[Show abstract][Hide abstract] ABSTRACT: Sustained release of methane (CH4) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH4 from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH4 emissions from this shelf are likely to be determined by the state of subsea permafrost degradation. We observed CH4 emissions from two previously understudied areas of the ESAS: the outer shelf, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH4 emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in ice extent could result in a significant increase in CH4 emissions from the ESAS.
Full-text · Article · Sep 2015 · Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences
[Show abstract][Hide abstract] ABSTRACT: Thick haze plagued north-eastern China in January 2013, strongly affecting both regional climate and human respiratory health. Here, we present dual carbon isotope-constrained (Δ(14)C and δ(13)C) source apportionment for combustion-derived black carbon aerosol (BC) for three key hotspot regions (megacities): North China Plain (NCP, Beijing), the Yangtze River Delta (YRD, Shanghai) and the Pearl River Delta (PRD, Guangzhou) for January 2013. BC is one of the most health-detrimental components of PM2.5 and a strong climate warming agent. The results show that these severe haze events were equally affected (~30%) by biomass combustion in all three regions, whereas the sources of the dominant fossil fuel component was dramatically different between north and south. In the NCP region, coal combustion accounted for 63 - 74% (95% C.I.) of the BC, whereas in the YRD and PRD regions, liquid fossil fuel combustion (e.g., traffic) stood for 43 - 68% and 58 - 69%, respectively. Taken together, these findings suggest the need for regionally-specific description of BC sources in climate models and regionally-tailored mitigation to combat severe air pollution events in E Asia.
Full-text · Article · Jan 2015 · Environmental Science and Technology
[Show abstract][Hide abstract] ABSTRACT: Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated estuarine sediments, we present a unique framework for deconvoluting the contrasting mobilization mechanisms of surface vs. deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular plant-derived lignin phenol (14)C contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast, plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions, where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. Because river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3-6% between 1985 and 2004. These findings suggest that although partly masked by surface carbon export, climate change-induced mobilization of old permafrost carbon is well underway in the Arctic.
Full-text · Article · Aug 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The limited understanding of black carbon (BC) aerosol emissions from incomplete combustion causes a poorly constrained anthropogenic climate warming that globally may be second only to CO2 and regionally, such as over East Asia, the dominant driver of climate change. The relative contribution to atmospheric BC from fossil fuel versus biomass combustion is important to constrain as fossil BC is a stronger climate forcer. The source apportionment is the underpinning for targeted mitigation actions. However, technology-based "bottom-up" emission inventories are inconclusive, largely due to uncertain BC emission factors from small-scale/household combustion and open burning. We use "top-down" radiocarbon measurements of atmospheric BC from five sites including 3 city sites and 2 regional sites to determine that fossil fuel combustion produces 80±6% of the BC emitted from China. This source-diagnostic radiocarbon signal in the ambient aerosol over East Asia establishes a much larger role for fossil fuel combustion than suggested by all fifteen BC emission inventory models, including one with monthly resolution. Our results suggest that current climate modelling should refine both BC emission strength and consider the stronger radiative absorption associated with fossil-fuel-derived BC. To mitigate near-term climate effects and improve air quality in East Asia, activities such as residential coal combustion and city traffic should be targeted.
[Show abstract][Hide abstract] ABSTRACT: Two-dimensional Compound Specific Isotope Analysis (2D-CSIA), combining stable carbon and chlorine isotopes, holds potential for monitoring of natural attenuation of chlorinated ethenes (CEs) in contaminated soil and groundwater. However, interpretation of 2D-CSIA data sets is challenged by a shortage of experimental Cl isotope enrichment factors. Here, isotope enrichments factors for C and Cl (i.e. εC and εCl) were determined for biodegradation of tetrachloroethene (PCE) and trichloroethene (TCE), using microbial enrichment cultures from a heavily CEs contaminated aquifer. The obtained values were εC = -5.6±0.7‰ (95% CI) and εCl = -2.0±0.5‰ for PCE degradation, and εC = -8.8±0.2‰ and εCl = -3.5±0.5‰ for TCE degradation. Combining the values for both εC and εCl yielded mechanism-diagnostic εCl/εC ratios of 0.35±0.11 and 0.37±0.11 for the degradation of PCE and TCE, respectively. Application of the obtained εC and εCl values to a previously investigated field site gave similar estimates for the fraction of degraded contaminant as in the previous study, but with a reduced uncertainty in assessment of the natural attenuation. Furthermore, 16S rRNA gene clone library analyses were performed on three samples from the PCE degradation experiments. A species closely related to Desulfitobacterium aromaticivorans UKTL dominated the reductive dechlorination process. This study contributes to the development of 2D-CSIA as a tool for evaluating remediation strategies of CEs at contaminated sites.
