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1

Lichenometry in the Cordillera Blanca, Peru: “Little Ice Agemoraine chronology  

NASA Astrophysics Data System (ADS)

This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 “Little Ice Agemoraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of “Little Ice Agemoraines. The time of deposition of the most prominent and numerous terminal and lateral moraines on the Pacific-facing side of the Cordillera Blanca (between AD 1590 and AD 1720) corresponds to the coldest and wettest phase in the tropical Andes as revealed by ice-core data. Less prominent advances occurred between AD 1780 and 1880.

Solomina, Olga; Jomelli, Vincent; Kaser, Georg; Ames, Alcides; Berger, Bernhard; Pouyaud, Bernard

2007-10-01

2

Ice Blocks on a Moraine  

Microsoft Academic Search

BLOCKS of ice, so far as I know and so far as I remember to have read, are not usual constituents of a moraine. So it may be well to call attention to an instance which I saw lately when walking over the Gorner Glacier with my friend Mr. J. Eccles, who is even more familiar than I am with

T. G. Bonney

1889-01-01

3

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

4

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

Microsoft Academic Search

An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier on Svalbard following its Little Ice Age maximum. Dead-ice appears mainly as ice-cored moraines, ice-cored eskers and ice- cored kames. The most common dead-ice landform is sediment gravity flows on ice-cored slopes surrounding a large ice-walled, moraine-dammed lake. The lake finally receives the sediment from the

A. Schomacker; K. H. Kjaer

2007-01-01

5

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

Microsoft Academic Search

We have established precise ages of two glacial events in the tropical Andean highlands of southern Peru. The field site is located on the flanks of Nevado Salcantay (6271 m asl; 13°20'S latitude), the highest peak in the Cordillera Vilcabamba. A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the south face

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

2008-01-01

6

Cosmogenic analysis reveals a blue-ice moraine in Antarctica survived the last glacial cycle  

NASA Astrophysics Data System (ADS)

Cosmogenic isotope analysis shows that the ice-cored blue-ice moraine at Patriot Hills has survived for at least 80 kyr, i.e. since before the Last Glacial Maximum. The implication is that a biological refuge may also have survived for as long. Strong winds sweep over the Patriot Hills causing accelerated ablation of the glacier edge at the hill foot. In compensation ice flows towards the hills and compressive flow at the margin brings a folded debris band, dipping at angles of 70-800, to the ice surface. Subglacially-derived clasts emerge at the surface and ablation then concentrates them at the ice margin to form the ice-cored moraine. Cosmogenic isotope analysis reveals exposure ages of zero on stones emerging on the ice surface and a range from a few hundred to 29 kyr on the present ice-cored moraine. Relict moraines are draped across the hillside up to a height of ~ 340 m above the ice margin and mark the thinning of the ice over the last ~16 kyr. These moraines contain a mix of boulder ages ranging from a few thousand to ~ 80 kyr with a few ages as old as 424 kyr. The implication is that the moraine has existed at the ice edge for much of at least the last glacial cycle, but that it has migrated up (?) and down the mountain front as the ice elevation has responded to global sea-level change. If substantiated, this discovery would explain why it is so difficult to date moraines reflecting Holocene thinning in Antarctica. Further, the presence of pre-LGM erratics could be used to argue that the West Antarctic Ice Sheet survived the last interglacial intact.

Sugden, D. E.; Fogwill, C. J.; Bentley, M. J.; Hein, A. S.

2009-04-01

7

Preservation of basal-ice sediment texture in ice-sheet moraines  

Microsoft Academic Search

Ice-sheet moraines near Kangerlussuaq in west Greenland inherit distinctive particle-size distributions from basal ice, although debris structures from the basal ice are commonly destroyed by deposition and resedimentation processes. The abundance of clay and silt in the “dispersed facies” basal ice at the ice-sheet margin is clearly reflected in the sedimentology of the ice-sheet moraine. Geographical variations in the texture

Peter G. Knight; Carrie J. Patterson; Richard I. Waller; Alison P. Jones; Zoe P. Robinson

2000-01-01

8

Rapid Communication Cosmogenic-nuclide ages for New England coastal moraines, Martha's Vineyard and Cape Cod, Massachusetts, USA  

Microsoft Academic Search

Cosmogenic-nuclide exposure ages for 13 glacially transported boulders atop the Martha's Vineyard moraine, MA, USA, indicate that the southeastern margin of the Laurentide ice sheet reached its maximum extent during the last glaciation 23,2007500 yr ago. Another 10 age determinations from the younger Buzzards Bay moraine near Woods Hole, MA, indicate that this moraine complex was formed 18,8007400 yr ago.

Greg Balco; John O. H. Stone; Stephen C. Porter; Marc W. Caffee

2002-01-01

9

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

USGS Publications Warehouse

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

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

1984-01-01

10

Hummocky moraine: sedimentary record of stagnant Laurentide Ice Sheet lobes resting on soft beds  

Microsoft Academic Search

Over large areas of the western interior plains of North America, hummocky moraine (HM) formed at the margins of Laurentide Ice Sheet (LIS) lobes that flowed upslope against topographic highs. Current depositional models argue that HM was deposited supraglacially from stagnant debris-rich ice (`disintegration moraine'). Across southern Alberta, Canada, map and outcrop data show that HM is composed of fine-grained

N. Eyles; J. I Boyce; R. W Barendregt

1999-01-01

11

Cross-Cutting Moraines, big Young ice, and Evidence for Multiple Late Quaternary Glaciations in the Southernmost Cordillera Blanca, Peru  

NASA Astrophysics Data System (ADS)

The glaciated Nevado Jeulla Rajo massif (10°00'S, 77°16'W, peaks ca. 5600 masl) lies at the southern end of the Cordillera Blanca in the central Peruvian Andes. The Conococha Plain (ca. 4050 masl) borders the western side of the massif. Large lateral moraines extend onto the Plain from west-facing valleys, and multiple moraine loops lie upvalley, closer to active ice margins. Most moraines on the western side of the massif are offset by the active, west-dipping, north-south-trending Cordillera Blanca Normal Fault. We are focusing on two southwest-facing valleys, Jeullesh Valley (JV) and Quenua Ragra Valley (QRV). Surface- exposure ages [10Be; Lal (1991)/Stone (2000) scaling] indicate that the largest lateral moraines from JV are compound features deposited during both the local last glacial maximum (LLGM; ca. 28-30 ka) and a late-glacial readvance (ca. 14-16 ka), whereas the lateral moraines from adjacent QRV are predominantly late-glacial (ca. 14-16 ka). In JV, two smaller inset moraine loops date to ca. 14 ka and 13 ka, suggesting relatively rapid, but not continuous, retreat from the maximum late-glacial ice extent. The LLGM/late-glacial moraines in JV cross-cut an older, smaller pair of lateral moraines (ca. 50-60 ka) that may be the first geomorphologically distinct evidence of an advance during marine isotope stage 4 identified in the region. We have found no moraines that date to the global LGM (ca. 19-24 ka), but see some evidence for an advance ca. 40-45 ka. The late-glacial moraines from JV and QRV are large, but do not represent the maximum ice extent in the region. Fluvial outwash deposits (ca. 45 ka) located beyond the termini of the moraines on the Conococha Plain are underlain by lodgement till that is up to 20 m thick and extends ca. 6 km across the width of the Plain. The wide distribution of till suggests that at least one older glaciation was far more extensive than any of the late Quaternary advances that we have dated by 10Be. The combination of high peaks, a high-altitude plateau, and an active fault may be ideal for enhancing preservation of older moraines and till.

Smith, J. A.; Rodbell, D. T.

2008-12-01

12

Morphology and GPR stratigraphy of a frontal part of an end moraine of the Laurentide Ice Sheet: Paris Moraine near Guelph, ON, Canada  

Microsoft Academic Search

During deglaciation, the Laurentide Ice Sheet developed lobate ice termini in the Great Lakes area. Where the lobes remained quasi-stationary for considerable time and sediment was supplied by the glacier, end moraines fronted by outwash plains were formed. One of the best examples in southern Ontario is the Paris Moraine formed by the Lake Ontario lobe. This study is a

S. Sadura; I. P. Martini; A. L. Endres; K. Wolf

2006-01-01

13

Submarine push moraine formation during the early Fennoscandian Ice Sheet deglaciation  

NASA Astrophysics Data System (ADS)

The glacial history in the topographically confined paleo-ice stream drainage route of Vestfjorden, North Norway, was analysed based on multi-beam bathymetric data, high-resolution seismic records and 14C AMS-dated gravity cores. The inner part of the fjord is characterised by axial-parallel megascale lineations. In the central part of the fjord, a succession of transverse ridges form a zigzag like morphology. The ridges become wider and more prominent down-fjord and the largest, up to 40 m high forms the distal part of the Værøy morainal bank system. A second series of similar transverse, zigzag ridges occur in the Røst morainal bank system. They also increase in size down-fjord to terminate by a ~100 m high ridge. A mound, interpreted as a raft of sediment displaced from a similar-sized depression in the Røst morainal bank system, is located ca 8 km beyond the bank, indicating sediment drag and deformation. Seismic records show thrusted and folded sediment blocks within the ridges. The inner ridges of the Røst system terminate at the Værøy system, indicating that the latter is younger than the Røst system. The landforms are inferred to reflect basal processes and the transition from warm-based (inner fjord) to cold-based (outer fjord) conditions, i.e. fast flow followed by basal freeze-on, sediment deformation and morainal bank formation. The moraines formed during the final part of two paleo-ice sheet re-advances. 14C AMS dating indicates a maximum age of 13.7 14C ka BP (16.2 cal ka BP) for the Røst system whereas the Værøy system is inferred to be slightly older than 12.5 14C ka BP (14.5 cal ka BP). This demonstrates that the northern part of the Fennoscandian Ice Sheet behaved in a much more dynamic way during the early deglaciation than previously assumed. Acknowledgement This work is a contribution to the SPONCOM and GlaciPet (http://www.ngu.no/glacipet/) projects. Financial support from the Research Council of Norway and StatoilHydro is gratefully acknowledged. Further reading Laberg, J.S., Eilertsen, R.S., Salomonsen, G.R., Vorren, T.O. 2007. Submarine push moraine formation during the early Fennoscandian Ice Sheet deglaciation. Quaternary Research 67, 453-462. Laberg, J.S., Eilertsen, R.S., Vorren, T.O. in press. The paleo-ice stream in Vestfjorden, North Norway over the last 35ka: glacial erosion and sediment yield. Geological Society of America Bulletin. Fløistad, K.R., Laberg, J.S., Vorren, T.O. in press. Morphology of Younger Dryas ice-proximal submarine landforms, inner Vestfjorden, northern Norway. Boreas.

Laberg, J. S.; Eilertsen, R. S.; Salomonsen, G. R.; Vorren, T. O.

2009-04-01

14

Bed Ribbing Instability Explanation: Testing a numerical model of ribbed moraine formation arising from coupled flow of ice and subglacial sediment  

Microsoft Academic Search

Ribbed moraines are large (up to 16 km long) ridges of sediment produced transverse to ice flow direction that formed widely beneath palaeo-ice sheets. Since ice sheet stability is sensitive to conditions operating at the bed, an understanding of ribbed moraine genesis will provide critical information on ice sheet dynamics. Currently, there is no consensus on ribbed moraine formation and

Paul Dunlop; Chris D. Clark; Richard C. A. Hindmarsh

2008-01-01

15

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

SciTech Connect

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

Birkeland, P.W.; Berry, M.E. (Univ. of Colorado, Boulder (USA)); Swanson, D.K. (Dept. of Agriculture, Fairbanks, Alaska (USA))

1991-03-01

16

Origin of Periodic, Transverse Moraines of the Des Moines Lobe Ice Stream, Iowa  

NASA Astrophysics Data System (ADS)

The late-glacial (~ 15 kyr B.P.) advance of the soft-bedded Des Moines Lobe, the marginal portion of an ice stream of the Laurentide Ice Sheet, deposited regularly-spaced, transverse moraines. These moraines have relief of 1-5 m and an average spacing of ~ 100 m. Transverse moraines of similar size and spacing have been revealed by high-resolution, sea-floor imagery on continental shelves outboard of modern ice streams in Antarctica and have been used to estimate rates of ice-margin retreat, assuming that the moraines form either annually or by tidal forcing. The internal structure and origin of the more accessible Des Moines Lobe moraines, which have been interpreted as either ice-marginal features or subglacial crevasse fills, may help constrain interpretations of submarine moraine ridges. A 70 m long, 3-5 m high cross-section through a moraine ridge in Story County, Iowa, revealed till with irregular, isolated lenses of silt, sand and gravel that generally dip steeply up-glacier. Preconsolidation pressures, measured from intact till and silt samples, and till densities indicate that these sediments were under the glacier. Anisotropy of magnetic susceptibility (AMS) of 3200 intact till samples was used to characterize till fabrics using orientations of principal susceptibilities. AMS fabrics were interpreted using ring-shear experiments that allow fabric orientation to be calibrated to the state of strain. AMS fabrics in the moraine are consistent with flow-parallel simple shear, with shear planes inclined up-glacier, together with flow-parallel shortening accompanied by vertical and lateral extension. This strain field is consistent with shearing and extrusion of weak basal till and subglacial fluvial sediments into basal crevasses during slip of the lobe—a conclusion supported by less detailed study of several nearby moraines. Periodicity of the moraines reflects the tendency for crevasses in extending glaciers to be regularly spaced. These results indicate that caution should be exercised in interpreting the periodicity of submarine ridges as necessarily resulting from temporal forcing.

Ankerstjerne, S. M.; Iverson, N. R.; Lagroix, F.

2010-12-01

17

Ages for the Big Stone Moraine and the oldest beaches of glacial Lake Agassiz: Implications for deglaciation chronology  

NASA Astrophysics Data System (ADS)

Glacial Lake Agassiz has been implicated as the trigger for numerous episodes of abrupt climate change at the close of the last ice age, yet the beginning age of the lake has never been determined. Here we report the first numerical age data on the Big Stone Moraine and the oldest beaches of glacial Lake Agassiz. Organic remains from lakes, bogs, and channels distal to, and inset to, the Big Stone Moraine require that glacial activity at this moraine ceased prior to 12,000 14C yr B.P. (13,950 cal [calendar] yr). A site near New Effington, South Dakota (United States), implies full glacial recession north of the topographic divide prior to 11,810 14C yr B.P. (13,670 cal yr), synchronous with the beginning of glacial Lake Agassiz. Lake Agassiz shorelines inset to the moraine yield optically stimulated luminescence (OSL) ages from 14,200-12,600 yr cal. Lower strandlines are younger, but the similarity of ages suggests that initial lake lowering was faster than OSL ages can currently resolve. Nevertheless, the OSL ages represent the first numerical age assignments for the Herman, Norcross, and Upham beach ridges, setting the stage for future numerical age assignments within the Lake Agassiz basin. These two dating methods yield strongly consistent results within stated uncertainties. The age of the Big Stone Moraine implies an interval of rapid retreat for the Des Moines lobe of the Laurentide Ice Sheet during the Bölling-Alleröd warm interval. The overlapping ages for the uppermost beach levels and abandonment of the highest Lake Agassiz spillway indicate a rapidly evolving lake until at least 13,500 yr cal.

Lepper, Kenneth; Fisher, Timothy G.; Hajdas, Irka; Lowell, Thomas V.

2007-07-01

18

Ice Ages  

NSDL National Science Digital Library

During most of the last one billion years the globe had no permanent ice. However, sometimes large areas of the globe were covered with vast ice sheets. Users can read and view pictures which help explain what ice ages are, when they occurred, and why they occur. This site, sponsored by the Illinois State Museum, has links to web pages on paleontology of the midwestern United States during the last ice age and to an animation showing the advance and retreat of the ice sheet in North America 20,000 years ago.

19

Correlating Ice Cores from Quelccaya Ice Cap with Chronology from Little Ice Age Glacial Extents  

NASA Astrophysics Data System (ADS)

Proxy records indicate Southern Hemisphere climatic changes during the Little Ice Age (LIA; ~1300-1850 AD). In particular, records of change in and around the tropical latitudes require attention because these areas are sensitive to climatic change and record the dynamic interplay between hemispheres (Oerlemans, 2005). Despite this significance, relatively few records exist for the southern tropics. Here we present a reconstruction of glacial fluctuations of Quelccaya Ice Cap (QIC), Peruvian Andes, from pre-LIA up to the present day. In the Qori Kalis valley, extensive sets of moraines exist beginning with the 1963 AD ice margin (Thompson et al., 2006) and getting progressively older down valley. Several of these older moraines can be traced and are continuous with moraines in the Challpa Cocha valley. These moraines have been dated at <1050-1350-AD (Mercer and Palacios, 1977) and interpreted to have been deposited during the Little Ice Age. We present a new suite of surface exposure and radiocarbon dates collected in 2008 and 2009 that constrain the ages of these moraines. Preliminary 10Be ages of boulder surfaces atop the moraines range from ~350-1370 AD. Maximum and minimum-limiting radiocarbon ages bracketing the moraines are ~0-1800 AD. The chronology of past ice cap extents are correlated with ice core records from QIC which show an accumulation increase during ~1500-1700 AD and an accumulation decrease during ~1720-1860 AD (Thompson et al., 1985; 1986; 2006). In addition, other proxy records from Peru and the tropics are correlated with the records at QIC as a means to understand climate conditions during the LIA. This work forms the basis for future modeling of the glacial system during the LIA at QIC and for modeling of past temperature and precipitation regimes at high altitude in the tropics.

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.

2010-12-01

20

Age of the Fjord Stade moraines in the Disko Bugt region, western Greenland, and the 9.3 and 8.2 ka cooling events  

NASA Astrophysics Data System (ADS)

Retreat of the western Greenland Ice Sheet during the early Holocene was interrupted by deposition of the Fjord Stade moraine system. The Fjord Stade moraine system spans several hundred kilometers of western Greenland's ice-free fringe and represents an important period in the western Greenland Ice Sheet's deglaciation history, but the origin and timing of moraine deposition remain uncertain. Here, we combine new and previously published 10Be and 14C ages from Disko Bugt, western Greenland to constrain the timing of Fjord Stade moraine deposition at two locations ˜60 km apart. At Jakobshavn Isfjord, the northern of two study sites, we show that Jakobshavn Isbræ advanced to deposit moraines ca 9.2 and 8.2-8.0 ka. In southeastern Disko Bugt, the ice sheet deposited moraines ca 9.4-9.0 and 8.5-8.1 ka. Our ice-margin chronology indicates that the Greenland Ice Sheet in two distant regions responded in unison to early Holocene abrupt cooling 9.3 and 8.2 ka, as recorded in central Greenland ice cores. Although the timing of Fjord Stade moraine deposition was synchronous in Jakobshavn Isfjord and southeastern Disko Bugt, within uncertainties, we suggest that Jakobshavn Isbræ advanced while the southeastern Disko Bugt ice margin experienced stillstands during the 9.3 and 8.2 ka events based on regional geomorphology and the distribution of 10Be ages at each location. The contrasting style of ice-margin response was likely regulated by site-specific ice-flow characteristics. Jakobshavn Isbræ's high ice flux results in an amplified ice-margin response to a climate perturbation, both warming and cooling, whereas the comparatively low-flux sector of the ice sheet in southeastern Disko Bugt experiences a more subdued response to climate perturbations. Our chronology indicates that the western Greenland Ice Sheet advanced and retreated in concert with early Holocene temperature variations, and the 9.3 and 8.2 ka events, although brief, were of sufficient duration to elicit a significant response of the western Greenland Ice Sheet.

Young, Nicolás E.; Briner, Jason P.; Rood, Dylan H.; Finkel, Robert C.; Corbett, Lee B.; Bierman, Paul R.

2013-01-01

21

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

NASA Astrophysics Data System (ADS)

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

Thompson, S. S.; Kulessa, B.

2010-12-01

22

Airborne SAR Determination of Relative Ages of Walker Valley Moraines, Eastern Sierra Nevada.  

National Technical Information Service (NTIS)

A regional study of the distribution and elevations of Pleistocene moraines in the Andes requires a method of determining relative age from space. One of our primary objectives is to establish the relative chronology of major climatic events responsible f...

A. Fox B. Isacks A. Bloom E. Fielding D. Mcmurry

1991-01-01

23

Combining Interannual Airborne Lidar and Diurnal Oblique Thermal Imagery to Investigate Glacial Ice-Cored Moraine Dynamics  

NASA Astrophysics Data System (ADS)

As glacier extents in the Canadian Rockies diminish, the influence of groundwater and other baseflow inputs to headwater river systems will gradually take on a more important role in terms of their contribution to the available water resource. It is believed that commensurate with decreasing exposed ice extents there is a volumetric increase in the reservoir of debris covered and therefore insulated ice cored moraines adjacent to and surrounding glacier margins. There is plenty of geomorphic evidence that clearly illustrates these storages of buried ice are increasing during the current period of glacier recession but to date little effort has focussed on investigating the relative proportions of buried ice melt vs. exposed ice melt in the Rockies, and the impact this might have on future water resources. In this paper, we present the results of multi-temporal lidar collections over the Peyto Glacier (2000, 2002, 2006, 2007) that accurately quantify rates of volumetric moraine downwasting. The spatial variability of lateral moraine downwasting is high but the average across the 7 year period was approximately 1.5 m p.a. While some of the downwasting can be attributed to slope creep, slumping and general mass wasting processes, the lack of debris volumes at the foot of slope clearly indicate that some other process is in operation and in fact dominates. By comparing the ratios of moraine to exposed ice downwasting, we find that up to 5% of the mass loss from the Peyto basin is from these marginal moraine areas, and we further hypothesize that most of this volume is lost in the form of melt water from ice cored moraines. This hypothesis was evaluated by collecting oblique diurnal thermal imagery to map the rise and decay in temperature signal over a large area of moraine adjacent to the Peyto Glacier. While no exposed ice was visible anywhere on the moraine slope, the presence of shallow ice core beneath the debris covered surface could be inferred in areas of slow temperature rise during daylight solar heating and rapid thermal decay after sunset. It is presumed that this apparent increased loss of heat in certain areas of the moraine is being used to drive internal melt processes. With some calibration and energy balance modeling, this technique will be further developed to map debris cover depth and assist in the parameterisation of glacial hydrological melt models.

Hopkinson, C.; Barlow, J.; Demuth, M.; Pomeroy, J.

2009-05-01

24

Thermoluminescence Measurements on Meteorites from the Elephant Moraine Region: L6 Showers and Regional Ice Movements  

NASA Astrophysics Data System (ADS)

As part of their initial characterization, we have completed natural and induced thermoluminescence (TL) measurements for over 800 Antarctic meteorites. We have previously discussed the implications of these data for pairing, terrestrial age, and meteorite concentration mechanism at the Lewis Cliff and Allan Hills sites (Benoit et al., 1992a,b). Here we report data for meteorites from the Elephant Moraine region (designated EET, see Huss, 1990, for description of region). Our present discussion is limited to meteorites collected in the 1986/87 and 1987/88 field seasons; measurement of samples from the 1990/91 field season are underway. The Elephant Moraine region encompasses at least five meteorite-bearing blue icefields, including Elephant Moraine proper (EM), Meteorite City (MC), Upper Meteorite City (UMC), Texas Bowl (TB), and the Northern Ice Patch (NIP). While MC, UMC, and TB are physically adjacent to each other, EM and NIP are separated from the others, the latter being approximately 40 km distant from UMC. We have previously identified numerous pairing groups within the EET database without regard for field location. While most pairing groups are found to be restricted to single fields, there are a significant number that span several fields. The howardite group EET87503 covers both TB and EM and several L6 groups either span TB and EM or span the physically adjacent TB, UMC, and MC icefields. Even the isolated NIP apparently shares a few pairing groups with UMC and TB, although the small number of samples from this field make comparison difficult. This result seems to indicate that, unlike the Allan Hills sites, the individual ice fields at EET are sampling the same meteorite population. Natural TL levels for EET meteorites (Fig. 1) are generally high, with a significant fraction having TL levels greater than 50 krad. This would suggest that, in general, these meteorites have small terrestrial ages, probably <100,000 years for most meteorites. In this sense, the region is comparable to the Yamato sites. The cumulative histogram and the data for TB show a large number of meteorites with low TL (<30 krad), which would suggest this field is older than the others. However, the low TL "hump" in the TB data is caused almost entirely by three large L6 pairing groups (EET87587, EET87596, and EET87601) that are probably paired with each other. This suggests that the TB data are dominated by a relatively old L6 shower, but that the meteorites at the site, in general, have short terrestrial ages similar to the other icefields. The short terrestrial ages of the EET meteorites might suggest a connection with the meteorites of the Farwestern icefield at Allan Hills. However, induced TL peak temperature and width data show that the unusual H5 group observed at the Allan Hills sites (including the Farwestern field, Benoit and Sears, 1992). is absent at all EET sites. This suggests that the meteorites at the EET sites have shorter terrestrial ages than those from the Farwestern field at Allan Hills, despite a possible link between these sites suggested by recent ice flow determinations (Schultz et al., 1990; Delisle and Sievers, 1991). Benoit P.H. and Sears D.W.G. (1992a) Science 255, 1685-1687. Benoit P.H., Sears H., and Sears D.W.G. (1992a) J. Geophys. Res. (in press). Benoit P.H., Sears H., and Sears D.W.G. (1992b) J. Geophys. Res. 97, 4629-4647. Delisle G. and Siever J. (1991) J. Geophys. Res. 96, 15577-15587. Huss G.R. (1990) Meteoritics 25, 41-56. Schultz L., Annexstad J.O., and Delisle G. (1990) Antarctic Journal the U.S. 25(5), 9495. Figure 1, which in the hard copy appears here shows the natural TL data for (A) EET ordinary chondrites, (B,C) broken down by icefield, and for ordinary chondrites from (D) Allan Hills Main and (E) Farwestern icefields.

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

1992-07-01

25

Quantifying glacial moraine age, denudation, and soil mixing with cosmogenic nuclide depth profiles  

Microsoft Academic Search

Glacial boulders and soils on moraines are often dated to quantify the timing of glaciations and\\/or rates of chemical weathering in moraine chronosequences. A common assumption is that moraine crest erosion and soil mixing are unimportant. However, several studies suggest moraine denudation may be substantial. We evaluate the magnitude of moraine denudation and soil mixing in the Pinedale (?21 ka)

M. Schaller; T. A. Ehlers; J. D. Blum; M. A. Kallenberg

2009-01-01

26

Geology Fieldnotes: Ice Age National Scientific Preserve  

NSDL National Science Digital Library

This National Park Service (NPS) site gives information on the Ice Age National Scientific Preserve in Wisconsin, including geology, park maps, a photo album, and other media (books, videos, CDs). There is also a selection of links to other geologic and conservation organizations, and to information for visitors. This preserve contains a wealth of glacial features associated with the most recent Pleistocene continental glaciation including drumlins, kames, kettles, moraines, erratics, and eskers. It also contains a segment of the Ice Age National Scenic Trail, a 1000-plus mile hiking and backpacking trail that passes through this unique glacial landscape.

27

Paleo Slide Set: The Ice Ages  

NSDL National Science Digital Library

This slide show will aid in the quest to understand the cause of the Pleistocene ice ages, an example of how scientists have used different types of evidence to understand earth processes. It traces the history of investigation of the ice ages, from the discovery of glacial erratics and moraines in the 1800s, and the theories of orbital variations in solar radiation, to recent investigations of the glacial-interglacial cycles using evidence found in ice cores and deep sea sediments. This slide set emphasizes how different types of geologic evidence can be used to understand how earth climate has varied in the past. The set includes photos of evidence of glaciers, pictures and graphs from ice cores and marine sediment cores, and pictures illustrating changes in the earths orbit. Each is accompanied by a comprehensive narrative and can be enlarged for better viewing.

28

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

USGS Publications Warehouse

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

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

2012-01-01

29

Upper Wisconsinan submarine end moraines off Cape Ann, Massachusetts  

USGS Publications Warehouse

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

Oldale, R. N.

1985-01-01

30

Ice age paleotopography  

SciTech Connect

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

Peltier, W.R. (Univ. of Toronto, Ontario (Canada))

1994-07-08

31

The Great Ice Age  

NSDL National Science Digital Library

The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. Mountain glaciers formed on all continents, the ice caps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across North America and Eurasia. This ice age, the most recent in the history of the Earth, took place from 20 million years to 6 thousand years ago (Quaternary Period). The development of our understanding and the evidence for this worldwide event are covered in this United States Geological Survey (USGS) publication.

Ray, Louis

32

A review of catastrophic drainage of moraine-dammed lakes in British Columbia  

Microsoft Academic Search

Moraine-dammed lakes are common in the high mountains of British Columbia. Most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the Little Ice Age. Many moraine dams in British Columbia are susceptible to failure because they are steep-sided, have relatively low width-to-height ratios, comprise loose, poorly sorted sediment, and may contain ice cores

John J. Clague; Stephen G. Evans

2000-01-01

33

Ice age terminations.  

PubMed

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

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

2009-10-01

34

Ice Age Terminations  

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

35

Portage Glacier and Portage Pass, Alaska: Little Ice Age dynamics and the chronology of glacial retreat  

Microsoft Academic Search

Portage Glacier currently acts as a lacustrine calving glacier discharging icebergs into Portage Lake, Alaska. This glacier advanced during the Little Ice Age, and from 1799 to 1911 completely filled the lake basin and deposited three large moraines downvalley of the modern lakeshore. During this time the glacial ablation regime was dominated by melting and a large outwash stream flowed

Kristine J. Crossen

2007-01-01

36

The little ice age  

Microsoft Academic Search

The Little Ice Age, a period of glacier expansion in alpine regions that began sometime between the twelfth and sixteenth centuries and lasted until late in the nineteenth century, was recorded not only in glacial features dated by geologic techniques but also in historical documents such as field sketches, land values, and weather records, especially in the Alps. Indirect evidence

J. M. Grove

1988-01-01

37

Ice Age Impetus  

NSDL National Science Digital Library

This radio broadcast considers the possibility that the current Ice Age was triggered when Panama rose up out of the sea to join North and South America, thereby separating the Atlantic and Pacific Oceans. There is an explanation of how this affected, in turn, the oceans, the Arctic, and ultimately the entire planet. The clip is 2 minutes in length.

38

A new moraine surface exposure chronology from the eastern Kunlun Shan (Lake Donggi Cona catchment, NE-Tibet): Early last glacial ice maxima and the 'missing' LGM  

NASA Astrophysics Data System (ADS)

Recent advances in obtaining reliable age control for late Pleistocene glaciations on the Tibetan Plateau and adjacent mountain areas have been critical for reconstructing past regional climate dynamics and long distance glacial correlations. In this debate, the analysis of mountain glacier records from the vast area of central and High Asia is particularly interesting as this region is influenced by several major atmospheric systems including the Siberian-Mongolian anticyclone, the mid-latitude Westerlies and the Asian Monsoon systems. During the late Quaternary, changes in the complex interplay between these systems caused substantial climatic variability, specifically in hydrological conditions, with major effects on the extent of regional glaciation. Pioneering studies from NE-Tibet (Anyemaqen Shan, Qilian Shan) have suggested significant late Pleistocene ice advances during MIS 3 and MIS 2 indicating that in some phases glacial mass balances responded strongly positive to increased monsoonal precipitation (during MIS 3) and at other times to insolation minima (during MIS 2). More recently, however, results from other areas of NE-Tibet (Bayan Shan) have shown that glaciation during MIS 2 was extremely limited or even missing, while the timing of the largest late Pleistocene glaciation remains unclear. To address this problem we collected a set of 23 rock samples from moraines in four glacial valleys of the eastern Kunlun Shan near Lake Donggi Cona on the northeastern Tibetan Plateau for in-situ 10Be exposure age dating. All samples were prepared and measured at the AMS laboratory of the Scottish Universities Environmental Research Centre (SUERC). Our results indicate that mountains in the northern part of the Donggi Cona catchment (up to 5000 m a.s.l.) experienced extensive glaciation between 100-90 ka (MIS 5) and between 60-50 ka (MIS 4) when valley glaciers advanced up to 20 km. By contrast, we find no evidence for any significant glaciation during MIS 2 or the LGM. In fact, results from a high resolution study conducted in one of the valleys where the entire up-valley directed moraine sequence was sampled, demonstrate that deglaciation had occurred by 40 ka and that the range remained essentially unglaciated since. We will present study details and discuss paleoclimatological implications.

Rother, Henrik; Lehmkuhl, Frank; Stauch, Georg; Freeman, Stewart; Davidson, Allan

2013-04-01

39

The little ice age  

SciTech Connect

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

Grove, J.M.

1988-01-01

40

Ice Age Floods Institute  

NSDL National Science Digital Library

Describes Ice Age glaciers and immense floods of glacial meltwater that swept across the Pacific Northwest (18,000-12,000 years ago and earlier), affecting the landscape from Montana to Washington and Oregon, sculpting the Columbia River Basin, and creating glacial lakes to rival the today's Great Lakes. This non-profit institute promotes scientific education about the floods, their causes and impacts. Proposes an interpretive geologic trail linking significant sites.

41

Sakami moraine, Quebec: A 500-km-long moraine without climatic control  

Microsoft Academic Search

The Laurentide ice sheet in eastern Canada disintegrated step by step, as evidenced by several morainic complexes. Although commonly interpreted as reflecting climatic events, it seems probable that the disintegration simply related to changes in the dynamics of the ice margin, without climatic control. From the example of the Late Glacial Sakami moraine in Quebec, formed during the drainage of

Claude Hillaire-Marcel; Serge Occhietti; Jean-Serge Vincent

1981-01-01

42

Recent ice ages on Mars  

Microsoft Academic Search

A key pacemaker of ice ages on the Earth is climatic forcing due to variations in planetary orbital parameters. Recent Mars exploration has revealed dusty, water-ice-rich mantling deposits that are layered, metres thick and latitude dependent, occurring in both hemispheres from mid-latitudes to the poles. Here we show evidence that these deposits formed during a geologically recent ice age that

John F. Mustard; Mikhail A. Kreslavsky; Ralph E. Milliken; David R. Marchant; James W. Head

2003-01-01

43

Components of the ice age circulation  

Microsoft Academic Search

Four general climate model (GCM) simulations are compared to investigate te the influence of ice age boundary conditions on atmospheric dynamics and regional climate patterns. Starting with a simulation of the current climate, the ice age distributions of (1) sea surface temperatures; (2) 10-m-thick land ice in locations of ice age ice sheets; and (3) ice sheets elevated to their

D. Rind

1987-01-01

44

Recent ice ages on Mars  

NASA Astrophysics Data System (ADS)

A key pacemaker of ice ages on the Earth is climatic forcing due to variations in planetary orbital parameters. Recent Mars exploration has revealed dusty, water-ice-rich mantling deposits that are layered, metres thick and latitude dependent, occurring in both hemispheres from mid-latitudes to the poles. Here we show evidence that these deposits formed during a geologically recent ice age that occurred from about 2.1 to 0.4 Myr ago. The deposits were emplaced symmetrically down to latitudes of ~30°-equivalent to Saudi Arabia and the southern United States on the Earth-in response to the changing stability of water ice and dust during variations in obliquity (the angle between Mars' pole of rotation and the ecliptic plane) reaching 30-35°. Mars is at present in an `interglacial' period, and the ice-rich deposits are undergoing reworking, degradation and retreat in response to the current instability of near-surface ice. Unlike the Earth, martian ice ages are characterized by warmer polar climates and enhanced equatorward transport of atmospheric water and dust to produce widespread smooth deposits down to mid-latitudes.

Head, James W.; Mustard, John F.; Kreslavsky, Mikhail A.; Milliken, Ralph E.; Marchant, David R.

2003-12-01

45

Paleotopography of glacial-age ice sheets  

Microsoft Academic Search

This is technical comment and response to the subject of paleotophography of glacial age ice sheets. The model presented by Peltier reconstructing the paleotopography of glacial age ice sheets has implications for atmospheric general circulation models of ice age climate. In addition, the model suggests that the glacial-age Antarctic Ice Sheet was significantly larger than today`s. The commentor, Edwards, suggests

R. L. Edwards

1995-01-01

46

Staggering through the ice ages  

SciTech Connect

Because the steady orbital cycles of earth, thought to control the ice ages, cannot easily account for the evidence of repeated rapid climatic shifts during the last ice age. Without knowing what made the iceage climate so in temperate, scientists cannot tell whether today's interglacial period is immune to the sudden swings. Information about climate instability has emerged from two drilling projects in the middle of Greenland where crews bored through the 3-kilometer think glacial cap. This paper describes the discoveries and the evidence for rapid climatic shifts, including conflicting results from different sites. The concerns about global warming are making questions about these shifts of increased interest. The possibility exists that modern climate harbors an inherently unstable element that could trigger wild wings in response to the atmospheric buildup of greenhouse gases. On the other hand sudden climatic shifts might have been unique to the ice-age Earth.

Monastersky, R.

1994-07-30

47

The Great Ice-Age  

Microsoft Academic Search

MR. GREEN, reviewing Mr. J. Geikie's work on the ``Great Ice-Age'' (NATURE, vol. ix. p. 318), expresses the opinion that a glacial period must have been one of intense cold. This is the general opinion, and yet I think it can be shown to rest on a misconception. If the climate at any given elevation is cold enough to form

J. J. Murphy

1874-01-01

48

Glaciology and the Ice Age.  

ERIC Educational Resources Information Center

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

Carozzi, Albert V.

1984-01-01

49

Glaciology and the Ice Age.  

ERIC Educational Resources Information Center

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

Carozzi, Albert V.

1984-01-01

50

Paleotopography of glacial-age ice sheets  

SciTech Connect

This is technical comment and response to the subject of paleotophography of glacial age ice sheets. The model presented by Peltier reconstructing the paleotopography of glacial age ice sheets has implications for atmospheric general circulation models of ice age climate. In addition, the model suggests that the glacial-age Antarctic Ice Sheet was significantly larger than today`s. The commentor, Edwards, suggests there is a discrepancy between data from Papua New Guinea and the model results.

Edwards, R.L. [Univ. of Minnesota, Minneapolis, MN (United States)

1995-01-27

51

Probability of moraine survival in a succession of glacial advances.  

USGS Publications Warehouse

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

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

1984-01-01

52

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

NASA Astrophysics Data System (ADS)

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

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

1994-01-01

53

How ice age climate got the shakes  

Microsoft Academic Search

Records in Greenland ice, ocean mud, and ancient corals are revealing abrupt climate shifts during the last ice age. The climate at the end of the last ice age apparently jumped from cold to warmer conditions, jumped back to cold, and then jumped into the present warm weather conditions. The mechanism for this erratic behavior is unknown, but appears to

R. A. Kerr

1993-01-01

54

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

NASA Astrophysics Data System (ADS)

Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007, Pages 303-313, ISSN 0033-5894, DOI: 10.1016/j.yqres.2007.07.013. DiPrinzio, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract C11C-0834, 2003

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

2009-12-01

55

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

Microsoft Academic Search

We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began

Faron S. Anslow; Peter U. Clark; Mark D. Kurz; Steven W. Hostetler

2010-01-01

56

SKB/TVO ice age scenario.  

National Technical Information Service (NTIS)

Ice ages have repeatedly occurred throughout geological history, and it is likely that they will also occur in the time-span considered for the disposal of nuclear fuel. Based on the present status of knowledge, this report discusses when future ice ages ...

K. Ahlbom T. Aeikaes L. O. Ericsson

1991-01-01

57

Modeling the ice-age climate  

Microsoft Academic Search

The last great (Wisconsin) ice age has long held the interest of climatologists, geologists, and geographers as the best documented of the several ice ages of the last million years. Although local glaciation maximums varied by several thousand years, the time 18,000 B.P. (years before present) is globally representative of this event. The changes of flora and fauna that accompanied

W. Lawrence Gates

1976-01-01

58

Dynamics of ice ages on Mars.  

PubMed

Unlike Earth, where astronomical climate forcing is comparatively small, Mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale. The geographic extent of the subsurface ice found poleward of approximately +/-60 degrees latitude on both hemispheres of Mars coincides with the areas where ice is stable. However, the tilt of Mars' rotation axis (obliquity) changed considerably in the past several million years. Earlier work has shown that regions of ice stability, which are defined by temperature and atmospheric humidity, differed in the recent past from today's, and subsurface ice is expected to retreat quickly when unstable. Here I explain how the subsurface ice sheets could have evolved to the state in which we see them today. Simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years. Today, this gives rise to pore ice at mid-latitudes and a three-layered depth distribution in the high latitudes of, from top to bottom, a dry layer, pore ice, and a massive ice sheet. Combined, these layers provide enough ice to be compatible with existing neutron and gamma-ray measurements. PMID:17851518

Schorghofer, Norbert

2007-09-13

59

Cosmogenic 10Be Dating of Early and Latest Holocene Moraines on Nevado Salcantay in the Southern Peruvian Andes  

NASA Astrophysics Data System (ADS)

A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the southwest flank of Nevado Salcantay (6271 m; ~13°S latitude), the highest peak in the Cordillera Vilcabamba of southern Peru. The field area is situated 25 km due south of the archaeological site of Machu Picchu. Outer and inner moraines in the sequence were deposited by valley glaciers that terminated ~5 km and ~3 km, respectively, from their headwall on the Salcantay summit massif. Cosmogenic 10Be surface exposure dating of granitic boulders sampled on the Salcantay moraines is underway and has provided the first numerical ages for these deposits. Initial results indicate ages of 8.1 ± 0.1 10Be ka for the outer moraine and 200 ± 20 10Be years for the sharp-crested inner moraine. These ages are derived using the CRONUS-Earth 10Be exposure age calculator (version 2.0) and expressed with respect to the Lal- Stone production rate scaling scheme using the standard atmosphere. The outer and inner moraine ages correspond to glacial events during the early and latest Holocene, respectively. Further 10Be dating of the mapped moraines and similar deposits observed in adjacent drainages on Nevado Salcantay is anticipated to yield a high-resolution chronology of valley glaciation in this segment of the southern Peruvian Andes. The new results bridge an important gap between existing Andean glacier records to the north and south, and complement available ice core and lacustrine paleoclimate records in the vicinity, thereby expanding spatial and temporal coverage for identifying patterns of Holocene climate change in the tropical Andes. Notably, the inner moraine age correlates with the timing of the Little Ice Age as defined in northern mid- and high latitude glacier records, and suggests considerable expansion of valley glaciers in the southern Peruvian Andes during this climatic minimum. Apart from their paleoclimatic significance, the initial results also demonstrate the utility of 10Be exposure dating for historical surface deposits.

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

2007-12-01

60

Late-glacial and Holocene history of changes in Quelccaya Ice Cap, Peru  

NASA Astrophysics Data System (ADS)

Quelccaya Ice Cap in the southeastern Peruvian Andes (~13-14° S latitude) is an icon for climate change. Its rapidly receding outlet, Qori Kalis Glacier, has been monitored since the 1970's. Cores from Quelccaya Ice Cap provide high-resolution information about temperature and precipitation during the past 1,500 years. We extend the understanding of past changes in Quelccaya Ice Cap based on mapping and dating of glacial moraines and associated deposits. Our results include fifty 10Be ages of moraines and bedrock as well as twenty-nine 14C ages of organic material associated with moraines. These results form the basis of a chronology of changes in Quelccaya Ice Cap from ~16,000 yr BP to late Holocene time. Results from 10Be and 14C dating indicate that Quelccaya Ice Cap experienced a significant advance at 12,700-11,400 yr BP. Subsequent to this advance, the ice margin deposited at least three recessional moraine sets. Quelccaya Ice Cap receded to near its present-day margin by ~10,000 yr BP. Neoglacial advances began by ~3,000 yr BP and culminated with a maximum advance during the Little Ice Age. This chronology fits well with prior work which indicates a restricted Quelccaya Ice Cap during middle Holocene time. Moreover, the overlap between moraine and ice core data for the last 1,500 years provides a unique opportunity to assess the influences of temperature and precipitation on past ice cap extents.

Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.; Finkel, R. C.

2008-12-01

61

Geological Evidence for Recent Martian Ice Ages  

NASA Astrophysics Data System (ADS)

Multiple lines of evidence for surface deposits formed as a result of quasi- periodic climate change on Mars are presented which are remarkably consistent with models of ground-ice stability and climate. These results are used to present a new model for martian ice ages.

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

2003-07-01

62

SKB/TVO ice age scenario.  

National Technical Information Service (NTIS)

Ice ages have repeatedly occurred throughout geological history, and it is likely that they will also occur in the future. The report discusses the principal processes predicted to occur during future glaciations, and which are likely to be of importance ...

K. Ahlbom T. Aeikaes L. Ericsson

1991-01-01

63

Numerical Simulation of an Ice Age Paleoclimate.  

National Technical Information Service (NTIS)

In order to simulate the climate of an ice age, a two-level, quasi-goestrophic, spectral general circulation model for the northern hemisphere is developed. Horizontal diffusion and vertical shearing stresses are incorporated along with a diabatic heating...

F. N. Alyea

1972-01-01

64

Mantle viscosity and ice-age ice sheet topography  

SciTech Connect

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

Peltier, W.R. [Univ. of Toronto, Ontario (Canada)

1996-09-06

65

Stationary Waves of the Ice Age Climate.  

NASA Astrophysics Data System (ADS)

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

Cook, Kerry H.; Held, Isaac M.

1988-08-01

66

How ice age climate got the shakes  

SciTech Connect

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

Kerr, R.A.

1993-05-14

67

Terminating the 100 kyr ice age cycle  

Microsoft Academic Search

We report a simulation of the most recent 100,000-year glaciation-deglaciation cycle of the late Pleistocene ice age, a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record. Our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing

Lev Tarasov; W. Richard Peltier

1997-01-01

68

Volcano-ice age link discounted  

SciTech Connect

Speculation that huge volcanic eruptions may have caused an immediate `volcanic winter` that devastated early humans and accelerated a slide into the Ice Age. However, further information from the Greenland ice sheet about the Toba errumption on the island of Sumatra 70,000 years ago, seems to indicate that such volcanic actions wasn`t a major climatic catalyst. This article discusses the evidence and further possibilities.

Kerr, R.A.

1996-05-10

69

Self-potential investigation of moraine dam seepage  

NASA Astrophysics Data System (ADS)

Self-potential (SP) and electrical resistivity measurements are used to investigate seepage at a remote moraine dam in the Sierra Nevada of California. The site is a small terminal moraine impounding roughly 300,000 m3 of water at ~ 3400 m a.s.l. Suspicious fine sediment in a small lake at the dam's downstream toe prompted initial concerns that anomalous seepage may be eroding matrix material from the moraine. 235 individual SP measurements covering the surface of the dam were collected in order to investigate electrokinetic current sources resulting from seepage, while resistivity soundings probed moraine stratigraphy and suggest that the till contains interstitial ice. Contoured SP data reveal a non-uniform voltage distribution over the moraine dam and two distinct negative SP anomalies. The first, located in the central area of the moraine, shows a broad negative SP zone around the crest and increasingly positive SP moving downhill towards both the upstream and downstream toes. This anomaly can be explained by shallow gravitational groundwater flow in the near subsurface combined with upward groundwater flux through evapotranspiration; numerical simulation of the combined effect matches field data well. The second SP anomaly has a tightly localized distribution and can be explained by vertically descending flow into a bedrock fault conduit. Our conceptual seepage model suggests that flow travels from Dana Lake first at the boundary of ice-filled moraine and bedrock before converging on a concentrated channel in the subvertical fault zone. Positive SP near the dam abutments results from groundwater inflow from adjacent hillslopes. Combined analyses suggest that seepage erosion is not currently affecting the moraine dam, and that the sediment observed on the bed of the downstream toe lake is likely a remnant of past outflow events.

