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Sample records for glaciales tierra del

  1. Do crustal deformations observed by GPS in Tierra del Fuego (Argentina) reflect glacial-isostatic adjustment?

    NASA Astrophysics Data System (ADS)

    Mendoza, L.; Richter, A.; Hormaechea, J. L.; Perdomo, R.; Del Cogliano, D.; Dietrich, R.; Fritsche, M.

    2010-09-01

    Vertical site velocities determined by geodetic GPS observations in the Lago Fagnano area, Tierra del Fuego main island, are interpreted with respect to their potential relation with the glacial-isostatic crustal response to ice mass changes. The spatial pattern of the uplift rates, in combination with the horizontal crustal deformation pattern, point towards a fault-tectonic rather than glacial-isostatic origin of the determined vertical crustal deformations. This implies rather small GIA effects pointing towards relatively small Holocene ice-mass changes in Tierra del Fuego. However, these findings are considered to be preliminary. They should be confirmed by additional observations covering an extended area with GPS sites.

  2. Synchronous acceleration of ice loss and glacial erosion, Glaciar Marinelli, Chilean Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Koppes, Michèle; Hallet, Bernard; Anderson, John

    To contribute to the understanding of the influence of climate on glacial erosion and on orogenic processes, we report contemporary glacial erosion rates from a calving glacier in the Southern Andes and elucidate the influence of ice dynamics on erosion. Using seismic profiles of sediments collected in a proglacial fjord and a documented history of retreat, we determine the time-varying sediment flux of Glaciar Marinelli as a measure of basin-wide erosion rates, and compare these rates with the annual ice budget reconstructed using NCEP-NCAR reanalysis climate data from 1950 to 2005. The rate of erosion of the largest tidewater glacier in Tierra del Fuego averaged 39±16 mm a-1 during the latter half of the 20th century, with an annual maximum approaching 130 mm a-1 following a decade of rapid retreat. A strong correlation emerges between the variable rate of ice delivery to the terminus and the erosion rate, providing quantitative insight into the relationship between ice fluxes and glacial erosion rates. For Glaciar Marinelli, as for other calving glaciers for which suitable data exist, the marked retreat and thinning over the past 50 years have resulted in a period of accelerated basal sliding and unusually rapid erosion.

  3. Glacial geomorphology of the Pleistocene Lake Fagnano ice lobe, Tierra del Fuego, southern South America

    NASA Astrophysics Data System (ADS)

    Coronato, A.; Seppälä, M.; Ponce, J. F.; Rabassa, J.

    2009-11-01

    A regional geomorphological study is presented of the southern and eastern coast of Lake Fagnano, one of the most extensive glacial areas of Tierra del Fuego Island, at the southernmost tip of South America. A palaeoglacial reconstruction is made, based on the location of erosional and depositional glacial landforms. The outlet glacier flowing eastwards from the Darwin Cordillera (Fuegian Andes, Chile) had more than 50 tributary glaciers. An alpine-type landscape, including arêtes, cirques, truncated spurs and hanging valleys developed in the western region of the present lake, whereas a piedmont-type landscape including lateral moraines, glaciofluvial and glaciolacustrine terraces and an ice-disintegration landscape developed in the eastern region. The glacier spread over the low ranges and lowlands through three different lobes, and was drained by four main outwash basins, directly into the Atlantic Ocean. The ice-covered area is estimated at 4000 km 2; the maximum length of the main lobe at 132 km, and the general slope at 8°. Four terminal positions of the glacier were recognized and related to the Inútil Bay and Beagle Channel glacial areas, located to the north and south, respectively. 14C dates from basal peats show that most of the area, especially the easternmost part and the southern coast, were free of ice by 12,300 years B.P. Fossil peat contained in the lower basal till deposits yield 14C dates of 31,000-48,200 years B.P., indicating that a glacial advance occurred in the area prior to the Last Glacial Maximum (ca. 25,000-23,000 cal. years B.P.).

  4. Erratic boulder trains and cosmogenic exposure dating of former glacial limits: A case-study from Tierra del Fuego, southernmost South America

    NASA Astrophysics Data System (ADS)

    Darvill, Christopher; Stokes, Chris; Bentley, Mike

    2014-05-01

    Erratic Boulder Trains (EBTs) are a spectacular yet poorly-understood glacial geomorphological feature. These linear clusters of glacial erratic boulders help to illustrate the flow-lines of former glaciers by pin-pointing the parent rock from which they have originated and are often used as targets for cosmogenic nuclide exposure dating. Consequently, there is a need to understand their geomorphological significance to improve ice-sheet reconstructions and provide important contextual information for dating studies. The EBTs in Tierra del Fuego are some of the finest examples of this feature in the world, and this paper presents the first comprehensive mapping and physical assessment of four boulder trains. Unlike most other examples, they were deposited laterally rather than medially and are tightly clustered, presenting linear features only a few kilometres long that contain hundreds to thousands of huge boulders (often >8 m in diameter). The size and angularity of the boulders strongly supports the hypothesis that they were deposited as a supraglacial rock avalanche. The boulders have been the subject of previous cosmogenic dating, which have yielded anomalously young ages from deposits thought to be hundreds of thousands of years old. Analysis of weathering proxies shows little difference between boulder trains thought to be of radically different ages, with important implications for the timing of glaciations and potentially contradicting previous age constraints on glacial limits in the region.

  5. Geomorphology and weathering characteristics of erratic boulder trains on Tierra del Fuego, southernmost South America: Implications for dating of glacial deposits

    NASA Astrophysics Data System (ADS)

    Darvill, Christopher M.; Bentley, Michael J.; Stokes, Chris R.

    2015-01-01

    Erratic boulder trains (EBTs) are a useful glacial geomorphological feature because they reveal former ice flow trajectories and can be targeted for cosmogenic nuclide exposure dating. However, understanding how they are transported and deposited is important because this has implications for palaeoglaciological reconstructions and the pre-exposure and/or erosion of the boulders. In this study, we review previous work on EBTs, which indicates that they may form subglacially or supraglacially but that large angular boulders transported long distances generally reflect supraglacial transport. We then report detailed observations of EBTs from Tierra del Fuego, southernmost South America, where their characteristics provide a useful framework for the interpretation of previously published cosmogenic nuclide exposure dates. We present the first comprehensive map of the EBTs and analyse their spatial distribution, size, and physical appearance. Results suggest that they were produced by one or more supraglacial rock avalanches in the Cordillera Darwin and were then transported supraglacially for 100 s of kilometres before being deposited. Rock surface weathering analysis shows no significant difference in the weathering characteristics of a sequence of EBTs, previously hypothesized to be of significantly different age (i.e., different glacial cycles). We interpret this to indicate that the EBTs are much closer in age than previous work has implied. This emphasises the importance of understanding EBT formation when using them for cosmogenic nuclide exposure dating.

  6. Extreme Environments in Tierra del Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Schultz, C.; D'Antoni, H.; Burgess, S.; Zamora, J.; Skiles, J.

    2007-12-01

    The upper timberline of the Andes Cordillera on the island of Tierra del Fuego at the tip of South America is an environment subject to extreme conditions. In order to further understand this environment, ecosystem parameters were measured within two transects of the Andes at Glaciar Martial and Cerro Guanaco. The measurements included pH, soil temperature, soil moisture, nitrogen, sodium and potassium concentration, chlorophyll absorbance, and irradiance in the ultraviolet range (200-400 nm). These data comprise a survey that serves as a baseline for an intensive research program. Chlorophyll concentration and soil data were within the range of our observations at several other sites, from Lapataia Bay on the southwestern boundary with Chile, through the eastern end of Lake Fagnano. However, unusual levels of solar irradiance were found in the open sites of both transects while those in the forest exhibited lower UV values, suggesting strong absorption and/or reflection by the forest canopy. High levels of UV radiation damage important biomolecules and may be partially responsible for the presence of life forms such as the krummholz belt in the upper timberline. These UV values may be due to the effects of global ozone depletion and the ozone hole. The low temperatures, strong winds, snow and ice-covered soil and especially the exposure to UV radiation make this area an extreme environment for life.

  7. Biological and behavioral determinants of fertility in Tierra del Fuego.

    PubMed

    Pascual, J; García-Moro, C E; Hernández, M

    2005-05-01

    The reproductive history of 182 women in postreproductive life or near menopause from the Chilean part of Tierra del Fuego was traced back by means of familial interviews. These postmenopausal women represent the population since almost the beginning of the settlement, and their reproductive years were spent on the island. Path analysis was applied to analyze fertility determinants of these women and to propose a complex model of interconnections among factors. The reproductive history of these women is characterized by a long fertile span, a short childbearing period, and low fertility. Age at menarche is relatively late, and the age of the women at first birth is mainly determined by their late age at marriage. The use of contraception is related to both spacing and stopping behaviors. The late age of women at marriage, the rhythm of conception, and practices of contraception are proposed as the main determinants of fertility in Tierra del Fuego.

  8. Bryophyte-cyanobacteria associations during primary succession in recently Deglaciated areas of Tierra del Fuego (Chile).

    PubMed

    Arróniz-Crespo, María; Pérez-Ortega, Sergio; De Los Ríos, Asunción; Green, T G Allan; Ochoa-Hueso, Raúl; Casermeiro, Miguel Ángel; de la Cruz, María Teresa; Pintado, Ana; Palacios, David; Rozzi, Ricardo; Tysklind, Niklas; Sancho, Leopoldo G

    2014-01-01

    Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronosequences in front of two receding glaciers with contrasting climatic conditions (wetter vs drier) at Cordillera Darwin (Tierra del Fuego) and found that most mosses had the capacity to support an epiphytic flora of cyanobacteria and exhibited high rates of N2 fixation. Pioneer moss-cyanobacteria associations showed the highest N2 fixation rates (4.60 and 4.96 µg N g-1 bryo. d-1) very early after glacier retreat (4 and 7 years) which may help accelerate soil development under wetter conditions. In drier climate, N2 fixation on bryophyte-cyanobacteria associations was also high (0.94 and 1.42 µg N g-1 bryo. d-1) but peaked at intermediate-aged sites (26 and 66 years). N2 fixation capacity on bryophytes was primarily driven by epiphytic cyanobacteria abundance rather than community composition. Most liverworts showed low colonization and N2 fixation rates, and mosses did not exhibit consistent differences across life forms and habitat (saxicolous vs terricolous). We also found a clear relationship between cyanobacteria genera and the stages of ecological succession, but no relationship was found with host species identity. Glacier forelands in Tierra del Fuego show fast rates of soil transformation which imply large quantities of N inputs. Our results highlight the potential contribution of bryophyte-cyanobacteria associations to N accumulation during post-glacial primary succession and further describe the factors that drive N2-fixation rates in post-glacial areas with very low N deposition.

  9. Bryophyte-Cyanobacteria Associations during Primary Succession in Recently Deglaciated Areas of Tierra del Fuego (Chile)

    PubMed Central

    Arróniz-Crespo, María; Pérez-Ortega, Sergio; De los Ríos, Asunción; Green, T. G. Allan; Ochoa-Hueso, Raúl; Casermeiro, Miguel Ángel; de la Cruz, María Teresa; Pintado, Ana; Palacios, David; Rozzi, Ricardo; Tysklind, Niklas; Sancho, Leopoldo G.

    2014-01-01

    Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronosequences in front of two receding glaciers with contrasting climatic conditions (wetter vs drier) at Cordillera Darwin (Tierra del Fuego) and found that most mosses had the capacity to support an epiphytic flora of cyanobacteria and exhibited high rates of N2 fixation. Pioneer moss-cyanobacteria associations showed the highest N2 fixation rates (4.60 and 4.96 µg N g−1 bryo. d−1) very early after glacier retreat (4 and 7 years) which may help accelerate soil development under wetter conditions. In drier climate, N2 fixation on bryophyte-cyanobacteria associations was also high (0.94 and 1.42 µg N g−1 bryo. d−1) but peaked at intermediate-aged sites (26 and 66 years). N2 fixation capacity on bryophytes was primarily driven by epiphytic cyanobacteria abundance rather than community composition. Most liverworts showed low colonization and N2 fixation rates, and mosses did not exhibit consistent differences across life forms and habitat (saxicolous vs terricolous). We also found a clear relationship between cyanobacteria genera and the stages of ecological succession, but no relationship was found with host species identity. Glacier forelands in Tierra del Fuego show fast rates of soil transformation which imply large quantities of N inputs. Our results highlight the potential contribution of bryophyte-cyanobacteria associations to N accumulation during post-glacial primary succession and further describe the factors that drive N2-fixation rates in post-glacial areas with very low N deposition. PMID:24819926

  10. Non-seasonality of births in Tierra del Fuego (Chile).

    PubMed

    Pascual, J; García-Moro, C; Hernández, M

    2000-01-01

    Tierra del Fuego is situated at the southern tip of the American continent, which conditions its environmental and climatic characteristics. The colonizing population arrived, at the end of the 19th century, from other Chilean regions (particularly from Chiloé) and diverse European countries, especially Britain and Croatia, but also Germany, Spain and Italy. In the present study, the existence of a seasonal pattern in 5430 births registered in the Chilean population of Tierra del Fuego from 1890 to 1995 was analysed. The analysis showed no seasonal distribution of births in the periods 1890-1920 and from 1946 to the present day, a phenomenon rarely reported in the literature. The absence of seasonality in birth distribution could be related to the great diversity in the origins of the population's families, the constant renovation of this and the declining importance of the administrative capital of the province of Tierra del Fuego, Porvenir, in favour of Punta Arenas, capital of the Magellanic region. In the period of maximum development of the capital of the province, a seasonal pattern was detected with a peak in April and a trough in October, which corresponds with a maximum of conceptions in July and, in general, during the early southern winter and a decline in births from late spring to mid-summer, with a trough in January. This birth distribution is interpreted as a subordination of activity and social life to the annual sheep cycle. In addition to temporal trends, the influence on the observed patterns of environmental parameters, father's occupation, seasonality of marriage and the origin of the parents were analysed.

  11. Taphonomy of guanaco bones in Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Borrero, Luis Alberto

    1990-11-01

    Guanaco carcasses are deposited in great quantities in Cabo San Pablo, Tierra del Fuego (Argentina), as a result of winter stress. Taphonomic studies indicate that the gnawing action of foxes on guanaco ( Lama guanicoe) carcasses produces only very tenuous marks on the bones. Lack of sustained interest in the carcasses by carnivores results in slow disarticulation. The articulated and disarticulated bones are exposed to heavy trampling by guanacos, a process that produces vertical migration of small/dense bones and fracturing of the most weathered bones. An understanding of this ongoing process is important for local archaeology, since modern bones are migrating into archaeological contexts. A regional approach to taphonomy is the most appropriate instrument to solve this and other related problems.

  12. Phytoseiid mites (Acari: Phytoseiidae) from Patagonia and Tierra del Fuego.

    PubMed

    Ferragut, Francisco; Navia, Denise

    2015-07-28

    Predatory phytoseiid mites have been intensively studied and surveyed in the last decades because of their economic importance as biocontrol agents of agricultural pests. However, many regions of the world remain unexplored and the diversity of the family worldwide is still fragmentary. Up to date no phytoseiid species have been collected in the southernmost part of the Earth down to latitude 45º S. In this study Phytoseiidae were sampled from native vegetation in southern Argentina and Chile in the regions of Patagonia and Tierra del Fuego Island. Thirteen species were collected, five of which were previously described and eight, Chileseius australis n. sp., Neoseiulus mapuche n. sp., Typhlodromips valdivianus n. sp., T. fissuratus n. sp., Amblyseius grandiporus n. sp., A. caliginosus n. sp., Typhlodromus (Anthoseius) anomalos n. sp. and Metaseiulus parabrevicollis n. sp. are proposed as new to science and are described and diagnosed.

  13. [Epidemiology of dog bite lesions in Tierra del Fuego, Argentina].

    PubMed

    Zanini, Fabián; Padinger, Patricia; Elissondo, María C; Pérez, Héctor

    2008-01-01

    The coexistence between man and dog has resulted in mutual benefits during thousands of years, nevertheless some problems have recently arisen where bite injuries have an important role. The aim of this work was to describe the epidemiological characteristics of dog bite lesions which occurred during a year in Tierra del Fuego. A descriptive observational, transversal study of patients who were admitted with dog bite injuries to clinic and pediatric emergency services of hospitals and health centers was carried out between 3/1/05 and 3/1/06. A total of 382 records were made. The children group represents 49.5%. The group between 5 and 9 year-old was the most affected (44.4%; IC95% 37.2-51.8). In the adult group, that between 15 and 24 year-old was the most affected (29.5%; IC95% 23.2-36.5). More lesions were registered in men (57.6%) than in women (42.4%) (chi2 = 8.6, p = 0.003). During spring and summer months, 56.5% of the lesions were registered. A 72.8% of the incidents occurred on the public highway. Dogs of big size were responsible of 49.7% (IC95% 44.6-54.9) of the injuries. The 89.8% of the incidents were caused by another person's dog. Of the lesions, 55.8% (IC95% 50.6-60.8) were registered in lower extremities and 11% (IC95% 8.1-14.7) in head and neck. These data show that dog bite lesions affect the health and impact in the quality of life of the population of Tierra del Fuego, Argentina.

  14. The Geologic and Geochemical Setting of Lago Fagnano, Tierra del Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Tingle, D.; Odle, K.; Knettel, P.; Redding, S.; Perry, E.; Ellins, K.; Ormiston, C.; Dovzak, N.; Anderson, S.

    2005-12-01

    Lago Fagnano, Tierra del Fuego, Argentina is the largest and southernmost ice-free lake on Earth. The isolated lake is unique because the geographic and geologic context provides information relating to the westerly wind patterns, interaction of multiple water sources (hot springs, glacial meltwater, precipitation, groundwater), and tectonic dynamics along a major transform fault. In March, 2005, four students and three teachers from Boerne High School, south-central Texas joined scientists from the United States, Argentina and Switzerland engaged in a geophysical survey of this lake. Lago Fagnano potentially contains within its sediments an undisturbed record of the geotectonic and global climate variability of past 20,000 years. The science team imaged the lake floor with a boat specially equipped to collect both high resolution data (high frequency), imaging the upper 10-15 meters of the sediment, and long range data (low frequency), penetrating 100 or more meters into the sediment. The group conducted field research of existing tectonic features at the eastern end of Tierra del Fuego, an activity directly tied to the research objectives of the science team. They also collected water and soil samples to assess chemical and isotopic trends in the Lago Fagnano region. The research performed can help to characterize the modern geochemical setting of the lake. Analyses of dissolved oxygen, NH4+, PO42-, pH (water) and N, P, and pH (soils) demonstrate a link between low nutrient levels and low biodiversity (which was confirmed by observation) in Tierra del Fuego. Water and soil data are incorporated into a database to facilitate comparisons to North American samples collected and analyzed during the Boerne High School summer field courses. Twenty-three ^18O and ^D analyses yielded a south-north isotopic trend across the Lago Fagnano region. ^18O and ^D transition from -11.92 to -3.53% and -87.81 to -40.26%, respectively, moving south to the Beagle Channel. These

  15. Holocene sedimentary record in Lago Fagnano (Tierra del Fuego): Paleoclimate implications

    NASA Astrophysics Data System (ADS)

    Vizcaino, Alexis; Anderson, Lysanna; Wahl, Dave; Dunbar, Rob; Guilderson, Tom; Moy, Chris

    2010-05-01

    Tierra del Fuego is the world's southernmost landmass outside of Antarctica. Together with Patagonia, it represents the only terrestrial region directly influenced by the southern hemisphere westerly winds. The climate of Tierra del Fuego is controlled by the Southern Ocean circumpolar flow and the South Pacific Gyre. This region is also a tectonically active area affected by volcanic and seismic activity related to South American and Scotia-Antarctic plate boundaries. Lago Fagnano is the largest lake in Tierra del Fuego. This E-W trending lake is 100 km long and 5-15 km wide. It lies along the Magallanes-Fagnano fault system that is part of the diffuse left-lateral Scotian Sea - South American plate boundary. Our investigations were carried out on an 8.4 m long piston core obtained at 69 m water depth in Bahía Grande (LF06-PC8), a southwestern lake sub-basin separated from the main lake by a shallow sill. Our studies are based on the integration of sediment, physical properties, pollen, and geochemical analyses. The age model for the core is based on tephrachronology and radiocarbon ages. Additionally, a 800 km long grid of high resolution seismic profiles support the sedimentary analyses and allow the correlation with other cores from within the lake basin. Three distinct intervals are observed in the core. The uppermost interval is characterized by laminated hemipelagic sedimentation with low frequency detrital depositional events. The second interval is affected by mass transport deposits including debris flow and turbidite events. And finally, the oldest interval is characterized by very thin and fine layers associated with high frequency detrital depositional events. Pollen and geochemical analyses (C/N) integrated with the sedimentological interpretation provide reliable proxy records of past variability in the westerly wind field as well as the regional precipitation regime. These records are compared to late glacial ice retreat in the neighboring areas

  16. Trichomycetes living in the guts of aquatic insects of Misiones and Tierra del Fuego, Argentina.

    PubMed

    López Lastra, Claudia C; Scorsetti, Ana C; Marti, Gerardo A; Coscarón, Sixto

    2005-01-01

    Fourteen species of Trichomycetes living in the guts of aquatic insects are reported from two provinces of Argentina, Misiones and Tierra del Fuego. Twelve of the species belong to the Harpellales and two are Amoebidiales. Five harpellid species are reported from Misiones in the extreme northeast of the country (Genistellospora homothallica, Harpella tica, Smittium culisetae, Smittium sp., Stachylina sp.) and seven are from Tierra del Fuego, the southern tip of South America (H. meridianalis, Glotzia sp., S. culicis, S. cellaspora, S. imitatum, Stachylina minima, Penella simulii). Insect hosts all were immature stages of Culicidae, Simuliidae, Chironomidae, Ceratopogonidae (Insecta: Diptera), and Ephemeroptera and Plecoptera. The lower diversity of Trichomycetes found at Misiones, which has a subtropical climate and rainforest vegetation, was due possibly to the warmer temperatures of the water (15-24 C), compared to the colder streams of Tierra del Fuego (9-15 C), with forests and steppes as typical vegetation.

  17. Epidemiological surveillance of ovine hydatidosis in Tierra del Fuego, Patagonia Argentina, 1997-1999.

    PubMed

    Zanini, Fabián; Gonzalo, Roberto; Pérez, Héctor; Aparici, Inés; Soto, Ximena; Guerrero, Juvenal; Cerrone, Gloria; Elissondo, Celina

    2006-06-15

    Cystic echinococcosis is the most prevalent zoonosis in Tierra del Fuego province, Argentina, with important economic, productive and public health consequences. The present work was performed to determine the ovine prevalence in Tierra del Fuego, Argentina, as well as to evaluate the quality of diagnostic systems in slaughterhouses. Moreover, genetic analyses to characterize the strain of Echinococcus granulosus involved in the region were done. The first actions to perform a diagnosis of the epidemiological situation of hydatidosis in Tierra del Fuego were done between 1976 and 1977. A canine prevalence of 80% and an ovine prevalence of 55% results were obtained. Since 1979 the control program of Hydatidosis of Tierra del Fuego was implemented. It was based on semiannual canine anthelmintic treatment with praziquantel at dose of 5mg/kg, and complemented with sanitary education and canine and ovine epidemiological surveillance. During May 1997-January 1999: 5,916 sheep coming from 20 farms of the programmatic area were evaluated. In the lamb category, hydatid cysts were not found. In the adults category, 62 infected animals were found (3.2%). The ovine prevalence was 1.1% and there was 100% of coincidence between diagnosis in the slaughterhouse, re-inspection in the laboratory and histopathological study. The marked decrease in the prevalence observed for sheep infection evidenced a destabilization of the biological cycle of the parasite. This could be explained by the application of a control program with uninterrupted systematic actions. Polymerase chain reaction-ribosomal ITS-1 DNA (rDNA) restriction fragment length polymorphism (PCR-RFLP) analysis and partial sequencing of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene were used to characterize E. granulosus isolates collected from different regions of Tierra del Fuego to determine which genotypes occurred in this region. The results revealed the presence of the G1 genotype (sheep-dog strain

  18. Gastrointestinal helminths of Commerson's dolphins Cephalorhynchus commersonii from central Patagonia and Tierra del Fuego.

    PubMed

    Berón-Vera, B; Pedraza, S N; Raga, J A; Gil de Pertierra, A; Crespo, E A; Alonso, M K; Goodall RNP

    2001-12-05

    The stomachs and intestines of 9 Commerson's dolphins incidentally caught in trawl nets in central Patagonia and 23 stranded on beaches in Tierra del Fuego were surveyed for helminth parasites. A total of 267 individuals belonging to 4 species of parasites (1 nematode, 3 digeneans) were found in the dolphins from the first area: Anisakis sp. (larvae type 1 = A. simplex), Braunina cordiformis, Hadwenius sp. and Pholeter gastrophilus. In the Tierra del Fuego dolphins, 142 specimens belonging to 3 species (2 nematodes, 1 digenean, 1 cestode) were found: A. simplex, Hadwenius sp. and Strobilocephalus triangularis. Only 2 of the helminth species were shared in the 2 study areas, A. simplex and Hadwenius sp., and both were more common in central Patagonia. Among the species, A. simplex was most prevalent and abundant in both study areas. In Tierra del Fuego, adults of A. simplex appeared in only 1 host. Hadwenius sp., P. gastrophilus and S. triangularis are new host records for Commerson's dolphin. Species diversity and species richness were low in both study areas. Helminth communities were more diverse in central Patagonia (t = 1.97, df = 258, p < 0.05) and species richness was higher in central Patagonia (S = 4). No differences in diversity were observed between females and males of central Patagonia (t = 1.97, df = 139, p < 0.05) and between females of central Patagonia and Tierra del Fuego. The results may suggest some differences in habitat use, diet and sex between Commerson's dolphin populations in the 2 study areas.

  19. Mitochondrial DNA diversity of feral pigs from Karukinka Natural Park, Tierra del Fuego Island, Chile.

    PubMed

    Aravena, P; Skewes, O; Gouin, N

    2015-04-28

    Control or eradication of exotic species is one of the greatest challenges facing biodiversity and ecosystem conservation. Domestic pigs (Sus scrofa domestica) were released and became feral in the southern region of Chilean Tierra del Fuego Island in the 1900s. Currently, they inhabit part of Karukinka Natural Park, an area of global conservation concern. To gain insight into the control of this invasive species, we analyzed genetic variation in the mitochondrial DNA control region to determine the origin and population subdivision of feral pigs in Tierra del Fuego. Sequences from a sample of 42 feral pigs, 10 domestic pigs from local farms, and references from other countries and commercial breeds revealed 2 highly differentiated populations, 1 in the western and the other in the eastern area of the park, each harboring a different haplotype, suggesting no connectivity between populations. Comparison of these haplotypes with reference sequences from other countries and commercial breeds indicated that feral pigs from Chilean Tierra del Fuego are of European origin, very likely from 2 separate introduction events. The haplotype found in the western feral population was also identified in domestic pigs from a farm. This raises concerns regarding the possible connectivity between stocks from local farms and the wild population. Based on these results, we recommend the development of strategies for controlling the population of this invasive species in Karukinka Natural Park.

  20. Heavy metal concentrations in litteral sediments from the Beagle Channel, Tierra del Fuego, Argentina.

    PubMed

    Amin, O; Ferrer, L; Marcovecchio, J

    1996-07-01

    For the first time the concentration of trace metals (Fe, Pb, Cu, Zn, Cd and total Hg) of sediments from the coastal zone of the Beagle Channel (Tierra del Fuego, in Southern Argentina) were measured. Atomic absorption spectrophotometry was utilized in order to determine the metal contents. The level of metals as observed in the sediments was recognized as the natural background, even though the use of normalization of lead, copper, and zinc to iron allowed the identification of the main sources of metal pollution for this environment. In order to develop future environmental monitoring programmes for the area of Ushuaia city and the Beagle Channel, the present results need to be considered.

  1. Holocene paleoclimate characterization in Lago Fagnano (Tierra del Fuego) using sedimentary, physical and geochemical proxies

    NASA Astrophysics Data System (ADS)

    Vizcaino Marti, A.; Dunbar, R. B.; Wahl, D.; Moy, C. M.; Mucciarone, D. A.; Anderson, L.; Guilderson, T. P.

    2010-12-01

    Tierra del Fuego is the world's southernmost landmass outside of Antarctica. Two features of ocean circulation control the climate of Tierra del Fuego: the Southern Ocean circumpolar flow and the South Pacific Gyre. Together with Patagonia, Tierra del Fuego is the only terrestrial region directly influenced by the southern hemisphere westerly winds. This region is also a tectonically active area affected by volcanic and seismic activity related to South American and Scotia-Antarctic plate boundaries. Accommodated along the Magallanes-Fagnano fault system, as part of the plate boundary, the Lago Fagnano is the largest lake in Tierra del Fuego. This E-W trending lake is 100 km long and 5-15 km wide. Our investigations were carried out on the upper 4 meters of an 8.4 m long piston core obtained at 69 m water depth in Bahía Grande (LF06-PC8); a southwestern lake sub-basin separated from the main lake by a shallow sill. Our studies are based on the integration of sediment description, physical properties, pollen, and geochemical analyses including C and N isotopes (1cm interval) and XRF scan (1mm interval). The age model for the core is based on radiocarbon ages and tephrochronology. Additionally, a 800 km long grid of high resolution seismic profiles support the sedimentary analyses and allow the correlation with other cores from within the lake basin. LF06-PC8 yields continuous and high accumulation-rate sedimentary sections for Lago Fagnano. The presented sediment record corresponds to a laminated hemipelagite with presence of a single but complex mass transport deposit interval. An accurate sedimentological interpretation of the core together with the radiocarbon ages and tephra dates allow to identify and characterize the main sedimentary processes occurring in the lake over the last 8 kyr. In addition, proxy data (C and N isotopes and XRF scan data) from the laminated hemipelagic interval provide a reliable record of past variability in the westerly wind field as

  2. Anomalous ocean load tide signal observed in lake-level variations in Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Richter, A.; Hormaechea, J. L.; Dietrich, R.; Perdomo, R.; Fritsche, M.; Del Cogliano, D.; Liebsch, G.; Mendoza, L.

    2009-03-01

    We demonstrate the application of a 100 km long lake as a sensor for studying the tidal effects on Tierra del Fuego main island. The lake-level variations observed in Lago Fagnano reflect both the direct response to the tidal potential and the indirect effect of the ocean tidal loading. Modeling both contributions explains the observed tidal signal in the lake to about 70%. Underestimated model load tide amplitudes are found to be probably responsible for the remaining difference. We interpret this discrepancy as a hint for regional elastic lithosphere properties differing substantially from those represented by currently available global models.

  3. Loss of helminth species diversity in the large hairy armadillo Chaetophractus villosus on the Tierra del Fuego Island, Argentina.

    PubMed

    Ezquiaga, M C; Abba, A M; Navone, G T

    2016-03-01

    The aim of this work is to compare the taxonomic diversity of parasite species of the large hairy armadillo Chaetophractus villosus in its native range and in another recently introduced population (Tierra del Fuego island), and to evaluate whether the isolation of the latter determines a decrease in its parasitic diversity. Forty specimens from Buenos Aires and Tierra del Fuego Provinces were collected and examined for helminths. Eleven parasite species were found in the native population, and only one species was present in Tierra del Fuego (Trichohelix tuberculata). This may be explained because isolation and climatic conditions prevent encounters between potential host species and infective forms of parasites. Further sampling will be needed throughout the entire Patagonia steppe to confirm how the characteristic parasitic fauna of C. villosus behaves across the armadillo's southern distribution.

  4. [Tierra del Fuego: the scientific-political construction of exclusion and counter-image of the ideal city dweller].

    PubMed

    Nacach, Gabriela

    2012-01-01

    Due to its late incorporation into the national State, the social, economic and political setting of the Argentine province Tierra del Fuego differed from that of the rest of the national territory. In the construction of dependent otherness, objectifications and representations were imposed by state-related and non-state-related institutions, among other agencies. In this context, the Salesian mission of La Candelaria and Ushuaia's Jail for recidivists stand out as spaces in which biopolitics was concretised. The native population and criminals in Tierra del Fuego were those to be subjugated. The thesis of the extinction of the Indian and the simultaneous exaltation of the criminal as the subject of progress identified the scientific and political mechanisms by which the exclusion of certain social groups (Tierra del Fuego's indigenous population) and the inclusion of others (criminals) were regulated.

  5. Isolation of Sphaerotilus-Leptothrix strains from iron bacteria communities in Tierra del Fuego wetlands.

    PubMed

    Schmidt, Bertram; Sánchez, Leandro A; Fretschner, Till; Kreps, Gastón; Ferrero, Marcela A; Siñeriz, Faustino; Szewzyk, Ulrich

    2014-11-01

    Sheath-forming iron- and manganese-depositing bacteria belonging to the Sphaerotilus-Leptothrix group (SLG) are widespread in natural and artificial water systems. Known requirements for their growth include the presence of organic substrates and molecular oxygen. High concentrations of reduced iron or manganese, although not necessary for most species, make their growth a noticeable phenomenon. Such microbial communities have been studied mostly in the Northern Hemisphere. Here, we present descriptions of diverse ochre-depositing microbial communities in Tierra del Fuego, Argentina, using a combined approach of microscopical examination, clone library construction and cultivation focused on SLG bacteria. To date, only few SLG type strains are available. The present work increases the number and diversity of cultivated SLG bacteria by obtaining isolates from biofilms and sediment samples of wetlands in Tierra del Fuego. Thirty isolates were selected based on morphological features such as sheath formation and iron/manganese deposition. Five operational taxonomic units (OTUs) were deduced. Sequencing of 16S rRNA genes showed that one OTU is identical to the Leptothrix mobilis Feox-1(T) -sequence while the four remaining OTUs show similarity values related to previously described type strains. Similarity values ranged from 96.5% to 98.8%, indicating possible new species and subspecies.

  6. Epidemiological surveillance of cystic echinococcosis in rural population of Tierra del Fuego, Argentina, 1997-2006.

    PubMed

    Zanini, Fabián; Suárez, Carlos; Pérez, Héctor; Elissondo, María C

    2009-03-01

    Cystic echinococcosis (CE) is the most prevalent zoonosis in Tierra del Fuego. In 1997, ulrasonography (US) was selected as the method of choice for the development of population surveys for epidemiological surveillance and early diagnosis in rural population. The aim of this work was to present the results of the epidemiological surveillance of CE by means of US in rural population of Tierra del Fuego, Argentina between 1997 and 2006. The ultrasonographic diagnostic was realized once a year. The population was stratified in children (4 to 17 years) and adults. From each individual, name, age, sex, actual residence and origin were registered. The images compatible with cysts were graded according to location, number and characteristics. A total of 1400 rural inhabitants were examined for CE. From the total of studied individuals, 27 (1.9%) exhibited images compatible with cysts on the abdominal ultrasound scan. Thirteen of these persons were finally diagnosed as having CE. The overall prevalence of CE was 0.9%. This value is in accordance with the decrease in the prevalence observed in the definitive host and the intermediate hosts (sheep and cattle). The absence of cases in children during the studied period, evidence no transmission of the disease to humans in the recent past.

  7. Atmospheric background trace elements deposition in Tierra del Fuego region (Patagonia, Argentina), using transplanted Usnea barbata lichens.

    PubMed

    Conti, Marcelo Enrique; Finoia, Maria Grazia; Bocca, Beatrice; Mele, Giustino; Alimonti, Alessandro; Pino, Anna

    2012-01-01

    Lichen, Usnea barbata, transplants taken from Tierra del Fuego (south Patagonia, Argentina) were tested as potential biomonitors of atmospheric airborne deposition in an apparently pristine environment. In 2005, lichens were sampled in a reference site (n = 31) and transplanted in the northern Region of Tierra del Fuego. After, respectively, 1 month and 1 year of exposure, we collected them. The aim of the study was to determine the bioaccumulation of 26 elements in order to evaluate the background levels in the selected area. Samples were analyzed by the sector field inductively coupled plasma mass spectrometry. Discriminant analysis on principal component analysis factors was applied in order to explore the relationship among the different elements as far as time and spatial variation in transplants regards. The analysis was tested by Monte Carlo test based on 999 replicates. The most important contamination source resulted to be the atmospheric soil particle deposition. Furthermore, the results were compared with those obtained from the lichens collected in central and southern Tierra del Fuego. This study confirms the ability of U. barbata to reflect the background levels of the 26 elements in that environment. Compared with other background sites in the world, we did confirm that Tierra del Fuego lichens have a low content of the studied elements. Tierra del Fuego turned out not to be a pristine environment as supposed, but it can be considered as a reference basal ecosystem for useful comparisons among different geographical areas. These findings can be very relevant and useful for environmental conservation programs.

  8. Deglacial environmental changes on Isla de los Estados (54.4°S), southeastern Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Unkel, Ingmar; Björck, Svante; Wohlfarth, Barbara

    2008-08-01

    The island of Isla de los Estados is situated at 54.5°S, 64°W, east of Argentinian Tierra del Fuego, and is located in a sensitive geographic position in relation to the zonal circulation between Antarctica and South America. Its terrestrial records of the last deglaciation, recording atmospheric conditions but within an oceanic setting, can help to clarify changes of regional circulation patterns, both atmospheric and marine. Here, we present geochemical analyses from 16-10 ka cal BP of a peat core from Lago Galvarne Bog at the northern coast of the island, and a lake sediment core from Laguna Cascada 3 km further south. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning on both cores as well as age-depth modeling based on AMS- 14C dating. Deglaciation and onset of peat formation in the coastal areas began before 16 ka cal BP followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland. Data suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14.5 ka cal BP. The warming trend slows down until ca 13.5 ka cal BP, followed by arid conditions culminating around 12.8 ka cal BP. Our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10.6 ka cal BP, contemporaneous with the onset of the Antarctic thermal optimum. This indicates large-scale shifts in the placement of zonal flow and the Westerlies at the beginning of the Holocene.

  9. Three new species and one new record of Tullbergiidae (Collembola: Onychiuroidea) from Tierra del Fuego.

    PubMed

    Arbea, Javier I

    2016-03-20

    Three new species, Tullbergia rapoporti sp. nov., Dinaphorura nerudai sp. nov. and Dinaphorura najtae sp. nov., and one new record, Tullbergia meridionalis Cassagnau & Rapoport, 1962 are described based on specimens from Tierra del Fuego. Tullbergia rapoporti sp. nov. is similar to T. crozetensis, but can be distinguished from it by the presence of an empodial appendage and the chaetotaxy of Abd VI. Dinaphorura nerudai sp. nov. is diagnosed by the dorsal pso formula, the seven spiniform processes on Abd VI, an elongate PAO, the absence of vesicle on Ant IV and the dorsal chaetotaxy. Dinaphorura najtae sp. nov. is characterised by the dorsal pso formula, the seven spiniform processes on Abd VI, a triangular PAO, the absence of vesicle on Ant IV and the dorsal chaetotaxy.

  10. Lack of founding Amerindian mitochondrial DNA lineages in extinct aborigines from Tierra del Fuego-Patagonia.

    PubMed

    Lalueza, C; Pérez-Pérez, A; Prats, E; Cornudella, L; Turbón, D

    1997-01-01

    Ancient DNA from bones and teeth of 60 individuals from four extinct human populations from Tierra del Fuego-Patagonia (Selknam, Yamana, Kaweskar and Aonikenk) has been extracted and the mitochondrial DNA (mtDNA) amplified by using the polymerase chain reaction. High-resolution analysis of endonuclease restriction site variation in the mtDNA and sequencing of its hypervariable non-coding control region, revealed complete absence of two of the four primary mitochondrial haplotype groups present in contemporary Amerinds, namely A and B. In contrast, haplogroups C and D were found in all but one sample with frequencies of approximately 38% and 60%. These results, together with the decreasing incidence of group A in more southerly latitudes in the American continent and the absence of cluster B above 55 degrees North in America and Asia, argue that the first settlers entering America 21000-14000 years ago already lacked both mtDNA lineages.

  11. Saprolegnia oliviae sp. nov. isolated from an Argentine river (Tierra del Fuego Province, Argentina).

    PubMed

    Steciow, Mónica Mirta

    2003-02-28

    Saprolegnia oliviae sp. nov. is described from litter (floating dead twigs, leaves and roots) in the Olivia River, Ushuaia Department, Tierra del Fuego Province (Argentina). The new species is illustrated and compared with other species of the genus. Distinguishing characteristics of S. oliviae are the production of smooth oogonia (with some lateral or terminal projections) and the absence of antheridial branches on the majority of the oogonia, but when present, they are mostly diclinous, at times oogonia are supplied with androgynous and monoclinous antheridial branches. The oogonial stalks are predominantly short and straight or long and bent, curved or many times coiled; oospores are distinctive subcentric, (1-) 15-50 (-70) per oogonium. Morphological details of the new species and its comparison with other described species are discussed here.

  12. Continental stretching preceding the opening of the Drake Passage: Evidence from Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Ghiglione, Matías C.; Yagupsky, Daniel; Ghidella, Marta; Ramos, Victor A.

    2008-08-01

    Age estimates for the onset of a seaway through the Drake Passagerange from middle Eocene to early Miocene, complicating interpretationsof the relation between ocean circulation and Cenozoic globalcooling. Here we present evidence for the presence of a latestPaleocene-early Eocene extensional basin (i.e., lateralrift) in Tierra del Fuego. An accurately dated postrift unconformityindicates that extensional faulting ended in the studied areaca. 49 Ma, in concurrence with a previously reported eightfoldincrease in South America-Antarctica separation rate,and the proposed onset of oceanic basins in the incipient DrakePassage. The coincidence of these facts indicates progressivestrain concentration on the zone of future crustal separation(i.e., Drake Passage) after abandonment of lateral rifts ca.49 Ma. Although the described extensional depocenters did notallow the exchange of water between the Pacific and AtlanticOceans, they represent a direct indication of continental lithosphericstretching preceding the recently proposed Eocene opening ofembryonic basins in the West Scotia Sea.

  13. Iridium, platinum and rhodium baseline concentration in lichens from Tierra del Fuego (South Patagonia, Argentina).

    PubMed

    Pino, Anna; Alimonti, Alessandro; Conti, Marcelo Enrique; Bocca, Beatrice

    2010-10-06

    Lichen samples of Usnea barbata were used as possible biomonitors of the atmospheric background level of iridium (Ir), platinum (Pt) and rhodium (Rh) in the remote region of Tierra del Fuego (South Patagonia, Argentina). Lichens were collected in 2006 at 53 sites covering 7 different areas of the region (24 transplanted lichens of the northern region and 29 native lichen samples of the central-southern region). A microwave acidic digestion procedure was used to mineralize the samples and a sector field inductively coupled plasma mass spectrometry method was developed to quantify the elements. The study of the influence of interferences on analyte signals and a quality control procedure were carried out. The analytical protocol was further applied to evaluate Ir, Pt and Rh bioaccumulation in lichens. The detection limits obtained were 0.010 ng g⁻¹, 0.013 ng g⁻¹ and 0.030 ng g⁻¹ for Ir, Pt and Rh, respectively. Recoveries at different fortification levels were between 96.3% and 106% and precision was 3.3% on average. The metals concentration (as dry weight) spanned the following ranges: Ir, <0.010-1.011 ng g⁻¹; Pt, 0.016-2.734 ng g⁻¹; and Rh, 0.063-1.298 ng g⁻¹. Data on 7 areas were similar suggesting that no specific source, for example traffic or anthropogenic activity, influenced directly the metal concentrations in Tierra del Fuego. Values detected are more likely influenced by the long-range atmospheric transport of these pollutants and, in comparison with densely populated areas in the world, they can represent the baseline for low impacted areas.

  14. Epidemiological studies on intestinal helminth parasites of the patagonian grey fox (Pseudalopex griseus) in Tierra del Fuego, Patagonia Argentina.

    PubMed

    Zanini, Fabián; Laferrara, Miguel; Bitsch, Matías; Pérez, Héctor; Elissondo, Maria Celina

    2006-03-31

    The present work was performed to study the intestinal helminths of the patagonian grey fox (Pseudalopex griseus) and to obtain information about its possible role in the sylvatic life cycle of Echinococcu granulosus in Tierra del Fuego, Patagonia Argentina. Eighty-one foxes were captured and subject to post-mortem analysis. Thirty-one foxes (38.3%) harboured helminths. A total of six helminth species were recovered. Only one adult of E. granulosus was found in the studied samples. The current study is the first report of the intestinal helminths of the patagonian grey fox in Tierra del Fuego, Argentina and showed that this specie is probably not an important reservoir host for E. granulosus.

  15. Large residuals on geoidal heights determined on the Fagnano Lake, Tierra del Fuego-Argentina

    NASA Astrophysics Data System (ADS)

    Gomez, M. E.; Del Cogliano, D.; Perdomo, R.

    2013-05-01

    A new geoid model was developed in Tierra del Fuego and it was evaluated in the area of Fagnano Lake. The model was developed by means of the Equivalent Source Technique combining gravity data, levelling information measured on the province and observations of a GPS buoy on the Fagnano Lake. Those GPS buoy measurements provide information of the mean lake level surface (Del Cogliano et al., 2007). A cross validation process was realized in order to evaluate the model on the lake. What allowed determining a 6 cm geoid in the area of Fagnano Lake. Also, an evaluation of the EGM2008 (Pavlis et al., 2008) was made on the lake. Its behaviour was compared to that observed on the levelling lines. Differences of several decimetres were found when EGM2008 undulations were compared to observed geoid undulations in the lake area. In the regions where EGM2008 has included real gravimetric observations, differences between model and observations were only of a few centimetres. Such model has the particularity that includes fill-in gravity in that region. The above mentioned evaluation derived in an analysis of the effect that not representative gravity information could have on the estimation of geoid undulations in high mountainous regions. We found that this effect could be significant if there is no real information in the computing area (Gomez et al, 2012).

  16. Lichen Usnea barbata as biomonitor of airborne elements deposition in the Province of Tierra del Fuego (southern Patagonia, Argentina).

    PubMed

    Conti, Marcelo Enrique; Pino, Anna; Botrè, Francesco; Bocca, Beatrice; Alimonti, Alessandro

    2009-05-01

    Lichen Usnea barbata was tested as a possible biomonitor of atmospheric deposition in a supposedly pristine environment Tierra del Fuego (Argentina). Lichen samples were collected in 2005 and again in 2006 in 71 sites covering almost the entire region. The aim of the study was to evaluate the bioaccumulation of 26 elements in order to define the background levels in the region. The quantification was carried out by the sector field inductively coupled plasma mass spectrometry. No relevant temporal accumulation patterns between 2005 and 2006 sampling campaigns were observed. Then, the results were submitted to multivariate statistical analysis (cluster and principal component analyses). Cluster analysis produced a dendrogram where the 71 sites were divided into four clusters at (Dlink/Dmax)100<30. The areas and the elements were correlated according to the element concentrations by principal component analysis. Four significant components that accounted for 67% were obtained. Cluster 1 was mainly composed of sites of Ushuaia-Road 3 (E area) and it was characterized by high levels of Cd, Co, Ni, Pb, Sb, and W in lichens. The present study has revealed the good capacity of U. barbata to reflect the baseline levels of elements in the environment at a regional scale level. The presence of certain level of elements in lichens agrees with the hypothesis that Tierra del Fuego is not a relatively pristine environment as occasionally supposed. However, when comparing our results with other countries, Tierra del Fuego lichens have a very low content of the measured elements.

  17. Rock Magnetic Properties of Laguna Carmen (Tierra del Fuego, Argentina): Implications for Paleomagnetic Reconstruction

    NASA Astrophysics Data System (ADS)

    Gogorza, C. G.; Orgeira, M. J.; Ponce, F.; Fernández, M.; Laprida, C.; Coronato, A.

    2013-05-01

    We report preliminary results obtained from a multi-proxy analysis including paleomagnetic and rock-magnetic studies of two sediment cores of Laguna Carmen (53°40'60" S 68°19'0" W, ~83m asl) in the semiarid steppe in northern Tierra del Fuego island, Southernmost Patagonia, Argentina. Two short cores (115 cm) were sampled using a Livingstone piston corer during the 2011 southern fall. Sediments are massive green clays (115 to 70 cm depth) with irregularly spaced thin sandy strata and lens. Massive yellow clay with thin sandy strata continues up to 30 cm depth; from here up to 10 cm yellow massive clays domain. The topmost 10 cm are mixed yellow and green clays with fine sand. Measurements of intensity and directions of Natural Remanent Magnetization (NRM), magnetic susceptibility, isothermal remanent magnetization, saturation isothermal remanent magnetization (SIRM), back field and anhysteretic remanent magnetization at 100 mT (ARM100mT) were performed and several associated parameters calculated (ARM100mT/k and SIRM/ ARM100mT). Also, as a first estimate of relative magnetic grain-size variations, the median destructive field of the NRM (MDFNRM), was determined. Additionally, we present results of magnetic parameters measured with vibrating sample magnetometer (VSM). The stability of the NRM was analyzed by alternating field demagnetization. The magnetic properties have shown variable values, showing changes in both grain size and concentration of magnetic minerals. It was found that the main carrier of remanence is magnetite with the presence of hematite in very low percentages. This is the first paleomagnetic study performed in lakes located in the northern, semiarid fuegian steppe, where humid-dry cycles have been interpreted all along the Holocene from an aeolian paleosoil sequence (Orgeira et el, 2012). Comparison between paleomagnetic records of Laguna Carmen and results obtained in earlier studies carried out at Laguna Potrok Aike (Gogorza et al., 2012

  18. Shallow temperatures and thermal regime in the hydrocarbon province of Tierra del Fuego

    SciTech Connect

    Zielinski, G.W.; Bruchhausen, P.M.

    1983-01-01

    A suite of shallow (<2 m deep) thermal measurements across the San Sebastian oil and gas field, northeastern Tierra del Fuego, indicates at least a 200 mWm/sup -2/ (5 HFU) thermal anomaly over the field. The anomaly appears to be of subsurface origin and, due to its magnitude, must be caused by a localized discharge of deep ground water. A single published heat flow value and deep bottom hole temperature data for the area suggest a regional heat flow that is at least 20 mWm/sup -2/ (0.5 HFU) higher than the world average for similar tectonic provinces (postPrecambrian non-orogenic). Maturation level estimates based on the heat flow and burial history of sediments suggest considerable lateral migration (at least 100 km) of hydrocarbons from deeper in the Magellan basin. From estimates of the timing of possible oil generation, minimum average migration velocity is within 1 or 2 orders of magnitude of the ground water velocity required to cause the local and regional heat flow anomalies. This suggests that ground water moving from deeper in the Magellan basin might simultaneously transport hydrocarbons and heat to the area. Volume flux estimates require that hydrocarbon concentrations significantly greater than possible via aqueous molecular solution.

  19. Shallow temperatures and thermal regime in the hydrocarbon province of Tierra del Fuego

    SciTech Connect

    Zielinski, G.W.; Bruchhausen, P.M.

    1983-01-01

    A suite of shallow (<2 m deep) thermal measurements across the San Sebastian oil and gas field, northeastern Tierra del Fuego, indicates at least a 200 mWm/sup -2/ (5 HFU) thermal anomaly over the field. The anomaly appears to be of subsurface origin and, due to its magnitude, must be caused by a localized discharge of deep groundwater. A single published heat flow value and deep bottom hole temperature data for the area suggest a regional heat flow that is at least 20 mWm/sup -2/ (0.5 HFU) higher than the world average for similar tectonic provinces (post-Precambrian non-orogenic). Maturation level estimates based on the heat flow and burial history of sediments suggest considerable lateral migration (at least 100 km) of hydrocarbons from deeper in the Magellan basin. From estimates of the timing of possible oil generation, minimum average migration velocity is within 1 or 2 orders of magnitude of the groundwater velocity required to cause the local and regional heat flow anomalies. This suggests that groundwater moving from deeper in the Magellan basin might simultaneously transport hydrocarbons and heat to the area. Volume flux estimates require hydrocarbon concentrations significantly greater than possible via aqueous molecular solution.

  20. Paleoseismic observations of an onshore transform boundary: The Magallanes-Fagnano fault, Tierra del Fuego, Argentina

    USGS Publications Warehouse

    Costa, C.H.; Smalley, R.; Schwartz, D.P.; Stenner, Heidi D.; Ellis, M.; Ahumada, E.A.; Velasco, M.S.

    2006-01-01

    We present preliminary information on the geomorphologic features and paleoseismic record associated with the ruptures of two Ms 7.8 earthquakes that struck Tierra del Fuego and the southernmost continental margin of South America on December 17, 1949. The fault scarp was surveyed in several places cast of Lago Fagnano and a trench across a secondary fault trace of the Magallanes-Fagnano fault was excavated at the Ri??o San Pablo. The observed deformation in a 9 kyr-old peat bog sequence suggests evidence for two, and possibly three pre-1949 paleoearthquakes is preserved in the stratigraphy. The scarp reaches heights up to 11 m in late Pleistocene-Holocence(?) deposits, but the vertical component of the 1949 events was always less than ???1 m. This observation also argues for the occurrence of previous events during the Quaternary. Along die part of the fault we investigated east of Lago Fagnano, the horizontal component of the 1949 rupture does not exceed 4 m and is likely lower than 0.4 m, which is consistent with the kinematics of a local releasing bend, or at the end of a strike-slip rupture zone. ?? 2006 Revista de la Asociacio??n Geolo??gica Argentina.