[Show abstract][Hide abstract] ABSTRACT: The use of stable chlorine isotopic signatures (δ37Cl) of organochlorine compounds has been suggested as a tool to determine both their origins and transformations in the environment. Here we investigated the δ37Cl fractionation of two important pathways for enzymatic natural halogenation: chlorination by chloroperoxidase (CPO) and flavin-dependent halogenases (FDH). Phenolic products of CPO were highly 37Cl depleted (δ37Cl = -12.6±0.9‰); significantly more depleted than all known industrially produced organochlorine compounds. In contrast, four FDH products did not exhibit any observable isotopic shifts (δ37Cl = -0.3±0.6‰). We attributed the different isotopic effect to the distinctly different chlorination mechanisms employed by the two enzymes. Furthermore, the δ37Cl in bulk organochlorines extracted from boreal forest soils were only slightly depleted in 37Cl relative to inorganic Cl. In contrast to previous suggestions that CPO plays a key role in production of soil organochlorines, this observation points to the additional involvement of either other chlorination pathways, or that dechlorination of naturally produced organochlorines can neutralize δ37Cl shifts caused by CPO chlorination. Overall, this study demonstrates that δ37Cl values are highly useful to understand sources and cycling of organochlorines in nature. Furthermore, this study presents δ37Cl values of FDH products as well of bulk organochlorines extracted from pristine forest soil for the first time.
No preview · Article · Jan 2013 · Environmental Science & Technology
[Show abstract][Hide abstract] ABSTRACT: The widespread use chlorinated phenols (CPs) as a wood preservative has led to numerous contaminated sawmill sites. However, it remains challenging to assess the extent of in situ degradation of CPs. We evaluated the use of compound specific chlorine and carbon isotope analysis (Cl- and C-CSIA) to assess CP biotransformation. In a laboratory system, we measured isotopic fractionation during oxidative 2,4,6-trichlorophenol dechlorination by representative soil enzymes (C. fumago chloroperoxidase, horseradish peroxidase, and laccase from T. versicolor). Using a mathematical model, the validity of the Rayleigh approach to evaluate apparent kinetic isotope effects (AKIE) was confirmed. A small but significant Cl-AKIE of 1.0022±0.0006 was observed for all three enzymes, consistent with a reaction pathway via a cationic radical species. For carbon, a slight inverse isotope effect was observed (C-AKIE = 0.9945±0.0019). This fractionation behavior is clearly distinguishable from reported reductive dechlorination mechanisms. Using CSIA we then assessed degradation and apportioned different types of technical CP mixtures used at two former sawmill sites. To our knowledge, this is the first study that makes use of two-element CSIA to study sources and transformation of CPs in the environment.
No preview · Article · Dec 2012 · Environmental Science & Technology
[Show abstract][Hide abstract] ABSTRACT: Chlorinated ethenes (CEs) are ubiquitous groundwater contaminants, yet there remains a need for a method to efficiently monitor their in situ degradation. We report here the first field application of combined stable carbon and chlorine isotope analysis of tetrachloroethene (PCE) and trichloroethene (TCE) to investigate their biodegradation in a heavily contaminated aquifer. The two-dimensional Compound Specific Isotope Analysis (2D-CSIA) approach was facilitated by a recently developed gas chromatography-quadrupole mass spectrometry (GCqMS) method for δ(37)Cl determination. Both C and Cl isotopes showed evidence of ongoing PCE transformation. Applying published C isotope enrichment factors (ε(C)) enabled evaluation of the extent of in situ PCE degradation (11-78%). We interpreted C and Cl isotopes using a numerical reactive transport model along a 60-m flow path. It revealed that combined PCE and TCE mass load was dechlorinated by less than 10%, and that cis-dichloroethene was not further dechlorinated. Furthermore, the 2D-CSIA approach allowed estimation of Cl isotope enrichment factors ε(Cl) (-7.8 to -0.8‰) and characteristic ε(Cl)/ε(C) values (0.42-1.12) for reductive PCE dechlorination at this field site. This investigation demonstrates the benefit of 2D-CSIA to assess in situ degradation of CEs and the applicability of Cl isotope fractionation to evaluate PCE and TCE dechlorination.
