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The paper reviews and evaluates a 30-year-long atmospheric CO2 data series measured at the Hegyhátsál tall-tower greenhouse gas monitoring site, a member of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW), US National Oceanic and Atmospheric Administration (NOAA), and pan-European Integrated Carbon Observation System (ICOS) networks. The paper also gives the technical description of the monitoring system and its changes over time and introduces the environment of the station. This low-elevation (248 m above mean sea level – m a.m.s.l.), mid-continental central European site shows a 3.90 ± 0.83 µmolmol-1 offset relative to the latitudinally representative marine boundary layer reference concentration, presumably due to European net anthropogenic emissions. The long-term trend (2.20 µmolmol-1yr-1) closely follows the global tendencies. In the concentration growth rate, the ENSO effect is clearly detectable with a 6–7-month lag time. The summer diurnal concentration amplitude is slightly decreasing due to the faster-than-average increase in the nighttime concentrations, which is related to the warming climate. The warming climate also caused a 0.96 ± 0.41 dyr-1 advance at the beginning of the summer CO2 -deficit season in the first half of the measurement period, which did not continue later. The summer CO2 -deficit season was extended by 9.0 ± 6.1 d during the measurement period. [ABSTRACT FROM AUTHOR]

Atmospheric emissions from anthropogenic hotspots, i.e., cities, power plants and industrial facilities, can be determined from remote sensing images obtained from airborne and space-based imaging spectrometers. In this paper, we present a Python library for data-driven emission quantification (ddeq) that implements various computationally light methods such as the Gaussian plume inversion, cross-sectional flux method, integrated mass enhancement method and divergence method. The library provides a shared interface for data input and output and tools for pre- and post-processing of data. The shared interface makes it possible to easily compare and benchmark the different methods. The paper describes the theoretical basis of the different emission quantification methods and their implementation in the ddeq library. The application of the methods is demonstrated using Jupyter notebooks included in the library, for example, for NO 2 images from the Sentinel-5P/TROPOMI satellite and for synthetic CO 2 and NO 2 images from the Copernicus CO 2 Monitoring (CO2M) satellite constellation. The library can be easily extended for new datasets and methods, providing a powerful community tool for users and developers interested in emission monitoring using remote sensing images. [ABSTRACT FROM AUTHOR]

Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. The Surface Ocean Carbon Dioxide (CO2) Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fugacity, fCO2. fCO2 is highly sensitive to temperature and the measurements are only valid for the instantaneous sea surface temperature (SST) that is measured concurrent with the in-water CO2 measurement. To create a climatology of fCO2 data suitable for calculating air-sea CO2 fluxes it is therefore desirable to calculate fCO2 valid for climate quality SST. This paper presents a method for creating such a climatology. We recomputed SOCAT's fCO2 values for their respective measurement month and year using climate quality SST data from satellite Earth observation and then extrapolated the resulting fCO2 values to reference year 2010. The data were then spatially interpolated onto a 1° × 1° grid of the global oceans to produce 12 monthly fCO2 distributions for 2010. The partial pressure of CO2 (pCO2) is also provided for those who prefer to use pCO2. The CO2 concentration difference between ocean and atmosphere is the thermodynamic driving force of the air-sea CO2 flux, and hence the presented fCO2 distributions can be used in air-sea gas flux calculations together with climatologies of other climate variables. [ABSTRACT FROM AUTHOR]

GeoCARB is a proposed instrument to measure column averaged concentrations of CO2, CH4 and CO from geostationary orbit using reflected sunlight in near-infrared absorption bands of the gases. The scanning options, spectral channels and noise characteristics of geoCARB and two descope options are described. The accuracy of concentrations from geoCARB data is investigated using end-to-end retrievals; spectra at the top of the atmosphere in the geoCARB bands are simulated with realistic trace gas profiles, meteorology, aerosol, cloud and surface properties, and then the concentrations of CO2, CH4 and CO are estimated from the spectra after addition of noise characteristic of geoCARB. The sensitivity of the algorithm to aerosol, the prior distributions assumed for the gases and the meteorology are investigated. The contiguous spatial sampling and fine temporal resolution that geoCARB could provide opens the possibility of monitoring localised sources such as power plants. Simulations of emissions from a power plant with a gaussian plume are conducted to assess the accuracy with which the emission strength may be recovered from geoCARB spectra. Scenarios for "clean" and "dirty" power plants are examined. It is found that a reliable estimate of the emission rate is possible, especially for power plants that have particulate filters, by averaging multiple snap-shots of the CO2 field surrounding the plant. The result holds even in the presence of partial cloud cover. [ABSTRACT FROM AUTHOR]

Ecosystem-scale manipulation experiments represent large science investments that require well-designed data acquisition and management systems to provide reliable, accurate information to project participants and third party users. The SPRUCE Project (Spruce and Peatland Responses Under Climatic and Environmental Change, http: //mnspruce.ornl.gov) is such an experiment funded by the Department of Energy's (DOE), Oce of Science, Terrestrial Ecosystem Science (TES) Program. The SPRUCE experimental mission is to assess ecosystem-level biological responses of vulnerable, high carbon terrestrial ecosystems to a range of climate warming manipulations and an elevated CO2 atmosphere. SPRUCE provides a platform for testing mechanisms controlling the vulnerability of organisms, biogeochemical processes, and ecosystems to climatic change (e.g., thresholds for organism decline or mortality, limitations to regeneration, biogeochemical limitations to productivity, the cycling and release of CO2 and CH4 to the atmosphere). The SPRUCE experiment will generate a wide range of continuous and discrete measurements. To successfully manage SPRUCE data collection, achieve SPRUCE science objectives, and support broader climate change research, the research staff has designed a flexible data system using proven network technologies and software components. The primary SPRUCE data system components are: 1. Data acquisition and control system - set of hardware and software to retrieve biological and engineering data from sensors, collect sensor status information, and distribute feedback to control components. 2. Data collection system - set of hardware and software to deliver data to a central depository for storage and further processing. 25 3. Data management plan - set of plans, policies, and practices to control consistency, protect data integrity, and deliver data. This publication presents our approach to meeting the challenges of designing and constructing an eficient data system for managing high volume sources of in-situ observations in a remote, harsh environmental location. The approach covers data flow starting from the sensors and ending at the archival/distribution points, discusses types of hardware and software used, examines design considerations that were used to choose them, and describes the data management practices chosen to control and enhance the value of the data. [ABSTRACT FROM AUTHOR]

The knowledge of Green House Gases GHGs fluxes at the air--sea interface at high resolution is crucial to accurately quantify the role of the ocean in the absorption and emission of GHGs. In this paper we present a novel method to reconstruct maps of surface ocean partial pressure of CO2, pCO2, and air--sea CO2 fluxes at super resolution (4 km) using Sea Surface Temperature (SST) and Ocean Colour (OC) data at this resolution, and CarbonTracker CO2 fluxes data at low resolution (110 km). Inference of super-resolution of pCO2, and air--sea CO2 fluxes is performed using novel nonlinear signal processing methodologies that prove efficient in the context of oceanography. The theoretical background comes from the Microcanonical Multifractal Formalism which unlocks the geometrical determination of cascading properties of physical intensive variables. As a consequence, a multiresolution analysis performed on the signal of the so-called singularity exponents allows the correct and near optimal cross-scale inference of GHGs fluxes, as the inference suits the geometric realization of the cascade. We apply such a methodology to the study offshore of the Benguela area. The inferred representation of oceanic partial pressure of CO2 improves and enhances the description provided by CarbonTracker, capturing the small scale variability. We examine different combinations of Ocean Colour and Sea Surface Temperature products in order to increase the number of valid points and the quality of the inferred pCO2 field. The methodology is validated using in-situ measurements by means of statistical errors. We obtain that mean absolute and relative errors in the inferred values of pCO2 with respect to in-situ measurements are smaller than for CarbonTracker. [ABSTRACT FROM AUTHOR]

