Aromatic acids in a Eurasian Arctic ice core: a 2,600-year proxy record of biomass burning

Wildfires and their emissions have significant impacts on ecosystems, climate, atmospheric chemistry, and carbon cycling. Well-dated proxy records are needed to study the long-term climatic controls on biomass burning and the associated climate feedbacks. There is a particular lack of information about long-term biomass burning variations in Siberia, the largest forested area in the Northern Hemisphere. In this study we report analyses of aromatic acids (vanillic and para-hydroxybenzoic acids) over the past 2600 years in the Eurasian Arctic Akademii Nauk ice core. These compounds are aerosol-borne, semi-volatile organic compounds derived from lignin combustion. The analyses were made using ion chromatography with electrospray mass spectrometric detection. The levels of these aromatic acids ranged from below the detection limit (0.01 to 0.05 ppb; 1 ppb  =  1000 ng L−1) to about 1 ppb, with roughly 30 % of the samples above the detection limit. In the preindustrial late Holocene, highly elevated aromatic acid levels are observed during three distinct periods (650–300 BCE, 340–660 CE, and 1460–1660 CE). The timing of the two most recent periods coincides with the episodic pulsing of ice-rafted debris in the North Atlantic known as Bond events and a weakened Asian monsoon, suggesting a link between fires and large-scale climate variability on millennial timescales. Aromatic acid levels also are elevated during the onset of the industrial period from 1780 to 1860 CE, but with a different ratio of vanillic and para-hydroxybenzoic acid than is observed during the preindustrial period. This study provides the first millennial-scale record of aromatic acids. This study clearly demonstrates that coherent aromatic acid signals are recorded in polar ice cores that can be used as proxies for past trends in biomass burning

Controlling Domain-Wall Nucleation in Ta/CoFeB/MgO Nanomagnets via Local Ga+ Ion Irradiation

Comprehensive control of the domain wall nucleation process is crucial for spin-based emerging technologies ranging from random-access and storage-class memories over domain-wall logic concepts to nanomagnetic logic. In this work, focused Ga+ ion-irradiation is investigated as an effective means to control domain-wall nucleation in Ta/CoFeB/MgO nanostructures. We show that analogously to He+ irradiation, it is not only possible to reduce the perpendicular magnetic anisotropy but also to increase it significantly, enabling new, bidirectional manipulation schemes. First, the irradiation effects are assessed on film level, sketching an overview of the dose-dependent changes in the magnetic energy landscape. Subsequent time-domain nucleation characteristics of irradiated nanostructures reveal substantial increases in the anisotropy fields but surprisingly small effects on the measured energy barriers, indicating shrinking nucleation volumes. Spatial control of the domain wall nucleation point is achieved by employing focused irradiation of pre-irradiated magnets, with the diameter of the introduced circular defect controlling the coercivity. Special attention is given to the nucleation mechanisms, changing from a Stoner-Wohlfarth particle's coherent rotation to depinning from an anisotropy gradient. Dynamic micromagnetic simulations and related measurements are used in addition to model and analyze this depinning-dominated magnetization reversal

The cryostratigraphy of the Yedoma cliff of Sobo-Sise Island (Lena delta) reveals permafrost dynamics in the central Laptev Sea coastal region during the last 52 kyr

