Thomas A. Douglas

Halogens in the coastal snow pack near Barrow, Alaska: Evidence for active bromine air-snow chemistry during springtime

Received 14 October 2004; revised 11 January 2005; accepted 25 January 2005; published 26 February 2005. [1] We measured halide concentrations of snow and frost flowers in the vicinity of Barrow, Alaska. We find that the ratio of bromide to sodium in frost flowers is slightly enhanced (10%) as compared to sea water. In contrast, the ratio of bromide to sodium in some snow samples is more than an order of magnitude enhanced, and in other samples is more than an order of magnitude depleted. We interpret the bromide depleted snow as having been processed by heterogeneous chemistry and providing reactive halogen compounds to the atmosphere. The eventual end product of reactive bromine chemistry is HBr that is then deposited over a wide region, enhancing bromide in inland snow samples. Although frost flowers or open leads are likely to be the original source of halides that become reactive halogen gases, we find that the bromide release often occurs subsequent to production of aerosol from marine sources. Citation: Simpson, W. R., L. Alvarez-Aviles, T. A. Douglas, M. Sturm, and F. Domine (2005), Halogens in the coastal snow pack near Barrow, Alaska: Evidence for active bromine air-snow chemistry during springtime, Geophys. Res. Lett., 32, L04811,

Rate of decrease of the specific surface area of dry snow : Isothermal and temperature gradient conditions

The specific surface area (SSA) of snow is the surface area available to gases per unit mass. It is an important variable for quantifying air-snow exchange of chemical species, and it is closely related to other variables such as albedo. Snow SSA decreases during metamorphism, but few data are available to quantify its rate of decrease. We have performed laboratory experiments under isothermal and temperature gradient conditions during which the SSA of snow samples was monitored for several months. We have also monitored the SSA of snowfalls subjected to large temperature gradients at a field site in the central Alaskan taiga. The same snow layers were also monitored in a manipulated snowpack where the temperature gradient was greatly reduced. In all cases, the SSA decay follows a logarithmic equation with three adjustable variables that are parameterized using the initial snow SSA and the time-averaged temperature of the snow. Two parameterizations of the three adjustable variables are found: One applies to the isothermal experiments and to the quasi-isothermal cases studied in Alaska (equitemperature (ET) metamorphism), and the other is applicable to both the laboratory experiments performed under temperature gradients and to the natural snowpack in Alaska (temperature gradient (TG) metamorphism). Higher temperatures accelerate the decrease in SSA, and this decrease is faster under TG than ET conditions. We discuss the conditions of applicability of these parameterizations and use them to speculate on the effect of climate change on snow SSA. Depending on the climate regime, changes in the rate of decay of snow SSA and hence in snow albedo may produce either negative or positive feedbacks on climate change.

Phylogenetic analysis of bacteria preserved in a permafrost ice wedge for 25,000 years

ABSTRACT Phylogenetic analysis of bacteria preserved within an ice wedge from the Fox permafrost tunnel was undertaken by cultivation and molecular techniques. The radiocarbon age of the ice wedge was determined. Our results suggest that the bacteria in the ice wedge adapted to the frozen conditions have survived for 25,000 years.

Convective forcing of mercury and ozone in the Arctic boundary layer induced by leads in sea ice

The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads (large transient channels of open water in the ice), which may affect atmospheric and biogeochemical cycles in the Arctic. Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic, caused by destruction of ozone along with oxidation of gaseous elemental mercury (Hg(0)) to oxidized mercury (Hg(ii)) in the atmosphere and its subsequent deposition to snow and ice. Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry, whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic, some of which can enter ecosystems during snowmelt. Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow, Alaska. We find that coastal depletion events are directly linked to sea-ice dynamics. A consolidated ice cover facilitates the depletion of Hg(0) and ozone, but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads. We attribute the rapid recoveries of Hg(0) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer, which mixes Hg(0) and ozone from undepleted air masses aloft. This convective forcing provides additional Hg(0) to the surface layer at a time of active depletion chemistry, where it is subject to renewed oxidation. Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems.

