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Sample records for glacial refugial site

  1. Reconstruction of full glacial environments and summer temperatures from Lago della Costa, a refugial site in Northern Italy

    NASA Astrophysics Data System (ADS)

    Samartin, Stéphanie; Heiri, Oliver; Kaltenrieder, Petra; Kühl, Norbert; Tinner, Willy

    2016-07-01

    Vegetation and climate during the last ice age and the Last Glacial Maximum (LGM, ∼23,000-19,000 cal BP) were considerably different than during the current interglacial (Holocene). Cold climatic conditions and growing ice-sheets during the last glaciation radically reduced forest extent in Europe to a restricted number of so-called "refugia", mostly located in the southern part of the continent. On the basis of paleobotanical analyses the Euganian Hills (Colli Euganei) in northeastern Italy have previously been proposed as one of the northernmost refugia of temperate trees (e.g. deciduous Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Abies alba, Fagus sylvatica, Carpinus and Castanea) in Europe. In this study we provide the first quantitative, vegetation independent summer air temperature reconstruction for Northern Italy spanning the time ∼31,000-17,000 cal yr BP, which covers the coldest periods of the last glacial, including the LGM and Heinrich stadials 1 to 3. Chironomids preserved in a lake sediment core from Lago della Costa (7m a.s.l.), a small lake at the south-eastern edge of the Euganean Hills, allowed quantitative reconstruction of Full and Late Glacial summer air temperatures using a combined Swiss-Norwegian temperature inference model based on chironomid assemblages from 274 lakes. Chironomid and pollen evidence from Lago della Costa derives from finely stratified autochthonous organic gyttja sediments, which excludes major sediment mixing or reworking. After reconstructing paleo-temperatures, we address the question whether climate conditions were warm enough to permit the local survival of temperate tree species during the LGM and whether local expansions and pollen-inferred contractions of temperate tree taxa coincided with chironomid-inferred climatic changes. Our results suggest that chironomids at Lago della Costa have responded to major climatic fluctuations such as temperature decreases during the LGM and Heinrich stadials. The

  2. Reconstruction of full glacial environments and summer air temperatures from Lago della Costa, a refugial site in northeastern Italy.

    NASA Astrophysics Data System (ADS)

    Samartin, S. V.; Heiri, O.; Boltshauser-Kaltenrieder, P.; Tinner, W.

    2014-12-01

    Vegetation and climate during the Last Glacial Maximum (LGM) were considerably different than during the current interglacial (Holocene). In Europe large areas north of 40°N were entirely covered by continental ice-sheets and widespread permafrost, with temperatures around 10-20°C lower than at present, whereas further south aridity and temperatures 7-10°C cooler than today occurred. Cool climatic conditions and growing ice-sheets during the LGM radically reduced forest extent and diversity in Europe to a restricted number of so-called "refugia", mostly located in the southern part of the continent. The Euganian Hills in northeastern Italy are supposed to be one of the northernmost refugia of thermophilous mixed oak forest species (e.g. deciduous Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Carpinus, Castanea) as well of some temperate mesophilous species (e.g. Fagus sylvatica, Abies alba) in Europe. In this study we present the first European chironomid-based quantitative temperature reconstruction for the LGM and address the question whether climate conditions were warm enough to permit the local survival of Quercetum mixtum species between ca. 31'000-17'000 cal yr BP. Chironomids preserved in a lake sediment core from Lago della Costa (7m a.s.l.), a lake on the border of the Euganean Hills in northeastern Italy, allowed quantitative reconstruction of Full and Late Glacial July air temperatures using a combined Swiss-Norwegian temperature inference model based on chironomid assemblages from 274 lakes. Our results suggest that July air temperatures never fell below 10°C which are considered necessary for forest growth. In general, mild climatic conditions prevailed between ca. 31'000-17'000 cal yr BP with temperatures ranging from ca. 11°C to 15.7°C. The expansion of thermophilous trees such as Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Carpinus, Castanea (Quercetum mixtum) between ca. 30'000-23'000 cal yr BP can most likely be explained by climate

  3. Did glacials and/or interglacials promote allopatric incipient speciation in East Asian temperate plants? Phylogeographic and coalescent analyses on refugial isolation and divergence in Dysosma versipellis.

    PubMed

    Qiu, Ying-Xiong; Guan, Bi-Cai; Fu, Cheng-Xin; Comes, Hans Peter

    2009-05-01

    To explore the evolutionary consequences of climate-induced fluctuations in presently fragmented temperate forest habitats in continental East Asia we investigated the phylogeography and demographic history of the temperate-deciduous forest endemic Dysosma versipellis from disjunct montane sites in Central-Southeast China. Based on a survey of chloroplast (cp) DNA sequence variation, our analyses show that this perennial herb consists of morphologically indistinguishable western and central/eastern cpDNA lineages. Coalescent analyses under the 'isolation with migration' (IM) model support an ancient (Mid-Pleistocene) divergence between these lineages, with the western lineage having persisted without significant population growth in a long-term refuge just east of the Tibetan (Qinghai-Xizang) Plateau. In contrast, for the central/eastern lineage, we found strong evidence for population expansion from a refuge located south of the middle and lower reaches of the Yangtze River, and likely coinciding with the last or penultimate interglacial, followed by considerable population isolation and divergence in situ over (at least) the latest glacial-interglacial cycle. In line with recent evidence from palaeomodeling of East Asian forest biomes, our results suggest that the same vicariance factor, i.e. climate-induced eco-geographic isolation through (a)biotic displacement of temperate-deciduous forested habitats, promoted the divergence of D. versipellis lineages and populations at different spatial-temporal scales and over glacial and interglacial periods. Thus, there is no evidence that populations of D. versipellis merged at lower elevations during the last glacial(s). As such, D. versipellis accords with the premise that Late Quaternary refugial isolation is likely to have enhanced allopatric (incipient) species formation of temperate plants in East Asia.

  4. Aspects of conducting site investigations in glacial terrain

    SciTech Connect

    Schilling, K.E. )

    1993-03-01

    Much of northern US is mantled by Pleistocene glacial drift consisting of heterogeneous deposits of fine to coarse-textured sediments. Hazardous waste site investigations in glacial settings can often present unique design and implementation considerations. Complex glacial stratigraphy encountered during drilling activities demands flexibility built into work plans to allow for field decisions based on field conditions. Continuous cores should be collected from boreholes on a routine basis for stratigraphic purposes with particular importance assigned to field identification of relative permeabilities of stratigraphic units. Selection of appropriate field screening methodology should be based on site conditions. Utilization of open borehole groundwater sampling is recommended for fine-textured glacial settings where soil gas and well point sampling are ineffective. Installation of boreholes allows for collection of stratigraphic information and enables more surface area exposed beneath the water table for groundwater recharge and sampling. Water level determinations can be made on open boreholes for an initial assessment of the horizontal direction of groundwater flow. Placement of screens for monitoring wells should be based on field determination of likely groundwater flow paths. Nested wells are necessary to define the vertical groundwater flow system at most sites. Evaluation of the vertical flow system can often dominate site investigations in fine-textured glacial terrain. Two case studies from Iowa illustrate the usefulness of incorporating the above considerations in planning and implementing in fine-textured glacial sediments. Field investigations utilizing open borehole groundwater sampling successfully delineated site glacial geology and hydrogeology for determination of the nature and extent of groundwater contamination and better located the horizontal and vertical placement of monitoring wells.

  5. Glacial lakes in the Indian Himalayas--from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes.

    PubMed

    Worni, Raphael; Huggel, Christian; Stoffel, Markus

    2013-12-01

    Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the world, but comparably little attention has been given to these topics in the Indian Himalayas. In this study we present a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial lakes >0.01 km(2). Lakes were detected in the five states spanning the Indian Himalayas, and lake distribution pattern and lake characteristics were found to differ significantly between regions. Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were then selected for a detailed risk assessment. Lake outburst probability, potential outburst magnitudes and associated damage were evaluated on the basis of high-resolution satellite imagery, field assessments and through the use of a dynamic model. The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to present moderate risks to downstream villages, whereas the lake in Sikkim severely threatens downstream locations. At the study site in Sikkim, a dam breach could trigger drainage of ca. 16×10(6)m(3) water and generate maximum lake discharge of nearly 7000 m(3) s(-). The identification of critical glacial lakes in the Indian Himalayas and the detailed risk assessments at three specific sites allow prioritizing further investigations and help in the definition of risk reduction actions. PMID:23218457

  6. Glacial lakes in the Indian Himalayas--from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes.

    PubMed

    Worni, Raphael; Huggel, Christian; Stoffel, Markus

    2013-12-01

    Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the world, but comparably little attention has been given to these topics in the Indian Himalayas. In this study we present a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial lakes >0.01 km(2). Lakes were detected in the five states spanning the Indian Himalayas, and lake distribution pattern and lake characteristics were found to differ significantly between regions. Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were then selected for a detailed risk assessment. Lake outburst probability, potential outburst magnitudes and associated damage were evaluated on the basis of high-resolution satellite imagery, field assessments and through the use of a dynamic model. The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to present moderate risks to downstream villages, whereas the lake in Sikkim severely threatens downstream locations. At the study site in Sikkim, a dam breach could trigger drainage of ca. 16×10(6)m(3) water and generate maximum lake discharge of nearly 7000 m(3) s(-). The identification of critical glacial lakes in the Indian Himalayas and the detailed risk assessments at three specific sites allow prioritizing further investigations and help in the definition of risk reduction actions.

  7. Refugial persistence and postglacial recolonization of North America by the cold-tolerant herbaceous plant Orthilia secunda.

    PubMed

    Beatty, Gemma E; Provan, Jim

    2010-11-01

    Previous phylogeographical and palaeontological studies on the biota of northern North America have revealed a complex scenario of glacial survival in multiple refugia and differing patterns of postglacial recolonization. Many putative refugial regions have been proposed both north and south of the ice sheets for species during the Last Glacial Maximum, but the locations of many of these refugia remain a topic of great debate. In this study, we used a phylogeographical approach to elucidate the refugial and recolonization history of the herbaceous plant species Orthilia secunda in North America, which is found in disjunct areas in the west and east of the continent, most of which were either glaciated or lay close to the limits of the ice sheets. Analysis of 596 bp of the chloroplast trnS-trnG intergenic spacer and five microsatellite loci in 84 populations spanning the species' range in North America suggests that O. secunda persisted through the Last Glacial Maximum (LGM) in western refugia, even though palaeodistribution modelling indicated a suitable climate envelope across the entire south of the continent. The present distribution of the species has resulted from recolonization from refugia north and south of the ice sheets, most likely in Beringia or coastal regions of Alaska and British Columbia, the Washington/Oregon region in the northwest USA, and possibly from the region associated with the putative 'ice-free corridor' between the Laurentide and Cordilleran ice sheets. Our findings also highlight the importance of the Pacific Northwest as an important centre of intraspecific genetic diversity, owing to a combination of refugial persistence in the area and recolonization from other refugia.

  8. Refugial persistence and postglacial recolonization of North America by the cold-tolerant herbaceous plant Orthilia secunda.

    PubMed

    Beatty, Gemma E; Provan, Jim

    2010-11-01

    Previous phylogeographical and palaeontological studies on the biota of northern North America have revealed a complex scenario of glacial survival in multiple refugia and differing patterns of postglacial recolonization. Many putative refugial regions have been proposed both north and south of the ice sheets for species during the Last Glacial Maximum, but the locations of many of these refugia remain a topic of great debate. In this study, we used a phylogeographical approach to elucidate the refugial and recolonization history of the herbaceous plant species Orthilia secunda in North America, which is found in disjunct areas in the west and east of the continent, most of which were either glaciated or lay close to the limits of the ice sheets. Analysis of 596 bp of the chloroplast trnS-trnG intergenic spacer and five microsatellite loci in 84 populations spanning the species' range in North America suggests that O. secunda persisted through the Last Glacial Maximum (LGM) in western refugia, even though palaeodistribution modelling indicated a suitable climate envelope across the entire south of the continent. The present distribution of the species has resulted from recolonization from refugia north and south of the ice sheets, most likely in Beringia or coastal regions of Alaska and British Columbia, the Washington/Oregon region in the northwest USA, and possibly from the region associated with the putative 'ice-free corridor' between the Laurentide and Cordilleran ice sheets. Our findings also highlight the importance of the Pacific Northwest as an important centre of intraspecific genetic diversity, owing to a combination of refugial persistence in the area and recolonization from other refugia. PMID:20958819

  9. The current refugial rainforests of Sundaland are unrepresentative of their biogeographic past and highly vulnerable to disturbance

    PubMed Central

    Cannon, Charles H.; Morley, Robert J.; Bush, Andrew B. G.

    2009-01-01

    Understanding the historical dynamics of forest communities is a critical element for accurate prediction of their response to future change. Here, we examine evergreen rainforest distribution in the Sunda Shelf region at the last glacial maximum (LGM), using a spatially explicit model incorporating geographic, paleoclimatic, and geologic evidence. Results indicate that at the LGM, Sundaland rainforests covered a substantially larger area than currently present. Extrapolation of the model over the past million years demonstrates that the current “island archipelago” setting in Sundaland is extremely unusual given the majority of its history and the dramatic biogeographic transitions caused by global deglaciation were rapid and brief. Compared with dominant glacial conditions, lowland forests were probably reduced from approximately 1.3 to 0.8 × 106 km2 while upland forests were probably reduced by half, from approximately 2.0 to 1.0 × 105 km2. Coastal mangrove and swamp forests experienced the most dramatic change during deglaciations, going through a complete and major biogeographic relocation. The Sundaland forest dynamics of fragmentation and contraction and subsequent expansion, driven by glacial cycles, occur in the opposite phase as those in the northern hemisphere and equatorial Africa, indicating that Sundaland evergreen rainforest communities are currently in a refugial stage. Widespread human-mediated reduction and conversion of these forests in their refugial stage, when most species are passing through significant population bottlenecks, strongly emphasizes the urgency of conservation and management efforts. Further research into the natural process of fragmentation and contraction during deglaciation is necessary to understand the long-term effect of human activity on forest species. PMID:19549829

  10. Glacial-Interglacial, Orbital and Millennial-Scale Climate Variability for the Last Glacial Cycle at Shackleton Site U1385 based on Dinoflagellate Cysts

    NASA Astrophysics Data System (ADS)

    Datema, M.

    2015-12-01

    The Shackleton Site (IODP Expedition 339 Site U1385), located off the West-Portuguese Margin, preserves a continuous high-fidelity record of millennial-scale climate variability for the last several glacial cycles (~1.4 Myr) that can be correlated precisely to patterns observed in polar ice cores. In addition, rapid delivery of terrestrial material to the deep-sea environment allows the correlation of these marine records to European terrestrial climate records. This unique marine-ice-terrestrial linkage makes the Shackleton Site the ideal reference section for studying Quaternary abrupt climate change. The main objective of studying Site U1385 is to establish a marine reference section of Pleistocene climate change. We generated (sub)millennial-scale (~600 year interval) dinoflagellate cyst (dinocyst) assemblage records from Shackleton Site U1385 (IODP Expedition 339) to reconstruct sea surface temperature (SST) and productivity/upwelling over the last 152 kyrs. In addition, our approach allows for detailed land-sea correlations, because we also counted assemblages of pollen and spores from higher plants. Dinocyst SST and upwelling proxies, as well as warm/cold pollen proxies from Site U1385 show glacial-interglacial, orbital and stadial-interstadial climate variability and correlate very well to Uk'37, planktic foraminifer δ18O and Ca/Ti proxies of previously drilled Shackleton Sites and Greenland Ice Core δ18O. The palynological proxies capture (almost) all Dansgaard-Oeschger events of the last glacial cycle, also before ~70 ka, where millennial-scale variability is overprinted by precession. We compare the performance and results of the palynology of Site U1385 to proxies of previously drilled Shackleton Sites and conclude that palynology strengthens the potential of this site to form a multi-proxy reference section for millennial scale climate variability across the Pleistocene-Holocene. Finally, we will present a long-term paleoceanographic perspective down

  11. A Complex System of Glacial Sub-Refugia Drives Endemic Freshwater Biodiversity on the Tibetan Plateau

    PubMed Central

    Clewing, Catharina; Albrecht, Christian

    2016-01-01

    Although only relatively few freshwater invertebrate families are reported from the Tibetan Plateau, the degree of endemism may be high. Many endemic lineages occur within permafrost areas, raising questions about the existence of isolated intra-plateau glacial refugia. Moreover, if such refugia existed, it might be instructive to learn whether they were associated with lakes or with more dynamic ecosystems such as ponds, wetlands, or springs. To study these hypotheses, we used pulmonate snails of the plateau-wide distributed genus Radix as model group and the Lake Donggi Cona drainage system, located in the north-eastern part of the plateau, as model site. First, we performed plateau-wide phylogenetic analyses using mtDNA data to assess the overall relationships of Radix populations inhabiting the Lake Donggi Cona system for revealing refugial lineages. We then conducted regional phylogeographical analyses applying a combination of mtDNA and nuclear AFLP markers to infer the local structure and demographic history of the most abundant endemic Radix clade for identifying location and type of (sub-)refugia within the drainage system. Our phylogenetic analysis showed a high diversity of Radix lineages in the Lake Donggi Cona system. Subsequent phylogeographical analyses of the most abundant endemic clade indicated a habitat-related clustering of genotypes and several Late Pleistocene spatial/demographic expansion events. The most parsimonious explanation for these patterns would be a scenario of an intra-plateau glacial refugium in the Lake Donggi Cona drainage system, which might have consisted of isolated sub-refugia. Though the underlying processes remain unknown, an initial separation of lake and watershed populations could have been triggered by lake-level fluctuations before and during the Last Glacial Maximum. This study inferred the first intra-plateau refugium for freshwater animals on the Tibetan Plateau. It thus sheds new light on the evolutionary history

  12. A Complex System of Glacial Sub-Refugia Drives Endemic Freshwater Biodiversity on the Tibetan Plateau.

    PubMed

    Clewing, Catharina; Albrecht, Christian; Wilke, Thomas

    2016-01-01

    Although only relatively few freshwater invertebrate families are reported from the Tibetan Plateau, the degree of endemism may be high. Many endemic lineages occur within permafrost areas, raising questions about the existence of isolated intra-plateau glacial refugia. Moreover, if such refugia existed, it might be instructive to learn whether they were associated with lakes or with more dynamic ecosystems such as ponds, wetlands, or springs. To study these hypotheses, we used pulmonate snails of the plateau-wide distributed genus Radix as model group and the Lake Donggi Cona drainage system, located in the north-eastern part of the plateau, as model site. First, we performed plateau-wide phylogenetic analyses using mtDNA data to assess the overall relationships of Radix populations inhabiting the Lake Donggi Cona system for revealing refugial lineages. We then conducted regional phylogeographical analyses applying a combination of mtDNA and nuclear AFLP markers to infer the local structure and demographic history of the most abundant endemic Radix clade for identifying location and type of (sub-)refugia within the drainage system. Our phylogenetic analysis showed a high diversity of Radix lineages in the Lake Donggi Cona system. Subsequent phylogeographical analyses of the most abundant endemic clade indicated a habitat-related clustering of genotypes and several Late Pleistocene spatial/demographic expansion events. The most parsimonious explanation for these patterns would be a scenario of an intra-plateau glacial refugium in the Lake Donggi Cona drainage system, which might have consisted of isolated sub-refugia. Though the underlying processes remain unknown, an initial separation of lake and watershed populations could have been triggered by lake-level fluctuations before and during the Last Glacial Maximum. This study inferred the first intra-plateau refugium for freshwater animals on the Tibetan Plateau. It thus sheds new light on the evolutionary history

  13. Records of glacial-interglacial variability during the Pliocene: IODP Expedition 318 - Site U1361

    NASA Astrophysics Data System (ADS)

    Gonzalez, J. J.; Escutia, C.; Espejo, F. J.; Williams, T.; McKay, R. M.; Passhier, S.; van de Flierdt, T.; Tauxe, L.; Brinkhuis, H.

    2012-04-01

    One of the aims of IODP Expedition 318 drilling on the East Antarctic Wilkes Land margin was to obtain the record of Antarctic climate and cryosphere variability during the past warm climates of the early-middle Pliocene. A complete Pliocene section was recovered from Site U1361, located on the continental rise eastern levee of the Jussieu Channel. We present the results from a continous high-resolution geochemical study (X-Ray Fluorescence (XRF) scanner and discrete XRF analysis) conducted on sediments from Site U1361. These records are compared with shipboard physical properties data measured on the core, clay mineralogy analyses and with a post-cruise revised sedimentary facies model. Age constrains for the studied sediments are provided by the age-depth model constructed shipboard and refined post-cruise, which indicated the studies sediments to be comprised between 5.18 and 2.46 Ma. The downcore variations of these multiple proxies is interpreted to result from changes in primary biogenic productivity, terrigenous supply, and sedimentary processes that allow us to reconstruct changes in paleoceanographic and paleoenvironmental conditions associated with glacial-interglacial cyclicity. In this sense it is remarkable the Ba/Al and Ca variations, associated to the diatomaceous-rich silty-clay facies, suggesting high-productivity during interglacial periods at our site. In addition to the glacial/interglacial cyclic variability, we also discuss a marked change in the compositional and physical properties variability patterns within the section that we interpret to correspond with the start of the Pliocene cooling trend in this margin. This contribution results from work funded by: the Integrated Ocean Drilling Program, CTM2009-08467-E (Spanish Ministry of Science and Education and FEDER funds); and the Spanish Ministry of Science and Innovation project CAGES (CTM2011-24079).

  14. Results of geophysical surveys of glacial deposits near a former waste-disposal site, Nashua, New Hampshire

    USGS Publications Warehouse

    Ayotte, Joseph D.; Dorgan, Tracy H.

    1995-01-01

    Geophysical investigations were done near a former waste-disposal site in Nashua, New Hampshire to determine the thickness and infer hydraulic characteristics of the glacial sediments that underlie the area. Approximately 5 miles of ground- penetrating radar (GPR) data were collected in the study area by use of dual-80 Megahertz antennas. Three distinct radar-reflection signatures were evident from the data and are interpreted to represent (1) glacial lake-bottom sediments, (2) coarse sand and gravel and (or) sandy glacial till, and (3) bedrock. The GPR signal penetrated as much as 70 feet of sediment in coarse-grained areas, but penetration depth was generally less than 40 feet in extensive areas of fine-grained deposits. Geologic features were evident in many of the profiles. Glacial-lake-bottom sediments were the most common features identified. Other features include deltas deposited in glacial Lake Nashua and lobate fans of sediment deposited subaqueously at the distal end of deltaic sediments. Cross-bedded sands were often identifiable in the deltaic sediments. Seismic-refraction data were also collected at five of the GPR data sites. In most cases, depths to the water table and to the till and (or) bedrock surface indicated by the seismic-refraction data compared favorably with depths calculated from the GPR data. Test holes were drilled at three locations to determine the true depths to radar reflectors and to determine the types of geologic material represented by the various reflectors.

  15. Fossil Arthropods from a Full-Glacial Site in Northeastern Italy

    NASA Astrophysics Data System (ADS)

    Foddai, Donatella; Minelli, Alessandro

    1994-05-01

    Fossil remains of beetles and oribatid mites from a peat deposit dated 18,870 ± 300 yr B.P. near Verona, northeastern Italy, represent the first insect fauna of its kind from the last glacial maximum to be described from Italy. The assemblage includes the ground beetle Amara alpina, whose distribution today in Europe is restricted to mountains in Scandinavia and Scotland. Ecological requirements and geographic distribution of recent populations of the identified species suggest mesic habitats with standing water and peat bogs during the glacial maximum. The paleoenvironment was comparable to present-day lowland moors in Scandinavia or mesic environments above 1000 m altitude on the southern slopes of the Alps. The climate is inferred to have been colder and wetter than today. Mean July temperature may have been 8-9°C lower than at present.

  16. Chlorine-36 and cesium-137 in ice-core samples from mid-latitude glacial sites in the Northern Hemisphere

    USGS Publications Warehouse

    Green, J.R.; Cecil, L.D.; Synal, H.-A.; Kreutz, K.J.; Wake, C.P.; Naftz, D.L.; Frape, S.K.

    2000-01-01

    Chlorine-36 (36Cl) concentrations, 36Cl/Cl ratios, and 36Cl fluxes in ice-core samples collected from the Upper Fremont Glacier (UFG) in the Wind River Mountain Range, Wyoming, United States and the Nangpai Gosum Glacier (NGG) in the Himalayan Mountains, Nepal, were determined and compared with published results from the Dye-3 ice-core drilling site on the Greenland Ice Sheet. Cesium-137 (137Cs) concentrations in the NGG also were determined. The background fluxes for 36Cl for each glacial site were similar: (1.6??0.3)??10-2 atoms/cm2 s for the UFG samples, (0.7??0.1)??10-2 atoms/cm2 s for the NGG samples, and (0.4??0.1)??10-2 atoms/cm2 s for the Dye-3 samples. The 36Cl fluxes in ice that was deposited as snow during peak atmospheric nuclear weapon test (1957-1958) were (33??1)??10-2 atoms/cm2 s for the UFG site, (291??3)??10-2 atoms/cm2 s for the NGG site, and (124??5)??10-2 atoms/ cm2 s for the Dye-3 site. A weapon test period 137Cs concentration of 0.79??0.05 Bq/kg in the NGG ice core also was detected in the same section of ice that contained the largest 36Cl concentration. ?? 2000 Elsevier Science B.V. All rights reserved.

  17. Deep-sea trace fossil and benthic foraminiferal assemblages across glacial Terminations 1, 2 and 4 at the "Shackleton Site" (IODP Expedition 339, Site U1385)

    NASA Astrophysics Data System (ADS)

    Rodríguez-Tovar, Francisco J.; Dorador, Javier; Grunert, Patrick; Hodell, David

    2015-10-01

    Numerous studies focused on the transitions between glacial and interglacial periods, the so-called terminations, due to the associated significant reorganizations of the ocean-atmosphere system. However, analyses combining macro- and micropaleontological information are near absent. In this research, an integrative study of trace fossils and benthic foraminiferal assemblages is conducted in order to improve the characterization of Terminations 1, 2 and 4, as revealing the response of the macro-and microbenthic habitats to the involved paleoenvironmental changes. For this purpose, selected cores from Site U1385 (IODP Expedition 339) located off the western Iberian Margin, have been studied. Changes in trace fossils and benthic foraminifera related to both long-term variations at the glacial/interglacial scale, and short-term millennial-scale climatic events. Food and oxygen availability have been identified as the main factors determining variations in the macro- and microbenthic community structure across glacial terminations in the context of changes in water mass distribution and productivity in the NE Atlantic. A deep-sea multi-tiered tracemaker community, consisting of biodeformational structures, Chondrites, ?Nereites, Palaeophycus, Planolites, Thalassinoides, and Zoophycos, suggest generally well-oxygenated bottom and pore-water conditions during interglacial as well as glacial intervals, with punctual decreases in oxygenation. Short-climatic events registered during Terminations 1, 2, and 4 induce a similar response of trace fossil and benthic foraminifera communities to the variable incidence of food and oxygen availability. Termination 1 shows a severe deterioration of oxic conditions and increasing food availability during the YD and HS 1, favoring appearance/dominance of Zoophycos, together with the lowest miliolid and the highest deep infaunal taxa abundances. Short-term climatic events (HS 11, IRE 10.1) associated with Terminations 2 and 4 are

  18. Glacial refugia and modern genetic diversity of 22 western North American tree species.

    PubMed

    Roberts, David R; Hamann, Andreas

    2015-04-01

    North American tree species, subspecies and genetic varieties have primarily evolved in a landscape of extensive continental ice and restricted temperate climate environments. Here, we reconstruct the refugial history of western North American trees since the last glacial maximum using species distribution models, validated against 3571 palaeoecological records. We investigate how modern subspecies structure and genetic diversity corresponds to modelled glacial refugia, based on a meta-analysis of allelic richness and expected heterozygosity for 473 populations of 22 tree species. We find that species with strong genetic differentiation into subspecies had widespread and large glacial refugia, whereas species with restricted refugia show no differentiation among populations and little genetic diversity, despite being common over a wide range of environments today. In addition, a strong relationship between allelic richness and the size of modelled glacial refugia (r(2) = 0.55) suggest that population bottlenecks during glacial periods had a pronounced effect on the presence of rare alleles. PMID:25761711

  19. Glacial refugia and modern genetic diversity of 22 western North American tree species

    PubMed Central

    Roberts, David R.; Hamann, Andreas

    2015-01-01

    North American tree species, subspecies and genetic varieties have primarily evolved in a landscape of extensive continental ice and restricted temperate climate environments. Here, we reconstruct the refugial history of western North American trees since the last glacial maximum using species distribution models, validated against 3571 palaeoecological records. We investigate how modern subspecies structure and genetic diversity corresponds to modelled glacial refugia, based on a meta-analysis of allelic richness and expected heterozygosity for 473 populations of 22 tree species. We find that species with strong genetic differentiation into subspecies had widespread and large glacial refugia, whereas species with restricted refugia show no differentiation among populations and little genetic diversity, despite being common over a wide range of environments today. In addition, a strong relationship between allelic richness and the size of modelled glacial refugia (r2 = 0.55) suggest that population bottlenecks during glacial periods had a pronounced effect on the presence of rare alleles. PMID:25761711

  20. Amsterdamøya: a key site for the post-glacial of Svalbard

    NASA Astrophysics Data System (ADS)

    Bakke, Jostein; Balascio, Nicholas; van der Bilt, Willem; D`Andrea, William; Bradley, Raymond; Gjerde, Marthe; Hormes, Anne; Olafsdottir, Sædis; Røthe, Torgeir; Vasskog, Kristian; De Wet, Greg; Werner, Johannes

    2016-04-01

    No other place on Earth is changing as fast as the Arctic in terms of climate. On average this region is warming twice as fast as the global average with a seasonal bias towards winter. A major retreat in sea ice extent accompanied by an even more massive thinning represents one of the most robust trends in the Arctic. This trend is anticipated to continue in the decades to come and, according to some models, will leave the Arctic Ocean open during summer some time between 2050-2100. Unabated reduction in the spring-snow cover represents another significant trend. The current warming is also expressed in the massive melting of the Greenland ice sheet as well as local glaciers and ice caps in the Arctic, which causes increased freshwater influx to the Arctic Ocean and adjacent seas. Climate modeling and scenarios are improving and becoming of growing importance, but without a firmer understanding of natural climate variability over longer timescale it is still hard to evaluate and best read the output from these models. In the SHIFTS project we have done an unparalleled effort to overcome this quandary, providing necessary empirical data on past climate which is critical for assessing past changes in atmospheric circulation patterns controlling Arctic hydroclimate. Our study site is located at the northwestern corner of Svalbard on the Island of Amsterdamøya, a site sensitive to changes in both oceanic and atmospheric forcing, at tail of the westward moving branch of the North Atlantic current. Here we have cored several lakes with the goal of providing quantitative data on temperature, hydrology and winter precipitation for the Holocene. Our approach has been to combine reconstruction of glaciers with lipid biomarkers and hydrogen isotopes with the goal of unravel the underlying signature of past climate in the Arctic. Chronological control is secured by radiocarbon dates on macrofossils combined with measurement of paleomagnetic secular variations. Here we

  1. Late glacial environments of peninsular Florida: evidence from the Little Salt Spring (LSS) site

    SciTech Connect

    Gifford, J.A.; Clausen, C.J.

    1985-01-01

    Located 20 km east of the Gulf of Mexico, Little Salt Spring (8 So 18) is a flooded, 60 m-deep collapse sinkhole in the Tampa Limestone. Excavation of an underwater ledge at the site has produced the oldest association - 12,000 ybp - of an artifact with a vertebrate faunal assemblage in the southeastern US. Ground water level in this feature circa 12,000 years ago was 20+/- 1 m below present mean sea level. Due to the porosity of the Florida carbonate platform, this would approximate the contemporaneous ground water table around the peninsula south of 29/sup 0/ N. latitude and below +25 m elevation. The authors theorize that a vegetation zone paralleling in the Gulf of Mexico paleocoastline (at -25 to -40 m) and extending up to present mean sea level probably resembled that of the present evergreen forest association of Florida; additionally, as far south as Fort Myers it may have included northern hardwood species. Gallery forests would have penetrated along intermittent drainageways into the interior of the peninsula but in general its quartz-rich surficial sand cover will have been desiccated, and landward of the paleocoastal forest zone the environment would have been semiarid to rid. The concomitant greatly-reduced biomass implies a decrease in carrying capacity and less available animal protein for a hunting economy. On the Florida peninsula, the critical independent variable controlling realistic models of the distribution of paleoindian habitation and land use is depth to ground water table.

  2. Faunal Change of Benthic Foraminifera to the Glacial Events during the Mid-Oligocene Interval in the Eastern Equatorial Pacific Sites (ODP Leg 199)

    NASA Astrophysics Data System (ADS)

    Takata, H.; Nomura, R.

    2007-12-01

    Deep-sea paleoceanographic environments considerably varied in the late Paleogene, in response to the fluctuation of the Antarctic ice volume and to the potentials of deep water formation in the Southern Ocean. Several glacial events with stable oxygen isotopic shift occurred during the Oligocene. Recently, many Oligocene paleoceanographic studies of Site 1218, ODP Leg 199 (the eastern equatorial Pacific Ocean) have been carried out (Coxall et al., 2005; Wade and Palike, 2004; Palike et al., 2006). These studies suggested that various orbital forcing, particularly long eccentricity and ~1.2 m.y.-obliquity amplitude modulation, affected not only glacial events but also the carbonate compensation depth or surface carbonate production via weathering process. Because the drilled section of this site contains well-preserved foraminifera in almost all samples, this section provides the opportunity for conducting a detailed study of faunal change to the Oligocene glacial events. The objectives of our study are to investigate the mid-Oligocene faunal succession (27.0 to 30.5 Ma) of benthic foraminifera and to consider their relation to paleoceanographic changes in the eastern equatorial Pacific Ocean. Based on a factor analysis to benthic foraminiferal fauna at Sites 1218 and 1219 (112 samples), three factor assemblages were recognized. The Factor 2 assemblage is characterized by typical deep-sea taxa under Oligotropic condition, such as Oridorsalis umbonatus, Cibicidoides spp. and Gyroidinoides spp., whereas the Factor 1 assemblage, characterized by Nuttallides umbonifer that is related to Southern Ocean deepwater flow and / or carbonate undersaturation of deep waters. Factor 1 assemblage was common around four glacial events (76Ol-C11r, 73Ol-C10m, 70Ol-C10n and 67Ol-C9n (Palike et al., 2006)). In addition, dominance of the assemblage became continuously after the 73Ol-C10m. Such occurrence suggests that influence of Southern Ocean deepwater flow and/or carbonate

  3. Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

    NASA Astrophysics Data System (ADS)

    Vidstrand, Patrik; Follin, Sven; Selroos, Jan-Olof; Näslund, Jens-Ove

    2014-09-01

    The impact of periglacial and glacial climate conditions on groundwater flow in fractured crystalline rock is studied by means of groundwater flow modeling of the Forsmark site, which was recently proposed as a repository site for the disposal of spent high-level nuclear fuel in Sweden. The employed model uses a thermal-hydraulically coupled approach for permafrost modeling and discusses changes in groundwater flow implied by the climate conditions found over northern Europe at different times during the last glacial cycle (Weichselian glaciation). It is concluded that discharge of particles released at repository depth occurs very close to the ice-sheet margin in the absence of permafrost. If permafrost is included, the greater part discharges into taliks in the periglacial area. During a glacial cycle, hydraulic gradients at repository depth reach their maximum values when the ice-sheet margin passes over the site; at this time, also, the interface between fresh and saline waters is distorted the most. The combined effect of advances and retreats during several glaciations has not been studied in the present work; however, the results indicate that hydrochemical conditions at depth in the groundwater flow model are almost restored after a single event of ice-sheet advance and retreat.

  4. Glacial-interglacial variations in sediment organic carbon accumulation and benthic foraminiferal assemblages on the Bermuda Rise (ODP Site 1063) during MIS 13 to 10

    NASA Astrophysics Data System (ADS)

    Poli, Maria Serena; Meyers, Philip A.; Thunell, Robert C.; Capodivacca, Marco

    2012-09-01

    We have determined organic carbon concentrations and isotopic compositions and benthic foraminiferal assemblages in sediments deposited between ˜500 and 340 ka at ODP Site 1063 on the northeastern flank of the Bermuda Rise. This time interval includes Marine Isotope Stage (MIS) 11, a particularly warm and long interglacial that was similar to today, and MIS 12, one of the most severe glacials of the last 600 kyr. During MIS 11.3, the peak of interglacial warming, organic carbon accumulation rates are low and benthic foraminiferal assemblages are dominated by Nuttallides umbonifera, a species indicative of oligotrophic environments. Higher accumulation rates during MIS 12 and 10 correspond with elevated sedimentation rates (33-36 cm/kyr). This pattern implies a combination of enhanced delivery and improved preservation of sediment organic matter during these glacial times. Organic δ13C values are less negative during MIS 12 and MIS 10 than during MIS 11, which is consistent with greater glacial-stage marine productivity. High relative abundances ofOridorsalis umbonatus during glacial intervals probably records a low but sustained flux of highly degraded organic material. Large, recurrent fluctuations in the abundance of Epistominella exiguaat the beginnings of the MIS 12 and MIS 10 glaciations suggest a marked increase in local phytoplankton blooms at these times and consequent delivery of phytodetritus to the seafloor. The most likely causes of these variations are changes in the position and strength of the Gulf Stream and its associated cold-ring eddies, combined with increased advection of terrigenous sediments from northerly locations during glacial lowstands.

  5. Glacial-Interglacial sea level reconstruction of the last 570 kyr: Inferences from a new benthic δ18O record of IODP Site U1386 (Gulf of Cadiz)

    NASA Astrophysics Data System (ADS)

    Kaboth, S.; Lourens, L. J.; de Boer, B.

    2015-12-01

    Sea level reconstructions on geological time scales are crucial for our understanding of glacial-interglacial cycles in the past, and thus offer context for current and projected changes. Global sea-level variations since the last glacial maximum have been well established based on numerous well-dated coral reef terraces and speleothem records. Throughout the Late Pleistocene, the coral and speleothem based data sets become more incomplete and reliable dated sea-level points, though showing the general amplitude of sea-level changes, are insufficient to establish the exact pattern and timing of millennial-scale changes. To gain further insight into glacial-interglacial sea level variations throughout the Late Pleistocene, we generated a new benthic δ18O record of IODP Site U1386 in the Gulf of Cadiz for the past ~ 570 kyr. Site U1386 is located within the Gulf of Cadiz Contourite Depositional System (CDS). These sediments are characterized by high sedimentation rate (~35 cm/kyr), providing a unique opportunity to study sea level oscillations in high resolution. To estimate ice volume and deep-water temperature changes we used an inverse forward modeling approach based on our benthic δ18O data. The coupled model includes four ice-sheet-shelf components that simulate glaciation on Eurasia, North America, Greenland and Antarctica, thereby explicitly accounting for all individual ice-volume contributions throughout the investigated time period. Our initial findings suggest that older glacial periods were characterized by repeated and substantial δ18O enrichment events preceding their respective glacial maximum. We argue that the observed δ18O enrichment events are not an expression of local hydrographic changes of salinity and/or temperature limited to the Gulf of Cadiz but probably relate to global ice volume changes. In this regard, our results contrast estimates derived from the global mean benthic δ18O LR04 stack. On a regional scale, our results show

  6. Evidence for Millennial-Scale Climate Variability in the Surface Waters Above ODP Site 980, NE Atlantic Ocean During the Last Glacial Interval (MIS 4-2)

    NASA Astrophysics Data System (ADS)

    Michaud, J. R.; Cullen, J. L.; McManus, J. F.; Oppo, D. W.

    2004-05-01

    Successful efforts to recover quality high sedimentation rate deep-sea sediment sections from the North Atlantic over the last decade have produced a number of studies demonstrating that climate instability at sub-orbital and even millennial time-scales is a pervasive component of Late Pleistocene North Atlantic climate. This is particularly true during Marine Isotope Stages (MIS) 4-2, i.e., the last glacial interval. One such high sedimentation rate section was recovered at ODP Site 980, Northeast Atlantic Ocean where sedimentation rates during MIS 4-2 exceed 15cm/kyr. Recently, we have begun to generate more detailed records from MIS 4-2 at Site 980 by reducing our sampling interval from 20 to around 2.5 cm, improving the resolution of our records an order of magnitude, from 1200-1300 to 100-200 years. 300 samples were used to generate high resolution records of changes in the input of ice-rafted detritus (IRD), along with limited data documenting changes in the relative abundance of the N. pachyderma, left coiling, which can be evaluated within the context of our previously generated lower resolution planktic and benthic oxygen isotope records used to generate our age model for this interval. Our previously published low resolution IRD record enabled us to identify Heinrich events 1-6 within the sediment interval deposited during the last glacial. Each event is characterized by IRD concentrations ranging from 500 to over 2500 lithic grains >150 microns per gram sediment. Superimposing our new high resolution IRD record reveals that Heinrich events 3,2,1 occurring at approximately 32, 23, and 17 kya, respectively, are each composed of a series of separate abrupt rapid increases in IRD concentrations approaching 1,000 grains per gram. An additional comparable event occurring at approximately 20 kya has also been identified. In the early part of the last glacial H6, H5, and H4 occurring at approximately 66, 47, and 38 kya, respectively, are recorded as much more

  7. Phylogeographic analysis of a temperate-deciduous forest restricted plant (Bupleurum longiradiatum Turcz.) reveals two refuge areas in China with subsequent refugial isolation promoting speciation.

    PubMed

    Zhao, Cai; Wang, Chang-Bao; Ma, Xiang-Guang; Liang, Qian-Long; He, Xing-Jin

    2013-09-01

    This study investigates the influence of climate-induced oscillations and complicated geological conditions on the evolutionary processes responsible for species formation in presently fragmented temperate forest habitats, located in continental East Asia. In addition to this, we also investigate the heavily debated issue of whether temperate forests migrated southwards during such glacial periods or, alternatively, whether there existed refugia within north China, enabling localized survival of temperate forests within this region. In order to achieve these, we surveyed the phylogeography of Bupleurum longiradiatum Turcz. (a herbaceous plant solely confined to temperate forests) constructed from sequence variation in three chloroplast (cp) DNA fragments: trnL-trnF, psbA-trnH and rps16. Our analyses show high genetic diversity within species (h(T)=0.948) and pronounced genetic differentiation among groups (yellow and purple flowers) with a significant phylogeographical pattern (N(ST)>G(ST), P<0.05). Forty-three haplotypes were identified and clustered into two lineages (the purple-flowered lineage and the yellow-flowered lineage). Two corresponding refuge areas, one in Qinling and its adjacent regions and one in the Changbai Mountains/eastern China, were revealed across the entire distribution ranges of Bupleurum longiradiatum. These results provide evidence for the hypothesis that independent refugia were maintained across the range of temperate forests in northern China during the last glacial maximum or earlier cold periods. Bupleurum longiradiatum var. porphyranthum formed a single taxon based on molecular data. This specific formation process suggests that the historical vicariance factors, i.e. climate-induced eco-geographic isolation through the biotic displacement of temperate-deciduous forest habitats, enhanced the divergence of the yellow and purple flower lineages at different spatial-temporal scales and over glacial and interglacial periods

  8. Phylogeographic analysis of a temperate-deciduous forest restricted plant (Bupleurum longiradiatum Turcz.) reveals two refuge areas in China with subsequent refugial isolation promoting speciation.

    PubMed

    Zhao, Cai; Wang, Chang-Bao; Ma, Xiang-Guang; Liang, Qian-Long; He, Xing-Jin

    2013-09-01

    This study investigates the influence of climate-induced oscillations and complicated geological conditions on the evolutionary processes responsible for species formation in presently fragmented temperate forest habitats, located in continental East Asia. In addition to this, we also investigate the heavily debated issue of whether temperate forests migrated southwards during such glacial periods or, alternatively, whether there existed refugia within north China, enabling localized survival of temperate forests within this region. In order to achieve these, we surveyed the phylogeography of Bupleurum longiradiatum Turcz. (a herbaceous plant solely confined to temperate forests) constructed from sequence variation in three chloroplast (cp) DNA fragments: trnL-trnF, psbA-trnH and rps16. Our analyses show high genetic diversity within species (h(T)=0.948) and pronounced genetic differentiation among groups (yellow and purple flowers) with a significant phylogeographical pattern (N(ST)>G(ST), P<0.05). Forty-three haplotypes were identified and clustered into two lineages (the purple-flowered lineage and the yellow-flowered lineage). Two corresponding refuge areas, one in Qinling and its adjacent regions and one in the Changbai Mountains/eastern China, were revealed across the entire distribution ranges of Bupleurum longiradiatum. These results provide evidence for the hypothesis that independent refugia were maintained across the range of temperate forests in northern China during the last glacial maximum or earlier cold periods. Bupleurum longiradiatum var. porphyranthum formed a single taxon based on molecular data. This specific formation process suggests that the historical vicariance factors, i.e. climate-induced eco-geographic isolation through the biotic displacement of temperate-deciduous forest habitats, enhanced the divergence of the yellow and purple flower lineages at different spatial-temporal scales and over glacial and interglacial periods

  9. Hydrogeologic framework, arsenic distribution, and groundwater geochemistry of the glacial-sediment aquifer at the Auburn Road landfill superfund site, Londonderry, New Hampshire

    USGS Publications Warehouse

    Degnan, James R.; Harte, Philip T.

    2013-01-01

    Leachate continues to be generated from landfills at the Auburn Road Landfill Superfund Site in Londonderry, New Hampshire. Impermeable caps on the three landfills at the site inhibit direct infiltration of precipitation; however, high water-table conditions allow groundwater to interact with landfill materials from below, creating leachate and ultimately reducing conditions in downgradient groundwater. Reducing conditions can facilitate arsenic transport by allowing it to stay in solution or by liberating arsenic adsorbed to surfaces and from geologic sources, such as glacial sediments and bedrock. The site occupies a 180-acre parcel of land containing streams, ponds, wetlands, and former gravel pits located in glacial sediment. Four areas, totaling 14 acres, including three landfills and one septage lagoon, were used for waste disposal. The site was closed in 1980 after volatile organic compounds associated with industrial waste dumping were detected. The site was added to the U.S. Environmental Protection Agency National Priority List in 1982, and the landfills were capped in 1996. Although volatile organic compound concentrations in groundwater have declined substantially, some measurable concentrations remain. Temporally variable and persistent elevated arsenic concentrations have been measured in groundwater affected by the landfill leachate. Microbial consumption of carbon found in leachate is a driver of reducing conditions that liberate arsenic at the site. In addition to sources of carbon in landfill leachate, wetland areas throughout the site also could contribute carbon to groundwater, but it is currently unknown if any of the wetland areas have downward or reversing gradients that could allow the infiltration of surface water to groundwater. Red-stained sediments and water indicate iron-rich groundwater discharge to surface water and are also associated with elevated concentrations of arsenic in sediment and groundwater. Ironrich groundwater seeps have

  10. Hydrogeologic framework, arsenic distribution, and groundwater geochemistry of the glacial-sediment aquifer at the Auburn Road landfill superfund site, Londonderry, New Hampshire

    USGS Publications Warehouse

    Degnan, James R.; Harte, Philip T.

    2013-01-01

    Leachate continues to be generated from landfills at the Auburn Road Landfill Superfund Site in Londonderry, New Hampshire. Impermeable caps on the three landfills at the site inhibit direct infiltration of precipitation; however, high water-table conditions allow groundwater to interact with landfill materials from below, creating leachate and ultimately reducing conditions in downgradient groundwater. Reducing conditions can facilitate arsenic transport by allowing it to stay in solution or by liberating arsenic adsorbed to surfaces and from geologic sources, such as glacial sediments and bedrock. The site occupies a 180-acre parcel of land containing streams, ponds, wetlands, and former gravel pits located in glacial sediment. Four areas, totaling 14 acres, including three landfills and one septage lagoon, were used for waste disposal. The site was closed in 1980 after volatile organic compounds associated with industrial waste dumping were detected. The site was added to the U.S. Environmental Protection Agency National Priority List in 1982, and the landfills were capped in 1996. Although volatile organic compound concentrations in groundwater have declined substantially, some measurable concentrations remain. Temporally variable and persistent elevated arsenic concentrations have been measured in groundwater affected by the landfill leachate. Microbial consumption of carbon found in leachate is a driver of reducing conditions that liberate arsenic at the site. In addition to sources of carbon in landfill leachate, wetland areas throughout the site also could contribute carbon to groundwater, but it is currently unknown if any of the wetland areas have downward or reversing gradients that could allow the infiltration of surface water to groundwater. Red-stained sediments and water indicate iron-rich groundwater discharge to surface water and are also associated with elevated concentrations of arsenic in sediment and groundwater. Ironrich groundwater seeps have

  11. Unusually limited pollen dispersal and connectivity of Pedunculate oak (Quercus robur) refugial populations at the species' southern range margin.

    PubMed

    Moracho, E; Moreno, G; Jordano, P; Hampe, A

    2016-07-01

    Low-latitudinal range margins of temperate and boreal plant species typically consist of scattered populations that persist locally in microrefugia. It remains poorly understood how their refugial habitats affect patterns of gene flow and connectivity, key components for their long-term viability and evolution. We examine landscape-scale patterns of historical and contemporary gene flow in refugial populations of the widespread European forest tree Pedunculate oak (Quercus robur) at the species' southwestern range margin. We sampled all adult trees (n = 135) growing in a 20 km long valley and genotyped 724 acorns from 72 mother trees at 17 microsatellite loci. The ten oak stands that we identified were highly differentiated and formed four distinct genetic clusters, despite sporadic historical dispersal being detectable. By far most contemporary pollination occurred within stands, either between local mates (85.6%) or through selfing (6.8%). Pollen exchange between stands (2.6%) was remarkably rare given their relative proximity and was complemented by long-distance pollen immigration (4.4%) and hybridization with the locally abundant Quercus pyrenaica (0.6%). The frequency of between-stand mating events decreased with increasing size and spatial isolation of stands. Overall, our results reveal outstandingly little long-distance gene flow for a wind-pollinated tree species. We argue that the distinct landscape characteristics of oaks' refugial habitats, with a combination of a rugged topography, dense vegetation and humid microclimate, are likely to increase plant survival but to hamper effective long-distance pollen dispersal. Moreover, local mating might be favoured by high tree compatibility resulting from genetic purging in these long-term relict populations. PMID:27146553

  12. A pulse in the delivery of ice-rafted debris at site 704 in the southeast Atlantic during glacial Termination V

    NASA Astrophysics Data System (ADS)

    Kanfoush, Sharon L.

    2016-03-01

    Termination V, the transition from glacial marine isotope stage 12 to interglacial stage 11-425 ka, is the largest deglaciation of the late Pleistocene and culminated with temperatures potentially warmer than present. Coastal geomorphic and stratigraphic evidence provides estimates of a sea-level high-stand 20 m above present at the time (Hearty et al. in Geology 27(4):375-378, 1999). Such sea-level rise would require disintegration of the Greenland Ice Sheet and West Antarctic Ice Sheet as well as part of the East Antarctic Ice Sheet (Raynaud et al. in Earth's climate and orbital eccentricity: the marine isotope stage 11 question. Geophysical monograph 137. American Geophysical Union, Washington, 2003). Lithic fragments in deep-sea sediments >150 μm at Site 704 in the South Atlantic Ocean were quantified. A large multipronged peak in concentration of this ice-rafted debris consisting of clear minerals, rose-colored transparent minerals, and ash punctuates glacial Termination V. It coincides with a brief two-pronged 1 ‰ reversal to heavier isotopic values from ~2.4 to ~3.4 ‰ at ~416 ka interpreted to reflect cooling resulting from influx of a large number of icebergs. The peak in ice-rafted debris also coincides with a 1 ‰ decrease in carbon isotopic ratios interrupting the ~2 ‰ increase in carbon isotope values across the entirety of Termination V. This is interpreted to reflect a reduction or shutdown in North Atlantic Deep Water formation and attendant Circumpolar Deep Water upwelling at the site and is also consistent with a shift in storage of carbon and carbonate from the deep sea to continental shelves resulting from a dramatic sea-level high-stand. Consequently, the lithic record at Site 704 lends support for the upper end of sea-level estimates based upon land-based evidence that requires a substantial contribution from the East Antarctic Ice Sheet. However, caution is warranted as differences with lithic records from Site 1089, 1090 and 1094

  13. Continuity of brown bear maternal lineages in northern England through the Last-glacial period

    NASA Astrophysics Data System (ADS)

    Edwards, Ceiridwen J.; Ho, Simon Y. W.; Barnett, Ross; Coxon, Peter; Bradley, Daniel G.; Lord, Tom C.; O'Connor, Terry

    2014-07-01

    Brown bears recolonised Europe rapidly after the Last Glacial Maximum (LGM), but there has been debate about whether bear populations were confined to separate glacial refugia in southern Europe, or if there was continuous gene flow among groups. To look in more detail at recolonisation routes into the British Isles after the LGM, 16 brown bear (Ursus arctos) samples from Lateglacial Yorkshire were analysed for mitochondrial DNA survival. The resulting data were compared with earlier work on Late Pleistocene and Holocene bears from Ireland (Edwards et al., 2011), as well as with both modern and ancient bears from across continental Europe. The results highlight the temporal and spatial continuity of brown bear maternal lineages through the Lateglacial period in northern England. While this region was not a refugial area in the LGM for the Irish Clade 2 brown bears, our data suggest that populations of brown bear in England did act as refugial sources for the later colonisation of Ireland, by Clade 1-i bears, during the Holocene. Our results contribute to a wider understanding of the phylogenetic relationships of brown bears through the Late Quaternary, and lend a valuable perspective on bear migration into peripheral Europe.

  14. Summer air temperature, reconstructions from the last glacial stage based on rodents from the site Taillis-des-Coteaux (Vienne), Western France

    NASA Astrophysics Data System (ADS)

    Royer, Aurélien; Lécuyer, Christophe; Montuire, Sophie; Primault, Jérôme; Fourel, François; Jeannet, Marcel

    2014-09-01

    The oxygen isotope composition of phosphate from tooth enamel of rodents (δ18Op) constitutes a valuable proxy to reconstruct past air temperatures in continental environments. This method has been applied to rodent dental remains from three genera, Arvicola sp., Microtus sp. and Dicrostonyx sp., coming from Taillis-des-Coteaux, Vienne, France. This archaeological site contains an exceptionally preserved sedimentary sequence spanning almost the whole Upper Palaeolithic, including seven stratigraphic layers dated from 35 to 17 cal ka BP. The abundant presence of rodent remains offers the opportunity to quantify the climatic fluctuations coeval of the various stages of human occupation of the site. Differences between δ18Op values of Arvicola sp. and Microtus sp. teeth are interpreted as the result of heterochrony in tooth formation as well as differences in ecology. Mean δ18Op values of Microtus sp. are preferentially used to reconstruct summer air temperatures, which range from 16.0 ± 3.7 to 19.1 ± 3.1°C throughout the sedimentary sequence; however, the highest variability is observed during the last glacial maximum.

  15. A New Late Glacial Site in the Central Appalachians of Virginia. Preliminary Findings From Paleobotany, Palynology, and Geomorphology

    NASA Astrophysics Data System (ADS)

    Schwartz, B. F.; Upchurch, G. R.; Willard, D. A.; Bernhardt, C. E.; Valella, P. A.

    2009-12-01

    Thick clay deposits in a recently identified paleo-lake bed in a central Appalachian karst system in Highland County, Virginia have yielded well-preserved pollen and macroflora that provide the opportunity to refine the understanding of Pleistocene climate, vegetation dynamics, and erosion in the region. A radiocarbon date of 22,000 14C yr B.P. on wood fragments near the top of the sequence establishes the age of the sediments. Pollen and plant macrofloras characteristic of modern boreal forests are present in sediments at this site. Pollen assemblages show a dominance of conifers, mostly Pinus banksiana and Picea, with Lycopodium as important ground cover. Leaf fossils sieved from the clay show a dominance of Picea needles and common dicot leaf fragments, suggesting that Pinus is either over-represented in the pollen flora or more distal to the paleo-lake. Macrofossil assemblages sieved from the clay contain a variety of non-leaf remains, including fruits, seeds, mosses, insects, feathers, and fungi. Test augering and geophysical results indicate that these clay deposits are at least 9m and perhaps as much as 15m thick. The amount and temporal distribution of sediment loads to the paleo-lake (a depositional environment) from the surrounding landscape (an erosional environment) will be modeled using analysis of sediment facies in and above (>12m) these clays, combined with sediment volume calculations and drainage basin analysis, and constrained by dates from the sediments themselves. Due to the rare occurrence of still-water depositional environments in the Appalachians, this site provides paleo-climate and sedimentological data that will refine regional models of landscape evolution and incision. This work also has implications for the development and modification of a significant karst system that surrounds and underlies the paleo-lake bed. The same karst system is responsible both for the formation of the paleo-lake (after the drain in a blind valley became

  16. (Lack of) genetic diversity in immune genes predates glacial isolation in the North American mountain goat (Oreamnos americanus).

    PubMed

    Shafer, Aaron B A; Fan, Chia Wei; Côté, Steeve D; Coltman, David W

    2012-01-01

    The major histocompatibility complex (MHC) plays an important role in an organism's ability to respond to pathogens. Immunogenetic diversity is advantageous as it permits the recognition of more external antigens. For this reason, MHC and immune gene variation are considered a barometer for the genetic health of wild populations. Mountain goats (Oreamnos americanus) were previously shown to have little variation at the MHC Class II Oram-DRB locus, which was attributed to population bottlenecks during the last glacial maximum (LGM). In this paper, we extended the analysis of immunogenetic variability in mountain goats to 5 genes representing the 3 classes of MHC gene (Class I OLA, Class II DRA and DRB, and Class III TNF-α) and the natural resistance-associated macrophage protein. We sequenced approximately 3000 bp from 31 individuals sampled across the range of mountain goats and found very low levels of diversity (1-3 polymorphic sites per gene) with the exception of the Class I Oram-OLA gene. Oram-OLA was nearly 30 times more diverse than the other immune genes and appears to represent a source of increased immunogenetic diversity. This diversity may be attributed to multiple loci, mediated by pathogen exposure, or potentially influenced by social factors. The distribution of SNPs was not associated with refugial history, suggesting that the current distribution of immunogenetic diversity was present prior to the LGM. These data suggest that although they have low levels of diversity at the 4 of 5 immune loci, mountain goats may be better equipped for future climate oscillations and pathogen exposure than previously thought. PMID:22268162

  17. (Lack of) genetic diversity in immune genes predates glacial isolation in the North American mountain goat (Oreamnos americanus).

    PubMed

    Shafer, Aaron B A; Fan, Chia Wei; Côté, Steeve D; Coltman, David W

    2012-01-01

    The major histocompatibility complex (MHC) plays an important role in an organism's ability to respond to pathogens. Immunogenetic diversity is advantageous as it permits the recognition of more external antigens. For this reason, MHC and immune gene variation are considered a barometer for the genetic health of wild populations. Mountain goats (Oreamnos americanus) were previously shown to have little variation at the MHC Class II Oram-DRB locus, which was attributed to population bottlenecks during the last glacial maximum (LGM). In this paper, we extended the analysis of immunogenetic variability in mountain goats to 5 genes representing the 3 classes of MHC gene (Class I OLA, Class II DRA and DRB, and Class III TNF-α) and the natural resistance-associated macrophage protein. We sequenced approximately 3000 bp from 31 individuals sampled across the range of mountain goats and found very low levels of diversity (1-3 polymorphic sites per gene) with the exception of the Class I Oram-OLA gene. Oram-OLA was nearly 30 times more diverse than the other immune genes and appears to represent a source of increased immunogenetic diversity. This diversity may be attributed to multiple loci, mediated by pathogen exposure, or potentially influenced by social factors. The distribution of SNPs was not associated with refugial history, suggesting that the current distribution of immunogenetic diversity was present prior to the LGM. These data suggest that although they have low levels of diversity at the 4 of 5 immune loci, mountain goats may be better equipped for future climate oscillations and pathogen exposure than previously thought.

  18. Refugial isolation and secondary contact in the dyeing poison frog Dendrobates tinctorius.

    PubMed

    Noonan, Brice P; Gaucher, Philippe

    2006-12-01

    Recent palaeoclimactic research suggests that fluctuating environmental conditions throughout the Pleistocene of Amazonia occurred with previously unrecognized frequency. This has resulted in a theoretical shift from glacially influenced fluctuations to those driven by precessional rhythms. This theoretical revolution has a profound impact on expectations of biotic diversity within biogeographical regions that have long been based on the idea of large-scale landscape fragmentation associated with increased aridity and glacial cycles. Generally speaking, this shifts phylogeographical expectations from that of (i) large areas of sympatry of closely related (but not sister) species whose origins lie in separate refugia, and current distributions are the results of cyclic connectivity of those two refugia (refuge hypothesis), to that of (ii) fine scale genetic structure, often associated with elevation, and divergence well below expected speciation levels [disturbance-vicariance (DV) hypothesis]. To date there have been few tests of the expectations of the DV hypothesis based on empirical studies of Neotropical floral and faunal communities. Herein we examine phylogeographical structure of Dendrobates tinctorius, an amphibian species endemic to the uplands of the eastern Guiana Shield, based on sampling of 114 individuals from 24 localities. Phylogenetic, nested clade, and dispersal-vicariance (DIVA) analyses of cytochrome b sequence data reveal the presence of two mitochondrial lineages that are associated with previously identified western and eastern uplands of this area. The geographical distribution of mitochondrial haplotypes and the results of DIVA and coalescent analyses suggest that there has been extensive secondary contact between these lineages indicating a complex history of connectivity between these western and eastern highlands, supporting the predictions of the DV hypothesis. PMID:17107474

  19. Refugial isolation and secondary contact in the dyeing poison frog Dendrobates tinctorius.

    PubMed

    Noonan, Brice P; Gaucher, Philippe

    2006-12-01

    Recent palaeoclimactic research suggests that fluctuating environmental conditions throughout the Pleistocene of Amazonia occurred with previously unrecognized frequency. This has resulted in a theoretical shift from glacially influenced fluctuations to those driven by precessional rhythms. This theoretical revolution has a profound impact on expectations of biotic diversity within biogeographical regions that have long been based on the idea of large-scale landscape fragmentation associated with increased aridity and glacial cycles. Generally speaking, this shifts phylogeographical expectations from that of (i) large areas of sympatry of closely related (but not sister) species whose origins lie in separate refugia, and current distributions are the results of cyclic connectivity of those two refugia (refuge hypothesis), to that of (ii) fine scale genetic structure, often associated with elevation, and divergence well below expected speciation levels [disturbance-vicariance (DV) hypothesis]. To date there have been few tests of the expectations of the DV hypothesis based on empirical studies of Neotropical floral and faunal communities. Herein we examine phylogeographical structure of Dendrobates tinctorius, an amphibian species endemic to the uplands of the eastern Guiana Shield, based on sampling of 114 individuals from 24 localities. Phylogenetic, nested clade, and dispersal-vicariance (DIVA) analyses of cytochrome b sequence data reveal the presence of two mitochondrial lineages that are associated with previously identified western and eastern uplands of this area. The geographical distribution of mitochondrial haplotypes and the results of DIVA and coalescent analyses suggest that there has been extensive secondary contact between these lineages indicating a complex history of connectivity between these western and eastern highlands, supporting the predictions of the DV hypothesis.

  20. Hydrostratigraphic mapping of the Milford-Souhegan glacial drift aquifer, and effects of hydrostratigraphy on transport of PCE, Operable Unit 1, Savage Superfund Site, Milford, New Hampshire

    USGS Publications Warehouse

    Harte, Philip T.

    2010-01-01

    The Savage Municipal Well Superfund site in the Town of Milford, New Hampshire, was underlain by a 0.5-square mile plume (as mapped in 1994) of volatile organic compounds (VOCs), most of which consisted of tetrachloroethylene (PCE). The plume occurs mostly within highly transmissive stratified-drift deposits but also extends into underlying till and bedrock. The plume has been divided into two areas called Operable Unit 1 (OU1), which contains the primary source area, and Operable Unit 2 (OU2), which is defined as the extended plume area outside of OU1. The OU1 remedial system includes a low-permeability barrier wall that encircles the highest detected concentrations of PCE and a series of injection and extraction wells to contain and remove contaminants. The barrier wall likely penetrates the full thickness of the sand and gravel; in many places, it also penetrates the full thickness of the underlying basal till and sits atop bedrock.From 1998 to 2004, PCE concentrations decreased by an average of 80 percent at most wells outside the barrier wall. However, inside the barrier, PCE concentrations greater than 10,000 micrograms per liter (μg/L) still exist (2008). The remediation of these areas of recalcitrant PCE presents challenges to successful remediation.The U.S. Geological Survey (USGS), in cooperation with the New Hampshire Department of Environmental Services (NHDES) and the U.S. Environmental Protection Agency (USEPA), Region 1, is studying the solute transport of VOCs (primarily PCE) in contaminated groundwater in the unconsolidated sediments (overburden) of the Savage site and specifically assisting in the evaluation of the effectiveness of remedial operations in the OU1 area. As part of this effort, the USGS analyzed the subsurface stratigraphy to help understand hydrostratigraphic controls on remediation.A combination of lithologic, borehole natural gamma-ray and electromagnetic (EM) induction logging, and test drilling has identified 11 primary

  1. Late-glacial recolonization and phylogeography of European red deer (Cervus elaphus L.).

    PubMed

    Meiri, Meirav; Lister, Adrian M; Higham, Thomas F G; Stewart, John R; Straus, Lawrence G; Obermaier, Henriette; González Morales, Manuel R; Marín-Arroyo, Ana B; Barnes, Ian

    2013-09-01

    The Pleistocene was an epoch of extreme climatic and environmental changes. How individual species responded to the repeated cycles of warm and cold stages is a major topic of debate. For the European fauna and flora, an expansion-contraction model has been suggested, whereby temperate species were restricted to southern refugia during glacial times and expanded northwards during interglacials, including the present interglacial (Holocene). Here, we test this model on the red deer (Cervus elaphus) a large and highly mobile herbivore, using both modern and ancient mitochondrial DNA from the entire European range of the species over the last c. 40,000 years. Our results indicate that this species was sensitive to the effects of climate change. Prior to the Last Glacial Maximum (LGM) haplogroups restricted today to South-East Europe and Western Asia reached as far west as the UK. During the LGM, red deer was mainly restricted to southern refugia, in Iberia, the Balkans and possibly in Italy and South-Western Asia. At the end of the LGM, red deer expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, Scandinavia, Germany, Poland and Belarus. Ancient DNA data cannot rule out refugial survival of red deer in North-West Europe through the LGM. Had such deer survived, though, they were replaced by deer migrating from Iberia at the end of the glacial. The Balkans served as a separate LGM refugium and were probably connected to Western Asia with genetic exchange between the two areas.

  2. Simulation of solute transport of tetrachloroethylene in ground water of the glacial-drift aquifer at the Savage Municipal Well Superfund Site, Milford, New Hampshire, 1960-2000

    USGS Publications Warehouse

    Harte, Philip T.

    2004-01-01

    The Savage Municipal Well Superfund site, named after the former municipal water-supply well for the town of Milford, is underlain by a 0.5-square mile plume of volatile organic compounds (VOCs), primarily tetrachloroethylene (PCE). The plume occurs mostly within a highly transmissive sand-and-gravel unit, but also extends to an underlying till and bedrock unit. The plume logistically is divided into two areas termed Operable Unit No. 1 (OU1), which contains the primary source area, and Operable Unit No. 2 (OU2), which is the extended plume area. PCE concentrations in excess of 100,000 parts per billion (ppb) had been detected in the OU1 area in 1995, indicating a likely Dense Non-Aqueous Phase Liquid (DNAPL) source. In the fall of 1998, the New Hampshire Department of Environmental Services (NHDES) and the U.S. Environmental Protection Agency (USEPA) installed a remedial system in OU1. The OU1 remedial system includes a low-permeability barrier that encircles the highest detected concentrations of PCE, and a series of injection and extraction wells. The barrier primarily sits atop bedrock and penetrates the full thickness of the sand and gravel; and in some places, the full thickness of the underlying basal till. The sand and gravel unit and the till comprise the aquifer termed the Milford-Souhegan glacial-drift aquifer (MSGD). Two-dimensional and three-dimensional finite-difference solute-transport models of the unconsolidated sediments (MSGD aquifer) were constructed to help evaluate solute-transport processes, assess the effectiveness of remedial activities in OU1, and to help design remedial strategies in OU2. The solute-transport models simulate PCE concentrations, and model results were compared to observed concentrations of PCE. Simulations were grouped into the following three time periods: an historical calibration of the distribution of PCE from the initial input (circa 1960) of PCE into the subsurface to the 1990s, a pre-remedial calibration from 1995

  3. Evidence for Differential Assortative Female Preference in Association with Refugial Isolation of Rainbow Skinks in Australia's Tropical Rainforests

    PubMed Central

    Dolman, Gaynor

    2008-01-01

    Background Divergence driven by female preference can give rise to pre-mating isolation more rapidly than post-mating isolation can evolve through the accumulation of allelic incompatibilities. Moreover pre-mating isolation may be more effective at maintaining morphological differentiation between divergent populations. In the context of Australian rainforest endemic skinks that were historically subjected to refugial isolation, this study examined the following predictions: 1) that assortative female preference is associated with more recent divergence of southern C. rubrigularis (S-RED) and C. rhomboidalis (BLUE), but not with deeply divergent S-RED and northern C. rubrigularis (N-RED); and 2) that upon secondary contact, morphological differentiation is maintained between S-RED and BLUE, whereas N-RED and S-RED remain morphogically indistinguishable. Principal Findings Female preference trials found no evidence for assortative female preference between N-RED and S-RED, supporting a previous genetic hybrid zone study which inferred post-mating but no pre-mating isolation. In contrast there is evidence for assortative female preference between S-RED and BLUE, with BLUE females preferring to associate with BLUE males, but S-RED females showing no preference. Multi-locus coalescent analyses, used to estimate post-divergence gene-flow between proximally located S-RED and BLUE populations, rejected zero gene-flow from BLUE to S-RED and thus RED and BLUE have maintained morphological differentiation despite secondary contact. Morphometric analyses confirmed a lack of morphological divergence between N-RED and S-RED and established that BLUE is morphologically divergent from RED in traits other than throat colour. Conclusions/Significance Long-term isolation has been sufficient to generate post-mating isolation but no morphological divergence between N-RED and S-RED. In contrast, greater morphological differentiation is associated with evidence for assortative female

  4. Glacial integrative modelling.

    PubMed

    Ganopolski, Andrey

    2003-09-15

    Understanding the mechanisms of past climate changes requires modelling of the complex interaction between all major components of the Earth system: atmosphere, ocean, cryosphere, lithosphere and biosphere. This paper reviews attempts at such an integrative approach to modelling climate changes during the glacial age. In particular, the roles of different factors in shaping glacial climate are compared based on the results of simulations with an Earth-system model of intermediate complexity, CLIMBER-2. It is shown that ice sheets, changes in atmospheric compositions, vegetation cover, and reorganization of the ocean thermohaline circulation play important roles in glacial climate changes. Another example of this approach is the modelling of two major types of abrupt glacial climate changes: Dansgaard-Oeschger and Heinrich events. Our results corroborate some of the early proposed mechanisms, which relate abrupt climate changes to the internal instability of the ocean thermohaline circulation and ice sheets. At the same time, it is shown that realistic representation of the temporal evolution of the palaeoclimatic background is crucial to simulate observed features of the glacial abrupt climate changes.

  5. Glacial integrative modelling.

    PubMed

    Ganopolski, Andrey

    2003-09-15

    Understanding the mechanisms of past climate changes requires modelling of the complex interaction between all major components of the Earth system: atmosphere, ocean, cryosphere, lithosphere and biosphere. This paper reviews attempts at such an integrative approach to modelling climate changes during the glacial age. In particular, the roles of different factors in shaping glacial climate are compared based on the results of simulations with an Earth-system model of intermediate complexity, CLIMBER-2. It is shown that ice sheets, changes in atmospheric compositions, vegetation cover, and reorganization of the ocean thermohaline circulation play important roles in glacial climate changes. Another example of this approach is the modelling of two major types of abrupt glacial climate changes: Dansgaard-Oeschger and Heinrich events. Our results corroborate some of the early proposed mechanisms, which relate abrupt climate changes to the internal instability of the ocean thermohaline circulation and ice sheets. At the same time, it is shown that realistic representation of the temporal evolution of the palaeoclimatic background is crucial to simulate observed features of the glacial abrupt climate changes. PMID:14558899

  6. Refugial isolation and range expansions drive the genetic structure of Oxyria sinensis (Polygonaceae) in the Himalaya-Hengduan Mountains.

