[PDF] A High Resolution Study Of A Late Pleistocene Interglacial Glacial Transition And Its Periodicity In Owens Lake California Core Ol 92 eBook

Author : Kirsten Margaret Menking
Publisher :
Page : 420 pages
File Size : 19,91 MB
Release : 1995
Category : Paleoclimatology
ISBN :

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In 1992, the U.S. Geological Survey cored Owens Lake to obtain a continuous paleoclimate record for the Sierra Nevada region. Owens Lake heads a chain of closed-basin lakes which are separated by a series of bedrock sills, received their water primarily from Sierra Nevadan precipitation, and overflowed during wet periods. The core records the histories of cyclic glaciation of the Sierra Nevada and water-balance of Owens Lake over the past 800 kyrs. A variety of paleoclimatic proxies have been studied, details of which may be found in Smith and Bischoff (1993). In this thesis, I report the results and interpretations of 1) grain-size and clay-mineralogical analyses performed on 3.5-m-long channel samples (%7500 years of sedimentation per sample) and point samples, 2) grain size, carbonate content, and oxygen isotopic measurements on 70-cm-long channel samples (%1500 years), and 3) a water-balance model used to infer the magnitude of runoff and evaporation changes necessary to fill the lakes in the Owens Lake system, and to determine the response time of the lake chain to climatic perturbations.

Author : Peter U. Clark
Publisher : Geological Society of America
Page : 326 pages
File Size : 14,32 MB
Release : 1992-01-01
Category : Science
ISBN : 0813722705

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Focuses on the last time glaciers spread across the continent, using the records of former ice sheets, glaciers, and pluvial lakes to understand the response of North American ice sheets and glaciers to the climate change that ended the last (before ours) interglacial period. The 21 papers, most fro

Author :
Publisher :
Page : 218 pages
File Size : 48,37 MB
Release : 1995
Category :
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Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relative weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before (approximately) 13,100 cal yr B.P. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic 1°Be and 26Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.

Author : Elizabeth Grayce Ceperley
Publisher :
Page : 102 pages
File Size : 19,89 MB
Release : 2014
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Due to cryosphere-albedo feedbacks mechanisms, climate change is amplified in the Arctic, making it sensitive to changes in temperature. Alpine glaciers grow and retreat depending on climate, and are excellent recorders of past climate fluctuations. By analyzing the landforms and sediment deposited by glaciers, high-resolution climate chronologies can be constructed and past glacier fluctuations can be inferred. 10Be ages and physical properties of lake sediment are used here to reconstruct Late Pleistocene and Holocene glacier activity from Alapah River valley and Shainin Lake in the north-central Brooks Range. 10Be ages from moraine boulders in Alapah River valley in the north-central Brooks Range were used to reconstruct the maximum glacier extent during the LGM. After eliminating outliers, the 10Be ages from a terminal moraine deposit in the Alapah River valley indicate that the local LGM culminated at 21. 0 ℗ł 0. 8 ka. This new 10Be chronology is the first to firmly constrain the timing of the local LGM in the Brooks Range, and is in agreement with LGM moraine records from other sites in Alaska and the globe. Two 10Be ages from boulders located on bedrock 14 km upvalley from the Itkillik II terminal moraine give an age of deglaciation in Alapah River valley of 18. 2 ℗ł 0. 8 ka. This indicates rapid retreat after the LGM and shows that deglaciation is synchronous with sites in Alaska but was initiated earlier than the age of 17 ka previously proposed for onset of LGM deglaciation in the western US. Physical and geochemical properties of lake sediment from a proglacial lake in Alapah River valley, Shainin Lake, were analyzed to investigate any glacial signals recorded in the lake sediment. Age-depth models for each core were established using 14C ages and analytical methods included magnetic susceptibility, wet bulk density (WBD), scanning X-Ray fluorescence (ITRAX) and visible scanning reflectance spectroscopy. The WBD record from Shainin Lake may serve as a proxy for glacial history of Alapah and Kayak Creek valleys. If interpreted correctly, glacial activity increased from 12,700 to ~10,000 cal yr, decreased from ~10,000 to ~5700 cal yr BP, then increased from ~5700 cal yr BP to the present. This indicates that there is evidence for early Holocene glacial activity, the retreating or stagnating glaciers in the middle Holocene until ~5700 cal yr BP, followed by expanding ice.

