A warming climate results in sea ice loss and impacts to the Arctic water cycle. The water isotope
parameter deuterium excess, a moisture source proxy, can serve as a tracer to help understand hydrological
changes due to sea ice loss. However, unlocking the sea ice change signal of isotopes from ice cores requires
understanding how sea ice changes impact deuterium excess, which is unknown. Here we present the first
isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values. Initial loss of

The reasons for the early Holocene temperature discrepancy between northern hemispheric model simulations and paleoclimate reconstructions—known as the Holocene temperature conundrum—remain unclear. Using hydrogenisotopes of fluid inclusion water extracted from stalagmites from the Milandre Cave in Switzerland, we established a mid-latitude European mean annual temperature reconstruction for the past 14,000 years.

In this paper, we present an innovative CH₄, δ¹³CH₄, and C₂H₆ instrument based on cavity ring-down spectroscopy (CRDS). The design and performance of the analyzer is presented in detail. The instrument is capable of precision of less than 1‰ on δ¹³CH₄ with 1 in. of averaging and about 0.1‰ in an hour. Using this instrument, we present a comprehensive approach to atmospheric methane emissions attribution.

We report the determination of ammonia (NH3) diffusive sampling rates for six different designs of commercial
diffusive samplers (CEH ALPHA sampler, Gradko diffusion tube, Gradko DIFRAM-400, Passam ammonia sampler,
and ICS Maugeri Radiello radial sampler (blue and white turbulence barriers)), together with the validation
test results for a pumped sampler (CEH DELTA denuder). The devices were all exposed in the UK's National
Physical Laboratory's (NPL) controlled atmosphere test facility (CATFAC). For each of the seven diffusive

As part of the DENCHAR (Development and Evaluation of Novel Compact Hygrometer for Airborne Research) inter-comparison campaign in northern Germany in 2011, a commercial cavity ring-down spectroscopy (CRDS) based gas analyzer (G2401-m, Picarro Inc., US) was installed on a Learjet to measure atmospheric water vapor, CO2, CH4, and CO. The CRDS components were identical to those chosen for integration aboard commercial airliners within the IAGOS (In-service Aircraft for a Global Observing System) project.

Carbon dioxide and oxygen are tightly coupled in land-biospheres CO2 - O2 exchange processes, while they are not coupled in oceanic exchange. For this reason, atmospheric oxygen measurements can be used to constrain the global carbon cycle, especially oceanic uptake. However, accurately quantifying the small (~1-100 ppm) variations in O2 is analytically challenging due to the very large atmospheric background which constitutes about 20.9 % (~209500 ppm) of atmospheric air.

A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH₃) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy.

Abstract. Cavity ring-down spectrometers have generally been designed to operate under conditions in which the background gas has a constant composition. However, there are a number of observational and experimental situations of interest in which the background gas has a variable composition. In this study, we examine the effect of background gas composition on a cavity ring-down spectrometer that measures δ¹⁸O–H2O and δ²H–H₂O values based on the amplitude of water isotopologue absorption features around 7184 cm−1 (L2120-i, Picarro, Inc.).

Rationale
Induction module cavity ring-down spectroscopy (IM-CRDS) has been proposed as a rapid and cost-effective alternative to cryogenic vacuum distillation (CVD) and isotope ratio mass spectrometry (IRMS) for the measurement of δ¹⁸O and δ²H values in matrix-bound waters. In the current study, we characterized the performance of IM-CRDS relative to CVD and IRMS and investigated the mechanisms responsible for differences between the methods.

A laboratory and field experiment compared fluxes of CO₂, CH₄ and N₂O measured with cavity ring-downspectroscopy (CRDS) and gas chromatography (GC). The comparison between CRDS and GC showed thataverage CO₂ fluxes were significantly higher for CRDS in both the laboratory and field, but the same experimental treatments effects were detected for both techniques. Compared to CRDS, the GC technique was severely limited in detecting CH₄ fluxes in both the laboratory and field.

