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Modelling micro- and macrophysical contributors to the dissipation of an Arctic mixed-phase cloud during the Arctic Summer Cloud Ocean Study (ASCOS)
No full textThe Arctic climate is changing; temperature changes in the Arctic are greater than at midlatitudes, and changing atmospheric conditions influence Arctic mixed-phase clouds, which are important for the Arctic surface energy budget. These low-level clouds are frequently observed across the Arctic. They impact the turbulent and radiative heating of the open water, snow, and sea-ice-covered surfaces and influence the boundary layer structure. Therefore the processes that affect mixed-phase cloud life cycles are extremely important, yet relatively poorly understood. In this study, we present sensitivity studies using semi-idealized large eddy simulations (LESs) to identify processes contributing to the dissipation of Arctic mixed-phase clouds. We found that one potential main contributor to the dissipation of an observed Arctic mixed-phase cloud, during the Arctic Summer Cloud Ocean Study (ASCOS) field campaign, was a low cloud droplet number concentration (CDNC) of about 2 cm-3. Introducing a high ice crystal concentration of 10 L-1 also resulted in cloud dissipation, but such high ice crystal concentrations were deemed unlikely for the present case. Sensitivity studies simulating the advection of dry air above the boundary layer inversion, as well as a modest increase in ice crystal concentration of 1 L-1, did not lead to cloud dissipation. As a requirement for small droplet numbers, pristine aerosol conditions in the Arctic environment are therefore considered an important factor determining the lifetime of Arctic mixed-phase clouds
Paleoglaciological study of the Ahlmannryggen, Borgmassivet and Kirwanveggen nunatak ranges, Dronning Maud Land, East Antarctica, using WorldView imagery
No full textPaleoglaciological reconstructions based on glacial geological and geomorphological evidence areused to constrain and test numerical models of ice sheet extent and dynamics. The MAGIC-DMLresearch project (“Mapping, Measuring and Modelling Antarctic Geomorphology and Ice Change, inDronning Maud Land”) is trying to reconstruct the timing and pattern of ice surface elevation changessince the mid-Pliocene across western Dronning Maud Land, East Antarctica. This reconstructionwill work as the basis for testing and constraining ice sheet numerical models to improve climateunderstanding in Antarctica. This master thesis project contributes to MAGIC-DML by adopting a high-resolution remote sensingbasedmapping of glacial geomorphology and ice sheet surface structures, for a coast-inland transectincluding the Ahlmannryggen, Borgmassivet, and Kirwanveggen nunatak ranges. The primary aimof this study is to investigate the glaciology and paleoglaciology of the study area, in order to mapevidence for a former thicker ice sheet on nunatak slopes and plateaus, and patterns of ice flow of thecurrent ice sheet surface. Meso-scale glacial landforms and ice flow features were identified andmapped using different remote sensing data sets: the LANDSAT Image Mosaic of Antarctica(LIMA), DigitalGlobe Worldview-2 (WV02) and Worldview-3 (WV03) panchromatic andmultispectral images, the Radarsat Antarctica Mapping Project (RAMP) Ice Surface Digital ElevationModel (DEM) version 2, and the Bedmap2 datasets. The satellite imagery was analysed in a multistepprocedure using ArcGIS, including image processing and mosaicking, visual feature recognition,and mapping. The identification of some key landforms required the adoption of assumptions, forexample in order to distinguish till cover from regolith or boulders derived from rock fall from glacialerratics. Present-day ice flow directions were traced according to the distribution of ice surfacefeatures such as blue ice areas, crevasse fields, longitudinal surface structures, and supraglacialmoraines. The occurrence of till cover and erratics above the present-day ice surface on somenunataks slopes and plateaus was considered indicative of a thicker ice sheet in the past. Paleo-iceflow directions were inferred from the proximity of locations to the closest ice streams, since thatlatter have been active since the Oligocene. Geomorphological and ice flow direction maps were obtained and used to infer the paleoglaciologyof the three nunatak ranges. Ice sheet thinning reconstructions reveal a minimum ice surface loweringof ~400–500 m in the Ahlmannryggen and Borgmassivet nunatak ranges, of ~300 m north of theKirwanveggen escarpment and of ~100 m on the edge of Amundsenisen polar plateau. The paleo-icesheet flow pattern probably differed from today, because ice flow has locally been influenced by anincreased topographical complexity, due to the thinning of the ice sheet and the emerging of nunatakoutcrops. According to dating studies conducted elsewhere in DML, the inferred ice surface decreasewas probably initiated in the Late Pliocene/Early Pleistocene, and continued after the Last GlacialMaximum interruption across the coastal sector of the ice sheet. The reliability of derived paleo-icesheet reconstructions, based on the mapping and interpretation of landforms, needs to be verified infuture field studies. This master thesis project has identified 34 well-suited locations for the samplingof erratic boulders and bedrock surfaces for cosmogenic nuclide (CN) surface exposure dating duringthe MAGIC-DML 2017/18 field season. The chronology derived from CN dating and fieldverification of the presented mapping will permit the delineation of ice sheet surface elevations astargets for ice sheet modelling.MAGIC DM
