Separating contributions from natural and anthropogenic sources in atmospheric methane from the Black Sea region,Romania

The Danube Delta-Black Sea region of Romania is an important wetland, and this preliminary study evaluates the significance of this region as a source of atmospheric CH₄. Measurements of the mixing ratio and δ¹³C in CH₄ are reported from air and water samples collected at eight sites in the Danube Delta. High mixing ratios of CH₄ were found in air (2500–14,000 ppb) and dissolved in water samples (∼1–10 μmol L⁻¹), demonstrating that the Danube Delta is an important natural source of CH₄. The intercepts on Keeling plots of about −62‰ show that the main source of CH₄ in this region is microbial, probably resulting primarily from acetate fermentation. Atmospheric CH₄ and CO data from the NOAA/ESRL (National Oceanic and Atmospheric Administration/Earth System Research Laboratory) were used to make a preliminary estimate of biogenic CH₄ at the Black Sea sampling site at Constanta (BSC). These data were used to calculate ratios of CH₄/CO in air samples, and using an assumed CH₄/CO anthropogenic emissions ratio of 0.6, fossil fuel emissions at BSC were estimated. Biogenic CH₄ emissions were then estimated by a simple mass balance approach. Keeling plots of well-mixed air from the BSC site suggested a stronger wetland source in summer and a stronger fossil fuel source in winter.     

Precise geodesy with the Very Long Baseline Array

We report on a program of geodetic measurements between 1994 and 2007 which used the Very Long Baseline Array (VLBA) and up to ten globally distributed antennas. One of the goals of this program was to monitor positions of the array at a 1 mm level of accuracy and to tie the VLBA into the international terrestrial reference frame. We describe the analysis of these data and report several interesting geophysical results including measured station displacements due to crustal motion, earthquakes, and antenna tilt. In terms of both formal errors and observed scatter, these sessions are among the very best geodetic very long baseline interferometry experiments.     

Multi‐transient electromagnetic repeatability experiment over the North Sea Harding field‡

We present results of synthetic time‐lapse and real repeatability multi‐transient electromagnetic surveys over the North Sea Harding field. Using Archie's law to convert porosity and fluid saturation to resistivity we created 3D isotropic models of the reservoir resistivity at different stages of production from the initial state in 1996 through to complete hydrocarbon production by 2016 and, for each stage, we simulated an east‐west transient electromagnetic survey line across Harding. Unconstrained 1D full‐waveform Occam inversions of these synthetic data show that Harding should be detectable and its lateral extent reasonably well‐defined. Resistivity changes caused by hydrocarbon production from initial pre‐production state to production of the oil rim in 2011 are discernible as are significant changes from 2011–2016 during the modelled gas blowdown phase. The 2D repeatability surveys of 2007 and 2008 tied two wells: one on and the other off the structure. Between the two surveys the segment of the field under investigation produced 3.9 million barrels of oil – not enough to generate an observable time‐lapse electromagnetic anomaly with a signal‐to‐noise ratio of 40 dB. Processing of the 2007 and 2008 data included deconvolution for the measured source current and removal of spatially‐correlated noise, which increased the signal‐to‐noise ratio of the recovered impulse responses by about 20 dB and resulted in a normalized root‐mean‐square difference of 3.9% between the data sets. 1D full‐waveform Occam inversions of the real data showed that Harding was detectable and its lateral extent was also reasonably well‐defined. The results indicate that the multi‐transient electromagnetic method is suitable for exploration, appraisal and monitoring hydrocarbon production.     

Pyritization of trace metals in estuarine sediments and the controlling factors: a case in Jiaojiang Estuary of Zhejiang Province,China

Three undisturbed sediment samples were collected from the intertidal zone of the Jiaojiang Estuary of Zhejiang Province, China. The sediments were found to contain remarkably low concentrations of organic carbon (<0.6%) and acid volatile sulfide (AVS) (<30 μmol g⁻¹). The availability of these two substrates likely constrained sulfate reduction and pyritization of several trace metals, respectively. This was especially true at one station where AVS concentrations in the upper 20 cm averaged less than 0.05 μmol g⁻¹. Although the depth dependence of the degree of trace metal pyritization was generally consistent with expectations based on redox conditions, depth profiles of reactive-metal and pyrite-metal concentrations in several cases revealed more complex behavior and a positive correlation between reactive-metal concentrations and pore water metal concentrations.     

