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1

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

Microsoft Academic Search

This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 “Little Ice Agemoraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then

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

2007-01-01

2

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

3

The effects of slope degradation on lichenometric dating of Little Ice Age moraines  

Microsoft Academic Search

Over the last four decades, lichenometry has been used globally to determine late Holocene moraine ages that are necessary for developing glacier-length chronologies. However, the influence of a variety of environmental factors that can affect the demographics of a lichen population in glacial landscapes led to the development of a variety of different methods of data collection and analysis. Although

Michael A. O’Neal

2006-01-01

4

'Little Ice Age' glacier variations in Jotunheimen, southern Norway: a study in regionallycontrolledlichenometricdatingof recessional moraines with implications for climate and lichen growth rates  

Microsoft Academic Search

A new approach to regional lichenometric dating is developed and applied to 'Little Ice Age' moraine-ridge sequences on 16 glacier forelands in Jotunheimen, southern Norway. Lichenometric-dating curves, based on the Rhizocarpon subgenus, are constructed independently for west, central and east Jotunheimen. Although there are differences between the subregions, a composite regional moraine chron- ology for Jotunheimen identifies 12 episodes of

John A. Matthews

5

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

USGS Publications Warehouse

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

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

2007-01-01

6

Analysis of plant colonization on an arctic moraine since the end of the Little Ice Age using remotely sensed data and a Bayesian approach  

Microsoft Academic Search

Young moraines less than 100 years old are considered as key areas for monitoring the effects of climate change since the end of the Little Ice Age. One way of documenting this change is by recognizing and characterizing the different plant colonization stages and trends that occur on these relatively new environments. Previous studies have shown that remotely sensed data

Myrtille Moreau; Dominique Laffly; Daniel Joly; Thierry Brossard

2005-01-01

7

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

8

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

9

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

10

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

11

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

NASA Astrophysics Data System (ADS)

Rock mass movements are dominant in the morphodynamics of high mountain rock slopes and are at the origin of significant risks for people who attend these areas and for infrastructures that are built on (mountain huts, cable cars, etc.). These risks are becoming greater because of permafrost degradation and glacier retreat, two consequences of the global warming. These two commonly associated factors may affect slope stability by changing mechanical properties of the interstitial ice and modifying the mechanical constraints in these rock slopes. Between 1977 and 1979, significant works were carried out on the Little Ice Age moraine of the Tortin glacier at the Col des Gentianes (2894 m), in the Mont Fort area (Verbier, Switzerland), for the construction of a cable car station and a restaurant. Since the early 1980s, the glacier drastically retreated and the moraine became unstable: its inner slope has retreated for several meters. Various observations and geoelectric measurements indicate that significant volume of massive ice mass is still present within the moraine (ice-cored moraine). Its melting could therefore increase the instability of the moraine. Since 2007, the moraine is surveyed by terrestrial laser scanning (TLS) in order to characterize its evolution: 8 campaigns were conducted between July 2007 and October 2011. The comparison of the high resolution 3D models so obtained allowed the detection and quantification of mass movements that have affected the moraine over this period, essentially by calculating difference maps (shortest oblique distances between two models). Between July 2007 and October 2011, 7 landslides were measured, involving volumes between 87 and 1138 m3. The most important of these occurred during the summers 2009 and 2011. TLS data also allowed identifying: (i) two main areas affected by slower but sometimes substantial movements (displacements of blocks on more than 2 m during a summer period); (ii) significant deposits of anthropogenic materials and their mechanical readjustments; and (iii) a loss of thickness of the glacier approaching 10 m at the foot of the moraine. Except for the morphological changes related to the landscaping of ski-runs, mass movements identified by TLS since 2007 are mainly resulting from glacier retreat and, to a lesser extent, to permafrost creep and degradation.

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

2012-04-01

12

How can blue-ice moraines constrain elevation changes of the West Antarctic Ice Sheet in the southern Ellsworth Mountains?  

NASA Astrophysics Data System (ADS)

Observational data in the Weddell Sea sector of the Antarctic Ice Sheet has 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 first 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 boulders and finer debris in the glacier ice and that they are related to ice structures and to basal debris emerging at the glacier surface, (b) exposure ages of surface debris reveals boulders both recently exposed and those pre-dating the Last Glacial Maximum (LGM), (c) during the LGM the ice was thicker and the limit is marked by a zone of perched boulders and, in topographic hollows, by buried glacier ice, (d) weathered high elevation deposits with exposure ages in excess of 400 ka have been overridden by glacier ice and thus may represent deposits of much greater age, (e) the relationship between blue-ice moraines and deposits from local wind-drift glaciers makes it possible to constrain the date and duration of Holocene thinning. A forthcoming field season in 2013-2014 to re-measure 90 stakes for horizontal movement and ablation should help quantify the rate of blue-ice moraine formation. We will also obtain rock cores to establish rates of weathering of the older deposits and thus constrain their age more tightly.

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

2013-12-01

13

Cosmogenic Dating of Moraines in the Central Transantarctic Mountains to Evaluate Past Behavior of the East Antarctic Ice Sheet  

NASA Astrophysics Data System (ADS)

One of the most prominent questions as global temperatures rise is how the world's large ice sheets will fare under a warmer climate. Our study aims to understand the past behavior of the East Antarctic Ice Sheet (EAIS) as it flowed through the central Transantarctic Mountains. In particular, we focus on the period prior to the Last Glacial Maximum (LGM). We are dating extensive ice-cored moraine sequences around the remote Mt. Howe and Mt. Achernar nunatack sites in connection with provenance study of moraine composition, specifically analyses of detrital zircon geochronology and pebble lithology. Mt. Howe and Mt. Achernar are located near the heads of the Scott and Law Glaciers, respectively. The dated moraines tell us about changes in the former height of the ice surface. We measured 10Be-26Al in quartz-bearing boulders and 3He in pyroxene-bearing boulders. At both sites, the oldest and youngest ages are ~500,000 and < 10,000 years, consistent with relative surface weathering, till thickness, and position of the landforms relative to the active ice margin. In more detail, existing data suggest the innermost moraine ridges formed since the LGM, but the majority of the moraine sequences were deposited well before. Most of the moraine complex at Mt. Howe appears to have formed over the last glacial cycle, whereas at Mt. Achernar the ages for most of the crests span the last two glacial cycles. The chronologic evidence points to relative stability of the EAIS at both interior ice sheet sites, possibly for the past hundred thousand years or more. This finding is consistent with provenance data from the same moraines. Additional 3He dating is underway on the dominant dolerite erratics, which will result in a more comprehensive set of data.

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

2012-12-01

14

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

15

Paraglacial adjustment of Little Ice Ace moraine slopes at the Gepatschferner glacier, Ötztal Alps, Austria  

NASA Astrophysics Data System (ADS)

In days of rapid glacier retreat, the morphodynamics of freshly exposed terrain have attained quite some interest. The availability of sediment for various geomorphic processes has been increasing since the end of the "Little Ice Age" (LIA) and will continue to do so. This is the case especially for large lateral moraines as they are frequently high and steep, and loose consolidation after the melting of glacier and underground ice. The adjustment to non-glacial conditions by the reworking of the glacigenic sediments through slope wash, fluvial and gravitational processes can be analysed within the theoretical framework of paraglacial geomorphology. Curry, Cleasby & Zukowskyj (2006) showed that lateral moraine morphology and process rates change over time since deglaciation and calibrated exhaustion curves of sediment availability to their study areas using a total station for data acquisition. Our approach was to use digital elevation models generated from high resolution airborne LiDAR data (> 10 pts/sqm) for a detailed morphometric analysis. Several test subsections of a chronosequence of deglaciation on the true-right LIA lateral moraine slope of the Gepatschferner glacier were defined and very high resolution DEMs of the subsections were generated from the LiDAR point cloud. Sediment budgets for each time interval and lateral moraine subsection were estimated from a reconstruction of the pre-incision moraine surface. Different glacial stages digitized from historical maps and multi-temporal orthophotos data were used to estimate the respective time passed since deglaciation. This space-for-time substitution approach makes it possible to estimate section specific erosion rates, to calibrate a sediment exhaustion curve for the Gepatschferner lateral moraine and to monitor the development of morphometric parameters (lateral slope angle, paraglacial gullying index, profiles, etc.) of the gullies dissecting the lateral moraines over time / distance from the glacier snout. The work presented here is part of the joint project PROSA (High-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) which deals with the generation of the sediment budget for an alpine catchment in the Austrian Alps.

