Alfred Wegener Institute for Polar and Marine Research
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Precise dating of deglacial Laptev Sea sediments via 14C and authigenic 10Be/9Be – assessing local 14C reservoir ages
Get PDFEstablishing accurate chronological frameworks is imperative for reliably identifying lead-lag dynamics within the climate system and enabling meaningful inter-comparisons across diverse paleoclimate proxy records over long time periods. Robust age models provide a solid temporal foundation for establishing correlations between paleoclimate records. One of the primary challenges in constructing reliable radiocarbon-based chronologies in the marine environment is to determine the regional marine radiocarbon reservoir age correction. Calculations of the local marine reservoir effect (ΔR) during deglaciation can be acquired using 14C-independent dating methods, such as synchronization with other well-dated archives. The cosmogenic radionuclide 10Be offers such a synchronization tool. Its atmospheric production rate is affected by the global modulations driven by fluctuations in the cosmic ray influx, caused by variations in solar activity and geomagnetic field strength. The resulting fluctuations in the meteoric deposition of 10Be are preserved in sediments and ice cores and can thus be utilized for their synchronization. In this study, for the first time, we use the authigenic 10Be/9Be record of a Laptev Sea sediment core for the period 8-14 kyr BP and synchronize it with the 10Be records from absolutely dated ice cores. Based on the resulting absolute chronology, a benthic ΔR value of +345±60 14C years was estimated for the Laptev Sea, which corresponds to a marine reservoir age of 848±90 14C years. The ΔR value was used to refine the age-depth model for core PS2458-4, establishing it as a reference chronology for the Laptev Sea. We also compare the calculated ΔR value with modern estimates from the literature and discuss its implications for the age-depth model
Five million years of Antarctic Circumpolar Current strength variability
Get PDFThe Antarctic Circumpolar Current (ACC) represents the world’s largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability1–3. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity4. Whereas palaeoceanographic reconstructions exhibit regional heterogeneity in ACC position and strength over Pleistocene glacial–interglacial cycles5–8, the long-term evolution of the ACC is poorly known. Here we document changes in ACC strength from sediment cores in the Pacific Southern Ocean. We find no linear long-term trend in ACC flow since 5.3 million years ago (Ma), in contrast to global cooling9 and increasing global ice volume10. Instead, we observe a reversal on a million-year timescale, from increasing ACC strength during Pliocene global cooling to a subsequent decrease with further Early Pleistocene cooling. This shift in the ACC regime coincided with a Southern Ocean reconfiguration that altered the sensitivity of the ACC to atmospheric and oceanic forcings11–13. We find ACC strength changes to be closely linked to 400,000-year eccentricity cycles, probably originating from modulation of precessional changes in the South Pacific jet stream linked to tropical Pacific temperature variability14. A persistent link between weaker ACC flow, equatorward-shifted opal deposition and reduced atmospheric CO2 during glacial periods first emerged during the Mid-Pleistocene Transition (MPT). The strongest ACC flow occurred during warmer-than-present intervals of the Plio-Pleistocene, providing evidence of potentially increasing ACC flow with future climate warming
Holocene thinning in central Greenland controlled by the Northeast Greenland Ice Stream
Get PDFIce-core records from the interior of the Greenland ice sheet suggest widespread thinning during the Holocene. However, the recurring underestimation of this thinning in numerical models raises concerns about both the veracity of such reconstructions and the reliability of glaciological models. Recent work suggests the 8000-year-old Northeast Greenland Ice Stream (NEGIS), including a now-extinct northern tributary, may have been an early influence on Greenland ice-sheet dynamics. Yet, the inaccurate reproduction of NEGIS-like dynamics in most models hampers investigation of whether this feature played a role in Holocene ice-sheet thinning. Here we show that grounding-line retreat in northeast Greenland triggers elevation changes at the northern summit via ice-dynamic effects modulated by the paleo NEGIS system. In our simulations, fast ice-stream flow caused by transiently imposed reduced basal shear stress following the northeast retreat explains 55% (± 18%) of the estimated ice thinning, showing that ice-stream dynamics is one of the main drivers of the NGRIP Holocene surface elevation drop. Our findings show that the ice-flow in northeast Greenland plays a large role in ice-surface elevation changes in central Greenland
Environmental changes on the northern Taymyr Peninsula (Russian Arctic) during the last 62 ka inferred from the lacustrine pollen record
Get PDFEnvironmental changes on the northern Taymyr Peninsula were reconstructed based on a new pollen record from a 46-m-long sediment core recovered from Lake Levinson-Lessing (latitude 74°27′54″N, longitude 98°39′58″E). The record is continuous and has a relatively good age control and high temporal resolution. Reaching a basal age of 62 cal. ka BP, it provides a unique environmental archive for the central Russian Arctic. The results reveal that open landscapes dominated 62.0–50.8 cal. ka BP, but presence of shrubs reflects a relatively warm summer climate. Numerous Pediastrum colonies in the sediments point to a rather low lake stand. A decrease in algae remains in the pollen spectra reflects a higher lake level after c. 50.8 cal. ka BP. From c. 47.8 to 25.5 cal. ka BP, lower contents of Betula and higher percentages of herb pollen point to colder and drier conditions. Besides, larger amounts of Pre-Quaternary palynomorphs and Pediastrum colonies point to increased erosion processes and a lower lake stand. After c. 