<p> Lipids preserved in soils and sediments are important proxies in paleoclimate research. However, various growth conditions that affect the organisms synthesizing the lipids can in turn affect the abundance and stable isotopic compositions of the lipids themselves, and, consequently, can introduce significant errors in the paleoclimatic inferences drawn from them. This work examines how two climate proxies based on lipids, namely, glycerol dialkyl glycerol tetraether (GDGT)-based paleotemperature proxies in soils, and paleohydrological proxies based on hydrogen isotopic composition of lipids, respond to variability in environmental and other growth conditions (e.g., carbon source).</p><p> In order to evaluate the role of annual precipitation amount on the distribution of soil GDGTs and on GDGT-based temperature proxies in soils, we studied GDGT distribution in soils collected from two environmental transects in the USA&mdash;a dry, western transect covering six western states and a wet, east coast transect from Maine to Georgia. Our results indicate a significant impact of precipitation amount on soil GDGT distribution, which is related to soil aeration that in turn depends on precipitation amount, and also to soil pH. Our results also indicate that below an annual precipitation of 700-800 mm yr^&ndash;1 the MBT/CBT-temperature proxy based on soil GDGTs is not applicable. Furthermore, due to the distinct GDGT distributions in soils under arid conditions, soil input into lacustrine or marginal marine environments cannot be estimated using BIT index.</p><p> In order to estimate the effects of variability in environmental conditions and utilization of different substrates on D/H_lipid, we studied two heterotrophic organisms&mdash;<i>Haloarcula marismortui</i>, a halophilic archaeon and <i>Tetrahymena thermophila</i>, a ciliated protozoan, in pure cultures. Our results from experiments with <i>H. marismortui</i> indicate that metabolism of different substrates leads to formation of reducing agents (mainly nicotinamide adenine dinucleotide phosphate or NADPH) with distinct D/H signatures, which is reflected in the significant D/H variations in isoprenoidal lipids (ca. 100&permil;). Growth temperature affects growth rate as well as enzyme activities, and salinity of the growth media affects mainly growth rate of <i>H. marismortui</i>, and both cause similar variations in D/H_lipid (ca. 20-30&permil;) that are smaller compared to the substrate-effect. <i>T. thermophila </i>, on the other hand, responds to variations in growth temperature in a different manner. Isoprenoid and fatty acids synthesized by <i> T. thermophila</i> generally become more D-enriched with temperature increase. The isoprenoid ranges from being D-depleted to D-enriched relative to water with temperature increase, but the fatty acids do not display similar patterns. Our results from <i>T. thermophila</i> culture experiments indicate that temperature has a critical control on the D/H ratios of NADPH and possibly also intracellular water, due probably to temperature effects on processes that are related to growth and metabolism of <i>T. thermophila. </i></p>

<p> The increased surface melting of the outlet glaciers of the Vatnaj&ouml;kull Ice Cap has a profound affect on the dynamics of the ice-bed couple and landform genesis. Soft-bedded glaciers are largely inaccessible, which creates a problem. One challenge is to understand the complex interactions of the glacier bed and its resultant depositional and deformational landform systems. This study investigates an outlet glacier from the Vatnaj&ouml;kull Ice Cap, described herein as the Fl&aacute;aj&ouml;kull glacier system. To circumvent some of these problems, three separate projects were conducted in this dissertation: (1) magnetic fabric study of effective pressure (difference between the ice-overburden pressure and pore-water pressure) and shear rate (glacier velocity) using a laboratory ring-shear device; (2) glaciological analysis of magnetic fabrics and c-axis orientations of dirty ice veins; and (3) investigation of drumlin formation using magnetic till fabrics and field relationships. Several hypotheses were addressed for each of these studies, which include: (1) to determine if fabric strength is independent of shear rate and effective pressure. This hypothesis was tested and the results confirmed that the fabric strength (S1 eigenvalue) was independent of shear rate and effective pressure. Based on these results, effective pressure and shear rate cannot be interpreted from fabric strength evidence from glacial deposits; (2) in the glaciological study, I hypothesized that the dirty ice veins were sub-vertically sheared from the bed near the ice front, but then moderately deformed. Results from the magnetic fabrics indicate that the maximum K1 susceptibility axis (77&deg; plunge) is approximately parallel to the vein margins verify that the injection was sub-vertical. The long axes of the recrystallized ice grains (parallel to foliation plane defined by K₁ &ndash; K₂) appeared to show a good correlation with the plunge of the maximum K₁ susceptibility. Also, the eigenvector plunge of the c-axes was approximately normal to the shear plane, which supports previous theory that c-axes rotate away from the shear plane toward the vertical. Multi-maximum girdle fabrics from the c-axes and associated textures from thin sections (e.g. nucleated grains, bulging of grain boundaries and slips band) suggest that some deformation likely occurred after emplacement; and (3) the Boulton hypothesis was tested using magnetic till fabrics and field relationships. According to this idea, drumlins form due to hydrologic heterogeneity (permeability differences in granular materials) causing a solid nucleus to form in the bed where sediment is accreted and sheared in the direction of ice flow. At Fl&aacute;aj&ouml;kull, the magnetic fabrics from sites B and C mimicked the glacier flow direction with the longitudinal flow plane (K₁ &ndash; K₃) approximately parallel to the NNW-SSE drumlin long axis. The drumlin cores consisted of outwash sand and gravels which likely acted as rigid obstacles in the bed. Ice overriding resulted in heterogeneous deformation of the drumlin cores following the deposition of the upper basal till carapace. These results support the Boulton hypothesis. </p><p> These studies demonstrate significant progress toward understanding fabric strength development of soft-bedded glaciers. In linking studies (1) and (3) the ring-shear device was used to provide insights into fabric strength development upon shear rate and effective pressure. In the third study previous ring-shear experiments, magnetic till fabrics and field relationships were used to understand modern drumlin genesis.</p>