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

2013-04-01

16

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

17

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

SciTech Connect

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

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

1991-03-01

18

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

PubMed

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

Hallet, B; Putkonen, J

1994-08-12

19

LITTLE ICE AGE HISTORY OF TZEETSAYTSUL GLACIER, TWEEDSMUIR PROVINCIAL PARK, BRITISH COLUMBIA  

Microsoft Academic Search

This paper describes licheno- metric and dendroglaciological investigations of Little Ice Age (LIA) deposits at Tzeetsaytsul Glacier, Tweedsmuir Provincial Park, British Columbia. The glacier originates from an ice- field on the northeast flank of Tzeetsaytsul Peak and terminates in a moraine-dammed lake. A stream draining the lake has incised the moraine dam and flows through nested moraines into a second

J. SMITH; Joseph R. DESLOGES; D. J. SMITH

20

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

21

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

22

Submerged Tioga and Tahoe age Moraines at Meeks Bay, Lake Tahoe, Calif. Implications to Late Pleistocene Lake Levels  

NASA Astrophysics Data System (ADS)

At Meeks Bay, a well-preserved right-lateral morainal complex is constructed of till from the Tioga (>20.4 +/- 0.7 ka B.P.) and Tahoe (>62.0 +/- 1.3 ka B.P.; Howle et al., 2005) glacial advances. High-resolution digital bathymetry merged with the terrestrial DEM reveals that the onshore Tioga and Tahoe moraines extend offshore below the modern lake level of 1,899m. Longitudinal profiles show that the sub-aerial moraine crests grade evenly with the submerged crests and that the slopes of the sub-aqueous crests match the profile of the adjacent submarine canyon. In the digital bathymetry, the Tioga and Tahoe moraines are recognizable to 1,844 and 1,768m respectively. In May of 2004 and 2005 the moraines were imaged with the remotely operated submersible Triton deployed from the UC Davis research vessel, John LeConte. The Tioga moraine goes down to 1,817m, and rests upon Pliocene (?) lacustrine sediments. Above 1,817m the moraine is comprised of unsorted gravel, cobbles, and angular granitic boulders up to 3m across, typical of the Tioga age till on land. The moraine crest is continuous from 1,817m up to the shoreline promontory where the Tioga till on land enters the lake. Between 1,868m and 1,838m, the submerged Tahoe moraine contains well-rounded granitic boulders up to 2m across. The degree of rounding is consistent with the Tahoe boulders on land. The lowest occurrence of the Tahoe moraine was not imaged, but the glacial origin of the crest was confirmed. The submerged Tioga and Tahoe lateral moraines place upper limiting constraints on lake elevation, because lateral moraines do not form in water deeper than the ice thickness. Instead, when the relatively thin terminal ice cliff of an ablating alpine glacier interacts with water the glacier either melts, disintegrates by calving, or detaches along crevasses and floats when submerged to about 0.9 of the ice thickness. Reconstructions of ice thickness at the lower limits of the Tioga and Tahoe moraines here yield estimates of the maximum lake elevations at the glacial maxima. During the Tioga and Tahoe glacial maxima (>20 and >62 ka B.P., respectively) the lake elevation was <1,810m and <1,765m. These data indicate that in the Tahoe basin, late Pleistocene lake low-stands occurred during the glacial maxima. Asynchrony between glacial and lacustrine maxima has also been documented at Pleistocene lakes Russell and Lahonton (Lajoie and Robinson, 1982). Evidence at Meeks Bay for a post-Tahoe and pre-Tioga high-stand between 1,914 and 1,920m is provided by a gently sloping bench cut into the Tahoe moraine. This correlates well with reports of a Tahoe age high-stand at 1,926m. Birkeland (1963) proposed a Tahoe age ice dam at that may have raised lake levels to about 1950m. However, there is no evidence of this at 1950m in the Tahoe moraine at Meeks Bay, and therefore any such high-stand must have predated the Tahoe maximum. Available data suggests that large fluctuations in lake elevation have occurred from a mid Pleistocene (?) high-stand of about 2073m (Birkeland, 1963) to <1,765m at the Tahoe glacial maximum, up to about 1,920m after the Tahoe advance, down to <1,810m at the Tioga glacial maximum, and finally up to elevations between 1876 and 1899m during the Holocene (Schweickert et al., 2000). We thank the IEEE Oceanic Engineering Society for partial funding and commend the engineering students of Santa Clara University for designing, building, and deploying the Triton. Special thanks to Bob Richards and Brant Allen, captains of the LeConte.

Howle, J. F.; Schweickert, R. A.; Finkel, R. C.; Kitts, C. A.; Ota, J.

2005-12-01

23

Ribbed moraine formation  

NASA Astrophysics Data System (ADS)

Ribbed (Rogen) moraines are conspicuous landforms found in interior parts of formerly glaciated areas. Two major theories for ribbed moraine formation have been suggested in recent years: (i) the shear and stack theory, which explains ribbed moraine formation by shearing and stacking of till slabs or englacially entrained material during compressive flow, followed by basal melt-out of transverse moraine ridges, and (ii) the fracturing theory, according to which ribbed moraines form by fracturing of frozen pre-existing till sheets, at the transition from cold- to warm-based conditions under deglaciating ice sheets. In this paper, we present new data on the distribution of ribbed moraines and their close association with areas of frozen-bed conditions under ice sheets. In addition, we show examples of ribbed moraine ridges that fit together like a jig-saw puzzle. These observations indicate that fracturing and extension of a pre-existing till sheet may be a predominant process in ribbed moraine formation. In summary, we conclude that all described characteristics of ribbed moraines are compatible with the fracturing theory, while the shear and stack theory is hampered by an inability to explain many conspicuous features in the distribution pattern and detailed morphology of ribbed moraines. One implication of the fracturing theory is that the distribution of ribbed moraines can be used to reconstruct the extent of areas that underwent a change from frozen-bed to thawed-bed conditions under former ice sheets.

Hättestrand, Clas; Kleman, Johan

24

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.

25

Resedimentation of debris on an ice-cored lateral moraine in the high-Arctic (Kongsvegen, Svalbard)  

NASA Astrophysics Data System (ADS)

In ice-cored landform assemblages, the process of resedimentation via sediment-flow is important in determining the morphology and sedimentary facies distribution after the ice core has melted. This paper documents the sediment-flow processes associated with the resedimentation of an ice-cored lateral moraine at Kongsvegen, Svalbard. Decay of the ice-cored lateral moraine is dominated by the development of a sediment-flow fan, which has an 'hour-glass' form in plan. The fan comprises a broad source area on the crest of the lateral moraine separated from the fan surface, composed of tessellated flow lobes, by a narrow ice-floored channel system. The principle sedimentary facies associated with this fan include matrix-supported diamictons, laminated silts and fine sands. The evolution of this fan and the likely end-products after complete deglaciation are discussed, and this paper contributes modern analogue data relevant to the interpretation of the Pleistocene landform and sediment record.

Bennett, Matthew R.; Huddart, David; Glasser, Neil F.; Hambrey, Michael J.

2000-10-01

26

A chronology of the Little Ice Age in the tropical Andes of Bolivia (16°S) and its implications for climate reconstruction  

Microsoft Academic Search

Dating moraines by lichenometry enabled us to reconstruct glacier recession in the Bolivian Andes since the Little Ice Age maximum. On the 15 proglacial margins studied, we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries. Moraines were dated by performing statistical analysis of lichen measurements based on the extreme

Antoine Rabatel; Bernard Francou; Vincent Jomelli; Philippe Naveau; Delphine Grancher

2008-01-01

27

Paleo Slide Set: The Ice Ages  

NSDL National Science Digital Library

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

28

10Be chronology of the Drygalski Moraines, central western Greenland  

NASA Astrophysics Data System (ADS)

Ice sheet margin fluctuations throughout the Holocene are increasingly well documented in Greenland, but fundamental gaps still exist. The Drygalski Moraines on the Nuussuaq Peninsula, central western Greenland, represent one of the few locations on Greenland where potential early Neoglacial (~2-5 ka) moraines have been identified. We used cosmogenic 10Be exposure dating of moraine boulders to test the hypothesis that the Drygalski Moraines are early Neoglacial in age, as was previously estimated using cross-cutting relationships with relative sea level. Alternative hypotheses are that the Drygalski Moraines represent the northern extent of the Ørkendalen Moraine (6.8 × 0.3 ka) or the Fjord Stade Moraines (~9.3 and ~8.2 ka). Results from 10Be dating of perched erratics outboard of the Drygalski Moraines suggest that deglaciation of the area occurred between ~10.4 × 0.3 ka and 9.5 × 0.3 ka. We dated three different crests of the Drygalski Moraine complex, which have mean ages of 8.6 × 0.4 ka (n=2), 8.5 × 0.2 ka (n=3), and 7.6 × 0.1 ka (n=2) from outer to inner. Perched erratics between the younger two moraines average 7.8×0.1 ka (n=2) and are consistent with the nearby moraine ages. These results allow us to reject the early Neoglacial and Ørkendalen hypotheses and generally support the Fjord Stade Moraine hypothesis because the Drygalski and Fjord Stade moraines are both early Holocene in age. However, we propose that the Drygalski and Fjord Stade moraines represent a different ice sheet response to early Holocene climate history. This may be attributed to the fast-flowing, marine-terminating nature of Jakobshavn Isbræ (the outlet glacier that deposited the Fjord Stade Moraines) in contrast with the land-based and slower-flowing lobe that deposited the Drygalski Moraines. Evidence suggests that Jakobshavn Isbræ is extremely sensitive to changes in climate, even on the centennial to decadal scale. As a result, Jakobshavn Isbræ may create discrete moraines in response to short-lived climate events (i.e. the 9.3 and 8.2 ka climate events). In contrast, the Drygalski Moraines may archive the centennial- to millennial-scale climate variability during the early Holocene and do not seem to be associated with specific early Holocene climate events.

