Abstract Ice cores in Antarctica and Greenland reveal ice-crystal fabrics that can be softer under simple shear compared with isotropic ice. Owing to the sparseness of ice cores in regions away from the ice divide, we currently lack information about the spatial distribution of ice fabrics and its association with ice flow. Radio-wave reflections are influenced by ice-crystal alignments, allowing them to be tracked provided reflections are recorded simultaneously in orthogonal orientations (polarimetric measurements). Here, we image spatial variations in the thickness and extent of ice fabric across Dome A in East Antarctica, by interpreting polarimetric radar data. We identify four prominent fabric units, each several hundred metres thick, extending over hundreds of square kilometres. By tracing internal ice-sheet layering to the Vostok ice core, we are able to determine the approximate depth–age profile at Dome A. The fabric units correlate with glacial–interglacial cycles, most noticeably revealing crystal alignment contrasts between the Eemian and the glacial episodes before and after. The anisotropy within these fabric layers has a spatial pattern determined by ice flow over subglacial topography.

Surface, unsaturated-zone, and saturated-zone hydrologic conditions at Yucca Mountain responded to past climate variations and are at least partly preserved by sediment, fossil, and mineral records. Characterizing past hydrologic conditions in surface and subsurface environments helps to constrain hydrologic responses expected under future climate conditions and improve predictions of repository performance. Furthermore, these records provide a better understanding of hydrologic processes that operate at time scales not readily measured by other means. Pleistocene climates in southern Nevada were predominantly wetter and colder than the current interglacial period. Cyclic episodes of aggradation and incision in Fortymile Wash, which drains the eastern slope of Yucca Mountain, are closely linked to Pleistocene climate cycles. Formation of pedogenic cement is favored under wetter Pleistocene climates, consistent with increased soil moisture and vegetation, higher chemical solubility, and greater evapotranspiration relative to Holocene soil conditions. The distribution and geochemistry of secondary minerals in subsurface fractures and cavities reflect unsaturated-zone hydrologic conditions and the response of the hydrogeologic system to changes in temperature and percolation flux over the last 12.8 m.y. Physical and fluid-inclusion evidence indicates that secondary calcite and opal formed in air-filled cavities from fluids percolating downward through connected fracture pathways in the unsaturated zone. Oxygen, strontium, and carbon isotope data from calcite are consistent with a descending meteoric water source but also indicate that water compositions and temperatures evolved through time. Geochronological data indicate that secondary mineral growth rates are less than 1–5 mm/m.y., and have remained approximately uniform over the last 10 m.y. or longer. These data are interpreted as evidence for hydrological stability despite large differences in surface moisture caused by climate shifts between the Miocene and Pleistocene and between Pleistocene glacial-interglacial cycles. Secondary mineral distribution and δ 18 O profiles indicate that evaporation in the shallower welded tuffs reduces infiltration fluxes. Several near-surface and subsurface processes likely are responsible for diverting or dampening infiltration and percolation, resulting in buffering of percolation fluxes to the deeper unsaturated zone. Cooler and wetter Pleistocene climates resulted in increased recharge in upland areas and higher water tables at Yucca Mountain and throughout the region. Discharge deposits in the Amargosa Desert were active during glacial periods, but only in areas where the modern water table is within 7–30 m of the surface. Published groundwater models simulate water-table rises beneath Yucca Mountain of as much as 150 m during glacial climates. However, most evidence from Fortymile Canyon up gradient from Yucca Mountain limits water-table rises to 30 m or less, which is consistent with evidence from discharge sites in the Amargosa Desert. The isotopic compositions of uranium in tuffs spanning the water table in two Yucca Mountain boreholes indicate that Pleistocene water-table rises likely were restricted to 25–50 m above modern positions and are in approximate agreement with water-table rises estimated from zeolitic-to-vitric transitions in the Yucca Mountain tuffs (less than 60 m in the last 11.6 m.y.).

