New Constraints on the Timing and Pattern of Deglaciation in the Húnaflói Bay Region of Northwest Iceland Using Cosmogenic 36CA Dating and Geomorphic Mapping

Understanding the evolution and timing of changes in ice sheet geometry and extent in Iceland during the Last Glacial Maximum (LGM) and subsequent deglaciation continues to stimulate much active research. Though many previous studies have advanced our knowledge of Icelandic ice sheet history preserved in marine and terrestrial settings (e.g., Andrews et al., 2000; Norðdahl et al., 2008), the timing of ice margin retreat remains largely unknown in several key regions. Recently published 36Cl surface exposure ages of bedrock surfaces and moraines in the West Fjords (Brynjólfsson et al., 2015) contribute important progress in establishing more precise age control of ice recession in northwest Iceland. In another recent study, the spatial pattern and style of deglaciation in northern Iceland have been revealed through geomorphic mapping and GIS analyses of glacial landforms (Principato et al., 2016). Additional insight comes from updated numerical modeling reconstructions, which now provide a series of glaciologically plausible Icelandic ice sheet configurations from the LGM through the last deglaciation (Patton et al., 2017). However, the optimization of ice sheet model simulations relies on critical comparisons with the available empirical record of glacial-geologic evidence and chronological control, which remains relatively limited and sparsely distributed throughout Iceland. Our investigation is motivated by the need for more accurate constraints on the deglacial history in northern Iceland, where dated terrestrial records of ice margin retreat are particularly scarce. (excerpt

Rates of erosion and landscape change along the Blue Ridge escarpment, southern Appalachian Mountains, estimated from in situ cosmogenic 10Be

The Blue Ridge escarpment, located within the southern Appalachian Mountains of Virginia and North Carolina, forms a distinct, steep boundary between the lower-elevation Piedmont and higher-elevation Blue Ridge physiographic provinces. To understand better the rate at which this landform and the adjacent landscape are changing, we measured cosmogenic 10Be in quartz separated from sediment samples (n = 50) collected in thirty-two streams and from three exposed bedrock outcrops along four transects normal to the escarpment, allowing us to calculate erosion rates integrated over 104–105 years. These basin-averaged erosion rates (5.4–49 m My-1) are consistent with those measured elsewhere in the southern Appalachians and show a positive relationship between erosion rate and average basin slope. Erosion rates show no relationship with basin size or relative position of the Brevard fault zone, a fundamental structural element of the region. The cosmogenic isotopic data, when considered along with the distribution of average basin slopes in each physiographic province, suggest that the escarpment is eroding on average more rapidly than the Blue Ridge uplands, which are eroding more rapidly than the Piedmont lowlands. This difference in erosion rates by geomorphic setting suggests that the elevation difference between the uplands and lowlands adjacent to the escarpment is being reduced but at extremely slow rates

Holocene glacier culminations in the Western Alps and their hemispheric relevance

The natural variability of Holocene climate defines the baseline to assess ongoing climate change. Greenland ice-core records indicate warming superimposed by abrupt climate oscillations in the early Holocene, followed by a general cooling trend throughout the middle and late Holocene that culminated during the Little Ice Age (LIA). Tropical precipitation changes correlate with these patterns throughout the Holocene. Here we use mountain glaciers in the European Alps to reconstruct the regional Holocene climate evolution and to test for a link between mid-latitude, North Atlantic, and tropical climate. Our precise 10Be chronology from Tsidjiore Nouve Glacier, western Swiss Alps, indicates a glacier culmination during the earliest Holocene ∼11.4 k.y. ago, likely related to the Preboreal Oscillation. Based on our data, no Holocene glacier advance of similar amplitude occurred until ∼3.8 k.y. ago, when the glacier reached LIA limits. The 10Be ages between 500 and 170 yr correspond to the LIA, while the youngest 10Be ages overlap with the historically recorded post-LIA glacier positions. Integrating our data with existing records, we propose a hemispheric climate link between the Alps, North Atlantic temperature, and tropical precipitation patterns for the Holocene, supporting the concept of a pervasive climate driver. These findings from northern mid-latitudes are consistent with the hypothesis formulated for the tropics that the Earth’s thermal equator, responding to North Atlantic temperature changes, might have migrated southward throughout the Holocene, reaching the southern turning point toward the end of the LIA