25.5 cal. ka BP, herb communities further increased. Poaceae and Artemisia show the highest contents between c. 20.3 and 19.2 cal. ka BP, suggesting the coldest and driest climatic conditions during the studied time interval coincident with the Last Glacial Maximum (LGM). Pollen spectra dated c. 19.20–16.05 cal. ka BP reflect a slightly warmer and wetter climate in comparison to the LGM. Increased amounts of coprophilous fungi spores indirectly indicate that grazing animals were abundant around the lake. After с. 16.05 cal. ka BP, increases in shrubs and sedges reflect somewhat warmer and/or wetter conditions. The pollen data also well document the Allerød warming and Younger Dryas cooling events, reflecting an Atlantic influence on the regional climate development during these times. The transition from the Lateglacial to the Holocene at c. 11.63 cal. ka BP is characterized by drastic increases in pollen of shrubs, which document a significant warming. The Early Holocene (c. 11.63–8.30 cal. ka BP) pollen spectra reflect the Holocene Thermal Maximum in the study region. After c. 8.3 cal. ka BP, gradual cooling prevailed and led to climate conditions similar to modern ones at c. 2 cal. ka BP
The role of New World vultures as carriers of environmental antimicrobial resistance
Get PDFAbstract
Background
Although antibiotics have significantly improved human and animal health, their intensive use leads to the accumulation of antimicrobial resistance (AMR) in the environment. Moreover, certain waste management practices create the ideal conditions for AMR development while providing predictable resources for wildlife. Here, we investigated the role of landfills in the potentiation of New World vultures to disseminate environmental AMR. We collected 107 samples (soil, water, and feces) between 2023 and 2024, in different bird use sites (roosts, landfills and boneyards).
Results
We isolated enterococci (EN), Escherichia coli (EC), and Salmonella spp. (SM), performed antibiotic susceptibility tests, and quantified the presence of antibiotic resistance genes (ARGs) within all samples. We identified EN, EC, and SM, in 50, 37, and 26 samples, from the three vulture use areas, respectively. AMR was mainly to aminoglycoside, cephalosporin, and tetracycline, and the prevalence of multidrug resistance (MDR) was 5.3% (EC), 78.2% (EN), and 17.6% (SM). Variations in bacterial abundance and AMR/MDR profiles were found based on the season, use site, and sample types, which was corroborated by ARG analyses.
Conclusions
Our study suggests that landfills constitute a source of zoonotic pathogens and AMR for wildlife, due to readily available refuse input. Using non-invasive molecular methods, we highlight an often-ignored ecosystem within the One Health paradigm.
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Screening the release of chemicals and microplastic particles from diverse plastic consumer products into water under accelerated UV weathering conditions
Get PDFPhotodegradation of plastic consumer products is known to accelerate weathering and facilitate the release of chemicals and plastic particles into the aquatic environment. However, these processes are complex. In our presented pilot study, eight plastic consumer products were leached in distilled water under strong ultraviolet (UV) light simulating eight months of Central European climate and compared to their respective dark controls (DCs). The leachates and formed plastic particles were exploratorily characterized using a range of chemical analytical tools to describe degradation and leaching processes. These techniques covered (a) microplastic analysis, showing substantial liberation of plastic particles further increased under UV exposure, (b) non-targeted mass spectrometric characterization of the leachates, revealing several hundreds of chemical features with typically only minor agreement between the UV exposure and the corresponding DCs, (c) target analysis of 71 organic analytes, of which 15 could be detected in at least one sample, and (d) metal(loid) analysis, which revealed substantial release of toxic metal(loid)s further enhanced under UV exposure. A data comparison with the US-EPA's ToxVal and ToxCast databases showed that the detected metals and organic additives might pose substantial health and environmental concerns, requiring further study and comprehensive impact assessments
Mechanisms Underpinning the Net Removal Rates of Dissolved Organic Carbon in the Global Ocean
Get PDFAbstract With almost 700 Pg of carbon, marine dissolved organic carbon (DOC) stores more carbon than all living biomass on Earth combined. However, the controls behind the persistence and the spatial patterns of DOC concentrations on the basin scale remain largely unknown, precluding quantitative assessments of the fate of this large carbon pool in a changing climate. Net removal rates of DOC along the overturning circulation suggest lifetimes of millennia. These net removal rates are in stark contrast to the turnover times of days to weeks of heterotrophic microorganisms, which are the main consumers of organic carbon in the ocean. Here, we present a dynamic “MICrobial DOC” model (MICDOC) with an explicit representation of picoheterotrophs to test whether ecological mechanisms may lead to observed decadal to millennial net removal rates. MICDOC is in line with >40,000 DOC observations. Contrary to other global models, the reactivity of DOC fractions is not prescribed, but emerges from a dynamic feedback between microbes and DOC governed by carbon and macronutrient availability. A colimitation of macronutrients and organic carbon on microbial DOC uptake explains >70% of the global variation of DOC concentrations, and governs characteristic features of its distribution. Here, decadal to millennial net removal rates emerge from microbial processes acting on time scales of days to weeks, suggesting that the temporal variability of the marine DOC inventory may be larger than previously thought. With MICDOC, we provide a foundation for assessing global effects on DOC related to changes in heterotrophic microbial communities in a future ocean.