ABSTRACT The Minneapolis Chain of Lakes is a focal point of natural beauty in the heart of the city. Given the recreational and aesthetic imperative, these urban waterbodies have for decades been heavily managed for water quality and lake level. In the early stages of development of Minneapolis’ civic infrastructure, the area’s lakes and streams, as well as the Mississippi River, were given special consideration for preservation. This did not, however, mean that the lakes were preserved in their “natural” state, for they were connected by channels, dredged and filled to turn wetlands into open water and dry land, and even reshaped to better conform to the prevailing fashion of design. These manipulations had dramatic effects on the Chain’s smallest lake, Brownie, which became meromictic after a rapid drop in lake level caused by ditching across the divide to Cedar Lake. The lakes and surrounding area were important sources of subsistence for Dakota and Ojibwe people through the middle of the nineteenth century, and some of the earliest substantive interactions between missionaries and Native Americans in Minnesota played out around the Chain of Lakes and nearby Mississippi River valley. The relative orientation of the lakes (and of other groups of lakes in the Twin Cities), and some lakes’ unusual depths relative to surface areas, result from their formation by melting of ice blocks buried in valley train fill during final retreat of the Laurentide ice sheet. Below tens to hundreds of feet of glacial material, mapping of bedrock surfaces indicates the presence of paleo–Mississippi River channels dating from at least two previous interglacials. The integration of multiple subdisciplines of geology and of various basic sciences within paleolimnology and limnogeology, as well as the relevance to students of historical and environmental information, makes lake sediment studies well suited to hands-on, place-based educational approaches as stand-alone courses or laboratories for a number of different core curriculum and nonmajor classes.

Abstract The Great Basin of the western United States offers tremendous potential for exploring the response of mountain glaciers and lowland lakes to climate changes during the Last Glacial Maximum (LGM, MIS-2, ca. 22–18 ka B.P.) and subsequent glacial-interglacial transition. The combination of well-distributed alpine moraine records and pluvial lake deposits offers an unparalleled opportunity to develop a more precise understanding of temperature and precipitation changes during the latest Pleistocene and into the Holocene. This field trip provides an overview of recent and ongoing work illuminating aspects of the glacial and pluvial history of northeastern Nevada from the LGM to the present. The route of this trip involves three full days of stops separated by two nights in Elko, Nevada. The first day focuses on glacial deposits at the type locality for the LGM Angel Lake Glaciation on the eastern side of the East Humboldt Range. The second day explores the geomorphic record of pluvial Lakes Franklin and Clover on the east side of the Ruby–East Humboldt Mountains and describes recent efforts to develop a chronology for the late Pleistocene regression of these lakes. The final day again focuses on glacial geology, starting with the type locality of the pre-LGM Lamoille Glaciation on the west side of the Ruby Mountains, and ending with several stops along the scenic drive up Lamoille Canyon.

Sediments deposited over the past 220,000 years in Bear Lake, Utah and Idaho, are predominantly calcareous silty clay, with calcite as the dominant carbonate mineral. The abundance of siliciclastic sediment indicates that the Bear River usually was connected to Bear Lake. However, three marl intervals containing more than 50% CaCO 3 were deposited during the Holocene and the last two interglacial intervals, equivalent to marine oxygen isotope stages (MIS) 5 and 7, indicating times when the Bear River was not connected to the lake. Aragonite is the dominant mineral in two of these three high-carbonate intervals. The high-carbonate, aragonitic intervals coincide with warm interglacial continental climates and warm Pacific sea-surface temperatures. Aragonite also is the dominant mineral in a carbonate-cemented microbialite mound that formed in the southwestern part of the lake over the last several thousand years. The history of carbonate sedimentation in Bear Lake is documented through the study of isotopic ratios of oxygen, carbon, and strontium, organic carbon content, CaCO 3 content, X-ray diffraction mineralogy, and HCl-leach chemistry on samples from sediment traps, gravity cores, piston cores, drill cores, and microbialites. Sediment-trap studies show that the carbonate mineral that precipitates in the surface waters of the lake today is high-Mg calcite. The lake began to precipitate high-Mg calcite sometime in the mid–twentieth century after the artificial diversion of Bear River into Bear Lake that began in 1911. This diversion drastically reduced the salinity and Mg 2+ :Ca 2+ of the lake water and changed the primary carbonate precipitate from aragonite to high-Mg calcite. However, sediment-trap and core studies show that aragonite is the dominant mineral accumulating on the lake floor today, even though it is not precipitating in surface waters. The isotopic studies show that this aragonite is derived from reworking and redistribution of shallow-water sediment that is at least 50 yr old, and probably older. Apparently, the microbialite mound also stopped forming aragonite cement sometime after Bear River diversion. Because of reworking of old aragonite, the bulk mineralogy of carbonate in bottom sediments has not changed very much since the diversion. However, the diversion is marked by very distinct changes in the chemical and isotopic composition of the bulk carbonate. After the last glacial interval (LGI), a large amount of endogenic carbonate began to precipitate in Bear Lake when the Pacific moisture that filled the large pluvial lakes of the Great Basin during the LGI diminished, and Bear River apparently abandoned Bear Lake. At first, the carbonate that formed was low-Mg calcite, but ~11,000 years ago, salinity and Mg 2+ :Ca 2+ thresholds must have been crossed because the amount of aragonite gradually increased. Aragonite is the dominant carbonate mineral that has accumulated in the lake for the past 7000 years, with the addition of high-Mg calcite after the diversion of Bear River into the lake at the beginning of the twentieth century.

