Search

The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) have been investigated using hourly water temperature and water level records covering a three year period (2009-2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. The data were used for numerical modeling with FLake software, and also to determine the physical indices of the lakes. The lakes vary in area, depths and volumes. The winter thermal regime is characterized by an ice cover up to 2 m thick that survives for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increase at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. The effects of solar radiation return prior to ice break-up, effectively warming the water beneath the ice cover and inducing convective mixing. Ice break-up starts the beginning of June and takes until the middle or end of June for completion. Mixing occurs within the entire water column from the start of ice break-up and continues during the ice-free periods, as confirmed by the Wedderburn numbers. Some of the lakes located closest to the Lena River are subjected to varying levels of spring flooding with river water, on an annual basis. Numerical modeling using FLake software indicates that the vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m-2 in summer and with heat released back into the water column at a~rate of less than 1 W m-2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C. [ABSTRACT FROM AUTHOR]

High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon stock will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under newly formed thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 peta-grams of carbon (Pg-C) (68 % range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42 to 141 Pg-C and 157 to 313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates only consider fluxes from newly thawed permafrost, not from soils already part of the seasonally thawed active layer under pre-industrial climate. Our simulated CH4 fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40 % of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest CH4 emission rates of about 50 Tg-CH4 per year around the middle of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is taken into account. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions crucially affects our simulated circumpolar CH4 fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts to about 0.03-0.14 °C (68 % ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario, adding 0.16 to 0.39 °C (68% range) to simulated global mean surface air temperatures in the year 2300. [ABSTRACT FROM AUTHOR]

High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon store will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost-carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 petagrammes of carbon (Pg-C) (68% range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42-141 and 157-313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates do only consider fluxes from newly thawed permafrost but not from soils already part of the seasonally thawed active layer under preindustrial climate. Our simulated methane fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40 % of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest methane emission rates of about 50Tg-CH4year-1 around the mid of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is accounted for. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions does crucially affect our simulated circumpolar methane fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts about 0.03-0.14°C (68% ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario with adding 0.16-0.39°C (68% range) to simulated global mean surface air temperatures in the year 2300. [ABSTRACT FROM AUTHOR]

Subgrid processes occur in various ecosystems and landscapes but, because of their small scale, they are not represented or poorly parameterized in climate models. These local heterogeneities are often important or even fundamental for energy and carbon balances. This is especially true for northern peatlands and in particular for the polygonal tundra, where methane emissions are strongly influenced by spatial soil heterogeneities. We present a stochastic model for the surface topography of polygonal tundra using Poisson-Voronoi diagrams and we compare the results with available recent field studies. We analyze seasonal dynamics of water table variations and the landscape response under different scenarios of precipitation income. We upscale methane fluxes by using a simple idealized model for methane emission. Hydraulic interconnectivities and large-scale drainage may also be investigated through percolation properties and thresholds in the Voronoi graph. The model captures the main statistical characteristics of the landscape topography, such as polygon area and surface properties as well as the water balance. This approach enables us to statistically relate large-scale properties of the system to the main small-scale processes within the single polygons. [ABSTRACT FROM AUTHOR]

Freeze/thaw (F/T) processes can be quite different under the various land surface types found in the heterogeneous polygonal tundra of the Arctic. Proper simulation of these different processes is essential for accurate prediction of the release of greenhouse gases under a warming climate scenario. In this study we have modified the dynamic organic soil version of the Terrestrial Ecosystem Model (DOS-TEM) to simulate F/T processes beneath the polygon rims, polygon centers (with and without water), and lakes that are common features in Arctic lowland regions. We first verified the F/T algorithm in the DOS-TEM against analytical solutions, and then compared the results with in situ measurements from Samoylov Island, Siberia. In the final stage, we examined the different responses of the F/T processes for different water levels at the various land surface types. The simulations revealed that (1) the DOS-TEM was very efficient and its results compared very well with analytical solutions for idealized cases, (2) the simulations compared reasonably well with in situ measurements although there were a number of model limitations and uncertainties, (3) the DOS-TEM was able to successfully simulate the differences in F/T dynamics under different land surface types, and (4) permafrost beneath water bodies was found to respond highly sensitive to changes in water depths between 1 and 2 m. Our results indicate that water is very important in the thermal processes simulated by the DOS-TEM; the heterogeneous nature of the landscape and different water depths therefore need to be taken into account when simulating methane emission responses to a warming climate. [ABSTRACT FROM AUTHOR]

