These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Little Ice Age on the Tibetan Plateau and its bordering mountains: Evidence from moraine chronologies  

NASA Astrophysics Data System (ADS)

Knowledge of the Little Ice Age (LIA) on the Tibetan Plateau (TP) is of critical importance for understanding the climate changes over the past millennium. However, the data associated with the extents and chronologies of TP LIA moraines are highly dispersed in literature. Lack of systematic integration of these data hampers us to further understand the nature of the LIA, especially from a perspective of whole TP. The paper reviews multiple types of dating on LIA moraines to examine the timing and nature of the LIA on the TP. These include ages of radiocarbon 14C, lichenometry, and cosmogenic radionuclide (CRN), by which we can cross-date the same or morphostratigraphically similar landforms. LIA moraines on the TP are usually present a few hundred to thousand meters beyond the contemporary glaciers. The morphological and stratigraphic evidence indicates multiple periods of glacier advance during the last millennium (LIA). At present, available chronology evidence allows to fully compare the timing of the LIA maximum extents. The glaciers reached and retreated from their LIA maximum extents by an asynchronous pattern between different parts of the TP. The majority of glaciers advanced to their LIA maximum extents at late-14th and early-14th century on the southern and northwestern TP, respectively. The glaciers retreated from their LIA maximum extents during 16th to early-18th, late-14th to early-15th and early-16th century on the southern, northwestern, and northeastern TP, respectively. In addition, the glacier advance period of late-18th to early-19th centuries and retreat period of late-19th century are common on the whole TP. Comparison with ice core records suggests that on the TP, the glacier fluctuations responded more strongly to temperature than to precipitation. By comparison of the LIA chronologies from a global perspective, this paper also concludes that the LIA maximum extents occurred commonly earlier on the TP than in North Atlantic and Southern Hemisphere regions, despite of the variability in the timing of LIA maximum extents on the TP and in the North Atlantic regions. Further, more chronology programs, especially in the central TP, are necessarily needed to improve our understanding of the LIA glacier fluctuations.

Xu, Xiangke; Yi, Chaolu

2014-05-01

2

Age of the Ørkendalen moraines, Kangerlussuaq, Greenland: constraints on the extent of the southwestern margin of the Greenland Ice Sheet during the Holocene  

NASA Astrophysics Data System (ADS)

Although Greenland ice core records register relatively stable Holocene climate conditions, the lower elevation margins of the Greenland Ice Sheet (GrIS) experienced significant Holocene fluctuations. These fluctuations include ice sheet recession during the Holocene Thermal Maximum (9-5 ka) and advance during the Little Ice Age (LIA; ˜A.D. 1350-1880). Determining the extent and timing of these fluctuations is important for understanding the response of the GrIS to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models. Sets of moraines marking past extents of the southwestern GrIS margin occur in the Kangerlussuaq region. We focus on the Ørkendalen moraines, a prominent moraine set located within 2 km of the modern ice margin and just outboard of the LIA moraines. We present the first 10Be ages of the Ørkendalen moraines indicating they were deposited at 6.8 ± 0.3 ka. The geomorphic relationship between the Ørkendalen and LIA moraines indicates that the ice sheet margin was inboard of its Ørkendalen extent between ˜6.8 ka and the culmination of the LIA. The age of the Ørkendalen moraines provides an important constraint on the extent of the southwestern GrIS during the middle Holocene.

Levy, Laura B.; Kelly, Meredith A.; Howley, Jennifer A.; Virginia, Ross A.

2012-10-01

3

A chronology of Holocene and Little Ice Age glacier culminations of the Steingletscher, Central Alps, Switzerland, based on high-sensitivity beryllium-10 moraine dating  

NASA Astrophysics Data System (ADS)

The amplitude and timing of past glacier culminations are sensitive recorders of key climate events on a regional scale. Precisely dating young moraines using cosmogenic nuclides to investigate Holocene glacier chronologies has proven challenging, but progress in the high-sensitivity 10Be technique has recently been shown to enable the precise dating of moraines as young as a few hundred years. In this study we use 10Be moraine dating to reconstruct culminations of the Steingletscher, a small mountain glacier in the central Swiss Alps, throughout the Holocene. The outermost-recorded positions of Steingletscher most likely occurred in the Early Holocene and appear nearly synchronous with glacier culminations reported from other regions in the Alps. A Late-Holocene position corroborates the evidence for a significant glacier advance of similar extent to that of the Little Ice Age (LIA) ?3 kyr ago. Finally, fourteen boulders from different moraines yield 10Be ages between 580 and 140 years with analytical precisions mostly <10%, dating Steingletscher advances during the LIA. Because these LIA 10Be ages are in stratigraphic order, we tentatively distinguish four LIA glacier culminations: about 1470 CE, 1650 CE, 1750 CE and 1820 CE, which are in good agreement with existing independent records during the LIA in the Swiss Alps. These findings illustrate the high potential of the 10Be moraine dating method to directly link paleo-glacier-chronologies to historical records and thus present-day glacier evolution.

Schimmelpfennig, Irene; Schaefer, Joerg M.; Akçar, Naki; Koffman, Tobias; Ivy-Ochs, Susan; Schwartz, Roseanne; Finkel, Robert C.; Zimmerman, Susan; Schlüchter, Christian

2014-05-01

4

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

E-print Network

in southern Greenland. Southern Greenland warming at w1.5 ka was also concurrent with the end of the Roman. The warming of southern Greenland and retreat of ice from the Narsarsuaq moraine is consistent with studies across Greenland suggest that general global cooling resulted in glacial maxima at different times during

5

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

NASA Astrophysics Data System (ADS)

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

Schomacker, A.; Kjaer, K. H.

2007-12-01

6

Different rates of reworking of Little Ice Age lateral moraines in the Kaunertal valley, Austrian Alps: A morphometric and morphodynamic case study using multi-epoch LiDAR surveys  

NASA Astrophysics Data System (ADS)

Little Ice Age (LIA) moraines in the proglacial areas of the Gepatsch and Weißsee glaciers in the Kaunertal valley, Austria reveal different degrees of reworking by gully incision and debris flows. The state and intensity of reworking appears to depend not only on the time since deglaciation, but also on morphometric properties of the respective locations, such as slope gradient and slope length. Moreover, moraine locations with a high morphodynamic intensity are directly connected to the fluvial system. In these areas, where slope processes and fluvial processes overlap, the accumulation zones of the slope processes are prone to fluvial erosion. This leads to a regular disturbance of the slope gradient at the foot of the slopes. A series of aerial photos, dating back to 1953, was used as a basis for a geomorphological map, where coupling states of the investigated moraine locations are evident from the digitized process areas. Spatial changes of single gullies and headward migration of the upper moraine ridges were also monitored on base of the series of aerial photos. In order to estimate the time since deglaciation for different locations, spatial extents of the glaciers, dating back to 1850 were used to interpolate an age surface grid. Airborne LiDAR data were acquired and a digital elevation model was derived from the LiDAR point clouds in order to quantify minimum erosion volumes. These LiDAR data are also suitable for analysis of morphometric properties as well as morphodynamic intensities on the moraine locations. The study presented here is part of the multidisciplinary joint research project PROSA (High-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) which deals with the quantification of the sediment budget of the upper Kaunertal valley, with a focus on the proglacial area.

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

2014-05-01

7

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

8

Glacier variations in Breheimen, southern Norway: relative-age dating of Holocene moraine complexes at six high-altitude glaciers  

Microsoft Academic Search

Lichenometric evidence and Schmidt hammer R-values are used to date Holocene moraine sequences in front of six high-altitude (> 1500 m) glaciers in Breheimen, central southern Norway. At three glacier forelands with southerly aspects (Høgsetbreen, Vestre Høybre and Østre Høybre), relatively small (?4 m high) discrete boulder moraine ridges are shown to date from the ‘Little Ice Age’. The remaining

Richard A. Shakesby; John A. Matthews; Stefan Winkler

2004-01-01

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

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

12

Surface Dating of Dynamic Landforms: Young Boulders on Aging Moraines  

Microsoft Academic Search

The dating of landforms is crucial to understanding the evolution, history, and stability of landscapes. Cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces. A pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data. Consideration of the dynamic nature

Bernard Hallet; Jaakko Putkonen

1994-01-01

13

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

USGS Publications Warehouse

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

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

2007-01-01

14

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

SciTech Connect

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

Danelski, T.C.; Moe, S.A.; Weeks, M.R.; Anderson, G.G. (St. Cloud State Univ., MN (United States). Dept. of Earth Sciences)

1993-03-01

15

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.

16

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

17

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

NASA Astrophysics Data System (ADS)

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

Burbank, Douglas W.; Cheng, Kang Jian

1991-07-01

18

Ice Ages  

NSDL National Science Digital Library

This online exhibit from the Illinois State Museum provides an introduction to glaciation in the midwestern United States since the last glacial advance 20,000 years ago. Topics include what ice ages are, when they occurred, and why. There is also an animation showing the advance and retreat if the ice sheet that covered much of North America from 18,000 to 8000 years ago.

19

Surface Exposure Dating of the Huancané III Moraines in Peru: A Record of Quelccaya Ice Cap's Maximum Extent during the Last Glacial Period  

NASA Astrophysics Data System (ADS)

The climatic conditions that influenced the tropics during the height of the last glacial period are not well defined and controversial. There are disparities in estimates of temperature anomalies (e.g., MARGO, 2009; Rind and Peteet, 1985; CLIMAP, 1976), and critical terrestrial paleotemperature proxy records in tropical regions are poorly dated (e.g., Porter, 2001). Defining these conditions is important for understanding the mechanisms that cause major shifts in climate, as the tropics are a primary driver of atmospheric and oceanic circulation. This study aims to constrain the timing of maximum glacier extents in the Cordillera Oriental in southern Peru during the last glacial period by applying surface exposure (beryllium-10) dating to the Huancané III (Hu-III) moraines. The Hu-III moraines mark the maximum extent of Quelccaya Ice Cap (QIC) (13.93°S, 70.83°W), the largest tropical ice cap, during the last ice age. The eight beryllium-10 ages presented here yield 17,056 ± 520 yrs ago as a minimum age for the onset of recession from the ice cap advance marked by the Hu-III moraines. Comparing this age to other paleoclimate records indicates that the ice cap advance marked by the Hu-III moraines is more likely associated with a North Atlantic climate event known as Heinrich I (H1; 16,800 yrs ago, Bond et al., 1992, 1993) than with global cooling at the Last Glacial Maximum (LGM; ~21,000 yrs ago, Denton and Hughes, 1981). This result suggests that climate processes in the North Atlantic region are linked to climatic conditions in the tropical Andes. A mesoscale climate model and an ice-flow model are currently being developed for QIC. The moraine data presented in this study will be used with these two models to test response of QIC to North Atlantic and global climate events.

Baranes, H. E.; Kelly, M. A.; Stroup, J. S.; Howley, J. A.; Lowell, T. V.

2012-12-01

20

High resolution record of paleoclimate since the Little Ice Age from the Tibetan ice cores  

Microsoft Academic Search

Climate changes during the Little Ice Age were studied based on oxygen isotope values (?18O) measured from ice cores recovered on, and nearby, the Qinghai-Tibetan Plateau. Three cold periods have been identified and are supported by three widely existing moraine ridges formed during the Little Ice Age. Importantly, the amplitude of the three cold periods differ in the cores studied.

Tandong Yao; Yafeng Shi; L. G. Thompson

1997-01-01

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

Groundwater flow beneath ice sheets: Part II — Its impact on glacier tectonic structures and moraine formation  

NASA Astrophysics Data System (ADS)

Meltwater flowing as groundwater from beneath the margin of an ice sheet determines the distribution of sub-surface heads and effective pressures. A subglacial groundwater flow model is used, together with an ice sheet loading model, to compute the magnitudes and directions of the principal effective stresses in the subsurface, from which the distribution of different types of sub-surface failure in the subglacial and proglacial zones are deduced. Zones of hydrofracturing, shear fracture and pervasive shear failure are distinguished. Beneath the ice sheet divide area, intact rocks of high tensile strength may fail. Hydrofracturing and liquefaction are two coupled processes which lead to the formation of upward-filled and downward-filled sediment dykes and till wedges. Quicksand conditions are developed where strong vertical seepage pressures occur, producing sediment diapirism. It is suggested that subglacial permeability magnitude may be the product of a self organising process. Certain types of moraine (extrusion moraines) are suggested to be a consequence of upward movement and surface extrusion of sediment driven by rising groundwater. It is suggested that groundwater over pressure associated with narrow proglacial permafrost plates are conductive to the formation of large push moraines, and that many large ancient and modern examples are produced in this setting.

Boulton, G. S.; Caban, P.

23

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

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

Airborne SAR determination of relative ages of Walker Valley moraines, eastern Sierra Nevada  

NASA Technical Reports Server (NTRS)

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 for glaciation in the Andes and other regions that are difficult to access on the ground and where suitable material for absolute age determination is lacking. The sensitivity of radar to surface roughness makes it possible to develop a remotely-based relative dating technique for landforms for which surface age and roughness can be correlated. We are developing such a technique with Airborne Synthetic Aperture Radar (AIRSAR) imagery of the eastern Sierra Nevada where independent evidence is available for the ages and physical characteristics of moraines. The Sierra Nevada moraines are similar in form and environmental setting to Andean moraines that we have targeted for study during the pending Shuttle Imaging Radar-C (SIR-C) mission. SAR imagery is used to differentiate the ages of five moraine sequences of Walker Valley in the eastern Sierra Nevada. Other aspects of this investigation are briefly discussed.

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

1991-01-01

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

The Ice Age  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 9-12. It explains what ice ages are, what causes ice ages to occur, plants and animals that lived during the last Ice Age, and why some Ice Age animals went extinct. It includes objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order that complement this lesson, an audio-enhanced vocabulary list, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

28

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

SciTech Connect

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

Metz, M.A.; Meyer, D.P.; Rogers, M.R.; Thorne, R.E.; Anderson, G.G. (St. Cloud State Univ., MN (United States))

1994-04-01

29

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

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 Sediment Wedge and an Instantaneous End-Moraine: a Twofold Ice-marginal Product of the 1890 Glacier Surge of Bruarjokull, Iceland  

NASA Astrophysics Data System (ADS)

Contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments. This study concerns the ice-marginal environment of the surge-type Brúarjökull in Iceland. The sediment distribution in the glacier forefield as well as the morphology, sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment/landform associations. As a result of substrate/bedrock decoupling during the 1890 surge, subglacial sediment was dislocated across the bedrock surface and deformed compressively, leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone. A drop in subglacial porewater pressure at the very end of the surge led to substrate/bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate. Simultaneously, the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine-ridge construction. Fine-grained and incompetent sediment deformed in ductile manner, resulting in a narrow rooted-fold-dominated moraine while coarse-grained and competent sediment deformed in brittle fashion, resulting in wide imbricated moraine. A new sequential model of subglacial and ice marginal processes operating during a glacier surge is proposed, illustrating the stepwise formation of a surging-glacier marginal sediment wedge and an instantaneous end moraine - a twofold, inseparable marginal end-product of the 1890 surge. As a result of high ice-flow velocities (100-120 m/day) the sediment wedge is thought to have formed in approximately five days and the end moraine in about one day.

Benediktsson, I. O.; Ingolfsson, O.; Per, M.; van der Meer, J. J.; Kjær, K. H.; Kruger, J.

2007-12-01

33

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

34

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

35

Ice Age Floods Institute  

NSDL National Science Digital Library

This site 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 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.

2011-12-30

36

Cracking the Ice Age  

NSDL National Science Digital Library

This web site is part of NOVA online from the Public Broadcasting System (PBS). It examines earth and atmospheric topics with a focus on historical and present climates, ice ages, glaciers, climactic change, Wilson cycles, the greenhouse effect, carbon dioxide, chlorofluorocarbons, plate tectonics, and Alfred Wegener. Tutorials are entitled: Big Chill, Greenhouse - Green Planet, Hot Science: Continents on the Move, and Related Links. Each topic has a brief report and includes scientific illustrations.

37

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

38

Mars Ice Age, Simulated  

NASA Technical Reports Server (NTRS)

December 17, 2003

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

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

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

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

2003-01-01

39

Melt-out till and ribbed moraine formation, a case study from south Sweden  

NASA Astrophysics Data System (ADS)

Hummocky moraine with dispersed agglomerations of ribbed moraine - here named 'Åsnen-type ribbed moraine' - forms a 20-40 km wide zone over Småland, south Sweden, terminated to the north by a sharp boundary to streamlined terrain. The hummocky/ribbed moraine zone can be geomorphologically linked to the subaqueous Göteborg Moraine, formed at an oscillation/stand-still phase during the deglaciation of the Swedish west coast. Based on detailed sedimentological and structural investigations of ribbed moraine ridges it is concluded that diamict sequences and associated sorted sediment were deposited due to passive melt-out from stagnant, debris-rich ice with synsedimentary deposition of sorted sediments, preferentially at a melting ice/bed interface. To accommodate for the geomorphological expression, such an interpretation further implies that debris-rich ice formed in an intermediate adfreezing zone between ice at the pressure-melting point and a frontal frozen zone at deglaciation. Basal debris-rich ice was stacked into transversally arranged zones (controlled moraine), forming ribbed moraine 'embryos', the active phase of ridge formation. The stacked sequences of debris-rich ice eventually melted out beneath a stable and melt-retarding supraglacial ablation complex to form the final moraine ridges, the passive phase of ridge formation. In areas with no stable supraglacial ablation complex, the resulting landform after final de-icing was a hummocky moraine landscape. Internal composition of moraine hummocks suggests that most of them are composed of sediment gravity flow sediments, intercalated with stream-deposited sediments, all resting on a platform of subglacial melt-out till. De-icing of the zone now occupied by hummocky and ribbed moraine took a considerable time; deglacial 14C age differences from lake basins on either side of the geomorphic boundary to the streamlined terrain indicate a separation between active and stagnant ice along that boundary, and that it took another 200-300 yr for the stagnant ice zone to melt during the final formation of present-day landforms.

Möller, Per

2010-12-01

40

Ice age paleotopography  

Microsoft Academic Search

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

W. R. Peltier

1994-01-01

41

Controlled moraines: origins, characteristics and palaeoglaciological implications  

NASA Astrophysics Data System (ADS)

Controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de-icing and possess clear linearity due to the inheritance of the former pattern of debris-rich folia in the parent ice. Linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt-out. As a result, moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris-rich ice was concentrated in frozen toe zones. Recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that: (a) controlled moraine development can be ascribed to a specific process (e.g. englacial thrusting or supercooling); and (b) controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts (e.g. ancient polythermal or supercooled snouts). These assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris-rich ice thickening mechanisms are seen to produce the same geomorphic features. Polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier-permafrost interface. End moraines lie on a process-form continuum constrained by basal thermal regime. The morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores, but the final deposits/landforms tend to consist of discontinuous transverse ridges with intervening hummocks, preserving only a weak impression of the former englacial structure. These are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice-walled lake plains and lying down flow of streamlined landforms produced by warm-based ice. A variety of debris entrainment mechanisms can produce the same geomorphic signature. Spatial and temporal variability in process-form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin.

Evans, David J. A.

2009-02-01

42

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

43

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

44

Dating of Holocene lateral moraines in the western Southern Alps, New Zealand, applying Schmidt-hammer exposure-age dating (SHD)  

NASA Astrophysics Data System (ADS)

Research on Holocene mountain glacier chronologies has recently intensified due to the importance of mountain glaciers as key indicators for past and present climate change. This progress is closely connected with major improvements in modern dating techniques and the application of multi-proxy approaches adapted to specific local/regional conditions. Despite recent progress there is, however, still a need for better spatial differentiation and a lack of generally accepted concepts for global and inter-hemispheric correlation of Holocene glacier chronologies. Furthermore, the "geomorphological uncertainty" inevitably connected with numerical dating of moraines in neotectonic active mountain ranges characterised by highly dynamic geomorphological process systems requires careful consideration of any subsequent palaeoclimatic interpretation. During the past few years Schmidt-hammer exposure-age dating (SHD) has revealed its potential to successfully challenge those specific circumstances. The Southern Alps of New Zealand have provided one of only a few suitable study sites for investigating Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere. Recent years have seen a significant increase in terrestrial cosmogenic nuclide dating (TCND)-ages published for the Southern Alps, mainly for the last Glaciation, but also for the Holocene. The availability of a regional 10Be-production curve has improved the calibration of TCND-ages. These studies applying TCND alongside previous chronological studies using a variety of different dating techniques focus, however, primarily on a few selected glacier forelands east of the Main Divide in Aoraki/Mt Cook National Park. Bad accessibility and methodological problems account for comparatively few investigations on glacier forelands west of the Main Divide. Chronological studies applying Schmidt-hammer exposure-age dating (SHD) were performed on six glacier forelands in the western part of the Southern Alps/New Zealand. Although lithological heterogeneity prevented a regional age-calibration curve to be established, local age-calibration curves for La Perouse and Strauchon Glaciers could be derived. They show similar linear equations and trends/slopes, and enabled a preliminary assessment of the representativeness of individual 10Be TCND-ages obtained from the other forelands. No mid- and early-Holocene advance periods were detected. Clusters of moraine ages date around 2800, 1850 - 1450, and 1100 - 900 years ago, followed by the Little Ice Age (LIA) commencing c. 500 years ago. There is no good agreement with earlier radiocarbon-based studies in the western part of the Southern Alps, as well as with recently published TCND-chronologies from glacier forelands east of The Main Divide. This at least partly could be the result of different approaches to the palaeoclimatic interpretation of the dated samples rather than of spatial differentiation. The results obtained from this recent study do not support an elsewhere proposed general asynchronous glacier behaviour between the mid-latitudinal northern and southern hemispheres. They also show that due to the specific environmental conditions in the Southern Alps, more investigations are needed before a "regional" Holocene glacier chronology robust enough to allow reliable intra-hemispheric and global correlations can be undertaken.

Winkler, Stefan

2014-05-01

45

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

46

Mass loss of the Greenland Ice Sheet since the Little Ice Age, implications on sea level  

NASA Astrophysics Data System (ADS)

The impact of mass loss from the Greenland Ice Sheet (GrIS) on 20th Century sea level rise (SLR) has long been subject to intense discussions. While globally distributed tide gauges suggest a global mean SLR of 15-20 cm, quantifying the separate components is of great concern - in particular for modeling sea level projections into the 21st Century. Estimates of the past GrIS contribution to SLR have been derived using a number of different approaches, e.g. surface mass balance (SMB) calculations combined with estimates of ice discharge found by in correlating SMB anomalies and calving rates. Here, we adopt a novel geometric approach to determine the post-Little Ice Age (LIA) mass loss of the GrIS. We use high quality aerial stereo photogrammetric imagery recorded between 1978 and 1987 to map morphological features such as trim lines (boundary between freshly eroded and non-eroded bedrock) and end moraines marking the ice extent of the LIA, which thereby enables us to obtain vertical point-based differences associated with changes in ice extent. These point measurements are combined with contemporary ice surface differences derived using NASA's Airborne Topographic Mapper (ATM) from 2002-2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, and NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, to estimate mass loss throughout the 20th and early 21st Century. We present mass balance estimates of the GrIS since retreat commence from the maximum extent of the LIA to 2010 derived for three intervals, LIAmax (1900) - 1978/87, 1978/87 - 2002, and 2002 - 2010. Results suggest that despite highly spatially- and temporally variable post-LIA mass loss, the total mass loss and thus the contribution from the GrIS to global SLR has accelerated significantly during the 20th Century.

Kjeldsen, K. K.; Kjaer, K.; Bjork, A. A.; Khan, S. A.; Korsgaard, N. J.; Larsen, N. K.; Long, A. J.; Woodroffe, S.; Milne, G. A.; Wahr, J. M.; Geruo, A.; Bamber, J. L.; van den Broeke, M. R.

2013-12-01

47

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

NASA Technical Reports Server (NTRS)

The natural TL survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to (1) identifying pairing, (2) providing an estimate of terrestrial age and residence time on the ice surface, (3) looking for differences in natural TL between ice fields, (4) looking for variations in natural TL level with location on the ice, (5) looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the @ost productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to (5) look for evidence for secular variation in the nature of the flux of meteorites to Earth, and (6) look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary chondrites from Grosvenor Mountains (39 meteorites), MacAlpine Hills (70 meteorites), Pecora Escarpment (60 meteorites), and Queen Alexandra Range (173 meteorites) and we have data for a further 101 samples from Elephant Moraine. The results are summarized in Table 1. We also have fairly minimal databases (10-15 meteorites) for Dominion Range, Graves Nunataks, Reckling Peak and Wisconsin Range that will not be discussed here.

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

2000-01-01

48

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

NASA Technical Reports Server (NTRS)

The natural TL (Thermoluminescence) survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET (Antarctic Search for Meteorites) samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to identifying pairing, providing an estimate of terrestrial age and residence time on the ice surface, looking for differences in natural TL between ice fields, looking for variations in natural TL level with location on the ice, looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the most productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to look for evidence for secular variation in the nature of the flux of meteorites to Earth, and look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary chondrites from Grosvenor Mountains (39 meteorites), MacAlpine Hills (70 meteorites), Pecora Escarpment (60 meteorites), and Queen Alexandra Range (173 meteorites) and we have data for a further 101 samples from Elephant Moraine. The results are summarized. We also have fairly minimal databases (10-15 meteorites) for Dominion Range, Graves Nunataks, Reckling Peak and Wisconsin Range that will not be discussed here.

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

1999-01-01

49

AN INTRODUCTION TO THE ICE AGES  

E-print Network

ASTRO 101A AN INTRODUCTION TO THE ICE AGES The Authors: Group 77* National University of Singapore courtesy of http://www.magicaweb.com #12;ASTRO 101A AN INTRODUCTION TO THE ICE AGES Notes from the authors This course is designed to introduce students to the basic idea of the astronomical aspects of the ice ages

Aslaksen, Helmer

50

Dynamics of Ice Ages Norbert Schorghofer  

E-print Network

.4 0.5 equilibrium Ice fraction (%) Depthbelowsurface J dry Vertical Growth Illustration of aDynamics of Ice Ages on Mars Norbert Schorghofer University of Hawaii July 2013 #12;Planet Mars K to 310 K #12;ice-free surface Phoenix on Mars May­November 2008 latitude: 68N ice buried by 5cm

Schörghofer, Norbert

51

Cosmogenic Be10 ages of Angel Lake and Lamoille moraines and late Pleistocene slip rate of the rangefront normal fault, Ruby Mountains, Basin and Range, Nevada  

Microsoft Academic Search

We use Be-10 cosmogenic radionuclide (CRN) exposure dating to quantify the timing of late Pleistocene glacial advances and to estimate the rangefront normal fault slip rate along the Ruby Mountains in the Basin and Range, Nevada. Ten Be-10 CRN exposure ages from the Angel Lake terminal moraine in Hennen Canyon limit deposition to between 15.4-23.1 ka (average = 18.2 ka;

R. W. Briggs; S. G. Wesnousky; F. J. Ryerson; R. C. Finkel; A. Meriaux

2004-01-01

52

Cosmogenic Be-10 ages of Angel Lake and Lamoille moraines and late Pleistocene slip rate of the rangefront normal fault, Ruby Mountains, Basin and Range, Nevada  

NASA Astrophysics Data System (ADS)

We use Be-10 cosmogenic radionuclide (CRN) exposure dating to quantify the timing of late Pleistocene glacial advances and to estimate the rangefront normal fault slip rate along the Ruby Mountains in the Basin and Range, Nevada. Ten Be-10 CRN exposure ages from the Angel Lake terminal moraine in Hennen Canyon limit deposition to between 15.4-23.1 ka (average = 18.2 ka; SD = 2.5 ka), an interval that overlaps with the Tioga glacial advances in the Sierra Nevada and Pinedale advances in the Rocky Mountains during MIS-2. The termination of the Angel Lake glaciation at ~15.4 ka is nearly synchronous with the final highstand and subsequent rapid desiccation of Lake Lahontan. Previous relative age dating studies in the Ruby Mountains have inferred deposition of Lamoille moraines during MIS-4 (~59-74 ka) or MIS-6 (~130-190 ka). However, fifteen Be-10 CRN exposure dates obtained from a Lamoille lateral moraine in Hennen Canyon (average = 30.7 ka; SD = 11.5; range = 19.3-66.5 ka) do not support these assignments and instead suggest that the moraine may have been deposited during MIS-3. Assuming the average Be-10 model age from the Lamoille surface represents a minimum age constraint, we obtain a maximum fault slip rate of 0.40-0.60 mm/year for a 60° dipping fault and 11-16 m of vertical separation across faulted Lamoille moraines. Accommodation of 0.4-0.6 mm/year of slip by the Ruby Mountains fault zone implies an average 0.2-0.3 mm/year of horizontal strain accumulation across the fault during the last ~31 ka, and thus characterization of the central Basin and Range as a geodetic microplate may be at odds with late Pleistocene horizontal displacement rates along the Ruby Mountains fault zone. If correct, the observed disparity between the CRN exposure dates and geologic correlations underscores the importance of quantitative age constraints for climate reconstruction, landscape evolution, and tectonic geomorphology.

Briggs, R. W.; Wesnousky, S. G.; Ryerson, F. J.; Finkel, R. C.; Meriaux, A.

2004-12-01

53

Mass loss from the southern half of the Greenland Ice Sheet since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The impact of mass loss from the Greenland Ice sheet (GrIS) on the 20th Century sea level rise (SLR) has long been subject to immense discussions. While globally distributed tide gauges suggest SLR of 15-20 cm computing the input constituents is of great concern - in particular for modeling sea level projections into the 21st Century. Estimates of the GrIS contribution to SLR have been derived using a number of different approaches, e.g. surface mass balance (SMB) calculations combined with estimates of ice discharge founded in correlating SMB anomalies and calving rates. Here, we show a novel geometric approach to determine the post-Little Ice Age (LIA) mass loss of the southern GrIS. We present mass balance estimates of the GrIS south of 71N since retreat commence from the maximum extent of the LIA to 2010. The mass loss estimates are derived for three intervals, LIAmax (1900) - 1981/85 (1), 1981/85 - 2002 (2), and 2002 - 2010 (3). We use high quality aerial stereo photogrammetric imagery recorded in 1981 and 1985 to map morphological features such as trim lines (boundary between freshly eroded and non-eroded bedrock) and end moraines marking the ice extent of the LIA, which thereby enables us to obtain vertical difference associated with former ice extent. We combine these with contemporary ice surface differences derived using NASA's Airborne Topographic Mapper (ATM) from 2002-2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, and NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, to estimate mass loss throughout the 20th and early 21st Century. Using our novel approach we find mass loss rates for the above periods (1) to (3) of 53 Gt/yr, 46 Gt/yr, and 109 Gt/yr, respectively. In southeast GrIS we find substantial and extensive mass loss reaching the ice divide while in southwestern GrIS mass loss is less and mainly associated with marine outlet glaciers. Furthermore, post-LIA mass loss is found to be highly variable, even within relative close proximity to other outlet glaciers and within comparable terminal environments.

Kjeldsen, Kristian K.; Kjær, Kurt H.; Bjørk, Anders A.; Khan, Shfaqat A.; Korsgaard, Niels J.; Funder, Svend; Larsen, Nicolaj K.; Vinther, Bo; Andresen, Camilla S.; Long, Antony J.; Woodroffe, Sarah A.; Steen Hansen, Eric; Olsen, Jesper

2013-04-01

54

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

USGS Publications Warehouse

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

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

2001-01-01

55

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

56

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

57

Dynamics of ice ages on Mars Norbert Schorghofer1  

E-print Network

to bottom, a dry layer, pore ice, and a massive ice sheet. Combined, these layers provide enough iceLETTERS Dynamics of ice ages on Mars Norbert Schorghofer1 Unlike Earth, where astronomical climate of redistributing ice on a global scale1­6 . The geo- graphic extent of the subsurface ice found poleward of approxi

Schörghofer, Norbert

58

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

59

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

60

Monday, November 29, 2010 Chapters 12 and 14 "Ice Ages"  

E-print Network

Monday, November 29, 2010 Chapters 12 and 14 ­ "Ice Ages" #12;Chapter 12 - Earth has had five six the earth cool. #12;The second ice age was ~2500 mya (Huronian) ­ removal of methane from the atmosphere due it is today, CO2 would need to be > 560 ppm to keep Earth ice-free. #12;Fourth and fifth ice ages 440 mya

Toohey, Darin W.