Cronauer, S. L.; Briner, J. P.; Kelley, S. E.; Zimmerman, S. R.

2013-12-01

29

Limnology of the Klutlan moraines, Yukon Territory, Canada*1  

NASA Astrophysics Data System (ADS)

Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600-1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an "ultraoligotrophic" category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceran Daphnia pulex. Surface-sediment samples contained a total of 16 species of chydorid Cladocera. Of these, Alonella excisa and Alona barbulata are apparently the pioneer species in the youngest lakes. Chydorus sphaericus only appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age.

Whiteside, M. C.; Bradbury, J. Platt; Tarapchak, S. J.

1980-07-01

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 formation of sawtooth moraine ridges in Bødalen, western Norway  

NASA Astrophysics Data System (ADS)

The forefield of the Bødalsbreen glacier, western Norway, exhibits a prominent set of end moraines. The outermost one, deposited at the Little Ice Age (LIA) maximum (A.D. ˜ 1755), is smooth, continuous and arcuate, thus reflecting an even ice front. In contrast, subsequently formed moraines (deposited A.D. ˜ 1767-1930) show a striking "sawtooth" morphology. In an attempt to elucidate the formation processes responsible for this complex landform assemblage, we have employed several methods of investigation including geomorphological mapping, sedimentological studies, and ground penetrating radar (GPR). In general, the detailed formation processes of all moraines include bulldozing and thrusting. Furthermore, the sediment composition and structure are similar for all the moraines containing recycled diamicton. The remaining major factor influencing the moraine morphology thus seems to be the shape of the glacier front. Due to the distinctive geometry of the Bødalen valley, the former glacier underwent strong changes of its transverse stress field. In the part where the valley was wider, splaying/radial crevasses developed. Further downvalley, where the valley again narrowed, these crevasses were closed. As previous studies have concluded, the change in valley morphology to a large extent explains the distinct morphology of the Bødalen valley moraines. This notion is further corroborated by studying sawtooth or sawtooth-like moraines elsewhere where valley geometry also seems to have been a major contributing factor for moraine morphology.

Burki, Valentin; Larsen, Eiliv; Fredin, Ola; Margreth, Aninna

2009-04-01

32

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

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

Cosmogenic 10Be dating of the Salpausselkä I Moraine in southwestern Finland  

NASA Astrophysics Data System (ADS)

We determined in situ cosmogenic 10Be ages for nine boulders sampled on the Salpausselkä I (Ss I) Moraine. Previous dating of this moraine indicated that it formed during the Younger Dryas Stadial along the southern margin of the Scandinavian Ice Sheet in southern Finland. Our new exposure ages range from 10.9±1.0 to 13.5±1.2 10Be ka, with an error-weighted mean age of 12.4±0.7 10Be ka. Our results confirm four previous 10Be ages obtained 40 km northeast of our sample location. The combined data (n=13) indicate that retreat from the Ss I Moraine occurred at 12.5±0.7 10Be ka, in excellent agreement with an age of 12.1 ka for retreat from the Ss I Moraine based on varve chronologies. These results identify the Ss I Moraine as among the best-dated margins associated with Late Quaternary ice sheets.

Rinterknecht, Vincent R.; Clark, Peter U.; Raisbeck, Grant M.; Yiou, Françoise; Brook, Edward J.; Tschudi, Silvio; Lunkka, Juha P.

2004-12-01

35

Ice age terminations.  

PubMed

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

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

2009-10-01

36

The Great Ice Age  

USGS Publications Warehouse

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

Ray, Louis L.

1992-01-01

37

Ancient Ice Ages  

Microsoft Academic Search

MESSRS. BLANFORD, in their letter (NATURE, p. 101) called forth by Dr. Wallace's notice of a palæozoic glacial conglomerate in Victoria, Australia, say:-``It has become an accepted article of faith amongst most European geologists that no ice-age occurred before the last glacial epoch.'' There is no doubt that the tendency of opinion has been in that direction, notwithstanding the evidences

T. Mellard Reade

1892-01-01

38

Ice Age Impetus  

NSDL National Science Digital Library

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

39

Simulating the climatic response of Hardangerjøkulen ice cap since the Little Ice Age with ISSM  

NASA Astrophysics Data System (ADS)

Glaciers and small ice caps respond considerably faster to climate change than the large ice sheets Greenland and Antarctica. We use the Ice Sheet System Model (ISSM) to model the dynamics and evolution of the maritime-continental Hardangerjøkulen ice cap (73 km^2, 60.55°N, 7.43°E) from the Little Ice Age (LIA) until today. ISSM is a finite element model with anisotropic mesh capabilities (resolution can be refined in regions of interest) and includes different approximations for the dynamics of ice flow, including the Shallow Ice Approximation (SIA) and Full-Stokes. The SIA neglects important stresses when topography is complex; however it has proved accurate in representing glacier volume fluctuations on decadal and longer timescales. As Hardangerjøkulen has relatively gentle slopes and lacks areas of very fast flow, we choose to use the SIA to study this ice cap on climatic time scales. As initial forcing for the ice flow model, we use a dynamically calibrated mass balance history corresponding to moraine evidence from the Little Ice Age maximum in 1750 AD, as well as later outlet glacier front positions from moraines, direct measurements and aerial photographs. For the 1900s, we use surface mass balance from a spatially distributed energy-balance model using data from meteorological stations as forcing. Glaciological mass balance records and front positions for the two main outlet glaciers, along with surface DEMs, are used for calibration. We investigate total ice volume and outlet glacier responses since the LIA. The sensitivity to surface mass balance as well as the applicability of the SIA to small ice caps is also discussed. Finally, our findings are compared and contrasted with previous model results for Hardangerjøkulen.

Åkesson, Henning; Nisancioglu, Kerim H.; Giesen, Rianne H.; Morlighem, Mathieu

2014-05-01

40

Ice Age Floods Institute  

NSDL National Science Digital Library

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

41

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

Microsoft Academic Search

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

Kristine J. Crossen

2007-01-01

42

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

43

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

44

Moraine Sediments  

NSDL National Science Digital Library

In this assignment students look at the provenance of glacial sediments and the size and shape of clasts to investigate the sources of moraine material and what happens as glaciers transport sediment. Students visit the field site to see sediment in place, collect a sample to sort in the lab, and compile and review a geologic map in ArcGIS.

Tranel, Lisa

45

The morphology, structural evolution and significance of push moraines  

Microsoft Academic Search

Push moraines (glaciotectonic ice-marginal moraines) have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing Pleistocene ice sheets, providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland. To the wider earth science community, push moraines are of interest as analogues for thin-skin tectonics within orogenic belts. This paper reviews

Matthew R. Bennett

2001-01-01

46

Genesis of De Geer moraines in Finland  

NASA Astrophysics Data System (ADS)

The proposed model of the genesis of De Geer moraines in Finland is based mainly on the distribution of the moraine areas in relation to the palaeohydrological environment, and on the composition and two- and three-dimensional fabrics of the material. In order to shed some light on the geochronological problem involved, the distances between successive ridges in a number of De Geer moraine series are also compared with clay varve data on deglaciation rates in Finland. Granulometrically, petrographically and morphometrically, De Geer moraine till does not differ significantly from tills of surrounding areas. Two-dimensional fabrics stress orientations at right angles to the ridge crest, and three-dimensional analyses reveal the slope-conformable character of pebble inclinations. Generally, spacings of the De Geer moraine ridges do not confirm annual deglaciation rates as conveyed by clay varve data. It is suggested the moraines were formed in basal crevasses of the ice, following active flow phases of a local surging nature. During the quiescent phase of the surge cycle, the ice subsided into a water-soaked till mattress, filling up basal cavities from the proximal or the distal side. Finnish De Geer moraines are thus neither annual nor end moraines. They are subglacial bedforms with no geochronological meaning, except that they formed during one single surge cycle. As the marginal zone of the ice sheet calved and thinned, it was lifted by proglacial water and the whole group of moraines became free of ice almost simultaneously.