Samoylov Island is centrally located within the Lena River Delta at 72° N, 126° E and lies within the Siberian zone of continuous permafrost. The landscape on Samoylov Island consists mainly of late Holocene river terraces with polygonal tundra, ponds and lakes, and an active floodplain. The island has been the focus of numerous multidisciplinary studies since 1993, which have focused on climate, land cover, ecology, hydrology, permafrost, and limnology. This paper aims to provide a framework for future studies by describing the characteristics of the island's meteorological parameters (temperature, radiation, and snow cover), soil temperature, and soil moisture. The land surface characteristics have been described using high resolution aerial images in combination with data from ground-based observations. Of note is that deeper permafrost temperatures have increased between 0.5 to 1 °C over the last five years. However, no clear warming of air and active layer temperatures is detected since 1998, though winter air temperatures during recent years have not been as cold as in earlier years. [ABSTRACT FROM AUTHOR]

Information on soil surface state is valuable for many applications such as climate studies and monitoring of permafrost regions. C-band scatterometer data indicate good potential to deliver information on surface freeze/thaw. Variation in state or amount of water contained in the soil causes significant alteration of dielectric properties of the soil which is markedly observable in scatterometer backscattered signal. A threshold-analysis method is developed to derive a set of parameters to be used in evaluating the normalized backscatter measurements through decision trees and anomaly detection modules for determination of freeze/thaw conditions. The model parameters are extracted from two years (2007-2008) backscatter data from ASCAT scatterometer onboard Metop satellite collocated with ECMWF ReAnalysis (ERA-Interim) soil temperature. Backscatter measurements are flagged as indicator of frozen/unfrozen surface, and snowmelt or existing water on the surface. The output product, so-called surface state flag (SSF), compares well with two modeled soil temperature data sets as well as the air temperature measurements from synoptic meteorological stations across the northern hemisphere. The SSF time series are also validated with soil temperature data available at four in situ observation sites in Siberian and Alaska regions showing the overall accuracy of about 80% to 90%. [ABSTRACT FROM AUTHOR]

The article presents a study on the use stochastic model based on Poisson-Voronoi Diagrams to analyze polygonal tundra. The study analyzes the landscape response and seasonal dynamics of water table variations under different precipitation income scenarios and the geometric characteristics of polygonal tundra and physical vapor deposition (PVD). Result shows that the model can show the statistical qualities of landscape topography like polygon area, water balance, and surface properties.

An abstract of the article "Page21: A Large-Scale International and Integrated Project to Measure the Impact of Permafrost Degradation on the Climate System," by Hans-Wolfgang Hubberten is presented.

Field campaigns were undertaken in May and June of 1992 and 1997 in order to study spectral reflectance characteristics of snow during melt-off. The investigations were performed on snow-covered tundra at Ny-Alesund, Svalbard (79 deg. N). Spectral measurements were acquired with spectroradiometers covering wavelengths from 350 to 2500 nm. Supporting measurements such as snow thickness, density, content of liquid water, grain size and shape, stratification of snowpack, as well as cloud observations and air temperature, were monitored throughout the field campaigns. Spectral measurements demonstrate that the near-infrared albedo is most affected by the ongoing snow metamorphism while the albedo in the visible wavelength range is more strongly affected by surface pollution. Comparisons of spectral measurements and spectrally integrated measurements emphasize the need for narrow-band to broad-band conversion when applying satellite-derived albedo to surface energy-balance calculations. As an example, Landsat TM Band 4 albedo is shown to produce slightly high albedo values compared to the spectrally integrated albedo (285-2800 nm). Daily albedo measurements from 1981-1997 show that the albedo normally drops from 80% to bare ground levels (10%) within two to four weeks and the date when the tundra becomes snow-free varies from early June to early July. Thus, the changing spectral characteristics of snow during melt-off combined with a general rapid decrease in albedo call for cautious use of satellite-derived albedo, especially when used as absolute numbers. Our data also illustrate the effect of cloud cover on surface albedo for an event in which the integrated albedo increased by 7% under cloudy conditions compared to clear skies without changes of surface properties. Finally, the reflectance of snow increases relative to nadir for measurements facing the sun and at azimuths 90 deg. and 180 deg. by 8, 15, 19, and 26% for viewing angles 15 deg. , 30 deg. , 45 deg. , an [ABSTRACT FROM AUTHOR]