    PubMed

    Meng, Lihua; Chen, Gang; Li, Zhonghu; Yang, Yongping; Wang, Zhengkun; Wang, Liuyang

    2015-01-01

    The formation of the Mekong-Salween Divide and climatic oscillations in Pleistocene were the main drivers for the contemporary diversity and genetic structure of plants in the Himalaya-Hengduan Mountains (HHM). To identify the relative roles of the two historical events in shaping population history of plants in HHM, we investigated the phylogeographic pattern of Oxyria sinensis, a perennial plant endemic to the HHM. Sixteen chloroplast haplotypes were identified and were clustered into three phylogenetic clades. The age of the major clades was estimated to be in the Pleistocene, falling into several Pleistocene glacial stages and postdating the formation of the Mekong-Salween Divide. Range expansions occurred at least twice in the early and middle Pleistocene, but the spatial genetic distribution rarely changed since the Last Glacial Maximum. Our results suggest that temporary mountain glaciers may act as barriers in promoting the lineage divergence in O. sinensis and that subsequential range expansions and secondary contacts might reshape the genetic distribution in geography and blur the boundary of population differentiation created in the earlier glacial stages. This study demonstrates that Pleistocene climatic change and mountain glaciers, rather than the Mekong-Salween Divide, play the primary role in shaping the spatial genetic structure of O. sinensis.

  7. Refugial isolation and range expansions drive the genetic structure of Oxyria sinensis (Polygonaceae) in the Himalaya-Hengduan Mountains

    PubMed Central

    Meng, Lihua; Chen, Gang; Li, Zhonghu; Yang, Yongping; Wang, Zhengkun; Wang, Liuyang

    2015-01-01

    The formation of the Mekong-Salween Divide and climatic oscillations in Pleistocene were the main drivers for the contemporary diversity and genetic structure of plants in the Himalaya-Hengduan Mountains (HHM). To identify the relative roles of the two historical events in shaping population history of plants in HHM, we investigated the phylogeographic pattern of Oxyria sinensis, a perennial plant endemic to the HHM. Sixteen chloroplast haplotypes were identified and were clustered into three phylogenetic clades. The age of the major clades was estimated to be in the Pleistocene, falling into several Pleistocene glacial stages and postdating the formation of the Mekong-Salween Divide. Range expansions occurred at least twice in the early and middle Pleistocene, but the spatial genetic distribution rarely changed since the Last Glacial Maximum. Our results suggest that temporary mountain glaciers may act as barriers in promoting the lineage divergence in O. sinensis and that subsequential range expansions and secondary contacts might reshape the genetic distribution in geography and blur the boundary of population differentiation created in the earlier glacial stages. This study demonstrates that Pleistocene climatic change and mountain glaciers, rather than the Mekong-Salween Divide, play the primary role in shaping the spatial genetic structure of O. sinensis. PMID:26013161

  8. Sources of glacial moisture in Mesoamerica

    USGS Publications Warehouse

    Bradbury, J.P.

    1997-01-01

    Paleoclimatic records from Mesoamerica document the interplay between Atlantic and Pacific sources of precipitation during the last glacial stage and Holocene. Today, and throughout much of the Holocene, the entire region receives its principal moisture in the summer from an interaction of easterly trade winds with the equatorial calms. Glacial records from sites east of 95?? W in Guatemala, Florida, northern Venezuela and Colombia record dry conditions before 12 ka, however. West of 95?? W, glacial conditions were moister than in the Holocene. For example, pollen and diatom data show that Lake Pa??tzcuaro in the central Mexican highlands was cool, deep and fresh during this time and fossil pinyon needles in packrat middens in Chihuahua, Sonora, Arizona, and Texas indicate cooler glacial climates with increased winter precipitation. Cold Gulf of Mexico sea-surface temperatures and reduced strength of the equatorial calms can explain arid full and late glacial environments east of 95?? W whereas an intensified pattern of winter, westerly air flow dominated hydrologic balances as far south as 20?? N. Overall cooler temperatures may have increased effective moisture levels during dry summer months in both areas. ?? 1997 INQUA/ Elsevier Science Ltd.

  9. Future intrusion of oxygenated glacial meltwaters into the Fennoscandian shield: a possibility to consider in performance assessments for nuclear-waste disposal sites?: Chapter 6

    USGS Publications Warehouse

    Glynn, Pierre

    2008-01-01

    Provost et al. (1998) and Glynn and Voss (1999; also published in Glynn et al., 1999) considered the possibility that during future glaciations, oxygenated glacial meltwaters from two- to three-kilometer thick ice sheets could potentially intrude to the 500 m depth of planned nuclear-waste repositories. This possibility has been of concern because of potential negative effects on the stability of the repository engineered environment, and because of the potential mobilization of radionuclides should the oxygenated waters come into contact with the radioactive waste. The above reports argued that given the current state of knowledge, it was hard to discount the possibility that oxygenated waters could penetrate to repository level depth. The reports also suggested that oxidizing conditions might be present in the fractured rock environment for significant amounts of time, on the order of thousands to tens of thousands of years. In some earlier reports, Swedish and Finnish governmental agencies in charge of nuclear-waste disposal had considered the possibility that oxygenated meltwaters might intrude to the repository depth (SKI: 1992; Martinerie et al, 1992; Ahonen and Vieno, 1994). Subsequent to the publication of Provost et al. (1998), Glynn et al. (1999) and Glynn and Voss (1999), the Swedish Nuclear Fuel and Waste Handling Company (SKB) commissioned efforts to examine more thoroughly the possibilities that oxygenated meltwaters might occur under ice-sheet conditions and intrude to the repository depth.

  10. Glacial Geology of Wisconsin.

    ERIC Educational Resources Information Center

    Madison Public Schools, WI.

    This publication is a teacher's resource and guidebook for the presentation of the three filmstrips in the "Glacial Geology of Wisconsin" series. The first filmstrip is subtitled, "Evidence of the Glaciers," the second "How the Glaciers Reshaped the Landscape," and the third "Fossils of the Ice Age." Included are a list of objectives, an outline…

  11. Glacial vicariance in Eurasia: mitochondrial DNA evidence from Scots pine for a complex heritage involving genetically distinct refugia at mid-northern latitudes and in Asia Minor

    PubMed Central

    Naydenov, Krassimir; Senneville, Sauphie; Beaulieu, Jean; Tremblay, Francine; Bousquet, Jean

    2007-01-01

    Background At the last glacial maximum, Fennoscandia was covered by an ice sheet while the tundra occupied most of the rest of northern Eurasia. More or less disjunct refugial populations of plants were dispersed in southern Europe, often trapped between mountain ranges and seas. Genetic and paleobotanical evidences indicate that these populations have contributed much to Holocene recolonization of more northern latitudes. Less supportive evidence has been found for the existence of glacial populations located closer to the ice margin. Scots pine (Pinus sylvestris L.) is a nordic conifer with a wide natural range covering much of Eurasia. Fractures in its extant genetic structure might be indicative of glacial vicariance and how different refugia contributed to the current distribution at the continental level. The population structure of Scots pine was investigated on much of its Eurasian natural range using maternally inherited mitochondrial DNA polymorphisms. Results A novel polymorphic region of the Scots pine mitochondrial genome has been identified, the intron 1 of nad7, with three variants caused by insertions-deletions. From 986 trees distributed among 54 populations, four distinct multi-locus mitochondrial haplotypes (mitotypes) were detected based on the three nad7 intron 1 haplotypes and two previously reported size variants for nad1 intron B/C. Population differentiation was high (GST = 0.657) and the distribution of the mitotypes was geographically highly structured, suggesting at least four genetically distinct ancestral lineages. A cosmopolitan lineage was widely distributed in much of Europe throughout eastern Asia. A previously reported lineage limited to the Iberian Peninsula was confirmed. A new geographically restricted lineage was found confined to Asia Minor. A new lineage was restricted to more northern latitudes in northeastern Europe and the Baltic region. Conclusion The contribution of the various ancestral lineages to the current

  12. Late glacial aridity in southern Rocky Mountains

    SciTech Connect

    Davis, O.K.; Pitblado, B.L.

    1995-09-01

    While the slopes of the present-day Colorado Rocky Mountains are characterized by large stands of subalpine and montane conifers, the Rockies of the late glacial looked dramatically different. Specifically, pollen records suggest that during the late glacial, Artemisia and Gramineae predominated throughout the mountains of Colorado. At some point between 11,000 and 10,000 B.P., however, both Artemisia and grasses underwent a dramatic decline, which can be identified in virtually every pollen diagram produced for Colorado mountain sites, including Como Lake (Sangre de Cristo Mountains), Copley Lake and Splains; Gulch (near Crested Butte), Molas Lake (San Juan Mountains), and Redrock Lake (Boulder County). Moreover, the same pattern seems to hold for pollen spectra derived for areas adjacent to Colorado, including at sites in the Chuska Mountains of New Mexico and in eastern Wyoming. The implications of this consistent finding are compelling. The closest modem analogues to the Artemisia- and Gramineae-dominated late-glacial Colorado Rockies are found in the relatively arid northern Great Basin, which suggests that annual precipitation was much lower in the late-glacial southern Rocky Mountains than it was throughout the Holocene.

  13. A new millipede, Austrotyla awishoshola n. sp., (Diplopoda, Chordeumatida, Conotylidae) from New Mexico, USA, and the importance of cave moss gardens as refugial habitats.

    PubMed

    Wynne, J Judson; Shear, William A

    2016-01-01

    Austrotyla awishoshola n. sp. is described from the moss gardens of one lava tube cave in El Malpais National Monument, Cibola Co., New Mexico. Most chordeumatidans require mesic conditions, and these environments are limited to moss gardens in several cave entrances and beneath cave skylights in El Malpais. Presently, this species is known from the moss gardens of a single of cave in the monument. We suggest A. awishoshola may be a climatic relict, having become restricted to the cave environment following the end of the Pleistocene. We discuss the importance of cave moss gardens as refugial and relictual habitats. Recommendations are provided to aid in the conservation and management of A. awishoshola and these habitats. PMID:27394265

  14. A new millipede, Austrotyla awishoshola n. sp., (Diplopoda, Chordeumatida, Conotylidae) from New Mexico, USA, and the importance of cave moss gardens as refugial habitats.

    PubMed

    Wynne, J Judson; Shear, William A

    2016-02-25

    Austrotyla awishoshola n. sp. is described from the moss gardens of one lava tube cave in El Malpais National Monument, Cibola Co., New Mexico. Most chordeumatidans require mesic conditions, and these environments are limited to moss gardens in several cave entrances and beneath cave skylights in El Malpais. Presently, this species is known from the moss gardens of a single of cave in the monument. We suggest A. awishoshola may be a climatic relict, having become restricted to the cave environment following the end of the Pleistocene. We discuss the importance of cave moss gardens as refugial and relictual habitats. Recommendations are provided to aid in the conservation and management of A. awishoshola and these habitats.

  15. Glacial atmospheric phosphorus deposition

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid; Dallmayr, Remi; Gabrieli, Jacopo; Goto-Azuma, Kumiko; Hirabayashi, Motohiro; Svensson, Anders; Vallelonga, Paul

    2016-04-01

    Phosphorus in the atmosphere is poorly studied and thus not much is known about atmospheric phosphorus and phosphate transport and deposition changes over time, though it is well known that phosphorus can be a source of long-range nutrient transport, e.g. Saharan dust transported to the tropical forests of Brazil. In glacial times it has been speculated that transport of phosphorus from exposed shelves would increase the ocean productivity by wash out. However whether the exposed shelf would also increase the atmospheric load to more remote places has not been investigated. Polar ice cores offer a unique opportunity to study the atmospheric transport of aerosols on various timescales, from glacial-interglacial periods to recent anthropogenic influences. We have for the first time determined the atmospheric transport of phosphorus to the Arctic by means of ice core analysis. Both total and dissolved reactive phosphorus were measured to investigate current and past atmospheric transport of phosphorus to the Arctic. Results show that glacial cold stadials had increased atmospheric total phosphorus mass loads of 70 times higher than in the past century, while DRP was only increased by a factor of 14. In the recent period we find evidence of a phosphorus increase over the past 50 yrs in ice cores close to human occupation likely correlated to forest fires. References: Kjær, Helle Astrid, et al. "Continuous flow analysis method for determination of dissolved reactive phosphorus in ice cores." Environmental science & technology 47.21 (2013): 12325-12332. Kjær, Helle Astrid, et al. "Greenland ice cores constrain glacial atmospheric fluxes of phosphorus." Journal of Geophysical Research: Atmospheres120.20 (2015).

  16. Late-glacial recolonization and phylogeography of European red deer (Cervus elaphus L.).

    PubMed

    Meiri, Meirav; Lister, Adrian M; Higham, Thomas F G; Stewart, John R; Straus, Lawrence G; Obermaier, Henriette; González Morales, Manuel R; Marín-Arroyo, Ana B; Barnes, Ian

    2013-09-01

    The Pleistocene was an epoch of extreme climatic and environmental changes. How individual species responded to the repeated cycles of warm and cold stages is a major topic of debate. For the European fauna and flora, an expansion-contraction model has been suggested, whereby temperate species were restricted to southern refugia during glacial times and expanded northwards during interglacials, including the present interglacial (Holocene). Here, we test this model on the red deer (Cervus elaphus) a large and highly mobile herbivore, using both modern and ancient mitochondrial DNA from the entire European range of the species over the last c. 40,000 years. Our results indicate that this species was sensitive to the effects of climate change. Prior to the Last Glacial Maximum (LGM) haplogroups restricted today to South-East Europe and Western Asia reached as far west as the UK. During the LGM, red deer was mainly restricted to southern refugia, in Iberia, the Balkans and possibly in Italy and South-Western Asia. At the end of the LGM, red deer expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, Scandinavia, Germany, Poland and Belarus. Ancient DNA data cannot rule out refugial survival of red deer in North-West Europe through the LGM. Had such deer survived, though, they were replaced by deer migrating from Iberia at the end of the glacial. The Balkans served as a separate LGM refugium and were probably connected to Western Asia with genetic exchange between the two areas. PMID:23927498

  17. Late Pleistocene ice margin fluctuations in the Nahanni National Park-UNESCO World Heritage Site and their impact on glacial lake formation and architecture of drainage systems across the Yukon-NWT continental divide

    NASA Astrophysics Data System (ADS)

    Duk-Rodkin, A.; Barendregt, R. W.

    2009-12-01

    In the late Pleistocene the southern Mackenzie region was glaciated by ice masses from a Cordilleran and continental source (Laurentide). Stratigraphic and geomorphologic evidence indicate that the two glaciers occupied this region at different times during the Late Pleistocene. The continental ice sheet advanced over the foothills and up major valleys reaching its maximum extent, ca. 30 ka. B. P. This took place when Cordilleran glaciers were in their initial stages of development. The Laurentide Ice Sheet blocked the drainage of the South Nahanni River near Virginia Falls, forming a glacial lake which inundated an area of approximately 900 km2 at its maximum stand, and had an outlet to the southwest, across the continental divide into the Yukon Territory and eventually into the Pacific Ocean. Lacustrine sediments at various sites reach thicknesses ranging from 110 to 120 metres, at an elevation of around 700 m. Cordilleran glaciers advanced eastward and approximately 5000 years later blocked this southwestward drainage, rerouting it to the east and north along the Mackenzie Mountain front. The drainage was confined between the mountains and continental ice margin where it incised major canyons into the limestone bedrock, and produced a spectacular karst landscape, which today forms part of the Nahanni National Park. During the retreat of the Laurentide and advance of Cordilleran glaciers, glacial Lake Nahanni cut an outlet to the east at First Canyon. This outlet drained into a continuous northbound network of marginal meltwater channels joining the north-flowing drainage that eventually reached the Arctic Ocean, and during further retreat of the ice sheet established the Mackenzie River in its modern location. The presence of Laurentide ice in this region is evidenced by large granite boulders carried from the Canadian Shield. Erratics are found up to 100 km west of the mountain front. Neotectonic activity in the area is interpreted from exposures such as those

  18. What happened to the coal forests during Pennsylvanian glacial phases?

    SciTech Connect

    Falcon-Lang, H.J.; Dimichele, W.A.

    2010-09-15

    Sequence stratigraphic analysis of Pennsylvanian coal-bearing strata suggests that glacial-interglacial fluctuations at high latitudes drove cyclic changes in tropical biomes. A literature review of plant assemblages in this paleoclimatic context suggests that coal forests dominated during humid interglacial phases, but were replaced by seasonally dry vegetation during glacial phases. After each glacial event, coal forests reassembled with largely the same species composition. This remarkable stasis implies that coal-forest refugia existed across the equatorial landscape during glacial phases, expanding to repopulate lowlands during and following deglaciation. One possibility is that refugia comprised small pockets of wetland forest strung out along valleys at some sites, but data are currently insufficient to test this hypothesis. The model presented here, if accepted, dramatically alters our understanding of the coal forests and helps explain aspects of their dynamics.

  19. Glacial history of the North Atlantic marine snail, Littorina saxatilis, inferred from distribution of mitochondrial DNA lineages.

    PubMed

    Panova, Marina; Blakeslee, April M H; Miller, A Whitman; Mäkinen, Tuuli; Ruiz, Gregory M; Johannesson, Kerstin; André, Carl

    2011-01-01

    The North Atlantic intertidal gastropod, Littorina saxatilis (Olivi, 1792), exhibits extreme morphological variation between and within geographic regions and has become a model for studies of local adaptation; yet a comprehensive analysis of the species' phylogeography is lacking. Here, we examine phylogeographic patterns of the species' populations in the North Atlantic and one remote Mediterranean population using sequence variation in a fragment of the mitochondrial cytochrome b gene (607 bp). We found that, as opposed to many other rocky intertidal species, L. saxatilis has likely had a long and continuous history in the Northwest Atlantic, including survival during the last glacial maximum (LGM), possibly in two refugia. In the Northeast Atlantic, several areas likely harboured refugial populations that recolonized different parts of this region after glacial retreat, resulting in strong population structure. However, the outlying monomorphic Venetian population is likely a recent anthropogenic introduction from northern Europe and not a remnant of an earlier wider distribution in the Mediterranean Sea. Overall, our detailed phylogeography of L. saxatilis adds an important piece to the understanding of Pleistocene history in North Atlantic marine biota as well as being the first study to describe the species' evolutionary history in its natural range. The latter contribution is noteworthy because the snail has recently become an important model species for understanding evolutionary processes of speciation; thus our work provides integral information for such endeavours. PMID:21412417

  20. Glacial history of the North Atlantic marine snail, Littorina saxatilis, inferred from distribution of mitochondrial DNA lineages.

    PubMed

    Panova, Marina; Blakeslee, April M H; Miller, A Whitman; Mäkinen, Tuuli; Ruiz, Gregory M; Johannesson, Kerstin; André, Carl

    2011-01-01

    The North Atlantic intertidal gastropod, Littorina saxatilis (Olivi, 1792), exhibits extreme morphological variation between and within geographic regions and has become a model for studies of local adaptation; yet a comprehensive analysis of the species' phylogeography is lacking. Here, we examine phylogeographic patterns of the species' populations in the North Atlantic and one remote Mediterranean population using sequence variation in a fragment of the mitochondrial cytochrome b gene (607 bp). We found that, as opposed to many other rocky intertidal species, L. saxatilis has likely had a long and continuous history in the Northwest Atlantic, including survival during the last glacial maximum (LGM), possibly in two refugia. In the Northeast Atlantic, several areas likely harboured refugial populations that recolonized different parts of this region after glacial retreat, resulting in strong population structure. However, the outlying monomorphic Venetian population is likely a recent anthropogenic introduction from northern Europe and not a remnant of an earlier wider distribution in the Mediterranean Sea. Overall, our detailed phylogeography of L. saxatilis adds an important piece to the understanding of Pleistocene history in North Atlantic marine biota as well as being the first study to describe the species' evolutionary history in its natural range. The latter contribution is noteworthy because the snail has recently become an important model species for understanding evolutionary processes of speciation; thus our work provides integral information for such endeavours.

  1. Glacial bed forms at Findelengletscher, Zermatt, Switzerland

    NASA Astrophysics Data System (ADS)

    Madella, Andrea; Nyffenegger, Franziska; Schlüchter, Christian

    2013-04-01

    The current glacier meltdown is increasingly unveiling the glacial bed forms produced by the most recent glacial advance of the 1980ies, such as flutes, mega-flutes and drumlins. This is a challenging opportunity to study these morphologies and the processes involved in their formation; in addition, our observation suggests a new question to be answered: why can't any of these features in units belonging to previous glacial advances be recognised? Similar forms could either have been washed away already, or never been built during LGM and since. The most beautiful and evident of the forms under investigation are the flutes and mega-flutes: elongated streamlined ridges of sediments either starting from an obstacle or just sticking out of the basal lodgement till. The way flutes have been initiated and then evolve is still partially unknown, due to their variety in shape, size and material. The glacial forefield at Findelengletscher under investigation deglaciated over the past two years, offers a well-preserved variety of such forms at all scales. Their material (basal lodgement till) is homogeneous and consistent all over the site, as well as their fabric. In addition, this silty sand shows a low plasticity index. These preliminary results support the idea that flutes build up very quickly during repeated seasonal advances in thin ice conditions with retreating trend (Coray, 2007), and that they could be equally easily and rapidly washed away. References: Coray Sandro (2007): Genesis and significance of flutes at Findelengletscher, Valais, Switzerland, Institute of Geological Sciences, University of Bern.

  2. Kennebunk glacial advance: A reappraisal

    NASA Astrophysics Data System (ADS)

    Smith, Geoffrey W.

    1981-06-01

    Evidence for the Kennebunk glacial advance (readvance) in southwestern Maine is discussed in light of recent geologic mapping. Orientations of glacially produced lineations record the response of ice to major topographic controls and do not indicate glacial readvance. Minor end moraines and large stratified end moraines associated with deformed marine sediments of the Presumpscot Formation occur throughout the southwestern coastal zone. These features outline the general pattern of ice retreat from this part of the coastal zone and suggest that withdrawal of the last ice from southwestern Maine occurred with minor stillstands and local frontal fluctuations but without significant readvance. The Kennebunk glacial advance (readvance) appears to have been one of many local fluctuations of the ice front during general recession, occurring at about 13,200 yr B.P.

  3. The last glacial maximum

    USGS Publications Warehouse

    Clark, P.U.; Dyke, A.S.; Shakun, J.D.; Carlson, A.E.; Clark, J.; Wohlfarth, B.; Mitrovica, J.X.; Hostetler, S.W.; McCabe, A.M.

    2009-01-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ???14.5 ka.

  4. The Last Glacial Maximum.

    PubMed

    Clark, Peter U; Dyke, Arthur S; Shakun, Jeremy D; Carlson, Anders E; Clark, Jorie; Wohlfarth, Barbara; Mitrovica, Jerry X; Hostetler, Steven W; McCabe, A Marshall

    2009-08-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level approximately 14.5 ka.

  5. Direct evidence of central European forest refugia during the last glacial period based on mollusc fossils

    NASA Astrophysics Data System (ADS)

    Juřičková, Lucie; Horáčková, Jitka; Ložek, Vojen

    2014-07-01

    Although there is evidence from molecular studies for the existence of central European last glacial refugia for temperate species, there is still a great lack of direct fossil records to confirm this theory. Here we bring such evidence in the form of fossil shells from twenty strictly forest land snail species, which were recorded in radiocarbon-dated late glacial or older mollusc assemblages of nine non-interrupted mollusc successions situated in the Western Carpathians, and one in the Bohemian Massif. We proposed that molluscs survived the last glacial period in central Europe in isolated small patches of broadleaf forest, which we unequivocally demonstrate for two sites of last glacial maximum age.

  6. Spatial patterns of AFLP diversity in Bulbophyllum occultum (Orchidaceae) indicate long-term refugial isolation in Madagascar and long-distance colonization effects in La Réunion.

    PubMed

    Jaros, U; Fischer, G A; Pailler, T; Comes, H P

    2016-05-01

    Bulbophyllum occultum, an epiphytic orchid mainly distributed in the rainforests of (north)eastern Madagascar and La Réunion, represents an interesting model case for testing the effects of anthropogenic vs historical (e.g., climate induced) habitat isolation and long-distance colonization on the genetic structure of plant species with disjunct distributions in the Madagascan region. To this aim, we surveyed amplified fragment length polymorphisms (AFLPs) across 13 populations in Madagascar and nine in La Réunion (206 individuals in total). We found overall high levels of population subdivision (Φ(PT)=0.387) and low within-population diversity (H(E), range: 0.026-0.124), indicating non-equilibrium conditions in a mainly selfing species. There was no impact of recent deforestation (Madagascar) or habitat disturbance (La Réunion) detectable on AFLP diversity. K-means clustering and BARRIER analyses identified multiple gene pools and several genetic breaks, both within and among islands. Inter-island levels of population genetic diversity and subdivision were similar, whereby inter-individual divergence in flower colour explained a significant part of gene pool divergence in La Réunion. Our results suggest that (i) B. occultum persisted across multiple isolated ('refugial') regions along the eastern rainforest corridor of Madagascar over recent climatic cycles and (ii) populations in La Réunion arose from either single or few independent introductions from Madagascar. High selfing rates and sufficient time for genetic drift likely promoted unexpectedly high population genetic and phenotypic (flower colour) differentiation in La Réunion. Overall, this study highlights a strong imprint of history on the genetic structure of a low-gene-dispersing epiphytic orchid from the Madagascan region. PMID:26883184

  7. Spatial patterns of AFLP diversity in Bulbophyllum occultum (Orchidaceae) indicate long-term refugial isolation in Madagascar and long-distance colonization effects in La Réunion.

    PubMed

    Jaros, U; Fischer, G A; Pailler, T; Comes, H P

    2016-05-01

    Bulbophyllum occultum, an epiphytic orchid mainly distributed in the rainforests of (north)eastern Madagascar and La Réunion, represents an interesting model case for testing the effects of anthropogenic vs historical (e.g., climate induced) habitat isolation and long-distance colonization on the genetic structure of plant species with disjunct distributions in the Madagascan region. To this aim, we surveyed amplified fragment length polymorphisms (AFLPs) across 13 populations in Madagascar and nine in La Réunion (206 individuals in total). We found overall high levels of population subdivision (Φ(PT)=0.387) and low within-population diversity (H(E), range: 0.026-0.124), indicating non-equilibrium conditions in a mainly selfing species. There was no impact of recent deforestation (Madagascar) or habitat disturbance (La Réunion) detectable on AFLP diversity. K-means clustering and BARRIER analyses identified multiple gene pools and several genetic breaks, both within and among islands. Inter-island levels of population genetic diversity and subdivision were similar, whereby inter-individual divergence in flower colour explained a significant part of gene pool divergence in La Réunion. Our results suggest that (i) B. occultum persisted across multiple isolated ('refugial') regions along the eastern rainforest corridor of Madagascar over recent climatic cycles and (ii) populations in La Réunion arose from either single or few independent introductions from Madagascar. High selfing rates and sufficient time for genetic drift likely promoted unexpectedly high population genetic and phenotypic (flower colour) differentiation in La Réunion. Overall, this study highlights a strong imprint of history on the genetic structure of a low-gene-dispersing epiphytic orchid from the Madagascan region.

  8. Spatial patterns of AFLP diversity in Bulbophyllum occultum (Orchidaceae) indicate long-term refugial isolation in Madagascar and long-distance colonization effects in La Réunion

    PubMed Central

    Jaros, U; Fischer, G A; Pailler, T; Comes, H P

    2016-01-01

    Bulbophyllum occultum, an epiphytic orchid mainly distributed in the rainforests of (north)eastern Madagascar and La Réunion, represents an interesting model case for testing the effects of anthropogenic vs historical (e.g., climate induced) habitat isolation and long-distance colonization on the genetic structure of plant species with disjunct distributions in the Madagascan region. To this aim, we surveyed amplified fragment length polymorphisms (AFLPs) across 13 populations in Madagascar and nine in La Réunion (206 individuals in total). We found overall high levels of population subdivision (ΦPT=0.387) and low within-population diversity (HE, range: 0.026–0.124), indicating non-equilibrium conditions in a mainly selfing species. There was no impact of recent deforestation (Madagascar) or habitat disturbance (La Réunion) detectable on AFLP diversity. K-means clustering and BARRIER analyses identified multiple gene pools and several genetic breaks, both within and among islands. Inter-island levels of population genetic diversity and subdivision were similar, whereby inter-individual divergence in flower colour explained a significant part of gene pool divergence in La Réunion. Our results suggest that (i) B. occultum persisted across multiple isolated (‘refugial') regions along the eastern rainforest corridor of Madagascar over recent climatic cycles and (ii) populations in La Réunion arose from either single or few independent introductions from Madagascar. High selfing rates and sufficient time for genetic drift likely promoted unexpectedly high population genetic and phenotypic (flower colour) differentiation in La Réunion. Overall, this study highlights a strong imprint of history on the genetic structure of a low-gene-dispersing epiphytic orchid from the Madagascan region. PMID:26883184

  9. Glacial marine sedimentation: Paleoclimatic significance

    SciTech Connect

    Anderson, J.B.; Ashley, G.M.

    1991-01-01

    This publication resulted from a symposium held during the 1988 Annual Meeting of the Geological Society of America. Many, but not all, contributors to the symposium have papers in this volume. This Special Paper consists of 14 chapters and a Subject/Geographic index. Each chapter has is own list of references. The papers cover a wide range of modem climate/ ocean environments, including papers on glacial marine sediments from Antarctica, the fiords of Alaska, and sediments from the Canadian High Arctic. In addition, three papers discuss [open quote]old[close quotes] glacial marine records (i.e., pre-Tertiary), and one paper discusses the Yakataga Formation of the Gulf of Alaska which is a Miocene-to-late-Pleistocene sequence. The last chapter in the book includes a survey and summary of the evidence for the paleoclimatic significance of glacial marine sediments by the two editors, John Anderson and Gail Ashley. It is worth noting that Anderson and Domack state in the Foreword that there is a considerable variation in terminology; hence they employ a series of definitions which they urge the other authors to employ. They define and explain what they mean by [open quotes]polar ice cap,[close quotes] [open quote]polar tundra (subpolar),[close quotes] and [open quotes]temperate oceanic and boreal[close quotes] in terms of the dominant glacial and glacial marine processes. Although one might quarrel with the terminology, the broad differences between these three glaciological regimes are indeed fundamental and need to be sought in the geological record. The flavor of the volume can be judged by some of the chapter titles. Contributions on Antarctica include a paper by Anderson and other entitled [open quote]Sedimentary facies associated with Antarctica's floating ice masses[close quotes] and a companion paper by Anderson and Domack which deals with the extremely complex glacial marine facies (13 facies are delimited) in McMurdo Sound, Antarctica.

  10. Sub-glacial volcanic eruptions

    USGS Publications Warehouse

    White, Donald Edward

    1956-01-01

    The literature on sub-glacial volcanic eruptions and the related flood phenomena has been reviewed as a minor part of the larger problem of convective and conductive heat transfer from intrusive magma. (See Lovering, 1955, for a review of the extensive literature on this subject.) This summary of data on sub-glacial eruptions is part of a program that the U.S. Geological Survey is conducting in connection with its Investigations of Geologic Processes project on behalf of the Division of Research, U.S. Atomic Energy Commission.

  11. Bering Sea Porewaters and Late Glacial Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Mix, A. C.; McKay, J. L.; Ross, A.; Okazaki, Y.; Scientific Team of IODP Expedition 323

    2011-12-01

    The combination of high-resolution porewater d18O and chlorinity, benthic and planktonic foraminiferal d18O in IODP Sites U1339 (1870 m depth) and U1344 (3172 m depth) constrain late glacial circulation in the Bering Sea. During the Last Glacial Interval, the water column below 1800 m approached the freezing point, and upper ocean stratification was lower than today. Both scenarios point to likely local ventilation, associated with brine formation, during glacial time. An additional deep ventilation event may have occurred during late Holocene (Neoglacial?) time, evidenced by relatively low d18O and high chlorinity porewaters. Intervals of high biological productivity appear to be associated with relatively high upper-ocean stratification, perhaps implying a role for nutrients or micronutrients sourced from the continents.

  12. Tectonic control on the persistence of glacially sculpted topography.

    PubMed

    Prasicek, Günther; Larsen, Isaac J; Montgomery, David R

    2015-08-14

    One of the most fundamental insights for understanding how landscapes evolve is based on determining the extent to which topography was shaped by glaciers or by rivers. More than 10(4) years after the last major glaciation the topography of mountain ranges worldwide remains dominated by characteristic glacial landforms such as U-shaped valleys, but an understanding of the persistence of such landforms is lacking. Here we use digital topographic data to analyse valley shapes at sites worldwide to demonstrate that the persistence of U-shaped valleys is controlled by the erosional response to tectonic forcing. Our findings indicate that glacial topography in Earth's most rapidly uplifting mountain ranges is rapidly replaced by fluvial topography and hence valley forms do not reflect the cumulative action of multiple glacial periods, implying that the classic physiographic signature of glaciated landscapes is best expressed in, and indeed limited by, the extent of relatively low-uplift terrain.

  13. Tectonic control on the persistence of glacially sculpted topography

    PubMed Central

    Prasicek, Günther; Larsen, Isaac J.; Montgomery, David R.

    2015-01-01

    One of the most fundamental insights for understanding how landscapes evolve is based on determining the extent to which topography was shaped by glaciers or by rivers. More than 104 years after the last major glaciation the topography of mountain ranges worldwide remains dominated by characteristic glacial landforms such as U-shaped valleys, but an understanding of the persistence of such landforms is lacking. Here we use digital topographic data to analyse valley shapes at sites worldwide to demonstrate that the persistence of U-shaped valleys is controlled by the erosional response to tectonic forcing. Our findings indicate that glacial topography in Earth's most rapidly uplifting mountain ranges is rapidly replaced by fluvial topography and hence valley forms do not reflect the cumulative action of multiple glacial periods, implying that the classic physiographic signature of glaciated landscapes is best expressed in, and indeed limited by, the extent of relatively low-uplift terrain. PMID:26271245

  14. Tectonic control on the persistence of glacially sculpted topography.

    PubMed

    Prasicek, Günther; Larsen, Isaac J; Montgomery, David R

    2015-01-01

    One of the most fundamental insights for understanding how landscapes evolve is based on determining the extent to which topography was shaped by glaciers or by rivers. More than 10(4) years after the last major glaciation the topography of mountain ranges worldwide remains dominated by characteristic glacial landforms such as U-shaped valleys, but an understanding of the persistence of such landforms is lacking. Here we use digital topographic data to analyse valley shapes at sites worldwide to demonstrate that the persistence of U-shaped valleys is controlled by the erosional response to tectonic forcing. Our findings indicate that glacial topography in Earth's most rapidly uplifting mountain ranges is rapidly replaced by fluvial topography and hence valley forms do not reflect the cumulative action of multiple glacial periods, implying that the classic physiographic signature of glaciated landscapes is best expressed in, and indeed limited by, the extent of relatively low-uplift terrain. PMID:26271245

  15. Phosphorus burial in the ocean over glacial-interglacial time scales

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2009-04-01

    The role of nutrients, such as phosphorus (P), and their impact on primary productivity and the fluctuations in atmospheric CO2 over glacial-interglacial periods are intensely debated. Suggestions as to the importance of P evolved from an earlier proposal that P actively participated in changing productivity rates and therefore climate change, to most recent ones that changes in the glacial ocean inventory of phosphorus were important but not influential if compared to other macronutrients, such as nitrate. Using new data coming from a selection of ODP sites, we analyzed the distribution of oceanic P sedimentary phases and calculate reactive P burial fluxes, and we show how P burial fluxes changed over the last glacial-interglacial period at these sites. Concentrations of reactive P are generally lower during glacial times, while mass accumulation rates (MAR) of reactive P show higher variability. If we extrapolate for the analyzed sites, we may assume that in general glacial burial fluxes of reactive P are lower than those during interglacial periods by about 8%, because the lack of burial of reactive P on the glacial shelf reduced in size, was apparently not compensated by burial in other regions of the ocean. Using the calculated changes in P burial, we evaluate their possible impact on the phosphate inventory in the world oceans. Using a simple mathematical approach, we find that these changes alone could have increased the phosphate inventory of glacial ocean waters by 17-40% compared to interglacial stages. Variations in the distribution of sedimentary P phases at the investigated sites seem to indicate that at the onset of interglacial stages, shallower sites experienced an increase in reactive P concentrations, which seems to point to P-richer waters at glacial terminations. All these findings would support the Shelf-Nutrient Hypothesis, which assumes that during glacial low stands nutrients are transferred from shallow sites to deep sea with possible

  16. Genome-wide set of SNPs reveals evidence for two glacial refugia and admixture from postglacial recolonization in an alpine ungulate.

    PubMed

    Sim, Zijian; Hall, Jocelyn C; Jex, Bill; Hegel, Troy M; Coltman, David W

    2016-08-01

    Past glaciation events have played a major role in shaping the genetic diversity and distribution of wild sheep in North America. The advancement of glaciers can isolate populations in ice-free refugia, where they can survive until the recession of ice sheets. The major Beringian refugium is thought to have held thinhorn sheep (Ovis dalli) populations during times of glacial advance. While isolation in the major refugium can account for much of the genetic and morphological diversity seen in extant thinhorn sheep populations, mounting evidence suggests the persistence of populations in smaller minor refugia. We investigated the refugial origins of thinhorn sheep using ~10 000 SNPs obtained via a cross-species application of the domestic sheep ovine HD BeadChip to genotype 52 thinhorn sheep and five bighorn sheep (O. canadensis) samples. Phylogenetic inference revealed a distinct lineage of thinhorn sheep inhabiting British Columbia, which is consistent with the survival of a group of thinhorn sheep in a minor refugium separate from the Beringian refugium. Isolation in separate glacial refugia probably mediated the evolution of the two thinhorn sheep subspecies, the white Dall's sheep (O. d. dalli), which persisted in Beringia, and the dark Stone's sheep (O. d. stonei), which utilized the minor refugium. We also found the first genetic evidence for admixture between sheep from different glacial refugia in south-central Yukon as a consequence of post glacial expansion and recolonization. These results show that glaciation events can have a major role in the evolution of species inhabiting previously glaciated habitats and the need to look beyond established refugia when examining the evolutionary history of such species.

  17. Genome-wide set of SNPs reveals evidence for two glacial refugia and admixture from postglacial recolonization in an alpine ungulate.

    PubMed

    Sim, Zijian; Hall, Jocelyn C; Jex, Bill; Hegel, Troy M; Coltman, David W

    2016-08-01

    Past glaciation events have played a major role in shaping the genetic diversity and distribution of wild sheep in North America. The advancement of glaciers can isolate populations in ice-free refugia, where they can survive until the recession of ice sheets. The major Beringian refugium is thought to have held thinhorn sheep (Ovis dalli) populations during times of glacial advance. While isolation in the major refugium can account for much of the genetic and morphological diversity seen in extant thinhorn sheep populations, mounting evidence suggests the persistence of populations in smaller minor refugia. We investigated the refugial origins of thinhorn sheep using ~10 000 SNPs obtained via a cross-species application of the domestic sheep ovine HD BeadChip to genotype 52 thinhorn sheep and five bighorn sheep (O. canadensis) samples. Phylogenetic inference revealed a distinct lineage of thinhorn sheep inhabiting British Columbia, which is consistent with the survival of a group of thinhorn sheep in a minor refugium separate from the Beringian refugium. Isolation in separate glacial refugia probably mediated the evolution of the two thinhorn sheep subspecies, the white Dall's sheep (O. d. dalli), which persisted in Beringia, and the dark Stone's sheep (O. d. stonei), which utilized the minor refugium. We also found the first genetic evidence for admixture between sheep from different glacial refugia in south-central Yukon as a consequence of post glacial expansion and recolonization. These results show that glaciation events can have a major role in the evolution of species inhabiting previously glaciated habitats and the need to look beyond established refugia when examining the evolutionary history of such species. PMID:27272944

  18. The Arctic: Glacial Refugium or Area of Secondary Contact? Inference from the Population Genetic Structure of the Thick-Billed Murre (Uria lomvia), with Implications for Management.

    PubMed

    Tigano, Anna; Damus, Martin; Birt, Tim P; Morris-Pocock, Jamie A; Artukhin, Yuri B; Friesen, Vicki L

    2015-01-01

    Quaternary glaciations affected the distribution of many species. Here, we investigate whether the Arctic represented a glacial refugium during the Last Glacial Maximum or an area of secondary contact following the ice retreat, by analyzing the genetic population structure of the thick-billed murre (Uria lomvia), a seabird that breeds throughout the North Atlantic, North Pacific and Arctic Oceans. The thick-billed murre is a species of socio-economic importance and faces numerous threats including hunting, oil pollution, gill netting, and climate change. We compared variation in the mitochondrial DNA (mtDNA) control region (n = 424), supplemented by 4 microsatellite loci (n = 445), among thick-billed murres sampled throughout their range. MtDNA data indicated that colonies comprise 4 genetically differentiated groups (Φst = 0.11-0.81): 1) Atlantic Ocean plus New Siberian Islands region, 2) Cape Parry, 3) Chukchi Sea, and 4) Pacific Ocean. Microsatellite variation differed between Atlantic and Pacific populations. Otherwise, little substructure was found within either ocean. Atlantic and Pacific populations appear to have been genetically isolated since the last interglacial period and should be considered separate evolutionary significant units for management. The Chukchi Sea and Cape Parry appear to represent areas of secondary contact, rather than arctic refugial populations.

  19. Geothermal activity helps life survive glacial cycles.

    PubMed

    Fraser, Ceridwen I; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L

    2014-04-15

    Climate change has played a critical role in the evolution and structure of Earth's biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this "geothermal glacial refugia" hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species.

  20. Geothermal activity helps life survive glacial cycles

    PubMed Central

    Fraser, Ceridwen I.; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L.

    2014-01-01

    Climate change has played a critical role in the evolution and structure of Earth’s biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this “geothermal glacial refugia” hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species. PMID:24616489

  1. Geothermal activity helps life survive glacial cycles.

    PubMed

    Fraser, Ceridwen I; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L

    2014-04-15

    Climate change has played a critical role in the evolution and structure of Earth's biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this "geothermal glacial refugia" hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species. PMID:24616489

  2. Imprints of multiple glacial refugia in the Pyrenees revealed by phylogeography and palaeodistribution modelling of an endemic spider.

    PubMed

    Bidegaray-Batista, Leticia; Sánchez-Gracia, Alejandro; Santulli, Giulia; Maiorano, Luigi; Guisan, Antoine; Vogler, Alfried P; Arnedo, Miquel A

    2016-05-01

    Mediterranean mountain ranges harbour highly endemic biota in islandlike habitats. Their topographic diversity offered the opportunity for mountain species to persist in refugial areas during episodes of major climatic change. We investigate the role of Quaternary climatic oscillations in shaping the demographic history and distribution ranges in the spider Harpactocrates ravastellus, endemic to the Pyrenees. Gene trees and multispecies coalescent analyses on mitochondrial and nuclear DNA sequences unveiled two distinct lineages with a hybrid zone around the northwestern area of the Catalan Pyrenees. The lineages were further supported by morphological differences. Climatic niche-based species distribution models (SDMs) identified two lowland refugia at the western and eastern extremes of the mountain range, which would suggest secondary contact following postglacial expansion of populations from both refugia. Neutrality test and approximate Bayesian computation (ABC) analyses indicated that several local populations underwent severe bottlenecks followed by population expansions, which in combination with the deep population differentiation provided evidence for population survival during glacial periods in microrefugia across the mountain range, in addition to the main Atlantic and Mediterranean (western and eastern) refugia. This study sheds light on the complexities of Quaternary climatic oscillations in building up genetic diversity and local endemicity in the southern Europe mountain ranges.

  3. Imprints of multiple glacial refugia in the Pyrenees revealed by phylogeography and palaeodistribution modelling of an endemic spider.

    PubMed

    Bidegaray-Batista, Leticia; Sánchez-Gracia, Alejandro; Santulli, Giulia; Maiorano, Luigi; Guisan, Antoine; Vogler, Alfried P; Arnedo, Miquel A

    2016-05-01

    Mediterranean mountain ranges harbour highly endemic biota in islandlike habitats. Their topographic diversity offered the opportunity for mountain species to persist in refugial areas during episodes of major climatic change. We investigate the role of Quaternary climatic oscillations in shaping the demographic history and distribution ranges in the spider Harpactocrates ravastellus, endemic to the Pyrenees. Gene trees and multispecies coalescent analyses on mitochondrial and nuclear DNA sequences unveiled two distinct lineages with a hybrid zone around the northwestern area of the Catalan Pyrenees. The lineages were further supported by morphological differences. Climatic niche-based species distribution models (SDMs) identified two lowland refugia at the western and eastern extremes of the mountain range, which would suggest secondary contact following postglacial expansion of populations from both refugia. Neutrality test and approximate Bayesian computation (ABC) analyses indicated that several local populations underwent severe bottlenecks followed by population expansions, which in combination with the deep population differentiation provided evidence for population survival during glacial periods in microrefugia across the mountain range, in addition to the main Atlantic and Mediterranean (western and eastern) refugia. This study sheds light on the complexities of Quaternary climatic oscillations in building up genetic diversity and local endemicity in the southern Europe mountain ranges. PMID:26878195

  4. Characterization methods for fractured glacial tills

    USGS Publications Warehouse

    Haefner, R.J.

    2000-01-01

    This paper provides a literature review of methods successfully employed to characterize finegrained and fractured or unfractured glacial deposits. Descriptions and examples are given for four major categories of characterization methods: physical, hydraulic, chemical, and indirect. Characterization methods have evolved significantly within the past ten years; however, there still exists uncertainty about the reliability of individual characterization methods applied to till deposits. Therefore, a combination of methods is best, the choice of which depends on the objectives of the work. Sampling methods, sampling scales, and reporting methods are extremely important and should be considered when interpreting and comparing results between sites. Recognition of these issues is necessary to ensure that decisions regarding the transport of fluids in fractured tills are not based on the assumption that poorly permeable tills are always an inhibitor of subsurface flow.

  5. Extraterrestrial accretion and glacial cycles

    NASA Technical Reports Server (NTRS)

    Muller, R. A.

    1994-01-01

    We propose that the approx. 100-k.y. cycle seen in terrestrial glaciation is due to changes in meteor flux that come from changes in the Earth's orbit. This model can explain a 70-k.y. 'anomalous' period in climate data and the apparent discrepancy between present extraterrestrial fluxes and those in oceanic sediments. It can be tested by measuring Ir densities in sediments and ice during glacials and interglacials.

  6. Glacial modification of granite tors in the Cairngorms, Scotland

    USGS Publications Warehouse

    Hall, A.M.; Phillips, W.M.

    2006-01-01

    A range of evidence indicates that many granite tors in the Cairngorms have been modified by the flow of glacier ice during the Pleistocene. Comparisons with SW England and the use of a space-time transformation across 38 tor groups in the Cairngorms allow a model to be developed for progressive glacial modification. Tors with deeply etched surfaces and no, or limited, block removal imply an absence of significant glacial modification. The removal of superstructure and blocks, locally forming boulder trains, and the progressive reduction of tors to stumps and basal slabs represent the more advanced stages of modification. Recognition of some slabs as tor stumps from which glacial erosion has removed all superstructure allows the original distribution of tors to be reconstructed for large areas of the Cairngorms. Unmodified tors require covers of non-erosive, cold-based ice during all of the cold stages of the Middle and Late Pleistocene. Deformation beneath cold-based glacier ice is capable of the removal of blocks but advanced glacial modification requires former wet-based glacier ice. The depth of glacial erosion at former tor sites remains limited largely to the partial or total elimination of the upstanding tor form. Cosmogenic nuclide exposure ages (Phillips et al., 2006) together with data from weathering pit depths (Hall and Phillips, 2006), from the surfaces of tors and large erratic blocks require that the glacial entrainment of blocks from tors occurred in Marine Isotope Stages (MIS) 4-2, 6 and, probably, at least one earlier phase. The occurrence of glacially modified tors on or close to, the main summits of the Cairngorms requires full ice cover over the mountains during these Stages. Evidence from the Cairngorms indicates that tor morphology can be regarded as an important indicator of former ice cover in many formerly glaciated areas, particularly where other evidence of ice cover is sparse. Recognition of the glacial modification of tors is important

  7. Contrasted evolution of glacial lakes along the Hindu Kush Himalaya mountain range between 1990 and 2009

    NASA Astrophysics Data System (ADS)

    Gardelle, Julie; Arnaud, Yves; Berthier, Etienne

    2011-01-01

    In this study, we present a first regional assessment of glacial lake distribution and evolution in the Hindu Kush Himalaya (HKH). Seven sites have been selected between Bhutan and Afghanistan, to capture the climatic variability along the 2000-km long mountain range. For each site, glacial lakes have been mapped with LANDSAT satellite imagery acquired in 1990, 2000 and 2009, using an automatic classification. In the East (India, Nepal and Bhutan), glacial lakes are bigger and more numerous than in the West (Pakistan, Afghanistan), and have grown continuously between 1990 and 2009 by 20% to 65%. On the other hand, during the same period, the glacial lake coverage has shrunk in the Hindu Kush (-50%) and the Karakorum (-30%). This east/west pattern of lake changes seems in agreement with sparse glaciological measurements that suggest less (or even no) ice loss in the western part of the HKH.

  8. Glacial Isostatic Adjustment Observed with VLBI and SLR

    NASA Technical Reports Server (NTRS)

    Argus, D.; Peltier, W.; Watkins, M.

    1999-01-01

    In global geodetic solutions vertical rates of site motion are usually estimated relative to the geocenter (center of figure) of the solid earth. The velocity of the geocenter is estimated assuming that the plates are rigid, that the velocities of the plates equal those in NUVEL-1A (DeMets et al. 1990, 1994) and that the uplift, subsidence, and intraplate deformation due to glacial isostatic adjustment is negligible.

  9. Glacial-Holocene Deep Atlantic Variability

    NASA Astrophysics Data System (ADS)

    Oppo, D.; Curry, W. B.; Huang, K.; Gebbie, G.; Keigwin, L. D.

    2012-12-01

    Despite decades of research on deep ocean circulation during the Last Glacial Maximum (LGM) and deglaciation, many uncertainties remain. Even first order questions such as whether Antarctic Intermediate Water (AAIW) influenced the North Atlantic in the past are unresolved. Here, we update the glacial western Atlantic benthic δ13C transect of Curry and Oppo (2005) including new data from four cores recovered between 450 and 1100 m water depth, at AAIW depths in the western tropical North Atlantic. Low glacial values are consistent with the presence of AAIW. However, in the modern ocean, remineralization of organic matter drives δ13C values at these water depths lower than expected from their end-member composition. As this may have also been the case in the past, insights from more conservative tracers like δ18O of calcite, the air-sea exchange δ13C signature (δ13Cas), and neodymium isotopes (ɛNd) are important. We evaluate new and published relevant data and present a new δ13Cas transect for the LGM (updated from Marchitto and Broecker, 2006). A preliminary inversion of LGM data using an ocean pathways model (Gebbie and Huybers, 2010) will be presented. δ13C values in these same four western tropical North Atlantic cores during the Heinrich Event are also consistent with, but may not require, a contribution of AAIW. δ13C values decrease further following the Heinrich event and remain low throughout the deglaciation, during which the records exhibit coherent millennial-scale oscillations. For much of the deglaciation, δ13C values in these cores appear to be lower than values at other sites from similar depths in the western North and South Atlantic, suggestive of non-conservative behavior. The benthic records exhibit high amplitude δ18O variability, which may reflect vertical movement of isopynals, in association with variations in geostrophic flow (e.g. Lynch-Stieglitz et al., 2011). Our new deglacial data will be discussed in the broader context of

  10. Displaced phylogeographic signals from Gyrodactylus arcuatus, a parasite of the three-spined stickleback Gasterosteus aculeatus, suggest freshwater glacial refugia in Europe.

    PubMed

    Lumme, Jaakko; Mäkinen, Hannu; Ermolenko, Alexey V; Gregg, Jacob L; Ziętara, Marek S

    2016-08-01

    We examined the global mitochondrial phylogeography of Gyrodactylus arcuatus, a flatworm ectoparasite of three-spined stickleback Gasterosteus aculeatus. In accordance with the suggested high divergence rate of 13%/million years, the genetic variation of the parasite was high: haplotype diversity h=0.985 and nucleotide diversity π=0.0161. The differentiation among the parasite populations was substantial (Φst=0.759), with two main allopatric clades (here termed Euro and North) accounting for 54% of the total genetic variation. The diversity center of the Euro clade was in the Baltic Sea, while the North clade was spread across the Barents and White Seas. A single haplotype within the North clade was found in the western and eastern Pacific Ocean. Divergence of main clades was estimated to be circa 200 thousand years ago. Each main clade was further divided into six distinct subclades, estimated to have diverged in isolation since 135 thousand years ago. This second division corresponds approximately to the Eemian interglacial predating the last glacial maximum. A demographic expansion of the subclades is associated with colonisation of northern Europe since the last glacial maximum, circa 15-40 thousand years ago. The parasite phylogeny is most likely explained by sequential isolated bottlenecks and expansions in numerous allopatric refugia. The postglacial intermingling and high variation in the marine parasite populations, separately in the Baltic and Barents Seas, suggest low competition of divergent parasite matrilines, coupled with a large population size and high rate of dispersal of hosts. The genetic contribution of the assumed refugial fish populations maintaining the parasite during the last glacial maximum was not detected among the marine sticklebacks, which perhaps were infected after range expansion. PMID:27155331

  11. Tracing the glacial sulphur cycle

    NASA Astrophysics Data System (ADS)

    Hansson, M. E.; Jonsell, U.; Bigler, M.; de Angelis, M.; Fischer, H.; Siggaard-Andersen, M.-L.; Steffensen, J. P.; Udisti, R.; Wolff, E.

    2003-04-01

    Sulphate aerosols are playing a major role in climate forcing in the present atmosphere and therefore possibly also during other climatic stages. The deposition of sulphur-containing species onto polar ice sheets provides a tool for determining variations in the sulphur cycle in the past. Relatively short atmospheric residence times for sulphate aerosols cause spatial gradients and a high sensitivity to variations in the general circulation of the atmosphere and the hydrological cycle. Several factors may influence the air-snow transfer functions and post-depositional process may modify the deposited signal. Therefore, both a large spatial and temporal coverage is needed to identify significant changes in the sulphur cycle in the past. The EPICA Dome C ice core from Antarctica is providing the longest records ever, spanning several glacial cycles. Unique high-resolution chemical records, from discontinuous samples analysed by Ion Chromatography (IC), are gradually evolving from the cooperation between the laboratories in the EPICA Chemistry Consortium. The EPICA DML ice core is analysed in parallel by the same laboratories and the profiles are growing with the progress of the drilling each season. The sulphate and methane sulphonate records are here in focus and will be presented as far as they reach at present. High-resolution chemical records are now also available from the NorthGRIP ice core from Greenland spanning the last glacial cycle. An interhemispheric comparison of sulphur-containing species during the glacial period will be presented, using both new high-resolution data and previous ice core data from a few locations as well as initial results from sulphur isotope measurements, with the aim to increase our understanding of variations in the global sulphur cycle with climate change.

  12. Phosphorus burial in the ocean over glacial-interglacial time scales

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2008-12-01

    The role of nutrients and their impact on primary productivity and the fluctuations in atmospheric CO2 over glacial-interglacial periods are intensely debated. One of the cornerstones is the role of phosphorus (P; in the form of phosphate). Suggestions as to the importance of P evolved from an earlier proposal that P actively participated in changing productivity rates and therefore climate change, to the most recent one that changes in the glacial ocean inventory of phosphorus were small and not influential if compared to other macronutrients, such as nitrogen. Using new data coming from a selection of ODP sites, we illustrate oceanic P sedimentary phases distribution and reactive P burial fluxes, and we show how P burial fluxes changed over the last glacial-interglacial period. Concentrations of reactive P are generally lower during glacial times, while mass accumulation rates (MAR) show higher variability. On a global scale, glacial burial fluxes of reactive P are lower than those during interglacial periods by 7-10%, because lack of burial of reactive P on the glacial reduced shelf was apparently not compensated by burial in other regions of the ocean. Using the calculated changes in P burial, we try to infer their possible impact on the phosphate inventory in the world oceans. Using a simple mathematical approach, we find that these changes alone could have increased the phosphate inventory of glacial ocean waters by 20-40% compared to interglacial stages. Variations in the C/P reactive ratios and in the P sedimentary phases distribution at the investigated sites seem to indicate that at the onset of interglacial stages, shallower sites experienced an increase in reactive P concentrations. This seems to point to P-richer waters at glacial terminations, supporting the shelf-nutrient hypothesis and giving phosphorus a role as a potential player in climate change.

  13. 20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U.S.A.

    USGS Publications Warehouse

    Molnia, B.F.; Post, A.; Carlson, P.R.

    1996-01-01

    Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacific Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake's basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of "present-day" glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake. In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations

  14. Preformed Nitrate in the Glacial North Atlantic

    NASA Astrophysics Data System (ADS)

    Homola, K.; Spivack, A. J.; D'Hondt, S.; Estes, E. R.; Insua, T. L.; McKinley, C. C.; Murray, R. W.; Pockalny, R. A.; Robinson, R. S.; Sauvage, J.

    2015-12-01

    Atmospheric CO2 abundances are highly correlated with global temperature variations over the past 800,000 years. Consequently, understanding the feedbacks between climate and CO2 is important for predictions of future climate. Leading hypotheses to explain this feedback invoke changes in ocean biology, circulation, chemistry, and/or gas exchange rates to trap CO2 in the deep ocean, thereby reducing the greenhouse effect of CO2 in the atmosphere. To test these hypotheses, we use sediment pore water profiles of dissolved nitrate and oxygen to reconstruct paleo-preformed nitrate concentrations at two deep-water sites in the western North Atlantic (23°N 57°W, 5557 m water depth; 30°N 58°W, 5367 m water depth). Preformed nitrate increases down-core to 22.7 μM (25.6 m core depth) at the northern site, and to 28.5 μM (27.8 m core depth) at the southern site. The large preformed nitrate gradient between these sites reveals a paleo-boundary between a southern water source high in preformed nitrate and a northern water source with lower concentrations, similar to today's ocean. However, the boundary between these water masses occurs north of where their modern counterparts meet, indicating that Antarctic Bottom Water (AABW) extended farther north during the Last Glacial Maximum (LGM). In addition, the southern source had a higher preformed nitrate concentration than today's AABW (25 μM), contradicting hypotheses that nutrient utilization was more efficient in the Southern Ocean deep-water formation regions during the LGM. Comparison to our previous Pacific data reveals that the average preformed nitrate concentration of the deep ocean was slightly higher during the LGM than today. This result implies that the CO2-climate feedback was not principally due to more efficient nitrate utilization.

  15. Obsidian hydration dates glacial loading?

    PubMed

    Friedman, I; Pierce, K L; Obradovich, J D; Long, W D

    1973-05-18

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow. PMID:17806883

  16. Obsidian hydration dates glacial loading?

    PubMed

    Friedman, I; Pierce, K L; Obradovich, J D; Long, W D

    1973-05-18

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

  17. Obsidian hydration dates glacial loading?

    USGS Publications Warehouse

    Friedman, I.; Pierce, K.L.; Obradovich, J.D.; Long, W.D.

    1973-01-01

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming . The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

  18. Microbial Succession in Glacial Foreland Soils of the Canadian Subarctic

    NASA Astrophysics Data System (ADS)

    Kazemi, S.; Lanoil, B. D.

    2014-12-01

    The Canadian arctic has experienced increasing temperatures over the past century leading to heightened rate of glacial retreat. Glacial retreat leads to subsequent exposure of foreland soils to atmospheric conditions, thus creating a sequence of change in these ecosystems. Microbes are critical for soil development and nutrient dynamics in glacial systems as they are the primary colonizers of these soils and have been demonstrated to play a role in geochemical weathering and nutrient cycling beneath the glacier. Although viable microbial communities exist beneath glaciers and are known to be important for the glacial ecosystem, the impact of glacial retreat on these communities and development of the resulting foreland ecosystem is not well understood. Here, we investigate how microbial communities respond to changing conditions brought on by glacial retreat and whether a pattern of succession, such as those found in well characterized plant systems, occurs along a soil foreland in these microbial communities. We hypothesis that time since deglaciation is the major determinant of structure and composition of microbial assemblages. To test this, soil samples were collected along two glacier forelands, Trapridge Glacier and Duke River Glacier, located in Kluane National Park, Yukon Territory. Chronosequence dating of satellite images using geographic information system software revealed sampling sites have been ice-free from ~30 years to over 60 years. Soil chemistry analysis of major nutrients revealed no change in chemical parameters along the chronosequence, suggesting that presence of microbes after exposure from subglacial environments does not significantly alter soil characteristics in the timeframe observed. Furthermore, next-generation IonTorrentTM sequencing performed on soil samples revealed over five million sequencing reads, suggesting prominent microbial presence within these soils. Further analysis on sequencing data is needed to establish the

  19. Pleistocene glacial evolution of Fuentes Carrionas (Cantabrian Range, NW Spain)

    NASA Astrophysics Data System (ADS)

    Pellitero, Ramon

    2014-05-01

    Fuentes Carrionas is a massif situated at the N of Spain, between Castilla y Leon and Cantabria regions. It is the second highest mountain massif of the Cantabrian Range after Picos de Europa, with peaks over 2500 m.a.s.l. and valleys well over 1000 m.a.s.l. Fuentes Carrionas was glaciated during Quaternary, and even during the Holocene and as far as Little Ice Age the presence of glaciers, or at least permafrost is controversial. Results from glacial geomorphology analysis of Fuentes Carrionas Massif are presented. Based on the interpretation of glacial landforms, glacial evolution since the Last Glacial Maximum until Pleistocene deglaciation is described. Four different glacial equilibrium phases are identified, the last one divided into two pulsations. Deglaciation process took place between 36 ka BP and 11 ka BP. Local Last Glacial Maximum is dated back to 36-38 ka. BP, therefore earlier than LGM. Glaciers reached 15 km. long and occupied valleys down to 1250 m.a.s.l. during this phase. By European LGM (20-18 ka.BP) glaciers had substantially retreated to fronts about 1700 m.a.s.l. A final stage with two marked pulsations shows only small glaciers located at cirques above 2000 m.a.s.l. and, finally, only small cirque glaciers at North and Northeast orientation above 2200 m.a.s.l. Both these phases have been correlated to Oldest and Younger Dryas, although no dates have been done yet. A palaeoenvironmental reconstruction is proposed, based on ELA (Equilibrium Line Altitude) rise. ELA has been calculated with the AAR method and 0.67 ratio. This reconstruction shows that temperatures ranged between 9°C and 10°C lower than present ones at the end of Pleistocene, depending on a precipitations variation between 30% higher and 20% lower than current ones. Further research will focus on these retreat phases, especially on Younger Dryas identification and reconstruction for this site and the rest of Cantabrian Range.

  20. Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change

    PubMed Central

    Cauvy-Fraunié, Sophie; Espinosa, Rodrigo; Andino, Patricio; Jacobsen, Dean; Dangles, Olivier

    2015-01-01

    Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we

  1. Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change.

    PubMed

    Cauvy-Fraunié, Sophie; Espinosa, Rodrigo; Andino, Patricio; Jacobsen, Dean; Dangles, Olivier

    2015-01-01

    Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we

  2. Record of glacial Lake Missoula floods in glacial Lake Columbia, Washington

    NASA Astrophysics Data System (ADS)

    Hanson, Michelle A.; Clague, John J.

    2016-02-01

    During the last glaciation (marine oxygen isotope stage 2), outburst floods from glacial Lake Missoula deposited diagnostic sediments within glacial Lake Columbia. Two dominant outburst flood lithofacies are present within glacial Lake Columbia deposits: a flood expansion bar facies and a finer-grained hyperpycnite facies. We conclude that the flood sediments have a glacial Lake Missoula source because: (1) current indicators indicate westward flow through the lake, and upvalley flow followed by downvalley flow in tributary valleys; (2) no flood sediments are found north of a certain point; (3) there is a dominance of Belt-Purcell Supergroup clasts in a flood expansion bar; and (4) some of the finer-grained beds have a pink colour, reflective of glacial Lake Missoula lake-bottom sediments. A new radiocarbon age of 13,400 ± 100 14C BP on plant detritus found below 37 flood beds helps constrain the timing of outburst flooding from glacial Lake Missoula.

  3. Quaternary glaciations recorded by glacial and fluvial landforms in the Shaluli Mountains, Southeastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Xu, Liubing; Zhou, Shangzhe

    2009-01-01

    The Shaluli Mountains, a tectonically controlled mountain range between the Jinsha and Yalong River Rifts, are located in southeastern Tibetan Plateau. In the central Shaluli Mountains, an ice cap of ~ 3600 km 2 once developed on the Haizi Shan. Abundant glacial landforms are present on the Haizi Shan and in the surrounding river valleys. Together with the outwash terraces in the Yazheku River, the northeastern part of the Haizi Shan provides an ideal site to examine the Quaternary glacial history of the region. Sedimentological and morphostratigraphical analysis, field mapping, and dating by electron spin resonance (ESR) define at least seven major glacier advances in the Haizi Shan area. Six major glacier advances likely occurred during marine oxygen isotope stage (MIS)-16, MIS-14/12, MIS-6, MIS-3, early MIS-2, and the global Last Glacial Maximum. These can be defined on the basis of ESR dating and stratigraphical analysis of the glacial landforms in front of the Kuzhaori glacial trough on the southern slope of the Haizi Shan. The outwash terraces in the Yazheku River also record four major glacier advances, which occurred during MIS-16, MIS-12, MIS-6, and MIS-2. In addition, the moraines preserved on the southwestern part of the Haizi Shan suggest that a glacial advance likely occurring during the Lateglacial. The extent of glaciation on the Haizi Shan decreased with time.

  4. Systematically enhanced subarctic Pacific stratification and nutrient utilization during glacials

    NASA Astrophysics Data System (ADS)

    Knudson, K. P.; Ravelo, A. C.

    2015-12-01

    The modern subarctic North Pacific is characterized as a high-nitrate, low-chlorophyll (HNLC) area, but evidence for increased nutrient utilization during the last glacial indicates that this region is highly dynamic. As such, this HNLC area is of particular interest in regard to understanding changes in the biological pump and carbon sequestration and predicting how biogeochemical processes will influence, or be influenced by, future climate change. While it has been suggested that changes in iron supply and/or ocean stratification could explain fluctuations in nutrient utilization and productivity in the subarctic Pacific, short records of nutrient utilization have previously hindered the evaluation of these potential mechanisms over long timescales. Here we present new, high-resolution records of bulk sediment δ15N from 0-1.2 Ma from Integrated Ocean Drilling Program Exp. 323 Site U1342, which are used to calculate Δδ15N (U1342 δ15Nbulk - ODP Site 1012 δ15Nbulk) as a nitrate utilization proxy. The unprecedented length and resolution of this new record allows us, for the first time, to determine orbital-scale systematic behavior in subarctic Pacific nutrient utilization over many glacial/interglacial cycles. Spectral analyses demonstrate that enhanced nutrient utilization was paced by climate on Milankovitch orbital cycles since the Mid-Pleistocene Transition (MPT; ~800 ka). Nitrate utilization maxima is statistically correlated with glacial maxima and enhanced dust/iron availability (represented by existing records of EPICA ice core dust, Southern Pacific Ocean sediment iron, and China loess) but shows low correlation to primary productivity, suggesting that stratification has systematically exerted an important control on subarctic Pacific nutrient utilization since the MPT. These findings imply that the presence of iron helped to change the region into a nitrate-limited, rather than iron-limited, region during glacials and that stratification, which

  5. Glacial and marine chronology of Mars

    NASA Technical Reports Server (NTRS)

    Strom, Robert G.; Kargel, Jeffrey S.; Johnson, Natasha; Knight, Christine

    1992-01-01

    A summary is given of the glacial and marine chronology of Mars. Hydrological models of oceans and ice sheets, the cratering record, hydrological cycling, and episodic glaciation are discussed. Evidence for a Noachian ocean is evaluated.

  6. A fresh look at glacial foods

    USGS Publications Warehouse

    Colman, Steven M.

    2002-01-01

    Over the last 20 years, it has become clear that ice ages are characterized by glacial as well as climatic instability on millennial time scales. In his Perspective, Colman highlights two recent papers investigating the role of glacial meltwater and continental drainage in this instability. The results suggest a fundamental instability feedback between ocean circulation and ice sheet dynamics and provides an explanation for why instability was greatest at times of intermediate ice volume.

  7. Phylogeographic patterns, genetic affinities and morphological differentiation between Epipactis helleborine and related lineages in a Mediterranean glacial refugium

    PubMed Central

    Tranchida-Lombardo, Valentina; Cafasso, Donata; Cristaudo, Antonia; Cozzolino, Salvatore

    2011-01-01

    Background and Aims In the Mediterranean basin, the Italian peninsula has been suggested to be one of the most important glacial refugia for temperate tree species. The orchid genus Epipactis is widely represented in the Italian peninsula by widespread species and several endemic, localized taxa, including selfing and outcrossing taxa. Here the phylogenetic and phylogeographic relationships in a group of closely related taxa in Epipactis are investigated with the aim of understanding the role of this refugial area for cladogenesis and speciation in herbaceous species, such as terrestrial orchids. Methods Ribosomal DNA (rDNA) was employed to assess phylogenetic relationships, and plastid sequence variation in the rbcL–accD spacer was used to reveal phylogeographic patterns among plastid haplotypes using a parsimony network. Key Results Low genetic variation and shared ribotypes were detected in rDNA, whereas high levels of sequence variation and a strong phylogeographic structure were found in the examined plastid region. The parsimony plastid haplotype network identified two main haplotype groups, one including E. atrorubens/microphylla/muelleri/leptochila and the other including all accessions of E. helleborine and several localized and endemic taxa, with a combination of widespread and rare haplotypes detected across the Italian peninsula. A greater genetic divergence separated the Italian and other European accessions of E. helleborine. Conclusions Phylogenetic and phylogeographic patterns support a working hypothesis in which the Italian peninsula has only recently been colonized by Epipactis, probably during the most recent phase of the Quaternary age and, nevertheless, it acted as a remarkable centre of diversification for this orchid lineage. Changes in pollination strategy and recurrent shifts in mating system (from allogamy to autogamy) could have represented the mechanism promoting this rapid diversification and the observed high taxonomic complexity

  8. A new record of post-glacial sedimentation in a glacial trough, offshore sub-Antarctic South Georgia

    NASA Astrophysics Data System (ADS)

    Meisel, Ove; Graham, Alastair; Kuhn, Gerhard

    2014-05-01

    Past studies of South Georgia's climatic history were constrained to land-based sedimentary records, such as peat bogs and coastal lakes, or to terrestrial geomorphology, such as terminal moraines. Hence, the current state of knowledge on past climatic changes in South Georgia is characterised by a complete absence of records from sedimentary marine archives in the fjords or coastal embayments of the region. This study comprises detailed examination of one of the first marine sediment cores recovered on its northeastern shelf in Royal Bay Glacial Trough. Alongside the analysis of new acoustic sub-bottom data, it is the first work to deliver extensive insight into South Georgia's post-glacial climatic history from a marine perspective. The glacial troughs on the South Georgia shelf radiate from the coast towards the shelf edge and represent major sediment traps as they form the only key large-scale depressions in the shelf bathymetry. Sedimentary records, covering a period since at least the Last Glacial Maximum, are thought likely to be recorded in most of them. The sediment core of this study covers sedimentation dated from a maximum of 15,346 ± 492 cal. yr BP until the present day. Physical core parameters indicate a major change in climatic conditions around 14,000 cal. yr BP, the time of the Antarctic Cold Reversal. Holocene climate variabilities are also recorded in the trough infill. The acoustic data show a major change in sedimentation and a pronounced unconformity at the core site, which appears to have had a widespread effect over a large area of the shelf. The origin of the unconformity remains unclear, though several hypotheses, including bottom-current erosion, glacial overriding and earthquake activity, are proposed and discussed. Another important finding at the core site is the presence of methane-derived authigenic carbonates. They form either as secondary precipitates in the subsurface or syndepositional at the seafloor as individual minerals or

  9. Changing glacial lakes and associated outburst floods risks in Nanda Devi Biosphere Reserve, Indian Himalaya

    NASA Astrophysics Data System (ADS)

    Mal, S.; Singh, R. B.

    2014-09-01

    Glacial lakes and associated outburst floods (GLOFs) have increased in the Himalayan region due to climate change during the last century that has led to huge losses to society. Therefore, the present study was undertaken to map glacial lakes, their increasing extent, and associated damage potential in Nanda Devi Biosphere Reserve (NDBR), Indian Himalaya. The glacial lakes were mapped on Landsat TM (3 November, 2009 and 6 November 2010) and Landsat MSS satellite images (15 November 1976 and 26 October 1979) to assess their changing area. Potential GLOFs sites have been identified and studied for their damage potentials using site characteristics and past occurrence of GLOFs. A total of 35 lakes were mapped, of which 14 lakes are located at more than 4500 m. The size and damage potentials of lakes have increased. Some lakes grew so much that they merged to form a big lake. All of these are potential GLOFs and can cause severe damage to society.

