Heavy hydrogen in the stratosphere

We report measurements of the deuterium content of molecular hydrogen (H2) obtained from a suite of air samples that were collected during a stratospheric balloon flight between 12 and 33 km at 40º N in October 2002. Strong deuterium enrichments of up to 400 permil versus Vienna Standard Mean Ocean Water (VSMOW) are observed, while the H2 mixing ratio remains virtually constant. Thus, as hydrogen is processed through the H2 reservoir in the stratosphere, deuterium is accumulated in H2 . Using box model calculations we investigated the effects of H2 sources and sinks on the stratospheric enrichments. Results show that considerable isotope enrichments in the production of H2 from CH4 must take place, i.e., deuterium is transferred preferentially to H2 during the CH4 oxidation sequence. This supports recent conclusions from tropospheric H2 isotope measurements which show that H2 produced photochemically from CH4 and non-methane hydrocarbons must be enriched in deuterium to balance the tropospheric hydrogen isotope budget. In the absence of further data on isotope fractionations in the individual reaction steps of the CH4 oxidation sequence, this effect cannot be investigated further at present. Our measurements imply that molecular hydrogen has to be taken into account when the hydrogen isotope budget in the stratosphere is investigated

Potential impact of the sea-ice ecosystem to the polar seas biogeochemistry

We used a one-dimensional vertical transport model, the sympagic-pelagic-benthic vertical transport model (SPBM) to explore the impact of sea-ice presence on phytoplankton phenology and biogeochemical dynamics. In the model, we introduced new parameter values for sympagic diatoms using ERSEM (European Regional Seas Ecosystem Model) in addition to the existing phytoplankton groups in the sea-ice model. We found that different groups of primary producers exhibit distinct spatial and temporal variabilities in both the sea-ice and water column depending on their physiological and biogeochemical properties. In particular, we discovered that the biomass of pelagic diatoms during the bloom season is strongly influenced by the release of sympagic algal cells during the early spring. This suggests the potential significance of sympagic algae seeding for the occurrence of pelagic diatom blooms in the Amundsen Sea. Notably, our model also indicates a potential connection between the earlier peak in particulate organic carbon flux and the release of sympagic-algae-associated particles from the sea ice, followed by their rapid sinking. Previous studies relying solely on observational data did not fully account for this mechanism. Our findings emphasize the importance of understanding the role of sympagic algae in the polar ecosystem and carbon cycle, and shed light on the complex biogeochemical dynamics associated with the sea-ice ecosystem in the polar seas

Abrupt reversal in emissions and atmospheric abundance of HCFC-133a (CF3CH2Cl)

Hydrochlorofluorocarbon HCFC-133a (CF3CH2Cl) is an anthropogenic compound whose consumption for emissive use is restricted under the Montreal Protocol. A recent study showed rapidly increasing atmospheric abundances and emissions. We report that, following this rise, the at- mospheric abundance and emissions have declined sharply in the past three years. We find a Northern Hemisphere HCFC-133a increase from 0.13 ppt (dry air mole fraction in parts-per-trillion) in 2000 to 0.50 ppt in 2012–mid-2013 followed by an abrupt reversal to 0.44 ppt by early 2015. Global emissions derived from these observations peaked at 3.1 kt in 2011, followed by a rapid decline of 0.5 kt yr−2 to 1.5 kt yr−1 in 2014. Sporadic HCFC-133a pollution events are detected in Europe from our high-resolution HCFC-133a records at three European stations, and in Asia from sam- ples collected in Taiwan. European emissions are estimated to be <0.1 kt yr−1 although emission hotspots were identi- fied in France

Atmospheric histories and emissions of chlorofluorocarbons CFC-13 (CClF3), ΣCFC-114 (C2Cl2F4), and CFC-115 (C2ClF5)

