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Hydroclimate Variability In Central America During The Holocene Inferred From Lacustrine Sediments In Lake Izabal Eastern Guatemala
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Book Synopsis Hydroclimate Variability in Central America During the Holocene Inferred from Lacustrine Sediments in Lake Izabal, Eastern Guatemala by : Edward Duarte
Download or read book Hydroclimate Variability in Central America During the Holocene Inferred from Lacustrine Sediments in Lake Izabal, Eastern Guatemala written by Edward Duarte and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Holocene hydroclimate reconstructions have contributed to our understanding of the mechanisms controlling precipitation in Central America. Recent hydroclimate proxy records from the region, however, have revealed considerable spatiotemporal complexity in precipitation variability. This complexity is hypothesized to result from the interaction between multiple oceanic-atmospheric processes that converge in the region. This project analyzed three sediment cores from Lake Izabal, eastern lowland Guatemala, with the goal of understanding changes in precipitation, lake productivity, and lake water chemistry during the Holocene. Our proxy results indicate that precipitation in the region increased from the early to the middle Holocene, when Lake Izabal became a meromictic lake following a marine incursion. Anoxic bottom waters lasted ~3,500 years, preserving 2,186 mm-scale dark and light laminae couplets that are distinctly different in color, composition, and texture. At ~4,800 calibrated years before present (cal yr BP), Lake Izabal became a polymictic lake, and precipitation in the region stabilized, remaining high until ~1,200 cal yr BP, with an abrupt decrease in precipitation thereafter. Our findings indicate that Lake Izabal is highly sensitive to changes in Caribbean sea level and Caribbean sea-surface temperatures, the former controlling lake water chemistry and the latter controlling precipitation. Our results also add to new hydroclimate proxy data from the region, highlighting the complexity in precipitation variability in the area. Additional paleoclimate proxy records from Central America are needed to improve our understanding of how global warming will affect environmental conditions and regional hydroclimate variability"--Abstract, page iv.
Download or read book Criminal Procedure Law written by and published by . This book was released on 1959 with total page 672 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A 5200 Year Record of Precipitation Changes in West-central Guatemala Inferred from Lacustrine Carbonate-based Stable Isotopes by : Jacob Ryan Feller
Download or read book A 5200 Year Record of Precipitation Changes in West-central Guatemala Inferred from Lacustrine Carbonate-based Stable Isotopes written by Jacob Ryan Feller and published by . This book was released on 2016 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: Guatemala is a drought-sensitive country that experiences varying amounts of precipitation in response to Atlantic and Pacific Ocean influences. A 5.5 m, finely-laminated sediment core from Lake San Francisco in the Huehuetenango province was collected in order to reconstruct precipitation changes over the last [almost equal to]5,200 years at a decadal-scale resolution. An age-depth model was developed based on 7 radiocarbon ages of charcoal as well as 210Pb dating of surface sediments. Authigenic calcite preserved in the sediment record provides an archive of lake-water isotopic variability in response to climate driven changes in hydrologic balance. Modern surface water isotope data taken from lakes throughout the region do not indicate evaporative enrichment relative to meteoric water. Within open-basin lakes within the Tropics, such as San Francisco, [delta]18O variation is often driven by the amount effect. This means that high [delta]18O reflects drier conditions within the record while lower [delta]18O values indicate wetter overall periods. Our data suggest relatively dry conditions within the region between 5-2 ka BP, with the driest period lasting from [almost equal to]4.2 to [almost equal to]3.2 ka. A shift to wetter conditions began at [almost equal to]2 ka and persisted until the past century. Correspondence between the San Francisco record and both North Atlantic Oscillation (NAO) and El Nino Southern Oscillation (ENSO) reconstructions suggest that both of these modes of variability drive precipitation change in this region of Guatemala. In general, positive (negative) phases of ENSO cause drier (wetter) conditions, while positive (negative) phases of NAO cause wetter (drier) conditions throughout the duration of the record. The detailed stratigraphy and well-resolved age model exhibited by the San Francisco record indicate a high potential to produce detailed paleoclimate data from Western Guatemala.
Book Synopsis Climate Change in Lowland Central America During the Late Deglacial and Early Holocene by :
Download or read book Climate Change in Lowland Central America During the Late Deglacial and Early Holocene written by and published by . This book was released on 2005 with total page 51 pages. Available in PDF, EPUB and Kindle. Book excerpt: The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition ((almost equal to)11,250 to 7,500 cal yr BP) inferred from sediment cores retrieved in Lake Peten Itza, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by (almost equal to)11,250 cal yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11,250 to 10,350 cal yr BP, during the Preboreal period, lithologic changes in sediments from deep-water cores (>50 m below modern water level) indicate several wet-dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1-4) occurred at 11,200, 10,900, 10,700, and 10,400 cal yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10,350 cal yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Peten Itza with other records from the circum-Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high-latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores-Bermuda high-pressure system. This mechanism operated on millennial-to-submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC).
