C41C-0525
A 720-kyear record of dust variability from the Dome Fuji ice core, Antarctica
Microparticles (dust) in deep ice cores in polar area are well-known as an indicator of terrestrial materials. Dust concentrations in deep ice cores vary with climate and environmental changes such as variations of dust origin areas, atmospheric transport intensity and atmospheric water cycle. Here we present a new dust record from deep ice core reached 3035.22 m depth in January 2007 at Dome Fuji, Antarctica (77°19'S, 39°42'E, 3,810m a.s.l.). The age of ice core in 3028-m depth was ca. 720 kyears ago, which corresponded to Marine Isotope Stage (MIS) 17. Dust concentrations in the ice core periodically varied high during glacial periods, especially the end stages of glacial periods, and low during interglacial periods with glacial-interglacial cycles from MIS 17 to Holocene. The amplitudes of dust variation on glacial-interglacial cycles were smaller than after ~ 430 kyears ago (MIS 12), so-called the Mid-Brunhes Event (MBE). Dust concentration variations and concentration levels of the Dome Fuji ice core were similar to those of EPICA Dome C. The ratios of dust larger than 1 micrometer in diameter were also high during the end stages of glacial periods and low during interglacial periods, suggesting that the intensity of atmospheric circulation, which transported dust to Antarctic inland plateau, was relatively greater in the ends of glacial periods.
C41C-0526 TI:
C41C-0527
Spatial Concentration Fields of Trace Elements and Major Ions Over a Large and Highly Inaccessible Area of Antarctica
Over-snow traverses, such as those conducted by the International Trans-Antarctic Scientific Expedition (ITASE), provide the data needed at a high enough spatial and temporal resolution to form a more accurate assessment of the regional chemical and climate differences between deep core sites. This study focuses on a collection of snow pits and surface snow samples collected along the 2002/03 (ITASE-02), 2003/04 (ITASE- 03), 2006/07 (ITASE-06), and 2007/08 (ITASE-07) US ITASE traverses - total distance >5000 km. The ITASE-02 traverse started from Byrd Station, West Antarctica, and progressed southward, ultimately ending at the South Pole. The ITASE-03 traverse began at the South Pole and proceeded over the interior of East Antarctica to the Automated Geophysical Observatory number 4 (AGO4). From AGO4 the traverse traveled northward along the Transantarctic Mountain seismic sensor line, passing through the area known as Megadunes, and finishing up at Taylor Dome. The ITASE-06 traverse began at Taylor Dome and traveled in a southwesterly direction ending up approximately 300 km inland from Byrd Glacier mouth. The ITASE-07 traverse began where the ITASE-06 traverse left off, and continued in a southwesterly direction for 200 km before heading directly south and ending up at South Pole. Several snow pits were collected along the traverses and >250 surface snow samples were collected every ~20-50 km. All samples were analyzed using an ion chromatograph for their soluble major ion content (Na, K, Mg, Ca, Cl, NO3, SO4). Additionally, the surface snow samples were all analyzed for their trace element content (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn) using inductively coupled plasma mass spectrometry. Snow pit data indicate summer concentration values for most of the surface snow samples. However, the seasonality of the surface snow samples is most uncertain between AGO4 and the Megadunes. The ice sheet surface around the Megadunes area is most likely composed of redistributed or reworked (probably through ablation processes) snow. The process of surface ablation has the effect of concentrating chemistry on the surface. Summer concentrations of several trace elements in West Antarctica are below detection limits. However, there are high concentrations around the South Pole and Megadunes areas. These concentration variations may be a consequence of chemical and/or precipitation differences between the traverse years.
C41C-0528
The measure for black carbon (BC) and dust in the glaciers of China: a review and prospect
During 2004-2006, black carbon concentrations were measured in the snow and ice sampled from the
glaciers in west China. The investigated regions could be aligned as follows based on the BC concentrations
in the surface snow for the glaciers: the Tianshan Mountains > the central Tibetan Plateau (TP) > the
Pamirs > the Qilian Mountians > the Himalayas. This distribution could be attributed to the elevations of
the glaciers (higher concentration at lower altitude), the topography of the TP, strong melting in some
glaciers, and more regional emissions. Probably significant impacts on the albedos of the glacier surfaces
could be caused by heavy BC deposits, and the estimated reduced albedos on the glaciers are 9.8%
(Zhadang glacier), 8.7% (Miao'ergou Riverhead No.3 glacier), and 6.8% (Haxilegen River No.48 glacier),
and 6.2% (Dongkemadi glacier), and 5.3% (La'nong glacier), and 4.2% (Muztagata glacier), and etc.
The East Rongbuk glacier was located on the central part of the Himalayas with a mean elevation higher than
6300 m, and in 2002 a shallow ice core was drilled on it. BC concentrations were measured throughout the
ice core. In the past 50 yrs, BC concentrations showed fluctuations in the earlier 40 yrs, whereas showed a
dramatic increasing tread in the most recent decade (since the 1990s) and exceeded 50 ¦Ìg kg-1 in the
summer of 2001. Trajectory analysis indicated BC was dominantly transported by monsoons in summers and
by westerlies in other seasons, and BC emitted from South Asia in summers dominated the varying trend of
concentrations in the ice core and caused higher concentration in summer than that in other season.
