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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.
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
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.
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.
This book studies the history and gives an analysis of extreme climate change on Earth. In order to provide a long-term perspective, the first chapter briefly reviews some of the wild gyrations that occurred in the Earth’s climate hundreds of millions of years ago: snowball Earth and hothouse Earth. Coming closer to modern times, the effects of continental drift, particularly the closing of the Isthmus of Panama are believed to have contributed to the advent of ice ages in the past three million years. This first chapter sets the stage for a discussion of ice ages in the geological recent past (i.e. within the last three million years, with an emphasis on the last few hundred thousand years). The second chapter discusses geological evidence for ice ages – how geologists surmised their existence prior to actual subsurface data that proved the theory. The following two chapters look at ice cores (primarily from Greenland and Antarctica). Chapter 3 discusses how ice core data is processed and Chapter 4 summarizes data obtained from ice cores. Chapter 5 discusses the processing of data obtained from ocean sediments, and summarizes the results, while the following chapter discusses data from other sources, such as "Devil’s Cave." Chapter 7 summarizes the experimental results from Chapters 4, 5, and 6. It provides the foundation for comparison with theories in later chapters. In a perfect world, this data would be totally separate and disconnected from theory. Unfortunately, as the author shows, dating of much of the data was accomplished by "tuning" to the astronomical theory, which introduces circular reasoning. Chapter 8 provides a brief overview of the various theories that have been devised to "explain" the patterns of alternating ice ages and interglacials that have occurred over the past three million years. This serves as an introduction to the following three chapters which presents the astronomical theory in its various manifestations, compare the astronomical theory with data, and then compare other theories with data. Finally, Chapter 12 summarizes what we think we know about ice ages and, more importantly, what we don’t know.
This dissertation reconstructs late Pleistocene oceanic circulation variability within the North Atlantic, a critical region of deep-water formation, using proxies that reconstruct surface and deepwater changes. Unlike other studies that examine North Atlantic circulation as a whole, my study focuses on changes in Iceland Scotland Overflow Water (ISOW), one of the largest contributors to Northern Component Water (NCW). Each NCW component reflects the regional climate within its formation region; thus, different climates may produce different deepwater states by changing the relative contribution from each component. Southern Gardar Drift is bathed by ISOW, thus the accumulating sediments are ideal for examining ISOW. A high-resolution record of the Younger Dryas cold event provides an analog for abrupt climate events. The benthic foraminiferal [delta]13C record from core 11JPC (2707m) on Gardar Drift reveals NCW shoaled during the early and late Younger Dryas. These reductions are coincident with increased meltwater from Northern Hemisphere ice sheets, linking surface freshening to NCW production changes on short-timescales. On longer time-scales, benthic foraminiferal [delta]13C records from Gardar Drift show ISOW density was paced by northern high-latitude summer insolation, particularly within the precessional band. Uniform benthic foraminiferal [delta]13C values on Gardar Drift indicate that the mixing zone between NCW and Southern Component Water (SCW) was positioned to the south of Gardar Drift during interglacial periods. Conversely a large north-south gradient in benthic foraminiferal [delta]13C values during glacial periods indicates that ISOW shoaled, allowing SCW to bathe southern Gardar Drift. High-frequency ISOW variability caused by surface freshening during intermediate climate states is superimposed on the orbitally paced variations. A study of the trace metal compositions in Krithe carapaces found in core top samples demonstrates that calcification temperature is the dominant control on magnesium incorporation. Carbonate ion concentration is a secondary control on magnesium to calcium (Mg/Ca) ratios at low temperatures (