The present study examines the formation history and cryolithological properties of the late-Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled at 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above river level (a.r.l.). The sequence differentiates into three cryostratigraphic units: Unit A, dated from ca. 52 to 28 cal kyr BP; Unit B, dated from ca. 28 to 15 cal kyr BP; Unit C, dated from ca. 7 to 0 cal kyr BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial marine isotope stage (MIS) 3 (36–29 cal kyr BP) as well as during stadial MIS 2 (20–17 cal kyr BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena river caused by repeated outburst floods from the glacial Lake Vitim in southern Siberia along the Lena river valley towards the Arctic Ocean. The hiatus during the MIS 2–1 transition (15–7 cal kyr BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island and are most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic, and ice components. Higher permafrost aggradation rates of 1 m kyr−1 with higher organic-matter (OM) stocks (29 ± 15 kg C m−3, 2.2 ± 1.0 kg N m−3; Unit A) and mainly coarse silt are found for the interstadial MIS 3 if compared to the stadial MIS 2 with 0.7 m kyr−1 permafrost aggradation, lower OM stocks (14 ± 8 kg C m−3, 1.4 ± 0.4 kg N m−3; Unit B), and pronounced peaks in the coarse-silt and medium-sand fractions. Geochemical signatures of intra-sedimental ice reflect the differences in summer evaporation and moisture regime by higher ion content and less depleted ratios of stable δ18O and stable δD isotopes but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The δ18O and δD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11 ‰ and 15 ‰ and surprisingly low δ18O and δD values. Hence, the isotopic difference between late-Pleistocene and Holocene ice wedges is more pronounced in d than in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation, and degradation over the last approximately 52 kyr as well as their climatic and morphodynamic controls on the regional scale of the central Laptev Sea coastal region in NE Siberia

Rapid Fluvio-Thermal Erosion of a Yedoma Permafrost Cliff in the Lena River Delta

The degradation of ice-rich permafrost deposits has the potential to release large amounts of previously freeze-locked carbon (C) and nitrogen (N) with local implications, such as affecting riverine and near-shore ecosystems, but also global impacts such as the release of greenhouse gases into the atmosphere. Here, we study the rapid erosion of the up to 27.7 m high and 1,660 m long Sobo-Sise yedoma cliff in the Lena River Delta using a remote sensing-based time-series analysis covering 53 years and calculate the mean annual sediment as well as C and N release into the Lena River. We find that the Sobo-Sise yedoma cliff, which exposes ice-rich late Pleistocene to Holocene deposits, had a mean long-term (1965–2018) erosion rate of 9.1 m yr–1 with locally and temporally varying rates of up to 22.3 m yr–1. These rates are among the highest measured erosion rates for permafrost coastal and river shoreline stretches. The fluvio-thermal erosion led to the release of substantial amounts of C (soil organic carbon and dissolved organic carbon) and N to the river system. On average, currently at least 5.2 × 106 kg organic C and 0.4 × 106 kg N were eroded annually (2015–2018) into the Lena River. The observed sediment and organic matter erosion was persistent over the observation period also due to the specific configuration of river flow direction and cliff shore orientation. Our observations highlight the importance to further study rapid fluvio-thermal erosion processes in the permafrost region, also because our study shows increasing erosion rates at Sobo-Sise Cliff in the most recent investigated time periods. The organic C and N transport from land to river and eventually to the Arctic Ocean from this and similar settings may have severe implications on the biogeochemistry and ecology of the near-shore zone of the Laptev Sea as well as for turnover and rapid release of old C and N to the atmosphere

Pressure dissociation of integration host factor–DNA complexes reveals flexibility-dependent structural variation at the protein–DNA interface

E. coli Integration host factor (IHF) condenses the bacterial nucleoid by wrapping DNA. Previously, we showed that DNA flexibility compensates for structural characteristics of the four consensus recognition elements associated with specific binding (Aeling et al., J. Biol. Chem. 281, 39236–39248, 2006). If elements are missing, high-affinity binding occurs only if DNA deformation energy is low. In contrast, if all elements are present, net binding energy is unaffected by deformation energy. We tested two hypotheses for this observation: in complexes containing all elements, (1) stiff DNA sequences are less bent upon binding IHF than flexible ones; or (2) DNA sequences with differing flexibility have interactions with IHF that compensate for unfavorable deformation energy. Time-resolved Förster resonance energy transfer (FRET) shows that global topologies are indistinguishable for three complexes with oligonucleotides of different flexibility. However, pressure perturbation shows that the volume change upon binding is smaller with increasing flexibility. We interpret these results in the context of Record and coworker's model for IHF binding (J. Mol. Biol. 310, 379–401, 2001). We propose that the volume changes reflect differences in hydration that arise from structural variation at IHF–DNA interfaces while the resulting energetic compensation maintains the same net binding energy

Holocene thermokarst and pingo development in the Kolyma Lowland (NE Siberia)