Significant increasing BC concentration caused increasing radiative forcing since the 1990s, which exceeded
4.5 W m-2 in the summer of 2001 as calculated by a Snow-Ice-Aerosol Radiative (SNICAR) model.
During the summer and fall of 2008, a plan of sampling snow in the snow pits on the nine glaciers distributed
on a transection from the north Altai Mountains (on the border of China, Russia, and Mongolia) to the south
Himalayas in west China would be exerted by a group of glaciological researchers. Seasonal variation of BC
and dust concentrations covering 1-2 years would be expected to obtain. Transport and sources of BC and
dust would be interpreted. Reduced albedo of snow and the radiative forcing of BC and dust would be
observed and calculated at a specific site, Nam Co Lake in the central Tibetan Plateau. We are expecting to
obtain a comprehensive interpretation on BC and its climate effects on the cryosphere in west China.
http://www.agu.org/mingjing
C41C-0529
Carbonaceous Particle and Dust Concentrations Since the Pre-Industrial Era from Asian Ice Cores
Carbonaceous particles (CP; i.e., black carbon) can significantly contribute to climate change by altering the Earth's radiative balance. In the atmosphere, CP absorb and scatter light and can act as cloud condensation nuclei. CP deposited on snow and ice can significantly reduce the surface albedo, resulting in rapid melting of snow and ice. Assessing CP concentrations in snow and ice from the Tibetan Plateau is key to understanding the climatic impacts of CP, as the atmospheric composition in this region is influenced by the largest sources of CP globally, and it is estimated that the largest climate forcing from CP in snow occurs over the Tibetan Plateau. Additionally, the atmosphere in this region can be heavily dust laden, further affecting the energy balance of the atmosphere and cryosphere. To date, there is little information regarding the CP composition of Tibetan Plateau snow and ice. We present records of CP and dust concentrations spanning pre-industrial to modern time from ice cores from the Tibetan Plateau (Mt. Nyainqentanglha and Mt. Geladandong). These records provide a quantitative measurement of CP and dust emissions and atmospheric concentrations as a function of time needed to estimate climate change related to CP forcing.
C41C-0530
Quantification of Impurities in Prairie Snowpacks and Evaluation and Assessment of Snow Parameters
Recent measurements of snow impurities collected in North American prairie snowpacks show deposition of significant quantities of atmospheric aerosols and local dust into the snowpack. While concern over the effects of soot and other impurities in atmospheric samplings has been a scientific focus for decades, few efforts have been made to determine the effects of these highly absorbing impurities on snow albedo. These impurities can lower snow albedo in the visible portion of the electromagnetic spectrum by 5-15% with concentrations of only 1 part per million by weight (ppmw). Mass impurities were measured in snowpacks in Dickinson County, Iowa taken at agricultural, lake and other sites during multiple days in 2007 and 2008. The sampling captured two snowfall events in 2008 with snowfall totals exceeding 290 mm. The contaminant contributions to light absorption were determined to be primarily from agricultural dust and black carbon which are identifiable by their wavelength dependence. Impurity concentrations are determined by optical methods. Snow meltwater was filtered through a Nuclepore filter and the filters were analyzed for light absorption using the Integrating Plate (IP) method at 16 equal interval wavelengths across the visible portion of the electromagnetic spectrum. Average impurity concentrations were found to range between 15 and 80 ngC/gm. These concentrations are higher than those typically measured in the Arctic and Antarctic.
C41C-0531
A 4-year shortwave and longwave radiation climatology in a dust-influenced mountain snow regime
In winter 2005, we established detailed radiation infrastructure in the Senator Beck Basin Study Area (SBBSA), which lies near Red Mountain Pass in the San Juan Mountains, SW Colorado, US. The San Juan Mountains are subject to multiple dust deposition events each year, primarily in spring and summer. In the period 2004-2008, the study site received 4 to 9 deposition events a year, with mass coming primarily from the Colorado Plateau. The loading observed today is approximately 500% greater than that prior to the disturbance of fragile desert surfaces in the southwest US in the 1870s when numbers of grazing cattle and sheep began to increase dramatically. Snowmelt model sensitivity analyses indicate that snow cover duration is reduced by 25-35 days as a result of enhanced absorption of shortwave radiation by dust in the snow cover. Land surface radiative forcing as a result of early removal of snowcover is of the order 150 W/m2. In this study, we describe the shortwave and longwave climatology (winter 2005 through summer 2008) at alpine and subalpine towers in the SBBSA. At each tower, we measure incident and reflected fluxes for broadband shortwave and NIR/SWIR (from which we infer the visible fluxes), longwave irradiance and snow surface temperature (from which we infer snow longwave exitance), and noontime diffuse irradiance. A CIMEL sunphotometer (NASA AERONET site RedMountainPass) is situated near the subalpine tower to measure aerosol optical depth coordinated with the above radiation measurements. During winter and spring, the top 30 cm of the snow column was sampled at 3 cm resolution to determine the stratigraphy of dust concentration contributing to enhanced absorption.
