ALBERT

Description: 〈span〉The Sentinel Bluffs Member is the youngest unit of the Grande Ronde Basalt, having typical physical characteristics of most large-volume Columbia River Basalt Group (CRBG) sheet flows. These flows have been studied for over 50 years, resulting in numerous scientific publications from academic institutions, federal and state regional mapping projects, more detailed mapping associated with the U.S. Department of Energy’s (USDOE) Hanford Site (southeastern Washington State), and borehole investigations focused in part on petroleum exploration in the Columbia Basin. The compositional heterogeneity of individual flows, although small, has been interpreted by many workers as being the result of magma chamber processes (e.g., Wright et al., 1973; Wright and Swanson, 1980; Mangan et al., 1986; Hooper, 2000; Reidel, 2005) combined in places with surficial mixing as the flows are emplaced (e.g., Reidel and Tolan, 2013). Sawlan (2018) argues instead that flow heterogeneity in the Sentinel Bluffs Member is largely the result of previously unrecognized chemical alteration of basalt in contact with aquifers, accompanied by significant mass loss (up to 50%). The fact that nearly all CRBG lava flows are in contact with the confined aquifer system, even those in the anticlinal ridges, suggests that such alteration, if it existed, could be widespread.The ramifications of widespread, hitherto undocumented alteration are compelling, in part because of the ambiguity such alteration would place on previous interpretations that rely on high-quality chemical data. Such data could be queried as problematic or invalid in a variety of studies that focus, for example, on chemostratigraphic correlations (e.g., Reidel, 2005; Conrey and Wolff, 2010; Vye-Brown et al., 2013; Martin et al., 2013; Wells et al., 2009) or on petrogenesis and evolution of the basalts (e.g., Davis et al., 2017; Blake et al., 2010; Martin, 1989; Wolff et al., 2008; Wolff and Ramos, 2013; Ramos et al., 2005, 2009, 2013; Tollstrup et al., 2002; Hooper, 1984; Hooper and Hawkesworth, 1993; Rodriguez and Sen, 2013; Thordarson and Self, 1998), as well as in paleomagnetic studies where the results are extremely sensitive to alteration especially in the case of iron minerals (e.g., magnetite, hematite) and rely on compositional data for flow identification (e.g., Wells et al., 1989; Hagstrum et al., 2010).Consideration and scrutiny of the Sawlan (2018) study is both timely and relevant to workers on the CRBG, but it is also pertinent to workers on other basalt provinces where aquifers are present (e.g., Hawaii, the Snake River Plain [Idaho], and the Oregon High Lava Plains). We therefore embrace debate on the potential role of these aquifers in modifying primary magmatic compositions. It is our contention that careful sample collection of the CRBG has generated largely unaltered chemical compositions, and that the alteration hypothesis of Sawlan (2018) is incorrect due to flawed methodology. As a contribution to this debate, we (1) examine long-established procedures and sampling techniques that have allowed workers to avoid significant alteration when collecting and analyzing CRBG flows; (2) describe data collection of the Sentinel Bluffs Member and chemical variations that have been attributed to both magmatic processes and secondary alteration; and (3) discuss the concerns we have on the rationale and analytical methodology that form the basis for Sawlan’s (2018) conclusions that compositional variations in the Sentinel Bluff Member are the result of chemical alteration from basalt-water interaction.〈/span〉

