Nitrate stable isotopes and major ions in snow and ice samples from four Svalbard sites

Increasing reactive nitrogen (N-r) deposition in the Arctic may adversely impact N-limited ecosystems. To investigate atmospheric transport of N-r to Svalbard, Norwegian Arctic, snow and firn samples were collected from glaciers and analysed to define spatial and temporal variations (1 10 years) in major ion concentrations and the stable isotope composition (delta N-15 and delta O-18) of nitrate (NO3-) across the archipelago. The delta N-15(NO3-) and delta O-18(NO3-) averaged -4 parts per thousand and 67 parts per thousand in seasonal snow (2010-11) and -9 parts per thousand and 74 parts per thousand in firn accumulated over the decade 2001-2011. East-west zonal gradients were observed across the archipelago for some major ions (non-sea salt sulphate and magnesium) and also for delta N-15(NO3-) and delta O-18(NO3-) in snow, which suggests a different origin for air masses arriving in different sectors of Svalbard. We propose that snowfall associated with long-distance air mass transport over the Arctic Ocean inherits relatively low delta N-15(NO3-) due to in-transport N isotope fractionation. In contrast, faster air mass transport from the north-west Atlantic or northern Europe results in snowfall with higher delta N-15(NO3-) because in-transport fractionation of N is then time-limited

Measurement and modelling of UV radiation penetration and photolysis rates of nitrate and hydrogen peroxide in Antarctic sea ice:An estimate of the production rate of hydroxyl radicals in first-year sea ice

Sea ice may be an oxidising medium owing to sunlight-driven reactions occurring within the ice. UV light transmission and albedo (320-450 nm) are reported for first-year sea ice in Terra Nova Bay, Antarctica, in conjunction with depth integrated photolysis rates for OH radical production from photolysis of hydrogen peroxide (H O ) and nitrate anion (NO). The albedo is 0.70-0.75 and the transmission is characterised by an e-folding depth of ∼50 cm or an extinction coefficient of ∼2 m . A coupled atmosphere-snowpack radiation-transfer model (TUV-snow) was applied to the experimental measurements so that scattering and absorption cross-sections of the ice could be deduced. These cross-sections were used to model actinic flux (spherical irradiance) profiles in the ice, and thus illustrate the enhancement of actinic flux around a depth of 10 cm in the sea ice for zenith angles smaller than 50°. The actinic flux-depth profiles demonstrate how extinction coefficients (measured at solar zenith angles greater than 50°) for the top 10-20 cm of sea ice are much larger than extinction coefficients measured deeper in the ice. The TUV model was also used to calculate photolysis frequencies for nitrate anions and hydrogen peroxide, which produce hydroxyl radicals within the sea ice. The depth integrated photolysis rate of hydrogen peroxide is an order of magnitude larger than the depth integrated photolysis rate of nitrate. However, the low concentrations of hydrogen peroxide in sea water and ice relative to nitrate result in a higher rate of production of OH radicals for nitrate than hydrogen peroxide. Approximate upper limits for depth integrated rate of production OH from nitrate photolysis in a 1 m deep sea ice block were found to be 0.06-2 μmol m h for solar zenith angles of 85-45°, respectively. The depth integrated production rate of OH radical from hydrogen peroxide photolysis is 0.01-0.3 μmol m h for solar zenith angles of 85-45°, respectively. Photolysis of nitrate in ice is an efficient route to the production of hydroxyl radicals and an oxidising ice. It must be stressed that these depth integrated rates of production are, however, approximate upper limits because the low porosity and the microphysical, chemical and photochemical process occurring in sea ice may reduce the depth integrated rate of production. In conclusion we suggest that first-year sea ice may be an efficient medium for photochemistry and that 85% of ice photochemistry may occur in the top 1 m of sea ice, assuming that the concentration of chromophore (nitrate or hydrogen peroxide) and photochemical efficiency are independent of depth in the sea ice

Inclined lidar observations of boundary layer aerosol particles above the Kongsfjord, Svalbard

An inclined lidar with vertical resolution of 0.4 m was used for detailed boundary layer studies and to link observations at Zeppelin Mountain (474 m) and Ny-Ålesund, Svalbard. We report on the observation of aerosol layers directly above the Kongsfjord. On 29 April 2007, a layer of enhanced backscatter was observed in the lowest 25 m above the open water surface. The low depolarization ratio indicated spherical particles. In the afternoon, this layer disappeared. The ultrafine particle concentration at Zeppelin and Corbel station (close to the Kongsfjord) was low. On 1 May 2007, a drying process in the boundary layer was observed. In the morning, the atmosphere up to Zeppelin Mountain showed enhanced values of the backscatter coefficient. Around noon, the top of the highly reflecting boundary layer decreased from 350 to 250 m. The top of the boundary layer observed by lidar was confirmed by radiosonde data

Microorganisms in Dry Polar Snow Are Involved in the Exchanges of Reactive Nitrogen Species with the Atmosphere

International audienceThe snowpack is a complex photochemical reactor that emits a wide variety of reactive molecules to the atmosphere. In particular, the photolysis of nitrate ions, NO 3-, produces NO, NO 2 , and HONO, which affects the oxidative capacity of the atmosphere. We report measurements in the European High Arctic where we observed for the first time emissions of NO, NO 2 , and HONO by the seasonal snowpack in winter, in the complete or near-complete absence of sunlight and in the absence of melting. We also detected unusually high concentrations of nitrite ions, NO 2-, in the snow. These results suggest that microbial activity in the snowpack is responsible for the observed emissions. Isotopic analysis of NO 2-and NO 3-in the snow confirm that these ions, at least in part, do not have an atmospheric origin and are most likely produced by the microbial oxidation of NH 4 + coming from clay minerals into NO 2-and NO 3-. These metabolic pathways also produce NO. Subsequent dark abiotic reactions lead to NO 2 and HONO production. The snow cover is therefore not only an active photochemical reactor but also a biogeochemical reactor active in the cycling of nitrogen and it can affect atmospheric composition all year round

Reactive nitrogen and sulphate wet deposition at Zeppelin Station, Ny-Ålesund, Svalbard

As a potent fertilizer, reactive nitrogen plays an important role in Arctic ecosystems. Since the Arctic is a nutrient-limited environment, changes in nitrogen deposition can have severe impacts on local ecosystems. To quantify the amount of nitrogen deposited through snow and rain events, precipitation sampling was performed at Zeppelin Station, Svalbard, from November 2009 until May 2011. The samples were analysed for , nss- and concentrations, and the deposition of single precipitation events was calculated using precipitation measurements taken at nearby Ny-Ålesund. The majority of observed events showed concentrations ranging from 0.01 to 0.1 mg L−1 N for and and from 0.02 to 0.3 mg L−1 S for nss-. The majority of calculated depositions ranged from 0.01 to 0.1 mg m−2 N for and and from 0.02 to 0.3 mg m−2 S for nss-. The budget was controlled by strong deposition events, caused by long-lasting precipitation episodes that lasted for several days and which had raised concentrations of nitrogen and sulphur. Three future scenarios of increasing precipitation in the Arctic were considered. The results showed that deposition is mainly controlled by the amount of precipitation, which leads to the conclusion that increased precipitation might cause increases in deposition of the same magnitude