  10. Ecology of invasive Melilotus albus on Alaskan glacial river floodplains

    USGS Publications Warehouse

    Conn, Jeff S.; Werdin-Pfisterer, Nancy R.; Beattie, Katherine L.; Densmore, Roseann V.

    2011-01-01

    Melilotus albus (white sweetclover) has invaded Alaskan glacial river floodplains. We measured cover and density of plant species and environmental variables along transects perpendicular to the Nenana, Matanuska, and Stikine Rivers to study interactions between M. albus and other plant species and to characterize the environment where it establishes. Melilotus albus was a pioneer species on recently disturbed sites and did not persist into closed canopy forests. The relationships between M. albus cover and density and other species were site-specific.Melilotus albus was negatively correlated with native species Elaeagnus commutata at the Nenana River, but not at the Matanuska River. Melilotus albus was positively correlated with the exotic species Crepis tectorumand Taraxacum officinale at the Matanuska River and T. officinale on the upper Stikine River. However, the high density of M. albus at a lower Stikine River site was negatively correlated with T. officinale and several native species including Lathyrus japonicus var. maritimus and Salix alaxensis. Glacial river floodplains in Alaska are highly disturbed and are corridors for exotic plant species movement. Melilotus albus at moderate to low densities may facilitate establishment of exotic species, but at high densities can reduce the cover and density of both exotic and native species.

  11. Bayesian analysis of radiocarbon chronologies: examples from the European Late-glacial

    NASA Astrophysics Data System (ADS)

    Blockley, S. P. E.; Lowe, J. J.; Walker, M. J. C.; Asioli, A.; Trincardi, F.; Coope, G. R.; Donahue, R. E.

    2004-02-01

    Although there are many Late-glacial (ca. 15 000-11 000 cal. yr BP) proxy climate records from northwest Europe, some analysed at a very high temporal resolution (decadal to century scale), attempts to establish time-stratigraphical correlations between sequences are constrained by problems of radiocarbon dating. In an attempt to overcome some of these difficulties, we have used a Bayesian approach to the analysis of radiocarbon chronologies for two Late-glacial sites in the British Isles and one in the Adriatic Sea. The palaeoclimatic records from the three sites were then compared with that from the GRIP Greenland ice-core. Although there are some apparent differences in the timing of climatic events during the early part of the Late-glacial (pre-14 000 cal. yr BP), the results suggest that regional climatic changes appear to have been broadly comparable between Greenland, the British Isles and the Adriatic during the major part of the Late-glacial (i.e. between 14 000 and 11 000 cal. yr BP). The advantage of using the Bayesian approach is that it provides a means of testing the reliability of Late-glacial radiocarbon chronologies that is independent of regional chronostratigraphical (climatostratigraphical) frameworks. It also uses the full radiocarbon inventory available for each sequence and makes explicit any data selection applied. Potentially, therefore, it offers a more objective basis for comparing regional radiocarbon chronologies than the conventional approaches that have been used hitherto. Copyright

  12. Contrasted evolution of glacial lakes along the Hindu-Kush Himalaya mountain range between 1990 and 2009

    NASA Astrophysics Data System (ADS)

    Gardelle, J.; Yves, A.; Berthier, E.

    2011-12-01

    In this study, we present the first assessment of glacial lake distribution and evolution in the Hindu Kush Himalaya (HKH). Seven sites have been selected between Bhutan and Afghanistan, to capture the climatic variability along the 2000-km long mountain range. For each site, glacial lakes have been mapped with LANDSAT satellite imagery acquired in 1990, 2000 and 2009, using an automatic classification. In the East (India, Nepal and Bhutan) glacial lakes are bigger and more numerous than in the West (Pakistan, Afghanistan), and have grown continuously between 1990 and 2009 by 20% to 65%. Conversely, during the same period, the glacial lake coverage has shrunk in the Hindu Kush (-50%) and the Karakorum (-30%). This east/west pattern of lake changes seems in agreement with sparse glaciological measurements that suggest less (or even no) ice loss in the western part of the HKH.

  13. Glacial influence on caldera-forming eruptions

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Bindeman, Ilya

    2010-05-01

    Investigation of Ar-Ar, U-Pb, and 14C ages of caldera-forming eruptions for the past million years in glaciated arc of Kamchatka has lead to observations that the majority of large-volume ignimbrites, which are associated with the morphologically-preserved calderas, correspond in time with 'maximum glacial' conditions. The latter are defined as the highest δ18O foraminifera values on the N Pacific SPECMAP stack. Additional evidence comes from clustering Kamchatka-derived marine ash layers with glacial moraines in DSDP cores. The strongest field evidence comes from glaciated multi-caldera volcanoes that hosted thick glacial ice caps. In this paper, we investigate how glacial load dynamics may alter eruption frequency in such glaciated multicaldera volcanoes. We present results of numerical simulations that include ice cap of different thickness (ranging from 0 to 1 km) on top of calderas of relevant sizes (5 to 40 km) with magma chambers at different depths. We also study the effects of an asymmetric ice distribution, a variable pre-caldera topography, glacial overpressure on volatiles solubility, and the subglacial intracaldera hydrothermal system on changing mechanical properties of roof rock. The results are: 1) Any ice cap retard ring-fall propagation and caldera formation; 2) Asymmetric distribution of ice plays no or minor role; 3) Glacial erosion of part of volcanic edifice or interglacial edifice failure may promote ring fracture; 4) hydrothermal system under an ice cap may have more acidic hydrothermal fluids leading to more effective hydrothermal rotting of the intracaldera roof rocks; 5) short period interstadial during maximal glaciation may play most important role in pressure fluctuations/volatite saturation condition; 6) Arching influence of the ice cap on roof rock may lead to ring fracture. Overall, the maximal glacial time represent the most dynamic time in a multi-caldera volcano life promoting physical and chemical feedbacks.

  14. Technical Note: Glacial influence in tropical mountain hydrosystems evidenced by the diurnal cycle in water levels

    NASA Astrophysics Data System (ADS)

    Cauvy-Fraunié, S.; Condom, T.; Rabatel, A.; Villacis, M.; Jacobsen, D.; Dangles, O.

    2013-12-01

    Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Determining the influence of glacial runoff to streams is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier-stream system interface. Here we propose quantifying the diurnal cycle amplitude of the streamflow to determine the glacial influence in glacierized catchments. We performed water-level measurements using water pressure loggers over 10 months at 30 min time steps in 15 stream sites in 2 glacier-fed catchments in the Ecuadorian Andes (> 4000 m a.s.l.) where no perennial snow cover is observed outside the glaciers. For each stream site, we performed wavelet analyses on water-level time series, determined the scale-averaged wavelet power spectrum at 24 h scale and defined three metrics, namely the power, frequency and temporal clustering of the diurnal flow variation. The three metrics were then compared to the percentage of the glacier cover in the catchments, a metric of glacial influence widely used in the literature. As expected, we found that the diurnal variation power of glacier-fed streams decreased downstream with the addition of non-glacial tributaries. We also found that the diurnal variation power and the percentage of the glacier cover in the catchment were significantly positively correlated. Furthermore, we found that our method permits the detection of glacial signal in supposedly non-glacial sites, thereby revealing glacial meltwater resurgence. While we specifically focused on the tropical Andes in this paper, our approach to determine glacial influence may have potential applications in temperate and arctic glacierized catchments. The measure of diurnal water

  15. History of glacial terminations from the Tiber River, Rome: Insights into glacial forcing mechanisms

    NASA Astrophysics Data System (ADS)

    Marra, Fabrizio; Florindo, Fabio; Boschi, Enzo

    2008-06-01

    We document the aggradational history of the Tiber River delta through the last 17,000 years by means of 17 new 14C ages from peat or wood collected from the delta sediment. An abrupt change in sediment clast size, grading from gravel to clay, occurred between 13.63 (±0.20) and 12.80 (±0.15) ka, indicating that it was synchronous with the last glacial termination, with no appreciable phase lag. Knowing this phase relationship enables us to reduce the magnitudes of age uncertainties for aggradational sections corresponding to glacial terminations IX through III, which we had dated previously by 40Ar/39Ar methods. Glacial terminations VIII, VI, and IV precede beyond 95% confidence the ages predicted by Northern Hemisphere summer insolation maxima. Additionally, we find that each of these seven glacial terminations follows particularly mild insolation minima, which we suggest may be regarded as the preconditioning factor to trigger a glacial termination.

  16. Evaluation of modeling for groundwater flow and tetrachloroethylene transport in the Milford-Souhegan glacial-drift aquifer at the Savage Municipal Well Superfund site, Milford, New Hampshire, 2011

    USGS Publications Warehouse

    Harte, Philip T.

    2012-01-01

    The U.S. Geological Survey and the New Hampshire Department of Environmental Services entered into a cooperative agreement to assist in the evaluation of remedy simulations of the MSGD aquifer that are being performed by various parties to track the remedial progress of the PCE plume. This report summarizes findings from this evaluation. Topics covered include description of groundwater flow and transport models used in the study of the Savage Superfund site (section 2), evaluation of models and their results (section 3), testing of several new simulations (section 4), an assessment of the representation of models to simulate field conditions (section 5), and an assessment of models as a tool in remedial operational decision making (section 6).

  17. Glacial history of Tranquilo glacier (Central Patagonia) since the Last Glacial Maximum through to the present.

    NASA Astrophysics Data System (ADS)

    Sagredo, E. A.; Araya, P. S.; Schaefer, J. M.; Kaplan, M. R.; Kelly, M. A.; Lowell, T. V.; Aravena, J. C.

    2014-12-01

    Deciphering the timing and the inter-hemispheric phasing of former glacial fluctuations is critical for understanding the mechanisms and climate signals underlying these glacial events. Here, we present a detailed chronology of glacial fluctuations for Río Tranquilo glacier (47°S), since the LGM, including up to the present. Río Tranquilo is a small glacial valley located on the northern flank of Monte San Lorenzo, an isolated granitic massif, ~70 km to the east of the southern limit of the Northern Patagonian Icefield. Although Mt. San Lorenzo is located on the leeward side of the Andes, it is one of the most glacierized mountains in the region, with an ice surface area of ~140 km2. Geomorphic evidence suggests that during past episodes of climate change several small glaciers that today occupy the headwalls of Río Tranquilo valley expanded and coalesced, depositing a series of moraines complexes along the flanks and bottom of the valley. We used two independent dating techniques to constrain the age of the glacial history of the area. 10Be surface exposure ages from boulders located atop moraine ridges reveal that Río Tranquilo valley underwent glacial expansion/stabilization during at least the LGM (late LGM?), Late glacial (ACR and Younger Dryas) and Mid-Holocene. Within the Mid-Holocene limits, tree-ring based chronology indicates that Río Tranquilo glacier expanded during the Late Holocene as well. Our results are the first detailed chronology of glacial fluctuations from a single valley glacier, spanning the entire period from the (end of the) LGM up to the present, in southern South America. By identifying different glacial episodes within a single alpine valley, this study provides baseline data for studying the relative magnitude of the climate events responsible for these glacial events.

  18. Last Glacial loess in the conterminous USA

    USGS Publications Warehouse

    Bettis, E. Arthur; Muhs, Daniel R.; Roberts, Helen M.; Wintle, Ann G.

    2003-01-01

    The conterminous United States contains an extensive and generally well-studied record of Last Glacial loess. The loess occurs in diverse physiographic provinces, and under a wide range of climatic and ecological conditions. Both glacial and non-glacia lloess sources are present, and many properties of the loess vary systematically with distance from loess sources. United States' mid-continent Last Glacial loess is probably the thickest in the world, and our calculated mass accumulation rates (MARs) are as high as 17,500 g/m2/yr at the Bignell Hill locality in Nebraska, and many near-source localities have MARs greater than 1500 g/m2/yr. These MARs are high relative to rates calculated in other loess provinces around the world. Recent models of LastGlacial dust sources fail to predict the extent and magnitude of dust flux from the mid-continent of the United States. A better understanding of linkages between climate, ice sheet behaviour, routing of glacial meltwater, land surface processes beyond the ice margin, and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region.

  19. Beyond the Seafloor: a Plio-Pleistocene Archive of Glacial Geomorphology from Basin-Wide 3D Seismic Reflection Data on the Mid-Norwegian Shelf

    NASA Astrophysics Data System (ADS)

    Newton, A.; Huuse, M.

    2015-12-01

    Oil and gas exploration on the mid-Norwegian shelf has created an extensive geophysical and geological database. As such, this margin has become one of the most comprehensively studied formerly-glaciated continental margins in the world. Industrial operations have concentrated on the structure and geohazard potential of glacial sediments whilst academic work has looked at reconstructing environmental conditions during and since the Last Glacial Maximum (LGM). This has generally consisted of mapping seafloor glacial geomorphology and a limited number of shallow sediment cores. Despite the increasingly large volume of 3D seismic reflection data available across the majority of the shelf, only limited work has been carried out investigating the oldest glaciations. A Plio-Pleistocene archive of glacial-interglacial history is preserved offshore and represents a unique study site because of the availability of 100s of 3D seismic reflection datasets. This database allows numerous different glacial erosion events and glacial landforms to be imaged throughout the glacially-derived NAUST Formation. We present an inventory of glacial history for the mid-Norwegian shelf and review the implications for the glacial history of Northwest Europe. This record shows glacial landforms such as iceberg scours, mega-scale glacial lineations and grounding-zone wedges, each of which provides an insight into ice characteristics. Dating is limited to a few tentative dates based on side-wall core data but we infer a further dating chronology based on dated sediments from the Voring Plateau, fluctuations in the benthic δ18O derived global sea level record, interpretation of seismic facies and the overall architecture. Glacial evidence is present regularly throughout the stratigraphy with the earliest evidence for marine terminating ice found at the base of the NAUST Formation at ~2.8 Ma.

  20. Laurentide Ice Sheet basal temperatures during the last glacial cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Pickler, C.; Beltrami, H.; Mareschal, J.-C.

    2016-01-01

    Thirteen temperature-depth profiles ( ≥ 1500 m) measured in boreholes in eastern and central Canada were inverted to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region that was covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0 °C throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, allowed basal flow and fast flowing ice streams at the base of the Laurentide Ice Sheet. Despite such conditions, which have been inferred from geomorphological data, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

  1. Laurentide Ice Sheet basal temperatures at the Last Glacial Cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Pickler, C.; Beltrami, H.; Mareschal, J.-C.

    2015-08-01

    Thirteen temperature-depth profiles (≥ 1500 m) measured in boreholes in eastern and central Canada were inverted to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0 °C throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, allowed basal flow and fast flowing ice streams at the base of the Laurentide Ice Sheet. Despite such conditions, which have been inferred from geomorphological data, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

  2. Laurentide Ice Sheet basal temperatures at the Last Glacial Cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Mareschal, Jean-Claude; Pickler, Carolyne; Beltrami, Hugo

    2016-04-01

    We measured and inverted thirteen temperature-depth profiles (≥1500 m) in boreholes in eastern and central Canada to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0oC throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, demonstrate that the southern portion of the Laurentide Ice Sheet was not frozen to the bed, allowing for basal flow and fast flowing ice streams at the base. Despite such conditions, which have been inferred from geomorphological data and models, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

  3. Monitoring of a recurring glacial lake outburst flood in north-western Nepal

    NASA Astrophysics Data System (ADS)

    Neckel, Niklas; Kropacek, Jan; Schröter, Benjamin; Tyrna, Bernd; Buchroithner, Manfred

    2014-05-01

    Since 2004 an almost annual recurring glacial lake outburst flood threatens Halji Village, located in Limi valley in one of the most remote regions of north-western Nepal. So far a considerable extent of rare fields and several houses have been destroyed. A cultural heritage site, the Halji Monastery which is the oldest Buddhist monastery in western Nepal is located only 30 m from the flood path. A supra-glacial lake at an altitude of 5300 m a.s.l. located approximately 6 km away from the village was identified as the source of the flood from recent satellite imagery. In November/December 2013 we carried out a field survey in this region in order to understand the drainage paths of the lake, to measure the volume of the glacial lake and to set up an Automatic Weather Station (AWS). To assess both the filling and draining of the glacial lake a terrestrial time-lapse camera was installed taking six photographs every day. These show the glacial lake and parts of the feeding water channels. The images combined with the AWS data will help us to understand the dependency of magnitude and timing of the outburst event to the temperature, snow conditions and glacier movements. The collected data will also help us to learn more about the flooding event and serve as the input for a two dimensional hydrodynamic model which simulates the flood extent under different flooding scenarios.

  4. Glacial geology, glacial recession, proglacial lakes, and postglacial environments, Fishers Island, New York

    SciTech Connect

    Sirkin, L. ); Funk, R.E. . Anthropological Survey)

    1993-03-01

    The Fishers Island Moraine, a complex of three parallel ice margin depositional trends, forms the west-central segment of a major recessional moraine of the Connecticut-Rhode Island Lobe of the late Wisconsinan glacier. As such, the moraine links the Orient Point Moraine of eastern Long Island and the Charlestown Moraine of western Rhode Island and marks a prominent recessional ice margin. The moraine is correlative with the Roanoke Point Moraine of the Connecticut Lobe of northeastern Long Island. Pollen stratigraphy of >13,180 ka bog sediments begins early in the spruce (A) pollen zone with evidence of a cold, late-glacial climate. The pine (B) pollen zone, beginning prior to 11,145 ka, and the oak (C) pollen zone, dating from about 9,000 ka with hickory and hemlock subzones, are well represented. However, after about 2,000 ka, the stratigraphic record in the bog sections is missing in most cases due to peat harvesting. Pollen spectra from several archeological sites fall within the late oak pollen zone, well within the land clearing interval with evidence of hardwood forests and locally holly and cedar. Evidence of cultigens in the pollen record is sparse. Marine deposits over fresh water bog and proglacial lake sediments show that some coastal bogs were drowned by sea level rise.

  5. Origin of glacial dust in four East Antarctica ice cores

    NASA Astrophysics Data System (ADS)

    Delmonte, B.; Petit, J. R.; Basile-Doelsh, I.; Jagoutz, E.; Michard, A.; Maggi, V.; Revel-Rolland, M.

    2003-04-01

    We investigated the geographic origin of mineral aerosol (dust) windblown from the Southern Hemisphere continents and preserved in four East Antarctica ices cores using 87Sr/86Sr -143Nd/144Nd isotopic systems. For the equivalent size range (diameter < 5 micron) the isotope composition is compared to the signature of Potential Source Areas (PSAs) of the Southern Hemisphere. Our initial collection of PSA samples was recently documented by new samples of loesses, fluvial and sands deposits from South America, South Africa, New Zealand and the Antarctic Dry Valleys. In addition, the isotopic fingerprint was measured on ice core from glacial climate (corresponding to even number of marine isotopic stages) for four different ice cores from the East Antarctic Plateau: EPICA-Dome C (75^o06'S, 123^o 24'E; Stage 2,4,6), Vostok (78^o S, 106^o E; Stage 6), Dome B (77^o05' S, 94^o 55' E; Stage 2) and Komsomolskaia (74^o 05' S, 97^o 29' E, Stage 2). The Sr-Nd signature of dust from the four sites appear very close from each other, and confirm the previous results from Basile (1997) from the Vostok ice core. Altogether, they define a restricted isotopic field, and suggest provenance from the same source(s). The comparison with the isotopic signature from the PSAs allows to exclude South Africa as possible candidate, but a partial overlap arises among Southern South America (Chile, Argentina), New Zealand and the Antarctic Dry Valleys. A possible contribution from all these three sources cannot be excluded. However New Zealand and Antarctic source and contribution to Antarctic ice seem quite negligible, an hypothesis as also supported by the absence of volcanic ashes from these area in the Vostok ice core. for the last four glacial/interglacial cycles. Our data confirm previous studies (Grousset et al., 1992, Basile et al., 1997) suggesting South America as the dominant source for dust in East Antarctica in glacial times.

  6. A Mars Analog for Wet-Based Glacial Alteration of Volcanic Terrains: Thermal Infrared Remote Sensing at Three Sisters, Oregon, U.S.A.

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Scudder, N. A.; Horgan, B.; Rampe, E. B.

    2016-09-01

    This study characterizes wet-based glacial weathering products at a volcanic Mars analog site using thermal infrared remote sensing. Decorrelation stretches are used to examine the geographic relationships between compositional units.

  7. Fast Vegetational Responses to Late-Glacial Climate Change

    NASA Astrophysics Data System (ADS)

    Williams, J. W.; Post, D. M.; Cwynar, L. C.; Lotter, A. F.; Levesque, A. J.

    2001-12-01

    How rapidly can natural ecosystems respond to rapid climate change? This question can be addressed by studying paired paleoecological and paleoclimatological records spanning the last deglaciation. Between 16 and 10 ka, abrupt climatic oscillations (e.g. Younger Dryas, Gerzensee/Killarney Oscillations) interrupted the general warming trend. Rates of climate change during these events were as fast or faster than projected rates of change for this century. We compiled a dozen high-resolution lacustrine records in North America and Europe with a pollen record and independent climatic proxy, a clear Younger Dryas signal, and good age control. Cross-correlation analysis suggests that vegetation responded rapidly to late-glacial climate change, with significant changes in vegetation composition occurring within the lifespan of individual trees. At all sites, vegetation lagged climate by less than 200 years, and at two-thirds of the sites, the initial vegetational response occurred within 100 years. The finding of rapid vegetational responses is consistent across sites and continents, and is similar to the 100-200 year response times predicted by gap-scale forest models. Likely mechanisms include 1) increased susceptibility of mature trees to disturbances such as fire, wind, and disease, thereby opening up gaps for colonization, 2) the proximity of these sites to late-glacial treeline, where climate may directly control plant population densities and range limits, 3) the presence of herbaceous taxa with short generation times in these plant communities, and 4) rapid migration due to rare long-distance seed dispersals. Our results are consistent with reports that plant ranges are already shifting in response to recent climate change, and suggest that these shifts will persist for the next several centuries. Widespread changes in plant distributions may affect surface-atmosphere interactions and will challenge attempts to manage ecosystems and conserve biodiversity.

  8. Glacial geography and native North American languages

    NASA Astrophysics Data System (ADS)

    Rogers, Richard A.

    1985-01-01

    This study tests the hypothesis that the number and distribution of some native American languages may be related to ice-margin changes of the Wisconsin glaciation. The analysis indicated that the number of languages per unit area is much greater in unglaciated areas of the last glacial maximum than in glaciated areas. The pattern of languge overlap between land areas sequentially exposed during deglaciation appears to indicate the direction of movement of populations from the periphery toward the core of the area once covered by the Wisconsin Ice Sheet. The data strongly indicate that North America was inhabited prior to the Wisconsin glacial maximum, because glacial maximum conditions apparently influenced linguistic distributions. Evidence suggests that ancestral Eskimo-Aleut and Na-Dene speakers occupied the northwestern edge of the continental ice mass, and that ancestral Algonquian speakers were south of the ice mass during the Wisconsin glacial maximum (approximately 18,000 yr ago). These three linguistic groups were the principal ones to spreas into areas exposed by the recession of the Wisconsin ice.

  9. Potential flood volume of Himalayan glacial lakes

    NASA Astrophysics Data System (ADS)

    Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

    2013-01-01

    Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the risk of such flooding, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes flooded. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e. the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability because it requires no particular expertise to carry out. We calculated PFVs for more than 2000 Himalayan glacial lakes using the ASTER data. The distribution follows a power-law function, and we identified 49 lakes with PFVs of over 10 million m3 that require further detailed field investigations.

  10. Central Michigan University's Glacial Park: Instruction through Landscaping.

    ERIC Educational Resources Information Center

    Pape, Bruce; Francek, Mark A.

    1992-01-01

    Describes the creation of a glacial park on a university campus. Suggests that the park is a useful instructional resource that helps students relate classroom material to outdoor phenomena by visualizing and identifying glacial landforms, recognizing their spatial relationships, and understanding how glacial features originated. Offers advice for…

  11. Glacial influence on caldera-forming eruptions

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Bindeman, Ilya

    2011-04-01

    It has been suggested that deglaciations have influenced volcanism in several areas around the world increasing productivity of mantle melting and eruptions from crustal magma chambers. However, the connection between glaciations and increased volcanism is not straightforward. Investigation of Ar-Ar, U-Pb, and 14C ages of caldera-forming eruptions for the past million years in the glaciated arc of Kamchatka has lead to the observation that the majority of large-volume ignimbrites, which are associated with the morphologically preserved calderas, correspond in time with "maximum glacial" conditions for the past several glacial cycles. In the field, the main proof is related to the fact that glaciated multi-caldera volcanoes hosted thick glacial ice caps. Additional evidence comes from clustering Kamchatka-derived marine ash layers with glacial moraines in DSDP cores. Here we present a set of new results from numerical modelling using the Finite Element Method that investigate how the glacial load dynamic may affect the conditions for ring-fault formation in such glaciated multi-caldera volcanoes. Different scenarios were simulated by varying: (1) the thickness and asymmetric distribution of the existing ice cap, (2) the depth and size of the magmatic reservoir responsible for the subsequent collapse event, (3) the thickness and mechanical properties of the roof rock due to the alteration by hydrothermal fluids, (4) the existence of a deeper and wider magmatic reservoir and (5) possible gravitational failure triggered, in part, by subglacial rock mass build up and hydrothermal alteration. The results obtained indicate that: (1) Any ice cap plays against ring fault formation; (2) Asymmetric distribution of ice may favour the initiation of trap-door type collapse calderas; (3) Glacial erosion of part of volcanic edifice or interglacial edifice failure may facilitate subsequent ring fault formation; (4) hydrothermal system under an ice cap may lead to a quite effective

  12. Glacial-marine and glacial-lacustrine sedimentation in Sebago Lake, Maine: Locating the marine limit

    SciTech Connect

    Johnston, R.A.; Kelley, J.T. ); Belknap, D. . Dept. of Geological Sciences)

    1993-03-01

    The marine limit in Maine marks a sea-level highstand at approximately 13 ka. It was inferred to cross Sebago Lake near Frye Island by Thompson and Borns (1985) on the Surficial Geological Map of Maine, dividing the lake into a northern glacial-lacustrine basin and a southern glacial-marine basin. This study examined the accuracy of the mapped marine limit in the lake and the nature of glacial-lacustrine and glacial-marine facies in Maine. Recognition of the marine limit is usually based on mapped shorelines, glacial-marine deltas, and contacts with glacial-marine sediments. This study, in Maine's second largest lake, collected 100 kilometers of side-scan sonar images, 100 kilometers of seismic reflection profiles, and one core. Side-scan sonar records show coarse sand and gravel and extensive boulder fields at an inferred grounding-line position near Frye Island, where the marine limit was drawn. ORE Geopulse seismic reflection profiles reveal a basal draping unit similar to glacial-marine units identified offshore. Later channels cut more than 30 m into the basal stratified unit. In addition, till and a possible glacial-tectonic grounding-line feature were identified. Slumps and possible spring disruptions are found in several locations. The top unit is an onlapping ponded Holocene lacustrine unit. Total sediment is much thicker in the southern basin; the northern basin, >97 m deep, north of the marine limit appears to have been occupied by an ice block. Retrieved sediments include 12 meters of rhythmites. Microfossil identifications and dating will resolve the environments and time of deposition in this core.

  13. Potential flood volume of Himalayan glacial lakes

    NASA Astrophysics Data System (ADS)

    Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

    2013-07-01

    Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

  14. Magnetic Properties of Bermuda Rise Sediments Controlled by Glacial Cycles During the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Roud, S.

    2015-12-01

    Sediments from ODP site 1063 (Bermuda Rise, North Atlantic) contain a high-resolution record of geomagnetic field behavior during the Brunhes Chron. We present rock magnetic data of the upper 160 mcd (<900 ka) from hole 1063D that show magnetic properties vary in concert with glacial cycles. Magnetite appears to be the main magnetic carrier in the carbonate-dominated interglacial horizons, yet exhibits contrasting grain size distributions depending on the redox state of the horizons. Higher contributions of single domain magnetite exist above the present day sulfate reduction zone (ca. 44 mcd) with relatively higher multidomain magnetite components below that likely arise from the partial dissolution of SD magnetite in the deeper, anoxic horizons. Glacial horizons on the other hand, characterized by enhanced terrigenous deposition, show no evidence for diagenetic dissolution but do indicate the presence of authigenic greigite close to glacial maxima (acquisition of gyro-remanence, strong magnetostatic interactions and SD properties). Glacial horizons contain hematite (maxima in HIRM and S-Ratio consistent with a reddish hue) and exhibit higher ARM anisotropy and pronounced sedimentary fabrics. We infer that post depositional processes affected the magnetic grain size and mineralogy of Bermuda rise sediments deposited during the late Pleistocene. Hematite concentration is interpreted to reflect primary terrigenous input that is likely derived from the Canadian Maritime Provinces. A close correlation between HIRM and magnetic foliation suggests that changes in sediment composition (terrigenous vs. marine biogenic) were accompanied by changes in the depositional processes at the site.

  15. Iceland Dust Storms Linked to Glacial Outwash Deposits and to Sub-Glacial Flood (Jökulhlaup) Events

    NASA Astrophysics Data System (ADS)

    Prospero, J. M.; Arnalds, Ó.; Olafsson, H.; Bullard, J.; Hodgkins, R.

    2008-12-01

    Studies of Arctic snow and ice cores reveal large temporal changes in dust concentrations, especially over glacial-interglacial cycles. Most efforts to model dust variability with climate have focused on sources in tropical and mid-latitude arid regions and have neglected high latitude emissions because of a lack of information on possible sources. Here we report on aerosol measurements which show that dust storms are common on Iceland and that major events are associated with glacial sedimentary environments. In July 1991 we established an aerosol sampling site on Heimaey, a small island located 18 km off the southeast coast of Iceland, with the objective of studying the transport of pollutant species to the Arctic. We found that although concentrations of nitrate and non-sea-salt sulfate were generally quite low, there were sporadic peaks that were primarily attributed to pollutant transport from Europe [Prospero et al., 1995]. Recently we expanded our analyses to include mineral dust, covering the period 1997 through 2004. Dust is present during much of the year (annual average 3.9 μg m-3) with a strong seasonal cycle (maximum in April, 14.0 μg m-3). However there are many spikes in the dust record, some exceeding 100 μg m-3, which are not associated with pollutant transport peaks. A search of NASA satellite web archives yielded six "dust storm" images that were acquired during our data period. These show prominent dust plumes streaming off the coast of Iceland. Here we show that each image could be closely linked to a major dust peak in our record (although there were many more peaks than satellite images). Most of these dust events were associated with dust emitted from glacial outwash (sandur) deposits. Some of the largest dust peaks were linked to jökulhlaups, an Icelandic term for sub-glacially generated outburst floods. The dust clouds were typically comprised of a series of well-defined plumes emitted from large "point" sources, mostly associated with

  16. Plio-Pleistocene glacial-interglacial productivity changes in the eastern equatorial Pacific upwelling system

    NASA Astrophysics Data System (ADS)

    Jakob, Kim A.; Wilson, Paul A.; Bahr, André; Bolton, Clara T.; Pross, Jörg; Fiebig, Jens; Friedrich, Oliver

    2016-03-01

    The eastern equatorial Pacific Ocean (EEP) upwelling system supports >10% of the present-day global ocean primary production, making it an important component in Earth's atmospheric and marine carbon budget. Traditionally, it has been argued that since intensification of Northern Hemisphere glaciation (iNHG, ~2.7 Ma), changes in EEP productivity have predominantly depended on trade wind strength-controlled upwelling intensity. An alternative hypothesis suggests that EEP productivity is primarily controlled by nutrient supply from the high southern latitudes via mode waters. Here we present new high-resolution data for the latest Pliocene/early Pleistocene from Ocean Drilling Program Site 849, located within the equatorial divergence system in the heart of the EEP upwelling regime. We use carbon isotopes in benthic and planktic foraminiferal calcite and sand accumulation rates to investigate glacial-interglacial (G-IG) productivity fluctuations between 2.65 and 2.4 Ma (marine isotope stages (MIS) G1 to 94). This interval includes MIS 100, 98, and 96, three large-amplitude glacials (~1‰ in benthic δ18O) representing the culmination of iNHG. Our results suggest that latest Pliocene/early Pleistocene G-IG productivity changes in the EEP were strongly controlled by nutrient supply from Southern Ocean-sourced mode waters. Our records show a clear G-IG cyclicity from MIS 100 onward with productivity levels increasing from full glacial conditions and peaking at glacial terminations. We conclude that enhanced nutrient delivery from high southern latitudes during full glacial conditions together with superimposed intensified regional upwelling toward glacial terminations strongly regulated primary productivity rates in the EEP from MIS 100 onward.

  17. Geomorphical and Geochronological Constrains of the Last Glacial Period in Southern Patagonia, Southern South America

    NASA Astrophysics Data System (ADS)

    García, J.; Hall, B. L.; Kaplan, M. R.; Vega, R. M.; Binnie, S. A.; Hein, A.; Gómez, G. N.; Ferrada, J. J.

    2013-12-01

    Despite the outer limits of the former Patagonian ice sheet (PIS, ~38-55S) having been extensively mapped, it remains unknown if the Patagonian glaciers fluctuated synchronously or asynchronously during the last glacial period. Previous work has revealed asynchronous spatiotemporal ice dynamics along the eastern and western ice-margins at the end of the last glaciation but it is not well understood if the northern and southern parts of the PIS reached concurrent maximum glaciation during the last glacial cycle. The Patagonian Andes is the only landmass involving the southern westerly wind belt latitudinal range, which is thought to have played a key role in past glacial and climate changes. Therefore, reconstructing southern Andes glacier history constitutes a key element for understanding the cause of glaciations in Patagonia and the role of the westerlies in climate change. Here, we discuss paleoglaciological and paleoclimatological implications of new 10Be and 14C data obtained from moraines and strategically selected mires in two contiguous glacially molded basins of south Patagonia (48-55S): Torres del Paine (51S) and Última Esperanza (52S). In this region, we focused our 10Be cosmogenic-dating efforts in the previously undated outer moraines deposited (supposedly) during the last glacial cycle. In order to crosscheck cosmogenic data we collected boulders embedded in moraines and cobbles from the main glaciofluvial plains grading from the outermost moraines. Geomorphic and cosmogenic dating affords evidence for glacial maximum conditions occurring between 40-50 ka (ka = thousand of years before present) in southern Patagonia, which is different from other chronologies within southern South America. We obtained 14C basal ages from sites located within moraine depressions and on former paleolake shorelines and thus these may provide key data on deglaciation and debated regional paleolake history.

  18. Subglacial morphology and glacial evolution of the Palmer deep outlet system, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Domack, Eugene; Amblàs, David; Gilbert, Robert; Brachfeld, Stefanie; Camerlenghi, Angelo; Rebesco, Michele; Canals, Miquel; Urgeles, Roger

    2006-04-01

    The Palmer Deep is an erosional, inner-shelf trough located at the convergence of ice flow from three distinct accumulation centers. It served as a funnel for ice flow out across the continental shelf of the Antarctic Peninsula. Swath mapping of 1440 km 2 of seafloor in and adjacent to the Palmer Deep basin defines a large paleo-ice stream that flowed 230 km across the Antarctic Peninsula continental shelf during the Last Glacial Maximum (MIS-2). The unique perspective and detail of the Palmer Deep physiography allow us to recognize several phases of erosion and deposition in the outlet basin. These events are uniquely constrained by two ODP drill cores (sites 1099 and 1098) that together recovered over 150 m of latest Pleistocene and Holocene sediment. We divide this region of the continental shelf into three zones based upon mega- to meso-scale bathymetric features and emphasize that all three were part of one glacial outlet during the most recent period of glaciation. These zones include from inner shelf to outer shelf: the Palmer Deep basin, the Palmer Deep Outlet Sill and the Hugo Island Trough. Specific seafloor features associated with these zones include: relict terraces, sub-glacial lake deltas, channels and levees, debris slopes, spindle and out bed forms, mega-scale glacial lineations, morainal banks, and bank breach points. The origin of many of these features can be linked to the development of a sub-glacial lake basin within the Palmer Deep during or prior to MIS-2, its subsequent drainage, and recession of the Palmer Deep ice stream system. This sub-glacial lake system is reconstructed at the head of a major paleo-ice stream.

  19. North Atlantic Deep Water Production during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Noble, Taryn L.; Mulitza, Stefan; Chiessi, Cristiano M.; Bayon, Germain

    2016-06-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial-interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.

  20. North Atlantic Deep Water Production during the Last Glacial Maximum.

    PubMed

    Howe, Jacob N W; Piotrowski, Alexander M; Noble, Taryn L; Mulitza, Stefan; Chiessi, Cristiano M; Bayon, Germain

    2016-01-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial-interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ(13)C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters. PMID:27256826

  1. Ice flow models and glacial erosion over multiple glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Headley, R. M.; Ehlers, T. A.

    2015-03-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological timescales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model yields erosion rates that vary spatially and by almost an order of magnitude from those of the SIA model. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered area that are greater than 30% those of the SIA model, again with larger differences for temperate ice. Over multiple glaciations and long timescales, these results suggest that higher-order glacial physics should be considered, particularly in temperate, mountainous settings.

  2. Stratification and Circulation of the Glacial Ocean: Reconstructing Watermass Geometry and Circulation with Nd Isotopes

    NASA Astrophysics Data System (ADS)

    Piotrowski, A. M.; Goldstein, S. L.; Hemming, S. R.

    2004-12-01

    One of the most important debates in paleoclimate research is the link between ocean circulation and climate change. On glacial-interglacial timescales, global climate is driven by Milankovich orbital cycles, though the resulting insolation variations are small and require amplifying mechanisms. Changes in the strength of global "conveyor-belt" ocean circulation is one possible amplifying mechanism, and abrupt switches between circulation modes may have triggered rapid climate changes. Understanding the ocean-climate link has been difficult because nutrient-based proxies of ocean circulation disagree with each other. During the last glacial period, benthic foraminiferal carbon isotopes suggest substantially weaker North Atlantic Deep Water (NADW) formation and export, while benthic Cd/Ca indicate a strong flow of North Atlantic -sourced water at intermediate depths. Non-circulatory effects (including fractionation during calcite dissolution, changes in global carbon budget, air-sea gas equilibration, and porewater effects) are known to overprint these proxies, likely causing this discrepancy. Neodymium isotopes can resolve this disagreement because it does not share the same sources of error as nutrient-based proxies. We report Nd isotopes measured on Fe-Mn leaches from sites located throughout the South Atlantic. These sites range in depth from 2000 - 5000 mbsl, allowing a three-dimensional perspective of South Atlantic watermass geometry. The leachates have marine Sr isotopic composition. Coretop samples have Nd isotopic compositions which match overlying bottom waters. This coretop calibration is consistent with known vertical and horizontal geometry of NADW and Antarctic Bottom Water. Samples from the last glacial maximum show a coherent glacial-interglacial pattern of circulation change which is most simply interpreted as indicating a reduction in the amount of NADW reaching the South Atlantic. The relative contribution of NADW to the glacial South Atlantic

  3. Glacial curvilineations: gradual or catastrophic origin?

    NASA Astrophysics Data System (ADS)

    Clark, Chris; Livingstone, Stephen

    2016-04-01

    Glacial curvilineations (GCLs) are enigmatic landforms that have recently been discovered in Poland (Lesemann et al., 2010, 2014). They comprise parallel sets of sinuous ridges separated by troughs that are found in tunnel valleys and replicate the morphology and pattern of the valley sides. The sedimentology for some has been reported to indicate that the sediment composition relates to a pre-GCL phase. So far just one theory for their formation exists - erosion by longitudinal-vortices within high-energy subglacial meltwater flows (Lesemann et al., 2010). Here, we provide an alternative hypothesis for their formation developed from observations of GCLs found along the southern sector of the Laurentide Ice Sheet. In all cases GCLs were found associated with tunnel valley widenings or hollows and occur as distinct parallel sets that mimic each other in terms of nicks and cusps. Using analogies from tree-rings and coral growth we take such mimicry as indicating either incremental growth or development from a template over time. Although without a strong physical explanation we find it much less likely that a series of parallel water channels would maintain such strong mimicry. We instead suggest that subglacial thawing of frozen ground in association with discrete water bodies (tunnel valleys or subglacial lakes) resulted in retrogressive bank failure, possibly along a glide plane provided by a frozen surface. References: Lesemann, J.-E., Piotrowski, J. a, Wysota, W., 2010. "Glacial curvilineations": New glacial landforms produced by longitudinal vortices in subglacial meltwater flows. Geomorphology 120, 153-161. Lesemann, J.-E., Piotrowski, J. a, Wysota, W., 2014. Genesis of the "glacial curvilineation" landscape by meltwater processes under the former Scandinavian Ice Sheet, Poland. Sediment. Geol. 312, 1-18.

  4. High genetic differentiation in the alpine plant Campanula alpina Jacq. (Campanulaceae): evidence for glacial survival in several Carpathian regions and long-term isolation between the Carpathians and the Alps.

    PubMed

    Ronikier, M; Cieślak, E; Korbecka, G

    2008-04-01

    A survey of amplified fragment length polymorphism (AFLP) and chloroplast DNA (cpDNA) variation was conducted to elucidate the phylogeography of Campanula alpina, a key species of silicicolous alpine grasslands in the Carpathians with a disjunct distribution in the Eastern European Alps. The Carpathians experienced a different glacial history from the Alps: local glaciers were present only in the highest massifs, while alpine habitats extended over larger areas related to their present distribution in this region. We asked: (i) whether in the Carpathians a high-mountain plant exhibits a complex phylogeographical structure or rather signatures of recent migrations, and (ii) whether the disjunct part of the species' distribution in the Alps resulted from a recent colonization from the Carpathians or from a restricted expansion from separate Eastern Alpine refugia. Our study revealed a clear phylogeographical pattern in AFLPs supported by congruent groups of distinct cpDNA haplotypes. Highest genetic differentiation was observed between the Alps and the Carpathians, indicating a long-term isolation between populations from these two mountain ranges. Further genetic division within the Carpathians suggests that current species' distribution is composed of several groups which have been isolated from each other for a long period. One genetic break separates Western from Southeastern Carpathian material, which is in line with a classical biogeographical boundary. A further, strongly supported genetic group was identified at the southwestern edge of the Carpathian arch. In the Eastern Alps, genetic traces of glacial survival in separate refugial areas in the calcareous northern part and the siliceous central part were found.

  5. Secondary uranium mineralization in southern Finland and its relationship to recent glacial events

    NASA Astrophysics Data System (ADS)

    Read, David; Black, Stuart; Buckby, Tracy; Hellmuth, Karl-Heinz; Marcos, Nuria; Siitari-Kauppi, Marja

    2008-02-01

    Uranium series dating has been carried out on secondary uranyl silicate minerals formed during sub-glacial and post-glacial weathering of Proterozoic uraninite ores in south west Finland. The samples were obtained from two sites adjacent to the Salpauselkä III ice marginal formation and cover a range of depths, from the surface to more than 60 m. Measured ages fall into three distinct groups, 70-100 ka, 28-36 ka and < 2500 yr. The youngest set is associated with surface exposures and the crystals display clear evidence of re-working. The most likely trigger for uranium release at depths below the surface weathering zone is intrusion of oxidising glacial melt water. The latter is often characterised by very high discharge rates along channels, which close once the overpressure generated at the ice margin is released. There is excellent correspondence between the two Finnish sites and published data for similar deposits over a large area of southern and central Sweden. None of the seventy samples analysed gave a U-Th age between 40 and 70 ka; a second hiatus is apparent at 20 ka, coinciding with the Last Glacial Maximum. Thus, the process responsible for uranyl silicate formation was halted for significant periods, owing to a change in geochemical conditions or the hydrogeological regime. These data support the presence of interstadial conditions during the Early and Middle Weichselian since in the absence of major climatic perturbations the uranium phases at depth are stable. When viewed in conjunction with proxy data from mammoth remains it would appear that the region was ice-free prior to the Last Glacial Maximum.

  6. Constraints on the glacial erosion rule

    NASA Astrophysics Data System (ADS)

    Herman, Frédéric

    2016-04-01

    It is thought that glaciers erode their underlying bedrock mainly through abrasion and quarrying. Theories predict erosion to be proportional to ice-sliding velocity raised to some power: ˙e = Kguls (1) where ė is the erosion rate, and Kg a proportionality constant and l an exponent. By implementing such a rule in numerical models, it has been possible to reproduce typical glacial landscape features, such as U-shape valleys, hanging valleys, glacial cirques or fjords. Although there have been great advances in the level of sophistication of these models, for example through the inclusion of high-order ice dynamics and subglacial hydrology, the proportionality constant, and the exponent have remained poorly constrained parameters. Recently, two independent studies in the Antarctic Peninsula and Patagonian Andes (Koppes et al., 2015) and the Franz Josef Glacier, New Zealand (Herman et al., 2015) simultaneously collected erosion rate and ice velocity data to find that erosion depends non-linearly on sliding velocity, and that the exponent on velocity is about 2. Such a nonlinear rule is appealing because it may, in part, explain the observed variations in erosion rates globally. Furthermore, an exponent about 2 closely matches theoretical predictions for abrasion. Although it is tempting to argue that abrasion is the dominant process for fast flowing glaciers like the Franz Josef Glacier, there is a clear need for more data and better quantification for the role of quarrying. Both studies also led to very similar values for the proportionality constant Kg. These new results therefore imply that glacial erosion processes might be better constrained than previously thought. Given that glacial velocity can nowadays be measured and modeled at an unprecedented resolution, it may potentially become possible to use glacial erosion models in a predictive manner. Herman, F. et al. "Erosion by an Alpine glacier." Science 350.6257 (2015): 193-195. Koppes, M. et al. "Observed

  7. Glacial Retreat and Associated Glacial Lake Hazards in the High Tien Shan

    NASA Astrophysics Data System (ADS)

    Smith, T. T.

    2013-12-01

    A number of studies have identified glacial retreat throughout the greater Himalayan region over the past few decades, but the Karakorum region remains an anomaly with large stagnating or advancing glaciers. The glacial behavior in the Tien Shan is still unclear, as few studies have investigated mass balances in the region. This study focuses on the highest peaks of the Tien Shan mountain range, in the region of Jengish Chokusu along the Kyrgyzstan-China-Kazakhstan border. In a first step, a 30-year time series of Landsat imagery (n=27) and ASTER imagery (n=10) was developed to track glacial growth and retreat in the region. Using a combination of spectral and topographic information, glacial outlines are automatically delineated. As several important glaciers in the study region contain medium to high levels of debris cover, our algorithm also improves upon current methods of detecting debris-covered glaciers by using topography, distance weighting methods, river networks, and additional spectral data. Linked to glacial retreat are glacial lake outburst floods (GLOFs) that have become increasingly common in High Mountain Asia over the last few decades. As glaciers retreat, their melt water is often trapped by weakly bonded moraines. These moraines have been known to fail due to overtopping caused by surge waves created by avalanches, rockslides, or glacial calving. A suite of studies throughout High Mountain Asia have used remotely-sensed data to monitor the formation and growth of glacial lakes. In a second step of the work, lake-area changes over the past 15 years were tracked monthly and seasonally using dense Landsat/ASTER coverage (n=30) with an automatic procedure based on spectral and topographic information. Previous work has identified GLOFs as a significant process for infrastructural damage in the southern Tien Shan/northern Pamir, as well as in the better studied Himalaya region. Lake identification and quantification of lake-growth rates is a valuable

  8. Current transition from glacial to periglacial processes in the Dolomites (South-Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Seppi, R.; Zanoner, T.; Carton, A.; Bondesan, A.; Francese, R.; Carturan, L.; Zumiani, M.; Giorgi, M.; Ninfo, A.

    2015-01-01

    A close relationship between glacial and periglacial landforms is frequently observed in alpine environments, where a transition from glacial to periglacial processes often took place after the end of the Little Ice Age (LIA). Understanding the origin of these landforms is challenging, and assessing the current spatial domain of glacial and periglacial processes may be a difficult task in high-relief areas, where thick and widespread debris cover often characterize rapidly decaying glaciers. Here we present a comprehensive study of a composite landform located in the Dolomites (South-Eastern Alps), combining geomorphological, geophysical and topographic surveys with ground surface temperature measurements. Results indicate that a debris-covered glacier persists in the upper part, rather large compared to the LIA extent, but currently inactive and rapidly losing mass. An active rock glacier exists in the lower part, surrounded by discontinuous permafrost. A frozen body about 10 m thick was detected in the rock glacier and geomorphological evidence suggests that this ice mass is completely detached from the debris-covered glacier. Our findings suggest that the lower part of the composite landform is probably a remnant of the ancient glacier tongue and is currently evolving under periglacial conditions. Periglacial processes are therefore replacing glacial processes which dominated in this site during the LIA.

  9. North Atlantic Deep Water Production during the Last Glacial Maximum

    PubMed Central

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Noble, Taryn L.; Mulitza, Stefan; Chiessi, Cristiano M.; Bayon, Germain

    2016-01-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters. PMID:27256826

  10. Earth's glacial record and its tectonic setting

    NASA Astrophysics Data System (ADS)

    Eyles, N.

    1993-09-01

    Glaciations have occurred episodically at different time intervals and for different durations in Earth's history. Ice covers have formed in a wide range of plate tectonic and structural settings but the bulk of Earth's glacial record can be shown to have been deposited and preserved in basins within extensional settings. In such basins, source area uplift and basin subsidence fulfill the tectonic preconditions for the initiation of glaciation and the accomodation and preservation of glaciclastic sediments. Tectonic setting, in particular subsidence rates, also dictates the type of glaciclastic facies and facies successions that are deposited. Many pre-Pleistocene glaciated basins commonly contain well-defined tectonostratigraphic successions recording the interplay of tectonics and sedimentation; traditional climatostratigraphic approaches involving interpretation in terms of either ice advance/retreat cycles or glacio-eustatic sea-level change require revision. The direct record of continental glaciation in Earth history, in the form of classically-recognised continental glacial landforms and "tillites", is meagre; it is probable that more than 95% of the volume of preserved "glacial" strata are glacially-influenced marine deposits that record delivery of large amounts of glaciclastic sediment to offshore basins. This flux has been partially or completely reworked by "normal" sedimentary processes such that the record of glaciation and climate change is recorded in marine successions and is difficult to decipher. The dominant "glacial" facies in the rock record are subaqueous debris flow diamictites and turbidites recording the selective preservation of poorly-sorted glaciclastic sediment deposited in deep water basins by sediment gravity flows. However, these facies are also typical of many non-glacial settings, especially volcanically-influenced environments; numerous Archean and Proterozoic diamictites, described in the older literature as tillites, have no

  11. Glacial isostatic uplift of the European Alps

    NASA Astrophysics Data System (ADS)

    Mey, Juergen; Scherler, Dirk; Wickert, Andrew D.; Egholm, David L.; Tesauro, Magdala; Schildgen, Taylor F.; Strecker, Manfred R.

    2016-04-01

    Present-day vertical movements of the Earth's surface are mostly due to tectonic deformation, volcanic processes, and crustal loading/unloading. In tectonically stable regions of North America and Scandinavia, vertical movements are almost entirely attributable to glacial isostatic rebound after the melting of the Laurentide and Fennoscandian ice sheets. In contrast, the Pleistocene Alpine icecap grew on a younger mountain belt that formed by collision of the European and African plates, still subject to shortening. Therefore, measured uplift is potentially a composite signal of tectonic shortening and unloading after deglaciation and concomitant erosion. Deciphering the contributions of tectonics and crustal unloading to present-day uplift rates in formerly-glaciated mountain belts is a prerequisite to using uplift data to estimate the viscosity structure of the Earth's mantle, a key variable in geodynamics. We evaluate the post-LGM glacial-isostatic rebound of the Alps following a 4-tiered procedure. First, we estimated the thickness distribution of sedimentary valley fills to create a bedrock map of the entire mountain belt. Second, this map was used as topographic basis for the reconstruction of the Alpine icecap using a numerical ice-flow model. Third, we estimated the equilibrium deflection of the Alpine lithosphere, using the combined loads of ice and sediments with a variable effective elastic thickness. Finally, we used an exponential decay function to infer the residual deflection and the present-day uplift rate for a range of upper mantle viscosities. Our analysis shows that virtually all of the geodetically measured surface uplift in the Swiss and the Austrian Alps can be attributed to glacial unloading and redistribution of sediments, assuming an upper-mantle viscosity lower than that inferred for an old craton (e.g., Fennoscandia), but higher than that for a region with recent crustal thinning (e.g., Basin and Range province).

  12. Paleoecology of central Kentucky since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Wilkins, Gary R.; Delcourt, Paul A.; Delcourt, Hazel R.; Harrison, Frederick W.; Turner, Manson R.

    1991-09-01

    Pollen grains and spores, plant macrofossils, and sponge spicules from a 7.2-m sediment core from Jackson Pond dating back to 20,000 yr B.P. are the basis for new interpretations of vegetational, limnological, and climatic changes in central Kentucky. During the full-glacial interval (20,400 to 16,800 yr B.P.) upland vegetation was closed spruce forest with jack pine as a subdominant. Aquatic macrophyte and sponge assemblages indicate that the site was a relatively deep, open pond with low organic productivity. During late-glacial time (16,800 to 11,300 yr B.P.) spruce populations continued to dominate while jack pine declined and sedge increased as the vegetation became a more open, taiga-like boreal woodland. Between 11,300 and 10,000 yr B.P., abundances of spruce and oak pollen oscillated reciprocally, possibly reflecting the Younger Dryas oscillation as boreal taxa underwent a series of declines and increases at the southern limit of their ranges before becoming extirpated and replaced by deciduous forest. In the early Holocene (10,000 to 7300 yr B.P.) a mesic deciduous woodland developed; it was replaced by xeric oak-hickory forest during the middle Holocene between 7300 and 3900 yr B.P. Grass increased after 3900 yr B.P., indicating that the presettlement vegetation mosaic of mixed deciduous forest and prairie (the "Kentucky Barrens") became established in central Kentucky after the Hypsithermal interval. Sponge spicules increased in number during the Holocene, reflecting reduced water depths in the pond. Sediment infilling, as well as climatic warming and the expansion of fringing shrub thickets, increased nutrient and habitat availability for freshwater sponges.

  13. Glacial disparities in Intermediate Mode Water advection in the South Pacific Gyre

    NASA Astrophysics Data System (ADS)

    Tapia, R.; Nuernberg, D.; Ronge, T.; Tiedemann, R.

    2014-12-01

    The Intermediate Mode Waters formed in the Southern Ocean are critical for the lower thermocline ventilation process in the Southern Hemisphere Gyres. They also might have served as the most relevant pathways transporting climatic signals from high to low latitudes via the "oceanic tunneling" on glacial/interglacial time scales. Despite the importance of the Southern Ocean Intermediate Waters (SOIWs), our understanding on the long-term evolution, exact advection paths, and impact on the South Pacific Gyre's thermocline is still fragmentary. Here, we present a 200 kyr record of paired Mg/Ca ratios and stable oxygen isotope from surface dweller and deep dwelling planktonic foraminifera, from the South Pacific Gyre (SPG). On average, the Mg/Ca-derived sea Surface Temperatures (Globigerina bulloides) show similar conditions during the LGM and Marine Isotope Stage (MIS) 6 (9.4 °C versus 9.9 °C). In contrast, our Mg/Ca-derived subsurface temperatures (Globorotalia inflata and Globorotalia truncatulinoides) suggest LGM from ~3 to ~2 °C colder than MIS 6. The reconstructed subsurface ice volume corrected stable oxygen isotope ratio of seawater (δ18Osw-ivc, proxy for local salinity changes) suggests opposing glacial subsurface conditions, i.e., slightly saltier-than-Holocene during MIS 6 to fresher-than-Holocene during MIS 2. Considering that subsurface hydrography at the core site is plausibly driven by the formation and/or advection of SOIWs from the South East Pacific, our results provide further support on the relevance of subsurface processes in the Southern Ocean transferring climatic signals (temperature and salinity) to the SPG. Furthermore, the contrasting subsurface glacial scenarios at the SPG's thermocline imply that the advection of SOIWs during glacial stages could be highly variable during different glacial stages.

  14. 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.

  15. Mapping Glacial Weathering Processes with Thermal Infrared Remote Sensing: A Case Study at Robertson Glacier, Canada

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Christensen, P. R.; Shock, E.; Canovas, P. A., III

    2014-12-01

    Geologic weathering processes in cold environments, especially subglacial chemical processes acting on rock and sediment, are not well characterized due to the difficulty of accessing these environments. Glacial weathering of geologic materials contributes to the solute flux in meltwater and provides a potential source of energy to chemotrophic microbes, and is thus an important component to understand. In this study, we use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to map the extent of glacial weathering in the front range of the Canadian Rockies using remotely detected infrared spectra. We ground-truth our observations using laboratory infrared spectroscopy, x-ray diffraction, and geochemical analyses of field samples. The major goals of the project are to quantify weathering inputs to the glacial energy budget, and to link in situ sampling with remote sensing capabilities. Robertson Glacier, Alberta, Canada is an excellent field site for this technique as it is easily accessible and its retreating stage allows sampling of fresh subglacial and englacial sediments. Infrared imagery of the region was collected with the ASTER satellite instrument. At that same time, samples of glacially altered rock and sediments were collected on a downstream transect of the glacier and outwash plain. Infrared laboratory spectroscopy and x-ray diffraction were used to determine the composition and abundance of minerals present. Geochemical data were also collected at each location, and ice and water samples were analyzed for major and minor elements. Our initial conclusion is that the majority of the weathering seems to be occurring at the glacier-rock interface rather than in the outwash stream. Results from both laboratory and ASTER data indicate the presence of leached weathering rinds. A general trend of decreasing carbonate abundances with elevation (i.e. residence time in ice) is observed, which is consistent with increasing calcium ion

  16. Characterization of a landfill-derived contaminant plume in glacial and bedrock aquifers, Dupage County, Illinois

    SciTech Connect

    Vagt, P.J.

    1987-01-01

    In this study of the Blackwell landfill, DuPage County, Illinois, the contaminant plume is delineated and related to the site history and hydrogeology. Leachate leakage is attributed partly to landfill construction problems. The landfill is located partly on a sand-and-gravel aquifer and partly on thick, low permeability till, all overlying an important dolomite aquifer. A roughly concentric contaminant plume surrounds the landfill in the glacial materials. It was calculated that the 30-acre landfill leaks at a rate of 2000 to 3000 cubic feet per day. The leakage volume was calculated from estimates of infiltration and observations of leachate-level change. The leachate leaks primarily into the shallow glacial aquifer where it is rapidly diluted; the TDS and chloride concentrations reach background levels within the forest preserve boundaries, (within several hundred feet of the landfill). Volatile organic compounds (VOC) are found at concentrations greater than 100 ppb in several glacial-aquifer monitoring wells close to the landfill, but concentrations decrease rapidly with distance. VOC have not been detected in the glacial aquifer at the property boundary. The contaminant plume appears to have reached equilibrium. The bedrock is probably in continuity with the glacial aquifer; however, the traces of volatile organics found therein are not clearly linked to the landfill plume, and other possible sources are located nearby. The Random Walk Solute Transport Model, published by Prickett, Naymik, and Lonnqust in 1981, was applied to the system. The flow simulation was used in both horizontal and vertical section and did support field-derived flow regime data. The solution of the horizontal flow pattern was able to replicate the steady-state contaminant distribution, but the profile simulation along a major flow line was too dependent upon estimates of dispersivity values to provide meaningful system evaluation.

  17. Glacial heritage: knowledge, inventory and promotion in the Chablais area (France, Switzerland)

    NASA Astrophysics Data System (ADS)

    Perret, A.; Reynard, E.; Delannoy, J.-J.

    2012-04-01

    This study is part of an Interreg IVA project (www.123chablais.com) dealing with the promotion of different types of natural and cultural heritage in the Chablais area (French and Swiss Prealps) and is linked to the candidature of the French Chablais territory for the European Geoparks Network. The objective of the study is to develop a strategy for the promotion of the glacial heritage (landforms, deposits) in an area where the geomorphological features are highly influenced by glacial history and where key concepts in the Quaternary sciences were developed (e.g. the theory of multiple glaciations by Morlot in 1859), but that is now nearly completely deglaciated. The challenge is to find solutions to explain why the glacial heritage is so important for the regional economy and how it influences the life of inhabitants (e.g. Evian and Thonon mineral water, extraction industry, landscape and tourism), even if glaciers are not so impressive than in other parts of the Alps. The research is divided in three parts. (1) The first one aims to enhance knowledge on glacial landforms and deposits. The study area, that is quite large, has been intensively studied for more than two centuries; nevertheless, some parts have been only poorly studied. Intensive field survey was carried out to fill in the gaps of knowledge and some landforms, such as erratic boulders, have been dated in order to establish a chronology of deglaciation. All of these different elements have been included in a Geographic Information System with the aim of establishing maps of glacial stages in the Chablais area. (2) From this, an inventory of glacial geosites has been carried out, using the assessment method developed by Reynard et al. (2007). A specific focus has been on the assessment of the potential of the selected sites for educational purposes and geotourist promotion. (3) The last part has been the preparation of adapted educational and promotional supports. In particular, an exhibition will be

  18. Range persistence during the last glacial maximum: Carex macrocephala was not restricted to glacial refugia.

    PubMed

    King, Matthew G; Horning, Matthew E; Roalson, Eric H

    2009-10-01

    The distribution of many species inhabiting northwestern North America has been heavily influenced by the climatic changes during the late Pleistocene. Several studies have suggested that species were restricted to glacial refugia north and/or south of the continental ice sheet front. It is also hypothesized that the coast of northwestern North America could have been a prime location for glacial refugia because of the lowering of the eustatic sea level and the concomitant rise of the continental shelf because of tectonic rebound. Alternatively, some coastal species distributions and demographics may have been unaffected in the long-term by the last glacial maximum (LGM). We tested the glacial refugium hypothesis on an obligate coastal plant species, Carex macrocephala by sampling 600 individuals from 41 populations with 11 nuclear microsatellite loci and the rpL16 plastid intragenic spacer region. The microsatellite data sets suggest a low level of population differentiation with a standardized G'(ST) = 0.032 and inbreeding was high with an F = 0.969. The homogenization of the populations along the coast was supported by a principal coordinate analysis, amovas and samova analyses. Analyses using the rpL16 data set support the results of the microsatellite analyses, with a low F(ST) of 0.042. Coalescent and mismatch analyses using rpL16 suggest that C. macrocephala has not gone through a significant bottleneck within the past 100,000 years, although a much earlier population expansion was indicated by the mismatch analysis. Carex macrocephala exhibits the characteristics of metapopulation dynamics and on the basis of these results, we concluded that it was not restricted to glacial refugia during the LGM, but that it existed as a large metapopulation.

  19. Glacial and periglacial geomorphology and its paleoclimatological significance in three North Ethiopian Mountains, including a detailed geomorphological map

    NASA Astrophysics Data System (ADS)

    Hendrickx, Hanne; Jacob, Miro; Frankl, Amaury; Nyssen, Jan

    2015-10-01

    Geomorphological investigations and detailed mapping of past and present (peri)glacial landforms are required in order to understand the impact of climatic anomalies. The Ethiopian Highlands show a great variety in past and contemporary climate, and therefore, in the occurrence of glacial and periglacial landforms. However, only a few mountain areas have been studied, and detailed geomorphological understanding is lacking. In order to allow a fine reconstruction of the impact of the past glacial cycle on the geomorphology, vegetation complexes, and temperature anomalies, a detailed geomorphological map of three mountain areas (Mt. Ferrah Amba, 12°51‧N 39°29‧E; Mt. Lib Amba, 12°04‧N 39°22‧; and Mt. Abuna Yosef, 12°08‧N 39°11‧E) was produced. In all three study areas, inactive solifluction lobes, presumably from the Last Glacial Maximum (LGM), were found. In the highest study area of Abuna Yosef, three sites were discovered bearing morainic material from small late Pleistocene glaciers. These marginal glaciers occurred below the modeled snowline and existed because of local topo-climatic conditions. Evidence of such Pleistocene avalanche-fed glaciers in Ethiopia (and Africa) has not been produced earlier. Current frost action is limited to frost cracks and small-scale patterned ground phenomena. The depression of the altitudinal belts of periglacial and glacial processes during the last cold period was assessed through periglacial and glacial landform mapping and comparisons with data from other mountain areas taking latitude into account. The depression of glacial and periglacial belts of approximately 600 m implies a temperature drop around 6 °C in the last cold period. This cooling is in line with temperature depressions elsewhere in East Africa during the LGM. This study serves as a case study for all the intermediate mountains (3500-4200 m) of the North Ethiopian highlands.

  20. Glacial CO2 Cycles: A Composite Scenario

    NASA Astrophysics Data System (ADS)

    Broecker, W. S.

    2015-12-01

    There are three main contributors to the glacial drawdown of atmospheric CO2 content: starvation of the supply of carbon to the ocean-atmosphere reservoir, excess CO2 storage in the deep sea, and surface-ocean cooling. In this talk, I explore a scenario in which all three play significant roles. Key to this scenario is the assumption that deep ocean storage is related to the extent of nutrient stratification of the deep Atlantic. The stronger this stratification, the larger the storage of respiration CO2. Further, it is my contention that the link between Milankovitch insolation cycles and climate is reorganizations of the ocean's thermohaline circulation leading to changes in the deep ocean's CO2 storage. If this is the case, the deep Atlantic d13C record kept in benthic foraminifera shells tells us that deep ocean CO2 storage follows Northern Hemisphere summer insolation cycles and thus lacks the downward ramp so prominent in the records of sea level, benthic 18O and CO2. Rather, the ramp is created by the damping of planetary CO2 emissions during glacial time intervals. As it is premature to present a specific scenario, I provide an example as to how these three contributors might be combined. As their magnitudes and shapes remain largely unconstrained, the intent of this exercise is to provoke creative thinking.

  1. Interhemispheric correlation of late pleistocene glacial events

    SciTech Connect

    Lowell, T.V.; Heusser, C.J.; Andersen, B.G.

    1995-09-15

    A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and {ge}33,500 carbon-14 years before present ({sup 14}C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000 {sup 14}C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720 {sup 14}C yr B.P., and at the beginning of the Younger Dryas at 11,050 {sup 14}C yr B.P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges. 51 refs., 3 figs., 1 tab.

  2. A coherent high-precision radiocarbon chronology for the Late-glacial sequence at Sluggan Bog, Co. Antrim, Northern Ireland

    NASA Astrophysics Data System (ADS)

    Lowe, J. J.; Walker, M. J. C.; Scott, E. M.; Harkness, D. D.; Bryant, C. L.; Davies, S. M.

    2004-02-01

    Seventy-five radiocarbon dates are presented from Sluggan Bog in Co. Antrim, Northern Ireland. The Holocene peats are underlain by Late-glacial sediments, which also appear to have accumulated largely in a mire environment. The radiocarbon dates, from the Late-glacial and early Holocene part of the profile, were obtained from the humic and humin fractions of the sedimentary matrix, and from plant macrofossils. The last-named were dated by AMS and the sediment samples by radiometric (beta counting) methods. Age-depth models for the three dating series show a very high level of agreement between the two fractions and the macrofossils. No statistically significant difference is found between the beta counting and AMS results. Three tephras were located in the profile, the uppermost of which is in a stratigraphical position suggestive of the Vedde Ash, but the geochemical and radiocarbon evidence do not support this interpretation. The lower ashes are in the correct stratigraphical position for the Laacher See and Borrobol tephras, attributions substantiated by the radiocarbon evidence, but not by the geochemical data. The Sluggan sequence has generated one of the most internally consistent radiocarbon chronologies for any Late-glacial site in the British Isles, and it is suggested that in future more effort should be devoted to the search for, and analysis of, Late-glacial mire sequences, rather than the limnic records that have formed the principal focus of Late-glacial investigations hitherto. Copyright

  3. Groundwater Transport of Strontium 90 in a Glacial Outwash Environment

    NASA Astrophysics Data System (ADS)

    Kipp, Kenneth L., Jr.; Stollenwerk, Kenneth G.; Grove, David B.

    1986-04-01

    As part of the investigation of groundwater contamination at a uranium-scrap recovery plant at Wood River Junction, Rhode Island, laboratory experiments led to the development of a model for predicting the transport of strontium 90 in glacial outwash sediments based on an approximate mechanism for ion exchange. The multicomponent system was simplified to two components by regarding all exchangeable cations other than strontium 90 as a single component. The binary ion-exchange parameter was a function of the variable, total ion concentration. A one-dimensional solute transport model was formulated to evaluate the time necessary for natural groundwater flow to remove the strontium 90 contamination plume from the groundwater system to the Pawcatuck River. The finite difference transport equations were solved sequentially for total ion concentrations, then strontium 90 concentrations. Clay-free quartz and feldspar sands at the study site have little potential for strontium 90 sorption, and high calcium, magnesium, and sodium concentrations compete for the few ion exchange sites. As the total ion concentration plume moves out of the system, ion exchange of strontium 90 increases, reducing the strontium 90 concentration in the groundwater. Cleanout times predicted using the binary ion exchange mechanism were about two thirds of those predicted using a constant distribution coefficient. It is suggested that this type of model can simulate solute transport more realistically in many groundwater systems where the total ion concentration is not constant.

  4. Contrasting scaling properties of interglacial and glacial climates

    PubMed Central

    Shao, Zhi-Gang; Ditlevsen, Peter D.

    2016-01-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard–Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. PMID:26980084

  5. Contrasting scaling properties of interglacial and glacial climates.

    PubMed

    Shao, Zhi-Gang; Ditlevsen, Peter D

    2016-01-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard-Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. PMID:26980084

  6. Quaternary Glacial Mapping in Western Wisconsin Using Soil Survey Information

    ERIC Educational Resources Information Center

    Oehlke, Betsy M.; Dolliver, Holly A. S.

    2011-01-01

    The majority of soils in the western Wisconsin have developed from glacial sediments deposited during the Quaternary Period (2.6 million years before present). In many regions, multiple advances and retreats have left a complex landscape of diverse glacial sediments and landforms. The soils that have developed on these deposits reflect the nature…

  7. Light attenuation characteristics of glacially-fed lakes

    NASA Astrophysics Data System (ADS)

    Rose, Kevin C.; Hamilton, David P.; Williamson, Craig E.; McBride, Chris G.; Fischer, Janet M.; Olson, Mark H.; Saros, Jasmine E.; Allan, Mathew G.; Cabrol, Nathalie

    2014-07-01

    Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400-700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.

  8. Quaternary glacial geomorphosites from the Cantabrian Mountains (northern Iberian Peninsula): the Redes Natural Reservation and Picos de Europa Regional Park

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María

    2013-04-01

    The Cantabrian Mountains is a mountain range 480 km-long and up to 2,648 m altitude (Torre Cerredo Peak) trending parallel to the Cantabrian Coastline between Pyrenees and the northwest corner of the Iberian Peninsula (~43oN 5oW). This mountain range is an outstanding area to research the climatic patterns across South Europe during the Quaternary glaciations since well-preserved glacial features evidence the occurrence of past mountain glaciations in a climatic environment marked by the transition from a maritime climate (Atlantic) to Mediterranean one across the mountain range. The available studies in the Cantabrian Mountains stand that the regional glacial maximum recorded here is prior to ca 38, and that glaciers were in some locations remarkably retreated by the time of the global Last Glacial Maximum (Jiménez-Sánchez et al., in press; Serrano et al., in press). This study is focused on an area about 800 km2 that includes 36 peaks over 2,000 m (Pico Mampodre; 2,192 m) and partially covers the Redes Natural Reservation and Picos de Europa Regional Park. A geomorphologic database in ArcGIS was produced for this area as a previous step to reconstruct in detail the extent, flow pattern and chronology of the former glaciers (PhD under progress). Here we present a selection of 18 glacial geomorphosites classified according to genetic criteria in sites that show: (i) a nicely preserved moraine sequence recording the transition from glacial to periglacial conditions; (ii) glacial erosion features; (iii) glacial and ice related deposits (like moraines, ice-dammed deposits, erratic boulders or fluvio-glacial deposits); (iv) slope instability related to glacial debuttressing (complex landslides and rock avalanches); and (v) the interaction between the landscape and human activity. The interest of the geomorphosites is supported by its good quality of preservation, allowing its use as a basis to reconstruct the glacial and paraglacial processes in this region during

  9. The RECAP ice core - recovering a full Glacial record from Eastern Greenland

    NASA Astrophysics Data System (ADS)

    Vinther, Bo

    2016-04-01

    During May-June 2015 the 584m an international team drilled the RECAP (REnland ice CAp Project) ice core to bedrock on the Renland ice cap in Eastern Greenland. The exact drill site selection was determined from a detailed radio echo sounding (RES) grid, that had been measured from the ice cap surface right before drilling operations began. The RES data suggested that the ice cap internal layers are horizontal almost right down to the bed at the selected site, and that ice from the Glacial period was present some 30-50m above bedrock. The RES results have now been confirmed by measurements on the RECAP core that shows the entire Glacial being nicely preserved in the 20m section indicated by the RES measurements. The RECAP core thus yields the first undisturbed ice core record from Eastern Greenland covering the last Glacial, a marked improvement compared to the landmark 1988 Renland ice core that was disturbed by ice flow features both during the mid-Holocene and especially during Marine Isotope Stages 4 and 5.