  1. Block modeling of crustal deformation in Tierra del Fuego from GNSS velocities

    NASA Astrophysics Data System (ADS)

    Mendoza, L.; Richter, A.; Fritsche, M.; Hormaechea, J. L.; Perdomo, R.; Dietrich, R.

    2015-05-01

    The Tierra del Fuego (TDF) main island is divided by a major transform boundary between the South America and Scotia tectonic plates. Using a block model, we infer slip rates, locking depths and inclinations of active faults in TDF from inversion of site velocities derived from Global Navigation Satellite System observations. We use interseismic velocities from 48 sites, obtained from field measurements spanning 20 years. Euler vectors consistent with a simple seismic cycle are estimated for each block. In addition, we introduce far-field information into the modeling by applying constraints on Euler vectors of major tectonic plates. The difference between model and observed surface deformation near the Magallanes Fagnano Fault System (MFS) is reduced by considering finite dip in the forward model. For this tectonic boundary global plate circuits models predict relative movements between 7 and 9 mm yr- 1, while our regional model indicates that a strike-slip rate of 5.9 ± 0.2 mm yr- 1 is accommodated across the MFS. Our results indicate faults dipping 66- 4+ 6° southward, locked to a depth of 11- 5+ 5 km, which are consistent with geological models for the MFS. However, normal slip also dominates the fault perpendicular motion throughout the eastern MFS, with a maximum rate along the Fagnano Lake.

  2. New species of dictyostelids from Patagonia and Tierra del Fuego, Argentina.

    PubMed

    Vadell, Eduardo M; Cavender, James C; Romeralo, Maria; Edwards, Sally M; Stephenson, Steven L; Baldauf, Sandra L

    2011-01-01

    In late Jan and early Feb 2005 samples for isolation of dictyostelid cellular slime molds (dictyostelids) were collected in five different provinces and from six national parks (all located 39-55°S) in Patagonia and Tierra del Fuego, Argentina. Southern beech (Nothofagus) forests represented the primary vegetation type investigated, but some samples were obtained from Patagonian steppe, alpine meadows, Valdivian temperate rainforests and coniferous forests dominated by Araucaria, Austrocedrus and Fitzroya. Among the dictyostelids isolated from the samples we collected were seven species new to science. These species (Dictyostelium austroandinum, D. chordatum, D. fasciculoideum, D. gargantuum, D. leptosomopsis, D. valdivianum and Polysphondylium patagonicum) are described herein on the basis of both morphology and molecular (SSU rDNA) data. One of the new species, D. gargantuum, is one of the largest representatives of the group reported to date. Another unusual species, D. chordatum, produces long interwoven sorocarps that do not appear to respond to a spacing gas similar to the condition first noted in D. implicatum.

  3. Baseline trace metals in gastropod mollusks from the Beagle Channel, Tierra del Fuego (Patagonia, Argentina).

    PubMed

    Conti, Marcelo Enrique; Stripeikis, Jorge; Finoia, Maria Grazia; Tudino, Mabel Beatriz

    2012-05-01

    With the aim to evaluate the mollusk Nacella (P)magellanica as biomonitor of elemental pollution in seawater of the Beagle Channel, more than one hundred individuals of the gastropod were sampled, separated in viscera and muscle, and then examined with respect to the accumulation of Cd, Cr, Cu, Ni, Pb and Zn. Collection was performed in seven strategic locations along 170 km of the coastal area of the Beagle Channel (Tierra del Fuego, Argentina) in two campaigns during 2005 and 2007. Samples of surrounding seawater in the different sites were obtained and tested for the same metals as well. The accumulation capacity of Nacella (P)magellanica and thus its aptitude as biomonitor, was evaluated through the calculus of the preconcentration factors of the metals assayed. A discussion involving the comparison with other mollusks previously tested will be given. Several statistical approaches able to analyze data with environmental purposes were applied. Non parametric univariate tests such as Kruskal-Wallis and Mann-Whitney were carried out to assess the changes of the metal concentrations with time (2005 and 2007) in each location. Multivariate methods (linear discriminant analysis on PCA factors) were also applied to obtain a more reliable site classification. Johnson's probabilistic method was carried out for comparison between different geographical areas. The possibility of employing these results as heavy metals' background levels of seawater from the Beagle Channel will be debated.

  4. Pressure tide gauge records from the Atlantic shelf off Tierra del Fuego, southernmost South America

    NASA Astrophysics Data System (ADS)

    Richter, Andreas; Mendoza, Luciano; Perdomo, Raúl; Hormaechea, José Luis; Savcenko, Roman; Bosch, Wolfgang; Dietrich, Reinhard

    2012-07-01

    Based on pressure tide gauge observations at three sites off the Atlantic coast of Tierra del Fuego main island, time series spanning one to seven months of bottom pressure and sea-level variations are derived and analysed to reveal the major driving mechanisms. Ocean tides account for 99.5% of the total energy of the sea-level variations. The amplitudes and phases of a comprehensive set of tidal constituents resulting from a harmonic tidal analysis are presented. Exceptionally large shallow-water tides are identified. The second largest contribution is due to the local inverse barometer model accounting for up to 65% of the variance of the tide residual sea-level variations. Close to the shore a significant topographic modulation of the sea-level variations is revealed. The in situ observations are compared with six recent global ocean tide models, official tide tables, and sea-surface heights derived from satellite altimetry data. The amplitudes and phases predicted by the ocean tide models for the semidiurnal and diurnal constituents agree with those derived from our tide gauge records on average within 2 cm and 5°, respectively. In the time domain the tidal signal represented by the models deviates typically by a few decimetres from that extracted from our records. Absolute altimeter biases were determined for the Jason-2, Jason-1 extended mission, and Envisat satellite altimeters. Relative sea-level variations are represented by the altimetry data with an accuracy of the order of 5 cm.

  5. Alkali basalts and enclosed ultramafic xenoliths near Ushuaia, Tierra Del Fuego, Argentina.

    PubMed

    Acevedo, Rogelio Daniel

    2016-01-01

    At the southernmost part of Tierra del Fuego a few outcrops and erratic boulders of alkali basaltic rocks with ultramafic enclaves have been studied. Alkali basalt plugs or pipes hitherto identified are scarce, and host rocks are constituted by slates that belong to Mesozoic deposition. The petrography, texture and composition of the basalt and xenoliths were investigated by petrographic microscope and electron microprobe analysis. Xenocrysts of amphibole and alkali feldspar, phenocrysts of nepheline, olivine, spinel, phlogopite and Fe-Ti minerals (10 %) and a diversity of xenoliths, mainly lherzolitic, pyroxenite and wehrlitic nodules (15 %), but also from metamorphic rocks provenance, are contained in the basalt groundmass (75 %). This finer-grained material is made up of laths or needles of plagioclase, pyroxene, opaque minerals, apatite and glass, with intersertal, hyalopilitic and pilotaxitic. Locally, rock has an even granoblastic texture. Former amygdules are filled by analcite, zeolites, sodalite and calcite. The normative classification, based on nepheline content, conclude that this rock is an alkali basalt. The chemical classification, considering immobile elements as Zr/TiO2 versus Nb/Y indicate an alkali basalt too and plots over the TAS diagram fall in the foidite (Na-rich or nephelinite) and basanite fields. The REE patterns are fractionated (La/Yb primitive mantle normalized is approximately 30). The K-Ar isotopic technique on individual macrocrysts gave ages of 146 ± 5 Ma (amphibole) and 127 ± 4 Ma (alkali feldspar); and K-Ar whole rock datum reported 8.3 ± 0.3 Ma. Nevertheless, fertile samples show geochemical features typical of deep derived material thus, based on the position in the actual tectonic setting, indicate that the basalt is older than its isotopic age.

  6. [Knowledge of the endoparasitic fauna of Lama guanicoe Muller, 1776, from the Mitre Peninsula, Tierra del Fuego, Argentina].

    PubMed

    Navone, G T; Merino, M L

    1989-01-01

    Parasitological fauna of Lama guanicoe in the Peninsula Mitre, Tierra del Fuego, Argentina, is analyzed in this paper. Coproparasitological tests of 58 samples were performed, and on this basis, the presence of the following genera was determined: Haemonchus, Marshallagia, Cooperia, Nematodirus, Ostertagia, Trichostrongylus, Oesophagostomun and Chavertia. Marshallagia and Chabertia are reported for the first time for this host. The dung piles are not considered as parasitic barriers. Infections occur in two seasons: at the beginning of the spring and at the beginning of summer, as a survival strategy of parasitic nematodes. Parasites of L. guanicoe would be secondarily acquired form cattle.

  7. Cold- maritime processes in the Fuegian Mountains (Tierra del Fuego, Argentina)

    NASA Astrophysics Data System (ADS)

    Pérez-Alberti, A.; Valcarcel-Diaz, M.; Castillo-Rodriguez, F.; Naya-Fernandez, S.; Carrera-Gomez, P.; Lopez-Bedoya, J.; Blanco-Chao, R.; Macias-Vazquez, F.

    2009-04-01

    Studies carried out since 2004 in the "Andes Fueguinos" (Tierra del Fuego, Argentina) demonstrate the great importance that cryogenic processes have at the present time. The current investigations are based on two directions of research: (1) the mapping of the existing cryonival forms, and (2) the measurement of their activity. First, the existing geomorphic forms have been identified and their positions located on a map by means of GPS; second, a number of ground control stations were established to provide environmental information for a variety of locations with differing conditions. In addition, grain size analysis of stones in different areas was undertaken to characterize the varying sediment characteristics. The first results demonstrate: 1. - The existence of numerous cryogenic geomorphic forms: sorted polygons and sorted stripes, rock glaciers, stratified slope deposits, solifluction lobes, and cryonival steps and debris flows. 2. - The importance of structural and lithological control on landforms and sediments. 3. - The presence of noticeable differences in the genesis and current dynamics of geomorphic forms due to topographic variables: orientation, slope and elevation. 4. - The importance of the role of the wind in the distribution of the snow and, consequently, in the degree of activity of the landforms. 5. - The role of the snow, as a factor of protection of the ground as well as a driving agent for the geomorphic processes. 6. - Differences in development between the presently active forms and those that have been produced in the recent past (which are now being colonized by vegetation). The installation of control stations to monitoring the temperature and moisture of ground and air has allowed us to know: 1. - The large variability in air temperatures (mean annual of - 3° C). 2. - The existence of marked differences in temperatures between the spring and the autumn with respect to the winter and the summer. 3. - The important role of frost heave

  8. Diversity of endosymbiotic Nostoc in Gunnera magellanica from Tierra del Fuego, Chile [corrected].

    PubMed

    Fernández-Martínez, M A; de Los Ríos, A; Sancho, L G; Pérez-Ortega, S

    2013-08-01

    Global warming is causing ice retreat in glaciers worldwide, most visibly over the last few decades in some areas of the planet. One of the most affected areas is the region of Tierra del Fuego (southern South America). Vascular plant recolonisation of recently deglaciated areas in this region is initiated by Gunnera magellanica, which forms symbiotic associations with the cyanobacterial genus Nostoc, a trait that likely confers advantages in this colonisation process. This symbiotic association in the genus Gunnera is notable as it represents the only known symbiotic relationship between angiosperms and cyanobacteria. The aim of this work was to study the genetic diversity of the Nostoc symbionts in Gunnera at three different, nested scale levels: specimen, population and region. Three different genomic regions were examined in the study: a fragment of the small subunit ribosomal RNA gene (16S), the RuBisCO large subunit gene coupled with its promoter sequence and a chaperon-like protein (rbcLX) and the ribosomal internal transcribed spacer (ITS) region. The identity of Nostoc as the symbiont was confirmed in all the infected rhizome tissue analysed. Strains isolated in the present study were closely related to strains known to form symbioses with other organisms, such as lichen-forming fungi or bryophytes. We found 12 unique haplotypes in the 16S rRNA (small subunit) region analysis, 19 unique haplotypes in the ITS region analysis and 57 in the RuBisCO proteins region (rbcLX). No genetic variability was found among Nostoc symbionts within a single host plant while Nostoc populations among different host plants within a given sampling site revealed major differences. Noteworthy, interpopulation variation was also shown between recently deglaciated soils and more ancient ones, between eastern and western sites and between northern and southern slopes of Cordillera Darwin. The cell structure of the symbiotic relationship was observed with low-temperature scanning

  9. Chronicles from the End of the Word: the Holocene climate variability in Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Waldmann, N.; Ariztegui, D.; Anselmetti, F.; Austin, J.; Moy, C.; Borromei, A.; Coronato, A.; Recasens, C.; Dunbar, R.; Martinez, M.; Olivera, D.

    2008-12-01

    Latest advances in the chronology and environmental importance of Antarctic paleoclimate records point towards a larger heterogeneity than previously thought. Thus, realistic inter-hemispheric correlations rely in the development of a tight array of well constrained records with a dense latitudinal coverage. Climatic records from southernmost Patagonia are hence critical corner-stones to link these Antarctic paleoclimatic archives with their South American counterparts. At 55° S on the Island of Tierra del Fuego, Lago Fagnano is located in one of the most substantially and extensively glaciated regions of southernmost South America during the Late Pleistocene. This elongated lake is the largest (~110 km long) and southernmost non-ice covered water body in the world. Existing on-shore geomorphological reconstructions combined with new lacustrine subsurface data, allowed us to better constrain the magnitude and chronology of the Fagnano glacier fluctuations since the LGM. The former Fagnano glacier flowed eastwards from the Darwin Cordillera fed by more than 50 tributary glaciers. The glacier spread over the low ranges and lowlands through three different lobes and was drained by four main outwash basins directly into the Atlantic Ocean. During the maximum ice-expansion, the ice-covered area was ca. 4000 km2 with a maximum length of ca. 132 km. A set of submerged frontal moraines covered by lacustrine infilling identified in the seismic survey suggests occasional eastward re-advances of the paleo-glacier within the overall westward deglaciation pattern. These re-advances may correspond to cold events such as the Antarctic Cold Reversal (ACR), the Huelmo- Mascardi Cold Event (HMCE) and/or the Younger Dryas Chronozone (YDC). The ongoing development of a robust age model blended with a multi-proxy dataset will potentially clarify remaining controversial issues dealing with the geographical extension and chronology of these cold episodes during the last deglaciation. A

  10. Effect of Resource Spatial Correlation and Hunter-Fisher-Gatherer Mobility on Social Cooperation in Tierra del Fuego

    PubMed Central

    Santos, José Ignacio; Pereda, María; Zurro, Débora; Álvarez, Myrian; Caro, Jorge; Galán, José Manuel; Briz i Godino, Ivan

    2015-01-01

    This article presents an agent-based model designed to explore the development of cooperation in hunter-fisher-gatherer societies that face a dilemma of sharing an unpredictable resource that is randomly distributed in space. The model is a stylised abstraction of the Yamana society, which inhabited the channels and islands of the southernmost part of Tierra del Fuego (Argentina-Chile). According to ethnographic sources, the Yamana developed cooperative behaviour supported by an indirect reciprocity mechanism: whenever someone found an extraordinary confluence of resources, such as a beached whale, they would use smoke signals to announce their find, bringing people together to share food and exchange different types of social capital. The model provides insight on how the spatial concentration of beachings and agents’ movements in the space can influence cooperation. We conclude that the emergence of informal and dynamic communities that operate as a vigilance network preserves cooperation and makes defection very costly. PMID:25853728

  11. Effect of resource spatial correlation and hunter-fisher-gatherer mobility on social cooperation in Tierra del Fuego.

    PubMed

    Santos, José Ignacio; Pereda, María; Zurro, Débora; Álvarez, Myrian; Caro, Jorge; Galán, José Manuel; Briz i Godino, Ivan

    2015-01-01

    This article presents an agent-based model designed to explore the development of cooperation in hunter-fisher-gatherer societies that face a dilemma of sharing an unpredictable resource that is randomly distributed in space. The model is a stylised abstraction of the Yamana society, which inhabited the channels and islands of the southernmost part of Tierra del Fuego (Argentina-Chile). According to ethnographic sources, the Yamana developed cooperative behaviour supported by an indirect reciprocity mechanism: whenever someone found an extraordinary confluence of resources, such as a beached whale, they would use smoke signals to announce their find, bringing people together to share food and exchange different types of social capital. The model provides insight on how the spatial concentration of beachings and agents' movements in the space can influence cooperation. We conclude that the emergence of informal and dynamic communities that operate as a vigilance network preserves cooperation and makes defection very costly.

  12. Long-range Receiver Function Profile of Crustal and Mantle Discontinuities From the Aleutian Arc to Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Spieker, Kathrin; Rondenay, Stéphane; Sawade, Lucas

    2016-04-01

    The Circum-Pacific belt, also called the Pacific Ring of Fire, is the most seismically active region on Earth. Multiple plate boundaries form a zone characterized by frequent volcanic eruptions and seismicity. While convergent plate boundaries such as the Peru-Chile trench dominate the Circum-Pacific belt, divergent and transform boundaries are present as well. The eastern section of the Circum-Pacific belt extends from the Aleutian arc, through the Cascadia subduction zone, San Andreas Fault, middle America trench and the Andean margin down to Tierra del Fuego. Due to the significant hazards posed by this tectonic activity, the region has been densely instrumented by thousands of seismic stations deployed across fifteen countries, over a distance of more than 15000 km. Various seismological studies, including receiver function analyses, have been carried out to investigate the crustal and mantle structure beneath local segments of the eastern Circum-Pacific belt (i.e., at ~100-500 km scale). However, to the best of our knowledge, no study to date has ever attempted to combine all available seismic data from the eastern Circum-Pacific belt to generate a continuous profile of seismic discontinuities extending from the Aleutians to Tierra del Fuego. Here, we use results from the "Global Imaging using Earthquake Records" (GLImER) P-wave receiver function database to create a long-range profile of crustal and upper mantle discontinuities across the entire eastern portion of the Circum-Pacific belt. We image intermittent crustal and mantle discontinuities along the profile, and examine them with regard to their behaviour and properties across transitions between different tectonic regimes.

  13. Rare earth element and Nd isotope geochemistry of an ombrotrophic peat bog at Karukinka (Chile, 53.9° S): a palaeo-record of Holocene dust deposition in Tierra del Fuego.

    NASA Astrophysics Data System (ADS)

    Vanneste, Heleen; De Vleeschouwer, François; Vanderstraeten, Aubry; Mattielli, Nadine; Triquet, Delphine; Piotrowska, Natalia; Le Roux, Gael

    2013-04-01

    The value of ombrotrophic peat bogs as past atmospheric dust records, has been increasingly recognized over the past 10 years. Their high accumulation rates provide high resolution archives of natural atmospheric dust deposition since the Late Glacial, often missing in marine, lake and ice core records. Consequently, peat deposits can be used as a proxy for atmospheric circulation patterns and thus palaeoclimate. In the Southern Hemisphere, the climate is considered to be driven by the Southern Westerly Wind belt (SSW), as it significantly affects the Antarctic Circumpolar Current and hence atmospheric CO2 levels. Palaeo SSW belt migrations have been observed in palaeoclimate records but, reconstructions of SSW shifts and associated climatic changes are incoherent, in particular for the Holocene. As peatlands thrive in southwest Tierra del Fuego due to its high annual precipitation, a remote ombrotrophic peat bog at Karukinka (southwest on the Isla Grande de Tierra del Fuego) was sampled, to investigate the Holocene palaeoclimate in southern South America based on dust deposition records. A 4,5 m long Russian D-core was recovered and subsequently subsampled for elemental and isotope geochemistry in addition to density and radiocarbon dating measurements. Initial results show a number of layers enriched in scandium, indicating the presence of lithogenic material, i.e. dust. Rare earth element patterns indicate at least 2 different sources. The most significant dust peak occurs at the base of the core at ~7300 Cal years B.P and has a neodymium isotopic composition of 2.2, suggesting a volcanic origin.

  14. Seismically-induced soft-sediment deformation structures associated with the Magallanes-Fagnano Fault System (Isla Grande de Tierra del Fuego, Argentina)

    NASA Astrophysics Data System (ADS)

    Onorato, M. Romina; Perucca, Laura; Coronato, Andrea; Rabassa, Jorge; López, Ramiro

    2016-10-01

    In this paper, evidence of paleoearthquake-induced soft-sediment deformation structures associated with the Magallanes-Fagnano Fault System in the Isla Grande de Tierra del Fuego, southern Argentina, has been identified. Well-preserved soft-sediment deformation structures were found in a Holocene sequence of the Udaeta pond. These structures were analyzed in terms of their geometrical characteristics, deformation mechanism, driving force system and possible trigger agent. They were also grouped in different morphological types: sand dykes, convolute lamination, load structures and faulted soft-sediment deformation features. Udaeta, a small pond in Argentina Tierra del Fuego, is considered a Quaternary pull-apart basin related to the Magallanes-Fagnano Fault System. The recognition of these seismically-induced features is an essential tool for paleoseismic studies. Since the three main urban centers in the Tierra del Fuego province of Argentina (Ushuaia, Río Grande and Tolhuin) have undergone an explosive growth in recent years, the results of this study will hopefully contribute to future analyses of the seismic risk of the region.

  15. A Geochemical and Sedimentary Record of High Southern Latitude Holocene Climate Evolution from Lago Fagnano, Tierra del Fuego

    SciTech Connect

    Moy, C M; Dunbar, R B; Guilderson, T P; Waldmann, N; Mucciarone, D A; Recasens, C; Austin, J A; Anselmetti, F S

    2010-11-19

    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55{sup o}S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8,000 years based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcan Hudson eruption. Combining bulk organic isotopic ({delta}{sup 13}C and {delta}{sup 15}N) and elemental (C and N) parameters with physical sediment properties allow us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8,000 years. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk {delta}{sup 13}C between 7,000 and 5,000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano {delta}{sup 13}C record shows similarities with Holocene records of sea surface

  16. A geochemical and sedimentary record of high southern latitude Holocene climate evolution from Lago Fagnano, Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Moy, Christopher M.; Dunbar, Robert B.; Guilderson, Thomas P.; Waldmann, Nicolas; Mucciarone, David A.; Recasens, Cristina; Ariztegui, Daniel; Austin, James A.; Anselmetti, Flavio S.

    2011-02-01

    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55°S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8000 yr based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcán Hudson eruption. Combining bulk organic isotopic (δ13C and δ15N) and elemental (C and N) parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8000 yr. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk δ13C between 7000 and 5000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano δ13C record shows similarities with Holocene records of sea surface temperature from the mid-latitude Chilean continental

  17. CO2 and CH4 fluxes of contrasting pristine bogs in southern Patagonia (Tierra del Fuego, Argentina)

    NASA Astrophysics Data System (ADS)

    Münchberger, Wiebke; Blodau, Christian; Kleinebecker, Till; Pancotto, Veronica

    2015-04-01

    South Patagonian peatlands cover a wide range of the southern terrestrial area and thus are an important component of the terrestrial global carbon cycle. These extremely southern ecosystems have been accumulating organic material since the last glaciation up to now and are - in contrast to northern hemisphere bogs - virtually unaffected by human activities. So far, little attention has been given to these pristine ecosystems and great carbon reservoirs which will potentially be affected by climate change. We aim to fill the knowledge gap in the quantity of carbon released from these bogs and in what controls their fluxes. We study the temporal and spatial variability of carbon fluxes in two contrasting bog ecosystems in southern Patagonia, Tierra del Fuego. Sphagnum-dominated bog ecosystems in Tierra del Fuego are similar to the ones on the northern hemisphere, while cushion plant-dominated bogs can almost exclusively be found in southern Patagonia. These unique cushion plant-dominated bogs are found close to the coast and their occurrence changes gradually to Sphagnum-dominated bogs with increasing distance from the coast. We conduct closed chamber measurements and record relevant environmental variables for CO2 and CH4 fluxes during two austral vegetation periods from December to April. Chamber measurements are performed on microforms representing the main vegetation units of the studied bogs. Gas concentrations are measured with a fast analyzer (Los Gatos Ultraportable Greenhouse Gas Analyzer) allowing to accurately record CH4 fluxes in the ppm range. We present preliminary results of the carbon flux variability from south Patagonian peat bogs and give insights into their environmental controls. Carbon fluxes of these two bog types appear to be highly different. In contrast to Sphagnum-dominated bogs, cushion plant-dominated bogs release almost no CH4 while their CO2 flux in both, photosynthesis and respiration, can be twice as high as for Sphagnum

  18. Hydro-Geomorphologic Effects Of Large Wood Jams On A Third-Order Stream (Tierra Del Fuego, Argentina)

    NASA Astrophysics Data System (ADS)

    Mao, L.; Andreoli, A.; Comiti, F.; Lenzi, M. A.; Iturraspe, R.; Burns, S.; Novillo, M. G.

    2007-05-01

    Dead wood pieces, especially when organized in jams, play an important geomorphic role in streams because of the effects on flow hydraulics, pool formation and sediments storage. The increase of stream morphological diversity and complexity also exerts also an important ecological role. This work reports on geomorphic role of large wood pieces and jams in a third order mountain stream located in the Southern Tierra del Fuego (Argentina), and draining an old-growth nothofagus forested basin not influenced by the beavers damming activity. Even if the in-stream number of wood pieces (length > 1m; diameter > 0.1 m) is comparable to what observed in other climatic areas, the slow growth of the nothofagus forest causes a lower wood abundance in terms of volumetric load. Since the relatively small dimensions of the surveyed large wood pieces, almost the 70% of them demonstrated to have been fluvial transported and the also wood jams reflect the apparent dynamic of wood in the channel. Wood jams exert a significant influence on the channel morphology, representing almost the half of the drop caused by steps and being responsible for the creation of 30% of the pools. The LW-forced pool volume is strongly and positively correlated to the height of the LW jam, and a significant inverse relationship between pool spacing and wood density within is evident if only the LW-forced pools are considered. The geomorphic influence of LW jams is also exerted by a considerable sediment storing capacity.

  19. Hepatic and renal metallothionein concentrations in Commerson's dolphins (Cephalorhynchus commersonii) from Tierra del Fuego, South Atlantic Ocean.

    PubMed

    Cáceres-Saez, Iris; Polizzi, Paula; Romero, Belén; Dellabianca, Natalia A; Ribeiro Guevara, Sergio; Goodall, R Natalie P; Cappozzo, H Luis; Gerpe, Marcela

    2016-07-15

    The Commerson's dolphin is the most common endemic odontocete of subantarctic waters of Tierra del Fuego, Argentina incidentally caught in fishing nets. The species is classified as "Data Deficient" by the IUCN. Metallothioneins (MTs) are considered as suitable biomarkers for health and environmental monitoring. The aims of the study were to assess MT concentrations in the liver and kidney of bycaught specimens. Moreover, correlations with Zn, Se, Cd, Ag and Hg, and the molar ratios of MT:metals were estimated to evaluate if there is an indication of their respective protective role against metal toxicity in tissues. Hepatic and renal MT concentrations were similar, ranging from 11.6 to 29.1nmol·g(-1) WW, and Kidney/Liver ratios ranging from 0.73 to 1.93 corresponded to normal ranges. Results suggest that MTs are related to physiological ranges for the species. This information constitutes the first MT report on Commerson's dolphins and possibly considered as baseline for species' conservation.

  20. Solar ultraviolet-B radiation affects plant-insect interactions in a natural ecosystem of Tierra del Fuego (southern Argentina).

    PubMed

    Rousseaux, M Cecilia; Ballaré, Carlos L; Scopel, Ana L; Searles, Peter S; Caldwell, Martyn M

    1998-10-01

    We examined the effects of solar ultraviolet-B radiation (UVB) on plant-herbivore interactions in native ecosystems of the Tierra del Fuego National Park (southern Argentina), an area of the globe that is frequently under the Antarctic "ozone hole" in early spring. We found that filtering out solar UVB from the sunlight received by naturally-occurring plants of Gunnera magellanica, a creeping perennial herb, significantly increased the number of leaf lesions caused by chewing insects. Field surveys suggested that early-season herbivory was principally due to the activity of moth larvae (Lepidoptera: Noctuidae). Manipulative field experiments showed that exposure to solar UVB changes the attractiveness of G. magellanica leaf tissue to natural grazers. In a laboratory experiment, locally caught moth caterpillars tended to eat more tissue from leaves grown without UVB than from leaves exposed to natural UVB during development; however, the difference between treatments was not significant. Leaves grown under solar UVB had slightly higher N levels than leaves not exposed to UVB; no differences between UVB treatments in specific leaf mass, relative water content, and total methanol-soluble phenolics were detected. Our results show that insect herbivory in a natural ecosystem is influenced by solar UVB, and that this influence could not be predicted from crude measurements of leaf physical and chemical characteristics and a common laboratory bioassay.

  1. [Impact of school closings on the influenza A (H1N1) outbreak in Tierra del Fuego, Argentina].

    PubMed

    Orellano, Pablo Wenceslao; Grassi, Aurora; Reynoso, Julieta Itatí; Palmieri, Abel; Uez, Osvaldo; Carlino, Orestes

    2010-03-01

    The impact of school closings on reducing the number of cases of influenza-like illness during an outbreak of influenza A (H1N1), which reached pandemic proportions, was assessed, along with other control measures, in the two main cities of Tierra del Fuego Province in southern Argentina. The incidence before and after the school closings in 2009 was compared by means of the t-test for related samples. By week 40, 6 901 cases of influenza-like illness had been detected, 281 of which were confirmed as influenza A (H1N1) through laboratory tests; 38 patients were hospitalized. After the intervention, there were nearly 10 times fewer cases than the average recorded in the health centers. The results indicate that closing schools during the influenza A (H1N1) outbreak resulted in a significantly lower incidence of influenza-like illness. However, the impact of other measures, such as case management and protection against exposure, should not be ignored. Timely implementation of this intervention, together with other measures, can help minimize the spread of influenza outbreaks.

  2. First evidence of testate amoebae in Lago Fagnano (54° S), Tierra del Fuego (Argentina): Proxies to reconstruct environmental changes

    NASA Astrophysics Data System (ADS)

    Caffau, Mauro; Lenaz, Davide; Lodolo, Emanuele; Zecchin, Massimo; Comici, Cinzia; Tassone, Alejandro

    2015-12-01

    We report here the first findings of testate amoebae at high southern latitudes (54° S) from four gravity cores recovered in the Lago Fagnano (Tierra del Fuego, Argentina), where twelve taxa have been recognized. Among them, Centropyxis constricta "constricta", Centropyxis elongata, Difflugia globulus, Difflugia oblonga "oblonga", and Difflugia protaeiformis "amphoralis" are always present, while other taxa are randomly distributed. According to the sand/silt ratio in the different cores, the Total Organic Carbon content and the Carbon/Nitrogen ratio, as well as the presence/disappearance and abundance of testate amoebae from cluster analysis, we infer a correlation between major textural/granulometrical changes found in the cores and environmental changes. A seismic event occurred on 1949, which substantially modified the morphology of the eastern Lago Fagnano shoreline and the supply pattern from two main eastern tributaries of the lake, is recorded in the studied cores. This event has in part modified the distribution of testate amoebae taxa within the studied cores. Present results show that testate amoebae represent important indicators to detect changes occurring in the environment in which they live.

  3. First isolation of mycobacterium avium subsp. Paratuberculosis from wild guanacos (Lama guanicoe) on Tierra del Fuego Island.

    PubMed

    Salgado, M; Herthnek, D; Bölske, G; Leiva, S; Kruze, J

    2009-04-01

    The aim of this study was to search for Mycobacterium avium subsp. paratuberculosis (Map) infection in a free-ranging wild animal species in a region where Johnes's disease has yet to be reported and to classify Map isolates using a genomic typing method. Fecal samples were obtained from 501 wild guanacos (Lama guanicoe) from Tierra del Fuego Island, Chile, in August 2006. Samples were cultured using Herrold's egg yolk medium with and without mycobactin J. After 9 mo of incubation, suspected Map colonies showing mycobactin dependence were confirmed by real-time polymerase chain reaction (PCR) based on IS900 and F57. Isolates were further tested using IS1311 PCR with restriction endonuclease analysis in order to type the guanaco Map strains. Twenty-one of 501 (4.2%) animals were fecal culture-positive for Map; identity was confirmed by real-time PCR and isolates were classified as cattle-type. Most culture-positive animals were located in four contiguous geographic areas, and the infection was most commonly found among adult animals. Prevalence was higher in females (5.9%) than males (3.1%) but the difference was not statistically significant. This represents the first isolation of Map from a free-ranging wildlife species in Chile. It expands the geographic range of paratuberculosis and the diversity of wildlife species that can become infected with Map.

  4. Environmental context shapes the bacterial community structure associated to Peltigera cyanolichens growing in Tierra del Fuego, Chile.

    PubMed

    Ramírez-Fernández, Lía; Zúñiga, Catalina; Carú, Margarita; Orlando, Julieta

    2014-03-01

    The structure of the associated bacterial community of bipartite cyanolichens of the genus Peltigera from three different environmental contexts in the Karukinka Natural Park, Tierra del Fuego, Chile, was assessed. The sampling sites represent different habitat contexts: mature native forest, young native forest and grassland. Recently it has been determined that the bacterial community associated to lichens could be highly structured according to the mycobiont or photobiont identities, to the environmental context and/or to the geographic scale. However, there are some inconsistencies in defining which of these factors would be the most significant on determining the structure of the microbial communities associated with lichens, mainly because most studies compare the bacterial communities between different lichen species and/or with different photobiont types (algae vs. cyanobacteria). In this work bipartite lichens belonging to the same genus (Peltigera) symbiotically associated with cyanobacteria (Nostoc) were analyzed by TRFLP to determine the structure of the bacterial community intimately associated with the lichen thalli and the one present in the substrate where they grow. The results indicate that the bacterial community intimately associated differs from the one of the substrate, being the former more influenced by the environmental context where the lichen grows.

  5. Assessment of land influence on a high-latitude marine coastal system: Tierra del Fuego, southernmost Argentina.

    PubMed

    Amin, Oscar; Comoglio, Laura; Spetter, Carla; Duarte, Claudia; Asteasuain, Raúl; Freije, Rubén Hugo; Marcovecchio, Jorge

    2011-04-01

    The study deals with the determination of physico-chemical parameters, inorganic nutrients, particulate organic matter, and photosynthetic pigments on a monthly basis during an annual cycle from nine sampling sites of the coastal zone of a high-latitude ecosystem (Tierra del Fuego, Argentina). Nitrites and phosphates concentrations were similar to other systems of the south Atlantic coast (median, 0.30 and 1.02 μM, respectively), while nitrates were higher in all sampling periods (median, 45.37 μM), and silicates were significantly smaller (median, 7.76 μM). Chlorophyll a and phaeopigments have shown median values of 0.38 and 0.85 mg m(-3), respectively, while saturated values of dissolved oxygen were recorded throughout the study. The analysis reflected that nutrient enrichment seems to be linked to an anthropogenic source, the presence of peatlands areas, and a sink of Nothofagus pumilio woods. The area could be characterized in three zones related to (1) high urban influence, (2) natural inputs of freshwater, and (3) mixed inputs coming from moderate urban impacts.

  6. U-Pb zircon constraints on the age and provenance of the Rocas Verdes basin fill, Tierra del Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Barbeau, David L.; Gombosi, David J.; Zahid, Khandaker M.; Bizimis, Michael; Swanson-Hysell, Nicholas; Valencia, Victor; Gehrels, George E.

    2009-12-01

    The Late Jurassic to Early Cretaceous Rocas Verdes basin constitutes one of the most poorly understood components of the southernmost Andes. As a result, accurate reconstructions and interpretations of deformation associated with the Andean orogeny and the kinematics of Scotia arc development also remain poorly constrained. In this data brief, we report U-Pb zircon ages from sandstones of the Rocas Verdes basin fill and from a crosscutting pluton in the southernmost Andes of Argentine Tierra del Fuego. Detrital samples contain predominant Early to early Middle Cretaceous (circa 130-105 Ma) U-Pb zircon age populations, with very small or single-grain middle Mesozoic and Proterozoic subpopulations. A very small subpopulation of Late Cretaceous ages in one sample raises the unlikely possibility that parts of the Rocas Verdes basin are younger than perceived. A sample from a crosscutting syenitic pegmatite yields a crystallization age of 74.7 +2.2/-2.0 Ma. The data presented herein encourage further geochronologic evaluation of the Rocas Verdes basin in order to better constrain the depositional ages and provenance of its contents.

  7. Holocene Paleoglacier History of Glaciar Dalla Vedova, Cordillera DARWIN, Tierra del Fuego, Chile

    NASA Astrophysics Data System (ADS)

    Reynhout, S.

    2015-12-01

    Southernmost South America is unique in its position immediately north of the present-day Antarctic Convergence, making it ideally suited for the evaluation of Antarctic influences on terrestrial paleoclimate. Here we present a glacial geomorphic interpretation of the paleoglacial history of Glaciar Dalla Vedova in Bahía Blanca, Cordillera Darwin, Chile (53°S). This interpretation is further constrained by radiocarbon dating, cosmogenic dating, dendrochronology, and historical photogrammetry. Preliminary field work suggests that Holocene glacier fluctuations have been constrained to within 3 km of the present glacier boundary, punctuated by rapid recent glacier retreat over the past century. By comparing the observed chronology with the record contained further north in Patagonia, we will evaluate possible mechanisms of regional climate variability over the Holocene across southernmost South America.

  8. Linking invasive exotic vertebrates and their ecosystem impacts in Tierra del Fuego to test theory and determine action

    NASA Astrophysics Data System (ADS)

    Valenzuela, Alejandro E. J.; Anderson, Christopher B.; Fasola, Laura; Cabello, José L.

    2014-01-01

    Understanding processes and impacts of biological invasions is fundamental for ecology and management. Recent reviews summarized the mechanisms by which invasive species alter entire ecosystems, but quantitative assessments of these mechanisms are lacking for actual assemblages to determine their relative importance, frequency and patterns. We updated information on introduced vertebrates in the Tierra del Fuego Archipelago (TDF) via an exhaustive literature review and new data to evaluate ecosystem impact mechanisms and provide management recommendations. To date, 24 exotic vertebrates have naturalized in TDF, outnumbering natives nearly 2:1, with the North American beaver (Castor canadensis) and muskrat (Ondatra zibethica) being the most widely distributed species and also impacting the ecosystem through the greatest number of mechanisms. Introduced vertebrates occupied most parts of the archipelago with human-inhabited islands having greater taxa richness. All exotics potentially altered ecosystems by one or more mechanisms: 100% food webs, 92% invasional meltdown, 42% habitat modification, 38% disease or parasite transmission, 21% soil property and disturbance regime changes. Impact to habitat structure was the main clustering criterion for this assemblage. Within the species that physically alter habitats, we found two sub-groups: 1) large herbivores and 2) "others" including beavers and muskrats. Species that did not alter habitat were divided further into those with predatory trophic effects (carnivorous mammals and trout, sub-group 4) and the rest with assorted impacts (sub-group 3). By establishing high quality information on archipelago-wide assemblage, distribution, impacts and mechanisms for exotic vertebrates, we recommend, based on ecological criteria, prioritizing the management of sub-group 2. A secondary priority might be given to the carnivores in sub-group 4, while species in sub-groups 1 and 3 are less urgent. As the first systematic survey of

  9. Mass balance evolution of Martial Este Glacier, Tierra del Fuego (Argentina) for the period 1960-2099

    NASA Astrophysics Data System (ADS)

    Buttstädt, M.; Möller, M.; Iturraspe, R.; Schneider, C.

    2009-12-01

    The Martial Este Glacier in southern Tierra del Fuego was studied in order to estimate the surface mass balance from 1960 until 2099. For this reason a degree-day model was calibrated. Air temperature and precipitation data obtained from 3 weather stations as well as glaciological measurements were applied. The model was driven using a vertical air temperature gradient of 0.69 K/100 m, a degree-day factor for snow of 4.7 mm w.e. K-1 day-1, a degree-day factor for ice of 9.4 mm w.e. K-1 day-1 and a precipitation gradient of 22%/100 m. For the purpose of surface mass balance reconstruction for the time period 1960 until 2006 a winter vertical air temperature gradient of 0.57 K/100 m and a summer vertical air temperature gradient of 0.71 K/100 m were added as well as a digital terrain model. The key finding is an almost continuous negative mass balance of -772 mm w.e. a-1 throughout this period. While the calculation of the mass balance for the period 1960-2006 is based on instrumental records, the mass balance for the years 2007 until 2099 was estimated based on the IPCC SRES A2-scenario. To accomplish this estimation, the dataset of the global climate model HadCM3 was statistically downscaled to fit local conditions at Martial Este Glacier. Subsequently, the downscaled air temperature and precipitation were applied to a volume-area scaling glacier change model. Findings reveal an enduring deglaciation resulting in a surface area reduction of nearly 93% until 2099. This implicates that the Martial Este Glacier might be melted off at the beginning of the 22nd century.

  10. Sand dispersal in the southeastern Austral Basin, Tierra del Fuego, Argentina: Outcrop insights from Eocene channeled turbidite systems

    NASA Astrophysics Data System (ADS)

    Torres Carbonell, Pablo J.; Olivero, Eduardo B.

    2012-02-01

    We made a detailed facies analysis of well exposed Eocene foredeep and wedge-top successions in the SE Austral Basin of eastern Tierra del Fuego, Argentina, contributing to a better understanding of its patterns of sand dispersal. The analysis reveals that these successions constitute portions of turbidite systems with recurrent facies associations, interpreted as channel, channel-margin and levée depositional elements. The channel facies, paleocurrents and interpreted paleogeography suggest that the studied successions form the transfer zone of the turbidite systems that fed the foreland basin. We hypothesize that the SE Austral Basin, which forms the transition between the Austral and Malvinas Basins, acted as an east-west conduit for sediments sourced at the Fuegian Andes and transported to a deeper depositional zone in the SW Malvinas Basin. The fill of the channels in the transfer zone involved a large amount of turbidity flows, which in addition to the evidence of levée confinement in the studied deposits suggests that the sandier portion of the flows was able to reach the depositional zone, were mostly unconfined (sheeted) sand bodies may have formed. In addition, overbank sand bodies were deposited within the transfer zone, associated to processes of flow overspill. Both types of sand bodies constitute potential reservoirs in this hydrocarbon producing basin, implying that the Eocene SE Austral Basin, and the ultimate zone of deposition in the SW Malvinas Basin may constitute major prospects for hydrocarbon exploration. The proposed model define a new perspective for future research on the sedimentologic and stratigraphic evolution of the SE portion of the Austral Basin.

  11. Present-day crustal deformation along the Magallanes-Fagnano Fault System in Tierra del Fuego from repeated GPS observations

    NASA Astrophysics Data System (ADS)

    Mendoza, L.; Perdomo, R.; Hormaechea, J. L.; Del Cogliano, D.; Fritsche, M.; Richter, A.; Dietrich, R.

    2011-03-01

    The present-day deformation of the earth crust in the Argentine part of Tierra del Fuego main island (southernmost South America) is here investigated based on repeated geodetic GPS observations. The island is traversed by the active transform boundary between the South American and Scotia tectonic plates, represented by the Magallanes-Fagnano fault system. Since 1993 a regional network comprising to date 29 GPS sites has been observed almost every year. The complete set of accumulated observations was processed using the Bernese GPS software and state-of-the-art processing strategies and models. The utilization of homogeneous GPS products resulting from a reprocessing of the global IGS network warrants a stable realization of a global reference frame. For each GPS site 3-D positions and linear velocities with error estimates were obtained. A strain analysis of the horizontal velocity components revealed the zones of major deformation activity. A 30-km-wide deformation belt centred on the main trace of the fault system was identified. This belt is bordered to the north (South America) and south (Scotia) by geodynamically stable zones, which move horizontally with a relative average velocity of 4.4 ± 0.6 (east) and -0.3 ± 0.4 (north) mm a-1. Within the deformation belt a maximum strain rate in the order of 0.25 μstrain per year has been detected. A pronounced change in the deformation style from transtension (east) to transpression (west) is observed. The area of predominating shortening of the crust coincides with a local rotation minimum and relative uplift. Throughout the period covered by the GPS observations the displacements and deformations occurred to be linear with time.

  12. Impacts of solar ultraviolet-B radiation on terrestrial ecosystems of Tierra del Fuego (southern Argentina). An overview of recent progress.

    PubMed

    Ballaré, C L; Rousseau, M C; Searles, P S; Zaller, J G; Giordano, C V; Robson, T M; Caldwell, M M; Sala, O E; Scopel, A L

    2001-09-01

    The southern part of Tierra del Fuego, in the southernmost tip of South America, is covered by dense Nothofagus spp. forests and Sphagnum-dominated peat bogs, which are subjected to the influence of ozone depletion and to increased levels of solar ultraviolet-B radiation (UV-B). Over the last 5 years we have studied some of the biological impacts of solar UV-B on natural ecosystems of this region. We have addressed two general problems: (i) do the fluctuations in UV-B levels under the influence of the Antarctic ozone 'hole' have any measurable biological impact, and (ii) what are the long-term effects of solar (ambient) UV-B on the Tierra del Fuego ecosystems? In this paper, we provide an overview of the progress made during the first 4 years of the project. We highlight and discuss the following results: (1) ambient UV-B has subtle but significant inhibitory effects on the growth of herbaceous and graminoid species of this region (growth reduction < or = 12%), whereas no consistent inhibitory effects could be detected in woody perennials; (2) in the species investigated in greatest detail, Gunnera magellanica, the inhibitory effect of solar UV-B is accompanied by increased levels of DNA damage in leaf tissue, and the DNA damage density in the early spring is clearly correlated with the dose of weighted UV-B measured at ground level; (3) the herbaceous species investigated thus far show little or no acclimation responses to ambient UV-B such as increased sunscreen levels and DNA repair capacity; and (4) ambient UV-B has significant effects on heterotrophic organisms, included marked inhibitory effects on insect herbivory. The results from the experiments summarized in this review clearly indicate that UV-B influences several potentially important processes and ecological interactions in the terrestrial ecosystems of Tierra del Fuego.

  13. Pathogenic and enzyme activities of the entomopathogenic fungus Tolypocladium cylindrosporum (Ascomycota: Hypocreales) from Tierra del Fuego, Argentina.

    PubMed

    Scorsetti, Ana C; Elíades, Lorena A; Stenglein, Sebastián A; Cabello, Marta N; Pelizza, Sebastián A; Saparrat, Mario C N

    2012-06-01

    Tolypocladium cylindrosporum is an entomopathogenic fungi that has been studied as a biological control agent against insects of several orders. The fungus has been isolated from the soil as well as from insects of the orders Coleoptera, Lepidoptera, Diptera and Hymenoptera. In this study, we analyzed the ability of a strain of T cylindrosporum, isolated from soil samples taken in Tierra del Fuego, Argentina, to produce hydrolytic enzymes, and to study the relationship of those activities to the fungus pathogenicity against pest aphids. We have made the traditional and molecular characterization of this strain of T cylindrosporum. The expression of hydrolase activity in the fungal strain was estimated at three incubation temperatures (4 degreeC, 12 degreeC and 24 degreeC), on different agar media supplemented with the following specific substrates: chitin azure, Tween 20, casein, and urea for chitinase, lipase, protease, and urease activity, respectively. The hydrolytic-enzyme activity was estimated qualitatively according to the presence of a halo of clarification through hydrolase action, besides was expressed semi-quantitatively as the ratio between the hydrolytic-halo and colony diameters. The pathogenicity of the fungus was tested on adults of the aphid Rhopalosiphum padi at three temperatures of incubation (4 degree C, 12 degree C and 24 degree C). The suspension was adjusted to a concentration of 1x10(7) conidia/ml. In pathogenicity assays at seven days post-inoculation, the fungus caused the mortality of adults of Ropalosiphum padi at different temperatures also showed a broad ability to grow on several agar-culture media, supplemented with different carbon sources at the three incubation temperatures tested. Although, the growth was greater with higher incubation temperatures (with maximum levels at 24 degreeC), the fungus reached similar colony diameters after 15 days of incubation on the medium supplemented with Tween 20 at the lower two incubation

  14. A second, cryptic species of the soft coral genus Incrustatus (Anthozoa: Octocorallia: Clavulariidae) from Tierra del Fuego, Argentina, revealed by DNA barcoding

    NASA Astrophysics Data System (ADS)

    McFadden, Catherine S.; van Ofwegen, Leen P.

    2013-03-01

    The encrusting soft coral Incrustatus comauensis is a common denizen of hard substrates in the shallow sub-tidal zone from the central Chilean fjords to the Cape Horn region of southern South America. DNA barcoding of specimens collected from the Beagle Channel, Tierra del Fuego, Argentina, revealed the presence of a second, cryptic species of Incrustatus that is syntopic with I. comauensis. We describe Incrustatus niarchosi, a new species that can be distinguished morphologically from I. comauensis by differences in the microscopic ornamentation of the coenenchymal sclerites. To date, I. niarchosi n. sp. is known only from the Beagle Channel. A population of I. comauensis discovered in the intertidal zone in eastern Tierra del Fuego represents a new record of the species for that habitat and geographic region. Although the intertidal population is also distinct genetically, it is morphologically indistinguishable from sub-tidal Chilean populations of I. comauensis, and at present, there is insufficient evidence to support its status as a separate species.

  15. The Last Glacial Maximum and Termination in the Torres del Paine Region, Southern South America

    NASA Astrophysics Data System (ADS)

    Garcia, J.; Hall, B. L.; Kaplan, M. R.; Vega, R. M.; Binnie, S.; Gómez, G.; Santana, F.

    2012-12-01

    Deciphering the timing, structure and termination of the local last glacial maximum (LGM) throughout Patagonia (42-55 S) remains one of the key unsolved paleoclimate questions in Quaternary sciences. During the last glaciation, the Patagonian ice sheet formed one ice body along the Patagonian Andes (42-55 S) in southern South America, but previous work has revealed different spatiotemporal ice dynamics along the eastern and western ice margins. The Patagonian Andes is the only landmass that exists at this latitude confronting the southern westerly wind belt, which seems 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 causes of glaciations in the Southern Hemisphere. Major progress has been made to document the local Late-Pleistocene glacier history, particularly in response to recent application of exposure-cosmogenic dating technique in the region, although only sparse well-dated paleoclimate records exist in this vast area. LGM moraine-based records in south Patagonia (~48-55 S) have been developed for the Strait of Magellan area, where full glacial conditions seems to have occurred between ~28.0 - 17.5 ka. Despite that these data seem to confirm previous glacial chronologies developed in north Patagonia and the Chilean Lake District (40-42 S), recent works in Torres del Paine and Última Esperanza basins (50-51 S), suggest that glacial maximum conditions may have occurred earlier (i.e., during Marine Isotope Stage 3) and that ice extent could have been twice the size of previously thought. Here, we discuss paleoclimatological implications from our 10Be and 26Al-dating program of moraines in the Torres del Paine region in southern Patagonia. We focused our efforts in the previously undated Río de las Viscachas (RV) I and II moraines, which occur distal to the late-glacial TDP II, III and IV moraines that enclose present lake bodies at the

  16. Teleseismic receiver function analysis in Tierra del Fuego Island: an estimation of crustal thickness and Vp/Vs velocity ratio

    NASA Astrophysics Data System (ADS)

    Buffoni, C.; Sabbione, N. C.; Schimmel, M.; Rosa, M. L.

    2012-04-01

    Tierra del Fuego Island (TdF) is situated in the southern part of South America, where the transform tectonic boundary between the Scotia and South America plates divides the island into two continental blocks. This boundary is represented by a mainly strike-slip lineament known as Magallanes-Fagnano fault system that runs from the western part of the north Scotia ridge to the Chile trench south of 50° S. This fault system is composed of many splays and diverse subparallel faults that overprint the fold-and-thrust belt and are the responsible for the complex tectonic setting that has TdF. Only a few studies have been carried out to constrain the crustal structure and Moho depth in TdF. We present the preliminary estimations on Moho depth and Vp/Vs velocity ratio in TdF Argentinian Island, from teleseismic receiver function analysis with data recorded at five permanent seismic stations. We analyzed data and selected among 40 and 120 events for each seismic station, according to data availability and quality. Earthquakes with magnitudes greater than 5.5 mb and epicentral distances between 30° and 90° were selected. We used Seismic Analysis Code software to pre-process the seismograms. After removing the mean and trend, the data were band-pass filtered using different ranges of frequencies: 0.5-2Hz, 0.08-2Hz and 0.02-1Hz. We applied an iterative deconvolution technique in order to isolate the P-to-S converted waves and obtain the Receiver Functions (RFs). A Gaussian factor of a= 2.5 ( ~1Hz) was selected to reduce the noise and improve the signal coherence in the RFs. Crustal thickness and Vp/Vs ratio were estimated using the H-K stacking method. Since our RFs were not as clear as those typically obtained for simple tectonic settings, we performed different resample techniques to asses the robustness of our results. RFs from clustered events were stacked to increase the signal-to-noise ratio. For this purpose we divided the events into three clusters according event

  17. HOLOCENE MASS-WASTING EVENTS IN LAGO FAGNANO, TIERRA DEL FUEGO (54°S): IMPLICATIONS FOR PALEOSEISMICITY OF THE MAGALLANES-FAGNANO TRANSFORM FAULT

    NASA Astrophysics Data System (ADS)

    Ariztegui, D.; Waldmann, N.; Austin, J. A.; Anselmetti, F.; Moy, C.; Dunbar, R. B.