A continuous, 120-m-long core (BL00-1) from Bear Lake, Utah and Idaho, contains evidence of hydrologic and environmental change over the last two glacial-interglacial cycles. The core was taken at 41.95°N, 111.31°W, near the depocenter of the 60-m-deep, spring-fed, alkaline lake, where carbonate-bearing sediment has accumulated continuously. Chronological control is poor but indicates an average sedimentation rate of 0.54 mm yr ‒1 . Analyses have been completed at multi-centennial to millennial scales, including (in order of decreasing temporal resolution) sediment magnetic properties, oxygen and carbon isotopes on bulk-sediment carbonate, organic- and inorganic- carbon contents, palynology; mineralogy (X-ray diffraction), strontium isotopes on bulk carbonate, ostracode taxonomy, oxygen and carbon isotopes on ostracodes, and diatom assemblages. Massive silty clay and marl constitute most of the core, with variable carbonate content (average = 31 ± 19%) and oxygen-isotopic values (δ 18 O ranging from ‒18‰ to ‒5‰ in bulk carbonate). These variations, as well as fluctuations of biological indicators, reflect changes in the water and sediment discharged from the glaciated headwaters of the dominant tributary, Bear River, and the processes that influenced sediment delivery to the core site, including lake-level changes. Although its influence has varied, Bear River has remained a tributary to Bear Lake during most of the last quarter-million years. The lake disconnected from the river and, except for a few brief excursions, retracted into a topographically closed basin during global interglaciations (during parts of marine isotope stages 7, 5, and 1). These intervals contain up to 80% endogenic aragonite with high δ 18 O values (average = ‒5.8 ± 1.7‰), indicative of strongly evaporitic conditions. Interglacial intervals also are dominated by small, benthic/tychoplanktic fragilarioid species indicative of reduced habitat availability associated with low lake levels, and they contain increased high-desert shrub and Juniperus pollen and decreased forest and forest-woodland pollen. The 87 Sr/ 86 Sr values (>0.7100) also increase, and the ratio of quartz to dolomite decreases, as expected in the absence of Bear River inflow. The changing paleoenvironments inferred from BL00-1 generally are consistent with other regional and global records of glacial-interglacial fluctuations; the diversity of paleoenvironmental conditions inferred from BL00-1 also reflects the influence of catchment-scale processes.

