Alfred Wegener Institute for Polar and Marine Research
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A simple method of purifying authigenic 10Be from sediments for AMS-analysis
Get PDFThe cosmogenic radionuclide 10Be is used for a variety of applications, its analysis however requires laborious purification methods. We developed a simple purification protocol for Be from sediment samples that works without strongly hazardous chemicals or time consuming and expensive ion exchange columns. The combination of hydroxide precipitations and precipitation in NaHCO3 was compared to an established protocol of hydroxide precipitations and ion exchange columns. The new method has a slightly lower Be-yield and purity of the resulting samples. However, this does not have a significant influence on performance during AMS-measurement where both methods performed equally well. The avoidance of column chromatography reduces sample preparation costs and space requirements in the lab allowing for more samples to be prepared simultaneously
Life Cycles and Polycyclicity of Mega Retrogressive Thaw Slumps in Arctic Permafrost Revealed by 2D/3D Geophysics and Long‐Term Retreat Monitoring
Get PDFMega retrogressive thaw slumps (MRTS, >106 m3) are a major threat to Arctic infrastructure, alter regional biogeochemistry, and impact Arctic carbon budgets. However, processes initiating and reactivating MRTS are insufficiently understood. We hypothesize that MRTS preferentially develop a polycyclic behavior because the material is thermally and mechanically prepared for subsequent generation failure. In contrast to remote sensing, geophysical reconnaissance reveals the inner structure and relative thermal state of MRTS decameters beneath slump surfaces, potentially controlling polycyclicity. Based on their life cycle development, five (M)RTS were studied on Herschel Island, an MRTS hotspot on the Canadian Beaufort coast. We combine >2 km of electrical resistivity tomography (ERT), 500 m of ground-penetrating radar (GPR) and annual monitoring of headwall retreat from 2004 to 2013 to reveal the thermal state, internal structure, and volume loss of slumps. ERT data were calibrated with unfrozen-frozen transitions from frost probing of active layer thickness and shallow boreholes. In initial stage MRTS, ERT displays surficial thermal perturbations a few meters deep, coincident with recent mud pool and mud flow development. In early stage polycyclic MRTS, ERT shows decameter deep-reaching thermal perturbations persisting even 300 years after the last activation. In peak-stage polycyclic MRTS, 3D-ERT highlights actively extending deep-reaching thermal perturbations caused by gully incisions, mud slides and mud flows. GPR and headwall monitoring reveal structural disturbance by historical mud flows, ice-rich permafrost, and a decadal quantification of headwall retreat and slump floor erosion. We show that geophysical signatures identify long-lasting thermal and mechanical disturbances in MRTS predefining their susceptibility to polycyclic reactivation
Vegetation and glacier dynamics are sensitive to summer (not winter) warming and the evidence for larch refugia in the ‘Northern Pole of Cold’ inferred from sedimentary ancient DNA and geochemistry
Get PDFClimate seasonality critically influences the functioning and dynamics of ecosystems in continental areas. The ecological importance of winter temperatures on high-latitude vegetation changes has recently been argued to be largely overlooked in comparison to summer temperatures. The Oymyakon region from eastern Siberia, with its strong continentality of extremely cold winters and moderately warm summers, is ideally suited to study the response of past vegetation to seasonal temperature changes based on long ecological time-series. However, few paleorecords are available from this area. The history of regional glacial activity and potential plant refugia since Marine Isotope Stage (MIS) 3 is not well understood. Here, we present geochemical and plant DNA metabarcoding records retrieved from a sediment core from Lake Ulu in the Oymyakon region, which provides detailed information on glacier and vegetation dynamics over the last 43 cal. ka BP. Our results suggest that glacial fluctuations were primarily driven by summer insolation, and Lake Ulu was likely initiated by glacial retreat during MIS 3. The catchment experienced multiple glacial advance/retreat cycles until the Last Glacial Maximum, and the glaciers fully retreated by 20 cal. ka BP. In addition, a tundra-steppe landscape dominated by Dryas, Papaver, Saliceae, and Anthemideae occupied the catchment for most of the time and began to collapse around 19 cal. ka BP following the expansion of trees and shrubs such as Larix, Betula, Alnus, and Vaccinium. Postglacial plant assemblages in the Oymyakon region exhibit a high sensitivity to summer temperature variations, with minimal impact from winter temperatures. This can be explained by the dominance of summer insolation amplitude, extreme continentality, extended plant growing season, and plant genetic adaptation to cold. Notably, our ancient DNA record show the earliest postglacial expansion of larch in eastern Siberia (around 18.6 cal. ka BP), which is likely related to the presence of local refugia. This implies that the Oymyakon region may be one of the earliest sources for larch recolonization and that more research should be implemented to provide insights into larch expansion and migration, and to better predict the future scenarios for Siberian larch forests
A Practical Approach to Utilize Deep-Learning Algorithms for Earthquake Catalog Compilation in Local OBS Networks
Get PDFIn land-based seismology, modern automatic earthquake detection and phase picking algorithms have proven to outperform classic methods, resulting in more comprehensive catalogs with significantly reduced manual workload. However, similar advancements in marine-based seismology have been more challenging, particularly with Ocean Bottom Seismometer (OBS) data, which typically show lower signal-to-noise ratio and have limited labeled datasets available for training deep-learning models. In this study, we apply modern event detection and land-based phase picking algorithms to a ~12-month local OBS dataset, comparing resulting earthquake catalogs and location accuracy. We compare manually detected events and visually revised picks to their automatic counterparts, revealing that seismicity patterns from automatic catalogs are comparable to manually revised catalogs after applying strict location quality control. We find PhaseNet more suitable for local OBS networks and suggest a pick-independent event detection approach like Lassie for initial catalog compilation. Furthermore, we find that catalog completeness cannot be reliably determined using automatic approaches. As automatic picks are not yet reliable enough for developing velocity models or interpreting small-scale seismicity patterns, we suggest to apply different manual re-picking schemes depending on the aim of the study