    2009-12-01

    High-resolution seismic imaging and sediment coring in Lago Fagnano, located along the Magallanes-Fagnano plate boundary in Tierra del Fuego, have revealed a chronologic catalog of Holocene mass-wasting events. These event layers are interpreted as resulting from slope instabilities that load the slope-adjacent lake floor during mass flow deposition thus mobilizing basin floor sediments through gravity spreading. A total of 22 mass flow deposits have been identified combining results from an 800 km-long dense grid of seismic profiles with a series of sediment cores. Successions of up to 6 m-thick mass-flow deposits pond the basin floor spreading eastward and westward following the main axis of the eastern sub-basin of Lago Fagnano. An age model on the basis of information from previous studies and from new radiocarbon dating allowed establishing a well-constrained chronologic mass-wasting event catalogue covering the last ~15000 years. Simultaneously-triggered basin-wide lateral slope failure and the formation of multiple debris flow and megaturbidite deposits are interpreted as the fingerprint of paleo-seismic activity along the Magallanes-Fagnano transform fault that runs along the entire lake basin. The slope failures and megaturbidites are interpreted as recording large earthquakes occurring along the transform fault since the early Holocene. The results from this study provide new data about the frequency and possible magnitude of Holocene earthquakes in Tierra del Fuego, which can be applied in the context of seismic hazard assessment in southernmost Patagonia.

  18. Glacial geomorphology of the Torres del Paine region (southern Patagonia): Implications for glaciation, deglaciation and paleolake history

    NASA Astrophysics Data System (ADS)

    García, Juan-Luis; Hall, Brenda L.; Kaplan, Michael R.; Vega, Rodrigo M.; Strelin, Jorge A.

    2014-01-01

    The processes affecting paleoclimate variability and Pleistocene glacial landscape development in the southern mid-latitudes remain poorly understood, in part because of the scarcity of comprehensive, well-studied records. Glacial landforms are invaluable for reconstructing past ice-sheet, climate, and associated environmental changes along the southern Andes, but there are significant spatial and temporal gaps in existing data. In this paper, we present new geomorphic and sedimentologic analyses, including surficial maps, for the Torres del Paine region (51°S, 73°W), southern South America. Our findings provide a new framework for understanding changes in the regional glacier history and Pleistocene landscape development. Glacial extent during the local last glacial maximum (LGM) remains unknown but new chronological data supported by geomorphic evidence afford evidence for a larger ice sheet at Torres del Paine than previously assumed. Deglaciation from the local LGM was underway by 17,400 ± 200 (1σ) cal. yr. BP. As opposed to previous suggestions, we have found that most of the moraines fringing the lakes in the Torres del Paine national park were deposited during a late-glacial expansion that occurred between 14,100 and 12,500 cal. yr. BP. Late-glacial advances also have been documented recently for the Última Esperanza and Lago Argentino basins to the south and north of Torres del Paine, respectively, suggesting an overall regional ice response to a climate signal. The Tehuelche paleolake accompanied each of the ice-sheet fluctuations in Torres del Paine. New data document at least three main phases of this paleolake, which drained eastward to the Atlantic Ocean, while the Andes gaps were blocked with ice. During the late phase of glacial lake formation, when water levels reached 125-155 m a.s.l., the lake likely merged with paleolake Consuelo in the Última Esperanza area at the end of the last glaciation. Lake Tehuelche in Torres del Paine had drained

  19. Fate of a broad spectrum of perfluorinated compounds in soils and biota from Tierra del Fuego and Antarctica.

    PubMed

    Llorca, Marta; Farré, Marinella; Tavano, Máximo Sebastián; Alonso, Bruno; Koremblit, Gabriel; Barceló, Damià

    2012-04-01

    In this study, the presence of 18 perfluorinated compounds was investigated in biota and environmental samples from the Antarctica and Tierra de Fuego, which were collected during a sampling campaign carried out along February and March 2010. 61 samples were analysed including fish, superficial soils, guano, algae, dung and tissues of Papua penguin by liquid chromatography coupled to tandem mass spectrometry. The concentrations of PFCs were ranging from 0.10 to 240 ng/g for most of the samples except for penguin dung, which presented levels between 95 and 603 ng/g for perfluorooctane sulfonate, and guano samples from Ushuaia, with concentration levels of 1190-2480 ng/g of perfluorohexanoic acid. PFCs acids presented, in general, the highest levels of concentration and perfluorooctanesulfonate was the most frequently found compound. The present study provides a significant amount of results, which globally supports the previous studies, related to the transport, deposition, biodegradation and bioaccumulation patterns of PFCs.

  20. Paleomagnetism of the Patagonian orocline (Tierra del Fuego, Argentina): Evidence for a pre-early Eocene (ca. 50 Ma) oroclinal bending.

    NASA Astrophysics Data System (ADS)

    Maffione, Marco; Speranza, Fabio; Faccenna, Claudio; Rossello, Eduardo

    2010-05-01

    The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a ~700 km long orogenic re-entrant with an interlimb angle of ~90° known as Patagonian orocline. No reliable paleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primary arc formed over an articulated paleomargin, or is due to bending of a previously less curved (or rectilinear) chain. Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) study carried out on 22 sites (298 oriented cores), predominantly sampled in Eocene marine clays from the external Magallanes belt of Tierra del Fuego. Five sites (out of six giving reliable paleomagnetic results) containing magnetite and subordinate iron sulphides yield a positive fold test at the 99% significance level, and document no significant rotation since ~50 Ma. Thus, the Patagonian orocline is either a primary bend, or an orocline formed after Cretaceous-earliest Tertiary rotations. Our data imply that the opening of the Drake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciation and global climate cooling), was definitely not related to the formation of the Patagonian orocline, but was likely the sole consequence of the 32±2 Ma Scotia plate spreading. Well-defined magnetic lineations gathered at 18 sites from the Magallanes belt are sub-parallel to (mostly E-W) local fold axes, while they trend randomly at two sites from the Magallanes foreland. Our and previous AMS data consistently show that the Fuegian Andes were characterized by a N-S compression and northward displacing fold-thrust sheets during Eocene-early Miocene times (50-20 Ma), an unexpected kinematics considering coeval South America-Antarctica relative motion. Both paleomagnetic and AMS data suggest no significant influence from the E-W left-lateral Magallanes-Fagnano strike-slip fault system (MFFS), running few kilometres south of our sampling

  1. Paleomagnetic evidence for a pre-early Eocene (˜ 50 Ma) bending of the Patagonian orocline (Tierra del Fuego, Argentina): Paleogeographic and tectonic implications

    NASA Astrophysics Data System (ADS)

    Maffione, Marco; Speranza, Fabio; Faccenna, Claudio; Rossello, Eduardo

    2010-01-01

    The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a ˜ 700 km long orogenic re-entrant with an interlimb angle of ˜ 90° known as Patagonian orocline. No reliable paleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primary arc formed over an articulated paleomargin, or is due to bending of a previously less curved (or rectilinear) chain. Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) study carried out on 22 sites (298 oriented cores), predominantly sampled in Eocene marine clays from the external Magallanes belt of Tierra del Fuego. Five sites (out of six giving reliable paleomagnetic results) containing magnetite and subordinate iron sulphides yield a positive fold test at the 99% significance level, and document no significant rotation since ˜ 50 Ma. Thus, the Patagonian orocline is either a primary bend, or an orocline formed after Cretaceous-earliest Tertiary rotations. Our data imply that the opening of the Drake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciation and global climate cooling), was definitely not related to the formation of the Patagonian orocline, but was likely the sole consequence of the 32 ± 2 Ma Scotia plate spreading. Well-defined magnetic lineations gathered at 18 sites from the Magallanes belt are sub-parallel to (mostly E-W) local fold axes, while they trend randomly at two sites from the Magallanes foreland. Our and previous AMS data consistently show that the Fuegian Andes were characterized by a N-S compression and northward displacing fold-thrust sheets during Eocene-early Miocene times (50-20 Ma), an unexpected kinematics considering coeval South America-Antarctica relative motion. Both paleomagnetic and AMS data suggest no significant influence from the E-W left-lateral Magallanes-Fagnano strike-slip fault system (MFFS), running a few kilometres south of our

  2. Early population differentiation in extinct aborigines from Tierra del Fuego-Patagonia: ancient mtDNA sequences and Y-chromosome STR characterization.

    PubMed

    García-Bour, Jaume; Pérez-Pérez, Alejandro; Alvarez, Sara; Fernández, Eva; López-Parra, Ana María; Arroyo-Pardo, Eduardo; Turbón, Daniel

    2004-04-01

    Ancient mtDNA was successfully recovered from 24 skeletal samples of a total of 60 ancient individuals from Patagonia-Tierra del Fuego, dated to 100-400 years BP, for which consistent amplifications and two-strand sequences were obtained. Y-chromosome STRs (DYS434, DYS437, DYS439, DYS393, DYS391, DYS390, DYS19, DYS389I, DYS389II, and DYS388) and the biallelic system DYS199 were also amplified, Y-STR alleles could be characterized in nine cases, with an average of 4.1 loci per sample correctly typed. In two samples of the same ethnic group (Aonikenk), an identical and complete eight-loci haplotype was recovered. The DYS199 biallelic system was used as a control of contamination by modern DNA and, along with DYS19, as a marker of American origin. The analysis of both mtDNA and Y-STRs revealed DNA from Amerindian ancestry. The observed polymorphisms are consistent with the hypothesis that the ancient Fuegians are close to populations from south-central Chile and Argentina, but their high nucleotide diversity and the frequency of single lineages strongly support early genetic differentiation of the Fuegians through combined processes of population bottleneck, isolation, and/or migration, followed by strong genetic drift. This suggests an early genetic diversification of the Fuegians right after their arrival at the southernmost extreme of South America.

  3. [Obesity and sedentary lifestyles in four-years old children attending two pre-schools in the city of Río Grande, Tierra del Fuego, Argentina].

    PubMed

    Berghtein, Ileana Ruth

    2014-12-01

    The precocious start of the adipocyte rebound, such as sedentarism, increases the risk of developing obesity and its comorbidities at later ages. The city of Río Grande is located in the Northwestern part of Tierra del Fuego and its monthly average temperature is the lowest in all of Argentina. It also possesses the largest juvenile population (in proportion to the total) as well as a very low mortality rate. According to the 2006 National Health and Nutrition Survey, the prevalence of obesity among its children was also one of the highest in the country. The objective of this investigation was to determine the prevalence of obesity and sedentarism in 4-year-old children; the sample was taken from two local kindergartens. In order to achieve this, the children were weighed and measured, their body mass index and waist perimeter, as well as their percentiles, were calculated. A structured questionnaire was applied to characterize the average weekly time allotted to sedentary activities. In this study, 27.3% of children were deemed to be overweight, while 18.2% were classified as obese. Furthermore, 23.6% presented a waist circumference in the > 90 percentile or higher and 70.1% fell in the sedentary classification. Both the predominance of sedentarism and the pattern of fat distribution are a clear alert towards the need to deepen the search for metabolic-risk syndrome factors in vulnerable groups.

  4. Glacial History of Southernmost South America and Implications for Movement of the Westerlies and Antarctic Frontal Zone

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Fogwill, C. J.; Hulton, N. R.; Sugden, D. E.; Peter, K. W.

    2004-12-01

    The ~1 Myr glacial geologic record in southern South American is one of the few available terrestrial paleoclimate proxies at orbital and suborbital time scales in the middle latitudes of the Southern Hemisphere. Presently, southernmost Patagonia lies about 3\\deg north of the Antarctic frontal zone and within the middle latitude westerlies and the climate is controlled by the surrounding maritime conditions. Thus, the long-term glacial record provides insight into the history of climatic boundaries over the middle and high latitude southern ocean, including the upwind SE Pacific Ocean, tectonic-glacial evolution of the Andes, and global climate. To date, cosmogenic nuclide and 14C dating have focused on glacial fluctuations between 51 and 53\\deg S (Torres del Paine to northern Tierra del Fuego) during the last glacial cycle, including the late glacial period. At least 4 advances occurred between ca. 25 and 17 ka, with the maximum expansion of ice ca. 25-24 ka. Major deglaciation commenced after ca. 17.5 ka, which was interrupted by a major glacial-climate event ca. 14-12 ka. Modelling experiments suggest that the ice mass needed to form the glacial maximum moraines required about a 6\\deg cooling and a slight drying relative to the present. Such a fundamental temperature reduction, despite high summer isolation, strongly suggests northward movement of the westerlies and the polar front on millennial timescales. The Patagonian record also indicates that on orbital timescales equatorward movement of climate boundaries and glacial growth was in phase with major Northern Hemisphere ice volume change, despite high local summer insolation. At suborbital timescales, the picture is more complex. While major facets of the last glacial maximum appear to be in phase between the hemispheres, at least some late glacial events may be in step with Antarctic climate change. Present and future research will further constrain the timing of glacial events over the last 1 Myr and

  5. Multi-proxy analyses of a peat bog on Isla de los Estados, easternmost Tierra del Fuego: a unique record of the variable Southern Hemisphere Westerlies since the last deglaciation

    NASA Astrophysics Data System (ADS)

    Björck, Svante; Rundgren, Mats; Ljung, Karl; Unkel, Ingmar; Wallin, Åsa

    2012-05-01

    We have analyzed an almost 14,000 year old peat sequence on the island of Isla de los Estados (55° S, 64° W), east of Tierra del Fuego, in the core of the Southern Hemisphere Westerlies. A multitude of methods have been used: high resolution 14C dating; detailed lithologic descriptions including humification degree; loss on ignition; magnetic susceptibility; bulk density; pollen and spore analysis and determination of Aeolian sand influx. By combining proxies for wind and precipitation we have been able to reconstruct how the westerlies have varied over time in the Atlantic sector of the Southern Ocean. It shows that this westerly wind belt was most intense at the onset of the record, 13,600-13,200 cal BP, coinciding with the mid to late part of the Antarctic Cold Reversal, followed by a gradual decline. At 12,200 cal BP the westerlies seem to have shifted to a position south of Tierra del Fuego and this phase, the calmest and driest period on the island throughout the sequence, ended at 10,000 cal BP when the westerlies moved equatorward again. Since then the westerlies have been present but with a variable impact on the 55° S latitude of the Atlantic. Mostly conditions have been fairly similar to today, but occasionally with a wider or narrower and/or weaker or stronger wind belt. At 7200 cal BP wind intensity began to increase and between 4500 and 3500 cal BP these southern latitudes experienced a distinct wind and precipitation maximum, both in terms of perseverance and intensity. Our results show a both wide and strong wind belt, with possible niveo-aeolian activity in Tierra del Fuego in winter, and possibly creating milder summers around the Antarctic Peninsula. In the later part of the Holocene, expansion-contraction phases of the wind belt, especially in winter, seem to have been a common phenomenon.

  6. Records of environmental changes during the Holocene from Isla de los Estados (54.4°S), southeastern Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Unkel, Ingmar; Fernandez, Marilen; Björck, Svante; Ljung, Karl; Wohlfarth, Barbara

    2010-12-01

    Southernmost Patagonia, located at the relatively narrow passage between Antarctica and South America, is a highly sensitive region for recording meridional and zonal changes in the pattern of oceanic and atmospheric circulation. The island of Isla de los Estados, situated at 54.5°S, 64°W, east of Argentinean Tierra del Fuego, provides an exceptional possibility, to investigate terrestrial records of atmospheric conditions in an oceanic setting during the last deglaciation and the Holocene. Here we present geochemical and diatom analyses from 10 600 to c. 1500 cal BP of one sequence (LGB) with peat, lake sediments and lagoon deposits at the northern coast of the island, and a lake sediment sequence (CAS) 3 km further inland. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning as well as age-depth modeling based on AMS- 14C dating on both cores. Diatom analysis of the CAS record complements the geochemical proxies. During the Holocene, our two sites have been impacted by two different forcings: changes in the regional climate regime largely influenced by the varying strength and position of the Southern Hemisphere Westerlies (SHW), while relative sea-level changes affected the deposits of the coastal site. In concert with the onset of the Antarctic thermal optimum, our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation on the island c. 10 600 cal BP. Between 8500 and 4500 cal BP geochemistry and diatoms from the CAS record indicate stronger Westerlies at this latitude, which means higher wind speed or higher storm frequency and more precipitation, resulting in more pronounced surface run-off. After 4500 cal BP, the geochemical proxies and large changes in diatom assemblages indicate a decrease in precipitation, weaker winds and possibly cooler conditions, probably as an effect of weaker SHW and/or a latitudinal shift. The depositional environment of CAS changed from gyttja to peat around 1000

  7. Los ojos de la NASA sobre la Tierra

    NASA Video Gallery

    La NASA cuenta con más de una decena de satélites que estudian la Tierra. Conoce la información que recaban los satélites, junto con Gilberto Colón, asistente especial del subdirector del Centro de...

  8. Current treatment and future prospects for the management of acute coronary syndromes: consensus recommendations of the 1997 ushuaia conference, tierra del fuego, Argentina.

    PubMed

    Gurfinkel, E

    1998-01-01

    Management of acute coronary syndromes, particularly unstable angina, acute myocardial infarction and non-Q-wave myocardial infarction, is one of the most common and costly problems facing modern medicine. Furthermore, the increasing availability of new research and clinical information relevant to the treatment of these conditions means that continuing reappraisal of management strategies is necessary. Accordingly, the Ushuaia conference, Tierra Del Fuego, Argentina, was convened to discuss current approaches and future treatment prospects for patients with these conditions. The conference was comprised of leading Argentinian cardiologists whose primary aim was to formulate consensus recommendations regarding the management of patients with acute coronary syndromes. The first of the major recommendations for the pharmacological management of acute coronary syndromes arising from the Ushuaia Consensus Conference was that aspirin (200 to 500mg initially, then 100 to 325 mg/day) should be administered to all patients except those for whom aspirin is absolutely (or relatively, depending on the clinician's discretion) contraindicated. In such cases, ticlopidine is a suitable alternative. Intravenous nitrates are indicated for patients with angina pain (24 to 48 hours' duration), ECG changes, recurrence of angina, or signs of heart failure; in other cases, oral, transdermal or sublingual nitrates may be administered. Use of beta-blockers is recommended except when absolutely contraindicated or when there is a strong suspicion of vasospasm as a dominant mechanism in angina. Intravenous administration of these agents is preferred in patients with tachycardia, arterial hypertension or angina. Calcium antagonists are generally not recommended as first choice therapy, but can be indicated (preferably using agents that decrease heart rate) when beta-blockers are contraindicated or when there is a strong suspicion of vasospasm as a dominant mechanism in angina. Calcium

  9. The effect of natural UV-B radiation on a perennial Salicornia salt-marsh in Bahía San Sebastián, Tierra del Fuego, Argentina: a 3-year field study.

    PubMed

    Bianciotto, O A; Pinedo, L B; San Roman, N A; Blessio, A Y; Collantes, M B

    2003-07-01

    The Antarctic ozone hole and a general depletion of the stratospheric ozone layer cause increased levels of ultraviolet-B solar radiation (UV-B) over Tierra del Fuego, the southernmost tip of South America. For three consecutive growing seasons (1997-2000), we studied the biological impacts (morphology, physiology, demography and phenology) of natural UV-B radiation on a perennial Salicornia ambigua Michx. community in San Sebastian Bay (53 degrees S and 68 degrees W), Tierra del Fuego, Argentina. This is the first UV-B screening experiment on a subantarctic halophytic community. The shortwave UV-B spectrum (280 to 320 nm) was excluded by covering plots with UV-B blocking film (Mylar). These plots were compared to controls covered with UV-B transparent (Aclar) plastic screens, and unscreened plots. Shoot length in Salicornia was not affected by UV-B. Exposure to natural UV-B reduced biomass and density (by 17% and 38%, respectively). Concentration of UV-shielding pigments and cuticle thickness were both significantly higher (25-48% and 21-40%, respectively) in plants receiving ambient UV-B. The increase in cuticle thickness persisted throughout the growing season, whereas pigment concentration was higher at the beginning of the growing season. Also, the number of dead shoots was higher in plants exposed to UV-B. At the end of the growing season (March) shoot mortality was higher in plants exposed to ambient UV-B, and post-flowering senescence was 30 days earlier. Slight changes in the relative composition of Salicornia to Puccinellia were seen. The reduction observed in Salicornia shoot density under ambient UV-B was cumulative over time; 23% in the first growing-season, rising to 38% by the third growing-season. A similar incremental increase in pigment absorption at 305 nm was seen; 25% in the first and 48% in the third growing season.

  10. La Enseñanza/Aprendizaje del Modelo Sol-Tierra Análisis de la Situación Actual y Propuesta de Mejora Para la Formación de los Futuros Profesores de Primaria

    NASA Astrophysics Data System (ADS)

    Martínez Sebastià, Bernat

    2004-12-01

    This work is an extened summary of the autor's PhD thesis. It deals with the teaching of astronomy (day/night, seasons) in primary school. At first, students teachers' undestanding of astronomical concepts related to Sun-Earth system have been analysed. Taking into account the results of the previous analysis and using a socio-constructivist approach a teaching sequence has been designed. This sequence has been tested with different groups of students teachers showing an improvement in their undestanding of elementary astronomical concepts. El trabajo que presentamos es un resumen extenso de la tesis doctoral del autor. El enfoque utilizado ha sido tratar de ligar la investigación sobre las ideas, razonamientos y obstáculos de los profesores de primaria con la planificación de la enseñanza del modelo Sol-Tierra que permite explicar el ciclo día/noche y las estaciones. En primer lugar, se ha procedido a realizar un análisis crítico de los resultados que se obtienen en el aprendizaje de los contenidos astronómicos en la enseñanza habitual. En segundo lugar se ha diseñado un curriculum potencialmente superador de esta situación desde una orientación que concibe la enseñanza y el aprendizaje como un proceso de construcción de conocimientos en una estructura problematizada. Finalmente, esta secuencia didáctica ha sido experimentada con diferentes grupos de estudiantes de magisterio, mostrando una mejora relevante en la comprensión de los conceptos astronómicos fundamentales.

  11. Modern rates of glacial sediment accumulation along a 15° S-N transect in fjords from the Antarctic Peninsula to southern Chile

    NASA Astrophysics Data System (ADS)

    Boldt, Katherine V.; Nittrouer, Charles A.; Hallet, Bernard; Koppes, Michele N.; Forrest, Brittany K.; Wellner, Julia S.; Anderson, John B.

    2013-12-01

    of glacial erosion in temperate climates rank among the highest worldwide, and the sedimentary products of such erosion record climatic and tectonic signals in many glaciated settings, as well as temporal changes in glacier behavior. Glacial sediment yields are expected to decrease with increasing latitude because decreased temperature and meltwater production reduce glacial sliding, erosion, and sediment transfer; however, this expectation lacks a solid supportive database. Herein we present modern 210Pb-derived sediment accumulation rates on decadal to century time scales for 12 fjords spanning 15° of latitude from the Antarctic Peninsula to southern Chile and interpret the results in light of glacimarine sediment accumulation worldwide. 210Pb records from the Antarctic Peninsula show surprisingly steady sediment accumulation throughout the past century at rates of 1-7 mm yr-1, despite rapid warming and glacial retreat. Cores from the South Shetland Islands reveal accelerated sediment accumulation over the past few decades, likely due to changes in the thermal state of the glaciers in this region, which straddles the boundary between subpolar and temperate conditions. In Patagonia and Tierra del Fuego, sediment accumulates faster (11-24 mm yr-1), and previously collected seismic profiles show that rates reach meters per year close to the glacier termini. This increase in sediment accumulation rates with decreasing latitude reflects the gradient from subpolar to temperate climates and is consistent with glacial erosion being much faster in the temperate climate of southern Chile than in the polar climate of the Antarctic Peninsula.

  12. Trace elements deposition in the Tierra del Fuego region (south Patagonia) by using lichen transplants after the Puyehue-Cordón Caulle (north Patagonia) volcanic eruption in 2011.

    PubMed

    Conti, Marcelo Enrique; Jasan, Raquel; Finoia, Maria Grazia; Iavicoli, Ivo; Plá, Rita

    2016-04-01

    Lichen Usnea barbata transplants were tested as a biomonitor of atmospheric deposition in an apparently pristine environment that is Tierra del Fuego region (Patagonia, Argentina). The present survey is connected with the volcanic eruption that started in north Patagonia on June 4, 2011 from the Puyehue-Cordón Caulle volcano, Chile (north Patagonia, at 1700 km of distance of our sampling sites). Lichens were collected in September 2011 (one month of exposure) and September 2012 (1 year of exposure) in 27 sites covering the northern region of the province where trees are not present. The atmospheric deposition of 27 elements by using Neutron Activation Analysis (NAA) was determined in the collected samples. The first aim of the study was to evaluate the influence of the volcanic eruption on the regional atmospheric deposition comparing our results with baseline data we determined in U. barbata in 2006 in the same sites. The second aim was to test possible patterns of bioaccumulation between the two sampling campaigns after the volcanic eruption. With respect to 2006 baseline levels, we found significant higher levels for As, Ba, Co, Cr, Cs, Na, Sb and U in lichens collected after 1 month of exposure (first sampling campaign--2011). Between the two sampling campaigns (2011-2012) after the eruption, lichens reflected the natural contamination by volcanic ashes with significantly higher median levels of Br, Cr, Fe, K, Na, Sc, and Se. Results confirmed the very good aptitude of U. barbata to reflect the levels of elements in the environment at global scale and to reflect the volcanic emissions at distant places. Volcanic eruptions cause the emission in the atmosphere of elevated levels of particulate matter. In this regard, our findings demonstrate the importance to evaluate the metal composition of the particles to avoid possible health effects.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    behaviour detected at the Pia glacial terminus results from a combination of climatic factors and elements derived from the dynamics of the glacial flow. García-Sancho, L. Palacios, D., Green, T.G.A., Vivas, M., Pintado, A. (2011): Extreme lichen growth rates detected in recent deglaciated areas in Tierra del Fuego. Polar Biology, 34 (6): 813-822. DOI: 10.1007/s00300-010-0935-4. Research funded by POL20060840 & CGL2009-7343 projects, Government of Spain.

  14. Mineralogical, IR-spectral and geochemical monitoring of hydrothermal alteration in a deformed and metamorphosed Jurassic VMS deposit at Arroyo Rojo, Tierra del Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Biel, C.; Subías, I.; Acevedo, R. D.; Yusta, I.; Velasco, F.

    2012-04-01

    The Arroyo Rojo Zn-Pb-Cu volcanogenic massive sulfide deposit is the main deposit of the Fin del Mundo District in the Fuegian Andes, Argentina. This deposit is hosted by a Middle Jurassic volcanic and volcanoclastic sequence forming the Lemaire Formation. The latter consists, from the base up, of the following: rhyolitic and dacitic porphyritic rocks, ignimbrite, tuff, and flow. It is underlain by a pre-Jurassic basement and overlain by the hyaloclastic andesites of the Yahgán Formation. The Arroyo Rojo consists of stacked lenticular lenses that are associated with disseminated mineralization in both the footwall and the hanging wall. The internal structure of the ore lenses is marked by the occurrence of massive, semi-massive and banded facies, along with stringer and brecciated zones and minor ore disseminations. The mineral assemblage comprises mainly pyrite and sphalerite, with minor amounts of galena and chalcopyrite and rare pyrrhotite, arsenopyrite, tetrahedrite and bournonite. The ores and the volcanic host rocks have metamorphosed to greenschist facies and were overprinted by a penetrative tectonic foliation, which led to the development of mylonitic, and cataclastic textures, recrystallization and remobilization. Primary depositional characteristics and regional and hydrothermal alteration patterns were preserved despite deformation and metamorphism. Therefore, primary banding was preserved between facies boundaries. In addition, some remnants of magmatic origin are recognizable in preserved phenocrysts and volcaniclastic phenoclasts. Most of the volcanic and volcaniclastic rocks of the host sequence show a rhyolitic to rhyo-dacitic composition. Regional seafloor alteration, characterized by the presence of clinozoisite, Fe-chlorite and titanite, along with quartz and albite, is partially obliterated by hydrothermal alteration. The hydrothermal alteration is stratabound with the following assemblages, which developed from the base to top: (1) Quartz

  15. La Memoria De Nuestra Tierra: Colorado

    ERIC Educational Resources Information Center

    Baca, Judy

    2005-01-01

    La Memoria de Nuestra Tierra combines a meticulously hand-painted landscape with historic photographs in a seamless blend imprinted on the holographic-like surface of a metallic coated substrate. The mural for the Denver International Airport, entitled La Memoria de Nuestra Tierra is a breakthrough in digital murals, printed digitally on a…

  16. Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America

    PubMed Central

    Vanneste, Heleen; De Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

    2015-01-01

    Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions. PMID:26126739

  17. Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America.

    PubMed

    Vanneste, Heleen; De Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

    2015-07-01

    Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions.

  18. Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America

    NASA Astrophysics Data System (ADS)

    Vanneste, Heleen; de Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

    2015-07-01

    Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions.

  19. Deforestation in Tierras Bajas, Bolivia

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This false-color image shows the gradual conversion of forest lands for agricultural use in the Tierras Bajas region of Santa Cruz, Bolivia, as observed by the Enhanced Thematic Mapper Plus (ETM+) flying aboard Landsat 5. Forest and woodland are represented as grey tones from Channel 5 in this ETM+ scene, collected in 1998. Other colors indicate the first year in which a site was developed for agriculture (see color scale in the image, which corresponds to years of development). In this scene, land use types are delineated with lines. Solid white lines show the locations of planned colonies, dashed white lines show spontaneous colonies, and dotted white lines show Mennonite colonies. All other regions of development are non-Mennonite industrial soybean farms. Natural vegetation formations in this image are delineated with black lines. Solid black lines show the locations of Northern Chaco Woodlands and dashed black lines show Cerrado regions. For more information, see this previous Image of the Day regarding Bolivian deforestation. Image courtesy Marc Steininger, NASA GSFC

  20. Geomorphological evolution of a paraglacial coastal system: Moat Sector, Beagle Channel, Tierra de Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Blanco-Chao, R.; Pérez-Alberti, A.; Martínez-Cortizas, A.; Valcárcel-Díaz, M.; Costa-Casais, M.

    2009-04-01

    The morphodynamics of paraglacial coastal systems is controlled by a number of factors, including rock basement structure, sediment disposal, changes in the relative sea-level and wave regime. Of great importance is the thickness and the particle size composition of the glacial deposits because they are not only the main source of material, but also a major element in the coast plan form and in the processes of sediment redistribution. The Moat sector in the Beagle Channel (Tierra del Fuego, Argentina), is a shallow embayment opened in a previously glaciated landscape, in which the Beagle glacier left several drumlins and moraines. After deglaciation the rising sea-level led to the erosion of the till sediments at least until 2550 yr BP, exposing the rock substrate in which up to three narrow shore platforms were modelled. The erosion of the till produced cliffs up to 18 m high, capped with Holocene sediments. After 2550 yr BP a fall in the relative sea-level enhanced wave dissipation on the rocky areas and forced the diffraction of the incoming waves. The limits of the sedimentary cell were then set and a shadow zone developed in the east section of the beach, where the cliff became stabilized meanwhile erosion persisted on the west section. The coarser till of the west cliff was then the main source of sediments, and the retreat of the cliff left a boulder pavement that created a secondary limit of the cell. The clasts were redistributed by a dominant west to east transport that still dominates today. The 14C dates obtained in the sedimentary deposit developed on top of the cliff suggest that, when the bluff retreat stopped at the east end, a phase of stabilization began and the talus was covered by a layer of organic-rich sediments. Later, an environmental change to drier conditions, occurred after 1310-1180 cal. yr BP, led to the desiccation and degradation of the organic-sediments of the talus, which started to be eroded exposing the till again

  1. Tierra Nueva -- A passive solar cohousing project

    SciTech Connect

    Haggard, K.; Cooper, P.

    1999-10-01

    California architects take on the formidable challenges of designing a cohousing project, and discover that the end result is well worth the effort. The Tierra Nueva Cohousing Project consists of living units, a common house, community orchard, community gardens, community play space, space for a future shop and at the periphery of the site, parking, carports and garages. The units use thermal mass, solar heating, passive solar cooling, perimeter insulation on slabs. Design was agreed to by the community as a whole.

  2. Phylogeography of the Patagonian otter Lontra provocax: adaptive divergence to marine habitat or signature of southern glacial refugia?

    PubMed Central

    2011-01-01

    Background A number of studies have described the extension of ice cover in western Patagonia during the Last Glacial Maximum, providing evidence of a complete cover of terrestrial habitat from 41°S to 56°S and two main refugia, one in south-eastern Tierra del Fuego and the other north of the Chiloé Island. However, recent evidence of high genetic diversity in Patagonian river species suggests the existence of aquatic refugia in this region. Here, we further test this hypothesis based on phylogeographic inferences from a semi-aquatic species that is a top predator of river and marine fauna, the huillín or Southern river otter (Lontra provocax). Results We examined mtDNA sequences of the control region, ND5 and Cytochrome-b (2151 bp in total) in 75 samples of L. provocax from 21 locations in river and marine habitats. Phylogenetic analysis illustrates two main divergent clades for L. provocax in continental freshwater habitat. A highly diverse clade was represented by haplotypes from the marine habitat of the Southern Fjords and Channels (SFC) region (43°38' to 53°08'S), whereas only one of these haplotypes was paraphyletic and associated with northern river haplotypes. Conclusions Our data support the hypothesis of the persistence of L. provocax in western Patagonia, south of the ice sheet limit, during last glacial maximum (41°S latitude). This limit also corresponds to a strong environmental change, which might have spurred L. provocax differentiation between the two environments. PMID:21356052

  3. 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.

  4. 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."…

  5. PALEOCLIMATE: Glacial Climate Instability.

    PubMed

    Labeyrie, L

    2000-12-08

    Throughout the last glacial period, rapid climatic changes called Dansgaard-Oeschger (D-O) events occurred in the Northern Hemisphere. As Labeyrie discusses in his Perspective, these events are ideal targets for testing our understanding of climate change and developing climatic change models. Important steps toward understanding D-O events, particularly regarding the role of the low latitudes, are now reported by Hughen et al. and Peterson et al.

  6. 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).

  7. Revealing the eruptive dynamics of post-glacial effusive volcanism in the western part of Laguna del Maule Volcanic Field: Insights into a complex magmatic system

    NASA Astrophysics Data System (ADS)

    Cáceres, F.; Castruccio, A.; Parada, M. Á.

    2015-12-01

    In this study we analyzed six Quaternary lava flows and one lava dome from Laguna del Maule Volcanic Field, in the Chilean Andes, in order to create a volcano-petrological eruptive model to get ideas about pre- and syn-eruptive stages, the main factors that control the broad distribution of vents and the architecture of magma reservoir. We estimated eruptive parameters such as effusion rates and erupted volumes, extrinsic and intrinsic lava flows emplacement controlling factors, magma ascent rates and pre-eruptive thermodynamics conditions to determine different stages in magma evolution from magma reservoir to emplacement of lava at surface. The analyzed lavas have andesitic-to-rhyolitic compositions, blocky morphology with volumes about a few cubic kilometers, thicknesses up to 140 m, maximum widths of 5 km and maximum lengths of 10 km. Modeling of the advance of these flows gives effusion rates of 10-1-102 m3s-1 and eruptions of a few months to years. Petrologic studies which include quantitative textural analyses and mineral and glass compositions, reveal similar provenance and crystalizing temperatures of similar minerals, coupled with similar pressures, H2O content and oxygen fugacity by similar lava composition, meanwhile individual chamber size estimations show an overlap sharing volume in near chambers indicating the equivalent provenance. Our main results about dynamics of lava flows suggest a crustal yield strength control in the emplacement over the internal viscosity of the flow for each lava. On the other hand, non-rhyolitic units appear to come from chambers located in similar depths and with coinciding volumes which indicate that the eruptions were triggered by the injection of different magma batches into a crystal-rich magma reservoir that could be divided into many sub-compartments which could explain the broad distribution of the vents. In addition, rhyolitic units also show similar thermodynamics conditions and coming from equivalent chambers.

  8. 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.

  9. 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.

  10. 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.

  11. Differences in Bacterial Diversity and Communities Between Glacial Snow and Glacial Soil on the Chongce Ice Cap, West Kunlun Mountains

    PubMed Central

    Yang, Guang Li; Hou, Shu Gui; Le Baoge, Ri; Li, Zhi Guo; Xu, Hao; Liu, Ya Ping; Du, Wen Tao; Liu, Yong Qin

    2016-01-01

    A detailed understanding of microbial ecology in different supraglacial habitats is important due to the unprecedented speed of glacier retreat. Differences in bacterial diversity and community structure between glacial snow and glacial soil on the Chongce Ice Cap were assessed using 454 pyrosequencing. Based on rarefaction curves, Chao1, ACE, and Shannon indices, we found that bacterial diversity in glacial snow was lower than that in glacial soil. Principal coordinate analysis (PCoA) and heatmap analysis indicated that there were major differences in bacterial communities between glacial snow and glacial soil. Most bacteria were different between the two habitats; however, there were some common bacteria shared between glacial snow and glacial soil. Some rare or functional bacterial resources were also present in the Chongce Ice Cap. These findings provide a preliminary understanding of the shifts in bacterial diversity and communities from glacial snow to glacial soil after the melting and inflow of glacial snow into glacial soil. PMID:27811967

  12. Differences in Bacterial Diversity and Communities Between Glacial Snow and Glacial Soil on the Chongce Ice Cap, West Kunlun Mountains.

    PubMed

    Yang, Guang Li; Hou, Shu Gui; Le Baoge, Ri; Li, Zhi Guo; Xu, Hao; Liu, Ya Ping; Du, Wen Tao; Liu, Yong Qin

    2016-11-04

    A detailed understanding of microbial ecology in different supraglacial habitats is important due to the unprecedented speed of glacier retreat. Differences in bacterial diversity and community structure between glacial snow and glacial soil on the Chongce Ice Cap were assessed using 454 pyrosequencing. Based on rarefaction curves, Chao1, ACE, and Shannon indices, we found that bacterial diversity in glacial snow was lower than that in glacial soil. Principal coordinate analysis (PCoA) and heatmap analysis indicated that there were major differences in bacterial communities between glacial snow and glacial soil. Most bacteria were different between the two habitats; however, there were some common bacteria shared between glacial snow and glacial soil. Some rare or functional bacterial resources were also present in the Chongce Ice Cap. These findings provide a preliminary understanding of the shifts in bacterial diversity and communities from glacial snow to glacial soil after the melting and inflow of glacial snow into glacial soil.

  13. 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.

  14. 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.

  15. Using glacial morphology to constrain the impact of the Chile active spreading ridge subduction in Central Patagonia

    NASA Astrophysics Data System (ADS)

    Scalabrino, B.; Ritz, J. F.; Lagabrielle, Y.

    2009-04-01

    The Central Patagonian Cordillera is a unique laboratory to study interaction between oceanic and continental lithospheres during the subduction of an active spreading ridge beneath a continent. The subduction of the South Chile spreading Ridge, which separates the Nazca plate from the Antarctic plate, started ca. 15-14 Ma at the southern tip of Patagonia (55°S latitude). The northwards migration of the Chile Triple Junction induces the subduction of several segments especially around 46°S latitude. There, three segments subducted at ca. 6, 3 and 0.3 Ma, leading to the formation of a large asthenospheric slab-window beneath Central Patagonia. Contemporaneously, the Central Patagonia reliefs are undergoing major glacial events since at least 7 Ma. These events are evidenced to the east of the Central Patagonian morphotectonic front within perched relict surfaces. Inset in these perched glacial surfaces are found mid-Pleistocene glacial valleys, as the Lake General Carrera-Buenos Aires amphitheatre (LGCBA), which formed between 1.1 Ma and 16 ka. We used the relationships between the glacial valleys and the volcanism associated with the asthenospheric slab-window to better constraints the structural evolution of the Patagonian Cordillera related to the subduction of the Chili active spreading Ridge. The present work focused within two well-preserved perched flat surfaces named Meseta del Lago Buenos Aires and Meseta del Cerro Galera: (i) The meseta del Lago Buenos Aires defines a plateau made of interbedded units of tills and lavas dated between 12 Ma and 3 Ma. The top surface of the meseta, ˜2000 meters high is dated at 3 Ma, and is shaped by four NE-SW trending glacial lobes characterized with kettles, lineations and moraines. The glacial valleys are beheaded westwards and define perched valleys 200 to 400 meters higher than the western Cordillera. This suggests recent vertical movement along N160 extensive/transtensive corridor located between the morphotectonic

  16. 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.

  17. Understanding the glacial methane cycle

    NASA Astrophysics Data System (ADS)

    Hopcroft, Peter O.; Valdes, Paul J.; O'Connor, Fiona M.; Kaplan, Jed O.; Beerling, David J.

    2017-02-01

    Atmospheric methane (CH4) varied with climate during the Quaternary, rising from a concentration of 375 p.p.b.v. during the last glacial maximum (LGM) 21,000 years ago, to 680 p.p.b.v. at the beginning of the industrial revolution. However, the causes of this increase remain unclear; proposed hypotheses rely on fluctuations in either the magnitude of CH4 sources or CH4 atmospheric lifetime, or both. Here we use an Earth System model to provide a comprehensive assessment of these competing hypotheses, including estimates of uncertainty. We show that in this model, the global LGM CH4 source was reduced by 28-46%, and the lifetime increased by 2-8%, with a best-estimate LGM CH4 concentration of 463-480 p.p.b.v. Simulating the observed LGM concentration requires a 46-49% reduction in sources, indicating that we cannot reconcile the observed amplitude. This highlights the need for better understanding of the effects of low CO2 and cooler climate on wetlands and other natural CH4 sources.

  18. Understanding the glacial methane cycle

    PubMed Central

    Hopcroft, Peter O.; Valdes, Paul J.; O'Connor, Fiona M.; Kaplan, Jed O.; Beerling, David J.

    2017-01-01

    Atmospheric methane (CH4) varied with climate during the Quaternary, rising from a concentration of 375 p.p.b.v. during the last glacial maximum (LGM) 21,000 years ago, to 680 p.p.b.v. at the beginning of the industrial revolution. However, the causes of this increase remain unclear; proposed hypotheses rely on fluctuations in either the magnitude of CH4 sources or CH4 atmospheric lifetime, or both. Here we use an Earth System model to provide a comprehensive assessment of these competing hypotheses, including estimates of uncertainty. We show that in this model, the global LGM CH4 source was reduced by 28–46%, and the lifetime increased by 2–8%, with a best-estimate LGM CH4 concentration of 463–480 p.p.b.v. Simulating the observed LGM concentration requires a 46–49% reduction in sources, indicating that we cannot reconcile the observed amplitude. This highlights the need for better understanding of the effects of low CO2 and cooler climate on wetlands and other natural CH4 sources. PMID:28220787

  19. Analysis of recent glacial earthquakes in Greenland

    NASA Astrophysics Data System (ADS)

    Olsen, K.; Nettles, M.

    2015-12-01

    Large calving events at Greenland's outlet glaciers produce teleseismically detectable glacial earthquakes. These events are observed in the seismic record for the past 22 years, but the complete catalog of glacial earthquakes still numbers only ~300. The annual occurrence of these long-period events has increased over time, which makes recent years especially valuable in expanding the global dataset. Glacial earthquakes from 1993- 2010 have been analyzed systematically (Tsai and Ekström, 2007; Veitch and Nettles, 2012). Here, we analyze more recent events using the same centroid—single-force (CSF) approach as previous authors, focusing initially on data from 2013. In addition, we perform a focused study of selected events from 2009-2010 to assess the reliability of the force azimuths obtained from such inversions. Recent spatial and temporal patterns of glacial earthquakes in Greenland differ from those in previous years. In 2013, three times as many events occurred on the west coast as on the east, and these events originated predominantly from two glaciers: Jakobshavn Glacier on the west coast and Helheim Glacier on the east. Kangerdlugssuaq Glacier, on the east coast, produced no glacial earthquakes in 2013, though it produced many events in earlier years. Previous CSF results for glacial earthquakes show force azimuths perpendicular to the glacier front during a calving event, with force plunges near horizontal. However, some azimuths indicate forces initially oriented upglacier, while others are oriented downglacier (seaward). We perform a set of experiments on events from 2009 and 2010 and find two acceptable solutions for each glacial earthquake, oriented 180° apart with plunges of opposite sign and centroid times differing by approximately one half of the assumed duration of the earthquake time function. These results suggest the need for a more complex time function to model glacial earthquakes more accurately.

  20. 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.

  1. Nutrient Dynamics in the Glacial Southern Ocean

    NASA Astrophysics Data System (ADS)

    Latimer, J. C.; Filippelli, G. M.

    2004-12-01

    The Southern Ocean (SO) was likely a key contributor to glacial/interglacial climate change resulting from variability either in biogeochemical cycles or ocean stratification and CO2 degassing. Many of the hypotheses to explain the interglacial to glacial difference in atmospheric CO2 suggest that higher glacial dust fluxes led to Fe fertilization of surface waters and increased export production in the SO because the modern-day Southern Ocean is co-limited by both Fe and light availability. Documented Fe sources include upwelled Upper Circumpolar Deep Water, eolian deposition, and melting sea-ice. However, the influence of these sources is variable with latitude and position relative to major frontal zones. Presumably these same Fe sources were important during glacial times albeit at potentially different rates and magnitudes. To examine this effect, we have compared sedimentary Fe fluxes with records of dust deposition. We have found that Fe fluxes are higher than can be explained by eolian deposition, supporting an additional hemipelagic source of Fe to the deep ocean during glacial intervals. Furthermore, different proxies used to evaluate export production and nutrient utilization during glacial intervals yield different and seemingly contradictory results-for example, different studies have concluded that net productivity increased, decreased, and/or remained constant in the SO. Results from phosphorus geochemistry suggest that maxima in export production actually occur at terminations rather than either full glacial or interglacial conditions adding yet another possibility. The focus here will be to try to reconcile the nutrient, export production, and Fe data into a coherent view of nutrient utilization and export production in the glacial SO.

  2. Tierra de Oportunidad Implementation Handbook. LAES: Latino Adult Education Services Project.

    ERIC Educational Resources Information Center

    Kissam, Ed; Dorsey, Holda

    This handbook is intended to help administrators and instructors of adult basic education and English-as-a-Second-Language programs use the 30 Tierra de Oportunidad (Land of Opportunity) instructional modules, which address four strands or clusters relating to the different major domains in which adults function: work life, family life, community,…

  3. Espectroscopia del Cometa Halley

    NASA Astrophysics Data System (ADS)

    Naranjo, O.; Fuenmayor, F.; Ferrin, L.; Bulka, P.; Mendoza, C.

    1987-05-01

    Se reportan observaciones espectroscópicas del cometa Halley. Los espectros fueron tomados usando el espectrógrafo del telescopio reflector de 1 metro del Observatorio Nacional de Venezuela. Se utilizó óptica azul, con una red de difracción de 600 lineas/min, obteniéndose una dispersión de 74.2 A/mm y una resolución de 2.5 A, en el rango espectral de 3500 a 6500 A. Seis placas fueron tomadas con emulsión IIa-O y dos con IIa-D. Los tiempos de exposición fueron entre 10 y 150 minutos. El cometa se encontraba entre 0.70 y 1.04 UA del Sol, y entre 1.28 y 0.73 UA de la Tierra. Las emisiones más prominentes en el espectro, son las del CN, C2, y C3. Otras emisiones detectadas corresponden a CH, NH2 y Na. Los espectros muestran un fuerte continuo, indicando un contenido significativo de polvo. Se detectó mayor intensidad del contínuo, en la dirección anti solar, lo cual es evidencia de la cola de polvo.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Glacial stages and post-glacial environmental evolution in the Upper Garonne valley, Central Pyrenees.

    PubMed

    Fernandes, M; Oliva, M; Palma, P; Ruiz-Fernández, J; Lopes, L

    2017-04-15

    The maximum glacial extent in the Central Pyrenees during the Last Glaciation is known to have occurred before the global Last Glacial Maximum, but the succession of cold events afterwards and their impact on the landscape are still relatively unknown. This study focuses on the environmental evolution in the upper valley of the Garonne River since the Last Glaciation. Geomorphological mapping allows analysis of the spatial distribution of inherited and current processes and landforms in the study area. The distribution of glacial records (moraines, till, erratic boulders, glacial thresholds) suggests the existence of four glacial stages, from the maximum expansion to the end of the glaciation. GIS modeling allows quantification of the Equilibrium Line Altitude, extent, thickness and volume of ice in each glacial stage. During the first stage, the Garonne glacier reached 460m in the Loures-Barousse-Barbazan basin, where it formed a piedmont glacier 88km from the head and extended over 960km(2). At a second stage of glacier stabilization during the deglaciation process, the valley glaciers were 12-23km from the head until elevations of 1000-1850m, covering an area of 157km(2). Glaciers during stage three remained isolated in the upper parts of the valley, at heights of 2050-2200m and 2.6-4.5km from the head, with a glacial surface of 16km(2). In stage four, cirque glaciers were formed between 2260m and 2590m, with a length of 0.4-2km and a glacial area of 5.7km(2). Also, the wide range of periglacial, slope, nival and alluvial landforms existing in the formerly glaciated environments allows reconstruction of the post-glacial environmental dynamics in the upper Garonne basin. Today, the highest lands are organized following three elevation belts: subnival (1500-1900m), nival (1900-2300m) and periglacial/cryonival (2300-2800m).

  9. Latest Pleistocene and Holocene glacier fluctuations in southernmost Tierra del Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Menounos, Brian; Clague, John J.; Osborn, Gerald; Davis, P. Thompson; Ponce, Federico; Goehring, Brent; Maurer, Malyssa; Rabassa, Jorge; Coronato, Andrea; Marr, Rob

    2013-10-01

    Some researchers propose that summer insolation controls long-term changes in glacier extent during the Holocene. If this hypothesis is correct, the record of glacier fluctuations at high latitudes in the Southern Hemisphere should differ from that in the Northern Hemisphere. Although the chronology of Holocene glacier fluctuations in the Northern Hemisphere is well established, much uncertainty remains in the ages of Holocene glacier fluctuations in the Southern Hemisphere, especially South America. Here we report on latest Pleistocene and Holocene glacier fluctuations at the southern end of the Andes north and west of Ushuaia, Argentina. Surface exposure ages (10Be) from glaciated bedrock beyond cirque moraines indicate that alpine areas were free of ice by ca 16.9 ka. One, and in some cases two, closely spaced moraines extend up to 2 km beyond Little Ice Age moraines within many of the cirques in the region. The mean age of five 10Be ages from two pre-Little Ice Age moraines is 14.27-12.67 ka, whereas a minimum limiting radiocarbon age for a smaller, recessional moraine in one cirque is 12.38-12.01 ka. Our ages imply that, following glacier retreat beginning about 18.52-17.17 ka, cirque glaciers first advanced during the Antarctic Cold Reversal (14.5-12.9 ka) and may have later advanced or stabilized in the Younger Dryas Chronozone (12.9-11.7 ka). Based on the distribution of thick, geochemically distinct, and well-dated Hudson tephra, no Holocene moraines appear to be older than 7.96-7.34 ka. At some sites, there is evidence for one or more advances of glaciers sometime between 7.96-7.34 ka and 5.29-5.05 ka to limits only tens of meters beyond Little Ice Age maximum positions. Taken together, the data: 1) do not support the summer insolation hypothesis to explain Holocene glacier fluctuations in southernmost Patagonia; 2) confirm paleobotanical evidence for a warm, dry early Holocene; and 3) suggest that some glaciers in the region reached extents comparable to those of the Little Ice Age shortly before 5.29-5.05 ka.

  10. Morphological differentiation of aboriginal human populations from Tierra del Fuego (Patagonia): implications for South American peopling.

    PubMed

    Perez, S Ivan; Bernal, Valeria; Gonzalez, Paula N

    2007-08-01

    This study aims to integrate the craniofacial morphological variation of southern South American populations with the results of mtDNA haplogroup variation, to discuss the South America peopling. Because the causes of morphological differentiation of Fueguian populations are still a controversial subject, the comparison with neutral variation could contribute to elucidate them. Samples of human remains from South America regions were used to analyze the evolutionary relationships. Several craniofacial traits observed in frontal and lateral view were analyzed by means of geometric morphometrics techniques, and the evolutionary relationships based on morphological and molecular data were established in base to ordination analyses. The results from the facial skeleton agree with those obtained from mtDNA haplogroup frequencies, with La Pampa/Chaco samples detached from the Patagonian samples. Hence, the same mechanism that accounts for the pattern of frequency of haplogroups could explain the variation found in facial skeleton among the samples. It is suggested that such geographic pattern of craniofacial and molecular diversity may reflect the effect of genetic drift that occurred in the small founding populations isolated by distance or geographic barriers. Conversely, the results obtained using the traits from the lateral view slightly differ from the molecular results, showing differences between southernmost Patagonian and the other samples. Therefore, mechanisms other than genetic drift (e.g., natural selection) could have acted to shape the pattern observed in some craniofacial structures present in the lateral view, characterized by the fact that the southernmost Patagonian samples display the most robust and dolichocephalic crania.