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

2011-08-01

70

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

NASA Astrophysics Data System (ADS)

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 14 C 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 14 C yrs BP to 13,450 ± 150 14 C 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 14 C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 14 C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 14 C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 14 C 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 had receded to just outboard of the outer Holocene moraines at Lago Frías and Lago Pearson (Anita) prior to 10,400 ± 40 14 C yrs BP (12,270 ± 100 cal yrs BP) and 9040 ± 45 14 C yrs BP (10,210 ± 50 cal yrs BP), respectively. The most extensive recession registered during the early Holocene was in Agassiz Este Valley, where the Upsala Glacier had pulled back behind the outer Holocene moraine, reaching close to the present-day glacier terminus before 8290 ± 40 14 C yrs BP (9300 ± 80 cal yrs BP). The radiocarbon-dated fluctuations of the Lago Argentino glacier in late-glacial time, given here, are in accord with changes in ocean mixed layer properties, predominately temperature, derived from the isotopic record given here of ODP Core 1233, taken a short distance off shore of the Chilean Lake District. It also matches recently published chronologies of late-glacial moraines in the Southern Alps of New Zealand on the opposite side of the Pacific Ocean from Lago Argentino. Finally, the timing of the late-glacial reversal of the Lago Argentino glacier fits the most recent chronology for the culmination of the Antarctic Cold Reversal (ACR) in the deuterium record of the EPICA Dome C ice core from high on the East Antarctic Plateau. Therefore, we conclude that the climate signature of the ACR was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe.

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

2011-09-01

71

Post Little Ice Age Collapse of the Glacier Bay Icefield, Alaska  

NASA Astrophysics Data System (ADS)

Glacier Bay provides an excellent example of the tidewater glacier cycle proposed by Austin Post. It has a complete record of an advancing phase, stability, rapid calving and drawdown, lengthy retreat, and then readvance behind protective sediments. Glacier Bay currently consists of numerous discrete glaciers and small isolated icefields, but it recently contained a huge continuous icefield up to 2 km thick that covered more than 6000 km2 at the peak of the Little Ice Age (LIA) (1750 AD). Rapid calving and associated upstream drawdown lead to its collapse. In less than 160 yrs, the main trunk of the icefield retreated 120 km in fjords as deep as 500 m. We evaluated the LIA volume and topography of the Glacier Bay Icefield based on mapping of trimlines, lateral moraines and terminal moraines. We used light aircraft to identify these geomorphic markers as well as analysis of vertical airphotos, hydrographs, seismic profiles, and the SRTM digital elevation model. Our reconstruction indicates an ice volume loss of over 3000 km3 during the post-LIA collapse. This localized ice wastage represents the largest post-LIA deglaciation known to us, and is greater than the volume lost from all Alaskan and neighboring Canadian Glaciers from 1955-2002, greater in volume than the Larsen B 2002 ice shelf collapse, comparable in volume to Lake Huron, and equivalent to a global rise in sea level (SLE) of 8 mm. The collapse of the Glacier Bay icefield stranded many tributary glaciers. Some were entirely isolated from any source of accumulation and are now simply wasting away (e.g., Burroughs Glacier). Other glaciers in the region have had their accumulations areas severely reduced as the icefields feeding the LIA tidewater glaciers disappeared (e.g., Casement and Brady Glaciers). The vast loss of ice has lead to some of the highest rates of glacier rebound presently occurring in the world (32 mm/yr) with total uplift since the 18th century of as much as 5.8 m. Facilitated by infill of fjords from erosion and remobilization of subglacial sediments, several glaciers are now in the advancing phase of the tidewater glacier cycle despite the regional trend of glacier wastage. Post-LIA Glacier Bay could provide an analogue to collapse of other tidewater glacier systems and outlet glaciers from polar ice sheets.

Motyka, R. J.; Larsen, C. F.

2005-12-01

72

Last glacial maximum climate inferences from cosmogenic dating and glacier modeling of the western Uinta ice field, Uinta Mountains, Utah  

Microsoft Academic Search

During the last glacial maximum (LGM), the western Uinta Mountains of northeastern Utah were occupied by the Western Uinta Ice Field. Cosmogenic 10Be surface-exposure ages from the terminal moraine in the North Fork Provo Valley and paired 26Al and 10Be ages from striated bedrock at Bald Mountain Pass set limits on the timing of the local LGM. Moraine boulder ages

Kurt A. Refsnider; Benjamin J. C. Laabs; Mitchell A. Plummer; David M. Mickelson; Bradley S. Singer; Marc W. Caffee

2008-01-01

73

Age characteristics in a multidecadal Arctic sea ice simulation  

SciTech Connect

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

Hunke, Elizabeth C [Los Alamos National Laboratory; Bitz, Cecllia M [UNIV. OF WASHINGTON

2008-01-01

74

Late-Wisconsin End Moraines in Northern Canada.  

PubMed

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

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

1965-02-01

75

Why could ice ages be unpredictable?  

NASA Astrophysics Data System (ADS)

It is commonly accepted that the variations of Earth's orbit and obliquity control the timing of Pleistocene glacial-interglacial cycles. Evidence comes from power spectrum analysis of palaeoclimate records and from inspection of the timing of glacial and deglacial transitions. However, we do not know how tight this control is. Is it, for example, conceivable that random climatic fluctuations could cause a delay in deglaciation, bad enough to skip a full precession or obliquity cycle and subsequently modify the sequence of ice ages? To address this question, seven previously published conceptual models of ice ages are analysed by reference to the notion of generalised synchronisation. Insight is being gained by comparing the effects of the astronomical forcing with idealised forcings composed of only one or two periodic components. In general, the richness of the astronomical forcing allows for synchronisation over a wider range of parameters, compared to periodic forcing. Hence, glacial cycles may conceivably have remained paced by the astronomical forcing throughout the Pleistocene. However, all the models examined here also show a range of parameters for which the structural stability of the ice age dynamics is weak. This means that small variations in parameters or random fluctuations may cause significant shifts in the succession of ice ages if the system were effectively in that parameter range. Whether or not the system has strong structural stability depends on the amplitude of the effects associated with the astronomical forcing, which significantly differ across the different models studied here. The possibility of synchronisation on eccentricity is also discussed and it is shown that a high Rayleigh number on eccentricity, as recently found in observations, is no guarantee of reliable synchronisation.

Crucifix, M.

2013-02-01

76

The importance of poligenic moraines in the paleoclimatic interpretation from cosmogenic dating  

NASA Astrophysics Data System (ADS)

The dating of moraine boulders by the surface exposure dating technique is increasingly frequent but does not always achieve homogeneous results. In the Iberian Peninsula, the use of this method has suggested several glaciations in the North and in the South, when in the centre only the last glaciation was identified. Moreover, the date of the last maximum advance of the Pleistocene in the Iberian Peninsula varies by more than 30 ka depending on the results obtained in different mountain ranges. This chronological discrepancy has been explained by the regional climatic behaviour during the glacial phases, especially in relation to precipitation. However, over the last years, as new results are known, the hypothesis of the regional climatic diversity is more difficult to accept. A similar pattern occurred in the tropical Andes where, as in the Iberian Peninsula, several glaciations were dated in some mountain ranges and just the last glaciation in others. Moreover, the dating results of the last maximum glacial advance of the Pleistocene give a difference of more than 20 ka. First, this advance was seen as much earlier than the global; then, the advance was suggested to be diachronic but consistent with its latitude; and finally, the different regional distribution of precipitation became the accepted explanation. As new results appear, the hypotheses which try to provide a general explanation of the glacial behaviour during the Pleistocene in central Andes loose consistency. In this work we analyse various cases from both geographic areas and we achieve a double-conclusion: cosmogenic methods only indicate a minimum age of the moraine forms and, in many cases, a moraine formation does not indicate a specific glacial phase but is the results of the overlapping during different phases. Thus, we can observe that in some valleys multiple glacial phases form a unique polygenic moraine and, in adjacent valleys, every glacial advance deposits its own moraine ridges. This uneven behaviour, most of all in ice caps, obeys to local factors, both microclimatic and derived from the specific glacial dynamics. The cosmogenic dating results are very diverse and diachronic on moraine formations in both study areas but, on the other hand, the results within the same areas and using the same methods are absolutely homogeneous and isochronic, reinforcing the hypothesis here presented. Research funded by CGL2009-7343 project, Government of Spain.

Palacios, D.; Andrés, N.; Úbeda, J.; Alcalá, J.; Marcos, J.; Vázquez-Selem, L.

2012-04-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

78

Abrupt onset and intensification of the Little Ice Age in Arctic Canada linked to explosive volcanism and sea-ice/ocean feedbacks  

NASA Astrophysics Data System (ADS)

At high northern latitudes the most reliable monitors of summer temperature are glaciers and ice caps. Small ice caps are multi-decadal integrators of climate. Precise 14C dates on rooted vegetation exposed by recent recession of more than 70 different ice caps that have remained perpetually frozen to their beds since their inception date ice-cap inception at that site. Unlike valley glacier moraines that are not formed until long after the initial climate shift, entombed plants date the moment of a persistent summer cooling. The composite probability density function of the 138 calibrated 14C ages indicates that ice caps expanded in four discrete intervals within the past 2 ka, with the most abrupt ice-cap growth ~1250 AD following three centuries of relative warmth, and intensified ice expansion ~1450 AD, with maximum ice cover ~1850 AD. These intervals of sudden and sustained ice expansion coincide with the three most volcanically perturbed half centuries of the past millennium. Separating the impacts of solar and volcanic forcings in the late Holocene has been vexing because decades of low solar irradiance largely coincide with decades of frequent explosive volcanism. Transient simulations with a fully coupled climate model show that the main features of our proxy data can be matched by decadally paced explosive volcanism alone, perpetuated by feedbacks related to consequent sea-ice expansion and export into the northern North Atlantic. Exported sea ice cools and freshens surface waters there, leading to a reduction in the AMOC and consequently perpetuation of an expanded sea ice state. The coincidence of low decadal solar irradiance with decades of explosive volcanism suggests that volcanic impacts may have been amplified by solar variability, but scaling the proxies of past solar irradiance remains uncertain. The persistence in the Eastern Canadian Arctic of some ice caps that formed 5000 years ago and remained intact until melting in the past decade, confirms that no subsequent century there was as warm as the most recent one, confirming the unusual character of present Arctic warming.

Miller, G. H.; Refsnider, K. A.; Zhong, Y.; Otto-Bliesner, B. L.; Lehman, S. J.; Southon, J. R.

2011-12-01

79

ConcepTest: Ocean Salinity During an Ice Age  

NSDL National Science Digital Library

One million years ago ice sheets covered much of the Earth's land surface during an ice age. How did this affect the salinity of the oceans? a. Oceans were saltier than today. b. Oceans were less salty than ...

80

‘Little Ice Age’ glacier fluctuations, Gran Campo Nevado, southernmost Chile  

Microsoft Academic Search

Moraine systems of Glaciar Lengua (unofficial name) and neighbouring glaciers of Gran Campo Nevado (53°S) in the southernmost Andes were mapped and dated by dendrochronological means. They were formed around AD 1628, 1872\\/1875, 1886, 1902, 1912 and 1941 with the advance in the 1870s being calendar dated. Recessional moraines within each moraine system correspond to brief standstills or minor readvances.

Johannes Koch; Rolf Kilian

2005-01-01

81

Why could ice ages be unpredictable?  

NASA Astrophysics Data System (ADS)

It is commonly accepted that the variations of Earth's orbit and obliquity control the timing of Pleistocene glacial-interglacial cycles. Evidence comes from power spectrum analysis of palaeoclimate records and from inspection of the timing of glacial and deglacial transitions. However, we do not know how tight this control is. Is it, for example, conceivable that random climatic fluctuations could cause a delay in deglaciation, bad enough to skip a full precession or obliquity cycle and subsequently modify the sequence of ice ages? To address this question, seven previously published conceptual models of ice ages are analysed by reference to the notion of generalised synchronisation. Insight is being gained by comparing the effects of the astronomical forcing with idealised forcings composed of only one or two periodic components. In general, the richness of the astronomical forcing allows for synchronisation over a wider range of parameters, compared to periodic forcing. Hence, glacial cycles may conceivably have remained paced by the astronomical forcing throughout the Pleistocene. However, all the models examined here show regimes of strong structural dependence on parameters. This means that small variations in parameters or random fluctuations may cause significant shifts in the succession of ice ages. Whether the actual system actually resides in such a regime depends on the amplitude of the effects associated with the astronomical forcing, which significantly differ across the different models studied here. The possibility of synchronisation on eccentricity is also discussed and it is shown that a high Rayleigh number on eccentricity, as recently found in observations, is no guarantee of reliable synchronisation.

Crucifix, M.

2013-10-01

82

Marginal formation of De Geer moraines and their implications to the dynamics of grounding-line recession  

Microsoft Academic Search

De Geer moraine ridges occur in abundance in the coastal zone of northern Sweden, preferentially in areas with proglacial water depths in excess of 150 m at deglaciation. From detailed sedimentological and structural investigations in machine-dug trenches across De Geer ridges it is concluded that the moraines formed due to subglacial sediment advection to the ice margin during temporary halts

MATTIAS LINDEN; PER MOLLER

83

On the causes of ice-ages  

Microsoft Academic Search

The distinction between homogeneous black ice and bubbly ice is well-known. Light entering homogeneous ice at normal incidence propagates without scattering until it is absorbed by the ice in a distance of ~10 m or more. Air bubbles serve as scattering centres, and if there are enough of them multiple scatterings turn the light around by a random walk before

Fred Hoyle

1984-01-01

84

A revisionist timetable for the ice ages  

SciTech Connect

In terms of sheer mass, there's no contest. In one corner, there's a land-based record of ice age climates that takes the form of a single carbonate cylinder about the size of the cardboard tube in a roll of paper towels. In the other corner, there's the marine record, which draws on the tons of deep-sea mud cored around the world during the past 20 years. But a group of researchers argues that the lone continental record, drilled from a wall of calcite in Devil's Hole, Nevada, is enough to unseat the conventional wisdom about the causes of the ice ages. The reason a single stick of carbonate has received all this attention is the unique resource it contains: a precisely dated continental climate record of the past 600,000 years. The record was deposited from ground water, which carried a measure of air temperature in the form of the water's oxygen isotope composition. As the water seeped into Devil's Hole - an open, water-filled fault zone - carbonate crystallized out, locking up some of the water's oxygen and building up a climate record layer by layer. Drilling into the walls of the fault, a core was retrieved spanning layers formed between 60,000 and 560,000 years ago, as measured by high-precision uranium thorium dating.

Kerr, R.A.

1992-10-09

85

Rapid Communication Huge Ice-age lakes in Russia  

Microsoft Academic Search

During an early phase of the Last Ice Age (Weichselian, Valdaian), about 90 000 yr ago, an ice sheet formed over the shallow Barents and Kara seas. The ice front advanced on to mainland Russia and blocked the north-flowing rivers (Yenissei, Ob, Pechora, Dvina and others) that supply most of the freshwater to the Arctic Ocean. The result was that

JAN MANGERUD; VALERY ASTAKHOV; MARTIN JAKOBSSON

2001-01-01

86

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

NASA Astrophysics Data System (ADS)

Quantitative assessment of the spatial and temporal scale of ice volume change of the West Antarctic ice sheet (WAIS) and Ross Ice Shelf since the last glacial maximum (LGM) ~20 ka is essential to accurately predict ice sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar ice sheets is uncertain and the timing of any such contribution is controversial. Mackintosh et al (2007) suggest that sectors of the EAIS, similar to those studied at Framnes Mountains where the ice sheet slowly calves at coastal margins, have made marginal contributions to global sea-level rise between 13 and 7 ka. In contrast, Stone et al (2003) document continuing WAIS decay during the mid-late Holocene, raising the question of what was the response of the WAIS since LGM and into the Holocene. Terrestrial evidence is restricted to sparse coastal oasis and ice free mountains which archive limits of former ice advances. Mountain ranges flanking the Darwin-Hatherton glaciers exhibit well-defined moraines, weathering signatures, boulder rich plateaus and glacial tills, which preserve the evidence of advance and retreat of the ice sheet during previous glacial cycles. Previous studies suggest a WAIS at the LGM in this location to be at least 1,000 meters thicker than today. As part of the New Zealand Latitudinal Gradient Project along the Transantarctic, we collected samples for cosmogenic exposure dating at a) Lake Wellman area bordering the Hatherton Glacier, (b) Roadend Nunatak at the confluence of the Darwin and Hatherton glaciers and (c) Diamond Hill which is positioned at the intersection of the Ross Ice Shelf and Darwin Glacier outlet. While the technique of exposure dating is very successful in mid-latitude alpine glacier systems, it is more challenging in polar ice-sheet regions due to the prevalence of cold-based ice over-riding events and absence of outwash processes which removes glacially transported debris. Our glacial geomorphic survey from ice sheet contact edge (~850 masl) to mountain peak at 1600 masl together with a suite of 10Be and 26Al exposure ages, documents a pre-LGM ice volume at least 800 meters thicker than current ice levels which was established at least 2 million years ago. However a complex history of exposure and re-exposure of the ice free regions in this area is seen in accordance with advance and retreat of the ice sheets that feeds into the Darwin -Hatherton system. A cluster of mid-altitude boulders, located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, have exposure ages ranging from 30 to 40 ka. Exposure ages for boulders just above the ice contact range from 1to 19 ka and allow an estimate of inheritance. Hence, we conclude that LGM ice volume was not as large as previously estimated and actually little different from what is observed today. These results raise rather serious questions about the implications of a reduced WAIS at the LGM, its effect on the development of the Ross Ice Shelf, and how the Antarctic ice sheets respond to global warming. J. O. Stone et al., Science v299, 99 (2003). A. Mackintosh, D. White, D. Fink, D. Gore et al, Geology, v 35; 551-554 (2007).

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

2010-05-01

87

Timing of Expansions of the Quelccaya Ice Cap, Peru, and Implications for Cosmogenic Nuclide Production Rate Calibration  

NASA Astrophysics Data System (ADS)

We calibrate the production rate of the cosmogenic nuclide beryllium-10 (10Be) at a low-latitude, high-elevation site, using nuclide concentrations measured in moraine boulders and an independent chronology determined with bracketing radiocarbon dates. The measurement of terrestrial cosmogenic nuclide (TCN) concentrations in earth surface materials has been an important development for understanding a host of earth surface processes. Uncertainty in cosmogenic nuclide production rates has hampered application of this method. Here, we contribute to the estimation of 10Be production rates by reporting both preliminary 10Be concentrations and independent radiocarbon dates from a low latitude, high elevation site. Our study site in the southeastern Peruvian Andes (~13.9°S, 70.9°W, 4850 m asl) is centered on a moraine set, known as the Huancané II moraines, that represents a ~4 km expansion of Quelccaya Ice Cap during late glacial time. At this location, organic material situated both stratigraphically below and above moraines in two adjacent valleys provide material for radiocarbon dating. Based on geomorphic arguments, we correlate results from the two valleys. The timing of ice cap margin advance is bracketed by 13 radiocarbon ages on organic material within the outermost Huancané II moraines that range from 13.6 to 12.5 ka. Two stratigraphic sections upvalley from the moraines yield 6 radiocarbon ages from 11.3 to 12.4 ka, indicating the time of retreat . We computed the probability density function that lies between these two sets of dates, and assign an age of 12.4 ka (+/-???) for the formation of the Huancané II moraines. Calculating beryllium-10 exposure dates from the measured concentrations yield exposure dates that significantly underestimate the independently determined age of the moraine (~8-30%), if existing production rate estimates are used. We suggest that the radiocarbon age for the moraines can be used as a robust independent calibration for 10Be production rates at this site.

Lowell, T. V.; Kelly, M. A.; Applegate, P. J.; Smith, C. A.; Phillips, F. M.; Hudson, A. M.

2010-12-01

88

Modeling dependence of moraine deposition on climate history: the effect of seasonality  

Microsoft Academic Search

A simple shallow-ice flowline glacier model coupled to a model of sediment transport and deposition is used to simulate formation and preservation of moraines. The number, positions, and volume of moraines formed all are sensitive to the climate history assumed. We drive the model with the GISP2 central-Greenland temperature record, and with reduced-millennial-amplitude versions of that record, to test the

David A. Vacco; Richard B. Alley; David Pollard

2009-01-01

89

Geological Evidence for Recent Ice Ages on Mars  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

90

Hydrothermal calcite in the Elephant Moraine  

SciTech Connect

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

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

1986-01-01

91

Ice Age Paleontology of Southeast Alaska  

NSDL National Science Digital Library

In 1990 vertebrate fossils were found in the caves of southeast Alaska, an area of impressive karst topography. Since then, large-scale paleontological and archaeological excavations have been conducted on northern Prince of Wales Island, and the research is now expanding to other islands and coastal mainland areas of southeast Alaska. The goal of this research is to establish a complete chronology of mammals, birds, and fish living in the region before, during, and following the Last Glacial Maximum, and up to the present day. This work is helping to establish the timing and extent of glaciation, the presence of Ice Age coastal refugia for land mammals, and the possibility that humans first entered North America by this coastal route. The results of this research are available at this site.

Heaton, Timothy

2002-01-01

92

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

NASA Astrophysics Data System (ADS)

The onset of deglaciation of the Lake Michigan lobe (LML) in the western Great Lakes region of North America is well-defined by radiocarbon ages from terrestrial plant material that was buried by proglacial lake sediment and till. A small portion of the lobe began its final retreat during the Marengo Phase at about 24,780 C-14 yr BP (29,630 cal yr BP) [CalPal]; most of the lobe began its final retreat during the Shelby Phase starting at about 19,350 C-14 yr BP (23,010 cal yr BP)[Calib 5.02]. New radiocarbon ages from tundra plant fossils encased in the deposits of ice-walled lakes allow estimation periods of ice stagnation vs. margin advance as well as constraining the age of important events during the late Wisconsin Episode. For example, radiocarbon ages from fossils in ice-walled deposits indicate the LML margin began its final retreat from Illinois at the onset of the Mackinaw lake phase by about 13,650 C-14 yr BP (16,250 cal yr BP). Located on the Marseilles Morainic System, the oldest dated ice-walled lake deposit known in Illinois began to form at 18,210 C-14 yr BP (21,680 cal yr BP). From its end moraine located near Peoria to Chicago on the shores of southern Lake Michigan, the LML extended about 230 km. Collectively, the ages indicate that the outer 100 km of the LML margin retreated about three times faster than the inner 130 km (7.5 x 10-2 km/yr vs. 2.4 x 10-2 km/yr). Changes in ice thickness and dynamics, debris concentration, climate, and regional drainage are some of the likely factors that affected the difference in rate. The existing data provide conservative estimates for the formation of two moraines, the lake-border Deerfield Moraine (720 cal yrs) and the Tinley Moraine (850 cal yrs). Periods of stagnations, marked by radiocarbon ages from fossils in the ice-walled lake sediments, include about 320 years (Deerfield Moraine), 520 cal yrs (Tinley Moraine), 500 cal yrs (Woodstock Moraine), and 710 years (Ransom Moraine). These and other ages indicate that ice stagnation occurred during at least 45% of the 5,430 year period when these and intervening moraines formed.

Curry, B.

2009-12-01

93

Simulation of the tropical climate of an ice age  

Microsoft Academic Search

Numerical time integrations of a general circulation model of the atmosphere are performed with both modern and ice age boundary conditions. It is shown that the climate of continental portions of the tropics in the ice age simulation is much drier than that of the modern climate simulation. According to comparisons of results from the two experiments, tropical continental aridity

Syukuro Manabe; Douglas G. Hahn

1977-01-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

95

Carbon-14 ages of Allan Hills meteorites and ice  

NASA Astrophysics Data System (ADS)

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

Fireman, E. L.; Norris, T.

96

Little ice age clearly recorded in northern Greenland ice cores  

Microsoft Academic Search

Four ice cores drilled in the little investigated area of northern and northeastern Greenland were evaluated for their isotopic (delta18O) and chemical content. From these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced, which reveals distinct climate cooling during the 17th and the first half of the 19th century. Timing of

H. Fischer; M. Werner; D. Wagenbach; M. Schwager; T. Thorsteinnson; F. Wilhelms; J. Kipfstuhl; S. Sommer

1998-01-01

97

Ice Age terrestrial carbon changes revisited  

NASA Astrophysics Data System (ADS)

N. Shackleton (1977) first proposed that changes in the marine ?13C record (??13C) could be used to infer ice age changes in carbon storage on land. The previously published best estimate from the marine record is equivalent to about 490 Gt (0.32 ??13C). However, Adams et al. (1990) utilized a pollen database to estimate a 1350 Gt change in carbon storage, which would cause a ??13C of about 0.90‰. The nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land. To address the nature of this discrepancy, I have reexamined the terrestrial carbon record based on a new pollen database compiled by R. Webb and the Cooperative Holocene Mapping Project (COHMAP) group. I estimate about 750-1050 Gt glacial-interglacial change in terrestrial carbon storage, with the range reflecting uncertainties in carbon storage values for different biomes. Additional uncertainties apply to rainforest and wetland extent and presence of C4 plants, which have a significantly different isotopic signature than C3 plants. Although some scenarios overlap a new estimate of carbon storage based on the oceanic ??13C record (revised to 0.40‰ and 610 Gt), most estimates seem to fall outside the envelope of uncertainty in the marine record. Several possible explanations for this gap involve: (1) a missing sink may be involved in land-sea carbon exchange (e.g., continental slopes); (2) the geochemistry of the exchange process is not understood; (3) carbon storage by biome may have changed under ice age boundary conditions; or (4) the standard interpretation of whole ocean changes in the marine ?13C record requires reevaluation. This latter conclusion receives some support from comparison of the ?13C records for ?18O Stages 2 and 6. For the Stage 6 glacial, the ?13C changes are 50-60% larger than for the Stage 2 glacial. Yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading. To summarize, the above analysis implies that, despite the uncertainties remaining in estimates of terrestrial carbon storage changes, a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine ?13C record.

Crowley, Thomas J.

1995-09-01

98

The Little Ice Age in Mesoamerica  

NASA Astrophysics Data System (ADS)

The spatial and seasonal distribution of rainfall is highly variable across the Yucatan Peninsula today, and is affected by climate variability of both Pacific (e.g., ENSO) and Atlantic (e.g., NAO) origin. The northwest coast is driest and is marked by a steep precipitation gradient from a low of 450 mm/yr near Progreso (21.3°N), increasing to 1000 mm/yr at Merida (21.0°N), and 1150 mm/yr at Abala (20.7°N), representing almost a 3-fold increase over a distance of only 65 km with negligible topographic relief. The region is highly attractive for paleoclimate study because of the steep rainfall gradient that is this sensitive to past changes in the position of the ITCZ. Consequently, we studied a 5.1-m sediment core from Aguada X'caamal (20.61°N, 89.72°W, max. depth = 12 m), a sinkhole lake located near the town of Abala, Mexico. Between 1400 and 1500 A.D., oxygen isotope ratios of the gastropod Pyrgophorus coronatus (spinose) increased by ~3‰ and the benthic foraminifer Ammonia beccarii became abundant in the sediment profile, providing strong evidence for a pronounced increase in evaporation/precipitation ratio (E/P) and the salinity of Aguada X'caamal. This interpretation is supported by historical accounts of intense drought in the mid-1400s described in the Book of Chilam Balam of Mani (Gill, 2000), a town located only 45 km southeast of Aguada X'caamal. Oxygen isotope values in sediment cores from Lake Chichancanab (19.9°N) and Lake Salpeten (17°N) to the south also show an increase in the mid 15th century, although the magnitude is less than that recorded in northwest Yucatan. Increased E/P on the Yucatan Peninsula in the 15th century coincided with the start of the Little Ice Age (LIA), and is synchronous with increased aridity inferred from trace metals (Fe and Ti) in the Cariaco Basin off Venezuela, and with expressions of the LIA in tropical and polar ice cores. Colder temperatures during the LIA are well known to have had a societal impact in Greenland and Europe, and decreased precipitation in Mesoamerica may have contributed to cultural change such as the collapse of the Mayapan hegemony in the mid 15th century (Gill, 2000). Gill, R.B. (2000). The Great Maya Droughts, University of New Mexico Press, Albuquerque.

Hodell, D. A.; Brenner, M.; Curtis, J. H.; Medina Gonzalez, R. M.; Rosenmeier, M. F.; Guilderson, T. P.

2002-12-01

99

Using geophysics on a terminal moraine damming a glacial lake: the Flatbre debris flow case, Western Norway  

NASA Astrophysics Data System (ADS)

A debris flow occurred on 8 May 2004, in Fjørland, Western Norway, due to a Glacial Lake Outburst Flood and a natural terminal moraine failure. The site was investigated in 2004 and 2005, using pre- and post-flow aerial photos, airborne laser scanning, and extensive field work investigations, resulting in a good understanding of the mechanics of the debris flow, with quantification of the entrainment and determination of the final volume involved. However, though the moraine had a clear weak point, with lower elevation and erosion due to overflowing in the melting season, the sudden rupture of the moraine still needs to be explained. As moraines often contain an ice core, a possible cause could be the melting of the ice, inducing a progressive weakening of the structure. Geophysical investigations were therefore carried out in September 2006, including seismic refraction, GPR and resistivity. All methods worked well, but none revealed the presence of ice, though the depth to bedrock was determined. On the contrary, the moraine appeared to be highly saturated in water, especially in one area, away from the actual breach and corresponding to observed water seepage at the foot of the moraine. To estimate future hazard, water circulation through the moraine should be monitored over time.

Lecomte, I.; Thollet, I.; Juliussen, H.; Hamran, S.-E.

2008-04-01

100

Amplification of European Little Ice Age by sea ice-ocean-atmosphere feedbacks  

NASA Astrophysics Data System (ADS)

The transition from the Medieval Climate Anomaly (~950-1250 AD) to the Little Ice Age (~1400-1700 AD) is believed to have been driven by an interplay of external forcing and climate system-internal variability. While the hemispheric signal seems to have been dominated by solar irradiance and volcanic eruptions, the understanding of mechanisms shaping the climate on continental scale is less robust. Examining an ensemble of transient model simulations as well as a new type of sensitivity experiments with artificial sea ice growth, we identify a sea ice-ocean-atmosphere feedback mechanism that amplifies the Little Ice Age cooling in the North Atlantic-European region and produces the temperature pattern expected from reconstructions. Initiated by increasing negative forcing, the Arctic sea ice substantially expands at the beginning of the Little Ice Age. The excess of sea ice is exported to the subpolar North Atlantic, where it melts, thereby weakening convection of the ocean. As a consequence, northward ocean heat transport is reduced, reinforcing the expansion of the sea ice and the cooling of the Northern Hemisphere. In the Nordic Seas, sea surface height anomalies cause the oceanic recirculation to strengthen at the expense of the warm Barents Sea inflow, thereby further reinforcing sea ice growth in the Barents Sea. The absent ocean-atmosphere heat flux in the Barents Sea results in an amplified cooling over Northern Europe. The positive nature of this feedback mechanism enables sea ice to remain in an expanded state for decades to centuries and explain sustained cold periods over Europe such as the Little Ice Age. Support for the feedback mechanism comes from recent proxy reconstructions around the Nordic Seas.

Lehner, Flavio; Born, Andreas; Raible, Christoph C.; Stocker, Thomas F.

2013-04-01

101

Late Pleistocene ice age scenarios based on observational evidence  

NASA Astrophysics Data System (ADS)

Ice age scenarios for the last glacial-interglacial cycle, based on observations of Boyle and Keigwin (1982) concerning the North Atlantic thermohaline circulation and of Barnola et al. (1987) concerning atmospheric CO2 variations derived from the Vostok ice cores, are analyzed. Northern Hemisphere continental ice sheets are simulated with an energy balance model (EBM) that is asynchronously coupled to vertically integrated ice sheet models based on the Glen flow law. The EBM includes both a realistic land-sea distribution and temperature-albedo feedback and is driven with orbital variations of effective solar insolation. With the addition of atmospheric CO2 and ocean heat flux variations, but not in their absence, a complete collapse is obtained for the Eurasian ice sheet but not for the North American ice sheet. Further feedback mechanisms, perhaps involving more accurate modeling of the dynamics of the mostly marine-based Laurentide complex, appear necessary to explain termination I.

Deblonde, G.; Peltier, W. R.

1993-04-01

102

Response of the Deep Sea to Ice Ages.  

ERIC Educational Resources Information Center

|During some ice ages, there has been an increase in the production of cold bottom water, whereas in others there has been a decrease. Researchers are investigating why this has occurred. (Author/BB)|

Lohmann, G. P.

1978-01-01

103

A Chronology of Late-Glacial and Holocene Advances of Quelccaya Ice Cap, Peru, Based on 10Be and Radiocarbon Dating  

NASA Astrophysics Data System (ADS)

The Quelccaya Ice Cap region in the southeastern Peruvian Andes (~13-14°S latitude) is a key location for the development of late-glacial and Holocene terrestrial paleoclimate records in the tropics. We present a chronology of past extents of Quelccaya Ice Cap based on ~thirty internally consistent 10Be dates of boulders on moraines and bedrock as well as twenty radiocarbon dates of organic material associated with moraines. Based on results from both dating methods, we suggest that significant advances of Quelccaya Ice Cap occurred during late-glacial time, at ~12,700-11,400 yr BP, and during Late Holocene time ~400-300 yr BP. Radiocarbon dating of organic material associated with moraines provides maximum and minimum ages for ice advances and recessions, respectively, thus providing an independent check on 10Be dates of boulders on moraines. The opportunity to use both 10Be and radiocarbon dating makes the Quelccaya Ice Cap region a potentially important low-latitude calibration site for production rates of cosmogenic nuclides. Our radiocarbon chronology provides a tighter constraint on maximum ages of late-glacial and Late Holocene ice advances. Upcoming field research will obtain organic material for radiocarbon dating to improve minimum age constrains for late-glacial and Late Holocene ice recessions.

Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.

2007-12-01

104

Apparent Slip Rates on the Cordillera Blanca Normal Fault, Peruvian Andes, Determined From Offset Moraine Crests  

NASA Astrophysics Data System (ADS)

In the glacierized Cordillera Blanca, Peru, where the active, west-dipping Cordillera Blanca Normal Fault (CBNF) vertically offsets the crests of numerous moraines, we are dating faulted moraines as a means of determining apparent slip rates on the CBNF. We profiled CBNF scarps on moraines in six valleys: Jeullesh, Quenua Ragra, and Tuco valleys in the Nevado Jeulla Rajo (NJR) massif (10°00'S, 77°16'W) at the southern end of the Cordillera Blanca; and Llaca, Cojup, and Querococha valleys in the central Cordillera Blanca (9°28'-45'S, 77°28'-21'W). The NJR massif hosts a number of small glaciers within a cirque on its southwest face, and large lateral moraines extend onto the Conococha Plain from west-facing valleys. Fault scarps on moraines and valley floors on the western side of NJR show the trace of the north-south-trending CBNF. Surface-exposure ages (10Be) indicate that the largest lateral moraines from Jeullesh Valley are compound features deposited during both the local last glacial maximum (ca. 27-32 ka) and a late-glacial readvance (ca. 15 ka), whereas the large compound lateral moraines from Quenua Ragra Valley are predominantly late-glacial (ca. 15-18 ka). To the north of NJR in the central Cordillera Blanca, the faulted Rurec moraine in Cojup Valley has a 10Be age of ca. 30 ka (Farber et al., 2005). These surface-exposure ages suggest an apparent slip rate of 1.2-1.4 mm/yr for the CBNF in Quenua Ragra Valley (based on moraine ages of 15-18 ka), and 0.5-0.6 mm/yr for Jeullesh Valley and 2.0-2.7 mm/yr for Cojup Valley (based on moraine ages of 30 ka). Samples for 10Be dating have been collected in the Tuco, Llaca, and Querococha valleys, where moraine crests are displaced vertically ca. 44 m , 46-50 m, and 17-26 m, respectively. Field observations suggest an age of 30 ka for faulted moraines in Tuco, Llaca, and Querococha Valleys, which would yield slip rates of ca. 1.5, 1.5-1.7 mm/yr, and 0.6-0.9 mm/yr, respectively. Our estimates are largely consistent with an apparent slip rate of 0.86-1.36 mm/yr calculated for the CBNF on the valley floor at Querococha Valley (Schwartz, 1988). Differences in slip rates along the length of the seismogenic CBNF are known to exist, with the fastest slip occurring to the north of the study area, coincident with the highest topography.

Smith, J. A.; Zehner, S. P., Jr.; Bowen, D. R.; Rodbell, D. T.; Graber, N. R.

2011-12-01

105

Ice ages and nuclear waste isolation  

Microsoft Academic Search

The greatest natural threats to the integrity of the geological barriers to nuclear wastes isolated in cavities mined at depths between 400 and 800m are likely during rapid retreats of future ice sheets. The next major glacial retreat is expected at ca 70ka, well within the lifetime of high grade nuclear waste, but it is not yet clear how long

C. J Talbot

1999-01-01

106

The rock avalanche sediment in moraines and its implication for palaeoclimate reconstruction  

NASA Astrophysics Data System (ADS)

Rock avalanches mobilise a large quantity of sediment that after deposition on a glacier may cause its regime to alter. The glacier response includes change of mass balance after the rock avalanche emplacement followed by re-deposition of the rock avalanche sediment as moraine (Reznichenko et al., 2010; Reznichenko et al., 2011). Such aclimatic glacier response to a supraglacial rock avalanche deposit can confound apparent climatic signals extracted from moraine chronologies, which are widely used to infer regional climate change and are often correlated globally. Therefore, the origin of any particular dated moraine must be clarified before that date can be used for paleoclimatic interpretation. We present a new method that identifies the presence of rock avalanche sediment in moraines, based on the characteristics of the finest sediment fraction which contrast with those of non-rock-avalanche-derived glacial sediment. Under the dry, high-stress conditions during rock avalanche emplacement, fragmenting grains form agglomerates, which are absent in the wet, lower-stress processes of sub- and en-glacial environments. We show that these agglomerates are present in some moraines in the Southern Alps of New Zealand that have been attributed to climate fluctuation. This technique has the potential to resolve long-standing arguments about the role of rock avalanches in moraine formation and to enhance the use of moraines in palaeoclimatological studies. Reznichenko, N.V., Davies, T.R.H., Shulmeister, J. and McSaveney, M.J., 2010. Effects of debris on ice-surface melting rates: an experimental study. Journal of Glaciology, Vol. 56, No. 197, 384-394 Reznichenko, N.V., Davies, T.R.H. and Alexander, D.J., 2011. Effects of rock avalanches on glacier behaviour and moraine formation. Geomorphology, v. 132, is.3-4, p. 327-338

Reznichenko, N.; Davies, T. R. H.; Shulmeister, J.; Winkler, S.

2012-04-01

107

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)

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

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

2012-04-01

108

Little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap  

SciTech Connect

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical condutivity records confirms the worldwide character of this event.

Thompson, L.G.; Mosley-Thompson, E.; Dansgaard, W.; Grootes, P.M.

1986-10-17

109

The Little Ice Age in the Canadian Rockies  

Microsoft Academic Search

This paper reviews the evidence and history of glacier fluctuations during the Little Ice Age (LIA) in the Canadian Rockies. Episodes of synchronous glacier advance occurred in the 12th–13th, early 18th and throughout the 19th centuries. Regional ice cover was probably greatest in the mid-19th century, although in places the early 18th century advance was more extensive. Glaciers have lost

B. H. Luckman

2000-01-01

110

Debris emergence at Fox Glacier, New Zealand and formation of an ablation-dominant medial moraine  

NASA Astrophysics Data System (ADS)

Medial moraines can form important routeways of sediment transport in valley glaciers, and may consist of sediment from a range of sources. Despite the presence of medial moraines on several glaciers in the New Zealand Southern Alps, medial moraines there have hitherto generally escaped attention. The evolving morphology and debris content of the 12.5 km-long Fox Glacier on the western flank of the Southern Alps is the focus of this study. This tests the hypothesis that medial moraine at Fox Glacier is the product of down-glacier lateral compression of accumulation zone rockfall material within a narrow valley tongue, followed by supraglacial emergence due to down-glacier ablation gradients. Using clast orientation, clast shape, and clast lithological data, combined with ablation rates and topographic surveys, this hypothesis is applicable to such a valley glacier with an accumulation area ratio (AAR) of 0.8. Metamorphic grade increases down-valley toward the Alpine Fault at the range front. Hence, as the debris consists of slabby, very angular to angular argillaceous mudstones that generally cleave, and very angular to subangular blocky sandstones, it is likely sourced from rocks located well above the equilibrium line altitude (ELA) near the Main Divide. The debris takes a medium-level to high-level passive transport pathway through the glacier, emerging at a point-source left of centerline in the lower icefall. As the debris layers progressively melt-out, down-glacier widening of the moraine occurs. This growth in moraine width is accompanied by an increase in local relief of the moraine above adjacent debris-free ice. This width and relief increase is itself accompanied by an increase in maximum cross-glacier slope of the moraine down-glacier, reaching around 30° toward the terminus. Cross-sections of the medial moraine exposed in chevron crevasses display a layer of debris around 5 cm thick, with exceptions at the base of steep slopes. Margins of the medial moraine are marked by a discontinuous cover of debris, grading to scattered clasts forming rock tables. Dirt cones are also prevalent along the margins, forming beneath <2 cm thick coarse/very coarse sand-sized (0.5-2 mm) 'fines'. Fabric of clasts reveals a consistent flow-parallel orientation, consistent with foliation and measured strain-rates and vectors. The proglacial area preserves limited evidence of the medial moraine, in the form of low-relief 'dumped' material at the terminus. However, this has low preservation potential due to continual switching of the proglacial river exit portal across the snout.

Brook, M.

2012-04-01

111

The sedimentary and structural evolution of a recent push moraine complex: Holmströmbreen, Spitsbergen  

Microsoft Academic Search

The glacier Holmströmbreen, in Spitsbergen, surged into the ice contact scarp of a proglacial outwash sequence at some time during its Neoglacial maximum. The outwash sediments were pushed along a decollement to produce a moraine in which deformation extended for 1.5 km beyon the furthest extent of the glacier front. The style of folding and faulting and the nature of

G. S. Boulton; D. J. Beets; J. K. Hart; G. H. J. Ruegg

2004-01-01

112

The sedimentary and structural evolution of a recent push moraine complex: Holmstrømbreen, Spitsbergen  

Microsoft Academic Search

The glacier Holmstrømbreen, in Spitsbergen, surged into the ice contact scarp of a proglacial outwash sequence at some time during its Neoglacial maximum. The outwash sediments were pushed along a decollement to produce a moraine in which deformation extended for 1.5km beyond the furthest extent of the glacier front. The style of folding and faulting and the nature of the

G. S. Boulton; D. J. Beets; J. K. Hart; G. H. J. Ruegg

1999-01-01

113

Surface exposure dating of the Great Aletsch Glacier Egesen moraine system, western Swiss Alps, using the cosmogenic nuclide10Be  

Microsoft Academic Search

Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide 10Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The 10Be dates

Meredith A. Kelly; Peter W. Kubik; Friedhelm Von Blanckenburg; Christian SchlÜchter

2004-01-01

114

Ice-age rain forest found moist, cooler  

SciTech Connect

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

Kerr, R.A.

1996-10-04

115

The Uummannaq Ice Stream System, West Greenland  

NASA Astrophysics Data System (ADS)

The offshore and coastal geomorphology of the Uummannaq region of West Greenland records evidence for the advance and decay of the Uummannaq Ice Stream system (UISS) during the Last Glacial Maximum (LGM). Regional ice flow patterns across this region show evidence for a large coalescent onset zone formed of smaller ice streams and fjord outlet glaciers which converged into the Uummannaq trough to form a single ice stream which flowed to the continental shelf break at the LGM. Ice stream surface elevation throughout the onset zone is constrained to a minimum of 1000m asl based on striae, bedform and moraine data, and is further supported by cosmogenic exposure ages on erratics that show warm based ice operating up to 975m asl in both ice stream and inter-stream areas. 14C and surface exposure ages along a transect from the mid-shelf to the present ice margin record initial ice surface down-wasting between 25 to 10.5 ka BP, though some ice stream marginal moraines show late stage ice re-thickening prior to extremely rapid ice stream collapse through the Uummannaq trough between 10.5 and 10.1 ka BP. We suggest this pattern of deglaciation reflects strong surface ablation associated with increased air temperatures running up to the Bolling Interstadial (GIS1e) at c. 14 ka BP, followed by ice re-thickening during the Younger Dryas, and late stage rapid marine calving driven by peak sea-level and bathymetric over-deepening at the start of the Holocene.

Roberts, D. H.; Rea, B.; Lane, T.; Schnabel, C.; Rodes, A.

2012-04-01

116

Late pleistocene ice age scenarios based on observational evidence  

SciTech Connect

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

DeBlonde, G. (Canada Center for Remote Sensing, Ottawa, Ontario (Canada)); Peltier, W.R. (Univ. of Toronto, Ontario (Canada))

1993-04-01

117

Evidence of Little Ice Age in an East Antarctica Ice Core  

NASA Astrophysics Data System (ADS)

An 80 meter ice core was retrieved from an East Antarctica location (76° S, 77° E) by the Chinese Antarctica Research Expedition in 1999. Chemical analysis of the ice core has yielded a record of ionic impurities in snow for the past 800 years (1200-1999 A.D.). The ice core is dated using a combination of annual layer counting and volcanic time stratigraphic horizons, resulting in an accurate chronology with high resolution. The ice core record demonstrates that, during the period of approximately 1300-1850 A.D., the concentrations of several chemical species, including nitrate and methanesulfonate, are sharply lower than the levels both prior to and after this period. This period coincides with the most recent neoglacial climatic episode, the "Little Ice Age (LIA)," that has been found in numerous Northern Hemisphere proxy and historic records. Additional evidence includes the sharply reduced net snow accumulation rates during this period. The significance of this new finding will be discussed in the context of LIA evidence in Antarctica ice cores, its probable regional and spatial variations, and chronological relationships to LIA signals in South America and in the Northern Hemisphere.

Cole-Dai, J.; Li, Y.; Zhou, L.

