The iron isotopic composition of subglacial streams draining the Greenland ice sheet

In this study, we present the first measurements of iron (Fe) stable isotopic composition (δ56Fe) of subglacial streams draining the Greenland Ice Sheet (GIS). We measure the δ56Fe values [(δ56Fe, ‰ = (56Fe/54Fe)sample/(56Fe/54Fe)standard − 1) × 103] of both dissolved and suspended sediment Fe in subglacial outflows from five distinct land-terminating glaciers. Suspended sediments have δ56Fe values that lie within the crustal array (δ56Fe ∼ 0‰). In contrast, the δ56Fe values of dissolved Fe in subglacial outflows are consistently less than 0‰, reaching a minimum of −2.1‰ in the outflow from the Russell Glacier. The δ56Fe values of dissolved Fe vary geographically and on daily time scales. Major element chemistry and mineral saturation state modeling suggest that incongruent silicate weathering and sulfide oxidation are the likely drivers of subglacial stream Fe chemistry, and that the extent of chemical weathering influences the δ56Fe of dissolved Fe. The largest difference in δ56Fe between dissolved and suspended load is −2.1‰, and occurs in the subglacial system from the Russell glacier (southwest GIS). Major element chemistry indicates this outflow to be the least chemically weathered, while more mature subglacial systems (i.e., that exhibit greater extents of subglacial weathering) have dissolved loads with δ56Fe that are indistinguishable from suspended sediments (Δ56Fesuspended-dissolved ∼ 0‰). Ultimately, the dissolved Fe generated in some subglacial systems from the GIS is a previously unrecognized source of isotopically light Fe into the hydrosphere. The data illustrate that the dissolved Fe supplied by subglacial weathering can have variable δ56Fe values depending on the degree of chemical weathering. Thus, Fe isotopes have potential as a proxy for subglacial chemical weathering intensity or mode. Finally, based on our regional Fe concentration measurements from each glacial outflow, we estimate a flux weighted continental scale dissolved iron export of 2.1 Gg Fe yr−1 to the coastal ocean, which is within the range of previous estimates

SNAPSHOT USA 2020: A second coordinated national camera trap survey of the United States during the COVID-19 pandemic

Managing wildlife populations in the face of global change requires regular data on the abundance and distribution of wild animals, but acquiring these over appropriate spatial scales in a sustainable way has proven challenging. Here we present the data from Snapshot USA 2020, a second annual national mammal survey of the USA. This project involved 152 scientists setting camera traps in a standardized protocol at 1485 locations across 103 arrays in 43 states for a total of 52,710 trap-nights of survey effort. Most (58) of these arrays were also sampled during the same months (September and October) in 2019, providing a direct comparison of animal populations in 2 years that includes data from both during and before the COVID-19 pandemic. All data were managed by the eMammal system, with all species identifications checked by at least two reviewers. In total, we recorded 117,415 detections of 78 species of wild mammals, 9236 detections of at least 43 species of birds, 15,851 detections of six domestic animals and 23,825 detections of humans or their vehicles. Spatial differences across arrays explained more variation in the relative abundance than temporal variation across years for all 38 species modeled, although there are examples of significant site-level differences among years for many species. Temporal results show how species allocate their time and can be used to study species interactions, including between humans and wildlife. These data provide a snapshot of the mammal community of the USA for 2020 and will be useful for exploring the drivers of spatial and temporal changes in relative abundance and distribution, and the impacts of species interactions on daily activity patterns. There are no copyright restrictions, and please cite this paper when using these data, or a subset of these data, for publication

SNAPSHOT USA 2019: a coordinated national camera trap survey of the United States

With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14-week period (17 August-24 November of 2019). We sampled wildlife at 1,509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian's eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the United States. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban-wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot-usa, as will future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species-specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication

Calcium isotope fractionation and its controlling factors over authigenic carbonates in the cold seeps of the northern South China Sea