[Show abstract][Hide abstract] ABSTRACT: Methyl bromide is the most important natural bromine contributor to stratospheric ozone depletion, yet there are still large uncertainties regarding quantification of its sources and sinks. The stable bromine isotope composition of CH(3)Br is potentially a powerful tool to apportion its sources and to study both its transport and its reactive fate. A novel compound-specific method to measure (81)Br/(79)Br isotope ratios in CH(3)Br using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry (GC/MCICPMS) was developed. Sample amounts of >40 ng could be measured with a precision of 0.1‰ (1σ, n = 3). The method results are reproducible over the long term as shown with 36 analyses acquired over 3 months, yielding a standard deviation (1σ) better than 0.4‰. This new method demonstrates for the first time Br isotope ratio determination in gaseous brominated samples. It is three orders of magnitude more sensitive than previously existing isotope ratio mass spectrometry methods for Br isotope determination of other organobromines, thus allowing applications towards ambient atmospheric samples.
No preview · Article · Sep 2011 · Rapid Communications in Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The bromine isotope composition is potentially diagnostic in both degradation monitoring and source apportionment of organobromines in the environment. A method for compound-specific bromine isotope analysis (delta(81)Br) based on gas chromatography multiple collector inductively coupled plasma mass spectrometry (GC/ICPMS) was developed for common brominated diaromatic compounds. Brominated diphenyl ethers (BDEs) in Bromkal 70-5DE, a technical flame-retardant mixture containing mainly BDEs #47, #99 and #100, were used as test substances, with standard bracketing for the samples achieved through co-injected monobromobenzene (MBB) with a known delta(81)Br of -0.39 per thousand vs. Standard Mean Ocean Bromine (SMOBr). Three different heated transfer lines were constructed and tested to achieve efficient conduction of the BDEs from the gas chromatograph to the ICPMS instrument. The MBB was analyzed with a precision of 0.4 per thousand (1 s, n = 18). The precision for BDEs was 1.4-1.8 per thousand (1 s, n = 10-12 depending on the congener). The lower precision for the BDEs than for MBB may reflect the heat required to prevent condensation of the analytes in ICP torch assembly. The use of an internal standard of similar chemical structure to the analytes alleviates this problem, as illustrated by a difference of 0.3 +/- 0.7 per thousand (1 s, n = 6) between the delta(81)Br values of co-injected methoxy BDE-47 and BDE-47 extracted from whale blubber. Improvements in precision and accuracy may be achieved by the use of a more efficient heating of the torch assembly in conjunction with a set of internal standards that match the target compounds.
No preview · Article · Jul 2010 · Rapid Communications in Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The physicochemical speciation of Fe and Fe-isotopes were measured in the Lena River freshwater plume during the International Siberian Shelf Study 2008 (ISSS-08). Particulate iron (>0.2 µm) decreased from 57000 nM to 1000 nM during the first 200 km of mixing, whereas iron in the ultrafiltered fraction (< 1000D) remained approximately constant, at 8 nM, throughout the transect. The delta56Fe value was around zero in the particulate fraction within the Lena River and close to the river mouth, but changed systematic to more negative values (-0.3 per mille) in the outer parts of the plume. Colloidal iron changed from -0.2 to +0.1per mille during mixing. Although the salinity was around 25 PSU at the outermost station (600 km) a relatively high concentration of total Fe, 150 nM, still remained in the surface water, indicating that a significant amount of river introduced Fe is reaching the open Arctic basin from the Lena River system. Removal of Fe from the freshwater plume is mainly due to sedimentation of particulate Fe (colloidal Fe decreased from 625 nM to 64 nM). We suggest that the changing delta56Fe pattern in the suspended particulate fraction is caused by sedimentation of Fe-oxyhydroxides with a positive delta56Fe value, leaving a particulate suspended fraction with more negative values in the outer parts of the freshwater plume. The positive value in the colloidal fraction at the outermost stations probably indicates small remaining oxyhydroxide particles (colloids).
[Show abstract][Hide abstract] ABSTRACT: Sustained release of methane to the atmosphere from thawing Arctic permafrost likely is a strong positive feedback to climate warming. A climate impact of Arctic methane releases is implied by past climate shifts and may play a role in the renewed growth of contemporary atmospheric methane. Observed Arctic warming in early 21st century is stronger than predicted by several degrees, which may accelerate thaw-release of methane. The East Siberian Arctic Shelf (ESAS, encompassing the Laptev, East Siberian and Russian part of the Chuckchi Seas) occupies an area of 2.1×106 km2, three times as great as terrestrial Siberian wetlands. It is a shallow seaward extension of the Siberian tundra that was flooded during the Holocene transgression 7-15 kyr ago. The ESAS sub-sea permafrost, (frozen sediments inter-layered with the flooded peatland) contains not only comparable amounts of carbon as still land-fast permafrost in the Siberian tundra, but also sequesters permafrost-related seabed deposits of CH4. Remobilization to the atmosphere of only a small fraction of the methane trapped in ESAS sediments could trigger abrupt climate warming. Currently it is hypothesized that sub-sea permafrost acts as a lid retaining this shallow methane reservoir. However, estimates of ESAS methane emissions based on recent observations indicate the current atmospheric budget, which arises from gradual diffusion and ebullition, is on par with estimates of methane emissions from the entire World Ocean. Large transient emissions remain to be assessed; yet initial data suggest this component could increase significantly annual emissions. These study results show methane leakage from the shallow ESAS needs consideration in interactions between the biogeosphere and a warming Arctic climate.