2003-12-01

118

Climate-forcing & Feedbacks of the Late Paleozoic Ice Age  

NASA Astrophysics Data System (ADS)

Evaluating climate-forcing and feedbacks during pre-Cenozoic ice ages requires reconstructing marine-terrestrial linkages between atmospheric composition, the regional hydroclimate expression of mean climate change, ice sheets, and sea-level. Here we evaluate the role of different climate parameters and their linkages during the Carboniferous icehouse through integration of a recently developed ID-TIMS U-Pb constrained sea-level history, brachiopod stable isotope time-series from shallow marine regions of paleotropical Pangaea, atmospheric pCO2 inferred from paleosol minerals and fossil leaf stomatal indices, ice sheet variations constrained by the distribution of high-latitude Gondwanan glacial deposits, and paleoclimate simulations. Within chronostratigraphic uncertainty, long-term sea-level lowstands coincide with glacial maxima defined from high-latitude Gondwanan basins, whereas long-term highstands are coeval with glacial minima suggesting a dynamic late Paleozoic icehouse. Superimposed shorter-term sea-level events define a stepwise onset (late Mississippian) and contraction of Carboniferous ice sheets prior to the initiation of Early Permian ice sheets. Sea level fluctuations, at different temporal scales parallel trends defined by brachiopod oxygen and carbon isotope compositions and paleo-atmospheric pCO2 estimates inferred using mineral and biologic proxies. A protracted (~9 my) stepwise sea level rise beginning in the middle Pennsylvanian and culminating in an earliest Gzhelian peak is coincident with overall increasing CO2 levels throughout this interval and substantially decreased effective moisture in paleotropical Pangaea. This possibly CO2-forced period of waning continental ice sheets and sea-level highstand encompassed a large-scale floral turnover across the mid-to-late Pennyslvanian boundary and the onset of the demise of paleotropical rainforests across much of Pangaea. Ocean-atmosphere-ice sheet climate simulations for this period reveal a possible mechanistic link between ice sheet extent and stability in high-latitudes and ocean-atmospheric dynamics in the tropics.

Montanez, I. P.; Brand, U.; Poulsen, C. J.; Horton, D. E.

2011-12-01

119

Population genetics of Ice Age brown bears  

PubMed Central

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

Leonard, Jennifer A.; Wayne, Robert K.; Cooper, Alan

2000-01-01

120

Mud aprons in front of Svalbard surge moraines: Evidence of subglacial deforming layers or proglacial glaciotectonics?  

NASA Astrophysics Data System (ADS)

Large debris-flow units commonly occur on the distal sides of subaqueous end moraines deposited by surges of Svalbard tidewater glaciers, but have rarely been described in terrestrial settings. Some researchers have argued that these kinds of debris flows reflect processes unique to the subaqueous environment, such as the extrusion of subglacial deforming layers or extensive failure of oversteepened moraine fronts. In this paper, we describe terrestrial and subaqueous parts of a single late Holocene moraine system deposited by a major surge of the tidewater glacier Paulabreen in west Spitsbergen. The ice-marginal landforms on land closely resemble the corresponding landforms on the seabed as evidenced by geomorphic mapping and geophysical profiles from both environments. Both onland and offshore, extensive areas of hummocky moraine occur on the proximal side of the maximum glacier position, and large mud aprons (interpreted as debris flows) occur on the distal side. We show that the debris-flow sediments were pushed in front of the advancing glacier as a continuously failing, mobile push moraine. We propose that the mud aprons are end members of a proglacial landforms continuum that has thrust-block moraines as the opposite end member. Two clusters of dates (~ 8000 YBP and ~ 700 YBP) have previously been interpreted to indicate two separate surges responsible for the moraine formation. New dates suggest that the early cluster indicates a local extinction of the abounded species Chlamys islandica. Other changes corresponding to the widespread 8.2 ka event within the fjord, may suggest that the extinction of the C. islandica corresponds to that time.

Kristensen, Lene; Benn, Douglas I.; Hormes, Anne; Ottesen, Dag

2009-10-01

121

Temperature differences between the hemispheres and ice age climate variability  

Microsoft Academic Search

The Earth became warmer and cooler during the ice ages along with changes in the Earth's orbit, but the orbital changes themselves are not nearly large enough to explain the magnitude of the warming and cooling. Atmospheric CO2 also rose and fell, but again, the CO2 changes are rather small in relation to the warming and cooling. So, how did

J. R. Toggweiler; David W. Lea

2010-01-01

122

Ice age True Polar Wander: raising debates and new analyses  

Microsoft Academic Search

Issues related to long time scale instability in the Earth's rotation, named True Polar Wander (TPW), have continuously been debated, after the pioneering works of the sixties. Since Maxwell Earth models with elastic or high viscosity viscoelastic lithospheres predict different ice-age TPW in the lower mantle viscosity range 1021 - 1022 Pa s, it has been recently suggested that the

Roberto Sabadini; Gabriele Cambiotti; Yanick Ricard

2010-01-01

123

Isotopes, ice ages, and terminal Proterozoic earth history  

Microsoft Academic Search

ABSTRACT Detailed correlations of ancient glacial de- posits, based on temporal records of carbon and strontium isotopes in seawater, indicate four (and perhaps five) discrete ice ages in the terminal Proterozoic Eon. The close and repeated stratigraphic relationship between C-isotopic excur- sions and glaciogenic rocks suggests that unusually high rates of organic carbon burial facilitated glaciation by reducing atmospheric greenhouse

Alan J. Kaufman; Andrew H. Knoll; Guy M. Narbonne

1997-01-01

124

Evaluating sun–climate relationships since the Little Ice Age  

Microsoft Academic Search

From the coldest period of the Little Ice Age to the present time, the surface temperature of the Earth increased by perhaps 0.8°C. Solar variability may account for part of this warming which, during the past 350 years, generally tracks fluctuating solar activity levels. While increases in greenhouse gas concentrations are widely assumed to be the primary cause of recent

Judith Lean; David Rind

1999-01-01

125

Global warming in the context of the Little Ice Age  

Microsoft Academic Search

Understanding the role of volcanic and solar variations in climate change is important not only for understanding the Little Ice Age but also for understanding and predicting the effects of anthropogenic changes in atmospheric composition in the twentieth century and beyond. The evaluate the significance of solar and volcanic effects, we use four solar reconstructions and three volcanic indices as

Melissa Free; Alan Robock

1999-01-01

126

Intermittent Thinning of Jakobshavns Isbrae Since the Little Ice Age, Reconstructed From Photogrammetry, Remote Sensing and Glacial Geologic Evidence  

NASA Astrophysics Data System (ADS)

Rapid thinning and velocity increase on major Greenland outlet glaciers (Jakobshavn Isbrae, west Greenland; Kangerlussuaq and Helheim glaciers in southeast Greenland) during the last two decades may indicate that these glaciers became unstable as a consequence of the Jakobshavn effect, with terminus retreat leading to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the ice sheet as it responds to the general warming following the Little Ice Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the calving front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as ice further upstream thins and accelerates. To address this issue, we compiled a history of surface elevation changes of Jakobshavn Isbrae since the LIA. We first combined data from historical records, ground surveys, airborne laser altimetry, and field mapping of lateral moraines and trimlines. This record shows two periods of rapid thinning by about 70 meters, in the early 1950s and since 1997. Observed changes in glacier behavior during these two events are markedly different. The recent thinning, which involved several episodes of retreat followed by large thinning, resulted in a rapid retreat of the calving front toward grounding line. Thinning in the 1950s occurred during a period when the calving front was stationary with only minor annual fluctuations. Nevertheless, aerial photographs collected in the 1940s and 50s indicate that thinning extended far inland.

Csatho, B.; van der Veen, C.; Schenk, T.; Thomas, R.

2005-12-01

127

Ice age True Polar Wander: raising debates and new analyses  

NASA Astrophysics Data System (ADS)

Issues related to long time scale instability in the Earth's rotation, named True Polar Wander (TPW), have continuously been debated, after the pioneering works of the sixties. Since Maxwell Earth models with elastic or high viscosity viscoelastic lithospheres predict different ice-age TPW in the lower mantle viscosity range 1021 - 1022 Pa s, it has been recently suggested that the observed fluid Love number should be used to describe the initial equatorial bulge rather than the tidal fluid limit resulting from the viscoelastic modelling itself. We show that different ice-age TPW predictions have to be expected due to the dependence of TPW on the Earth's initial state, characterized by a larger and stress-free equatorial bulge for the viscoelastic lithosphere, compared to the elastic one, and that there is no shortcomings or errors in the traditional approach based on the use of tidal Love number from the model. The use of the observed fluid Love number represents in fact a simplified attempt to couple the effects on TPW from mantle convection and glacial forcing, by including the non-hydrostatic flattening due to mantle convection but not its driving part. This partial coupling freezes in space the non-hydrostatic contribution due to mantle convection, thus damping the present-day ice-age TPW and forcing the axis of instantaneous rotation to come back to its initial position when ice ages started. In this perspective, we discuss the implication of self-consistent convection calculations of the non-hydrostatic contribution and its impact on the long-term Earth's rotation stability during ice-age. We develop a full compressible model, based on the numerical integration in the radial variable of the momentum and Poisson equations and on the contour integration in the Laplace domain, which allows us to deal with the non-modal contribution from continuous radial rheological variations. We quantify the effects of the compressible rheology, compared to the widely used incompressible ones

Sabadini, Roberto; Cambiotti, Gabriele; Ricard, Yanick

2010-05-01

128

The cause of the ice ages  

Microsoft Academic Search

A composite deep-sea core, normalized on the basis of sedimentary averages from seven cores from the Caribbean and one from the Pacific, reveals the occurrence of ten major glaciations during the past 730,000 years and affords a close estimate of their ages. Spacing of glaciation through time ranges from 50,000 to > 100,000 years. Obliquity minima caused significant lowering of

Cesare Emiliani

1978-01-01

129

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

Federal Register 2010, 2011, 2012, 2013

...Environmental Impact Statement for the Ice Age Complex at Cross Plains, Cross Plains...Environmental Impact Statement for the Ice Age Complex at Cross Plains, Wisconsin...may also send comments to Superintendent, Ice Age National Scenic Trail, 700...

2012-03-12

130

Simulating and Investigating the 100ka ice age cycle with a three dimensional ice sheet model and GCM  

Microsoft Academic Search

One of the challenges of earth system modelling is to confirm the theories of ice age cycle by simulating the realistic response of the climate system to the change of orbital parameters, known as Milankovitch forcing, by phisically based models instead of conceptual models. Here we simulate the ice age cycle and investigate the origin of 100ka cycle using a

A. Abe-Ouchi; F. Saito; T. Segawa

2004-01-01

131

Glimpses of the Ice Age from I-81  

NSDL National Science Digital Library

This United States Geological Survey (USGS) publication is part of a series entitled "Geologic Wonders of the George Washington and Jefferson National Forests". The article covers an area from Strasburg to Harrisonburg, Virginia along I-81 that shows evidence of glaciation. A description of the Ice Age, block fields and how they formed, and uses of block fields are discussed. Additional reading resources are also suggested.

132

Chilly ice-age tropics could signal climate sensitivity  

SciTech Connect

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

Kerr, R.A.

1995-02-17

133

Ice Ages on the Earth and their astronomical implications  

Microsoft Academic Search

It is pointed out that while the long-periodic variations of the elements of the terrestrial orbit around the Sun are probably sufficient to account for the frequency-spectrum of recurrent ice-ages established from the geological record of climatic changes experiences by the Earth in the course of the past half a million years, such kinematic phenomena cannot account naturally for the

Zdenek Kopal

1980-01-01

134

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

135

The Little Ice Age: Understanding Climate and Climate Change  

NSDL National Science Digital Library

This is a classroom activity about the forcing mechanisms for the most recent cold period: the Little Ice Age (1350-1850). Students receive data about tree ring records, solar activity, and volcanic eruptions during this time period. By comparing and contrasting time intervals when tree growth was at a minimum, solar activity was low, and major volcanic eruptions occurred, they draw conclusions about possible natural causes of climate change and identify factors that may indicate climate change.

Gardiner, Lisa; University Corporation for Atmospheric Research (UCAR)

136

Architecture and sedimentation pattern of Skeidarárjökull end moraine at Gigjukvisl gap, Iceland  

NASA Astrophysics Data System (ADS)

A complex assemblage of ice marginal and proglacial sediments and their geological architecture were preliminary studied at the Skeidarárjökull marginal zone along the western slope of Gigju River gap, south Iceland. Catastrophic jökulhlaup of 1996 have widened the gap in the end moraine dated to the end of the 19th century exposing the glacigenic sediment sequence. Erosion as a result of the heavy waters flow provided the possibility of detailed structural analysis of the section at the proximal part of the end moraine as well as its architecture study at extra-marginal part. The study was supplemented with some geomorphological observations of the area. The end moraine exposed at the Gigjukvisl gap is composed of the sediments from melting-ice, glaciofluvial, glaciolacustrine, mass -transport and probably other facies related to terminoglacial and proglacial subenvironments. The melting-ice facies is presented by the variety of deposits ranging from gravelly-boulder to sandy-silty diamicton. The meltwater streams have formed the stratified sands and gravels mostly laid in form of fans or small sandurs at the ice front. Glaciolacustrine sandy silt sediments possess seasonal lamination. Partly glaciotectonically disturbed series of diamicton, silt, sand and gravel with the originally stratified structure preserved in many places reveal the complex geological structure of the end moraine. Sedimentary succession reflects the dynamic change of the position of ice margin and sedimentation pattern during short time interval in quite narrow area on Skeiðarársandur, the largest active outwash plain in the world. This study was financed by the Research Council of Lithuania (No. MIP-045/2011).

Šink?nas, P.; Karmaza, B.; Karmazien?, D.; Kazakauskas, V.; Waller, R.

2012-04-01

137

Rapid onset of Little Ice Age summer cold in the northern North Atlantic derived from precisely dated ice cap records (Invited)  

Microsoft Academic Search

Precise radiocarbon dates on dead vegetation emerging beneath retreating non-erosive ice caps in NE Arctic Canada define the onset of ice cap growth, and provide a Holocene context for 20th Century warming. Although most plateau ice caps melted during the Medieval Warm Period, a few that are now disappearing remained intact since at least 350 AD. Little Ice Age ice

G. H. Miller; D. Larsen; A. Geirsdottir; K. A. Refsnider; C. Anderson

2009-01-01

138

What controls dead-ice melting under different climate conditions?  

Microsoft Academic Search

In the geological record, hummocky dead-ice moraines represent the final product of the melt-out of dead- ice. Processes and rates of dead-ice melting in ice-cored moraines and at debris-covered glaciers are commonly believed to be governed by climate. Here, backwasting rates from 14 dead-ice areas are assessed in relation to mean annual air temperature, mean summer air temperature, mean annual

A. Schomacker

2008-01-01

139

Ice Ages and the Asteroid Belt: A Surprising Connection  

SciTech Connect

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

Muller, Richard A. (Lawrence Berkeley Lab)

2001-05-23

140

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

141

Exposure-age record of Holocene ice sheet and ice shelf change in the northeast Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

This paper describes glacial-geologic observations and cosmogenic-nuclide exposure ages from ice-free areas adjacent to the Sjögren, Boydell, and Drygalski Glaciers of the northeast Antarctic Peninsula. These provide a record of Holocene glacier and ice shelf change in this region. Early Holocene ice surface elevation near the present coastline was locally at least 500 m above present sea level, but our observations do not constrain the maximum thickness of Last Glacial Maximum (LGM) ice or the time at which it was attained. The boundary between frozen-based and wet-based ice reached a maximum elevation of 100-150 m above present sea level. The ice surface elevation decreased from 300-500 m elevation to near present sea level between 9 ka and ca 4 ka. Below 160 m elevation, we observed a bimodal distribution of apparent exposure ages in which a population of glacially transported clasts with mid-Holocene exposure ages coexists with another that has exposure ages of 100-600 years. We consider the most likely explanation for this to be i) complete deglaciation of currently ice-free areas, which presumably required the absence of ice shelves, at 3.5-4.5 ka, followed by ii) subsequent ice shelf formation and grounding line advance after ca 1.4 ka, and iii) complete re-exposure of the sites after ice shelf breakup and glacier surface lowering in recent decades. This explanation is consistent with marine sedimentary records indicating that ice shelves in the Prince Gustav Channel and Larsen A embayment were absent in the middle to late Holocene and were re-established within the last 2000 years.

LARISSA Group Balco, Greg; Schaefer, Joerg M.

2013-01-01

142

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

PubMed

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

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

2010-09-03

143

A rapidly growing moraine-dammed glacial lake on Ngozumpa Glacier, Nepal  

NASA Astrophysics Data System (ADS)

Moraine-dammed glacial lakes are becoming increasingly common in the Himalaya as a result of glacier mass loss, causing concern about glacier lake outburst flood risk. In addition to extant lakes, the potential exists for many more to form, as more glaciers ablate down to the level of potential moraine dams. In this paper, we document the recent rapid growth of, a moraine-dammed lake on Ngozumpa Glacier, Nepal. Using a combination of ground-based mapping and sonar surveys, aerial photographs (< 1 m resolution), and ASTER imagery (15 m resolution), processes and rates of lake expansion have been determined. The lake first formed between 1984 and 1992 when collapse of an englacial conduit allowed water to accumulate at the level of a gap in the lateral moraine, ~km from the glacier terminus. Lake growth was initially slow, but since 2001 it has undergone exponential growth at an average rate of 10% y-1. In 2009, the lake area was 300,000 m2, and its volume was at least 2.2 million m3. Calving, subaqueous melting, and melting of subaerial ice faces all contribute to the expansion of the lake; but large-scale, full-height slab calving is now the dominant contributor to growth. Comparison with other lakes in the region indicate that lake growth will likely continue unchecked whilst the spillway remains at its current level and may attain a volume of hundreds of millions of cubic metres within the next few decades.

Thompson, Sarah S.; Benn, Douglas I.; Dennis, Kathryn; Luckman, Adrian

2012-04-01

144

Isotopes, ice ages, and terminal Proterozoic earth history.  

PubMed

Detailed correlations of ancient glacial deposits, based on temporal records of carbon and strontium isotopes in seawater, indicate four (and perhaps five) discrete ice ages in the terminal Proterozoic Eon. The close and repeated stratigraphic relationship between C-isotopic excursions and glaciogenic rocks suggests that unusually high rates of organic carbon burial facilitated glaciation by reducing atmospheric greenhouse capacity. The emerging framework of time and environmental change contributes to the improved resolution of stratigraphic and evolutionary pattern in the early fossil record of animals. PMID:11038552

Kaufman, A J; Knoll, A H; Narbonne, G M

1997-06-24

145

A high glacier opens a view of the ice age tropics  

SciTech Connect

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

Mlot, C.

1995-07-07

146

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

ERIC Educational Resources Information Center

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

Mattioli, Denee J.; Drake, Frederick

1999-01-01

147

Paleoclimatology: Second clock supports orbital pacing of the ice ages  

SciTech Connect

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

Kerr, R.A.

1997-05-02

148

Medieval Warmth, Little Ice Age Cooling, and 20th Century Warming Reconstructed from Icelandic Lake Sediments  

Microsoft Academic Search

Historical records from Iceland provide one of the most compelling lines of evidence for North Atlantic warmth and reduced sea ice during Medieval times, colder summers and expanded sea ice during the Little Ice Age, followed by ameliorated conditions during the 20th century. Icelandic terrestrial records, particularly those derived from lake sediments, tend instead to be over-printed by the ancillary

A. Geirsdottir; G. Miller; M. Wooller; Y. Wang

2004-01-01

149

Statistical, remote sensing-based approach for estimating the probability of catastrophic drainage from moraine-dammed lakes in southwestern British Columbia  

NASA Astrophysics Data System (ADS)

Safe development of glacierized regions requires a systematic and objective method for assessing the hazard posed by moraine-dammed lakes. Empirical relations exist for estimating outburst flood magnitude, but, until now, no standardized procedures have been developed for estimating outburst flood probability. To make quick and inexpensive preliminary assessments that are reproducible, we propose using a statistical, remote sensing-based approach to estimate the probability of catastrophic drainage of moraine-dammed lakes. We completed a comprehensive inventory of 175 moraine-dammed lakes in the southern Coast Mountains of British Columbia, Canada. By applying logistic regression analysis to the data set, we identified and weighted the following four independent predictor variables that best discriminate drained lakes from undrained lakes: moraine height-to-width ratio, presence/absence of an ice-core in the moraine, lake area, and main rock type forming the moraine. With an appropriate classification cutoff value, the predictive model correctly classifies 70% of drained lakes and 90% of undrained lakes, for an overall accuracy of 88%. Our model provides engineers and geoscientists with a tool for making first-order estimates of the probability of catastrophic drainage from moraine-dammed lakes in southwestern British Columbia.

McKillop, Robin J.; Clague, John J.

2007-03-01

150

Annual push moraines as climate proxy  

NASA Astrophysics Data System (ADS)

We reconstruct the terminus position of a mountain glacier in British Columbia, Canada from annual push moraines formed between 1959 and 2007. Our reconstruction represents the longest, annually-resolved record of length change for a North American glacier. Comparison of annual recession with climate records indicates that glacier recession is controlled by air temperatures during the ablation season and accumulation season precipitation during the previous decade. Analysis among records of glacier frontal variation and mass balance in western North America similarly reveals an immediate terminus reaction to summer and net balance and a delayed reaction to winter and net balance. Other mountain ranges may contain long series of push moraines that could be exploited as climate proxies, and to improve understanding of glacier response to climate.

Beedle, Matthew J.; Menounos, Brian; Luckman, Brian H.; Wheate, Roger

2009-10-01

151

Cosmogenic 3 He and 10 Be chronologies of the late Pinedale northern Yellowstone ice cap, Montana, USA  

Microsoft Academic Search

Cosmogenic 3 He and 10 Be ages measured on surface boulders from the moraine sequence deposited by the northern outlet glacier of the Yellowstone ice cap indicate that the outlet glacier reached its terminal position at 16.5 6 0.4 3 He ka and 16.2 6 0.3 10 Be ka, respectively. Concordance of these ages supports the scaled pro- duction rates

Joseph M. Licciardi; Peter U. Clark

2001-01-01

152

Medial moraines of glaciers of the Copper River Basin, Alaska: Discrete landslides dominate over other sources  

NASA Astrophysics Data System (ADS)

Medial moraines are visually dominant structures of most large valley glaciers in the Copper River Basin (CRB), Alaska. Areally extensive but thin (usually <20 cm) accumulations of debris pose challenges for glacier mapping based on multispectral imagery, as done, for instance, in the GLIMS project. The sources of this material include large discrete landslides from wallrocks and from lateral moraines; diffuse contributions from rock falls and talus creep; rocks delivered via snow and ice avalanches; ingestion of lateral moraines along tributary convergences; and basal erosional debris. Evidence indicates that in CRB glaciers, discrete large avalanches predominate as the major contributors of moraine mass. Subglacial erosional debris is predominantly pulverized to small grain sizes and flushed. Many large, young avalanches exist on CRB glaciers. Evidence from colorimetry indicates that many medial moraines actually are landslides that have been sheared and swept downglacier, thus mimicking the form of other types of medial moraines formed where tributaries coalesce and flow down valley. Landcover classification of ASTER imagery, qualitative observations from air photos, and semiquantitative field-based estimations of rock color types indicate that on Allen Glacier, and other CRB glaciers, landslides are the sources of most medial moraines. On Allen and Root Glacier, for example, we see very few boulders with obvious signs of basal abrasion, whereas nearly all boulders exhibit signs of irregular fracture, for example in landslides. Such landslides have large effects on the thermal and mass balance of CRB glaciers, sometimes opposing or in other cases accentuating the effects of global/regional climate change. Considering the link between landslides and seismicity, and that Magnitude 8-9 earthquakes may occur nearby only about once a century, which is also the characteristic response time of large glaciers to climate shifts, seismicity must be considered along with climate change induced glacier responses in the CRB. Ultimately, climate has the final word, and already this is evident in the glacier record. Glacial flour is probably almost entirely from bed erosion. We will present estimates of the contributions of landslides and subglacially pulverized glacial rock flour to the overall rock mass budget of Allen Glacier. Each of the components of the rock mass budget differs in its probable distribution on the surface and within a typical glacier. We will present some preliminary empirical determinations of the influence of various thicknesses of supraglacial rock debris on the local mass balance of Allen Glacier; the net zero influence is exhibited for debris thicknesses on the order of 1 cm of fine debris or ~50% coverage by cobbles or boulders.

Kargel, J. S.; Fischer, L.; Furfaro, R.; Huggel, C.; Korup, O.; Leonard, G. J.; Uhlmann, M.; Wessels, R. L.; Wolfe, D. F.

2009-12-01

153

Evidence for multiple glacier advances in Svalbard recorded by push moraine complex-meltwater channel relationships: the case studies of Finsterwalderbreen and Grønfjordbreen  

NASA Astrophysics Data System (ADS)

Large ice-marginal push moraine complexes, also known as composite ridge systems, have a restricted distribution at active glacier margins, and are thought to be associated with a combination of specific glaciological conditions and the availability of deformable material in the glacier foreland. In Svalbard, it has been recognised that they are often found at the margins of glaciers thought to be of surge-type, and therefore may be a useful indicator of palaeo-surging when found in a Quaternary context elsewhere, although specific case studies are needed to confirm this. We describe geomorphological evidence from large push moraine complexes in front of Finsterwalderbreen and Grønfjordbreen, both of which have been described as surge-type glaciers but have never been observed to surge. A combination of fieldwork, aerial photographs and a digital elevation model were used to assess the relationship between individual ridges within the moraine complexes and meltwater channels, from which it is possible to identify multiple advances of both glaciers. Specifically, there is clear evidence for relict channels and associated outwash fans which breach outer ridges but have been blocked off by a ridge or ridges formed during a subsequent advance. Using this approach, it is possible to identify four separate advances of Finsterwalderbreen and two of Grønfjordbreen, which is consistent with their classification as surge-type glaciers. Further support is provided by both quantitative and qualitative relative-age indicators for the different ridges, including lichenometry, vegetation cover, frost-shattered lithologies and overall ridge morphology and composition. It is anticipated that this relatively simple way to detect multiple advances within composite ridge systems has a wider application across Svalbard as a method for identifying possible surge-type glaciers and, if used in conjunction with dating techniques, could provide important information on the frequency and magnitude of glacier advances and/or surges in Svalbard during the Holocene.

Lovell, Harold; Lukas, Sven; Benn, Douglas; Swift, Darrel; Spagnolo, Matteo; Clark, Chris; Yde, Jacob

2013-04-01

154

Climate Discovery Teacher's Guide: The Little Ice Age Case Study  

NSDL National Science Digital Library

In this unit, students explore how scientists study climates of the past by modelling their methods through inquiry activities and investigating real data. The lessons address the difference between weather and climate, direct and indirect evidence of climate change, and natural indicators of climate such as tree rings. They will also examine what conditions were like in the 'Little Ice Age', a period of unusually cool conditions that occurred between 1300 and 1850 A.D. A lesson on glaciers uses imagery to show how they respond to climate change, and a lesson on sunspots uses real data to show the connection between sunspot activity and terrestrial climate. There is also a lesson on the effect of volcanism on climate and a summary activity that brings together all these concepts to draw conclusions about possible natural causes of climate change.

2007-12-12

155

The rotational stability of a triaxial ice-age Earth  

NASA Astrophysics Data System (ADS)

Mitrovica et al. (2005), following calculations by Nakada (2002), demonstrated that the traditional approach for computing rotation perturbations driven by glacial isostatic adjustment significantly overestimates present-day true polar wander (TPW) speeds by underestimating the background oblateness on which the ice-age loading is superimposed. The underestimation has two contributions: the first originates from the treatment of the hydrostatic form and the second from the neglect of the Earth's excess ellipticity supported by mantle convection. In Mitrovica et al. (2005), the second of these two contributions was computed assuming a biaxial nonhydrostatic form (i.e., the principal equatorial moments of inertia were assumed to be equal to their mean value). In this article we outline an extended approach that accounts for a triaxial planetary form. We show that differences in the TPW speed predicted using the Mitrovica et al. (2005) approach and our triaxial theory are relatively minor (˜0.1°/Myr) and are limited to Earth models with lower mantle viscosity less than ˜5 × 1021 Pa s. However, for this same class of Earth models, the angle of TPW predicted for a triaxial Earth is rotated westward (toward the axis of maximum equatorial inertia) by as much as ˜20° relative to the biaxial case. We demonstrate that these effects are a consequence of the geometry of the ice-age forcing, which has a dominant equatorial direction that is intermediate to the axes defining the principal equatorial moments of inertia of the planet. We complete the study by computing updated Frechet kernels for the TPW speed datum, which provide a measure of the detailed depth-dependent sensitivity of the predictions to variations in mantle viscosity. We show, in contrast to earlier efforts to explore this sensitivity based on the traditional rotation theory, that the datum does not generally have a sensitivity to viscosity that peaks near the base of the mantle.

Matsuyama, I.; Mitrovica, J. X.; Daradich, A.; Gomez, N.

2010-05-01

156

Simulation of the Northern Hemisphere Ice sheet throughout ice age cycles: Impact of Mass-Balance-related parameters  

Microsoft Academic Search

One of the challenges of earth system modeling is to confirm the theories of ice age cycle by simulating it using physically based models. Here we simulate the glacial cycle known as saw-tooth shape 100ka cycle time sequence using a three dimensional ice sheet model, IcIES (Saito and Abe-Ouchi, 2004), which includes the thermo-mechanical coupling processes (used for simulations of

A. Abe-Ouchi; F. Saito; T. Segawa

2005-01-01

157

How did the Greenland ice sheet respond to abrupt warming at the end of the last Ice Age?  

Microsoft Academic Search

During the Younger Dryas-Preboreal transition (YD\\/Pb), 11,700 years ago, temperatures at the top of the ice sheet rose c. 8Ë? C over a period of 60 years, marking the end of the last Ice Age. After slight cooling phase, The Preboreal Oscillation (PBO), 11,500-11,400 years ago, renewed abrupt warming raised temperatures a further 4Ë? C over a few years. The

S. Funder

2009-01-01

158

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

NASA Astrophysics Data System (ADS)

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

Martin, C.; Gudmundsson, G. H.

2011-12-01

159

Dating New York - Tracking the Retreat of the Laurentide Ice Sheet  

NASA Astrophysics Data System (ADS)

The Laurentide Ice Sheet (LIS) covered the New York City area during the Last Glacial Maximum (LGM) and when it retreated carved out the present topography, exposing fresh bedrock. Although modernization has led to the modification of much of the present landscape, the New York area still features many attributes of the glacial sculpting. These attributes: glacially polished bedrock, erratic boulders and glacial moraines, remain as evidence of past climate change. Long Island represents a terminal moraine of the LIS, while areas in Central Park, Inwood (northern Manhattan) and the Hudson valley display beautiful retreat features. We present surface exposure dates of samples removed from these areas from the measurement of 10Be in them. This allows us to better understand the dynamics of the Laurentide Ice Sheet at the end of the last ice age. We will match the data with existing moraine records from the LIS as well as with mountain glacier records to determine whether or not (i) the LIS and the Scandinavian Ice Sheet were in sync; (ii) the huge LIS reacted more inertial than smaller systems to the climate reorganizations; (iii) the retreat pattern of the LIS.

Edwards, A. R.; Schaefer, J.; Rinterknecht, V.; Ivy-Ochs, S.

2004-12-01

160

Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area  

NASA Astrophysics Data System (ADS)

We use a full-Stokes thermo-mechanically coupled ice-flow model to study the dynamics of the glacier inside Scharffenbergbotnen valley, Dronning Maud Land, Antarctica. The domain encompasses a high accumulation rate region and, downstream a sublimation-dominated bare ice ablation area. The ablation ice area is notable for having old ice at its surface since the vertical velocity is upwards, and horizontal velocities are almost stagnant there. We compare the model simulation with field observations of velocities and the age distribution of the surface ice. A satisfactory match with simulations using an isotropic flow law was not found because of too high horizontal velocities and too slow vertical ones. However, the existence of a pronounced ice fabric may explain the present day surface velocity distribution in the inner Scharffenbergbotnen blue ice area. Near absence of data on the temporal evolution of Scharffenbergbotnen since the Late Glacial Maximum necessitates exploration of the impact of anisotropy using prescribed ice fabrics: isotropic, single maximum, and linear variation with depth, in both two-dimensional and three dimensional flow models. The realistic velocity field simulated with a non-collinear orthotropic flow law, however produced surface ages in significant disagreement with the few reliable age measurements and suggests that the age field is not in a steady state and that the present distribution is a result of a flow reorganization at about 15 000 yr BP. In order to fully understand the surface age distribution a transient simulation starting from the Late Glacial Maximum including the correct initial conditions for geometry, age, fabric and temperature distribution would be needed. It is the first time that the importance of anisotropy has been demonstrated in the ice dynamics of a blue ice area. This is useful to understand ice flow in order to better interpret archives of ancient ice for paleoclimate research.

Zwinger, T.; Schäfer, M.; Martín, C.; Moore, J. C.

2013-06-01

161

Age and competition level on injuries in female ice hockey.  

PubMed

The objective of this study was to describe the number, types and locations of known injuries occurring across different age categories and levels of competition in female ice hockey within the Ontario Women's Hockey Association from 2004/05 to 2007/08. We further examined under which aforementioned factors and combination of factors an unusually high or low number of injuries was recorded. Secondary analysis of anonymized injury data was conducted. The most common known injury type was strain/sprain, followed by concussion while the most frequent injury location was head/face/mouth. Analysis of deviance indicated that a significantly higher than expected number of sprain/strain, concussion and laceration injuries were recorded compared to all other injury types. In addition, there were a higher number of injuries recorded at the AA level compared to all other levels of competition. Finally, the age categories of Peewee, Midget and Intermediate within the AA level of competition, as well as Senior/Adult within the Houseleague level of competition also recorded a significantly higher number of injuries compared to other combinations of descriptive factors. Further research with female youth is needed to better understand the high number of injuries, including concussions, reported overall. PMID:23516144

Keightley, M; Reed, N; Green, S; Taha, T

2013-03-20

162

The whole world had a case of the ice age shivers  

SciTech Connect

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

Kerr, R.A.

1993-12-24

163

Duration of Greenland Stadial 22 and ice-gas ?age from counting of annual layers in Greenland NGRIP ice core  

NASA Astrophysics Data System (ADS)

High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (?age) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP ?depth (5.49 to 5.85 m) and ?age (498 to 601 yr) at the warming onset of GI-21 as well as the ?age range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the ?15N proxy) increases before CH4 concentration by no more than a few decades.

Vallelonga, P.; Bertagna, G.; Blunier, T.; Kjær, H. A.; Popp, T. J.; Rasmussen, S. O.; Steffensen, J. P.; Stowasser, C.; Svensson, A. S.; Warming, E.; Winstrup, M.; Bigler, M.; Kipfstuhl, S.

2012-11-01

164

Duration of Greenland Stadial 22 and ice-gas ?age from counting of annual layers in Greenland NGRIP ice core  

NASA Astrophysics Data System (ADS)

The NorthGRIP ice core chronology GICC05modelext is composed of the annual-layer counted GICC05 chronology to 60 kyr before 2000 AD (b2k), and an ice flow model dating the deepest part of the ice core to 123 kyr b2k. Determination of annual strata in ice beyond 60 kyr b2k has been challenged by the thinning of annual layers to <1 cm and the appearance of microfolds in some early glacial strata. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses, constraining the duration of the Greenland Stadial (GS-22) between Greenland Interstadials (GIs) 21 and 22 which occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21) depending on the chronology used. Multiple analytes (insoluble dust particles, electrolytic conductivity, ammonium and sodium) were determined in annual layers of ice often thinner than 1 cm. From annual layer counting, we find that GS-22 lasted 2894 ± 198 yr and was followed by a GI-21 pre-cursor event lasting 350 ± 19 yr. Our layer-based counting agrees with the duration of GS-22 determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr). These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the NorthGRIP ice depth-gas depth (5.67 ± 0.18 m) and ice age-gas age (550 ± 52 yr) differences at the warming onset of GI-21, observing that ?15N increases before CH4 concentration by no more than a few decades.

Vallelonga, P.; Bertagna, G.; Blunier, T.; Kjær, H. A.; Popp, T. J.; Rasmussen, S. O.; Steffensen, J. P.; Stowasser, C.; Svensson, A. S.; Warming, E.; Winstrup, M.; Bigler, M.; Kipfstuhl, S.

2012-07-01

165

Revised interpretation of Mueller Glacier moraines, Southern Alps, New Zealand  

NASA Astrophysics Data System (ADS)

A sequence of moraine ridges on the Mueller Glacier foreland, Southern Alps, New Zealand has previously formed part of a database used to develop a local/regional palaeoclimate chronology; however, it is possible that factors other than climate may have caused or influenced these moraine formations. Rock avalanches that deposit large volumes of rock debris on glacier ablation zones can affect glacier behaviour and cause moraine formation that does not necessarily reflect a climatically-driven advance (Reznichenko et al., 2011). Therefore, prior to the correlation of dated moraines with regional climate alterations, it is required to determine the genesis of these features. In previous studies the possible formation of some Mueller moraines by large-scale mass movements has been neglected that could have resulted in wrong assumptions of moraine positions having been entirely forced by climate change. The presence of modern rock avalanche deposits on glaciers in the Aoraki/Mt. Cook area indicates the probable contribution of supraglacial rock avalanches to the formation of these moraines in the past. This argument was recently supported by the presence of rock-avalanche-indicating agglomerates found in the sediment from two Mueller Glacier moraine ridges (Reznichenko et al., 2012). Previous interpretations of these ridges are inconsistent and are usually attributed to reflecting several glacial climatic-driven advances. In current research presented morphological and sedimentological analysis evidence that this feature is a single moraine (the "Mueller Memorial Moraine") formed following supraglacial transport of a large volume of rock avalanche debris to the glacier snout. Because a moraine formed by this process has no necessary association with a climate event, this finding raises concerns about the palaeoclimatic significance of this moraine; and, by implication, of other moraines in similar situations. References Reznichenko, N.V., Davies, T.R. and Alexander, D.J., 2011. Effects of rock avalanches on glacier behavior and moraine formation. Geomorphology 132: 327-338. Reznichenko, N.V., Davies, T.R., Shulmeister, J.P. and Larsen, S.H., 2012. A new technique for identifying rock avalanche-sourced sediment in moraines and some palaeoclimatic implications. Geology 40: 319-322.

Reznichenko, Natalya; Davies, Tim; Winkler, Stefan

2013-04-01

166

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

SciTech Connect

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

Zreda, M.G.; Phillips, F.M. [New Mexico Tech., Socorro, NM (United States); Elmore, D. [Purdue Univ., West Lafayette, IN (United States)

1994-11-01

167

Little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap  

Microsoft Academic Search

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that

L. G. Thompson; E. Mosley-Thompson; P. M. Grootes

1986-01-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

169

The effect of surrounding topography on the thermal water circulation in moraine-dammed glacial lakes:  

NASA Astrophysics Data System (ADS)

The observations in the pre-monsoon seasons of 1996 and 1997 indicated that two moraine-dammed glacial lakes, Tsho Rolpa and Imja, in the Nepal Himalayas have the different thermal structure in spite of the similar solar radiation, air temperature and wind system at the weather stations. The difference of thermal conditions in the lakes possibly results from the depletion in wind velocity over Imja Lake, which is caused by the screening of the upwind end-moraine to dead-ice zone 20-25 m higher than the lake surface. In order to clarify the topographic screening effect, three-dimensional numerical simulations of airflow around Tsho Rolpa and Imja Lakes were performed by building up a topographic model of actual size in the calculation domain. Simulated results indicated that the wind velocity at 2 m above the Imja Lake surface is 33-42 % smaller than that above the Tsho Rolpa Lake surface for the constant wind velocites of 1-5 m/s at 2 m above the points corresponding to the weather stations. This evidences the significant screening effect on the thermal structure of Imja Lake, since the wind force per unit lake area is proportional to the square of wind velocity at a certain height above the lake surface. The airflow simulations indicate that, as a barrier, the glacier terminus (ice cliff) leeward of Imja Lake decreases the wind velocity near the lake surface as much as does the upwind end-moraine to dead-ice zone.

Chikita, Kazuhisa A.

170

The Little Ice Age in the Canadian Rockies  

NASA Astrophysics Data System (ADS)

This paper reviews the evidence and history of glacier fluctuations during the Little Ice Age (LIA) in the Canadian Rockies. Episodes of synchronous glacier advance occurred in the 12th-13th, early 18th and throughout the 19th centuries. Regional ice cover was probably greatest in the mid-19th century, although in places the early 18th century advance was more extensive. Glaciers have lost over 25% of their area in the 20th century. Selective preservation of the glacier record furnishes an incomplete chronology of events through the 14th-17th centuries. In contrast, varve sequences provide continuous, annually resolved records of sediments for at least the last millennium in some highly glacierized catchments. Such records have been used to infer glacier fluctuations. Evaluation of recent proxy climate reconstructions derived from tree-rings provides independent evidence of climate fluctuations over the last millennium. Most regional glacier advances follow periods of reduced summer temperatures, reconstructed from tree rings particularly ca. 1190-1250, 1280-1340, 1690s and the 1800s. Reconstructed periods of higher precipitation at Banff, Alberta since 1500 are 1515-1550, 1585-1610, 1660-1680 and the 1880s. Glacier advances in the early 1700s, the late 1800s and, in places, the 1950-1970s reflect both increased precipitation and reduced summer temperatures. Negative glacier mass balances from 1976 to 1995 were caused by decreased winter balances. The glacier fluctuation record does not contain a simple climate signal: it is a complex response to several interacting factors that operate at different timescales. Evaluation of climate proxies over the last millennium indicates continuous variability at several superimposed timescales, dominated by decade-century patterns. Only the 19th century shows a long interval of sustained cold summers. This suggests that simplistic concepts of climate over this period should be abandoned and replaced with more realistic records based on continuous proxy data series. The use of the term LIA should be restricted to describing a period of extended glacier cover rather than being used to define a period with specific climate conditions.

Luckman, B. H.

2000-03-01

171

Atlantic forcing of Amazonian climates in the last ice age  

NASA Astrophysics Data System (ADS)

An absence of study sites means that the relative influence of orbitally driven presession cycles and millenial scale variability upon ice-age Amazonian precipitation is unknown. Here we present a continuous isotopic (?O18 and C13) record spanning the period from ~93-8 ka, from the aseasonal forests of Amazonian Ecuador. The variability in ?O18 depletion is probably related to the relative strength of evapotranspired moisture (less depleted) and tropical Atlantic moisture carried across the basin by the South American Low Level Jet (more depleted). Times of strengthened South American Low Level Jet probably correspond to increased overall moisture availability and hence elevated precipitation. The occurrence of markedly depleted ?O18 signatures during Heinrich events suggests a strong influence of the Atlantic Ocean on this system, and that these northern hemispheric stadials induced wet episodes in western Amazonia. Weakening of the Atlantic Meridional Overturning Circulation (AMOC) has been suggested to strengthen the South American Low Level Jet. The isotopic records reveal strong cohesion with previously published records from southern Brazil. A precessional influence amplifies the north Atlantic signal between c. 93 ka and 50 ka. However, after c. 50 ka the precessional signal weakens, perhaps sugesting that at a critical size the Laurentide ice mass exerted a strong influence on Neotropical climates suppressing the weaker forcing associated with precession. Contrary to long-standing expectation, the Last Glacial Maximum (21 ± 2 ka) does not stand out as time of aridity in this record. However, between c. 35 ka and 18 ka there is a drift toward less depleted rainfall. One hypothesis to account for this observation is that the climate was becoming more seasonal as the Intertropical Convergence Zone (ITCZ) formed further south than its modern location. The resulting weakened influence of the South American Summer Monsoon (SASM) would probably reduce wet season precipitation to this region of Amazonia. About 18 ka a marked shift toward less isotopically depleted moisture is consistent with a strengthening influence of SASM as the ITCZ migrated northward. The southerly movement and northerly return of the SASM influence between c. 35 and 18 ka has the temporal asymmetry common to many glacial events. In the deglacial period, the dominance of precession appears to be re-asserted, but the signal of Heinrich events is lost.

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

2011-12-01

172

How did the Greenland ice sheet respond to abrupt warming at the end of the last Ice Age?  

NASA Astrophysics Data System (ADS)

During the Younger Dryas-Preboreal transition (YD/Pb), 11,700 years ago, temperatures at the top of the ice sheet rose c. 8Ë? C over a period of 60 years, marking the end of the last Ice Age. After slight cooling phase, The Preboreal Oscillation (PBO), 11,500-11,400 years ago, renewed abrupt warming raised temperatures a further 4Ë? C over a few years. The ice margin response to this abrupt warming is here investigated from available onshore and offshore records. During YD most of Greenland was still ice covered, but some areas in the south and east had been cleared of ice already before YD, and contain a record of late glacial change. However, the evidence from these sites leaves a rather confusing picture: In Scoresby Sund, East Greenland, glaciers advanced in YD, but retreat probably did not start until after PBO. Contrary to this, the Kangerlussuaq area to the south apparently saw glacier-melting through YD, but the melting was reduced already before the end of YD. Further to the south (Skjoldungen) a record from the shelf shows no oceanographic change over YD/Pb and PBO. Finally, a lake in the extreme south has the only Greenland record of rapid warming at YD/Pb. From coastal areas in the rest of Greenland 14C dates on marine and organic lake sediments generally don't go back further than c. 11,000 years, indicating that deglaciation did not commence until some hundred years after the YD/Pb warming. There is therefore so far no positive evidence from Greenland that the ice sheet margin responded to the large and fast YD/Pb warming, while it may be the smaller post-PBO warming that triggered large scale ice margin retreat in all parts of the country. This suggests that in spite of the large temperature jump during YD/Pb warming, much of the ice surface remained below freezing point, probably because the warming was mainly in the winter. Only in the extreme south were summer temperatures high enough to melt the ice. In other parts the warming after PBO may have started ice margin recession which proceeded over the next 3-4 millenia at a rate determined by local climate and topography. The rate and amplitude of YD/Pb warming is comparable to the most pessimistic IPCC prediction for Greenland in our century, but took place in a different temperature regime. Still, one lesson that can be learned from history seems to be that different parts of the ice sheet may react very differently to rapid change.

Funder, S.

2009-04-01

173

Climatic warming, glacier recession and runoff from Alpine basins after the Little Ice Age maximum  

Microsoft Academic Search

Records of discharge of rivers draining Alpine basins with between 0 and ˜70% ice cover, in the upper Aare and Rhône catchments, Switzerland, for the period 1894-2006 have been examined together with climatic data for 1866-2006, with a view to assessing the effects on runoff from glacierized basins of climatic warming coupled with glacier recession following the Little Ice Age

David N. Collins

2008-01-01

174

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

SciTech Connect

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

Dahms, D.E. (Univ. of Northern Iowa, Cedar Falls, IA (United States). Geography Dept.)

1992-01-01

175

Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles  

NASA Astrophysics Data System (ADS)

Ice nucleation in the atmosphere is central to the understanding the microphysical properties of mixed-phase and cirrus clouds. Ambient conditions such as temperature (T) and relative humidity (RH), as well as aerosol properties such as chemical composition and mixing state play an important role in predicting ice formation in the troposphere. Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measurements despite the long-range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 < T < 263 K. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone concentrations of 0.4-4.3 ppmv in a stainless steel aerosol tank. The portable ice nucleation counter (PINC) and immersion chamber combined with the Zurich ice nucleation chamber (IMCA-ZINC) are used to conduct deposition and immersion mode measurements, respectively. Ice active fractions as well as ice active surface site densities (ns) are reported and observed to increase as a function of decreasing temperature. We present first results that demonstrate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode due to ageing. We also present the first results to show a suppression of heterogeneous ice nucleation activity without the condensation of a coating of (in)organic material. In immersion mode, low ozone exposed Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka, whereas high ozone exposed ATD particles showed suppressed ice nucleation requiring a median freezing temperature of 3 K colder than that of untreated ATD. In deposition mode, low exposure Ka had ice active fractions of an order of magnitude higher than untreated Ka, whereas high ozone exposed ATD had ice active fractions up to a factor of 4 lower than untreated ATD. From our results, we derive and present parameterizations in terms of ns(T) that can be used in models to predict ice nuclei concentrations based on available aerosol surface area.

