Proxy Signals Research Articles

Testing tree-ring cellulose δ18O with water isotopes for Holocene lake δ18O interpretations in the central Rocky Mountains USA

Stable isotopes of water preserved in geologic archives, primarily as oxygen (δ18O), have proven critical for documenting Earth’s climatic and hydrologic systems past and present. However, timescale differences of water isotope inputs to proxy systems and the signal embedded in long paleorecords often confound translation to observed hydroclimatic metrics. Here, a unique 20-year dataset of meteorology, hydrology, and the isotopic composition of weekly meteoric and surface water samples (δ18O, δ2H) are combined with paleoclimate δ18O data from tree-ring cellulose and lake carbonate to better understand proxy signals of Upper Colorado river basin drought. Annual tree-ring cellulose δ18O from Picea engelmannii growing within a glacier-fed creek and a spring discharge area were used to derive annual source water δ18O using a cellulose source-water isotope model. Comparisons with the monitoring record indicates that tree-ring cellulose δ18O tracks variations in wet and dry hydroclimatic extremes. Source water isotopes are shown to reflect the hydroclimate of the current year and some number of previous years as an effective moisture-discharge proxy rather than a precipitation isotope proxy. Results contextualize Holocene lake carbonate δ18O data. The contemporary-to-paleo comparison identifies changes in seasonal precipitation extremes during recent millennia and several earlier arid and monsoon-dominated Holocene periods that exceed the arid maximum of the calibration period.

The Origin of Magnetofossil Coercivity Components: Constraints From Coupled Experimental Observations and Micromagnetic Calculations

AbstractBiogenic magnetite crystals produced by magnetotactic bacteria (MTB) and associated magnetofossils in sediments are characterized by variable morphologies, grain sizes, and chain structures. Magnetofossils are widely used in paleomagnetic and paleoenvironmental studies, but the complex magnetofossil shapes and particle arrangements significantly affect magnetic properties, hampering their magnetic detection and proxy interpretation. Here we perform coupled experimental and micromagnetic modeling analyses of typical magnetofossil‐rich sediments, where the effects of magnetofossil crystal forms and microstructures on magnetic properties can be quantitatively separated. Since the in situ magnetofossil chain structures in sediments remain poorly known, we compare results from magnetic measurements and micromagnetic simulations based on realistic magnetofossil shapes and grain size distributions. Our results suggest that bullet‐shaped magnetofossils certainly contribute to the biogenic hard (BH) coercivity component with a minor contribution from elongated prismatic particles, and collapsed equidimensional grains to the biogenic soft (BS) component. Micromagnetic simulations with different collapse models of bullet‐shaped magnetofossils produce variable FORC (first‐order reversal curve) central‐ridge contributions with similar coercivity distributions. Sensitivity test suggests that samples containing different forms of magnetofossils can produce the BH coercivity component if the proportion of the bullet‐shaped particles is more than ∼2%. Magnetofossil assemblages with a higher proportion of bullet‐shaped particles have higher coercivities, squareness ratios, and larger BH contents. Our data shed new light on understanding the origin of magnetofossil coercivity components and the in situ magnetofossil microstructures in sediments, which is widely useful for interpreting magnetofossil proxy signals in geological records.

Estimating Carbon Dioxide Emissions from Power Plant Water Vapor Plumes Using Satellite Imagery and Machine Learning

Combustion power plants emit carbon dioxide (CO2), which is a major contributor to climate change. Direct emissions measurement is cost-prohibitive globally, while reporting varies in detail, latency, and granularity. To fill this gap and greatly increase the number of power plants worldwide with independent emissions monitoring, we developed and applied machine learning (ML) models using power plant water vapor plumes as proxy signals to estimate electric power generation and CO2 emissions using Landsat 8, Sentinel-2, and PlanetScope imagery. Our ML models estimated power plant activity on each image snapshot, then an aggregation model predicted plant utilization over a 30-day period. Lastly, emission factors specific to region, fuel, and plant technology were used to convert the estimated electricity generation into CO2 emissions. Models were trained with reported hourly electricity generation data in the US, Europe, and Australia and were validated with additional generation and emissions data from the US, Europe, Australia, Türkiye, and India. All results with sufficiently large sample sizes indicate that our models outperformed the baseline approaches. In validating our model results against available generation and emissions reported data, we calculated the root mean square error as 1.75 TWh (236 plants across 17 countries over 4 years) and 2.18 Mt CO2 (207 plants across 17 countries over 4 years), respectively. Ultimately, we applied our ML method to plants that constitute 32% of global power plant CO2 emissions, as estimated by Climate TRACE, averaged over the period 2015–2022. This dataset is the most comprehensive independent and free-of-cost global power plant point-source emissions monitoring system currently known to the authors and is made freely available to the public to support global emissions reduction.