Nutritional thermal ecology: investigating the combined influence of temperature and nutrient availability on plant‐ectotherm trophic interactions
Get PDFMany primary consumers in freshwater, marine and terrestrial systems are ectotherms (e.g. zooplankton and insects), whose metabolisms, and therefore nutritional demands, are modulated by temperature. Further, nutrient availability largely influences the quality of resources consumed by these organisms, and hence affects whether nutritional demands of consumers are fulfilled. From these considerations, a crucial question arises: how do temperature and nutrient availability together modulate trophodynamics at the basis of food webs? Addressing this question for zooplankton and insects is essential since these consumers are the most abundant metazoans on Earth, and they link primary production to higher trophic levels. Here, we synthesize the existing literature and offer avenues to guide future scientific endeavours. We highlight that the vast majority of studies on the combined influence of temperature and nutrient availability published to date focus on at least one of the following research topics: 1) metabolic requirements of ectotherms; 2) feeding behaviour; 3) eco‐evolutionary processes; and 4) trophodynamics. We pose that further advances in this field of research may provide a robust understanding of how modulations of consumer metabolic requirements and resource quality define consumer–producer interactions across marine, freshwater and terrestrial ecosystems. This research effort would enable to combine the fields of Ecological stoichiometry and of Metabolic theory of ecology, and create an integrated approach, which we propose to call Nutritional thermal ecology.</jats:p
Erfassung und Charakterisierung geschützter Meeresboden-Biotope in der Nordsee mit Hilfe von Unterwasservideos
Get PDFCharacteristics and sources of fluorescent aerosols in the central Arctic Ocean
Get PDFThe Arctic is sensitive to cloud radiative forcing. Due to the limited number of aerosols present throughout much of the year, cloud formation is susceptible to the presence of cloud condensation nuclei and ice nucleating particles (INPs). Primary biological aerosol particles (PBAP) contribute to INPs and can impact cloud phase, lifetime, and radiative properties. We present yearlong observations of hyperfluorescent aerosols (HFA), tracers for PBAP, conducted with a Wideband Integrated Bioaerosol Sensor, New Electronics Option during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition (October 2019–September 2020) in the central Arctic. We investigate the influence of potential anthropogenic and natural sources on the characteristics of the HFA and relate our measurements to INP observations during MOSAiC. Anthropogenic sources influenced HFA during the Arctic haze period. But surprisingly, we also found sporadic “bursts” of HFA with the characteristics of PBAP during this time, albeit with unclear origin. The characteristics of HFA between May and August 2020 and in October 2019 indicate a strong contribution of PBAP to HFA. Notably from May to August, PBAP coincided with the presence of INPs nucleating at elevated temperatures, that is, &gt;−9°C, suggesting that HFA contributed to the “warm INP” concentration. The air mass residence time and area between May and August and in October were dominated by the open ocean and sea ice, pointing toward PBAP sources from within the Arctic Ocean. As the central Arctic changes drastically due to climate warming with expected implications on aerosol–cloud interactions, we recommend targeted observations of PBAP that reveal their nature (e.g., bacteria, diatoms, fungal spores) in the atmosphere and in relevant surface sources, such as the sea ice, snow on sea ice, melt ponds, leads, and open water, to gain further insights into the relevant source processes and how they might change in the future.</jats:p
Sediment Freeze‐On and Transport Near the Onset of a Fast‐Flowing Glacier in East Antarctica
Get PDFUnderstanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice‐sheet dynamics. Yet, direct data are sparse and difficult to acquire. Here, we employ ultra‐wideband radar to map high‐backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. Our backscatter analysis reveals that the basal ice in an area of ∼10,000 km² is composed of along‐flow oriented sediment‐laden basal ice units connected to the basal substrate, extending up to several hundred meters thick. Three‐dimensional thermomechanical modeling supports that these units form via basal freeze‐on of subglacial water that originated from further upstream. Our findings suggest that basal freeze‐on, and the entrainment and transport of subglacial material play a significant role in an accurate representation of material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice‐sheet modeling
The Chemical Effect of Increased Water Vapor From the Hunga Tonga‐Hunga Ha'apai Eruption on the Antarctic Ozone Hole
Get PDFThe eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 was one of the most explosive eruptions of the last decades. The amount of water vapor injected into the stratosphere was unprecedented in the observational record, increasing the stratospheric water vapor burden by about 10%. Using model runs from the ATLAS chemistry and transport model and Microwave Limb Sounder (MLS) satellite observations, we show that while 20%–40% more water vapor than usual was entrained into the Antarctic polar vortex in 2023 as it formed, the direct chemical effect of the increased water vapor on Antarctic ozone depletion in June through October was minor (less than 4 DU). This is because low temperatures in the vortex, as occur every year in the Antarctic, limit water vapor to the saturation pressure and thus reset any anomalies through the process of dehydration before they can affect ozone loss