CO2 release from thawing permafrost is both a consequence of, and a driver for, global warming, making accurate information on the Arctic carbon cycle essential for climate predictions. Eddy covariance data obtained from Bayelva (Svalbard) in 2015, using well‐established processing and quality control techniques, indicate that most of the annual net CO2 uptake is due to high CO2 flux events in winter that are associated with strong winds and probably relate to technical limitations of the gas analyzer. Emission events may relate to either (unidentified) instrumental limitations or to physical processes such as CO2 advection. Excluding the high winter uptake events yields an annual CO2 budget close to zero; whether or not these events are included can, therefore, have a considerable effect on carbon budget calculations. Further investigation will be crucial to pinpoint the factors causing these high CO2 flux events and to derive scientifically substantiated flux processing standards. Plain Language Summary: Global warming is making Arctic soils thaw, with formerly frozen organic material decomposing and producing the greenhouse gas CO2. This CO2 release further amplifies the rise in temperature. In order to predict how our climate will develop in the future, we, therefore, need to investigate how much CO2 is released into the atmosphere and how much is taken up by plants. Strong CO2 release or uptake signals are not expected during the Arctic winter due to the reduced microbial and plant activity but have nevertheless been observed at Arctic sites. We have investigated CO2 exchanges during the winter of 2015 at the Bayelva site, Svalbard, using the eddy covariance technique. We found that high levels of CO2 emission and uptake occurred during periods with high wind speed and have a significant impact on the calculated net annual CO2 exchange. The apparent CO2 uptake is likely to be an artefact resulting from technical limitations of the instruments, while the high levels of CO2 emission are probably a result of physical processes. However, known physical mechanisms alone, such as episodic outbursts of CO2 stored within the snow, cannot adequately explain our observations. Additional measurements will be required to identify the processes at play. Key Points: High levels of CO2 exchange during the Arctic winter, associated with high wind speeds, have a marked effect on the annual carbon budgetConventional flux measurement and calculation techniques are subject to large uncertainties under Arctic low‐flux conditionsLocal abiotic processes cannot explain the high‐flux events, suggesting advective flux contributions or unidentified instrumental limitations [ABSTRACT FROM AUTHOR]

The accelerated warming of the Arctic climate may alter the local and regional surface energy balances, for which changing land surface temperatures (LSTs) are a key indicator. Modeling current and anticipated changes in the surface energy balance requires an understanding of the spatio-temporal interactions between LSTs and land cover, both of which can be monitored globally by measurements from space. This paper investigates the accuracy of the MODIS LST/Emissivity Daily L3 Global 1 km V005 product and its spatio-temporal sensitivity to land surface properties in a Canadian High Arctic permafrost landscape. The land cover ranged from fully vegetated wet sedge tundra to barren rock. MODIS LSTs were compared with in situ radiometer measurements from wet tundra areas collected over a 2-year period from July 2008 to July 2010 including both summer and winter conditions. The accuracy of the MODIS LSTs was − 1.1 °C with a root mean square error of 3.9 °C over the entire observation period. Agreement was lowest during the freeze-back periods where MODIS LST showed a cold bias likely due to the overrepresentation of clear-sky conditions. A multi-year analysis of LST spatial anomalies, i.e., the difference between MODIS LSTs and the MODIS LST regional mean, revealed a robust spatio-temporal pattern. Highest variability in LST anomalies was found during freeze-up and thaw periods as well as for open water surface in early summer due to the presence or absence of snow or ice. The summer anomaly pattern was similar for all three years despite strong differences in precipitation, air temperature and net radiation. Summer periods with regional mean LSTs above 5.0 °C showed the greatest spatial diversity with four distinct 2.0 °C classes. Summer anomalies ranged from − 4.5 °C to 2.6 °C with an average standard deviation of 1.8 °C. Dry ridge areas heated up the most, while wetland areas and dry areas of sparsely vegetated bedrock with a high albedo remained coolest. The observed summer LST anomalies can be used as a baseline against which to evaluate both past and future changes in land surface properties that relate to the surface energy balance. Summer anomaly classes mainly reflected a combination of albedo and surface wetness. The potential to use this tool to monitor surface drying and wetting in the Arctic should therefore be further explored. A multi-sensor approach combining thermal satellite measurements with optical and radar imagery promises to be an effective tool for a dynamic, process-based ecosystem monitoring scheme. [ABSTRACT FROM AUTHOR]

