Glacier motion responds dynamically to changing meltwater inputs, but the multi-decadal response of basal sliding to climate remains poorly constrained due to its sensitivity across multiple ...timescales. Observational records of glacier motion provide critical benchmarks to decode processes influencing glacier dynamics, but multi-decadal records that precede satellite observation and modern warming are rare. Here we present a record of motion in the ablation zone of Saskatchewan Glacier that spans seven decades. We combine in situ and remote-sensing observations to inform a first-order glacier flow model used to estimate the relative contributions of sliding and internal deformation on dynamics. We find a significant increase in basal sliding rates between melt-seasons in the 1950s and those in the 1990s and 2010s and explore three process-based explanations for this anomalous behavior: (i) the glacier surface steepened over seven decades, maintaining flow-driving stresses despite sustained thinning; (ii) the formation of a proglacial lake after 1955 may support elevated basal water pressures; and (iii) subglacial topography may cause dynamic responses specific to Saskatchewan Glacier. Although further constraints are necessary to ascertain which processes are of greatest importance for Saskatchewan Glacier's dynamic evolution, this record provides a benchmark for studies of multi-decadal glacier dynamics.
Glacier-bed characteristics that are poorly known and modeled are important in projected sea-level rise from ice-sheet changes under strong warming, especially in the Thwaites Glacier drainage of ...West Antarctica. Ocean warming may induce ice-shelf thinning or loss, or thinning of ice in estuarine zones, reducing backstress on grounded ice. Models indicate that, in response, more-nearly-plastic beds favor faster ice loss by causing larger flow acceleration, but more-nearly-viscous beds favor localized near-coastal thinning that could speed grounding-zone retreat into interior basins where marine-ice-sheet instability or cliff instability could develop and cause very rapid ice loss. Interpretation of available data indicates that the bed is spatially mosaicked, with both viscous and plastic regions. Flow against bedrock topography removes plastic lubricating tills, exposing bedrock that is eroded on up-glacier sides of obstacles to form moats with exposed bedrock tails extending downglacier adjacent to lee-side soft-till bedforms. Flow against topography also generates high-ice-pressure zones that prevent inflow of lubricating water over distances that scale with the obstacle size. Extending existing observations to sufficiently large regions, and developing models assimilating such data at the appropriate scale, present large, important research challenges that must be met to reliably project future forced sea-level rise.
•We present a formal model of tool manufacture, use, and discard.•We model trade-offs in the use of generalized vs. specialized tools.•Generalized tools are favored when subsistence tasks are evenly ...distributed.•Increases in task predictability and payoff certainty favor more specialized tools.•California plant processing tools are modeled relative to acorn intensification.
The question investigated by this study is: how much behavioral specialization is necessary before tool specialization is worthwhile? The toolkits of hunter–gatherers vary considerably over space and through time from simple and multifunctional, to complex and specialized. The decision to use one tool over another can be modeled as a fairly straightforward consideration of costs and benefits, but the problem becomes more complex when individual tools are employed in multiple tasks. We introduce a formal model that helps explain when and why multi-use, or flexible tools, might outperform specific-use, or specialized tools, or vice versa. This model is used to help understand the adoption of mortars when acorns became a staple food in prehistoric California. The model suggests specialized tools win out when tasks they are designed for are performed often enough, or occur with enough certainty, to make their added cost worthwhile.
Although use-wear analysis of prehistoric stone tools using conventional microscopy has proven useful to archaeologists interested in tool function, critics have questioned the reliability and ...repeatability of the method. The research presented here shows it is possible to quantitatively discriminate between various contact materials (e.g., wood, antler) using laser scanning confocal microscopy in conjunction with conventional edge damage data. Experiments with replica and prehistoric tools suggest the quantitative method presented here provides valid functional inferences and is flexible enough to accommodate other relevant sources of data on tool function.
Here we report on a phenanthridine derivative which has a covalently linked fluorescein molecule in order to increase the light absorption and hence fluorescence signal intensity when bound to duplex ...RNA. Steady-state fluorescence shows that the energy transfer efficiency from the fluorescein to the phenanthridine fluorophore is approximately 77%, which results in the probe being over 5× brighter than other phenanthridine derivatives when bound to RNA. Due to the relatively long lifetime (∼20 ns) of the probe, time-resolved fluorescence is used to increase the signal to background ratio in cell growth medium from 7 (steady-state value) to over 40. Moreover, fluorescence images of cells containing the probe show that the fluorescein signal is readily apparent along with that of the intercalated fluorophore, allowing this probe to be used as a dual color probe which simultaneously reports the probesʼ location and that of RNA.
The WAIS (West Antarctic Ice Sheet) Divide deep ice core was recently completed to a total depth of 3405 m, ending 50 m above the bed. Investigation of the visual stratigraphy and grain ...characteristics indicates that the ice column at the drilling location is undisturbed by any large-scale overturning or discontinuity. The climate record developed from this core is therefore likely to be continuous and robust. Measured grain-growth rates, recrystallization characteristics, and grain-size response at climate transitions fit within current understanding. Significant impurity control on grain size is indicated from correlation analysis between impurity loading and grain size. Bubble-number densities and bubble sizes and shapes are presented through the full extent of the bubbly ice. Where bubble elongation is observed, the direction of elongation is preferentially parallel to the trace of the basal (0001) plane. Preferred crystallographic orientation of grains is present in the shallowest samples measured, and increases with depth, progressing to a vertical-girdle pattern that tightens to a vertical single-maximum fabric. This single-maximum fabric switches into multiple maxima as the grain size increases rapidly in the deepest, warmest ice. A strong dependence of the fabric on the impurity-mediated grain size is apparent in the deepest samples.