Description: 〈div data-abstract-type="normal"〉〈p〉We experimentally investigate the two-phase interplay in an open-channel turbulent boundary layer laden with finite-size particles at global volume fractions between 4 and 25 %. The working fluid (water) and the dispersed phase (hydrogel spheres) have closely matched refractive indices, allowing us to measure the properties of both phases using particle image velocimetry and particle tracking velocimetry, respectively. The particles have a diameter of approximately 9 % of the channel depth and are slightly denser than the fluid. The negative buoyancy causes a strong vertical concentration gradient, characterized by discrete and closely spaced particle layers parallel to the wall. Even at the lowest considered volume fractions, the near-wall fluid velocity and velocity gradients are strongly reduced, with large mean shear throughout most of the channel height. This indicates that the local effective viscosity of the suspension is greatly increased due to the friction between particle layers sliding over one another. The particles consistently lag the fluid and leave their footprint on its mean and fluctuating velocity profiles. The turbulent activity is damped near the wall, where the nearly packed particles disrupt and suppress large-scale turbulent fluctuations and redistribute some of the kinetic energy to smaller scales. On the other hand, in the outer region of the flow where the local particle concentration is low, the mean shear produces strong Reynolds stresses, with enhanced sweeps and ejections and frequent swirling events.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Chemically defended benthic macroalgae that dominate shallow, hard bottom communities along the western Antarctic Peninsula support very high densities of mesograzers, particularly amphipods but also small gastropods. Previous studies have demonstrated that the macroalgae and amphipods form a mutualistic relationship. The chemically defended macroalgae provide the amphipods with a refuge from predation while the macroalgae benefit from the amphipods greatly reducing surface fouling by smaller algae. One of the three most important macroalgae in terms of overstory cover, 〈span〉Himantothallus grandifolius〈/span〉, forms huge blades that can carpet the benthos. Field observations suggest that gastropods may be higher in relative abundance in proportion to amphipods on 〈span〉H. grandifolius〈/span〉 than on other overstory macroalgae. The present study documents the finding that natural abundances of gastropods on 〈span〉H. grandifolius〈/span〉 maintained in mesocosms reduce fouling by microscopic algae, primarily diatoms. However, amphipods are probably also important in keeping the macroalga clean of diatoms in nature. In a smaller scale experiment, three gastropod species were differentially effective at reducing diatom coverage on 〈span〉H. grandifolius.〈/span〉 The hypothesis that gastropods benefit from associating with 〈span〉H. grandifolius〈/span〉 in potentially gaining a refuge from sea-star predation was also tested but not supported by the experimental results.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Mountain glaciers integrate climate processes to provide an unmatched signal of regional climate forcing. However, extracting the climate signal via intercomparison of regional glacier mass-balance records can be problematic when methods for extrapolating and calibrating direct glaciological measurements are mixed or inconsistent. To address this problem, we reanalyzed and compared long-term mass-balance records from the US Geological Survey Benchmark Glaciers. These five glaciers span maritime and continental climate regimes of the western United States and Alaska. Each glacier exhibits cumulative mass loss since the mid-20th century, with average rates ranging from −0.58 to −0.30 m w.e. a〈span〉−1〈/span〉. We produced a set of solutions using different extrapolation and calibration methods to inform uncertainty estimates, which range from 0.22 to 0.44 m w.e. a〈span〉−1〈/span〉. Mass losses are primarily driven by increasing summer warming. Continentality exerts a stronger control on mass loss than latitude. Similar to elevation, topographic shading, snow redistribution and glacier surface features often exert important mass-balance controls. The reanalysis underscores the value of geodetic calibration to resolve mass-balance magnitude, as well as the irreplaceable value of direct measurements in contributing to the process-based understanding of glacier mass balance.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Various paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ〈span〉13〈/span〉C, δ〈span〉15〈/span〉N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.〈/p〉〈/div〉

Description: During the late Pleistocene, multiple floods from drainage of glacial Lake Missoula further eroded a vast anastomosing network of bedrock channels, coulees, and cataracts, forming the Channeled Scabland of eastern Washington State (United States). However, the timing and exact pathways of these Missoula floods remain poorly constrained, thereby limiting our understanding of the evolution of this spectacular landscape. Here we report cosmogenic 10 Be ages that directly date flood and glacial features important to understanding the flood history, the evolution of the Channeled Scabland, and relationships to the Cordilleran Ice Sheet (CIS). One of the largest floods occurred at 18.2 ± 1.5 ka, flowing down the northwestern Columbia River valley prior to blockage of this route by advance of the Okanogan lobe of the CIS, which dammed glacial Lake Columbia and diverted later Missoula floods to more eastern routes through the Channeled Scabland. The Okanogan and Purcell Trench lobes of the CIS began to retreat from their maximum extent at ca. 15.5 ka, likely in response to onset of surface warming of the northeastern Pacific Ocean. Upper Grand Coulee fully opened as a flood route after 15.6 ± 1.3 ka, becoming the primary path for later Missoula floods until the last ones from glacial Lake Missoula at 14.7 ± 1.2 ka. The youngest dated flood(s) (14.0 ± 1.4 ka to 14.4 ± 1.3 ka) came down the northwestern Columbia River valley and were likely from glacial Lake Columbia, indicating that the lake persisted for a few centuries after the last Missoula flood.

