Download or read book Holocene Climate and Environmental Changes Inferred from a Subfossil Chironomid Record in a Small Lake Near Bolshoe Toko Southeastern Yakutia Russia written by Laura Weniger and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Climate and Environmental Change in the Great Basin of the Western United States written by Scott Alan Reinemann and published by . This book was released on 2013 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: In this dissertation, I have completed a research project that focused on reconstructing past climate and environmental conditions in the Great Basin of the western United States. This research project incorporates four discrete but interrelated studies. (1) The geochemistry of lake sediments was used to identify anthropogenic factors influencing aquatic ecosystems of sub-alpine lakes in the western United States during the past century. Sediment cores were recovered from six high elevation lakes in the central Great Basin of the United States. Mercury (Hg) flux varied among lakes but all exhibited increasing fluxes during the mid-20th century and declining fluxes during the late 20th century. Peak Spheroidal Carbonaceous Particles (SCP) flux for all lakes occurred at approximately 1970, after which SCP flux was greatly reduced. Atmospheric deposition is the primary source of Hg and anthropogenically produced SCPs to these pristine high elevation lakes during the late 20th century. (2) Chironomids are used to develop centennial length temperature reconstructions for six sub-alpine and alpine lakes in the central Great Basin of the United States. Chironomid-inferred temperature estimates indicate that four of the six lakes were characterized by above average air temperatures during the post-AD 1980 interval and below average temperatures during the early 20th century. This study adds to the growing body of evidence that sub-alpine and alpine lakes in the western United States have been, and are increasingly being affected by anthropogenic climate change in the early 21st century. (3) A sediment core representing the past two millennia was recovered from Stella Lake in the Snake Range of the central Great Basin in Nevada. The core was analyzed for sub-fossil chironomids and sediment organic content. The chironomid-based mean July air temperature (MJAT) reconstruction suggests that the Medieval Climate Anomaly (MCA), was characterized by MJAT elevated 1.0°C above the subsequent Little Ice Age (LIA), but likely not as warm as recent conditions. The Stella Lake record provides evidence that elevated summer temperature contributed to the increased aridity that characterized the western United States during the MCA. (4) Lake sediment cores spanning roughly the last 7,000 years were recovered from four small sub-alpine and alpine lakes located in central Great Basin of the United States. Reconstructions of MJAT were developed for each of the study sites using a chironomid-based inference model for MJAT (two-component Weighted Averaging-Partial Least Squares (WA-PLS)). The elevated temperature that characterizes the mid-Holocene at Stella Lake is surpassed only during the Medieval Climate Anomaly and in the post-AD 1800 interval. The reconstructions for the sites located in the northern portion of the study transect are characterized by greater variability, likely reflecting the influence of both radiative forcing and catchment-specific conditions.

Download or read book Late Holocene Climate and Environmental Change Inferred from Arctic Lake Sediment written by Darrell S. Kaufman and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book 7700 Years of Holocene Climatic Variability in Sermilik Valley Southeast Greenland Inferred from Lake Sediments written by Samuel Hallett Davin and published by . This book was released on 2013 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the latter half of the 20th century until present day there has been an unprecedented rise in global annual mean temperatures accompanied by rising sea levels and a decrease in Northern Hemisphere snow cover, which if it continues will lead to widespread disruption of climate patterns, ecosystems, and present-day landscapes. It is therefore of critical importance to establish an expanded network of paleoclimate records across the globe in order to better assesses how the global climate system has changed in the past, that we may create a metric by which to address modern change. Herein is presented a7,700 years record of Holocene climatic and environmental variability in Sermilik Valley, located on Ammassalik Island, SE Greenland. This objective of this study is to determine the timing of major Holocene climate transitions as expressed in the physical, elemental, and geochemical parameters preserved in the 484 cm sediment record of Lower Sermilik Lake. Major transitions observed in this study include the deglaciation of Sermilik Valley, the onset and termination of the Holocene Climatic Optimum, the transition into neoglacial conditions, and the Little Ice Age.