Physical soil properties create lags between temperature change and corresponding soil responses, which obscure true Q10 values and other biophysical parameters such as depth of production. This study examines an inversion approach for estimating Q10 and depth of production (Zp) using physically based soil models, constrained by observed high-frequency surface fluxes and/or concentrations. Our inversion strategy uses a 1-D multi-layered soil model that simulates realistic temperature and gas diffusion. We tested inversion scenarios on synthetic data using a range of constraining parameters, time averaging techniques, mechanisms to improve computational efficiency, and various methods of incorporating real data into the model. Overall, we have found that with carefully constrained data, inversion was possible. While inversions using exclusively surface flux measurements could succeed, constraining the inversion using multiple shallow subsurface CO2 measurements proved to be most successful. Inversions constrained by these shallow measurements returned Q10 and Zp values with average errors of 1.85 and 0.16 % respectively. This work is a first step toward building a reliable framework for removing physical effects from high frequency soil CO2 data. Ultimately, we hope that this process will lead to better estimates of biophysical soil parameters and their variability on short timescales. [ABSTRACT FROM AUTHOR]

Earth surface systems are controlled by a combination of global and local factors, which cannot be understood without accounting for both the local and global components. The system dynamics cannot be recovered from the global or local controls alone. Ground forest inventory is able to accurately estimate forest carbon stocks at sample plots, but these sample plots are too sparse to support the spatial simulation of carbon stocks with required accuracy. Satellite observation is an important source of global information for the simulation of carbon stocks. Satellite remote-sensing can supply spatially continuous information about the surface of forest carbon stocks, which is impossible from ground-based investigations, but their description has considerable uncertainty. In this paper, we validated the Lund-Potsdam-Jena dynamic global vegetation model (LPJ), the Kriging method for spatial interpolation of ground sample plots and a satellite-observation-based approach as well as an approach for fusing the ground sample plots with satellite observations and an assimilation method for incorporating the ground sample plots into LPJ. The validation results indicated that both the data fusion and data assimilation approaches reduced the uncertainty of estimating carbon stocks. The data fusion had the lowest uncertainty by using an existing method for high accuracy surface modeling to fuse the ground sample plots with the satellite observations (HASM-SOA). The estimates produced with HASM-SOA were 26.1 and 28.4% more accurate than the satellite-based approach and spatial interpolation of the sample plots, respectively. Forest carbon stocks of 7.08 Pg were estimated for China during the period from 2004 to 2008, an increase of 2.24 Pg from 1984 to 2008, using the preferred HASM-SOA method. [ABSTRACT FROM AUTHOR]

Laser Absorption Spectroscopy (LAS) has been used over the last several decades for the measurement of trace gasses in the atmosphere. For over a decade, LAS measurements from multiple sources and tens of retroreflectors have been combined with sparse-sample tomography methods to estimate the 2-D distribution of trace gas concentrations and underlying fluxes from pointlike sources. In this work, we consider the ability of such a system to detect and estimate the position and rate of a single point leak which may arise as a failure mode for carbon dioxide storage. The leak is assumed to be at a constant rate giving rise to a plume with a concentration and distribution that depend on the wind velocity. We demonstrate the ability of our approach to detect a leak using numerical simulation and a preliminary measurement. [ABSTRACT FROM AUTHOR]

The annual average CO2 difference between baseline data from Mauna Loa and the southern Hemisphere increased by ~ 0.8 µmolmol-1 (0.8 ppm) between 2009 and 2010, a step unprecedented in over 50 years of reliable data. We find no evidence for coinciding, sufficiently large and rapid, source/sink changes. A statistical anomaly is unlikely due to the highly systematic nature of the variation in observations. An explanation for the step, and the subsequent 5 year stability in this north-south difference, involves inter-hemispheric atmospheric exchange variation. The selected data describing this episode provide a critical test for studies that employ atmospheric transport models that interpret global carbon budgets and inform management of anthropogenic emissions. [ABSTRACT FROM AUTHOR]

In a globalised world, the transfer of carbon between regions, either physically or embodied in production, represents a substantial fraction of global carbon emissions. The resulting emission transfers are important for balancing regional carbon budgets and for understanding the drivers of regional emissions. In this paper we synthesise current understanding in two parts: (1) embodied CO2 emissions from the production of goods and services produced in one country but consumed in others, (2) physical carbon flows in fossil fuels, petroleum-derived products, harvested wood products, crops, and livestock. We describe the key differences between studies and provide a consistent set of estimates using the same definitions, modelling framework, and consistent data. We find the largest trade flows of carbon in international trade in 2004 were fossil fuels (2673MtC, 37% of global emissions), CO2 embodied in traded goods and services (1661MtC, 22% of global emissions), livestock (651MtC, 20% of total livestock carbon), crops (522MtC, 31% of total harvested crop carbon), petroleum-based products (183MtC, 50% of their total production), and harvested wood products (149MtC, 40% of total roundwood extraction). We find that for embodied CO2 emissions estimates from independent studies are robust. We found that differences between individual studies is not representative of the uncertainty in consumption-based estimates as different studies use different production-based emission estimates as input and different definitions of allocating emissions to international trade. After adjusting for these issues, results across independent studies converge to give less uncertainty than previously assumed. For physical carbon ?ows there are relatively few studies to be synthesised, but differences between existing studies are due to the method of allocating to international trade with some studies using "apparent consumption" as opposed to "final consumption" in more comprehensive approaches. While results across studies are robust to be used in further applications, more research is needed to understand the differences between methods and to harmonise definitions for particular applications. [ABSTRACT FROM AUTHOR]

The article discusses the study which estimates the quantification of the greenhouse gas methane emissions for anthropogenic activity and natural phenomena in global climate change. The study used the optical remote sensing instrument MAMAP data, which is operated from aircraft to better understand point sources of the greenhouse gases, carbon dioxide, and methane. The study utilised the added information from a turbulence probe operated on-board an aircraft to enhance the emission quality.

Distributions of surface water partial pressure of carbon dioxide (pCO2) were measured on nine cruises in the Delaware Estuary (USA). The Delaware River was highly supersaturated in pCO2 with respect to the atmosphere during all seasons while the Delaware Bay was undersaturated in pCO2 during spring and late summer and moderately supersaturated during midsummer, fall, and winter. While the upper tidal river was a strong CO2 source (24.6 ± 2.2 mol C m-2 year-1), the bay was a weak source (1.8 ± 0.2 mol C m-2 year-1), the latter of which had a much greater area than the former. In turn, the Delaware Estuary acted as a relatively weak CO2 source (2.4 ± 0.3 mol C m-2 year-1), which is in great contrast to many other estuarine systems. Seasonally, pCO2 changes were greatest at low salinities (0 = S< 5) with pCO2 values in the summer nearly three-fold greater than those observed in the spring and fall. Undersaturated pCO2 was observed over the widest salinity range (7.5 = S< 30) during spring. Near to supersaturated pCO2 was generally observed in mid- to high salinity waters (20 = S< 30) except during spring and late summer. Strong seasonal trends in internal estuarine production and consumption of CO2 were observed throughout both the upper tidal river and lower bay. Comparably, positive correlations between river-borne and air-water CO2 fluxes in the upper estuary emphasize the significance of river-borne CO2 degassing to overall CO2 fluxes. While river-borne CO2 degassing heavily influenced CO2 dynamics in the upper tidal river, these forces were largely compensated by internal biological processes within the extensive bay system of the lower estuary. [ABSTRACT FROM AUTHOR]

