This thesis explores the factors controlling the distribution of black carbon (BC) in the atmosphere/troposphere and its implications for climate forcing. BC is of great climate interest because of its warming potential. Estimates of BC climate forcing have large uncertainty, in part due to poor knowledge of the distribution of BC in the atmosphere. This dissertation first examines the factors controlling the sources of BC in the Arctic in winter and spring using a global chemical transport model (GEOS-Chem). Emission inventories of BC and wet scavenging of aerosols in the model are updated to reproduce observed atmospheric concentrations of BC as well as observed snow BC content in the Arctic in winter-spring. The simulation shows a dominant contribution of fuel (fossil fuel and biofuel) combustion to BC in Arctic spring. Arctic snow BC content is dominated by fuel combustion sources in winter, but has equal contributions from open fires and fuel combustion in spring. The estimated decrease in Arctic snow albedo due to BC deposition in spring is 0.6%, resulting in a regional surface radiative forcing of 1.2 W m-2. The dissertation then extends the evaluation of the BC simulation to the global scale using aircraft observations over source regions, continental outflow and remote regions and ground-based measurements. The observed low BC concentrations over the remote oceans imply more efficient BC removal than is currently implemented in models. The simulation that has total BC emissions of 6.5 Tg C a-1 and a mean tropospheric lifetime of 4.2 days for 2009 (vs. 6.8 &plusmn 1.8 days for the AeroCom models) captures the principal features of observed BC. The simulation estimates a global mean BC absorbing aerosol optical depth of 0.0017 and a top-of-atmosphere direct radiative forcing (DRF) of 0.19 W m-2, with a range of 0.17-0.31 W m-2 based on uncertainties in the BC atmospheric distribution. The DRF is lower than previous estimates, which could be biased high because of excessive BC concentrations over the oceans and in the free troposphere. / Engineering and Applied Sciences

No description available.

In June, 1959, I entered into a contract with the United States Atomic Energy Commission (Contract No. AT(04-3-315) to direct a programme of human geographical studies in Northwestern Arctic Alaska. These studies were part of the bio-environmental programme for Project Chariot. They were centred on the Eskimo village of Point Hope but included the villages of Noatak and Point Lay. Although the contract terminated on June 1st, 1961 I remained in arctic Alaska for an additiona1 year of research. [...]

Glaciated areas offer a unique opportunity to study the dispersal of animals. During glaciation the fauna of glaciated areas was either destroyed or forced into unglaciated refugia. When the icesheets retreated the glaciated regions were open to reinvasion. [...]

