The study of long-term climatic change in the Arctic, a region both particularly sensitive to the effects of a warming climate and an important driver of global climate, is pertinent to understanding the rates and magnitude of current ecosystem changes. Analyses on geological time frames provide insight into the variability of Arctic climate, allowing a contextualized understanding of recent ecosystem changes that have been documented across the Arctic. Lake CF8, a mid-Arctic lake on Clyde Foreland, Baffin Island, contains a unique sedimentary archive of the present and last two interglacial periods, due to past non-erosive glaciation patterns, providing an opportunity to study interglacial climate trends. Diatom assemblages were analyzed through the organic sediment record of the past three interglacials. Trends in the ontogeny of this lake were revealed: the early, post-glacial environment was dominated by species of the colonial Fragilaria genera, which transitioned into high relative abundances of tychoplanktonic Aulacoseira species. Benthic/periphytic taxa, such as Psammothidium marginulatum, tended to increase in relative abundance in the mid- to late-interglacial periods. The ecological interpretation of this pattern is examined in this study, and suggests that climate drives the succession of the diatom community primarily through indirect effects on lake ice and pH. The extent of ice cover likely plays a large role in the biotic community of this lake; the diatom assemblages within the past ~ 50 years indicate increasing littoral habitat complexity with a peak in Eunotia species and a slightly acidic pH, which is discussed in relation to changing habitat availability associated with decreasing ice cover. In-lake production was examined through the use of spectrally-inferred chlorophyll a trends, which also indicate elevated production in the past ~ 50 years. As climate change becomes an increasingly significant threat to the stability of Arctic ecosystems, interest in paleoclimate records that extend into past, non-anthropogenically mediated warm periods, is increasing. This sediment record extends our understanding of past environmental trends beyond the longest records in this part of the Arctic, the Greenland ice core records, and enhances our understanding of the variability of Arctic climate. / Thesis (Master, Biology) -- Queen's University, 2009-05-06 17:04:38.302

This thesis presents new insights into the chemical composition of semi-volatile compounds in aerosol samples collected in the central Arctic Ocean close to the North Pole in September 2018. The central Arctic Ocean is an inaccessible location due to the lack of land areas along with heavy pack ice conditions. Therefore, large knowledge gaps remain to understand the Arctic climate system, and in particular the role of aerosol particles in its pristine atmosphere. The chemical composition of the aerosol samples was analysed on a molecular level using High Resolution Time-of-Flight Chemical Ionization Mass Spectrometry coupled to a Filter Inlet for Gases and AEROsols (FIGAERO-HRToF-CIMS). The analysis revealed a significant signal from compounds that are likely from marine sources. One important precursor for marine aerosols is dimethyl sulfide (DMS), a gas released by phytoplankton and ice algae in the Arctic Ocean. DMS oxidises in the atmosphere to produce oxidation products that can contribute to aerosol growth. Analysis of air mass origin with backward trajectories showed that the highest ambient DMS concentrations originated from marine areas around the pack ice. However, no correlation could be shown within the pack ice between ambient DMS and its oxidation product methanesulfonic acid (MSA) in the particle phase. As FIGAERO-HRToF-CIMS is commonly used in areas with higher particle concentrations and has never been used in the central Arctic before, this thesis further demonstrates its suitability for measurements of aerosol chemical composition in this remote region. / Denna avhandling ämnar att presentera nya kunskaper om den kemiska sammansättningen av halvflyktiga föreningar i aerosolprover som samlades in i Norra ishavet nära Nordpolen i september 2018. Den innersta delen av Norra ishavet är svårtillgängligt på grund av bristen på fasta landområden ihop med kompakt packis. Därför kvarstår stora kunskapsluckor i förståelsen av klimatsystemet i Arktis, och i synnerhet aerosolpartiklars roll i dess orörda atmosfär. Den kemiska sammansättningen av aerosolproverna analyserades på molekylnivå med högupplöst kemisk joniseringsmasspektrometri kopplad till ett filterinsläpp för gaser och aerosoler (FIGAERO-HRToF-CIMS). Analysen visade på en tydlig signal från föreningar som sannolikt har marina källor. En viktig kemisk föregångare till marina aerosoler är dimetylsulfid (DMS), en gas som frigörs av fytoplankton och isalger i Ishavet. DMS oxiderar i atmosfären till oxidationsprodukter som kan bidra till en storleksökning av aerosoler. Genom analys av provluftens ursprung med trajektorieanalys visades att de högsta DMS-koncentrationerna kom från havsområdena runt packisen. Ingen korrelation kunde emellertid visas inom packisområdet mellan DMS i gasfas och dess oxidationsprodukt metansulfonsyra (MSA) i partikelfas. Eftersom FIGAERO-HRToF-CIMS ofta används i områden med högre partikelkoncentrationer och aldrig har använts i de inre delarna av Arktis tidigare, visar denna avhandling även att tekniken är lämplig för att mäta den kemiska sammansättningen av aerosoler i detta avlägsna polarområde.