Zilliacus, Harry

1989-05-01

47

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

48

Ribbed moraine formation  

Microsoft Academic Search

Ribbed (Rogen) moraines are conspicuous landforms found in interior parts of formerly glaciated areas. Two major theories for ribbed moraine formation have been suggested in recent years: (i) the shear and stack theory, which explains ribbed moraine formation by shearing and stacking of till slabs or englacially entrained material during compressive flow, followed by basal melt-out of transverse moraine ridges,

Clas Hättestrand; Johan Kleman

1999-01-01

49

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

50

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

51

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

52

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

53

Paleotopography of glacial-age ice sheets  

SciTech Connect

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

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

1995-01-27

54

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

Microsoft Academic Search

Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric

J. H. Kennedy; E. C. Pettit

2009-01-01

55

Mantle viscosity and ice-age ice sheet topography  

Microsoft Academic Search

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

W. R. Peltier

1996-01-01

56

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

57

Components of the ice age circulation  

NASA Technical Reports Server (NTRS)

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

Rind, D.

1987-01-01

58

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

59

Modeling the ice-age climate  

Microsoft Academic Search

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

W. Lawrence Gates

1976-01-01

60

The ‘Little Ice Age’ – only temperature?  

Microsoft Academic Search

Understanding the climate of the last few centuries, including the ‘Little Ice Age’, may help us better understand modern-day natural climate variability and make climate predictions. The conventional view of the climate development during the last millennium has been that it followed the simple sequence of a ‘Mediaeval Warm Period’, a cool ‘Little Ice Age’ followed by warming in the

Atle Nesje; Svein Olaf Dahl

2003-01-01

61

Ribbed moraines in Sweden — distribution pattern and palaeoglaciological implications  

Microsoft Academic Search

A detailed map of ribbed moraines in central and northern Sweden is presented. They are frequent features over much of the mapped area, and the distribution has well defined limits. The most abundant ribbed moraines are situated in close connection to areas that are inferred to have been cold-based during the retreat of the Late Weichselian Ice Sheet, while outer,

Clas Hättestrand

1997-01-01

62

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

63

Hummocky moraines of piedmont glaciers from Geyikda?, Central Tauride Mountains, Turkey; insights from cosmogenic 36Cl dating  

NASA Astrophysics Data System (ADS)

For the first time we report the presence of Late Quaternary piedmont glaciers represented by the largest hummocky moraine field in Turkey. The piedmont glaciers developed in the Central Taurides, 50 km north of the Mediterranean Sea. They were located on the north-facing hill-slopes of the Namaras Valley situated around 2000-2050 m above sea-level (a.s.l) in Geyikda?. The hummocky moraines resulted from in situ deposition of stagnant glacier ice (or dead-ice) where debris cover was heterogeneously distributed on the glacier surface. Twenty-six boulders from hummocky, lateral and terminal moraines from the Namaras Valley and the tributary Susam Valley were dated by cosmogenic 36Cl surface exposure dating. The moraine ages indicate three phases of glacial advances during the Late Quaternary. The oldest glacial advance occurred in the Namaras Valley at the end of the Last Glacial Maximum (18.0±0.4 ka, ka: thousands years ago) and is recorded entirely by the sequence of hummocky moraines in the mountain. Glaciers retreated towards the Susam Valley (2100-2200 m a.s.l.) and became stagnant during the Late Glacial (14.3±1.3 ka) as observed from hummocky and terminal moraines at the interior and outlet of the valley. Glaciers re-advanced at around 11.5±1.0 ka ago (Younger Dryas) which is represented by several lateral moraines that are at least 50 m higher than the surrounding hummocky moraines in both valleys. Comparable glacial chronologies were obtained from other Turkish mountains and from other Mediterranean mountains.

Ciner, Attila; Akif Sar?kaya, Mehmet; Y?ld?r?m, Cengiz

2014-05-01

64

Dynamics of ice ages on Mars.  

PubMed

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

Schorghofer, Norbert

2007-09-13

65

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

NASA Astrophysics Data System (ADS)

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

Brynjólfsson, Skafti; Schomacker, Anders; Ingólfsson, Ólafur

2014-05-01

66

The Little Ice Age and Solar Activity  

Microsoft Academic Search

We analyze the ice winter severity index on the Baltic region since 1501-1995. We found that the variability of this index is modulated among other factors by the secular solar activity. The little ice ages that have appeared in the North Hemisphere occurred during periods of low solar activity. Seemingly our star is experiencing a new quiet stage compared with

Victor Manuel Velasco Herrera; C. M. Carmen Leal Silva; Graciela Velasco Herrera

2010-01-01

67

Components of the ice age circulation  

NASA Astrophysics Data System (ADS)

Four general climate model (GCM) simulations are compared to investigate the influence of ice age boundary conditions on atmospheric dynamics and regional climate patterns. Starting with a simulation of the current climate, the ice age distributions of (1) sea surface temperatures; (2) 10-m-thick land ice in locations of ice age ice sheets; and (3) ice sheets elevated to their proper altitude were added sequentially. The results show that these different boundary conditions often impart conflicting influences, with the full ice age simulation representing a compromise between different tendencies inherent in the different boundary components. In particular, the ice age sea surface temperatures stablize the atmosphere over the oceans, increase the frequency of storms tracking through central North America, and amplify transient eddy energy without increasing baroclinic generation. Low-elevation ice generates low pressure over eastern North America and southern Europe in winter, while increasing cloud cover and cooling the land in summer. Elevation of the ice sheets cools the land in winter, further intensifies storms off northeastern North America, induces subsidence warming downstream of the European ice sheets in summer, and increases both transient and stationary eddy energy through increased baroclinicity. In all of the experiments the atmosphere is transporting a similar amount of energy poleward, consistent with the similarity in sea surface temperature gradients, but the eddy characteristics employed in the process vary with the longitudinal distribution of the boundary conditions. Other results show that the Broad raised ice sheets have both a topographic and a thermal effect (due to the reduced optical thickness above) which occur simultaneously and lead to a greater stationary eddy forcing of the zonal mean flow. The stationary wave change in the northern hemisphere is accompanied by a similar change in the southern hemisphere, implying a dynamical interhemispheric connection. The Walker circulation and the July Hadley circulation weaken as a result of the altered sea surface temperature patterns, but the poleward extent of the Hadley cell and the zonally averaged jet stream show little difference from current climate values. The results are compared with two-dimensional model expectations, paleoclimate evidence, and previous ice age simulations.

Rind, D.

1987-04-01

68

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

NASA Astrophysics Data System (ADS)

Between 1977 and 1979, important civil engineering works were made on the moraine of "Col des Gentianes", which is situated 2894 meters above the sea level in the region of Mt-Fort, Valais, Switzerland. Two cableway station arrivals, a departure station to the Mt-Fort and a restaurant were built on. This moraine was formed during the last advance of the Tortin glacier during the Little Ice Age. Since 1980, the glacier has melted dramatically and the moraine is creeping. The moraine in front of the cableway departure station to the Mt-Fort sagged by 2 to 4 meters in 30 years. A large volume of ice is still present within the moraine and melting of the ice would make its stability even more precarious. Since 2007 the moraine is monitored by terrestrial laser scanning (TLS). Two TLS campaigns were made in July and October 2008 and compared to datasets acquired in 2007. The comparison of sequential TLS point clouds enabled the detection and quantification of movements in the moraine: (1) by computing oblique (shortest) or vertical differences, (2) by creating displacement vectors and (3) by profiles across the TLS point clouds. Between July and October 2008 the Tortin glacier melted by 1 to 2.5 m and the moraine creeped in direction of the glacier by 0.25 to 0.75 m. During the same period, a landslide zone has been clearly identified downslope of the cableway departure station to the Mt-Fort. Important movements between 1.5 to 5 meters were measured on this landslide through the creation of displacement vectors. This landslide scarp is delimited by 0.5 and 1 meter downward displacements in two month. Already in 2007, a less important landslide was identified and some ice had been observed in the scarp zone. The TLS permitted to analyze the distribution of these movements on the entire moraine and not only on few measurement points like given by D-GPS. The computed TLS displacement vectors are in good agreement with annual D-GPS measurements performed on this moraine. In this study, two types of movements have been identified: (1) Superficial movements, like the landslide, and (2) general creep movements. To explain these movements, two parameters are crucial: (1) The annual melting rate of the glacier below the moraine reached up to 4 m, which has certainly an impact on the stability of the moraine (important movements observed in the landslide zone). The glacier acted as a buttress stabilizing the moraine. The observed glacier retreat and shrinkage causes the destabilisation of the moraine and finally leads to the measured surface movements. (2) The degradation of permafrost (deduced from thermal profiles acquired in a borehole in the moraine), destabilizes the moraine and causes an increase of the creep displacements measured for the whole moraine. The acceleration of the movements is now actively monitored because they can influence the stability of man-made infrastructures. This study was also the opportunity to test the ability of TLS in monitoring of glacial and periglacial landforms like moraines.