In this study, we analyzed stable calcium isotope results of authigenic carbonates from two cold seep areas of the Dongsha area and the Baiyun Sag in the northern South China Sea. The stable isotopes of carbon and oxygen as well as the mineral composition of authigenic carbonates were used to investigate control calcium isotope fractionation. The δ 44/40Ca ratios of the southwestern Dongsha area samples ranged from 1.21‰ to 1.52‰ and the ratio of the Baiyun Sag sample was 1.55‰ of the SRM915a isotope standard. X-ray diffraction analysis showed that the carbonate samples consisted of dolomite, calcite and aragonite, with small amounts of high-Mg calcite and siderite. The δ 13C values of the carbonates of the southwestern Dongsha area varied between −49.21‰ and −16.86‰ of the Vienna PeeDee Belemnite (VPDB) standard and the δ 18O values ranged from 2.25‰ to 3.72‰ VPDB. The δ 13C value of the Baiyun Sag sample was 2.36‰ VPDB and the δ 18O value was 0.44‰ VPDB. The δ 13C values of the carbonates of the southwestern Dongsha area revealed there is methane seeping into this area, with a variable contribution of methane-derived carbon. The sampled carbonates covered a range of δ 13C values suggesting a dominant methane carbon source for the light samples and mixtures of δ 13C values for the heavier samples, with possibly an organic or seawater carbon source. The δ 18O values indicated that there is enrichment in 18O, which is related to the larger oxygen isotope fractionation in dolomite compared to calcite. The results of the Baiyun Sag sample exhibited normal seawater carbon and oxygen isotopic values, indicating that this sample is not related to methane seepage but instead to precipitation from seawater. The relatively high δ 44/40Ca values indicated either precipitation at comparatively high rates in pore-water regimes with high alkalinity, or precipitation from an evolved heavy fluid with high degrees of Ca consumption (Raleigh type fractionation). The dolomite samples from the Dongsha area revealed a clear correlation between the carbon and calcium isotope composition, indicating a link between the amount and/or rate of carbonate precipitation and methane contribution to the bicarbonate source. The results of the three stable isotope systems, mineralogy and petrography, show that mineral composition, the geochemical environment of authigenic carbonates and carbon source can control the calcium isotope fractionation.This work was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-GJ03-01), the National Natural Science Foundation of China (40706022, U0733003 and 41176052), the National Basic Research Program of China (2009CB219502-4) and the Knowledge Innovation Program of South China Sea Institute of Oceanology, Chinese Academy of Sciences (LYQY200806). The authors thank the University of Aveiro and Universität Münster for the facilities provided for this research. We appreciate the thoughtful and constructive comments provided by editors and reviewers, which improve the manuscript.publishe

SNAPSHOT USA 2019 : a coordinated national camera trap survey of the United States

This article is protected by copyright. All rights reserved.With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14-week period (17 August - 24 November of 2019). We sampled wildlife at 1509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian's eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the USA. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban-wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot-usa, as well as future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species-specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication.Publisher PDFPeer reviewe

Mammal responses to global changes in human activity vary by trophic group and landscape

Wildlife must adapt to human presence to survive in the Anthropocene, so it is critical to understand species responses to humans in different contexts. We used camera trapping as a lens to view mammal responses to changes in human activity during the COVID-19 pandemic. Across 163 species sampled in 102 projects around the world, changes in the amount and timing of animal activity varied widely. Under higher human activity, mammals were less active in undeveloped areas but unexpectedly more active in developed areas while exhibiting greater nocturnality. Carnivores were most sensitive, showing the strongest decreases in activity and greatest increases in nocturnality. Wildlife managers must consider how habituation and uneven sensitivity across species may cause fundamental differences in human–wildlife interactions along gradients of human influence.Peer reviewe

The Ca isotopic composition of dust-producing regions: Measurements of surface sediments in the Black Rock Desert, Nevada

Dust is a relatively unconstrained flux in the geochemical cycle of Ca. The isotopic composition of dust-derived Ca has not been studied, though it is an important part of any attempt at deciphering Ca isotope-based proxy records. Accordingly, this study reports the elemental and calcium isotope geochemistry of 30 surface (upper ∼0.5 cm) sediments from an arid dust producer, the Black Rock Desert in northwestern Nevada. Geochemical data for sequential water and 0.5 N HCl leaches, meant to sample mobile Ca, and selected leached residues are presented, along with X-ray diffraction (XRD) determinations of major mineralogy. Bulk playa sediments have Ca concentrations between 0.28 and 40 wt.% (median: 6.8 wt.%) and calcite concentrations of 2–32%. Isotopically, Ca sampled by water leaches (60% of total Ca), though the degree of fractionation (Δw-a) varies between 0‰ and 0.6‰. Acid leaches, which are the primary component of mobile Ca in the sediments, have δ44CaSRM-915a values of 0.78 ± 0.08‰, similar to the δ44Ca of modern nannofossil ooze and modern rivers. This means that dust produced in closed continental basins likely has little isotopic leverage to change the ocean’s isotopic composition, and suggests that the Ca isotopic composition of dust is tied to rivers/weathering. In addition, while the Ca concentration data in the water leach suggest that evaporative evolution controls the amount of Ca in this reservoir, the isotope data are inconsistent with this conclusion. Instead, we hypothesize that adsorption of Ca on clays controls the Ca isotope systematics in the water leach. This hypothesis requires that there is no significant isotopic fractionation during evaporite mineral precipitation and may suggest that sorption at rates appropriate for natural systems might fractionate differently than sorption at laboratory rates

