Geochemical and Sedimentological Analysis of Marine Sediments from ODP Site 696 and Implications for the Onset of Antarctic Glaciation

The Eocene-Oligocene Transition (EOT) approximately 34 million years ago (Ma) marks the shift from the warm greenhouse conditions of the Eocene to today’s icehouse, and was accompanied by the establishment of the East and West Antarctic Ice Sheets. Details surrounding the timing, magnitude, and regional expansion of glaciation are poorly constrained primarily due to low core recovery and lack of reliable age models, and therefore warrant continued investigation. A recently updated age model applied to Ocean Drilling Program (ODP) Site 696, located in the northwest sector of the Weddell Sea, indicates Core 55R represents a high-recovery succession encompassing the EOT. This project presents a high-resolution, multimethod analysis of this sediment core. Laser particle size analysis was performed throughout the core, and inductively coupled plasma mass spectrometry and optical emission spectrometry are used to quantify major, trace, and rare earth elemental concentrations on samples with \u3e80% mud. Paleoclimate proxies are calculated to characterize the dominant weathering regime and degree of glacial influence on sediment. Results indicate a cool, dry climate and sediment with a strong glacial signature, as evidenced by low chemical index of alteration (CIA) values and significant contribution of glacial rock flour. Trace and REE ratios do not suggest major changes in source material, and felsic versus mafic plots indicate 55R sediment is felsic to intermediate in composition. Sediment remains well sorted throughout, and therefore elemental enrichments are likely related to grain-size partitioning. Results of this study have implications for the investigation into continental glacial history of Antarctic through the EOT; 55R sediments reflect a similar climate to shelf sediments retrieved from Prydz Bay and Wilkes Land Margins and are consistent with significant terrestrial cooling across East Antarctica during the late Eocene. Studies from West Antarctica, however, suggest a later onset with less glacial stability. Similar high-resolution studies are thusly needed to further improve our understanding of Antarctic ice dynamics in response to climate perturbations

Advances in understanding subglacial meltwater drainage from past ice sheets

Meltwater drainage beneath ice sheets is a fundamental consideration for understanding ice–bed conditions and bed-modulated ice flow, with potential impacts on terminus behavior and iceshelf mass balance. While contemporary observations reveal the presence of basal water movement in the subglacial environment and inferred styles of drainage, the geological record of former ice sheets, including sediments and landforms on land and the seafloor, aids in understanding the spatiotemporal evolution of efficient and inefficient drainage systems and their impact on ice-sheet behavior. We highlight the past decade of advances in geological studies that focus on providing process-based information on subglacial hydrology of ice sheets, how these studies inform theory, numerical models and contemporary observations, and address the needs for future research

Modelling Primordial Gas in Numerical Cosmology

We have reviewed the chemistry and cooling behaviour of low-density (n<10^4 cm^-3) primordial gas and devised a cooling model wich involves 19 collisional and 9 radiative processes and is applicable for temperatures in the range (1 K < T < 10^8 K). We derived new fits of rate coefficients for the photo-attachment of neutral hydrogen, the formation of molecular hydrogen via H-, charge exchange between H2 and H+, electron detachment of H- by neutral hydrogen, dissociative recombination of H2 with slow electrons, photodissociation of H2+, and photodissociation of H2. Further it was found that the molecular hydrogen produced through the gas-phase processes, H2+ + H -> H2 + H+, and H- + H -> H2 + e-, is likely to be converted into its para configuration on a faster time scale than the formation time scale. We have tested the model extensively and shown it to agree well with former studies. We further studied the chemical kinetics in great detail and devised a minimal model which is substantially simpler than the full reaction network but predicts correct abundances. This minimal model shows convincingly that 12 collisional processes are sufficient to model the H, He, H+, H-, He+, He++, and H2 abundances in low density primordial gas for applications with no radiation fields.Comment: 26 pages of text, 4 tables, and 6 eps figures. The paper is also available at http://zeus.ncsa.uiuc.edu:8080/~abel/PGas/bib.html Submitted to New Astronomy. Note that some of the hyperlinks given in the paper are still under constructio

Advances in understanding subglacial meltwater drainage from past ice sheets

Meltwater drainage beneath ice sheets is a fundamental consideration for understanding ice–bed conditions and bed-modulated ice flow, with potential impacts on terminus behavior and ice-shelf mass balance. While contemporary observations reveal the presence of basal water movement in the subglacial environment and inferred styles of drainage, the geological record of former ice sheets, including sediments and landforms on land and the seafloor, aids in understanding the spatiotemporal evolution of efficient and inefficient drainage systems and their impact on ice-sheet behavior. We highlight the past decade of advances in geological studies that focus on providing process-based information on subglacial hydrology of ice sheets, how these studies inform theory, numerical models and contemporary observations, and address the needs for future research

The micro-structure of the intergalactic medium I: the 21cm signature from dynamical minihaloes