Deuterium (dD) and oxygen (d18O) isotopes are powerful tracers of the hydrological cycle and have been extensively used for paleoclimate reconstructions as they can provide information on past precipitation,temperature and atmospheric circulation. More recently, the use of 17O excess derived from precise measurement of d17O and d18O gives new and additional insights in tracing the hydrological cycle whereas uncertainties surround this proxy.

Laser-based spectroscopic techniques, such as cavity ring-down spectroscopy (CRDS), provide a new, costeffective and more widely available approach to measure the oxygen isotope ratio in water molecules, H218O/H216O (d18O), and are used increasingly to measure d18O in the world’s oceans. Here, we present results froman interlaboratory comparison designed to evaluate the quality of CRDS-derived measurements, and theirconsistency with values measured by isotope ratio mass spectrometry (IRMS).

The isotopic composition of near surface (or planetary boundary layer) water vapor on the south coast of Iceland (63.83°N, 21.47°W) has been monitored in situ between November 2011 and April 2013. The calibrated data set documents seasonal variations in the relationship between δ¹⁸O and local humidity (ppmv) and between deuterium excess and δ¹⁸O. These seasonal variations are attributed to seasonal changes in atmospheric transport.

Insights into the effects of stormwater control measures (SCMs) on urban stream hydrology and in-stream processes are required to understand their effectiveness in mitigating the environmental problems associated with urbanization. Stable water isotopes were applied to understand processes occurring within SCMs and their effects on water sourcing in urban streams. We sampled ten events from June to November 2013 at four locations along a 360-m headwater stream reach in North Carolina and at four SCMs (two ponds, one wetland and one bioretention) that contribute to the reach.

Temperature reconstructions across Heinrich stadials 1–3 are presented from an absolute-dated speleothem from Abaco Island in the Bahamas to understand the nature of climate change across these intervals in the subtropical Atlantic. The stalagmite carbonate record, dated by the U–Th geochronometry technique, includes higher δ¹⁸O and δ¹³C values within Heinrich stadials 1, 2, and 3 followed by rapid declines at the end of the stadials.

A portable Wavelength Scanned-Cavity Ring-Down Spectrometer (Picarro L2120) fitted with a diffusion sampler (DS-CRDS) was used for the first time to continuously measure δ¹⁸O and δ²H of stream water. The experiment took place during a storm event in a wet tropical agricultural catchment in north-eastern Australia.

This study presents two methods for estimating methane emissions from a waste water treatment plant (WWTP) along with results from a measurement campaign at a WWTP in Valence, France. These methods, chamber measurements and tracer release, rely on Fourier transform infrared spectroscopy and cavity ring-down spectroscopy instruments. We show that the tracer release method is suitable for quantifying facility- and some process-scale emissions, while the chamber measurements provide insight into individual process emissions. Uncertainties for the two methods are described and discussed.

We present a study of methane emissions from oil and gas producing well pad facilities in the Barnett Shale region of Texas, measured using an innovative ground-based mobile flux plane (MFP) measurement system, as part of the Barnett Coordinated Campaign. Using only public roads, we measured the emissions from nearly 200 well pads over 2 weeks in October 2013.

The replacement of native species by invasive Phragmites australis in coastal wetlands may impact ecosystem processes including fluxes of the greenhouse gases (GHGs) carbon dioxide (CO₂) and methane (CH₄).

Fugitive greenhouse gas emissions from unconventional gas extraction processes (e.g. shale gas, tight gas and coal bed methane/coal seam gas) are poorly understood due in part to the extensive area over which these emissions may occur. We apply a rapid qualitative approach for source assessment at the scale of a large gas field.

Floods frequently produce deoxygenation and acidification in waters of artificially drained coastal acid sulfate soil (CASS) wetlands. These conditions are ideal for carbon dioxide and methane production. We investigated CO₂ and CH₄ dynamics and quantified carbon loss within an artificially drained CASS wetland during and after a flood.

