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Nitrate stable isotopes and major ions in snow and ice from Svalbard
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing atmospheric reactive nitrogen (Nr), as consequence of human activities, has generated accumulation of nitrate (NO3-) in Arctic regions. The Arctic has fragile nitrogen limited ecosystems that can be altered by increases of dry or wet deposition of Nr. Ice cores have shown increments of twofold in nitrogen deposition over Greenland and Svalbard during the 20th century. Ice core NO3- stable isotopes, (δ15N-NO3- and δ18O-NO3-), have the potential to serve as proxy of nitrogen oxides (NOx) sources and atmospheric oxidation pathways. NO3- is difficult to interpret in ice since it has several sources and experiences post-depositional processes, e.g. photolysis, relocation, evaporation and diffusion. The present work shows the results of NO3- and NO3- stable isotopes analyses of ice cores, snow and precipitation from Svalbard, in order to obtain records of natural and anthropogenic sources of NO3-. In addition, meltwater percolation effects on the snowpack ion content were also studied. A comparison between NO3- records from different Svalbard ice cores and NOx and SOx emission profiles from different regions shows that the major source regions affecting Svalbard are Western Europe and North America, followed by Central Europe and former USSR. Post-1950s δ15N-NO3- measured at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions, and forest fires. There is an east-west gradient in snow NO3- stable isotopes during 2010/2011, with lower δ15N-NO3- and higher δ18O-NO3- values at eastern sites; the results evidence differences in the origin of air masses arriving at Svalbard sites, mainly Eurasia, to the eastern sites, and Northern Europe to the western sites. The effects of post-depositional change on the ice core chemistry were studied, finding that 45% of annual snowpack suffers melt at Lomonosovfonna during the last 60 years. Percolation lengths were estimated as ≈1 m for most of ions; therefore, it is expected that the atmospheric ionic signal is preserved at annual or bi-annual resolution within the last 60 years at the Lomonosovfonna summit. The results presented here suggest that NO3- stable isotopes from Svalbard ice cores are useful to describe different sources and source regions of NOx, contributing to the assessment of nitrogen enrichment for this region.

Abstract [sv]

Halten av reaktivt kväve (Nr) har ökat i atmosfären som en följd av mänskliga aktiviteter och har lett till en anrikning av nitrat (NO3-) nedfallet i Arktis. Ekosystemen i de Arktiska områdena är mycket sköra och extremt anpassade till den låga tillgången på tillgängligt kväve, ett förhållande som drastiskt kan ändras genom en ökad våt och torr deposition av Nr. Studier av iskärnor från både Grönland och Svalbard har visat på en fördubbling av kvävenedfallet under de senaste hundra åren. Potentiellt så kan analyser av kvävets och syrets stabila isotoper (δ15N-NO3- and δ18O-NO3-) i nitrat från iskärnor ge information om de kväveoxidkällor, oxidations- och transportvägar som påverkar nitrat halten i Arktis. Dock är nitrat sammansättningen i is svårtolkat eftersom det nitrat som återfinns i isen kan härstamma från flera olika källor och där även flera post-depositionsprocesser har beskrivits, t.ex. fotolys, evaporation, diffusion och omlokalisering som följd av snösmältning. Denna doktorsavhandling använder såväl nitrat halter som des stabila isotoper från iskärnor, snö- och nederbördsprover från Svalbard, för att fastställa de naturliga och antropogena källor av nitrat som influerar denna del av Arktis. I tillägg till detta så har även snösmältningsförsök gjorts för att undersöka hur nitratet påverkas av perkolationsprocesser. En jämförelse av nitratkompositionen mellan iskärnor och snöprofiler från olika delar av Svalbard visar att de huvudsakliga källregionerna för Nr till denna del av Arktis är Västeuropa och Nordamerika, följt av Centraleuropa och forna Sovjetunionen. För perioden 1950 och fram till i dag så påvisar δ15N-NO3- värden mätt från en Lomonosovfonna (centrala Svalbard) iskärna en stark influens från förbränning av fossila bränslen följt av utsläpp från åkermarker samt för de sista tio åren en influens av Ryska skogsbränder. Generellt så finns det även en öst-västlig gradient bland de stabila isotoperna av nitrat, med lägre δ15N-NO3- och högre δ18O-NO3- värden på Svalbards östsida i 2010/2011. Resultaten visar på en skillnad i ursprungskällan av luftmassor, där östra Svalbard påverkas mest av luft från Eurasien medan västra Svalbard påverkas med av Nordeuropa. När det gäller perkolationens effekt på jonkoncentrationen, så påvisar 60 års iskärnedata att 45% av den årliga vinterackumulationen smälts bort under sommaren på Lomonosovfonna. Detta medför en förflyttning av de flesta joner nedåt i snön, med en perkolationslängd på ca 1 m, och den ursprungliga nitrat sammansättningen förväntas därför bevaras på årlig eller vartannat års basis. Resultaten som presenteras här tyder på att iskärnedata, vad gäller nitrat och dess stabila isotoper, från Svalbard är representativa för att beskriva de olika källor och regioner som bidrar till kvävetillförseln i denna del av Arktis.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1142
Keyword [en]
nitrate stable isotopes, nitrate, NOx proxies, ice cores, percolation, ion relocation, Svalbard
Keyword [sv]
stabila isotoper av nitrat, nitrat, indikator för kväveoxider, iskärnor, perkolation, joniska omlokalisering, Svalbard
National Category
Natural Sciences
Research subject
Earth Science with specialization in Physical Geography
Identifiers
URN: urn:nbn:se:uu:diva-221780ISBN: 978-91-554-8931-1 (print)OAI: oai:DiVA.org:uu-221780DiVA: diva2:709995
Public defence
2014-05-27, Hörsalen, Villavägen 18, Uppsala, 11:00 (English)
Opponent
Supervisors
Available from: 2014-04-30 Created: 2014-04-03 Last updated: 2014-06-30
List of papers
1. First Ice Core Records of NO3- Stable Isotopes from Lomonosovfonna, Svalbard
Open this publication in new window or tab >>First Ice Core Records of NO3- Stable Isotopes from Lomonosovfonna, Svalbard
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2015 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 1, 313-330 p.Article in journal (Refereed) Published
Abstract [en]