Kanji, Z. A.; Welti, A.; Chou, C.; Stetzer, O.; Lohmann, U.

2013-09-01

176

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

NASA Astrophysics Data System (ADS)

Knowledge of the West Antarctic Ice Sheet (WAIS) response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future. The timing and extent of past interior WAIS elevation changes provides insight to WAIS behavior and constraints for ice sheet models. Constraints prior to the Last Glacial Maximum (LGM) however, are rare. Surface exposure ages of glacial erratics near the WAIS divide at Mt. Waesche in Marie Byrd Land, and at the Ohio Range in the Transantarctic Mountains, range from ˜10 ka to >500 ka without a dependence on elevation. The probability distribution functions (PDF) of the exposure ages at both locations, are remarkably similar. During the last glaciation, maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka. However, most exposure ages are older than the LGM and cluster around ˜40 ka and ˜80 ka. The peak in the exposure age distributions at ˜40 ka includes ages of alpine moraine boulders at Mercer Ridge in the Ohio Range. Comparison of the PDF of exposures ages from the Ohio Range and Mt. Waesche with the temperature record from the Fuji Dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the Last Glacial termination. A prominent peak in the Ohio Range PDF corresponds to the penultimate termination (stage 5e). During the intervening glacial period, there is not a consistent relationship between the peaks in the PDF at each location and temperature. A combined ice sheet/ice shelf model with forcing scaled to marine ?18O predicts that interior WAIS elevations near the ice divide have varied ˜300 m over the Last Glacial cycle. Peaks in the PDF correspond to model highstands over the last 200 ka. In the simulated elevation history, maximum ice elevations at Ohio Range (+100 m) and Mt. Waesche (+60 m) occur at ˜10 ka, in agreement with observations from these sites. During collapse of the marine portion of the WAIS, ice elevations at Ohio Range and Mt. Waesche are drawn down at least 200 m below the present ice elevation. The good correspondence between the model results and observations at both the Ohio Range and Mt. Waesche supports the conclusion that interior WAIS highstands do not occur during glacial maximums. Rather, the highstands are controlled primarily by increased accumulation during temperature maximums that occur early in the interglacials. Interior down-draw events follow highstands, resulting from the arrival of a wave of thinning triggered by retreat of the WAIS grounding line coupled with decreasing accumulation rates.

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

2013-04-01

177

Predicted age-depth scales for Siple Dome and Inland WAIS Ice Cores in west Antarctica  

NASA Astrophysics Data System (ADS)

Geophysical data are used with ice flow models and generalized accumulation histories to estimate age and annual layer thickness versus depth for two anticipated ice core sites in West Antarctica: Siple Dome (81.65°S, 148.81°W) and an inland site on the West Antarctic Ice Sheet (WAIS). This modeling experiment predicts that 104 year-old ice is at ?50% depth and 105 year-old ice is at ?90% depth at both sites. Both of these cores could contain climate information through the last glacial cycle with annual resolution through the Holocene. The predicted similarity in resolution and record length between the two cores suggests that they could be compared in detail to obtain both spatial and temporal information about the paleoclimate and history of the West Antarctic ice sheet.

Nereson, N. A.; Waddington, E. D.; Raymond, C. F.; Jacobson, H. P.

178

The influence of continental ice sheets on the climate of an ice age  

Microsoft Academic Search

The climate influence of the land ice that existed 18,000 years before present (18K B.P.) is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean. Simulated climates are obtained from two versions of the model; one with the land ice distribution of the present and the other with that of 18K

S. Manabe; A. J. Broccoli

1985-01-01

179

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

USGS Publications Warehouse

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

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

1996-01-01

180

Glacial age precipitation and temperature estimates for the tropical Guatemalan highlands  

NASA Astrophysics Data System (ADS)

The Sierra Cuchumatanes of Western Guatemala supported a large ice cap of approximately 44 square km area, and a group of 5-6 small valley glaciers during the local last glacial maximum (LLGM). We propose that a temperature reduction during the Guatemalan LLGM was between -4.5 degrees C and -6.0 degrees C from present accompanied by precipitation totals that fall between 80-100% of present day levels. Our new field work on moraine limits expands upon previous reconnaissance-level studies. Here we present a comprehensive reconstruction of the Guatemalan glacial geomorphology on a high limestone plateau; including delineations between morphologically different moraine sequences, boundaries of sub-glacial till deposits and locations of dry moraine dammed lakes. The glacial geologic map was produced via field mapping and GPS surveying, coupled with aerial photographic analysis. A 50m digital elevation model (DEM) created for the mapping portion was employed as input for a physically based GIS mass-balance model, developed by Plummer and Phillips (2003). The mass-balance model data was calculated for varying precipitation, temperature, environmental lapse rates, cloudiness, wind speed and humidity. A sensitivity analysis using variations in temperature and precipitation provided constraints on Guatemalan highland paleoclimate. Although the ages of the glaciations are unconstrained, a qualitative assessment of moraine morphology suggests correlation with the LLGM (20 - 17.5 ka) moraines of Mexico.

Roy, A. J.; Lachniet, M. S.

2007-12-01

181

Rapid Grounding Line Retreat Followed by Collapse of the Ross Ice Shelf : Response to Meltwater Pulse 1A  

NASA Astrophysics Data System (ADS)

Mega-scale glacial lineations within troughs have been used to reconstruct paleodrainage of the expanded ice sheet within Ross Sea during the Last Glacial Maximum. The variable number and distribution of grounding zone wedges from trough to trough indicate that individual ice streams behaved independently during retreat from the shelf. Deep iceberg furrows that extend to ~650 m water depth indicate periodic calving at the grounding line of the ice sheet, suggestive of rapid retreat and ice shelf break-up. Here we present geomorphological evidence for rapid grounding line retreat and associated collapse of the ice shelf in the JOIDES Basin (western Ross Sea) and in the Little America Basin (eastern Ross Sea). Evidence for collapse of the ice shelf exists in the form of regularly spaced ridges, which in JOIDES Basin have an average spacing of 28.6 m and occur in water depths of 626 m to 647 m. We call these features fishbone moraines and interpret them as having formed by tidally driven up and down motion of a collapsed ice shelf at or very near the grounding line as it exited the Ross Sea. The fishbone moraines extend seaward into low-relief wedges that are interpreted as DeGeer moraines, which are annual features. This interpretation is based on sediment flux estimates and the general size of these features compared to DeGeer moraines found elsewhere. They indicate retreat of the grounding line of 20 km in 34 years (.58 km/yr) prior to the ice sheet stabilizing for about two centuries to form a more prominent grounding zone wedge just prior to ice shelf collapse. Iceberg furrows with internal ridges similar in scale to fishbone moraines exist in the outer portion of the trough. These features are interpreted as having been formed by tide-driven up and down motion of icebergs that were part of a coherent mass of floating ice. Seaward, these furrows cross each other at high angles. This marks the location where icebergs began to drift freely out of Ross Sea. We also imaged fishbone moraines in a portion of Little America Basin where the trough floor is relatively flat, as in the JOIDES Basin. The timing of WAIS retreat from eastern Ross Sea is poorly constrained, so it is not possible to determine when the fishbone moraines in Little America Basin were formed. However, radiocarbon ages from glacimarine sediments indicate that the JOIDES Basin was free of grounded ice and an ice shelf by 14,620 to 13,120 ka, which is coincident with Meltwater Pulse 1A (MWP1A). Thus, while debate continues as to the contribution of the WAIS to MWP1A, our results leave little doubt that this rapid sea-level rise contributed to grounding line instability, especially where the ice sheet was grounded in relatively deep and flat troughs, such as in the JOIDES and Little America Basins.

Anderson, J. B.; Stolldorf, T. D.; Jakobsson, M.

2010-12-01

182

History of ice sheet elevation in East Antarctica: Paleoclimatic implications  

NASA Astrophysics Data System (ADS)

The multi-disciplinary study of past ice surface elevations in the Grove Mountains of interior East Antarctica provides direct land-based data on the behavior of the East Antarctic Ice Sheet since the Pliocene. The glacial geology, the ages of cold desert soils, the depositional environment of younger moraine sedimentary boulders and their spore-pollen assemblages combine to imply a possible significant shrinkage of the Ice Sheet before the Middle Pliocene Epoch, with the Ice Sheet margin retreating south of the Grove Mountains (˜ 450 km south from its present coastal position). Exposure age measurements of bedrock indicate that the elevation of the ice surface in the Grove Mountains region subsequently rose at about mid-Pliocene to at least 200 m higher than today's levels. The ice surface then progressively lowered, with some minor fluctuations. Middle to Late Pleistocene exposure ages found on the lowest samples, at the ice/bedrock contact line, indicate a long period with ice surface elevations kept at the current level or complex fluctuation history during the Quaternary Epoch.

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

2010-02-01

183

Out of Tibet: Pliocene woolly rhino suggests high-plateau origin of Ice Age megaherbivores.  

PubMed

Ice Age megafauna have long been known to be associated with global cooling during the Pleistocene, and their adaptations to cold environments, such as large body size, long hair, and snow-sweeping structures, are best exemplified by the woolly mammoths and woolly rhinos. These traits were assumed to have evolved as a response to the ice sheet expansion. We report a new Pliocene mammal assemblage from a high-altitude basin in the western Himalayas, including a primitive woolly rhino. These new Tibetan fossils suggest that some megaherbivores first evolved in Tibet before the beginning of the Ice Age. The cold winters in high Tibet served as a habituation ground for the megaherbivores, which became preadapted for the Ice Age, successfully expanding to the Eurasian mammoth steppe. PMID:21885780

Deng, Tao; Wang, Xiaoming; Fortelius, Mikael; Li, Qiang; Wang, Yang; Tseng, Zhijie J; Takeuchi, Gary T; Saylor, Joel E; Säilä, Laura K; Xie, Guangpu

2011-09-01

184

Ice  

NSDL National Science Digital Library

When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.

Harris, Kathryn L.

185

The development and preservation of tabular massive ground ice in permafrost regions  

NASA Astrophysics Data System (ADS)

An investigation of tabular massive ground ice was conducted to ascertain if ground ice has distinctive characteristics that could be measured and used to determine the origin of the ice. Initial studies were conducted on Bylot Island in the eastern Canadian Arctic, where some glaciers are rapidly retreating, resulting in buried massive ground ice. The environments with the greatest potential for the burial and preservation of massive ice were first examined and the processes of burial identified. It was determined that glacier end and lateral moraines have the greatest potential for preserving massive ice. Ground penetrating radar (GPR) methodology was developed for imaging the subsurface geometry and structure of glaciers, icing, and ground ice bodies. GPR was shown to be effective for mapping icing and glacier geometry, hydrology and subbottom structure, and possibly thermal conditions. GPR also proved effective at delineating the size and thickness of massive ground ice bodies. This revealed that the ice core in lateral and end moraines around Stagnation Glacier are continuous and extensive. Physical property analyses indicated that some ice types could not be differentiated on their physical properties alone. A methodology was thus developed for extracting and analyzing the gaseous component of ice which would provide a differentiating technique. This method enabled the measurement of the chemical and isotopic composition of the ice and gases, and direct age determination of the ice by radiocarbon dating of the COsb2 in the bubbles. In testing the technique in the proglacial environment on Bylot Island, the environmental history of the site was linked to the more extensive ice core records from Greenland and Devon Island. Along with the other ice property analysis techniques, the gas analysis techniques were applied to three sites across the western Canadian Arctic (Peninsula Point, North Point, and Herschel Island). It was discovered that ground ice bodies in the Tuktoyaktuk Peninsula and on Herschel Island were considerably younger than had been reported previously. In a detailed study of the massive ground ice at Peninsula Point it was determined that the ice mass developed from the segregation of ice formed from a ground water source. The ground water probably originated as glacial meltwater, with several different sources, each with different isotopic signatures.

Moorman, Brian James

186

General Humid Little Ice Age In Westerly Dominated Western China  

Microsoft Academic Search

Eleven major humidity proxy records and other supplementary evidence, including natural archives such as ice-cores, sedimentary records, river terraces, lake-level fluctuations, as well as historical documents, have been used to reconstruct the variability of humidity in the Westerly dominated Western China (WDWC) including Arid China and north part of the Tibet Plateau, over the last 1000 years. The results show

F. Chen; J. Chen

2008-01-01

187

Ice ages and the thermal equilibrium of the earth, II  

USGS Publications Warehouse

The energy required to sustain midlatitude continental glaciations comes from solar radiation absorbed by the oceans. It is made available through changes in relative amounts of energy lost from the sea surface as net outgoing infrared radiation, sensible heat loss, and latent heat loss. Ice sheets form in response to the initial occurrence of a large perennial snowfield in the subarctic. When such a snowfield forms, it undergoes a drastic reduction in absorbed solar energy because of its high albedo. When the absorbed solar energy cannot supply local infrared radiation losses, the snowfield cools, thus increasing the energy gradient between itself and external, warmer areas that can act as energy sources. Cooling of the snowfield progresses until the energy gradients between the snowfield and external heat sources are sufficient to bring in enough (latent plus sensible) energy to balance the energy budget over the snowfield. Much of the energy is imported as latent heat. The snow that falls and nourishes the ice sheet is a by-product of the process used to satisfy the energy balance requirements of the snowfield. The oceans are the primary energy source for the ice sheet because only the ocean can supply large amounts of latent heat. At first, some of the energy extracted by the ice sheet from the ocean is stored heat, so the ocean cools. As it cools, less energy is lost as net outgoing infrared radiation, and the energy thus saved is then available to augment evaporation. The ratio between sensible and latent heat lost by the ocean is the Bowen ratio; it depends in part on the sea surface temperature. As the sea surface temperature falls during a glaciation, the Bowen ratio increases, until most of the available energy leaves the oceans as sensible, rather than latent heat. The ice sheet starves, and an interglacial period begins. The oscillations between stadial and interstadial intervals within a glaciation are caused by the effects of varying amounts of glacial meltwater entering the oceans as a surface layer that acts to reduce the amount of energy available for glacial nourishment. This causes the ice sheet to melt back, which continues the supply of meltwater until the ice sheet diminishes to a size consistent with the reduced rate of nourishment. The meltwater supply then decreases, the rate of nourishment increases, and a new stadial begins. ?? 1975.

Adam, D. P.

1975-01-01

188

Wobbly winds in an ice age: The mutual interaction between the great continental ice sheets and atmospheric stationary waves  

NASA Astrophysics Data System (ADS)

The ice sheets of the last glacial maximum (about 21 thousand years ago) covered a significant fraction of the high latitude land mass, reached up to 3km in height, and had length scales of thousands of kilometers. They represented, significant obstacles to the westerly flow of the atmosphere. As the atmospheric flow is forced to deviate around such topographic features, stationary waves-large scale standing patterns in the winds and temperatures-are established within the atmosphere. It is not possible to integrate full dynamical climate models for the long time scales appropriate to ice sheet dynamics (>103 yrs). Previous studies have typically either used general circulation models (GCMs) for `snapshot' climate simulations with prescribed ice age insolation and boundary conditions, or used long integrations of energy balance models (EBMs), which do not account for atmospheric dynamics. We aim for an intermediate approach-including some of the important dynamical features of the climate within a framework which is nonetheless simple enough to do long term calculations with. The effects explored above in the rather restrictive two- dimensional approach are further studied using a fully three-dimensional ice sheet model coupled to a ?- plane channel stationary wave model, which is quasi- geostrophic, steady state, and linear. The two components of the model interact via the accumulation and ablation parameterizations which are, of necessity, very simplified representations. The ablation parameterization is the positive degree day model which has been used to model the modern ice sheets. The accumulation parameterization places particular emphasis on the topographic influence on precipitation. When the stationary wave model is applied to a reconstruction of the topography at the last glacial maximum, the results suggest that the stationary wave patterns due to Tibet and the Rockies may have played a role in preconditioning different regions for ice sheet initiation. Once established, the Laurentide ice sheet exerted a strong influence on the climate over the Fennoscandian ice sheet (over northern Europe) due to the downstream propagation of the stationary wave it created. (Copies available exclusively from MIT Libraries, Rm. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.)

Roe, Gerard Hugh

189

Extending Glacier Monitoring into the Little Ice Age and Beyond  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

190

The Greenland Ice Sheet Project 2 depth-age scale: Methods and results  

Microsoft Academic Search

The Greenland Ice Sheet Project 2 (GISP2) depth-age scale is presented based on a multiparameter continuous count approach, to a depth of 2800 m, using a systematic combination of parameters that have never been used to this extent before. The ice at 2800 m is dated at 110,000 years B.P. with an estimated error ranging from 1 to 10% in

D. A. Meese; A. J. Gow; R. B. Alley; G. A. Zielinski; P. M. Grootes; M. Ram; K. C. Taylor; P. A. Mayewski; J. F. Bolzan

1997-01-01

191

Ice-age atmospheric concentration of nitrous oxide from an Antarctic ice core  

Microsoft Academic Search

Results from Antarctic ice cores are reported which show that the atmospheric N2O concentration was about 30 percent lower during the Last Glacial Maximum than during the Holocene epoch. The data also show that present-day N2O concentrations are unprecedented in the past 45 kyr and hence provide evidence that recent increases in atmospheric N2O are of anthropogenic origin.

Markus Leuenberger; Ulrich Siegenthaler

1992-01-01

192

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

SciTech Connect

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

Naftz, D.L. [Geological Survey, Salt Lake City, UT (United States); Klusman, R.W. [Colorado School of Mines, Golden, CO (United States); Michel, R.L. [Geological Survey, Menlo Park, CA (United States)] [and others

1996-02-01

193

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

SciTech Connect

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

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

1992-03-01

194

Internal layer tracing and age-depth-accumulation relationships for the northern Greenland ice sheet  

NASA Astrophysics Data System (ADS)

Clues to previous ice sheet structure and long-term glaciological processes are preserved in the internal layering configuration of the Greenland ice sheet. Information about these internal layers has been retrieved over many parts of the ice sheet with the University of Kansas ice-penetrating radar. We report on the coherence of these layers over very large distances, describe a method of tracing these layers along thousands of kilometers of flight line, and do so for one flight during the 1999 Program for Arctic Regional Climate Assessment (PARCA) aircraft campaign. We determine the ages of these layers, based on information at the GRIP ice core site, and extend these ages along the flight line to Camp Century, where they are compared to modeled-derived age estimates. These ages agree with each other to between 2 and 15%, differences that can be substantially reduced with minor changes to the model parameters (accumulation rate and shear layer depth). Finally, we are able to derive estimates of accumulation rates along the flight line by fitting the age-depth data from layer tracing to a Dansgaard-Johnsen model with a minimization technique, providing estimates that match recent accumulation patterns within a few centimeters per year.

Fahnestock, M.; Abdalati, W.; Luo, S.; Gogineni, S.

2001-12-01

195

Ages and composition of gas trapped in Allan Hills and Byrd core ice  

NASA Astrophysics Data System (ADS)

Gas is extracted from large (6-31 kg) Antarctic ice samples to obtain sufficient CO 2 for 14C measurements with small low-level proportional counters. The 14C ages of Byrd core ice are in accord with glaciological estimates ranging from (2.2 -1.1+1.4)×10 3 yr at 271 m depth to more than 8 × 10 3 yr at 1071 m depth. The CO 2 abundances in gas extracted from Byrd core ice range from 0.0216 to 0.051%, with below present-day atmosphere CO 2 abundances for ice from 1068 and 1469 m depths. The CO 2 abundance in gas from Allan Hills surface ice samples ranges between four and six times the atmospheric value and the CO 2 had a specific activity three times that of contemporary carbon. A possible explanation for the anomalously high specific activity is surface melting with the incorporation into CO 2 of 14C produced by cosmic ray spallation of oxygen in ice. The CO 2 abundance in gas extracted from subsurface Allan Hills ice ranged from 0.030 to 0.065%, and the specific activities are below contemporary carbon, indicating ages greater than ˜5×10 3 yr. The 18O/ 16O ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the 18O/ 16O ratio in the ice. The O 2, N 2, and Ar abundances and isotopic compositions are similar to those in contemporary air, except for positive 15N/ 14N ratios in a few samples.

Fireman, E. L.; Norris, T. L.

1982-10-01

196

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

USGS Publications Warehouse

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

Kaye, Clifford A.

1976-01-01

197

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

SciTech Connect

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

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

1992-09-01

198

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

NASA Astrophysics Data System (ADS)

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

Anslow, Faron S.; Clark, Peter U.; Kurz, Mark D.; Hostetler, Steven W.

2010-08-01

199

Long time management of fossil fuel resources to limit global warming and avoid ice age onsets  

Microsoft Academic Search

There are about 5000 billion tons of fossil fuel carbon in accessible reserves. Combustion of all this carbon within the next few centuries would force high atmospheric CO2 content and extreme global warming. On the other hand, low atmospheric CO2 content favors the onset of an ice age when changes in the Earth's orbit lead to low summer insolation at

Gary Shaffer

2009-01-01

200

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

SciTech Connect

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

Peltier, W.R.; Jiang, X. [Univ. of Toronto, Ontario (Canada)

1994-10-01

201

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

ERIC Educational Resources Information Center

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

Glenn, William Harold

1996-01-01

202

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

ERIC Educational Resources Information Center

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

Glenn, William Harold

1996-01-01

203

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

USGS Publications Warehouse

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

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

1999-01-01

204

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

NASA Astrophysics Data System (ADS)

The importance and annual amount of sea ice volume produced during polyna opening events in the Siberian Laptev Sea is still controversially discussed. So far, published information about sea ice volume production are purely based on indirect thickness measurements of thin ice using remote sensing techniques or on computer simulations of sea ice growth based on reanalysis climate data. We recorded a sea ice thickness transect of approximately 160 km length using helicopter electromagnetics (HEM) in the region of the so called West New Siberian (WNS) Polynya located directly north of the Lena delta in April 2008. In addition, a time series of synthetic aperture radar (SAR) images covering the complete polynya region was analyzed and ice area fragments were tracked from their origin to the moment when we recorded their thickness. Both data sets together, HEM and SAR, provide the opportunity to classify overflown ice areas in terms of age, area and thickness and therefore in terms of volume. From December 2007 to April 2008 approximately 50.000 km2 of sea-ice area was produced in the WNS polynya, which is more than the size of Switzerland. The youngest surveyed sea-ice was 6 days old and had a mean total and a mean level-ice thickness of 0.2 m. The oldest surveyed ice floe had an age of 104 days and a mean total thickness of 2.4 +/- 0.3 m and a mean level ice thickness of 1.8 +/- 0.3 m. The error is based on the HEM instrument accuracy and a lag of snow thickness data. Assuming that ice thickness along the HEM transect was representative for entire overflown ice areas, our calculations result that the produced sea ice area contained a volume of approximately 86 km3. This is about 1.8 % of the Arctic wide ice production between October 2007 and March 2008, as it was published by Kwok et al. 2009 on the basis of ICE-Sat ice thickness data. The combined HEM and SAR study enabled us furthermore to analyze thickness vs. age relations of first year ice floes. Mean thickness showed to be a bad indicator for ice age determination and vice versa, due to the dynamic component of sea-ice growth. The most surprising result was a 16 days old ice floe which was piled up to deformed sea ice with a mean thickness of 2.4 m. Mean level-ice thickness is a far better indicator for ice age, although we found mean thickness variations for level ice of the same age of about 0.5 m. Reference: Kwok, R., Cunningham, G.F., Wensnahan, M., Rigor, I., Zwally, H.J., Yi,D., Thinning and volume loss of the Arctic Ocean sea ice cover: 2003-2008, Journal of Geophysical Research, 114, 2009

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

2012-04-01

205

Northern Hemisphere Meltwater Discharge and the Last Ice-Age Termination (Invited)  

NASA Astrophysics Data System (ADS)

The transient climate evolution of last Ice-Age termination (21,000 to 7,000 years ago) provides key observations for constraining climate sensitivity and understanding global carbon cycle. Here we present the first complete simulation of the last Ice-Age termination in a synchronously coupled atmosphere-ocean general circulation model. Our simulation reproduces many major features of the deglacial climate evolution in Greenland, Antarctic, tropical Pacific, Southern and Deep Ocean, suggesting our model exhibits reasonable climate sensitivity in those regions and is capable of simulating abrupt climate change events. In particular, our simulation supports the view that the last deglaciation is triggered by the enhanced spring-summer insolation locally in the Northern Hemisphere. Northern Hemisphere meltwater discharge is able to induce the early deglacial warming of the Southern and Deep Ocean, and accounts for the lead-lag relationship among the Southern Ocean, tropical Pacific and Northern Hemisphere observed during the last Ice-Age termination. Furthermore, by inducing deep ocean warming and Southern Ocean sea ice retreat, Northern Hemisphere meltwater discharge likely plays an active role in deglacial CO2 rise and gives an explanation for the associations between Heinrich events and atmospheric CO2 rise.

He, F.; Liu, Z.; Otto-Bliesner, B. L.; Clark, P. U.; Carlson, A. E.; Brady, E. C.; Brook, E.; Lynch-Stieglitz, J. M.; Kutzbach, J. E.; Rosenbloom, N. A.

2010-12-01

206

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

SciTech Connect

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

Straw, W.T.; Kehew, A.E.; Passero, R.N. (Western Michigan Univ., Kalamazoo, MI (United States). Dept. of Geology)

1993-03-01

207

Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide  

NASA Astrophysics Data System (ADS)

The largest climate anomaly of the last 1000 years in the Northern Hemisphere was the Little Ice Age (LIA) from 1400-1850 C.E., but little is known about the signature of this event in the Southern Hemisphere, especially in Antarctica. We present temperature data from a 300 m borehole at the West Antarctic Ice Sheet (WAIS) Divide. Results show that WAIS Divide was colder than the last 1000-year average from 1300 to 1800 C.E. The temperature in the time period 1400-1800 C.E. was on average 0.52 ± 0.28°C colder than the last 100-year average. This amplitude is about half of that seen at Greenland Summit (GRIP). This result is consistent with the idea that the LIA was a global event, probably caused by a change in solar and volcanic forcing, and was not simply a seesaw-type redistribution of heat between the hemispheres as would be predicted by some ocean-circulation hypotheses. The difference in the magnitude of the LIA between Greenland and West Antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions.

Orsi, Anais J.; Cornuelle, Bruce D.; Severinghaus, Jeffrey P.

2012-05-01

208

Carbon isotope composition of atmospheric CO2 during the last ice age from an Antarctic ice core  

NASA Astrophysics Data System (ADS)

The most likely mechanisms for the reduction in atmospheric CO2 during the last Glacial Maximum involve either a decrease in dissolved CO2 in surface waters because of a more efficient 'biological pump' transporting carbon to deep waters, or a higher alkalinity in the glacial ocean as a consequence of changes in carbonate dissolution or sedimentation. Changes in the biological pump would alter the carbon isotope composition of atmospheric CO2, whereas changes in alkalinity would in themselves have no such effect. Measurements of the carbon isotope content of CO2 in ice cores from Byrd Station, Antarctica, are examined in an attempt to distinguish the two mechanisms. It is found that during the ice age the reduced isotope ratio delta C-13 was more negative than preindustrial values by 0.3 +/- 0.2 per mil. Although this result does not permit definite discrimination between the two possible causes of lower glacial atmospheric CO2, it does indicate that change in the strength of the biological pump cannot alone have been responsible.

Leuenberger, Markus; Siegenthaler, Ulrich; Langway, Chester C.

1992-06-01

209

Sea Ice Age/Edge Motion. Visible/Infrared Imager/Radiometer Suite Algorithm Theoretical Basis Document. Version 5, Revision 1.  

National Technical Information Service (NTIS)

This Sea Ice Age and Edge Motion Algorithm Theoretical Basis Document (ATBD) describes the background, theory, and analysis of the algorithmic process required to create the Sea Ice Age and Edge Motion Environmental Data Record (EDR) from the Sensor Data ...

K. A. Jensen I. Appel

2002-01-01

210

Chlorine-36 and 14C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet  

USGS Publications Warehouse

The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to ???20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald's Beringian ice-sheet hypothesis. ?? 2003 Elsevier Science (USA). All rights reserved.

Brigham-Grette, J.; Gualtieri, L. M.; Glushkova, O. Y.; Hamilton, T. D.; Mostoller, D.; Kotov, A.

2003-01-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

212

The Oldest Dryas last significant fluctuation of the Scandinavian ice sheet margin in Eastern Baltic and problems of its regional correlation  

NASA Astrophysics Data System (ADS)

Ice marginal formations, glaciotectonic phenomena, directional ice-flow features and new absolute age dating results of the Pleistocene deposits were subjected to systematic analyses and re-interpretation for clarification of deglaciation history, especially on the timing and position of the glacial margin of the Linkuva (North Lithuanian, Haanja, Luga) phase. The oldest Dryas - the last significant fluctuation of the ice margin - locally termed as the Linkuva stage in Latvia, is probably best known deglaciation stage event in south eastern sector of the Scandinavian Ice Sheet, yet problems of its cross border correlation are still present. The timing of the North Lithuanian phase occurred at the end of the Oldest Dryas cold stage. Its minimum age is currently dated to 15.9-15.6 ka BP in Latvia (calibrated from 13.2-13.4 ka 14C BP), and correlative to the Haanja stade in Estonia , Middle Lithuanian phase in Lithuania, Slupsk Bank phase in northern Poland, and most likely by Krasnogorodsk phase in Russia. These ages are older than the error-weighted mean age (13.1 ± 0.3 10Be ka) of the North Lithuanian moraine. Here we present re-interpreted map of the Linkuva stage glacial marginal position in the territory of Latvia correlated with adjacent territories. The map is based on cumulative results of the mapping of ice marginal formations and spatial arrangement of streamlined bedforms (drumlins, flutes and megalineations), OSL and radiocarbon data available cosmogenic datings, and previous reconstructions of these stage glacial marginal positions. The results allow: (1) to draw complex interplay of the Scandinavian ice sheet lobate structure during the Linkuva deglaciation phase; (2) to conclude that the fast ice flow in many places with surging pattern were common for ice lobes and tongues; (3) to attest that mapping of the marginal shear moraines can be used as a tool for reconstruction of active ice marginal positions. The results suggest that there is no evidence of the ice margin retreat followed by ice re-advance as suggested earlier to form the Linkuva phase ice marginal formations. Rather penultimate areal ice stagnation was replaced by reactivation of individual comparatively small ice flows forming ice lobes and tongues. Fluctuations of the ice lobes were controlled not only by variations in climate but also by changes in the dynamics of glacial system, and concentration of the active ice draining in the wider depressions, while stagnation and decay occurring over adjacent elevated areas.

Saks, T.; Zelcs, V.; Nartiss, M.; Kalvans, A.

2009-12-01

213

Age of the crowfoot advance in the Canadian Rocky Mountains. A glacial event coeval with the Younger Dryas oscillation  

SciTech Connect

A suite of sediment core samples was recovered from two lakes, Crowfoot and Bow lakes, that are adjacent to the Crowfoot moraine type locality, to identify and radiocarbon date sediments related to the Crowfoot advance. The Crowfoot moraine system, widely recognized throughout northwestern North America, represents a glacial advance that is post-Wisconsin and pre-Mazama tephra in age. An interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca. 11,330 and 10,100 [sup 14]C yr B.P. is associated with the Crowfoot moraine. The Crowfoot advance is therefore approximately synchronous with the European Younger Dryas cold event (ca. 11,000-10,000 [sup 14]C yr B.P.). Furthermore, the termination of the Crowfoot advance also appears to have been abrupt. These findings illustrate that the climatic change responsible for the European Younger Dryas event extended beyond the northern Atlantic basin and western Europe. Equilibrium-line altitude (ELA) depressions associated with the Crowfoot advance are similar to those determined for the Little Ice Age advance, whereas Younger Dryas ELA depressions in Europe significantly exceed Little Ice Age ELA depressions. 26 refs., 3 figs., 1 tab.

Reasoner, M.A.; Rutter, N.W. (Univ. of Alberta, Edmonton, Alberta (Canada)); Osborn, G. (Univ. of Calgary, Alberta (Canada))

1994-05-01

214

A novel radiocarbon dating technique applied to an ice core from the Alps indicating late Pleistocene ages  

Microsoft Academic Search

Ice cores retrieved from high-altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions. Because of the specific flow behavior of ice, their age-depth relationship is nonlinear, preventing the application of common dating methods such as annual layer counting in the deepest and oldest part. Here we present a new approach and technique, allowing

Theo M. Jenk; Sönke Szidat; David Bolius; Michael Sigl; Heinz W. Gäggeler; Lukas Wacker; Matthias Ruff; Carlo Barbante; Claude F. Boutron; Margit Schwikowski

2009-01-01

215

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

SciTech Connect

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

Keigwin, L.D. [Woods Hole Oceanographic Institution, Woods Hole, MA (United States)

1996-11-29

216

Surface age of the ice-dust mantle deposit in Malea Planum, Mars  

NASA Astrophysics Data System (ADS)

The mid- and high-latitudes of Mars are covered by a smooth young mantle that is interpreted as an atmospherically derived air-fall deposit of ice and dust related to recent climate changes. In order to determine relative and absolute ages of this surface unit within the southern hemisphere, a systematic survey of all available HiRISE and CTX images in the Malea Planum region from 55-60°S latitude and 50-70°E longitude was performed and the distribution and the morphology of small impact craters on the mantle deposit were investigated. Using crater size-frequency measurements, we derived absolute model ages of ˜3-5 Ma for the surface of the mantle, immediately south of the Hellas basin rim. Morphologic observations of the mantle, its fresh appearance, very low number of craters, and superposition on older units support this very young Amazonian age. Nearly all observed craters on the smooth mantle in Malea Planum are small and show signs of erosion, evidence for the ongoing modification of the ice-dust mantle. However, this modification has not been strong enough to reset the surface age. Compared to the ice-dust mantle at higher latitudes in the northern and southern hemisphere, the surface of the mantle in Malea Planum is older and thus has been relatively stable during obliquity changes in the last ˜3-5 Ma. This is consistent with the hypothesis that the ice-dust mantle is a complex surface deposit of different layers, that shows a strong latitude dependence in morphology and has been deposited and degraded at different times in martian history.

Willmes, Malte; Reiss, Dennis; Hiesinger, Harald; Zanetti, Michael

2012-01-01

217

Ice-age cycles: Earth's rotation instabilities and sea-level changes  

Microsoft Academic Search

A new class of multilayered, viscoelastic Earth models based on PREM is applied to the modeling of Earths's rotation instabilities and associated sea-level changes, induced by the occurrence of Pleistocene ice-age cycles that match the oxygen isotope records over the last 0.8 Myr. The novelty of our approach stands on the usage, for the first time in post-glacial rebound induced

R. Sabadini; L. L. A. Vermeersen

1997-01-01

218

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

SciTech Connect

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

Fivez, J.; Thoen, J. [Laboratorium voor Akoestiek en Thermische Fysica, Department Natuurkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

2004-11-15

219

Calendar-dated, early 'Little Ice Age' glacier advance at Robson Glacier, British Columbia, Canada  

Microsoft Academic Search

Dendrochronological studies at Robson and Bennington Glaciers have provided the first calendar dating of an early 'Little Ice Age' glacier advance in North America. Dates derived from in-situ stumps indicate that Robson Glacier began over-riding forest between c. AD 1142 and 1150 and continued until at least AD 1350. The highest rates of glacier advance (c. 3.8 m yr-1 )

B. H. Luckman

1995-01-01

220

Exposure dating of underwater rocks: potential application to studies of land bridges during the Ice Ages  

Microsoft Academic Search

10Be concentrations for four underwater rock samples from the Tsugaru Strait, Japan were obtained. Most of the 10Be concentrations of these samples are higher than the expected steady state concentration at the relevant underground depth, implying that most samples have been pre-exposed during the last ice age. The model calculation of 10Be production using recent rates for underground production and

K. J Kim; M. Imamura

2004-01-01

221

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

Microsoft Academic Search

We present a 6-year simulation of the ice age atmosphere using the T21 Atmospheric General Circulation Model (AGCM) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The lower boundary conditions (18 kyr B.P.) were taken from CLIMAP Project Members (1981). The analysis is restricted to the surface climatology for two reasons: The surface fields are the test data derived

M. Lautenschlager; K. Herterich

1990-01-01

222

The ‘Little Ice Age’ glacial expansion in western Scandinavia: summer temperature or winter precipitation?  

Microsoft Academic Search

Reconstructing the temporal and spatial climate development on a seasonal basis during the last few centuries, including the\\u000a ‘Little Ice Age’, may help us better understand modern-day interplay between natural and anthropogenic climate variability.\\u000a The conventional view of the climate development during the last millennium has been that it followed a sequence of a Medieval\\u000a Warm Period, a cool ‘Little

A. Nesje; S. O. Dahl; T. Thun; Ø. Nordli

2008-01-01

223

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

Microsoft Academic Search

The sensitivity of the tropics to climate change, particularly the amplitude of glacial-to-interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no-analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods. A

Alan C. Mix; Ann E. Morey; Nicklas G. Pisias; Steven W. Hostetler

1999-01-01

224

Weak chemical weathering during the Little Ice Age recorded by lake sediments  

Microsoft Academic Search

Low magnetic susceptibility, low Sr content and hence high Rb\\/Sr ratio in the lake sediment sequence indicate a weak chemical\\u000a weathering process under arid and cold climate of the Little Ice Age in a single closed lake watershed. According to different\\u000a geochemical behavior between rubidium and strontium in earth surface processes, variation of Rb\\/Sr ratios in the lake sediment\\u000a sequence

Zhangdong Jin; Sumin Wang; Ji Shen; Enlou Zhang; Junfeng Ji; Fuchun Li

2001-01-01

225

El Niño's tropical climate and teleconnections as a blueprint for pre-Ice Age climates  

Microsoft Academic Search

At ~2.7 million years ago the warm equable climates of early and ``middle'' Pliocene time (used here to mean from ~5 to ~2.7 Ma) were replaced by recurring ice ages. Most attempts to explain the change appeal either to changes in CO2 in the atmosphere or reduced heat transport by the Atlantic Ocean. The sources of the strongest teleconnections in

Peter Molnar; Mark A. Cane

2002-01-01

226

A latest Pliocene age for the earliest and most extensive Cordilleran Ice Sheet in northwestern Canada  

NASA Astrophysics Data System (ADS)

The Klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive Cordilleran Ice Sheet (CIS) in NW North America. New terrestrial cosmogenic nuclide (TCN) burial ages indicate this gravel was emplaced 2.64+0.20/-0.18 Ma (1?). Coupled with previously interpreted paleomagnetic stratigraphy, this numerical age constrains the timing of the earliest CIS to the late Gauss Chron and provides a minimum age for the Upper White Channel gravel, a significant placer gold source in the Yukon. This implies the first CIS glacial maximum pre-dates the maximum extent of the Laurentide Ice Sheet, indicating that during the initial stages of northern hemisphere glaciation, the most extensive glaciers were present in the relatively cold and high elevation northern Cordillera. Our results verify the CIS as a likely source of persistent coeval ice-rafted debris in the northern Pacific, and suggest that the first CIS formed as a response to the establishment of the northern Pacific halocline and emergence of the 41 ka obliquity cycle during the Plio-Pliocene transition.

Hidy, Alan J.; Gosse, John C.; Froese, Duane G.; Bond, Jeffrey D.; Rood, Dylan H.

2013-02-01

227

A non-linear climate oscillator controlled by biogeochemical cycling in the ocean: an alternative model of Quaternary ice age cycles  

Microsoft Academic Search

A new, biogeochemical model of ice age cycles is developed and applied which explains major features of climate variations in the late Quaternary —rapid ice age terminations, large glacial-interglacial amplitudes and ~ 100-kyr cycles — in a way consistent with the paleorecord. Existing models which invoke non-linear, ice-sheet-earth-crust dynamics to explain ice age cycles are not consistent with simultaneous terminations

Gary Shaffer

1990-01-01

228

Polar Synchronization: A mechanism for interhemispheric timing of millennial climate variability during the last ice age  

NASA Astrophysics Data System (ADS)

Ice core records from Greenland and Antarctica show that the inter-hemispheric timing of climatic responses is not synchronous during the last ice age. The relatively precise methane synchronized data indicate that Antarctic warming events lead Dansgaard-Oeschger events (DO) by 1.5-3ka, which implies the average north-south phase shift is 90°. However, the underlying mechanism about this phase relationship is unclear. Here we suggest that climate variability in millennial-scale is controlled by polar synchronization. The term synchronization here is to describe the nonlinear frequency and phase locking that occurs when two or more coupled oscillators adjust their initially different rhythms to a common frequency and constant relative phase, which can be either in-phase, anti-phase, or out-of-phase. So, polar synchronization is not contradictory with inter-hemispheric asynchrony in geological records. With our numerical method, Greenland ice core wiggle can be transformed to Antarctic ice core wiggle and vice versa. Besides, the observed phase relationship can be successfully captured by our synchronization model.

Zhang, Y.; Rial, J. A.

2011-12-01

229

Characterization of Surface Water-Groundwater Interactions in a Proglacial Moraine Using Heat and Solute Tracers  

NASA Astrophysics Data System (ADS)

Alpine watersheds represent the headwaters of many major rivers in western North America. Understanding the groundwater systems in these watersheds is critical to understanding the timing of water release and late season stream flow, especially given the predicted shifts in precipitation patterns due to climate change. Recent water-balance studies of alpine lakes have shown the importance of groundwater, and suggest that moraines may play an important role in its storage and release. Due to challenging terrain and the inability to install wells, the use of conventional hydrogeological methods to characterize groundwater flow is not possible on most moraines. Thus, alternative methods are needed if these features are to be adequately incorporated into future physically-based modelling attempts. As part of an integrated alpine hydrology study of the Lake O'Hara research basin in the Canadian Rockies, we used a small tarn (~ 600 m3) on a partially ice-cored, proglacial moraine as a well surrogate. The lack of surface water inflows or outflows to the tarn means that tarn water level can be used to indicate the local groundwater table and that flow rates through the tarn can be used to represent local groundwater flow rates. Here we present the results of two experiments performed on the tarn to determine local flow rates. 1) A chloride-dilution tracer experiment was performed, in which the chloride decay-rate after a one-time addition of NaCl was used to determine the volumetric flow rate through the tarn. Chloride concentration was determined from daily water samples and interpolated from half hourly electrical conductivity measurements. 2) Detailed energy-balance measurements for the tarn were made and flow rates through the tarn were determined based on the advection component of the energy balance equation. Both experiments used a digital elevation model of the tarn to determine tarn volume changes, and therefore solute mass and energy storage changes based on water level data. We compare the above methods in terms of the calculated flow rates and accuracy. Our results provide a significant step forward in parameterizing future hydrological modelling attempts in challenging alpine environments.

Langston, G.; Hayashi, M.; Roy, J. W.

2009-05-01

230

Evidence for long-lasting landform surface instability on hummocky moraines in the Pamir Mountains (Tajikistan) from 10Be surface exposure dating  

Microsoft Academic Search

Surface exposure dating is a new, but already widely used tool in geomorphological studies, aiming, e.g. at the establishment of glacial chronologies. Sometimes, however, results from samples taken from one and the same moraine scatter widely and thus interpretation turns out to be difficult. Here we assess sample-specific effects (topographic shielding, sample geometry and erosion) on 17 surface exposure ages

Roland Zech; Bruno Glaser; Pjotr Sosin; Peter W. Kubik; Wolfgang Zech

2005-01-01

231

CO2 Climate-Glaciation linkages During the Late Paleozoic Ice Age and the Earth's Penultimate Deglaciation  

Microsoft Academic Search

The Late Paleozoic Ice Age (LPIA) was the longest-lived (330 to 260 Myr) and most intense glaciation of the past half-billion years. Emerging high-latitude Southern Hemisphere records document a much more dynamic ice age - one defined by multiple short-lived (1 to 7 myr duration) icehouse periods punctuated by warmer periods of glacial minima. These major climate shifts throughout the

I. P. Montanez

2007-01-01

232

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

SciTech Connect

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

Monastersky, R.

1994-02-19

233

Constraining the Late Wisconsinan retreat of the Laurentide ice sheet from western Canada using luminescence ages from postglacial aeolian dunes  

Microsoft Academic Search

Optically stimulated luminescence (OSL) dating of quartz extracts from postglacial aeolian dunes from central Alberta in western Canada points to a landscape that was free of ice as early as 15 ka. Data from profiles where multiple ages have been obtained indicate an increase in depositional age with depth, suggesting that older aeolian sands underlie the dated sequences. The OSL ages

Kennedy Munyikwa; James K. Feathers; Tammy M. Rittenour; Heather K. Shrimpton

2011-01-01

234

Coherent Tropical Ocean Response to Plio-Pleistocene Ice Age Cycles (Invited)  

NASA Astrophysics Data System (ADS)

Despite the enormous progress made in unravelling the history of high latitude glaciations during Plio-Pleistocene time, assessing the sensitivity of the tropical regions of the globe to these climate perturbations has proved controversial. Ocean Drilling provides a unique capability to address this question with a globally distributed data base. We present here alkenone-based tropical sea surface temperature (SST) records from the major ocean basins that span 3.5 Myr, at the sample resolution of the orbital cycles that pace glaciation. The SST data are aligned to each other and to a common timescale via benthic oxygen isotope measurements made on the same samples used for SST determinations. Despite the fact that the modern oceanography of the four sites is quite different, the paleo-SST records display remarkable similarity. All show coherent glacial-interglacial temperature changes on the order of 1-3 °C that closely align with (but slightly lead) the global record of ice volume and deep ocean cooling recorded by oxygen isotopes (?18O) in benthic foraminifera. Tropical temperatures became tightly coupled with benthic ?18O and orbital forcing after 2.7 Ma, and thereafter follow a similar spectral and amplitude evolution. The amplitude of the tropical SST cycles increases toward the present, as does the fraction of variance shared between the sites. We interpret the broad synchroneity of tropical SST with the ice ages, in dynamically dissimilar regions, to represent a “top-down” forcing of SST through the atmosphere, which would lead to a common temperature imprint across the tropics. The tropical SST response became increasingly similar toward the present, as the magnitude of the greenhouse forcing during ice ages increased. According to this interpretation, the critical sequence of events that led to a sustained pattern of northern hemisphere ice ages involved the inception of a strong CO2/greenhouse gas feedback and amplification of orbital forcing at ~2.7 Ma which has connected the fate of northern hemisphere ice sheets with tropical ocean temperatures since that time. The coherent tropical SST response would serve to significantly amplify CO2 forcing through water vapor and perhaps cloud effects.

Herbert, T.; Lawrence, K. T.; Liu, Z.; Peterson, L. C.

2010-12-01

235

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments.  