Automated cavity ring down spectroscopy was used to make continuous measurements of dissolved methane, nitrous oxide, and carbon dioxide in a coral reef lagoon for 2 weeks (Heron Island, Great Barrier Reef). Radon (²²²Rn) was used to trace the influence of tidally driven pore water exchange on greenhouse gas dynamics. Clear tidal variation was observed for CH₄, which correlated to ²²²Rn in lagoon waters.

Estuaries have high rates of primary production and respiration and can be hotspots for carbon dioxide and methane enriched submarine groundwater discharge.

Automated in situ instrumentation captured high-resolution surface water pCO₂, CH₄ and²²²Rn data at the creek mouth, and ∼500 m upstream in a sub-tropical mangrove ecosystem (Southern Moreton Bay, Australia, S27.78°, E153.38°) over a spring-neap-spring tidal cycle (∼15 days) during November 2013.

We present a novel determination of the dissolution kinetics of inorganic calcite in seawater.

Laser spectroscopy is an emerging technology for measuring nitrous oxide (N₂O) dynamics in the environment, but most studies have focused on atmospheric applications. We have coupled a commercially available cavity ring-down spectroscope (CRDS) (Picarro G5101-i isotopic N₂O analyzer) to an air/water gas equilibration device to collect continuous in situ dissolved N₂O molar concentration and bulk nitrogen isotopic (δ¹⁵N-N₂O) data.

The most common currency for estimating N₂ fixation is acetylene reduction to ethylene. Real-time estimates of nitrogen fixation are needed to close the global nitrogen budget and these remain a critical gap in both laboratory and field experiments. We present a new method for continuous real-time measurements of ethylene production: Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectroscopy (ARACAS).

Production of natural gas from shale formations is bringing drilling and production operations to regions of the United States that have seen little or no similar activity in the past, which has generated considerable interest in potential environmental impacts. This study focused on the Barnett Shale Fort Worth Basin in Texas, which saw the number of gas-producing wells grow from 726 in 2001 to 15,870 in 2011.

Methane is a greenhouse gas (GHG) and the anthropogenic emission of methane to the atmosphere contributes to global warming. There are several anthropogenic methane sources, and the quantification of methane from these emission sources are often based on emission factors and model calculations making reporting uncertain. Reducing the methane emission is an effective way of reducing the overall greenhouse gas emission. Methane reductions can often be difficult to quantify and document, as accurate measurements methods are lacking and not commercial available.

Methane is emitted to the atmosphere from both anthropogenic and natural sources. One of the major anthropogenic sources is methane produced by bacteria in anaerobic environments such as rice pads and landfills. Land filling has for many years been the preferred waste disposal method, resulting in a large methane production with a large contribution to the global increase in atmospheric green house gas concentration. Several steps have been taken to reduce the emission of methane from landfills.

The performance of eight fast-response methane (CH₄) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions.

With the recent advent of commercial laser absorption spectrometers, field studies measuring stable isotope ratios of hydrogen and oxygen in water vapor have proliferated. These pioneering analyses have provided invaluable feedback about best strategies for optimizing instrumental accuracy, yet questions still remain about instrument performance and calibration approaches for multi-year field deployments.

Here we test an experimental approach that produces estimates of the location, timing and extent of water uptake by individual plant species in the field. A tracer injection experiment was used to estimate the proportion of active roots across soil depths. These proportions were multiplied by species-specific estimates of evapotranspiration. This approach was repeated in early- and late-season conditions in adjacent native- and non-native-dominated shrub-steppe plant communities. Resulting estimates of water uptake by depth were compared to soil water content.

We provide sedimentological, geochemical, mineral magnetic, stable carbon isotope, charcoal, and pollen-based evidence from a guano/clay sequence in Gaura cu Muscă Cave (SW Romania), from which we deduced that from ~ 1230 BC to ~ AD 1240 climate oscillated between wet and dry. From ~ 1230 BC to AD 1000 the climate was wetter than the present, prompting flooding of the cave, preventing bats from roosting, and resulting in a slow rate of clay accumulation.