C41C-0532
The Effect of Aerosol Deposition on Snow Albedo Reduction in the Sierra Nevada Mountains
We investigate snow cover and albedo changes in the Sierra Nevada regions due to deposition of black carbon and dust particles from East Asia. We note that coal combustion reaches maximum in the winter, while dust storms originate in the Gobi Desert occur most frequently in April. We selected snow and albedo data from MODIS/Terra to examine albedo reduction in March and April from 2000 to 2008. To eliminate the contamination of albedo by bare land, only the pixels with 100% snow cover in the entire period were used. Analysis using the 8-day average snow cover and 16-day average surface albedo reveals that there is a small increasing trend of albedo reduction. We also show that a large snow albedo reduction in 2001 is possibly due to the strong dust storm event that occurred in April, 2001. Finally, composite time series have been made using daily data to demonstrate decrease in snow albedo after each snowfall event. We illustrate that the rate of albedo reduction increases by 0.01/day per year from 2000 to 2008.
C41C-0533
Springtime Warming and Reduced Snow Cover from Carbonaceous Particles
Boreal spring climate is uniquely susceptible to solar warming mechanisms because it has expansive snow cover and receives relatively strong insolation. Carbonaceous particles can influence snow coverage by warming the atmosphere, reducing surface-incident solar energy ("dimming"), and reducing snow reflectance after deposition ("darkening"). Applying a column radiative transfer model, we show that darkening caused by very small concentrations of absorbing particles within snow exceeds the loss of absorbed energy from concurrent dimming, thereby driving net heating of the snowpack as well as atmosphere. Over global snow, we estimate 6-fold greater surface forcing from darkening than dimming, caused by black carbon (BC) and organic matter (OM). Equilibrium climate experiments suggest that fossil fuel and biofuel emissions of BC+OM induce 95% as much springtime snow cover loss over Eurasia as anthropogenic carbon dioxide, a consequence of strong snow-albedo feedback and large BC+OM emissions from Asia. Finally, of 22 climate models contributing to the IPCC Fourth Assessment Report, 21 underpredict the rapid warming (0.64 degrees/decade) observed over springtime Eurasia since 1979. Darkening from natural and anthropogenic sources of BC and mineral dust exerts 3-fold greater forcing on springtime snow over Eurasia (3.9 W/m2) than North America (1.2 W/m2), and inclusion of this forcing significantly improves simulated continental warming trends. The forcing also reduces, but does not reconcile, the low bias in rate of Eurasian spring snow cover decline exhibited by all models.
C41C-0534
Recent increase in snow-melt area in the Greenland Ice sheet as an indicator of the effect of reduced surface albedo by snow impurities
Recent rapid decline of cryosphere including mountain glaciers, sea ice, and seasonal snow cover tends to be associated with global warming. However, positive feedback is likely to operate between the cryosphere and air temperature, and then it may not be so simple to decide the cause-and-effect relation between them. The theory of heat budget for snow surface tells us that sensible heat transfer from the air to the snow by atmospheric warming by 1°C is about 10 W/m2, which is comparable with heat supply introduced by reduction of the snow surface albedo by only 0.02. Since snow impurities such as black carbon and soil- origin dusts have been accumulated every year on the snow surface in snow-melting season, it is very important to examine whether the snow-melting on the ice sheets, mountain glaciers, and sea ice is caused by global warming or by accumulated snow impurities originated from atmospheric pollutants. In this paper we analyze the dataset of snow-melt area in the Greenland ice sheet for the years 1979 – 2007 (available from the National Snow and Ice Data Center), which is reduced empirically from the satellite micro-wave observations by SMMR and SMM/I. It has been found that, seasonally, the snow-melt area extends most significantly from the second half of June to the first half of July when the sun is highest and sunshine duration is longest, while it doesn't extend any more from the second half of July to the first half of August when the air temperature is highest. This fact may imply that sensible heat required for snow-melting comes from the solar radiation rather than from the atmosphere. As for the interannual variation of snow-melt area, on the other hand, we have found that the growth rate of snow-melt area gradually increases from July, to August, and to the first half of September as the impurities come out to and accumulated at the snow surface. However, the growth rate is almost zero in June and the second half of September when fresh snow of high albedo covers the surface. This fact may imply that the combined operation of solar radiation and snow impurities is responsible for the recent global decline of cryosphere. Discussion about other research works will be given in the presentation in order to support the above idea.
C41C-0535
Albedo reduction by dirty snow: measurements and implications
Industrial and biomass burning emissions of black carbon (BC) from low- and mid-latitudes dominate the radiative forcing by absorbing impurities trapped in snow and ice at mid- and high- northern latitudes. Correct model representation of albedo reduction by BC-contaminated snow is crucial because our GCM simulations show that dirty snow can explain about 30% of the observed 20th century Arctic warming. Until now, measurements of actual snow darkening by BC have been attempted only in the field, under non- reproducible conditions, and limited to the environmental BC concentration. We have conducted the first measurements of the direct effect of BC-contamination on snow albedo by in a controlled environment. We doped natural snow with a commercially available BC-analogue and measured the resulting albedo change at visible and near-infrared wavelengths. Snow albedo was measured in a (portable) integrating sphere system. Snow grain size is estimated from the near-infrared albedo. Snow density, temperature, and BC properties were known a priori. The albedo measurement reproducibility is about 1% for natural snow. Our measurements agree with model predictions that BC concentrations from 250 ppbm to 200 ppmm darken snow albedo by 1--70%. Our results lend confidence to the current model representations of surface darkening in the cryosphere. Applying these methods to impurity records in polar ice cores yields surface radiative forcing estimates that can be extrapolated to regional scales.
