Arctic landscape dynamics: modern processes and pleistocene legacies

Thesis (Ph.D.) University of Alaska Fairbanks, 2017The Arctic Cryosphere (AC) is sensitive to rapid climate changes. The response of glaciers, sea ice, and permafrost-influenced landscapes to warming is complicated by polar amplification of global climate change which is caused by the presence of thresholds in the physics of energy exchange occurring around the freezing point of water. To better understand how the AC has and will respond to warming climate, we need to understand landscape processes that are operating and interacting across a wide range of spatial and temporal scales. This dissertation presents three studies from Arctic Alaska that use a combination of field surveys, sedimentology, geochronology and remote sensing to explore various AC responses to climate change in the distant and recent past. The following questions are addressed in this dissertation: 1) How does the AC respond to large scale fluctuations in climate on Pleistocene glacial-interglacial time scales? 2) How do legacy effects relating to Pleistocene landscape dynamics inform us about the vulnerability of modern land systems to current climate warming? and 3) How are coastal systems influenced by permafrost and buffered from wave energy by seasonal sea ice currently responding to ongoing climate change? Chapter 2 uses sedimentology and geochronology to document the extent and timing of ice-sheet glaciation in the Arctic Basin during the penultimate interglacial period. Chapter 3 uses a combination of surficial geology mapping and remote sensing to explore the distribution and vulnerability of modern day landscapes on the North Slope of Alaska to thermokarst caused by rapid warming. Chapter 4 uses high spatial and temporal resolution remote sensing data and field surveys to show how sea ice decline is causing AC coastlines to become more geomorphologically dynamic. Together the results of this research show that the AC is a highly dynamic system that can respond to climate warming in complex and non-linear ways. Chapter 2 provides terrestrial evidence that ice-sheet glaciation occurred offshore in the Arctic Ocean in the later stages of the last interglacial period at a time when lower latitude sections of the Laurentide and Cordilleran were in retreat. These findings have important implications for how Arctic ice sheets respond to increased moisture availability caused by sea ice decline and atmospheric warming. This study also provides a new approach to reconstructing and establishing an absolute chronology for periods of Arctic Ocean glaciation during the mid- to late-Pleistocene. Chapter 3 illustrates how Pleistocene-legacy effects exert important influences over the vulnerability of Arctic lowlands to climate warming. Striking differences are revealed in Holocene thermokarst activity between different surficial geology units. During the Holocene, regions of marine silts have been the most susceptible to thermokarst, while regions of ice-poor aeolian sand have seen the least thermokarst activity. In future decades, areas of ice-rich aeolian silt will be most vulnerable to rapid warming because these areas contain large amounts of ground ice that have so far undergone little thermokarst development during the Holocene. Findings from this study have important implications for understanding future landscape evolution and carbon cycling in the Arctic. Chapter 4 shows that permafrost coastlines in the Kotzebue Sound region are already responding to ongoing climate change. Remote sensing data demonstrates that declines in the extent and timing of sea ice are causing an increasingly dynamic coastal system. Rates of change along the coast are more dynamic now than at any time during the past 64 years, and these geomorphic responses to sea ice decline are non-linear. Furthermore, future coastal change will not necessarily be characterized by higher erosion rates, because accretion rates are simultaneously rising. In general, the research described in this dissertation illustrates that the future response of AC components to ongoing climate change will be complex and nonlinear. These results serve to emphasize the value of using past responses of the AC to better understand its possible future trajectories. They also highlight the importance of taking into account a wide variety of processes operating across a wide range of spatial and temporal scales to refine future projected changes.Chapter 1 General Introduction -- Chapter 2 Marine transgressions in northern Alaska indicate out-of-phase Beaufort Sea glaciation during the last interglacial -- Chapter 3 Spatial distribution of thermokarst terrain in Arctic Alaska -- Chapter 4 High variability in shoreline response to declining sea ice in northwest Alaska -- Chapter 5 General Conclusions