Soil carbon stored in high-latitude permafrost landscapes is threatened by warming, and could contribute significant amounts of carbon to the atmosphere and hydrosphere as permafrost thaws. Permafrost disturbances, especially active layer detachments and retrogressive thaw slumps, have increased in frequency and magnitude across the Fosheim Peninsula, Ellesmere Island, Canada. To determine the effects of retrogressive thaw slumps on net ecosystem exchange (NEE) of CO2 in high Arctic tundra, we used two eddy covariance (EC) tower systems to simultaneously and continuously measure CO2 fluxes from a disturbed site and the surrounding undisturbed tundra. During the 32-day measurement period in the 2014 growing season the undisturbed tundra was a small net sink (NEE = −0.12 g C m-2 d-1); however, the disturbed terrain of the retrogressive thaw slump was a net source (NEE = +0.39 g C m-2 d-1). Over the measurement period, the undisturbed tundra sequestered 3.84 g C m-2, while the disturbed tundra released 12.48 g C m-2. Before full leaf out in early July, the undisturbed tundra was a small source of CO2, but shifted to a sink for the remainder of the sampling season (July), whereas the disturbed tundra remained a source of CO2 throughout the season. A static chamber system was also used to measure fluxes in the footprints of the two towers, in both disturbed and undisturbed tundra, and fluxes were partitioned into ecosystem respiration (Re) and gross primary production (GPP). Average GPP and Re found in disturbed tundra were smaller (+0.41 μmol m-2 s-1 and +0.50 μmol m-2 s-1, respectively) than those found in undisturbed tundra (+1.21 μmol m-2 s-1 and +1.00 μmol m-2 s-1, respectively). Our measurements indicated clearly that the permafrost disturbance changed the high Arctic tundra system from a sink to a source for CO2 during the growing season. [ABSTRACT FROM AUTHOR]

Stratospheric profiles of methane (CH4) and carbon dioxide (CO2) have been derived from solar occultation measurements of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY). The retrieval is performed using a method called "Onion Peeling DOAS" (ONPD) which combines an onion peeling approach with a weighting function DOAS (Differential Optical Absorption Spectroscopy) fit. By use of updated pointing information and optimisation of the data selection and of the retrieval approach the altitude range for reasonable CH4 could be extended to about 17 to 45 km. Furthermore, the quality of the derived CO2 has been assessed such that now the first stratospheric profiles of CO2 from SCIAMACHY are available. Comparisons with independent data sets yield an estimated accuracy of the new SCIAMACHY stratospheric profiles of about 5-10 % for CH4 and 2-3 % for CO2. The accuracy of the products is currently mainly restricted by the appearance of unexpected vertical oscillations in the derived profiles which need further investigation. Using the improved ONPD retrieval, CH4 and CO2 stratospheric data sets covering the whole SCIAMACHY time series (August 2002-April 2012) and the latitudinal range between about 50 and 70° N have been derived. Based on these time series, CH4 and CO2 trends have been estimated, which are in reasonable agreement with total column trends for these gases. This shows that the new SCIAMACHY data sets can provide valuable information about the stratosphere. [ABSTRACT FROM AUTHOR]

The closed chamber technique is widely used to measure the exchange of methane (CH4) and carbon dioxide (CO2) from terrestrial ecosystems. There is, however, large uncertainty about which model should be used to calculate the gas flux from the measured gas concentrations. Due to experimental uncertainties the robust linear regression model (first order polynomial) is often applied, even though theoretical considerations of the technique suggest the application of other, curvilinear models. High-resolution automatic chamber systems which sample gas concentrations several hundred times per flux measurement make it possible to resolve the curvilinear behavior and study the information imposed by the natural variability of the temporal concentration changes. We used more than 50 000 such flux measurements of CH4 and CO2 from five field sites located in peat forming wetlands to calculate fluxes with different models. The flux differences from independent linear estimates are generally found to be smaller than the local flux variability on the plot scale. The curvilinear behavior of the gas concentrations within the chamber is strongly influenced by wind driven chamber leakage, and less so by changing gas concentration gradients in the soil during chamber closure. Such physical processes affect both gas species equally, which makes it possible to isolate biochemical processes affecting the gases differently, such as photosynthesis limitation by chamber headspace CO2 concentrations under high levels of incoming solar radiation. We assess the possibility to exploit this effect for a partitioning of the net CO2 flux into photosynthesis and ecosystem respiration and argue that high-resolution automatic chamber measurements could be used for purposes beyond the estimation of the net gas flux. [ABSTRACT FROM AUTHOR]

The article presents a study which measures ground-based high-resolution fourier transform spectrometers through carbon dioxide and methane aircraft measurements. The study also compares the aforementioned measurements to Greenhouse Gases Observing Satellite (GOSAT) data measurement. It also gives details of the measurement instruments onboard the aircraft and ground sites.

The article presents a study which looks into the remote sensing of carbon dioxide (CO) and atmospheric methane (CH4) through solar absorption spectrometry. The study operates the high resolution instrument as part of the Total Carbon Column Observing Network (TCCON). It concludes that a low resolution Fourier Transform Spectrometry (FTS) instrument is effective in measuring XCO2.

Climatologies, which depict mean fields of oceanographic variables on a regular geographic grid, and atlases, which provide graphical depictions of specific areas, play pivotal roles in comprehending the societal vulnerabilities linked to ocean acidification (OA). This significance is particularly pronounced in coastal regions where most economic activities, such as commercial and recreational fisheries and aquaculture industries, occur. In this paper, we unveil a comprehensive data product featuring coastal ocean acidification climatologies and atlases, encompassing the fugacity of carbon dioxide, pH on the total scale, total hydrogen ion content, free hydrogen ion content, carbonate ion content, aragonite saturation state, calcite saturation state, Revelle factor, total dissolved inorganic carbon content, and total alkalinity content. These variables are provided on 1° × 1° spatial grids at 14 standardized depth levels, ranging from the surface to a depth of 500 m, along the North American ocean margins, defined as the region between the coastline and a distance of 200 nautical miles (∼370 km) offshore. The climatologies and atlases were developed using the World Ocean Atlas (WOA) gridding methods of the NOAA National Centers for Environmental Information (NCEI) based on the recently released Coastal Ocean Data Analysis Product in North America (CODAP-NA), along with the 2021 update to the Global Ocean Data Analysis Project version 2 (GLODAPv2.2021) data product. The relevant variables were adjusted to the index year of 2010. The data product is available in NetCDF (https://doi.org/10.25921/g8pb-zy76 , Jiang et al., 2022b) on the NOAA Ocean Carbon and Acidification Data System: https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0270962.html (last access: 15 July 2024). It is recommended to use the objectively analyzed mean fields (with "_an" suffix) for each variable. The atlases can be accessed at https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/synthesis/nacoastal.html (last access: 15 July 2024). [ABSTRACT FROM AUTHOR]