Background: Transjugular intrahepatic portosystemic shunt (TIPSS) is highly effective for treatment of variceal bleeding; however, factors contributing to rebleeding complications remain unclear., Aims: In this study, we aim to determine risk factors for recurrent portal hypertensive gastrointestinal bleeding following TIPSS., Methods: Utilising the Advancing Liver Therapeutic Approaches multicentre database, we retrospectively identified adult patients who underwent TIPSS for secondary prophylaxis of variceal bleeding and had a gastrointestinal rebleeding event within 1 year. We developed multivariable logistic regression models to identify clinical/procedural characteristics associated with rebleeding., Results: We identified 476 patients, predominately middle-aged (mean age 57), male (62%) and White (65%), with mean MELD-Na 16. 16% (n = 77) had a rebleeding event; these patients were more likely to be male (p = 0.016), with higher serum creatinine (p = 0.005), MELD-Na (p = 0.0002), portal hypertensive gastropathy on pre-TIPSS upper endoscopy (p = 0.000) and with higher incidence of TIPSS revision (p = 0.000). There were no significant differences in type of TIPSS endoprosthesis, concurrent embolotherapy, and post-TIPSS pressure gradients between those who experienced rebleeding and those who did not. After adjusting for TIPSS revision, multivariable analysis revealed MELD-Na and presence of portal hypertensive gastropathy on pre-TIPSS endoscopy were independently associated with rebleeding., Conclusions: In this retrospective analysis of a multicentre, nationally representative database, we found that apart from TIPSS-related factors, high MELD-Na and portal hypertensive gastropathy on pre-TIPSS endoscopy were independent predictors of rebleeding within 1 year following TIPSS. These variables may be used to identify high-risk patients who may require additional monitoring following TIPSS., (© 2024 John Wiley & Sons Ltd.)

Arctic soil microbial communities may shift with increasing temperatures and water availability from climate change. We examined temperature and volumetric liquid water content (VWC) in the upper 80 cm of permafrost-affected soil over 2 years (2018-2019) at the Bayelva monitoring station, Ny Ålesund, Svalbard. We show VWC increases with depth, whereas in situ temperature is more stable vertically, ranging from -5°C to 5 °C seasonally. Prokaryotic metagenome-assembled genomes (MAGs) were obtained at 2-4 cm vertical resolution collected while frozen in April 2018 and at 10 cm vertical resolution collected while thawed in September 2019. The most abundant MAGs were Acidobacteriota, Actinomycetota, and Chloroflexota. Actinomycetota and Chloroflexota increase with depth, while Acidobacteriota classes Thermoanaerobaculia Gp7-AA8, Blastocatellia UBA7656, and Vicinamibacteria Vicinamibacterales are found above 6 cm, below 6 cm, and below 20 cm, respectively. All MAGs have diverse carbon-degrading genes, and Actinomycetota and Chloroflexota have autotrophic genes. Genes encoding β -glucosidase, N-acetyl-β-D-glucosaminidase, and xylosidase increase with depth, indicating a greater potential for organic matter degradation with higher VWC. Acidobacteriota dominate the top 6 cm with their classes segregating by depth, whereas Actinomycetota and Chloroflexota dominate below ∼6 cm. This suggests that Acidobacteriota classes adapt to lower VWC at the surface, while Actinomycetota and Chloroflexota persist below 6 cm with higher VWC. This indicates that VWC may be as important as temperature in microbial climate change responses in Arctic mineral soils. Here we describe MAG-based Seqcode type species in the Acidobacteriota, Onstottus arcticum, Onstottus frigus, and Gilichinskyi gelida and in the Actinobacteriota, Mayfieldus profundus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier GmbH.)

Purpose: This study aimed to present the institutional experience and algorithm for performing biliary interventions in liver transplant patients using the modified Hutson loop access (MHLA) and the impact of percutaneous endoscopy via the MHLA on these procedures., Methods: Over 13 years, 201 MHLA procedures were attempted on 52 patients (45 liver transplants; 24 living and 21 deceased donors) for diagnostic (e.g., cholangiography) and therapeutic (e.g., stent/drain insertion and cholangioplasty) purposes. The most common indications for MHLA were biliary strictures (60%) and bile leaks (23%). Percutaneous endoscopy was used to directly visualize the biliary-enteric anastomosis, diagnose pathology (e.g., ischemic cholangiopathy), and help in biliary hygiene (removing debris/casts/stones/stents) in 138/201 (69%) procedures. Technical success was defined as cannulating the biliary-enteric anastomosis and performing diagnostic/therapeutic procedure via the MHLA., Results: The technical success rate was 95% (190/201). The failure rate among procedures performed with and without endoscopy was 2% (3/138) versus 13% (8/63) (P = 0.0024), and the need for new transhepatic access (to aid the procedure) was 12% (16/138) versus 30% (19/63) (P = 0.001). Despite endoscopy, failure in 2% of the cases resulted from inflamed/friable anastomosis (1/3) and high-grade stricture (2/3) obstructing retrograde cannulation of biliary-enteric anastomosis. Major adverse events (bowel perforation and injury) occurred in 1% of the procedures, with no procedure-related mortality., Conclusions: MHLA-based percutaneous biliary intervention is a safe and effective alternative to managing complications after liver transplant. Percutaneous endoscopy via the MHLA improves success rates and may reduce the need for new transhepatic access. Level of Evidence Level 4., (© 2024. Springer Science+Business Media, LLC, part of Springer Nature and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE).)