<p>The boundary layer is the part of the atmosphere that is in direct contact with the ground via turbulent motion. At mid-latitudes the boundary layer is usually one or a few kilometers deep, while in the Arctic it is much more shallow, typically a few hundred meters or less. The reason is that here the absolute temperature increases in the lowest kilometer, making the boundary layer semi-permanently stably stratified. The exchange of heat, momentum and tracers between the atmosphere, ocean and ground under stable stratification is discussed from an observational, modeling and climate-change point of view. A compilation of six observational datasets, ordered by the Richardson number (rather than the widely used Monin-Obukhov length) reveals new information about turbulence in the very stably stratified regime. An essentially new turbulence closure model, based on the total turbulent energy concept and these observational datasets, is developed and tested against large-eddy simulations with promising results. The role of mesoscale motion in the exchange between the atmosphere and surface is investigated both for observations and in idealized model simulations. Finally, it is found that the stably stratified boundary layer is more sensitive to external surface forcing than its neutral and convective counterparts. It is speculated that this could be part of the explanation for the observed Arctic amplification of climate change.</p>

The boundary layer is the part of the atmosphere that is in direct contact with the ground via turbulent motion. At mid-latitudes the boundary layer is usually one or a few kilometers deep, while in the Arctic it is much more shallow, typically a few hundred meters or less. The reason is that here the absolute temperature increases in the lowest kilometer, making the boundary layer semi-permanently stably stratified. The exchange of heat, momentum and tracers between the atmosphere, ocean and ground under stable stratification is discussed from an observational, modeling and climate-change point of view. A compilation of six observational datasets, ordered by the Richardson number (rather than the widely used Monin-Obukhov length) reveals new information about turbulence in the very stably stratified regime. An essentially new turbulence closure model, based on the total turbulent energy concept and these observational datasets, is developed and tested against large-eddy simulations with promising results. The role of mesoscale motion in the exchange between the atmosphere and surface is investigated both for observations and in idealized model simulations. Finally, it is found that the stably stratified boundary layer is more sensitive to external surface forcing than its neutral and convective counterparts. It is speculated that this could be part of the explanation for the observed Arctic amplification of climate change.

Water chemistry and bioindicators (diatoms and invertebrates) were examined for freshwater lakes, ponds and streams in two regions within Sirmilik National Park, northern Baffin Island, Nunavut. Significant differences were recorded between the water chemistry and diatom and invertebrate assemblages of the two regions. Modern diatom assemblages were explained mainly by specific conductivity, ORP, pH, temperature, elevation and distance from the coast. Paleolimnological techniques were applied to a sediment core from Lake BY14 on Bylot Island. Fossil diatom assemblages indicate increases in nutrients and temperature since 1935 AD. The diatom biostratigraphy does not show as large an increase in diversity and production since the middle 20th century as has been noted elsewhere, and this may be a reflection of the more nutrient-rich status of the lake relative to other Arctic lakes.

Water chemistry and bioindicators (diatoms and invertebrates) were examined for freshwater lakes, ponds and streams in two regions within Sirmilik National Park, northern Baffin Island, Nunavut. Significant differences were recorded between the water chemistry and diatom and invertebrate assemblages of the two regions. Modern diatom assemblages were explained mainly by specific conductivity, ORP, pH, temperature, elevation and distance from the coast. Paleolimnological techniques were applied to a sediment core from Lake BY14 on Bylot Island. Fossil diatom assemblages indicate increases in nutrients and temperature since 1935 AD. The diatom biostratigraphy does not show as large an increase in diversity and production since the middle 20th century as has been noted elsewhere, and this may be a reflection of the more nutrient-rich status of the lake relative to other Arctic lakes.