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

2009-04-01

69

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

70

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

71

Little Ice Age fluctuations of Glaciar Río Manso in the north Patagonian Andes of Argentina  

NASA Astrophysics Data System (ADS)

Little Ice Age (LIA) fluctuations of Glaciar Río Manso, north Patagonian Andes, Argentina are studied using information from previous work and dendrogeomorphological analyses of living and subfossil wood. The most extensive LIA expansion occurred between the late 1700s and the 1830-1840s. Except for a massive older frontal moraine system apparently predating ca. 2240 14C yr BP and a small section of a south lateral moraine ridge that is at least 300 yr old, the early nineteenth century advance overrode surficial evidence of any earlier LIA glacier events. Over the past 150 yr the gently sloping, heavily debris-covered lower glacier tongue has thinned significantly, but several short periods of readvance or stasis have been identified and tree-ring dated to the mid-1870s, 1890s, 1900s, 1920s, 1950s, and the mid-1970s. Ice mass loss has increased in recent years due to calving into a rapidly growing proglacial lake. The neighboring debris-free and land-based Glaciar Frías has also retreated markedly in recent years but shows substantial differences in the timing of the peak LIA advance (early 1600s). This indicates that site-specific factors can have a significant impact on the resulting glacier records and should thus be considered carefully in the development and assessment of regional glacier chronologies.

Masiokas, M. H.; Luckman, B. H.; Villalba, R.; Ripalta, A.; Rabassa, J.

2010-01-01

72

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

73

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

74

Age characteristics in a multidecadal Arctic sea ice simulation  

Microsoft Academic Search

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.

Elizabeth C. Hunke; Cecilia M. Bitz

2009-01-01

75

Ice Age Geomorphology of North America  

NASA Astrophysics Data System (ADS)

The Last Glacial Cycle in North America dramatically modified drainage patterns and geomorphology on a continental scale. As a consequence, the evolution of river systems holds information on the patterns of glaciation and isostatic response. This information can, in principle, be used to reconstruct the volumes of ice sheet sectors and eroded material by connecting the upstream ice sheets with stable isotope and other sedimentary records in offshore basins. Here we integrate this coupled geomorphic-hydrologic-glacial-sedimentary-paleoceanographic system to solve both the forward problem, how rivers evolve in response to Ice Age forcing, as well as the inverse problem, how fluvial systems record Quaternary history. The connections that define this system provide a link between climate and geomorphology that extends beyond the traditionally considered watershed-to-landscape scale by incorporating solid Earth deformations, large-scale shoreline migration, and the high amplitude changes in climate that drive the growth and decay of major ice sheets and water delivery to the bounding river systems. We address this continental scale problem using a valley-resolving drainage reconstruction that incorporates a realistic ice sheet history, a gravitationally self-consistent treatment of ice-age sea-level changes that includes shoreline migration, and precipitation and evapotranspiration retrodicted using general circulation model (GCM) runs. Drainage divides over the flat-lying North American interior migrate hundreds to thousands of kilometers in response to dynamic interactions between ice sheets and solid Earth response, and these changes coupled with post last glacial maximum (LGM) ice sheet melting drive high-amplitude variability in water and sediment discharge to the oceans. The Mackenzie River Delta records a sedimentary record produced by a highly non-eustatic sea level history and massive glacial sediment inputs routed along the axis that divided the Cordilleran and Laurentide Ice sheets. The upper Missouri River was re-routed northward during multiple deglacial periods due to isostatic depression of the Canadian interior; this re-routing is in addition to its known pre-Illinoian bedrock course to the Northeast. The Missouri River and many of its northerly tributaries hug the Laurentide ice margin, a sign that they were trapped between the ice sheet and its forebulge on the eastward-sloping High Plains. In contrast, the Upper Mississippi flows due south and contains a broad bedrock overdeepening along the Illinois border that records where this river must have sliced through one or more forebulges associated with Laurentide Ice Sheets. Offshore, sedimentary records coupled with these drainage reconstructions can be used as an independent geologic constraint on ice sheet volumes. Our drainage reconstructions provide a new paleogeographic backdrop to understand the North America's glacial past and a framework for tackling new problems at the interface of geomorphology, ice age geodynamics, and paleoclimate.

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

2012-12-01

76

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

77

Self-potential investigation of moraine dam seepage  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

78

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 ...

79

Intermittent thinning of Jakobshavn Isbræ, West Greenland, since the Little Ice Age  

NASA Astrophysics Data System (ADS)

Rapid thinning and velocity increase on major Greenland outlet glaciers during the last two decades may indicate that these glaciers became unstable as a consequence of the Jakobshavn effect (Hughes, 1986), with terminus retreat leading to increased discharge from the interior and consequent further thinning and retreat. To assess whether recent trends deviate from longer-term behavior, we measured glacier surface elevations and terminus positions for Jakobshavn Isbræ, West Greenland, using historical photographs acquired in 1944, 1953, 1959, 1964 and 1985. These results were combined with data from historical records, aerial photographs, ground surveys, airborne laser altimetry and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the Little Ice Age (LIA). We identified three periods of rapid thinning since the LIA: 1902-13, 1930-59 and 1999-present. During the first half of the 20th century, the calving front appears to have been grounded and it started to float during the late 1940s. The south and north tributaries exhibit different behavior. For example, the north tributary was thinning between 1959 and 1985 during a period when the calving front was stationary and the south tributary was in balance. The record of intermittent thinning, combined with changes in ice-marginal extent and position of the calving front, together with changes in velocity, imply that the behavior of the lower parts of this glacier represents a complex ice-dynamical response to local climate forcings and interactions with drainage from the interior.

Csatho, Bea; Schenk, Toni; van der Veen, C. J.; Krabill, William B.

80

New constraints on the gas age-ice age difference along the EPICA ice cores, 0-50 kyr  

Microsoft Academic Search

Gas is trapped in polar ice sheets at ~50-120 m below the surface and is therefore younger than the surrounding ice. Firn densification models are used to evaluate this ice age-gas age difference (Deltaage) in the past. However, such models are not well tested on low accumulation and cold sites of the East Antarctic plateau, especially for periods with different

L. Loulergue; F. Parrenin; T. Blunier; J.-M. Barnola; R. Spahni; A. Schilt; G. Raisbeck; J. Chappellaz

2007-01-01

81

Morphological characteristics, formation and glaciological significance of Rogen moraine in northern Scotland  

NASA Astrophysics Data System (ADS)

Rogen moraine are enigmatic landforms whose exact origin is still debated. We use NEXTMap digital surface models and aerial photographs to map the distribution of previously unreported fields of Rogen moraine in the vicinity of Loch Shin, northern Scotland. Existing models of formation are tested against detailed morphological Rogen moraine characteristics obtained from the remote sensing data and field observations. Detailed morphometric analyses combined with their geographical setting lead us to postulate a likely mechanism of formation. Rogen moraine appear to have formed in areas where there were strong basal ice-flow velocity gradients. Thrusting by compression, or fracturing by extension of preexisting partially frozen sediment probably occurred in these areas, resulting in Rogen moraine formation. A general down-ice increase in ridge crest spacing suggests that the latter process may have been dominant, and is consistent with the location of Rogen moraine in the lee of topographic obstructions, in areas that experienced overall extensional ice flow. We also suggest that at least one field of Rogen moraine formed where lateral basal ice-flow velocity gradients were strongest — possibly in a subglacial shear margin setting. Given their location, the landforms may be consistent with formation during headward scavenging of the Moray Firth palaeo-ice stream into a shrinking core of cold-based ice.

