Winter Ecosystem Respiration and Sources of CO2 From the High Arctic Tundra of Svalbard: Response to a Deeper Snow Experiment

Currently, there is a lack of understanding on how the magnitude and sources of carbon (C) emissions from High Arctic tundra are impacted by changing snow cover duration and depth during winter. Here we investigated this issue in a graminoid tundra snow fence experiment on shale-derived gelisols in Svalbard from the end of the growing season and throughout the winter. To characterize emissions, we measured ecosystem respiration (Reco) along with its radiocarbon (14C) content. We assessed the composition of soil organic matter (SOM) by measuring its bulk-C and nitrogen (N), 14C content, and n-alkane composition. Our findings reveal that greater snow depth increased soil temperatures and winter Reco (25 mg C m−2 d−1 under deeper snow compared to 13 mg C m−2 d−1 in ambient conditions). At the end of the growing season, Reco was dominated by plant respiration and microbial decomposition of C fixed within the past 60 years (Δ14C = 62 ± 8‰). During winter, emissions were significantly older (Δ14C = −64 ± 14‰), and likely sourced from microorganisms decomposing aged SOM formed during the Holocene mixed with biotic or abiotic mineralization of the carbonaceous, fossil parent material. Our findings imply that snow cover duration and depth is a key control on soil temperatures and thus the magnitude of Reco in winter. We also show that in shallow Arctic soils, mineralization of carbonaceous parent materials can contribute significant proportions of fossil C to Reco. Therefore, permafrost-C inventories informing C emission projections must carefully distinguish between more vulnerable SOM from recently fixed biomass and more recalcitrant ancient sedimentary C sources

The Biodiversity and Geochemistry of Cryoconite Holes in Queen Maud Land, East Antarctica

Cryoconite holes are oases of microbial diversity on ice surfaces. In contrast to the Arctic, where during the summer most cryoconite holes are ‘open’, in Continental Antarctica they are most often ‘lidded’ or completely frozen year-round. Thus, they represent ideal systems for the study of microbial community assemblies as well as carbon accumulation, since individual cryoconite holes can be isolated from external inputs for years. Here, we use high-throughput sequencing of the 16S and 18S rRNA genes to describe the bacterial and eukaryotic community compositions in cryoconite holes and surrounding lake, snow, soil and rock samples in Queen Maud Land. We cross correlate our findings with a broad range of geochemical data including for the first time 13C and 14C analyses of Antarctic cryoconites. We show that the geographic location has a larger effect on the distribution of the bacterial community compared to the eukaryotic community. Cryoconite holes are distinct from the local soils in both 13C and 14C and their isotopic composition is different from similar samples from the Arctic. Carbon contents were generally low (≤0.2%) and older (6–10 ky) than the surrounding soils, suggesting that the cryoconite holes are much more isolated from the atmosphere than the soils

Assessment of hydropyrolysis as a method for the quantification of black carbon using standard reference materials

A wide selection of thermal, chemical and optical methods have been proposed for the quantification of black carbon (BC) in environmental matrices, and the results to date differ markedly depending upon the method used. A new approach is hydropyrolysis (hypy), where pyrolysis assisted by high hydrogen pressures (150 bar) facilitates the complete reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum (defined as BChypy). Here, the potential of hypy for the isolation and quantification of BC is evaluated using the 12 reference materials from the International BC Ring Trial, comprising BC-rich samples, BC-containing environmental matrices and BC-free potentially interfering materials. By varying the hypy operating conditions, it is demonstrated that lignocellulosic, humic and other labile organic carbon material (defined as non-BChypy) is fully removed by 550 °C, with hydrogasification of the remaining BChypy not commencing until over 575 °C. The resulting plateau in sample mass and carbon loss is apparent in all of the environmental samples, facilitating BC quantification in a wide range of materials. The BChypy contents for all 12 ring trial samples fall within the range reported in the BC inter-comparison study, and systematic differences with other methods are rationalised. All methods for BC isolation, including hypy are limited by the fact that BC cannot be distinguished from extremely thermally mature organic matter; for example in high rank coals. However, the data reported here indicates that BChypy has an atomic H/C ratio of less than 0.5 and therefore comprises a chemically well-defined polyaromatic structure in terms of the average size of peri-condensed aromatic clusters of >7 rings (24 carbon atoms), that is consistent across different sample matrices. This, together with the sound underlying rationale for the reductive removal of labile organic matter, makes hypy an ideal approach for matrix independent BC quantification. The hypy results are extremely reproducible, with BChypy determinations from triplicate analyses typically within ±2% across all samples, limited mainly by the precision of the elemental analyser

Conceptual Design of a Liquid Helium Vertical Test-Stand for 2m long Superconducting Undulator Coils

Superconducting Undulators (SCUs) can produce higher photon flux and cover a wider photon energy range compared to permanent magnet undulators (PMUs) with the same vacuum gap and period length. To build the know-how to implement superconducting undulators for future upgrades of the European XFEL facility, the test stand SUNDAE1 for the characterization of SCU is being developed. The purpose of SUNDAE1 is the training, tuning and development of new SCU coils by means of precise magnetic field measurements. The experimental setup will allow the characterization of magnets up to 2m in length. These magnets will be immersed in a Helium bath at 4K or 2K temperature. In this article, we describe the experimental setup and highlight its expected performances