  11. QBO modulation of the mesopause gravity wave momentum flux over Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Wit, R. J.; Janches, D.; Fritts, D. C.; Hibbins, R. E.

    2016-04-01

    The interannual variability of the mesosphere and lower thermosphere (MLT) gravity wave momentum flux over southern midlatitudes (53.7°S) has been studied using more than 7 years of meteor radar observations at Río Grande, Argentina. A modulation, with periods similar to that of the equatorial stratospheric quasi-biennial oscillation (QBO), is observed in the vertical flux of zonal as well as meridional momentum. The QBO signal is largest in the zonal component during summer and is in phase with the stratospheric QBO at 50 hPa (˜21 km). The relation between the stratospheric QBO and the QBO modulation in the MLT gravity wave forcing (derived from the divergence of the momentum flux) was found to be consistent with that expected from the Holton-Tan effect coupled to the interhemispheric coupling mechanism. These results provide the first observational support for the existence of the midlatitude gravity wave forcing anomalies as hypothesized in the interhemispheric coupling mechanism.

  12. Mössbauer study of archaeological ceramics from Valle del Alto Sinu (Colombia)

    NASA Astrophysics Data System (ADS)

    Useche, L. A.; Gaviria, S.; Alabart, J. R.; Fontcuberta, J.

    1990-07-01

    A physico-chemical characterization of ceramic samples from the arachaeological sites of El Cabrero, El Gallo, and El Frasquillo (Valle del Alto Sinú) is presented. Extensive use of Mössbauer spectroscopy data reveals that the currently used typological classification scheme of Dolmatoff is related to the production technology of the different artifacts. In addition, a model for firing conditions for “Rojo Sencillo”, “Tierra Impresa”, “Tierra Incisa”, and “Blanco” types of ceramics is proposed.

  13. Geochronology, structural evolution of the Tierra Colorada area, and tectonic implications for southern Mexico and Chortís block connections

    NASA Astrophysics Data System (ADS)

    Solari, L. A.; Torres de Leon, R.; Hernandez Pineda, G.; Sole', J.; Solis Pichardo, G.; Hernandez Treviño, T.

    2006-05-01

    The Tierra Colorada area is considered the best exposure of the northern limit between the Xolapa Complex and the Paleozoic-Precambrian Mixteca and Zapotecan terranes of southern Mexico. Geochemistry (major, trace, and REE) and geochronology on deformed granitoids in Tierra Colorada area show evidence of subduction-related magmatism during Mesozoic and Cenozoic. El Pozuelo granite, dated at 129 Ma (concordant U-Pb single-zircon age) is a foliated body, with local porphyric facies. Foliation is penetrative and characterized by oriented micas and stretched quartz. Geochemically it shows a metaluminous character, with arc-related trace and REE patterns. Because it cuts across high-grade gneisses of the Xolapa Complex, its intrusion postdates the second phase of metamorphism in the Xolapa Complex (> 130 Ma), which generated the orthogneisses-migmatites sequence. El Salitre granite (55 Ma, Rb-Sr 4 point isochron) is a foliated peraluminous body with a pronounced negative Zr anomaly. The protomylonitic Las PiÑas granite (54 +/- 6 Ma, U-Pb lower intercept) is characterized by ductile fabric, recognized by cinematic indicators such as mica fish, and indicates a top-to-the NNW sense of shear, dated at 50 +/- 1 Ma and 45.3 +/- 2 Ma (K-Ar on Bt, and Rb-Sr Bt-WR isochron, respectively), ages that indicate the time of ductile deformation along La Venta shear zone, as N-dipping detachment under low greenschist facies conditions. El Salitre and Las PiÑas granites are linked because of their similar HREE patterns. The Tierra Colorada, Xaltianguis and San Juan del Reparo granites, with calcalkaline subduction-related geochemistry, lack of penetrative deformation, and their ages of 30-34 Ma (U-Pb on zircons) constitute the last recognized granitic pulse in this area, post-dating the S-verging thrust of the Morelos limestones on top of sheared granites and volcanics. Together with previously published ages of magmatism in the studied area, we demonstrate here that calcalkaline

  14. 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.

  15. Glacial Lake Lind, Wisconsin and Minnesota

    USGS Publications Warehouse

    Johnson, M.D.; Addis, K.L.; Ferber, L.R.; Hemstad, C.B.; Meyer, G.N.; Komai, L.T.

    1999-01-01

    Glacial Lake Lind developed in the pre-late Wisconsinan St. Croix River valley, Minnesota and Wisconsin, and lasted more than 1000 yr during the retreat of the Superior lobe at the end of the Wisconsinan glaciation. Lake Lind sediment consists primarily of red varved silt and clay, but also includes mud-flow deposits, nearshore silt (penecontemporaneously deformed in places), nearshore rippled sand, and deltaic sand. Lake Lind varved red clay is not part of glacial Lake Grantsburg, as suggested by earlier authors, because the red varves are separated from overlying glacial Lake Grantsburg silt and clay by a unit of deltaic and fluvial sand. Furthermore, varve correlations indicate that the base of the red varves is younger to the north, showing that the basin expanded as the Superior lobe retreated and was not a lake basin dammed to the southwest by the advancing Grantsburg sublobe. Varve correlations indicate that the Superior lobe retreated at a rate of about 200 m/yr. Uniform winter-clay thickness throughout most of the varve couplets suggests thermal stratification in the lake with clay trapped in the epilimnion; some clay would exit the lake at the outlet prior to winter freeze. Zones of thicker winter-clay layers, in places associated with mud-flow layers, indicate outlet incision, lake-level fall, and shoreline erosion and resuspension of lake clay. The most likely outlet for glacial Lake Lind was in the southwest part of the lake near the present site of Minneapolis, Minnesota. Nearshore sediment indicates that the lake level of glacial Lake Lind was around 280 m. The elevation of the base of the Lake Lind sediments indicates water depth was 20 to 55 m. Evidence in the southern part of the lake basin suggests that the Superior lobe readvanced at least once during the early stages of glacial Lake Lind. Lake Lind ended not by drainage but by being filled in by prograding deltas and outwash plains composed of sand derived from the retreating Superior lobe. It

  16. 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

  17. 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.

  18. Variations in Glacial Erosion over Multiple Glacial-Interglacial Cycles: A Numerical Modelling Approach

    NASA Astrophysics Data System (ADS)

    Headley, Rachel M.; Ehlers, Todd A.

    2013-04-01

    Mountain topography is constructed through a variety of interacting processes. As one of these processes, glacial erosion plays an important role in the development of landscapes by the formation of distinctive topographic features. Glacial landscape evolution models reproduce many observed features at the orogen scale. Detailed comparisons at the scale of individual valleys holds potential for quantifying the influence of glacial physics in glacial erosion models. Over long timescales (>10,000 yr), glacial erosion has typically been simulated using a modified shallow ice approximation (SIA) approach. In this study, we compare the strengths and weaknesses of shallow ice and high-order, Stokes-flow glacial landscape evolution models. Our emphasis is placed on the patterns and rates of glacial erosion over multiple glacial-interglacial cycles. We present a comparison of two different numerical models for glacial erosion. For both approaches, a modified version of the ICE Cascade model is used to develop and evolve topography. This model calculates hillslope and fluvial erosion and sediment transport, isostasy, temporally variable orographic precipitation, and a range of glaciological processes: glacial mass balance, snow avalanching, basal ice superfreezing, and basal water buoyancy feedback in large overdeepenings. Within this framework, we compare the predicted ice-flow field and erosion patterns using a modified SIA as well as predictions from a nested, thermally-coupled, Stokes-flow model calculated using COMSOL Multiphysics. Simulations are conducted for a range of amplitudes and periodicity in surface temperature change between glacial and interglacial periods. We investigate these simulations, as well as the effects of each model for various initial topographies and with a temperature-dependent ice rheology. In general, both models predict visually similar patterns in sliding velocity, and resulting erosion rates, assuming the erosion rate scales with the

  19. 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

    2016-06-03

    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.

  20. Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

    NASA Astrophysics Data System (ADS)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Winckler, Gisela; Hall, Brenda L.; Todd, Claire E.; Rademaker, Kurt M.

    2009-11-01

    Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions. Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological time scales, 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 has a larger impact on the erosion rate, with variations of almost an order of magnitude. 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 that are greater than 30%, again with larger differences for temperate ice. Over multiple glaciations and long-time scales, these results suggest that consideration of higher-order glacial physics may be necessary, particularly in temperate, mountainous settings.

  2. 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.

  3. 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.

  4. 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.

  5. Late Glacial ice advances in southeast Tibet

    NASA Astrophysics Data System (ADS)

    Strasky, Stefan; Graf, Angela A.; Zhao, Zhizhong; Kubik, Peter W.; Baur, Heinrich; Schlüchter, Christian; Wieler, Rainer

    2009-03-01

    The sensitivity of Tibetan glacial systems to North Atlantic climate forcing is a major issue in palaeoclimatology. In this study, we present surface exposure ages of erratic boulders from a valley system in the Hengduan Mountains, southeastern Tibet, showing evidence of an ice advance during Heinrich event 1. Cosmogenic nuclide analyses ( 10Be and 21Ne) revealed consistent exposure ages, indicating no major periods of burial or pre-exposure. Erosion-corrected (3 mm/ka) 10Be exposure ages range from 13.4 to 16.3 ka. This is in agreement with recalculated exposure ages from the same valley system by [Tschudi, S., Schäfer, J.M., Zhao, Z., Wu, X., Ivy-Ochs, S., Kubik, P.W., Schlüchter, C., 2003. Glacial advances in Tibet during the Younger Dryas? Evidence from cosmogenic 10Be, 26Al, and 21Ne. Journal of Asian Earth Sciences 22, 301-306.]. Thus this indicates that local glaciers advanced in the investigated area as a response to Heinrich event 1 cooling and that periglacial surface adjustments during the Younger Dryas overprinted the glacial morphology, leading to deceptively young exposure ages of certain erratic boulders.

  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. 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.

  8. 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

  9. 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

  10. Excitation of the earth's rotational axis by recent glacial discharges

    NASA Technical Reports Server (NTRS)

    Gasperini, P.; Sabadini, R.; Yuen, D. A.

    1986-01-01

    The effects of present-day glacial discharges and the growth of the Antarctic ice sheet on exciting the earth's rotational axis are studied. Glacial forcing could cause a maximum change in J2 of about one-third of the observed amount, for the Maxwell rheology and for Burgers' body models with a long-term, lower-mantle viscosity greater than about 10 to the 23rd P. For transient rheologies the amount of excitation due to glacial melting decreases. Polar wander is not much excited by recent glacial melting for the various types of rheologies examined.

  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. The role of meltwater in glacial processes

    NASA Astrophysics Data System (ADS)

    Eyles, Nick

    2006-08-01

    Water plays a dominant role in many glacial processes and the erosional, depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized. At its maximum extent c. 20,000 years ago, the volume of the Laurentide ice sheet was 33 × 10 6 km 3 (about the same as the volume of all ice present today on planet Earth). The bulk of this was released as water in little more than 10,000 years. Pulses of meltwater flowing to the Atlantic Ocean from large ice dammed lakes altered thermohaline circulation of the world's oceans and global climate. One such discharge event via Hudson Bay at 8200 years BP released 160,000 km 3 of water in 12 months. Global sea levels recovered from glacial maximum low stands reached at about 20,000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods, rates as high as 4 m per hundred years. Meltwaters played a key role in lubricating ice sheet motion (and thus areal abrasion) across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the Canadian Shield. The recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments (till) by sliding-induced shearing and deformation of overpressured sediment and soft rock. The transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates. Some workers credit catastrophic subglacial 'megafloods' with the formation of drumlins and flutes on till surfaces. Subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins; it has been estimated that less than 6% of the total volume of glaciclastic sediment produced during the Pleistocene remains on land. Fluvioglacial and

  13. New mechanism proposed for glacial cycles

    NASA Astrophysics Data System (ADS)

    Newman, Alan

    Were the ice ages triggered by an influx of extraterrestrial dust or meteoroids hitting Earth's upper atmosphere? A controversial and still unproven new theory recently described by Muller and MacDonald [1995] in Nature links the 100,000 year glacial cycle with changes in Earth's orbital inclination relative to the plane of the solar system. And, say the theory developers, the only logical mechanism they can find for the connection is increasing amounts of extraterrestrial material entering the atmosphere whenever Earth's orbit sweeps through the solar plane. Climate researchers are just beginning to test the model's predictions.

  14. Geological constraints on Earth system sensitivity to CO2 during glacial and non-glacial times

    NASA Astrophysics Data System (ADS)

    Royer, D. L.; Park, J. J.; Pagani, M.; Beerling, D. J.

    2011-12-01

    Earth system climate sensitivity (ESS) is the long-term (>103 yr) response of global surface temperature to doubled CO2 that integrates fast and slow climate feedbacks. ESS has energy policy implications because global temperatures are not expected to decline appreciably for many centuries, even if anthropogenic greenhouse-gas emissions drop to zero. We report ESS estimates for the last 420 Myr of Earth history of 3 °C or higher during many non-glacial times and ~6-8 °C during glacial times. Analyses include both direct comparison of CO2 and temperature records, and fitting Berner's long-term carbon cycle model GEOCARBSULFvolc to proxy CO2 records while using ESS as a tunable parameter (Park & Royer, 2011, American Journal of Science 311: 1-26). Our ESS estimates are generally higher than climate sensitivities simulated from global climate models for the same ancient periods (~3 °C). Our two-fold amplification during glacial times is probably caused by long-term continental ice-sheet dynamics, a mechanism consistent with other studies. Even for non-glacial times, climate models do not capture the full suite of positive climate feedbacks. These absent feedbacks may be related to clouds, trace greenhouse gases, seasonal snow cover, and/or vegetation, especially in polar regions. Better characterization and quantification of these feedbacks is a priority given the current accumulation of atmospheric greenhouse gases.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. Interhemispheric Correlation of Late Pleistocene Glacial Events

    NASA Astrophysics Data System (ADS)

    Lowell, T. V.; Heusser, C. J.; Andersen, B. G.; Moreno, P. I.; Hauser, A.; Heusser, L. E.; Schluchter, C.; Marchant, D. R.; Denton, G. H.

    1995-09-01

    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 >=33,500 carbon-14 years before present (14C 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 14C 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 14C yr B.P., and at the beginning of the Younger Dryas at 11,050 14C 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.

  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. 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…

  2. 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

  3. Contrasting scaling properties of interglacial and glacial climates.

    PubMed

    Shao, Zhi-Gang; Ditlevsen, Peter D

    2016-03-16

    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.

  4. Hydrogeology of glacial drift, Mesabi Iron Range, northeastern Minnesota

    USGS Publications Warehouse

    Winter, Thomas C.

    1973-01-01

    Practical sustained yield of aquifers in glacial drift is estimated to be as much as 40 million gallons per day from known aquifers. Assuming that the ratio of area underlain by aquifer to total area is constant for the study area (about 20 percent where mapped in detail), as much as 80 million gallons per day could be developed from glacial-drift aquifers.

  5. Glacial-interglacial vegetation change in the Zambezi catchment

    NASA Astrophysics Data System (ADS)

    Dupont, L. M.; Kuhlmann, H.

    2017-01-01

    Changes in the environment are thought to have had strong impact on human evolution. The pollen record of GeoB9311, retrieved offshore of the Zambezi River mouth, indicates glacial-interglacial changes in the vegetation of southern East Africa with enhanced forests in the coastal area during interglacials, more Afromontane forest and ericaceous bushland during glacials and an increase in mopane woodland during the transitional periods. C4 swamps, probably with papyrus, might have spread during the more humid phases of the glacial, while mangroves responded sensitively to changes in sea level. The spread of open ericaceous bushland and Afromontane forest during glacials is found for most of Southern Africa with the exception of the extreme south and southwest regions. In contrast to the western part of the continent, forest and woodland in East Africa did not completely disappear during the glacial. It seems that on a regional scale climatic perturbations of the vegetation are less severe than in West Africa.

  6. Glacial isostatic uplift of the European Alps

    PubMed Central

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

    2016-01-01

    Following the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth's viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions. PMID:27830704

  7. Measurements of Glacial Isostatic Adjustment in Greenland

    NASA Astrophysics Data System (ADS)

    Khan, Shfaqat Abbas; Bamber, Jonathan; Bevis, Michael; Wahr, John; van dam, Tonie; Wouters, Bert; Willis, Michael

    2015-04-01

    The Greenland GPS network (GNET) was constructed to provide a new means to assess viscoelastic and elastic adjustments driven by past and present-day changes in ice mass. Here we assess existing glacial isostatic adjustments (GIA) models by analysing 1995-present data from 61 continuous GPS receivers located along the edge of the Greenland ice sheet. Since GPS receivers measure both the GIA and elastic signal, we isolate the GIA signal, by removing the elastic adjustments of the crust due to present-day mass loss using high-resolution ice surface elevation change grids derived from satellite and airborne altimetry measurements (ERS1/2, ICESat, ATM, ENVISAT, and CryoSat-2). In general, our observed GIA rates contradict models, suggesting GIA models and hence their ice load history for Greenland are not well constrained.

  8. Bacterial recovery from ancient glacial ice.

    PubMed

    Christner, Brent C; Mosley-Thompson, Ellen; Thompson, Lonnie G; Reeve, John N

    2003-05-01

    Ice that forms the bottom 18 m of a 308 m ice core drilled from the Guliya ice cap on the Qinghan-Tibetan plateau in Western China is over 750000 years old and is the oldest glacial ice known to date. Fourteen bacterial isolates have been recovered from samples of this ice from approximately 296 m below the surface (mbs). Based on 16S rDNA sequences, these are members of the alpha- and beta-proteobacterial, actinobacterial and low-G + C Gram-positive bacterial lineages. 16S rDNA molecules have also been amplified directly, cloned and sequenced from the ice-core melt water. These originated from Pseudomonas and Acinetobacter gamma-proteobacterial species. These results demonstrate that bacteria can be recovered from water ice that has frozen for time periods relevant to biological survival through terrestrial ice ages or during interplanetary transport.

  9. Quaternary glacial stratigraphy and chronology of Mexico

    NASA Astrophysics Data System (ADS)

    White, Sidney E.

    The volcano Iztaccihuatl in central Mexico was glaciated twice during the middle Pleistocene, once probably in pre-Illinoian (or pre-Bull Lake) time, and once in late Illinoian (or Bull Lake) time. Glaciation during the late Pleistocene was restricted to the late Wisconsin (or Pinedale). A maximum advance and one readvance are recorded in the early part, and one readvance in the latter part. Three or four small neoglacial advances occurred during the Holocene. Two other volcanoes nearby, Ajusco and Malinche, have a partial record of late Pleistocene and Holocene glaciations. Three others, Popocatépetl, Pico de Orizaba, and Nevado de Toluca, have a full Holocene record of three to five glacial advances during Neoglaciation.

  10. Glacial isostatic uplift of the European Alps.

    PubMed

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

    2016-11-10

    Following the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth's viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions.

  11. Glacial isostatic uplift of the European Alps

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    Following the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ~90% of the geodetically measured rock uplift in the Alps can be explained by the Earth's viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions.

  12. 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.

  13. 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.

  14. 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."

  15. TIERRAS: A package to simulate high energy cosmic ray showers underground, underwater and under-ice

    NASA Astrophysics Data System (ADS)

    Tueros, Matías; Sciutto, Sergio

    2010-02-01

    In this paper we present TIERRAS, a Monte Carlo simulation program based on the well-known AIRES air shower simulations system that enables the propagation of particle cascades underground, providing a tool to study particles arriving underground from a primary cosmic ray on the atmosphere or to initiate cascades directly underground and propagate them, exiting into the atmosphere if necessary. We show several cross-checks of its results against CORSIKA, FLUKA, GEANT and ZHS simulations and we make some considerations regarding its possible use and limitations. The first results of full underground shower simulations are presented, as an example of the package capabilities. Program summaryProgram title: TIERRAS for AIRES Catalogue identifier: AEFO_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFO_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 36 489 No. of bytes in distributed program, including test data, etc.: 3 261 669 Distribution format: tar.gz Programming language: Fortran 77 and C Computer: PC, Alpha, IBM, HP, Silicon Graphics and Sun workstations Operating system: Linux, DEC Unix, AIX, SunOS, Unix System V RAM: 22 Mb bytes Classification: 1.1 External routines: TIERRAS requires AIRES 2.8.4 to be installed on the system. AIRES 2.8.4 can be downloaded from http://www.fisica.unlp.edu.ar/auger/aires/eg_AiresDownload.html. Nature of problem: Simulation of high and ultra high energy underground particle showers. Solution method: Modification of the AIRES 2.8.4 code to accommodate underground conditions. Restrictions: In AIRES some processes that are not statistically significant on the atmosphere are not simulated. In particular, it does not include muon photonuclear processes. This imposes a limitation on the application of this package to a depth of

  16. Conversation with Lara about the Earth and Land. (Spanish Title: Conversando con Lara sobre la Tierra y la Teirra.) Conversando com Lara sobre a Terra e a Terra

    NASA Astrophysics Data System (ADS)

    da Conceição Barbosa-Lima, Maria

    2010-12-01

    The present article is the analysis of a conversation between the author and Lara, a four-yearold- girl, enrolled in nursery school, while she makes a drawing of the Earth. It took place outside school environment and without any other person around to avoid interference during the interview. According to Ferreira & Silva (2004), a researcher can only comprehend a child's drawing, or form, by listening to him/her while he/she is creating it. Lara presented the traditional flat drawing, picturing the sky parallel to the ground, as reported by Nardi & Carvalho (1996). However, when asked to draw the World - term used by Butterworth et al. (2002), in order to avoid unnecessary confusion - she represented it by a circle, with herself on the surface. Her drawings led to the conclusion that such girl does not know yet the World in which she lives is the Earth, and probably because of that, within her age and consequent maturity, she accurately differentiates the concepts of land and Earth. El presente artículo analiza una entrevista libre, mientras una niña de 4 años y 4 meses, matriculada en el pregrado, dibuja la Tierra. Esta entrevista se realizó fuera del ambiente escolar y sin otra persona alrededor que pudiera interferir. De acuerdo con Ferreira Silva (2004), para quien investiga es posible conocer realmente lo que un niño o una niña pone en el papel a través de grafismos y/o dibujos si se lo escucha durante el proceso de creación de la escritura con imágenes. La niña, en este caso, representa la Tierra con el tradicional dibujo plano y el "cielo" paralelo al suelo, conforme analizaron Nardi & Carvalho (1996). Pero, cuando se Le solicita dibujar el "Mundo" - palabra empleada en un trabajo de Butterworth et al. (2002), con intención de no provocar "confusiones" innecesarias a sus sujetos de investigación- lo representa de forma circular, poniéndose sobre su superficie. Sus dibujos llevan a concluir que esta niña aún no tiene conocimiento que el mundo

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. Early Circum-Arctic Glacial Decay Following the Last Glacial Maximum?

    NASA Astrophysics Data System (ADS)

    Snow, T.; Alonso-Garcia, M.; Flower, B. P.; Shevenell, A.; Roehl, U.; Goddard, E.

    2012-12-01

    Recent rapid warming, glacial retreat, and sea ice reduction observed in the Arctic suggest extreme regional environmental sensitivity to ongoing anthropogenic climate change. To place these recent environmental changes in context and better understand the forcings and feedbacks involved in Arctic climate change, regional studies of past intervals of rapid warming are required. Paleoceanographic studies from the high-latitude North Atlantic indicate close relationships between meltwater discharges from circum-Arctic ice sheets, perturbations of Atlantic Meridional Overturning Circulation (AMOC), and global climate variations on sub-orbital timescales during the Late Quaternary. During the last glacial-interglacial transition (25-10 ka), when atmospheric temperatures over Greenland warmed 10-15°C and the AMOC experienced millennial-scale variability, low-resolution stable isotope studies from Fram Strait sediment cores indicate that the circum-Arctic ice sheets began to melt earlier than lower latitude Northern Hemisphere ice sheets, discharging their meltwater into the high latitude North Atlantic. Fram Strait, located at the gateway between the Atlantic and Arctic Oceans, is the only region where Arctic meltwater can exchange with the world oceans on both glacial and interglacial timescales. Thus, high-resolution paleoceanographic studies of Fram Strait sediments are critically required for understanding changes in Arctic meltwater flux to the North Atlantic on sub-orbital timescales. Here we present the first high-resolution (<100 yr) multi-proxy dataset from Fram Strait (ODP Site 986; 77°20.43'N, 9°04.66'E; water depth: 2063 m) to assess the timing of circum-Arctic ice sheet decay since the Last Glacial Maximum. Foraminiferal isotopic and elemental, scanning X-Ray Fluorescence, and ice-rafted debris records are used to isolate Arctic meltwater and iceberg discharge signals. Sharp increases in productivity and changes in water mass ventilation are inferred

  9. 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.

  10. New exposure ages for the Last Glacial Cycle in the Sanabria Lake region (northwestern Spain)

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María Jose; Rinterknecht, Vincent; Pallàs, Raimon; Braucher, Régis; Bourlès, Didier; Valero-Garcés, Blas

    2013-04-01

    ., 2011. Last deglaciation in northwestern Spain: New chronological and geomorphologic evidence from the Sanabria region. Geomorphology 135, 48-65. Palacios, D., Andrés, N., Úbeda, J., Alcalá, J., Marcos, J., Vázquez-Selem, L., 2012. The importance of poligenic moraines in the paleoclimatic interpretation from cosmogenic dating. Geophysical Research Abstracts 14, EGU2012-3759-1. Pérez-Alberti, A., Valcárcel-Díaz, M., Martini, I.P., Pascucci, V., Andrucci, S., 2011. Upper Pleistocene glacial valley-junction sediments at Pias, Trevinca Mountains, NW Spain. In: Martini, I.P., French, H.M., Pérez-Alberti, A. (Eds.), Ice-Marginal and Periglacial Processes and Sediments. Geological Society (London) Special Publication 354, pp. 93-110. Research funded by the projects LIMNOCLIBER (REN2003-09130-C02-02), IBERLIMNO (CGL2005-20236-E/CLI), LIMNOCAL (CGL2006-13327-C04-01) and GRACCIE (CSD2007-00067) of the Spanish Inter-Ministry Commission of Science and Technology (CICYT). Additional funding was provided by the Fundación Patrimonio Natural de Castilla y León through the project "La investigacion en el Lago de Sanabria dentro del proyecto CALIBRE: perspectivas y posibilidades", and by the projects Consolider Ingenio 2006 (CSD2006-0041, Topo-Iberia), 2003 PIRA 00256, HF02.4, and RISKNAT (2009SGR520). L. Rodríguez-Rodríguez has developed her research under a Severo Ochoa Programme fellowship (FICYT- Asturias).

  11. Neoproterozoic Glacial Extremes: How Plausible is the

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.

    2004-05-01

    The suggestion that the glaciation events of the Neoproterozoic could have been global in extent, so-called "snowball" glaciations, during which the oceans were entirely covered by sea ice and the continents by massive continental ice sheets, is an idea tha is recurrent in the geological and climate dynamics literature. It is an idea that haa both critics and defenders but concensus concerning it's plausiblity has yet to emerge. Previous work on this problem has led to the suggestion that a more likely scenario than the "hard snowball" is one in which open water continues to persist at the equator, thus enabling biological evolution into the Cambrian to proceed, perhaps stimulated by the transition from the cold conditions of the Neoproterozoic to the warm condition of the Cambrian, thus leading to the Cambrian "explosion of life". We will discuss recent extensions of our previous efforts to model the extreme climate of the Neoproterozoic, using both the University of Toronto Glacial Systems Model and the NCAR Community Climate System Model. With an appropriate choice for the albedo of sea ice, the former model conntinues to deliver hysteresis in the surface temperature vs. CO2 concentration space when solar luminosity is reduced by 6% below modern, and thus continues to suggest the existence of the previously hypothesized "CO2 attractor". We argue here that the system could be locked onto this attractor by the strong "out of equilibrium" effects of the carbon cycle recently discussed by Rothman et al. (PNAS, 2003). The open water solution is confirmed as the preferred mode of the system by the detailed CCSM integrations that we have performed.

  12. 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.

  13. Geochemical Weathering in Glacial and Proglacial Environments

    NASA Astrophysics Data System (ADS)

    Tranter, M.

    2003-12-01

    It seems counterintuitive that chemical erosion in glaciated regions proceeds at rates comparable to those of temperate catchments with comparable specific runoff (Anderson et al., 1997). All the usual factors that are associated with elevated rates of chemical weathering ( Drever, 1988, 1994), such as water, soil, and vegetation, are either entirely absent or absent for much of the year. For example, glaciated regions are largely frozen for significant periods each year, the residence time of liquid water in the catchment is low ( Knight, 1999), there are thin, skeletal soils at best, and vegetation is either absent or limited ( French, 1997). Other chapters in this volume have highlighted how these factors are important in other, more temperate and tropical environments. Even so, chemical erosion rates in glaciated terrain are usually near to or greater than the continental average ( Sharp et al., 1995; Wadham et al., 1997; Hodson et al., 2000). This is because glaciated catchments usually have high specific runoff, there are high concentrations of freshly comminuted rock flour, which is typically silt sized and coated with microparticles, and adsorbed organic matter or surface precipitates that may hinder water-rock interactions are largely absent ( Tranter, 1982). In short, the rapid flow of water over fine-grained, recently crushed, reactive mineral surfaces maximizes both the potential rates of chemical weathering and chemical erosion.A range of both lab- and field-based studies of glacial chemical weathering have been undertaken, mainly on the smaller glaciers of Continental Europe (e.g., Brown et al., 1993a, b), Svalbard (e.g., Hodson et al., 2002), and North America (e.g., Anderson et al., 2000). The field-based studies typically generate hydrographs of glacier runoff, which show a characteristic diurnal cycle during summer in low latitudes ( Figure 1), and more subdued diurnal cycles at high latitudes (Figure 2 and Figure 3). The concentration of ions in

  14. 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.

  15. Changes in the weathering of rock surfaces in different geomorphological environments: glacial, nival and coastal.

    NASA Astrophysics Data System (ADS)

    Feal-Pérez, A.; Blanco-Chao, R.; Pérez-Alberti, A.; López-Bedoya, J.; Valcárcel-Díaz, M.

    2009-04-01

    The sclerometer or Schmidt Rock Test Hammer has been broadly applied in geomorphology to estimate the strength of different rock types and to measure the degree of rock weathering. It has been proved that for a rock type, the rebound values are lower in weathered than in fresh rock surfaces. This evidence suggests that if there is any factor that causes a gradual change in the weathering degree, it must be possible to identify a distinctive tendency with the sclerometer. There are two types of factors that can cause gradual changes in the weathering degree. First, those related with the time of exposure of a rock surface, which are the basis of works that attempt to use the sclerometer as a tool for relative chronology. Second, those related with the frequency or duration at which the weathering agents operate, which are the basis for the studies focused on the efficacy of weathering. In both cases it is essential to understand how the factors of weathering are spatially distributed in order to achieve a good sampling procedure. We applied the sclerometer in three different environments: rock coasts, glacially exposed surfaces and rock surfaces subjected to nival processes. The sclerometer was used in a receding glacier in Tierra de Fuego, Argentina, assuming that the rock surface must be more weathered as more time passed since the exposure. The hypothesis was confirmed by the negative correlation between rebound values and the distance to the glaciar front. In rocky coasts, it was proved by field and laboratory data that one of the main factors responsible for variations in rock strength is the degree of weathering by tidally-induced wetting and drying. We found negative correlations between rebound values and tidal elevation in very different coastal environments in the NW of Spain and in the Beagle Channel. We also found that the absence of this relationship may be caused by processes of mechanical erosion, but they also can respond to disequilibrium of the

  16. Obliquity pacing of the late Pleistocene glacial terminations.

    PubMed

    Huybers, Peter; Wunsch, Carl

    2005-03-24

    The 100,000-year timescale in the glacial/interglacial cycles of the late Pleistocene epoch (the past approximately 700,000 years) is commonly attributed to control by variations in the Earth's orbit. This hypothesis has inspired models that depend on the Earth's obliquity (approximately 40,000 yr; approximately 40 kyr), orbital eccentricity (approximately 100 kyr) and precessional (approximately 20 kyr) fluctuations, with the emphasis usually on eccentricity and precessional forcing. According to a contrasting hypothesis, the glacial cycles arise primarily because of random internal climate variability. Taking these two perspectives together, there are currently more than thirty different models of the seven late-Pleistocene glacial cycles. Here we present a statistical test of the orbital forcing hypothesis, focusing on the rapid deglaciation events known as terminations. According to our analysis, the null hypothesis that glacial terminations are independent of obliquity can be rejected at the 5% significance level, whereas the corresponding null hypotheses for eccentricity and precession cannot be rejected. The simplest inference consistent with the test results is that the ice sheets terminated every second or third obliquity cycle at times of high obliquity, similar to the original proposal by Milankovitch. We also present simple stochastic and deterministic models that describe the timing of the late-Pleistocene glacial terminations purely in terms of obliquity forcing.

  17. Glacial ocean circulation and stratification explained by reduced atmospheric temperature.

    PubMed

    Jansen, Malte F

    2017-01-03

    Earth's climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.

  18. Glacial ocean circulation and stratification explained by reduced atmospheric temperature

    NASA Astrophysics Data System (ADS)

    Jansen, Malte F.

    2017-01-01

    Earth’s climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5–10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.

  19. Reconciling Glacial Snow Lines With Tropical Sea Surface Temperatures

    NASA Astrophysics Data System (ADS)

    Lorenz, S. J.; Lohmann, G.

    Reconstructions of tropical snow lines during the last glacial maximum (LGM) 21,000 years ago are incompatible with the sea surface temperature (SST) reconstructions of the CLIMAP project, when assuming present day atmospheric lapse rates (e.g. Pe- teet and Rind 1985). Since proxy data for the vertical structure of the atmosphere during glacial times do not exist, numerical experiments with an atmospheric gen- eral circulation model for glacial and interglacial climates have been performed. Our model experiments reveal that slightly cooler tropical SSTs relative to the ones by CLIMAP (1981) are sufficient to simulate proper glacial freezing temperature levels. The depression of tropical snow lines in our LGM experiment can be attributed to two effects: Less moisture content provides an increased environmental lapse rate in the free atmosphere. This effect is strongest in the tropical middle troposphere where we observe an additional two degrees cooling. Secondly, the surface temperature near tropical glaciers is further cooled by a longer duration of snow cover. Our model result provides a consistent view of the last glacial maximum climate with much colder tem- peratures than today in the tropical mountains in concordance with moderate lowering of tropical SSTs.

  20. Somma-Vesuvius ground deformation over the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Marturano, Aldo; Aiello, Giuseppe; Barra, Diana

    2013-04-01

    Vertical ground movements at Somma-Vesuvius during the last glacial cycle have been inferred from micropalaeontological and petrochemical analyses of rock samples from boreholes drilled at the archaeological sites of Herculaneum and Pompeii as well as on the apron of the volcano and the adjacent Sebeto and Sarno Valleys. Opposing movements occurred during the periods preceding and following the Last Glacial Maximum (LGM). The uplift began 20 ka ago with marine deposits rising several tens of metres up to 25 m a.s.l., recovering previous subsidence which occurred during the Late glacial period, suggesting a strict connection between volcano-tectonic and glacial cycles. Here we present the analysis of deposits predating the LGM, which confirms subsidence of the Campanian Plain where Mt. Somma-Vesuvius is located, shows variable surface loading effects and highlights the volcano-tectonic stages experienced by the volcano. The self-balancing mechanism of the volcanic system, evolving towards an explosive, subaerial activity 60 ka ago, is testified to by a large ground oscillation in phase with sea level change during the last glacial cycle.

  1. Evaluating Object-Based Image Analysis on Glacial Micromorphology

    NASA Astrophysics Data System (ADS)

    Chin, K. S.; Sjogren, D. B.

    2007-12-01

    Micromorphology has recently been applied more in analyzing glacial sediments at a microscopic level. It provides additional information and details that may help to explain glacial processes in areas where macro- scale observations cannot yield sufficient information. However, the process of interpreting thin sections has been very subjective, and reaching general consensus about glacial processes is difficult. Remote sensing technology is increasingly helpful in the development and advancement of many sciences; the concepts that lie behind the technology in object cognition used in other fields, such as landscape ecology, can be applied to micromorphology. Similar to what has been done to landscape ecology in the past, automating the process of interpreting objects in glacial sediments may potentially simplify and decrease the subjectivity of the process. Definiens Professional 5 is an object-based image analysis program that imitates human cognitive methods; it is used in this study to identify objects apart from background matrices in multiple thin section images of glacial sediments. The program's initial results proved that more work was needed to be done for better results, but overall the software produced promising results. The method is repeatable and continues to generate consistent results with no bias or ambiguity, so the application of this method to micromorphology and other areas alike will be valuable.

  2. Early Diagnosis of Congenital Trypanosoma cruzi Infection, Using Shed Acute Phase Antigen, in Ushuaia, Tierra del Fuego, Argentina

    PubMed Central

    Mallimaci, María Cristina; Sosa-Estani, Sergio; Russomando, Graciela; Sanchez, Zunilda; Sijvarger, Carina; Alvarez, Isabel Marcela; Barrionuevo, Lola; Lopez, Carlos; Segura, Elsa Leonor

    2010-01-01

    Chagas' disease, or American trypanosomiasis, is caused by the protozoan parasite Trypanasoma cruzi. It is estimated that 15,000 new cases of congenital T. cruzi transmission occur in the Americas each year. The aim of this study was to estimate the rate of congenital T. cruzi infection in infants born to infected women living in Ushuaia, Argentina, as well to assess a serologic test using Shed Acute Phase Antigen (SAPA) for a timely diagnosis of congenital infection. The rate of congenital infection among children in the study was 4.4% (3/68). Our results show that for infants younger than 30 days of age, matched blood samples from mother and infant were capable of identifying congenital transmission of infection using an enzyme-linked immunosorbent assay with SAPA. For infants older than 3 months, congenital infection could be ruled out using the same procedure. PMID:20064996

  3. The southernmost Andean Mountain soils: a toposequence from Nothofagus Forest to Sub Antarctic Tundra at Ushuaia, Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Firme Sá, Mariana M.; Schaefer, Carlos E.; Loureiro, Diego C.; Simas, Felipe N.; Francelino, Marcio R.; Senra, Eduardo O.

    2015-04-01

    Located at the southern tip of the Fuegian Andes Cordilhera, the Martial glacier witnessed a rapid process of retreat in the last century. Up to now little is known about the development and genesis of soils of this region. A toposequence of six soils, ranging from 430-925 m a.s.l, was investigated, with emphasis on genesis, chemical and mineralogical properties. The highest, youngest soil is located just below the Martial Glacier Martial Sur sector, and the lowest soils occur on sloping moraines under Nothofagus pumilio forests. Based on chemical, physical and mineralogical characteristics, the soils were classified according to the Soil taxonomy, being keyed out as Inceptisols and Entisols. Soil parent material of the soil is basically moraines, in which the predominant lithic components dominated by metamorphic rocks, with allochthonous contributions of wind-blown materials (very small fragments of volcanic glass) observed by hand lens in all horizons, except the highest profile under Tundra. In Nothofagus Deciduous Forests at the lowest part of the toposequence, poorly developed Inceptisols occur with Folistic horizons, with mixed "andic" and "spodic" characters, but with a predominance of andosolization (Andic Drystrocryepts). Under Tundra vegetation, Inceptisols are formed under hydromorphism and andosolization processes (Oxiaquic Dystrocrepts and Typic Dystrocrepts). On highland periglacial environments, soils without B horizon with strong evidence of cryoturbation and cryogenesis occur, without present-day permafrost down to 2 meters (Typic Cryorthents and Lithic Haploturbels). The mountain soils of Martial glacier generalize young, stony and rich in organic matter, with the exception of barely vegetated Tundra soils at higher altitudes. The forest soils are more acidic and have higher Al3+activity. All soils are dystrophic, except for the highest profile of the local periglacial environment. The organic carbon amounts are higher in forest soils and decrease with altitude. Clay content is low and varies little along the topossequence, indicating an overall low chemical weathering. The clay mineralogy indicates predominance of primary minerals and high proportion of low crystalline Fe and Al minerals, bound to organic matter.

  4. Polynuclear aromatic and chlorinated hydrocarbons in mussels from the coastal zone of Ushuaia, Tierra del Fuego, Argentina.

    PubMed

    Amin, Oscar A; Comoglio, Laura I; Sericano, José L

    2011-03-01

    Mussels (Mytilus edulis chilensis) were collected from 12 coastal locations in Ushuaia Bay, Argentina, and the surrounding area in October 1999 and again in October 2003. Concentrations of polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and selected chlorinated pesticides were determined to assess the impact of a fast-growing population in the area. Total PAH concentrations ranged from 2.24 to an extremely high concentration of 2,420 µg/g lipid measured in mussels collected near an oil jetty used to discharge to shore storage tanks. The composition of PAHs in these samples indicates that the source of these compounds inside Ushuaia Bay is predominantly petrogenic, with some pyrogenic background, whereas mostly pyrogenic-related PAHs were evident in areas outside the bay. Total concentrations of PCBs ranged between 12.8 and 8,210 ng/g lipid, with the highest concentration, detected inside Ushuaia harbor, representing a 10-fold increase when compared with historical data. Chlorinated pesticides were detected at comparatively lower concentrations, with 4-4'- 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene being the most common. The aggressive increase in population and related activities observed in the city of Ushuaia over the last two decades might have affected the environmental quality of the local bay. Moreover, the oceanographic and atmospheric conditions existing in Ushuaia Bay and surrounding areas may favor the accumulation and long-term presence of these organic pollutants in all compartments of this fragile environment.

  5. Sources and distribution of aliphatic and polyaromatic hydrocarbons in coastal sediments from the Ushuaia Bay (Tierra del Fuego, Patagonia, Argentina).

    PubMed

    Commendatore, Marta G; Nievas, Marina L; Amin, Oscar; Esteves, José L

    2012-03-01

    The environmental quality of Ushuaia Bay, located at the southernmost tip of South America, is affected by the anthropogenic pressure of Ushuaia city. In this study, levels and sources of hydrocarbons in coastal sediments were assessed. Aliphatic hydrocarbon fractions ranged between 5.5 and 1185.3 μg/g dry weight and PAHs from not detected to 360 ng/g. Aliphatic diagnostic indices, the nalkanes homologous series occurrence, Aliphatic Unresolved Complex Mixtures (AliUCMs), and pristane and phytane isoprenoids indicated a petrogenic input. Some sites showed biogenic features masked by the anthropogenic signature. Particularly in port areas biodegradation processes were evident. PAH ratios showed a mixture of petrogenic and pyrogenic sources. Aliphatic and aromatic UCMs were strongly correlated, reflecting chronic pollution. Three areas were distinguished inside the bay: (1) east, with low hydrocarbons impact; (2) central, where hydrocarbons accumulation was related to source proximity and sediment characteristics; (3) south-west, where sediment characteristics and current circulation favour hydrocarbons accumulation.

  6. Early diagnosis of congenital Trypanosoma cruzi infection, using shed acute phase antigen, in Ushuaia, Tierra del Fuego, Argentina.

    PubMed

    Mallimaci, María Cristina; Sosa-Estani, Sergio; Russomando, Graciela; Sanchez, Zunilda; Sijvarger, Carina; Alvarez, Isabel Marcela; Barrionuevo, Lola; Lopez, Carlos; Segura, Elsa Leonor

    2010-01-01

    Chagas' disease, or American trypanosomiasis, is caused by the protozoan parasite Trypanasoma cruzi. It is estimated that 15,000 new cases of congenital T. cruzi transmission occur in the Americas each year. The aim of this study was to estimate the rate of congenital T. cruzi infection in infants born to infected women living in Ushuaia, Argentina, as well to assess a serologic test using Shed Acute Phase Antigen (SAPA) for a timely diagnosis of congenital infection. The rate of congenital infection among children in the study was 4.4% (3/68). Our results show that for infants younger than 30 days of age, matched blood samples from mother and infant were capable of identifying congenital transmission of infection using an enzyme-linked immunosorbent assay with SAPA. For infants older than 3 months, congenital infection could be ruled out using the same procedure.

  7. 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.

  8. 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.

  9. 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

  10. GLOF, Glacial Lake Mapping an ESA DUE Innovator 2 Project

    NASA Astrophysics Data System (ADS)

    Wiesmann, Andreas; Strozzi, Tazio; Kaab, Andreas

    2010-12-01

    Glacier lake outbursts have repeatedly been the cause of major fatal events and damage in, for instance, the Himalayas, Central Asia, Andes, Caucasus, and the European Alps. The related hazards may even currently increase due to climate change as glaciers worldwide retreat and leave under certain circumstances glacier lakes behind. As a particularly far-reaching glacier- related hazard, glacier lake outburst floods may have devastating impact on populated areas that are located far downstream of the source area. Glacial lakes are often located in inaccessible areas, or can only be accessed with a substantial effort and cost to investigate their condition. While e.g. in Switzerland a network is setup to monitor glacier changes and help prevent glacial hazards, large and inaccessible areas e.g. in the Pamir and Himalayan mountains cannot be easily monitored from ground and air. Spaceborne remote sensing data are therefore a valuable and important information source to collect information on glacial lakes in these areas.

  11. Deglaciation and post-glacial environmental evolution in the Western Massif of Picos de Europa

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesús; Oliva, Marc; García, Cristina; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

    2014-05-01

    This study examines the process of deglaciation of the Western Massif of Picos de Europa through field work, geomorphological mapping, sedimentary records and absolute datings of 14C. This massif has several peaks over 2,400 m a.s.l. (Peña Santa de Castilla, 2,596 m; Torre Santa María, 2,486 m; Torre del Mediu, 2,467 m). It is composed mainly by Carboniferous limestones. This area has been intensively affected by karstic dissolution, Quaternary glaciers and fluvio-torrential processes (Miotke, 1968; Moreno et al, 2010; Ruiz-Fernández et al, 2009; Ruiz-Fernández, 2013). At present day, periglacial processes are active at the highest elevations (Ruiz-Fernández, 2013). We have identified four main glacial stages regarding the deglaciation of the massif: (i) maximum advance corresponding to the Last Glaciation, (ii) retreat and stabilization after the maximum advance, (iii) Late Glacial, and (iv) Little Ice Age. Sedimentological studies also contribute data to the understanding of the chronological framework of these environmental changes. The datings of the bottom sediments in two long sequences (8 and 5.4 m) provided a minimum age of 18,075 ± 425 cal BP for the maximum advance stage and 11,150 ± 900 cal BP for retreat and stabilization in the phase following the maximum advance. The ongoing analyses of these sequences at very high resolution will provide new knowledge about the environmental conditions prevailing since the deglaciation of the massif. References Miotke, F.D. (1968). Karstmorphologische studien in der glazial-überformten Höhenstufe der Picos de Europa, Nordspanien. Hannover, Selbtverlag der Geografischen Gessellschaft, 161 pp. Moreno, A., Valero, B.L., Jiménez, M., Domínguez, M.J., Mata, M.P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J.P. & Rico, M. (2010). The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Ruiz

  12. 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.

  13. Productivity of the glacial ocean: Discussion of the iron hypothesis

    SciTech Connect

    Berger, W.H. ); Wefer, G. )

    1991-12-01

    An increase in the productivity of the glacial-age Southern Ocean has been postulated to explain the decrease in pCO{sub 2} of the atmosphere observed in ice cores. A plausible mechanism has been proposed elsewhere that productivity is limited by the availability of Fe in this region and that the greater supply of eolian dust during glacial time removed this limit. Recently published evidence from cores from the Southern Ocean suggests that in fact there was no change in productivity in the assumed manner. Glacial-age productivity was indeed greatly increased in the equatorial Pacific and in the eastern boundary upwelling systems. The cause, presumably, was the mechanical action of glacial-age winds rather than a greater supply of Fe. However, a role of increased supply of micronutrients from the continents in the increase of equatorial productivity during glacial time cannot be excluded. Such enhancement from increased supply of dust would have the interesting corollary of more efficient export transfer to depth, possibly contributing to nutrient depletion in glacial-age, deep intermediate waters. There is some indication, as well, of a general decrease in nutrient content in the tropical thermocline in the western Pacific during the last several million years, a depletion that may have been fostered by increasing supply of dust from emerging Asian highlands. Alternative explanations are available. The case for Fe as a major modifier of productivity and biogenic sedimentation on geological time scales cannot be made in the absence of criteria diagnostic for Fe supply as opposed to stirring and upwelling.

  14. Geometric dependency of Tibetan lakes on glacial runoff

    NASA Astrophysics Data System (ADS)

    Phan, V. H.; Lindenbergh, R. C.; Menenti, M.

    2013-10-01

    The Tibetan Plateau is an essential source of water for Southeast Asia. The runoff from its ~34 000 glaciers, which occupy an area of ~50 000 km2, feeds Tibetan lakes and major Asian rivers like the Indus and Brahmaputra. Reported glacial shrinkage likely has an impact on the runoff. Unfortunately, accurate quantification of glacial changes is difficult over the high-relief Tibetan Plateau. However, it has recently been shown that it is possible to directly assess water level changes of a significant number of the ~900 Tibetan lakes with an area over 1 km2. This paper exploits different remote sensing products to create drainage links between Tibetan glaciers, lakes and rivers. The results allow us to differentiate between lakes with and without outlet. In addition, we introduce the notion of geometric dependency of a lake on glacial runoff, defined as the ratio between the total area of glaciers draining into a lake and the total area of the lake catchment. We determined these dependencies for all ~900 sufficiently large Tibetan lakes. To do so, we combined three remote sensing products: the CAREERI glacier mask product, a lake mask product based on the MODIS MOD44W water product and the HydroSHEDS river network product derived from Shuttle Radar Topography Mission (SRTM) elevation data. Using a drainage network analysis, we determined all drainage links between glaciers and lakes. The results show that 25.3% of the total glacier area directly drains into one of 244 Tibetan lakes. The results also give the geometric dependency of each lake on glacial runoff. For example, there are ten lakes with direct glacial runoff from at least 240 km2 of glacier. Three case studies, including one of the well-studied Nam Tso Lake, demonstrate how the geometric dependency of a lake on glacial runoff can be directly linked to hydrological processes.

  15. Geometric dependency of Tibetan lakes on glacial runoff

    NASA Astrophysics Data System (ADS)

    Phan, V. H.; Lindenbergh, R. C.; Menenti, M.

    2013-01-01

    The Tibetan plateau is an essential source of water for South-East Asia. The run-off from its ~ 34 000 glaciers, which occupy an area of ~ 50 000 km2, feed Tibetan lakes and major Asian rivers like Indus and Brahmaputra. Reported glacial shrinkage likely has its impact on the run-off. Unfortunately, accurate quantification of glacial changes is difficult over the high relief Tibetan plateau. However, it has been recently shown that it is possible to directly assess water level changes of a significant part of the ~ 900 Tibetan lakes greater than one square kilometer. This paper exploits different remote sensing products to explicitly create links between Tibetan glaciers, lakes and rivers. The results allow us first to differentiate between lakes with and without outlet. In addition, we introduce the notion of geometric dependency of a lake on glacial runoff, defined as the ratio between the total area of glaciers draining into a lake and the area of the catchment of the lake. These dependencies are determined for all ~ 900 Tibetan lakes. To obtain these results, we combine the so-called CAREERI glacier mask, a lake mask based on the MODIS MOD44W water product and the HydroSHEDS river network product derived from SRTM elevation data. Based on a drainage network analysis, all drainage links between glaciers and lakes are determined. The results show that 25.3% of the total glacier area directly drains into one of 244 Tibetan lakes. The results also give the geometric dependency of each lake on glacial runoff. For example, there are 10~lakes with direct glacial runoff from at least 240 km2 of glacier. Three case studies, including one over the well-studied Nam Tso, demonstrate how the geometric dependency of a lake on glacial runoff can be directly linked to hydrological processes.

  16. Noble Gas Signatures in Greenland - Tracing Glacial Meltwater Sources

    NASA Astrophysics Data System (ADS)

    Niu, Y.; Castro, M. C.; Hall, C. M.; Aciego, S.; Stevenson, E. I.; Arendt, C. A.

    2014-12-01

    This study is meant to explore the information noble gases can provide in glacial environments with respect to glacial meltwater sources, relative source contributions, water residence times, and spatial location where this glacial meltwater originates in the ice sheet. Ultimately, we seek to improve our understanding on the dynamics of these massive ice sheets, critical for the major role they play on climate change. This is possible due to the conservative nature of noble gases and temperature dependency of their concentrations in water in equilibrium with the atmosphere (ASW) allowing for calculation of noble gas temperatures (NGTs) and, under certain assumptions, estimation of the altitude at which glacial meltwater originated. In addition, crustally produced isotopes such as He accumulate in water over time, allowing for estimation of water residence times. Glacial meltwater samples were collected and analyzed for noble gas concentrations and isotopic ratios at five different locations in southern Greenland, between sea level and 1221 m. All samples are enriched in He with respect to ASW and are depleted in all other noble gases. Two patterns are apparent. The first one presents a relative Ar enrichment with respect to Ne, Kr, and Xe, a pattern first observed in high-altitude springs in the Galápagos Islands. The second one displays a mass-dependent pattern, a pattern first observed in Michigan rainwater samples. Most samples point to equilibration temperatures at ~0°C and altitudes between 1000 m and 2000 m, values which are consistent with both temperatures and elevations in Greenland. He concentrations vary between 1.1 and 7 times that of ASW and suggest glacial meltwater ages between ~170 and 1150 yrs, a result which is consistent with a preliminary tritium analysis. He isotopes point to surface (precipitation as snow and rainfall) contributions for most samples between ~60% and 90% with a ~10% - 40% crustal contribution from groundwater.