Finlayson, Andrew G.; Bradwell, Tom

2008-11-01

82

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

83

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

84

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

Microsoft Academic Search

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

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

2008-01-01

85

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

Microsoft Academic Search

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

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

2010-01-01

86

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

87

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

88

NEW 10 BE COSMOGENIC AGES FROM THE VIMMERBY MORAINE CONFIRM THE TIMING OF SCANDINAVIAN ICE SHEET DEGLACIATION IN SOUTHERN SWEDEN  

Microsoft Academic Search

S1 b1722 208 57.3947 14.9039 1.0000 0.975 7.61±0.43 12.4±1.3 (0.7) S3 b1723 211 57.3866 14.8983 0.9809 0.975 8.98±0.47 14.9±1.5 (0.8) S4 b2474 217 57.3808 14.8787 0.9731 0.967 8.00±0.41 13.4±1.3 (0.7) S7 b1727 145 57.6695 15.8057 1.0000 0.975 7.62±0.40 13.3±1.3 (0.7) S8 b1434 136 57.6700 15.8064 0.9761 0.975 7.99±0.42 14.4±1.4 (0.7) S9 b1808 140 57.6688 15.8031 1.0000 0.967 7.51±0.58 13.2±1.5 (1.0)

TIMOTHY F. JOHNSEN; HELENA ALEXANDERSON; DEREK FABEL; STEWART P. H. T. FREEMAN

2009-01-01

89

Geological Evidence for Recent Ice Ages on Mars  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

90

Carbon-14 ages of Allan Hills meteorites and ice  

NASA Technical Reports Server (NTRS)

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

Fireman, E. L.; Norris, T.

1982-01-01

91

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

92

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

NASA Astrophysics Data System (ADS)

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

Waitt, Richard B.; Yount, James C.; Davis, P. Thompson

1982-03-01

93

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

94

Processes of annual moraine formation at a temperate alpine valley glacier: glacier dynamics and climatic controls  

NASA Astrophysics Data System (ADS)

This paper presents the first detailed sedimentological study of annual moraines formed by an alpine valley glacier. The moraines have been formed since at least AD 1980 by a subsidiary lobe of Gornergletscher, Switzerland, that advances up a reverse bedrock slope. They reach heights of 0.5-1.5 m, widths of up to 6 m and lengths of up to several hundreds of metres. Sediments in these moraines comprise proglacial outwash and debris flow units; subglacial traction till is absent entirely. Based on four representative sections, three genetic process combinations have been identified. (1) Inefficient bulldozing of a gently-sloping ice margin transfers proglacial sediments onto the ice, causing differential ablation and dead-ice incorporation upon retreat. (2) Terrestrial ice-contact fans are formed by the dumping of englacial and supraglacial material from point sources such as englacial conduit fills. Debris flows and associated fluvial sediments are stacked against a temporarily stationary margin at the start, and deformed during glacier advance in the remainder, of the accumulation season. (3) A steep ice margin without supraglacial input leads to efficient bulldozing and deformation of pre-existing foreland sediments by wholesale folding. Ice surface slope appears to be a key control on the type of process responsible for moraine formation in any given place and year. The second and third modes result in stable and higher moraines that have a higher preservation potential than those containing dead ice. Analysis of the spacing and climatic records at Gornergletscher reveal that winter temperature controls marginal retreat and hence moraine formation. However, any climatic signal is complicated by other factors, most notably the presence of a reverse bedrock slope, so that the extraction of a clear climatic signal is not straightforward. This study highlights the complexity of annual moraine formation in high-mountain environments and suggests avenues for further research.

Lukas, S.

2012-04-01

95

Impact of thermomechanical ice sheet coupling on a model of the 100 kyr ice age cycle  

Microsoft Academic Search

Simulations of the most recent 100 kyr glaciation-deglaciation cycle of the late Pleistocene Ice Age are presented which feature a newly constructed thermomechanically coupled three-dimensional ice sheet model which is itself coupled to a previously employed global energy balance climate model with realistic geography. The model incorporates both orbital insolation forcing due to the slow time evolution of orbital geometry

L. Tarasov; W. Richard Peltier

1999-01-01

96

Spatial and Temporal Characteristics of the Little Ice Age: The Antarctic Ice Core Record.  

National Technical Information Service (NTIS)

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 tem...

E. Mosley-Thompson L. G. Thompson

1992-01-01

97

A common and optimized age scale for Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Dating ice cores is a complex problem because 1) there is a age shift between the gas bubbles and the surrounding ice 2) there are many different ice cores which can be synchronized with various proxies and 3) there are many methods to date the ice and the gas bubbles, each with advantages and drawbacks. These methods fall into the following categories: 1) Ice flow (for the ice) and firn densification modelling (for the gas bubbles); 2) Comparison of ice core proxies with insolation variations (so-called orbital tuning methods); 3) Comparison of ice core proxies with other well dated archives; 4) Identification of well-dated horizons, such as tephra layers or geomagnetic anomalies. Recently, an new dating tool has been developped (DATICE, Lemieux-Dudon et al., 2010), to take into account all the different dating information into account and produce a common and optimal chronology for ice cores with estimated confidence intervals. In this talk we will review the different dating information for Antarctic ice cores and show how the DATICE tool can be applied.

Parrenin, F.; Veres, D.; Landais, A.; Bazin, L.; Lemieux-Dudon, B.; Toye Mahamadou Kele, H.; Wolff, E.; Martinerie, P.

2012-04-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

99

Mapping and analysis of the glacier inventory data at the maximum of the `Little Ice Age' in Jotunheimen, Norway  

NASA Astrophysics Data System (ADS)

Glaciers are determined by variations of several climatic parameters and, therefore, good indicators for climate change. In Norway, there is a long history of glacier monitoring, mainly due to their importance for hydro power generation. Therefore, a detailed and accurate data basis is available. Within southern Norway, there is a strong climatological gradient from the coast eastwards to the drier and, therefore, more continental interior. Jotunheimen represents the most continental glacier area of Norway. For any characterisation of the recent glacier dynamics and for verification of existing models of their future behaviour, it is essential to understand the glacier reaction in the most recent past, e.g. during the so-called ‘Little Ice age'. However, related previously investigations focussed on selected single glaciers. In this study, the glacier extent at the maximum of the Little Ice Age (LIA) in the glacier area Jotunheimen, South Central Norway, was mapped on a regional scale by using remote sensing. For its verification, ground truth data of different sources were applied. Furthermore, the inventory data of the LIA-glaciers, e.g. flow length or maximum height, was assessed with a digital elevation model (DEM). These data were compared with the existing modern inventories. The change of glacier area and length since about the last 250 years was calculated on that basis. Further parameters and fluctuation data was estimated by application of a simple but robust parameterisation for distinct time steps between the maximum of the LIA and AD 2003. In detail, glacier extent at the maximum of the LIA was mapped on a Landsat TM image 2003 and vertical air photos. The maximum LIA- extent is indicated by the outermost Neoglacial moraine and the sparsely vegetation cover inside the glacier foreland. The actual dating of the outermost moraines was taken from the literature. Chronological studies at several individual glaciers using e.g. lichenometry, Schmidt-Hammer, or radiocarbon dating indicated that there are no pre-LIA Neoglacial moraines in the glacier forelands. The only exceptions are some ice-cored moraines on high-lying glaciers mainly in the eastern part of Jotunheimen. Maps of these glaciers and own field-work data were used for verification of the remote-sensing mapping and a sensitivity analysis was made to confirm the accurateness of the mapping. Following this results, 233 glaciers existed during the LIA-maximum in Jotunheimen, comprising a total glacier area of about 290 km2. The mean glacier flow length was about 1550 m. Three glaciers showed an areal extent exceeding 10 km2. The majority of all glaciers (about 41 %), however, belongs to the area class of less than 0.5 km2. In comparison to the inventory data of AD 2003, the glacier area shrank about 35% and the flow length about 34%. By contrast to the westwards located Jostedalsbreen ice cap with its maritime glaciological regime, the glaciers of Jotunheimen showed a rather continuous area and flow length decrease following LIA-maximum until AD 2003.

Baumann, S.; Winkler, S.

2009-04-01

100

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

101

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.

Ahn, Jinho; Brook, Edward J.

2014-01-01

102

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

103

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

NASA Astrophysics Data System (ADS)

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.

Ahn, Jinho; Brook, Edward J.