C41C-0536
Concentration and 14C Content of Total Organic Carbon and Black Carbon in Small (<100 ug C) Samples from Low-Latitude Alpine Ice Cores
Many low latitude glaciers are receding with consequences for the regional energy budget and hydrology. Ice loss has been linked to climate change and the deposition of organic aerosols such as black carbon (BC) which is formed during incomplete combustion. Little is known about how the contents of BC and total organic carbon (TOC) in aerosols change over time and how anthropogenic activities (e.g. land-use change) impact this variability. Low-latitude ice cores are located closer to population centers than polar ice caps and can provide a regional synthesis of TOC and BC variability. Radiocarbon (14C) may be used to partition BC aerosols into fossil (>50 kyrs) and modern sources (e.g. fossil-fuels vs. wildfires). We quantified TOC, BC, and their 14C content in three low-latitude ice cores: Naimona'nyi (30°27'N, 81°91'E) and Dasuopu (28°23'N, 85°43'E), Tibet, and Quelccaya (13°56'S; 70°50'W), Peru. Aerosols (52-256 g ice on filters) were separated into TOC and BC using thermal oxidation (CTO- 375). 14C was measured by AMS. TOC contents were 0.11-0.87, 0.05-0.43, and 0.06-0.19 μg C (g ice) -1 for Naimona'nyi, Dasuopu, and Quelccaya, respectively. BC contents were 18±8, 27±4, and 29±12 %TOC. Procedural blanks were 0.8 ± 0.4 μg C (TOC) and 1.2 ± 0.6 μg C (BC). In ice cores well dated through annual layer counting and/or independent ages (e.g. volcanic horizons) such as Quelccaya, the ability to separate BC from TOC, as well as partition BC into fossil and modern contributions has potential for reconstructing pre- and post-industrial changes in aerosol composition and their impact on the energy budget.
C41C-0537
Raman Probing of Gaseous Constituents and Water Isotopes in Deep Glacial Ice
We propose and demonstrate the nondestructive analysis of several trace components of glacial ice and ice bubbles using Raman spectroscopy. Trace components of water-ice, such as isotopic heavy water (HDO) and gases trapped in bubbles, have significant correlations with parameters of prehistoric climate such as temperature and aridity. Raman spectroscopy identifies characteristic vibration frequencies of trace molecules and can map the presence of chemicals throughout an ice sample without causing any physical or chemical damage. As a proof of principle, we first studied the isotopic characteristics of glacial ice samples using a confocal Raman microscope with a low-power (20mW) argon laser (514.4nm). In the GISP2 1000m and 3000m samples, the stretching mode of oxygen-deuterium bond (O-D) (2400cm-1 - 2500cm-1) was readily detected, indicating the presence of deuterium. As a calibration, we performed Raman spectroscopy on prepared highly diluted heavy water (D2O) solutions. Results showed that concentrations of H-O-D as low as 0.03% (as in VSMOW) can be readily detected with a 5 minutes collection time at a temperature of - 5°C. Gaseous contents in trapped air bubbles inside the ice sample were also examined. In the GISP2 513m samples, the vibration lines of nitrogen (2332cm-1) and oxygen (1550cm-1) are clearly visible inside the trapped bubbles. The O2/N2 ratio was found to be around one-third, which is close to the atmospheric level. By scanning the nitrogen (2330cm-1 - 2340cm-1) and water (3100cm-1 - 3200cm-1) Raman lines, a chemical map of bubbles and concentration gradients across the bubble-ice boundary was observed.
C41C-0538
The Photolysis of Frozen Hydrogen Peroxide Solutions Revisited
Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities of past atmospheres. Published laboratory experiments on the photolysis of liquid and frozen HOOH solutions indicate that the photolytic lifetime of HOOH in Polar environments should be on the order of days to weeks. However, ice cores show that HOOH in snow/ice can be preserved for longer than this and buried beneath the photic zone. HOOH photolysis produces OH radicals which easily react with trace organics, and thus HOOH reaction rates in the laboratory are commonly derived through proxy measurements of stable organic products. In this work we describe results from a different approach: HOOH photolysis kinetics were followed directly through HPLC measurements of HOOH. The derived HOOH lifetimes were about 3 times longer than those based on OH proxy measurements; for typical summertime conditions at Summit, Greenland, for example, the HOOH lifetime was derived as ca. 1100 hrs. This is long enough for the surface snow to get buried and remove HOOH from the reactive photic zone. Kinetic modeling on the photochemical HOOH reactions and subsequent reactions of organics and OH in solution is presented to help understand the discrepancy between the direct and the proxy measurements of HOOH photolysis rates.
