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Long-term atmospheric CO2 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.

In order to reliably predict the climate of our planet, and to help inform political conventions on greenhouse gas emissions such as the Paris Agreement of 2015, adequate knowledge of both natural and anthropogenic sources of the greenhouse gases Carbon dioxide (CO2) and methane (CH4) and their feedbacks is needed. Despite the recognized importance of this issue, our current understanding about sources and sinks of CO2 and CH4 is still inadequate. This is particularly true for the Arctic, where large wetlands and permafrost areas constitute the most relevant but least quantified ecosystems for the global carbon budget.The CoMet 2.0 Arctic mission wants to help remedy this deficiency with a multi-disciplinary approach providing relevant measurements from Arctic regions using a suite of sophisticated scientific instrumentation onboard the German research aircraft HALO (High Altitude and LOng Range Research Aircraft, https://halo-research.de) to support state-of-the-art Earth System Models. At the same time, CoMet intends to support and improve current and future satellite missions, which still struggle to make high-quality measurements given the low sun elevation, low albedo, and adverse cloud conditions in the Arctic.CoMet 2.0 Arctic (https://comet2arctic.de/) has successfully been conducted within a six-week intensive operation period from August 10th to September 16th, 2022 targeting greenhouse gas emissions from boreal wetlands and permafrost areas in the Canadian Arctic, from wildfires, and from anthropogenic emission sources such oil, gas, and coal extraction sites and landfills.For that mission, HALO was equipped with a suite of remote sensing and in-situ instruments for the measurement of greenhouse gases and meteorological parameters. The remote sensing package comprised the CH4 and CO2 lidar CHARM-F (operated by DLR), the imaging spectrometer MAMAP2D-Light (operated by University of Bremen) and the hyperspectral imager specMACS (operated by LMU Munich). The remote sensors were supported by several in-situ instruments (operated by MPI Jena and DLR) to measure the main greenhouse gases and related trace species as well as an air sampler that collects air samples at flight level for later analysis (e.g. w.r.t. isotopes) in the laboratory. Furthermore, instruments to provide detailed information about the standard meteorological parameters (pressure, wind, humidity) were operated and several small meteorological sondes were launched in order to link those in-flight data to profiles.A total of 135 flight hours including a test flight to landfills in Spain and transfer flights from Europe have been performed. 16 scientific flights took place out of Edmonton, Alberta, to various regions all over Canada.CoMet 2.0 Arctic has partly been coordinated with the Arctic-Boreal Vulnerability Experiment field program by NASA (ABoVE, https://above.nasa.gov/). Both missions, ABoVE and CoMet 2.0 Arctic, are linked through the transatlantic initiative AMPAC (Arctic Methane and Permafrost Challenge, https://www.ampac-net.info/) that has recently been inaugurated by the US and European Space Agencies, NASA and ESA.Thus, a valuable data set was acquired to help better understand the methane and carbon dioxide cycles in the Arctic and emissions from natural and anthropogenic sources.

Arctic and boreal wetlands and lakes are experiencing complex ecological changes as a result of warming. The potential for rapidly thawing permafrost to promote large increases in methane (CH4) emissions via ground subsidence and ponding (thermokarst), and permafrost carbon mineralization is of particular concern for accelerating the permafrost carbon feedback (PCF) [Turetsky et al. 2020]. However, complex hydrological dynamics produce large uncertainties regarding the sign and magnitude of carbon loss in modeling and forecasting efforts. Determining CH4’s current and future contributions to the PCF is challenging due to sparse observations, high spatiotemporal variability, and heterogeneous Arctic landscapes. As a result, top-down (observation-based) and bottom-up (model/inventory-based) evaluations of annual Arctic and boreal CH4 emissions disagree by 50-200% [McGuire et al. 2012; Peltola et al. 2019]. Constraining the current budget and forecast uncertainty in future Arctic emissions will require scale-bridging approaches that reconcile fine spatiotemporal variability and regional to continental scale coverage. To this end, we compiled multiple large remote sensing datasets to study relationships between Arctic lake and thermokarst landscape morphology trends with remotely-sensed (AVIRIS-NG) CH­4 emission hotspot detections. Preliminary analyses from a lake-and-wetland-rich 1,750 km2 study area of the Yukon Kuskokwim Delta, AK, USA reveal discrete correlations between recently wetted areas and CH4 hotspot detections. However, in an analysis of over 1,200 lakes > 1 ha, hotspots were detected in greater abundance surrounding lakes that have shrunk in area since 1999 (p < 0.05) (Fig. 2). Our preliminary results imply a complex response of CH4 emissions surrounding dynamic permafrost environments. Ongoing analyses seek to further elucidate patterns related to waterbody size, permafrost ice and carbon contents, and relationships between terrestrial and limnetic hotspot detections.