Elucidating modern geochemical cycles at local, regional, and global scales using calcium isotopes

In Earth's surface environment, calcium (Ca) is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases, being cycled and recycled during various biogeochemical processes. With the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of Ca can be measured, revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems. More than three decades of work reveal systematic variations in the partitioning of Ca isotopes due to both abiotic and biological processes. An overview of processes that fractionate Ca isotopes at local, regional, and global scales is outlined here. We present detailed examples of instances in which Ca isotopes have provided unique insight into the functioning of Earth surface processes and the cycling of Ca at multiple scales. Future studies should target questions for which Ca isotopic analysis provide unique insight and, when combined with other isotope and trace element multi-proxy studies, better constrain the system of interest. At the same time, we challenge the scientific community to explore new frontiers including polar regions and other extreme environments

Effects of ocean acidification on the marine calcium isotope record at the Paleocene–Eocene Thermal Maximum

Highlights • δ44Ca was measured in bulk carbonate and barite at two sites over the PETM. • Diagenetic effects on δ44Ca are observed associated with ocean acidification. • Multiple sites and proxy archives necessary to reconstruct the past accurately. Abstract Carbonates are used extensively to reconstruct paleoclimate and paleoceanographic conditions over geologic time scales. However, these archives are susceptible to diagenetic alteration via dissolution, recrystallization and secondary precipitation, particularly during ocean acidification events when intense dissolution can occur. Despite the possible effects of diagenesis on proxy fidelity, the impacts of diagenesis on the calcium isotopic composition (δ44Ca) of carbonates are unclear. To shed light on this issue, bulk carbonate δ44Ca was measured at high resolution in two Pacific deep sea sediment cores (ODP Sites 1212 and 1221) with considerably different dissolution histories over the Paleocene–Eocene Thermal Maximum (PETM, ∼55 Ma∼55 Ma). The δ44Ca of marine barite was also measured at the deeper Site 1221, which experienced severe carbonate dissolution during the PETM. Large variations (∼0.8‰∼0.8‰) in bulk carbonate δ44Ca occur in the deeper of the two sites at depths corresponding to the peak carbon isotope excursion, which correlate with a large drop in carbonate weight percent. Such an effect is not observed in either the 1221 barite record or the bulk carbonate record at the shallower Site 1212, which is also less affected by dissolution. We contend that ocean chemical changes associated with abrupt and massive carbon release into the ocean–atmosphere system and subsequent ocean acidification at the PETM affected the bulk carbonate δ44Ca record via diagenesis in the sedimentary column. Such effects are considerable, and need to be taken into account when interpreting Ca isotope data and, potentially, other geochemical proxies over extreme climatic events that drive sediment dissolution

Calcium isotope ratios from marine barite and carbonate over Paleocene-Eocene Boundary (ODP Sites 1212 and 1221)

Carbonates are invaluable archives of the past, and have been used extensively to reconstruct paleoclimate and paleoceanographic conditions over geologic time scales. Such archives are susceptible to diagenetic alteration via dissolution, recrystallization and secondary precipitation, particularly during ocean acidification events when intense dissolution can occur. Despite the importance of diagenesis on proxy fidelity, the effects of diagenesis on the calcium isotopic composition (d44Ca) of carbonates are unclear. Accordingly, bulk carbonate d44Ca was measured at high resolution in two Pacific deep sea sediment cores (ODP Sites 1212 and 1221) with considerably different dissolution histories over the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma). The d44Ca of marine barite was also measured at the deeper Site 1221, which experienced severe carbonate dissolution during the PETM. Large (~0.8 per mil) variations in bulk carbonate d44Ca occur in the deeper site near the peak carbon isotope excursion, and are correlated with a large drop in carbonate weight percent. Such an effect is seen in neither the 1221 barite record nor the bulk carbonate record at the shallower, less dissolved Site 1212. We contend that ocean chemical changes associated with the abrupt and massive carbon release into the ocean-atmosphere system and subsequent ocean acidification at the PETM affected the bulk carbonate d44Ca record via diagenesis in the sedimentary column. Such changes are considerable, and need to be taken into account when interpreting and modeling Ca isotope data over extreme climatic events associated with ocean chemical evolution