[Show abstract][Hide abstract] ABSTRACT: We present some results of our biogeochemical and hydrological studies conducted in the East Siberian Arctic seas (ESAS) in 1994-2008, and along the Lena River stream during July-August, 2003 and after flood season in late August-early September, 1995 and 1998. We focus on the carbon cycle, including horizontal dissolved and particulate organic and inorganic carbon and vertical carbon dioxide (CO2) and methane (CH4) fluxes, and the geochemistry of the surface seafloor sediments in connection with the effects of coastal erosion and riverine solid and liquid discharge. We directly observed particulate matter (PM) fluxes along the Lena River down to the Laptev Sea during late August - early September of 1997 and 1999, and June-August of 2003. Our results demonstrate that almost all riverine PM settles in the delta; this was true even during the spring/summer floods that occurred in June-July 2003. Values of PM, particulate organic carbon (POC), and d13C in POC ranged between -300/00 and -250/00 with a mean value near -270/00. A similar range of d13C/POC variability was found by Rachold and Hubberten in 1999 in the Lena, Khatanga, and Yana basins. In general, the riverine POC had a light "terrestrial signature", while a few samples contained small particles of coal which is common in this area. Using mean PM concentration = 20 mg/l and annual Lena discharge = 525 km3 we calculated "mean" solid discharge to the delta channels to be 10.5 Tg, The annual discharge of POC may be evaluated as equal to 0.38 Tg, if we use a mean POC value = 0.75mg/l; this value was obtained in 2003 along the entire Lena River. If we accept the Lisytsin statement (1994) that 85-95% of total PM (and POC) precipitates on the marginal "filter", only about 1Tg of PM, and 0.03-0.04 Tg of POC reaches the Laptev Sea with the Lena River (flood season is not considered). In summer-fall the solid discharge of the major East Siberian Sea rivers, the Indigirka and Kolyma, is also limited by the near-mouth areas (Ivanov and Piskun, 1999). Thus, we suggest that the modern solid river discharge plays only a small role in sedimentation of terrestrial OC in the entire ESAS area, but the Lena plays a major role in transporting dissolved organic carbon (DOC). It has been found also that the seabed is a major CH4 source over the ESAS while the riverine export is negligible (N.Shakhova et al., this session). Results of our earlier studies performed in the Dmitry Laptev Strait in 1999 and 2000 demonstrate the existence of high rates of seaward PM flux, up to 189-290 mg/l km, which are similar to those found near the Mekong River delta. The most recent evaluation demonstrates that about 4 Tg of POC is transported into the Laptev and East-Siberian seas along with coastal eroded material (M. Grigoriev, this session). Thus, we argue that transport of eroded material plays a major role in the accumulation of carbon in this part of the Arctic Ocean. Moreover, the eroded carbon is biodegradable and its oxidation plays an important role in CO2 supersaturation, with respect to the atmosphere, in the shallow ESAS (I.Pipko et al. and I.Semiletov et al., this session) References Ivanov, V.V. and A.A. Piskun (1999), Distribution of river water and suspended sedimentloads in the deltas of rivers in the basins of the Laptev and East-Siberian Seas, In: Land-Ocean Systems in the Siberian Arctic: Dynamics and History, edited by H. Kassens et al., Springer-Verlag, Berlin, pp. 239-250. Lisytsin, A.P. (1994) Ocean marginal filters, Oceanologiya, 34 (5), 735-747 (translated in English). Rachold, V., and H.-W.Hubberten (1999), Carbon isotope composition of particulate organic material in East Siberian rivers, In: Land-Ocean Systems in the Siberian Arctic, edited by H. Kassens et al., Springer-Verlag, Berlin , pp. 223-237.