Quantifying landscape change in an arctic coastal lowland using repeat airborne LiDAR

Increases in air, permafrost, and sea surface temperature, loss of sea ice, the potential for increased wave energy, and higher river discharge may all be interacting to escalate erosion of arctic coastal lowland landscapes. Here we use airborne light detection and ranging (LiDAR) data acquired in 2006 and 2010 to detect landscape change in a 100 km2 study area on the Beaufort Sea coastal plain of northern Alaska. We detected statistically significant change (99% confidence interval), defined as contiguous areas (>10 m2) that had changed in height by at least 0.55 m, in 0.3% of the study region. Erosional features indicative of ice-rich permafrost degradation were associated with ice-bonded coastal, river, and lake bluffs, frost mounds, ice wedges, and thermo-erosional gullies. These features accounted for about half of the area where vertical change was detected. Inferred thermo-denudation and thermo-abrasion of coastal and river bluffs likely accounted for the dominant permafrost-related degradational processes with respect to area (42%) and volume (51%). More than 300 thermokarst pits significantly subsided during the study period, likely as a result of storm surge flooding of low-lying tundra (<1.4 m asl) as well as the lasting impact of warm summers in the late-1980s and mid-1990s. Our results indicate that repeat airborne LiDAR can be used to detect landscape change in arctic coastal lowland regions at large spatial scales over sub-decadal time periods.

Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests

We examined the effects of fire disturbance on permafrost degradation and thaw settlement across a series of wildfires (from ~1930 to 2010) in the forested areas of collapse-scar bog complexes in the Tanana Flats lowland of interior Alaska. Field measurements were combined with numerical modeling of soil thermal dynamics to assess the roles of fire severity and climate history in postfire permafrost dynamics. Field-based calculations of potential thaw settlement following the loss of remaining ice-rich permafrost averaged 0.6 m. This subsidence would cause the surface elevations of forests to drop on average 0.1 m below the surface water level of adjacent collapse-scar features. Up to 0.5 m of thaw settlement was documented after recent fires, causing water impoundment and further thawing along forest margins. Substantial heterogeneity in soil properties (organic layer thickness, texture, moisture, and ice content) was attributed to differing site histories, which resulted in distinct soil thermal regimes by soil type. Model simulations showed increasing vulnerability of permafrost to deep thawing and thaw settlement with increased fire severity (i.e., reduced organic layer thickness). However, the thresholds of fire severity that triggered permafrost destabilization varied temporally in response to climate. Simulated permafrost dynamics underscore the importance of multiyear to multidecadal fluctuations in air temperature and snow depth in mediating the effects of fire on permafrost. Our results suggest that permafrost is becoming increasingly vulnerable to substantial thaw and collapse after moderate to high-severity fire, and the ability of permafrost to recover is diminishing as the climate continues to warm.

The specific surface area and chemical composition of diamond dust near Barrow, Alaska

2006, when conditions were similar. The SSA of DD ranges from 79.9 to 223 m 2 kg � 1 . The calculated ice surface area in the atmosphere reaches 11000 (� 70%) mm 2 cm � 3 , much higher than the aerosol surface area. However, the impact of DD on the downwelling and upwelling light fluxes in the UV and visible is negligible. The composition of DD is markedly different from that of snow on the surface. Its concentrations in mineral ions are much lower, and its overall composition is acidic. Its concentrations in aldehydes, DOC, H2O2 and mercury are much higher than in surface snows. Our interpretation is that DOC from the oceanic surface microlayer, coming from open leads in the ice off of Barrow, is taken up by DD. Active chemistry in the atmosphere takes place on DD crystal surfaces, explaining its high concentrations in aldehydes and mercury. After deposition, active photochemistry modifies DD composition, as seen from the modifications in its absorption spectra and aldehyde and H2O2 content. This probably leads to the emissions of reactive species to the atmosphere.

A time series investigation of the stability of nitramine and nitroaromatic explosives in surface water samples at ambient temperature.

We investigated the fate of nitramine and nitroaromatic explosives compounds in surface water to determine how surface water biogeochemistry affects the stability of explosives compounds. Five river water samples and 18.2 MOmega deionized water were spiked with 10 explosives compounds and the samples were held at ambient temperatures (20 degrees C) for 85 d. Surface water represented three rivers with a range of total organic carbon concentrations and two rivers draining glacial watersheds with minimal organic carbon but high suspended solids. 18.2 MOmega deionized water exhibited no explosives transformation. Nitroaromatic compound loss from solution was generally: tetryl>1,3,5-TNB>TNT>1,3-DNB>2,4-DNT. The HMX, RDX, 2,6-DNT, 2ADNT, and 4ADNT concentrations remained somewhat stable over time. The surface water with the highest total organic carbon concentration exhibited the most dramatic nitroaromatic loss from solution with tetryl, 1,3,5-TNB and TNT concentrations decreasing to below detection within 10d. The two water samples with high suspended solid loads exhibited substantial nitroaromatic explosives loss which could be attributable to adsorption onto fresh mineral surfaces and/or enhanced microbiologic biotransformation on mineral surfaces. An identical set of six water samples was spiked with explosives and acidified with sodium bisulfate to a pH of 2. Acidification maintained stable explosives concentrations in most of the water samples for the entire 85 d. Our results suggest sampling campaigns for explosives in surface water must account for biogeochemical characteristics. Acidification of samples with sodium bisulfate immediately following collection is a robust way to preserve nitroaromatic compound concentrations even at ambient temperature for up to three months.

