Rück stände setzen sich neben Quarz hauptsächlich aus Tonmineralen der Illit-Gruppe (mixed layers) zusammen. Sr-Gehalte sind eindeutig an den Kalkanteil, Fe und Cr überwiegend an Tonminerale gebunden. Zn, Mn und Cu liegen gleichwertig in Bindung an Tonminerale wie an das Karbonatgitter vor. Pb scheint überwiegend an den Kar bonatanteil gebunden zu sein. Extrem hohe Spurenelementkonzentrationen ("Ausreißer") von Pb, Zn, Fe, Cu und Mn werden auf einzelne, zufällig erfaßte Sulfid-, Oxyd- und Karbonatminerale dieser Elemente zurückgeführt. Die Analyse der Pb-Daten erwies sich nicht in allen Belangen als befriedigend. Die Gehalte von Pb in Karbonatgesteinen bewegen sich für den Entwicklungsstand des hier benutzten Analysegeräts zu nahe an der Nachweisgrenze. Die Auswertung erbrachte: - Stratiforme Anomalien, die über mehrere Probennahmeprofile verfolgbar und an bestimmte stratigraphische Niveaus gebunden sind. - Diskordante Anomalien, die in der Umgebung von bekannten Erzkörpern durch primäre oder sekundäre Migration hervorgerufen wurden. Die oberen Partien des Alpinen Muschelkalks sind meist hornsteinführend, insbesondere in der räumlichen und zeitlichen Nachbarschaft der Vulkanite. Dabei ist besonders auffällig, daß der Si02-Anteil im Liegenden und Hangenden von Tuff-Lagen (Pietra verde, 4 Zyklen) ungewöhnlich ansteigt. Dort entnommene Karbonatgesteinsproben zeigen stratiform anomal erhöhte Spurenelementkonzentrationen von Pb und Zn, fallweise begleitet von anomal er höhten F-, Fe-, Mn- und Cr-Werten. Stratiforme Anomalien von Zn-Pb-F, lokal auch von Fe-Cu-Mn-Cr, konnten regional über die Flexenpaß-Profile, Profil Zugspitze N und Martinswand verfolgt werden. In gleichem stratigraphischem Niveau wurden an anderer Stelle (Profile Davos-Silberberg, Krabachjoch u. St.Veith) diskordante Pb-Zn, F-, Fe-Mn- oder Cu-Anomalien be obachtet. Durch die wesentlich höheren Spurenelementkonzentrationen in diskordanten Anomalien wird die hier zu erwartende stratiforme Anomalie verdeckt. Im unteren und mittleren Teil des Alpinen Muschelkalks lokal auftretende, anomal erhöhte Spurenelementkonzentrationen waren dagegen regional nicht stratigraphisch korrelierbar. Geochemische Untersuchungen an Karbonatgesteinen aus den Südlichen Kalkalpen (Profile Valle Ambata/Auronzo und Topla/Mezica) lieferten keine Hinweise auf die Möglichkeit der Korrelation mit den Stratiformen Anomalien der Nördlichen Kalkalpen. Gegenüber den Karbonatgesteinen, Mergeln und Tonsteinen zeigt die Pietra verde signifkant erhöhte Gehalte von Zn und F. Diese deuten einen genetischen Zusammenhang zwischen einer zeitgleichen Zufuhr mit den Pyroklastika und einer Konzentration von Zn und F in den zwischengeschalteten Karbonatgesteinen an. Die Elemente Zn und F zeigten untereinander eine deutliche Korrelation. Bei der Suche nach schichtgebundenen Pb/Zn-Vorkommen in Karbonatgesteinen kann daher die Analyse der F-Gehalte als geochemische Prospektionshilfe (proximity indicator) herangezogen werden.