Based on observations of the chlorofluorocarbons CFC-13 (chlorotrifluoromethane), ΣCFC-114 (combined measurement of both isomers of dichlorotetrafluoroethane), and CFC-115 (chloropentafluoroethane) in atmospheric and firn samples, we reconstruct records of their tropospheric histories spanning nearly 8 decades. These compounds were measured in polar firn air samples, in ambient air archived in canisters, and in situ at the AGAGE (Advanced Global Atmospheric Gases Experiment) network and affiliated sites. Global emissions to the atmosphere are derived from these observations using an inversion based on a 12-box atmospheric transport model. For CFC-13, we provide the first comprehensive global analysis. This compound increased monotonically from its first appearance in the atmosphere in the late 1950s to a mean global abundance of 3.18 ppt (dry-air mole fraction in parts per trillion, pmol mol1) in 2016. Its growth rate has decreased since the mid-1980s but has remained at a surprisingly high mean level of 0.02 ppt yr⁻¹ since 2000, resulting in a continuing growth of CFC-13 in the atmosphere. ΣCFC-114 increased from its appearance in the 1950s to a maximum of 16.6 ppt in the early 2000s and has since slightly declined to 16.3 ppt in 2016. CFC-115 increased monotonically from its first appearance in the 1960s and reached a global mean mole fraction of 8.49 ppt in 2016. Growth rates of all three compounds over the past years are significantly larger than would be expected from zero emissions. Under the assumption of unchanging lifetimes and atmospheric transport patterns, we derive global emissions from our measurements, which have remained unexpectedly high in recent years: mean yearly emissions for the last decade (2007–2016) of CFC-13 are at 0.48 ± 0.15 kt yr⁻¹ (> 15 % of past peak emissions), of ΣCFC-114 at 1.90 ± 0.84 kt yr⁻¹ (∼ 10 % of peak emissions), and of CFC-115 at 0.80 ± 0.50 kt yr⁻¹(> 5 % of peak emissions). Mean yearly emissions of CFC-115 for 2015–2016 are 1.14 ± 0.50 kt yr⁻¹ and have doubled compared to the 2007–2010 minimum. We find CFC-13 emissions from aluminum smelters but if extrapolated to global emissions, they cannot account for the lingering global emissions determined from the atmospheric observations. We find impurities of CFC-115 in the refrigerant HFC-125 (CHF₂CF₃) but if extrapolated to global emissions, they can neither account for the lingering global CFC-115 emissions determined from the atmospheric observations nor for their recent increases. We also conduct regional inversions for the years 2012–2016 for the northeastern Asian area using observations from the Korean AGAGE site at Gosan and find significant emissions for ΣCFC-114 and CFC-115, suggesting that a large fraction of their global emissions currently occur in northeastern Asia and more specifically on the Chinese mainland

Continuous-flow isotope analysis of the deuterium/ hydrogen ratio in atmospheric hydrogen

A convenient method is described for analyzing the deuterium/hydrogen (D/H) ratio of atmospheric molecular hydrogen (H2) based on mass spectrometric isotope-ratio monitoring. The method requires small amounts of air ( 300mL STP), is operated on-line, and comprises four steps: (1) the condensation of the air matrix at 40 K; (2) the collection of the non-condensed components of the air sample (H2, Ne, He, and traces of N2) in a 5A° molecular sieves pre-concentration trap at 63 K; (3) gas chromatographic purification of H2 in a flow of He; and (4) quantification of the D/H ratio in an isotope-ratio mass spectrometer. The precision of the determination of the D/H ratio is better than 2%, which is comparable to, or better than, that obtained by conventional duel-inlet off-line analysis. There are, however, discrepancies relative to the D/H ratios determined by conventional duel-inlet analysis. This is due to differences in peak shape between reference and sample air, depending on the amount of H2 injected. Consequently, calibration runs are required. After the calibration of the system, we obtained an accuracy of 1.5%, so that the accumulated uncertainty is estimated to be less than 4%. The method also allows determination of the H2 concentration, with an uncertainty estimated to be 2%

Measuring Biogenic Volatile Organic Compounds in the Marine Boundary Layer over the North Pacific Ocean using Proton Transfer Reaction Mass Spectrometry and Solid Absorbent Cartridges

<p>Approximately 70% of Earth's surface is covered by the ocean and the cryosphere. It has been recognized that these environments play an important role in exerting feedbacks on the global climate system. For instance, in the marine boundary layer, it is hypothesized that the emission of biogenic volatile compounds (BVOCs) contributes to cloud formation with resulting changes in temperature and radiation initiating climate feedback. However, measurements of BVOC concentrations are limited, thus the concentration and emission of BVOCs are typically derived and estimated using satellite-observed phytoplankton abundance (i.e., chlorophyll-a concentration). To help validate the modeled relationship between chlorophyll-a concentration and BVOC emission (i.e., isoprene) that current chemistry models are using, BVOCs were measured during the 2012 SHIPPO (SHIp-borne Pole-to-Pole Observations) cruise over the Yellow Sea, the East Sea (or the Sea of Japan), the North Pacific Ocean, and the Bering Sea from 13 July to 29 July. BVOCs were measured using two different methods: Proton Transfer Reaction Mass Spectrometry (PTRMS) and solid absorbent cartridges. The results from these two different measurement techniques will be presented and discussed. In addition, observed BVOC concentrations will be discussed in relation to phytoplankton abundance and other biological and meteorological parameters measured along the cruise track.</p