<p> The age of the Ruby Ranch Member (RRM) of the Cedar Mountain Formation in East-Central Utah was recently constrained using carbon isotope chemostratigraphy to span known excursions associated with the late Aptian. The RRM is characterized by calcrete horizons that are thought to occur across the C10 carbon isotope excursion. Along with carbonate stable isotope analyses and the region&rsquo;s paleo-position in a depositional basin on the leeward rain shadow of the Sevier Orogenic belt, this interval is hypothesized to coincide with an aridification event. Our research objective is to quantify the extent of this aridity using clumped isotope paleothermometry (<i>n</i> = 7) and paleoprecipitation proxies (n = 51) for samples collected across the C10 chemostratigraphic interval. Two weathering indices, CIA-K and CALMAG, were applied to data obtained using X-ray fluorescence spectrometry. Using these proxies, we determined mean annual precipitation across the RRM at its type section. Precipitation values (<i> n</i> = 27) obtained through CIA-K for identified paleosol horizons ranged between 795 and 1275 mm/year, and through CALMAG ranged between 735 and 1042 mm/year. Precipitation values decreased through the C10 interval which may indicate increased aridity. Clumped isotopes provided ?47 values ranging from 0.647 to 0.693&permil;. Paleotemperature measurements (n = 4) from accepted carbonate samples were between 27.9 and 46.3 &deg;C. Isotopic compositions of water calculated from carbonates ranged between -4.4&permil; and -1.9&permil; VSMOW. Precipitation values and temperatures were not lowest during the C10 interval. Temperatures peaked at the end of the C10 interval and decreased afterward, indicating a potential for cooler, more arid conditions. These results suggest that carbon cycle changes during the mid-Cretaceous may have influenced paleoclimate conditions experienced in terrestrial settings.</p><p>

<p> Multi-proxy comparative analyses of sediment from Eagle Lake, including TOC, &delta;13C and &delta;15N composition of bulk organic material, n-alkane distribution, and biogenic silica, was used to document hydroclimatic changes during the early and late Holocene. Eagle Lake is currently located near the transition zone of the North American Precipitation Dipole, with the timing of precipitation showing a winter-wet scenario common to the Pacific Northwest, but overall precipitation (e.g. aridity) showing a Pacific Southwest pattern. The width and position of this transition is poorly constrained during the Holocene and is hypothesized to have migrated, particularly in response to the North American Monsoon. Eagle Lake is thus ideal in providing insights to the past positions of the dipole. Multi-proxy analyses results in differences between the early and late Holocene at Eagle Lake. TOC is lower in the early Holocene, however C:N ratios are much more variable indicating a transition from algal source material to terrestrial and back to algal material prior to the Mazama ash. There are also greater fluctuations of biogenic silica during the early Holocene, suggesting rapid changes in productivity. </p><p> To place these Holocene changes within the context of known climatic and anthropogenic conditions of the 20th century, a ~100 year record of hydrologic change is compared to drought and lake-level drops induced by the formation of the Bly Tunnel. Importantly, the effects of the tunnel on lake level is superimposed on the 1930s drought, making it difficult to disentangle the two impacts. However, the TOC and C:N ratios clearly mirror variations in lake level suggesting that they are effective indicators of Holocene variations. </p><p>

No description available.