Previous research has shown that stratospheric aerosol causes only a small temperature change per unit forcing because they produce stronger cooling in the tropical Indian Ocean and the western Pacific Ocean than in the global mean. The enhanced temperature change in this so-called "warm-pool" region activates strongly negative local and remote feedbacks, which dampen the global mean temperature response. This paper addresses the question of why stratospheric aerosol forcing affects warm-pool temperatures more strongly than CO 2 forcing, using idealized MPI-ESM simulations. We show that the aerosol's enhanced effective forcing at the top of the atmosphere (TOA) over the warm pool contributes to the warm-pool-intensified temperature change but is not sufficient to explain the effect. Instead, the pattern of surface effective forcing, which is substantially different from the effective forcing at the TOA, is more closely linked to the temperature pattern. Independent of surface temperature changes, the aerosol heats the tropical stratosphere, accelerating the Brewer–Dobson circulation. The intensified Brewer–Dobson circulation exports additional energy from the tropics to the extratropics, which leads to a particularly strong negative forcing at the tropical surface. These results show how forced circulation changes can affect the climate response by altering the surface forcing pattern. Furthermore, they indicate that the established approach of diagnosing effective forcing at the TOA is useful for global means, but a surface perspective on the forcing must be adopted to understand the evolution of temperature patterns. [ABSTRACT FROM AUTHOR]

Through 1959-2012, an airborne fraction (AF) of 44% of total anthropogenic CO2 emissions remained in the atmosphere, with the rest being taken up by land and ocean CO2 sinks. Understanding of this uptake is critical because it greatly alleviates the emissions reductions required for climate mitigation. An observable quantity that reflects sink properties more directly than the AF is the CO2 sink rate (kS), the combined land-ocean CO2 sink flux per unit excess atmospheric CO2 above preindustrial levels. Here we show from observations that kS declined over 1959-2012 by a factor of about 1/3, implying that CO2 sinks increased more slowly than excess CO2. We attribute the decline in kS to four mechanisms: slower-than-exponential CO2 emissions growth (~ 35% of the trend), volcanic eruptions (~ 25 %), sink responses to climate change (~ 20 %), and nonlinear responses to increasing CO2, mainly oceanic (~ 20 %). The first of these mechanisms is associated purely with extrinsic forcings, and the last two with intrinsic, nonlinear responses of sink processes to changes in climate and atmospheric CO2. Our results indicate that the effects of these intrinsic, nonlinear responses are already detectable in the global carbon cycle. Although continuing future decreases in kS will occur under all plausible CO2 emission scenarios, the rate of decline varies between scenarios in non-intuitive ways because extrinsic and intrinsic mechanisms respond in opposite ways to changes in emissions: extrinsic mechanisms cause kS to decline more strongly with increasing mitigation, while intrinsic mechanisms cause kS to decline more strongly under high-emission, low-mitigation scenarios as the carbon- climate system is perturbed further from a near-linear regime. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the most important anthropogenic greenhouse gases. Variation in soil moisture can be very dynamic, and it is one of the dominant factors controlling the net exchange of these three greenhouse gases (GHG). Although technologies for high frequency, precise measurements of CO2 have been available for years, methods for measuring soil fluxes of CH4 and N2O at high temporal frequency have been hampered by lack of appropriate technology for in situ real-time measurements. A previously developed automated chamber system for measuring CO2 flux from soils was configured to run in-line with a new quantum cascade laser (QCLAS) instrument that measures N2O and CH4. Here we present data from a forested wetland in Maine and an agricultural field in North Dakota, which provided examples of both net uptake and production for N2O and CH4. The objective was to provide a range of conditions in which to run the new system and to compare results to a traditional manual static chamber method. The high precision and more than ten-times lower minimum detectable flux of the QCLAS system, compared to the manual system, provided confidence in measurements of small N2O uptake in the forested wetland. At the agricultural field, the greatest difference between the automated and manual sampling systems came from the effect of the relatively infrequent manual sampling of the high spatial variation, or "hot spots", in GHG fluxes. "Hot spots" greatly influenced the seasonal estimates, particularly for N2O, over one 74 day alfalfa crop cycle. The high temporal frequency of the automated system clearly characterized the transient response of all three GHG's to precipitation and demonstrated a clear diel pattern related to temperature for GHG's. A combination of high frequency automated, and spatially distributed chambers would be ideal for characterizing "hot spots" and "hot moments" of GHG fluxes. [ABSTRACT FROM AUTHOR]

Ocean acidification is a predictable consequence of rising atmospheric carbon dioxide (CO2), and is highly likely to impact the entire marine ecosystem - from plankton at the base to fish at the top. Factors which are expected to be impacted include reproductive health, organism growth and species composition and distribution. Predicting when critical threshold values will be reached is crucial for projecting the future health of marine ecosystems and for marine resources planning and management. The impacts of ocean acidification will be first felt at the seasonal scale, however our understanding how seasonal variability will influence rates of future ocean acidification remains poorly constrained due to current model and data limitations. To address this issue, we first quantified the seasonal cycle of aragonite saturation state utilizing new data-based estimates of global ocean surface dissolved inorganic carbon and alkalinity. This seasonality was then combined with earth system model projections under different emissions scenarios (RCPs 2.6, 4.5 and 8.5) to provide new insights into future aragonite under-saturation onset. Under a high emissions scenario (RCP 8.5), our results suggest accounting for seasonality will bring forward the initial onset of month-long undersaturation by 17 years compared to annual-mean estimates, with differences extending up to 35 ± 17 years in the North Pacific due to strong regional seasonality. Our results also show large-scale under-saturation once atmospheric CO2 reaches 486 ppm in the North Pacific and 511 ppm in the Southern Ocean independent of emission scenario. Our results suggest that accounting for seasonality is critical to projecting the future impacts of ocean acidification on the marine environment. [ABSTRACT FROM AUTHOR]

A new coastal background site has been established for observations of greenhouse gases (GHGs) in the central Namib Desert at Gobabeb, Namibia. The location of the site was chosen to provide observations for a data-poor region in the global sampling network for GHGs. Semi-automated, continuous measurements of carbon dioxide, methane, nitrous oxide, carbon monoxide, atmospheric oxygen, and basic meteorology are made at a height of 21ma.g.l., 50 km from the coast at the northern border of the Namib Sand Sea. Atmospheric oxygen is measured with a differential fuel cell analyzer (DFCA). Carbon dioxide and methane are measured with an early-model cavity ring-down spectrometer (CRDS); nitrous oxide and carbon monoxide are measured with an off-axis integrated cavity output spectrometer (OA-ICOS). Instrument-specific water corrections are employed for both the CRDS and OA-ICOS instruments in lieu of drying. The performance and measurement uncertainties are discussed in detail. As the station is located in a remote desert environment, there are some particular challenges, namely fine dust, high diurnal temperature variability, and minimal infrastructure. The gas handling system and calibration scheme were tailored to best fit the conditions of the site. The CRDS and DFCA provide data of acceptable quality when base requirements for operation are met, specifically adequate temperature control in the laboratory and regular supply of electricity. In the case of the OA-ICOS instrument, performance is significantly improved through the implementation of a drift correction through frequent measurements of a working tank. [ABSTRACT FROM AUTHOR]

Planetary boundary layer (PBL) CO2 mole fraction data are needed by transport models and carbon budget models as both input and reference for validation. The height of in situ CO2 mole fraction measurements is usually different from that of the model levels where the data are needed; data from short towers, in particular, are dificult to utilize in atmospheric models that do not simulate the surface layer well. Tall tower CO2 mole fraction measurements observed at heights ranging from to 115ma.g.l. at a rural site in Hungary and regular airborne vertical mole fraction profile measurements (136 vertical profiles) above the tower allowed us to estimate how well a tower of a given height could estimate the CO2 mole fraction above the tower in the PBL. The statistical evaluation of the height-dependent bias between the real PBL CO2 mole fraction profile (measured by the aircraft) and the measurement at a given elevation above the ground was performed separately for the summer and winter half years to take into account the different dynamics of the lower troposphere and the different surface CO2 flux in the dif15 ferent seasons. The paper presents: (1) how accurately the vertical distribution of CO2 in the PBL can be estimated from the measurements on the top of a tower of height H, (2) how tall a tower would be needed for the satisfaction of different requirements on the accuracy of the estimation of the CO2 vertical distribution, (3) how accurate a CO2 vertical distribution estimation can be expected from the existing towers; and (4) how much improvement can be achieved in the accuracy of the estimation of CO2 vertical distribution applying the virtual tall tower concept. [ABSTRACT FROM AUTHOR]