The impact of the abnormal salinity enrichment in pore water on the thermodynamic stability of marine natural gas hydrates in the Arctic region

In this study, the thermodynamic and structural characteristics of natural gas hydrates (NGHs) retrieved from gas hydrate mounds (ARAON Mound 03 (AM03) and ARAON Mound 06 (AM06)) in the Chukchi Sea in the Arctic region were investigated. The gas compositions, crystalline structure, and cage occupancy of the NGHs at AM03 and AM06 were experimentally measured using gas chromatography (GC), C-13 nuclear magnetic resonance (NMR), Raman spectroscopy, and powder X-ray diffraction (PXRD). In the NGHs from AM03 and AM06, a significantly large fraction of CH4 (&gt; 99%) and a very small amount of H2S were enclathrated in small (5(12)) and large (5(12)6(2)) cages of sl hydrate. The NGHs from AM03 and AM06 were almost identical in composition, guest distri- butions, and existing environment to each other. The salinity of the residual pore water in the hydrate-bearing sediment (AM06) was measured to be 50.32 parts per thousand, which was much higher than that of seawater (34.88 parts per thousand). This abnormal salinity enrichment in the pore water of the low-permeability sediment might induce the dissociation of NGHs at a lower temperature than expected. The saturation changes in the NGHs that corresponded with an increase in the seawater temperature were also predicted on the basis of the salinity changes in the pore water. The experimental and predicted results of this study would be helpful for understanding the thermodynamic stability of NGHs and potential CH4-releasing phenomena in the Arctic region. (C) 2021 Elsevier B.V. All rights reserved

Methylmercury mass budgets and distribution characteristics in the Western Pacific Ocean.

International audienceMethylmercury (MeHg) accumulation in marine organisms poses serious ecosystem and human health risk, yet the sources of MeHg in the surface and subsurface ocean remain uncertain. Here, we report the first MeHg mass budget for the Western Pacific Ocean estimated based on cruise observations. We found the major net source of MeHg in surface water to be vertical diffusion from the subsurface layer (1.8 to 12 nmol m-2 yr-1). A higher upward diffusion in the North Pacific (12 nmol m-2 yr-1) than in the Equatorial Pacific (1.8-5.7 nmol m-2 yr-1) caused elevated surface MeHg concentrations observed in the North Pacific. We furthermore found that the slope of the linear regression line for MeHg versus apparent oxygen utilization was about twofold higher in the Equatorial Pacific than the North Pacific. We suggest this could be explained by redistribution of surface water in the tropical convergence-divergence zone, supporting active organic carbon decomposition in the Equatorial Pacific Ocean. Base on this study, we predict oceanic regions with high organic carbon remineralization to have enhanced MeHg concentrations in both surface and subsurface waters

DataSheet_1_Identification of ventilated and submarine glacial meltwaters in the Amundsen Sea, Antarctica, using noble gases.pdf

To delineate the glacial meltwater distribution, we used five noble gases for optimum multiparameter analysis (OMPA) of the water masses in the Dotson-Getz Trough (DGT), Amundsen Sea. The increased number of tracers allowed us to define potential source waters at the surface, which have not been possible with a small set of tracers. The highest submarine meltwater (SMW) fraction (~0.6%) was present at the depth of ~450 m near the Dotson Ice Shelf. The SMW appeared to travel beyond the continental shelf break along an isopycnal layer. Air-equilibrated freshwater (up to 1.5%), presumably ventilated SMW (VMW) and surface melts, was present in the surface layer (-1 for the adjacent ice shelves, assuming that the SMW fractions represent accumulation since the previous Winter Water formation. The Meteoric Water (MET) fractions, consisting of SMW and VMW, comprised 24% of those derived from oxygen isotopes, indicating that the annual input from basal melting is far less than the inventory of meteoric water, represented by MET.</p