Sedimentology of thermokarst lakes forming within yedoma on the Northern Seward Peninsula

Thesis (M.S.) University of Alaska Fairbanks, 2012Thermokarst lakes forming in yedoma (organic-rich permafrost containing massive syngenetic Pleistocene ice wedges) play an important role in periglacial landscape evolution. These lakes alter landscape elevation and topography, as well as redistribute upland sediment into lower basins. However, sediment deposition within yedoma thermokarst lakes is not well understood. Sedimentological, biogeochemical and macrofossil analyses enabled identification of five prominent fades in yedoma thermokarst lakes in my study region on the northern Seward Peninsula, Alaska. These include a Yedoma Taberal Silt facies situated below a sub-lacustrine unconformity, three types of basal facies and a Lacustrine Silt facies. A preliminary geomorphological model based on sediment cores from mature yedoma thermokarst lakes illustrates how fades distribution changes through the different stages of lake development. First-generation lakes (those forming in undisturbed upland) and later-generation lakes (those forming in thermokarst-affected lowland) were present on the northern Seward Peninsula. A comparison between these two lake types indicates that the depositional environments of later-generation lakes are much more variable than first-generation lakes. Understanding the depositional history and development of yedoma thermokarst lakes is critical to understanding their role in landscape evolution and the carbon cycle

Landsat-based lake distribution and changes in western Alaska permafrost regions between the 1970s and 2010s

Lakes are an important ecosystem component and geomorphological agent in northern high latitudes and it is important to understand how lake initiation, expansion and drainage may change as high latitudes continue to warm. In this study, we utilized Landsat Multispectral Scanner System (MSS) images from the 1970s (1972, 1974, and 1975) and Operational Land Imager (OLI) images from the 2010s (2013, 2014, and 2015) to assess broad-scale distribution and changes of lakes larger than 1 ha across the four permafrost zones (continuous, discontinuous, sporadic, and isolated extent) in western Alaska. Across our ca 70,000 km2study area, we saw a decline in overall lake coverage across all permafrost zones with the exception of the sporadic permafrost zone. In the continuous permafrost zone lake area declined by -6.7 % (-65.3 km2), in the discontinuous permafrost zone by -1.6 % (-55.0 km2), in the isolated permafrost zone by -6.9 % (-31.5 km2) while lake cover increased by 2.7 % (117.2 km2) in the sporadic permafrost zone. Overall, we observed a net drainage of lakes larger than 10 ha in the study region. Partial drainage of these medium to large lakes created an increase in the area covered by small water bodies <10 ha, in the form of remnant lakes and ponds by 7.1 % (12.6 km2) in continuous permafrost, 2.5 % (15.5 km2) in discontinuous permafrost, 14.4 % (74.6 km2) in sporadic permafrost, and 10.4 % (17.2 km2) in isolated permafrost. In general, our observations indicate that lake expansion and drainage in western Alaska are occurring in parallel. As the climate continues to warm and permafrost continues to thaw, we expect an increase in the number of drainage events in this region leading to the formation of higher numbers of small remnant lakes

Alaskan Marine Transgressions Record Out-of-Phase Arctic Ocean Glaciation During the Last Interglacial

Ongoing climate change focuses attention on the Arctic cryosphere’s responses to past and future climate states. Although it is now recognized the Arctic Ocean Basin was covered by ice sheets and their associated floating ice shelves several times during the Late Pleistocene, the timing and extent of these polar ice sheets remain uncertain. Here we relate a relict barrier-island system on the Beaufort Sea coast of northern Alaska to the isostatic effects of a previously unrecognized ice shelf grounded on the adjacent continental shelf. A new suite of optically stimulated luminescence dates show that this barrier system formed during one or more marine transgressions occurring late in Marine Isotope Stage 5 (MIS 5) between 113 ka and 71 ka. Because these transgressions occurred after the warmest part of the last interglacial (ca. 123 ka) and did not coincide with the global eustatic sea-level maximum during MIS 5e, this indicates Arctic ice sheets developed out-of-phase with lower-latitude sectors of the Laurentide and Fennoscandian ice sheets. We speculate that Arctic ice sheets began development during full interglacial conditions when abundant moisture penetrated to high latitudes, and low summer insolation favored glacier growth. These ice sheets reached their full extents at interglacial-glacial transitions, then wasted away at the heights of mid-latitude glaciations because of moisture limitations