PubMed

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550-1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems. PMID:23716658

La Farge, Catherine; Williams, Krista H; England, John H

2013-05-28

236

Cosmogenic exposure-age chronologies of Pinedale and Bull Lake glaciations in greater Yellowstone and the Teton Range, USA  

USGS Publications Warehouse

We have obtained 69 new cosmogenic 10Be surface exposure ages from boulders on moraines deposited by glaciers of the greater Yellowstone glacial system and Teton Range during the middle and late Pleistocene. These new data, combined with 43 previously obtained 3He and 10Be ages from deposits of the northern Yellowstone outlet glacier, establish a high-resolution chronology for the Yellowstone-Teton mountain glacier complexes. Boulders deposited at the southern limit of the penultimate ice advance of the Yellowstone glacial system yield a mean age of 136??13 10Be ka and oldest ages of ???151-157 10Be ka. These ages support a correlation with the Bull Lake of West Yellowstone, with the type Bull Lake of the Wind River Range, and with Marine Isotope Stage (MIS) 6. End moraines marking the maximum Pinedale positions of outlet glaciers around the periphery of the Yellowstone glacial system range in age from 18.8??0.9 to 16.5??1.4 10Be ka, and possibly as young as 14.6??0.7 10Be ka, suggesting differences in response times of the various ice-cap source regions. Moreover, all dated Pinedale terminal moraines in the greater Yellowstone glacial system post-date the Pinedale maximum in the Wind River Range by ???4-6 kyr, indicating a significant phase relationship between glacial maxima in these adjacent ranges. Boulders on the outermost set and an inner set of Pinedale end moraines enclosing Jenny Lake on the eastern Teton front yield mean ages of 14.6??0.7 and 13.5??1.1 10Be ka, respectively. The outer Jenny Lake moraines are partially buried by outwash from ice on the Yellowstone Plateau, hence their age indicates a major standstill of an expanded valley glacier in the Teton Range prior to the Younger Dryas, followed closely by deglaciation of the Yellowstone Plateau. These new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the Rocky Mountains during the Pleistocene. ?? 2008 Elsevier Ltd. All rights reserved.

Licciardi, J. M.; Pierce, K. L.

2008-01-01

237

Detecting Seepage Through a Natural Moraine Dam Using the Self-Potential Method  

NASA Astrophysics Data System (ADS)

We conducted a self-potential (SP) survey of the Dana Lake moraine dam to investigate seepage flow through a natural moraine. Seepage erosion, along with overtopping, are the two primary mechanisms that cause moraine dams to fail. Specifically, localized seepage paths can entrain dam matrix material and may lead to undermining and partial collapse. Our survey included 200+ self-potential measurements spaced between 2 to 10 meters apart. The Dana Lake moraine dam is located in the Sierra Nevada, California. The moraine is likely between 4000 and 11,000 years old, and impounds approximately 3 x 105 m3 of water. The moraine also has two small lakes (unofficially East and West lakes) at its downstream toe, which are fed in part by seepage from Dana Lake. Intriguingly, West Lake is primarily sand and silt bedded while gravel and boulders dominate the bed of East Lake, despite them being ~40 meters apart. We concentrated our study on the west side of the moraine dam because 1) we observed active seepage flow on that side and 2) the lake bed material difference between East and West lakes suggests seepage may be removing fines from the western side of the moraine. Preliminary analysis of our self-potential data indicates nonuniform seepage flow through the moraine. On the western side, a broad positive SP anomaly is spatially coincident with observed seepage outlets and a sub-moraine bedrock knob visible at the surface. Additionally, a large negative anomaly coincides with the edge of the bedrock knob and may represent a vertical seepage path. On the eastern side of the moraine, groundwater flow appears to originate at the lake margin and follows an arcuate path towards West Lake. Other localized positive SP anomalies indicate possible seepage outlets. Future work includes forward modeling to resolve seepage flow rates and resulting stresses for use in a full seepage erosion analysis of the moraine dam.

Moore, J. R.; Sanders, J. W.; Clague, J. J.; Glaser, S. D.

2004-12-01

238

Impact of ice ages on circumpolar molecular diversity: insights from an ecological key species.  

PubMed

We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal 'Amphi-Atlantic lineage' included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal 'Beringian lineage' included seven haplotypes restricted to Beringia and the Pacific coast of USA. The 'Arctic-Alpine lineage' included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions. PMID:16029475

Alsos, I G; Engelskjøn, T; Gielly, L; Taberlet, P; Brochmann, C

2005-08-01

239

Changes in Attitude on Equatorial Latitudes: Tropical Climate Evolution During the Ice Ages  

NASA Astrophysics Data System (ADS)

Some 50 years ago, Cesare Emiliani published the first oxygen isotope records from marine sediment cores taken in the Caribbean Sea. He interpreted the observed oscillations as a consequence of 6 deg cooler tropical sea surface temperatures (SSTs) during the Ice Ages. In the following decades, this interpretation was discarded in favor of the dominant role of high latitude ice volume on oxygen isotope variability. Consequently, and as bolstered by a lack of faunal evidence for significant tropical changes, the Ice Ages were regarded as largely high and mid latitude phenomenon, with minimal involvement of the tropics. This view began to change when evidence emerged from terrestrial archives, from new proxies of tropical SST, and from tropical sites with rapidly accumulating sediments such as the Cariaco Basin, for an active climate role for the tropics on both orbital and millennial timescales. Today it is largely accepted that tropical SSTs cooled by about 3 deg during glacial episodes, and that at least some parts of the tropics played a dynamical role in the abrupt millennial scale events first identified in high latitude ice cores. What is still controversial is: 1) the timing of tropical changes, with some records strongly suggesting that tropical changes pre-dated northern hemisphere high latitude changes, including ice volume changes; 2) the climate forcing that drove tropical changes, with greenhouse gas forcing and high latitude shifts the most likely sources; and 3) the role of the tropics in triggering, amplifying or even driving large scale climate evolution. This talk will address these three critical questions and survey the most recent evidence. In particular, I will present new evidence that supports an early deglacial warming of the tropics in response to greenhouse gas forcing. If this interpretation is correct, it suggests that tropical warming might have played a key role in driving deglaciation. It also suggests that past tropical changes under known forcing can be used to gauge climate sensitivity, both in the narrow sense of temperature response, and in the broad sense of how tropical climate and circulation evolved. Ultimately, I will argue that tropical paleoclimate records inform predictions of how both the tropics and the global climate system will respond to rising greenhouse gases in the atmosphere.

Lea, D. W.

2007-12-01

240

Delta N-15 of N[sub 2] in air trapped in polar ice - a tracer of gas transport in the firn and a possible constraint on ice age-gas age differences  

SciTech Connect

Factors which influence the distribution of air in present-day firn are examined on the basis of the analysis of delta N-15 of trapped N[sub 2] in 12 ice-core samples taken from Greenland and Antarctica, and this information is used to determine how air may have been mixed in glacial firn. The upper and the lower limits of ice-age/gas-age differences (Delta age) are then calculated for the ice core at the Vostok, the Dome C, and the Byrd locations, and the results are compared with previous estimates. Finally, the surface-temperature and CO[sub 2] records from Byrd and Vostok over the last 30,000 years are compared to provide independent means of establishing the best estimates of the Delta age difference for Vostok, and of the nature of gas transport in firn during the last glacial termination. 39 refs.

Sowers, T.; Bender, M.; Raynaud, D.; Korotkevich, IU.S. (Rhode Island Univ., Narragansett (United States) CNRS, Lab. de Glaciologie et Geophysique de l'Environnement, St.-Martin-d'Heres (France) Arctic and Antarctic Research Inst., St. Petersburg (Russian Federation))

1992-10-01

241

A novel radiocarbon dating technique applied to an ice core from the Alps indicating late Pleistocene ages  

NASA Astrophysics Data System (ADS)

Ice cores retrieved from high-altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions. Because of the specific flow behavior of ice, their age-depth relationship is nonlinear, preventing the application of common dating methods such as annual layer counting in the deepest and oldest part. Here we present a new approach and technique, allowing dating of any such ice core at arbitrary depth for the age range between ˜500 years B.P. and the late Pleistocene. This new, complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies. Using small to ultrasmall sample size (100 ?g > carbon content > 5 ?g) accelerator mass spectrometry, we take advantage of the ice-included, water-insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon (14C) dating. Analysis and dating of the bottom ice of the Colle Gnifetti glacier (Swiss-Italian Alps, 45°55'50?N, 7°52'33?E, 4455 m asl) has been successful in a first application, and the results revealed the core to cover most of the Holocene at the least with indication for late Pleistocene ice present at the very bottom.

Jenk, Theo M.; Szidat, SöNke; Bolius, David; Sigl, Michael; GäGgeler, Heinz W.; Wacker, Lukas; Ruff, Matthias; Barbante, Carlo; Boutron, Claude F.; Schwikowski, Margit

2009-07-01

242

Cosmogenic exposure dating of boulders and bedrock in Denmark: wide range in ages reflect strong dependence of post-depositional stability related to specific glacial landforms  

NASA Astrophysics Data System (ADS)

The timing of ice-sheet fluctuations, as indicated by glacier advances and retreats, is detected from a wide range of geochronological techniques, including varve counting, and radiocarbon and luminescence dating of proglacial and inter till sediments. A robust Late Weichselian chronology of deglacial ice sheet fluctuations in southwestern Scandinavia indicates that the decline of the Scandinavian Ice Sheet from the Last Glacial Maximum position at c. 23-21 kyr (thousands of years) ago in central Denmark occurred through recessional stages and readvances. Active glaciers withdrew from eastern Denmark 17-16 kyr ago and left the southwestern Baltic basin ice free at the beginning of the Bølling interstade c. 14.5 kyr ago. The withdrawal left behind belts of elongate end moraines and streamlined ground moraine as large ice masses were successively isolated causing massive down wasting until c. 12 - 11 kyr ago. In Eastern Denmark and southernmost Sweden this lead to formation of complex superimposed glacial landscapes originally covered with a wealth of erratic boulders. Hitherto untried cosmogenic nuclide surface exposure dating was applied to sites in Eastern Denmark to test the method against independent chronologies. Samples collected from erratics, moraines and ice-sculpted bedrock were prepared at the Cosmogenic Nuclide Laboratory at the University of Glasgow and AMS measurements were carried out at the Scottish Universities Environmental Research Centre (SUERC) AMS facility. Procedural blank corrected 10Be concentrations were converted to in situ 10Be surface exposure ages using the online CRONUS-Earth 10Be-26Al exposure age calculator Version 2.2. Exposure ages from 35 samples range between 11.5 and 20 kyr, 18 of which lie within the expected age envelope. Two samples show overestimated ages apparently due to cosmogenic nuclide inheritance from previous exposure episodes. The remaining 17, two of which have suffered from exhumation, are younger than predicted. Dating of boulders and adjacent bedrock on the island of Bornholm in the western Baltic reveal almost similar ages and fit the independent chronology. This indicates that very little if any inherited nuclides are present in the boulders. Moreover, ages from Bornholm seem to become younger with descending height above sea level, suggesting that the island was progressively exposed as glaciers in the Baltic downwasted. In mainland Denmark ages that fit the age model are situated on top of end moraines or located on streamlined ground moraine. Boulders with underestimated ages were sampled in dead ice moraines and down wasting landscapes. These results are interpreted as providing landform stabilisation ages since these boulders appear to have first melted out of dead ice and came to rest after 15 until about 12 kyr ago. We conclude that cosmogenic nuclide surface exposure dating is very sensitive to landscape stability, and that when used for dating glacier fluctuations surface stability should be thoroughly evaluated before sampling.

Houmark-Nielsen, Michael; Linge, Henriette; Fabel, Derek; Xu, Sheng

2010-05-01

243

Variability in the timing of the late Holocene maximum extent of the southwest Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Boreal summer climate generally cooled across the mid to late Holocene, driving growth of the Greenland Ice Sheet. The timing of maximum late Holocene Greenland Ice Sheet extent is usually assigned to the Little Ice Age (LIA), although earlier more extensive Neoglacial advances may have occurred. Here we present new 10-Be surface exposure ages from erratic boulders on bedrock just outside of historical moraines deposited during the LIA near Kangerlussuaq, Paamiut and Narsarsuaq in southwest Greenland to date when ice was more extensive than during the LIA. A more extensive Neoglacial advance at ~2 ka was previously proposed near Kangerlussuaq. Our cosmogenic dates just outside the historical moraine at Kangerlussuaq indicate, however, that ice has been within its historical limit since 6.8±0.1 ka (n=6, 1 std. error), which is similar to recently published age constraints further north in the Disko Bugt region of west Greenland. Near Narsarsuaq in south Greenland, cosmogenic boulder dates indicate that at 1.2±0.2 ka (n=4, 1 std. error), the outlet glacier Kiagtût sermiat was ~200 m thicker than its historical limit. The timing of thicker ice near Narsarsuaq is likely concurrent with an ~8 km advance the same outlet glacier relative to the modern ice margin previously inferred from one minimum limiting radiocarbon date of 1.2±0.1 ka (1?). Cosmogenic dates from near Paamiut in southwest Greenland and additional Narsarsuaq dates are forthcoming. The timing of ice thinning and retreat near Narsarsuaq beginning at ~1.2 ka is concurrent with a switch from the dominance of Arctic- to Atlantic-sourced water masses within southern Greenland fjords, inferred from changes in fjord faunal assemblages. Modern switches in the source of fjord waters are related to variations in the North Atlantic Oscillation (NAO), with a switch from a positive to a negative phase causing the incursion of relatively warm Irminger Current waters around southern Greenland. We hypothesize that similar variations in North Atlantic atmospheric-oceanic circulation at centennial time-scales could have resulted in relatively cold southern Greenland fjord waters prior to ~1.2 ka during a positive NAO-like state, which forced a more extensive Neoglacial advance in southern Greenland than during the LIA. Conversely, during the LIA, warmer Atlantic waters may have dominated southern Greenland fjords, resulting in less extensive ice. The importance of this effect may have diminished northward up the coast, such that at Kangerlussuaq and further north, temperatures reached Holocene minima and the ice sheet margin its Holocene maximum extent during the LIA.

Carlson, A. E.; Winsor, K.; Ullman, D. J.; Murray, D. S.; Rood, D. H.; Axford, Y.

2011-12-01

244

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

NASA Astrophysics Data System (ADS)

230Th/234U and 14C dating of Barbados corals has extended the calibration of 14C years B.P. to calendar years B.P. beyond the 9200 year tree ring series (Bard et al., 1990). This now permits the conversion of 14C chronozones, which delimit major climate shifts in western Europe, to calendar years. The Younger Dryas chronozone, defined as 11,000 to 10,000 14C years B.P., corresponds to 13,000 to 11,700 calendar years B.P. This calibration affects the interpretation of an intensely studied example of the "Younger Dryas climate event," the ?18O anomaly between 1785 and 1793 m in Dye 3 ice core. The end of the ?18O anomaly in Dye 3 ice core has been dated by measurements of 14C in air bubbles (Andree et al., 1984, 1986) and by annual layer counting (Hammer et al., 1986). The older 14C dates fall out of the range of the tree ring calibration series but can now be calibrated to calendar years using the Barbados 230Th/234U calibration. The 14Ccorrected age for the end of the ?18O event is 10,300 ± 400 calendar years B.P. compared to the annual layer counting age of 10,720 ± 150 years B.P. Thus, the "Younger Dryas" event in the Dye 3 ice core ends in the Preboreal chronozone (11,700 to 10,000 calendar years B.P.) and is not correlative with the end of the Younger Dryas event identified in pollen records marking European vegetation changes. The end of the Dye 3 ?18O event is, however, correlative with the end of meltwater pulse IB (Fairbanks, 1989), marking a period of intense deglaciation with meltwater discharge rates exceeding 13,000 km³/yr.

Fairbanks, R. G.; Bard, E.

1990-12-01

245

Future ice ages and the challenges related to final disposal of nuclear waste: The Greenland Ice Sheet Hydrology Project  

NASA Astrophysics Data System (ADS)

A deep geological repository for nuclear waste is designed to keep radiotoxic material separated from mankind and the environment for several hundreds of thousands of years. Within this time perspective glacial conditions are expected in high latitudes/Canada and North Europe. Climate induced changes such as the growth of ice sheets and permafrost will influence and alter the ground surface and subsurface environment, which may impact repository safety. In order to understand how climate change, particularly cooling and glaciation, might affect a repository in the long term, the use of present-day analogues helps to reduce the uncertainties and support the assumptions made in safety assessments. There are major uncertainties concerning hydrological processes related to glacial conditions. The impact of glaciations on any planned repository is a key consideration when performing safety assessments as it is one of the strongest perturbations related to climate change in the long term. The main aspects that need to be further investigated include: 1) to what extent does the meltwater produced by an ice sheet penetrates into the bedrock; 2) what is the pressure situation under an ice sheet, driving ground water flow; 3) how much oxygenated water will reach repository depth; 4) to what depth does glacial meltwater penetrate into the bedrock ; 5)what chemical composition does such water has when and if it reaches repository depth; and 6) can taliks (unfrozen ground in a permafrost area) act as concentrated discharge points of deep groundwater potentially transporting radionuclides in case of repository failure? Field data is needed in order to achieve a better and integrated understanding of the problems discussed above. Thus, research in a natural analogue site in Greenland has been planned and initiated by the Finnish (Posiva), Swedish (SKB) and Canadian (NWMO) nuclear waste management companies. The Greenland ice sheet and the Kangerlussuaq area (west Greenland) provides a good analogue for this purpose due to similarities in geology (in the selected study area), and the climate conditions and ice sheet size in Kangerlussuaq resemble the expected conditions in Fennoscandia during future glaciations. In 2005 and 2008 reconnaissance field trips were made to Kangerlussuaq, which confirmed the suitability of the area for the planned studies. According to the present Work Programme the investigations will be carried out in 2009-2012. The project is divided into four subprojects (SPA, SPB, SPC and SPD) addressing specific and different topics at or in relation to the ice margin: SPA (ice sheet hydrology and glacial groundwater formation); SPB (subglacial ice sheet hydrology), SPC (hydrogeochemistry and hydrogeology) and SPD (periglacial environment: biosphere and permafrost). The main objectives of SPA and SPB are to gain a better process understanding of supra- and subglacial hydrology. Qualitative and quantitative knowledge of the mechanisms, rates and distribution of the melt water recharge through the ice down to the bed, location and extension of warm-based areas and hydraulic pressure conditions at the base are the key issues to be studied. This will be made by meteorological observations, GPS measurements, radar surveys, drilling through the ice sheet and by ice sheet modelling. SPC will further study the fate of melt water by extending the investigations into the bedrock. It is assumed that the high hydraulic pressures at the ice sheet bed force water into the fracture network prevailing in the bedrock. However, it is not known how the fracture network behaves under loading, what is the proportion of recharging water compared to the drainage through the bed sediments, what is the intrusion depth, how long the meltwater can sustain its oxic nature and what chemical composition the recharging water has when and if it reaches repository depth (400-700 m). SPC seeks to answer these questions by drilling and instrumenting boreholes drilled into the bedrock and below the ice sheet. SPD is aiming at describing and studying proce

Lehtinen, A.; Claesson-Liljedahl, L.; Näslund, J.-O.; Ruskeeniemi, T.

2009-04-01

246

The Impact of the Little Ice Age on Coccolithophores in the Central Mediterranea Sea  

NASA Astrophysics Data System (ADS)

The Little Ice Age (LIA) is the last episode of a series of Holocene climatic anomalies. There is still little knowledge on the response of the marine environment to the pronounced cooling of the LIA and to the transition towards the 20th century global warming. Here we present decadal-scale coccolithophore data from four short cores recovered from the central Mediterranean Sea (northern Sicily Channel and Tyrrhenian Sea), which on the basis of 210Pb activity span the last 200-350 years. The lowermost part of the record of one of the cores from the Sicily Channel, Station 407, which extends down to 1650 AD, is characterized by drastic changes in productivity. Specifically, below 1850 AD, the decrease in abundance of F. profunda and the increase of placoliths, suggest increased productivity. The chronology of this change is related to the main phase of the Little Ice Age, which might have impacted the hydrography of the southern coast of Sicily and promoted vertical mixing in the water column. The comparison with climatic forcings points out the importance of stronger and prolonged northerly winds, together with decreased solar irradiance.

Incarbona, A.; Ziveri, P.; di Stefano, E.; Lirer, F.; Mortyn, G.; Patti, B.; Pelosi, N.; Sprovieri, M.; Tranchida, G.; Vallefuoco, M.; Albertazzi, S.; Bellucci, L. G.; Bonanno, A.; Bonomo, S.; Censi, P.; Ferraro, L.; Giuliani, S.; Mazzola, S.; Sprovieri, R.

2010-12-01

247

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

USGS Publications Warehouse

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

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

1999-01-01

248

Beryllium-10 dating of Mount Everest moraines indicates a strong monsoon influence and glacial synchroneity throughout the Himalaya  

NASA Astrophysics Data System (ADS)

Moraine successions in glaciated valleys south of Mount Everest provide evidence for at least eight glacial advances during the late Quaternary. Cosmogenic radionuclide (CRN) surface exposure dating of moraine boulders defines the timing of each glacial advance and refines the previous glacial chronologies. The CRN data show that glaciation was most extensive during the early part of the last glacial (marine oxygen isotype stage [MIS] 3 and earlier), but limited during MIS 2 (the global Last Glacial Maximum) and the Holocene. A previously assumed Neoglacial advance is dated to 3.6 ± 0.3 ka and the CRN dates confirm a glacial advance ca. 1 ka. These results show that glaciations on the south side of Everest were not synchronous with the advance of Northern Hemisphere ice sheets, yet glaciations within the Himalaya, the world's highest mountain belt, were synchronous during the late Quaternary. The existence of glacial advances during times of increased insolation suggests that enhanced moisture delivered by an active south Asian summer monsoon is largely responsible for glacial advances in this part of the Himalaya. These data allow us to quantify the importance of global climate change and monsoon influence on glaciation in the Himalaya.

Finkel, Robert C.; Owen, Lewis A.; Barnard, Patrick L.; Caffee, Marc W.

2003-06-01

249

The chronology and rate of ice-sheet margin retreat in the major fjords of Western Norway during the Early Holocene  

NASA Astrophysics Data System (ADS)

Hardangerfjorden is up to 900 m deep and about 170 km long. The well defined Younger Dryas (YD) end moraine is located 40 km inside the fjord mouth. Lateral moraines show that the surface gradient near the ice front was steep and the glacier was grounded. These moraines can be traced up to 1000 m a.s.l. about 40 km inland, where the fjord is 600 m deep, indicating a total ice thickness of 1600 m. The YD margin terminated on a threshold and the fjord gets much deeper on the proximal side of the moraine. Therefore, the ice margin must have been floating as soon as retreat from the YD position began and calving was certainly an important process during deglaciation. The break up of the glacier ice in the fjord must also have led to a considerable draw down of the ice-sheet surface further inland. According to our dating results the retreat started at 11,500 cal yr BP (Bondevik and Mangerud 2002; Lohne 2007). We have used three methods to estimate the up-fjord retreat: 1) 14C dating of organic material deposited during or soon after deglaciation (Romundset et al., 2009), 2) age determination of ice-marginal deltas by using a shore-line diagram we constructed from data in Lohne et al (2007) and Romundset et al (2009), 3) 10Be exposure dating of a number of large ice-transported boulders. All three methods provide consistent ages in the interval 10,900-11,100 cal yr BP for the deglaciation of the fjord head, which yields a mean retreat rate of 220-330 m/year. The ages for Hardangerfjorden can also be used for the even longer (220 km) and deeper (1300 m) Sognefjorden, giving a retreat rate of 370-550 m/year, because the relevant YD and Early Holocene moraines have been mapped and correlated (Vorren and Mangerud 2008). Bondevik, S. and Mangerud, J., 2002. A calendar age estimate of a very late Younger Dryas ice sheet maximum in western Norway. Quaternary Science Reviews 21, 1661-1676. Lohne, Ø.S., 2007. Late Weichselian relative sea-level changes and glacial history in Hordaland, Western Norway. PhD, Dept. Earth Sc., Univ. Bergen. Lohne, Ø.S., Bondevik, S., Mangerud, J. and Svendsen, J.I., 2007. Sea-level fluctuations imply that the Younger Dryas ice-sheet expansion in western Norway commenced during the Allerød. Quaternary Science Reviews 26, 2128-2151. Romundset, A., Lohne, Ø., Mangerud, J. and Svendsen, J., 2009. The first Holocene relative sea-level curve from the middle part of Hardangerfjorden, western Norway. Boreas (in press). Vorren, T. and Mangerud, J., 2008. Glaciations come and go. Pleistocene, 2.6 million-11,500 years ago. In: I. Ramberg et al (Eds.). The making of a land - Geology of Norway, pp. 480-533. Norsk Geologisk Forening, Trondheim, Norway.

Mangerud, J.; Lohne, O. S.; Goehring, B. M.; Svendsen, J.; Gyllencreutz, R.; Schaefer, J. M.

2009-12-01

250

Several million years of stability among insect species because of, or in spite of, Ice Age climatic instability?  

PubMed Central

There is a curious paradox in the evolutionary legacy of Ice Ages. Studies of modern species suggest that they are currently evolving in response to changing environments. If extrapolated into the context of Quaternary Ice Ages, this evidence would suggest that the frequent climatic changes should have stimulated the evolutionary process and thus increased the rates of change within species and the number of speciation events. Extinction rates would, similarly, be high. Quaternary insect studies call into question these interpretations. They indicate that insect species show a remarkable degree of stability throughout the Ice Age climatic oscillations. The paradox arises from the apparent contradiction between abundant evidence of incipient speciation in insect populations at the present day and the evidence that, in the geological past, this apparently did not lead to sustained evolution.

Coope, G R

2004-01-01

251

Medial moraines of glaciers of the Copper River Basin, Alaska: Discrete landslides dominate over other sources  

Microsoft Academic Search

Medial moraines are visually dominant structures of most large valley glaciers in the Copper River Basin (CRB), Alaska. Areally extensive but thin (usually <20 cm) accumulations of debris pose challenges for glacier mapping based on multispectral imagery, as done, for instance, in the GLIMS project. The sources of this material include large discrete landslides from wallrocks and from lateral moraines;

J. S. Kargel; L. Fischer; R. Furfaro; C. Huggel; O. Korup; G. J. Leonard; M. Uhlmann; R. L. Wessels; D. F. Wolfe

2009-01-01

252

Contribution of Icelandic ice caps to sea level rise: Trends and variability since the Little Ice Age  

NASA Astrophysics Data System (ADS)

In total, Icelandic ice caps contain ˜3600 km3 of ice, which if melted would raise sea level by ˜1 cm. Here, we present an overview of mass changes of Icelandic ice masses since the end of the 19th century. They have both gained and lost mass during this period. Changes in ice volume have been estimated both through surface mass balance measurements (performed annually since ˜1990) and differencing of digital elevation models derived from various satellite and airborne observations. While the glaciers showed little mass loss as the 20th century began, losses increased rapidly after 1925, peaked in the 1930s and 1940s, and remained significant until the 1960s. After being near-zero or even positive during the 1980s and early 1990s, glacier mass budgets declined considerably, and have since the mid-1990s shown an average annual loss of 9.5±1.5 Gt a-1, contributing ˜0.03 mm a-1 to sea level rise. Since 1995 interannual variability in mass loss is high, ranging from 2.7 to 25.3±1.5 Gt a-1, corresponding to surface mass balances of -0.2 to -2.2 ± 0.15 m we a-1. This variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions.

Björnsson, Helgi; Pálsson, Finnur; Gudmundsson, Sverrir; Magnússon, Eyjólfur; Adalgeirsdóttir, Gudfinna; Jóhannesson, Tómas; Berthier, Etienne; Sigurdsson, Oddur; Thorsteinsson, Thorsteinn

2013-04-01

253

Breath from the little ice age makes non-sorted circles CO2 sources  

NASA Astrophysics Data System (ADS)

The mass-movement of soil induced by differential heave and thaw cycles (cryoturbation) is thought to reduce respiration losses from high latitude soils as it translocate carbon into cold mineral soil layers where microbial processes proceeds at slow rates (Bockheim, 2007). However, it is not straightforward to always view cryogenic processes as processes that contribute positively to the build-up of carbon in patterned ground systems, such as non-sorted circles. In these systems differential heave and ice-formation may affect plant growth negatively and thus lower the carbon input to the soil. In this study, we test the hypothesis that; increased cryogenic activity within non-sorted circles reduces the rate in which plant fixate CO2 from the atmosphere. To test our hypothesis we measured gross ecosystem photosynthesis (GEP) and soil respiration (R) in 3 fields of non-sorted circles (total amount of 15 circles, total 190 measurements) formed along a permafrost gradient close to Abisko, Northern Sweden. Measurements were conducted every second week for one summer and GEP and R fluxes were used to calculate the net ecosystem exchange (NEE) of CO2 in the fields. In the fields, the churning of carbon into mineral soil layers by cryoturbation occurred mainly in the past under different climatic conditions, i.e. mainly during the little ice age and a period around 1100 AD as indicated by 14C dating (Becher et al., 2013). In contrary to our hypothesis, we did not find any major difference in GEP between the fields in the permafrost gradient that seems to depend on contemporary cryogenic activity in the centre of the circles. However, we note that all circles respired more carbon than was fixated by photosynthesis. We therefore suggest that respiration losses from the pool buried mainly during the little ice age is strongly affecting the carbon balance of the circles. Consequently, non-sorted circles in northern Sweden may currently act as carbon sources. References Becher, M., C. Olid, and J. Klaminder, 2013. Buried Soil Organic Inclusions in Non-sorted Circles Fields in Northern Sweden: Age and Paleoclimatic Context. J. Geophys. Re., in press. Bockheim, J.G., 2007. Importance of Cryoturbation in Redistributing Organic Carbon in Permafrost-Affected Soils. Soil Sci. Soc. Am. J., 71:1335-1342.

Becher, Marina; Olofsson, Johan; Klaminder, Jonatan

2013-04-01

254

Extreme carbonate super-saturation of the ocean and Neoproterozoic ice ages  

NASA Astrophysics Data System (ADS)

In the modern ocean, reduction in carbonate deposition on the continental shelves can be compensated for by the increased preservation in deep sea sediments of biogenic carbonate originating from planktic calcifiers living in the open ocean. The result is that ocean carbonate chemistry is strongly buffered and the carbon-climate system relatively stable. However, before the advent of metazoan biomineralization in the Cambrian and proliferation of calcareous plankton during the Mesozoic, carbonate deposition would have been largely restricted to shallow water photic environments. Such a system is highly susceptible to positive feedback between sea level fall, reduced shallow water carbonate deposition, increased carbonate saturation of the ocean, atmospheric CO2 draw-down, and ice-sheet growth. This is consistent with the occurrence of ice ages of near-global extent during the Neoproterozoic. Both the widespread occurrence and observed thickness of `cap' (dolostone) carbonate deposited during postglacial transgression are explicit predictions of this hypothesis. The enigmatic cap facies thus record the rapid removal of accumulated alkalinity from an ocean that has reached an extreme degree of carbonate super-saturation by the end of the glacial period.

Ridgwell, A. J.; Kennedy, M.

2004-05-01

255

Three Holocene and late Pleistocene glacial stages inferred from moraines in the Lingshi and Thanza village areas, Bhutan  

Microsoft Academic Search

Moraines formed by valley glaciers in Lingshi area, northwestern Bhutan constitute three distinct stages with contrasts in the spatial distribution and size of moraines, and surface features such as clasts, soils and vegetation. Moraines in the Thanza Village area, northern Bhutan, show three stages with similar characteristics to those in the Lingshi area. Using morphostratigraphic criteria, these three stages correlate

Shuji Iwata; Chiyuki Narama; Karma

2002-01-01

256

Sedimentary facies and depositional architecture of ice-contact glaciomarine systems  

Microsoft Academic Search

The characteristics of ice-contact glaciomarine systems are reviewed, based on a range of Weichselian and Holocene examples from the fjordal basins in Norway and Svalbard. These depositional systems occur as large morphological ridges, “end-moraines” (including “push-moraines”), which are coarse grained and show large-scale foreset bedding. The paper addresses some of the major problems with regard to the recognition, classification and

Ida Lønne

1995-01-01

257

Assessing the Response of Alaska's Glaciers to Post-Little Ice Age Climate Change  

NASA Astrophysics Data System (ADS)

A comprehensive survey of the eleven mountain ranges and three island areas in Alaska that presently support glaciers was conducted to determine how glaciers in each area have responded to post-Little Ice Age (LIA) climate change. Today, glaciers cover 5 percent of Alaska, about 75,000 sq. km., range in elevation from 6,000 m to below sea level, and span latitudes from south of 55 degrees N to north of 69 degrees N. During the LIA, Alaskan glaciers expanded significantly, covering 10 percent more area than today. Many different types of data were used to construct baselines and determine glacier change. These include: published descriptions of glaciers (1794 - 2000), historic and modern maps (1794 - 2000), aerial photography (1926 - 2001), ground photography (1884 - 2001), airborne radar (1981 - 1991), satellite radar (1978 - 1998), space photography (1984 - 1994), multi-spectral satellite imagery (1972 - 2001), aerial reconnaissance and field observations by the author (1968 - 2001), and various types of proxy data. Data available varied for each region and glacier. Every mountain range and island group investigated is characterized by significant glacier retreat, thinning, and/or stagnation, especially at lower elevations. At some locations, glaciers have completely disappeared during the twentieth century. In other areas, retreat that started as early as the early eighteenth century, has continued into the twenty-first century. Ironically, in several areas, retreat is resulting in the number of glaciers is actually increasing, but the volume and area of ice is decreasing. The key survey findings are: ALEXANDER ARCHIPELAGO, KODIAK ISLAND, ALEUTIAN ISLANDS: every glacier examined showed evidence of thinning and retreat. Some have disappeared since last being mapped in the mid-twentieth century; COAST MOUNTAINS, ST. ELIAS MOUNTAINS, CHUGACH MOUNTAINS, KENAI MOUNTAINS, WRANGELL MOUNTAINS, ALASKA RANGE, AND THE ALEUTIAN RANGE: more than 95 percent of glaciers ending below an elevation of 1,500 m are retreating, thinning, and/or stagnating. Some advancing glaciers have tidewater termini. The two largest glaciers, Bering and Malaspina Glaciers, are thinning and retreating, losing several cubic kilometers of ice each year to melting and calving; TALKEETNA MOUNTAINS, AHKLUN-WOOD RIVER MOUNTAINS, KIGLUAIK MOUNTAINS, AND THE BROOKS RANGE: every glacier examined is retreating. Some disappeared during the twentieth century. Glaciers at higher elevations show little or no change. Perhaps, at these locations, regional climate change has not resulted in temperatures being elevated to a level where they impact existing glacier ice. Increases in precipitation may also be compensating for increases in melting. Throughout Alaska, in response to post-Little Ice Age climate change, all but a few glaciers that descent below an elevation of 1,500 m have thinned, stagnated, and/or retreated. Of the nearly 700 named Alaskan glaciers, less than a dozen are currently advancing.

Molnia, B. F.

2001-12-01

258

Rapid reorganization in ocean biogeochemistry off Peru towards the end of the Little Ice Age  

NASA Astrophysics Data System (ADS)

Climate and ocean ecosystem variability has been well recognized during the twentieth century but it is unclear if modern ocean biogeochemistry is susceptible to the large, abrupt shifts that characterized the Late Quaternary. Time series from marine sediments off Peru show an abrupt centennial-scale biogeochemical regime shift in the early nineteenth century, of much greater magnitude and duration than present day multi-decadal variability. A rapid expansion of the subsurface nutrient-rich, oxygen-depleted waters resulted in the present-day higher biological productivity, including pelagic fish. The shift was likely driven by a northward migration of the Intertropical Convergence Zone and the South Pacific Subtropical High to their present day locations, coupled with a strengthening of Walker circulation, towards the end of the Little Ice Age. These findings reveal the potential for large reorganizations in tropical Pacific climate with immediate effects on ocean biogeochemical cycling and ecosystem structure.

Gutiérrez, D.; Sifeddine, A.; Field, D. B.; Ortlieb, L.; Vargas, G.; Chávez, F. P.; Velazco, F.; Ferreira, V.; Tapia, P.; Salvatteci, R.; Boucher, H.; Morales, M. C.; Valdés, J.; Reyss, J.-L.; Campusano, A.; Boussafir, M.; Mandeng-Yogo, M.; García, M.; Baumgartner, T.

2009-05-01

259

Rapid reorganization in ocean biogeochemistry off Peru towards the end of the Little Ice Age  

NASA Astrophysics Data System (ADS)

Climate and ocean ecosystem variability has been well recognized during the twentieth century but it is unclear if modern ocean biogeochemistry is susceptible to the large, abrupt shifts that characterized the Late Quaternary. Time series from marine sediments off Peru show an abrupt centennial-scale biogeochemical regime shift in the early nineteenth century, of much greater magnitude and duration than present day multi-decadal variability. A rapid expansion of the subsurface nutrient-rich, oxygen-depleted waters resulted in higher biological productivity, including pelagic fish. The shift was likely driven by a northward migration of the Intertropical Convergence Zone and the South Pacific Subtropical High to their present day locations, coupled with a strengthening of Walker circulation, towards the end of the Little Ice Age. These findings reveal the potential for large reorganizations in tropical Pacific climate with immediate effects on ocean biogeochemical cycling and ecosystem structure.

Gutiérrez, D.; Sifeddine, A.; Field, D. B.; Ortlieb, L.; Vargas, G.; Chávez, F.; Velazco, F.; Ferreira, V.; Tapia, P.; Salvatteci, R.; Boucher, H.; Morales, M. C.; Valdés, J.; Reyss, J.-L.; Campusano, A.; Boussafir, M.; Mandeng-Yogo, M.; García, M.; Baumgartner, T.

2008-09-01

260

Abrupt Decrease in Tropical Pacific Sea Surface Salinity at End of Little Ice Age  

NASA Astrophysics Data System (ADS)

A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores from the Great Barrier Reef, Australia, indicates that sea surface temperature and salinity were higher in the 18th century than in the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific.

Hendy, Erica J.; Gagan, Michael K.; Alibert, Chantal A.; McCulloch, Malcolm T.; Lough, Janice M.; Isdale, Peter J.

2002-02-01

261

Ice age initiation by an ocean-atmospheric circulation change in the Labrador Sea  

Microsoft Academic Search

The contrast between the large Greenland ice sheet and the nearly ice-free area of Canada to the west exemplifies the critical role of the moisture supply in glaciation. The trigger for new ice-sheet growth in Canada at the end of the last interglacial was probably an increase in the moisture supply rather than regional cooling. Triggering is attributed to stronger

R. G. Johnson

1997-01-01

262

Relative sea-level change in Greenland during the last 700 yrs and ice sheet response to the Little Ice Age  

NASA Astrophysics Data System (ADS)

This paper presents new evidence regarding relative sea-level (RSL) changes and vertical land motions at three sites in Greenland since 1300 A.D., a time interval that spans the later part of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We observe RSL rise at two sites in central west Greenland from c. - 0.80 ± 0.20 m at c. 1300 A.D. to c. - 0.20 m ± 0.25 m at c. 1600 A.D., after which RSL slowed and then stabilised. At a third site in south Greenland, we observe RSL rise from c. - 1.40 ± 0.20 m at c. 1400 A.D. until c. 1750 A.D., after which RSL slowed and was stable during at least the latter part of the 20th century. The c. 1600 A.D. RSL slow-down seen at the two former sites is surprising because it occurs during the LIA when one might expect the ice sheet to be gaining mass and causing RSL to rise. We interpret this RSL slowdown to indicate a period of enhanced regional mass loss from central west Greenland since c. 1600 A.D. and propose two hypotheses for this loss: first, a reduction in precipitation during cold and dry conditions and second, higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards. The latter hypothesis is compatible with a well-established temperature seesaw between western Greenland and northern Europe and, potentially, a previously identified shift from a positive to generally more negative NAO conditions around 1400 to 1600 A.D. Our study shows how RSL data from Greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern Europe the ice sheet in west Greenland gained mass.

Long, Antony J.; Woodroffe, Sarah A.; Milne, Glenn A.; Bryant, Charlotte L.; Simpson, Matthew J. R.; Wake, Leanne M.

2012-01-01

263

Asynchronous Little Ice Age glacier fluctuations in Iceland and European Alps linked to shifts in subpolar North Atlantic circulation  

NASA Astrophysics Data System (ADS)

Records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume. In the North Atlantic region, glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover. However, the majority of glacier records are discontinuous and temporally restricted, owing in part to the extensive advance of Northern Hemisphere glaciers during the Little Ice Age (LIA), the most recent and severe climate anomaly of the Neoglacial period. Here, we combine an absolutely dated and continuous record of Langjökull ice marginal fluctuations with new reconstructions of sediment flux through the past 1.2 ka using varved sediments from Hvítárvatn, a proglacial lake in Iceland's central highlands. Large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles. Sediment data reveal two discrete phases of ice expansion occurring ca. 1400 to 1550 AD and ca. 1680 to 1890 AD. These advances are separated by a persistent interval of ice retreat, suggesting that a substantial period of warming interrupted LIA cold. The pattern of Icelandic glacier activity contrasts with that of European glaciers but shows strong similarities to reconstructed changes in North Atlantic oceanographic conditions, indicating differing regional responses to coupled ocean-atmosphere-sea ice variations. Our data suggest that subpolar North Atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid LIA and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments.

Larsen, Darren J.; Miller, Gifford H.; Geirsdóttir, Áslaug

2013-10-01

264

Variations of soil profile characteristics due to varying time spans since ice retreat in the inner Nordfjord, western Norway  

NASA Astrophysics Data System (ADS)

In the Erdalen and Bødalen drainage basins located in the inner Nordfjord in western Norway the soils have been formed after deglaciation. The climate in the upper valley part is sub-arctic oceanic with an annual areal precipitation of ca 1500 mm. The lithology in Erdalen and Bødalen consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. Parts of the valleys were affected by the Little Ice Age glacier advance with the maximum glacier extent around 1750 BP. In this study five sites on moraine and colluvium materials were selected to examine the main soil properties of the most representative soils found in the region. The objective was to assess if soil profile characteristics and pattern of fallout radionuclides (FRN's) and environmental radionuclides (ERN's) are affected by different stages of ice retreat. Soil profiles were sampled at 5 cm depth interval increments until 20 cm depth. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. At P2 profile where ice retreated earlier (ca., 1767) depth profile activities of FR?s are more homogenous than in P1 that became ice-free since ca. 1930. The sampled soils on the colluviums outside the LIA glacier limit became ice free during the Preboral. The Regosols present better developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Lower activities of FR?s in soils on the moraines are related to the predominant sand material that has less capacity to fix the radionuclides. Lower 40K activities in Erdalen as compared to Bødalen are likely related to soil mineralogical composition. All profiles show disequilibrium in the uranium and thorium series. These results indicate differences in soil development that are consistent with the age of ice retreat. In addition, the pattern distribution of 137Cs and 210Pbexactivities differs in the soils related to the LIA glacier limits in the drainage basins.

Navas, Ana; Laute, Katja; Beylich, Achim A.; Gaspar, Leticia

2013-04-01

265

Larsen Ice Shelf Collapse (WMS)  

NSDL National Science Digital Library

The Larsen ice shelf at the northern end of the Antarctic Peninsula experienced a dramatic collapse between January 31 and March 7, 2002. First, melt ponds appeared on the ice shelf during these summer months (seen in blue on the shelf), then a minor collapse of about 800 square kilometers occurred. Finally, a 2600 square kilometer collapse took place, leaving thousands of sliver icebergs and berg fragments where the shelf formerly lay. Brownish streaks within the floating chunks mark areas where rocks and morainal debris are exposed from the former underside and interior of the shelf. These images were acquired by the MODIS instrument on the Terra satellite.

Snodgrass, Stuart; Mitchell, Horace; Haran, Terry

2005-03-04

266

Close-range photogrammetric reconstruction of moraine dam failures  

NASA Astrophysics Data System (ADS)

Glacial Lake Outburst Floods (GLOFs) from moraine-dammed lakes represent a high magnitude, low frequency catastrophic glacio-fluvial phenomena, with the potential to cause significant damage to property and infrastructure in high-mountain regions. Detailed accounts of GLOF dynamics, in particular the initiation and propagation of dam breaching are extremely rare, owing to their occurrence in often remote, inaccessible areas, as well as the impracticalities associated with attempting to directly instrument such high magnitude, turbulent flows. In addition to the dearth of detailed, first-hand observations of dam failures, reconstruction of breaches and failure mechanisms derived from morphological evidence is hampered by the lack of high-quality, high-resolution DTMs of remote alpine areas. Previous studies have therefore resorted to the use of coarse resolution data products (SRTM, ASTER GDEM) to quantify characteristics of failure events, e.g. pre-flood lake volume, dam height/width, which may give rise to considerable uncertainty in related numerical simulations and assessments of downstream flood hazards. In this paper we employ a novel low-cost, close-range photogrammetric technique, termed 'Structure-from-Motion' (SfM) to provide detailed in-situ reconstructions of dam and valley topography for two moraine dam complexes which have produced historical GLOFs in the Khumbu Himal, Nepal. Requiring little more than a consumer-grade digital camera and suitable ground control for implementation, the resolution of the final data products are comparable to that obtained using ground-based or airborne LiDAR. These data facilitate the extraction of precise estimates of dam (and breach) geometry, volumes of water and sediment removed during the outburst events, and the downstream channel topography. We conclude by directly comparing such key metrics derived from low-resolution topographic datasets, with those acquired in situ using the SfM technique, and discuss the implications for the reconstruction of flood dynamics.

Westoby, M. J.; Brasington, J.; Glasser, N. F.; Hambrey, M. J.; Reynolds, J. M.

2012-04-01

267

Post–Little Ice Age record of coarse and fine clastic sedimentation in an Alaskan proglacial lake  

Microsoft Academic Search

Many assessments of glacial sediment yield rely solely on mea- surements of fine-grained suspended sediment. We show that sus- pended sediment contributes ,20% of the total clastic sediment discharge into Iceberg Lake, an Alaskan proglacial lake. Drainage of this lake in 1999 exposed outcrops of varved lacustrine sediment that record suspended sediment deposition. Since a Little Ice Age highstand two

Michael G. Loso; Robert S. Anderson; Suzanne P. Anderson

2004-01-01

268

Evidence from northwest European bogs shows ‘Little Ice Age’ climatic changes driven by variations in solar activity  

Microsoft Academic Search

Fluctuations in Holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity. Analyses of both 10Be and 14C nuclides con” rm that production-rate changes during the Holocene were largely modulated by solar activity. Analyses of peat samples from two intact European ombrotrophic bogs show that climatic deteriorations during the ‘Little Ice Age’ are associated with

Dmitri Mauquoy; Bas van Geel; Maarten Blaauw; Johannes van der Plicht

2002-01-01

269

Glacial recession in the Tropical Andes from the Little Ice Age: the case of Ampato Volcanic Complex (Southern Peru  

Microsoft Academic Search

Data published over the last decade reveal substantial glacial recession in the tropical Andes since the Little Ice Age (LIA), (Ramirez, et al., 2001; Rabatel, et al., 2005; Rabatel, et al., 2008; Vuille, et al., 2008; Hastenrath, 2009; Jomelli, et al., 2009), and a growing rate of recession since the 1980's caused by global warming (Ramirez, et al., 2001; Vuille,

J. Alcalá; D. Palacios; J. J. Zamorano

2010-01-01

270

Horns of the woolly rhinoceros Coelodonta antiquitatis (Blumenbach, 1799) in the Ice Age Museum collection (Moscow, Russia)  

Microsoft Academic Search

The Ice Age Museum (Moscow, Russia) houses the most representative collection of woolly rhinoceros horns in the world. It consists in about 30 complete and fragmentary specimens from the Late Pleistocene deposits of Northern Yakutia and Chukotka. This collection includes five complete sets of nasal and frontal horns of the same individual (two sets with their own proper skull); series

Fedor K. Shidlovskiy; Irina V. Kirillova; John Wood

271

The geomorphic impact of catastrophic glacier ice loss in mountain regions  

Microsoft Academic Search

Perhaps the most dramatic manifestation of global warming is catastrophic glacier ice loss in mountain regions. The geomorphic impact of this process was first outlined by Evans and Clague in 1994 and includes mountain slope instability, glacier avalanching, the formation and failure of moraine dammed lakes, and the formation and failure of ice dammed lakes. The present paper is an

S. G. Evans

2006-01-01

272

Changing Low-Latitude Paleoenvironments During the Onset of the Late Paleozoic Ice Age.  