Samples from two ice cores drilled at Lomonosovfonna, Svalbard, covering the period 1957-2009, and 1650-1995, respectively, were analyzed for NO(3)(-)concentrations, and NO3- stable isotopes (N-15 and O-18). Post-1950 N-15 has an average of (-6.91.9), which is lower than the isotopic signal known for Summit, Greenland but agrees with values observed in recent Svalbard snow and aerosol. Pre-1900 N-15 has an average of (4.21.6)parts per thousand suggesting that natural sources, enriched in the N-15 isotope, dominated before industrialization. The post-1950 O-18 average of (75.1 +/- 4.1)parts per thousand agrees with data from low and polar latitudes, suggesting similar atmospheric NOy (NOy=NO+NO2+HNO3) processing pathways. The combination of anthropogenic source N-15 and transport isotope effect was estimated as -29.1 parts per thousand for the last 60years. This value is below the usual range of NOx (NOx=NO+NO2) anthropogenic sources which is likely the result of a transport isotope effect of -32 parts per thousand. We suggest that the N-15 recorded at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions, and forest fires; the first and second being responsible for the marked decrease in N-15 observed in the post-1950s record with soil emissions being associated to the decreasing trend in N-15 observed up to present time, and the third being responsible for the sharp increase of N-15 around 2000.

National Category
Earth and Related Environmental Sciences
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-221776 (URN)10.1002/2013JD020930 (DOI)000349104700020 ()
Available from: 2014-04-03 Created: 2014-04-03 Last updated: 2017-12-05Bibliographically approved
2. Nitrate stable isotopes and major ions in snow and ice samples from four Svalbard sites
Open this publication in new window or tab >>Nitrate stable isotopes and major ions in snow and ice samples from four Svalbard sites
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2015 (English)In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 34, 23246Article, review/survey (Refereed) Published
Abstract [en]

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.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-221777 (URN)10.3402/polar.v34.23246 (DOI)000353050700001 ()
Available from: 2014-04-03 Created: 2014-04-03 Last updated: 2017-12-05Bibliographically approved
3. Analysis of chemical elution and percolation length in an ice field site experiencing periodical melt events-Lomonosovfonna, Svalbard
Open this publication in new window or tab >>Analysis of chemical elution and percolation length in an ice field site experiencing periodical melt events-Lomonosovfonna, Svalbard
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-221778 (URN)
Available from: 2014-04-03 Created: 2014-04-03 Last updated: 2014-12-08
4. Nitrate and Sulfate Anthropogenic Trends in the 20th Century from Five Svalbard Ice Cores
Open this publication in new window or tab >>Nitrate and Sulfate Anthropogenic Trends in the 20th Century from Five Svalbard Ice Cores
2012 (English)In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 44, no 4, 490-499 p.Article in journal (Refereed) Published
Abstract [en]

Sulfate and nitrate records from 5 ice cores spread across Svalbard were compared and revealed strong temporal similarities with previously published global estimates of SO2 and NOx anthropogenic emissions during the 20th century. A significant departure from the early century sulfate and nitrate levels was evident at all drilling sites starting from the mid-1940s. A steady increase was observed in both sulfate and nitrate profiles at most sites until the late 1960s, when the annual concentrations started to increase at a higher rate. This peak activity lasted for about a decade, and was observed to decrease steadily from the early 1980s on, when sulfate levels declined significantly and when nitrate levels finally reached sulfate levels for the first time in 20th century. The timing of these trends in Svalbard with global SO2 and NOx concentration profiles was best appraised when considering composite concentration profiles of all Svalbard ice cores for sulfate and nitrate, respectively. Composite profiles were also found to provide a convenient mean for distinguishing between the most important world source regions. Based on correlation analysis, the major pollutant sources appeared to be Western Europe and North America for both sulfate and nitrate, followed by Central Europe and former U.S.S.R. in generally similar proportions.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-189157 (URN)10.1657/1938-4246-44.4.490 (DOI)000311010700010 ()
Available from: 2012-12-25 Created: 2012-12-25 Last updated: 2017-12-06Bibliographically approved
5. Reactive nitrogen and sulphate wet deposition at Zeppelin Station, Ny-Alesund, Svalbard
Open this publication in new window or tab >>Reactive nitrogen and sulphate wet deposition at Zeppelin Station, Ny-Alesund, Svalbard
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2013 (English)In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 32, UNSP 19136- p.Article in journal (Refereed) Published
Abstract [en]

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 NO3-; nss-SO42- and NH4+ concentrations, and the deposition of single precipitation events was calculated using precipitation measurements taken at nearby Ny-Alesund. The majority of observed events showed concentrations ranging from 0.01 to 0.1 mg L-1 N for NO3- and NH4+ and from 0.02 to 0.3 mg L-1 S for nss-SO42-. The majority of calculated depositions ranged from 0.01 to 0.1 mg m(-2) N for NO3- and NH4+ and from 0.02 to 0.3 mg m(-2) S for nss-SO42-. 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.

Keyword
Nitrogen, sulphur, Arctic, precipitation, sampling, NSINK
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-200129 (URN)10.3402/polar.v32i0.19136 (DOI)000317580400001 ()
Available from: 2013-05-21 Created: 2013-05-20 Last updated: 2017-12-06Bibliographically approved

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