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.

Studying the mean state and variability of past climate provides important insight into the dynamically coupled climate system, directly aiding projections of future climate. Reconstruction of past climate conditions can be achieved using geochemical proxies including the novel clumped isotope paleothermometer. In this thesis I use multiple proxies to study climate variability during the last glacial period and at the onset of Antarctic glaciation. Greenland ice cores record repeated millennial-scale fluctuations in climate during the last glacial period known as Dansgaard-Oeschger (DO) cycles. We measure 18O of bulk sediment and planktonic foraminifera (Neogloboquadrina Pachyderma) in sediment cores from the North Atlantic to investigate fluctuations in sediment properties on the timescale of DO cycles. We find evidence of episodic deposition of carbonate ice-rafted debris near Iceland. Integrating these observations with published data and modeling studies, we propose a new hypothesis to explain DO cycles. We suggest that a large ice shelf in the Nordic Seas acted in concert with sea ice to set the slow and fast timescales of DO cycles. The ice shelf was periodically removed by subsurface warming with the timescale of shelf regrowth setting the duration of each interstadial. We utilize the clumped isotope proxy to reconstruct the climate history during a key period of the Cenozoic - the onset of Antarctic glaciation. To facilitate this work, a new inlet is developed to streamline sample preparation and reduce sample size requirements. We decrease the required sample size from 5-8mg to 1-2mg per replicate, while still achieving external precision of 0.005-0.010o/oo, equivalent to previous methods. This new capability increases the range of possible applications for the clumped isotope paleothermometer, specifically in the field of paleoceanography. We apply the clumped isotope paleothermometer to thermocline-dwelling foraminifera (Subbotina angiporoides and Subbotina utilisindex) from the Southern Ocean core ODP689 across the Eocene-Oligocene transition. With the clumped isotope paleothermometer we separate the contributions of near- surface temperature change and ice sheet growth on the ~1o/oo increase in 18O observed in planktonic foraminifera from this site. We measure no change in temperature, and 0.8±0.2o/oo change in 18Osw, equivalent to 124-140% of the modern Antarctic ice sheet volume. / Earth and Planetary Sciences

In this research, the relationship of climatic changes between 130k to 28k years BP to concurrent morphological variations in Neanderthals was tested. Traditional anthropological studies attribute robust Neanderthal morphological traits as an adaptation to a cold environment. A database of previously completed terrestrial paleoclimatic reconstructions in Europe and the Mediterranean was compiled and used to create a series of GIS-generated timeslice maps. Regional climatic conditions were then related to changes in Neanderthal appearances, morphology and disappearances as evident in the archaeological record. To establish climatic conditions, existing studies were compiled from two regions: Europe and the Mediterranean. The European data are based on pollen assemblage sequences from terrestrial lacustrine cores. The Mediterranean data are based on established ƒÔ18O/16O and ƒÔ13C/12C maximum and minimum events recorded in speleothems. The GIS perspective allows these changes to be viewed at significant time to better correlate regional climatic changes with known Neanderthal morphological variation and to extend the investigation both temporally, including Stage 4 and Stage 5e, and geographically, into the Mediterranean from similarly completed studies.

Stable isotopes of water preserved in glaciers and icesheets have revolutionized our understanding of terrestrial paleoclimate. Post-deposition alteration of the stable water isotope ratios in snow and ice can obscure the original meteoric signal, therefore altering the interpretation of δ18O and δD as records of paleo-temperatures in ice. The effects of sublimation on δ18O and δD are not well-understood for massive (non-snow) ice and have been largely overlooked, particularly within the experimental literature. We present results from a series of environmental chamber experiments investigating alteration of the in-situ signal following sublimation. Our data suggest that sublimation enriches the ice remaining after sublimation in 18O and D. This is observed both in surface ice and in the signal of the ice at depth. These results could have important implications for studies utilizing surface ice δ18O and δD for reconstructions of paleoclimate.

No description available.

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>

<p> Sediment cores from Cascade Lake (68.38&deg;N, 154.60&deg;W) and Shainin Lake (68.34&deg;N, 151.05&deg;W), Arctic Alaska were selected for paleomagnetic analysis to assess 210Pb-14C age control using paleomagnetic secular variation (PSV) and relative paleointensity (RPI) features, and to quantify environmental magnetic variability during the Holocene and late Pleistocene. U-channels were studied through alternating field (AF) demagnetization of the natural remanent magnetization (NRM), and laboratory-induced magnetizations including anhysteretic remanent magnetization (ARM) acquisition, ARM demagnetization, isothermal remanent magnetization (IRM), and hysteresis experiments to determine magnetic mineralogy and grain-size variability. </p><p> Cascade Lake sediment yields a strong, well-defined characteristic remanent magnetization with average maximum angular deviation values of &lt; 2&deg; and average inclinations within 4&deg; of the expected geocentric axial dipole. Correlation of inclination changes with geomagnetic field models, as well as the Burial Lake record ~ 200 km to the west, indicates a variable offset between the Cascade Lake radiometric chronology and the preferred PSV-derived age model (PSV-1), reaching a maximum offset of 1.5&ndash;2.8 kyr during the mid-Holocene. This offset likely results from either a hard-water effect or the incorporation of watershed-stored terrestrial carbon into ¹⁴C samples. The PSV-1 age model extends the Cascade Lake age model to ~ 21 ka. Cascade Lake sediment may be suitable for RPI estimation using the IRM as a normalizer, however three methods of normalization (magnetic susceptibility (kLF), ARM, and IRM) produce similar normalized remanence results. </p><p> Hysteresis experiments and S-ratios for Cascade Lake glacial till and Shainin Lake sediment supports the hypothesis that local bedrock hosts predominantly high-coercivity magnetic material. However, S-ratios from Cascade Lake (~ 21 ka to present) and Shainin Lake (~ 12.6 ka to present) do not appear consistent with Burial Lake S-ratios, and most S-ratio variability is therefore interpreted as a result of site-specific sedimentation processes and background magnetic assemblages. A Younger-Dryas-aged peak in Shainin Lake S-ratios may be revealed by the increased sensitivity of the S-ratio parameter to magnetite at high-coercivity background levels. Cascade Lake S-ratios increase from 10.3 ka to present, potentially indicating Holocene biogenic magnetite production, down-core magnetic dissolution, or eolian input from a fine-grained, low-coercivity magnetic source that is clearly distinct from eolian magnetite at Burial Lake. Anhysteretic susceptibility (k<p style="font-variant: small-caps">ARM</p>)/k<p style="font-variant: small-caps">LF</p> may be a better indicator of this fine-grained magnetite population observed in the north-central Brooks Range, however the origin of this magnetic component remains unclear. This research highlights the potential advantages of supplementing ¹⁴C dating with additional dating methods, and will benefit from ongoing efforts to improve age control (e.g., cryptotephra exploration) and additional magnetic experiments to constrain the source of fine-grained magnetite.</p>