NASA Astrophysics Data System (ADS)

The Carboniferous is one of the critical stepwise transitions in the evolution of the Earth System when rapid changes in climate and atmospheric composition (rise in oxygen/carbon dioxide) coincided with key events in biological evolution (the proliferation of land plants) and increased rates of tectonic plate reorganisation. The paleoequatorial Carboniferous sedimentary successions of Britain and Ireland were deposited in a shallow epicontinental seaway and record high magnitude and high frequency eustatic changes as ice sheets waxed and waned on Gondwana during the onset of the Late Paleozoic ice age. In the Asbian and Brigantian (ca.334-326 Ma) widespread shallow and marginal marine conditions are recorded by mixed carbonate and siliciclastic deposition and carbonate successions on platforms and shelves. In the mid-Brigantian, a marine transgression reduced deposition on the carbonate platforms and connected previously separate sub-basins in central Scotland. Data used to interpret global climate for this time slice are contradictory. A warmer global climate is suggested by the widespread extent of a Gondwanan macrofloral realm that requires frost-free conditions whereas isotope data suggest a cold Asbian followed by a warm, ice-free Brigantian. In the Pendleian to Yeadonian (ca.326-317 Ma), increasingly light oxygen isotope data indicate a return to cold conditions. Well- constrained periods of Gondwanan glacial sedimentation (e.g. in SE Australia), of 1 and 3 Myr duration, coincide with major paleoevironmental changes across Britain and Ireland, including the end of significant carbonate production and the earliest examples of large-scale river paleovalleys (with 20-80 m of erosional relief). Depositional environments (fluvial, deltaic) and basin bathymetry (distinct shelf edges) provided optimal conditions for the effects of sea-level change to be recorded in sedimentary successions of this time slice. These late Mississippian and early Pennsylvanian siliciclastic and carbonate successions generally reflect shifts in global climate, including glacial periods, but temporal changes in paleoenvironments and local climate overprint the record. These data provide useful constraints for modelling climate change in deep time.

Davies, S.

2007-12-01

273

End of the Little Ice Age in the Alps forced by industrial black carbon.  

PubMed

Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Alpine temperature and precipitation records suggest that glaciers should instead have continued to grow until circa 1910. Radiative forcing by increasing deposition of industrial black carbon to snow may represent the driver of the abrupt glacier retreats in the Alps that began in the mid-19th century. Ice cores indicate that black carbon concentrations increased abruptly in the mid-19th century and largely continued to increase into the 20th century, consistent with known increases in black carbon emissions from the industrialization of Western Europe. Inferred annual surface radiative forcings increased stepwise to 13-17 W?m(-2) between 1850 and 1880, and to 9-22 W?m(-2) in the early 1900s, with snowmelt season (April/May/June) forcings reaching greater than 35 W?m(-2) by the early 1900s. These snowmelt season radiative forcings would have resulted in additional annual snow melting of as much as 0.9 m water equivalent across the melt season. Simulations of glacier mass balances with radiative forcing-equivalent changes in atmospheric temperatures result in conservative estimates of accumulating negative mass balances of magnitude -15 m water equivalent by 1900 and -30 m water equivalent by 1930, magnitudes and timing consistent with the observed retreat. These results suggest a possible physical explanation for the abrupt retreat of glaciers in the Alps in the mid-19th century that is consistent with existing temperature and precipitation records and reconstructions. PMID:24003138

Painter, Thomas H; Flanner, Mark G; Kaser, Georg; Marzeion, Ben; Vancuren, Richard A; Abdalati, Waleed

2013-09-03

274

End of the Little Ice Age in the Alps forced by industrial black carbon  

PubMed Central

Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Alpine temperature and precipitation records suggest that glaciers should instead have continued to grow until circa 1910. Radiative forcing by increasing deposition of industrial black carbon to snow may represent the driver of the abrupt glacier retreats in the Alps that began in the mid-19th century. Ice cores indicate that black carbon concentrations increased abruptly in the mid-19th century and largely continued to increase into the 20th century, consistent with known increases in black carbon emissions from the industrialization of Western Europe. Inferred annual surface radiative forcings increased stepwise to 13–17 W?m?2 between 1850 and 1880, and to 9–22 W?m?2 in the early 1900s, with snowmelt season (April/May/June) forcings reaching greater than 35 W?m?2 by the early 1900s. These snowmelt season radiative forcings would have resulted in additional annual snow melting of as much as 0.9 m water equivalent across the melt season. Simulations of glacier mass balances with radiative forcing-equivalent changes in atmospheric temperatures result in conservative estimates of accumulating negative mass balances of magnitude ?15 m water equivalent by 1900 and ?30 m water equivalent by 1930, magnitudes and timing consistent with the observed retreat. These results suggest a possible physical explanation for the abrupt retreat of glaciers in the Alps in the mid-19th century that is consistent with existing temperature and precipitation records and reconstructions.

Painter, Thomas H.; Flanner, Mark G.; Kaser, Georg; Marzeion, Ben; VanCuren, Richard A.; Abdalati, Waleed

2013-01-01

275

Ion microprobe U-Pb dating of phosphates in lunar basaltic breccia, Elephant Moraine 87521  

NASA Astrophysics Data System (ADS)

We report ion microprobe U-Pb dating of phosphates in lunar meteorite ``Elephant Moraine 87521 (EET87521),'' which is a fragmental breccia consisting of Very-Low Ti (VLT) basaltic clasts and a small component of highland-derived materials. The observed Pb-Pb age of phosphates in EET87521 is 3503 +/- 140 Ma, which is distinct from the results from previous chronological studies on VLT mare basalt of 3.2-3.3 Ga for LUNA-24. This suggests that the VLT basalt volcanism appears to have been prolonged on the Moon. Moreover, the age is apparently different from those of other VLT meteorites (3.8 Ga for QUE94281 and 4.0 & 4.4 Ga for Yamato793274), which are proposed to have been launched by a single impact event based on the similarity of launching ages, mineralogical and geochemical signatures. This evidence questions the validities of bulk age analyses for the Yamato & QUE meteorites in the literature and/or the hypothesis of a single-crater origin.

Terada, Kentaro; Saiki, Tomoyo; Oka, Yoshimi; Hayasaka, Yasutaka; Sano, Yuji

2005-10-01

276

Little Ice Age to modern climate transition of Meso-American climate derived from speleothems  

NASA Astrophysics Data System (ADS)

We present a high-resolution (annual) reconstruction of hydrological variability from a speleothem located in a cave under the Guatemala/Belize (G/B) border. Our age model is highly constrained by annual layering in the speleothem and nine U/Th MC ICPMS dates. Our ?18O record from 1640 to 2005 A.D. shows two large, abrupt decreases in inferred precipitation rates that appear to coincide with historical, large volcanic eruptions, superimposed on a general drying trend. The first abrupt increase in aridity occurred synchronously with the Tambora eruption in 1815, followed by another sharp decrease in Meso-American precipitation coincident with the eruption of Krakatau in 1883. Both drying events extend for thirty to forty years after the initial eruption, in good agreement with the 19th century drying and the "volcanic dust veil index" from Lamb (1970). Preliminary analysis indicates that the Meso-Americas may be highly sensitive to volcanic forcing because they receive considerable climate input from both Atlantic (primary) and Pacific (secondary) influences. Past volcanic aerosol model loading patterns from the Mt. Pinatubo eruption produced global and in particular, North Atlatic cooling. This could have moved the Atlantic ITCZ southwards and caused drying in Meso-America. Wavelet analysis of the speleothem data also shows ENSO scale variability. Our results highlight the need for better understanding of the consequences of volcanic eruptions and their patterns of climate variability, in particular during the transition from the Little Ice Age to the modern industrial era.

Winter, A.; Miller, T.; Kushnir, Y.; Black, D. E.; Estrella, J.; Burnett, A.; Haug, G. H.; Breitenbach, S.; Beaufort, L.; Edwards, R.

2011-12-01

277

The northern Uummannaq Ice Stream System, West Greenland: ice dynamics and and controls upon deglaciation  

NASA Astrophysics Data System (ADS)

At the Last Glacial Maximum (LGM), the Uummannaq Ice Stream System comprised a series coalescent outlet glaciers which extended along the trough to the shelf edge, draining a large proportion of the West Greenland Ice Sheet. Geomorphological mapping, terrestrial cosmogenic nuclide (TCN) exposure dating, and radiocarbon dating constrain warm-based ice stream activity in the north of the system to 1400 m a.s.l. during the LGM. Intervening plateaux areas (~ 2000 m a.s.l.) either remained ice free, or were covered by cold-based icefields, preventing diffluent or confluent flow throughout the inner to outer fjord region. Beyond the fjords, a topographic sill north of Ubekendt Ejland prevented the majority of westward ice flow, forcing it south through Igdlorssuit Sund, and into the Uummannaq Trough. Here it coalesced with ice from the south, forming the trunk zone of the UISS. Deglaciation of the UISS began at 14.9 cal. ka BP, rapidly retreating through the overdeepened Uummannaq Trough. Once beyond Ubekendt Ejland, the northern UISS retreated northwards, separating from the south. Retreat continued, and ice reached the present fjord confines in northern Uummannaq by 11.6 kyr. Both geomorphological (termino-lateral moraines) and geochronological (14C and TCN) data provide evidence for an ice marginal stabilisation at within Karrat-Rink Fjord, at Karrat Island, from 11.6-6.9 kyr. The Karrat moraines appear similar in both fjord position and form to 'Fjord Stade' moraines identified throughout West Greenland. Though chronologies constraining moraine formation are overlapping (Fjord Stade moraines - 9.3-8.2 kyr, Karrat moraines - 11.6-6.9 kyr), these moraines have not been correlated. This ice margin stabilisation was able to persist during the Holocene Thermal Maximum (~7.2 - 5 kyr). It overrode climatic and oceanic forcings, remaining on Karrat Island throughout peaks of air temperature and relative sea-level, and during the influx of the warm West Greenland Current into the Uummannaq region. Based upon analysis of fjord bathymetry and width, this ice marginal stabilisation has been shown to have been caused by increases in topographic constriction at Karrat Island. The location of the marginal stillstand is coincident with a dramatic narrowing of fjord width and bed shallowing. These increases in local lateral resistance reduces the ice flux necessary to maintain a stable grounding line, leading to ice margin stabilisation. This acted to negate the effects of the Holocene Thermal Maximum. Following this stabilisation, retreat within Rink-Karrat Fjord continued, driven by calving into the overdeepened Rink Fjord. Rink Isbræ reached its present ice margin or beyond after 5 kyr, during the Neoglacial. In contrast, the southern UISS reached its present margin at 8.7 kyr and Jakobshavn Isbræ reached its margin by 7 kyr. This work therefore provides compelling evidence for topographically forced asynchronous, non-linear ice stream retreat between outlet glaciers in West Greenland. In addition, it has major implications for our understanding and reconstruction of mid-Holocene ice sheet extent, and ice sheet dynamics during the Holocene Thermal Maximum to Neoglacial switch.

Lane, Timothy; Roberts, David; Rea, Brice; Cofaigh, Colm Ó.; Vieli, Andreas

2013-04-01

278

Little Ice Age and Medieval Warm Periods in Eastern China as Read from the Speleothem Records  

NASA Astrophysics Data System (ADS)

The long-term climatic pace has often been interrupted by short-term abrupt changes. The Little Ice Age and Medieval Warm Period represent the two most important such changes over the last two millennia. Largely due to a dearth of high-resolution climatic records, our knowledge on the spatial extent, duration, and moisture characteristics of these two events is incomplete, and this has hampered our understanding of the driving force causing them as well as the recent global warming trend. Here we present high-resolution climatic records reflected by the ? 18O and ? 13C in three stalagmites from limestone caves in China: S312 from Shihua Cave (about 50 km southwest of Beijing), SF from Buddha Cave (about 80 km south of Xian), and F4 from Fengyu Cave (about 100 km south of Guilin). The chronologies of the stalagmites were determined by lamination counting and by the 210Pb and 230Th (TIMS) methods. S312 (3,600 years old) and F4 (600 years old) have mean growth rates of 0.035 and 0.24 mm/yr, respectively; whereas SF (10,000 years old) has a growth rate of 0.087 mm/yr for the top 1.6 cm and a rate of 0.0163 mm/yr below. We measured ? 18O and ? 13C at a resolution of 1-10 years for the last 1,000 years or so in all three stalagmites. These measurements were extended to the past 4,000 years at lower resolutions in S312 and SF. A total of 1052 pairs of ? 18O and ? 13C data thus obtained forms the basis for our reconstruction of the temperature (using ? 18O as proxy) and moisture (using ? 13C as proxy) variability in eastern China over the last four millennia. From the measured cave-water ? 18O and cave temperature at each location, we calculated the ? 18O values for calcites precipitated under isotopic equilibrium and found them to be similar to the observed ? 18O values in modern stalagmite layers. Measured ? 18O values in S312 and SF average -8.8\\permil and -9.1\\permil, respectively, reflecting a similar mean temperature of about14°C. The average ? 18O value of F4 is 2.2\\permil heavier than those of S312 and SF, indicating an annual mean temperature in Fengyu Cave that is about 5°C warmer than those of the two northern caves. Although the three caves are more than 1000 km apart, their long-term ? 18O records show patterns that are remarkably similar. The records show that in eastern China, the Medieval Warm Period started around 1000 AD and lasted until 1500 AD. A brief cooling during this warm interval occurred around 1150 AD. The Little Ice Age in China started at around 1500 AD and ended in the mid-1800s. Since then, all three locations show a warming trend that has been observed elsewhere in the world. The records of S312 and SF show that for the past 4,000 years, the two locations has had similar temperature variations with five distinct warming trends, but a different moisture variability which is probably more sensitive to local atmospheric circulation changes than temperature. In general, it was relatively dry during the Medieval Warm Period and wet during the Little Ice Age in eastern China. Of the five warming trends, the most recent one is the strongest.

Li, H.; Ku, T.

2002-12-01

279

Ages of rampart craters in equatorial regions on Mars: Implications for the past and present distribution of ground ice  

NASA Astrophysics Data System (ADS)

We are testing the idea of Squyres et al. (1992) that rampart craters on Mars may have formed over a significant time period and therefore the onset diameter (minimum diameter of a rampart crater) only reflects the ground ice depth at a given time. We measured crater size frequencies on the layered ejecta of rampart craters in three equatorial regions to derive absolute model ages and to constrain the regional volatile history. Nearly all rampart craters in the Xanthe Terra region are ˜3.8 Gyr old. This corresponds to the Noachian fluvial activity that region. Rampart crater formation declines in the Hesperian, whereas onset diameters (minimum diameter) increase. No new rampart craters formed after the end of the Hesperian (˜3 Gyr). This indicates a lowering of the ground ice table with time in the Xanthe Terra region. Most rampart craters in the Valles Marineris region are around 3.6 Gyr old. Only one large, probably Amazonian-aged (˜2.5 Gyr), rampart crater exists. These ages indicate a volatile-rich period in the Early Hesperian and a lowering of the ground ice table with time in the Valles Marineris study region. Rampart craters in southern Chryse Planitia, which are partly eroded by fluvial activity, show ages around 3.9 Gyr. Rampart craters superposed on channels have ages between ˜1.5 and ˜0.6 Gyr. The onset diameter (3 km at ˜1.5 Gyr) in this region may indicate a relatively shallow ground ice table. Loss of volatiles due to diffusion and sublimation might have lowered the ground ice table even in the southern Chryse Planitia region afterwards. In general, our study implies a formation of the smallest rampart craters within and/or shortly after periods of fluvial activity and a subsequent lowering of the ground ice table indicated by increasing onset diameter to the present. These results question the method to derive present equatorial ground ice depths from the onset diameter of rampart craters without information about their formation time.

Reiss, D.; van Gasselt, S.; Hauber, E.; Michael, G.; Jaumann, R.; Neukum, G.

2006-10-01

280

Palaeoclimatic interpretation of moraines: Identifying limitations and future tasks (the case study Southern Alps/New Zealand)  

NASA Astrophysics Data System (ADS)

During the past 20 years, the widespread deployment of terrestrial cosmogenic nuclide dating (TCND) alongside other substantial geochronological advances in laboratory precision and model calibration have seen an impressive increase in both number and claimed resolution of well-dated geomorphological reconstructions of mountain glacier fluctuations. Correlations at local, regional and hemispheric scales have frequently been performed on basis of those studies that partly include sophisticated probability analyses for reducing the statistical uncertainty of moraine ages, and analyses of glacier sensitivity to temperature and precipitation forcing. Although these recent advances especially with dating modern dating techniques are acknowledged, some basic conceptual issues still remain. It seems that in certain cases "technical" progress and improved modelling skills have encouraged us to over-reach our interpretive limits and overstate our optimism regarding "reliability" of glacier chronologies and their correlation. Critical evaluation of the interpretative limitations of chronological studies is not always recognised to the necessary extent. Interdisciplinary approaches - indispensable for the complex subject covering Geochronology, Glaciology, Glacial Geomorphology and Palaeoclimatology - are still not necessarily the norm. Based on a brief theoretical outline of the requirements for "reliable" palaeoclimatic interpretation of moraines (cf. Winkler & Matthews 2010, Kirkbride & Winkler 2012), one of the high-potential key sites for the investigation of Holocene glacier variation, the Southern Alps of New Zealand, are taken as case study to highlight a few of the practical limitations and outline future tasks that need improvement. Those tasks are - among others - identified as: (1) minimise the "geomorphological" uncertainty with the numerical dating of moraines, (2) identify possible non-glacial influence on the formation of moraines and address the potential misleading effect of large-scale mass movements on their subsequent palaeoclimatic interpretation, (3) improve the control on spatial coherence of existing data, and finally (4) include glaciological considerations and critical evaluation of the proposed resolution with any attempts of intra-hemispheric and global correlation. References: Kirkbride, M.P. & Winkler, S. (2012): Correlation of Late Quaternary glacier chronologies: impact of climate variability, glacier response, and chronological resolution. Quaternary Science Reviews 46, 1 - 29. Winkler, S. & Matthews, J.A. (2010): Holocene glacier chronologies: Are 'high-resolution' global and inter-hemispheric comparisons possible? The Holocene 20, 1137 - 1147.

Winkler, Stefan; Kirkbride, Martin

2013-04-01

281

Radiocarbon Isochrones of the Retreat of the Laurentide Ice Sheet.  

National Technical Information Service (NTIS)

A Map of northern North America is presented which shows isochrones of the outer limit of the Laurentide ice sheet from about 13,000 years ago until the present. The data points are radiocarbon dates of moraines, basal peat, and lacustrine deposits which ...

R. A. Bryson W. M. Wendland

1967-01-01

282

Climatic warming, glacier recession and runoff from Alpine basins after the Little Ice Age maximum  

Microsoft Academic Search

Records of discharge of rivers draining Alpine basins with between 0 and ?? 70% ice cover, in the upper Aare and Rhone catchments, Switzerland, for the period 1894-2006 have been examined together with climatic data for 1866-2006, with a view to assessing the effects on runoff from glacierized basins of climatic warming coupled with glacier recession following the Little Ice

David N. Collins

2008-01-01

283

Chronology of glacial and periglacial deposits in front of the 1850 moraine of the Goldberg-Glacier, Sonnblick area (Salzburg/Austria)  

NASA Astrophysics Data System (ADS)

Since the Sonnblick-Observatory (3705 m) was founded in 1887, the nearby situated Goldberg Glacier (also termed Goldbergkees) was subject to numerous glaciological investigations. During the Würm glaciation the Goldberg Glacier covered the Rauris Valley and flew to the north. A giant landslide occurred in the upper Rauris Valley partly overlying moraines at an altitude of 1700 m. Based on morphostratigraphic relationships relative age sequences were established in the 1960ies. The 1850 moraine of the Goldberg Glacier was mapped at an altitude of 2200 m, and scarce remnants of older and younger moraines are preserved. Applying several new methods we want to date moraine stages in front of the 1850 moraine. Based on a detailed geological and geomorphological mapping using LIDAR topography we selected boulders on glacial stadials and on landslides for dating their surface exposure using the cosmogenic nuclide Be-10. The lithology of boulders on stadials is mostly gneiss whereas boulders of landslides are mostly biotite schist, garnet-mica schist and quartzite. We also applied the Schmidt-Hammer method as a proxy for estimating the degree of weathering of exposed boulders in order to establish a relative chronology of their deposition. In addition C-14 dating of peat deposits bordering the landslide will be used for establishing a robust time frame of glacier retreat and events of mass movements. The field work revealed temporal relationships of cross-cutting landscape elements due to the fact that the dominant glacial stadial overlies the giant landslide of the upper Rauris Valley, and the supposed Egesen stadial moraine itself is topped by a younger landslide of smaller dimension. Our goal is to decipher the chronologic evolution of the Goldberg Glacier as well as the landscape development of the Rauris Valley from the Alpine Lateglacial to the Holocene. Especially the effects of the cold spells of the Younger Dryas (12.7-11.6 ka BP) and of the "8,2 ka event" in this inner-Alpine mountain range, both linked to circulation changes in the North Atlantic, are of the essence for Quaternary stratigraphy and paleo-climatological reconstructions.

Bichler, M.; Reindl, M.; Häusler, H.; Reitner, J. M.

2012-04-01

284

Global warming and ice ages: I. prospects for physics based modulation of global change  

SciTech Connect

It has been suggested that large-scale climate changes, mostly due to atmospheric injection of greenhouse gases connected with fossil-fired energy production, should be forestalled by internationally-agreed reductions in, e.g., electricity generation. The potential economic impacts of such limitations are obviously large: greater than or equal to $10{sup 11}/year. We propose that for far smaller - less than 1% - the mean thermal effects of greenhouse gases may be obviated in any of several distinct ways, some of them novel. These suggestions are all based on scatterers that prevent a small fraction of solar radiation from reaching all or part of the Earth. We propose research directed to quite near-term realization of one or more of these inexpensive approaches to cancel the effects of the greenhouse gas injection. While the magnitude of the climatic impact of greenhouse gases is currently uncertain, the prospect of severe failure of the climate, for instance at the onset of the next Ice Age, is undeniable. The proposals in this paper may lead to quite practical methods to reduce or eliminate all climate failures.

Teller, E.; Wood, L.; Hyde, R.

1996-08-15

285

Millennial-scale variations of sea-ice expansion in the southwestern part of the Okhotsk Sea during the past 120 kyr: Age model and ice-rafted debris in IMAGES Core MD01-2412  

NASA Astrophysics Data System (ADS)

A 58-m-long sediment core IMAGES MD01-2412 was recovered in the southwestern part of the Okhotsk Sea for high resolution paleocenography. An age model of the core was obtained by accelerator mass spectrometry (AMS) 14C dating of planktonic foraminifer shells, oxygen isotope stratigraphy of benthic foraminifer calcite, and tephrochronology, resulting in a core-bottom age of 115 kyr. Sea-ice expansion in the Okhotsk Sea was reconstructed by ice-rafted debris (IRD) based on measurement of dropstone, coarse fraction, sand fractions of terrigenous particles, and the magnetic properties. The SW Okhotsk Sea has not had perennial but seasonal sea-ice conditions during the 115 kyr. Seasonal sea ice fluctuated with large amplitudes on millennial scale during the glacials (Marine isotope stage: MIS 2, 3, and 4) and varied relatively little during the Holocene (MIS 1) and the last interglacial (MIS 5). Enhanced polar atmospheric circulation during the glacial resulted in strong wind fields over the Okhotsk Sea and accelerated the large sea-ice expansion during the glacials (MIS 2, 3, and 4). During the interglacials (MIS 1 and 5), sea ice also expanded by small amplitudes. During these periods, decrease of the Amur River discharge would be one of the possible factors for sea-ice expansion. The two main factors of polar atmospheric circulation and Amur River discharge would be responsible for sea-ice expansion during 120 kyr.

Sakamoto, Tatsuhiko; Ikehara, Minoru; Uchida, Masao; Aoki, Kaori; Shibata, Yasuyuki; Kanamatsu, Toshiya; Harada, Naomi; Iijima, Koichi; Katsuki, Kota; Asahi, Hiroshi; Takahashi, Kozo; Sakai, Hideo; Kawahata, Hodaka

2006-08-01

286

The Medieval Warm Period, the Little Ice Age and simulated climatic variability  

NASA Astrophysics Data System (ADS)

The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for ‘present’ climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Since no external forcing was permitted during the model run all such fluctuations are attributed to naturally occurring climatic variability associated with the nonlinear processes inherent in the climatic system. Comparison of simulated climatic time series for different geographical locations highlighted the lack of synchronicity between these series. The model was found to be able to simulate climatic extremes for selected observations for century timescales, as well as identifying the associated spatial characteristics. Other examples of time series simulated by the model for the USA and eastern Russia had similar characteristics to those attributed to the MWP and the LIA, but smaller amplitudes, and clearly defined spatial patterns. A search for the frequency of occurrence of specified surface temperature anomalies, defined via duration and mean value, revealed that these were primarily confined to polar regions and northern latitudes of Europe, Asia and North America. Over the majority of the oceans and southern hemisphere such climatic fluctuations could not be sustained, for reasons explained in the paper. Similarly, sustained sea ice anomalies were mainly confined to the northern hemisphere. An examination of mechanisms associated with the sustained climatic fluctuations failed to identify a role for the North Atlantic Oscillation, the El Niño-Southern Oscillation or the Pacific Decadal Oscillation. It was therefore concluded that these fluctuations were generated by stochastic processes intrinsic to the nonlinear climatic system. While a number of characteristics of the MWP and the LIA could have been partially caused by natural processes within the climatic system, the inability of the model to reproduce the observed hemispheric mean temperature anomalies associated with these events indicates that external forcing must have been involved. Essentially the unforced climatic system is unable to sustain the generation of long-term climatic anomalies.

Hunt, B. G.

2006-12-01

287

A model study of the Little Ice Age and beyond: changes in ocean heat content, hydrography and circulation since 1500  

Microsoft Academic Search

The Earth System Climate Model from the University of Victoria is used to investigate changes in ocean properties such as\\u000a heat content, temperature, salinity, density and circulation during 1500 to 2000, the time period which includes the Little\\u000a Ice Age (LIA) (1500–1850) and the industrial era (1850–2000). We force the model with two different wind-stress fields which\\u000a take into account

Jan Sedlácek; Lawrence A. Mysak

2009-01-01

288

Social vulnerability to climate in the ``Little Ice Age?: an example from Central Europe in the early 1770s  

Microsoft Academic Search

The paper is oriented on social vulnerability to climate in Switzerland and in the Czech Lands during the early 1770s. Documentary sources of climate related to man-made archives are discussed. Methods of temperature and precipitation reconstruction based on this evidence as well as climate impact analyses are presented. Modelling of Little Ice Age-type Impacts (LIATIMP) is applied to highlight climate

C. Pfister; R. Brázdil

2006-01-01

289

The spatial-temporal pattern of the Medieval Climate Anomaly and the Little Ice Age in the Northern Hemisphere  

Microsoft Academic Search

Knowledge of how climate has changed in the past is essential for understanding present climate changes and for separating anthropogenic influence from natural variability. The amplitude and geographical coherency of the late-Holocene pre-industrial temperature variability have been much discussed and the occurrence of a distinct Medieval Climate Anomaly (c. AD 800-1300) and a Little Ice Age (c. AD 1300-1900) on

Fredrik Charpentier Ljungqvist; Paul J. Krusic; Anders Moberg; Hâkan Grudd; Hanna S. Sundqvist

2010-01-01

290

Glacier change in Garibaldi Provincial Park, southern Coast Mountains, British Columbia, since the Little Ice Age  

Microsoft Academic Search

Fluctuations of glaciers during the 20th century in Garibaldi Provincial Park, in the southern Coast Mountains of British Columbia, were reconstructed from historical documents, aerial photographs, and fieldwork. Over 505 km2, or 26%, of the park, was covered by glacier ice at the beginning of the 18th century. Ice cover decreased to 297 km2 by 1987–1988 and to 245 km2 (49% of the

Johannes Koch; Brian Menounos; John J. Clague

2009-01-01

291

The Little Ice Age: evidence from a sediment record in Gullmar Fjord, Swedish west coast  

NASA Astrophysics Data System (ADS)

We discuss the climatic and environmental changes during the last millennium in NE Europe based on a ca. 8-m long high-resolved and well-dated marine sediment record from the deepest basin of Gullmar Fjord (SW Sweden). According to the 210Pb- and 14C-datings, the record includes the period of the late Holocene characterised by anomalously cold summers and well-known as the Little Ice Age (LIA). Using benthic foraminiferal stratigraphy, lithology, bulk sediment geochemistry and stable carbon isotopes we reconstruct various phases of the cold period, identify its timing in the study area and discuss the land-sea interactions occurring during that time. The onset of the LIA is indicated by an increase in cold-water foraminiferal species Adercotryma glomerata at ~ 1350 AD The first phase of the LIA was characterised by a stormy climate and higher productivity, which is indicated by a foraminiferal unit of Nonionella iridea and Cassidulina laevigata. Maximum abundances of N. iridea probably mirror a short and abrupt warming event at ~ 1600 AD. It is likely that due to land use changes in the second part of the LIA there was an increased input of terrestrial organic matter to the fjord, which is indicated by lighter ?13C values and an increase of detritivorous and omnivorous species such as Textularia earlandi and Eggerelloides scaber. The climate deterioration during the climax of the LIA (1675-1704 AD), as suggested by the increase of agglutinated species, presence of Hyalinea balthica, and a decline of N. iridea may have driven the decline in primary productivity during this time period.

Polovodova Asteman, I.; Nordberg, K.; Filipsson, H. L.

2013-03-01

292

The Medieval Climate Anomaly and the Little Ice Age in the Eastern Ecuadorian Andes  

NASA Astrophysics Data System (ADS)

To better characterize the climate variability of the last millennium in the high Andes, we analysed the pollen content of a 1100-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the Eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined to distinguish the atmospheric moisture from the soil moisture content of the páramo. Results showed that between 900 AD and 1230 AD, the Medieval Climate Anomaly interval was warm and moist with high T/P index linked to a high ENSO variability and a weak South American Summer Monsoon (SASM) activity. Between 1230 and 1650 AD, a dry climate prevailed characterized by an abrupt decrease in the T/P index related to lower ENSO variability with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed, first a wet phase between 1650 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic SSTs favored the return of a wet páramo, and a cold and dry phase between 1750 and 1810 AD associated with low ENSO variability and weak SASM activity resulting in drying of the páramo. The Current Warm Period marks the beginning of a climate characterized by high convective activity, the highest in the last millennium, and weaker SASM activity modifying the water stock of the páramo. Our results show that the páramo is progressively loosing its capacity for water storage and that the variability of both tropical Pacific and Atlantic SSTs matters for Andean climate patterns although many teleconnection mechanisms are still poorly understood.

Ledru, M.-P.; Jomelli, V.; Samaniego, P.; Vuille, M.; Hidalgo, S.; Herrera, M.; Ceron, C.

2012-09-01

293

Evidence for early Pleistocene Glaciation(s) in tropical Africa: Stratigraphy, Paleomagnetism, Paleosols and Paleoclimate of the Gorges Moraine System, Mount Kenya  

NASA Astrophysics Data System (ADS)

Moraines marking an Early Pleistocene glaciation on Mt. Kenya are known from several valleys marking the lowermost extent of the Early Pleistocene Gorges Glaciation (2850 m a.s.l.). The lowermost paleosols at these sites formed either in till predating the Gorges Glaciation or in weathered phonolitic bedrock and related lavas, similar to the lithology forming the base of the Mt. Kenya volcanic series of Miocene/Pliocene age. Paleomagnetism and weathering characteristics have been used to refine the age of sediments assigned to the Gorges Glaciation. These deposits are normally magnetized but carry a persistent reversed overprint, suggesting that they were deposited during one of the normal subchrons within the Matuyama Reversed Chron. They are underlain either by a reversely magnetized weathered till (GOR 68), or weathered bedrock (GOR 64 and GOR 69), the latter exhibiting normal magnetization (Gauss?) with reversed overprint (Matuyama?). The sediments are overlain at all three sites by normally magnetized loesses and paleosols of presumable Brunhes age. The normal magnetization and reversed overprint recorded in sediments of the Gorges Glaciation most likely span a considerable portion of the Olduvai subchron (1.78-1.950 Ma.), which persisted for sufficient time to accommodate an extensive montane glaciation and prolonged period of weathering and soil formation. While the somewhat younger Jaramillo subchron cannot be ruled out, the extensive sediment and weathering record is more easily accommodated within the longer-lived Olduvai subchron. The characteristics of the lowermost buried paleosols and weathered bedrock substrate indicate wetter conditions prior to the onset of Pleistocene glaciation, a period that initially may have fostered a higher elevation forest cover of substantial spatial extent. These wetter conditions, punctuated with dry events, depict a progressive transition to alpine grassland at the start of the Quaternary. In light of new paleomagnetic and paleosol evidence, at least two tropical glaciations during the Matuyama Reversed Chron are documented from Mt. Kenya, suggesting this volcanic edifice had attained sufficient relief to form an ice mass and outlet glaciers, despite its equatorial latitude.

Mahaney, W. C.; Barendregt, R. W.; Hamilton, T.; Hancock, R.

2011-12-01

294

Cratering Evidence For The Age And Thickness Of An Extensive Ice-Rich Mantle In Western Utopia Planitia, Mars  

NASA Astrophysics Data System (ADS)

Polygonal features with characteristic dimensions of 100 +/- 30 m, bounded by cracks, are commonly observed on the martian northern plains. These features have previously been attributed to thermal cracking, in direct analogy to ice-wedge polygons in terrestrial polar regions. Polygons were mapped in the northern mid latitudes (30 to 65 N) using all Mars Orbiter Camera (MOC) narrow-angle images (5 m per pixel) from September 1997 through September 2003. Three fourths of MOC images showing polygons are centered in western Utopia Planitia (40 to 50 N; 258 to 288 W). This region, notable for its dense concentration of polygonal terrain, is otherwise non-unique in its mapped geology, topography, gravity, or albedo. Previous authors have suggested that this concentration of polygons indicates the presence of a generally continuous ice-rich mantle. Ice stability models, neutron spectroscopy data, and the common occurrence of thermokarst indicate that the ice is concentrated below 1 m depth and is currently subliming. The MOC images show 687 craters, with diameters between 100 m and 4 km, on polygonal terrain. The size-frequency distribution of these craters larger than 1 km is concordant with the Barlow distribution for craters larger than 8 km in western Utopia, indicating preservation of a late Hesperian crater population. Approximately 20 of the 687 craters on polygonal terrain postdate the adjacent polygonal cracks, indicating Amazonian-age deposition or activation of the ice-rich layer. The size-frequency distribution of craters on polygonal terrain shows a marked deficiency of craters smaller than 1 km, suggestive of mantling. Some such craters with diameters between 460 m and 1.1 km are buried to their rims by polygonal terrain; below this range all rims are buried, and above all rims are exposed. Based on the MOLA-derived relationship between rim height and crater diameter, this range indicates that the ice-rich layer is locally 30 to 40 m thick. These findings are in accord with recent models of obliquity-driven deposition and sublimation of ice-rich mantles in the northern mid latitudes of Mars.

Allen, C. C.; Bell, M. S.; Kanner, L. C.; McBride, S. A.

2004-12-01

295

Terrestrial Kr-81-Kr ages of Antarctic meteorites  

NASA Astrophysics Data System (ADS)

The production rate of Ar-38 in meteorites P(38), has been determined, as a function of the sample's chemical composition, from Kr-81-Kr exposure ages of four eucrite falls. The cosmogenic Kr-78/Kr-83 ratio is used to estimate the shielding dependence of P(38). From the 'true' Ar-38 exposure ages and the apparent Kr-81-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 300,000 ages (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017, and A81009) have within the limits of error the same exposure age (15.2 x 10 to the 6th ages) and the same terrestrial age (110,000 ages). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case is the Elephant Moraine polymict eucrites A79005, A79006, and 82600 with an exposure age of 26 x 10 to the 6th ages and a terrestrial age of 180,000 ages. EETA 79004 may be different from this group because its exposure age and terrestrial age are 21 x 10 to the 6th ages and 250,000 ages, respectively. The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: directly deposited falls and meteorites transported to the Allen Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering 'half-life' is about 160,000 ages. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations.

Freundel, M.; Schultz, L.; Reedy, R. C.

1986-12-01

296

Ice front configuration and torrential flow features of the Late Wisconsinan interlobate region of southcentral Michigan  

SciTech Connect

A large re-entrant, bordered on three sides by ice of the Michigan, Saginaw and Huron-Erie lobes, developed over a five-county area in southcentral Michigan during ice retreat of the Port Bruce Stade of the Woodfordian Substage. At this time, ice occupied positions marked by the Sturgies, Tekonsha, and Kalamazoo Moraines. The presence of numerous boulder beds within outwash deposits attests to frequent episodes of torrential flow. A major source of the discharge was the draining of short-lived proglacial and subglacial lakes identified by lacustrine deposits which occur at different altitudes within moraine belts. Tunnel valleys, meltwater channels, and narrow chutes carried the high discharges of water that were partly responsible for the Kankakee torrent of northeastern Illinois. The configuration of abandoned meltwater channels in eastern Calhoun and western jackson counties, between the Kalamazoo Moraine on the northeast and the Tekonsha Moraine to the southwest, indicates that a large ice-collapsed depression, 30 km long and 8 km to 16 km wide, developed within the Saginaw lobe just behind its margin. For a short period of time it contained intermittent glacial lakes one of which drained through the Kesler Lakes sluiceway. A large outwash plain, the Union City-Mendon sluiceway, heads at the Tekonsha Moraine in southcentral Calhoun County and extends southwest through northeastern Branch County to the Sturgis Moraine. Several abandoned narrow chutes, up to 1.6 km long and 60 m to 300 m wide, are incised in the outwash plain in the vicinity of Union City. Channel geometry indicates that flow exceeded 850 cms (30,000 cfs) during bankfull discharge and came from the overflow of a lake dammed by ice blocks in the ancient St. Joseph River floodplain.

Taylor, L.D. (Albion Coll., MI (United States). Dept. of Geological Sciences)

1994-04-01

297

The Medieval Climate Anomaly and the Little Ice Age in the eastern Ecuadorian Andes  

NASA Astrophysics Data System (ADS)

To better characterize the climate variability of the last millennium in the high Andes, we analyzed the pollen content of a 1150-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the Andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined. This index was used to distinguish changes in the atmospheric moisture from the soil moisture content of the páramo and their associated patterns of interdecadal El Niño-Southern Oscillation (ENSO) variability and South American summer monsoon (SASM) activity. Results show that between 850 and 1250 AD, the Medieval Climate Anomaly interval was warm and moist with a high transported pollen/Poaceae pollen (T/P) index linked to high ENSO variability and weak SASM activity. Between 1250 and 1550 AD, a dry climate prevailed, characterized by an abrupt decrease in the T/P index and therefore no upslope cloud convection, related to lower ENSO variability and with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed: first, a wet phase between 1550 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic sea surface temperatures (SSTs) favored the return of a wet páramo, and then a cold and dry phase between 1750 and 1800 AD associated with low ENSO variability and weak SASM activity resulted in drying of the páramo. The current warm period marks the beginning of a climate characterized by high convective activity - the highest in the last millennium - and weaker SASM activity modifying the water storage of the páramo. Our results show that the páramo is progressively losing its capacity for water storage and that the interdecadal variability of both tropical Pacific and Atlantic SSTs matter for Andean climate patterns, although many teleconnection mechanisms are still poorly understood.

Ledru, M.-P.; Jomelli, V.; Samaniego, P.; Vuille, M.; Hidalgo, S.; Herrera, M.; Ceron, C.

2013-02-01

298

Replicated Stalagmite Records of Rainfall Variability in the Solomon Islands since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The tropical west Pacific warm pool (WPWP) and south Pacific convergence zone (SPCZ) play integral roles in global climate variability. Convection over the WPWP is a source of latent heat and moisture to extratropical latitudes and, in the region of the SPCZ, forms a center of action for the rising component of the zonal Pacific Walker circulation. The nature of pre-instrumental, and therefore pre-industrial, variability of convection associated with the WPWP since the Little Ice Age (LIA) is known only from sparse and spatially disparate records. As a result, it is difficult to form a robust framework on which to base estimates of future variability of zonal atmospheric circulation within the region, an important prospect given predicted weakening in the Pacific Walker circulation under global warming conditions. Here we present absolutely dated, subannually resolved, partially replicated oxygen isotope records, spanning 1420-2010 CE, from two fast growing (~2 mm yr-1) calcite speleothems from a cave in northern Guadalcanal, Solomon Islands (9.5° S, 160° E). Guadalcanal is located both within the WPWP and under the zonally oriented portion of the SPCZ. A strong degree of reproducibility between the two stalagmite ?18O time series, within dating uncertainties, favors the interpretation that the stalagmite ?18O variability is a reflection of climatic conditions over the cave, however we continue to assess the possibility of influence by any potential non-climatic processes. We assert that speleothem ?18O variability reflects changes in rainfall based on the isotope "amount effect" observed in the tropics. We find rainfall here has varied considerably on decadal to multidecadal timescales since the LIA and hypothesize a relationship between this variability and variability in the strength of shallow Pacific meridional overturning circulation (PMOC). Changes in the PMOC are thought to be responsible for decadal variability in central and eastern equatorial Pacific SST anomalies as well as anomalies in Pacific tradewind strength. Such variability could affect convergence and vertical motion in the zonally oriented portion of the SPCZ. We find no clear long-term trend associated with changes in total solar irradiance since the LIA, in contrast to equatorial and northern hemisphere proxy records of tropical Pacific ocean-atmosphere variability.

Maupin, C. R.; Partin, J. W.; Quinn, T. M.; Shen, C.; Banner, J. L.; lin, K.; Taylor, F. W.; Sinclair, D.

2011-12-01

299

Late Quaternary ice extent in Far NE Russia  

NASA Astrophysics Data System (ADS)

The extent of glaciation in Far NE Russia during the Last Glacial Maximum is a matter of considerable controversy. Views range from the belief that the region was occupied by a series of extensive ice sheets, to the belief that glaciers were little more than 20 km in length, and restricted to only the highest mountains. In order to address this uncertainty, a remote sensing approach is adopted to the systematic mapping of end moraines across the entire region of Far NE Russia, extending east from the Lena River to the Pacific coast. The distribution of the 1800+ mapped moraines indicates that much of the, now largely ice-free, region was formerly occupied by glaciers, centred upon the region’s uplands, and typically less than 100 km in length. As such, the data lend little support to the view that vast ice sheets occupied the region at the LGM or during any other recent phase of glaciation.

Barr, I.; Clark, C. D.

2009-12-01

300

On the age vs depth and optical clarity of deep ice at South Pole  

Microsoft Academic Search

The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the South Pole. During the 1995-96 season an additional six strings will be deployed at greater depths. Provided absorption, scattering, and refraction of visible light are sufficiently small, the trajectory of a

1995-01-01

301

Reconstructing the history of major Greenland glaciers since the Little Ice Age  

Microsoft Academic Search

The Greenland Ice Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from

B. M. Csatho; A. F. Schenk; C. J. van der Veen; L. Stearns; G. S. Babonis

2008-01-01

302

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica  

NASA Astrophysics Data System (ADS)

A new deep ice core drilling program, TALDICE, has been successfully handled by a European team at Talos Dome, in the Ross Sea sector of East Antarctica, down to 1620 m depth. Using stratigraphic markers and a new inverse method, we produce the first official chronology of the ice core, called TALDICE-1. We show that it notably improves an a priori chronology resulting from a one-dimensional ice flow model. It is in agreement with a posteriori controls of the resulting accumulation rate and thinning function along the core. An absolute uncertainty of only 300 yr is obtained over the course of the last deglaciation. This uncertainty remains lower than 600 yr over Marine Isotope Stage 3, back to 50 kyr BP. The phasing of the TALDICE ice core climate record with respect to the central East Antarctic plateau and Greenland records can thus be determined with a precision allowing for a discussion of the mechanisms at work at sub-millennial time scales.

Buiron, D.; Chappellaz, J.; Stenni, B.; Frezzotti, M.; Baumgartner, M.; Capron, E.; Landais, A.; Lemieux-Dudon, B.; Masson-Delmotte, V.; Montagnat, M.; Parrenin, F.; Schilt, A.

2011-01-01

303

Relative sea-level response to Little Ice Age ice mass change in south central Alaska: Reconciling model predictions and geological evidence  

NASA Astrophysics Data System (ADS)

Integration of geological data and glacio-isostatic adjustment (GIA) modelling shows that it is possible to decouple complex mechanisms of relative sea-level (RSL) change in a tectonically active glacial environment. We model a simplest solution in which RSL changes in upper Cook Inlet, Alaska, are a combination of the interplay of tectonic and isostatic processes driven by the unique rheology of this tectonically active location. We calculate interseismic uplift during latter part of the penultimate earthquake cycle to vary from 0.3 to 0.7 mm/yr. Diatom based reconstructions of RSL from tidal marsh sediment sequences coupled with detailed age models, from AD 1400 to the AD 1964 great earthquake, show deviations from a purely tectonically driven model of regional RSL. Glacial isostatic modelling, constrained by GPS data, predicts up to 70 cm sea-level change due to mountain glacier mass balance changes during the Little Ice Age. Misfits between the GIA model predictions and RSL reconstructions in the 19th and 20th century highlight that the tidal marshes of upper Cook Inlet potentially record a hemispheric-wide acceleration in sea level and that other more complex Earth process combinations may contribute to regional RSL change.

Barlow, Natasha L. M.; Shennan, Ian; Long, Antony J.

2012-01-01

304

Cosmogenic 10Be Dating of Early and Latest Holocene Moraines on Nevado Salcantay in the Southern Peruvian Andes  

Microsoft Academic Search

A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the southwest flank of Nevado Salcantay (6271 m; ~13°S latitude), the highest peak in the Cordillera Vilcabamba of southern Peru. The field area is situated 25 km due south of the archaeological site of Machu Picchu. Outer and inner moraines in the sequence

J. M. Licciardi; J. M. Schaefer; D. C. Lund

2007-01-01

305

Beryllium10 dating of Mount Everest moraines indicates a strong monsoon influence and glacial synchroneity throughout the Himalaya  

Microsoft Academic Search

Moraine successions in glaciated valleys south of Mount Everest provide evidence for at least eight glacial advances during the late Quaternary. Cosmogenic radionuclide (CRN) surface exposure dating of moraine boulders defines the timing of each glacial advance and refines the previous glacial chronologies. The CRN data show that glaciation was most extensive during the early part of the last glacial

Robert C. Finkel; Lewis A. Owen; Patrick L. Barnard; Marc W. Caffee

2003-01-01

306

Sr and Nd isotope ratios and REE abundances of moraines in the mountain areas surrounding the Taklimakan Desert, NW China  

Microsoft Academic Search

The first systematic data of Sr and Nd isotopic ratios, REE abundances, major element and mineral compositions are reported for the Chinese moraines from the western Kunlun Mts. and southern and north- ern flanks of the Tianshan Mts. and soils from the Tibet Plateau. This study was conducted in order to characterize the isotopic and geochemical features of these moraines

QING CHANG; TAKASHI MISHIMA; SADAYO YABUKI; YOSHIO TAKAHASHI; HIROSHI SHIMIZU

307

Early Pliocene (pre–Ice Age) El Niño–like global climate: Which El Niño?  