2014-04-01

104

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

NASA Astrophysics Data System (ADS)

The main purpose of the paper is to study the deglaciation process, including the retreat of the glaciers and the occurrence of short advances with the deposition of new, relatively recent tills in two head valleys of the central-southern Pyrenees: The Upper Gállego Valley, with the main peak Balaitus (42°46'0' N, 0° 15'0'W, 3151 m), and the Marbore Cirque, at the head of the Cinca Valley, on the north face of the Monte Perdido Peak (42º400' N; 0.5º0'W; 3355 m). The deglaciation process was studied through geomorphological mapping and 36Cl cosmogenic exposure ages obtained from morainic and rock glacier boulders and polished bedrocks. Even though the exact position of the front glacier during the global Last Glacial Maximum is not known, there is evidence that the different ice tongues retreated until headwater positions, causing the subdivision of the main glaciers into various individual glaciers. Two clear climate reversals within the general trend to deglaciation have been detected: First of all, the Oldest Dryas, coinciding with the Heinrich Event 1 (ca 17-15 ka) and, secondly, the Younger Dryas (ca 13-11.7 ka). Between both stadials, the Bølling/Allerød Interstadial (ca 15-13 ka) represented an intense glacial retreat up to the cirque headwalls. During the Bølling/Allerød Interstadial the retreat was very rapid, although the occurrence of a short readvance of small glaciers during the Older Dryas must not be ruled out. The Younger Dryas is represented by a new glacial push with the deposition of distinct types of tills. During these late glacier advances, small glaciers and rock glaciers developed close to the cirque headwalls, and coexisted under the same climatic conditions. After the Younger Dryas, new glacial advances has not been detected until the Little Ice Age, except in the Marbore Cirque, where glacial expansion occurred during the Mid and Late Holocene (5.1 ± 0.1 ka), represented by a large push moraine. A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 ka (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. A melting period occurred during the Medieval Climate Anomaly following a glacial expansion during the Dark Age Cold Period (1.4-1.2 ka). The Little Ice Age represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and 1830 AD (Dalton Minimum).

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

2014-05-01

105

The Late Paleozoic Ice Age: An Evolving Paradigm  

NASA Astrophysics Data System (ADS)

The late Paleozoic icehouse was the longest-lived ice age of the Phanerozoic, and its demise constitutes the only recorded turnover to a greenhouse state. This review summarizes evidence for the timing, extent, and behavior of continental ice on Pangea in addition to the climate and ecosystem response to repeated transitions between glacial and interglacial conditions. Combined empirical and climate modeling studies argue for a dynamic ice age characterized by discrete periods of glaciation separated by periods of ice contraction during intermittent warmings, moderate-size ice sheets emanating from multiple ice centers throughout southern Gondwana, possible glaciation of the Northern Hemisphere, and atmospheric CO2 as a primary driver of both ice sheet and climate variability. The glacioeustatic response to fluctuations of these smaller ice sheets was likely less extreme than previously suggested. Modeling studies, stratigraphic relationships, and changes in both the geographic patterns and community compositions of marine fauna and terrestrial flora indicate the potential for strong responses to high-latitude glacial conditions in both ocean circulation and low-latitude climate. The forcings and feedbacks of these linkages, as well as existing climate paradoxes, define research targets for future studies of the late Paleozoic.

Montañez, Isabel P.; Poulsen, Christopher J.

2013-05-01

106

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

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the ice sheet as it responds to the general warming following the Little Ice Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the calving front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as ice further upstream thins and accelerates. To assess whether recent trends deviate from longer-term behavior, we examined three rapidly thinning and retreating outlet glaciers, Jakobshavn Isbrae in west, Kangerdlussuaq Glacier in east and Petermann Glacier in northwest Greenland. Glacier surface and trimline elevations, as well as terminus positions were measured using historical photographs and declassified satellite imagery acquired between the 1940s and 1985. These results were combined with data from historical records, ground surveys, airborne laser altimetry, satellite observations and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the (LIA) up to the present. We identified several episodes of rapid thinning and ice shelf break-up, including thinning episodes that occurred when the calving front was stationary. Coastal weather station data are used to assess the influence of air temperatures and intensity of surface melting, and to isolate glacier changes likely associated with changes in glacier dynamics. We also examined the potential influence of geologic control, including the effect of increased heat flux and high rates of subglacial melt suggested by geophysical data.

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

2008-12-01

107

Radiometric age of the snout ice of Nehnar glacier  

Microsoft Academic Search

The surface ice taken from the snout of the Nehnar glacier (Kashmir) in western Himalaya has been dated using radioisotopes32Si and210Pb to be 500 years. Based on the age distribution of ice and the expected activity of32Si in the fallout, the average rate of glacier movement over a period of the last few centuries is estimated to be about 6

N. Bhandari; D. I. Bhatt; V N Nijampurkar; R K Singh; D. Srivatsava; C P Vohra

1981-01-01

108

Preliminary 10Be Chronology for the Last Deglaciation of the Southern Scandinavian Ice Sheet  

NASA Astrophysics Data System (ADS)

Prominent moraines crossing the Baltic region mark the late Pleistocene maximum extent and recessional phases of the southern margin of the Scandinavian Ice Sheet (SIS). Five moraines present between the advance during the Last Glacial Maximum (LGM) and the Younger-Dryas Salpausselkä Moraines in Finland dated at 11.6 \\pm 0.5 10Be ka (Tschudi et al., 2000) suggest a millennial-scale signal for this sector of the ice sheet. However, dating control constraining the age of the LGM and retreat phases of the southern SIS margin in the region is all but lacking. We have sampled boulders for surface exposure dating with the cosmogenic nuclide 10Be from moraines along a broad south-to-north transect spanning Poland, Lithuania, Latvia, Belarus, Estonia, and Finland. Here we report 10Be concentrations on 63 boulders measured by accelerator mass spectrometry at the Tandetron facility, Gif-sur-Yvette, France. We used a production rate of 5.1 \\pm 0.3 atoms g-1 yr-1 scaled for latitude and altitude according to Stone's factors. No corrections for snow cover or erosion have been applied. Six boulders from the LGM have a weighted mean age of 18.5 \\pm 0.6 10Be ka. Twenty four samples from the Pomeranian Moraine have a weighted mean age of 14.6 \\pm 0.2 10Be ka. Eight samples from the Middle Lithuanian Moraine have a weighted mean age of 14.3 \\pm 0.4 10Be ka. Ten samples from the North Lithuanian Moraine have a weighted mean age of 13.1 \\pm 0.3 10Be ka. A single boulder on the Pandivere Moraine was dated at 14.4 \\pm 1.3 10Be ka. These results define a preliminary time frame for the deglaciation of SIS southern margin in this region. The chronology will be further refined based on 10Be results from an additional 97 samples.

Rinterknecht, V. R.; Raisbeck, G. M.; Yiou, F.; Clark, P. U.; Bitinas, A.; Marks, L.; Piotrowski, J. A.; Zelucs, V.; Brook, E. J.

2002-12-01

109

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

110

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

111

10Be Dating of the Last Retreat of the Southern Margin of the Scandinavian Ice Sheet: Preliminary Results  

NASA Astrophysics Data System (ADS)

Prominent moraines crossing the Baltic region mark the late Pleistocene maximum extent and recessional phases of the southern margin of the Late Pleistocene Scandinavian Ice Sheet (SIS). The presence of five main moraines between the advance during the Last Glacial Maximum (LGM) and the Younger-Dryas Salpausselkä Moraines in southern Finland dated at 11.6 \\pm 0.5 10Be ka suggest a strong millennial-scale signal for this sector of the ice sheet. However, dating control constraining the age of the LGM and retreat phases of the southern SIS margin in this region is all but lacking. We have sampled boulders for surface exposure dating (10Be) from moraines along a broad south-to-north transect spanning Poland, Lithuania, Latvia, Belarus, Estonia, and Finland. Here we report 10Be concentrations on 16 boulders measured by AMS at the Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse. We used a production rate of 5.1 \\pm 0.3 atoms g-1 yr-1 scaled for latitude and altitude according to Lal's factors. No corrections for sample thickness, snow cover nor erosion have been applied. One boulder from the Gruda Moraine representing the last glacial maximum in Lithuania was dated at 17.2 \\pm 1.4 10Be ka. Seven samples from the Pomeranian Moraine in Poland have a weighted mean age of 16.6 \\pm 0.7 10Be ka. Two samples from the Middle Lithuanian Moraine in Lithuania have a weighted mean age of 15.4 \\pm 0.8 10Be ka, and five samples from the North Lithuanian Moraine in Latvia date to 14.1 \\pm 0.7 10Be ka. A single boulder on the Pandivere Moraine was dated at 14.6 \\pm 1.3 10Be ka. We are processing an additional 144 samples for 10Be dating that will further refine this chronology.

Rinterknecht, V. R.; Clark, P. U.; Raisbeck, G. M.; Yiou, F.; Bitinas, A.; Marks, L.; Zelcs, V.