  10. The sequence and timing of large late Pleistocene floods from glacial Lake Missoula

    NASA Astrophysics Data System (ADS)

    Hanson, Michelle A.; Lian, Olav B.; Clague, John J.

    2012-01-01

    Glacial Lake Missoula formed when the Purcell Trench lobe of the Cordilleran ice sheet dammed Clark Fork River in Montana during the Fraser Glaciation (marine oxygen isotope stage 2). Over a period of several thousand years, the lake repeatedly filled and drained through its ice dam, and floodwaters coursed across the landscape in eastern Washington. In this paper, we describe the stratigraphy and sedimentology of a significant new section of fine-grained glacial Lake Missoula sediment and compare this section to a similar, previously described sequence of sediments at Ninemile Creek, 26 km to the northwest. The new exposure, which we informally term the rail line section, is located near Missoula, Montana, and exposes 29 units, each of which consists of many silt and clay couplets that we interpret to be varves. The deposits are similar to other fine-grained sediments attributed to glacial Lake Missoula. Similar varved sediments overlie gravelly flood deposits elsewhere in the glacial Lake Missoula basin. Each of the 29 units represents a period when the lake was deepening, and all units show evidence for substantial draining of glacial Lake Missoula that repeatedly exposed the lake floor. The evidence includes erosion and deformation of glaciolacustrine sediment that we interpret happened during draining of the lake, desiccation cracks that formed during exposure of the lake bottom, and fluvial sand deposited as the lake began to refill. The floods date to between approximately 21.4 and 13.4 cal ka ago based on regional chronological data. The total number of varves at the rail line and Ninemile sites are, respectively, 732 and 583. Depending on lake refilling times, each exposure probably records 1350-1500 years of time. We present three new optical ages from the rail line and Ninemile sites that further limit the age of the floods. These ages, in calendar years, are 15.1 ± 0.6 ka at the base of the Ninemile exposure, and 14.8 ± 0.7 and 12.6 ± 0.6 ka midway

  11. Vegetation of the Central Beringian Lowlands: Evidence of a Glacial Refugium Found in IODP Expedition 323 Sediment

    NASA Astrophysics Data System (ADS)

    Westbrook, R.; Fowell, S. J.; Bigelow, N. H.; VanLaningham, S.

    2011-12-01

    The lowlands of central Beringia may have acted as a glacial refugium for boreal vegetation, which expanded into eastern and western Beringia as climate changed and glaciers retreated. Persistence of trees, shrubs and mesic-adapted vegetation in the vicinity of the modern Bering Strait and Bering Sea Shelf could have presented a barrier to migrating fauna during Pleistocene glacial stages. These hypotheses have been difficult to test, because sampling has been restricted to lacustrine sediment and peat deposits accessible in eastern and western Beringia. Pollen analysis of cores from IODP Expedition 323 (Bering Sea Expedition) sites U1339 and U1343, on the edge of the Bering Sea Shelf, permits reconstruction of the terrestrial vegetation of adjacent south-central Beringia. Palynological assemblages extracted from sediment that accumulated during Marine Isotope Stages 2 and 6 are dominated by grass (Poaceae ≥ 15%) and sedge (Cyperaceae ≥ 20%). Spruce (Picea ≥ 5%), birch (Betula ≥ 10%) and alder (Alnus ≥ 5%) are also consistently present throughout glacial/interglacial cycles, suggesting that small populations of trees and shrubs remained in central Beringia during glacial maxima. These results support the refugium hypothesis. Although it is possible that some of the boreal plant pollen deposited during glacial stages is derived from interglacial sediment reworked by rivers flowing across the emergent shelf, we postulate that such sources only contribute about 1-5% of the total sediment found at these Bering slope sites. Thus we consider the palynological assemblages from IODP Expedition 323 a robust proxy for the glacial vegetation of central Beringia.

  12. Technical Note: Using wavelet analyses on water depth time series to detect glacial influence in high-mountain hydrosystems

    NASA Astrophysics Data System (ADS)

    Cauvy-Fraunié, S.; Condom, T.; Rabatel, A.; Villacis, M.; Jacobsen, D.; Dangles, O.

    2013-04-01

    Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is currently modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Assessing the contribution of glacier run-off to stream discharge is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier-stream system interface. Here we propose a new methodological approach based on wavelet analyses on water depth time series to determine the glacial influence in glacierized catchments. We performed water depth measurement using water pressure loggers over ten months in 15 stream sites in two glacier-fed catchments in the Ecuadorian Andes (> 4000 m). We determined the global wavelet spectrum of each time series and defined the Wavelet Glacier Signal (WGS) as the ratio between the global wavelet power spectrum value at a 24 h-scale and its corresponding significance value. To test the relevance of the WGS we compared it with the percentage of the glacier cover in the catchments, a metric of glacier influence often used in the literature. We then tested whether one month data could be sufficient to reliably determine the glacial influence. As expected we found that the WGS of glacier-fed streams decreased downstream with the increasing of non-glacial tributaries. We also found that the WGS and the percentage of the glacier cover in the catchment were significantly positively correlated and that one month data was sufficient to identify and compare the glacial influence between two sites, provided that the water level time series were acquired over the same period. Furthermore, we found that our method permits to detect glacial signal in supposedly non-glacial sites, thereby evidencing glacial meltwater infiltrations. While we specifically focused on the

  13. Dating the Little Ice Age Advance of Jakobshavn Isbrae, Greenland, Using Pro-glacial Lake Sediments.

    NASA Astrophysics Data System (ADS)

    Stewart, H. A.; Briner, J. P.; Csatho, B. M.

    2009-05-01

    The Greenland Ice Sheet's (GIS) largest and fastest outlet glacier, Jakobshavn Isbrae, is one of the most significant contributors to GIS mass loss, draining an estimated 6.5% of the GIS area (Rignot and Kanagaratnam, 2006). Jakobshavn Isbrae has retreated significantly since the Little Ice Age (LIA, ca. 1250- 1900; Csatho et al., 2008), and continues to exhibit rapid changes in velocity and ice calving front position (Joughin et al., 2004). However, it is unknown for how long Jakobshavn Isbrae was at or near its extensive LIA position because there is a lack of chronological control on the LIA advance phase. We collected sediment cores from lakes just beyond the LIA margin to constrain the time when the advancing glacier's silt-laden meltwater entered the lake basins. Sediment cores from South Oval and Ice Boom lakes (informal names), which no longer receive glacial meltwater from Jakobshavn Isbrae because it has retreated out of their catchments, contain gyttja/glacial-silt/gyttja sequences that represent their non-glacial/pro-glacial/non-glacial histories. One additional site, ice-dammed Lake Morten (informal name), completely drained sometime between 1985 and 2001 AD. Outcrops of laminated sediments in the lake basin overly an intact tundra landscape. Four AMS radiocarbon dates from macrofossils immediately below the LIA sediments from the three lake basins reveal that Jakobshavn Isbrae reached its LIA maximum extent between 530±10 and 370±60 cal yr BP (1400-1640 AD). Furthermore, the continuous nature of the LIA-sediment units in all sites indicates that Jakobshavn Isbrae remained at or near its LIA maximum position between 1400-1640 AD and into the 20th century. Finally, pre-LIA organic-rich sediments at all sites continue uninterrupted down to basal sediments deposited during regional deglaciation in the Early Holocene. AMS radiocarbon ages on macrofossils from basal sediments at all sites range from 7220±40 to 8130±60 cal yr BP. We therefore interpret

  14. The influence of glacial ice sheets on Atlantic meridional overturning circulation through atmospheric circulation change under glacial climate

    NASA Astrophysics Data System (ADS)

    Sherriff-Tadano, Sam; Abe-Ouchi, Ayako; Yoshimori, Masakazu; Oka, Akira; Chan, Wing-Le

    2016-04-01

    Recent coupled modeling studies have shown that the existence of the glacial ice sheets intensifies the Atlantic meridional overturning circulation (AMOC). Since this may play an important role in maintaining a strong AMOC over the last glacial period, which is suggested by recent reconstruction study, it is very important to understand the process by which glacial ice sheets intensify the AMOC. Here, a decoupled simulation is conducted to investigate the effect of wind change due to glacial ice sheets on the AMOC, the crucial region where wind modifies the AMOC and the mechanism, which remained elusive in previous studies. First, from atmospheric general circulation model (AGCM) experiments, the effect of glacial ice sheets on the surface wind is evaluated. Second, from ocean general circulation model (OGCM) experiments, the influence of the wind stress change on the AMOC is evaluated by applying only the changes in the surface wind as a boundary condition, while leaving surface heat and freshwater fluxes unchanged. Moreover, several sensitivity experiments are conducted. Using the AGCM, glacial ice sheets are applied individually. Using the OGCM, changes in the wind are applied regionally or at different magnitudes, ranging from the full glacial to modern levels. These experiments demonstrate that glacial ice sheets intensify the AMOC through an increase in the wind stress curl mainly at the North Atlantic mid-latitudes. This intensification is caused by the increased Ekman upwelling and gyre transport of salt while the change in sea ice transport works as a negative, though minor, feedback.

  15. Wind Stress Increases Glacial Atlantic Overturning

    NASA Astrophysics Data System (ADS)

    Muglia, J.; Schmittner, A.

    2015-12-01

    Previous Paleoclimate Model Intercomparison Project (PMIP) simulations of the Last Glacial Maximum (LGM) Atlantic Meridional Overturning Circulation (AMOC) showed ambiguous results on transports and structure. Here we analyze the most recent PMIP3 models, which show a consistent increase (on average by 41%) and deepening (580 m) of the AMOC for all models with respect to pre-industrial control (PIC) simulations (see Figure), in contrast to some reconstructions. Changes in wind stress alone lead to similar AMOC responses in a climate-ocean circulation model, suggesting that atmospheric circulation changes in the North Atlantic due to the presence of ice sheets are an important control in the PMIP3 models' LGM response. These results improve our understanding of the LGM AMOC's driving forces and are relevant for the evaluation of models that are used in the IPCC's Assessment Reports for future climate projections, as well as for the currently ongoing design of the next round of PMIP.

  16. Glacial terminations and the global water budget

    SciTech Connect

    Broecker, W.S. . Lamont-Doherty Geological Observatory)

    1992-01-01

    Evidence suggests that the last glacial period came to an abrupt close about 13,500 years ago. This evidence indicates: (1) that the melting of the North American ice sheet commenced abruptly at this time; (2) that surface temperatures in the northern Atlantic rose sharply at this time; (3) that surface water conditions in the Antarctic changed abruptly at this time; (4) that the salinity of the Red Sea dropped abruptly at this time; and (5) that accumulation rate of planktonic foraminifera in the South China Sea underwent an abrupt five-fold increase at this time. This project has been directed toward better developing and documenting our explanation for the abruptness of these changes. This project has supported investigation of several aspects of this hypothesis. We suggest that the Greenland climate changes are driven by oscillations in salt content which modulate the strength of the Atlantic's conveyor circulation.

  17. Understanding Antarctic Climate and Glacial History

    NASA Astrophysics Data System (ADS)

    DeConto, Rob; Escutia, Carlota

    2010-01-01

    First Antarctic Climate Evolution Symposium; Granada, Spain, 7-11 September 2009; Antarctic Climate Evolution (ACE; http://www.ace.scar.org), a scientific research project of the Scientific Committee on Antarctic Research and a core International Polar Year project, held its first international symposium in Spain in September 2009. ACE's mission is to facilitate the study of Antarctic climate and glacial history through integration of numerical modeling with geophysical and geological data. Nearly 200 international scientists from the fields of climate, ocean, and ice modeling joined geologists, geophysicists, and geochemists for 5 days of intense interaction. Oral sessions were plenary and were limited to allow time for poster viewing, discussion, and workshops (http://www.acegranada2009.com/).

  18. Dissolved organic matter export in glacial and non-glacial streams along the Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Hood, E. W.; Scott, D.; Jeffery, A.; Schreiber, S.; Heavner, M.; Edwards, R.; D'Amore, D. V.; Fellman, J.

    2009-12-01

    The Gulf of Alaska drainage basin contains more than 75,000 km2 of glaciers, many of which are rapidly thinning and receding. We are using a paired watershed approach to evaluate how changes in glacier ecosystems will impact the export dissolved organic matter (DOM) into the Gulf of Alaska. Our primary study watersheds, Lemon Creek and Montana Creek, are similar in size, bedrock lithology and elevation range and extend from near sea level to the margin or interior of the Juneau Icefield. Lemon Creek has a glacial coverage of ~60%, while Montana Creek is free of glacier ice. Our goal is to evaluate seasonal differences in the quantity, chemical character and reactivity of DOM being exported from these watersheds to downstream near-shore marine ecosystems. In addition, we are monitoring a variety of physical parameters that influence instream DOM metabolism in both watersheds. Our initial results from the 2009 runoff season indicate that concentrations of dissolved organic carbon (DOC) are substantially higher in the non-glacial watershed. However, fluorescence analyses indicate that DOM from the glacier watershed has a higher protein and lower humic material content compared to DOM from the non-glacial watershed. After the spring snowmelt season, physical parameters between the two watersheds diverged, with higher streamflow and turbidity as well as colder water temperatures in the glacial watershed. Although our previous yield calculations show significantly higher DOC fluxes from the forested watershed, our results here suggest that glacier watersheds may be an important source of labile carbon to the near shore marine ecosystem. The contrast in the physical habitat between the two rivers (e.g glacier stream = cold, low light penetration, unstable substrate) supports the hypothesis that that in-stream DOM processing is limited within glacier dominated rivers, therefore delivering a higher percentage of labile DOM downstream.

  19. Late Glacial lakes - uniform or contrasting ecosystems?

    NASA Astrophysics Data System (ADS)

    Zawiska, Izabela; Rzodkiewicz, Monika; Noryśkiewicz, Agnieszka M.; Obremska, Milena; Ott, Florian; Kramkowski, Mateusz; Słowiński, Michał; Błaszkiewicz, Mirosław; Brauer, Achim

    2015-04-01

    Climate changes are one of the most investigated topic in paleolimnology. The Late Glacial and Early Holocene time are specially interesting as than most abrupt changes happened. Lake sediments are known to be great source of information of the past environments. They are functioning as natural archives because in them preserve animal and plants remains. In this study we investigated three cores of the biogenic sediments from the lakes located in close vicinity in Tuchola Forest (Northern Poland): paleolake Trzechowskie, Lake Czechowskie-deepest part and Lake Czechowskie-bay. We made Cladocera, diatom and pollen analysis, the chronology was determined by varve counting, Laacher See Tephra (12,880 yrs BP) and 14C dating. The aim of our research was to find out the response of zooplankton, phytoplankton, lake and catchment vegetation to abrupt climate changes. We were interested in similarities and differences between those three locations in response of entire communities but also species composition. The preliminary results revealed that the Cladocera, diatoms and plants communities were sensitive to climatic shifts and it is well shown in the results of ordination method (PCA). However in the Cladocera and diatoms assemblages, which reflect well lake environment conditions, the dominant species and total number of species present, were different in all three locations. Especially great difference was noted between paleolake Trzechowskie and Lake Czechowskie (core from the deepest part). The results of our research shows that in Late Glacial time landscape in Lake Czechowskie region (Tuchola Forest, Northern Poland) had mosaic character. Local factors such as relief, edaphic conditions strongly modified type of vegetation and in close vicinity existed lakes that had very diverse environments.

  20. Numerical simulation of Glacial Isostatic Adjustment

    NASA Astrophysics Data System (ADS)

    Miglio, E.

    2015-12-01

    In the Earth's crust, stress can be subdivided into tectonic background stress, overburden pressure, and pore-fluid pressure. The superposition of the first two and the variation of the third part are key factors in controlling movement along faults. Furthermore, stresses due to sedimentation and erosion contribute to the total stress field. In deglaciated regions, an additional stress must be considered: the rebound stress, which is related to rebounding of the crust and mantle after deglaciation. During the growth of a continental ice sheet, the lithosphere under the iceload is deformed and the removal of the ice load during deglaciation initiates a rebound process. The uplift is well known in formerly glaciated areas, e.g.North America and Scandinavia, and in currently deglaciating areas, e.g.Alaska, Antarctica, and Greenland. The whole process of subsiding and uplifting during the growth and melting of an iceload and all related phenomena is known as glacial isostatic adjustment. During the process of glaciation, the surface of the lithosphere is depressed underneath the ice load and compressional flexural stresses are induced in the upper lithosphere, whereas the bottom of the lithosphere experiences extensional flexural stresses; an additional vertical stress due to the ice load is present and it decreases to zero during deglaciation. During rebound, flexural stresses relax slowly. These stresses are able to change the original stress directions and regime.In this work we aim to study the effect of the GIA process in the context of petroleum engineering. The main aspect we will focus on is the mathematical and numerical modeling of the GIA including thermal effects. We plan also to include a preliminary study of the effect of the glacial erosion. All these phenomena are of paramount importance in petroleum engineering: for example some reservoir have been depleted due to tilting caused by both GIA, erosion and thermal effects.

  1. Fault slip during a glacial cycle

    NASA Astrophysics Data System (ADS)

    Steffen, Rebekka; Wu, Patrick; Steffen, Holger; Eaton, Dave

    2013-04-01

    Areas affected by glacial isostatic adjustment (GIA) generally show uplift after deglaciation. These regions are also characterized by a moderate past and present-day seismicity, at seismic moment release rates that exceed those expected under stable tectonic conditions. Several faults have been found in North America and Europe, which have been activated during or after the last deglaciation. Large-magnitude earthquakes have generated fault offsets of up to 120 m. Due to the recent melting of Greenland and Antarctic ice sheets, an understanding of the occurrence of these earthquakes is important. With a new finite-element model, we are able to estimate, for the first time, fault slip during a glacial cycle for continental ice sheets. A two-dimensional earth model based on former GIA studies is developed, which is loaded with a hyperbolic ice sheet. The fault is able to move in a stress field consisting of rebound stress, tectonic background stress, and lithostatic stress. The sensitivity of this fault is tested regarding lithospheric and crustal thickness, viscosity structure of upper and lower mantle, ice-sheet thickness and width, and fault parameters including coefficient of friction, depth, angle and location. Fault throws of up to 30 m are obtained using a fault of 45° dipping below the ice sheet centre. The thickness of the crust is one of the major parameters affecting the total fault throw, e.g. higher values for a thinner crust. Most faults start to move close to the end of deglaciation, and movement stops after one thrusting/reverse earthquake. However, certain conditions may also lead to several fault movements after the end of glaciations.

  2. Glacial onset predated Late Ordovician climate cooling

    NASA Astrophysics Data System (ADS)

    Pohl, Alexandre; Donnadieu, Yannick; Le Hir, Guillaume; Ladant, Jean-Baptiste; Dumas, Christophe; Alvarez-Solas, Jorge; Vandenbroucke, Thijs R. A.

    2016-06-01

    The Ordovician glaciation represents the acme of one of only three major icehouse periods in Earth's Phanerozoic history and is notorious for setting the scene for one of the "big five" mass extinction events. Nevertheless, the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained. Here using an Earth system model with an innovative coupling method between ocean, atmosphere, and land ice accounting for climate and ice sheet feedback processes, we report simulations portraying for the first time the detailed evolution of the Ordovician ice sheet. We show that the emergence of the ice sheet happened in two discrete phases. In a counterintuitive sequence of events, the continental ice sheet appeared suddenly in a warm climate. Only during the second act, and set against a background of decreasing atmospheric CO2, followed steeply dropping temperatures and extending sea ice. The comparison with abundant sedimentological, geochemical, and micropaleontological data suggests that glacial onset may have occurred as early as the Middle Ordovician Darriwilian, in agreement with recent studies reporting third-order glacioeustatic cycles during the same period. The second step in ice sheet growth, typified by a sudden drop in tropical sea surface temperatures by ˜8°C and the further extension of a single, continental-scale ice sheet over Gondwana, marked the onset of the Hirnantian glacial maximum. By suggesting the presence of an ice sheet over Gondwana throughout most of the Middle and Late Ordovician, our models embrace the emerging paradigm of an "early Paleozoic Ice Age."

  3. High-precision radiogenic strontium isotope measurements of the modern and glacial ocean: Limits on glacial-interglacial variations in continental weathering

    NASA Astrophysics Data System (ADS)

    Mokadem, Fatima; Parkinson, Ian J.; Hathorne, Ed C.; Anand, Pallavi; Allen, John T.; Burton, Kevin W.

    2015-04-01

    Existing strontium radiogenic isotope (87Sr/86Sr) measurements for foraminifera over Quaternary glacial-interglacial climate cycles provide no evidence for variations in the isotope composition of seawater at the ±9-13 ppm level of precision. However, modelling suggests that even within this level of uncertainty significant (up to 30%) variations in chemical weathering of the continents are permitted, accounting for the longer-term rise in 87Sr/86Sr over the Quaternary, and the apparent imbalance of Sr in the oceans at the present-day. This study presents very high-precision 87Sr/86Sr isotope data for modern seawater from each of the major oceans, and a glacial-interglacial seawater record preserved by planktic foraminifera from Ocean Drilling Program (ODP) Site 758 in the north-east Indian ocean. Strontium isotope 87Sr/86Sr measurements for modern seawater from the Atlantic, Pacific and Indian Oceans are indistinguishable from one another (87Sr/86Sr = 0.7091792 ± 0.0000021, n = 17) at the level of precision obtained in this study (±4.9 ppm 2σ). This observation is consistent with the very long residence time of Sr in seawater, and underpins the utility of this element for high precision isotope stratigraphy. The 87Sr/86Sr seawater record preserved by planktic foraminifera shows no resolvable glacial-interglacial variation (87Sr/86Sr = 0.7091784 ± 0.0000035, n = 10), and limits the response of seawater to variations in the chemical weathering flux and/or composition to ±4.9 ppm or less. Calculations suggest that a variation of ±12% around the steady-state weathering flux can be accommodated by the uncertainties obtained here. The new data cannot accommodate a short-term weathering pulse during de-glaciation, although a more a diffuse weathering pulse accompanying protracted ice retreat is permissible. However, these results still indicate that modern weathering fluxes are potentially higher than average over the Quaternary, and such variations through

  4. Variations in glacial and interglacial marine conditions over the last two glacial cycles off northern Greenland

    NASA Astrophysics Data System (ADS)

    Löwemark, Ludvig; Chao, Weng-Si; Gyllencreutz, Richard; Hanebuth, Till J. J.; Chiu, Pin-Yao; Yang, Tien-Nan; Su, Chih-Chieh; Chuang, Chih-Kai; León Dominguez, Dora Carolina; Jakobsson, Martin

    2016-09-01

    Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<<5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10-20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MIS 5 appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a

  5. High-resolution Geophysical Mapping of Submarine Glacial Landforms

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Dowdeswell, J. A.; Canals, M.; Todd, B. J.; Dowdeswell, E. K.; Hogan, K. A.; Mayer, L. A.

    2014-12-01

    Glacial landforms are generated from the activity of glaciers and display spatial dimensions ranging from below one meter up to tens of kilometers. Glacial landforms are used as diagnostic features of past activity of ice sheets and glaciers; they are specifically important in the field of palaeoglaciology. Mapping of submarine glacial landforms is largely dependent on geophysical survey methods capable of imaging the seafloor and sub-bottom through the water column. Full "global" seafloor mapping coverage, equivalent to what exists for land elevation, is to-date only achieved by the powerful method of deriving bathymetry from altimeters on satellites like GEOSAT and ERS-1. The lateral resolution of satellite derived bathymetry is, however, limited by the footprint of the satellite and the need to average out local wave and wind effects resulting in values of around 15 km. Consequently, mapping submarine glacial landforms requires for the most part higher resolution than is achievable by satellite derived bathymetry. The most widely-used methods for mapping submarine glacial landforms are based on echo-sounding principles. This presentation shows how the evolution of marine geophysical mapping techniques, in particular the advent of side-scan and multibeam bathymetric sonars, has made it possible to study submarine glacial landforms in unprecedented detail. Examples are shown from the Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient, which will be published in late 2015 in the Memoir Series of the Geological Society of London.

  6. Extensive glaciation in Transbaikalia, Siberia, at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Margold, Martin; Jansen, John D.; Gurinov, Artem L.; Codilean, Alexandru T.; Fink, David; Preusser, Frank; Reznichenko, Natalya V.; Mifsud, Charles

    2016-01-01

    Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic 10Be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved.

  7. Glacial and periglacial buzzsaws: fitting mechanisms to metaphors

    NASA Astrophysics Data System (ADS)

    Hall, Adrian M.; Kleman, Johan

    2014-03-01

    The buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier Equilibrium Line Altitudes (ELAs), irrespective of uplift rates, rock type or pre-existing topography. Here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and ELAs, and whether the glacial system can produce low-relief surfaces or limit summit heights. Plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited, pre-glacial relief. Summit heights may correlate with ELAs but no causal link need be implied as summit erosion rates are low, cirque headwalls may not directly abut summits and, on passive margins, cirques are cut into pre-existing mountain topography. Any simple links between ELAs and glacial erosion break down on passive margins due to topographic forcing of ice-sheet growth, and to the km-scale vertical swaths through which ELAs have shifted through the Quaternary. Glaciers destroy rather than create low-relief rock surfaces through the innate tendency for ice flow to be faster, thicker and warmer along valleys. The glacial buzzsaw cuts down.

  8. The interglacial-glacial cycle and geochemical evolution of Canadian and Fennoscandian Shield groundwaters

    NASA Astrophysics Data System (ADS)

    Stotler, R. L.; Frape, S. K.; Ruskeeniemi, T.; Pitkänen, P.; Blowes, D. W.

    2012-01-01

    Results from cryogenic column experiments are compared with the geochemical data collected in the Canadian and Fennoscandian Shields over the past 25 years to investigate the relative influence of the glacial-interglacial cycle; specifically, the impact of continental glaciers, permafrost, and methane hydrate, on the evolution of groundwater from crystalline shield environments. Several different geochemical indicators of freezing processes (either glacial or permafrost-related) were utilized: comparisons of Na/Cl and Br/Cl ratios, δ 18O and δ 2H values, and δ 18O values and Cl - concentration. During freezing, fluids with different dominant cations follow distinctly different linear trends when Na/Cl and Br/Cl ratios are compared. Significantly, none of the freezing trends follows the trend hypothesized by Herut et al. (1990) for the evolution of seawater chemistry during freezing. Intrusion of glacial meltwater and in situ freezing (i.e., permafrost formation) result in a similar end-member when comparing δ 18O values and Cl - concentration. The geochemical influence of a freezing process on fresh, brackish, and some saline fluids was identified at some, but not all Canadian Shield sites, regardless of site location with respect to modern-day permafrost. Appreciably, physical and geochemical data do not support the formation of brines through any freezing process in the Canadian and Fennoscandian Shields, as hypothesized by Starinsky and Katz (2003). Rather, on all diagnostic freezing plots, brines are an end-member, indicating a different evolutionary pathway. Significant depletions in 18O with respect to modern precipitation, an indication of either glacial meltwater or a freezing process, were identified at depths of up to 1 km at some sites in the Canadian Shield, and to shallower depths in the Fennoscandian Shield. The potential of this fluid to reach such depths could be attributable to artificial gradients and mixing, glacial recharge, permafrost or

  9. Regional Analysis of the Hazard Level of Glacial Lakes in the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Chisolm, Rachel E.; Jhon Sanchez Leon, Walter; McKinney, Daene C.; Cochachin Rapre, Alejo

    2016-04-01

    of glacial lakes and their hazard potential. This phase of glacial lake hazard assessment aims to be geographically comprehensive in order to identify potentially dangerous lakes that may have previously been ignored. A second phase of analysis that includes site visits will be necessary for a thorough analysis at each lake to determine the potential hazard for downstream communities. The objective of the work presented here is to identify potentially dangerous lakes that warrant further study rather than provide a final hazard assessment for each lake of the glacial lake inventory in the Cordillera Blanca. References: Emmer, A. and Vilímek, V.: New method for assessing the potential hazardousness of glacial lakes in the Cordillera Blanca, Peru, Hydrol. Earth Syst. Sci. Discuss., 11, 2391-2439, 2014. UGRH - Unidad de Glaciologia y Recursos Hidricos. Inventario de Lagunas Glaciares del Peru. Ministerio de Agricultura y Riego, Autoridad Nacional del Agua, Direcccion de Conservacion y Planeamiento de Recursos Hidricos, Huaraz, Peru, 2014. Wang, W., Yao, T., Gao, Y., Yang, X., and Kattel, D. B.: A first-order method to identify potentially dangerous glacial lakes in a region of the southeastern Tibetan Plateau, Mountain Res. Develop., 31, 122-130, 2011.

  10. Ocean Drilling Program Leg 178 (Antarctic Peninsula): Sedimentology of glacially influenced continental margin topsets and foresets

    USGS Publications Warehouse

    Eyles, N.; Daniels, J.; Osterman, L.E.; Januszczak, N.

    2001-01-01

    Ocean Drilling Program Leg 178 (February-April 1998) drilled two sites (Sites 1097 and 1103) on the outer Antarctic Peninsula Pacific continental shelf. Recovered strata are no older than late Miocene or early Pliocene (<4.6 Ma). Recovery at shallow depths in loosely consolidated and iceberg-turbated bouldery sediment was poor but improved with increasing depth and consolidation to allow description of lithofacies and biofacies and interpretation of depositional environment. Site 1097 lies on the outer shelf within Marguerite Trough which is a major outlet for ice expanding seaward from the Antarctic Peninsula and reached a maximum depth drilled of 436.6 m below the sea floor (mbsf). Seismic stratigraphic data show flat-lying upper strata resting on strata that dip gently seaward. Uppermost strata, to a depth of 150 mbsf, were poorly recovered, but data suggest they consist of diamictites containing reworked and abraded marine microfauna. This interval is interpreted as having been deposited largely as till produced by subglacial cannibalization of marine sediments (deformation till) recording ice sheet expansion across the shelf. Underlying gently dipping strata show massive, stratified and graded diamictite facies with common bioturbation and slump stuctures that are interbedded with laminated and massive mudstones with dropstones. The succession contains a well-preserved in situ marine microfauna typical of open marine and proglacial marine environments. The lower gently dipping succession at Site 1097 is interpreted as a complex of sediment gravity flows formed of poorly sorted glacial debris. Site 1103 was drilled in that part of the continental margin that shows uppermost flat-lying continental shelf topsets overlying steeper dipping slope foresets seaward of a structural mid-shelf high. Drilling reached a depth of 363 mbsf with good recovery in steeply dipping continental slope foreset strata. Foreset strata are dominated by massive and chaotically

  11. Assimilation of aged organic carbon in a glacial river food web

    NASA Astrophysics Data System (ADS)

    Fellman, J.; Hood, E. W.; Raymond, P. A.; Bozeman, M.; Hudson, J.; Arimitsu, M.

    2013-12-01

    Identifying the key sources of organic carbon supporting fish and invertebrate consumers is fundamental to our understanding of stream ecosystems. Recent laboratory bioassays highlight that aged organic carbon from glacier environments is highly bioavailable to stream bacteria relative to carbon originating from ice-free areas. However, there is little evidence suggesting that this aged, bioavailable organic carbon is also a key basal carbon source for stream metazoa. We used natural abundance of Δ14C, δ13C, and δ15N to determine if fish and invertebrate consumers are subsidized by aged organic carbon in a glacial river in southeast Alaska. We collected biofilm, leaf litter, three different species of macroinvertebrates, and resident juvenile salmonids from a reference stream and two sites (one site is directly downstream of the glacial outflow and one site is upstream of the tidal estuary) on the heavily glaciated Herbert River. Key producers, fish, and invertebrate consumers in the reference stream had carbon isotope values that ranged from -26 to -30‰ for δ13C and from -12 to 53‰ for Δ14C, reflecting a food web sustained mainly on contemporary primary production. In contrast, biofilm in the two glacial sites was highly Δ14C depleted (-203 to -215‰) relative to the reference site. Although biofilm may consist of both bacteria and benthic algae utilizing carbon depleted in Δ14C, δ13C values for biofilm (-24.1‰), dissolved inorganic carbon (-5.9‰), and dissolved organic carbon (-24.0‰) suggest that biofilm consist of bacteria sustained in part by glacier-derived, aged organic carbon. Invertebrate consumers (mean Δ14C of -80.5, mean δ13C of -26.5) and fish (mean Δ14C of -63.3, mean δ13C of -25.7) in the two glacial sites had carbon isotope values similar to biofilm. These results similarly show that aged organic carbon is incorporated into the metazoan food web. Overall, our findings indicate that continued watershed deglaciation and

  12. Late Ordovician (Ashgillian) glacial deposits in southern Jordan

    NASA Astrophysics Data System (ADS)

    Turner, Brian R.; Makhlouf, Issa M.; Armstrong, Howard A.

    2005-11-01

    The Late Ordovician (Ashgillian) glacial deposits in southern Jordan, comprise a lower and upper glacially incised palaeovalley system, occupying reactivated basement and Pan-African fault-controlled depressions. The lower palaeovalley, incised into shoreface sandstones of the pre-glacial Tubeiliyat Formation, is filled with thin glaciofluvial sandstones at the base, overlain by up to 50 m of shoreface sandstone. A prominent glaciated surface near the top of this palaeovalley-fill contains intersecting glacial striations aligned E-W and NW-SE. The upper palaeovalley-fill comprises glaciofluvial and marine sandstones, incised into the lower palaeovalley or, where this is absent, into the Tubeiliyat Formation. Southern Jordan lay close to the margin of a Late Ordovician terrestrial ice sheet in Northwest Saudi Arabia, characterised by two major ice advances. These are correlated with the lower and upper palaeovalleys in southern Jordan, interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest. Thus, four ice advances are now recorded from the Late Ordovician glacial record of southern Jordan. Disturbed and deformed green sandstones beneath the upper palaeovalley-fill in the Jebel Ammar area, are confined to the margins of the Hutayya graben, and have been interpreted as structureless glacial loessite or glacial rock flour. Petrographic and textural analyses of the deformed sandstones, their mapped lateral transition into undeformed Tubeiliyat marine sandstones away from the fault zone, and the presence of similar sedimentary structures to those in the pre-glacial marine Tubeiliyat Formation suggest that they are a locally deformed facies equivalent of the Tubeiliyat, not part of the younger glacial deposits. Deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre-existing faults, previously weakened by epeirogenesis, triggering sediment

  13. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle.

  14. 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

  15. Isotopic evidence for reduced productivity in the glacial Southern Ocean

    SciTech Connect

    Shemesh, A. ); Macko, S.A. ); Charles, C.D. ); Rau, G.H. )

    1993-10-15

    Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.

  16. Controls of the Northern Hemisphere Hadley circulation over the last five glacial cycles

    NASA Astrophysics Data System (ADS)

    Meckler, A. N.; Roehl, U.; Adkins, J. F.; Haug, G. H.

    2012-12-01

    Sediments off the coast of Mauritania have proven to be sensitive recorders of climate in the adjacent Sahel zone and Saharan desert. It has been shown that climate in this region is highly sensitive to both local insolation forcing, dominated by orbital precession, and high latitude millennial-scale cooling events. However, most available high-resolution records are relatively short, covering at most the last glacial cycle. Here we extend the existing grain-size-based humidity record from core GeoB7920-2 (Tjallingii et al., Nature Geoscience, 2008) back to 550 kyr BP, using sediments from ODP Site 658 at the same location. We employ the XRF-scanning-derived Zr/Al ratio as a proxy for grain-size, which corresponds well to the published humidity index over the last 110 kyr. Grain-size is expected to be a mixed signal of continental aridity and wind strength, whereby the Northeasterly trade winds are the dominant source of dust at this site. The data from Site 658 should therefore reflect the northern components of the low-latitude Hadley circulation, with larger grain-sizes reflecting stronger NE trade winds and/or increased aridity (related to atmospheric subsidence). Reconstructions of precipitation in tropical Borneo (Meckler et al., Science, 2012), at the heart of the convective limb of the Hadley cell, show many similarities. In combination, the two data sets therefore likely reflect variations in strength of the Northern Hemisphere Hadley circulation. The records show clear precession-related cyclicity. In addition, the 100-kyr glacial-interglacial cycles are also apparent, with maxima in grain-size at Site 658 characterizing all glacial periods. Finally, shorter, millennial-scale events are evident at both locations. The presented data therefore reveal a persistent triumvirate of forcing factors, consisting of local insolation, high-latitude ice volume, and millennial-scale high-latitude cooling.

  17. Glacial magnetite dissolution in abyssal NW Pacific sediments - evidence for carbon trapping?

    NASA Astrophysics Data System (ADS)

    Korff, Lucia; von Dobeneck, Tilo; Frederichs, Thomas; Kasten, Sabine; Kuhn, Gerhard; Gersonde, Rainer; Diekmann, Bernhard

    2016-04-01

    The abyssal North Pacific Ocean's large volume, depth, and terminal position on the deep oceanic conveyor make it a candidate site for deep carbon trapping as postulated by climate theory to explain the massive glacial drawdown of atmospheric CO2. As the major basins of the North Pacific have depths of 5500-6500m, far below the modern and glacial Calcite Compensation Depths (CCD), these abyssal sediments are carbonate-free and therefore not suitable for carbonate-based paleoceanographic proxy reconstructions. Instead, paleo-, rock and environmental magnetic methods are generally well applicable to hololytic abyssal muds and clays. In 2009, the international paleoceanographic research cruise SO 202 INOPEX ('Innovative North Pacific Experiment') of the German RV SONNE collected two ocean-spanning EW sediment core transects of the North Pacific and Bering Sea recovering a total of 50 piston and gravity cores from 45 sites. Out of seven here considered abyssal Northwest Pacific piston cores collected at water depths of 5100 to 5700m with mostly coherent shipboard susceptibility logs, the 20.23m long SO202-39-3, retrieved from 5102 m water depth east of northern Shatsky Rise (38°00.70'N, 164°26.78'E), was rated as the stratigraphically most promising record of the entire core transect and selected for detailed paleo- and environmental magnetic, geochemical and sedimentological investigations. This core was dated by correlating its RPI and Ba/Ti records to well-dated reference records and obviously provides a continuous sequence of the past 940 kyrs. The most striking orck magnetic features are coherent magnetite-depleted zones corresponding to glacial periods. In the interglacial sections, detrital, volcanic and even submicron bacterial magnetite fractions are excellently preserved. These alternating magnetite preservation states seem to reflect dramatic oxygenation changes in the deep North Pacific Ocean and hint at large-scale benthic glacial carbon trapping

  18. Climate versus geological controls on glacial meltwater micronutrient production in southern Greenland

    NASA Astrophysics Data System (ADS)

    Aciego, S. M.; Stevenson, E. I.; Arendt, C. A.

    2015-08-01

    Low concentrations of micronutrients in subarctic North Atlantic surface waters limit phytoplankton growth. Iron, phosphorous, and silicon are all potentially bio-limiting nutrients; iron is the most well documented in the subarctic North Atlantic. Manganese, nickel, copper and zinc are also essential trace metals for phytoplankton cell function. However, the spatial and temporal variability in the flux of these elements to the subarctic North Atlantic is undercharacterized. Here we show new data from the meltseason peak in 2013 indicating that glacial meltwater from the southern tip of Greenland has elevated dissolved major and trace metal concentrations compared to glacial meltwater draining shorter melt season glacial catchments to the north. Fe concentrations range from 0.13 to 6.97 μM, Zn from 4 to 95 μM, and Si from 4 to 36 μM, all higher than the depleted surface waters of the subarctic North Atlantic. Measured hydrochemical data modeled by PHREEQC indicates meltwater is undersaturated in pyrite and silicate phases but supersaturated with respect to oxyhydroxides, hematite and goethite, all phases that precipitate Fe as colloids, of which the nanoparticle phases should remain biologically available. The variability in geologic units between the sites indicates that subglacial lithology is a minor but not the dominant control on meltwater chemistry. The disparity in concentrations is directly correlated with climate, and an extended melt season, suggesting that future warming in Greenland will lead to increased trace element, and potential micronutrient, flux to the subarctic North Atlantic surface waters.

  19. Hydrogeology and hydrogeochemistry of fine-grained glacial till, northeastern Indiana

    SciTech Connect

    Ferguson, V.R. . Geosciences Dept.); Fleming, A.H. ); Krothe, N.C.; Steen, W.J. )

    1992-01-01

    Ground water chemistry, including environmental isotopes, indicate that significant recharge is occurring through a thick sequence of fine-grained glacial till. [delta]D and [delta] O-18 values correspond well with the current mean average annual values for precipitation at the site, and suggest that the entire glacial sequence, as well as the bedrock aquifer, has been completely recharged since the end of the Pleistocene. Bomb tritiated water is present to a depth of 20 feet, and possibly below 80 feet as well. This strongly suggests that macropore flow, perhaps via fractures, may be occurring. Nitrogen isotope analysis suggest that the nitrates at a depth of 37 feet have animal waste as their source. The age of the water in the upper 37 feet of the profile is therefore between 40 and 140 years, based on historical farming practices. In addition, major ion chemistry suggests that the upper clay rich till unit is acting as a semipermeable membrane and retarding the downward migration of most of the major ions. When compared to similar studies conducted in slightly different geologic settings, it can be concluded that recharge through fine-grained glacial materials may greatly vary.

  20. Testing Models of Modern Glacial Erosion of the St. Elias Mountains, Alaska Using Marine Sediment Provenance

    NASA Astrophysics Data System (ADS)

    Penkrot, M. L.; Jaeger, J. M.; Loss, D. P.; Bruand, E.

    2015-12-01

    The glaciated coastal St. Elias Range in Alaska is a primary site to examine climate-tectonic interactions. Work has primarily focused on the Bering-Bagley and Malaspina-Seward ice fields, utilizing detrital and bedrock zircon and apatite geochronology to examine local exhumation and glacial erosion (Berger et al., 2008; Enkelmann et al., 2009; Headly et al., 2013). These studies argue for specific regions of tectonically focused or climatically widespread glacial erosion. Analyzed zircon and apatite grains are sand size, however glacial erosion favors the production of finer-grained sediments. This study focuses on the geochemical provenance of the silt-size fraction (15-63μm) of surface sediments collected throughout the Gulf of Alaska (GOA) seaward of the Bering and Malaspina glaciers to test if the exhumation patterns observed in zircon and apatites are also applicable for the silt size fraction. Onshore bedrock Al-normalized elemental data were used to delineate sediment sources, and a subset of provenance-applicable elements was chosen. Detrital thermochronologic data suggest that sediment produced by the Bagley/Bering system is derived from bedrock on the windward side with input from the Chugach Metamorphic Complex (CMC) underlying the Bagley only during glacial surge events (Headly et al., 2013). Geochemical observations of GOA silt deposited during the 1994-95 surge event confirm input of CMC sediment (elevated in Cr, Ni, Sc, Sr, depleted in Hf, Pb and Rb relative to Kultieth and Poul Creek formations). We also observe a windward-side sediment source (Kultieth and Poul Creek). It is hypothesized that the sediment carried by the Malaspina is primarily from CMC rock underlying the Seward ice field mixed with Yakataga formation rock that underlies the Seward throat (Headly et al., 2013). Geochemical observations of GOA silt support this hypothesis.

  1. Paraglacial rock mass damage during repeat glacial cycles in preparing slope instabilities (Aletsch region, Switzerland)

    NASA Astrophysics Data System (ADS)

    Grämiger, Lorenz; Moore, Jeffrey R.; Gischig, Valentin S.; Loew, Simon

    2016-04-01

    Glacier advance and retreat imposes mechanical stress cycles on underlying bedrock. Stress changes propagate rock mass damage and act as preparatory factors for slope instabilities, however, the mechanics of paraglacial rock slope damage remains poorly understood. In this study, we present results of detailed, conceptual numerical models, based on extensive field mapping and characterization at our Aletsch valley study site, Switzerland. We illustrate how simple stress changes associated with repeat glacial cycles can propagate fractures, enhance slip along discontinuities, and lead to failure of intact rock bridges, conditioning adjacent valley slopes for failure. We describe the timing and location of induced damage, stress redistribution, and displacement associated with Late Pleistocene and Holocene glacial cycles, and compare numerical predictions with the spatial and temporal distribution of landslides around the Great Aletsch Glacier. Our results help clarify mechanical linkages between glacial cycles and damage propagation in alpine valley rock slopes. In our simulations, most damage occurs during first deglaciation. This is in good agreement with the relative initiation timing (post-LGM / post-Egesen) for the majority of identified landslides at Aletsch. Large Holocene glacial cycles with high amplitude ice elevation changes in our models have a significant impact on displacement patterns in adjacent slopes. This correlates with a concentrated area of landslides located around the present-day glacier terminus, where the Great Aletsch Glacier fluctuated most during the Holocene. The kinematics and dimensions of an unstable rock slope produced in our models also generally resembles field observations of toppling-mode landslides on the eastern slope. No substantial displacement was generated on the western slope, although compound rock slides are observed on the western flank in the Aletsch.

  2. Cyclic 100-ka (glacial-interglacial) migration of subseafloor redox zonation on the Peruvian shelf

    PubMed Central

    Contreras, Sergio; Meister, Patrick; Liu, Bo; Prieto-Mollar, Xavier; Hinrichs, Kai-Uwe; Khalili, Arzhang; Ferdelman, Timothy G.; Kuypers, Marcel M. M.; Jørgensen, Bo Barker

    2013-01-01

    The coupling of subseafloor microbial life to oceanographic and atmospheric conditions is poorly understood. We examined diagenetic imprints and lipid biomarkers of past subseafloor microbial activity to evaluate its response to glacial-interglacial cycles in a sedimentary section drilled on the Peruvian shelf (Ocean Drilling Program Leg 201, Site 1229). Multiple and distinct layers of diagenetic barite and dolomite, i.e., minerals that typically form at the sulfate−methane transition (SMT), occur at much shallower burial depth than the present SMT around 30 meters below seafloor. These shallow layers co-occur with peaks of 13C-depleted archaeol, a molecular fossil of anaerobic methane-oxidizing Archaea. Present-day, non-steady state distributions of dissolved sulfate also suggest that the SMT is highly sensitive to variations in organic carbon flux to the surface shelf sediments that may lead to shoaling of the SMT. Reaction-transport modeling substantiates our hypothesis that shallow SMTs occur in response to cyclic sediment deposition with a high organic carbon flux during interglacials and a low organic carbon flux during glacial stages. Long diffusion distances expectedly dampen the response of deeply buried microbial communities to changes in sediment deposition and other oceanographic drivers over relatively short geological time scales, e.g., glacial-interglacial periods. However, our study demonstrates how dynamically sediment biogeochemistry of the Peru Margin has responded to glacial-interglacial change and how these changes are now preserved in the geological record. Such changes in subsurface biogeochemical zonation need to be taken into account to assess the role of the subseafloor biosphere in global element and redox cycling. PMID:24145422

  3. The taphonomy of human remains in a glacial environment.

    PubMed

    Pilloud, Marin A; Megyesi, Mary S; Truffer, Martin; Congram, Derek

    2016-04-01

    A glacial environment is a unique setting that can alter human remains in characteristic ways. This study describes glacial dynamics and how glaciers can be understood as taphonomic agents. Using a case study of human remains recovered from Colony Glacier, Alaska, a glacial taphonomic signature is outlined that includes: (1) movement of remains, (2) dispersal of remains, (3) altered bone margins, (4) splitting of skeletal elements, and (5) extensive soft tissue preservation and adipocere formation. As global glacier area is declining in the current climate, there is the potential for more materials of archaeological and medicolegal significance to be exposed. It is therefore important for the forensic anthropologist to have an idea of the taphonomy in this setting and to be able to differentiate glacial effects from other taphonomic agents. PMID:26917542

  4. Enigmatic sediment ridges in the German Bight - glacial vs post-glacial morphologies?

    NASA Astrophysics Data System (ADS)

    Unnithan, Vikram; Pio Rossi, Angelo; Praeg, Daniel

    2014-05-01

    The German Wadden Sea extends over 1000 km from the Dutch coast to that of Sweden and consists of a long chain of barrier islands and ephemeral sand banks punctuated by estuaries and rivers. The sedimentary environment is currently shaped and characterised by storm surges, high tidal and wave energy levels. However, this part of the North Sea has been repeatedly covered by continental ice sheets, and it remains unclear how glacial to interglacial sedimentary processes may have influenced seabed morphology in the region. The study area is situated approximately 70 km north of Cuxhaven, and 5 km due east of the islands of Helgoland and Dune. It covers an approximate area of 5 km square with water depths ranging from 50 m in the south to about 20 m in the north. High resolution multibeam (Simrad EM710) and parametric echosounder (Innomar SES2000) data were acquired during graduate and undergraduate teaching excursions on the RV Heincke in Spring 2010 (HE-324) and 2011 (HE-349). The seabed swath bathymetric data reveal distinctive linear seabed ridges. The ridges trend NNW-SSE, are 1-5 m in height, have wavelengths on the order of 100 m and crest lengths ranging from 100-2500 m. The ridge crests are broadly anastomosing. They bifurcate towards the north to form more subdued structures, while they converge and disappear to the south. Profiles across the ridges show an asymmetric structure, with steeper slopes trending west in the western part of the study area but trending east in the eastern part. These enigmatic sedimentary structures have not been previously mapped in the Wadden Sea, and their origin remains uncertain. Possible interpretations to be tested include sub-crop structural control on seabed morphology, relict glacial or glaciofluvial landforms and post-glacial marine bedforms linked to processes of sediment redistribution.

  5. Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Weber, M. E.; Clark, P. U.; Ricken, W.; Mitrovica, J. X.; Hostetler, S. W.; Kuhn, G.

    2012-04-01

    The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood because only a few findings with robust chronologies exist for Antarctic ice sheets. We developed a chronology for the Weddell Sea sector of the East Antarctic ice sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates the advance to their maximum extent at 29 -28 ka, and retreat from their maximum extent at 19 ka was nearly synchronous with Northern Hemisphere ice sheets (Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G. (2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. - Science, 334, 1265-1269, doi: 10.1126:science.1209299). As for the deglaciation, modeling studies suggest a late ice-sheet retreat starting around 14 ka BP and ending around 7 ka BP with a large impact of an unstable West Antarctic Ice Sheet (WAIS) and a small impact of a stable East Antarctic Ice Sheet (EAIS). However, the Weddell Sea sites studied here, as well as sites from the Scotia Sea, provide evidence that specifically the EAIS responded much earlier, possibly provided a significant contribution to the last sea-level rise, and was much more dynamic than previously thought. Using the results of an atmospheric general circulation we conclude that surface climate forcing of Antarctic ice mass balance would likely cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Furthermore, our new data support teleconnections involving a sea-level fingerprint forced from Northern Hemisphere ice sheets as indicated by gravitational modeling. Also, changes in North Atlantic Deepwater formation and attendant heat flux to Antarctic grounding lines may have contributed to synchronizing the hemispheric ice sheets.

  6. Greenland ice cores constrain glacial atmospheric fluxes of phosphorus

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid; Dallmayr, Remi; Gabrieli, Jacopo; Goto-Azuma, Kumiko; Hirabayashi, Motohiro; Svensson, Anders; Vallelonga, Paul

    2015-10-01

    Phosphorus is a limiting nutrient for primary productivity, but little is known about past atmospheric fluxes to the open ocean. In this study, phosphate and phosphorus concentrations have been determined in the North Greenland Eemian Ice Drilling Project ice core for selected periods during the last glacial. Phosphate was determined continuously by using a molybdenum blue spectroscopic absorption method and discretely using an ion chromatograph. Total P was determined discretely using an inductively coupled plasma sector field mass spectrometer. For the last glacial period, we found concentrations of between 3 and 62 nM PO43- and 7 and 929 nM P. We find glacial atmospheric fluxes of phosphorus to Greenland were 4 to 11 times higher than in the past century, with the highest input during the cold glacial stadials (GS). Changes in P and PO43- fluxes between mild glacial interstadials (GI) and GS correlate positively with dust variability. The soluble fraction of P is larger in the mild GIs as compared to the dust-rich GSs. For the very high phosphate and phosphorus loads during the Last Glacial Maximum, the relationship between phosphate and dust is weaker than in GIs and milder GSs, suggesting either secondary phosphate sources or multiple dust sources. Based on crustal abundances, we find that dust inputs are sufficient to account for all P deposited during all periods investigated except the Last Glacial Maximum. During the glacial, sea salts contributed 10-3 nM P, while land biogenic emissions were a minor source of P.

  7. Oceanographic gradients and seabird prey community dynamics in glacial fjords

    USGS Publications Warehouse

    Arimitsu, Mayumi L.; Piatt, John F.; Madison, Erica N.; Conaway, Jeff; Hillgruber, N.

    2012-01-01

    Glacial fjord habitats are undergoing rapid change as a result of contemporary global warming, yet little is known about how glaciers influence marine ecosystems. These ecosystems provide important feeding, breeding and rearing grounds for a wide variety of marine organisms, including seabirds of management concern. To characterize ocean conditions and marine food webs near tidewater glaciers, we conducted monthly surveys of oceanographic variables, plankton, fish and seabirds in Kenai Fjords, Alaska, from June to August of 2007 and 2008. We also measured tidal current velocities near glacial features. We found high sediment load from glacial river runoff played a major role in structuring the fjord marine ecosystem. Submerged moraines (sills) isolated cool, fresh, stratified and silt-laden inner fjord habitats from oceanic influence. Near tidewater glaciers, surface layers of turbid glacial runoff limited availability of light to phytoplankton, but macrozooplankton were abundant in surface waters, perhaps due to the absence of a photic cue for diel migration. Fish and zooplankton community structure varied along an increasing temperature gradient throughout the summer. Acoustic measurements indicated that low density patches of fish and zooplankton were available in the surface waters near glacial river outflows. This is the foraging habitat occupied most by Kittlitz's murrelet (Brachyramphus brevirostris), a rare seabird that appears to be specialized for life in glacially influenced environments. Kittlitz's murrelets were associated with floating glacial ice, and they were more likely to occur near glaciers, in deeper water, and in areas with high acoustic backscatter. Kittlitz's murrelet at-sea distribution was limited to areas influenced by turbid glacial outflows, and where prey was concentrated near the surface in waters with low light penetration. Tidewater glaciers impart unique hydrographic characteristics that influence marine plankton and fish

  8. Glacial Erosion Rates from Bayesian Inversion of Cosmogenic Nuclide Concentrations in a Bedrock Core, Streaked Mtn., ME

    NASA Astrophysics Data System (ADS)

    Ploskey, Z. T.; Stone, J. O.

    2014-12-01

    Glacial erosion is an important source of sediment and could be an important coupling to glacier and ice sheet models that track sediment. However, glacial erosion is difficult to quantify, and models of glacial erosion can benefit from independent erosion rate estimates. Here we present the results of a Bayesian Markov chain Monte Carlo (MCMC) inversion of a cosmogenic nuclide (CN) geomorphic model for glacial erosion rates on a bedrock landform formerly eroded beneath the Laurentide ice sheet. The CN 10Be was measured in quartz to 8 m depth in a bedrock core from the summit of Streaked Mountain, ME. The accumulation of 10Be was modeled over multiple glacial cycles of alternating exposure and glacial erosion. This model was invertedfor glacial erosion rates and burial history using MCMC algorithms implemented in PyMC (Patil et al., 2010). This Bayesian approach allows us to incorporate prior constraints on ice cover history, including oxygen isotope records and radiometric dates, which is otherwise difficult to differentiate from erosion in rapidly eroding areas. We compare these results to depth profile and surface CN measurements elsewhere in Maine (Ploskey and Stone, 2013).The forward model of CN production used in the inversion is part of Cosmogenic (github.com/cosmolab/cosmogenic), an open-source Python-based software library we developed for modeling the growth and decay of in-situ CN inventories in rock during geomorphic evolution. It includes calibrated production rates for 10Be and 26Al in quartz and 36Cl in K-feldspar by both neutrons and muons, with more isotopic production pathways and material targets to be added in the future. Production rates are scaled to the site altitude and latitude using modular scaling schemes. Cosmogenic includes a variety of functions representing common geomorphic histories, and can be used to model any arbitrary exposure, erosion and burial history that can be defined as Python function.ReferencesPatil, A., D. Huard and C

  9. Glacial ocean and continental climate variability off southernmost Chile during the past 60 kyr

    NASA Astrophysics Data System (ADS)

    Lamy, F.; Caniupan, M.; Arz, H. W.; Hebbeln, D.; Kaiser, J.; Kilian, R.; Kissel, C.; Lange, C.; Mollenhauer, G.; Ninnemann, U.

    2009-04-01

    We present paleoceanographic and continental paleoclimate data from sediment core MD07-3128 recovered during IMAGES XV-MD159-PACHIDERME cruise off southernmost Chile. The coring site is located at ~53°S at the continental slope (~1000 m water depth) off the Pacific entrance of the Strait of Magellan. Based on the preliminary stratigraphy (14C and paleomagnetic evidence), the Holocene sequence is very condensed and largely consists of foraminifera sand, whereas enhanced terrestrial sediment input provides high time-resolution during the last glacial back to ca. 65 kyr BP. The alkenone SST record reveals a very strong warming of ca. 8˚C over the last termination and millennial-sale variability in the order of 2-4˚C in the glacial (MIS 2-4). The timing and structure of the termination and some of the millennial-scale fluctuations in the glacial are very similar to those observed in the well-dated SST record from the Chilean margin ODP Site 1233 (41°S) and in the temperature reconstructions from Antarctic ice-cores. There are however important differences in the new southernmost Chilean margin record, e.g. regarding a long-term warming trend over the MIS 3 followed by a cooling towards the LGM. Opal/CaCO3 ratios are generally higher and alkenone concentrations lower during millennial-scale cold intervals suggesting SST-related shifts in the calcareous and siliceous plankton communities. The cold period between ~25 to ~19 kyr BP is accompanied by a significant increase in ice rafted debris and alkenone C37:4 content in particular at ~21, ~20 and ~18 kyr BP that correlate with reduced iron contents (most likely due to Quarz-rich IRD). These changes may be related with glacier advances documented in the Strait of Magellan region or wind-driven changes in the advection of ice-bergs to the site.

  10. Rapid loss of glacial ice reveals stream community assembly processes

    PubMed Central

    Brown, Lee E; Milner, Alexander M

    2012-01-01

    Glacial retreat creates new habitat which is colonized and developed by plants and animals during the process of primary succession. While there has been much debate about the relative role of deterministic and stochastic processes during terrestrial succession, evidence from freshwater ecosystems remains minimal and a general consensus is lacking. Using a unique 27 years record of community assembly following glacial recession in southeast Alaska, we demonstrate significant change in the trait composition of stream invertebrate communities as catchment glacial cover decreased from ∼70% to zero. Functional diversity increased significantly as glacier cover decreased and taxonomic richness increased. Null modelling approaches led to a key finding that niche filtering processes were dominant when glacial cover was extensive, reflecting water temperature and dispersal constraints. Thereafter the community shifted towards co-occurrence of stochastic and deterministic assembly processes. A further novel discovery was that intrinsic functional redundancy developed throughout the study, particularly because new colonizers possessed similar traits to taxa already present. Rapid glacial retreat is occurring in Arctic and alpine environments worldwide and the assembly processes observed in this study provide new fundamental insights into how glacially influenced stream ecosystems will respond. The findings support tolerance as a key primary successional mechanism in this system, and have broader value for developing our understanding of how biological communities in river ecosystems assemble or restructure in response to environmental change.

  11. Millennial-Scale Climate Variability for the Last Glacial Cycle along the Iberian Margin based on Dinoflagellate Cysts

    NASA Astrophysics Data System (ADS)

    Datema, M.; Sangiorgi, F.; Reichart, G. J.; Lourens, L. J.; Sluijs, A.

    2014-12-01

    The Shackleton Site (IODP Expedition 339 Site U1385), located off the West-Portuguese Margin, preserves a continuous high-fidelity record of millennial-scale climate variability for the last several glacial cycles (~1.4 Myr) that can be correlated precisely to patterns observed in polar ice cores. In addition, rapid delivery of terrestrial material to the deep-sea environment allows the correlation of these marine records to European terrestrial climate records. This unique marine-ice-terrestrial linkage makes the Shackleton Site the ideal reference section for studying Quaternary abrupt climate change. The main objective of studying site U1385 is to establish a marine reference section of Pleistocene climate change. We generated millennial-scale dinoflagellate cyst (dinocyst) assemblage records from the Shackleton Site (IODP Expedition 339) to reconstruct upwelling, sea surface temperature (SST) and productivity across the last two glacial-interglacial cycles. We quantify the validity of dinocyst-based paleoenvironmental reconstructions based on multivariate statistics on dinocyst assemblages and multi-proxy data from regional core-tops and the last glacial cycle. This allows us to conclude that the strength of the West Iberian Margin upwelling system changed from relatively intense upwelling during the last glacial to upwelling relaxation during the Holocene as a result of reduced (strength of the) Portuguese trade winds. Secondly, SST, productivity/upwelling, strength of Portuguese trade winds and climate on the Iberian Peninsula co-vary on stadial-interstadial timescales and correspond to Greenland stadial-interstadial variability (δ18O). Finally, we will present a long-term paleoceanographic perspective down to ~120 ka.

  12. Exceptionally well-preserved early Oligocene diatoms from glacial sediments of Prydz Bay, East Antarctica

    USGS Publications Warehouse

    Barron, J.A.; Mahood, A.D.

    1993-01-01

    An exceptionally well-preserved early Oligocene diatom assemblage is documented and illustrated from the internal sediment of a gastropod shell, which was collected from glacial sedments recovered at ODP Site 739, Prydz Bay, Antarctica. The diatoms were deposited between 35.9 and 34.8 Ma according to diatom and calcareous nannofossil stratigraphy, apparently soon after a period of major ice sheet advance across the Prydz Bay continental shelf. The diatom assemblage is neritic in character, but it can readily be correlated with open ocean assemblages from the Southern Ocean as well as with similar material recovered from the CIROS-1 drillhole in the Ross Sea. -Authors

  13. A procedure for objective preliminary assessments of outburst flood hazard from glacial lakes in Aosta Valley

    NASA Astrophysics Data System (ADS)

    Bal, Germain; Godio, Alberto; Theodule, Alex

    2010-05-01

    GLOFs represent a major natural hazards in glaciated mountain regions, because of their fair-reaching capacity and of the difficulty in detecting source areas (especially in case of internal water pockets) and in forecasting the breakdown moment. GLOFs hazard is probably increasing because of the current glaciers retreat, and its prevention and management requires a multi-disciplinary approach, in order to (i) detect dangerous sites, (ii) assess danger, (iii) define and measure triggering factors and parameters and (iv) assess potential reaching areas so to define risk. Such a study was carried out in Aosta Valley, a mountainous territory with more than 200 glaciers covering an area of about 130 km2 (about 5% of the whole territory). The aim was double: to inventory and analyse all existing glacial lakes focusing on the newborn lakes and on potentially dangerous sites; to test surveying and modeling methods to be applied for hazard mapping and prevention. First, an inventory was compiled by means of GIS analysis of ortophotos (taken in 2005). The images were compared with previous ones to detect morphological evolution. Ground-based and helicopter surveys were also carried out. Historical data have been analyzed in order to recognize most dangerous sites and situations and to classify most recurrent phenomena. In case of recognized dangerous situations, some parameters are needed in order to evaluate the potential water volume and runout distance. Ground-penetrating radar (GPR) technique was tested to detect the presence of glacial internal cavities and water pockets on a well known situation (a glacier with well known collapse cavities). The same technique was also used to measure the bathymetry of a glacial lake. The technique was carried out successfully, allowing to estimate with a good resolution the lake depth and bottom morphology; encouraging results were also obtained in detecting glacial cavities and drainage channels. To perform the downstream runoff

  14. Status of glacial Lake Columbia during the last floods from glacial Lake Missoula

    USGS Publications Warehouse

    Atwater, B.F.

    1987-01-01

    The last floods from glacial Lake Missoula, Montana, probably ran into glacial Lake Columbia, in northeastern Washington. In or near Lake Columbia's Sanpoil arm, Lake Missoula floods dating from late in the Fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves. The highest three interflood intervals each contain only one or two varves, and about 200-400 successive varves conformably overlie the highest flood bed. This sequence suggests that jo??kulhlaup frequency progressively increased until Lake Missoula ended, and that Lake Columbia outlasted Lake Missoula. The upper Grand Coulee, Lake Columbia's late Fraser-age outlet, contains a section of 13 graded beds, most of them sandy and separated by varves, that may correlate with the highest Missoula-flood beds of the Sanpoil River valley. The upper Grand Coulee also contains probable correlatives of many of the approximately 200-400 succeeding varves, as do nearby parts of the Columbia River valley. This collective evidence casts doubt on a prevailing hypothesis according to which one or more late Fraser-age floods from Lake Missoula descended the Columbia River valley with little or no interference from Lake Columbia's Okanogan-lobe dam. ?? 1987.

  15. Should precise numerical dating overrule glacial geomorphology?

    NASA Astrophysics Data System (ADS)

    Winkler, Stefan

    2016-04-01

    Numerical age dating techniques, namely different types of terrestrial cosmogenic nuclide dating (TCND), have achieved an impressive progress in both laboratory precision and regional calibration models during the past few decades. It is now possible to apply precise TCND even to young landforms like Late Holocene moraines, a task seemed hardly achievable just about 15 years ago. An increasing number of studies provide very precise TCND ages for boulders from Late Holocene moraines enabling related reconstruction of glacier chronologies and the interpretation of these glacial landforms in a palaeoclimatological context. These studies may also solve previous controversies about different ages assigned to moraines obtained by different dating techniques, for example relative-age dating techniques or techniques combining relative-age dating with few fixed points derived from numerical age dating. There are a few cases, for example Mueller Glacier and nearby long debris-covered valley glacier in Aoraki/Mt.Cook National Park (Southern Alps, New Zealand), where the apparent "supremacy" of TCND-ages seem to overrule glacial geomorphological principles. Enabled by a comparatively high number of individual boulders precisely dated by TCND, moraine ridges on those glacier forelands have been primarily clustered on basis of these boulder ages rather than on their corresponding morphological position. To the extreme, segments of a particular moraine complex morphologically and sedimentologically proven to be formed during one event have become split and classified as two separate "moraines" on different parts of the glacier foreland. One ledge of another moraine complex contains 2 TCND-sampled boulders apparently representing two separate "moraines"-clusters of an age difference in the order of 1,500 years. Although recently criticism has been raised regarding the non-contested application of the arithmetic mean for calculation of TCND-ages for individual moraines, this

  16. Post-glacial sea-level changes around the Australian margin: a review

    NASA Astrophysics Data System (ADS)

    Lewis, Stephen E.; Sloss, Craig R.; Murray-Wallace, Colin V.; Woodroffe, Colin D.; Smithers, Scott G.

    2013-08-01

    It has been known since Rhodes Fairbridge's first attempt to establish a global pattern of Holocene sea-level change by combining evidence from Western Australia and from sites in the northern hemisphere that the details of sea-level history since the Last Glacial Maximum vary considerably across the globe. The Australian region is relatively stable tectonically and is situated in the 'far-field' of former ice sheets. It therefore preserves important records of post-glacial sea levels that are less complicated by neotectonics or glacio-isostatic adjustments. Accordingly, the relative sea-level record of this region is dominantly one of glacio-eustatic (ice equivalent) sea-level changes. The broader Australasian region has provided critical information on the nature of post-glacial sea level, including the termination of the Last Glacial Maximum when sea level was approximately 125 m lower than present around 21,000-19,000 years BP, and insights into meltwater pulse 1A between 14,600 and 14,300 cal. yr BP. Although most parts of the Australian continent reveals a high degree of tectonic stability, research conducted since the 1970s has shown that the timing and elevation of a Holocene highstand varies systematically around its margin. This is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice-melt, including a process known as ocean siphoning (i.e. glacio-hydro-isostatic adjustment processes). Several seminal studies in the early 1980s produced important data sets from the Australasian region that have provided a solid foundation for more recent palaeo-sea-level research. This review revisits these key studies emphasising their continuing influence on Quaternary research and incorporates relatively recent investigations to interpret the nature of post-glacial sea-level change around Australia. These include a synthesis of research from the Northern

  17. Glacial geology and stratigraphy of Western New York Nuclear Service Center and vicinity, Cattaraugus and Erie Counties, New York

    USGS Publications Warehouse

    LaFleur, Robert G.

    1979-01-01

    A detailed glacial geologic map at a scale of 1:24,000, embracing a 165 square-mile area in Erie and Cattaraugus Counties, NY, shows 27 mapping units, including the till complex in which the West Valley radioactive-waste burial site is located. Stratigraphic relationships at 24 boreholes at the burial site and 6 newly described exposures indicate the age of the till complex to be early late Woodfordian (post-Kent, pre-Lake Escarpment, Valley Heads), equivalent to the Lavery glacial advance. Correlations of mapping units and measured sections with Woodfordian and older glacial and deglacial episodes are proposed. The Lavery till is confined to the valleys of Cattaraugus Creek and its major tributaries. At the waste-burial site in Buttermilk Creek Valley, the Lavery is an interfingering complex of clayey-silt till and thinner beds of deformed, poorly stratified lacustrine clay and silt. Ice readvance after the Kent glacial recession and Erie Interstade erosion imponded proglacial lake water in Buttermilk Creek Valley and covered post-Kent kame deltas and Erie channel gravels with as much as 130 feet of till. The Lavery till thins southward to a thickness of 80 feet at the waste-burial site and to less than 16 feet near the hamlet of West Valley. Water from the Lavery till may flow through subjacent Erie channel gravel and Kent-recessional kame delta sand to the bluffs along Buttermilk Creek, where discharge of water from these exposed pervious deposits appears to cause major slumps. (USGS)

  18. Precipitation Isotopes Reveal Intensified Indonesian Monsoon Circulation During the Dry Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Konecky, B. L.; Russell, J. M.; Vogel, H.; Bijaksana, S.; Huang, Y.

    2014-12-01

    The Indo-Pacific Warm Pool (IPWP) invigorates the oceanic-atmospheric circulation in the tropics, with far-reaching climate impacts that extend into the high latitudes. A growing number of deglacial proxy reconstructions from the region have revealed the importance of both high- and low-latitude climate processes to IPWP rainfall during the late Pleistocene. Many of these proxies reconstruct the oxygen and hydrogen isotopic composition of rainfall (δ18Oprecip, δDprecip), a powerful tool for understanding changes in climate. However, an increasing number of studies from the region have highlighted the tendency for δ18Oprecip and δDprecip to reflect regional and/or remote circulation processes rather than local rainfall amounts, complicating the reconstruction of IPWP hydroclimate. To better understand high- and low-latitude drivers of late Pleistocene hydroclimate in the IPWP, precipitation isotopic reconstructions must be constrained with both modern observations and independent proxies for rainfall amount. We present a reconstruction of δDprecip using leaf wax compounds preserved in the sediments of Lake Towuti, Sulawesi, from 60,000 years before present to today. We interpret our proxy record with the aid of a new precipitation isotopic dataset from our study site, with daily rainfall isotope measurements to constrain the processes controlling δDprecip. Our Lake Towuti δDwax record is strikingly similar to a speleothem δ18O record from southern Indonesia (Ayliffe et al., 2013) and shares features with other nearby records spanning the Last Glacial Maximum to present. Together, these records indicate that monsoon circulation was intensified in central and southern Indonesia during the glacial period. However, other independent rainfall proxies from Lake Towuti indicate that dry conditions accompanied the intensified monsoon. Regional-scale isotopic depletion during the dry glacial period may have arisen from dynamical and other fractionating processes that

  19. Uncertainty in the Himalayan energy–water nexus: estimating regional exposure to glacial lake outburst floods

    NASA Astrophysics Data System (ADS)

    Schwanghart, Wolfgang; Worni, Raphael; Huggel, Christian; Stoffel, Markus; Korup, Oliver

    2016-07-01

    Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia’s soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysis remains elusive. To this end we estimate the regional exposure of 257 Himalayan HPP to GLOFs, using a flood-wave propagation model fed by Monte Carlo-derived outburst volumes of >2300 glacial lakes. We interpret the spread of thus modeled peak discharges as a predictive uncertainty that arises mainly from outburst volumes and dam-breach rates that are difficult to assess before dams fail. With 66% of sampled HPP are on potential GLOF tracks, up to one third of these HPP could experience GLOF discharges well above local design floods, as hydropower development continues to seek higher sites closer to glacial lakes. We compute that this systematic push of HPP into headwaters effectively doubles the uncertainty about GLOF peak discharge in these locations. Peak discharges farther downstream, in contrast, are easier to predict because GLOF waves attenuate rapidly. Considering this systematic pattern of regional GLOF exposure might aid the site selection of future Himalayan HPP. Our method can augment, and help to regularly update, current hazard assessments, given that global warming is likely changing the number and size of Himalayan meltwater lakes.