  17. 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

  18. The role of ocean-atmosphere reorganizations in glacial cycles

    NASA Astrophysics Data System (ADS)

    Broecker, Wallace S.; Denton, George H.

    A case is made that glacial-to-interglacial transitions involve major reorganizations of the ocean-atmosphere system. Such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere. Only in this way can the rapidity of glacial terminations, the hemispheric synchroneity and symmetry of mountain glaciation, and the large polar air temperature and dustiness variations be accounted for. If these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes, then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean's salinity distribution.

  19. The role of ocean-atmosphere reorganizations is glacial cycles

    NASA Astrophysics Data System (ADS)

    Broecker, Wallace S.; Denton, George H.

    1989-10-01

    A case is made that glacial-to-interglacial transitions involve major reorganizations of the ocean-atmosphere system. Such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere. Only in this way can the rapidity of glacial terminations, the hemispheric synchroneity and symmetry of mountain glaciation, and the large polar air temperature and dustiness variations be accounted for. If these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes, then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean's salinity distribution.

  20. The last glacial-Holocene transition in southern Chile.

    PubMed

    Bennett, K D; Haberle, S G; Lumley, S H

    2000-10-13

    Warming at the last glacial termination in the North Atlantic region was interrupted by a period of renewed glacial activity during the Younger Dryas chronozone (YDC). The underlying mechanism of this cooling remains elusive, but hypotheses turn on whether it was a global or a North Atlantic phenomenon. Chronological, sedimentological, and palaeoecological records from sediments of small lakes in oceanic southern Chile demonstrate that there was no YDC cooling in southern Chile. It is therefore likely that there was little or no cooling in southern Pacific surface waters and hence that YDC cooling in the North Atlantic was a regional, rather than global, phenomenon.

  1. Last Glacial - Present Glacial Activity in East Greenland Fjords Inferred from Swath Bathymetry and High-Resolution Seismic Data

    NASA Astrophysics Data System (ADS)

    Forwick, M.; Laberg, J. S.; Husum, K.; Olsen, I. L.

    2014-12-01

    Swath bathymetry and high-resolution penetration echo sounder (chirp) data from fjords and sounds between Kong Oscars Fjord and Bredefjord, East Greenland, reveal glacial landforms and sedimentary processes that can be used to infer glacial activity from the last glacial to the present. Relatively straight, linear features oriented parallel to the fjord axes, as well as beyond the mouths of some fjords, are interpreted to be glacial lineations providing evidence of fast-flowing grounded ice draining the eastern parts of the Greenland Ice Sheet during the last glacial. In some areas, the glacial lineations are the only preserved glacigenic landfjorms (e.g. beyond the mouth of Bredefjord). However, in other areas, they are covered with multiple transverse ridges interpreted to be small terminal moraines (e.g. in Youngsund). Whereas the absence of such moraines is suggested to represent a rapid ice retreat due to lift-up and disintegration during parts of the deglaciation, their presence reflects that multiple halts and/or re-advances interrupted the retreat. Acoustically stratified sediment sequences dominate the fjord-fill stratigraphies (up to 180 ms two-way travel time). These deposits are suggested to reflect repeatedly changing lithological compositions in a glacimarine environment where deposition mainly occurred from suspension fall-out, in addition to ice rafting from icebergs calving off from tidewater glaciers, and sea ice. The stratified deposits form often relatively uniform drapes indicating that the tidewater glaciers were mainly located near the fjord heads since the last deglaciation. However, acoustically transparent bodies with irregular geometries, intercalated within the stratified deposits, occur in some of the inner fjords. These are suggested to be glacigenic sediment wedges (debris-flow lobes) that formed during relatively recent advances of tidewater glaciers (e.g. in Nordfjord and Moskusoksefjord).

  2. 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.

  3. 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

  4. 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

  5. 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...

  6. 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.

  7. Glacial melting: an overlooked threat to Antarctic krill

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  8. 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...

  9. 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

  10. Volcanic fire and glacial ice: Mount Rogers National Recreation Area

    USGS Publications Warehouse

    ,; ,

    2007-01-01

    In addition to containing the highest point in Virginia (Mount Rogers, elevation 5,729 feet), the Mount Rogers National Recreation Area (NRA) of the Jefferson National Forest is a window on the history of ancient volcanic eruptions and glacial movement.

  11. 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

  12. 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.

  13. 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.

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

    PubMed

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

    2015-06-26

    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.

  15. 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.

  16. 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

  17. Large spatial variations in glacial erosion detected with detrital thermochronology

    NASA Astrophysics Data System (ADS)

    Ehlers, T. A.; Stock, G. M.; Farley, K. A.; Densmore, M. S.; Rushlow, C.

    2008-12-01

    Studies of drainage basin erosion and landform evolution are often limited by not knowing where sediment is sourced from and how climate change influences catchment erosion. Detrital thermochronometer cooling ages collected from Quaternary glacial moraines and modern river sediments provide a promising tool to address these problems. We present an application of detrital thermochronology to quantify spatial variations in alpine glacial erosion during the Last Glacial Maximum (LGM). Results are compared to the distribution of recent erosion recorded in samples from modern river sediments. The elevation dependence of detrital apatite (U-Th)/He (AHe) ages is used as a sediment tracer to track the elevations where glacially eroded sediment is produced from bedrock. We measured ~204 AHe single grain ages from three moraines located between 2.3 and 3.7 km elevation in the Lone Pine catchment, Sierra Nevada, California. Ages from the lowest elevation moraine were measured on fine (<250 um) and coarse (>250 um) grained fractions of the sample to assess potential variations in sediment supply from different erosional processes. Measured AHe age probability density functions (PDFs) were compared with predicted PDFs, calculated by convolving bedrock age-elevation relationships with catchment hypsometries clipped at different elevations to reflect variable source elevations of sediment. Statistical comparison of the PDFs using a Monte Carlo approach and Kuiper test are used to evaluate the spatial distribution of erosion in the catchments. Results from the lowest elevation moraine indicate sediment is produced from the lower ~50-70% of catchment elevations at the 95% confidence level, indicating erosion near the base and sides of the glacier proportionally outweigh erosion from higher elevation head wall retreat and rock fall onto the glacier. Furthermore, grain-age distributions from the fine and coarse grain fractions are virtually indistinguishable, suggesting either both

  18. 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.

  19. 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.

  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. A first 10Be cosmogenic glacial chronology from the High Atlas, Morocco, during the last glacial cycle.

    NASA Astrophysics Data System (ADS)

    Fink, David; Hughes, Philip; Fenton, Cassie

    2014-05-01

    Glacial geomorphological mapping, 10Be cosmogenic exposure ages of 21 erratics from cirque-valley systems and paleo-glacier climate modelling in the High Atlas Mountains, Morocco (31.1° N, 7.9° W), provides new and novel insights as to the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence of extensive and multiple Late Pleistocene glaciations whose extent is significantly larger than that recognised by previous workers. The largest glaciers formed in the Toubkal massif where we find 3 distinct phases of glacial advances within the last glacial cycle. The oldest moraines occurring at the lowest elevations have yielded eight 10Be ages ranging from 30 to 88 ka. Six of eight samples from moraines at intermediate elevations gave ages of 19 to 25 ka (2 outliers) which correlates well with the global Last Glacial Maximum (ca. 26-21 ka) and the last termination during marine isotope stage 2. Five erratics from the youngest and most elevated moraines yielded a suite of normally distributed exposure ages from 11 to 13 ka which supports a correlation with the northern hemisphere Younger Dryas (12.9-11.7 ka). The glacial record of the High Atlas effectively reflects moisture supply to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The plaeo equilibrium line altitudes (ELA) of these three glacier phases was more than 1000 m lower than the predicted ELA based on today's temperatures. Glacier-climate modelling indicates that for each of these glacier phases climate was not only significantly cooler than today, but also much wetter. The new evidence on the extent, timing and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages.

  3. 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.

  4. Radiocarbon chronology of the late-glacial Puerto Bandera moraines, Southern Patagonian Icefield, Argentina

    NASA Astrophysics Data System (ADS)

    Strelin, J. A.; Denton, G. H.; Vandergoes, M. J.; Ninnemann, U. S.; Putnam, A. E.

    2011-09-01

    We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages ( n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 14C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 14C yrs BP to 13,450 ± 150 14C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance. Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 14C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 14C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 14C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 14C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini

  5. Simulation and understanding the nature of Quaternary glacial cycles

    NASA Astrophysics Data System (ADS)

    Ganopolski, A.; Calov, R.

    2012-04-01

    Although it is generally accepted that, as postulated by the Milankovitch theory, Earth's orbital variations play an important role in Quaternary climate dynamics, the mechanism of glacial cycles still remains poorly understood. Among remaining scientific challenges are an understanding of the nature of 100 kyr cycles that dominated global ice volume and climate variability over the late part of Quaternary and the causes of the transition from the "40 kyr world" to the "100 kyr world" around one million years ago. Using the Earth system model of intermediate complexity CLIMBER-2, we demonstrate that both strong 100 kyr periodicity in the ice volume variations and the timing of glacial terminations during past 800 kyr can be successfully simulated as direct, strong nonlinear responses of the climate-cryosphere system to orbital forcing alone. We show that the sharp 100 kyr peak in the power spectrum of ice volume results from the phase locking of the long glacial cycles to the corresponding eccentricity cycles. Variations in obliquity and CO2 concentration are not required to simulate strong 100 kyr cyclicity if the atmospheric CO2 concentration stays below its typical interglacial value. The existence of long glacial cycles is primarily attributed to the North American ice sheet and it requires the presence of a large continental area with exposed rocks. In case when the continents are completely covered by a thick sediment layer, for the realistic range of CO2 concentrations (180-300 ppm), the long glacial cycles can not be simulated. In the experiment with fixed CO2 concentration, ice volume variations contain both strong precessional and obliquity cycles, which apparently is in odd with empirical data that suggest complete dominance of the obliquity cycle. However, in the experiments with interactive carbon cycle, simulated obliquity component becomes much stronger, especially, in the deep ocean temperature. This is explained by the direct and indirect (via the

  6. 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

  7. 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

  8. 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.

  9. 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

  10. Representations of Mexican American Migrant Childhood in Rivera's "...y no se lo trago la tierra" and Viramontes's "Under the Feet of Jesus"

    ERIC Educational Resources Information Center

    Beck, Scott A.; Rangel, Dolores E.

    2009-01-01

    This article gives an analysis of two books: Thomas Rivera's "...y no se lo trago la tierra" and Helena Maria Viramontes's "Under the Feet of Jesus". The two books are strong and important literary texts that stand in close relation to each other. Both texts treat the subject of migrant childhood by affirming central themes of Chicano literature.…

  11. 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

  12. 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.

  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.

  14. Hemispheric sea ice distribution sets the glacial tempo

    NASA Astrophysics Data System (ADS)

    Lee, Jung-Eun; Shen, Aaron; Fox-Kemper, Baylor; Ming, Yi

    2017-01-01

    The proxy record of global temperature shows that the dominant periodicity of the glacial cycle shifts from 40 kyr (obliquity) to 100 kyr (eccentricity) about a million years ago. Using climate model simulations, here we show that the pace of the glacial cycle depends on the pattern of hemispheric sea ice growth. In a cold climate the sea ice grows asymmetrically between two hemispheres under changes to Earth's orbital precession, because sea ice growth potential outside of the Arctic Circle is limited. This difference in hemispheric sea ice growth leads to an asymmetry in absorbed solar energy for the two hemispheres, particularly when eccentricity is high, even if the annual average insolation is similar. In a warmer climate, the hemispheric asymmetry of the sea ice decreases as mean Arctic and Antarctic sea ice decreases, diminishing the precession and eccentricity signals and explaining the dominant obliquity signal (40 kyr) before the mid-Pleistocene transition.

  15. 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

  16. 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

  17. 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

  18. Requirements for extracting mantle viscosity from glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Cathles, L. M.

    2012-04-01

    Extracting mantle viscosity from glacial isostatic adjustment (GIA) data is challenging because it requires a correctly posed rheological model, an accurate description of the ice and water load redistributions that occurred over at least the last glacial cycle, and the ability to interact model predictions with a large amount of observational data. To address sealevel changes, models must be based on an appropriate rheology. Daly focused attention on this critical issue 78 years ago with his down-punching hypothesis. Observing the sympathetic uplift behavior of areas peripheral to continental glacial loads, he suggested a thick lithosphere was required to force this behavior on asthenosphere flow. At the same time Haskell pointed out that deep flow in a constant viscosity Newtonian mantle would produce the observed peripheral bulge behavior without a thick lithosphere. This debate is important today because sealevel changes are particularly impacted by deep mantle viscosity and mantle rheology. Lithosphere and asthenosphere properties are another much discussed topic. The commonly observed substantial short wavelength response requires both a thin (~40 km thick) lithosphere and an asthenosphere ~25 times more fluid than the mantle. Because the manner of local ice removal can affect rebound calculations greatly, it is critical to have accurate ice and water load redistributions. Load redistributions must include changes in the levels of large lakes. Recent studies indicate how important it is to take into account sediment redistribution over the last glacial cycle. Finally, evaluation of the calculated emergence requires the comparison to large amounts of accurate (or at least critically vetted) sea level, emergence, GPS, and other kinds of data. These issues will be discussed and illustrated with some recent calculations.

  19. 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.

  20. 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

  1. Glacial oceanographic contrasts explain phylogeography of Australian bull kelp.

    PubMed

    Fraser, Ceridwen I; Spencer, Hamish G; Waters, Jonathan M

    2009-05-01

    The evolutionary effects of Southern Hemisphere Pleistocene oceanographic conditions - marked by fluctuations in sea levels and water temperatures, and redirected currents - are poorly understood. The southeastern tip of Australia presents an intriguing model system for studying the biological impacts of palaeoceanography. In particular, contrasting oceanographic conditions that existed on eastern vs. western sides of the Bassian Isthmus during Pleistocene glacial periods allow for natural comparisons between putative refugial vs. re-invading populations. Whereas many western Tasmanian marine taxa were likely eliminated by cold subantarctic water during the last glacial period, eastern Tasmanian populations would have persisted in relatively warm temperatures mediated by the ongoing influence of the East Australian Current (EAC). Here we test for the effects of contrasting palaeoceanographic conditions on endemic bull kelp, Durvillaea potatorum, using DNA sequence analysis (COI; rbcL) of more than 100 individuals from 14 localities in southeastern Australia. Phylogenetic reconstructions reveal a deep (maximum divergence 4.7%) genetic split within D. potatorum, corresponding to the 'eastern' and 'western' geographical regions delimited by the Bassian Isthmus, a vicariant barrier during low Pleistocene sea levels. Concordant with the western region's cold glacial conditions, samples from western Tasmania and western Victoria are genetically monomorphic, suggesting postglacial expansion from a mainland refugium. Eastern samples, in contrast, comprise distinct regional haplogroups, suggesting the species persisted in eastern Tasmania throughout recent glacial periods. The deep east-west divergence seems consistent with earlier reports of morphological differences between 'western' and 'eastern' D. potatorum, and it seems likely that these forms represent reproductively isolated species.

  2. 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.

  3. 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.

  4. 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.

  5. Ocean Cooling Pattern at the Last Glacial Maximum

    DOE PAGES

    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.

  6. Comparative phylogeography of two North American 'glacial relict' crustaceans.

    PubMed

    Dooh, R T; Adamowicz, S J; Hebert, P D N

    2006-12-01

    The Pleistocene glaciations represent the most recent and dramatic series of habitat changes since the Cretaceous. The impact of these events was particularly acute for aquatic taxa with poor powers of dispersal, but few organisms have evolutionary histories more intimately entwined with the advance and retreat of ice than the 'glacial relicts'. In this study, we used a mitochondrial gene, cytochrome c oxidase subunit I (COI), to examine and compare the phylogeographical structure of two glacial relict crustaceans (Limnocalanus macrurus and members of the Mysis relicta species group) across North America. In both cases, we found a sharp phylogenetic division between populations from inland lakes formed during glacial retreat, and arctic lakes isolated from polar seas via isostatic rebound. However, the depth of this phylogenetic partition varied between taxa. In L. macrurus, nucleotide sequence divergence of 2.2% between these zones is consistent with its current status as a single morphologically variable species, but in Mysis the split occurred among recently described, morphologically conserved species, at a divergence of 8.2%. The disparity in the depth of divergence indicates a history of recurrent freshwater invasions from the arctic seas, in concordance with previous studies of Eurasian glacial relicts. However, we suggest further consideration of a largely overlooked explanation that could account for some of the discrepancies between molecular divergences and glaciation events. Many cladogenetic events could have occurred in arctic seas prior to the transition to inland waters, a possibility supported both by the complex physical and ionic history of arctic seas and by high marine and estuarine lineage diversity in the north.

  7. Floating glacial ice caps in the arctic ocean.

    PubMed

    Broecker, W S

    1975-06-13

    Two arguments are presented, one in favor of the existence of thicker ice in the Arctic Ocean during glacial time, and the other in favor of a full-fledged Arctic ice cap. The first is based on the Greenland air temperature record obtained from isotopic studies of the Camp Century ice core. The second is based on the oxygen isotope record of benthic foraminifera from a deep Pacific Ocean core.

  8. Evidence of strong ocean heating during glacial periods

    NASA Astrophysics Data System (ADS)

    Zimov, S. A.; Zimov, N.

    2013-12-01

    Numerous hypotheses have addressed glacial-interglacial climatic dynamics, but none of them explain the sharp 25C temperature increase in Greenland in the last deglaciation (Cuffey et al. 1995; Dahl-Jensen et al. 1998). These robust data were obtained through analyzing the temperature profile in the Greenland ice sheet where cold from the last glaciation is preserved in the depth of the glacial sheet. We suggest that during glaciations the ocean accumulated energy: interior ocean water heated up to ~20-30C and during deglaciation this energy is released. In the analogy with reconstructing the ice sheet temperature profiles, the most reliable proof of ocean interior warming during the last glaciation is the heat flux profiles in the bottom sediments. In the final reports based on temperature measurements conducted during the DSDP (Deep Sea Drilling Project) it is stated that heat flux in the bottom sediments doesn't vary with depth and consequently there were no substantial temperature changes in the ocean interior during the last glacial cycle, and heat flux on the surface of the ocean bottom is the geothermal heat flux (Erickson et al., 1975, Hyndman et al., 1987). However, we have critically investigated data in all initial reports of all deep sea drilling projects and have noticed that all temperature data show that heat flow decreases strongly with depth (a minimum of 40 mW/m2), i.e. most of the heat flux detected on the surface of the ocean floor is not the geothermal heat flux but remaining heat that bottom sediments release. Sharp shifts in heat flow are seen within boreholes at depths crossing gas hydrate bottom. All this means that during the last glacial period interior water temperature was on 25-30C degrees warmer. Conversely, in isolated seas heat flow in the sediments shows little change with depth.

  9. 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.

  10. An interhemispheric mechanism for glacial abrupt climate change

    NASA Astrophysics Data System (ADS)

    Banderas, Rubén; Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2015-05-01

    The last glacial period was punctuated by abrupt climate changes that are widely considered to result from millennial-scale variability of the Atlantic meridional overturning circulation (AMOC). However, the origin of these AMOC reorganizations remains poorly understood. The climatic connection between both hemispheres indicated by proxies suggests that the Southern Ocean (SO) could regulate this variability through changes in winds and atmospheric CO concentration. Here, we investigate this hypothesis using a coupled climate model forced by prescribed CO and SO wind-stress variations. We find that the AMOC exhibits an oscillatory behavior between weak and strong circulation regimes which is ultimately caused by changes in the meridional density gradient of the Atlantic Ocean. The evolution of the simulated climatic patterns matches the amplitude and timing of the largest events that occurred during the last glacial period and their widespread climatic impacts. Our results suggest the existence of an internal interhemispheric oscillation mediated by the bipolar seesaw that could promote glacial abrupt climate changes through variations in atmospheric CO levels, the strength of the SO winds and AMOC reorganizations, and provide an explanation for the pervasive Antarctic-like climate signal found in proxy records worldwide.

  11. Intra-crater glacial processes in central Utopia Planitia, Mars

    NASA Astrophysics Data System (ADS)

    Pearce, Geoffrey; Osinski, Gordon R.; Soare, Richard J.

    2011-03-01

    We describe and interpret a series of previously unidentified glacial-like lobes (34-43°N; 107-125°E) that were discovered as part of a survey of large (D > 5 km) impact craters in Utopia Planitia, one of the great northern plains of Mars. The lobes have characteristics that are consistent with a glacial origin. Evidence includes curvilinearity of form, lineations and ridges, and surface textures that are thought to form by the sublimation of near-surface volatiles. The lobes display morphologies that range from wedge-shaped to near-circular to elongate. The flow directions are towards the northern walls in the case of craters with large single lobes, and in all directions in the case of the largest (D > 30 km) craters. Concentric crater fill is also interspersed within craters of our study region, with such craters having much higher filling rates than those with flow lobes. We suggest that the impact crater population in south-west Utopia Planitia demonstrates a spectrum of glacial modifications, from low levels of filling in the case of craters with elongate lobes at one extreme, to concentric crater fill in highly-filled craters at the other.

  12. 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

  13. Massive remobilization of permafrost carbon during post-glacial warming

    NASA Astrophysics Data System (ADS)

    Tesi, T.; Muschitiello, F.; Smittenberg, R. H.; Jakobsson, M.; Vonk, J. E.; Hill, P.; Andersson, A.; Kirchner, N.; Noormets, R.; Dudarev, O.; Semiletov, I.; Gustafsson, Ö.

    2016-11-01

    Recent hypotheses, based on atmospheric records and models, suggest that permafrost carbon (PF-C) accumulated during the last glaciation may have been an important source for the atmospheric CO2 rise during post-glacial warming. However, direct physical indications for such PF-C release have so far been absent. Here we use the Laptev Sea (Arctic Ocean) as an archive to investigate PF-C destabilization during the last glacial-interglacial period. Our results show evidence for massive supply of PF-C from Siberian soils as a result of severe active layer deepening in response to the warming. Thawing of PF-C must also have brought about an enhanced organic matter respiration and, thus, these findings suggest that PF-C may indeed have been an important source of CO2 across the extensive permafrost domain. The results challenge current paradigms on the post-glacial CO2 rise and, at the same time, serve as a harbinger for possible consequences of the present-day warming of PF-C soils.

  14. Microbial genesis, life and death in glacial ice.

    PubMed

    Price, P Buford

    2009-01-01

    Arguments are given that terrestrial RNA and DNA may have originated in a frozen environment more than 4 billion years ago. Scenarios are developed for atmospheric transport of microbes onto glacial ice, their adaptation to subzero temperatures in the ice, and their incorporation into one of three habitats - liquid veins, mineral grain surfaces, or isolated inside 1 of the crystals that make up polycrystalline ice. The Arrhenius dependence of microbial metabolic rate on temperature is shown to match that required to repair damage owing to spontaneous DNA depurination and amino acid racemization. Even for the oldest glacial ice, microbial lifetime is shown not to be shortened by radiation damage from 238U, 232Th, or 40K in mineral dust in ice, by phage-induced lysis, or by penetrating cosmic radiation. Instead, death of those cells adapted to the hostile conditions in glacial ice is probably due to exhaustion of available nutrients. By contrast, in permafrost microbial death is more likely due to alpha-particle radiation damage from U and Th in the soil and rocks intermixed with ice. For residence times in ice longer than a million years, spore formers may be unable to compete in longevity with vegetative cells that are able to repair DNA damage via survival metabolism.

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

    PubMed

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

    2015-07-07

    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. How long do U-shaped valleys last? The lifespan of glacial topography set by tectonics.

    NASA Astrophysics Data System (ADS)

    Prasicek, Günther; Larsen, Isaac; Montgomery, David

    2015-04-01

    More than 10 kyr after the last major glaciation the topography of mountain ranges world-wide remains dominated by characteristic glacial landforms such as U-shaped valleys, but the transition from a glacial to a fluvial landscape is poorly constrained and it remains unclear how long glacial morphology persists following deglaciation. The longevity of glacial topography influences glacial extent and erosion in subsequent glaciations and hence the cumulative impact of Pleistocene glacial cycles on the evolution of mountain ranges. We tested whether tectonic forcing and erosional response control the timescale over which glacial topography persists into inter-glacial periods in the western Southern Alps of New Zealand and other mountain ranges worldwide, including the syntaxes of the Himalaya and Taiwan. We quantified the degree of glacial imprint by exploiting the conventional interpretation of V-shaped fluvial and U-shaped glacial valleys. Valley cross sections were automatically extracted from digital terrain models and power-laws were fitted to each cross section to quantify the shape of the valley flanks. A power-law exponent of 1 characterizes the straight valley flanks of a V-shaped cross section and greater exponents are indicative of progressively more U-shaped valleys. Our results show that tectonic forcing is a first-order control on landscape evolution and on the persistence of glacial morphology worldwide. In Earth's most rapidly uplifting mountain ranges the lifespan of glacial topography is on the order of one interglacial period, preventing the development of a cumulative glacial signal. In contrast, in most alpine landscapes more than 100 kyr are required for the transformation from glacial back to fluvial topography and glacial landforms have not or have only partially been erased during the current interglacial. Thus we suggest, emphasizing the influence of glacially preconditioned topography on glacial extent and erosion, that tectonic forcing

  17. 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

  18. 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

  19. 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.

  20. [Distribution patterns of canopy and understory tree species at local scale in a Tierra Firme forest, the Colombian Amazonia].

    PubMed

    Barreto-Silva, Juan Sebastian; López, Dairon Cárdenas; Montoya, Alvaro Javier Duque

    2014-03-01

    The effect of environmental variation on the structure of tree communities in tropical forests is still under debate. There is evidence that in landscapes like Tierra Firme forest, where the environmental gradient decreases at a local level, the effect of soil on the distribution patterns of plant species is minimal, happens to be random or is due to biological processes. In contrast, in studies with different kinds of plants from tropical forests, a greater effect on floristic composition of varying soil and topography has been reported. To assess this, the current study was carried out in a permanent plot of ten hectares in the Amacayacu National Park, Colombian Amazonia. To run the analysis, floristic and environmental variations were obtained according to tree species abundance categories and growth forms. In order to quantify the role played by both environmental filtering and dispersal limitation, the variation of the spatial configuration was included. We used Detrended Correspondence Analysis and Canonical Correspondence Analysis, followed by a variation partitioning, to analyze the species distribution patterns. The spatial template was evaluated using the Principal Coordinates of Neighbor Matrix method. We recorded 14 074 individuals from 1 053 species and 80 families. The most abundant families were Myristicaceae, Moraceae, Meliaceae, Arecaceae and Lecythidaceae, coinciding with other studies from Northwest Amazonia. Beta diversity was relatively low within the plot. Soils were very poor, had high aluminum concentration and were predominantly clayey. The floristic differences explained along the ten hectares plot were mainly associated to biological processes, such as dispersal limitation. The largest proportion of community variation in our dataset was unexplained by either environmental or spatial data. In conclusion, these results support random processes as the major drivers of the spatial variation of tree species at a local scale on Tierra Firme

  1. 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

  2. Timing the last interglacial-glacial transition in glacial sedimentary sequences of the Hudson Bay lowlands (Canada)

    NASA Astrophysics Data System (ADS)

    Roy, M.; Allard, G.; Ghaleb, B.; Lamothe, M.

    2010-12-01

    Paleoclimate records (oxygen isotopes and speleothems) indicate that the onset of the last glacial cycle was characterized by rapid and large-scale growth of continental ice sheets. The timing of the inception of the Laurentide ice sheet (LIS) and its subsequent evolution (extent) remain, however, largely unconstrained. The depositional record of the Hudson Bay Lowlands (HBL) is of particular interest to these issues because this region is located near the former geographic center of the LIS. The presence of nonglacial deposits in HBL glacial sedimentary sequences thus implies drastic changes in ice sheet configuration, but constraining these ice volume changes through absolute dating of nonglacial sediments has been so far inconclusive. Here we use radiocarbon, U-series, and optical stimulated luminescence (OSL) methods to constrain the age of an extensive nonglacial unit containing abundant wood fragments enclosed in compacted clay lying below several meters of glacial deposits along the Nottaway River, in the southeastern sector of the HBL. This region is particularly interesting because it lies near one of the inception centers of the LIS. Radiocarbon dating of a wood fragment yielded a nonfinite 14C age of >55.2 ka, in agreement with similar dating attempts throughout the HBL. Measurements of U and Th concentrations and isotope ratios on fossil wood samples revealed consistent 230Th/U ages, indicating that the wood fragments were subject to a single episode of uranium uptake, with apparently no subsequent disturbance of the geochemical system. Despite mechanical cleaning of the wood outer surfaces, non-authigenic 230Th was found in most samples and correction for this detrital contamination yielded an isochron age of 106.8 (+12.3, -10.3) ka, which represents a minimum age for this unit. The 230Th/U age constraint is nonetheless supported by a series of OSL ages obtained for the overlying fluvial sands, thereby assigning the Nottaway nonglacial unit to the end

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. Caribbean Salinity Variation During the Last Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Schmidt, M. W.; Spero, H. J.; Lea, D. W.

    2003-12-01

    Evaporation exceeds precipitation in the tropical Atlantic, resulting in a net freshwater removal across the Central American Isthmus. Because most of the north Atlantic's subtropical gyre water circulates through the Caribbean before flowing north to sub-polar regions via the Gulf Stream, changes in tropical atmospheric circulation have the potential to affect the salinity and density structure of the entire north Atlantic, thereby influencing glacial-interglacial oscillations in North Atlantic Deep Water (NADW) formation. Here, we combine Mg/Ca measurements (a proxy for the temperature of calcification) and δ 18O analyses of shells from the surface-dwelling foraminifera Globigerinoides ruber s.s. (white var.) from the western Caribbean Colombian Basin at ODP Site 999A (2827m; 4cm/ka sed. rate) and VM28-122 (3623m; 4-10cm/ka sed. rate) to produce the first continuous record of western tropical Atlantic δ 18OSEAWATER (δ 18OSW) during the last 130ka. In order to generate a record for sea surface salinity (SSS) due to regional hydrological change, we removed the δ 18OSW signal due to glacial ice volume variation and normalized the residual to the modern δ 18OSW value for the Colombian Basin (0.8‰ ). The resulting ice volume-free (Δ δ 18OIVF-SW) record shows that Caribbean Δ δ 18OIVF-SW increased by ˜0.5‰ during the Last Glacial Maximum and Marine Isotope Stage 4. Using a modern western Caribbean δ 18OSW:SSS relationship, these enriched δ 18OSW values suggest glacial Caribbean salinities were 2.3 - 2.8‰ higher than modern after removing the influence of ice-volume. Our data supports the hypothesis that the tropics might have been in a state more similar to the modern El Nino mode, characterized by a more southerly position of the ITCZ, during cold phases of the last glacial cycle. Within the resolution of our Δ δ 18OIVF-SW record from VM28-122, elevated glacial Caribbean salinity decreased to modern levels at the onset of the Bolling-Allerod (B

  9. 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.

  10. 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.

  11. 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.

  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

    1995-06-02

    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.

  13. 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.

  14. Last Glacial Maximum and deglaciation of the Iberian Central System.

    NASA Astrophysics Data System (ADS)

    Palacios, D.; Andrés, N.; Vieira, G.; Marcos, J.; Vázquez-Selem, L.

    2012-04-01

    The Central System runs E-W across the centre of the Iberian Peninsula and is composed mainly of crystalline rocks. A glacial morphology is well preserved on many of its most important summit areas especially towards the Atlantic. Research has recently been carried out in three of the sierras of this mountain system, with the aim of establishing the absolute chronology of the maximum glacial advance and of the deglaciation in the whole system. The method used is cosmogenic 36Cl surface exposure dating of moraine boulders and glacially polished outcrops. The selected areas are the Sierra de Guadarrama (Palacios et al. 2012) close to Peñalara Peak (40°51'N, 3°57'W; 2428 m), the Sierra de Gredos (Palacios et al. 2011) close to Almanzor Peak (40°14'N, 5°17'W; 2592 m), and the Sierra de la Estrela (Vieira and Palacios, 2010) close to Alto de la Torre summit (40°20'N, 7°34'W; 1993 m). These areas are representative of the whole Central System from west to east. The results are highly homogeneous. Moraines dating from earlier than the last glaciation were not found in any of the sierras. On the contrary, in all cases the oldest moraines from the last glaciation rest on intensely weathered crystalline surfaces. The oldest moraines date from between 31 and 26 ka. In most cases, the deposition of these moraine ridges was followed by minor advances and retreats which left a sequence of ridges very close together, lasting until 18-16 ka. A fast retreat occurred after 16-15 ka, when glaciers completely abandoned the valleys, disappearing in most cases by 13-14 ka. The ice lasted until 11-10 ka, but only in small cirques found on sheltered rock-walls below the highest peaks.

  15. 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.

  16. 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.

  17. Linking the Holocene glacial and oceanographic variability in northern Spitsbergen

    NASA Astrophysics Data System (ADS)

    Bartels, Martin; Hebbeln, Dierk

    2015-04-01

    The Svalbard area can be considered as a key region for Arctic heat transfer. The archipelago is located where relatively warm Atlantic Water is reaching further north than at any other Arctic location at similar latitudes. The Holocene variability of Atlantic Water advection is well documented for the western coasts of Spitsbergen whereas records from northern Svalbard are still rare. Here we present a sedimentary record from Woodfjorden in northern Spitsbergen where the influence of Atlantic Water is fading out and glaciers are responding much more sensitive to oceanographic variations than at the western coasts of Spitsbergen. We analyzed the foraminiferal fauna and the distribution of Ice Rafted Debris (IRD) to trace the interplay between the oceanographic and glacial variability, respectively. The appearance of Nonionellina labradorica, a species which is adapted to warm Atlantic Water, shows that the advection of Atlantic-derived water correlates positively with summer insolation. The amount of IRD - increasing during the Allerød interstadial - diminished subsequently with intensifying inflow of Atlantic Water. During the Mid-Holocene, the strong influence of these relative warm water masses concurs with very low IRD values, possibly reflecting the retreat of tidewater glaciers from the coast to a further inland position disconnecting glacier dynamics from the respective marine archives at that time. With declining inflow of Atlantic Water during the late Holocene sea ice expanded, indicated by increased percentages of Islandiella norcrossi. The appearance of this species shows a similar trend as reported for sea-ice biomarkers in the eastern Fram Strait. Thus, variations of Atlantic Water inflow directly affected glacial activity as well as sea-ice coverage. Combining marine and terrestrial proxies enabled us to reconstruct regional (sea-ice) as well as local (glacial expansion) changes over time.

  18. 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

  19. 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

  20. Dendroclimatic trend and glacial fluctuations in the Central Italian Alps

    NASA Astrophysics Data System (ADS)

    Pelfini, M.; Santilli, M.; D Agata, C.; Diolaiuti, G.; Smiraglia, C.

    2003-04-01

    In the Alpine environment, one of the main limiting factors for tree growth is the thermal conditions of the vegetative season. The conifers at high altitude, if not subject to others disturbs, such as geomorphological processes or biological interferences, undergo a development, from which the width of annual rings depends. Five chronologies few centuries long, obtained for the species Larix decidua Mill. and Pinus cembra L. from different valleys of the Central Italian Alps (Alpisella, Valfurva, Gavia and Solda) in proximity of timberline (2000-2550 m of altitude), were analysed and their climatic signal gained; this last one was then related to the recent glacial fluctuations. The chronologies are the averages of many dendrochronological indicized curves obtained from dominant trees with regular growth and extended from 13th-17th century up to the present. The time intervals of the chronologies are the following ones: Pinus cembra: 1752-1999 for Valfurva; 1607-1999 for Gavia; 1593-1999 for Val Solda. With regard to Larix decidua: 1252-1998 for Val Solda; 1784-2001 for Alpisella. The good correspondence between the various chronologies allows to consider them representative of the climatic regional signal. In order to evidence climatic evolution, linear trends based on running mean with period of 11 years have been constructed. Those curves have been compared between them and then overlapped and mediated in order to obtain a climatic signal of regional value that excludes eventual local anomalies. Finally, the growth variations in the chronologies have been compared to known alpine climatic variations and glacial fluctuations. In particular time-distance curves (curves of cumulated frontal variations) of some glaciers from the Ortles-Cevedale Group were utilized. The periods of tree rings growth rate reduction appear well correlated to glacial advancing phases of the Little Ice Age and of the following phases. In particular, growth rate reductions are observable

  1. 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.

  2. 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

  3. 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.

  4. 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

  5. Inverting Glacial Isostatic Adjustment beyond linear viscoelasticity using Burgers rheology

    NASA Astrophysics Data System (ADS)

    Caron, L.; Greff-Lefftz, M.; Fleitout, L.; Metivier, L.; Rouby, H.

    2014-12-01

    In Glacial Isostatic Adjustment (GIA) inverse modeling, the usual assumption for the mantle rheology is the Maxwell model, which exhibits constant viscosity over time. However, mineral physics experiments and post-seismic observations show evidence of a transient component in the deformation of the shallow mantle, with a short-term viscosity lower than the long-term one. In these studies, the resulting rheology is modeled by a Burgers material: such rheology is indeed expected as the mantle is a mixture of materials with different viscosities. We propose to apply this rheology for the whole viscoelastic mantle, and, using a Bayesian MCMC inverse formalism for GIA during the last glacial cycle, study its impact on estimations of viscosity values, elastic thickness of the lithosphere, and ice distribution. To perform this inversion, we use a global dataset of sea level records, the geological constraints of ice-sheet margins, and present-day GPS data as well as satellite gravimetry. Our ambition is to present not only the best fitting model, but also the range of possible solutions (within the explored space of parameters) with their respective probability of explaining the data. Our first results indicate that compared to the Maxwell models, the Burgers models involve a larger lower mantle viscosity and thicker ice over Fennoscandia and Canada.

  6. 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.

  7. A study of Glacial Isostatic Adjustment in Greenland

    NASA Astrophysics Data System (ADS)

    Nielsen, Jens Emil; Sandberg Sørensen, Louise; Adalgeirsdottir, Gudfinna; Spada, Giorgio

    2010-05-01

    Glacial isostatic adjustment (GIA) is the viscoelastic response of the Earth caused by changes in ice loads during glaciations and deglaciations. Knowledge of the GIA signal is particularly important in cryospheric applications of satellite gravimetry and altimetry, where the origin of the observed changes must be separated into past and present response. Modeling the present-day GIA signal must include knowledge of both the ice loading history and the Earth's rheology. Neither of these models are well constrained in Greenland, and hence the GIA estimates here are uncertain. In this paper we implement a loading history of the Greenland Ice Sheet derived from the ice sheet model SICOPOLIS, and we study the present-day gravity changes and vertical crustal motion derived from using this ice history. The results are compared with those derived from the widely used ICE-5G ice history. For calculation of present day GIA signal, we assume the Earth's rheology to be a simplified version of the VM2 Earth model. The calculated GIA signal in Greenland, derived from the two ice loading histories are compared with geodetic measurements of vertical crustal motion from GPS time series and with repeated gravity measurements in Greenland. The free code SELEN is used for calculating the effects of the Earth model and different ice loading histories. This study is performed within the Working Group 4 of the ESF COST Action ES0701 "Improved constraints on models of Glacial Isostatic Adjustment".

  8. Glacial-Age Dust Provenance in West Antarctica

    NASA Astrophysics Data System (ADS)

    Borunda, A.; Winckler, G.; Goldstein, S. L.; Kaplan, M. R.

    2015-12-01

    Antarctic ice cores contain insoluble dust particles that may have been transported for thousands of miles, from distal continental sources, before being deposited on the ice sheet and incorporated into the ice core record. Knowing the dust sources, and observing how those sources have changed over time, informs our understanding of regional climate conditions in the potential source areas, as well as informing our reconstructions of atmospheric transport between the sources and the poles. Patagonia has been identified as a key dust source to East Antarctica during Ice Age climates; however, the dust sources to West Antarctica during these times have remained unknown. We present radiogenic isotope (Sr, Nd, Pb isotopes) and trace element data of the insoluble dust extracted from 15 WAIS Divide ice core and 4 Byrd ice core samples between ~40ky and the end of the Last Glacial Maximum, and combine these with a novel set of observations on potential sources of dust from around the Pacific sector of the polar Southern Hemisphere. We use these geochemical tools to identify, in a multi-dimensional view, the source(s) of dust to West Antarctica. We also identify the sources of dust across two millennial-scale climate events. The data indicate that Patagonia was a dominant source of dust for West Antarctica during glacial periods, highlighting the importance of southern South America as a dust source for broad swaths of the polar and sub-polar Southern Hemisphere.

  9. 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.

  10. Massive remobilization of permafrost carbon during post-glacial warming

    PubMed Central

    Tesi, T.; Muschitiello, F.; Smittenberg, R. H.; Jakobsson, M.; Vonk, J. E.; Hill, P.; Andersson, A.; Kirchner, N.; Noormets, R.; Dudarev, O.; Semiletov, I.; Gustafsson, Ö

    2016-01-01

    Recent hypotheses, based on atmospheric records and models, suggest that permafrost carbon (PF-C) accumulated during the last glaciation may have been an important source for the atmospheric CO2 rise during post-glacial warming. However, direct physical indications for such PF-C release have so far been absent. Here we use the Laptev Sea (Arctic Ocean) as an archive to investigate PF-C destabilization during the last glacial–interglacial period. Our results show evidence for massive supply of PF-C from Siberian soils as a result of severe active layer deepening in response to the warming. Thawing of PF-C must also have brought about an enhanced organic matter respiration and, thus, these findings suggest that PF-C may indeed have been an important source of CO2 across the extensive permafrost domain. The results challenge current paradigms on the post-glacial CO2 rise and, at the same time, serve as a harbinger for possible consequences of the present-day warming of PF-C soils. PMID:27897191

  11. 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

  12. Molecular evidence for an active endogenous microbiome beneath glacial ice.

    PubMed

    Hamilton, Trinity L; Peters, John W; Skidmore, Mark L; Boyd, Eric S

    2013-07-01

    Geologic, chemical and isotopic evidence indicate that Earth has experienced numerous intervals of widespread glaciation throughout its history, with roughly 11% of present day Earth's land surface covered in ice. Despite the pervasive nature of glacial ice both today and in Earth's past and the potential contribution of these systems to global biogeochemical cycles, the composition and phylogenetic structure of an active microbial community in subglacial systems has yet to be described. Here, using RNA-based approaches, we demonstrate the presence of active and endogenous archaeal, bacterial and eukaryal assemblages in cold (0-1 °C) subglacial sediments sampled from Robertson Glacier, Alberta, Canada. Patterns in the phylogenetic structure and composition of subglacial sediment small subunit (SSU) ribosomal RNA (rRNA) assemblages indicate greater diversity and evenness than in glacial surface environments, possibly due to facilitative or competitive interactions among populations in the subglacial environment. The combination of phylogenetically more even and more diverse assemblages in the subglacial environment suggests minimal niche overlap and optimization to capture a wider spectrum of the limited nutrients and chemical energy made available from weathering of bedrock minerals. The prevalence of SSU rRNA affiliated with lithoautotrophic bacteria, autotrophic methane producing archaea and heterotrophic eukarya in the subglacial environment is consistent with this hypothesis and suggests an active contribution to the global carbon cycle. Collectively, our findings demonstrate that subglacial environments harbor endogenous active ecosystems that have the potential to impact global biogeochemical cycles over extended periods of time.

  13. Molecular evidence for an active endogenous microbiome beneath glacial ice

    PubMed Central

    Hamilton, Trinity L; Peters, John W; Skidmore, Mark L; Boyd, Eric S

    2013-01-01

    Geologic, chemical and isotopic evidence indicate that Earth has experienced numerous intervals of widespread glaciation throughout its history, with roughly 11% of present day Earth's land surface covered in ice. Despite the pervasive nature of glacial ice both today and in Earth's past and the potential contribution of these systems to global biogeochemical cycles, the composition and phylogenetic structure of an active microbial community in subglacial systems has yet to be described. Here, using RNA-based approaches, we demonstrate the presence of active and endogenous archaeal, bacterial and eukaryal assemblages in cold (0–1 °C) subglacial sediments sampled from Robertson Glacier, Alberta, Canada. Patterns in the phylogenetic structure and composition of subglacial sediment small subunit (SSU) ribosomal RNA (rRNA) assemblages indicate greater diversity and evenness than in glacial surface environments, possibly due to facilitative or competitive interactions among populations in the subglacial environment. The combination of phylogenetically more even and more diverse assemblages in the subglacial environment suggests minimal niche overlap and optimization to capture a wider spectrum of the limited nutrients and chemical energy made available from weathering of bedrock minerals. The prevalence of SSU rRNA affiliated with lithoautotrophic bacteria, autotrophic methane producing archaea and heterotrophic eukarya in the subglacial environment is consistent with this hypothesis and suggests an active contribution to the global carbon cycle. Collectively, our findings demonstrate that subglacial environments harbor endogenous active ecosystems that have the potential to impact global biogeochemical cycles over extended periods of time. PMID:23486249

  14. 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.

  15. 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.

  16. Mapping Post-Glacial expansions: The Peopling of Southwest Asia

    PubMed Central

    Platt, Daniel E.; Haber, Marc; Dagher-Kharrat, Magda Bou; Douaihy, Bouchra; Khazen, Georges; Ashrafian Bonab, Maziar; Salloum, Angélique; Mouzaya, Francis; Luiselli, Donata; Tyler-Smith, Chris; Renfrew, Colin; Matisoo-Smith, Elizabeth; Zalloua, Pierre A.

    2017-01-01

    Archaeological, palaeontological and geological evidence shows that post-glacial warming released human populations from their various climate-bound refugia. Yet specific connections between these refugia and the timing and routes of post-glacial migrations that ultimately established modern patterns of genetic variation remain elusive. Here, we use Y-chromosome markers combined with autosomal data to reconstruct population expansions from regional refugia in Southwest Asia. Populations from three regions in particular possess distinctive autosomal genetic signatures indicative of likely refugia: one, in the north, centered around the eastern coast of the Black Sea, the second, with a more Levantine focus, and the third in the southern Arabian Peninsula. Modern populations from these three regions carry the widest diversity and may indeed represent the most likely descendants of the populations responsible for the Neolithic cultures of Southwest Asia. We reveal the distinct and datable expansion routes of populations from these three refugia throughout Southwest Asia and into Europe and North Africa and discuss the possible correlations of these migrations to various cultural and climatic events evident in the archaeological record of the past 15,000 years. PMID:28059138

  17. 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.

  18. 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.

  19. Glacial Isostatic Adjustment and Contemporary Sea Level Rise: An Overview

    NASA Astrophysics Data System (ADS)

    Spada, Giorgio

    2017-01-01

    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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. Paleoclimate of northern Guatemala during the Last Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Hodell, D. A.; Anselmetti, F.; Ariztegui, D.; Brenner, M.; Curtis, J.; Gilli, A.; Mueller, A.

    2006-12-01

    Lake Peten Itza (zmax = 165 m) in northern Guatemala is the deepest lake in the lowlands of Central America. Annual rainfall averages ~1600 mm and is highly seasonal with over 90% occurring in the months from May to October. As part of an ICDP project, we recovered 1327 m of lake sediment at seven sites using the GLAD800 superbarge. Preliminary research has focused on Site PI-6 at a water depth of 71 m. Three holes were drilled and recovered a complete stratigraphic section to a maximum depth of 75.9 mblf. Radiocarbon dates on terrestrial organic matter display a regular increase in age with depth, and indicate a mean sedimentation rate of ~100 cm per 1000 yrs (1mm/yr). The top 10.8 mcd were deposited during the Holocene and consist primarily of gray carbonate clay with abundant charcoal. The Pleistocene/Holocene boundary at 10.8 mcd is marked by a transition to Holocene clay from underlying, interbedded dense gypsum sand and clay deposited during the Late Glacial period from ~17 to 9.3 kyrs. This transition represents a switch to moist climate during the early Holocene from more arid conditions during the Late Glacial. Arid conditions during the Late Glacial period may coincide with episodic delivery of seasonal meltwater to the Gulf of Mexico (Aharon, 2003, Paleoceanography, 18, 1079). In contrast to the Late Glacial period, the earlier Last Glacial Maximum (LGM), from 23 to 17 kyrs, consists of gray carbonate clay that is very similar to Holocene deposits, suggesting high detrital input and high lake level. This finding contradicts previous results suggesting that the LGM was dry in the Peten lowlands. We speculate that a cold, wet LGM may have been caused by increased winter precipitation when the Laurentide Ice Sheet (LIS) was at its southernmost extent. The mechanism may have been related to increased frequency of polar outbreaks and "Norte" winds, which occasionally bring rain to the Peten today during the dry season. Similar increases in winter

  5. 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

  6. Glacial and post-glacial history of Lake Windermere, The Lake District, UK: integrating high resolution multibeam bathymetry, airborne LiDAR, and sediment cores

    NASA Astrophysics Data System (ADS)

    Miller, H.; Bull, J. M.; Cotterill, C.; Vardy, M. E.; Dix, J. K.; Henstock, T.

    2013-12-01

    High resolution multibeam bathymetry and airborne LiDAR (light detection and ranging) data, supplemented by geomorphological and geological field mapping have been used to investigate the glacial and post-glacial history of Windermere, the largest natural lake in England. In addition, recently acquired piston cores, supplemented with 2D and 3D seismic reflection data from previous surveys have been used to examine the well preserved sequence stratigraphy. The data is used to generate a present-day landscape map, revealing a complex landform record, characterised by nine sub-basins separated by steps, ridges and isolated topographic highs related to the retreat of the British and Irish Ice Sheet (BIIS). Debris flows and anthropogenic features are superimposed on the general bathymetric framework formed since the Last Glacial Maximum. There is also evidence of glacial features preserved onshore, which identify a series of depositional environments that accompanied ice advance, ice retreat and post-glacial deposition within the Lake District. Core analysis has identified a sequence of sand with finely laminated sand, silt and clay, fining upwards into varved clays, overlain by organic rich lacustrine gyttja. The stratigraphic units correlate with existing seismic stratigraphic facies, suggesting the sequence extends through an overlying drape of Holocene gyttja into glaciolacustrine and lacustrine sediment fill relating to Interstadial/BIIS retreat, and further penetrates to the till surface. Analysis of geophysical core properties reveals coarser layers in the varved clay are correlated with peaks in magnetic susceptibility and iron, suggesting retreat was punctuated by surges in ice movement leading to the deposition of coarser layers rich in iron bearing minerals. This study indicates that an integrated approach, using high resolution geophysical datasets combined with sediment coring is capable of deriving an in-depth understanding of glacial and post-glacial

  7. 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,...

  8. 78 FR 3909 - Big Oaks National Wildlife Refuge, IN; Glacial Ridge National Wildlife Refuge, MN; Northern...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-17

    ... Fish and Wildlife Service Big Oaks National Wildlife Refuge, IN; Glacial Ridge National Wildlife Refuge... conservation plans (CCP) and associated environmental documents for the Big Oaks, Glacial Ridge, Northern... refuge at the following addresses: Attention: Refuge Manager, Big Oaks NWR, 1661 West JPG Niblo...