Description: ABSTRACT In order to determinate geochemical proximity indicators of the ore-bearing (upper) parts of the 'Alpiner Muschelkalk' (Anisian s. str.) rock samples have been taken from 11 standard profiles in the 'Nördliche Kalk alpen', and for comparison 2 standard profiles in the 'Südliche Kalkalpen'. Sampling was done systematically in aproximative homogeneous carbonate sequences and (facies-) differentiated in inhomogeneous sequences in the middle and upper parts of the 'Alpiner Muschelkalk'. 652 samples collected over 1.750 meters in total have been upgraded for geochemical analysis. Contents of Mg and trace elements like Sr, Zn, Pb, Fe, Mn, Cu and Cr have been determined by atomic absorption spectrophotometry. The F-analysis was done by a fluoride ion activity electrode (potentiometric fluorid analysis). Insoluble residues have been determined gravimetrically and occasionally examined by x-ray-diffraction. The analysis of about 10.600 data obtained has been processed by computer programme. Ca-data, correlation coefficients, geometric means and scattering have been computed by mathematical systems. Besides conventional statistics of geochemical analysis data like determination of regional backgrounds and thresholds, local backgrounds and thresholds have been computed, too, for showing and making comparable local anomalies of regional representative standard profiles. The border to the hanging wall had to be determined by conventional lithological conception. A more exact stratigraphical correlation of standard profiles was made possible by tuffs as far as they outcropped. Correlation coefficients showed the mineralogical bounding of elements as well as the primary and secondary concentrations in the sedimentary sequences. The major elements Ca and Mg originate predominantly from calcite and dolomite. Insoluble residues consist essentially of clay minerals of Illite-group (mixed layers) and quartz. Sr is clearly bound to calcite, Fe and Cr are linked to clay minerals as well as to calcite. Extremely high trace element concentrations of Pb, Zn, Fe, Mn and Cu are considered to originate from accidently caught sulfides, oxides or carbonates of these elements. Analysis of Pb data was not satisfactory in each matter, as the contents of Pb in carbonate rocks are to close to the noise of used AAS. The evaluation showed: — Stratiform anomalies, which can be correlated in several standard profiles and which are bound to distinct stratigraphic levels. -Discordantanomalies, which are caused by primary or secondary migration from ore bodies nearby. In the upper parts of the 'Alpiner Muschelkalk occur cherty limestones, especially in regional and stra tigraphical neighbourhood of volcanics. It is conspicuous, that carbonates belonging to the foot wall and hanging wall of tuffs (Pietra verde) are unusual rich of silica. Carbonate samples of this matter show stra tiform anomalous high trace element concentrations of Pb and Zn, occasionally accompanied by anomalous high concentrations of F, Fe, Mn and Cr. Stratiform anomalies of Zn-Pb-F, in some profiles also of Fe-Mn-Cu-Cr, can be correlated regionally in the Flexenpass-profiles and the profiles Zugspitze and Martinswand. At the same stratigraphical level there have been observed anomalies of Pb-, Zn-, F-, Fe-, Mn- or Cu at other places (profiles Davos-Silberberg, Kra bachjoch and St. Veith). Here the expected stratiform anomalies are masked by the higher trace element con centrations of discordant anomalies. The trace element concentrations of the lower and middle part of the 'Alpiner Muschelkalk' however, are not stratigraphically correlated. Geochemical data of the two profiles from the 'Südliche Kalkalpen' (profiles Valle Ambata/Auronzo and Topla/Me2ica) do not indicate a correlation with stratiform anomalies of the 'Nördliche Kalkalpen'. In opposition to the carbonates, marls and clays, the 'Pietra verde' shows significant higher contents of Zn and F. This indicates a genetic connection between the pyroclastics and the concentration of Zn and F in the intercalated carbonates. The elements Zn and F exhibit an evident correlation. The analysis of F may find application as a proximity indicator for exploration of stratabound lead-zinc occurrences in carbonate rocks.