The Northward Course of the Anthropocene : Transformation, Temporality and Telecoupling in a Time of Environmental Crisis
No full textThe Arctic—warming at twice the rate of the rest of the planet—is a source of striking imagery of amplified environmental change in our time, and has come to serve as a spatial setting for climate crisis discourse. The recent alterations in the Arctic environment have also been perceived by some observers as an opportunity to expand economic exploitation. Heightened geopolitical interest in the region and its resources, contradicted by calls for the protection of fragile Far North ecosystems, has rendered the Arctic an arena for negotiating human interactions with nature, and for reflecting upon the planetary risks and possibilities associated with the advent and expansion of the Anthropocene—the proposed new epoch in Earth history in which humankind is said to have gained geological agency and become the dominant force over the Earth system. With the Arctic serving as a nexus of crosscutting analytical themes spanning contemporary history (the late twentieth and the early twenty-first century until 2015), this dissertation examines defining characteristics of the Anthropocene and how the concept, which emerged from the Earth system science community, impacts ideas and assumptions in historiography, social sciences and the environmental humanities, including the fields of environmental history, crisis management and security studies, political geography, and science and technology studies (STS). The primary areas of empirical analysis and theoretical investigation encompass constructivist perspectives and temporal conceptions of environmental and climate crisis; the role of science and expertise in performing politics and shaping social discourse; the geopolitical significance of telecoupling—a concept that reflects the interconnectedness of the Anthropocene and supports stakeholder claims across wide spatial scales; and implications of the recent transformation in humankind’s long duration relationship with the natural world. Several dissertation themes were observed in practice at the international science community of Ny-Ålesund on Svalbard, where global change is made visible through a concentration of scientific activity. Ny-Ålesund is furthermore a place of geopolitics, where extra-regional states attempt to enhance their legitimacy as Arctic stakeholders through the performance of scientific research undertakings, participation in governance institutions, and by establishing a physical presence in the Far North. This dissertation concludes that this small and remote community represents an Anthropocene node of global environmental change, Earth system science, emergent global governance, geopolitics, and stakeholder construction in an increasingly telecoupled world.QC 20151211</p
Boreal earliest Triassic biotas elucidate globally depauperate hard substrate communities after the end-Permian mass extinction
No full textThe end-Permian mass extinction constituted the most devastating biotic crisis of the Phanerozoic. Its aftermath was characterized by harsh marine conditions incorporating volcanically induced oceanic warming, widespread anoxia and acidification. Bio-productivity accordingly experienced marked fluctuations. In particular, low palaeolatitude hard substrate communities from shallow seas fringing Western Pangaea and the Tethyan Realm were extremely impoverished, being dominated by monogeneric colonies of filter-feeding microconchid tubeworms. Here we present the first equivalent field data for Boreal hard substrate assemblages from the earliest Triassic (Induan) of East Greenland. This region bordered a discrete bio-realm situated at mid-high palaeolatitude (> 30 degrees N). Nevertheless, hard substrate biotas were compositionally identical to those from elsewhere, with microconchids encrusting Claraia bivalves and algal buildups on the sea floor. Biostratigraphical correlation further shows that Boreal microconchids underwent progressive tube modification and unique taxic diversification concordant with changing habitats over time. We interpret this as a post-extinction recovery and adaptive radiation sequence that mirrored coeval subequatorial faunas, and thus confirms hard substrate ecosystem depletion as a hallmark of the earliest Triassic interval globally
Ice export from the Laptev and East Siberian Sea derived from delta O-18 values
