Science.gov

Sample records for ice age moraines

  1. Biogeomorphic interactions and patterns on Little Ice Age lateral moraines

    NASA Astrophysics Data System (ADS)

    Eichel, Jana; Schmidtlein, Sebastian; Dikau, Richard

    2014-05-01

    Glaciers and their forefields are strongly affected by climate change. This leads to increasing geomorphological and ecological dynamics in these environments. Glacier recession exposes high volumes of unconsolidated sediments, with lateral moraines being among the most important sediment storages. Their sediment is reworked by a variety of slope processes, e.g. sheet wash, debris flows or gullying. At the same time, these landforms are colonized by plants and other organisms, proceeding into vegetation succession. It is believed that this process ultimately leads to sediment stabilization which is an important factor for reservoir management in glacier forefields. Recent biogeomorphic research revealed a strong coupling of geomorphic and ecologic processes and complex feedbacks. Geomorphic processes disturb vegetation while at the same time, certain plant species, 'geomorphic-engineer species', can influence geomorphic properties and processes. The strength of these interactions changes during biogeomorphic succession. Corresponding patterns of vegetation and geomorphic forms and processes arise at the mesoscale. The resulting spatial heterogeneity can be mapped as patches. In our study, we investigate patterns of vegetation and geomorphic forms and processes on Little Ice Age lateral moraines in the Turtmann glacier forefield, Switzerland. Despite higher terrain age, these landforms show strongly heterogeneous vegetation as well as geomorphic activity patterns, indicating that sediment stabilization has not yet been accomplished. This could result from varying strengths of biogeomorphic interactions. To assess this influence, vegetation and geomorphic properties of 50 vegetation plots were sampled and statistically analyzed. Results showed that vegetation composition does not relate to terrain age, rather, geomorphic disturbances seem to be a dominant influencing factors, producing patch dynamics. Certain species compositions can be related to specific geomorphic

  2. Investigating age and origin of ice-cored moraines in Jotunheimen and Breheimen/Southern Norway

    NASA Astrophysics Data System (ADS)

    Winkler, Stefan; Matthews, John; Wilson, Peter

    2015-04-01

    Ice-cored moraines characteristic for the high-alpine zones in the Jotunheimen and Breheimen mountain regions of southern Norway have been recognised, described, and studied as early as during the 1950s and 1960s. These complex multiple-ridged, ramp-like moraines of up to 50 m in height occurring at comparatively small but high-lying glaciers differ considerably from those typical for the other glaciers at lower altitudes. The existence of their ice-core beneath rather thin debris cover and a spatial concentration in the north-eastern part of the regions with a higher snow line and stronger climatic continentality points towards their link with alpine permafrost. Until today, there is no consensus about either the mechanisms of their formation or their age constraints. Based on few (possibly less reliable) radiocarbon ages retrieved from dust within the ice cores the innermost (proximal) ridges were, for example, interpreted as rather old and the outermost ridges as youngest. Consequently, the innermost ridges need to have survived successive overriding during more extensive glacier advances. Alternatively, these ice-cored moraines have also been interpreted as initial rock glaciers and the younger ages of the outer ridges explained by 'pressing-out' of material from the base of the moraine by its own weight and gravity. Other theories developed include also a mixture of traditional push moraine processes and deformation structures caused by the glacier advancing in a permafrost environment ('push-deformation moraine'). Because reliable age constraints for individual ridges of those complex ice-cored moraine complexes are crucial for any interpretation of their mode of formation, this study aims to provide insights into their age and origin by applying high-precision Schmidt-hammer exposure-age dating (SHD). Local SHD calibration curves using moraine ridges dating from the last 50 years to the Preboreal (c. 9700 years ago) have been used to give age estimates for

  3. Lichenometric Dating of Little Ice Age Moraines in the Cordillera Vilcabamba, Southern Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Taggart, J. R.; Licciardi, J. M.

    2008-12-01

    Lateral and end moraines deposited by two valley glaciers were mapped on the south side of Nevado Tucarhuay (5910 m asl) and on the east side of Nevado Salcantay (6271 m asl) in the Cordillera Vilcabamba in the southern Peruvian Andes (~13°S latitude). The geomorphic expression of outer and inner moraine sequences in these two drainages mimics that of a previously studied pair of moraines in the upper Rio Blanco valley on the south side of Nevado Salcantay. Cosmogenic 10Be surface exposure dating has yielded ages of 9.0 ± 0.3 ka and 195 ± 24 years, respectively, for these outer and inner Rio Blanco moraines. In all three valleys, prominent outer moraines occur ~3-5 km from headwalls and inner moraine ridges are found ~2.5-3 km from headwalls. Recessional moraines found exclusively on the east side of Salcantay indicate multiple early- to late-Holocene glacier pauses, rather than continuous retreat, prior to the latest Holocene glacier readvance. Diameters of the lichen Rhizocarpon subgenus Rhizocarpon were measured on moraine boulders from the inner moraines in all three valleys. Lichen diameters on the two undated inner moraines are consistent with diameters on the inner 10Be-dated Rio Blanco moraine, which signifies similar lichenometric ages and supports synchronous glacier culminations in all three drainages during the Little Ice Age. The new lichen measurements and age estimates provide a critical link between previous lichen studies in the Cordillera Blanca to the north and in the Cordillera Real to the south, thereby increasing spatial coverage of terrestrial paleoclimate information. Moreover, the extensive lichen measurements gathered on the inner 10Be-dated Rio Blanco moraine define a new control point for the Rhizocarpon subgenus Rhizocarpon growth curve in the tropical Peruvian- Bolivian Andes, which will increase the accuracy of lichenometric age estimates in this region. 10Be exposure dating of the inner moraines in adjacent valleys is underway

  4. Numerical Modeling of the Last Glacial Maximum Yellowstone Ice Cap Captures Asymmetry in Moraine Ages

    NASA Astrophysics Data System (ADS)

    Anderson, L. S.; Wickert, A. D.; Colgan, W. T.; Anderson, R. S.

    2014-12-01

    The Last Glacial Maximum (LGM) Yellowstone Ice Cap was the largest continuous ice body in the US Rocky Mountains. Terminal moraine ages derived from cosmogenic radionuclide dating (e.g., Licciardi and Pierce, 2008) constrain the timing of maximum Ice Cap extent. Importantly, the moraine ages vary by several thousand years around the Ice Cap; ages on the eastern outlet glaciers are significantly younger than their western counterparts. In order to interpret these observations within the context of LGM climate in North America, we perform two numerical glacier modeling experiments: 1) We model the initiation and growth of the Ice Cap to steady state; and 2) We estimate the range of LGM climate states which led to the formation of the Ice Cap. We use an efficient semi-implicit 2-D glacier model coupled to a fully implicit solution for flexural isostasy, allowing for transient links between climatic forcing, ice thickness, and earth surface deflection. Independent of parameter selection, the Ice Cap initiates in the Absaroka and Beartooth mountains and then advances across the Yellowstone plateau to the west. The Ice Cap advances to its maximum extent first to the older eastern moraines and last to the younger western and northwestern moraines. This suggests that the moraine ages may reflect the timescale required for the Ice Cap to advance across the high elevation Yellowstone plateau rather than the timing of local LGM climate. With no change in annual precipitation from the present, a mean summer temperature drop of 8-9° C is required to form the Ice Cap. Further parameter searches provide the full range of LGM paleoclimate states that led to the Yellowstone Ice Cap. Using our preferred parameter set, we find that the timescale for the growth of the complete Ice Cap is roughly 10,000 years. Isostatic subsidence helps explain the long timescale of Ice Cap growth. The Yellowstone Ice Cap caused a maximum surface deflection of 300 m (using a constant effective elastic

  5. 10Be dating of the Narsarsuaq moraine in southernmost Greenland: evidence for a late-Holocene ice advance exceeding the Little Ice Age maximum

    NASA Astrophysics Data System (ADS)

    Winsor, K.; Carlson, A. E.; Rood, D. H.

    2014-08-01

    In southernmost Greenland near Narsarsuaq, the terminal Narsarsuaq moraine was deposited well outside of a historical Little Ice Age (LIA) moraine adjacent to the modern ice margin. Using 10Be surface exposure dating, we determine Narsarsuaq moraine abandonment at 1.51 ± 0.11 ka. A second set of 10Be ages from a more ice-proximal position shows that ice has been within or at its historical (i.e., LIA) extent since 1.34 ± 0.15 ka. Notably, Narsarsuaq moraine abandonment was coincident with climate amelioration in southern Greenland. Southern Greenland warming at ˜1.5 ka was also concurrent with the end of the Roman Warm Period as climate along the northern North Atlantic sector of Europe cooled into the Dark Ages. The warming of southern Greenland and retreat of ice from the Narsarsuaq moraine is consistent with studies suggesting possible anti-phase centennial-scale climate variability between northwestern Europe and southern Greenland. Other southernmost Greenland ice-margin records do not preclude a pre-LIA ice-margin maximum, potentially concurrent with a Narsarsuaq advance prior to ˜1.51 ka, but also lack sufficient ice-margin control to confirm such a correlation. We conclude that there is a clear need to further determine whether a late-Holocene pre-LIA maximum was a local phenomenon or a regional southern Greenland ice maximum, and if this advance and retreat reflects a regional fluctuation in climate.

  6. Precise Surface Exposure Dating of Early Holocene and Little Ice Age Moraines in the Cordillera Vilcabamba of Southern Peru

    NASA Astrophysics Data System (ADS)

    Licciardi, J. M.; Schaefer, J. M.; Lund, D. C.; Taggart, J. R.

    2008-12-01

    We have established precise ages of two glacial events in the tropical Andean highlands of southern Peru. The field site is located on the flanks of Nevado Salcantay (6271 m asl; 13°20'S latitude), the highest peak in the Cordillera Vilcabamba. A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the south face of Salcantay. Well-defined outer and inner moraines were deposited by valley glaciers that terminated 5 km and 3 km, respectively, from their head on the Salcantay massif. Cosmogenic 10Be surface exposure dating of boulders on the outer (n = 7) and inner (n = 7) moraine crests expands upon initial age control for these deposits and improves substantially on the precision of earlier 10Be measurements. The new results yield mean ages of 9.0 ± 0.3 ka for the outer moraine and 195 ± 24 years for the inner moraine, corresponding to glacial events during the early and latest Holocene. These ages are derived using the CRONUS-Earth 10Be exposure age calculator with Lal-Stone production rate scaling and the default height-pressure relationship. The inner moraine age correlates with the timing of the Little Ice Age as defined from northern mid- and high latitude records, and indicates considerable expansion of glaciers heading on Nevado Salcantay during this climatic minimum. Recent geomorphic mapping has identified similar sequences of moraines in adjacent drainages on and near Salcantay, suggesting a broader regional signal of two prominent Holocene glacial events in this segment of the southern Peruvian Andes; 10Be dating of these additional moraines is underway. Our new glacier chronologies complement ice core and lacustrine paleoclimate records in the vicinity, thereby increasing spatial and temporal coverage for identifying patterns of climate change in the tropical Andes during the Holocene. Apart from their paleoclimatic significance, the results also demonstrate a newly- developed capability of 10Be exposure

  7. Net ecosystem production in a Little Ice Age moraine: the role of plant functional traits

    NASA Astrophysics Data System (ADS)

    Varolo, E.; Zanotelli, D.; Tagliavini, M.; Zerbe, S.; Montagnani, L.

    2015-07-01

    Current glacier retreat allows vast mountain ranges available for vegetation establishment and growth. Little is known about the effective carbon (C) budget of these new ecosystems and how the presence of different vegetation communities, characterized by their specific physiology and life forms influences C fluxes. In this study, using a comparative analysis of the C fluxes of two contrasting vegetation types, we intend to evaluate if the different physiologies of the main species have an effect on Ecosystem Respiration (Reco), Gross Primary Production (GPP), annual cumulated Net Ecosystem Exchange (NEE), and long-term carbon accumulation in soil. The NEE of two plant communities present on a Little Ice Age moraine in the Matsch glacier forefield (Alps, Italy) was measured over two growing seasons. They are a typical C3 grassland, dominated by Festuca halleri All. and a community dominated by CAM rosettes Sempervivum montanum L. on rocky soils. Using transparent and opaque chambers, we extrapolated the ecophysiological responses to the main environmental drivers and performed the partition of NEE into Reco and GPP. Soil samples were collected from the same site to measure long-term C accumulation in the ecosystem. The two communities showed contrasting GPP but similar Reco patterns and as a result significantly different in NEE. The grassland acted mainly as a carbon sink with a total cumulated value of -46.4 ± 35.5 g C m-2 NEE while the plots dominated by the CAM rosettes acted as a source with 31.9 ± 22.4 g C m-2. In spite of the NEE being different in the two plant communities, soil analysis did not reveal significant differences in carbon accumulation. Grasslands showed 1.76 ± 0.12 kg C m-2, while CAM rosettes showed 2.06 ± 0.23 kg C m-2. This study demonstrates that carbon dynamics of two vegetation communities can be distinct even though the growing environment is similar. The physiological traits of the dominant species determine large differences in

  8. Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2 cal ka, and Little Ice Age events

    USGS Publications Warehouse

    Benson, L.; Madole, R.; Kubik, P.; McDonald, R.

    2007-01-01

    Surface-exposure (10Be) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-m-long Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to ???3.0 10Be ka.11Surface-exposure ages in this paper are labeled 10Be; radiocarbon ages are labeled 14C ka, calendar and calibrated radiocarbon ages are labeled cal ka, and layer-based ice-core ages are labeled ka. 14C ages, calibrated 14C ages, and ice core ages are given relative to AD 1950, whereas 10Be ages are given relative to the sampling date. Radiocarbon ages were calibrated using CALIB 5.01 and the INTCAL04 data base Stuiver et al. (2005). Ages estimated using CALIB 5.01 are shown in terms of their 1-sigma range. Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 10Be ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0-11.7 10Be ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in

  9. Architecture and structural evolution of an early Little Ice Age terminal moraine at the surge-type glacier Múlajökull, Iceland

    NASA Astrophysics Data System (ADS)

    Benediktsson, Ívar &Oum; lrn; Schomacker, Anders; Johnson, Mark D.; Geiger, Alessa J.; Ingólfsson, Ólafur; Gudmundsdóttir, Esther Ruth

    2015-09-01

    The internal architecture and structural evolution of the Arnarfellsmúlar terminal moraine at Múlajökull, a surge-type glacier in central Iceland, is described in order to demonstrate submarginal and proglacial glaciotectonic processes during glacier surging, as well as constraining the age of the maximum extent of the glacier. The moraine is 4-7 m high, 50-100 m wide, and composed of a highly deformed sequence of loess, peat, and tephra that is draped by till up to the crest. The internal architecture is dominated by steep, high-amplitude overturned folds and thrusts in the crest zone but open, low-amplitude folds on the distal slope. Section balancing suggests a basal detachment (décollement) depth of 1.4 m and a total horizontal shortening of around 59%. This implies that the glacier coupled to the foreland about 70 m up glacier from its terminal position to initiate the formation of the moraine. The structural evolution is polyphase in that the formation commenced with low-amplitude open folding of the foreland, followed by overfolding and piggyback thrusting. Radiocarbon dating and analysis of tephra layers, along with historical references, indicate that the most likely time of moraine formation was between A.D. 1717 and 1760, which suggests that Múlajökull had its Little Ice Age maximum and most extensive surge earlier than many other surge-type glaciers in Iceland.

  10. Approaching sediment dynamics on Little Ice Age (LIA) lateral moraines in Upper Kaunertal valley, Austria using long-lived radionuclide 129I

    NASA Astrophysics Data System (ADS)

    Kamleitner, Sarah; Czarnowsky, Verena; Lachner, Johannes; Steier, Peter; Morche, David; Kraushaar, Sabine

    2016-04-01

    The Upper Kaunertal, as many other valleys situated in the Eastern Alps, has recently undergone large deglaciation processes as a result of global warming, leaving behind large moraines exposed to geomorphic processes. Steep lateral moraines represent large and easily erodible sources of material within an Alpine sediment cascade. In order to quantify the amount of sediments provided by the moraines, methods of surface change detection such as aerial and terrestrial laser scanning or sfm (structure from motion) generated Digital Elevation Models (DEM) are being applied. However, morphological changes due to the melt out of persisted ice are overlain by processes of mass movement, slope wash, and fluvial erosion, and therefore often remain unnoticed. Yet melting alone could account for a volume reduction in the sediment matrix of up to 13%, the additional leaching of water to a further unknown amount. Hence, the hydrological situation on the lateral moraines needs to be clarified. Previous investigations of springs evolving from the LIA lateral moraine were showing light isotope signatures comparable to those of glacier ice, and resulted in first assumption about the presence of ice lenses within the moraines (Kraushaar et al. 2014). Stable isotope measurements applied by Czarnowsky et al. 2015 confirm former findings. However, fail to distinguish between recently developed ice and dead ice lenses originating from former glacial maxima. This study therefore aims to date evolving spring waters on lateral moraines of the Gepatschferner, sampled between May and October 2015, using the radioactive isotope iodine-129. The environmental abundance of this long-lived radionuclide has been, analogue to tritium, significantly altered due to human activity since Nuclear Age, and is therefore believed to provide feasible relative age estimations. Hence, measurements will allow the clarification of the hydrological situation on site and the specification of processes causing

  11. Nature and origin of a Pleistocene-age massive ground-ice body exposed in the Chapman Lake moraine complex, central Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Lacelle, Denis; Lauriol, Bernard; Clark, Ian D.; Cardyn, Raphaelle; Zdanowicz, Christian

    2007-09-01

    A massive ground-ice body was found exposed in the headwall of a thaw flow developed within the Chapman Lake terminal moraine complex on the Blackstone Plateau (Ogilvie Mountains, central Yukon Territory), which is contemporaneous to the Reid glaciation. Based on visible cryostructures in the 4-m-high headwall, two units were identified: massive ground ice, overlain sharply by 2 m of icy diamicton. The nature and origin of the Chapman Lake massive ground ice was determined using cryostratigraphy, petrography, stable O-H isotopes and the molar concentration of occluded gases (CO 2, O 2, N 2 and Ar) entrapped in the ice, a new technique in the field of periglacial geomorphology that allows to distinguish between glacial and non-glacial intrasedimental ice. Collectively, the results indicate that the Chapman Lake massive ground ice formed by firn densification with limited melting-refreezing and underwent deformation near its margin. Given that the massive ground-ice body consists of relict glacier ice, it suggests that permafrost persisted, at least locally, on plateau areas in the central Yukon Territory since the middle Pleistocene. In addition, the d value of Chapman Lake relict glacier ice suggests that the ice covering the area during the Reid glaciation originated from a local alpine glaciation in the Ogilvie Mountains.

  12. Constraining the Timing of Neoglaciation: Moraine Exposure Ages from Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Crump, S. E.; Miller, G. H.

    2014-12-01

    A long-term Neoglacial cooling trend, beginning ~6 ka, is well documented across the Arctic and correlates with a monotonic decline in Northern Hemisphere summer insolation. However, paleoclimate proxy records point to decadal- to millennial-scale variability superimposed on overall cooling. This climate variability is reflected in the fluctuations of Arctic glaciers over the course of several millennia. The most recent Neoglacial advance, the Little Ice Age (LIA; ~1275-1850 AD), was generally more extensive than pre-LIA advances and thus destroyed most evidence of previous advances. As such, the timing and extent of earlier Neoglacial advances are not well constrained. However, several extant glaciers on Cumberland Peninsula, Baffin Island, are fronted by nested ice-cored moraine sequences in which multiple pre-LIA moraines are preserved. We have generated absolute ages on moraine sequences for Snow Creek and Throne Glaciers using 10Be in moraine boulders. Nine 10Be ages from the two most distal moraine crests at Snow Creek Glacier range from ~1.8 ka to ~5.7 ka, and twelve ages from the two most distal moraine crests at Throne Glacier range from ~1.1 ka to ~4.6 ka. The wide spread of exposure ages in these settings is likely due to the degradation of moraine ice cores and the disturbance of older moraines by younger readvances. Because these processes result in the exposure of new clasts on the moraine post-emplacement, the oldest ages in these datasets likely provide the best estimates for the earliest Neoglacial advances. These data also indicate that in some settings, early Neoglacial alpine glacier advances reached similar extents as their LIA maxima, possibly due to large ice-cored moraines impeding LIA advances. Glacier modeling efforts and complementary lacustrine sediment records will help to unravel the complex Neoglacial history in this region.

  13. Using blue-ice moraines to constrain elevation changes of the West Antarctic Ice Sheet in the southern Ellsworth Mountains

    NASA Astrophysics Data System (ADS)

    Sugden, David; Woodward, John; Dunning, Stuart; Hein, Andy; Marrero, Shasta; Le-Brocq, Anne

    2014-05-01

    Observations in the Weddell Sea sector of the Antarctic Ice Sheet have not yet allowed the dating of elevated glacier trimlines and associated deposits in the Ellsworth Mountains. This uncertainty limits the value of models of changing ice-sheet configuration, volume and, by extension, sea level during glacial cycles and earlier. Here we present the emerging results of a study into the origin and evolution of blue-ice moraines in the Heritage Range, southern Ellsworth Mountains, and begin to unravel the long record of ice-sheet history they hold. Our findings so far are: (a) Ground Penetrating Radar shows that the blue-ice moraines are equilibrium forms bringing basal debris to the ice surface; the compressive ice flow is caused by enhanced ablation at the mountain foot. (b) Moraines are concentrated in embayments that focus katabatic winds and their location is largely controlled by topography. (c) The elevated blue-ice moraines in the southern Ellsworth Mountains hold a continuous record of West Antarctic Ice Sheet history going back 600,000 years; so far we have not found evidence of de-glacial intervals. (d) Thinning since the LGM (~40 ka?) is < 450 m and agrees with views of modest changes in the Weddell Sea sector during glacial cycles; most thinning occurred in the Holocene (6-3 ka). (e) Downslope flow of debris-covered ice in embayments follows ice surface lowering; it transports old clasts downslope and exposes fresh clasts, thus complicating the interpretation of exposure ages. We hope that a second field season in 2014 to re-measure 90 stakes for horizontal movement and ablation will help quantify the rate of blue-ice moraine formation.

  14. Are Late-Pleistocene Climate Reconstructions from Cirque and Valley Moraines Possible in Regions of Decaying Ice Sheets?

    NASA Astrophysics Data System (ADS)

    Menounos, B.; Goehring, B. M.; osborn, G.; Clague, J. J.; Davis, P. T.; Lakeman, T.; Schaefer, J. M.; Koch, J.; Clarke, G. K.

    2012-12-01

    The extent of glaciers in the past has commonly been used to infer past climates. Both abrupt climate change and geomorphic factors, however, are required to explain the timing and apparent magnitude of latest Pleistocene advances at high latitudes in western Canada and southernmost Patagonia. At the southern end of the Andes, north and west of Ushuaia, Argentina, 10Be surface exposure ages from glaciated bedrock beyond cirque moraines indicate that alpine areas were deglaciated by ca. 15.5 ka (kilo calendar yr BP). One, and in some cases two, closely spaced moraines extend up to 2 km beyond Little Ice Age moraines within many cirques in this region. The mean of five 10Be ages from two of the moraines is 14.82-13.16 ka, whereas a smaller recessional moraine in one cirque returned a minimum-limiting AMS radiocarbon age of 12.38-12.01 ka. The ages imply that following regional deglaciation, cirque glaciers first advanced during the Antarctic Cold Reversal (ACR) [14.5-12.9 ka] and then advanced again or remained near their ACR limits during the Younger Dryas Chronozone (YD) [12.9-11.7 ka]. The moraines are restricted to topographic highs that were deglaciated before 15.5 ka. In western Canada, glaciers also advanced during the YD, but the magnitude of this advance differs markedly throughout the region. 10Be and 14C ages on moraines at high elevations in the Canadian Rockies and the southern Coast Mountains indicate that many glaciers built moraines during the YD that were only hundreds of meters beyond those constructed during the later part of the Little Ice Age [0.30-0.15 ka]. In contrast, 10Be ages [13.10-12.00 ka] on three moraines in northwest British Columbia indicate that glaciers up to 10 km beyond LIA glacier limits during the YD. We argue that the different responses of alpine glaciers in western Canada to climate deterioration during the YD is due to the presence of the decaying Cordilleran ice sheet. Top-down melting of the Cordilleran ice sheet allowed

  15. Glaciotectonic origin of the Massachusetts coastal end moraines and a fluctuating late Wisconsinan ice margin.

    USGS Publications Warehouse

    Oldale, R.N.; O'Hara, C. J.

    1984-01-01

    Late Wisconsinan end moraines on Cape Cod and islands south and west of Cape Cod are believed to be glaciotectonic features formed by advancing ice fronts. Evidence for major ice readvances during general recession includes the moraines themselves, till atop stratified drift, and the numerous basal tills that are inferred to exist beneath Cape Cod Bay. The Thompson Glacier end moraine in the Canadian Arctic Archipelago is considered to be a modern example of how late Wisconsinan end moraines on Cape Cod and the islands were formed. It is overriding its outwash plain, displacing outwash deposits forward and upward beyond the ice front. New sheets are added to the base of the moraine as the ice overrides it. Retreat of the ice from Cape Cod and the islands may have been similar to the retreat of the Lake Michigan lobe, deposits of which contain evidence of at least 12 moraine-building episodes caused by readvancing ice.-from Authors

  16. Evolution of a highly vulnerable ice-cored moraine: Col des Gentianes, Swiss Alps

    NASA Astrophysics Data System (ADS)

    Ravanel, L.; Lambiel, C.; Oppikofer, T.; Mazotti, B.; Jaboyedoff, M.

    2012-04-01

    Rock mass movements are dominant in the morphodynamics of high mountain rock slopes and are at the origin of significant risks for people who attend these areas and for infrastructures that are built on (mountain huts, cable cars, etc.). These risks are becoming greater because of permafrost degradation and glacier retreat, two consequences of the global warming. These two commonly associated factors may affect slope stability by changing mechanical properties of the interstitial ice and modifying the mechanical constraints in these rock slopes. Between 1977 and 1979, significant works were carried out on the Little Ice Age moraine of the Tortin glacier at the Col des Gentianes (2894 m), in the Mont Fort area (Verbier, Switzerland), for the construction of a cable car station and a restaurant. Since the early 1980s, the glacier drastically retreated and the moraine became unstable: its inner slope has retreated for several meters. Various observations and geoelectric measurements indicate that significant volume of massive ice mass is still present within the moraine (ice-cored moraine). Its melting could therefore increase the instability of the moraine. Since 2007, the moraine is surveyed by terrestrial laser scanning (TLS) in order to characterize its evolution: 8 campaigns were conducted between July 2007 and October 2011. The comparison of the high resolution 3D models so obtained allowed the detection and quantification of mass movements that have affected the moraine over this period, essentially by calculating difference maps (shortest oblique distances between two models). Between July 2007 and October 2011, 7 landslides were measured, involving volumes between 87 and 1138 m3. The most important of these occurred during the summers 2009 and 2011. TLS data also allowed identifying: (i) two main areas affected by slower but sometimes substantial movements (displacements of blocks on more than 2 m during a summer period); (ii) significant deposits of

  17. Quantification of Dead-ice Melting in Ice-Cored Moraines at the High-Arctic Glacier Holmströmbreen, Svalbard

    NASA Astrophysics Data System (ADS)

    Schomacker, A.; Kjaer, K. H.

    2007-12-01

    An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier on Svalbard following its Little Ice Age maximum. Dead-ice appears mainly as ice-cored moraines, ice-cored eskers and ice- cored kames. The most common dead-ice landform is sediment gravity flows on ice-cored slopes surrounding a large ice-walled, moraine-dammed lake. The lake finally receives the sediment from the resedimentation processes. Dead-ice melting is described and quantified through field studies and analyses of high-resolution, multi-temporal aerial photographs and satellite imagery. Field measurements of backwasting of ice-cored slopes indicate short-term melting rates of c. 9.2 cm/day. Long-term downwasting rates indicate a surface lowering of ice-cored moraines of c. 0.9 m/yr from 1984-2004. Different measures for dead-ice melting are assessed in relation to the temperature record from Svalbard since the termination of the Little Ice Age. The most prominent impact of dead-ice melting is the evolution of the ice-walled lake with an area increasing near-exponentially over the last 40 years. As long as backwasting and mass movement processes prevent build-up of an insulating debris-cover and expose ice-cores to melting, the de-icing continues even though the area is characterized by continuous permafrost.

  18. Changes in ice-margin processes and sediment routing during ice-sheet advance across a marginal moraine

    USGS Publications Warehouse

    Knight, P.G.; Jennings, C.E.; Waller, R.I.; Robinson, Z.P.

    2007-01-01

    Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice-marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice-proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris-rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations. ?? 2007 Swedish Society for Anthropology and Geography.

  19. Ice-thrust Wadena drift in the southern St. Croix moraine, Stearns Co. , Minnesota

    SciTech Connect

    Danelski, T.C.; Moe, S.A.; Weeks, M.R.; Anderson, G.G. . Dept. of Earth Sciences)

    1993-03-01

    A sequence of Wisconsinan drift including loess, outwash and till with Wadena lobe characteristics has been found in structural contact above Cretaceous mudstones at the southern most location of the St. Croix moraine in southeastern Stearns County, Minnesota. This drift has been thrust faulted in a minimum of 3 places along a north-south transect about 300 meters in length. The parallel fault planes strike roughly east-west, dip to the north at about 30 to 45 degrees, and parallel several topographical ridges which were probably formed at the same time by the advancing Superior lobe ice. Fault surfaces are defined by steeply dipping contacts, and till units with high concentrations of large Cretaceous mudstone clasts at the base. The highest elevation of the exposed Cretaceous mudstone outcrop is about 15 meters above the base of the St. Croix moraine, suggesting that the moraine is bedrock cored, and that the moraine may well have located at that position at least partially as a result of the Superior lobe ice not being capable of surmounting the topographical high. A 30 meter thick accumulation of Des Moines lobe outwash just to the east of the moraine end could be interpreted to be a Superior lobe tunnel valley formed by meltwater flowing beneath rapidly melting glacial ice shortly after the ice-thrust ridges were produced. This tunnel valley breeched the moraine, scoured a deep bifurcating channelway, and formed a topographical low through which the northern edge of the later Grantsburg sublobe could more easily pass.

  20. Use of soil catena field data for estimating relative ages of moraines

    SciTech Connect

    Birkeland, P.W.; Berry, M.E. ); Swanson, D.K. )

    1991-03-01

    Soils at the crests of moraines are commonly used to estimate the relative ages of moraines. However, for various pedologic and geomorphic reasons, soil development at crest sites may not truly reflect the time since moraine formation; for example, some crest soils on moraines of greatly different age are similar in morphology and development. Soil catena data for soils at several sites aligned downslope from the crest can greatly improve on the usefulness of soil data for estimating moraine ages. For this purpose, the authors use the weighted mean catena profile development index, which condenses field data for all of the soils in each catena into a single value.

  1. Surface dating of dynamic landforms: young boulders on aging moraines.

    PubMed

    Hallet, B; Putkonen, J

    1994-08-12

    The dating of landforms is crucial to understanding the evolution, history, and stability of landscapes. Cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces. A pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data. Consideration of the dynamic nature of landforms and of the ever-present processes of erosion, deposition, and weathering leads to a resolution of this inconsistency and, more generally, offers guidance for realistic interpretation of exposure ages. PMID:17782145

  2. Cosmogenic 10Be Exposure Age for the Cut Bank Creek terminal moraine, Glacier National Park, MT

    NASA Astrophysics Data System (ADS)

    Quirk, B.; Laabs, B. J.; Leonard, E. M.; Caffee, M. W.

    2012-12-01

    Mountain glaciers are highly sensitive to temperature and precipitation with geologic records that are superb proxies of climate change. In the Rocky Mountains of the western United States, abundant records of Late Pleistocene glaciation provide an opportunity for understanding paleoclimate throughout this region, especially in places where the chronology of glaciation is precisely known. Cosmogenic 10Be exposure dating has been widely applied to glacial deposits in the Rocky Mountains, providing precise numerical ages and improving the understanding of glacial chronologies in this region. Despite these improvements, the chronology of the last Pleistocene glaciation of the northernmost Rocky Mountains is not completely understood. Cosmogenic 10Be exposure dating was applied to the Cut Bank Creek valley in the Lewis Range of the Northern Rocky Mountains, where a discrete mountain glacier deposited a broad terminal moraine during the last Pleistocene glaciation. Exposure ages of eight quartzite and sandstone boulders at the crest of the ice-distal sector of the terminal moraine indicate that abandonment occurred at 15.6 ± 0.8 ka. This age is consistent with age limits of several terminal moraines elsewhere in the Northern Rocky Mountains, suggesting that the last Pleistocene glaciation culminated in this region after the global Last Glacial Maximum.

  3. Relative dating of Quaternary moraines, Rongbuk valley, Mount Everest, Tibet: Implications for an ice sheet on the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Burbank, Douglas W.; Cheng, Kang Jian

    1991-07-01

    Relative-dating studies applied to high-altitude moraines (5000-5500 m) in the Rongbuk valley on the northern flank of Mt. Everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests. These differences serve to define three intervals of major Pleistocene glaciation that, on the basis of the degree of weathering, are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation. Either interpretation indicates that some of these moraines are considerably older than their previously assigned ages. The magnitude of equilibrium-line lowering during Neoglacial and late Pleistocene times is calculated to be ca. 50-100 and 350-450 m, respectively. The data described here are incompatible with the recently proposed model ( Kuhle, 1987) for large-scale ice-sheet development on the Tibetan Plateau. The reconstructed equilibrium-line lowering in the Everest region is only 30% of that cited in the ice-sheet model. Moreover, the flow patterns and geometry of the former Rongbuk glaciers are in opposition to those proposed by the model. Based on the data from the Everest region, it appears that valley glaciation, rather than ice-sheet growth, characterized the southern margin of the Tibetan Plateau during the middle and late Pleistocene glaciations.

  4. Interannual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

    NASA Astrophysics Data System (ADS)

    Westoby, Matthew J.; Dunning, Stuart A.; Woodward, John; Hein, Andrew S.; Marrero, Shasta M.; Winter, Kate; Sugden, David E.

    2016-06-01

    Multi-temporal and fine-resolution topographic data products are increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3-D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of structure from motion with multi-view stereo (SfM-MVS) photogrammetry to a set of aerial photographs acquired from an unmanned aerial vehicle (UAV). Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ~ 0.10 m) and surface lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin, although we are unable to validate the latter. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow and debris supply within moraine ice.

  5. Hydrogeophysical characterisation of ice-marginal moraines, with reference to moraine dam stability, Miage Glacial Lake, Italy

    NASA Astrophysics Data System (ADS)

    Thompson, S. S.; Kulessa, B.

    2010-12-01

    In mountain regions, potentially hazardous glacial lakes are becoming increasingly common as a consequence of climatically driven glacier recession. Lakes can expand rapidly in the space between downwasting or receding glacier fronts and terminal or lateral moraines, and are prone to catastrophic drainage if the moraine dam is breached. Lake drainage can have severe impacts on both fragile mountain ecosystems and local economies. In addition to the moraine-dammed lakes currently in existence, it is likely that many more will form in the coming decades as more glaciers cross the threshold required for rapid lake expansion. A key factor in assessing the stability and future evolution of such systems is a better understanding of the subsurface structure and hydrology of the moraine dams. Here results are presented from electrical geophysical work carried out across the breach moraine complex at the Miage Glacial Lake, Italy. A combination of induced polarisation, normalised induced polarisation and self potentials have been used to characterise the local water table and to identify the subsurface connections between two moraines dammed glacial lakes. The results not only show the depth and distribution of subsurface flow but also the preferential flow pathways, indicating areas of maximum discharge. The results highlight the areas of the moraines where hydrological processes are causing internal degradation and impacting upon the longer term stability of the system. This model therefore, can be employed on much larger systems where the risk of outburst has far greater consequences.

  6. Blue-ice moraines in Antarctica: long-term formation and short-term change

    NASA Astrophysics Data System (ADS)

    Woodward, J.; Dunning, S.; Sugden, D.; Hein, A.; Marrero, S.

    2013-12-01

    The Heritage Range at the southern end of the Ellsworth Mountains lies across the main flow of the West Antarctic Ice Sheet (WAIS) just 50 km from the grounding line of the Filchner-Ronne Ice Shelf. If the long-term record of ice sheet change can be understood from the Blue Ice Moraines (BIM) found along the hills it becomes a critical location to understand the past behaviour of the ice sheet, and therefore, to better understand the future behaviour of WAIS in a warming climate. We present integrated geophysical data from Unmanned Aerial Vehicles (UAV), Terrestrial Laser Scanning (TLS) and ground penetrating radar (GPR) that helps us understand the long-term formation, and short-term mophological changes of BIMs. BIMs along the front of Patriot Hills (part of the Heritage Range) are associated with katabatic winds enhancing ablation and sublimation to create depressions that are then compensated for by ice-flow from the main trunk glacier at right angles to the main flow direction. This ice flow brings basal debris from the trunk glacier that can reside for long-periods of time rather than being removed by the dominant mountain parallel ice-flow. Using GPR we have imaged debris bands from the trunk glacier arriving directly into the lowest BIMs, and also emerging at the ice surface as folded debris bands in the moraine-marginal depressions that do not have a dense enough debris cover to prevent ablation. High resolution elevation models derived from TLS, and a UAV quantify the changing topography associated with this debris arriving into the BIM, and the surface change over a summer melt season. This work was funded by NERC Standard Grant NE/I025840/1

  7. Age of the Tahoe moraine at Bloody Canyon, Mono County, California

    SciTech Connect

    Soles, S. . Dept. of Geology); Sarna-Wojcicki, A.M.; Meyer, C.E.; Wan, E. )

    1993-04-01

    The age of the Tahoe moraines on the east side of the Sierra Nevada has been subject of considerable discussion over about the last 60 years. Two schools of thought prevail: that the moraines were formed about 65--75 ka BP, roughly equivalent in age to oxygen isotope stage four; or that they were formed about 135--170 ka BP, roughly equivalent to stage six. A major reason for this uncertainty is that most available dating techniques have large errors or poor reproducibility when applied to moraines, till materials, or stratigraphically related volcanic rocks within this age range. The authors attempted to bracket the age of the Tahow moraine at Bloody Canyon by (1) searching for volcanic shards in the soil formed on the moraine and in the fine fraction of the till below the soil; (2) physically separating the shads and analyzing them by electron microprobe; and (3) comparing the chemical composition of the shards to those in tephra layers of known age. They dug four pits near the crest of the moraine and sampled continuously at intervals of 15 can to depths of 2.5 m. The authors conclude that (1) the soil formed on the Tahoe moraine is at least 75 to 95 ka in age, and thus that the underlying till must be at least as old as stage six; and (2) that translocation or mechanical mixing of fine particles from the surface of the soil must extend down to at least 2.5 m in the Tahoe till.

  8. Deglaciation chronology of the Scandinavian Ice Sheet from the Lake Onega Basin to the Salpausselkä End Moraines

    NASA Astrophysics Data System (ADS)

    Saarnisto, Matti; Saarinen, Timo

    2001-11-01

    Several long sediment cores (max. 12 m) from various parts (up to 150 km apart) of Lake Onega, Russian Karelia, have been studied for lithology, varve chronology and palaeomagnetism. The two longest varve records from the central basin contain 1300 varves. These indicate the length of the deglaciation period from these localities to the north of Lake Onega, where the drainage of glacial meltwaters was directed towards the White Sea and the deposition of varves in the Onega basin terminated. An estimate of the duration of deglaciation of the whole Onega basin is 1500 years. Natural remanent magnetization (NRM) is strong and stable in these sediments and accurately records changes in the Earth's magnetic field. A distinct change in the magnetic field, when the declination shifted from east to west by at least 60° in 350 varve years, is clearly identifiable in all cores. This palaeomagnetic feature was used for core to core correlation together with other variations in magnetic parameters and widely distributed lithological marker horizons. On the basis of the correlations between the cores and calibration of AMS radiocarbon dates from varves obtained from the northern archipelago of Lake Onega, the age of the westerly declination peak is dated to 13 090 cal. BP and accordingly the deglaciation of the Onega basin took place between 14 250 and 12 750±100 cal. BP. The westerly declination peak was also recognized earlier by Bakhmutov and Zagniy in the Helylä varved clay sequence near Sortavala on the northern shore of Lake Ladoga. Helylä is situated outside the Salpausselkä end moraines and the accumulation of varved clays continued there 1500 years after the declination peak, up until the drainage of the Baltic Ice Lake, which more or less coincides with the ice margin retreat from Salpausselkä II end moraine and the termination of the Younger Dryas event. The date thus arrived at for this event is 11 590±100 cal. BP, close to the recent results from Greenland

  9. Is there still ice in the lateral moraines? Hydrochemical analyses of episodic springs from lateral moraines and their implications for the interpretation of geomorphological process studies

    NASA Astrophysics Data System (ADS)

    Kraushaar, Sabine; Czarnowsky, Verena; Kamleitner, Sarah; Morche, David; Knöller, Kay; Lachner, Johannes

    2016-04-01

    The Gepatschferner glacier in the Upper Kaunertal valley in western Austria is recently one of the fastest melting glaciers in the region of the Eastern Alps. With a retreat rate of around 100m/year in the last years unconsolidated sediments of steep lateral moraines have been exposed to erosion. The earth surface changes in the proglacial area are often quantified and monitored using high resolution change detection methods, such as ALS, TLS or SFM and assume erosion to be the dominant factor of volume change. The existence of episodic springs dwelling from the lateral moraines fostered the hypothesis that a potential significant morphological change may result from the melt out of ice lenses and the leaching of the water from the moraines, and is so far not considered in contemporary measurement campaigns. The present study aims to identify the spring water's origin and displays first attempts of quantifying the leached volume. In a one year monitoring campaign in 2015 around 40 samples were monthly derived from the glacier, various springs, and a precipitation collector. In order to differentiate the spring water's origin between infiltrated rain and/or ice the samples were analyzed for temperature, EC, and the stable isotope compositions of O18 and deuterium. Additional monthly precipitation averages of 30 years continuous isotopic measurements in similar altitude from the Global Network for Isotopes were used as comparison. Results support the hypothesis that certain springs derive from melting ice of similar isotopic signature as the glacier. In a second step, chosen samples were examined for the long-lived anthropogenic radionuclide 129I. Since the 1950s this radioactive isotope has been significantly increased in the atmosphere mainly due to releases by reprocessing plants. Its abundance hints surface contact of the waters in the last 65 years. Springs of ice origin show little to no 129I content and thus are believed to derive of dead ice by the glacier

  10. Blue Ice Moraines as an Archive of Past EAIS dynamics: Mt. Achernar as a Case Study in the Central Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Licht, K.; Winckler, G.; Schaefer, J. M.; Mathieson, C.; Bader, N.

    2014-12-01

    Observations from the interior of East Antarctica are essential for placing direct constraints on the ice sheet's history over multiple glacial cycles, which also can be used to test numerical modeling of its past dynamics. In particular, laterally extensive, blue ice or ablation moraines are important archives of the former behavior of the EAIS and WAIS during at least the Pleistocene and Holocene. We can now quantify changes in the former ice surfaces using such deposits, which have been studied for decades, but have lacked chronological information. We are carrying out 10Be-26Al-3He dating and provenance initiatives at Mt. Achernar, near the head of the Law Glacier, where there is a well-preserved archive of ice sheet history extending spatially over 5-10 km and temporally over the last few hundred thousand years, during which time the climate swung between full glacial and warm interglacial changes. Here, concentric moraines are continuous and well preserved, and the entire complex is no higher than about ~30 meters above the modern EAIS surface. The cosmogenic ages steadily progress away from the EAIS, over 103 to 105 timescales. In addition, agreement of 10Be and 26Al concentrations indicate that, at least over the long term, blue ice deposits at Mt Achernar do not have a complicated history of burial and re-exposure. This is consistent with the inferred process of blue ice moraine formation that involves debris coming up from below and accumulating on the surface, when ice encounters the Transantarctic Mountains. Based on our findings we conclude that the interior of EAIS has been relatively stable for the last few 100 kyr, with ice surface elevation changes on the order of tens of meters, including 20-30 meters since the LGM. In a net sense, the EAIS has also been getting slightly lower over the last half million years or so. We hypothesize that if the interior of the EAIS had undergone major lowering or more pronounced surface changes over the time

  11. Inter-annual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

    NASA Astrophysics Data System (ADS)

    Westoby, M. J.; Dunning, S. A.; Woodward, J.; Hein, A. S.; Marrero, S. M.; Winter, K.; Sugden, D. E.

    2015-11-01

    Multi-temporal and fine resolution topographic data products are being increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3-D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of Structure-from-Motion (SfM) photogrammetry to a set of aerial photographs taken from an unmanned aerial vehicle (UAV). Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ∼ 0.10 m), with lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow, and debris supply within moraine ice.

  12. The influence of basement block tectonics on ice thrust Wadena drift in the southern St. Croix moraine, Stearns Co, Minnesota

    SciTech Connect

    Metz, M.A.; Meyer, D.P.; Rogers, M.R.; Thorne, R.E.; Anderson, G.G. )

    1994-04-01

    Cretaceous mudstones containing horizontal bedding are found in the St. Croix moraine in southern Stearns County, Minnesota, These sediments are probably in-situ because they have been drilled to 14.5 m. and have horizontal bedding, based upon the orientation of concretions. The north end of this outcrop is truncated by a fault striking N90[degree]W and dipping north at 35 degrees. The orientation of concretions near the fault suggest normal fault displacement. A single water well log two miles northwest shows similar Cretaceous mudstones 70 m. lower. A significant aeromagnetic lineament striking N70[degree]W is located between the two sites and parallel to the orientation of the St. Croix moraine. Superior lobe ice may have depressed the northern block to produce a topographic barrier which stalled the ice and was at least partially responsible for the ice thrust glacial sediments located in the interior of the moraine. Deformed glacial sediments rest unconformably upon horizontal Cretaceous mudstones and consist of Wadena till, Superior till, perhaps an older pre-Wisconsinian till, glacial lacustrine sediments intercalated with till, wind-blown fine sand and outwash. After the northern basement block was depressed, a small normal fault developed in the Cretaceous sediments moving wind blown fine sand down. Older glacial materials were then ice-thrust onto this topographic high developed by ice loading. Structural features include at least 3 N90[degree]W, north-dipping thrust faults with materials tectonically transported from a depression located more than 3,000 feet to the north.

  13. An Initial AUV Investigation of the Morainal Bank and Ice-Proximal Submarine Processes of the Advancing Hubbard Glacier, Southeast Alaska

    NASA Astrophysics Data System (ADS)

    Lawson, D. E.; Gulick, S. P. S.; Goff, J. A.; O'Halloran, W.

    2014-12-01

    The movement of an advancing tidewater glacier occurs in concert with the morainal bank that underlies its terminus. The mechanics of motion and sedimentological processes responsible for this advance of the morainal bank with the calving terminus are not well-defined and based largely on inferences from geophysical analyses of remnant morainal banks on fjord floors. There is a general absence of in situ or direct observation of the submarine margin because it is nearly impossible to access the immediate area of the ice face by boat safely. In order to obtain such data, in June 2014 we tested the ability of a Bluefin 9M AUV (autonomous underwater vehicle) to acquire high resolution swath bathymetry and sidescan backscatter across a ~2 km long section of the ice face of Hubbard Glacier (see also Goff et al., this meeting). Additionally onboard oceanographic measurements were taken that can be compared with surface cast CTD profiles obtained during AUV deployment, including locations with subglacial discharges. The AUV test provides details on the geometry of the morainal bank and nature of the fjord wall surfaces. The decimeter-scale imagery of the seabed reveals numerous erosional and depositional bedforms and gravitational features on the morainal bank's proximal slope. Closer to the ice face, the morainal bank surface appears much coarser, with textural patterns of unknown origin, and gravel lags including boulder fields. Comparing the water depth from the AUV survey with that of NOAA bathymetric data from 2004/2006 shows the morainal bank continued to advance in pace with ice advance into fjord waters over 200m deep, water depths shoaling up to 100m near the present ice margin. The glimpse of the morainal bank afforded by the AUV test clearly demonstrated the value of this technology to ice marginal submarine investigations.

  14. Ice-cored moraine degradation mapped and quantified using an unmanned aerial vehicle: A case study from a polythermal glacier in Svalbard

    NASA Astrophysics Data System (ADS)

    Tonkin, T. N.; Midgley, N. G.; Cook, S. J.; Graham, D. J.

    2016-04-01

    Ice-cored lateral-frontal moraines are common at the margins of receding high-Arctic valley glaciers, but the preservation potential of these features within the landform record is unclear. Recent climatic amelioration provides an opportunity to study the morphological evolution of these landforms as they de-ice. This is important because high-Arctic glacial landsystems have been used as analogues for formerly glaciated areas in the mid-latitudes. This study uses SfM (Structure-from-Motion) photogrammetry and a combination of archive aerial and UAV (unmanned aerial vehicle) derived imagery to investigate the degradation of an ice-cored lateral-frontal moraine at Austre Lovénbreen, Svalbard. Across the study area as a whole, over an 11-year period, the average depth of surface lowering was - 1.75 ± 0.89 m. The frontal sections of the moraine showed low or undetectable rates of change. Spatially variable rates of surface lowering are associated with differences in the quantity of buried ice within the structure of the moraine. Morphological change was dominated by surface lowering, with limited field evidence of degradation via back-wastage. This permits the moraine a greater degree of stability than previously observed at other sites in Svalbard. It is unclear whether the end point will be a fully stabilised ice-cored moraine, in equilibrium with its environment, or an ice-free lateral-frontal moraine complex. Controls on geomorphological change (e.g. topography and climate) and the preservation potential of the lateral-frontal moraine are discussed. The methods used by this research also demonstrate the potential value of SfM photogrammetry and unmanned aerial vehicles for monitoring environmental change and are likely to have wider applications in other geoscientific sub-disciplines.

  15. Ice age paleotopography

    SciTech Connect

    Peltier, W.R. )

    1994-07-08

    A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.

  16. Glaciotectonic deformation associated with the Orient Point-Fishers Island moraine, westernmost Block Island Sound: further evidence of readvance of the Laurentide ice sheet

    USGS Publications Warehouse

    Poppe, Lawrence J.; Oldale, Robert N.; Foster, David S.; Smith, Shepard M.

    2012-01-01

    High-resolution seismic-reflection profiles collected across pro-glacial outwash deposits adjacent to the circa 18 ka b.p. Orient Point–Fishers Island end moraine segment in westernmost Block Island Sound reveal extensive deformation. A rhythmic seismic facies indicates the host outwash deposits are composed of fine-grained glaciolacustrine sediments. The deformation is variably brittle and ductile, but predominantly compressive in nature. Brittle deformation includes reverse faults and thrust faults that strike parallel to the moraine, and thrust sheets that extend from beneath the moraine. Ductile deformation includes folded sediments that overlie undisturbed deposits, showing that they are not drape features. Other seismic evidence for compression along the ice front consists of undisturbed glaciolacustrine strata that dip back toward and underneath the moraine, and angular unconformities on the sea floor where deformed sediments extend above the surrounding undisturbed correlative strata. Together, these ice-marginal glaciotectonic features indicate that the Orient Point–Fishers Island moraine marks a significant readvance of the Laurentide ice sheet, consistent with existing knowledge for neighboring coeval moraines, and not simply a stillstand as previously reported.

  17. Geomorphology and Ice Content of Glacier - Rock Glacier &ndash; Moraine Complexes in Ak-Shiirak Range (Inner Tien Shan, Kyrgyzstan)

    NASA Astrophysics Data System (ADS)

    Bolch, Tobias; Kutuzov, Stanislav; Rohrbach, Nico; Fischer, Andrea; Osmonov, Azamat

    2015-04-01

    Meltwater originating from the Tien Shan is of high importance for the runoff to the arid and semi-arid region of Central Asia. Previous studies estimate a glaciers' contribution of about 40% for the Aksu-Tarim Catchment, a transboundary watershed between Kyrgyzstan and China. Large parts of the Ak-Shiirak Range drain into this watershed. Glaciers in Central and Inner Tien Shan are typically polythermal or even cold and surrounded by permafrost. Several glaciers terminate into large moraine complexes which show geomorphological indicators of ice content such as thermo-karst like depressions, and further downvalley signs of creep such as ridges and furrows and a fresh, steep rock front which are typical indicators for permafrost creep ("rock glacier"). Hence, glaciers and permafrost co-exist in this region and their interactions are important to consider, e.g. for the understanding of glacial and periglacial processes. It can also be assumed that the ice stored in these relatively large dead-ice/moraine-complexes is a significant amount of the total ice storage. However, no detailed investigations exist so far. In an initial study, we investigated the structure and ice content of two typical glacier-moraine complexes in the Ak-Shiirak-Range using different ground penetrating radar (GPR) devices. In addition, the geomorphology was mapped using high resolution satellite imagery. The structure of the moraine-rock glacier complex is in general heterogeneous. Several dead ice bodies with different thicknesses and moraine-derived rock glaciers with different stages of activities could be identified. Few parts of these "rock glaciers" contain also massive ice but the largest parts are likely characterised by rock-ice layers of different thickness and ice contents. In one glacier forefield, the thickness of the rock-ice mixture is partly more than 300 m. This is only slightly lower than the maximum thickness of the glacier ice. Our measurements revealed that up to 20% of

  18. A more complex deglaciation chronology of Southern Norway than previously thought. New geochronological constraints based on cosmogenic exposure ages of marginal moraines

    NASA Astrophysics Data System (ADS)

    Fredin, Ola; Akçar, Naki; Romundset, Anders; Reber, Regina; Ivy-Ochs, Susan; Kubik, Peter; Høgaas, Fredrik; Schlüchter, Christian

    2015-04-01

    Glacial landforms from the last deglaciation in southern Norway were mapped by the famous glacial geologist Bjørn Andersen already in the early 1950s, using basic aerial photographs and topographic maps. Andersen reconstructed two distinct glacial sub-stages (the Lista stage and Spangereid stage) that were older than the Younger Dryas (YD), and one main glacial stage of assumed YD age (the Ra stage). This interpretation has remained largely untested and is still used in reconstructions of the Fennoscandian ice sheet. However, absolute chronological control has been lacking and only a handful radiocarbon dates has been used to support the deglaciation chronology. In this study we test the reconstruction of Andersen by remapping the whole area using newly aquired LiDAR data (high resolution laser scanning of terrain), together with in-situ cosmogenic nuclide exposure ages of boulders on marginal moraines. The study comprises mapping of more than 6000 km2 of forested and dissected landscape, 53 10Be ages from boulders/bedrock, one cosmogenic 10Be depth profile in a coarse-grained glaciofluvial deposit, and finally one lake record. Our study shows that the oldest of Andersen's glacial stages, the Lista stage right on the outermost Norwegian south coast, should likely be rejected since it consists of consolidated subglacial till and therefore is not an end moraine system. However, our cosmogenic depth profile indicates that this area might have been ice free already by around 19 ka BP, approximately 4000 years earlier than previously thought. At the same time the ice sheet surface slowly lowered, and the first inland hills of about 450 m. asl. became ice free at around 17 ka BP. Ice retreat continued slowly 10-15 km inland and halted as a calving fjord stage at the Spangereid stage with an approximate age of 15 ka BP. Then the deglaciation appears to have been very rapid and the ice front retreated 30-50 km inland to a position inside of the Ra stage, until a readvance

  19. Ice age terminations.

    PubMed

    Cheng, Hai; Edwards, R Lawrence; Broecker, Wallace S; Denton, George H; Kong, Xinggong; Wang, Yongjin; Zhang, Rong; Wang, Xianfeng

    2009-10-01

    230Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO2 and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO2 and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO2. PMID:19815769

  20. Ice Age Terminations

    NASA Astrophysics Data System (ADS)

    Cheng, Hai; Edwards, R. Lawrence; Broecker, Wallace S.; Denton, George H.; Kong, Xinggong; Wang, Yongjin; Zhang, Rong; Wang, Xianfeng

    2009-10-01

    230Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO2 and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO2 and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO2.

  1. The Great Ice Age

    USGS Publications Warehouse

    Ray, Louis L.

    1992-01-01

    The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. During the Pleistocene Epoch of the geologic time scale, which began about a million or more years ago, mountain glaciers formed on all continents, the icecaps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across northern North America and Eurasia. So extensive were these glaciers that almost a third of the present land surface of the Earth was intermittently covered by ice. Even today remnants of the great glaciers cover almost a tenth of the land, indicating that conditions somewhat similar to those which produced the Great Ice Age are still operating in polar and subpolar climates.

  2. Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

    USGS Publications Warehouse

    Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

    2007-01-01

    The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

  3. Ribbed moraines in northern Manitoba, Canada: characteristics and preservation as part of a subglacial bed mosaic near the core regions of ice sheets

    NASA Astrophysics Data System (ADS)

    Trommelen, Michelle S.; Ross, Martin; Ismail, Ahmed

    2014-03-01

    Ribbed moraines are enigmatic glacial landforms for which different models, with contrasting paleoglaciologic implications, have been proposed to explain their formation. Despite the great deal of attention this type of landform has received over the last several decades, ribbed moraine fields in northern Manitoba, Canada are among the largest in the world but have been seldom studied. Ribbed moraines in this part of the world overlie the low-relief Canadian Shield, are not constrained by topography, and are part of a spatial subglacial-landform assemblage associated with drumlinoid ridges within palimpsest and relict-type Glacial Terrain Zones. Field observations herein provide new insights into the characteristics of these transverse-to ice-flow ridges at landscape (mapping and spatial analysis) and landform (internal structure using high-resolution shear wave (S-wave) seismic reflection surveys, sedimentological characteristics, clast-fabric analyses) scales. Two main types of ribbed moraine are recognized: 'pristine', high amplitude straight-crested ridges and secondarily-modified subdued 'drumlinized' ridges. Ribbed moraine in northeast Manitoba consist of massive, matrix-supported till at surface, which is similar in matrix texture and composition to the regional till sheet, though pristine moraines show a higher concentration of boulders. A seismic profile reveals subparallel-to surface layered stratigraphy with only minor folding and no major unconformities (stacking or faulting).

  4. The little ice age

    SciTech Connect

    Grove, J.M.

    1988-01-01

    The Little Ice Age, a period of glacier expansion in alpine regions that began sometime between the twelfth and sixteenth centuries and lasted until late in the nineteenth century, was recorded not only in glacial features dated by geologic techniques but also in historical documents such as field sketches, land values, and weather records, especially in the Alps. Indirect evidence of its impact in other parts of the world includes the records of sea-ice extent near Iceland and Greenland, the fate of the Viking settlements in Greenland, and many other suggestions that the climate was colder in the recent past than it is today. Jean Grove's book is an authoritative, superbly documented, and excellently written summary of the abundant evidence of climatic change during the last few centuries in the context of broader climatic variations of the last 10,000 years. This summary provides a much-needed perspective for considering the magnitude and frequency of natural climatic variations in the past, given predictions for the future. In the final chapter, Grove notes that natural climatic variations, including another minor ice age, might be expected in the future but at the end of the Little Ice Age coincided with the increased burning of fossil fuels during the industralization of Europe and North America. This coincidence does indeed suggest that modern scientists already have had a significant impact on the global climate.

  5. Quantification of the ice-cored moraines' short-term dynamics in the high-Arctic glaciers Ebbabreen and Ragnarbreen, Petuniabukta, Svalbard

    NASA Astrophysics Data System (ADS)

    Ewertowski, Marek W.; Tomczyk, Aleksandra M.

    2015-04-01

    Extensive ice-cored moraine complexes are common elements, marking the last advance of many Svalbard glaciers. Sediment gravity flows are among the most dynamic processes, transforming these landforms. The short-term (yearly and weekly) dynamics of mass-wasting processes were studied in a cm-scale using repetitive topographic scanning. We monitored several active sites on the forelands of two glaciers, Ebbabreen and Ragnarbreen, both of which are located near Petuniabukta at the northern end of Billefjorden in Spitsbergen. The surveys indicate high dynamic rates of landforms' transformation. The mean annual volume loss of sediments and dead-ice for the most active parts of the moraines was up to 1.8 m a- 1. However, most of the transformation occurred during summer, with the short-term values of mean elevation changes as high as - 104 mm day- 1. In comparison, the dynamics of the other (i.e. non-active) parts of the ice-cored moraines were much lower, namely, the mean annual lowering (attributed mainly to dead-ice downwasting) was up to 0.3 m a-1, whereas lowering during summer was up to 8 mm day- 1. Our results indicate that in the case of the studied glaciers, backwasting was much more effective than downwasting in terms of landscape transformation in the glacier forelands. However, despite the high activity of localised mass movement processes, the overall short-term dynamics of ice-cored moraines for the studied glaciers were relatively low. We suggest that as long as debris cover is sufficiently thick (thicker than the permafrost's active layer depths), the mass movement activity would occur only under specific topographic conditions and/or due to occurrence of external meltwater sources and slope undercutting. In other areas, ice-cored moraines remain a stable landsystem component in a yearly to decadal time-scale.

  6. Sedimentary and structural evolution of a Pleistocene small-scale push moraine in eastern Poland: New insight into paleoenvironmental conditions at the margin of an advancing ice lobe

    NASA Astrophysics Data System (ADS)

    Włodarski, Wojciech; Godlewska, Anna

    2016-08-01

    Recent studies of push moraines have focused on the interplay between the dynamics of ice margins and the environmental variables of the foreland into which they advance. These studies showed that the spatial distribution, geometry and style of the glaciotectonic deformation of push moraines are controlled by ice-induced stresses, the strain rate, the rheology of the deposits and hydraulic conductivity. In this work, we provide new insight into this interplay at a small spatio-temporal scale, specifically, the ancient glacial system of the Liwiec ice lobe within the younger Saalian ice sheet in eastern Poland. The paleoenvironmental variables that are analysed here refer to the dynamics of the hydrological processes that affected the patterns and sediment deposition rate on the terminoglacial fan and the resulting mechanical stratigraphy and hydraulic conductivity of the foreland. We document the progradational sequence of the fan deposits that developed as a result of the ice lobe thickening and the steepening of its stationary front. The sedimentary features of the fan, the lithology of its basement and the hydraulic conductivity of the foreland strongly influenced the geometry and kinematics of fold growth during the advance of the ice lobe. The predominance of flexural slip and the development of fractures, including fold-accommodation faults, were interpreted to be an effect of buckle folding due to horizontal shortening induced by ice advance. The partial overriding of the push moraine by the ice lobe and, thus, the submarginal conditions for deformation were inferred from the significant hinge migration and internal deformation of the strata under undrained conditions in one of the folds. The synfolding deposition pattern of the fan growth strata allowed us to suggest that the push moraine was probably formed by a sustained advance rather than surge.

  7. First Younger Dryas moraines in Greenland

    NASA Astrophysics Data System (ADS)

    Funder, Svend; Larsen, Nicolaj K.; Linge, Henriette; Möller, Per; Schomacker, Anders; Fabel, Derek; Kjær, Kurt H.; Xu, Sheng

    2016-04-01

    Over the Greenland ice sheet the Younger Dryas (YD) cold climate oscillation (12.9-11.7 kaBP) began with up to 10°C drop in temperatures and ended with up to 12°C abrupt warming. In the light of the present warming and melting of the ice sheet, and its importance for future climate change, the ice sheet's response to these dramatic changes in the past is of great interest. However, even though much effort has gone into charting YD ice margin behaviour around Greenland in recent years, no clear-cut signal of response to the oscillation has been uncovered. Here we show evidence to suggest that three major outlets from a local ice cap at Greenland's north coast advanced and retreated synchronously during YD. The evidence comprises OSL (optically stimulated luminescence) dates from a marine transgression of the coastal valleys that preceded the advance, and exposure ages from boulders on the moraines, formed by glaciers that overrode the marine sediment. The OSL ages suggest a maximum age of 12.4 ±0.6 kaBP for the marine incursion, and 10 exposure ages on boulders from the three moraines provide an average minimum age of 12.5 ±0.7 kaBP for the moraines, implying that the moraines were formed within the interval 11.8-13.0 kaBP. Elsewhere in Greenland evidence for readvance has been recorded in two areas. Most notably, in the East Greenland fjord zone outlet glaciers over a stretch of 800 km coast advanced through the fjords. In Scoresby Sund, where the moraines form a wide belt, an extensive 14C and exposure dating programme has shown that the readvance here probably culminated before YD, while cessation of moraine formation and rapid retreat from the moraine belt did not commence until c. 11.5 kaBP, but no moraines have so far been dated to YD. Readvance is also seen in Disko Bugt, the largest ice sheet outlet in West Greenland. However, here the advance and retreat of the ice stream took place in mid YD times, and lasted only a few hundred years, while YD in

  8. Upper Wisconsinan submarine end moraines off Cape Ann, Massachusetts

    USGS Publications Warehouse

    Oldale, R.N.

    1985-01-01

    Seismic profiles across the southwest end of Jeffreys Ledge, a bathymetric high north of Cape Ann, Massachusetts, reveal two end moraines. The moraines overlie upper Wisconsinan glacialmarine silty clay and are composed mostly of subaqueous ice-contact deposits and outwash. They were formed below sea level in water depths of as much as 120 m during fluctuations of a calving ice front. The moraines are late Wisconsinan in age and were formed after the Cambridge readvance, about 14,000 yr B.P., and before the Kennebunk readvance, about 13,000 yr B.P. They represent fluctuations of the ice front during overall retreat of Laurentide ice from the Gulf of Maine and New England. ?? 1985.

  9. Mars Ice Age, Simulated

    NASA Technical Reports Server (NTRS)

    2003-01-01

    December 17, 2003

    This simulated view shows Mars as it might have appeared during the height of a possible ice age in geologically recent time.

    Of all Solar System planets, Mars has the climate most like that of Earth. Both are sensitive to small changes in orbit and tilt. During a period about 2.1 million to 400,000 years ago, increased tilt of Mars' rotational axis caused increased solar heating at the poles. A new study using observations from NASA's Mars Global Surveyor and Mars Odyssey orbiters concludes that this polar warming caused mobilization of water vapor and dust into the atmosphere, and buildup of a surface deposit of ice and dust down to about 30 degrees latitude in both hemispheres. That is the equivalent of the southern Unites States or Saudi Arabia on Earth. Mars has been in an interglacial period characterized by less axial tilt for about the last 300,000 years. The ice-rich surface deposit has been degrading in the latitude zone of 30 degrees to 60 degrees as water-ice returns to the poles.

    In this illustration prepared for the December 18, 2003, cover of the journal Nature, the simulated surface deposit is superposed on a topography map based on altitude measurements by Global Surveyor and images from NASA's Viking orbiters of the 1970s.

    Mars Global Surveyor and Mars Odyssey are managed by NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, for the NASA Office of Space Science, Washington.

  10. Geomorphic change detection using repetitive topographic surveys and DEMs of Differences: Implementation for short-term transformation of the ice-cored moraines in the Petuniabukta, Svalbard

    NASA Astrophysics Data System (ADS)

    Tomczyk, Aleksandra; Ewertowski, Marek

    2015-04-01

    The exposed glacial forelands are supposed to be intensively transformed by geomorphological processes due to the paraglacial adjustment of the topography. To recognize how high is the activity of such processes, we monitored the transformation rates of ice-cored moraines on the forelands of two glaciers, Ebbabreen and Ragnarbreen, both of which are located near the Petuniabukta at the northern end of the Billefjorden. The main objectives were to: (1) analyse the spatial and temporal aspects of debris flow activity in cm-scale, (2) quantify the short-term (seasonal and intra-seasonal) rate of volume changes, (3) compare transformations of the ice-cored moraine surfaces due to active geomorphic processes (including dead-ice backwasting and debris mass movements) with transformations caused by dead-ice downwasting only. The short-term (yearly and weekly) dynamics of mass-wasting processes were studied in a cm-scale using repetitive topographic scanning. In total, four different locations were scanned, containing seven active debris flows or other mass wasting processes, and including non-active surfaces. Sites were chosen to ensure representation from different parts of the end moraine, different types of dominant processes (debris flows, debris falls, etc.) as well as different types of morphology (exposed ice cliffs, steep debris slope, gentle debris flows lobes, etc.). Altogether, the total scanned area was about 14,200 m2, of which 5,500 m2 were transformed by the active mass movement processes. Ten measurement sessions were carried out: three in summer of 2012, three in summer of 2013, and four in summer of 2014, which allowed for assessing the seasonal (annual) and intra-seasonal (weekly) variations. The results of the surveys in the form of cloud points were used to generate digital elevation models (DEMs) with cell size 0.05 m. Subtracting DEMs from subsequent time periods created DEMs of Differences - DoDs, which enabled us to investigate the volume of and

  11. Annual to sub-annual 3D surface evolution of an Antarctic blue-ice moraine using multi-platform, multi-temporal high resolution topography

    NASA Astrophysics Data System (ADS)

    Westoby, Matthew; Dunning, Stuart; Woodward, John; Hein, Andrew; Marrero, Shasta; Winter, Kate; Sugden, David

    2016-04-01

    High-resolution topographic data products are now routinely used for the geomorphological characterisation of Earth surface landforms and landscapes, whilst the acquisition and differencing of such datasets are swiftly becoming the preferred method for quantifying the transfer of mass through landscapes at the spatial scales of observation at which many processes operate. In this research, we employ 3-D differencing of repeat high-resolution topography to quantify the surface evolution of a 0.3 km2 blue-ice moraine complex in front of Patriot Hills, Antarctica. We used terrestrial laser scanning (TLS) to acquire multiple overlapping 3D datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey campaign in 2014. An additional topographic dataset was acquired at the end of season 1 through the application of a Structure-from-Motion with Multi-View Stereo (SfM-MVS) workflow to a set of aerial photographs acquired during a single unmanned aerial vehicle (UAV) sortie. 3D cloud-to-cloud differencing was undertaken using the M3C2 algorithm. The results of 3D differencing revealed net uplift (median ~0.05 m) and lateral (xy) movement (median 0.02 m) of the moraine crests within season 1. Analysis of results from the longest differencing epoch (start of season 1 to season 2) suggests gradual but persistent surface uplift (median ~0.11 m) and sustained lateral movement (median ~0.05 m). Locally, lowering of a similar magnitude to uplift was observed in inter-moraine troughs and close to the current ice margin. This research demonstrates that it is possible to detect dynamic surface topographic change across glacial moraines over short timescales through the acquisition and differencing of high-resolution topographic datasets. Such data and methods of analysis offer new opportunities to understand glaciological and geomorphological process linkages in remote glacial environments.