Purpose: To evaluate recovery of platelet count after transjugular intrahepatic portosystemic shunt (TIPS) creation and patient factors predicting platelet recovery after TIPS creation., Materials and Methods: Adults with cirrhosis who underwent TIPS creation at 9 U.S. hospitals from 2010 to 2015 were included in this retrospective analysis. Change in platelets from before TIPS to 4 months after TIPS creation was characterized. Logistic regression was used to assess factors associated with top quartile percentage platelet increase after TIPS. Subgroup analyses were performed among patients with a pre-TIPS platelet count of ≤50 ×10 9 /L., Results: A total of 601 patients were included. The median absolute change in platelets was 1 × 10 9 /L (-26 × 10 9 /L to 25 × 10 9 /L). Patients with top quartile percent platelet increase experienced ≥32% platelet increase. In multivariable analysis, pre-TIPS platelet counts (odds ratio [OR], 0.97 per 10 9 /L; 95% CI, 0.97-0.98), age (OR, 1.24 per 5 years; 95% CI, 1.10-1.39), and pre-TIPS model for end-stage liver disease (MELD) scores (OR, 1.06 per point; 95% CI, 1.02-1.09) were associated with top quartile (≥32%) platelet increase. Ninety-four (16%) patients had a platelet count of ≤50 × 10 9 /L before TIPS. The median absolute platelet change was 14 × 10 9 /L (2 × 10 9 /L to 34 × 10 9 /L). Fifty-four percent of patients in this subgroup were in the top quartile for platelet increase. In multivariable logistic regression, age (OR, 1.50 per 5 years; 95% CI, 1.11-2.02) was the only factor associated with top quartile platelet increase in this subgroup., Conclusions: TIPS creation did not result in significant platelet increase, except among patients with a platelet count of ≤50 × 10 9 /L before TIPS. Lower pre-TIPS platelet counts, older age, and higher pre-TIPS MELD scores were associated with top quartile (≥32%) platelet increase in the entire cohort, whereas only older age was associated with this outcome in the patient subset with a pre-TIPS platelet count of ≤50 × 10 9 /L., (Copyright © 2023. Published by Elsevier Inc.)

Long-term atmospheric CO 2 concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Glecaprevir/pibrentasvir in combination with sofosbuvir may serve as a safe and effective option for treatment of recurrent hepatitis C virus post-liver transplant in patients who previously failed direct-acting antivirals., Competing Interests: Conflict-of-interest statement: Martin MT and Patel S serve on the speakers’ bureau for AbbVie and Gilead. Martin MT has received grant funding from Gilead and Merck, served on the advisory board for AbbVie and Gilead, and is a minor shareholder of AbbVie, Gilead, and Merck stock., (©The Author(s) 2023. Published by Baishideng Publishing Group Inc. All rights reserved.)

Purpose: To evaluate the outcomes of splenic artery aneurysm (SAA) embolization and compare adverse event (AE) rates after embolization in patients with and without portal hypertension (PHTN)., Materials and Methods: A retrospective review of all patients who underwent embolization of SAAs at 2 institutions was performed (34 patients from institution 1 and 7 patients from institution 2). Baseline demographic characteristics, preprocedural imaging, procedural techniques, and postprocedural outcomes were evaluated. Thirty-day postprocedural severe and life-threatening AEs were evaluated using the Society of Interventional Radiology guidelines. Thirty-day mortality and readmission rates were also evaluated. t test, χ 2 test, and/or Fisher exact test were used for the statistical analysis., Results: There was no statistically significant difference between patients with and without PHTN in the location, number, and size of SAA(s). All procedures were technically successful. There were 13 (32%) patients with and 28 (68%) patients without PHTN. The 30-day mortality rate (31% vs 0%; P = .007), readmission rates (61% vs 7%; P < .001), and severe/life-threatening AE rates (69% vs 0%; P < .001) were significantly higher in patients with PHTN than in those without PHTN., Conclusions: There was a significantly higher mortality and severe/life-threatening AE rate in patients with PHTN than in those without PHTN. SAAs in patients with PHTN need to be managed very cautiously, given the risk of severe/life-threatening AEs after embolization., (Copyright © 2022 SIR. Published by Elsevier Inc. All rights reserved.)

Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994-2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm -2 ) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types., (© 2022. The Author(s).)

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km 2 resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km 2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Arctic warming is affecting snow cover and soil hydrology, with consequences for carbon sequestration in tundra ecosystems. The scarcity of observations in the Arctic has limited our understanding of the impact of covarying environmental drivers on the carbon balance of tundra ecosystems. In this study, we address some of these uncertainties through a novel record of 119 site-years of summer data from eddy covariance towers representing dominant tundra vegetation types located on continuous permafrost in the Arctic. Here we found that earlier snowmelt was associated with more tundra net CO 2 sequestration and higher gross primary productivity (GPP) only in June and July, but with lower net carbon sequestration and lower GPP in August. Although higher evapotranspiration (ET) can result in soil drying with the progression of the summer, we did not find significantly lower soil moisture with earlier snowmelt, nor evidence that water stress affected GPP in the late growing season. Our results suggest that the expected increased CO 2 sequestration arising from Arctic warming and the associated increase in growing season length may not materialize if tundra ecosystems are not able to continue sequestering CO 2 later in the season., (© 2022. The Author(s).)

The active layer of permafrost in Ny Ålesund, Svalbard (79°N) around the Bayelva River in the Leirhaugen glacier moraine is measured as a small net carbon sink at the brink of becoming a carbon source. In many permafrost-dominating ecosystems, microbes in the active layers have been shown to drive organic matter degradation and greenhouse gas production, creating positive feedback on climate change. However, the microbial metabolisms linking the environmental geochemical processes and the populations that perform them have not been fully characterized. In this paper, we present geochemical, enzymatic, and isotopic data paired with 10 Pseudomonas sp. cultures and metagenomic libraries of two active layer soil cores (BPF1 and BPF2) from Ny Ålesund, Svalbard, (79°N). Relative to BPF1, BPF2 had statistically higher C/N ratios (15 ± 1 for BPF1 vs. 29 ± 10 for BPF2; n = 30, p < 10 -5 ), statistically lower organic carbon (2% ± 0.6% for BPF1 vs. 1.6% ± 0.4% for BPF2, p < 0.02), statistically lower nitrogen (0.1% ± 0.03% for BPF1 vs. 0.07% ± 0.02% for BPF2, p < 10 -6 ). The d 13 C values for inorganic carbon did not correlate with those of organic carbon in BPF2, suggesting lower heterotrophic respiration. An increase in the δ 13 C of inorganic carbon with depth either reflects an autotrophic signal or mixing between a heterotrophic source at the surface and a lithotrophic source at depth. Potential enzyme activity of xylosidase and N-acetyl-β-D-glucosaminidase increases twofold at 15°C, relative to 25°C, indicating cold adaptation in the cultures and bulk soil. Potential enzyme activity of leucine aminopeptidase across soils and cultures was two orders of magnitude higher than other tested enzymes, implying that organisms use leucine as a nitrogen and carbon source in this nutrient-limited environment. Besides demonstrating large variability in carbon compositions of permafrost active layer soils only ∼84 m apart, results suggest that the Svalbard active layer microbes are often limited by organic carbon or nitrogen availability and have adaptations to the current environment, and metabolic flexibility to adapt to the warming climate., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Sipes, Paul, Fine, Li, Liang, Boike, Onstott, Vishnivetskaya, Schaeffer and Lloyd.)

Purpose: To evaluate hepatocellular carcinoma (HCC) treatment allocation, deviation from BCLC first-treatment recommendation, and outcomes following multidisciplinary, individualized approach., Methods: Treatment-naïve HCC discussed at multidisciplinary tumor board (MDT) between 2010 and 2013 were included to allow minimum 5 years of follow-up. MDT first-treatment recommendation (resection, transplant, ablation, transarterial radioembolization (Y90), transarterial chemoembolization, sorafenib, palliation) was documented, as were subsequent treatments. Overall survival (OS) analyses were performed on an intention-to-treat (ITT) basis, stratified by BCLC stage., Results: Three hundred and twenty-one patients were treated in the 4-year period. Median age was 62 years, predominantly male (73%), hepatitis C (41%), and Y90 initial treatment (52%). There was a 76% rate of BCLC-discordant first-treatment. Median OS was not reached (57% alive at 10 years), 51.0 months, 25.4 months and 13.4 months for BCLC stages A, B, C and D, respectively., Conclusion: Deviation from BCLC guidelines was very common when individualized, MDT treatment recommendations were made. This approach yielded expected OS in BCLC A, and exceeded general guideline expectations for BCLC B, C and D. These results suggest that while guidelines are helpful, implementing a more personalized approach that incorporates center expertise, patient-specific characteristics, and the known multi-directional treatment allocation process, improves patient outcomes.