No full textIce export from the vast Arctic Siberian shelf is calculated using O-18 values and salinity data for water samples collected during the International Siberian Shelf Study between August and September 2008 (ISSS-08). The samples represent a wide range of salinities and O-18 values due to river water inputs and sea ice removal. We estimate the fraction of water that has been removed as ice by interpreting observed O-18 values and salinities as a result of mixing between river water and sea water end-members as well as to fractional ice removal. This method does not assume an ice end-member of fixed composition, which is especially important when applied on samples with large differences in salinity. The results show that there is net transport of ice from both the Laptev and the Eastern Siberian Seas, and in total 3000 km(3) of sea ice is exported from the shelf. The annual total export of ice from the entire region, calculated from the residence time of water on the shelf, is estimated to be 860 km(3) yr(-1). Thus, changes in ice production on the shelf may have great impact on sea ice export from the Arctic Ocean
Distribution and activity of nitrogen-fixing bacteria in marine and estuarine waters
No full textIn aquatic environments the availability of nitrogen (N) generally limits primary production. N2-fixing prokaryotes (diazotrophs) can convert N2 gas into ammonium and provide significant input of N into the oceans. Cyanobacteria are thought to be the main N2-fixers but diazotrophs also include a wide range of heterotrophic bacteria. However, their activity and regulation in the water column is largely unknown. In this thesis the distribution, diversity, abundance, and activity of marine and estuarine heterotrophic diazotrophs was investigated. With molecular methods targeting the nifH gene, encoding the nitrogenase enzyme for N2 fixation, it was shown that diverse nifH genes affiliating with heterotrophic bacteria were ubiquitous in surface waters from ten marine locations world-wide and the estuarine Baltic Sea. Through enrichment cultures of Baltic Sea surface water in anaerobic N-free medium, heterotrophic N2 fixation was induced showing that there was a functional N2-fixing community present and isolates of heterotrophic diazotrophs were obtained. In Sargasso Sea surface waters, transcripts of nifH related to heterotrophic bacteria were detected indicating heterotrophic N2-fixing activity. Nitrogenase expression is thought to be highly regulated by the availability of inorganic N and the presence of oxygen. Low oxygen zones within the water column can be found in association with plankton. The presence of diazotrophs as symbionts of heterotrophic dinoflagellates was investigated and nifH genes related to heterotrophic diazotrophs rather than the cyanobacterial symbionts were found, suggesting that a symbiotic co-existence prevailed. Oxic-anoxic interfaces could also be potential sites for heterotrophic N2 fixation. The Baltic Sea contains large areas of anoxic bottom water. At the chemocline and in anoxic deep water heterotrophic diazotrophs were diverse, abundant and active. These findings extend the currently known regime of N2 fixation to also include ammonium-rich anaerobic waters. The results of this thesis suggest that heterotrophic diazotrophs are diverse and widely distributed in marine and estuarine waters and that they can also be active. However, limits in the knowledge on their physiology and factors which regulate their N2 fixation activity currently prevent an evaluation of their importance in the global marine N budget
Treeline dynamics in short and long term perspectives : observational and historical evidence from the southern Swedish Scandes
No full textTreelines in high-mountain regions are constrained by heat deficiency, although the working mechanisms are still not entirely understood. Observational and paleoecological studies on treeline performance may contribute to increased understanding of the treeline phenomenon in general. The present thesis addresses elevational shifts of alpine treelines in the Swedish Scandes. By various analytical tools, the studies embrace widely different temporal scales. The concept treeline refers to the elevation (m a.s.l.) at a specific site of the upper individual tree of a certain tree species, at least 2 m tall. All the principal tree species in the Scandes are concerned, i.e. mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). Paper I deals with regional treeline dynamics at more than 100 sites over the past 100 years. Concurrent with temperature rise by c. 1.4 °C over the same period, maximum treeline advances of all species amount to about 200 m. Thus, under ideal conditions, treelines respond in close equilibrium with air temperature evolution. However, over most parts of the landscape, treeline upshifts have been much smaller than 200 m, which relates to the combined action of geomorphology, wind, snow distribution and soil depth. After 1975, the birch has lost its role as the most rapidly advancing tree species, being superseded by pine and spruce. Paper II is a short-term (2005/2007-2010/2011) study of mountain birch treeline performance along a regional maritimity-continentality