  12. The probable importance of snow and sediment shielding on cosmogenic ages of north-central Colorado Pinedale and pre-Pinedale moraines

    USGS Publications Warehouse

    Benson, L.; Madole, R.; Phillips, W.; Landis, G.; Thomas, T.; Kubik, P.

    2004-01-01

    Eight uncorrected 36Cl ages for Pinedale boulders in north-central Colorado fall in the range 16.5 to 20.9 kyr. 10Be age determinations on four of five boulders are in close agreement (???6% difference) with 36Cl determinations. Hypothetical corrections for snow shielding increased the 36Cl ages of Pinedale boulder surfaces by an average of ???12%. Most ages for pre-Pinedale (Bull Lake) boulders fall within marine-isotope stage (MIS) 5, a time when continental and Sierran ice accumulations were small or nonexistent. Under the assumption that these boulders were deposited on moraines that formed before the end of MIS 6 (???140 kyr BP), calculations indicated that rock-surface erosion rates would have had to range from 5.9 to 10.7 mm kyr-1 to produce the observed 36Cl values. When compared to rates that have been documented for the past 20 kyr, these erosion rates are extremely high. Snow shielding accounts for 0-48% of the additional years needed to shift pre-Pinedale dates to MIS 6. This suggests that some combination of snow shielding, sediment shielding, or 36Cl leakage has greatly decreased the apparent ages of most pre-Pinedale boulders. Inability to account for the effects of these processes seriously hinders the use of cosmogenic ages of pre-Pinedale boulders as estimators of the timing of alpine glaciation.

  13. Preliminary Vertical Slip Rate for the West Tahoe Fault from six new Cosmogenic 10Be Exposure Ages of Late Pleistocene Glacial Moraines at Cascade Lake, Lake Tahoe, California

    NASA Astrophysics Data System (ADS)

    Pierce, I. K. D.; Wesnousky, S. G.; Kent, G. M.; Owen, L. A.

    2015-12-01

    The West Tahoe Fault is the primary range bounding fault of the Sierra Nevada at the latitude of Lake Tahoe. It is a N-NW striking, east dipping normal fault that has a pronounced onshore quaternary scarp extending from highway 50 southwest of Meyers, CA to Emerald Bay. At Cascade Lake, the fault cuts and progressively offsets late Pleistocene right lateral moraines. The fault vertically offsets the previously mapped Tahoe moraine ~83 m and the Tioga moraine ~23 m, measured from lidar data. Seventeen samples were collected for 10Be cosmogenic age analysis from boulders on both the hanging and footwalls of the fault along the crests of these moraines.We report here the initial analysis of 6 of these boulders and currently await processing of the remainder. The 10Be exposure ages of 3 boulders each on the younger Tioga and older Tahoe moraines range from 12.7 +/- 1.6 to 20.7 +/- 3.3 ka and 13.3 +/- 2.1 to 72.5 +/- 8.8 ka, respectively. Using the oldest ages as minima, these preliminary results suggest that the slip rate has averaged ~1 mm/yr since the penultimate glaciation, in accord with estimates of previous workers, and place additional bounds on the age of glaciation in the Lake Tahoe basin. The Last Glacial Maxima and penultimate glaciation near Lake Tahoe thus appear to coincide with the Tioga and Tahoe II glaciations of the Eastern Sierra.

  14. Glaciology and the Ice Age.

    ERIC Educational Resources Information Center

    Carozzi, Albert V.

    1984-01-01

    Discusses: (1) the beginning of glaciology; (2) origin of erratic boulders, meteorites, volcanic explosions, floods, and drift; (3) ice age hypothesis in Europe and the United States; (4) development of glacial theory; (5) and a unified explanation of glacial events. A bibliography of classical research on glaciology is included. (BC)

  15. Cosmogenic 10Be constraints on Little Ice Age glacial advances in the eastern Tian Shan, China

    NASA Astrophysics Data System (ADS)

    Li, Yanan; Li, Yingkui; Harbor, Jon; Liu, Gengnian; Yi, Chaolu; Caffee, Marc W.

    2016-04-01

    Presumed Little Ice Age (LIA) glacial advances, represented by a set of fresh, sharp-crested, boulder covered and compact moraines a few hundred meters downstream from modern glaciers, have been widely recognized in the Central Asian highlands. However, few studies have constrained the formation ages of these moraines. We report 31 10Be exposure ages from presumed LIA moraines in six glacial valleys in the Urumqi River headwater area and the Haxilegen Pass area of the eastern Tian Shan, China. Our results reveal that the maximum LIA glacial extent occurred mainly around 430 ± 100 yr, a cold and wet period as indicated by proxy data from ice cores, tree rings, and lake sediments in Central Asia. We also dated a later glacial advance to 270 ± 55 yr. However, 10Be exposure ages on several presumed LIA moraines in front of small, thin glaciers are widely scattered and much older than the globally recognized timing of the LIA. Historical topographic maps indicate that most glaciers were more extensive in the early 1960s, and two of our 10Be sample sites were located close to the ice front at that time. Boulders transported by these small and thin glaciers may be reworked from deposits originally formed prior to the LIA glacial advances, producing apparently old and widely scattered exposure ages due to varied nuclide inheritance. Other published ages indicated an earlier LIA advance around 790 ± 300 yr in the easternmost Tian Shan, but in our study area the more extensive advance around 430 ± 100 yr likely reworked or covered deposits from this earlier event.

  16. Climate Data Records (CDRs) for Ice Motion and Ice Age

    NASA Astrophysics Data System (ADS)

    Tschudi, M. A.; Fowler, C.; Maslanik, J. A.; Stroeve, J. C.

    2011-12-01

    Climate Data Records (CDRs) for remotely-sensed Arctic sea ice motion and sea ice age are under development by our group at the University of Colorado, Boulder. The ice motion product, archived at NSIDC, has a considerable history of use, while sea ice age is a relatively new product. Our technique to estimate sea ice motion utilizes images from SSM/I, as well as SMMR and the series of AVHRR sensors to estimate the daily motion of ice parcels. This method is augmented by incorporating ice motion observations from the network of drifting buoys deployed as part of the International Arctic Buoy Program. Our technique to calculate ice age relies on following the actual age of the ice for each ice parcel, categorizing the parcel as first-year ice, second-year, ice, etc. based on how many summer melt seasons the ice parcel survives. Both of these research-grade products have been interpolated onto 25x25 km grid points spanning the entire Arctic Ocean using the Equal-Area Scalable Earth (EASE) grid. Datasets generated from this program have shown that the Arctic ice cover has experienced a significant (> 70%) decline in multiyear ice over the last 20 years, leaving a younger ice cover in 2011. By comparing ice age derived by the Lagrangian tracking method to ice thickness estimated by Ice, Cloud and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) data, it is observed that ice age is linearly related to ice thickness, up to an age of 10 years. Therefore, the shift in dominance of multiyear ice to first-year ice relates to a significant thinning of the ice. This thinning is estimated to correspond to a 40% reduction in ice volume in the last 20 years. An ancillary dataset (APP-X) produced by the University of Wisconsin, Madison has been combined with the ice motion product to monitor the properties of the sea ice parcels tracked by the ice motion product. This dataset includes ice surface and 2-meter air temperature, albedo, downwelling shortwave

  17. Little Ice Age glaciers in Britain: Glacier–climate modelling in the Cairngorm Mountains

    SciTech Connect

    Stephan Harrison; Ann V. Rowan; Neil F. Glasser; Jasper Knight; Mitchell A. Plummer; Stephanie C. Mills

    2014-02-01

    It is widely believed that the last glaciers in the British Isles disappeared at the end of the Younger Dryas stadial (12.9–11.7 cal. kyr BP). Here, we use a glacier–climate model driven by data from local weather stations to show for the first time that glaciers developed during the Little Ice Age (LIA) in the Cairngorm Mountains. Our model is forced from contemporary conditions by a realistic difference in mean annual air temperature of -1.5 degrees C and an increase in annual precipitation of 10%, and confirmed by sensitivity analyses. These results are supported by the presence of small boulder moraines well within Younger Dryas ice limits, and by a dating programme on a moraine in one cirque. As a result, we argue that the last glaciers in the Cairngorm Mountains (and perhaps elsewhere in upland Britain) existed in the LIA within the last few hundred years, rather than during the Younger Dryas.

  18. The Natural Thermoluminescence Survey of Antarctic Meteorites: Ordinary Chondrites at the Grosvenor Mountains, MacAlpine Hills, Pecora Escarpment and Queen Alexandra Range, and New Data New Data for the Elephant Moraine, Ice Fields

    NASA Technical Reports Server (NTRS)

    Benoit, Paul H.; Sears, Derek W. G.

    2000-01-01

    The natural TL survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to (1) identifying pairing, (2) providing an estimate of terrestrial age and residence time on the ice surface, (3) looking for differences in natural TL between ice fields, (4) looking for variations in natural TL level with location on the ice, (5) looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the @ost productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to (5) look for evidence for secular variation in the nature of the flux of meteorites to Earth, and (6) look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary

  19. The Natural Thermoluminescence Survey of Antarctic Meteorites: Ordinary Chondrites at the Grosvenor Mountains, Macalpine Hills, Pecora Escarpment and Queen Alexandra Range, and New Data for the Elephant Moraine, Ice Fields

    NASA Technical Reports Server (NTRS)

    Benoit, Paul H.; Sears, Derek W. G.

    1999-01-01

    The natural TL (Thermoluminescence) survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET (Antarctic Search for Meteorites) samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to identifying pairing, providing an estimate of terrestrial age and residence time on the ice surface, looking for differences in natural TL between ice fields, looking for variations in natural TL level with location on the ice, looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the most productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to look for evidence for secular variation in the nature of the flux of meteorites to Earth, and look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable

  20. Examination of surface exposure age of Antarctic moraines using in situ produced [sup 10]Be and [sup 26]Al

    SciTech Connect

    Brown, E.T.; Edmond, J.M. ); Raisbeck, G.M.; Yiou, F. ); Kurz, M.D.; Brook, E.J. )

    1991-08-01

    Concentrations of [sup 10]Be (t[sub 1/2] = 1.5 [times] 10[sup 6]y) and [sup 26]Al (t[sub 1/2] = 0.72 [times] 10[sup 6]y) have been determined by accelerator mass spectrometry (AMS) in a suite of quartz samples taken from sandstone boulders in several moraines in Arena Valley, a dry valley adjacent to the Taylor Glacier in the Quatermain Mountains, Southern Victoria Land, East Antarctica. These isotopes are produced in surficial quartz by cosmic ray spallation of O and Si. The concentrations in these samples ranged from 6.1 [times] 10[sup 5] to 3.0 [times] 10[sup 7] at g[sup [minus]1] for [sup 10]Be and from 9.4 [times] 10[sup 6] to 1.2 [times] 10[sup 8] at g[sup [minus]1] for [sup 26]Al, depending upon the extent of exposure at the surface. Production rates of 17[sub [minus]4][sup +16] at g[sup [minus]1]y[sup [minus]1] for [sup 10]Be and 113[sub [minus]16][sup +54] at g[sup [minus]1]y[sup [minus]1] for [sup 26]Al at 1300 m and 87[degree]S and a [sup 26]Al:[sup 10]Be production ratio of 6.5[sub [minus]1.3][sup +1.3] were calculated from the data. These values correspond to sea-level production rates at high geomagnetic latitude of 6.4 at g[sup [minus]1]y[sup [minus]1] and 41.7 at g[sup [minus]1]y[sup [minus]1] for [sup 10]Be and [sup 26]Al, respectively, consistent with determinations based on [approximately]11 Ky glacially polished surfaces in the Sierra Nevada in California. These production rates imply exposure ages for the various moraines ranging from 50 Ky to 2.5 My, in accordance with other geological evidence. The [sup 10]Be and [sup 26]Al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of [sup 3]He.

  1. A preliminary report on a possible stromatolite find from the Elephant Moraine, Antarctica: A potential directional indicator for ice movement

    NASA Technical Reports Server (NTRS)

    Sipiera, P. P.; Landis, C. A.

    1986-01-01

    During the 1983 to 1984 Antarctic Search for Meteorites field season, numerous specimens of a shiny black rock were collected from among the glacial debris at the Elephant Moraine. From a distance these black rocks gave the appearance of meteorites, but upon closer inspection, distinct layering and radial crystal growth patterns became clearly visible. Laboratory investigations showed that these unusual specimens are primarily composed of carbonate minerals. Petrographically, microscopic examination of twelve randomly collected specimens revealed a variety in the habits of the carbonates, but the overall trend tends to be one of radiating acicular crystals that have the appearance of a pseudo-cellular structure reminiscent of stromatolites. It is not possible at this time to specifically identify this possible stromatolite material or its source locality.

  2. Cosmogenic Be-10 Constraints of the "Little Ice Age" Glacial Advances in the Eastern Tian Shan, China

    NASA Astrophysics Data System (ADS)

    Li, Y.; Liu, G.; Chen, Y.

    2014-12-01

    The Little Ice Age (LIA) glacial advances, represented as a set of "fresh and bouldery" moraines a few hundred meters downstream from modern glaciers, have been widely recognized in Central Asian highlands. However, few studies have been conducted to constrain the formation ages of these moraines. Glaciers provide critical freshwater supply in Central Asia, so understanding the dynamics of glaciers, especially in the past a few hundreds of years, is of great importance. In a NSF funded project reported here, we aim to constrain the formation ages of these putative LIA moraines in the eastern Tian Shan, China, using cosmogenic 10Be surface exposure dating. Our initial results showed 10Be exposure ages ranging from 0.17±0.10 ka to 0.28±0.10 ka, from 0.38±0.03 ka to 0.86±0.08 ka, and from 0.36±0.04 ka to 0.41±0.10 ka for these moraines from the Bayinbuluke Valley in the Nalati Range, the Turgan Valley in the Karlik Range, and the Daxi Valley in the Tianger Range, respectively. We are currently processing 30 samples for the "LIA" moraines in six valleys located in the Heigou Valley of the Bogeda Range, the Haxilegen Pass in the Borohoro Range, and the Urumqi River headwaters in the Tianger Range. Except for one older age of 5.1±0.6 ka, which might be an outlier, our recently measured four ages range from 0.19±0.04 ka to 0.61±0.10 ka. These ages suggest that these fresh moraines were formed during the LIA, but glaciers might advance to their maximum extents slightly differently in different sites. This work demonstrates the importance of absolute dating in reconstructing past glacial fluctuations, and provides quantitative evidence in assessing the impact of glacier change on the ecosystem and society in recent centuries.

  3. Components of the ice age circulation

    NASA Technical Reports Server (NTRS)

    Rind, D.

    1987-01-01

    The effects of ice age boundary conditions on atmospheric dynamics and regional climate patterns are investigated using four GCM simulations. Particular consideration is given to sea surface temperature-sea ice distribution, the appearance of land ice, and the increased elevation of land ice. It is observed that the ice-age sea surface temperature stabilizes the atmosphere over the oceans, increases the frequency of storm tracking through central North America, and amplifies transient eddy energy without increasing baroclinic generation. It is detected that low-elevation ice generates low pressure over eastern North America and southern Europe in winter, while increasing cloud cover and cooling the land in summer. Elevation of the ice sheets cools the land in winter, further intensifies storms off northeastern North America, induces subsidence warming downstream of the European ice sheets in summer, and increases the transient and stationary eddy energy through increased baroclinicity.

  4. Evolution of crystal fabric: Ice-Age ice versus Holocene ice

    NASA Astrophysics Data System (ADS)

    Kennedy, J. H.; Pettit, E. C.

    2009-12-01

    Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007

  5. Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Lakeman, Thomas R.; Clague, John J.; Menounos, Brian

    2008-03-01

    Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550-10,250 cal yr BP (9230 ± 50 14C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances.

  6. Quantifying the character and short-term evolution of blue-ice moraines, Heritage Range, Antarctica: Integration and comparison of repeat UAV, TLS and dGPS-derived datasets

    NASA Astrophysics Data System (ADS)

    Westoby, M.; Dunning, S.; Woodward, J.; Sugden, D.; Hein, A.; Marrero, S.; Reid, K.

    2014-12-01

    Blue-ice moraines are associated with katabatic winds that enhance ablation and sublimation at the base of nunataks which create surface depressions that are compensated for by ice-flow from an adjacent trunk glacier, and at right-angles to the main flow direction. It is hypothesised that this flow regime transports basal debris which emerges glacier surface at the base of the nunatak, where it resides for long periods of time. Quantifying the long- and short-term evolution and persistence of these features is central to refining estimates of, and constraining the principles drivers of long-term ice-sheet stability. High resolution digital elevation models derived from sUAV photography and Structure-from-Motion (SfM) photogrammetry, and Terrestrial Laser Scanning have been used to quantify rates and patterns of topographic change across a blue-ice moraine in the Heritage Range, West Antarctica, between the 2012/13 and 2013/14 melt seasons, and within the 2012/13 melt season. We benchmark these SfM-TLS derived change detection data against coincident dGPS ablation and movement stake data, with a view to assessing the utility of the different approaches for resolving small-scale (centimetric to sub-centimetric) surface change in ice-marginal areas over annual and sub-annual timescales.

  7. Debris flows from failures Neoglacial-age moraine dams in the Three Sisters and Mount Jefferson wilderness areas, Oregon

    USGS Publications Warehouse

    O'Connor, J. E.; Hardison, J.H.; Costa, J.E.

    2001-01-01

    The highest concentration of lakes dammed by Neoglacial moraines in the conterminous United States is in the Mount Jefferson and Three Sisters Wilderness Areas in central Oregon. Between 1930 and 1980, breakouts of these lakes have resulted in 11 debris flows. The settings and sequences of events leading to breaching and the downstream flow behavior of the resulting debris flows provide guidance on the likelihood and magnitude of future lake breakouts and debris flows.

  8. Geomorphology and the Little Ice Age extent of the Drangajökull ice cap, NW Iceland, with focus on its three surge-type outlets

    NASA Astrophysics Data System (ADS)

    Brynjólfsson, Skafti; Schomacker, Anders; Ingólfsson, Ólafur

    2014-05-01

    Detailed geomorphological maps from the forefields of three surging outlets of the Drangajökull ice cap, northwest Iceland, are presented. The maps are based on field studies in 2011-2013, high resolution orthorectified aerial photographs recorded in 2005-2006, and airborne LiDAR data from 2011. The maps cover an area of about 40-60 km2 each. Furthermore, we present an overview map that covers the area surrounding the Drangajökull ice cap. Landforms and sediments were manually registered in a geographic information system (ESRI ArcGIS 10). We mapped glacial landforms such as flutes, ice-sculpted bedrock, hummocky moraine, kame terraces, and moraines. Fluvial landforms include outwash plains/sandur, pitted sandur, and eskers. In addition raised beaches were mapped. The Little Ice Age (LIA) maximum extent of Drangajökull and its outlet glaciers are fingerprinted by surficial till deposits and freshly glacially scoured bedrock. Sediments distal to the LIA deposits were recorded and consist mainly of late Weichselian and early Holocene sediments and locally weathered bedrock. Periglacial activity is demonstrated by patterned ground, mainly occurring on the 500-700 m high plateaux, and three rock glaciers. At least 3-4 surge events are described from each of the outlet glaciers, occurring over the last three centuries. In contrast to most other surge-type outlets from Icelandic ice caps, the Drangajökull outlets are confined within valleys, which affect the forefield geomorphology. Glaciofluvial landforms, moraines, and a thin sheet of till with numerous boulders are characteristic for the forefields of the Drangajökull outlets.

  9. Mantle viscosity and ice-age ice sheet topography

    SciTech Connect

    Peltier, W.R.

    1996-09-06

    Ice-age paleotopography and mantle viscosity can both be inferred from observations of Earth`s response to the most recent deglaciation event of the current ice age. This procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment. Results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ICE-4G model. The accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process, thus resolving a fundamental issue concerning mantle rheology. The combined model also explains postglacial sea level histories for the east cost of the United States. 28 refs., 9 figs.

  10. Stationary Waves of the Ice Age Climate.

    NASA Astrophysics Data System (ADS)

    Cook, Kerry H.; Held, Isaac M.

    1988-08-01

    A linearized, steady state, primitive equation model is used to simulate the climatological zonal asymmetries (stationary eddies) in the wind and temperature fields of the 18 000 YBP climate during winter. We compare these results with the eddies simulated in the ice age experiments of Broccoli and Manabe, who used CLIMAP boundary conditions and reduced atmospheric CO2 in an atmospheric general circulation model (GCM) coupled with a static mixed layer ocean model. The agreement between the models is good, indicating that the linear model can be used to evaluate the relative influences of orography, diabatic heating, and transient eddy heat and momentum transports in generating stationary waves. We find that orographic forcing dominates in the ice age climate. The mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies. This concept of the ice age climate is complicated by the sensitivity of the stationary eddies to the large increase in the magnitude of the zonal mean meridional temperature gradient simulated in the ice age GCM.

  11. Probability of moraine survival in a succession of glacial advances.

    USGS Publications Warehouse

    Gibbons, A.B.; Megeath, J.D.; Pierce, K.L.

    1984-01-01

    Emplacement of glacial moraines normally results in obliteration of older moraines deposited by less extensive glacial advances, a process we call 'obliterative overlap'. Assuming randomness and obliterative overlap, after 10 glacial episodes the most likely number of surviving moraines is only three. The record of the Pleistocene is in agreement with the probability analysis: the 10 glaciations during the past 0.9 Myr inferred from the deep-sea record resulted in moraine sequences in which only two or three different-aged moraine belts can generally be distinguished. -from Authors

  12. The natural thermoluminescence of meteorites. 7: Ordinary chondrites from the Elephant Moraine region, Antarctica

    NASA Technical Reports Server (NTRS)

    Benoit, P. H.; Roth, J.; Sears, H.; Sears, D. W. G.

    1994-01-01

    We report natural and induced thermoluminescence (TL) measurements for meteorites from the Elephant Moraine region (76 deg 17 min S, 157 deg 20 min E) of Antarctica. We use our data to identify fragmented meteorites (i.e., 'pairings'); our dataset of 107 samples represents at most 73 separate meteorite falls. Pairing groups are generally confined to single icefields, or to adjacent icefields, but a small proportion cross widely separated icefields in the region, suggesting that the fields can be considered as a single unit. Meteorites from this region have high natural TL levels, which indicates that they have small terrestrial surface exposure ages (less than 12,500 years). There do not appear to be significant differences in natural TL levels (and hence surface exposure ages) between individual blue icefields in the region. The proportion of reheated meteorites from the Elephant Moraine region is similar to that of other Antarctic sites and modern falls, consistent with the uniformity of the meteoritic flux in this regard. An unusual subset of H-chondrites, with high induced TL peak temperatures, is absent among the data for meteorites collected in the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine icefields formed through shallow ablation of the ice. Unlike the Allan Hills sites to the south, lateral transport is probably less important relative to the infall of meteorites in concentrating meteorites on these icefields.

  13. How ice age climate got the shakes

    SciTech Connect

    Kerr, R.A.

    1993-05-14

    Records in Greenland ice, ocean mud, and ancient corals are revealing abrupt climate shifts during the last ice age. The climate at the end of the last ice age apparently jumped from cold to warmer conditions, jumped back to cold, and then jumped into the present warm weather conditions. The mechanism for this erratic behavior is unknown, but appears to be an interaction of North Atlantic ocean currents and the ice sheets themselves. Warm water from the tropics would evaporate and become more saline and dense as it moved north. The colder, denser water would then sink and flow back to the tropics. The melting of ice caused by the warm water would decrease the salinity of the North Atlantic current, the water would not sink, the return current would be shut down, and the waters surrounding the ice sheets would become colder, slowing melting of the sheets. The cycle could be started again by collapse of the ice sheets from their internal heat. There may be other switches that could cause sudden climate change, as may be evidenced by links between changes in the Pacific and a decade of erratic weather in North America. Researcher would like to identify these switches to prevent them from being activated by human activity.

  14. Engineering geology and ground water considerations for sanitary landfills in Wisconsin-aged morainal deposits of central Indiana

    SciTech Connect

    West, T.R.

    1985-01-01

    In the past five years the author has been engaged as an engineering geology consultant concerning a number of existing and proposed landfills, located in the Wisconsin morainal plains of central Indiana. Work has involved the representation of landfill owners in some cases and opposing citizens in others. For each case except one, municipal waste or conventional waste landfills were involved with the other involving hazardous waste disposal. Several major geologic considerations are involved in proper sitting of landfills in this region. These include: (1) Type, nature and stratigraphy of unconsolidated materials; (2) Thickness of unconsolidated material; (3) Type and nature of bedrock below unconsolidated material: (4) Groundwater supplies in vicinity; (5) Topography of site including flood potential; and (6) Groundwater table and water bearing zones involved. Engineering details of landfill construction and monitoring must also be considered in regard to the site geology. Aspects of leachate generation and containment must be addressed as well.

  15. Coeval fluctuations of the Greenland ice sheet and a local glacier, central East Greenland, during late glacial and early Holocene time

    NASA Astrophysics Data System (ADS)

    Levy, Laura B.; Kelly, Meredith A.; Lowell, Thomas V.; Hall, Brenda L.; Howley, Jennifer A.; Smith, Colby A.

    2016-02-01

    We present a 10Be chronology of late glacial to early Holocene fluctuations of a Greenland ice sheet outlet glacier and the adjacent Milne Land ice cap in central East Greenland. Ages of boulders on bedrock indicate that both ice masses receded during the Younger Dryas (YD), likely due to rising summer temperatures. Since Greenland ice core records register cold mean annual temperatures throughout the YD, these ice-marginal data support climate conditions characterized by strong seasonality. The ice sheet outlet glacier and ice cap deposited inner Milne Land Stade moraines at 11.4 ± 0.8 ka and 11.4 ± 0.6 ka, respectively (mean moraine ages and 1σ uncertainties). Based on the coeval moraine ages, we suggest that both ice masses responded to climate conditions acting on the ice margins, specifically ablation. Moreover, the ice sheet responded sensitively (i.e., on the same time scale as a small ice cap) to climate conditions.

  16. Cosmogenic 10Be Chronologies of Moraines and Glacially Scoured Bedrock in the Teton Range, with Implications for Paleoclimatic Events and Tectonic Activity

    NASA Astrophysics Data System (ADS)

    Licciardi, J. M.; Pierce, K. L.; Thackray, G. D.; Finkel, R. C.; Zimmerman, S. R. H.

    2015-12-01

    At its Pleistocene maximum, the greater Yellowstone glacial system consisted of an ice cap on the Yellowstone Plateau joined by glaciers from adjacent high mountains, including the Teton Range. In prior research, we obtained 112 exposure ages from moraines and bedrock in this region. These chronologies identified asynchronous outlet glacier culminations around the periphery of the Yellowstone glacier complex, supporting a model of spatial and temporal progressions in buildup and decay of the various ice source regions. Here we build on this previous work and present >30 recently developed 10Be exposure ages on glacial features in the Teton Range. Although the Tetons harbored a relatively small portion of the greater Yellowstone ice complex, glaciers in this range left behind some of the region's best-preserved moraine sequences and scoured bedrock. Ongoing investigations are focused on developing moraine chronologies in several drainages on the eastern and western Teton Range fronts, and obtaining exposure ages along scoured bedrock transects in glacial troughs upvalley from the dated moraines to define rates of ice recession. Notably, our dating campaign includes lateral moraines that are offset by the Teton fault, providing a rare opportunity to establish direct constraints on integrated long-term slip rates. All new and previously obtained 10Be ages are calculated using recently published calibrations and scaling of 10Be production rates. Initial results show that massive lateral moraines in selected drainages are several thousands of years older than adjacent distal end moraines, implying that the laterals were constructed during an earlier phase of the last glaciation and then acted to topographically confine subsequent ice advances. Mean ages of ca. 17-16 ka from terminal moraine loops along with limiting ages from scoured bedrock upvalley of the moraines indicate glacier culminations followed by the onset of rapid ice retreat long after the end of the global

  17. Monitoring of glacial and periglacial landforms using terrestrial laser scanning.The case of the Col des Gentianes moraine (Valais, Switzerland)

    NASA Astrophysics Data System (ADS)

    Mazotti, B.; Oppikofer, T.; Riff, F.; Lambiel, C.; Loye, A.; Jaboyedoff, M.

    2009-04-01

    Between 1977 and 1979, important civil engineering works were made on the moraine of "Col des Gentianes", which is situated 2894 meters above the sea level in the region of Mt-Fort, Valais, Switzerland. Two cableway station arrivals, a departure station to the Mt-Fort and a restaurant were built on. This moraine was formed during the last advance of the Tortin glacier during the Little Ice Age. Since 1980, the glacier has melted dramatically and the moraine is creeping. The moraine in front of the cableway departure station to the Mt-Fort sagged by 2 to 4 meters in 30 years. A large volume of ice is still present within the moraine and melting of the ice would make its stability even more precarious. Since 2007 the moraine is monitored by terrestrial laser scanning (TLS). Two TLS campaigns were made in July and October 2008 and compared to datasets acquired in 2007. The comparison of sequential TLS point clouds enabled the detection and quantification of movements in the moraine: (1) by computing oblique (shortest) or vertical differences, (2) by creating displacement vectors and (3) by profiles across the TLS point clouds. Between July and October 2008 the Tortin glacier melted by 1 to 2.5 m and the moraine creeped in direction of the glacier by 0.25 to 0.75 m. During the same period, a landslide zone has been clearly identified downslope of the cableway departure station to the Mt-Fort. Important movements between 1.5 to 5 meters were measured on this landslide through the creation of displacement vectors. This landslide scarp is delimited by 0.5 and 1 meter downward displacements in two month. Already in 2007, a less important landslide was identified and some ice had been observed in the scarp zone. The TLS permitted to analyze the distribution of these movements on the entire moraine and not only on few measurement points like given by D-GPS. The computed TLS displacement vectors are in good agreement with annual D-GPS measurements performed on this moraine

  18. Time needed for first lichen colonization of terminal moraines in the Tröllaskagi peninsula (North Iceland)

    NASA Astrophysics Data System (ADS)

    Andres, Nuria; Palacios, David; Brynjólfsson, Skafti; Sæmundsson, Þorsteinn

    2015-04-01

    , lichen thalli were located and their greatest diameters measured, examining the surface, boulder by boulder, along a 100 m stretch of each moraine and counting those with existing lichen thalli and those without them. The results from the two moraines are very similar: a) Only 15 - 18% of the boulders presented some type of thallus. b) There is little variety in the thallus size on one specific boulder, but great variety between different boulders, even when they are very close together. c) The largest thalli of the moraine only appear on isolated boulders, between 3 and 0.7%. d) In the Rizocarpon geographicum thalli, exceptional sizes were found of isolated thalli with max. diameter of up to 2,8 mm. The most frequent size observed on boulders with homogeneous thalli is 1 - 2 mm. e) Some sectors of the two moraines still have ice under the boulders, which may explain the uneven lichen colonization in different parts of the moraine. These observations should be taken into consideration when examining the age of the moraines using lichenometry. 8-10 years after a moraine separated from the glacial terminus, only a minimum number of its boulders are stable enough to allow lichen colonization. As time passes, the blocks gradually become stabilized and allow lichen colonization. This may explain the widely varying thalli sizes found between different blocks in the same moraine. Research funded by Cryocrisis project (CGL2012-35858), Government of Spain, and Nils Mobility projects (EEA GRANTS)

  19. Ice Age Geomorphology of North America

    NASA Astrophysics Data System (ADS)

    Wickert, A. D.; Anderson, R. S.; Mitrovica, J. X.; Picard, K.

    2012-12-01

    The Last Glacial Cycle in North America dramatically modified drainage patterns and geomorphology on a continental scale. As a consequence, the evolution of river systems holds information on the patterns of glaciation and isostatic response. This information can, in principle, be used to reconstruct the volumes of ice sheet sectors and eroded material by connecting the upstream ice sheets with stable isotope and other sedimentary records in offshore basins. Here we integrate this coupled geomorphic-hydrologic-glacial-sedimentary-paleoceanographic system to solve both the forward problem, how rivers evolve in response to Ice Age forcing, as well as the inverse problem, how fluvial systems record Quaternary history. The connections that define this system provide a link between climate and geomorphology that extends beyond the traditionally considered watershed-to-landscape scale by incorporating solid Earth deformations, large-scale shoreline migration, and the high amplitude changes in climate that drive the growth and decay of major ice sheets and water delivery to the bounding river systems. We address this continental scale problem using a valley-resolving drainage reconstruction that incorporates a realistic ice sheet history, a gravitationally self-consistent treatment of ice-age sea-level changes that includes shoreline migration, and precipitation and evapotranspiration retrodicted using general circulation model (GCM) runs. Drainage divides over the flat-lying North American interior migrate hundreds to thousands of kilometers in response to dynamic interactions between ice sheets and solid Earth response, and these changes coupled with post last glacial maximum (LGM) ice sheet melting drive high-amplitude variability in water and sediment discharge to the oceans. The Mackenzie River Delta records a sedimentary record produced by a highly non-eustatic sea level history and massive glacial sediment inputs routed along the axis that divided the Cordilleran

  20. Age characteristics in a multidecadal Arctic sea ice simulation

    SciTech Connect

    Hunke, Elizabeth C; Bitz, Cecllia M

    2008-01-01

    Results from adding a tracer for age of sea ice to a sophisticated sea ice model that is widely used for climate studies are presented. The consistent simulation of ice age, dynamics, and thermodynamics in the model shows explicitly that the loss of Arctic perennial ice has accelerated in the past three decades, as has been seen in satellite-derived observations. Our model shows that the September ice age average across the Northern Hemisphere varies from about 5 to 8 years, and the ice is much younger (about 2--3 years) in late winter because of the expansion of first-year ice. We find seasonal ice on average comprises about 5% of the total ice area in September, but as much as 1.34 x 10{sup 6} km{sup 2} survives in some years. Our simulated ice age in the late 1980s and early 1990s declined markedly in agreement with other studies. After this period of decline, the ice age began to recover, but in the final years of the simulation very little young ice remains after the melt season, a strong indication that the age of the pack will again decline in the future as older ice classes fail to be replenished. The Arctic ice pack has fluctuated between older and younger ice types over the past 30 years, while ice area, thickness, and volume all declined over the same period, with an apparent acceleration in the last decade.

  1. Late Pleistocene piedmont glaciations in the Eastern Mediterranean; insights from cosmogenic 36Cl dating of hummocky moraines in southern Turkey

    NASA Astrophysics Data System (ADS)

    Çiner, Attila; Sarıkaya, Mehmet Akif; Yıldırım, Cengiz

    2015-05-01

    We report the presence of Late Pleistocene piedmont glaciers represented by the largest hummocky moraine field observed in the Eastern Mediterranean. The piedmont glaciers originated from the Geyikdağ ice cap (∼40 km2), situated between 2350 and 2650 m above sea level (a.s.l.) (Central Tauride Mountains of Turkey), and deeply carved the north-facing hillslopes before reaching the Namaras Valley (2000-2050 m a.s.l). The hummocky moraines resulted from in-situ deposition of stagnant glacier ice where debris cover was heterogeneously distributed on the glacier surface. Thirty-four boulders from hummocky, disintegration, lateral and terminal moraines from the Namaras Valley and the tributary Susam Valley (2100-2200 m a.s.l.) were dated by cosmogenic 36Cl surface exposure dating. The moraine ages indicate three phases of deglaciation during the Late Pleistocene. The oldest deglaciation occurred in the Namaras Valley at 18.0 ± 1.1 ka (ka: thousand years ago) towards the end of the Last Glacial Maximum (LGM) and is recorded entirely by hummocky moraines. We speculate that hummocky moraine forming processes with cycles of relief inversion gave rise to boulder apparent ages up to a few thousand years younger in our study area. Therefore, 18.0 ± 1.1 ka should be regarded as a minimum age with a probable true age much closer to the local-LGM values (∼20 ka) as observed in the surrounding mountains. Paleo-piedmont glaciers also deposited several lateral moraines that are ∼50 m higher than the hummocky moraines. Although the lateral moraines probably represent the build-up and the hummocky moraines the final phase of the same local-LGM-pulse, both lateral moraines started to retreat from the Late-glacial (14.0 ± 2.7 ka) and gradually disappeared by mid-Holocene (5.2 ± 1.0 ka), encompassing the Younger Dryas (YD) stadial. In the Susam Valley, the Late-glacial is represented by a terminal moraine (13.4 ± 1.5 ka). The glacier retreat was very fast as indicated by an

  2. A glacial chronology for post Little Ice Age glacier changes based on proglacial geomorphology, tree rings, OSL- and 14C-dating at Mt. Pulongu, southeastern Tibet

    NASA Astrophysics Data System (ADS)

    Loibl, David; Hochreuther, Philipp; Hülle, Daniela; Zhu, Haifeng; Lehmkuhl, Frank

    2014-05-01

    The remote eastern Nyainqêntanglha Range contains numerous temperate monsoonal glaciers which are highly sensitive to climate change. However, there is still a great lack of information on late Holocene glacier fluctuations and the factors driving these changes. We conducted field work at two large debris covered glaciers on the northern and southern slopes of Mt. Pulongu (~6,300 m a.s.l.). Detailed geomorphological mapping of the proglacial settings revealed similar patterns of two major and three minor/recessional glacial advances. At the northern glacier, tree ring dating for the moraines of the two major advances resulted in minimum ages of ~1670 AD and ~1745 AD, respectively. These Little Ice Age (LIA) ages are supported by geochemical measurements on glacial and glacio-fluvial sediments from these settings showing almost no signs of chemical weathering. Further evidence, including 14C-age and depositional characteristics of a buried tree, and moraine topography, suggest that the second advance was stronger but was hampered by a dead ice relict of the previous advance. At the northern glacier, this obstacle led to an ice tailback and subsequently to lateral moraine oversteepening and breaching, resulting in a large lateral glacier lobe. At the southern glacier, the valley is narrower and hence did not allow the formation of a lateral glacier lobe. However, the proglacial setting, i.e. pronounced push moraines, suggests a similar sequence of events. Furthermore, both settings contain two moraine-dammed lakes in similar positions. A combination of OSL-dating, tree ring based reconstruction of the local climate, and constraints from the proglacial geomorphological setting enabled the inclusion of the 3 minor moraine stages into the glacial chronology. This multiproxy-approach resulted in a well-established morphochronology with multiple direct and indirect dates that allow the reconstruction of the glacial fluctuations at Mt. Pulongu since the LIA. A regional

  3. About Weichselian Ice-Marginal Positions South of the Baltic Sea - Stratigraphy and Critical Discussion of Age Estimates

    NASA Astrophysics Data System (ADS)

    Boese, Margot; Hardt, Jacob

    2015-04-01

    In the classical research area of glacial morphology south of the Baltic Sea, the supposed main ice-marginal positions of the Weichselian glaciation have been documented on various maps. The lines in the maps suggest a similar timing of the ice margin along these hypothetical lines and represent a traditional morphostratigraphical approach. Nevertheless, more recent research resulting in stratigraphical interpretations of the related sediments give controversial results about the connectivity of ice-marginal features in the landscape. In addition, the development of new dating techniques reveals more diversified ice dynamics of the Scandinavian ice sheet as well as a time transgressiveness of the formation of major end moraine belts. On the other hand, age estimates generated by various methods don't give an unambiguous pattern of ice advances and retreat phases. The interpretation of geochronological data is a highly sensitive challenge in respect to the methods themselves and in respect to landscape processes induced by Late Glacial climatic phases, the relief, and by human impact during the Holocene. The Pomeranian ice margin will be taken as an example for the diverse interpretations of data obtained by Surface Exposure Dating, Optically Stimulated Luminescence, and Radiocarbon data. The dating methods require material of different origin, such as boulders at the surface, fine grained sediment, and organic material. All methods have been applied for dating the same ice marginal position. The remaining question is to which extent the reactions of the ice margins of the Scandinavian Ice Sheet can be brought into accordance with the general climatic record of long term climate archives or whether local weather conditions linked to changes in the atmospheric flow pattern influenced small scale ice advances or retreat along the fringe of the Scandinavian Ice Sheet.

  4. A 300 Year Surge History of the Drangajökull Ice Cap, Northwest Iceland: Surge Frequency and Little Ice Age Maximum

    NASA Astrophysics Data System (ADS)

    Brynjolfsson, S.; Schomacker, A.; Ingolfsson, O.; Gudmundsdottir, E. R.

    2014-12-01

    Over the last 300 years, each of the three surge-type outlet glaciers of the Drangajökull ice cap in north-west Iceland has surged 2-4 times. There is valuable historical information available on the surge frequencies since the Little Ice Age (LIA) maximum because of the proximity of the surging outlets, Reykjarfjarðarjökull, Leirufjarðarjökull and Kaldalónsjökull to farms and pastures. We have reconstructed the surge history of the Drangajökull ice cap, based on geomorphological mapping, sedimentary studies and review of historical records. Geomorphological mapping of the glacier forefields revealed twice as many end-moraines than previously recognized. This indicates a higher surge frequency than previously perceived. A clear relationship between the surge frequency and climate cannot be established, however, surges were more frequent during the 19th century and the earliest 20th century compared to the cool 18th century and the warmer late part of the 20th century. We have estimated the magnitude of the LIA maximum surge events by reconstruction of Digital Elevation Models (DEMs) that can be compared with modern DEMs. As reference points for the digital elevation modelling we used the recently mapped lateral moraines and historical information on the exposure timing of nunataks. During the LIA maximum surge events the outlet glaciers extended 3-3.5 km further down-valley than at present. Their ice volumes were at least 2-2.5 km3 greater than after their most recent surges in the beginning of the 21st century.

  5. Appearance of De Geer moraines in southern and western Finland - Implications for reconstructing glacier retreat dynamics

    NASA Astrophysics Data System (ADS)

    Ojala, Antti E. K.

    2016-02-01

    LiDAR digital elevation models (DEMs) from southern and western Finland were investigated to map and discriminate features of De Geer moraines, sparser and more scattered end moraines, and larger end moraine features (i.e., ice-marginal complexes). The results indicate that the occurrence and distribution of De Geer moraines and scattered end moraine ridges in Finland are more widespread than previously suggested. This is probably attributed to the ease of detecting and mapping these features with high-resolution DEMs, indicating the efficiency of LiDAR applications in geological and geomorphological studies. The variable appearance and distribution of moraine ridges in Finland support previous interpretations that no single model is likely to be appropriate for the genesis of De Geer moraines at all localities and for all types of end moraines. De Geer moraine appearances and interdistances probably result from a combination of the general rapidity of ice-margin recession during deglaciation, the proglacial water depth in which they were formed, and local glacier dynamics related to climate and terrain topography. The correlation between the varved clay-based rate of deglaciation and interdistances of distinct and regularly spaced De Geer moraine ridges indicates that the rate of deglaciation is probably involved in the De Geer ridge-forming process, but more thorough comparisons are needed to understand the extent to which De Geer interdistances represent an annual rate of ice-margin decay and the rapidity of regional deglaciation.

  6. Determination of the age distribution of sea ice from Lagrangian observations of ice motion

    SciTech Connect

    Kwok, R.; Cunningham, G.F.; Rothrock, D.A.; Stern, H.L.

    1995-03-01

    A procedure for monitoring the local age distribution of the Arctic sea ice cover is presented. The age distribution specifies the area covered by ice in different age classes. In the authors` approach, a regular array of grid points is defined initially on the first image of a long time series, and an ice tracker finds the positions of those points in all subsequent images of the series. These Lagrangian points mark the corners of a set of cells that move and deform with the ice cover. The area of each cell changes with each new image or time step. A positive change indicates that ice in a new age class was formed in the cell. A negative change is assumed to have ridged the youngest ice in the cell, reducing its area. The ice in each cell ages as it progresses through the time series. The area of multiyear ice in each cell is computed using an ice classification algorithm. Any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first-year ice. They thus have a fine age resolution in the young end of the age distribution, and coarse resolution for older ice. The age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing-degree days and ice thickness, or using a more complicated thermodynamic model. They describe a general scheme for implementing this procedure for the Arctic Ocean from fall freeze-up until the onset of melt in the spring. The concept is illustrated with a time series of five ERS-1 SAR images spanning a period of 12 days. Such a scheme could be implemented with RADARSAT SAR imagery to provide basin-wide ice age and thickness information.

  7. Self-potential investigation of moraine dam seepage

    NASA Astrophysics Data System (ADS)

    Moore, Jeffrey R.; Boleve, Alexandre; Sanders, Johnny W.; Glaser, Steven D.

    2011-08-01

    Self-potential (SP) and electrical resistivity measurements are used to investigate seepage at a remote moraine dam in the Sierra Nevada of California. The site is a small terminal moraine impounding roughly 300,000 m 3 of water at ~ 3400 m a.s.l. Suspicious fine sediment in a small lake at the dam's downstream toe prompted initial concerns that anomalous seepage may be eroding matrix material from the moraine. 235 individual SP measurements covering the surface of the dam were collected in order to investigate electrokinetic current sources resulting from seepage, while resistivity soundings probed moraine stratigraphy and suggest that the till contains interstitial ice. Contoured SP data reveal a non-uniform voltage distribution over the moraine dam and two distinct negative SP anomalies. The first, located in the central area of the moraine, shows a broad negative SP zone around the crest and increasingly positive SP moving downhill towards both the upstream and downstream toes. This anomaly can be explained by shallow gravitational groundwater flow in the near subsurface combined with upward groundwater flux through evapotranspiration; numerical simulation of the combined effect matches field data well. The second SP anomaly has a tightly localized distribution and can be explained by vertically descending flow into a bedrock fault conduit. Our conceptual seepage model suggests that flow travels from Dana Lake first at the boundary of ice-filled moraine and bedrock before converging on a concentrated channel in the subvertical fault zone. Positive SP near the dam abutments results from groundwater inflow from adjacent hillslopes. Combined analyses suggest that seepage erosion is not currently affecting the moraine dam, and that the sediment observed on the bed of the downstream toe lake is likely a remnant of past outflow events.

  8. Push moraines in the upper valley of Santa Cruz river, southwest Argentina. Structural analysis and relationship with Late Pleistocene paleoclimate

    NASA Astrophysics Data System (ADS)

    Goyanes, Gabriel; Massabie, Armando

    2015-01-01

    The upper cliff of the Santa Cruz River was used to assess the proglacial environments of the Argentino Glacier outlet of Late Pleistocene age. These cliffs show glaciolacustrine, fluvioglacial and till deposits, where only the first one are deformed. Glacial landforms in the area and these structures suggest that the ice mass advanced, topographically controlled, towards the east from the Patagonian Ice Sheet pushing up the proglacial sediments. The spatial arrangement of thrusts and overturned folds, the drumlins-flutes moraine directions and the end moraines shape, allow inferring the dynamic and the Argentino glacier profile. Detailed analyses of the glaciotectonic structures indicate that these have two origins: load in the north with stress transfer to the southeast, and push from the west. Through the analysis of deformed sediments, their thickness and their sedimentary and structural features, three zones of deformations were recognized. Each of these zones was associated to glacial advances because of changes of the regional climate conditions.

  9. Dendrogeomorphic reconstruction of Little Ice Age paraglacial activity in the vicinity of the Homathko Icefield, British Columbia Coast Mountains, Canada

    NASA Astrophysics Data System (ADS)

    Hart, Sarah J.; Clague, John J.; Smith, Dan J.

    2010-09-01

    Moraine and glacier dams bordering the Homathko Icefield in the southern British Columbia Coast Mountains failed in the 1980s and 1990s, causing catastrophic downstream floods. The largest of the floods occurred in August 1997 and was caused by overtopping and rapid breaching of the moraine dam that impounds Queen Bess Lake. The floodwaters from Queen Bess Lake eroded Holocene-age sedimentary deposits along the west fork of Nostetuko River and caused a steep rise in the hydrograph of Homathko River at the head of Bute Inlet, ˜ 115 km downstream. A field investigation of the eroded valley fill in 2008, revealed multiple paraglacial valley-fill units, many of which are capped by in situ stumps and woody detritus. Dendrogeomorphological field techniques were employed to develop a chronology for the buried forests. A regional tree-ring chronology spanning the interval CE 1572-2007 was constructed from living subalpine fir ( Abies lasiocarpa) trees at seven sites in the southern Coast Mountains. In cases where subfossil stumps and boles predated the regional chronology, relative death dates constrained by radiocarbon ages were assigned to floating chronologies. By combining these dendrogeomorphological dating methods, we identified six floodplain aggradation episodes within the past 1200 years. Comparison to local and regional glacial histories suggests that these events reflect climate-induced Little Ice Age changes in local glacier cover.

  10. Climate Data Records (CDRs) for Ice Motion, Ice Age, and Melt Pond Fraction

    NASA Astrophysics Data System (ADS)

    Tschudi, M. A.; Maslanik, J. A.; Fowler, C.; Stroeve, J. C.; Rigor, I. G.

    2010-12-01

    Remotely-sensed Arctic sea ice motion, sea ice age, and melt pond coverage have been proposed for development into full CDRs. The first has a considerable history of use, while the latter two are relatively new products. Our technique to estimate sea ice motion utilizes images from SSM/I, as well as the Scanning Multichannel Microwave Radiometer (SMMR) and the series of Advanced Very High Resolution Radiometer (AVHRR) sensors to estimate the daily motion of ice parcels. This method is augmented by incorporating ice motion observations from the network of drifting buoys deployed as part of the International Arctic Buoy Program. Our technique to calculate ice age relies on following the actual age of the ice for each ice parcel, categorizing the parcel as first-year ice, second-year ice, etc. based on how many summer melt seasons the ice parcel survives. Our method to estimate melt pond coverage on sea ice involves solving a set of linear equations that relate each surface feature’s individual reflectance within the sensor’s (currently using the MODIS surface reflectance product, MOD09) pixel to the overall reflectance in that pixel. These three research-grade products have been interpolated onto 25x25 km grid points spanning the entire Arctic Ocean using the Equal-Area Scalable Earth (EASE) grid.

  11. Geological Evidence for Recent Ice Ages on Mars

    NASA Astrophysics Data System (ADS)

    Head, J. W.; Mustard, J. F.; Kreslavsky, M. A.; Milliken, R. E.; Marchant, D. R.

    2003-12-01

    A primary cause of ice ages on Earth is orbital forcing from variations in orbital parameters of the planet. On Mars such variations are known to be much more extreme. Recent exploration of Mars has revealed abundant water ice in the near-surface at high latitudes in both hemispheres. We outline evidence that these near-surface, water-ice rich mantling deposits represent a mixture of ice and dust that is layered, meters thick, and latitude dependent. These units were formed during a geologically recent major martian ice age, and were emplaced in response to the changing stability of water ice and dust on the surface during variations in orbital parameters. Evidence for these units include a smoothing of topography at subkilometer baselines from about 30o north and south latitudes to the poles, a distinctive dissected texture in MOC images in the +/-30o-60o latitude band, latitude-dependent sets of topographic characteristics and morphologic features (e.g., polygons, 'basketball' terrain texture, gullies, viscous flow features), and hydrogen concentrations consistent with the presence of abundant ice at shallow depths above 60o latitude. The most equatorward extent of these ice-rich deposits was emplaced down to latitudes equivalent to Saudi Arabia and the southern United States on Earth during the last major martian ice age, probably about 0.4-2.1 million years ago. Mars is currently in an inter-ice age period and the ice-rich deposits are presently undergoing reworking, degradation and retreat in response to the current stability relations of near-surface ice. Unlike Earth, martian ice ages are characterized by warmer climates in the polar regions and the enhanced role of atmospheric water ice and dust transport and deposition to produce widespread and relatively evenly distributed smooth deposits at mid-latitudes during obliquity maxima.

  12. Carbon-14 ages of Allan Hills meteorites and ice

    NASA Technical Reports Server (NTRS)

    Fireman, E. L.; Norris, T.

    1982-01-01

    Allan Hills is a blue ice region of approximately 100 sq km area in Antarctica where many meteorites have been found exposed on the ice. The terrestrial ages of the Allan Hills meteorites, which are obtained from their cosmogenic nuclide abundances are important time markers which can reflect the history of ice movement to the site. The principal purpose in studying the terrestrial ages of ALHA meteorites is to locate samples of ancient ice and analyze their trapped gas contents. Attention is given to the C-14 and Ar-39 terrestrial ages of ALHA meteorites, and C-14 ages and trapped gas compositions in ice samples. On the basis of the obtained C-14 terrestrial ages, and Cl-36 and Al-26 results reported by others, it is concluded that most ALHA meteorites fell between 20,000 and 200,000 years ago.

  13. Alteration of Heterogeneous Ice Nucleation Properties Induced by Particle Aging

    NASA Astrophysics Data System (ADS)

    Sullivan, R. C.; Polen, M.; Beydoun, H.; Lawlis, E.; Ahern, A.; Jahn, L.; Hill, T. C. J.

    2015-12-01

    Aerosol particles that can serve as ice nuclei frequently experience rapid and extensive chemical aging during atmospheric transport. This is known to significantly alter some ice nucleation modes of the few types of ice nucleation particle systems where aging effects have been simulated, such as for mineral dust. Yet much of our understanding of atmospheric particle freezing properties is derived from measurements of fresh or unaged particles. We know almost nothing regarding how atmospheric aging might alter the freezing properties of biomass burning aerosol or biological particle nucleants. We have investigated the effects of simulated aging using a chamber reactor on the heterogeneous ice nucleation properties of biomass burning aerosol (BBA) and ice-active bacteria particles. Some types of aging were found to enhance the freezing ability of BBA, exhibited as a shift in a portion of the droplet freezing curve to warmer temperatures by a few °C. Ice-active bacteria were found to consistently loose their most ice-active nucleants after repeated aging cycles. The bacterial systems always retained significantly efficient ice active sites that still allowed them to induce freezing at mild/warm temperatures, despite this decrease in freezing ability. A comprehensive series of online single-particle mass spectrometry and offline spectromicroscopic analysis of individual particles was used to determine how the aging altered the aerosol's composition, and gain mechanistic insights into how this in turn altered the freezing properties. Our new ice nucleation framework that uses a continuous distribution of ice active site ability (contact angle) was used to interpret the droplet freezing spectra and understand how aging alters the internal and external variability, and rigidity, of the ice active sites.

  14. Radiostratigraphy and age structure of the Greenland Ice Sheet

    PubMed Central

    MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Paden, John D; Prasad Gogineni, S; Young, S Keith; Rybarski, Susan C; Mabrey, Alexandria N; Wagman, Benjamin M; Morlighem, Mathieu

    2015-01-01

    Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet. Key Points Phase information predicts reflection slope and simplifies reflection tracing Reflections can be dated away from ice cores using a simple ice flow model Radiostratigraphy is often disrupted near the onset of fast ice flow PMID:26213664

  15. 10Be exposure dating of Holocene moraines in the Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Hidy, Alan; Zimmerman, Susan; Finkel, Robert; Schaefer, Jeorg; Clark, Douglas

    2016-04-01

    Constraint on the extent and timing of Holocene glaciations is critical to addressing standing hypotheses that ascribe climatic fluctuations to changes in atmospheric and oceanic circulation patterns, or anthropogenic forcing. In the terrestrial record, such constraint typically relies on chronologies obtained from 10Be exposure dating of moraine deposits. However, the short exposure time of Holocene moraines, particularly those formed during the Little Ice Age (LIA), makes obtaining precise chronologies extremely challenging. To date, only a handful of LIA deposits in two locations (New Zealand and the Swiss Alps) have been successfully dated with 10Be. Here, we report new 10Be exposure ages from LIA and Neoglacial moraines from multiple sites in the Sierra Nevada (Lyell, Maclure, and Palisade glaciers). The Sierran LIA record will be compared to those from New Zealand and the Swiss Alps to test whether LIA deglaciation was globally synchronous. This result would support the contention that the LIA was terminated by anthropogenically-driven warming. Chronology from the neoglacial deposits will be used to test whether the timing of the return to glacial conditions in the Sierras correlates to a southward shift in the Intertropical Convergence Zone, which has been hypothesized to increase El Nino-like conditions in the Pacific Ocean. This record should be ideal for testing this hypothesis since precipitation in the Sierras is highly sensitive to El Nino conditions.

  16. Late-Wisconsin End Moraines in Northern Canada.

    PubMed

    Falconer, G; Andrews, J T; Ives, J D

    1965-02-01

    A system of end moraines nearly 2240 kilometers long has been identified by field investigation and aerial photography. It extends through northeastern Keewatin, Melville Peninsula, and Baffin Island and marks the border of a late-Wisconsin ice sheet centered over Foxe Basin and Hudson Bay 8000 or 9000 years ago. PMID:17783266

  17. Rate and style of ice stream retreat constrained by new surface-exposure ages: The Minch, NW Scotland

    NASA Astrophysics Data System (ADS)

    Bradwell, Tom; Small, David; Fabel, Derek; Dove, Dayton; Cofaigh, Colm O.; Clark, Chris; Consortium, Britice-Chrono

    2016-04-01

    Chronologically constrained studies of former ice-sheet extents and dynamics are important for understanding past cryospheric responses and modelling future ice-sheet and sea-level change. As part of the BRITICE-CHRONO project, we present new geomorphological and chronological data from a marine-terminating ice stream system in NW Europe that operated during the Late Weichselian Glaciation. A suite of 51 cosmogenic-nuclide exposure ages from ice sheet moraines and glacially transported boulders constrain the maximum extent of the ice sheet on the continental shelf (~28 ka BP) and its subsequent retreat, between ~27 and 16 ka BP, into a large marine embayment (ca. 7000 km2; the Minch, NW Scotland). Recently acquired swath bathymetry and acoustic sub-bottom profiler data reveal several large transverse grounding-zone wedges up to 40 m thick and 5 km wide with diagnostic acoustic-facies architecture. These seabed sediment wedges mark former quasi-stable positions of grounded marine-terminating ice-stream fronts; their size and thickness suggest long-lived stillstands of the order of centuries. Statistically significant clusters of exposure ages from glacial deposits on islands and intervening headlands shed important new light on the age of these marine grounding-zone wedges and, by inference, the rate and timing of Minch palaeo-ice stream retreat. We find strong evidence for episodic ice stream retreat on the continental shelf between ~28-24 ka BP, in the outer Minch between ~24-22 ka BP, and in the central Minch between 22-18.5 ka BP. In contrast, final ice stream deglaciation (<18 ka) across the deepest parts of the inner Minch embayment, was probably rapid and uninterrupted - with the ice sheet margin at or close to the present-day coastline in NW Scotland by 16.1 ka BP. It is hoped that these results will form the empirical basis for future ice-sheet modelling of this dynamically sensitive sector of the British-Irish Ice Sheet.

  18. The genetic history of Ice Age Europe.

    PubMed

    Fu, Qiaomei; Posth, Cosimo; Hajdinjak, Mateja; Petr, Martin; Mallick, Swapan; Fernandes, Daniel; Furtwängler, Anja; Haak, Wolfgang; Meyer, Matthias; Mittnik, Alissa; Nickel, Birgit; Peltzer, Alexander; Rohland, Nadin; Slon, Viviane; Talamo, Sahra; Lazaridis, Iosif; Lipson, Mark; Mathieson, Iain; Schiffels, Stephan; Skoglund, Pontus; Derevianko, Anatoly P; Drozdov, Nikolai; Slavinsky, Vyacheslav; Tsybankov, Alexander; Cremonesi, Renata Grifoni; Mallegni, Francesco; Gély, Bernard; Vacca, Eligio; Morales, Manuel R González; Straus, Lawrence G; Neugebauer-Maresch, Christine; Teschler-Nicola, Maria; Constantin, Silviu; Moldovan, Oana Teodora; Benazzi, Stefano; Peresani, Marco; Coppola, Donato; Lari, Martina; Ricci, Stefano; Ronchitelli, Annamaria; Valentin, Frédérique; Thevenet, Corinne; Wehrberger, Kurt; Grigorescu, Dan; Rougier, Hélène; Crevecoeur, Isabelle; Flas, Damien; Semal, Patrick; Mannino, Marcello A; Cupillard, Christophe; Bocherens, Hervé; Conard, Nicholas J; Harvati, Katerina; Moiseyev, Vyacheslav; Drucker, Dorothée G; Svoboda, Jiří; Richards, Michael P; Caramelli, David; Pinhasi, Ron; Kelso, Janet; Patterson, Nick; Krause, Johannes; Pääbo, Svante; Reich, David

    2016-06-01

    Modern humans arrived in Europe ~45,000 years ago, but little is known about their genetic composition before the start of farming ~8,500 years ago. Here we analyse genome-wide data from 51 Eurasians from ~45,000-7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3-6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans. Whereas there is no evidence of the earliest modern humans in Europe contributing to the genetic composition of present-day Europeans, all individuals between ~37,000 and ~14,000 years ago descended from a single founder population which forms part of the ancestry of present-day Europeans. An ~35,000-year-old individual from northwest Europe represents an early branch of this founder population which was then displaced across a broad region, before reappearing in southwest Europe at the height of the last Ice Age ~19,000 years ago. During the major warming period after ~14,000 years ago, a genetic component related to present-day Near Easterners became widespread in Europe. These results document how population turnover and migration have been recurring themes of European prehistory. PMID:27135931

  19. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

    PubMed

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-01-01

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas. PMID:25908601

  20. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics

    PubMed Central

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-01-01

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas. PMID:25908601

  1. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-04-01

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ~3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

  2. Constraints on ice volume changes of the WAIS and Ross Ice Shelf since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Fink, David; Storey, Bryan; Hood, David; Joy, Kurt; Shulmeister, James

    2010-05-01

    glacially transported debris. Our glacial geomorphic survey from ice sheet contact edge (~850 masl) to mountain peak at 1600 masl together with a suite of 10Be and 26Al exposure ages, documents a pre-LGM ice volume at least 800 meters thicker than current ice levels which was established at least 2 million years ago. However a complex history of exposure and re-exposure of the ice free regions in this area is seen in accordance with advance and retreat of the ice sheets that feeds into the Darwin -Hatherton system. A cluster of mid-altitude boulders, located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, have exposure ages ranging from 30 to 40 ka. Exposure ages for boulders just above the ice contact range from 1to 19 ka and allow an estimate of inheritance. Hence, we conclude that LGM ice volume was not as large as previously estimated and actually little different from what is observed today. These results raise rather serious questions about the implications of a reduced WAIS at the LGM, its effect on the development of the Ross Ice Shelf, and how the Antarctic ice sheets respond to global warming. J. O. Stone et al., Science v299, 99 (2003). A. Mackintosh, D. White, D. Fink, D. Gore et al, Geology, v 35; 551-554 (2007).

  3. Potential improvement of Schmidt-hammer exposure-age dating (SHD) of moraines in the Southern Alps, New Zealand, by application of the new electronic Schmidt-hammer (SilverSchmidt)

    NASA Astrophysics Data System (ADS)

    Winkler, Stefan; Corbett, David

    2014-05-01

    The Southern Alps of New Zealand are among the few key study sites for investigating Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere. Their characteristic highly dynamic geomorphological process systems prove, however, to be a considerable challenge for all attempts to date and palaeoclimatologically interpret the existing Holocene moraines record. As a multi-proxy approach combining 10Be terrestrial cosmogenic nuclide dating (TCND) with Schmidt-hammer testing, the recently developed Schmidt-hammer exposure-age dating (SHD) has already shown its potential in this study area (cf. Winkler 2005, 2009, 2013). An electronic Schmidt-hammer (named SilverSchmidt) was introduced by the manufacturer of the original mechanical Schmidt-hammer (Proceq SA) a few years ago. It offers, in particular, facilities for much easier data processing and constitutes a major improvement and potential replacement for the mechanical Schmidt-hammer. However, its different approach to the measurement of surface hardness - based on Q-(velocity) values instead of R-(rebound) values - is a potential drawback. This difference effectively means that measurements from the two instruments are not easily interconvertible and, hence, that the instruments cannot be used interchangeably without previous comparative tests of both instruments under field conditions. Both instruments used in this comparative study were N-type models with identical impact energy of 2.207 Nm for the plunger. To compare both instruments and explore interconvertibility, parallel measurements were performed on a selected number of boulders (10 boulders per site with 5 impacts each, at least 2 sites per moraine) on moraines of homogeneous lithology but different established ages covering the entire Holocene and the Late Glacial. All moraines are located east of the Main Divide of the Southern Alps at Mueller Glacier, Tasman Glacier, and in the outer Tasman River Valley. All paired samples (n = 50) were

  4. Timing and Structure of Glacial Fluctuations at the end of the Last Ice Age in SW Patagonia

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Moreno, P. I.; Villa-Martínez, R. P.; Kubik, P. W.

    2006-12-01

    In the mid to high southern latitudes much of the controversy regarding synchrony or bipolar asynchrony has centered on late glacial time, especially in South America as it is one of the few land masses south of 45°S, outside Antarctica. To help resolve this controversy, and in general understand this important time interval, we studied in detail the timing, structure, and relative amplitude of climate changes during the late glacial period at 50°S in SW Patagonia. We combined two independent dating approaches including cosmogenic dating of moraines and radiocarbon of lake sediment cores, in addition to paleoecologic studies of key sections. We measured the 10Be concentrations in erratics from maximum and retreat glacial deposits from the Lago Nordenskjöld and Río Paine ice lobes. The 10Be ages from the two areas indicate a maximum extent prior to ~13 ka (4 ages), followed by slightly less extensive but sustained ice until ~12-11±1 ka. Excluding ages from deposits clearly related to retreat, the mean 10Be age for the two lobes falls between 13-12 ka, and the maximum ages from the two areas are 14.3±1.1 and 13.8±1.8 ka, respectively. This timing agrees well with minimum 14C ages for glacial geomorphic features associated with the maximum and retreat ice positions. We interpret the onset of organic sedimentation in the area occupied by a former ice-dammed lake at 12.6 cal ka as the closest minimum age for ice recession from the maximum ice extent. The pollen data indicate extreme cold conditions between 14.8-12.5 ka, slight amelioration between 12.5-10.9 ka, followed by warming in the early Holocene Period. We conclude that 1) a major cold reversal took place in SW Patagonia overlapping in time with the Antarctic Cold Reversal and 2) ice retreated slowly but lingered close to the maximum position throughout Younger Dryas time until ~10.7±0.9 ka under cold and, possibly, wet conditions. We speculate that southern latitude air- ocean dynamics, such as that of

  5. Paired moraine-dammed lakes: a key landform for glaciated high mountain areas in the tropical Andes of Peru

    NASA Astrophysics Data System (ADS)

    Iturrizaga, Lasafam

    2016-04-01

    The tropical mountain range of the Cordillera Blanca hosts one of the main concentrations of proglacial lakes in high-mountain settings worldwide, which have formed as a result of the dominant trend of modern glacier retreat. Based on empirical data from field research in over 20 valleys and the analysis of air and satellite images, a genetic classification of major lake types with their barriers and a generalized model for the distribution of the present lakes and paleolakes was set up. The origin of the lakes and their recurrent distribution pattern are associated with the individual stages of the Pleistocene to modern glaciation and their corresponding geomorphological landforms. Characteristic repetitive moraine sequences are found in the upper parts of numerous valleys of the Cordillera Blanca. In terms of the spatial arrangement of the lake types, combined lakes are classified as a distinct composite lake type. These lakes occur at nearly the same elevation or at successively lower elevations, and form characteristic lake sequences of two or more lakes. They may occur as multi-moraine-dammed lakes or mixed combined lakes such as moraine-rock-dammed lakes or multi-debris-dammed lakes. From special interest are in this study the paired moraine-dammed lakes (e.g. Lagunas Qoyllurcochas, Lagunas Safuna Alta and Baja). They are composed of the Great Endmoraine (GEM), primarily formed during the Little Ice Age and earlier, and the pre-GEM, formed during the Holocene. Both moraines are located in rather close vicinity to each other at a distance of 1-3 km. In contrast to the prominent sharp-crested GEM, the pre-GEM is a low-amplitude end-moraine complex, which usually does not exceed a few meters to tens of meters in height. The latter is often composed of several inserted moraine ridges or an irregular hummocky moraine landscape. It is argued here that the process of formation of these combined lakes is mainly controlled by a combination of distinct topographical

  6. Formation of minor moraines in high-mountain environments independent of a primary climatic driver

    NASA Astrophysics Data System (ADS)

    Wyshnytzky, Cianna; Lukas, Sven

    2016-04-01

    Closely-spaced minor moraines allow observations of moraine formation and ice-marginal fluctuations on short timescales, helping to better understand glacier retreat and predict its geomorphological effects (e.g. Sharp, 1984; Boulton, 1986; Bradwell, 2004; Lukas, 2012). Some minor moraines can be classified as annual moraines given sufficient chronological control, which implies a seasonal climatic driver of minor ice-front fluctuations. This leads to annual moraines being utilised as very specific and short-term records of glacier fluctuations and climate change. However, such research is sparse in high-mountain settings (Hewitt, 1967; Ono, 1985; Beedle et al., 2009; Lukas, 2012). This study presents the detailed sedimentological results of minor moraines at two high-mountain settings in the Alps. Minor moraines at Schwarzensteinkees, Austria, formed as push moraines in two groups, separated by a flat area and sloping zone with scattered boulders and flutings. The existence of a former proglacial lake, evident from ground-penetrating radar surveys and geomorphological relationships, appears to have exerted the primary control on minor moraine formation. Minor moraines at Silvrettagletscher, Switzerland, exist primarily on reverse bedrock slopes. The presence of these bedrock slopes, and in some areas medial moraines emerging beyond the ice front, appear to exert the primary controls on minor moraine formation. These findings show that climate may only play a small role in minor moraine formation at these study sites, echoing similar findings from another glacier in the Alps (Lukas, 2012). These two glaciers and valleys are differentiated primarily by geometry, sedimentation, and mechanisms of minor moraine formation. Despite these crucial differences, valley geometry and pre-existing geomorphology play a large, if not dominant, role in minor moraine formation and are at odds with a primarily-climatic control of minor moraine formation in lowland settings. This

  7. Radiostratigraphy and age structure of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    MacGregor, Joseph A.; Fahnestock, Mark A.; Catania, Ginny A.; Paden, John D.; Prasad Gogineni, S.; Young, S. Keith; Rybarski, Susan C.; Mabrey, Alexandria N.; Wagman, Benjamin M.; Morlighem, Mathieu

    2015-02-01

    Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.

