One of the defining characteristics of our current epoch—the Anthropocene—is modification of nutrient cycles. At regional to global scales, humans have fundamentally reshaped the availability of carbon, nitrogen, and phosphorus. These changes are particularly apparent in freshwater ecosystems, which receive surface and groundwater inputs of nutrients from agriculture, fossil fuel use, and wastewater. In this thesis, I investigated how the addition of nutrients affects microbial community and biogeochemistry in two extreme environments: the hypereutrophic shallow Utah Lake and nutrient-limited Arctic permafrost streams. In my first chapter, I used bioassay and dilution bioassay experiments to identify what factors control harmful algal blooms in Utah Lake. Specifically, I measured phytoplankton and cyanobacteria growth, cyanotoxin production, and aquatic N-fixation potential. I included physical factors, such as temperature, light, nutrient concentrations, and pH, as well as biological factors, such as top-down control by zooplankton grazers. Phytoplankton showed a threshold behavior at 0.005 mg/L for soluble reactive phosphorus and 0.14 mg/L for dissolved inorganic nitrogen. Surprisingly, nitrogen fixation rates were only high in active bloom samples and were augmented by the addition of both nitrogen and phosphorus. Also contrary to our hypothesis, zooplankton preferentially grazed cyanobacteria over total phytoplankton. In my second chapter, I investigated how permafrost degradation might influence dissolved organic matter (DOM) in Arctic stream networks. Specifically, I used nutrient and labile carbon additions to simulate the effects of permafrost thaw DOM degradation and microbial community in three distinct permafrost-covered catchments on the North Slope of Alaska. The alpine catchment had higher biodegradability but lower DOM concentration across seasons compared with the lake-influenced and tundra catchments. For all catchments, there were strong seasonal changes in microbial community and distinct responses to nutrient addition. The addition of nutrients stimulated DOM biodegradation in the late season—the period of the year when permafrost DOM release typically occurs. Microbial communities differed by catchment type, but overall diversity was similar. Together, these experiments highlight the diverse downstream consequences of human alteration of global carbon, nitrogen, and phosphorus cycles. Even in extreme systems, alteration of the microbial community regulating many of these cycles has potential to exacerbate ecosystem and climate change, so understanding our influence over biogeochemical cycles and microbial interactions is vital for informing future management practices and planetary boundaries.

No description available.

Arctic tundra wetlands support abundant waterbirds, but invertebrate prey communities may change with climate warming. Increased influx of nutrients and labile dissolved organic matter (DOM) from thawing permafrost may alter the relative importance of organic matter (OM) sources, with associated changes in relative biomass of taxa dependent on different sources. In six wetland types, we used stable isotopes (δ13C, δ15N) to compare contributions of four OM sources (periphytic microalgae, cyanobacteria, macrophytes, and peat) to the diets of nine macroinvertebrate taxa. Relative OM contributions within invertebrate taxa were similar among wetland types. Cyanobacteria comprised only 2–7% of OM sources for all taxa in shallow wetland types (<1 m), but up to 25% for oligochaetes and Physidae in deeper wetlands. Macrophytes were minor OM sources (<13%) in all wetland types except deep open lakes (21–26%). Peat typically comprised 20–40% of OM sources except for Physidae (mostly 50–80%). Microalgae were the dominant OM source for most taxa (47–78%, mean ⁓60%), although less for Oligochaeta and much less for Physidae (9–32%). High periphyton production with very depleted δ13C values likely results from continuous daylight illuminating shallow depths, high N and P levels, and very high pCO2 derived from bacterial respiration of DOM leached from thawing permafrost. Invertebrate consumption of microalgae and peat appears often to involve bacterial intermediates. Impacts of warming on invertebrate prey availability will likely depend not on shifts in OM sources, but on changes in overall area or number of shallow ponds.

This thesis analyses ice-rich mountain permafrost with regard to its genesis, distribution, deformation and interaction with other environmental factors. The processes influencing ground ice formation in ice-rich and ice-poor mountain permafrost are highlighted. Factors influencing the presence of ice-rich permafrost are identified and their individual or combined effect on frozen ground is determined. Based on these findings, a new permafrost distribution map of Switzerland was created, which specifies permafrost temperature and ice contents and considers rock glacier creep paths. The deformation of rock glaciers is investigated with newly developed monitoring systems and concepts. This enables a better understanding of the processes leading to rock glacier acceleration at different time scales.

Climate warming is increasing fire severity in boreal forests and can alter forest structure and carbon (C) dynamics in Cajander larch (Larix cajanderi) forests of Siberia, which occur over C and ice-rich yedoma permafrost. Altered forest structure may impact understory vegetation through changing canopy cover, permafrost thaw depth, and soil temperatures. The primary objective of this study was to assess the long-term impacts of fire-driven changes in tree density on understory composition, diversity, and C pools and the underlying soil organic layer (SOL). Shrubs dominated low density stands, likely from reduced canopy cover and thaw depth, while mosses dominated high density stands. Consequently, understory C pools decreased from 415.46 to 158.87 g C m-2. Total SOL C pools remained unchanged as tree density increased. These findings suggest that fire-driven changes in tree density may alter understory composition and C pools, which could impact nutrient/water cycling and permafrost stability.