Cosmogenic ^(10)Be and ^(36)Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone

The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right-lateral strike-slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high-resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ∼297 ± 9 m of right-lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic ^(10)Be and ^(36)Cl geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/−20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on ^(36)Cl depth profiles is 63 ± 8 ka. Combining the offset measurement with the cosmogenic ^(10)Be date yields a geologic fault slip rate of 4.2 +1.9/−1.1 mm yr^(−1), whereas the ^(36)Cl data indicate 4.7 +0.9/−0.6 mm yr^(−1) of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ∼8.5 to 10 mm yr^(−1). This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant

Dating the Siple Dome (Antarctica) Ice Core By Manual and Computer Interpretation of Annual Layering

The Holocene portion of the Siple Dome (Antarctica) ice core was dated by interpreting the electrical, visual and chemical properties of the core. The data were interpreted manually and with a computer algorithm. The algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the GISP2 (Greenland Ice Sheet Project 2) ice core, (BE)-B-10 stratigraphic ties to the dendrochronology C-14 record and the dated volcanic stratigraphy. The algorithm interpretation is more consistent and better quantified than the tedious and subjective manual interpretation

ASCR/HEP Exascale Requirements Review Report

This draft report summarizes and details the findings, results, and recommendations derived from the ASCR/HEP Exascale Requirements Review meeting held in June, 2015. The main conclusions are as follows. 1) Larger, more capable computing and data facilities are needed to support HEP science goals in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of the demand at the 2025 timescale is at least two orders of magnitude -- and in some cases greater -- than that available currently. 2) The growth rate of data produced by simulations is overwhelming the current ability, of both facilities and researchers, to store and analyze it. Additional resources and new techniques for data analysis are urgently needed. 3) Data rates and volumes from HEP experimental facilities are also straining the ability to store and analyze large and complex data volumes. Appropriately configured leadership-class facilities can play a transformational role in enabling scientific discovery from these datasets. 4) A close integration of HPC simulation and data analysis will aid greatly in interpreting results from HEP experiments. Such an integration will minimize data movement and facilitate interdependent workflows. 5) Long-range planning between HEP and ASCR will be required to meet HEP's research needs. To best use ASCR HPC resources the experimental HEP program needs a) an established long-term plan for access to ASCR computational and data resources, b) an ability to map workflows onto HPC resources, c) the ability for ASCR facilities to accommodate workflows run by collaborations that can have thousands of individual members, d) to transition codes to the next-generation HPC platforms that will be available at ASCR facilities, e) to build up and train a workforce capable of developing and using simulations and analysis to support HEP scientific research on next-generation systems.Comment: 77 pages, 13 Figures; draft report, subject to further revisio

The last glaciation of Bear Peninsula, central Amundsen Sea Embayment of Antarctica: Constraints on timing and duration revealed by in situ cosmogenic 14C and 10Be dating