Tomitella biformata gen. nov., sp. nov., a new member of the suborder Corynebacterineae isolated from a permafrost ice wedge.

Gram-reaction-positive, aerobic, non-spore-forming, irregular rod-shaped bacteria, designated AHU1821(T) and AHU1820, were isolated from an ice wedge in the Fox permafrost tunnel, Alaska. The strains were psychrophilic, growing at -5 to 27°C. Phylogenetic analysis of the 16S rRNA and gyrB gene sequences indicated that the ice-wedge isolates formed a clade distinct from other mycolic-acid-containing bacteria within the suborder Corynebacterineae. The cell wall of strains AHU1821(T) and AHU1820 contained meso-diaminopimelic acid, arabinose and galactose, indicating chemotype IV. The muramic acids in the peptidoglycan were glycolated. The predominant menaquinone was MK-9(H(2)). The polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides and an unidentified glycolipid. The major fatty acids were hexadecenoic acid (C(16 : 1)), hexadecanoic acid (C(16 : 0)), octadecenoic acid (C(18 : 1)) and tetradecanoic acid (C(14 : 0)). Tuberculostearic acid was present in relatively small amounts (1 %). Strains AHU1821(T) and AHU1820 contained mycolic acids with 42-52 carbons. The DNA G+C content of the two strains was 69.3-71.6 mol% (T(m)). 16S rRNA, rpoB and recA gene sequences were identical between strains AHU1821(T) and AHU1820 and those of the gyrB gene showed 99.9 % similarity. Based on phylogenetic and phenotypic evidence, strains AHU1821(T) and AHU1820 represent a single novel species of a novel genus, for which the name Tomitella biformata gen. nov., sp. nov. is proposed. The type strain of Tomitella biformata is AHU1821(T) (=DSM 45403(T) =NBRC 106253(T)).

Glaciibacter superstes gen. nov., sp. nov., a novel member of the family Microbacteriaceae isolated from a permafrost ice wedge

Gram-positive, aerobic, non-spore-forming, irregular rod-shaped bacteria, designated strains AHU1791(T) and AHU1810, were isolated from a permafrost ice wedge in Alaska. Cells were motile by means of a polar flagellum. The strains were psychrophilic, growing at -5 to 25 degrees C. Phylogenetic analysis of 16S rRNA gene sequences indicated that the ice-wedge isolates formed a clade distinct from other genera affiliated with the family Microbacteriaceae. The novel strains showed highest levels of 16S rRNA gene sequence similarity with members of the genera Agreia and Subtercola (95.6-95.9 %). The level of 16S rRNA gene sequence similarity between strains AHU1791(T) and AHU1810 was 99.8 %. The cell-wall peptidoglycan type of the two strains was B2gamma, containing 2,4-diaminobutyric acid as the diagnostic amino acid. The predominant menaquinones were MK-12 and MK-13 (strain AHU1791(T)) and MK-11 and MK-12 (strain AHU1810). The major fatty acids of the two strains were 12-methyl tetradecanoic acid (anteiso-C(15 : 0)), 14-methyl hexadecanoic acid (anteiso-C(17 : 0)), 14-methyl pentadecanoic acid (iso-C(16 : 0)) and 13-methyl tetradecanoic acid (iso-C(15 : 0)). The DNA G+C contents of strains AHU1791(T) and AHU1810 were approximately 65 mol%. These phenotypic characteristics differentiated the ice-wedge strains from their closest phylogenetic neighbours, namely Subtercola boreus and the two recognized species of the genus Agreia. The sequences of the housekeeping genes coding for DNA gyrase subunit B (gyrB), RNA polymerase subunit B (rpoB) and recombinase A (recA) were almost identical between strains AHU1791(T) and AHU1810. Although the predominant menaquinones found in strains AHU1791(T) and AHU1810 were different, no other distinct differences were found with regard to other phenotypic and genotypic characteristics, indicating that the two strains were members of the same species. Accordingly, strains AHU1791(T) and AHU1810 are considered to represent a single novel species of a new genus, for which the name Glaciibacter superstes gen. nov., sp. nov. is proposed. The type strain of Glaciibacter superstes is AHU1791(T) (=DSM 21135(T) =NBRC 104264(T)).