This is a descriptive study reviewing the outcomes of mammalian target of rapamycin inhibitors (mTORs) in intestinal (IT) and multivisceral transplantation (MVT). This study included 22 patients, 20 adults, and two children, and an overall mean age of 46 years old at the time of transplantation. Twelve patients (54.5%) received IT, and the remainder (45.5%) MVT. The mean time between transplantation and mTORs initiation was 24 months. The indication was worsening renal function in 13 patients (59%), with 9/13 (69.2%) noted to have an increase in glomerular filtration rate of at least 10 ml/min/1.73m 2 . The indication for four patients (18.2%) was a history of neuroendocrine tumor. After mTOR initiation, 50% of patients were reduced or weaned off tacrolimus and 13.7% off prednisone. mTORs were discontinued in 11/22 patients. Six patients (54.5%) stopped due to side effects, two (18.1%) for surgery, and one (9%) for acute cellular rejection. Side effects were edema (33.3%), headaches (33.3%), diarrhea (16.7%), and oral ulcers (16.7%). The average duration of mTORs prior to discontinuation due to side effects was 7 months. mTORs may function in their own niche of patients due to the potential renal safety profile, but use is most limited by tolerance to side effects., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background and Aims: Radioembolization (yttrium-90 [Y90]) is used in hepatocellular carcinoma (HCC) as a bridging as well as downstaging liver-directed therapy to curative liver transplantation (LT). In this study, we report long-term outcomes of LT for patients with HCC who were bridged/downstaged by Y90., Approach and Results: Patients undergoing LT following Y90 between 2004 and 2018 were included, with staging by United Network for Organ Sharing (UNOS) tumor-node-metastasis criteria at baseline pre-Y90 and pre-LT. Post-Y90 toxicities were recorded. Histopathological data of HCC at explant were recorded. Long-term outcomes, including overall survival (OS), recurrence-free survival (RFS), disease-specific mortality (DSM), and time-to-recurrence, were reported. Time-to-endpoint analyses were estimated using Kaplan-Meier. Univariate and multivariate analyses were performed using a log-rank test and Cox proportional-hazards model, respectively. During the 15-year period, 207 patients underwent LT after Y90. OS from LT was 12.5 years, with a median time to LT of 7.5 months [interquartile range, 4.4-10.3]. A total of 169 patients were bridged, whereas 38 were downstaged to LT. Respectively, 94 (45%), 60 (29%), and 53 (26%) patients showed complete, extensive, and partial tumor necrosis on histopathology. Three-year, 5-year, and 10-year OS rates were 84%, 77%, and 60%, respectively. Twenty-four patients developed recurrence, with a median RFS of 120 (95% confidence interval, 69-150) months. DSM at 3, 5, and 10 years was 6%, 11%, and 16%, respectively. There were no differences in OS/RFS for patients who were bridged or downstaged. RFS was higher in patients with complete/extensive versus partial tumor necrosis (P < 0.0001). For patients with UNOS T2 treated during the study period, 5.2% dropped out because of disease progression., Conclusions: Y90 is an effective treatment for HCC in the setting of bridging/downstaging to LT. Patients who achieved extensive or complete necrosis had better RFS, supporting the practice of neoadjuvant treatment before LT., (© 2020 by the American Association for the Study of Liver Diseases.)