A unified description is provided for the 21cm signatures arising from minihaloes against a bright background radio source and against the Cosmic Microwave Background (CMB), within the context of a dynamical collapsing cosmological spherical halo model. The equivalent width distribution of the resulting 21cm forest is computed for LCDM cosmologies, along with the brightness temperature differential relative to the CMB. The effects of an ambient Ly-alpha radiation field and heating of the IGM on the signatures are included. It is shown that the dynamical effects of heating substantially suppress absorption features in the 21cm forest with observed equivalent widths exceeding 0.15 kHz. It is demonstrated how measurements of excess fluctuations beyond detector noise could make a statistical detection of the weaker absorption features against a bright background radio source. It is also shown that a Ly-alpha radiation field only a few percent the thermalisation rate is sufficient to render the minihalo signal against the CMB negligible compared with the signal from the diffuse IGM component. The 21cm signals are found to be very sensitive to the amount of small scale power in the primordial density fluctuation spectrum. The effects of gas cooling via radiative atomic and molecular processes and of star formation on setting the maximum mass of the minihaloes giving rise to a 21cm signal are included, with allowance made for the suppression of molecular hydrogen formation by an ambient UV radiation field.Comment: Substantial revision: paper restructured; hydrodynamical model with heating included; discussion of statistical detection of absorption fluctuations from 21cm forest added. 34 pages; 34 figures. Definitive version published in Monthly Notice

Synchronous retreat of Thwaites and Pine Island glaciers in response to external forcings in the presatellite era

Today, relatively warm Circumpolar Deep Water is melting Thwaites Glacier at the base of its ice shelf and at the grounding zone, contributing to significant ice retreat. Accelerating ice loss has been observed since the 1970s; however, it is unclear when this phase of significant melting initiated. We analyzed the marine sedimentary record to reconstruct Thwaites Glacier’s history from the early Holocene to present. Marine geophysical surveys were carried out along the floating ice-shelf margin to identify core locations from various geomorphic settings. We use sedimentological data and physical properties to define sedimentary facies at seven core sites. Glaciomarine sediment deposits reveal that the grounded ice in the Amundsen Sea Embayment had already retreated to within ~45 km of the modern grounding zone prior to ca. 9,400 y ago. Sediments deposited within the past 100+ y record abrupt changes in environmental conditions. On seafloor highs, these shifts document ice-shelf thinning initiating at least as early as the 1940s. Sediments recovered from deep basins reflect a transition from ice proximal to slightly more distal conditions, suggesting ongoing grounding-zone retreat since the 1950s. The timing of ice-shelf unpinning from the seafloor for Thwaites Glacier coincides with similar records from neighboring Pine Island Glacier. Our work provides robust new evidence that glacier retreat in the Amundsen Sea was initiated in the mid-twentieth century, likely associated with climate variability

Global Landscape Review of Serotype-Specific Invasive Pneumococcal Disease Surveillance among Countries Using PCV10/13: The Pneumococcal Serotype Replacement and Distribution Estimation (PSERENADE) Project.

Serotype-specific surveillance for invasive pneumococcal disease (IPD) is essential for assessing the impact of 10- and 13-valent pneumococcal conjugate vaccines (PCV10/13). The Pneumococcal Serotype Replacement and Distribution Estimation (PSERENADE) project aimed to evaluate the global evidence to estimate the impact of PCV10/13 by age, product, schedule, and syndrome. Here we systematically characterize and summarize the global landscape of routine serotype-specific IPD surveillance in PCV10/13-using countries and describe the subset that are included in PSERENADE. Of 138 countries using PCV10/13 as of 2018, we identified 109 with IPD surveillance systems, 76 of which met PSERENADE data collection eligibility criteria. PSERENADE received data from most (n = 63, 82.9%), yielding 240,639 post-PCV10/13 introduction IPD cases. Pediatric and adult surveillance was represented from all geographic regions but was limited from lower income and high-burden countries. In PSERENADE, 18 sites evaluated PCV10, 42 PCV13, and 17 both; 17 sites used a 3 + 0 schedule, 38 used 2 + 1, 13 used 3 + 1, and 9 used mixed schedules. With such a sizeable and generally representative dataset, PSERENADE will be able to conduct robust analyses to estimate PCV impact and inform policy at national and global levels regarding adult immunization, schedule, and product choice, including for higher valency PCVs on the horizon

Grain size determination from coastal outcrop samples of Cliffside from Whidbey Island, Washington state

These grainsize data were collected by a BetterSize S3 Plus Particle Analyzer at the University of Virginia, organized in the spreadsheet by site. Each sample has a unique row with differential percentages of the binned grainsize data output in microns. Code to plot these data was developed by Dr. Allison Lepp and is available upon request to Dr. Marion McKenzie

XRF data from coastal outcrop samples of Fort Casey 1 from Whidbey Island, Washington state

These trace element data were collected by a Niton XLF X-ray fluorescence machine (units in ppm), while magnetic susceptibility (MS) data (units in SI) were collected using a Bartington MS2 meter. Within the spreadsheet, this data is organized by site and each sample has a unique row of data. This spreadsheet also lists the difference between "field" labels (in centimeters from the beach) and "lab" labels (in centimeters from the top of the column) presented in the associated manuscript. Code to plot these data is available upon request to Dr. Marion McKenzie