  9. The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination

    NASA Astrophysics Data System (ADS)

    Schaefer, Joerg M.; Putnam, Aaron E.; Denton, George H.; Kaplan, Michael R.; Birkel, Sean; Doughty, Alice M.; Kelley, Sam; Barrell, David J. A.; Finkel, Robert C.; Winckler, Gisela; Anderson, Robert F.; Ninneman, Ulysses S.; Barker, Stephen; Schwartz, Roseanne; Andersen, Bjorn G.; Schluechter, Christian

    2015-04-01

    Glacial maxima and their terminations provide key insights into inter-hemispheric climate dynamics and the coupling of atmosphere, surface and deep ocean, hydrology, and cryosphere, which is fundamental for evaluating the robustness of earth's climate in view of ongoing climate change. The Last Glacial Maximum (LGM, ∼26-19 ka ago) is widely seen as the global cold peak during the last glacial cycle, and its transition to the Holocene interglacial, dubbed 'Termination 1 (T1)', as the most dramatic climate reorganization during this interval. Climate records show that over the last 800 ka, ice ages peaked and terminated on average every 100 ka ('100 ka world'). However, the mechanisms pacing glacial-interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood. Here we show evidence for a full glacial maximum in the Southern Hemisphere 65.1 ± 2.7 ka ago and its 'Unfinished Termination'. Our 10Be chronology combined with a model simulation demonstrates that New Zealand's glaciers reached their maximum position of the last glacial cycle during Marine Isotope Stage-4 (MIS-4). Southern ocean and greenhouse gas records indicate coeval peak glacial conditions, making the case for the Southern Glacial Maximum about halfway through the last glacial cycle and only 15 ka after the last warm period (MIS-5a). We present the hypothesis that subsequently, driven by boreal summer insolation forcing, a termination began but remained unfinished, possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the North Atlantic through Heinrich Stadial 6 to drive a full termination. Yet the Unfinished Termination left behind substantial ice on the northern continents (about 50% of the full LGM ice volume) and after another 45 ka of cooling and ice sheet growth the earth was at inter

  10. 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

  11. Midlatitude land surface temperature impacts the timing and structure of glacial maxima

    NASA Astrophysics Data System (ADS)

    Thomas, Elizabeth K.; Clemens, Steven C.; Sun, Youbin; Huang, Yongsong; Prell, Warren; Chen, Guangshan; Liu, Zhengyu; Loomis, Shannon

    2017-01-01

    Orbitally modulated insolation is thought to be among the key mechanisms driving ice sheet change. Yet, late Pleistocene ice sheets attained maximum marginal extents prior to summer insolation minima, suggesting that additional mechanisms influenced ice growth and decay. Continuous orbital-scale terrestrial temperature records can help define the role that temperature near ice sheet margins plays on the timing and structure of glacial maxima. We hypothesize, based on a 360 kyr long air temperature record from the Chinese Loess Plateau and shorter records from North America and Europe, that midlatitude terrestrial temperature influenced the rate of ice sheet growth prior to and during glacial maxima; cold conditions prior to glacial maxima enhanced ice sheet growth, while warming during glacial maxima inhibited further growth, despite low summer insolation. Thus, the midlatitude surface energy budget may be an important component of understanding and modeling ice volume, particularly for intervals prior to and during glacial maxima, when ice sheet margins reached midlatitudes.

  12. Late Glacial and Late Holocene Paleohydrology of Central Asia

    NASA Astrophysics Data System (ADS)

    Aichner, B.; Feakins, S. J.; Mischke, S.; Herzschuh, U.; Liu, X.; Rajabov, I.; Wang, Y.; Heinecke, L.

    2013-12-01

    The goal of this study is to deepen the understanding of past climatological, ecological and hydrological changes in Central Asia, by means of organic geochemical proxies and in close cooperation with other work groups providing biological and sedimentological data. We analysed an 8 m sediment core from Lake Karakuli, a small open freshwater lake situated at an altitude of 3,657 m between the massifs of Muztagh Ata (7,546 m) and Kongur Shan (7,719 m) in western China. Additional work is in progress on a 12 m core derived from Lake Karakul in Tajikistan, a large closed saline lake situated in a tectonic graben structure at an altitude of 3,928 m. The distance between the two lakes is 130 km and basal ages of the cores are ca. 4.7 ka BP (China) and ca. 27 ka BP (Tajikistan). The lake catchments may be classified as alpine steppe to alpine deserts with mean annual temperature of ca. 0 °C and mean annual precipitation of ca. 100 mm, respectively. Summer precipitation, associated with the Indian monsoon, accounts for <30% of the annual total, whereas most precipitation is supplied by mid-latitude Westerlies between March and May. In the small Chinese lake long-chain fatty acids (FAs) were mainly attributed to terrestrial sources by compound-specific carbon isotopic analyses. In contrast δ13C values up to -14‰ for abundant mid-chain FAs suggest aquatic origins in the large Lake Karakul. Hydrogen isotopic variability is ca. 15‰ in the mid-Holocene record and ca. 60‰ in the first data derived from the Late Glacial record. In the latter, the most pronounced change from higher to lower δD-values of aquatic biomarkers is tentatively interpreted as change from arid to more humid conditions at the Late Glacial to Holocene transition. Since in Central Asia isotopic variability of precipitation mainly correlates with temperature, we interpret high resolution δD data of terrestrial long-chain FAs in the younger core to mainly reflect mid-Holocene temperature variations

  13. Attenuation of acoustic waves in glacial ice and salt domes

    NASA Astrophysics Data System (ADS)

    Price, P. B.

    2006-02-01

    Two classes of natural solid media, glacial ice and salt domes, are under consideration as media in which to deploy instruments for detection of neutrinos with energy ≥1018 eV. Though insensitive to 1011 to 1016 eV neutrinos for which observatories (e.g., AMANDA and IceCube) that utilize optical Cherenkov radiation detectors are designed, radio and acoustic methods are suited for searches for the very low fluxes of neutrinos with energies >1017 eV. This is because owing to the very long attenuation lengths of radio and acoustic waves produced by interactions of such neutrinos in ice and salt, detection modules can be spaced at horizontal distances ˜1 km, in contrast to the 0.12 km distances between strings of IceCube modules. In this paper, I calculate the absorption and scattering coefficients as a function of frequency and grain size for acoustic waves in glacial ice and salt domes and show that experimental measurements on laboratory samples and in glacial ice and salt domes are consistent with theory. For South Pole ice with grain size ˜0.2 cm at depths ≤600 m, scattering lengths are calculated to be 2000 and 25 km at frequencies 10 and 30 kHz, respectively; for grain size ˜0.4 cm at 1500 m (the maximum depth to be instrumented acoustically), scattering lengths are calculated to be 250 and 3 km. These are within the range of frequencies where most of the energy of the acoustic wave is concentrated. The absorption length is calculated to be 9 ± 3 km at all frequencies above ˜100 Hz. For NaCl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 and 1.4 km at 10 and 30 kHz, and absorption lengths are calculated to be 3 × 104 and 3300 km at 10 and 30 kHz. Existing measurements are consistent with theory. For ice, absorption is the limiting factor; for salt, scattering is the limiting factor. Both media would be suitable for detection of acoustic waves from ultrahigh-energy neutrino interactions.

  14. 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

  15. Delineating Glacial Till Bed Kinematics using AMS and Pebble Fabrics

    NASA Astrophysics Data System (ADS)

    Gentoso, M. J.; Evenson, E.; Kodama, K. P.

    2010-12-01

    Anisotropy of magnetic susceptibility (AMS) and pebble fabric analysis was used to explore glacial till bed kinematics in streamlined glacial landforms of the Weedsport Drumlin field of north central New York State. Five wave-truncated drumlins were sampled at two locations each along the shore of Lake Ontario. A total of 500 pebble orientations and 250 AMS samples were collected from 10 sampling sites in the drumlins. Six flutes were also sampled at 10 sampling sites for a total of 500 pebble orientations and 200 AMS measurements. All AMS measurements were conducted on a KLY-3s Kappabridge. The average orientation of the maximum principal susceptibility axes for the drumlins (N2°E) was parallel, within 95% confidence limits, to the average pebble long-axis orientations (N5°W) and parallel to the N-S trend of the drumlins. Both AMS and pebble average orientations plunge toward the north in the “up glacier” direction indicating an imbrication due to ice flow. The clustering of the AMS principal axis directions indicates that the strength of the AMS drumlin fabric is highly variable, at 3 of the 10 sites it is as strong as fabrics developed in a ring shear device (Iverson et al., 2008) at intermediate shear strains. AMS fabrics in the flutes are stronger and more unidirectional than for the drumlins with the average pebble direction (N4°E) parallel to the average AMS maximum susceptibility direction (N12°E), but not at the 95% confidence level. Northward plunge of these average orientations indicates an imbrication. The flutes trend N10°W, so the fabric orientations are not as closely parallel to the glacial landforms for the flutes as they are for the drumlins. Thermal demagnetization of three orthogonal components of an isothermal remanent magnetization indicates that the AMS is carried primarily by maghemite. The stronger AMS fabric in the flutes compared to the drumlins suggests that the till of the flutes has been subjected to higher strains and perhaps

  16. 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

  17. 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

  18. 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

  19. Glacial lake expansion in the central Himalayas by Landsat images, 1990-2010.

    PubMed

    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.

  20. The tropical lapse rate steepened during the Last Glacial Maximum

    PubMed Central

    Loomis, Shannon E.; Russell, James M.; Verschuren, Dirk; Morrill, Carrie; De Cort, Gijs; Sinninghe Damsté, Jaap S.; Olago, Daniel; Eggermont, Hilde; Street-Perrott, F. Alayne; Kelly, Meredith A.

    2017-01-01

    The gradient of air temperature with elevation (the temperature lapse rate) in the tropics is predicted to become less steep during the coming century as surface temperature rises, enhancing the threat of warming in high-mountain environments. However, the sensitivity of the lapse rate to climate change is uncertain because of poor constraints on high-elevation temperature during past climate states. We present a 25,000-year temperature reconstruction from Mount Kenya, East Africa, which demonstrates that cooling during the Last Glacial Maximum was amplified with elevation and hence that the lapse rate was significantly steeper than today. Comparison of our data with paleoclimate simulations indicates that state-of-the-art models underestimate this lapse-rate change. Consequently, future high-elevation tropical warming may be even greater than predicted. PMID:28138544

  1. 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.

  2. Magnetostratigraphy of continental glacial deposits in southernmost Patagonia

    NASA Astrophysics Data System (ADS)

    Griffing, C. Y.; Barendregt, R. W.; Clague, J. J.; Roberts, N. J.; Corbella, H.; Ercolano, B.; Rabassa, J.

    2012-12-01

    Southernmost Patagonia has well preserved records of continental and alpine glaciations. It is the only region in the Southern Hemisphere outside Antarctica where large Pleistocene ice sheets developed, thus it offers a unique opportunity to enhance understanding of global climate variability. Previous research on the glacial history of Patagonia is largely based on geomorphology, with limited study of stratigraphy and relatively few absolute ages. Consequently, the number, ages, and geographic extent of individual glaciations are not well understood. Geomorphic evidence of multiple Quaternary glaciations is widespread in the region and includes moraines, erratics, drumlin fields, and outwash plains. Exposures of glacial sediments are common along the Atlantic coast, the Strait of Magellan, meltwater channels, and in gravel pits. Most of the glacial deposits are beyond the range of radiocarbon dating. K-Ar and Ar-Ar dating have been used to determine the ages of basalt flows interlayered with till and outwash in the southern Andes to the west and in the Rio Gallegos valley near the Atlantic coast. These absolute ages suggest that glaciation in Patagonia began in the late Miocene and that the Pleistocene Patagonian ice sheet may have decreased in size with each successive advance. We conducted a paleomagnetic study of glacial sediments to further constrain the timing of continental glaciations. The sediments are stably magnetized, providing clear directional data from which polarity can be determined. Most sediments in the area are normally magnetized, but some sediments near the outer limit of glaciation, within areas covered by the Patagonian ice sheet during the Great Patagonian Glaciation (GPG), are reversely magnetized. Recent field work indicates that drift of the GPG comprises deposits of several glaciations. Our paleomagnetic results suggest that the first continental glaciation(s) in the region occurred during the Matuyama Reversed Chron (2.6 - 0.78 Ma) and

  3. 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.

  4. 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.

  5. Mediterranean Ocean Climate for the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Mikolajewicz, Uwe

    2010-05-01

    To correctly reproduce past climate changes is one of the prerequistes for reliably predicting anthropogenic climate change. Here, results from an attempt to simulate the climate of the Last Glacial Maximum (LGM, 21.000 years ago) for the Mediterranean Sea are pesented. For this time slice, precompiled proxy data sets exist. One key problem in regional ocean modelling for past time slices is to obtain atmospheric forcing data. A multi-step approach is used. A coarse resolution earth system model consisting of coupled atmospheric-oceanic general circulation models (ECHAM5_T31/MPIOM_GR3) with a dynamical vegetation model (LPJ) was integrated for several thousand years to steady state. The surface conditions derived from these model simulations (sea surface temperature (SST), sea ice and vegetation) were used as lower boundary conditions for a short (20 years plus 9 years of spinup) simulation with a high resolution stand-alone atmosphere model (ECHAM5_T106). The continental runoff was calculated using a hydrological discharge model. This procedure was performed both for the Last Glacial Maximum as well as for a preindustrial control simulation. Atmospheric composition, earth orbital parameters, topography and ice sheet distribution were prescribed following the protocol for the PMIP2 project. The simulations of the Mediterranean ocean climate were performed with a regional version of MPIOM. The model has a horizontal resolution of approximately 25 km and 29 levels. The surface heat fluxes are calculated with bulk fomulas using the model SST. Freshwater forcing consists of evaporation (calculated from the latent heat flux), precipitation and river runoff. The model uses daily forcing for the atmospheric input derived from the high resolution atmosphere model. In the Atlantic box a restoring to observed hydrography is applied. For the LGM the anomalies from the coupled model are added to observations. This model has been integrated in each of the cases for more than

  6. The tropical lapse rate steepened during the Last Glacial Maximum.

    PubMed

    Loomis, Shannon E; Russell, James M; Verschuren, Dirk; Morrill, Carrie; De Cort, Gijs; Sinninghe Damsté, Jaap S; Olago, Daniel; Eggermont, Hilde; Street-Perrott, F Alayne; Kelly, Meredith A

    2017-01-01

    The gradient of air temperature with elevation (the temperature lapse rate) in the tropics is predicted to become less steep during the coming century as surface temperature rises, enhancing the threat of warming in high-mountain environments. However, the sensitivity of the lapse rate to climate change is uncertain because of poor constraints on high-elevation temperature during past climate states. We present a 25,000-year temperature reconstruction from Mount Kenya, East Africa, which demonstrates that cooling during the Last Glacial Maximum was amplified with elevation and hence that the lapse rate was significantly steeper than today. Comparison of our data with paleoclimate simulations indicates that state-of-the-art models underestimate this lapse-rate change. Consequently, future high-elevation tropical warming may be even greater than predicted.

  7. 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.

  8. 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).

  9. 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.

  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. Glacial landscape evolution by subglacial quarrying: A multiscale computational approach

    NASA Astrophysics Data System (ADS)

    Ugelvig, Sofie V.; Egholm, David L.; Iverson, Neal R.

    2016-11-01

    Quarrying of bedrock is a primary agent of subglacial erosion. Although the mechanical theory behind the process has been studied for decades, it has proven difficult to formulate the governing principles so that large-scale landscape evolution models can be used to integrate erosion over time. The existing mechanical theory thus stands largely untested in its ability to explain postglacial topography. In this study we relate the physics of quarrying to long-term landscape evolution with a multiscale approach that connects meter-scale cavities to kilometer-scale glacial landscapes. By averaging the quarrying rate across many small-scale bedrock steps, we quantify how regional trends in basal sliding speed, effective pressure, and bed slope affect the rate of erosion. A sensitivity test indicates that a power law formulated in terms of these three variables provides an acceptable basis for quantifying regional-scale rates of quarrying. Our results highlight the strong influence of effective pressure, which intensifies quarrying by increasing the volume of the bed that is stressed by the ice and thereby the probability of rock failure. The resulting pressure dependency points to subglacial hydrology as a primary factor for influencing rates of quarrying and hence for shaping the bedrock topography under warm-based glaciers. When applied in a landscape evolution model, the erosion law for quarrying produces recognizable large-scale glacial landforms: U-shaped valleys, hanging valleys, and overdeepenings. The landforms produced are very similar to those predicted by more standard sliding-based erosion laws, but overall quarrying is more focused in valleys, and less effective at higher elevations.

  12. 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.

  13. 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.

  14. 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.

  15. Glacial Delineation and Ice Retreat on Pico de Orizaba, Mexico

    NASA Astrophysics Data System (ADS)

    Colby, A. E.; Weissling, B.; Xie, H.

    2011-12-01

    Pico de Orizaba, a dormant stratovolcano at the eastern end of the Trans-Mexican Volcanic Belt at approximately 19 degrees of latitude and the third largest peak in North America (5636 m), hosts what is likely the last significant tropical zone glacier (Jamapa Glacier) in the Northern Hemisphere. Not since the International Geophysical Year of 1957-58 has Pico's glacial environment been studied with any focused effort, perhaps due to the general innaccessibility, high altitude, and steep slopes. As are most glaciers around the world, the Jamapa Glacier is retreating, with a remarkable loss of ice in the past 2 decades. The rate and pattern of retreat is important to understanding climate change forcing as well as understanding environmental and water supply impacts to a substantial human population who live along the base of the volcano. Through the use of satellite imagery (LandSat, ASTER, IKONOS), legacy hand-drawn maps, aerial photographs, and first-hand accounts from climber's expeditions, a reasonably accurate map of almost 60 years of glacial retreat has been produced. Legacy hand-drawn maps of the ice edge, that pre-date the satellite era, did not fit perfectly with modern images when layered in ArcGIS. Oblique perspectives in Google Earth and various aerial and surface-based photographs of the mountain were used to help fit the ice edge to the actual topography. The disparity of satellite image pixel resolution (from 1 m IKONOS to 60 m LandSat) was addressed using various imagery analysis tools (eg. edge detection convolution filters and pixel unmixing) in order to delineate an approximate ice edge for the respective image date. The final map shows the nature of ice edge retreat on Pico de Orizaba from 1945 up until the present (Feb 2011).

  16. 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.

  17. A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice

    NASA Astrophysics Data System (ADS)

    Petrenko, Vasilii Victorovich

    Ice core records from Greenland and Antarctica reveal large and rapid variations in atmospheric methane concentrations ([CH4]) in response to abrupt climate change. Two such events occurred at the Oldest Dryas (OD) - Bolling and Younger Dryas (YD) - Preboreal (PB) climatic transitions during the last glacial termination. A record of 14C of atmospheric CH4 (14CH4) through these transitions can help to identify the sources of the [CH4] increases and constrain the fossil fraction of paleo CH4 budgets. Very large (˜100 L STP) samples of paleoatmospheric air are needed for such 14CH4 measurements. To obtain these samples, ancient ice outcropping at an ice-margin ablation site in West Greenland was explored. Ice sections dating to the last glacial termination were identified and found to contain high-quality gas records. A new method for large-scale air extraction from glacial ice was developed and twelve large air samples from the YD-PB and the OD-Bolling transitions were obtained. New methods were also developed for processing this air for 14CH4 . 14CH4 procedural blanks were greatly reduced through the construction of a new CH4 conversion line utilizing platinized quartz wool for CH4 combustion and the use of an ultra high purity iron catalyst for graphitization. The overall 14CH 4 processing blank was 0.75 +/- 0.38 pMC. Measured 14CH4 values were too high by 14--38% as compared to the highest expected values based on paleoatmospheric 14CO2. In-situ production of CH4 and direct cosmogenic production of 14CH4 molecules in ablating ice were identified as the two most likely mechanisms that elevated 14CH4. Sample 14CH4 was then corrected for both mechanisms, however these corrections are speculative and do not allow any definite conclusions to be drawn from the results. Corrected 14CH4 results suggest that there was a 7% increase in the fossil CH4 fraction from the YD to the PB. The corrected 14CH4 results also suggest no large changes in the fossil fraction between the

  18. The early rise and late demise of New Zealand’s last glacial maximum

    PubMed Central

    Rother, Henrik; Fink, David; Shulmeister, James; Mifsud, Charles; Evans, Michael; Pugh, Jeremy

    2014-01-01

    Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30–20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28–16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26–19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19–16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28–20 ka, and gradual deglaciation until at least 15 ka. PMID:25071171

  19. The early rise and late demise of New Zealand's last glacial maximum.

    PubMed

    Rother, Henrik; Fink, David; Shulmeister, James; Mifsud, Charles; Evans, Michael; Pugh, Jeremy

    2014-08-12

    Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30-20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28-16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26-19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19-16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28-20 ka, and gradual deglaciation until at least 15 ka.

  20. On the glacial and inter-glacial thermohaline circulation and the associated transports of heat and freshwater

    NASA Astrophysics Data System (ADS)

    Ballarotta, M.; Falahat, S.; Brodeau, L.; Döös, K.

    2014-03-01

    The change of the thermohaline circulation (THC) between the Last Glacial Maximum (LGM, ≈ 21 kyr ago) and the present day climate are explored using an Ocean General Circulation Model and stream functions projected in various coordinates. Compared to the present day period, the LGM circulation is reorganised in the Atlantic Ocean, in the Southern Ocean and particularly in the abyssal ocean, mainly due to the different haline stratification. Due to stronger wind stress, the LGM tropical circulation is more vigorous than under modern conditions. Consequently, the maximum tropical transport of heat is slightly larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes and reorganising the freshwater transport. The LGM circulation is represented as a large intrusion of saline Antarctic Bottom Water into the Northern Hemisphere basins. As a result, the North Atlantic Deep Water is shallower in the LGM simulation. The stream functions in latitude-salinity coordinates and thermohaline coordinates point out the different haline regimes between the glacial and interglacial period, as well as a LGM Conveyor Belt circulation largely driven by enhanced salinity contrast between the Atlantic and the Pacific basin. The thermohaline structure in the LGM simulation is the result of an abyssal circulation that lifts and deviates the Conveyor Belt cell from the area of maximum volumetric distribution, resulting in a ventilated upper layer above a deep stagnant layer, and an Atlantic circulation more isolated from the Pacific. An estimation of the turnover times reveal a deep circulation almost sluggish during the LGM, and a Conveyor Belt cell more vigorous due to the combination of stronger wind stress and shortened circulation route.

  1. A long pollen record from lowland Amazonia: Forest and cooling in glacial times

    SciTech Connect

    Colinvaux, P.A.; Moreno, J.E.; Bush, M.B.

    1996-10-04

    A continuous pollen history of more than 40,000 years was obtained from a lake in the lowland Amazon rain forest. Pollen spectra demonstrate that tropical rain forest occupied the region continuously and that savannas or grasslands were not present during the last glacial maximum. The data suggest that the western Amazon forest was not fragmented into refugia in glacial times and that the lowlands were not a source of dust. Glacial age forests were comparable to modern forests but also included species now restricted to higher evaluations by temperature, suggesting a cooling of the order of 5{degrees} to 6{degrees}C. 23 refs., 22 tabs.

  2. Effect of low glacial atmospheric CO{sub 2} on tropical African montane vegetation

    SciTech Connect

    Jolly, D.; Haxeltine, A.

    1997-05-02

    Estimates of glacial-interglacial climate change in tropical Africa have varied widely. Results from a process-based vegetation model show how montane vegetation in East Africa shifts with changes in both carbon dioxide concentration and climate. For the last glacial maximum, the change in atmospheric carbon dioxide concentration alone could explain the observed replacement of tropical montane forest by a scrub biome. This result implies that estimates of the last glacial maximum tropical cooling based on tree-line shifts must be revised. 30 refs., 2 figs.

  3. Architecture of Late Ordovician glacial valleys in the Tassili N'Ajjer area (Algeria)

    NASA Astrophysics Data System (ADS)

    Deschamps, Rémy; Eschard, Rémi; Roussé, Stéphane

    2013-05-01

    The architecture of three Late Ordovician glacial valleys was studied in detail in the Tassili N'Ajjer (SE Algeria) outcrops. The valleys are oriented south-north, 2 to 5 km wide, and up to 250 m deep. The valley-fills revealed a very complex sedimentary architecture with significant lateral facies changes. Several glacial cycles induced the formation of Glacial Erosion Surfaces (GES) at the base and within the glacial valleys. The first type of GES shows a sharp and steep-angled contact without striations or associated syn-sedimentary deformation, suggesting that subglacial meltwater was the dominant erosive agent. A second type associated with the deformation of pre-glacial and syn-glacial sediment, suggests that ice was in contact with the valley floor. Four facies associations are proposed: FA1: subglacial tillite; FA2: Sub-to pro-glacial ice contact fans; FA3: Proglacial sub-aqueous gravity flows; and FA4: outwash fans. The stratigraphic architecture of three of the main valleys reveals a complex polyphase infill. At least two main cycles of ice-sheet advance and retreat can be interpreted from the sedimentary succession of each valley. Minor glacial cycles by ice oscillations also occur locally. GES morphology and the facies sequence suggest that the Iherir valleys were initiated by meltwater erosion in subglacial channels, whereas the Dider and Ouarsissen valleys were part of a large ice stream pathway. Above the valley-fill and the interfluves, a sand-rich unit of stacked lobes and channels is interpreted as submarine outwash fans deposited during final ice retreat. A glacial sequence found between two GES comprises fluvio-glacial or ice-contact fan deposits, fluvio-glacial eskers and tills. These sediments were deposited subglacially or at the glacier front during the ice maximum phase and/or the early ice retreat phase. During the ice retreat, interbedded subaqueous gravity flow deposits and diamictites filled the glacially cut topography as the sea

  4. Instability of glacial climate in a model of the ocean- atmosphere-cryosphere system.

    PubMed

    Schmittner, Andreas; Yoshimori, Masakazu; Weaver, Andrew J

    2002-02-22

    In contrast to the relatively stable climate of the past 10,000 years, during glacial times the North Atlantic region experienced large-amplitude transitions between cold (stadial) and warm (interstadial) states. In this modeling study, we demonstrate that hydrological interactions between the Atlantic thermohaline circulation (THC) and adjacent continental ice sheets can trigger abrupt warming events and also limit the lifetime of the interstadial circulation mode. These interactions have the potential to destabilize the THC, which is already more sensitive for glacial conditions than for the present-day climate, thus providing an explanation for the increased variability of glacial climate.

  5. Gigantic landslides versus glacial deposits: on origin of large hummock deposits in Alai Valley, Northern Pamir

    NASA Astrophysics Data System (ADS)

    Reznichenko, Natalya

    2015-04-01

    As glaciers are sensitive to local climate, their moraines position and ages are used to infer past climates and glacier dynamics. These chronologies are only valid if all dated moraines are formed as the result of climatically driven advance and subsequent retreat. Hence, any accurate palaeoenvironmental reconstruction requires thorough identification of the landform genesis by complex approach including geomorphological, sedimentological and structural landform investigation. Here are presented the implication of such approach for the reconstruction of the mega-hummocky deposits formation both of glacial and landslide origin in the glaciated Alai Valley of the Northern Pamir with further discussion on these and similar deposits validity for palaeoclimatic reconstructions. The Tibetan Plateau valleys are the largest glaciated regions beyond the ice sheets with high potential to provide the best geological record of glacial chronologies and, however, with higher probabilities of the numerous rock avalanche deposits including those that were initially considered of glacial origin (Hewitt, 1999). The Alai Valley is the largest intermountain depression in the upper reaches of the Amudarja River basin that has captured numerous unidentified extensive hummocky deposits descending from the Zaalai Range of Northern Pamir, covering area in more than 800 km2. Such vast hummocky deposits are usually could be formed either: 1) glacially by rapid glacial retreat due to the climate signal or triggered a-climatically glacial changes, such as glacial surge or landslide impact, or 2) during the landslide emplacement. Combination of sediment tests on agglomerates forming only in rock avalanche material (Reznichenko et al., 2012) and detailed geomorphological and sedimentological descriptions of these deposits allowed reconstructing the glacial deposition in the Koman and Lenin glacial catchments with identification of two gigantic rock avalanches and their relation to this glacial

  6. Terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the Himalayan orogen: Ladakh Range, northern India

    USGS Publications Warehouse

    Owen, L.A.; Caffee, M.W.; Bovard, K.R.; Finkel, R.C.; Sharma, M.C.

    2006-01-01

    Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya. The glacial stages that have been identified are: the Indus Valley glacial stage, dated at older than 430 ka; the Leh glacial stage occurring in the penultimate glacial cycle or older; the Karglacial stage, occurring during the early part of the last glacial cycle; the Bazgo glacial stage, at its maximum during the middle of the last glacial cycle; and the early Holocene Khalling glacial stage. The exposure ages of the Indus Valley moraines are the oldest observed to date throughout the Himalayan orogen. We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation. A possible explanation is that uplift of Himalayan ranges to the south and/or of the Karakoram Mountains to the west of the region may have effectively blocked moisture supply by the south Asian summer monsoon and mid-latitude westerlies, respectively. Alternatively, this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the Pleistocene. ?? 2006 Geological Society of America.

  7. Holocene Glacial Retreat at Walgreen Coast, West Antarctica

    NASA Astrophysics Data System (ADS)

    Lindow, J.; Johnson, J.; Castex, M.; Wittmann, H.; Smith, J.; Lisker, F.; Gohl, K.; Spiegel, C.

    2012-12-01

    The Walgreen Coast of West Antarctica represents one of the most rapidly changing sectors of the West Antarctic Ice Sheet (WAIS). With the fastest ice streams in the whole Antarctic, the WAIS is characterised by rapid thinning and grounding line retreat. Airborne and satellite-based short-term observations show a doubling of the negative net mass balance between 1996-2006 (Rignot et al., 2008). Furthermore, because the WAIS is largely grounded below sea level, continued inland thinning and grounding line retreat could result in rapid ice sheet collapse, which would raise global sea level by between 3-5 m. However, due to remoteness and challenging accessibility, onshore data is limited to a few isolated nunataks making it difficult to assess the long-term evolution of the glacial dynamics along Walgreen Coast. To address this we present new data from two key areas of the Walgreen Coast; the Kohler Range and the Pine Island Bay. Our 10Be surface exposure ages from erratic boulders in the Kohler Range are the first and reveal that this area became ice-free between 8.3 and 12.3 ka. This implies a long-term thinning rate of 3.3 cm/yr and agrees with similar data published from glaciers eastward. Our ages are also consistent with recent deglaciation models which suggest strong thinning after 15 ka and off-shore sediments shows a concurrent lateral ice-shelf front retreat. Our results suggest an ice-cover at least 300 m thicker in the Kohler Range during the early Holocene and that subsequent average thinning occurred on rates one order of magnitude slower than recent satellite measurements show. This implies that the recent trend in ice-sheet thinning results from a recent dynamic changes rather than a response to long-term thinning. To further constrain the lateral deglaciation history along the eastern Walgreen Coast, namely the Pine Island Glacier, we collected additional samples from a chain of islands, located flow-parallel and downstream of the ice-shelf front. We

  8. Glacial history and behaviour of Mackay Glacier, Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Selwyn Jones, Richard; Mackintosh, Andrew; Norton, Kevin; Golledge, Nicholas; Fogwill, Christopher

    2014-05-01

    The configuration of Antarctic ice sheets is inherently linked to changes in climate and the encircling oceans. Direct observations of Antarctica have shown that changes are possible on the timescale of years to decades (Pritchard et al., 2012), but ice sheets also respond on longer timescales. Understanding the changes that occurred since the Last Glacial Maximum (LGM) is therefore vital for evaluating longer-term drivers of ice sheet changes. The Ross Sea embayment drains both the marine-based West Antarctic Ice Sheet (WAIS) as well as some of the East Antarctic Ice Sheet (EAIS) through the Transantarctic Mountains. At the LGM, grounded ice extended to the outer continental shelf (Shipp et al., 1999; Anderson et al., 2002). Timing of the subsequent deglaciation currently indicates that deglaciation in the Ross Sea Embayment initiated at ca. 14 ka (Licht et al., 1999), continued during the Holocene and slowed and/or stopped in recent millennia. To the east of the Ross Sea Embayment in West Antarctica, surface-exposure dating indicates thinning was underway by 11 ka (Stone et al., 2003) and in a similar manner to the Ross Sea, continued throughout the Holocene. A very rapid and large global sea level rise, known as Meltwater Pulse 1a, occurred during the last global deglaciation, between around 15 and 14 ka. Existing chronologies appear to indicate that Antarctic deglaciation slightly post-dated this event (e.g. Stone et al., 2003; Bentley et al., 2006; Mackintosh et al., 2011). In contrast, relative sea level evidence (Deschamps et al., 2012) and reinterpretation of geological data (Carlson & Clark, 2012) suggest that Antarctica was a significant contributor. Further direct constraints on the timing of deglaciation from Antarctica are required to test these competing hypotheses. This project aims to better reconstruct the configurations of the EAIS and WAIS in the Transantarctic Mountains region at the LGM, specifically of the Mackay Glacier system which has not

  9. An inventory of glacial lakes in the Austrian Alps

    NASA Astrophysics Data System (ADS)

    Buckel, Johannes; Otto, Jan-Christoph; Keuschnig, Markus; Götz, Joachim

    2016-04-01

    The formation of lakes is one of the consequences of glacier retreat due to climate change in mountain areas. Numerous lakes have formed in the past few decades in many mountain regions around the globe. Some of these lakes came into focus due to catastrophic hazard events especially in the Himalayas and the Andes. Glacial lake development and lifetime is controlled by the complex interplay of glacier dynamics, geomorphological process activity and geological boundary conditions. Besides the hazard potential new lakes in formerly glaciated areas will significantly contribute to a new landscape setting and to changing geomorphologic, hydrologic and ecologic conditions at higher alpine altitudes. We present an inventory of high alpine lakes in the Austrian Alps located above an altitude of 1700 m asl. Most of these lakes are assumed to be of glacial origin, but other causes for development, like mass movements are considered as well. The inventory is a central part of the project FUTURELAKES that aims at modelling the potential development of glacial lakes in Austria (we refer to the presentation by Helfricht et al. during the conference for more details on the modelling part). Lake inventory data will serve as one basis for model validation since modelling is performed on different time steps using glacier inventory data. The purpose of the lake inventory is to get new insights into boundary conditions for lake formation and evolution by analysing existing lake settings. Based on these information the project seeks to establish a model of lake sedimentation after glacier retreat in order to assess the potential lifetime of the new lakes in Austria. Lakes with a minimum size of 1000 m² were mapped using multiple aerial imagery sources. The dataset contains information on location, geometry, dam type, and status of sedimentation for each lake. Additionally, various geologic, geomorphic and morphometric parameters describe the lake catchments. Lake data is related to

  10. Indonesian Throughflow variability over the last glacial cycle (Invited)

    NASA Astrophysics Data System (ADS)

    Holbourn, A. E.; Kuhnt, W.; Regenberg, M.; Xu, J.; Hendrizan, M.; Schröder, J.

    2013-12-01

    The transfer of surface and intermediate waters from the Pacific Ocean to the Indian Ocean through the Indonesian archipelago (Indonesian Throughflow: ITF) strongly influences the heat and freshwater budgets of tropical water masses, in turn affecting global climate. Key areas for monitoring past ITF variations through this critical gateway are the narrow passages through the Makassar Strait and Flores Sea and the main outflow area within the Timor Sea. Here, we integrate high-resolution sea surface temperature and salinity reconstructions (based on paired planktic foraminiferal Mg/Ca and δ18O) with X-ray fluorescence runoff data and benthic isotopes from marine sediment cores retrieved in these regions during several cruises with RV'Sonne' and RV'Marion Dufresne'. Our results show that high latitude climate variability strongly influenced ITF intensity on millennial to centennial timescales as well as on longer glacial-interglacial timescales. Marked declines in ITF strength occurred during Heinrich events and the Younger Dryas, most likely related to slowdown of the global thermohaline circulation during colder northern hemisphere climate spells, when deep water production decreased and the deep ocean became more stratified. Additionally, the surface component of the ITF strongly reflects regional windstress and rainfall patterns, and thus the spatial extent and intensity of the tropical convection over the Indonesian archipelago. Our runoff and salinity estimates reveal that the development of the tropical convection was intricately linked to the latitudinal migration of the Inter Tropical Convergence Zone (ITCZ). In particular, our data show that the Australian monsoon intensified during the major deglacial atmospheric CO2 rise through the Younger Dryas and earliest Holocene (12.9-10 ka). This massive intensification of the Australian monsoon coincided with a southward shift of the ITCZ, linked to southern hemisphere warming and enhanced greenhouse forcing

  11. Glacial termination hydroclimate in the Indo-Pacific Warm Pool

    NASA Astrophysics Data System (ADS)

    Yuan, S.; Wang, X.; Chiang, H. W.; Bijaksana, S.; Jiang, X.; Imran, A. M.; Wicaksono, S. A.

    2014-12-01

    Hydroclimatic change in the Indo-Pacific Warm Pool (IPWP), the largest center of atmospheric deep convection on Earth, can have a profound influence on the global moisture and energy budgets. Although it has been extensively studied, the history of IPWP hydroclimate remains elusive, partially due to the scarcity of well-resolved hydroclimiate records from the region. Here we report a U/Th dated, high-resolution, calcite d18O record on IPWP hydroclimatic change, spanning the last glacial termination (termination-I or T-I) and the interval of time from the Marine Isotope Stage (MIS) 12 to MIS11 (termination-V or T-V). The record was obtained using speleothems collected from Southwest Sulawesi (S5o1', E119o44'), Indonesia. During T-I, the Sulawesi speleothem δ18O shows a few millennial-scale events, possibly a drier climate during the Younger Dryas (YD) and Heinrich Stadial 1 (HS1), but a relatively wet climate during the last glacial maximum (LGM) and the Bolling-Allerod (B-A). The pattern resembles those registered in the speleothem records from eastern China and Borneo. However, the Sulawesi d18O varies from ~ -5.8‰ to ~ -7.3‰ during the last termination, which is much smaller than the magnitudes shown in China and Borneo cave samples (~ 4‰). On the other hand, the Sulawesi cave record is anti-correlated with the Flores speleothem record in terms of their millennial-scale events. Yet, the two Indonesian records share a similar, small d18O variation (~1.5‰). Such observations therefore suggest that the Intertropical Convergence Zone (ITCZ) probably became narrower when responding to the northern high-latitude climatic forcing during the T-I, and it centered zonally between the two Indonesian locations. Interestingly, Sulawesi speleothem d18O has a larger magnitude of shift during T-V, from ~ -5.7‰ in MIS12 to ~ -8.7‰ at the peak of MIS11. Given that Sulawesi cave d18O is not sensitive to sea level change and orbital forcing, we suspect that a much lower

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

    NASA Astrophysics Data System (ADS)

    Katz, R. F.; Crowley, J. W.; Langmuir, C. H.

    2012-12-01

    Glacial cycles redistribute water between the oceans and continents, causing long-wavelength changes of static pressure in the upper mantle. Previous work has shown that subaerial, glaciated volcanoes respond to these changes with variation in eruption rates (Jull & McKenzie 1996, Huybers & Langmuir 2009), and has suggested that the magmatic flux at mid-ocean ridges may vary with changes in sea-level (Huybers & Langmuir 2009, Lund & Asimow 2011). The latter is speculative, however, because previous theory has assumed highly simplified melt transport and neglected the dependence of the ridge thermal structure on spreading rate. Moreover, it remains a challenge to connect model predictions of variations arising from sea-level change with sea-floor observations. Here we present results from a theoretical model of a mid-ocean ridge based on conservation of mass, momentum, energy, and composition for two phases (magma & mantle) and two thermodynamic components (enriched & depleted) (Katz 2008, 2010). The model is driven by imposed variations in the static pressure within the mantle. We consider both the geochemically inferred record of past sea-level variation, as well as simpler harmonic and instantaneous variations. The output of these models is compared with observations of bathymetry at ridges that are undisturbed by off-axis volcanism. The comparison is preliminary but suggests that some abyssal hills on the sea-floor are, at least in part, the result of glacial cycles. To understand the simulation results in more detail, we develop analytical solutions for a reduced-complexity model. This model is derived according to the idea that the melting induced by sea-level changes can be thought of as a small perturbation to a steady-state system. We obtain a Green's function solution for crustal thickness as a function of sea-level change with the associated dependencies on geophysical parameters of the magma/mantle system. We show that this solution captures much of the

  13. Noble Gas Signatures in Athabasca Glacier - Tracing Glacial Meltwater Sources

    NASA Astrophysics Data System (ADS)

    Niu, Y.; Hall, C. M.; Castro, M. C.; Aciego, S.; Arendt, C. A.

    2015-12-01

    We present a noble gas study in glacial meltwater (GMW) from the Athabasca Glacier (AG) in the Columbia Icefield, Canada. It constrains the relative contributions of GMW sources, water residence times, and spatial locations where the GMW originates in the alpine glacier. This is possible due to the conservative nature of noble gases and temperature dependency of their concentrations in water in equilibrium with the atmosphere (ASW) which allows for estimation of the altitude at which GMW originated. In addition, crustal He accumulates in water over time, allowing for estimation of water residence times. Water samples were collected in the morning on selected dates in May and July 2011 at two locations about 200 m apart near the terminus area at altitudes between 2000 m and 2100 m. Eight samples were collected in six different days. Results show that the major source of subglacial meltwater is ASW rather than old, compressed glacial ice, which has a distinct noble gas signature not seen in our samples. Given that, GMW samples from the AG do deviate to a certain extent from the ASW values corresponding to measured water temperature and altitude at collection points. Two patterns are observed in the concentrations of the AG samples. The first one presents a relative Ar enrichment with respect to Ne, Kr, and Xe, first observed in high-altitude springs in the Galápagos Islands (Warrier et al., 2012). The second one displays a mass-dependent pattern, first observed in Michigan rainwater (Warrier et al., 2013). A preliminary Xe analysis indicates equilibration altitudes between 2500 m and 3400 m, values compatible with local topography. Samples present He excess of 4% to 91%, and suggest an average residence time of ~400 yrs. References:Warrier, R. B., Castro, M. C., and Hall, C. M. (2012), Recharge and source-water insights from the Galapagos Islands using noble gases and stable isotopes, Water Resour. Res., 48, W03508, doi:10.1029/2011WR010954. Warrier, R. B., Castro

  14. A comparison of eastern North American seismic strain-rates to glacial rebound strain-rates

    NASA Technical Reports Server (NTRS)

    James, Thomas S.; Bent, Allison L.

    1994-01-01

    Glacial rebound strain-rates computed using a simple Laurentide glacial loading model are of the order of 10(exp -9) per year within the region of glaciation and extending several hundred kilometers beyond. The horizontal strain-rates receive approximately equal contributions from horizontal and vertical velocities, a consequence of the spherical geometry adopted for the Earth model. In the eastern United States and southeastern Canada the computed strain-rates are 1-3 orders of magnitude greater than an estimate of the average seismic strain-rate (Anderson, 1986) and approximately 1 order of magnitude greater than predicted erosional strain-rates. The predicted glacial rebound strain-rates are not, in general, oriented in such a way as to augment the observed state of deviatoric stress, possibly explaining why the seismic strain-rates are much smaller than the glacial rebound strain-rates. An exception to this may be seismically active regions in the St. Lawrence valley.

  15. The Dorsa Argentea Formation and the Noachian-Hesperian Transition: Climate and Glacial Flow Modeling

    NASA Astrophysics Data System (ADS)

    Scanlon, K. E.; Head, J. W.; Fastook, J. L.; Wordsworth, R. D.

    2016-09-01

    We used early Mars GCM and glacial flow model simulations to constrain climates allowing development, basal melting, and recession of an ice sheet consistent with the Noachian-Hesperian landforms and geologic units at the south pole of Mars.

  16. Glacial landforms in Ius Chasma, Mars — Indicators of Two Glaciation Episodes

    NASA Astrophysics Data System (ADS)

    Dębniak, K. T.; Kromuszczyńska, O.

    2016-06-01

    Results of geomorphological mapping of glacial landforms in Ius Chasma, Valles Marineris, Mars are presented. The results indicate at least two episodes of glaciations which occurred in the trough system.

  17. Lithological and structural controls for glacial valley development in the Valais, Swiss Alps

    NASA Astrophysics Data System (ADS)

    Valla, P. G.; Herman, F.; Champagnac, J.-D.

    2009-04-01

    Quaternary glaciations affected most modern mountain ranges and shaped glacial landscapes including U-shaped valleys, overdeepenings, cirques and ridgelines. Glacial valley formation has been explained using qualitative morphometric evidence or small-scale models (e.g., MacGregor et al., 2000); however glacial erosion rates and the timing of glacial valley formation are presently poorly understood. Glacial erosion is often approximated by scaling erosion rates to the basal sliding velocity of ice (e.g., Herman and Braun, 2008); and several studies show that the faster erosion occurs at the Equilibrium Line Altitude (ELA, e.g., Anderson et al., 2006). Furthermore it has been proposed that lithology and structural control influence glacial erosion (Harbor, 1995). The Valais in the Swiss Alps is an ideal natural laboratory to better understand these issues. This area is mainly drained by the Rhône valley, a large and overdeepened U-shaped valley; with several high relief transverse valleys. The geology of the area is contrasted, most transverse valleys cut into Penninic metamorphic rocks, whereas the Rhône valley lies mainly on soft Mesozoic sedimentary sequences, highly fracturated by the long-lived Rhône-Simplon fault zone (e.g., Hubbard and Mancktelow, 1992; Champagnac et al., 2003). This context is thus ideal to test potential lithological and/or structural controls on glacial valley formation. We used a 2D numerical model (Herman and Braun, 2008) that is calibrated using the sediment budget record since the Last Glacial Maximum (Hinderer, 2001), LGM ice-surface geometry (Kelly et al., 2004), and field observations. We first explore the effects of initial topographic conditions on the computed erosion patterns. Using a uniform lithology, the predicted glacial erosion patterns do not enable explaining the contrast between the overdeepened Rhône valley and its lateral tributaries. Lithological dependent erosion law is therefore necessary to explain these spatial

  18. Millennial climatic fluctuations are key to the structure of last glacial ecosystems.

    PubMed

    Huntley, Brian; Allen, Judy R M; Collingham, Yvonne C; Hickler, Thomas; Lister, Adrian M; Singarayer, Joy; Stuart, Anthony J; Sykes, Martin T; Valdes, Paul J

    2013-01-01

    Whereas fossil evidence indicates extensive treeless vegetation and diverse grazing megafauna in Europe and northern Asia during the last glacial, experiments combining vegetation models and climate models have to-date simulated widespread persistence of trees. Resolving this conflict is key to understanding both last glacial ecosystems and extinction of most of the mega-herbivores. Using a dynamic vegetation model (DVM) we explored the implications of the differing climatic conditions generated by a general circulation model (GCM) in "normal" and "hosing" experiments. Whilst the former approximate interstadial conditions, the latter, designed to mimic Heinrich Events, approximate stadial conditions. The "hosing" experiments gave simulated European vegetation much closer in composition to that inferred from fossil evidence than did the "normal" experiments. Given the short duration of interstadials, and the rate at which forest cover expanded during the late-glacial and early Holocene, our results demonstrate the importance of millennial variability in determining the character of last glacial ecosystems.

  19. Paraglacial Geomorphology on Mars: A Conceptual Framework for Post-Glacial Geomorphic Processes

    NASA Astrophysics Data System (ADS)

    Jawin, E. R.; Head, J. W.; Marchant, D. R.

    2014-07-01

    The paraglacial period is a terrestrial post-glacial phase that describes the environmental response to deglaciation. We use this period as a framework for analyzing martian impact craters that bear evidence of ice accumulation, flow, and loss.

  20. Perennial mounds in Utopia Planitia: (HiRISE) Evidence of a Glacial Origin

    NASA Astrophysics Data System (ADS)

    Soare, R. J.; Osinski, G. R.; Thomson, L.

    2009-03-01

    Here, we use HiRISE and high-resolution MOC images to discuss sub-kilometer pingo-like mounds in Utopia Planita. The mounds show geological characteristics consistent with formation by glacial accumulation, and ablation by sublimation.

  1. Glacial Acetic Acid Adverse Events: Case Reports and Review of the Literature

    PubMed Central

    Doles, William; Wilkerson, Garrett; Morrison, Samantha

    2015-01-01

    Glacial acetic acid is a dangerous chemical that has been associated with several adverse drug events involving patients over recent years. When diluted to the proper concentration, acetic acid solutions have a variety of medicinal uses. Unfortunately, despite warnings, the improper dilution of concentrated glacial acetic acid has resulted in severe burns and other related morbidities. We report on 2 additional case reports of adverse drug events involving glacial acetic acid as well as a review of the literature. A summary of published case reports is provided, including the intended and actual concentration of glacial acetic acid involved, the indication for use, degree of exposure, and resultant outcome. Strategies that have been recommended to improve patient safety are summarized within the context of the key elements of the medication use process. PMID:26448660

  2. Glacial refugia and the phylogeography of Steller's sea lion (Eumatopias jubatus) in the North Pacific.

    PubMed

    Harlin-Cognato, A; Bickham, J W; Loughlin, T R; Honeycutt, R L

    2006-05-01

    Mitochondrial DNA sequence data were used to examine the phylogeographic history of Steller's sea lions (Eumetopias jubatus) in relation to the presence of Plio-Pleistocene insular refugia. Cytochrome b and control region sequences from 336 Steller's sea lions reveal phylogenetic lineages associated with continental refugia south of the ice sheets in North America and Eurasia. Phylogenetic analysis suggests the genetic structure of E. jubatus is the result of Pleistocene glacial geology, which caused the elimination and subsequent reappearance of suitable rookery habitat during glacial and interglacial periods. The cyclic nature of geological change produced a series of independent population expansions, contractions and isolations that had analogous results on Steller's sea lions and other marine and terrestrial species. Our data show evidence of four glacial refugia in which populations of Steller's sea lions diverged. These events occurred from approximately 60,000 to 180,000 years BP and thus preceded the last glacial maximum.

  3. Glacial and Quaternary geology of the northern Yellowstone area, Montana and Wyoming

    USGS Publications Warehouse

    Pierce, Kenneth L.; Licciardi, Joseph M.; Krause, Teresa R.; Whitlock, Cathy

    2014-01-01

    This field guide focuses on the glacial geology and paleoecology beginning in the Paradise Valley and progressing southward into northern Yellowstone National Park. During the last (Pinedale) glaciation, the northern Yellowstone outlet glacier flowed out of Yellowstone Park and down the Yellowstone River Valley into the Paradise Valley. The field trip will traverse the following Pinedale glacial sequence: (1) deposition of the Eightmile terminal moraines and outwash 16.5 ± 1.4 10Be ka in the Paradise Valley; (2) glacial recession of ~8 km and deposition of the Chico moraines and outwash 16.1 ± 1.7 10Be ka; (3) glacial recession of 45 km to near the northern Yellowstone boundary and moraine deposition during the Deckard Flats readjustment 14.2 ± 1.2 10Be ka; and (4) glacial recession of ~37 km and deposition of the Junction Butte moraines 15.2 ± 1.3 10Be ka (this age is a little too old based on the stratigraphic sequence). Yellowstone's northern range of sagebrush-grasslands and bison, elk, wolf, and bear inhabitants is founded on glacial moraines, sub-glacial till, and outwash deposited during the last glaciation. Floods released from glacially dammed lakes and a landslide-dammed lake punctuate this record. The glacial geologic reconstruction was evaluated by calculation of basal shear stress, and yielded the following values for flow pattern in plan view: strongly converging—1.21 ± 0.12 bars (n = 15); nearly uniform—1.04 ± 0.16 bars (n = 11); and strongly diverging—0.84 ± 0.14 bars (n = 16). Reconstructed mass balance yielded accumulation and ablation each of ~3 km3/yr, with glacial movement near the equilibrium line altitude dominated by basal sliding. Pollen and charcoal records from three lakes in northern Yellowstone provide information on the postglacial vegetation and fire history. Following glacial retreat, sparsely vegetated landscapes were colonized first by spruce parkland and then by closed subalpine forests. Regional fire activity

  4. The Last Glacial Maximum experiment in PMIP4-CMIP6

    NASA Astrophysics Data System (ADS)

    Kageyama, Masa; Braconnot, Pascale; Abe-Ouchi, Ayako; Harrison, Sandy; Lambert, Fabrice; Peltier, W. Richard; Tarasov, Lev

    2016-04-01

    The Last Glacial Maximum (LGM), around 21,000 years ago, is a cold climate extreme. As such, it has been the focus of many studies on modelling and climate reconstruction, which have brought knowledge on the mechanisms explaining this climate, in terms of climate on the continents and of the ocean state, and in terms relationships between climate changes over land, ice sheets and oceans. It is still a challenge for climate or Earth System models to represent the amplitude of climate changes for this period, under the following forcings: - Ice sheets, which represent perturbations in land surface type, altitude and land/ocean distribution - Atmospheric composition - Astronomical parameters Feedbacks from the vegetation and dust are also known to have played a role in setting up the LGM climate but have not been accounted for in previous PMIP experiments. In this poster, we will present the experimental set-up of the PMIP4 LGM experiment, which is presently being discussed and will be finalized for March 2016. For more information and discussion of the PMIP4-CMIP6 experimental design, please visit: https://wiki.lsce.ipsl.fr/pmip3/doku.php/pmip3:cmip6:design:index

  5. Evidence of late glacial runoff in the lower Mississippi Valley

    NASA Astrophysics Data System (ADS)

    Saucier, Roger T.

    Thousands of cubic kilometers of massive coarse-grained glacial outwash underlie the alluvial plain of the Lower Mississippi Valley between Cairo, Illinois, and the Gulf of Mexico. However, valley trains deposited by braided streams characterize less than one-third of the valley area, and those attributable to runoff from the Laurentide Ice Sheet cover less than 15,000 km2, mostly in the St. Francis Basin segment of the valley. There they form a series of subdued terraces that reflect episodes of meltwater release and possibly catastrophic flood events. Radiocarbon-dated sediment cores establish that the initial runoff entered the basin about 16.3 ka BP and continued without a significant lull for about 5000 years. The distribution of archeological sites tends to support an effective brief cessation of runoff to the valley about 11.0 ka BP when meltwater is thought to have been diverted from the Mississippi River Valley to the St. Lawrence Valley. Both radiocarbon dates and archeological evidence document a final pulse of outwash to the (Lower) Mississippi Valley about 10.0 ka BP when the Mississippi River occupied Thebes Gap near Cairo and created the Charleston Fan. All outwash deposition ended, and the river adopted a meandering regime not later than 9.8 ka BP.