Book Synopsis Holocene Climate Change in the Eastern United States and Canada Inferred from Lake Sedimentation Rates by : John Warren Dunham
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:
Book Synopsis Holocene glacier fluctuations and tephra fall inferred from lacustrine sediment, Emerald Lake, Alaska by : Taylor S. LaBrecque
Download or read book Holocene glacier fluctuations and tephra fall inferred from lacustrine sediment, Emerald Lake, Alaska written by Taylor S. LaBrecque and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Late Holocene Oxygen Isotope Record of Hydroclimate Variability in Nicaragua from Lake Asososca by : Stephen Perdziola
Download or read book Late Holocene Oxygen Isotope Record of Hydroclimate Variability in Nicaragua from Lake Asososca written by Stephen Perdziola and published by . This book was released on 2018 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: Investigation of hydroclimate requires a higher level of spatial and temporal detail than what currently exists for Central America. High resolution lake sediment archives are critical to gaining a more complete understanding of late Holocene climate variability in the region. The climate of Central America is influenced by both tropical Atlantic and Pacific Ocean-atmosphere processes. A better understanding of how these processes have impacted regional hydroclimate is important as it will enable more accurate predictions of future climate changes associated with shifting conditions in a drought sensitive region. Here a 1,000-year carbonate oxygen isotope record is presented from Lake Asososca, located in western Nicaragua. In this record, high delta 18O values indicate drier conditions, while lower ?18O values indicate drier conditions. My data indicate wet conditions at the start of the Medieval Climate Anomaly (MCA) and a trend towards drier conditions until A.D. 1200. The transitional period between the MCA and the Little Ice Age (LIA) from A.D. 1200 - 1400 experienced a shift towards wetter conditions. The LIA from A.D. 1400 -- 1850 was a period of variable conditions. My record indicates a shift from wet to dry conditions from A.D. 1400 - 1600. A pronounced period of wetter conditions occurred from A.D. 1650-1700 during the Maunder Minimum solar event. From A.D 1700 -- 1800 the record indicates variable conditions that alternated between shifts towards dry and wet. After the LIA, the record indicates a trend towards drier conditions. The El Nino Southern Oscillation (ENSO), the North American Oscillation (NAO), and the Atlantic Multidecadal Oscillation (AMO), were often temporally correlated with the Lake Asososca record and suggest that these modes have impacted regional hydroclimate over the late Holocene. Correspondence between the Lake Asososca record and solar variability highlight a potential linkage. Climate models indicate that the Atlantic Meridional Overturning Circulation responds to changes in solar variability and can have impacts on Atlantic SSTs, and therefore may be provide a mechanism to amplify changes in solar variability to Central American hydroclimate. Comparison of the Lake Asososca delta18O record to regional hydroclimate proxies across show little correspondence over the past millennium. While some similarities exist between the Lake Asososca record and other regional proxies, the lack of a coherent hydroclimate signal over the late Holocene suggests temporally and spatially variability hydroclimate shifts. More hydroclimate reconstructions and modelling studies need to be performed in order to fully resolve hydroclimate variability in Central America over the past millennium. This record adds to the network of regional paleoclimate reconstructions in Central America and indicates that modes of variability in both the Atlantic and Pacific Ocean basins have impacted regional hydroclimate over the past millennium.