The cost of success or failure for proxy signals in ecological problems.

Two of John et al.'s examples of proxy failures in ecological situations are not failures: Runaway sexual selection and marsupial neonate competition. Instead, more appropriate ecological examples may be paternal genetic kin recognition and warning coloration. These differ in proxy effectiveness and failure in ways that illustrate the importance of "costs" in the evolution of ecological proxy traits.

The influence of fluid inclusions, organics, and calcite fabric on trace element distributions in stalagmites

Trace elements and calcite fabrics in stalagmites are increasingly employed as indicators of past environmental conditions. The drivers of trace element concentrations and fabrics reflect a complex interplay of factors during crystal growth, and accurate interpretation of geochemical proxies requires a clear understanding of the incorporation of the proxy signal in the stalagmite. We employ a series of non-destructive techniques to compare the spatial distribution of water, organic components, and trace elements and in relationship with calcite fabrics, and evaluate if these distributions are consistent with recent hypotheses about controlling factors on crystal fabrics, fluid inclusions, and element incorporation. We use for the first time Fourier Transformation Infrared Focal-Plane Array (FTIR-FPA) imaging to show the distribution of molecular water (3,400 cm−1 absorbance) and organic matter (2,983 cm−1) in calcite. To test if entrapped water in speleothem calcite affects the abundance or distribution of trace elements, the element distribution (Na, Mg, Sr, U, Al, Y, and Zn) is mapped by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Transmitted Light Microscope imaging constrains crystal fabrics. We find that stalagmite areas with strong Organic Matter fluorescence via Confocal Laser Scanning Microscopy coincide with areas of high Fourier Transformation Infrared absorbance at 2,983 cm−1, suggesting common co-location of multiple organic matter types in the stalagmite. While microscopic fluid inclusions visible in transmitted light are also detected by FTIR 3400 cm−1 absorbance, the FTIR additionally detects submicroscopic fluid inclusions, but not evident in transmitted light microscopy. In most samples, Na concentration is elevated in regions of high fluid inclusion density, suggesting that a significant portion of Na may be hosted in entrapped water rather than in the calcite. Only samples with 100-fold higher Y, feature Na concentrations which appear dominated by coupled Y-Na substitution and little influenced by fluid inclusion hosted Na. Our analysis provides new evidence of the influence of fluid inclusions on trace element content of stalagmites and illustrates the utility of several non-destructive imaging techniques to improve interpretations of proxy signals based on trace elements.

Contextual Gaps in Machine Learning for Mental Illness Prediction: The Case of Diagnostic Disclosures

Getting training data for machine learning (ML) prediction of mental illness on social media data is labor intensive. To work around this, ML teams will extrapolate proxy signals, or alternative signs from data to evaluate illness status and create training datasets. However, these signals' validity has not been determined, whether signals align with important contextual factors, and how proxy quality impacts downstream model integrity. We use ML and qualitative methods to evaluate whether a popular proxy signal, diagnostic self-disclosure, produces a conceptually sound ML model of mental illness. Our findings identify major conceptual errors only seen through a qualitative investigation -- training data built from diagnostic disclosures encodes a narrow vision of diagnosis experiences that propagates into paradoxes in the downstream ML model. This gap is obscured by strong performance of the ML classifier (F1 = 0.91). We discuss the implications of conceptual gaps in creating training data for human-centered models, and make suggestions for improving research methods.