61

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

62

Holocene Deglaciation of the Scandinavian Ice Sheet: Preliminary 10Be Ages  

NASA Astrophysics Data System (ADS)

The response of ice sheets to a warming climate is not well understood. Because we are limited in our understanding of present dynamics, reconstructing the deglaciation of former ice sheets allows for a better understanding of how past ice sheets responded to a warming climate along with their contribution to sea-level rise. These reconstructions also serve as critical constraints for ice sheet modeling efforts. Here, we present a suite of new 10Be ages from erratic boulders along three transects spanning southern to northern Sweden and Finland, that improve our understanding of the deglaciation of the Scandinavian Ice Sheet (SIS) beginning ~ 11.7ka through its final demise during the early Holocene. Preliminary dates from southern Finland, beginning at the Salpausselka Youngers Dryas moraine (11.5 ± 0.7 ka, n=2), inland southern Finland near Jyvaskyla (11.5 ± 0.5ka, n=2), and coastal Finland (~60km from Gulf of Bothnia) near Vimpeli (11.5 ± 0.4ka, n=1) indicate a rapid retreat following the Younger Dryas for Southern Finland (~500km within uncertainty of ages). Preliminary dates also exist for Northern Finland, near Inari (10.3 ± 0.5ka, n=2). Additional ages now being processed at PRIME Lab, Purdue University, which will establish a basis for SIS retreat from all sampled sites, will also be presented. These new data will help to constrain the Holocene deglaciation of the SIS and its associated retreat rates, and establish the SIS contribution to Holocene sea level rise, which will improve our understanding of ice-sheet response to a warming climate.

Cuzzone, J. K.; Clark, P. U.; Marcott, S. A.; Pekka Lunka, J.; Wohlfarth, B.; Carlson, A. E.

2012-12-01

63

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

64

Tree-ring derived Little Ice Age temperature trends from the central British Columbia Coast Mountains, Canada  

NASA Astrophysics Data System (ADS)

Most glaciers in the British Columbia Coast Mountains reached their maximum Holocene extent during the Little Ice Age. Early- and late-Little Ice Age intervals of expansion and retreat fluctuations describe a mass-balance response to changing climates. Although existing dendroclimatic records provide insights into these climatic fluctuations over the last 400 yr, their short durations prohibit evaluation of early-Little Ice Age climate variability. To extend the duration of these records, submerged coarse woody debris salvaged from a high-elevation lake was cross-dated to living chronologies. The resulting chronology provides the opportunity to reconstruct a regional June-July air-temperature anomaly record extending from AD 1225 to 2010. The reconstruction shows that the intervals AD 1350-1420, 1475-1550, 1625-1700 and 1830-1940 characterized distinct periods of below-average June-July temperature followed by periods of above-average temperature. Our reconstruction provides the first annually resolved insights into high-elevation climates spanning the Little Ice Age in this region and indicates that Little Ice Age moraine stabilization corresponds to persistent intervals of warmer-than-average temperatures. We conclude that coarse woody debris submerged in high-elevation lakes has considerable potential for developing lengthy proxy climate records, and we recommend that researchers focus attention on this largely ignored paleoclimatic archive.

Pitman, Kara J.; Smith, Dan J.

2012-11-01

65

Origin of Ice Ages as a Simple Newtonian Problem  

NASA Astrophysics Data System (ADS)

The physics of ice and the related geophysics are essentially unknown. Thus the origin of ice ages should be a straightforward application of the Newtonian theory. But it has remained an unsolved mystery for a century. This cannot be due to anything but naive, juvenile mistakes which are more than one. (1) Forgetting the initial condition of the Newtonian theory. The next ice age must be spawned from the present polar icesheets (and the same for all previous and future ice ages). But this initial condition of permanent ice on earth is ignored by all ice age theories. Result: they all predict ice ages before Pleistocene without permanent polar icesheets and this is 99% wrong factually. (2) Forgetting ice and the heat of fusion of ice in the ice age. The Milankovitch eccentricity theory gives the right periodicity and the right heat of fusion needed to produce all the ice of an ice age but was dismissed by the double forgetfulness, because of a climate theory (Sellers) based on permanen-ice free earth. The true solution was missed by the shoulder. The correct Milankovitch forcing with the right initial conditions will lead to the prediction of glacier advances and retreats of the existing icesheets (like the seasonal changes of the iceshelves), spawning a new ice age, the only unanswered question being why the effect is so large (the new icesheet is of continental size). This cannot happen in stable equilibrium but can happen in neutral equilibrium. The origin of ice ages can thus be answered simply by one sentence in thermodynamics -- the ice-water phase equilibrium (between icesheet and ocean) is in a neutral equilibrium (dS=0, not dS>0).

Fong, Peter

1998-11-01

66

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 ...

67

Late-Wisconsinan submarine moraines along the north shore of the Estuary and Gulf of St. Lawrence (Eastern Canada)  

NASA Astrophysics Data System (ADS)

A series of ice-contact submarine fans and morainal banks along the Québec North-Shore of the Estuary and Gulf of St. Lawrence (Eastern Canada), between the Manicouagan River delta and the Mingan Islands, have been revealed with great detail by recent multibeam echosounder and high-resolution subbottom profiler surveys. These grounding-line landforms are observed between 65 and 190 m water depths and were constructed as the marine-based margin of the Laurentide Ice Sheet (LIS) stabilized or readvanced. Radiocarbon ages obtained from shells sampled in sediment cores collected in glaciomarine deposits 6 km south of a grounding line in the Sept-Iles area indicate a stabilisation that took place around 11 000 14C yr BP (12.5 ka cal BP with a ?R=120 ± 40 yr). In the Mingan Islands area, organic matter collected in distal deposits of an ice-contact fan is dated at 10 800 14C yr BP (11.6 ka cal BP). The position of the Sept-Iles and Mingan deposits, 20 km south of the ~9.7-9.5 14C kyr BP North-Shore Moraine, suggests that these ice marginal landforms were constructed during the Younger Dryas (YD) cold episode and that they might be the eastward submarine extent of the early YD St. Narcisse morainic system. Superimposed till sheets and morainal banks observed within grounding line deposits indicate that this stability phase was interrupted by local readvances that were marked in some cases by ice streaming. Segments of this morainic system are also visible along the shoreline in some sectors, where they have been generally washed out of fine fragments by waves. Another series of ice-contact deposits and landforms of similar nature observed farther offshore and at greater depths (100-190 m) were formed during a previous phase of stabilisation of the LIS margin. This older morainic system was probably deposited immediately after the opening of the Estuary and Gulf of the St. Lawrence.

Lajeunesse, Patrick; St-Onge, Guillaume

2013-04-01

68

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

69

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

SciTech Connect

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

Kwok, R.; Cunningham, G.F. [California Inst. of Tech., Pasadena, CA (United States). Jet Propulsion Lab.] [California Inst. of Tech., Pasadena, CA (United States). Jet Propulsion Lab.; Rothrock, D.A.; Stern, H.L. [Univ. of Washington, Seattle, WA (United States)] [Univ. of Washington, Seattle, WA (United States)

1995-03-01

70

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

71

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

72

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

73

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

Microsoft Academic Search

Remotely-sensed Arctic sea ice motion, sea ice age, and melt pond coverage have been proposed for development into full CDRs. The first has a considerable history of use, while the latter two are relatively new products. Our technique to estimate sea ice motion utilizes images from SSM\\/I, as well as the Scanning Multichannel Microwave Radiometer (SMMR) and the series of

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

2010-01-01

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

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

76

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

77

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

NASA Astrophysics Data System (ADS)

The Southern Alps of New Zealand are among the few key study sites for investigating Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere. Their characteristic highly dynamic geomorphological process systems prove, however, to be a considerable challenge for all attempts to date and palaeoclimatologically interpret the existing Holocene moraines record. As a multi-proxy approach combining 10Be terrestrial cosmogenic nuclide dating (TCND) with Schmidt-hammer testing, the recently developed Schmidt-hammer exposure-age dating (SHD) has already shown its potential in this study area (cf. Winkler 2005, 2009, 2013). An electronic Schmidt-hammer (named SilverSchmidt) was introduced by the manufacturer of the original mechanical Schmidt-hammer (Proceq SA) a few years ago. It offers, in particular, facilities for much easier data processing and constitutes a major improvement and potential replacement for the mechanical Schmidt-hammer. However, its different approach to the measurement of surface hardness - based on Q-(velocity) values instead of R-(rebound) values - is a potential drawback. This difference effectively means that measurements from the two instruments are not easily interconvertible and, hence, that the instruments cannot be used interchangeably without previous comparative tests of both instruments under field conditions. Both instruments used in this comparative study were N-type models with identical impact energy of 2.207 Nm for the plunger. To compare both instruments and explore interconvertibility, parallel measurements were performed on a selected number of boulders (10 boulders per site with 5 impacts each, at least 2 sites per moraine) on moraines of homogeneous lithology but different established ages covering the entire Holocene and the Late Glacial. All moraines are located east of the Main Divide of the Southern Alps at Mueller Glacier, Tasman Glacier, and in the outer Tasman River Valley. All paired samples (n = 50) were collected so that the plunger impacts of both instruments were set close together on the rock surface (to avoid any influence of modifications to the surface by consecutive impacts on the same spot). In order to test their performance at the higher and lower end of surface hardness, similar paired sample tests were also made on the full-metal test anvil. The results of paired samples for all sites/moraines reveal that Q-/R-value pairs are closely clustered for young surfaces but more scattered for the older ones with a corresponding moderate R2 for a calculated linear trend. The greater variability of the older, weathered surfaces with greater scatter and hence higher standard deviations and broader confidence intervals has been recognised in numerous previous Schmidt-hammer studies and is elated to the effects of micro-scale lithological variability, which becomes a more pronounced influence with time exposed to subaerial weathering. But most important, Q-values and R-values are closely related and Q-values are systematically higher than R-values by c. 10 - 12 units over most of the operational range of both instruments. Linear conversion equations indicate a conversion factor in the order of + 11 units is applicable when converting R-values to Q-values. These estimates agree well with data obtained on the standard test anvil. Given the apparent interconvertibility of the two instruments, the SilverSchmidt is regarded as a potential replacement for the mechanical Schmidt hammer. This enables, moreover, continuity in study areas with existing R-value data archives. However, when comparing data sets of different age, adjustments must be made for any changes to the instrumental calibration value over time. References: Winkler, S. (2005): The 'Schmidt hammer' as a relative-age dating technique: potential and limitations of its application on Holocene moraines in Mt Cook National Park, Southern Alps, New Zealand. New Zealand Journal of Geology and Geophysics 48, 105 - 116. Winkler, S. (2009): First attempt to combine terrestrial cosmogenic nuclide (10Be) and Schmidt

Winkler, Stefan; Corbett, David

2014-05-01

78

Holocene Deglaciation of the Scandinavian Ice Sheet: Preliminary 10Be Ages  

NASA Astrophysics Data System (ADS)

The response of ice sheets to a warming climate is not well understood. Because we are limited in our understanding of present dynamics, reconstructing the deglaciation of former ice sheets allows for a better understanding of how past ice sheets responded to a warming climate along with their contribution to sea-level rise. These reconstructions also serve as critical constraints for ice sheet modeling efforts. Here, we present a suite of new 10Be ages from erratic boulders along three transects spanning southern to northern Sweden and Finland, that improve our understanding of the deglaciation of the Scandinavian Ice Sheet (SIS) beginning ~ 11.7ka through its final demise during the early Holocene. Dates from southern Finland, beginning at the Salpausselka Younger Dryas moraine (11.5 × 0.7 ka, n=4), inland southern Finland near Jyvaskyla (11.5 × 0.5ka, n=2), and coastal Finland (~60km from Gulf of Bothnia) near Vimpeli (11.5 × 0.4ka, n=4) indicate a rapid retreat following the Younger Dryas for Southern Finland (~500km within uncertainty of ages). Preliminary dates also exist for Northern Finland, near Inari (10.8 × 0.5ka, n=4) and near Oulu (10.5 × 0.6 ka, n = 4) suggesting a later retreat in the north. Dates from southern Sweden, near Skovde (12.73 × 0.8ka, n=4) to Mora (10.41 × 0.6ka, n=5) suggest a slower retreat (over ~400km). Lastly, dates in Northwestern Sweden suggest a final termination of the SIS around 9.4 × 0.7ka (n = 3). Additional ages are now being processed at PRIME Lab, Purdue University, which will further strengthen our understanding of SIS retreat from all sampled sites. These new data will help to constrain the Holocene deglaciation of the SIS and its associated retreat rates, and establish the SIS contribution to Holocene sea level rise, which will improve our understanding of ice-sheet response to a warming climate.

Cuzzone, J. K.; Clark, P. U.; Marcott, S. A.; Lunkka, J.; Wohlfarth, B.; Caffee, M. W.; Carlson, A. E.

2013-12-01

79

Late Quaternary glaciations in Far NE Russia; combining moraines, topography and chronology to assess regional and global glaciation synchrony  

NASA Astrophysics Data System (ADS)

During various periods of Late Quaternary glaciation, small ice-sheets, -caps, -fields and valley glaciers, occupied the mountains and uplands of Far NE Russia (including the Verkhoyansk, Suntar-Khayata, and Chersky Mountains; the Kolyma-Anyuy and Koryak Highlands; and much of the Kamchatka and Chukchi Peninsulas). Here, the margins of former glaciers across this region are constrained through the comprehensive mapping of moraines from remote sensing data (Landsat 7 ETM+ satellite images; ASTER Global Digital Elevation Model (GDEM2); and Viewfinder Panorama DEM data). A total of 8414 moraines are mapped, and this record is integrated with a series of published age-estimates (n = 25), considered to chronologically-constrain former ice-margin positions. Geomorphological and chronological data are compiled in a Geographic Information System (GIS) to produce 'best estimate' reconstructions of ice extent during the global Last Glacial Maximum (gLGM) and, to a lesser degree, during earlier phases of glaciation. The data reveal that much of Far NE Russia (˜1,092,427 km2) preserves a glaciated landscape (i.e. is bounded by moraines), but there is no evidence of former ice masses having extended more than 270 km beyond mountain centres (suggesting that, during the Late Quaternary, the region has not been occupied by extensive ice sheets). During the gLGM, specifically, glaciers occupied ˜253,000 km2, and rarely extended more than 50 km in length. During earlier (pre-gLGM) periods, glaciers were more extensive, though the timing of former glaciation, and the maximum Quaternary extent, appears to have been asynchronous across the region, and out-of-phase with ice-extent maxima elsewhere in the Northern Hemisphere. This glacial history is partly explained through consideration of climatic-forcing (particularly moisture-availability, solar insolation and albedo), though topographic-controls upon the former extent and dynamics of glaciers are also considered, as are topographic-controls upon moraine deposition and preservation. Ultimately, our ability to understand the glacial and climatic history of this region is restricted when the geomorphological-record alone is considered, particularly as directly-dated glacial deposits are few, and topographic and climatic controls upon the moraine record are difficult to distinguish.

Barr, Iestyn D.; Clark, Chris D.

2012-10-01

80

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

81

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

NASA Astrophysics Data System (ADS)

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

Kirkbride, Martin; Everest, Jez; Benn, Doug

2014-05-01

82

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

NASA Astrophysics Data System (ADS)

Iztaccíhualt Volcano (19°10'20''N, 98°38'30''W, 5230 m asl) preserves an important moraine complex from the Little Ice Age (LIA), which stretches to 4300 m asl. These moraines are different from former ones because they are not covered by ash fall from the last plinian explosive phases of the nearby Popocatépetl volcano. In fact, the last emission of those pyroclasts took place during the XI century (Vázquez-Selem, 2000). The summit area of the Iztaccíhualt volcano still has glaciers whose terminus are located around 5000 m asl. From the end of the LIA until present the glacier terminus have ascended 700 m. To study the deglaciation process in Iztaccíhualt volcano from the LIA maximum to present, the Ayoloco valley was selected as it is the most important valley of the western slope of the volcano. Taking this valley as a reference, we determined the limits of glaciers in different dates by georeferencing the aerial and panoramic photographs (from 1897 to 2000) and analysing the 1958 field cartography of the glacial limits (Lorenzo, 1964). On the one hand, we carried out a statistical analysis of the size of the Rhizocarpon geographicum thallus and, on the other hand, we undertook a statistical study of the biodiversity of the lichen species through a number of cross-sections from the lowest LIA moraines to the current glacier snouts. This methodology allowed dating the exact moment in which the glacier retreated over certain points of the analysed cross-sections and determining the ecesis and the growth curve of the Rhizocarpon geographicum specie. In the Ayoloco valley the average growth rate is of 0.23 mm per year. From this information, we could deduce the evolution of the glacier from the LIA maximum to present. The results indicate that two main advances took place during the XVII and the XIX centuries. At the beginning of the XX century the glacier terminus were very close to the moraines of the maximum advance. An intense glacial retreat took place during the 40s and 50s, which was however interrupted during the 60s and 70s by a period of stabilization and re-advance. Since the mid-80s, we obreved an accelerated glacial retreat, that increased during the first decade of the XXI century. If this rate of retreat remains, the glaciers from Iztaccíhualt could disappear in 20 years. Research funded by POL2006-08405 & CGL2009-7343 project, Government of Spain.

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

2012-04-01

83

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

84

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

85

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

NASA Astrophysics Data System (ADS)

At the Last Glacial Maximum and during Termination-1 (~20-10 ka), marine evidence indicates that the grounding line of the West Antarctic Ice Sheet (WAIS) advanced northwards into the Ross Ice Shelf (RIS), blocking drainage of the Darwin and Hatherton outlet glaciers through the Transantarctic Mountains (TM) resulting in significant downstream thickening of glacier profiles. These outlet glaciers provide geological and glaciological records of EAIS expansion through the TMs as well as WAIS fluctuations which together suggest an LGM thickness of ~800 m lager than today at their confluence with the Ross Embayment. About 80 cosmogenic 10Be and 26Al exposure ages of erratics from 3 locations flanking the Hatherton Glacier (Dubris Valley near the EAIS source region, from Lake Wellman at its midpoint and Diamond Hill at its terminus) taken along transects covering 800 m in differential elevation from ice-sheet contact to mountain peaks documents 2.5 Ma of ice volume evolution of the Hatherton allowing a reconstruction of its quaternary paleo-ice surface. Pleistocene ice thickness is some 800 to 400 meters thicker between 2.5 to 0.5 Ma years ago than today . However at all 3 locations, exposure ages of mapped glacial drifts younger than 0.5 Ma at lower elevations down to current ice margin did not show any evidence for a distinct LGM advance. At Lake Wellman a cluster of mid-elevation moraine boulders from the Britannia Drift, previously taken to demarcate the LGM advance, have exposure ages ranging from 30 to 40 ka. At Dubris Valley, the same drift returned ages of 120-125 ka. At Diamond Hill, the confluence of the Darwin Glacier and RIS, two transects were sampled that cover an altitude range of 1100 meters. Cosmogenic dates show a similar trend to that seen further upvalley - the WAIS was approximately 900 meters thicker than the current Rose Ice Shelf configuration at ~1.5Ma and with only minor advances in the last 10ka and an absence of any LGM ages. The absence of a LGM signal is perplexing. We suggest the idea that while WAIS expansion during the early Pleistocene was large, LGM ice volume in the Darwin-Hatherton Glaciers was not as large as previously estimated and perhaps little different from what is observed today (at most 50 m above current ice surface). These results raise serious questions about the implications of a reduced East Antarctic ice Sheet at the LGM, and how the Antarctic ice sheets respond to global warming. Similar conclusions from 10Be exposure ages from coastal sites of the East Antarctic Ice Sheet in the Lambert Glacier-Amery Ice Shelf and at the Framnes Mountains also indicate a far reduced LGM ice volume at ~15ka than previously assumed.

Fink, David; Joy, Kurt; Storey, Bryan

2013-04-01

86

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

NASA Astrophysics Data System (ADS)

Recent rapid warming across the Antarctic Peninsula has resulted in ice-sheet thinning, dramatic ice-shelf collapse, acceleration of ice-flow velocities and widespread glacier recession. Reconstructing past rates, volumes and magnitudes of cryospheric change, particularly with respect to the former configuration of ice sheets and ice shelves, and their response to changing oceanic and climatic regimes, is vital in providing a context for this change, in order to improve predictions of future ice-sheet behaviour, and to provide glacio-isostatic adjustment corrections for gravimetric measurements of contemporary ice loss. This research aimed to investigate valley glacier and ice-shelf interactions during the Last Glacial Maximum (LGM) and Holocene Epoch across George VI Sound and Alexander Island, western Antarctic Peninsula, an area with a well-preserved but poorly dated record. We identify four principal stratigraphic units: (1) a high-elevation drift with Alexander Island erratics only (interpreted as recording older advances of ice from the interior of the island), (2) a lower-elevation drift with exotic Palmer Land erratics (interpreted as ice-shelf moraine, representing incursions of George VI Ice Shelf onto Ablation Point Massif), (3) multiple overlapping sequences of valley glacier moraine and ice-shelf moraine, presumed to be Holocene in age, and (4) more recent processes and units, including frozen epishelf lakes, slope processes and alluvial fans. On-going cosmogenic nuclide dating on these sediments (in progress; 25 10Be exposure ages) has the potential to unlock the complex history and interactions of ice streams, valley glaciers and ice shelves in this area. This work will also provide the first long-term record of sea-level indicators, allowing the first estimates of glacial unloading, rates of uplift and ice-sheet thinning to be calculated. The Holocene record of the ice shelf, preserved in the younger ice-shelf moraines and in the overlapping sequence of ice-shelf and valley-glacier moraines in Erratic Valley, will assist not only in tying together limnological records from the epishelf lakes and the onshore geomorphological record, but will also allow inferences about Holocene ice-shelf collapse to be made. Dating these samples will provide a sensitive record of the geomorphological impact of Holocene climatic variations.

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

2014-05-01

87

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

PubMed

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

Ahn, Jinho; Brook, Edward J

2014-01-01

88

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

PubMed Central

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

Ahn, Jinho; Brook, Edward J.

2014-01-01

89

First attempt to combine terrestrial cosmogenic nuclide ( 10 Be) and Schmidt hammer relative-age dating: Strauchon Glacier, Southern Alps, New Zealand  

Microsoft Academic Search

This study provides the first attempt to combine terrestrial (in situ) cosmogenic nuclide (10Be) surface exposure dating with Schmidt hammer relative-age dating for the age estimation of Holocene moraines at Strauchon\\u000a Glacier, Southern Alps, New Zealand. Numerous Schmidt hammer tests enable a multi-ridged lateral moraine system to be related\\u000a to three late-Holocene ‘Little Ice Age’-type events. On the basis of

Stefan Winkler

2009-01-01

90

Sea ice volume and age: Sensitivity to physical parameterizations and thickness resolution in the CICE sea ice model  

NASA Astrophysics Data System (ADS)

New dynamics parameterizations in Version 5 of the Los Alamos Sea Ice Model, CICE, feature an anisotropic rheology and variable drag coefficients. This study investigates their effect on Arctic sea ice volume and age simulations, along with the effects of several pre-existing model options: a parameter that represents the mean cumulative area of ice participating in ridging, the resolution of the ice thickness distribution, and the resolution of the vertical temperature and salinity profiles. By increasing shear stress between floes, the anisotropic rheology slows the ice motion, producing a thicker, older ice pack. The inclusion of variable drag coefficients, which depend on modeled roughness elements such as deformed ice and melt pond edges, leads to thinner ice and a more realistic simulation of sea ice age. Several feedback processes act to enhance differences among the runs. Notably, if less open water is produced mechanically through ice deformational processes, the simulated ice thins relative to runs with more mechanically produced open water. Thermodynamic processes can have opposing effects on ice age and volume; for instance, growth of new ice increases the volume while decreasing the age of the pack. Therefore, age data provides additional information useful for differentiating among process parameterization effects and sensitivities to other model parameters. Resolution of thicker ice types is crucial for proper modeling of sea ice volume, because the volume of ice in the thicker ice categories determines the total ice volume. Model thickness categories tend to focus resolution for thinner ice; this paper demonstrates that 5 ice thickness categories are not enough to accurately resolve the ice thickness distribution for simulations of ice volume.

Hunke, Elizabeth C.

2014-10-01

91

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

NASA Astrophysics Data System (ADS)

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

Seiser, Bernd; Fischer, Andrea

2014-05-01

92

Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion.  

NASA Astrophysics Data System (ADS)

It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum occurred prior to the Antarctic LGM (18-22 ka). No evidence based on cosmogenic ages for post-LGM or Holocene advances were found. These results support an extensive exposure age data set from the nearby Darwin-Hatherton Glacier system that indicates an absence of EAIS expansion across the Transantarctic Mnts during the global LGM period.

Fink, David; Joy, Kurt; Storey, Bryan

2014-05-01

93

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

94

Palaeogeography of South Lithuania during the last ice age  

NASA Astrophysics Data System (ADS)

The palaeogeographical development of South Lithuania during the last ice age (Nemunas = Weichselian) was reconstructed by various methods. The recurring permafrost and cryogenic structures in the ground were an important phenomenon of the southeastern periglacial zone. The 3-4 lithocomplexes of the extraglacial cover correlate with the Lithuanian and Mid-European Late Pleistocene Weichselian (Nemunas) biostratigraphic divisions. In the northwest, the palaeogeography is influenced by the deglaciation during the Žiogeliai (Frankfurt) Phase and the Baltija (Pomeranian) Stage of the last ice age. The deglatiation process is shown in a series of palaeogeography maps. During the Weichselian, the SW-NE oriented middle part of the area, commonly regarded as part of the Vilnius-Warsaw-Berlin Urstromtal (ice-marginal streamway), underwent intensive interstadial fluvial erosion and accumulation, glacial erosion and sedimentation, followed by subsequent glaciofluvial accumulation on sandurs and glaciolacustrine sedimentation in a series of small basins.

Baltr?nas, Valentinas; Švedas, K?stutis; Pukelyt?, Violeta

2007-01-01

95

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

96

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

97

PalaeobotanyIce-age steppe vegetation in east Beringia  

Microsoft Academic Search

The landmass known as Beringia is an extensive region that existed during the Pleistocene epoch and included the land bridge between present-day Siberia and Alaska, now submerged beneath the Bering Strait. It must have been covered with vegetation even during the coldest part of the most recent ice age (some 24,000 years ago) because it supported large populations of woolly

Grant D. Zazula; Duane G. Froese; Charles E. Schweger; Rolf W. Mathewes; Alwynne B. Beaudoin; Alice M. Telka; C. Richard Harington; John A. Westgate

2003-01-01

98

"Little Ice Age" climate of the North Atlantic sector  

E-print Network

­ p.7 #12;Motivation simulations of past climate quite good on hemispheric scale less good on regional scales "Little Ice Age" climate of the North Atlantic sector ­ p.8 #12;Motivation simulations of past with assimilating paleodata II no `ordinary' data-assimilation excercise low-temporal resolution low-density network

Schrier, Gerard van der

99

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

100

Milutin Milankovitch: Seeking the Cause of the Ice Ages  

NSDL National Science Digital Library

This online article, from Earth: Inside and Out, reports on how mathematician Milutin Milankovitch developed a complete astronomical theory of glaciers. It discusses his work charting the ice ages of the Pleistocene, which incorporated new information about how the gravitational tug of other planets causes small variations in the tilt of the Earth's axis.

101

The genetic legacy of the Quaternary ice ages  

Microsoft Academic Search

Global climate has fluctuated greatly during the past three million years, leading to the recent major ice ages. An inescapable consequence for most living organisms is great changes in their distribution, which are expressed differently in boreal, temperate and tropical zones. Such range changes can be expected to have genetic consequences, and the advent of DNA technology provides most suitable

Godfrey Hewitt

2000-01-01

102

Friday April 19, 2013 Chapters 12 and 14 "Ice Ages"  

E-print Network

­ "Ice Ages" Note ­ because campus was closed due to snow on Monday and Exam 3 was postponed until is that this glaciation was caused by the formation of an organic haze layer in the upper atmosphere that reflected light

Toohey, Darin W.

103

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

NASA Astrophysics Data System (ADS)

Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ˜26,500-˜19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the 'local LGM' (LLGM). We used 10Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr-1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the Ohau glacier record. The modeling experiments indicate that a snowline lowering of 920 ± 50 m and temperature depression of 6.25 ± 0.5 °C below modern values allows for the Ohau glacier to grow to an equilibrium position within the LGM moraine belt. Taken together with a glaciological simulation reported from the Irishman Stream valley, snowlines and temperatures increased by at least ˜520 m and ˜3.6 °C, respectively, between ˜18,000 and ˜13,000 yrs ago. Climate parameters derived from the Ohau glacier reconstruction are similar to those derived from glacier records from Patagonia, to air temperature indicators from Antarctica, as well as to sea-surface temperature and stratification signatures of the Southern Ocean. We think that the best explanation for the observed southern LLGM is that southern winter duration modulated Southern Ocean sea ice, which in turn influenced Southern Ocean stratification and made the surface ocean cooler. Orbitally induced cooling of the Southern Ocean provides an explanation for the LLGM in the Southern Alps having been coincident with the northern LGM. We argue further that the global effect of North Atlantic stadials led to disturbance of Southern Ocean stratification, southward shifts of the subtropical front, and retreat of Southern Alps glaciers. Collapse of Southern Ocean stratification during Heinrich Stadial-1, along with attendant sea-surface warming, triggered the onset of the Last Glacial termination in the Southern Alps of New Zealand.

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

2013-02-01

104

On the age of the young morainic morphology in the area ascribed to the maximum extent of the Weichselian glaciation in north-eastern Germany  

Microsoft Academic Search

In this case study, the first numerical ages from the area ascribed to the maximum extent of the Weichselian glaciation in north-eastern Germany are presented. The ages were derived from fluvioglacial (sandur) sediments of the Luckenwalde area using Optically Stimulated Luminescence dating techniques for the dating of quartz. The ages reveal a primary formation of the Luckenwalde outwash plain in

Christopher Lüthgens; Margot Böse; Matthias Krbetschek

2010-01-01

105

Intense storm activity during the Little Ice Age on the French Mediterranean coast L. Dezileau a,  

E-print Network

Intense storm activity during the Little Ice Age on the French Mediterranean coast L. Dezileau a November 2010 Available online 13 November 2010 Keywords: Lagoon Storm Little Ice Age North Atlantic increase in intense storms around 250 years ago occurs during the latter half of the Little Ice Age, a time

Demouchy, Sylvie

106

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

107

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

USGS Publications Warehouse

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.

2013-01-01

108

On the Origins of the Ice Ages: Insolation Forcing, Age Models, and Nonlinear Climate Change  

E-print Network

On the Origins of the Ice Ages: Insolation Forcing, Age Models, and Nonlinear Climate Change by Peter Huybers Submitted to the Department of Earth, Atmospheric and Planetary Sciences in partial .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Department of Earth, Atmospheric and Planetary Sciences May, 2004 Certified by

Huybers, Peter

109

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

110

Spatial pattern of mass loss processes across the Greenland Ice Sheet from the Little Ice Age to 2010  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet loses mass through surface meltwater runoff and discharge from marine terminating outlet glaciers. The spatial variability and magnitude of these processes have been studied and described in detail for the past decades. Here, we combine the mass loss between the LIA to 2010 with a SMB model extending back to ~1900 in order to investigate the spatial distribution of mass loss processes. We use high quality aerial stereo photogrammetric imagery recorded between 1978 and 1987 to map morphological features such as trim lines and end moraines marking the maximum ice extent of the LIA, which enables us to obtain vertical point-based differences associated with former ice extent. These point measurements are combined with contemporary ice surface differences derived using NASA's Airborne Topographic Mapper (ATM) from 2003-2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, and ASTER (Silcast AST14DMO) co-registered to ICESat, to estimate mass loss throughout the 20th and early 21st Century. The mass balance estimates of the GrIS since retreat from maximum LIA is combined with a SMB model for the period for three intervals, LIAmax (~1900) - 1978/87, 1978/87 - 2003, and 2003 - 2010. Across the GrIS the total mass loss if found to be spatially- and temporally variable. However, when assessing the mass loss due to SMB and mass loss due to dynamic ice loss, we find that that the ratios between these components are variable between the different sectors of the GrIS, e.g. in the southeast sector of the GrIS we find substantial mass loss, possibly driven by high precipitation rates but also the presence of a large number of marine terminating glaciers. Furthermore many areas currently undergoing changes correspond to those that experienced considerable thinning throughout the 20th century. Consequently, comparing the 20th century thinning pattern to that of the last decade, and assuming a similar warming pattern, we argue that the present sensitivity distribution will hold also for future ice sheet mass loss until marine outlet glaciers become grounded.