Book Synopsis Late Glacial to Holocene Climate and Vegetation Changes on the Tibetan Plateau Inferred from Fossil Pollen Records in Lacustrine Sediments by : Yongbo Wang
Download or read book Late Glacial to Holocene Climate and Vegetation Changes on the Tibetan Plateau Inferred from Fossil Pollen Records in Lacustrine Sediments written by Yongbo Wang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The past climate in central Asia, and especially on the Tibetan Plateau (TP), is of great importance for an understanding of global climate processes and for predicting the future climate. As a major influence on the climate in this region, the Asian Summer Monsoon (ASM) and its evolutionary history are of vital importance for accurate predictions. However, neither the evolutionary pattern of the summer monsoon nor the driving mechanisms behind it are yet clearly understood. For this research, I first synthesized previously published Late Glacial to Holocene climatic records from monsoonal central Asia in order to extract the general climate signals and the associated summer monsoon intensities. New climate and vegetation sequences were then established using improved quantitative methods, focusing on fossil pollen records recovered from Tibetan lakes and also incorporating new modern datasets. The pollen-vegetation and vegetation-climate relationships on the TP were also evaluated in order to achieve a better understanding of fossil pollen records. The synthesis of previously published moisture-related palaeoclimate records in monsoonal central Asia revealed generally different temporal patterns for the two monsoonal subsystems, i.e. the Indian Summer Monsoon (ISM) and East Asian Summer Monsoon (EASM). The ISM appears to have experienced maximum wet conditions during the early Holocene, while many records from the area affected by the EASM indicate relatively dry conditions at that time, particularly in north-central China where the maximum moisture levels occurred during the middle Holocene. A detailed consideration of possible driving factors affecting the summer monsoon, including summer solar insolation and sea surface temperatures, revealed that the ISM was primarily driven by variations in northern hemisphere solar insolation, and that the EASM may have been constrained by the ISM resulting in asynchronous patterns of evolution for these two subsystems. This hypothesis is further supported by modern monsoon indices estimated using the NCEP/NCAR Reanalysis data from the last 50 years, which indicate a significant negative correlation between the two summer monsoon subsystems. By analogy with the early Holocene, intensification of the ISM during coming decades could lead to increased aridification elsewhere as a result of the asynchronous nature of the monsoon subsystems, as can already be observed in the meteorological data from the last 15 years. A quantitative climate reconstruction using fossil pollen records was achieved through analysis of sediment core recovered from Lake Donggi Cona (in the north-eastern part of the TP) which has been dated back to the Last Glacial Maximum (LGM). A new data-set of modern pollen collected from large lakes in arid to semi-arid regions of central Asia is also presented herein. The concept of "pollen source area" was introduced to modern climate calibration based on pollen from large lakes, and was applied to the fossil pollen sequence from Lake Donggi Cona. Extremely dry conditions were found to have dominated the LGM, and a subsequent gradually increasing trend in moisture during the Late Glacial period was terminated by an abrupt reversion to a dry phase that lasted for about 1000 years and coincided with the first Heinrich Event of the northern Atlantic region. Subsequent periods corresponding to the warm Bølling-Allerød period and the Younger Dryas cold event were followed by moist conditions during the early Holocene, with annual precipitation of up to about 400 mm. A slightly drier trend after 9 cal ka BP was then followed by a second wet phase during the middle Holocene that lasted until 4.5 cal ka BP. Relatively steady conditions with only slight fluctuations then dominated the late Holocene, resulting in the present climatic conditions. In order to investigate the relationship between vegetation and climate, temporal variations in the possible driving factors for vegetation change on the northern TP were examined using a high resolution late Holocene pollen record from Lake Kusai. Moving-window Redundancy Analyses (RDAs) were used to evaluate the correlations between pollen assemblages and individual sedimentary proxies. These analyses have revealed frequent fluctuations in the relative abundances of alpine steppe and alpine desert components, and in particular a decrease in the total vegetation cover at around 1500 cal a BP. The climate was found to have had an important influence on vegetation changes when conditions were relatively wet and stable. However, after the 1500 cal a BP threshold in vegetation cover was crossed the vegetation appears to have been affected more by extreme events such as dust storms or fluvial erosion than by the general climatic trends. In addition, pollen spectra over the last 600 years have been revealed by Procrustes analysis to be significantly different from those recovered from older samples, which is attributed to an increased human impact that resulted in unprecedented changes to the composition of the vegetation. Theoretical models that have been developed and widely applied to the European area (i.e. the Extended R-Value (ERV) model and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model) have been applied to the high alpine TP ecosystems in order to investigate the pollen-vegetation relationships, as well as for quantitative reconstructions of vegetation abundance. The modern pollen-vegetation relationships for four common pollen species on the TP have been investigated using Poaceae as the reference taxa. The ERV Submodel 2 yielded relatively high PPEs for the steppe and desert taxa (Artemisia Chenopodiaceae), and low PPEs for the Cyperaceae that are characteristic of the alpine Kobresia meadows. The plant abundances on the central and north-eastern TP were quantified by applying these PPEs to four post-Late Glacial fossil pollen sequences. The reconstructed vegetation assemblages for the four pollen sequences always yielded smaller compositional species turnovers than suggested by the pollen spectra, indicating that the strength of the previously-reported vegetation changes may therefore have been overestimated. In summary, the key findings of this thesis are that (a) the two ASM subsystems show asynchronous patterns during both the Holocene and modern time periods, (b) fossil pollen records from large lakes reflect regional signals for which the pollen source areas need to be taken into account, (c) climate is not always the main driver for vegetation change, and (d) previously reported vegetation changes on the TP may have been overestimated because they ignored inter-species variations in pollen productivity
Book Synopsis Holocene Paleohydrologic Change Inferred from the Sediment Record at Sunrise Lake, Michigan by : Amanda Toomey
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.