C41C-0539
An in situ Method for the Detection of Hydroxyl Radicals at the Air—Ice Interface
The photolysis of species such as nitrate and hydrogen peroxide in terrestrial snowpacks can lead to the formation of hydroxyl radicals. Chemical reaction with hydroxyl radicals is often the most important removal pathway for organic contaminants both in the gas phase and in natural waters. Recent laboratory investigations indicate that this is likely not the case for organic species present at the surface of frozen aqueous solutions. This highlights the difference between ice and liquid water as reaction media, and demonstrates the importance of tracking the fate of hydroxyl radicals in ice. We have developed a technique that uses a chemical trap combined with glancing-angle laser-induced fluorescence detection to monitor the formation of hydroxyl radicals in situ at the air—ice interface. Here we will demonstrate the potential of this method and present some initial results.
C41C-0540
Snowpack and Air Interactions of (Semi)volatile Organic Compounds at Alert, Nunavut
Eighteen different (semi)volatile organic compounds (halogenated, aromatic and oxygenates) were determined in surface snow (0-10~cm) together with concurrent measurements of surface air samples. Subsequently, atmosphere-snow interactions were investigated. Samples were collected in the Canadian Arctic (Alert, Nunavut; 82° 29' 58" N, 62° 20' 05" W) between May 22 and June 2, 2006 during the snowmelt and rising temperatures. Snow samples analysed on site using solid-phase microextraction with gas chromatography and flame ionisation detection (GC/FID) and air samples analysed after transfer to Montreal employing a home-built cryo-trap GC/FID system showed a drop in concentration below the detection limit for a number of compounds (e.g. trichloroethene, benzene) in snow on May 30 that corresponded to a sudden increase in ground ozone concentrations and a shift in the origin auf air masses passing the sampling location 72 hrs prior to the sampling event from polar to South-Westerly source regions. Additionally, the warming of the boundary layer and subsequently the snow pack was accompanied by a transformation from dendritic to highly metamorphous snow. Sorption coefficient were used for the estimation of acetone concentrations in snow from air data and vice versa and comparison with measured values showed discrepancies of up to 3 orders of magnitude, indicating highly non-equilibrium conditions. Attempts were made to evaluate the gas/snow interactions using several thermodyanmic calculations, the results of which will be discussed.
C41C-0541
Nitrogen oxides and ozone in and above the snowpack at Summit, Greenland: Continuous observations of photochemical release and uptake
Photochemical reactions in the polar snowpack are known to alter concentrations of NOx (NO + NO2) and O3 in the interstitial air, releasing NOx and destroying O3. This results in an efflux of NOx and uptake of O3 at the air-snow interface, with additional impacts on photochemical processes in the atmospheric boundary layer. Here, we present a set of new continuous measurements of NOx and O3 gradients in the snow and overlying atmosphere at Summit, Greenland. These observations were obtained during summer 2008. They will be continued during spring-summer 2009 as the first of a set of three similar studies in varying snowpacks, in polar, midlatitude, and boreal tundra regions, which will be used to improve the simulation of air-snow interactions in a global chemistry-climate model. These new observations will be complemented by an overview of prior field observations of NOx in polar snowpacks and a discussion of the degree to which variations in field observations of NOx release are characterized and understood.
C41C-0542
Determining the kinetics and concentrations of singlet molecular oxygen on natural snow
Singlet molecular oxygen (1O2*), the first electronically excited state of molecular oxygen, reacts rapidly with several classes of environmental pollutants such as furans, phenols, and polycyclic aromatic hydrocarbons (PAHs). Its formation requires the absorption of light by a chromophore (a.k.a. sensitizer), which subsequently transfers energy to ground state molecular oxygen. In prior work, we have shown that the rate of formation (Rf) and steady state concentration ([1O2*]) of 1O2* can be orders of magnitude higher in frozen ice relative to the same laboratory solution studied as a liquid. Here we discuss how we have modified our method to determine Rf and [1O2*] on natural snow, which required overcoming several difficulties: the total solute concentrations are low, the 1O2* sensitizing species are unknown, and other oxidants could be interfering with the measured loss of our chemical probe. The new method is similar to the one used previously, as both use furfuryl alcohol (FFA) as a probe for photoformed 1O2*. The total rate of FFA decay is the sum of its direct photolysis and the rate of all its reactions with other species. Introducing a sink for other oxidants and taking the difference between this measured decay rate and the rate of direct photolysis yields the rate of decay due specifically 1O2*. As a second validation, experiments were also conducted in D2O. In liquid solution, water is the dominant sink for 1O2* where physical quenching controls the lifetime, and thus the steady state concentration, of 1O2*. D2O has a rate constant for quenching of 1O2* much lower than for water. This difference in rate constants is then used to derive [1O2*] in a manner independent of other reactions that may occur. Results from these experiments allowed us to measure Rf and [1O2*] in snow from polar regions and from a mid-latitude site in the Sierra Nevada mountains of California. In addition to describing the technique and its results, we will also give a preliminary assessment of 1O2* to the decay of organic pollutants in cold regions.