Kjaer, K.; Korsgaard, N. J.; Kjeldsen, K. K.; Bjork, A. A.; Khan, S. A.; Funder, S.; Nuth, C.; Larsen, N. K.; Vinther, B.; Andresen, C. S.; Long, A. J.; Woodroffe, S.; Hansen, E. S.; Odgaard, B. V.; Olsen, J.; Bamber, J. L.; van den Broeke, M. R.; Box, J. E.; Willerslev, E.

2013-12-01

111

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

NASA Astrophysics Data System (ADS)

Millennial-scale temperature variations in Antarctica during the period 80,000 to 18,000 years ago are known to anti-correlate broadly with winter-centric cold-warm episodes revealed in Greenland ice cores. However, the extent to which climate fluctuations in the Southern Hemisphere beat in time with Antarctica, rather than with the Northern Hemisphere, has proved a controversial question. In this study we determine the ages of a prominent sequence of glacial moraines in New Zealand and use the results to assess the phasing of millennial climate change. Forty-four 10Be cosmogenic surface-exposure ages of boulders deposited by the Pukaki glacier in the Southern Alps document four moraine-building events from Marine Isotope Stage 3 (MIS 3) through to the end of the Last Glacial Maximum (?18,000 years ago; LGM). The earliest moraine-building event is defined by the ages of nine boulders on a belt of moraine that documents the culmination of a glacier advance 42,000 years ago. At the Pukaki locality this advance was of comparable scale to subsequent advances that, from the remaining exposure ages, occurred between 28,000 and 25,000, at 21,000, and at 18,000 years ago. Collectively, all four moraine-building events represent the LGM. The glacier advance 42,000 years ago in the Southern Alps coincides in Antarctica with a cold episode, shown by the isotopic record from the EPICA Dome C ice core, between the prominent A1 and A2 warming events. Therefore, the implication of the Pukaki glacier record is that as early as 42,000 years ago an episode of glacial cold similar to that of the LGM extended in the atmosphere from high on the East Antarctic plateau to at least as far north as the Southern Alps (?44°S). Such a cold episode is thought to reflect the translation through the atmosphere and/or the ocean of the anti-phased effects of Northern Hemisphere interstadial conditions to the southern half of the Southern Hemisphere. Regardless of the mechanism, any explanation for the cold episode at 42,000 years ago must account for its widespread atmospheric footprint not only in Antarctica but also within the westerly wind belt in southern mid-latitudes.

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

2014-11-01

112

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

113

Soil translocation by water erosion from agricultural cropland into wet depressions (morainic kettle holes)  

Microsoft Academic Search

Wet depressions are important habitats in the agricultural landscape. In NE Germany, many of these depressions are morainic kettle holes containing temporary or permanent water bodies. Such kettle holes were formed at the end of the last glaciation, about 12,000 yr ago, by slowly melting blocks of buried dead ice. Because of the considerable relief in the resulting small inland

Martin Frielinghaus; Wilhelm-Günther Vahrson

1998-01-01

114

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

SciTech Connect

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

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

1992-03-01

115

Slope stability of moraines, Cordillera Blanca, Peru  

NASA Astrophysics Data System (ADS)

Landslides originating from inner slopes of moraine dams are often capable of producing glacial lakes outburst floods (GLOFs). Therefore assessing stability conditions of the moraines is important for predicting this potentially damaging phenomenon. Characteristics of the basic mechanical properties of the material and geophysical investigations were applied to collect necessary information for slope stability assessment of the Palcacocha Lake moraine dam, Peru. The lake is situated in the Cordillera Blanca Mts. at the altitude of about 4,500m asl and produced catastrophic GLOF in 1941. Another minor flood originated in 2003 due to landslide impact into the lake. Detailed investigations of this landslide site included geomorphological mapping, geophysical investigations and characterization of basic mechanical properties of the forming material. Geomorphological mapping identified dormant landslide with scarp up to 2m high which developed on the edge of the inner moraine slope. It is conditioned by set of parallel extension trenches which also affected the origin of 2003 landslide. Within its scarp area, significant water bearing layer was noticed around 10 m bellow the moraine surface. Three profiles were investigated using electric resistivity tomography performed on 4poing light instrument with 24 electrodes and with spacing ranging from 1 to 4m. Results helped to verify geometry of the main shear plane of the mapped landslide as well as the spacing and depth of extension trenches. Significant heterogeneity in the moraine resistivity characteristics was found. The high resistivity regions are explained by rock block accumulation whereas the low resistivity may represent wet layers within the moraine body. Grain size distribution of 33 disturbed soil samples originating from moraine material within the Cordillera Blanca Mts., Peru were determined and classified according to the UCSC classification system. The samples were taken from moraine dams and slopes covered by moraine material. 11 samples were also tested for the angle of repose. These results were compared with literature data relating grains size distribution of similar soil types with measured shear strength characteristics to assess peak shear strength ?max of the analyzed samples. Rough estimates of these values indicate that the moraine material gains 35°-38o. These estimates are verified by measured angle of repose. Results of the grain size distribution were also used to estimate average hydraulic conductivity applying Hazen formula. This estimates show that investigated moraine material range from 6x10-6 to 3x10-4 m/s.

Klimes, J.; Novotny, J.

2012-12-01

116

Subdivision of Late Pleistocene Moraines in the Cordillera Blanca, Peru, Based on Rock-Weathering Features, Soils, and Radiocarbon Dates  

NASA Astrophysics Data System (ADS)

The progressive development of unusual rock-weathering features and soils and minimum-limiting radiocarbon dates provide a basis for subdividing four groups of late Pleistocene moraines on the west side of the Cordillera Blanca, northern Peru (9°20'1°000'S, 77°10'-77°30'W). Boulders on the youngest late Pleistocene moraines have 10 to 14-cm-tall weathering posts; soils on these moraines yield mean profile development index (PDI) values of 0.05 ± 0.04 (±1?). These moraines date between ca. 13,500 and 9700 ± 500 yr B.P., older than previously postulated. The next older moraines have boulders with weathering-post heights between 20 and 25 cm and soils with PDI values of 0.08 ± 0.07, and were deposited prior to 13,280 ± 190 yr B.P., probably during the last glacial maximum (marine isotope stage 2). Moraines from an older glaciation have boulders with weathering posts between 39 and 50 cm high, soils that yield PDI values of 0.21 ± 0.07, and are older than 19,700 ± 340 yr B.P. Boulders on moraines from a still older glaciation have lost ca. 50% of their above-ground volume, and have weathering posts between 62 and 70 cm high. PDI values for soils on these moraines are 0.32 ± 0.06. Linear and logarithmic models of weathering-post and soil development with time are used to estimate minimum and maximum ages for the two oldest moraine groups. Linear models suggest that the second oldest moraines are between ca. 20,500 and 46,500 yr B.P., and that the oldest moraines are between ca. 29,000 and 72,000 yr B.P. In contrast, logarithmic models suggest ages of greater than ca. 75,500 yr B.P. and greater than ca. 500,000 yr B.P., respectively.

Rodbell, Donald T.

1993-03-01

117

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

NASA Astrophysics Data System (ADS)

Hillslopes in glacially formed landscapes are typically characterized by talus cones developed beneath free rock faces. Studying hillslopes as sedimentary source, storage and transfer zones as well as surface processes acting on hillslopes since the end of the deglaciation is of importance in order to gain a better understanding of the complex sedimentary source-to-sink fluxes in cold climate environments. Hillslopes function as a key component within the geomorphic process response system. Large areas of the Norwegian fjord landscapes are covered by hillslopes and are characterized by the influences of the glacial inheritance. This PhD project is part of the NFR funded SedyMONT-Norway project within the ESF TOPO-EUROPE SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) programme. The focus of this study is on geomorphic influences of the Little Ice Age glacial advance on postglacial hillslope systems in four distinct headwater areas of the Erdalen and Bødalen valleys in the Nordfjord valley-fjord system (inner Nordfjord, Western Norway). Both valleys can be described as steep, U-shaped and glacier-fed, subarctic tributary valleys. Approximately 14% of the 49 km2 large headwater areas of Erdalen are occupied by hillslope deposits and 41% by rock surfaces; in Bødalen hillslope deposits occupy 12% and rock surfaces occupy 38% of the 42 km2 large headwater areas. The main aims of this study are (i) to analyze and compare the morphometric characteristics as well as the composition of hillslope systems inside and outside of the Little Ice Age glacial limit, (ii) to detect possible changes within the mass balances of these hillslope systems, (iii) to identify the type and intensity of currently acting hillslope processes as well as (iv) to determine possible sediment sources and delivery pathways within the headwater areas of the catchments. The process-based approach includes orthophoto- and topographical map interpretation, hillslope profile surveying, photo monitoring, geomorphological mapping as well as GIS and DEM computing. Two appropriate hillslope test sites within each headwater area are selected in order to follow the main aims of this study. The designed monitoring instrumentation of the slope test sites includes nets for collecting freshly accumulated rockfall debris, stone tracer lines for measuring surface movements, wooden sticks for monitoring of slow surface creep movements and peg lines for depth-integrated measurements of slow mass movements. In addition, remote site cameras for monitoring rapid mass movement events (avalanches, slush- and debris flows) and slope wash traps for analyzing slope wash denudation are installed and measurements of solute concentrations at small hillslope drainage creeks for investigating the role of chemical denudation are conducted. Measurements of morphometric characteristics and longitudinal profiles along the main axis of the talus cones are carried out at each test site. The manually obtained longitudinal profile data are combined with data derived from a DEM in order to generate complete longitudinal hillslope profiles reaching from the apex until the slope foot. Preliminary results show a steepening trend of the talus cones located inside the Little Ice Age glacier limit which is due to erosion during the Little Ice Age glacial advance. In addition, some of these talus cones are characterized by a recognizable more complex talus cone morphometry and composition, resulting from implementation of Little Ice Age glacier side moraines. The combination of (i) steepened talus cones and (ii) complex composition seems to increase currently acting hillslope processes which leads to a higher sediment delivery from these slopes as compared to hillslopes outside the Little Ice Age glacier limit. The implementation of moraine material but also the increased intensity of denudative processes has a recognizable influence on the mass balance of the hillslope systems inside the Little Ice Age glacier limit. Research on the complex developmen

Laute, Katja; Beylich, Achim A.

2010-05-01

118

Glacier retreat since the Little Ice Age in the eastern Nyainqêntanglha Range, southeastern Tibet  

NASA Astrophysics Data System (ADS)

The remote eastern Nyainqêntanglha Range in southeastern Tibet is situated in a transition zone between warm-wet subtropical and cold-dry plateau climate conditions. In this high mountain environment, intense summer monsoon rainfalls support numerous temperate glaciers despite the latitude of ~29° to ~31°N. Due to the outstanding importance of the monsoonal airmasses for the water cycle of the whole region, it is a key area to study climate and subsequent glacier change in High Asia. Here, we present the results of a study in which 1964 glaciers were mapped by remote sensing from a Landsat ETM+ scene and subsequently parameterized by DEM supported measurements. Geomorphological evidence, such as glacier trimlines and latero-frontal moraines, was used to delineate the Little Ice Age (LIA) maximum glacier advance terminus positions. Statistical analysis of glacier length change revealed an average retreat of ~40 % and a trend towards stronger retreat for smaller glaciers. Calculated ELAs show a southeast-northwest gradient ranging from 4,400 to 5,600 m a.s.l. and an average ELA rise of ~98 m since the LIA. Due to the large amount of measurements the ELA distribution reveals topographic effects down to the catchment scale, i.e. orographic rainfall and leeward shielding. This gives numerous hints on the relief-climate-glacier interactions and allows a simplified reconstruction of the flow patterns of the monsoonal air masses. Contrasting to the expectations for subtropical settings, glaciers on south facing slopes have not retreated strongest and ELAs on south facing slopes did not rise furthest. Instead, highly heterogeneous spatial patterns emerge that show a strong imprint of both, topography and monsoonal dynamics. Our results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings due to the coincidence of accumulation and ablation phases. First, monsoon intensity directly controls the amount of precipitation and additionally influences temperature through cloud cover. Second, many glaciers in the study area have steep upper accumulation areas. In these settings, temperature rise rapidly reduces the size of the accumulation areas. Additionally, the larger portion of precipitation that is falling as rain instead of snow results in increased melting through lowered albedos and the effects of liquid water in the glacier system.

Loibl, David; Grießinger, Jussi; Lehmkuhl, Frank

2014-05-01

119

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

NASA Astrophysics Data System (ADS)

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

Martin, C.; Gudmundsson, G. H.

2012-04-01

120

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

121

Instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of Brúarjökull, Iceland  

NASA Astrophysics Data System (ADS)

Contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments. This study concerns the ice-marginal environment of the surge-type Brúarjökull in Iceland. The sediment distribution in the glacier forefield as well as the morphology, sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment/landform associations. As a result of substrate/bedrock decoupling during the 1890 surge, subglacial sediment was dislocated across the bedrock surface and deformed compressively, leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone. A drop in subglacial porewater pressure at the very end of the surge led to substrate/bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate. Simultaneously, the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine-ridge construction. Fine-grained and incompetent sediment deformed in ductile manner, resulting in a narrow moraine dominated by rooted folds, while coarse-grained and competent sediment deformed in brittle fashion, resulting in a wider moraine dominated by thrust blocks. A new sequential model of subglacial and ice-marginal processes operating during a glacier surge is proposed, illustrating the stepwise formation of a marginal sediment wedge and an end moraine—a twofold, inseparable marginal end-product that formed during the last days of the 1890 surge.

Benediktsson, Ívar Örn; Möller, Per; Ingólfsson, Ólafur; van der Meer, Jaap J. M.; Kjær, Kurt H.; Krüger, Johannes

2008-02-01

122

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

USGS Publications Warehouse

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

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

2005-01-01

123

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

124

Ice Age Epochs and the Sun's Path Through the Galaxy  

E-print Network

We present a calculation of the Sun's motion through the Milky Way Galaxy over the last 500 million years. The integration is based upon estimates of the Sun's current position and speed from measurements with Hipparcos and upon a realistic model for the Galactic gravitational potential. We estimate the times of the Sun's past spiral arm crossings for a range in assumed values of the spiral pattern angular speed. We find that for a difference between the mean solar and pattern speed of Omega_Sun - Omega_p = 11.9 +/- 0.7 km/s/kpc the Sun has traversed four spiral arms at times that appear to correspond well with long duration cold periods on Earth. This supports the idea that extended exposure to the higher cosmic ray flux associated with spiral arms can lead to increased cloud cover and long ice age epochs on Earth.

D. R. Gies; J. W. Helsel

2005-03-14

125

Variations in the age of Arctic sea-ice and summer sea-ice extent Ignatius G. Rigor1,2  

E-print Network

. On time scales of days to weeks, wind stresses from storms produce ridges of sea-ice and areas of open. The number of storms that any given parcel of ice has experienced is cumulative, and hence the amountVariations in the age of Arctic sea-ice and summer sea-ice extent Ignatius G. Rigor1,2 and John M

Rigor, Ignatius G.

126

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

127

The possible role of Brazilian promontory in Little Ice Age  

NASA Astrophysics Data System (ADS)

The Gulf Stream, one of the strongest currents in the world, transports approximately 31 Sv of water (Kelly and Gille, 1990; Baringer and Larsen, 2001; Leaman et al., 1995) and 1.3 × 1015 W (Larsen, 1992) of heat into the Atlantic Ocean, and warms the vast European continent. Thus any change of the Gulf Stream could lead to the climate change in the European continent, and even worldwide (Bryden et al., 2005). Past studies have revealed a diminished Gulf Stream and oceanic heat transport that was possibly associated with a southward migration of intertropical convergence zone (ITCZ) and may have contributed to Little Ice Age (AD ?1200 to 1850) in the North Atlantic (Lund et al., 2006). However, the causations of the Gulf Stream weakening due to the southward migration of the ITCZ remain uncertain. Here we use satellite observation data and employ a model (oceanic general circulation model - OGCM) to demonstrate that the Brazilian promontory in the east coast of South America may have played a crucial role in allocating the equatorial currents, while the mean position of the equatorial currents migrates between northern and southern hemisphere in the Atlantic Ocean. Northward migrations of the equatorial currents in the Atlantic Ocean have little influence on the Gulf Stream. Nevertheless, southward migrations, especially abrupt large southward migrations of the equatorial currents, can lead to the increase of the Brazil Current and the significant decrease of the North Brazil Current, in turn the weakening of the Gulf Stream. The results from the model simulations suggest the mean position of the equatorial currents in the Atlantic Ocean shifted at least 180-260 km southwards of its present-day position during the Little Ice Age based on the calculations of simple linear equations and the OGCM simulations.

Zou, Youjia; Xi, Xiangying

2014-09-01

128

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

129

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

130

Readvance of the last British-Irish Ice Sheet during Greenland Interstade 1 (GI-1): the Wester Ross Readvance, NW Scotland  

NASA Astrophysics Data System (ADS)

Fourteen samples obtained from Torridon sandstone boulders on four moraines marking the limit of the Wester Ross Readvance (WRR) in NW Scotland yielded tightly clustered 10Be exposure ages confirming contemporaneous or penecontemporaneous moraine deposition. Collectively, the 14 samples yield mean ages of 13.5 ± 1.2 ka to 14.0 ± 1.7 ka, depending on choice of geomagnetic scaling and sampling surface erosion rates. All fourteen moraine ages are significantly younger than an age of ca 16.3 ka previously proposed for the WRR, and also younger than most samples obtained from rock outcrops within the WRR limits. The ages obtained for the WRR moraines appear to confirm that a substantial cover of glacier ice persisted over low ground in NW Scotland during at least the early part of the Lateglacial Interstade (?Greenland Interstade 1). We infer that the WRR probably occurred in response to rapid short-lived cooling during the Older Dryas climatic reversal (?Greenland Interstade 1d), though the possibilities that the WRR represents ice-margin response to a later climatic reversal during the Lateglacial Interstade or stabilization and readvance of the ice margin following rapid offshore calving cannot be discounted.

Ballantyne, Colin K.; Schnabel, Christoph; Xu, Sheng

2009-05-01

131

ForPeerReview Ice age True Polar wander in a compressible and non  

E-print Network

ForPeerReview Ice age True Polar wander in a compressible and non hydrostatic Earth Journal approach" to the Earth's rotation developed during the eighties and nineties, both for ice age and mantle of Earth Sciences "A. Desio" Ricard, Yanick; ENS Lyon, Earth's Sciences Keywords: Earth rotation variations

132

Response of the Greenland ice sheet to ice age cycles and to recent climate changes  

Microsoft Academic Search

The Greenland ice sheet is seldom in a steady state, because of climate change and transient ice dynamic response. Observations on elevation both by geodetic methods on the ground and by satellite alti- metry suggest a slight change in elevation of about 10 mm per year at the centre part of the ice sheet. The aims of this work are

AYAKO ABE-OUCHI

1994-01-01

133

Foraminiferal isotope evidence of reduced nitrogen fixation in the ice age Atlantic Ocean.  

PubMed

Fixed nitrogen (N) is a limiting nutrient for algae in the low-latitude ocean, and its oceanic inventory may have been higher during ice ages, thus helping to lower atmospheric CO2 during those intervals. In organic matter within planktonic foraminifera shells in Caribbean Sea sediments, we found that the 15N/14N ratio from the last ice age is higher than that from the current interglacial, indicating a higher nitrate 15N/14N ratio in the Caribbean thermocline. This change and other species-specific differences are best explained by less N fixation in the Atlantic during the last ice age. The fixation decrease was most likely a response to a known ice age reduction in ocean N loss, and it would have worked to balance the ocean N budget and to curb ice age-interglacial change in the N inventory. PMID:19095896

Ren, H; Sigman, D M; Meckler, A N; Plessen, B; Robinson, R S; Rosenthal, Y; Haug, G H

2009-01-01

134

The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia  

NASA Astrophysics Data System (ADS)

The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field mapping, GIS analysis, statistical associations between landslides and terrain attributes, and a comparison between Neoglaciated and non-Neoglaciated terrain within each basin. The bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the LIA trimline. Valleys carved in weak Quaternary volcanics show significant erosional oversteepening and contain deep-seated slope movement features, active rock fall, rock slides, and rock avalanches near glacial trimlines. Basins in stronger granitic rock rarely show increased bedrock instability resulting from post-LIA retreat, except for shallow-seated rock slides along some trimlines and failures on previously unstable slopes. In surficial materials, landslides associated with post-LIA retreat originate in till or colluvium, as debris slides or debris avalanches, and are concentrated along lateral moraines or glacial trimlines. Significant spatial association was also observed between recent catastrophic failures, gravitational slope deformation, and slopes that were oversteepened then debuttressed by glacial erosion. Eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep-seated gravitational slope movement, implying that this type of deformation is a precursor to catastrophic detachment.

Holm, Kris; Bovis, Michael; Jakob, Matthias

2004-02-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

137

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. No satisfactory match using an isotropic flow law could be found because of too high vertical velocities and much too high horizontal ones in simulations despite varying enhancement factor, geothermal heat flux and surface temperatures over large ranges. However, the existence of a pronounced ice fabric may explain the observed present-day surface velocity and mass balance 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 noncollinear 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. This is the first time that the importance of anisotropy has been demonstrated in the ice dynamics of a blue ice area and demonstrates the need 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.

2014-04-01

138

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 sulphate 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 that will represent ageing but not internal mixing with in(organic) compounds. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone exposures 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 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. Additionally, these are also the first results to show a suppression of heterogeneous ice nucleation without the condensation of a coating of (in)organic material. In immersion mode, low exposure Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka whereas high exposure 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, where as high exposure ATD had ice active fractions up to a factor of 4 lower than untreated ATD. Based on our results, we present parameterizations in terms of ns(T) that can represent ice nucleation of atmospherically aged and non-aged particles for both immersion and deposition mode. We find excellent agreement (to within less than a factor of 2) with field measurements when parameterizations derived from our results are used to predict ice nuclei concentrations in the troposphere.

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

2013-04-01

139

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

140

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

141

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

USGS Publications Warehouse

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

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

2005-01-01

142

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

NASA Technical Reports Server (NTRS)

The valleys of the Mono Basin contain several sets of lateral and terminal moraines representing multiple stages of glaciation. The semi-arid climate with slow weathering rates preserved sequences of nested younger moraines within older ones. There is a well established relative chronology and recently exposure dating provided a new set of numerical dates. The moraines span the late Wisconsin (11-25 ka) to the Illinoian (130-190 ka) glaciations. The Mono Basin area was used as a 'calibration site' to establish remote dating techniques for eventual transfer to the more inaccessible but geomorphically and climatically similar moraines of the South American Andes Mountains. Planned polarimetric synthetic aperture radar (SAR) imagery acquired by JPL AIRSAR (South American Campaign) and SIR-C (Andes super-site) are analyzed to establish chronologies of previously undated moraine sequences in a study of Pleistocene climatic change in the Southern Hemisphere. The dry climate and sparse vegetation is also favorable for correlation of ground surface roughness with radar polarization signature. The slow weathering processes acting over thousands of years reduce the size, frequency, and angularity of surface boulders while increasing soil development on the moraines. Field observations based on this hypothesis result in relative ages consistent with those inferred from nested position within the valley. Younger moraines, therefore, will appear rougher than the older smoother moraines at scales measurable at AIRSAR wavelengths. Previously documented effects of ground surface roughness on polarization signatures suggest that analysis of moraine polarization signatures can be useful for relative dating. The technique may be extended to predict numerical ages. The data set reported were acquired on 8 Sep. 1989 with the JPL Airborne SAR (AIRSAR) collecting polarimetric imagery at C- (5.6 cm), L- (24 cm), and P-band (68 cm) with a flight-line parallel to the strike of the mountains. Phase calibration was performed on the analyzed scene by setting the co-phase of a smooth lake to zero as described. Absolute amplitude calibration was not possible because corner reflectors were not deployed.

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

1992-01-01

143

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

USGS Publications Warehouse

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

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

1989-01-01

144

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

NASA Astrophysics Data System (ADS)

Mountain glaciers are highly sensitive to variations in temperature and precipitation, and so moraine records from such systems are strong indicators of climate change. Due to the prevailing trend of retreat of the majority of mountain glaciers globally over the last few decades, there are limited opportunities to observe moraine formation, especially at temperate alpine glaciers. In the Southern Alps of New Zealand, while glaciers have all experienced a major retreat since the late 19th century, within this loss of ice mass, there has been a distinct variance in individual glacier response. Indeed, while Tasman Glacier, the longest glacier in the Southern Alps has thinned and entered into the current phase of calving retreat in the early 1990s, the steeper, more responsive glaciers to the west of the Main Divide, such as Franz Josef and Fox Glacier have experienced more elaborate advance/retreat phases. We focus on moraine formation at Fox Glacier, a c. 12.5 km long valley glacier terminating at 300 m above sea level. Fox Glacier retreated substantially since the 1930s, before advancing 800 m between the mid-1980s and 1999. A minor retreat then followed until 2005, succeeded by a 300 m re-advance until 2007-8. Continued retreat and down-wasting has since followed. Superimposed on this alternating advance/retreat cycle, have been minor winter re-advances. Sedimentological and morphological information were combined with detailed observations, historical photos and recent time-lapse photography of the terminus. Characteristics of several modes of moraine formation have been observed: (1) the late 20th century advance culminated in a broad <5 m high terminal moraine, formed by an admixture of "bulldozed" proglacial sediments and dumping of supraglacial material; (2) the 21st century short-lived advances were characterized by 1-2 m high (often multi-crested) ridges with a "saw-tooth" plan-form controlled by longitudinal crevasses outcropping at the terminus; (3) time-lapse imagery identified thrusting and subsequent melt-out of fine-grained englacial material along reverse faults intersecting the terminal face as a significant contributor to the subdued terminal moraines forming during the most recent phase of recent recession; (4) collapse of lateral moraines due to post-2008 down-wasting is now proceeding. Overall, even short-term preservation of glacigenic sediment-landform associations on the Fox Glacier sandur is limited by the glacial meltwater regime, with lateral migration of the proglacial river continually reworking morainic material.

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

2012-04-01

145

The WAIS-Divide deep ice core WD2014 chronology - Part 2: Methane synchronization (68-31 ka BP) and the gas age-ice age difference  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet (WAIS)-Divide ice core (WAIS-D) is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WAIS-D gas age-ice age difference (?age) using a combination of firn densification modeling, ice flow modeling, and a dataset of ?15N-N2, a proxy for past firn column thickness. The largest ?age at WAIS-D occurs during the last glacial maximum, and is 525 ± 100 years. Internally consistent solutions can only be found when assuming little-to-no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WAIS-D chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu speleothem record. The small ?age at WAIS-D provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the bipolar "seesaw".

Buizert, C.; Cuffey, K. M.; Severinghaus, J. P.; Baggenstos, D.; Fudge, T. J.; Steig, E. J.; Markle, B. R.; Winstrup, M.; Rhodes, R. H.; Brook, E. J.; Sowers, T. A.; Clow, G. D.; Cheng, H.; Edwards, R. L.; Sigl, M.; McConnell, J. R.; Taylor, K. C.

2014-08-01

146

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

147

The Pangean ice age: studies with a coupled climate-ice sheet model  

Microsoft Academic Search

Application of an ice sheet model developed for the Pleistocene to the extensive Carboniferous glaciation on Gondwana yields\\u000a an ice sheet which has several features consistent with observations. While complete deglaciation is not achieved without\\u000a CO2 changes, the Milankovich-induced fluctuations in ice sheet volume are comparable to Pleistocene glacial\\/ interglacial signals.\\u000a This result is shown to hold for a large

W. T. Hyde; T. J. Crowley; L. Tarasov; W. R. Peltier

1999-01-01

148

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

149

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

NASA Astrophysics Data System (ADS)

The age of ice in permafrost is an indicator of past climate history, and of the resilience and response of high-latitude ecosytems to global change. Methods such as radiocarbon dating and tephrachronology are limited in permafrost because they provide indirect age control, and could overestimate ages when ice is intermittently absent. Development of geochemical indicators of water/ice residence time in permafrost is critical for understanding the circumstances and primary controls of permafrost formation, preservation, and thaw in response to climate change. We analyzed uranium isotopes to evaluate the age of segregated ice in ice-rich loess permafrost (yedoma) cores from central Alaska. Activity ratios of 234U vs. sup>238U (234/238U ARs) in thawed waters exceed 1.000 due to extended contact of ice with mineral surfaces over time. Ice is expected to increase in age with depth at this location based on the presence of deep loess, cryostructures associated with syngenetic permafrost aggracation, high segregated ice content, and frequent wedge ice. These features indicate that permafrost formed syngenetically as loess was deposited. Consequently, (234/238U ARs are expected to increase with depth as recoil 234U, derived from in situ decay of (238U in loess particles, accumulates in ice without being flushed over time. Values of (234/238U ARs measured for ice from a series of five neighboring cores up to 21 m deep increase with depth, consistent with downhole increases in permafrost age. Additional variability of (234/238U ARs with depth can be attributed to variations in surface area of solids determined by analysis of particle size distribution. Radiocarbon analysis of dissolved organic carbon indicates that the ages of ice are greater than ~36ky below the upper few meters, consistent with previous work on soil organic-matter profiles in this area. Using these measured parameters, a model of (234/238U AR evolution indicates minimum ages up to a minimum of ~100ky in the deepest core. Our results suggest that in this area of deep, ice-rich, syngenetic loess permafrost, ice bodies below the modern active layer (uppermost ~1 m) were formed during the last glacial period, starting 110 ky ago, and were preserved through subsequent fluctuations in climate and vegetation.

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

2010-12-01

150

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

151

'Little Ice Age' summer temperature variations: their nature and relevance to recent global warming trends  

Microsoft Academic Search

Climatic changes resulting from greenhouse gases will be superimposed on natural climatic variations. High-resolution proxy records of past climate can be used to extend our perspective on regional and hemispheric changes of climate back in time by several hundred years. Using historical, tree-ring and ice core data, we examine climatic variations during the period commonly called the 'Little Ice Age'.

Raymond S. Bradley; Philip D. Jonest

1993-01-01

152

OSL ages on glaciofluvial sediment in northern Lower Michigan constrain expansion of the Laurentide ice sheet  

E-print Network

dating; Laurentide ice sheet Introduction Grayling Fingers is the name given to a large, upland landform ice sheet Randall J. Schaetzl a,, Steven L. Forman b a Department of Geography, 128 Geography BuildingOSL ages on glaciofluvial sediment in northern Lower Michigan constrain expansion of the Laurentide

Schaetzl, Randall

153

The 100 Kyr Ice Age Cycle: Inception and Demise  

Microsoft Academic Search

The quasi-periodic variation of continental ice volume that has been a dominant characteristic of low frequency climate variability since approximately 900 ka continues to defy detailed explanation. Although the linkage between this \\

R. W. Peltier

2001-01-01

154

Neoglacial fluctuations of terrestrial, tidewater, and calving lacustrine glaciers, Blackstone-Spencer Ice Complex, Kenai Mountains, Alaska  

NASA Astrophysics Data System (ADS)

The glaciers surrounding the Blackstone-Spencer Ice Complex display a variety of termini types: Tebenkov, Spencer, Bartlett, Skookum, Trail, Burns, Shakespeare, Marquette, Lawrence, and Ripon glaciers end in terrestrial margins; Blackstone and Beloit glaciers have tidewater termini; and Portage Glacier has a calving lacustrine margin. In addition, steep temperature and precipitation gradients exist across the ice complex from the maritime environment of Prince William Sound to the colder, drier interior. The Neoglacial history of Tebenkov Glacier, as based on overrun trees near the terminus, shows advances ca. 250- 430 AD (calibrated date), ca. 1215-1275 AD (calibrated date), and ca. 1320-1430 AD (tree ring evidence), all intervals of glacier advance around the Gulf of Alaska. However, two tidewater glaciers in Blackstone Bay retreated from their outermost moraines by 1350 AD, apparently asynchronously with respect to the regional climate signal. The most extensive Kenai Mountain glacier expansions during Neoglaciation occurred in the late Little Ice Age. The outermost moraines are adjacent to mature forest stands and bog peats that yield dates as old as 5,600 BP. Prince William Sound glaciers advanced during two Little Ice Age cold periods, 1380-1680 and 1830-1900 AD. The terrestrial glaciers around the Blackstone-Spencer Ice Complex all built moraines during the 19th century and began retreating between 1875 and 1900 AD. Portage and Burns glaciers began retreating between 1790 and 1810 AD, but their margins remained close to the outermost moraines during the 19th century. Regional glacier fluctuations are broadly synchronous in the Gulf of Alaska region. With the exception of the two tidewater glaciers in Blackstone Bay, all glaciers in the Kenai Mountains, no matter their sizes, altitudes, orientations, or types of margins, retreated at the end of the Little Ice Age. The climate signal, especially temperature, appears to be the strongest control on glacier behavior during the last millennium.