gradient. Upshift by 3.0 yr-1 in the maritime part of the gradient contrasts to retreat by 0.4 m yr-1 in the continental part. In the latter area, earlier and more complete melting of late-lying snow patches has seemingly progressed to a state when soil drought sets back the vigour of existing birches and precludes sexual regeneration and upslope advance of the treeline. In the maritime area, extensive and deep snow packs still exist above the treeline and constrain its position, although some release is taking place in the current warm climate. Paper III explores treeline change by phenotypic transformation of old-established stunted and prostrate spruce individuals (krummholz) growing high above the treeline and is based on analyses of radiocarbon-dated megafossils, preserved in the soil underneath clonal groups of spruce. Living spruce clones, which in some cases may date back to the early Holocene (9500 cal. yr BP), suggests that spruce immigrated from “cryptic” ice age refugia much closer to Scandinavia than conventionally thought. As the krummholz form presupposes open and windy habitats, it is inferred that permanently open spots prevailed in the high-mountain landscape even during periods when treelines in general were much higher than today. Paper IV reports radiocarbon dates of wood samples, retrieved from newly exposed glacier forefields at three main sites, located high above the modern treelines and embracing the entire Swedish Scandes. It appears that pine colonized early emerging nunataks already during the Late Glacial. Around 9600-9500 cal. yr BP a first massive wave of tree establishment, birch and pine, took place in “empty” glacier cirques. Both species grew 400-600 m above their present day treeline position and accordingly, the summer temperatures may have been 3.5 °C warmer than present (uncorrected for land uplift). During the entire interval 9600 to 4400 cal. yr BP, birch prospered 100-150 m above the uppermost pines. In response to Neoglacial cooling, treelines of both birch and pine descended until their final disappearance from the record 4400 and 5900 cal. yr BP, respectively. Thereafter, these habitats experienced increased snow accumulation and glacier inception.Avhandlingen belyser förskjutningar i olika tidsskalor av den alpina trädgränsens läge i de svenska Skanderna. Trädgränsen definieras som den högsta nivån (m ö.h.) för minst 2 m höga individer av en viss art i en definierad del av en fjällsluttning. Avhandlingen består av fyra separata uppsatser, publicerade i olika välrenommerade vetenskapliga tidskrifter. I Paper I analyseras förändringar av trädgränserna för fjällens vanligaste trädarter, fjällbjörk, gran och tall (Betula pubescens ssp. czerepanovii, Picea abies och Pinus sylvestris) mellan 1915 och 2007. Undersökningen omfattar ett 8000 km2 stort, naturgeografiskt heterogent område, med mer än 100 lokaler. De maximala trädgränsförskjutningarna för samtliga trädarter uppgår till omkring 200 m. Resultaten motsvarar de trädgränsförskjutningar som teoretiskt kan förutsägas utifrån den temperaturhöjning med cirka 1,4 °C som skett under samma tidsperiod, förutsatt ideala förhållanden. För större delen av området råder emellertid andra, icke-ideala förhållanden, varför trädgränsernas uppflyttning i allmänhet blivit avsevärt mindre än 200 m. Den främsta anledningen till detta är lokala topoklimatiska begränsningar, d.v.s. kombinerade effekter av geomorfologi, vind, snöfördelning, jorddjup, etc., som i stora delar av det starkt brutna fjällandskapet mer eller mindre effektivt hindrar träden från att nå sina potentiellt högst belägna växtplatser betingade av temperaturen. Efter 1975 har björken förlorat sin roll som arten med den snabbast expanderande trädgränsen. I stället har tall och gran avancerat med större hastighet. Det innebär att även om klimatets uppvärmning fortsätter, så kommer det subalpina björkbältet att expandera i avsevärt mindre omfattning än vad som ofta förebådats. Möjligtvis kommer det att ersättas av tall. Paper II behandlar björkens trädgränsdynamik under perioden 2005/2007-2010/2011 längs en regional klimatgradient med avseende på maritimitet/kontientalitet. Trädgränsen har under den aktuella perioden avancerat 3,0 m/år i den maritimt präglade delen av gradienten, vilket kontrasterar signifikant mot en sänkning med 0,4 m/år i området med mer kontinentalt klimat. Skillnaderna diskuteras i termer av klimatförändringens varierande effekter på snötäckets utbredning och varaktighet och dess inverkan på markfuktigheten. En allt tidigare total utsmältning av snölegorna i de kontinentala områdena har av allt att döma resulterat i vattenbrist under sommaren. Torka medför reducerad vitalitet för existerande björkar och förhindrar både sexuell förökning och uppflyttning av trädgränsen. I de maritima delarna kvarligger alltjämt mycket snö under en stor del av sommaren. Trädgränsens position har därför kunnat bibehållas eller flyttas upp. Vissa omständigheter tyder på att trädgränsens stigning i högre grad har varit baserad på fröföryngring efter 1975, jämfört med perioden 1915-1975. Utgångspunkten för Paper III är