Antarctic Ice Sheet Stability During Warm Periods: Integrating Numerical Modeling With Geologic Data, Anna Ruth W. Halberstadt

Doctoral Dissertations

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Sea level rise is one of the major social and environmental challenges that threatens modern civilization, yet the response of polar ice sheets to future warming is deeply uncertain. Mass loss from the Antarctic Ice Sheet is projected to dominate global sea level rise in the near future, but how much, and when, remains a key unknown. The challenges associated with projecting Antarctica’s future sea level contribution are derived from a knowledge gap of physical ice sheet processes in a world warmer than today, and a lack of understanding of climatic thresholds that drive potentially irreversible retreat. Future and even …

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Modeling The Pleistocene History Of The Greenland Ice Sheet, Benjamin Andrew Keisling

Doctoral Dissertations

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One of the most profound and immediate consequences of anthropogenic climate change is sea level rise, which in large part is driven by the melting of polar ice sheets. The Greenland Ice Sheet (GrIS) contains enough ice to raise global sea level by ~7 meters. Fluctuations of the GrIS in response to past climate change provide an opportunity to better understanding the stability of the ice sheet during periods of climatic change. In this thesis, we use numerical ice-sheet models to understand the causes and consequences of past fluctuations of the Greenland ice sheet. In Chapters 3 and 4, we …

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Middle To Late Pleistocene Paleoenvironmental Reconstructions From Lake El'gygytgyn, Arctic Russia, Mary Helen Habicht

Doctoral Dissertations

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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 …

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Wildfires In The Northeastern United States: Evaluating Fire Occurrence And Risk In The Past, Present, And Future, Daniel R. Miller

Doctoral Dissertations

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Climate change is one of the most complex and challenging issues facing the world today. A changing climate will affect humankind in many ways and alter our physical environment, presenting ethical challenges in how we respond. The impact of climate change will likely be exacerbated in heavily populated regions of the planet, such as the Northeastern United States (NEUS). The NEUS is comprised of complex, sprawling urban centers and rural regions, both of which are vital to the economic and cultural character of the region. Furthermore, both urban and rural areas in the NEUS contain communities that have been historically …

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Mid-Pliocene To Early Pleistocene Sea Surface And Land Temperature History Of Nw Australia Based On Organic Geochemical Proxies From Site U1463, Rebecca Smith

Masters Theses

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Ocean gateways facilitate water circulation between ocean basins, and therefore directly impact thermohaline circulation and global climate. In order to better predict the effects of future climate change, it is critical to constrain past changes in ocean gateway behavior, and corresponding changes in thermohaline circulation, particularly during analogue periods for modern climate change. The Indonesian Throughflow (ITF) is a primary ocean gateway and vital component of the global conveyor that transports water from the Pacific Ocean into the Indian Ocean, however due to a lack of long and continuous sedimentary records from locations under its influence, changes in ITF behavior …

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Eccentricity Modulation Of Precessional Variation In The Earth’S Climate Response To Astronomical Forcing: A Solution To The 41-Kyr Mystery, Rajarshi Roychowdhury

Doctoral Dissertations

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The 41,000-year variability of Earth’s glacial cycles during the late Pliocene-early Pleistocene is usually attributed to variations in Earth’s obliquity (axial tilt). However, a satisfactory explanation for the lack of precessional variation in marine d¹⁸O records, a proxy for ocean temperature and ice-volume, remains contested. Here, a physically based climate model is used to show that the climatic effect of precession is muted in global isotope records due to two different mechanisms, with each dominating as a function of eccentricity. At low eccentricities (e0.019), the time-integrated summer insolation and number of positive degree-days impacting ice sheets varies at …

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Arctic And North Atlantic Paleo-Environmental Reconstructions From Lake Sediments, Gregory A. De Wet

Doctoral Dissertations

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ABSTRACT

ARCTIC AND NORTH ATLANTIC PALEO-ENVIRONMENTAL RECONSTRUCTIONS FROM LAKE SEDIMENTS MAY 2017 GREGORY A. DE WET, B.Sc., BATES COLLEGE M.Sc., UNIVERSITY OF MASSSCHUSETTS, AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS, AMHERST Directed by: Drs. Raymond S. Bradley and Isla S. Castañeda There are few fields in the discipline of Earth Science that hold more relevancy in 2017 than studies of earth’s climate. Called the “perfect problem” considering its complexity and magnitude, climate change will continue to be one of the greatest challenges humanity will face in the 21^st century. And while numerical models provide valuable information on conditions in the future, …