Constraining Water Depth Influence on Organic Paleotemperature Proxies Using Sedimentary Archives

AbstractThe TEX86 paleothermometer has been extensively used to reconstruct past sea water temperatures, but it remains unclear which export depths the proxy represents. Here we used a novel approach to better constrain the proxy recording depths by investigating paleotemperature proxies (TEX86, , RI−OH and RI−OH′) from two pairs of proximal (<12 km apart) cores from Chilean and Angola margins, respectively. These cores are from steep continental slopes and lower shelves, which leads to a substantial difference in water depth between them despite being closely located. Surprisingly, the deep and the shallow records at the Chilean margin show dissimilarities, in contrast to the similar records from the Angola margin, which may be due to post‐depositional alteration at the former sites. In contrast, the TEX86 records were statistically indistinguishable between the sites at both the locations, even though the GDGT [2]/[3] ratio suggests GDGTs derived from potentially different archaeal communities residing at different depths. A short‐lived difference between the TEX86 records is observed during the last glacial period at the Angola margin, possibly due to a contribution of Antarctic Intermediate Waters to the deep site. Modelling suggests that the TEX86 source signal at our core sites reaches its peak abundance at water depths shallower than 350 m. The RI−OH and RI−OH′ records show similar variability as the TEX86 records, although regional differences in their absolute temperature estimates exist. Our approach using proximal sediment cores at steep slopes appears useful to constrain the export depth of organic proxy signals for paleo‐reconstructions.

Low-phosphorus concentrations and important ferric hydroxide scavenging in Archean seawater.

The availability of nutrients in seawater, such as dissolved phosphorus (P), is thought to have regulated the evolution and activity of microbial life in Earth's early oceans. Marine concentrations of bioavailable phosphorus spanning the Archean Eon remain a topic of debate, with variable estimates indicating either low (0.04 to 0.13 μM P) or high (10 to 100 μM P) dissolved P in seawater. The large uncertainty on these estimates reflects in part a lack of clear proxy signals recorded in sedimentary rocks. Contrary to some recent views, we show here that iron formations (IFs) are reliable recorders of past phosphorus concentrations and preserved a primary seawater signature. Using measured P and iron (Fe) contents in Neoarchean IF from Carajás (Brazil), we demonstrate for the first time a clear partitioning coefficient relationship in the P-Fe systematics of this IF, which, in combination with experimental and Archean literature data, permits us to constrain Archean seawater to a mean value of 0.063 ± 0.05 μM dissolved phosphorus. Our data set suggests that low-phosphorus conditions prevailed throughout the first half of Earth's history, likely as the result of limited continental emergence and marine P removal by iron oxyhydroxide precipitation, supporting prior suggestions that changes in ancient marine P availability at the end of the Archean modulated marine productivity, and ultimately, the redox state of Earth's early oceans and atmosphere. Classification: Physical Sciences, Earth, Atmospheric and Planetary Sciences.

Creativity as privilege

Organizational gatekeepers rely on tacit proxy signals of quality to evaluate creative work: status and status characteristics, elite networks, cultural capital, and a set of signals we refer to as symbolic dexterity. We argue that this reliance is due to the “push” of uncertainty and the “pull” of the culturally dominant person-centered view of creativity. Evaluators are “pushed” toward these proxy signals because the quality of creative work is fundamentally uncertain. Evaluators are “pulled” toward these proxy signals because the person-centered view of creativity makes these signals legitimate and easily available decision heuristics. Since members of privileged social groups are advantaged in producing and understanding the importance of such signals, we argue that access to creative work and success within it are largely a privilege. Given that privilege-based selection in creative work is both entrenched and ethically problematic, we explore its implications for organizational performance and organizational reputation and propose strategies that may help organizations reduce its discriminatory impact. We conclude by presenting questions for future research arising at the intersection of the literatures on evaluation in creative work and on social inequality.

Grain size controls on long-chain diol distributions and proxy signals in marine sediments