Crossen, Kristine June

1997-12-01

155

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

156

Records of past ice sheet fluctuations in interior East Antarctica  

USGS Publications Warehouse

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

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

2007-01-01

157

Climatic basis for sluggish macroevolution during the late Paleozoic ice age  

NASA Astrophysics Data System (ADS)

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

Powell, Matthew G.

2005-05-01

158

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

159

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

160

Estimations of the age of the ice beneath Dome A, Antarctica  

NASA Astrophysics Data System (ADS)

The drilling of a deep ice core at the Chinese Kunlun station, Dome A, East Antarctica, is about to start with high expectations on obtaining the oldest possible ice so far. The Alpine type bedrock of the Gamburtsev mountains in combination with a largely undetermined geothermal heat flux distribution raises questions on the basal thermal conditions that via the melting rate have a strong feedback on the vertical flow velocity and in consequence on the age/depth horizons. Additionally, the undetermined ice fabric introducing anisotropic effects in rheology have to be taken into account. By deploying a full Stokes ice sheet model (http://elmerice.elmerfem.org) we investigate the influence of those parameters, namely anisotropy as well as geothermal heat flux values, on the spatial distribution of the age close to the bedrock. Results are compared with dated radar isochrones in the upper one third of the ice sheet. We find that a non-unique combination of parameters is able to closely reproduce those measured values, leading to the conclusion, that without additional information, the basal age beneath Kunlun station remains undetermined. However, our simulations suggest that vast spatial variation of basal melting rates and, in consequence, the age/depth distribution over a relative small domain exists, increasing the motivation for ice coring, obtaining both high resolution as well as possibly oldest ice from the same site.

Zwinger, Thomas; Sun, Bo; Liyun, Liyun; Moore, John C.; Steinhage, Daniel; Martin, Carlos

2014-05-01

161

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

162

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

163

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Age Characteristics in a Multidecadal Arctic Sea Ice1  

E-print Network

in a Multidecadal Arctic Sea Ice1 Simulation2 Elizabeth C. Hunke T-3 Fluid Dynamics and Solid Mechanics Group T November 3, 2008, 12:14pm D R A F T #12;X - 2 HUNKE AND BITZ: SEA ICE AGE CHARACTERISTICS Abstract. Results from adding a tracer for age of sea ice to a sophisti-6 cated sea ice model that is widely used

Bitz, Cecilia

164

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

NASA Astrophysics Data System (ADS)

The consequences of the ongoing temperature rise in alpine regions force glaciers to rapid melting and thus new surfaces are exposed to generate numerous geomorphic processes. Steep Little Ice Age (LIA) moraines and other glacial depositional landforms contain huge masses of sediments, that are subject to progressive (re-)mobilization by gullying, slope wash, debris flows and other mass movements. The material is frequently re-deposited in secondary storage landforms; these storages themselves are then subject to depletion. Increased morphodynamics with a maximum shortly after deglaciation, and a slow decrease afterwards, are predicted by the conceptual model of paraglacial response. In addition to these "self-organising" changes following deglaciation, our study area has been experiencing changes in precipitation and (meltwater) discharge for decades; these climatic factors are known to influence morphodynamics, e.g. by triggering mass movements and by driving slope wash and fluvial erosion. While overall precipitation appears to decrease, heavy rainfall events become more intense, and discharge rates of glacial melt water channels show a significant increase. The PROSA joint project (High-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) uses terrestrial and airborne LiDAR data and digital Photogrammetry to monitor surface changes in the Upper Kaunertal, Austrian Central Alps (64 km²). These are related to the deglaciation since the end of the LIA and to changes in hydrometeorological parameters since several decades ago. The aim of this study is to investigate a possible relationship between climate change signals and erosion rates in the proglacial area of the Gepatschferner. The morphodynamics of steep LIA moraines are assessed on multiple temporal scales: Long-term changes are analyzed based on multitemporal airborne images dating back to 1953. The recent development is measured using digital elevation models (DEM) generated from multitemporal airborne (2006, July 2012, September 2012) and terrestrial (July 2010, August 2010, September 2011, July 2012, September 2012) LiDAR surveys. Seasonal climate data of more than 40 years are analyzed to detect trends. Precipitation and discharge data of two extreme events in 2011 and 2012 that triggered slope-type debris flows are examined in detail. The moved sediment masses are quantified and related to the precipitation record.

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

2014-05-01

165

Reconstructing glacier retreat since the Little Ice Age in SE Tibet by glacier mapping and equilibrium line altitude calculation  

NASA Astrophysics Data System (ADS)

Temperate glaciers in the eastern Nyainqêntanglha Range, southeastern Tibet, are highly sensitive to climate change and therefore of particular high interest for research on late Holocene changes of the monsoonal climate in High Asia. However, because of the remoteness of the area, the scarcity of empirical data, and the challenges to remote sensing work posed by cloud and snow cover, knowledge about the glacier dynamics and changes in this region is still very limited. In this study, we applied a remote sensing approach in which 1964 glaciers were mapped from a Landsat ETM+ scene and subsequently parameterized by DEM-supported measurements. Geomorphological evidence, i.e., trimlines and latero-frontal moraines, were used to obtain quantitative data on the glaciers' morphological characteristics and the changes since the Little Ice Age (LIA) maximum glacier advance. Statistical analysis of glacier length change revealed an average retreat of ~ 27% and a trend toward stronger retreat for smaller glaciers. An evaluation of different methods to calculate equilibrium line altitudes (ELAs) indicates that an optimized toe-to-ridge altitude method (TRAM) is more suitable than other methods in settings with complex topography and a lack of mass balance measurements. A large number of glacier measurements are crucial for high quality of TRAM results, and special attention has to be paid to different glacier characteristics. In order to determine the best-fitting TRAM ratio value and to test the quality of the calculated ELAs, a remote sensing approach was applied: for each investigated glacier, the altitudes of transient snowlines visible in the late summer Landsat scene were measured from the DEM and compared to TRAM results. The interpolated ELA results show a SE-NW gradient ranging from 4400 to 5600 m asl and an average ELA rise of ~ 136 m since the LIA. Because of the high spatial resolution of measurements, the ELA distribution reveals topographic effects down to the catchment scale, specifically orographic rainfall and leeward shielding. The interpretation of these patterns reveals that the eastern Nyainqêntanglha Range is influenced by both, the Indian (ISM) and East Asian summer monsoon (EASM). However, the EASM does not reach the western part of the study area. The results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings owing to the coincidence of accumulation and ablation phases.

Loibl, David; Lehmkuhl, Frank; Grießinger, Jussi

2014-06-01

166

Regional scale trends in the timing and magnitude of Little Ice Age glacial maxima in Europe and the North Atlantic  

NASA Astrophysics Data System (ADS)

Reconstructing the configuration of atmospheric/oceanic circulation during past climate perturbations is crucial for understanding how the climate system responds to changing forcing mechanisms. The most recent Holocene climatic perturbation, the Little Ice Age (LIA), covered the period ca AD 1200-1900 and has been widely recorded in a series of documented, early instrumental and palaeo-proxy data. Past research has used such data from the European/North Atlantic regions to elucidate the spatio-temporal distribution of heat and moisture related to possible changes in dominant modes of atmospheric/oceanic circulation such as the North Atlantic Oscillation. Despite this, interpretations of climate dynamics based on such reconstructions are often contradictory, for example in terms of constraining the prevailing position of the North Atlantic storm track. Until recently, glacial variability during the LIA has been considered somewhat separately from the large-scale climate dynamics which are thought to have characterised the period. Several recent studies have suggested that apparent asynchrony in the timing of the LIA glacial maximum between regions in Europe and the North Atlantic was controlled by shifts in large-scale oceanic/atmospheric circulation patterns. However, such interpretations have been based predominantly on single glacier comparisons and no understanding of regional-scale trends has been presented. This research aims to synthesise published data on the timing and maximum extent of glacier advances across Europe and the North Atlantic during the LIA. A standardised approach for estimating the glacier equilibrium line altitude (ELA) associated with the LIA maximum was systematically applied to digitised moraine outlines derived from the published literature. This involved using an equilibrium profile equation to reconstruct palaeo-glacier surface geometry and estimating ELA from appropriate balance ratios. ELA was reconstructed for over 150 glaciers and stored in a database alongside information relating to the timing of the LIA maximum, based on published dates using a variety of methods. An attempt was also made to correct for the lag time between glacier frontal response and the climatic drivers of glacier retreat. Trends in the timing and magnitude of the LIA glacial maximum were then mapped at a regional scale in order to analyse proposed changes to oceanic/atmospheric circulation patterns in the context of a more complete understanding of glacial variability than has been presented hitherto.

Frew, Craig R.; Rea, Brice R.; Spagnolo, Matteo; Edwards, Kevin J.; Schofield, J. Edward

2014-05-01

167

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

168

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

169

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

170

Sedimentology of latero-frontal moraines and fans on the west coast of South Island, New Zealand  

NASA Astrophysics Data System (ADS)

Exposures through the LGM latero-frontal moraine loops at sites along the west coast of South Island, New Zealand reveal a depositional environment that was dominated by the progradation of steep fronted, debris flow-fed fans, manifest in crudely stratified to massive diamictons, arranged in sub-horizontal to steeply dipping clinoforms and containing discontinuous bodies of variably sorted, stratified sediment (LFA 1). The fans were constructed by debris-covered glaciers advancing over outwash plains, as recorded by well stratified and horizontally bedded gravels, sands and diamicts (LFA 0). The ice-contact slopes of the fans are offlapped by retreat phase deposits in the form of glacilacustrine depo-centres (LFA 2), which record the existence of moraine-dammed lakes. Interdigitation of lake rhythmites and subaerial to subaqueous sediment gravity flow deposits documents intense debris-flow activity on unstable moraine/fan surfaces. Glacier readvances in all catchments are documented by glacitectonic disturbance and localized hydrofracturing of LFA 2, followed by the emplacement of schist-dominated debris flow-fed fans (LFA 3) inside and over the top of the earlier latero-frontal moraine/fan loops. Contorted and disturbed bedding in LFA 3 reflects its partial deposition in supraglacial positions. Clast lithologies in LFAs 1 and 3 reveal that two distinct transport pathways operated during moraine construction, with an early period of latero-frontal fan construction involving mixed lithologies and a later period of ice-contact/supraglacial fan construction dominated by schist lithologies from the mountains. These two periods of deposition were separated by a period of moraine abandonment and paraglacial reworking of ice-contact slopes to produce LFA 2. The occurrence of LFA 3 at all sites indicates that the glacier readvance phase responsible for its deposition was not localized or glacier-specific, and involved the transfer of large volumes of schist, possibly due to rock slope failures, onto glacier surfaces. The absence of any sediment that could be unequivocally classified as subglacial till reflects the dominance of debris flow and glacifluvial processes in latero-frontal moraine construction in this hyper-humid west coast setting.

Evans, David J. A.; Shulmeister, James; Hyatt, Olivia

2010-12-01

171

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

PubMed

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

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

2014-03-21

172

Recent Ice Ages on Mars: The role of radiatively active clouds and cloud microphysics  

NASA Astrophysics Data System (ADS)

Global climate models (GCMs) have been successfully employed to explain the origin of many glacial deposits on Mars. However, the latitude-dependent mantle (LDM), a dust-ice mantling deposit that is thought to represent a recent "Ice Age," remains poorly explained by GCMs. We reexamine this question by considering the effect of radiatively active water-ice clouds (RACs) and cloud microphysics. We find that when obliquity is set to 35°, as often occurred in the past 2 million years, warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter-thick ice mantle poleward of 30° in each hemisphere during winter. This mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low-altitude clouds. We outline a scenario for its deposition and preservation that compares favorably with the characteristics of the LDM.

Madeleine, J.-B.; Head, J. W.; Forget, F.; Navarro, T.; Millour, E.; Spiga, A.; Colaïtis, A.; Määttänen, A.; Montmessin, F.; Dickson, J. L.

2014-07-01

173

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

USGS Publications Warehouse

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

Curry, B.; Petras, J.

2011-01-01

174

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

175

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

SciTech Connect

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

Mann, D.H. (Univ. of Alaska, Fairbanks, AK (United States). Alaska Quaternary Center)

1992-01-01

176

E THE SECOND INTERNATIONAL CONFERENCE ON GLOBAL WARMING AND THE NEXT ICE AGE  

E-print Network

of the current rapid warming of the North Atlantic is due to an accelerating thermohaline circulation related thermohaline circulation (THC) slowdown starting in about the next decade, which could be enhancedE THE SECOND INTERNATIONAL CONFERENCE ON GLOBAL WARMING AND THE NEXT ICE AGE What: More than 120

Zender, Charles

177

OSL ages on glaciofluvial sediment in northern Lower Michigan constrain expansion of the Laurentide ice sheet  

NASA Astrophysics Data System (ADS)

We report new ages on glaciofluvial (outwash) sediment from a large upland in northern Lower Michigan—the Grayling Fingers. The Fingers are cored with > 150 m of outwash, which is often overlain by the (informal) Blue Lake till of marine isotope stage (MIS) 2. They are part of an even larger, interlobate upland comprised of sandy drift, known locally as the High Plains. The ages, determined using optically stimulated luminescence (OSL) methods, indicate that subaerial deposition of this outwash occurred between 25.7 and 29.0 ka, probably associated with a stable MIS 2 ice margin, with mean ages of ca. 27 ka. These dates establish a maximum-limiting age of ca. 27 ka for the MIS 2 (late Wisconsin) advance into central northern Lower Michigan. We suggest that widespread ice sheet stabilization at the margins of the northern Lower Peninsula, during this advance and later during its episodic retreat, partly explains the thick assemblages of coarse-textured drift there. Our work also supports the general assumption of a highly lobate ice margin during the MIS 2 advance in the Great Lakes region, with the Fingers, an interlobate upland, remaining ice-free until ca. 27 ka.

Schaetzl, Randall J.; Forman, Steven L.

2008-07-01

178

Ice age climate, evolutionary constraints and diversity patterns of European dung beetles  

E-print Network

LETTER Ice age climate, evolutionary constraints and diversity patterns of European dung beetles with historical dispersal events and climatic oscillations, generate region-specific patterns that must Abstract Current climate and Pleistocene climatic changes are both known to be associated with geographical

Rodríguez, Miguel Ángel

179

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

180

Deep water formation in the North Atlantic Ocean during the last ice age  

Microsoft Academic Search

Oxygen-18 records of benthic foraminifera from northeastern Atlantic and Southern Ocean cores are significantly different. This difference indicates that the deep water in the northeastern Atlantic Ocean during the last Ice Age was at least 1.3 °C cooler than in modern times. We show here that the occurrence of such a cold deep water mass implies that the North Atlantic

Jean-Claude Duplessy; J. Moyes; C. Pujol

1980-01-01

181

Solar modulation of Little Ice Age climate in the tropical Andes  

E-print Network

Solar modulation of Little Ice Age climate in the tropical Andes P. J. Polissar*, M. B. Abbott, A sediments. Four glacial advances occurred be- tween anno Domini (A.D.) 1250 and 1810, coincident with solar- activity minima. Temperature declines of 3.2 1.4°C and precip- itation increases of 20% are required

Wolfe, Alexander P.

182

Solar modulation of Little Ice Age climate in the tropical Andes  

E-print Network

Solar modulation of Little Ice Age climate in the tropical Andes P. J. Polissar* , M. B. Abbott , A sediments. Four glacial advances occurred be- tween anno Domini (A.D.) 1250 and 1810, coincident with solar- activity minima. Temperature declines of 3.2 1.4°C and precip- itation increases of 20% are required

Polissar, Pratigya J.

183

Some genetic consequences of ice ages, and their role in divergence and speciation  

Microsoft Academic Search

The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a

GODFREY M. HEWITT

1996-01-01

184

Climatic Change and Witchhunting: the Impact of the Little Ice Age on Mentalities  

Microsoft Academic Search

In addition to objective climatic data, subjective or social reactions can also serve as indicators in the assessment of climatic changes. Concerning the Little Ice Age the conception of witchcraft is of enormous importance. Weather-making counts among the traditional abilities of witches. During the late 14th and 15th centuries the traditional conception of witchcraft was transformed into the idea of

Wolfgang Behringer

1999-01-01

185

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age  

E-print Network

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age Alfredo Martínez-García,1 of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused is uniquely consistent with Subantarctic iron fertilization. The associated strengthening of the Southern

Gilli, Adrian

186

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

187

Subdivision of Glacial Deposits in Southeastern Peru Based on Pedogenic Development and Radiometric Ages  

Microsoft Academic Search

The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13°30?–14°00?S; 70°40?–71°25?W) contains a detailed record of late Quaternary glaciation in the tropical Andes. Quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history. Secondary iron and clay increase linearly in Quelccaya soils and clay accumulates at a linear rate in

Adam Y. Goodman; Donald T. Rodbell; Geoffrey O. Seltzer; Bryan G. Mark

2001-01-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

189

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

190

Modern pollen assemblages and vegetational history of the moraines of the Klutlan Glacier and its surroundings, Yukon Territory, Canada*1  

NASA Astrophysics Data System (ADS)

Modern pollen assemblages have been studied from surficial lake muds and moss polsters collected from five vegetated ice-cored moraines of the Klutlan Glacier. The youngest vegetated moraine (K-II) is characterized by high pollen values for Salix and Hedysarum, K-III by high Salix and Shepherdia canadensis and low Hedysarum and Picea, K-IV by high Betula, Salix, and Shepherdia, and K-V and the Harris Creek moraine (HCM) by high Picea. Variations are summarized by canonical variates analysis. A percentage pollen diagram from Gull Lake on the upland east of the glacier records vegetational development since the deposition of the White River volcanic ash 1220 14C yr ago. An initial species-rich treeless vegetation was replaced by birch-alder-willow shrub-tundra, and this by open Picea glauca forest similar to present vegetation around the lake. Sites on HCM show two basic stratigraphies. Triangle Lake reflects vegetational succession from Salix-Shepherdia canadensis scrub similar to that on K-III today, through open Picea woodland of K-IV type, to closed Picea forests of K-V and HCM. Heart Lake and Cotton Pond reflect vegetational development following melting of ice underlying the spruce forests of HCM. These two types are summarized by positioning the fossil spectra on the first two canonical variate axes of the modern surface spectra.

Birks, H. J. B.

1980-07-01

191

The 100,000Year Ice-Age Cycle Identified and Found to Lag Temperature, Carbon Dioxide, and Orbital Eccentricity  

Microsoft Academic Search

The deep-sea sediment oxygen isotopic composition (delta18O) record is dominated by a 100,000-year cyclicity that is universally interpreted as the main ice-age rhythm. Here, the ice volume component of this delta18O signal was extracted by using the record of delta18O in atmospheric oxygen trapped in Antarctic ice at Vostok, precisely orbitally tuned. The benthic marine delta18O record is heavily contaminated

Nicholas J. Shackleton

2000-01-01

192

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

NASA Astrophysics Data System (ADS)

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

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

193

Glacial geomorphology of terrestrial-terminating fast flow lobes/ice stream margins in the southwest Laurentide Ice Sheet  

NASA Astrophysics Data System (ADS)

Glacial geomorphological mapping of southern Alberta, Canada, reveals landform assemblages that are diagnostic of terrestrial-terminating ice streams/fast flowing outlet glaciers with lobate snouts. Spatial variability in features that comprise the landform assemblages reflects changes in (a) palaeo-ice stream activity (switch on/off); and (b) snout basal thermal regimes associated with climate sensitive, steady state flow. Palaeo-ice stream tracks reveal distinct inset sequences of fan-shaped flowsets indicative of receding lobate ice stream margins. Former ice lobe margins are demarcated by (a) major, often glacially overridden transverse moraine ridges, commonly comprising glacitectonically thrust bedrock; and (b) minor, closely spaced recessional push moraines and hummocky moraine arcs. Details of these landform types are well exhibited around the former southern margins of the Central Alberta Ice Stream, where larger scale, more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges (MTR types 1-3), hummocky terrain (HT types 1-3), flutings, and meltwater channels/spillways. The MTR type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined. The MTR type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts. The MTR type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain. The close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin, where the HT type 3 hummocks represent former ice-walled lake plains. The ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern Alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream/fast flow lobes of the southern Laurentide Ice Sheet, where alternate cold, polythermal, and temperate marginal conditions associated with climate sensitive, steady state flow sequentially gave way to more dynamic streaming and surging activity.

Evans, David J. A.; Young, Nathaniel J. P.; Ó Cofaigh, Colm

2014-01-01

194

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

NASA Astrophysics Data System (ADS)

Sea-level changes over the last ice age cycle were instrumental in steering Earth's topographic evolution. These sea-level variations were driven by changes in surface mass loads, including not only ice and ocean mass variations but also the transfer of rock from eroding mountains to sedimentary deposits. Here we use an extended numerical model of ice age sea level (Dalca et al., 2013) to explore how sediment erosion and deposition affected global sea-level variations over the last ice age cycle. The model takes histories of ice and sediment loads as inputs, and it computes gravitationally self-consistent sea level responses by accounting for the deformational, gravitational, and rotational perturbations in the Earth's viscoelastic form. In these model simulations, we use published estimates of erosion rates, sedimentation rates, and ice sheet variations to constrain sediment and ice loading since the Last Interglacial. We explore sea-level responses to several erosional and depositional scenarios, and in each we quantify the relative contributions of crustal deformation and gravitational perturbation to the computed sea-level change. We also present a case study to illustrate the effects that sediment transfer can have on sea level at the regional scale. In particular, we focus on the region surrounding the Indus River, where fluvial sediment fluxes are among the highest on Earth. Preliminary model results suggest that sediment fluxes from Asia to the ocean are large enough to produce a significant response in sea level along the northeastern coast of the Arabian Sea. Moreover, they suggest that modeled sea-level histories are sensitive to the timing and spatial distribution of sediment erosion and deposition. For instance, sediment deposition along the continental shelf - which may have been the primary site of Indus River sediment deposition during the Holocene - produces a different sea-level response than sediment deposition on the deep-sea Indus Fan, where most of the Indus sediment may have been deposited during the glacial period preceding the Holocene. These simulations highlight the role that massive continent-to-ocean sediment fluxes can play in driving sea-level patterns over thousands of years. References: Dalca A.V., Ferrier K.L., Mitrovica J.X., Perron J.T., Milne G.A., Creveling J.R., 2013. On postglacial sea level - III: Incorporating sediment redistribution. Geophys. J. Int., doi: 10.1093/gji/ggt089.

Ferrier, K.; Mitrovica, J. X.

2013-12-01

195

Little Ice Age Cold Interval in West Antarctica: Evidence from Borehole Temperature at the West Antarctic Ice Sheet (WAIS) Divide.  

E-print Network

Antarctic Ice Sheet (WAIS) Divide. Anais J. Orsi1 , Bruce D. Cornuelle1 and Jeffrey P. Severinghaus1 . 1/ice, and Q the heat production term, taking into account ice deformation and firn compaction. WAIS Divide from WAIS Divide and Byrd station (AMRC, SSEC, UW-Madison). Tsea(t) = 10(cos(2t) + 0.3cos(4t)) (in K

Severinghaus, Jeffrey P.

196

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

PubMed Central

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

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

2004-01-01

197

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

NASA Astrophysics Data System (ADS)

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 high northern latitudes. Here I present Earth System Model projections showing that typical reduction targets for fossil fuel use in the present century could limit ongoing global warming to less than one degree Celcius above present. Furthermore, the projections show that combustion pulses of remaining fossil fuel reserves could then be tailored to raise atmospheric CO2 content high and long enough to parry forcing of ice age onsets by summer insolation minima far into the future. Our present interglacial period could be extended by about 500,000 years in this way.

Shaffer, Gary

2009-02-01

198

Ages and significance of glacial and mass movement deposits on the west side of Boulder Mountain, Utah, USA  

Microsoft Academic Search

Using air photos, satellite images, and field observations we mapped Quaternary glacial and mass movement deposits on the west side of Boulder Mountain in south-central Utah, USA. Prominent glacial moraines were deposited by outlet glaciers that emanated from an ice cap that existed atop Boulder Mountain. Cosmogenic 3He exposure ages of these deposits range from 20.2±1.5 to 22.5±2.5 ka and indicate

David W. Marchetti; Thure E. Cerling; John C. Dohrenwend; William Gallin

2007-01-01

199

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

NASA Astrophysics Data System (ADS)

Surficial mapping and more than 70 radiometric ages 10Be, 14C] constrain the evolution of the Cordilleran Ice Sheet (CIS) and associated mountain glaciers in western Canada during the latest Pleistocene. Our data suggest that: i) there is widespread evidence for the Younger Dryas (YD) throughout the mountains of western Canada; ii) late Pleistocene climate reconstructions based solely on alpine moraines may be misleading in regions with decaying ice sheets; iii) extensive interfluves in some mountain regions were ice-free between 16 ka and 13 ka (kilo calibrated yrs BP). Initial decay of the CIS from its maximum extent around 16 ka was likely due to a combination of climatic (surface melting) and dynamical factors. Climate amelioration during the Bølling-Allerød Warm Period [14.7-12.9 ka], likely the cause for the major phase of CIS decay, resulted in ice sheet equilibrium line altitudes (ELAs) ranging from 2500 m asl in southern BC to around 2000 m asl along the BC-Yukon border. Hence, before the onset of the Younger Dryas (YD) Cold Period [12.9-11.7 ka], the ice sheet shrank and became a labyrinth of individual and coalescing valley glaciers fed by major accumulation zones centered on the Coast Mountains and other high ranges of NW Canada. The response of remnant ice and cirque glaciers to the YD climate deterioration was highly variable. In some cases, small glaciers (0.5-2 km2) built YD moraines that were only hundreds of meters beyond those constructed during the Little Ice Age (LIA) [0.30-0.15 ka]. Our dating also reveals that much larger glaciers persisted in nearby valleys that lie hundreds of meters below the cirques. Hence, we infer that many cirques were completely deglaciated prior the YD, in contrast to low-lying valleys where ice sheet remnants persisted. Glaciers also advanced in north-central British Columbia during the YD, but here glaciers constructed large terminal and lateral moraines. In the Cassiar and northern Coast mountains, for example, 25 10Be [13.10-12.00 ka] and four minimum-limiting 14C ages from lakes impounded by moraines show that glaciers existed up to 10 km beyond LIA glacier limits during the YD. These glaciers thus had ELAs that were 300-500 m lower than contemporary glaciers. We are currently performing high-resolution (

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

2014-05-01

200

Evidences for a more restricted Icelandic Ice cap re-advance after the Bølling warming period  

NASA Astrophysics Data System (ADS)

Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using 36Cl and 3He cosmogenic nuclides. We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary 36Cl ages of the northernmost moraine at Skessugarðura, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 ± 1.2 ka to 13.4 ± 1.4 ka with an average at 12.2 ± 1.0 ka (±1?, n=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models. References: Licciardi et al., EPSL 267 (2008) 365-377.

Meriaux, Anne-Sophie; Delunel, Romain; Merchel, Silke; Finkel, Robert

2013-04-01

201

Evidences for a more restricted Icelandic Ice cap re-advance after the Bølling warming period  

NASA Astrophysics Data System (ADS)

Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using 36Cl and 3He cosmogenic nuclides. We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary 36Cl ages of the northernmost moraine at Skessugardur, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 ± 1.2 ka to 13.4 ± 1.4 ka with an average at 12.2 ± 1.0 ka (±1?, n=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models. References: Licciardi et al., EPSL 267 (2008) 365-377.

Meriaux, A.; Delunel, R.; Merchel, S.; Finkel, R. C.

2012-12-01

202

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

203

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

204

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

NASA Astrophysics Data System (ADS)

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 cap inception occurred in two pulses, centered on 1250-1300 AD and around 1450 AD, with ice caps remaining in an expanded state until the warming of the past few decades. Ice cap inception occurred simultaneously (±10 years) over a 200 m elevational range, suggesting an abrupt onset of Little Ice Age cold, rather than a slow cooling over many decades. Similarly, a 3000 year annually resolved lacustrine record of glacier power and a complementary independent proxy for landscape instability in the highlands of central Iceland show an initial jump in both glacier power and landscape instability between 1250 and 1300 AD, with a second step-increase around 1450 AD, and dramatic increases in both proxies around 1800 AD, retracting in the 20th Century. A sub-decadal record of hillslope stability and within-lake primary productivity in sediments from a low-elevation lake in northern Iceland shows parallel changes at similar times. Sea ice proxies and historical records document the first appearance of sea ice around Iceland following Medieval time about 1250 AD. The similarity in the onset and intensification of Little Ice Age cold-weather proxies across a wide region of the northern North Atlantic suggests at least a regional driver of abrupt climate change. The time intervals for which these abrupt changes occur coincide with the three most intense episodes of multiple explosive volcanic eruptions that introduced large volumes of sulfate aerosols into the stratosphere during the past millennium. Although the direct impacts of volcanic aerosols have a duration of only a few years, the memory stored by the cooled ocean surface waters allows a cumulative effect to have a longer-term impact. To explain the apparent irreversible shift to colder summers following volcanic eruptions requires additional strong positive feedbacks, most likely a consequence of expanded sea ice cover.

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

2009-12-01

205

Little Ice Age events (or not) in the middle to high latitudes of the Southern Hemisphere?  

NASA Astrophysics Data System (ADS)

The use of 'Little Ice Age' is prevalent in the literature on past Southern Hemisphere climates. We make a case that during the Little Ice Age period in Europe, terrestrial observations in the southern middle latitudes, specifically landform- and stratigraphic-based records, indicate that glaciers were typically not the most extensive of the Holocene. We summarize recently obtained findings from Patagonia and New Zealand. In both places, notable glacier advances did occur between ca. 1400 AD and 1850 AD and snowline depressions were about 100 m or more below present. Thus, Southern Hemisphere glaciers exhibited advances broadly at a similar time as during the European Little Ice Age. However, in contrast, glaciers in New Zealand and in at least some parts of Patagonia were consistently more extensive in the early or middle Holocene, respectively, when snowlines were 200 to 300 m below present-day. In addition, on both sides of the South Pacific region, we observe that glacier advances between ~1400 and 1600 AD were more extensive than those between 1600 and 1900 AD. We conclude that during the Holocene there were important differences in how glaciers behaved in the Northern and Southern hemispheres.

Kaplan, M. R.; Schaefer, J. M.; Denton, G. H.; Putnam, A. E.; Strelin, J.; García, J.; Sagredo, E. A.; Finkel, R. C.; Schwartz, R.

2013-12-01

206

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

USGS Publications Warehouse

We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5??2.5ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3km upslope for ~4.5-5.0kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ~15.4ka corresponds to a large reduction of the Atlantic meridional overturning circulation (AMOC) following Heinrich Event 1. Subsequent ice-margin retreat began at 14.6??1.9ka, corresponding to a rapid resumption of the AMOC and onset of the B??lling warm interval, with the ice cap melting rapidly to complete deglaciation. Additional 3He ages obtained from a flood deposit date the catastrophic outburst of a moraine-dammed lake roughly coeval with the Younger Dryas cold interval, suggesting a more active hydrological cycle on Mauna Kea at this time. A coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of LLGM and readvance sizes. The depression of the LLGM equilibrium line altitude requires atmospheric cooling of 4.5??1??C, whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present. We hypothesize (1) that the LLGM temperature depression was associated with global cooling, (2) that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the North Atlantic, and (3) that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter-tropical convergence zone (ITCZ). Such a 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. ?? 2010 Elsevier B.V.

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

2010-01-01

207

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

208

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

209

Climate Variability in the GODTHÅBSFJORD Area (sw Greenland) Since the Little Ice Age: a Multiproxy Approach  

NASA Astrophysics Data System (ADS)

We will present data from a high-resolution sediment core retrieved from the Godthåbsfjord area, SW Greenland. A network of sedimentological (e.g. grain size distribution), geochemical (XRF) and biological proxies (e.g. dinoflagellate cysts) have been applied to this record in order to reconstruct fjord-ice conditions, sea surface temperature, and changes in ocean-fjord water mass exchange since the Little Ice Age. The results will be compared against extensive data collected within the framework of the Greenland Ecosystem Monitoring (GEM) programme, aimed at obtaining insight into long-term ecosystem changes and climate change effects in the Arctic. Furthermore, phytoplankton resting stages preserved in the sediment core have been germinated in order to test the impact of climate variability on the genetic structure and variability of Arctic primary producers.