C41C-0543
The Kinetics of Hydroxyl Radical on Ice
The hydroxyl radical (OH) is likely one of the dominant sinks for organic species and other trace contaminants on snow and ice. However, because we know very little about the formation rates, lifetimes, or steady-state concentrations of OH on illuminated snow and ice, we cannot currently estimate the OH- mediated lifetimes of organics and other contaminants. To address this gap, we have measured OH kinetics in illuminated snow samples from both Summit, Greenland and Dome C, Antarctica. Our results show that the rates of formation of OH on ice samples can be explained essentially by photolysis of hydrogen peroxide, although gas-to-snow transport of OH is calculated to be of similar importance in the field. The lifetimes of OH are on the order of tens of microseconds; it appears that organic compounds are the dominant sinks for OH in these polar snow samples. Finally, the steady-state concentrations of OH in illuminated ice are on the order of several femtomolar. These concentrations suggest that reactions with OH will be an important sink for many organic contaminants in snow, but quantifying the organic lifetimes is complicated by the fact that HOOH (as the OH source) and organics (as the OH sink) might not be collocated in snow grains.
C41C-0544
Results from the ANTCI 2005 Antarctic Plateau Airborne Study
The 2005 Antarctic Tropospheric Chemistry Investigation (ANTCI 2005) was conducted from late November to mid December 2005. Extensive sampling of the Antarctic Plateau was performed on five of the twelve research flights. The measurements made during those flights extend the database of NO and NMHC observations made during the ANTCI 2003 mission and provide airborne measurements of O3, HNO3, HO2NO2, and SO2 across the Plateau. Vertical chemical profiles compiled from all five Plateau-focused flights are presented. Comparisons with South Pole measurements are made where appropriate. NO, HNO3, and HO2NO2 concentrations all exhibited strong vertical trends with the highest levels observed closest to the surface. Horizontal chemical profiles from the two most geographically diverse flights are also presented. The movement of a high pressure ridge across Antarctica during the study period provided for very different meteorological conditions during these two flights as well, which makes ascription of the differences in chemistry challenging. Although concentrations of short-lived species varied across the Plateau, they were still higher than would be expected in the remote troposphere. This confirms the fact that the Plateau can be considered an expansive chemical reactor. Lastly, the results of a brief firn air experiment conducted at Midpoint C are presented for comparison with South Pole and Summit, Greenland snow experiments.
C41C-0545
Mercury and major element snowmelt chemistry at an Alaskan Arctic coastal site
Mercury is deposited to snow in Polar Regions during the late winter and early spring. This deposition is driven by photochemical reactions that involve reactive halogens and snow and ice surfaces. The Arctic also receives trace metals, sulfate and black carbon during spring time Arctic haze events. Mercury, Arctic haze metals and sulfate in Arctic snow are likely mobilized during metamorphism, melt and surface runoff in the spring. To investigate this we implemented a daily sampling campaign for mercury and major elements during spring snow melt near Barrow, Alaska in 2008. The area is underlain by continuous permafrost and there is no base flow in the winter. We focused on a small (52,000 m2) ephemeral stream watershed to quantify chemical fluxes at the microscale. Prior to the melt the snow pack was 35 cm high with a density of 0.3 g/cm3. The snow pack height was measured daily at 15 locations along two 1 kilometer long transects throughout the melt to track snow pack loss. Discharge in our micro watershed was measured using a sonic sounder above a small dam constructed in the stream bed and by quantifying flow through a PVC pipe at the dam outlet. Percolation columns began to migrate downward through the snow pack on May 26 and within two days the snow pack was isothermal. Flow in the micro watershed began as a slushy trickle on May 28 that increased to a steady flow by June 4. Peak discharge rates of slightly over 3 L/sec were measured in the late afternoons on June 7, 8 and 9. By June 9 slightly more than half the tundra surface was exposed and snow was relegated to low lying areas. The first melt water to pool at the base of the snow pack had the highest cation (sodium, potassium, magnesium, calcium, and ammonium) and anion (chloride, bromide, sulfate, nitrate, bicarbonate) concentrations of all inorganic ions measured in snow, melt water or surface runoff. These major element concentrations were 5 to 10 times higher than pre melt snow pack values. The pre-melt snow pack surface 1 cm yielded a mercury concentration of 56 ng/L with three other layers comprising the remainder of the snow pack yielding mercury concentrations between 11 and 19 ng/L. Snow melt water at the base of the snow pack on May 28 yielded initial mercury concentrations of 55 ng/L and melt water mercury values remained between 25 and 102 ng/L until June 6 when discharge began to increase markedly. As discharge increased the mercury concentrations decreased to between 10 and 25 ng/L. Taken in total, our results suggest that there is an "ionic pulse" of major elements and mercury from the snow pack during the initial stages of snow melt. Though we cannot address the bioavailability of mercury in the Arctic ecosystem during snow melt our results suggest that mercury monitoring campaigns should focus on spring melt.