Ground ice and sedimentary records of a pingo exposure reveal insights into Holocene permafrost, landscape and climate dynamics. Early to mid‐Holocene thermokarst lake deposits contain rich floral and faunal paleoassemblages, which indicate lake shrinkage and decreasing summer temperatures (chironomid‐based TJuly) from 10.5 to 3.5 cal kyr BP with the warmest period between 10.5 and 8 cal kyr BP. Talik refreezing and pingo growth started about 3.5 cal kyr BP after disappearance of the lake. The isotopic composition of the pingo ice (δ18O − 17.1 ± 0.6‰, δD −144.5 ± 3.4‰, slope 5.85, deuterium excess −7.7± 1.5‰) point to the initial stage of closed‐system freezing captured in the record. A differing isotopic composition within the massive ice body was found (δ18O − 21.3 ± 1.4‰, δD −165 ± 11.5‰, slope 8.13, deuterium excess 4.9± 3.2‰), probably related to the infill of dilation cracks by surface water with quasi‐meteoric signature. Currently inactive syngenetic ice wedges formed in the thermokarst basin after lake drainage. The pingo preserves traces of permafrost response to climate variations in terms of ground‐ice degradation (thermokarst) during the early and mid‐Holocene, and aggradation (wedge‐ice and pingo‐ice growth) during the late Holocene

The Yedoma cliff of Sobo Sise Island, eastern Lena Delta - insights into past and modern permafrost dynamics and related organic matter stock and release

The Lena Delta in eastern Siberia is the largest Arctic delta. Its terrestrial surface is shaped by four geomorphologic units. The oldest unit is built of remnants of late Pleistocene Yedoma Ice Complex (IC) and its degradation features. The studied Yedoma cliff on Sobo Sise Island in the South-Eastern part of the delta ranges from the river level to about 28 m height and is about 1.7 km long. During a field campaign in 2018, the entire permafrost sequence of the Sobo Sise Yedoma cliff has been sampled in 0.5-m vertical intervals. The geochronological record of the Sobo Sise Yedoma spans the last 52 ka cal BP based on radiocarbon dating and age-height modelling. The sequence differentiates into three cryostratigraphic units that are MIS3 Yedoma IC (52–28 ka cal BP), MIS2 Yedoma IC (28–15 ka cal BP) and MIS1 Holocene cover (7–0 ka cal BP). The cryostratigraphic sequence is not continuous, but has chronological gaps at 36–32.5 ka cal BP, at 20.5–18 ka cal BP and at 12.5–9 cal ka BP. These gaps represent traces of past changes in permafrost deposition and/or erosion regimes and climatic conditions. The cryostratigraphic units of the Yedoma cliff are characterized by differing properties of their clastic, organic and ice components. All units are built of poorly sorted sandy silt but differ in prevalent grain-size fractions ranging from fine silt to middle sand. The organic matter (OM) content is highest in the thin MIS1 Holocene cover (TOC of 11.3±9.9 wt%, TN of 0.6±0.3 wt%), but still substantial in MIS3 Yedoma IC (TOC of 4.5±2.5 wt%, TN of 0.3±0.1 wt%) and in MIS2 Yedoma IC (TOC of 2.1±1.3 wt%, TN of 0.2±0.1 wt%). The presence of syngenetic ice wedges in all units and the high content of intrasedimentary ice amount to a total volumetric ice content of 88.4 vol%. The high ice content in combination with the exposition of the cliff towards the main river channel results in a very high susceptibility to thaw and thermo-erosion. The high mean cliff erosion rate of 10.3 m yr−1 (1975-2018) results in large OM quantities entering the Lena River (3.2±2.1 kt organic carbon per year, 0.3±0.1 kt nitrogen per year along the 1.7 km long Yedoma cliff). Ongoing fluvial dynamics and changing runoff regimes with extended ice-free seasons and warmer water will most likely maintain high permafrost cliff erosion rates in the future and further facilitate high fluxes of terrestrial fossil OM into the riverine and eventually marine ecosystems

The Yedoma cliff of Sobo Sise Island - insights into past and modern permafrost dynamics and related organic matter stock and release