Ribeiro, S.; Ellegaard, M.; Andersen, T. J.; Kuijpers, A.; Mikkelsen, N.; Pedersen, N. N.; Rysgaard, S.

2013-12-01

210

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

211

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

PubMed Central

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.

2013-01-01

212

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

NASA Astrophysics Data System (ADS)

The Late Palaeozoic sediments in northern Ethiopia record a series of depositional environments during and after the Late Paleozoic ice age (LPIA). These sediments are up to 200 m thick and exceptionally heterogeneous in lithofacies composition. A differentiation of numerous types of lithofacies associations forms the basis for the interpretation of a large range of depositional processes. Major glacigenic lithofacies associations include: (1) sheets of diamictite, either overlying glacially eroded basement surfaces or intercalated into the sediment successions, and representing subglacial tillites, (2) thick massive to weakly stratified muddy clast-poor diamictites to lonestone-bearing laminated mudstones originating from a combination of suspension settling of fines and iceberg rainout, (3) lensoidal or thin-bedded diamictites deposited from debris flows, (4) wedges of traction and gravity transported coarse-grained sediments deposited in outwash fans, (5) irregular wedges or sheets of mudstones deformed primarily by extension and incorporating deformed beds or rafts of other lithofacies formed by slumping, and (6) irregular bodies of sandstone, conglomerate and diamictite deformed by glacial pushing. The dominance of laminated or massive clast-bearing mudstones in most successions indicates ice-contact water bodies as the major depositional environment. Into this environment, coarse-grained sediments were transported by various gravity driven transport processes, including dropstone activity of ice-bergs, slumping, cohesive debris flow, hyperconcentrated to concentrated flow, hyperpycnal flow, and by turbidity flow. Close to glacier termini, wedge-shaped bodies of conglomerate, sandstone, diamictite and mudstone were deposited primarily in subaqueous outwash-fans. Soft-sediment deformation of these sediments either records ice push during glacier advance or re-sedimentation by slumping. Apart from an initial glacier advance when thick ice of temperate or polythermal glaciers covered the whole basin, many sections document at least a second major phase of ice advance and retreat, and some sections additional minor advance-retreat cycles. Whether most of the LPIA sediments in northern Ethiopia were deposited in lakes or in fjords is not yet clear. Although univocal evidence of marine conditions is missing, the presence of carbonate-rich beds and the trace fossil assemblage are compatible with a restricted marine environment such as broad palaeofjords affected by strong freshwater discharge during deglaciation. A restricted marine environment for most of the sediments in northern Ethiopia could challenge models of the LPIA sediments in Arabia as primarily glaciolacustrine and glaciofluviatile deposits.

Bussert, Robert

2014-11-01

213

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

214

Deposition ice nucleation on fresh, cloud processed, internally mixed and oxidatively aged ?-pinene secondary organic aerosol  

NASA Astrophysics Data System (ADS)

There are many uncertainties related to role of organic aerosol (OA) as ice nuclei (IN). To that end, the ice nucleating abilities of fresh, cloud processed, internally mixed, and oxidatively aged secondary organic aerosol (SOA) particles were investigated with the University of Toronto continuous flow diffusion chamber (UT-CFDC) at temperatures relevant for cirrus cloud formation. Our SOA particles were produced by ?-pinene ozonolysis which took place in a flow tube (FT) and a smog chamber (SC). The FT-SOA particles mimicked freshly formed particles while the water soluble organic compound (WSOC) experiments from both the flow tube (FT-WSOC-SOA) and the smog chamber (SC-WSOC-SOA) capture the character of aged and cloud processed SOA particles. The FT-SOA particles exhibited low ice nucleation efficiency, i.e. relative humidities with respect to ice (RHi) of 152×4% and 157×4% were required to activate 0.1% of the aerosol particles in deposition mode at 223K and 218K, respectively. Similarly, the IN efficiencies of the FT-WSOC-SOA and SC-WSOC-SOA particles were found to be comparably low between 233K and 214K. However, if both the FT-WSOC-SOA and the SC-WSOC-SOA particles were pre-cooled at 233K prior to entering the UT-CFDC they nucleate ice at between 6 to 9% lower relative humidities, probably due to decreased viscosity. We also observed that an increase in the oxygen to carbon ratio (from 0.39 to 0.78) of the SC-WSOC-SOA particles from aqueous oxidative processing did not modify IN abilities. Finally, given that SOA is commonly mixed with inorganic salts, especially when arising through cloud processing, it was found that internally mixed particles of SC-WSOC-SOA and ammonium sulfate (AS) had a significantly higher RHi (140×5% at 219K) than pure AS particles of the same size (125×4%). Overall conclusions are that SOA-containing particles may act as IN only in regions where more efficient are not present. The SOA component will serve to suppress the IN abilities of efficient IN when internally mixed.

Ladino Moreno, L.; Zhou, S.; Aljawhary, D.; Yakobi-Hancock, J.; Abbatt, J.

2013-12-01

215

Effects of chemical aging on the ice nucleation activity of soot and polycyclic aromatic hydrocarbon aerosols.  

PubMed

The role of soot particles as ice nuclei (IN) in heterogeneous freezing processes in the atmosphere remains uncertain. Determination of the freezing efficiency of soot is complicated by the changing properties of soot particles undergoing atmospheric aging processes. In this study, the heterogeneous freezing temperatures of droplets in contact with fresh and oxidized soot particles were determined using an optical microscope apparatus equipped with a sealed cooling stage and a CCD video camera. Experiments were also conducted using fresh and oxidized polycyclic aromatic hydrocarbons (PAHs), including anthracene, pyrene, and phenanthrene, as potential ice nuclei. Chemical changes at the surface of the aerosols caused by exposure to ozone were characterized using Fourier transform infrared spectroscopy with horizontal attenuated total reflectance (FTIR-HATR). In addition, Brunauer-Emmett-Teller (BET) measurements were used to determine the specific surface areas of the soot particles. Mean freezing temperatures on fresh particles ranged from -19 to -24 °C, depending on the IN composition and size. In all cases, exposure to ozone facilitated ice nucleation at warmer temperatures, by 2-3 °C, on average. In addition, nucleation rate coefficients for a single temperature and IN type increased by as much as 4 orders of magnitude because of oxidation. Furthermore, a fraction of the oxidized soot particles froze at temperatures above -10 °C. A modified version of classical nucleation theory that accounts for a range of contact angles on nucleation sites within an IN population was used to derive the probability of freezing as a function of temperature for each type of IN. In summary, our results suggest that atmospheric oxidation processes may both extend the range over which particles can act as ice nuclei to warmer temperatures and increase heterogeneous nucleation rates on soot and pollutant aerosols. PMID:25280086

Brooks, Sarah D; Suter, Katie; Olivarez, Laura

2014-10-30

216

An explanation of the 100 kyr ice age cycle using a simple box model  

NASA Astrophysics Data System (ADS)

We have developed a conceptually simple box model, similar in philosophy to those of Saltzman, with a view to explaining the 100 kyr period of the most recent ice age signals. Here we explain in detail how and why the various components of the model have been constructed, and we show how the model can be analysed in order to explain its behaviour. We find that the model can explain the 100 kyr cycles as a self-sustaining oscillation, and in addition we can explain the 40 kyr -100 kyr transition, and indeed the post-Eocene cooling, through the variation of weathering rate over geologic time. The central component of the model is an ocean carbon balance, which receives input from the weathering of silicates and carbonates, and loses CaCO3 by the burial of calcareous biomass. It is therefore necessary to also balance calcium and biomass, and thence phosphorus, which we take to be rate limiting. Charge balance is effected through estimates of the conservative ions Na+, Cl-, etc. To this ocean chemistry model we add a simple ice sheet model of the Weertman/Oerlemans/Ghil type, and we allow for rapid deglaciation through an enhanced wastage rate associated with the growth of proglacial lakes like Agassiz. The oscillations which result are due to the interaction of the hysteretic ice sheet growth (allowing for the elevation-accumulation feedback), and a similar hysteresis in the proglacial lake volume. The effect of this on the atmospheric carbon is controlled by the lowering of the carbonate ion which results when the ice sheet meltwater flows into the ocean.

Fowler, A. C.; Rickaby, R. E. M.; Wolff, E. W.

2012-04-01

217

Landscape history and man-induced landscape changes in the young morainic area of the North European Plain — a case study from the Bäke Valley, Berlin  

NASA Astrophysics Data System (ADS)

The Bäke creek valley is part of the young morainic area in Berlin. Its origin is related to meltwater flow and dead-ice persistence resulting in a valley with a lake-creek system. During the Late Glacial, the slopes of the valley were affected by solifluction. A Holocene brown soil developed in this material, whereas parts of the lakes were filled with limnic-telmatic sediments. The excavation site at Goerzallee revealed Bronze Age and Iron Age burial places at the upper part of the slope, as well as a fireplace further downslope, but the slope itself remained stable. Only German settlements in the 12th and 13th centuries changed the processes in the creek-lake system: the construction of water mills created a retention system with higher ground water levels in the surrounding areas. On the other hand, deforestation on the till plain and on the slope triggered erosion. Therefore, in medieval time interfingering organic sediments and sand layers were deposited in the lower part of the slope on top of the Holocene soil. The new soil which formed on top of these sediments was transformed by ploughing until the 19th century. In 1905/06 the lower part of the slope was reshaped by the construction of the Teltow Canal, following the valley of the former Bäke creek. Finally, the whole area was levelled by infill after World War II.

Böse, Margot; Brande, Arthur

2010-10-01

218

The Media, Planning and the Oak Ridges Moraine  

E-print Network

actually happened. It is generally accepted that the media does have an influence over public opinionARTICLE The Media, Planning and the Oak Ridges Moraine R. CHRISTOPHER EDEY, MARK SEASONS & GRAHAM WHITELAW Introduction The role of the media with respect to urban planning has not been well

219

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

220

Holocene history of North Ice Cap, northwestern Greenland  

NASA Astrophysics Data System (ADS)

Although much research has focused on the past extents of the Greenland Ice Sheet, less is known about the smaller ice caps on Greenland and how they have evolved over time. These small ice caps respond sensitively to summer temperatures and, to a lesser extent, winter precipitation, and provide valuable information about climatic conditions along the Greenland Ice Sheet margins. Here, we investigate the Holocene history of North Ice Cap (76°55'N 68°00'W), located in the Nunatarssuaq region near Thule, northwest Greenland. Our results are based on glacial geomorphic mapping, 10Be dating, and analyses of sediment cores from a glacially fed lake. Fresh, unweathered and unvegetated boulders comprise moraines and drift that mark an extent of North Ice Cap ~25 m outboard of the present ice margin. It is likely that these deposits were formed during late Holocene time and we are currently employing 10Be surface exposure dating to examine this hypothesis. Just outboard of the fresh moraines and drift, boulders and bedrock show significant weathering and are covered with lichen. Based on glacial geomorphic mapping and detailed site investigations, including stone counts, we suggest that the weathered boulders and bedrock were once covered by erosive Greenland Ice Sheet flow from southeast to northwest over the Nunatarssuaq region. Five 10Be ages from the more weathered landscape only 100-200 m outboard of the modern North Ice Cap margin are 52 and 53 ka (bedrock) and 16, 23, and 31 ka (boulders). These ages indicate that recent ice cover has likely been cold-based and non-erosive, failing to remove inherited cosmogenic nuclides from previous periods of exposure, although the youngest boulder may provide a maximum limiting deglaciation age. Sediment cores collected from Delta Sø, a glacially-fed lake ~1.5 km outside of the modern North Ice Cap margin, contain 130 cm of finely laminated sediments overlying coarse sands and glacial till. Radiocarbon ages from just above the sands are 14,940 and 14,560 cal yr BP (medians of two-sigma ranges). Our results thus far suggest that the Nunatarssuaq region preserves a long and complex glacial history, including glaciation by the Greenland Ice Sheet and potentially North Ice Cap, as well as glaciation by both erosive and non-erosive ice. Based on the basal ages from Delta Sø and the youngest boulder 10Be age, recession at the end of the most recent glacial period likely occurred by ~15 ka. This is considerably earlier than most other terrestrial margins of Greenland that did not become ice free until ~10 ka. Our ongoing research is developing proxy and further chronological data from sediment cores from Delta Sø and nearby ice-marginal lakes to constrain the Holocene fluctuations of North Ice Cap.

Corbett, L. B.; Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Roy, E. P.; Thompson, J. T.

2013-12-01

221

Deglaciation dynamics following the Little Ice Age on Svalbard: Implications for shaping of landscapes at high latitudes  

Microsoft Academic Search

The late culmination of the Little Ice Age (LIA) on Svalbard allows a detailed reconstruction of the landscape's response to the subsequent climatic warming. The study area comprises a small glacier (400–1000 m a.s.l.), on the south side of Adventfjorden (78°11?N) that was polythermal during the LIA and turned into a passively down-wasting cold-based ice-mass prior to 1936. Reconstruction of

Ida Lønne; Astrid Lyså

2005-01-01

222

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

223

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

Microsoft Academic Search

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

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

2001-01-01

224

Quantitative Biostratigraphic Age Control of Glacimarine Sediments, ANDRILL 1B Drillcore, McMurdo Ice Shelf  

NASA Astrophysics Data System (ADS)

Interpretation of glacimarine sedimentary records from Antarctic shelf drillholes has been greatly hampered by the ambiguous age of strata where erosional unconformities and coarse diamictite deposits truncate or omit the mangetostratigraphic and biostratigraphic units used for correlation. However, new quantitative biostratigraphic techniques enable the correlation of sparse, incomplete, and reworking-prone Plio- Pleistocene records of Ross Sea fossil diatom flora with the more extensively documented but potentially diachronous offshore history of species' first and last appearances (FAs and LAs). The approach uses a comprehensive regional database of fossil records and computer-automated search algorithms to (a) find the multidimensional line of correlation (LOC) that best fits local observations, and (b) map out confidence intervals based on the full range of equally parsimonious composite FA/LA sequences and local range-end adjustments. An integrated, quantitative chronostratigraphic model for the AND-1B drillcore was constructed iteratively: the initial LOC was based solely on preliminary on-ice observations of fossil diatom highest and lowest occurrences (HOs and LOs) and their correlation with a database of other local event records from 24 DVDP, CIROS, and IODP drillcore sections. The model was subsequently updated as off-ice work yielded additional biostratigraphic marker events and revised event horizons, Ar/Ar ages for volcanic material, better- constrained magnetostratigraphic interpretations, and refinements to computational/analytical methodology. The current quantitative biostratigraphic age model for the AND-1B hole integrates the local ranges of 29 diatom taxa, 5 dated ashes, and independently constrained ages of 5 paleomagnetic reversals. Results corroborate almost all of the on-ice geomagnetic polarity reversal age interpretations, but identify a previously unrecognized major disconformity (~800kyr hiatus) near 440mbsf. It is significant to note that in spite of drastic augmentation and progressive refinement of, the original AND- 1B input dataset, successive iterations of the output LOC retain the same fundamental structure/shape with only relatively minor, fine-scale differences. The age model's remarkable stability indicates that quantitative biostratigraphic analysis is capable of constructing robust and reliable regional correlation schemes and local section chronologies, even where records are somewhat rough or unfinished and include some errors and low-quality content, or lack independent age control. Large discrepancies between observed and expected HO/LO horizons reveal significant diachronism in the timing of a few species' FAs and LAs on the shelf vs. offshore. In other cases, positions of HOs and LOs that were predicted by the quantitative analysis were subsequently validated by collection of additional microfossil count data that documented occurrences of the taxon near the stratigraphic limits predicted by regional correlations. Quantitative biostratigraphic analysis of this type could potentially be useful in guiding more intensive, supplementary off-ice or post-cruise sampling and investigation.

Cody, R.; Levy, R.; Crampton, J.; Wilson, G.; Naish, T.; Harwood, D.; Winter, D.; Scherer, R.

2008-12-01

225

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

226

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

227

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

Microsoft Academic Search

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

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

2009-01-01

228

Lacustrine Basal Ages Constrain the Last Deglaciation in the Uinta Mountains, Utah, USA  

NASA Astrophysics Data System (ADS)

Basal radiocarbon ages from 21 high-elevation lakes limit the timing of final Pleistocene deglaciation in the Uinta Mountains of northeastern Utah, USA. The lakes are located in glacial valleys and cirques 5 to 20 km upstream from LGM terminal moraines at elevations from 2830 to 3475 m. Many are impounded behind recessional moraines. Cores were retrieved from a floating platform with a percussion corer driven to the point of refusal. All penetrated inorganic silty clay beneath gyttja. AMS radiocarbon analyses were made on terrestrial macrofossils, daphnia ephippia, pollen concentrates, and bulk sediment retrieved from the base of each core. No radiocarbon reservoir effect was observed when bulk dates were checked against terrestrial material. Radiocarbon results were converted to calendar years using the IntCal09 calibration curve in OxCal 4.1. Given the stratigraphy observed in the cores, these calibrated basal ages are considered close limits on the timing of the local deglaciation and lake formation. The oldest three lakes have basal radiocarbon ages that calibrate to a few centuries after the Bölling/Alleröd warming, indicating that the landscape was becoming ice free at this time. These are followed by an overlapping group of five lakes with basal ages between 13.5 and 13.0 ka BP. Five more cores, from four separate lakes, have basal ages tightly clustered between 13.0 and 12.5 ka BP. Three of these lakes are dammed by moraines, suggesting glacial activity during the early part of the Younger Dryas interval. The lone kettle lake in the study yielded a basal age of 12.3 ka BP, considerably younger than the basal age of 13.9 ka BP from a nearby lake filling a bedrock basin, indicating that buried ice may have been locally stable for more than a millennium after deglaciation. The remaining seven lakes have basal ages between 12.0 and 11.0 ka BP. Four of these lakes are also dammed by moraines. These two non-overlapping clusters of basal ages for moraine-dammed lakes, with maximum probabilities ca. 12.7 and 11.3 ka BP, suggest that active glaciers were present in the Uinta Mountains during the Younger Dryas, and that Younger Dryas glacier activity was concentrated in two separate intervals.

Munroe, Jeffrey; Laabs, Benjamin

2013-04-01

229

The glacial sedimentology and geomorphological evolution of an outwash head/moraine-dammed lake, South Island, New Zealand  

NASA Astrophysics Data System (ADS)

Extensive exposures through the glacial landforms around southern Lake Pukaki, New Zealand, comprise seven lithofacies (LFs 1-7). LFs 1-3 are grouped together as LFA 1 (Pukaki Member) and record pulsed subaqueous grounding line fan progradation, cohesionless debris flows, underflow activity and rhythmite deposition by suspension settling, iceberg rafting of dropstones, and pulsed traction current activity. Localized disturbance of these deposits by glacitectonic deformation and multi-generational hydrofracture fills records minor readvances by the glacier snout and the emplacement of a glacitectonite (LF 4) derived from cannibalization of glacilacustrine sediments. LFs 4-6 are grouped together as LFA 2 (Twizel Member) and record direct glacigenic deposition of glacitectonite (LF 4), subglacial traction till (LF 5) and supraglacially dumped boulder rubble (LF 6). Stratigraphic relationships between LFA 1 with LFA 2 record the oscillatory behaviour of the former Tasman Glacier snout when it formed a calving margin in a proglacial and locally supraglacial lake dammed by a glacitectonically disturbed outwash head and lateral moraine ridges. This is entirely consistent with the landform-sediment record of its coeval terrestrial margins, where flutings and push moraines are diagnostic of active temperate glacier recession from a glacially overridden outwash head, the latter being recorded by the vertically stacked sub-horizontally bedded and coarse-grained gravels of LF 7 (Waitaki Member). Previous proposals that late Pleistocene lake damming was initiated by an ice-cored moraine arc appear unfounded, because the glacilacustrine deposits only lie above the altitude of the outwash head/lateral moraine arc in locations where they have been glacitectonically compressed. Alternatively, it is proposed that the overdeepened subglacial topography was produced by the construction of an outwash head, leading to a glacilacustrine sediment sink which operates at times when the expanded Tasman Glacier actively retreats from the outwash head apex. The changing landsystem imprint related to the shrinkage of the Tasman Glacier records spatio-temporal landsystem change, involving evolution from a coupled landsystem to a moraine-dammed to an uncoupled landsystem.

Evans, David J. A.; Rother, Henrik; Hyatt, Olivia M.; Shulmeister, James

2013-02-01

230

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age  

NASA Astrophysics Data System (ADS)

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO.

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-02-01

231

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age.  

PubMed

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-01-01

232

Increase in penguin populations during the Little Ice Age in the Ross Sea, Antarctica  

PubMed Central

Penguins are an important seabird species in Antarctica and are sensitive to climate and environmental changes. Previous studies indicated that penguin populations increased when the climate became warmer and decreased when it became colder in the maritime Antarctic. Here we determined organic markers in a sediment profile collected at Cape Bird, Ross Island, high Antarctic, and reconstructed the history of Adélie penguin colonies at this location over the past 700 years. The region transformed from a seal to a penguin habitat when the Little Ice Age (LIA; 1500–1800?AD) began. Penguins then became the dominant species. Penguin populations were the highest during ca. 1490 to 1670?AD, a cold period, which is contrary to previous results in other regions much farther north. Different responses to climate change may occur at low latitudes and high latitudes in the Antarctic, even if for same species. PMID:23969993

Hu, Qi-Hou; Sun, Li-Guang; Xie, Zhou-Qing; Emslie, Steven D.; Liu, Xiao-Dong

2013-01-01

233

Global signatures and dynamical origins of the Little Ice Age and Medieval Climate Anomaly.  

PubMed

Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña-like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation-Arctic Oscillation. PMID:19965474

Mann, Michael E; Zhang, Zhihua; Rutherford, Scott; Bradley, Raymond S; Hughes, Malcolm K; Shindell, Drew; Ammann, Caspar; Faluvegi, Greg; Ni, Fenbiao

2009-11-27

234

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age  

PubMed Central

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400–1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-01-01

235

Regionally coherent Little Ice Age cooling in the Atlantic Warm Pool  

USGS Publications Warehouse

We present 2 new decadal-resolution foraminiferal Mg/Ca-SST records covering the past 6-8 centuries from the northern Gulf of Mexico (GOM). These records provide evidence for a Little Ice Age (LIA) cooling of 2??C, consistent with a published Mg/Ca record from Pigmy Basin. Comparison of these 3 records with existing SST proxy records from the GOM-Caribbean region show that the magnitude of LIA cooling in the Atlantic Warm Pool (AWP) was significantly larger than the mean hemispheric cooling of <1??C. We propose that a reduction in the intensity and spatial extent of the AWP during the LIA, combined with associated changes in atmospheric circulation may account for the regional SST patterns observed in the GOM-Caribbean region during the LIA. Copyright 2009 by the American Geophysical Union.

Richey, J.N.; Poore, R.Z.; Flower, B.P.; Quinn, T.M.; Hollander, D.J.

2009-01-01

236

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

237

The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth  

E-print Network

The short term variability of the Galactic cosmic ray flux (CRF) reaching Earth has been previously associated with variations in the global low altitude cloud cover. This CRF variability arises from changes in the solar wind strength. However, cosmic ray variability also arises intrinsically from variable activity of and motion through the Milky Way. Thus, if indeed the CRF climate connection is real, the increased CRF witnessed while crossing the spiral arms could be responsible for a larger global cloud cover and a reduced temperature, thereby facilitating the occurrences of ice ages. This picture has been recently shown to be supported by various data (Shaviv, 2001). In particular, the variable CRF recorded in Iron meteorites appears to vary synchronously with the appearance ice ages. Here we expand upon the original treatment with a more thorough analysis and more supporting evidence. In particular, we discuss the cosmic ray diffusion model which considers the motion of the Galactic spiral arms. We also elaborate on the structure and dynamics of the Milky Way's spiral arms. In particular, we bring forth new argumentation using HI observations which imply that the galactic spiral arm pattern speed appears to be that which fits the glaciation period and the cosmic-ray flux record extracted from Iron meteorites. In addition, we show that apparent peaks in the star formation rate history, as deduced by several authors, coincides with particularly icy epochs, while the long period of 1 to 2 Gyr before present, during which no glaciations are known to have occurred, coincides with a significant paucity in the past star formation rate.

Nir J. Shaviv

2002-09-12

238

Evidence for more extensive ice shelves along the Western Antarctic Peninsula during the Little Ice Age: observations from the LARISSA project in Barilari Bay, Graham Land  

NASA Astrophysics Data System (ADS)

Barilari Bay, west Antarctic Peninsula, lies 12 nautical miles northwest from ice-core site Beta on the Bruce Plateau, which is an area of regionally high snow accumulation rates and ice velocity. This area has experienced recent rapid regional warming (Vaughan, 2003), and aerially-documented ice shelf disintegration since the 1940’s . A 133cm Kasten core (KC54) was collected aboard the Nathaniel B. Palmer in 2010 (NBP1001), allowing for the investigation of whether the inner fjord of Barilari Bay has experienced fluctuations in glacial dynamics throughout Marine Isotope Stage 2e to present, or if the recent observations are unique to the last century. KC-54 was collected in the tributary region of the Weir and Lawrie glaciers. Multibeam bathymetric mapping delineated that the core was collected landward of a prominent grounding zone wedge, in a zone of paleo-ice streaming, indicated by mega-scale glacial lineations. The glacial stratigraphy has been established based on a multi-proxy data-set, including: grain size; preserved total organic carbon; ?13C; diatom abundance and assemblages; physical properties including magnetic susceptibility and porosity; and geophysical data. The lower-most unit is a homogeneous, poorly-sorted, diamicton with low porosity and no diatoms. Unconformably overlying the basal unit is a laminated mud with low diatom abundance. This unit grades upwards into a zone of abundant ice rafted debris. The top unit is a finely laminated, diatom-rich mud. The facies change from glacial till to sandy-silt to laminated, diatomaceous sediments from the NPB1001 KC54 documents a transition from sub-glacial to sub-ice shelf to open marine conditions in the inner fjord of Barilari Bay. The chronology of this change was determined using radiocarbon and 210Pb radio-isotope dating. The cyclicity of sediment flux to the basin was examined through x-ray analysis of laminations deposited above the diamicton. This helps to constrain the controlling factor in depositional behavior in inner Barilari Bay during the Late Holocene. The general retreat history of the bay may be related to post-Little Ice Age warming, which has been documented from other marine records along the western Antarctic Peninsula. This work stems from a NSF summer program related to the LARISSA (LARsen Ice Shelf System, Antarctica) project, through the International Antarctic Institute and Hamilton College.

Kirshner, A. E.; Christ, A.; Allinger, T.; Armbruster, G.; Crawford, A.; Elking, N.; Gao, J.; Gunter, M.; Kirievskaya, D.; Jeong, S.; Peers, C.; Povea de Castro, P.; Reardon, D.; Sanchez Cervera, C.; Talaia-Murray, M.; Verreydt, W.; Ward, M.; Larissa Summer School

2010-12-01

239

Distribution of tunnel valleys along the southern margin of the former Laurentide Ice Sheet  

NASA Astrophysics Data System (ADS)

The formation of tunnel valleys remains enigmatic, having variously been attributed to: (i) gradual formation by subglacial sediment deformation into channels under steady-state conditions; (ii) time-transgressive formation close to the ice margin by drainage of supraglacial meltwater to the bed or of meltwater temporarily impounded behind a permafrost wedge; and (iii) by catastrophic subglacial meltwater floods. We present comprehensive mapping of the distribution of tunnel valleys and their relation to moraines and outwash fans along the southern sector of the former Laurentide Ice Sheet. The results permit a detailed morphometric and spatial analysis of tunnel valleys, and are compared against potential subglacial lake locations derived from a simple diagnostic approach that applies the Shreve equation to modelled ice and bed elevation data. A comparison of the two allows us to decipher the possible contribution of subglacial lake drainage events to tunnel valley formation. A relative age of the tunnel valleys, based on their association with moraines (i.e. whether they are incised through or overlain by them), is used to resolve when individual tunnel valleys and networks were eroded.

Livingstone, Stephen; Clark, Chris

2014-05-01

240

Reconstructing the late Holocene expansion of mountain ice caps in west-central Greenland  

NASA Astrophysics Data System (ADS)

The retreat of glaciers is one of the most profound visual manifestations of global warming. Yet without the longer-term context of glacier history, the magnitude of retreat observed today is less meaningful. We are reconstructing the late Holocene history of mountain ice caps in west-central Greenland to determine: 1) the precedence of their current size, 2) the pattern of Neoglaciation across the northwestern North Atlantic, and 3) how their record of Neoglaciation compares with that of the adjacent Greenland Ice Sheet. Our chronology is built on radiocarbon ages from in situ surface moss emerging from receding ice cap margins. We assert that the moss died during ice cap expansion across tundra surfaces, and has since been entombed beneath non-erosive ice cap sectors that we strategically target. Although this project is in its beginning stages, two initial radiocarbon ages from in situ moss that recently were exposed in front of Lyngmarksbræen, a plateau ice cap on southern Disko island, are 3580-3700 and 3450-3570 cal yr BP. The moss became ice free sometime during the summer in which they were collected, and historical imagery shows the sites are tens of meters behind the ice margin in August 23, 2004. The radiocarbon ages indicate that Lyngmarksbræen has not been as small as it is today since ~3500 yr ago. Other age constraints on Neoglaciation from the Disko Bugt region are similar to the ages we obtained here: reworked marine fauna in Greenland Ice Sheet moraines indicate ice sheet growth at this time, and relative sea level records indicate that landscape submergence (due to ice sheet growth) initiated around this time. Furthermore, ice cap melt records demonstrate that ice caps in this sector of the Arctic are melting more today than they have in the past 4000 years. Additional ages from multiple ice cap margins on Disko island, the Nuussuaq peninsula and various locations in the Uummannaq region will be presented. This dataset of ice cap expansion in western Greenland will be compared to similar constraints on late Holocene ice cap expansion on Baffin Island and in Liverpool Land, eastern Greenland.

Briner, J. P.; Schweinsberg, A.; Miller, G. H.; Bennike, O.; Lifton, N. A.

2013-12-01

241

Neogene History of Antarctic Sea-ice and Development of the Sea-ice Diatom Community  

NASA Astrophysics Data System (ADS)

Sea-ice plays an important role in the modern Antarctic climate system and in this region's linkage to lower latitude regions. Today, the seasonal sea-ice cover decouples oceanic heat transfer to the atmosphere, which amplifies winter's low temperatures and shifts sources of moisture far to the north. The sea-ice zone is an important site for biological productivity and bottom water formation, through cooling and brine exclusion. The absence of the sea-ice during past and future periods of elevated temperatures would significantly impact the biology, oceanography, glaciology and meteorology of the Antarctic region. A unique diatom assemblage is adapted to life in and around the sea-ice, and serves as an increasingly useful proxy to mark the presence, extent and duration of sea-ice cover. This assemblage dominates Antarctic shelf sediments today and back through most of the Quaternary. The oldest fossil diatom flora with a similar composition and structure to that of the modern sea-ice community was identified in a late Miocene mudstone erratic MB-244C in coastal moraine from McMurdo Sound. This assemblage did not persist through to the present day, and it is absent, or significantly reduced, in numerous marine diatom-bearing strata of late Miocene, Pliocene and Quaternary age, including the upper Miocene McLeod Beds of the Battye Glacier Formation, Prince Charles Mountains, the lower Pliocene Sorsdal Formation in the Vestfold Hills, the Pliocene sediments from the DVDP and CIROS drillcores, and the lower Quaternary carbonate unit in the Cape Roberts Project drillcore CRP-1. The sea-ice diatom community likely persisted in low numbers in interior fjords and basins, adjacent to glacier margins during these times. The history of sea-ice development and fluctuation during the Neogene appears to be complex, with substantial variability in sea-ice cover. Core records are currently insufficient to document the details of this history, and variation in the diatom assemblages through times of climate transition, but potential is high to utilize the diatom record as a proxy indicator for sea-ice cover. Sea-ice likely existed in Antarctic waters prior to the late Miocene, and morphological analyses of species within several diatom genera recovered in the erratic sample may provide a means of extending sea-ice interpretations back in time.