Ice streams in the Pine Island-Thwaites region of West Antarctica currently dominate contributions to sea level rise from the Antarctic ice sheet. Predictions of future ice-mass loss from this area rely on physical models that are validated with geological constraints on past extent, thickness and timing of ice cover. However, terrestrial records of ice sheet history from the region remain sparse, resulting in significant model uncertainties. We report glacial-geological evidence for the duration and timing of the last glaciation of Hunt Bluff, in the central Amundsen Sea Embayment. A multi-nuclide approach was used, measuring cosmogenic 10Be and in situ14C in bedrock surfaces and a perched erratic cobble. Bedrock 10Be ages (118–144 ka) reflect multiple periods of exposure and ice-cover, not continuous exposure since the last interglacial as had previously been hypothesized. In situ14C dating suggests that the last glaciation of Hunt Bluff did not start until 21.1 ± 5.8 ka – probably during the Last Glacial Maximum – and finished by 9.6 ± 0.9 ka, at the same time as ice sheet retreat from the continental shelf was complete. Thickening of ice at Hunt Bluff most likely post-dated the maximum extent of grounded ice on the outer continental shelf. Flow re-organisation provides a possible explanation for this, with the date for onset of ice-cover at Hunt Bluff providing a minimum age for the timing of convergence of the Dotson and Getz tributaries to form a single palaeo-ice stream. This is the first time that timing of onset of ice cover has been constrained in the Amundsen Sea Embayment

Outbreak of Cyclosporiasis Associated with Imported Raspberries, Philadelphia, Pennsylvania, 2000

An outbreak of cyclosporiasis occurred in attendees of a wedding reception held in Philadelphia, Pennsylvania, on June 10, 2000. In a retrospective cohort study, 54 (68.4%) of the 79 interviewed guests and members of the wedding party met the case definition. The wedding cake, which had a cream filling that included raspberries, was the food item most strongly associated with illness (multivariate relative risk, 5.9; 95% confidence interval, 3.6 to 10.5). Leftover cake was positive for Cyclospora DNA by polymerase chain reaction analyses. Sequencing of the amplified fragments confirmed that the organism was Cyclospora cayetanensis. The year 2000 was the fifth year since 1995 that outbreaks of cyclosporiasis definitely or probably associated with Guatemalan raspberries have occurred in the spring in North America. Additionally, this is the second documented U.S. outbreak, and the first associated with raspberries, for which Cyclospora has been detected in the epidemiologically implicated food item

High-precision 10Be chronology of moraines in the Southern Alps indicates synchronous cooling in Antarctica and New Zealand 42,000 years ago

Millennial-scale temperature variations in Antarctica during the period 80,000 to 18,000 years ago are known to anti-correlate broadly with winter-centric cold–warm episodes revealed in Greenland ice cores. However, the extent to which climate fluctuations in the Southern Hemisphere beat in time with Antarctica, rather than with the Northern Hemisphere, has proved a controversial question. In this study we determine the ages of a prominent sequence of glacial moraines in New Zealand and use the results to assess the phasing of millennial climate change. Forty-four 10Be cosmogenic surface-exposure ages of boulders deposited by the Pukaki glacier in the Southern Alps document four moraine-building events from Marine Isotope Stage 3 (MIS 3) through to the end of the Last Glacial Maximum (∼18,000 years ago; LGM). The earliest moraine-building event is defined by the ages of nine boulders on a belt of moraine that documents the culmination of a glacier advance 42,000 years ago. At the Pukaki locality this advance was of comparable scale to subsequent advances that, from the remaining exposure ages, occurred between 28,000 and 25,000, at 21,000, and at 18,000 years ago. Collectively, all four moraine-building events represent the LGM. The glacier advance 42,000 years ago in the Southern Alps coincides in Antarctica with a cold episode, shown by the isotopic record from the EPICA Dome C ice core, between the prominent A1 and A2 warming events. Therefore, the implication of the Pukaki glacier record is that as early as 42,000 years ago an episode of glacial cold similar to that of the LGM extended in the atmosphere from high on the East Antarctic plateau to at least as far north as the Southern Alps (∼44°S). Such a cold episode is thought to reflect the translation through the atmosphere and/or the ocean of the anti-phased effects of Northern Hemisphere interstadial conditions to the southern half of the Southern Hemisphere. Regardless of the mechanism, any explanation for the cold episode at 42,000 years ago must account for its widespread atmospheric footprint not only in Antarctica but also within the westerly wind belt in southern mid-latitudes