Comparing coastal dynamics between two geomorphologically distinct permafrost affected coastlines in NW Alaska

Arctic clastic coastlines are some of the most dynamic in the world and have a large impact on cultural and natural resources. Sea ice plays an important role in the erosion and accretion dynamics of these coastlines, and sea ice cover is currently declining at >10% per decade. As a result of declining sea ice cover and an increase in the duration of open water days in the Arctic Ocean, we need to know more about coastal processes in polar seas, specifically how sea ice decline changes coastal processes, the rate at which such coastal changes can occur, and how the effects of declining sea ice interacts with local coastline characteristics including wave fetch, bathymetry, permafrost properties onshore, and pre-existing coastal geomorphology. To assess the influence of sea ice decline on permafrost coastal dynamics we selected two segments of the coastline in NW Alaska with contrasting geography, surficial geology and geomorphology. Study site A, Cape Krusenstern National Monument (CAKR), has a wave-dominated, west- to south-west facing, coarseclastic shoreline. Accreted beach ridges, barrier-closed lagoons, permafrost bluffs, longshore gravel bars, and gravelly beaches characterize coastal geomorphology. Study site B, the Bering Land Bridge National Park and Preserve (BELA), has a north-facing coastline with a shoreline characterized by yedoma and thermokarst basin permafrost bluffs, aggrading spits, sandy barrier islands, and open lagoons. To establish rates of coastal change and identify key geomorphological processes, we digitally mapped the shoreline of both study areas using aerial photographs (1-meter resolution or better) and sub-meter resolution World View-2 satellite imagery from 2003 and 2014, respectively. We compared our data to the results of previous studies based on imagery taken between 1950 and 2003 (Lestak et al., 2010). To better understand the relationship between geomorphology and rates of change, we established geomorphological landform classes for both study areas. We mapped coastal changes within a subset of each study area, using sub meter resolution imagery, over annual time steps to help us better quantify variations in the rate of event driven coastline change. Mapping results for the period 2003 to 2014 suggest a change in erosion rates within both study sites. Erosion rates for the period 1950 to 2003 in BELA and CAKR were -0.12 m/yr and -0.98 m/yr respectively, where the negative signs indicate shoreline retreat (Gorokhovich and Leiserowiz, 2012). These rates, for the period between 2003 and 2014, increased in CAKR to -0.86 and decreased in BELA to -0.69 m/yr. Rates of erosion were found to vary according to geomorphology, with overwash fans in BELA exhibiting the highest rates of change at -1.3 m/yr. Significant changes in geomorphology were observed for this time period including the development of a 200-meter long spit in CAKR, degradation of ice wedges on upland yedoma bluffs in BELA, and the infilling of numerous barrier island ponds due to overwash events in BELA. Our results illustrate the complexity of coastal responses along Arctic coastlines even within close proximity. To ensure robust projections of future coastal change, further mapping and analysis at intraannual and sub-meter spatial resolution is necessary to firmly tie together cause and effect of arctic coastal processes with a changing climate. References: 1. Gorokhovich, Y., Leiserowiz, A., 2012. Historical and Future Coastal Changes in Northwest Alaska. J. Coast. Res. 28, 174–186. 2. Lestak, L.R., Manley, W.F., Parrish, E.G., 2010. Digital Shoreline Analysis of Coastal Change in Bering Land Bridge NP (BELA) and Cape Krusenstern NM (CAKR), Northwest Alaska: Fairbanks, AK: National Park Service, Arctic Network I&M Program. Geospatial Dataset-2184176