Harwood, D. M.; Bohaty, S. M.; Whitehead, J. M.

2002-12-01

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

The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia  

Microsoft Academic Search

The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field

Kris Holm; Michael Bovis; Matthias Jakob

2004-01-01

244

Project EARTH-13-RK1: Ice ages, sea level, and mid-ocean ridge magmatism: coupled oscillations  

E-print Network

Project EARTH-13-RK1: Ice ages, sea level, and mid-ocean ridge magmatism: coupled oscillations is also an important element in the melting region beneath mid-ocean ridges, because it lowers the solidus an exisiting numerical model of coupled magma/mantle flow beneath a mid-ocean ridge to account for the presence

Henderson, Gideon

245

Palynology as an age-control tool for ice cores. First results of PAMOGIS - Pollen Analyses of the Mt. Ortles Glacier Ice Samples  

NASA Astrophysics Data System (ADS)

Glacier ice cores from the mid latitude are capable of retaining essential information on past climate, environmental and human activities on a seasonal/annual time resolution. However, for a correct interpretation of the ice record a good chronological control is essential. Absolute time markers such as 3H peaks and Sahara dust horizons, together with radiometric methods such as 210Pb, radiocarbon from carbonaceous aerosol particles and AMS-dating are commonly used to obtain the age depth model of ice cores. In this frame we present the first pollen-based chronology from the Eastern Alps. Results of pollen analyses performed on a 10 m firn core taken on the top of Alto dell'Ortles Glacier (3905 m a.s.l.) will be discussed. Palynological data are compared and complemented with stable isotopes, major ions and trace elements analyses. Based on the single species flowering periods, our results show that the pollen spectrum presents seasonal and inter-annual variability that enables to distinguish snow accumulated in the three different flowering seasons and winter snow. According to these four components a seasonal and annual chronology was established, proving that the 10 m firn core encompasses four years of snow accumulation and presents a clear seasonal palynological signal. These first results reveal the potential of pollen content of glacier snow and ice as a chronological tool that can contribute to the construction of a robust chronological model with a seasonal to annual resolution. This study is the first step and the base for future research on deeper ice cores on the Alto dell'Ortles Glacier (Ortles project: www.ortles.org).

Festi, Daniela; Kofler, Werner; Gabrielli, Paolo; Oeggl, Klaus

2014-05-01

246

Decreasing frequency of forest fires in the southern boreal zone of Québec and its relation to global warming since the end of the 'Little Ice Age'  

Microsoft Academic Search

Although an increasing frequency of forest fires has been suggested as a consequence of global warming, there are no empirical data that have shown a climatically driven change in fire frequency since the warming that has followed the end of the 'Little Ice Age'. We present here evidence from fire and tree-ring chronologies that the post-'Little Ice Age' climate change

Yves Bergeron; Sylvain Archambault

1993-01-01

247

Terrestrial Ages of Meteorites MIL 07710 (L4) and MIL 091010 (CV3) Found in the Ice at Miller Range, Antarctica  

NASA Astrophysics Data System (ADS)

Cosmogenic nuclides were measured in two meteorites (MIL 07710 and 091010) found in the ice at Miller Range, Antarctica. Terrestrial and exposure ages were determined. The terrestrial ages were 16–19kyr.

Jull, A. J. T.; Nishiizumi, K.; Caffee, M. W.; Junk, N.; Burr, G. S.

2014-09-01

248

Solar Cycle Variations in Ice Acidity at the End of the Last Ice Age: Possible Marker of a Climatically Significant Interstellar Dust Incursion  

E-print Network

Hammer et al. [1997] report the presence of regularly spaced acidity peaks (H+, F-, Cl-) in the Byrd Station, Antarctica ice core. The event has a duration of about one century and falls at the beginning of the deglacial warming. Volcanism appears to be an unlikely cause since the total acid deposition of this event was about 18 fold greater than the largest known volcanic eruption, and since volcanic eruptions are not known to recur with such regularity. We show that the recurrence period of these peaks averages to 11.5 +/- 2.4 years, which approximates the solar cycle period, and suggest that this feature may have an extraterrestrial origin. We propose that this material may mark a period of enhanced interstellar dust and gas influx modulated by the solar cycle. The presence of this material could have made the Sun more active and have been responsible for initiating the warming that ended the last ice age.

Paul LaViolette

2005-02-04

249

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

250

Carbon cycle instability as a cause of the late Pleistocene ice age oscillations - Modeling the asymmetric response  

NASA Technical Reports Server (NTRS)

A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model.

Saltzman, Barry; Maasch, Kirk A.

1988-01-01

251

Possible effects of anthropogenically-increased CO2 on the dynamics of climate - Implications for ice age cycles  

NASA Technical Reports Server (NTRS)

A dynamical model, developed to account for the observed major variations of global ice mass and atmospheric CO2 during the late Cenozoic, is used to provide a quantitative demonstration of the possibility that the anthropogenically-forced increase of atmospheric CO2, if maintained over a long period of time (perhaps by tectonic forcing), could displace the climatic system from an unstable regime of oscillating ice ages into a more stable regime representative of the pre-Pleistocene. This stable regime is characterized by orbitally-forced oscillations that are of much weaker amplitude than prevailed during the Pleistocene.

Saltzman, Barry; Maasch, Kirk A.; Verbitsky, Mikhail YA.

1993-01-01

252

Acidity decline in Antarctic ice cores during the Little Ice Age linked to changes in atmospheric nitrate and sea salt concentrations  

NASA Astrophysics Data System (ADS)

is an important chemical variable that impacts atmospheric and snowpack chemistry. Here we describe composite time series and the spatial pattern of acidity concentration (Acy = H+ - HCO3-) during the last 2000 years across the Dronning Maud Land region of the East Antarctic Plateau using measurements in seven ice cores. Coregistered measurements of the major ion species show that sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) determine greater than 98% of the acidity value. The latter, also described as excess chloride (ExCl-), is shown mostly to be derived from postdepositional diffusion of chloride with little net gain or loss from the snowpack. A strong inverse linear relationship between nitrate concentration and inverse accumulation rate provides evidence of spatially homogenous fresh snow concentrations and reemission rates of nitrate from the snowpack across the study area. A decline in acidity during the Little Ice Age (LIA, 1500-1900 Common Era) is observed and is linked to declines in HNO3 and ExCl- during that time. The nitrate decline is found to correlate well with published methane isotope data from Antarctica (?13CH4), indicating that it is caused by a decline in biomass burning. The decrease in ExCl- concentration during the LIA is well correlated to published sea surface temperature reconstructions in the Atlantic Ocean, which suggests increased sea salt aerosol production associated with greater sea ice extent.

Pasteris, Daniel; McConnell, Joseph R.; Edwards, Ross; Isaksson, Elizabeth; Albert, Mary R.

2014-05-01

253

The search for refractory interplanetary dust particles from preindustrial aged Antarctic ice  

NASA Technical Reports Server (NTRS)

In a study of refractory interplanetary dust particles, preindustrial-aged Antarctic ice samples have been collected, melted, and filtered to separate the particle load. Particles containing a significant amount of aluminum, titanium, and/or calcium were singled out for detailed SEM and STEM characterization. The majority of these particles are shown to be volcanic tephra from nearby volcanic centers. Six spherical aggregates were encountered that consist of submicron-sized grains of rutile within polycrystalline cristobalite. These particles are probably of terrestrial volcanic origin, but have not been previously reported from any environment. One aggregate particle containing fassaite and hibonite is described as a probable interplanetary dust particle. The constituent grain sizes of this particle vary from 0.1 to 0.3 microns, making it significantly more fine-grained than meteoritic calcium-aluminum-rich inclusions. This particle is mineralogically and morphologically similar to recently reported refractory interplanetary dust particles collected from the stratosphere, and dissimilar to the products of modern spacecraft debris.

Zolensky, Michael E.; Webb, Susan J.; Thomas, Kathie

1988-01-01

254

Conference Summary: First International Conference on Global Warming and the Next Ice Age  

NASA Technical Reports Server (NTRS)

The First International Conference on Global Warming and the Next Ice Age was convened in Halifax, Nova Scotia, August 19-24, 2001. The conference program began each day with a 30 minute live classical music performances of truly international quality before the beginning business. Ample time for panel discussions was also scheduled. The general public was invited to attend and participate in a special evening panel session on the last day of the conference. The unusual and somewhat provocative title of the conference was designed to attract diverse views on global climate change. This summary attempts to accurately reflect the tone and flavor of the lively discussions which resulted. Presentations ranged from factors forcing current climate to those in effect across the span of time from the Proterozoic "snowball Earth" epoch to 50,000 years in the future. Although, as should be expected, attendees at the conference arrived with opinions on some of the controversial issues regarding climate change, and no-one openly admitted to a 'conversion' from their initial point of view, the interdisciplinary nature of the formal presentations, poster discussions, panels, and abundant informal discourse helped to place the attendees' personal perspectives into a broader, more diversified context.

Wetzel, Peter J.; Chylek, Petr; Lesins, Glen; Starr, David OC. (Technical Monitor)

2002-01-01

255

The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean  

USGS Publications Warehouse

A new 2400-year paleoclimate reconstruction from Chesapeake Bay (CB) (eastern US) was compared to other paleoclimate records in the North Atlantic region to evaluate climate variability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Using Mg/Ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation-driven estuarine hydrography, results show that warmest temperatures in CB reached 16-17. ??C between 600 and 950. CE (Common Era), centuries before the classic European Medieval Warm Period (950-1100. CE) and peak warming in the Nordic Seas (1000-1400. CE). A series of centennial warm/cool cycles began about 1000. CE with temperature minima of ~. 8 to 9. ??C about 1150, 1350, and 1650-1800. CE, and intervening warm periods (14-15. ??C) centered at 1200, 1400, 1500 and 1600. CE. Precipitation variability in the eastern US included multiple dry intervals from 600 to 1200. CE, which contrasts with wet medieval conditions in the Caribbean. The eastern US experienced a wet LIA between 1650 and 1800. CE when the Caribbean was relatively dry. Comparison of the CB record with other records shows that the MCA and LIA were characterized by regionally asynchronous warming and complex spatial patterns of precipitation, possibly related to ocean-atmosphere processes. ?? 2010.

Cronin, T.M.; Hayo, K.; Thunell, R.C.; Dwyer, G.S.; Saenger, C.; Willard, D.A.

2010-01-01

256

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

257

Ice-age survival of Atlantic cod: agreement between palaeoecology models and genetics  

PubMed Central

Scant scientific attention has been given to the abundance and distribution of marine biota in the face of the lower sea level, and steeper latitudinal gradient in climate, during the ice-age conditions that have dominated the past million years. Here we examine the glacial persistence of Atlantic cod (Gadus morhua) populations using two ecological-niche-models (ENM) and the first broad synthesis of multi-locus gene sequence data for this species. One ENM uses a maximum entropy approach (Maxent); the other is a new ENM for Atlantic cod, using ecophysiological parameters based on observed reproductive events rather than adult distribution. Both the ENMs were tested for present-day conditions, then used to hindcast ranges at the last glacial maximum (LGM) ca 21?kyr ago, employing climate model data. Although the LGM range of Atlantic cod was much smaller, and fragmented, both the ENMs agreed that populations should have been able to persist in suitable habitat on both sides of the Atlantic. The genetic results showed a degree of trans-Atlantic divergence consistent with genealogically continuous populations on both sides of the North Atlantic since long before the LGM, confirming the ENM results. In contrast, both the ENMs and the genetic data suggest that the Greenland G. morhua population post-dates the LGM. PMID:17999951

Bigg, Grant R; Cunningham, Clifford W; Ottersen, Geir; Pogson, Grant H; Wadley, Martin R; Williamson, Phillip

2007-01-01

258

Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay  

USGS Publications Warehouse

We present paleoclimate evidence for rapid (< 100 years) shifts of ??? 2-4??C in Chesapeake Bay (CB) temperature ???2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (???1400-1900 AD) and the Medieval Warm Period (???800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between ???450 and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous temperature maxima between 2200 and 250 years BP (average ???70 years) suggests that multi-decadal processes typical of the North Atlantic Oscillation (NAO) are an inherent feature of late Holocene climate. However, late 19th and 20th century temperature extremes in Chesapeake Bay associated with NAO climate variability exceeded those of the prior 2000 years, including the interval 450-1000 AD, by 2-3??C, suggesting anomalous recent behavior of the climate system. ?? 2002 Elsevier Science B.V. All rights reserved.

Cronin, T.M.; Dwyer, G.S.; Kamiya, T.; Schwede, S.; Willard, D.A.

2003-01-01

259

Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.  

PubMed Central

Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes. PMID:15101574

Hooghiemstra, Henry; Van der Hammen, Thomas

2004-01-01

260

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

261

Middle to Late Amazonian tropical mountain glaciers on Mars: The ages of the Tharsis Montes fan-shaped deposits  

NASA Astrophysics Data System (ADS)

Fan-shaped deposits (FSDs) extending to the northwest of the Tharsis Montes on Mars are the remnants of Amazonian-aged, cold-based, tropical mountain glaciers. We use high-resolution images to perform new impact crater size-frequency distribution (CSFD) analyses on these deposits in an effort to constrain the timing and duration of ice accumulation at tropical latitudes on Mars. This analysis revises the current understanding of the chronology regarding the formation of the glaciers and of the ridged facies in the Arsia Mons deposit, a deposit interpreted to be formed from recessional cold-based drop moraines. We develop a conceptual model that illustrates the effect of moving glacial ice on superposed impact craters of various sizes, including the buffering of underlying geologic units from impacts caused by the presence of the ice for extended periods of time, and the interpretation of crater retention ages of the subsequent glacial deposits following the periods of active glaciation. The new CSFD analyses establish best-fit crater retention ages for each entire Tharsis Montes FSD; these are ~220 Ma for the Ascraeus FSD at 8.35°S, ~125 Ma for the Pavonis FSD at 1.48°N, and ~210 Ma for the Arsia FSD at 11.92°N. Because the age for each deposit represents a combination of the stratigraphically older ridged facies and the younger knobby and smooth facies, the crater retention ages are most likely to represent dates subsequent to the onset of glaciation and prior to its final cessation. Estimates of the time necessary to build the deposits using net accumulation rates from atmospheric general circulation models and emplacement rates from glacial flow models suggest durations of ~45-150 Ma, depending on the specific obliquity history. These surface crater retention ages and related age estimates require that massive volumes of ice (on the order of 105 km3) were emplaced at tropical latitudes on Mars during the Middle to Late Amazonian. Additionally, we determined CSFD ages of three adjacent drop moraine units at Arsia Mons (725 Ma, 475 Ma and 345 Ma) and used these to calculate the average amount of time needed to form one of the approximately 185 drop moraines forming these deposits; we found that a typical drop moraine formation time in the Arsia FSD ridged facies to be on the order of ~106 years. These formation ages are considerably longer than that required for typical moraine systems alongside dynamic, wet-based glaciers on Earth, but are in approximate accord with recent geomorphological and geochemical data that document long-term, ice-margin stability for several cold-based glaciers in interior Antarctica. The difference in the ages of the ridged facies and non-ridged portion of the Arsia FSD suggests that the tropical mountain glaciers may have been emplaced over a period spanning many hundreds of millions of years. CSFD measurements for lava flows predating and postdating the Arsia Mons FSD suggest a maximum possible age of <750 Ma and a minimum age for the late stage, post FSD lava flows of ~105 Ma. Taken together, this evidence supports a scenario in which ice has been present and stable in substantial quantities (~105-106 km3) at tropical latitudes during extended periods of the Middle to Late Amazonian history of Mars. This implies that during this time, Mars sustained periods of spin-axis obliquity in the vicinity of 45°, during which time polar ice deposits were substantially reduced in volume or perhaps even absent.

Kadish, Seth J.; Head, James W.; Fastook, James L.; Marchant, David R.

2014-02-01

262

Evidence for rapid sedimentation in a tunnel channel, Oak Ridges Moraine, southern Ontario, Canada  

Microsoft Academic Search

In south-central Ontario, a Late Wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of Lake Ontario. The tunnel channels are locally infilled and the unconformity buried by sediment of the Oak Ridges Moraine. Based on seismic reflection profiling and drillcore, the tunnel channels are known to continue beneath the moraine. Detailed sedimentological analysis of ?300

H. A. J Russell; R. W. C Arnott; D. R Sharpe

2003-01-01

263

A REVIEW OF LICHENOMETRIC DATING OF GLACIAL MORAINES IN ALASKA The authors 2010  

E-print Network

OF GLACIAL MORAINES IN ALASKA BY GREGORY C. WILES1, DAVID J. BARCLAY2 AND NICOLÁS E.YOUNG3 1Department.C., Barclay, D.J. and Young, N.E., 2010: A review of li- chenometric dating of glacial moraines in Alaska 2000 years (Barclay et al. 2009). However, many other glacier forefields in Alaska are beyond

Barclay, David J.

264

Optical ages on loess derived from outwash surfaces constrain the advance of the Laurentide Ice Sheet out of the Lake Superior Basin, USA  

E-print Network

such an application: the timing of the advance of the Laurentide Ice Sheet in Wisconsin. Considerable de- bate existsOptical ages on loess derived from outwash surfaces constrain the advance of the Laurentide Ice Sheet out of the Lake Superior Basin, USA Randall J. Schaetzl a, , Steven L. Forman b , John W. Attig c

Schaetzl, Randall

265

Meltback of Hesperian-aged ice-rich deposits near the south pole of Mars: Evidence for drainage channels and lakes  

E-print Network

Meltback of Hesperian-aged ice-rich deposits near the south pole of Mars: Evidence for drainage. The eastern margin of these deposits displays further evidence for meltback, ponding, and drainage and are interpreted to represent drainage of water, ice, and sediment from the DAF. Channels connecting these craters

Head III, James William

266

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

267

Reconstruction of late Wisconsinan Ice Sheet and sea-level implications  

NASA Technical Reports Server (NTRS)

The Ross Sea exhibits north-south oriented troughs associated with modern ice streams and outlet glaciers. Seismic reflection profiles across the troughs show evidence that they were glacially eroded. Seismic records show morphologic features interpreted as till tongues, morainal banks, and possibly glacial deltas formed near the grounding line of the former marine ice sheet. Piston cores from the continental shelf penetrated diamictons whose origin and age is problematic. Detailed petrographic analyses of the minerals and rocks comprising these diamictons were conducted to determine subglacial versus glacial marine origin, and to reconstruct the glacial setting of the Ross Sea during the most recent glacial maximum. The most detailed work, conducted in the western Ross Sea, shows that diamictons do occur in distinct petrologic provinces. This is consistent with deposition from the basal debris zone of either an ice sheet or an ice shelf. Overcompaction, in conjunction with the widespread nature of these deposits, favors deposition from marine ice sheets; ice shelves are believed to deposit their basal debris close to the grounding lines. Other results from the investigation are briefly discussed.

Anderson, John B.

1993-01-01

268

Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific 15N/14N isotopic ratios (?15N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, ?15N decreases between 1850 and the present. The total shift in ?15N of -2 per mil over this period is comparable to the total change in global mean sedimentary ?15N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

Sherwood, Owen A.; Guilderson, Thomas P.; Batista, Fabian C.; Schiff, John T.; McCarthy, Matthew D.

2014-01-01

269

Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age.  

PubMed

The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific (15)N/(14)N isotopic ratios (?(15)N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, ?(15)N decreases between 1850 and the present. The total shift in ?(15)N of -2 per mil over this period is comparable to the total change in global mean sedimentary ?(15)N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age. PMID:24336216

Sherwood, Owen A; Guilderson, Thomas P; Batista, Fabian C; Schiff, John T; McCarthy, Matthew D

2014-01-01

270

Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages  

USGS Publications Warehouse

The extent of the last British-Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23-19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright ?? 2008 John Wiley & Sons, Ltd.

Phillips, W. M.; Hall, A. M.; Ballantyne, C. K.; Binnie, S.; Kubik, P. W.; Freeman, S.

2008-01-01

271

Abrupt change in atmospheric CO2 during the last ice age Jinho Ahn,1  

E-print Network

in Antarctica varied in a similar fashion on millennial time scales, but previous work indicates understanding of future climate-carbon cycle feedbacks [Friedlingstein et al., 2006]. Previous ice core work

Schmittner, Andreas

272

Using proglacial-threshold lakes to constrain fluctuations of the Jakobshavn Isbræ ice margin, western Greenland, during the Holocene  

NASA Astrophysics Data System (ADS)

The future response of the Greenland Ice Sheet (GIS) and its potential contribution to sea level rise are uncertain. Rapid changes of Greenland's outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future. This significant short-term variability highlights the need for longer-term, geologic (e.g., Holocene) records of ice margin fluctuations. However, a major challenge with reconstructing the GIS during the Holocene stems from it having been smaller than it is at present, thus traditional glacial geologic approaches are not suitable. We use radiocarbon-dated sediment sequences from seven proglacial-threshold lakes spanning ˜50 km of the western GIS margin near Jakobshavn Isbræ to constrain the timing of early Holocene deglaciation, the duration that this sector of the western GIS was smaller than its present configuration, and the timing of its advance during Neoglaciation. Our reconstructions suggest deglaciation ˜7300 cal yr BP, minimum ice extent ˜6000-5000 cal yr BP and smaller-than-present ice configuration until at least ˜2300 cal yr BP for the ice margin south of Jakobshavn Isbræ, and until ˜400 cal yr BP for the ice margin north of Jakobshavn Isbræ. One relatively large proglacial lake that became briefly ice-free during the middle Holocene lies in a catchment that likely extends 10s of km inland beneath the GIS, suggesting significant middle Holocene retreat of this portion of the GIS. The overall pattern of ice sheet change is inconsistent with existing ice sheet model reconstructions for this region, but is consistent with numerous paleoclimate proxy and relative sea level data. These continuous lacustrine records corroborate, but provide closer age control than, existing non-continuous records of radiocarbon-dated reworked bivalves from historical moraines in the region. Reconstructing ice margin change from proglacial-threshold lakes is one of few approaches with the potential to constrain smaller-than-present ice sheet extent.

Briner, J. P.; Stewart, H. A. M.; Young, N. E.; Philipps, W.; Losee, S.

2010-12-01

273

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

274

Tropical North Atlantic Hydrologic Cycle Variability in the Florida Straits During the Last Ice Age  

E-print Network

Sheet MIS Marine Isotope Stage[s] NGRIP North Greenland Ice Core Project SSS Sea Surface Salinity SST Sea Surface Temperature TNA Tropical North Atlantic ix TABLE OF CONTENTS Page ABSTRACT... discovered by analyzing the oxygen isotopic composition of Greenland ice cores [Dansgaard et al., 1969; Dansgaard et al., 1993]. Recent evidence suggested that these abrupt changes influenced climate on a global scale [e.g., Peterson et al., 2000; Wang...

Them, Theodore

2012-10-19

275

Area, volume and mass changes of southeast Vatnajökull ice cap, Iceland, from the Little Ice Age maximum in the late 19th century to 2010  

NASA Astrophysics Data System (ADS)

Area and volume changes and the average geodetic mass balance of the non-surging outlet glaciers of southeast Vatnajökull ice cap, Iceland, during different time periods between ~1890 and 2010, are derived from a multi-temporal glacier inventory. A series of digital elevation models (DEMs) (∼1890, 1904, 1936, 1945, 1989, 2002, 2010) have been compiled from glacial geomorphological features, historical photographs, maps, aerial images, DGPS measurements and a LiDAR survey. Given the mapped bedrock topography we estimate relative volume changes since the end of the Little Ice Age (LIA) ~1890. The variable dynamic response of the outlets, assumed to have experienced similar climate forcing, is related to their different hypsometry, bedrock topography, and the presence of proglacial lakes. In the post-LIA period the glacierized area decreased by 164 km2 and the glaciers had lost 10-30% of their ~1890 area by 2010. The glacier surface lowered by 150-270 m near the terminus and the outlet glaciers collectively lost 60 ± 8 km3 of ice, which is equivalent to 0.154 ± 0.02 mm of sea level rise. The relative volume loss of individual glaciers was in the range of 15-50%, corresponding to a geodetic mass balance between -0.70 and -0.32 m w.e. a-1. The rate of mass loss was most negative in the period 2002-2010, on average -1.34 ± 0.12 m w.e. a-1, which lists among the most negative mass balance values recorded worldwide in the early 21st century. From the data set of volume and area of the outlets, spanning the 120 years post-LIA period, we evaluate the parameters of a volume-area power law scaling relationship.

Hannesdóttir, H.; Björnsson, H.; Pálsson, F.; Aðalgeirsdóttir, G.; Guðmundsson, S.

2014-09-01

276

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

277

Exploring controls on ice stream destabilisation during the LGM/Holocene transition in West Greenland  

NASA Astrophysics Data System (ADS)

Newly emerging onshore and offshore deglacial chronologies from West Greenland enable investigation of the role of both climate and topography in controlling ice stream dynamics The Uummannaq ice stream system (UIS) now has a comprehensive deglacial chronology (eg. Lane et al; 2013; Ó Cofaigh et al., 2013; Roberts et al., 2013) which includes four dimensional control i.e. location and geometry of the ice margin and ice stream trunk and rates of thinning and retreat. This provides a framework for interpreting the main drivers and controls on ice stream dynamics under changing climatic conditions. Deglaciation of the UIS began on the outer shelf at ~14.8 ka, with Ubekendt Ejland becoming ice free at ~12.4 ka. Staircases of lateral moraines on the southern flanks of Ubekendt point to step-wise thinning of the UIS as ice retreated from the shelf edge. This period of retreat coincided with a rise in air temperature between 16 -14.5 ka, increasing JJA solar radiation as well sea-level rise. The wide, mid-shelf trough (> 30km; which harboured the main UIS trunk zone) also had few constrictions which facilitated grounding line retreat. The UIS then withdrew rapidly with 80 - 100 km of retreat by ~11.4 ka - 10.8 ka as the northern and southern feeder zones unzipped. This coincided with increasing insolation and peak sea-level, but topography and bathymetry were also influential on margin retreat (i.e. reverse slope over-deepening and fjord widening). This retreat occurred despite Younger Dryas air temperature cooling. Along the southern arm of the UIS the grounding line retreated towards Store Gletscher becoming topographically pinned at ~11.4 - 11.0 ka, but from 9.3 ka onwards retreat rates increased with the ice reaching the present Store Gletscher margin by 8.7 ka. This coincided with increased air temperatures and peak summer insolation at the start of the Holocene. The northern arm of the UIS also deglaciated quickly from Ubekendt, calving northward into Karrat/Rinks and Ingia Fjords. Lateral moraines north of Karrat again point to step-wise thinning of the UIS as ice retreated. At ~11.3 ka the ice front in Karrat/Rinks Isfjord stabilised until ~6.5 ka and seemingly became unresponsive to both climate and marine forcing for 5000yrs due to topographic pinning. Ice sheet surface profile reconstructions based on two equilibrium models (perfectly plastic v Weertman-sliding profile; Roberts et al., 2013) combined with surface exposure ages have constrained likely minimum and maximum Last Glacial Maximum (LGM) ice surface geometries for the UIS.A 2D model, however, can simulate grounding line-retreat behaviour and surface thinning through time (e.g. Jamieson et al., 2012). Initial model results indicate that the non-linear retreat of the UIS is influenced by vertical and lateral constrictions in the marine trough system which partially regulates grounding line stability. It is apparent that during periods of rapid retreat the ice surface thins rapidly inland. Conversely, if the grounding line is pinned and relatively stable, surface thinning decelerates. This period of relatively slow ice surface thinning may be evidenced by the lateral moraine staircases which infer slow, incremental thinning along the margins of the UIS during different periods of retreat.

Roberts, David H.; Rea, Brice R.; Lane, Tim P.; Jamieson, Stewart S. R.; Cofaigh, Colm Ó.; Vieli, Andreas

2014-05-01

278

Evidence for rapid sedimentation in a tunnel channel, Oak Ridges Moraine, southern Ontario, Canada  

NASA Astrophysics Data System (ADS)

In south-central Ontario, a Late Wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of Lake Ontario. The tunnel channels are locally infilled and the unconformity buried by sediment of the Oak Ridges Moraine. Based on seismic reflection profiling and drillcore, the tunnel channels are known to continue beneath the moraine. Detailed sedimentological analysis of ˜300 m of continuous core from two drillholes located ˜7 km apart in subparallel tunnel channels identified three facies. The gravel facies is 17 m thick and occurs in only one of the cores. It directly overlies the unconformity and may include a number of upward-fining units. Seismic reflection data suggests the gravel forms stacked gravel mesoforms or quasi-horizontal gravel layers (bed load sheets deposited from fluidal flows). Along the deep channel axis, the graded massive sand facies up to 37 m thick is the most common facies and consists of silty, medium sand with minor coarse sand. Strata are reverse-graded, normal-graded, or massive with isolated silt intraclasts and evidence locally for dewatering. This facies is interpreted to have been deposited from hyperconcentrated dispersions downflow of a hydraulic jump (or major channel confluence). The third facies consists of medium-scale and small-scale cross-stratified sand. Medium-scale cross-stratification occurs predominantly in the lower 37 m of the core and is interbedded with the graded massive sand facies; small-scale cross-stratified sand is progressively more common upward in core. Medium- and small-scale cross-stratified sands was deposited, respectively, by subaqueous dunes and ripples formed in dilute fluid flows. The complete succession is interpreted to have been deposited very rapidly within a subglacial tunnel channel before discharge ceased along the channel. Deposition followed closely, and in part coincided with rapid expansion of the channel by erosion in a hydraulic jump or at a major channel confluence along the grounding line of a subglacial lake. Scour into unconsolidated sediment contributed to the sediment flux and quickly overloaded the flow with suspended sediment, which in turn resulted in extremely high rates of sedimentation immediately downflow. Such depositional conditions support the notion that tunnel channels in the study area formed and/or served as conduits for subglacial jökulhlaup discharges, and that the Laurentide Ice Sheet most probably did not generally drain by steady state processes, but instead by short-lived catastrophic events.

Russell, H. A. J.; Arnott, R. W. C.; Sharpe, D. R.

2003-08-01

279

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

280

Radiocarbon ages of terrestrial gastropods extend duration of ice-free conditions at the Two Creeks forest bed, Wisconsin, USA  

USGS Publications Warehouse

Analysis of terrestrial gastropods that underlie the late Pleistocene Two Creeks forest bed (~ 13,800–13,500 cal yr BP) in eastern Wisconsin, USA provides evidence for a mixed tundra-taiga environment prior to formation of the taiga forest bed. Ten new AMS 14C analyses on terrestrial gastropod shells indicate the mixed tundra-taiga environment persisted from ~ 14,500 to 13,900 cal yr BP. The Twocreekan climatic substage, representing ice-free conditions on the shore of Lake Michigan, therefore began near the onset of peak warming conditions during the Bølling–Allerød interstadial and lasted ~ 1000 yr, nearly 600 yr longer than previously thought. These results provide important data for understanding the response of continental ice sheets to global climate forcing and demonstrate the potential of using terrestrial gastropod fossils for both environmental reconstruction and age control in late Quaternary sediments.

Rech, Jason A.; Nekola, Jeffrey C.; Pigati, Jeffrey S.

2012-01-01

281

The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories  

NASA Astrophysics Data System (ADS)

A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in viscous response to the early Holocene unloading of ice from the current locations of the ice shelf centers. ICE-6G_C (VM5A) fits the horizontal observations well (wrms residual speed of 0.7 mm yr-1), there being no need to invoke any influence of lateral variation in mantle viscosity. ICE-6G_C (VM5A) differs in several respects from the recently published W12A model of Whitehouse et al. First, the upper-mantle viscosity in VM5a is 5 × 1020 Pa s, half that in W12A. The VM5a profile, which is identical to that inferred on the basis of the Fennoscandian relaxation spectrum, North American relative sea level histories and Earth rotation constraints, when coupled with the revised ICE-6G_C deglaciation history, fits all of the available constraints. Secondly, the net contribution of Antarctica ice loss to global sea level rise is 13.6 m, 2/3 greater than the 8 m in W12A. Thirdly, ice loss occurs quickly from 12 to 5 ka, and the contribution to global sea level rise during Meltwater Pulse 1B (11.5 ka) is large (5 m), consistent with sedimentation constraints from cores from the Antarctica ice shelf. Fourthly, in ICE-6G_C there is no ice gain in the East Antarctica interior, as there is in W12A. Finally, the new model of Antarctic deglaciation reconciles the global constraint upon the global mass loss during deglaciation provided by the Barbados record of relative sea level history when coupled with the Northern Hemisphere counterpart of this new model.

Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

2014-07-01

282

Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age  

NASA Astrophysics Data System (ADS)

For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (?30Siopal) and nitrogen (?15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (?Nd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, ?15Nsed values of ~ +5‰ and intermediate ?30Siopal values of ~+0.97‰. At the same time the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were caused by permanent El Niño-like conditions characterized by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, ?30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by ?15Nsed of up to ~ +7‰, and by the highest degree of silicate utilisation with ?30Siopal reaching values of +1.1‰. At the same time detrital ?Nd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA indicating significantly increased nutrient availability. Comparison between the ?30Siopal and ?15Nsed signatures suggests that during the past 650 years the ?15Nsed signature in the Peruvian Upwelling area has most likely primarily been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column.

Ehlert, C.; Grasse, P.; Gutiérrez, D.; Salvatteci, R.; Frank, M.

2014-08-01

283

Vertical dimensions and age of the Wicklow Mountains ice dome, Eastern Ireland, and implications for the extent of the last Irish Ice Sheet  

Microsoft Academic Search

Patterns of erratic distribution show that the Wicklow Mountains formerly supported an independent ice cap or ice dome. Geomorphological mapping of the upper limits of evidence for glaciation (ice-scoured and moulded bedrock, perched boulders) and the distribution of features indicative of prolonged periglacial conditions (tors, frost-shattered rock, blockfields) indicates that along the main axis of high ground erosive warm-based ice

Colin K. Ballantyne; Danny McCarroll; John O. Stone

2006-01-01

284

Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic  

E-print Network

Antarctic Ice Sheet (WAIS) Divide Anais J. Orsi,1 Bruce D. Cornuelle,1 and Jeffrey P. Severinghaus1 Received (WAIS) Divide. Results show that WAIS Divide was colder than the last 1000-year average from 1300 Sheet (WAIS) Divide, Geophys. Res. Lett., 39, L09710, doi:10.1029/2012GL051260. 1. Introduction 1

Severinghaus, Jeffrey P.

285

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

286

Preservation of ancient ice at Pavonis and Arsia Mons: Tropical mountain glacier deposits on Mars  

NASA Astrophysics Data System (ADS)

Large tropical mountain glacier (TMG) deposits on the northwest flanks of the Tharsis Montes and Olympus Mons volcanoes are interpreted to be the record of ancient climates characteristic of Mars several hundred million years ago when planetary spin-axis obliquity was ~45°. During this era, polar volatiles (predominantly H2O) were mobilized and transferred equatorward, undergoing adiabatic cooling on the Tharsis volcano flanks, and precipitating snow and ice to form cold-based tropical mountain glaciers up to several kilometers in thickness. Subsequent climate change resulted in retreat, sublimation and collapse of the tropical mountain glaciers, leaving the three typical facies observed today: (1) concentric ridges, the ridged facies, interpreted as drop moraines; (2) knobby facies, interpreted as debris-dominated sublimation residue; and (3) the smooth facies, interpreted as remnant alpine glacial deposits. Ring-mold craters (RMCs) are distinctive features formed by impacts into debris-covered ice. We describe a set of relatively fresh ring-mold craters superposed on the Arsia and Pavonis Mons TMG deposits; we interpret these to indicate that the impact events penetrated a veneer of sublimation lag and excavated buried remnant glacial ice, despite the lack of detection of buried ice by orbital radar instruments. The diameter distribution of the RMCs suggest that the remnant ice lies at a depth of at least 16 m. The TMG deposit ages suggest that these ice deposits date from a period in the range of 125-220 million years before the present; the remnant ice may thus preserve records of the ancient atmospheric gas content and microbiota, as is common in terrestrial glacial ice. Preservation of this ice and the lack of any associated fluvial features suggest that the post-glacial climate has been cold, and related surface temperatures have not been sufficient to bring the buried deposits to the melting point of water.

Head, James W.; Weiss, David K.

2014-11-01

287

European floods during the winter 1783/1784: scenarios of an extreme event during the `Little Ice Age'  

NASA Astrophysics Data System (ADS)

The Lakagígar eruption in Iceland during 1783 was followed by the severe winter of 1783/1784, which was characterised by low temperatures, frozen soils, ice-bound watercourses and high rates of snow accumulation across much of Europe. Sudden warming coupled with rainfall led to rapid snowmelt, resulting in a series of flooding phases across much of Europe. The first phase of flooding occurred in late December 1783-early January 1784 in England, France, the Low Countries and historical Hungary. The second phase at the turn of February-March 1784 was of greater extent, generated by the melting of an unusually large accumulation of snow and river ice, affecting catchments across France and Central Europe (where it is still considered as one of the most disastrous known floods), throughout the Danube catchment and in southeast Central Europe. The third and final phase of flooding occurred mainly in historical Hungary during late March and early April 1784. The different impacts and consequences of the above floods on both local and regional scales were reflected in the economic and societal responses, material damage and human losses. The winter of 1783/1784 can be considered as typical, if severe, for the Little Ice Age period across much of Europe.

Brázdil, Rudolf; Demarée, Gaston R.; Deutsch, Mathias; Garnier, Emmanuel; Kiss, Andrea; Luterbacher, Jürg; MacDonald, Neil; Rohr, Christian; Dobrovolný, Petr; Kolá?, Petr; Chromá, Kate?ina

2010-03-01

288

Influences of the Little Ice Age glacier advance on hillslope morphometry and development in paraglacial valley systems around the Jostedalsbreen ice cap in Western Norway  

NASA Astrophysics Data System (ADS)

This paper focuses on the influence of the "Little Ice Age" (LIA) glacier advance on hillslope morphometry and development in selected U-shaped and (para)glacial tributary valleys, which are still occupied in their upper parts by outlet glaciers of the Jostedalsbreen ice cap in Western Norway. Especially the morphometric influences and geomorphic consequences of the LIA glacier advance on the development of the valley-side hillslope systems and associated denudative processes are assessed by comparing hillslope systems located inside and outside of the LIA glacier maximum extent. The process-based approach applied includes orthophoto- and topographical map interpretation as well as hillslope profile surveying in field for morphometric analyses and detailed geomorphological mapping for process analyses. In addition GIS and DEM computing as well as geophysical measurements (georadar) for storage analyses are performed. It is found that hillslopes inside the LIA glacier limit have steepened lower hillslope segments due to a negative sediment net balance of removal and deposition of material by the advancing LIA glacier front. There are significant differences in the present-day slope debris thickness and composition between hillslopes inside or outside the LIA glacier limit. Slope debris from hillslopes inside the glacier maximum extent are clearly less thick and display a different internal structure originating from a combination of debris from gravitational processes and reworked modern glacial deposits. Compared to that slope debris covers on hillslopes outside the LIA glacier limit are in general noticeable thicker and less influenced by glacial deposits. The combined effects of modified slope morphometry and altered composition of material covering lower hillslope segments have generated a higher intensity of post-LIA denudative hillslope processes.

Laute, Katja; Beylich, Achim A.

2012-09-01

289

Continental shelf record of the East Antarctic Ice Sheet evolution: seismo-stratigraphic evidence from the George V Basin  

NASA Astrophysics Data System (ADS)

The late Quaternary ice sheet/ice shelf extent in the George V Basin (East Antarctica) has been reconstructed through analyses of Chirp sub-bottom profiles, integrated with multi-channel seismic data and sediment cores. Four glacial facies, related to the advance and retreat history of the glaciated margin, have been distinguished: Facies 1 represents outcrop of crystalline and sedimentary rocks along the steep inner shelf and comprises canyons once carved by glaciers; Facies 2 represents moraines and morainal banks and ridges with a depositional origin along the middle-inner shelf; Facies 3 represents glacial flutes along the middle-outer shelf; Facies 4 is related to ice-keel turbation at water depths <500 m along the outer shelf. A sediment drift deposit, located in the NW sector of the study area, partly overlies facies 2 and 3 and its ground-truthing provides clues to understanding their age. We have distinguished: (a) an undisturbed sediment drift deposit at water depth >775 m, with drape/sheet and mound characters and numerous undisturbed sub-bottom sub-parallel reflectors (Facies MD1); (b) a fluted sediment drift deposit at water depth <775 m, showing disrupted reflectors and a hummocky upper surface (Facies MD2). Radiocarbon ages of sediment cores indicate that the glacial advance producing facies MD2 corresponds to the Last Glacial Maximum (LGM) and that during the LGM the ice shelf was floating over the deep sector of the basin, leaving the sediment drift deposit undisturbed at major depths (Facies MD1). This observation further implies that: (a) glacial facies underneath the sediment drift were the result of a grounding event older than the LGM, (b) this sector of the East Antarctic fringe was sensitive to sea-level rise at the end of the LGM; thus potentially contributing to meltwater discharge during the last deglaciation.

Presti, Massimo; De Santis, Laura; Brancolini, Giuliano; Harris, Peter T.

2005-05-01

290

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

291

Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada  

NASA Astrophysics Data System (ADS)

Glacially-deformed massive ice and icy sediments (MI-IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in Alaska, Greenland and Iceland; (2) ice crystal fabrics similar to those from basal ice in Antarctica and ice-cored moraines on Axel Heiberg Island, Canada; and (3) a thaw or erosional unconformity along the top of the MI-IS, buried by glacigenic or aeolian sediments. Intrasedimental ice consists of pore ice and segregated ice formed within Pleistocene sands deposited before glacial overriding. The co-existence of basal and intrasedimental ice within the MI-IS records their occurrence within the basal ice layer of the Laurentide Ice Sheet. Stagnation of the ice sheet and melt-out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale. The widespread occurrence of supraglacial melt-out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost.

Murton, J. B.; Whiteman, C. A.; Waller, R. I.; Pollard, W. H.; Clark, I. D.; Dallimore, S. R.

2005-03-01

292

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

293

A continental shelf sedimentary record of Little Ice Age to modern glacial dynamics: Bering Glacier, Alaska  

NASA Astrophysics Data System (ADS)

The Bering Glacier System is the world's largest surging temperate glacier with seven events occurring over the past century under a range of north Pacific climatic conditions. Onshore records reveal changes in glacial termini positions and evidence of late Holocene glacial advances, but the Little Ice Age (LIA) record of potential glacial surging and associated flooding has not been examined. A 13.6 m-long jumbo core collected on the adjacent continental shelf reveals a 600-yr-long record of sedimentation associated with changing glacifluvial discharge. The chronology is based on 210Pb geochronology and five radiocarbon dates, and the core can be separated into three distinct lithologic units based on the examination of X-radiographs and physical properties: (1) an uppermost unit dating from ?125 cal yr BP to the present characterized by bioturbated mud interbedded with laminated, thick (5-20 cm) low-bulk density clay-rich beds; (2) a middle unit dating from ?120-400 cal yr BP that includes numerous interlaminated-to-interbedded low- and high-bulk density beds with infrequent evidence of bioturbation; thick laminated clay-rich beds are rare; (3) a lowermost unit that predates ?400 cal yr BP and is composed of rare laminated beds grading down into mottled to massive mud. In each of these units, the laminated lithofacies from this mid-shelf location indicates both flood deposition and likely sediment transport in the wave-current bottom-boundary layer. The thick low-density, clay-rich beds in the uppermost unit correlate with historic outburst floods associated with known surge events. Based on previous terrestrial studies, the terminus was at its Holocene Neoglacial maximum extent close to the modern coastline at some point in the middle to late stages of the LIA in southern Alaska (100-350 cal yr BP). During the LIA, preservation of bioturbated intervals is rare while laminated intervals are common. This style of interbedding indicates frequent (<10 yr recurrence interval) event-scale mud deposition, suggesting that frequent summer flooding and redistribution by winter storms were more prevalent during the LIA rather than the outburst flooding typical of the past century. Rare event-scale bedding indicative of outburst flooding and possible surge events is found within the middle unit, and may correspond to periods with similar climatic trends as in the 20th century. The infrequent deposition of event layers in the lowermost unit could be attributed to the less frequent flooding and/or enhanced diversion of glacial drainage to the eastern terminus instead of present day Seal River. The thickness and depositional frequency of event-scale bedding can be related to Gulf of Alaska tree-ring proxy temperature reconstructions, where more numerous event bed formation occurs when there are more frequent, higher-amplitude temperature excursions. These frequent fluctuations may have prevented the decadal-long periods of positive mass balance required to enable numerous surge events during this period.

Jaeger, John M.; Kramer, Branden

2014-09-01

294

www.sciencemag.org SCIENCE VOL 302 14 NOVEMBER 2003 1111 Algal Clues to Antarctic Ice Shelf Ages  

E-print Network

The naturally high variability of sea ice extent in Antarctica and the short duration of instrumental records have combined to obscure any clear record of sea ice coverage change. Curran et al. (p. 1203; see at the edges of ice shelves, which they show is related to the position of the nearby winter-spring sea ice

Nori, Franco

295

Geodiversity characterization and assessment of the Morainic Amphitheatre of Rivoli -Avigliana (NW-Italy)  

NASA Astrophysics Data System (ADS)

The concept of Geodiversity in its wide sense refers specifically to particular geosystems that are in themselves complex (e.g diverse) assemblages of bedrock, landform, and soil features. Therefore, geodiversity assessment is strictly related to landscape structure, whose studies are in the field of complex Physical Geography. Moreover, Geodiversity studies provide a fundamental base for geoconservation and environmental management in a holistic way. This is particularly true within complex geomorphological environments, where many intrinsic and extrinsic factors are interconnected. Various procedures has been already applied for the creation of geodiversity maps in different geomorphological context, but especially in wide areas with a large geodiversity of landforms. Pleistocene morainic amphitheatres of the Alpine piedmont regions are indeed particular and complex environments: not only for the geological and geomorphological points of view, but also for their relationships with biotic components and human life. The aim of this study is to carry out a geodiversity characterization of the Rivoli-Avigliana Morainic Amphitheatre (AMRA; NW Italy). The AMRA separates the lower Susa Valley from the middle course of the Sangone River; it is a set of low hills and depressions related to glacial pulsations aged between 750,000 and 12,000 years ago. Earth Sciences knowledge of the area has been compared to detailed field geomorphological and territorial data in order to determine qualitative and quantitative landscape parameters and to evaluate their validity for geodiversity assessment. A first qualitative characterization of the AMRA and an estimation of its geodiversity have been performed by means of geomorphological mapping and stratigraphic studies, including geomorphosites assessment for the same area. Then, geodiversity characterization and evaluation have been performed through the definition and application of quantitative parameters (landform energy, slope, land use, roughness, and other geomorphologic, hydrologic and geologic indexes). After acquisition of vector data, satellite and aerial images, GIS procedures allowed to manage and to process images and data: this allowed to interpret morphometric indexes and to obtain thematic maps with 3D views. Finally, results from the calculation of geodiversity and geomorphosites have been compared. Results turned out to be very effective for the study and for the reconstruction of the AMRA evolutionary stages, also for interpreting scenarios of future natural hazards, land occupation and risks posed to geodiversity for natural and anthropogenic causes. Geomatics devices and digital data demonstrated to be really suitable for improved analysis and representation of the observed phenomena. They can be easily integrated within GIS for decision support requirements. In this way, field and remote sensing data, together with indexes of biotic and abiotic aspects can generate synthetic information, to produce effective spatial interpolations and impressive 3D scenarios useful for Earth Science simulations and environmental/territorial advertising.

Giordano, Enrico; Lucchesi, Stefania; Perotti, Luigi; Giardino, Marco

2014-05-01

296

Designing for effective stationkeeping in ice  

E-print Network

. Sea ice management Sea ice observation and monitoring: · Ice concentration, floe size distribution, etc. · Ice geometry, ice age, density, salinity, etc. · Sea ice tracking (drift speed and directionDesigning for effective stationkeeping in ice CeSOS Highlights and AMOS Visions Conference

Nørvåg, Kjetil

297

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

298

Extensive mapping of ice marginal landforms in northern Russia (25°E - 112°E); new precise constraints on ice sheet limits of the Eurasian ice sheets in Russia  

NASA Astrophysics Data System (ADS)

Ice sheet extent for the last glaciation(s) are well established in most previously glaciated areas, most notably in North America and Europe. However, in Russia, which have hosted major sectors of the Scandinavian-, Barents sea-, and Kara sea ice sheets, knowledge of exact ice marginal positions is sporadic. Most evidence of ice sheet extent so far, have been from drift distribution, and only limited attempts have been made to use remote sensing data to precisely locate ice marginal zones. This is probably because of difficulties in using optical remote sensing data (typically Landsat ETM+ and ASTER) in low relief, densely forested areas (Taiga), and sheer scale of the mapped areas. Furthermore, no reliable elevation model has existed north of 60°N, aiding interpretation of optical remote sensing data. We have used recently digitized Russian topographic maps (scale 1:100,000) and the new ASTER GDEM 15 m resolution elevation model to map ice marginal moraines in Russia (25°E - 112°E), thereby covering most formerly glaciated areas in Russia. The majority of the mapping was made using shaded relief maps. Critical interpretation was made using the ASTER GDEM elevation model combined with multispectral Landsat ETM+ data to construct a synthetic stereo-model, which was analyzed in 3D using ERDAS Stereo Analyst® software. Several operators have worked independently to insure unbiased interpretation of the landforms. So far we have mapped about 2.1E6 km2. Many of the mapped moraines are distinct at the mapping scale, with a typical relief of 20 - 120 m, and a cross-sectional width of 500 - 1500 m. Moreover, several moraines are hundreds kilometers long! Many mapped ice marginal moraines exhibit a very lobate morphology, reflecting low gradient ice lobes extending into the low relief river valleys. We infer very low basal shear stresses in the valleys, indicating glacier flow on soft sediments and possible flotation of ice tongues on ice dammed lakes. There are relatively little mapped ice marginal deposits on relative highs in the terrain, indicating less ice movement slightly higher up in the topography. We have also mapped large zones of hummocky moraine, tentatively correlated to an early-/mid-Weichselian Barents Sea advance, indicating down-wasting in a stagnant fashion. We regard the mapping as robust, and expect it to reliably depict major ice marginal zones in Russia. The current mapping conforms well with, and, expands upon previous remote sensing efforts in NW Russia. Important results from this study show that the Scandivian LGM ice sheet extended significantly further southeast (~150 km) than previously thought in the Severnaya Dvina and Vychegda river basins. Furthermore many previously unknown ice marginal moraines have been mapped in great detail all the way east into the Taymyr region. We have only tentatively correlated the mapped moraines to known glacial stages, but we are confident that the new mapping effort is a big step forward in understanding the geometry of former ice extent in Russia.

Fredin, O.; Rubensdotter, L.; van Welden, A.; Larsen, E.; Lyså, A.; Jensen, M.

2009-12-01

299

Vostok Ice Core: Excel (Mac or PC)  

NSDL National Science Digital Library

Students use Excel to graph and analyze Vostok ice core data (160,000 years of Ice core data from Vostok Station). Data includes ice age, ice depth, carbon dioxide, methane, dust, and deuterium isotope relative abundance.

Professor Stephanie Pfirman, Barnard College. Based on data of J. Chapellaz, Laboratoire de Glaciologie et Geophysique de l'Environment, Grenoble. Archived at: Lamont-Dohert Earth Observatory (more info) . Starting Point page organized by R.M. MacKay.

300

Cosmogenic 10Be Exposure Age Limits on the Angel Lake Glaciation, Ruby Mountains, Northeastern Nevada  

NASA Astrophysics Data System (ADS)

Evidence of Pleistocene glaciations in the northern Great Basin of the interior western U.S. has been known for decades. Nonetheless, this area has received considerably less attention than the eastern and western extremes of the Great Basin, despite being centrally located among numerous well-dated Pleistocene glacial chronologies and in a setting where such chronologies can provide clues to the influence of North American ice sheets, Great Basin paleolakes, and atmospheric circulation changes on climate change. Among the most extensively glaciated mountains in the Great Basin are the Ruby and East Humboldt Mountains in northeastern Nevada, where the type localities for the last two Pleistocene glaciations in the region, the Lamoille and Angel Lake Glaciations, are found. The glacial record in these two ranges includes sequences of moraines deposited during the Angel Lake Glaciation, displaying abundant material suitable for terrestrial cosmogenic 10Be surface-exposure dating. Exposure ages of boulders from atop a sequence of well-preserved moraines in Seitz Canyon in the western Ruby Mountains limit the end of the Angel Lake Glaciation to 19.3 ± 1.0 ka. This preliminary age limit verifies that the Angel Lake Glaciation coincided with marine oxygen-isotope stage 2 and the global Last Glacial Maximum, and suggests that mountain glaciers in northeastern Nevada began retreating in step with the Laurentide Ice Sheet. When compared to glacial chronologies from elsewhere in the region, this age limit indicates an early start of the last deglaciation relative to the Sierra Nevada and the Wasatch Mountains, at the western and eastern extremes of the Great Basin respectively. Furthermore, this age limit suggests that ice retreat began before the highstands of the largest Great Basin paleolakes, Lakes Bonneville and Lahontan. Further development of the glacial chronology of the northern Great Basin is needed to evaluate the significance of these apparent age differences, and will provide a useful framework for resolving the pattern of climate change during the last glacial-interglacial transition.

Laabs, B. J.; Munroe, J. S.; Best, L. C.; Caffee, M. W.

2011-12-01

301

The Little Ice Age signature and subsequent warming seen in borehole temperature logs versus solar forcing model  

NASA Astrophysics Data System (ADS)

The `low' in the transient temperature versus depth borehole profiles around 120 m seen from deep temperature logs in the Canadian Prairies (southern Alberta-southern Saskatchewan), as well as in some of the European data, has been interpreted to be related to the Little Ice Age (LIA). Data point to the lowest ground surface and subsurface temperatures occurring in the very late eighteenth to nineteenth centuries. Inversion of these logs shows that surface temperature lows were followed by a recent warming period. Further, the synthetic profiles built on the basis of solar forcing history, stretching as far back as the beginning of the seventeenth century, suggest that the LIA signatures interpreted from the inversion of the borehole temperature logs would be difficult to be explained by known published models of past solar irradiation despite large range of assumed sensitivities for the couplings assumed, and that further forcing needs to be considered.

Majorowicz, Jacek; Šafanda, Jan; Przybylak, Rajmund

2014-06-01

302

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

303

Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations  

NASA Astrophysics Data System (ADS)

Mountain glaciers sample a combination of climate fields - temperature, precipitation and radiation - by accumulation and melting of ice. Flow dynamics acts as a transfer function that maps volume changes to a length response of the glacier terminus. Long histories of terminus positions have been assembled for several glaciers in the Alps. Here I analyze terminus position histories from an ensemble of seven glaciers in the Alps with a macroscopic model of glacier dynamics to derive a history of glacier equilibrium line altitude (ELA) for the time span 400-2010 C.E. The resulting climatic reconstruction depends only on records of glacier variations. The reconstructed ELA history is similar to recent reconstructions of Alpine summer temperature and Atlantic Multidecadal Oscillation (AMO) index, but bears little resemblance to reconstructed precipitation variations. Most reconstructed low-ELA periods coincide with large explosive volcano eruptions, hinting at a direct effect of volcanic radiative cooling on mass balance. The glacier advances during the LIA, and the retreat after 1860, can thus be mainly attributed to temperature and volcanic radiative cooling.

Lüthi, M. P.

2014-04-01

304

Molecular evidence of the survival of subterranean amphipods (Arthropoda) during Ice Age underneath glaciers in Iceland.  

PubMed

A Two endemic groundwater arthropod crustacean species, Crangonyx islandicus and Crymostygius thingvallensis, were recently discovered on the mid-Atlantic volcanic island of Iceland. The extent of morphological differences from closest relatives, endemism, along with the geographic isolation of Iceland and its complete coverage by glaciers 21,000 years ago, suggests that these two species have survived glaciation periods in sub-glacial refugia. Here we provide strong support for this hypothesis by an analysis of mitochondrial genetic variation within Crangonyx islandicus. Our results show that the species is divided into several distinct monophyletic groups that are found along the volcanic zone in Iceland, which have been separated by 0.5 to around 5 million years. The genetic divergence between groups reflects geographic distances between sampling sites, indicating that divergence occurred after the colonization of Iceland. The genetic patterns, as well as the dependency of genetic variation on distances from the tectonic plate boundary and altitude, points to recent expansion from several refugia within Iceland. This presents the first genetic evidence of multicellular organisms as complex as crustacean amphipods which have survived glaciations beneath an ice sheet. This survival may be explained by geothermal heat linked to volcanic activities, which may have maintained favourable habitats in fissures along the tectonic plate boundary in Iceland during glaciations. PMID:20465590

Kornobis, Etienne; Pálsson, Snaebjörn; Kristjánsson, Bjarni K; Svavarsson, Jörundur

2010-06-01

305

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. PMID:16894151

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

2006-01-01

306

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

2006-08-15

307

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

2010-11-01

308

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

309

Rock avalanches on a glacier and morainic complex in Haut Val Ferret (Mont Blanc Massif, Italy)  

NASA Astrophysics Data System (ADS)

Deposits in upper Val Ferret (Mont Blanc Massif, Italy) have been attributed to glacier advances and to a rock avalanche of 12 September AD 1717. We review evidence for the timing and mode of emplacement of the deposit, and present a new geomorphic interpretation and relative and absolute dating to show that the AD 1717 deposit is less extensive than previously thought. The landslide was deflected along one side of the valley floor, preserving older slope and morainic sediments along the other side. An earlier rock avalanche onto the Triolet Glacier occurred before AD 1000. The deposits of these landslides partly cover older moraine several kilometres downstream from the present glacier front, and have affected the glacier regimen and construction of its moraines. This study highlights the geomorphic impact of rock avalanches in glacierized high mountains.

Deline, Philip; Kirkbride, Martin P.

2009-01-01

310

Glacier changes since the Little Ice Age maximum in the western Qilian Shan, northwest China, and consequences of glacier runoff for water supply  

Microsoft Academic Search

Based on aerial photographs, topographical maps and the Landsat-5 image data, we have analyzed fluctuations of glaciers in the western Qilian Shan, northwest China, from the Little Ice Age (LIA) to 1990. The areas and volumes of glaciers in the whole considered region decreased 15% and 18%, respectively, from the LIA maximum to 1956.This trend of glacier shrinkage continued and

Liu Shiyin; Sun Wenxin; Shen Yongping; Li Gang

2003-01-01

311

The ages of pedestal craters on Mars: Evidence for a late-Amazonian extended period of episodic emplacement of decameters-thick mid-latitude ice deposits  

NASA Astrophysics Data System (ADS)

There is significant geomorphologic evidence for the past presence of longitudinally widespread, latitudinally zoned deposits composed of ice-rich material at the northern and southern mid latitudes on Mars (lobate debris aprons, lineated valley fill, concentric crater fill, pedestal craters, etc.). Among these features, pedestal craters (Pd) are impact craters interpreted to have produced a protective layer on top of decameters-thick ice deposits now missing in intercrater regions. The time during which these various deposits were present is still highly debated. To address this question we have analyzed the distribution and characteristics of pedestal craters; here, we use a population of 2287 pedestal craters (Pd) to derive a crater retention age for the entire population, obtaining a minimum timescale of formation of ~90 Myr. Given that the ice-rich deposit has not been continuously present for this duration, the timescale of formation is necessarily longer than ~100 Myr. We then compiled impact crater size-frequency distribution dates for 50 individual pedestal craters in both hemispheres to further assess the frequency distribution of individual ages. We calculated pedestal crater ages that ranged from ~1 Myr to ~3.6 Gyr, with a median of ~140 Myr. In addition, 70% of the pedestal ages are less than 250 Myr. During the 150 Myr period between 25 Ma and 175 Ma, we found at least one pedestal age every 15 Myr. This suggests that the ice-rich paleodeposit accumulated frequently during that time period. We then applied these results to the relationship between obliquity and latitudinal ice stability to suggest some constraints on the obliquity history of Mars over the past 200 Myr. Atmospheric general circulation models indicate that ice stability over long periods in the mid latitudes is favored by moderate mean obliquities in the ~35° range. Models of spin-axis/orbital parameter evolution predict that the average obliquity of Mars is ~38°. Our data represent specific observational evidence that ice-rich deposits accumulated frequently during the past 200 Myr, supporting the prediction that Mars was characterized by this obliquity range during an extensive part of that time period. Using these results as a foundation, the dating of other non-polar ice deposits will permit the specific obliquity history to be derived and lead to an assessment of volatile transport paths in the climate history of Mars.

Kadish, Seth J.; Head, James W.

2014-02-01

312

LAST ICE AGE MILLENNIAL SCALE CLIMATE CHANGES RECORDED IN HUON PENINSULA CORALS  

Microsoft Academic Search

Uranium series and radiocarbon ages were measured in corals from the uplifted coral terraces of Huon Penin- sula (HP), Papua New Guinea, to provide a calibration for the 14C time scale beyond 30 ka (kilo annum). Improved analytical procedures, and quantitative criteria for sample selection, helped discriminate diagenetically altered samples. The base-line of the calibration curve follows the trend of

Yusuke Yokoyama; Tezer M Esat; Kurt Lambeck; L Keith Fifield

2000-01-01

313

The Sea of Okhotsk: A Window on the Ice Age Ocean  

NASA Astrophysics Data System (ADS)

The modern Sea of Okhotsk and the high-latitude glacial ocean share similar radiolarian faunas suggesting they also share environmental similarities. This sea favors deep- (>200 m) over shallow-living species as evidenced by collections of sediment traps set at 258 and 1061 m in the central part of the Sea. Of the twelve dominant polycystine radiolarian species, four live above and eight below 258 m. The shallow-living species' productivity maxima coincide with spring and fall phytoplankton blooms while deep-living species' annual production, nearly twice that of the shallow-living species, is concentrated in fall. Previous workers have shown that summer plankton tows collect higher concentrations of polycystine Radiolaria below than above 200 m and that Radiolaria, fish and zooplankton have unusual concentration maxima between 200 and 500 m. The paucity of Radiolaria and other consumers above 200 m coincides with an upper (0-150 m) cold (-1.5°C to 1.5°C), low salinity layer while higher concentrations below 200 m occur within warmer saltier water. This unusual biological structure must produce a lower ratio of shallow (<200 m) to deep carbon remineralization than elsewhere in the world ocean. Deep-living radiolarian species, similar to those of the modern Sea of Okhotsk, dominate glacial high-latitude deep-sea sediments. If the hydrographic and biological structures that produced these glacial faunas were like those of the modern Sea of Okhotsk, then glacial high-latitude oceans would have differed from today's in at least two respects. Surface waters were less saline and more stable enhancing the spread of winter sea ice. This stability, combined with a deepening of nutrient regeneration would have reduced surface water nutrients contributing to a reduction of atmospheric carbon dioxide.

Hays, James D.; Morley, Joseph J.

2004-04-01

314

The Sea of Okhotsk: A Window on the Ice Age Ocean  

NASA Astrophysics Data System (ADS)

The modern Sea of Okhotsk and the high-latitude glacial ocean share similar radiolarian faunas suggesting they also share environmental similarities. This sea favors deep- (>200 m) over shallow-living species as evidenced by collections of sediment traps set at 258 and 1061 m in the central part of the Sea. Of the twelve dominant polycystine radiolarian species, four live above and eight below 258 m. The shallow-living species' productivity maxima coincide with spring and fall phytoplankton blooms while deep-living species' annual production, nearly twice that of the shallow-living species, is concentrated in fall. Previous workers have shown that summer plankton tows collect higher concentrations of polycystine Radiolaria below than above 200 m and that Radiolaria, fish and zooplankton have unusual concentration maxima between 200 and 500 m. The paucity of Radiolaria and other consumers above 200 m coincides with an upper (0-150 m) cold (-1.5°C to 1.5°C), low salinity layer while higher concentrations below 200 m occur within warmer saltier water. This unusual biological structure must produce a lower ratio of shallow (<200 m) to deep carbon remineralization than elsewhere in the world ocean. Deep-living radiolarian species, similar to those of the modern Sea of Okhotsk, dominate glacial high-latitude deep-sea sediments. If the hydrographic and biological structures that produced these glacial faunas were like those of the modern Sea of Okhotsk, then glacial high-latitude oceans would have differed from today's in at least two respects. Surface waters were less saline and more stable enhancing the spread of winter sea ice. This stability, combined with a deepening of nutrient regeneration, reduced surface water nutrients contributing to a reduction of atmospheric carbon dioxide.

Hays, James D.; Morley, Joseph J.