The Arctic is considered as a focal region in the ongoing climate change debate. The currently observed and predicted climate warming is particularly pronounced in the high northern latitudes. Rising temperatures in the Arctic cause progressive deepening and duration of permafrost thawing during the arctic summer, creating an ‘active layer’ with high bioavailability of nutrients and labile carbon for microbial consumption. The microbial mineralization of permafrost carbon creates large amounts of greenhouse gases, including carbon dioxide and methane, which can be released to the atmosphere, creating a positive feedback to global warming. However, to date, the microbial communities that drive the overall carbon cycle and specifically methane production in the Arctic are poorly constrained. To assess how these microbial communities will respond to the predicted climate changes, such as an increase in atmospheric and soil temperatures causing increased bioavailability of organic carbon, it is necessary to investigate the current status of this environment, but also how these microbial communities reacted to climate changes in the past. This PhD thesis investigated three records from two different study sites in the Russian Arctic, including permafrost, lake shore and lake deposits from Siberia and Chukotka. A combined stratigraphic approach of microbial and molecular organic geochemical techniques were used to identify and quantify characteristic microbial gene and lipid biomarkers. Based on this data it was possible to characterize and identify the climate response of microbial communities involved in past carbon cycling during the Middle Pleistocene and the Late Pleistocene to Holocene. It is shown that previous warmer periods were associated with an expansion of bacterial and archaeal communities throughout the Russian Arctic, similar to present day conditions. Different from this situation, past glacial and stadial periods experienced a substantial decrease in the abundance of Bacteria and Archaea. This trend can also be confirmed for the community of methanogenic archaea that were highly abundant and diverse during warm and particularly wet conditions. For the terrestrial permafrost, a direct effect of the temperature on the microbial communities is likely. In contrast, it is suggested that the temperature rise in scope of the glacial-interglacial climate variations led to an increase of the primary production in the Arctic lake setting, as can be seen in the corresponding biogenic silica distribution. The availability of this algae-derived carbon is suggested to be a driver for the observed pattern in the microbial abundance. This work demonstrates the effect of climate changes on the community composition of methanogenic archae. Methanosarcina-related species were abundant throughout the Russian Arctic and were able to adapt to changing environmental conditions. In contrast, members of Methanocellales and Methanomicrobiales were not able to adapt to past climate changes. This PhD thesis provides first evidence that past climatic warming led to an increased abundance of microbial communities in the Arctic, closely linked to the cycling of carbon and methane production. With the predicted climate warming, it may, therefore, be anticipated that extensive amounts of microbial communities will develop. Increasing temperatures in the Arctic will affect the temperature sensitive parts of the current microbiological communities, possibly leading to a suppression of cold adapted species and the prevalence of methanogenic archaea that tolerate or adapt to increasing temperatures. These changes in the composition of methanogenic archaea will likely increase the methane production potential of high latitude terrestrial regions, changing the Arctic from a carbon sink to a source. / Die Arktis ist in den gegenwärtigen Diskussionen zum Klimawandel von besonderem Interesse. Die derzeitig beobachtete globale Erwärmung ist in den hohen nördlichen Breiten besonders ausgeprägt. Dies führt dazu, dass ehemals gefrorene Böden zunehmend tiefer auftauen und daher im Boden enthaltene Kohlenstoffquellen für die mikrobielle Umsetzung und Mineralisierung zur Verfügung stehen. Aufgrund dieser Prozesse entstehen klimarelevant Gase, darunter Kohlendioxid und Methan, die aus den Böden und Sedimenten freigesetzt werden können. Wenn man bedenkt, dass in den nördlichen Permafrostgebieten die Hälfte des weltweit unter der Bodenoberfläche gelagerten Kohlenstoffs gelagert ist, wird die Bedeutung dieser Region für das Verständnis des globalen Kohlenstoffkreislaufes und der möglichen Treibhaus-gasemissionen sichtbar. Trotz dieser Relevanz, sind die am Kohlenstoffumsatz beteiligten Mikroorganismen in der Arktis wenig untersucht und ihre Anpassungsfähigkeit an die gegenwärtigen Klimaveränderungen unbekannt. Die vorliegende Arbeit untersucht daher, wie sich Klimaveränderungen in der Vergangenheit auf die Anzahl und Zusammensetzung der mikrobiellen Gemeinschaften ausgewirkt haben. Dabei liegt ein besonderer Fokus auf die methanbildenden Archaeen, um das Verständnis der mikrobiellen Methandynamik zu vertiefen. Im Rahmen dieser Arbeit wurden drei Bohrkerne aus zwei verschiedenen Standorten in der russischen Arktis untersucht, darunter terrestrischer Permafrost und Seesedimente aus Sibirien und Chukotka, Russland. Mittels der Identifikation und Quantifizierung von mikrobiellen Genen und charakteristischen Bestandteilen der mikrobiellen Zellmembran war es möglich, fossile mikrobielle Gemeinschaften in Seesedimenten mit einem Alter von bis zu 480 000 Jahren und in Permafrostablagerungen mit einem Alter von bis zu 42 000 Jahren zu rekonstruieren. Es wurde gezeigt, dass es während vergangener warmen Perioden zu einem Wachstum von Bakterien und Archaeen in allen untersuchten Standorten gekommen ist. Dieser Trend konnte auch für die Gemeinschaft der methanogenen Archaeen gezeigt werden, die während warmen und insbesondere feuchten Klimabedingungen in großer Anzahl und Diversität vorhanden waren, was wiederrum Rückschlüsse auf mögliche Methanemissionen erlaubt. In den terrestrischen Permafroststandorten wird der Temperaturanstieg als direkte Ursache für die gefundene Reaktion der mikrobiellen Gemeinschaft vermutet. Im Gegenzug dazu, führte der Temperaturanstieg im untersuchten arktischen See wahrscheinlich zu einer erhöhten Primärproduktion von organischem Kohlenstoff, die wiederum das Wachstum der Mikroorganismen antrieb. Weiterhin konnte im Rahmen dieser Arbeit gezeigt werden, dass Methanosarcina-verwandte Spezies in der Russischen Arktis weit verbreitet sind und sich an veränderte Umweltbedingungen gut anpassen können. Im Gegensatz dazu stehen Vertreter von Methanocellales und Methano-microbiales, die nicht in der Lage sich an veränderte Lebensbedingungen anzupassen. Im Rahmen dieser Arbeit konnte erstmalig gezeigt werden, dass es in früheren Warmphasen zu einem vermehrten Wachstum der an der Umsetzung des organischen Kohlenstoffs beteiligten Mikroorganismen in der Russischen Arktis gekommen ist. Im Zusammenhang mit der zukünftigen Erwärmung der Arktis kann also von einer Veränderung der am Kohlenstoffkreislauf beteiligten Mikroorganismen ausgegangen werden kann. Mit den steigenden Temperaturen werden sich einige Vertreter der methanproduzierenden Mikroorganismen an die veränderten Bedingungen anpassen können, während Temperatur-empfindliche Vertreter aus dem Habitat verdrängt werden. Diese Veränderungen in der mikrobiellen Gemeinschaft können die Methanproduktion der hohen noerdlichen Breiten erhoehen und dazu beitragen, dass aus der Arktis als eine Kohlenstoffsenke eine Kohlenstoffquelle wird.