  8. 500,000-year temperature record challenges ice age theory

    USGS Publications Warehouse

    Snow, K. Mitchell

    1994-01-01

    Just outside the searing heat of Death Valley lies Devils Hole (fig. 1), a fault-created cave that harbors two remnants of the Earth's great ice ages. The endangered desert pupfish (Cyprinodon diabolis) has long made its home in the cave. A 500,000-year record of the planet's climate that challenges a widely accepted theory explaining the ice ages also has been preserved in Devils Hole.

  9. Coeval fluctuations of the Greenland Ice Sheet and a local ice cap during the Younger Dryas: implications for late-glacial climate

    NASA Astrophysics Data System (ADS)

    Levy, Laura; Kelly, Meredith; Lowell, Tom; Hall, Brenda; Howley, Jennifer; Smith, Colby

    2016-04-01

    Although the Younger Dryas (YD) has been recorded in ice cores atop the Greenland Ice Sheet, past glacier extents on Greenland dating to the YD are rare. In part, this is due to much of the Greenland Ice Sheet being located offshore until early Holocene time. The Scoresby Sund region (~71°N, 26°W) of central East Greenland, however, is one of only a few locations where the margins of the Greenland Ice Sheet and glaciers independent of the ice sheet were located at least partially on land by late-glacial time. In this region, two distinct sets of moraines, known as the inner and outer Milne Land Stade moraines, have been defined and mark a significant readvance or stillstand during deglaciation from the last glacial maximum. Previous work has dated these moraines to late-glacial and early Holocene time. We present a new 10Be chronology on fluctuations of both the Greenland Ice Sheet and the adjacent Milne Land ice cap from the type locality of the Milne Land Stade moraines in Milne Land. 10Be ages of boulders on bedrock distal to the inner Milne Land Stade moraines range from 12.3 to 11.5 ka and indicate that both ice masses retreated during the YD, likely in response to rising summer temperatures. Since Greenland ice-cores register cold mean annual temperatures throughout the YD, these ice-marginal data support climate conditions characterized by strong seasonality. The mean ages (± 1σ uncertainty) of the inner Milne Land Stade moraines date to 11.4 ± 0.8 ka (Greenland Ice Sheet) and 11.4 ± 0.6 ka (ice cap) indicating that they were formed during Preboreal time or at the end of the YD. Based on these coeval moraine ages, we suggest that both ice masses responded to climate conditions acting on the ice margins, specifically ablation. Moreover, our data show that the ice sheet responded sensitively (i.e., on the same time scale as a small ice cap) to late-glacial and early Holocene climate conditions.

  10. Siple Dome ice reveals two modes of millennial CO2 change during the last ice age

    PubMed Central

    Ahn, Jinho; Brook, Edward J.

    2014-01-01

    Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

  11. Constraints on ice volume changes of the East Antarctic Ice Sheet and Ross Ice Shelf since the LGM based on cosmogenic exposure ages from Darwin-Hatherton outlet glaciers.

    NASA Astrophysics Data System (ADS)

    Fink, David; Joy, Kurt; Storey, Bryan

    2013-04-01

    At the Last Glacial Maximum and during Termination-1 (~20-10 ka), marine evidence indicates that the grounding line of the West Antarctic Ice Sheet (WAIS) advanced northwards into the Ross Ice Shelf (RIS), blocking drainage of the Darwin and Hatherton outlet glaciers through the Transantarctic Mountains (TM) resulting in significant downstream thickening of glacier profiles. These outlet glaciers provide geological and glaciological records of EAIS expansion through the TMs as well as WAIS fluctuations which together suggest an LGM thickness of ~800 m lager than today at their confluence with the Ross Embayment. About 80 cosmogenic 10Be and 26Al exposure ages of erratics from 3 locations flanking the Hatherton Glacier (Dubris Valley near the EAIS source region, from Lake Wellman at its midpoint and Diamond Hill at its terminus) taken along transects covering 800 m in differential elevation from ice-sheet contact to mountain peaks documents 2.5 Ma of ice volume evolution of the Hatherton allowing a reconstruction of its quaternary paleo-ice surface. Pleistocene ice thickness is some 800 to 400 meters thicker between 2.5 to 0.5 Ma years ago than today . However at all 3 locations, exposure ages of mapped glacial drifts younger than 0.5 Ma at lower elevations down to current ice margin did not show any evidence for a distinct LGM advance. At Lake Wellman a cluster of mid-elevation moraine boulders from the Britannia Drift, previously taken to demarcate the LGM advance, have exposure ages ranging from 30 to 40 ka. At Dubris Valley, the same drift returned ages of 120-125 ka. At Diamond Hill, the confluence of the Darwin Glacier and RIS, two transects were sampled that cover an altitude range of 1100 meters. Cosmogenic dates show a similar trend to that seen further upvalley - the WAIS was approximately 900 meters thicker than the current Rose Ice Shelf configuration at ~1.5Ma and with only minor advances in the last 10ka and an absence of any LGM ages. The absence of a

  12. A Lateglacial to late Holocene glacial chronology for the Cairngorm Mountains (Scotland): effects of boulder inheritance and snow shielding on age distributions.

    NASA Astrophysics Data System (ADS)

    Kirkbride, Martin; Everest, Jez; Benn, Doug

    2014-05-01

    It is thought that British glaciers disappeared after the Younger Dryas Stadial (YDS, 12.9 - 11.7 k yr). We present cosmogenic 10Be ages of cirque moraines in the Cairngorm Mountains which include two Lateglacial advances, a speculative early Holocene advance, and a late Holocene moraine probably deposited by a Little Ice Age glacier ( 17th - 18th century AD). One cirque (CLE) contains evidence of a YDS advance peaking at c. 12.3 k yr, and a probable Little Ice Age (LIA) advance dated to <0.9 k yr. Another cirque (CLW) has an outer moraine dated to between 15.3 and 12.0 k yr. An inner moraine, conventionally regarded as YDS in age, yields 10Be ages of 11.5 to 8.3 k yr (Lal/Stone time-dependent production model). The putative YDS moraines are well dated in cirque CLE, but appear too "young" in CLW. We consider how snow-shielding and boulder recycling may have affected age distributions. If these ages are minima from a YDS moraine, snow-shielding and delayed deposition from debris-covered ice may explain low 10Be concentrations, but this does not explain why similar adjustments are not needed in the neighbouring cirque. Alternatively, ages may be maxima from an early Holocene moraine which incorporated existing boulders. The LIA moraine in CLE contains a high proportion of inherited boulders, but the YDS moraine here contains few. Therefore the proportion of inherited boulders is estimated to be a function of the ratio of debris production during the glacial period and debris production during the preceding paraglacial period. The ratio describes the likelihood of sampling an inherited boulder if the geomorphological history is understood. By this reasoning, an alternative interpretation of the "YDS" moraine in CLW is that an early Holocene glacier (speculatively, the 8.2 k event?) incorporated post-YDS paraglacial rock fall debris.

  13. Modelling the climate, ice sheet and thermohaline circulation during the ice age termination

    NASA Astrophysics Data System (ADS)

    Abe-Ouchi, A.; Saito, F.; Kawamura, K.; Ohgaito, R.; Chikamoto, M. O.; Oka, A.; Yoshimori, M.; Yokoyama, Y.

    2009-12-01

    One of the challenges of earth system modeling is to explain the mechanism of ice age cycle by simulating it and to understand the uniqueness or necessity of the present state of climate and cryosphere. Whether Milankovitch cycle or CO2 is the driver and why the dominant periodicity of ice age cycle switched from 40 ka cycle to 100ka cycle and why a sharp termination occur for each ice age cycle have been remained unsolved. Here we simulate the glacial cycle and investigate the origin of saw-tooth shape 100ka cycle using a three dimensional ice sheet model with the input examined by GCM. The model is forced by the orbital parameters (Berger, 1978) and atmospheric CO2 content obtained by ice cores (Vostok, EPICA and DomeF), whose dating is partly given by a new method using the N2/O2 ratio. The ice sheet model includes the thermo-mechanical coupling process of ice sheet with the process of delayed isostatic rebound with a typical time constant. In order to estimate the climate sensitivity to Milankovitch forcing and atmospheric CO2 indicated by ice core data we used an atmospheric GCM (part of MIROC GCM) coupled to a slab ocean and full MIROC AOGCM in part of the work. Within the range of possibilities of the model, ice age cycles with a saw-tooth shape 100 ka cycle, the major NH ice sheets’ volume and the geographical distribution at the glacial maximum are successfully simulated. Moreover the role of Atmospheric stationary wave feedback are found to be important to sharpen the termination. It is shown by sensitivity studies that this 100ka cycle is mainly obtained by the slowly acting ice sheet response to Milankovitch forcing even without the CO2 cycle. The CO2 change amplifies the cycle and affects the global climate change, while the delay of crustal rebound sharpens the termination of every ice age cycle. In order to study the effect of thermohaline circulation, the sensitivity of AOGCM (by MIROC) is separately studied by applying time slice experiments of

  14. The deglaciaton of the Pyreenes: from the Oldest Dryas to the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Palacios, David; de Andrés, Nuria; López-Moreno, Juan I.; García-Ruiz, José M.

    2014-05-01

    The main purpose of the paper is to study the deglaciation process, including the retreat of the glaciers and the occurrence of short advances with the deposition of new, relatively recent tills in two head valleys of the central-southern Pyrenees: The Upper Gállego Valley, with the main peak Balaitus (42°46'0' N, 0° 15'0'W, 3151 m), and the Marbore Cirque, at the head of the Cinca Valley, on the north face of the Monte Perdido Peak (42º400' N; 0.5º0'W; 3355 m). The deglaciation process was studied through geomorphological mapping and 36Cl cosmogenic exposure ages obtained from morainic and rock glacier boulders and polished bedrocks. Even though the exact position of the front glacier during the global Last Glacial Maximum is not known, there is evidence that the different ice tongues retreated until headwater positions, causing the subdivision of the main glaciers into various individual glaciers. Two clear climate reversals within the general trend to deglaciation have been detected: First of all, the Oldest Dryas, coinciding with the Heinrich Event 1 (ca 17-15 ka) and, secondly, the Younger Dryas (ca 13-11.7 ka). Between both stadials, the Bølling/Allerød Interstadial (ca 15-13 ka) represented an intense glacial retreat up to the cirque headwalls. During the Bølling/Allerød Interstadial the retreat was very rapid, although the occurrence of a short readvance of small glaciers during the Older Dryas must not be ruled out. The Younger Dryas is represented by a new glacial push with the deposition of distinct types of tills. During these late glacier advances, small glaciers and rock glaciers developed close to the cirque headwalls, and coexisted under the same climatic conditions. After the Younger Dryas, new glacial advances has not been detected until the Little Ice Age, except in the Marbore Cirque, where glacial expansion occurred during the Mid and Late Holocene (5.1 ± 0.1 ka), represented by a large push moraine. A melting phase occurred at

  15. Late Pleistocene ice-shelf, valley-glacier and ice-sheet interactions on Alexander Island, Antarctic Peninsula: implications for climatic and ice-volume changes

    NASA Astrophysics Data System (ADS)

    Davies, Bethan; Hambrey, Michael; Glasser, Neil; Smellie, John; Carrivick, Jonathan; Bentley, Michael

    2014-05-01

    Recent rapid warming across the Antarctic Peninsula has resulted in ice-sheet thinning, dramatic ice-shelf collapse, acceleration of ice-flow velocities and widespread glacier recession. Reconstructing past rates, volumes and magnitudes of cryospheric change, particularly with respect to the former configuration of ice sheets and ice shelves, and their response to changing oceanic and climatic regimes, is vital in providing a context for this change, in order to improve predictions of future ice-sheet behaviour, and to provide glacio-isostatic adjustment corrections for gravimetric measurements of contemporary ice loss. This research aimed to investigate valley glacier and ice-shelf interactions during the Last Glacial Maximum (LGM) and Holocene Epoch across George VI Sound and Alexander Island, western Antarctic Peninsula, an area with a well-preserved but poorly dated record. We identify four principal stratigraphic units: (1) a high-elevation drift with Alexander Island erratics only (interpreted as recording older advances of ice from the interior of the island), (2) a lower-elevation drift with exotic Palmer Land erratics (interpreted as ice-shelf moraine, representing incursions of George VI Ice Shelf onto Ablation Point Massif), (3) multiple overlapping sequences of valley glacier moraine and ice-shelf moraine, presumed to be Holocene in age, and (4) more recent processes and units, including frozen epishelf lakes, slope processes and alluvial fans. On-going cosmogenic nuclide dating on these sediments (in progress; 25 10Be exposure ages) has the potential to unlock the complex history and interactions of ice streams, valley glaciers and ice shelves in this area. This work will also provide the first long-term record of sea-level indicators, allowing the first estimates of glacial unloading, rates of uplift and ice-sheet thinning to be calculated. The Holocene record of the ice shelf, preserved in the younger ice-shelf moraines and in the overlapping

  16. Regional significance of an early Holocene moraine in Enchantment Lakes basin, North Cascade Range, Washington

    USGS Publications Warehouse

    Waitt, R.B., Jr.; Yount, J.C.; Davis, P.T.

    1982-01-01

    The upper Enchantment Lakes basin in the North Cascade Range of Washington displays two moraine belts, each recording an episode of glacier advance after the end of the last glaciation. The inner belt, the Brynhild, 0.1 to 0.5 km beyond existing glaciers, postdates Mount St. Helens Wn tephra (???450 yr old), which lies only beyond the moraines. The morainal surface is only slightly weathered, is almost barren of lichens, and is devoid of soil, evidence suggesting that the Brynhild moraines are no more than a century old. The outer moraine, the Brisingamen, 0.3 to 0.7 km beyond existing glaciers, is weathered and is covered with large lichens. On and behind the Brisingamen moraine the Mazama ash (6900 yr old) is present beneath the Mount St. Helens Yn and Wn tephras. Despite more than 7 millennia of weathering, the rock surface behind the Brisingamen moraine is measurably less weathered than the surface beyond, which was last glaciated during the Rat Creek advance about 13,000 yr ago. The age of the Brisingamen moraine therefore is probably early Holocene. The Brisingamen moraine evidently correlates with moraines near Glacier Peak, near Mount Rainier, in northeastern and central Oregon, in the southern Canadian Rockies, and in the northern U.S. Rocky Mountains. These regional effects suggest that a climatic episode of cooling or increased snowfall affected the entire region some time during the early Holocene. ?? 1982.

  17. Ice-age simulations with a caving ice-sheet model

    SciTech Connect

    Pollard, D.

    1982-01-01

    Further extensions and results of a simple northern hemispheric ice-sheet model are described for the Quaternary ice ages. The basic model predicts ice thickness and bedrock deformation in a north-south cross section, with a prescribed snow-budget distribution shifted uniformly in space to represent the orbital perturbations. An ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level. As in Pollard (1982a) the basic model produces a large approx. 100,000-yr response and agrees fairly well with the delta/sup 18/O deep-sea core records. Three extensions of the model are described: an alternative treatment of bedrock deformation, a more realistic ice-shelf model of ice calving, and a generalized parameterization for such features as the North Atlantic deglacial meltwater layer. Much the same ice-age simulations and agreement with the delta/sup 18/O records as with the original model are still obtained. The observed phase-correlation between the 100,000-yr cycles and eccentricity is examined. First, the model is shown to give a approx. 100,000-yr response to nearly any kind of higher-frequency forcing. Although over the last two million years the model phase is mainly controlled by the precessional modulation due to eccentricity, over just the last 600,000-yr the observed phase can also be simulated with eccentricity held constant. A definitive conclusion on the phase-control of the Quaternary ice ages is prevented by uncertainty in the deep-sea core time scales before approx. 600,000-yr B.P. In an appendix the model is applied to West Antarctica where unforced internal oscillations occur with periods of about 50,000-yr.

  18. Little Ice Age glaciers in the Mediterranean mountains

    NASA Astrophysics Data System (ADS)

    Hughes, Philip

    2014-05-01

    Only a few small glaciers survive today in the Mountains of the Mediterranean. Notable examples are found in the Pyrenees, Maritime Alps, Italian Apennines, the Dinaric and Albanian Alps and the mountains of Turkey. Many glaciers disappeared during the 20th Century. Glaciers were much larger and more numerous during the Little Ice Age (Hughes, 2014). Small glaciers even existed as far south as the High Atlas of Morocco and the Sierra Nevada of southern Spain. In more northerly areas, such as the western Balkans, glaciers and permanent snow patches occupied hundreds of cirques on relatively low-lying mountains. In the High Atlas and the Sierra Nevada no glaciers exist today, whilst in the Balkans only a few modern glaciers have been reported. A similar situation is apparent throughout the mountains of the Mediterranean region. New evidence for glacier change since the Little Ice Age will be published soon in Hughes (2014) and this paper reviews the extent, timing and climatic significance of Little Ice Age glaciation in the Mediterranean region. Reference: Hughes, P.D. (2014) Little Ice Age glaciers in the Mediterranean mountains. In: Carozza, J.-M., Devillers, B., Morhange, C. (eds) Little Ice Age in the Mediterranean, Méditerranée, volume 123.

  19. Measurements of Past Ice Sheet Elevations in Interior West Antarctica.

    PubMed

    Ackert; Barclay; Borns; Calkin; Kurz; Fastook; Steig

    1999-10-01

    A lateral moraine band on Mount Waesche, a volcanic nunatak in Marie Byrd Land, provides estimates of past ice sheet surface elevations in West Antarctica. Helium-3 and chlorine-36 surface exposure ages indicate that the proximal part of the moraine, up to 45 meters above the present ice surface, was deposited about 10,000 years ago, substantially later than the maximum ice extent in the Ross Embayment. The upper distal part of the moraine may record multiple earlier ice sheet high stands. A nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at Mount Waesche relative to the maximum ice extent in the Ross Sea. The glacial geologic evidence, coupled with the ice sheet model, indicates that the contribution of the Ross Sea sector of the West Antarctic Ice Sheet to Holocene sea level rise was only about 3 meters. These results eliminate West Antarctic ice as the principle source of the large meltwater pulse during the early Holocene. PMID:10514368

  20. Ice Nucleation Properties of Amospherically Aged Biomass Burning Aerosol

    NASA Astrophysics Data System (ADS)

    Polen, M.; Lawlis, E.; Sullivan, R. C.

    2015-12-01

    Biomass burning can sometimes emit surprisingly active ice nucleating particles, though these emissions are not at all consistent between biomass fuel sources and burns. Soot from biomass combustion has been attributed to some but not all of the ice nucleating potential of biomass burning aerosol (BBA), while fossil fuel combustion soot emits very weak ice nucleants. The causes of the sometimes significant but variable ice nucleating ability of BBA are still largely unknown. BBA experiences significant atmospheric aging as the plume evolves and mixes with background air, yet almost no reports exploring the effects of atmospheric aging on the freezing properties of BBA have been made. We have performed some of the first experiments to determine the effects of simulated atmospheric aging on these ice nucleation properties, using a chamber reactor. The fresh and aged BBA was collected for subsequent droplet freezing array analysis using an impinger sampler to collect aerosol in water, and by deposition onto substrates in a MOUDI sampler. Droplets containing the chamber particles were then suspended in oil on a cold plate for freezing temperature spectrum measurement. Aging of Sawgrass flaming-phase combustion BBA by exposure to hydroxyl radicals (from H2O2 photolysis) enhanced the ice nucleation ability, observed by a shift to warmer droplet freezing temperatures by ~2-3°C. The changes in the aerosol's chemical composition during aging were observed using a laser ablation single-particle mass spectrometer and a soot-particle aerosol mass spectrometer. We will report our observations of the effects of other types of simulated aging (including photochemistry under high and low NOx conditions, dark ozonolysis, and nitric acid exposure) on Sawgrass and BBA from other grass and palm fuels.

  1. Hydrothermal calcite in the Elephant Moraine

    SciTech Connect

    Faure, G.; Taylor, K.S.; Jones, L.M.

    1986-01-01

    In the course of geologic mapping of the Elephant Moraine on the east antarctic ice sheet, Faure and Taylor (1985) collected several specimens of black botryoidal calcite, composed of radiating acicular crystals that resemble stromatolites. Calcite from this and other specimens is significantly enriched in strontium-87 (the strontium-87/strontium-86 ratio equals 0.71417 +/- 0.00002), carbon-12 (delta carbon-13 equals -22.9 parts per thousand, PDB standard) and oxygen-16 (delta oxygen-18 equals -21.1 parts per thousand, standard mean ocean water) compared with calcite of marine origin. The enrichment in carbon-12 is similar to that of calcite associated with coal in the Allan Hills. The enrichment in oxygen-16 indicates that the calcite from the Elephant Moraine could only have precipitated in isotopic equilibrium with glacial melt water. Therefore, the temperature at which the black calcite precipitated from water of that isotope composition was about 85/sup 0/C. A temperature of this magnitude implies that the black calcite formed as a result of volcanic activity under the east antarctic ice sheet. The enrichment of the black calcite in carbon-12 suggests that it formed in part from carbon dioxide derived from the coal seams of the Weller Formation in the Beacon Supergroup. The isotopic composition of strontium in the black calcite is similar to that of carbonate beds and concretions in the Beacon rocks of southern Victoria Land. A volcanic-hydrothermal origin is also consistent with the very low total organic carbon content of 0.15% in the calcite.

  2. Ice-age rain forest found moist, cooler

    SciTech Connect

    Kerr, R.A.

    1996-10-04

    Climate researchers have argued for years about whether the tropics cooled a little or a lot during the height of the last ice age 18000 years ago. The answer will offer clues to the sensitivity of the Earth`s climate system to the strengthening greenhouse effect. On a different front, arguments have raged about how the Amazon flora and fauna became so divers. A single study of lake mud from deep in the Amazon rain forest sheds new light on both of these controveries by point toward a cool, but still wet ice age Amazon. This article goes on to discuss the background of the study, other view points, and the implications.

  3. An ice age recorded in the polar deposits of Mars

    NASA Astrophysics Data System (ADS)

    Smith, Isaac B.; Putzig, Nathaniel E.; Holt, John W.; Phillips, Roger J.

    2016-05-01

    Layered ice deposits at the poles of Mars record a detailed history of accumulation and erosion related to climate processes. Radar investigations measure these layers and provide evidence for climate changes such as ice advance and retreat. We present a detailed analysis of observational data showing that ~87,000 cubic kilometers of ice have accumulated at the poles since the end of the last ice age ~370,000 years ago; this volume is equivalent to a global layer of ~60 centimeters. The majority of the material accumulated at the north pole. These results provide both a means to understand the accumulation history of the polar deposits as related to orbital Milankovitch cycles and constraints for better determination of Mars’ past and future climates.

  4. An ice age recorded in the polar deposits of Mars.

    PubMed

    Smith, Isaac B; Putzig, Nathaniel E; Holt, John W; Phillips, Roger J

    2016-05-27

    Layered ice deposits at the poles of Mars record a detailed history of accumulation and erosion related to climate processes. Radar investigations measure these layers and provide evidence for climate changes such as ice advance and retreat. We present a detailed analysis of observational data showing that ~87,000 cubic kilometers of ice have accumulated at the poles since the end of the last ice age ~370,000 years ago; this volume is equivalent to a global layer of ~60 centimeters. The majority of the material accumulated at the north pole. These results provide both a means to understand the accumulation history of the polar deposits as related to orbital Milankovitch cycles and constraints for better determination of Mars' past and future climates. PMID:27230372

  5. Laurentide Ice Sheet dynamics in the Bay of Fundy, Canada, revealed through multibeam sonar mapping of glacial landsystems

    NASA Astrophysics Data System (ADS)

    Todd, Brian J.; Shaw, John

    2012-12-01

    Recent multibeam sonar data collected in the Bay of Fundy, Canada, interpreted in conjunction with geophysical profiling and sediment sampling, reveal in unprecedented detail a suite of glacial landforms associated with the southwest margin of the Laurentide Ice Sheet. These landforms constitute four glacial landsystems. 1) Subglacial landsystem I: In southwestern Bay of Fundy, the elongated Grand Manan Basin contains ice-contact sediments of possible mid-Wisconsinan age overlain by late-Wisconsinan ice-contact sediments strongly imprinted by iceberg furrows and pits. In places, possible mid-Wisconsinan glaciomarine sediments have been eroded by late-Wisconsinan ice, creating streamlined landforms. Eroded bedrock and megafluted ice-contact sediment on the flanks of Grand Manan Basin indicate the southwest direction of topographically-steered ice. 2) Subglacial landsystem II: Along the southern margin of the Bay of Fundy, an array of drumlins, with superimposed esker complexes, was formed by glacial ice that emanated northwest from the interior of Nova Scotia and was deflected to the southwest by the ice flowing out of the Bay of Fundy to the Gulf of Maine. The esker complexes formed later when the Nova Scotia ice sheet stagnated and meltwater escaped northwest via topographic gaps. 3) Ice-marginal landsystem I: In northern Bay of Fundy, both small De Geer moraines and larger, basin-bounding moraines were created when retreating late-Wisconsinan ice became grounded in relatively shallow water. New radiocarbon ages show that the Owen Basin Moraine in this landsystem was abandoned prior to c. 14,600 14C yr BP (cal BP 17,015-17,270 [0.7], 17,286-17,405 [0.3]). 4) Ice-marginal landsystem II: This distinctive landsystem consists of numerous arcuate moraines, commonly superimposed on one another. This landsystem was formed by thin (170 m), lightly grounded ice that retreated northeast into the Bay of Fundy. The splayed pattern of the ice margin was a response to a large

  6. The deglacial history of the Lake Michigan lobe in Illinois, USA, fleshed out by chronologies associated with ice-walled lakes

    NASA Astrophysics Data System (ADS)

    Curry, B.

    2009-12-01

    The onset of deglaciation of the Lake Michigan lobe (LML) in the western Great Lakes region of North America is well-defined by radiocarbon ages from terrestrial plant material that was buried by proglacial lake sediment and till. A small portion of the lobe began its final retreat during the Marengo Phase at about 24,780 C-14 yr BP (29,630 cal yr BP) [CalPal]; most of the lobe began its final retreat during the Shelby Phase starting at about 19,350 C-14 yr BP (23,010 cal yr BP)[Calib 5.02]. New radiocarbon ages from tundra plant fossils encased in the deposits of ice-walled lakes allow estimation periods of ice stagnation vs. margin advance as well as constraining the age of important events during the late Wisconsin Episode. For example, radiocarbon ages from fossils in ice-walled deposits indicate the LML margin began its final retreat from Illinois at the onset of the Mackinaw lake phase by about 13,650 C-14 yr BP (16,250 cal yr BP). Located on the Marseilles Morainic System, the oldest dated ice-walled lake deposit known in Illinois began to form at 18,210 C-14 yr BP (21,680 cal yr BP). From its end moraine located near Peoria to Chicago on the shores of southern Lake Michigan, the LML extended about 230 km. Collectively, the ages indicate that the outer 100 km of the LML margin retreated about three times faster than the inner 130 km (7.5 x 10-2 km/yr vs. 2.4 x 10-2 km/yr). Changes in ice thickness and dynamics, debris concentration, climate, and regional drainage are some of the likely factors that affected the difference in rate. The existing data provide conservative estimates for the formation of two moraines, the lake-border Deerfield Moraine (720 cal yrs) and the Tinley Moraine (850 cal yrs). Periods of stagnations, marked by radiocarbon ages from fossils in the ice-walled lake sediments, include about 320 years (Deerfield Moraine), 520 cal yrs (Tinley Moraine), 500 cal yrs (Woodstock Moraine), and 710 years (Ransom Moraine). These and other ages

  7. Greenhouse effect and ice ages: historical perspective

    NASA Astrophysics Data System (ADS)

    Bard, Edouard

    2004-06-01

    This article provides a brief historical perspective on the first scientific research on the greenhouse effect and glaciations. While these two aspects of our climate can be investigated separately, naturalists, physicists and chemists during the 19th century were interested jointly in both issues, as well as the possible relationship between them. The contributions of famous pioneers are mentioned, ranging from scholars with encyclopaedic knowledge such as Horace-Bénédict de Saussure, to modern scientists like Svante Arrhenius, who was first to predict global warming as a consequence of using fossil fuels. Despite fragmentary observations, these pioneers had prophetic insights. Indeed, the main fundamental concepts used nowadays have been developed during the 19th century. However, we must wait until the second half of the 20th century to see a true revolution of investigative techniques in the Earth Sciences, enabling full access to previously unknown components of the climate system, such as deep oceans and the interior of the polar ice caps. To cite this article: E. Bard, C. R. Geoscience 336 (2004).

  8. Population genetics of ice age brown bears.

    PubMed

    Leonard, J A; Wayne, R K; Cooper, A

    2000-02-15

    The Pleistocene was a dynamic period for Holarctic mammal species, complicated by episodes of glaciation, local extinctions, and intercontinental migration. The genetic consequences of these events are difficult to resolve from the study of present-day populations. To provide a direct view of population genetics in the late Pleistocene, we measured mitochondrial DNA sequence variation in seven permafrost-preserved brown bear (Ursus arctos) specimens, dated from 14,000 to 42,000 years ago. Approximately 36,000 years ago, the Beringian brown bear population had a higher genetic diversity than any extant North American population, but by 15,000 years ago genetic diversity appears similar to the modern day. The older, genetically diverse, Beringian population contained sequences from three clades now restricted to local regions within North America, indicating that current phylogeographic patterns may provide misleading data for evolutionary studies and conservation management. The late Pleistocene phylogeographic data also indicate possible colonization routes to areas south of the Cordilleran ice sheet. PMID:10677513

  9. Airborne LiDAR DEMs as a tool for deriving information on past glacier extent and ice flow

    NASA Astrophysics Data System (ADS)

    Seiser, Bernd; Fischer, Andrea

    2014-05-01

    The quantification of ice volumes and the identification of ice flow regimes within historical glacier systems are important steps towards understanding historical phases of glacier advance and disintegration in the context of Holocene climate fluctuation. Topographic LiDAR DEMs provide an excellent tool for gaining various kinds of spatially distributed information. Several case studies have been performed in the Austrian Alps, where LiDAR DEMs are available for almost the entire glacier area. LiDAR DEMs achieve vertical accuracies of few decimetres and can be used to calculate hillshade images with flat incidence angles, so that the surface structures of moraines and other glacial deposits can be identified. These hillshade images were used together with aerial photographs to identify the LIA (Little Ice Age) moraines and the elevation of the lateral moraines, so that, together with information on today's ice volume, a lower limit for the LIA ice volume could be calculated. The resulting LIA glacier areas showed good coincidence with former reconstructions based on field mapping and airborne photogrammetry. In addition to that, historical ice flow directions could be derived from the structure of basal moraines. These data allow an interpretation of the changing contribution of specific tributary glaciers to a joint glacier tongue, which may result in an important switch in ice dynamics leading to fast glacier advances recorded by frontal moraines. The combination of terrestrial long-term observations and LiDAR data documents the genesis of specific geomorphological features in the periglacial area by recording the processes occurring during the disintegration of glacier tongues. For example, the deposition of the material from former medial moraines in the newly formed periglacial area can be identified and quantified from the LiDAR data as well as debris flows or rock falls from the LIA moraines.

  10. Late pleistocene ice age scenarios based on observational evidence

    SciTech Connect

    DeBlonde, G. ); Peltier, W.R. )

    1993-04-01

    Ice age scenarios for the last glacial interglacial cycle, based on observations of Boyle and Keigwin concerning the North Atlantic thermohaline circulation and of Barnola et al. concerning atmospheric CO[sub 2] variations derived from the Vostok ice cores, are herein analyzed. Northern Hemisphere continental ice sheets are simulated with an energy balance model (EBM) that is asynchronously coupled to vertically integrated ice sheets models based on the Glen flow law. The EBM includes both a realistic land-sea distribution and temperature-albedo feedback and is driven with orbital variations of effective solar insolation. With the addition of atmospheric CO[sub 2] and ocean heat flux variations, but not in their absence, a complete collapse is obtained for the Eurasian ice sheet but not for the North American ice sheet. We therefore suggest that further feedback mechanisms, perhaps involving more accurate modeling of the dynamics of the mostly marine-based Laurentide complex appears necessary to explain termination I. 96 refs., 12 figs., 2 tabs.

  11. Recent Deglaciation of Darwin Mountains (Tierra de Fuego) after Little Ice Age: monitoring by photogrammetry, lichenometry, dendrochronology and field studies.

    NASA Astrophysics Data System (ADS)

    García-Sancho, L.; Palacios, D.; Zamorano, J. J.; Green, A.; Vivas, M.; Pintado, A.

    2012-04-01

    Glaciers from the Darwin mountain range have been retreating since the Little Ice Age (LIA). However, the amount of retreat varies and is minimal for some glacial snouts and substantial for others. Possible explanations for this different behaviour include climatic and glacial dynamic causes. The aim of this work was to analyse the impact of climate change on these glaciers. The research site was the terminus of glacier Pia, which descends to the south of Mount Darwin (2488 m asl, 54°45'S, 69°29'W) and reaches the coastline at the Beagle Channel. The terminus is situated some hundreds of meters above the LIA moraine but, whereas one sector retreated rapidly and then stabilized, another sector has had several advances and retreats leaving a number of moraine arches. To better understand the origin of this dynamic behaviour, we undertook a study of the evolution of the terminus of glacier Pia over the last 60 years. We used aerial photographs and satellite images to determine the exact location of the glacial terminus in certain years (1943, 1963, 1987, 1990, 2001 and 2006). These results were completed in 2008 and 2009 through field work. We also carried out lichenometric studies of the two most abundant lichen species that rapidly colonize the moraine boulders abandoned by the glacier: Placopsis perrugosa and Rhizocarpon geographicum. By comparing results from field work carried out in 2008 and 2009, we were able to determine the growth rate of these two species (García-Sancho et al. 2011). In addition, we also carried out a dendrochronological study of Nothofagus antarctica and N. betuloides. The use of the four techniques involved in this study (photogrammetry, lichenometry, dendrochronology and multiyear field work) allowed us to establish the ecesis period of each species as well as their growth curves, from which we can deduce the movements of the glacial terminus from the end of the LIA to the present. From this study we can infer that the different

  12. Airborne LiDAR detection of postglacial faults and Pulju moraine in Palojärvi, Finnish Lapland

    NASA Astrophysics Data System (ADS)

    Sutinen, Raimo; Hyvönen, Eija; Middleton, Maarit; Ruskeeniemi, Timo

    2014-04-01

    Postglacial faults (PGFs) are indicative of young tectonic activity providing crucial information for nuclear repository studies. Airborne LiDAR (Light Detection And Ranging) data revealed three previously unrecognized late- or postglacial faults in northernmost Finnish Lapland. Under the canopies of mountain birch (Betula pubescens ssp. czerepanovii) we also found clusters of the Pulju moraine, typically found on the ice-divide zone of the former Fennoscandian ice sheet (FIS), to be spatially associated with the fault-scarps. Tilt derivative (TDR) filtered LiDAR data revealed the previously unknown Palojärvi fault that, by the NE-SW orientation parallels with the well documented Lainio-Suijavaara PGF in northern Sweden. This suggests that PGFs are more extensive features than previously recognized. Two inclined diamond drill holes verified the fractured system of the Palojärvi fault and revealed clear signs of postglacial reactivation. Two other previously unrecognized PGFs, the W-E trending Paatsikkajoki fault and the SE-NW trending Kultima fault, differ from the Palojärvi faulting in orientation and possibly also with regard to age. The Pulju moraine, a morphological feature showing transitions from shallow (< 2-m-high) circular/arcuate ridges to sinusoidal/anastomosing esker networks was found to be concentrated within 6 km from the Kultima fault-scarp. We advocate that some of the past seismic events took place under the retreating wet-base ice sheet and the increased pore-water pressure triggered the sediment mass flows and formation of the Pulju moraine-esker landscape.

  13. 10Be ages of glacial and meltwater features northwest of Lake Superior: a chronology of Laurentide Ice sheet deglaciation and eastward flooding from Glacial Lake Agassiz

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Fisher, T. G.; Lowell, T.; Barnett, P.; Schaefer, J. M.; Schwartz, R.

    2009-12-01

    Significant controversy exists as to the role of Laurentide Ice Sheet meltwater in causing the Younger Dryas cold event. Recently, Lowell et al. (2009) presented a radiocarbon chronology of Laurentide Ice Sheet deglaciation along a north-south transect located northwest of Lake Superior. These authors concluded that the presence of the Laurentide Ice Sheet precluded an eastward drainage of glacial Lake Agassiz until mid-Younger Dryas time. Here, we use 10Be surface exposure dating to examine the timing of the eastward drainage of Lake Agassiz. We present 10Be ages of moraines and erratic boulders in meltwater pathways along the same transect as Lowell et al. (2009), northwest of Lake Superior. In general, 10Be ages of glacial features are similar to, or slightly older than, basal radiocarbon ages of nearby lakes. Based on the 10Be chronology, deglaciation of the Laurentide Ice Sheet in this region occurred between ~13,000 and 10,000 yr BP. We also present the first direct ages of flood deposits in bedrock channels presumably associated with the eastern drainage of Lake Agassiz. Evidence for flooding includes extensive channels incised into bedrock and enormous bedforms located north of Lake Superior. 10Be ages of two flood deposits near the Roaring River and Mundell Lake yield mean 10Be ages of ~11,700 and 11,000 yr BP, respectively. These ages indicate that occupation of the channels postdates initiation of the Younger Dryas by more than 1,000 years and are in general agreement with a basal radiocarbon age from nearby Lower Vail Lake (Teller et al., 2005). Preliminary paleohydrological estimates based on bedform clast sizes and channel geometries are velocities and discharges of 2.8-19.8 ms-1 and 4,200-30,000 m3s-1 at the Roaring River location and 2.5-17.5 ms-1 and 49,000-349,000 m3s-1 at the Mundell Lake location.

  14. Moraine-dammed lake failures in Patagonia and assessment of outburst susceptibility in the Baker Basin

    NASA Astrophysics Data System (ADS)

    Iribarren Anacona, P.; Norton, K. P.; Mackintosh, A.

    2014-12-01

    Glacier retreat since the Little Ice Age has resulted in the development or expansion of hundreds of glacial lakes in Patagonia. Some of these lakes have produced large (≥ 106 m3) Glacial Lake Outburst Floods (GLOFs) damaging inhabited areas. GLOF hazard studies in Patagonia have been mainly based on the analysis of short-term series (≤ 50 years) of flood data and until now no attempt has been made to identify the relative susceptibility of lakes to failure. Power schemes and associated infrastructure are planned for Patagonian basins that have historically been affected by GLOFs, and we now require a thorough understanding of the characteristics of dangerous lakes in order to assist with hazard assessment and planning. In this paper, the conditioning factors of 16 outbursts from moraine-dammed lakes in Patagonia were analysed. These data were used to develop a classification scheme designed to assess outburst susceptibility, based on image classification techniques, flow routine algorithms and the Analytical Hierarchy Process. This scheme was applied to the Baker Basin, Chile, where at least seven moraine-dammed lakes have failed in historic time. We identified 386 moraine-dammed lakes in the Baker Basin of which 28 were classified with high or very high outburst susceptibility. Commonly, lakes with high outburst susceptibility are in contact with glaciers and have moderate (> 8°) to steep (> 15°) dam outlet slopes, akin to failed lakes in Patagonia. The proposed classification scheme is suitable for first-order GLOF hazard assessments in this region. However, rapidly changing glaciers in Patagonia make detailed analysis and monitoring of hazardous lakes and glaciated areas upstream from inhabited areas or critical infrastructure necessary, in order to better prepare for hazards emerging from an evolving cryosphere.

  15. Meteorites constrain the age of Antarctic ice at the Frontier Mountain blue ice field (northern Victoria Land)

    NASA Astrophysics Data System (ADS)

    Folco, L.; Welten, K. C.; Jull, A. J. T.; Nishiizumi, K.; Zeoli, A.

    2006-08-01

    We show that meteorites can provide chronological constraints upon the age of the ice cropping out at the Frontier Mountain meteorite trap (Antarctica) when their terrestrial age is placed in a glaciological context. Amongst the over 700 meteorites found so far, Frontier Mountain (FRO) 84001, 99028, 93005 and 93054 were most likely not wind-drifted across the ice field, since their masses (772-1665 g) are much heavier than the local ˜ 200 g wind transport threshold. The four meteorites were found along a stretch of ice where a representative section of the Frontier Mountain blue ice crops out. Based on the bedding of englacial tephra layers, the structure of the ice along the section appears to be essentially an up-glacier dipping monocline. The 14C terrestrial age of FRO 8401, 99028 and 93005 are 13 ± 2, 21 ± 3 and 27 ± 2 ky, respectively; the 41Ca/ 36Cl age of FRO 93054 is 40 ± 10 ky. The terrestrial ages of the four meteorites increase from the top to the bottom layers of the monocline. This geographic distribution is best explained by delivery of meteorites at the ice surface through the "ice-flow model" (i.e., englacial transport from the snow accumulation zone and exhumation in the blue ice area through ablation) rather than direct fall. Since the effect of ablation in decoupling terrestrial ages of meteorites and the age of the ice on which they sit must have been minor (most likely ≤ 7 ky) based on the local ice dynamics, we conclude that the age of the bulk of the ice body currently under ablation at Frontier Mountain is up to ˜ 50 ky old. This result has implications on both the meteorite concentrations mechanism at Frontier Mountain and the regional ice dynamics.

  16. Chilly ice-age tropics could signal climate sensitivity

    SciTech Connect

    Kerr, R.A.

    1995-02-17

    A classic 1976 study, CLIMAP, indicated that the tropical ocean cooled less than 2C during the worst of the last ice age while the rest of the world experienced a 5C chill. However, this climatic buffering in the tropics has come under attack with new evidence and possible errors in the original study. This article discusses new evidence about climate sensitivity in the tropics and reinterpertation in climate models.

  17. Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

    USGS Publications Warehouse

    Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

    2013-01-01

    Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

  18. Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

    NASA Astrophysics Data System (ADS)

    Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

    2013-06-01

    Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

  19. The Last Glacial Maximum at 44°S documented by a 10Be moraine chronology at Lake Ohau, Southern Alps of New Zealand

    NASA Astrophysics Data System (ADS)

    Putnam, Aaron E.; Schaefer, Joerg M.; Denton, George H.; Barrell, David J. A.; Birkel, Sean D.; Andersen, Bjørn G.; Kaplan, Michael R.; Finkel, Robert C.; Schwartz, Roseanne; Doughty, Alice M.

    2013-02-01

    Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ˜26,500-˜19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the 'local LGM' (LLGM). We used 10Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr-1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the

  20. Unblocking temperatures of viscous remanent magnetism in displaced granitic boulders, Icicle Creek glacial moraines (Washington, USA)

    NASA Astrophysics Data System (ADS)

    Crider, Juliet G.; Globokar, Danika M.; Burmester, Russell F.; Housen, Bernard A.

    2015-12-01

    Viscous remanent magnetization (VRM) may partially overprint original magnetization in rocks displaced by geomorphic events. An established theoretical relationship between the time and temperature of acquisition of VRM and the time and temperature of demagnetization suggests that laboratory demagnetization (unblocking) of VRM can be used to estimate the displacement age of rocks. We test this hypothesis at four nested glacial moraines in the Icicle Creek drainage of central Washington, the ages of which were previously determined by cosmogenic surface exposure dating. The moraines are composed primarily of granodiorite boulders, and magnetic remanence is carried dominantly by magnetite. Both the maximum and average pVRM demagnetization temperatures (TD) increase with relative age of the moraines. For the three younger moraines, the average TD yields an age comparable to the cosmogenic age, within uncertainty of pVRM acquisition temperature. Uncertainty in the acquisition and demagnetization temperatures can limit the utility of pVRM for absolute dating.

  1. Fluctuations of the Greenland Ice Sheet since the last ice age: comparisons of the response of marine and land-terminating ice margins to Holocene climate changes

    NASA Astrophysics Data System (ADS)

    Levy, Laura; Larsen, Nicolaj; Kelly, Meredith; Kjær, Kurt; Bjørk, Anders; Kjeldsen, Kristian; Funder, Svend; Applegate, Patrick; Howley, Jennifer; Virginia, Ross

    2016-04-01

    Fluctuations of the margins of the Greenland Ice Sheet (GrIS) in response to Holocene climate change may be used as a proxy for how they may respond to future climate change. Here, we present records of Holocene fluctuations of the margins of the GrIS in southeastern and southwestern Greenland based on geomorphic mapping and 10Be dating of boulders on moraines and boulders on bedrock. We show that in southeastern Greenland the marine-terminating outlet glaciers retreated from the outer coast between 10.4 and 9.4 ka and responded rapidly to early Holocene warming, retreating up-fjord at a rate of ~70-100 m yr-1. These rates are comparable, or higher than, modern retreat rates of 30-100 m yr-1. In contrast, the terrestrial margin of the GrIS in the Kangerlussuaq region of southwestern Greenland retreated only ~25 m yr-1 throughout the early and middle Holocene. These data indicate that forcings such as warm ocean waters, fjord geometry, fjord bathymetry and ice dynamics are potential mechanisms that caused differences in retreat rates between marine and terrestrial-terminating margins of the ice sheet. Additionally, they show that the margins of the GrIS responded sensitively to Holocene climate change.

  2. Ice Age Sea Level Change on a Dynamic Earth

    NASA Astrophysics Data System (ADS)

    Austermann, J.; Mitrovica, J. X.; Latychev, K.; Rovere, A.; Moucha, R.

    2014-12-01

    Changes in global mean sea level (GMSL) are a sensitive indicator of climate variability during the current ice age. Reconstructions are largely based on local sea level records, and the mapping to GMSL is computed from simulations of glacial isostatic adjustment (GIA) on 1-D Earth models. We argue, using two case studies, that resolving important, outstanding issues in ice age paleoclimate requires a more sophisticated consideration of mantle structure and dynamics. First, we consider the coral record from Barbados, which is widely used to constrain global ice volume changes since the Last Glacial Maximum (LGM, ~21 ka). Analyses of the record using 1-D viscoelastic Earth models have estimated a GMSL change since LGM of ~120 m, a value at odds with analyses of other far field records, which range from 130-135 m. We revisit the Barbados case using a GIA model that includes laterally varying Earth structure (Austermann et al., Nature Geo., 2013) and demonstrate that neglecting this structure, in particular the high-viscosity slab in the mantle linked to the subduction of the South American plate, has biased (low) previous estimates of GMSL change since LGM by ~10 m. Our analysis brings the Barbados estimate into accord with studies from other far-field sites. Second, we revisit estimates of GMSL during the mid-Pliocene warm period (MPWP, ~3 Ma), which was characterized by temperatures 2-3°C higher than present. The ice volume deficit during this period is a source of contention, with estimates ranging from 0-40 m GMSL equivalent. We argue that refining estimates of ice volume during MPWP requires a correction for mantle flow induced dynamic topography (DT; Rowley et al., Science, 2013), a signal neglected in previous studies of ice age sea level change. We present estimates of GIA- and DT-corrected elevations of MPWP shorelines from the U.S. east coast, Australia and South Africa in an attempt to reconcile these records with a single GMSL value.

  3. 10Be cosmic-ray exposure dating of moraines and rock avalanches in the Upper Romanche valley (French Alps): Evidence of two glacial advances during the Late Glacial/Holocene transition

    NASA Astrophysics Data System (ADS)

    Chenet, Marie; Brunstein, Daniel; Jomelli, Vincent; Roussel, Erwan; Rinterknecht, Vincent; Mokadem, Fatima; Biette, Melody; Robert, Vincent; Léanni, Laëtitia

    2016-09-01

    Cosmic-ray exposure (CRE) dating of moraines allow glacier fluctuations and past climate change reconstructions. In the French Alps, there is a lack of moraine dating for the Late Glacial/Holocene transition period. Here we present a chronology of glacier advances in the Upper Romanche valley (French Alps - Massif des Ecrins) based on 10Be CRE dating. CRE ages of moraines of 13.0 ± 1.1 ka and 12.4 ± 1.5 ka provide evidence for two stages of glacial advance or standstill at the end of the Late Glacial. The CRE dating of a rock avalanche deposit at 12.2 ± 1.5 ka is attributed to post-glacial debuttressing and reveals rapid deglaciation at the end of the Late Glacial. A CRE age of 7.1 ± 0.7 ka of a second mass-wasting, whose triggering factor is unidentified so far, indicates that up to an altitude of 2300 m a.s.l., the valley was ice-free as of ∼7 kyr at the latest. The re-evaluation of 21 moraine 10Be CRE ages from nine glacial valleys across the Alps shows multiple glacial advances occurring at the Late Glacial/Holocene transition. These results lead to a re-evaluation of the importance of cooling events during the Allerød and the Younger Dryas in the Alps.

  4. Identifying signals of Late Pleistocene climate change from cosmogenic 10Be chronologies of moraines in the western U.S.

    NASA Astrophysics Data System (ADS)

    Laabs, B. J. C.; Licciardi, J. M.; Leonard, E. M.; Munroe, J. S.

    2015-12-01

    Cosmogenic 10Be exposure dating has become the most widely applied method of developing ages of terminal moraines in the western U.S. Advances in the precision of analytical measurements along with a more accurate understanding of spatial and temporal variations in the production of in situ 10Be have improved the accuracy of cosmogenic exposure dating of moraines. Such improvements afford more accurate assessment of the impact of regional and global-scale climate changes of the Late Pleistocene on glaciation in the western U.S. A great number of new and recalculated cosmogenic 10Be exposure ages of moraines are considered here to identify the most probable drivers of changes in ice extent at the end of the last glacial period. The last Pleistocene glaciation culminated in the western U.S. during marine oxygen isotope stage 2, before or during the onset of the global Last Glacial Maximum at ca. 26.5 ka. Terminal moraine abandonment in several ranges corresponds to the end of the Last Glacial Maximum at ca. 19.0 ka. This observation indicates that most mountain glaciers started retreating in step with the decline of global ice volume, and possibly in response to rising insolation at northern middle latitudes. In some regions, such as the Northern Rocky Mountains and the Great Basin, mountain glaciers apparently advanced to or persisted near their maximum terminus positions well after the start of global deglaciation, during the interval of the Oldest Dryas/Heinrich Stadial 1 (ca. 19.0-14.6 ka). Although changes in atmospheric circulation and precipitation patterns during this time likely affected mountain glacier extent, rapid ice retreat commenced in nearly all settings by 17.0-16.0 ka. This indication of warming prior to the onset of the Bølling-Allerød interval at ca. 14.6 ka is consistent with records from elsewhere at northern middle latitudes, and supports the hypothesis that warming of the region was in phase with a global rise in atmospheric CO2. This

  5. Spatial and temporal characteristics of the Little Ice Age: The Antarctic ice-core record

    SciTech Connect

    Mosley-Thompson, E.; Thompson, L.G.

    1992-03-01

    Recently, ice core records from both hemispheres, in conjunction with other proxy records (e.g., tree rings, speleothems and corals), have shown that the Little Ice Age (LIA) was spatially extensive, extending to the Antarctic. This paper examines the temporal and spatial characteristics of the dust and delta 18O information from Antarctic ice cores. Substantial differences exist in the records. For example, a 550-year record of delta 18O and dust concentrations from Siple Station, Antarctica suggests that, less dusty conditions prevailed from A.D. 1600 to 1830. Alternately, dust and delta 18O data from South Pole Station indicate that opposite conditions (e.g., cooler and more dusty) were prevalent during the LIA. Three additional Antarctic delta 18O records are integrated with the Siple and South Pole histories for a more comprehensive picture of LIA conditions. The records provide additional support for the LIA temperature opposition between the Antarctic Peninsula region and East Antarctica. In addition, periods of strongest LIA cooling are not temporally synchronous over East Antarctica. These strong regional differences demonstrate that a suite of spatially distributed, high resolution ice core records will be necessary to characterize the LIA in Antarctica.

  6. 40Ar-39Ar age determinations of lunar basalt meteorites Asuka 881757, Yamato 793169, Miller Range 05035, La Paz Icefield 02205, Northwest Africa 479, and basaltic breccia Elephant Moraine 96008

    NASA Astrophysics Data System (ADS)

    Fernandes, Vera A.; Burgess, Ray; Morris, Adam

    2009-06-01

    40Ar-39Ar data are presented for the unbrecciated lunar basaltic meteorites Asuka (A-) 881757, Yamato (Y-) 793169, Miller Range (MIL) 05035, LaPaz Icefield (LAP) 02205, Northwest Africa (NWA) 479 (paired with NWA 032), and basaltic fragmental breccia Elephant Moraine (EET) 96008. Stepped heating 40Ar-39Ar analyses of several bulk fragments of related meteorites A-881757, Y-793169 and MIL 05035 give crystallization ages of 3.763 ± 0.046 Ga, 3.811 ± 0.098 Ga and 3.845 ± 0.014 Ga, which are comparable with previous age determinations by Sm-Nd, U-Pb Th-Pb, Pb-Pb, and Rb-Sr methods. These three meteorites differ in the degree of secondary 40Ar loss with Y-793169 showing relatively high Ar loss probably during an impact event ˜200 Ma ago, lower Ar loss in MIL 05035 and no loss in A-881757. Bulk and impact melt glass-bearing samples of LAP 02205 gave similar ages (2.985 ± 0.016 Ga and 2.874 ± 0.056 Ga) and are consistent with ages previously determined using other isotope pairs. The basaltic portion of EET 96008 gives an age of 2.650 ± 0.086 Ga which is considered to be the crystallization age of the basalt in this meteorite. The Ar release for fragmental basaltic breccia EET 96008 shows evidence of an impact event at 631 ± 20 Ma. The crystallization age of 2.721 ± 0.040 Ga determined for NWA 479 is indistinguishable from the weighted mean age obtained from three samples of NWA 032 supporting the proposal that these meteorites are paired. The similarity of 40Ar-39Ar ages with ages determined by other isotopic systems for multiple meteorites suggests that the K-Ar isotopic system is robust for meteorites that have experienced a significant shock event and not a prolonged heating regime.

  7. The present flora and vegetation of the moraines of the Klutlan Glacier, Yukon Territory, Canada: A study in plant succession*1

    NASA Astrophysics Data System (ADS)

    Birks, H. J. B.

    1980-07-01

    The flora and vegetation of six ice-cored moraines of the Klutlan Glacier were analyzed in 65 plots by European plant-sociological techniques. The age of each plot was estimated from annual growth rings of shrubs or trees in the plots. Nine major vegetation types are distinguished: Crepis nana, Dryas drummondii, Hedysarum mackenzii, Hedysarum-Salix, Salix-Shepherdia canadensis, Picea-Salix, Picea-Arctostaphylos, Picea-Ledum, and Picea-Rhytidium. These contain plants aged 2-6, 9-23, 10-20, 24-30, 32-58, 58-80, 96-178, 177-240, and >163- >339 yr, respectively. Six other vegetation types are described from windthrow areas, drainage channels, volcanic tephra slopes, lake margins, fens, and drained lakes. The major vegetation types reflect a vegetational succession related to moraine age and stability, with the Crepis nana type as the pioneer vegetation developing through the other vegetation types to the Picea-Rhytidium type on the oldest moraines. Changes in species diversity and soil development, particularly humus accumulation, parallel the vegetational succession. This succession differs from patterns of revegetation of deglaciated landscapes in Alaska and British Columbia today and in Minnesota in late-Wisconsin times because of differences in climate, plant migration, and local ecology.

  8. Ice Ages and the Asteroid Belt: A Surprising Connection

    SciTech Connect

    Muller, Richard A.

    2001-05-23

    Oxygen isotope records preserved in glacial ice, seafloor cores and lake beds, show that the climate for the past million years has been one of a nearly continuous ice age, with short 10-20 kyr interglacials that occur every 100 kyr. (All of civilization has developed during the current interglacial.) Spectral analysis shows narrow peaks that imply the cycles are astronomically driven, but the spectrum is incompatible with the climate 'standard model' -- otherwise known as Milankovitch theory. An alternative theory attributes the cycles to the Earth's orbital changes, and the resulting variations in the influx of extraterrestrial dust which originates in the asteroid belt. Recent measurements of dust influx verify a prediction of this new model.

  9. Last Glacial Maximum cirque glaciation in Ireland and implications for reconstructions of the Irish Ice Sheet

    NASA Astrophysics Data System (ADS)

    Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; McCabe, A. Marshall; Caffee, Marc

    2016-06-01

    Reconstructions of the extent and height of the Irish Ice Sheet (IIS) during the Last Glacial Maximum (LGM, ∼19-26 ka) are widely debated, in large part due to limited age constraints on former ice margins and due to uncertainties in the origin of the trimlines. A key area is southwestern Ireland, where various LGM reconstructions range from complete coverage by a contiguous IIS that extends to the continental shelf edge to a separate, more restricted southern-sourced Kerry-Cork Ice Cap (KCIC). We present new 10Be surface exposure ages from two moraines in a cirque basin in the Macgillycuddy's Reeks that provide a unique and unequivocal constraint on ice thickness for this region. Nine 10Be ages from an outer moraine yield a mean age of 24.5 ± 1.4 ka while six ages from an inner moraine yield a mean age of 20.4 ± 1.2 ka. These ages show that the northern flanks of the Macgillycuddy's Reeks were not covered by the IIS or a KCIC since at least 24.5 ± 1.4 ka. If there was more extensive ice coverage over the Macgillycuddy's Reeks during the LGM, it occurred prior to our oldest ages.

  10. Last Glacial Maximum cirque glaciation in Ireland and implications for reconstructions of the Irish Ice Sheet

    NASA Astrophysics Data System (ADS)

    Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; McCabe, A. Marshall; Caffee, Marc

    2016-06-01

    Reconstructions of the extent and height of the Irish Ice Sheet (IIS) during the Last Glacial Maximum (LGM, ∼19-26 ka) are widely debated, in large part due to limited age constraints on former ice margins and due to uncertainties in the origin of the trimlines. A key area is southwestern Ireland, where various LGM reconstructions range from complete coverage by a contiguous IIS that extends to the continental shelf edge to a separate, more restricted southern-sourced Kerry-Cork Ice Cap (KCIC). We present new 10Be surface exposure ages from two moraines in a cirque basin in the Macgillycuddy's Reeks that provide a unique and unequivocal constraint on ice thickness for this region. Nine 10Be ages from an outer moraine yield a mean age of 24.5 ± 1.4 ka while six ages from an inner moraine yield a mean age of 20.4 ± 1.2 ka. These ages show that the northern flanks of the Macgillycuddy's Reeks were not covered by the IIS or a KCIC since at least 24.5 ± 1.4 ka. If there was more extensive ice coverage over the Macgillycuddy's Reeks during the LGM, it occurred prior to our oldest ages.

  11. Fan type end moraine related glaciofluvial deposits of Last Glaciation from Lithuania

    NASA Astrophysics Data System (ADS)

    Šinkūnė, Eglė; Šinkūnas, Petras

    2015-04-01

    Several alluvial-fan type end moraine related sites were chosen for detailed sedimentological analyses in ice marginal zone of the last glaciation in Lithuania. Such glaciofluvial ice-marginal fans are formed close to linear ice-sheet front and have semi-conical form or represent simple asymmetric hill forms or more complex ridges with steep proximal and gentler distal slopes. Sedimentary sequences of ice-marginal fans studied consist mainly of waterlain sandy and gravelly deposits with pebbles and boulders. In some sequences a debris-flow deposits are observed as well as beds of sorted material interbedded with dominating high energy sheetflow deposits. Sediment grain size, sorting, structure and bedding characteristics dependent on ice proximity and hydrodynamic conditions were analysed. Highly pulsatory water discharge can be interpreted from depositional architecture of the end moraine related fans. The inferred character of sedimentation suggests that landforms consisting of deposits studied are genetically similar to the alluvial fans. According to the sedimentation features the investigated landforms are an intermediate between the marginal glaciofluvial ridges and sandur fans. Are they a transition zone of sedimentation between the end moraines and proximal outwash plains, or can be the end moraine related fans distinguished as a separate type of glaciofluvial deposits? This question is still open.

  12. The deglaciation of Iztaccíhuatl volcano (Mexico) from the Little Ice Age maximum to the present, determined by photogrametry and lichenometry

    NASA Astrophysics Data System (ADS)

    Palacios, D.; García-Sancho, L.; Zamorano, J. J.; Andrés, N.; Pintado, A.

    2012-04-01

    Iztaccíhualt Volcano (19°10'20''N, 98°38'30''W, 5230 m asl) preserves an important moraine complex from the Little Ice Age (LIA), which stretches to 4300 m asl. These moraines are different from former ones because they are not covered by ash fall from the last plinian explosive phases of the nearby Popocatépetl volcano. In fact, the last emission of those pyroclasts took place during the XI century (Vázquez-Selem, 2000). The summit area of the Iztaccíhualt volcano still has glaciers whose terminus are located around 5000 m asl. From the end of the LIA until present the glacier terminus have ascended 700 m. To study the deglaciation process in Iztaccíhualt volcano from the LIA maximum to present, the Ayoloco valley was selected as it is the most important valley of the western slope of the volcano. Taking this valley as a reference, we determined the limits of glaciers in different dates by georeferencing the aerial and panoramic photographs (from 1897 to 2000) and analysing the 1958 field cartography of the glacial limits (Lorenzo, 1964). On the one hand, we carried out a statistical analysis of the size of the Rhizocarpon geographicum thallus and, on the other hand, we undertook a statistical study of the biodiversity of the lichen species through a number of cross-sections from the lowest LIA moraines to the current glacier snouts. This methodology allowed dating the exact moment in which the glacier retreated over certain points of the analysed cross-sections and determining the ecesis and the growth curve of the Rhizocarpon geographicum specie. In the Ayoloco valley the average growth rate is of 0.23 mm per year. From this information, we could deduce the evolution of the glacier from the LIA maximum to present. The results indicate that two main advances took place during the XVII and the XIX centuries. At the beginning of the XX century the glacier terminus were very close to the moraines of the maximum advance. An intense glacial retreat took place

  13. An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

    NASA Technical Reports Server (NTRS)

    Pollard, D.

    1978-01-01

    The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

  14. Sedimentary and tectonic architecture of a large push moraine: a case study from Hagafellsjökull-Eystri, Iceland

    NASA Astrophysics Data System (ADS)

    Bennett, Matthew R.; Huddart, David; Waller, Richard I.; Cassidy, Nigel; Tomio, Alexandre; Zukowskyj, Paul; Midgley, Nicholas G.; Cook, Simon J.; Gonzalez, Silvia; Glasser, Neil F.

    2004-12-01

    Using a combination of geological and geophysical techniques (Ground Penetrating Radar), we explore the tectonic architecture of a push moraine formed just after the 1890 Neoglacial ice maximum of Hagafellsjökull-Eystri, in central Iceland. The push moraine formed by a re-advance, perhaps a surge, of the glacier against a moraine bank-delta sometime between 1890 and 1929. Different tectonic architectures exist in two adjacent parts of the same push moraine complex. In one location, the ice advance pushed the delta pro-glacially to form a prominent single-crested push moraine. Deformation occurred along a single listric décollement over which a large nappe moved, as a result of ice-marginal pushing. In an adjacent location, the ice-margin mounted and advanced over the ice-contact delta to create a push moraine at the limit of the advance by subglacial gravity-spreading. In this case, deformation occurred along a series of listric thrusts and by folding within the distal parts of the over-ridden delta. The geomechanical causes of these two contrasting styles of deformation, present in adjacent sectors of the same ice-marginal flow unit, are discussed and a range of possible controls identified. These include variation along the former ice-margin and foreland in: (1) glacier-foreland coupling; (2) foreland shear strength; and (3) the frictional characteristics of the décollement. Some combination of these variables provides the most likely cause. The case study presented in this paper provides an example of the potential for rapid variation in the tectonic architecture of a push moraine along strike.

  15. Multiple ice-age refugia in Pacific cod, Gadus macrocephalus.

    PubMed

    Canino, Michael F; Spies, Ingrid B; Cunningham, Kathryn M; Hauser, Lorenz; Grant, W Stewart

    2010-10-01

    Pleistocene ice-ages greatly influenced the historical abundances of Pacific cod, Gadus macrocephalus, in the North Pacific and its marginal seas. We surveyed genetic variation at 11 microsatellite loci and mitochondrial (mt) DNA in samples from twelve locations from the Sea of Japan to Washington State. Both microsatellite (mean H = 0.868) and mtDNA haplotype (mean h = 0.958) diversities were large and did not show any geographical trends. Genetic differentiation between samples was significantly correlated with geographical distance between samples for both microsatellites (FST = 0.028, r(2) = 0.33) and mtDNA (FST = 0.027, r(2) = 0.18). Both marker classes showed a strong genetic discontinuity between northwestern and northeastern Pacific populations that likely represents groups previously isolated during glaciations that are now in secondary contact. Significant differences appeared between samples from the Sea of Japan and Okhotsk Sea that may reflect ice-age isolations in the northwest Pacific. In the northeast Pacific, a microsatellite and mtDNA partition was detected between coastal and Georgia Basin populations. The presence of two major coastal mtDNA lineages on either side of the Pacific Ocean basin implies at least two ice-age refugia and separate postglacial population expansions facilitated by different glacial histories. Northward expansions into the Gulf of Alaska were possible 14-15 kyr ago, but deglaciation and colonization of the Georgia Basin probably occurred somewhat later. Population expansions were evident in mtDNA mismatch distributions and in Bayesian skyline plots of the three major lineages, but the start of expansions appeared to pre-date the last glacial maximum. PMID:20819160

  16. Acting Out History from the Ice Age to the Modern Age.

    ERIC Educational Resources Information Center

    Mattioli, Denee J.; Drake, Frederick

    1999-01-01

    Addresses the teaching methods of Michael Welch, a seventh grade teacher, who incorporates the humanities, such as drama and literature, into his history classroom in order to help students learn to question, think analytically, solve problems, and make decisions. Summarizes a particular unit on the Ice Age. (CMK)

  17. A high glacier opens a view of the ice age tropics

    SciTech Connect

    Mlot, C.

    1995-07-07

    This article discusses new information about the ice age tropics as cores from a mountain glacier in the Peruvian Andes are analysed. Chemical markers in the ice of the two cores (160 and 166 meters long), covering 20,000 years, are starting to provide detailed support for understanding the ice age in the tropics. they show that climate in the tropics experience sharp oscillations at the end of the ice ages as it did in more northerly regions. Information about El Ninos and how the tropics respond to global climate changes is forthcoming. Comments on the actual expedition to obtain the ice cores are included.

  18. Glacial culmination and decay sequences: new data from a core in the Ivrea end-moraine system (NW Italy)

    NASA Astrophysics Data System (ADS)

    Gianotti, Franco; Forno, Maria Gabriella; Hajdas, Irka; Monegato, Giovanni; Pini, Roberta; Ravazzi, Cesare

    2016-04-01

    The Ivrea end-moraine system extends on a surface of about 500 kmq at the outlet of the Aosta Valley, being one of the largest amphitheatres on the southern side of the Alps. Along with the Rivoli-Avigliana amphitheatre, the Ivrea end-moraine system was the first to be studied in Italy during the XIX century, drawing the attention of several scientists from all over Europe for its impressive geomorphology. Most part of the stratigraphic researches on the Ivrea amphitheatre was traditionally performed on outcrops. In 2013 a 55-m long continuous core was drilled (ProGEO Project) in the western flank of the system, choosing an inward palaeolake location (Torre Canavese) related to the damming by one of the main terminal moraine, within a wide group of moraines whose age is still debated (the so called "Serra Synthem"). The aim was to make available a complete stratigraphic record of the ice-contact lake developed inward to the moraine at time of glacial culmination, or shortly later. This core crossed the entire local glacigenic succession down to the preglacial substrate at 53 m depth. Hopefully, the geochronometric and stratigraphic information obtained from this lake succession may provide time constrains for the glacial culmination. The Torre Canavese core displays a double sequence of subglacial till passing to glaciolacustrine and finally to fully lacustrine conditions. At its base, the sequence preserves a 12-m thick glacial till, resting on Lower Pleistocene fluvial gravels coming from a different catchment. A lacustrine unit made of laminated silty-clayey sands extends from 41.6 to 29 m depth, directly resting over the glacial till. As shown by a radiocarbon AMS age, this unit is older than 45 ka cal BP. An overconsolidated, 19-m thick glacial till lays on this lacustrine unit and is covered by a further, uppermost lacustrine unit from 10.26 to 0.34 m depth. A thin Holocene alluvial layer ends the sequence at the top. Both lacustrine units were sampled for

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

    NASA Astrophysics Data System (ADS)

    Kelley, Samuel E.; Kaplan, Michael R.; Schaefer, Joerg M.; Andersen, Bjørn G.; Barrell, David J. A.; Putnam, Aaron E.; Denton, George H.; Schwartz, Roseanne; Finkel, Robert C.; Doughty, Alice M.

    2014-11-01

    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

  20. Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages

    NASA Technical Reports Server (NTRS)

    Croft, S. K.; Kieffer, S. W.; Ahrens, T. J.

    1979-01-01

    The paper reports on a series of low-velocity impact experiments performed in ice and ice-saturated sand. It is found that crater diameters in ice-saturated sand were about 2 times larger than in the same energy and velocity range in competent blocks of granite, basalt and cement, while craters in ice were 3 times larger. It is shown that if this dependence of crater size on strength persists to large hypervelocity impact craters, then surface of geologic units composed of ice or ice-saturated soil would have greater crater count ages than rocky surfaces with identical influx histories. Among the conclusions are that Martian impact crater energy versus diameter scaling may also be a function of latitude.

  1. Increased Ice-age Influence of Antarctic Intermediate Water.

    NASA Astrophysics Data System (ADS)

    Muratli, J.; McManus, J.; Mix, A.; Chase, Z.