C41C-0546
Photochemical Recycling of Hydrogen Peroxide on Snow in the Presence of Organic Compounds
Hydrogen peroxide (HOOH), an important tropospheric oxidant, is also present in polar ice cores and surface snow. In the presence of sunlight, HOOH in the photic zone of snow photolyzes to form hydroxyl radical (•OH), which can react with organics and other compounds in the snow to form a variety of products, including volatile compounds. Based on past reports, the photolytic lifetime of HOOH in polar surface snow during the summer is less than a month, yet ice core data shows that snowpack HOOH survives through the summer. Chemical reactions producing HOOH are known to exist in water drops and aerosol particles, but have not been studied in snow or ice matrices. Recycling of HOOH due to reactions with organic compounds may represent a significant source in polar snows. Our work evaluates the ability of organic compounds to recycle HOOH in water and ice matrices. The recycling of HOOH can occur through the following cycle: (1) HOOH is photolyzed to two molecules of •OH; (2) reaction of •OH with an organic molecule forms hydroperoxyl radical (HO2•), and (3) two HO2• combine to reform HOOH: •OH + organic → HO2• + products HO2• + HO2• → HOOH + O2 Our findings in solution (5° C) indicate that a variety of organic compounds recycle •OH back into HOOH; typically 10 to 60% of the HOOH that is photolyzed is recycled via this mechanism. For organic acids, decreases in solution pH increase the efficiency of HOOH production. Other organics have not shown pH dependent production rates. Organics studied have also shown direct photoformation of HOOH, although the contribution of this pathway to the overall HOOH concentration is minor compared to the recycling reaction. Evaluation of organics-mediated HOOH recycling in an ice matrix is underway, and will also be presented. Assuming recycling efficiencies in an ice matrix are similar to those in aqueous solution, HOOH recycling could be responsible for extending the lifetime of HOOH in polar snowpacks. Once buried by additional snow, this recycled HOOH would no longer be subject to photolysis and would be preserved, explaining the presence of HOOH in ice cores.
C41C-0547
The Interaction of PNA with ice Surfaces
It has been proposed that PNA (HNO4) might be an important reservoir species of nitrogen oxides in colder regions of the atmosphere. Here we present studies to investigate the adsorption of HNO4 on snow or ice surfaces, which might present an important sink of HNO4 and thus of atmospheric NOx. For this a gas-phase synthesis of HNO4 labeled with the radioactive 13N isotope has been set-up based on the reaction of 13NO2 with HO2 in the gas-phase. The synthesis was monitored by simultaneously determining HNO4 as well as important side products such as H2O2, O3, HNO3 and NO2 using a chemical ionization mass spectrometer. The adsorption behavior of HNO4 was investigated using a packed bed flow tube. The use of radioactive 13N-HNO4 allowed observing the migration of HNO4 along the packed bed flow tube in-situ and in real-time. From the temporal evolution of the migration, information on the diffusion into the bulk ice and on the reversible adsorption can be gained. First results on the diffusive uptake and on the adsorption of HNO4 in/on snow will be discussed.
C41C-0548
Frost Flower Chemistry and Physics: a Hudson Bay Field Study
Frost flowers are an important part of air-ice surface exchange in the polar regions and play a role in halogen chemistry in the troposphere. Their presence affects our ice core interpretation, understanding of past atmospheric circulation and climate modeling. Frost flowers were observed and collected in areas of differing salinity from sea ice on the Hudson Bay, Quebec in March 2008. Specific surface areas of the frost flower samples were obtained using CH4 adsorption at 77K in a volumetric apparatus, followed by Brunuaer- Emmett-Teller analysis. The enrichment or depletion in certain ions in frost flowers helps us understand their contributions to atmospheric chemistry. Chemical analysis was performed on the frost flower melt and on local seawater and brine, and we examine sulfate and bromide enrichment factors (with respect to chloride). We present this data together with photomicrographs of frost flowers from the area to illustrate the effects of temperature and salinity on frost flower morphology and composition.
C41C-0549
Chemical characteristics of surface snow on the way from coastal area to Dome Fuji, Antarctica
The sea salt components are transported from the coastal area to the inland area in Antarctica. On the other hand, there is a route transported directly from the stratosphere to the ice sheet in the inland region. The chemical characteristic in the surface snow is different according to the difference of these transportation routes. It is thought that the chemical species concentration in surface snow has changed because the amount of accumulation is different in the coastal area and the inland area. In this study, we aimed to clarify a chemical characteristic in the surface snow from the coastal area (S17) to the Dome Fuji, Antarctica. The samples were collected by the 47th Japanese Antarctic Research Expedition. They was left the S17 in October 2006 and arrived at the Dome Fuji in November 2006. They collected the surface snow every 10 km in about 1000 km trip. The samples were collected by scooped up the surface snow directly with pre-washed polypropylene bottle. The samples were taken to Japan without melting, and stored at -20 degree C until analysis. We analyzed the pH, electric conductivity, stable isotope of water (δ18O, δD), and major anions and cations. The stable isotope of water has lowered by rising of the altitude of sampling site. The pH and the electric conductivity showed the mirror image relation. As for a pH and electric conductivity, the drastic change was seen on the altitude 3000 m or more. Whenever the altitude was rising, the pH of the surface snow decreased and was less than 5.0. It is suggested that the depositional environment was changed. Whenever the altitude was rising, NO3- concentration increases and became 1.8 ppm at the maximum. It is thought that this is a cause of the surface snow acidification.