Cavity ring-down spectrometers (CRDS) have the capacity to make isotopic measurements of CO₂ where concentrations range from atmospheric (~ 400 ppm) to 6000 ppm. Following field trials, it has come to light that the spectrographic lines used for CO₂ have an interference with elevated (higher than ambient) amounts of hydrogen sulfide (H₂S), which causes significant depletions in the δ¹³C measurement by the CRDS.

Anthropogenic modification of the water cycle involves a diversity of processes, many of which have been studied intensively using models and observations. Effective tools for measuring the contribution and fate of combustion-derived water vapor in the atmosphere are lacking, however, and this flux has received relatively little attention. We provide theoretical estimates and a first set of measurements demonstrating that water of combustion is characterized by a distinctive combination of H and O isotope ratios.

Rapid Arctic warming is associated with important water cycle changes: sea ice loss, increasing atmospheric humidity, permafrost thaw, and water-induced ecosystem changes. Understanding these complex modern processes is critical to interpreting past hydrologic changes preserved in paleoclimate records and predicting future Arctic changes. Cyclones are a prevalent Arctic feature and water vapor isotope ratios during these events provide insights into modern hydrologic processes that help explain past changes to the Arctic water cycle.

Dissolved oxygen (DO) is commonly recognized as an important factor influencing nitrous oxide (N₂O) production by ammonia-oxidizing bacteria (AOB). However, it has been difficult to separate the true effect of DO from that of nitrite, as DO variation often affects nitrite accumulation. The effect of DO on N₂O production by an enriched nitrifying sludge, consisting of both AOB and nitrite-oxidizing bacteria (NOB), was investigated in this study. Nitrite accumulation was minimized by augmenting nitrite oxidation through the addition of an enriched NOB sludge.

RATIONALE

Traditionally, stable isotope analysis of plant and soil water has been a technically challenging, labour-intensive and time-consuming process. Here we describe a rapid single-step technique which combines Microwave Extraction with Isotope Ratio Infrared Spectroscopy (ME-IRIS).

METHODS

High-precision analysis of the ¹⁷O / ¹⁶O isotope ratio in water and water vapor is of interest in hydrological, paleoclimate, and atmospheric science applications. Of specific interest is the parameter ¹⁷O excess (Δ¹⁷O), a measure of the deviation from a‾linear relationship between ¹⁷O / ¹⁶O and ¹⁸O / ¹⁶O ratios.

A reliable and precise in situ CO₂ and CO analysis system has been developed and deployed at eight sites in the NOAA Earth System Research Laboratory's (ESRL) Global Greenhouse Gas Reference Network. The network uses very tall (> 300 m) television and radio transmitter towers that provide a convenient platform for mid-boundary-layer trace-gas sampling. Each analyzer has three sample inlets for profile sampling, and a complete vertical profile is obtained every 15 min.

There is a pressing need to verify air pollutant and greenhouse gas emissions from anthropogenic fossil energy sources to enforce current and future regulations. We demonstrate the feasibility of using simultaneous remote sensing observations of column abundances of CO₂, CO, and NO₂ to inform and verify emission inventories.

A dedicated system for airborne ship emission measurements of SO₂, NO_x and particles has been developed and used from several small aircraft. The system has been adapted for fast response measurements at 1 Hz, and the use of several of the instruments is unique. The uncertainty of the given data is about 20% for SO₂ and 24% for NO_x emission factors.

Suitable predictors of degradability are sought to support the identification of biochars with large potential to increase C sequestration in soils. We determined the biodegradation of 9 chars from hydrothermal carbonization and pyrolysis in two agricultural soils. The 200- and 115-day degradation correlated strongly with the O:C- and slightly with the H:C-atomic ratio of 9 and 14 biochars, respectively. Highest temperature treatment and ash content did not show similar correlations.

The East Scotia Ridge is an active back-arc spreading centre located to the west of the South Sandwich island arc in the Southern Ocean. Initial exploration of the ridge by deep-tow surveys provided the first evidence for hydrothermal activity in a back-arc setting outside of the western Pacific, and we returned in 2010 with a remotely operated vehicle to precisely locate and sample hydrothermal sites along ridge segments E2 and E9.