    2008-12-01

    A depth transect of three ODP sites collected along the central Chile Margin constrain Antarctic Intermediate Water (AAIW) distributions and regional export production over the last 30 ka. Reduced Re and Cd, and increased Mn are proxies for higher bottom water oxygenation; 230Th-normalized burial of opal is a proxy for productivity. Mn/Al is high during the glacial interval at all three sites, suggesting high oxygenation and the retreat of the oxygen minimum zone during this period. At Site 1233, within the core of modern AAIW, Re and Cd are unchanged from detrital values throughout the last 30 ky, implying continuously oxic conditions. In contrast, at the northern sites 1234 and 1235, which reside below and above AAIW respectively, Re and Cd rise rapidly from low glacial values at ~15ka, signifying lower oxygen concentrations at the sea floor during Holocene time relative to ice-age conditions. Local productivity, recorded in Th-normalized opal burial, is highest during the glacial interval at both sites 1233 and 1234, and varies independently from the redox proxies. We conclude that local productivity does not drive bottom water oxygenation here, and that ventilation of the shallow subsurface southeast Pacific increased during the last ice age, with an expanded depth range of AAIW relative to the present.

  2. Paleoclimatology: Second clock supports orbital pacing of the ice ages

    SciTech Connect

    Kerr, R.A.

    1997-05-02

    For a while, it looked as if a water-filled crack in the Nevada desert might doom the accepted explanation of the ice ages. Twenty years ago, the so-called astronomical theory had carried the day. Oceanographers had found evidence implying that the march of ice ages over the last million years was paced by the cyclical stretching and squeezing of Earth`s orbit around the sun, which would have altered the way sunlight fell on the planet`s surface. But in 1988, researchers scuba diving in Nevada`s Devils Hole came up with a climate record--captured in carbonate deposits in the crack-that seemed to contradict this chronology. This article discusses the findings and the puzzles that still remain. The records of sea-level change in Barbados coral appear to be right and the astronomical theory is on solid ground using a new clock based on the radioactive decay of uranium-235 to protactinium-231. However, the Devils Hole record also seems to be correct.

  3. Ground Ice in Iceland: Possible Analogs for Equatorial Mars

    NASA Astrophysics Data System (ADS)

    Helgason, J.

    2000-08-01

    Ground ice preservation in nonglaciated regions on Earth is normally terminated annually outside permafrost terrains. In Iceland old ice has been found under at least three different conditions that may serve as potential Martian analogs or lead the way where to look for ground ice on Mars. Three reconnaissance cases of ancient ground ice in Iceland are briefly reported: (1) Basaltic Scoria/Ice (ice residence: >64 yr). The main event of the AD 1875 volcanic eruption in Askja was first observed on January 3rd that year. The spattering lava material agglutinated to form a one to two meter thick layer on snow that had fallen earlier that winter. In 1939 a roughly two meter thick compact snow was photographed under the solidified lava material from 1875. No intervening material is recorded between the ice and the overlying chilled lava material. Collapse structures where the ice has melted are commonly seen in the AD 1875 basalt lava flow. (2) Moraine/Ice (ice residence: >100 yr?). In the Grimsvotn joekulhlaup of October and November 1996 the meltwater erosion exposed buried ice banking up against the Sandgigur terminal moraines. The age of the Sandgigur is dated at about 2200 year BP. The moraine material on top of the ice was approximately four meters thick and the exposed ice wall was also about four meters high. The contact between ice and moraine was made up of fine grained material. The ice differs from normal glacier ice in being a mixture of sand and ice. A few large ice blocks of this kind were found on the sandur plain below in between the large ice blocks that broke off the Skeidardrjokull glacier suggesting a somewhat large source than observed the in situ exposure. While the age of this ice is unconfirmed it was found in situ on the upward side of the Sandgigur terminal moraine, that are located five kilometers south of the present ice margin. (3) Ash deposit/Ice (ice residence: >600 yr?). A less well documented case is that of the rhyolite ash deposit

  4. Effects of nonlinear rheology and anisotropy on the relationship between age and depth at ice divides

    NASA Astrophysics Data System (ADS)

    Martin, C.; Gudmundsson, G. H.

    2012-04-01

    Ice-cores need to be accurately dated to reveal, in detail, past environmental conditions. The ice-core chronology is always incomplete because of ice stratigraphy thinning and distortion due to flow, and timeline extraction is often reliant on simplified models to predict the age of ice. Through numerical modelling using a full Stokes solver and a non-linear anisotropic rheology, we investigate the effects of ice flow on the age versus depth relationship at ice divides. We compare our results with analytical approximations commonly employed in age-depth prediction. Our main findings are: Firstly, once the ice has developed a significant single maximum or vertical girdle fabric, the analytical approximations tend to underestimate the age of ice. Secondly, ice fabric enhance the effect of the bedrock topography on the ice flow. We show that the presence of single maximum fabric close to the bedrock affects strongly the ice stratigraphy and the age-depth relationship. We also study the coupling between anisotropic viscosity and internal heating. It does produce a warm spot and softer ice at the base of the divide when compared with surrounding areas. Finally we study the age-depth distribution in divides that show double-peaked Raymond bump in their radar stratigraphy. They provide ideal locations fore ice-core drilling as they have been stable for a long time when compared with their characteristic time (ice thickness divide by accumulation). Our model shows that the ice in these areas can be up to one order of magnitude older that ice at the same depth both at the flanks of the divide area or on similar divides that have not been stable for that long.

  5. Role of Atmospheric CO2 in the Ice Ages (Invited)

    NASA Astrophysics Data System (ADS)

    Toggweiler, J. R.

    2010-12-01

    Ice cores from Antarctica provide our most highly resolved records of glacial-interglacial climate change. They feature big transitions every 100,000 years or so in which Antarctica warms by up to 10 deg. C while the level of atmospheric CO2 rises by up to 100 ppm. We have no other records like these from any other location, so the assumption is often made that the Earth's mean temperature varies like the temperatures in Antarctica. The striking co-variation between the two records is taken to mean 1) that there is a causal relationship between the global temperature and atmospheric CO2 and 2) that atmospheric CO2 is a powerful agent of climate change during the ice ages. The problem is that the mechanism most often invoked to explain the CO2 variations operates right next to Antarctica and, as such, provides a fairly direct way to explain the temperature variations in Antarctica as well. If so, Antarctic temperatures go up and down for the same reason that atmospheric CO2 goes up and down, in which case no causation can be inferred. Climate models suggest that the 100-ppm CO2 increases during the big transitions did not increase surface temperatures by more than 2 deg. C. This is not nearly enough to explain the observed variability. A better reason for thinking that atmospheric CO2 is important is that its temporal variations are concentrated in the 100,000-yr band. In my presentation I will argue that atmospheric CO2 is important because it has the longest time scale in the system. We observe empirically that atmospheric CO2 remains low for 50,000 years during the second half of each 100,000-yr cycle. The northern ice sheets become especially large toward the ends of these intervals, and it is large ice sheets that make the Earth especially cold. This leads me to conclude that atmospheric CO2 is important because of its slow and persistent influence on the northern ice sheets over the second half of each 100,000-yr cycle.

  6. Extremely eroded or incredibly young - 10Be depth profile dating of moraines in the Swiss Midlands

    NASA Astrophysics Data System (ADS)

    Wüthrich, Lorenz; Zech, Roland; Haghipour, Negar; Gnägi, Christian; Christl, Markus; Ivy-Ochs, Susan; Veit, Heinz

    2014-05-01

    During the Pleistocene, glaciers advanced repeatedly from the Alps into the Swiss Midlands. The exact extent and timing are still under debate, even for the last glacial advances. Decalcification depths, for example, increase from west to east in the western Swiss Midlands and have been interpreted to indicate that the Valais (Rhone) glacier may have been less extensive during the global Last Glacial Maximum (LGM) at 20 ka than assumed so far [1]. In an attempt to provide more quantitative age control, we applied 10Be depth profile dating [2] on moraines at two locations. Steinhof has previously been dated to the global LGM based on exposure ages from four boulders [3], and Niederbuchsiten presumably lies outside the last glacial ice extent [1]. The 10Be concentrations at both sites decrease consistently with depth, but are very similar. Assuming only a few decimeters of erosion since moraine deposition, we obtain apparent exposure ages of ~20 ka. Niederbuchsiten would thus be unexpectedly young, implying a much more extensive extent of the LGM glacier than assumed so far. Alternatively, if the till at Niederbuchsiten was deposited during or before the penultimate glaciation (>130 ka), the surprisingly low 10Be concentrations indicate several meters of erosion during the last glacial cycle and/or the Holocene, which seems to be at odds with the deep and intensive soil formation. References: [1] Bitterli et al. (2011) Geologischer Atlas der Schweiz, Blatt 1108. [2] Hidy et al. (2010) Geochem. Geophys. Geosyst. 11, doi:10.1029/2010GC003084. [3] Ivy- Ochs et al. (2004) Ecl. Geol. Helv. 97, 47-55.

  7. Spatial and temporal variations in the age structure of Arctic sea ice

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

    2005-01-01

    Spatial and temporal variations in the age structure of Arctic sea ice are investigated using a new reverse chronology algorithm that tracks ice-covered pixels to their location and date of origin based on ice motion and concentration data. The Beaufort Gyre tends to harbor the oldest (>10 years old) sea ice in the western Arctic while direct ice advection pathways toward the Transpolar Drift Stream maintain relatively young (10 years old (10+ year age class) were observed during 1989-2003. Since the mid-1990s, losses to the 10+ year age class lacked compensation by recruitment due to a prior depletion of all mature (6-10 year) age classes. Survival of the 1994 and 1996-1998 sea ice generations reestablished most mature age classes, and thereby the potential to increase extent of the 10+ year age class during the mid-2000s.

  8. Slope stability of moraines, Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Klimes, J.; Novotny, J.

    2012-12-01

    Landslides originating from inner slopes of moraine dams are often capable of producing glacial lakes outburst floods (GLOFs). Therefore assessing stability conditions of the moraines is important for predicting this potentially damaging phenomenon. Characteristics of the basic mechanical properties of the material and geophysical investigations were applied to collect necessary information for slope stability assessment of the Palcacocha Lake moraine dam, Peru. The lake is situated in the Cordillera Blanca Mts. at the altitude of about 4,500m asl and produced catastrophic GLOF in 1941. Another minor flood originated in 2003 due to landslide impact into the lake. Detailed investigations of this landslide site included geomorphological mapping, geophysical investigations and characterization of basic mechanical properties of the forming material. Geomorphological mapping identified dormant landslide with scarp up to 2m high which developed on the edge of the inner moraine slope. It is conditioned by set of parallel extension trenches which also affected the origin of 2003 landslide. Within its scarp area, significant water bearing layer was noticed around 10 m bellow the moraine surface. Three profiles were investigated using electric resistivity tomography performed on 4poing light instrument with 24 electrodes and with spacing ranging from 1 to 4m. Results helped to verify geometry of the main shear plane of the mapped landslide as well as the spacing and depth of extension trenches. Significant heterogeneity in the moraine resistivity characteristics was found. The high resistivity regions are explained by rock block accumulation whereas the low resistivity may represent wet layers within the moraine body. Grain size distribution of 33 disturbed soil samples originating from moraine material within the Cordillera Blanca Mts., Peru were determined and classified according to the UCSC classification system. The samples were taken from moraine dams and slopes

  9. Stable Isotope Systematics of Cryogenic Evaporite Deposits from Lewis Cliff Ice Tongue, Antarctica: A Mars Analog

    NASA Astrophysics Data System (ADS)

    Socki, R. A.; Harvey, R. P.; Bish, D. L.; Tonui, E.; Bao, H.

    2008-03-01

    We report stable isotope results of evaporite mounds and associated moraine materials from Lewis Cliff, Antarctica. Data suggest evaporite mineral formation likely occurred sub-glacially, influenced by secondary glacial ice and/or moraine lake water.

  10. Cryosphere: Antarctic ice growth and retreat

    NASA Astrophysics Data System (ADS)

    Evans, Jeffrey

    2015-08-01

    Antarctic Ice Sheet change during the last glacial cycle is unclear. The timing of moraine development in the Ross basin suggests that the ice sheet reached maximum thickness under the warming temperatures of the last termination.

  11. Seismic reflection study of recessional moraines beneath Lake Superior and their relationship to regional deglaciation

    USGS Publications Warehouse

    Landmesser, C.W.; Johnson, T.C.; Wold, R.J.

    1982-01-01

    Approximately 8000 km of continuous seismic reflection profiles throughout Lake Superior were examined for evidence of recessional moraines and other ice-margin deposits associated with the retreat of late Wisconsin ice. These features are correlated with the record of glacial-lake evolution in western Lake Superior. An offlapping sequence of glacial and glacial-lacustrine dediments overlying bedrock is recognized in west-central Lake Superior that is progressively younger to the northeast. The sequence underlies more recent glaical-lacustrine and postglacial sediments. Four facies are recognized on the basis of geomorphologic and acoustic properties and are interpreted to represent a southwest-to-northeast assemblage of: proglacial stratified drift (facies A), drift in major end moraines (facies B), till deposited as glacial retreat resumed, or possibly late-stage ablation till (facies C), and basal till (facies D). The prominent moraines of facies B are unusually thick and are believed to mark the ice-margin shorelines of successive major proglacial lakes that formerly occupied parts of western Lake Superior. The moraines are tentatively correlated with Glacial Lake Duluth (unit 1), Glacial Lake Washburn (unit 2), and Glacial Lake Beaver Bay (unit 3), the most prominent of lakes drained via the progressively lower outlets via the Moose Lake/ Brule-St. Croix Rivers, the Huron Mountains, and the Au Train-Whitefish regions, respectively. ?? 1982.

  12. Seismic reflection study of recessional moraines beneath Lake Superior and their relationship to regional deglaciation*1

    NASA Astrophysics Data System (ADS)

    Landmesser, C. W.; Johnson, T. C.; Wold, R. J.

    1982-03-01

    Approximately 8000 km of continuous seismic reflection profiles throughout Lake Superior were examined for evidence of recessional moraines and other ice-margin deposits associated with the retreat of late Wisconsin ice. These features are correlated with the record of glacial-lake evolution in western Lake Superior. An offlapping sequence of glacial and glacial-lacustrine dediments overlying bedrock is recognized in west-central Lake Superior that is progressively younger to the northeast. The sequence underlies more recent glaical-lacustrine and postglacial sediments. Four facies are recognized on the basis of geomorphologic and acoustic properties and are interpreted to represent a southwest-to-northeast assemblage of: proglacial stratified drift (facies A), drift in major end moraines (facies B), till deposited as glacial retreat resumed, or possibly late-stage ablation till (facies C), and basal till (facies D). The prominent moraines of facies B are unusually thick and are believed to mark the ice-margin shorelines of successive major proglacial lakes that formerly occupied parts of western Lake Superior. The moraines are tentatively correlated with Glacial Lake Duluth (unit 1), Glacial Lake Washburn (unit 2), and Glacial Lake Beaver Bay (unit 3), the most prominent of lakes drained via the progressively lower outlets via the Moose Lake/ Brule-St. Croix Rivers, the Huron Mountains, and the Au Train-Whitefish regions, respectively.

  13. Alpine Cliff Backwearing Rates Derived From Cosmogenic 10-Be in Active Medial Moraines

    NASA Astrophysics Data System (ADS)

    Ward, D. J.; Anderson, R. S.

    2008-12-01

    We use cosmogenic 10Be concentrations in rock samples from an active, ice-cored medial moraine to constrain glacial valley sidewall backwearing rates in the Kichatna Mountains, Alaska Range, Alaska. Kilometer-tall granite walls that tower over active glaciers are some of the most dramatic landscape features of the Alaska Range. The sheer scale of the relief speaks to the relative rates of valley incision by glaciers and rockwall retreat, but these rates are difficult to determine independently of one another. We present a method that uses cosmogenic nuclides to measure rockwall backwearing rates in glaciated settings on timescales of 103 yr, with a straightforward sampling strategy that exploits active medial moraines. Ablation-dominated medial moraines form by exhumation of debris-rich ice in the ablation zone of a glacier. Exhumed debris insulates the underlying ice and reduces its ablation rate relative to bare ice, promoting formation of a ridge-like, ice cored moraine. The rock debris is primarily derived from supraglacial rockfalls, which become incorporated in the ice along the glacier margins in the accumulation area. These lateral bands of debris-rich ice merge to form a medial debris band when glacial tributaries converge. The debris is minimally mixed until it is exhumed on the moraine crest. In the simplest case, such a system serves as a conveyor belt, bringing material from a specific part of the ablation zone valley wall to a specific point on a medial moraine in the ablation zone. We collected 5 grab samples, each consisting of ~30 2-10 cm rock fragments of the same lithology, from a 4.5 km longitudinal transect on the crest of the medial moraine of the Shadows glacier. We sampled the crest to minimize the amount of post-exhumation transport and mixing that may have occurred; each sample probably contains rocks from only one to a few rockfall events. Measured 10Be concentrations range from 1.5x104 to 3x104 at/g-qtz and are higher downvalley. First

  14. Effects of nonlinear rheology and anisotropy on the relationship between age and depth at ice divides

    NASA Astrophysics Data System (ADS)

    Martin, C.; Gudmundsson, G. H.

    2011-12-01

    Through numerical modelling using a full-system Stokes thermomechanical model, the effects of nonlinear rheology and strain-induced anisotropy on the age versus depth relation at ice divides are investigated. We compare our numerical results with field examples and analytical approximations commonly employed in age-depth prediction. We show that both the rheological index and strain-induced anisotropy profoundly affect the age distribution with depth, and caution must be exercised when estimating age of ice from ice cores with an isotropic age-depth model. Our main findings are: First, once the ice has developed a significant single maximum or vertical girdle fabric, the analytical approximations tend to underestimate the age of ice. Second, Bedrock topography and divide migration have a strong influence on the orientation of the ice fabric. They can force the development of single maximum and vertical girdle fabrics that are not aligned in the vertical. The orientation of the ice fabric can show sharp horizontal gradients and it has a significant effect on the age-depth relationship. We also study the coupling between anisotropic viscosity and internal heating. It does produce a warm spot and softer ice at the base of the divide when compared with surrounding areas. Finally we study the age-depth distribution in divides that show double-peaked Raymond bump in their radar stratigraphy and concavities in the surface parallel to and at both sides of the ridge. They provide ideal locations fore ice-core drilling as they have been stable for a long time when compared with their characteristic time (ice thickness divide by accumulation). Our model shows that the ice in these areas can be up to one order of magnitude older that ice at the same depth both at the flanks of the divide area or on similar divides that have not been stable for that long.

  15. Glimpses of the Ice Age from I-81: Lee Ranger District

    USGS Publications Warehouse

    U.S. Geological Survey; U.S. Forest Service

    1998-01-01

    Travelers on Interstate Highway 81 can see remnants of the Ice Age on the mountains between Strasburg and Harrisonburg, Virginia. Scattered along the miles of green, forested mountains are many gray patches without any forests. These treeless patches, or openings, in the steep mountain forests are block fields - geologic features that owe their origin to the Ice Age.

  16. Origin of washboard moraines of the Des Moines Lobe: Spatial analyses with LiDAR data

    NASA Astrophysics Data System (ADS)

    Cline, Mitchell D.; Iverson, Neal R.; Harding, Chris

    2015-10-01

    The Des Moines Lobe (DML)-the largest lobe along the southern margin of the Laurentide ice sheet-deposited low-relief (1-5 m) transverse moraine ridges, herein called washboard moraines, that are most prominent in central Iowa. Their origin as either subglacial or ice-marginal features bears on the dynamics of the lobe, geomorphic reconstructions of it, and interpretations of similar ridges elsewhere. Data from airborne laser swath mapping provide the first digital elevation models with sufficient spatial resolution to study in detail the geometric attributes of these topographically subtle features. Spectral analysis of profiles perpendicular to ridge crests indicates that most of them are spaced with statistically significant periodicities, with dominant wavelengths of 70-150 m. Normalizing and stacking these profiles indicate that, on average, they display no systematic asymmetry. Locally, washboard moraines are intersected by discontinuous longitudinal ridge segments. Trends of the crests of moraines are scalloped, with cusps that point upglacier and are coincident with outwash trains, which were overridden by the lobe. Our interpretation of these data is that the moraines formed subglacially as crevasse-squeeze ridges. Overridden outwash trains likely supported low basal water pressures and resulted in anomalously slow basal slip, causing upglacier deflection of crevasses that extended to the bed. This crevasse-squeeze interpretation reinforces evidence that the DML surged to its maximum position. Bering Glacier, as a temperate, surge-type glacier that deposited crevasse-squeeze ridges similar to the washboard moraines of the DML, may be a good analog for the lobe.

  17. Can Volcanic Eruptions Produce Ice Ages or Mass Extinctions?

    NASA Astrophysics Data System (ADS)

    Robock, A.; Ammann, C.; Oman, L.; Shindell, D.; Stenchikov, G.

    2006-12-01

    Volcanic eruptions are well known to be important causes of interannual and even interdecadal climate change. But can very large eruptions initiate ice ages, as has been suggested for the Toba eruption ~74,000 years ago? Could flood basalt eruptions, such as the Deccan Traps 65,000,000 years ago or the Siberian Traps 250,000,000 years ago, have produced climate change large enough and long-lasting enough, along with other atmospheric pollution, to have caused mass extinctions? Here we conduct climate model simulations of the effects of a volcanic eruption 100 times larger than the 1991 Pinatubo eruption as a test of the climatic effects of Toba. We use two different state-of-the-art climate models, CCSM 3.0 from the National Center for Atmospheric Research and ModelE from the NASA Goddard Institute for Space Studies, to investigate the dependence of the results on the climate model used. We find that although the "Toba" eruption produces very large global cooling for a couple years, of up to 10°C, the volcanic aerosols leave the atmosphere quickly and the climate largely recovers in a decade. We investigated the mechanism of vegetation response to the cold and dark, but this mechanism was not strong enough to prolong the response enough to allow ice sheets to grow. On the other hand, continuous emissions from massive flood basalt eruptions lasting several decades could make it so cold and dark at the Earth's surface that many species would find it hard to survive. On longer time scales, however, continued large greenhouse gas emissions would have a significant warming effect. With good estimates of the amount and timing of gas and particle emissions into the atmosphere, we have the climate modeling tools to calculate their impact on climate.

  18. Spatial Pattern of the Glacier Shrinkages over the Tibetan Plateau since the Little Ice Age and the Role of the Summer Freezing Level

    NASA Astrophysics Data System (ADS)

    Wang, N.; Yao, T.; Thompson, L. G.; Mosley-Thompson, E.

    2015-12-01

    Many Asian large rivers originate from glaciers over the Tibetan Plateau. The changes of glaciers in this region have a significant impact on water supply. In recent years, the Karakoram Anomaly, i.e., the glaciers in Karakoram remained stable and even expanded in contrast to the receding of the glaciers nearby and worldwide, has attracted much attention. There have been many attempts to explain this phenomenon. In order to better understand the causes of this phenomenon, the spatial pattern of the variations of the glaciers in the whole Tibetan Plateau should be explored on a longer time scale. During the Little Ice Age (LIA), the glaciers over the Tibetan Plateau advanced and formed easily recognizable end and lateral moraines, which could be used to identify the extents of glaciers. Using remote sensing images and aerial photos, along with field works, we recognized the distributions of the LIA's moraines of about 2000 glaciers over the Tibetan Plateau. It was found that the glacier areas have reduced by larger than 25% in the southeast Tibetan Plateau and the northeast margin of the Tibetan Plateau while less than 10% in the northwest Tibetan Plateau (including the Karakoram) since the LIA. A similar spatial pattern of the shrinkages of the glaciers was also revealed over the past decades. It's noted that the summer freezing level is much higher than the glacier median elevation in the southeast Tibetan Plateau while much lower in the northwest Tibetan Plateau, and the summer freezing level showed a decreasing trend in the northwest Tibetan Plateau (including the Karakoram) while increasing in the southeast Tibetan Plateau over the past decades. These imply that the summer freezing level play an important role in the spatial variations of the glaciers over the Tibetan Plateau.

  19. Effect of photochemical ageing on the ice nucleation properties of diesel and wood burning particles

    NASA Astrophysics Data System (ADS)

    Chou, C.; Kanji, Z. A.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

    2013-01-01

    A measurement campaign (IMBALANCE) conducted in 2009 was aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro without emission aftertreatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical ageing did not play a role in modifying their ice nucleation behaviour. Only one diesel experiment where α-pinene was added for the ageing process, showed an ice nucleation enhancement at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical ageing also did not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C whereas no ice nucleation was observed at -30 °C. Photochemical ageing did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -40 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical ageing on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

  20. Effect of photochemical aging on the ice nucleation properties of diesel and wood burning particles

    NASA Astrophysics Data System (ADS)

    Chou, C.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Kanji, Z. A.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

    2012-06-01

    A measurement campaign (IMBALANCE) was conducted in 2009 and aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro with no emission after-treatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical aging did not play a role in modifying their ice nucleation behavior. Only one diesel experiment where α-pinene was added, showed an ice nucleation enhancement after the aging at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical aging did also not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C with no ice nucleation observed at -30 °C for wood burning particles. Photochemical aging did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -30 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical aging on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

  1. The whole world had a case of the ice age shivers

    SciTech Connect

    Kerr, R.A.

    1993-12-24

    There is now worldwide evidence of short-term increases in the earth's temperature during the last ice ages. This evidence comes from South American glaciers, Antarctic ice cores, and sediment cores from the tropical oceans, as well as Greenland ice cores. Researcher are unsure of the causes of these fluctuations. Some speculate a means for transmitting a climate signal from the North Atlantic to the rest of the world, while others look to some shorter-term version of the orbital variations that pace the cycle of the ice ages.

  2. Veiki-moraine-like landforms in Nereidum Montes on Mars: Insights from analogues in northern Sweden.

    NASA Astrophysics Data System (ADS)

    Johnsson, Andreas; Reiss, Dennis; Hauber, Ernst; Johnson, Mark D.; Olvmo, Mats; Hiesinger, Harald

    2016-04-01

    Mars is a cold hyper-arid planet where liquid water is extremely rare [1]. The observable water budget is instead found in a number of frozen reservoirs such as the polar caps, near surface ground ice and as glacier ice. Previously, numerous studies reported on glacier landforms such as viscous flow features and lobate debris aprons where water-ice is believed to be present under insulating debris cover [2]. This notion was confirmed by SHARAD measurements [3]. However, very little is known about glacial landforms in which water is an important factor. Most studies have focused on moraine-like ridges that are associated to gully systems [4], glacial landforms at the equatorial volcanic province [5] and possible drop-moraines from CO2 glaciers [6]. Here we report on an unusual lobate assemblage of irregular ring-shaped landforms within a mountain complex in Nereidum Montes, Mars. These landforms are well-preserved and may suggest recent ablation of a debris-covered glacier. These martian ring-shaped landforms show a striking morphological resemblance to the Veiki moraine in northern Sweden. Veiki moraines are believed to have formed at the lobate margins of a stagnant ice-sheet during the first Weichselian glaciation [7]. As it sharply ends to the east it may represent the maximum extent of this former ice sheet. The Veiki moraine is characterized by ridged plateaus that are more or less circular and surrounded by a rim ridge. The newly acquired national LiDAR data over Sweden enable us studying these landforms in unprecedented detail. They also enable us exploring geomorphological similarities between Earth and Mars in large spatial contexts. This study aims to increase our understanding of glacial landforms on Mars by comparison to terrestrial analogues. Questions addressed are: (1) How morphological similar are the Martian landforms to the Veiki moraine of Sweden? (2) How does the ring-shaped landforms relate to other possible glacial landforms within the

  3. Late glacial fluctuations of the Laurentide Ice Sheet in the White Mountains of Maine and New Hampshire, U.S.A.

    NASA Astrophysics Data System (ADS)

    Bromley, Gordon R. M.; Hall, Brenda L.; Thompson, Woodrow B.; Kaplan, Michael R.; Garcia, Juan Luis; Schaefer, Joerg M.

    2015-05-01

    Prominent moraines deposited by the Laurentide Ice Sheet in northern New England document readvances, or stillstands, of the ice margin during overall deglaciation. However, until now, the paucity of direct chronologies over much of the region has precluded meaningful assessment of the mechanisms that drove these events, or of the complex relationships between ice-sheet dynamics and climate. As a step towards addressing this problem, we present a cosmogenic 10Be surface-exposure chronology from the Androscoggin moraine complex, located in the White Mountains of western Maine and northern New Hampshire, as well as four recalculated ages from the nearby Littleton-Bethlehem moraine. Seven internally consistent 10Be ages from the Androscoggin terminal moraines indicate that advance culminated ~ 13.2 ± 0.8 ka, in close agreement with the mean age of the neighboring Littleton-Bethlehem complex. Together, these two datasets indicate stabilization or advance of the ice-sheet margin in northern New England, at ~ 14-13 ka, during the Allerød/Greenland Interstadial I.

  4. Spatial and temporal variations in the age structure of Arctic sea ice

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

    2005-01-01

    Spatial and temporal variations in the age structure of Arctic sea ice are investigated using a new reversechronology algorithm that tracks ice-covered pixels to their location and date of origin based on ice motion and concentration data. The Beaufort Gyre tends to harbor the oldest (>10 years old) sea ice in the western Arctic while direct ice advection pathways toward the Transpolar Drift Stream maintain relatively young (???5 years) ice in the eastern Arctic. Persistent net losses (-4.2% yr-1) in extent of ice >10 years old (10+ year age class) were observed during 1989-2003. Since the mid-1990s, losses to the 10+ year age class lacked compensation by recruitment due to a prior depletion of all mature (6-10 year) age classes. Survival of the 1994 and 1996-1998 sea ice generations reestablished most mature age classes, and thereby the potential to increase extent of the 10+ year age class during the mid-2000s. Copyright 2005 by the American Geophysical Union.

  5. The genesis of the northern Kettle Moraine, Wisconsin

    NASA Astrophysics Data System (ADS)

    Carlson, A. E.; Mickelson, D. M.; Principato, S. M.; Chapel, D. M.

    2005-04-01

    Interpreting past glacial dynamics from the glacial record requires that the depositional environments of glacial sediments and landforms be understood. In the case of interlobate deposits, models that incorporate various components of pro, supra and subglacial deposition have been developed and tested in the northern Kettle Moraine (nKM), Wisconsin; a large interlobate deposit that formed between the Green Bay and Lake Michigan lobes of the Laurentide Ice Sheet during the last deglaciation. In this paper, we interpret a new genesis for the nKM using sediment analysis and distribution along with landform distribution. In Sheboygan County, the nKM consists of two steep-sided, high-relief, hummocky ridges separated by a low elevation and low-relief central axis. Gravel in the bounding hummocky ridges is well-sorted and well-rounded. Some bedding is collapsed. Large, isolated moulin kames are restricted to the axis area and composed of relatively poorly sorted, more angular gravel and diamicton. The distribution of these different sediments and landforms are explained by the accumulation of supraglacial debris that insulated the ice below the axis of the nKM, while the melting of cleaner ice on either side formed channels on the ice surface. As deglaciation proceeded, a substantial thickness of well-rounded, stream-deposited sand and gravel accumulated on ice in the bounding channels. Eventual collapse of this sediment formed the two hummocky ridges. Poorly sorted debris along the axis fell and slid into moulins and larger collapse areas in the ice. Thus, differential debris insulation and ice ablation controlled the mainly supraglacial deposition of this part of the nKM.

  6. Spatial manifestation of the Little Ice Age in Alaska

    NASA Astrophysics Data System (ADS)

    Clegg, B. F.; Tinner, W.; Henderson, A.; Bigler, C.; Hu, F.

    2005-12-01

    We present here climate reconstructions of the past 1000 years on the basis of multiproxy sediment analyses at six lakes in three regions of Alaska: the northwestern Alaskan Range (Farewell Lake), the southern Brooks Range (Takahula, Malamute, and Omega Lakes), and the Copper River Basin in southeastern Alaska (Grizzly and Moose Lakes). All three regions show a consistent decline in summer temperature of roughly 1.5 to 2 degrees C during Little Ice Age (LIA, 1480 - 1850 AD), in good agreement with previous estimates. However, effective-moisture reconstructions vary greatly among these regions. Oxygen isotopes, carbonate trace elements, and chironomid assemblages suggest that the SW and N portions of the Alaskan interior experienced a considerable effective-moisture increase and elevated lake levels during the LIA. At Takahula Lake, oxygen isotope analysis reveals that the rise in effective moisture occurred predominantly as a result of increased winter precipitation. In contrast, diatom-inferred water depths at Grizzly Lake dropped dramatically during the LIA, suggesting that the Copper River Basin became drier. The heterogeneity of the LIA moisture changes across our sites is consistent with the expected spatial pattern based on recent reconstructions of the position of the Aleutian Low (AL) during the LIA. Thus, variation of the strength/position of the AL appears to have been a major driver of the Alaskan climate over the last millennium.

  7. Veiki-moraine-like landforms in the Nereidum Montes region on Mars: Insights from analogues in northern Sweden.

    NASA Astrophysics Data System (ADS)

    Johnsson, A.; Reiss, D.; Hauber, E.; Johnson, M. D.; Olvmo, M.; Hiesinger, H.

    2015-10-01

    Mars is a cold hyper-arid planet where liquid water is extremely rare [1]. Most water is instead locked in a number of frozen reservoirs such as the polar caps, latitude-dependent near surface ground ice and as glacier ice. Previously, numerous studies reported on glacier landforms such as viscous flow features and lobate debris aprons where water-ice is believed to be present under insulating debris cover[2].This notion was confirmed by SHARAD measurements [3].However, very little is known about glacial landforms in which water is an important factor. Most studies have focused on moraine- like ridges that are associated to gully systems in crater environments[4], glacier landforms at the equatorial volcanic province [5]and drop-moraines from CO2 glaciers [6]. Here we report on unusual irregular ring-shaped landforms within a mountain complex in Nereidum Montes, Mars. These landforms are well-preserved and may suggest recent ablation of a debris-covered,cold-based glacier. These martian ring-shaped moraine-like landforms show a striking resemblance to the Veiki moraine in northern Sweden. Veiki moraines are believed to have formed at the lobate margins of a stagnant ice- sheet during the first Weich selian glaciation as it sharply ends to the east [7].The Veiki-moraine is characterized by ridged plateaus that are more or less circular and surrounded by a rim ridge. The newly acquired national LiDAR data over Sweden enable us studying these landforms in unprecedented detail. They also enable us exploring geomorphological similarities between Earth and Mars in large spatial contexts. This study aims to increase our understanding of glacial landforms on Mars by comparison to terrestrial analogues. Questions addressed are: (1) how morphological similar are the Martian landforms to the Veiki moraine of Sweden? (2) How does the moraine-like landform relate to other, well-preserved, glacial landforms within the mountain complex? (3) Do the moraine-like land forms indicate

  8. Atlantic forcing of Amazonian climates in the last ice age

    NASA Astrophysics Data System (ADS)

    Bush, M. B.; Mosblech, N.; Valencia, B. G.; Hodell, D. A.; Gosling, W. D.; Van Calsteren, P. W.; Thomas, L. E.; Curtis, J. H.

    2011-12-01

    An absence of study sites means that the relative influence of orbitally driven presession cycles and millenial scale variability upon ice-age Amazonian precipitation is unknown. Here we present a continuous isotopic (δO18 and C13) record spanning the period from ~93-8 ka, from the aseasonal forests of Amazonian Ecuador. The variability in δO18 depletion is probably related to the relative strength of evapotranspired moisture (less depleted) and tropical Atlantic moisture carried across the basin by the South American Low Level Jet (more depleted). Times of strengthened South American Low Level Jet probably correspond to increased overall moisture availability and hence elevated precipitation. The occurrence of markedly depleted δO18 signatures during Heinrich events suggests a strong influence of the Atlantic Ocean on this system, and that these northern hemispheric stadials induced wet episodes in western Amazonia. Weakening of the Atlantic Meridional Overturning Circulation (AMOC) has been suggested to strengthen the South American Low Level Jet. The isotopic records reveal strong cohesion with previously published records from southern Brazil. A precessional influence amplifies the north Atlantic signal between c. 93 ka and 50 ka. However, after c. 50 ka the precessional signal weakens, perhaps sugesting that at a critical size the Laurentide ice mass exerted a strong influence on Neotropical climates suppressing the weaker forcing associated with precession. Contrary to long-standing expectation, the Last Glacial Maximum (21 ± 2 ka) does not stand out as time of aridity in this record. However, between c. 35 ka and 18 ka there is a drift toward less depleted rainfall. One hypothesis to account for this observation is that the climate was becoming more seasonal as the Intertropical Convergence Zone (ITCZ) formed further south than its modern location. The resulting weakened influence of the South American Summer Monsoon (SASM) would probably reduce wet

  9. 77 FR 14567 - Draft General Management Plan/Environmental Impact Statement for the Ice Age Complex at Cross...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-12

    ... Ice Age National Scenic Trail headquarters at the address above. FOR FURTHER INFORMATION CONTACT... National Park Service Draft General Management Plan/Environmental Impact Statement for the Ice Age Complex... Statement for the Ice Age Complex at Cross Plains, Wisconsin DATES: The draft General Management...

  10. Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks

    NASA Astrophysics Data System (ADS)

    Miller, Gifford H.; Geirsdóttir, Áslaug; Zhong, Yafang; Larsen, Darren J.; Otto-Bliesner, Bette L.; Holland, Marika M.; Bailey, David A.; Refsnider, Kurt A.; Lehman, Scott J.; Southon, John R.; Anderson, Chance; Björnsson, Helgi; Thordarson, Thorvaldur

    2012-01-01

    Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes. However, the causes of superposed century-scale cold summer anomalies, of which the Little Ice Age (LIA) is the most extreme, remain debated, largely because the natural forcings are either weak or, in the case of volcanism, short lived. Here we present precisely dated records of ice-cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430-1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required.

  11. Uranium isotopes in Pleistocene permafrost: evaluating the age of ancient ice

    NASA Astrophysics Data System (ADS)

    Ewing, S. A.; Paces, J. B.; O'Donnell, J.; Kanevskiy, M. Z.; Aiken, G.; Jorgenson, T.; Shur, Y.; Striegl, R. G.

    2010-12-01

    The age of ice in permafrost is an indicator of past climate history, and of the resilience and response of high-latitude ecosytems to global change. Methods such as radiocarbon dating and tephrachronology are limited in permafrost because they provide indirect age control, and could overestimate ages when ice is intermittently absent. Development of geochemical indicators of water/ice residence time in permafrost is critical for understanding the circumstances and primary controls of permafrost formation, preservation, and thaw in response to climate change. We analyzed uranium isotopes to evaluate the age of segregated ice in ice-rich loess permafrost (yedoma) cores from central Alaska. Activity ratios of 234U vs. sup>238U (234/238U ARs) in thawed waters exceed 1.000 due to extended contact of ice with mineral surfaces over time. Ice is expected to increase in age with depth at this location based on the presence of deep loess, cryostructures associated with syngenetic permafrost aggracation, high segregated ice content, and frequent wedge ice. These features indicate that permafrost formed syngenetically as loess was deposited. Consequently, (234/238U ARs are expected to increase with depth as recoil 234U, derived from in situ decay of (238U in loess particles, accumulates in ice without being flushed over time. Values of (234/238U ARs measured for ice from a series of five neighboring cores up to 21 m deep increase with depth, consistent with downhole increases in permafrost age. Additional variability of (234/238U ARs with depth can be attributed to variations in surface area of solids determined by analysis of particle size distribution. Radiocarbon analysis of dissolved organic carbon indicates that the ages of ice are greater than ~36ky below the upper few meters, consistent with previous work on soil organic-matter profiles in this area. Using these measured parameters, a model of (234/238U AR evolution indicates minimum ages up to a minimum of ~100ky in

  12. Age of Allan Hills 82102, a meteorite found inside the ice

    NASA Technical Reports Server (NTRS)

    Nishiizumi, K.; Jull, A. J. T.; Bonani, G.; Suter, M.; Woelfli, W.

    1989-01-01

    The terrestrial age of a meteorite that was recovered from below the surface of Antarctic ice is reported, and it is argued that this represents a measurement of the age of the ice itself. The cosmogenic radionuclides Be-10, C-14, Al-26, Cl-36, and Mn-53 are measured in the meteorite and Be-10 and Cl-36 in the ice. A terrestrial age of 11,000 yr is obtained for the meteorite, which suggests that the snow accumulation area where it fell was only a few tens of km away.

  13. Timing of the East Antrim Coastal Readvance: phase relationships between lowland Irish and upland Scottish ice sheets during the Last Glacial Termination

    NASA Astrophysics Data System (ADS)

    McCabe, A. M.; Williams, G. D.

    2012-12-01

    A submillennial ice readvance from upland centres of ice dispersal in west central Scotland into northeastern Ireland post-dates the retreat of lowland Irish ice immediately after the Killard Point Stadial (max. 16.5 cal ka BP). The dimensions of this southerly and westerly ice sheet readvance on the margins of the North Channel are reconstructed from subglacial bedform patterns, subglacial tectonic deformation of Tertiary lignite and glacigenic sediment, limiting moraines/outwash and glacial stratigraphy. Morainic ridges at Rams Island and Sandy Bay on the eastern margin of the Lough Neagh basin which mark this ice limit are perpendicular to a well-defined field of subglacial bedforms across east County Antrim. At the ice readvance limits glacial lakes impounded in the Lagan Valley were partially infilled with subaqueous outwash known as the Malone Sands. This water body drained south along the Dundonald/Comber Gap spillway providing sediment which formed extensive, late-glacial marine terraces at the northern end of Strangford Lough around 15-15.5 cal ka BP. The East Antrim Coastal Readvance is part of a much more extensive readvance southwards along the North Channel and adjacent lowlands associated with ice sheet reorganisation and ice sheet growth in west central Scotland. It is now termed the North Channel Readvance and may be similar in age to the Wester Ross Readvance moraines in northwestern Scotland.

  14. Neoproterozoic ice ages, boron isotopes, and ocean acidification

    NASA Astrophysics Data System (ADS)

    Kasemann, S. A.; Prave, A. R.; Fallick, A. E.; Hawkesworth, C. J.; Hoffmann, K.

    2010-12-01

    the Sturtian-aged glacial aftermath do not indicate extreme ocean pH (~8.3) conditions and do not support a contemporaneous major ocean acidification event and associated high pCO2 at the time of the older Cryogenian glaciation and deglaciation. That leads us to speculate that the ocean during the older glaciation was not totally frozen and that the hydrological cycle was functioning2. 1Hoffman, P.F., Kaufman, A.J., Halverson, G.P. and Schrag, D.P. (1998). A Neoproterozoic Snowball Earth. Science, 281, 1342-1346. 2Kasemann, S.A., Prave, A.R., Fallick, A.E., Hawkesworth, C.J. and Hoffmann, K.H. (2010). Neoproterozoic ice ages, boron isotopes, and ocean acidification: Implications for a snowball Earth. Geology, 38, 775-778.

  15. Remedial Reading Students at Moraine Valley.

    ERIC Educational Resources Information Center

    Reis, Elizabeth

    In an effort to assess the effectiveness of their remedial reading courses, Moraine Valley Community College (MVCC) in Palos Hills, Illinois, undertook a study of the retention, course completion, and graduation rates of students who completed one of three remedial reading courses: RDG-040, basic skills for students reading below the 7th grade…

  16. Cultural Implications of Out-of-Phase Weather across northern Alaska after 500 CE: Regional Variability during the Medieval Climate Anomaly and Little Ice Age

    NASA Astrophysics Data System (ADS)

    Mason, O. K.; Alix, C. M.; Bigelow, N. H.; Hoffecker, J. F.

    2014-12-01

    From a global perspective, a diverse mélange of paleoclimate data reveal that Northwest Alaska is partially out of phase with northwest Europe, witnessing cooler periods during the Medieval Climate Anomaly ca. CE 1000 and warmer conditions in the 16th and 17th centuries. The search for climatic forcers in northern Alaska relies on integration of data drawn from tree-rings, lacustrine varves and moraines, diatoms, beach ridges and dunes. At Cape Espenberg, northern Seward Peninsula, a 1500-year reconstruction of settlement, landscape evolution and climatic variability employs >100 14C ages from accreting dunes with shell-laden storm beds, intercalated driftwood and superimposed soils, archaeological sites and marsh peats within swale ponds. Large storms occurred along the Chukchi Sea from Cape Espenberg and Deering (Kotzebue Sound) to Point Barrow prior to 1000 CE, and at decadal intervals during the Little Ice Age (LIA) from 1300 to 1700. Architecural driftwood logs from several excavated houses capped by sand dunes yield several 14C dated floating chronologies covering intervals from 700 to 1700, suggest the identification of cooler intervals 800 to 1000 and intermittently after 1300. Peat aggradation followed isolation from the sea from 500 onward, and was interrupted by two pulses of fresh water, one ca. 1300 and a second ca. 1800, with diatoms suggesting relative aridity during the LIA. The occupation history of Cape Espenberg generally follows dune growth, and may be inversely related to cooler temperatures.

  17. Borax in the supraglacial moraine of the Lewis Cliff, Buckley Island quadrangle--first Antarctic occurrence

    USGS Publications Warehouse

    Fitzpatrick, J.J.; Muhs, D.R.

    1989-01-01

    During the 1987-1988 austral summer field season, membersof the south party of the antarctic search for meteorites south-ern team* working in the Lewis Cliff/Colbert Hills region dis-covered several areas of unusual mineralization within theLewis Cliff ice tongue and its associated moraine field (figure1). The Lewis Cliff ice tongue (84°15'S 161°25'E) is a meteorite-stranding surface of ablating blue ice, about 2.3 by 7.0 kilo-meters, bounded on the west by the Lewis Cliff, on the northand northeast by a large supraglacial moraine, and on the eastby the Colbert Hills. To the south it opens to the Walcott Névé.Because it is a meteorite-stranding surface, the major component of ice motion in the area is believed to be vertical(Whillans and Cassidy 1983). The presence of Thule-Baffinmoraines at the northern terminus of the blue ice tends tosupport the hypothesis that the area underlying the moraineis essentially stagnant and that ice arriving from the south ispiling up against it. Areas containing mineral deposits werefound within the moraine field to the north and east of theblue ice margin and also along the east margins of the blue iceitself. Subsequent X-ray diffraction analyses of these depositshave shown that they are composed predominantly of nah-colite (NaHCO3), trona [Na3(CO3)(HCO3) · 2H20], borax[Na2B405(OH)4 · 8H20], and a new hexagonal hydrous sulfatespecies. This paper reports the details of the borax occurrence,because it is the first known on the continent.

  18. Climatic basis for sluggish macroevolution during the late Paleozoic ice age

    NASA Astrophysics Data System (ADS)

    Powell, Matthew G.

    2005-05-01

    Rates of origination and extinction for marine invertebrates fell at the onset of the late Paleozoic ice age in late Mississippian time and remained low until glaciation ended in middle Permian time. Through the use of a database of stratigraphic and geographic occurrences of brachiopod genera, these macroevolutionary changes are traced to the loss of genera with narrow latitudinal ranges, which had intrinsically high turnover rates, at the onset of glaciation in late Viséan time. When glaciation waned in late Sakmarian time, narrowly distributed genera rebounded abruptly and restored the global fauna to its pre ice-age configuration. Because narrowly distributed brachiopod genera had dominated tropical diversity, the major biotic effects of the late Paleozoic ice age were felt at low latitudes. The climatic regime of this ice age thus altered the marine ecosystem to one characterized by broadly adapted, long-lived genera.

  19. Ice-age Ice-sheet Rheology: Constraints from the Last Glacial Maximum Form of the Laurentide Ice Sheet

    NASA Technical Reports Server (NTRS)

    Peltier, W. Richard; Goldsby, David L.; Kohlstedt, David L.; Tarasov, Lev

    2000-01-01

    State-ot-the-art thermomechanical models of the modern Greenland ice and the ancient Laurenticle ice sheet that covered Canada at the Last Glacial Maximum (LGM) are not able to explain simultaneously the observed forms of these cryospheric structures when the same, anisotropy-enhanced, version of the conventional Glen flow law is employed to describe their rheology. The LGM Laurenticle ice sheet. predicted to develop in response to orbital climate forcing, is such that the ratio of its thickness to its horizontal extent is extremely large compared to the aspect ratio inferred on the basis of surface-geomorphological and solid-earth-geophysical constraints. We show that if the Glen flow law representation of the rheology is replaced with a new rheology based upon very high quality laboratory measurements of the stress-strain-rate relation, then the aspect ratios of both the modern Greenland ice sheet and the Laurenticle ice sheet, that existed at the LGM, are simultaneously explained with little or no retuning of the flow law.

  20. Preliminary results of polarization signatures for glacial moraines in the Mono Basin, Eastern Sierra Nevada

    NASA Technical Reports Server (NTRS)

    Forster, Richard R.; Fox, Andrew N.; Isacks, Bryan

    1992-01-01

    The valleys of the Mono Basin contain several sets of lateral and terminal moraines representing multiple stages of glaciation. The semi-arid climate with slow weathering rates preserved sequences of nested younger moraines within older ones. There is a well established relative chronology and recently exposure dating provided a new set of numerical dates. The moraines span the late Wisconsin (11-25 ka) to the Illinoian (130-190 ka) glaciations. The Mono Basin area was used as a 'calibration site' to establish remote dating techniques for eventual transfer to the more inaccessible but geomorphically and climatically similar moraines of the South American Andes Mountains. Planned polarimetric synthetic aperture radar (SAR) imagery acquired by JPL AIRSAR (South American Campaign) and SIR-C (Andes super-site) are analyzed to establish chronologies of previously undated moraine sequences in a study of Pleistocene climatic change in the Southern Hemisphere. The dry climate and sparse vegetation is also favorable for correlation of ground surface roughness with radar polarization signature. The slow weathering processes acting over thousands of years reduce the size, frequency, and angularity of surface boulders while increasing soil development on the moraines. Field observations based on this hypothesis result in relative ages consistent with those inferred from nested position within the valley. Younger moraines, therefore, will appear rougher than the older smoother moraines at scales measurable at AIRSAR wavelengths. Previously documented effects of ground surface roughness on polarization signatures suggest that analysis of moraine polarization signatures can be useful for relative dating. The technique may be extended to predict numerical ages. The data set reported were acquired on 8 Sep. 1989 with the JPL Airborne SAR (AIRSAR) collecting polarimetric imagery at C- (5.6 cm), L- (24 cm), and P-band (68 cm) with a flight-line parallel to the strike of the mountains

  1. Little Ice Age evidence from a south-central North American ice core, U.S.A.

    USGS Publications Warehouse

    Naftz, D.L.; Klusman, R.W.; Michel, R.L.; Schuster, P.F.; Ready, M.M.; Taylor, H.E.; Yanosky, T.M.; McConnaughey, E.A.

    1996-01-01

    In the past, ice-core records from mid-latitude glaciers in alpine areas of the continental United States were considered to be poor candidates for paleoclimate records because of the influence of meltwater on isotopic stratigraphy. To evaluate the existence of reliable paleoclimatic records, a 160-m ice core, containing about 250 yr of record was obtained from Upper Fremont Glacier, at an altitude of 4000 m in the Wind River Range of south-central North America. The ??18O (SMOW) profile from the core shows a -0.95??? shift to lighter values in the interval from 101.8 to 150 m below the surface, corresponding to the latter part of the Little Ice Age (LIA). Numerous high-amplitude oscillations in the section of the core from 101.8 to 150 m cannot be explained by site-specific lateral variability and probably reflect increased seasonality or better preservation of annual signals as a result of prolonged cooler temperatures that existed in this alpine setting. An abrupt decrease in these large amplitude oscillations at the 101.8-m depth suggests a sudden termination of this period of lower temperatures which generally coincides with the termination of the LIA. Three common features in the ??18O profiles between Upper Fremont Glacier and the better dated Quelccaya Ice Cap cores indicate a global paleoclimate linkage, further supporting the first documented occurrence of the LIA in an ice-core record from a temperate glacier in south-central North America.

  2. Formation and evolution of the Waiho Loop terminal moraine, New Zealand

    NASA Astrophysics Data System (ADS)

    Alexander, David; Davies, Tim; Shulmeister, James

    2015-04-01

    The terminal moraine of the Franz Josef Glacier in New Zealand, known as the Waiho Loop, has been subject to intense scientific research since it was identified as potential evidence of a Southern Hemisphere Younger Dryas (~12000 yrs BP) event in the late 1980s and early 1990s. As a result, the large, arcuate moraine has been interpreted to indicate inter-hemispheric connectivity and synchronicity of climate change, and in turn has been inferred to indicate a major late-glacial cooling event in New Zealand. In recent times, it has been postulated that the Loop moraine may not reflect climate variation at all, but rather it may have been the result of a landslide sourced from the upper Franz Josef catchment due to its rock-avalanche-debris-dominated composition. New evidence from shallow seismic studies between the Loop and the range front (~3 km) suggests (i) that the presence of an overdeepened trough may be a critical component influencing glacier behaviour and moraine formation; and (ii) that the volume of the Waiho Loop is significantly greater than previously thought. Using a one-dimensional flowline model, two rock-avalanche-based scenarios for the formation of Loop are tested: first, that a rock avalanche generated a significant advance of the glacier terminus from a location within the confined mountain valley to the Loop; and second, that the rock avalanche occurred while the glacier was retreating from its long-occupied terminus at the distal margin of its overdeepened trough close to the position of the Loop during the Last Glacial Interglacial Transition (LGIT) 13000-11000 yrs BP. Results from the first test demonstrate that a rock avalanche could not have generated a significant advance of the Franz Josef Glacier terminus from a location within the confined mountain valley to form the Loop, because most of the rock avalanche debris could not be advected to the terminus to form a sufficiently high moraine before the ice in the upper catchment becomes

  3. Moraine formation during an advance/retreat cycle at a temperate alpine glacier

    NASA Astrophysics Data System (ADS)

    Brook, M.; Quincey, D.; Winkler, S.

    2012-04-01

    Mountain glaciers are highly sensitive to variations in temperature and precipitation, and so moraine records from such systems are strong indicators of climate change. Due to the prevailing trend of retreat of the majority of mountain glaciers globally over the last few decades, there are limited opportunities to observe moraine formation, especially at temperate alpine glaciers. In the Southern Alps of New Zealand, while glaciers have all experienced a major retreat since the late 19th century, within this loss of ice mass, there has been a distinct variance in individual glacier response. Indeed, while Tasman Glacier, the longest glacier in the Southern Alps has thinned and entered into the current phase of calving retreat in the early 1990s, the steeper, more responsive glaciers to the west of the Main Divide, such as Franz Josef and Fox Glacier have experienced more elaborate advance/retreat phases. We focus on moraine formation at Fox Glacier, a c. 12.5 km long valley glacier terminating at 300 m above sea level. Fox Glacier retreated substantially since the 1930s, before advancing 800 m between the mid-1980s and 1999. A minor retreat then followed until 2005, succeeded by a 300 m re-advance until 2007-8. Continued retreat and down-wasting has since followed. Superimposed on this alternating advance/retreat cycle, have been minor winter re-advances. Sedimentological and morphological information were combined with detailed observations, historical photos and recent time-lapse photography of the terminus. Characteristics of several modes of moraine formation have been observed: (1) the late 20th century advance culminated in a broad <5 m high terminal moraine, formed by an admixture of "bulldozed" proglacial sediments and dumping of supraglacial material; (2) the 21st century short-lived advances were characterized by 1-2 m high (often multi-crested) ridges with a "saw-tooth" plan-form controlled by longitudinal crevasses outcropping at the terminus; (3) time

  4. An instability theory for the formation of ribbed moraine, drumlins and mega-scale glacial lineations

    PubMed Central

    Fowler, A. C.; Chapwanya, M.

    2014-01-01

    We present a theory for the coupled flow of ice, subglacial water and subglacial sediment, which is designed to represent the processes which occur at the bed of an ice sheet. The ice is assumed to flow as a Newtonian viscous fluid, the water can flow between the till and the ice as a thin film, which may thicken to form streams or cavities, and the till is assumed to be transported, either through shearing by the ice, squeezing by pressure gradients in the till, or by fluvial sediment transport processes in streams or cavities. In previous studies, it was shown that the dependence of ice sliding velocity on effective pressure provided a mechanism for the generation of bedforms resembling ribbed moraine, while the dependence of fluvial sediment transport on water film depth provides a mechanism for the generation of bedforms resembling mega-scale glacial lineations. Here, we combine these two processes in a single model, and show that, depending largely on the granulometry of the till, instability can occur in a range of types which range from ribbed moraine through three-dimensional drumlins to mega-scale glacial lineations. PMID:25383019

  5. An instability theory for the formation of ribbed moraine, drumlins and mega-scale glacial lineations.

    PubMed

    Fowler, A C; Chapwanya, M

    2014-11-01

    We present a theory for the coupled flow of ice, subglacial water and subglacial sediment, which is designed to represent the processes which occur at the bed of an ice sheet. The ice is assumed to flow as a Newtonian viscous fluid, the water can flow between the till and the ice as a thin film, which may thicken to form streams or cavities, and the till is assumed to be transported, either through shearing by the ice, squeezing by pressure gradients in the till, or by fluvial sediment transport processes in streams or cavities. In previous studies, it was shown that the dependence of ice sliding velocity on effective pressure provided a mechanism for the generation of bedforms resembling ribbed moraine, while the dependence of fluvial sediment transport on water film depth provides a mechanism for the generation of bedforms resembling mega-scale glacial lineations. Here, we combine these two processes in a single model, and show that, depending largely on the granulometry of the till, instability can occur in a range of types which range from ribbed moraine through three-dimensional drumlins to mega-scale glacial lineations. PMID:25383019

  6. Records of past ice sheet fluctuations in interior East Antarctica

    USGS Publications Warehouse

    Liu, Xiaohan; Huang, Feixin; Kong, Ping; Fang, Aimin; Li, Xiaoli

    2007-01-01

    The results of a land-based multi-disciplinary study of the past ice surface elevation in the Grove Mountains of interior East Antarctica support a dynamic evolution of the East Antarctic Ice Sheet (EAIS). Moraine boulders of sedimentary rocks and spore pollen assemblage imply a significant shrinkage of the EAIS, with its margin retreating south of the Grove Mountains (~450 km south of recent coast line) before the middle Pliocene. The exposure ages indicate that the ice sheet subsequently re-advanced, with the ice surface rising locally at least 450 m higher than today. It then went back down constantly from before 2.3 Ma to 1.6 Ma. The glacial topography and existence of soil show that the ice surface fluctuation continued since the early Quaternary, but with highest levels never exceeding ~100 m higher than today.

  7. First geomorphological record and glacial history of an inter-ice stream ridge on the West Antarctic continental shelf

    NASA Astrophysics Data System (ADS)

    Klages, J. P.; Kuhn, G.; Hillenbrand, C.-D.; Graham, A. G. C.; Smith, J. A.; Larter, R. D.; Gohl, K.

    2013-02-01

    Inter-ice stream areas cover significant portions of Antarctica's formerly glaciated shelves, but have been largely neglected in past geological studies because of overprinting by iceberg scours. Here, we present results of the first detailed survey of an inter-ice stream ridge from the West Antarctic continental shelf. Well-preserved sub- and proglacial bedforms on the seafloor of the ridge in the eastern Amundsen Sea Embayment (ASE) provide new insights into the flow dynamics of this sector of the West Antarctic Ice Sheet (WAIS) during the Last Glacial cycle. Multibeam swath bathymetry and PARASOUND acoustic sub-bottom profiler data acquired across a mid-shelf bank, between the troughs of the Pine Island-Thwaites (PITPIS) and Cosgrove palaeo-ice streams (COPIS), reveal large-scale ribbed moraines, hill-hole pairs, terminal moraines, and crevasse-squeeze ridges. Together, these features form an assemblage of landforms that is entirely different from that in the adjacent ice-stream troughs, and appears to be unique in the context of previous studies of Antarctic seafloor geomorphology. From this assemblage, the history of ice flow and retreat from the inter-ice stream ridge is reconstructed. The bedforms indicate that ice flow was significantly slower on the inter-ice stream ridge than in the neighbouring troughs. While terminal moraines record at least two re-advances or stillstands of the ice sheet during deglaciation, an extensive field of crevasse-squeeze ridges indicates ice stagnation subsequent to re-advancing ice, which deposited the field of terminal moraines in the NE. The presented data suggest that the ice flow behaviour on the inter-ice stream ridge was substantially different from that in the adjacent troughs. However, newly obtained radiocarbon ages on two sediment cores recovered from the inter-ice stream ridge suggest a similar timing in the deglaciation of both areas. This information closes an important gap in the understanding of past WAIS

  8. Ice ages and the thermal equilibrium of the earth, II

    USGS Publications Warehouse

    Adam, D.P.

    1975-01-01

    The energy required to sustain midlatitude continental glaciations comes from solar radiation absorbed by the oceans. It is made available through changes in relative amounts of energy lost from the sea surface as net outgoing infrared radiation, sensible heat loss, and latent heat loss. Ice sheets form in response to the initial occurrence of a large perennial snowfield in the subarctic. When such a snowfield forms, it undergoes a drastic reduction in absorbed solar energy because of its high albedo. When the absorbed solar energy cannot supply local infrared radiation losses, the snowfield cools, thus increasing the energy gradient between itself and external, warmer areas that can act as energy sources. Cooling of the snowfield progresses until the energy gradients between the snowfield and external heat sources are sufficient to bring in enough (latent plus sensible) energy to balance the energy budget over the snowfield. Much of the energy is imported as latent heat. The snow that falls and nourishes the ice sheet is a by-product of the process used to satisfy the energy balance requirements of the snowfield. The oceans are the primary energy source for the ice sheet because only the ocean can supply large amounts of latent heat. At first, some of the energy extracted by the ice sheet from the ocean is stored heat, so the ocean cools. As it cools, less energy is lost as net outgoing infrared radiation, and the energy thus saved is then available to augment evaporation. The ratio between sensible and latent heat lost by the ocean is the Bowen ratio; it depends in part on the sea surface temperature. As the sea surface temperature falls during a glaciation, the Bowen ratio increases, until most of the available energy leaves the oceans as sensible, rather than latent heat. The ice sheet starves, and an interglacial period begins. The oscillations between stadial and interstadial intervals within a glaciation are caused by the effects of varying amounts of

  9. Quantifying Sea Ice Advection Through Key "Gates" in the Arctic Using the Sea Ice Motion and Age Data Products at the University of Colorado, Boulder With Applications to Studying Changes in the Arctic Ice Pack.

    NASA Astrophysics Data System (ADS)

    Tooth, M.; Tschudi, M. A.

    2015-12-01

    The past several decades have seen an alarming decline in sea ice extent, and a trend toward thinner, first-year ice throughout the Arctic. This younger ice has a lower probability of surviving the next melt season, and features different surface properties than multi-year ice floes typically possess. Through the combination of satellite passive microwave observations and buoy data, the motion and age of the ice pack in the Arctic are tracked and analyzed using datasets produced at the University of Colorado, Boulder that are archived at the National Snow and Ice Data Center. The ice motion product is produced daily from 1978 to the present, and the weekly age data span from 1985 onward. Using these products, the advection of first-year and multi-year ice is tracked through several key ice "gates" throughout the Arctic on relatively short time scales. Understanding the "sinks" that sea ice travels to and melts in will provide a more complete picture of the underlying causes in the decline in sea ice extent and volume in the Arctic. Through tracking the trajectory and locations of ice parcels in our ice motion product, we can also use other co-located data products to assess the impact of radiative and other climate component forcing on the Arctic ice pack.

  10. Extending Glacier Monitoring into the Little Ice Age and Beyond

    NASA Astrophysics Data System (ADS)

    Nussbaumer, S. U.; Gärtner-Roer, I.; Zemp, M.; Zumbühl, H. J.; Masiokas, M. H.; Espizua, L. E.; Pitte, P.

    2011-12-01

    Glaciers are among the best natural proxies of climatic changes and, as such, a key variable within the international climate observing system. The worldwide monitoring of glacier distribution and fluctuations has been internationally coordinated for more than a century. Direct measurements of seasonal and annual glacier mass balance are available for the past six decades. Regular observations of glacier front variations have been carried out since the late 19th century. Information on glacier fluctuations before the onset of regular in situ measurements have to be reconstructed from moraines, historical evidence, and a wide range of dating methods. The majority of corresponding data is not available to the scientific community which challenges the reproducibility and direct comparison of the results. Here, we present a first approach towards the standardization of reconstructed Holocene glacier front variations as well as the integration of the corresponding data series into the database of the World Glacier Monitoring Service (www.wgms.ch), within the framework of the Global Terrestrial Network for Glaciers (www.gtn-g.org). The concept for the integration of these reconstructed front variations into the relational glacier database of the WGMS was jointly elaborated and tested by experts of both fields (natural and historical sciences), based on reconstruction series of 15 glaciers in Europe (western/central Alps and southern Norway) and 9 in southern South America. The reconstructed front variation series extend the direct measurements of the 20th century by two centuries in Norway and by four in the Alps and in South America. The storage of the records within the international glacier databases guarantees the long-term availability of the data series and increases the visibility of the scientific research which - in historical glaciology - is often the work of a lifetime. The standardized collection of reconstructed glacier front variations from southern Norway

  11. Little Ice Age climate and oceanic conditions of the Ross Sea, Antarctica from a coastal ice core record

    NASA Astrophysics Data System (ADS)

    Rhodes, R. H.; Bertler, N. A. N.; Baker, J. A.; Steen-Larsen, H. C.; Sneed, S. B.; Morgenstern, U.; Johnsen, S. J.

    2012-07-01

    Increasing paleoclimatic evidence suggests that the Little Ice Age (LIA) was a global climate change event. Understanding the forcings and associated climate system feedbacks of the LIA is made difficult by the scarcity of Southern Hemisphere paleoclimate records. We use a new glaciochemical record of a coastal ice core from Mt. Erebus Saddle, Antarctica, to reconstruct atmospheric and oceanic conditions in the Ross Sea sector of Antarctica over the past five centuries. The LIA is identified in stable isotope (δD) and lithophile element records, which respectively demonstrate that the region experienced 1.6 ± 1.4 °C cooler average temperatures prior to 1850 AD than during the last 150 yr and strong (>57 m s-1) prevailing katabatic winds between 1500 and 1800 AD. Al and Ti concentration increases of an order of magnitude (>120 ppb Al) are linked to enhanced aeolian transport of complex silicate minerals and represent the strongest katabatic wind events of the LIA. These events are associated with three 12-30 yr intervals of cooler temperatures at ca. 1690 AD, 1770 AD and 1840 AD. Furthermore, ice core concentrations of the biogenic sulphur species MS- suggest that biological productivity in the Ross Sea polynya was ~80% higher prior to 1875 AD than at any subsequent time. We propose that cooler Antarctic temperatures promoted stronger katabatic winds across the Ross Ice Shelf, resulting in an enlarged Ross Sea polynya during the LIA.

  12. Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

    NASA Astrophysics Data System (ADS)

    Ewing, S. A.; Paces, J. B.; O'Donnell, J. A.; Jorgenson, M. T.; Kanevskiy, M. Z.; Aiken, G. R.; Shur, Y.; Harden, J. W.; Striegl, R.

    2015-03-01

    The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10-100 ky BP), despite subsequent fluctuations in

  13. Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

    USGS Publications Warehouse

    Ewing, Stephanie A.; Paces, James B.; O'Donnell, J.A.; Jorgenson, M.T.; Kanevskiy, M.Z.; Aiken, George R.; Shur, Y.; Harden, Jennifer W.; Striegl, Rob

    2015-01-01

    The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10–100 ky BP), despite subsequent

  14. Detailed sedimentology and geomorphology elucidate mechanisms of formation of modern and historical sequences of minor moraines in the European Alps

    NASA Astrophysics Data System (ADS)

    Wyshnytzky, Cianna; Lukas, Sven

    2016-04-01

    Suites of closely-spaced minor moraines may help further understanding of glacier retreat and predict its geomorphological effects through the observations of moraine formation on short timescales. This research is common in lowland, maritime settings (Sharp, 1984; Boulton, 1986; Krüger, 1995; Reinardy et al., 2013), but remains sparse in high-mountain settings (Hewitt, 1967; Ono, 1985; Beedle et al., 2009; Lukas, 2012). This research presents detailed sedimentological and geomorphological research on minor moraines at two high-mountain settings in the Alps: Silvrettagletscher, Switzerland, as a modern setting and Schwarzensteinkees, Austria, as a historical setting. Geomorphological investigations included mapping and measurements through field observations and assessing aerial imagery. Additionally, terrestrial laser scanning and ground-penetrating radar data were collected in the Schwarzensteinkees foreland. Detailed sedimentological investigations followed excavation of seven moraines at Silvrettagletscher and five moraines at Schwarzensteinkees and include multiple scales of observation and measurements to support interpretations of sediment transport and deposition (e.g. Evans and Benn, 2004). The modern moraines at Silvrettagletscher, in the immediately proglacial foreland, have been forming since before 2003. Four mechanisms of formation show distinct sedimentological signatures: formerly ice-cored moraines (e.g. Kjær & Krüger, 2001; Lukas, 2012; Reinardy et al., 2013) , push moraine formation on a reverse bedrock slope (e.g. Lukas, 2012), push moraine formation incorporating sediments deposited in a former proglacial basin, and basal freeze-on (e.g. Andersen & Sollid, 1971; Krüger, 1995; Reinardy et al., 2013). Schwarzensteinkees still exists but is currently restricted to steeply-dipping bedrock slabs above the main valley. This study therefore investigates the moraines in the foreland that formed between approximately 1850 and 1930. The minor

  15. Applications of Cosmogenic He-3 and Ne-21 Dating to Glacial Moraines in Antarctica and California

    NASA Astrophysics Data System (ADS)

    Sams, S.; Morgan, D. J.; Balco, G.; Putkonen, J.; Bibby, T.