  20. Uncertainty in the Himalayan energy-water nexus: estimating regional exposure to glacial lake outburst floods

    NASA Astrophysics Data System (ADS)

    Schwanghart, Wolfgang; Worni, Raphael; Huggel, Christian; Stoffel, Markus; Korup, Oliver

    2016-07-01

    Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia’s soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysis remains elusive. To this end we estimate the regional exposure of 257 Himalayan HPP to GLOFs, using a flood-wave propagation model fed by Monte Carlo-derived outburst volumes of >2300 glacial lakes. We interpret the spread of thus modeled peak discharges as a predictive uncertainty that arises mainly from outburst volumes and dam-breach rates that are difficult to assess before dams fail. With 66% of sampled HPP are on potential GLOF tracks, up to one third of these HPP could experience GLOF discharges well above local design floods, as hydropower development continues to seek higher sites closer to glacial lakes. We compute that this systematic push of HPP into headwaters effectively doubles the uncertainty about GLOF peak discharge in these locations. Peak discharges farther downstream, in contrast, are easier to predict because GLOF waves attenuate rapidly. Considering this systematic pattern of regional GLOF exposure might aid the site selection of future Himalayan HPP. Our method can augment, and help to regularly update, current hazard assessments, given that global warming is likely changing the number and size of Himalayan meltwater lakes.

  1. Simulated Last Glacial Maximum Δ14CATM and the Deep Glacial Ocean Reservoir

    NASA Astrophysics Data System (ADS)

    Mariotti, V.; Paillard, D.; Roche, D. M.; Bouttes, N.; Bopp, L.

    2012-12-01

    Δ14Catm has been estimated at 420 ± 80‰ (INTCAL09) during the Last Glacial Maximum (LGM) compared to preindustrial times (0‰), but mechanisms explaining this difference are not yet resolved. Δ14Catm is a function of cosmogenic production in high atmosphere and of carbon cycling in the Earth system (through carbon exchange with the superficial reservoirs, ocean and continental biosphere). 10Be-based reconstructions show a contribution of the cosmogenic production term of only 200 ± 200‰ at the LGM. The remaining 220‰ of Δ14Catm variation between the LGM and preindustrial times have thus to be explained by changes in the carbon cycle. Recently, Bouttes et al. (2010) proposed to explain most of the difference in atmospheric pCO2 between glacial and interglacial times by brine-induced ocean stratification in the Southern Ocean. This mechanism involves the formation of very saline water masses that can store Dissolved Inorganic Carbon (DIC) in the deep ocean. During glacial times, the sinking of brines is enhanced and more DIC is stored in the deep ocean, lowering atmospheric pCO2. Such an isolated ocean reservoir would be characterized by a low Δ14C signature. Evidence of such 14C-depleted deep waters during the LGM has recently been found in the Southern Ocean (Skinner et al., 2010). The degassing of this carbon with low Δ14C would then reduce Δ14Catm throughout the deglaciation. We have further developed the CLIMBER-2 model to include a cosmogenic production of 14C as well as an interactive atmospheric 14C reservoir. We investigate the role of both sinking of brines and cosmogenic production, alongside iron and vertical diffusion mechanisms to explain changes in Δ14Catm during the last deglaciation. In our simulations, not only the sinking of brine mechanism is consistent with past Δ14C data but also it explains most of the differences in atmospheric pCO2 and Δ14C between LGM and preindustrial times.

  2. Radar remote sensing of glacial features, Malaspina Glacier, Alaska

    SciTech Connect

    Molnia, B.F.; Jones, J.E. )

    1990-05-01

    Two types of radar investigations were conducted at Malaspina glacier, the largest piedmont glacier lobe in North America. Digital x-band side-looking airborne radar (SLAR) data were collected to image surface features; ice-surface, ice-penetrating radar was employed to measure ice thickness and to identify the configuration of subglacial bed rock SLAR revealed a complex pattern of surface backscatter responses related to three types of channellike features on the glacier surface, which mimic the configuration of its underlying bed rock. The features resemble (1) glacially eroded valleys with cirque-like indentations, (2) dendritic stream valleys, and (3) a greater than 40-km-long, arcuate, east-west lineament that corresponds to the Fairweather fault. Field examinations of the three types of features were made to determine relief, slope, and other conditions. The channel-like features had elevations as much as 40 m lower than adjacent high areas and were characterized by fewer crevasses, minimal surface relief, a sediment veneer, and standing and running water. Hundred-m-spaced ice-penetrating radar soundings showed that the ice thickness over these low areas is much greater than over adjacent highs. About 50 ice-thickness measurements were made elsewhere on the glacier. The maximum ice thickness measured exceeded 850 m, whereas the minimum thickness was less than 150 m. Comparison of ice-thickness measurements and ice-surface elevations at each site suggests that the Malaspina Glacier occupies a deep basin or series of basins extending well below sea level.

  3. Precise prediction of glacial cycle with its rhythm

    NASA Astrophysics Data System (ADS)

    Lai, C.; Tseng, Y.; Yu, W.; Chueh, P.

    2010-12-01

    An ability to explain and predict the paleoclimatic cycles is one of necessary conditions for reliable predictions of future climate without and with anthropogenic forcing. Here, we solved a big puzzle. Quaternary glacial cycles, as represented by climate proxy data of benthic δ18O, can be divided into four typical periods (TP) with four characteristic points (CP). The cyclic sequence of them goes in the following order: (1) Onset point of glacial termination, (2) Glacial termination period, (3) Zip point of glacial termination, (4) Inter-glacial period, (5) Inception point of glaciations, (6) Period for glacial maturation, (7) Glacial maximum point, and (8) Period for glacial hibernation. The glacial termination (GT) is a swift transition period of about 6,500 years only. A precise prediction of its onset point is a great challenge to the theorem of orbital-forcing that is being developed since Milankovitch. We consider the climate system as a stack of heat capacitors that get warmed up by absorbing part of the insolation and cooled down via gray-body radiation. Part of the insolation is transformed into chemical energy through photosynthesis (CETP) and eventually gets accumulated in the clathrate hydrate (CH) in seawater. We found that, during the last 1.7 million years, every Onset point of GT falls in a very precise time-window defined with three conditions: (1) the eccentricity (E) of Earth’s orbit is increasing, (2) the obliquity (T) is also increasing, and (3) the phase angle of precession (P) falls between 7π/8 and 5π/4. The CETP is converted into sensible heat via oxidation of gases released from dissociated CH. The dissociation of CH depends on its floating level and dissociating level. Those levels are controlled by seawater temperature and the density of CH. The Zip point of GT comes when the average temperature of seawater at 150 m depth is about 18 C, which is mostly influenced by the H2S in the CH. We define the Inception point of glaciations as

  4. Glacial climate states and abrupt climate change in MIROC AOGCM

    NASA Astrophysics Data System (ADS)

    Abe-Ouchi, Ayako; Ohgaito, Rumi; Takahashi, Kunio; Yoshimori, Masa; Kawamura, Kenji; Oka, Akira; Chan, Wing-Le; Sherriff-Tadano, Sam

    2016-04-01

    Millennial climate change such as D-O cycles and AIM recorded in ice cores in both Hemispheres is known to show a relatively higher amplitude in the middle-level of a glacial cycle than in the interglacial state or severe glacial state. Here we ran several sensitivity experiments using a coupled atmosphere and ocean GCM (MIROC4m, renamed from MIROC3.2.2) and show that the response to fresh water release to the ocean and bipolar response is highly dependent on the background climate. The experiments were conducted with 500 years water hosing of 0.05 to 0.1 Sv (where 1 Sv is equivalent to the water flux of 10m sea level rise in 100 years) in the North Atlantic 50-70N under different basic states; modern climate state with the pre-industrial condition, middle glacial climate state and full glacial condition, mainly differing in the ice sheet configuration and atmospheric amount of Greenhouse Gases. The results under middle glacial condition show largest cooling/warming response in North Atlantic and a reasonable bipolar warming/cooling signal revealed in the ice core data of the both hemisphere. We discuss the responses under different background climates which involve the strong coupling between atmosphere, ocean and sea ice and their dependence on the configuration of ice sheet.

  5. Crevassing and calving of glacial ice

    NASA Astrophysics Data System (ADS)

    Kenneally, James Patrick

    Calving of ice is a relatively new area of research in the still young field of glaciology. In the short time that calving has been studied, it has been mainly treated as an afterthought, with the predominant mode of thinking being that it will happen so to concern oneself with why is not important. Many studies dealt with observations of calving front positions over time vs. ice velocity in an attempt to quantify the calving rate as the difference between the two, while others have attempted to deduce some empirical relationship between calving rate and variables such as water depth or temperature. This study instead addresses the question of why, where, and when ice will first become crevassed, which is an obviously necessary condition for a later calving event to occur. Previous work examining the causes of calving used ideas put forth from a variety of fields, including civil engineering, materials science, and results from basic physics and mechanics. These theories are re-examined here and presented as part of a larger whole. Important results from the field of fracture mechanics are utilized frequently, and these results can be used as a predictor of ice behavior and intrinsic properties of ice, as well as properties like back stresses induced by local pinning points and resistive shears along glacial ice boundaries. A theory of fracture for a material experiencing creep is also presented with applications to ice shelves and crevasse penetration. Finally, a speculative theory regarding large scale iceberg formation is presented. It is meant mainly as an impetus to further discussion on the topic, with the hope that a model relating crevasse geometries to flow parameters can result in crevasse spacings that could produce the tabular icebergs which are so newsworthy. The primary focus of this thesis is to move away from the "after the fact" studies that are so common in calving research, and instead devote energy to determining what creates the conditions that

  6. Spawning distribution of sockeye salmon in a glacially influenced watershed: The importance of glacial habitats

    USGS Publications Warehouse

    Young, D.B.; Woody, C.A.

    2007-01-01

    The spawning distribution of sockeye salmon Oncorhynchus nerka was compared between clear and glacially turbid habitats in Lake Clark, Alaska, with the use of radiotelemetry. Tracking of 241 adult sockeye salmon to 27 spawning locations revealed both essential habitats and the relationship between spawn timing and seasonal turbidity cycles. Sixty-six percent of radio-tagged sockeye salmon spawned in turbid waters (???5 nephelometric turbidity units) where visual observation was difficult. Spawning in turbid habitats coincided with seasonal temperature declines and associated declines in turbidity and suspended sediment concentration. Because spawn timing is heritable and influenced by temperature, the observed behavior suggests an adaptive response to glacier-fed habitats, as it would reduce embryonic exposure to the adverse effects of fine sediments. ?? Copyright by the American Fisheries Society 2007.

  7. Late Glacial beech forest: an 18,000 5000-BP pollen record from Auckland, New Zealand

    NASA Astrophysics Data System (ADS)

    Lancashire, A. K.; Flenley, J. R.; Harper, M.

    2002-07-01

    Australia, New Zealand and South America are the main sources of terrestrial climate change records for midlatitudes in the Southern Hemisphere. The advantage of studying the New Zealand record is that its vegetation has been subject to human influence for only the last thousand years. Vegetation records for Auckland are important because earlier work indicates that during the Last Glacial Maximum, the boundary between scrubland and forest lay in the Auckland region. Auckland is situated in a volcanic field and the coring site was in the crater of a small extinct volcano (Crater Hill, formed about 29 ka BP). The 4-m long core contained sediment dating from c. 5 to c. 18 ka BP. We present pollen and diatom records from this core. The pollen records from basal clays indicate southern beech forest (mainly Nothofagus menziesii) was present in the region around Crater Hill from 18 to 14.5 ka BP. At this time, there were areas of scrub in the crater surrounding a hardwater lake. The southern forest limit could well have been close to the site. Records from overlying peat indicate beech forest was replaced by Podocarp broadleaf forest as the Last Glacial ended. Metrosideros spp. (coastal forest trees) peak in the early Holocene. This coincides with an impoverished diatom flora which indicates drier conditions in the basin. When the lake reformed in the Holocene on peat its water was more acidic.

  8. Full-glacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Sanborn, Paul T.; Smith, C. A. Scott; Froese, Duane G.; Zazula, Grant D.; Westgate, John A.

    2006-07-01

    Perennially frozen loess deposits in the Klondike goldfields include paleosols formed in full-glacial environments, correlated by Alaskan distal tephra with Marine Isotope Stages (MIS) 2 and 4. Patterns of organic and inorganic carbon and clay distribution, microstructures, and profile morphologies indicate that soil formation occurred in a base-rich environment in which organic matter accreted predominantly as root detritus. At sites approximately 20 km apart, the expression of cryoturbation and ice wedge development decreases in strength upward in loess-paleosol sequences correlated with MIS 4, suggesting increasing aridity. Configurations of cryoturbation features and ice-wedge thaw unconformities, the presence of numerous ground squirrel burrows, and an absence of peat accumulation suggest that these substrates were predominantly well-drained, with active layers of equal or greater thickness than in modern soils on similar sites in the west-central Yukon. Some characteristics of these paleosols are similar to those of modern steppe and tundra soils, consistent with plant macrofossil evidence for local ecological diversity during full-glacial conditions in eastern Beringia.

  9. EDITORIAL: Cryospheric ecosystems: a synthesis of snowpack and glacial research

    NASA Astrophysics Data System (ADS)

    Hodson, Andy; Brock, Ben; Pearce, David; Laybourn-Parry, Johanna; Tranter, Martyn

    2015-11-01

    The fourteen letters that contributed to this focus issue on cryospheric ecosytems provide an excellent basis for considering the state of the science following a marked increase in research attention since the new millennium. Research letters from the focus issue provide significant insights into the biogeochemical and biological processes associated with snow, glacier ice and glacial sediments. This has been achieved via a significant, empirical effort that has given particular emphasis to glacier surface habitats. However, far less is known about aerobiology, glacial snow covers, supraglacial lakes and sub-ice sedimentary habitats, whose access for sampling and in-situ monitoring remains a great challenge to scientists. Furthermore, the use of models to explore key fluxes, processes and impacts of a changing glacial cryosphere are conspicuous by their absence. As a result, a range of process investigations and modelling studies are required to address the increasing urgency and uncertainty that is associated with understanding the response of cryospheric ecosystems to global change.

  10. Glacial geology of the Hellas region on Mars

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S.; Strom, Robert G.; Johnson, Natasha

    1991-01-01

    A glacial geologic interpretation was recently presented for Argyre, which is herein extended to Hellas. This glacial event is believed to constitute an important link in a global cryohydric epoch of Middle Amazonian age. At glacial maximum, ice apparently extended far beyond the regions of Argyre and Hellas, and formed what is termed as the Austral Ice Sheet, an agglomeration of several ice domes and lobes including the Hellas Lobe. It is concluded that Hellas was apparently heavily glaciated. Also glaciation was young by Martian standards (Middle Amazonian), and ancient by terrestrial standards. Glaciation appears to have occurred during the same period that other areas on Mars were experiencing glaciation and periglacial activity. Glaciation seems to have occurred as a geological brief epoch of intense geomorphic activity in an era characterized by long periods of relative inactivity.

  11. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle. PMID:15860623

  12. Development of a glacially dominated shelf-slope-fan system in tectonically active southeast Alaska: Results of IODP Expedition 341 core-log-seismic integrated studies at glacial cycle resolution

    NASA Astrophysics Data System (ADS)

    Gulick, Sean; Jaeger, John; Mix, Alan; Swartz, John; Worthington, Lindsay; Reece, Robert

    2014-05-01

    100 kyr glacial-interglacial cycles. Examination of the sink for both of these systems, which includes the Surveyor Fan and Aleutian Trench wedge, demonstrates a clear climatic driver for sediment flux to the deep sea. The first appearance of ice-rafted debris at our distal drill site closely approximates the start of the Pleistocene and a doubling of sediment accumulation accompanies the MPT. Converting sediment volumes just within the deep-sea sinks back to erosion rates in the orogen and correlating with changes in exhumation rates from thermochronology demonstrates a lack of accelerated tectonic response to the intensification of Northern Hemisphere glaciations at the start of the Pleistocene but increased shortening and exhumation of sediments at the MPT. The form of tectonic response differs between out-of-sequence thrusting or antiformal stacking within the fold and thrust belt to the west and a near vertical advection of material in a tectonic aneurysm in the core of the orogen to the east.

  13. Timing of Pleistocene glacial oscillations recorded in the Cantabrian Mountains (North Iberia): correlation of glacial and periglacial sequences from both sides of the range using a multiple-dating method approach

    NASA Astrophysics Data System (ADS)

    Rodriguez-Rodriguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María; Rinterknecht, Vincent; Pallàs, Raimón; Bourlès, Didier

    2015-04-01

    The Cantabrian Mountains is a coastal mountain range up to 2648 m altitude located at 43oN latitude and directly influenced by the North Atlantic climate oscillations. Although nowadays it is fully deglaciatied, glacial sediments and landforms are clearly preserved elsewhere above 1600 m. Particularly, glacial evidence in the central Cantabrian Mountains suggests the formation of an icefield in the headwaters of the Porma and Esla catchments drained by glaciers up to 1-6 km in length in the northern slope and 19 km-long in the southern slope, with their fronts at minimum altitudes of 900 and 1150 m asl respectively (Rodríguez-Rodríguez et al., 2014). Numerical ages obtained from the base of the Brañagallones ice-dammed deposit and one of the lateral moraines that are damming this deposit suggest that the local glacial maximum was prior to ca 33.5 cal ka BP in the Monasterio Valley (see data compiled in Rodriguez-Rodríguez et al., in press). Currently, our research is focused on developing a full chronology of glacial oscillations in both sides of the range and investigating their paleoclimate significance and relationship with glacial asymmetry through the combined use of surface exposure, OSL and radiocarbon dating methods. In this work, we present 47 10Be surface exposure ages obtained from boulders in moraines, glacial erratic boulders and rock glaciers in the Monasterio and Porma valleys. The glacial record of these valleys was chosen because of: (i) its good preservation state; (ii) the occurrence of a quartz-rich sandstone formation; and (iii) the availability of previous 14C and OSL numerical ages. Sampling sites were selected considering the relative age of glacial stages to cover as complete as possible the history of Pleistocene glaciations in the studied area, from the glacial maximum stage to the prevalence of periglacial conditions. Preliminary results suggest the occurrence of several glacial advances of similar extent at ca 150 - 50 ka followed

  14. The vegetation cover of New Zealand at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Newnham, Rewi; McGlone, Matt; Moar, Neville; Wilmshurst, Janet; Vandergoes, Marcus

    2013-08-01

    A new reconstruction of the vegetation cover for New Zealand at the Last Glacial Maximum (LGM) is presented, based primarily on a database of 66 pollen site records and a more limited range of plant macrofossil and coleopteran records. Extensive forest is evident only from Auckland northwards. Conifer-broadleaf forest similar to that in the region today, but with Agathis australis scarce, persisted in the far north, whilst Nothofagus trees and a range of shrub taxa characterised the more open forests elsewhere in Northland. Survival of Nothofagus-dominated forest in coastal and exposed continental shelf locations to the southwest of Auckland and northwestern South Island is also indicated. Beyond these regions, vegetation cover comprised shrubland- and grassland-dominant communities, with the latter more prominent in eastern areas, to the south and presumably at higher altitudes. Nevertheless the survival of forest trees is indicated unambiguously in most regions apart from the eastern South Island. Thus the concept of 'micro glacial forest refugia' in New Zealand remains supported by this latest glacial vegetation reconstruction and we draw possible parallels with the developing but contentious concept of 'northern cryptic refugia' in Europe. Recent assertions that pollen and beetle reconstructions of the New Zealand LGM vegetation patterns diverge significantly are not supported by this analysis. Rather, the two proxies are readily reconciled if the term 'woody' as indicated by coleoptera is not restricted to tall forest trees but extended to the widespread woody shrub and small tree elements of the New Zealand flora. Regional distinctions in the LGM vegetation reconstruction concur broadly with the contemporary vegetation pattern, suggesting that, along with temperature depression and likely drier growing conditions, a zonal circulation regime with prominent southern westerly winds was important at 21 ka, as it is today. Pollen-climate modelling of the extent of

  15. Erosion and transport by Byrd Glacier, Antarctica during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Licht, K. J.; Palmer, E. F.

    2013-02-01

    Glacial till samples from seven, modern-Holocene Byrd Glacier moraines were characterized using particle size analysis, sand petrography and detrital zircon geochronology and compared to Ross Sea tills deposited during the Last Glacial Maximum. The goal was to identify the paleoflow path for Byrd Glacier and assess the use of multiple provenance techniques. The coarse sand fraction of Byrd Glacier tills is dominated by lithic fragments of adjacent bedrock outcrops, except samples from the Lonewolf Nunataks, which have a higher proportion of mineral to lithic fragments, as well as a recognizable exotic component. Cluster analysis shows that Byrd Glacier tills, with the exception of the two Lonewolf Nunataks sites, do not cluster strongly with Ross Sea samples because they have a higher proportion of lithic fragments. This indicates that comminution must be an active subglacial process beneath East Antarctic outlet glaciers. Byrd Glacier tills are also typically coarser grained that Ross Sea tills and their maturity is a reflection of both glacial processes and rock type. Measured U/Pb ages of detrital zircons from Byrd Glacier tills range from Triassic to Archean (240-3540 Ma) with a dominance of grains 530-600 Ma. Ross Sea till samples show spatial variability in U/Pb age distributions, with the core sites west of the 180° longitude line showing similarity to most Byrd Glacier tills, whereas core NBP9407-39, east of 180° long., is dominated by ˜100 Ma grains. Ross Sea tills also contain a recognizable detrital zircon fraction eroded inland of the Transantarctic Mountains. Both provenance methods indicate that the ice flow line for Byrd Glacier during the LGM was to the east of Ross Island and extended on either side of Ross Bank, with the majority of ice flowing to the Ross Sea's Central Basin. Our analysis shows that sand petrography and detrital zircon U/Pb age spectra provide complementary datasets that produce similar ice flow reconstructions and reveal

  16. Giant glacial cirques of non-mountainous terrains

    NASA Astrophysics Data System (ADS)

    Amantov, A.; Amantova, M.

    2012-04-01

    Cirques are usually considered as specific landforms of hill and mountain terrains produced by alpine glaciers, and/or slope failures (landslides). However, glacial cirques seem to be present also in non-mountainous terrains that underwent extensive Pleistocene ice-sheet glaciations and strong glacial and fluvio-glacial erosion. The largest form in the Baltic region is Severoladozhsky (North Lake Ladoga) cirque, probably the world's largest representative, with the length and width close to 100 km. Another example is the deepest Landsort basin of the Baltic Sea. In those cases Meso-Neoproterozoic sediments were subject to selected erosion, with evident overdeepening of the bedrock surface in comparison with surrounding crystalline frame. The bowl headwall shape of the cirque-like landforms was determined by the outline of the margin of exhumed basin. The origin of the major basins of margins of the Baltic and Canadian shields are similar. However, direct analogues of giant cirques are not well developed in this part of North America due to geological deviations and dominant directions of ice movement. Comparable landforms (like the South Chippewa basin of the Lake Michigan) are therefore less mature. We define glacial cirque as an amphitheatre-shape depression with comparable values of length and width, steep headwall with adjacent side slopes and gentle lip with commonly increased glacial accumulation. They are usually located within an ice stream that created typical relief profile with normal horseshoe overdeepening, and in areas predefined by geological and geomorphological peculiarities. This definition likely fits both classic mountain cirques, and giant ones created in favorable conditions in domains that underwent extensive glaciations and relevant selective glacial erosion. Length/width ratio typical for giant cirques group is close to 1:1, being comparable with classical alpine ones. Major differences (like length/height ratio of other order and possible

  17. Is rate of glacial retreat accelerated in Indian Himalaya? (Invited)

    NASA Astrophysics Data System (ADS)

    Kulkarni, A. V.

    2013-12-01

    The Himalaya has one of the largest concentration of glaciers and rivers like Indus, Ganga and Bramhputra originate from this region. The snow and glacier melt is an important source of water for these rivers. However, this source of water may get affected in the near future due to changes in the cryosphere. Therefore, retreat of Himalayan glaciers are discussed extensively in scientific and public forums in India. Conventionally health of glaciers is assessed using changes in glacial length, as it is widely measured. However changes in glacial length and loss in areal extent near terminus needs to be interpreted carefully, as these changes can be influenced by numerous terrain and climatically sensitive parameters. The terrain parameters which can influence glacial retreat are slope, area altitude distribution, debris cover and orientation. In addition, climatically sensitive parameters like mass balance, glacial lakes and black carbon can also influence glacier retreat. These multiple influences can produce a complex pattern of glacial retreat. In this paper long-term glacier retreat in three river basins in the Indian Himalaya as Tista, Baspa and Parbati will be discussed. These basins are located in different climatically sensitive regions and each basin has unique dominant process of mass wasting. In addition to terrain parameters, influence of process like formation and expansion of moraine dammed lakes in Tista basin, deposition of black carbon on accumulation area in Baspa basin and debris cover in Parbati basin will also be discussed. This will provide understanding on varying influence of different mass wasting processes on glacial retreat during last five decades in the Indian Himalaya.

  18. The Southern Ocean's biological pump during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Anderson, Robert F.; Chase, Zanna; Fleisher, Martin Q.; Sachs, Julian

    Ice core records from Antarctica show large (˜80 ppm) and regular climate-related changes in atmospheric CO 2, with minimum values during glacial periods and maximum values during peak interglacials. The suggested role of the Southern Ocean in driving these changes is based on either the potential for increased utilization of surface nutrients or the potential for decreased ventilation of deep waters during glacial times. Several recent studies have invoked increased stratification of the Southern Ocean to explain lower glacial atmospheric CO 2 levels in terms of reduced exchange of CO 2 between the deep sea and the atmosphere. A northward displacement and/or substantial weakening of the westerly winds during glacial periods are implicit in the scenarios that invoke enhanced stratification. However, both circulation models and proxy results argue against a weakening of the westerlies. In fact, the mean flow of the Antarctic Circumpolar Current and wind-driven upwelling during the Last Glacial Maximum (LGM) are thought to be at least as vigorous as those which exist today. Given these boundary conditions, we offer two (competing) scenarios for ecosystem structure and export production of the glacial Southern Ocean. The first scenario satisfies all proxy records for nutrient utilization and phytoplankton growth rate, and requires increased (relative to today) nitrate utilization south of the Antarctic Polar Front (APF) by phytoplankton other than diatoms, together with a shift in the zone of maximum diatom growth from south (interglacials) to north (glacials) of the APF. The second scenario has reduced growth of all phytoplankton species south of the APF during glacials, and a shift in the zone of maximum export production to the north of the Polar Front. The principal weakness of the first scenario is that there is little sedimentary evidence to support the increased export of particulate organic carbon required by the inferred increase in nitrate utilization south

  19. The glacial iron cycle from source to export

    NASA Astrophysics Data System (ADS)

    Hawkings, J.; Wadham, J. L.; Tranter, M.; Raiswell, R.; Benning, L. G.; Statham, P. J.; Tedstone, A. J.; Nienow, P. W.; Telling, J.; Bagshaw, E.; Simmons, S. L.

    2014-12-01

    Nutrient availability limits primary production in large sectors of the world's oceans. Iron is the major limiting nutrient in around one third of the oceanic euphotic zone, most significantly in the Southern Ocean proximal to Antarctica. In these areas the availability of bioavailable iron can influence the amount of primary production, and thus the strength of the biological pump and associated carbon drawdown from the atmosphere. Despite experiencing widespread iron limitation, the Polar oceans are among the most productive on Earth. Due to the extreme cold, remoteness and their perceived "stasis", ice sheets have previously been though of as insignificant in global biogeochemical cycles. However, large marine algal blooms have been observed in iron-limited areas where glacial influence is large, and it is possible that these areas are stimulated by glacial bioavailable iron input. Here we discuss the importance of the Greenland and Antarctic ice sheets in the global iron cycle. Using field collected trace element data, bulk meltwater chemistry and mineralogical analysis, including photomicrographs, EELS and XANES, we present, for the first time, a conceptual model of the glacial iron cycle from source to export. Using this data we discuss the sources of iron in glacial meltwater, transportation and alteration through the glacial system, and subsequent export to downstream environments. Data collected in 2012 and 2013 from two different Greenlandic glacial catchments are shown, with the most detailed breakdown of iron speciation and concentrations in glacial areas yet reported. Furthermore, the first data from Greenlandic icebergs is presented, allowing meltwater-derived and iceberg-derived iron export to be compared, and the influence of both in marine productivity to be estimated. Using our conceptual model and flux estimates from our dataset, glacial iron delivery in both the northern and southern hemisphere is discussed. Finally, we compare our flux

  20. Retreat history of the East Antarctic Ice Sheet since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Mackintosh, Andrew N.; Verleyen, Elie; O'Brien, Philip E.; White, Duanne A.; Jones, R. Selwyn; McKay, Robert; Dunbar, Robert; Gore, Damian B.; Fink, David; Post, Alexandra L.; Miura, Hideki; Leventer, Amy; Goodwin, Ian; Hodgson, Dominic A.; Lilly, Katherine; Crosta, Xavier; Golledge, Nicholas R.; Wagner, Bernd; Berg, Sonja; van Ommen, Tas; Zwartz, Dan; Roberts, Stephen J.; Vyverman, Wim; Masse, Guillaume

    2014-09-01

    The East Antarctic Ice Sheet (EAIS) is the largest continental ice mass on Earth, and documenting its evolution since the Last Glacial Maximum (LGM) is important for understanding its present-day and future behaviour. As part of a community effort, we review geological evidence from East Antarctica that constrains the ice sheet history throughout this period (˜30,000 years ago to present). This includes terrestrial cosmogenic nuclide dates from previously glaciated regions, 14C chronologies from glacial and post-glacial deposits onshore and on the continental shelf, and ice sheet thickness changes inferred from ice cores and continental-scale ice sheet models. We also include new 14C dates from the George V Land - Terre Adélie Coast shelf. We show that the EAIS advanced to the continental shelf margin in some parts of East Antarctica, and that the ice sheet characteristically thickened by 300-400 m near the present-day coastline at these sites. This advance was associated with the formation of low-gradient ice streams that grounded at depths of >1 km below sea level on the inner continental shelf. The Lambert/Amery system thickened by a greater amount (800 m) near its present-day grounding zone, but did not advance beyond the inner continental shelf. At other sites in coastal East Antarctica (e.g. Bunger Hills, Larsemann Hills), very little change in the ice sheet margin occurred at the LGM, perhaps because ice streams accommodated any excess ice build up, leaving adjacent, ice-free areas relatively unaffected. Evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the LGM, an observation supported by ice cores, which suggest that interior ice sheet domes were ˜100 m lower than present at this time. Ice sheet recession may have started ˜18,000 years ago in the Lambert/Amery glacial system, and by ˜14,000 years ago in Mac.Robertson Land. These early pulses of deglaciation may have been responses to abrupt sea-level rise

  1. Environmental transformations and cultural changes: A multidisciplinary case study for the Late Glacial and Final Palaeolithic from Northern Germany

    NASA Astrophysics Data System (ADS)

    Turner, F.; Tolksdorf, J. F.; Viehberg, F.; Schwarz, A.; von Bramann, U.; Bittmann, F.; Kaiser, K.; Schwalb, A.; Staesche, U.; Breest, K.; Pott, R.; Veil, S.

    2012-04-01

    In contrast to younger periods, studies integrating archaeological and environmental records for the Palaeolithic are still rare. Especially our knowledge about interactions between the drastic climatic/environmental changes and cultural developments during the Late Glacial is very limited. This multidisciplinary case study from river Jeetzel, a western Elbe tributary in Northern Germany, combines high resolution palaeoenvironmental investigations with fine-scaled archaeological research on stratified and surface sites. Various dating methods (palynostratigraphy, radiocarbon- and OSL-dating) and analyses of environmental and climatological proxies (pollen and plant macro-remains, ostracods, diatoms and green algae) on river palaeochannel sediments allow detailed reconstruction of interactions between Late Glacial climate, vegetation and fluvial developments. Biostratigraphical analyses on stratified archaeological sites and dating of charcoal / bone fragments from artefact scatters place the Late Palaeolithic occupation of Early Federmesser groups in an environmental context. Thus the former production of hitherto unknown amber art (amongst others a figurine representing a moose) can be ascribed to the Older Dryas and Early Allerød, which are the periods of main Late Glacial afforestation. Therewith our investigations suggest that Final Palaeolithic cultural changes may have been triggered by climatic and environmental transformations.

  2. Variability of neodymium isotopes associated with planktonic foraminifera in the Pacific Ocean during the Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hu, Rong; Piotrowski, Alexander M.; Bostock, Helen C.; Crowhurst, Simon; Rennie, Victoria

    2016-08-01

    The deep Pacific Ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales. The circulation of the deep Pacific during the Last Glacial Maximum (LGM), however, is not well understood. Neodymium (Nd) isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography. In this study, we present Nd isotope compositions (εNd) of planktonic foraminifera for the Holocene and the LGM obtained from 55 new sites widely distributed in the Pacific Ocean. The Holocene planktonic foraminiferal εNd results agree with the proximal seawater data, indicating that they provide a reliable record of modern bottom water Nd isotopes in the deep Pacific. There is a good correlation between foraminiferal εNd and seawater phosphate concentrations (R2 = 0.80), but poorer correlation with silicate (R2 = 0.37). Our interpretation is that the radiogenic Nd isotope is added to the deep open Pacific through particle release from the upper ocean during deep water mass advection and aging. The data thus also imply the Nd isotopes in the Pacific are not likely to be controlled by silicate cycling. In the North Pacific, the glacial Nd isotopic compositions are similar to the Holocene values, indicating that the Nd isotope composition of North Pacific Deep Water (NPDW) remained constant (-3.5 to -4). During the LGM, the southwest Pacific cores throughout the water column show higher εNd corroborating previous studies which suggested a reduced inflow of North Atlantic Deep Water to the Pacific. However, the western equatorial Pacific deep water does not record a corresponding radiogenic excursion, implying reduced radiogenic boundary inputs during the LGM probably due to a shorter duration of seawater-particle interaction in a stronger glacial deep boundary current. A significant negative glacial εNd excursion is evident in

  3. Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larea tridentata

    USGS Publications Warehouse

    Hunter, Kimberly L.; Betancourt, Julio L.; Riddle, Brett R.; Van Devender, Thomas R.; Cole, K.L.; Spaulding, W.G.

    2001-01-01

    1. A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). 2 Glacial/early Holocene (26a??10 14C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 14C kyr bp. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr bp. Hexaploids appeared by 8.5 14C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37A?N) in the Mohave Desert between 5.6 and 3.9 14C kyr bp. 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

  4. Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

    USGS Publications Warehouse

    Hunter, K.L.; Betancourt, J.L.; Riddle, B.R.; Van Devender, T. R.; Cole, K.L.; Geoffrey, Spaulding W.

    2000-01-01

    1 A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). 2 Glacial/early Holocene (26-10 14C kyr BP or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ???4.0 14C kyr BP. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr BP. Hexaploids appeared by 8.5 14C kyr BP in the lower Colorado River Basin, reaching their northernmost limits (???37??N) in the Mohave Desert between 5.6 and 3.9 14C kyr BP. 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture. ?? 2001 Blackwell Science Ltd.

  5. Glacial to Interglacial Climate and Sea Level Changes Recorded in Submerged Speleothems, Argentarola, Italy

    NASA Astrophysics Data System (ADS)

    Folz-Donahue, K.; Dutton, A.; Antonioli, F.; Richards, D. A.; Nita, D. C.; Lambeck, K.

    2014-12-01

    Direct records of Quaternary sea level change can provide insight on the timing and nature of ice sheet retreat during glacial terminations. Such records are generally rare, particularly prior to the last deglaciation, due in part to the difficulty of recovering material from sites that have been submerged by subsequent sea-level rise. A suite of stalagmites recovered from a submerged cave on Argentarola Island in the Tyrrhenian Sea contains hiatuses that were formed when the cave became submerged by seawater. These hiatuses are remarkable due to the presence of calcite tubes secreted by serpulid worms, providing direct evidence of marine inundation. As sea level drops during the following glacial inception, the cave is drained and dense spelean calcite encases the serpulid worm tubes, forming alternating layers of spelean and serpulid calcite. U-Th dates of spelean calcite directly above and below these serpulid layers has previously been used to constrain timing and amplitude of sea level highstands in the Mediterranean. Stable isotope records from the same cave have also been used to indicate increased precipitation across the Mediterranean during Sapropel 6 (175 ka). Here we present U-Th dates and stable isotope records for three Argentarola stalagmites. These specimens were recovered from -22, -18, and -14 m relative to present sea level (rpsl), and complement previously published data for Argentarola stalagmites at -21, -18.5, and -18 m rpsl. The timing and elevation of spelean calcite directly above and below serpulid tube layers provide rare insight on rates of sea-level change between -14 and -22 m during glacial terminations and inceptions prior to the last termination. Stable isotope records from the same stalagmites are used to investigate changes in western Mediterranean climate and potential relationships to Mediterranean sapropel events.

  6. An evaluation of stream characteristics in glacial versus fluvial process domains in the Colorado Front Range

    NASA Astrophysics Data System (ADS)

    Livers, Bridget; Wohl, Ellen

    2015-02-01

    Many of the conceptual models developed for river networks emphasize progressive downstream trends in morphology and processes. Such models can fall short in describing the longitudinal variability associated with low-order streams. A more thorough understanding of the influence of local variability of process and form in low-order stream channels is required to remotely and accurately predict channel geometry characteristics for management purposes, and in this context designating process domains is useful. We define process domains with respect to glacial versus fluvial valleys and lateral confinement of valley segments. We evaluated local variability of process domains in the Colorado Front Range by systematically following streams, categorizing them into stream morphologic type and process domain, and evaluating a number of channel geometry characteristics. We evaluated 111 stream reaches for significant differences in channel geometry among stream types and process domains, location and clustering of stream types on a slope-drainage area (S-A) plot and downstream hydraulic geometry relationships. Although individual channel geometry variables differed significantly between individual stream types in glacial and fluvial process domains, no single channel geometry variable consistently differentiated all stream types between process domains. Hypothetical S-A boundaries between bedrock- and alluvial-bed channels proposed in previous studies did not reliably divide bedrock and alluvial reaches for our study sites. Although downstream hydraulic geometry relationships are well-defined using all reaches in the study area, reaches in glacial valleys display much more variability in channel geometry characteristics than reaches in fluvial valleys, less pronounced downstream hydraulic geometry relationships, and greater scatter of reaches on an S-A plot. Local spatial variability associated with process domains at the reach scale (101-103 m) overrides progressive

  7. Sensitivity of Last Glacial Maximum climate to uncertainties in tropical and subtropical ocean temperatures

    USGS Publications Warehouse

    Hostetler, S.; Pisias, N.; Mix, A.

    2006-01-01

    The faunal and floral gradients that underlie the CLIMAP (1981) sea-surface temperature (SST) reconstructions for the Last Glacial Maximum (LGM) reflect ocean temperature gradients and frontal positions. The transfer functions used to reconstruct SSTs from biologic gradients are biased, however, because at the warmest sites they display inherently low sensitivity in translating fauna to SST and they underestimate SST within the euphotic zones where the pycnocline is strong. Here we assemble available data and apply a statistical approach to adjust for hypothetical biases in the faunal-based SST estimates of LGM temperature. The largest bias adjustments are distributed in the tropics (to address low sensitivity) and subtropics (to address underestimation in the euphotic zones). The resulting SSTs are generally in better agreement than CLIMAP with recent geochemical estimates of glacial-interglacial temperature changes. We conducted a series of model experiments using the GENESIS general atmospheric circulation model to assess the sensitivity of the climate system to our bias-adjusted SSTs. Globally, the new SST field results in a modeled LGM surface-air cooling relative to present of 6.4 ??C (1.9 ??C cooler than that of CLIMAP). Relative to the simulation with CLIMAP SSTs, modeled precipitation over the oceans is reduced by 0.4 mm d-1 (an anomaly -0.4 versus 0.0 mm d-1 for CLIMAP) and increased over land (an anomaly -0.2 versus -0.5 mm d-1 for CLIMAP). Regionally strong responses are induced by changes in SST gradients. Data-model comparisons indicate improvement in agreement relative to CLIMAP, but differences among terrestrial data inferences and simulated moisture and temperature remain. Our SSTs result in positive mass balance over the northern hemisphere ice sheets (primarily through reduced summer ablation), supporting the hypothesis that tropical and subtropical ocean temperatures may have played a role in triggering glacial changes at higher latitudes.

  8. Glacial landforms of the southern Ungava Bay region (Canada): implications for the late-glacial dynamics and the damming of glacial Lake Naskaupi

    NASA Astrophysics Data System (ADS)

    Dube-Loubert, Hugo; Roy, Martin

    2014-05-01

    The Laurentide ice sheet played an important role in the late Pleistocene climate, notably through discharges of icebergs and meltwater. In this context, the Ungava Bay region in northern Quebec-Labrador appears particularly important, especially during the last deglaciation when the retreating ice margin dammed major river valleys, creating large proglacial lakes (e.g., McLean, aux Feuilles). The history of these lakes is closely related to the temporal evolution of the Labrador-Quebec ice dome. There are, however, large uncertainties regarding the position of its ice divide system through time, thereby limiting our understanding of the history of these glacial lakes. Here we focus on glacial and deglacial landforms present in the George River valley, south of Ungava Bay, in order to bring additional constraints on the late-glacial ice dynamics of this region, which also comprised glacial Lake Naskaupi. This work is based on surficial mapping using aerial photos and satellite imagery, combined with extensive fieldwork and sediment sampling. Our investigation showed significant differences in the distribution of glacial landforms across the region. The area east of the George River is characterized by well-developed Naskaupi shorelines while the elevated terrains show a succession of geomorphological features indicative of cold-based ice or ice with low basal velocities. In the easternmost part of this sector, ice flow directional data indicate that the ice was flowing towards ENE, against the regional slope. Eskers show paleocurrent directions indicating a general ice retreat from east to west. In the western part of this sector, near the George River valley, eskers are absent and the region is covered by felsenmeer and ground moraine that likely reflect the presence of a residual ice mass that was no longer dynamic. The presence of a stagnant ice represents the best mechanism to explain the formation of glacial lakes in the George River valley and its main

  9. A method for selecting potential geosites. The case of glacial geosites in the Chablais area (French and Swiss Prealps)

    NASA Astrophysics Data System (ADS)

    Perret, Amandine; Reynard, Emmanuel

    2014-05-01

    Since 2009, an Interreg IVA project (123 Chablais), dealing with the promotion of natural and cultural heritage in the Chablais area, has been developed. It is linked to the creation of the Chablais Geopark. In a context of development of smart forms of tourism, the objective was to develop a strategy promoting the glacial heritage to a wide public in an area where the glaciers have almost disappeared. The recognition of specific places as geoheritage is the result of a double process: a scientific one, based on more or less sophisticated methods, and a social one, that is the acknowledgment by the society. One of the first scientific tasks is to produce a list of "potential geosites" that will be assessed in more details. However, this selection is often a weak point of inventories. It often seems like a "black box" without any transparency. In this project (123 Chablais) we carried out an inventory of glacial geosites, using the method developed by Reynard et al. (2007, 2012). However, a method has been created to enlighten the selection process, and to enhance choices in geoheritage management. As it was not possible to consider all sites in the Chablais area, a mixed selection approach was developed, halfway between completeness and specificity (Martin, 2012). The first step was the creation of a list of "points of interest", established using different sources: literature review, fieldwork and use of GIS to cross information. A selection was then performed according to two criteria: correspondence with a glacial stage (time axis) and belonging to a type of forms (spatial axis). Finally, selected sites aimed at providing a representative overview of the regional glacial witnesses. Therefore, representative sites of the regional geology were selected as well as sites presenting regional peculiarities Temporal and spatial attributes were given to the 101 points of interest identified. From a temporal point of view, this inventory aimed at presenting the main

  10. Petaloid Organs Preserved in an Arctic Plant Macrofossil Assemblage from Full-Glacial Sediments in Southeastern Minnesota

    NASA Astrophysics Data System (ADS)

    Baker, R. G.; Mason, J. A.; Maher, L. J.

    1999-11-01

    A small suite of plant macrofossils indicates that southeastern Minnesota supported subarctic to arctic vegetation 18,700 yr B.P. Fossil tepals of Polygonum viviparum are exceptionally well preserved; they occur with more fragmentary remains of Dryas integrifolia, Vaccinium uliginosum var. alpinum, and probable species of arctic Salix, S. cf. herbacea, and S. cf. arctica. The pollen spectrum from this site is dominated by Picea, Pinus, and Cyperaceae, which are typical of midwestern full-glacial sequences. Tundra-like conditions with permafrost were present in southeastern Minnesota during full-glacial time. Local environments 18,700 yr B.P. reconstructed from both physical and paleobotanical evidence include wind-swept ridge tops with thin loess, outcrops of dolostone and sandstone on valley walls, colluvial slopes, sandy to gravelly floodplains, shallow floodplain pools, wet meadows, and peaty turfs, all in a treeless or nearly treeless environment.

  11. Trends in stomatal density and 13C/12C ratios of Pinus flexilis needles during last glacial-interglacial cycle

    USGS Publications Warehouse

    Van De Water, Peter K.; Leavitt, Steven W.; Betancourt, J.L.

    1994-01-01

    Measurements of stomatal density and ?? 13C of limber pine (Pinus flexilis) needles (leaves) preserved in pack rat middens from the Great Basin reveal shifts in plant physiology and leaf morphology during the last 30,000 years. Sites were selected so as to offset glacial to Holocene climatic differences and thus to isolate the effects of changing atmospheric CO2 levels. Stomatal density decreased ~17 percent and ?? 13C decreased ~1.5 per mil during deglaciation from 15,000 to 12,000 years ago, concomitant with a 30 percent increase in atmospheric CO2. Water-use efficiency increased ~15 percent during deglaciation, if temperature and humidity were held constant and the proxy values for CO2 and ?? 13C of past atmospheres are accurate. The ??13C variations may help constrain hypotheses about the redistribution of carbon between the atmosphere and biosphere during the last glacial-interglacial cycle.

  12. Morphologic Map of Glacial and Periglacial Features in the Northwestern Argyre Basin, Mars

    NASA Astrophysics Data System (ADS)

    Raack, J.; Hiesinger, H.; Reiss, D.

    2010-03-01

    We produced a morphological map of the northwestern rim of the Argyre Basin with focus on glacial and periglacial features. We report on features such as gullies, pingo-like forms and glacial remnants which are observed.

  13. The Influence of Glacial Ice Sheets on Atlantic Meridional Overturning Circulation Through Atmospheric Circulation Change under Glacial Climate

    NASA Astrophysics Data System (ADS)

    Sherriff-Tadano, S.; Abe-Ouchi, A.; Yoshimori, M.; Oka, A.; Chan, W. L.

    2014-12-01

    It is well known that glacial ice sheets (Laurentide, Fennoscandian and Antarctic ice sheets) exert a large influence on the climate including the atmospheric circulation. Moreover, recent climate modeling studies suggest that glacial ice sheets have a large impact on the Atlantic meridional overturning circulation (AMOC). However, the process by which the ice sheets impact on the AMOC is not yet fully understood. On the other hand, recent studies showed that surface wind changes play a crucial role on changes to the AMOC under glacial climate. Therefore, in this study, we investigate in detail, the process by which the ice sheet modifies the AMOC through surface wind change. Here we conduct numerical experiments using an atmospheric general circulation model (AGCM) and an ocean general circulation model (OGCM) separately. Our method consists of 2 steps. First, from AGCM experiments, we evaluate the effect of glacial ice sheets on the surface wind. Second, from OGCM experiments, we evaluate the influence of the wind stress change on the AMOC by applying the surface wind change as a boundary condition, while leaving other boundary conditions (surface heat and water fluxes) unchanged. In addition, we conduct several sensitivity experiments. Using the AGCM, we explore individual ice sheet effect, ice sheet topography effect and albedo effect on surface wind change. Moreover, using the OGCM, we change the surface wind gradually or apply the surface wind change only at a specific region in order to explore the wind change effect in detail. We find that glacial ice sheets largely intensify the AMOC by surface wind change under glacial climate. Compare to other regions, it reveals that the wind change at the North Atlantic (NA) is a key region. There, the northern glacial ice sheet topography intensifies the Icelandic Low and anti-cyclonic circulation over the Laurentide ice sheet. However, this wind effect is effective only when the NA is not widely covered by sea ice

  14. Reconstructing Oceanographic Conditions From the Holocene to the Last Glacial Maximum in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Miller, J.; Dekens, P. S.; Weber, M. E.; Spiess, V.; France-Lanord, C.

    2015-12-01

    The International Ocean Discovery Program (IODP) Expedition 354 drilled 7 sites in the Bay of Bengal, providing a unique opportunity to improve our understanding of the link between glacial cycles, tropical oceanographic changes, and monsoon strength. Deep-sea sediment cores of the Bengal Fan fluctuate between sand, hemipelagic and terrestrial sediment layers. All but one of the sites (U1454) contain a layer of calcareous clay in the uppermost part of the core that is late Pleistocene in age. During Expedition 354 site U1452C was sampled at high resolution (every 2cm) by a broad group of collaborators with the goal of reconstructing monsoon strength and oceanographic conditions using a variety of proxies. The top 480 cm of site U1452C (8ºN, 87ºE, 3671m water depth) contains primarily nannofossil rich calcareous clay. The relatively high abundance of foraminifera will allow us to generate a high resolution record of sea surface temperature (SST) and sea surface salinity (SSS) using standard foraminifera proxies. We will present oxygen isotopes (δ18O) and Mg/Ca data of mixed layer planktonic foraminifera from the top 70cm of the core, representing the Holocene to the last glacial maximum. δ18O of planktonic foraminifera records global ice volume and local SST and SSS, while Mg/Ca of foraminifera is a proxy for SST. The paired Mg/Ca and δ18O measurements on the same samples of foraminifera, together with published estimates with global ocean δ18O, can be used to reconstruct both SST and local δ18O of seawater, which is a function of the evaporation/precipitation balance. In future work, the local SSS and SST during the LGM will be paired with terrestrial and other oceanic proxies to increase our understanding of how global climate is connected to monsoon strength.

  15. Do post-glacial river valleys in northern New England store mill-dam legacy sediments?

    NASA Astrophysics Data System (ADS)

    Strouse, S.; Snyder, N. P.

    2010-12-01

    Dam-influenced floodplain morphology has not been studied extensively in post-glacial rivers with high densities of colonial-era milldams. Fluvial restoration in the eastern U.S. often focuses on understanding the natural, or pre-Colonial, floodplain processes. Recent work by Walter and Merritts (2008) in the piedmont of the U.S. Mid-Atlantic region suggests milldams significantly impact sedimentation by creating surfaces composed of post-dam legacy sediment that are often abandoned by the river and function as fill terraces. This work has not yet been tested in a post-glacial environment. I analyze channel morphology and sedimentation patterns upstream of two breached dams on the Sheepscot River in Mid-Coastal Maine using lidar digital elevation models, historical aerial photographs, radiocarbon dating, and hydraulic modeling. In the past several decades, observable channel morphologic changes occurred at the two study sites: Maxcy’s Mills dam (built in 1809, it was 4-m high and breached in the late 1950s), and at Head Tide dam (built in the 1760s, it is 6-m high and was partially breached in 1952). The Sheepscot River is one of Maine’s eight rivers with native anadromous Atlantic salmon populations. Because Atlantic salmon are a federally listed endangered species, understanding the existence and transport of legacy sediment has become an important component of habitat restoration efforts in the region. The goal of this investigation is to determine the extent of legacy sediment in order to better understand how historical dam sites affect morphology and sediment transport in a post-glacial, low-gradient river system. Field and remote sensing analyses indicate that surfaces (up to 2-m high) composed of mud and sand function as floodplains 1.5-2.5 km upstream of both former dam sites. Preliminary analysis of seven radiocarbon dates from pieces of tree bark sampled from the stratigraphy (58-187 cm below the surface) of the two study sites suggest at least 1.8 m

  16. The impact of glacial fluctuations on the shallow proglacial groundwater systems of two SE Icelandic glaciers.

    NASA Astrophysics Data System (ADS)

    Levy, A.; Robinson, Z.; Krause, S.; Waller, R.

    2012-04-01

    Groundwater represents a key component of the complex hydrological processes of glaciated basins, where models project significant changes in glacial extent and mass balance. Exchange fluxes between groundwater and surface water can significantly impact discharge and stream level dynamics, biogeochemical cycling and aquifer and river habitat conditions. Understanding the spatial patterns and temporal dynamics of groundwater - surface water exchange fluxes is important for effective water resources management, especially considering the increasing pressures on groundwater and surface water systems resulting from environmental changes. This study investigates the shallow groundwater systems at two proglacial locations in SE Iceland. Impacted by the interaction between volcanic activity and glaciers, Skeiðarársandur is the world's largest active proglacial outwash plain (sandur). Skeiðarársandur contains an extensive unconfined aquifer whose thickness varies between 100-250m. Skaftafellsjökull, the second site of investigation, is a temperate valley glacier. This site is dominated by moraines and confined channels. Vegetation cover is higher than on the sandur. Groundwater seepage at both sites have potential impacts on eco-hydrological habitat conditions. Automated groundwater monitoring took place between July - mid August 2011. Preliminary results suggest strong coupling between rivers and the aquifer. This was illustrated by an increase in groundwater level following high, episodic increases in the discharge of the river Súla, western Skeiðarársandur. Results from the Skaftafellsjökull margin also suggest high river-aquifer coupling. A strong diurnal signal was detected in a well located between a large groundwater-fed lake and the glacial-fed river Skaftafellsà. Fluctuations in groundwater level, temperature and EC suggest strong response of the aquifer to changes in river level. This was illustrated during a flood event, in which an increase in

  17. The vegetation and climate during the Last Glacial Cold Period, northern South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Callard, S. Louise; Newnham, Rewi M.; Vandergoes, Marcus J.; Alloway, Brent V.; Smith, Carol

    2013-08-01

    Pollen assemblages from Howard Valley, South Island, New Zealand, were used to reconstruct the palaeovegetation and infer past climate during the period ca 38-21 cal. ka, which encompasses the Marine Isotope Stage (MIS) 3/2 transition and Last Glacial Cold Period (LGCP). A glacier occupied the upper Howard Valley during the Last Glacial, whilst extensive glaciofluvial outwash surfaces were constructed in the lower valley. Episodic periods of fluvial aggradation and incision have produced a complex sequence of terraces flanking the main Howard River and its tributaries. Sedimentary sequences from three exposed valley fills, sampled for palynological analysis and radiocarbon dating, consist of a complex vertical and lateral arrangement of coarse textured cobbly sandy gravels interbedded with organic-rich silt deposits. Palynology of these organic-rich horizons was directly compared to an existing beetle record from these same horizons. During late MIS 3 the site was dominated by marshy shrubland vegetation interspersed with mixed beech forest, indicating temperatures ˜2-3 °C cooler than present. Climate cooling began as early as 35.7 cal. ka and coincides with evidence of cooling from other sites in New Zealand, South America and with an Antarctic cooling signature. A three phase vegetation and inferred climate pattern occurs at the site during the LGCP beginning with a transition to an alpine/sub-alpine grassland comparable to communities growing near treeline today marking the change to glacial conditions before 31 cal. ka. A small increase in tree abundance between ca 25.8 and 22.7 cal. ka suggests minor climate amelioration during the mid-LGCP. During this phase, a possible volcanically induced vegetation disruption caused by the deposition of the Kawakawa Tephra at 25 cal. ka is evident in the pollen record. This is followed by a further decline in tree pollen and increase in alpine grassland and herb pollen indicating further deterioration of conditions and a

  18. Ecology of invasive Melilotus alba on Alaskan glacial river floodplains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    White sweetclover has recently invaded glacial river floodplains in Alaska. We sampled vegetation and measured environmental variables along transects located along the Nenana, Matanuska, and Stikine Rivers to describe plant communities and to determine the effects of white sweetclover on other plan...

  19. Obliquity Control On Southern Hemisphere Climate During The Last Glacial

    PubMed Central

    Fogwill, C.J.; Turney, C.S.M.; Hutchinson, D.K.; Taschetto, A.S.; England, M.H.

    2015-01-01

    Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent. PMID:26115344

  20. Terrestrial glacial eskers: Analogs for Martian sinuous ridges

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S.; Strom, Roger G.

    1991-01-01

    A glacial model was introduced last year for the Argyre region, a concept which is now extended, and which was recently integrated with a Global Hydrologic Model incorporating many other aspects of Martian geology. Despite wide agreement that the Martian ridges strongly resemble glacial eskers, this hypothesis has been presented with great equivocation due to a perceived lack of other glacial landforms. Quite to the contrary, it is shown that the Martian ridges actually do occur in logical ordered sequences with many other types of characteristically glacial appearing landforms. Herein, the esker hypothesis is further supported in isolation from considerations of regional landform assemblages. It is concluded that Martian sinuous ridges are similar in every respect to terrestrial eskers: scale, morphology, planimetric pattern, and associations with other probable glaciogenic landforms. It is found that the esker hypothesis is well supported. Eskers are glaciofluvial structures, and owe their existence to large scale melting of stagnant temporate glaciers. Thus, eskers are indicators of an ameliorating climatic regime after a protracted episode of cold, humid conditions.

  1. Glacial melting: an overlooked threat to Antarctic krill

    PubMed Central

    Fuentes, Verónica; Alurralde, Gastón; Meyer, Bettina; Aguirre, Gastón E.; Canepa, Antonio; Wölfl, Anne-Cathrin; Hass, H. Christian; Williams, Gabriela N.; Schloss, Irene R.

    2016-01-01

    Strandings of marine animals are relatively common in marine systems. However, the underlying mechanisms are poorly understood. We observed mass strandings of krill in Antarctica that appeared to be linked to the presence of glacial meltwater. Climate-induced glacial meltwater leads to an increased occurrence of suspended particles in the sea, which is known to affect the physiology of aquatic organisms. Here, we study the effect of suspended inorganic particles on krill in relation to krill mortality events observed in Potter Cove, Antarctica, between 2003 and 2012. The experimental results showed that large quantities of lithogenic particles affected krill feeding, absorption capacity and performance after only 24 h of exposure. Negative effects were related to both the threshold concentrations and the size of the suspended particles. Analysis of the stomach contents of stranded krill showed large quantities of large particles ( > 106 μm3), which were most likely mobilized by glacial meltwater. Ongoing climate-induced glacial melting may impact the coastal ecosystems of Antarctica that rely on krill. PMID:27250339

  2. Obliquity Control on Southern Hemisphere Climate during the Last Glacial

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Hutchinson, D. K.; Turney, C. S.; Taschetto, A.; England, M. H.

    2015-12-01

    Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent.

  3. Glacial isostatic stress shadowing by the Antarctic ice sheet

    NASA Technical Reports Server (NTRS)

    Ivins, E. R.; James, T. S.; Klemann, V.

    2005-01-01

    Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

  4. Glacial Influences on Solar Radiation in a Subarctic Sea.

    EPA Science Inventory

    Understanding macroscale processes controlling solar radia­tion in marine systems will be important in interpreting the potential effects of global change from increasing ultraviolet radiation (UV) and glacial retreat. This study provides the first quantitative assessment of UV i...

  5. Alaskan mountain glacial melting observed by satellite gravimetry

    NASA Astrophysics Data System (ADS)

    Chen, J. L.; Tapley, B. D.; Wilson, C. R.

    2006-08-01

    We use satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) as an indication of mass change to study potential long-term mountain glacial melting in southern Alaska and West Canada. The first 3.5 yr of GRACE monthly gravity data, spanning April 2002-November 2005, show a prominent glacial melting trend in the mountain regions around the Gulf of Alaska (GOA). GRACE-observed surface mass changes correlate remarkably well with available mass balance data at Gulkana and Wolverine, two benchmark glaciers of the U.S. Geological Survey (USGS), although the GRACE signals are smaller in magnitude. In addition, terrestrial water storage (TWS) changes estimated from an advanced land surface model show significant mass loss in this region during the same period. After correcting for the leakage errors and removing TWS contributions using model estimates, we conclude that GRACE-observed glacial melting in the GOA mountain region is equivalent to ˜ - 101 ± 22 km 3/yr, which agrees quite well with the assessment of ˜ - 96 ± 35 km 3/yr based on airborne laser altimetry data, and is consistent with an earlier estimate based on the first 2 yr of GRACE data. This study demonstrates the significant potentials of satellite gravity measurements for monitoring mountain glacial melting and regional climate change.

  6. Sulfur/Carbonate Springs and Life in Glacial Ice

    NASA Technical Reports Server (NTRS)

    Allen, C. C.; Grasby, S.; Longazo, T.

    2001-01-01

    Glacial springs are useful analogs to channels and seeps issuing from frozen strata on Mars. Mineralized water can move through, and discharge from, solid ice. This water, even near freezing, can support microbial life and bring it to the surface. Additional information is contained in the original extended abstract.

  7. Oxygen-isotope variations in post-glacial Lake Ontario

    NASA Astrophysics Data System (ADS)

    Hladyniuk, Ryan; Longstaffe, Fred J.

    2016-02-01

    The role of glacial meltwater input to the Atlantic Ocean in triggering the Younger Dryas (YD) cooling event has been the subject of controversy in recent literature. Lake Ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the Laurentide Ice Sheet (LIS) to the Atlantic Ocean via the lower Great Lakes. Here, we use the oxygen-isotope compositions of ostracode valves and clam shells from three Lake Ontario sediment cores to identify glacial meltwater contributions to ancient Lake Ontario since the retreat of the LIS (∼16,500 cal [13,300 14C] BP). Differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime. The average lakewater δ18O of -17.5‰ (determined from ostracode compositions) indicates a significant contribution from glacial meltwater. Upon LIS retreat from the St. Lawrence lowlands, ancient Lake Ontario (glacial Lake Iroquois) lakewater δ18O increased to -12‰ largely because of the loss of low-18O glacial meltwater input. A subsequent decrease in lakewater δ18O (from -12 to -14‰), accompanied by a median sediment grain size increase to 9 μm, indicates that post-glacial Lake Ontario received a final pulse of meltwater (∼13,000-12,500 cal [11,100-10,500 14C] BP) before the onset of hydrologic closure. This meltwater pulse, which is also recorded in a previously reported brief freshening of the neighbouring Champlain Valley (Cronin et al., 2012), may have contributed to a weakening of thermohaline circulation in the Atlantic Ocean. After 12,900 cal [11,020 14C] BP, the meltwater presence in the Ontario basin continued to inhibit entry of Champlain seawater into early Lake Ontario. Opening of the North Bay outlet diverted upper Great Lakes water from the lower Great Lakes causing a period (12,300-8300 cal [10,400-7500 14C] BP) of hydrologic closure in Lake Ontario (Anderson and Lewis, 2012). This change is demarcated by a shift to higher δ18Olakewater

  8. Vegetation and climate changes in western Amazonia during a previous Interglacial- Glacial transition

    NASA Astrophysics Data System (ADS)

    Cardenas, M. L.; Gosling, W. D.; Sherlock, S. C.; Poole, I.; Pennington, R. T.

    2009-12-01

    Amazonia is one of the most biodiverse areas of the world and its vegetation plays a crucial role in controlling the global climate through the regulation of the levels of atmospheric CO2. However, Amazonian ecosystems and their role in the climate system are threatened by ongoing the human impact (already estimated loss of 60% of the species in western Amazonia) and predicted climate change (+1.1-6.4oC by 2100). Unfortunately, there is absence of data relating to the ecological baseline function and response to global climate change of western Amazonian ecosystems in the absence of humans. To help anticipate the impact of future climate change predictions an improved understanding of the natural responses of tropical vegetation to known past climate change is required. Here we present the first study that shows the response of pristine tropical ecosystems in western Amazonia biodiversity hotspot to a major global climate change event (a Quaternary Interglacial-Glacial transition). Pleistocene lake/swamp sediments preserved at the Erazo study site (Lat. 00o 33’S, Long. 077o 52’W, 1927m alt.) today within tropical cloud forest vegetation provide a unique opportunity to examine the impact of past climate shifts. The sediment are >40,000 years old (radiocarbon infinite) and younger than 1 million years (presence of Alder biomarker) and consist of organic layers interbedded with volcanic ash (tephra). This study presents data from multiple proxies (fossil pollen, wood macrofossils and charcoal) to establish a comprehensive picture of regional and local vegetation change prior to human arrival. Our data show a change of vegetation from palm-dominated forest indicative of warm and wet conditions similar to the present at the base of this record, to a forest dominated by Podocarpus sp. suggesting cold and wet conditions at the top of the record. The transition between these two vegetation communities appears to be progressive with small sharp changes along the

  9. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-21

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  10. Negligible glacial-interglacial variation in continental chemical weathering rates.

    PubMed

    Foster, Gavin L; Vance, Derek

    2006-12-14

    Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide, and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide. However, variations in chemical weathering rates over glacial-interglacial cycles remain uncertain. During glacial periods, cold and dry conditions reduce the rate of chemical weathering, but intense physical weathering and the exposure of carbonates on continental shelves due to low sea levels may increase this rate. Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years. Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering, we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods. This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves, indicating that chemical weathering rates remained relatively constant on glacial-interglacial timescales. On timescales of more than a million years, however, we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide, creating a positive feedback on global climate that, once initiated, promotes cooling and further glaciation.

  11. Abrupt glacial climate shifts controlled by ice sheet changes

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-01

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  12. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-21

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials. PMID:25119027

  13. Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile.

    PubMed

    Moreno, P I; Jacobson, G L; Lowell, T V; Denton, G H

    2001-02-15

    Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.

  14. Evidence of late glacial paleoseismicity from submarine landslide deposits within Lac Dasserat, northwestern Quebec, Canada

    NASA Astrophysics Data System (ADS)

    Brooks, Gregory R.

    2016-09-01

    An integrated seismo- and chronostratigraphic investigation at Lac Dasserat, northwestern Quebec, identified 74 separate failures within eight event horizons. Horizons E and B, and H and G have strong or moderately-strong multi-landslide signatures, respectively, composed of 11-23 failures, while horizons F, D, C, and A have minor landslide signatures consisting of a single or pair of deposit(s). Cores collected at six sites recovered glacial Lake Ojibway varve deposits that are interbedded with the event horizons. The correlation of the varves to the regional Timiskaming varve series allowed varve ages or ranges of varve ages to be determined for the event horizons. Horizons H, G, E, and B are interpreted to be evidence of paleoearthquakes with differing levels of interpretative confidence, based on the relative strength of the multi-landslide signatures, the correlation to other disturbed deposits of similar age in the region, and the lack or possibility of alternative aseismic mechanisms. The four interpreted paleoearthquakes occurred between 9770 ± 200 and 8470 ± 200 cal yr BP, when glacial Lake Ojibway was impounded behind the Laurentide Ice Sheet during deglaciation. They probably represent an elevated period of seismicity at deglaciation that was driven by crustal unloading.

  15. Last Glacial mammals in South America: a new scenario from the Tarija Basin (Bolivia).

    PubMed

    Coltorti, M; Abbazzi, L; Ferretti, M P; Iacumin, P; Rios, F Paredes; Pellegrini, M; Pieruccini, P; Rustioni, M; Tito, G; Rook, L

    2007-04-01

    The chronology, sedimentary history, and paleoecology of the Tarija Basin (Bolivia), one of the richest Pleistocene mammalian sites in South America, are revised here based on a multidisciplinary study, including stratigraphy, sedimentology, geomorphology, paleontology, isotope geochemistry, and (14)C geochronology. Previous studies have indicated a Middle Pleistocene age for this classic locality. We have been able to obtain a series of (14)C dates encompassing all the fossil-bearing sequences previously studied in the Tarija Basin. The dated layers range in age from about 44,000 to 21,000 radiocarbon years before present (BP), indicating that the Tarija fauna is much younger than previously thought. Glacial advances correlated to marine isotopic stages (MIS) 4 and 2 (ca. 62 and 20 ka BP, respectively) are also documented at the base and at the very top of the Tarija-Padcaya succession, respectively, indicating that the Bolivian Altiplano was not dry but sustained an ice cap during the Last Glacial Maximum. The results of this multidisciplinary study enable us to redefine the chronological limits of the Tarija sequence and of its faunal assemblage and to shift this paleontological, paleoclimatological, and paleoecological framework to the time interval from MIS 4 to MIS 2. PMID:17180614

  16. Early and late Holocene glacial fluctuations and tephrostratigraphy, Cabin Lake, Alaska

    USGS Publications Warehouse

    Zander, Paul D.; Kaufman, Darrell S.; Kuehn, Stephen C.; Wallace, Kristi L.; Anderson, R. Scott

    2013-01-01

    Marked changes in sediment types deposited in Cabin Lake, near Cordova, Alaska, represent environmental shifts during the early and late Holocene, including fluctuations in the terminal position of Sheridan Glacier. Cabin Lake is situated to receive meltwater during periods when the outwash plain of the advancing Sheridan Glacier had aggraded. A brief early Holocene advance from 11.2 to 11.0 cal ka is represented by glacial rock flour near the base of the sediment core. Non-glacial lake conditions were restored for about 1000 years before the water level in Cabin Lake lowered and the core site became a fen. The fen indicates drier-than-present conditions leading up to the Holocene thermal maximum. An unconformity spanning 5400 years during the mid-Holocene is overlain by peat until 1110 CE when meltwater from Sheridan Glacier returned to the basin. Three intervals of an advanced Sheridan Glacier are recorded in the Cabin Lake sediments during the late Holocene: 1110–1180, 1260–1540 and 1610–1780 CE. The sedimentary sequence also contains the first five reported tephra deposits from the Copper River delta region, and their geochemical signatures suggest that the sources are the Cook Inlet volcanoes Redoubt, Augustine and Crater Peak, and possibly Mt Churchill in the Wrangell Volcanic field.

  17. Authigenic uranium in Atlantic sediments of the last glacial stage — a diagenetic phenomenon

    NASA Astrophysics Data System (ADS)

    Thomson, J.; Wallace, H. E.; Colley, S.; Toole, J.

    1990-05-01

    Cores from three different Atlantic localities (equatorial, Cape Verde Rise and Porcupine Abyssal Plain) are shown to have anomalous high U contents (5-8 ppm total) in sediments laid down during the last glacial stage (12-24 ky BP). Radiocarbon data demonstrate that the sediments hosting the peak U levels were accumulated at rates similar to those immediately above and below. All the cores exhibit maximum Mn levels, characteristic colour changes, and maximum U levels in the same sequence with increasing depth in core. On the evidence of the similarities between the cores, and pore water U data from a Porcupine Abyssal Plain site, it is proposed that the authigenic U enrichments are syndiagenetic and possibly active. No correlation is observed between sediment authigenic U and C org contents. The source of enrichment is bottom water U which has diffused downwards into the sediments to be sorbed at a particular redox level, located 10-30 cm below the oxic/post-oxic boundary marked by the colour change. The magnitude of the enrichments is caused by the persistence of this boundary at a particular level as a result of the decrease in mean sediment accumulation rate between the last glacial stage (5.2 up to at least 19.1 cm ky -1) and the Holocene (2.2-4.1 cm ky -1). Similar accumulation rate contrasts are expected to be widespread in the Atlantic, and the implications for previous reported work, particularly from the Mid-Atlantic Ridge, are discussed.

  18. Potentially dangerous glacial lakes in Kyrgyzstan - Research overview of 2004-2015

    NASA Astrophysics Data System (ADS)

    Jansky, Bohumir; Yerokhin, Sergey; Sobr, Miroslav; Engel, Zbynek; Cerny, Michal; Falatkova, Kristyna; Kocum, Jan; Benes, Vojtech

    2016-04-01

    Global warming causes intensive melting and retreat of glaciers in most of high mountains all over the world. This process is also evident in the mountain regions of central Tien Shan. Glacier melt water affects changes in hydrological regime of water streams and causes overfilling of high mountain lake basins. The dams of many lakes are very unstable and can burst open. To determine the degree of such risk, it is necessary to analyse the genesis of lakes, to characterize the morphology of the lake basins and to know the particularities of their hydrological regime. According to the latest inventory within territory of Kyrgyzstan, a total of 1328 lakes have been identified as potentially dangerous, 12 lakes are considered as currently dangerous, other 25 feature high potential hazard. Since 1952 more than 70 disastrous cases of lake outburst have been registered. The hazardous alpine lakes are studied in Kyrgyzstan systematically since 1966. Since 2004, Czech-Kyrgyz research team has been operating in Kyrgyzstan in the field of dangerous glacial lakes. Projects were focused primarily on high-mountain glacial lakes risk assessment, propositions of risk mitigation measures, establishment of permanent research station near one of the studied glacier complexes, preparation of risk analysis for selected endangered valleys, evaluation of climatic and hydrological data and glacier development within observed regions. The most significant portion of data and information has been gathered during field work, complemented by satellite image analysis and surveillance flights over the monitored sites.

  19. Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska

    USGS Publications Warehouse

    Roberts, H.M.; Muhs, D.R.; Wintle, A.G.; Duller, G.A.T.; Bettis, E. Arthur

    2003-01-01

    A high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35-50 ??m quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil's Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr-much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values. ?? 2003 Elsevier Science (USA). All rights reserved.

  20. Thriving in the Cold: Glacial Expansion and Post-Glacial Contraction of a Temperate Terrestrial Salamander (Plethodon serratus)

    PubMed Central

    Newman, Catherine E.; Austin, Christopher C.