Description: thesis

Description: DFG, SUB Göttingen

Description: Es wird die These, daß Zinn-führende Granite eine besondere geochemische Spezialisierung aufweisen, an den Beispielen des Sarrabus- (1), San-Vito- (2), Quirra- (3), Arburese- (4) und Monte-Linas-Granites (5) in S-Sardinien geprüft. Sie repräsentieren herzynische Plutongranite mit relativ hohem Intrusionsstockwerk und scharf ausgebildeten Intrusivkontakten zu schwach metamorphen altpaläozoischen Rahmengesteinen der Grünschieferfazies. Zinnlagerstätten treten nur im Umfeld der Massive (4) und (5), Mo-W-Vererzungen im Bereich der Massive (3) und (5) auf. Petrologisch bestehen die Massive hauptsächlich aus Leukogranit, untergeordnet und lokal treten auch Monzogranit, Granodiorit und Tonalit auf. Typisch für die Massive (3), (4) und (5) sind Zweiglimmergranite und Greisenbildungen mit unbedeutenden Anreicherungen der Elemente Sr, Mo, W, Zn und Cu. Petrochemisch sind die Granitoide als raum-zeitliche Differentationsreihen kalkalkalischer Magmen aufzufassen, an deren Ende Zweiglimmergranite als höchst spezialisierte Differentiate stehen. Ihre Sr^87/Sr^96 - Zusammensetzung deutet auf eine krustale Herkunft der Ausgangsschmelzen hin. Die Konzentration signifikanter Elemente der Frühkristallisation (Ti, Zr, Mg, Fe, P, Ca, Ba und Sr) nimmt zu den sauren Differentiaten hin ab, die der Spätkristallisation (F, B, Sn, Rb, Li) diametral zu. Danach erreichte der Quirra-Granit ein höchstes Differentationsniveau. Die Entwicklung der Massive im Einzelnen wird von folgenden Mechanismen kontrolliert: 1. Durch in-situ-Differentation bei der Entwicklung aller Massive, 2. durch emanative Differentation bei der Entwicklung des Quirra- (3), Monte-Linas- (5) und, mit Einschränkung, auch des Arburese-Granites (4), 3. durch nachträgliche metasomatische Stoffverschiebungen hauptsächlich bei der Entwicklung des Quirra- (3), Arburese- (4) und Monte-Linas-Granites (5). Bei Letzteren treten auch anomale Zinngehalte in Flußsedimenten, im granitischen Festgestein und seiner Biotite sowie in den Kontaktgesteinen auf. Die Häufigkeit anomaler Werte von 17 Indikatorgrößen, ihre Mittelwerte und Streuungen sowie die Intensität der geochemischen Spezialisierung in Bezug auf Sn, Rb, Li und F grenzen die Massive (3), (4) und (5) einhellig als für weitere Prospektionsarbeiten interessante Gebiete ab. Die absolute Intensität der Spezialisierung erreicht aber nicht das Ausmaß bekannter Zinnprovinzen. So sind für diese Granite z. B. relativ niedrige Bor- und z. T. auch Fluorwerte charakteristisch. Allgemein sind die Indikatorgrößen deutlich vom Intrusionsniveau eines Granites abhängig. Der Vergleich mit Literaturdaten führt zu einer Klassifizierung in geochemisch spezialisierte Granite 1. und 2. Ordnung im Rb-Ba-Sr- und K/Rb-Rb/Sr-Diagramm. Zinn-führende Granite heben sich also innerhalb gewisser geochemischer Variationsbreiten deutlich von sterilen Graniten ab.