The present study of the permafrost exposed the Sobo-Sise Yedoma cliff in the eastern Lena Delta provides a comprehensive cryostratigraphic and organic matter (OM) inventory, insights into permafrost aggradation and degradation over the last about 52 thousand years and their climatic and morphodynamic controls on regional scale of the Central Laptev Sea coastal region in NE Siberia

A method for continuous239Pu determinations in Arctic and Antarctic ice cores

Atmospheric nuclear weapons testing (NWT) resulted in the injection of plutonium (Pu) into the atmosphere and subsequent global deposition. We present a new method for continuous semi-quantitative measurement of 239Pu in ice cores, which was used to develop annual records of fallout from NWT in ten ice cores from Greenland and Antarctica. The 239Pu was measured directly using an Inductively Coupled Plasma – Sector Field Mass Spectrometer, thereby reducing analysis time and increasing depth-resolution with respect to previous methods. To validate this method, we compared our one year averaged results to published 239Pu records and other records of NWT. The 239Pu profiles from four Arctic ice cores reflected global trends in NWT and were in agreement with discrete Pu profiles from lower latitude ice cores. The 239Pu measurements in the Antarctic ice cores tracked low latitude NWT, consistent with previously published discrete records from Antarctica. Advantages of the continuous 239Pu measurement method are (1) reduced sample preparation and analysis time; (2) no requirement for additional ice samples for NWT fallout determinations; (3) measurements are exactly co-registered with all other chemical, elemental, isotopic, and gas measurements from the continuous analytical system; and (4) the long half-life means the 239Pu record is stable through time

Late Quaternary palaeo-environmental history of Muostakh Island, Northern Siberia based on sedimentological and geocryological studies

Muostakh Island (N 71°36’; E 129°57’) is a spectacular site in the Siberian Arctic due to its very high coastal erosion rates of up to 20 m/year as well as substantial permafrost subsidence (Günther et al., 2015). The island extends about 7.5 km in the N-S direction and up to 500m in E-W direction and has been connected to the mainland until a few thousand years ago. Sediments and ground ice of the Yedoma type (the so called Ice Complex; Schirrmeister et al., 2011) form up to 20 m high coastal cliffs on Muostakh Island. The main aim of this multi-proxy study is to cover the complete sedimentological and geocryological sequence for a detailed palaeoenvironmental interpretation of the island. In general, the sedimentary sequence from Muostakh Island is divided into three stratigraphic units and consists of sediments of late Pleistocene to Holocene age. The lowermost unit A is approximately 8 m thick, rich in ground ice and comprises mostly sandy silt alternating with thin peat layers. At the top of this unit, a prominent 1 m thick peat layer is found in many sections on the island. In unit A, the ice wedges may reach widths of up to 5 m. At ca. 10m a.s.l., a hiatus from ca. 41.6 kyr BP to ca. 19.7 kyr BP is indicated by an erosional plane sharply intersecting ice wedges and sedimentary structures as well as by geocryological observations, i.e. distinctly narrower ice wedges above the discordance. Above this erosional plane, unit B, which is composed of 8-9 m of coarse-grained material, is indicative for fast and highly-energetic deposition, absent in many other sites of Ice Complex exposures in the Laptev Sea region (i.e. at nearby Mamontovy Khayata outcrop on Bykovsky Peninsula; Meyer et al., 2002). The upper (and youngest) sedimentary unit C reaches a maximum thickness of about 4-5 m and is laterally discontinuous. About 10 m wide peaty patches of Holocene organic-rich and ice-rich sandy silts cover the underlying deposits. Peat patches are intersected by ice wedges of generally less than 1 m wide, but in exceptions also reaching 3-5 m in width, penetrating downwards into the older layers. Here we present the complete sedimentological sequence of Muostakh Island including new AMS 14C radiocarbon ages both from sediment and ice wedges. Sedimentological, geochemical and geocryological data include the coarse-grained layer for the first time, which highlights an episode of erosion and rapid deposition in Siberian Ice Complex during the Last Glacial Maximum. Stable isotope data from ice wedges complement this study with winter season paleoclimate information. This multidisciplinary study will re-evaluate the Late Quaternary depositional and palaeo-environmental history of the region