ObjectiveTo report a case of early pregnancy loss successfully managed by hysteroscopic resection, review the literature comparing hysteroscopic resection to dilation and curettage for retained products of conception, and review potential advantages of hysteroscopic resection over dilation and curettage for management of early pregnancy loss.DesignCase report.SettingPrivate practice.PatientsOne woman with early pregnancy loss.InterventionsHysteroscopic resection using a mechanical morcellation device.Main outcome measuresComplete uterine evacuation after hysteroscopic resection as demonstrated by a normal transvaginal ultrasound and cessation of bleeding 2 weeks after surgery.ResultsThe hysteroscopic fluid deficit was 365 ml, with minimal blood loss. Products of conception were confirmed on pathologic examination. There were no intraoperative or postoperative complications. A saline infusion sonogram obtained 4 months after surgery demonstrated a normal endometrial cavity with no intrauterine adhesions.ConclusionsSurgical management of early pregnancy loss may be complicated by retained products of conception (RPOC) or intrauterine adhesion formation, which can lead to adverse fertility outcomes in the future. Hysteroscopic resection of RPOC has been associated with fewer cases of intrauterine adhesions, more cases of complete tissue removal, and earlier time to conception compared with dilation and curettage. Early pregnancy loss can also be characterized as RPOC with potentially similar benefits from hysteroscopic resection. Thus, hysteroscopic resection can be considered as an alternative surgical technique for management of early pregnancy loss. This case report demonstrates the successful application of hysteroscopic resection in a case of early pregnancy loss.

Arctic-boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic-boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (Reco), net ecosystem CO2 exchange (NEE; Reco − GPP), and terrestrial methane (CH4) emissions for the Arctic-boreal zone using a satellite data-driven process-model for northern ecosystems (TCFM-Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM-Arctic to obtain daily 1-km2 flux estimates and annual carbon budgets for the pan-Arctic-boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO2-C year−1. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH4 emissions from tundra and boreal wetlands (not accounting for aquatic CH4) were estimated at 35 Tg CH4-C year−1. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high-latitude carbon status and also indicates a continued need for integrated site-to-regional assessments to monitor the vulnerability of these ecosystems to climate change.

We used full polarimetric L-band and P-band synthetic aperture radar (SAR) data collected from the recent NASA Arctic Boreal Vulnerability Experiment (ABoVE) airborne campaign and Sentinel-1 C-band dual-polarization data to understand the sensitivity of radar backscatter intensity and phase to fire-induced changes in the surface and subsurface soil processes in Arctic tundra underlain by permafrost. The 2007 Anaktuvuk River fire on the Alaska North Slope was used as a case study. At ~10-year post-fire, we observed strong increases (> ~3-4 dB) in the low frequency radar backscatter in severely burned areas during the thaw season, in contrast to limited ( 1 dB) in burned areas than adjacent unburned areas. Polarimetric decomposition analysis indicated a general trend towards more random surface scattering, and strong increases in double-bounce and volume scattering power at both P- and L-band in the burned areas. The ice-rich yedoma region shows largest backscatter increases in burned areas, and the highest correlation with burn severity and microtopography changes. The above backscatter changes are attributed to increasing surface roughness and microtopography due to ice wedge degradation and thermokarst development, and increasing subsurface scattering due to an overall drier and deeper active layer in burned areas. Among all frequencies, P-band shows consistently larger contrast in backscatter power and phase between burned and unburned areas, which makes it potentially more useful to study fire-permafrost interactions in the Arctic over decadal time scales.

Atmospheric methane observations are used to test methane emission inventories as the sum of emissions should correspond to observed methane concentrations. Typically, concentrations are inversely projected to a net flux through an atmospheric chemistry-transport model. Current methods to partition net fluxes to underlying sector-based emissions often scale fluxes based on the relative weight of sectors in a prior inventory. However, this approach imposes correlation between emission sectors which may not exist. Here we present a Bayesian optimal estimation method that projects inverse methane fluxes directly to emission sectors while accounting uncertainty structure and spatial resolution of prior fluxes and emissions. We apply this method to satellite-derived fluxes over the U.S. and at higher resolution over the Permian Basin to demonstrate that we can characterize a sector-based emission budget. This approach provides more robust comparisons between different top-down estimates, critical for assessing the efficacy of policies intended to reduce emissions. Sector-based methane emissions can be backed out from observed methane fluxes, using a Bayesian optimal estimation method. This could help with monitoring gas leaks from industry.