  6. Numerical modelling of iceberg calving force responsible for glacial earthquakes

    NASA Astrophysics Data System (ADS)

    Sergeant, Amandine; Yastrebov, Vladislav; Castelnau, Olivier; Mangeney, Anne; Stutzmann, Eleonore; Montagner, Jean-Paul

    2016-04-01

    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 geometric factors on the force history, amplitude and duration at the laboratory and field scales. We show first insights into the force and the generated seismic waves exploring different scenarios for iceberg capsizing.

  7. Glacial Isostatic Adjustment - a hot topic in cold regions

    NASA Astrophysics Data System (ADS)

    Whitehouse, Pippa

    2016-04-01

    Glacial Isostatic Adjustment (GIA) modelling tackles the classic geodynamical problem of determining the solid Earth response to surface load changes by ice and ocean water whilst at the same time solving for the gravitationally-consistent redistribution of ice sheet meltwater across the global ocean. Understanding this process is important for quantifying both present-day ice mass balance and the response of ice sheets to past and future climatic change. The two fundamental unknowns in this problem are (i) the rheology of the solid Earth, and (ii) the history of global ice sheet change. In this talk I will discuss the myriad of approaches that are used to constrain these two components. In particular, I will focus on Antarctica, where the presence of a continuously-evolving ice sheet, situated on top of one of the most rheologically-diverse regions of the planet, provides us with a challenge that can only be resolved by drawing on knowledge from across the fields of geodynamics, glaciology, geology, geodesy and seismology.

  8. Climate driven thresholds for post-glacial soil development (Invited)

    NASA Astrophysics Data System (ADS)

    Dixon, J. L.; Chadwick, O.

    2013-12-01

    We explore thresholds in soil development along a strong climate gradient in the South Island of New Zealand. Soils are developed in thin (~1m) loess deposits that mantle LGM and post LGM moraines and outwash in the Waitaki catchment, extending from Lake Benmore in the south to just below the Tasman glacier in the north. We sampled 28 soil profiles across a strong precipitation gradient spanning 400-4000 mm/yr. Base cations in soils are increasingly leached as rainfall increases and soil pH decreases along the climate gradient. The pools of exchangeable iron and aluminum increase with rainfall while pools of plant available nutrients decrease. Several soil processes are nonlinearly affected by rainfall and we identify two important thresholds for soil development in these loessal soils. The first occurs at approximately 800 mm/yr where the soil leaching intensity increases markedly with rainfall, likely associated with the transition to a positive water balance. The second occurs at high rainfall (~2000 mm/yr) where soils become depleted in labile nutrients and base cations, and extractable Al and Fe concentrations no longer increase with increasing rainfall. Together these data identify nonlinear changes in weathering intensity with rainfall, and show clear climate control on relatively young, post-glacial soil development.

  9. The cryosphere and glacial permafrost as its integral component

    NASA Astrophysics Data System (ADS)

    Dobiński, Wojciech

    2012-12-01

    Since Earth sciences have undertaken studies of other celestial bodies, its various fields have moved beyond the scope of study assigned to them by name. Interest in space makes it necessary to abandon research geocentrism and reverse relations when comparing the structure of the Earth with other celestial bodies. As an exceptional place in the universe, it should not be the Earth which constitutes a reference point, especially in cryospheric research, but rather the other celestial bodies of our planetary system. This approach, referred to as "Spatial Uniformitarianism," is the basis for determining the place of ice in the environment and for assigning it to the lithosphere. Ice can be penetrated by frost just as other minerals and rocks, so the occurrence of permafrost may yet be attributed to glaciers and ice-caps. In the article, the occurrence of glacial permafrost has been worked out on the basis of a thermal classification of glaciers with a thorough understanding of the phenomenon. This allows us to specify permafrost's presence beneath glaciers and ice-caps, a concept which had been needlessly vague. Further, by considering rock glaciers as a mixture of two types of rocks, and by understanding the importance of movement in their evolution, we are now closer to fruitfully determining their role in the environment, their geomorphological significance.

  10. Identifying spatial variations in glacial catchment erosion with detrital thermochronology

    NASA Astrophysics Data System (ADS)

    Ehlers, Todd A.; Szameitat, Annika; Enkelmann, Eva; Yanites, Brian J.; Woodsworth, Glenn J.

    2015-06-01

    Understanding the spatial distribution of glacial catchment erosion during glaciation has previously proven difficult due to limited access to the glacier bed. Recent advances in detrital thermochronology provide a new technique to quantify the source elevation of sediment. This approach utilizes the tendency of thermochronometer cooling ages to increase with elevation and provides a sediment tracer for the elevation of erosion. We apply this technique to the Tiedeman Glacier in the heavily glaciated Mount Waddington region, British Columbia. A total of 106 detrital apatite (U-Th)/He (AHe) and 100 apatite fission track (AFT) single-grain ages was presented from the modern outwash of the Tiedemann Glacier with catchment elevations between 530 and 3960 m. These data are combined with nine AHe and nine AFT bedrock ages collected from a ~2400 m vertical transect to test the hypotheses that erosion is uniformly or nonuniformly distributed in the catchment. A Monte Carlo sampling model and Kuiper statistical test are used to quantify the elevation range where outwash sediment is sourced. Model results from the AHe data suggest nearly uniform erosion in the catchment, with a preference for sediment being sourced from ~2900 to 2700 m elevation. Ages indicated that the largest source of sediment is near the present-day ELA. These results demonstrate the utility of AHe detrital thermochronology (and to a lesser degree AFT data) to quantify the distribution of erosion by individual geomorphic processes, as well as some of the limitations of the technique.

  11. N2 glacial flow on and onto Sputnik Planum

    NASA Astrophysics Data System (ADS)

    Umurhan, O. M.; Moore, J. M.; Howard, A. D.; McKinnon, W. B.; Nimmo, F.; Schenk, P.; White, O. L.; Grundy, W. M.; Stern, A.; Olkin, C.; Weaver, H. A., Jr.; Young, L. A.; Ennico Smith, K.

    2015-12-01

    Sputnik Planum (SP)[1,2] is the high albedo crater-free western portion of Tombaugh Regio imaged in July by the New Horizons LORRI instrument. The relatively high resolution (400 m/pix) LORRI mosaics of the northern portions of the planum bordered by the Cousteau Rupes (CR) scarp reveal surface patterns highly suggestive of viscous flow dynamics. Spectroscopic measurements of SP taken by the New Horizons LEISA instrument also indicate that SP is a region containing (among others) a significant amount of N2 [2]. Taken together these observations suggest the possibility that the high albedo material on SP is glacial N2 ice atop a bedrock-like substrate and the notable lack of craters on SP means that these processes are acting on relatively fast geologic timescales. Using the known properties of N2 ice in the temperature range of interest, we formulate and implement a numerical landform evolution model in order to examine a number of hypothetical evolutionary scenarios for SP and its environs. [1] All place names on Pluto and Charon are informally known as such as of the writing of this abstract. [2] Stern, S. A et al. 2015 Science.

  12. Remote sensing for defining aquifers in glacial drift

    NASA Technical Reports Server (NTRS)

    Myers, V. I.

    1970-01-01

    Investigations were undertaken to determine the properties of shallow aquifers and related features that influence electromagnetic energy, to determine how these properties can be detected remotely, and to establish remote sensing procedures for aiding in ground water mapping. The direct influence of aquifier characteristics on surface thermal contrasts is discussed. Conclusions reached for late summer, predawn missions were: (1) Dynamic thermal changes near the surface can be used for thermal infrared sensing to detect shallow aquifers in glacial drift. (2) Under ideal conditions, surface temperatures may be used to predict certain features related to the occurrence of shallow aquifers. (3) The timing of missions and the optimum meteorological conditions occurring prior to and during the mission are critical for night thermal missions. (4) Repetitive flights made under variable conditions provide additional evidence to verify the occurrence of shallow aquifers. (5) Imagery from this investigation, along with ERTS-simulated imagery, indicates the feasibility of applying ERTS A and B data to reconnaissance studies for detection of shallow aquifers.

  13. Ground movement at Somma-Vesuvius from Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Marturano, Aldo; Aiello, Giuseppe; Barra, Diana; Fedele, Lorenzo; Morra, Vincenzo

    2012-01-01

    Detailed micropalaeontological and petrochemical analyses of rock samples from two boreholes drilled at the archaeological excavations of Herculaneum, ~ 7 km west of the Somma -Vesuvius crater, allowed reconstruction of the Late Quaternary palaeoenvironmental evolution of the site. The data provide clear evidence for ground uplift movements involving the studied area. The Holocenic sedimentary sequence on which the archaeological remains of Herculaneum rest has risen several meters at an average rate of ~ 4 mm/yr. The uplift has involved the western apron of the volcano and the Sebeto-Volla Plain, a populous area including the eastern suburbs of Naples. This is consistent with earlier evidence for similar uplift for the areas of Pompeii and Sarno valley (SE of the volcano) and the Somma -Vesuvius eastern apron. An axisimmetric deep source of strain is considered responsible for the long-term uplift affecting the whole Somma -Vesuvius edifice. The deformation pattern can be modeled as a single pressure source, sited in the lower crust and surrounded by a shell of Maxwell viscoelastic medium, which experienced a pressure pulse that began at the Last Glacial Maximum.

  14. Self-organization of mega-scale glacial lineations

    NASA Astrophysics Data System (ADS)

    Martin, Carlos; Hilmar Gudmundsson, G.; Hogan, Kelly A.; King, Edward; Stokes, Chris R.

    2015-04-01

    Mega-scale glacial lineations (MSGL) are elongate corrugations in sediment that develop under fast-flowing regions in ice sheets. Their distinctive shape and distribution contains information about ice and sediment that is essential to understand the mass imbalance of present and past glaciated areas. Here we use a high-resolution full-Stokes numerical model of coupled flow of ice and sediment to investigate the genesis and evolution of MSGL. We compare our results with field examples from the base of Rutford Ice Stream, Antarctica, and from the now-exposed beds of paleo-ice streams at Anvers Trough, West Antarctic Peninsula, Dotson-Getz Trough, Amundsen Sea, and Dubawnt Lake in the Canadian Shield. We show that the origin of MSGL could be explained by naturally occurring perturbations in the geometry or mechanical properties of the sediment. These original perturbations grow, redistribute and elongate, as the sediment is transported downstream, until they reach a steady configuration. We find that MSGL amplitude is dependent of the strength of the original perturbation; their length is related to the time elapsed from the genesis of the feature; and the lateral spacing between lineations depends mainly on the macroscopic mechanical properties of the sediment. Finally, we conclude that MSGL can be understood as a self-organized system as their geometry and distribution is determined by local interactions between individual lineations and not as a response to the global flow of ice and sediment.

  15. A singularity free approach to post glacial rebound calculations

    NASA Technical Reports Server (NTRS)

    Fang, Ming; Hager, Bradford H.

    1994-01-01

    Calculating the post glacial response of a viscoelastic Earth model using the exponential decay normal mode technique leads to intrinsic singularities if viscosity varies continuously as a function of radius. We develop a numerical implementation of the Complex Real Fourier transform (CRFT) method as an accurate and stable procedure to avoid these singularities. Using CRFT, we investigate the response of a set of Maxwell Earth models to surface loading. We find that the effect of expanding a layered viscosity structure into a continuously varying structure is to destroy the modes associated with the boundary between layers. Horizontal motion is more sensitive than vertical motion to the viscosity structure just below the lithosphere. Horizontal motion is less sensitive to the viscosity of the lower mantle than the vertical motion is. When the viscosity increases at 670 km depth by a factor of about 60, the response of the lower mantle is close to its elastic limit. Any further increase of the viscosity contrast at 670 km depth or further increase of viscosity as a continuous function of depth starting from 670 km depth is unlikely to be resolved.

  16. Bioprospecting glacial ice for plant growth promoting bacteria.

    PubMed

    Balcazar, Wilvis; Rondón, Johnma; Rengifo, Marcos; Ball, María M; Melfo, Alejandra; Gómez, Wileidy; Yarzábal, Luis Andrés

    2015-08-01

    Glaciers harbor a wide diversity of microorganisms, metabolically versatile, highly tolerant to multiple environmental stresses and potentially useful for biotechnological purposes. Among these, we hypothesized the presence of bacteria able to exhibit well-known plant growth promoting traits (PGP). These kinds of bacteria have been employed for the development of commercial biofertilizers; unfortunately, these biotechnological products have proven ineffective in colder climates, like the ones prevailing in mountainous ecosystems. In the present work, we prospected glacial ice collected from two small tropical glaciers, located above 4.900 m in the Venezuelan Andes, for cold-active PGP bacteria. The initial screening strategy allowed us to detect the best inorganic-P solubilizers at low temperatures, from a sub-sample of 50 bacterial isolates. Solubilization of tricalcium phosphate, aluminum- and iron-phosphate, occurred in liquid cultures at low temperatures and was dependent on medium acidification by gluconic acid production, when bacteria were supplied with an appropriate source of carbon. Besides, the isolates were psychrophilic and in some cases exhibited a broad range of growth-temperatures, from 4 °C to 30 °C. Additional PGP abilities, including phytohormone- and HCN production, siderophore excretion and inhibition of phytopathogens, were confirmed in vitro. Nucleotidic sequence analysis of 16S rRNA genes allowed us to place the isolates within the Pseudomonas genus. Our results support the possible use of these strains to develop cold-active biofertilizers to be used in mountainous agriculture.

  17. Interferometric swath processing of Cryosat data for glacial ice topography

    NASA Astrophysics Data System (ADS)

    Gray, L.; Burgess, D.; Copland, L.; Cullen, R.; Galin, N.; Hawley, R.; Helm, V.

    2013-12-01

    We have derived digital elevation models (DEMs) over the western part of the Devon Ice Cap in Nunavut, Canada, using "swath processing" of interferometric data collected by Cryosat between February 2011 and January 2012. With the standard ESA (European Space Agency) SARIn (synthetic aperture radar interferometry) level 2 (L2) data product, the interferometric mode is used to map the cross-track position and elevation of the "point-of-closest-approach" (POCA) in sloping glacial terrain. However, in this work we explore the extent to which the phase of the returns in the intermediate L1b product can also be used to map the heights of time-delayed footprints beyond the POCA. We show that there is a range of average cross-track slopes (~ 0.5 to ~ 2°) for which the returns will be dominated by those beneath the satellite in the main beam of the antenna so that the resulting interferometric phase allows mapping of heights in the delayed range window beyond the POCA. In this way a swath of elevation data is mapped, allowing the creation of DEMs from a sequence of L1b SARIn Cryosat data takes. Comparison of the Devon results with airborne scanning laser data showed a mean difference of order 1 m with a standard deviation of about 1 m. The limitations of swath processing, which generates almost 2 orders of magnitude more data than traditional radar altimetry, are explored through simulation, and the strengths and weaknesses of the technique are discussed.

  18. The Antarctic Circumpolar Current during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, J.; Ito, T.

    2014-12-01

    The circulation and climate of the modern Southern Ocean is dominated by the Antarctic Circumpolar Current (ACC) and associated frontal structures that separate the cold, nutrient-rich Antarctic water masses from the subantarctic and subtropical waters of northern basins. The structure in seawater density across the ACC puts strong constraints on the intensity of the eastward flow. Here we investigate the density structure across the ACC during the Last Glacial Maximum (LGM). We explore the relationship between the lateral density contrast across the ACC and the vertical density stratification north of the ACC in General Circulation Models (GCMs). We employ a compilation of paleoceanographic constraints from the literature, including the oxygen isotopic composition of benthic foraminifera and the chlorinity and oxygen isotopic composition of pore waters in order to reconstruct these vertical and lateral density contrasts south of Australia during the LGM. We infer that the density contrast across the ACC is slightly reduced relative today's. While some model simulations produce a density stratification and ACC much stronger than today's during the LGM, we find the bulk of the paleoceanographic data do not support such a scenario.

  19. Assessment of Glacial Isostatic Adjustment in Greenland using GPS

    NASA Astrophysics Data System (ADS)

    Khan, S. A.; Bevis, M. G.; Sasgen, I.; van Dam, T. M.; Wahr, J. M.; Wouters, B.; Bamber, J. L.; Willis, M. J.; Knudsen, P.; Helm, V.; Kuipers Munneke, P.; Muresan, I. S.

    2015-12-01

    The Greenland GPS network (GNET) was constructed to provide a new means to assess viscoelastic and elastic adjustments driven by past and present-day changes in ice mass. Here we assess existing glacial isostatic adjustments (GIA) predictions by analysing 1995-2015 data from 61 continuous GPS receivers located along the margin of the Greenland ice sheet. Since GPS receivers measure both the GIA and elastic signals, we isolate GIA, by removing the elastic adjustments of the lithosphere due to present-day mass changes using high-resolution fields of ice surface elevation change derived from satellite and airborne altimetry measurements (ERS1/2, ICESat, ATM, ENVISAT, and CryoSat-2). For most GPS stations, our observed GIA rates contradict GIA predictions; particularly, we find huge uplift rates in southeast Greenland of up to 14 mm/yr while models predict rates of 0-2 mm/yr. Our results suggest possible improvements of GIA predictions, and hence of the poorly constrained ice load history and Earth structure models for Greenland.

  20. Eyjabakkajokull Glacial Landsystem, Iceland: Geomorphic Impact of Multiple Surges

    NASA Astrophysics Data System (ADS)

    Ingolfsson, O.; Schomacker, A.; Benediktsson, I.

    2013-12-01

    A new glacial geomorphological map of the Eyjabakkajökull forefield in Iceland is presented. The map covers c. 60 km2 and is based on high-resolution aerial photographs recorded in August 2008 as well as field checking. Landforms are manually registered in a geographical information system (ArcGIS) based on inspection of orthorectified imagery and digital elevation models of the area. We mapped subglacially streamlined landforms such as flutes and drumlins on the till plain, supraglacial landforms such as ice-cored moraine, pitted outwash, and concertina eskers, and ice-marginal landforms such as the large, multi-crested 1890 surge end moraine and smaller single-crested end moraines. The glaciofluvial landforms are represented by outwash plains, minor outwash fans, and sinuous eskers. Extramarginal sediments were also registered and consist mainly of old sediments in wetlands or locally weathered bedrock. Eyjabakkajökull has behaved as a surge-type glacier for 2200 years; hence, the mapped landforms originate from multiple surges. Landforms such as large glaciotectonic end moraines, hummocky moraine, long flutes, crevasse-fill ridges, and concertina eskers are characteristic for surge-type glaciers. The surging glacier landsystem of Eyjabakkajökull serves as a modern analog to the landsystems of terrestrial paleo-ice streams.

  1. Preliminary map showing the thickness of glacial deposits in Ohio

    USGS Publications Warehouse

    Soller, D.R.

    1986-01-01

    In contrast to the extreme variations in drift thickness encountered in the vicinity of buried channels, drift on the upland arcus is generally thinner and the variations in thickness are much less pronounced. Worthy of note, however, are three large areas where the drift sheet is relatively thick. In northwestern Ohio, a large volume of drift was deposited along the flanks of the Erie ice lobe (fig. 2) near the interlobate position with the Saginaw lobe to the northwest; drift thickness there exceeds 200 ft. Thick drift was also deposited in a roughly cast-west band across the Miami lobe. The mechanism that produced this band of thick drift is not obvious, but it may have been influenced in part by bedrock topography. Bedrock control of drift thickness is more clearly indicated to the cast of Columbus, along the eastern flank of the Scioto lobe, where ice slow was resisted by rocks of the Allegheny plateau. The edge of the plateau, or the Allegheny escarpment, is obscured by glacial deposits but its likely position (Fenneman, 1938; Stout and others, 1913; Dove, 1960; and Root and others, 1961) is shown on the map. Southward from the ice margin's reentrant position in southern Richland County, ice flowing eastward from the Scioto lobe encountered the topographically higher plateau, which constrained the ice and caused drift to accumulate in significant thicknesses just to the west of the escarpment.

  2. Glacial biogeography of North American coho salmon (Oncorhynchus kisutch).

    PubMed

    Smith, C T; Nelson, R J; Wood, C C; Koop, B F

    2001-12-01

    To study the glacial biogeography of coho we examined 20 microsatellite loci and mitochondrial DNA D-loop sequence in samples from Alaska to California. Microsatellite data divided our samples among five biogeographic regions: (1) Alaska and northern coastal British Columbia; (2) the Queen Charlotte Islands; (3) the mainland coast of British Columbia and northern Washington State; (4) the Thompson River; and (5) Oregon and California. The D-loop sequence data suggested three geographical regions: (1) Oregon and California; (2) the Thompson River; and (3) all the other sites north of the southern ice margin. Microsatellite data revealed no difference in the number of alleles in different regions, but mitochondrial DNA data revealed a cline of decreasing diversity from south to north. We suggest that the two signals presented by these different marker types illuminate two time frames in the history of this species. Endemic microsatellite diversity in Alaska and on the Queen Charlotte Islands provides evidence in favour of Fraser Glaciation refugia in these regions. The loss of mitochondrial variation from south to north suggests that one of the earlier, more extensive, Pleistocene glaciations eliminated coho from its northern range.

  3. Antarctic glacial history from numerical models and continental margin sediments

    USGS Publications Warehouse

    Barker, P.F.; Barrett, P.J.; Cooper, A. K.; Huybrechts, P.

    1999-01-01

    The climate record of glacially transported sediments in prograded wedges around the Antarctic outer continental shelf, and their derivatives in continental rise drifts, may be combined to produce an Antarctic ice sheet history, using numerical models of ice sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about ice sheet history. The ice sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the ice sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene-Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the Antarctic Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene ice sheet varied considerably in size and areal extent, but the late Miocene ice sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the Antarctic continental margin. Present-day numerical models of ice sheet development are sufficient to guide current sampling plans, but sea-ice formation, polar wander, basal topography and ice streaming can be identified as factors meriting additional modelling effort in the future.

  4. Water quality of two glacial alpine Italian lakes.

    PubMed

    Zelano, Vincenzo; Zambrotta, Maria; Defilippi, Albino; Torazzo, Annamaria

    2005-01-01

    The purpose of this study was to characterize, in a period of one year, two glacial lakes, Alice and Meugliano, located in an alpine reservoir on the basis of physical and chemical features. The two lakes show two periods of mixing: one in the spring and one in the autumn, so can be classified as dimictic lakes. They are characterized by pH, alkalinity, low conductivity and and quite dilute ionic concentrations. With regard to nutrients, most nitrogen occurred in the nitric form in the superficial layers. During the period of thermal stratification, in the anoxic layer NO3- decreases and NH4+ increases, confirming the activity of the anaerobic denitrificant bacteria. Total and soluble phosphorus levels show homogeneity during the cold period at different depths, while with stratification concentrations increase in the hypolimnium and metalimnium. In both lakes there is an inverse correlation between transparency and chlorophyll a. To evaluate the trophic state the conventional criteria of Nurnberg 2 and four lake trophic indices (TSIs) are used. Both evaluations suggest that the two lakes are eutrophic, with worse conditions in Alice. Deviations of the trophic states, based on the relation between TSIs, indicate that factors other than phosphorous limit the algal biomass, and that non-algal particles influence light attenuation

  5. A fundamental Precambrian-Phanerozoic shift in earth's glacial style?

    NASA Astrophysics Data System (ADS)

    Evans, D. A. D.

    2003-11-01

    It has recently been found that Neoproterozoic glaciogenic sediments were deposited mainly at low paleolatitudes, in marked qualitative contrast to their Pleistocene counterparts. Several competing models vie for explanation of this unusual paleoclimatic record, most notably the high-obliquity hypothesis and varying degrees of the snowball Earth scenario. The present study quantitatively compiles the global distributions of Miocene-Pleistocene glaciogenic deposits and paleomagnetically derived paleolatitudes for Late Devonian-Permian, Ordovician-Silurian, Neoproterozoic, and Paleoproterozoic glaciogenic rocks. Whereas high depositional latitudes dominate all Phanerozoic ice ages, exclusively low paleolatitudes characterize both of the major Precambrian glacial epochs. Transition between these modes occurred within a 100-My interval, precisely coeval with the Neoproterozoic-Cambrian "explosion" of metazoan diversity. Glaciation is much more common since 750 Ma than in the preceding sedimentary record, an observation that cannot be ascribed merely to preservation. These patterns suggest an overall cooling of Earth's longterm climate, superimposed by developing regulatory feedbacks involving an increasingly complex biosphere.

  6. A subtropical fate awaited freshwater discharged from glacial Lake Agassiz

    SciTech Connect

    Condron, Alan; Winsor, Peter

    2011-02-10

    The 8.2 kyr event is the largest abrupt climatic change recorded in the last 10,000 years, and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the North Atlantic Ocean. Using a high-resolution (1/6°) global, ocean-ice circulation model we present an alternative view that freshwater discharged from glacial Lake Agassiz would have remained on the continental shelf as a narrow, buoyant, coastal current, and would have been transported south into the subtropical North Atlantic. The pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburst spread over most of the sub-polar North Atlantic, and covered the deep, open-ocean, convection regions. This coastally confined freshwater pathway is consistent with the present-day routing of freshwater from Hudson Bay, as well as paleoceanographic evidence of this event. In this study, using a coarse-resolution (2.6°) version of the same model, we demonstrate that the previously reported spreading of freshwater across the sub-polar North Atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows, producing instead a diffuse circulation that advects freshwater away from the boundaries. To understand the climatic impact of freshwater released in the past or future (e.g. Greenland and Antarctica), the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow, coastal buoyant flows.

  7. 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.

  8. Sea-level variability over five glacial cycles.

    PubMed

    Grant, K M; Rohling, E J; Ramsey, C Bronk; Cheng, H; Edwards, R L; Florindo, F; Heslop, D; Marra, F; Roberts, A P; Tamisiea, M E; Williams, F

    2014-09-25

    Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum 'natural' (pre-anthropogenic forcing) sea-level rise rates below 2 m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2 kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records.

  9. Seasonal variations in vertical migration of glacier lanternfish, Benthosema glaciale.

    PubMed

    Dypvik, Eivind; Røstad, Anders; Kaartvedt, Stein

    2012-01-01

    The seasonal variations in glacier lanternfish (Benthosema glaciale) vertical distribution and diel vertical migration (DVM) were studied by use of a bottom-mounted upward-facing 38 kHz echo sounder deployed at 392 m depth and cabled to shore in Masfjorden (~60°52'N, ~5°24'E), Norway. Acoustic data from July 2007-October 2008 were analyzed, and scattering layers below ~220 m during daytime were attributed to glacier lanternfish based on net sampling in this, and previous studies, as well as from analysis of the acoustic data. At these depths, three different diel behavioral strategies were apparent: normal diel vertical migration (NDVM), inverse DVM (IDVM), and no DVM (NoDVM). NoDVM was present all year, while IDVM was present in autumn and winter, and NDVM was present during spring and summer. The seasonal differences in DVM behavior seem to correlate with previously established seasonal distribution of prey. We hypothesize that in regions with seasonally migrating zooplankton, such as where calanoid copepods overwinter at depth, similar plasticity in DVM behavior might occur in other populations of lanternfishes.

  10. Neoproterozoic cap-dolostone deposition in stratified glacial meltwater plume

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Wang, Zhengrong; Raub, Timothy D.; Macdonald, Francis A.; Evans, David A. D.

    2014-10-01

    Neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of Snowball Earth. Interpretation of these features has remained contentious, with hypotheses hinging upon timescale and synchronicity of deposition, and whether or not geochemical signatures of cap carbonates represent those of a well-mixed ocean. Here we present new high-resolution Sr and Mg isotope results from basal Ediacaran cap dolostones in South Australia and Mongolia. Least-altered Sr and Mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis. These data can be explained by the formation of these cap dolostones involving two chemically distinct solutions, a glacial meltwater plume enriched in radiogenic Sr, and a saline ocean residue with relatively lower 87Sr/86Sr ratios. Model simulations suggest that these water bodies remained dynamically stratified during part of cap-dolostone deposition, most likely lasting for ∼8 thousand years. Our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints. Geochemical data from cap carbonates used to interpret the nature of Snowball Earth and its aftermath should be recast in terms of a chemically distinct meltwater plume.

  11. Large arctic temperature change at the Wisconsin-Holocene glacial transition

    USGS Publications Warehouse

    Cuffey, Kurt M.; Clow, G.D.; Alley, R.B.; Stuiver, M.; Waddington, E.D.; Saltus, R.W.

    1995-01-01

    Analysis of borehole temperature and Greenland Ice Sheet Project II ice-core isotopic composition reveals that the warming from average glacial conditions to the Holocene in central Greenland was large, approximately 15??C. This is at least three times the coincident temperature change in the tropics and mid-latitudes. The coldest periods of the last glacial were probably 21??C colder than at present over the Greenland ice sheet.

  12. Large arctic temperature change at the Wisconsin-Holocene glacial transition

    SciTech Connect

    Cuffey, K.M.; Clow, G.D.; Alley, R.B.

    1995-10-20

    Analysis of borehole temperature and Greenland Ice Sheet Project II ice-core isotopic composition reveals that the warming from average glacial conditions to the Holocene in central Greenland was large, approximately 15{degrees}C. This is at least three times the coincident temperature change in the tropics and mid-latitudes. The coldest periods of the last glacial were probably 21{degrees}C colder than at present over the Greenland ice sheet. 47 refs., 3 figs., 1 tab.

  13. Strong and deep Atlantic meridional overturning circulation during the last glacial cycle.

    PubMed

    Böhm, E; Lippold, J; Gutjahr, M; Frank, M; Blaser, P; Antz, B; Fohlmeister, J; Frank, N; Andersen, M B; Deininger, M

    2015-01-01

    Extreme, abrupt Northern Hemisphere climate oscillations during the last glacial cycle (140,000 years ago to present) were modulated by changes in ocean circulation and atmospheric forcing. However, the variability of the Atlantic meridional overturning circulation (AMOC), which has a role in controlling heat transport from low to high latitudes and in ocean CO2 storage, is still poorly constrained beyond the Last Glacial Maximum. Here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima. Our results are based on a reconstruction of both the strength and the direction of the AMOC during the last glacial cycle from a highly resolved marine sedimentary record in the deep western North Atlantic. Parallel measurements of two independent chemical water tracers (the isotope ratios of (231)Pa/(230)Th and (143)Nd/(144)Nd), which are not directly affected by changes in the global cycle, reveal consistent responses of the AMOC during the last two glacial terminations. Any significant deviations from this configuration, resulting in slowdowns of the AMOC, were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials. Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage, probably as a result of increased fresh-water input. In contrast, the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states, and an active AMOC prevailed during Dansgaard-Oeschger interstadials (Greenland warm periods).

  14. Reduced ventilation and enhanced magnitude of the deep Pacific carbon pool during the last glacial period

    NASA Astrophysics Data System (ADS)

    Skinner, L.; McCave, I. N.; Carter, L.; Fallon, S.; Scrivner, A. E.; Primeau, F.

    2015-02-01

    It has been proposed that the ventilation of the deep Pacific carbon pool was not significantly reduced during the last glacial period, posing a problem for canonical theories of glacial-interglacial CO2 change. However, using radiocarbon dates of marine tephra deposited off New Zealand, we show that deep- (> 2000 m) and shallow sub-surface ocean-atmosphere 14C age offsets (i.e. "reservoir-" or "ventilation" ages) in the southwest Pacific increased by ˜1089 and 337 yrs respectively, reaching ˜2689 and ˜1037 yrs during the late glacial. A comparison with other radiocarbon data from the southern high-latitudes suggests that broadly similar changes were experienced right across the Southern Ocean. If, like today, the Southern Ocean was the main source of water to the glacial ocean interior, these observations would imply a significant change in the global radiocarbon inventory during the last glacial period, possibly equivalent to an increase in the average radiocarbon age > 2 km of ˜ 700 yrs. Simple mass balance arguments and numerical model sensitivity tests suggest that such a change in the ocean's mean radiocarbon age would have had a major impact on the marine carbon inventory and atmospheric CO2, possibly accounting for nearly half of the glacial-interglacial CO2 change. If confirmed, these findings would underline the special role of high latitude shallow sub-surface mixing and air-sea gas exchange in regulating atmospheric CO2 during the late Pleistocene.

  15. Late-Glacial to Late-holocene Shifts in Global Precipitation Delta(sup 18)O

    NASA Technical Reports Server (NTRS)

    Jasechko, S.; Lechler, A.; Pausata, F.S.R.; Fawcett, P.J.; Gleeson, T.; Cendon, D.I.; Galewsky, J.; LeGrande, A. N.; Risi, C.; Sharp, Z. D.; Welker, J. M.; Werner, M.; Yoshimura, K.

    2015-01-01

    Reconstructions of Quaternary climate are often based on the isotopic content of paleo-precipitation preserved in proxy records. While many paleo-precipitation isotope records are available, few studies have synthesized these dispersed records to explore spatial patterns of late-glacial precipitation delta(sup 18)O. Here we present a synthesis of 86 globally distributed groundwater (n 59), cave calcite (n 15) and ice core (n 12) isotope records spanning the late-glacial (defined as 50,000 to 20,000 years ago) to the late-Holocene (within the past 5000 years). We show that precipitation delta(sup 18)O changes from the late-glacial to the late-Holocene range from -7.1% (delta(sup 18)O(late-Holocene) > delta(sup 18)O(late-glacial) to +1.7% (delta(sup 18)O(late-glacial) > delta(sup 18)O(late-Holocene), with the majority (77) of records having lower late-glacial delta(sup 18)O than late-Holocene delta(sup 18)O values. High-magnitude, negative precipitation delta(sup 18)O shifts are common at high latitudes, high altitudes and continental interiors.

  16. Intermittent glacial sliding velocities explain variations in long-timescale denudation

    NASA Astrophysics Data System (ADS)

    Yanites, Brian J.; Ehlers, Todd A.

    2016-09-01

    Quantifying controls on glacial erosion over geologic timescales is central to understanding the role of Cenozoic climate change on the development of modern mountain belts, yet the mechanisms that produce the distinct relief and topography visible in glaciated regions remain poorly constrained. We test the hypothesis that commonly assumed glacial sliding parameterizations control denudation rates over geologic timescales. We do this by modeling glacier dynamics over a glacial-interglacial cycle and compare with a dense dataset of (U-Th)/He thermochronometer derived denudation rates from the southern Coast Mountains, BC. Results indicate zones of rapid Quaternary erosion correspond to locations where the model predicts the highest averaged sliding velocities. The results are consistent with the hypothesis that sliding influences the rate of glacial erosion. Regression between sliding predicted by the model and erosion rates shows a statistically significant correlation (r2 = 0.6). The coefficient of the regression (10-5) is smaller than previous estimates based on data from much shorter timescales. The model results also reveal that for a specific location, active subglacial sliding, and hence erosion, occurs for only ∼10-20% of a glacial-interglacial cycle, suggesting high temporal variations in erosion rates. This intermittency of erosion requires instantaneous erosion rates to be greater than long term averages, explaining how timescale averaging can impact estimates of glacial erosion rates.

  17. Speleothem Paleoclimatology of the Last Glacial Maximum and Deglaciation in Yucatan, Mexico

    NASA Astrophysics Data System (ADS)

    Gentry, C. L.; Hodell, D. A.; Curtis, J. H.; Brenner, M.; Gallup, C.; Endsley, E.

    2006-12-01

    Two speleothems were collected in August 2005 from Columnas Cave near Tzucacab, Yucatan, Mexico. Both stalagmites have basal ages placing the initial growth during the Last Glacial Maximum (LGM). The first sample, Hobo 3, has a basal U/Th age of 21,089 +/- 221 years and the second sample, Hobo 4, has a basal U/Th age of 21,823 +/- 261 years. Oxygen isotopes were measured on calcite samples drilled every 0.5mm along the growth axis of these speleothems. Oxygen isotope values are relatively low at the base of both Hobo 3 and 4 during the LGM, and increase during the period inferred to represent the Late Glacial. Lower oxygen isotopic values during the LGM suggest a cold, wet climate in Yucatan followed by more arid conditions during the Late Glacial. This interpretation is consistent with recent findings from sediment cores from Lake Peten Itza, Guatemala (Hodell et al., 2006). We speculate that a cold, wet LGM may have been caused by increased winter precipitation related to polar outbreaks and "Norte" winds, which bring rain to Yucatan today during the dry season. Arid conditions during the Late Glacial may coincide with delivery of glacial meltwater to the Gulf of Mexico via the Mississippi River. Although additional U/Th dates are needed to constrain the chronology, our preliminary results suggest that Hobo 3 and 4 stalagmites will provide a detailed history of climate change for the northern Yucatan Peninsula during the last glacial cycle.

  18. Glacial-interglacial changes in bottom-water oxygen content on the Portuguese margin

    NASA Astrophysics Data System (ADS)

    Hoogakker, Babette A. A.; Elderfield, Henry; Schmiedl, Gerhard; McCave, I. Nick; Rickaby, Rosalind E. M.

    2015-01-01

    During the last and penultimate glacial maxima, atmospheric CO2 concentrations were lower than present, possibly in part because of increased storage of respired carbon in the deep oceans. The amount of respired carbon present in a water mass can be calculated from its oxygen content through apparent oxygen utilization; the oxygen content can in turn be calculated from the carbon isotope gradient within the sediment column. Here we analyse the shells of benthic foraminifera occurring at the sediment surface and the oxic/anoxic interface on the Portuguese Margin to reconstruct the carbon isotope gradient and hence bottom-water oxygenation over the past 150,000 years. We find that bottom-water oxygen concentrations were 45 and 65 μmol kg-1 lower than present during the last and penultimate glacial maxima, respectively. We calculate that concentrations of remineralized organic carbon were at least twice as high as today during the glacial maxima. We attribute these changes to decreased ventilation linked to a reorganization of ocean circulation and a strengthened global biological pump. If the respired carbon pool was of a similar size throughout the entire glacial deep Atlantic basin, then this sink could account for 15 and 20 per cent of the glacial PCO2 drawdown during the last and penultimate glacial maxima.

  19. Glacial to postglacial transformation of organic input pathways in Arctic Ocean basins

    NASA Astrophysics Data System (ADS)

    Yunker, Mark B.; MacDonald, Robie W.; Snowdon, Lloyd R.

    2009-12-01

    The Arctic Ocean is undergoing rapid loss in ice cover with yet unknown consequences for the cycling of organic material. Here we examine persistent terrigenous (land-based) alkane and polycyclic aromatic hydrocarbons with vascular plant, combustion, and petrogenic sources in seven cores collected from all major basins of the Arctic Ocean for insight as to how organic cycling at the Last Glacial Maximum compares to the present day. We find only modest changes between the glacial and postglacial sediments for atmospherically transported hydrocarbon biomarkers, demonstrating that glacial sea ice was not a barrier to atmospheric inputs. In stark contrast, particle-associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the postglacial period. Evidently the capture of organic matter shifted from the slopes to the shelves as the latter flooded during the Holocene, and the Transpolar Drift and Beaufort Gyre evolved from minor carriers of plant detritus from the glacial ocean margins to major modern transporters of shelf sediment to the basins. This suggests that changes in organic transport currently accompanying the loss of sea ice are likely to be very different from those that occurred at the end of the last glacial period.

  20. Glacial history of the Haizishan Plateau reconstructed from geomorphology, exposure dating and numerical modelling

    NASA Astrophysics Data System (ADS)

    Fu, Ping; Seguinot, Julien; Stroeven, Arjen P.; Harbor, Jonathan M.

    2014-05-01

    The Haizishan Plateau is a low-relief formerly glaciated highland located at a crossroads of continental climate on the Tibetan Plateau and the south-west Asian monsoon. It is surrounded by deeply-cut glacial and fluvial valleys on its flanks, deep basins, and high mountain peaks. Using geomorphological mapping, 10Be exposure dating, and numerical glacier modelling we provide a detailed reconstruction of the Haizishan Plateau glacial history. An ice cap measuring almost 4 000 km2 formed at or before marine oxygen isotope stage 6 (with minimum ages of 102.3±10.0 - 183.6±17.0 ka), and, with a slightly smaller extent, during the global last glacial maximum (21.6±2.0 ka). The dating results are consistent with geomorphology in showing a pattern of patchy glacial erosion on the Haizishan Plateau. Modelling results also support this inference through a patchy pattern of basal temperatures on the plateau surface, and warm-based ice at outlet valleys. Finally, our simulations show that only ca. 3 °C of cooling is required for glacial inception and expansion of the ice cap to its geomorphologically inferred maximum extent, which is consistent with glacial modelling results obtained at other locations on the Tibetan Plateau and consistent with climate modelling.

  1. Constraining the Late Mesozoic and Early Tertiary Tectonic Evolution of Southern Mexico: Structure and Deformation History of the Tierra Caliente Region.

    PubMed

    Cabral-Cano; Draper; Lang; Harrison

    2000-07-01

    We analyze the structure and assess the deformation history of the Tierra Caliente Metamorphic Complex (TCMC) of southern Mexico, where Laramide accretion of exotic terranes is in debate. The TCMC consists of a south-plunging antiform fault that is bounded on both its eastern and western flanks. Tierra Caliente Metamorphic Complex rocks show at least two phases of compressional deformation. The first and most prominent records a mean tectonic transport direction of 068 degrees. This phase is responsible for east-verging asymmetrical folding and thrusting of both metamorphic and superjacent sedimentary rocks. The second phase has an average transport direction of 232 degrees and is restricted to the western portion of the TCMC. A third phase is responsible for normal faulting. Lack of discernible deformation before Late Cretaceous time indicates that the main deformation phase is coincident with Laramide orogenesis elsewhere in the North American Cordillera. The stratigraphy, structure, and deformational history of the TCMC do not require accretion of exotic terranes. We explain the Mesozoic tectonostratigraphic evolution of the TCMC in terms of deposition and deformation of Mesozoic volcanic and sedimentary strata over the attenuated continental crust of the North American plate.

  2. Glacial landscape evolution and sediment export: insights from digital topographic analyses and numerical modelling (Invited)

    NASA Astrophysics Data System (ADS)

    Brocklehurst, S. H.; MacGregor, K. R.

    2013-12-01

    Sediment accumulation rates in the Gulf of Alaska and low-temperature thermochronology from the European Alps, amongst other lines of evidence, indicate accelerated glacial incision and sediment export associated with the Middle Pleistocene Transition (MPT), ~1 Ma. At this time, the change from symmetrical 40-kyr temperature cycles to larger amplitude, asymmetric 100-kyr cycles would have allowed larger, longer lived glaciers to develop, which is inferred as a key contributor to accelerated glacial erosion. Digital topographic analyses comparing glaciated drainage basins of different sizes in the Southern Alps, New Zealand, and Teton Range, western US, amongst others, indicate the importance of scale in glacial landscape development. In smaller drainage basins, or those at the limit of glaciation, landscape modification is primarily restricted to carving characteristic cirques at the heads of valleys. Glaciers may have occasionally spilled from these to carve U-shaped cross-sections downvalley, but without substantial vertical incision. In larger drainage basins with a longer history of glacial occupation, glacial incision has produced shallower downvalley profiles with characteristic glacial steps, presumably accompanied by greater sediment export. A numerical glacial longitudinal profile evolution model, driven by temperature cycles representing either side of the MPT, is used to compare glacial erosion and sediment export from initial Pleistocene glaciations with post-MPT behaviour. The modelled landscape response to the MPT is strongly dependent on the tectonic setting and the behaviour of the fluvial system downstream of the glacier. With no imposed tectonic rock uplift, the major change in the landscape is the carving of cirque forms and glacial longitudinal profiles at the start of the Pleistocene; the MPT would have had little impact on landscape morphology or sediment export. Imposing tectonic as well as isostatic rock uplift, alongside inefficient fluvial

  3. Linking glacial deposits and lake sediments for paleoclimate studies in the Northern Romanian Carpathians

    NASA Astrophysics Data System (ADS)

    Zamosteanu, Andrei; Mindrescu, Marcel; Anselmetti, Flavio; Akçar, Naki; Lowick, Sally E.; Vogel, Hendrik

    2015-04-01

    Timing and extent of glaciations in the Carpathian mountains are still controversely discussed, mostly due to the lack of well dated geomorphological and geochronological studies. We present the preliminary results of geomorphological and sedimentological analyses of glacial and lacustrine deposits in Bistricioara Valley located in the Rodna Mountains (Northern Romanian Carpathians). Most of the glacial deposits in the Romanian Carpathians, such as moraines, typically occur above 1600 m a.s.l. marking the maximum lowering of past glaciations. Most of the glacial lakes occur between 1800 and 2000 m a.s.l. Field surveys included mapping of moraines and erratic boulders using detailed topographical maps and aerial photos. A Digital Elevation Model (DEM) was derived using GIS (ArcMap 10.1) from 1:25000 topographic maps, which was further completed by field survey data. The resulting geomorphological map shows a series of moraines, which indicate the occurrence of several glacial phases in the study area. Sediment samples were collected from a peat bog (1630 m a.s.l.) dammed by a large lateral moraine within Bistricioara Mare, one of the largest glacial cirques in the Romanian Carpathians. A Russian corer was used to extract the sediment profile from the peat bog (approx. 5 m long sediment core). A X-ray computed tomography (CT) system was employed for the study of sedimentary and deformation structures and X-ray fluorescence spectroscopy (XRF) for multi-element analysis at high resolution. Glacial deposits from the lateral moraine in front of the peat bog were also sampled, as well as from the frontal moraines, upstream and downstream of the peat bog. This set of samples from multiple archives allows to link and merge the chronologies and the paleoenvironmental records of glacial deposits and lake sediments. Moreover, we employed cosmogenic nuclide dating for the reconstruction of glacial stages and their paleoclimatic implications during deglaciation in this area of

  4. Quaternary glacial landforms and evolution in the Cantabrian Mountains (Northern Spain): a synthesis from current data

    NASA Astrophysics Data System (ADS)

    Serrano, Enrique; José González-Trueba, Juan; Pellitero, Ramón; González-García, María; Gómez-Lende, Manuel

    2014-05-01

    In Northern Iberian Peninsula are located the Cantabrian Mountains, a mountain system of 450 km length, reaching 2648 m in the Picos de Europa. It is an Atlantic mountain in the North slope, with a Atlantic Mediterranean transitional climate in the South slope.More than thirty-five massifs developed glaciers during the Pleistocene. Studies on glacial morphology are known from the XIX century and they have focused mainly on the maximum extent of glaciers. Nowadays there are detailed geomorphological maps, morphostratigraphic surveys and estimation of Equilibrium Line Altitude in different massifs and on different stages. During the last decade studies on glacial evolution and glaciation phases have been made, and the first chronological data have been published. In this work we presents the reconstruction of the glacial evolution in the Cantabrian Mountains during the Pleistocene and Holocene, based on recent chronological data (30 dates made using OSL, AMS and C14) and morphostratigraphic correlations obtained by several research groups. The number of reconstructed glacial stages varies among the different massifs, form one to four different stages. The highest massifs located in the central portion of the Cantabrian Mountains have the most complex glacial features, with at least four different moraine complexes stepped between the 400 m a.s.l in the Northern slope and 800 m a.s.l. in the Southern slope for the lowest moraine complexes, and the highest and youngest, located above 2100 m a.s.l. An ancient glacial phase has been pointed to MIS 12 -more than 400 ka-, disconnected from the present day glacial morphology. During Upper Pleistocene three main stages have been identified. The first one, the local glacial maximum, could be prior to the LGM, as all dates refer to chronologies prior to 28-38 ka. Some authors locate this stage prior to 45 and 65 ka, during the 50-70 ka cold stage. It could be a wet stage, when the main fronts reached the Iberian Peninsula from

  5. Pb Isotopes as Tracers of Weathering in Glacial Systems

    NASA Astrophysics Data System (ADS)

    Martin, E. E.; Deuerling, K. M.; Scribner, C. A.; Martin, J. B.; Clements, K.

    2013-12-01

    Incongruent chemical weathering of freshly exposed continental material produces weathering solutions with Sr and Pb isotopic values that are distinctly more radiogenic than the parent material. As soils age, weathering becomes more congruent and the isotopic ratio in the solution approaches the composition of parent material. In light of this response, rapid increases in seawater Pb isotopes in the North Atlantic over the last deglacial have been attributed to incongruent weathering of fine grained glacial sediment exposed as the ice sheet retreated. This theory has not been tested using modern glacial river systems due to concerns about contamination by anthropogenic Pb. In this study we analyzed Pb isotopes from: 1) leachates of moraine material, 2) bedload and river water samples along a proglacial river, and 3) sediment and water samples from closed basin lakes in deglaciated terrains, from the Kangerlussuaq region of western Greenland. As expected, 0.1N HCl leachates of moraine soils exhibit 206,207,208Pb/204Pb ratios that are more radiogenic than the bulk soil. Samples from a Little Ice Age moraine close to the Russell Glacier exhibit greater offsets between the leachate and bulk soil Pb isotopes than samples from Orkendalen moraines (6.8 ka), which also record a slightly greater offset than Umivit-Keglen moraines (7.3 ka). Proglacial Watson (Akuliarusuarsuup Kuua) River water samples collected closest to the Russell Glacier also record the most radiogenic Pb isotopes and the largest increase relative to bedload values. Bedload 206Pb/204Pb ratios along the 40 km length of the proglacial river are 14.7+/0.6. Values for all water samples are distinctly more radiogenic than bedload, with the highest value (18.02) closest to the glacier and a general decreasing trend to ~15.82 farthest from the glacier. For comparison to anthropogenic Pb isotopes, 206Pb/207Pb ratios are 1.00+/-.03 for bedload, with water values ranging from 1.18 to 1.06 in a decreasing trend

  6. On the issue of equifinality in glacial geomorphology

    NASA Astrophysics Data System (ADS)

    Möller, Per; Dowling, Thomas; Cleland, Carol; Johnson, Mark

    2016-04-01

    A contemporary trend in glacial geomorphology is the quest for some form of unifying theory for drumlin and/or ribbed moraine formation: there MUST be ONE explanation. The result of this is attempts to apply 'instability theory' to the formation of all drumlinoid and ribbed moraine formation or, as an alternative to this, the 'erodent layer hypothesis' for single processes driven formation. However, based on field geology evidence on internal composition and architecture and the internals relation to the exterior, i.e. the shape of drumlins or ribbed moraine, many glacial sedimentologists would argue that it is instead different processes in their own or in combination that lead to similar form, i.e. look-alike geomorphologic expression or equifinality in spite of different process background for their formation. As expressed by Cleland (2013) from a philosophical point of view of a 'common cause explanation', as exemplified with mass extinctions through geologic time, there is probably a 'common cause explanation' for the K/T boundary extinction (massive meteorite impact on Earth), but this is not a common explanation for every other mass extinction. The parallel to our Quaternary enigma is that there can of course be a single common cause for explaining a specific drumlinoid flow set (a particular case), but that does not have to be the explanation of another flow set showing other sedimentological/structural attributes, in turn suggesting that the particular case cause cannot be used for explaining the general case, i.e. all drumlins over glaciated terrain on the globe. We argue in the case of streamlined terrain, which often have considerable morphologic difference between features at local landscape scale whilst still remaining part of the drumlinoid continuum on regional scale, is a product of different processes or process combinations (erosion/deformation/accumulation) in the subglacial system, tending towards the most efficient obstacle shape and thus

  7. Relative contribution of structural inheritance and glacial morphology on the post-glacial slope destabilization. The Séchilienne slope case study (French western Alps).

    NASA Astrophysics Data System (ADS)

    Schwartz, Stéphane; Zerathe, Swann; Audin, Laurence; Dumont, Thierry; Jarre, Raphael; Jongmans, Denis; Carcaillet, Julien; Dubois, Laurent

    2016-04-01

    In the main Alpine valleys, the chronological constraints about the onset of the slope movements following glacial retreat are scarse. The southern part of the Belledonne massif (French western Alps) along the Romanche valley is affected by numerous slope destabilizations. A detailed geomorphological study using a high resolution LIDAR digital model elevation, allows to characterize the structural framework, the evolution of the glacial retreat and the distribution of the gravitational instabilities. The systematic survey of (i) the main fracturing and (ii) the glacial and gravity morphological witness along the slopes of the Romanche valley coupled with (iii) cosmogenic 10Be dating provides a regional view of the dynamics of slope destabilisation in this area. The proposed scenario allows to evaluate the relative influence of different triggering factors such as seismo-tectonic stresses and climatic changes. These data also allow to propose a consistent dynamic destabilization model of a major lanslide (> 100×106 m3) in relation with the last episode of glacial retreat ~ 21ka ago.

