Richard B. Alley's research while affiliated with Pennsylvania State University and other places

Publications (551)

Article
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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 tha...
Article
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Rapid retreat of the Larsen A and B ice shelves has provided important clues about the ice shelf destabilization processes. The Larsen C Ice Shelf, the largest remaining ice shelf on the Antarctic Peninsula, may also be vulnerable to future collapse in a warming climate. Here, we utilize multisource satellite images collected over 1963–2020 to deri...
Article
Marine-terminating glaciers lose mass through melting and iceberg calving, and we find that meltwater drainage systems influence calving timing at Helheim Glacier, a tidewater glacier in East Greenland. Meltwater feeds a buoyant subglacial discharge plume at the terminus of Helheim Glacier, which rises along the glacial front and surfaces through t...
Article
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Bedforms of Thwaites Glacier, West Antarctica both record and affect ice flow, as shown by geophysical data and simple models. Thwaites Glacier flows across the tectonic fabric of the West Antarctic rift system with its bedrock highs and sedimentary basins. Swath radar and seismic surveys of the glacier bed have revealed soft‐sediment flutes 100 m...
Preprint
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Glacier motion responds dynamically to changes in climate, but the multi-decadal trajectory of slip-facilitated motion remains poorly constrained due to its sensitivity to climate variability across a significant range of timescales. Long-running observational records of glacier motion provide critical benchmarks to decode the processes influencing...
Article
Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Anta...
Article
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The Paris Agreement aims to limit global mean warming in the twenty-first century to less than 2 degrees Celsius above preindustrial levels, and to promote further efforts to limit warming to 1.5 degrees Celsius¹. The amount of greenhouse gas emissions in coming decades will be consequential for global mean sea level (GMSL) on century and longer ti...
Article
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The grounding zone of Whillans Ice Stream, West Antarctica, exhibits an abrupt transition in basal properties from the grounded ice to the ocean cavity over distances of less than 0.5–1 km. Active-source seismic methods reveal the downglacier-most grounded portion of the ice stream is underlain by a relatively stiff substrate (relatively high shear...
Article
While twentieth century sea-level rise was dominated by thermal expansion of ocean water, mass loss from glaciers and ice sheets is now a larger annual contributor. There is uncertainty on how ice sheets will respond to further warming, however, reducing confidence in twenty-first century sea-level projections. In 2019, to address the uncertainty,...
Article
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Plain Language Summary Glacier beds and tectonic faults may at first appear to be quite different, but they share important characteristics. In both cases, motion may be smooth (aseismic creep) or earthquake‐producing “stick‐slip.” A powerful physical constitutive relationship called rate‐and‐state friction has been developed to understand earthqua...
Article
Thwaites Glacier (TG), West Antarctica, is losing mass in response to oceanic forcing. Future evolution could lead to deglaciation of the marine basins of the West Antarctic Ice Sheet, depending on ongoing and future climate forcings, but also on basal topography/bathymetry, basal properties, and physical processes operating within the grounding zo...
Preprint
Full-text available
The grounding zone of Whillans Ice Stream, West Antarctica, exhibits an abrupt transition in basal properties from the grounded ice to the ocean cavity over distances of less than 0.5–1 km. Active source seismic methods reveal the grounded portion of the ice stream is underlain by a relatively stiff substrate (relatively high shear wave velocities)...
Article
Ice sheets reshape Earth’s surface. Maps of the landscape formed by past ice sheets are our best tool for reconstructing historic ice sheet behavior. But models of glacier erosion and deposition that explain mapped features are relatively untested, and without observations of landforms developing in situ, postglacial landscapes can provide only qua...
Article
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We describe elongate, wet, subglacial bedforms in the shear margins of the NE Greenland Ice Stream and place some constraints on their formation. Lateral shear margin moraines have been observed across the previously glaciated landscape, but little is known about the ice-flow conditions necessary to form these bedforms. Here we describe in situ sed...
Article
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Over the past decade, the Arctic has warmed by 0.75°C, far outpacing the global average, while Antarctic temperatures have remained comparatively stable. As Earth approaches 2°C warming, the Arctic and Antarctic may reach 4°C and 2°C mean annual warming, and 7°C and 3°C winter warming, respectively. Expected consequences of increased Arctic warming...
Article
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Glacier-erosion rates range across orders of magnitude, and much of this variation cannot be attributed to basal sliding rates. Subglacial till acts as lubricating ‘fault gouge’ or ‘sawdust’, and must be removed for rapid subglacial bedrock erosion. Such erosion occurs especially where and when moulin-fed streams access the bed and are unconstraine...
Article
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Recent seismic measurements from upper Thwaites Glacier indicate that the bed-type variability is closely related to the along-flow basal topography. In high-relief subglacial highlands, stoss sides of topographic highs have a relatively higher acoustic impedance (‘hard’ bed) with lower acoustic impedance (‘soft’ till) on lee sides. This pattern is...