The northern Scotia Sea contains the largest seasonal uptake of atmospheric carbon dioxide yet measured in the Southern Ocean. This study examines one of the main routes by which this carbon fluxes to the deep ocean, through the production of faecal pellets (FPs) by the zooplankton community. Deep sediment traps were deployed in two sites with contrasting ocean productivity regimes (P3, naturally iron-fertilized and P2, iron-limited), within the same water mass. The magnitude and seasonal pattern of particulate organic carbon (POC) and FPs in the traps was markedly different between the two sites. Maximum fluxes at P3 (22.91mgCm-2 d-1; 2534x10 FPm-2 d-1 ) were an order of magnitude higher than at P2 (4.01mgCm-2 d-1 ; 915x10 FPm-2 d-1), with flux at P3 exhibiting a double seasonal peak, compared to a single flatter peak at P2. The maximum contribution of FP carbon to the total amount of POC was twice as high at P3 (91%) compared to P2 (40%). The dominant FP category at P3 varied between round, ovoidal, cylindrical and tabular over the course of the year while, at P2, ovoidal FPs were consistently dominant, always making up more than 60% of the FP assemblage. There was also a difference in the FP state between the two sites, with FPs being relatively intact at P3, while FPs were often fragmented with broken peritrophic membranes at P2. The exception was ovoidal FPs, which were relatively intact at both sites. Our observations suggest that there was community shift from an herbivorous to an omnivorous diet from spring through to autumn at P3 while detritivores had a higher relative importance over the year at P2. Furthermore, the flux was mainly a product of the vertically migrating zooplankton community at P3 while the FP flux was more likely to be generated by deeper-dwelling zooplankton feeding on recycled material at P2. The results demonstrate that the feeding behavior and vertical distribution of the zooplankton community plays a critical role in controlling the magnitude of carbon export to the deep ocean in this region. [ABSTRACT FROM AUTHOR]

We monitored CO2 and CH4 fluxes using eddy covariance from 19 May to 27 September 2011 in a poor fen located in northern Michigan. The objectives of this paper are to: (1) quantify the flux of CH4 from a sub-boreal peatland, and (2) determine which abiotic and biotic factors were the most correlated to the flux of CHv over the measurement period. Net daily CH4 fluxes increased from 70 mgm-2 d-1 to 220mgm-2 d-1 from mid May to mid July. After July, CH4 losses steadily declined to approximately 50 mgm-2 d-1 in late September. During the study period, the peatland lost 17.4 g CH4 m-2. Both abiotic and biotic variables were correlated with changes in CH4 flux. When the different variables were analyzed together, the preferred model included mean daily soil temperature at 20cm, daily net ecosystem exchange (NEE) and the interaction between mean daily soil temperature at 20 cm and NEE (R² = 0.47, p value < 0.001). The interaction was important because the relationship between daily NEE and mean daily soil temperature with CH4 flux changed in conjunction with changes in daily NEE. On days when daily NEE was negative, 25% of the CH4 flux could be explained by changes in NEE, however on days when daily NEE was positive, there was no correlation between daily NEE and the CH4 flux. In contrast, daily mean soil temperature at 20 cm was poorly correlated to changes in CH4 when NEE was negative (17%), but the correlation increased to 34% when NEE was positive. The interaction between daily NEE and mean daily soil temperature at 20 cm indicates shifting environmental controls on the CH4 flux throughout the growing season. [ABSTRACT FROM AUTHOR]

While radiocarbon (14C) abundance in standing stocks of soil carbon has been used to evaluate rates of soil carbon turnover on timescales of several years to centuries, soil-respired 14CO2 measurements are an important tool for identifying more immediate responses to disturbance and climate change. Soil 14CO2 data are often temporally sparse, however, and could be interpreted better with more context for typical seasonal ranges and trends. We report on a semi-high-frequency sampling campaign to distinguish physical and biological drivers of soil 14CO2 at a temperate forest site in Northern Wisconsin, USA. We sampled 14CO2 profiles every three weeks during snow-free months through 2012, in three intact plots and one trenched plot that excluded roots. Respired 14CO2 declined through the summer in intact plots, shifting from an older C composition that contained more bomb 14C, to a younger composition more closely resembling present 14C levels in the atmosphere. In the trenched plot respired 14C was variable but remained comparatively higher than in intact plots, reflecting older bomb- enriched 14C sources. Although respired 14CO2 from intact plots correlated with soil moisture, related analyses did not support a clear cause-and-effect relationship with moisture. The initial decrease in 14CO2 from spring to midsummer could be explained by increases in 14C-deplete root respiration; however, 14CO2 continued to decline in late summer after root activity decreased. We also investigated whether soil moisture impacted vertical partitioning of CO2 production, but found this had little effect on respired 14CO2 because CO2 contained modern bomb-C at depth, even in the trenched plot. This surprising result contrasted with decades to centuries-old pre-bomb CO2 produced in lab incubations of the same soils. Our results suggest that root-derived C and other recent C sources had dominant impacts on 14CO2 in situ, even at depth. We propose that 14CO2 may have declined through late summer in intact plots because of continued microbial turnover of root-derived C, following declines in root respiration. Our results agree with other studies showing large seasonal fluctuations in respired Δ14CO2, and suggest root C inputs are an important driver. [ABSTRACT FROM AUTHOR]

Knowledge of all the mechanisms and processes involved in soil CO2 emissions is essential to close the global carbon cycle. Apart from molecular diffusion, the main physical component of such CO2 exchange is soil ventilation. Advective CO2 transport, through soil or snow, has been correlated with the wind speed, friction velocity or pressure (p). Here we examine variations in subterranean CO2 molar fractions (Χc) over two years within a vertical profile (1.5 m) in a semiarid ecosystem, as influenced by short-timescale p changes. Analyses to determine the factors involved in the variations in subterranean Χc were differentiated between the growing period and the dry period. In both periods it was found that variations in deep Χc (0.5-1.5 m) were due predominantly to static p variations and not to wind or biological influences. Within a few hours, the deep Χc can vary by fourfold showing a pattern with two cycles per day, due to p oscillations caused by atmospheric tides. By contrast, shallow Χc (0.15 m) generally has one cycle per day as influenced by biological factors like soil water content and temperature in both periods, while the wind was an important factor in shallow Χc variations only during the dry period. Evidence of emissions was registered in the atmospheric boundary layer by eddy covariance during synoptic pressure changes when subterranean CO2 was released; days with rising barometric pressure -- when air accumulated belowground, including soil-respired CO2 -- showed greater ecosystem uptake than days with falling pressure. Future assessments of the net ecosystem carbon balance should not rely exclusively on Fick's law to calculate soil CO2 effluxes from profile data. [ABSTRACT FROM AUTHOR]