    2015-01-01

    The dynamic geologic history of the southeastern United States has played a major role in shaping the geographic distributions of amphibians in the region. In the phylogeographic literature, the predominant pattern of distribution shifts through time of temperate species is one of contraction during glacial maxima and persistence in refugia. However, the diverse biology and ecology of amphibian species suggest that a “one-size-fits-all” model may be inappropriate. Nearly 10% of amphibian species in the region have a current distribution comprised of multiple disjunct, restricted areas that resemble the shape of Pleistocene refugia identified for other temperate taxa in the literature. Here, we apply genetics and spatially explicit climate analyses to test the hypothesis that the disjunct regions of these species ranges are climatic refugia for species that were more broadly distributed during glacial maxima. We use the salamander Plethodon serratus as a model, as its range consists of four disjunct regions in the Southeast. Phylogenetic results show that P. serratus is comprised of multiple genetic lineages, and the four regions are not reciprocally monophyletic. The Appalachian salamanders form a clade sister to all other P. serratus. Niche and paleodistribution modeling results suggest that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species. PMID:26132077

  1. Thriving in the Cold: Glacial Expansion and Post-Glacial Contraction of a Temperate Terrestrial Salamander (Plethodon serratus).

    PubMed

    Newman, Catherine E; Austin, Christopher C

    2015-01-01

    The dynamic geologic history of the southeastern United States has played a major role in shaping the geographic distributions of amphibians in the region. In the phylogeographic literature, the predominant pattern of distribution shifts through time of temperate species is one of contraction during glacial maxima and persistence in refugia. However, the diverse biology and ecology of amphibian species suggest that a "one-size-fits-all" model may be inappropriate. Nearly 10% of amphibian species in the region have a current distribution comprised of multiple disjunct, restricted areas that resemble the shape of Pleistocene refugia identified for other temperate taxa in the literature. Here, we apply genetics and spatially explicit climate analyses to test the hypothesis that the disjunct regions of these species ranges are climatic refugia for species that were more broadly distributed during glacial maxima. We use the salamander Plethodon serratus as a model, as its range consists of four disjunct regions in the Southeast. Phylogenetic results show that P. serratus is comprised of multiple genetic lineages, and the four regions are not reciprocally monophyletic. The Appalachian salamanders form a clade sister to all other P. serratus. Niche and paleodistribution modeling results suggest that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species.

  2. Timing of maximum glacial extent and deglaciation from HualcaHualca volcano (southern Peru), obtained with cosmogenic 36Cl.

    NASA Astrophysics Data System (ADS)

    Alcalá, Jesus; Palacios, David; Vazquez, Lorenzo; Juan Zamorano, Jose

    2015-04-01

    Andean glacial deposits are key records of climate fluctuations in the southern hemisphere. During the last decades, in situ cosmogenic nuclides have provided fresh and significant dates to determine past glacier behavior in this region. But still there are many important discrepancies such as the impact of Last Glacial Maximum or the influence of Late Glacial climatic events on glacial mass balances. Furthermore, glacial chronologies from many sites are still missing, such as HualcaHualca (15° 43' S; 71° 52' W; 6,025 masl), a high volcano of the Peruvian Andes located 70 km northwest of Arequipa. The goal of this study is to establish the age of the Maximum Glacier Extent (MGE) and deglaciation at HualcaHualca volcano. To achieve this objetive, we focused in four valleys (Huayuray, Pujro Huayjo, Mollebaya and Mucurca) characterized by a well-preserved sequence of moraines and roches moutonnées. The method is based on geomorphological analysis supported by cosmogenic 36Cl surface exposure dating. 36Cl ages have been estimated with the CHLOE calculator and were compared with other central Andean glacial chronologies as well as paleoclimatological proxies. In Huayuray valley, exposure ages indicates that MGE occurred ~ 18 - 16 ka. Later, the ice mass gradually retreated but this process was interrupted by at least two readvances; the last one has been dated at ~ 12 ka. In the other hand, 36Cl result reflects a MGE age of ~ 13 ka in Mollebaya valley. Also, two samples obtained in Pujro-Huayjo and Mucurca valleys associated with MGE have an exposure age of 10-9 ka, but likely are moraine boulders affected by exhumation or erosion processes. Deglaciation in HualcaHualca volcano began abruptly ~ 11.5 ka ago according to a 36Cl age from a polished and striated bedrock in Pujro Huayjo valley, presumably as a result of reduced precipitation as well as a global increase of temperatures. The glacier evolution at HualcaHualca volcano presents a high correlation with

  3. Late Glacial Tropical Savannas in Sundaland Inferred From Stable Carbon Isotope Records of Cave Guano

    NASA Astrophysics Data System (ADS)

    Wurster, C. M.; Bird, M. I.; Bull, I.; Dungait, J.; Bryant, C. L.; Ertunç, T.; Hunt, C.; Lewis, H. A.; Paz, V.

    2008-12-01

    During the Last Glacial Period (LGP), reduced global sea level exposed the continental shelf south of Thailand to Sumatra, Java, and Borneo to form the contiguous continent of Sundaland. However, the type and extent of vegetation that existed on much of this exposed landmass during the LGP remains speculative. Extensive bird and bat guano deposits in caves throughout this region span beyond 40,000 yr BP, and contain a wealth of untapped stratigraphic palaeoenvironmental information. Stable carbon isotope ratios of insectivorous bird and bat guano contain a reliable record of the animal's diet and, through non-specific insect predation, reflect the relative abundance of major physiological pathways in plants. Various physiological pathways of carbon fixation in plants yield differing stable carbon isotope ratios. Stable carbon isotope values of C3 plants are lower than C4 vegetation due to different enzymatic discriminations of the heavy isotope through the carbon fixing pathways. In tropical locales, grasses nearly always follow the C4 photosynthetic pathway, whereas tropical rainforest uses C3 photosynthesis, providing a proxy for vegetation and therefore climate change in the past. Here we discuss four guano stable-isotope records, based on insect cuticle and n-alkane analysis, supplemented by pollen analysis. All sites suggest a C3 dominated ecosystem for the Holocene, consistent with the wet tropical forest vegetation present at all locations. Two sites from Palawan Island, Philippines, record stable carbon isotope values of guano that document a drastic change from C3 (forest) to C4 (savanna) dominated ecosystems during the Last Glacial Maximum (LGM). A third location, at Niah Great Cave, Malaysia, indicates C3-dominant vegetation throughout the record, but does display variation in stable carbon isotope values likely linked to humidity changes. A fourth location, Batu Caves in Peninsular Malaysia, also indicates open vegetation during the LGM. Vegetation

  4. Quaternary glacial and post-glacial depositional history associated with the Green Bay lobe, east-central Wisconsin

    SciTech Connect

    Thieme, L.D.; Smith, G.L. . Dept. of Geology)

    1993-03-01

    Multiple layers of peat and wood fragments indicate that Quaternary glaciation of the east-central region of Wisconsin was punctuated by at least two interglacial periods. Till, outwash, and glaciolacustrine deposits suggest that deposition took place in alternating glacial and non-glacial environments due to oscillations in the position of the Green Bay Lobe terminus. The data for this study consists of 36 auger borings, 70 geologic logs and 100 well-construction reports from water wells. Nine vibracores were taken at the northern margin of Lake Winnebago in order to document in detail the post-glacial history of Glacial Lake Oshkosh/Lake Winnebago. Local bedrock consists of limestones and dolomites of the Middle Ordovician Sinnipee Group. Bedrock elevations range from 211--237 m; bedding dips regionally to the southeast at 1--2 degrees. Bedrock is overlain by a 3--13 m-thick layer of alternating red clay and gray silty-clay (basal Kewaunee Formation ) perhaps deposited in a proglacial lake. These sediments are overlain by apeat/wood layer indicating marsh deposition. This peat/wood layer is overlain by more proglacial lake sediment, 3--10 m of gray brown clay to silty-clay. A second peat/wood layer overlies the gray/brown sediment and may correlate with the Two Creeks buried forest bed. The uppermost unit consists of 2--3 m red silty-clay till (Middle Inlet Member of the Kewaunee Formation). Along the northern margin of present-day Lake Winnebago, red silty-clay is overlain by silty-sand deposited by Glacial Lake Oshkosh. Future work includes obtaining radiocarbon dates from buried peat/wood layers to verify these tentative correlations between east-central Wisconsin and the Lake Michigan Basin.

  5. The Post-Glacial Species Velocity of Picea glauca following the Last Glacial Maximum in Alaska.

    NASA Astrophysics Data System (ADS)

    Morrison, B. D.; Napier, J.; Kelly, R.; Li, B.; Heath, K.; Hug, B.; Hu, F.; Greenberg, J. A.

    2015-12-01

    Anthropogenic climate change is leading to dramatic fluctuations to Earth's biodiversity that has not been observed since past interglacial periods. There is rising concern that Earth's warming climate will have significant impacts to current species ranges and the ability of a species to persist in a rapidly changing environment. The paleorecord provides information on past species distributions in relation to climate change, which can illuminate the patterns of potential future distributions of species. Particularly in areas where there are multiple potential limiting factors on a species' range, e.g. temperature, radiation, and evaporative demand, the spatial patterns of species migrations may be particularly complex. In this study, we assessed the change in the distributions of white spruce (Picea glauca) from the Last Glacial Maxima (LGM) to present-day for the entire state of Alaska. To accomplish this, we created species distribution models (SDMs) calibrated from modern vegetation data and high-resolution, downscaled climate surfaces at 60m. These SDMs were applied to downscaled modern and paleoclimate surfaces to produce estimated ranges of white spruce during the LGM and today. From this, we assessed the "species velocity", the rate at which white spruce would need to migrate to keep pace with climate change, with the goal of determining whether the expansion from the LGM to today originated from microclimate refugia. Higher species velocities indicate locations where climate changed drastically and white spruce would have needed to migrate rapidly to persist and avoid local extinction. Conversely, lower species velocities indicated locations where the local climate was changing less rapidly or was within the center of the range of white spruce, and indicated locations where white spruce distributions were unlikely to have changed significantly. Our results indicate the importance of topographic complexity in buffering the effects of climate change

  6. Glacially-developed weathering rinds at the micro-scale: Mineralogy and chemistry

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Edwards, C. S.; Christensen, P. R.

    2013-12-01

    Glacial weathering of rock and sediment is difficult to study, but important to understand as it contributes to solute flux in meltwaters and provides potential energy sources to chemotrophic microbes. In this study we characterize weathering rinds present on samples from a glaciated silicate-carbonate system using microscopic thermal infrared (TIR) spectroscopy and complementary electron microprobe analyses. The major goals of the project are to: 1) characterize the mineralogy and chemistry of glacially-derived weathering rinds at the micro-scale, 2) compare the microscopic spectroscopy measurements to previously measured bulk TIR spectra of the samples to assess the sensitivity of remote sensing data to small scale weathering rinds, and 3) to quantify weathering inputs to the glacial energy budget. Robertson Glacier in Alberta, Canada is our field site for this technique as its retreating stage allows sampling of fresh subglacial and englacial sediments. This site is significant to microbiology studies, as methanogenic and iron-reducing microbial communities have been identified in the local subglacial till. Samples of glacially altered rock and sediments were collected on a downstream transect of the glacier in 2011. In this work, we use an innovative laboratory technique, microscopic TIR emission spectroscopy, to investigate these weathering rinds. The MicroLab at Arizona State University was designed to quantitatively determine sample mineralogy at a spot size of ~85 μm. TIR spectroscopy is especially powerful for identifying crystalline minerals, as molecular bonds vibrate at specific wavelengths of light, creating absorption bands at characteristic TIR wavelengths. To first order, TIR spectra add linearly with area, making this technique especially useful for determining quantitative mineral abundances, especially when the number of areal components is small. We also measure the chemistry of these rinds using an electron microprobe, the JEOL JXA-8530F

  7. The Glacial BuzzSaw, Isostasy, and Global Crustal Models

    NASA Astrophysics Data System (ADS)

    Levander, A.; Oncken, O.; Niu, F.

    2015-12-01

    The glacial buzzsaw hypothesis predicts that maximum elevations in orogens at high latitudes are depressed relative to temperate latitudes, as maximum elevation and hypsography of glaciated orogens are functions of the glacial equilibrium line altitude (ELA) and the modern and last glacial maximum (LGM) snowlines. As a consequence crustal thickness, density, or both must change with increasing latitude to maintain isostatic balance. For Airy compensation crustal thickness should decrease toward polar latitudes, whereas for Pratt compensation crustal densities should increase. For similar convergence rates, higher latitude orogens should have higher grade, and presumably higher density rocks in the crustal column due to more efficient glacial erosion. We have examined a number of global and regional crustal models to see if these predictions appear in the models. Crustal thickness is straightforward to examine, crustal density less so. The different crustal models generally agree with one another, but do show some major differences. We used a standard tectonic classification scheme of the crust for data selection. The globally averaged orogens show crustal thicknesses that decrease toward high latitudes, almost reflecting topography, in both the individual crustal models and the models averaged together. The most convincing is the western hemisphere cordillera, where elevations and crustal thicknesses decrease toward the poles, and also toward lower latitudes (the equatorial minimum is at ~12oN). The elevation differences and Airy prediction of crustal thickness changes are in reasonable agreement in the North American Cordillera, but in South America the observed crustal thickness change is larger than the Airy prediction. The Alpine-Himalayan chain shows similar trends, however the strike of the chain makes interpretation ambiguous. We also examined cratons with ice sheets during the last glacial period to see if continental glaciation also thins the crust toward

  8. Glacially induced stresses in sedimentary rocks of northern Poland

    NASA Astrophysics Data System (ADS)

    Trzeciak, Maciej; Dąbrowski, Marcin

    2016-04-01

    During the Pleistocene large continental ice sheets developed in Scandinavia and North America. Ice-loading caused bending of the lithosphere and outward flow in the mantle. Glacial loading is one of the most prominent tectono-mechanical event in the geological history of northern Poland. The Pomeranian region was subjected several times to a load equivalent of more than 1 km of rocks, which led to severe increase in both vertical and horizontal stresses in the upper crustal rocks. During deglaciation a rapid decrease in vertical stress is observed, which leads to destabilization of the crust - most recent postglacial faults scarps in northern Sweden indicate glacially induced earthquakes of magnitude ~Mw8. The presence of the ice-sheet altered as well the near-surface thermal structure - thermal gradient inversion is still observable in NW Poland. The glacially related processes might have left an important mark in the sedimentary cover of northern Poland, especially with regard to fracture reopening, changes in stress state, and damage development. In the present study, we model lithospheric bending caused by glacial load, but our point of interest lies in the overlying sediments. Typical glacial isostatic studies model the response of (visco-) elastic lithosphere over viscoelastic or viscous asthenosphere subjected to external loads. In our model, we introduce viscoelastic sedimentary layers at the top of this stack and examine the stress relaxation patterns therein. As a case study for our modelling, we used geological profiles from northern Poland, near locality of Wejherowo, which are considered to have unconventional gas potential. The Paleozoic profile of this area is dominated by almost 1 km thick Silurian-Ordovician shale deposits, which are interbedded with thin and strong limestone layers. This sequence is underlain by Cambrian shales and sandstones, and finally at ~3 km depth - Precambrian crystalline rocks. Above the Silurian there are approximately

  9. Glacial landscape evolution on Hall Peninsula, Baffin Island, since the Last Glacial Maximum: insights into switching glacial dynamics and thermo-mechanical conditions

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Ross, M.

    2012-12-01

    Ice cover in north central Hall Peninsula, Baffin Island has evolved from full Laurentide Ice Sheet (LIS) cover during the Last Glacial Maximum (LGM) to a thin ice cap that now covers about 800 km2 in the northeast sector. The exposed subglacial landscape consists of contrasting geomorphological zones which allude to complex spatial and temporal changes in basal ice dynamics and thermal regime since LGM. We used satellite imagery, field observations, a large till geochemical database, and terrestrial cosmogenic isotopes to get new insights into subglacial erosion intensity, ice flow dynamics, and glacial history. Fields of streamlined bedrock-cored ridges (e.g. drumlins) have been mapped and their elongation ratios calculated. The density of bedrock-controlled lakes, which has traditionally been used as a proxy for subglacial erosion intensity on Baffin Island, has been re-examined using modern GIS techniques. This work has revealed a mosaic of glacial terrain zones each consisting of characteristics that are distinct from the other zones. Five glacial terrain zones (GTZ) have been recognized. One zone (GTZ 1) is characterized by a broad flowset of northeast trending streamlined hills and parallel paleo-flow indicators. It also has the highest streamlined hill density, longest elongation ratios, and the highest lake density of the study area. This northeast flowset is crosscut locally by ice flow indicators that converge into troughs that now form a series of fjords. Landforms and ice flow indicators of this younger system (GTZ 2) are traced inland showing propagation of the channelized system into this portion of the LIS. The central area of the peninsula contains a zone of thicker till and rolling topography (GTZ 3) as well as a zone consisting of southeast trending features and associated perpendicular moraines (GTZ 4). The modern ice cap and its past extension form the last zone (GTZ 5). The preservation of the northeast system (GTZ 1) outside of the

  10. Ice-walled-lake plains: Implications for the origin of hummocky glacial topography in middle North America

    USGS Publications Warehouse

    Clayton, L.; Attig, J.W.; Ham, N.R.; Johnson, M.D.; Jennings, C.E.; Syverson, K.M.

    2008-01-01

    Ice-walled-lake plains are prominent in many areas of hummocky-till topography left behind as the Laurentide Ice Sheet melted from middle North America. The formation of the hummocky-till topography has been explained by: (1) erosion by subglacial floods; (2) squeezing of subglacial till up into holes in stagnant glacial ice; or (3) slumping of supraglacial till. The geomorphology and stratigraphy of ice-walled-lake plains provide evidence that neither the lake plains nor the adjacent hummocks are of subglacial origin. These flat lake plains, up to a few kilometers in diameter, are perched as much as a few tens of meters above surrounding depressions. They typically are underlain by laminated, fine-grained suspended-load lake sediment. Many ice-walled-lake plains are surrounded by a low rim ridge of coarser-grained shore sediment or by a steeper rim ridge of debris that slumped off the surrounding ice slopes. The ice-walled lakes persisted for hundreds to thousands of years following glacial stagnation. Shells of aquatic molluscs from several deposits of ice-walled-lake sediment in south-central North Dakota have been dated from about 13 500 to 10 500??B.P. (calibrated radiocarbon ages), indicating a climate only slightly cooler than present. This is confirmed by recent palaeoecological studies in nearby non-glacial sites. To survive so long, the stagnant glacial ice had to be well-insulated by a thick cover of supraglacial sediment, and the associated till hummocks must be composed primarily of collapsed supraglacial till. ?? 2007 Elsevier B.V. All rights reserved.

  11. Hydrogeologic for the Saco River valley glacial aquifer from Bartlett, New Hampshire to Fryeburg, Maine; October 1983 through January 1986

    USGS Publications Warehouse

    Johnson, C.D.; Tepper, D.H.; Morrissey, D.J.

    1987-01-01

    Hydrogeologic data was collected for a study of the Saco River valley glacial aquifer. The study area extends along the Saco River from Bartlett, New Hampshire to Fryeburg, Maine. The study was done in cooperation with the Maine Geological Survey (Department of Conservation), the New Hampshire Water Supply and Pollution Control Commission, the New Hampshire Water Resources Board, and the Town of Conway, New Hampshire. The data include information on 54 well-inventory sites, 69 exploration-hole logs , analyses of grain-size distribution in 130 samples of glacial sediments, monthly water-table measurements in 100 wells, and continuous water-table measurements in 7 wells. Discharge data are presented from 6 stream-gaging stations operated for this study during the 1984 and 1985 water years. Data from 50 sets of seepage runs and 15 miscellaneous discharge measurements conducted on the mainstream of the Saco River and on 7 tributary streams during the 1984 and 1985 water years are also presented. Water quality analyses of groundwater samples from 92 sites and surface water samples from 12 sites are presented. Field determinations include pH, temperature, and specific conductance. Laboratory determinations include nutrients, common inorganic anions and cations, selected volatile organic compounds, and detergents. Maps show the locations of data-collection sites. (USGS)

  12. The unstable geomagnetic field during the last glacial

    NASA Astrophysics Data System (ADS)

    Nowaczyk, Norbert; Frank, Ute; Kind, Jessica; Plessen, Birgit; Arz, Helge

    2013-04-01

    Detailed stratigraphic analyses of a sediment composite record from three different sites in the southeastern Black Sea yielded a high-resolution, well-dated paleomagnetic record of the past 14 to 68 ka. Age constraints are provided by 16 AMS 14C ages, identification of the Campanian Ignimbrite tephra (39.28±0.11 ka), and by detailed tuning of sedimentologic parameters of the Black Sea sediments to the oxygen isotope record from the Greenland NGRIP ice core. Dansgaard-Oeschger events 3 through 18 are very well expressed in the Black Sea sedimentary records of Ca-content, oxygen isotopes as well as in records of ice-rafted detritus. Though hampered by some larger hiatusses at one site, and patchy contaminations by diagenetically formed greigite, the paleomagnetic composite record obtained from the preserved primary detrital magnetite phase reflects a highly dynamic geomagnetic field during the last glacial period. Relative variations of paleointensity inferred from the sediments' magnetisations were converted into a record of the virtual axial dipole moment (VADM). Thus, the Black Sea paleomagnetic record comprises evidence for the Norwegian-Greenland-Sea excursion at 64.5 ka (VADM = 1.5×1022 Am2), a full reversal of the geomagnetic field during the Laschamp excursion at 41 ka and several subsequent excursions with low northern virtual geomagnetic pole (VGP) latitudes, including the Mono Lake excursion at 34.5 ka (VADM = 3.0×1022 Am2). According to the derived age model, VGP positions during the Laschamp excursion persisted at high southern latitudes in Antarctica for an estimated 440 years, making the Laschamp excursion a short-lived event with fully reversed polarity directions. Recorded field reversals of the Laschamp excursion, lasting only an estimated ~250 years, are characterized by very low paleointensities with VADMs as low as 0.50×1022 Am2. The reversed phase of the Laschamp excursion is associated with a significant field recovery with a VADM of 2.0

  13. Glacial cycles drive variations in the production of oceanic crust.

    PubMed

    Crowley, John W; Katz, Richard F; Huybers, Peter; Langmuir, Charles H; Park, Sung-Hyun

    2015-03-13

    Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of Earth's interior. Using Plio-Pleistocene sea-level variations as a forcing function, theoretical models of mid-ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters. New bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills, one of the most common bathymetric features on Earth, record the magmatic response to changes in sea level. The models and data support a link between glacial cycles at the surface and mantle melting at depth, recorded in the bathymetric fabric of the sea floor. PMID:25766231

  14. Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse

    NASA Astrophysics Data System (ADS)

    Ladant, Jean-Baptiste; Donnadieu, Yannick

    2016-09-01

    The historical view of a uniformly warm Cretaceous is being increasingly challenged by the accumulation of new data hinting at the possibility of glacial events, even during the Cenomanian-Turonian (~95 Myr ago), the warmest interval of the Cretaceous. Here we show that the palaeogeography typifying the Cenomanian-Turonian renders the Earth System resilient to glaciation with no perennial ice accumulation occurring under prescribed CO2 levels as low as 420 p.p.m. Conversely, late Aptian (~115 Myr ago) and Maastrichtian (~70 Myr ago) continental configurations set the stage for cooler climatic conditions, favouring possible inception of Antarctic ice sheets under CO2 concentrations, respectively, about 400 and 300 p.p.m. higher than for the Cenomanian-Turonian. Our simulations notably emphasize that palaeogeography can crucially impact global climate by modulating the CO2 threshold for ice sheet inception and make the possibility of glacial events during the Cenomanian-Turonian unlikely.

  15. Evidence for Obliquity Forcing of Glacial Termination II

    NASA Astrophysics Data System (ADS)

    Drysdale, R. N.; Hellstrom, J. C.; Zanchetta, G.; Fallick, A. E.; Sánchez Goñi, M. F.; Couchoud, I.; McDonald, J.; Maas, R.; Lohmann, G.; Isola, I.

    2009-09-01

    Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth’s obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 ± 2500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth’s obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

  16. Glacial geomorphic evidence for a late climatic change on Mars

    NASA Technical Reports Server (NTRS)

    Kargel, J. S.; Strom, R. G.

    1992-01-01

    In a series of preliminary reports, we documented evidence of former glacial epochs on Mars. Apparent glacial landforms seemed to be concentrated primarily at middle to high southern latitudes. We now have additional evidence supporting the view that Martian glaciation appears to have been more extensive than previously recognized. The growth and collapse of ice sheets on Mars seems closely analogous to the growth and decline of Earth's great Pleistocene ice sheets. This implies that climate change was probably somewhat comparable on the two planets, although in the case of Mars the entire planet seems to have changed rapidly to a cold, dry present-day environment after the collapse of the ice sheets.

  17. Climate model benchmarking with glacial and mid-Holocene climates

    NASA Astrophysics Data System (ADS)

    Harrison, S. P.; Bartlein, P. J.; Brewer, S.; Prentice, I. C.; Boyd, M.; Hessler, I.; Holmgren, K.; Izumi, K.; Willis, K.

    2014-08-01

    Past climates provide a test of models' ability to predict climate change. We present a comprehensive evaluation of state-of-the-art models against Last Glacial Maximum and mid-Holocene climates, using reconstructions of land and ocean climates and simulations from the Palaeoclimate Modelling and Coupled Modelling Intercomparison Projects. Newer models do not perform better than earlier versions despite higher resolution and complexity. Differences in climate sensitivity only weakly account for differences in model performance. In the glacial, models consistently underestimate land cooling (especially in winter) and overestimate ocean surface cooling (especially in the tropics). In the mid-Holocene, models generally underestimate the precipitation increase in the northern monsoon regions, and overestimate summer warming in central Eurasia. Models generally capture large-scale gradients of climate change but have more limited ability to reproduce spatial patterns. Despite these common biases, some models perform better than others.

  18. The Role of Glacial Erosion in Limiting Ice Sheet Extents

    NASA Astrophysics Data System (ADS)

    Jamieson, S.; Hulton, N.

    2007-12-01

    We aim to identify and quantify feedbacks between ice dynamics and glacial erosion. Whilst geological and geomorphological evidence indicates that ice sheets generally oscillate in time with orbital forcing, their extents are not necessarily a direct function of the amplitude of this forcing. Benthic δ18O records document glacial-interglacial fluctuations and indicate that maximum Pleistocene global ice volume occurs around 400 ka. However, geomorphological evidence in a number of regions is contradictory, with the most extensive ice masses often occurring 100's of kyrs prior to peaks in the δ18O record. For example, the glacial landforms of Patagonia preserve a record of just such behaviour with each successive glacial advance since 1.15 Ma covering an area less extensive than the previous expansion. This implies that other processes are modifying the linkages between ice sheets and climate. We ask: Could glacial erosion of bedrock have caused ice sheets to self-regulate their extents? Ground-breaking experiments by Oerlemans (1984) demonstrated that erosion induced margin retreat was indeed possible. He showed that retreat could be achieved but only where eroding ice streams were smaller in width than the wavelength of lithospheric response. In Patagonia however, the scales of retreat are much larger than this lithospheric wavelength - but could erosion still be an important factor? We use the GLIMMER 3-D thermomechanical ice sheet model (Payne, 1999) with an added erosion component to simulate long-term landscape evolution under theoretical ice sheets (Jamieson et al., 2007). We show that models of glacial erosion can generate feedbacks on a significant scale such that ice sheets can self-limit their extents over periods of 105 - 106 years regardless of the flexural response of the land surface. Erosion around the ELA enables increasingly efficient ice drainage, and the mass balance of the ice sheet thus shifts towards a more negative state. At the same time

  19. Pre-glacial, Early Glacial, and Ice Sheet Stratigraphy Cored During NBP1402, Sabrina Coast, East Antarctic Margin

    NASA Astrophysics Data System (ADS)

    Domack, E. W.; Gulick, S. P. S.; Fernandez-Vasquez, R. A.; Frederick, B.; Lavoie, C.; Leventer, A.; Shevenell, A.; Saustrup, S., Sr.; Bohaty, S. M.; Sangiorgi, F.

    2014-12-01

    Western Wilkes Land provides an unusual setting with regard to passive margin subsidence and exposure of Cenozoic sedimentary units across the continental shelf, due to the unique rift to drift history off of the Australian-Antarctic Discordance and subsequent deep glacial erosion of the evolved continental shelf. The first factor has provided extensive accommodation space for the preservation of stratigraphic sequences that in turn represent critical periods in the climate evolution of Antarctica. Glacial erosion has then provided access to this stratigraphy that is usually inaccessible to all but deep drilling programs. Such stratigraphies are well exposed to within cm of the seafloor off the Sabrina Coast. Cruise NBP1402 investigated this region via a combination of multi-channel seismic imaging and innovative, strategic coring. The geophysical data imaged the geologic evolution of the margin, which exhibits a continuum from non-glacial, partly glaciated, to fully glaciated depo- and erosional systems. Based on the seismic stratigraphy, we collected dredges and one barrel Jumbo Piston Cores (JPCs) across areas of outcropping strata imaged seismically, a unique strategy that allowed us to identify and sample specific reflectors. The stratigraphically deepest coring targeted sections for which the seismic character suggested a pre-glacial context, with non-glaciated continental margin sequences including deltas. Coring recovered dark organic rich siltstones and sandy mudstones, and a large concretion whose center contained a cm-sized plant fossil. In addition, the sediments contain a fossil snail. These fossils provide a glimpse into the pre-glacial terrestrial environment in Antarctica. Overlying this section, coring recovered similar dark siltstones with a 20 cm thick horizon with abundant large angular clasts of variable lithology, interpreted to be ice-rafted debris and indicative of early glacial ice in Antarctica. Finally, JPCs targeting a younger part of

  20. Sedimentary architecture of the Amundsen Sea Embayment shelf, West Antarctica, from pre-glacial to glacial processes

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten; Uenzelmann-Neben, Gabriele; Hillenbrand, Claus-Dieter; Larter, Robert; Nitsche, Frank

    2013-04-01

    Studies of the sedimentary architecture and characteristics of Antarctic shelves provide clues of past ice sheet advance-retreat cycles and help improve constraints for paleo-ice dynamic models since early glacial periods. A first seismostratigraphic analysis of the Amundsen Sea Embayment shelf and slope of West Antarctica reveals insights into the structural architecture of the continental margin and shows stages of sediment deposition, erosion and transport history from pre-glacial times to early glaciation and to the most recent glacial periods. The shelf geometry consists of a large pre- and syn-rift basin in the middle shelf region between outcropping basement of the inner shelf and basement ridges and highs beneath the outer shelf. A middle shelf sub-basin exists which may have formed as a result of motion along an early West Antarctic Rift System branch. At least 4 km of pre-glacial strata has been eroded from the present inner shelf and coastal hinterland by ice sheet advances since the onset of glaciation. Some of the eroded sediments were deposited as a progradational wedge extending the outer shelf by 25 to 65 km oceanward of the pre-glacial shelf-break. Comparing the observed seismic characteristics with those of other Antarctic shelf sequences, we assign an Early Cretaceous age for bottom sedimentary unit ASS-1, a Late Cretaceous to Oligocene age for unit ASS-2, an Early to Mid-Miocene age for unit ASS-3, a Mid-Miocene age for unit ASS-4, a Late Miocene to Early Pliocene age for unit ASS-5, and a Pliocene to Pleistocene age for the top unit ASS-6. The survival of buried grounding zone wedges in the upper part of unit ASS-5 of the outer shelf is consistent with the onset of a long warming phase and a retreated ice sheet in the early Pliocene as observed for the Ross Sea shelf and reconstructed from paleo-ice sheet models. Our data also reveal that the paleo-ice flow paths of the central Pine Island Trough system have remained stationary across the

  1. Mercury fluxes out of glacial and non-glacial streams, as determined by continuous measurements of turbidity and CDOM

    NASA Astrophysics Data System (ADS)

    Vermilyea, A.; Nagorski, S. A.; Lamborg, C. H.; Scott, D.; Hood, E. W.

    2011-12-01

    Glaciers and icefields along the Alaskan coast contribute nearly half of the freshwater discharge to the Gulf of Alaska and can play an important role in near-shore marine ecosystems. In southeastern Alaska, glaciers are rapidly thinning and retreating and are being replaced by temperate forests and wetlands. This ongoing landscape evolution is altering the sensitivity of coastal watersheds to atmospheric Hg inputs. The influence of glacial runoff with high suspended sediment loads on in-stream mercury fluxes and dynamics is poorly understood. In contrast, numerous studies have shown that streams with large contributions from wetlands typically carry high dissolved organic matter (DOM) and filtered methylmercury (FMHg) loads. This study compares and contrasts the mercury concentrations, fluxes, partitioning, and speciation in two coastal watersheds in southeastern Alaska. The two watersheds are separated by only 23 km and are relatively similar in area, however one is heavily glaciated (Lemon Creek) and one is dominated by temperate forest and wetlands (Peterson Creek). Grab samples for unfiltered total mercury (UTHg), particulate total mercury (PTHg), filtered total mercury (FTHg), and FMHg were taken during three, 4-day sampling periods within the glacial melt season (May-Sept) while continuously monitoring in-situ chromophoric dissolved organic matter (CDOM) fluorescence and stream turbidity. While UTHg concentration-discharge relationships were poor (R2=0.38-0.55) in both streams, flux estimates for UTHg were greatly improved using CDOM fluorescence (R2=0.82) for Peterson Creek, and turbidity (R2=0.81) for Lemon Creek. UTHg concentrations were consistently greater in Peterson Creek (factor of 1.7-2.3); however, the watershed area normalized UTHg flux was 3-6 times greater in glacial Lemon Creek than Peterson Creek across all time periods. In Peterson Creek, the majority of the UTHg was in the filtered phase, whereas in Lemon Creek the majority of the mercury

  2. Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period

    USGS Publications Warehouse

    Bay, R.C.; Bramall, N.E.; Price, P.B.; Clow, G.D.; Hawley, R.L.; Udisti, R.; Castellano, E.

    2006-01-01

    We perform a Monte Carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies in Greenland and East Antarctica determined by continuous core chemistry, together with West Antarctic volcanic ash layers determined by remote optical borehole logging and core assays. We find that the Antarctic record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% (???3??) significance level and that volcanic depositions at the three locations match at levels exceeding 3??, likely indicating that many common horizons represent single eruptive events which dispersed material world wide. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. The striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated. Copyright 2006 by the American Geogphysical Union.

  3. Reduced El Niño-Southern Oscillation during the Last Glacial Maximum.

    PubMed

    Ford, Heather L; Ravelo, A Christina; Polissar, Pratigya J

    2015-01-16

    El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate.

  4. Reduced El Niño-Southern Oscillation during the Last Glacial Maximum.

    PubMed

    Ford, Heather L; Ravelo, A Christina; Polissar, Pratigya J

    2015-01-16

    El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate. PMID:25593181

  5. An Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Dowdeswell, J. A.; Canals, M.; Todd, B. J.; Dowdeswell, E. K.; Hogan, K. A.

    2014-12-01

    In the past two decades there have been several advances that make the production of an atlas of submarine glacial landforms timely. First is the development of high-resolution imaging technologies; multi-beam echo-sounding or swath bathymetry that allows the detailed mapping of the sea floor at water depths of tens to thousands of metres across continental margins, and 3-D seismic methods that enable the visualisation of palaeo-continental shelves in Quaternary sediments and ancient palaeo-glacial rocks (e.g. Late Ordovician of Northern Africa). A second technological development is that of ice-breaking or ice-strengthened ships that can penetrate deep into the ice-infested waters of the Arctic and Antarctic, to deploy the multibeam systems. A third component is that of relevance - through both the recognition that the polar regions, and especially the Arctic, are particularly sensitive parts of the global environmental system and that these high-latitude margins (both modern and ancient) are likely to contain significant hydrocarbon resources. An enhanced understanding of the sediments and landforms of these fjord-shelf-slope systems is, therefore, of increasing importance to both academics and industry. We are editing an Atlas of Submarine Glacial Landforms that presents a series of individual contributions that describe, discuss and illustrate features on the high-latitude, glacier-influenced sea floor. Contributions are organised in two ways: first, by position on a continental margin - from fjords, through continental shelves to the continental slope and rise; secondly, by scale - as individual landforms and assemblages of landforms. A final section provides discussion of integrated fjord-shelf-slope systems. Over 100 contributions by scientists from many countries contain descriptions and interpretation of swath-bathymetric data from both Arctic and Antarctic margins and use 3D seismic data to investigate ancient glacial landforms. The Atlas will be

  6. EPICA Dome C record of glacial and interglacial intensities

    NASA Astrophysics Data System (ADS)

    Masson-Delmotte, V.; Stenni, B.; Pol, K.; Braconnot, P.; Cattani, O.; Falourd, S.; Kageyama, M.; Jouzel, J.; Landais, A.; Minster, B.; Barnola, J. M.; Chappellaz, J.; Krinner, G.; Johnsen, S.; Röthlisberger, R.; Hansen, J.; Mikolajewicz, U.; Otto-Bliesner, B.

    2010-01-01

    Climate models show strong links between Antarctic and global temperature both in future and in glacial climate simulations. Past Antarctic temperatures can be estimated from measurements of water stable isotopes along the EPICA Dome C ice core over the past 800 000 years. Here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile. The consistency between stable isotope-derived temperature and other environmental and climatic proxies measured along the EDC ice core is analysed at the orbital scale and compared with estimates of global ice volume. MIS 2, 12 and 16 appear as the strongest glacial maxima, while MIS 5.5 and 11 appear as the warmest interglacial maxima. The links between EDC temperature, global temperature, local and global radiative forcings are analysed. We show: (i) a strong but changing link between EDC temperature and greenhouse gas global radiative forcing in the first and second part of the record; (ii) a large residual signature of obliquity in EDC temperature with a 5 ky lag; (iii) the exceptional character of temperature variations within interglacial periods. Focusing on MIS 5.5, the warmest interglacial of EDC record, we show that orbitally forced coupled climate models only simulate a precession-induced shift of the Antarctic seasonal cycle of temperature. While they do capture annually persistent Greenland warmth, models fail to capture the warming indicated by Antarctic ice core δD. We suggest that the model-data mismatch may result from the lack of feedbacks between ice sheets and climate including both local Antarctic effects due to changes in ice sheet topography and global effects due to meltwater-thermohaline circulation interplays. An MIS 5.5 sensitivity study conducted with interactive Greenland melt indeed induces a slight Antarctic warming. We suggest that interglacial EDC optima are caused by transient heat transport redistribution comparable with

  7. Ocean Cooling Pattern at the Last Glacial Maximum

    DOE PAGESBeta

    Zhuang, Kelin; Giardino, John R.

    2012-01-01

    Ocean temperature and ocean heat content change are analyzed based on four PMIP3 model results at the Last Glacial Maximum relative to the prehistorical run. Ocean cooling mostly occurs in the upper 1000 m depth and varies spatially in the tropical and temperate zones. The Atlantic Ocean experiences greater cooling than the rest of the ocean basins. Ocean cooling is closely related to the weakening of meridional overturning circulation and enhanced intrusion of Antarctic Bottom Water into the North Atlantic.

  8. Uncovering the glacial history of the Irish continental shelf (Invited)

    NASA Astrophysics Data System (ADS)

    Dunlop, P.; Benetti, S.; OCofaigh, C.

    2013-12-01

    In 1999 the Irish Government initiated a €32 million survey of its territorial waters known as the Irish National Seabed Survey (INSS). The INSS is amongst the largest marine mapping programmes ever undertaken anywhere in the world and provides high-resolution multibeam, backscatter and seismic data of the seabed around Ireland. These data have been used to provide the first clear evidence for extensive glaciation of the continental shelf west and northwest of Ireland. Streamlined drumlins on the mid to outer shelf record former offshore-directed ice flow towards the shelf edge and show that the ice sheet was grounded in a zone of confluence where ice flowing onto the shelf from northwest Ireland merged with ice flowing across the Malin Shelf from southwest Scotland. The major glacial features on the shelf are well developed nested arcuate moraine systems that mark the position of the ice sheet margin and confirm that the former British Irish Ice Sheet was grounded as far as the shelf edge around 100 km offshore of west Donegal at the last glacial maximum. Distal to the moraines, on the outermost shelf, prominent zones of iceberg plough marks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. Since 2008 several scientific cruises have retrieved cores from the shelf and slope to help build a more detailed understanding of glacial events in this region. This presentation will provide an overview of the glacial history of the Irish shelf and will discuss ongoing research programmes that are building on the initial research findings to produce a better understanding of the nature and timing of ice sheet events in this region.

  9. Case for periodic, colossal jokulhlaups from Pleistocene glacial Lake Missoula.

    USGS Publications Warehouse

    Waitt, R.B., Jr.

    1985-01-01

    Lake Missoula (2500 km3) remained sealed as long as any segment of the glacial dam remained grounded; when the lake rose to a critical level c.600 m in depth, the glacier bed at the seal became buoyant, initiating underflow from the lake. Subglacial tunnels then grew exponentially, leading to catastrophic discharge. Calculations of the water budget for the lake basin (including input from the Cordilleran ice sheet) suggest that the lake filled every three to seven decades. -from Author

  10. Glacial History of the Pirrit Hills, West Antarctica

    NASA Astrophysics Data System (ADS)

    Spector, P. E.; Stone, J. O.

    2014-12-01

    We present new ice-thickness constraints from the Pirrit Hills, a small, far-flung group of nunataks located in the Weddell Sector. At the Pirrit Hills, fresh glacial erratics indicate ice levels ~350-450 m above present during the last ice age. The highest erratics have preliminary 10Be exposure ages of ~16 ka, and the ages generally decrease with decreasing elevation, recording the thinning of the ice in the region. Despite the evidence of thicker ice, weathered bedrock extends down to the present ice level, implying prolonged subaerial weathering prior to the last ice age. These features, and the lack of evidence for wet-based glacial erosion, indicate cold-based and non-erosive ice cover. Over the elevation range in which we found glacial erratics, bedrock 10Be, 26Al, and 21Ne concentrations are consistent with modest ice cover, and have exposure ages ranging from ~0.3-1.5 Myr. Around 450 m above the present ice level, bedrock 10Be, 26Al, and 21Ne concentrations increase by a factor of ~4-5 and do not indicate past ice cover. This height coincides with a break in the otherwise steep slopes of the Pirrit Hills, and the bedrock above is more weathered than the bedrock below. This transition marks the height above which ice cover, if it has occurred in the past few million years, has been very rare, brief, and cold-based. This feature may relate to the trimline imprinted on ridges in the Ellsworth Mountains. In both cases, alpine landscapes have been preserved by a polar climate and glacial highstands rising only partway up the mountain flanks.

  11. Tectonic stress feedback loop explains U-shaped glacial valleys

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2014-03-01

    In the shadow of the Matterhorn, the broad form of the Matter Valley—like so many throughout the Alps—is interrupted by a deep U-shaped glacial trough. Carved into a landscape reflecting millennia of tectonic uplift and river erosion, growing evidence suggests the 100-meter-deep U-shaped groove was produced shortly after a shift toward major cycles of Alpine glaciation almost a million years ago. Subsequent glaciations may have therefore had little effect on the landscape.

  12. Sulfur/Carbonate Springs and Life in Glacial Ice

    NASA Technical Reports Server (NTRS)

    Allen, Carlton; Grasby, Stephen; Longazo, Teresa

    2001-01-01

    Ice in the near subsurface of Mars apparently discharges liquid water on occasion. Cold-tolerant microorganisms are known to exist within terrestrial glacial ice, and may be brought to the surface as a result of melting events. We are investigating a set of springs that deposit sulfur and carbonate minerals, as well as evidence of microbial life, on the surface of a glacier in the Canadian arctic. Additional information is contained in the original extended abstract.

  13. Southern Hemisphere Westerly Wind Changes during the Last Glacial Maximum: Paleo-data Synthesis

    NASA Astrophysics Data System (ADS)

    Kohfeld, Karen; Graham, Robert; De Boer, Agatha; Sime, Louise; Wolff, Eric; Le Quéré, Corinne; Bopp, Laurent

    2013-04-01

    Changes in the strength and position of Southern Hemisphere westerly winds during the last glacial cycle have been invoked to explain glacial-interglacial climate fluctuations. However, neither paleo models nor paleodata agree on the magnitude, or even the sign, of the change in wind strength and latitude during the Last Glacial Maximum (LGM), compared to the recent past. This study synthesizes paleo-environmental data that have been used to infer changes in winds during the LGM compared with the late Holocene. These compilations include changes in terrestrial moisture, dust deposition, and ocean productivity, along with summaries of previously published information on sea surface temperatures (SSTs) and ocean dynamics in the Southern Hemisphere. Our compilations of terrestrial moisture from 94 sites and dust deposition from 87 sites show generally drier conditions for the LGM between 0 and 40°S, with wetter conditions along the west coasts and drying along the east coasts of continents. LGM dust deposition rates ranged from 2 to 4.5 times higher over the Southern Ocean and about 13 times higher over the Antarctic continent. For the oceans, reconstructed changes in SSTs show maximum cooling (>4°C) in the modern-day Subantarctic Zone, coincident with a region of enhanced export production during the LGM compared with today. We find that any hypothesis of LGM wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents, cooler temperatures and higher productivity in the Subantarctic Zone, and reductions in Agulhas leakage around southern Africa. Our comparison suggests that an overall strengthening, an equatorward displacement, or no change at all in winds could all be interpreted as consistent with observations. If a single cause related to the southern westerlies is sought for all the evidence presented, then an equatorward displacement or strengthening of the winds would be consistent with the largest

  14. Glacial aridity in central Indonesia coeval with intensified monsoon circulation

    NASA Astrophysics Data System (ADS)

    Konecky, Bronwen; Russell, James; Bijaksana, Satria

    2016-03-01

    The Last Glacial Maximum was cool and dry over the Indo-Pacific Warm Pool (IPWP), a key region driving global oceanic-atmospheric circulation. Both low- and high-latitude teleconnections with insolation, ice sheets, and sea level have been suggested to explain the pervasive aridity observed in paleoecological and geomorphic data. However, proxies tracking the H- and O-isotopic composition of rainfall (e.g., speleothems, sedimentary biomarkers) suggest muted aridity or even wetter conditions than the present, complicating interpretations of glacial IPWP climate. Here we use multiproxy reconstructions from lake sediments and modern rainfall isotopic measurements from central Indonesia to show that, contrary to the classical "amount effect," intensified Australian-Indonesian monsoon circulation drove lighter H- and O-isotopic composition of IPWP rainfall during the LGM, while at the same time, dry conditions prevailed. Precipitation isotopes are particularly sensitive to the apparent increase in monsoon circulation and perhaps also decreased moisture residence time implied by our data, explaining contrasts among proxy records while illuminating glacial IPWP atmospheric circulation, a key target for climate models.

  15. Human population dynamics in Europe over the Last Glacial Maximum.

    PubMed

    Tallavaara, Miikka; Luoto, Miska; Korhonen, Natalia; Järvinen, Heikki; Seppä, Heikki

    2015-07-01

    The severe cooling and the expansion of the ice sheets during the Last Glacial Maximum (LGM), 27,000-19,000 y ago (27-19 ky ago) had a major impact on plant and animal populations, including humans. Changes in human population size and range have affected our genetic evolution, and recent modeling efforts have reaffirmed the importance of population dynamics in cultural and linguistic evolution, as well. However, in the absence of historical records, estimating past population levels has remained difficult. Here we show that it is possible to model spatially explicit human population dynamics from the pre-LGM at 30 ky ago through the LGM to the Late Glacial in Europe by using climate envelope modeling tools and modern ethnographic datasets to construct a population calibration model. The simulated range and size of the human population correspond significantly with spatiotemporal patterns in the archaeological data, suggesting that climate was a major driver of population dynamics 30-13 ky ago. The simulated population size declined from about 330,000 people at 30 ky ago to a minimum of 130,000 people at 23 ky ago. The Late Glacial population growth was fastest during Greenland interstadial 1, and by 13 ky ago, there were almost 410,000 people in Europe. Even during the coldest part of the LGM, the climatically suitable area for human habitation remained unfragmented and covered 36% of Europe.

  16. A northern glacial refugium for bank voles (Clethrionomys glareolus).

    PubMed

    Kotlík, Petr; Deffontaine, Valérie; Mascheretti, Silvia; Zima, Jan; Michaux, Johan R; Searle, Jeremy B

    2006-10-01

    There is controversy and uncertainty on how far north there were glacial refugia for temperate species during the Pleistocene glaciations and in the extent of the contribution of such refugia to present-day populations. We examined these issues using phylogeographic analysis of a European woodland mammal, the bank vole (Clethrionomys glareolus). A Bayesian coalescence analysis indicates that a bank vole population survived the height of the last glaciation (approximately 25,000-10,000 years B.P.) in the vicinity of the Carpathians, a major central European mountain chain well north of the Mediterranean areas typically regarded as glacial refugia for temperate species. Parameter estimates from the fitted isolation with migration model show that the divergence of the Carpathian population started at least 22,000 years ago, and it was likely followed by only negligible immigration from adjacent regions, suggesting the persistence of bank voles in the Carpathians through the height of the last glaciation. On the contrary, there is clear evidence for gene flow out of the Carpathians, demonstrating the contribution of the Carpathian population to the colonization of Europe after the Pleistocene. These findings are consistent with data from animal and plant fossils recovered in the Carpathians and provide the clearest phylogeographic evidence to date of a northern glacial refugium for temperate species in Europe. PMID:17001012

  17. Human population dynamics in Europe over the Last Glacial Maximum

    PubMed Central

    Tallavaara, Miikka; Luoto, Miska; Korhonen, Natalia; Järvinen, Heikki; Seppä, Heikki

    2015-01-01

    The severe cooling and the expansion of the ice sheets during the Last Glacial Maximum (LGM), 27,000–19,000 y ago (27–19 ky ago) had a major impact on plant and animal populations, including humans. Changes in human population size and range have affected our genetic evolution, and recent modeling efforts have reaffirmed the importance of population dynamics in cultural and linguistic evolution, as well. However, in the absence of historical records, estimating past population levels has remained difficult. Here we show that it is possible to model spatially explicit human population dynamics from the pre-LGM at 30 ky ago through the LGM to the Late Glacial in Europe by using climate envelope modeling tools and modern ethnographic datasets to construct a population calibration model. The simulated range and size of the human population correspond significantly with spatiotemporal patterns in the archaeological data, suggesting that climate was a major driver of population dynamics 30–13 ky ago. The simulated population size declined from about 330,000 people at 30 ky ago to a minimum of 130,000 people at 23 ky ago. The Late Glacial population growth was fastest during Greenland interstadial 1, and by 13 ky ago, there were almost 410,000 people in Europe. Even during the coldest part of the LGM, the climatically suitable area for human habitation remained unfragmented and covered 36% of Europe. PMID:26100880

  18. Pennsylvanian tropical rain forests responded to glacial-interglacial rhythms

    NASA Astrophysics Data System (ADS)

    Falcon-Lang, Howard J.

    2004-08-01

    Pennsylvanian tropical rain forests flourished during an icehouse climate mode. Although it is well established that Milankovitch-band glacial-interglacial rhythms caused marked synchronous changes in Pennsylvanian tropical climate and sea level, little is known of vegetation response to orbital forcing. This knowledge gap has now been addressed through sequence- stratigraphic analysis of megafloral and palynofloral assemblages within the Westphalian D Cantabrian Sydney Mines Formation of eastern Canada. This succession was deposited in a low- accommodation setting where sequences can be attributed confidently to glacio-eustasy. Results show that long-lived, low-diversity peat mires dominated by lycopsids were initiated during deglaciation events, but were mostly drowned by rising sea level at maximum interglacial conditions. Only upland coniferopsid forests survived flooding without significant disturbance. Mid- to late interglacial phases witnessed delta-plain progradation and establishment of high-diversity, mineral-substrate rain forests containing lycopsids, sphenopsids, pteridosperms, cordaites, and tree ferns. Renewed glaciation resulted in sea-level fall, paleovalley incision, and the onset of climatic aridity. Glacial vegetation was dominated by cordaites, pteridosperms, and tree ferns; hydrophilic lycopsids and sphenopsids survived in paleovalley refugia. Findings clearly demonstrate the dynamic nature of Pennsylvanian tropical ecosystems and are timely given current debates about the impact of Quaternary glacial-interglacial rhythms on the biogeography of tropical rain forest.

  19. Testing hypotheses about glacial cycles against the observational record

    NASA Astrophysics Data System (ADS)

    Kaufmann, Robert K.; Juselius, Katarina

    2013-01-01

    We estimate an identified cointegrated vector autoregression model of the climate system to test hypotheses about the physical mechanisms that may drive glacial cycles during the late Pleistocene. Results indicate that a permanent doubling of CO2 generates a 11.1°C rise in Antarctic temperature. Large variations in atmospheric CO2 over glacial cycles are driven by changes in sea ice and sea surface temperature in southern oceans and marine biological activity. The latter can be represented by a two-step process in which iron dust increases biological activity and the increase in biological activity reduces CO2 concentrations. Glacial variations in ice volume, as proxied by δ18O are driven by changes in CO2 concentrations, global and high latitude solar insolation, latitudinal gradients in solar insolation, and the atmospheric concentration of CO2. The model is able to quantify the effects of ice volume and temperature on sea level, such that in the long-run, sea level rises 14 m per 0.11‰ δ18O and about 17 m/°C of sea surface temperature in southern oceans. Beyond these specific results, the multivariate model suggests omitted variables may bias bivariate analyses of these mechanisms.

  20. 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.

  1. Application of the surface azimuthal electrical resistivity survey method to determine patterns of regional joint orientation in glacial tills

    USGS Publications Warehouse

    Carlson, D.

    2010-01-01

    Joints within unconsolidated material such as glacial till can be primary avenues for the flow of electrical charge, water, and contaminants. To facilitate the siting and design of remediation programs, a need exists to map anisotropic distribution of such pathways within glacial tills by determining the azimuth of the dominant joint set. The azimuthal survey method uses standard resistivity equipment with a Wenner array rotated about a fixed center point at selected degree intervals that yields an apparent resistivity ellipse. From this ellipse, joint set orientation can be determined. Azimuthal surveys were conducted at 21 sites in a 500-km2 (193 mi2) area around Milwaukee, Wisconsin, and more specifically, at sites having more than 30 m (98 ft) of glacial till (to minimize the influence of underlying bedrock joints). The 26 azimuthal surveys revealed a systematic pattern to the trend of the dominant joint set within the tills, which is approximately parallel to ice flow direction during till deposition. The average orientation of the joint set parallel with the ice flow direction is N77??E and N37??E for the Oak Creek and Ozaukee tills, respectively. The mean difference between average direct observation of joint set orientations and average azimuthal resistivity results is 8??, which is one fifth of the difference of ice flow direction between the Ozaukee and Oak Creek tills. The results of this study suggest that the surface azimuthal electrical resistivity survey method used for local in situ studies can be a useful noninvasive method for delineating joint sets within shallow geologic material for regional studies. Copyright ?? 2010 The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.

  2. A vadose zone Transport Processes Investigation within the glacial till at the Fernald Environmental Management Project.

    SciTech Connect

    Schwing, J.; Roepke, Craig Senninger; Brainard, James Robert; Glass, Robert John, Jr.; Mann, Michael J. A.; Holt, Robert M.; Kriel, Kelly

    2007-08-01

    This report describes a model Transport Processes Investigation (TPI) where field-scale vadose zone flow and transport processes are identified and verified through a systematic field investigation at a contaminated DOE site. The objective of the TPI is to help with formulating accurate conceptual models and aid in implementing rational and cost effective site specific characterization strategies at contaminated sites with diverse hydrogeologic settings. Central to the TPI are Transport Processes Characterization (TPC) tests that incorporate field surveys and large-scale infiltration experiments. Hypotheses are formulated based on observed pedogenic and hydrogeologic features as well as information provided by literature searches. The field and literature information is then used to optimize the design of one or more infiltration experiments to field test the hypothesis. Findings from the field surveys and infiltration experiments are then synthesized to formulate accurate flow and transport conceptual models. Here we document a TPI implemented in the glacial till vadose zone at the Fernald Environmental Management Project (FEMP) in Fernald, Ohio, a US Department of Energy (DOE) uranium processing site. As a result of this TPI, the flow and transport mechanisms were identified through visualization of dye stain within extensive macro pore and fracture networks which provided the means for the infiltrate to bypass potential aquatards. Such mechanisms are not addressed in current vadose zone modeling and are generally missed by classical characterization methods.

  3. Imaging Quaternary glacial deposits and basement topography using the transient electromagnetic method for modeling aquifer environments

    NASA Astrophysics Data System (ADS)

    Simard, Patrick Tremblay; Chesnaux, Romain; Rouleau, Alain; Daigneault, Réal; Cousineau, Pierre A.; Roy, Denis W.; Lambert, Mélanie; Poirier, Brigitte; Poignant-Molina, Léo

    2015-08-01

    Aquifer formations along the northern shore of the Saint-Lawrence River in Quebec (Canada) mainly consist of glacial and coastal deposits of variable thickness overlying Precambrian bedrock. These deposits are important because they provide the main water supply for many communities. As part of a continuing project aimed at developing an inventory of the groundwater resources in the Charlevoix and Haute-Côte-Nord (CHCN) regions of the province of Quebec in Canada, the central loop transient electromagnetic (TEM) method was used to map the principal hydrogeological environments in these regions. One-dimensional smooth inversion models of the TEM soundings have been used to construct two-dimensional electrical resistivity sections, which provided images for hydrogeological validation. Electrical contour lines of aquifer environments were compared against available well logs and Quaternary surface maps in order to interpret TEM soundings. A calibration table was achieved to represent common deposits and basements. The calibration table was then exported throughout the CHCN region. This paper presents three case studies; one in the Forestville site, another in the Les Escoumins site and the other in the Saint-Urbain site. These sites were selected as targets for geophysical surveys because of the general lack of local direct hydrogeological data related to them.

  4. The influence of glacier ice temperature on the long-term evolution of longitudinal valley profiles: Can a landscape escape from the "glacial buzzsaw"?

    NASA Astrophysics Data System (ADS)

    Dühnforth, M.; Anderson, R. S.; Colgan, W.

    2012-04-01

    The long-term pattern of glacial erosion in alpine valleys leads to characteristic longitudinal valley profiles. While landscape evolution models commonly take glacier sliding velocity to be the dominant control on erosion, the influence of spatial and temporal variations in glacier ice temperature on the efficiency of erosion over long timescales (>1 Ma) remains largely unexplored. Yet, the thermal field of a glacier can strongly influence the pattern of sliding. Temperate glaciers, with basal temperatures at the pressure melting point (PMP), slide whenever and wherever the glacial hydrology produces high water pressures. In contrast, in polythermal glaciers, erosion efficiency is strongly linked to basal ice temperature; when and where basal ice temperatures are below the PMP sliding, and hence erosion, are limited. We present results from numerical models in which we explore the influence of variations in glacier ice temperature on long-term glacial erosion processes in alpine valleys. These simulations are motivated by the persistent appeal of geomorphologists to polar glacial conditions to explain sites of unusually low glacial erosion rates. We employ a transient 1D (flowline) ice flow model that numerically solves the continuity equation for ice, and includes a depth-averaged approximation for longitudinal coupling stress. We prescribe separate winter and summer surface mass balance profiles: a capped elevation-dependent snowfall pattern in winter, and we capture both daily and seasonal oscillations in ablation using a positive degree day algorithm in summer. The steady-state ice temperature within the glacier is calculated using the conventional 2D (cross-sectional) heat equation (i.e. diffusion, advection and production terms) at a prescribed interval. The ice temperature model uses the surface temperature at the end of each melt season as the surface boundary condition, and a prescribed geothermal gradient as the basal boundary condition. Basal sliding is

  5. Localized sub-glacial deep karst formation due to water infiltration into glacier crevasses: A case study from Asiago, Italy

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Frehner, Marcel; Busellato, Leonardo; Grasselli, Giovanni

    2015-04-01

    In karstic plateaus, deep karst phenomena (e.g. abysses) are the preferential pathways for surface water to penetrate the Earth's crust. After percolation along diaclases and meanders, the infiltrated water often springs at the foot of the karstic plateau, potentially representing a valuable water resource. Thus, it is crucial to understand the formation and distribution of deep karst phenomena, for instance to predict karstic groundwater flow paths or to preserve water resources from pollution. The role of glaciers in enhancing the formation of deep karst is not yet clear. On the one hand, chilly water retains more CO2 which increases its acidity and efficiency in corroding carbonates. On the other hand, glaciers obliterate the soil and vegetation covering the developing karst decreasing the quantity of humic acids dissolved in the surface water. Nevertheless, ice-caps may play a key role in controlling how and where surface water can access the developing karstic system. Due to the presence of a glacier, some sub-glacial areas may not be reached by surface water, which prevents karstification, while other areas may be connected to intra- or sub-glacial flow paths possibly leading to localized kartification in these areas. Here we investigate the relationship between sub-glacial topography and the development of preferred intra-glacier flow paths and how this relationship leads to localized sub-glacial karstification. As a case study site, we use the karstic plateau of Asiago in Northern Italy. The Asiago plateau (https://goo.gl/maps/bLezx) is mainly composed of Permian to Cretaceous rocks. The northern and southern boundaries of the plateau are marked by two Alpine trusts, which uplifted the plateau during the Alpine orogeny to ~1500 m above the Po flood plain delimiting the plateau to the South. The Asiago plateau extends for ~600 km2 and contains ~2100 natural caves, including many significantly deep caves such as the deepest cave of Veneto: the 1011 m deep

  6. Climatic Instability and Regional Glacial Advances in the Late Ediacaran

    NASA Astrophysics Data System (ADS)

    Hannah, J. L.; Stein, H. J.; Marolf, N.; Bingen, B.

    2014-12-01

    The Ediacaran Period closed out the environmentally raucous Neoproterozoic Era with the last of multiple glacial events and the first ephemeral glimmer of multicellular life. As such, evolution of Earth's biosphere and the marine environments that nurtured this nascent biota are of particular interest. Because the Ediacaran biota appear in the stratigraphic record just above tillites in many localities, inferences are naturally drawn to link glaciation to bioevolution. Here we review known controls on the timing and extent of the late Ediacaran Gaskier and Varanger glacial events, bolstered by new constraints on the Moelv tillite of South Norway. The elusive mid-Ediacaran glacial strata are poorly dated, patchy in distribution, and relatively limited in thickness. The type Gaskier glaciogenic units in Newfoundland are 582 to 584 Ma, based on U-Pb zircon ages from intercalated ash beds [1]. The Varanger glaciogenic deposits in northern Norway, in contrast, remain only roughly constrained to ca. 630 to 560 Ma. Post-Gaskier negative carbon isotope excursions (CIEs) have been reported from multiple localities in both China and SW United States, suggesting climatic instability in the late Ediacaran. Although most localities lack solid geochronology, paleontologic constraints place the Hongtiegou glacial diamictite and accompanying CIE in the Chaidam Basin, NW China, in the latest Ediacaran, ca. 555 Ma [2]. We previously suggested that the Moelv tillite in south Norway was roughly equivalent to the Gaskier, based on an imprecise Re-Os age of ~560 Ma [3] for the underlying Biri shale. Reanalysis of these data shows that the upper part of the shale section was disturbed by a redox front during the Caledonian orogeny. The undisturbed lower part of the section yields a more precise Model 1 isochron age of 559.5 ± 6.2 Ma, clearly post-dating the Gaskier event well outside analytical uncertainty. These new results bolster arguments that the Gaskier glaciation was not a global

  7. Transience and Glacial Erosion in South Central Alaska

    NASA Astrophysics Data System (ADS)

    Valentino, J.; Spotila, J. A.; Owen, L. A.; Buscher, J.

    2013-12-01

    It is documented that a glacial presence in active orogenic belts undergoing rapid rock uplift will increase erosion rates often matching rates of rock uplift. Glacial erosion seems to have shaped the mass balance of numerous mountain ranges and tectonic settings, but the Kenai Peninsula and Chugach Mountains of south central Alaska do not conform to this pattern. The Kenai Peninsula is an uplifted forearc forming above the Aleutian subduction zone and the Chugach Mountains are the continuation of the orogenic belt around Prince William Sound. This mountain belt is comprised of accreted Mesozoic island arcs, which were sequentially metamorphosed from the cretaceous through the Tertiary. Geomorphic analysis and past studies, including Buscher et al. (2008) and Arkle et al. (2013), show that the Chugach Mountains and Kenai Peninsula are similar to the Saint Elias Mountains in the Yakutat collision zone with regards to topographic ruggedness. The region is dominated by alpine glaciers, ice fields, and extensive valley glaciers that are actively eroding the topography through headwall erosion and valley glacier down cutting. Despite this, there is a low background long term erosion rate of <0.1-0.2 mm/yr (Buscher et al, 2008). This suggests a transient landscape that has not yet fully adjusted to onset of erosive glacial conditions. Through the use of four dating techniques spanning different timescales, we aim to quantify erosion rates in the Kenai and Chugach Mountains. (U-TH)/He thermochronometry (106-7 yr), He/He thermochronometry (105-6 yr), OSL thermochronometry (105-6 yr), and 10Be and 36CL cosmogenic dating (103-4 yr), are being used in conjunction to test if short-term rates exceed long-term rates, thereby indicating a transient response to late Cenozoic glaciations. This analysis will also address how landscapes respond to the onset of glacial conditions and subsequent climate fluctuations. The history of exhumation and erosion will also characterize the role

  8. Optically Stimulated Luminescence Dating of Glacial Outwash Spanning the Last Glacial Cycle on the Western Olympic Peninsula, Washington, USA

    NASA Astrophysics Data System (ADS)

    Marshall, K. J.; Thackray, G. D.; Rittenour, T. M.

    2012-12-01

    Valley glaciers in the Olympic Mountains, Washington coalesced and advanced onto the Pacific coastal lowlands six times during Late Pleistocene time. With each advance, the valley glaciers constructed extensive landforms and thick stratigraphic sequences. Along the coast of the Olympic Peninsula, between the Hoh and Queets Rivers, wave-cut sea cliffs expose alternating sequences of outwash fans formed during periods of glacial advance and marine transgressive facies formed during periods of sea-level high stand. Previous work, encompassing geomorphic mapping of inland and coastal outcrops, stratigraphy, stratigraphic correlation, and radiocarbon dating, established a provisional glacial chronology for the Olympic coast, but was limited to the range of radiocarbon dating. Within the sea cliffs, three primary units of outwash were identified: the Hoh Oxbow (MIS 3), Lyman Rapids (MIS 4 or 5b), and Steamboat Creek outwash (MIS 6 or older). The outwash units are generally bounded by interglacial sea-level high stand sediments or interstadial terrestrial sediment. Our new investigations utilize detailed sedimentology and stratigraphy, mapping of geomorphic sequences, and optically stimulated luminescence (OSL) dating to extend and solidify the coastal glacial chronology. OSL methods provide a means to date outwash sequences directly and enable dating of previously undateable older sediments. The quartz in these sediments appears to be fully bleached and retains the luminescence signal. Furthermore, at two locations where both radiocarbon and OSL methods were applied on the same sediments, the ages are indistinguishable, indicating that OSL is reliable in these settings. Preliminary OSL ages from the outwash units indicate valley glacier advances on the Olympic Peninsula during Hoh Oxbow (MIS 3, ca. 30-50 ka), Lyman Rapids (MIS 4, ca. 50-80 ka), and Steamboat Creek (MIS 5d or older, >/= 105 ka). Additionally, general sediment fining up-section suggests a decrease in

  9. Modelling of Gas Hydrate Dissociation During The Glacial-Inter-glacial Cycles, Case Study The Chatham Rise, New Zealand

    NASA Astrophysics Data System (ADS)

    Oluwunmi, P.; Pecher, I. A.; Archer, R.; Moridis, G. J.; Reagan, M. T.

    2015-12-01

    Seafloor depressions covering an area of >20,000 km2 on the Chatham Rise, south east of New Zealand, have been interpreted as pockmarks which are related to past fluid releases. It is proposed that the seafloor depressions were caused by sudden escape of overpressured gas generated by gas hydrate dissociation during glacial sea-level lowering. We are attempting to simulate the evolution of the gas hydrate system through glacial-interglacial cycles in the study area using TOUGH-Hydrate. The Chatham Rise offers a unique opportunity for studying the effect of depressurization from sealevel lowering to gas hydrate systems because it is a bathymetric barrier preventing the Subtropical Front separating subtropical and subantarctic waters from migrating during glacial-interglacial cycles. Hence, bottom-water temperatures can be assumed to remain constant. Recent results from paleoceanographic studies however, indicate that bottom-temperature may have varied locally. These temperature changes may have a more significant effect on the shallow gas hydrate system in the study area than the relatively gradual decrease of pressure associated with sealevel lowering.

  10. Stratigraphy and sedimentology of pre-late Wisconsin catastrophic glacial flood sediments, western Walla Walla Valley, Washington

    SciTech Connect

    Robertson, J.L.; Spencer, P.K. . Geology Dept.)

    1993-04-01

    The Cummins Bridge site in the western Walla Walla Valley exhibits clear evidence for pre-late Wisconsin catastrophic glacial flooding. The section consists of an unstratified, poorly sorted diamict with angular basaltic clasts in a matrix of sand and silt, and a large number of well-rounded clasts of exotic lithology in the coarse fraction, gradationally overlain by a coarse, angular gravel that is matrix poor and exotic-free; this unit grades upward into a matrix-rich diamict with a well-developed caliche in the upper portion. Above this is a sand and silt unit showing vague cross-stratification, lamination, and graded beds; this unit may represent local temporary ponding of the ancestral drainage. Overlying this on a pronounced erosional surface are rhythmically stratified sand-to-salt beds assigned to the late Wisconsin Toughet Beds. The section is capped by a thin bed of Holocene loess. Stratigraphic and sedimentologic criteria suggest that the lowermost units represent an indirect record of catastrophic glacial flooding. Flood sediments were deposited on an adjacent topographic high and subsequently mass-wasted via mudflow into their present position. Normal fluvial processes alternated with mass-wasting events to concentrate the angular, matrix-poor basaltic gravel. The lower diamict shows characteristics similar to documented pre-late Wisconsin catastrophic flood sediments at a nearby site, including rounded exotic clasts, angular basaltic clasts, lack of stratification, and poor sorting. The two sites may represent the same pre-late Wisconsin flood event.

  11. Interpreting last glacial to Holocene dust changes at Talos Dome (East Antarctica): implications for atmospheric variations from regional to hemispheric scales

    NASA Astrophysics Data System (ADS)

    Albani, S.; Delmonte, B.; Maggi, V.; Baroni, C.; Petit, J.-R.; Stenni, B.; Mazzola, C.; Frezzotti, M.

    2012-04-01

    Central East Antarctic ice cores preserve stratigraphic records of mineral dust originating from remote sources in the Southern Hemisphere, and represent useful indicators of climatic variations on glacial-interglacial time scales. The peripheries of the East Antarctic Ice Sheet, where ice-free areas with the potential to emit dust exist, have been less explored from this point of view. Here, we present a new profile of dust deposition flux and grain size distributions from an ice core drilled at Talos Dome (TALDICE, Northern Victoria Land, East Antarctica), where there is a significant input of dust from proximal Antarctic ice-free areas. We analyze dust and stable water isotopes variations from the Last Glacial Maximum to the Late Holocene, and compare them to the EPICA Dome C profiles from central East Antarctica. The smaller glacial-interglacial variations at Talos Dome compared to Dome C and a distinctive decreasing trend during the Holocene characterize the TALDICE dust profile. By deciphering the composite dust signal from both remote and local sources, we show the potential of this combined proxy of source activity and atmospheric transport to give information on both regional and larger spatial scales. In particular, we show how a regional signal, which we relate to the deglaciation history of the Ross Sea embayment, can be superimposed to the broader scale glacial-interglacial variability that characterizes other Antarctic sites.

  12. Interpreting last glacial to Holocene dust changes at Talos Dome (East Antarctica): implications for atmospheric variations from regional to hemispheric scales

    NASA Astrophysics Data System (ADS)

    Albani, S.; Delmonte, B.; Maggi, V.; Baroni, C.; Petit, J.-R.; Stenni, B.; Mazzola, C.; Frezzotti, M.

    2012-01-01

    Central East Antarctica ice cores preserve stratigraphic records of mineral dust originating from remote sources in the Southern Hemisphere, and represent useful indicators of climatic variations on glacial-interglacial time scales. The peripheries of the East Antarctic Ice Sheet, where ice-free areas with the potential to emit dust exist, have been less explored from this point of view. Here we present a new profile of dust deposition flux and grain size distributions from an ice core drilled at Talos Dome (Northern Victoria Land, East Antarctica), where there is a significant input of dust from proximal Antarctic ice-free areas. We analyze dust and stable water isotopes variations from the Last Glacial Maximum to the Late Holocene, and compare them to the EPICA Dome C profiles from Central East Antarctica. The smaller glacial-interglacial variations at Talos Dome compared to Dome C, and a distinctive decreasing trend during the Holocene, characterize the TALDICE dust profile. By deciphering the composite dust signal from both remote and local sources, we show the potential of this combined proxy of source activity and atmospheric transport to give information on both regional and larger spatial scales. In particular, we show how a regional signal, which we related to the deglaciation history of the Ross Sea embayment, can be superimposed to the broader scale glacial-interglacial variability that characterizes other Antarctic sites.