Throughout the late 20th and early 21st century, the global temperature has been on the rise, a process that has been accelerated in the Arctic. The Arctic surface temperatures have risen at a factor of 3 greater rate than the global average, leading to the term Arctic Amplification of climate change. In this study, the enhanced warming of the Arctic, and the enhancement at the Arctic surface in comparison to the warming of the atmosphere aloft, is investigated through a reconstruction of the past surface energy balance by a model driven by downwelling irradiance reconstructed using radiosonde profiles and the radiative transfer code SBDART. The downwelling irradiance is shown to be increasing over the time-period of 1994-2009, and the sources of this increase are diagnosed. The time-evolution of the surface flux terms are discussed, and the sensitivity of the surface temperature to changes in atmospheric temperature is investigated.

Until recently it has been widely believed that significant anthropogenic influences on the environment began in Canada following the onset of European colonization. However, our paleolimnological data indicate that centuries prior to European settlement, ponds on Ellesmere and Bathurst Island were impacted by Thule Inuit whalers, whose activities altered nutrient levels in nearby ponds. Two Thule Inuit whaling sites were selected based on input from several archaeologists, to ensure good coverage of the Thule geographic range and proximity to freshwater ponds. Multiple independent paleolimnological proxies have been used to analyze a pond from Ellesmere Island, showing taxonomic shifts in diatoms assemblages coinciding with 1.5 - 2‰ shifts in d15N, during the period of Thule occupation (ca. 1000 – 1670 AD). Increases in the relative abundance of Amphora ovalis, indicate nutrient concentrations above average for the High Arctic. Elevated levels of nitrogen and phosphorus were observed in the pond indicating the continuing influence of nutrient inputs centuries after the abandonment of the camp. Meanwhile, on Bathurst Island, the orientation of the Deblicquy site, such that the large majority of the Thule nutrient inputs are focused towards one of our two study ponds, provided us with the opportunity to compare two ponds that are essentially identical with the exception of the degree of Thule influence. In our “impacted” site, a marked increase in Stephanodiscus minutulus, coincides with a 2‰ shift in d15N. While our a priori determined control site shows no major changes in geochemistry or algal composition. Previous research on Bathurst Island used water chemistry and surface sediment diatoms to construct a diatom-inferred total nitrogen model for Bathurst Island. However, this study was limited by excluding unbuffered, low pH sites which characterize the western half of Bathurst Island. By expanding the previous Bathurst Island dataset to include western sites, we have been able to construct a diatom-inferred pH model which will prove invaluable in future climate research in this region. Together, these three studies serve to highlight the sensitivity of freshwater ecosystems to relatively minor anthropogenic disturbances and represent some of the earliest known anthropogenic impacts on North American aquatic ecosystems. / Thesis (Master, Biology) -- Queen's University, 2007-12-20 15:20:46.342