2003-12-01

315

Ice Sheet Deglaciation, Younger Dryas Readvance and Palaeoclimatic Implications in the Cairngorm Mountains, Scotland.  

NASA Astrophysics Data System (ADS)

The Cairngorm Mountains contain an outstanding assemblage of glacial landforms from both the deglaciation of the last British-Irish Ice Sheet and the Younger Dryas Readvance; these can provide a wealth of information about palaeoclimate and glacier-climate interaction. Previous interpretations have left doubt over the extent and style of the Younger Dryas readvance. In addition, although the ice sheet deglaciation of the northern margin of the Cairngorms is relatively well understood, the pattern and timing of deglaciation on the southern margin and particularly how local and external ice masses interacted is unclear. New geomorphological mapping from aerial images and fieldwork has been compiled in a GIS for a 600km² area of the Cairngorm Mountains. This systematic mapping covers all previously reconstructed Younger Dryas glaciers and the landform assemblages associated with ice sheet deglaciation. For the first time, Cairngorm-wide patterns of deglaciation have been mapped and comparisons between the northern and southern margins made. Interpretations suggest that during ice sheet deglaciation, outlet glaciers were fed by locally-sourced plateau ice caps. On both the northern and southern margin of the Cairngorms, large ice-dammed lakes formed between locally sourced ice and neighbouring ice masses. The presence of these lakes indicates that ice masses in the Cairngorms began to recede early in deglaciation, most likely as a result of precipitation starvation. Detailed mapping, combined with new surface exposure ages taken from areas of 'hummocky moraine' previously subject to differing interpretation, will assist in determining the extent of Younger Dryas glaciation. The new ages will also guide new modelling of snow delivery to the surface of Younger Dryas glaciers. Preliminary results suggest snow blow factors cannot account for the low ELAs of some previously reconstructed valley glaciers. As a result, either very strong precipitation gradients existed within the Cairngorms during the Younger Dryas or previously reconstructed glaciers did not occur simultaneously. The geomorphological evidence and palaeoclimatic inferences are important alongside a growing number of palaeoglaciological studies in acting as evaluation areas for current numerical models of ice sheet growth and decay.

Standell, Matthew; Graham, David; Hodgkins, Richard; Rodés, Ángel

2013-04-01

316

A first-order global model of Late Cenozoic climatic change: Orbital forcing as a pacemaker of the ice ages  

NASA Technical Reports Server (NTRS)

The development of a theory of the evolution of the climate of the earth over millions of years can be subdivided into three fundamental, nested, problems: (1) to establish by equilibrium climate models (e.g., general circulation models) the diagnostic relations, valid at any time, between the fast-response climate variables (i.e., the 'weather statistics') and both the prescribed external radiative forcing and the prescribed distribution of the slow response variables (e.g., the ice sheets and shelves, the deep ocean state, and the atmospheric CO2 concentration); (2) to construct, by an essentially inductive process, a model of the time-dependent evolution of the slow-response climatic variables over time scales longer than the damping times of these variables but shorter than the time scale of tectonic changes in the boundary conditions (e.g., altered geography and elevation of the continents, slow outgassing, and weathering) and ultra-slow astronomical changes such as in the solar radiative output; and (3) to determine the nature of these ultra-slow processes and their effects on the evolution of the equilibrium state of the climatic system about which the above time-dependent variations occur. All three problems are discussed in the context of the theory of the Quaternary climate, which will be incomplete unless it is embedded in a more general theory for the fuller Cenozoic that can accommodate the onset of the ice-age fluctuations. We construct a simple mathematical model for the Late Cenozoic climatic changes based on the hypothesis that forced and free variations of the concentration of atmospheric greenhouse gases (notably CO2), coupled with changes in the deep ocean state and ice mass, under the additional 'pacemaking' influence of earth-orbital forcing, are primary determinants of the climate state over this period. Our goal is to illustrate how a single model governing both very long term variations and higher frequency oscillatory variations in the Pleistocene can be formulated with relatively few adjustable parameters.

Saltzman, Barry

1992-01-01

317

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

318

Ice-cored drumlins at the surge-type glacier Brúarjökull, Iceland: a transitional-state landform  

NASA Astrophysics Data System (ADS)

This paper presents data on a glacial landform that, to our knowledge, has not previously been described in the literature: the ice-cored drumlin. The study area is the forefield of the surge-type glacier Brúarjökull at the northeastern margin of the Vatnajökull ice cap, East Iceland. Based on sedimentological field investigations and aerial photograph interpretation, a qualitative model for the formation of ice-cored drumlins is proposed. The drumlin core consists of stagnant glacier ice from a previous advance and bubbly ice formed by snowdrifts, which were incorporated during the most recent advance - the 1963-64 surge. This advance deposited a mantle of basal till and streamlined the ice-cored moraines. Till deformation and deposition on the drumlin ice-core is facilitated by a substratum of low-permeability ice-cored moraines.In the present climate, the ice-core is subject to melting and the drumlin landform will degrade. The ongoing melting of the core and re-sedimentation of the till cover cause the originally streamlined subglacial landform to develop into a patch of hummocky moraine surrounded by a basal till sheet. Thus, ice-cored drumlins are a transitional-state landform in the surging glacier landsystem at Brúarjökull rather than a final landform.

Schomacker, Anders; Krüger, Johannes; Kjær, Kurt H.

2006-01-01

319

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

320

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

321

Late Pleistocene earthquake-triggered moraine dam failure and outburst of Lake Zurich, Switzerland  

Microsoft Academic Search

Lakes impounded by moraines may be considered hazardous in glaciated areas throughout the world because dams can fail suddenly producing destructive floods with peak discharges far in excess of normal flows. Here we present a comprehensive case study in the Zurich, Switzerland, area that reveals several independent lines of evidences for the occurrence of a Late Pleistocene (~13,760 calibrated years

M. Strasser; C. Schindler; F. S. Anselmetti

2008-01-01

322

Late Pleistocene earthquake-triggered moraine dam failure and outburst of Lake Zurich, Switzerland  

Microsoft Academic Search

Lakes impounded by moraines may be considered hazardous in glaciated areas throughout the world because dams can fail suddenly producing destructive floods with peak discharges far in excess of normal flows. Here we present a comprehensive case study in the Zurich, Switzerland, area that reveals several independent lines of evidences for the occurrence of a Late Pleistocene (?13,760 calibrated years

M. Strasser; C. Schindler; F. S. Anselmetti

2008-01-01

323

Late Pleistocene earthquake-triggered moraine dam failure and outburst of Lake Zurich, Switzerland  

E-print Network

Late Pleistocene earthquake-triggered moraine dam failure and outburst of Lake Zurich, Switzerland hazardous in glaciated areas throughout the world because dams can fail suddenly producing destructive of $20,600 m3 sÃ?1 . We also discuss long-term causes and short-term trigger mechanisms of the dam failure

Gilli, Adrian

324

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. PMID:22666462

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

325

Steppe lion remains imported by Ice Age spotted hyenas into the Late Pleistocene Perick Caves hyena den in northern Germany  

NASA Astrophysics Data System (ADS)

Upper Pleistocene remains of the Ice Age steppe lion Panthera leo spelaea (Goldfuss, 1810) have been found in the Perick Caves, Sauerland Karst, NW Germany. Bones from many hyenas and their imported prey dating from the Lower to Middle Weichselian have also been recovered from the Perick Cave hyena den. These are commonly cracked or exhibit deep chew marks. The absence of lion cub bones, in contrast to hyena and cave bear cub remains in the Perick Caves, and other caves of northern Germany, excludes the possibility that P. leo spelaea used the cave for raising cubs. Only in the Wilhelms Cave was a single skeleton of a cub found in a hyena den. Evidence of the chewing, nibbling and cracking of lion bones and crania must have resulted from the importation and destruction of lion carcasses (4% of the prey fauna). Similar evidence was preserved at other hyena den caves and open air sites in Germany. The bone material from the Perick and other Central European caves points to antagonistic hyena and lion conflicts, similar to clashes of their modern African relatives.

Diedrich, Cajus G.

2009-05-01

326

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

327

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

328

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

329

Global Glacial Isostasy and the Surface of the Ice-Age Earth: The ICE-5G (VM2) Model and GRACE  

NASA Astrophysics Data System (ADS)

The 100 kyr quasiperiodic variation of continental ice cover, which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of Earth history, has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n-body effects in the Solar System on the geometry of Earth's orbit around the Sun. The impacts of the changing surface ice load upon both Earth's shape and gravitational field, as well as upon sea-level history, have come to be measurable using a variety of geological and geophysical techniques. These observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid Earth and on the detailed spatiotemporal characteristics of glaciation history. This review focuses upon the most recent advances that have been achieved in each of these areas, advances that have proven to be central to the construction of the refined model of the global process of glacial isostatic adjustment, denoted ICE-5G (VM2). A significant test of this new global model will be provided by the global measurement of the time dependence of the gravity field of the planet that will be delivered by the GRACE satellite system that is now in space.

Peltier, W. R.

2004-05-01

330

Simulations of Western North American Hydroclimate during the Little Ice Age and Medieval Climate Anomaly  

NASA Astrophysics Data System (ADS)

Despite the immense impact that large, modern North American droughts, such as those of the 1930s and 1950s, have had on economic, social, aquacultural, and agricultural systems, they are smaller in duration and magnitude than the multidecadal megadroughts that affected North America, in particular the western United States, during the Medieval Climate Anomaly (MCA, ~ 900-1300 AD) and the Little Age (LIA, ~1450-1850 AD). Although various proxy records have been used to reconstruct the timing of these MCA and LIA megadroughts in the western United States, there still exists great uncertainty in the magnitude and spatial coherence of such droughts in the Pacific Northwest region, especially on decadal to centennial timescales. This uncertainty motivates the following study to establish a causal link between the climate forcing that induced these megadroughts and the spatiotemporal response of regional North American hydroclimates to this forcing. This study seeks to establish a better understanding of the influence of tropical Pacific and North Atlantic SSTs on North American drought during the MCA and LIA. We force NCAR's Community Atmospheric Model version 5.1.1 (CAM 5) with prescribed proxy-reconstructed tropical Pacific and North Atlantic SST anomalies from the MCA and LIA, in order to investigate the influence that these SST anomalies had on the spatiotemporal patterns of drought in North America. To isolate the effects of individual ocean basin SSTs on the North American climate system, the model experiments use a variety of SST permutations in the tropical Pacific and North Atlantic basin as external forcing. In order to quantify the spatiotemporal response of the North American climate system to these SST forcing permutations, temperature and precipitation data derived from the MCA and LIA model experiments are compared to lake sediment isotope and tree ring-based hydroclimate reconstructions from the Pacific Northwest. The spatiotemporal temperature and precipitation patterns from the model experiments indicate that in the Pacific Northwest, the MCA and LIA were anomalously wet and dry periods, respectively, a finding that is largely supported by the lake sediment records. This pattern contrasts with the dry MCA/wet LIA pattern diagnosed in model experiments for the U.S Southwest and indicated by tree ring-based proxy data. Thus, the CAM 5 model experiments confirm the wet/dry dipole pattern suggested by proxy data for the western U.S. during the MCA and LIA and highlights the role that the natural variability of tropical Pacific and North Atlantic SSTs played in driving this spatiotemporal climate pattern and its related teleconnections.

Simon, S. M.; Mann, M. E.; Steinman, B. A.; Feng, S.; Zhang, Y.; Miller, S. K.

2013-12-01

331

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

332

Carbon dioxide effects of Antarctic stratification, North Atlantic Intermediate Water formation, and subantarctic nutrient drawdown during the last ice age: Diagnosis and synthesis in a geochemical box model  

Microsoft Academic Search

In a box model synthesis of Southern Ocean and North Atlantic mechanisms for lowering CO2 during ice ages, the CO2 changes are parsed into their component geochemical causes, including the soft-tissue pump, the carbonate pump, and whole ocean alkalinity. When the mechanisms are applied together, their interactions greatly modify the net CO2 change. Combining the Antarctic mechanisms (stratification, nutrient drawdown,

Mathis P. Hain; Daniel M. Sigman; Gerald H. Haug

2010-01-01

333

Marine Climate Archives across the Medieval Climate Anomaly-Little Ice Age Transition from Viking and Medieval Age Shells, Orkney, Scotland  

NASA Astrophysics Data System (ADS)

Proxy records reconstructing marine climatic conditions across the transition between the Medieval Climate Anomaly (MCA; ~900-1350 AD) and Little Ice Age (LIA; ~1350-1850) are strongly biased towards decadal to annual resolution and summer/growing seasons. Here we present new archives of seasonal variability in North Atlantic sea surface temperature (SST) from shells of the European limpet, Patella vulgata, which accumulated in Viking and medieval shell and fish middens at Quoygrew on Westray, Orkney. SST was reconstructed at submonthly resolution using oxygen isotope ratios preserved in shells from the 12th and mid 15th centuries (MCA and LIA, respectively). MCA shells recorded warmer summers and colder winters by ~2 degrees C relative to the late 20th Century (1961-1990). Therefore, seasonality was higher during the MCA relative to the late 20th century. Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~1°C. This conclusion is broadly true for the summer season, but not true for the winter season. Higher seasonality and cooler winters during early medieval times may result from a weakened North Atlantic Oscillation index. In contrast, the LIA shells have a more a variable inter-annual pattern. Some years record cooler summers and winters relative to the MCA shells and late 20th century, whereas other years record warmer summers and cooler winters similar to the MCA shells. Our findings provide a new test for the accuracy of seasonal amplitudes resulting from paleoclimate model experiments.

Surge, D. M.; Barrett, J. H.

2013-12-01

334

Simulating LGM retreat of the Uummannaq Ice Stream and Rinks Isbrae, Western Greenland using a 1-D ice-stream model constrained by a suite of marine and terrestrial data  

NASA Astrophysics Data System (ADS)

We aim to understand what controlled the retreat pattern of the Uummannaq Ice Stream (UIS) during the last deglaciation. Evidence for the pattern of retreat is found in both the marine and terrestrial realms, but because the evidence is temporally and spatially discontinuous, it is challenging to coherently reconstruct both grounding-line retreat and ice-surface thinning such that they are in agreement. Marine stratigraphic and geophysical evidence indicates that the ice stream was grounded close to the continental shelf edge at the Last Glacial Maximum, and retreated rapidly and nonlinearly after 14.8 ka. Cosmogenic nuclide exposure dating on Ubekendt Island at the convergence zone of multiple feeder ice streams show that the ice surface thinned progressively and that the island became ice-free by ca. 12.4 ka. The ice stream then collapsed over the next 1-1.6 kyrs and the ice stream separated into a series of distinct inland arms. In the northernmost Rinks system, there is a 'staircase' of evidence showing ice surface thinning over time, but it is unclear where the grounding line was located during this phase of thinning. Furthermore, it is currently unclear what controlled the nonlinear retreat pattern identified in the Uummannaq system. We develop a numerical model of ice-stream retreat using the marine geophysical data and measurements of sediment strength on the continental shelf to control the boundary conditions. The model has the capability to dynamically and robustly simulate grounding line-retreat behaviour over millennial timescales. We simulate the retreat of the UIS grounding line into the northernmost Rinks system in response to enhanced ocean warming, rising sea level and warming climate. We compare the simulated dynamic behaviour of the UIS against the geomorphological and cosmogenic exposure evidence for ice surface thinning onshore and against dated marine grounding line positions. Our model results enable us to match grounding-line positions in the marine trough to distinct onshore ice-surface heights, and therefore provide a 2-dimensional reconstruction of the geometry of the UIS as it retreated after the LGM. We find that the nonlinearity in retreat rate is conditioned by the locations of vertical and lateral constrictions in the Uummannaq/Rink trough which provide temporary pinning points for the grounding line. When the grounding line retreats rapidly between pinning points, the ice surface thins rapidly inland. When the grounding line is pinned, thinning of the ice surface becomes much slower in locations corresponding to the deposition of moraines. We suggest that the slowdowns in retreat identified in the marine domain are therefore reflected by the generation of moraines in the terrestrial domain. Finally, we generate hypotheses about the timing of marine grounding-line retreat based upon the published terrestrial cosmogenic exposure ages.

Jamieson, Stewart; Roberts, Dave; Rea, Brice; Lane, Timothy; Vieli, Andreas; Cofaigh, Colm Ó.

2014-05-01

335

Simulation of Little Ice Age Initiation on Baffin Island Using Coupled Model Intercomparison Project / Paleoclimate Modeling Intercomparison Project (CMIP5/PMIP3) Models  

NASA Astrophysics Data System (ADS)

Geological evidence collected from Northern Baffin Island suggests several abrupt cooling events during the descent into the Little Ice Age (LIA) in the late 13th century CE. Ice caps from this period did not start to melt until roughly a century ago, and as they did vegetation was uncovered from their margins and dated. During these abrupt cooling events, the snow line elevation descended by hundreds of meters in a matter of decades. During the height of the Little Ice Age (early to mid 1800's) the snow line was at least 600 m lower than it is today. Modeling efforts have suggested that the LIA could have been induced with four decadally paced volcanic eruptions causing an expanded sea ice state, but these results were sensitive to the conditions of the North Atlantic Ocean when the eruptions took place. Here, we investigate whether any of four CMIP5/PMIP3 Last Millennium simulations (Goddard Institute for Space Studies ModelE (GISS-E), Beijing Climate Center Climate System Model (BCC-CSM1.1), Max-Planck Institute Earth System Model (MPI-ESM), Community Climate Systems Model (CCSM4)) produced enough cooling and a sudden enough change in snow line elevation to match the observations from Baffin Island. We compare the amplitude of cooling, snow cover and sea ice expansion, and circulation patterns during the transition into the LIA between models. We focus on summer seasons directly after volcanic eruptions at the onset of the LIA, particularly the 1258 Unknown (Rinjani?) Eruption, since this is when the effect of a snow line elevation descent would be evident.

Berdahl, M.; Robock, A.

2012-12-01

336

Cryoconite and Ice-bubble Microbial Ecosystems in Antarctica  

NASA Technical Reports Server (NTRS)

During the Antarctica 2000 Expedition samples of rocks and ice bubbles entrained in ice were collected from the blue ice fields near the Moulton Escarpment of the Thiel Mountains (85S, 94W) and the Morris Moraine of the Patriot Hills (80S, 8 1 W) Ellsworth Mountains of Antarctica. Investigation of the microbiota of these cryoconite and ice bubble ecosystems are now being conducted to help refine chemical and morphological biomarkers of potential significance to Astrobiology. The Antarctica 2000 Expedition will be discussed and the preliminary results of the studies of the ice bubble and cryoconite microbial ecosystems discussed. Recent ESEM images of the Antarctic microbiota will be presented a the relevance of ice ecosystems to Astrobiology will be discussed.

Hoover, Richard B.; Rose, M. Franklin (Technical Monitor)

2000-01-01

337

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

338

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

339

Pacing the post-Last Glacial Maximum demise of the Animas Valley glacier and the San Juan Mountain ice cap, Colorado  

NASA Astrophysics Data System (ADS)

During the Last Glacial Maximum (LGM), a 5000 km2 ice cap covered the San Juan Mountains of southwest Colorado. The largest valley glacier draining this ice cap occupied the Animas Valley and flowed 91 km to the south. To characterize the post-LGM demise of the Animas Valley glacier, we employ cosmogenic 10Be to date the LGM terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples. The 10Be depth profile within the terrace sediments suggests abandonment at 19.4 ± 1.5 ka. As deglaciation began, the ponding of Glacial Lake Durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment. The age of the terrace therefore records the initiation of LGM retreat. Negligible 10Be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory. Glacial polish exposure ages monotonically decrease up-valley from 17.1 to 12.3 ka, with the single exception of a sample collected from a quartzite rib, yielding an average retreat rate of 15.4 m/yr. This trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history. Retreat of the Animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes. Deglaciation lasted for ˜7.2 k.y., and was complete by 12.3 ± 1.0 ka. The retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying.

Guido, Zackry S.; Ward, Dylan J.; Anderson, Robert S.

2007-08-01

340

Moraine Molded Plastics, Inc.: Industrial Energy Assessment Finds Opportunities to Save $24,000 in Annual Operating Costs  

SciTech Connect

Industrial Technologies Program's BestPractices case study based on a comprehensive plant assessment conducted at the Moraine Molded Plastics by ITP's Industrial Assessment Center in conjunction with The Society of the Plastics Industry, Inc.

Not Available

2005-09-01

341

Planning for long, wide conservation corridors on private lands in the Oak Ridges Moraine, Ontario, Canada.  

PubMed

We explored the role of conservation biology in the planning of a natural-heritage system that includes long, wide conservation corridors situated primarily on private lands, and established to connect natural core areas in the Oak Ridges Moraine of Ontario, Canada. We based our review on government documents, semi-structured interviews with participants involved in this land-use planning process, and our involvement with the issue from 1990 through 2002. Conservation biology had a major influence on the outcome of the land-use planning process for this moraine. The landform was identified as an area of value by the environmental movement within the context of a number of ongoing government studies that began in the late 1980s and early 1990s. Conservation biologists and planners in government, the environmental movement, and the private sector carried out work related to conservation biology, including inventories and the development and application of criteria for the delineation of core areas and conservation corridors. Once the political timing was favorable (2001-2002), decision makers linked the science of conservation biology to planning policies and law in Ontario. The Oak Ridges Moraine land-use planning process was precedent setting in Canada, and possibly internationally. To our knowledge this is the first time long, wide conservation corridors on private lands were regulated through land-use-planning legislation and led to restrictions on urban development and aggregate resource extraction. PMID:17531046

Whitelaw, Graham S; Eagles, Paul F J

2007-06-01

342

Marine geophysical evidence for Late Pleistocene ice sheet extent and recession off northwest Ireland  

NASA Astrophysics Data System (ADS)

Multibeam swath bathymetry data collected through the Irish National Seabed Survey provides direct evidence for extensive glaciation of the continental shelf off northwest Ireland. Streamlined subglacial bedforms on the inner shelf record former offshore-directed ice flow. The major glacial features, however, consist of well developed, nested arcuate moraines which mark the position of former ice sheet margins on the shelf. Distal to these moraines, on the outermost shelf, prominent zones of iceberg ploughmarks give way into a well developed system of gullies and canyons which incise the continental slope. The large-scale, nested, arcuate moraines record the episodic retreat, probably punctuated by minor readvances or oscillations, of a lobate grounded ice sheet across this sector of the continental shelf during deglaciation. Initial retreat from the outer shelf was associated with an episode of ice sheet break-up and calving as recorded by extensive zones of iceberg ploughmarks distal to the outermost moraine. It is conceivable that this initial phase of retreat could have been driven by rising sea level. The data indicate a major reorganisation of the Irish Ice Sheet on the northwest 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.

Cofaigh, Colm Ó.; Dunlop, Paul; Benetti, Sara

2012-06-01

343

What controls dead-ice melting under different climate conditions?  

NASA Astrophysics Data System (ADS)

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 precipitation, mean summer precipitation, and the sum of degree days > 0 deg. C. The highest correlation was found between backwasting rate and mean annual air temperature. However, the correlation between melt rates and climate parameters is low, stressing that processes and topography play a major role in governing the rates of backwasting. The rates of dead-ice melting from modern glacial environments should serve as input to de-icing models for ancient dead-ice areas in order to assess the mode and duration of deposition. A challenge for future explorations of dead-ice environments is to obtain long-term records of field-based monitoring of melt progression. Furthermore, many modern satellite-borne sensors have high potentials for recordings of multi-temporal Digital Elevation Models (DEMs) for detection and quantification of changes in dead-ice environments. However, time series of high-resolution aerial photographs remain essential for both visual inspection and high-resolution stereographic DEM production. Reference: Schomacker, A. 2008. What controls dead-ice melting under different climate conditions? Earth- Science Reviews, in press.

Schomacker, A.

2008-12-01

344

Persistence across Pleistocene ice ages in Mediterranean and extra-Mediterranean refugia: phylogeographic insights from the common wall lizard  

PubMed Central

Background Pleistocene climatic oscillations have played a major role in structuring present-day biodiversity. The southern Mediterranean peninsulas have long been recognized as major glacial refugia, from where Northern Europe was post-glacially colonized. However, recent studies have unravelled numerous additional refugia also in northern regions. We investigated the phylogeographic pattern of the widespread Western Palaearctic lizard Podarcis muralis, using a range-wide multilocus approach, to evaluate whether it is concordant with a recent expansion from southern glacial refugia or alternatively from a combination of Mediterranean and northern refugia. Results We analyzed DNA sequences of two mitochondrial (cytb and nd4) and three nuclear (acm4, mc1r, and pdc) gene fragments in individuals from 52 localities across the species range, using phylogenetic and phylogeographic methods. The complex phylogeographic pattern observed, with 23 reciprocally monophyletic allo- parapatric lineages having a Pleistocene divergence, suggests a scenario of long-term isolation in multiple ice-age refugia across the species distribution range. Multiple lineages were identified within the three Mediterranean peninsulas – Iberia, Italy and the Balkans - where the highest genetic diversity was observed. Such an unprecedented phylogeographic pattern - here called “refugia within all refugia” – compasses the classical scenario of multiple southern refugia. However, unlike the southern refugia model, various distinct lineages were also found in northern regions, suggesting that additional refugia in France, Northern Italy, Eastern Alps and Central Balkans allowed the long-term persistence of this species throughout Pleistocene glaciations. Conclusions The phylogeography of Podarcis muralis provides a paradigm of temperate species survival in Mediterranean and extra-Mediterranean glacial refugia. Such refugia acted as independent biogeographic compartments for the long-term persistence of this species, for the differentiation of its genetic lineages, and for the short-distance post-glacial re-colonization of neighbouring areas. This finding echoes previous findings from recent phylogeographic studies on species from temperate ecoregions, thus suggesting the need for a reappraisal of the role of northern refugia for glacial persistence and post-glacial assembly of Holarctic biota. PMID:23841475

2013-01-01

345

Spatial rainfall gradients in equatorial Africa during the Little Ice Age: ITCZ migration and tropical SST variability  

NASA Astrophysics Data System (ADS)

Climate proxy data and general circulation models indicate that tropical regions experience broad, zonal changes in precipitation driven by shifts in the mean position of the Intertropical Convergence Zone (ITCZ) during millennial-scale coolings and warmings in the North Atlantic. These ITCZ movements affected the climate of tropical Africa, where paleolimnological records from the northern and southern tropics indicate southerly (northerly) ITCZ displacement during high-latitude coolings (warmings). High-resolution paleosalinity data from Lake Edward, a rift lake situated on the equator in central Africa, indicate that equatorial Africa experienced drought during both high latitude coolings and warmings of the mid- to late Holocene, consistent with zonal displacement of the ITCZ away from the equator. New, sub-decadally resolved analyses of the Mg concentration in authigenic calcite in five cores from Lake Edward and stratigraphic analyses of sediment cores from western Ugandan crater lakes indicate that central equatorial Africa experienced strong droughts during the Little Ice Age (LIA, 1400-1750 AD), when the ITCZ was presumably displaced southward. However, records from easternmost equatorial Africa, particularly that of Lake Naivasha located on the equator ~1000 km east of Lake Edward, suggest a wet LIA. Drought in central equatorial Africa and humid conditions in easternmost equatorial Africa during the LIA are supported by multiple proxy records, suggesting an east-west dipole pattern in tropical African rainfall during the LIA. This pattern is not consistent with the climate anomalies that should arise from north/south displacement of the ITCZ. We suggest that this east/west dipole in tropical Africa is driven by changes in the position of the ITCZ together with a shift towards a more El Niño-like SST pattern in the tropical Pacific, an interpretation supported by continental records from South America, Asia, and Indonesia. This spatial pattern could arise as a result of solar forcing of tropical climate during the LIA, but solar forcing cannot explain all of the droughts observed in central Africa during the late Holocene.

Russell, J. M.; Johnson, T. C.

2006-12-01

346

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

347

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

348

VOL. 59, NO. 1 (MARCH 2006) P. 1420 Tree-Ring Dates for the Maximum Little Ice Age Advance of Kaskawulsh Glacier,  

E-print Network

white spruce trees, Picea glauca (Moench) Voss, that had been sheared, tilted, and killed by deposition glacier Kaskawulsh fournit la première datation de calendrier de l'avancée glaciaire dupetitâgeglaciaire,danslenord-estdesmontagnesSt.Elias,territoireduYukon.Lessériesdecernesd'épinettesblanches,Picea glauca (Moench) Voss, qui avaient été abattues, inclinées et tuées par le dépôt de till à la moraine

Ward, Brent C.

349

Radiocarbon Age Constraints on Rates of Advance and Retreat of the Puget Lobe of the Cordilleran Ice Sheet during the Last Glaciation  

NASA Astrophysics Data System (ADS)

Calibrated radiocarbon dates of organic matter below and above till of the last (Fraser) glaciation provide limiting ages that constrain the chronology and duration of the last advance-retreat cycle of the Puget Lobe in the central and southeastern Puget Lowland. Seven dates for wood near the top of a thick proglacial delta have a weighted mean age of 17,420 ± 90 cal yr B.P., which is the closest limiting age for arrival of the glacier near the latitude of Seattle. A time-distance curve constructed along a flowline extending south from southwestern British Columbia to the central Puget Lowland implies an average glacier advance rate of ca. 135 m/yr. The glacier terminus reached its southernmost limit ca. 16,950 yr ago and likely remained there for ca. 100 yr. In the vicinity of Seattle, where the glacier reached a maximum thickness of 1000 m, ice covered the landscape for ca. 1020 yr. Postglacial dates constraining the timing of ice retreat in the central lowland are as old as 16,420 cal yr B.P. and show that the terminus had retreated to the northern limit of the lowland within three to four centuries after the glacial maximum. The average rate of retreat was about twice the rate of advance and was enhanced by rapid calving recession along flowline sectors where the glacier front crossed deep proglacial lakes.

Porter, Stephen C.; Swanson, Terry W.

1998-11-01

350

Age and origin of ice-rich Yedoma silts at Duvanny Yar, northeast Siberia: a record of Beringian environmental change since the last interglacial  

NASA Astrophysics Data System (ADS)

Silty Yedoma deposits at the important Beringian site of Duvanny Yar (68o,37’ N; 159o08’ E) in northeast Siberia, have been interpreted before as both loess and nival deposits. The yedoma deposits form a stratigraphic unit more than 30 m thick that comprises sandy silts which are generally massive and rich in ground ice and organic material. The ground ice includes pore ice, segregated ice and wedge ice (both syngenetic and epigenetic), and much of it accumulated more or less coevally with deposition of the silt and upward growth of permafrost. Organic material includes pervasive rootlets of former steppe-tundra vegetation (e.g. grasses), vertebrate bones (e.g. mammoth, bison, horse), pollen, insect remains, and plant macrofossils. A number of cryoturbated organic horizons within the silts are interpreted as incipient palaeosols. The sedimentary properties of the silts (particle size and magnetic susceptibility) and the palaeocological characteristics of the contained organic material are both consistent with deposition of silts primarily as loess and loess-sand intergrades, sedimentologically similar to known aeolian deposits in northwest Europe (e.g. Pegwell Bay, UK). Deposition primarily by snow meltwater is unlikely because the nearest uplands where snow could have accumulated and hillslopes could have provided runoff sites are many kilometers distant. The remnants of the original landsurface—prior to thermokarst activity during the late-glacial and Holocene—indicate an essentially flat landscape during dust deposition. Radiocarbon dating of mainly in situ rootlets indicates a complete record of dust deposition during the Last Glacial Maximum (LGM), potentially one of the best terrestrial records of LGM palaeoenvironments. Older radiocarbon dates suggest at least two periods of soil formation between the LGM and about 40,000 radiocarbon years BP (within Marine Isotope Stage 3). Optical dating is currently being undertaken to constrain the ages of older dust deposits and palaeosols. U-series dating of wood contained within thaw-lake deposits at the base of the sequence provides an age from the Last Interglacial. Overall, dating of the yedoma sequence constrains interpretation of ancient soil DNA contained within the silts and provides a basis for reconstructing LGM palaeo-wind conditions associated with the Siberian high-pressure cell.

Murton, J.; Edwards, M. E.; Murton, D.; Bateman, M.; Haile, J.

2010-12-01

351

Sorting Out Mixed Messages from Till Provenance: Bulk Sediment Isotopic Compositions vs. U-Pb Detrital Zircon Ages from Antarctica  

NASA Astrophysics Data System (ADS)

Understanding how basal erosion by ice sheets takes place as a function of time and position is critical to models of sub-ice landscape evolution and to determining whether isotopic and chem