The Arctic is an important component of the Earth’s climate system, and it is a region dynamically coupled to climate phenomena at lower latitudes, through both atmospheric and oceanic paths. The coupling has significant effects on the hydroclimate variability in the Arctic, including effects on sea ice and Arctic precipitation. In this dissertation, we explore the coupling of the lower latitudes and the Arctic hydroclimate through atmospheric mechanisms with dynamical and thermodynamical components, with a focus on the following examples of variability: i) the decadal variability of boreal winter Arctic precipitation, ii) the variability of the strength of the stratospheric polar vortex in boreal winter, and iii) the initial melt of Arctic sea ice in late boreal spring. The goal of the research is to understand what drives the Arctic hydroclimate variability in each of these examples through improved knowledge of the mechanisms linking them to the tropics and Northern Hemisphere midlatitudes. In the first part of the analysis, we explore the mechanisms responsible for the decadal variability of boreal winter Arctic precipitation. We find that the decadal variability of cool-season Arctic precipitation is at least partly connected to decadal modulation of tropical central Pacific sea surface temperatures related to the El Niño-Southern Oscillation (ENSO). The modulation can be described as the oscillation between periods favoring central and eastern Pacific warming events [CPW and EPW, respectively], which are two common types of ENSO variability. By analyzing a collection of CPW and EPW events in reanalysis data, we establish the following connecting mechanism. First, the increase of central Pacific SSTs drive a Rossby wave train that destructively interferes with the zonal wavenumber 1 component of the background extratropical planetary wave in the subpolar region. Next, as a result of this interference, the magnitude of the vertical Rossby wave propagation from the troposphere to the stratosphere decreases and the stratospheric polar vortex strengthens. Finally, the strengthening of the vortex translates into a tendency towards a positive Arctic Oscillation (AO) in the troposphere and a poleward shift of the Northern Hemisphere midlatitude storm tracks, increasing moisture transport from lower latitudes and increasing total Arctic precipitation. In a further investigation of a crucial component of the above mechanism, the initial response of the stratospheric polar vortex to the influence of CPW and EPW is investigated. A 20-member ensemble run of an idealized model experiment in the NCAR Whole Atmosphere Community Climate Model (WACCM) is conducted with prescribed CPW and EPW pattern SST anomalies. Both CPW and EPW events weaken the polar vortex in the ensemble mean. The weakening is mainly tied to changes in the eddy-driven mean meridional circulation, with some contribution from eddy momentum flux convergence. There is a significant spread between ensemble members with identical CPW and EPW forcing, where a few of the ensemble members exhibit a weak strengthening response. The initial conditions of the extratropical atmosphere and subsequent internal variability after the introduction of the CPW and EPW forcing help drive the spread in response between individual members. In the last part of the analysis, using MERRA reanalysis data, the means by which atmospheric eddies affect the trend and variability of the initial melt of Arctic sea ice are explored. We focus specifically on the effects of lower troposphere (i.e. 1000-500 mb average) meridional heat transport by atmospheric eddies, a dynamical component of the atmospheric eddy mechanism, and eddy-generated surface downwelling shortwave and longwave radiation anomalies, a thermodynamical component. Although in a climatological sense, atmospheric eddies in all major frequency bands transport heat poleward into the Arctic, we find that the lower-troposphere eddy meridional heat transport does not contribute to the trend of an earlier initial melt date. However, eddy heat transport still plays an important role in the initialization of individual episodes of initial melt with large areal coverage. In the investigation of two specific episodes, the meridional heat transport term that represents the interaction between the eddy wind and mean temperature fields (i.e. the product of the meridional eddy wind and the mean temperature fields) is most associated with the initial melt in both episodes. Additionally, melt in one of the episodes is also associated with surface downwelling longwave and shortwave radiation anomalies, a result of eddy-generated cloud cover anomalies. Therefore, in individual melt events, the combination of direct eddy meridional heat transport and surface longwave and eddy-driven shortwave radiation anomalies may significantly contribute to the initial melt of Arctic sea ice. This combination may be especially important in episodes where significant initial melt occurs over a large area and over a period of a few days.