    2015-12-01

    The depositional age of moraines can be determined through cosmogenic nuclide exposure dating. These ages are useful in establishing a glacial history of an area and ascribing age constraints to transport processes. Be-10 is the most common nuclide used for exposure dating today, but this method is both expensive and time consuming because it requires analysis by accelerator mass spectrometry (AMS). He-3 and Ne-21 can be analyzed using noble gas mass spectrometry, which is more cost efficient than AMS and requires less chemical preparation. We collected samples from areas in Moraine Canyon, Antarctica (86.10° S, 157.75° W), which is a dry valley in the Transantarctic Mountains. Dolerite boulders along a transect of recessional moraines were sampled in the typical fashion of using a large piece of the boulder for analysis. Pyroxene minerals have been separated from these samples following the method of Bromley et al. (2014) using hydrofluoric acid. Exposure ages will be calculated from the He-3 concentrations in them. In the Mono Lake area of California, moraines were sampled from Bloody Canyon and McGee Creek sites. Instead of collecting a sample from an individual boulder, we collected approximately 25 granitic pebbles (1-3 cm) from 4-6 sites along the crest of the moraines following the method of Briner (2009). Each suite of pebbles was crushed together, and quartz minerals were separated from the agglomeration of pebbles. Cosmogenic Ne-21 will be measured from these samples to determine their exposure age. From these two field sites, we will use He-3 and Ne-21 to better understand the timing and extent of glaciation in these areas.

  16. Combination of in situ cosmogenic nuclide (10Be) and Schmidt-hammer dating for the investigation of Late-Holocene lateral moraines in the Southern Alps of New Zealand

    NASA Astrophysics Data System (ADS)

    Winkler, S.

    2009-04-01

    The investigation of Holocene glacier chronologies in high mountain regions is important for use of glaciers as indicators for climate change. Only detailed Holocene glacier chronologies offer the opportunity to improve our knowledge on the relationship between glaciers and climate factors, and to verify models of the future glacier development. The Southern Alps of New Zealand represent the southern hemispheric study area within the complex comparative current research project "MaMoGla" (Holocene and recent dynamics of maritime mountain glaciers). Among other goals, new methodological attempts to date the dominating lateral moraines in the Southern Alps in order to revise existing glaciers chronologies have been integrated in this project. The need for improvement of the existing Holocene glacier chronology of the Southern Alps/New Zealand is mainly caused by methodological uncertainties and the focus on Tasman Glaciers as unreliable key locality. Previously, radiocarbon (14C) dating of organic material (plant remains, organic-rich soil layers etc.) buried beneath or within the complex lateral moraines was the predominating ‘absolute' dating technique applied. In addition to older studies using the measurement of weathering rind thickness on boulders, the potential of the Schmidt-hammer as relative-age dating technique has clearly been demonstrated by the successful application on several lateral and latero-frontal moraine sequences in the Mt Cook/Aoraki National Park. The relatively homogenous and weathering/erosion-resistant bedrock yielded comparatively small standard errors and, thus, a relatively high time resolution of up to 200 - 300 years. Supported by statistical treatment of the raw field data, the Schmidt-hammer provided sufficient information to group the individual moraine ridges into moraine sequences and relate them to separate Little Ice Age-type events. However, the final ‘absolute' age dating of the moraine sequences remained open. As an

  17. Little Ice Age Glaciation in Alaska: A record of recent global climatic change

    SciTech Connect

    Calkin, P.E.; Wiles, G.C.

    1992-03-01

    General global cooling and temperature fluctuation accompanied by expansion of mountain glaciers characterized the Little Ice Age of about A.D. 1200 through A.D. 1900. The effects of such temperature changes appear first and are strongest at high latitudes. Therefore the Little Ice Age record of glacial fluctuation in Alaska may provide a good proxy for these events and a test for models of future climatic change. Holocene expansions began here as early as 7000 B.P. and locally show a periodicity of 350 years after about 4500 years B.P. The Little Ice Age followed a late Holocene interval of minor ice advance and a subsequent period of ice margin recession lasting one to seven centuries. The timing of expansions since about A.D. 1200 have often varied between glaciers, but these are the most pervasive glacial events of the Holocene in Alaska and frequently represent ice marginal maxima for this interval. At least two major expansions are, apparent in forefields of both land-terminating and fjord-calving glaciers, but the former display the most reliable and detailed climatic record. Major maxima occurred by the 16th century and into the mid-18th century. Culmination of advances occurred throughout Alaska during the 19th century followed within a few decades by general glacial retreat. Concurrently, equilibrium line altitudes have been raised 100-400 m, representing a rise of 2-3 deg C in mean summer temperature.

  18. Characteristics of recessional moraines at a temperate glacier in SE Iceland: Insights into patterns, rates and drivers of glacier retreat

    NASA Astrophysics Data System (ADS)

    Chandler, Benjamin M. P.; Evans, David J. A.; Roberts, David H.

    2016-03-01

    Icelandic glaciers are sensitive to climate variability on short-term timescales owing to their North Atlantic maritime setting, and have been undergoing ice-marginal retreat since the mid-1990s. Recent patterns, rates and drivers of ice-frontal retreat at Skálafellsjökull, SE Iceland, are examined using small-scale recessional moraines as a geomorphological proxy. These small-scale recessional moraines exhibit distinctive sawtooth planform geometries, and are constructed by a range of genetic processes associated with minor ice-margin re-advance, including (i) combined push/squeeze mechanisms, (ii) bulldozing of pre-existing proglacial material, and (iii) submarginal freeze-on. Remote-sensing investigations and lichenometric dating highlight sequences of annually-formed recessional moraines on the northern and central parts of the foreland. Conversely, moraines are forming on a sub-annual timescale at the southeastern Skálafellsjökull margin. Using annual moraine spacing as a proxy for annual ice-margin retreat rates (IMRRs), we demonstrate that prominent periods of glacier retreat at Skálafellsjökull are coincident with those at other Icelandic outlet glaciers, as well as those identified at Greenlandic outlet glaciers. Analysis of IMRRs and climate data suggests summer air temperature, sea surface temperature and the North Atlantic Oscillation have an influence on IMRRs at Skálafellsjökull, with the glacier appearing to be most sensitive to summer air temperature. On the basis of further climate data analyses, we hypothesise that sea surface temperature may drive air temperature changes in the North Atlantic region, which in turn forces IMRRs. The increase in sea surface temperature over recent decades may link to atmospheric-driven variations in North Atlantic subpolar gyre dynamics.

  19. Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.; Argus, D. F.; Drummond, R.

    2015-01-01

    A new model of the last deglaciation event of the Late Quaternary ice age is here described and denoted as ICE-6G_C (VM5a). It differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available Global Positioning System (GPS) measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal. Additional space geodetic constraints have also been applied to specify the reference frame within which the GPS data are described. The focus of the paper is upon the three main regions of Last Glacial Maximum ice cover, namely, North America, Northwestern Europe/Eurasia, and Antarctica, although Greenland and the British Isles will also be included, if peripherally, in the discussion. In each of the three major regions, the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the Gravity Recovery and Climate Experiment satellites as an independent means of verifying the improvement of the model achieved by applying the GPS constraints. Several aspects of the global characteristics of this new model are also discussed, including the nature of relative sea level history predictions at far-field locations, in particular the Caribbean island of Barbados, from which especially high-quality records of postglacial sea level change are available but which records were not employed in the development of the model. Although ICE-6G_C (VM5a) is a significant improvement insofar as the most recently available GPS observations are concerned, comparison of model predictions with such far-field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration.

  20. Little ice age evidence from a south-central North American ice core, U.S.A.

    SciTech Connect

    Naftz, D.L.; Klusman, R.W.; Michel, R.L.

    1996-02-01

    In the past, ice-core records from mid-latitude glaciers in alpine areas of the continental United States were considered to be poor candidates for paleoclimate records because of the influence of meltwater on isotopic stratigraphy. To evaluate the existence of reliable paleoclimatic records, a 160-m ice core, containing about 250 yr of record was obtained from Upper Fremont Glacier, at an altitude of 4000 m in the Wind River Range of south-central North America. The {gamma}{sup 18}O (SMOW) profile from the core shows a -0.95{per_thousand} shift to lighter values in the interval from 101.8 to 150 m below the surface, corresponding to the latter part of the Little Ice Age (LIA). Numerous high-amplitude oscillations in the section of the core from 101.8 to 150 m cannot be explained by site-specific lateral variability and probably reflect increased seasonality or better preservation of annual signals as a result of prolonged cooler temperatures that existed in this alpine setting. An abrupt decrease in these large amplitude oscillations at the 101.8-m depth suggests a sudden termination of this period of lower temperatures which generally coincides with the termination of the LIA. Three common features in the {gamma}{sup 18}O profiles between Upper Fremont Glacier and the better dated Quelccaya Ice Cap cores indicate a global paleoclimate linkage, further supporting the first documented occurrence of the LIA in an ice-core record from a temperate glacier in south-central North America.

  1. Establishing a Reliable Depth-Age Relationship for the Denali Ice Core

    NASA Astrophysics Data System (ADS)

    Wake, C. P.; Osterberg, E. C.; Winski, D.; Ferris, D.; Kreutz, K. J.; Introne, D.; Dalton, M.

    2015-12-01

    Reliable climate reconstruction from ice core records requires the development of a reliable depth-age relationship. We have established a sub-annual resolution depth-age relationship for the upper 198 meters of a 208 m ice core recovered in 2013 from Mt. Hunter (3,900 m asl), Denali National Park, central Alaska. The dating of the ice core was accomplished via annual layer counting of glaciochemical time-series combined with identification of reference horizons from volcanic eruptions and atmospheric nuclear weapons testing. Using the continuous ice core melter system at Dartmouth College, sub-seasonal samples have been collected and analyzed for major ions, liquid conductivity, particle size and concentration, and stable isotope ratios. Annual signals are apparent in several of the chemical species measured in the ice core samples. Calcium and magnesium peak in the spring, ammonium peaks in the summer, methanesulfonic acid (MSA) peaks in the autumn, and stable isotopes display a strong seasonal cycle with the most depleted values occurring during the winter. Thin ice layers representing infrequent summertime melt were also used to identify summer layers in the core. Analysis of approximately one meter sections of the core via nondestructive gamma spectrometry over depths from 84 to 124 m identified a strong radioactive cesium-137 peak at 89 m which corresponds to the 1963 layer deposited during extensive atmospheric nuclear weapons testing. Peaks in the sulfate and chloride record have been used for the preliminary identification of volcanic signals preserved in the ice core, including ten events since 1883. We are confident that the combination of robust annual layers combined with reference horizons provides a timescale for the 20th century that has an error of less than 0.5 years, making calibrations between ice core records and the instrumental climate data particularly robust. Initial annual layer counting through the entire 198 m suggests the Denali Ice

  2. Combination of in situ cosmogenic nuclide (10Be) and Schmidt-hammer dating for the investigation of Late-Holocene lateral moraines in the Southern Alps of New Zealand

    NASA Astrophysics Data System (ADS)

    Winkler, S.

    2009-04-01

    The investigation of Holocene glacier chronologies in high mountain regions is important for use of glaciers as indicators for climate change. Only detailed Holocene glacier chronologies offer the opportunity to improve our knowledge on the relationship between glaciers and climate factors, and to verify models of the future glacier development. The Southern Alps of New Zealand represent the southern hemispheric study area within the complex comparative current research project "MaMoGla" (Holocene and recent dynamics of maritime mountain glaciers). Among other goals, new methodological attempts to date the dominating lateral moraines in the Southern Alps in order to revise existing glaciers chronologies have been integrated in this project. The need for improvement of the existing Holocene glacier chronology of the Southern Alps/New Zealand is mainly caused by methodological uncertainties and the focus on Tasman Glaciers as unreliable key locality. Previously, radiocarbon (14C) dating of organic material (plant remains, organic-rich soil layers etc.) buried beneath or within the complex lateral moraines was the predominating ‘absolute' dating technique applied. In addition to older studies using the measurement of weathering rind thickness on boulders, the potential of the Schmidt-hammer as relative-age dating technique has clearly been demonstrated by the successful application on several lateral and latero-frontal moraine sequences in the Mt Cook/Aoraki National Park. The relatively homogenous and weathering/erosion-resistant bedrock yielded comparatively small standard errors and, thus, a relatively high time resolution of up to 200 - 300 years. Supported by statistical treatment of the raw field data, the Schmidt-hammer provided sufficient information to group the individual moraine ridges into moraine sequences and relate them to separate Little Ice Age-type events. However, the final ‘absolute' age dating of the moraine sequences remained open. As an

  3. Iron fertilization of the Subantarctic ocean during the last ice age.

    PubMed

    Martínez-García, Alfredo; Sigman, Daniel M; Ren, Haojia; Anderson, Robert F; Straub, Marietta; Hodell, David A; Jaccard, Samuel L; Eglinton, Timothy I; Haug, Gerald H

    2014-03-21

    John H. Martin, who discovered widespread iron limitation of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused the ice age reduction in atmospheric carbon dioxide (CO2). In a sediment core from the Subantarctic Atlantic, we measured foraminifera-bound nitrogen isotopes to reconstruct ice age nitrate consumption, burial fluxes of iron, and proxies for productivity. Peak glacial times and millennial cold events are characterized by increases in dust flux, productivity, and the degree of nitrate consumption; this combination is uniquely consistent with Subantarctic iron fertilization. The associated strengthening of the Southern Ocean's biological pump can explain the lowering of CO2 at the transition from mid-climate states to full ice age conditions as well as the millennial-scale CO2 oscillations. PMID:24653031

  4. Controls on interior West Antarctic Ice Sheet Elevations: inferences from geologic constraints and ice sheet modeling

    NASA Astrophysics Data System (ADS)

    Ackert, Robert P.; Putnam, Aaron E.; Mukhopadhyay, Sujoy; Pollard, David; DeConto, Robert M.; Kurz, Mark D.; Borns, Harold W.

    2013-04-01

    Knowledge of the West Antarctic Ice Sheet (WAIS) response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future. The timing and extent of past interior WAIS elevation changes provides insight to WAIS behavior and constraints for ice sheet models. Constraints prior to the Last Glacial Maximum (LGM) however, are rare. Surface exposure ages of glacial erratics near the WAIS divide at Mt. Waesche in Marie Byrd Land, and at the Ohio Range in the Transantarctic Mountains, range from ∼10 ka to >500 ka without a dependence on elevation. The probability distribution functions (PDF) of the exposure ages at both locations, are remarkably similar. During the last glaciation, maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka. However, most exposure ages are older than the LGM and cluster around ∼40 ka and ∼80 ka. The peak in the exposure age distributions at ∼40 ka includes ages of alpine moraine boulders at Mercer Ridge in the Ohio Range. Comparison of the PDF of exposures ages from the Ohio Range and Mt. Waesche with the temperature record from the Fuji Dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the Last Glacial termination. A prominent peak in the Ohio Range PDF corresponds to the penultimate termination (stage 5e). During the intervening glacial period, there is not a consistent relationship between the peaks in the PDF at each location and temperature. A combined ice sheet/ice shelf model with forcing scaled to marine δ18O predicts that interior WAIS elevations near the ice divide have varied ∼300 m over the Last Glacial cycle. Peaks in the PDF correspond to model highstands over the last 200 ka. In the simulated elevation history, maximum ice elevations at Ohio Range (+100 m) and Mt. Waesche (+60 m) occur at ∼10 ka, in agreement with observations from these sites

  5. The effect of rainfall events with changing frequency and magnitude on reworking conditions of proglacial moraines

    NASA Astrophysics Data System (ADS)

    Dusik, Jana-Marie; Heckmann, Tobias; Neugirg, Fabian; Hilger, Ludwig; Haas, Florian; Becht, Michael

    2014-05-01

    The consequences of the ongoing temperature rise in alpine regions force glaciers to rapid melting and thus new surfaces are exposed to generate numerous geomorphic processes. Steep Little Ice Age (LIA) moraines and other glacial depositional landforms contain huge masses of sediments, that are subject to progressive (re-)mobilization by gullying, slope wash, debris flows and other mass movements. The material is frequently re-deposited in secondary storage landforms; these storages themselves are then subject to depletion. Increased morphodynamics with a maximum shortly after deglaciation, and a slow decrease afterwards, are predicted by the conceptual model of paraglacial response. In addition to these "self-organising" changes following deglaciation, our study area has been experiencing changes in precipitation and (meltwater) discharge for decades; these climatic factors are known to influence morphodynamics, e.g. by triggering mass movements and by driving slope wash and fluvial erosion. While overall precipitation appears to decrease, heavy rainfall events become more intense, and discharge rates of glacial melt water channels show a significant increase. The PROSA joint project (High-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) uses terrestrial and airborne LiDAR data and digital Photogrammetry to monitor surface changes in the Upper Kaunertal, Austrian Central Alps (64 km²). These are related to the deglaciation since the end of the LIA and to changes in hydrometeorological parameters since several decades ago. The aim of this study is to investigate a possible relationship between climate change signals and erosion rates in the proglacial area of the Gepatschferner. The morphodynamics of steep LIA moraines are assessed on multiple temporal scales: Long-term changes are analyzed based on multitemporal airborne images dating back to 1953. The recent development is measured using digital elevation models (DEM

  6. Reaching and abandoning the furthest ice extent during the Last Glacial Maximum in the Alps

    NASA Astrophysics Data System (ADS)

    Ivy-Ochs, Susan; Wirsig, Christian; Zasadni, Jerzy; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

    2016-04-01

    During the Last Glacial Maximum (LGM) in the European Alps (late Würm) local ice caps and extensive ice fields in the high Alps fed huge outlet glaciers that occupied the main valleys and extended onto the forelands as piedmont lobes. Records from numerous sites suggest advance of glaciers beyond the mountain front by around 30 ka (Ivy-Ochs 2015 and references therein). Reaching of the maximum extent occurred by about 27-26 ka, as exemplified by dates from the Rhein glacier area (Keller and Krayss, 2005). Abandonment of the outermost moraines at sites north and south of the Alps was underway by about 24 ka. In the high Alps, systems of transection glaciers with transfluences over many of the Alpine passes dominated, for example, at Grimsel Pass in the Central Alps (Switzerland). 10Be exposure ages of 23 ± 1 ka for glacially sculpted bedrock located just a few meters below the LGM trimline in the Haslital near Grimsel Pass suggest a pulse of ice surface lowering at about the same time that the foreland moraines were being abandoned (Wirsig et al., 2016). Widespread ice surface lowering in the high Alps was underway by no later than 18 ka. Thereafter, glaciers oscillated at stillstand and minor re-advance positions on the northern forelands for several thousand years forming the LGM stadial moraines. Final recession back within the mountain front took place by 19-18 ka. Recalculation to a common basis of all published 10Be exposure dates for boulders situated on LGM moraines suggests a strong degree of synchrony for the timing of onset of ice decay both north and south of the Alps. Ivy-Ochs, S., 2015, Cuadernos de investigación geográfica 41: 295-315. Keller, O., Krayss, E., 2005, Vierteljahrschr. Naturforsch. Gesell. Zürich 150: 69-85. Wirsig, C. et al., 2016, J. Quat. Sci. 31: 46-59.

  7. Geomorphic influences of the Little Ice Age glacial advance on selected hillslope systems in Nordfjord, Western Norway (Erdalen and Bødalen valleys)

    NASA Astrophysics Data System (ADS)

    Laute, Katja; Beylich, Achim A.

    2010-05-01

    interpretation, hillslope profile surveying, photo monitoring, geomorphological mapping as well as GIS and DEM computing. Two appropriate hillslope test sites within each headwater area are selected in order to follow the main aims of this study. The designed monitoring instrumentation of the slope test sites includes nets for collecting freshly accumulated rockfall debris, stone tracer lines for measuring surface movements, wooden sticks for monitoring of slow surface creep movements and peg lines for depth-integrated measurements of slow mass movements. In addition, remote site cameras for monitoring rapid mass movement events (avalanches, slush- and debris flows) and slope wash traps for analyzing slope wash denudation are installed and measurements of solute concentrations at small hillslope drainage creeks for investigating the role of chemical denudation are conducted. Measurements of morphometric characteristics and longitudinal profiles along the main axis of the talus cones are carried out at each test site. The manually obtained longitudinal profile data are combined with data derived from a DEM in order to generate complete longitudinal hillslope profiles reaching from the apex until the slope foot. Preliminary results show a steepening trend of the talus cones located inside the Little Ice Age glacier limit which is due to erosion during the Little Ice Age glacial advance. In addition, some of these talus cones are characterized by a recognizable more complex talus cone morphometry and composition, resulting from implementation of Little Ice Age glacier side moraines. The combination of (i) steepened talus cones and (ii) complex composition seems to increase currently acting hillslope processes which leads to a higher sediment delivery from these slopes as compared to hillslopes outside the Little Ice Age glacier limit. The implementation of moraine material but also the increased intensity of denudative processes has a recognizable influence on the mass balance of

  8. Improved age constraints for the retreat of the Irish Sea Ice Stream

    NASA Astrophysics Data System (ADS)

    Smedley, Rachel; Chiverrell, Richard; Duller, Geoff; Scourse, James; Small, David; Fabel, Derek; Burke, Matthew; Clarke, Chris; McCarroll, Danny; McCarron, Stephen; O'Cofaigh, Colm; Roberts, David

    2016-04-01

    BRITICE-CHRONO is a large (> 45 researchers) consortium project working to provide an extensive geochronological dataset constraining the rate of retreat of a number of ice streams of the British-Irish Ice Sheet following the Last Glacial Maximum. When complete, the large empirical dataset produced by BRITICE-CHRONO will be integrated into model simulations to better understand the behaviour of the British-Irish Ice Sheet in response to past climate change, and provide an analogue for contemporary ice sheets. A major feature of the British-Irish Ice Sheet was the dynamic Irish Sea Ice Stream, which drained a large proportion of the ice sheet and extended to the proposed southern limit of glaciation upon the Isles of Scilly (Scourse, 1991). This study will focus on a large suite of terrestrial samples that were collected along a transect of the Irish Sea basin, covering the line of ice retreat from the Isles of Scilly (50°N) in the south, to the Isle of Man (54°N) in the north; a distance of 500 km. Ages are determined for both the eastern and western margins of the Irish Sea using single-grain luminescence dating (39 samples) and terrestrial cosmogenic nuclide dating (10 samples). A Bayesian sequence model is then used in combination with the prior information determined for deglaciation to integrate the geochronological datasets, and assess retreat rates for the Irish Sea Ice Stream. Scourse, J.D., 1991. Late Pleistocene stratigraphy and palaeobotany of the Isles of Scilly. Philosophical Transactions of the Royal Society of London B334, 405 - 448.

  9. Sedimentology and architecture of De Geer moraines in the western Scottish Highlands, and implications for grounding-line glacier dynamics

    NASA Astrophysics Data System (ADS)

    Golledge, Nicholas R.; Phillips, Emrys

    2008-07-01

    Sedimentary exposures in moraines in a Scottish Highland valley (Glen Chaorach), reveal stacked sequences of bedded and laminated silt, sand and gravel, interspersed or capped with diamicton units. In four examples, faults and folds indicate deformation by glaciotectonism and syndepositional loading. We propose that these sediments were laid down in an ice-dammed lake, close to the last ice margin to occupy this glen. Individual units within cross-valley De Geer moraine ridges are interpreted by comparison with examples from similar environments elsewhere: stratified diamictons containing laminated or bedded lenses are interpreted as subaqueous ice-marginal debris-flow deposits; massive fine-grained deposits as hyperconcentrated flow deposits, and massive gravel units as high-density debris-flow deposits. Using an allostratigraphic approach we argue that glaciotectonically deformed coarsening-upward sand and gravel sequences that culminate in deposition of subglacial diamicton represent glacier advances into the ice-marginal lake, whereas undisturbed cross-bedded sand and gravel reflects channel or fan deposits laid down during glacier retreat. A flat terrace of bedded sand and gravel at the northern end of Glen Chaorach is interpreted as subaerial glaciofluvial outwash. On the basis of these inferences we propose the following three stage deglacial event chronology for Glen Chaorach. During glacier recession, ice separation and intra-lobe ponding first led to subaquaeous deposition of sorted and unsorted facies. Subsequent glacier stabilisation and ice-marginal oscillation produced glaciotectonic structures in the ice-marginal sediment pile and formed De Geer moraines. Finally, drainage of the ice-dammed lake allowed a subaerial ice-marginal drainage system to become established. Throughout deglaciation, deposition within the lake was characterized by abrupt changes in grain size and in the architecture of individual sediment bodies, reflecting changing delivery

  10. New land, new opportunitites. Vegetation succession and soil formation within the heterogenous moraines formed by the Skaftafellsjökull and Breiðamerkurjökull outlet glaciers in Southeast Iceland.

    NASA Astrophysics Data System (ADS)

    Vilmundardóttir, Olga K.; Gísladóttir, Guðrún; Lal, Rattan

    2016-04-01

    Retreating glaciers expose heterogenous landscapes where primary vegetation succession becomes active. These glacier forelands are excellent sites to study the effects of landscape on vegetation establishment and the commencing soil formation. Where the location of the glacier terminus is known in time, a chronosequence can be established, thus allowing for assessing the role of time on both vegetation succession and soil development. In Iceland, glaciers have been more or less retreating since the end of the Little Ice Age in ~1890, exposing thick moraines mostly composed of ground basaltic material of volcanic origin. In a research from southeast Iceland, soil formation was studied in front of two outlet glaciers, Skaftafellsjökull and Breiðamerkurjökull, and the developing soil properties analyzed with regards to the age of the surface, vegetation, avifauna and topography. At Skaftafellsjökull, soils were sampled along three moraines of known age. The vegetation was dominated by mosses but dwarf shrubs and shrubs (willows and birch) characterized the older moraines. Vegetation cover and plant group cover was affected by the profile position (summit, shoulder, backslope, footslope, toeslope) and the shape of the topographic features (ridge, slope, depression). The cover was significantly greater in toeslopes and footslopes when compared to the backslopes and featured significantly more shrub cover. The vegetation cover was significantly denser in depressions than on ridges and slopes, predominantly comprising mosses and shrubs. On the other hand, macro-lichens predominated on ridges. The vegetation cover and soil properties showed the strongest relation between total vegetation cover, cover of mosses, macro-lichens and dwarf shrubs. The concentration of SOC, N and ammonium oxalate extractable Al increased significantly with increase in vegetation cover and showed similar trends of increase in the cover by mosses, macro-lichens and dwarf shrubs. Profile

  11. Cosmogenic {sup 36}Cl accumulation in unstable landforms 2. Simulations and measurements on eroding moraines

    SciTech Connect

    Zreda, M.G.; Phillips, F.M.; Elmore, D.

    1994-11-01

    Cosmogenic {sup 36}Cl ages of boulders from late Pleistocene moraines in Bishop Creek, Sierra Nevada, California, provided valuable details about {sup 36}Cl surface exposure dating and the nature of post depositional processes that modify glacial landforms. The natural variability of the apparent {sup 36}Cl ages among morainal boulders is due to soil erosion and gradual exposure of boulders at the surface. Two mechanisms are responsible for the resulting distributions of the apparent {sup 36}Cl ages. Variability of the initial burial depth among boulders and variability in the chemical composition of boulders from the same depth both result in different {sup 36}Cl ages due to the dependence of the depth production profile on the boulder chemistry. The authors measured cosmogenic {sup 36}Cl in boulders from a late Pleistocene moraine. The distribution of the calculated apparent ages allowed them to calculate the true age of 85 kyr and the erosion rate of 570 g cm{sup -2}. These results are in excellent agreement with independently estimated values of 87 kyr and 600 g cm{sup -2} for the age and erosion depth, respectively. These results indicate that the model satisfactorily simulates effects of erosion processes and can thus aid in surface exposure dating of eroding landforms.

  12. The Impact of Gravitationally Self-Consistent Ice Age Sea-Level Variations on the Evolution of the Antarctic Ice Sheet (Invited)

    NASA Astrophysics Data System (ADS)

    Gomez, N. A.; Pollard, D.; Mitrovica, J. X.

    2013-12-01

    We couple a three-dimensional ice sheet-shelf model to a gravitationally self-consistent global sea-level model in order to investigate the ice age stability of the Antarctic Ice Sheet. The coupled model incorporates deformational and gravitational perturbations to a viscoelastic, rotating Earth and it captures the complex spatiotemporal geometry of post-glacial sea-level change, including at the grounding lines of marine-based ice. We apply the coupled model to simulate the evolution of the Antarctic Ice Sheet over the last 40,000 years, focusing in particular on ice distributions and sea levels from the Last Glacial Maximum to present. The results demonstrate, in support of our earlier work based on simplified, one-dimensional ice-sheet models, that the sea-level feedback has a significant stabilizing influence on marine ice-sheets, acting to slow down grounding-line migration relative to ice sheet model simulations that do not include the sea-level coupling. We also explore the sensitivity of the results to adopted Earth and ice model parameters and compare our model predictions to relative sea level (RSL) histories and GPS-derived present-day uplift rates at sites around the periphery of Antarctica. We find that the coupled model yields improved fits to uplift rates. The model also yields fits to the RSL observations that are comparable to those reported in recent, uncoupled simulations in which the viscoelastic Earth model was varied to obtain a best fit.

  13. Simulating Dust Cycling during the Late Paleozoic Ice Age

    NASA Astrophysics Data System (ADS)

    Heavens, N. G.; Mahowald, N. M.; Soreghan, G. S.; Soreghan, M. J.; Shields, C. A.; Albani, S.

    2012-12-01

    Upper Carboniferous and Lower Permian strata preserve evidence for significant deposition of mineral dust, an aerosol with strong potential influence on the climate. Some equatorial marine carbonate records from this interval appear to record massive influxes of fine dust (diameter < 10 μm) after rapid sea level fall, suggesting that the pacing of dust deposition was connected to the expansion and contraction of ice sheets during the important icehouse climate interval of Carboniferous and Permian time. Nearby continental strata record high accumulations of coarse dust (loess) during periods of increasing aridity (apparent glacial intervals) and of fine dust (paleosols) during periods of increasing humidity (apparent interglacial intervals), though the pacing of this deposition may be more strongly associated with orbital forcing than ice sheet dynamics. Significant dust deposition continued in many of these areas during the emergence of the Earth's climate from icehouse conditions during Middle Permian time. Understanding the dynamics of dust cycling during the depths of the icehouse is the first step to investigating dust records from the most recent icehouse termination of Earth's history. Here, we attempt to reconstruct the cycling and some of the potential climate impacts of mineral dust during this interval, using version 3 of the Community Climate System Model (CCSM3) and the best available records of dust deposition. Modeled sensitivity simulations suggest that climatic controls on dust cycling that act on relatively short timescales (primarily meteorological and vegetation-related) cannot explain the large variability in dust deposition rates inferred from marine carbonate records. Processes acting on longer timescales, particularly those that control the availability of wind-erodible sediment, likely are more important. We also consider whether exposure of sedimentary basins during sea level fall and glaciogenic dust production could modulate dust

  14. Dual-band infrared imaging applications: Locating buried minefields, mapping sea ice, and inspecting aging aircraft

    SciTech Connect

    Del Grande, N.K.; Durbin, P.F.; Perkins, D.E.

    1992-09-01

    We discuss the use of dual-band infrared (DBIR) imaging for three quantitative NDE applications: location buried surrogate mines, mapping sea ice thicknesses and inspecting subsurface flaws in aging aircraft parts. Our system of DBIR imaging offers a unique combination of thermal resolution, detectability, and interpretability. Pioneered at Lawrence Livermore Laboratory, it resolves 0.2 {degrees}C differences in surface temperatures needed to identify buried mine sites and distinguish them from surface features. It produces both surface temperature and emissivity-ratio images of sea ice, needed to accurately map ice thicknesses (e.g., by first removing clutter due to snow and surface roughness effects). The DBIR imaging technique depicts subsurface flaws in composite patches and lap joints of aircraft, thus providing a needed tool for aging aircraft inspections.

  15. Late Pleistocene glacial chronology of the Retezat Mts, Southern Carpathians, using 10Be exposure ages

    NASA Astrophysics Data System (ADS)

    Ruszkiczay-Rüdiger, Zsófia; Kern, Zoltán; Urdea, Petru; Braucher, Régis; Madarász, Balázs; Schimmelpfennig, Irene

    2015-04-01

    Our knowledge on the timing of glacial advances in the Southern Carpathians is limited. Recently, some attempts have been made to develop an improved temporal framework for the glaciations of the region using cosmogenic 10Be exposure dating. However, glacial chronology of the Romanian Carpathians remains contradictory. E.g. the timing of the maximum ice advance appears to be asynchronous within the area and also with other dated glacial events in Europe. Main objective of our study is to utilize cosmogenic in situ produced 10Be dating to disentangle the contradictions of the Southern Carpathian Late Pleistocene glacial chronology. Firstly, previously published 10Be data are recalculated in accordance with the new half-life, standardization and production rate of 10Be. The recalculated 10Be exposure ages of the second largest (M2) moraines in the Retezat Mts. appear to be ca. 19-24% older than exposure ages calculated by Reuther et al. (2007, Quat. Int. 164-165, 151-169). This contradicts the earlier conclusions suggesting post LGM age of M2 glacial advance and suggests that M2 moraines can be connected to the end of the LGM with final stabilization possibly at the beginning of the Late Glacial. We emphasize that it is ambiguous to correlate directly the exposure-dated glacier chronologies with millennial scale climate changes due to uncertainties in sample collection and in computation of exposure ages from measured nuclide concentrations. New 10Be samples were collected in order to determine the 10Be exposure age of moraines outside the most prominent generation (M2) including the largest and oldest moraine (M1) and the landforms connected to the smallest ice advances (M4), which remained undated so far. The new exposure ages of M2 moraines are well in harmony with the recalculated ages of Reuther at al. (2007). 10Be exposure age of boulders on the smallest moraine suggest that the last glaciers disappeared in the area during the Late Glacial, indicating no

  16. Foraminiferal faunal estimates of paleotemperature: Circumventing the no-analog problem yields cool ice age tropics

    USGS Publications Warehouse

    Mix, A.C.; Morey, A.E.; Pisias, N.G.; Hostetler, S.W.

    1999-01-01

    The sensitivity of the tropics to climate change, particularly the amplitude of glacial-to-interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no-analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods. A new calibration strategy developed here, which uses past variability of species to define robust faunal assemblages, solves the no-analog problem and reveals ice age cooling of 5??to 6??C in the equatorial current systems of the Atlantic and eastern Pacific Oceans. Classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core-top assemblages misrepresented the ice age faunal assemblages. Our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981] and thus may help to resolve a long-standing controversy. Our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems, however, and supports CLIMAP's inference of stability of the subtropical gyre centers.

  17. The precession constant of the Earth: Variations through the ice-age

    SciTech Connect

    Peltier, W.R.; Jiang, X.

    1994-10-01

    We directly calculate the history of variations in Earth`s precession constant H that are forced by variations in surface mass associated with late Pleistocene ice-age glaciation and deglaciation events. Our analyses show that the magnitude of Delta H/H(sub zero) is lower than that required to cause the recently hypothesized resonant reduction of the precession period.

  18. Integrating Teaching about the Little Ice Age with History, Art, and Literature.

    ERIC Educational Resources Information Center

    Glenn, William Harold

    1996-01-01

    Discusses climate change during the Little Ice Age as experienced during several historical events, including the settlement and demise of the Norse Greenland colonies, the landing of the Pilgrims at Plymouth, and both the Battle of Trenton and Washington's encampment at Valley Forge during the American Revolution. Associated artistic and literary…

  19. Pacing, Forcing, or Chance? Milankovitch Plays Dice and Scores Ice Ages. (Invited)

    NASA Astrophysics Data System (ADS)

    Mix, A. C.

    2010-12-01

    Understanding the role of orbital forcing in the ice ages has now occupied paleoclimatologists and paleoceanographers for many decades, and still we don’t really know how this works. Are ice ages directly forced by orbits, or are orbits a pacemaker that organize ice-age oscillations that would occur anyway (i.e., in the absence of orbital forcing)? Tuning of marine d18O (and other) records gives plausibly satisfying results in many contexts, but radiometric dates have led some to suggest that that glacial terminations can precede presumed forcing, and thus must be independent of, or at least only very weakly coupled to, Earth’s orbital variations. Several early efforts sought to separate the background variability and organized orbital pacing of ice ages, and concluded that a large fraction of climate change is stochastic. Simple models of various types imply that thresholds and limits must exist within the glacial system. Combining these ideas of stochasticity and thresholds implies that the timing of glacial-interglacial transition must be to some extent indeterminate, and if so the precise dating of any particular event is not important to defining the orbital controls of climate. Instead the overall pattern of variation in multiple parts of the climate system, if sufficiently constrained in a sequence, may provide better insights.

  20. Dynamics of the intertropical convergence zone over the western Pacific during the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Yan, Hong; Wei, Wei; Soon, Willie; An, Zhisheng; Zhou, Weijian; Liu, Zhonghui; Wang, Yuhong; Carter, Robert M.

    2015-04-01

    Precipitation in low latitudes is primarily controlled by the position of the intertropical convergence zone, which migrates from south to north seasonally. The Little Ice Age (defined as AD 1400-1850) was associated with low solar irradiance and high atmospheric aerosol concentrations as a result of several large volcanic eruptions. The mean position of the intertropical convergence zone over the western Pacific has been proposed to have shifted southwards during this interval, which would lead to relatively dry Little Ice Age conditions in the northern extent of the intertropical convergence zone and wet conditions around its southern limit. However, here we present a synthesis of palaeo-hydrology records from the Asian-Australian monsoon area that documents a rainfall distribution that distinctly violates the expected pattern. Our synthesis instead documents a synchronous retreat of the East Asian Summer Monsoon and the Australian Summer Monsoon into the tropics during the Little Ice Age, a pattern supported by the results of our climate model simulation of tropical precipitation over the past millennium. We suggest that this pattern over the western Pacific is best explained by a contraction in the latitudinal range over which the intertropical convergence zone seasonally migrates during the Little Ice Age. We therefore propose that rather than a strict north-south migration, the intertropical convergence zone in this region may instead expand and contract over decadal to centennial timescales in response to external forcing.

  1. Chronological framework for the deglaciation of the Lake Michigan lobe of the Laurentide ice sheet from ice-walled lake deposits

    USGS Publications Warehouse

    Curry, B.; Petras, J.

    2011-01-01

    A revised chronological framework for the deglaciation of the Lake Michigan lobe of the south-central Laurentide Ice Sheet is presented based on radiocarbon ages of plant macrofossils archived in the sediments of low-relief ice-walled lakes. We analyze the precision and accuracy of 15 AMS 14C ages of plant macrofossils obtained from a single ice-walled lake deposit. The semi-circular basin is about 0.72km wide and formed of a 4- to 16-m-thick succession of loess and lacustrine sediment inset into till. The assayed material was leaves, buds and stems of Salix herbacea (snowbed willow). The pooled mean of three ages from the basal lag facies was 18 270??50 14C a BP (21 810cal. a BP), an age that approximates the switch from active ice to stagnating conditions. The pooled mean of four ages for the youngest fossil-bearing horizon was 17 770??40 14C a BP (21 180cal. a BP). Material yielding the oldest and youngest ages may be obtained from sediment cores located at any place within the landform. Based on the estimated settling times of overlying barren, rhythmically bedded sand and silt, the lacustrine environment persisted for about 50 more years. At a 67% confidence level, the dated part of the ice-walled lake succession persisted for between 210 and 860cal. a (modal value: 610cal. a). The deglacial age of five moraines or morainal complexes formed by the fluctuating margin of the Lake Michigan lobe have been assessed using this method. There is no overlap of time intervals documenting when ice-walled lakes persisted on these landforms. The rapid readvances of the lobe during deglaciation after the last glacial maximum probably occurred at some point between the periods of ice-walled lake sedimentation. ?? 2011 John Wiley & Sons, Ltd.

  2. Detailed sedimentology and geomorphology elucidate mechanisms of formation of modern and historical sequences of minor moraines in the European Alps

    NASA Astrophysics Data System (ADS)

    Wyshnytzky, Cianna; Lukas, Sven

    2016-04-01

    Suites of closely-spaced minor moraines may help further understanding of glacier retreat and predict its geomorphological effects through the observations of moraine formation on short timescales. This research is common in lowland, maritime settings (Sharp, 1984; Boulton, 1986; Krüger, 1995; Reinardy et al., 2013), but remains sparse in high-mountain settings (Hewitt, 1967; Ono, 1985; Beedle et al., 2009; Lukas, 2012). This research presents detailed sedimentological and geomorphological research on minor moraines at two high-mountain settings in the Alps: Silvrettagletscher, Switzerland, as a modern setting and Schwarzensteinkees, Austria, as a historical setting. Geomorphological investigations included mapping and measurements through field observations and assessing aerial imagery. Additionally, terrestrial laser scanning and ground-penetrating radar data were collected in the Schwarzensteinkees foreland. Detailed sedimentological investigations followed excavation of seven moraines at Silvrettagletscher and five moraines at Schwarzensteinkees and include multiple scales of observation and measurements to support interpretations of sediment transport and deposition (e.g. Evans and Benn, 2004). The modern moraines at Silvrettagletscher, in the immediately proglacial foreland, have been forming since before 2003. Four mechanisms of formation show distinct sedimentological signatures: formerly ice-cored moraines (e.g. Kjær & Krüger, 2001; Lukas, 2012; Reinardy et al., 2013) , push moraine formation on a reverse bedrock slope (e.g. Lukas, 2012), push moraine formation incorporating sediments deposited in a former proglacial basin, and basal freeze-on (e.g. Andersen & Sollid, 1971; Krüger, 1995; Reinardy et al., 2013). Schwarzensteinkees still exists but is currently restricted to steeply-dipping bedrock slabs above the main valley. This study therefore investigates the moraines in the foreland that formed between approximately 1850 and 1930. The minor

  3. Late Holocene South American and Indian summer monsoon variability: Assessing the regional significance of the Medieval Climate Anomaly and Little Ice Age

    NASA Astrophysics Data System (ADS)

    Bird, B. W.; Rudloff, O. M.; Escobar, J.; Polissar, P. J.; Steinman, B. A.; Thompson, L. G.; Yao, T.

    2014-12-01

    The response of Earth's major climate systems to natural forcings during the last 2000 years can provide valuable insight into the affect that ongoing climate change may have on these systems. Understanding the relationship between temperature, monsoonal hydroclimate and radiative forcing is of particular interest because hydrologic responses in these systems have the ability to impact over half of the global population. Here, late Holocene variability in the South American and Indian summer monsoon regions is examined using sedimentological, geochemical and isotopic proxies from high altitude lake sediment archives from the Colombian Andes and the southeastern Tibetan Plateau. New results from Laguna de Ubaque, a small moraine dammed lake at 2060 m ASL in the Eastern Cordillera of the Colombian Andes, suggest a reduction in Andean South American summer monsoon (SASM) rainfall during the Medieval Climate Anomaly (MCA; 900 to 1200 CE) that is consistent with other records from the Andes. During the Little Ice Age (LIA; 1450 to 1900 CE), Ubaque shows wet conditions between 1450 and 1600 CE and drier conditions from1600 to 1900 CE. This pattern is similar to accumulation at the Quelccaya Ice Cap, but differs from ice core, speleothem and lake sediment oxygen isotope records of synoptic-scale monsoonal precipitation, suggesting that Andean rainfall anomalies may have differed from upstream monsoonal trends over the Amazon. In contrast, results from Badi Namco and Paru Co on the southeastern Tibetan Plateau suggest that the MCA and LIA were relatively minor hydroclimate events superimposed on a larger millennial scale variation in Indian summer monsoon precipitation (1200 to 200 cal yr B.P.) that was associated with changes in the position of the ITCZ, surface air temperature over the Tibetan Plateau and sea surface temperatures in the western tropical Pacific. The unique hydroclimate variations in the ISM and SASM regions supports the idea that while spatially

  4. Initial AUV Investigation of the Dynamic Morainal Bank Environment of the Advancing Hubbard Glacier, Alaska

    NASA Astrophysics Data System (ADS)

    Lawson, D. E.; Gulick, S. P. S.; Goff, J. A.

    2015-12-01

    Hubbard Glacier has been steadily advancing into tidewater > 200 years; advance over last 40 years has averaged ~34 m/yr, although at spatially variable rates across the terminus (14-80 m/yr) and with a seasonal advance and retreat cycle of ~100 m to 300 m, but as much as 600 m. The advance of the terminus is synchronous with the movement of the morainal bank that underlies it. The mechanics of this motion and the related sedimentological processes responsible for this coordinated advance of the grounding line are based largely on inferences from geophysical surveys of remnant morainal banks. In situ and repeated observations of the submarine margin are required to improve our understanding of how the terminus advances into deep fjords. We conducted initial submarine observations using a Bluefin 9M AUV (Autonomous Underwater Vehicle) and acquired high-resolution swath bathymetry and sidescan backscatter along a ~2 km long section of the ice face of the glacier. Onboard oceanographic measurements and surface CTD casts were obtained during AUV deployment. Decimeter-scale imagery of the seabed reveals numerous erosional and depositional bedforms and gravitational features next to the ice face and down the morainal bank's proximal slope. The moraine surface adjacent to the ice face is coarse, apparently swept clear of finer materials, exhibits gravel stripes and boulder lags. The slope into the fjord displays a sequence of bedforms from barchan-shaped dunes up to 15 m on a side to barchanoid transverse ridges >50 m long to transverse ridges >100 m long. This transition implies increased sand supply to the bed downslope. Channels, erosional gullies and scours cross the upper slope, while localized slump and flow failures occur sporadically across the face. We speculate that high concentration bottom flows originating from turbulent subglacial discharge are likely processes creating the barchan forms and that the flow velocity reduces with distance from the grounding

  5. Buried soils of Late Quaternary moraines of the Wind River Mountains, Wyoming

    SciTech Connect

    Dahms, D.E. . Geography Dept.)

    1992-01-01

    Buried soils occur on kettle floors of four Pinedale moraine catenas of the western Wind River Mountains of Wyoming. Radiocarbon ages from bulk samples of Ab horizons indicate the soils were buried during the mid-Holocene. Soils on kettle floors have silty A and Bw horizons that overlie buried A and B horizons that also formed in silt-rich sediments. Crests and backslope soils also have A and Bw horizons of sandy loam formed over 2BCb and 2Cb horizons of stony coarse loamy sand. Recent data show the silty textures of the A and B horizons are due to eolian silt and clay from the Green River Basin just west of the mountains. The buried soils appear to represent alternate periods of erosion and deposition on the moraines during the Holocene. The original soils developed on higher slopes of the moraines were eroded during the mid-Holocene and the 2BC and 2C horizons exposed at the surface. Eroded soil sediments were transported downslope onto the kettle floors. Following erosion, silt-rich eolian sediments accumulated on all surfaces and mixed with the BC and C horizons (the mixed loess of Shroba and Birkeland). The present surface soils developed within this silt-rich material. Stone lines often occur at the Bw-2BCb/2Cb boundary, and mark the depth to which the earlier soils were eroded. Thus, soil profiles at the four localities result from two periods of soil formation, interrupted by an interval of erosion during the mid-Holocene. Moraines of this study are adjacent to the Fremont Lake type area for the Pinedale glaciation of the Rocky Mountains. Buried soils in kettles of the moraines indicates the soil characteristics of the Pinedale type region are not necessarily due to continuous post-Pinedale development, but may result from more than one episode of soil formation.

  6. Middle and Late Pennsylvanian cyclothems, American Midcontinent: Ice-age environmental changes and terrestrial biotic dynamics

    NASA Astrophysics Data System (ADS)

    Blaine Cecil, C.; DiMichele, William A.; Elrick, Scott D.

    2014-07-01

    The Pennsylvanian portion of the Late Paleozoic Ice Age was characterized by stratigraphic repetition of chemical and siliciclastic rocks in the equatorial regions of the Pangean interior. Known as “cyclothems”, these stratigraphic successions are a 105 yr-record of glacial waxing and waning, superimposed on longer term, 106 yr intervals of global warming and cooling and a still longer term trend of increasing equatorial aridity. During periods of maximum ice-minimum sea level, the interior craton was widely exposed. Epicontinental landscapes were initially subjected to dry subhumid climate when first exposed, as sea level fell, but transitioned to humid climates and widespread wetlands during maximum lowstands. During interglacials (ice-minima) seasonally dry vegetation predominated. The wetland and seasonally dry biomes were compositionally distinct and had different ecological and evolutionary dynamics.

  7. Age and thickness distribution of polynya sea ice in the Laptev Sea determined by satellite SAR imagery and airborne EM

    NASA Astrophysics Data System (ADS)

    Rabenstein, L.; Krumpen, T.; Hendricks, S.; Hoelemann, J.

    2012-04-01

    The importance and annual amount of sea ice volume produced during polyna opening events in the Siberian Laptev Sea is still controversially discussed. So far, published information about sea ice volume production are purely based on indirect thickness measurements of thin ice using remote sensing techniques or on computer simulations of sea ice growth based on reanalysis climate data. We recorded a sea ice thickness transect of approximately 160 km length using helicopter electromagnetics (HEM) in the region of the so called West New Siberian (WNS) Polynya located directly north of the Lena delta in April 2008. In addition, a time series of synthetic aperture radar (SAR) images covering the complete polynya region was analyzed and ice area fragments were tracked from their origin to the moment when we recorded their thickness. Both data sets together, HEM and SAR, provide the opportunity to classify overflown ice areas in terms of age, area and thickness and therefore in terms of volume. From December 2007 to April 2008 approximately 50.000 km2 of sea-ice area was produced in the WNS polynya, which is more than the size of Switzerland. The youngest surveyed sea-ice was 6 days old and had a mean total and a mean level-ice thickness of 0.2 m. The oldest surveyed ice floe had an age of 104 days and a mean total thickness of 2.4 +/- 0.3 m and a mean level ice thickness of 1.8 +/- 0.3 m. The error is based on the HEM instrument accuracy and a lag of snow thickness data. Assuming that ice thickness along the HEM transect was representative for entire overflown ice areas, our calculations result that the produced sea ice area contained a volume of approximately 86 km3. This is about 1.8 % of the Arctic wide ice production between October 2007 and March 2008, as it was published by Kwok et al. 2009 on the basis of ICE-Sat ice thickness data. The combined HEM and SAR study enabled us furthermore to analyze thickness vs. age relations of first year ice floes. Mean thickness

  8. End of the "Little Ice Age" in the Alps not forced by industrial black carbon

    NASA Astrophysics Data System (ADS)

    Sigl, Michael; Osmont, Dimtri; Gabrieli, Jacopo; Barbante, Carlo; Schwikowski, Margit

    2016-04-01

    Light absorbing aerosols present in the atmosphere and cryosphere play an important role in the climate system. Their presence in ambient air and snow changes radiative properties of these media, thus contributing to increased atmospheric warming and snowmelt. High spatio-temporal variability of aerosol concentrations in these media and a shortage of long-term observations contribute to large uncertainties in properly assigning the climate effects of these aerosols through time. Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Radiative forcing by increasing deposition of industrial black carbon to snow has been suggested as the main driver of the abrupt glacier retreats in the Alps (Painter et al. 2012). Basis for this hypothesis were model simulations using ice-core measurements of elemental carbon at low temporal resolution from two ice cores in the Alps. Here we present sub-annually resolved, well replicated ice-core measurements of refractory black carbon (rBC; using a SP2 soot photometer), mineral dust (Fe, Ca), biomass burning (NH4, K) and distinctive industrial pollution tracers (Bi, Pb, SO4) from an ice core in the Alps covering the past 250 years. These reconstructions allow to precisely compare the timing of observed acceleration of glacier melt in the mid-19th century with that of the increase of soot deposition on ice-sheets caused by the industrialization of Western Europe. Our study suggests that at the time when European rBC emission rates started to significantly increase Alpine glaciers have already experienced more than 70% of their total 19th century length reduction. Industrial BC emissions can therefore not been considered as the primary forcing of the rapid deglaciation at the end of the Little Ice Age in the Alps. References: Painter, T. H., M. G. Flanner, G. Kaser, B. Marzeion, R. A. VanCuren, and W. Abdalati (2013), End of the Little Ice

  9. Past and future ice age initiation: the role of an intrinsic deep-ocean millennial oscillation

    NASA Astrophysics Data System (ADS)

    Johnson, R. G.

    2014-05-01

    This paper offers three interdependent contributions to studies of climate variation: (1) the recognition and analysis of an intrinsic millennial oceanic oscillation that affects both Northern and Southern high latitude climates, (2) The recognition of an oceanographic switch to ice-free seas west of Greenland that explains the initiation of the Last Ice Age, and (3) an analysis of the effect of increasing salinity in the seas east of Greenland that suggests the possibility of the initiation of an ice age threshold climate in the near future. In the first contribution the millennial oscillation in the flow of the North Atlantic Drift reported by Bond et al. (1997) is proposed to be part of a 1500 yr intrinsic deep ocean oscillation. This oscillation involves the exchange of North Atlantic intermediate-level deep water (NADW) formed in the seas east of Greenland with Antarctic Bottom Water formed in a shallow-water zone at the edge of the Antarctic continent. The concept of NADW formation is already well known, with details of the sinking water flowing out of the Greenland Sea observed by Smethie et al. (2000) using chlorofluorocarbon tracers. The concept of Antarctic Bottom Water formation is also already well established. However, its modulation by the changing fraction of NADW in the Southern Ocean, which I infer from the analysis of Weyl (1968), has not been previously discussed. The modulated lower-salinity Antarctic Bottom Water that reaches the northern North Atlantic then provides negative feedback for the cyclic variation of NADW formation as proposed here. This causes the 1500 yr bipolar oscillation. The feedback suggests the possible sinusoidal character of the proposed oscillation model. The model is consistent with the cooling of the Little Ice Age (Lamb, 1972, 1995), and it also correctly predicts NASA's observation of today's record maximum area of winter sea ice on the Southern Ocean and the present observed record low rate of Antarctic Bottom Water

  10. High resolution dating of moraines on Kodiak Island, Alaska links Atlantic and North Pacific climatic changes during the late glacial

    SciTech Connect

    Mann, D.H. . Alaska Quaternary Center)

    1992-01-01

    Much less is known about the paleoclimate and paleoceanography of the North Pacific than the North Atlantic despite the North Pacific's important role in the global ocean-climate system. Kodiak Island lies in the northwestern Gulf of Alaska astride the eastern end of the Aleutian Low. On southwestern Kodiak Island, coastal bluffs section a series of moraines, kettle ponds, and bogs formed between 15 and 9 ka BP. Distinctive tephras from volcanoes on the Alaska Peninsula provide time-lines within the stratigraphy. Deformation events recorded in sediment stacks from basins within glaciotectonic landforms allows precise dating of glacial events. An ice cap occupied the Kodiak archipelago during the last glaciation. Three glacial advances of the southwestern margin of this ice cap occurred after 15 ka BP. At 13.4 ka, piedmont ice lobes formed large push moraines extending into Shelikof Strait during the Low Cape Advance. The less-extensive Tundra Advance culminated between 12 and 11.7 ka BP followed by glacier retreat then readvance to form the prominent Olga Moraine system between 11 and 10 ka BP. The timing of the Tundra and Olga Advances correlates closely with that of the Older and Younger Dryas cold episodes in northwestern Europe suggesting that these climatic oscillations were synchronous throughout the northern hemisphere.

  11. Microphysical characteristics of aging anvils and cirrus sampled during TWP- ICE

    NASA Astrophysics Data System (ADS)

    McFarquhar, G.; Freer, M.; Um, J.; Mace, G.; Kok, G.; McCoy, R.; Tooman, T.

    2006-12-01

    Observations of anvils at various stages in their life cycle and in generic cirrus were made during the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) using the Atmospheric Radiation Measurement Program's Uninhabited Aerospace Vehicle's (ARM UAV) payload of in-situ cloud microphysics probes on the Scaled Composites Proteus. The probes, including the Cloud and Aerosol Precipitation Spectrometer (CAPS), the Cloud Droplet Probe (CDP), the Cloud Particle Imager (CPI), the Cloud Spectrometer and Impactor Probe (CSI) and the Cloud Integrating Nephelometer (CIN), give number concentrations as a function of size, bulk parameters such as total water content and extinction, and information on ice crystal habits. Bulk measurements of total water content are also derived from co-located remote sensing measurements which are compared against the in-situ mass contents. In this presentation, data from the composite of probes are examined in an effort to determine the importance of ice crystals with maximum dimensions less than 100 micrometers to the total number, extinction and mass of the cirrus with varying ages. The variation of dominant ice crystal habit, median mass diameter and other bulk microphysical quantities with cirrus age and origin are also investigated. Implications of these results for cloud modeling studies are discussed.

  12. Life and extinction of megafauna in the ice-age Arctic.

    PubMed

    Mann, Daniel H; Groves, Pamela; Reanier, Richard E; Gaglioti, Benjamin V; Kunz, Michael L; Shapiro, Beth

    2015-11-17

    Understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal Pleistocene and today. Our study area is Alaska's North Slope, a place where humans were rare when these extinctions occurred. After developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones, we compare the temporal patterns of bone abundance with climate records. Megafaunal abundance tracked ice age climate, peaking during transitions from cold to warm periods. These results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice-age biogeography at high latitudes. It follows that long-distance dispersal was crucial for the long-term persistence of megafaunal species living in the Arctic. Such dispersal was only possible when their rapidly shifting range lands were geographically interconnected. The end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable, interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes. PMID:26578776

  13. Life and extinction of megafauna in the ice-age Arctic

    NASA Astrophysics Data System (ADS)

    Mann, Daniel H.; Groves, Pamela; Reanier, Richard E.; Gaglioti, Benjamin V.; Kunz, Michael L.; Shapiro, Beth

    2015-11-01

    Understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal Pleistocene and today. Our study area is Alaska's North Slope, a place where humans were rare when these extinctions occurred. After developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones, we compare the temporal patterns of bone abundance with climate records. Megafaunal abundance tracked ice age climate, peaking during transitions from cold to warm periods. These results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice-age biogeography at high latitudes. It follows that long-distance dispersal was crucial for the long-term persistence of megafaunal species living in the Arctic. Such dispersal was only possible when their rapidly shifting range lands were geographically interconnected. The end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable, interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes.

  14. Life and extinction of megafauna in the ice-age Arctic

    PubMed Central

    Mann, Daniel H.; Groves, Pamela; Reanier, Richard E.; Gaglioti, Benjamin V.; Kunz, Michael L.; Shapiro, Beth

    2015-01-01

    Understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal Pleistocene and today. Our study area is Alaska's North Slope, a place where humans were rare when these extinctions occurred. After developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones, we compare the temporal patterns of bone abundance with climate records. Megafaunal abundance tracked ice age climate, peaking during transitions from cold to warm periods. These results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice-age biogeography at high latitudes. It follows that long-distance dispersal was crucial for the long-term persistence of megafaunal species living in the Arctic. Such dispersal was only possible when their rapidly shifting range lands were geographically interconnected. The end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable, interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes. PMID:26578776

  15. Aging affects the ice-nucleating properties of volcanic ash aerosol

    NASA Astrophysics Data System (ADS)

    Bingemer, H.; Klein, H.; Ebert, M.; Haunold, W.; Bundke, U.; Herrmann, T.; Kandler, K.; Müller-Ebert, D.; Weinbruch, S.; Judt, A.; Wéber, A.; Nillius, B.; Ardon-Dryer, K.; Levin, Z.; Curtius, J.

    2012-04-01

    The effectiveness of volcanic ash as ice nuclei (IN) has been debated in the past. While some reported enhanced IN concentrations in volcanic plumes, others found no evidence for that. Here we show that "aged" volcanic particles sampled from the atmosphere in central Germany when the ash cloud of the 2010 Eyjafjallajökull eruption was present are very effective IN, as compared to particles of aerosolized "fresh" volcanic sediment that had been collected close to the eruption site in Iceland. The number concentration of atmospheric IN was measured with the same method both at the Taunus Observatory in central Germany and at Tel Aviv University, Israel, as well as in laboratory-generated aerosol of volcanic ash. Aerosol was sampled by electrostatic precipitation of particles onto silicon substrates and was subsequently analyzed at - 8° to -18°C (deposition and condensation nucleation modes) in the isothermal static vapor diffusion chamber FRIDGE. The composition of individual atmospheric IN was analyzed by environmental scanning electron microscopy (ESEM) with EDX. Our daily measurements show a significant enhancement of atmospheric IN when the dispersed ash cloud reached central Europe in April 2010 and the eastern Mediterranean in May 2010. Pure volcanic ash accounts for at least 53-68% of the 239 individual ice nucleating particles that were analyzed by ESEM-EDX in aerosol samples collected at Taunus Observatory during the volcanic peak of April 2010. Volcanic ash samples that had been collected close to the eruption site were aerosolized in the laboratory and measured by FRIDGE. Our analysis confirms the relatively poor ice nucleating efficiency (at -18°C and 119% ice-saturation) of such "fresh" volcanic ash, as it had recently been found by other workers. We find that both the fraction of the aerosol that is active as ice nuclei as well as the density of ice-active sites on the aerosol surface are three orders of magnitude larger in the samples collected

  16. Mesoscale variability of water vapor, surface ice aging and precipitation in the Martian polar regions

    NASA Astrophysics Data System (ADS)

    Evdokimova, Nadezda; Rodin, Alexander V.; Kuzmin, Ruslan; Fedorova, Anna

    We present the results of analysis of the H2 O and CO2 ices and the atmospheric water vapor distribution in the polar regions of Mars, based on the OMEGA C channel data obtained during the period of MY 26-27. We employ observations of the North polar cap (NPC) obtain during the aphelion campaigns of 26-27 MY, and corresponding South polar cap (SPC) observations obtained during the perihelion season. In both cases ices were mapped using spectral indices corresponding to specific adsorption bands. At the NPC where H2 O ices is presented during the spring-summer season we used square-based index of the 1.5 µm for estimation of the net ice content and one of the 1.25 µm band for the analysis of ice microstructure. At the SPC square indices are unreliable because of contamination of narrow CO2 absorption bands, so the relative depth of 1.5 µm was used for mapping of H2 O ice. CO2 ice was mapped using 1.57 µm band. In both hemispheres, wave-2 and wave-3 structures were observed in the circumpolar regions during limited period of time. At the NPC wave-2 pattern was found in the 1.25 µm index distribution during early aphelion season that presumably reflects enhanced aging rates of the NPC frost caused by cyclonic wind system in the circumpolar vortex, resulting in enlargement of grains in the optically active skin layer. Later in the aphelion season, wave-2 pattern is followed by wave-3 which is a consequence of change of the leading wavenumber in the polar vortex. At the SPC, wave-3 pattern is observed during the shot period when seasonal CO2 ice cap retreats. We interpret this structure as the outcropping of H2 O ice deposits accumulated during south hemisphere for autumn-winter season. Water vapor distribution inferred from OMEGA data also demonstrates zonal variations correlating with such wave structures. GCM simulations with comprehensive treatment of the water cycle reproduce stationary cyclonic eddies during the string-summer, and transient wave-3 system

  17. Marine ice sheets of Pleistocene age on the East Siberian Continental Margin (Invited)

    NASA Astrophysics Data System (ADS)

    Niessen, F.; Hong, J.; Hegewald, A.; Matthiessen, J. J.; Stein, R. H.; Kim, H.; Kim, S.; Jensen, L.; Jokat, W.; Nam, S.; Kang, S.

    2013-12-01

    Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present results of the RV "Polarstern' cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA03B (2012), which investigated an area between the Chukchi Borderland and the East Siberian Sea between 165°W and 170°E. At the southern end of the Mendeleev Ridge, close to the Chukchi and East Siberian shelves, evidence is found for the existence of Pleistocene ice sheets/ice shelves, which have grounded several times in up to 1200 m present water depth. We found mega-scale glacial lineations associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, accentuated by a conspicuous truncation of pre-glacial strata typically capped with mostly thin layers of diamicton draped by pelagic sediments. Our tentative age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3. The oldest and deepest event predates MIS 6. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. They were possibly linked to previously suggested ice sheets on the Chukchi Borderland and the New Siberian Islands. We propose that the ice sheets extended northward as thick ice shelves, which grounded on the Mendeleev Ridge to an area up to 78°N within MIS 5 and/or earlier. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for global sea-level variations, albedo, ocean-atmosphere heat exchange, freshwater export from the Arctic Ocean at glacial terminations and the formation of submarine permafrost. The existence of km-thick Pleistocene ice sheets in the western Arctic Ocean during glacial times predating

  18. Sea-level responses to sediment transport over the last ice age cycle

    NASA Astrophysics Data System (ADS)

    Ferrier, K.; Mitrovica, J. X.

    2013-12-01

    Sea-level changes over the last ice age cycle were instrumental in steering Earth's topographic evolution. These sea-level variations were driven by changes in surface mass loads, including not only ice and ocean mass variations but also the transfer of rock from eroding mountains to sedimentary deposits. Here we use an extended numerical model of ice age sea level (Dalca et al., 2013) to explore how sediment erosion and deposition affected global sea-level variations over the last ice age cycle. The model takes histories of ice and sediment loads as inputs, and it computes gravitationally self-consistent sea level responses by accounting for the deformational, gravitational, and rotational perturbations in the Earth's viscoelastic form. In these model simulations, we use published estimates of erosion rates, sedimentation rates, and ice sheet variations to constrain sediment and ice loading since the Last Interglacial. We explore sea-level responses to several erosional and depositional scenarios, and in each we quantify the relative contributions of crustal deformation and gravitational perturbation to the computed sea-level change. We also present a case study to illustrate the effects that sediment transfer can have on sea level at the regional scale. In particular, we focus on the region surrounding the Indus River, where fluvial sediment fluxes are among the highest on Earth. Preliminary model results suggest that sediment fluxes from Asia to the ocean are large enough to produce a significant response in sea level along the northeastern coast of the Arabian Sea. Moreover, they suggest that modeled sea-level histories are sensitive to the timing and spatial distribution of sediment erosion and deposition. For instance, sediment deposition along the continental shelf - which may have been the primary site of Indus River sediment deposition during the Holocene - produces a different sea-level response than sediment deposition on the deep-sea Indus Fan, where

  19. Impact of Ice Ages on the genetic structure of trees and shrubs.

    PubMed Central

    Lascoux, Martin; Palmé, Anna E; Cheddadi, Rachid; Latta, Robert G

    2004-01-01

    Data on the genetic structure of tree and shrub populations on the continental scale have accumulated dramatically over the past decade. However, our ability to make inferences on the impact of the last ice age still depends crucially on the availability of informative palaeoecological data. This is well illustrated by the results from a recent project, during which new pollen fossil maps were established and the variation in chloroplast DNA was studied in 22 European species of trees and shrubs. Species exhibit very different levels of genetic variation between and within populations, and obviously went through very different histories after Ice Ages. However, when palaeoecological data are non-informative, inferences on past history are difficult to draw from entirely genetic data. On the other hand, as illustrated by a study in ponderosa pine, when we can infer the species' history with some certainty, coalescent simulations can be used and new hypotheses can be tested. PMID:15101576

  20. The little ice age and medieval warm period in the Sargasso Sea

    SciTech Connect

    Keigwin, L.D.

    1996-11-29

    Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbondated box core show that SST was {approximately} 1{degree}C cooler than today {approximately} 400 years ago (the Little Ice Age) and 1700 years ago, and {approximately} 1{degree}C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation. 39 refs., 4 figs., 1 tab.

  1. Cosmogenic 36Cl exposure ages reveal a 9.3 ka BP glacier advance and the Late Weichselian-Early Holocene glacial history of the Drangajökull region, northwest Iceland

    NASA Astrophysics Data System (ADS)

    Brynjólfsson, Skafti; Schomacker, Anders; Ingólfsson, Ólafur; Keiding, Jakob K.

    2015-10-01

    We present twenty-four new cosmogenic isotope (36Cl) surface exposure ages from erratic boulders, moraine boulders and glacially eroded bedrock that constrain the late Weichselian to Holocene glacial history of the Drangajökull region, northwest Iceland. The results suggest a topographically controlled ice sheet over the Vestfirðir (Westfjords) peninsula during the last glaciation. Cold based non-erosive sectors of the ice sheet covered most of the mountains while fjords and valleys were occupied with erosive, warm-based ice. Old36Cl exposure ages from highlands and mountain plateaux (L8; 76.5 ka and H1; 41.6 ka) in combination with younger erratic boulders (L7; 26.2 and K1-K4; 15.0-13.8 ka) superimposed on such surfaces suggest the presence of non-erosive ice over uplands and plateaux in the Vestfirðir peninsula during the last glaciation. Glacially scoured terrain and erratic boulders yielding younger exposure ages (L1-L6; 11.3-9.1 ka and R1, R6-R7; 10.6-9.4 ka) in the lowland areas indicate that the valleys and fjords of the Vestfirðir peninsula were occupied by warm-based, dynamic ice during the last glaciation. The deglaciation of mountain Leirufjall by 26.2 ka BP suggests that ice thinning and deglaciation of some mountains and plateaux preceded any significant lateral retreat of the ice sheet. Subsequently this initial ice thinning was followed by break-up of the shelf based ice sheet off Vestfirðir about 15 ka BP. Hence, the new exposure ages suggest a stepwise asynchronous deglaciation on land, following the shelf break-up with some valleys and most of the highlands, ice free by 14-15 ka BP. The outermost moraine at the mouth of Leirufjörður is dated to 9.3 ka BP, and we suggest the moraine to be formed by a glacier re-advance in response to a cooler climate forced by the reduced Atlantic Meridional Overturning Circulation at around 9.3 ka BP. A system of moraines proximal to the 9.3 ka moraine in Leirufjörður as well as a 9.4 ka deglaciation age

  2. Zonal temperature-anomaly maps of Indian ocean surface waters: modern and ice-age patterns.

    PubMed

    Prell, W L; Hutson, W H

    1979-10-26

    Maps of sea surface temperature anomalies in the Indian Ocean in modern and ice-age times reveal striking changes in its surface circulation. During the last glacial maximum (18,000 years before the present), the Indian Ocean had colder average zonal surface temperatures, a cooler and less extensive Agulhas Current, a distinct eastern boundary current, and decreased upwelling and a weaker southwest monsoon in its northwestern region. PMID:17809371

  3. Effects of sudden mixing in the solar core on solar neutrinos and ice ages.

    NASA Technical Reports Server (NTRS)

    Ezer, D.; Cameron, A. G. W.

    1972-01-01

    Some numerical experiments with a solar model have been conducted in connection with the hypothesis regarding the effects of mixing in the solar core. Questions concerning a plausible mechanism by which such a mixing could be produced are explored. The variation of solar luminosity throughout the numerical experiments is shown. In connection with a great change in luminosity after a second mixing, it is suggested that the earth is presently undergoing an ice age.