  8. Late glacial 10Be ages for glacial landforms in the upper region of the Taibai glaciation in the Qinling Mountain range, China

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Liu, Liang; Chen, Yixin; Liu, Beibei; Harbor, Jonathan M.; Cui, Zhijiu; Liu, Rui; Liu, Xiao; Zhao, Xu

    2016-01-01

    Glacial landforms are well preserved on Taibai Mountain (3767 m), the main peak of the Qinling mountain range located south of the Loess Plateau and east of the Qinghai-Tibet Plateau. The timing and extent of Quaternary glaciation in the study area is important for reconstructing Quaternary environmental change however numerical ages for glaciation in this study area have not previously been well resolved. Using terrestrial in situ cosmogenic nuclides we dated four samples collected from two glacially eroded rock steps in the upper part of a valley near the main peak, in an area previously identified as having been occupied by ice during the Taibai glaciation. The 10Be results are all late glacial in age: 18.6 ± 1.1 ka, 16.9 ± 1.0 ka, 16.9 ± 1.1 ka and 15.1 ± 1.0 ka. The spatial pattern of ages in the valley suggests fast retreat, with horizontal and vertical retreat rates estimated to be on the order of 0.4 and 0.09 m a-1, respectively. A simple extrapolation of these retreat rates from the ages at the two sample sites suggests that the glacier retreat began during Last Glacial Maximum and that glaciers disappeared from the main peak by about 15 ka.

  9. 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.

  10. Structures and fabrics in glacial ice: A review

    NASA Astrophysics Data System (ADS)

    Hudleston, Peter J.

    2015-12-01

    Glaciers, ice sheets and ice caps represent tectonic systems driven by gravity. Their movement can be studied in real time and the rheological properties and strength of ice determined from laboratory experiments and field measurements. All glacial ice has primary stratification, exhibited by variations in grain size, bubble content and debris content. As it deforms, with deformation dominated by plastic flow and recrystallization, accompanied locally by fracture under tension, a suite of structures develops that reflects the primary fabric of the ice and the anisotropy that develops as a result of cumulative deformation. Initial variations in solid impurity content and strain dependent anisotropy as a result of a crystallographic fabric give rise to effective viscosity increases or decreases compared to isotropic polycrystalline ice of about a factor of ten. Foliation develops from inherited (mostly stratification) or introduced (mostly ice veins or fracture traces) fabric elements and from dynamic recrystallization. It is largely dependent on the accumulated strain, which is highest at the base and near the margins of glaciers, ice sheets and ice streams. Folds develop largely passively due to initial amplification of irregularities in the primary stratification, to variations in flow with time or to inhomogeneous flow associated with shear zones and ductile accommodation around open fractures. Buckle folds and boudinage, mostly on a small scale, occur where viscosity contrast is large, mostly in basal ice. Thrusting and wrench faulting are documented in surging glaciers but theoretically most unlikely and rare or absent elsewhere. Many structures interpreted as faults are not due to shear failure but rather result from shear displacements during opening and closing of tensile fractures.

  11. A subtropical fate awaited freshwater discharged from glacial Lake Agassiz

    DOE PAGES

    Condron, Alan; Winsor, Peter

    2011-02-10

    The 8.2 kyr event is the largest abrupt climatic change recorded in the last 10,000 years, and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the North Atlantic Ocean. Using a high-resolution (1/6°) global, ocean-ice circulation model we present an alternative view that freshwater discharged from glacial Lake Agassiz would have remained on the continental shelf as a narrow, buoyant, coastal current, and would have been transported south into the subtropical North Atlantic. The pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburstmore » spread over most of the sub-polar North Atlantic, and covered the deep, open-ocean, convection regions. This coastally confined freshwater pathway is consistent with the present-day routing of freshwater from Hudson Bay, as well as paleoceanographic evidence of this event. In this study, using a coarse-resolution (2.6°) version of the same model, we demonstrate that the previously reported spreading of freshwater across the sub-polar North Atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows, producing instead a diffuse circulation that advects freshwater away from the boundaries. To understand the climatic impact of freshwater released in the past or future (e.g. Greenland and Antarctica), the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow, coastal buoyant flows.« less

  12. Organic carbon in glacial fjords of Chilean Patagonia

    NASA Astrophysics Data System (ADS)

    Pantoja, Silvio; Gutiérrez, Marcelo; Tapia, Fabián; Abarzúa, Leslie; Daneri, Giovanni; Reid, Brian; Díez, Beatriz

    2016-04-01

    The Southern Ice Field in Chilean Patagonia is the largest (13,000 km2) temperate ice mass in the Southern hemisphere, yearly transporting ca. 40 km3 of freshwater to fjords. This volume of fresh and cold water likely affects adjacent marine ecosystems by changing circulation, productivity, food web dynamics, and the abundance and distribution of planktonic and benthic organisms. We hypothesize that freshwater-driven availability of inorganic nutrient and transport of organic and inorganic suspended matter, as well as microbes, become a controlling factor for productivity in the fjord associated with the Baker river and Jorge Montt glacier. Both appear to be sources of silicic acid, but not of nitrate and particulate organic carbon, especially during summer, when surface PAR and glacier thawing are maximal. In contrast to Baker River, the Jorge Montt glacier is also a source of dissolved organic carbon towards a proglacial fjord and the Baker Channel, indicating that a thorough chemical description of sources (tidewater glacier and glacial river) is needed. Nitrate in fiord waters reaches ca. 15 μM at 25 m depth with no evidence of mixing up during summer. Stable isotope composition of particulate organic nitrogen reaches values as low as 3 per mil in low-salinity waters near both glacier and river. Nitrogen fixation could be depleting δ15N in organic matter, as suggested by the detection at surface waters of nif H genes belonging to diazotrophs near the Montt glacier. As diazotrophs have also been detected in other cold marine waters (e.g. Baltic Sea, Arctic Ocean) as well as glaciers and polar terrestrial waters, there is certainly a potential for both marine and freshwater microbes to contribute and have a significant impact on the Patagonian N and C budgets. Assessing the impact of freshwater on C and N fluxes and the microbial community structure in Patagonian waters will allow understanding future scenarios of rapid glacier melting. This research was funded

  13. Ongoing glacial isostatic contributions to observations of sea level change

    NASA Astrophysics Data System (ADS)

    Tamisiea, Mark E.

    2011-09-01

    Studies determining the contribution of water fluxes to sea level rise typically remove the ongoing effects of glacial isostatic adjustment (GIA). Unfortunately, use of inconsistent terminology between various disciplines has caused confusion as to how contributions from GIA should be removed from altimetry and GRACE measurements. In this paper, we review the physics of the GIA corrections applicable to these measurements and discuss the differing nomenclature between the GIA literature and other studies of sea level change. We then examine a range of estimates for the GIA contribution derived by varying the Earth and ice models employed in the prediction. We find, similar to early studies, that GIA produces a small (compared to the observed value) but systematic contribution to the altimetry estimates, with a maximum range of -0.15 to -0.5 mm yr-1. Moreover, we also find that the GIA contribution to the mass change measured by GRACE over the ocean is significant. In this regard, we demonstrate that confusion in nomenclature between the terms 'absolute sea level' and 'geoid' has led to an overestimation of this contribution in some previous studies. A component of this overestimation is the incorrect inclusion of the direct effect of the contemporaneous perturbations of the rotation vector, which leads to a factor of ˜two larger value of the degree two, order one spherical harmonic component of the model results. Aside from this confusion, uncertainties in Earth model structure and ice sheet history yield a spread of up to 1.4 mm yr-1 in the estimates of this contribution. However, even if the ice and Earth models were perfectly known, the processing techniques used in GRACE data analysis can introduce variations of up to 0.4 mm yr-1. Thus, we conclude that a single-valued 'GIA correction' is not appropriate for sea level studies based on gravity data; each study must estimate a bound on the GIA correction consistent with the adopted data-analysis scheme.

  14. 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.

  15. Distortions of glacial landform sizes by manual mapping

    NASA Astrophysics Data System (ADS)

    Hillier, John K.; Smith, Mike J.

    2016-04-01

    Mapped topographic features are important for understanding processes that sculpt the Earth's surface. Subjective manual techniques are commonly used for mapping, yet how effective they are in quantitative terms is poorly constrained. Here 12,121 outlines drawn by 25 interpreters searching for a total of 21,625 drumlins in 5 synthetic DEMs are interpreted in terms of how the manual mapping process distorts the height (H), width (W) and length (L) of the reported features. Bias in the size-frequency distributions is caused by the sub-set of the forms 'found', even assuming perfect extraction of sizes, and is governed by H driving detectability. Bias is then compounded in sizes that are extracted using the mapped outlines but, remarkably, the size-frequency distribution is not altered further when mappers' incorrect guesses (i.e. outline corresponds to no input synthetic drumlin) are then included; it seems possible that, once mappers have their 'eye in' based on the most clearly defined features, they are very effective at identifying similar morphologies. Of the metrics available to quantify the size of a population, maximum size and λ, the exponent of its tail, are the most robust to these distortions. The drumlins in the study area resemble UK drumlins, permitting extrapolation of the conclusions. These are the first results to give such granular insights into the impacts of the various stages in manually mapping glacial landforms, permitted by the development of the synthetic DEMs. Arguments will always exist about how realistic any synthetic is, but this work demonstrates another use of synthetic DEMs that may be applied more widely in geomorphology.

  16. Glacial lake evolution in the southeastern Tibetan Plateau and the cause of rapid expansion of proglacial lakes linked to glacial-hydrogeomorphic processes

    NASA Astrophysics Data System (ADS)

    Song, Chunqiao; Sheng, Yongwei; Ke, Linghong; Nie, Yong; Wang, Jida

    2016-09-01

    Glacial lakes, as an important component of the cryosphere in the southeastern Tibetan Plateau (SETP) in response to climate change, pose significant threats to the downstream lives and properties of people, engineering construction, and ecological environment via outburst floods, yet we currently have limited knowledge of their distribution, evolution, and the driving mechanism of rapid expansions due to the low accessibility and harsh natural conditions. By integrating optical imagery, satellite altimetry and digital elevation model (DEM), this study presents a regional-scale investigation of glacial lake dynamics across two river basins of the SETP during 1988-2013 and further explores the glacial-hydrogeomorphic process of rapidly expanding lakes. In total 1278 and 1396 glacial lakes were inventoried in 1988 and 2013, respectively. Approximately 92.4% of the lakes in 2013 are not in contact with modern glaciers, and the remaining 7.6% includes 27 (1.9%) debris-contact lakes (in contact with debris-covered ice) and 80 (5.7%) cirque lakes. In categorizing lake variations, we found that debris-contact proglacial lakes experienced much more rapid expansions (∼75%) than cirque lakes (∼7%) and non-glacier-contact lakes (∼3%). To explore the cause of rapid expansion for these debris-contact lakes, we further investigated the mass balance of parent glaciers and elevation changes in lake surfaces and debris-covered glacier tongues using time-series Landsat images, ICESat altimetry, and DEM. Results reveal that the upstream expansion of debris-contact proglacial lakes was not directly associated with rising water levels but with a geomorphological alternation of upstream lake basins caused by melting-induced debris subsidence at glacier termini. This suggests that the hydrogeomorphic process of glacier thinning and retreat, in comparison with direct glacial meltwater alone, may have played a dominant role in the recent glacial lake expansion observed across the

  17. Quantifying Landscape Response to Past (Last Glacial) and Present Day Erosion with Detrital Thermochronology

    NASA Astrophysics Data System (ADS)

    Ehlers, Todd A.; Stock, Greg M.; Farley, Kenneth A.; Yanites, Brian

    2010-05-01

    Quantifying landscape response to climate change is limited by insufficient knowledge of spatial and temporal variations in catchment erosion. Detrital cooling ages collected from Quaternary glacial moraines and modern river sediments provide a tool to address these problems. We use detrital thermochronology to quantify spatial variations in alpine glacial erosion during the Last Glacial Maximum (LGM). Results are compared to the distribution of present-day erosion recorded in samples from modern river sediments, and predicted patterns in glacial erosion from a plan-form (shallow-ice approximation) glacial erosion model. The elevation dependence of detrital apatite (U-Th)/He (AHe) ages is used as a sediment tracer to track the elevations where glacially eroded sediment is produced from bedrock. We measured ~204 AHe single grain ages from three moraines located between 2.3 and 3.7 km elevation in the Lone Pine catchment, Sierra Nevada, California. Measured AHe age probability density functions (PDFs) were compared with predicted PDFs, calculated by convolving bedrock age-elevation relationships with catchment hypsometries clipped at different altitudes to reflect variable source elevations of sediment. Statistical comparison of the PDFs using a Monte Carlo approach and Kuiper test are used to evaluate the spatial distribution of erosion in the catchments. Results from the lowest elevation moraine indicate sediment is produced from the lower 50-70% of catchment elevations at the 95% confidence level, suggesting erosion near the base and sides of the glacier outweigh erosion from higher elevation head wall retreat and rock fall onto the glacier. Furthermore, grain-age distributions from different sediment size fractions are virtually indistinguishable, suggesting either both size fractions are sourced from similar elevations, and/or a significant disaggregation of coarse-grained material into finer material during transport. Finally, the intermediate to high

  18. Linking glacial erosion and low-relief landscapes in tropical orogens

    NASA Astrophysics Data System (ADS)

    Cunningham, M.; Stark, C. P.; Kaplan, M. R.; Schaefer, J. M.; Galewsky, J.; Yoo, J.

    2015-12-01

    One significant way that climate influences orogenic evolution is by modulating glacial erosion. At mid-latitudes it is hypothesized that this climate-tectonic interplay is so strong that a "glacial buzzsaw" acting throughout the Quaternary outpaced tectonic uplift in most mountain belts and concentrated topography in a zone defined by the bounds of ELA fluctuation. Less attention has been paid to how the buzzsaw might manifest itself at low latitudes, where many mountain belts are just high enough to have been glaciated at the LGM but today sit well below the ELA. We have focused on the glacial history of Costa Rica and Taiwan, where we find evidence of ice cap erosion coincident with low-relief landscapes near the LGM ELA. Previous attempts to understand the formation of these perched, low-relief landscapes has mostly concerned interactions between fluvial erosion and geodynamics. Our work aims instead to describe the role that glacial erosion played in the evolution of these landscapes, and how they fit in the buzzsaw paradigm. At Cerro Chirripó in Costa Rica we use 10-Be surface exposure age dating of moraine boulders and scoured bedrock, field mapping, and remote sensing to constrain the timing, areal extent, and pattern of glacial erosion. We made similar observations of ice extent at Nanhudashan in Taiwan, where surface exposure age dating has previously been applied to glacial landforms (e.g. Hebenstreit et al., 2011; Siame et al., 2007). In Costa Rica, our 10-Be dates from scoured bedrock near the highest peak and terminal/lateral moraines show signs of ice-cap erosion until 22 ka. Similar arguments for LGM ice cap erosion have been made for Nanhudashan. Regional climate simulations (WRF) further constrain the timing and spatial extent of glaciation in these places, and the combination of field data and climate modeling will inform estimates of the magnitude of glacial erosion on perched landscapes.

  19. Determining Erosion Rates and Processes in the Pro-Glacial Area over a 28-Year Period

    NASA Astrophysics Data System (ADS)

    Delaney, I. A.; Huss, M.; Weidmann, Y.

    2015-12-01

    Glacially fed hydropower reservoirs in the Swiss Alps have experienced substantial increases in sedimentation recently. This sedimenation causes reduced reservoir capacity, turbine abrasion and increased need for sediment flushing, all of which reduce the efficiency and economic viability of hydropower in the region. Although the issue is largely attributed to regional glacier retreat, there is a need for greater understanding of the specific processes that contribute to the increased sedimentation. To evaluate these processes, we examine the Griesgletscher catchment, which lies in the central Swiss Alps and its runoff feeds a hydropower reservoir. The recent exposure of the glacier's fore-field (roughly 1986) due to the glacier's retreat beyond the reservoir's margin, along with its simple catchment area make it an ideal location to examine pro-glacial erosion. Here we present a time-series from 1986 to 2014 of digital elevation models (DEM) created from aerial photographs of the Griesgletscher's fore-field from each year except for 2. Comparison of DEMs from subsequent years yields erosion volumes and sediment balance over the 28 year period for the pro-glacial area. Bathymetry of the pro-glacial reservoir for select years allows us to speculate if the erosion of the recently exposed glacier fore-field is the sole source of sediment to the reservoir, or if alternative processes such as increased glacial erosion or mobilization of sub-glacial sediments could contribute. We correlate erosion amounts with runoff volumes from the Griesgletscher and changes in the the glacier's morophology and coverage. Additionally, implimentation of the Glacier Evolution Runoff Model allows us to examine the variability in the glacier's runoff on the hourly to daily scale. By examining these relationships we constrain the processes contributing to the erosion of the Griesgletscher's pro-glacial area.

  20. Evolution of the floor of Hellas Basin, Mars: Implications for regional glacial processes

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Christensen, P. R.

    2009-12-01

    Geologic features on Mars show clear evidence of modification by water and water ice. Studies have suggested that ice remains just below the martian surface today buried beneath tens of centimeters of soil. Past obliquity variations have been theorized to have promoted the formation and stability of ground ice near the equator, possibly promoting the accumulation of glaciers and the subsequent formation of periglacial terrain. Potential glacial and periglacial features have also been observed on the rim and floor of Hellas Basin; these include esker-like ridges, drumlin-like hills, grooved terrain (possible glacial scour), moraine-like deposits, lacustrine deposits, lobate debris aprons, and hourglass craters containing flow features. These potential glacial features could indicate present-day near-surface ice, with implications for global hydrologic cycle modeling, astrobiology studies, and the search for resources in the Solar System. We assess the geologically recent effects of ice on the evolution of the surface of this region of Mars by evaluating the spatial distribution of glacial features within and surrounding Hellas Basin. An in-depth survey of visible images and new nighttime infrared images from the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey and visible images from the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO) is undertaken in order to extend high quality coverage of the basin floor and its features. Initial findings confirm widespread morphologic evidence for glacial and periglacial processes on the basin floor, including moraine deposits, flow features and sublimation terrain. Preliminary analyses reveal correlations between glacial features and fluvial and lacustrine deposits, providing insights into the past hydrologic cycle of the region. We quantitatively model the depth to present-day, near-surface ice at glacial and periglacial feature locations throughout the region using

  1. Persistence of full glacial conditions in the central Pacific until 15,000 years ago.

    PubMed

    Blard, P-H; Lavé, J; Pik, R; Wagnon, P; Bourlès, D

    2007-10-04

    The magnitude of atmospheric cooling during the Last Glacial Maximum and the timing of the transition into the current interglacial period remain poorly constrained in tropical regions, partly because of a lack of suitable climate records. Glacial moraines provide a method of reconstructing past temperatures, but they are relatively rare in the tropics. Here we present a reconstruction of atmospheric temperatures in the central Pacific during the last deglaciation on the basis of cosmogenic 3He ages of moraines and numerical modelling of the ice cap on Mauna Kea volcano, Hawaii--the only highland in the central Pacific on which moraines that formed during the last glacial period are preserved. Our reconstruction indicates that the Last Glacial Maximum occurred between 19,000 and 16,000 years ago in this region and that temperatures at high elevations were about 7 degrees C lower than today during this interval. Glacial retreat began about 16,000 years ago, but temperatures were still about 6.5 degrees C lower than today until 15,000 years ago. When combined with estimates of sea surface temperatures in the central Pacific Ocean, our reconstruction indicates that the lapse rate during the Last Glacial Maximum was higher than at present, which is consistent with the proposal that the atmosphere was drier at that time. Furthermore, the persistence of full glacial conditions until 15,000 years ago is consistent with the relatively late and abrupt transition to warmer temperatures in Greenland, indicating that there may have been an atmospheric teleconnection between the central Pacific and North Atlantic regions during the last deglaciation.

  2. 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

  3. Micropaleontological Record of Post-glacial History in Lake Champlain and Adjacent Regions: Implications for Glacial Lake Drainage and Abrupt Climate Events

    NASA Astrophysics Data System (ADS)

    Cronin, T. M.; Manley, P. L.; Guilbault, J.; Berke, M.; Rayburn, J. A.; Franzi, D. A.; Knuepfer, P. L.

    2005-12-01

    Post-glacial lacustrine and marine sediments of the Lake Champlain region range from 20 to >50 meters in thickness presenting an opportunity to assess the timing of North American glacial lake drainage at multidecadal timescales and evaluate its effect on North Atlantic salinity and abrupt climate events 13.5 to 10 kyr B.P. High-resolution analysis of foraminifera and ostracodes from cores taken onshore in the Plattsburgh, N.Y. vicinity and southern Quebec and offshore in southern Lake Champlain reveal complex changes in salinity during and after the transition from pro-glacial Lake Vermont (Lake Candona in Canada) to marine sedimentation in the Champlain Sea. The microfaunal sequence (bottom to top) includes: non-marine ostracodes ( Candona) in lacustrine varves, foraminiferal assemblages (common Cassidulina reniforme), another interval of Candona-bearing sediments (sometimes containing foraminifera), and, finally, sediments from the main phase of the Champlain sea episode containing diverse foraminiferal and marine ostracode assemblages. A decrease in salinity during the Champlain Sea is also in evidence from the shift in dominance of distinct variants of Elphidium in the deep basin. The marine episode ended with a progressive salinity decrease and the formation of Lake Champlain about 10 kyr B.P. Observed salinity changes could be caused by catastrophic fresh-water influx from large glacial lakes west of the Lake Champlain region, meltwater from the retreating Laurentide Ice Sheet margin, diminished influx of marine water from the St. Lawrence due to changes in the position of the ice sheet margin and isostatic adjustment, or a combination of factors. The ages of these events were determined by estimating the reservoir effect on radiocarbon dates on marine shells through comparison with AMS dates on plant material and palynology, and shed light on the hypothesis that glacial lake discharges catalyzed abrupt climate events.

  4. Use of biomarkers in resident organisms as a tool for environmental monitoring in a cold coastal system, Tierra del Fuego Island.

    PubMed

    Comoglio, L; Amin, O; Botté, S; Marcovecchio, J

    2011-03-01

    Antioxidant status of Nacella (P) magellanica and Mytilus edulis related with heavy metal in sediment and tissues were analysed in five stations close to Ushuaia city in winter and spring. The principal component analysis produced a two-dimensional pattern of the degree of similarity between sites. The Industrial-Urban Contamination Index (IUCI) showed that the Industrial Zone (IZ) and Oil Marine Station (OMS) represent areas with anthropic inputs. Heavy metals have differential association with biomarkers depending on the species. In limpets, digestive gland presented major activities of enzyme defence in winter and gonads have shown higher values of Catalase (CAT) during spring while lipid peroxidation (LPO) presented higher values in IZ. For mussels CAT and LPO increased in spring time. For superoxide dismutase (SOD) peaks have been detected in IZ and NW stations for winter. Differences in biomarker responses due to seasons did not influence the grouping of the sites into references and contaminated groups.

  5. Heavy metal concentrations and biomarkers of oxidative stress in native mussels (Mytilus edulis chilensis) from Beagle Channel coast (Tierra del Fuego, Argentina).

    PubMed

    Duarte, Claudia A; Giarratano, Erica; Amin, Oscar A; Comoglio, Laura I

    2011-08-01

    The aim of this study was to evaluate the usefulness of oxidative stress biomarkers of pollution in native mussels Mytilus edulis chilensis from the Beagle Channel. Spatial and seasonal variations of catalase, glutathione-S-transferase and lipid peroxidation in gills and digestive gland were analyzed in relation to environmental parameters, heavy metals in sediment and in tissue. Four sites with anthropogenic impact and a control site were selected and monitored during the four seasons of 2007. We found significant differences among sites in concentrations of dissolved nutrients and heavy metals in sediments, with the highest values recorded at sites with anthropogenic pressure. Different patterns were observed between concentrations of metals in tissues and in sediments suggesting differences in bioavailability. There were also significant differences in biomarker responses among sites, despite the strong seasonal variability. Our results showed relatively moderate levels of pollution in the study area as a result of urban influences.

  6. [Production of soy bean inoculants. Behavior of supports based on peat from Tierra del Fuego sterilized by vapor and ethylene oxide].

    PubMed

    Balatti, A P; Mazza, L A

    1979-01-01

    The survival of Rhizobium japonicum was studied in neutralized and sterilized peats from Ushuaia and Rio Grande. The carriers were sterilized by ethylene oxide and by autoclaving. Similar counts for Rhizobium (5 x 10(8) cel/g) were obtained in peat-cultures sterilized by both methods, after eight months. A good nodulation and nitrogen fixation capacity was observed with inoculated soybean plants. Using the strain Rhizobium japonicum E-45, no appreciable difference in symbiotic effectiveness was found between the inoculants prepared with the two peats.

  7. Flat-slab subduction, orogenesis, intraplate deformation, and glacial erosion in southern Alaska: A tectonic-glacial progression from STEEP

    NASA Astrophysics Data System (ADS)

    Pavlis, T. L.; Gulick, S. S.; Bruhn, R. L.; Christeson, G. L.; Enkelmann, E.; Freymueller, J. T.; Hallet, B.; Horton, B. K.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Ridgway, K. D.; Spotila, J. A.; Van Avendonk, H. J.

    2012-12-01

    The ST. Elias Erosion and tectonics Project (STEEP) is a Continental Dynamics multidisciplinary collaboration involving offshore and onshore studies of a modern example of an oceanic plateau collision with a continental margin in southern Alaska. These studies constrain erosion-tectonic interactions and clarify the timeline of northern Cordilleran orogenesis. At ~55 Ma an oceanic plateau formed on either the Kula-Farallon or Farallon-Resurrection spreading center. From 50-46 Ma, this plateau attempted to subduct beneath an accretionary complex, the Yakutat Group (YG), near offshore British Columbia. The YG was thrust onto the plateau to form what is now the Yakutat Terrane. From ~40 to as late as 33 Ma the Yakutat Terrane was part of North America and the proto-Transition Fault was active moving the remnant Kula Plate towards the Aleutian Trench, slicing off the southern edge of the Yakutat Terrane, and emplacing Pacific crust adjacent to the Terrane. From ~33 to 6 Ma the Yakutat Terrane moved northward with the Pacific Plate. There is some Oligocene paleogeographic uncertainly, but upper plate deformation and basin development starting ~ 20-25 Ma may be Yakutat related. At ~6 Ma the Pacific Plate underwent a clockwise shift in motion reactivating the Transition Fault, albeit at a slow rate, and this motion drove a component of oblique convergence along the Fairweather Fault and orogenesis in the St. Elias. Rejuvenation of the Transition Fault formed a stable triple junction with the Aleutian Trench and the Yakutat-North American subduction front. Uplift in the orogen seeded glacial systems that reached tidewater by ~5.5 Ma and the sediments produced were the glaciomarine, syn-orogenic Yakataga Formation. The eastern syntaxis of the St. Elias orogen began to focus exhumation as thickened crust generated along the transpressive Fairweather system was fed into the fully contractional core of the orogen. Between 4 and 3 Ma, the thicker portions of the Yakutat Terrane

  8. Enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands: A sink for atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Wan, Shiming; Clift, Peter D.; Zhao, Debo; Hovius, Niels; Munhoven, Guy; France-Lanord, Christian; Wang, Yinxi; Xiong, Zhifang; Huang, Jie; Yu, Zhaojie; Zhang, Jin; Ma, Wentao; Zhang, Guoliang; Li, Anchun; Li, Tiegang

    2017-03-01

    Atmospheric CO2 and global climate are closely coupled. Since 800 ka CO2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature, humidity, and erosion rates, chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition. Cooler and drier conditions and lower non-glacial erosion rates suppressed in situ chemical weathering rates during glacial periods. However, using systematic variations in major element geochemistry, Sr-Nd isotopes and clay mineral records from Ocean Drilling Program Sites 1143 and 1144 in the South China Sea spanning the last 1.1 Ma, we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials. We attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for ∼9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial-interglacial variation of ∼80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric CO2 during cold stages of the Quaternary. This in turn would have caused an intensification of glacial cycles.

  9. Luminescence dating of glacial deposits near the eastern Himalayan syntaxis using different grain-size fractions

    NASA Astrophysics Data System (ADS)

    Hu, Gang; Yi, Chao-Lu; Zhang, Jia-Fu; Liu, Jin-Hua; Jiang, Tao

    2015-09-01

    Numerical dating of glacial deposits is important for understanding Quaternary glacial evolution. Optically stimulated luminescence (OSL) dating is one of the techniques widely used on such sediments. Owing to the short distances traveled before deposition, the incomplete bleaching of luminescence signals in glacial sediments may introduce serious dating problems vis-à-vis glacial and any associated sediments. Here, we report a comparison of OSL ages obtained from the fine (4-11 μm) and medium (38-63 μm) grain size fractions of quartz extracted from glaciofluvial sediments and from glacial tills in the Basongcuo catchment near the eastern Himalayan syntaxis. Initially, four glacial stages were identified based on field observations of moraine distribution and geomorpho-stratigraphic relations. A total of 39 OSL samples were then collected from glaciofluvial sand layers or lenses and from till. Quartz grains in the fine (4-11 μm) and medium (38-63 μm) size fractions were extracted from each sample, and dated using the single-aliquot regeneration (SAR) protocol. The modern supraglacial sediment sample was dated to ˜0.2 (fine grain) to ˜0.7 (medium grain) ka, suggesting that the sediment was not completely bleached on deposition. Contrary to previous experience suggesting that coarse grains are usually better bleached than fine grains prior to deposition, our results show that estimated OSL ages for fine grains are generally younger than those for medium grains. This suggests that the two fractions may have come from different sources and thus have different bleaching histories, and that fine-grained quartz may be more suitable for OSL dating of these materials. Applying the minimum age model to data from medium-grained quartz yields ages close to those obtained from fine-grained quartz, suggesting that both can be used for dating glacial advances. The OSL dates suggest that glaciers in the studied area advanced at 0.1-1.3 ka, ˜7.5 ka and 11-13 ka, and were

  10. Long-term evolution of hillslopes and drainage networks under repeated impact of glacial erosion

    NASA Astrophysics Data System (ADS)

    Salcher, Bernhard; Baumann, Sebastian; Kober, Florian; Robl, Jörg

    2015-04-01

    The morphology of hillslopes is an important indicator of landscape change and erosion. In nonglacial catchments, its characteristics depend to a large extent on channel processes and are a function of climate, tectonic and underlying bedrock. These factors may however become secondary when affected by glacial erosion as it is the case in many mid- to high-latitude mountain belts. The perturbation of the initial steady state hillslope morphology (where uplift is balanced by surface lowering rates) will tend to become successively larger if the repeated action of glacial processes exceeds the potential of fluvial readjustment during deglaciated periods. In the limiting case that fluvial or colluvial readjustments to the topography are smaller than modifications by glacial action, the history of glacial erosion rate may be faithfully archived in the form of hillslopes and the channel network (Salcher et al., 2014). This relation is furthermore important as significant mass is generally mobilized and eroded in the hillslope domain delivering material to the channel system. Here we analyzed the glacially modified topography of the European Central Alps, a region which has been multiply glaciated during the Quaternary and were tectonic processes have largely ceased. The higher elevated catchments suffered a more intense impact of glacial erosion than lower elevated catchments whereas fluvial (steady state) processes dominate the alpine foothills or regions outside the former ice sheets. To investigate variations to the hillslope domain we utilized digital elevation models to define hillslope parameters (area, length relief) as function of channel head locations. Channel heads are then calculated as a function of minimum channel plan curvature. Our results show that hillslope area, relief and length increases with the cumulative impact of glacial action. This relation is however only valid were individual tributary glaciers and associated headward erosion could evolve

  11. Differentiating Hydrothermal, Pedogenic, and Glacial Weathering in a Cold Volcanic Mars-Analog Environment

    NASA Technical Reports Server (NTRS)

    Scudder, N. A.; Horgan, B.; Havig, J.; Rutledge, A.; Rampe, E. B.; Hamilton, T.

    2016-01-01

    Although the current cold, dry environment of Mars extends back through much of its history, its earliest periods experienced significant water- related surface activity. Both geomorphic features (e.g., paleolakes, deltas, and river valleys) and hydrous mineral detections (e.g., clays and salts) have historically been interpreted to imply a "warm and wet" early Mars climate. More recently, atmospheric modeling studies have struggled to produce early climate conditions with temperatures above 0degC, leading some studies to propose a "cold and icy" early Mars dominated by widespread glaciation with transient melting. However, the alteration mineralogy produced in subglacial environments is not well understood, so the extent to which cold climate glacial weathering can produce the diverse alteration mineralogy observed on Mars is unknown. This summer, we will be conducting a field campaign in a glacial weathering environment in the Cascade Range, OR in order to determine the types of minerals that these environments produce. However, we must first disentangle the effects of glacial weathering from other significant alteration processes. Here we attempt a first understanding of glacial weathering by differentiating rocks and sediments weathered by hydrothermal, pedogenic, and glacial weathering processes in the Cascades volcanic range.

  12. Causes of atmospheric CO2 variations over the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Kemppinen, K. M.; Holden, P.; Edwards, N.; Ridgwell, A. J.; Friend, A. D.; Wolff, E.

    2013-12-01

    During glacial-interglacial cycles, atmospheric CO2 increases by about 100 ppmv during brief interglacials. Despite years of research, the causes of this change are still not entirely understood. Here we attempt to explain the change in CO2 using, for the first time, an ensemble of coupled climate-carbon cycle simulations designed to consider the processes that are thought to contribute to variability of atmospheric CO2 on glacial/interglacial timescales. We begin by running the ensemble to equilibrium with Last Glacial Maximum (LGM; 21 kyr BP) forcings. By comparing the simulations with ice core data, we find that a small subset of the ensemble produces plausible atmospheric CO2 concentrations and climate. We build emulators of the full model with respect to atmospheric CO2, and perform sensitivity analyses on them to quantify the contributions of atmospheric, sea ice, ocean, and vegetation processes to variability in atmospheric CO2 under glacial forcings. We find that the variability is dominated by a few key parameters. We also use singular vector decomposition to investigate the parameter interactions required for achieving plausible CO2 at the LGM. This work is ongoing, and if plausible states are found, a transient ensemble will be run over the last glacial-interglacial cycle (126 kyr) using the associated parameter sets. This experiment will be the first of its kind as it allows simulated atmospheric CO2 to feedback to the physical climate model in an unconstrained manner.

  13. Constraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Margo Project Members; Waelbroeck, C.; Paul, A.; Kucera, M.; Rosell-Melé, A.; Weinelt, M.; Schneider, R.; Mix, A. C.; Abelmann, A.; Armand, L.; Bard, E.; Barker, S.; Barrows, T. T.; Benway, H.; Cacho, I.; Chen, M.-T.; Cortijo, E.; Crosta, X.; de Vernal, A.; Dokken, T.; Duprat, J.; Elderfield, H.; Eynaud, F.; Gersonde, R.; Hayes, A.; Henry, M.; Hillaire-Marcel, C.; Huang, C.-C.; Jansen, E.; Juggins, S.; Kallel, N.; Kiefer, T.; Kienast, M.; Labeyrie, L.; Leclaire, H.; Londeix, L.; Mangin, S.; Matthiessen, J.; Marret, F.; Meland, M.; Morey, A. E.; Mulitza, S.; Pflaumann, U.; Pisias, N. G.; Radi, T.; Rochon, A.; Rohling, E. J.; Sbaffi, L.; Schäfer-Neth, C.; Solignac, S.; Spero, H.; Tachikawa, K.; Turon, J.-L.

    2009-02-01

    Observation-based reconstructions of sea surface temperature from relatively stable periods in the past, such as the Last Glacial Maximum, represent an important means of constraining climate sensitivity and evaluating model simulations. The first quantitative global reconstruction of sea surface temperatures during the Last Glacial Maximum was developed by the Climate Long-Range Investigation, Mapping and Prediction (CLIMAP) project in the 1970s and 1980s (refs 2, 3). Since that time, several shortcomings of that earlier effort have become apparent. Here we present an updated synthesis of sea surface temperatures during the Last Glacial Maximum, rigorously defined as the period between 23 and 19 thousand years before present, from the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) project. We integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records. Our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins, in contrast to the simulations of the Last Glacial Maximum climate available at present.

  14. Role of Stationary wave feedback in shaping the glacial ice sheets

    NASA Astrophysics Data System (ADS)

    Abe-Ouchi, A.; Takahashi, K.; Saito, F.; Blatter, H.

    2015-12-01

    The large northern hemisphere ice sheets significantly affected the atmospheric circulation and in return, their evolution and geographical pattern is influenced by the changed atmospheric circulation. In this work, we suggest that the atmospheric stationary planetary wave feedback leads to the contrasting asymmetrical evolution of ice sheet in the Northern Hemisphere during the glacial cycles. Model results suggest that the stationary wave induced by the glacial ice sheet topography suppresses the cooling of the land in the central Asia and prevents the ice sheet growth of the east-southern part of the Fennoscandian ice sheet and enables its faster retreat at the ice age termination. Because of the smaller eccentricity during the last 120 ka compared to the penultimate glacial during 230 to 130 ka, the Laurentide ice sheet grew to a larger size at the Last Glacial Maximum (LGM) than the Penultimate Glacial Maximum (PGM). This, in turn, resulted in the Fennoscandian ice sheet to be smaller in LGM than PGM through the stationary wave feedback mechanism.

  15. Quaternary fluvial response to climate change in glacially influenced river systems

    NASA Astrophysics Data System (ADS)

    Cordier, Stéphane; Adamson, Kathryn; Delmas, Magali; Calvet, Marc; Harmand, Dominique

    2016-04-01

    Over the last few decades, many studies in Europe and other continents have focused on the fluvial response to climate forcing in unglaciated basins. However, glacial activity may have a profound impact on the behaviour of the fluvial systems located downstream. In comparison to ice-free basins, these systems are characterised by distinctive hydrological and sediment supply regimes. Over Quaternary timescales, the fluvial records are influenced by periglacial (in non-glaciated areas), proglacial, and paraglacial processes. Understanding the impacts of these processes on the formation and preservation of the Quaternary geomorphological and sedimentary archives is key for our understanding of glacial-fluvial interactions. We investigate the impact of Quaternary glacial activity on fluvial sediment transfer, deposition, and preservation. Using existing studies from across Europe, we create a database of glaciofluvial geomorphology, sedimentology, and geochronology. This is used to examine how glacial forcing of fluvial systems varies spatially in different basin settings, and temporally over successive Milankovitch cycles. In particular, we focus on the ways in which the primary glacial-fluvial depositional signal could be distinguished from periglacial and paraglacial reworking and redeposition.

  16. Life hung by a thread: endurance of Antarctic fauna in glacial periods.

    PubMed

    Thatje, Sven; Hillenbrand, Claus-Dieter; Mackensen, Andreas; Larter, Rob

    2008-03-01

    Today, Antarctica exhibits some of the harshest environmental conditions for life on Earth. During the last glacial period, Antarctic terrestrial and marine life was challenged by even more extreme environmental conditions. During the present interglacial period, polar life in the Southern Ocean is sustained mainly by large-scale primary production. We argue that during the last glacial period, faunal populations in the Antarctic were limited to very few areas of local marine productivity (polynyas), because complete, multiannual sea-ice and ice shelf coverage shut down most of the Southern Ocean productivity within today's seasonal sea-ice zone. Both marine sediments containing significant numbers of planktonic and benthic foraminifera and fossil bird stomach oil deposits in the adjacent Antarctic hinterland provide indirect evidence for the existence of polynyas during the last glacial period. We advocate that the existence of productive oases in the form of polynyas during glacial periods was essential for the survival of marine and most higher-trophic terrestrial fauna. Reduced to such refuges, much of today's life in the high Antarctic realm might have hung by a thread during the last glacial period, because limited resources available to the food web restricted the abundance and productivity of both Antarctic terrestrial and marine life.

  17. A case report of a chemical burn due to the misuse of glacial acetic acid.

    PubMed

    Yoo, Jun-Ho; Roh, Si-Gyun; Lee, Nae-Ho; Yang, Kyung-Moo; Moon, Ji-Hyun

    2010-12-01

    As young and elastic skin is what everyone dreams of, various measures have been implemented including chemical, laser resurfacing and dermabrasion to improve the condition of ageing skin. However, the high cost of these procedures prevents the poor from having access to treatment. Glacial acetic acid is widely used as a substitute for chemical peeling because it is readily easily available and affordable. However, its use can result in a number of serious complications. A 28-year-old female patient was admitted to our hospital with deep second-degree chemical burns on her face caused by the application of a mixture of glacial acetic acid and flour for chemical peeling. During a 6-month follow-up, hypertrophic scarring developed on the both nasolabial folds despite scar management. Glacial acetic acid is a concentrated form of the organic acid, which gives vinegar its sour taste and pungent smell, and it is also an important reagent during the production of organic compounds. Unfortunately, misleading information regarding the use of glacial acetic acid for chemical peeling is causing serious chemical burns. Furthermore, there is high possibility of a poor prognosis, which includes inflammation, hypertrophic scar formation and pigmentation associated with its misuse. Therefore, we report a case of facial chemical burning, due to the misuse of glacial acetic acid, and hope that this report leads to a better understanding regarding the use of this reagent.

  18. Decadal-scale climate drivers for glacial dynamics in Glacier National Park, Montana, USA

    USGS Publications Warehouse

    Pederson, G.T.; Fagre, D.B.; Gray, S.T.; Graumlich, L.J.

    2004-01-01

    Little Ice Age (14th-19th centuries A.D.) glacial maxima and 20th century retreat have been well documented in Glacier National Park, Montana, USA. However, the influence of regional and Pacific Basin driven climate variability on these events is poorly understood. We use tree-ring reconstructions of North Pacific surface temperature anomalies and summer drought as proxies for winter glacial accumulation and summer ablation, respectively, over the past three centuries. These records show that the 1850's glacial maximum was likely produced by ???70 yrs of cool/wet summers coupled with high snowpack. Post 1850, glacial retreat coincides with an extended period (>50 yr) of summer drought and low snowpack culminating in the exceptional events of 1917 to 1941 when retreat rates for some glaciers exceeded 100 m/yr. This research highlights potential local and ocean-based drivers of glacial dynamics, and difficulties in separating the effects of global climate change from regional expressions of decadal-scale climate variability. Copyright 2004 by the American Geophysical Union.

  19. Millenial-scale lag times in vegetation response to glacial climate in Siberia

    NASA Astrophysics Data System (ADS)

    Herzschuh, Ulrike; Birks, John H.; Andreev, Andrei; Melles, Martin; Brigham-Grette, Julie

    2016-04-01

    Vegetation change on all relevant temporal scales is assumed to be primarily driven by contemporary climate change, which would imply that vegetation-climate feedbacks become effective without long-term delay. However, our results from multivariate analyses of pollen assemblages from Lake Eĺgygytgyn (NE Siberia) and other data covering the Mid-Pliocene-Warm-Period and the Plio-Pleistocene-Transition challenge this concept of broad-scale vegetation-climate equilibrium. Our results indicate that interglacial vegetation during the Plio-Pleistocene transition mainly reflects the condition of the preceding glacial instead of contemporary interglacial climate. We assume that the observed vegetation-climate disequilibrium, in particular the absence of pine and spruce in interglacials following strong glacial stages, originates from the combined effects of permafrost persistence, distant glacial refugia, and fire plus possible interactions. Our results imply that today's widespread larch ecosystem on permafrost is not in climate-equilibrium but rather represents a transient vegetation type which is still responding to the extreme glacial condition of the last glacial. This also implies that feedback between vegetation and climate and between permafrost and climate in northern mid- and high latitudes becomes active with long-term delay, which is of relevance for global climate change.

  20. High-resolution mapping of glacial landforms in the North Alpine Foreland, Austria

    NASA Astrophysics Data System (ADS)

    Salcher, Bernhard C.; Hinsch, Ralph; Wagreich, Michael

    2010-10-01

    In this study results from traditional field mapping were merged with precise elevation information from airborne LiDAR (Light detection and ranging) surveys. Morphological and sedimentological data provide new results from the Austrian (eastern) part of the Salzach piedmont glacier during times of and shortly after the Last Glacial Maximum (LGM). The variations in meltwater discharge had a major impact on the development of glacial landforms. In areas with high meltwater supply erosional or debris reworking processes play a major role, represented by drainage channels, drumlins and kettled, low relief hummocky moraine with low slope angles. Low discharge areas are associated with distinct depositional forms such as high relief end moraines (up to 30 m) and hummocky moraine (averaging 20 m) with high slope angles. Isolated conical kames may reach heights up to 45 m. Fluvial activity is supposed to rise towards the end of the glacial cycle causing high melting rates and comprehensive debris reworking. The formation of terminal lakes and associated widespread, inorganic lake clays are the last deposits within the study area before the Salzach Glacier completely receded to its main valley. The survey of glacial landforms through the combination of field mapping and high-resolution DEM derived from airborne LiDAR missions gives precise information on transport and deposition during the last glacial cycle of the eastern Salzach Glacier piedmont lobe.

  1. Glacial wetland distribution and methane emissions estimated from PMIP2 climate simulations

    NASA Astrophysics Data System (ADS)

    Weber, Nanne; Drury, Annajoy; Toonen, Willem; van Weele, Michiel

    2010-05-01

    It is an open question to what extent wetlands contributed to the interglacial-glacial decrease in atmospheric methane concentration. Here we estimate methane emissions from glacial wetlands, using newly available PMIP2 simulations of the Last Glacial Maximum (LGM) climate from coupled atmosphere-ocean and atmosphere-ocean-vegetation models. Emissions are computed from the dominant controls of water table depth, soil temperature and plant productivity and we analyse the relative role of each factor in the glacial decline. It is found that latitudinal changes in soil moisture, in combination with ice-sheet expansion, cause boreal wetlands to shift southward in all simulations. This southward migration is instrumental in maintaining the boreal wetland source at a significant level. The temperature effect is found to be moderate, while reduced plant productivity contributes equally to the total reduction. Model results indicate a relatively small boreal and large tropical source during the LGM, consistent with the low interpolar difference in glacial methane concentrations derived from ice-core data.

  2. Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars

    NASA Astrophysics Data System (ADS)

    Gallagher, Colman; Balme, Matthew

    2015-12-01

    Although glacial landsystems produced under warm/wet based conditions are very common on Earth, even here, observations of subglacial landforms such as eskers emerging from extant glaciers are rare. This paper describes a system of sinuous ridges emerging from the in situ but now degraded piedmont terminus of a Late Amazonian-aged (∼150 Ma) glacier-like form in the southern Phlegra Montes region of Mars. We believe this to be the first identification of martian eskers that can be directly linked to their parent glacier. Together with their contextual landform assemblage, the eskers are indicative of significant glacial meltwater production and subglacial routing. However, although the eskers are evidence of a wet-based regime, the confinement of the glacial system to a well-defined, regionally significant graben, and the absence of eskers elsewhere in the region, is interpreted as evidence of sub-glacial melting as a response to locally enhanced geothermal heat flux rather than climate-induced warming. These observations offer important new insights to the forcing of glacial dynamic and melting behaviour on Mars by factors other than climate.

  3. Carbonaceous matter deposition in the high glacial regions of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Li, Chaoliu; Chen, Pengfei; Kang, Shichang; Yan, Fangping; Li, Xiaofei; Qu, Bin; Sillanpää, Mika

    2016-09-01

    Carbonaceous matter at glacial region plays important role in river ecosystems fed by glacier and albedo reduction of glacier surface. However, currently, limited knowledge are available on the carbonaceous matter within the glacial region of the Tibetan Plateau (TP). In this study, the data from six snowpits in the glacial region across the TP were reported. The results showed that dissolved organic carbon (DOC) concentrations of snowpit samples of the TP were comparable to those of European Alps and the Arctic. The ratio of DOC to carbonaceous matter (40.25 ± 8.98%) was lower than that of Alpine glaciers, thus indicating greater particulate carbon content in the TP glacial region. In addition, the DOC was significantly correlated with insoluble particulate carbon (IPC), indicating that IPC and DOC likely came from the same sources. Spatially, the DOC concentration decreased from the north (0.42 ± 0.29 mg-C L-1) to the south TP (0.15 ± 0.06 mg-C L-1), which was consistent with variations in the distribution of dust storm on the TP. Principal component analysis of major ions and DOC showed that mineral dust contributed the major part of DOC, followed by biogenic sources such as agriculture and livestock. Finally, based on DOC concentrations and precipitation amounts at different periods, the mean annul flux of DOC in the glacial region of the TP was calculated to be 0.11 ± 0.05 g-C m-2 yr-1.

  4. An overview of how glacial depositional processes control characteristics of outwash aquifers

    SciTech Connect

    Fraser, G.S. )

    1994-04-01

    Sedimentological processes, acting on a variety of scales, are among the more important factors that determine the hydraulic properties of outwash aquifers. On a regional scale, the heterogeneity imposed on aquifer systems by such processes affects the shape of an aquifer and its relationships to enclosing units, the location and hydraulic properties of discharge and recharge areas, and the occurrence of low-permeable material. At the scale of individual aquifers, sedimentary heterogeneity is commonly a major control on the rate and complexity of groundwater movement. Glacial facies models can provide important insights into the characteristics of aquifers, aquifer systems and confining units. Outwash is produced and transported differently along active glacial margins and on active ice sheets, within stagnant ice sheets, and down glacial sluiceways, and these differences are reflected in regional-scale variations of the characteristics of aquifers and aquifer system. An understanding of such models are especially important to regional planners who must have knowledge of aquifer sensitivity when determining land-use policy. An understanding of how sedimentological processes act within glacial regimes can help determine local variations in aquifer characteristics on intermediate or small scales. Variations in grain size within outwash aquifers are the result of lateral and/or temporal changes in the intensity of the hydraulic regime imposed by proximity to melting ice and variations in meltwater flow. Examples will be provided that show how these processes operated during the evolution of glacial outwash sequences in various terrains in Indiana.

  5. A new remote hazard and risk assessment framework for glacial lakes in the Nepal Himalaya

    NASA Astrophysics Data System (ADS)

    Rounce, David R.; McKinney, Daene C.; Lala, Jonathan M.; Byers, Alton C.; Watson, C. Scott

    2016-08-01

    Glacial lake outburst floods (GLOFs) pose a significant threat to downstream communities and infrastructure due to their potential to rapidly unleash stored lake water. The most common triggers of these GLOFs are mass movement entering the lake and/or the self-destruction of the terminal moraine due to hydrostatic pressures or a buried ice core. This study initially uses previous qualitative and quantitative assessments to understand the hazards associated with eight glacial lakes in the Nepal Himalaya that are widely considered to be highly dangerous. The previous assessments yield conflicting classifications with respect to each glacial lake, which spurred the development of a new holistic, reproducible, and objective approach based solely on remotely sensed data. This remote hazard assessment analyzes mass movement entering the lake, the stability of the moraine, and lake growth in conjunction with a geometric GLOF to determine the downstream impacts such that the present and future risk associated with each glacial lake may be quantified. The new approach is developed within a hazard, risk, and management action framework with the aim that this remote assessment may guide future field campaigns, modeling efforts, and ultimately risk-mitigation strategies. The remote assessment was found to provide valuable information regarding the hazards faced by each glacial lake and results were discussed within the context of the current state of knowledge to help guide future efforts.

  6. Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Wickert, Andrew D.

    2016-11-01

    Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas, and sometimes delivered enough meltwater to the oceans in the right places to influence global climate. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges, by combining models of past ice sheets, glacial isostatic adjustment, and climate. The result is a time series of synthetic paleohydrographs and drainage basin maps from the Last Glacial Maximum to present for nine major drainage basins - the Mississippi, Rio Grande, Colorado, Columbia, Mackenzie, Hudson Bay, Saint Lawrence, Hudson, and Susquehanna/Chesapeake Bay. These are based on five published reconstructions of the North American ice sheets. I compare these maps with drainage reconstructions and discharge histories based on a review of observational evidence, including river deposits and terraces, isotopic records, mineral provenance markers, glacial moraine histories, and evidence of ice stream and tunnel valley flow directions. The sharp boundaries of the reconstructed past drainage basins complement the flexurally smoothed GIA signal that is more often used to validate ice-sheet reconstructions, and provide a complementary framework to reduce nonuniqueness in model reconstructions of the North American ice-sheet complex.

  7. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

    PubMed Central

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-01-01

    Reduced surface–deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface–subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring–summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall–winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink. PMID:26382319

  8. Downstream channel adjustment in a low-relief, glacially conditioned watershed

    NASA Astrophysics Data System (ADS)

    Thayer, James B.; Phillips, Roger T. J.; Desloges, Joseph R.

    2016-06-01

    River management practices are often informed by theoretical expectations of downstream channel adjustment, which may not be valid in low relief, glacially conditioned watersheds such as those in the lower North American Great Lakes region. Downstream trends in channel morphology and bed material size within a low-relief, glacially conditioned watershed are explored here and compared to a theoretical watershed model where slope and grain size are expected to decline exponentially. The observed channel morphology is then tested against a theoretical concept of reach-scale channel grade. The downstream hydraulic geometry relations wbf ∝ Qbf0.51S- 0.02 and dbf ∝ Qbf0.32S- 0.21 were found to best describe downstream changes in channel morphology and are consistent with some prior studies. Bed material size varies irregularly down the channel. Slope-controlled downstream fining trends are evident where inputs from glacial materials and tributaries are negligible but are masked by cobble/boulder lag deposits where the channel is cut into these glacial deposits. The asynchronous variability in slope and grain size produces downstream variations in graded and nongraded, understeepened conditions separated at τ*ex = 0. Graded reaches exist where τ*ex > 0, but an upper boundary with nongraded, oversteepened reaches is less clear. The results emphasize the geomorphic legacy of inherited slopes and sediment sources in dictating the modern downstream patterns of fluvial characteristics and morphologies in glacially conditioned, and similarly complex, watersheds.