The stratigraphic and regional distributions of paleosol morphology in latest Pennsylvanian through Early Permian strata in Colorado, Utah, Arizona, New Mexico, Texas, and Oklahoma are presented in this paper. This regional extent corresponds to a paleolatitudinal gradient spanning ~5°S to 10°N. Morphological trends from this region delineate significant and systematic temporal and spatial changes in Permian-Carboniferous paleoenvironment and paleoclimate. The inferred latest Pennsylvanian (Virgilian) through early Early Permian environmental pattern is complex, but it indicates persistently dry, semiarid to arid conditions in Colorado, Utah, and Arizona, at paleolatitudes north of ~2°N, whereas lower paleolatitude (~2°S to 2°N) tropical regions in New Mexico exhibit a stepwise shift from subhumid to semiarid and variably seasonal conditions throughout late Pennsylvanian and the first half of Early Permian (Virgilian through Wolfcampian) time, followed by a subsequent shift to more arid conditions during the latter part of the Early Permian (Leonardian). Notably, strata from the southernmost paleosites, in Texas and Oklahoma, exhibit the most significant and abrupt climate changes through this period; they show a rapid transition from nearly ever-wet latest Pennsylvanian climate (at ~5°S) to drier and seasonal climate across the Permian-Carboniferous system boundary, and finally to arid and seasonal climate by Leonardian time (at ~2–4°N). The inferred climate patterns show no robust long-term correlation with the high-latitude Gondwanan records of glaciation. Rather, the long-term record of Permian-Pennsylvanian climate indicators from the southwestern United States is most simply explained by an ~8° northward tectonic drift through (essentially) static climate zones over western tropical Pangea during the interval of study. However, the relatively rapid perturbations to climate recorded by these pedogenic archives appear to be too rapid for tectonic forces and might correspond to changes in climate drivers, such as atmospheric p CO 2 , atmospheric circulation, and glacial-interglacial cycles.

Planetary and synoptic-scale atmospheric features are important because they set the stage for differing climate regimes in the Yucca Mountain area—whether in past, present, or future time. Climate proxy records in the region show that numerous climate regimes occurred during the past 800 k.y. ranging from warm interglacial periods (similar to modern climate) to cool or cold and wet glacial periods. The current climate at Yucca Mountain is arid, with an annual average precipitation of ∼17.7 cm/yr. Most of the annual precipitation occurs during winter or during July and August monsoons. Annual average temperatures generally range from 15° to 18 °C but can exceed 40 °C during summer. Continuously deposited calcite at Devils Hole, Nevada, provides a precise chronology that can be used to calibrate other climate proxy data that provide estimates of the nature and magnitude of past climate events. During past glacial periods, mean annual temperature may have been as much as 10° to 15 °C cooler than present temperatures, with mean annual precipitation as much as 1.4–3 times present precipitation. These records of past climate are used to bound estimates of future climate to assess future potential infiltration. Five maximum infiltration scenarios are estimated to occur within the next 500 k.y. providing that anthropogenic disturbance does not modify or alter long-term climate change.

A coupled ocean-atmosphere general circulation model was used to perform multi-centennial climate simulations of the Eemian interglacial and the subsequent glacial inception. The simulations were performed as equilibrium experiments with orbital parameters and greenhouse gas concentrations set to values of 125,000 and 115,000 yr before present (B.P.). These dates represent periods with enhanced and weakened seasonal cycles of insolation in the Northern Hemisphere. A consistent reaction of seasonal temperatures is simulated for most continental regions. Comparisons with pollen-based reconstructions of European temperatures show that the model simulates realistic spatial temperature patterns for the warm phase of the Eemian. In the case of the simulation for 115,000 yr B.P., the model reacts with a long-term cooling trend. This trend is associated with a continuous increase in Northern Hemisphere sea-ice volume and an expansion of the permanently snow-covered areas over North America. Although summer precipitation is reduced in this region, the changes in seasonality of temperature lead to significant higher amounts of summer snowfall. The strengthened North Atlantic circulation does not compensate the cooling of the Northern Hemisphere. The snow accumulation starts in northeastern Canada where southward winds transport cold Arctic air into the continent. The accumulated snow volume on the North American continent is equivalent to a reduction of sea level at a rate of ∼10 cm per century at the end of the simulation.