Bubble number densities from the West Antarctic Ice Sheet (WAIS) Divide deep core in West Antarctica record relatively stable temperatures during the middle Holocene followed by late Holocene ...cooling. We measured bubble number density, shape, size, and arrangement on new samples of the main WAIS Divide deep core WDC06A from ~580 m to ~1600 depth. The bubble size, shape, and arrangement data confirm that the samples satisfy the requirements for temperature reconstructions. A small correction for cracks formed after core recovery allows extension of earlier work through the “brittle ice” zone, and a site‐specific calibration reduces uncertainties. Using an independently constructed accumulation rate history and a steady state bubble number density model, we determined a temperature reconstruction that agrees closely with other independent estimates, showing a stable middle Holocene, followed by a cooling of ~1.25°C in the late Holocene. Over the last ~5 millennia, accumulation has been higher during warmer times by ~12%°C−1, somewhat stronger than for thermodynamic control alone, suggesting dynamic processes.
Key Points
Bubble number density climate reconstruction was successfully extended for the WAIS Divide site
Climate reconstruction agrees with independent estimates and reveals a late Holocene cooling
Accumulation was higher during warmer times over the past ~5 millennia at the WAIS Divide site
The impact of western philosophy, with a particular focus on the Enlightenment, formed an epistemic default that elevated the intellectual ways of knowing at the expense of any other forms of ...knowing. This paper used John David Trentham's hermeneutical approach, the Inverse Consistency Protocol, as the framework for exploring the what and the why of this epistemic default. Trentham's first step, "envision redemptive maturity," was used to frame the doctrinal presuppositions that undergird a call for combating the limits of the isolating and dichotomous nature of the epistemic default. The second and third steps, "read for receptivity" and "employ reflective discernment," revealed the need for an integrated knowing that recognizes the holistic nature of the imago Dei and the impact of Jesus Christ as the truth. The work in the first three steps of Trentham's protocol set the stage for Christian schools to make application to their particular context as they engage in Trentham's fourth interpretive step, "identify appropriate outlets." By using Trentham's four steps, Christian schools may reflect on their practices and move toward an epistemology of integrated knowing that serves as the foundation for developing a culture focused on learning as formation.
Ice‐age cycling of the Greenland ice sheet likely contributed to locally elevated subglacial geothermal heat fluxes (GHFs), based on recent thermal modeling. Borehole and geophysical data indicate ...higher GHF in some areas than suggested by current knowledge of underlying geology, particularly at the head of the Northeast Greenland Ice Stream. Changes in lithospheric loading during ice‐sheet growth and decay cycles produce large and geologically rapid changes in the effective stress state beneath and near the ice sheet. Oscillations in melt fraction from cyclic loading through multiple ice‐age cycles will enhance upward magma migration through the nonlinear increase of melt migration velocity with melt fraction. We simulate periodic ice‐sheet loading scenarios along an east‐west transect across central Greenland on an Elastic Lithosphere, Relaxed Asthenosphere Earth model. Under likely parameter ranges, deviatoric stresses in the elastic lithosphere across widespread regions are sufficiently high to meaningfully enhance dike emplacement and also allow vug‐wave propagation in some scenarios. Stress patterns migrate laterally in response to ice‐sheet dynamics, favoring multistage magma ascent. If melt occurs at depth, our modeling suggests that ice‐age cycling could help it migrate upward to shallow depth or erupt, contributing to the high observed GHF. Furthermore, shallow magma emplacement might feed hydrothermal systems exploiting enhanced faulting or fracturing from ice‐age cycling, adding to elevated GHF. The preglacial passage of the Iceland‐Jan Mayen hot spot could have sourced such magmas. Direct observations of these lithospheric processes needed to further constrain our models are limited, highlighting the value of more targeted geophysical studies informing future modeling.
Key Points
Ice‐sheet growth and decay produce geologically rapid changes in lithospheric loading and stress
Simulated differential stresses from loading are of a similar magnitude to those needed for dike and vug‐wave magma migration processes
Cyclic loading might aid magma ascent and eruption, enhancing subglacial geothermal heat flux
Here we report that the phenanthridine derivative covalently linked to a fluorescein moiety (FLEth) can act as a fluorescence based probe for duplex short interfering RNA (siRNA) and that this probe ...can also be used to report on protein−RNA interactions. A fluorescence resonance energy transfer (FRET) signal that is observed at 600 nm occurs when FLEth is complexed with siRNA. At least 2 molecules of FLEth can bind to 21 nt duplex siRNA, and the dissociation constants for these interactions are reported. We find that FLEth can also report on the interaction of siRNAs with the Carnation Italian ringspot viral suppressor of RNA silencing p19. FLEth does not bind to the siRNA−p19 complex nor can p19 bind to the siRNA−FLEth complex; rather FLEth can report on the fraction of siRNA that is unbound. FLEth can also bind siRNA in delivery systems such as liposomes. Once the siRNA reaches the interior of Huh 7.5 cells, FLEth dissociates from the siRNA and is found in the nucleoli suggesting that FLEth cannot bind to siRNAs that are associated with the RNA silencing machinery.
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