Article
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The South Pole Ice Core (SPICEcore) was drilled in 2014–2016 to provide a detailed multi-proxy archive of paleoclimate conditions in East Antarctica during the Holocene and late Pleistocene. Interpretation of these records requires an accurate depth–age relationship. Here, we present the SPICEcore (SP19) timescale for the age of the ice of SPICEcor...
Article
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Basal ice of glaciers and ice sheets frequently contains a well-developed stratification of distinct, semi-continuous, alternating layers of debris-poor and debris-rich ice. Here, the nature and distribution of shear within stratified basal ice are assessed through the anisotropy of magnetic susceptibility (AMS) of samples collected from Matanuska...
Article
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Floating ice shelves of fast-flowing ice streams are prone to rift initiation and calving originating along zones of rapid shearing at their margins. Predicting future ice-shelf destabilization under a warming ocean scenario, with the resultant reduced buttressing, faster ice flow, and sea-level rise, therefore requires an understanding of the proc...
Article
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Ice core data record significant and abrupt past climate changes that are associated with large and rapid changes in atmospheric greenhouse gases, such as methane. Due to the gradual close‐off of gas bubbles and the relatively fast diffusion of gases within the firn column, even a discrete or quick step increase in air composition may be smoothed o...
Article
Integrating Earth science research and observations into adaptation planning helps identify effective strategies to manage climate risks.
Article
Large-ensemble perturbed-parameter forward ice-flow modeling can provide useful insights to uncertainties in inversions for basal drag or other ice-flow parameters. Inversion and data assimilation provide estimates of poorly known parameters that are essential for accurate prognostic modeling. Because ice flow depends on many such parameters with t...
Article
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38 The South Pole Ice Core (SPICEcore) was drilled in 2014-2016 to provide a 39 detailed multi-proxy archive of paleoclimate conditions in East Antarctica during the 40 Holocene and late Pleistocene. Interpretation of these records requires an accurate depth-41 age relationship. Here, we present the SP19 timescale for the age of the ice of SPICEcor...
Article
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The spatially variable basal flow law suggested by geophysical data from Thwaites Glacier, West Antarctica produces modeled ice-flow response to warming that differs notably from the response of commonly assumed spatially uniform flow laws, with implications for future sea-level rise. Unlike many ice-sheet outlets, Thwaites flows across rather than...
Conference Paper
The deformation of glacial ice is strongly influenced and often enhanced by several factors, including ice crystal size, solute concentrations and debris content. Since strain is concentrated near the base of glaciers and ice in the basal zone is characterized by high concentrations of debris, it is important to understand the effects of debris con...
Article
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Retrogressive slumping could accelerate sea-level rise if ice-sheet retreat generates ice cliffs much taller than observed today. The tallest ice cliffs, which extend roughly 100 m above sea level, calve only after ice-flow processes thin the ice to near flotation. Above some ice-cliff height limit, the stress state in ice will satisfy the material...
Article
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Plain Language Summary Accurate estimates of regional‐scale CO2 surface fluxes are essential to improve our understanding of the carbon cycle and to verify human CO2 emission inventories. CO2 surface fluxes can be inferred from atmospheric CO2 measurements through inversion methods, which use atmospheric transport models to relate CO2 concentration...
Article
Seismic measurements on Thwaites Glacier show a spatially variable bed character, with implications for ice-sheet stability. The West Antarctic Ice Sheet is losing mass rapidly through outlet glaciers and ice streams in the Amundsen Sea Embayment, including Thwaites Glacier, where limited observations and modeling suggest that ice-flow rates depend...
Article
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Plain Language Summary Snow that falls on ice sheets is squeezed to ice under its own weight. Old snow during its transformation to ice is called firn. Ice sheets in Greenland and Antarctica are covered in 10–100 m of firn, and many studies on ice sheets require knowledge of firn properties. Observations of the firn, however, are logistically diffi...
Article
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The history of the Greenland Ice Sheet has been influenced by the geodynamic response to ice sheet fluctuations, and this interaction may help explain past deglaciations under modest climate forcing. We hypothesize that when the Iceland hot spot passed beneath north-central Greenland, it thinned the lithosphere and left anomalous heat likely with p...
Article
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Rapidly retreating thick ice fronts can generate large amounts of mélange (floating ice debris), which may affect episodes of rapid retreat of Antarctic marine ice. In modern Greenland fjords, mélange provides substantial back pressure on calving ice faces, which slows ice front calving rates. On the much larger scales of West Antarctica, it is unk...
Article
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Measurements of a sample from ~580 m depth in the WAIS Divide (WDC06A) ice core reveal that bubbles are preferentially elongated in the basal plane of their parent grain, as expected if bubble shape preserves the record of dominant basal glide. This suggests that a method using bubbles as strain gauges could provide insights to grain-scale ice defo...
Article
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We present a high-resolution shear-wave velocity model of Greenland’s lithosphere from regional and teleseismic Rayleigh-waves recorded by the Greenland Ice Sheet Monitoring Network supplemented with observations from several temporary seismic deployments. To construct Rayleigh-wave group-velocity maps, we integrated signals from regional and teles...