Ablation of Enpp6 results in transient bone hypomineralization

C.F. was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) via an Institute Strategic Programme Grant Funding (BB/J004316/1). S.D. was supported through a BBSRC EASTBIO Doctoral Training Partnership studentship award (1803936) and N.M.M. was supported by a Wellcome Trust New Investigator Award (100981/Z/13/Z). S.D. wrote the manuscript. S.D., K.S., S-N.H., and L.A.S. carried out experimental work. W.P.C., R.W. and N.M.M. provided reagents and materials. A.J.S., F.N. and C.F. contributed to conceptualization of the study and experimental design. All authors reviewed and edited the manuscript and approved the final version. All authors state that they have no conflicts of interest.Biomineralization is a fundamental process key to the development of the skeleton. The phosphatase orphan phosphatase 1 (PHOSPHO1), which likely functions within extracellular matrix vesicles, has emerged as a critical regulator of biomineralization. The biochemical pathways which generate intravesicular PHOSPHO1 substrates are however currently unknown. We hypothesized that the enzyme ectonucleotide pyrophosphatase/phosphodiesterase (ENPP6) is an upstream source of PHOSPHO1 substrate. To test this, we characterized skeletal phenotypes of mice homozygous for a targeted deletion of Enpp6 (Enpp6‒/‒). Micro-computed tomography of the trabecular compartment revealed transient hypomineralization in Enpp6‒/‒ tibiae (p 0.01) and osteoid surface (p < 0.05) which recovered by 12 weeks but was not accompanied by changes in osteoblast or osteoclast number. This study is the first to characterize the skeletal phenotype of Enpp6‒/‒ mice, revealing transient hypomineralization in young animals compared to wild-type controls. These data suggest that ENPP6 is important for bone mineralization and may function upstream of PHOSPHO1 as a novel means of generating its substrates inside matrix vesicles.Publisher PDFPeer reviewe

Dynamics of Arctic Permafrost Coasts in the 21st Century

Climate warming is particularly pronounced in the Arctic with temperatures rising twice as much as in the rest of the world. It seems natural that this warming has profound effects on the speed of erosion of Arctic coasts, since the majority consists of permafrost, composed of unlithified material and hold together by ice. Permafrost stores approximately 1307 Gt of carbon, which is almost 60 % more than currently being contained in the atmosphere. Understanding the main drivers and dynamics of permafrost coastal erosion is of global relevance, especially since floods and erosion are both projected to intensify. However, the assessment of the impacts of climate warming on Arctic coasts is impaired by little data availability. We reviewed relevant scientific literature on changing dynamics of Arctic coast, potential drivers of these changes and the impacts on the human and natural environment. We provide a comprehensive overview over the state of the art and share our thoughts on how we envision potential pathways of future Arctic coastal research. We found that the overwhelming majority of all studied Arctic coasts is erosive and that in most cases erosion rates per year are increasing, threatening coastal settlements, infrastructure, cultural sites and archaeological remains. The impacts on the natural environment are also manifold and reach from changing sediment fluxes which limit light availability in the water column to a higher input of carbon and nutrients into the nearshore zone with the potential to influence food chains

Remote sensing-based statistical approach for defining drained lake basins in a continuous Permafrost region, North Slope of Alaska