Paleoclimatic research in the Canadian Arctic has increased in recent decades; however, there is still much to learn about the nature and extent of past climate change in this vast, environmentally sensitive region. This thesis uses diatom assemblages in dated lake sediment cores as proxy indicators to infer how climate has changed over the Holocene in two very different lakes in the central Canadian Arctic: one located in a poorly-studied geographical region, and another possessing limnological characteristics that are unusual in an Arctic context. Lake TK-2 is located in the low Arctic tundra. Paleolimnological studies from this region are lacking, as most have centered on sites in the High Arctic Archipelago or around Subarctic treeline. Marked changes in the diatom assemblages in TK-2 throughout the Holocene included potential evidence for the 8.2k cooling event, which has not been previously reported from other Canadian Arctic paleolimnological studies. In addition, diatom shifts occurring ~7000 and ~3500 cal yr BP are indicative of mid-Holocene warming and subsequent Neoglacial cooling, respectively, the timings of which agree with those from other studies farther south. Finally, shifts in the diatom assemblages in the upper sediment layers, beginning in the early-to-mid 19th century, are consistent with reduced ice cover, related to recent warming. Stygge Nunatak Pond, a small, closed-basin pond located on a nunatak in the High Arctic on Ellesmere Island, is characterized by unusually high ionic concentrations for an inland Arctic pond. As in TK-2, Stygge’s diatom assemblages changed substantially throughout the Holocene, but especially in the most recent sediments. Diatom shifts near ~10,500 cal yr BP suggest an early onset for the Holocene Thermal Maximum (and for the successive Neoglacial cooling trend) in this region, consistent with previous studies from the High Arctic. Marked diatom assemblage changes occurred in the most recent sediments, and are indicative of climate warming and reduced ice cover, as well as increased ionic concentration due to enhanced evaporative concentration. The dynamic nature of the diatom assemblage changes at the Stygge site suggests that sediments from these rare athalassic ponds represent an especially sensitive archive of Arctic climatic and environmental change. / Thesis (Master, Biology) -- Queen's University, 2008-11-12 16:46:47.174

Soil nitrogen availability to plants is a fundamental control on the structure and functioning of arctic tundra ecosystems. Despite recent evidence that biogeochemical and microbial dynamics during the non-growing season impact nitrogen availability to plants in tundra ecosystems, very little is known about soil microbial patterns and mechanisms for nutrient mobilization in the winter, spring and fall. In this dissertation I have examined the environmental and microbial controls on seasonal nitrogen mobilization in a widespread Canadian low arctic birch hummock tundra ecosystem. In particular, I have investigated the potential for increased winter snow depth and different above-ground vegetation-types to alter soil microbial community patterns and nutrient mobilization from organic matter into plant-available pools. First, I demonstrated that experimentally deepened winter snow altered soil microbial physiology during winter, defined as increased microbial carbon limitation to growth and activity. Second, I established that deepened snow enhanced spring nutrient mobilization during distinct environmental phases, producing large peaks in the soil microbial biomass and soil solution carbon, nitrogen and phosphorus during snow thaw. Third, I showed that laboratory predictions of early-spring air temperature freeze-thaw cycles promoting tundra soil nitrogen loss are not relevant, as the soil environment and soil biogeochemistry were relatively stable after snow melt and before plant growth began. Fourth, I demonstrated that microbial functional groups did not differ strongly under different tundra vegetation types, but higher quality shrub litter induced positive feedbacks on soil carbon availability and soil nitrogen mineralization in the late summer. Finally, I illustrated that annual patterns of tundra soil microbial community structure and composition were strongly linked to soil biogeochemistry and that significant shifts in fungal/bacterial ratios occur during snowmelt. This research suggests two broad conclusions: a) that soil microbial activity is responsive to changes in above-ground vegetation; and b) that seasonal changes in microbial community structure and microbial biochemistry are strongly correlated. Therefore, the synchronicity of microbial seasonal succession and plant species-specific timing of nitrogen uptake is a critical factor restricting the potential for ecosystem N losses at spring thaw and ultimately in supplying growth-limiting nutrients to plants in the following summer. / Thesis (Ph.D, Biology) -- Queen's University, 2009-09-25 23:29:53.103

No description available.