Description: The attribution of past glacier length fluctuations to changes in climate requires characterizing glacier mass-balance variability. Observational records, which are relatively short, are consistent with random fluctuations uncorrelated in time, plus an anthropogenic trend. However, longer records of other climate variables suggest that, in fact, there is a degree of temporal persistence associated with internal (i.e. unforced) climate variability, and that it varies with location and climate. Therefore, it is likely that persistence does exist for mass balance, but records are too short to confirm its presence, or establish its magnitude, with conventional statistical tests. Extending the previous work, we explore the impact of potential climatic persistence on glacier length fluctuations. We use a numerical model and a newly developed analytical model to establish that persistence, even of a degree so small as to be effectively undetectable in the longest mass-balance records, can significantly enhance the resulting glacier length fluctuations. This has a big impact on glacier-excursion probabilities: what was an extremely unlikely event (〈1%) can become virtually certain (〉99%), when persistence is incorporated. Since the actual degree of climatic persistence that applies to any given glacier is hard to establish, these results complicate the attribution of past glacier changes.

Description: Recent studies have suggested a physical link between Ca++ ions and an increase in the ductility or 'softening' of polycrystalline ice. In order to investigate the potential effects of Ca++ on deformation, we created sets of both undoped and CaSO4-doped specimens of polycrystalline ice for testing in uniaxial tension or compression. Deformation tests in tension were carried out under a constant load at an initial stress of 0.75 MPa and a temperature of -6 degrees C. Compression tests were carried out at -10 and -20 degrees C at constant strain rates of 1 x 10(-4) s(-1), 1 x 10(-5) s(-1) and 1 x 10(-6) s(-1) and taken to 5% strain. Our results show that CaSO4 increases the strength of polycrystalline ice at higher strain rates and lower temperatures, an effect that decreases with decreasing strain rate and higher temperatures. A microstructural analysis of the post-test compression specimens reveals mean grain diameters much larger in the CaSO4-doped specimens tested at the lowest applied strain rate of 1 x 10(-6) s(-1). Precipitates were found to have formed along grain boundaries in some doped specimens and evidence of intergranular fracture was observed in all specimens tested at 1 x 10(-4) and 1 x 10(-5) s(-1). In tension-tested specimens, there was no difference in the mean grain diameter between doped and undoped specimens at 25% strain.

Description: The following list comprises measurements made since those reported in NPL III and is complete to the end of November 1965.Ages are relative to A.D. 1950 and are calculated using a half-life of 5568 yr. The measurements, corrected for fractionation (quoted δC13 values are relative to the P.D.B. standard), are referred to 0.950 times the activity of the NBS oxalic acid as contemporary reference standard. The quoted uncertainty is one standard deviation derived from a proper combination of the parameter variances as described in detail in NPL III. These variances are those of the standard and background measurements over a rolling twenty week period, of the sample δC14 and δC13 measurements and of the de Vries effect (assumed to add an additional uncertainty equivalent to a standard deviation of 80 yr). Any uncertainty in the half-life has been excluded so that relative C14 ages may be correctly compared. Absolute age assessments, however, should be made using the accepted best value for the half-life and the appropriate uncertainty then included. If the net sample count rate is less than 4 times the standard error of the difference between the sample and background count rates, a lower limit to the age is reported corresponding to a net sample count rate of 4 times the standard error of this difference.