The permafrost region covers a vast area of land surface on the northern hemisphere,storing large amounts of carbon. Unfortunately, climate warming leads to permafrostthaw altering the hydrothermal state of permafrost soils. Due to the remoteness of thepermafrost region, access to field measurements is restricted. Therefore, remotesensing is an asset to study the permafrost region. Since permafrost is a sub-surfacephenomenon it cannot be directly observed from space. However, by using differenttypes of satellites the soil properties of the top soil layer, down to 10 cm depth, can beaccessed. To establish soil properties for the deeper soil layers modelling is required.The ERA5-Land (ERA5L) soil moisture is modelled based on climate reanalysis. Inthis study in-situ soil moisture data from the International Soil Moisture Network(ISMN) is used to evaluate the performance of the ERA5L soil moisture data withinthe permafrost region. The performance of the ERA5L soil moisture is found toperform best in soil layer 1 (0-7 cm depth) and worst in soil layer 3 (28-100 cm depth).For both soil layer 1 and 2 (0-7 and 7-28 cm depth) a moderate correlation(0.309 &lt; R &lt; 0.335) was found between ERA5L and in-situ soil moisture data, in Julyand August. The performance of the ERA5L soil moisture is best in Europe and worstin North-America. Compared to other evaluations of ERA5L soil moisture, within thepermafrost region, this study found a relatively low correlation. Therefore, this studyconcludes that on a global scale the ERA5L soil moisture is not ideal for directlyinforming permafrost research and decision making. However, integrating multisourcedatasets, resampled to a finer spatial resolution, could improve the performance ofERA5L soil moisture model on a global level. Moreover, on a local scale theapplication of a bias correction could also improve the performance of the ERA5L soilmoisture model.

Current climate change poses a threat to the Arctic due to increasing temperatures, which cause the permafrost and glaciers to melt and thaw. This thesis focused on analyzing water balances in Tarfala catchment between 2000 and 2020 and using GIS as a support for tracer test results measured in Tarfala in 2021. The results suggest that high resolution DEM data are more useful compared to low resolution DEM when it comes to understanding local hydrology. In addition, analyses regarding tracer test data suggest that permafrost can act both as a hinder and water flow pathway changer in Tarfala. Water balance calculations show that the area is highly affected by snow, permafrost and climate change and may come to change towards wetter and snow and permafrost free conditions due to climate change. / Den pågående klimatförändringen har en markant effekt på det arktiska ekosystemet på grund av de stigande temperaturerna vilket orsakar permafrosttining. Denna uppsats fokuserade på att analysera vattenbalanser mellan 2000 och 2020 i Tarfalas avrinningsområde samt diskutera hur spårämnesförsök och GIS kan användas för att analysera de lokala förhållandena i områden med permafrost. Resultaten tyder på att högupplöst DEM data kan användas som stöd för spårämnestester som påverkas starkt av jordartssammansättningen och permafrost i Tarfalas avrinningsområde. Resultaten tyder också på att vattenbalans i Tarfala påverkas och har påverkats av flera olika faktorer såsom permafrost, snö och klimatförändringar och kan komma att förändras i framtiden till mer våta samt snö- och permafrostfria förhållanden.

The McMurdo Dry Valley region is the largest ice-free area of Antarctica. Harsh abiotic conditions of the polar desert ecosystem, including extreme cold, aridity, and limited nutrient availability select for unique taxa. The comparatively simple terrestrial ecosystem is well-suited for investigating edaphic influences on microbial presence, activity, and community structuring. The Dry Valleys are viewed as a useful analog for Mars astrobiology investigations. However, most biotic investigations have been focused on lower elevations, where an understanding of edaphic effects on microbial communities within its generally more favorable conditions has emerged. Transiently wetted Dry Valley water tracks may be analogous to recurring slope lineae on Mars. Dry permafrost is rare on Earth, and unique to high-elevation Antarctica soils, but is ubiquitous on Mars. Identifying if abiotic properties known to structure microbial communities within low elevation soils holds true for water tracks and dry permafrost is not known. My dissertation investigates edaphic effects on microbial communities within water track soils and dry permafrost. First, I review the ecological effects of transient wetting within hyperarid environments of the Atacama Desert of Chile and the Dry Valleys of Antarctica and apply the findings to possible habitability of modern and early (i.e., ~3.5 bya) Mars surface environments. I show that deliquescent hygroscopic salts facilitate biological response where little or no biotic activity would occur otherwise, yet the salts can also inhibit life. Transient wetting alone may also not be enough to support life. Secondly, I examine bacterial community composition, richness, and diversity on and off water track soils in Taylor Valley and show they are significantly different in composition, which likely influence ecosystem functioning. Salinity is shown as the best predictor of composition. Third, I examine a bacterial community from a Beacon Valley water track, which we believe is among the highest, driest, and coldest soils on Earth that still experiences brief seasonal wetting. I show a small but diverse community is present, with some viable cells, yet no detectable RNA is expressed by the community when tested within a suite of simulated Martin soils. Finally, I examine bacterial and fungal communities in dry permafrost of Arena Valley. I show a strikingly minimal microbial community severely restricted by the extreme cold, oligotrophy, and aridity. Several abundant taxa are related to those within maritime, costal, and endolithic habitats, indicating that they are foreign inoculum. The communities appear to be inactive to such a degree that they are not meaningfully structured by the broad suite of measured abiotic properties. Dry permafrost soils and water track environments are extremely challenging habitats, but they are generally more favorable than conditions observed on Mars. My research has important ecological value for investigating terrestrial thresholds of microbial habitability on Earth and for Mars astrobiology investigations.