[Show abstract][Hide abstract] ABSTRACT: The Arctic Ocean is surrounded by permafrost, which is being degraded at
an increasing rate under conditions of warming which are most pronounced
in Siberia and Alaska . A major constraint on our ability to understand
linkages between the Arctic Ocean and the global climate system is the
scarcity of observational data in the Siberian Arctic marginal seas
where major fresh water input and terrestrial CNP fluxes exist. The
East-Siberian Sea has never been investigated by modern techniques
despite the progress that has been made in new technologies useful for
measuring ocean characteristics of interest. In this multi-year
international project which joins scientists from 3 nations
(Russia-USA-Sweden), and in cooperation with scientists from other
countries (UK, Netherlands) we focus on he ESAS which is poorly explored
areas located west from the U.S.-Russia boundary. In this report we
overview the main field activities and present some results obtained
during the last decade (1999-2009). Siberian freshwater discharge to the
Arctic Ocean is expected to increase with increasing temperatures,
potentially resulting in greater river export of old terrigenous organic
carbon to the ocean. We suggest that rivers integrate variability in the
components of the hydrometeorological regime, including soil condition,
permafrost seasonal thaw, and thermokarst development, all the variables
that determine atmospheric and ground water supply for the rivers and
chemical weathering in their watershed.. It has been found that 1)
carbon dioxide and methane fluxes are significant (and non-counted)
components of the carbon cycling in the Arctic Ocean; 2) transport of
eroded terrestrial material plays a major role in the accumulation of
carbon in the ESAS (Dudarev et al., Gustafsson et al., Vonk et al.,
Sanchez-Garcia et al., Charkin et al., Semiletov et al., this session) ;
3) the seabed is a major CH4 source over the ESAS (N.Shakhova et al.,
this session); 3) eroded carbon is biodegradable (all reports, this
session); 4) oxidation of eroded carbon onshore and offshore is a strong
source of carbon dioxide (Piko et al. and Semiletov et al., this
session). Thus studying carbon cycling in the East Siberian Arctic
marginal seas has a high scientific priority in order to establish the
carbon budget and evaluate the role of the Arctic region in global
carbon cycling, especially in the coastal zone where the redistribution
of carbon between terrestrial and marine environments occurs and the
characteristics of carbon exchange with atmosphere are unknown. Initial
scientific plan for the next decade is discussed. This study was
supported by the Russian Foundation for Basic Research (since 1994),
International (Soros) Scientific Foundation, ISF (1994-1995), Russian
Government and ISF (1995), McArthur Foundation (2000-2001), FEBRAS/RAS
(since 2003), IARC (since 2001), NSF (since 2003), NOAA (since 2005), SU
(since 2007), and Wallenberg Foundation (since 2008).
[Show abstract][Hide abstract] ABSTRACT: To test how environmental conditions in the Arctic and the resulting ecological adaptations affect accumulation of persistent organic pollutants (POPs) in the marine food web, bioaccumulation of four polychlorinated biphenyls (PCBs) in an arctic (Barents Sea 77 degrees N-82 degrees N) and a temperate marine (Baltic Sea 54 degrees N-62 degrees N) food web were compared. Three different trophic levels were studied (zooplankton, fish, and seal), representing the span from first-level consumer to top predator. Previously published high-quality data on PCB water concentrations in the two areas were used for calculation of bioaccumulation factors (BAF). BAF was calculated as the ratio of the PCB concentration in the organism ([PCB](org); pg/kg lipid) to the dissolved water concentration (C(w); pg/L). The BAF(Arctic):BAF(Temperate) ratios were above 1 for all four PCB congeners in zooplankton (6.4-13.8) and planktivorous fish (2.9-5.0)), whereas the ratios were below 1 in seal. The mean ratio between arctic and temperate BAFs for all trophic levels and congeners (BAF(Arcti):BAF(Temperate)) was 4.8. When the data were corrected for the seawater temperature difference between the two ecosystems, the ratio was 2.0. We conclude that bioaccumulation differences caused by ecological or physiological adaptations of organisms between the two ecosystems were well within a water concentration variability of 50%. Further, our data support the hypothesis that lower seawater temperature lead to a thermodynamically favoured passive partitioning to organic matrices and thus elevated ambient BAFs in the Arctic compared to the Baltic Sea. This would imply that bioaccumulation in the Arctic may be described in the same way as bioaccumulation in temperate regions, e.g. by the use of mechanistic models parameterised for the Arctic.
No preview · Article · Apr 2010 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments
could trigger abrupt climate warming, yet it is believed that sub-sea permafrost acts as a lid to keep this shallow methane
reservoir in place. Here, we show that more than 5000 at-sea observations of dissolved methane demonstrates that greater than
80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere.
The current atmospheric venting flux, which is composed of a diffusive component and a gradual ebullition component, is on
par with previous estimates of methane venting from the entire World Ocean. Leakage of methane through shallow ESAS waters
needs to be considered in interactions between the biogeosphere and a warming Arctic climate.