Download or read book Holocene Environmental Variability Inferred from Lake Sediments Southwest Yukon Territory Canada written by Joan Bunbury and published by . This book was released on 2009 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ecosystem Responses to Holocene Climate Variability Through the Analysis of High resolution Lake Sediment Cores from Southwestern Qu bec Canada written by Karen Neil and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Lake biotic responses to natural climate variability, fire disturbances, and human impacts over the Holocene were studied at two proximate sites in southwestern Québec. Sediments from Lac Noir and Lac Brûlé had annually deposited laminations (varves), enabling for the precise dating of continuous time-series and high-resolution analysis of subfossil diatom assemblages. The Lac Noir (45°46'31"N, 75°8'23"W, 176 m a.s.l.) record spanned ~11000 years of the Holocene. Stratigraphic changes in diatom assemblages of the lake could be divided into early, mid-, and late periods, broadly paralleling Milankovitch-scale climate intervals and vegetation changes inferred from regional palynological records. The early Holocene (11.1-8.0 ka) climate was cooler and dry, vegetation in the region was comprised of Picea-dominated woodlands, and the lake diatom flora included primarily benthic taxa. Warming in the mid-Holocene (8.0-3.6 ka) allowed for stabilization of soils and forests in the catchment, stronger thermal stratification in the lake, and resultant increases in oligo-mesotrophic diatom taxa such as Discostella stelligera. During the late Holocene (3.6 ka to present), an increase in the abundance of deciduous trees (e.g. Betula and Alnus) in response to cooling led to nutrient-enrichment and higher overall lake productivity. The record from Lac Brûlé (45°43'09"N, 75°26'32"W, 270 m a.s.l.) encompassed the last ~1200 years of the late Holocene. Generalized additive models (GAM) revealed a tight coupling between diatoms and catchment-mediated processes (e.g. vegetation and disturbances), which were closely aligned with climate variations. During the Medieval Warm Period (800-1300 CE), pollen-based inferences of warmer summer temperatures were associated with high abundances of Cyclotella bodanica var. intermedia and Cyclotella rossii; this signalled oligotrophic lake conditions and prolonged thermal stratification. The onset of the Little Ice Age (1450-1850 CE) marked a cooling in the region, and a decline in Tabellaria flocculosa str. IIIp indicated increased nutrient loading from the catchment area. Situated less than 300m from Lac Brûlé are remnants of the Wallingford-Back Mine, which ran from 1924-1972 CE; activities at the mine resulted in local changes to nutrient availability and primary productivity at this site. In previous studies of both Lac Noir and Lac Brûlé, pollen records had indicated overall similarities in the vegetation histories in response to climate variability during the late Holocene. Diatom assemblages were influenced by individual lake conditions and were thus unique to each site; nevertheless, they were closely linked with local and regional patterns of vegetation composition. A main point of difference in the paleo-records from both lakes was attributed to a local fire in the Lac Brûlé catchment at 1345 CE, which caused an early decline in hemlock (Tsuga). The decrease in hemlock was seen at Lac Noir only centuries later, and diatoms in each lake responded according to vegetation changes within their own respective catchments. This research shows that high-resolution sampling of lake sediments is able to detect diatom responses to both long-term and abrupt changes in the environment. Individual sites show similarly timed responses of other proxy-indicators, such as pollen and cladocera, to climate and land-use changes. However, distinct differences in the aquatic biota of well-dated proximate sites can be used to identify influences of regional climate variations, which are sometimes masked by localized, non-climatic processes.

Download or read book Holocene Climate and Environmental Variability in NE Germany Inferred from Annually Laminated Lake Sediments written by Nadine Dräger and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the role of natural climate variability under the pressure of human induced changes of climate and landscapes, is crucial to improve future projections and adaption strategies. This doctoral thesis aims to reconstruct Holocene climate and environmental changes in NE Germany based on annually laminated lake sediments. The work contributes to the ICLEA project (Integrated CLimate and Landscape Evolution Analyses). ICLEA intends to compare multiple high-resolution proxy records with independent chronologies from the N central European lowlands, in order to disentangle the impact of climate change and human land use on landscape development during the Lateglacial and Holocene. In this respect, two study sites in NE Germany are investigated in this doctoral project, Lake Tiefer See and palaeolake Wukenfurche. While both sediment records are studied with a combination of high-resolution sediment microfacies and geochemical analyses (e.g. μ-XRF, carbon geochemistry and stable isotopes), detailed proxy understanding mainly focus