No description available.

Natural climate variability over the past hundreds of thousands of years provides a uniquewindow into the drivers and processes that connect different parts of our climate system. This thesis investigates interactions between Earth’s mantle, its oceans, and ice sheets over the Quaternary. The dominant process that connects these spheres is glacial isostatic adjustment (GIA), which is the deformation of Earth’s mantle (and consequently its surface, gravity field, and sea level) in response to changes in ice and ocean mass loading. This dissertation focuses on time periods during which surface temperatures were warming or warmer than today to understand how these warm intervals affected ice sheets, permafrost, and sea level. I put my results in the context of current and future warming to improve predictions of future change and compare natural to anthropogenic variability. The thesis opens with an investigation of relative (i.e., local) sea level around Norway overthe last 16 thousand years (ka). Postglacial Norwegian sea level, though dominated by postglacial rebound and associated sea-level fall, is punctuated by two periods of sea-level rise. The causes of these episodes, named the ‘Tapes’ and ‘Younger Dryas’ transgressions, remain debated despite more than a century of study. I produce the first standardized and quality-controlled compilation of Norwegian sea-level data, then employ an ensemble of empirical Bayesian hierarchical statis- tical models to estimate relative sea level along the Norwegian coastline. The resulting model enables an examination of the relative contributions of isostatic rebound and global mean sea-level (GMSL) rise to the Tapes transgression, and lays the foundation for future applications such as in- version of sea-level data for Fennoscandian ice-sheet volume and the comparison of modern rates of Norwegian sea-level rise to pre-industrial rates. Chapter Two aims to better understand sea-level and Antarctic ice-sheet variability during the Holocene, which is the last time global temperatures may have exceeded early industrial (1850 CE) values. Both the Greenland and Antarctic ice sheets likely retreated inland of their present- day extents during the Holocene, yet previous GMSL reconstructions suggest that Holocene GMSL never surpassed early industrial levels. I use relative sea-level observations, GIA predictions, and new estimates of postglacial thermosteric sea-level and mountain glacier evolution to show that the available evidence is consistent with GMSL that exceeded early industrial levels in the mid- Holocene (8-4 ka) and an Antarctic Ice Sheet that was smaller than present at some time in the last 6000 years. I also demonstrate that Antarctic ice retreat lags Antarctic temperature by 250 years, which highlights the vulnerability of the future Antarctic ice sheet to 20th and 21st century warming. Comparing our reconstruction to projections for the future indicates that GMSL rise in the next 125 years will very likely (?>0.9) be faster than at any time in the last 5000 years, and that by 2080 GMSL will more likely than not be the highest of any time in the past 115,000 years. In Chapter Three, I explore the effect of GIA on subsea permafrost. Subsea permafrost forms when sea-level rise submerges terrestrial permafrost. Subsea permafrost underlies ∼1.8 million km² of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial–interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for GIA, which leads to deviations of local sea level from the global mean. I incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces estimates of present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects and deformation related to Northern Hemisphere ice sheets. Additionally, I extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change’s sixth assessment report. I find that subsea permafrost is preserved under a low-emissions scenario but mostly disappears under a high-emissions scenario. In the final chapter, I turn to the Last Interglacial (LIG, 129–116 ka), a time interval considered a partial analogue for future warming due to its elevated temperatures. Observations of oscillations in LIG local sea level, combined with an assumption that the Laurentide Ice Sheet collapsed prior to the LIG, have been used to infer Antarctic and Greenland ice-sheet melt histories as well as oscillations in LIG global mean sea level. However, evidence of a Laurentide Ice Sheet outburst flood at ∼125 ka suggests that Laurentide Ice Sheet remnants may have persisted longer into the LIG than typically thought. Here we explore the effect on LIG sea level of a Laurentide collapse that occurred during rather than prior to the LIG and a West Antarctic Ice Sheet that collapsed in the early LIG. We find that due to GIA, this asynchronous ice-sheet evolution produces a global pattern of sea-level oscillations that is similar to field observations. We demonstrate that the oscillation pattern can be produced by the combination of ongoing GIA from the penultimate deglaciation with the fingerprint of West Antarctic collapse. By showing that LIG Laurentide persistence would lead to an RSL oscillation that accords with field evidence, we highlight the need for LIG climate simulations to consider Laurentide ice-sheet dynamics and for more constraints on the LIG history of the Laurentide Ice Sheet.