  4. Evidence for a little ice age and recent warming from a borehole temperature data inversion procedure

    SciTech Connect

    Fivez, J.; Thoen, J.

    2004-11-15

    In this article, we apply our analytical theory, published earlier in this journal, to obtain information on the earth surface temperature history from some borehole temperature data. Compared to the results of the five different methods applied to the same temperature data, our method seems to be easier, assumption-free, and yields internally consistent results. The results suggest a cooling a few centuries ago, followed by a continuing warming up to these days, in agreement with a little ice age scenario.

  5. OSL ages in central Norway support a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

    NASA Astrophysics Data System (ADS)

    Johnsen, Timothy F.; Olsen, Lars; Murray, Andrew

    2012-06-01

    Recent work has suggested that the Scandinavian ice sheet was much more dynamic than previously believed, and its western marine-based margin can provide an analogue to the rapid-paced fluctuations and deglaciation observed at the margins of the Antarctic and Greenland ice sheets. In this study we used a complimentary dating technique, OSL (Optically Stimulated Luminescence dating), to support the existence of the Trofors interstadial in central Norway; an ice-free period that existed from ˜25 to 20 ka recorded at multiple sites throughout Norway (cf. Andøya interstadial) and that divides the Last Glacial Maximum (LGM) into two stadials. OSL signal component analysis was used to optimize data analysis, and internal (methodological) tests show the results to be of good quality. Both large and small aliquots gave consistent OSL ages (22.3 ± 1.7 ka, n = 7) for sub-till glaciofluvial/fluvial sediments at the Langsmoen stratigraphic site, and an apparent old age (˜100 ka) for a poorly-bleached sample of glaciolacustrine sediment at the nearby stratigraphically-related Flora site. Eight radiocarbon ages of sediment from the Flora site gave consistent ages (20.9 ± 1.6 cal ka BP) that overlap within 1σ with OSL ages from the nearby Langsmoen site. The similarity in age within and between these stratigraphically-related sites and using different geochronological techniques strongly suggests that this area was ice-free around ˜21 or 22 ka. The existence of the Trofors interstadial along with other interstadials during the Middle and Late Weichselian (MIS 3 and MIS 2) indicates that not only the western margin, but the whole western part of the Scandinavian ice sheet, from the ice divide to the ice margin was very dynamic. These large changes in the ice margin and accompanying drawdown of the ice surface would have affected the eastern part of the ice sheet as well.

  6. Contraction of the Western Pacific Intertropical Convergence Zone During the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Yan, H.; Wei, W.; Soon, W.; Zhou, W.; An, Z.

    2015-12-01

    Both palaeoclimate reconstructions and climate modeling have demonstrated thatprecipitation in low latitudes is primarily controlled by north- south migration of the globalIntertropical Convergence Zone on millennial to orbital timescales. These migrations areassociated with the occurrence of opposite rainfall variations between the twohemispheres. However, the pattern of rainfalls around the marine-continental tropicalwestern Pacific region over the last millennium remains unclear. Several recent studiessuggest a southward migration of the Intertropical Convergence Zone during the Little IceAge (~AD 1400-1850). Concomitantly, dry Little Ice Age conditions should have occurred inthe northern extent of the Intertropical Convergence Zone and wet conditions around thesouthern limit. However, our synthesis of proxy hydrology records from the Asian-Australian monsoon area documents a distinctly different rainfall pattern that violates thisexpectation, suggesting instead the occurrence of synchronous retreat of the East AsianSummer Monsoon and the Australian Summer Monsoon during the Little Ice Age. Thus wepropose an alternative dynamic scenario: rather than strict north-south migration, theapparent mode of multi-decadal to centennial change for the western Pacific IntertropicalConvergence Zone is contraction/expansion in response to external forcings such as solarirradiance variation and large volcanic eruptions.

  7. Moraine Valley College: A School With a Philosophy

    ERIC Educational Resources Information Center

    Kee, Byron E.

    1974-01-01

    In the architecture and arrangement of the physical plant, in the organization of its programs, and in the activities of its faculty and staff Moraine Valley Community College embodies a distinctive philosophy of education. (Author/RK)

  8. Radiocarbon dating of palaeosol components in moraines in Lapland, northern Sweden

    NASA Astrophysics Data System (ADS)

    Hormes, Anne; Karlén, Wibjörn; Possnert, Göran

    2004-10-01

    Accurate geochronologies are the key for comparison of palaeoclimate records. In order to clarify problems concerning the geochronology of glacier fluctuations we dated palaeosols in moraines in the Kebnekaise mountain region of Swedish Lapland. These palaeosols already have been dated several years ago using bulk samples of the palaeosols and yielded ages of 6180-5790 and 2750-2100 cal yr BP. In an attempt to evaluate the sources of contamination associated with bulk samples these soils were re-dated by using Coleoptera fragments, Cenococcum geophilum spores, humic acids and woody plant tissues. The new dates reveal that the two palaeosols found within the moraines represent much longer periods of time than was previously assumed. Soil formation periods can be distinguished for periods 7800-7580, 6300-4080, 2450-2000 and 1170-740 cal yr BP. These age groups point to differentiated soil formation processes, resedimentation, bioturbation and/or cryoturbation. The results show that dated terrestrial macrofossils from glacial moraines indicate climate changes that are in accordance with other proxy records in northern and central Scandinavia and in certain times off-phase with glacier fluctuations in southern maritime Norway. This throws light on possible changing interaction of forcing factors during the Holocene.

  9. Middle to late Holocene fluctuations of the Vindue glacier, an outlet glacier of the Greenland Ice Sheet, central East Greenland.

    NASA Astrophysics Data System (ADS)

    Levy, L.; Hammer, S. K.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.; Howley, J. A.; Wilcox, P.; Medford, A.

    2014-12-01

    The margins of the Greenland Ice Sheet are currently responding to present-day climate changes. Determining how the ice sheet margins have responded to past climate changes provides a means to understand how they may respond in the future. Here we present a multi-proxy record used to reconstruct the Holocene fluctuations of the Vindue glacier, an ice sheet outlet glacier in eastern Greenland. Lake sediment cores from Qiviut lake (informal name), located ~0.75 km from the present-day Vindue glacier margin contain a sharp transition from medium sand/coarse silt to laminated gyttja just prior to 6,340±130 cal yr BP. We interpret this transition to indicate a time when the Vindue glacier retreated sufficiently to cease glacial sedimentation into the lake basin. Above this contact the core contains laminated gyttja with prominent, ~0.5 cm thick, silt layers. 10Be ages of boulders on bedrock located between Qiviut lake and the present-day ice margin date to 6.81 ± 0.67 ka (n = 3), indicating the time of deglaciation. These ages also agree well with the radiocarbon age of the silt-gyttja transition in Qiviut lake cores. 10Be ages on boulders on bedrock located more proximal to the ice margin (~0.5 km) yield ages of 2.67 ± 0.18 ka (n = 2). These ages indicate either the continued recession of the ice margin during the late Holocene or an advance at this time. Boulders on the historical moraines show that ice retreated from the moraine by AD 1620 ± 20 yrs (n = 2). These results are in contrast with some areas of the western margin of the ice sheet where 10Be ages indicate that the ice sheet was behind its Historical limit from the middle Holocene (~6-7 ka) to Historical time. This may indicate that the eastern margin may have responded to late Holocene cooling more sensitively or that the advance associated with the Historical moraines overran any evidence of late Holocene fluctuations along the western margin of the ice sheet.

  10. Past and future ice age initiation: the role of an intrinsic deep-ocean millennial oscillation

    NASA Astrophysics Data System (ADS)

    Johnson, R. G.

    2014-05-01

    This paper offers three interdependent contributions to studies of climate variation: (1) the recognition and analysis of an intrinsic millennial oceanic oscillation that affects both Northern and Southern high latitude climates, (2) The recognition of an oceanographic switch to ice-free seas west of Greenland that explains the initiation of the Last Ice Age, and (3) an analysis of the effect of increasing salinity in the seas east of Greenland that suggests the possibility of the initiation of an ice age threshold climate in the near future. In the first contribution the millennial oscillation in the flow of the North Atlantic Drift reported by Bond et al. (1997) is proposed to be part of a 1500 yr intrinsic deep ocean oscillation. This oscillation involves the exchange of North Atlantic intermediate-level deep water (NADW) formed in the seas east of Greenland with Antarctic Bottom Water formed in a shallow-water zone at the edge of the Antarctic continent. The concept of NADW formation is already well known, with details of the sinking water flowing out of the Greenland Sea observed by Smethie et al. (2000) using chlorofluorocarbon tracers. The concept of Antarctic Bottom Water formation is also already well established. However, its modulation by the changing fraction of NADW in the Southern Ocean, which I infer from the analysis of Weyl (1968), has not been previously discussed. The modulated lower-salinity Antarctic Bottom Water that reaches the northern North Atlantic then provides negative feedback for the cyclic variation of NADW formation as proposed here. This causes the 1500 yr bipolar oscillation. The feedback suggests the possible sinusoidal character of the proposed oscillation model. The model is consistent with the cooling of the Little Ice Age (Lamb, 1972, 1995), and it also correctly predicts NASA's observation of today's record maximum area of winter sea ice on the Southern Ocean and the present observed record low rate of Antarctic Bottom Water

  11. Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages.

    USGS Publications Warehouse

    Croft, S.K.; Kieffer, S.W.; Ahrens, T.J.

    1979-01-01

    We produced a series of decimeter-sized impact craters in blocks of ice near 0oC and -70oC and in ice-saturated sand near -70oC as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar satellites. Crater diameters in the ice-saturated sand were 2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were c.3 times larger. Martian impact crater energy versus diameter scaling may thus be a function of latitude. -from Authors

  12. Coral's chilling tale: Ancient reefs may resolve an ice-age paradox

    SciTech Connect

    Monastersky, R.

    1994-02-19

    At the end of the Pleistocene epoch, the peak of the last ice age, the land that would become New York City lay hidden beneath a sheet of ice more than twice the height of the Empire State Building. However, researchers have found contradictory evidence about how the low latitudes fared during the ice age. Deep sea sediments seem to indicate that the tropical seas weathered the glacial epoch with remarkable stability while the continental record indicates evidence of marked cooling. This discrepancy is a problem for climate researchers because it raises the possibility that climate models may lack a critical element that will hinder their ability to accurately predict future changes. However, studies of an ancient coral species may help. The coral occasionally incorporates strontium into its shell, a situation which occurs more frequently in cold water. Looking at the ratio of strontium to calcium in coral, researchers have proposed that the surface waters off Barbados were 5[degree]C colder than today. The article discusses the scientific debate set off by this finding.

  13. Holocene fluctuations of Bregne ice cap, Scoresby Sund, eastern Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.

    2011-12-01

    TML. 10Be ages of boulders and bedrock just outside these moraines indicate that deglaciation occurred at 10.4±0.5 ka and that the moraines mark the maximum ice extent during the Holocene. Beginning in the early Holocene, the ice cap then had either entirely retreated from the TML basin or contributed minimal sediment input until ~2,800 cal yr BP when clay-rich, finely laminated sediments begin to occur. This chronology is in contrast to small ice caps located in Liverpool Land, 130 km east of Milne Land. In Liverpool Land, lake sediment records indicate that the onset of Neoglaciation occurred at ~800 cal yr BP. The difference between the onset of Neoglaciation in western and eastern Scoresby Sund may be due to differences in basin position relative to the ice cap or may represent a temperature gradient between the inland, high elevation of Bregne ice cap and the coastal, low elevation Liverpool Land ice caps. Other records, such as GRIP borehole temperatures and the δ18O record from the Renland ice cap show cooling from ~4,500-2,000 yr BP suggesting that the terrestrial advances of ice caps in Scoresby Sund lagged behind temperatures registered in ice cores or ice core records are not good proxies for changes at the ice margins.

  14. The complex behavior of the Cordilleran Ice Sheet and mountain glaciers to abrupt climate change during the latest Pleistocene

    NASA Astrophysics Data System (ADS)

    Menounos, Brian; Goehring, Brent; Osborn, Gerald; Clarke, Garry K. C.; Ward, Brent; Margold, Martin; Bond, Jeff; Clague, John J.; Lakeman, Tom; Schaefer, Joerg; Koch, Joe; Gosse, John; Stroeven, Arjen P.; Seguinot, Julien; Heyman, Jakob; Fulton, Robert

    2014-05-01

    Surficial mapping and more than 70 radiometric ages 10Be, 14C] constrain the evolution of the Cordilleran Ice Sheet (CIS) and associated mountain glaciers in western Canada during the latest Pleistocene. Our data suggest that: i) there is widespread evidence for the Younger Dryas (YD) throughout the mountains of western Canada; ii) late Pleistocene climate reconstructions based solely on alpine moraines may be misleading in regions with decaying ice sheets; iii) extensive interfluves in some mountain regions were ice-free between 16 ka and 13 ka (kilo calibrated yrs BP). Initial decay of the CIS from its maximum extent around 16 ka was likely due to a combination of climatic (surface melting) and dynamical factors. Climate amelioration during the Bølling-Allerød Warm Period [14.7-12.9 ka], likely the cause for the major phase of CIS decay, resulted in ice sheet equilibrium line altitudes (ELAs) ranging from 2500 m asl in southern BC to around 2000 m asl along the BC-Yukon border. Hence, before the onset of the Younger Dryas (YD) Cold Period [12.9-11.7 ka], the ice sheet shrank and became a labyrinth of individual and coalescing valley glaciers fed by major accumulation zones centered on the Coast Mountains and other high ranges of NW Canada. The response of remnant ice and cirque glaciers to the YD climate deterioration was highly variable. In some cases, small glaciers (0.5-2 km2) built YD moraines that were only hundreds of meters beyond those constructed during the Little Ice Age (LIA) [0.30-0.15 ka]. Our dating also reveals that much larger glaciers persisted in nearby valleys that lie hundreds of meters below the cirques. Hence, we infer that many cirques were completely deglaciated prior the YD, in contrast to low-lying valleys where ice sheet remnants persisted. Glaciers also advanced in north-central British Columbia during the YD, but here glaciers constructed large terminal and lateral moraines. In the Cassiar and northern Coast mountains, for example

  15. Rapid thinning of the Welsh Ice Cap at 20-19 ka based on 10Be ages

    NASA Astrophysics Data System (ADS)

    Hughes, Philip D.; Glasser, Neil F.; Fink, David

    2016-01-01

    New 10Be ages from the summits of three mountain areas of North Wales reveal a very similar exposure timing as the Welsh Ice Cap thinned after the global Last Glacial Maximum. Eight bedrock and one boulder sample gave a combined arithmetic mean exposure age of 19.08 ± 0.80 ka (4.2%, 1σ). Similar exposure ages over a 320 m vertical range (824 to 581 m altitude) show that ice cap thinning was very rapid and spatially uniform. Using the same production rate and scaling scheme, we recalculated six published 10Be exposure ages from the nearby Arans, which also covered a similar elevation range from 608 to 901 m and obtained an arithmetic mean of 19.41 ± 1.45 ka (7.5%, 1σ). The average exposure age of all 15 accepted deglaciation ages is 19.21 ± 1.07 (5.6%, 1σ). The complete dataset from North Wales provides very strong evidence indicating that these summits became exposed as nunataks at 20-19 ka. This result provides important insight to the magnitude of ice surface lowering and behavior of the Welsh Ice Cap during the last deglaciation that can be compared to other ice masses that made up the British-Irish Ice Sheet.

  16. Glacier dynamics at Helheim and Kangerdlugssuaq glaciers, southeast Greenland, since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Khan, S. A.; Kjeldsen, K. K.; Kjær, K. H.; Bevan, S.; Luckman, A.; Aschwanden, A.; Bjørk, A. A.; Korsgaard, N. J.; Box, J. E.; van den Broeke, M.; van Dam, T. M.; Fitzner, A.

    2014-08-01

    Observations over the past decade show significant ice loss associated with the speed-up of glaciers in southeast Greenland from 2003, followed by a deceleration from 2006. These short-term, episodic, dynamic perturbations have a major impact on the mass balance on the decadal scale. To improve the projection of future sea level rise, a long-term data record that reveals the mass balance beyond such episodic events is required. Here, we extend the observational record of marginal thinning of Helheim and Kangerdlugssuaq glaciers from 10 to more than 80 years. We show that, although the frontal portion of Helheim Glacier thinned by more than 100 m between 2003 and 2006, it thickened by more than 50 m during the previous two decades. In contrast, Kangerdlugssuaq Glacier underwent minor thinning of 40-50 m from 1981 to 1998 and major thinning of more than 100 m after 2003. Extending the record back to the end of the Little Ice Age (prior to 1930) shows no thinning of Helheim Glacier from its maximum extent during the Little Ice Age to 1981, while Kangerdlugssuaq Glacier underwent substantial thinning of 230 to 265 m. Comparison of sub-surface water temperature anomalies and variations in air temperature to records of thickness and velocity change suggest that both glaciers are highly sensitive to short-term atmospheric and ocean forcing, and respond very quickly to small fluctuations. On century timescales, however, multiple external parameters (e.g. outlet glacier shape) may dominate the mass change. These findings suggest that special care must be taken in the projection of future dynamic ice loss.

  17. Precise interpolar phasing of abrupt climate change during the last ice age

    USGS Publications Warehouse

    WAIS Divide Project Members; Buizert, Christo; Adrian, Betty M.; Ahn, Jinho; Albert, Mary; Alley, Richard B.; Baggenstos, Daniel; Bauska, Thomas K.; Bay, Ryan C.; Bencivengo, Brian B.; Bentley, Charles R.; Brook, Edward J.; Chellman, Nathan J.; Clow, Gary D.; Cole-Dai, Jihong; Conway, Howard; Cravens, Eric; Cuffey, Kurt M.; Dunbar, Nelia W.; Edwards, Jon S.; Fegyveresi, John M.; Ferris, Dave G.; Fitzpatrick, Joan J.; Fudge, T. J.; Gibson, Chris J.; Gkinis, Vasileios; Goetz, Joshua J.; Gregory, Stephanie; Hargreaves, Geoffrey Mill; Iverson, Nels; Johnson, Jay A.; Jones, Tyler R.; Kalk, Michael L.; Kippenhan, Matthew J.; Koffman, Bess G.; Kreutz, Karl; Kuhl, Tanner W.; Lebar, Donald A.; Lee, James E.; Marcott, Shaun A.; Markle, Bradley R.; Maselli, Olivia J.; McConnell, Joseph R.; McGwire, Kenneth C.; Mitchell, Logan E.; Mortensen, Nicolai B.; Neff, Peter D.; Nishiizumi, Kunihiko; Nunn, Richard M.; Orsi, Anais J.; Pasteris, Daniel R.; Pedro, Joel B.; Pettit, Erin C.; Price, P. Buford; Priscu, John C.; Rhodes, Rachael H.; Rosen, Julia L.; Schauer, Andrew J.; Schoenemann, Spruce W.; Sendelbach, Paul J.; Severinghaus, Jeffrey P.; Shturmakov, Alexander J.; Sigl, Michael; Slawny, Kristina R.; Souney, Joseph M.; Sowers, Todd A.; Spencer, Matthew K.; Steig, Eric J.; Taylor, Kendrick C.; Twickler, Mark S.; Vaughn, Bruce H.; Voigt, Donald E.; Waddington, Edwin D.; Welten, Kees C.; Wendricks, Anthony W.; White, James W. C.; Winstrup, Mai; Wong, Gifford J.; Woodruff, Thomas E.

    2015-01-01

    The last glacial period exhibited abrupt Dansgaard–Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives1. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard–Oeschger cycle and vice versa2, 3, suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw4, 5, 6. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events7, 8, 9. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision2, 3,10. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2σ) for Dansgaard–Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard–Oeschger dynamics.

  18. Precise interpolar phasing of abrupt climate change during the last ice age.

    PubMed

    2015-04-30

    The last glacial period exhibited abrupt Dansgaard-Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard-Oeschger cycle and vice versa, suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2σ) for Dansgaard-Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard-Oeschger dynamics. PMID:25925479

  19. An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes

    NASA Astrophysics Data System (ADS)

    Moreno-Chamarro, Eduardo; Zanchettin, Davide; Lohmann, Katja; Jungclaus, Johann H.

    2016-04-01

    We investigate the mechanism of a decadal-scale weakening shift in the strength of the subpolar gyre (SPG) that is found in one among three last millennium simulations with a state-of-the-art Earth system model. The SPG shift triggers multicentennial anomalies in the North Atlantic climate driven by long-lasting internal feedbacks relating anomalous oceanic and atmospheric circulation, sea ice extent, and upper-ocean salinity in the Labrador Sea. Yet changes throughout or after the shift are not associated with a persistent weakening of the Atlantic Meridional Overturning Circulation or shifts in the North Atlantic Oscillation. The anomalous climate state of the North Atlantic simulated after the shift agrees well with climate reconstructions from within the area, which describe a transition between a stronger and weaker SPG during the relatively warm medieval climate and the cold Little Ice Age respectively. However, model and data differ in the timing of the onset. The simulated SPG shift is caused by a rapid increase in the freshwater export from the Arctic and associated freshening in the upper Labrador Sea. Such freshwater anomaly relates to prominent thickening of the Arctic sea ice, following the cluster of relatively small-magnitude volcanic eruptions by 1600 CE. Sensitivity experiments without volcanic forcing can nonetheless produce similar abrupt events; a necessary causal link between the volcanic cluster and the SPG shift can therefore be excluded. Instead, preconditioning by internal variability explains discrepancies in the timing between the simulated SPG shift and the reconstructed estimates for the Little Ice Age onset.

  20. Exposure history of the lunar meteorite, Elephant Moraine 87521

    NASA Technical Reports Server (NTRS)

    Vogt, S.; Herzog, G. F.; Eugster, O.; Michel, TH.; Niedermann, S.; Kraehenbuhl, U.; Middleton, R.; Dezfouly-Arjomandy, B.; Fink, D.; Klein, J.

    1993-01-01

    We report the noble gas concentrations and the Al-26, Be-10, Cl-36, and Ca-41 activities of the Antarctic lunar meteorite Elephant Moraine 87521. Although the actual exposure history of the meteorite may have been more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation for about 1 Ma at a depth of 1-5 g/sq cm followed, not necessarily directly, by a second one for 26 Ma at about 565 g/sq cm; launch from the moon less than 0.1 Ma ago; and arrival on earth 15-50 ka ago. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 87521 spent less than 1 Ma at a lunar depth less than 1 g/sq cm. EET 87521 has a K/Ar age in the range 3.0-3.4 Ga, which is typical for lunar mare basalts.

  1. Detailed Reconstructions of Fluctuations of Seven Glaciers during the "little Ice Age" in the Northern Caucasus, Russian Federation

    NASA Astrophysics Data System (ADS)

    Bushueva, I.

    2012-12-01

    The main task of this work is the development of detailed reconstructions of mountain glaciers' fluctuations with precise spatial references in the Northern Caucasus, their analyses in terms of glacier length, area and volume changes and identification of climate role in these fluctuations. The studied glaciers (Alibek, Ullukam, Terskol, Kashkatash, Bezingi, Mijirgi, Tsey) are situated along the Bolshoy Caucasus Range from the very west (Teberda river basin) to the east (Tseydon river basin). These valley glaciers have different size, aspect and percent of debris-cover. Basing on instrumental data (since the middle of 20th century), remote sensing images (CORONA, Geoeye, Cartosat, IRS, ASTER, etc.), aerial photos of 1950s-1980s, maps (since 1887), old photographs, as well as proxy data (historical descriptions, lichenometry, dendrochronology, 14C, 10Be), we reconstructed 15-20 positions of the glaciers tongues for each glacier and produced maps showing variations of the glaciers with precise spatial reference since their maximum in the mid 17th or first half of 19th century. For example, for Alibek glacier seven former front positions and eleven moraines were photo-identified and dated. We obtained the carbon dating of intermorainal peat-bog (103%), moraine dating based on isotopes of 10Be (1900±12) and determined minimum age of most distant moraine according to dendrochronological analysis of trees (Abies nordmanniana), growing on its surface (more than 200 years). At that time (1895) the glacier was 290 m longer than today, its surface was 0.31 km2 larger (5.94 km2 in 1895, 5.63 km2 in 2008). We calculated glaciers' length and area changes, using different methods (GLIMS; Bhambri et al., 2012) and analyzed advantages and disadvantages of each method in case of their application for Caucasian glaciers. Based on our measurements we evaluated changes of equilibrium line altitude and volume. Volume changes have been reconstructed using the model offered by Lüthi et

  2. Little Ice Age Recorded in Mn/Fe Precipitates by Pb and Nd Isotopes

    NASA Astrophysics Data System (ADS)

    Liebetrau, V.; Eisenhauer, A.; Frei, R.; Bock, B.; Kronz, A.; Hansen, B. T.; Leipe, T.

    2002-12-01

    Ferromanganese precipitates of the Baltic Sea can be dated by the 226Raexcess/Ba-method (Liebetrau et al., 2002). Recent investigations have shown that these precipitates may represent perfect archives for the postglacial history of the circum Baltic area. In particular, these precipitates offer the possibility to study short term variations of the Scandinavian shield erosion and climate change during the Little Ice Age. The Nd isotope record of a selected Mn/Fe crust from the Mecklenburg Bay of the Baltic Sea shows a significant change of the ɛ Nd-value from around -13 for ages older than 1100 years AD to approx. -18 around 1600 years AD. This shift can be explained by increased erosion and input of Nd from Archean Scandinavian sources and/or a reduced inflow of North Atlantic water (ɛ Nd = -13) to the Baltic Sea. Comparison with a temperature reconstruction for Fennoscandia (Mann, 2001) documents a close relationship of the ɛ Nd record with temperature variations during the Little Ice Age because negative ɛ Nd-value tend to correlate with lower temperature during the last 1000 years. In contrast, the pattern of 207Pb/206Pb record closely correlates with historically known changes of anthropogenic activities during the industrial revolution and times of enhanced Ag and Pb mining. Nd and Pb are correlated before 1100 AD but are decoupled after at about 1100 years AD. We propose that Pb appears to be more sensitive to anthropogenic activities since about 1100 AD. Liebetrau V., Eisenhauer A., Gussone N., W”rner G., Hansen B.T., and Leipe T., 2002, 226Raexcess/Ba growth rates and U-Th-Ra-Ba systematic of Baltic Mn/Fe crusts, Geochim. Cosmochim. Acta, 66, 73-83 Mann M.E., 2001, The Little Ice Age, in: Encyclopedia of Environmental Global Change

  3. Age and stability of sublimation till over buried glacier ice, inferred from 21Ne measurements, Ong Valley, Antarctica

    NASA Astrophysics Data System (ADS)

    Bibby, T.; Putkonen, J.; Morgan, D. J.; Balco, G.

    2014-12-01

    Ong Valley, in the Central Transantarctic Mountains, contains three distinct glacial drifts deposited by past advances of the Argosy glacier into the valley. Massive ice occurs below two of the till deposits. Potentially, such buried ice under shallow regolith cover could provide access to past climate and biological records more easily than deep ice coring. We measured cosmic-ray produced 21Ne in these tills as a means of constraining the age and stability of the three drifts, as well as the ice below them. We collected samples in vertical profiles from two hand-dug sections through each drift. The pits from two drifts overlying buried ice extended to the buried ice surface. The hypothesis that these are sublimation tills implies that 21Ne concentrations are a function of i) any inheritance from prior exposure; ii) the age since emplacement of the ice and till; iii) the sublimation rate of the ice; and iv) the surface erosion rate of the till. 21Ne concentrations in the youngest drift are ca. 10 M atoms/g and invariant with depth, indicating that they are predominantly due to inheritance, and provide only a weak maximum age constraint of ca. 0.1 Mya. The two older drifts have surface 21Ne concentrations of 200-250 M atoms/ g and depth concentration profiles consistent with a sublimation till origin. Given that 21Ne concentrations in the deepest samples in each of the two older drifts provide an upper limit on the inherited 21Ne concentration, these imply minimum ages of 1 Mya for the middle drift and 1.6 Mya for the oldest. This implies a 1 Mya minimum age for the ice underlying the middle drift.

  4. Agreement between the Moraine Park Vocational, Technical and Adult Education District and the Moraine Park Federation of Teachers, Local 3338, July 1, 1989--June 30, 1991.

    ERIC Educational Resources Information Center

    Moraine Park Vocational, Technical and Adult Education District, Fond du Lac, WI.

    The collective bargaining agreement between the Moraine Park Vocational, Technical and Adult Educational District Board and the Moraine Park Federation of Teachers is presented. This contract, covering full-time faculty, guidance counselors, and school health nurses at Moraine Park Technical College, applies to the period from July 1, 1989 through…

  5. Paired proglacial lake sediment and cosmogenic ages reveal the timing of Late Glacial and Holocene glacier fluctuations in the Huaguruncho Massif of Peru

    NASA Astrophysics Data System (ADS)

    Stansell, Nathan; Rodbell, Donald; Licciardi, Joseph; Schweinsberg, Avriel; Huss, Elizabeth; Finkel, Robert; Zimmerman, Susan

    2015-04-01

    The pairing of cosmogenic ages on moraine boulders and radiocarbon-dated lake sediments provides a powerful tool for reconstructing past climates based on former ice positions. Surface exposure ages (10Be) and clastic sediment records from a proglacial lake at Nevado Huaguruncho, Peru, document the waxing and waning of tropical alpine glaciers in the Eastern Cordillera during the last ca. 15 ka. Moraine ages indicate that glaciers were advanced at ca. 14.1 ± 0.4 ka, a pattern that is consistent with cooling associated with the Antarctic Cold Reversal. Yanacocha is located immediately upvalley from this 14.1 ka moraine, and lake sediments and cosmogenic ages also suggest that glaciers advanced just prior to, or at the start of, the Younger Dryas from 13.1 to 12.5 ka. Lake sediments and cosmogenic ages then indicate that glaciers retreated after ca. 12.5 ka, and again advanced during the early Holocene between ca. 12 and 9 ka. Short-lived increases in clastic lake sediment values suggest that ice margins advanced briefly at times through the middle Holocene from ca. 8 to 4 ka, and the lack of moraine boulders dating to this interval suggest that glaciers were less extensive than during the late Holocene. Lake sediments suggest that glaciers experienced a relatively limited advance at the start of the late Holocene from ca. 4 to 2 ka, followed by retreat until the start of the Medieval Climate Anomaly at ca. 1.1 ka. Clastic sediment values in the lake sediments then suggest that ice began advancing during the MCA, and the most pronounced Holocene advance at Huaguruncho occurred during the Little Ice Age (ca. 0.4 to 0.2 ka) under colder and wetter conditions. The pattern of glacier variability in Huaguruncho during the Late Glacial and Holocene provides further evidence that tropical Atlantic Ocean conditions drove much of the observed temperature and precipitation changes along the Eastern Cordillera.

  6. Soil development on recent end moraines of the Klutlan Glacier, Yukon Territory, Canada*1

    NASA Astrophysics Data System (ADS)

    Jacobson, G. L.; Birks, H. J. B.

    1980-07-01

    Data on soils with six Neoglacial moraines of the Klutlan Glacier have been compared with those from moraines at the warm, moist coastal site of Glacier Bay, 160 km south. Percentage organic matter increases rapidly for the first 100 to 150 yr of soil development and then continues to rise gradually for the next 100 yr. Soil pH falls from 8.0 in recent till to approximately 6.0 in 200-yr-old soils. Nitrogen levels in the mineral soil increase from near zero in recent tills to 0.7% in soils 175-200 yr old; organic horizons of soils associated with spruce forests in later successional stages contain approximately 1% nitrogen. Concentrations of certain inorganic phosphate ions in the different-aged soils increase continually throughout the succession. Data for nine chemical variables were subjected to a principal components analysis; the major pattern in the data reflects the differences between soils of low organic content and high pH present in early successional stages, and nutrient-rich soils with high organic content and low pH present after succession has progressed toward the spruce forest. These trends in soil development with time are strikingly similar to those reported from Glacier Bay, except that the changes in soil properties appear to be delayed by 50-100 yr at the Klutlan terminus. Although numerous signs of nitrogen deficiency have been identified in plants growing on new soils at Glacier Bay, none was observed visually in living plants or in nutrients measured in samples of foliage from three plant taxa ( Epilobium latifolium, Salix spp., and Populus balsamifera) taken from the Klutlan moraines. Concentrations of nitrogen and other nutrients (Ca, Mg, K, total P) in the foliage samples show no clear trends with increasing soil development. Low temperatures, a short growing season, and very low mean annual precipitation probably limit plant growth and account for the delayed soil development on the Klutlan moraines.

  7. Glacial and climatic evolution from the Little Ice Age last Maximum to the present in Tröllaskagi Peninsula (North Iceland): the case of Gljúlfurárjökull

    NASA Astrophysics Data System (ADS)

    María Fernández, Jose; Andres, Nuria; Tanarro, Luis Miguel; Palacios, David

    2015-04-01

    This paper presents the evolution of the Gljúlfurárjökull glacier (65°42'48'' N, 18°39'13'' W; 980 m), located at the headwall of the Skiðadalur valley, on the Tröllaskagi peninsula (N. Iceland). This is one of many small glaciers situated on the bottom of the Tröllaskagi valleys. This glacier is one of the few "clean" glaciers, i.e. not covered with boulders, as is the case with most of the glaciers on this peninsula. This makes the glacier especially sensitive to climate change, and it has retreated and advanced many times since its last maximum during the Little Ice Age (LIA) maximum in the mid- 19th century (Caseldine and Stötter, 1993), leaving a large number of moraine ridges. This paper analyses the change in this glacier from the LIA up to the present day, with reference to the variations in the surface, ELA and volume. Lichenometry and geomorphological field analysis were used to establish the exact limits of the glacier during the LIA last maximum. An aerial photo from 1946 and two orthophotos from 2000 and 2013 were also used. Using photointerpretation and Geographical Information Systems (GIS), the aerial photos were georeferenced to delimit the glacier in different years, analyse the surface and volume variations, and calculate the ELA for each date. The ELA analysis was carried out using the method: Accumulation Area Ratio (AAR 0.67). The results obtained with this method are: Little Ice Age Maximum: 945 m a.s.l. (almost the same ELA proposed by Caseldine and Stötter, 1993) 1946: 970 m a.s.l. 2000: 980 m a.s.l. 2013: 990 m a.s.l. The ice volume lost from LIA to 2000 was: 111.68 hm3 Reference Caseldine, C., Stötter, J., 1993. "Little Ice Age" glaciation of Tröllaskagi Peninsula, northern Iceland: Climatic implications for reconstructed equilibrium line altitudes (ELAs). Holocene 3: 357-366. Research funded by Cryocrisis project (CGL2012-35858), Government of Spain, and Nils Mobility projects (EEA GRANTS)

  8. Geochronology and paleoclimatic implications of the last deglaciation of the Mauna Kea Ice Cap, Hawaii

    USGS Publications Warehouse

    Anslow, Faron S.; Clark, P.U.; Kurz, M.D.; Hostetler, S.W.

    2010-01-01

    We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5??2.5ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3km upslope for ~4.5-5.0kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ~15.4ka corresponds to a large reduction of the Atlantic meridional overturning circulation (AMOC) following Heinrich Event 1. Subsequent ice-margin retreat began at 14.6??1.9ka, corresponding to a rapid resumption of the AMOC and onset of the B??lling warm interval, with the ice cap melting rapidly to complete deglaciation. Additional 3He ages obtained from a flood deposit date the catastrophic outburst of a moraine-dammed lake roughly coeval with the Younger Dryas cold interval, suggesting a more active hydrological cycle on Mauna Kea at this time. A coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of LLGM and readvance sizes. The depression of the LLGM equilibrium line altitude requires atmospheric cooling of 4.5??1??C, whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present. We hypothesize (1) that the LLGM temperature depression was associated with global cooling, (2) that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the North Atlantic, and (3) that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter-tropical convergence zone (ITCZ). Such a

  9. Late-Holocene Fluctuations of the Greenland Ice Sheet: Insights from a south Greenland threshold lake

    NASA Astrophysics Data System (ADS)

    Sinclair, G.; Carlson, A. E.; Reilly, B.

    2015-12-01

    Several centennial-scale climate fluctuations during the late-Holocene make it an ideal test case for examining the effects of climate change on sea level at societally-relevant timescales. Across much of the Arctic, glaciers and ice sheets reached their maximum late-Holocene extent during the Little Ice Age (LIA, 1400-1900 C.E.), approximately coincident with the global temperature minima observed during this time. However, ongoing work suggests the south Greenland Ice Sheet (sGrIS) may have behaved differently during the late-Holocene, with several outlet glaciers retreating, rather than advancing, during the LIA, possibly due to regional warming in the region different from the Arctic trend. The Qassimiut lobe, a low-lying piedmont-like extension of the sGrIS, may be especially sensitive to late-Holocene climate changes. Geomorphic evidence outboard of Naujaat Sermia, an outlet glacier draining the Qassimiut lobe, suggests three distinct periods of land exposure. We hypothesize these occurred during the last deglacial period, after an advance from near or behind the present margin during the Neoglacial, and during warming following the Little Ice Age in the last 1-2 centuries. Here, we present data from threshold lake cores immediately outboard of the presumed Neoglacial moraine. A sharp contact divides glacial sands and silts from organic gyttja, indicating glacial retreat from the moraine and subsequent meltwater diversion. The contact is accompanied by several geochemical changes, including increased Fe/Ti ratios, increased Br, and decreased Si and K, indicating a switch from more clastic to organic sedimentation. Radiocarbon ages from eight macrofossils immediately above this contact are calibrated to 1350-1950 C.E., suggesting the ice sheet may have retreated from its late-Holocene maximum during the Little Ice Age, but the wide range in ages suggests reworking of organic material may be significant in this region.

  10. Depositional environments during the Late Palaeozoic ice age (LPIA) in northern Ethiopia, NE Africa

    NASA Astrophysics Data System (ADS)

    Bussert, Robert

    2014-11-01

    The Late Palaeozoic sediments in northern Ethiopia record a series of depositional environments during and after the Late Paleozoic ice age (LPIA). These sediments are up to 200 m thick and exceptionally heterogeneous in lithofacies composition. A differentiation of numerous types of lithofacies associations forms the basis for the interpretation of a large range of depositional processes. Major glacigenic lithofacies associations include: (1) sheets of diamictite, either overlying glacially eroded basement surfaces or intercalated into the sediment successions, and representing subglacial tillites, (2) thick massive to weakly stratified muddy clast-poor diamictites to lonestone-bearing laminated mudstones originating from a combination of suspension settling of fines and iceberg rainout, (3) lensoidal or thin-bedded diamictites deposited from debris flows, (4) wedges of traction and gravity transported coarse-grained sediments deposited in outwash fans, (5) irregular wedges or sheets of mudstones deformed primarily by extension and incorporating deformed beds or rafts of other lithofacies formed by slumping, and (6) irregular bodies of sandstone, conglomerate and diamictite deformed by glacial pushing. The dominance of laminated or massive clast-bearing mudstones in most successions indicates ice-contact water bodies as the major depositional environment. Into this environment, coarse-grained sediments were transported by various gravity driven transport processes, including dropstone activity of ice-bergs, slumping, cohesive debris flow, hyperconcentrated to concentrated flow, hyperpycnal flow, and by turbidity flow. Close to glacier termini, wedge-shaped bodies of conglomerate, sandstone, diamictite and mudstone were deposited primarily in subaqueous outwash-fans. Soft-sediment deformation of these sediments either records ice push during glacier advance or re-sedimentation by slumping. Apart from an initial glacier advance when thick ice of temperate or

  11. Iron fertilization of the Subantarctic Ocean during the last ice age

    NASA Astrophysics Data System (ADS)

    Martinez-Garcia, A.

    2015-12-01

    Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean. The scarcity of iron limits marine productivity and carbon uptake in one-quarter of the world ocean where the concentration of major nutrients (phosphorus and nitrogen) is perennially high. The Southern Ocean is the region where variations in iron availability can have the largest effect on Earth's carbon cycle through its fertilizing effect on marine ecosystems. Paleoceanographic records from the Subantarctic Atlantic have revealed a remarkable correlation between phytoplankton productivity and aeolian iron flux during glacial periods supporting the iron fertilization hypothesis. In addition, a recent study has shown that peak glacial times and millennial cold events were nearly universally associated not only with increases in dust flux and export production, but also with an increase in nutrient consumption (the last indicated by higher foraminifera-bound δ15N) (Martinez-Garcia et al. 2014). This combination of changes is uniquely consistent with ice age iron fertilization of the Subantarctic Atlantic. The strengthening of the biological pump associated with the observed increase in Subantarctic nutrient consumption during the high-dust intervals of the last two ice ages can explain up to ~40 ppm of the CO2 decrease that characterizes the transitions from mid-climate states to full ice age conditions. However, the impact of iron fertilization in other sectors of the Southern Ocean characterized by lower ice age dust fluxes than the Atlantic remains unclear. A series of recently published records from the Subantarctic Pacific indicate that dust deposition and marine export production were three times higher during glacial periods than during interglacials (Lamy et al. 2014). Here we present new measurements of foraminifera-bound nitrogen isotopes in a sediment core located in the

  12. No iron fertilization in the equatorial Pacific Ocean during the last ice age.

    PubMed

    Costa, K M; McManus, J F; Anderson, R F; Ren, H; Sigman, D M; Winckler, G; Fleisher, M Q; Marcantonio, F; Ravelo, A C

    2016-01-28

    The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron. Greater atmospheric dust deposition could have fertilized the equatorial Pacific with iron during the last ice age--the Last Glacial Period (LGP)--but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain. Here we present meridional transects of dust (derived from the (232)Th proxy), phytoplankton productivity (using opal, (231)Pa/(230)Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ(15)N) from six cores in the central equatorial Pacific for the Holocene (0-10,000 years ago) and the LGP (17,000-27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region. Thus, ice-age iron fertilization in the

  13. Predictions of the onset of mini ice age in the 25th solar cycle

    NASA Astrophysics Data System (ADS)

    Kumar, Rajiv

    2016-07-01

    Predictions of the ir-regularty in the 11 year heartbeat of the sun due to asyncronous of the two layered dynamo effect would result in mini ice age as in the Maunder minimum.The onset of this event is expected in the begining of 25th solar cycle and would go to its maximum in the 26th solar cycle.The minimum temperature is expected in 2028 due to the fall of solar activity by 60 % termed as solar hibernation.The predictions are based on the observations obtained by the Royal Greenwich observatory since 1874. Keywords: Dynamo effect,munder minimum,Solar hybernation

  14. Growth of a post-Little Ice Age submarine fan, Glacier Bay, Alaska

    USGS Publications Warehouse

    Carlson, P.R.; Cowan, E.A.; Powell, R.D.; Cai, J.

    1999-01-01

    A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed in the early 1900s at the head of Queen Inlet. The Late Holocene Queen fan is comparable to large Pleistocene fans that formed in the Gulf of Alaska and differs from trough-mouth fans formed by cooler climate glacier systems.

  15. Climate hazards, adaptation and "resilience" of societies (early Little Ice Age, west of France).

    NASA Astrophysics Data System (ADS)

    Athimon, Emmanuelle; Maanan, Mohamed

    2016-04-01

    Over the past ten to fifteen years, climate hazards and adaptation have received more attention due to the current climate change. Climate historians have gathered strong evidence that the world's climate has evolved over the past millennium and one of the most significant changes took place during the Little Ice Age. Recently, a set of questions has emerged: what were the effects of the Little Ice Age on human's societies? How did humans adapt to these climate changes? How did they react to extreme weather-related events? Using examples of climate hazards from the West of France during the beginning of the Little Ice Age (xivth-xviith centuries) such as storms, flooding, drought, harsh winters, the poster aims at showing how the past societies can constitute a source of inspiration for present ones. Through schemas, this research exposes the system's rebound capacity, points out the importance of the historical depth in research on human's adaptation and resilience and shows the value of integrating a historical approach. It reveals that History contributes to the knowledge of the relationship between societies and climate hazards. Data on climate hazards and adaptation of societies stem from historical sources such as chronicles, diaries, books of accounts, records of cities repairs. To protect themselves and their goods, medieval and modern societies had developed specific skills, practices and strategies. From the xivth to the xviiith century, there is an increase of defense by dikes in the low Loire, as for example the construction of those amongst Longué and Ponts-de-Cé between the early xivth century and 1407. The French kingdom's authorities also tried increasingly to provide technical, material, logistical and fiscal support: for instance, during the winter 1564-1565, several bridges have been destroyed by a river flooding in Nantes. The King Charles IX then offered to people of Nantes part of the funds from taxes on the main activities such as the

  16. Surface exposure dating of moraines and alluvial fans in the Southern Central Andes

    NASA Astrophysics Data System (ADS)

    Terrizzano, Carla; Zech, Roland; García Morabito, Ezequiel; Haghipour, Negar; Christl, Marcus; Likermann, Jeremías; Tobal, Jonathan; Yamin, Marcela

    2016-04-01

    The role of tectonics versus climate in controlling the evolution of alluvial fans in discussed controversially. The southern Central Andes and their forelands provide a perfect setting to study climate versus tectonic control of alluvial fans. On the one hand, the region is tectonically active and alluvial fan surfaces are offset by faults. The higher summits, on the other hand, are glaciated today, and glacial deposits document past periods of lower temperatures and increased precipitation. We applied 10Be surface exposure dating on 5 fan terraces 4 moraines of the Ansilta range (31.6°S - 69.8°W) using boulders and amalgamated pebbles to explore their chronological relationship. From youngest to oldest, the alluvial fan terraces yield minimum ages of 15 ± 1 ka (T1), 97 ± 9 ka (T2), 141 ± 9 ka (T3), 286 ± 14 ka (T4) and 570 ± 57 ka (T5). Minimum ages derived from moraines are 14 ± 1 ka (M1), 22 ± 2 ka (M2), 157 ± 14 ka (M3) and 351 ± 33 ka (M4), all calculations assuming no erosion and using the scaling scheme for spallation based on Lal 1991, Stone 2000. The moraines document glacial advances during cold periods at the marine isotope stages (MIS) 2, 6 and 10. The terraces T1, T3 seem to be geomorphologic counterparts during MIS 2 and 6. We suggest that T2, T4 and T5 document aggradation during the cold periods MIS 5d, 8 and 14 in response to glacial advances, although the respective moraines are not preserved. Our results highlight: i) the arid climate in the Southern Central Andes favors the preservation of glacial and alluvial deposits allowing landscape and climate reconstructions back to ~570 ka), ii) alluvial deposits correlate with moraines or fall into cold glacial times, so that climate, and in particular the existence of glaciers, seems to be the main forcing of alluvial fan formation at our study site. References Lal, D., 1991: Cosmic ray labeling of erosion surfaces: In situ nuclide production rates and erosion models. Earth and Planetary

  17. Evolution of Ossoue Glacier (French Pyrenees) since the end of the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Marti, R.; Gascoin, S.; Houet, T.; Ribière, O.; Laffly, D.; Condom, T.; Monnier, S.; Schmutz, M.; Camerlynck, C.; Tihay, J. P.; Soubeyroux, J. M.; René, P.

    2015-09-01

    Little is known about the fluctuations of the Pyrenean glaciers. In this study, we reconstructed the evolution of Ossoue Glacier (42°46' N, 0.45 km2), which is located in the central Pyrenees, from the Little Ice Age (LIA) onwards. To do so, length, area, thickness, and mass changes in the glacier were generated from historical data sets, topographical surveys, glaciological measurements (2001-2013), a ground penetrating radar (GPR) survey (2006), and stereoscopic satellite images (2013). The glacier has receded considerably since the end of the LIA, losing 40 % of its length and 60 % of its area. Three periods of marked ice depletion were identified: 1850-1890, 1928-1950, and 1983-2013, as well as two short periods of stabilization: 1890-1894, 1905-1913, and a longer period of slight growth: 1950-1983; these agree with other Pyrenean glacier reconstructions (Maladeta, Coronas, Taillon glaciers). Pyrenean and Alpine glaciers exhibit similar multidecadal variations during the 20th century, with a stable period detected at the end of the 1970s and periods of ice depletion during the 1940s and since the 1980s. Ossoue Glacier fluctuations generally concur with climatic data (air temperature, precipitation, North Atlantic Oscillation, Atlantic Multidecadal Oscillation). Geodetic mass balance over 1983-2013 was -1.04 ± 0.06 w.e.a-1 (-31.3 ± 1.9 m w.e.), whereas glaciological mass balance was -1.45 ± 0.85 m w.e. a-1 (-17.3 ± 2.9 m w.e.) over 2001-2013, resulting in a doubling of the ablation rate in the last decade. In 2013 the maximum ice thickness was 59 ± 10.3 m. Assuming that the current ablation rate remains constant, Ossoue Glacier will disappear midway through the 21st century.

  18. No iron fertilization in the equatorial Pacific Ocean during the last ice age

    NASA Astrophysics Data System (ADS)

    Costa, K. M.; McManus, J. F.; Anderson, R. F.; Ren, H.; Sigman, D. M.; Winckler, G.; Fleisher, M. Q.; Marcantonio, F.; Ravelo, A. C.

    2016-01-01

    The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron. Greater atmospheric dust deposition could have fertilized the equatorial Pacific with iron during the last ice age—the Last Glacial Period (LGP)—but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain. Here we present meridional transects of dust (derived from the 232Th proxy), phytoplankton productivity (using opal, 231Pa/230Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ15N) from six cores in the central equatorial Pacific for the Holocene (0–10,000 years ago) and the LGP (17,000–27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region. Thus, ice-age iron fertilization in the

  19. The age and origin of the "Younger Dryas climate event" in Greenland ice cores

    NASA Astrophysics Data System (ADS)

    Fairbanks, R. G.; Bard, E.

    1990-12-01

    230Th/234U and 14C dating of Barbados corals has extended the calibration of 14C years B.P. to calendar years B.P. beyond the 9200 year tree ring series (Bard et al., 1990). This now permits the conversion of 14C chronozones, which delimit major climate shifts in western Europe, to calendar years. The Younger Dryas chronozone, defined as 11,000 to 10,000 14C years B.P., corresponds to 13,000 to 11,700 calendar years B.P. This calibration affects the interpretation of an intensely studied example of the "Younger Dryas climate event," the δ18O anomaly between 1785 and 1793 m in Dye 3 ice core. The end of the δ18O anomaly in Dye 3 ice core has been dated by measurements of 14C in air bubbles (Andree et al., 1984, 1986) and by annual layer counting (Hammer et al., 1986). The older 14C dates fall out of the range of the tree ring calibration series but can now be calibrated to calendar years using the Barbados 230Th/234U calibration. The 14Ccorrected age for the end of the δ18O event is 10,300 ± 400 calendar years B.P. compared to the annual layer counting age of 10,720 ± 150 years B.P. Thus, the "Younger Dryas" event in the Dye 3 ice core ends in the Preboreal chronozone (11,700 to 10,000 calendar years B.P.) and is not correlative with the end of the Younger Dryas event identified in pollen records marking European vegetation changes. The end of the Dye 3 δ18O event is, however, correlative with the end of meltwater pulse IB (Fairbanks, 1989), marking a period of intense deglaciation with meltwater discharge rates exceeding 13,000 km³/yr.

  20. Episodic Neoglacial Cryosphere Expansion Reconstructed from 14C Ages of Ice-Entombed Plants on Svalbard

    NASA Astrophysics Data System (ADS)

    Miller, G. H.; Lehman, S.; Landvik, J. Y.

    2015-12-01

    The Northern Hemisphere cryosphere's response to the monotonic decline in summer insolation through the Holocene has been irregular expansion, interrupted by periods of retreat, culminating in the Little Ice Age, when most glaciers attained their maximum late Holocene dimensions. This non-linear response to near-linear forcing implies other factors modulate the radiative effects of the regular insolation decline. Understanding how the Earth system accomplishes this modulation is relevant to the development of reliable models for future climate change. Accurately dating the onset of persistent summer coolings across the Arctic is a first step toward developing this understanding. Here we report 52 precise radiocarbon dates on rooted plants emerging from beneath receding glaciers on Svalbard that define times when colder summers led to snowline depression and an expanded cryosphere. The earliest persistent depression of snowline documented by our dates occurred between 4.0 and 3.4 ka, but with little additional summer cooling until early in the first millennium AD. Episodes of subsequent summer cooling were centered on 240-340, 410-540 and 670-770 AD, followed by additional cooling between 1000 and 1230 AD, and between 1300 and 1470 AD. Cooling that occurred after 1470 AD, includes of the Little Ice Age when the Svalbard cryosphere reached its maximum Neoglacial dimensions. We suggest that in addition to insolation forcing, irregular reductions in the strength of the North Atlantic Current and expansions of Arctic Ocean sea ice were dominant factors that led to episodic snowline depression over Svalbard, but the extent to which these changes are linked to radiative forcing from volcanism or solar irradiance as opposed to unforced variability remains unclear. The widespread exposure of entombed plants dating from the first millennium AD suggests that Svalbard's average summer temperatures of the past century now exceed those of any century since at least 700 AD

  1. Beacon Hill end moraine, Boston: new explanation of an important urban feature

    USGS Publications Warehouse

    Kaye, Clifford A.

    1976-01-01

    The usefulness of geology to engineers is in direct proportion to how well it helps us predict the subsurface; these predictions, in turn, depend on our knowledge of the geomorphic processes that molded the terrain. The uncertainties of interpretation are particularly great in glaciated terrain because our understanding of both glacial processes and history is so incomplete, a fact well illustrated in Beacon Hill. Recent construction activities in the eastern part of the hill, until now classified as a drumlin, have shown that it is better interpreted as an end moraine formed by a Wisconsonian glacial readvance. Instead of the firm till that was anticipated as foundation material, excavations exposed a complex of sand, gravel, and clay, with only minor zones of till. The structure of these deposits strongly suggests that originally they were plates of the glacial bed that froze to the glacier and were transported englacially. Thrust faulting and other deformations are glacial structures formed within the ice in the glacier's terminal zone. In spite of the complex englacial history, these deposits lost little of their original appearance and intergranular relationships. Upon deglaciation, the frozen moraine thawed, and slumping formed complex secondary structures on the ridge's lower flanks.

  2. The Asian monsoon over the past 640,000 years and ice age terminations.

    PubMed

    Cheng, Hai; Edwards, R Lawrence; Sinha, Ashish; Spötl, Christoph; Yi, Liang; Chen, Shitao; Kelly, Megan; Kathayat, Gayatri; Wang, Xianfeng; Li, Xianglei; Kong, Xinggong; Wang, Yongjin; Ning, Youfeng; Zhang, Haiwei

    2016-06-30

    Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record's length and temporal precision allow us to test the idea that insolation changes caused by the Earth's precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record's timing, the terminations are separated by four or five precession cycles, supporting the idea that the '100,000-year' ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and 'unfinished terminations'. PMID:27357793

  3. Ice-nucleating particle emissions from photochemically aged diesel and biodiesel exhaust

    NASA Astrophysics Data System (ADS)

    Schill, G. P.; Jathar, S. H.; Kodros, J. K.; Levin, E. J. T.; Galang, A. M.; Friedman, B.; Link, M. F.; Farmer, D. K.; Pierce, J. R.; Kreidenweis, S. M.; DeMott, P. J.

    2016-05-01

    Immersion-mode ice-nucleating particle (INP) concentrations from an off-road diesel engine were measured using a continuous-flow diffusion chamber at -30°C. Both petrodiesel and biodiesel were utilized, and the exhaust was aged up to 1.5 photochemically equivalent days using an oxidative flow reactor. We found that aged and unaged diesel exhaust of both fuels is not likely to contribute to atmospheric INP concentrations at mixed-phase cloud conditions. To explore this further, a new limit-of-detection parameterization for ice nucleation on diesel exhaust was developed. Using a global-chemical transport model, potential black carbon INP (INPBC) concentrations were determined using a current literature INPBC parameterization and the limit-of-detection parameterization. Model outputs indicate that the current literature parameterization likely overemphasizes INPBC concentrations, especially in the Northern Hemisphere. These results highlight the need to integrate new INPBC parameterizations into global climate models as generalized INPBC parameterizations are not valid for diesel exhaust.

  4. Atmospheric response to Ice Age conditions: Climatology near the Earth's surface

    NASA Astrophysics Data System (ADS)

    Lautenschlager, M.; Herterich, K.

    1990-12-01

    We present a 6-year simulation of the ice age atmosphere using the T21 Atmospheric General Circulation Model (AGCM) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The lower boundary conditions (18 kyr B.P.) were taken from CLIMAP Project Members (1981). The analysis is restricted to the surface climatology for two reasons: The surface fields are the test data derived from the geological record on land, and they define the upper boundary conditions for simulating the glacial ocean. Model results are shown for the mean annual surface fields of temperature, wind, and precipitation. In the global average the surface temperature was 4.7°C cooler compared to the present temperature. The wind strength increased in mid-latitudes and decreased in tropical trade wind regions. Precipitation did not change significantly in the global average; however, precipitation decreased over land and increased over the ocean. Most of the difference patterns between the present conditions and the ice age climate were statistically significant. The simulated surface climatology is roughly consistent with the paleogeological evidence and with numerical AGCM simulations of other authors. This suggests that presently available AGCMs, including the ECMWF model (T21), are able to describe climates far away from the present, although internal parameterizations were tuned to present data sets.

  5. Reassessment of ice-age cooling of the tropical ocean and atmosphere

    USGS Publications Warehouse

    Hostetler, S.W.; Mix, A.C.

    1999-01-01

    The CLIMAP project's reconstruction of past sea surface temperature inferred limited ice-age cooling in the tropical oceans. This conclusion has been controversial, however, because of the greater cooling indicated by other terrestrial and ocean proxy data. A new faunal sea surface temperature reconstruction, calibrated using the variation of foraminiferal species through time, better represents ice-age faunal assemblages and so reveals greater cooling than CLIMAP in the equatorial current systems of the eastern Pacific and tropical Atlantic oceans. Here we explore the climatic implications of this revised sea surface temperature field for the Last Glacial Maximum using an atmospheric general circulation model. Relative to model results obtained using CLIMAP sea surface temperatures, the cooler equatorial oceans modify seasonal air temperatures by 1-2??C or more across parts of South America, Africa and southeast Asia and cause attendant changes in regional moisture patterns. In our simulation of the Last Glacial Maximum, the Amazon lowlands, for example, are cooler and drier, whereas the Andean highlands are cooler and wetter than the control simulation. Our results may help to resolve some of the apparent disagreements between oceanic and continental proxy climate data. Moreover, they suggest a wind-related mechanism for enhancing the export of water vapour from the Atlantic to the Indo-Pacific oceans, which may link variations in deep-water production and high-latitude climate changes to equatorial sea surface temperatures.

  6. The Asian monsoon over the past 640,000 years and ice age terminations

    NASA Astrophysics Data System (ADS)

    Cheng, Hai; Edwards, R. Lawrence; Sinha, Ashish; Spötl, Christoph; Yi, Liang; Chen, Shitao; Kelly, Megan; Kathayat, Gayatri; Wang, Xianfeng; Li, Xianglei; Kong, Xinggong; Wang, Yongjin; Ning, Youfeng; Zhang, Haiwei

    2016-06-01

    Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record’s length and temporal precision allow us to test the idea that insolation changes caused by the Earth’s precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record’s timing, the terminations are separated by four or five precession cycles, supporting the idea that the ‘100,000-year’ ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and ‘unfinished terminations’.

  7. Sturgis and Tekonsha ice advances: Evidence for thin ice sheets in southern Michigan

    SciTech Connect

    Straw, W.T.; Kehew, A.E.; Passero, R.N. . Dept. of Geology)

    1993-03-01

    Advance of an ice sheet through the Saginaw Lowland to the position of Sturgis, in St. Joseph County, Michigan initially produced the Sturgis Moraine and adjacent outwash apron. As this ice sheet down wasted, meltwater impounded by it overtopped ice divides to form meltwater streams that cut canyons in the ice and underlying glacial sediments. Continued wasting was attended by formation of supraglacial streams that developed waterfalls as they eroded headward. Complete melting of the ice revealed a subglacial topography marked by drumlins, many of which are irregular, attesting to formation near the attenuated margin of the ice sheet. Prior to complete wasting of this stagnant ice mass, ice of the Lake Michigan Lobe advanced from the west-northwest to form the Tekonsha Moraine. Exposed only where this relatively thin ice sheet advanced onto a highland in east-central Kalamazoo County, the southwestern extension of this moraine was buried by outwash from ice that formed the very prominent Kalamazoo Moraine. That the Tekonsha ice sheet stagnated and wasted in place is revealed by two prominent elongate kames, several escarpments, lake and wetland basins produced by melting of ice masses buried by glacial outwash, and sequential filling of the lowland produced by melting of this ice sheet by a series of alluvial fans. The sequence of fan emplacement is indicated by marginal relationships of the fans and the number and size of depressions formed by melting of relic blocks of ice. The first-formed Dry Prairie fan is marked by numerous large depressions while the Prairie Ronde, the last formed fan exhibits only small widely spaced depressions formed by melting of the last vestiges of this ice sheet.

  8. Reconstruction of mass balance of Nevado Coropuna glaciers (Southern Peru) for Late Pleistocene, Little Ice Age and the present.

    NASA Astrophysics Data System (ADS)

    Ubeda, J.; Palacios, D.

    2009-04-01

    The Nevado Coropuna volcanic complex (15th 31'S-72 ° 39 ° W) is the quaternary stratovolcano northernmost of the central volcanic zone (CVZ) in the western flank of the Central Andes (Southern Peru). This consists in four adjacent volcanic buildings that are occupied over 5.100-5.700 masl by a system of glaciers covering an area of 47 Km2 in 2007 (Ubeda et al, 2008). The maximum expansion of glaciers during the Pleistocene affected an area of ~449 Km2, dropping to altitudes around 3.600-4800 m (Ubeda et al, 2007). In this work were mapped several hundreds of moraines which constitute a record of climate change since the last glacial maximum (LGM). Current glacier system is formed by dozen of glaciers descending slope down in all directions. Coropuna complex is an excellent laboratory for to investigate the control that climate change, tectonics and volcanism exert on the dynamics of glaciers, a scale of tens of years (by studying current glaciers) and also of tens of thousands of years (by analyzing the geomorphological evidence of its evolution in the past). Ubeda et al. (2008) analyzed the evolution of eighteen glaciers of Nevado Coropuna using indicators as surfaces and Equilibrium Line Altitudes (ELAs) of ice masses in 2007, 1986, 1955, Little the Ice Age (LIA) and Last Glacial Maximum (LGM). The glaciers were grouped into two sets: NE group (seven glaciers) and SE group (eleven glaciers). The work included statistical series of ELAs in each phase, estimates by Area x Altitud Balance Ratio (AABR) method, which was proposed by Osmaston (2005), in addition with estimates of timing (~17Cl36 Ka) and magnitude (~ 782-911 m) of ELA depression during LGM. The work included statistical series of ELAs in each phase, estimates by the method Area x Altitud Balance Ratio (AABR) proposed by Osmaston (2005), and in addition estimates of the timing (~17Cl36 Ka) and magnitude (~ 782-911 m) of ELA depression during LGM. The objective of this work is to estimate the current

  9. Atmospheric aging of dust ice nucleating particles - a combined laboratory and field approach

    NASA Astrophysics Data System (ADS)

    Boose, Yvonne; Rodríguez, Sergio; García, M. Isabel; Linke, Claudia; Schnaiter, Martin; Zipori, Assaf; Crawford, Ian; Lohmann, Ulrike; Kanji, Zamin A.; Sierau, Berko

    2016-04-01

    than the rather fresh dust at Izaña. This suggests that atmospheric aging and processing decreases the ice nucleation efficiency of Saharan dust during advection to Central Europe.

  10. Controls on small-scale biogeomorphic interactions on lateral moraine slopes and their linkage to large-scale geomorphic and vegetation patterns

    NASA Astrophysics Data System (ADS)

    Eichel, Jana; Meyer, Nele; Draebing, Daniel; Schmidtlein, Sebastian; Dikau, Richard

    2016-04-01

    Glacier forelands are characterized by simultaneous and coupled geomorphic and vegetation development following glacier retreat. For lateral moraine slopes, it has been shown that once geomorphic activity decreases sufficiently, ecosystem engineer species (e.g., Dryas octopetala) can establish and a 'biogeomorphic feedback window' is entered, in which the engineer (e.g., through high cover) amplifies the decrease in geomorphic activity and changes the dominant process from erosional (e.g., slope wash) to bound solifluction processes, until it is suppressed by later successional species (Eichel et al., 2015). This temporal sequence is termed 'biogeomorphic succession' and has been found in a glacier foreland (Eichel et al., 2013). However, it remains unclear (1) if and how further factors, e.g., soil properties and thermal and snow conditions, influence small-scale biogeomorphic feedbacks and (2) how biogeomorphic succession dynamics relate to geomorphic and vegetation patterns in space. Consequently, the objectives of this study are (1) to evaluate controlling factors for small-scale biogeomorphic interactions, (2) to identify geomorphic and vegetation patterns in space and (3) to link small-scale interactions with large-scale vegetation and geomorphic patterns and dynamics. A biogeomorphic approach was carried out on Little Ice Age lateral moraine slopes in the Turtmann glacier foreland (Switzerland), consisting of (1) a permanent plot survey (2x2 m) to assess geomorphic and vegetation properties, combined with soil sampling and iButton temperature loggers for thermal and snow properties, and (2) a detailed (1:1000) geomorphic and vegetation mapping. Plot data was analysed using multivariate statistics and compared to geomorphic and vegetation maps. Combined results of multivariate statistics and mapping show a strong relationship between geomorphic properties and species composition. These are independent from terrain age, but controlled by a toposequence

  11. Holocene history of North Ice Cap, northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Corbett, L. B.; Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Roy, E. P.; Thompson, J. T.

    2013-12-01

    Although much research has focused on the past extents of the Greenland Ice Sheet, less is known about the smaller ice caps on Greenland and how they have evolved over time. These small ice caps respond sensitively to summer temperatures and, to a lesser extent, winter precipitation, and provide valuable information about climatic conditions along the Greenland Ice Sheet margins. Here, we investigate the Holocene history of North Ice Cap (76°55'N 68°00'W), located in the Nunatarssuaq region near Thule, northwest Greenland. Our results are based on glacial geomorphic mapping, 10Be dating, and analyses of sediment cores from a glacially fed lake. Fresh, unweathered and unvegetated boulders comprise moraines and drift that mark an extent of North Ice Cap ~25 m outboard of the present ice margin. It is likely that these deposits were formed during late Holocene time and we are currently employing 10Be surface exposure dating to examine this hypothesis. Just outboard of the fresh moraines and drift, boulders and bedrock show significant weathering and are covered with lichen. Based on glacial geomorphic mapping and detailed site investigations, including stone counts, we suggest that the weathered boulders and bedrock were once covered by erosive Greenland Ice Sheet flow from southeast to northwest over the Nunatarssuaq region. Five 10Be ages from the more weathered landscape only 100-200 m outboard of the modern North Ice Cap margin are 52 and 53 ka (bedrock) and 16, 23, and 31 ka (boulders). These ages indicate that recent ice cover has likely been cold-based and non-erosive, failing to remove inherited cosmogenic nuclides from previous periods of exposure, although the youngest boulder may provide a maximum limiting deglaciation age. Sediment cores collected from Delta Sø, a glacially-fed lake ~1.5 km outside of the modern North Ice Cap margin, contain 130 cm of finely laminated sediments overlying coarse sands and glacial till. Radiocarbon ages from just above

  12. The episodic influx of tin-rich cosmic dust particles during the last ice age

    NASA Astrophysics Data System (ADS)

    LaViolette, Paul A.

    2015-12-01

    This paper presents evidence of the first detection of interstellar dust in ice age polar ice. Neutron activation analysis (NAA) results are reported for 15 elements found in dust filtered from eight samples of Camp Century Greenland ice dating from 40 to 78 kyrs BP. High concentrations of Sn, Sb, Au, Ag, Ir, and Ni were found to be present in three out of these eight samples. One compositionally anomalous dust sample from an ice core depth of 1230.5 m (age ∼49 kyrs BP, near the beginning of D/O stadial No. 13) was found to contain tin with an average weight percent of 49% as determined by energy dispersive X-ray analysis (EDS). This sample was also found to contain high concentrations of Pb with an average weight abundance of 8.4% and matching the Sn:Pb ratio observed in interstellar spectra. Dust particles in this sample generally have a platy morphology and range from submicron size up to a size as large as 120 μm, a particle consisting almost entirely of SnO2 and being the largest monomineralic extraterrestrial dust particle so far discovered. One porous aggregate tin-bearing particle was found to contain nanometer sized chondrules indicating an extraterrestrial origin. The extraterrestrial origin for the tin is also indicated by the presence of isotopic anomalies in the 114Sn, 115Sn and 117Sn isotopes. Follow up isotopic measurements of this tin-rich dust need to be performed to improve confidence in the anomalies reported here. High abundances of the low melting point elements Ag, Au, and Sb are also present in this tin-rich sample along with elevated abundances of the siderophiles Ir, Ni, Fe, and Co, the latter being present in chondritic proportions and indicating that about 9% of the dust has a C1 chondrite component. Measurements indicate that about 97% of this dust is of extraterrestrial origin with a 3% residual being composed of terrestrial windblown dust. EDS analysis of another tin-rich Camp Century ice core dust sample dating to ∼130 kyrs BP

  13. Evolution of Ossoue Glacier (French Pyrenees) since the end of the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Marti, R.; Gascoin, S.; Houet, T.; Ribière, O.; Laffly, D.; Condom, T.; Monnier, S.; Schmutz, M.; Camerlynck, C.; Tihay, J. P.; Soubeyroux, J. M.; René, P.