Long chain alkyl diols (LCDs) are lipid biomarkers that occur ubiquitously in sediments. Their abundance and distributions are increasingly used as the basis of molecular proxies for environmental parameters such as sea surface temperature (SST) via the Long chain Diol Index (LDI), and upwelling intensity and nutrient conditions (parametrized as diol indices, DI-2, and Nutrient Diol Index, NDI, respectively). Their marine producers remain the subject of debate, but in cultures, they can be found within the outer wall (algaenan) of eustigmatophytes or in Proboscia diatoms. LCDs appear to be well preserved in sediments, potentially as a result of their association with algaenan and/or minerals, but little is known of their pre-depositional histories, in particular transport dynamics. Here, 15 surface continental margin sediments as well as one high-deposition-rate sediment core (50 cm, spanning the last ~30 years) were analyzed in order to evaluate the impact of organo-mineral associations, lateral transport, and hydrodynamic sorting on sedimentary LCD signals. The abundance and distribution of LCDs in bulk sediments and corresponding grain-size fractions was determined. The highest proportion of all LCD isomers is found in the fine fraction (2 – 10 µm), which also holds the highest proportion of organic matter in relation to the other grain-size fractions. However, LCDs are also found in the other fractions (sand, coarse silt, and clay), and their concentrations are not correlated with bulk organic carbon content, indicating different preservation or transport mechanisms. LDI-SST in the bulk sediment is comparable to the mean annual SST at all sites except those influenced by upwelling and characterized by strong seasonal SST gradients. To the contrary of other biomarker-related proxies (e.g., alkenones), lateral transport does not appear to strongly affect LDI-SST in size fractions, suggesting that the intimate relationship of LCD with the algaenan may counteract the influence of hydrodynamic mineral sorting processes on related proxy signals. The difference between the fraction-weighted LCD concentration and bulk sedimentary LCD concentration indicates potential release of LCD during laboratory fractionation, suggesting degradation of algaenan or dissolution of opal frustules.

Mesocrystalline Architecture in Hyaline Foraminifer Shells Indicates a Non‐Classical Crystallisation Pathway

AbstractCalcareous foraminifer shells (tests) represent one of the most important archives for paleoenvironmental and paleoclimatic reconstruction. To develop a mechanistic understanding of the relationship between environmental parameters and proxy signals, knowledge of the fundamental processes operating during foraminiferal biomineralization is essential. Here, we apply microscopic and diffraction‐based methods to address the crystallographic and hierarchical structure of the test wall of different hyaline foraminifer species. Our results show that the tests are constructed from micrometer‐scale oriented mesocrystals built of nanometer‐scale entities. Based on these observations, we propose a mechanistic extension to the biomineralization model for hyaline foraminifers, centered on the formation and assembly of units of metastable carbonate phases to the final mesocrystal via a non‐classical particle attachment process, possibly facilitated by organic matter. This implies the presence of metastable precursors such as vaterite or amorphous calcium carbonate, along with phase transitions to calcite, which is relevant for the mechanistic understanding of proxy incorporation in the hyaline foraminifers.

Holocene vegetation reconstruction in the forest–steppe of Mongolia based on leaf waxes and macro-charcoals in soils

Abstract. Vegetation and climate reconstruction in the forest–steppe of Mongolia is still challenging regarding the pattern of forest and grassland distribution during the Holocene. Different sediments containing paleosols and humic layers provide geomorphological archives for landscape development in Mongolia. n-Alkane and macro-charcoal ratios represent specific indicators to distinguish the share between grasses and trees. In a preliminary study, we investigated the applicability of these two paleo-proxies from soils for vegetation reconstruction comparing different relief positions and site conditions in the northern Khangai Mountains of Mongolia. n-Alkanes that are deposited from leaf waxes in the soil have the potential to indicate vegetation composition on a local scale. Depending on site-specific environmental conditions, n-alkanes are subjected to different degrees of microbiological decomposition, which is more intensive in soils of dry steppe than of forests. Mongolian forests are often underlain by permafrost that may reduce microbiological activity. In steppe soils, the decomposition of n-alkanes increases the quantity of mid-chain n-alkanes that adulterate the biomarker proxy signal to indicate more forest share. Macro-charcoals in soils have a site-specific component, but additional eolian input of macro-charcoals from long-distance transport can provide a distinct proportion in sediments. Thus, eolian influx of wood-derived macro-charcoal can dominate the proxy signal at sites where trees were few or had never existed. Radiometric dating of several paleosols and humic layers has shown that both proxies coincide as evidence for high grassland-to-forest ratios during the Early Holocene. By contrast, the proxy signals diverge for the Late Holocene. For this period, n-alkanes generally indicate more grassland, whereas macro-charcoals show increased wood-derived proportions. We imply that this difference is caused by increased forest fires and simultaneously spreading steppe area. A main portion of leaf waxes and charcoal particles in soils directly derive from the covering and nearby vegetation, whereas large lakes and glacier may receive these biomarkers from a larger catchment area. Thus, we conclude that soil archives provide proxies on a more local and site-specific scale than other archives do. Although the temporal resolution of soil archives is lower than for the other ones, biomarker proxies for paleosols and humic layer can be related to periods of distinct geomorphological processes. Further investigations comparing the multi-proxy data of different geomorphological archives are necessary to improve the paleo-ecological reconstruction for landscape development in Mongolia.