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A High-Resolution Paleoenvironmental And Paleoclimatic History Of Extreme Events On The Laminated Sediment Record From Basin Pond, Fayette, Maine, U.S.A., Daniel R. Miller

Masters Theses

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Future impacts from climate change can be better understood by placing modern climate trends into perspective through extension of the short instrumental records of climate variability. This is especially true for extreme climatic events, such as extreme precipitation and wildfires, as the period of instrumental records provides only a few examples and these have likely have been influenced by anthropogenic warming. Multi-parameter records showing the past range of climate variability can be obtained from lakes. Lakes are particularly good recorders of climate variability because sediment from the surrounding environment accumulates in lakes, making them sensitive recorders of climate variability and …

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Examining The Mid- Brunhes Event In The Terrestrial Arctic: An Organic Geochemical Record From Lake El’Gygytgyn, Russia, Mary Helen Habicht

Masters Theses

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The characteristic glacial and interglacial cycles of the Pleistocene underwent a climatic transition at ~430 ka known as the Mid- Brunhes Event (MBE). Many studies, particularly from the Southern Hemisphere have noted that after this transition, the amplitude of the climatic cycles increased. Despite the indication of an MBE signal in many globally distributed paleoclimate records, the geographic extent of the climatic transition remains unknown and its presence in northern hemisphere and terrestrial records is debated. Lake El’gygytgyn is located in the far- east Russian Arctic and provides the longest, most continuous record of Arctic climate (3.6 Ma). This study …

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Arctic Environmental Change Across The Pliocene-Pleistocene Transition, Benjamin Andrew Keisling

Masters Theses

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Environmental change in the Arctic proceeds at an unprecedented rate. The Pliocene epoch (5-2.65 million years ago) represents an analog for future climate conditions, with pCO₂ and continental configurations similar to present. Yet conditions in the Pliocene Arctic are poorly characterized because of sparse sampling. The records that do exist indicate periods of extreme warmth, as well as the first expansion of large ice-sheets in the Northern Hemisphere, took place from the end of the Pliocene into the early Pleistocene. Understanding these deposits and their implications for our future requires developing a sense of climatic evolution across the …

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Sedimentological, Geochemical And Isotopic Evidence For The Establishment Of Modern Circulation Through The Bering Strait And Depositional Environment History Of The Bering And Chukchi Seas During The Last Deglaciation, Ben M. Pelto

Masters Theses

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Sea level regression during the Last Glacial Maximum exposed the Bering Land Bridge, and cut off the connection between the North Pacific and Arctic Ocean, ending the exchange of North Pacific Water through the Bering Strait. Exchange of North Pacific Water comprises a major portion of fresh water input to the Arctic Ocean, and is of vital importance to North Atlantic Deep Water formation, a vital component of Atlantic Meridional Overturning Circulation. Bering Strait throughflow thus plays an integral role in global climate stability. A suite of four cores was selected, three in the Bering Sea and one in the …

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Compound-­Specific Hydrogen Isotopes Of Lipid Biomarkers In Lake El’Gygytgyn, Ne Russia, Kenna M. K. Wilkie

Open Access Dissertations

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Recent successful drilling operations at Lake El'gygytgyn, NE Russia have recovered sediment cores back to 3.6Ma, representing the longest time-continuous sediment record of past climate change in the terrestrial Arctic. Analysis of the hydrogen isotopic ratio (δD) of specific organic biomarkers allows reconstruction of past hydrological conditions, thereby providing a powerful tool for reconstructing past Arctic climate changes. Compound specific isotopic analysis of sedimentary lipids from this remote basin provides new insights into the climate evolution of the Arctic, capturing the mechanisms and dynamics of the last two glacial-interglacial transitions, potentially enhancing the accuracy of modeled future climate change projections …

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Lacustrine Records Of Holocene Climate And Environmental Change From The Lofoten Islands, Norway, Nicholas L. Balascio

Open Access Dissertations

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Lakes sediments from the Lofoten Islands, Norway, can be used to generate well resolved records of past climate and environmental change. This dissertation presents three lacustrine paleoenvironmental reconstructions that show evidence for Holocene climate changes associated with North Atlantic climate dynamics and relative sea-level variations driven by glacio-isostatic adjustment. This study also uses distal tephra deposits (cryptotephra) from Icelandic volcanic eruptions to improve the chronologies of these reconstructions and explores new approaches to crypto-tephrochronology. Past and present conditions at Vikjordvatnet, Fiskebølvatnet, and Heimerdalsvatnet were studied during four field seasons conducted from 2007-2010. Initially, each lake was characterized by measuring water …

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