Lake formation and drainage are pervasive phenomena in permafrost regions. Drained lake basins (DLBs) are often the most common landforms in lowland permafrost regions in the Arctic (50% to 75% of the landscape). However, detailed assessments of DLB distribution and abundance are limited. In this study, we present a novel and scalable remote sensing-based approach to identifying DLBs in lowland permafrost regions, using the North Slope of Alaska as a case study. We validated this first North Slope-wide DLB data product against several previously published sub-regional scale datasets and manually classified points. The study area covered \u3e71,000 km2, including a \u3e39,000 km2 area not previously covered in existing DLB datasets. Our approach used Landsat-8 multispectral imagery and ArcticDEM data to derive a pixel-by-pixel statistical assessment of likelihood of DLB occurrence in sub-regions with different permafrost and periglacial landscape conditions, as well as to quantify aerial coverage of DLBs on the North Slope of Alaska. The results were consistent with previously published regional DLB datasets (up to 87% agreement) and showed high agreement with manually classified random points (64.4–95.5% for DLB and 83.2– 95.4% for non-DLB areas). Validation of the remote sensing-based statistical approach on the North Slope of Alaska indicated that it may be possible to extend this methodology to conduct a comprehensive assessment of DLBs in pan-Arctic lowland permafrost regions. Better resolution of the spatial distribution of DLBs in lowland permafrost regions is important for quantitative studies on landscape diversity, wildlife habitat, permafrost, hydrology, geotechnical conditions, and high-lat-itude carbon cycling

Mitochondrial dysfunction and mitophagy blockade contribute to renal osteodystrophy in chronic kidney disease-mineral bone disorder

Chronic kidney disease–mineral and bone disorder (CKD-MBD) presents with extra-skeletal calcification and renal osteodystrophy (ROD). The origins of ROD likely lie with elevated uremic toxins and/or an altered hormonal profile but the cellular events responsible remain unclear. Here, we report that stalled mitophagy contributes to mitochondrial dysfunction in bones of a CKD-MBD mouse model, and also human CKD-MBD patients. RNA-seq analysis exposed an altered expression of genes associated with mitophagy and mitochondrial function in tibia of CKD-MBD mice. The accumulation of damaged osteocyte mitochondria and the expression of mitophagy regulators, p62/SQSTM1, ATG7 and LC3 was inconsistent with functional mitophagy, and in mito-QC reporter mice with CKD-MBD, there was a 2.3-fold increase in osteocyte mitolysosomes. Altered expression of mitophagy regulators in human CKD-MBD bones was also observed. To determine if uremic toxins were possibly responsible for these observations, indoxyl sulfate treatment of osteoblasts revealed mitochondria with distorted morphology and whose membrane potential and oxidative phosphorylation were decreased, and oxygen-free radical production increased. The altered p62/SQSTM1 and LC3-II expression was consistent with impaired mitophagy machinery and the effects of indoxyl sulfate were reversible by rapamycin. In conclusion, mitolysosome accumulation from impaired clearance of damaged mitochondria may contribute to the skeletal complications, characteristic of ROD. Targeting mitochondria and the mitophagy process may therefore offer novel routes for intervention to preserve bone health in patients with ROD. Such approaches would be timely as our current armamentarium of anti-fracture medications has not been developed for, or adequately studied in, patients with severe CKD-MBD

Climate Change Drives Widespread and Rapid Thermokarst Development in Very Cold Permafrost in the Canadian High Arctic

Climate warming in regions of ice‐rich permafrost can result in widespread thermokarst development, which reconfigures the landscape and damages infrastructure. We present multisite time series observations which couple ground temperature measurements with thermokarst development in a region of very cold permafrost. In the Canadian High Arctic between 2003 and 2016, a series of anomalously warm summers caused mean thawing indices to be 150–240% above the 1979–2000 normal resulting in up to 90 cm of subsidence over the 12‐year observation period. Our data illustrate that despite low mean annual ground temperatures, very cold permafrost (<−10 °C) with massive ground ice close to the surface is highly vulnerable to rapid permafrost degradation and thermokarst development. We suggest that this is due to little thermal buffering from soil organic layers and near‐surface vegetation, and the presence of near‐surface ground ice. Observed maximum thaw depths at our sites are already exceeding those projected to occur by 2090 under representative concentration pathway version 4.5