Download or read book Holocene Climate and Environmental Change from White Owl Lake Sediments White River Plateau Colorado written by Marian Esther Kramer and published by . This book was released on 2009 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Environmental Variability Inferred from Lake Diatoms and Sediment Geochemistry in Northeastern Siberia Russia written by Boris K. Biskaborn and published by . This book was released on 2012 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Multi proxy Study of Holocene Atmospheric Circulation Dynamics Recorded in Lake Sediments in Fennoscandia written by Natalie Ann St. Amour and published by . This book was released on 2009 with total page 253 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cellulose-inferred lake water oxygen-isotope records were obtained from five throughflow lakes situated along a north-south transect across Fennoscandia to help develop a better picture of Holocene changes in atmospheric circulation in the region. This research addresses prior evidence for the existence of non-temperature-dependent shifts in d18O of precipitation in the early Holocene attributed to changes in atmospheric circulation. The validity of this hypothesis is tested through the development of oxygen-isotope records from lake sediments and their interpretation in the context of independent reconstructions of temperature and precipitation from pollen and chironomid head-capsules collected from the same or nearby sites, and well-documented changes in vegetation composition. Records of carbon and nitrogen elemental content and isotopic composition and magnetic susceptibility are included in this multi-proxy investigation. Extensive modern isotope hydrology datasets spanning several years at four of the five sites also help to inform interpretations of the cellulose d18O records. Key results from this research are: 1) Elevated d18O in relation to prevailing temperature occurred during the early Holocene (c. 10,000-6000 cal. BP) for sites in northern Fennoscandia (Lake Tibetanus, Lake Spåime), in harmony with previous interpretations suggesting that strong zonal atmospheric circulation led to deepening of the precipitation and isotope shadows in the lee of the Scandes Mountains. 2) Evidence from a southern site (Arbovatten) reveals a previously unrecognized negative offset in the d18O-temperature relation during the early Holocene, apparently transferred directly from the North Atlantic without the orographic effects associated with a topographic barrier. 3) The modern d18O-temperature relation appears to have been established throughout Fennoscandia by c. 6000-4000 cal. BP, probably due to generally weaker circumpolar atmospheric circulation in response to lower summer insolation. 4) Comparison of two sites (Lake Spåime, Svartkälstjärn) in a west-east transect across central Fennoscandia reveals higher-frequency variability in atmospheric circulation at submillennial scales throughout the Holocene, which appears to be analogous to contemporary variability in the North Atlantic Oscillation (NAO) at seasonal-to-decadal time-scales. Evidence of such NAO-like variability also exists at two northern sites (Lake Keitjoru, Oikojärvi) during the Holocene, likely reflecting variations in summer and winter atmospheric circulation. 5) Complex lake-specific changes in productivity occurred in response to Holocene climate change, as revealed by carbon and nitrogen elemental and isotopic data in lake sediments. A major shift in atmospheric circulation pattern occurring at c. 4000 cal. BP probably led to a reduction in soil-derived 13C-depleted nutrients in five lakes (Lake Keitjoru, Oikojärvi, Lake Spåime, Svartkälstjärn, Arbovatten) associated with changes in terrestrial vegetation. Changes in sediment nitrogen isotope composition also occurred in these lakes at c. 4000 cal. BP, possibly reflecting changing nutrient supply dynamics because of enhanced nitrogen losses during spring snowmelt.

Download or read book Holocene Climate Change in the Eastern United States and Canada Inferred from Lake Sedimentation Rates written by John Warren Dunham and published by . This book was released on 1986 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Palaeoecological Study of Holocene Environmental Change in a Small Upland Lake from the Kola Peninsula Russia written by Nadezhda Solovieva and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Climate and Vegetation Change During the Late glacial early Holocene Transition Inferred from Multiple Proxy Records from Blacktail Pond Yellowstone National Park USA written by Teresa R. Krause and published by . This book was released on 2013 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of environmental changes from late-glacial ice recession through the early Holocene are revealed in a 7000-yr-long record of pollen, charcoal, geochemistry, and stable isotopes from Blacktail Pond, a closed-basin lake in Yellowstone National Park. Prior to 11,500 cal yr BP, cool conditions dominated, fire activity was low, and alpine tundra and Picea parkland grew on the landscape. A step-like climate change to warm summer conditions occurred at 11,500 cal yr BP. In response, fire activity increased facilitating a transition from Picea parkland to closed Pinus forest. From 11,500 to 8280 cal yr BP, warm summers and abundant moisture mostly likely from high winter snowfall supported closed Pinus contorta forests. Cooler drier summer conditions prevailed beginning 8280 cal yr BP due to decreased summer insolation and winter snowpack, and lower parkland developed. The timing of vegetation change in the Blacktail Pond record is similar to other low- and middle-elevation sites in the northern Rocky Mountains during the late-glacial period, suggesting local plant communities responded to regional-scale climate change; however, the timing of vegetation changes was spatially variable during the early and middle Holocene due to the varying influences of strengthened summer monsoons and subtropical high on regional precipitation patterns.