    2015-04-01

    Long-term climate records are rare at high elevations in Southern Europe. Here, we reconstructed the evolution of Ossoue Glacier (42°46' N, 0.45 km2), located in the Pyrenees (3404 m a.s.l.), since the Little Ice Age (LIA). Glacier length, area, thickness and mass changes indicators were generated from historical datasets, topographic surveys, glaciological measurements (2001-2013), a GPR survey (2006) and stereoscopic satellite images (2013). The glacier has receded considerably since the end of the LIA, losing 40 % of its length and 60% of its area. Three periods of marked ice depletion can be identified: 1850-1890, 1928-1950 and 1983-2013, as well as two periods of stabilization or slightly growth: 1905-1928 and 1950-1983; these agree with climatic datasets (air temperature, precipitation, North Atlantic Oscillation, Atlantic Multidecadal Oscillation). In the early 2000s, the area of the glacier dropped below 50% of its area at the end of the LIA. Geodetic mass balance measurements over 1983-2013 indicated -30.1 ± 1.7 m w.e. (-1 m w.e. yr-1) whereas glaciological mass balance measurements show -17.36 ± 2.9 m w.e. (-1.45 m w.e. yr-1) over 2001-2013, resulting in a doubling of the ablation rate in the last decade. In 2013 the maximum ice thickness was 59 ± 10.3 m. Assuming that the current ablation rate stays constant, Ossoue Glacier will disappear midway through the 21st century.

  14. Chlorine-36 and 14C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet

    USGS Publications Warehouse

    Brigham-Grette, J.; Gualtieri, L.M.; Glushkova, O.Y.; Hamilton, T.D.; Mostoller, D.; Kotov, A.

    2003-01-01

    The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to ???20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald's Beringian ice-sheet hypothesis. ?? 2003 Elsevier Science (USA). All rights reserved.

  15. A new Little Ice Age chronology of the Franz Josef Glacier, New Zealand

    NASA Astrophysics Data System (ADS)

    McKinzey, K. M.; Lawson, W.; Kelly, D.

    2003-04-01

    The Little Ice Age (LIA) chronology of the Franz Josef Glacier (FJG), New Zealand, was reassessed due to previous uncertainty surrounding the timing of its maximum extent, eg. 1450 (Burrows 1990), 1600 (Wardle 1973) or 1750 AD (Lawrence and Lawrence 1965). Tree age-size relationships based on data from 75 ring counts and diameters collected from southern rata (Metrosideros umbellata) and kamahi (Weinmannia racemosa) allowed the ages of 1340 trees measured within fifty, 150 m2 quadrats in the Waiho Valley to be predicted. Ages of the oldest trees were then used to determine the time elapsed since deglaciation, or alternatively, the culmination of the preceding advance. The revised chronology showed that the LIA maximum of the FJG culminated by c. 1470-1530 AD, when the terminus was located approximately 4.5 km down-valley of its position in 2001. Subsequent, but smaller magnitude, re-advances culminated by c. 1580-1610 and c. 1790-1840 AD. Average terminus retreat rates after the LIA maximum varied between 7-9 m a-1 and reached 23 m a-1 by the early to mid-1800's, which suggests that climatic amelioration signalling the end of the LIA occurred in New Zealand by the early 19th Century.

  16. Implementation of an all-ages mandatory helmet policy for ice skating.

    PubMed

    Thibault-Halman, Ginette; Fenerty, Lynne; Wheadon-Hore, Kathie; Walling, Simon; Cusimano, Michael D; Clarke, David B

    2015-12-01

    Ice skaters sustain a significant number of head injuries each winter. We are the first to implement an all-ages helmet policy at a university-based Canadian arena. We report our experience from a cross-sectional observational study as well as the policy's consequences on helmet use and skating participation. Educational programming was provided prior to policy implementation. Observations of helmet use, falls and skater demographics were conducted prior to education/implementation and after policy implementation. The number of skaters observed was essentially unchanged by the policy; 361 skaters were observed pre-implementation, while 358 were observed post-implementation during the same number of observation-hours. Pre-implementation, helmet use ranged from 97% among children under 12 to 10% among adults; post-implementation use in all skaters was 99%. Falls were observed among all age groups, with preponderance among those aged 4-12. An all-ages helmet policy was successful both in achieving helmet use among all skaters and in maintaining participation rates. PMID:25681515

  17. Temporal and Spatial Changes of Permafrost in the Tien Shan Mountains Since the Little Ice Age.

    NASA Astrophysics Data System (ADS)

    Marchenko, S.; Romanovsky, V.

    2006-12-01

    During the Late Holocene there were numerous periods of warming and cooling in the Tien Shan Mountains, Central Asia. Ground temperatures and permafrost area in the Tien Shan have been subjected to repeated fluctuations during the last millennia brought about by the general planetary changes in climate. The altitudinal oscillations of the mean annual air temperature (MAAT) zero Centigrade isotherm had a range of about 300 m during that time. Air temperature in the Tien Shan Mountains has increased at a higher rate than the global mean during the 20th century. Climate warming in the high-mountains regions could induce the further near-surface permafrost degradation, which may lead to slope instability and permafrost-related hazards. The main objectives of the modeling process were to estimate the permafrost thermal regime and assess the area where permafrost disappeared since the second part of the nineteenth century. To estimate the effect of climate change on permafrost a one-dimensional process-based model was used to simulate the ground thermal regime of the Tien Shan at a resolution of a half-degree latitude-longitude since the Little Ice Age up to present. The results of numerical simulation show that at an altitude of 2500 m a.s.l. the permafrost temporary formed at least three times during the last 500 years. At the lover altitudinal boundary of permafrost distribution the permafrost temperatures now are close to 0°C and at some sites permafrost degradation has already started. Analysis of measured active layer and permafrost temperatures coupled with numerical thermal modeling (permafrost temperature reanalysis) shows that most of the recently thawed permafrost was formed during the Little Ice Age. The modeling of alpine permafrost dynamics shows that the altitudinal lower boundary of permafrost distribution has shifted by about 150-200 m upward since the end of the Little Ice Age (circa 1850). During the same period, the area of permafrost distribution

  18. A sequential Bayesian approach for the estimation of the age-depth relationship of Dome Fuji ice core

    NASA Astrophysics Data System (ADS)

    Nakano, S.; Suzuki, K.; Kawamura, K.; Parrenin, F.; Higuchi, T.

    2015-06-01

    A technique for estimating the age-depth relationship in an ice core and evaluating its uncertainty is presented. The age-depth relationship is mainly determined by the accumulation of snow at the site of the ice core and the thinning process due to the horizontal stretching and vertical compression of ice layers. However, since neither the accumulation process nor the thinning process are fully understood, it is essential to incorporate observational information into a model that describes the accumulation and thinning processes. In the proposed technique, the age as a function of depth is estimated from age markers and δ18O data. The estimation is achieved using the particle Markov chain Monte Carlo (PMCMC) method, in which the sequential Monte Carlo (SMC) method is combined with the Markov chain Monte Carlo method. In this hybrid method, the posterior distributions for the parameters in the models for the accumulation and thinning processes are computed using the Metropolis method, in which the likelihood is obtained with the SMC method. Meanwhile, the posterior distribution for the age as a function of depth is obtained by collecting the samples generated by the SMC method with Metropolis iterations. The use of this PMCMC method enables us to estimate the age-depth relationship without assuming either linearity or Gaussianity. The performance of the proposed technique is demonstrated by applying it to ice core data from Dome Fuji in Antarctica.

  19. Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record

    NASA Astrophysics Data System (ADS)

    Greenwood, Sarah L.; Clark, Chris D.

    2009-12-01

    The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one 'flowsets' comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset cross-cutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative 'age-stack' of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset - its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, 'smudged' landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories

  20. Future ice ages and the challenges related to final disposal of nuclear waste: The Greenland Ice Sheet Hydrology Project

    NASA Astrophysics Data System (ADS)

    Lehtinen, A.; Claesson-Liljedahl, L.; Näslund, J.-O.; Ruskeeniemi, T.

    2009-04-01

    A deep geological repository for nuclear waste is designed to keep radiotoxic material separated from mankind and the environment for several hundreds of thousands of years. Within this time perspective glacial conditions are expected in high latitudes/Canada and North Europe. Climate induced changes such as the growth of ice sheets and permafrost will influence and alter the ground surface and subsurface environment, which may impact repository safety. In order to understand how climate change, particularly cooling and glaciation, might affect a repository in the long term, the use of present-day analogues helps to reduce the uncertainties and support the assumptions made in safety assessments. There are major uncertainties concerning hydrological processes related to glacial conditions. The impact of glaciations on any planned repository is a key consideration when performing safety assessments as it is one of the strongest perturbations related to climate change in the long term. The main aspects that need to be further investigated include: 1) to what extent does the meltwater produced by an ice sheet penetrates into the bedrock; 2) what is the pressure situation under an ice sheet, driving ground water flow; 3) how much oxygenated water will reach repository depth; 4) to what depth does glacial meltwater penetrate into the bedrock ; 5)what chemical composition does such water has when and if it reaches repository depth; and 6) can taliks (unfrozen ground in a permafrost area) act as concentrated discharge points of deep groundwater potentially transporting radionuclides in case of repository failure? Field data is needed in order to achieve a better and integrated understanding of the problems discussed above. Thus, research in a natural analogue site in Greenland has been planned and initiated by the Finnish (Posiva), Swedish (SKB) and Canadian (NWMO) nuclear waste management companies. The Greenland ice sheet and the Kangerlussuaq area (west Greenland

  1. Geochemical record of high emperor penguin populations during the Little Ice Age at Amanda Bay, Antarctica.

    PubMed

    Huang, Tao; Yang, Lianjiao; Chu, Zhuding; Sun, Liguang; Yin, Xijie

    2016-09-15

    Emperor penguins (Aptenodytes forsteri) are sensitive to the Antarctic climate change because they breed on the fast sea ice. Studies of paleohistory for the emperor penguin are rare, due to the lack of archives on land. In this study, we obtained an emperor penguin ornithogenic sediment profile (PI) and performed geochronological, geochemical and stable isotope analyses on the sediments and feather remains. Two radiocarbon dates of penguin feathers in PI indicate that emperor penguins colonized Amanda Bay as early as CE 1540. By using the bio-elements (P, Se, Hg, Zn and Cd) in sediments and stable isotope values (δ(15)N and δ(13)C) in feathers, we inferred relative population size and dietary change of emperor penguins during the period of CE 1540-2008, respectively. An increase in population size with depleted N isotope ratios for emperor penguins on N island at Amanda Bay during the Little Ice Age (CE 1540-1866) was observed, suggesting that cold climate affected the penguin's breeding habitat, prey availability and thus their population and dietary composition. PMID:27261428

  2. Saponaria pumila (caryophyllaceae) and the ice age in the European alps.

    PubMed

    Tribsch, Andreas; Schönswetter, Peter; Stuessy, Tod F

    2002-12-01

    The polymerase chain reaction (PCR)-based amplified fragment length polymorphism (AFLP) technique was applied to elucidate the glacial history of the alpine cushion plant Saponaria pumila in the European Alps. Special emphasis was given to a dense sampling of populations. Our data support a survival of S. pumila during the last ice age in at least three refugia, which are characterized by unique marker sets. Patterns of genetic diversity and divergence can be explained by survival in peripheral refugia and additional in situ survival within the ice sheet on peripheral nunataks. A nunatak survival in interior parts of the Alps needs not be postulated to explain our results. The level of genetic diversity is dramatically different between populations (Shannon's diversity index: 0.87-19.86). Some peripheral populations are characterized by a high number of rare fragments indicating long isolation, but not necessarily by a high level of genetic diversity. Parts of the present distributional area were recolonized via recent long-distance dispersal, leading to severely bottlenecked populations lacking private or rare fragments. The combination of our data with palaeogeological and palaeoclimatological evidence allows us to confine Pleistocene refugia to certain regions and to draw a detailed scenario of the glacial and postglacial history of S. pumila. PMID:21665631

  3. Bibliographic Instruction at Moraine Valley Community College: A Position Paper.

    ERIC Educational Resources Information Center

    Miller, Larry A.; And Others

    This paper presents a plan for implementing bibliographic instruction at Moraine Valley Community College in Palos Hills, Illinois. The definition and purpose of bibliographic instruction are reviewed, educational strategies in bibliographic instruction are discussed, and an implementation proposal is presented. The proposal describes three phases…

  4. Age of the crowfoot advance in the Canadian Rocky Mountains. A glacial event coeval with the Younger Dryas oscillation

    SciTech Connect

    Reasoner, M.A.; Rutter, N.W. ); Osborn, G. )

    1994-05-01

    A suite of sediment core samples was recovered from two lakes, Crowfoot and Bow lakes, that are adjacent to the Crowfoot moraine type locality, to identify and radiocarbon date sediments related to the Crowfoot advance. The Crowfoot moraine system, widely recognized throughout northwestern North America, represents a glacial advance that is post-Wisconsin and pre-Mazama tephra in age. An interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca. 11,330 and 10,100 [sup 14]C yr B.P. is associated with the Crowfoot moraine. The Crowfoot advance is therefore approximately synchronous with the European Younger Dryas cold event (ca. 11,000-10,000 [sup 14]C yr B.P.). Furthermore, the termination of the Crowfoot advance also appears to have been abrupt. These findings illustrate that the climatic change responsible for the European Younger Dryas event extended beyond the northern Atlantic basin and western Europe. Equilibrium-line altitude (ELA) depressions associated with the Crowfoot advance are similar to those determined for the Little Ice Age advance, whereas Younger Dryas ELA depressions in Europe significantly exceed Little Ice Age ELA depressions. 26 refs., 3 figs., 1 tab.

  5. Constraints on southern hemisphere tropical climate change during the Little Ice Age and Younger Dryas based on glacier modeling of the Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Malone, Andrew G. O.; Pierrehumbert, Raymond T.; Lowell, Thomas V.; Kelly, Meredith A.; Stroup, Justin S.

    2015-10-01

    Improving the late Quaternary paleoclimate record through climate interpretations of low-latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past, present, and future climate change. Paleotemperature reconstructions at low-latitude glaciers are uniquely fruitful because they can provide both site-specific information and enhanced understanding of regional-scale variations due to the structure of the tropical atmosphere. We produce Little Ice Age (LIA) and Younger Dryas (YD) paleoclimate reconstructions for the Huancané outlet glacier of the Quelccaya Ice Cap (QIC) and low-latitude southern hemisphere regional sea surface temperatures (SSTs) using a coupled ice-flow and energy balance model. We also model the effects of long-term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the Huancané glacier length. We find temperature to be the dominant climate driver of glacier length change. Also, we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record, necessitating that these features were formed during past colder climates. To constrain our LIA reconstruction, we incorporate the QIC ice core record, finding a LIA air temperature cooling at the ice cap of between ˜0.7 °C and ˜1.1 °C and ˜0.4 °C and regional SSTs cooling of ˜0.6 °C. For the YD paleoclimate reconstructions, we propose two limits on the precipitation rate, since the ice core record does not extend into the Pleistocene: 1) the precipitation rate scales with the Clausius-Clapeyron relationship (upper limit on cooling) and 2) the precipitation rate increases by 40% (lower limit on cooling), which is an increase about twice as great as the regional increases realized in GCM simulations for the period. The first limit requires ˜1.6 °C cooling in ice cap air temperatures and ˜0.9 °C cooling in SSTs, and the

  6. Glacier change from the early Little Ice Age to 2005 in the Torngat Mountains, northern Labrador, Canada

    NASA Astrophysics Data System (ADS)

    Way, Robert G.; Bell, Trevor; Barrand, Nicholas E.

    2015-10-01

    The glaciers of the Torngat Mountains of northern Labrador are the southernmost of the Canadian Arctic and the easternmost of continental North America. Currently, 195 small mountain glaciers cover an area in excess of ~ 24 km2, confined mostly to small cirques and upland depressions. Using a combination of field and remote sensing methods this study reconstructs and dates the areal extent of Torngat glaciers at their Neoglacial maximums, enabling the first assessment of regional glacier change over the past several centuries. Mapped glacier paleomargins (n = 165) are compared to current (2005) glaciers and ice masses, showing a 52.5% reduction in glacier area, with at least 11 former glaciers altogether disappearing. Glacier change is spatially homogenous and independent of most geographic and topographic factors; however, glacier elevation and glacier size mitigated total change. Previously established lichen growth stations were revisited, and growth rates recalculated based on ~ 30-year-long records, enabling the construction of locally derived low- and high-altitude lichen growth curves. Using growth rates and in situ lichen measurements, the retreat from maximum Neoglacial moraine extents are suggested to have occurred between A.D. 1581 and 1673. These findings indicate a similar magnitude of post-LIA retreat to mountain glaciers elsewhere, yet a much earlier timing (~ 200 years) of retreat than other glaciers in the eastern Canadian Arctic. Though no definitive answer explaining this discrepancy is presented, evidence suggests that regional climate dynamics and the importance of solar radiation for Torngat glaciers may play an important role in local glacierization.

  7. Dynamical excitation of the tropical Pacific Ocean and ENSO variability by Little Ice Age cooling

    NASA Astrophysics Data System (ADS)

    Rustic, Gerald T.; Koutavas, Athanasios; Marchitto, Thomas M.; Linsley, Braddock K.

    2015-12-01

    Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Niño-Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galápagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500-1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900-1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Niña pattern.

  8. Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age.

    PubMed

    Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

    2014-01-01

    The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

  9. Increase in penguin populations during the Little Ice Age in the Ross Sea, Antarctica

    PubMed Central

    Hu, Qi-Hou; Sun, Li-Guang; Xie, Zhou-Qing; Emslie, Steven D.; Liu, Xiao-Dong

    2013-01-01

    Penguins are an important seabird species in Antarctica and are sensitive to climate and environmental changes. Previous studies indicated that penguin populations increased when the climate became warmer and decreased when it became colder in the maritime Antarctic. Here we determined organic markers in a sediment profile collected at Cape Bird, Ross Island, high Antarctic, and reconstructed the history of Adélie penguin colonies at this location over the past 700 years. The region transformed from a seal to a penguin habitat when the Little Ice Age (LIA; 1500–1800 AD) began. Penguins then became the dominant species. Penguin populations were the highest during ca. 1490 to 1670 AD, a cold period, which is contrary to previous results in other regions much farther north. Different responses to climate change may occur at low latitudes and high latitudes in the Antarctic, even if for same species. PMID:23969993

  10. Global signatures and dynamical origins of the Little Ice Age and Medieval Climate Anomaly.

    PubMed

    Mann, Michael E; Zhang, Zhihua; Rutherford, Scott; Bradley, Raymond S; Hughes, Malcolm K; Shindell, Drew; Ammann, Caspar; Faluvegi, Greg; Ni, Fenbiao

    2009-11-27

    Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña-like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation-Arctic Oscillation. PMID:19965474

  11. Dynamical excitation of the tropical Pacific Ocean and ENSO variability by Little Ice Age cooling.

    PubMed

    Rustic, Gerald T; Koutavas, Athanasios; Marchitto, Thomas M; Linsley, Braddock K

    2015-12-18

    Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Niño-Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galápagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500-1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900-1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Niña pattern. PMID:26634438

  12. Little Ice Age wetting of interior Asian deserts and the rise of the Mongol Empire

    NASA Astrophysics Data System (ADS)

    Putnam, Aaron E.; Putnam, David E.; Andreu-Hayles, Laia; Cook, Edward R.; Palmer, Jonathan G.; Clark, Elizabeth H.; Wang, Chunzeng; Chen, Feng; Denton, George H.; Boyle, Douglas P.; Bassett, Scott D.; Birkel, Sean D.; Martin-Fernandez, Javier; Hajdas, Irka; Southon, John; Garner, Christopher B.; Cheng, Hai; Broecker, Wallace S.

    2016-01-01

    The degree to which warming of the planet will alter Asia's water resources is an important question for food, energy, and economic security. Here we present geological evidence, underpinned by radiometric dating and dendrochronology, and bolstered by hydrological modeling, indicating that wetter-than-present conditions characterized the core of the inner Asian desert belt during the Little Ice Age, the last major Northern Hemispheric cold spell of the Holocene. These wetter conditions accompanied northern mid-latitude cooling, glacier expansion, a strengthened/southward-shifted boreal jet, and weakened south Asian monsoons. We suggest that southward migration of grasslands in response to these wetter conditions aided the spread of Mongol Empire steppe pastoralists across Asian drylands. Conversely, net drying over the 20th century has led to drought that is unprecedented for the past ∼830 years, and that could intensify with further heating of the Asian continent.

  13. Regionally coherent Little Ice Age cooling in the Atlantic Warm Pool

    USGS Publications Warehouse

    Richey, J.N.; Poore, R.Z.; Flower, B.P.; Quinn, T.M.; Hollander, D.J.

    2009-01-01

    We present 2 new decadal-resolution foraminiferal Mg/Ca-SST records covering the past 6-8 centuries from the northern Gulf of Mexico (GOM). These records provide evidence for a Little Ice Age (LIA) cooling of 2??C, consistent with a published Mg/Ca record from Pigmy Basin. Comparison of these 3 records with existing SST proxy records from the GOM-Caribbean region show that the magnitude of LIA cooling in the Atlantic Warm Pool (AWP) was significantly larger than the mean hemispheric cooling of <1??C. We propose that a reduction in the intensity and spatial extent of the AWP during the LIA, combined with associated changes in atmospheric circulation may account for the regional SST patterns observed in the GOM-Caribbean region during the LIA. Copyright 2009 by the American Geophysical Union.

  14. Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age

    PubMed Central

    Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

    2014-01-01

    The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400–1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

  15. Variations of soil profile characteristics due to varying time spans since ice retreat in the inner Nordfjord, western Norway

    NASA Astrophysics Data System (ADS)

    Navas, A.; Laute, K.; Beylich, A. A.; Gaspar, L.

    2014-06-01

    In the Erdalen and Bødalen drainage basins located in the inner Nordfjord in western Norway the soils were formed after deglaciation. The climate in the uppermost valley areas is sub-arctic oceanic, and the lithology consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. The Little Ice Age glacier advance affected parts of the valleys with the maximum glacier extent around AD 1750. In this study five sites on moraine and colluvium materials were selected to examine main soil properties, grain size distribution, soil organic carbon and pH to assess if soil profile characteristics and patterns of fallout radionuclides (FRNs) and environmental radionuclides (ERNs) are affected by different stages of ice retreat. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. The sampled soils on the colluviums outside the LIA glacier limit became ice-free during the Preboral. The Regosols present better-developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Significantly lower mass activities of FRNs were found in soils on the moraines than on colluviums. Variations of ERN activities in the valleys were related to characteristics of soil mineralogical composition. These results indicate differences in soil development that are consistent with the age of ice retreat. In addition, the pattern distribution of 137Cs and 210Pbex activities differs in the soils related to the LIA glacier limits in the drainage basins.

  16. Variations of soil profile characteristics due to varying time spans since ice retreat in the inner Nordfjord, western Norway

    NASA Astrophysics Data System (ADS)

    Navas, A.; Laute, K.; Beylich, A. A.; Gaspar, L.

    2014-01-01

    In the Erdalen and Bødalen drainage basins located in the inner Nordfjord in western Norway the soils have been formed after deglaciation. The climate in the uppermost valley areas is sub-arctic oceanic and the lithology consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. The Little Ice Age glacier advance affected parts of the valleys with the maximum glacier extent around AD 1750. In this study five sites on moraine and colluvium materials were selected to examine the main soil properties to assess if soil profile characteristics and pattern of fallout radionuclides (FRNs) and environmental radionuclides (ERNs) are affected by different stages of ice retreat. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. The sampled soils on the colluviums outside the LIA glacier limit became ice-free during the Preboral. The Regosols present better-developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Significant lower mass activities of FRNs are found in soils on the moraines than on colluviums. Variations of ERNs activities in the valleys are related to characteristics soil mineralogical composition. These results indicate differences in soil development that are consistent with the age of ice retreat. In addition, the pattern distribution of 137Cs and 210Pbex activities differs in the soils related to the LIA glacier limits in the drainage basins.

  17. Plio-Pleistocene history of Ferrar Glacier, Antarctica: Implications for climate and ice sheet stability

    NASA Astrophysics Data System (ADS)

    Staiger, J. W.; Marchant, D. R.; Schaefer, J. M.; Oberholzer, P.; Johnson, J. V.; Lewis, A. R.; Swanger, K. M.

    2006-03-01

    The areal distribution and elevation of glacial drifts in Vernier Valley, southern Victoria Land, are used to reconstruct the Plio-Pleistocene history of upper Ferrar Glacier. 21Ne cosmogenic-nuclide analyses of surface cobbles on four moraines, Ferrar 1, 2, 3, and 4, provide age control. A minimum-age estimate for Ferrar Drifts calculated by assuming zero surface erosion indicates that the oldest moraine, Ferrar 4, was deposited at least ˜ 3400 ka. Our preferred age model, which applies a very conservative erosion rate of 5 cm Ma - 1 in age calculations, suggests that Ferrar 4 is ˜ 4000 ka; Ferrar 3 is ˜ 1200 ka; and Ferrar 2 is ˜ 700 ka. Based on glacial geologic data, Ferrar 1 is modern; cosmogenic ages for cobbles on this moraine suggest a value for nuclide inheritance of ˜ 50 ka. The Ferrar drifts are most easily interpreted in terms of a progressive reduction in the ice-surface elevation of upper Ferrar Glacier during Plio-Pleistocene time. Relative to today, the surface of upper Ferrar Glacier was ˜ 100 to 125 m higher during the Pliocene Climatic Optimum and ˜ 50 m higher during early to mid Quaternary time. Conversely, during MIS 2, the ice-surface elevation of upper Ferrar Glacier was likely no larger than today and may have stood below modern levels. The texture and sedimentology of all Ferrar drifts indicate that during ice recession from Vernier Valley the upper Ferrar Glacier lacked surface-melting ablation zones, even during the Pliocene Climatic Optimum. Results from a simple 2-D glaciological flow-band model demonstrate that upper Ferrar Glacier also lacked basal-melting zones during ice recession. We show that the development of weathering pits and desert varnish on cobbles exposed at the surface of Ferrar drifts varies in accord with cosmogenic age. The mean width and depth of the largest surface pits on boulders from Ferrar drifts increases by ˜ 10 mm Ma - 1 and ˜ 6.7 mm Ma - 1 , respectively; the maximum thickness of desert varnish on

  18. Geomorphic relations among glacial Lake Algonquin and the Munising and Grand Marais moraines in eastern Upper Michigan, USA

    NASA Astrophysics Data System (ADS)

    Blewett, William L.; Drzyzga, Scott A.; Sherrod, Laura; Wang, Hong

    2014-08-01

    Data obtained from ground-penetrating radar (GPR), optically stimulated luminescence (OSL) dating, and geostatistical reconstructions of Lake Algonquin water planes indicate that high-standing outwash aprons flanking the Munising moraine's southern margin in eastern Upper Michigan terminate as large, coalescing Gilbert-type ice-contact deltas graded to the Main level of Lake Algonquin. Nearly 30 km of GPR imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition. Landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation. In time, these deltas aggraded to the Main Lake Algonquin level as the ice margin stabilized. An OSL date of 12.5 ± 1.1 ka on a nearby beach ridge associated with the Main Algonquin shoreline is consistent with this interpretation. These new data, coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta, indicate that Lake Algonquin was falling as delta deposition waned, eventually reaching a level concordant with the Lower Orillia level before final abandonment. Large, regionally extensive heads of outwash marking the crest of the Munising moraine are graded to the upper margins of these deltas and, by inference, must also correlate with Main Lake Algonquin and the associated Two Rivers deglaciation ca. 13-12.5 ka. The deltas, in turn, are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group Lake Algonquin shoreline. Because these aforementioned heads of outwash, part of Drexler and others' Grand Marais moraine, correlate with the Marquette moraine farther west, they likely date to the Marquette advance ca. 11.5 ka. Thus, landforms related to Two Rivers and to Marquette glaciations appear to comingle across the study area. In the absence of extensive exposures and datable materials, our work

  19. A sequential Bayesian approach for the estimation of the age-depth relationship of the Dome Fuji ice core

    NASA Astrophysics Data System (ADS)

    Nakano, Shin'ya; Suzuki, Kazue; Kawamura, Kenji; Parrenin, Frédéric; Higuchi, Tomoyuki

    2016-02-01

    A technique for estimating the age-depth relationship in an ice core and evaluating its uncertainty is presented. The age-depth relationship is determined by the accumulation of snow at the site of the ice core and the thinning process as a result of the deformation of ice layers. However, since neither the accumulation rate nor the thinning process is fully known, it is essential to incorporate observational information into a model that describes the accumulation and thinning processes. In the proposed technique, the age as a function of depth is estimated by making use of age markers and δ18O data. The age markers provide reliable age information at several depths. The data of δ18O are used as a proxy of the temperature for estimating the accumulation rate. The estimation is achieved using the particle Markov chain Monte Carlo (PMCMC) method, which is a combination of the sequential Monte Carlo (SMC) method and the Markov chain Monte Carlo method. In this hybrid method, the posterior distributions for the parameters in the models for the accumulation and thinning process are computed using the Metropolis method, in which the likelihood is obtained with the SMC method, and the posterior distribution for the age as a function of depth is obtained by collecting the samples generated by the SMC method with Metropolis iterations. The use of this PMCMC method enables us to estimate the age-depth relationship without assuming either linearity or Gaussianity. The performance of the proposed technique is demonstrated by applying it to ice core data from Dome Fuji in Antarctica.

  20. End of the Little Ice Age in the Alps forced by industrial black carbon.

    PubMed

    Painter, Thomas H; Flanner, Mark G; Kaser, Georg; Marzeion, Ben; VanCuren, Richard A; Abdalati, Waleed

    2013-09-17

    Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Alpine temperature and precipitation records suggest that glaciers should instead have continued to grow until circa 1910. Radiative forcing by increasing deposition of industrial black carbon to snow may represent the driver of the abrupt glacier retreats in the Alps that began in the mid-19th century. Ice cores indicate that black carbon concentrations increased abruptly in the mid-19th century and largely continued to increase into the 20th century, consistent with known increases in black carbon emissions from the industrialization of Western Europe. Inferred annual surface radiative forcings increased stepwise to 13-17 W⋅m(-2) between 1850 and 1880, and to 9-22 W⋅m(-2) in the early 1900s, with snowmelt season (April/May/June) forcings reaching greater than 35 W⋅m(-2) by the early 1900s. These snowmelt season radiative forcings would have resulted in additional annual snow melting of as much as 0.9 m water equivalent across the melt season. Simulations of glacier mass balances with radiative forcing-equivalent changes in atmospheric temperatures result in conservative estimates of accumulating negative mass balances of magnitude -15 m water equivalent by 1900 and -30 m water equivalent by 1930, magnitudes and timing consistent with the observed retreat. These results suggest a possible physical explanation for the abrupt retreat of glaciers in the Alps in the mid-19th century that is consistent with existing temperature and precipitation records and reconstructions. PMID:24003138

  1. Virus etiology of schizophrenia: the characteristics of the "*Little Ice Age" and its consequences.

    PubMed

    Pavlović, Eduard; Peitl, Marija Vucić; Proloscić, Josko; Petrić, Daniela

    2014-12-01

    The data of the "Little Ice Age" (1500-1850) in Croatia and those which applied to human health were especially emphasized were analyzed. They are some which stand out like: importance of the sort of soil and relief, the influence of cutting down of woods and cattle-breeding and especially the war which lasted for 250 years in the territory of Croatia. The important interactions between those parameters were defined. The important correlations were also defined between freezing and long winters as well as wet springs and summers which caused starvation, malnutrition and the increase of infant mortality and also epidemics with enormous psychological stress among people in that period. The result was witch-hunting and burning (which was also advocated in the other parts of Europe) and they sometimes reached the levels of madness. Considering that such events were unknown in the earlier periods (in such proportions) and that (even today) the influence of the slow virus is emphasized in connection to the etiology of schizophrenia so why should't it be supposed that the "Litlle Ace Age" could be the cause of the larger prevalence of schizophrenia in the teritory of Croatia. PMID:25842752

  2. Reconstruction of surface area and volume variations of a small alpine valley glacier since the Little Ice Age the case-study of Dosdè Est Glacier (central Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Diolaiuti, G.; D Agata, C.; Pavan, M.; Belo, M.; Smiraglia, C.

    2003-04-01

    Reconstructing past glacier fluctuations and understanding them to forecast future trend of water availability in the Alps is an aim of general interest. For this reason continuous monitoring on sample glaciers is required to collect mass balance data, area and volume changes, ice thickness variations. The case-study of Dosdè Est Glacier, Piazzi-Campo Group, Italian Alps, representative of Italian small valley glaciers, is a good example of long term documentation of the evolution of this kind of glacier in the Central Alps. Dosdè Est Glacier is a North facing valley glacier, located in Italian Lombardy Alps (46 23 30 N, 10 13 05 E). In 2002 its area was approximately 2 kmq, extending from 2580 to 3294 m a.s.l., with a maximum widht of about 1000 m and a maximum lenght of about 2000 m. Observations to monitor the evolution of the glacier and to reconstruct past areas and volumes involve (in descending order of accuracy) direct mass balance measurements since 1995, topographic surveys (GPS) since 1996, GPR survey in order to evaluate ice thickness in 1999, seismic prospection and geoelectrical survey (VES) in 1997, glacier terminus variations field measurements from 1934 up to now (thanks to CGI operators), reconstruction of the 20th century maximum and of the LIA maximum using the well preserved moraines. Since hydrological year 1995-1996, mass balance of the glacier has been surveyed every year by glaciological field method. The stakes position is calculated by GPS technique and is used also to evaluate glacier surface velocity. The net mass balance during the 7 years of measurements was almost always negative with only one positive value recorded in the year 2001. During the 7 years of measures Dosdè Est Glacier lost about 7 m of ice thickness, it means 14.000.000 mc w.e. The mean yearly value of mass balance on 7 years of measures is -0,85 m w.e. and the mass balance gradient is 0,60 m w.e./100 m of altitude. Since 1925 Dosdè Est Glacier terminus variations

  3. Carbon cycle instability as a cause of the late Pleistocene ice age oscillations - Modeling the asymmetric response

    NASA Technical Reports Server (NTRS)

    Saltzman, Barry; Maasch, Kirk A.

    1988-01-01

    A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model.

  4. Possible effects of anthropogenically-increased CO2 on the dynamics of climate - Implications for ice age cycles

    NASA Technical Reports Server (NTRS)

    Saltzman, Barry; Maasch, Kirk A.; Verbitsky, Mikhail YA.

    1993-01-01

    A dynamical model, developed to account for the observed major variations of global ice mass and atmospheric CO2 during the late Cenozoic, is used to provide a quantitative demonstration of the possibility that the anthropogenically-forced increase of atmospheric CO2, if maintained over a long period of time (perhaps by tectonic forcing), could displace the climatic system from an unstable regime of oscillating ice ages into a more stable regime representative of the pre-Pleistocene. This stable regime is characterized by orbitally-forced oscillations that are of much weaker amplitude than prevailed during the Pleistocene.

  5. Cosmogenic exposure age evidence for rapid Laurentide deglaciation of the Katahdin area, west-central Maine, USA, 16 to 15 ka

    NASA Astrophysics Data System (ADS)

    Davis, P. Thompson; Bierman, Paul R.; Corbett, Lee B.; Finkel, Robert C.

    2015-05-01

    Katahdin, the highest peak in Maine and part of the second highest mountain range in New England, provides an opportunity to assess the timing and style of continental ice sheet surface lowering during deglaciation. We collected 14 samples from boulders on the adjacent Basin Ponds moraine, from bedrock and boulders on the upper part of the mountain, and from boulders in the surrounding area to estimate the age at which they were exposed by deglaciation of the Laurentide Ice Sheet. Measurements of in situ produced 10Be, which are consistent with measurements of 26Al, indicate that the Katahdin edifice became exposed from under ice by 15.3 ± 2.1 ka (n = 6), an age indistinguishable from the adjacent Basin Ponds moraine (16.1 ± 1.2 ka, n = 5). A boulder in the lowlands several km south of the moraine dates to 14.5 ± 0.8 ka, and a boulder deposited at Pineo Ridge, about 170 km SE of Katahdin, dates to 17.5 ± 1.1 ka. These data show that samples collected over an elevation range of 1.6 km and a distance of >170 km all have exposure ages that are indistinguishable within uncertainties. Together these data suggest that the Laurentide Ice Sheet surface dropped rapidly and the ice sheet margin retreated quickly across Maine between about 16 and 15 ka, perhaps influenced by calving of the marine-based ice sheet in the St. Lawrence Lowlands to the north and the Penobscot basin to the south.

  6. Ice formation and development in aged, wintertime cumulus over the UK: observations and modelling

    NASA Astrophysics Data System (ADS)

    Crawford, I.; Bower, K. N.; Choularton, T. W.; Dearden, C.; Crosier, J.; Westbrook, C.; Capes, G.; Coe, H.; Connolly, P. J.; Dorsey, J. R.; Gallagher, M. W.; Williams, P.; Trembath, J.; Cui, Z.; Blyth, A.

    2012-06-01

    In situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of a line of small cumulus clouds, using Radar and Lidar, as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than -8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed, near cloud top, temperatures (-7.5 °C). The role of mineral dust particles, consistent with concentrations observed near the surface, acting as high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L-1) could be produced by secondary ice particle production providing the observed small amount of primary ice (about 0.01 L-1) was present to initiate it. This emphasises the need to understand primary ice formation in slightly supercooled clouds. It is shown using simple calculations that the Hallett-Mossop process (HM) is the likely source of the secondary ice. Model simulations of the case study were performed with the Aerosol Cloud and Precipitation Interactions Model (ACPIM). These parcel model investigations confirmed the HM process to be a very important mechanism for producing the observed high ice concentrations. A key step in generating the high concentrations was the process of collision and coalescence of rain drops, which once formed fell rapidly through the cloud, collecting ice particles which caused them to freeze and form instant large riming particles. The

  7. Cosmogenic exposure-age chronologies of Pinedale and Bull Lake glaciations in greater Yellowstone and the Teton Range, USA

    USGS Publications Warehouse

    Licciardi, J.M.; Pierce, K.L.

    2008-01-01

    We have obtained 69 new cosmogenic 10Be surface exposure ages from boulders on moraines deposited by glaciers of the greater Yellowstone glacial system and Teton Range during the middle and late Pleistocene. These new data, combined with 43 previously obtained 3He and 10Be ages from deposits of the northern Yellowstone outlet glacier, establish a high-resolution chronology for the Yellowstone-Teton mountain glacier complexes. Boulders deposited at the southern limit of the penultimate ice advance of the Yellowstone glacial system yield a mean age of 136??13 10Be ka and oldest ages of ???151-157 10Be ka. These ages support a correlation with the Bull Lake of West Yellowstone, with the type Bull Lake of the Wind River Range, and with Marine Isotope Stage (MIS) 6. End moraines marking the maximum Pinedale positions of outlet glaciers around the periphery of the Yellowstone glacial system range in age from 18.8??0.9 to 16.5??1.4 10Be ka, and possibly as young as 14.6??0.7 10Be ka, suggesting differences in response times of the various ice-cap source regions. Moreover, all dated Pinedale terminal moraines in the greater Yellowstone glacial system post-date the Pinedale maximum in the Wind River Range by ???4-6 kyr, indicating a significant phase relationship between glacial maxima in these adjacent ranges. Boulders on the outermost set and an inner set of Pinedale end moraines enclosing Jenny Lake on the eastern Teton front yield mean ages of 14.6??0.7 and 13.5??1.1 10Be ka, respectively. The outer Jenny Lake moraines are partially buried by outwash from ice on the Yellowstone Plateau, hence their age indicates a major standstill of an expanded valley glacier in the Teton Range prior to the Younger Dryas, followed closely by deglaciation of the Yellowstone Plateau. These new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the Rocky Mountains during the Pleistocene

  8. Evolution of Glacier Snowline Since the End of the Last Ice Age in New Zealand

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Putnam, A. E.; Schaefer, J. M.; Denton, G. H.; Chinn, T. J.; Barrell, D.; Doughty, A. M.; Mackintosh, A. N.; Andersen, B. G.

    2012-12-01

    An important problem in paleoclimatology is how Southern Hemisphere climate changed since the end of the last ice age. The terrestrial glacier record reflects past snowline (=equilibrium line altitude) variability and is one of the few direct proxies available, in the middle latitudes, of former atmospheric properties. We reconstruct changes in snowline since ~15 ka on the South Island of New Zealand using geomorphologic mapping, 10Be surface-exposure dating, accumulation-area ratio (AAR) methods and numerical modeling. The snowline data are a proxy for the 0°C atmospheric isotherm, which occurs above 1500 m asl in the central Southern Alps, and trends in temperature since ~15 ka. Our findings show that snowline was depressed during the Antarctic Cold Reversal. Subsequently, snowline rose ~100 m during the Younger Dryas stadial in Europe. These late glacial changes appear coherent across the southern middle latitudes. In the early Holocene, snowline was depressed >200 m relative to modern in the Southern Alps. Between 11 ka and 600 years ago, short-term oscillations punctuated a multi-millennia trend of decreasing glacier extent as snowline rose ~100 m. Since ~600 yrs ago, net snowline has continued progressively to rise. The record implies long-term warming in New Zealand since the Late Glacial period. During the Holocene, the lowest snowlines and most extensive glaciers occurred in the early part of the epoch. Snowline reconstruction and numerical modeling allow us to estimate that temperature depression during the Late Glacial was ~2.1±0.4°C (relative to modern) and increased about 0.6 to 1°C between the early and late Holocene. Our terrestrial glacier and snowline records show coherence and also they are consistent with marine records in the Australian sector, documenting a regional climate pattern. However, the climate of the southwest Pacific region was fundamentally different from that observed in the Northern Hemisphere, where the most extensive

  9. Acidity decline in Antarctic ice cores during the Little Ice Age linked to changes in atmospheric nitrate and sea salt concentrations

    NASA Astrophysics Data System (ADS)

    Pasteris, Daniel; McConnell, Joseph R.; Edwards, Ross; Isaksson, Elizabeth; Albert, Mary R.

    2014-05-01

    Acidity is an important chemical variable that impacts atmospheric and snowpack chemistry. Here we describe composite time series and the spatial pattern of acidity concentration (Acy = H+ - HCO3-) during the last 2000 years across the Dronning Maud Land region of the East Antarctic Plateau using measurements in seven ice cores. Coregistered measurements of the major ion species show that sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) determine greater than 98% of the acidity value. The latter, also described as excess chloride (ExCl-), is shown mostly to be derived from postdepositional diffusion of chloride with little net gain or loss from the snowpack. A strong inverse linear relationship between nitrate concentration and inverse accumulation rate provides evidence of spatially homogenous fresh snow concentrations and reemission rates of nitrate from the snowpack across the study area. A decline in acidity during the Little Ice Age (LIA, 1500-1900 Common Era) is observed and is linked to declines in HNO3 and ExCl- during that time. The nitrate decline is found to correlate well with published methane isotope data from Antarctica (δ13CH4), indicating that it is caused by a decline in biomass burning. The decrease in ExCl- concentration during the LIA is well correlated to published sea surface temperature reconstructions in the Atlantic Ocean, which suggests increased sea salt aerosol production associated with greater sea ice extent.

  10. The glacial sedimentology and geomorphological evolution of an outwash head/moraine-dammed lake, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Evans, David J. A.; Rother, Henrik; Hyatt, Olivia M.; Shulmeister, James

    2013-02-01

    Extensive exposures through the glacial landforms around southern Lake Pukaki, New Zealand, comprise seven lithofacies (LFs 1-7). LFs 1-3 are grouped together as LFA 1 (Pukaki Member) and record pulsed subaqueous grounding line fan progradation, cohesionless debris flows, underflow activity and rhythmite deposition by suspension settling, iceberg rafting of dropstones, and pulsed traction current activity. Localized disturbance of these deposits by glacitectonic deformation and multi-generational hydrofracture fills records minor readvances by the glacier snout and the emplacement of a glacitectonite (LF 4) derived from cannibalization of glacilacustrine sediments. LFs 4-6 are grouped together as LFA 2 (Twizel Member) and record direct glacigenic deposition of glacitectonite (LF 4), subglacial traction till (LF 5) and supraglacially dumped boulder rubble (LF 6). Stratigraphic relationships between LFA 1 with LFA 2 record the oscillatory behaviour of the former Tasman Glacier snout when it formed a calving margin in a proglacial and locally supraglacial lake dammed by a glacitectonically disturbed outwash head and lateral moraine ridges. This is entirely consistent with the landform-sediment record of its coeval terrestrial margins, where flutings and push moraines are diagnostic of active temperate glacier recession from a glacially overridden outwash head, the latter being recorded by the vertically stacked sub-horizontally bedded and coarse-grained gravels of LF 7 (Waitaki Member). Previous proposals that late Pleistocene lake damming was initiated by an ice-cored moraine arc appear unfounded, because the glacilacustrine deposits only lie above the altitude of the outwash head/lateral moraine arc in locations where they have been glacitectonically compressed. Alternatively, it is proposed that the overdeepened subglacial topography was produced by the construction of an outwash head, leading to a glacilacustrine sediment sink which operates at times when the

  11. Lacustrine Basal Ages Constrain the Last Deglaciation in the Uinta Mountains, Utah, USA

    NASA Astrophysics Data System (ADS)

    Munroe, Jeffrey; Laabs, Benjamin

    2013-04-01

    Basal radiocarbon ages from 21 high-elevation lakes limit the timing of final Pleistocene deglaciation in the Uinta Mountains of northeastern Utah, USA. The lakes are located in glacial valleys and cirques 5 to 20 km upstream from LGM terminal moraines at elevations from 2830 to 3475 m. Many are impounded behind recessional moraines. Cores were retrieved from a floating platform with a percussion corer driven to the point of refusal. All penetrated inorganic silty clay beneath gyttja. AMS radiocarbon analyses were made on terrestrial macrofossils, daphnia ephippia, pollen concentrates, and bulk sediment retrieved from the base of each core. No radiocarbon reservoir effect was observed when bulk dates were checked against terrestrial material. Radiocarbon results were converted to calendar years using the IntCal09 calibration curve in OxCal 4.1. Given the stratigraphy observed in the cores, these calibrated basal ages are considered close limits on the timing of the local deglaciation and lake formation. The oldest three lakes have basal radiocarbon ages that calibrate to a few centuries after the Bölling/Alleröd warming, indicating that the landscape was becoming ice free at this time. These are followed by an overlapping group of five lakes with basal ages between 13.5 and 13.0 ka BP. Five more cores, from four separate lakes, have basal ages tightly clustered between 13.0 and 12.5 ka BP. Three of these lakes are dammed by moraines, suggesting glacial activity during the early part of the Younger Dryas interval. The lone kettle lake in the study yielded a basal age of 12.3 ka BP, considerably younger than the basal age of 13.9 ka BP from a nearby lake filling a bedrock basin, indicating that buried ice may have been locally stable for more than a millennium after deglaciation. The remaining seven lakes have basal ages between 12.0 and 11.0 ka BP. Four of these lakes are also dammed by moraines. These two non-overlapping clusters of basal ages for moraine

  12. Simple energy balance model resolving the seasons and the continents - Application to the astronomical theory of the ice ages

    NASA Technical Reports Server (NTRS)

    North, G. R.; Short, D. A.; Mengel, J. G.

    1983-01-01

    An analysis is undertaken of the properties of a one-level seasonal energy balance climate model having explicit, two-dimensional land-sea geography, where land and sea surfaces are strictly distinguished by the local thermal inertia employed and transport is governed by a smooth, latitude-dependent diffusion mechanism. Solutions of the seasonal cycle for the cases of both ice feedback exclusion and inclusion yield good agreements with real data, using minimal turning of the adjustable parameters. Discontinuous icecap growth is noted for both a solar constant that is lower by a few percent and a change of orbital elements to favor cool Northern Hemisphere summers. This discontinuous sensitivity is discussed in the context of the Milankovitch theory of the ice ages, and the associated branch structure is shown to be analogous to the 'small ice cap' instability of simpler models.

  13. Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties

    NASA Astrophysics Data System (ADS)

    Ankerstjerne, Suzanne; Iverson, Neal R.; Lagroix, France

    2015-11-01

    Geometric characteristics of the washboard moraines of the Des Moines Lobe (DML) of the Laurentide ice sheet agree with their proposed origin as crevasse-squeeze ridges, but study of their sediments is required to help further test this hypothesis. A 70-m-long, 3-5 m high section through a moraine ridge in central Iowa revealed till with irregular, isolated lenses of silt, sand, and gravel that dip to varying extents upglacier. The texture and density of the till are like those of the basal till of the DML studied elsewhere in Iowa, and preconsolidation pressures determined from tests on till and silt of the ridge indicate that it developed subglacially rather than at the glacier margin. Preconsolidation pressures additionally demonstrate that pore-water pressures in the bed supported most of the glacier's weight, which would have contributed to till mobility. Fabrics based on the anisotropy of magnetic susceptibility of 3125 intact till specimens collected at 125 locations in the section indicate two end-member states of strain that varied with location in the ridge and caused sediment mounding: simple shear that was directed downglacier along shear planes inclined upglacier, together with pure shear where an overlying crevasse allowed the sediment bed to extend upward and laterally. Meltwater that likely flowed along the crevasse deposited sorted sediments that were incorporated in till, deformed, and rotated. This positive test of the crevasse-squeeze hypothesis indicates that the DML was in longitudinal extension near its margin, reinforcing previous arguments that the lobe surged. The predominance of fabrics caused by simple shear demonstrates that crevasse filling was underway before the surge had fully halted. This study should prompt caution in using similar transverse ridges, such as those geophysically imaged in some submarine glacier forefields, as indicators of retreat rates.

  14. A method for estimating the age-depth relationship of Dome Fuji Ice Core using a sequential Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Nakano, Shinya; Suzuki, Kazue; Kawamura, Kenji; Parrenin, Frederic; Higuchi, Tomoyuki

    2015-04-01

    A technique for estimating the age-depth relationship and its uncertainty in ice cores has been developed. The age-depth relationship is mainly determined by the accumulation of snow at the site of the ice core and the thinning process due to the horizontal stretching and vertical compression of an ice layer. However, both the accumulation process and the thinning process are not fully known. In order to appropriately estimate the age as a function of depth, it is crucial to incorporate observational information into a model describing the accumulation and thinning processes. In the proposed technique, the age as a function of depth is estimated from age markers and time series of δ18O data. The estimation is achieved using a method combining a sequential Monte Carlo method and the Markov chain Monte Carlo method as proposed by Andrieu et al. (2010). In this hybrid method, the posterior distributions for the parameters in the models for the accumulation and thinning processes are basically computed using a way of the standard Metropolis-Hastings method. Meanwhile, sampling from the posterior distribution for the age-depth relationship is achieved by using a sequential Monte Carlo approach at each iteration of the Metropolis-Hastings method. A sequential Monte Carlo method normally suffers from the degeneracy problem, especially in cases that the number of steps is large. However, when it is combined with the Metropolis-Hastings method, the degeneracy problem can be overcome by collecting a large number of samples obtained by many iterations of the Metropolis-Hastings method. We will demonstrate the result obtained by applying the proposed technique to the ice core data from Dome Fuji in Antarctica.

  15. Ice formation and development in aged, wintertime cumulus over the UK : observations and modelling

    NASA Astrophysics Data System (ADS)

    Crawford, I.; Bower, K. N.; Choularton, T. W.; Dearden, C.; Crosier, J.; Westbrook, C.; Capes, G.; Coe, H.; Connolly, P.; Dorsey, J. R.; Gallagher, M. W.; Williams, P.; Trembath, J.; Cui, Z.; Blyth, A.

    2011-11-01

    In-situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of Radar and Lidar as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than ~-8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed near cloud top temperatures (~-7 °C). The role of biological particles, consistent with concentrations observed near the surface, acting as potential efficient high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L-1) could be produced by powerful secondary ice particle production emphasising the importance of understanding primary ice formation in slightly supercooled clouds. Aircraft penetrations at -3.5 °C, showed peak ice crystal concentrations of up to 100 L-1 which together with the characteristic ice crystal habits observed (generally rimed ice particles and columns) suggested secondary ice production had occurred. To investigate whether the Hallett-Mossop (HM) secondary ice production process could account for these observations, ice splinter production rates were calculated. These calculated rates and observations could only be reconciled provided the constraint that only droplets >24 μm in diameter could lead to splinter production, was relaxed slightly by 2 μm. Model simulations of the case study were also performed with the WRF (Weather, Research and Forecasting) model and ACPIM (Aerosol Cloud and

  16. Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.

    PubMed Central

    Hooghiemstra, Henry; Van der Hammen, Thomas

    2004-01-01

    Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes. PMID:15101574

  17. Ecological changes in Coyotes (Canis latrans) in response to the ice age megafaunal extinctions.

    PubMed

    Meachen, Julie A; Janowicz, Adrianna C; Avery, Jori E; Sadleir, Rudyard W

    2014-01-01

    Coyotes (Canis latrans) are an important species in human-inhabited areas. They control pests and are the apex predators in many ecosystems. Because of their importance it is imperative to understand how environmental change will affect this species. The end of the Pleistocene Ice Age brought with it many ecological changes for coyotes and here we statistically determine the changes that occurred in coyotes, when these changes occurred, and what the ecological consequences were of these changes. We examined the mandibles of three coyote populations: Pleistocene Rancho La Brean (13-29 Ka), earliest Holocene Rancho La Brean (8-10 Ka), and Recent from North America, using 2D geometric morphometrics to determine the morphological differences among them. Our results show that these three populations were morphologically distinct. The Pleistocene coyotes had an overall robust mandible with an increased shearing arcade and a decreased grinding arcade, adapted for carnivory and killing larger prey; whereas the modern populations show a gracile morphology with a tendency toward omnivory or grinding. The earliest Holocene populations are intermediate in morphology and smallest in size. These findings indicate that a niche shift occurred in coyotes at the Pleistocene/Holocene boundary - from a hunter of large prey to a small prey/more omnivorous animal. Species interactions between Canis were the most likely cause of this transition. This study shows that the Pleistocene extinction event affected species that did not go extinct as well as those that did. PMID:25551387

  18. Solar and Volcanic Modulation of Little Ice Age Climate in the Tropical Andes, Venezuela

    NASA Astrophysics Data System (ADS)

    Polissar, P. J.; Abbott, M. B.; Wolfe, A. P.; Rull, V.; Bezada, M.

    2004-12-01

    The underlying causes of late-Holocene climate variability in the tropics are incompletely understood. Here, we report a 1500-year reconstruction of climate history in the Venezuelan Andes using lake sediment records from four sites. This reconstruction is based upon accelerator mass spectrometry (AMS) radiocarbon and Pb-210 dating, sedimentology, magnetic susceptibility, geochemistry, pollen and stable isotope (C, N) measurements. In the Laguna Mucubaji watershed four distinct glacial advances occurred between 1250 and 1810 A.D. The earliest advance began during an extended period of higher global volcanic activity. The subsequent three advances were coincident with minima in solar activity (reconstructed from Be-10 and C-14 records). The Mucubají glacial activity in the Venezuelan Andes coincides with other records of Little Ice Age (LIA) glacial advances in S. America. Comparison of modern glacier equilibrium line altitudes (ELAs) in Venezuela with the Mucubaji LIA glacier ELA indicates an ELA depression of at least 300 m. Both a decline in temperature and increase in precipitation are required to explain the ELA depression. The precipitation increase is supported by increased catchment erosion recorded in L. Blanca sediments. Pollen records from two sites in the Venezuelan Andes also indicate wetter and colder conditions during the LIA.

  19. Possible Mechanisms of a Southward Shift in Tropical Precipitation During the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Atwood, A.; Wu, E.; Battisti, D. S.; Frierson, D. M.; Sachs, J. P.

    2015-12-01

    A number of tropical hydroclimate reconstructions provide evidence for substantial changes in tropical rainfall patterns over the last millennium. One of the hypothesized features of the climate during the Little Ice Age (LIA; ca. 1300-1800 CE) is a more southerly position of the Intertropical Convergence Zone (ITCZ). We evaluate the evidence for, and mechanisms of, a southward shift of tropical precipitation during the LIA, utilizing the last millennium simulations in the Coupled Model Intercomparison Project Phase 5/Paleoclimate Intercomparison Project Phase 3 archive. Six out of the seven model simulations analyzed demonstrate a southward shift in tropical precipitation during the LIA in (as determined by a decrease in tropical precipitation asymmetry between the Northern Hemisphere and Southern Hemisphere). While a southward shift of tropical precipitation during the LIA appears to be a robust feature across model simulations, the change is small and is manifested in the different model simulations in largely disparate ways. However, some common features emerge. We compare the simulated precipitation changes to proxy records and discuss to what extent the precipitation changes appear to be driven by thermodynamic scaling principles (i.e. a wet-get-drier, dry-get-wetter scenario associated with global cooling) and to what extent they appear to be tied to circulation changes in the atmosphere (e.g. a southward shift of the Intertropical Convergence Zone).

  20. Global Warming and Ice Ages: I. Prospects For Physics Based Modulation of Global Change

    DOE R&D Accomplishments Database

    Teller, E.; Wood, L.; Hyde, R.

    1996-08-15

    It has been suggested that large-scale climate changes, mostly due to atmospheric injection of greenhouse gases connected with fossil-fired energy production, should be forestalled by internationally-agreed reductions in, e.g., electricity generation. The potential economic impacts of such limitations are obviously large: greater than or equal to $10{sup 11}/year. We propose that for far smaller - less than 1% - the mean thermal effects of greenhouse gases may be obviated in any of several distinct ways, some of them novel. These suggestions are all based on scatterers that prevent a small fraction of solar radiation from reaching all or part of the Earth. We propose research directed to quite near-term realization of one or more of these inexpensive approaches to cancel the effects of the greenhouse gas injection. While the magnitude of the climatic impact of greenhouse gases is currently uncertain, the prospect of severe failure of the climate, for instance at the onset of the next Ice Age, is undeniable. The proposals in this paper may lead to quite practical methods to reduce or eliminate all climate failures.

  1. Tracing the effects of the Little Ice Age in the tropical lowlands of eastern Mesoamerica.

    PubMed

    Lozano-García, Ma del Socorro; Caballero, Margarita; Ortega, Beatriz; Rodríguez, Alejandro; Sosa, Susana

    2007-10-01

    The causes of late-Holocene centennial to millennial scale climatic variability and the impact that such variability had on tropical ecosystems are still poorly understood. Here, we present a high-resolution, multiproxy record from lowland eastern Mesoamerica, studied to reconstruct climate and vegetation history during the last 2,000 years, in particular to evaluate the response of tropical vegetation to the cooling event of the Little Ice Age (LIA). Our data provide evidence that the densest tropical forest cover and the deepest lake of the last two millennia were coeval with the LIA, with two deep lake phases that follow the Spörer and Maunder minima in solar activity. The high tropical pollen accumulation rates limit LIA's winter cooling to a maximum of 2 degrees C. Tropical vegetation expansion during the LIA is best explained by a reduction in the extent of the dry season as a consequence of increased meridional flow leading to higher winter precipitation. These results highlight the importance of seasonal responses to climatic variability, a factor that could be of relevance when evaluating the impact of recent climate change. PMID:17913875

  2. Conference Summary: First International Conference on Global Warming and the Next Ice Age

    NASA Technical Reports Server (NTRS)

    Wetzel, Peter J.; Chylek, Petr; Lesins, Glen; Starr, David OC. (Technical Monitor)

    2002-01-01

    The First International Conference on Global Warming and the Next Ice Age was convened in Halifax, Nova Scotia, August 19-24, 2001. The conference program began each day with a 30 minute live classical music performances of truly international quality before the beginning business. Ample time for panel discussions was also scheduled. The general public was invited to attend and participate in a special evening panel session on the last day of the conference. The unusual and somewhat provocative title of the conference was designed to attract diverse views on global climate change. This summary attempts to accurately reflect the tone and flavor of the lively discussions which resulted. Presentations ranged from factors forcing current climate to those in effect across the span of time from the Proterozoic "snowball Earth" epoch to 50,000 years in the future. Although, as should be expected, attendees at the conference arrived with opinions on some of the controversial issues regarding climate change, and no-one openly admitted to a 'conversion' from their initial point of view, the interdisciplinary nature of the formal presentations, poster discussions, panels, and abundant informal discourse helped to place the attendees' personal perspectives into a broader, more diversified context.

  3. Ecological Changes in Coyotes (Canis latrans) in Response to the Ice Age Megafaunal Extinctions

    PubMed Central

    Meachen, Julie A.; Janowicz, Adrianna C.; Avery, Jori E.; Sadleir, Rudyard W.

    2014-01-01

    Coyotes (Canis latrans) are an important species in human-inhabited areas. They control pests and are the apex predators in many ecosystems. Because of their importance it is imperative to understand how environmental change will affect this species. The end of the Pleistocene Ice Age brought with it many ecological changes for coyotes and here we statistically determine the changes that occurred in coyotes, when these changes occurred, and what the ecological consequences were of these changes. We examined the mandibles of three coyote populations: Pleistocene Rancho La Brean (13–29 Ka), earliest Holocene Rancho La Brean (8–10 Ka), and Recent from North America, using 2D geometric morphometrics to determine the morphological differences among them. Our results show that these three populations were morphologically distinct. The Pleistocene coyotes had an overall robust mandible with an increased shearing arcade and a decreased grinding arcade, adapted for carnivory and killing larger prey; whereas the modern populations show a gracile morphology with a tendency toward omnivory or grinding. The earliest Holocene populations are intermediate in morphology and smallest in size. These findings indicate that a niche shift occurred in coyotes at the Pleistocene/Holocene boundary – from a hunter of large prey to a small prey/more omnivorous animal. Species interactions between Canis were the most likely cause of this transition. This study shows that the Pleistocene extinction event affected species that did not go extinct as well as those that did. PMID:25551387

  4. Climate change on the Yucatan Peninsula during the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Hodell, David A.; Brenner, Mark; Curtis, Jason H.; Medina-González, Roger; Ildefonso-Chan Can, Enrique; Albornaz-Pat, Alma; Guilderson, Thomas P.

    2005-03-01

    We studied a 5.1-m sediment core from Aguada X'caamal (20° 36.6'N, 89° 42.9'W), a small sinkhole lake in northwest Yucatan, Mexico. Between 1400 and 1500 A.D., oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2.2‰ and the benthic foraminifer Ammonia beccarii parkinsoniana appeared in the sediment profile, indicating a hydrologic change that included increased lake water salinity. Pollen from a core in nearby Cenote San José Chulchacá showed a decrease in mesic forest taxa during the same period. Oxygen isotopes of shell carbonate in sediment cores from Lakes Chichancanab (19° 53.0'N, 88° 46.0'W) and Salpeten (16° 58.6'N, 89° 40.5'W) to the south also increased in the mid-15th century, but less so than in Aguada X'caamal. Climate change in the 15th century is also supported by historical accounts of cold and famine described in Maya and Aztec chronicles. We conclude that climate became drier on the Yucatan Peninsula in the 15th century A.D. near the onset of the Little Ice Age (LIA). Comparison of results from the Yucatan Peninsula with other circum-Caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the LIA. At that time, sea surface temperatures cooled and aridity in the circum-Caribbean region increased.

  5. The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean

    USGS Publications Warehouse

    Cronin, T. M.; Hayo, K.; Thunell, R.C.; Dwyer, G.S.; Saenger, C.; Willard, D.A.

    2010-01-01

    A new 2400-year paleoclimate reconstruction from Chesapeake Bay (CB) (eastern US) was compared to other paleoclimate records in the North Atlantic region to evaluate climate variability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Using Mg/Ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation-driven estuarine hydrography, results show that warmest temperatures in CB reached 16-17. ??C between 600 and 950. CE (Common Era), centuries before the classic European Medieval Warm Period (950-1100. CE) and peak warming in the Nordic Seas (1000-1400. CE). A series of centennial warm/cool cycles began about 1000. CE with temperature minima of ~. 8 to 9. ??C about 1150, 1350, and 1650-1800. CE, and intervening warm periods (14-15. ??C) centered at 1200, 1400, 1500 and 1600. CE. Precipitation variability in the eastern US included multiple dry intervals from 600 to 1200. CE, which contrasts with wet medieval conditions in the Caribbean. The eastern US experienced a wet LIA between 1650 and 1800. CE when the Caribbean was relatively dry. Comparison of the CB record with other records shows that the MCA and LIA were characterized by regionally asynchronous warming and complex spatial patterns of precipitation, possibly related to ocean-atmosphere processes. ?? 2010.

  6. Global warming and ice ages: I. prospects for physics based modulation of global change

    SciTech Connect

    Teller, E.; Wood, L.; Hyde, R.

    1996-08-15

    It has been suggested that large-scale climate changes, mostly due to atmospheric injection of greenhouse gases connected with fossil-fired energy production, should be forestalled by internationally-agreed reductions in, e.g., electricity generation. The potential economic impacts of such limitations are obviously large: greater than or equal to $10{sup 11}/year. We propose that for far smaller - less than 1% - the mean thermal effects of greenhouse gases may be obviated in any of several distinct ways, some of them novel. These suggestions are all based on scatterers that prevent a small fraction of solar radiation from reaching all or part of the Earth. We propose research directed to quite near-term realization of one or more of these inexpensive approaches to cancel the effects of the greenhouse gas injection. While the magnitude of the climatic impact of greenhouse gases is currently uncertain, the prospect of severe failure of the climate, for instance at the onset of the next Ice Age, is undeniable. The proposals in this paper may lead to quite practical methods to reduce or eliminate all climate failures.

  7. From Shakespeare to Defoe: malaria in England in the Little Ice Age.

    PubMed Central

    Reiter, P.

    2000-01-01

    Present global temperatures are in a warming phase that began 200 to 300 years ago. Some climate models suggest that human activities may have exacerbated this phase by raising the atmospheric concentration of carbon dioxide and other greenhouse gases. Discussions of the potential effects of the weather include predictions that malaria will emerge from the tropics and become established in Europe and North America. The complex ecology and transmission dynamics of the disease, as well as accounts of its early history, refute such predictions. Until the second half of the 20th century, malaria was endemic and widespread in many temperate regions, with major epidemics as far north as the Arctic Circle. From 1564 to the 1730s the coldest period of the Little Ice Age malaria was an important cause of illness and death in several parts of England. Transmission began to decline only in the 19th century, when the present warming trend was well under way. The history of the disease in England underscores the role of factors other than temperature in malaria transmission. PMID:10653562

  8. Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.

    PubMed

    Hooghiemstra, Henry; Van der Hammen, Thomas

    2004-02-29

    Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes. PMID:15101574

  9. Little Ice Age Wetting of Interior Asian Deserts and the Rise of the Mongol Empire

    NASA Astrophysics Data System (ADS)

    Putnam, A. E.; Putnam, D.; Andreu-Hayles, L.; Cook, E. R.; Palmer, J. G.; Clark, E. H.; WANG, C.; Chen, F.; Denton, G.; Boyle, D. P.; Bassett, S.; Birkel, S. D.; Martin Fernandez, J.; Hajdas, I.; Southon, J. R.; Garner, C.; Broecker, W. S.

    2015-12-01

    Documenting hydrological responses to past climate changes may provide insights into how ongoing warming will alter the distribution of Earth's water resources. Here we report evidence suggesting that wetter-than-present conditions persisted during the past millennium in the deserts of the Tarim Basin, western China, located at the heart of Asia - Earth's largest and most populous continent. Our assessment is based on observations of landforms composed of waterlain sediments occurring throughout the Taklamakan and Lop Deserts of the Tarim Basin. These landforms are associated with subfossil phreatophyte trees, reeds, and mollusk shells. We applied 14C and dendrochronological dating techniques to construct a chronology for when the Tarim Basin was wetter than today. We also employed hydrological modeling to estimate plausible climatic conditions under which the observed wet environment could have been sustained. Our results indicate that the core of the Asian desert belt was dominantly wetter than today during the last major cold spell of the Holocene: The Little Ice Age. Wetter conditions in the Tarim Basin deserts accompanied northern cooling, snowline lowering, a strengthened boreal jet, and coeval weakening of south Asian monsoons. Southward migration of grasslands in response to wetter conditions may have aided the spread of the Mongol Empire across Asian drylands. On the other hand, net drying over the 20th century has led to drought that is unprecedented for at least the past ~830 years, and which could intensify with further warming.

  10. Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Kamiya, T.; Schwede, S.; Willard, D.A.

    2003-01-01

    We present paleoclimate evidence for rapid (< 100 years) shifts of ??? 2-4??C in Chesapeake Bay (CB) temperature ???2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (???1400-1900 AD) and the Medieval Warm Period (???800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between ???450 and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous temperature maxima between 2200 and 250 years BP (average ???70 years) suggests that multi-decadal processes typical of the North Atlantic Oscillation (NAO) are an inherent feature of late Holocene climate. However, late 19th and 20th century temperature extremes in Chesapeake Bay associated with NAO climate variability exceeded those of the prior 2000 years, including the interval 450-1000 AD, by 2-3??C, suggesting anomalous recent behavior of the climate system. ?? 2002 Elsevier Science B.V. All rights reserved.

  11. Preliminary Cosmogenic Surface Exposure Ages on Laurentide Ice-sheet Retreat and Opening of the Eastern Lake Agassiz Outlets

    NASA Astrophysics Data System (ADS)

    Leydet, D.; Carlson, A. E.; Sinclair, G.; Teller, J. T.; Breckenridge, A. J.; Caffee, M. W.; Barth, A. M.

    2015-12-01

    The chronology for the eastern outlets of glacial Lake Agassiz holds important consequences for the cause of Younger Dryas cold event during the last deglaciation. Eastward routing of Lake Agassiz runoff was originally hypothesized to have triggered the Younger Dryas. However, currently the chronology of the eastern outlets is only constrained by minimum-limiting radiocarbon ages that could suggest the eastern outlets were still ice covered at the start of the Younger Dryas at ~12.9 ka BP, requiring a different forcing of this abrupt climate event. Nevertheless, the oldest radiocarbon ages are still consistent with an ice-free eastern outlet at the start of the Younger Dryas. Here we will present preliminary 10-Be cosmogenic surface exposure ages from the North Lake, Flat Rock Lake, glacial Lake Kaministiquia, and Lake Nipigon outlets located near Thunder Bay, Ontario. These ages will date the timing of the deglaciation of the Laurentide ice sheet in the eastern outlet region of glacial Lake Agassiz. This will provide an important constraint for the hypothesized freshwater forcing of the cause of Younger Dryas cold event.