Book Synopsis 7700 Years of Holocene Climatic Variability in Sermilik Valley, Southeast Greenland Inferred from Lake Sediments by : Samuel Hallett Davin
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.
Book Synopsis Mechanisms of Tropical Pacific Climate Change During the Holocene by : Alyssa Regine Atwood
Download or read book Mechanisms of Tropical Pacific Climate Change During the Holocene written by Alyssa Regine Atwood and published by . This book was released on 2015 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: A novel set of hydroclimate reconstructions is presented from the eastern equatorial Pacific that spans the last 9100 years. Past changes in total climatological rainfall and rainfall associated with El Niño events were reconstructed using the sedimentary distribution, accumulation rate, and hydrogen isotope composition of four lipid biomarkers in the sediment of El Junco Lake, San Crist??bal Island. Possible mechanisms of the multi-decadal to millennial scale rainfall variations inferred at El Junco Lake are evaluated in light of tropical hydroclimate and global climate reconstructions through the Holocene. Tropical hydroclimate changes are further investigated during the so-called "8.2 ka event" and the Little Ice Age (LIA) using climate model simulations. We propose that rainfall changes at El Junco Lake ca. 8500-8000 yr BP were produced by a large meltwater pulse in the North Atlantic that caused a southward shift of the ITCZ (via reduced northward ocean heat transport and expanded Arctic sea ice) and weakened El Niño/Southern Oscillation (ENSO) variability (via tropical Pacific mean state changes that increased the stability of the coupled ocean-atmosphere system). We provide support for this concept using simulations with a fully coupled global climate model (CESM) and a linearized ocean-atmosphere model of the tropical Pacific (LOAM), Tropical hydroclimate changes and their mechanisms during the LIA were investigated in the CMIP5/PMIP3 last millennium simulations. Climate forcings and feedbacks were quantified using the Approximate Partial Radiative Perturbation and radiative kernel methods, highlighting the role of volcanic forcing and the water vapor, lapse rate, and surface albedo feedbacks during the LIA. A weak southward shift in zonally averaged tropical precipitation was found during the LIA in the model simulations in association with anomalous northward cross-equatorial atmospheric energy transport that was driven by greater volcanic forcing and greater snow and sea ice response in the Northern (versus Southern) Hemisphere. A second theme of this dissertation is the influence of tropical Pacific mean state changes on ENSO variability. This concept is explored through simulations of the 8.2 ka event, as well as through analysis of the large, unforced, multi-decadal changes in ENSO variability in the General Circulation Model GFDL CM2.1. Experiments using LOAM suggest that a two-way feedback operates between ENSO and the mean state of the tropical Pacific in CM2.1, whereby random forcing and nonlinear dynamics produce low frequency changes in ENSO variance that are then counteracted by mean state feedbacks.
Book Synopsis Late Holocene Climate and Environmental Change Inferred from Arctic Lake Sediment by : Darrell S. Kaufman
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:
Book Synopsis Holocene climate and vegetation change in the main Ethopian Rift Valley, inferred from the composition of lacustrine organic matter by : A.L. Lamb
Download or read book Holocene climate and vegetation change in the main Ethopian Rift Valley, inferred from the composition of lacustrine organic matter written by A.L. Lamb and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Holocene Environmental Variability Inferred from Lake Sediments, Southwest Yukon Territory, Canada by : Joan Bunbury
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:
Book Synopsis Late Holocene Spatiotemporal Hydroclimatic Variability Over Fennoscandia Inferred from Tree-rings by :
Download or read book Late Holocene Spatiotemporal Hydroclimatic Variability Over Fennoscandia Inferred from Tree-rings written by and published by . This book was released on 2014 with total page 47 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Holocene Flood Variability and Glacier Fluctuations in the Central Alps Revealed by Lacustrine Sediments by : Lukas Glur
Download or read book Holocene Flood Variability and Glacier Fluctuations in the Central Alps Revealed by Lacustrine Sediments written by Lukas Glur and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Climatic Changes Inferred from Analyses of Lake-sediment Cores, Walker Lake, Nevada ; Prepared in Cooperation with the U.S. Department of Energy by : In Che Yang
Download or read book Climatic Changes Inferred from Analyses of Lake-sediment Cores, Walker Lake, Nevada ; Prepared in Cooperation with the U.S. Department of Energy written by In Che Yang and published by . This book was released on 1989 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