Dust correlation and oxygen isotope stratigraphy in the Southern Ocean over the last 450 kyrs: An Indian sector perspective

The chronology of Southern Ocean (SO) marine sediment cores forms the basis of understanding the SO paleoceanography, with significant implications for global climate. Because tuning of the oxygen isotope (δ18O) record of a marine sediment core to a δ18O stack (δ18O stratigraphy) is difficult in the SO because of a general paucity of calcareous foraminifera, tuning of the dust proxy signal of a marine sediment core to the dust record of an ice core (dust correlation) is a promising way to construct an age–depth model. However, the reliability of dust correlation has not been established, especially beyond the last ∼300 kyrs, and such work has been performed more in the Atlantic and Pacific sectors of the SO than in the Indian sector. Here we present a new dust correlation using the rock magnetic record, together with continuous δ18O stratigraphy, for a marine sediment core in the Indian sector of the SO over the last ∼410 kyrs. The δ18O stratigraphy is consistent with the dust correlation within their chronological uncertainties, supporting the reliability of the latter chronology for glacial–interglacial timescales. However, the dust correlation often produces older ages than the δ18O stratigraphy by up to 3 kyrs (410–126 ka and 84–50 ka). We additionally compiled, based on dust correlation, available dust proxy records in the circum-Antarctic SO for the last 450 kyrs to discuss variations in the dust proxy record within the Indian sector and between all three sectors. For the Indian sector, there is a marked difference in dust proxy signals for Marine Isotope Stage (MIS) 6 between two cores that have markedly different latitudinal positions relative to the oceanic fronts. Increased biogenic magnetite production by iron fertilization in the Subantarctic Zone during MIS 6 may partly explain the difference between the two cores. For the circum-Antarctic SO, moving correlation coefficients were computed between the marine sediment-core dust proxy signals and the dust flux of an Antarctic ice core. Strong correlation was recognized for intervals of high dust flux in the ice core, except for MIS 6. Although minor, the slightly lower correlation in the Indian sector than in the other sectors indicates a contribution from local dust source and volcanic materials and thus suggests the necessity for caution when performing dust correlation in the Indian sector of the SO.

Aqueous system-level processes and prokaryote assemblages in the ferruginous and sulfate-rich bottom waters of a post-mining lake

Abstract. In the low-nutrient, redox-stratified Lake Medard (Czechia), reductive Fe(III) dissolution outpaces sulfide generation from microbial sulfate reduction (MSR) and ferruginous conditions occur without quantitative sulfate depletion. The lake currently has marked overlapping C, N, S, Mn and Fe cycles occurring in the anoxic portion of the water column. This feature is unusual in stable, natural, redox-stratified lacustrine systems where at least one of these biogeochemical cycles is functionally diminished or undergoes minimal transformations because of the dominance of another component or other components. Therefore, this post-mining lake has scientific value for (i) testing emerging hypotheses on how such interlinked biogeochemical cycles operate during transitional redox states and (ii) acquiring insight into redox proxy signals of ferruginous sediments underlying a sulfatic and ferruginous water column. An isotopically constrained estimate of the rates of sulfate reduction (SRRs) suggests that despite high genetic potential, this respiration pathway may be limited by the rather low amounts of metabolizable organic carbon. This points to substrate competition exerted by iron- and nitrogen-respiring prokaryotes. Yet, the planktonic microbial succession across the nitrogenous and ferruginous zones also indicates genetic potential for chemolithotrophic sulfur oxidation. Therefore, our SRR estimates could rather be portraying high rates of anoxic sulfide oxidation to sulfate, probably accompanied by microbially induced disproportionation of S intermediates. Near and at the anoxic sediment–water interface, vigorous sulfur cycling can be fuelled by ferric and manganic particulate matter and redeposited siderite stocks. Sulfur oxidation and disproportionation then appear to prevent substantial stabilization of iron monosulfides as pyrite but enable the interstitial precipitation of microcrystalline equant gypsum. This latter mineral isotopically recorded sulfur oxidation proceeding at near equilibrium with the ambient anoxic waters, whilst authigenic pyrite sulfur displays a 38 ‰ to 27 ‰ isotopic offset from ambient sulfate, suggestive of incomplete MSR and open sulfur cycling. Pyrite-sulfur fractionation decreases with increased reducible reactive iron in the sediment. In the absence of ferruginous coastal zones today affected by post-depositional sulfate fluxes, the current water column redox stratification in the post-mining Lake Medard is thought relevant for refining interpretations pertaining to the onset of widespread redox-stratified states across ancient nearshore depositional systems.