Plain Language Summary The ocean stores more carbon as dissolved organic compounds (DOC) than all animals and plants on land and the oceans combined. However, numerical models used for future climate scenarios lack an implementation of processes transforming DOC back to CO 2 by marine microorganisms. Here, we present a global dynamical ocean model that explicitly considers the processes of DOC degradation by marine microorganisms. In the present ocean, the availability of organic carbon but also nitrogen and phosphorus control the amount of carbon stored as DOC, as the lack of these nutrients inhibits its degradation by bacteria. The identification of these ecological controls allows a quantitative assessment of the fate of this large carbon reservoir in the future. The findings indicate that the marine DOC reservoir is potentially more dynamic than previously thought, since decadal to millennial scale net removal rates might be a result of microbial processes acting on shorter time scales.
Key Points A model to reconcile millennial‐scale bulk dissolved organic carbon degradation rates and short‐term microbial turnover times is presented Macronutrient colimitation can explain observed concentration patterns of dissolved organic carbon in the surface ocean Continuous microbial reworking suggests a higher temporal variability of the marine dissolved organic matter inventory than previously though
Phase Field Modeling of Cracks in Ice
Get PDFCalving of iceberg at ice shelves and floating glacier tongues is a poorly understood process, hence a physically motivated calving law is not yet existing. The demands on developing appropriate models for calving is large, as calving rates are needed for large scale ice sheet models that simulate the evolution of ice sheets. Here, we present a new approach for simulating fracture in ice. Our model is based on a finite strain theory for a viscoelastic Maxwell material, as the large simulation time leads to high strains. The fracturing process is simulated using a fracture phase field model that takes into account the elastic strain energy. We conduct simulations for a typical calving front geometry, with ice rises governing the formation of cracks. To represent the stress state adequately, we first conduct a spin-up to allow the viscous contribution to develop before the fracture phase field is computed. The analysis comprises the assessment of the crack path in comparison to observations, the influence of the spin-up, as well as elastic versus viscous strain contributions based on Hencky strain. Additionally, an estimate of released energy based on high resolution optical imagery of a Greenlandic calving front is presented
Extracting Spatial Spectra Using Coarse‐Graining Based On Implicit Filters
Get PDFScale analysis based on coarse-graining has been proposed recently as an alternative to Fourier analysis. It requires interpolation to a regular mesh for data from unstructured-mesh models. We propose an alternative coarse-graining method which relies on implicit filters using powers of discrete Laplacians. This method can work on arbitrary (structured or unstructured) meshes and is applicable to the direct output of unstructured-mesh models. Illustrations and detailed discussions are provided for discrete fields placed at vertices of triangular meshes. The case with placement on triangles is also briefly discussed
Digital twins: fast flyby X-ray CT of polar firn
Get PDFIn this study we report on the first continuous records of three dimensional firn structure reconstructions using archive pieces of firn cores that cover the whole depth range of firn starting from surface down to the transition to bubbly ice. The CT-measurements have been performed on 1m-core segments with the means of the AWI-X-ray-computer tomograph especially designed for ice applications. Flyby recording in helical mode under a time-optimized measurement protocol enabled us to reduce the scanning time to 25 minutes per meter firn. The reconstructed volumes have a spatial resolution of 120 µm, giving about 1 million cross-section images per firn core. The analytical work flow includes three steps of pre-processing with denoising, image segmentation and a manual check for outliers at break positions and a layer-wise (5.5 mm thick) calculation of several geometrical parameters like density, ice and pore cluster sizes, intercept lengths, autocorrelation functions, structural anisotropy, Euler number (connectivity), coordination number, bubble number density, closed and open porosity.
The method was applied to archive pieces of EGRIP-S6 (firn air pumping site, 2018, North-East-Greenland, 75.6°N ,35.9°W), B40 (Kohnen station, 2013, Dronning Maud Land, East Antarctica, 75.0°S, 0.1°E) and B51 (CoFi-Traverse 2013, Dronning Maud Land, East Antarctica, 75.1°S ,15.4°E). Temperature and accumulation rates at the different core sites vary between -30°C and -50°C and 130 mm w.eq./a and 40 mm w.eq./a respectively. The selected sites cover a wide range of recent environmental conditions of polar regions.
In this contribution we present several fundamental relationships between the derived geometrical parameters. The evolution of firn structure with depth will be discussed in respect to the dominant processes acting at different sintering/densification stages. The potential value for densification modelling, gas transport and enclosure modelling will be highlighted