Download or read book Late Holocene Environmental Change written by V. N. Panizzo and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Climatic Change in the Alaskan Arctic as Inferred from Oxygen isotope and Lake sediment Analyses at Wahoo Lake written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Seasonal Variability Inferred from Multiple Proxy Records from Crevice Lake Yellowstone National Park USA written by Cathy Whitlock and published by . This book was released on 2012 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: A 9400-yr-old record from Crevice Lake, a semi-closed alkaline lake in northern Yellowstone National Park, was analyzed for pollen, charcoal, geochemistry, mineralogy, diatoms, and stable isotopes to develop a nuanced understanding of Holocene environmental history in a region of northern Rocky Mountains that receives both summer and winter precipitation. The limited surface area, conical bathymetry, and deep water (> 31 m) of Crevice Lake create oxygen-deficient conditions in the hypolimnion and preserve annually laminated sediment (varves) for much of the record. Pollen data indicate that the watershed supported a closed Pinus-dominated forest and low fire frequency prior to 8200 cal yr BP, followed by open parkland until 2600 cal yr BP, and open mixed-conifer forest thereafter. Fire activity shifted from infrequent stand-replacing fires initially to frequent surface fires in the middle Holocene and stand-replacing events in recent centuries. Low values of ó18O suggest high winter precipitation in the early Holocene, followed by steadily drier conditions after 8500 cal yr BP. Carbonate-rich sediments before 5000 cal yr BP imply warmer summer conditions than after 5000 cal yr BP. High values of molybdenum (Mo), uranium (U), and sulfur (S) indicate anoxic bottom-waters before 8000 cal yr BP, between 4400 and 3900 cal yr BP, and after 2400 cal yr BP. The diatom record indicates extensive water-column mixing in spring and early summer through much of the Holocene, but a period between 2200 and 800 cal yr BP had strong summer stratification, phosphate limitation, and oxygen-deficient bottom waters. Together, the proxy data suggest wet winters, protracted springs, and warm effectively wet summers in the early Holocene and less snowpack, cool springs, warm dry summers in the middle Holocene. In the late Holocene, the region and lake experienced extreme changes in winter, spring, and summer conditions, with particularly short springs and dry summers and winters during the Roman Warm Period (~ 2000 cal yr BP) and Medieval Climate Anomaly (1200?800 cal yr BP). Long springs and mild summers occurred during the Little Ice Age, and these conditions persist to the present. Although the proxy data indicate effectively wet summer conditions in the early Holocene and drier conditions in the middle and late Holocene, none point specifically to changes in summer precipitation as the cause. Instead, summer conditions were governed by multi-seasonal controls on effective moisture that operated over multiple time scales.

Download or read book Holocene Paleohydrologic Change Inferred from the Sediment Record at Sunrise Lake Michigan written by Amanda Toomey and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hydroclimate of the Great Lakes region likely changed significantly during the Holocene, or the past 11.7 ka, but determining the patterns of change, how they compare to those in adjacent regions, and their relationship to the region’s ecological history requires the development of new paleohydrologic records. In lower Michigan, which lies between Great Lakes, annual precipitation declines from lake-effect snowbelts in the west to dry areas in the east, while temperature declines northward. Climate changes on orbital to interannual timescales could have influenced both gradients, altering the availability of moisture, and producing ecological consequences. Here, to constrain this history, we present a record of water-level changes at Sunrise Lake, Michigan based on physical and chemical characteristics of the preserved sedimentary record. Geophysical surveys paired with bulk density, loss-on-ignition, and grain size analyses of four cores collected at different water depths revealed multiple distinct changes in shoreline position since lake development. Lake levels initially rose at 5.15 cal ka BP and subsequently stabilized for multiple millennia. A prominent drop in water level then followed after 3.4 cal ka BP, leading to a low water level until 1.8 cal ka BP. The highest level appears to have developed by ca. 350 years ago and persisted until today. The record displays similarities to general trends seen on regional scales with additional local influences imposed. Additionally, water-level changes at Sunrise Lake provide context for regional forest changes recorded by fossil pollen stratigraphies from the region.