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 and presenting an opportunity to estimate past polar amplification of climate change. The results of this research document the first continuous, high fidelity continental record of reconstructed δD in precipitation from terrestrial plant leaf waxes in the High Arctic spanning the last 120 ka. The hydrogen isotopic composition of lipid biomarkers were determined from previously obtained Lake El'gygytgyn sediment cores and compared with other multi-proxy evidence of past climate change within the lake basin. The modern isotope hydrology and controls on the δD lipid signal were first established within the El'gygytgyn Basin from modern precipitation, stream and lake waters, ice cover as well as modern vegetation, water column and lake bottom surface sediments in order to provide a modern context to properly constrain and interpret paleoclimatic proxy data. Reconstructed δD records of paleoprecipitation and temperature at Lake El'gygytgyn lead other northern hemisphere climate records (e.g. North Greenland Ice Core Project, NGRIP δ18O records) and are in phase with other continental and Antarctic climate records, suggesting early high northern latitude continental warming prior to established glacial-interglacial transitions. The data set generated here leads to multiple avenues of future work and provides critical insights into Arctic paleoclimate and paleohydrology, contributing to our understanding of high latitude environmental change over geological timescales. Collectively, the results of this dissertation research will provide a context for paleoclimate reconstructions and future organic geochemical and stable isotope analysis. Future application of compound-specific H isotope analyses to long drill cores (recovered in 2009; ∼315m of sediment) will potentially provide a quantitative high-resolution record of paleoclimatic and paleoenvironmental changes spanning the last 3.6 Ma.

The revised age models for the upper Oligocene to middle Miocene interval of the Marion Plateau have been used to identify eleven sequence boundaries and sequences sets at the Marion Plateau; MSA1.2 (23.1 Ma), MSA1.4 (22.1 Ma), MSA2.1 (21.2 Ma), MSB1.1 (18.4 Ma), MSB1.2 (17.3 Ma), MSB2.1 (16.5 Ma), MSB2.2 (15.6 Ma), MSB2.3 (14.8 Ma), MSB3.1 (13.6 Ma), MSB3.2 (12.9 Ma), and MSB3.3 (11.8 Ma). The complementary Miocene oxygen isotope events Mi1, Mi1a, Mi1aa, Mi2, Mi2b, Mi3a, Mi3, Mi4, Mi5a, Mi5, and Mi6 are recognized in the Marion Plateau sequences. In addition correlation to sequences on the New Jersey margin, the Gulf of Papua, Great Australian Bight, and McMurdo Sound Antarctica indicate that these sequences are controlled by glacio-eustasy, primarily the increase of ice volume on Antarctica. Changes in the preservation, assemblage structure and diversity of calcareous nannofossils as well as %planktic foraminifera, %neritics coincide with transgressive phases and sequence boundaries. The principles of `highstand shedding' are illustrated at the Marion Plateau by enhanced preservation of calcareous nannofossil, deposition of glauconite, unconformities and condensed intervals associated with early to middle Miocene sequence boundaries. Variations in surface water nutrient and temperature conditions at the Marion Plateau throughout the Miocene coincide with climatic events of the early Miocene (23 – 17 Ma), the Middle Miocene Climatic Optimum (17.6 – 15.4 Ma), and Middle Miocene Climatic Transition (14.8 – 13.8 Ma), and the stepwise growth of ice sheets on Antarctica. Calcareous nannofossil communities show evidence for precessional and eccentricity orbital forcing during the Middle Miocene Climatic Optimum, as well as a significantly cooler surface water mass at the Marion Plateau coinciding with the onset of the Middle Miocene Climatic Transition and Mi3a (14.8 Ma) glacial event. Changes in surface water fertility and temperature during the Middle Miocene Climatic Optimum agree with other studies that posit growth of significant ice volume on Antarctica starting as early as ∼17.35 Ma. Further evidence for significant cooling at the Mi3a (14.8 Ma) glacial event agrees with studies suggesting a step-wise cooling for the formation of a semi- permanent Antarctic ice sheet and thermohaline circulation, starting first at 14.8 Ma (Mi3a) and intensifying at 13.9 Ma (Mi3).