Global-scale evidence for the refractory nature of riverine black carbon

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Nature Geoscience 11 (2018): 584-588, doi:10.1038/s41561-018-0159-8.Wildfires and incomplete combustion of fossil fuel produce large amounts of black carbon. Black carbon production and transport are essential components of the carbon cycle. Constraining estimates of black carbon exported from land to ocean is critical, given ongoing changes in land use and climate, which affect fire occurrence and black carbon dynamics. Here, we present an inventory of the concentration and radiocarbon content (∆14C) of particulate black carbon for 18 rivers around the globe. We find that particulate black carbon accounts for about 15.8 ± 0.9% of river particulate organic carbon, and that fluxes of particulate black carbon co-vary with river-suspended sediment, indicating that particulate black carbon export is primarily controlled by erosion. River particulate black carbon is not exclusively from modern sources but is also aged in intermediate terrestrial carbon pools in several high-latitude rivers, with ages of up to 17,000 14C years. The flux-weighted 14C average age of particulate black carbon exported to oceans is 3,700 ± 400 14C years. We estimate that the annual global flux of particulate black carbon to the ocean is 0.017 to 0.037 Pg, accounting for 4 to 32% of the annually produced black carbon. When buried in marine sediments, particulate black carbon is sequestered to form a long-term sink for CO2.A.C. acknowledges financial support from the University of Zurich Forschungskredit Fellowship and the University of Zurich (grant No. STWF-18-026). M.R., S.A. and M.S. acknowledge support from the University Research Priority Projection Global Change and Biodiversity (URPP-GCB). M.Z. acknowledges support from the National Natural Science Foundation of China (No. 41521064). T.E. acknowledges support from the Swiss National Science Foundation (“CAPS-LOCK” and “CAPS-LOCK2” #200021_140850). V.G. acknowledges financial support from an Independent Study Award from the Woods Hole Oceanographic Institution

SUNDAE1: A Liquid Helium Vertical Test-Stand for 2m Long Superconducting Undulator Coils

Superconducting Undulators (SCUs) can produce higher photon flux and cover a wider photon energy range compared to permanent magnet undulators (PMUs) with the same vacuum gap and period length. To build the know-how to implement superconducting undulators for future upgrades of the European XFEL facility, two magnetic measurement test stands named SUNDAE 1 and 2 (Superconducting UNDulAtor Experiment) are being developed. SUNDAE1 will facilitate research and development on magnet design thanks to the possibility of training new SCU coils and characterizing their magnetic field. The experimental setup will allow the characterization of magnets up to 2m in length. These magnets will be immersed in a Helium bath at 2K or 4K temperature. In this article, we describe the experimental setup and highlight its expected performances

Marked isotopic variability within and between the Amazon River and marine dissolved black carbon pools

Riverine dissolved organic carbon (DOC) contains charcoal byproducts, termed black carbon (BC). To determine the significance of BC as a sink of atmospheric CO2 and reconcile budgets, the sources and fate of this large, slow-cycling and elusive carbon pool must be constrained. The Amazon River is a significant part of global BC cycling because it exports an order of magnitude more DOC, and thus dissolved BC (DBC), than any other river. We report spatially resolved DBC quantity and radiocarbon (Δ14C) measurements, paired with molecular-level characterization of dissolved organic matter from the Amazon River and tributaries during low discharge. The proportion of BC-like polycyclic aromatic structures decreases downstream, but marked spatial variability in abundance and Δ14C values of DBC molecular markers imply dynamic sources and cycling in a manner that is incongruent with bulk DOC. We estimate a flux from the Amazon River of 1.9–2.7 Tg DBC yr−1 that is composed of predominately young DBC, suggesting that loss processes of modern DBC are important

The NA48 LKr calorimeter readout electronics

The NA48 experiment at the CERN SPS accelerator is making a measurement of the direct CP violation parameter $\epsilon'/\epsilon$ by comparing the four rates of decay of $K_{S}$ and $K_{L}$ into $2\pi^{0}$ and $\pi^{+}\pi^{-}$. To reconstruct the decays into $2\pi^{0}$ the information from the almost 13500 channels of a quasi-homogeneous liquid krypton electromagnetic calorimeter is used. The readout electronics of the calorimeter has been designed to provide a dynamic range from a few MeV to about 50 GeV energy deposition per cell, and to sustain a high rate of incident particles. The system is made by cold charge preamplifiers (working at 120 degrees K), low-noise fast shapers followed by digitizer electronics at 40 MHz sampling rate that employs a gain switching technique to expand the dynamic range, where the gain can be selected for each sample individually (i.e. every 25 ns). To reduce the amount of data collected the system contains a zero suppression circuit based on halo expansion

Highlights from the Pierre Auger Observatory

The Pierre Auger Observatory is the world's largest cosmic ray observatory. Our current exposure reaches nearly 40,000 km$^2$ str and provides us with an unprecedented quality data set. The performance and stability of the detectors and their enhancements are described. Data analyses have led to a number of major breakthroughs. Among these we discuss the energy spectrum and the searches for large-scale anisotropies. We present analyses of our X$_{max}$ data and show how it can be interpreted in terms of mass composition. We also describe some new analyses that extract mass sensitive parameters from the 100% duty cycle SD data. A coherent interpretation of all these recent results opens new directions. The consequences regarding the cosmic ray composition and the properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray Conference, Rio de Janeiro 201