  12. Ice Age Reboot: Thermohaline Circulation Crisis during the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Pena, L.; Goldstein, S. L.

    2014-12-01

    The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41- to 100-kyr cycles and developed higher amplitude climate variability. Because it took place without significant changes in the Milankovitch forcing, this fundamental change must reflect either non-linear responses of the climate system to these external forcings, or internal changes in the ocean-atmosphere-cryosphere system that led to longer periodicities and more intense glacial periods. We document using Nd isotopes a major disruption of the ocean thermohaline circulation (THC) system during the MPT between MIS 25-21 at ~950-860 ka, which effectively marks the first 100-kyr cycle, including an exceptional weakening through critical interglacial MIS 23 at ~900 ka. The data are from ODP Sites 1088 (41°8.163'S, 13°33.77'E, 2082m) and 1090 (42°54.82'S, 8°53.98E', 3702m) in the SE Atlantic Subantarctic Zone, near the upper and lower boundaries of NADW and Circumpolar Deep Water (CDW). Given evidence for nearly stable NADW and North Pacific Water (NPW) ɛNd-values over the last 2 Ma, we interpret the ɛNd variations to reflect changes in the NADW:NPW mixing fractions. During the studied pre-MPT 41-kyr world (MIS 31-25, 1,100-950 ka), at both sites the differences in glacial and interglacial ɛNd-values are small, indicating strong glacial as well as interglacial export of NADW. A major weakening of NADW export occurred during MIS 24-22, including MIS 23, which is unique as the only known interglacial in which the THC did not strengthen, and thus can be considered as a 'trans-glacial' period. The recovery into the post-MPT 100-kyr world is characterized by continued weak glacial THC. We conclude that the MPT ocean circulation crisis 'rebooted' the pacing and intensity of ice ages and facilitated the coeval drawdown of atmospheric CO2 and high latitude ice sheet growth, generating the conditions that stabilized 100-kyr cycles.

  13. Historical reconstruction of storms in the West of France in the early Little Ice Age.

    NASA Astrophysics Data System (ADS)

    Athimon, Emmanuelle; Maanan, Mohamed

    2016-04-01

    This research offers to : 1) identify, as accurately as possible, the storms and the coastal flooding in the early Little Ice Age, 2) expose their impacts on the environment and populations, 3) query the « resilience » and adaptation of medieval and modern coastal societies in the West of France by presenting their perceptions and reactions. The space-time frame of the study is located in France, from Brittany to Gascony, between the xivth and the xvith century. Sensitive and brittle, this area is regularly battered by violent winds. It also undergoes episodic sea flooding that can cause ruptures of balance. Hence, the historical reconstruction and analysis of storms and coastal flooding in a long period appear fundamental. A thorough knowledge of past meteo-marine hazards allows to recreate a link with the territory, particularly through the (re)construction of an effective memory of these phenomena. This process is essential however difficult because of many documentary gaps. They are due to historical contingencies such as wars, French Revolution, or archival disasters like the fire of the Chamber of Accounts in Paris in 1737. Many limits must also be taken into account and discussed as inaccurate dates, exaggerated or undervalued descriptions, strict spatial demarcation almost impossible to achieve for the xivth-xvith centuries. Furthermore, during this period, no death toll, material and economic balance was done after a climate disaster. Yet, many historical records - especially narrative sources, books of accounts or cities repairs - expose the impacts of storms and marine submersion on agriculture, environment, infrastructures, etc. For instance, a violent storm hit the coast on June 24th 1452. It washed away part of the roof of a castle on Noirmoutier island and knocked down the bell towers of two churches in Angers. Storms and sea flooding have affected activities, constructions and populations' lives. They have therefore forced societies to adapt

  14. Multiple Nonconformities in Ice-Walled Lake Successions Indicate Periods with Cold Summers (24.4 - 22.5 ka, 21.1 - 19.2 ka, 18.5 - 18.1 ka) during the Last Deglaciation in Northeastern Illinois, USA

    NASA Astrophysics Data System (ADS)

    Curry, B. B.

    2014-12-01

    Unprecedented age control on many last glacial stratigraphic units and morainal ice-margin positions are interpreted from AMS radiocarbon ages of tundra plant macrofossils archived in low-relief ice-walled lake plain (IWLP) deposits the Lake Michigan Lobe (south-central Laurentide Ice Sheet). IWLPs are periglacial features that formed on morainal dead-ice permafrost. Lacustrine sediment, and the fossils contained therein, had physical and temporal proximity to the glacier which formed the underlying moraine. In modern ice-walled lakes, as the lake's ice cover begins to melt, moats form which allows access of sloughing tundra-mantled active layer sediment (soil) into the lakes. Multiple AMS ages from two sites with proglacial sediment buried by glacial max LIS diamicton, and IWLPs reveal evidence of episodic plant growth and sedimentation including ca. 24.0 to 24.4 ka (post Shelby Phase), 22.5 to 21.1 ka (post Livingston Phase), 18.1 to 17.4 ka (post Woodstock Phase). Although presently based on negative evidence, the associated nonconformities (listed in title) indicate periods when cold conditions did not promote development of the estival moat. Although the evidence does not preclude tundra growth during the cold summers, there was little landscape modification due to limited thawing of the active layer. At approximately the onset of the 19.2-18.5 "warm" period, at least two large deglacial discharge events flooded the Fox and Kankakee tributary valleys of the Illinois River. The latter, known as the Kankakee Torrent, occurred at 19.05 - 18.85 ka (σ1 range) at the Oswego channel complex. The temporal coincidence of the torrents and sedimentation in ice-walled lakes suggests that the post-Livingston Phase nonconformity (21.1 - 19.2 ka) was a period of lessened meltwater discharge through subglacial conduits (tunnel valleys) as the frozen toe promoted formation of subglacial lakes, buildup of pore-water pressures, and the release of subglacial water as "torrents

  15. The Little Ice Age and its Spatial Variability across the Balkans

    NASA Astrophysics Data System (ADS)

    Kulkarni, C.; Peteet, D. M.; Boger, R. A.

    2015-12-01

    Using biological proxies (pollen, spores, and charcoal), geochemical signals through X-ray fluorescence, and AMS 14C based chronology, we present a correlation between two new high resolution Little Ice Age (LIA) records from the Central Balkans that are part of one of the least studied regions of Europe. The sediments extracted from a western sinkhole and central Serbian oxbow lake are analyzed at 8-10-cm intervals to capture the nature and magnitude of the LIA at a resolution of 20 years. During the 15th-19th CE, indigenous tree (e.g. Quercus, Acer, Pinus) and herbaceous (e.g. Poaceae, Chenopodiaceae, Artemisia) pollen from these records demonstrate fluctuations in woodland-grassland dynamics. While tree populations from Central Serbia remain comparatively stable (40-60%), the trees of western Serbia vacillate drastically between 15% and 50%. Similarly, central Serbian grasses show variations of ~18-36% whereas the western Serbian grass populations exhibit abrupt oscillations between high (55%) and low (19%) percentages. As a proxy for surface erosion and clastic input into the lakes, the 1-cm resolution potassium and titanium counts are in strong agreement with varying herbaceous taxa. These variations in ecological signals across the cores can account for local factors including altitude, terrain exposure, soils etc., however, the dynamic human component of the landscape is evident through crop pollen (e.g. Cerealia, Juglans) and microscopic charcoal highlighting the dominant role of people in ecological changes. Although the two sites show certain differences in charcoal concentration, extremely high charcoal indicates accelerated land clearance between the 15th and 17th CE. Until the beginning of 18th CE, the cultivars (e.g. Secale, Triticum) occur with very low percentages and then peak to suggest improved agriculture in the region. In the post-LIA era, the 20th CE exhibits increased arboreal percentages and declining grasslands in both the two Central

  16. The Medieval Climate Anomaly and the Little Ice Age in the Eastern Ecuadorian Andes

    NASA Astrophysics Data System (ADS)

    Ledru, M.-P.; Jomelli, V.; Samaniego, P.; Vuille, M.; Hidalgo, S.; Herrera, M.; Ceron, C.

    2012-09-01

    To better characterize the climate variability of the last millennium in the high Andes, we analysed the pollen content of a 1100-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the Eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined to distinguish the atmospheric moisture from the soil moisture content of the páramo. Results showed that between 900 AD and 1230 AD, the Medieval Climate Anomaly interval was warm and moist with high T/P index linked to a high ENSO variability and a weak South American Summer Monsoon (SASM) activity. Between 1230 and 1650 AD, a dry climate prevailed characterized by an abrupt decrease in the T/P index related to lower ENSO variability with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed, first a wet phase between 1650 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic SSTs favored the return of a wet páramo, and a cold and dry phase between 1750 and 1810 AD associated with low ENSO variability and weak SASM activity resulting in drying of the páramo. The Current Warm Period marks the beginning of a climate characterized by high convective activity, the highest in the last millennium, and weaker SASM activity modifying the water stock of the páramo. Our results show that the páramo is progressively loosing its capacity for water storage and that the variability of both tropical Pacific and Atlantic SSTs matters for Andean climate patterns although many teleconnection mechanisms are still poorly understood.

  17. Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Sherwood, Owen A.; Guilderson, Thomas P.; Batista, Fabian C.; Schiff, John T.; McCarthy, Matthew D.

    2014-01-01

    The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific 15N/14N isotopic ratios (δ15N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, δ15N decreases between 1850 and the present. The total shift in δ15N of -2 per mil over this period is comparable to the total change in global mean sedimentary δ15N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

  18. Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages

    USGS Publications Warehouse

    Phillips, W.M.; Hall, A.M.; Ballantyne, C.K.; Binnie, S.; Kubik, P.W.; Freeman, S.

    2008-01-01

    The extent of the last British-Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23-19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright ?? 2008 John Wiley & Sons, Ltd.

  19. The chronology and rate of ice-sheet margin retreat in the major fjords of Western Norway during the Early Holocene

    NASA Astrophysics Data System (ADS)

    Mangerud, J.; Lohne, O. S.; Goehring, B. M.; Svendsen, J.; Gyllencreutz, R.; Schaefer, J. M.

    2009-12-01

    Hardangerfjorden is up to 900 m deep and about 170 km long. The well defined Younger Dryas (YD) end moraine is located 40 km inside the fjord mouth. Lateral moraines show that the surface gradient near the ice front was steep and the glacier was grounded. These moraines can be traced up to 1000 m a.s.l. about 40 km inland, where the fjord is 600 m deep, indicating a total ice thickness of 1600 m. The YD margin terminated on a threshold and the fjord gets much deeper on the proximal side of the moraine. Therefore, the ice margin must have been floating as soon as retreat from the YD position began and calving was certainly an important process during deglaciation. The break up of the glacier ice in the fjord must also have led to a considerable draw down of the ice-sheet surface further inland. According to our dating results the retreat started at 11,500 cal yr BP (Bondevik and Mangerud 2002; Lohne 2007). We have used three methods to estimate the up-fjord retreat: 1) 14C dating of organic material deposited during or soon after deglaciation (Romundset et al., 2009), 2) age determination of ice-marginal deltas by using a shore-line diagram we constructed from data in Lohne et al (2007) and Romundset et al (2009), 3) 10Be exposure dating of a number of large ice-transported boulders. All three methods provide consistent ages in the interval 10,900-11,100 cal yr BP for the deglaciation of the fjord head, which yields a mean retreat rate of 220-330 m/year. The ages for Hardangerfjorden can also be used for the even longer (220 km) and deeper (1300 m) Sognefjorden, giving a retreat rate of 370-550 m/year, because the relevant YD and Early Holocene moraines have been mapped and correlated (Vorren and Mangerud 2008). Bondevik, S. and Mangerud, J., 2002. A calendar age estimate of a very late Younger Dryas ice sheet maximum in western Norway. Quaternary Science Reviews 21, 1661-1676. Lohne, Ø.S., 2007. Late Weichselian relative sea-level changes and glacial history in

  20. Radiocarbon deglaciation chronology of the Thunder Bay, Ontario area and implications for ice sheet retreat patterns

    NASA Astrophysics Data System (ADS)

    Lowell, Thomas V.; Fisher, Timothy G.; Hajdas, I.; Glover, K.; Loope, H.; Henry, T.

    2009-08-01

    The sensitivity of ice sheets to climate change influences the return of meltwater to the oceans. Here we track the Laurentide Ice Sheet along a ˜400 km long transect spanning about 6000 yr of retreat during the major climate oscillations of the lateglacial. Thunder Bay, Ontario is near a major topographic drainage divide, thus terrestrial ablation processes are the primary forcers of ice margin recession in the study area. During deglaciation three major moraine sets were produced, and have been assigned minimum ages of 13.9 ± 0.2, 12.3 ± 0.2-12.1 ± 0.1, and 11.2 ± 0.2 cal ka BP from south to north. These define a slow retreat (˜10-50 m/a) prior to major climate oscillations which was then followed by a factor of ˜2 increase during the Bölling-Alleröd, and an additional increase during the early Holocene. When compared to retreat rates in other terrestrial settings of the ice sheet, nearly identical patterns emerge. However this becomes problematic because a key control on retreat rates is the surface slope of the ice sheet and this should vary considerably over areas of so-called hard and soft beds. Further these ice margin reconstructions would not allow meltwater sourced in the Hudson Basin to drain into the Atlantic basin until after Younger Dryas time.

  1. Reconstruction of late Wisconsinan Ice Sheet and sea-level implications

    NASA Technical Reports Server (NTRS)

    Anderson, John B.

    1993-01-01

    The Ross Sea exhibits north-south oriented troughs associated with modern ice streams and outlet glaciers. Seismic reflection profiles across the troughs show evidence that they were glacially eroded. Seismic records show morphologic features interpreted as till tongues, morainal banks, and possibly glacial deltas formed near the grounding line of the former marine ice sheet. Piston cores from the continental shelf penetrated diamictons whose origin and age is problematic. Detailed petrographic analyses of the minerals and rocks comprising these diamictons were conducted to determine subglacial versus glacial marine origin, and to reconstruct the glacial setting of the Ross Sea during the most recent glacial maximum. The most detailed work, conducted in the western Ross Sea, shows that diamictons do occur in distinct petrologic provinces. This is consistent with deposition from the basal debris zone of either an ice sheet or an ice shelf. Overcompaction, in conjunction with the widespread nature of these deposits, favors deposition from marine ice sheets; ice shelves are believed to deposit their basal debris close to the grounding lines. Other results from the investigation are briefly discussed.

  2. Diatom-bound 15N/14N: New support for enhanced nutrient consumption in the ice age subantarctic

    NASA Astrophysics Data System (ADS)

    Robinson, Rebecca S.; Sigman, Daniel M.; Difiore, Peter J.; Rohde, Melissa M.; Mashiotta, Tracy A.; Lea, David W.

    2005-09-01

    Diatom-bound 15N/14N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from both the Pacific and Indian sectors show δ15N of 5 to 6‰ during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as 2‰. The effect of either diatom assemblage or physiological change on the diatom-bound 15N/14N is unknown and cannot yet be ruled out as a possible explanation for the observed change. However, the consistency between Indian and Pacific sector records and with other paleoceanographic data suggests that the glacial-interglacial difference in diatom-bound 15N/14N was driven by higher consumption of nitrate in the subantarctic surface during the last ice age. Such a change in nutrient consumption may have resulted from atmospheric iron fertilization and/or decreased glacial mixed layer depths associated with sea ice melting. Enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of CO2 in the ice age atmosphere. It also would have reduced the preformed nutrient content of the low-latitude thermocline, leading to decreases in low-latitude productivity, suboxia, and denitrification.

  3. Beryllium-10 dating of Mount Everest moraines indicates a strong monsoon influence and glacial synchroneity throughout the Himalaya

    NASA Astrophysics Data System (ADS)

    Finkel, Robert C.; Owen, Lewis A.; Barnard, Patrick L.; Caffee, Marc W.

    2003-06-01

    Moraine successions in glaciated valleys south of Mount Everest provide evidence for at least eight glacial advances during the late Quaternary. Cosmogenic radionuclide (CRN) surface exposure dating of moraine boulders defines the timing of each glacial advance and refines the previous glacial chronologies. The CRN data show that glaciation was most extensive during the early part of the last glacial (marine oxygen isotype stage [MIS] 3 and earlier), but limited during MIS 2 (the global Last Glacial Maximum) and the Holocene. A previously assumed Neoglacial advance is dated to 3.6 ± 0.3 ka and the CRN dates confirm a glacial advance ca. 1 ka. These results show that glaciations on the south side of Everest were not synchronous with the advance of Northern Hemisphere ice sheets, yet glaciations within the Himalaya, the world's highest mountain belt, were synchronous during the late Quaternary. The existence of glacial advances during times of increased insolation suggests that enhanced moisture delivered by an active south Asian summer monsoon is largely responsible for glacial advances in this part of the Himalaya. These data allow us to quantify the importance of global climate change and monsoon influence on glaciation in the Himalaya.

  4. Carbon cycle instability as a cause of the late Pleistocene ice age oscillations - Modeling the asymmetric response

    SciTech Connect

    Saltzman, B.; Maasch, K.A. )

    1988-06-01

    A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model. 35 refs.

  5. Radiocarbon ages of terrestrial gastropods extend duration of ice-free conditions at the Two Creeks forest bed, Wisconsin, USA

    USGS Publications Warehouse

    Rech, Jason A.; Nekola, Jeffrey C.; Pigati, Jeffrey S.

    2012-01-01

    Analysis of terrestrial gastropods that underlie the late Pleistocene Two Creeks forest bed (~ 13,800–13,500 cal yr BP) in eastern Wisconsin, USA provides evidence for a mixed tundra-taiga environment prior to formation of the taiga forest bed. Ten new AMS 14C analyses on terrestrial gastropod shells indicate the mixed tundra-taiga environment persisted from ~ 14,500 to 13,900 cal yr BP. The Twocreekan climatic substage, representing ice-free conditions on the shore of Lake Michigan, therefore began near the onset of peak warming conditions during the Bølling–Allerød interstadial and lasted ~ 1000 yr, nearly 600 yr longer than previously thought. These results provide important data for understanding the response of continental ice sheets to global climate forcing and demonstrate the potential of using terrestrial gastropod fossils for both environmental reconstruction and age control in late Quaternary sediments.

  6. The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories

    NASA Astrophysics Data System (ADS)

    Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

    2014-07-01

    A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in

  7. Replicated Stalagmite Records of Rainfall Variability in the Solomon Islands since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Maupin, C. R.; Partin, J. W.; Quinn, T. M.; Shen, C.; Banner, J. L.; lin, K.; Taylor, F. W.; Sinclair, D.

    2011-12-01

    The tropical west Pacific warm pool (WPWP) and south Pacific convergence zone (SPCZ) play integral roles in global climate variability. Convection over the WPWP is a source of latent heat and moisture to extratropical latitudes and, in the region of the SPCZ, forms a center of action for the rising component of the zonal Pacific Walker circulation. The nature of pre-instrumental, and therefore pre-industrial, variability of convection associated with the WPWP since the Little Ice Age (LIA) is known only from sparse and spatially disparate records. As a result, it is difficult to form a robust framework on which to base estimates of future variability of zonal atmospheric circulation within the region, an important prospect given predicted weakening in the Pacific Walker circulation under global warming conditions. Here we present absolutely dated, subannually resolved, partially replicated oxygen isotope records, spanning 1420-2010 CE, from two fast growing (~2 mm yr-1) calcite speleothems from a cave in northern Guadalcanal, Solomon Islands (9.5° S, 160° E). Guadalcanal is located both within the WPWP and under the zonally oriented portion of the SPCZ. A strong degree of reproducibility between the two stalagmite δ18O time series, within dating uncertainties, favors the interpretation that the stalagmite δ18O variability is a reflection of climatic conditions over the cave, however we continue to assess the possibility of influence by any potential non-climatic processes. We assert that speleothem δ18O variability reflects changes in rainfall based on the isotope "amount effect" observed in the tropics. We find rainfall here has varied considerably on decadal to multidecadal timescales since the LIA and hypothesize a relationship between this variability and variability in the strength of shallow Pacific meridional overturning circulation (PMOC). Changes in the PMOC are thought to be responsible for decadal variability in central and eastern equatorial

  8. The Medieval Climate Anomaly and the Little Ice Age in the eastern Ecuadorian Andes

    NASA Astrophysics Data System (ADS)

    Ledru, M.-P.; Jomelli, V.; Samaniego, P.; Vuille, M.; Hidalgo, S.; Herrera, M.; Ceron, C.

    2013-02-01

    To better characterize the climate variability of the last millennium in the high Andes, we analyzed the pollen content of a 1150-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the Andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined. This index was used to distinguish changes in the atmospheric moisture from the soil moisture content of the páramo and their associated patterns of interdecadal El Niño-Southern Oscillation (ENSO) variability and South American summer monsoon (SASM) activity. Results show that between 850 and 1250 AD, the Medieval Climate Anomaly interval was warm and moist with a high transported pollen/Poaceae pollen (T/P) index linked to high ENSO variability and weak SASM activity. Between 1250 and 1550 AD, a dry climate prevailed, characterized by an abrupt decrease in the T/P index and therefore no upslope cloud convection, related to lower ENSO variability and with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed: first, a wet phase between 1550 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic sea surface temperatures (SSTs) favored the return of a wet páramo, and then a cold and dry phase between 1750 and 1800 AD associated with low ENSO variability and weak SASM activity resulted in drying of the páramo. The current warm period marks the beginning of a climate characterized by high convective activity - the highest in the last millennium - and weaker SASM activity modifying the water storage of the páramo. Our results show that the páramo is progressively losing its capacity for water storage and that the interdecadal variability of both tropical Pacific and Atlantic SSTs matter for Andean climate

  9. Central Tropical Pacific SST and Salinity Variability over the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Sayani, H. R.; Cobb, K. M.; Khare, A.; Stone, C.; Grothe, P. R.; Chen, T.; Cheng, H.; Lu, Y.; Edwards, R. L.

    2015-12-01

    Anthropogenic trends are difficult to separate from natural variability in the tropical Pacific, where instrumental data coverage is sparse. Of particular interest are variations of climate in the pre-industrial era, but instrumental data from this time period is virtually nonexistent. Corals allow for the investigation of pre-industrial climate variability, but most living coral colonies rarely span more than a century. Fossil corals provide a valuable archive of climate variability over the past millennia [Cobb et al., 2013] and are best suited to the reconstruction of ENSO. For the reconstruction of mean climate, systematic offsets between proxy records from contemporaneous corals translates to large error bars on the resulting reconstructions [e.g. Felis et al., 2003; Pfeiffer et al., 2009]. By building composite paleoclimate records using multiple corals from the Line Islands (2°N - 6°N, 157°W - 162°W), we quantify mean climate state and climate variability in the central tropical Pacific (CTP) during the Little Ice Age (LIA). We compare paired d18O and Sr/Ca records from Line Island fossil corals to a large collection of modern coral d18O and Sr/Ca records from the same islands to estimate SST and salinity changes from the LIA to the late 20th century. Taken together, Sr/Ca records from three Palmyra Atoll fossil corals spanning 1630-1703CE suggest CTP temperatures may have been 1.7±0.9˚C cooler during much of the 17th century. Reconstructed seawater d18O values are indicative of drier conditions at Palmyra, consistent with a southward shift of the ITCZ during the LIA documented in sediments from the Line Islands [Sachs et al., 2009]. We compare the results from seven LIA-dated fossil corals from nearby Christmas Island (Kiritimati; 2˚N, 157˚W) to the results obtained from Palmyra, enabling us to resolve potential shifts in the meridional gradients of SST and hydrology in this region during the LIA. References:Cobb, K. M., et al. (2013) Science. doi

  10. Middle to Late Amazonian tropical mountain glaciers on Mars: The ages of the Tharsis Montes fan-shaped deposits

    NASA Astrophysics Data System (ADS)

    Kadish, Seth J.; Head, James W.; Fastook, James L.; Marchant, David R.

    2014-02-01

    Fan-shaped deposits (FSDs) extending to the northwest of the Tharsis Montes on Mars are the remnants of Amazonian-aged, cold-based, tropical mountain glaciers. We use high-resolution images to perform new impact crater size-frequency distribution (CSFD) analyses on these deposits in an effort to constrain the timing and duration of ice accumulation at tropical latitudes on Mars. This analysis revises the current understanding of the chronology regarding the formation of the glaciers and of the ridged facies in the Arsia Mons deposit, a deposit interpreted to be formed from recessional cold-based drop moraines. We develop a conceptual model that illustrates the effect of moving glacial ice on superposed impact craters of various sizes, including the buffering of underlying geologic units from impacts caused by the presence of the ice for extended periods of time, and the interpretation of crater retention ages of the subsequent glacial deposits following the periods of active glaciation. The new CSFD analyses establish best-fit crater retention ages for each entire Tharsis Montes FSD; these are ~220 Ma for the Ascraeus FSD at 8.35°S, ~125 Ma for the Pavonis FSD at 1.48°N, and ~210 Ma for the Arsia FSD at 11.92°N. Because the age for each deposit represents a combination of the stratigraphically older ridged facies and the younger knobby and smooth facies, the crater retention ages are most likely to represent dates subsequent to the onset of glaciation and prior to its final cessation. Estimates of the time necessary to build the deposits using net accumulation rates from atmospheric general circulation models and emplacement rates from glacial flow models suggest durations of ~45-150 Ma, depending on the specific obliquity history. These surface crater retention ages and related age estimates require that massive volumes of ice (on the order of 105 km3) were emplaced at tropical latitudes on Mars during the Middle to Late Amazonian. Additionally, we determined

  11. Accurate age scale of the Dome Fuji ice core, Antarctica from O2/N2 ratio of trapped air

    NASA Astrophysics Data System (ADS)

    Kawamura, K.; Aoki, S.; Nakazawa, T.; Suzuki, K.; Parrenin, F.

    2012-04-01

    Chronology of the first Dome Fuji deep ice core (core length: 2,500 m, ice thickness: 3,035 m) for the age range from 80 kyr to 340 kyr ago was established by orbital tuning of measured O2/N2 ratios in trapped air to local summer insolation, with precision better than about 2,000 years (Kawamura et al., 2007). The O2/N2 ratios found in polar ice cores are slightly lower than the atmospheric ratio because of size-dependent molecular fractionation during bubble close-off. The magnitude of this gas fractionation is believed to be governed by the magnitude of snow metamorphism when the layer was originally at the surface, which in turn is controlled by local summer insolation (Fujita et al., 2009). A strong advantage of the O2/N2 chronology is that there is no need to assume a lag between climatic records in the ice core and orbital forcings, becacuse O2/N2 ratios record local insolation through physical processes. Accuracy of the chronology was validated by comparing the O2/N2 chronology with U-Th radiometric chronology of speleothem records (Cheng et al., 2009) for the ends of Terminations II, III and IV, as well as several large climatic events, for which both ice-core CH4 and speleothem δ18O (a proxy for precipitation) show abrupt shifts as seen in the last glacial period. All ages from O2/N2 and U-Th chronology agreed with each other within ~2,000 yr. The O2/N2 chronology permits comparisons between Antarctic climate, greenhouse gases, astronomically calculated orbital parameters, and radiometrically-dated sea level and monsoon records. Here, we completed the measurements of O2/N2 ratios of the second Dome Fuji ice core, which reached bedrock, for the range from 2,400 to 3,028 m (320 - 700 kyr ago) at approximately 2,000-year time resolution. We made significant improvements in ice core storage practices and mass spectrometry. In particular, the ice core samples were stored at about -50 ° C until the air extraction, except during short periods of transportation

  12. Variations of soil profile characteristics due to varying time spans since ice retreat in the inner Nordfjord, western Norway

    NASA Astrophysics Data System (ADS)

    Navas, Ana; Laute, Katja; Beylich, Achim A.; Gaspar, Leticia

    2013-04-01

    In the Erdalen and Bødalen drainage basins located in the inner Nordfjord in western Norway the soils have been formed after deglaciation. The climate in the upper valley part is sub-arctic oceanic with an annual areal precipitation of ca 1500 mm. The lithology in Erdalen and Bødalen consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. Parts of the valleys were affected by the Little Ice Age glacier advance with the maximum glacier extent around 1750 BP. In this study five sites on moraine and colluvium materials were selected to examine the main soil properties of the most representative soils found in the region. The objective was to assess if soil profile characteristics and pattern of fallout radionuclides (FRN's) and environmental radionuclides (ERN's) are affected by different stages of ice retreat. Soil profiles were sampled at 5 cm depth interval increments until 20 cm depth. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. At P2 profile where ice retreated earlier (ca., 1767) depth profile activities of FRŃs are more homogenous than in P1 that became ice-free since ca. 1930. The sampled soils on the colluviums outside the LIA glacier limit became ice free during the Preboral. The Regosols present better developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Lower activities of FRŃs in soils on the moraines are related to the predominant sand material that has less capacity to fix the radionuclides. Lower 40K activities in Erdalen as compared to Bødalen are likely related to soil mineralogical composition. All

  13. Substantial agreement on the timing and magnitude of Late Holocene ice cap expansion between East Greenland and the Eastern Canadian Arctic: a commentary on Lowell et al., 2013

    NASA Astrophysics Data System (ADS)

    Miller, Gifford H.; Briner, Jason P.; Refsnider, Kurt A.; Lehman, Scott J.; Geirsdóttir, Áslaug; Larsen, Darren J.; Southon, John R.

    2013-10-01

    Lowell et al. (2013) present a large series of radiocarbon dates on tundra plants preserved beneath ice caps and cosmogenic nuclide exposure ages on moraine boulders and bedrock that document changes in the dimensions of Istorvet, an independent coastal ice cap on East Greenland. They argue that their reconstruction of Istorvet advances during the Late Holocene is inconsistent with the reconstructions of Miller et al. (2012) for Arctic Canada. Here we show that a careful interpretation of their data reveals a remarkable similarity with the compilation of radiocarbon dates on rooted tundra plants long-entombed beneath over 50 different ice masses in a 1000 km transect along Baffin Island, Arctic Canada and with the high-resolution record from an Icelandic ice cap (Miller et al., 2012). Collectively, these results suggest synchronous responses of ice masses across the northwestern sector of the North Atlantic Arctic during recent millennia. We also emphasize that the interpretation of radiocarbon ages of rooted plants exposed by receding ice depends to a large extent on the collection protocols employed. The sampling protocols outlined below maximize the value of these key new datasets to provide unambiguous constraints on past climates and changes in glacier dimensions. Examples of settings that meet these criteria are shown in Figs. 1 and 2.ice caps

  14. Effect of ageing of K-feldspar on its ice nucleating efficiency in immersion, deposition and contact freezing modes

    NASA Astrophysics Data System (ADS)

    Peckhaus, Andreas; Bachmann, Felix; Hoffmann, Nadine; Koch, Michael; Kiselev, Alexei; Leisner, Thomas

    2015-04-01

    Recently K-feldspar was identified as one of the most active atmospheric ice nucleating particles (INP) of mineral origin [1]. Seeking the explanation to this phenomena we have conducted extensive experimental investigation of the ice nucleating efficiency of K-feldspar in three heterogeneous freezing modes. The immersion freezing of K-feldspar was investigated with the cold stage using arrays of nanoliter-size droplets containing aqueous suspension of polydisperse feldspar particles. For contact freezing, the charged droplets of supercooled water were suspended in the laminar flow of the DMA-selected feldspar-containing particles, allowing for determination of freezing probability on a single particle-droplet contact [2]. The nucleation and growth of ice via vapor deposition on the crystalline surfaces of macroscopic feldspar particles have been investigated in the Environmental Scanning Electron Microscope (ESEM) under humidified nitrogen atmosphere. The ice nucleation experiments were supplemented with measurements of effective surface area of feldspar particles and ion chromatography (IC) analysis of the leached framework cations (K+, Na+, Ca2+, Mg2+). In this contribution we focus on the role of surface chemistry influencing the IN efficiency of K-feldspar, in particular the connection between the degree of surface hydroxylation and its ability to induce local structural ordering in the interfacial layer in water molecules (as suggested by recent modeling efforts). We mimic the natural process of feldspar ageing by suspending it in water or weak aqueous solution of carbonic acid for different time periods, from minutes to months, and present its freezing efficiency as a function of time. Our immersion freezing experiments show that ageing have a nonlinear effect on the freezing behavior of feldspar within the investigated temperature range (-40°C to -10°C). On the other hand, deposition nucleation of ice observed in the ESEM reveals clear different pattern

  15. Relative sea-level response to Little Ice Age ice mass change in south central Alaska: Reconciling model predictions and geological evidence

    NASA Astrophysics Data System (ADS)

    Barlow, Natasha L. M.; Shennan, Ian; Long, Antony J.

    2012-01-01

    Integration of geological data and glacio-isostatic adjustment (GIA) modelling shows that it is possible to decouple complex mechanisms of relative sea-level (RSL) change in a tectonically active glacial environment. We model a simplest solution in which RSL changes in upper Cook Inlet, Alaska, are a combination of the interplay of tectonic and isostatic processes driven by the unique rheology of this tectonically active location. We calculate interseismic uplift during latter part of the penultimate earthquake cycle to vary from 0.3 to 0.7 mm/yr. Diatom based reconstructions of RSL from tidal marsh sediment sequences coupled with detailed age models, from AD 1400 to the AD 1964 great earthquake, show deviations from a purely tectonically driven model of regional RSL. Glacial isostatic modelling, constrained by GPS data, predicts up to 70 cm sea-level change due to mountain glacier mass balance changes during the Little Ice Age. Misfits between the GIA model predictions and RSL reconstructions in the 19th and 20th century highlight that the tidal marshes of upper Cook Inlet potentially record a hemispheric-wide acceleration in sea level and that other more complex Earth process combinations may contribute to regional RSL change.

  16. a Snowball's Chance in Death Valley: Re-Evaluation of the Number and Magnitude of Neoproterozoic Ice Ages

    NASA Astrophysics Data System (ADS)

    Kaufman, A. J.; Corsetti, F. A.; Marenco, P. J.

    2002-05-01

    The Neoproterozoic Ibex Formation, previously considered to represent a basinal facies of platform carbonates in the lower Noonday Dolomite, Great Basin, USA, is shown to rest on the eroded surface of the lower Noonday and older units. At the type section, the basal Ibex Formation consists of polymict conglomerate and laminated mudstone; the upper surface of the mudstone is pierced by large angular clasts of all underlying units, including distinctive lower Noonday tube stromatolites. A thin, finely laminated pink dolostone unit that records negative carbon isotope values caps the Ibex conglomerate. We interpret the erosional unconformity upon which the basal Ibex Formation is deposited to be glacioeustatic in origin, the basal conglomerate-pierced mudstone to be glaciogenic, and the overlying dolostone to be a classic cap carbonate. Above the cap dolostone marine transgression led to the deposition of deeper water ferruginous shale and limestone, which is overlain by dolostone as water depths again shallowed. These post-glacial Ibex carbonates also record negative carbon isotope values similar to upper Noonday lithofacies preserved on the platform. A notable oxidized paleosol occurs at the top of the upper Ibex dolostone immediately below a coarse sandstone correlative with the basal Johnnie Formation. Combined with the record of glacial sediments and cap carbonates from underlying units, in particular the Kingston Peak Formation, the Death Valley succession unambiguously records three discrete Neoproterozoic ice ages in a single continuous section. These new observations provide the lithological and geochemical proof that at least three, and potentially more, ice ages characterized Neoproterozoic time. As each sustained global glaciation represents a critical environmental hurdle, the number and the magnitude of discrete ice ages is an important constraint on the tempo of metazoan evolution.

  17. Bedforms of the Keewatin Ice Sheet, Canada

    NASA Astrophysics Data System (ADS)

    Aylsworth, J. M.; Shilts, W. W.

    1989-05-01

    By compiling glacial bedforms on a map that covers most of one sector of the Laurentide Ice Sheet, it is possible to make some suggestions about their genesis based largely on spatial relationships. It can be concluded that drumlins and ribbed moraine form at the base of actively flowing ice under similar dynamic conditions. For either landform to exist, however, there must have been enough sediment available in the base of the glacier to leave or form a feature large enough to be recognizable. The presence or absence of sufficient load is related to the geology of the glacier bed and has little to do with regionally changing dynamics of the ice-water system. Likewise, given sufficient load, it is evident that whether drumlins formed or whether ribbed moraine formed in a certain area is a function of the physical nature of the load which is, again, related to geology of the source outcrops. Whether the physical characteristics come into play after the sediment has been released from the ice and is being reshaped by basal drag, streamlining, etc., or whether the nature of the load while entrained changes the behaviour of the basal part of the ice is unclear. Physical characteristics of the basal sediment load have apparently promoted internal thrusting of coherent slabs of entrained debris and ice to form ribbed moraine on melting, whereas drumlins may reflect moulding of plastic subglacial debris or erosional streamlining of both the unconsolidated glacial substrate and bedrock. The observation that many eskers cross drumlin fields at nearly right angles to their orientation suggests that conditions producing streamlining and those pertaining to subglacial drainage are separated in time and circumstance. The general occurrence of drumlins and eskers throughout the sediment-rich portions of the Keewatin Ice Sheet, from Zone 1 to its edge, is difficult to reconcile with the restriction and intimate association of these forms with ribbed moraine almost exclusively in

  18. Bluefin 9M AUV Survey of the Hubbard Glacier Morainal Bank: Proof-of-Concept Study of Autonomous Underwater Vehicle Investigations Proximal to a Tidewater Glacier

    NASA Astrophysics Data System (ADS)

    Goff, J. A.; Gulick, S. P. S.; Lawson, D. E.; O'Halloran, W.

    2014-12-01

    Hubbard Glacier is one of the few advancing tidewater glaciers in the world, offering a premier opportunity for studying ice/sediment/seawater interactions at a tidewater glacier front that is in contact with the stabilizing submarine morainal bank. However, the seafloor and water column proximal to the ice face of a marine-terminating glacier is one of the most challenging and extreme environments imaginable for marine survey work. Frequently choked with constantly-shifting mélange ice at the sea surface and at risk from calving, surface vessels cannot operate safely proximal to the ice face. AUV (Autonomous Underwater Vehicle) technology provides an opportunity to survey in areas where surface vessels cannot. Operating well below the sea surface the AUV can operate without hindrance or danger to human operators. In addition, the AUV can be programmed to operate close to the seafloor at a constant altitude, enabling the finest-detail currently possible for acoustic seafloor mapping and consistent resolution irrespective of water depth. With these considerations in mind, we conducted a proof-of-concept survey of the Hubbard Glacier morainal bank in June, 2014. We utilized the Bluefin 9M, the smallest of their line of AUVs. Its size enabled deployment and recovery from a small charter fishing vessel well-suited to navigating through mélange-choked waters. The AUV's payload included a Klein UUV-3500 interferometric sonar (455/900 kHz), which enables acquisition of sidescan backscatter and swath bathymetry up to ~75 m to each side of the instrument from ~10 m altitude over the seabed, and sensors for measuring conductivity, temperature, depth (CTD) and optical backscatter (OBS). Although our operations were shortened due to an unfortunate failure in the sonar electronics, sufficient data were collected along the morainal bank to clearly prove the viability of AUV operations in this harsh environment. The data provide centimeter-scale seafloor detail close to the

  19. Ion microprobe U-Pb dating of phosphates in lunar basaltic breccia, Elephant Moraine 87521

    NASA Astrophysics Data System (ADS)

    Terada, Kentaro; Saiki, Tomoyo; Oka, Yoshimi; Hayasaka, Yasutaka; Sano, Yuji

    2005-10-01

    We report ion microprobe U-Pb dating of phosphates in lunar meteorite ``Elephant Moraine 87521 (EET87521),'' which is a fragmental breccia consisting of Very-Low Ti (VLT) basaltic clasts and a small component of highland-derived materials. The observed Pb-Pb age of phosphates in EET87521 is 3503 +/- 140 Ma, which is distinct from the results from previous chronological studies on VLT mare basalt of 3.2-3.3 Ga for LUNA-24. This suggests that the VLT basalt volcanism appears to have been prolonged on the Moon. Moreover, the age is apparently different from those of other VLT meteorites (3.8 Ga for QUE94281 and 4.0 & 4.4 Ga for Yamato793274), which are proposed to have been launched by a single impact event based on the similarity of launching ages, mineralogical and geochemical signatures. This evidence questions the validities of bulk age analyses for the Yamato & QUE meteorites in the literature and/or the hypothesis of a single-crater origin.

  20. Little Ice Age wintertime climate cooling linked to N-Atlantic subpolar gyre warming

    NASA Astrophysics Data System (ADS)

    Kuijpers, Antoon; Seidenkrantz, Marit-Solveig; Sicre, Marie-Alexandrine; Andresen, Camilla S.; Staines-Urías, Francisca

    2015-04-01

    Traditionally, the Little Ice Age (LIA) in the North Atlantic is believed to have been marked by negative Sea Surface Temperature (SST) anomalies. In apparent contrast, we present evidence from sediment core records from the N-Atlantic Subpolar Gyre showing prevalence of warm SST conditions. Our proxy data include both alkenone-based SST reconstructions and results from faunal and geochemical foraminiferal studies. Subpolar Gyre SST warming after the Medieval Climate Anomaly is observed in the Labrador Current close to the Gulf Stream boundary off Newfoundland, which agrees with previously reported increased influence of warmer, Gulf Stream-derived Slope Water off southern Newfoundland(1). Our core records from the West- and East Greenland Current realm off southern Greenland, as well as sites in Faroese waters, correspondingly indicate increased influence of warm, saline North Atlantic / Irminger Current waters. Other recently published studies also report LIA SST warming in the northern subpolar North Atlantic(2) as well as increased heat transport into the Arctic via the West Spitsbergen Current(3). Growing evidence indicates that positive SST anomalies in the North Atlantic Ocean can promote negative NAO conditions, thus be linked with cold wintertime conditions in Northwestern Europe. A published modeling study using ensemble simulations with an atmospheric GCM forced with reconstructed SST data for the period 1871-1999 shows weakening of the westerly winds around 60o N with SST anomalies that have the same sign across the North Atlantic(4). Six other climate models show that with some years of delay, an intensified Atlantic Meridional Overturning Circulation leads to a weak negative North Atlantic Oscillation (NAO) phase during winter(5). Furthermore, it was recently found that the stratosphere is a key element of extra-tropical response to ocean variability. Observational analysis and atmospheric model experiments indicate that large-scale Atlantic Ocean

  1. Sedimentary processes on the NW Iberian Continental Shelf since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Martins, Virgínia; Figueira, Rubens Cesar Lopes; França, Elvis Joacir; Ferreira, Paulo Alves de Lima; Martins, Paula; Santos, José Francisco; Dias, João Alveirinho; Laut, Lazaro L. M.; Monge Soares, António M.; Silva, Eduardo Ferreira da; Rocha, Fernando

    2012-05-01

    The OMEX core CD110 W90, retrieved from the Douro Mud Patch (DMP) off the River Douro in the north of Portugal, records the period since the beginning of Little Ice Age (LIA). The core chronology is based upon the data attributes for 210Pb, 137Cs and a 14C dating from a level near the core base. Geochemical, granulometric, microfaunal (benthic foraminifera) and compositional data suggest the occurrence of precipitation changes which may have been, at least partially, influenced by the North Atlantic Oscillation (NAO), that contributes to the regulation of the ocean-atmosphere dynamics in the North Atlantic. Southwesterly Atlantic storm track is associated with the negative phases of the NAO, when the Azores High is anomalously weak, higher oceanographic hydrodynamism, downwelling events and increased rainfall generally occurs. Prevalence of these characteristics during the LIA left a record that corresponds to phases of major floods. During these phases the DMP received a higher contribution of relatively coarse-grained terrigenous sediments, enriched in quartz particles, which diluted the contribution of other minerals, as indicated by reduced concentrations of several lithogenic chemical elements such as: Al, As, Ba, Ce, Co, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Rb, Sc, Sn, Th, V and Y. The presence of biogenic carbonate particles also underwent dilution, as revealed by the smaller abundance of foraminifera and correlative lower concentrations of Ca and Sr. During this period, the DMP also received an increased contribution of organic matter, indicated by higher values of lignin remains and a benthic foraminifera high productivity index, or BFHP, which gave rise to early diagenetic changes with pyrite formation. Since the beginning of the 20th century this contribution diminished, probably due to several drier periods and the impact of human activities in the river basins, e.g. construction of dams, or, on the littoral areas, construction of hard

  2. A continental shelf sedimentary record of Little Ice Age to modern glacial dynamics: Bering Glacier, Alaska

    NASA Astrophysics Data System (ADS)

    Jaeger, John M.; Kramer, Branden

    2014-09-01

    The Bering Glacier System is the world's largest surging temperate glacier with seven events occurring over the past century under a range of north Pacific climatic conditions. Onshore records reveal changes in glacial termini positions and evidence of late Holocene glacial advances, but the Little Ice Age (LIA) record of potential glacial surging and associated flooding has not been examined. A 13.6 m-long jumbo core collected on the adjacent continental shelf reveals a 600-yr-long record of sedimentation associated with changing glacifluvial discharge. The chronology is based on 210Pb geochronology and five radiocarbon dates, and the core can be separated into three distinct lithologic units based on the examination of X-radiographs and physical properties: (1) an uppermost unit dating from ∼125 cal yr BP to the present characterized by bioturbated mud interbedded with laminated, thick (5-20 cm) low-bulk density clay-rich beds; (2) a middle unit dating from ∼120-400 cal yr BP that includes numerous interlaminated-to-interbedded low- and high-bulk density beds with infrequent evidence of bioturbation; thick laminated clay-rich beds are rare; (3) a lowermost unit that predates ∼400 cal yr BP and is composed of rare laminated beds grading down into mottled to massive mud. In each of these units, the laminated lithofacies from this mid-shelf location indicates both flood deposition and likely sediment transport in the wave-current bottom-boundary layer. The thick low-density, clay-rich beds in the uppermost unit correlate with historic outburst floods associated with known surge events. Based on previous terrestrial studies, the terminus was at its Holocene Neoglacial maximum extent close to the modern coastline at some point in the middle to late stages of the LIA in southern Alaska (100-350 cal yr BP). During the LIA, preservation of bioturbated intervals is rare while laminated intervals are common. This style of interbedding indicates frequent (<10 yr

  3. Preservation of ancient ice at Pavonis and Arsia Mons: Tropical mountain glacier deposits on Mars

    NASA Astrophysics Data System (ADS)

    Head, James W.; Weiss, David K.

    2014-11-01

    Large tropical mountain glacier (TMG) deposits on the northwest flanks of the Tharsis Montes and Olympus Mons volcanoes are interpreted to be the record of ancient climates characteristic of Mars several hundred million years ago when planetary spin-axis obliquity was ~45°. During this era, polar volatiles (predominantly H2O) were mobilized and transferred equatorward, undergoing adiabatic cooling on the Tharsis volcano flanks, and precipitating snow and ice to form cold-based tropical mountain glaciers up to several kilometers in thickness. Subsequent climate change resulted in retreat, sublimation and collapse of the tropical mountain glaciers, leaving the three typical facies observed today: (1) concentric ridges, the ridged facies, interpreted as drop moraines; (2) knobby facies, interpreted as debris-dominated sublimation residue; and (3) the smooth facies, interpreted as remnant alpine glacial deposits. Ring-mold craters (RMCs) are distinctive features formed by impacts into debris-covered ice. We describe a set of relatively fresh ring-mold craters superposed on the Arsia and Pavonis Mons TMG deposits; we interpret these to indicate that the impact events penetrated a veneer of sublimation lag and excavated buried remnant glacial ice, despite the lack of detection of buried ice by orbital radar instruments. The diameter distribution of the RMCs suggest that the remnant ice lies at a depth of at least 16 m. The TMG deposit ages suggest that these ice deposits date from a period in the range of 125-220 million years before the present; the remnant ice may thus preserve records of the ancient atmospheric gas content and microbiota, as is common in terrestrial glacial ice. Preservation of this ice and the lack of any associated fluvial features suggest that the post-glacial climate has been cold, and related surface temperatures have not been sufficient to bring the buried deposits to the melting point of water.

  4. Terrestrial Kr-81-Kr ages of Antarctic meteorites

    NASA Technical Reports Server (NTRS)

    Freundel, M.; Schultz, L.; Reedy, R. C.

    1986-01-01

    The production rate of Ar-38 in meteorites P(38), has been determined, as a function of the sample's chemical composition, from Kr-81-Kr exposure ages of four eucrite falls. The cosmogenic Kr-78/Kr-83 ratio is used to estimate the shielding dependence of P(38). From the 'true' Ar-38 exposure ages and the apparent Kr-81-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 300,000 ages (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017, and A81009) have within the limits of error the same exposure age (15.2 x 10 to the 6th ages) and the same terrestrial age (110,000 ages). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case is the Elephant Moraine polymict eucrites A79005, A79006, and 82600 with an exposure age of 26 x 10 to the 6th ages and a terrestrial age of 180,000 ages. EETA 79004 may be different from this group because its exposure age and terrestrial age are 21 x 10 to the 6th ages and 250,000 ages, respectively. The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: directly deposited falls and meteorites transported to the Allen Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering 'half-life' is about 160,000 ages. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations.

  5. Volcanic ash layers in blue ice fields (Beardmore Glacier Area, Antarctica): Iridium enrichments

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian

    1988-01-01

    Dust bands on blue ice fields in Antarctica have been studied and have been identified to originate from two main sources: bedrock debris scraped up from the ground by the glacial movement (these bands are found predominantly at fractures and shear zones in the ice near moraines), and volcanic debris deposited on and incorporated in the ice by large-scale eruptions of Antarctic (or sub-Antractic) volcanoes. Ice core studies have revealed that most of the dust layers in the ice cores are volcanic (tephra) deposits which may be related to some specific volcanic eruptions. These eruptions have to be related to some specific volcanic eruptions. These eruptions have to be relatively recent (a few thousand years old) since ice cores usually incorporate younger ice. In contrast, dust bands on bare blue ice fields are much older, up to a few hundred thousand years, which may be inferred from the rather high terrestrial age of meteorites found on the ice and from dating the ice using the uranium series method. Also for the volcanic ash layers found on blue ice fields correlations between some specific volcanoes (late Cenozoic) and the volcanic debris have been inferred, mainly using chemical arguments. During a recent field expedition samples of several dust bands found on blue ice fields at the Lewis Cliff Ice Tongue were taken. These dust band samples were divided for age determination using the uranium series method, and chemical investigations to determine the source and origin of the dust bands. The investigations have shown that most of the dust bands found at the Ice Tongue are of volcanic origin and, for chemical and petrological reasons, may be correlated with Cenozoic volcanoes in the Melbourne volcanic province, Northern Victoria Land, which is at least 1500 km away. Major and trace element data have been obtained and have been used for identification and correlation purposes. Recently, some additional trace elements were determined in some of the dust band

  6. Development of lysozyme-combined antibacterial system to reduce sulfur dioxide and to stabilize Italian Riesling ice wine during aging process

    PubMed Central

    Chen, Kai; Han, Shun-yu; Zhang, Bo; Li, Min; Sheng, Wen-jun

    2015-01-01

    For the purpose of SO2 reduction and stabilizing ice wine, a new antibacterial technique was developed and verified in order to reduce the content of sulfur dioxide (SO2) and simultaneously maintain protein stability during ice wine aging process. Hazardous bacterial strain (lactic acid bacteria, LAB) and protein stability of Italian Riesling ice wine were evaluated in terms of different amounts of lysozyme, SO2, polyphenols, and wine pH by single-factor experiments. Subsequently, a quadratic rotation-orthogonal composite design with four variables was conducted to establish the multiple linear regression model that demonstrated the influence of different treatments on synthesis score between LAB inhibition and protein stability of ice wine. The results showed that, synthesis score can be influenced by lysozyme and SO2 concentrations on an extremely significant level (P < 0.01). Furthermore, the lysozyme-combined antibacterial system, which is specially designed for ice wine aging, was optimized step by step by response surface methodology and ridge analysis. As a result, the optimal proportion should be control in ice wine as follows: 179.31 mg L−1 lysozyme, 177.14 mg L−1 SO2, 0.60 g L−1 polyphenols, and 4.01 ice wine pH. Based on this system, the normalized synthesis score between LAB inhibition and protein stability can reach the highest point 0.920. Finally, by the experiments of verification and comparison, it was indicated that lysozyme-combined antibacterial system, which was a practical and prospective method to reduce SO2 concentration and effectively prevent contamination from hazardous LAB, can be used to stabilize ice wine during aging process. PMID:26405531

  7. Late glacial and Early Holocene climatic conditions along the margin of the Greenland Ice Sheet, registered by glacial extents in Milne Land, east Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.

    2010-12-01

    Determining the mechanisms that caused past abrupt climate changes is important for understanding today’s rapidly warming climate and, in particular, whether we may be faced with abrupt climate change in the future. Scientists, policy makers and the public are concerned about ongoing warming because it is sending our climate into unprecedented territory at a rapid pace. The Younger Dryas cold event (~12,850-11,650 cal yr B.P.) was an abrupt climate event that occurred during the last transition from glacial to interglacial conditions. Due to its abrupt nature and the magnitude of temperature change that occurred, the Younger Dryas has been the focus of extensive research, however, the mechanisms that caused this cold event are still not well understood. Wide belts (up to 5 km) of moraines, known as the Milne Land stade moraines, are present in the Scoresby Sund region of central east Greenland. Previous work in the region using a combination of equilibrium line altitudes, surface exposure dating of moraines, and relative sea level changes indicates that mountain glacier advances during Younger Dryas time represent only moderate summer temperature cooling (~3-4C colder than at present). In contrast, Greenland ice cores, which register mean annual temperatures, indicate that Younger Dryas temperatures over the ice sheet were ~15C colder than at present. This mismatch between the two nearby paleoclimate records is interpreted to result from strong seasonality (very cold winters and only moderately cold summers) during Younger Dryas time. We are examining seasonality during Younger Dryas time by developing records of summer temperatures from local glaciers in Milne Land (71.0°N, 25.6°W). These mountain glaciers are located adjacent to the Greenland Ice Sheet, less than 50 km from the location of Renland Ice core and only ~250 km from the locations of the GISP2 and GRIP cores. We present new 10Be ages of local glacial extents in Milne Land. Ages range from 11,880 yr

  8. Glacier change in Garibaldi Provincial Park, southern Coast Mountains, British Columbia, since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Koch, Johannes; Menounos, Brian; Clague, John J.

    2009-04-01

    Fluctuations of glaciers during the 20th century in Garibaldi Provincial Park, in the southern Coast Mountains of British Columbia, were reconstructed from historical documents, aerial photographs, and fieldwork. Over 505 km 2, or 26%, of the park, was covered by glacier ice at the beginning of the 18th century. Ice cover decreased to 297 km 2 by 1987-1988 and to 245 km 2 (49% of the early 18th century value) by 2005. Glacier recession was greatest between the 1920s and 1950s, with typical frontal retreat rates of 30 m/a. Many glaciers advanced between the 1960s and 1970s, but all glaciers retreated over the last 20 years. Times of glacier recession coincide with warm and relatively dry periods, whereas advances occurred during relatively cold periods. Rapid recession between 1925 and 1946, and since 1977, coincided with the positive phase of the Pacific Decadal Oscillation (PDO), whereas glaciers advanced during its negative phase (1890-1924 and 1947-1976). The record of 20th century glacier fluctuations in Garibaldi Park is similar to that in southern Europe, South America, and New Zealand, suggesting a common, global climatic cause. We conclude that global temperature change in the 20th century explains much of the behaviour of glaciers in Garibaldi Park and elsewhere.

  9. Environmental Change in the Prelude to a Neoproterozoic Ice Age: Sulfur Isotope Evidence from the Shaler Supergroup, Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Kaufman, A. J.; Williams, B. P.; Johnston, D. T.; Farquhar, J.; Knoll, A. H.; Butterfield, N. J.; Rainbird, R.

    2006-05-01

    The >723 Ma Shaler Supergroup on Victoria Island in the Northwest Territories of Canada is unusual for marginal marine Neoproterozoic successions insofar as thickly bedded sulfate evaporites are preserved. This unique sedimentary window for the Neoproterozoic allows us to investigate isotopic changes in the oxidized sulfur reservoir in the run up to a potential ice age, which is evidenced by a strong negative δ13C excursion in Kilian Formation carbonates at the top of the interval. Similar carbon isotope anomalies are recorded in carbonates beneath glacial diamictites of broadly the same age from the Mackenzie Mountains in Canada and in the Otavi Group of northern Namibia. Stratigraphically coincident with the 8‰ drop in 13C abundances in the Kilian Formation is a 15‰ rise in 34S of bedded sulfates, to a maximum of near +30‰. Anti-correlated isotope trends of smaller magnitude are recorded in mixed carbonates and evaporites at the top of the underlying Minto Inlet Formation. Comparison of 33S and 34S abundances of Shaler sulfates with values modeled from the results of culture experiments suggests that both anaerobic sulfate reducers and aerobic sulfur disproportionators populated the shallow open ocean. Notably, the profound 34S enrichment in the Kilian Formation is not coupled with similar enrichments in 33S. This observation is consistent with a system primarily driven by an increase in pyrite burial. Given the presence of shallow marine evaporites it is unlikely that sulfate concentrations were limited at this time. We hypothesize that this flux was enhanced during sea level fall at the onset of an ensuing ice age by the spread of anoxic conditions in deep oceans populated by sulfate reducing bacteria.

  10. Evidences for a more restricted Icelandic Ice cap re-advance after the Bølling warming period

    NASA Astrophysics Data System (ADS)

    Meriaux, Anne-Sophie; Delunel, Romain; Merchel, Silke; Finkel, Robert

    2013-04-01

    Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using 36Cl and 3He cosmogenic nuclides. We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary 36Cl ages of the northernmost moraine at Skessugarðura, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 ± 1.2 ka to 13.4 ± 1.4 ka with an average at 12.2 ± 1.0 ka (±1σ, n=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models. References: Licciardi et al., EPSL 267 (2008) 365-377.

  11. Evidences for a more restricted Icelandic Ice cap re-advance after the Bølling warming period

    NASA Astrophysics Data System (ADS)

    Meriaux, A.; Delunel, R.; Merchel, S.; Finkel, R. C.

    2012-12-01

    Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using 36Cl and 3He cosmogenic nuclides. We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary 36Cl ages of the northernmost moraine at Skessugardur, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 ± 1.2 ka to 13.4 ± 1.4 ka with an average at 12.2 ± 1.0 ka (±1σ, n=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models. References: Licciardi et al., EPSL 267 (2008) 365-377.

  12. Palaeoclimatic interpretation of moraines: Identifying limitations and future tasks (the case study Southern Alps/New Zealand)

    NASA Astrophysics Data System (ADS)

    Winkler, Stefan; Kirkbride, Martin

    2013-04-01

    During the past 20 years, the widespread deployment of terrestrial cosmogenic nuclide dating (TCND) alongside other substantial geochronological advances in laboratory precision and model calibration have seen an impressive increase in both number and claimed resolution of well-dated geomorphological reconstructions of mountain glacier fluctuations. Correlations at local, regional and hemispheric scales have frequently been performed on basis of those studies that partly include sophisticated probability analyses for reducing the statistical uncertainty of moraine ages, and analyses of glacier sensitivity to temperature and precipitation forcing. Although these recent advances especially with dating modern dating techniques are acknowledged, some basic conceptual issues still remain. It seems that in certain cases "technical" progress and improved modelling skills have encouraged us to over-reach our interpretive limits and overstate our optimism regarding "reliability" of glacier chronologies and their correlation. Critical evaluation of the interpretative limitations of chronological studies is not always recognised to the necessary extent. Interdisciplinary approaches - indispensable for the complex subject covering Geochronology, Glaciology, Glacial Geomorphology and Palaeoclimatology - are still not necessarily the norm. Based on a brief theoretical outline of the requirements for "reliable" palaeoclimatic interpretation of moraines (cf. Winkler & Matthews 2010, Kirkbride & Winkler 2012), one of the high-potential key sites for the investigation of Holocene glacier variation, the Southern Alps of New Zealand, are taken as case study to highlight a few of the practical limitations and outline future tasks that need improvement. Those tasks are - among others - identified as: (1) minimise the "geomorphological" uncertainty with the numerical dating of moraines, (2) identify possible non-glacial influence on the formation of moraines and address the potential

  13. Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD

    NASA Astrophysics Data System (ADS)

    Büntgen, Ulf; Myglan, Vladimir S.; Ljungqvist, Fredrik Charpentier; McCormick, Michael; di Cosmo, Nicola; Sigl, Michael; Jungclaus, Johann; Wagner, Sebastian; Krusic, Paul J.; Esper, Jan; Kaplan, Jed O.; de Vaan, Michiel A. C.; Luterbacher, Jürg; Wacker, Lukas; Tegel, Willy; Kirdyanov, Alexander V.

    2016-03-01

    Climatic changes during the first half of the Common Era have been suggested to play a role in societal reorganizations in Europe and Asia. In particular, the sixth century coincides with rising and falling civilizations, pandemics, human migration and political turmoil. Our understanding of the magnitude and spatial extent as well as the possible causes and concurrences of climate change during this period is, however, still limited. Here we use tree-ring chronologies from the Russian Altai and European Alps to reconstruct summer temperatures over the past two millennia. We find an unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 AD (ref. ), which was probably sustained by ocean and sea-ice feedbacks, as well as a solar minimum. We thus identify the interval from 536 to about 660 AD as the Late Antique Little Ice Age. Spanning most of the Northern Hemisphere, we suggest that this cold phase be considered as an additional environmental factor contributing to the establishment of the Justinian plague, transformation of the eastern Roman Empire and collapse of the Sasanian Empire, movements out of the Asian steppe and Arabian Peninsula, spread of Slavic-speaking peoples and political upheavals in China.

  14. Y-Chromosome evidence for a northward migration of modern humans into Eastern Asia during the last Ice Age.

    PubMed

    Su, B; Xiao, J; Underhill, P; Deka, R; Zhang, W; Akey, J; Huang, W; Shen, D; Lu, D; Luo, J; Chu, J; Tan, J; Shen, P; Davis, R; Cavalli-Sforza, L; Chakraborty, R; Xiong, M; Du, R; Oefner, P; Chen, Z; Jin, L

    1999-12-01

    The timing and nature of the arrival and the subsequent expansion of modern humans into eastern Asia remains controversial. Using Y-chromosome biallelic markers, we investigated the ancient human-migration patterns in eastern Asia. Our data indicate that southern populations in eastern Asia are much more polymorphic than northern populations, which have only a subset of the southern haplotypes. This pattern indicates that the first settlement of modern humans in eastern Asia occurred in mainland Southeast Asia during the last Ice Age, coinciding with the absence of human fossils in eastern Asia, 50,000-100,000 years ago. After the initial peopling, a great northward migration extended into northern China and Siberia. PMID:10577926

  15. An investigation into the use of color as a device to convey memes during the Little Ice Age

    NASA Astrophysics Data System (ADS)

    White, Peter A.

    Color is used as a tool in visual communication to express ideas in a symbolic fashion. It can also be used as a guide to assist the viewer in the visual narrative. Artwork created in the period of time between 1300 to 1850 in northern and central Europe provides a comprehensive perspective in the use of color as symbol and color as an elucidative devise. This period of time is known as the Little Ice Age, the duration of which spans European history between the Medieval period and the Romantic era. The extreme climatic conditions of this era caused profound changes in society on many levels and influenced the use of color in paintings throughout this chapter in history. The new paradigm of the science of ideas, called memetics, provides a framework to analyze the expression of ideas through the use of color within this span of time.

  16. Depressed rates of origination and extinction during the late Paleozoic ice age: A new state for the global marine ecosystem

    NASA Astrophysics Data System (ADS)

    Stanley, Steven M.; Powell, Matthew G.

    2003-10-01

    Rates of origination and extinction for marine animal genera dropped to low levels in latest Mississippian time, immediately after massive glaciers formed in the Southern Hemisphere and a second-order mass extinction occurred. Evolutionary turnover and diversity remained low for ˜50 m.y., shifting markedly upward precisely when extensive glaciation ended in Early Permian time. All diverse taxa with good fossil records experienced low rates of origination and extinction during this major ice age. Such sluggish rates would be predicted for faunas of shallow seas on or adjacent to a heavily glaciated supercontinent such as Pangea, where cool and highly seasonal thermal regimes should dictate that species have broad ecological niches, widespread geographic distributions, and large and relatively stable populations.

  17. IODP Expedition 325: Great Barrier Reefs Reveals Past Sea-Level, Climate and Environmental Changes Since the Last Ice Age

    NASA Astrophysics Data System (ADS)

    Yokoyama, Y.; Webster, J. M.; Cotterill, C.; Braga, J. C.; Jovane, L.; Mills, H.; Morgan, S.; Suzuki, A.; IODP Expedition 325 Scientists, the

    2011-09-01

    The timing and courses of deglaciations are key components in understanding the global climate system. Cyclic changes in global climate have occurred, with growth and decay of high latitude ice sheets, for the last two million years. It is believed that these fluctuations are mainly controlled by periodic changes to incoming solar radiation due to the changes in Earth's orbit around the sun. However, not all climate variations can be explained by this process, and there is the growing awareness of the important role of internal climate feedback mechanisms. Understanding the nature of these feedbacks with regard to the timing of abrupt global sea-level and climate changes is of prime importance. The tropical ocean is one of the major components of the feedback system, and hence reconstructions of temporal variations in sea-surface conditions will greatly improve our understanding of the climate system. The Integrated Ocean Drilling Program (IODP) Expedition 325 drilled 34 holes across 17 sites in the Great Barrier Reef, Australia to recover fossil coral reef deposits. The main aim of the expedition was to understand the environmental changes that occurred during the last ice age and subsequent deglaciation, and more specifically (1) establish the course of sea-level change, (2) reconstruct the oceanographic conditions, and (3) determine the response of the reef to these changes. We recovered coral reef deposits from water depths down to 126 m that ranged in age from 9,000 years to older than 30,000 years ago. Given that the interval of the dated materials covers several paleoclimatologically important events, including the Last Glacial Maximum, we expect that ongoing scientific analyses will fulfill the objectives of the expedition. doi:10.2204/iodp.sd.12.04.2011

  18. Multiproxy Evidence for a Positive Hydrological Budget during the Little Ice Age in the East African Rift, Kenya

    NASA Astrophysics Data System (ADS)

    Goman, M.; Ashley, G. M.; Hover, V. C.; Owen, R.

    2011-12-01

    Hominin evolution took place in Africa during the Plio-Pleistocene and climate change is thought to be a factor, with Africa experiencing a general cooling and increasing aridification over the last several million years. Today, the climate of the East African Rift Valley of Kenya is characterized as semi-arid with evapotranspiration four times precipitation. Water resources are a valuable commodity for the many millions of inhabitants of the Valley. The short instrumental record shows precipitation fluctuates at sub-decadal timeframes as a result of the ENSO cycle; while during prehistory variations in monsoonal precipitation occurred on Milankovitch timescales (i.e. African Humid Period). Both timescales exhibit significant impacts on the distribution of surface water. However, little is known regarding precipitation variability over sub-millennial timescales. Emerging paleoclimate data indicates that the near surface presence of water has also varied over century length timescales. We present paleoclimate data from multiple sites along a north-south 600 km transect of the Gregory Rift Valley (Kenya) that indicate the region experienced wetter conditions during the Little Ice Age (A.D. 1400-1850). Our reconstructions of landscape and climate during this time frame rely upon a multiproxy and interdisciplinary approach. We discuss data from a variety of environmental settings (e.g. lakes, wetlands, and springs) that indicate an overall increase in hydrologic balance. Evidence is derived from biologic microfossils such as pollen, diatom and testate amoebae assemblages as well as inorganic components of the sedimentary record and geomorphic changes. The data differs significantly from studies undertaken to the west in Uganda and the Congo, where negative hydrologic balances occurred during the Little Ice Age. While the atmospheric dynamics causing this disparity are not yet recognized, interactions between the Intertropical Convergence Zone and the Congo Air Boundary

  19. Lake carbonate-δ18 records from the Yukon Territory, Canada: Little Ice Age moisture variability and patterns

    USGS Publications Warehouse

    Anderson, Lesleigh; Finney, Bruce P.; Shapley, Mark D.

    2011-01-01

    A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water δ18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake’s hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water δ18O values decrease. Past lake-water δ18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate δ18O, supplemented by those in carbonate and organic δ13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ∼AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ∼AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake δ18O, a similarly small, stratified, alkaline lake located ∼250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances.

  20. Geodiversity characterization and assessment of the Morainic Amphitheatre of Rivoli -Avigliana (NW-Italy)

    NASA Astrophysics Data System (ADS)

    Giordano, Enrico; Lucchesi, Stefania; Perotti, Luigi; Giardino, Marco

    2014-05-01

    The concept of Geodiversity in its wide sense refers specifically to particular geosystems that are in themselves complex (e.g diverse) assemblages of bedrock, landform, and soil features. Therefore, geodiversity assessment is strictly related to landscape structure, whose studies are in the field of complex Physical Geography. Moreover, Geodiversity studies provide a fundamental base for geoconservation and environmental management in a holistic way. This is particularly true within complex geomorphological environments, where many intrinsic and extrinsic factors are interconnected. Various procedures has been already applied for the creation of geodiversity maps in different geomorphological context, but especially in wide areas with a large geodiversity of landforms. Pleistocene morainic amphitheatres of the Alpine piedmont regions are indeed particular and complex environments: not only for the geological and geomorphological points of view, but also for their relationships with biotic components and human life. The aim of this study is to carry out a geodiversity characterization of the Rivoli-Avigliana Morainic Amphitheatre (AMRA; NW Italy). The AMRA separates the lower Susa Valley from the middle course of the Sangone River; it is a set of low hills and depressions related to glacial pulsations aged between 750,000 and 12,000 years ago. Earth Sciences knowledge of the area has been compared to detailed field geomorphological and territorial data in order to determine qualitative and quantitative landscape parameters and to evaluate their validity for geodiversity assessment. A first qualitative characterization of the AMRA and an estimation of its geodiversity have been performed by means of geomorphological mapping and stratigraphic studies, including geomorphosites assessment for the same area. Then, geodiversity characterization and evaluation have been performed through the definition and application of quantitative parameters (landform energy, slope