  13. Interannual physiological responses of glacial trees to changes in atmospheric [CO2] since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Gerhart, L. M.; Harris, J. M.; Ward, J. K.

    2009-12-01

    During the Last Glacial Maximum, atmospheric [CO2] were as low as 180 ppm and have currently risen to a modern value of 385 ppm as a result of fossil fuel combustion and deforestation. In order to understand how changing [CO2] influenced the physiology of trees over the last 50,000 years, we analyzed carbon isotope ratios of individual tree rings from juniper wood specimens from the Rancho La Brea tar pits in southern California and kauri wood specimens from peat bogs in New Zealand (North Island). Modern trees from different altitudes were compared to account for changes in precipitation and temperature through time in order to isolate the effects of changing [CO2]. We hypothesized that over the last 50,000 years, the ratio of ci (intracellular [CO2]) to ca (atmospheric [CO2]) would be maintained within each species. Consequently, ci values would be significantly lower in glacial trees due to lower ca levels during the LGM. In addition, we hypothesized that low [CO2] (which does not vary between years during the LGM) dominated tree physiology during the LGM as evidenced by low levels of inter-annual variation in ci/ca ratios relative to modern trees (which are known to respond to high frequency variation in water and temperature between years). In both kauri and juniper trees, mean ci/ca values remained constant throughout 50,000 years despite major climatic and [CO2] changes, indicating that there is a long-term physiological set point in these species. Limitations on the ci values of glacial junipers suggest that 90 ppm CO2 represents a survival compensation point for this species. In addition, glacial trees showed very low inter-annual variation in ci/ca values compared to modern trees. This suggests that glacial tree physiology may have been dominated by low CO2 that was constant between years, whereas modern trees may be dominated by climatic factors that vary substantially between years. Consequently, while each species maintained mean ci/ca values over time

  14. The stratotype and facies of the glacial Lower Vendian Nichatka Formation, Chara River basin, Central Siberia

    NASA Astrophysics Data System (ADS)

    Chumakov, N. M.; Kernitskii, V. V.

    2016-07-01

    Sediments of the Nichatka Formation are facially studied and thoroughly described, the sections are correlated, and the subformations are recognized. The formation represents a key stratigraphic unit to reveal the origin of the Central Siberian glacial horizon and to correlate it with glacial horizons in other regions of the world, namely, with the Laplandian Horizon of the Lower Vendian, Nantou and Marino tillites, etc. The Nichatka Formation is correlated with the glacial Bolshoi Patom (Dzhemkukan) Formation of the Vendian reference section at the Ura Uplift. Unlike the latter, it is mainly composed of continental glacial deposits and is marked by a complex facies composition. The glacial origin of the Nichatka Formation is reliably determined on the basis of a set of diagnostic characters. This permits a more complete reconstruction of the Early Vendian depositional environments. In addition to typical basal tillites and marginal moraine deposits, the formation includes glaciolacustrine and fluvioglacial sediments along with aquatillites, allotillites, and the glacial fan, including subaqueous, deposits.

  15. Glacial inception during the late Holocene without carbon emissions from early agriculture: lessons from the stage-19 glacial inception

    NASA Astrophysics Data System (ADS)

    He, F.; Vavrus, S. J.; Kutzbach, J. E.; Ruddiman, W. F.; Tzedakis, P. C.

    2013-12-01

    Decreases in orbitally-forced summer insolation along with downward trends in greenhouse gases (GHG) have been precursors to incipient glaciation in the past. In the last several thousand years of the current interglacial, while summer insolation has decreased, there was a reversal of the downward trends in CH4 and CO2 concentration within the Holocene around 5,000 and 7,000 years ago. While the cause of this reversal remains unresolved, a leading hypothesis is Ruddiman's Early Anthropogenic Hypothesis that early agriculture, starting several thousand years ago, caused emissions of GHG large enough to reverse natural downward trends in CO2 and CH4 and kept Earth's climate anomalously warm, with the corollary that this may have prevented incipient glaciation during the late Holocene. Here we use the 1-degree, fully coupled Community Climate System Model version 4 (CCSM4) with climate forcings (orbital parameters and GHG) of a previous glacial inception to investigate whether glacial inception should have occurred prior to the industrial revolution if the concentrations of CH4 and CO2 had followed their natural downward trends throughout the Holocene. Tzedakis et al. [2012] show that for the previous eight interglacials, Stage 11 and Stage 19 are the best analogs of the Holocene because of their low eccentricities, and Stage 19 is a better analog than Stage 11 for the Holocene due to the in-phase relationship between obliquity and precession. Furthermore, their study suggests that 777 ka BP (777,000 years before present) is the timing of glacial inception for Stage 19, based on the occurrence of the earliest bipolar seesaw event associated with glacial melting. Not only do the orbital parameters at 777 ka BP resemble pre-industrial conditions, but the concentrations of CO2 at that time were essentially the same as their expected 'natural' pre-industrial values in the absence of anthropogenic greenhouse emissions. Our multi-millennial coupled CCSM4 simulations show

  16. Surface exposure dating of glacial lake shorelines: implications for constraining ice margin positions and meltwater outbursts during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Dube-Loubert, Hugo; Roy, Martin; Schaefer, Joerg

    2016-04-01

    The Laurentide ice sheet (LIS) played an important role in the climate variability of the last deglaciation, notably through large discharges of meltwater to the North Atlantic that disturbed the ocean's circulation and heat transport. Deglaciation of the northeastern sector of the LIS was complex and included the development of large ice-dammed lakes that were confined within the main river valleys draining northward into Ungava Bay. The history of these lakes is closely related to the temporal evolution of the Labrador ice dome, but large uncertainties regarding the position and dynamic of the ice margin through time currently limit our understanding of these glacial lakes. In the Ungava lowlands, glacial lake Naskaupi invaded the George River valley, leaving a series of well-developed shorelines and deltas. These spectacular raised shorelines are 10 to 20 meters wide and can be followed for several kilometers. Our field investigations and remote sensing analysis indicate that Lake Naskaupi experienced a complex history, as shown by the succession of shorelines that likely reflect the opening of new topographic outlets during ice retreat. Constraining the timing of the different phases of the lake and its drainage has traditionally been challenging, as organic material suitable for radiocarbon dating is scarce or lacking. Recent progress in Surface Exposure Dating (SED) by cosmogenic nuclides now inspires novel approaches to glacial and deglacial geomorphology. Here we apply 10Be SED to boulders that form part of these shorelines and mark the main (high-level) stage of Lake Naskaupi. We sampled 4-6 multi-meter size boulders at 4 different sites. Preliminary results show high internal consistency and, indicate that the main lake phase developed very late in the regional deglaciation, which extends from about 8500 to 6800 cal. yr BP (Dyke and Prest, 1987). We also present SED results from boulders deposited by a substantial outburst flood presumably associated with

  17. Last-glacial dustiness and enhanced gustiness: deciphering the record of Peoria Loess deposition at Loveland, western Iowa

    NASA Astrophysics Data System (ADS)

    Roberts, H. M.; Muhs, D. R.; Bettis, E. A., III; Harlan, S. S.; Paces, J. B.; Reynolds, R. L.

    2013-12-01

    The Loveland Paratype Section (N41.50052°, W95.88934°) in western Iowa, USA, preserves one of the thickest deposits of last-glacial (Peoria) loess in the world. As such, this site offers an ideal opportunity to test the recently proposed idea that the enhanced global ';dustiness' which is widely noted across a range of Quaternary records during the Last Glacial Maximum (LGM), was primarily driven by increased ';gustiness' in the form of stronger, more frequent winds (McGee et al., 2010). Twenty-two quartz optically stimulated luminescence (OSL) ages taken from the Pisgah and Peoria Loess units at Loveland give ages that are stratigraphically consistent within uncertainties. Mass Accumulation Rates (MARs) calculated for the loess using both a linear accumulation rate model and also a Bayesian model of accumulation, show that the MAR varies significantly between the Pisgah and Peoria Loess. The MARs calculated for the Peoria Loess are among the highest last-glacial MARs in the world, but they are also shown to vary significantly over time within the Peoria Loess unit. The maximum Peoria Loess MARs are observed at ~23 ka, and they coincide with an increase in grain size identified for the middle Peoria unit by Muhs and Bettis (2000), implying a strengthening of winds at Loveland. At this time, the Laurentide Ice Sheet was at its maximum southward extent and insolation was at a minimum at high latitudes in North America, giving rise to an enhanced latitudinal temperature contrast. Such conditions, and the MAR and grain-size observations at Loveland, support the hypothesis that enhanced gustiness, generated by a steepened meridional temperature gradient, may have been a primary driver of last-glacial dustiness. References McGee, D., Broecker, W.S., and Winckler, G., 2010. Gustiness: the driver of glacial dustiness? Quaternary Science Reviews 29, 2340-2350. Muhs, D.R., and Bettis III, E.A., 2000. Geochemical variations in Peoria Loess of western Iowa indicate

  18. Characterizing the variability in precipitation-bearing storms over Central Greenland during the last glacial period

    NASA Astrophysics Data System (ADS)

    Winstrup, Mai; Svensson, Anders M.; Rasmussen, Sune O.; Ditlevsen, Peter; Kipfstuhl, Sepp; Steig, Eric J.

    2013-04-01

    A few ice core records are of sufficiently high resolution that they are able to record individual weather events. In this study, we are looking into one of these, namely the visual stratigraphy of the NGRIP ice core record from Central Greenland. We consider the evidence these data contains on variability in past precipitation-bearing storm tracks over Central Greenland during the rapid climatic changes of the last glacial. This information has implications for the variability of past circulation patterns in the North Atlantic region and their governing climate mechanisms. From the NGRIP ice core, Central Greenland, very detailed images of the visual stratigraphy in the core has been obtained. For the ice deposited during the last glacial period, the images show a clear banding of small-scale layers with a range of thicknesses. These layers are believed to be the result of individual precipitation events, which can be distinguished due to differences in their impurity concentrations. This assumption is justified by a qualitative comparison of contemporary Central Greenland weather data to the layering in early Holocene visual stratigraphy data. In combination with an accurate layer-counted chronology for the NGRIP ice core, the data allows us to look into the variability of past storminess over Central Greenland. This variability is quantified in terms of the changes in frequency and intensity of precipitation-bearing storms over the warm and cold phases of the last glacial period. Preliminary investigations show that whereas the average amount of precipitation per storm event is relatively constant with climate, the frequency of storms is changing significantly: A considerably larger number of precipitating storms per year are reaching the NGRIP drill site, Central Greenland, during the interstadials. On the other hand, inter-annual variability in the frequency of major storm occurrences is observed to be largest during the cold periods. We hypothesize that the

  19. The Salzach Valley overdeeping: A most precise bedrock model of a major alpine glacial basin

    NASA Astrophysics Data System (ADS)

    Pomper, Johannes; Salcher, Bernhard; Eichkitz, Christoph

    2016-04-01

    sedimentary succession, representing multiple cycles of massive gravels and lacustrine fines, indicate that the valley was not fully excavated during the last glacial coverage at the LGM. Through its model accuracy related to a comprehensive geodatabase and a relatively homogenous rock erodibility, the Salzach Valley overdeepening might be a highly suitable testing site for future numerical simulations.

  20. Changes on a glacial-interglacial timescale in the oceanic inventory of phosphorus and its relation to climate change

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2003-12-01

    Phosphorus (P) is an important nutrient, which, along with other macro- and micronutrients, limits productivity in oceans. On a glacial-interglacial timescale, potential variations in the oceanic inventory of P, which are invoked by changes in the continental weathering regime, may have an impact on global primary production, on CO2 drawdown from the atmosphere, and on climate. It is crucial, therefore, to constrain P inventory changes throughout glacial and interglacial periods. We present new data that illustrate how P is distributed in marine sediments and how its inventory changed during the last 150,000 years. We have applied the SEDEX techinique (Ruttenberg, 1992) on sediments from eight different Ocean Drilling Program (ODP) Sites (Northeastern Atlantic; Peru margin; Oman margin; Japan Sea; Ontong Java plateau; North Atlantic; South China Sea). Authigenic and Fe-bound minerals, and organic material represent the principal sinks of reactive P in oceanic sediments. Regardless of the environmental setting and type of sediment, P phases have been detected at all sites. Moreover, average reactive P concentrations are in the same range of values, between 0.3 and 0.6 mg/g. Only concentrations at the Oman and the Peru margin sites fall outside this interval, showing concentrations characteristic of phosphogenesis. Average concentrations calculated over glacial and interglacial periods do not show any significant difference. Changes in P distribution and concentrations in the sediments, and mass accumulation rates seem closely linked to local climatic and oceanographic conditions, but still reflect global processes (i.e., oceanic circulation and climate). On a global average, P accumulation rates in the sediments increased during the last glacial, suggesting a positive relationship between cold climate, increased physical weathering and P sink in the ocean sediments. Reactive P inventory variations seem paced by the precessional cycle (23 kyr), pointing at the

  1. Millennial-scale climate variability in response to changing glacial and orbital boundary conditions during the Mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Ferretti, Patrizia; Crowhurst, Simon; Drysdale, Russell; Bajo, Petra; Barbante, Carlo

    2016-04-01

    The Mid-Pleistocene transition represents perhaps the most important climate transition in the Quaternary period, yet it is one of the most poorly understood. Although the exact timing and mechanism of the onset of the "100 kyr" regime remain a matter of debate, it is well established that the overall periodicity of the glacial-interglacial cycles changed from a dominant 41 kyr obliquity periodicity prior to ~0.9 Ma to a dominant late Pleistocene 100 kyr variance. This change in the frequency domain was associated with an increase in the amplitude of global ice volume variations that, superimposed on a long-term climatic trend towards more glacial conditions over millions of years, produced some of the most extreme glaciations recorded. This interval of time has often been considered to be important in relation to long-term Milankovitch-scale climate variability. In contrast, here, special emphasis will be placed on assessing the presence and the characteristics of the suborbital-scale variability, and reconstructing the evolution of millennial-scale climate variability as the average climate state evolve toward generally colder conditions with larger ice sheets, and the spectral character of climate variability shifted from dominantly 41 kyr to 100 kyr. Appealing evidence suggests that millennial-scale climate variability is amplified during times of intense forcing changes, but this rapid variability has not been thoroughly explored yet at the time when the major changes in climate periodicity occurred. To address these questions, we have examined the record of climatic conditions from Marine Isotope Stages 25 to 16 (~970-650 ka) using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess millennial-scale changes in sea-surface and deep-water conditions, the dynamics of thermohaline deep-water circulation

  2. A chronology for glacial Lake Agassiz shorelines along Upham's namesake transect

    NASA Astrophysics Data System (ADS)

    Lepper, Kenneth; Buell, Alex W.; Fisher, Timothy G.; Lowell, Thomas V.

    2013-07-01

    Four traditionally recognized strandline complexes in the southern basin of glacial Lake Agassiz are the Herman, Norcross, Tintah and Campbell, whose names correspond to towns in west-central Minnesota that lie on a linear transect defined by the Great Northern railroad grade; the active corridor for commerce at the time when Warren Upham was mapping and naming the shorelines of Lake Agassiz (ca.1880-1895). Because shorelines represent static water planes, their extension around the lake margin establishes time-synchronous lake levels. Transitions between shoreline positions represent significant water-level fluctuations. However, geologic ages have never been obtained from sites near the namesake towns in the vicinity of the southern outlet. Here we report the first geologic ages for Lake Agassiz shorelines obtained at field sites along the namesake transect, and evaluate the emerging chronology in light of other paleoclimate records. Our current work from 11 sampling sites has yielded 16 independent ages. These results combined with a growing OSL age data set for Lake Agassiz's southern basin provide robust age constraints for the Herman, Norcross and Campbell strandlines with averages and standard deviations of 14.1 ± 0.3 ka, 13.6 ± 0.2 ka, and 10.5 ± 0.3 ka, respectively.

  3. Last glacial megafaunal death assemblage and early human occupation at Lake Menindee, southeastern Australia

    NASA Astrophysics Data System (ADS)

    Cupper, Matthew L.; Duncan, Jacqui

    2006-09-01

    The Tedford subfossil locality at Lake Menindee preserves a diverse assemblage of marsupials, monotremes and placental rodents. Of the 38 mammal taxa recorded at the site, almost a third are of extinct megafauna. Some of the bones are articulated or semi-articulated and include almost complete skeletons, indicating that aeolian sediments rapidly buried the animals following death. New optical ages show the site dates to the early part of the last glacial (55,700 ± 1300 yr weighted mean age). This is close to the 51,200-39,800 yr Australia-wide extinction age for megafauna suggested by Roberts et al. [2001, Science 292:1888-1892], but like all previous researchers, we cannot conclusively determine whether humans were implicated in the deaths of the animals. Although an intrusive hearth at the site dating to 45,100 ± 1400 yr ago is the oldest evidence of human occupation of the Darling River, no artifacts were identified in situ within the sub-fossil-bearing unit. Non-anthropogenic causes, such as natural senescence or ecosystem stress due to climatic aridity, probably explain the mortality of the faunal assemblage at Lake Menindee.

  4. The state and their implication of Himalayan glacial lake changes from satellite observations

    NASA Astrophysics Data System (ADS)

    Nie, Y.; Sheng, Y.; Liu, Q.; Liu, L.; Liu, S.; Zhang, Y.; Song, C.

    2015-12-01

    Glacial lake outburst floods (GLOFs)generally result in catastrophic damages and fatalities. The Himalayas, the world's highest mountains hosting large number of glaciers, have frequently suffered from GLOFs events in the past decades. Climatic warming-induced melting and retreating glaciers make glacial lakes expand obviously and urge the potential risk of GLOFs in Himalayas. However, our knowledge on the state of glacial lakes in the entire Himalayas is still limited. This study conducts a systematically satellite-based inventory to firstly reveal the evolution complex, regional difference and causes of Himalayan glacial lake changes in the whole Himalayas. Hundreds of Landsat images and Google Earth high resolution imagery were employed to extract the extents of glacial lakes at four epochs (circa1990, circa 2000, circa 2005 and circa 2010). Object-oriented mapping method was used to automatically map the lakes. In association with published glacier data (e.g., China Glacier Inventory, Randolph and GLIMS Glacier data), visual inspections and iterative checks for individual lake guarantee the accuracy of our results. This study demonstrates the spatial and topographic distributions, differences, heterogeneity of glacial lake changes and their causes. Our results show that Himalayan glacial lakes present a rapidly expanding state in general. Both disappeared lakes and new-formed lakes were observed, however, pre-existing glacial lakes contributed most to the total areal expansion. Himalayan glacial lakes appeared a clear altitudinal difference between north side and south side of main range. Evolutions of glacial lakes between eastern, western and central Himalaya were different, and the most rapidly expanding areas need to be more concerned. Climatic and geomorphic controls result in the heterogeneity of glacial lake changes. This study will help assess the potential risk of GLOFs and promote the public awareness of glacial disasters in high mountain areas.

  5. Approach to estimating the maximum depth for glacially induced hydraulic jacking in fractured crystalline rock at Forsmark, Sweden

    NASA Astrophysics Data System (ADS)

    Lönnqvist, M.; Hökmark, H.

    2013-09-01

    Hydraulic jacking is a significant dilation of a fracture that occurs when the pore pressure within it exceeds the sum of the fracture's normal stress and tensile strength. This phenomenon may occur during a glacial period because of changes in hydraulic and mechanical boundary conditions. Since hydraulic jacking may alter flow patterns and the transport capacity of the rock mass, its possible effects on the long-term performance of a nuclear waste repository should be considered. We develop an approach to assess glacially induced hydraulic jacking in fractured crystalline rock and establish bounding estimates of the maximum jacking depth for the Swedish Nuclear Fuel and Waste Management Company's (SKB) repository site at Forsmark. The pore pressure is estimated using mechanically uncoupled two-dimensional poroelastic continuum models with hydraulic and mechanical conditions based on SKB's reconstruction of the Weichselian glaciation at this site (120-0 ka B.P.). For warm-based conditions, the water pressure at the ice/bed interface is set at 98% of the mechanical load, whereas for glacial conditions with extensive proglacial permafrost, the corresponding water pressure is set at a (lower) annual average value. We demonstrate that the pore pressure within the uppermost kilometer of rock is mainly governed by the water pressure at the ice/bed interface and that the mechanical impact of the ice load on the pore pressure is sufficiently small to be ignored. Given the current and estimated future stress conditions at Forsmark, hydraulic jacking is mainly of concern for subhorizontal fractures, i.e., it is sufficient to consider situations when the pore pressure exceeds the vertical stress. We conclude that hydraulic jacking at Forsmark will be confined to the uppermost 200 m of the rock mass.

  6. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-?15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J. A.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2013-12-01

    Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air- δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model- δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

  7. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2013-05-01

    Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model-δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

  8. Glacial hazards: communicating the science and managing the risk

    NASA Astrophysics Data System (ADS)

    Reynolds, J. M.

    2009-04-01

    The recession of glaciers worldwide has received huge media coverage over the last few years in association with the issue of climate change. Young people at schools and colleges are increasingly aware of the environmental pressures due to ‘global warming'. Yet simultaneously, there appears to be an increasing move away from studying science both at pre-university and undergraduate levels. One of the oft cited reasons is that students cannot see the application of the subjects being taught them. Glacial hazards are one of the most obvious adverse effects of climate change, with many, often poor, communities in remote mountain areas being the most affected by frequently devastating Glacial Lake Outburst Floods (GLOFs). When students are exposed to examples of these hazards and the science behind them, many become enthused by the subject and want to study it further. There has been a huge increase in the number of students selecting projects on glacial hazards as well as a large increase in the number of institutions offering to teach modules on this subject. In an effort to provide a basic visualisation, Peter Kennett has taken the principle of GLOFs and developed a cheap but highly visual demonstration of the potentially devastating effect of melting ice within a moraine leading to subsidence and subsequent dam failure. This is available on www.earthlearningidea.com as ‘Dam burst danger - modelling the collapse of a natural dam in the mountains - and the disaster that might follow'. Furthermore, the methods by which glacial hazards are assessed provide excellent applications of geophysics, geology, geography (physical and Human), engineering, mathematics, and glaciology. By exploring the potential vulnerability of communities downstream, the applications can be extended to include sociology, economics, geopolitics and even psychology. Glacial hazards have been the subject of presentations to the Earth Science Teachers Association (ESTA) in the UK to demonstrate

  9. Turbidite megabeds in an Oceanic Rift Valley recording jokulhlaups of late Pleistocene glacial lakes of the western United States

    USGS Publications Warehouse

    Zuffa, G.G.; Normark, W.R.; Serra, F.; Brunner, C.A.

    2000-01-01

    Escanaba Trough is the southernmost segment of the Gorda Ridge and is filled by sandy turbidites locally exceeding 500 m in thickness. New results from Ocean Drilling Program (ODP) Sites 1037 and 1038 that include accelerator mass spectrometry (AMS) 14C dates and revised petrographic evaluation of the sediment provenance, combined with high-resolution seismic-reflection profiles, provide a lithostratigraphic framework for the turbidite deposits. Three fining-upward units of sandy turbidites from the upper 365 m at ODP Site 1037 can be correlated with sediment recovered at ODP Site 1038 and Deep Sea Drilling Program (DSDP) Site 35. Six AMS 14C ages in the upper 317 m of the sequence at Site 1037 indicate that average deposition rates exceeded 10 m/k.yr. between 32 and 11 ka, with nearly instantaneous deposition of one ~60-m interval of sand. Petrography of the sand beds is consistent with a Columbia River source for the entire sedimentary sequence in Escanaba Trough. High-resolution acoustic stratigraphy shows that the turbidites in the upper 60 m at Site 1037 provide a characteristic sequence of key reflectors that occurs across the floor of the entire Escanaba Trough. Recent mapping of turbidite systems in the northeast Pacific Ocean suggests that the turbidity currents reached the Escanaba Trough along an 1100-km-long pathway from the Columbia River to the west flank of the Gorda Ridge. The age of the upper fining-upward unit of sandy turbidites appears to correspond to the latest Wisconsinan outburst of glacial Lake Missoula. Many of the outbursts, or jokulhlaups, from the glacial lakes probably continued flowing as hyperpycnally generated turbidity currents on entering the sea at the mouth of the Columbia River.

  10. Mid-late Pleistocene glacial evolution in the Grove Mountains, East Antarctica, constraints from cosmogenic 10Be surface exposure dating of glacial erratic cobbles

    NASA Astrophysics Data System (ADS)

    Dong, Guocheng; Huang, Feixin; Yi, Chaolu; Liu, Xiaohan; Zhou, Weijian; Caffee, Marc W.

    2016-08-01

    Glacial histories from the East Antarctic Ice Sheet (EAIS) provide keys to understanding correlations between the EAIS and global climate. They are especially helpful in the assessment of global sea level change, and as a means of quantifying the magnitude of past glacial activity and the rate at which ice responded to climate change. Given the significance of EAIS glacial histories, it is imperative that more glacial chronologic data for this region be obtained, especially for the mid-to-late Pleistocene. We report cosmogenic 10Be surface exposure dating results from glacially transported cobbles embedded in blue-ice moraine material at Mount Harding, the Grove Mountains, EAIS. Forty exotic cobbles sampled along two profiles (A and B) on this blue-ice moraine present apparent exposure-ages ranging from 7.2 to 542.2 ka. We explore this scattered dataset by using Principal Component Analysis (PCA) to identify statistically significant trends in the data. We identify a correlation between exposure-age and distance of the cobbles from Mount Harding. In profile A, cobbles further from Mount Harding yield older exposure-ages than those that are relatively close. In profile B, cobbles closer to Mount Harding are found to have relatively older exposure-ages. In term of glacial history we suggest that the direction of ice flow changed during the period from ∼60 to 200 ka, and that multiple glacial fluctuations occurred in the mid-late Pleistocene.

  11. Beryllium-10 dating of the duration and retreat of the last pinedale glacial sequence.

    PubMed

    Gosse, J C; Klein, J; Lawn, B; Middleton, R; Evenson, E B

    1995-06-01

    Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 +/- 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 +/- 500 beryllium-10 years.

  12. Beryllium-10 dating of the duration and retreat of the last pinedale glacial sequence.

    PubMed

    Gosse, J C; Klein, J; Lawn, B; Middleton, R; Evenson, E B

    1995-06-01

    Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 +/- 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 +/- 500 beryllium-10 years. PMID:17778979

  13. Beryllium-10 dating of the duration and retreat of the last pinedale glacial sequence

    SciTech Connect

    Gosse, J.C. |; Klein, J.; Evenson, E.B.

    1995-06-02

    Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 {+-} 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 {+-} 500 beryllium-10 years.

  14. SEM microfabric analysis of glacial varves, Geneseo, N. Y

    SciTech Connect

    Pietraszek, S.R. . Geology Dept.)

    1993-03-01

    A detailed study of the microfabric of Pleistocene varved silty-clay from Geneseo Valley (Geneseo, N.Y.) indicates rapid deposition of sediment in a flocculated state into a glacial lake. Ten varve couplets of a 10 cm thick sample were studied using the Scanning Electron Microscope to determine their microfabric. Each varve ranges from 0.5 cm to 2.0 cm and represents an annual ( ) deposit. Varves consists of a lower light colored, coarse zone of silt and clay, and an upper darker colored, organic fine clayey zone. Graded bedding is observed in each couplet, and random clay particle orientation is dominant throughout a varve, with the exception of the top 0.5 mm of the fine layer. The upper and lower contacts are sharp. Fabric features are instrumental in reconstructing a depositional environment. Microfabric results of the glacial unit indicate that an initial heavy concentration of clay and silt was introduced into the basin in a single pulse during spring runoff. The majority of silt settled together with clay in a flocculated or aggregated state, forming the lower coarse zone of random orientation. As the silt concentration diminished, the clay continued to flocculate and settled as a fine clay aggregate. It is proposed that the settling took place during the spring and summer months. Finally, during the winter months, the sediment surface of the varve was disturbed by nemotode burrows, which reoriented the clay flakes into a zone of preferred fabric. Microfabric analysis of these glacial varves, thus suggests that sediment was rapidly deposited in a flocculated state.

  15. Glacial greenhouse-gas fluctuations controlled by ocean circulation changes.

    PubMed

    Schmittner, Andreas; Galbraith, Eric D

    2008-11-20

    Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO(2)) and nitrous oxide (N(2)O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N(2)O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO(2). Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature, as well as CO(2) and N(2)O fluctuations. Despite significant changes in the land carbon inventory, CO(2) variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N(2)O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO(2) and N(2)O fluctuations on millennial timescales.

  16. Assessment of Potentially Dangerous Glacial Lakes in Chinese Himalayas

    NASA Astrophysics Data System (ADS)

    Xiaojun, Yao; Shiyin, Liu; Xin, Wang

    2010-05-01

    Glacial lake outburst floods (GLOFs) are catastrophic discharges of water resulting primarily from melting glaciers. In the face of global warming, most Himalayan glaciers have been retreating at a rate that ranges from a few meters to several tens of meters per year, resulting in an increase in the number and size and size of glacial lakes and a concomitant increase in the threat of GLOFs. In the past 50 years, 16 GLOF events which were reported in Tibet had caused the loss of human lives as well as severe damage to local infrastructure. Based on the combination of temperature and precipitation of these 14 failed moraine-dammed lakes, the climatic background could be classified into 4 types, that is, warm-wet, warm-arid, cold-wet and near common weather condition. Under different climatic background types, the outburst mechanisms can be further divided into 5 types and 21 modes based on the analysis of 31 failed moraine-dammed lakes documented all over the world. As to a potentially dangerous moraine-dammed lake, all possible breach modes under each climatic background are firstly described and its qualitative possibilities are given by experts, then the decision-making trees are formed and the breach probability of the potentially dangerous moraine-dammed lake can be calculate. The breaching probabilities of the 143 potentially dangerous moraine-dammed lakes were calculated one by one using the decision-making trees model in Chinese Himalayas. The calculating results show that there are 44 lakes with very high breaching probability, 47 lakes with high breaching probability, 24 lakes with median breaching probability, 24 lakes with low breaching probability, 4 lakes with very low breaching probability. The 91 lakes with very high and high breaching probability rate should be requested in the next steps of detailed assessment and should be took into account in local infrastructure construction, such as road, hydropower station and residential plan, etc. Key words

  17. Analysis of glacial and periglacial processes using structure from motion

    NASA Astrophysics Data System (ADS)

    Piermattei, L.; Carturan, L.; de Blasi, F.; Tarolli, P.; Dalla Fontana, G.; Vettore, A.; Pfeifer, N.

    2015-11-01

    Close-range photo-based surface reconstruction from the ground is rapidly emerging as an alternative to lidar (light detection and ranging), which today represents the main survey technique in many fields of geoscience. The recent evolution of photogrammetry, incorporating computer vision algorithms such as Structure from Motion (SfM) and dense image matching such as Multi-View Stereo (MVS), allows the reconstruction of dense 3-D point clouds for the photographed object from a sequence of overlapping images taken with a digital consumer camera. The objective of our work was to test the accuracy of the ground-based SfM-MVS approach in calculating the geodetic mass balance of a 2.1 km2 glacier in the Ortles-Cevedale Group, Eastern Italian Alps. In addition, we investigated the feasibility of using the image-based approach for the detection of the surface displacement rate of a neighbouring active rock glacier. Airborne laser scanning (ALS) data were used as benchmarks to estimate the accuracy of the photogrammetric DTMs and the reliability of the method in this specific application. The glacial and periglacial analyses were performed using both range and image-based surveying techniques, and the results were then compared. The results were encouraging because the SfM-MVS approach enables the reconstruction of high-quality DTMs which provided estimates of glacial and periglacial processes similar to those achievable by ALS. Different resolutions and accuracies were obtained for the glacier and the rock glacier, given the different survey geometries, surface characteristics and areal extents. The analysis of the SfM-MVS DTM quality allowed us to highlight the limitations of the adopted expeditious method in the studied alpine terrain and the potential of this method in the multitemporal study of glacial and periglacial areas.

  18. Deepwater redox changes in the southern Okinawa Trough since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Dou, Yanguang; Yang, Shouye; Li, Chao; Shi, Xuefa; Liu, Jihua; Bi, Lei

    2015-06-01

    In this study, rare earth element (REE) was treated as a paleo-redox proxy to investigate the changes of depositional environment in the southern Okinawa Trough since the last glacial maximum. The acid-leachable fraction (leachate) of the sediments recovered from the ODP Site 1202B is dominated by biogenic and authigenic components while detrital contamination is minor. The significant enrichment of middle REE suggests a large contribution from authigenic Mn oxyhydroxides and cerium (Ce) anomaly can indicate deepwater redox change. The REE parameters including Ce anomaly in the leachate exhibit remarkable and abrupt changes in the early Holocene (∼9.5 ka) and during LGM (∼20 ka). An increase of Ce anomaly at 28-22 ka implies the suboxic deepwater condition probably caused by increased primary productivity. Weak positive Ce anomalies during the last glacial maximum and deglaciation suggest an oxic depositional environment responding to the enhanced deepwater ventilation with the advection of the North Pacific Intermediate Water and/or South China Sea Intermediate Water into the trough. A decrease of Ce anomaly in the early Holocene might be caused by the intrusion and strengthening of the Kuroshio Current in the trough that enhanced the water stratification and induced a gradual development of suboxic depositional condition. Furthermore, an abrupt change of chemical composition at ca. 4 ka probably indicates a decrease of dissolved oxygen in deepwater and a weakening of ventilation in the Okinawa Trough. This study suggests that REE proxy can provide new insights into the linkage among surface current, deepwater circulation and sediment record in the continental margin where terrigenous input dominates.

  19. Simulating soil organic carbon in yedoma deposits during the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Zhu, Dan; Peng, Shushi; Ciais, Philippe; Zech, Roland; Krinner, Gerhard; Zimov, Sergey; Grosse, Guido

    2016-04-01

    Substantial quantities of organic carbon (OC) are stored in the thick, ice-rich and organic-rich silty sediments called yedoma deposits, distributed in Eastern Siberia and Alaska today. Yedoma deposits were accumulated during tens of thousands of years of the last ice age, under very dry and cold conditions favoring dust deposition and hill-slope erosion to build up thick deposits in unglaciated lowlands and hillslopes. Quantifying yedoma carbon stocks during the glacial period is important for understanding how much carbon was stored on land and, subsequently, how much could have been decomposed during the last deglaciation. Yet processes that yield to the formation of thick frozen carbon stocks in yedoma deposits are missing in land carbon cycle models. Here we incorporate sedimentation parameterizations into the ORCHIDEE global land surface model that was run across the Northern Hemisphere with Last Glacial Maximum (LGM) climate conditions. Sedimentation coupled to vertical mixing of soil carbon by cryoturbation and frozen soil hydrology led to reasonable modeled OC vertical distribution and regional budgets, compared with site-specific observations and inventories for today's non-degraded yedoma region. Simulated total soil OC stock over the full depth in the model (0-47.5m) for the northern permafrost region during the LGM is 1536~1592 PgC, including non-yedoma frozen carbon (1146 PgC) and yedoma OC within today's yedoma region only (390~446 PgC). This result is an underestimation since we did not account for the potentially much larger area of yedoma during the LGM than present-day.

  20. Carbonate chemistry of intermediate waters in the Southwest Pacific Ocean since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Allen, K. A.; Sikes, E. L.; Elmore, A.; Hoenisch, B.; deMenocal, P. B.; Rosenthal, Y.

    2013-12-01

    Shifts in ocean circulation and marine carbon storage likely played an important role in the termination of the last ice age, but the mechanisms driving these changes have not yet been fully explained. It has been suggested that a greater amount of CO2 was stored in the deep sea during glacial periods via the biologic pump and/or increased uptake by a more alkaline ocean. To quantify the relative roles of such processes, more constraints on past deep ocean alkalinity are needed. Here, we present a new record of deep water carbonate chemistry for the last 30,000 years derived from a sediment core located at 1,627 meters depth in New Zealand's Bay of Plenty. Today, this core site lies at the boundary between relatively fresh Antarctic/Tasman Intermediate Water (above), and Circumpolar Deep Water (below) with more corrosive Pacific Deep Water also intruding from the north. Trace element and stable isotopic composition of foraminiferal calcite (the epibenthic species Cibicidoides wuellerstorfi) reveal changes in bottom water carbonate chemistry during periods of atmospheric CO2 change. The boron to calcium ratio (B/Ca) in these shells indicates that deep water saturation (ΔCO32-) during the last glacial maximum (LGM) was only 5 μmol kg-1 less than the modern value of ~ 20 μmol/kg, consistent with previous work identifying the Pacific as a 'well-buffered' ocean basin on long timescales. However, reconstructed ΔCO32- values fluctuated by as much as 30 μmol/kg across the deglaciation, exhibiting the most pronounced changes between 17 and 13 ka. Together with shifts in carbon isotopes, these results imply changes in circulation and/or respired CO2 storage, and support a series of events in which major oceanographic changes are intimately linked with shifts in atmospheric circulation.

  1. Isolation and preliminary characterization of aerobic heterotrophic bacteria isolated from sub-glacial Antarctic water samples

    NASA Astrophysics Data System (ADS)

    Palma-Alvarez, R.; Lanoil, B. D.

    2002-05-01

    Recently, evidence has been accumulating supporting the presence of biogeochemically active microbial communities in cold, dark, and isolated subglacial environments. These environments are important sites of rock weathering, provide insight into global biogeochemistry during glacial periods, and are potential analogues for ancient Snowball Earth events and the ice-covered oceans of the Jovian moon, Europa. However, the extent of microbial influence on subglacial geochemistry is unclear. As part of an ongoing project to address the extent of that influence, we isolated aerobic heterotrophic bacteria from sediment-laden water from beneath Ice Stream C, a fast moving region of the Western Antarctic Ice Sheet (WAIS). Plates of a standard environmental media (R2A) were prepared at three dilutions (1x, 0.1x, 0.01x) and inoculated in duplicate in a HEPA-filtered environment. One replicate was incubated at 4oC, the other at room temperature in the dark. All plates showed abundant growth, although colony size was positively correlated with media concentration. One-hundred eighty-one colonies total were picked, grown in liquid R2A (1x concentration) at the same initial temperature, and characterized for Gram character, cell shape, cell size, and production of a diffusible yellow pigment with similar chemical characteristics to the siderophore, pyoverdine. Based on these characters, a moderate level of diversity was observed in these isolates. A few types dominated the samples, with several others found only rarely. Further characterization of these isolates is ongoing, and results of these studies and their possible implications for sub-glacial biogeochemistry are discussed.

  2. Bathymetry and temperature of some glacial lakes in Wyoming

    PubMed Central

    Leopold, Luna B.

    1980-01-01

    On the west flank of the Wind River Mountains, Wyoming, are several large lakes occupying glacially scoured depressions dammed by terminal moraines. Fremont, Willow, and New Fork Lakes, having maximal depths of 185, 85, and 62 m, respectively, are not only deep, but in 1970-1978 they had no measurable coliform. They have exceptionally low values of total dissolved solids; Fremont Lake has only 12.8 mg/liter, probably the second most dilute large lake in coterminus United States. Summer mixing is restricted to the uppermost 10 m, below which the lakes are essentially isothermal at the maximum density temperature, about 3.9°C. PMID:16592797

  3. Bathymetry and temperature of some glacial lakes in Wyoming.

    PubMed

    Leopold, L B

    1980-04-01

    On the west flank of the Wind River Mountains, Wyoming, are several large lakes occupying glacially scoured depressions dammed by terminal moraines. Fremont, Willow, and New Fork Lakes, having maximal depths of 185, 85, and 62 m, respectively, are not only deep, but in 1970-1978 they had no measurable coliform. They have exceptionally low values of total dissolved solids; Fremont Lake has only 12.8 mg/liter, probably the second most dilute large lake in coterminus United States. Summer mixing is restricted to the uppermost 10 m, below which the lakes are essentially isothermal at the maximum density temperature, about 3.9 degrees C.

  4. Bathymetry and temperature of some glacial lakes in Wyoming.

    PubMed

    Leopold, L B

    1980-04-01

    On the west flank of the Wind River Mountains, Wyoming, are several large lakes occupying glacially scoured depressions dammed by terminal moraines. Fremont, Willow, and New Fork Lakes, having maximal depths of 185, 85, and 62 m, respectively, are not only deep, but in 1970-1978 they had no measurable coliform. They have exceptionally low values of total dissolved solids; Fremont Lake has only 12.8 mg/liter, probably the second most dilute large lake in coterminus United States. Summer mixing is restricted to the uppermost 10 m, below which the lakes are essentially isothermal at the maximum density temperature, about 3.9 degrees C. PMID:16592797

  5. Early Pleistocene Glacial Cycles and the Integrated Summer Insolation Forcing

    NASA Astrophysics Data System (ADS)

    Huybers, Peter

    2006-07-01

    Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun.

  6. Glacial processes and morphologies in the southern hemisphere of Mars

    NASA Astrophysics Data System (ADS)

    Banks, Maria Elaine

    2009-06-01

    Understanding the history of ice on Mars provides important insight into Martian geologic and climatic history. A model capable of ice reconstruction that requires few input parameters, and a detailed analyses of landforms in an area with hypothesized glacial modification, Argyre Planitia, provide further understanding of Martian ice. A threshold-sliding model was developed to model perfectly-plastic deformation of ice that is applicable to ice bodies that deform when a threshold basal shear stress is exceeded. The model requires three inputs describing bed topography, ice margins, and a function defining the threshold basal shear stress. The model was tested by reconstructing the Greenland ice sheet and then used to reconstruct ice draping impact craters on the margins of the Martian South Polar Layered Deposits using an average constant basal shear stress of ~0.6 bars for the majority of Martian examples. This inferred basal shear stress value is almost 1/3 of the average basal shear stress calculated for the Greenland ice sheet. Reasons for the lower Martian basal shear stress are unclear but could involve the strain-weakening behavior of ice. The threshold- sliding model can be used for ice reconstruction and forward modeling of erosion and deposition to provide further insight into the history of ice on Mars. To test the glacial hypothesis in the Argyre region, landforms are examined using images from the High Resolution Imaging Science Experiment (HiRISE) and other Martian datasets. Linear grooves and streamlined hills are consistent with glacial erosion. Deep semi-circular embayments in mountains resemble cirques. U-shaped valleys have stepped longitudinal profiles and tributary valleys have hanging valley morphology similar to terrestrial glacial valleys. Boulders blanketing a valley floor resemble ground moraine. Sinuous ridges cross topography, have layers, occur in troughs, and have variations in height that appear related to the surrounding surface

  7. Early Pleistocene glacial cycles and the integrated summer insolation forcing.

    PubMed

    Huybers, Peter

    2006-07-28

    Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun. PMID:16794041

  8. Glacial-to-interglacial Changes in NADW Fluxes?

    NASA Technical Reports Server (NTRS)

    Mix, A. C.; Fairbanks, R. G.

    1984-01-01

    Interglacial gradients in delta 13C between Atlantic and Pacific deep waters reflect differences between low-nutrient, 13C-enriched North Atlantic Deep Water (NADW) and high-nutrient, 13C-depleted Pacific Deep Water. Reduced Atlantic-Pacific delta 13C and cadmium gradients at the last glacial maximum have been used to suggest substantial replacement of NADW with nutrient-rich Antarctic Bottom Water (Boyle and Keigwin, 1982; Shackleton et al., 1983). We show that the Atlantic delta 13C signal is linked directly to North Atlantic polar-front migration, as reflected by planktonic foraminiferal faunas.

  9. Last Glacial vegetation and climate change in the southern Levant

    NASA Astrophysics Data System (ADS)

    Miebach, Andrea; Chen, Chunzhu; Litt, Thomas

    2015-04-01

    Reconstructing past climatic and environmental conditions is a key task for understanding the history of modern mankind. The interaction between environmental change and migration processes of the modern Homo sapiens from its source area in Africa into Europe is still poorly understood. The principal corridor of the first human dispersal into Europe and also later migration dynamics crossed the Middle East. Therefore, the southern Levant is a key area to investigate the paleoenvironment during times of human migration. In this sense, the Last Glacial (MIS 4-2) is particularly interesting to investigate for two reasons. Firstly, secondary expansions of the modern Homo sapiens are expected to occur during this period. Secondly, there are ongoing discussions on the environmental conditions causing the prominent lake level high stand of Lake Lisan, the precursor of the Dead Sea. This high stand even culminated in the merging of Lake Lisan and Lake Kinneret (Sea of Galilee). To provide an independent proxy for paleoenvironmental reconstructions in the southern Levant during the Last Glacial, we investigated pollen assemblages of the Dead Sea/Lake Lisan and Lake Kinneret. Located at the Dead Sea Transform, the freshwater Lake Kinneret is nowadays connected via the Jordan with the hypersaline Dead Sea, which occupies Earth's lowest elevation on land. The southern Levant is a transition area of three different vegetation types. Therefore, also small changes in the climate conditions effect the vegetation and can be registered in the pollen assemblage. In contrast to the Holocene, our preliminary results suggest another vegetation pattern during the Last Glacial. The vegetation belt of the fragile Mediterranean biome did no longer exist in the vicinity of Lake Kinneret. Moreover, the vegetation was rather similar in the whole study area. A steppe vegetation with dwarf shrubs, herbs, and grasses predominated. Thermophilous elements like oaks occurred in limited amounts. The

  10. Glacial evolution of the Ampato Volcanic Complex (Peru)

    NASA Astrophysics Data System (ADS)

    Alcalá, J.; Palacios, D.; Zamorano, J. J.; Vázquez, L.

    2009-04-01

    Ice masses on the Western range of the Central Andes are a main source of water resources and act as a geoindicator of variations in the climate of the tropics (Mark, 2008). The study of their evolution is of particular interest since they are situated in the transition zone between the tropical and mid-latitude circulation areas of the atmosphere (Zech et al., 2007). The function of this transition area is currently under debate, and understanding it is essential for the development of global climate models (Kull et al, 2008; Mark, 2008). However our understanding of the evolution of glaciers and their paleoclimatic factors for this sector of the Central Andes is still at a very basic level. This paper presents initial results of a study on the glacial evolution of the Ampato volcanic complex (15°24´- 15° 51´ S, 71° 51´ - 73° W; 6288 m a.s.l.) located in the Western Range of the Central Andes in Southern Peru, 70 km NW of the city of Arequipa. The main objectives are to identify the number of glacial phases the complex has undergone using geomorphological criteria to define a time frame for each phase, based on cosmogenic 36Cl dating of a sequence of moraine deposits; and to estimate the glacier Equilibrium Line Altitude (ELA) of each phase. The Ampato volcanic complex is formed by 3 great andesitic stratovolcanoes, the Nevados HualcaHualca-Sabancaya-Ampato, which started forming between the late Miocene and early Quaternary (Bulmer et al., 1999), aligned N-S and with summits covered with glaciers. The Sabancaya volcano is fully active, with its latest eruption occurring in 2001. Glacial landforms were identified and mapped using photointerpretation of vertical aerial photographs from 1955 (1:35,000 scale, National Geographic Institute of Peru), oblique photographs from 1943 (Aerophotographical Service of Peru), and a geo-referenced high-resolution Mrsid satellite image from 2000 (NASA). This cartography was corrected and improved through fieldwork. It was

  11. Deciphering the Glacial-Interglacial Landscape History in Greenland Based on Markov Chain Monte Carlo Inversion of Existing 10Be-26Al Data

    NASA Astrophysics Data System (ADS)

    Strunk, A.; Knudsen, M. F.; Larsen, N. K.; Egholm, D. L.; Jacobsen, B. H.

    2015-12-01

    Surface exposure dating with cosmogenic nuclides is a dating method under continuous development. It is particularly useful for dating ice-sheet fluctuations in glacial environments, which is essential to increase our understanding of past climate fluctuations and glacial dynamics. Constraining the landscape history in previously glaciated terrains may be difficult, however, due to unknown erosion rates and the presence of inherited nuclides. The potential use of cosmogenic nuclides in landscapes with a complex history of exposure and erosion is therefore often quite limited. In this study, we investigate the landscape history in eastern and western Greenland by applying a novel Markov Chain Monte Carlo (MCMC) inversion approach to the existing 10Be-26Al data from these regions. The new MCMC approach allows us to constrain the most likely landscape history based on comparisons between simulated and measured cosmogenic nuclide concentrations. It is a fundamental assumption of the model approach that the exposure history at the site/location can be divided into two distinct regimes: i) interglacial periods characterized by zero shielding due to overlying ice and a uniform interglacial erosion rate, and ii) glacial periods characterized by 100 % shielding and a uniform glacial erosion rate. We incorporate the exposure/burial history in the model framework by applying a threshold value to the global marine benthic d18O record and include the threshold value as a free model parameter, hereby taking into account global changes in climate. The other free parameters include the glacial and interglacial erosion rates as well as the timing of the Holocene deglaciation. The model essentially simulates numerous different landscape scenarios based on these four parameters and zooms in on the most plausible combination of model parameters. Here, we apply the MCMC-model to the concentrations of 10Be and 26Al measured in three previous studies of glacial fluctuations in Greenland

  12. Evidence of macroalgal colonization on newly ice-free areas following glacial retreat in Potter Cove (South Shetland Islands), Antarctica.

    PubMed

    Quartino, María Liliana; Deregibus, Dolores; Campana, Gabriela Laura; Latorre, Gustavo Edgar Juan; Momo, Fernando Roberto

    2013-01-01

    Climate warming has been related to glacial retreat along the Western Antarctic Peninsula. Over the last years, a visible melting of Fourcade Glacier (Potter Cove, South Shetland Islands) has exposed newly ice-free hard bottom areas available for benthic colonization. However, ice melting produces a reduction of light penetration due to an increase of sediment input and higher ice impact. Seventeen years ago, the coastal sites close to the glacier cliffs were devoid of macroalgae. Are the newly ice-free areas suitable for macroalgal colonization? To tackle this question, underwater video transects were performed at six newly ice-free areas with different degree of glacial influence. Macroalgae were found in all sites, even in close proximity to the retreating glacier. We can show that: 1. The complexity of the macroalgal community is positively correlated to the elapsed time from the ice retreat, 2. Algae development depends on the optical conditions and the sediment input in the water column; some species are limited by light availability, 3. Macroalgal colonization is negatively affected by the ice disturbance, 4. The colonization is determined by the size and type of substrate and by the slope of the bottom. As macroalgae are probably one of the main energy sources for the benthos, an expansion of the macroalgal distribution can be expected to affect the matter and energy fluxes in Potter Cove ecosystem.

  13. Sensitivity of palaeotidal models of the northwest European shelf seas to glacial isostatic adjustment since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ward, Sophie L.; Neill, Simon P.; Scourse, James D.; Bradley, Sarah L.; Uehara, Katsuto

    2016-11-01

    The spatial and temporal distribution of relative sea-level change over the northwest European shelf seas has varied considerably since the Last Glacial Maximum, due to eustatic sea-level rise and a complex isostatic response to deglaciation of both near- and far-field ice sheets. Because of the complex pattern of relative sea level changes, the region is an ideal focus for modelling the impact of significant sea-level change on shelf sea tidal dynamics. Changes in tidal dynamics influence tidal range, the location of tidal mixing fronts, dissipation of tidal energy, shelf sea biogeochemistry and sediment transport pathways. Significant advancements in glacial isostatic adjustment (GIA) modelling of the region have been made in recent years, and earlier palaeotidal models of the northwest European shelf seas were developed using output from less well-constrained GIA models as input to generate palaeobathymetric grids. We use the most up-to-date and well-constrained GIA model for the region as palaeotopographic input for a new high resolution, three-dimensional tidal model (ROMS) of the northwest European shelf seas. With focus on model output for 1 ka time slices from the Last Glacial Maximum (taken as being 21 ka BP) to present day, we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea-level distribution. The new high resolution palaeotidal model is considered a significant improvement on previous depth-averaged palaeotidal models, in particular where the outputs are to be used in sediment transport studies, where consideration of the near-bed stress is critical, and for constraining sea level index points.

  14. Glacial sequence stratigraphy reveal the Weichselian glacial history of the SE sector of the Eurasian Ice Sheet

    NASA Astrophysics Data System (ADS)

    Räsänen, Matti

    2016-04-01

    Reconstructions of the last Weichselian glacial cycle 117,000-11,700 years (kyr) ago propose that S Finland, adjacent Russia and the Baltic countries in the SE sector of the Eurasian Ice Sheet (EIS), were glaciated during the Middle Weichselian time [marine isotope stage (MIS) 4, 71-57 kyr ago] and that this glaciation was preceded in S Finland by an Early Weichselian interstadial (MIS 5c, 105-93 kyr ago) with pine forest. Here glacial sequence stratigraphy (Powell and Cooper 2002) is applied to isolated Late Pleistocene onshore outcrop sections in S Finland. The analysed sedimentary records have traditionally been investigated, interpreted and published separately by different authors without an attempt to a methodologically more systematic survey. By putting new field data and old observations into a regional sequence stratigraphic framework it is shown how previously unnoticed regularities can be found in the lithofacies and fossil successions. It is shown that the proposed Middle Weichselian glaciation or the pine dominated interstadial did not take place at all (Räsänen et al. 2015). The one Late Weichselian glaciation (MIS 2, 29-11 kyr ago) at the SE sector of EIS was preceded in S Finland by a nearly 90 kyr long still poorly known non-glacial period, featuring tundra with permafrost and probably birch forest. The new Middle Weichselian paleoenvironmental scenario revises the configuration and hydrology of the S part of EIS and gives new setting for the evolution of Scandinavian biota. References Powell, R. D., and Cooper, J. M., 2002, A glacial sequence stratigraphic model for temperate, glaciated continental shelves, in Dowdeswell, J. A., and Cofaig, C. Ó. eds., Glacier-Influenced Sedimentation on High-Latitude Continental Margins: The Geological Society of London, London, Geological Society London, Special Publication v. 203, p. 215-244. Räsänen, M.E., Huitti, J.V., Bhattarai, S. Harvey, J. and Huttunen, S. 2015, The SE sector of the Middle

  15. Tentative correlation of midcontinent glacial sequence with marine chronology

    SciTech Connect

    Dube, T.E.

    1985-01-01

    A tentative glacial-interglacial 3-million-year chronology is synthesized by regional correlation of Midcontinent tills and paleosols to marine paleotemperature/eustatic cycles and oxygen isotope stages. The paleotemperature curves of Beard et al. (1982), based on planktonic foraminiferal abundances, correspond directly with eustatic cycles during the last 3 Ma. These generalized curves are shown to correlate reasonably well with standard oxygen isotope stages at least for the past 900 ka. This indicates that paleotemperature and Vail-type eustatic cycles have been glacially induced during the last 3 Ma. The chronology developed here utilizes both paleotemperature and oxygen isotope stages; however, below the Jaramillo magnetic subchron, isotope curves are more variable and only paleotemperature stages are used. Tills and paleosols at type localities in the Midcontinent area of the US are correlated to the SPECMAP oxygen isotope time scale. Because mid-Brunhes events are poorly constrained by radiometric dates, alternative correlations are possible. The oldest known Midcontinent tills correlate to the first Plio-Pleistocene cold paleotemperature stage and drop in sea level at 2.4 Ma. This Late Pliocene event also corresponds to the first major isotopic enrichment and the onset of late Cenozoic ice-rafting in the North Atlantic region.

  16. Intensified deep Pacific inflow and ventilation in Pleistocene glacial times.

    PubMed

    Hall, I R; McCave, I N; Shackleton, N J; Weedon, G P; Harris, S E

    2001-08-23

    The production of cold, deep waters in the Southern Ocean is an important factor in the Earth's heat budget. The supply of deep water to the Pacific Ocean is presently dominated by a single source, the deep western boundary current east of New Zealand. Here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep-water properties and speed changes during the Pleistocene epoch. In physical and isotope proxies we find evidence for intensified deep Pacific Ocean inflow and ventilation during the glacial periods of the past 1.2 million years. The changes in throughflow may be directly related to an increased production of Antarctic Bottom Water during glacial times. Possible causes for such an increased bottom-water production include increasing wind strengths in the Southern Ocean or an increase in annual sea-ice formation, leaving dense water after brine rejection and thereby enhancing deep convection. We infer also that the global thermohaline circulation was perturbed significantly during the mid-Pleistocene climate transition between 0.86 and 0.45 million years ago.

  17. The importance of equilibration in glacial climate simulations

    NASA Astrophysics Data System (ADS)

    Brandefelt, Jenny; Kjellström, Erik; Näslund, Jens-Ove; Strandberg, Gustav; Voelker, Antje; Wohlfarth, Barbara

    2010-05-01

    Last Glacial Maximum (21 000 yrs BP; LGM) and Greenland Stadial 12 (44 000 yrs BP; GS12) climate has been simulated with the National Centre for Atmospheric Research (NCAR) Community Climate System Model version 3 (CCSM3). Although the simulations were initiated from simulated glacial climates, both simulations required 1500 years of additional integration to reach equilibrium under the imposed boundary conditions and forcings. The annual global mean surface temperature changes by only 0.1oC during the last 1000 years of the 1500 year long GS12 simulation. Despite this small global change the slow equilibration is important for the simulated regional climate. The corresponding change in the annual mean surface air temperature in the North Atlantic region is more than 3oC with a maximum of 8oC in south-eastern Greenland. This regional change is coupled to a decrease of the sea ice extent in the North Atlantic region. Both climates are compared to available proxy data of sea surface temperature (SST). The simulated SST changes by up to 2oC in the North Atlantic region during the last 1000 years of the GS12 integration which leads to a better agreement with proxy data. Simulated LGM SSTs are colder than the proxy data but show similar spatial patterns. Simulated GS12 SSTs are in better agreement with the available proxy data.

  18. Numerical modeling of glacial earthquakes induced by iceberg capsize

    NASA Astrophysics Data System (ADS)

    Sergeant, A.; Yastrebov, V.; Castelnau, O.; Mangeney, A.; Stutzmann, E.; Montagner, J. P.; Burton, J. C.

    2015-12-01

    Glacial earthquakes is a class of seismic events of magnitude up to 5, occurring primarily in Greenland, in the margins of large marine-terminated glaciers with near-grounded termini. They are caused by calving of cubic-kilometer scale unstable icebergs which penetrate the full-glacier thickness and, driven by the buoyancy forces, capsize against the calving front. These phenomena produce seismic energy including surface waves with dominant energy between 10-150 s of period whose seismogenic source is compatible with the contact force exerted on the terminus by the iceberg while it capsizes. A reverse motion and posterior rebound of the terminus have also been measured and associated with the fluctuation of this contact force. Using a finite element model of iceberg and glacier terminus coupled with simplified fluid-structure interaction model, we simulate calving and capsize of icebergs. Contact and frictional forces are measured on the terminus and compared with laboratory experiments. We also study the influence of various factors, such as iceberg geometry, calving style and terminus interface. Being extended to field environments, the simulation results are compared with forces obtained by seismic waveform inversion of registered glacial earthquakes.

  19. Mapping bedrock beneath glacial till using CDP seismic reflection methods

    SciTech Connect

    Keiswetter, D.; Black, R.; Steeples, D.

    1994-03-01

    This paper is a case history demonstrating the applicability of the common depth point (CDP) seismic reflection method to image bedrock beneath glacial till in northwestern Iowa. Reflections from the base of the 40-m thick glacial till are clearly observable on field files at around 45 to 50 ms two-way traveltime and possess a dominant frequency of around 100 Hz. The bedrock reflection is confirmed by drill data. The seismic data are of sufficient quality to detect local bedrock topographic changes and to interpret discontinuities along the till-bedrock interface. Finite-difference synthetic seismograms substantiate the interpreted reflections and the diffraction signatures from faults observed on the field files. At some locations along the seismic line, intra-till reflections are apparent on the field files. These intra-till features are on the order of tens of meters in length along the line traverse and reflections from them are not enhanced by common depth point processing. Intra-till reflections could be indicative of gravels or other alluvial materials that may serve as local aquifers.

  20. Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse

    PubMed Central

    Ladant, Jean-Baptiste; Donnadieu, Yannick

    2016-01-01

    The historical view of a uniformly warm Cretaceous is being increasingly challenged by the accumulation of new data hinting at the possibility of glacial events, even during the Cenomanian–Turonian (∼95 Myr ago), the warmest interval of the Cretaceous. Here we show that the palaeogeography typifying the Cenomanian–Turonian renders the Earth System resilient to glaciation with no perennial ice accumulation occurring under prescribed CO2 levels as low as 420 p.p.m. Conversely, late Aptian (∼115 Myr ago) and Maastrichtian (∼70 Myr ago) continental configurations set the stage for cooler climatic conditions, favouring possible inception of Antarctic ice sheets under CO2 concentrations, respectively, about 400 and 300 p.p.m. higher than for the Cenomanian–Turonian. Our simulations notably emphasize that palaeogeography can crucially impact global climate by modulating the CO2 threshold for ice sheet inception and make the possibility of glacial events during the Cenomanian–Turonian unlikely. PMID:27650167

  1. Deep Arctic Ocean warming during the last glacial cycle

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Farmer, J.; Bauch, H.A.; Spielhagen, R.F.; Jakobsson, M.; Nilsson, J.; Briggs, W.M.; Stepanova, A.

    2012-01-01

    In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1–2 °C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.

  2. Mapping of glacial landforms from Seasat radar images

    NASA Technical Reports Server (NTRS)

    Ford, J. P.

    1984-01-01

    Glacial landforms in the drumlin drift belt of Ireland and the Alaska Range can be identified and mapped from Seasat synthetic-aperture radar (SAR) images. Drumlins cover 60 percent of the Ireland scene. The width/length ratio of individual drumlins can be measured on the SAR images, allowing regional differences in drumlin shape to be mapped. This cannot be done with corresponding Landsat multispectral scanner (MSS) images because of lower spatial resolution and because of shadowing effects that vary seasonally. The Alaska scene shows the extent and nature of morphological features such as medial and lateral moraines, stagnant ice, and fluted ground moraine in glaciated valleys. Perception of these features on corresponding Landsat MSS images is limited by seasonal diffrences in solar illumination. Because SAR is not affected by such differences or by cloud cover, it is particularly well suited for monitoring glacial movement. The disadvantage of distorted high-relief features on Seasat SAR images can be reduced in future SAR systems by modifying the radar illumination geometry.

  3. Intensified deep Pacific inflow and ventilation in Pleistocene glacial times.

    PubMed

    Hall, I R; McCave, I N; Shackleton, N J; Weedon, G P; Harris, S E

    2001-08-23

    The production of cold, deep waters in the Southern Ocean is an important factor in the Earth's heat budget. The supply of deep water to the Pacific Ocean is presently dominated by a single source, the deep western boundary current east of New Zealand. Here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep-water properties and speed changes during the Pleistocene epoch. In physical and isotope proxies we find evidence for intensified deep Pacific Ocean inflow and ventilation during the glacial periods of the past 1.2 million years. The changes in throughflow may be directly related to an increased production of Antarctic Bottom Water during glacial times. Possible causes for such an increased bottom-water production include increasing wind strengths in the Southern Ocean or an increase in annual sea-ice formation, leaving dense water after brine rejection and thereby enhancing deep convection. We infer also that the global thermohaline circulation was perturbed significantly during the mid-Pleistocene climate transition between 0.86 and 0.45 million years ago. PMID:11518963

  4. A Novel Seismic Method for Glacial Calving Localization

    NASA Astrophysics Data System (ADS)

    Mei, M. Y. J.; Holland, D. M.; Zheng, T.

    2015-12-01

    Glacial calving is a significant contributor to sea level rise, but the dynamics of how and why calving happens is not yet understood. A novel method of determining calving location using seismic wave arrival times from two local seismic stations at Helheim Glacier is presented. The difference in wave arrival times is used to define a locus (hyperbola) of possible origins, which intersects uniquely with the calving front. Our method is motivated by difficulties with traditional seismic location methods that fail due to both the emergent nature of calving, which obscures the P and S-wave onsets, as well as the proximity of the seismometers, which combines body and surface waves into one arrival. This method is calibrated via known calving events at Helheim Glacier in August 2014, then applied to other calving events in both 2013-2014 and 2014-2015. Extending this method with an additional station allows for triangulation of the calving location, which removes the need for up-to-date imagery of the calving front. Additionally, this method can be extended to allow for three-dimensional localization. By getting more precise locations of glacial calving, we may improve our understanding of why and how glaciers calve.

  5. Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse.

    PubMed

    Ladant, Jean-Baptiste; Donnadieu, Yannick

    2016-01-01

    The historical view of a uniformly warm Cretaceous is being increasingly challenged by the accumulation of new data hinting at the possibility of glacial events, even during the Cenomanian-Turonian (∼95 Myr ago), the warmest interval of the Cretaceous. Here we show that the palaeogeography typifying the Cenomanian-Turonian renders the Earth System resilient to glaciation with no perennial ice accumulation occurring under prescribed CO2 levels as low as 420 p.p.m. Conversely, late Aptian (∼115 Myr ago) and Maastrichtian (∼70 Myr ago) continental configurations set the stage for cooler climatic conditions, favouring possible inception of Antarctic ice sheets under CO2 concentrations, respectively, about 400 and 300 p.p.m. higher than for the Cenomanian-Turonian. Our simulations notably emphasize that palaeogeography can crucially impact global climate by modulating the CO2 threshold for ice sheet inception and make the possibility of glacial events during the Cenomanian-Turonian unlikely. PMID:27650167

  6. Historical distribution of Sundaland's Dipterocarp rainforests at Quaternary glacial maxima.

    PubMed

    Raes, Niels; Cannon, Charles H; Hijmans, Robert J; Piessens, Thomas; Saw, Leng Guan; van Welzen, Peter C; Slik, J W Ferry

    2014-11-25

    The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpaceae trees dominate the rainforests of Sundaland, and their distributions serve as a proxy for rainforest extent. We used species distribution models (SDMs) of 317 Dipterocarp species to estimate the geographic extent of appropriate climatic conditions for rainforest on Sundaland at the last glacial maximum (LGM). The SDMs suggest that the climate of central Sundaland at the LGM was suitable to sustain Dipterocarp rainforest, and that the presence of a previously suggested transequatorial savannah corridor at that time is unlikely. Our findings are supported by palynologic evidence, dynamic vegetation models, extant mammal and termite communities, vascular plant fatty acid stable isotopic compositions, and stable carbon isotopic compositions of cave guano profiles. Although Dipterocarp species richness was generally lower at the LGM, areas of high species richness were mostly found off the current islands and on the emergent Sunda Shelf, indicating substantial species migration and mixing during the transitions between the Quaternary glacial maxima and warm periods such as the present.

  7. Towards accurate observation and modelling of Antarctic glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    King, M.

    2012-04-01

    The response of the solid Earth to glacial mass changes, known as glacial isostatic adjustment (GIA), has received renewed attention in the recent decade thanks to the Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE measures Earth's gravity field every 30 days, but cannot partition surface mass changes, such as present-day cryospheric or hydrological change, from changes within the solid Earth, notably due to GIA. If GIA cannot be accurately modelled in a particular region the accuracy of GRACE estimates of ice mass balance for that region is compromised. This lecture will focus on Antarctica, where models of GIA are hugely uncertain due to weak constraints on ice loading history and Earth structure. Over the last years, however, there has been a step-change in our ability to measure GIA uplift with the Global Positioning System (GPS), including widespread deployments of permanent GPS receivers as part of the International Polar Year (IPY) POLENET project. I will particularly focus on the Antarctic GPS velocity field and the confounding effect of elastic rebound due to present-day ice mass changes, and then describe the construction and calibration of a new Antarctic GIA model for application to GRACE data, as well as highlighting areas where further critical developments are required.

  8. Mechanisms of abrupt climate change of the last glacial period

    NASA Astrophysics Data System (ADS)

    Clement, Amy C.; Peterson, Larry C.

    2008-12-01

    More than a decade ago, ice core records from Greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales. Since their discovery, there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the North Atlantic region and also to reveal the mechanisms that were responsible for them. In this paper, we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms. Three different mechanisms are then reviewed: ocean thermohaline circulation, sea ice feedbacks, and tropical processes. Each mechanism is tested for its ability to explain the key features of the observations, particularly with regard to the abruptness, millennial recurrence, and geographical extent of the observed changes. It is found that each of these mechanisms has explanatory strengths and weaknesses, and key areas in which progress could be made in improving the understanding of their long-term behavior, both from observational and modeling approaches, are suggested. Finally, it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes, as well as the potential for feedbacks between them. Some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given.

  9. Glacial Isostatic Adjustment and Contemporary Sea Level Rise: An Overview

    NASA Astrophysics Data System (ADS)

    Spada, Giorgio

    2016-08-01

    Glacial isostatic adjustment (GIA) encompasses a suite of geophysical phenomena accompanying the waxing and waning of continental-scale ice sheets. These involve the solid Earth, the oceans and the cryosphere both on short (decade to century) and on long (millennia) timescales. In the framework of contemporary sea-level change, the role of GIA is particular. In fact, among the processes significantly contributing to contemporary sea-level change, GIA is the only one for which deformational, gravitational and rotational effects are simultaneously operating, and for which the rheology of the solid Earth is essential. Here, I review the basic elements of the GIA theory, emphasizing the connections with current sea-level changes observed by tide gauges and altimetry. This purpose is met discussing the nature of the "sea-level equation" (SLE), which represents the basis for modeling the sea-level variations of glacial isostatic origin, also giving access to a full set of geodetic variations associated with GIA. Here, the SLE is employed to characterize the remarkable geographical variability of the GIA-induced sea-level variations, which are often expressed in terms of "fingerprints". Using harmonic analysis, the spatial variability of the GIA fingerprints is compared to that of other components of contemporary sea-level change. In closing, some attention is devoted to the importance of the "GIA corrections" in the context of modern sea-level observations, based on tide gauges or satellite altimeters.

  10. Glacial Refugium of Pinus pumila (Pall.) Regel in Northeastern Siberia

    SciTech Connect

    Shilo, N A; Lozhkin, A V; Anderson, P M; Brown, T A; Pakhomov, A Y; Solomatkina, T B

    2007-02-10

    One of the most glowing representatives of the Kolyma flora [1], ''Pinus pumila'' (Pall.) Regel (Japanese stone pine), is a typical shrub in larch forests of the northern Okhotsk region, basins of the Kolyma and Indigirka rivers, and high-shrub tundra of the Chukchi Peninsula. It also forms a pine belt in mountains above the forest boundary, which gives way to the grass-underbrush mountain tundra and bald mountains. In the southern Chukchi Peninsula, ''Pinus pumila'' along with ''Duschekia fruticosa'' (Rupr.) Pouzar and ''Betula middendorffii'' Trautv. et C. A. Mey form trailing forests transitional between tundra and taiga [2]. Pinus pumila pollen, usually predominating in subfossil spore-and-pollen spectra of northeastern Siberia, is found as single grains or a subordinate component (up 2-3%, rarely 10%) in spectra of lacustrine deposits formed during the last glacial stage (isotope stage 2) in the Preboreal and Boreal times of the Holocene. Sometimes, its content increases to 15-22% in spectra of lacustrine deposits synchronous to the last glacial stage near the northern coast of the Sea of Okhotsk [3], evidently indicating the proximity of Japanese stone pine thickets.

  11. Seasonality in the Arabian Sea over glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    de Nooijer, L. J.; Tjallingii, R.; Brummer, G. J.; Reichart, G. J.

    2012-04-01

    The Indian monsoon system controls seasonal precipitation alterations over the Indian continent and upwelling of nutrient-rich waters to the surface in the northern Arabian Sea. Functioning and strength of this weather system due to climate change is one of the important issues in predicting the effects of global warming on the region's economy, agriculture and social welfare. The strength of the Indian monsoon system through time can be studied by changes in seawater temperature and chemistry from single-specimen analysis of planktic foraminiferal calcite. Temperature reconstructions based on many single specimens allow reconstruction of past seasonal sea water temperatures ranges and thus seasonal temperature variability. . Here we present seawater reconstructions based on single-specimen Mg/Ca of the surface dweller Globigerinoides ruber and the deeper-living G. dutertrei of two sediment cores of the western equatorial Indian Ocean off Tanzania and the northern Arabian Sea. From both cores, specimens are analyzed for calcitic Mg/Ca using laser ablation-ICP-MS of time-intervals representing the Holocene optimum, Last Glacial Maximum, Marine Isotope Stage 4, MIS 5 and MIS6. The resulting temperature ranges allow reconstruction of variability in the strength of the Indian Monsoon as well as cross-equatorial heat transport during glacials and interglacials.

  12. Glacial and Holocene climates of Australia reconstructed by vegetation-model inversion

    NASA Astrophysics Data System (ADS)

    Harrison, S. P.; Willis, K.; Wang, H.; Herbert, A.; Prentice, I. C.