Description: Summary Summary The thesis that tin bearing granites exhibit a significant geochemical character is tested by investigations of the Sarrabus (1), San Vito (2), Quirra (3), Arburese (4), and Monte Linas (5) Granite, all situated in south Sardinia. These massifs represent Hercynian granitic intrusives of high intrusion level and knife-like contacts to the adjacent rocks of Lower Palaeozoic age of greenshist facies. Endogenous tin deposits exist only spatially to the massifs (4) and (5), Mo-W-mineralizations in connection to the massifs (3) and (5). Petrologically all massifs consist principally of leucogranite. Monzogranite, granodiorite, and tonalite are rare and occure only locally. A peculiarity within the massifs (3), (4), and (5) are muscovite biotite granites and greisen with unimportant concentrations of the elements Sn, Mo, W, Zn, and Cu. Petrochemically the granitoids represent a spatial and temporal suite of a calc-alkaline magma with the muscovite biotite granites as highest specialized members. The crustal origin of the primary magmas is proven by Sr^87/Sr^96 datas. Generally the concentration of significant elements characterizing the early cristallization of a magma (Ti, Zr, Mg, Fe, P, Ca, Ba, and Sr) increase in direction of the later differentiates. The granitophile elements (F, B, Sn, Rb, Li) against that are enriched. The magmatic evolution of the massifs is governed by the following processes: 1. By in situ differentiation in the formation of all massifs, 2. by emanative differentiation in the formation of the massifs (3) and (5), with reservation also massif (4), 3. by later metasomatic chemical changes that occurred during greisenization especially in the formation of the massifs (3), (4), and (5). Anomalous tin contents are observed in alluvial sediments, leucogranites, and their biotites and country rocks distinctly of massif (5). The abundance of anomalous values of 17 proximity indicators, their mean and dispersion values and the degree of total geochemical specialization of Sn, Rb, Li, and F in the leucogranites determine uniformely the massifs (3), (4), and (5) as most interesting prospects for further detail exploration activities. The intensity of metallogenetic specialization is not as high as in other provinces. So the intrusives have extreme low concentrations of B and relative low contents of F. Generally the proximity indicators are dependent on the intrusion level of the granites. Together with reference datas from other areas one can establish geochemically specialized intrusives of first and second order. Tin bearing granites are distinguished within certain levels of clustering distinctly from barren granites.

Description: thesis

Description: DFG, SUB Göttingen

Description: The isotopic composition of Si in biogenic silica (BSi), such as opal buried in the oceans' sediments, has changed over time. Paleorecords suggest that the isotopic composition, described in terms of δ30Si, was generally much lower during glacial times than today. There is consensus that this variability is attributable to differing environmental conditions at the respective time of BSi production and sedimentation. The detailed links between environmental conditions and the isotopic composition of BSi in the sediments remain, however, poorly constrained. In this study, we explore the effects of a suite of offset boundary conditions during the Last Glacial Maximum (LGM) on the isotopic composition of BSi archived in sediments in an Earth System Model of intermediate complexity (EMIC). Our model results suggest that a change in the isotopic composition of Si supply to the glacial ocean is sufficient to explain the observed overall low(er) glacial δ30Si in BSi. All other processes explored trigger model responses of either wrong sign or magnitude or are inconsistent with a recent estimate of bottom water oxygenation in the Atlantic Sector of the Southern Ocean. Caveats, mainly associated with generic uncertainties in today's pelagic biogeochemical modules, remain.

Description: No abstract available

Description: No abstract available

Description: Atmospheric Rivers (ARs) are responsible for much of the precipitation along the west coast of the United States. In order to accurately predict AR events in numerical weather prediction, subseasonal and seasonal timescales, it is important to understand the large-scale meteorological influence on extreme AR events.Here, characteristics of ARs that result in an extreme precipitation event are compared to typical ARs on the coast of WashingtonState. In addition to more intense water vapor transport, notable differences in the synoptic forcing are present during extreme precipitation events that are not present during typical AR events.In particular, a negatively tilted low pressure system is positioned to the west in the Gulf of Alaska, alongside an upper level jet streak. Subseasonal and seasonal teleconnection patterns are known to influence the weather in the Pacific Northwest. The Madden JulianOscillation (MJO) is shown to be particularly important in determining the strength of precipitation associated with in AR ont he Washington coast.