Microsoft Academic Search

Paleoceanographic data from sites near the equator in the eastern and western Pacifi c Ocean show that sea-surface temperatures, and apparently also the depth and tempera- ture distribution in the thermocline, have changed markedly over the past ~4 m.y., from those resembling an El Niño state before ice sheets formed in the Northern Hemisphere to the present-day marked contrast between

Peter Molnar; Mark A. Cane

2007-01-01

308

Southern California Hydrographic Shifts During the Medieval Climate Anomaly and the Little Ice Age.  

NASA Astrophysics Data System (ADS)

We present records of the marine environmental change that occurred as regional climate shifted from the Medieval Climate Anomaly (MCA) into the Little Ice Age (LIA) based on planktonic foraminiferal and diatom assemblages alongside geochemical evidence of surface water temperature and salinity change from Santa Barbara Basin (SBB). The present climate reconstructions available in SBB clearly demonstrate that ocean and atmospheric circulation changes are occurring during the MCA and LIA. Records of sinistral Neogloboquadrina pachyderma absolute and relative abundance from ODP Site 893 suggest that surface waters cooled at ~600 years BP (varve chronology) or ~800 years BP (radiocarbon chronology). SSTs must have dropped below 8-10°C during winter through these intervals to provide favorable environmental conditions as sinistral N. pachyderma does not inhabit the modern SBB where annual SSTs range from 13-17°C. These results conflict with assemblage records of planktonic diatoms from the same core where increased relative abundance of Fragilariopsis doliolus occurred during the LIA. F. doliolus is a subtropical diatom associated with warm gyral waters that has been used extensively on the northern California Margin as an indicator of surface water warming and weak California Current (CC) flow. However, 20th century records suggest a close relationship of F. doliolus relative abundance to spring SSTs in the basin. Preliminary planktonic foraminiferal Mg/Ca results ( Globigerina bulloides) from core MV0508-32TC indicate that during the MCA, SBB surface waters were between 15 and 16°C, similar to modern warm season temperatures in the region, and cooled to 14°C during the LIA. This is consistent with the planktonic foraminiferal and radiolarian assemblage records from the region, which suggest a warm CC during the MCA, but stands in contrast with the ?18O and diatom assemblage records. ?18O records from ODP Site 893 indicate a cooling of surface waters during the MCA and warming during the LIA (demonstrated by a ?18O decrease during the LIA of ~0.4‰). Mg/Ca and ?18O records can only be reconciled if surface salinity decreased dramatically during the LIA. The following scenario may explain the record. As upwelling cools surface waters, warming of surface waters indicated by the presence of F. doliolus suggests reduced spring upwelling during the LIA. The presence of sinistral N. pachyderma suggests that during a portion of the year during the LIA surface waters in the basin were extremely cool perhaps cooled by the advection of subpolar water into the region via the CC. Reduced salinity during the LIA may be the result of either increased upwelling of low salinity water (although this conflicts with the diatom evidence), or advection of subpolar water from the NE Pacific. In contrast the MCA appeared to be associated with more saline, warmer surface waters and spring upwelling. These surface water shifts maybe related to ocean and atmospheric circulation changes associated with the PDO.

Hendy, I. L.; Pak, D. K.; Barron, J. A.; David, L. W.

2007-12-01

309

Soil development along primary succession sequences on moraines of Hailuogou Glacier, Gongga Mountain, Sichuan, China  

Microsoft Academic Search

Soil properties related to soil development were measured in six profiles over approximately 180 years of soil development on recessional moraines of the Hailuogou Glacier, Sichuan of southwestern China. It is hypothesized that soil development is strictly time-dependent. Field and laboratory work indicate that as soil develops from initially coarse gravel outwash, the properties undergo a progressive physical and chemical change

Lei He; Ya Tang

2008-01-01

310

Incremental planning and land-use conflict in the Toronto region's Oak Ridges Moraine  

Microsoft Academic Search

The Greater Toronto Area is the largest urban concentration in Canada and one of the most significant built regions in North America. Toronto's growth legacy has created a legacy of sprawl development. Growth has not occurred without controversy. On the Oak Ridges Moraine, an environmentally sensitive landform located along Toronto's northern suburban edge, development has been the catalyst for activism

Kevin Hanna; Steven Webber

2010-01-01

311

Morphology and Significance of Transverse Ridges (De Geer Moraines) Adjacent to the Moray Firth, NE Scotland  

Microsoft Academic Search

High-resolution NEXTMap digital surface models and aerial photographs are used to map suites of transverse ridges at Tarbat Ness and to the west of Elgin, along the margins of the Moray Firth in northeast Scotland. Based on their morphology, configuration and location, interpret these landforms as De Geer moraines which formed at or near former grounding line positions of the

Andrew Finlayson; Tom Bradwell; Nick Golledge; Jon Merritt

2007-01-01

312

Lichenometry as Applied to Moraines in Alaska, U.S.A., and Kamchatka, Russia  

Microsoft Academic Search

A selective review of lichenometry as used to date Holocene moraines in five diverse regions of Alaska and in southeastern Kamchatka suggests that growth curves for this North Pacific area may be improved by attention to several factors. These included lichen identification, control point number and distribution, radiocarbon calibration, alternative curve models, and compatibility of lichen growth rate with climate.

Olga Solomina; Parker E. Calkin

2003-01-01

313

Controls on Groundwater Flow in an Alpine Talus-Moraine Complex  

Microsoft Academic Search

Since alpine watersheds are the headwaters of rivers acting as major sources of water, there is growing concern over water shortages in areas dependent on mountain runoff. Talus and moraine complexes, as well as fractured bedrock, are a dominant hydrologic response unit within the Lake O'Hara Research Basin (LORB) in Yoho National Park, British Columbia. In this alpine environment, previous

D. L. Muir; M. Hayashi; L. R. Bentley

2009-01-01

314

Cosmogenic age constraints on the last deglaciation in Southern Patagonia (49 - 50°S)  

NASA Astrophysics Data System (ADS)

The glacial-to-interglacial transition since the Last Glacial Maximum (LGM) reflects climate system dynamics and the mechanisms that force climate change. Numerous studies of glacier behavior, mainly in the Northern Hemisphere, have sought to delineate the LGM termination as well as post-LGM climate reversals. We know far less about the Southern Hemisphere, where the extent and timing of climate shifts, and the degree of linkage to changes in the Northern Hemisphere, remain uncertain. Quantifying the temperature and precipitation changes across southern South America can help assess the migration of precipitation patterns tied to the position of the Southern Westerlies and the Antarctic Polar Front. This data can also be used to detect the extent of temperature reversals across and between continents, such as the Antarctic Cold Reversal, if present. The testing of hypotheses regarding changes in global atmospheric and oceanic circulation since the LGM is partly dependent on the deconvolution of these two parameters. Glacial activity in the Southern Patagonian Icefield is highly sensitive to changes in temperature and precipitation, while the adjacent Andean rainshadow desert preserves a remarkably complete set of glacial deposits that span a wide transect of the southern mid-latitudes. These deposits are ideal for surface exposure dating, which in turn can provide a proxy for glacial activity and for changes in the factors that govern glacial mass balance. We use a new beryllium-10 production rate calibrated to the southern mid-latitudes to recalculate published surface exposure chronologies from Patagonia (46 to 53°S). The revised temporal framework indicates the presence of expansive ice from ~30 ka until regional retreat 17-18 ka, with a significant late-glacial re-advance or still-stand ending ~13 ka. This latitudinal transect is notable for a gap in glacial records between 49 and 50°S. New surface exposure age determinations from the Santa Teresita moraine along the western shores of the large outlet valley of Lago Viedma, and from several moraines within the narrow pre-Cordilleran Rio Guanaco mountain valley begin to fill this gap. Initial results from a moraine in Rio Guanaco valley indicate ice retreat at ~18 ka, correlative with final LGM moraines at Lago Buenos Aires and Lago Pueyrredon to the north (46 - 47°S) and to the south near Torres del Paine and the Straits of Magellan (51 - 53°S). Exposure ages for the Santa Teresita moraine indicate ice retreat at ~13 ka, coincident with the well-dated Puerto Banderas moraine (Ackert et al., 2008, Science) in the Lago Argentino outlet valley to the south. These surface exposure chronologies are consistent with other regional records. Moreover, the emerging chronology is consistent with results of a fully-coupled transient general circulation model that predicts minimal deglacial precipitation change with significant temperature and equilibrium line altitude lowering during the last deglaciation at 50°S near 14 ka, followed by resumed warming from ~13.5 ka into the Holocene. These findings suggest that unlike more northerly portions of Patagonia, the Antarctic Cold Reversal impacted the Andes as far north as 50°S.

Murray, D. S.; Singer, B. S.; Carlson, A. E.; Caffee, M. W.

2010-12-01

315

Saginaw Lobe tunnel channels (Laurentide Ice Sheet) and their significance in south-central Michigan, USA  

Microsoft Academic Search

A network of tunnel channels in southern Michigan records substantial subglacial meltwater activity beneath the Saginaw Lobe of the Laurentide Ice Sheet. The channels are incompletely filled with outwash, contain eskers, and in many places crosscut and continue beyond upland ridges previously mapped as recessional moraines. The presence of the tunnel channels and drumlins on these upland ridges indicate that

Timothy G. Fisher; Harry M. Jol; Amber M. Boudreau

2005-01-01

316

Marine geophysical evidence for ice sheet extension and recession on the Irish continental shelf  

NASA Astrophysics Data System (ADS)

Multibeam swath bathymetry data collected by the Irish National Seabed Survey provides evidence for extensive glaciation of the continental shelf west and northwest of Ireland. Streamlined subglacial bedforms on the mid to outer shelf record former offshore-directed ice flow and indicate the ice sheet was grounded in a zone of confluence between ice flowing onto the shelf from northwest Ireland and southwest Scotland. The major glacial features, however, consist of well developed arcuate moraines which mark the position of former ice sheet margins on various parts of the shelf. Distal to these moraines, on the outermost shelf, prominent zones of iceberg ploughmarks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. The moraines record the episodic retreat of lobate grounded ice sheets across this sector of the continental shelf during deglaciation. Initial retreat from the outer shelf was associated with an episode of ice sheet breakup and calving as recorded by extensive zones of iceberg ploughmarks distal to the outermost moraines. This initial phase of retreat may have been driven by rising sea level. The data indicate a major reorganisation of the British Irish Ice Sheet on the shelf during deglaciation; an initial elongate ice sheet configuration extending along the shelf edge changed to a pronounced lobate form during retreat. Consideration of dated, marine stratigraphic records from the wider northwest margin suggests that ice sheet advance to the shelf edge likely occurred at about 29-27 cal ka BP, but that retreat from this shelf edge position did not take place until after 24 cal ka BP. Large-scale contrasts in continental margin morphology west of Ireland, from trough mouth fans in the north to gully/canyon systems further to south, reflects a combination of factors including spatial variations in sediment flux related to palaeo-glaciology.

Dunlop, Paul; Benetti, Sara; OCofaigh, Colm

2013-04-01

317

Was the Little Ice Age the result of a volcanically-triggered regime shift in the North Atlantic ocean circulation?  

NASA Astrophysics Data System (ADS)

One of the most important events in the climate history of the North Atlantic region during the last millennium is the transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), a transition that had substantial impact on societies in medieval Europe. The origin of this shift in regional climate, however, is not fully understood. Volcanic eruptions and changes in the total solar irradiance (TSI) as well as internal climate variability on multi-centennial time-scales might have contributed, and it is likely that an interplay of a variety of forcings in combination with regional climate feedbacks is needed to understand the MCA-LIA transition. Here, we present transient last millennium simulations of the fully-coupled model Climber 3?. Based on reconstructions for the North Atlantic Oscillation (NAO), the dominant mode of North Atlantic atmospheric climate variability, as well as on observational data, we stochastically generated wind field ensembles over the last millennium. We performed ensemble simulations prescribing atmospheric and natural forcings and also separated the individual forcings. We find good agreement with paleo reconstructions of Nordic Sea sea-ice cover and AMOC strength over the last millennium. The ensemble spread for different stochastic wind fields reconstructions is substantial, thus highlighting the importance of atmospheric dynamics for North-Atlantic oceanic climate variability. However, when separating individual forcings, pure atmospheric forcing alone as well as in combination with TSI forcing are found to be insufficient to reproduce key features of the MCA-LIA transition as apparent in paleo reconstructions, whereas volcanic forcing can generate a transition in agreement with the reconstructions. Our results indicate a coupled sea-ice ocean feedback mechanism behind the MCA-LIA transition and decadally-paced volcanic eruptions as a potential trigger. The latter will lead to a substantial sea-ice increase in the Nordic Seas, hindering convection and subsequently weakening the overflows over the Greenland-Scotland Ridge. This in turn leads to a strengthening of the subpolar gyre circulation and eventually a weakening of the Atlantic Meridional Overturning Circulation (AMOC). The subsequent basin-wide cooling helps to maintain a greater sea-ice cover in absence of external forcing and thereby stabilises the new circulation regime. Our results demonstrate the possibility of a persistent regime shift in the North Atlantic oceanic circulation regime in response to a short-lived external forcing in a fully coupled climate model and highlight the importance of regional climate feedbacks in order to advance the understanding of past and future climate. References: C. F. Schleussner, G. Feulner: A volcanically triggered regime shift in the subpolar North Atlantic ocean as a possible origin of the Little Ice Age, Clim. Past Discuss. 8 (2012), 6199-6219, doi:10.5194/cpd-8-6199-2012.

Schleussner, Carl-Friedrich; Feulner, Georg

2013-04-01

318

Millennial-scale variations of sea-ice expansion in the southwestern part of the Okhotsk Sea during the past 120 kyr: Age model and ice-rafted debris in IMAGES Core MD01-2412  

Microsoft Academic Search

A 58-m-long sediment core IMAGES MD01-2412 was recovered in the southwestern part of the Okhotsk Sea for high resolution paleocenography. An age model of the core was obtained by accelerator mass spectrometry (AMS) 14C dating of planktonic foraminifer shells, oxygen–isotope stratigraphy of benthic foraminifer calcite, and tephrochronology, resulting in a core-bottom age of 115 kyr. Sea-ice expansion in the Okhotsk Sea

Tatsuhiko Sakamoto; Minoru Ikehara; Masao Uchida; Kaori Aoki; Yasuyuki Shibata; Toshiya Kanamatsu; Naomi Harada; Koichi Iijima; Kota Katsuki; Hiroshi Asahi; Kozo Takahashi; Hideo Sakai; Hodaka Kawahata

2006-01-01

319

Zircons and clay from morainal Permian siltstone at Mt Rymill (73°S, 66°E), Prince Charles Mountains, Antarctica, reflect the ancestral Gamburtsev Subglacial Mountains–Vostok Subglacial Highlands complex  

Microsoft Academic Search

Clasts of red siltstone with Glossopteris from moraine around Mt Rymill in the southern Prince Charles Mountains, East Antarctica, can be traced upslope in the Lambert Graben system to the nearby Gamburtsev Subglacial Mountains (GSM). The clasts contain zircons with SHRIMP U–Pb ages of 620–460 Ma and 1300–970 Ma from host rocks of intermediate to mafic rocks, and a clay fraction with

J. J. Veevers; A. Saeed; N. Pearson; E. Belousova; P. D. Kinny

2008-01-01

320

Ice Age Methane Revisited: Oceans, Lightning, and the Steady Wetland Source  

NASA Astrophysics Data System (ADS)

The concentrations of reactive greenhouse gases in the atmosphere are a result of the interplay between sources on land and in the oceans and the atmospheric sink. Methane (CH4) is the most important of the major, long-lived reactive trace gases, and over the past 400,000 years it has more closely paralleled the higher-frequency component of polar temperature records than any other measured gas. Analyses of ice core CH4 concentrations and carbon isotope composition (? 13CH4) have suggested that changing CH4 emissions from wetlands drove prehistoric changes in ice-core CH4. As a reactive trace gas, the global CH4 budget is controlled not just by changes in source strength, but also by climate, changes in the flux of other reactive trace gases, and the nonlinear dynamics of atmospheric chemistry. To investigate the effect of long-term climate change on the atmospheric concentration of CH4 we coupled climate, vegetation, and atmospheric chemistry models to simulate the natural emissions and atmospheric chemistry of the major reactive trace gases. Climate was simulated by a coupled AGCM/mixed-layer ocean model with simulations at 1000-year intervals from the Last Glacial Maximum (LGM, ca. 21 ka) to present. Terrestrial CH4 and Biogenic Volatile Organic Compound (BVOC) emissions were simulated using the BIOME4-TG global vegetation model, with simple algorithms for determining wetland area based on topography and soil moisture, CH4 emissions based on ecosystem carbon turnover in wet soils, and BVOC emissions based on vegetation type and density. We simulated atmospheric chemistry and transport with the LMDz-INCA 3D chemistry-transport model, and included a full prognostic simulation of nitrogen oxide (NOx) emissions from lightning based on simulated convective precipitation. Global wetland area decreased by 1x106 km2 from the LGM to the present (nearly 15%). However, CH4 emissions - 110 Tg yr-1 - were nearly unchanged over this same period. During the Pleistocene-Holocene transition CH4 emissions reached a maximum of ca. 130 Tg. LGM CH4 emissions were ca. 2\\permil more depleted in ? 13CH4 compared to present because of the increase in tropical wetland activity relative to northern wetlands. Wetland CH4 emissions did not change drastically during the deglaciation because new wetland areas formed as ice sheets retreated, while other wetland areas were flooded by rising sea-level. Global emissions of BVOC increased significantly from the LGM to present, (350 Tg C yr-1 or 150%) because of increased vegetation density from warming climate and increased atmospheric CO2 concentrations. The simulated increase in sea surface temperatures (SST) from the LGM to present led to increased convective precipitation and a 10-30% increase in NOx emissions from lightning. Observed rapid changes in atmospheric CH4 concentrations over the last 21 ka cannot be completely attributed to climate change on millennial time-scales. However, the simulated changes in both the atmospheric BVOC and NOx burdens, which compete with CH4 as an OH sink, may have increased the lifetime of CH4 on the order of 30% at the present compared to LGM. This strong reduction in CH4 oxidation potential would have had long-term consequences for atmospheric CH4 concentrations and may explain much of the ice-core CH4 record without requiring major changes in the wetland CH4 source.

Kaplan, J. O.; Folberth, G.; Hauglustaine, D.

2004-05-01

321

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

NASA Astrophysics Data System (ADS)

The Sanabria Lake region is located in the Trevinca Massif, a mid-latitude mountain area up to 2128 m asl in the northwest corner of the Iberian Peninsula (42oN 6oW). An ice cap glaciation took place during the Last Glacial Cycle in this massif, with an equilibrium line altitude of 1687 m for the Tera glacial outlet at its local maximum (Cowton et al., 2009). A well preserved glacial sequence occurs on an area of 45 km2 around the present Sanabria Lake (1000 m asl) and is composed by lateral and end moraines in close relationship with glaciolacustrine deposits. This sequence shows the ice snout oscillations of the former Tera glacier during the Last Glacial Cycle and offers a good opportunity to compare radiocarbon and OSL- based chronological models with new cosmogenic isotope dates. The new dataset of 10Be exposure ages presented here for the Sanabria Lake moraines is based on measurements conducted on 23 boulders and is compared with previous radiocarbon and OSL data conducted on ice related deposits (Pérez-Alberti et al., 2011; Rodríguez-Rodríguez et al., 2011). Our results are coherent with the available deglaciation radiocarbon chronology, and support a last deglaciation origin for the whole set of end moraines that are downstream the Sanabria Lake (19.2 - 15.7 10Be ka). Discrepancies between results of the different dating methods concern the timing of the local glacial maximum, with the cosmogenic exposure method always yielding the youngest minimum ages. As proposed to explain similar observations made elsewhere (Palacios et al., 2012), reconciling the ages from different dating methods would imply the occurrence of two glacial advances close enough in extent to generate an overlapping polygenic moraine. Cowton, T., Hughes, P.D., Gibbard, P.L., 2009. Palaeoglaciation of Parque Natural Lago de Sanabria, northwest Spain. Geomorphology 108, 282-291. Rodríguez-Rodríguez, L., Jiménez-Sánchez, M., Domínguez-Cuesta, M.J., Rico, M.T., Valero-Garcés, B., 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).

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

2013-04-01

322

Highly branched isoprenoid (HBI) biomarkers as an Antarctic sea-ice proxy in deep ocean glacial age sediments  

NASA Astrophysics Data System (ADS)

Antarctic sea-ice plays a primary role in the climate system, potentially modulating interhemispheric millennial-scale climate change and deglacial warming. Recently, microfossil proxy data have provided important insights into this potential forcing. However, additional proxies for glacial sea-ice reconstructions are required, to support the microfossil data and to control for potential preservation issues. We consider highly branched isoprenoids (HBIs) as a sea-ice proxy, building on earlier studies in the Arctic and Antarctic. This study focussed on measuring HBIs in glacial deposits in Southern Ocean deep ocean sediment cores. These deep-water sites provided a study location away from the local sea ice complexities associated with previously studied coastal and shallow water sites and, for the first time, allowed an evaluation of HBIs during several phases of glacial sea-ice variability inferred from microfossils. Down-core profiles of HBIs diene (II) and triene (III) were compared with diatom-based reconstructions of Antarctic sea-ice derived in three high-resolution sediment cores recovered from a transect across the Scotia Sea, Southwest Atlantic. High quality chronological control was achieved through a combination of abundance stratigraphy, relative geomagnetic palaeointensity data, and down-core magnetic susceptibility/ice core dust correlation. Positive correlations, observed between (II) and sea-ice presence, and a strong coupling between (III) and marginal ice zone conditions indicated that the two HBIs are both closely related to sea-ice edge dynamics. Strong down-core correlations between the HBIs indicate coeval sedimentation related to the summer breakdown of sea-ice melt-induced stratification. Combined, the two HBIs and diatoms demonstrated their potential as proxies for permanent sea-ice cover and sea-ice seasonality, two parameters poorly resolved in current climate models. The sea-ice reconstructions presented confirmed that HBIs are a viable proxy for glacial Antarctic sea-ice and sea ice dynamics back to at least 60 cal ka BP.

Collins, L. G.; Allen, C. S.; Pike, J.; Hodgson, D. A.; Weckström, K.; Massé, G.

2012-04-01

323

Y-Chromosome Evidence for a Northward Migration of Modern Humans into Eastern Asia during the Last Ice Age  

PubMed Central

Summary The timing and nature of the arrival and the subsequent expansion of modern humans into eastern Asia remains controversial. Using Y-chromosome biallelic markers, we investigated the ancient human-migration patterns in eastern Asia. Our data indicate that southern populations in eastern Asia are much more polymorphic than northern populations, which have only a subset of the southern haplotypes. This pattern indicates that the first settlement of modern humans in eastern Asia occurred in mainland Southeast Asia during the last Ice Age, coinciding with the absence of human fossils in eastern Asia, 50,000–100,000 years ago. After the initial peopling, a great northward migration extended into northern China and Siberia.

Su, Bing; Xiao, Junhua; Underhill, Peter; Deka, Ranjan; Zhang, Weiling; Akey, Joshua; Huang, Wei; Shen, Di; Lu, Daru; Luo, Jingchun; Chu, Jiayou; Tan, Jiazhen; Shen, Peidong; Davis, Ron; Cavalli-Sforza, Luca; Chakraborty, Ranajit; Xiong, Momiao; Du, Ruofu; Oefner, Peter; Chen, Zhu; Jin, Li

1999-01-01

324

Tropical Atlantic climate response to low-latitude and extratropical sea-surface temperature: A Little Ice Age perspective  

NASA Astrophysics Data System (ADS)

Proxy reconstructions and model simulations suggest that steeper interhemispheric sea surface temperature (SST) gradients lead to southerly Intertropical Convergence Zone (ITCZ) migrations during periods of North Atlantic cooling, the most recent of which was the Little Ice Age (LIA; ˜100-450 yBP). Evidence suggesting low-latitude Atlantic cooling during the LIA was relatively small (<1°C) raises the possibility that the ITCZ may have responded to a hemispheric SST gradient originating in the extratropics. We use an atmospheric general circulation model (AGCM) to investigate the relative influence of low-latitude and extratropical SSTs on the meridional position of the ITCZ. Our results suggest that the ITCZ responds primarily to local, low-latitude SST anomalies and that small cool anomalies (<0.5°C) can reproduce the LIA precipitation pattern suggested by paleoclimate proxies. Conversely, even large extratropical cooling does not significantly impact low-latitude hydrology in the absence of ocean-atmosphere interaction.

Saenger, Casey; Chang, Ping; Ji, Link; Oppo, Delia W.; Cohen, Anne L.

2009-06-01

325

Controls on Groundwater Flow in an Alpine Talus-Moraine Complex  

NASA Astrophysics Data System (ADS)

Since alpine watersheds are the headwaters of rivers acting as major sources of water, there is growing concern over water shortages in areas dependent on mountain runoff. Talus and moraine complexes, as well as fractured bedrock, are a dominant hydrologic response unit within the Lake O'Hara Research Basin (LORB) in Yoho National Park, British Columbia. In this alpine environment, previous studies have shown that groundwater plays an important hydrological role. Although little is known about groundwater storage in these media, they are likely a significant groundwater reservoir and an important control on groundwater flow. The goals of this study are to develop a conceptual model of the talus and moraine complex and the fractured bedrock. The approximately 0.3km2 Babylon drainage basin within the LORB was chosen as the study site as it contains a talus and moraine complex that drains into one gaugeable stream. The conceptual model of this basin has been developed using geophysical, hydrological and hydrogeological methods. Three Ground Penetrating Radar (GPR) and Electrical Resistivity Imaging (ERI) surveys were used to characterize the subsurface structure and water distribution within the talus and moraine complex. The bedrock surface is clearly defined in the GPR profiles and its elevation agrees with that in the ERI inversions. Highly resistive talus material is observable in the ERI results, and areas of low resistivity are found within the bedrock. Hydraulic conductivity estimates of the geologic media, calculated using tracer slug injection and baseflow recession analysis methods, fall within the ranges from gravel to fractured rock. Isotopic hydrograph separations indicate that groundwater is a significant contributor to stream discharge. Linear reservoir models show basin response times of up to 16 hours. The geophysical and hydrological evidence points toward two flow systems operating in the Babylon basin, those of flow through the fractured bedrock and flow through the talus and moraine complex. Understanding the hydrologic characteristics of alpine talus and moraine complexes and fractured bedrock is of great importance to increasing our knowledge of alpine hydrology. The results from this study will enable the estimation of hydrologic parameters of these geologic media and provide valuable information for the predictive modelling of mountain streams.

Muir, D. L.; Hayashi, M.; Bentley, L. R.

2009-05-01

326

CO2 Climate-Glaciation linkages During the Late Paleozoic Ice Age and the Earth's Penultimate Deglaciation  

NASA Astrophysics Data System (ADS)

The Late Paleozoic Ice Age (LPIA) was the longest-lived (330 to 260 Myr) and most intense glaciation of the past half-billion years. Emerging high-latitude Southern Hemisphere records document a much more dynamic ice age - one defined by multiple short-lived (1 to 7 myr duration) icehouse periods punctuated by warmer periods of glacial minima. These major climate shifts throughout the LPIA and its demise at the close of the Early Permian provide the only 'vegetated-Earth' analogues of major climate change in an icehouse. As our climate system departs from the well-studied Pleistocene glacial-interglacial cycles, a 'deep-time' perspective of pCO2-climate- glaciation linkages during past icehouse-to-greenhouse transitions provides a unique perspective into what may be the Earth's most epic deglaciation. Here we apply the carbon isotopic compositions of soil-formed carbonates and fossil plant material (cuticle, coals, charcoals) from several terrestrial basins in North America to a soil CO2-diffusion model and Monte Carlo modeling to estimate atmospheric pCO2 for the LPIA and its transition to the ensuing Mesozoic greenhouse state. Best estimates of Late Paleozoic pCO2 indicate repeated shifts from present-day levels to values of up to 2500 to 3000 ppmv during periods of glacial minima and possibly fully deglaciated greenhouse states. To evaluate the nature of the CO2-climate relationship during these major climate transitions, we developed a time-equivalent record of paleotropical sea-surface temperatures (SSTs) using ?18O values from a global compilation of well-preserved latest Permo-Carboniferous tropical shallow-water brachiopods. The observed covariance between shifts in inferred paleotropical SSTs, pCO2 and high- latitude Gondwanan glaciation implies a strong CO2-climate-glaciation linkage that is consistent with the range predicted by Permian climate simulations for a change in radiative CO2-forcing from 1 to 8 fold present-day levels. This apparent CO2-climate-glaciation link suggests that atmospheric CO2 levels may have been the primary driver for the repeated buildup and retreat of continental ice sheets during the Late Paleozoic. Integration of these climate proxy records with newly developed tropical paleobotanical records for paleotropical Euramerica reveals repeated major restructuring of flora in-step with climate and pCO2 shifts illustrating the impact on tropical floral ecosystems associated with past CO2-forced climate transitions.

Montanez, I. P.

2007-12-01

327

The Medieval Warm Period-Little Ice Age Relative Sea Level Slowdown in Western Greenland: A response of the Greenland Ice Sheet to a phase shift of the North Atlantic Oscillation?  

NASA Astrophysics Data System (ADS)

Changes in mass balance can force spatially variable sea-level changes in both the near- and far-field of an ice sheet (Farrell and Clark, 1976; Mitrovica et al. 2001). During the period spanning the Medieval Warm Period and the Little Ice Age (LIA), reconstructions of century-scale relative sea-level (RSL) extracted from salt marsh deposits in Greenland (Long et al. 2011, Woodroffe and Long, 2009) reveal that the century-scale RSL trends differ significantly to millennial-scale trends inferred from isolation basin data in their respective areas. At sites in west Greenland (Sisimiut: 68.6oN, 52.6oW; Aasiaat: 68.6oN, 52.6oW), RSL rise slows from ~3 mm/yr to ~0 mm/yr at ~1600AD and is stable thereafter. In south Greenland (Nanortalik, 60oN, 44.7oW), a similar trend is observed, but the slowdown occurs 200 years later. Sensitivity tests show that substantial contributions from oceanographic changes can be ruled out as drivers of RSL slowdown at Aasiaat and Sisimiut but could be more important at Nanortalik. Dynamic ice loss from Jakobshavn Isbrae is predicted to produce an extremely localised RSL signal and is likely to be only a secondary contributor to RSL changes at Aasiaat. For Sisimiut and Aasiaat, regional-scale changes in ice load are the most likely candidate to explain the observed RSL signals. Marginal ice loss in western Greenland beginning around 1600AD is required to initiate local sea-level fall to counteract the background viscous sea-level rise associated with GIA from non-Greenland sources. However, ice loss is deemed an unlikely scenario since this is incompatible with widely-perceived climatic conditions associated with the Little Ice Age. Recently it has been shown that the North Atlantic Oscillation (NAO) was predominantly in a positive phase prior to the LIA (Trouet et al., 2009), switching to a variable positive/negative phase since ~1600AD. This offers a mechanism to explain the RSL changes at Sisimiut and Aasiaat at 1600AD. We present the results of a sensitivity study which support the hypothesis first proposed in Long et al. (2011) that the western part of the Greenland Ice Sheet may have been losing mass as a result of warmer conditions associated with NAO-, during a time when the many glaciers around the world were expanding.

Wake, L. M.; Milne, G. A.; Long, A. J.; Woodroffe, S. A.

2012-04-01

328

The phylogeography of an alpine leaf beetle: divergence within Oreina elongata spans several ice ages.  

PubMed

The genetic landscape of the European flora and fauna was shaped by the ebb and flow of populations with the shifting ice during Quaternary climate cycles. While this has been well demonstrated for lowland species, less is known about high altitude taxa. Here we analyze the phylogeography of the leaf beetle Oreina elongata from 20 populations across the Alps and Apennines. Three mitochondrial and one nuclear region were sequenced in 64 individuals. Within an mtDNA phylogeny, three of seven subspecies are monophyletic. The species is chemically defended and aposematic, with green and blue forms showing geographic variation and unexpected within-population polymorphism. These warning colors show pronounced east-west geographical structure in distribution, but the phylogeography suggests repeated origin and loss. Basal clades come from the central Alps. Ancestors of other clades probably survived across northern Italy and the northern Adriatic, before separation of eastern, southern and western populations and rapid spread through the western Alps. After reviewing calibrated gene-specific substitution rates in the literature, we use partitioned Bayesian coalescent analysis to date our phylogeography. The major clades diverged long before the last glacial maximum, suggesting that O. elongata persisted many glacial cycles within or at the edges of the Alps and Apennines. When analyzing additional barcoding pairwise distances, we find strong evidence to consider O. elongata as a species complex rather than a single species. PMID:20807580

Borer, Matthias; Alvarez, Nadir; Buerki, Sven; Margraf, Nicolas; Rahier, Martine; Naisbit, Russell E

2010-08-31

329

The evolution of fish ectoparasite communities--the role of the ice ages.  

PubMed

The monogenean ectoparasite genera Dactylogyrus and Gyrodactylus are hyperdiverse, and yet monogenean communities infecting freshwater fish in the northern Holarctic are variable and often impoverished. This is a result of extinctions during periods of glaciation when the host fishes experienced range contraction. Fish species recolonised northern Europe by one of three routes; stenohaline fishes recolonised from the Black Sea basin via Danube-Rhine or Dnieper-Dniester-Vistula connections. These fish retain complex rich monogenean faunas with numerous species of Dactylogyrus and Paradiplozoon. Anadromous fishes, recolonising via marine migrations along the coast, and cold-water fishes surviving in refugia close to the ice sheets, have impoverished monogenean faunas, characterised by gyrodactylid and ancyrocephalid species. However, there may be great complexity, due to the evolution of new host-parasite interactions within specific watersheds before, during and after the Last Glacial Maximum (LGM). This is demonstrated using examples from the sticklebacks (Gasterosteus aculeatus) and the bullheads (Cottus gobio). Finally, the evolution of Gyrodactylus salaris from a clade of G. thymalli is described, and the role of glaciation in stimulating the evolution of numerous clades of the latter is discussed. This latter example represents a unique opportunity to study speciation by host shift in real time. PMID:19338218

Harris, Philip D

2008-01-01

330

Ice-age endurance: DNA evidence of a white spruce refugium in Alaska  

PubMed Central

Paleorecords offer key information for evaluating model simulations of species migration in response to forecast climatic change. However, their utility can be greatly compromised by the existence of glacial refugia that are undetectable in fossil records (cryptic refugia). Despite several decades of investigation, it remains controversial whether Beringia, the largely unglaciated area extending from northeastern Siberia to the Yukon Territory, harbored small populations of certain boreal tree species during the last glaciation. Here, we present genetic evidence for the existence of a glacial refuge in Alaska that helps to resolve this long-standing controversy. We sequenced chloroplast DNA (cpDNA) of white spruce (Picea glauca), a dominant boreal tree species, in 24 forest stands across northwestern North America. The majority of cpDNA haplotypes are unique, and haplotype diversity is relatively high in Alaska, arguing against the possibility that this species migrated into the region from areas south of the Laurentide Ice Sheet after the end of the last glaciation. Thus, white spruce apparently survived long glacial episodes under climatic extremes in a heterogeneous landscape matrix. These results suggest that estimated rates of tree migration from fossil records may be too high and that the ability of trees to track anthropogenic warming may be more limited than previously thought.

Anderson, Lynn L.; Hu, Feng Sheng; Nelson, David M.; Petit, Remy J.; Paige, Ken N.

2006-01-01

331

Ice-age endurance: DNA evidence of a white spruce refugium in Alaska.  

PubMed

Paleorecords offer key information for evaluating model simulations of species migration in response to forecast climatic change. However, their utility can be greatly compromised by the existence of glacial refugia that are undetectable in fossil records (cryptic refugia). Despite several decades of investigation, it remains controversial whether Beringia, the largely unglaciated area extending from northeastern Siberia to the Yukon Territory, harbored small populations of certain boreal tree species during the last glaciation. Here, we present genetic evidence for the existence of a glacial refuge in Alaska that helps to resolve this long-standing controversy. We sequenced chloroplast DNA (cpDNA) of white spruce (Picea glauca), a dominant boreal tree species, in 24 forest stands across northwestern North America. The majority of cpDNA haplotypes are unique, and haplotype diversity is relatively high in Alaska, arguing against the possibility that this species migrated into the region from areas south of the Laurentide Ice Sheet after the end of the last glaciation. Thus, white spruce apparently survived long glacial episodes under climatic extremes in a heterogeneous landscape matrix. These results suggest that estimated rates of tree migration from fossil records may be too high and that the ability of trees to track anthropogenic warming may be more limited than previously thought. PMID:16894151

Anderson, Lynn L; Hu, Feng Sheng; Nelson, David M; Petit, Rémy J; Paige, Ken N

2006-08-07

332

Detailed chronology of mid-altitude fluvial system response to changing climate and societies at the end of the Little Ice Age (Southwestern Alps and Cévennes, France)  

Microsoft Academic Search

Over a historical timescale, landscapes have been strongly affected by fluctuations in climate and by the impact of human societies. This study examines the historical evolution of mid-altitude fluvial systems in the Western Alps and Cévennes (SE Massif Central) in the context of marked climate and anthropogenic change at the end of the Little Ice Age (late 19th century). This

Laurent Astrade; Nicolas Jacob-Rousseau; Jean-Paul Bravard; Françoise Allignol; L. Simac

2011-01-01

333

'Little Ice Age' aridity in the North American Great Plains: a high-resolution reconstruction of salinity fluctuations from Devils Lake, North Dakota, USA  

Microsoft Academic Search

The 'Little Ice Age' was an interval between about AD 1500 and 1850, characterized by advancing glaciers in mountainous regions of Europe and western North America. However, it is unclear whether this cool moist period was truly global in extent, or how it was manifested in other regions with different climatic controls. A high-resolution reconstruction of salinity fluctuations in Devils

Sherilyn C. Fritz; Daniel R. Engstrom; Brian J. Haskell

1994-01-01

334

Kr-81 and Kr-85 analysis for the determination of water/ice age  

NASA Astrophysics Data System (ADS)

The Atom Trap Trace Analysis (ATTA) method has enabled us to measure radiokrypton isotopes 81Kr (half-life = 229,000 yr, atmospheric isotopic abundance ~1E-12) and 85Kr (half-life = 10.8 yr, isotopic abundance ~1E-11) in environmental samples (groundwater, geothermal steam, air, etc.). This in turn opens the door to new applications in the earth sciences. The first prototype ATTA instrument could measure both 81Kr and 85Kr in atmospheric Kr gas samples with an efficiency of 1E-7 [1]. Through modifications to the instrument, the efficiency of ATTA was subsequently improved to ~1E-4. At this efficiency, the first earth science applications became feasible using the current-generation instrument, ATTA-2 [2]. 81Kr measurements of groundwater samples from the Nubian Aquifer in the Western Desert of Egypt showed residence times approaching one million years, in good agreement with 36Cl data and numerical hydrodynamic models [3]. However, a sample of >1,000 liters of water was required for these groundwater measurements, making the method inconvenient for routine scientific applications. Recent developments in our lab have made it possible to further improve both the counting rate and counting efficiency of the ATTA method. We are developing a new apparatus (ATTA-3) to count 81Kr atoms with the goal of reaching a counting efficiency of 1%, which would reduce the required sample size down to 10 liters of water or ice. ATTA-3 will enable a wide range of applications in the earth sciences. This work is supported by NSF, Division of Earth Sciences, under Award No. EAR-0651161, and by DOE, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. [1] Chen C.Y. et al. (1999) Science 286, 1139-1141. [2] Du X. et al. (2003) Geophys. Res. Lett. 30, 2068. [3] Sturchio N.C. et al. (2004) Geophys. Res. Lett. 31, L05503.

Lu, Z.; Bailey, K.; Cheng, C.; Davis, A. M.; Ding, Y.; Dunford, R. W.; Hu, S.; Jiang, W.; Mueller, P.; O'Connor, T. P.; Purtschert, R.; Sturchio, N. C.; Sun, Y. R.; Yokochi, R.; Young, L.; Williams, W.

2009-12-01

335

Extensive Hesperian-aged south polar ice sheet on Mars: Evidence for massive melting and retreat, and lateral flow and ponding of meltwater  

Microsoft Academic Search

Local and regional Mars Orbiter Laser Altimeter (MOLA) topographic data support the presence of an extensive Hesperian-aged volatile-rich south polar deposit (the Dorsa Argentea Formation, Hd, and related units) underlying the present Amazonian-aged polar cap (Api, residual ice, and Apl, layered terrain) and covering a surface area that could be as large as 2.94×106km2 (about 2% of the surface of

James W. Head; Stephen Pratt

2001-01-01

336

History of late glacial runoff from the southern Laurentide ice sheet in Indiana  

SciTech Connect

The history of late glacial runoff from the southern Laurentide ice sheet in Indiana is one of long periods of normal'' meltwater flow punctuated by extreme flows. Meltwater flow down the Wabash began about 26 ka when ice of the Lake Michigan lobe entered the headwaters of its northern and western tributaries. This flow was augmented by meltwater from the Huron-Erie lobe which entered the basin about 24 ka, and there ensued a period when normal meltwater flow and outwash sedimentation prevailed through successive advances from these two sources. This ended about 17 ka ( ) when two extreme flow events occurred. The first involved a subglacial breakout of stored water in a stagnating sheet of Erie-Huron lobe ice and the second occurred when a proglacial lake stored behind a Huron-Erie Lobe recessional moraine in northeastern Indiana drained catastrophically into the Wabash. A second period of normal flow and sedimentation followed as successive episodes of advance and active backwasting of Huron-Erie lobe ice left a series of recessional moraines in northeastern Indiana. Lake Maumee (of ancestral Lake Erie) formed behind the last of these, and the final extreme flow down the Wabash occurred about 14 ka ( ) when this moraine was breached. During the final stages of glaciation in Indiana, very large volumes of meltwater were supplied to the Illinois river system through the Kankakee sluiceway by both the Lake Michigan lobe and the Saginaw lobe. For the most part, these were not extreme flows, but catastrophic subglacial outburst(s) of water from the Lake Michigan lobe did occur about 13 ka ( ) along the Valparaiso Moraine. Most of this meltwater was directed down the Kankakee sluiceway and into the Illinois River, but some may have flowed around the east end of the iroquois Moraine and into the Wabash River.

Fraser, G.S. (Indiana Univ., Bloomington, IN (United States)); Fleming, A.H. (Indiana Geological Survey, Bloomington, IN (United States))

1992-01-01

337

Evaluating highly branched isoprenoid (HBI) biomarkers as a novel Antarctic sea-ice proxy in deep ocean glacial age sediments  

NASA Astrophysics Data System (ADS)

Antarctic sea-ice plays a primary role in the climate system, potentially modulating interhemispheric millennial-scale climate change and deglacial warming. Recently, microfossil proxy data have provided important insights into this potential forcing. However, additional proxies for glacial sea-ice reconstructions are required, to support the microfossil data and to control for potential preservation issues. We considered highly branched isoprenoids (HBIs) as a sea-ice proxy, building on earlier studies in the Arctic and Antarctic. This study focused on measuring HBIs in glacial deposits in Southern Ocean deep ocean sediment cores. These deep ocean sites provided a study location away from the local sea-ice complexities associated with coastal and shallow water sites and allowed the comparison of HBIs during several phases of glacial sea-ice variability inferred from microfossils. Down-core profiles of di- and tri-unsaturated HBI isomers diene II and triene III were compared with diatom-based reconstructions of Antarctic sea-ice derived in three high resolution sediment cores recovered from a transect across the Scotia Sea, Southwest Atlantic. High quality chronological control was achieved through a combination of abundance stratigraphy, relative geomagnetic palaeointensity data, and down-core magnetic susceptibility/ice core dust correlation. Significant positive correlations, observed between HBI diene II and sea-ice presence, and between HBI triene III and open waters in the Marginal Ice Zone indicated that the two HBIs are both closely related to sea-ice and sea-ice edge dynamics, respectively. Highly significant down-core correlations between the HBIs indicate coeval sedimentation related to the summer breakdown of sea-ice melt-induced stratification. Combined, the two HBIs and diatoms demonstrated their potential as proxies for permanent sea-ice cover and sea-ice seasonality, two parameters poorly resolved in current climate models. The sea-ice reconstructions presented have developed our knowledge regarding HBIs and their relationship with the surface ocean environment and further highlight their potential as an important proxy for glacial Antarctic sea-ice and sea-ice dynamics back to at least ˜60 ka.

Collins, Lewis G.; Allen, Claire S.; Pike, Jennifer; Hodgson, Dominic A.; Weckström, Kaarina; Massé, Guillaume

2013-11-01

338

Regional drainage of meltwater beneath a Hesperian-aged south circumpolar ice sheet on Mars  

Microsoft Academic Search

Five sinuous valleys that begin near the margins of the Hesperian-aged Dorsa Argentea Formation (DAF) are examined using Mars Global Surveyor Mars Orbiter Laser Altimeter data. These valleys are carved into the surrounding Noachian cratered terrain and extend away from the DAF for lengths up to 1600 km before terminating in the Argyre basin 1–3 km below their starting elevations.