Decoding the Brain's Surface to Track Deeper Activity.

Neural activity can be readily and non-invasively recorded from the scalp using electromagnetic and optical signals, but unfortunately all scalp-based techniques have depth-dependent sensitivities. We hypothesize, though, that the cortex's connectivity with the rest of the brain could serve to construct proxy signals of deeper brain activity. For example, functional magnetic resonance imaging (fMRI)-derived models that link surface connectivity to deeper regions could subsequently extend the depth capabilities of other modalities. Thus, as a first step toward this goal, this study examines whether or not surface-limited support vector regression of resting-state fMRI can indeed track deeper regions and distributed networks in independent data. Our results demonstrate that depth-limited fMRI signals can in fact be calibrated to report ongoing activity of deeper brain structures. Although much future work remains to be done, the present study suggests that scalp recordings have the potential to ultimately overcome their intrinsic physical limitations by utilizing the multivariate information exchanged between the surface and the rest of the brain.

Masting effect on canopy greenness and climate response on seed production of Fagus grandifolia subsp. mexicana across the Sierra Madre Oriental, Mexico

Specific proximate mechanisms as climate spatial fluctuations modify the pattern of synchronic reproduction (masting) or seed production at population level in the Fagus genus worldwide. However, phenological processes as mass flowering, beechnut development and seed rain have attracted attention to understand the masting behavior in relict-endangered tree species. The normalized difference vegetation index (NDVI), temperature and precipitation could act as proxy signals resembling the onset of mast-seeding events. We studied a masting event in 2017 in ten relict-endangered Mexican beech forests (Fagus grandifolia subsp. mexicana) in eastern Mexican montane cloud forests. Our aims were 1) test if NDVI shows a particular pattern before and after masting event in 2017 at 10 sites; 2) explore how monthly temperature and precipitation change two years before and during the masting across the Mexican beech forests; and 3) assess how the beechnut amount and quality was affected by spatial and temporal specific climatic variables in the recorded masting event among the beech forests. We found that the masting was related to the canopy greenness variation (2015–2018) in the beech forests. Nut production variability among beech forests was related to temperature and precipitation fluctuations. We found that maximum and mean temperature and high precipitation during May to August were decisive to trigger the synchronic Mexican beech masting spatial behavior.

Local-scale deposition of surface snow on the Greenland ice sheet

Abstract. Ice cores from polar ice sheets and glaciers are an important climate archive. Snow layers, consecutively deposited and buried, contain climatic information from the time of their formation. However, particularly low-accumulation areas are characterised by temporally intermittent precipitation, which can be further redistributed after initial deposition, depending on the local surface features at different spatial scales. Therefore, the accumulation conditions at an ice core site influence the quantity and quality of the recorded climate signal in proxy records. This study aims to characterise the local accumulation patterns and the evolution of the snow height to describe the contribution of the snow (re-)deposition to the overall noise level in climate records from ice cores. To this end, we applied a structure-from-motion photogrammetry approach to generate near-daily elevation models of the surface snow for a 195 m2 area in the vicinity of the deep drilling site of the East Greenland Ice-core Project in northeast Greenland. Based on the snow height information we derive snow height changes on a day-to-day basis throughout our observation period from May to August 2018 and find an average snow height increase of ∼ 11 cm. The spatial and temporal data set also allows an investigation of snow deposition versus depositional modifications. We observe irregular snow deposition and erosion causing uneven snow accumulation patterns, a removal of more than 60 % of the deposited snow, and a negative relationship between the initial snow height and the amount of accumulated snow. Furthermore, the surface roughness decreased by approximately a factor of 2 throughout the spring and summer season at our study site. Finally, our study shows that structure from motion is a relatively simple method to demonstrate the potential influences of depositional processes on proxy signals in snow and ice.