Black shales and Mn carbonates interbedded with glacial deposits from the Neoproterozoic of southern China exhibit extremely heavy values of pyrite S isotopes that may reflect the peculiar environment of Earth at this time. δ 34 S averages +30‰ at Tanganshan and +44‰ at Xiangtan, compared with typical values of 0‰ to +5‰ found in younger deposits. Furthermore there is no distinction between the shales and the Mn carbonate ores in the Neoproterozoic, unlike the younger deposits, which show much lighter δ 34 S in the shales than in the Mn ores (the spread is 25‰). Most other chemical parameters are very similar to both the younger Mn deposits and those from the Paleoproterozoic. The exception is the rare earth elements (REE). All Neoproterozoic Fe ores and most Neoproterozoic Mn ores lack the positive Eu anomaly that characterizes Archean and Paleoproterozoic Fe-Mn accumulations. On the other hand, Neoproterozoic Mn deposits have positive Ce anomalies on North American Shale Composite (NASC) normalized plots, in contrast to other MnCO 3 ores. The ΣREE is also higher than in other Mn deposits, but lower than in modern deep-sea crusts. Sulfide S values in all Neoproterozoic shales tend to be exceptionally variable and to often show much heavier values than can be found in marine strata from the Phanerozoic. Therefore the anomalous δ 34 S values we observed reflect peculiar conditions in the world oceans at this time rather than purely local effects. Times of enrichment of seawater sulfate in 34 S do not correspond to periods of glaciation, so the likely cause of the S isotope patterns is not worldwide glaciation, but a generally low level of dissolved sulfate S in the Neoproterozoic oceans that allowed modest increases in the amounts of S removed as pyrite to drive down the oceanic S reservoir enough to produce strong Rayleigh reservoir effects. The abundance worldwide of Sturtian-age Mn and Fe deposits indicates an increase in Fe flux to the oceans that would have been sufficient to depress SO 4 2- levels severely and to result in residual dissolved S extremely enriched in 34 S. REE evidence indicates that most of this enhanced Fe and Mn flux came from diagenetic remobilization of detrital oxides rather than from ridge-crest hydrothermal systems, in contrast to the Paleoproterozoic banded iron formations. Rapid introduction of lateritic soil residues to restricted basins by low-latitude glaciation could have provided the needed excess Fe and Mn to drive this system.

Understanding and quantifying fluvial transport and bedrock abrasion processes have become major concerns in modeling landform response to tectonic and climatic forcing. Recent theoretical and experimental investigations have in particular stressed the importance of sediment supply and size in controlling bedrock incision rate. Many studies on the downstream evolution of pebble size have focused on unraveling the respective roles of selective sorting and abrasion, without paying much attention to sediment sources. In order to track sediment supply and characteristics from source to sink in an active tectonic setting, where long-term selective deposition can be excluded, we systematically measured sediment size and lithology on gravel bars along the Marsyandi River and its tributaries (Himalayas of central Nepal), and also in sediment source material from hillslopes (landslides, moraines, terrace deposits). The downstream evolution in lithological distribution is found to be in close agreement with common views on pebble abrasion and present views on denudation in the range: (1) pebbles from the more rapidly uplifted and eroded Higher Himalayan gneissic units are over-represented, due to their major contribution to sediment influx, (2) easily erodible lithologies such as schists, sandstones, and limestone are under-represented relative to resistant rock types like quartzite. More surprisingly, we observe a general downstream coarsening of gravel bar material along the middle and lower Marsyandi River, whereas downstream sediment fining is typical of most river systems. A simple integrative model that tracks pebbles from hillslope to the main stem of the river and includes abrasion coefficients for the different Himalayan lithologies and size distribution of hillslopes sediment supplies accounts for both changing lithologic proportion along the Marsyandi and for the downstream coarsening of gravel bar material. This coarsening mainly results from differences in sediment sources along the Marsyandi Valley, in particular from differences in size distributions of landslide and moraine material. However, the median pebble size of subsurface material in gravel bars is coarser than median size of the blocky material in the source. The choice of the measurement methods and their potential bias are discussed but cannot explain this surprising feature displayed by our measurements. We suspect that due to sediment transport modalities in active tectonic settings, the subpavement grain-size distribution on gravel bars is not representative of the average bed-load size distribution. Consequently, pebble abrasion is more easily demonstrated by description of pebble lithology than by the downstream evolution of pebble size. Our study also shows, in contrast with previous studies, that experimentally derived abrasion coefficients can account for the downstream evolution of pebbles without calling for additional fining processes. We conclude that the eroded lithology and hillslope sediment source exert a major influence on the downstream evolution of sediment characteristics, on bedload ratio, and probably on bedrock erosion efficiency. These conclusions have important implications in terms of river profile evolution, landscape denudation, internal erosion coupling, and the response of the fluvial network to glacial-interglacial fluctuations.