Gil J. Ghatan; James W. Head

2004-01-01

339

Reevaluation of paleo-accumulation parameterization over Northern Hemisphere ice sheets during the ice age examined with a high-resolution AGCM and a 3-D ice-sheet model  

Microsoft Academic Search

Simulations of the Northern Hemisphere ice sheet at the Last Glacial Maximum (LGM; 21 kyr BP) are performed using a high-resolution atmospheric general circulation model (AGCM) in order to re-evaluate the conventional surface temperature- or elevation-based parameterization. The influence of precipitation change on the steady-state topography of the Laurentide ice sheet at the LGM is estimated using an AGCM with

Takateru Yamagishi; Ayako Abe-Ouchi; Fuyuki Saito; Tomonori Segawa; Teruyuki Nishimura

2005-01-01

340

Interpreting ancient ice in a shallow ice core from the South Yamato (Antarctica) blue ice area using flow modeling and compositional matching to deep ice cores  

Microsoft Academic Search

We explore methods of dating a 101 m ice core from a bare ice ablation area in the Yamato Mountains, Dronning Maud Land, East Antarctica. There are two unknowns, the age of the ice at the surface and the age spanned by the core. The ice crystal growth rate was used to estimate the age span of the core at

John C. Moore; Fumihiko Nishio; Shuji Fujita; Hideki Narita; Elizabeth Pasteur; Aslak Grinsted; Anna Sinisalo; Norikazu Maeno

2006-01-01

341

Sensitivity of sea ice to wind-stress and radiative forcing since 1500: a model study of the Little Ice Age and beyond  

Microsoft Academic Search

Three different reconstructed wind-stress fields which take into account variations of the North Atlantic Oscillation, one\\u000a general circulation model wind-stress field, and three radiative forcings (volcanic activity, insolation changes and greenhouse\\u000a gas changes) are used with the UVic Earth System Climate Model to simulate the surface air temperature, the sea-ice cover,\\u000a and the Atlantic meridional overturning circulation (AMOC) since 1500,

Jan Sedlácek; Lawrence A. Mysak

2009-01-01

342

Mount Logan Ice Core Evidence for Changes in the Hadley and Walker Circulations Following the End of the \\\\Little Ice Age  

Microsoft Academic Search

The Hadley and Walker circulations dominate the climate of the tropics and contribute to extratropical climate variability\\u000a through the forcing of planetary waves that result in the long-range correlation of atmospheric circulation patterns known\\u000a as teleconnections. Previous work showed that an annually resolved 301-year ice core record of annual snow accumulation from\\u000a a highelevation site on Mount Logan in northwestern

G. W. K. Moore; Keith Alverson; Gerald Holdsworth

2004-01-01

343

Glacial Dynamics and Deglaciation Pattern of the Svalbard ice Sheet From Seafloor Morphology  

NASA Astrophysics Data System (ADS)

The configuration and dynamics for the Svalbard Ice Sheet (SIS) have been reconstructed on the basis of detailed and regional bathymetric data acquired in the fjords and continental shelf of Svalbard. The main drainage routes along the margins of the former Svalbard Ice Sheet have been identified as the major fjords and their connected cross-shelf troughs that extend to the shelf edge. On the west coast of Svalbard four major ice sheet outlet systems existed; Hornsund and Hornsundrenna, Bellsund (Van Keulen/Van Mijen), Isfjorden and Isfjordrenna, Kongsfjorden and Kongsfjordrenna. Along the northern Svalbard margin three major systems exist; Woodfjorden-Moffenrenna, Wijdefjorden-Hinlopenstredet and Kvitoyrenna. Storfjorden drained the southern and eastern part of the Svalbard Ice Sheet as well as parts of Barentsoya and Edgeoya and parts of the northeastern Barents Sea Ice Sheet. In the cross-shelf troughs an extensive pattern of glacial lineations record fast ice flow or palaeo-ice streams. Lateral ice stream moraines several tens of kilometres in length have been mapped along the margins of some of these cross-shelf troughs, identifying the border zone between fast ice flow and stagnant or slow-flowing ice on intervening shelf banks. A grounding zone for the SBIS has been mapped on the shelf edge some 10-20 km off the NW Svalbard coast. The grounding zone probably locates the maximum position of the SIS during the LGM, and shows that the LGM glaciers did not enter the adjacent Yermak Plateau. A large system of retreat moraines on the shallow bank areas on the shelf west and north of Svalbard have been mapped. The moraines are largely parallel with the coast line, and based on these ridges and the general sea floor morphology a new model for the deglaciation of western Svalbard is suggested.

Ottesen, D.; Dowdeswell, J.; Landvik, J.; Mienert, J.

2005-12-01

344

Dust Provenance and Radiometric U-Series Ages as Evidence for an Eemian Ice Sheet in Greenland  

Microsoft Academic Search

The mineralogy and geochemistry of air-transported mineral particles, dust, reflect the prior history of the source material as well as influence the chemistry of the settling locations (rivers, ice sheets and ultimately the oceans). When applied to ice sheets, the atmospheric circulation patterns gleaned from the chemical characteristics of the dust may provide some additional constraints on size and shape

S. Aciego; B. Bourdon; J. Schwander; T. F. Stocker

2009-01-01

345

Phylogeographic Analysis Elucidates the Influence of the Ice Ages on the Disjunct Distribution of Relict Dragonflies in Asia  

PubMed Central

Unusual biogeographic patterns of closely related groups reflect events in the past, and molecular analyses can help to elucidate these events. While ample research on the origin of disjunct distributions of different organism groups in the Western Paleartic has been conducted, such studies are rare for Eastern Palearctic organisms. In this paper we present a phylogeographic analysis of the disjunct distribution pattern of the extant species of the strongly cool-adapted Epiophlebia dragonflies from Asia. We investigated sequences of the usually more conserved 18 S rDNA and 28 S rDNA genes and the more variable sequences of ITS1, ITS2 and CO2 of all three currently recognised Epiophlebia species and of a sample of other odonatan species. In all genes investigated the degrees of similarity between species of Epiophlebia are very high and resemble those otherwise found between different populations of the same species in Odonata. This indicates that substantial gene transfer between these populations occurred in the comparatively recent past. Our analyses imply a wide distribution of the ancestor of extant Epiophlebia in Southeast Asia during the last ice age, when suitable habitats were more common. During the following warming phase, its range contracted, resulting in the current disjunct distribution. Given the strong sensitivity of these species to climatic parameters, the current trend to increasing global temperatures will further reduce acceptable habitats and seriously threaten the existences of these last representatives of an ancient group of Odonata.

Busse, Sebastian; von Grumbkow, Philipp; Hummel, Susanne; Shah, Deep Narayan; Tachamo Shah, Ram Devi; Li, Jingke; Zhang, Xueping; Yoshizawa, Kazunori; Wedmann, Sonja; Hornschemeyer, Thomas

2012-01-01

346

Late Holocene Environment in the Lower Hudson Valley, New York: Medieval Warming, Little Ice Age, and European Impact  

NASA Astrophysics Data System (ADS)

Two sediment cores from Piermont Marsh, located in the southern Hudson River Valley, provide a well-dated bi-decadal record of vegetation, climate, land use, and fire frequency. The classic Medieval Warm Period is evident through striking increases in charcoal and Pinus dominance from A.D.800-1350, paralleling records southward along the Atlantic seaboard. Higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions. Increases in Picea and Tsuga with corresponding decreases in Liquidambar, coupled with increasing organic percentages due to cooler, moister conditions indicate the presence of the Little Ice Age. European impact is manifested by increased weedy plant cover (i.e., Ambrosia, Plantago, and Rumex), decline in arboreal pollen due to land clearance, and increase in inorganic particles to the watershed. Radionuclide dating using Cs-137 and Pb-210 from the southern end of the marsh shows that little disturbance of sediments has occurred, adding validity to the high resolution results and supporting the sedimentation rates obtained using radiocarbon dating. Comparison with other marsh records in the Hudson River estuary shows general agreement in chronology with interesting differences in species changes and sedimentation rates.

Pederson, D. C.; Peteet, D. M.; Kurdyla, D.; Guilderson, T.

2004-05-01

347

Tropical Atlantic climate response to low-latitude and extratropical sea-surface temperature: A Little Ice Age perspective  

NASA Astrophysics Data System (ADS)

Proxy reconstructions and model simulations suggest that changes to the interhemispheric sea surface temperature (SST) gradient lead to southerly Intertropical Convergence Zone (ITCZ) migrations during periods of North Atlantic cooling. The Little Ice Age (LIA; ~100-450 yBP) was a recent interval of widespread North Atlantic cooling. Evidence suggesting that low-latitude Atlantic cooling during the LIA was relatively small (<1°C) raises the possibility that the ITCZ may have responded to a hemispheric SST gradient originating in the extratropics. We use an atmospheric general circulation model (AGCM) to investigate the relative influence of low-latitude and extratropical SSTs on the meridional position of the ITCZ. Our results suggest that the ITCZ responds primarily to local, low-latitude SST anomalies and that small cool anomalies (<0.5°C) can reproduce the LIA precipitation pattern suggested by paleoclimate proxies. Conversely, even large extratropical cooling does not significantly impact low-latitude hydrology in the absence of ocean-atmosphere interaction.

Saenger, C. P.; Chang, P.; Ji, L.; Oppo, D.; Cohen, A. L.

2009-12-01

348

Nd isotope signature of Holocene Baltic Mn/Fe precipitates as monitor of climate change during the Little Ice Age  

NASA Astrophysics Data System (ADS)

Neodymium (Nd) isotope profiles were analyzed on two Baltic Mn/Fe precipitates (99/2 and TL1) from shallow water (20 m) of the Mecklenburg Bay. The age range of these Mn/Fe precipitates determined by 226Raex/Ba dating reaches from recent growth back to ˜4300 and 1000 yr BP, respectively. Over this time range, the Nd isotope composition varies from ?Nd (0) = -13.1 to -17.5 in the selected Baltic precipitates indicating substantial changes in the Nd isotope composition of the Baltic Sea. The lowest ?Nd values were recorded during the time interval of the Little Ice Age (LIA, AD ˜1350 to 1850). These minimum values indicate either an increase of the input of less radiogenic Nd from Scandinavian Archean-Proterozoic sources (?Nd about -22) to the Baltic Sea or a decrease of the input of more radiogenic Nd from continental European sources (?Nd about -12) and/or North Sea water (?Nd about -10). Variations of both, erosive continental input and North Sea inflow may indicate a direct response of the Nd isotope signal in the Baltic Sea to climate changes during the LIA and be related to cyclic shifts in the atmospheric circulation triggered by the North Atlantic Oscillation (NAO). Another aspect that possibly influenced the input of trace elements and Nd isotopes into the Baltic Sea is the population development in the circum Baltic area during the LIA. The lowest ?Nd values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland. The reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the Baltic Sea by rivers which in turn may have resulted in a change of the Nd isotope composition of Baltic Sea water.

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

2005-05-01

349

Benthic foraminiferal ?18O in the ocean's temperature-salinity-density field: Constraints on Ice Age thermohaline circulation  

NASA Astrophysics Data System (ADS)

Benthic ?18O data from 95 core sites are used to infer possible temperature-salinity (T-S) fields of the Atlantic and Pacific oceans at the Last Glacial Maximum (LGM). A constraint of stable density stratification yields logically consistent scenarios for both T and S. The solutions are not unique but are useful as a thinking tool. Using GEOSECS data, we solve for the modem relationship between ?18Owater (?w) and salinity in the deep sea: ?w (SMOW) = 1.529 * S - 53.18. As a starting point, we assume that the slope of this equation applies to LGM conditions and predict ?18Ocalcite (?c) gradients in equilibrium with probable T-S fields of LGM deep and bottom waters. Benthic foraminiferal ?18O data from the deep Pacific (2-4 km depth), and the bottom Atlantic (> 4 km depth), are 0.1-0.2‰ lower than from the deep Atlantic (2-4 km depth) at the LGM. If the modern ?w-S slope applies, Atlantic deep and bottom waters were more dense than Pacific deep waters. This assumption would imply bottom waters both fresher (?S >0.5) and colder (?T ˜3°C) than overlying deep waters, in conflict with other data, suggesting ice age deep water much colder than at present. It is also possible that the observed ?c gradients are an artifact of laboratory intercalibration. If Atlantic deep and bottom water ?c values were similar to deep Pacific values, this would be consistent with the hypothesis of a stronger southern ocean versus North Atlantic source for deep-ocean ventilation at the LGM. Taking the observed gradients at face value, however, a solution could be that the LGM ?w-S slope in deep and bottom waters was higher than at present, conceivably because of a stronger contribution of salt to the deep ocean via more intense sea ice freezing. This would allow Pacific deep waters and Atlantic bottom waters to have a common source, again in the Antarctic. Both would be more dense than Atlantic deep waters, even though the deep waters were much colder than at present. To better constrain these inferences drawn from the spatial distribution of benthic ?18O, we must reduce scatter in the ?18O data with more high-quality measurements in high sedimentation rate cores. This is especially true at bottom water sites. Also, we must intercalibrate mass spectrometers at different isotope laboratories more accurately, to insure our isotope data are compatible.

Zahn, Rainer; Mix, Alan C.

1991-02-01

350

Little Ice Age and recent treeline fluctuations at the Columbia Icefield, Alberta  

SciTech Connect

Vegetation dynamics at two treeline sites (north- and south-facing) were reconstructed using tree-ring and age-structure studies. Trees, seedlings and snags were mapped in two, 30m x 275m plots running upslope from continuous forest to alpine tundra. The Athabasca Glacier advanced against the base of the south-facing slope ca. 1714 and in the 1840`s. Snags on this slope indicate that treeline was higher than present prior to ca. 1200 A.D. and between 1400-1700 A.D. Many trees died between 1650-1700 A.D. during the advance of the Athabasca Glacier. Tree establishment took place in the late 1700`s and the 1800`s as well as during periods of warmer climate in the 1940`s and 1960`s. Both Picea engelmannii and Abies lasiocarpa form treeline at this site. On the north-facing slope (8 km south) treeline dynamics are different. A. lasiocarpa dominates the vegetation and P. engelmannii is rare. There is no strong evidence of historical fluctuations of treeline at the north-facing site. Tree establishment is primarily due to expansion of tree clumps by layering at the north-facing site, whereas treeline expansion at the south-facing site is due to seedling establishment. At both sites tree establishment by seed appears to be limited to periods of warmer climate, whereas population expansion by layering occurs continuously.

Kavanagh, T.A.; Luckman, B.H. [Univ. of Western Ontario, London (Canada)

1995-06-01

351

Modern and Little Ice Age equilibrium-line altitudes on Outlet Valley glaciers from Jostedalsbreen, western Norway: An evaluation of different approaches to their calculation  

SciTech Connect

The modern and Little Ice Age (LIA) equilibrium-line altitude (ELA) of 20 outlet valley glacier from Jostedalsbreen, western Norway, has been calculated using different approaches. Using an accumulation area ratio (AAR) of 0.6 [+-] 0.05 gave a mean little Ice Age ELA depression of 70 m. A method developed by M. Kuhle, taking the influence by topography into account gave a mean ELA depression of 35-255 m, the median elevation of glaciers 115 m, and the toe-to-headwall altitude ration 140 m. Differences in the ELA estimates can be attributed to the differences in topography and morphology of the glaciers. The AAR method appears to provide the most reliable results. This will aid in determining mean global temperatures during the LIA. 34 refs., 9 figs., 5 tabs.

Torsnes, I.; Rye, N. (Univ. of Bergen (Norway)); Nesje, A. (Univ. of Bergen, Bergen-Sandviken (Norway))

1993-05-01

352

Simulation of the surface temperature anomalies in the North Hemisphere during the last 300 years of the Little Ice Age using a thermodynamic model.  

NASA Astrophysics Data System (ADS)

The last 300 years of the Little Ice Age, are characterised by two minimum in total solar irradiance (TSI): known as Maunder Minimum and Dalton Minimum, during which the reconstruction of surface temperature show anomalies smaller than -0.7°C. The experiments with a energy balance model called Thermodynamic Climate Model (TCM), show that the changes in CO2 and TSI at the end of the Little Ice Age, relative to period 1961-1990, have a significant effect in the descent of temperature, mainly in the Maunder Minimum major to 0.2°C. Nevertheless the incorporation of changes in low cloud cover, which we assumed are induced by the galactic cosmic ray flux, which varies inversely with solar activity, produced the greater descent of the surface temperature in the North Hemisphere. The results of the TCM are corroborated trough a comparison with the reconstruction of surface temperature anomalies developed by some authors.

Mendoza, V. M.; Mendoza, B.; Garduño, R.; Adem, J.

2009-04-01

353

Glacial recession in the Tropical Andes from the Little Ice Age: the case of Ampato Volcanic Complex (Southern Peru  

NASA Astrophysics Data System (ADS)

Data published over the last decade reveal substantial glacial recession in the tropical Andes since the Little Ice Age (LIA), (Ramirez, et al., 2001; Rabatel, et al., 2005; Rabatel, et al., 2008; Vuille, et al., 2008; Hastenrath, 2009; Jomelli, et al., 2009), and a growing rate of recession since the 1980’s caused by global warming (Ramirez, et al., 2001; Vuille, et al., 2008). Today there is great interest in the evolution of these ice masses due to heightened awareness of climate change and of the strategic importance that glaciers have as a hydrologic resource for communities in arid climate zones in the tropical Andes (Mark, 2008; Vuille et al., 2008). Cordillera Blanca forms part of the Andes Mountains of northern Peru, and is a chosen site for many studies on glacier evolution. Vuille et al. 2008 determined that a considerable area of ice mass was lost at Huascarán-Chopicalqui glacier (18% from 1920-1970) and Astesonraju glacier (20% from 1962-2003). Studies at Coropuna volcano, which has the most extensive glacier field in the western range of southern Peru, also report a strong melting trend that began with only minimal recession from 1955-1986 (4%), but increased to 14% from 1986-2007 (Úbeda et al., 2009). Only a few of the Andes glaciers are consistently monitored, and the most comprehensive data are for Chacaltaya and Zongo glaciers (16º S) in Bolivia. Since the maximum LIA, Chacaltaya has lost 89% of its surface area, particularly in recent years. By 1983, the totaled loss was five times the shrinkage for the period 1940-1963 (Ramirez, et al., 2001). Zongo glacier maintained equilibrium from 1956-1975, but later experienced a period dominated by continuous recession (Soruco, et al., 2009). This study expands current knowledge of glacier evolution since the LIA in the Central Volcanic Zone (CVZ; 14º - 27º S) (Stern, 2004) of the Andes. The study site was chosen in an area that had never been used for preliminary research of this type, concretely the Ampato volcanic complex (15º24´- 15º 51´ S, 71º 51´ - 73º W; 6.288 masl), one of the most important complexes of the northern sector of the CVZ. Photointerpretation of aerial photographs and teledetection through satellite images of Huayuray Valley (15º 41´ 14´´ S - 71º 51´ 53´´ W), located to the north of the complex, aided in accurately reconstructing the area occupied by the ice mass at different times (LIA, 1955, 2000 and 2008). Also the paleo-ELA (Equilibrium Line Altitude) and the ELA were calculated using the Accumulation Area (AA) method (Kaser and Osmaston, 2002; Osmaston, 2005) in a GIS. The ELA shows the relationship between climate and glacier mass balance (González Trueba, 2005). The data from Huayuray Valley show that the glaciers reached a minimum altitude of 5400 masl and covered an area of ~2.81 Km2 during the LIA. The paleo-ELA was located at ~5780 masl, ~120 m below the current ELA (~5900 m). Based on a vertical thermal gradient of 0.65ºC/100 m, the temperature during this event would have been about 0.7º C colder than present temperature in the Ampato volcanic complex. In 1955, Huayuray glacier covered ~2.45 km2, 12.8% less than in the LIA. In the same year, the glaciers in the Huayuray valley reached a minimum elevation of ~5660 masl and the ELA rose ~20 m, to 5800 masl. In only 45 years (1955 - 2000) the surface area of the ice was significantly reduced (~1 km2), i.e. 40.8%. The ELA continued to rise, until it reached 5890 masl in 2000. From 2000 - 2008, the Huayuray glacier was reduced to ~0.78 km2 and the ELA rised ~10 m to reach the 5900 masl These results from the CVZ confirm the dramatic recession of the glaciers in the tropical Andes during recent decades. They also suggest that if the rate of recession associated with the period 2000-2008 continues, glaciers in the Ampato volcanic complex will disappear in 10 years approximately. References González Trueba, J.J. (2005): La Pequeña Edad del Hielo en los Picos de Europa (Cordillera Cantábrica, NO de España). Análisis morfológico y reconstrucción del avance

Alcalá, J.; Palacios, D.; Zamorano, J. J.

2010-03-01

354

Aircraft Icing  

Microsoft Academic Search

Full-scale icing experiments and, therefore, certification time and cost can be significantly reduced by developing calculation methods to evaluate the aircraft and system performance for a wide range of icing conditions. This article summarizes calculation methods for icing that include ice accretion, ice system performance, and icing effects on aircraft.

Tuncer Cebeci; Fassi Kafyeke

2003-01-01

355

Multiple, discrete till sheets created in differently sourced ice streams are deposited in the Des Moines lobe, USA  

NASA Astrophysics Data System (ADS)

During review of the deposits of the Des Moines lobe--linked to drawdown of the southern Laurentide ice sheet--seven (upstream) and five (downstream) tills were distinguished within what had been considered a more homogenous deposit. Using lithology of the 1-2 mm sand fraction and texture of over 12,000 samples, several discrete till sheets were correlated for over 1,000 kilometers parallel to the flow direction. Lateral boundaries of till sheets are marked by abrupt lithologic and textural discontinuities and subtle geomorphic features including a broad, flow-parallel ridge overlain by pockets of sorted sediment. Deeply scalloped portions of moraine segments correspond to individual till sheets; cross-cutting subglacial landforms appear in areas where tills of similar age overlap; a till sheet is compositionally and texturally uniform in vertical section except for the lowermost few centimeters. We suggest that unique till sheets are created by ice from different ice-stream source areas, each with unique bed lithology. Substrate is incorporated and till homogenized where ice streams are confined by the ice sheet, but till is just exported as ice moves beyond these confines. A reduction in basal shear stress decreases the thickness of the deforming horizon, deposits till from the bottom up, and eliminates incorporation of new material. Independent behavior of flow zones derives from the activity of the ice stream source areas as well as the ability of the ice receiving area to maintain inherited initial conditions, i.e. ice thickness, velocity, and water pressure. Interplay between ice streams while still in the ice shed (e.g., capture) affects till provenance over time, but these changes take time to be transmitted down-ice and will result in a more subtle admixture of material. Contrasting velocity and/or ice thickness of neighboring flow zones may be apparent. The broad, flow-parallel ridge is interpreted as a subglacial feature, evidenced by oriented, striated clasts, overlain by sorted sediment that must have concentrated in an ice-surface low between two ice flows of contrasting velocity or thickness. The transverse- to diagonal- orientation of flanking stagnation landforms is consistent with the crevasse pattern expected in the stress field of a shear zone. Evidence of flow zones stagnating at different times comes from widespread ponding of meltwater over a zone that was confined by a more active ice flow. Ice margins are marked by a thickening of the till sheet, with basal melt-out till capped by supraglacial debris. This is interpreted as a result of freezing-on of subglacial material as ice slows and then stagnates. Sudden loss of subglacial water could help produce an ice-marginal thrust block and lead to subsequent incorporation of underlying, older material if thrust blocks with a deep detachment surface are overridden.

Jennings, C. E.; Lusardi, B. A.; Harris, K. L.

2008-12-01

356

Sea Ice  

NSDL National Science Digital Library

In this resource, students will discover that there are notable differences between sea ice and fresh-water ice, such as density. In on segment, students learn that the first sign of freezing on the sea is an oily appearance of the water caused by the formation of needle-like crystals. The site explains the relationship between growth and the rate at which heat flows from the water and that the ice pack can alter its shape and dimension due to the movement of winds, currents, thermal expansion, and contraction of the ice. Types of ice described here include new ice, nilas, young ice, first-year ice, and old ice while the forms of ice covered include pancake ice, brash ice, ice cake, floe, and fast ice. The site also explains the meteorological and oceanographic factors that control the amount and movement of ice.

357

Ice Age Sea Level Change: Lessons From Studies of the Mid-Pliocene Climate Optimum, the Last Glacial Maximum and the 20th Century.  

NASA Astrophysics Data System (ADS)

Renewed interest in geophysical models of ice age sea-level change has been motivated by three factors. First, the theory underlying these models has been progressively improved to take into account more complex viscoelastic Earth models and processes such as shoreline migration, changes in the extent of grounded marine-based ice sectors, and the impact on sea level of contemporaneous perturbations in the Earth's rotation. Second, results generated from these state-of-the-art models have highlighted the important information inherent to the geographic variability of sea-level change - information that is lost in analyses that are based on global (i.e., eustatic) averages. Third, there has been growing appreciation, through the application of the geophysical models, that accurate analyses of ancient sea level data sets can help to inform our understanding of future ice sheet stability in a warming world. In this talk we begin by summarizing a series of recent improvements in post-glacial sea-level theory and describe several applications that highlight important pitfalls in any effort to map sea-level measurements into estimates of past ice volumes. These applications include, in particular, studies of sea-level records from the mid-Pliocene climate optimum and the Last Glacial Maximum. We end by discussing an ongoing effort to use the geographic variability of rates obtained from tide gauge data and satellite altimetry records to estimate the dominant contributors to modern sea-level change.

Mitrovica, J. X.; Raymo, M. E.; Morrow, E.; Hay, C.

2011-12-01

358

36Cl Exposures Ages and Equilibrium Line Altitude (ELA) of the Ampato Volcanic Complex (Southern Peru).  

NASA Astrophysics Data System (ADS)

In this work we present the results obtained from the reconstruction of the ancient glacial Equilibrium Line Altitude (paleoELA) and the dating of various glacial phases on the Ampato volcanic complex (15°24´S-15°51´S, 73° W; 6.288 m asl), in the Central Andes. In order to calculate the paleoELAs we used two methods: the Accumulation Area Ratio (AAR) and the Area X Altitude Balance Ratio (AABR). The dating was obtained by cosmogenic methods (36Cl). We sampled: 1) boulders, in a stable position, larger than 1m and located on the crest of the moraines; and 2) polished and striated bedrock outcrops, which indicate the retreat of ice. In every studied valley we found voluminous moraines related to the Local Last Glacial Maximum of the Pleistocene (LLGMP). The dating obtained from the sampled boulders ranges from 17.9 ± 0.1 to 13.6 ± 0.1 kyr. We estimate that the most significant deglaciation process started at 12 ka on the Ampato volcanic complex and adjacent areas also covered by ice, such as the Patapampa altiplano. In certain valleys we found re-advance moraines such as in Huayuray valley, located on the Northern slope of the volcanic complex, dated at 11.4 ± 0.21 kyr. The last generalised advance is related to the Little Ice Age (LIA). During this event the glaciers formed small moraines which are close to the current glacial fronts. In Huayuray valley we estimated a paleoELA (AAR) of ~5,200 m during the LLGMP asl and ~5.810 m asl during the LIA. Similar data was obtained using the AABR method: ~5.150 m asl during the LLGMP, and ~5.750 m asl during the LIA. In Mollebaya valley (East face of the volcanic complex) the paleoELA (AAR) during the LLGMP was at ~5.350 m asl and during the LIA it reached ~5.740 m asl. Using the AABR method the LLGMP and LIA paleoELAs are ~5.070 and ~5.700 m asl, respectively. In Pujro-Huayjo valley, to the Soutwest, the paleoELA (AAR) during the LLGMP was ~5.390 m asl. LIA moraines are absent in this valley. We calculated the ELA from the glacier in 1955 at ~5.725 m asl. Using the AABBR method, the ELA was lower: ~4.940 m asl during LLGMP and ~5.635 m asl in 1955. Finally, in the Mucurca valley, West face of the volcanic complex, the LLGMP paleoELA was at ~4.930 m asl and at 5.100 m asl during the most recent advance (Lateglacial phase). Using the AABR method we obtained a value of ~4.865 m asl for the LLGMP paleoELA and ~5.015 m asl for the Late glacial phase. On average the the LLGMP ELA was 5220 m asl (AAR) and 5010 m asl (AABR). Based on the modern (1955) ELA from Pujro-Hayjo valley, the LLGMP ELA lowering was ~550 m (AAR) and ~625 m (AABR). Research funded by CGL2009-7343 project, Government of Spain.

Alcalá, J.; Palacios, D.; Vázquez-Selém, L.

2012-04-01

359

Vegetation and fire dynamics in different geological settings since the last ice age, Klamath Mountains, northwestern, CA  

NASA Astrophysics Data System (ADS)

The Klamath Mountains of northwestern California are a floristic hotspot and their diversity likely results from a combination of geological, ecological and historical factors (e.g., long-term climate change). To evaluate how climate change has influenced past composition, structure, and disturbance regime of the Klamath forests in different geological settings, vegetation and fire histories from four sites, Bolan (1), Sanger (in prog.), Campbell (in prog.), and Bluff (2) lakes are compared. Bolan and Sanger lakes are underline by nutrient-rich diorite soils, Campbell Lake by nutrient-poor and poorly-drained soils derived from mudstone and shales and Bluff Lake by ultramafics which pose severe nutrient limitations to plants. All sites experience the same modern climate and vegetation. The vegetation and fire records from the four sites suggest that substrates have influenced the sensitivity of plant communities and fire regimes to past variations in climate. Cool, dry late-glacial (>11ka cal yr BP) conditions resulted in a subalpine parkland in the Klamath region. P. jeffreyi and Abies were the main tree species at Bluff Lake and fires occurred frequently. Campbell Lake supported more species than Bluff (excluding P. jeffreyi) such as P. monticola, Picea and T. mertensiana and experienced few fires. Bolan and Sanger Lake harbored similar species as Campbell, as well as a small population of Pseudotsuga and experienced few fires. Warm, dry Early Holocene (7-11ka cal yr BP) conditions led to an increase in C. decurrens and a slight decrease in P. jeffreyi at Bluff Lake than before and fires were very frequent. At Campbell Lake, P. monticola increased, C. decurrens became more abundant than before, and Abies, Picea and T. mertensiana were scarce. Similar vegetation occurred at Bolan and Sanger lakes although the sites continued to harbor Pseudotsuga. Campbell, Bolan and Sanger all experienced frequent fires. Cool, wet conditions in the Middle Holocene (3-7ka cal yr BP) allowed P. jeffreyi to increase at the expense of C. decurrens at Bluff Lake. At Campbell, Sanger and Bolan lakes there was a decrease in P. monticola and a significant increase in Abies than before. Bolan and Sanger lakes still maintained a significant population of Pseudotsuga. Fire frequency at all sites was moderate. Modern (3ka cal yr BP to present) climate conditions in the Late Holocene resulted in increases in P. jeffreyi and Abies than before at Bluff Lake. P. monticola and Abies were abundant at Campbell Lake with minor amounts of Pseudotsuga and T. mertensiana. Most tree species occurred at Bolan and Sanger Lake (with the exception of P. jeffreyi at both sites and T. mertensiana at Sanger Lake). Abies and P.monticola were the primary species in the Bolan, Sanger and Campbell lake forests. Fires were frequent at all sites. In conclusion, Bluff Lake was dominated by ultramafic tolerant taxa such as Pinus jeffreyi, Calocedrus decurrens and Abies, while Bolan and Sanger lakes harbored mostly ultramafic intolerant species such as Pinus monticola, Pseudotsuga, Picea, and Tsuga mertensiana since the last ice age. The forest at Campbell Lake was more open, was dominated by Pinus monticola and had less Picea and T. mertensiana than Bolan and Sanger lakes since the last ice age. REFS. 1 Briles, C. et al 2005. Quaternary Research 64. 2 Mohr, J.A. et al 2000. The Holocene 10.

Briles, C.; Whitlock, C.; Bartlein, P.

2006-12-01

360

Tropical North Atlantic Coral-Based Sea Surface Temperature and Salinity Reconstructions From the Little Ice Age and Early Holocene  

NASA Astrophysics Data System (ADS)

Understanding the magnitude and spatial extent of tropical sea surface temperature (SST) cooling during the Little Ice Age (~1400-1850 A.D.; LIA) is important for elucidating low-latitude paleoclimate, but present estimates are poorly constrained. We used Sr/Ca and ?18O variability within the aragonitic skeleton of the coral genus Montastrea to reconstruct SST and sea surface salinity (SSS) during the LIA and early Holocene (EH) in the tropical Atlantic. Four seasonally-resolved coral Sr/Ca records from St. Croix, U.S. Virgin Islands, and Bermuda indicate SST is highly correlated (r2 = 0.94) with modern Montastrea Sr/Ca and mean annual coral extension. A Sr/Ca -SST calibration that combines temperature and growth rate effects on coral Sr/Ca was applied to fossil St. Croix corals to reconstruct Caribbean climate during 5-10 year intervals of the LIA (440 ± 30 yBP) and EH (7200 ± 30; EH). Contrary to previous coral-based LIA proxy reconstructions, we find mean SST during the LIA was similar to today, but approximately 1.2°C cooler during the EH. Both periods exhibited higher amplitude seasonal variability indicating other SST estimates may be seasonally biased. Based on residual coral ?18O, we find the LIA and EH were saltier, which suggests previous cooling estimates of 1-3°C relative to today may be exaggerated by changes in seawater ?18O. Our results are consistent with a southerly migration of the Intertropical Convergence Zone (ITCZ) during the LIA, but their corroboration requires longer, high-resolution proxy reconstructions that place our two brief multi-annual coral records from the LIA and EH, respectively, within the context of multi-decadal variability.

Saenger, C.; Cohen, A.; Oppo, D.; Hubbard, D.

2006-12-01

361

Microbial community structure in moraine lakes and glacial meltwaters, Mount Everest.  

PubMed

The bacterial diversity and abundance in two moraine lakes and two glacial meltwaters (5140, 5152, 5800 and 6350 m above sea level, respectively) in the remote Mount Everest region were examined through 16S rRNA gene clone library and flow cytometry approaches. In total, 247 clones were screened by RFLP and 60 16S rRNA gene sequences were obtained, belonging to the following groups: Proteobacteria (8% alpha subdivision, 21% beta subdivision, and 1% gamma subdivision), Cytophaga-Flavobacteria-Bacteroides (CFB) (54%), Actinobacteria (4%), Planctomycetes (2%), Verrucomicrobia (2%), Fibrobacteres (1%) and Eukaryotic chroloplast (3%), respectively. The high dominance of CFB distinguished the Mount Everest waters from other mountain lakes. The highest bacterial abundance and diversity occurred in the open moraine lake at 5152 m, and the lowest in the glacial meltwater at 6350 m. Low temperature at high altitude is considered to be critical for component dominancy. At the same altitude, nutrient availability plays a role in regulating population structure. Our results also show that the bacteria in Mount Everest may be derived from different sources. PMID:17107422

Liu, Yongqin; Yao, Tandong; Jiao, Nianzhi; Kang, Shichang; Zeng, Yonghui; Huang, Sijun

2006-12-01

362

Ice, Ice, Baby!  

NASA Astrophysics Data System (ADS)

The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an outreach program based on hands-on activities called "Ice, Ice, Baby". These lessons are designed to teach the science principles of displacement, forces of motion, density, and states of matter. These properties are easily taught through the interesting topics of glaciers, icebergs, and sea level rise in K-8 classrooms. The activities are fun, engaging, and simple enough to be used at science fairs and family science nights. Students who have participated in "Ice, Ice, Baby" have successfully taught these to adults and students at informal events. The lessons are based on education standards which are available on our website www.cresis.ku.edu. This presentation will provide information on the activities, survey results from teachers who have used the material, and other suggested material that can be used before and after the activities.

Hamilton, C.

2008-12-01

363

Measuring U-Series Isotopes in Polar Ice: Toward an Absolute Ice Chronometer  

Microsoft Academic Search

Comparison of ice records between ice sheets, alpine glaciers, and marine records currently rely on a combination of ice layer counting, matching relative time scales, and interpolation. U-series recoil from mineral aerosols (dust) into the ice matrix is one possible technique for determining the absolute age of ice, independent of any other parameters. However, the low concentrations of the U-series

S. M. Aciego; B. Bourdon; J. Schwander; T. Stocker

2007-01-01

364

GRACE satellite data and cosmogenic exposure ages in Enderby Land, Antarctica: ice mass increase or uncorrected post-glacial rebound?  

NASA Astrophysics Data System (ADS)

Measuring present day changes in the volume of the Antarctic ice sheet has traditionally been difficult, due to its remote nature and vast size. Over the past decade, the GRACE (Gravity Recovery and Climate Experiment) and ICEsat (Ice, Cloud and land Elevation) satellite systems have vastly improved these measurements by accurately measuring changes in the gravity exerted by the ice sheet, and the ice sheet surface height respectively. However, data sets from both these systems require various corrections related to an understanding of the rate of post-glacial rebound across the continent in order to make accurate measurements of ice loss or gain. GRACE measurements have consistently observed a substantial apparent gain in ice mass in the Enderby Land region of East Antarctica (e.g. Chen et al., 2006). This large region has until recently been given little attention and there is an absence of detailed geomorphic and geologic studies with no present-day assessment of uplift. This in turn places some doubt on the implications of the Enderby Land GRACE data and its relationship to modern day climate change. To address this problem, a reconnaissance survey to the Rayner Glacier region in Enderby Land was conducted during Polarstern Cruise ANT XXIII/9 in 2007. Observations of relatively unweathered erratics on Demidov Island and the Condon Hills provided strong evidence that the Rayner Glacier has lowered by at least 400 m, and retreated by at least 10 km during the late Quaternary. 10Be and 26Al dating of erratics and bedrock collected from three sites during this survey indicate that this deglaciation occurred early in the Holocene (~7 to 9 ka BP), and that ice retreat and lowering were effectively synchronous. The timing of this deglaciation is about the same as that used to model the post-glacial rebound in previous GRACE measurements (Ivins and James, 2005). However, these models assumed as little as 1-200 m of ice loss at this time, which is much less than that observed in the field. Thus, it is likely that the post-glacial rebound model underestimates the required correction in this area. This in turn, will mean that the overall rate of mass loss calculated by GRACE measurements that have been corrected using the Ivins and James post-glacial rebound model will underestimate the true rate of modern ice loss in East Antarctica. Chen, J.L., Wilson, C.R., Blankenship, D.D., Tapley. B.D., 2006. Antarctic Mass rates from GRACE, Geophysical Research Letters, 33, L11502. Ivins, E., James, T., 2005. Antarctic glacial isostatic adjustment: a new assessment. Antarctic Science, 17 (4), 541-553.

White, Duanne; Fink, David; Winkler, Stephan

2010-05-01

365

Question of Ages of Cenozoic Volcanic Centers Inferred Beneath the West Antarctic Ice Sheet (WAIS) in the West Antarctic Rift System (WR) from Coincident Aeromagnetic and Radar Ice Sounding Surveys  

NASA Astrophysics Data System (ADS)

The recently acquired radar ice sounding surveys (Holt, et al., 2006) extending the 1990s Central West Antarctica (CWA) aerogeophysical survey to the Amundsen and Bellingshausen sea coasts allows us to revise a thought experiment reported by Behrendt et al., 1991 from very limited bed elevation data. Were the ice of the WAIS flowing through the WR to be compressed to the density of crustal rock, almost all of the area beneath the WAIS would be at or above sea level, much >1 km elevation. There are only about 10-20% of the very deep areas (such as the Bentley subglacial trench and the Byrd Subglacial Basin) filled with 3-4-km thick ice that would be well below sea level. The age of the 5-7-km high rift shoulder bounding the asymmetric WR from northern Victoria Land through the Horlick Mountains (where it diverges from the Transantarctic Mountains) to the Ellsworth Mountains has been reported as old as Cretaceous. Volcanic exposures associated with the West Antarctic rift system in the present WAIS area extend at least to 34 Ma and the West Antarctic ice sheet has flowed through the rift possibly as far back in time as 25 Ma. Active volcanism has been reported for the WR at only a few widely scattered locations, so speculations about present volcanic activity beneath the WAIS are quite uncertain, and it is probably quite rare. The Central West Antarctic aeromagnetic and radar ice sounding survey carried out in the 1990s revealed about 1000 "volcanic centers" characterized by 100-1000 nT shallow source magnetic anomalies, at least 400 of which have associated bed topography. About 80% of these show relief <200 m and have been interpreted as smoothed off as they were erupted (injected) into the moving WAIS. Several kilometer-thick highly magnetic sources are required to fit these anomalies requiring high remanent magnetizations in the present field direction. We interpreted these sources as subvolcanic intrusions which must be younger than about 100 Ma because the Antarctic plate has been in its approximately present position since that time. Eighteen anomalies have >600 bed relief and were interpreted as erupted subaerially at a time when the WAIS was absent. At least one of these subaerially erupted peaks (Mt. Resnik, having 2 km bed relief) was erupted through a magnetic reversal. About 100 "volcanic" anomalies show reversed magnetic polarization indicating these must be at least as old as the Brunes-Matayama reversal at about 780 Ka. Essentially no volcanic rocks or detritus has been reported from the few drill holes that have penetrated the WAIS, although some have speculated, from the presence of smectite recovered from rock cores into the Ross Sea continental shelf, that this mineral has resulted from alteration of volcanic rock erupted beneath the WAIS. We consider the absence of volcanic samples from beneath the WAIS is not evidence of their absence. This seems particularly true considering the long time of the apparently coincident volcanism beneath the WAIS, possibly as great as 25 Ma, and the relatively brief age of the ice presently comprising the WAIS, about 200 Ka at most (e.g. perhaps the bulk of the volcanic centers are >10 Ma). Because none of the volcanic rocks or subvolcanic intrusions inferred to underlie the "volcanic centers" marked by high amplitude anomalies and low relief bed topography has been directly sampled, the question of their age cannot be answered.

Behrendt, J. C.; Finn, C. A.; Blankenship, D. D.

2007-12-01

366

A Changing Ice Sheet  

NSDL National Science Digital Library

This animation shows the retreat of glacial ice, changes in the shoreline, and the disappearance of the land bridge across the Bering Sea which occurred at the end of the last ice age, beginning just over 21,000 years ago.

367

Investigating Ice Worlds  

NSDL National Science Digital Library

In this activity about the solar system, learners use various light sources to examine ice with different components to understand how NASA studies planets and moons from space. This detailed lesson guide includes background information about distant ice worlds in the outer solar system, literature connections, instructions for a pre-activity demonstration, modified activities by age, tips, discussion questions, and resources.

Education, Carnegie I.

2011-01-01

368

The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach  

NASA Astrophysics Data System (ADS)

Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of -0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. Reconstructed geopotential height at 1,000 hPa (z1000) suggests enhanced southwesterly flow across New Zealand occurred during the LIA to generate the terrestrial temperature anomalies. The mean atmospheric circulation pattern for summer resulted from a crucial reduction of the `HSE'-blocking synoptic type (highs over and to the west of NZ; largely settled conditions) and increases in both the `T'- and `SW'-trough synoptic types (lows passing over NZ; enhanced southerly and southwesterly flow) relative to normal. Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Niño-Modoki in the tropical Pacific and negative Southern Annular Mode activity.

Lorrey, Andrew; Fauchereau, Nicolas; Stanton, Craig; Chappell, Petra; Phipps, Steven; Mackintosh, Andrew; Renwick, James; Goodwin, Ian; Fowler, Anthony

2013-07-01

369

Calcareous nannofossil assemblages from the Central Mediterranean Sea over the last four centuries: the impact of the little ice age  

NASA Astrophysics Data System (ADS)

We present decadal-scale calcareous nannofossil data from four short cores (Station 272, 37° 17' N, 12° 48' E, 226 m depth; St 342, 36° 42' N, 13° 55' E, 858.2 m depth; St 407, 36° 23' N, 14° 27' E, 345.4 m depth; C90-1M, 40° 36' N, 14° 42' E, 103.4 m depth) recovered in the central Mediterranean Sea (northern Sicily Channel and Tyrrhenian Sea), which, on the basis of 210Pb activity span the last 200-350 years. Assemblages are dominated by placoliths, mostly Emiliania huxleyi, while, at least in the Sicily Channel sediments, Florisphaera profunda was an important part of the coccolithophore community. The paleoenvironmental reconstruction, based on ecological preference of species and groups, suggests that the Tyrrhenian core C90-1M maintained higher productivity levels over recent centuries, with respect to the Sicily Channel sites, possibly because of more pronounced winter phytoplankton blooms, in agreement with modern primary productivity variations over the last ten years. The lowermost part of the record of one of the cores from the Sicily Channel, Station 407, which extends down to 1650 AD, is characterized by drastic changes in productivity. Specifically, below 1850 AD, the decrease in abundance of F. profunda and the increase of placoliths, suggest increased productivity. The chronology of this change is related to the main phase of the Little Ice Age, which might have impacted the hydrography of the southern coast of Sicily and promoted vertical mixing in the water column. The comparison with climatic forcings points out the importance of stronger and prolonged northerlies, together with decreased solar irradiance. The identification of the LIA in the northern Sicily Channel cover the Bond cycle BO that was missing in a previous study of Holocene climatic anomalies in the Sicily Channel. Finally, we suggest that major abundance changes in reworked nannofossil specimens, recorded in the Tyrrhenian core C90-1M, might be linked to variations in terrigenous supply from land. Paradoxically, higher amounts of reworking correspond to dry periods. We argue that soil and rock vulnerability is enhanced during times of prolonged drought and vegetation cover loss.

Incarbona, A.; Ziveri, P.; di Stefano, E.; Lirer, F.; Mortyn, G.; Patti, B.; Pelosi, N.; Sprovieri, M.; Tranchida, G.; Vallefuoco, M.; Albertazzi, S.; Bellucci, L. G.; Bonanno, A.; Bonomo, S.; Censi, P.; Ferraro, L.; Giuliani, S.; Mazzola, S.; Sprovieri, R.

2010-05-01

370

Profit-Making as Character Education: Social Education in the Moraine Park School and Antioch College, 1916-1933  

ERIC Educational Resources Information Center

|Arthur E. Morgan and other self-made business leaders opened Moraine Park School in 1917 to provide a form of character training that they feared had ended in the United States. These men believed that young people gained the best social education when they had to run their own companies because such opportunities enabled students to acquire the…

Watras, Joseph

2009-01-01

371

Paleoclimatic tracers: An investigation using an atmospheric general circulation model under ice age conditions. 2. Water isotopes  

Microsoft Academic Search

The linear relationship observed between the water isotopic contents of precipitation and surface air temperatures leads to the use of water isotopes, H218O and HDO, in paleoclimatology. Applied to the measurements of the isotopic content of paleowaters, like groundwaters and deep ice cores, this relationship is used to infer paleotemperatures. However, this interpretation of paleo-isotopic contents is only valid if

Sylvie Joussaume; Jean Jouzel

1993-01-01

372

Paleoclimatic tracers: An investigation using an atmospheric general circulation model under ice age conditions. 1. Desert dust  

Microsoft Academic Search

Many studies with atmospheric general circulation models (AGCMs) have demonstrated their usefulness in reconstructing past climates. In a new approach, we have used an AGCM to investigate the link between tracer cycles and climate. We consider in this paper the atmospheric cycle of windblown dust material from desertic areas and in part 2 the water isotope cycles. Studies from ice

Sylvie Joussaume

1993-01-01

373

Late Glacial Dynamics of the Greenland Ice Sheet on NE-Greenland  

NASA Astrophysics Data System (ADS)

The reconstruction of large ice masses in the past is a crucial element for current climate models as correct input and base line parameter as well as for the implementation of associated ice sheet dynamics. For a long time, the ice sheet extent of the Greenland Ice Sheet (GIS) was reconstructed mainly on the basis of terrestrial work. Accordingly, the outer limit of the GIS during the Late Glacial Maximum (LGM) was placed close to the current coastline. Advances in our understanding on the dynamic behaviour of the GIS,especially offshore NE-Greenland, came from hydro-acoustic surveys which indicated a much larger extent of GIS during the LGM. Here, we present hydro-acoustic data acquired with RV "Polarstern" from fjord systems to the shelf edge of NE-Greenland, including the first hydro-acoustic data of Dijmphna and Hekla Sunds. We found morphological evidence for fast-flowing ice filling the fjords, extending onto the shelf as ice stream and reaching the shelf break. Mega-scale glacial lineation, recessional moraines and grounding line wedges document a highly dynamic behaviour of this Westwind Ice Stream of the GIS on NE-Greenland. The ice advance was followed by a rapid retreat to a mid-shelf position where the ice margin repeatedly deposited sets of recessional moraines