A profound understanding of temporal and spatial variabilities of CO2, CH4 and N2O fluxes between terrestrial ecosystems and the atmosphere is needed to reliably quantify these fluxes and to develop future mitigation strategies. For managed grassland ecosystems, temporal and spatial variabilities of these three greenhouse gas (GHG) fluxes are due to environmental drivers as well as to fertilizer applications, grazing and cutting events. To assess how these affect GHG fluxes at Swiss grassland sites, we studied three sites along an altitudinal gradient that corresponds to a management gradient: from 400ma.s.l. (intensively managed) to 1000ma.s.l. (moderately intensive managed) to 2000 ma.s.l. (extensively managed). Temporal and spatial variabilities of GHG fluxes were quantified along small-scale transects of 16 static soil chambers at each site. We then established functional relationships between drivers and the observed fluxes on diel and annual time scales. Furthermore, spatial variabilities and their effect on representative site-specific mean chamber GHG fluxes were assessed using geostatistical semivariogram approaches. All three grasslands were N2O sources, with mean annual fluxes ranging from 0.15 to 1.28 nmol m-2 s-1. Contrastingly, all sites were net CH4 sinks, with uptake rates ranging from -0.56 to -0.15 nmol m-2 s-1. Mean annual respiration losses of CO2, as measured with opaque chambers, ranged from 5.2 to 6.5 µmol m-2 s-1. While the environmental drivers and their respective explanatory power for N O emissions differed considerably among the three grasslands (adjusted r² ranging from 0.19 to 0.42), CH4 and CO2 fluxes were much better constrained (adjusted r² ranging from 0.41 to 0.83), in particular by soil water content and air temperature, respectively. Throughout the year, spatial heterogeneity was particularly high for N2O and CH4 fluxes. We found permanent hot spots for N2O emissions and CH4 up- take at the extensively managed site. Including these hot spots in calculating the mean chamber flux was essential to obtain a representative mean flux for this ecosystem. At the intensively managed grassland, management effects clearly dominated over effects of environmental drivers on N2O fluxes. For CO2 and CH4, the importance of management effects did depend on the status of the vegetation. [ABSTRACT FROM AUTHOR]

1. We investigated the relative importance of CH4 and CO2 fluxes from soil and termite mounds at four different sites in the tropical savannas of Northern Australia near Darwin and assessed different methods to indirectly predict CH4 fluxes based on CO2 fluxes and internal gas concentrations. 2. The annual flux from termite mounds and surrounding soil was dominated by CO2 with large variations among sites. On a CO2-e basis, annual CH4 flux estimates from termite mounds were 5- to 46-fold smaller than the concurrent annual CO2 flux estimates. Differences between annual soil CO2 and soil CH4 (CO2-e) fluxes were even greater, soil CO2 fluxes being almost three orders of magnitude greater than soil CH4 (CO2-e) fluxes at site. 3. There were significant relationships between mound CH4 flux and mound CO2 flux, enabling the prediction of CH4 flux from measured CO2 flux, however, these relationships were clearly termite species specific. 4. We also observed significant relationships between mound flux and gas concentration inside mound, for both CH4 and CO2, and for all termite species, thereby enabling the prediction of flux from measured mound internal gas concentration. However, these relationships were also termite species specific. Using the relationship between mound internal gas concentration and flux from one species to predict mound fluxes from other termite species (as has been done in past) would result in errors of more than 5-fold for CH4 and 3-fold for CO2. 5. This study highlights that CO2 fluxes from termite mounds are generally more than one order of magnitude greater than CH4 fluxes. There are species-specific relationships between CH4 and CO2 fluxes from a mound, and between the inside mound concentration of a gas and the mound flux emission of the same gas, but these relationships vary greatly among termite species. Consequently, there is no generic relationship that will allow for the prediction of CH4 fluxes from termite mounds of all species. [ABSTRACT FROM AUTHOR]

The article discusses the study which compares the measurements of carbon dioxide CO2 δ(O2/N2) and δ13CO2 to assess the measurement compatibility of three European laboratories. It says that the standard deviation of the average differences between the laboratories are the same. It mentions that the required compatibility goals are not met by the laboratories.

The article discusses the study which assesses the cavity ring-down spectroscopy (CRDS) CO2CH4CO/H2O analyzer performance operating on an aircraft. The study used the CRDS analyzer to describe the system for making greenhouse gas measurements. Results show that the stability is not affected by pressure or temperature variation.

The article presents a study which evaluates the cavity ring-down spectrometer (CRDS) for 13carbon dioxide (CO)2's in situ observations. It states that a cylinder with known δ13CO2 was used to characterize the drift behavior and noise of the instrument. Results show that the performance of the laser detector and laser precision is governed by the noise.

The article discusses the measurement of dry mole fractions of greenhouse gases in humid air particularly carbon dioxide and methane. It says that greenhouse gas analyzers have been developed to provide high accuracy measurement of carbon dioxide, methane, and water vapor to meet the Global Atmospheric Watch program of the World Meteorological Organization (WMO/GAW) inter-laboratory compatibility goals. It adds that the dry-mole fraction measurements have met the compatibility goals of GAW.

Air-sea carbon dioxide (CO2) fluxes have recently been reported for the US South Atlantic Bight (SAB), a low-latitude shallow continental shelf bordered landward by abundant salt marshes and rivers. In this study, influences of terrestrial inputs on sea surface partial pressure of CO2 (pCO2) in the SAB are quantified. After re- moving pCO2 variations due to the annual temperature cycle and air-sea gas ex- change from the in situ pCO2, temperature and gas exchange corrected (TG-corrected) pCO2 is derived. Contributions from the river, marsh, and continental shelf to the TG-corrected pCO2 are then calculated. Findings show that CO2 contributions from the river [ΔpCO2 (river)] are highest close to the coast and decrease with distance off-shore. For example, ΔpCO2 (river) was up to 30 µatm on the inner shelf but averaged only 0--3 µatm on the outer shelf during January and March 2005. CO2 contributions from salt marshes [ΔpCO2 (marsh)] show similar spatial and seasonal distributions as ΔpCO2 (river), with the magnitude of ΔpCO2 (marsh) being about three times as high as that of ΔpCO2 (river). CO2 contributions from within the shelf [ΔpCO2 (shelf)] are highest among the three components. Compared to ΔpCO2 (river) and ΔpCO2 (marsh), ΔpCO2 (shelf) show the smallest onshore-offshore gradients. Despite large uncertainties, this study clearly demonstrates the importance of terrestrial impacts on coastal ocean CO2 distribution. [ABSTRACT FROM AUTHOR]

The article presents a study that determines the effectiveness of a new method in translating modeled terrestrial net ecosystem exchange (NEE) fluxes of carbon with seasonal cycles in atmospheric carbon dioxide. It describes the method of the study that observes the method based on the pulse-response functions from the atmospheric tracer transport model (ATM) intercomparison. It outlines the result of the research, which shows the effectiveness of the model in identifying ATM uncertainties.

The article discusses the synthesis and calculation of climate-based emission metrics of different species. It integrates radiative forcing (RF) with temperature change to a reference gas. It mentions several methods such as the Life Cycle Assessment (LCA), Impulse Response Function (IRF) and Bern Carbon Cycle. It concludes that the importance of short lived climate forcers (SLCFs) varies depending on the metric used.