Author : Mary Helen Habicht
Publisher :
Page : pages
File Size : 33,30 MB
Release : 2019
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Climate change is a major issue challenging the world today. Our global society faces rising temperatures, variable weather patterns, and rising sea level among other associated issues. Our action (or inaction) to address current changes will have serious ramifications for life on our planet in the coming centuries and millennia. In order to provide context for these present and future changes, we can utilize the paleo record to understand the natural variability of Earth's climate system. One region of the world is changing more rapidly than the global average. Over recent decades, the Arctic has experienced warmer temperatures, reduced sea ice, melting permafrost, and shifts in the amount and seasonality of precipitation. Unfortunately, paleoclimate and environmental records from the terrestrial Arctic, particularly beyond the last 120 ka, are few. This is due to the repeated extensive glaciation of the northern hemisphere high latitudes during the ice ages of the Quaternary. One area of the Arctic, in the Anadyr mountains of Chukotka, has remained unglaciated through the Pleistocene. Lake El'gygytgyn, a meteorite impact crater lake formed 3.6 million years ago lies in this area and so provides a continuous sedimentary sequence from the Mid-Pliocene to present. This dissertation includes four studies of Lake El'gygytgyn sediments over the last 800 thousand years. A variety of biogeochemical and stable isotope proxies are used to reconstruct climate and environmental variability throughout the study interval. These studies provide novel information about the natural variations of terrestrial Arctic climate on glacial-interglacial timescales. Chapter 2 of this dissertation involves the analysis of bacterial membrane lipids called branched glycerol dialkyl glycerol tetraethers (brGDGTs) and plant leaf wax n-alkanes to provide records of relative temperature change and terrestrial vegetation turnover in response to aridity during the glacial-intergacial cycles of the Mid-Pleistocene. Our data suggests that regional temperature is strongly influenced by local summer insolation while aridity changes derive from sea level driven changes in continentality. Comparison of our data with previously published paleoclimate records from Lake El'gygytgyn highlights the difference in proxy response to climatic variables and the utility of a multi-proxy approach. Additionally, we use our extensive records to identify the presence of a global climatic transition, the Mid-Brunhes Event (MBE), for the first time in the terrestrial Arctic. In Chapter 3, we analyze algal lipid biomarkers from the same samples used in Chapter 2. We also incorporate stable carbon and nitrogen isotopes to determine changes in primary production and organic matter preservation in Lake El'gygytgyn across multiple glacial-interglacial cycles. Chapter 4 spans the Holocene and Late Pleistocene (280 ka to present). We use the hydrogen isotopic composition of long chain plant leaf wax n-alkanes to reconstruct temperature and hydroclimate changes. We find that MIS 7 was a stronger interglacial period than MIS 5e in the terrestrial Arctic and attribute the variability in hydrogen isotopes predominantly to temperature and moisture source changes. In Chapter 5, we compare the hydrogen isotope composition of n-alkanes measured in Chapter 4 to the isotopic composition of n-alkanoic acids in the same samples previously analyzed by Wilkie (2012). This is a novel approach for paleoclimate records. Our results indicate that the type of compound selected for analysis can have a significant impact on the paleoclimatic interpretations of a study. Finally in Chapter 6, a summary and avenues for future research are provided. Overall, this dissertation is a testament to the utility of biomarkers and stable isotopes in Arctic lake sediments. Each study provides unique information about the terrestrial Arctic climate during the Quaternary and contributes to our understanding of climatic variability and the dynamics of this sensitive region.

Author : Nathan W. Dickey
Publisher :
Page : 144 pages
File Size : 36,79 MB
Release : 2016
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Glaciers are sensitive to local and global climate variations, especially to changes in precipitation and temperature over sub-millennial timescales. Therefore, glacial deposits are excellent tools for reconstructing past climates. The western United States exhibits an excellent record of glaciation, but ongoing work across the region shows complex and yetunexplained variation in timing and extent of deglaciation between different mountain ranges at the end of the Last Glacial Maximum (LGM). The Trinity Alps of the southern Klamath Mountains in Northern California contain an excellent record of Pleistocene glaciation which I use to fill a significant spatial gap in published glacial chronologies and to provide a bridge between the Sierra Nevada and the Cascades. The Trinity Alps Wilderness is a 2,130 sq. km. federally designated area located at 41.00° N, 123.00°W, approximately 60 km southwest of Mt. Shasta in Northern California. Glacial deposits in the Trinity Alps were located using Google Earth and previously published maps, and were confirmed in the field. Building on a series of previous expeditions, in the summer of 2015 twenty-four samples from five moraines were taken for 10Be exposure dating, as well as three samples from striated bedrock. Of these, six samples were selected for exposure age analysis: five from two early LGM moraines and one from an older moraine. These ages, in addition to twenty-four ages determined in a previous study, provide evidence for at least two stages of post-LGM glaciation of similar extent throughout the Trinity Alps: the first ending at 16.83 ± 1.85 ka, the second at 12.29 ± 1.23 ka. These ages correlate with the regional LGM (~17 ka) and the global Younger Dryas (~12 ka) cooling event, respectively. The moraine maps were then used to constrain results from a climate-driven 2D numerical model of glacier mass balance and flow. This model was used to determine the potential precipitation and temperature difference from modern climate that would generate the mapped glaciers. Comparison of the resulting paleoclimate curves with nearby proxies and global climate models suggest that an approximate 5.5°C decrease in temperature and 0 to 25% increase in precipitation drove LGM glaciation in the region. Additionally, these results suggest that a similarly wet but slightly warmer-than-LGM climate drove a regionally asynchronous re-advance in the Trinity Alps linked with the Younger Dryas cooling event.