We dedicate this manuscript to Dr. Cipora Klein, who studied the historic levels of the Dead Sea . This paper reviews the research and lake level reconstruction of the late Pleistocene and Holocene lakes in the Dead Sea basin. Lake Lisan and the Dead Sea occupied the Dead Sea basin during the past 70 k.y., and responded to and amplified regional climatological variations in the Eastern Mediterranean. Overall, the lake level history is correlative with global climate patterns. The Lake Lisan high levels correspond to the last Glacial period (marine isotope stages 2–4); its dramatic level drop to the transition to the Holocene, and the Dead Sea low stands to the current interglacial period. The Lisan level record also appears to show relationships to millennial events in Greenland ice and deep-sea cores. The paper describes the methodologies applied to identify indicators of lake level elevations and the determination of their ages. It is divided to (1) the early research history (mainly commencing at the nineteenth century) in the Dead Sea basin; (2) the early efforts of lake level curve reconstructions; and (3) the most recent studies that yield well-dated, high resolution lake level chronologies.

Evidence of former equilibrium line elevations on Mount Olympus, Greece, coupled with estimates of uplift rate, point to more extensive Pleistocene glaciation and far colder climates than previous studies have indicated. These findings are supported by the record of glacial deposition both on the mountain and across the adjacent piedmont. The data not only provide evidence of significant equilibrium line altitude depression from a present-day elevation as much as 600 m above the mountain's summit (2917 m), but also show that Mount Olympus was glaciated on several occasions, and that the first episode of glaciation significantly predated the late Pleistocene. Piedmont sediments east and west of Mount Olympus record three discrete stages of deposition, each of which can be related to glacial activity on the mountain. Soils that separate these sedimentary units correspond to nonglacial intervals and can be correlated to a dated soil succession south of Olympus. This correlation suggests that the oldest soils correspond to the isotope stage 7 (Mindel/Riss) interglacial event (ca. 210,000 yr before present; U/Th disequilibrium) and that the oldest Pleistocene sediments record isotope stage 8 (Mindel) glaciation in the Olympus region. Subsequent stages of deposition are interpreted to record glaciation on the mountain during the isotope stage 6 (Riss) and isotope stages 4–2 (Würm) glacial events. Sedimentary units defined on the piedmont are also recognized on the Olympus upland and within valley-head cirques, where they correspond to three stages of cirque development. The distribution of these materials, as well as the occurrence of glacial erosional and depositional landforms, indicates that Mount Olympus supported upland ice during the first and second episodes of glaciation and that the first glaciation was sufficiently extensive to produce piedmont ice lobes that covered parts of the eastern, northern, and western piedmont of the mountain. Uplift-corrected cirque floor elevations, coupled with the distribution of glacial sediments, indicate that the Pleistocene equilibrium line altitude during each episode of glaciation was depressed at least 1400–1500 m, to elevations of 2000–2100 m above present sea level (asl). Assuming that lowering of the equilibrium line was solely a function of temperature, this would correspond to a mean annual temperature decrease of 8–9 °C. This contrasts with previous studies of the Mount Olympus region, which suggest that glaciation was restricted to small valley glaciers in upland and valley-head positions, that the regional Pleistocene equilibrium line was lowered only to elevations of 2200–2400 m asl, and that active glaciation was restricted to the latest Pleistocene (Würm). Study of the neotectonic history of Mount Olympus suggests that uplift persisted throughout the mid-Pleistocene–Holocene at a rate of ∼1.6 m/k.y.