    2013-12-01

    We present reconstructions of temperature and moisture variables for Australia at key periods in the last glacial and the Holocene. The reconstructions were made by inversion of a simple, semi-empirical plant-functional type (PFT) based vegetation model developed using a Process-Oriented Niche Specification (PONS) approach, which makes it possible to take into account the effect of changing orbital parameters and CO2 concentration on plant water relations and therefore on the climatic implications of observed vegetation shifts. The data are PFT abundance ';scores' derived from site-based pollen assemblages in nearly 2000 records. The procedure used to calculate these scores involves assigning all living taxa that could contribute to a given pollen taxon to PFTs (independently, based on major plant traits), and using Bayes' theorem to re-allocate the share of the pollen sum represented by ';ambiguous' taxa to the different PFTs they could represent, given information on the other taxa present. In each case the vegetation model was run with a large set of alternative climates corresponding to systematic perturbations around the modern climate. The reconstructed anomaly of each climate variable is the difference between the best-fit climate (for which the dissimilarity between the modelled and observed profile of PFT scores is a minimum) and the modern climate at the site. This minimum is identified by fitting a second-degree polynomial surface to the dissimilarity values as a function of climate variables. The method also allows the assignment of a confidence interval using the second derivative of the fitted surface. We demonstrate that this inversion technique reproduces modern climates from surface samples collected at the fossil pollen sites, with only modest uncertainties, implying that the reconstructions are plausible. This work provides the first quantitative reconstructions of climate changes across Australia over the last glacial-interglacial cycle, and

  13. Reduced Surface Ocean Temperature Variability in the Eastern Equatorial Pacific During the Late Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ford, H. L.; Ravelo, A. C.; Polissar, P. J.

    2012-12-01

    El Niño-Southern Oscillation is the largest source of global interannual variability with far-reaching climatic effects. Climate model simulations of future warming exhibit widely divergent behavior indicating an incomplete understanding of the factors that dictate tropical climate variability. Generating records of past tropical Pacific variability during times with different climate states is one approach to deepening our understanding of tropical climate change processes and improving predictions of future change. Here we reconstruct tropical Pacific ocean variability from the Last Glacial Maximum (LGM) and from the Holocene at ODP Sites 806 and 849, located in the western equatorial Pacific (WEP) warm pool and eastern equatorial Pacific (EEP) cold tongue, respectively. We reconstruct ocean temperature variability using the intra-sample distribution of Mg/Ca values from individual foraminifera. Sea surface temperature variability is reconstructed from individual specimens of G. sacculifer analyzed for Mg/Ca values with laser ablation ICP-MS (Photon Machines Analyte.193 with HelEx sample cell coupled with a Thermo ElementXS ICP-MS, LA-ICP-MS). Subsurface temperature variability is reconstructed from individual specimens of G. tumida analyzed for Mg/Ca values by ICP-OES. Our results indicate that the cooling of last glacial maximum SSTs was greater in the WEP compared to the EEP. Furthermore, we show this cooling is not an artifact of changes in seasonal or interannual foraminiferal fluxes, but rather, reflects overall cooler temperatures and thus changes in seasonal/interannual heat fluxes. At Site 806 in the WEP, variability during the Holocene and LGM was similar, suggesting the cooling was a direct response to pCO2-radiative forcing. In contrast, at Site 849, sea surface temperature variability during the LGM was greatly diminished in comparison to the Holocene suggesting reduced ENSO and seasonal variability. Therefore conditions in the EEP responded to both

  14. Overdeepening development in a glacial landscape evolution model with quarrying

    NASA Astrophysics Data System (ADS)

    Ugelvig, S. V.; Egholm, D. L.; Brædstrup, C. F.; Iverson, N. R.

    2013-12-01

    In glacial landscape evolution models, subglacial erosion rates are often related to basal sliding or ice discharge by a power-law. This relation can be justified when considering bed abrasion, where rock debris transported in the basal ice drives erosion. However, the relation is not well supported when considering models for quarrying of rock blocks from the bed. Field observations indicate that the principal mechanism of glacial erosion is quarrying, which emphasize the importance of a better way of implementing erosion by quarrying in glacial landscape evolution models. Iverson (2012) introduced a new model for subglacial erosion by quarrying that operates from the theory of adhesive wear. The model is based on the fact that cavities, with a high level of bedrock differential stress, form in the lee of bed obstacles when the sliding velocity is too high to allow for the ice to creep around the obstacles. The erosion rate is quantified by considering the likelihood of rock fracturing on topographic bumps. The model includes a statistical treatment of the bedrock weakness, which is neglected in previous quarrying models. Sliding rate, effective pressure, and average bedslope are the primary factors influencing the erosion rate of this new quarrying model [Iverson, 2012]. We have implemented the quarrying model in a depth-integrated higher-order ice-sheet model [Egholm et al. 2011], coupled to a model for glacial hydrology. In order to also include the effects of cavitation on the subglacial sliding rate, we use a sliding law proposed by Schoof (2005), which includes an upper limit for the stress that can be supported at the bed. Computational experiments show that the combined influence of pressure, sliding rate and bed slope leads to realistically looking landforms such as U-shaped valleys, cirques, hanging valleys and overdeepenings. The influence of the effective pressure leads naturally to overdeepenings. However, in contrast to previously used erosion models

  15. Causes of strong ocean heating during glacial periods

    NASA Astrophysics Data System (ADS)

    Zimov, N.; Zimov, S. A.

    2013-12-01

    During the last deglaciation period, the strongest climate changes occurred across the North Atlantic regions. Analyses of borehole temperatures from the Greenland ice sheet have yielded air temperature change estimates of 25°C over the deglaciation period (Dahl-Jensen et al. 1998). Such huge temperature changes cannot currently be explained in the frames of modern knowledge about climate. We propose that glacial-interglacial cycles are connected with gradual warming of ocean interior waters over the course of glaciations and quick transport of accumulated heat from ocean to the atmosphere during the deglaciation periods. Modern day ocean circulation is dominated by thermal convection with cold waters subsiding in the Northern Atlantic and filling up the ocean interior with cold and heavy water. However during the glaciation thermal circulation stopped and ocean circulation was driven by 'haline pumps' -Red and Mediterranean seas connected with ocean with only narrow but deep straights acts as evaporative basins, separating ocean water into fresh water which returns to the ocean surface (precipitation) and warm but salty, and therefore heavy, water which flows down to the ocean floor. This haline pump is stratifying the ocean, allowing warmer water locate under the colder water and thus stopping thermal convection in the ocean. Additional ocean interior warming is driven by geothermal heat flux and decomposition of organic rain. To test the hypothesis we present simple ocean box model that describes thermohaline circulation in the World Ocean. The first box is the Red and Mediterranean sea, the second is united high-latitude seas, the third is the ocean surface, and the fourth the ocean interior. The volume of these water masses and straight cross-sections are taken to be close to real values. We have accepted that the exchange of water between boxes is proportional to the difference in water density in these boxes, Sun energy inputs to the ocean and sea surface

  16. Dichotomy Boundary Glaciation Models: Implications for Timing and Glacial Processes

    NASA Astrophysics Data System (ADS)

    Fastook, J. L.; Head, J. W.

    2008-12-01

    An integrated system with glacial features exists at 34E, 41N in the Deuteronilus-Protonilus Mensae region. This 30,000 km2 valley system is typical of dozens of fretted valleys in this region along the dichotomy boundary. We compare features described in current geological observations with results from the University of Maine Ice Sheet Model (UMISM) that we feel support the glacial interpretation of these features and also allow speculation as to the timing and processes responsible for the formation of these features. Geological observations identify evidence for a number of features that are felt to be indicative of glacial flow. These include: 1) localized alcoves from which emanate narrow, lobate concentric-ridged flows interpreted to be remnants of debris-covered glaciers; 2) alcove depressions perhaps indicating sublimation of material from relict ice-rich accumulation zones; 3) plateau-ridge remnants between alcoves typical of glacially eroded aretes; 4) horseshoe-shaped ridges upstream of topographic obstacles; 5) convergence and merging of LVF fabric in the down-valley direction; 6) deformation, distortion and folding of LVF in the vicinity of convergence; 7) LVF with pits and elongated troughs in distorted areas; 8) distinctive lobe-shaped termini with associated pitting where the LVF emerges into the northern lowlands. This evidence defines a coherent, unified flow regime extending from the upper valley reaches down to the northern lowlands. Additional support for the glacial hypothesis comes from a GCM for a dusty-atmosphere Mars with obliquity set to 35o and a water source in the Tharsis region. The GCM generates a pattern of ice accumulation in good agreement with these geological observations. This climate is what one might expect to follow a high- obliquity excursion of the sort that built ice sheets on the Tharsis volcanoes. UMISM as used here is an adaptation for the Martian environment of a thermo-mechanically coupled shallow- ice approximation

  17. Detection of Supra-Glacial Lakes on the Greenland Ice Sheet Using MODIS Images

    NASA Astrophysics Data System (ADS)

    Verin, Gauthier; Picard, Ghislain; Libois, Quentin; Gillet-Chaulet, Fabien; Roux, Antoine

    2015-04-01

    During melt season, supra-glacial lakes form on the margins of the Greenland ice sheet. Because of their size exceeding several kilometers, and their concentration, they affect surface albedo leading to an amplification of the regional melt. Furthermore, they foster hydro-fracturing that propagate liquid water to the bedrock and therefore enhance the basal lubrication which may affect the ice motion. It is known that Greenland ice sheet has strongly responded to recent global warming. As air temperature increases, melt duration and melt intensity increase and surface melt area extends further inland. These recent changes may play an important role in the mass balance of the Greenland ice sheet. In this context, it is essential to better monitor and understand supra-glacial spatio-temporal dynamics in order to better assess future sea level rise. In this study MODIS (Moderate Resolution Imaging Spectroradiometer) images have been used to detect supra-glacial lakes. The observation site is located on the West margin of the ice sheet, between 65°N and 70°N where the concentration of lake is maximum. The detection is performed by a fully automatic algorithm using images processing techniques introduced by Liang et al. (2012) which can be summarized in three steps: the selection of usable MODIS images, mainly we exclude images with too many clouds. The detection of lake and the automatic correction of false detections. This algorithm is capable to tag each individual lake allowing a survey of all lake geometrical properties over the entire melt season. We observed a large population of supra-glacial lakes over 14 melt seasons, from 2000 to 2013 on an extended area of 70.000 km2. In average, lakes are observed from June 9 ± 8.7 days to September 13 ± 13.9 days, and reach a maximum total area of 699 km2 ± 146 km2. As the melt season progresses, lakes form higher in altitude up to 1800 m above sea level. Results show a very strong inter-annual variability in term of

  18. Last glacial maximum environments in northwestern Patagonia revealed by fossil small mammals

    NASA Astrophysics Data System (ADS)

    Tammone, Mauro N.; Hajduk, Adan; Arias, Pablo; Teta, Pablo; Lacey, Eileen A.; Pardiñas, Ulyses F. J.

    2014-07-01

    Comparisons of historical and modern assemblages of mammals can yield important insights into patterns and processes of environmental change. Here, we present the first analyses of small mammal assemblages present in northern Patagonia during the last glacial maximum (LGM). Using remains obtained from owl pellets excavated from an archeological cave site (Arroyo Corral I, levels VII-V, carbon dates of 22,400-21,530 cal yr BP), we generate estimates of the minimum number of individuals for all species detected; these estimates, in turn are used to determine relative species abundances. Comparisons of these data with similar analyses of small mammal remains obtained from a second archeological site (ACoII, levels IV-V, carbon dates of 10,010-9220 cal yr BP) as well as from modern owl pellets reveal pronounced changes in relative species abundance since the LGM. In particular, Euneomys chinchilloides and Ctenomys sociabilis - the predominant species during the LGM - declined markedly, suggesting a change from open, bare habitat punctuated by patches of wet meadows and shrubs to the more densely vegetated mosaic of ecotone habitats found in this region today. These data provide important new insights into the environmental changes that have occurred in northern Patagonia over the last 20,000 years.

  19. The Isotopic Composition of Nitrate in West Antarctica at Present and Since the Last Glacial Stage

    NASA Astrophysics Data System (ADS)

    Buffen, A.; Hastings, M. G.

    2014-12-01

    Nitrate is one of the major ions found in polar and alpine snow. The oxygen isotopic composition of nitrate offers unique potential for examining the oxidation chemistry of past atmospheres. Additionally, nitrogen isotope ratios may contain information abut the contribution of the nitrogen oxide precursors (NOx = NO + NO2) to atmospheric nitrate from different sources (e.g., fossil fuel combustion, biomass burning, soil microbial emissions, lightning and stratospheric injection). Nitrate in snow, however, is sensitive to post-depositional processing and isotopic alteration, thereby obscuring the atmospheric record ultimately archived in an ice core. At sites with very low snow accumulation rates (such as East Antarctica), nitrate is particularly vulnerable to photolytic loss due to long residence times near the surface. However, under higher accumulation regimes (such as Summit, Greenland), previous work has shown that loss can be more limited and nitrate isotopic composition preserved. Here we present results from a two-part study assessing the modern and paleo isotopic composition of nitrate in West Antarctica. We present seasonally-resolved snowpit and shallow core records from 7 West Antarctic sites which span a range of accumulation rates in order to evaluate the spatial heterogeneity of deposited nitrate and how preservation varies with snowfall. This work is requisite to an accurate interpretation of a new nitrate isotopic record from the West Antarctic Ice Sheet Divide deep ice core, from which we show decadal- to centennial-scale measurements since the last glacial stage.

  20. Across-shelf sediment transport since the Last Glacial Maximum, southern California margin

    USGS Publications Warehouse

    Sommerfield, C.K.; Lee, H.J.

    2004-01-01

    Correlation of continental shelf-slope stratigraphy in Santa Monica Bay (southern California) with Ocean Drilling Program records for nearby slope-basin sites has illuminated the timing and scale of terrigenous sediment dispersal on margin since the Last Glacial Maximum (LGM). Marine flooding surfaces preserved in a transgressive sequence on the Santa Monica Shelf provide a key link between base-level elevation and sediment transport across shelf. Sediment-accumulation rates at slope-basin sites were maximal ca. 15-10 ka, well after the LGM, decreased during the 12-9 ka transition from fluvial-estuarine to fully marine conditions on the shelf, and decelerated throughout the Holocene to 30%-75% of their values at the LGM. The deceleration is interpreted to manifest a landward shift in the margin depocenter with the onset of transgressive sedimentation beginning when sea level surmounted the shelf edge ca. 13 ka, as predicted by sequence-stratigraphic models. However, the records make clear that factors other than base level modulated slope-basin accumulation rates during the deglaciation. ?? 2004 Geological Society of America.

  1. 76 FR 50476 - Application To Export Electric Energy; Glacial Energy of Texas, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Application To Export Electric Energy; Glacial Energy of Texas, Inc. AGENCY: Office of Electricity Delivery and Energy Reliability, DOE. ACTION: Notice of Application. SUMMARY: Glacial Energy of Texas,...

  2. Climate Change as the Dominant Control on Glacial-Interglacial Variations in C3 and C4 Plant Abundance

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Street-Perrott, F. A.; Metcalfe, S. E.; Brenner, M.; Moreland, M.; Freeman, K. H.

    2001-08-01

    Although C4 plant expansions have been recognized in the late Miocene, identification of the underlying causes is complicated by the uncertainties associated with estimates of ancient precipitation, temperature, and partial pressure of atmospheric carbon dioxide (PCO2). Here we report the carbon isotopic compositions of leaf wax n-alkanes in lake sediment cores from two sites in Mesoamerica that have experienced contrasting moisture variations since the last glacial maximum. Opposite isotopic trends obtained from these two sites indicate that regional climate exerts a strong control on the relative abundance of C3 and C4 plants and that in the absence of favorable moisture and temperature conditions, low PCO2 alone is insufficient to drive an expansion of C4 plants.

  3. Co-variation of nitrogen isotopes and redox states through glacial-interglacial cycles in the Black Sea

    NASA Astrophysics Data System (ADS)

    Quan, Tracy M.; Wright, James D.; Falkowski, Paul G.

    2013-07-01

    In all aquatic environments, nitrogen cycling within the water column is strongly influenced by oxygen. We hypothesize that the nitrogen isotopic composition (δ15N) of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition. We tested the hypothesis by measuring the bulk sedimentary δ15N values in a drill core from the Black Sea, a basin that alternates between oxic, less saline conditions and anoxic, marine conditions on glacial-interglacial time scales. We reconstructed these changes in Black Sea redox conditions using sedimentary δ15N, total organic carbon (TOC), total nitrogen (TN), redox-sensitive metals, and micropaleontological data from a deep-sea core (DSDP Site 380). The sedimentary data reveal that during the transitions between oxic and anoxic conditions, δ15N values increased relative to the preceding and succeeding quasi-steady-state oxic and anoxic periods. The results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification; during the quasi-stable oxic and anoxic states (characterized by glacial fresh water and interglacial marine conditions) nitrification and complete nitrate utilization, respectively, dominate the nitrogen cycle. While other factors may influence the δ15N record, our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the Black Sea subphotic zone on glacial-interglacial time scales, and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems. Our model suggests that the nitrogen isotopic composition of marine sediments, on geological time scales, can be used to reconstruct the redox state of the overlying water column.

  4. 21st century Himalayan hydropower: Growing exposure to glacial lake outburst floods?

    NASA Astrophysics Data System (ADS)

    Schwanghart, Wolfgang; Worni, Raphael; Huggel, Christian; Stoffel, Markus; Korup, Oliver

    2014-05-01

    Primary energy demand in China and India has increased fivefold since 1980. To avoid power shortages and blackouts, the hydropower infrastructure in the Hindu Kush-Himalaya region is seeing massive development, a strategy supported by the policy of the World Bank and in harmony with the framework of the Kyoto Protocol. The targeted investments in clean energy from water resources, however, may trigger far-reaching impacts to downstream communities given that hydropower projects are planned and constructed in close vicinity to glaciated areas. We hypothesize that the location of these new schemes may be subject to higher exposure to a broad portfolio of natural hazards that proliferate in the steep, dissected, and tectonically active topography of the Himalayas. Here we focus on the hazard from glacial lake outburst floods (GLOF), and offer an unprecedented regional analysis for the Hindu Kush-Himalaya orogen. We compiled a database of nearly 4,000 proglacial lakes that we mapped from satellite imagery; and focus on those as potential GLOF sources that are situated above several dozen planned and existing hydropower plants. We implemented a scenario-based flood-wave propagation model of hypothetic GLOFs, and compared thus simulated peak discharges with those of the local design floods at the power plants. Multiple model runs confirm earlier notions that GLOF discharge may exceed meteorological, i.e. monsoon-fed, flood peaks by at least an order of magnitude throughout the Hindu Kush-Himalaya. We further show that the current trend in hydropower development near glaciated areas may lead to a >15% increase of projects that may be impacted by future GLOFs. At the same time, the majority of the projects are to be sited where outburst flood modelling produces its maximum uncertainty, highlighting the problem of locating minimum risk sites for hydropower. Exposure to GLOFs is not uniformly distributed in the Himalayas, and is particularly high in rivers draining the Mt

  5. Terrestrial cosmogenic surface exposure dating of glacial and associated landforms in the Ruby Mountains-East Humboldt Range of central Nevada and along the northeastern flank of the Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Wesnousky, Steven G.; Briggs, Richard W.; Caffee, Marc W.; Ryerson, F. J.; Finkel, Robert C.; Owen, Lewis A.

    2016-09-01

    Deposits near Lamoille in the Ruby Mountains-East Humboldt Range of central Nevada and at Woodfords on the eastern edge of the Sierra Nevada each record two distinct glacial advances. We compare independent assessments of terrestrial cosmogenic nuclide (TCN) surface exposure ages for glacial deposits that we have determined to those obtained by others at the two sites. At each site, TCN ages of boulders on moraines of the younger advance are between 15 and 30 ka and may be associated with marine oxygen isotope stage (MIS) 2. At Woodfords, TCN ages of boulders on the moraine of the older advance are younger than ~ 60 ka and possibly formed during MIS 4, whereas boulders on the correlative outwash surface show ages approaching 140 ka (~ MIS 6). The TCN ages of boulders on older glacial moraine at Woodfords thus appear to severely underestimate the true age of the glacial advance responsible for the deposit. The same is possibly true at Lamoille where clasts sampled from the moraine of the oldest advance have ages ranging between 20 and 40 ka with a single outlier age of ~ 80 ka. The underestimations are attributed to the degradation and denudation of older moraine crests. Noting that boulder ages on the older advances at each site overlap significantly with MIS 2. We speculate that erosion of the older moraines has been episodic, with a pulse of denudation accompanying the inception of MIS 2 glaciation.

  6. Climatic evolution of the central equatorial Pacific since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Seo, Inah; Lee, Yuri; Lee, Yong Il; Yoo, Chan Min; Hyeong, Kiseong

    2016-08-01

    This paper investigates paleoceanographic changes at a central equatorial Pacific site (6°40'N, 177°28'W) since the last glacial maximum using planktic foraminifera assemblages, together with the oxygen isotope (δ18O) and Mg/Ca compositions of three species (Globigerinoides sacculifer, Pulleniatina obliquiloculata, and Globorotalia tumida) that dwell in the mixed layer, upper thermocline, and lower thermocline, respectively. While the Mg/Ca-derived temperatures of the mixed layer and lower thermocline varied within a narrow range from 18 ka onward, the upper thermocline temperature increased by as much as 3°C during the last deglaciation (18-12 ka) with a simultaneous decrease of δ18O. These changes are best explained by an enhanced mixing of the upper ocean and a reduced habitat depth separation between P. obliquiloculata and G. sacculifer during the 18-12 ka interval. The planktic foraminifera assemblage during the same period resembles modern composition at subtropical central Pacific sites that are strongly influenced by the northeasterly Trades and North Equatorial Current (NEC). We suggest that the study site, presently under the control of the Intertropical Convergence Zone (ITCZ)-North Equatorial Countercurrent, had been influenced by the northeasterly Trades and NEC during the 18-12 ka interval. This interpretation is consistent with previous documentation of a more southerly location of the ITCZ during two Northern Hemisphere cooling events; the Heinrich Stadial 1 and the Younger Dryas, and implies that the mean annual position of the ITCZ was located south of the study site, by at least 2° of latitude.

  7. Paleoceanographic history of the Lower Bengal Fan during the last glacial cycle - IODP Expedition 354

    NASA Astrophysics Data System (ADS)

    Dekens, P. S.; Weber, M. E.; Lantzsch, H.; Das, S. K.; Williams, T.; Adhikari, R. R.; Jia, G.; Fox, L. R.; Ge, J.; Manoj, M. C.; Savian, J. F.; Reilly, B. T.; Selkin, P. A.; Meynadier, L.; Spiess, V.; France-Lanord, C.; Sharma, B.

    2015-12-01

    IODP Expedition 354 drilled a ~320 km long transect of seven sites on the Lower Bengal Fan at 8o N in the Northern Indian Ocean. The sediments cores recovered record a complex relationship between turbiditic and hemipelagic environments. This variability offers a unique opportunity to link our understanding of tectonic and terrestrial processes with climate and oceanography. With the exception the westernmost Site U1454, all sites show a several meter thick, hemipelagic top layer, usually representing Late Quaternary sediment. We present physical, geochemical and stable isotopic properties of this interval to establish a time frame and assess the paleoceanographic development of the region during the last glacial cycle. We sampled Site U1452C-1H continuously for the uppermost 480 cm of hemipelagic sediment in 2-cm increments. Preliminary results indicate the Toba Ash 1 (0.74 ka) is a distinct time marker in all physical properties. Furthermore, wet-bulk density as well as color reflectance b* (the red-green component) and L* (the lightness) show a dominant precession cyclicity. Hence, we are able to provide an insolation-tuned chronology for the last 200 ka (MIS1 - 7) as a preliminary age model. These records agree well with d18O records retrieved from Chinese caves. We will present a preliminary paleoceanographic proxy data to reconstruct sea-surface temperature (SST), sea-surface salinity (SSS), ice volume, marine biological productivity, nutrient supply, and deep-water circulation. These oceanographic and climate conditions are linked to changes in monsoonal strength and terrestrial input using sedimentary proxies to reconstruct chemical weathering and sediment sources and transport time. This work addresses one of the primary cruise objectives - linking monsoon variability, regional and global climate, and Bay of Bengal sediment deposition.

  8. Glacial lakes amplify glacier recession in the central Himalaya

    NASA Astrophysics Data System (ADS)

    King, Owen; Quincey, Duncan; Carrivick, Jonathan; Rowan, Ann

    2016-04-01

    The high altitude and high latitude regions of the world are amongst those which react most intensely to climatic change. Across the Himalaya glacier mass balance is predominantly negative. The spatial and temporal complexity associated with this ice loss across different glacier clusters is poorly documented however, and our understanding of the processes driving change is limited. Here, we look at the spatial variability of glacier hypsometry and glacial mass loss from three catchments in the central Himalaya; the Dudh Koshi basin, Tama Koshi basin and an adjoining section of the Tibetan Plateau. ASTER and SETSM digital elevation models (2014/15), corrected for elevation dependant biases, co-registration errors and along or cross track tilts, are differenced from Shuttle Radar Topographic Mission (SRTM) data (2000) to yield surface lowering estimates. Landsat data and a hypsometric index (HI), a classification scheme used to group glaciers of similar hypsometry, are used to examine the distribution of glacier area with altitude in each catchment. Surface lowering rates of >3 m/yr can be detected on some glaciers, generally around the clean-ice/debris-cover boundary, where dark but thin surface deposits are likely to enhance ablation. More generally, surface lowering rates of around 1 m/yr are more pervasive, except around the terminus areas of most glaciers, emphasising the influence of a thick debris cover on ice melt. Surface lowering is only concentrated at glacier termini where glacial lakes have developed, where surface lowering rates are commonly greater than 2.5 m/yr. The three catchments show contrasting hypsometric distributions, which is likely to impact their future response to climatic changes. Glaciers of the Dudh Koshi basin store large volumes of ice at low elevation (HI > 1.5) in long, debris covered tongues, although their altitudinal range is greatest given the height of mountain peaks in the catchment. In contrast, glaciers of the Tama Koshi

  9. Edges and Blocks Matter on Hillslopes, Rivers, and Glacial Landscapes

    NASA Astrophysics Data System (ADS)

    Anderson, R. S.

    2014-12-01

    Many landforms display sharp corners, or edges, that are maintained as they migrate laterally. Our present landscape models, cast largely in terms of patterns of vertical erosion, fail to capture the essence of these landscapes, including flatirons, hogbacks, cliffs, and lumpy outcropped hillslopes; roche moutonée and glacial steps, and river knickpoints. Yet these are the very landscape signatures of rock type and structure. Block sizes, and the fracture distributions that bound the blocks, vary from one rock type or geological setting to another. Removal and transportation of discrete blocks of rock maintains a sharp edge, and results in their upvalley/upslope migration. Our challenge in developing numerical landscapes is to capture the essential variation, noisiness, and roughness of natural landscapes and their dependence on rock type and structure. The rate of lowering of the landscape is governed by the product of the spatial density of edges, their step height, and their rate of migration. I present cellular automata-like models in which I explicitly incorporate blocks, and utilize algorithms for the susceptibility of any block to motion, and the forces imposed on the surface by the environment. Susceptibility of a block to release is governed by its size, the geometry of the pocket in which it sits, the frictional properties of the bounding discontinuities, and the cohesion across these discontinuities. This is akin to coordination number and bond strengths of atoms in mineral dissolution studies; their atoms are our blocks. Removal of a block requires an event of sufficient magnitude to overcome its resistance. The relevant events include fluctuations in water pressure at the bed of glaciers, turbulence and sediment impacts in rivers, and root throw or earthquakes in hillslopes. Preliminary models capture the essence of migrating edges. The systems self-organize to produce suites of steps. In glacial beds, for example, migration of steps produces upvalley

  10. Glacial Geomorphic Characteristics of the Antarctic Peninsula Fjords

    NASA Astrophysics Data System (ADS)

    Wellner, J. S.; Munoz, Y. P.; Mead, K. A.; Hardin, L. A.

    2011-12-01

    A distinctive suite of subglacial geomorphic features, representing the grounding of an ice sheet and its subsequent retreat, has been well documented for many parts of the Antarctic continental shelf. Geomorphic features include meltwater channels, drumlins, mega-scale glacial lineations, and gullies cut into the upper slope. Many of these same features occur in more recently deglaciated fjords, but at different scales and in different combinations. We have surveyed twelve fjords on the Antarctic Peninsula, from the Graham Land Coast to Hope Bay as well as on Anvers Island and in the South Shetland Islands. Surveys include multibeam swath bathymetry, CHIRP 3.5 kHz seismic, and sediment cores. Recently, we have reprocessed much of the multibeam data using new software allowing higher-resolution imagery. Unlike on the outer continental shelf of the Antarctic Peninsula, where there is a relatively simple suite of geomorphic features and a uniform retreat history, the fjords on the inner shelf show a complex geomorphic pattern representing somewhat unique glacial retreat histories for each fjord. Several fjords have distinctive grounding zone wedge deposits, and some fjords have such wedges in multiple locations, representing multiple pauses in the retreat history, or a stepped retreat of the ice. Drumlins and mega-scale glacial lineations are present in the fjords, but extend for kms rather than the tens of kms that are typical of the outer shelf. If drumlins are interpreted to indicate acceleration of grounded ice, as they are on the outer shelf, then there must have been multiple zones of acceleration across the flow path of the ice as drumlin sets occur in multiple zones in a single flow path. The inner parts of many fjords along the coast of the peninsula are characterized by features interpreted as erosional meltwater channels, although such features are not common in fjords in the islands off the peninsula, despite the similar scale of the fjords themselves

  11. Tooth enamel stable isotopes of Holocene and Pleistocene fossil fauna reveal glacial and interglacial paleoenvironments of hominins in Indonesia

    NASA Astrophysics Data System (ADS)

    Janssen, Renée; Joordens, Josephine C. A.; Koutamanis, Dafne S.; Puspaningrum, Mika R.; de Vos, John; van der Lubbe, Jeroen H. J. L.; Reijmer, John J. G.; Hampe, Oliver; Vonhof, Hubert B.

    2016-07-01

    The carbon (δ13C) and oxygen (δ18O) isotope compositions of fossilized animal tissues have become important proxies of paleodiet and paleoenvironment, but such stable isotope studies have not yet been extensively applied to the fossil assemblages of Sundaland (the biogeographical region comprising most of the Indonesian Archipelago). Here, we use the isotope composition of tooth enamel to investigate the diet and habitat of bovids, cervids, and suids from several Holocene and Pleistocene sites on Java and Sumatra. Our carbon isotope results indicate that individual sites are strongly dominated by either C3-browsers or C4-grazers. Herbivores from the Padang Highlands (Sumatra) and Hoekgrot (Java) cave faunas were mainly C3-browsers, while herbivores from Homo erectus-bearing sites Trinil and Sangiran (Java) utilized an almost exclusive C4 diet. The suids from all sites show a wide range of δ13C values, corroborating their omnivorous diet. For the dataset as a whole, oxygen and carbon isotope values are positively correlated. This suggests that isotopic enrichment of rainwater and vegetation δ18O values coincides with an increase of C4-grasslands. We interpret this pattern to mainly reflect the environmental contrast between glacial (drier, more C4) and interglacial (wetter, more C3) conditions. Intermediate herbivore δ13C values indicating mixed C3/C4 feeding is relatively rare, which we believe to reflect the abruptness of the transition between glacial and interglacial precipitation regimes in Sundaland. For seven Homo erectus bone samples we were not able distinguish between diagenetic overprint and original isotope values, underlining the need to apply this isotopic approach to Homo erectus tooth enamel instead of bone. Importantly, our present results on herbivore and omnivore faunas provide the isotopic framework that will allow interpretation of such Homo erectus enamel isotope data.

  12. Glacial Lake Expansion in the Central Himalayas by Landsat Images, 1990–2010

    PubMed Central

    Nie, Yong; Liu, Qiao; Liu, Shiyin

    2013-01-01

    Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed. PMID:24376778

  13. Glacial history of sub-Antarctic South Georgia based on the submarine geomorphology of its fjords

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Graham, Alastair G. C.; Griffiths, Huw J.; Roberts, Stephen J.; Cofaigh, Colm O.; Bentley, Michael J.; Evans, David J. A.

    2014-05-01

    We present multibeam swath bathymetric surveys of the major fjords surrounding the sub-Antarctic island of South Georgia to characterise the glacial geomorphology and to identify the relative timings and extent of past glacial advance and retreat. Bathymetry data revealed a range of glacial features including terminal, retreat and truncated moraines, deep (distal) outer and shallow (proximal) inner basins and cross shelf troughs. These provide evidence of glacial advance and retreat through several glacial cycles. A near consistent pattern of large scale submarine geomorphological features was observed in the different fjords suggesting a similar response of margins of the island ice cap to past climate forcing. A relative chronology based on the relationships between the submarine features with their radiocarbon and cosmogenic isotope dated terrestrial counterparts suggests that widely observed inner basin moraines date from the last major glacial advance or Last Glacial Maximum, while deep basin moraines may date from an earlier (pre-LGM) more extensive glaciation, which we speculate corresponds to MIS6. On the sides of the deep basins a series of truncated moraines show ice advance positions from preceding glacial periods. The cross shelf troughs, and mid-trough moraines are interpreted as the product of much more extensive glaciations that predate the fjord geomorphology mapped here, thus possibly older than MIS6. This hypothesis would suggest that South Georgia followed a glacial history similar to that of central Patagonia (46deg S)where a series of Pleistocene glaciations (of MIS 20 and younger) extended beyond LGM limits, with the most extensive glacial advance occurring at c. 1.1 Ma.

  14. Glacial history of sub-Antarctic South Georgia based on the submarine geomorphology of its fjords

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Graham, Alastair G. C.; Griffiths, Huw J.; Roberts, Stephen J.; Cofaigh, Colm Ó.; Bentley, Michael J.; Evans, David J. A.

    2014-04-01

    We present multibeam swath bathymetric surveys of the major fjords surrounding the sub-Antarctic island of South Georgia to characterise the glacial geomorphology and to identify the relative timings and extent of past glacial advance and retreat. Bathymetry data revealed a range of glacial features including terminal, retreat and truncated moraines, deep (distal) outer and shallow (proximal) inner basins and cross shelf troughs. These provide evidence of glacial advance and retreat through several glacial cycles. A near consistent pattern of large scale submarine geomorphological features was observed in the different fjords suggesting a similar response of margins of the island ice cap to past climate forcing. A relative chronology based on the relationships between the submarine features with their radiocarbon and cosmogenic isotope dated terrestrial counterparts suggests that widely observed inner basin moraines date from the last major glacial advance or Last Glacial Maximum, while deep basin moraines may date from an earlier (pre-LGM) more extensive glaciation, which we speculate corresponds to MIS6. On the sides of the deep basins a series of truncated moraines show ice advance positions from preceding glacial periods. The cross shelf troughs, and mid-trough moraines are interpreted as the product of much more extensive glaciations that predate the fjord geomorphology mapped here, thus possibly older than MIS6. This hypothesis would suggest that South Georgia followed a glacial history similar to that of central Patagonia (46°S) where a series of Pleistocene glaciations (of MIS 20 and younger) extended beyond LGM limits, with the most extensive glacial advance occurring at c. 1.1 Ma.

  15. Comparison of eastern tropical Pacific TEX86 and Globigerinoides ruber Mg/Ca derived sea surface temperatures: Insights from the Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hertzberg, Jennifer E.; Schmidt, Matthew W.; Bianchi, Thomas S.; Smith, Richard W.; Shields, Michael R.; Marcantonio, Franco

    2016-01-01

    The use of the TEX86 temperature proxy has thus far come to differing results as to whether TEX86 temperatures are representative of surface or subsurface conditions. In addition, although TEX86 temperatures might reflect sea surface temperatures based on core-top (Holocene) values, this relationship might not hold further back in time. Here, we investigate the TEX86 temperature proxy by comparing TEX86 temperatures to Mg/Ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical Pacific (on the Cocos and Carnegie Ridges) across the Holocene and Last Glacial Maximum. Core-top and Holocene TEX86H temperatures at both study regions agree well, within error, with the Mg/Ca temperatures of Globigerinoides ruber, a surface dwelling planktonic foraminifera. However, during the Last Glacial Maximum, TEX86H temperatures are more representative of upper thermocline temperatures, and are offset from G. ruber Mg/Ca temperatures by 5.8 °C and 2.9 °C on the Cocos Ridge and Carnegie Ridge, respectively. This offset between proxies cannot be reconciled by using different TEX86 temperature calibrations, and instead, we suggest that the offset is due to a deeper export depth of GDGTs at the LGM. We also compare the degree of glacial cooling at both sites based on both temperature proxies, and find that TEX86H temperatures greatly overestimate glacial cooling, especially on the Cocos Ridge. This study has important implications for applying the TEX86 paleothermometer in the eastern tropical Pacific.

  16. Post-glacial sea-level history for NE Ireland (Belfast Lough) based on offshore evidence

    NASA Astrophysics Data System (ADS)

    Quinn, R.; Plets, R. M.; Callard, L.; Cooper, A.; Long, A. J.; Belknap, D. F.; Edwards, R.; Jackson, D.; Kelley, J. T.; Long, D.; Milne, G. A.; Monteys, X.

    2013-12-01

    Glacio-isostatic adjustment (GIA) models suggest a complex relative sea-level (RSL) pattern around the Irish Sea Basin after the Last Glacial Maximum (LGM), with modelled sea-level lowstands ranging from -12 m in the north to greater than -60 m in the south of the Basin. However, these GIA models are poorly constrained by observational data offshore. Belfast Lough, on the NE coast of Ireland, is one of seven sites chosen to investigate this complex RSL history as part of the project ';Late Glacial Sea level minima in the Western British Isles' (NERC NE/H024301/1). Belfast Lough was chosen as one of the candidate sites on the basis of location (at the northern end of the Irish Sea Basin), sedimentary environment (grossly depositional) and the fact that the lowstand predicted for the Belfast Lough area by a recent version of the GIA model (-16.5 m) differs significantly from the (limited) extant observational data, which interprets the lowstand at -30 m. In 2011 and 2012 we gathered new multi-beam echo-sounder data, >200 km trackline pinger- and boomer- seismic reflection data and 46 vibrocores in Belfast Lough. Radiocarbon dating and palaeoenvironmental analysis are used to constrain the interpretation of the seismic and sediment data. Five seismo-stratigraphic units are interpreted, with a distinct erosional surface between U3 and U4 interpreted as a transgressive surface associated with sea level rise post-dating a RSL lowstand. Foraminiferal evidence indicates an increase in marine species (from lagoonal/estuarine to fully marine) from U4 to U5. Integration of the seismic and core data indicate an erosional event prior to 12.7 cal yr BP resulting in a planated surface in the inner Lough and wave-eroded drumlins at the mouth of the Lough between -15 and -22 m, interpreted as a possible slowstand. On the basis of seismic evidence in the outer Lough, an as yet undated lowstand at -42 m is tentatively interpreted to pre-date this stillstand. These results will be

  17. Post-glacial sea-level history for NE Ireland (Belfast Lough) based on offshore evidence

    NASA Astrophysics Data System (ADS)

    Quinn, Rory; Plets, Ruth; Callard, Louise; Cooper, Andrew; Antony, Long; Daniel, Belknap; Robin, Edwards; Derek, Jackson; Joseph, Kelley; David, Long; Glenn, Milne; Xavier, Monteys

    2014-05-01

    Glacio-isostatic adjustment (GIA) models suggest a complex relative sea-level (RSL) pattern around the Irish Sea Basin after the Last Glacial Maximum (LGM), with modelled sea-level lowstands ranging from -12 m in the north to greater than -60 m in the south of the Basin. However, these GIA models are poorly constrained by observational data offshore. Belfast Lough, on the NE coast of Ireland, is one of seven sites chosen to investigate this complex RSL history as part of the project 'Late Glacial Sea level minima in the Western British Isles' (NERC NE/H024301/1). Belfast Lough was chosen as one of the candidate sites on the basis of location (at the northern end of the Irish Sea Basin), sedimentary environment (grossly depositional) and the fact that the lowstand predicted for the Belfast Lough area by a recent version of the GIA model (-16.5 m) differs significantly from the (limited) extant observational data, which interprets the lowstand at -30 m. In 2011 and 2012 we gathered new multi-beam echo-sounder data, >200 km trackline pinger- and boomer- seismic reflection data and 46 vibrocores in Belfast Lough. Radiocarbon dating and palaeoenvironmental analysis are used to constrain the interpretation of the seismic and sediment data. Five seismo-stratigraphic units are interpreted, with a distinct erosional surface between U3 and U4 interpreted as a transgressive surface associated with sea level rise post-dating a RSL lowstand. Foraminiferal evidence indicates an increase in marine species (from lagoonal/estuarine to fully marine) from U4 to U5. Integration of the seismic and core data indicate an erosional event prior to 12.7 cal yr BP resulting in a planated surface in the inner Lough and wave-eroded drumlins at the mouth of the Lough between -15 and -22 m, interpreted as a possible slowstand. On the basis of seismic evidence in the outer Lough, an as yet undated lowstand at -42 m is tentatively interpreted to pre-date this stillstand. These results will be used

  18. High resolution record of the Last Glacial Maximum in eastern Australia

    NASA Astrophysics Data System (ADS)

    Petherick, Lynda; Moss, Patrick; McGowan, Hamish

    2010-05-01

    A continuous, high resolution (average ca. 22 year) record encompassing the Last Glacial Maximum (LGM) has been developed using multiple proxies (aeolian sediment flux, grain size, pollen and charcoal) in lake sediment from Tortoise Lagoon (TOR), North Stradbroke Island, Queensland, Australia. The presence of Asteraceae tubilifloreae and spineless Asteraceae (common indicators of glacial conditions in Australia) at TOR indicates significantly cooler temperatures (mean annual temperature up to 6oC lower than today). In addition to the palaeoclimatic reconstruction, a record of palaeodust transport pathways for eastern Australia was developed using ICP-MS trace element analysis and geochemical "fingerprinting" of TOR aeolian sediment to continental dust source areas. Vectors between dominant dust source areas and North Stradbroke Island allowed the reconstruction of the position and intensity of LGM dust transport pathways. Furthermore, changes in likely synpotic scale conditions can be postulated based on the position of the dust transport corridors. Similarities between the vegetation at TOR during the LGM and that at temperate sites e.g. Caledonia Fen, Victoria (Kershaw et al. 2007), Redhead Lagoon, New South Wales (Williams et al. 2006) and Barrington Tops, New South Wales (Sweller and Martin 2001) suggests that this record reflects regional conditions across southeastern Australia. The TOR record also correlates well with that from nearby Native Companion Lagoon which suggests that the LGM was actually an extended period of ca. 8 - 10 kyr, characterised by 2 periods of increased aridity (ca. 30 - 26.5 kyr and 21 - 19.5 kyr) (Petherick et al. 2008). A growing number of records from across the Southern Hemisphere e.g. New Zealand (Suggate and Almond 2003; Alloway et al. 2007; Newnham et al. 2007), Chile (Denton et al. 1999), Antarctica (Röthlisberger et al. 2002; EPICA 2006) and Australia (Smith 2009) also show evidence that the LGM encompassed a longer period of

  19. Patagonian glacier response during the late glacial-Holocene transition.

    PubMed

    Ackert, Robert P; Becker, Richard A; Singer, Brad S; Kurz, Mark D; Caffee, Marc W; Mickelson, David M

    2008-07-18

    Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (50 degrees S), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 +/- 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49 degrees S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation-reflecting changes in the Southern Westerly circulation-rather than regional cooling.

  20. Deformation of Eemian and Glacial ice at NEEM, Greenland

    NASA Astrophysics Data System (ADS)

    Keegan, Kaitlin; Dahl-Jensen, Dorthe; Montagnat, Maurine; Weikusat, Ilka; Kipfstuhl, Sepp

    2015-04-01

    New findings from deep Greenland ice cores and airborne radio echo sounding (RES) images show that basal ice flow is very unstable, and a basal layer of disturbed ice is often observed. At NEEM, Greenland this folding occurs at the boundary between the Eemian and glacial ice regimes, suggesting that differences in physical properties of the ice play a role in the disturbance. Past work in metallurgy (Burke, 1957) and ice (Hammer et al., 1978; Langway et al., 1988; Dahl-Jensen et al., 1997), suggests that impurity content controls grain evolution, and therefore deformation, which we hypothesize to be analogous to the differences in ice flow seen deep in the NEEM ice core. Here we present results of fabric, grain size, impurity content, and deformation studies from samples above and below this unstable boundary in the ice sheet.

  1. Atmospheric CO2 concentrations over the last glacial termination.

    PubMed

    Monnin, E; Indermühle, A; Dällenbach, A; Flückiger, J; Stauffer, B; Stocker, T F; Raynaud, D; Barnola, J M

    2001-01-01

    A record of atmospheric carbon dioxide (CO2) concentration during the transition from the Last Glacial Maximum to the Holocene, obtained from the Dome Concordia, Antarctica, ice core, reveals that an increase of 76 parts per million by volume occurred over a period of 6000 years in four clearly distinguishable intervals. The close correlation between CO2 concentration and Antarctic temperature indicates that the Southern Ocean played an important role in causing the CO2 increase. However, the similarity of changes in CO2 concentration and variations of atmospheric methane concentration suggests that processes in the tropics and in the Northern Hemisphere, where the main sources for methane are located, also had substantial effects on atmospheric CO2 concentrations.

  2. Patagonian glacier response during the late glacial-Holocene transition.

    PubMed

    Ackert, Robert P; Becker, Richard A; Singer, Brad S; Kurz, Mark D; Caffee, Marc W; Mickelson, David M

    2008-07-18

    Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (50 degrees S), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 +/- 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49 degrees S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation-reflecting changes in the Southern Westerly circulation-rather than regional cooling. PMID:18635799

  3. Modeling East African tropical glaciers during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Doughty, Alice; Kelly, Meredith; Russell, James; Jackson, Margaret; Anderson, Brian; Nakileza, Robert

    2016-04-01

    The timing and magnitude of tropical glacier fluctuations since the last glacial maximum could elucidate how climatic signals transfer between hemispheres. We focus on ancient glaciers of the East African Rwenzori Mountains, Uganda/D.R. Congo, where efforts to map and date the moraines are on-going. We use a coupled mass balance - ice flow model to infer past climate by simulating glacier extents that match the mapped and dated LGM moraines. A range of possible temperature/precipitation change combinations (e.g. -15% precipitation and -7C temperature change) allow simulated glaciers to fit the LGM moraines dated to 20,140±610 and 23,370±470 years old.

  4. Hydrogeologic setting of the Glacial Lake Agassiz Peatlands, northern Minnesota

    USGS Publications Warehouse

    Siegel, Donald I.

    1981-01-01

    Seven test holes drilled in the Glacial Lake Agassiz Peatlands indicate that the thickness of surficial materials along a north-south traverse parallel to Minnesota Highway 72 ranges from 163 feet near Blackduck, Minnesota to 57 feet about 3 miles south of Upper Red Lake. Lenses of sand and gravel occur immediately above bedrock on the Itasca moraine and are interbedded with lake clay and till under the peatlands. Vertical head gradients measured in a piezometer nest near Blackduck on the moraine are downward, indicative of recharge to the regional ground-water-flow system. Vertical head gradients are upward in a piezometer nest on a sand beach ridge in the peatlands 12 miles north of Upper Red Lake. Numerical sectional models indicate that this discharge probably comes from local flow systems recharged from ground-water mounds located under large raised bogs.

  5. Inverse vertical migration and feeding in glacier lanternfish (Benthosema glaciale).

    PubMed

    Dypvik, Eivind; Klevjer, Thor A; Kaartvedt, Stein

    2012-01-01

    A bottom-mounted upward-facing 38-kHz echo sounder was deployed at ~400 m and cabled to shore in Masfjorden (~60(°)52'N, ~5(°)24'E), Norway. The scattering layers seen during autumn (September-October) 2008 were identified by trawling. Glacier lanternfish (Benthosema glaciale) were mainly distributed below ~200 m and displayed three different diel behavioral strategies: normal diel vertical migration (NDVM), inverse DVM (IDVM) and no DVM (NoDVM). The IDVM group was the focus of this study. It consisted of 2-year and older individuals migrating to ~200-270 m during the daytime, while descending back to deeper than ~270 m during the night. Stomach content analysis revealed increased feeding during the daytime on overwintering Calanus sp. We conclude that visually searching glacier lanternfish performing IDVM benefit from the faint daytime light in mid-waters when preying on overwintering Calanus sp. PMID:24391270

  6. Space-geodetic constraints on glacial isostatic adjustment in Fennoscandia.

    PubMed

    Milne, G A; Davis, J L; Mitrovica, J X; Scherneck, H G; Johansson, J M; Vermeer, M; Koivula, H

    2001-03-23

    Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisfies independent geologic constraints and bounds both the average viscosity in the upper mantle (5 x 10(20) to 1 x 10(21) pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +/- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than approximately 1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field. PMID:11264528

  7. Space-Geodetic Constraints on Glacial Isostatic Adjustment in Fennoscandia

    NASA Astrophysics Data System (ADS)

    Milne, G. A.; Davis, J. L.; Mitrovica, Jerry X.; Scherneck, H.-G.; Johansson, J. M.; Vermeer, M.; Koivula, H.

    2001-03-01

    Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisfies independent geologic constraints and bounds both the average viscosity in the upper mantle (5 × 1020 to 1 × 1021 pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +/- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than ~1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field.

  8. Post-glacial rebound and asthenosphere viscosity in Iceland

    SciTech Connect

    Sigmundsson, F. )

    1991-06-01

    During the Weichselian glaciation Iceland was covered with an ice cap which caused downward flexure of the Earth's surface. The post-glacial rebound in Iceland was very rapid, being completed in about 1,000 years. The length of this time interval constrains the maximum value of asthenosphere viscosity in Iceland to be 1 {times} 10{sup 19} Pa s or less. Further clarification of the ice retreat and uplift history may reveal lower viscosity. Current changes in the mass balance of Icelandic glaciers must lead to measurable elevation changes considering this low viscosity. Expected current elevation changes around the Vatnajoekull ice cap are of the order of 1 cm per year, due to mass balance change in this century.

  9. Simulations of cataclysmic outburst floods from Pleistocene Glacial Lake Missoula

    USGS Publications Warehouse

    Denlinger, Roger P.; O'Connell, D. R. H.

    2009-01-01

    Using a flow domain that we constructed from 30 m digital-elevation model data of western United States and Canada and a two-dimensional numerical model for shallow-water flow over rugged terrain, we simulated outburst floods from Pleistocene Glacial Lake Missoula. We modeled a large, but not the largest, flood, using initial lake elevation at 1250 m instead of 1285 m. Rupture of the ice dam, centered on modern Lake Pend Oreille, catastrophically floods eastern Washington and rapidly fills the broad Pasco, Yakima, and Umatilla Basins. Maximum flood stage is reached in Pasco and Yakima Basins 38 h after the dam break, whereas maximum flood stage in Umatilla Basin occurs 17 h later. Drainage of these basins through narrow Columbia gorge takes an additional 445 h. For this modeled flood, peak discharges in eastern Washington range from 10 to 20 × 106 m3/s. However, constrictions in Columbia gorge limit peak discharges to 6 m3/s and greatly extend the duration of flooding. We compare these model results with field observations of scabland distribution and high-water indicators. Our model predictions of the locations of maximum scour (product of bed shear stress and average flow velocity) match the distribution of existing scablands. We compare model peak stages to high-water indicators from the Rathdrum-Spokane valley, Walulla Gap, and along Columbia gorge. Though peak stages from this less-than-maximal flood model attain or exceed peak-stage indicators along Rathdrum-Spokane valley and along Columbia gorge, simulated peak stages near Walulla Gap are 10–40 m below observed peak-stage indicators. Despite this discrepancy, our match to field observations in most of the region indicates that additional sources of water other than Glacial Lake Missoula are not required to explain the Missoula floods.

  10. On the Timing of Glacial Terminations in the Equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Khider, D.; Ahn, S.; Lisiecki, L. E.; Lawrence, C.; Kienast, M.

    2015-12-01

    Understanding the mechanisms through which the climate system responds to orbital insolation changes requires establishing the timing of events imprinted on the geological record. In this study, we investigate the relative timing of the glacial terminations across the equatorial Pacific in order to identify a possible mechanism through which the tropics may have influenced a global climate response. The relative termination timing between the eastern and western equatorial Pacific was assessed from 15 published SST records based on Globigerinoides ruber Mg/Ca or alkenone thermometry. The novelty of our study lies in the accounting of the various sources of uncertainty inherent to paleoclimate reconstruction and timing analysis. Specifically, we use a Monte-Carlo process allowing sampling of possible realizations of the time series that are functions of the uncertainty of the benthic δ18O alignment to a global benthic curve, of the SST uncertainty, and of the uncertainty in the change point, which we use as a definition for the termination timing. We find that the uncertainty on the relative timing estimates is on the order of several thousand years, and stems from age model uncertainty (60%) and the uncertainty in the change point detection (40%). Random sources of uncertainty are the main contributor, and, therefore, averaging over a large datasets and/or higher resolution records should yield more precise and accurate estimates of the relative lead-lag. However, at this time, the number of records is not sufficient to identify any significant differences in the timing of the last three glacial terminations in SST records from the Eastern and Western Tropical Pacific.

  11. Mega-scale glacial lineations and drumlins: a morphological continuum?

    NASA Astrophysics Data System (ADS)

    Spagnolo, M.; Stokes, C. R.; Clark, C. D.; Dunstone, R. B.

    2012-04-01

    Mega-scale glacial lineations (MSGL) are highly elongate ridges that maintain a parallel conformity over length of 10s of km. Investigation of relict MSGL suggests that they form under fast flowing ice streams. This has now been verified by direct imaging of the bed of Rutford ice stream, West Antarctica. However, the mechanism(s) of MSGL formation is rather poorly understood, although some divergent theories and models have been suggested. Some of these theories have developed from concepts and models initially proposed to explain the formation of another glacial bedform, the drumlin. This would support the idea of a subglacial bedform continuum, i.e. that a distinction amongst related bedforms is artificial because each 'type' of landform gradually evolves into the other and they are the expression of the same fundamental process of formation. To date, very few (if any?) studies have attempted to systematically quantify the morphometric (size and shape) differences and similarities between drumlins and MSGL using a large database. In this paper, we present the result of an extensive analysis of drumlins and MSGL that are found within a single flow-set formed by the Dubawnt lake palaeo-ice stream on the central Canadian Shield. Thousands of MSGL and drumlins have been mapped there for analysis of bedform length, width, elongation, shape (planar asymmetry) and spatial distribution. Results are also compared to other published studies. Altogether, they strongly suggest that the morphometric difference between a 'drumlin' and 'MSGL' is subtle and that, for most variables, the frequency distribution of one landform population largely overlap with that of the other. This supports the idea that the same process might indeed be responsible for the formation of both.

  12. A benchmark study for glacial isostatic adjustment codes

    NASA Astrophysics Data System (ADS)

    Spada, G.; Barletta, V. R.; Klemann, V.; Riva, R. E. M.; Martinec, Z.; Gasperini, P.; Lund, B.; Wolf, D.; Vermeersen, L. L. A.; King, M. A.

    2011-04-01

    The study of glacial isostatic adjustment (GIA) is gaining an increasingly important role within the geophysical community. Understanding the response of the Earth to loading is crucial in various contexts, ranging from the interpretation of modern satellite geodetic measurements (e.g. GRACE and GOCE) to the projections of future sea level trends in response to climate change. Modern modelling approaches to GIA are based on various techniques that range from purely analytical formulations to fully numerical methods. Despite various teams independently investigating GIA, we do not have a suitably large set of agreed numerical results through which the methods may be validated; a community benchmark data set would clearly be valuable. Following the example of the mantle convection community, here we present, for the first time, the results of a benchmark study of codes designed to model GIA. This has taken place within a collaboration facilitated through European Cooperation in Science and Technology (COST) Action ES0701. The approaches benchmarked are based on significantly different codes and different techniques. The test computations are based on models with spherical symmetry and Maxwell rheology and include inputs from different methods and solution techniques: viscoelastic normal modes, spectral-finite elements and finite elements. The tests involve the loading and tidal Love numbers and their relaxation spectra, the deformation and gravity variations driven by surface loads characterized by simple geometry and time history and the rotational fluctuations in response to glacial unloading. In spite of the significant differences in the numerical methods employed, the test computations show a satisfactory agreement between the results provided by the participants.

  13. Global Ice-loading History Reconstructed Over Five Glacial Cycles

    NASA Astrophysics Data System (ADS)

    Williams, F. H.; Grant, K. M.; Tamisiea, M. E.; Rohling, E. J.; Hibbert, F. D.

    2014-12-01

    High resolution ice-loading reconstructions are a vital tool not only for palaeoclimate studies, but also for providing a palaeoenvironmental context to human development. Here we present a global ice-loading history developed using the high resolution, Red Sea relative sea-level (RSL) record. (Siddall et al. 2003, Rohling et al. 2009, Grant et al. in submission) We use glacial isostatic adjustment modelling to determine a set of corrections to the Red Sea RSL record, which is then translated into a global mean sea level. This global mean sea level allows us to calculate a global ice volume. Global ice volume is geographically distributed within our ice-loading history according to currently available data regarding ice margins, their timing, and constraints on maximum ice load. Where constraints are sparse we use a combination of ICE-5G (Peltier, 2004) and the de Boer coupled ice sheet model (de Boer et al, 2014) as a template for ice distribution. Although an ice-loading history for the past 5 Myr exists, this is the first time that geographic constraints have been applied to global ice volumes over 5 glacial cycles. Our ice-loading reconstruction is further supported by the high resolution of our source RSL data. Our ice-loading history is tested against a global compilation of coral sea-level indicators (Hibbert et al., in prep.), and compared with ice histories developed from alternate ice volume reconstructions or RSL records, including a global ice history based on that developed by de Boer et al. (2014), the sea-level record of Waelbroeck et al. (2002) and a simple ice history based on the δ18O stack of Lisiecki and Raymo (2005).

  14. No change in the neodymium isotope composition of deep water exported from the North Atlantic on glacial-interglacial timescales

    NASA Astrophysics Data System (ADS)

    Vance, D.; Foster, G.

    2005-12-01

    Sea Water. Our data require that the NADW mix during glacial periods resulted in a co-incidentally similar Nd isotope composition despite the changes in the sites of convection that models of the circulation seem to demand2. 1 Piotrowski, A. et al. 2005, Science 307, 1933 2 Rahmstorf, S. 2002, Nature 419, 207

  15. Does Temperature (Rather than Precipitation) Dictate the Geomorphic Legacy of Glacial Intervals in Unglaciated Mid-Latitude Terrains?

    NASA Astrophysics Data System (ADS)

    Marshall, J. A.; Roering, J. J.; Bartlein, P. J.; Praskievicz, S. J.; Gavin, D. G.; Hales, T. C.; Granger, D. E.

    2014-12-01

    Whereas glaciated landscapes record increased erosional efficiency through moraines and U-shaped valleys, unglaciated hillslopes and rivers lack a mechanistic theory for climate controls on their dynamics and form. Changes in precipitation and associated aggradation due to vegetation loss or incision due to increased river discharge are commonly invoked when considering the effect of glacial intervals on unglaciated terrains, but there is scant evidence supporting or discounting these hypotheses. Surprisingly, there is little consideration that temperature, rather than precipitation, may dictate the frequency, magnitude, or style of erosion in unglaciated landscapes during glacial intervals. Here, we present results combining a mechanistic frost-cracking model with downscaled general circulation model output to predict the extent and intensity of sediment production via frost processes across the unglaciated Oregon Coast Range (OCR) during the Last Glacial Maximum (LGM). Our results show that in this mid-latitude region, well south of the Cordilleran ice sheet, frost-driven processes likely shaped 90% of the present-day landmass during the LGM. A suite of geomorphic and vegetation data from a 50-ky sediment core from a paleo landslide-dammed lake in the OCR support our model results. Our study site, Little Lake, is located in the central portion of the OCR, over 400 m south of the maximum extent of the Cordilleran ice sheet. Based on 10Be-derived erosion rates, present-day catchment erosion rates average 0.07 ± 0.03 mm/yr (mean ± sd), while LGM erosion rates remained constant around 0.19 ± 0.01 mm/yr. These LGM values are nearly 3X greater than present-day erosion rates and coincide with high frost cracking intensity predicted by our model. We also observe a transition from finely laminated lacustrine clays and sands to coarse lacustrine blue-grey sands at ~ 28 ka, during the transition to the LGM. The presence of Picea sitchensis (Sitka spruce) and Abies

  16. Dansgaard-Oeschger Oscillations and the Bi-Polar SeeSaw in a Comprehensive Model of Glacial Climate

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.; Vettoretti, G.

    2013-12-01

    The millennial timescale variability characteristic of Marine Oxygen Isotopic Stage 3 that is observed most clearly in Summit, Greenland ice-cores has never been adequately explained. The mechanism responsible for the bi-polar seesaw relationship between the Polar Regions that accompanies these events has remained similarly enigmatic. This situation has continued to exist in large part as a consequence of the fact that the D-O oscillation has never been shown to arise in a comprehensive coupled model of glacial climate. We will describe a series of very long timescale high resolution integrations of the NCAR CESM1 model under glacial boundary conditions in which the continental ice cover is assumed to be fixed to that of the new ICE-6G (VM5a) model. Greenhouse gases are also fixed to those inferred in the basis of Antarctic ice-core measurements. In order that the equilibrium dynamical state of the ocean not be prejudiced by the initial conditions, the ocean is initialized from a state of rest with modern ocean heat content. The spin-up of the model to statistical equilibrium is characterized by the existence of a series of cooling thresholds which, once crossed, lead the climate system into full glacial cold conditions in which sea ice cover has significantly expanded. In the high spatial resolution version of CESM1, the same resolution employed in CMIP5 experiments, we find that the glacial state is unsteady and characterized by millennium timescale oscillations, each of which has the form of a relaxation oscillation with the fast timescale warming phase of the oscillation caused by a rapid onset of deep water production in the North Atlantic due to convective instability of the water column. The subsequent slow timescale phase of each oscillation is associated with a slow expansion of sea ice cover which leads the system back into stadial conditions. These characteristics accurately mimic the GRIP and NGRIP records of individual D-O oscillations, not only in

  17. Constraining the timing of last glacial plucking of tors on Cumberland Peninsula, Baffin Island, Eastern Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Margreth, Annina; Gosse, John; Dyke, Arthur

    2014-05-01

    Highly-weathered rock outcrops (tors) often occur on regolith-covered, low-relief upland plateaus in formerly glaciated polar landscapes. Owing to their advanced weathering degree and lack of glacial erosional or depositional features, they have traditionally been interpreted to have escaped ice sheet coverage as nunatak refugia for flora and fauna. However, in many places terrestrial cosmogenic nuclide (TCN) exposure dated erratic blocks deposited on the regolith and the asymmetric streamlining of tor outcrops allude to past ice coverage. Complex cosmic ray exposure histories of ice cover have been deciphered using two radiogenic nuclides with dissimilar decay rates. However, while 26Al/10Be ratios can indicate that the rock had been previously buried by ice, the ratios alone cannot determine when the cover occurred. Thus, interpretation that ice cover occurred during the last glacial maximum (LGM) may be flawed. We have developed a novel approach to interpret ratios of TCN in the context of complex exposure histories accounting for recurring burial by cold-based ice and address the problem of episodic glacial plucking. First, we establish the average exposure:cover ratio for the tor sites we visited. Assuming orbital pacing of glacial-interglacial cycles, we model plausible exposure histories of periodic exposure and burial intervals. The majority of the 26 samples collected from highly-weathered tors on Cumberland Peninsula interfjord plateaus require average relative exposure durations of 20% within a glacial-interglacial cycle (i.e., 20 ka of exposure and 80 ka of ice coverage). Three samples located along narrow, highly-weathered coastal ridges indicate ice-free conditions throughout their entire exposure history. Minimum total exposure durations range from 320 ka up to 1.8 Ma, which are approximately twice as long as previous estimates of total exposure histories. This model assumes ice coverage during LGM, but a Monte Carlo simulation has shown that several

  18. Monitoring of Bashkara glacial lakes (the Central Caucasus) and modelling of their potential outburst.

    NASA Astrophysics Data System (ADS)

    Krylenko, I.; Norin, S.; Petrakov, D.; Tutubalina, O.; Chernomorets, S.

    2009-04-01

    models, based on solving of two-dimensional Saint-Venant equations -"River" (the Russia, author V.Belikov) and "Flo-2D" (the USA, authors J.S.O'Brien, R.Garcia) were used. The "River" model is based on the irregular triangular grid, therefore it is possible to calculate flow in details. On the other hand there is no debris flow block in this model yet and "Flo-2D" was applied to calculate potential debris flow parameters, because transformation of flood into debris flow is likely here. Input data for simulation were following: digital terrain model of Adylsu valley, made on the on the basis of map with scale 1:25000, outburst hydrograph, calculated for case of englacial drainage channels formation (Vinogradov's model, Russia), some empirical relationships between volume of the glacial lake and maximum discharge of outburst (i.e. Clague and Mathews, Walder and Costa) were also applied. The mean value of the maximum discharge for potential outburst obtained by different methods was about 150 m3 /c. According to results of hydrodynamic modelling, movement of flood wave downstream the valley will be fast, peak of flood will cover distance from upper part of valley to lowest (8 km) for about half an hour. The depth of the flow on the floodplain is about 1-1.5 m and could reach 6 m in some sites. There are hotel, large camping site and several bridges in the hazardous zone. In 2008 early warning system was designed and installed at the Bashkara lake.

  19. Glacial deposits at the Boyne Bay Limestone Quarry, Portsoy, and their place in the late Pleistocene history of northeast Scotland

    NASA Astrophysics Data System (ADS)

    Peacock, J. Douglas; Merritt, Jon W.

    2000-07-01

    The glacial deposits at the Boyne Bay Limestone Quarry near Portsoy, a key Quaternary Site of Special Scientific Interest, comprise (i) a sandy, partly weathered diamicton (Craig of Boyne Till Formation, CBTF) resting on decomposed bedrock, (ii) a central, variably glaciotectonised assemblage of dark clay, diamicton and sand, with rafts of sand and weathered diamicton (Whitehills Glacigenic Formation, WGF), and (iii) an upper dark sandy diamicton (Old Hythe Till Formation, OHTF). The CBTF was probably derived from the west or southwest, and the WGF from seawards. Structures within the OHTF conform to deposition by east- or southeast-moving ice from the Moray Firth, but some erratics indicate derivation from the south. The CBTF is believed to pre-date the last (lpswichian) interglacial, but the WGF and OHTF both post-date the early Middle Devensian, and are probably of Late Devensian age. It is proposed that the OHTF was deposited by ice from inland which was directed eastwards near the coast by a vigorous glacier in the Moray Firth, and that the complex, Late Devensian glacial history of the south coast of the Moray Firth as a whole is the result of the interplay of these two contemporary ice-masses. British Geological Survey. © NERC 2000.

  20. New Benthic δ18o Stacks and Age Models for the Last Glacial Cycle (0-150 kyr ago)

    NASA Astrophysics Data System (ADS)

    Lisiecki, L. E.; Stern, J. V.

    2014-12-01

    The δ18O of formainiferal calcite is a common paleoceanographic proxy, which measures ice volume and deep water temperature change. Foraminiferal δ18O is also often used to create marine sediment core age models by aligning down-core variations in δ18O to a global stack, or average. However, the most commonly used stack, known as "LR04," has an outdated age model, assumes global benthic δ18O synchrony, and is biased to the Atlantic [Lisiecki and Raymo, 2005]. Here we present six regional benthic δ18O stacks of the last glacial cycle (0-150 kyr) that are combined to form a volume-weighted global stack with data from 263 sites. We develop new benthic δ18O age models using regional radiocarbon dates from 0-40 ka and correlations to the GICC05 layer-counted Greenland age model from 40-56 ka [Svensson et al., 2008] and U-Th-dated Chinese speleothems from 56-150 kyr [Wang et al., 2001; Cheng et al., 2009; Barker et al, 2011]. Additional features of the new stacks are diachronous benthic δ18O changes during the last two glacial terminations and explicit age uncertainty estimates throughout. Our new global stack indicates that some portions of the LR04 stack are up to 4 kyr too young. We estimate corrections to the LR04 age model throughout the Pleistocene that imply faster climate responses to orbital forcing than previously estimated.

  1. Radiocarbon Anomalies of Surface Waters in the Glacial-to-Deglacial Low-to-Mid-Latitude Atlantic

    NASA Astrophysics Data System (ADS)

    Sarnthein, M.; Balmer, S.; Mudelsee, M.

    2015-12-01

    14C reservoir ages of surface waters are crucial for dating marine sediment records of the last 40,000 yr. In the low-latitude Atlantic, time series of 14C reservoir ages were reconstructed for five sites using the 14C plateau-tuning technique and supplemented by a reservoir age record from southern mid-latitudes (Skinner et al., 2010). Results suggest small-scale spatial and short-term (multi-centennial-scale) changes in reservoir age over last glacial-to-deglacial times, thus modify previously assigned calendar age chronologies by up to 500-2500 yr. During late peak glacial, enhanced summer winds off South Brazil and strengthened southerly trades off Namibia induced local reservoir ages of up to 900-1100 yr, whereas surface water ages in the Cariaco lagoon fell close to zero, a result of dominant CO2 exchange with the atmosphere. Near 16.05 ka, reservoir ages dropped to a minimum of 170-420 yr all over the South Atlantic, possibly the response to an immediately preceding short-term major rise in atmospheric pCO2 and East Antarctic temperatures. Our 14C reservoir ages provide a first basis for systematic data-model comparisons. They largely confirm model-based estimates for the LGM (Butzin et al., 2012) that have been derived from changes in both atmospheric 14C concentration and reductions in AMOC. Deviations are constrained to coastal upwelling zones in part insufficiently resolved by numerical models.

  2. Simulating soil organic carbon in yedoma deposits during the Last Glacial Maximum in a land surface model

    NASA Astrophysics Data System (ADS)

    Zhu, D.; Peng, S.; Ciais, P.; Zech, R.; Krinner, G.; Zimov, S.; Grosse, G.

    2016-05-01

    Substantial quantities of organic carbon (OC) are stored in the thick, ice-rich, and organic-rich sediments called yedoma deposits, distributed in eastern Siberia and Alaska today. Quantifying yedoma carbon stocks during the glacial period is important for understanding how much carbon could have been decomposed during the last deglaciation. Yet processes that yield the formation of thick frozen OC in yedoma deposits are missing in global carbon cycle models. Here we incorporate sedimentation parameterizations into the Organizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE-MICT) land surface model, which leads to reasonable results in OC vertical distribution and regional budgets, compared with site-specific observations and inventories for today's nondegraded yedoma region. Simulated total soil OC stock for the northern permafrost region during the Last Glacial Maximum (LGM) is 1536-1592 Pg C, of which 390-446 Pg C is within today's yedoma region. This result is an underestimation since we did not account for the potentially much larger yedoma area during the LGM than the present day.

  3. The high-level marine shell-bearing deposits of Clava, Inverness-shire, and their origin as glacial rafts

    NASA Astrophysics Data System (ADS)

    Merritt, J. W.

    The enigmatic high-level, till-covered, cold water marine shell-bearing deposits at Clava, Inverness-shire, are described systematically in the light of new observations made at sites documented in the literature. The marine deposits, named here as the Clava Shelly Formation, include three members, the unfossiliferous Clava sand, the underlying Clava shelly clay and a shelly diamicton known as the Clava shelly till. The first two members form a conformable coarsening-upwards sequence containing a shallow water, high-boreal to low-Arctic fauna and flora. The Clava shelly till is essentially glacially re-sedimented glaciomarine clay containing a sparse fauna, but its stratigraphic relationship and age are not absolutely clear. The shelly clay is ascribed to a Mid-Devensian interstadial episode on the basis of amino-acid dating. It is concluded that the Clava shelly clay, and several discrete masses of Clava sand and shelly till, are glacially transported allochthons derived from the Great Glen. The rafts were probably detached as a result of high pore water pressure building up in laterally restricted aquifers beneath a confined glacier that flowed north-eastwards across the Loch Ness basin. This glacier was deflected eastwards and upwards towards Clava by ice flowing from the northern Highlands along the Beauly Firth during the build-up of the last Scottish ice-sheet. The rafts were stacked at the ice margin when the glacier entered the Nairn Valley before being overriden by the expanding ice-sheet.

  4. Correlation and interpretation of paleosols and loess across European Russia and Asia over the last interglacial-glacial cycle

    NASA Astrophysics Data System (ADS)

    Rutter, Nathaniel W.; Rokosh, Dean; Evans, Michael E.; Little, Edward C.; Chlachula, Jiri; Velichko, Andrei

    2003-07-01

    Loess-paleosol sequences of the last interglacial-glacial cycle are correlated from European Russia to central Siberia and the Chinese Loess Plateau. During cold periods represented by marine oxygen isotope stages (OIS) 2 and 4, loess deposition dominated in the Russian Plain and the Loess Plateau. In central Siberia, loess deposition took place also, but five to seven thin, weakly developed pale