The seasonal cycle of snow and sea ice is a fundamental feature of the Arctic climate system. In the Northern Hemisphere, about 55 million km2 of sea ice and snow undergo complete melt and freeze processes every year. Because snow and sea ice are much brighter (higher albedo) than the underlying surface, their presence reduces absorption of incoming solar energy at high latitudes. Therefore, changes of the sea-ice and snow cover have a large impact on the Arctic climate and possibly at lower latitudes. One of the most important determining factors of the seasonal snow and sea-ice cover is the timing of the seasonal melt-freeze transitions. Hence, in order to better understand Arctic climate variability, it is key to continuously monitor these transitions. This thesis presents an algorithm for obtaining melt-freeze transitions using scatterometers over both the land and sea-ice domains. These satellite-borne instruments emit radiation at microwave wavelengths and measure the returned signal. Several scatterometers are employed: QuikSCAT (1999–2009), ASCAT (2009–present), and OSCAT (2009–present). QuikSCAT and OSCAT operate at Ku-band (λ=2.2 cm) and ASCAT at C-band (λ=5.7 cm), resulting in slightly different surface interactions. This thesis discusses these dissimilarities over the Arctic sea-ice domain, and juxtaposes the time series of seasonal melt-freeze transitions from the three scatterometers and compares them with other, independent datasets. The interactions of snow and sea ice with other components of the Arctic climate system are complex. Models are commonly employed to disentangle these interactions. But this hinges upon robust and well-formulated models, reached by perpetual testing against observations. This thesis also presents an evaluation of how well eleven state-of-the-art global climate models reproduce the Arctic sea-ice cover and the summer length—given by the melt-freeze transitions—using surface observations of air temperature. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 4: Submitted.</p>

Insect pollinators serve a critical role in maintaining plant biodiversity and are especially susceptible to changes within their environment. To study the possible effects of seasonal variation in temperature, as well as climatic temperature increase on the plant-pollinator community, the relationship between bumblebee and flowering plant traits along an elevational gradient, representing warming-induced changes in plant community, were examined. Two hypotheses were tested; 1) if plant traits can predict visiting bumblebee proboscis length, and 2) if the relationship between plant traits and proboscis length is influenced by elevation, and the progression of the growing season. The study took place along an elevational gradient on Mt. Nuolja in Abisko National Park, Sweden. During surveys bumblebees were caught and measured. Flowers visited by captured bumblebees were collected, categorized by restrictiveness (i.e., whether or not the flower require a certain proboscis length, in order to access the nectar and pollen rewards) and floral traits measured (e.g., petal length). The results revealed that petal length was a significant predictor of bumblebee proboscis length, when taking restrictiveness into account. Furthermore, the relationship became weaker with increasing elevation for restrictive flowers but stronger for unrestrictive flowers. These findings show that trait-matching between bumblebees and flowers is an influential factor for flower selection and is affected by climatic temperature. This highlights the importance of considering individual-level traits when studying plant preference and creates a framework for assessing plant-pollinator networks. Future studies should examine additional traits that could explain the apparent size matching between unrestrictive flowers and proboscis.

As the climate warms, Arctic bumblebee species face the loss of habitat and must deal with increased competition from southern species tracking their thermal and habitat niches north, for example Bombus terrestris. Previous studies demonstrate that bumblebees follow Bergmann’s rule, i.e., larger body sizes at higher latitudes, despite bumblebees not being considered truly ectothermic, as they can generate heat through muscular activity (i.e., beating their wings). This study seeks to confirm and understand the relationship between body size and temperature using an elevational gradient as a proxy for climate. In this study, I examined 13 plots (420-1164 m.a.s.l.) set along the 3.4 km transect up the slope of Mt. Nuolja in Abisko National Park, Sweden. For body size, I chose to use the commonly accepted proxy distance between the base of the wings (i.e., intertegular distance). For temperature, I chose the mean temperature at time of visitation. Results show that climate is a significant explanatory variable for bumblebee body size, with an overall increasing body size with increasing elevation (i.e., colder climate), although most of the variance is explained by caste, i.e., queens having a larger body size than workers. Body size also shows some correlation with day of capture, which can be explained by changes in environmental conditions (e.g., temperature, flowering plant species) during the growing season experienced by the different emerging times for the castes. Given that caste was the most useful explanatory variable for body size, future studies could look at a larger environmental gradient, for example, by sampling at multiple locations along the entire Scandes mountain range to see if the effects found are localized. Further, specific habitat and specific traits of preferred plants may also help to elucidate body-size differences between species and castes. For example, many bumblebee species’ castes emerge at a specific time of year when only certain flowering plant species in specific habitats are available. This important research would also help to illuminate whether bumblebees and the species of plants they pollinate remain synchronous as climate warming accelerates. Nevertheless, my results show an overall positive relationship between bumblebee body size and elevation, indicating that a warming climate will result in reduced body sizes among bumble bee species. Future studies will have to investigate what consequences this will have for Arctic bumblebee populations – and for the plants that rely on bumblebee visits for their pollination.