Site-level observations have shown pervasive cold season CO2 release across Arctic and boreal ecosystems, impacting annual carbon budgets. Still, the seasonality of CO2 emissions are poorly quantified across much of the high latitudes due to the sparse coverage of site-level observations. Space-based observations provide the opportunity to fill some observational gaps for studying these high-latitude ecosystems, particularly across poorly sampled regions of Eurasia. Here, we show that data-driven net ecosystem exchange (NEE) from atmospheric CO2 observations implies strong summer uptake followed by strong autumn release of CO2 over the entire cold northeastern region of Eurasia during the 2015–2019 study period. Combining data-driven NEE with satellite-based estimates of gross primary production (GPP), we show that this seasonality implies less summer heterotrophic respiration (Rh) and greater autumn Rh than would be expected given an exponential relationship between respiration and surface temperature. Furthermore, we show that this seasonality of NEE and Rh over northeastern Eurasia is not captured by the TRENDY v8 ensemble of dynamic global vegetation models (DGVMs), which estimate that 47 %–57 % (interquartile range) of annual Rh occurs during August–April, while the data-driven estimates suggest 59 %–76 % of annual Rh occurs over this period. We explain this seasonal shift in Rh by respiration from soils at depth during the zero-curtain period, when sub-surface soils remain unfrozen up to several months after the surface has frozen. Additional impacts of physical processes related to freeze–thaw dynamics may contribute to the seasonality of Rh. This study confirms a significant and spatially extensive early cold season CO2 efflux in the permafrost-rich region of northeast Eurasia and suggests that autumn Rh from subsurface soils in the northern high latitudes is not well captured by current DGVMs.

The Arctic cryosphere is collapsing, posing overlapping environmental risks. In particular, thawing permafrost threatens to release biological, chemical and radioactive materials that have been sequestered for tens to hundreds of thousands of years. As these constituents re-enter the environment, they have the potential to disrupt ecosystem function, reduce the populations of unique Arctic wildlife and endanger human health. Here, we review the current state of the science to identify potential hazards currently frozen in Arctic permafrost. We also consider the cascading natural and anthropogenic processes that may compound the impacts of these risks, as it is unclear whether the highly adapted Arctic ecosystems have the resilience to withstand new stresses. We conclude by recommending research priorities to address these underappreciated risks. Thawing permafrost in the Arctic may release microorganisms, chemicals and nuclear waste that have been stored in frozen ground and by cold temperatures. This Review discusses the current state of potential hazards and their risks under warming to identify prospective threats to the Arctic.

Recent increases in boreal forest burned area, which have been linked with climate warming, highlight the need to better understand the composition of wildfire emissions and their atmospheric impacts. Here we quantified emission factors for CO and CH 4 from a massive regional fire complex in interior Alaska during the summer of 2015 using continuous high-resolution trace gas observations from the Carbon in Arctic Reservoirs Vulnerability Experiment (CRV) tower in Fox, Alaska. Averaged over the 2015 fire season, the mean CO / CO 2 emission ratio was 0.142 ± 0.051, and the mean CO emission factor was 127 ± 40 g kg −1 dry biomass burned. The CO / CO 2 emission ratio was about 39 % higher than the mean of previous estimates derived from aircraft sampling of wildfires from boreal North America. The mean CH 4 / CO 2 emission ratio was 0.010 ± 0.004, and the CH 4 emission factor was 5.3 ± 1.8 g kg −1 dry biomass burned, which are consistent with the mean of previous reports. CO and CH 4 emission ratios varied in synchrony, with higher CH 4 emission factors observed during periods with lower modified combustion efficiency (MCE). By coupling a fire emissions inventory with an atmospheric model, we identified at least 34 individual fires that contributed to trace gas variations measured at the CRV tower, representing a sample size that is nearly the same as the total number of boreal fires measured in all previous field campaigns. The model also indicated that typical mean transit times between trace gas emission within a fire perimeter and tower measurement were 1–3 d, indicating that the time series sampled combustion across day and night burning phases. The high CO emission ratio estimates reported here provide evidence for a prominent role of smoldering combustion and illustrate the importance of continuously sampling fires across time-varying environmental conditions that are representative of a fire season.