C41C-0550
Photochemical Transformation of Organochlorine POPs in Frozen Aqueous Systems: Field Studies at Barrow, Alaska
Volatile and semi-volatile organochlorine compounds such as aldrin, dieldrin, endosulfan and PCBs have frequently been identified as pollutants in remote polar regions, far from their anthropogenic sources. Bioaccumulation of these compounds has been previously documented and poses a potential threat to the health of individuals in Arctic subsistence communities as well as to the broader polar ecosystem. These compounds are normally regarded as persistent organic pollutants (POPs) in that they are environmentally long-lived and only undergo significant transformation once they enter living organisms. However, recent studies in our laboratory have demonstrated that some organochlorine POPs – including but not limited to aldrin and dieldrin – are degraded by near-ultraviolet light in both liquid and frozen aqueous media. From March – June 2008, a field campaign was conducted near Barrow, Alaska to determine whether the reactions observed in the laboratory also occurred under environmental conditions. The photochemical degradation of microgram quantities of aldrin, dieldrin, endosulfan (alpha and beta), hexachlorobenzene and 3,3',4,5'- tetrachlorobiphenyl dissolved in either MilliQ purified water or locally-collected melted snow was monitored under ambient temperature and light conditions. Of these, all but the PCB are shown to be degraded by sunlight. We present decay rates and estimated half-lives for these pollutants both at the snow's surface and at nominal depths of up to 10cm into the snowpack. Further, we have data confirming that in almost all cases, degradation occurs faster in predominantly frozen systems than in liquid ones. The significance of these results and their potential implications for Arctic environmental systems will be discussed.
C41C-0551
Photochemical Activity of Aldrin and Dieldrin in Liquid and Frozen Aqueous Systems: Field and Laboratory Studies
The phenomenon of global distillation generates significant accumulation of volatile, anthropogenic persistent organic pollutants (POPs) in polar regions. Bioaccumulation presents serious concerns for human health within Arctic subsistence communities. In the recent past, the photochemical processes of POPs have been observed in the laboratory. Despite some established knowledge regarding photochemical processes in reactive frozen media, little published literature exists regarding the chemical transformations and fate of POPs in the Arctic. Here, we consider the photochemical transformations of aldrin and dieldrin, two structurally similar organochlorine pollutants whose presence has been confirmed in the Arctic. Their photochemical transformation, resulting from ultraviolet exposure, was investigated by both field studies in Barrow, AK and controlled laboratory experiments. Pollutant degradation and photoproduct formation were monitored by GC-ECD analysis. Based on kinetic studies of liquid and frozen samples and identification of photoproducts, we will propose potential reaction mechanisms for the transformations of aldrin and dieldrin. Further implications for environmental processes will be discussed.
C41C-0552
The Distribution, Transport, and Fate of Organochlorine Pollutants in the Arctic
Anthropogenic pollutants, emitted primarily in low and mid latitude regions, have made their way north and settled in some of the most pristine areas in the world. Through the process of global distillation these compounds evaporate and are transported from temperate climates to cooler, higher latitudes where they accumulate. There is little research available on the fate of the deposited pollutants, what chemical and physical interactions they have with snow and ice, and where they go upon snowmelt. Fieldwork has been carried out in Barrow, Alaska in order to investigate these issues. Snow, ice, water, and air samples were collected and analyzed for levels of a variety of different pesticides and PCBs. The sampling continued to the end of the melt period at which point samples from the runoff water of the melting snowpack were collected. Due to extended periods of sunlight during the spring and summer months in the Arctic photochemical transformations of pollutants can occur in the chemically reactive ice. Alongside the collection of field samples photochemical degradation experiments were performed to investigate the photochemical fate of organochlorine pollutants. This chemistry may impact the distribution and ultimate fate of organic pollutants. Combining data from the photochemistry experiments with measurements of pollutant distribution will form a more complete picture of how these transplanted pollutants move, transform, and impact the Arctic environment.
C41C-0553
Sr-Nd isotopic study of surface snow near Dome Fuji, Antarctica
Snow ice sample in Antarctica contains particulate matter. Particulates originate from continent, volcano, sea, space, and organism. The particulate matter of continental origin contains many elements from minerals and rocks. The isotopic ratio of an element reflects the origin and the history of the particle. Since the isotopic composition of Strontium (Sr) or Neodymium (Nd) depends on the formation ages of the earth crust, the information about the source of the particulate matter of continental origin can be estimated by analyzing the isotopic ratio of Sr or Nd. In this research, isotopic ratio of Sr and Nd in surface snow collected at the sampling site DF80 near Dome Fuji in Antarctica were analyzed. 1 kg of surface snow sample was condensed by heat, then microwave decomposition was carried out with the mixture of nitric acid and hydrofluoric acid. The quantitative analyses of Sr and Nd were performed using the quadrupole type inductively-coupled plasma mass spectrometer (ICP-MS). The concentrations of Sr and Nd contained in surface snow were ca. 40 ppt and ca. 1 ppt, respectively. In order to avoid the interference by isobars, Sr and Rb were isolated by solid-phase extraction. Sr and Nd isotopic ratio were measured using the multi-collector type ICP-MS. For this sample, the preliminary value of the ratio 87Sr/86Sr = 0.7096 was acquired. Further results and discussion about the origin of particulate matter will be presented.