Stem CO2 efflux was investigated with an open gas exchange system while stand microclimate and stem temperature were continuously monitored in a Schima superba plantation in South China for several days in August and December, 2010. The temperature response of respiration over the di?erent seasons, the vertical variation in stem CO2 efflux along the stem and the stand-level stem CO2 efflux were examined. Stem volume was identi?ed as the better correlate for stem CO2 efflux and was used as scaling scalar for the stand-level estimates of stem CO2 efflux in this S. superba plantation. Volume-based stem CO2 efflux was higher at 2 m than at 1.3m. Mean stem CO2 efflux was 268.9 and 104.6 µmol m-3 s-1 in August and December, respectively, indicating a dramatic seasonal variation of stem CO2 efflux. The temperature response of stem CO2 efflux was constant during our study period with Q10 values of 1.9 and 1.8. In this subtropical S. superba plantation, the averaged stem CO2 efflux per unit ground area was 3.36 and 1.26 µmol m-2 s-1 in August and December, respectively, which was underestimated due to the vertical variation of stem CO2 efflux along the stem. Our results suggest that stem CO2 efflux has a constant temperature response on the stand scale, and the seasonal variation in stem CO2 efflux is mainly controlled by stem temperature, and the vertical variation in stem CO2 efflux needs to be considered at the stand-level estimation. [ABSTRACT FROM AUTHOR]

Accurately monitoring tropical forest carbon stocks is an outstanding challenge. Allometric models that consider tree diameter, height and wood density as predictors are currently used in most tropical forest carbon studies. In particular, a pantropical biomass model has been widely used for approximately a decade, and its most recent version will certainly constitute a reference in the coming years. However, this reference model shows a systematic bias for the largest trees. Because large trees are key drivers of forest carbon stocks and dynamics, understanding the origin and the consequences of this bias is of utmost concern. In this study, we compiled a unique tree mass dataset on 673 trees measured in five tropical countries (101 trees > 100 cm in diameter) and an original dataset of 130 forest plots (1 ha) from central Africa to quantify the error of biomass allometric models at the individual and plot levels when explicitly accounting or not accounting for crown mass variations. We first showed that the proportion of crown to total tree aboveground biomass is highly variable among trees, ranging from 3 to 88%. This proportion was constant on average for trees < 10 Mg (mean of 34%) but, above this threshold, increased sharply with tree mass and exceeded 50% on average for trees = 45 Mg. This increase coincided with a progressive deviation between the pantropical biomass model estimations and actual tree mass. Accounting for a crown mass proxy in a newly developed model consistently removed the bias observed for large trees (> 1 Mg) and reduced the range of plot-level error from -23-16 to 0-10%. The disproportionally higher allocation of large trees to crown mass may thus explain the bias observed recently in the reference pantropical model. This bias leads to far-from-negligible, but often overlooked, systematic errors at the plot level and may be easily corrected by accounting for a crown mass proxy for the largest trees in a stand, thus suggesting that the accuracy of forest carbon estimates can be significantly improved at a minimal cost. [ABSTRACT FROM AUTHOR]

The management of agroecosystems plays a crucial role in the global carbon cycle with soil tillage leading to known organic carbon redistributions within soils and changes in soil CO2 emissions. Yet, discrepancies exist on the impact of tillage on soil CO2 emissions and on the main soil and environmental controls. A meta-analysis was conducted using 46 peer-reviewed publications totaling 174 paired observations comparing CO2 emissions over entire seasons or years from tilled and untilled soils across different climates, crop types and soil conditions with the objective of quantifying tillage impact on CO2 emissions and assessing the main controls. On average, tilled soils emitted 21% more CO2 than untilled soils, which corresponded to a significant difference at P < 0.05. The difference increased to 29% in sandy soils from arid climates with low soil organic carbon content (SOCC < 1%) and low soil moisture, but tillage had no impact on CO2 fluxes in clayey soils with high background SOCC (> 3%). Finally, nitrogen fertilization and crop residue management had little effect on the CO2 responses of soils to no-tillage. These results suggest no-tillage is an effective mitigation measure of carbon dioxide losses from dry land soils. They emphasize the importance of including information on soil factors such as texture, aggregate stability and organic carbon content in global models of the carbon cycle. [ABSTRACT FROM AUTHOR]

Wildfires are by far the largest contributor to global biomass burning and constitute a large global source of atmospheric traces gases and aerosols. Such emissions have a considerable impact on air quality and constitute a major health hazard. Biomass burning also influences the radiative balance of the atmosphere and is thus not only of societal, but also of significant scientific interest. There is a common perception that climate change will lead to an increase in emissions as hot and dry weather events that promote wildfire will become more common. However, even though a few studies have found that the inclusion of CO2 fertilization of photosynthesis and changes in human population patterns will tend to somewhat lower predictions of future wildfire emissions, no such study has included full ensemble ranges of both climate predictions and population projections, including the effect of different degrees of urbanisation. Here, we present a series of 124 simulations with the LPJ-GUESS-SIMFIRE global dynamic vegetation -wildfire model, including a semi-empirical formulation for the prediction of burned area based on fire weather, fuel continuity and human population density. The simulations comprise Climate Model Intercomparison Project 5 (CMIP5) climate predictions from eight Earth system models using two Representative Concentration Pathways (RCPs) and five scenarios of future human population density based on the series of Shared Socioeconomic Pathways (SSPs), sensitivity tests for the effect of climate and CO2, as well as a sensitivity analysis using two alternative parameteri-sations of the semi-empirical burned-area model. Contrary to previous work, we find no clear future trend of global wildfire emissions for the moderate emissions and climate change scenario based on the RCP 4.5. Only historical population change introduces a decline by around 15 % since 1900. Future emissions could either increase for low population growth and fast urbanisation, or continue to decline for high population growth and slow urbanisation. Only for high future climate change (RCP8.5), wildfire emissions start to rise again after ca. 2020 but are unlikely to reach the levels of 1900 by the end of the 21st century. We find that climate warming will generally increase the risk of fire, but that this is only one of several equally important factors driving future levels of wildfire emissions, which include population change, CO2 fertilisation causing woody thickening, increased productivity and fuel load, and faster litter turnover in a warmer climate. [ABSTRACT FROM AUTHOR]

Stream networks were recently discovered as major but poorly constrained natural greenhouse gas (GHG) sources. A fundamental problem is that several measurement approaches have been used without cross comparisons. Flux chambers represent a potentially powerful methodological approach if robust and reliable ways 5 to use chambers on running water can be defined. Here we compare the use of anchored and freely drifting chambers on various streams having different flow velocities. The study clearly shows that (1) drifting chambers have a very small impact on the water turbulence under the chamber and thus generate more reliable fluxes, (2) anchored chambers enhance turbulence under the chambers and thus elevate fluxes, (3) the bias of the anchored chambers greatly depends on chamber design and sampling conditions, and (4) there is a promising method to reduce the bias from anchored chambers by using a flexible plastic foil seal to the water surface rather than having rigid chamber walls penetrating into the water. Altogether, these results provide novel guidance on how to apply flux chambers in running water, which will have important consequences for measurements to constrain the global GHG balances. [ABSTRACT FROM AUTHOR]

Fluxes of carbon dioxide (CO2) and methane (CH4) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chambers (FC) technique, however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at the lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO2 (pCO2 w ) in the EC flux footprint. The methods agree better for CH4 fluxes, it is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events. [ABSTRACT FROM AUTHOR]

Exchangeable organic carbon (OC) dynamics and CO2 fluxes in the Antarctic Peninsula region during austral summer are highly variable. By stations, the region is a weak source of CO2 to the atmosphere, however, continuous records of CO2 revealed this area as a weak sink. OC fluxes are also in both directions but generally towards the ocean and much higher than CO2 fluxes, sometimes by a factor of 10. Surface exchangeable dissolved organic carbon (EDOC) measurements had a 43±3 μmolCL-1 overall mean, while the gaseous organic carbon equilibrated in water as given by the Henry's Law constant (H') resulted in (GOC H'-1) concentrations of 46±3 μmolCL-1. EDOC represents around 66% of surface dissolved organic carbon (DOC) in Antarctic waters. There is a tendency towards low partial pressures of CO2 in waters with high Chlorophyll a (Chl a) content and high fCO2 in areas with high krill densities. However, such relationships were not found for EDOC. Depth profiles of EDOC were also quite variable and followed Chl a profiles, but only in some instances, while diel cycles of EDOC revealed two distinct peaks around midday and middle of the short austral dark period concurrent with solar radiation maxima and krill night migration patterns. However, there was no evident diel pattern for GOC H'-1. The pool of exchangeable OC reveals itself as an important compartment of the carbon budget in the Antarctic Peninsula and adds to previous studies highlighting its importance in the redistribution of carbon in marine environments. [ABSTRACT FROM AUTHOR]