Solar Scintillometry: Calibration of Signals and its Use for Seeing Measurements

Since 1993 it is known that there is a good correlation between the scintillation in the solar irradiance and solar image quality (Seykora, 1993). This effect is now being used in a number of experiments to evaluate solar image quality and to measure site seeing. In this paper we explore further the calibration of this scintillation (_I) in terms of the Fried parameter (_r0) taking into account variations in the refractive index structure constant C _N ² with height (h), zenith distance () dependence and the effects of wind velocities. A variant in the scintillometer setup is proposed which decreases sharply the dependance on C _N ² , , and the wind velocities. It uses an array of scintillometers. The same array can be used to measure theC _N ² profile with height. Some preliminary results of the calibration of current NSO site survey measurements are presented.     

Identifying uncertainties in Arctic climate change projections

Wide ranging climate changes are expected in the Arctic by the end of the 21st century, but projections of the size of these changes vary widely across current global climate models. This variation represents a large source of uncertainty in our understanding of the evolution of Arctic climate. Here we systematically quantify and assess the model uncertainty in Arctic climate changes in two CO₂ doubling experiments: a multimodel ensemble (CMIP3) and an ensemble constructed using a single model (HadCM3) with multiple parameter perturbations (THC-QUMP). These two ensembles allow us to assess the contribution that both structural and parameter variations across models make to the total uncertainty and to begin to attribute sources of uncertainty in projected changes. We find that parameter uncertainty is an major source of uncertainty in certain aspects of Arctic climate. But also that uncertainties in the mean climate state in the 20th century, most notably in the northward Atlantic ocean heat transport and Arctic sea ice volume, are a significant source of uncertainty for projections of future Arctic change. We suggest that better observational constraints on these quantities will lead to significant improvements in the precision of projections of future Arctic climate change.     

Laser ablation ICP-MS screening of corals for diagenetically affected areas applied to Tahiti corals from the last deglaciation

Fossil corals are unique archives of past seasonal climate variability, providing vital information about seasonal climate phenomena such as ENSO and monsoons. However, submarine diagenetic processes can potentially obscure the original climate signals and lead to false interpretations. Here we demonstrate the potential of laser ablation ICP-MS to rapidly detect secondary aragonite precipitates in fossil Porites colonies recovered by Integrated Ocean Drilling Program (IODP) Expedition 310 from submerged deglacial reefs off Tahiti. High resolution (100 μm) measurements of coralline B/Ca, Mg/Ca, S/Ca, and U/Ca ratios are used to distinguish areas of pristine skeleton from those afflicted with secondary aragonite. Measurements of coralline Sr/Ca, U/Ca and oxygen isotope ratios, from areas identified as pristine, reveal that the seasonal range of sea surface temperature in the tropical south Pacific during the last deglaciation (14.7 and 11 ka) was similar to that of today.     

Upholding labour productivity under climate change: an assessment of adaptation options

Changes in labour productivity feed through directly to national income. An external shock, like climate change, which may substantially reduce the productivity of workers is therefore a macroeconomic concern. The biophysical impact of higher temperatures on human performance is well documented. Less well understood are the wider effects of higher temperatures on the aggregate productivity of modern, diversified economies, where economic output is produced in contexts ranging from outdoor agriculture to work in air-conditioned buildings. Working conditions are at least to some extent the result of societal choices, which means that the labour productivity effects of heat can be alleviated through careful adaptation. A range of technical, regulatory/infrastructural and behavioural options are available to individuals, businesses and governments. The importance of local contexts prevents a general ranking of the available measures, but many appear cost-effective. Promising options include the optimization of working hours and passive cooling mechanisms. Climate-smart urban planning and adjustments to building design are most suitable to respond to high base temperature, while air conditioning can respond flexibly to short temperature peaks if there is sufficient cheap, reliable and clean electricity.

Key policy insights

• The effect of heat stress on labour productivity is a key economic impact of climate change, which could affect national output and workers’ income.

• Effective adaptation options exist, such as shifting working hours and cool roofs, but they require policy intervention and forward planning.

• Strategic interventions, such as climate-smart municipal design, are as important as reactive or project-level adaptations.

• Adaptation solutions to heat stress are highly context specific and need to be assessed accordingly. For example, shifting working hours could be an effective way of reducing the effect of peak temperatures, but only if there is sufficient flexibility in working patterns.