erfarenheter från Paper I, som visar att trädgränsens uppflyttning för gran och björk huvudsakligen är resultatet av ökad höjdtillväxt av äldre, i vissa fall flertusenåriga, mer eller mindre buskformiga individer (krummholz), som vuxit på nivåer långt ovanför trädgränsen. Som ett svar på de senaste hundra årens varmare klimat har dessa antagit trädform, varigenom trädgränsen höjts. För en fördjupad förståelse av den här mekanismen har megafossil, d.v.s. grova vedrester bevarade i marken under gamla grankloner i trädgränsekotonen, 14C-daterats. Resultaten tyder på att granar i exponerad fjällmiljö kan uppnå i det närmaste ”evigt” liv genom sin förmåga till vegetativ förökning och möjligheten att växla mellan busk- och trädform i takt med klimatets växlingar. Vissa nu levande kloner existerade av allt att döma redan för 9500 år sedan. Den nu dokumenterat tidiga förekomsten av gran, bekräftar den på senare tid allt tydligare bilden av granen som en tidig invandrare till fjällkedjan. Möjligtvis har granen ”övervintrat” den senaste istiden närmare Skandinavien än vad som till helt nyligen varit den gängse uppfattningen. Paper IV behandlar en för Skandinavien ny metod för historisk trädgränsrekonstruktion. I uppsatsen analyseras 14C-dateringar av totalt 78 större veddelar (megafossil) som nyligen exponerats i anslutning till smältande glaciäris och ”perenna” snölegor i tre huvudområden, Helags-Sylarna, Tärna och Abisko, högt ovanför dagens trädgräns. Det framkommer att tall (Pinus sylvestris) koloniserade tidigt framsmälta nunatakker redan under senglacial tid. För omkring 9600-9500 år sedan inträffade en första massiv våg av björk- och talletablering i isfria glaciärnischer. Båda arterna växte 400-600 m ovanför sina nuvarande trädgränspositioner, i ett klimat som kan ha varit 3,5 °C varmare än idag. Under intervallet 9600 till 4400 BP uppträdde björken i ett 100-150 m brett bälte ovanför de översta tallarna. Som ett svar på klimatets successiva avkylning under senare delen av Holocen sänktes både björkens och tallens trädgränser i de aktuella miljöerna, till dess de för 4400 respektive 5900 år sedan helt försvann från lokaler där glaciärer och perenna snöfält började bildas. De analyserade trädresterna, som länge bevarats av glaciäris och perenn snö representerar en period med ett klimat långt varmare än under det senaste århundradet. Med denna analogi från det förflutna kan det därför antas att i en framtid där sommartemperaturerna rent hypotetiskt är 3,5 °C högre än i nutiden, skulle trädgränserna lokalt kunna flyttas upp med ungefär 600 m
Birds and mammals of the northern coast of Argentina: first report of an association between birds and a feeding Pygmy Right Whale Caprea marginata : Fåglar och däggdjur utanför Argentinas norra kust: första rapporten om fåglar födosökande tillsammans med dvärgrätval Caprea marginata
No full textWhen the icebreaker Oden passed between 39°36’S, 57°46’W and 39°59’S, 58°11’W on 20 November 2007, an extraordinary observation was made. A feeding Pygmy Right Whale Caprea marginata, a species rarely seen, was attended by eight Grey Phalaropes Phalaropus fulicarius, two Slender-billed Prions Pachyptila belcheri, and four Wilson’s Storm Petrels Oceanites oceanicus. The birds returned to feed around the head of the whale every time it surfaced, presumably copepod plankton straining out between the baleen. The site is off Rio de la Plata estuary where nutrient rich freshwater meets cold water of the Malvinas (Falkland) Current, creating a hotspot with high levels of plankton food. The conditions were extraordinarily favourable for observation with a calm sea, no wind and only a very weak swell. Six multispecies feeding groups were seen with a total of 42 species of birds, eleven species of whales, dolphins and porpoises, and three species of seals. Dusky Dolphins Lagenorhynchus obscurus and Great Shearwaters Puf¿- nus gravis were predominant in the groups
Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres : the importance of nitric oxide
No full textThe relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic K indices) is examined. Calibrated PMSE reflectivities for the period May 2006-February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68 degrees N, geomagnetic latitude 65 degrees) and at two different sites in Queen Maud Land, Antarctica (73 degrees/72 degrees S, geomagnetic latitudes 62 degrees/63 degrees). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle precipitation, the delayed response can largely be explained by changes in nitric oxide concentrations. Observations of nitric oxide concentration at PMSE heights by the Odin satellite support this hypothesis. Sensitivity to geomagnetic disturbances, including nitric oxide produced during these disturbances, can explain previously reported differences between sites in the auroral zone and those at higher or lower magnetic latitudes. The several-day lifetime of nitric oxide can also explain earlier reported discrepancies between high correlations for average conditions (year-by-year PMSE reflectivities and K indices) and low correlations for minute-to-day timescales