We built an automatic chamber system to measure greehouse gas (GHG) exchange in forested peatland ecosystems. We aimed to build a system robust enough which would work throughout the year and could measure through a changing snowpackin addition to producing annual GHG fluxes by integrating the measurements without the need of using models. The system worked rather well throughout the year, but it was not service free. Gap filling of data was still necessary. We observed problems in carbon dioxide (CO2) flux estimation during calm summer nights, when a CO2 concentration gradient from soil/moss system to atmosphere builds up. Chambers greatly overestimated the nighttime respiration. This was due to the disturbance caused by the chamber to the soil-moss CO2 gradient and consequent initial pulse of CO2 to the chamber headspace. We tested different flux calculation and measurement methods to solve this problem. The estimated flux was strongly dependent on (1) the type of the fit (linear and polynomial), (2) the starting point of the fit after closing the chamber, (3) the length of the fit, (4) the speed of the fan mixing the air inside the chamber, and (5) atmospheric turbulence (friction velocity, u*). The best fitting method (the most robust, least random variation) was linear fitting with the period of 120-240 s after chamber closure. Furthermore, the fan should be adjusted to spin at minimum speed to avoid the pulse-effect, but it should be kept on to ensure mixing. If nighttime problems cannot be solved, emissions can be estimated using daytime data from opaque chambers. [ABSTRACT FROM AUTHOR]

The considerable uncertainties in the carbon budget of the Southern Ocean are largely attributed to unresolved variability, in particular at seasonal time scale and small spatial scale (~ 100 km). In this study, the variability of surface pCO2 and DIC at seasonal and small-spatial scales is examined using a dataset of surface drifters including ~ 80 000 measurements at high spatio-temporal resolution. On spatial scales of 100 km, we find gradients ranging from 5 to 50 μatm for pCO2 and 2 to 30 µmol kg-1 for DIC, with highest values in energetic and frontal regions. This result is supported by a second estimate obtained with SST satellite images and local DIC/SST relationships derived from drifters observations. We find that dynamical processes drives the variability of DIC at small spatial scale in most regions of the Southern Ocean, the cascade of large-scale gradients down to small spatial scales leading to gradients up to 15 µmol kg-1 over 100 km. Although the role of biological activity is more localized, it enhances the variability up to 30 µmol kg-1 over 100 km. The seasonal cycle of surface DIC is reconstructed following Mahadevan et al. (2011), using an annual climatology of DIC and a monthly climatology of mixed layer depth. This method is evaluated using drifters observations and proves to be a reasonable first-order estimate of the seasonality in the Southern Ocean, which could be used to validate models simulations. We find that small spatial scales structures are a non negligible source of variability for DIC, with amplitudes of about a third of the variations associated with the seasonality and up to 10 times the magnitude of large-scale gradients. The amplitude of small-scale variability reported here should be kept in mind when inferring temporal changes (seasonality, inter-annual variability, decadal trends) of the carbon budget from low resolution observations and models. [ABSTRACT FROM AUTHOR]

Gross primary production (GPP), separated from flux tower measurements of net ecosystem exchange (NEE) of CO2, is used increasingly to validate process-based simulators and remote sensing-derived estimates of simulated GPP at various time steps. Proper validation should include the uncertainty associated with this separation at different time steps. This can be achieved by using a Bayesian framework. In this study, we estimated the uncertainty in GPP at half hourly time steps. We used a nonrectangular hyperbola (NRH) model to separate GPP from flux tower measurements of NEE at the Speulderbos forest site, The Netherlands. The NRH model included the variables that influence GPP, in particular radiation, and temperature. In addition, the NRH model provided a robust empirical relationship between radiation and GPP by including the degree of curvature of the light response curve. Parameters of the NRH model were fitted to the measured NEE data for every 10-day period during the growing season (April to October) in 2009. Adopting a Bayesian approach, we defined the prior distribution of each NRH parameter. Markov chain Monte Carlo (MCMC) simulation was used to update the prior distribution of each NRH parameter. This allowed us to estimate the uncertainty in the separated GPP at half-hourly time steps. This yielded the posterior distribution of GPP at each half hour and allowed the quantification of uncertainty. The time series of posterior distributions thus obtained allowed us to estimate the uncertainty at daily time steps. We compared the informative with non-informative prior distributions of the NRH parameters. The results showed that both choices of prior produced similar posterior distributions GPP. This will provide relevant and important information for the validation of process-based simulators in the future. Furthermore, the obtained posterior distributions of NEE and the NRH parameters are of interest for a range of applications. [ABSTRACT FROM AUTHOR]

Recently, it has been proposed that alkalinity release from sediments can play an important role in the carbonate dynamics on continental shelves, lowering the pCO2 of seawater and hence increasing the CO2 uptake from the atmosphere. To test this hypothesis, sedimentary alkalinity generation was quantified within permeable and muddy sediments across the North Sea during two cruises in September 2011 (basinwide) and June 2012 (Dutch coastal zone). Benthic fluxes of alkalinity (AT) and dissolved inorganic carbon (DIC) were determined using shipboard closed sediment incubations. These results show that sediments can be an important source for alkalinity, particularly in the shallow southern North Sea, where high AT and DIC fluxes were recorded in near shore sediments of the Belgian, Dutch and German coastal zone. In contrast, fluxes of AT and DIC are substantially lower in the deeper, seasonally stratified, northern part of the North Sea. Overall, our results show that sedimentary alkalinity generation should be considered an important factor in the CO2 dynamics of shallow coastal systems. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is likely to have an effect on the fertilizing potential of desert dust in high-nutrient, low-chlorophyll oceanic regions, either by modifying Fe speciation and bioavailability, or by altering phytoplankton Fe requirements and acquisition. To address this issue, short incubations (4 days) of northeast subarctic Pacific waters enriched with either FeSO4 or dust, and set at pH 8.0 (in situ) and 7.8 were conducted in August 2010. We assessed the impact of a decrease in pH on dissolved Fe concentration, phytoplankton biomass, taxonomy and productivity, and the production of dimethylsulfide (DMS) and its algal precursor dimethylsulfoniopropionate (DMSP). Chlorophyll a (chl a) remained unchanged in the controls and doubled in both the FeSO4-enriched and dust-enriched incubations, confirming the Fe-limited status of the plankton assemblage during the experiment. In the acidified treatments, a significant reduction (by 16-38%) of the final concentration of chl a was measured compared to their non-acidified counterparts, and a 15% reduction in particulate organic carbon (POC) concentration was measured in the dust-enriched acidified treatment compared to the dust-enriched non-acidified treatment. FeSO4 and dust additions had a fertilizing effect mainly on diatoms and cyanobacteria. Lowering the pH affected mostly the haptophytes, but pelagophyte concentrations were also reduced in some acidified treatments. Acidification did not significantly alter DMSP and DMS concentrations. These results show that dust deposition events in a low-pH iron-limited Northeast subarctic Pacific are likely to stimulate phytoplankton growth to a lesser extent than in today's ocean during the few days following fertilization and point to a low initial sensitivity of the DMSP and DMS dynamics to OA. [ABSTRACT FROM AUTHOR]