Purpose: The purpose of this study was to present the institutional experience of performing endoscopy, cholangiography, and biliary interventions through the modified Hutson loop by interventional radiology., Materials and Methods: A total of 61 of 64 modified Hutson loop access procedures were successful. This single-center retrospective study included 61 successful procedures of biliary interventions using existing modified Hutson loops (surgically affixed subcutaneous jejunal limb adjacent to biliary anastomosis or anastomoses) for diagnostic or therapeutic purposes in 21 patients. Seventeen of 21 patients (81%) had undergone liver transplantation. Indications included biliary strictures (n = 18) and biliary leaks (n = 3). The clinical success and complications were evaluated., Results: There were 3 of 26 modified Hutson loop retrograde biliary intervention failures (12%) before introduction of endoscopy and no failures (0 of 38 [0%]) subsequently (P = .06). Endoscopy or cholangioscopy was performed in 19 procedures by interventional radiologists. Retrograde biliary interventions included diagnostic cholangiography (n = 26), cholangioplasty (n = 25), stent placement (n = 29), stent retrieval (n = 25), and biliary drainage catheter placement (n = 5). No procedure-related mortality occurred. There was 1 major complication (duodenal perforation) (1.6%) and 12 minor complications (19%). In the 9 patients undergoing therapeutic interventions for biliary strictures, there was a significant decrease in median alkaline phosphatase (288.5 to 174.5 U/L; P = .03). There was a trend toward decrease in median bilirubin levels (1.7 to 1 mg/dL; P = .06) at 1 month post-intervention., Conclusions: The modified Hutson loop provided interventional radiologists a safe and effective alternative access to manage biliary complications in patients with biliary-enteric anastomoses. Introduction of the endoscope in interventional radiology has improved the success rate of these procedures., (Copyright © 2020 SIR. Published by Elsevier Inc. All rights reserved.)

Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long-term average thermal conditions at coarse spatial resolutions only. Hence, many climate-forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold-air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free-air temperatures, microclimatic ground and near-surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near-surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes., (© 2020 John Wiley & Sons Ltd.)

The liver transplantation (LT) population is aging, with the need for transplant being driven by the growing prevalence of nonalcoholic steatohepatitis (NASH). Older LT recipients with NASH may be at an increased risk for adverse outcomes after LT. Our objective is to characterize outcomes in these recipients in a large multicenter cohort. All primary LT recipients ≥65 years from 2010 to 2016 at 13 centers in the Re-Evaluating Age Limits in Transplantation (REALT) consortium were included. Of 1023 LT recipients, 226 (22.1%) were over 70 years old, and 207 (20.2%) had NASH. Compared with other LT recipients, NASH recipients were older (68.0 versus 67.3 years), more likely to be female (47.3% versus 32.8%), White (78.3% versus 68.0%), Hispanic (12.1% versus 9.2%), and had higher Model for End-Stage Liver Disease-sodium (21 versus 18) at LT (P < 0.05 for all). Specific cardiac risk factors including diabetes with or without chronic complications (69.6%), hypertension (66.3%), hyperlipidemia (46.3%), coronary artery disease (36.7%), and moderate-to-severe renal disease (44.4%) were highly prevalent among NASH LT recipients. Graft survival among NASH patients was 90.3% at 1 year and 82.4% at 3 years compared with 88.9% at 1 year and 80.4% at 3 years for non-NASH patients (log-rank P = 0.58 and P = 0.59, respectively). Within 1 year after LT, the incidence of graft rejection (17.4%), biliary strictures (20.9%), and solid organ cancers (4.9%) were comparable. Rates of cardiovascular (CV) complications, renal failure, and infection were also similar in both groups. We observed similar posttransplant morbidity and mortality outcomes for NASH and non-NASH LT recipients. Certain CV risk factors were more prevalent in this population, although posttransplant outcomes within 1 year including CV events and renal failure were similar to non-NASH LT recipients., (Copyright © 2020 by the American Association for the Study of Liver Diseases.)

The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

The ice- and organic-rich permafrost of the northeast Siberian Arctic lowlands (NESAL) has been projected to remain stable beyond 2100, even under pessimistic climate warming scenarios. However, the numerical models used for these projections lack processes which induce widespread landscape change termed thermokarst, precluding realistic simulation of permafrost thaw in such ice-rich terrain. Here, we consider thermokarst-inducing processes in a numerical model and show that substantial permafrost degradation, involving widespread landscape collapse, is projected for the NESAL under strong warming (RCP8.5), while thawing is moderated by stabilizing feedbacks under moderate warming (RCP4.5). We estimate that by 2100 thaw-affected carbon could be up to three-fold (twelve-fold) under RCP4.5 (RCP8.5), of what is projected if thermokarst-inducing processes are ignored. Our study provides progress towards robust assessments of the global permafrost carbon-climate feedback by Earth system models, and underlines the importance of mitigating climate change to limit its impacts on permafrost ecosystems.

The original version of this Article contained an error in the author affiliations. Affiliation 5 incorrectly read 'Tyumen State Oil and Gas University, Tyumen, Tyument. Oblast, Russian Federation, 625000'.This has now been corrected in both the PDF and HTML versions of the Article.