This thesis aims to combine long high-resolution sediment data with information on sedimentation processes in and around Saanich Inlet, to better understand the seasonal sedimentation mechanisms in Saanich Inlet from the late Pleistocene to the early Holocene. These understandings are used to establish sediment provenance in Saanich Inlet with seasonal to sub-seasonal resolution, and to help understand paleoclimatic variations between 10700 and 2150 14C calibrated (cal) a BP (= cal yr BP). In Saanich Inlet, elemental variability within laminated sediments is largely controlled by mineralogical changes in the sediment caused by changes in sediment provenance and primary productivity. In particular, on Vancouver Island, gold and platinum group elements (PGE), occurring in soils as a result of weathering of metamorphic and igneous rocks during the process of pedogenesis, are only observed within a restricted area of naturally occurring minerals, which concentrate those elements in soil. Therefore, preferential deposition of such minor elements can be strongly related to a change in sediment provenance. Chalcophile elements, such as Cu, have successfully proven to be reliable indicators of heterogenic-origin and/or bottom water redox conditions. Furthermore, sediment provenance along the western slope basin near Bamberton are distinguished and identified by a strong expression of enriched excess CaCO3 in both organic (high Ca/Ti and Sr/Ca) and inorganic (high Ca/Ti and low Sr/Ca) forms. This dissertation is divided into five related and complementary parts. The first chapter introduces Saanich Inlet and provides an overview of climatic and oceanographic patterns. The second chapter explains the methodology used in this work, and the third and fourth chapters, which are intended for publication, examine paleoclimatic and oceanographic variability during selected intervals of the Holocene in sub-seasonal (third chapter) and multi-annual to decadal (fourth chapter) scales. The last chapter summarizes the conclusions. Because of this format, some repetition of the introductory material exists in the main chapters.

No description available.

<p> I present a high- resolution record of Southeast Asian Monsoon (SEAM) evolution compiled from &delta;¹⁸O measurements conducted on five U-Th dated speleothems from Tham Mai Cave in northern Laos (20.75N, 102.65E), a key site at the interface between the Indian and East Asian monsoon systems. The speleothem oxygen isotope records are tied to robust uranium-series dates and indicate the records span from 0.79 to 13 kyr BP with sub-decadal resolution. During the Holocene, the Tham Mai speleothem &delta;¹⁸O records are characterized by lower values during the early to mid-Holocene with increasing values towards the late Holocene. This is similar to trends seen throughout the Asian monsoon region, reflecting the strong insolation control on monsoon strength and ITCZ position. The Younger Dryas is characterized by an abrupt &delta;¹⁸O increase and is synchronous with the even observed in Chinese speleothem records and Greenland ice cores within age uncertainties. This suggests that the SEAM weakened in sync with high-latitude abrupt cooling events.</p><p> Four speleothems from Tham Mai cave grew contemporaneously from 4,300 years BP to 9,000 years BP. These four samples show a similar &delta;¹⁸O pattern, despite a 1.2&permil; between sample &delta;¹⁸O variability is observed. A lumped parameter forward model method (KarstFor model) is used to assess to which extent this 1.2&permil; discrepancy can be attributed to hydrological variability. Results suggested that this 1.2&permil; discrepancy can be generated due to hydrological variability within one cave.</p><p> To better interpret interannual &delta;¹⁸O variability in high-resolution oxygen isotope records in the Asian Monsoon region, I utilize existing simulations from a spectrally nudged isotope-enabled general circulation model (IsoGSM) to investigate the climatic controls on &delta;¹⁸<i> O_p</i> at four cave locations along the Asian monsoon region. Results show that &delta;¹⁸<i>O_p</i> at the four cave sites reflects large-scale ocean-atmosphere processes, instead of local precipitation amount. Spatial correlation with vertical wind shear indicates that &delta;¹⁸<i>O_p</i> at all sites is significantly related to monsoon strength and Walker circulation. The spatial correlations with SST and precipitation, suggest that the ENSO likely does play a role and that central Pacific type El Ni&ntilde;o events influence precipitation &delta;¹⁸O in Oman and northern Laos, in particular.</p>