Article
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Rapidly retreating thick ice fronts can generate large amounts of mélange (floating ice debris), which may affect episodes of rapid retreat of Antarctic marine ice. In modern Greenland fjords, mélange provides substantial back pressure on calving ice faces, which slows ice-front velocities and calving rates. On the much larger scales of West Antarc...
Article
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Observations at the West Antarctic Ice Sheet (WAIS) Divide site show that near-surface snow is strongly altered by weather-related processes such as strong winds and temperature fluctuations, producing features that are recognizable in the deep ice core. Prominent glazed surface crusts develop frequently at the site during summer seasons. Surface,...
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The flood hazard in New York City depends on both storm surges and rising sea levels. We combine modeled storm surges with probabilistic sea-level rise projections to assess future coastal inundation in New York City from the preindustrial era through 2300 CE. The storm surges are derived from large sets of synthetic tropical cyclones, downscaled f...
Article
Despite the importance of grounding zone sedimentation for ice sheet stability and ice sheet history, evidence for sedimentary deposits beneath West Antarctica's modern grounding zone remains sparse. Seismic surveying shows that Kamb Ice Stream has no detectable grounding zone deposit. As grounding zone deposition relies strongly on ice flow, the a...
Article
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This article provides concise documentation of the ongoing retreat of glaciers, along with the implications that the ice loss presents, as well as suggestions for geoscience educators to better convey this story to both students and citizens. We present the retreat of glaciers—the loss of ice—as emblematic of the recent, rapid contraction of the cr...
Article
The complex flow fields of the Antarctic and Greenland ice sheets deform layers deposited as snow at the ice sheet surface, leaving a record of the regional flow history and/or local transitions in basal boundary conditions within the geometry of ice sheet layers. Ice-penetrating radar reveals these layers, but radar data interpretations are limite...
Article
Constraining how much and how fast the West Antarctic Ice Sheet (WAIS) will change in the coming decades has recently been identified as the highest priority in Antarctic research (National Academies, 2015). Here we review recent research on WAIS and outline further scientific objectives for the area now identified as the most likely to undergo nea...
Article
Amplitude analysis of reflection seismic data reveals the presence of highly variable bed conditions under the main sticky spot and adjacent regions of the Kamb Ice Stream (KIS—formerly ice stream C). The sticky spot, which is a zone of bed that imparts high basal resistance to ice flow, is situated on a local topographic high composed of consolida...
Article
Recent estimates suggest that global mean sea level rise could exceed 2 m by 2100. These projections are higher than previous ones and are based on the latest understanding of how the Antarctic Ice Sheet has behaved in the past and how sensitive it is to future climate change. They pose a challenge for scientists and policy-makers alike, requiring...
Data
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The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses n...
Article
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The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses n...
Article
The Greenland Ice Sheet (GIS) contains the equivalent of 7.4 metres of global sea-level rise. Its stability in our warming climate is therefore a pressing concern. However, the sparse proxy evidence of the palaeo-stability of the GIS means that its history is controversial (compare refs 2 and 3 to ref. 4). Here we show that Greenland was deglaciate...
Article
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Using Arctic sea-ice concentration derived from passive microwave satellite observations in autumn and early winter over the 1979–2014 period, the Arctic region was objectively classified into several smaller regions based on the interannual sea-ice variability through self-organizing map analyses. The trend in regional sea-ice extent (RSIE) in eac...
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We present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice-sheet instability. Following a subsequent 60% drop in ocean...
Article
We present a comprehensive ice-penetrating radar survey of a subglacial embayment and adjacent peninsula along the grounding zone of Whillans Ice Stream, West Antarctica. Through basal waveform and reflectivity analysis, we identify four distinct basal interfaces: (1) an ice–water-saturated till interface inland of grounding; (2) a complex interfac...
Article
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Marine diatoms in tillites along the Transantarctic Mountains (TAMs) have been used to suggest a diminished East Antarctic Ice Sheet (EAIS) during Pliocene warm periods. Updated ice-sheet modelling shows significant Pliocene EAIS retreat, creating marine embayments into the Wilkes and Aurora basins that were conducive to high diatom productivity an...
Article
For common-offset radar data, there is no clear way to disentangle path effects from reflector characteristics, so efforts to determine the physical properties at the bed using reflection amplitude are inherently limited by the constraints on englacial attenuation. In this study, we identify the theoretical considerations required for interpreting...
Article
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The significance and robustness of the link between Arctic sea ice loss and changes in midlatitude weather patterns is investigated through a series of model simulations from the Community Atmosphere Model, version 5.3, with systematically perturbed sea ice cover in the Arctic. Using a large ensemble of 10 sea ice scenarios and 550 simulations, it...
Article
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Ice-age cycling of the Greenland Ice Sheet likely contributed to locally elevated subglacial geothermal heat fluxes (GHF), 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. Change...
Article
We predict the perturbation to the Earth's length-of-day (LOD) over the Common Era using a recently derived estimate of global sea-level change for this time period. We use this estimate to derive a time series of “clock error”, defined as the difference in timing of two clocks, one based on a theoretically invariant time scale (terrestrial time) a...