A model for marine sedimentary carbonate diagenesis and paleoclimate proxy signal tracking: IMP v1.0

Abstract. The preservation of calcium carbonate in marine sediments is central to controlling the alkalinity balance of the ocean and, hence, the ocean–atmosphere partitioning of CO2. To successfully address carbon cycle–climate dynamics on geologic (≫1 kyr) timescales, Earth system models then require an appropriate representation of the primary controls on CaCO3 preservation. At the same time, marine sedimentary carbonates represent a major archive of Earth history, as they have the potential to preserve how seawater chemistry, isotopic composition, and even properties of planktic and benthic ecosystems, change with time. However, changes in preservation and even chemical erosion of previously deposited CaCO3, along with the biogenic reworking of upper portions of sediments, whereby sediment particles are translocated both locally and nonlocally between different depths in the sediments, all act to distort the recorded signal. Numerical models can aid in recovering what the “true” environmental changes might have been, but only if they appropriately account for these processes. Building on a classical 1-D reaction-transport framework, we present a new diagenetic model – IMP (Implicit model of Multiple Particles (and diagenesis)) – that simulates biogeochemical transformations in carbonate-hosted proxy signals by allowing for populations of solid carbonate particles to possess different physicochemical characteristics such as isotopic value, solubility and particle size. The model also utilizes a variable transition matrix to implement different styles of bioturbation. We illustrate the utility of the model for deciphering past environmental changes using several hypothesized transitions of seawater proxies obscured by sediment mixing and chemical erosion. To facilitate the use of IMP, we provide the model in Fortran, MATLAB and Python versions. We described IMP with integration into Earth system models in mind, and we present the description of this coupling of IMP with the “cGENIE.muffin” model in a subsequent paper.

Two-dimensional impurity imaging in deep Antarctic ice cores: snapshots of three climatic periods and implications for high-resolution signal interpretation

Abstract. Due to its micrometer-scale resolution and inherently micro-destructive nature, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is particularly suited to exploring the thin and closely spaced layers in the oldest sections of polar ice cores. Recent adaptions to the LA-ICP-MS instrumentation mean we have faster washout times allowing state-of-the-art 2-D imaging of an ice core. This new method has great potential especially when applied to the localization of impurities on the ice sample, something that is crucial, to avoiding misinterpretation of the ultra-fine-resolution signals. Here we present the first results of the application of LA-ICP-MS elemental imaging to the analysis of selected glacial and interglacial samples from the Talos Dome and EPICA Dome C ice cores from central Antarctica. The localization of impurities from both marine and terrestrial sources is discussed, with special emphasis on observing a connection with the network of grain boundaries and differences between different climatic periods. Scale-dependent image analysis shows that the spatial significance of a single line profile along the main core axis increases systematically as the imprint of the grain boundaries weakens. It is demonstrated how instrumental settings can be adapted to suit the purpose of the analysis, i.e., by either employing LA-ICP-MS to study the interplay between impurities and the ice microstructure or to investigate the extremely thin climate proxy signals in deep polar ice.

Art Writing and Allegory in the Anthropocene

Abstract This essay traces the emergence of a rich and densely layered field of art writing within the Anthropocene. We ask: If the Anthropocene is all around us, where is it in art writing? We identify the emergence of Anthropocenic art writing: writing that is not art writing about the Anthropocene per se but rather art writing that takes its cue from the operations and outcomes of the Anthropocene itself, including its flagrant disregard for boundaries (disciplinary and otherwise), and its agency. We find such strategies already at work, particularly, in writing by artists such as Hito Steyerl, Martha Rosler, and Chris Kraus, as well as in writing that is polyphonic either through the collaboration of multiple writers or through collage. We map art writing's strata (its past and present delineations, some of its cardinal points) in order to identify sites of resistance to the accelerations of the contemporary era, which is to say places where deceleration and deliberation may be possible. Anthropocenic art writing claims such modes as its own. While for scientists the Anthropocene has been marked by the contestation of golden spikes, in art writing these proxy signals go far beyond employing “nature” and the environment as a theme or topic, taking the Anthropocene as an allegorical mode itself.