2001-12-01

112

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

113

Age vs depth of glacial ice at South Pole  

NASA Astrophysics Data System (ADS)

Knowledge of age as a function of depth in glacial ice is important for both glaciology and paleoclimatology. For sites near a ridge or dome, an ice flow model together with information on accumulation rate provides a first approximation. If the accumulation rate is high enough, annual layering of isotopes and dust measured in a solid core can provide a precise age vs depth relationship. For South Pole, the flow geometry is not simple and no deep core exists. Nevertheless, by remotely sensing peaks in scattering and absorption of light from pulsed sources buried at depths down to 2200 m, we have been able to determine age vs depth for ages up to 65,000 years. Analysis of radar isochrons by Siegert and Hodgkins provides a rough extension of the age vs depth model to ?165,000 years near bedrock.

Price, P. B.; Woschnagg, K.; Chirkin, D.

114

History of ice sheet elevation in East Antarctica: Paleoclimatic implications  

Microsoft Academic Search

The multi-disciplinary study of past ice surface elevations in the Grove Mountains of interior East Antarctica provides direct land-based data on the behavior of the East Antarctic Ice Sheet since the Pliocene. The glacial geology, the ages of cold desert soils, the depositional environment of younger moraine sedimentary boulders and their spore–pollen assemblages combine to imply a possible significant shrinkage

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

2010-01-01

115

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

116

Greenhouse effect and ice ages: historical perspective  

NASA Astrophysics Data System (ADS)

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

Bard, Edouard

2004-06-01

117

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

118

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

119

Using Radar Layer Data and AN Inverse Ice Flow Model to Constrain the Vostok Ice Core Age-Depth Relationship  

Microsoft Academic Search

Dating of the ice in the Vostok core has been by a combination of ice-flow modelling and the matching of isotopic variation to data from other sites. We present an inverse ice flow model that uses radar layer (isochronic data from near Vostok) to compute the age-depth distribution. We use an optimal method to invert for accumulation rate and melting

R. C. Hindmarsh; M. J. Siegert

2002-01-01

120

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

121

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

122

Glimpses of the Ice Age from I-81  

NSDL National Science Digital Library

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

123

Chilly ice-age tropics could signal climate sensitivity  

SciTech Connect

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

Kerr, R.A.

1995-02-17

124

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

125

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

NASA Astrophysics Data System (ADS)

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

Brook, M.

2012-04-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

127

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

128

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

Microsoft Academic Search

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

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

2009-01-01

129

Glacial Advances and Retreats in Tectonic Southeast Alaska During the Little Ice Age and Last Glacial Maximum: Preliminary Results from EW0408  

NASA Astrophysics Data System (ADS)

In glacially dominated environments climate is linked directly to the earth processes of erosion and sediment deposition with some of the smallest time lags of any geological process. A cruise on the R/V Maurice Ewing that combines high-resolution seismic reflection surveys with ultra-high resolution chirp, EM1002 swath mapping, jumbo piston-coring, multicoring, multi-sensor track logging, and CTD/water sampling from Aug. to Sept., 2004, examined these processes in 30 sites throughout the fjords and continental shelf of tectonically-active southeast Alaska. Geophysical imaging of shelf depocenters and fjord sub-basins allows for tracking of Last Glacial Maximum (LGM) and Little Ice Age (LIA) ice streaming (advances) and glacial retreats. Glacial advances through ice streaming can be tracked by the presence of terminal and lateral morainal banks and extensive deposystems. We present patterns of ice streaming and the resulting sediments from the Lynn Canal/Glacier Bay systems, the Malaspina/ Hubbard glaciers, the Bering glacier, and the glaciers within Prince William Sound. Patterns of convergent and divergent ice flow result in differing deposition patterns and are sometimes reflected in modern shelf topography in features such as shelf valleys and banks. Glacial retreat can be incredibly rapid with the Glacier Bay systems retreating 100 km in < 250 years. The dominant pattern of glacial retreat both for the LIA and LGM retreats are a series of sub-basins imaged within the structurally-controlled fjords showing an episodic retreat style with the greatest volumes of sediments being deposited ice proximally, and the amount of post-glacial drape being dependent on time since the retreat. Rates of sediment deposition are extreme; for example, the second sub-basin of Muir Inlet has accumulated 65 m of paraglacial sediment in the 45 years since direct glacial influence.

Gulick, S. S.; Powell, R. D.; Jaeger, J. M.; Cowan, E. A.; Mayer, L. A.; Mix, A. C.; Finney, B. P.; Pisias, N. G.; Prahl, F.; Stoner, J. S.

2004-12-01

130

Palaeo-ice streams in the northern Keewatin sector of the Laurentide ice sheet  

NASA Astrophysics Data System (ADS)

Evidence for ice streams in the Laurentide ice sheet is widespread. In the region of northern Keewatin and the Boothia Peninsula, Nunavut, Canada, palaeo-ice streams have been recognized, but their location, size and potential role in ice-sheet dynamics are poorly constrained. Based on the interpretation of satellite imagery, we produce a palaeo-ice-stream map of this region. Glacial directional landforms, eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model. Palaeo-frozen bed areas were also identified. Relative age of the geomorphic swarms was assessed by cross-cutting relationships and radiocarbon ages where available. Using this information we obtained a glaciologically plausible picture of ice-stream evolution within the northernmost Laurentide ice sheet. On the M'Clintock Channel corridor, three generations of pure ice streams are found. On Baffin Island and the Gulf of Boothia, glaciation was dominated by frozen-bed zones located on high plateaus and ice streams running along the troughs, i.e. topographic ice streams. A massive convergent pattern at the head of Committee Bay drained ice from both the Keewatin and Foxe sectors and was probably one of the main deglaciation channels of the Laurentide ice sheet. Finally, our results indicate that streaming flow was present in the deep interior of the Laurentide ice sheet, as recently shown for the Greenland and Antarctic ice sheets.

de Angelis, Hernán; Kleman, Johan

131

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

NASA Technical Reports Server (NTRS)

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

Pollard, D.

1978-01-01

132

Far-flung moraines: Exploring the feedback of glacial erosion on the evolution of glacier length  

NASA Astrophysics Data System (ADS)

Over many glacial cycles, the glacial erosion of alpine valleys can be sufficient to reduce the length of glaciers in the most recent cycles. We document field cases illustrative of this erosional feedback and model the long-term evolution of glacier lengths analytically and numerically. The general feature we target is a moraine deposited well beyond the last glacial maximum (LGM) limit, which we refer to as a "far-flung" moraine. Firstly, we assemble published observations to illustrate that far-flung moraines are documented around the world. The observations suggest that the downvalley distance to such far-flung moraines can exceed the distance to LGM moraines by up to twofold. Secondly, we address the problem analytically, making several simplifying assumptions, to demonstrate that glacier length scales linearly with erosion depth. Finally, we employ a numerical model to test the analytical solution. This 1D (depth-integrated) flowline model includes: (i) a depth-averaged longitudinal coupling stress approximation, (ii) prescribed winter and summer surface mass balance profiles, (iii) evolving ice temperature calculated via the conventional heat equation, and (iv) glacier sliding velocity parameterized as a function of basal ice temperature and spatially and temporally variable prescribed flotation fraction. The simulated alpine landscape is modified through the competing processes of glacier erosion, which is dependent on glacier sliding velocity and prescribed bedrock erodibility, and prescribed uplift rate. The climate controlling surface mass balance is prescribed by time series of air temperature and snowfall approximated by the sum of two sinusoidal cycles. The recurrence statistics of these prescribed climate drivers closely match those of the marine isotopic record; hence the prescribed climate drivers faithfully mimic observed long-term climate drivers. Consistent with earlier landscape evolution studies, we find that the primary effect of repeated glaciations is to flatten a valley floor and steepen its headwall, effectively cutting a longitudinal notch in a fluvial valley profile. Analytical and numerical model results also demonstrate that far-flung moraines are an inevitable consequence of repeated glaciations: glaciers in tectonically inactive regions can sufficiently erode their valleys so that the earliest glaciations leave moraines many kilometers down-valley from moraines left by the latest glaciations, despite similar climates. This suggests that a different landscape, rather than a different climate, is capable of explaining the early glacier extents. As a corollary, the long-term drift toward reduced glacier length favors the survival of early moraines in the face of later glacial advances. Finally, rock uplift can defeat this erosional feedback, while rock subsidence enhances the feedback.

Anderson, Robert S.; Dühnforth, Miriam; Colgan, William; Anderson, Leif

2012-12-01

133

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

PubMed

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

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

2010-09-01

134

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

ERIC Educational Resources Information Center

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

Mattioli, Denee J.; Drake, Frederick

1999-01-01

135

Isotopes, ice ages, and terminal Proterozoic earth history  

PubMed Central

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

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

1997-01-01

136

Milutin Milankovitch: Seeking the Cause of the Ice Ages  

NSDL National Science Digital Library

This 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. His conclusion was that Earth's orbit alternates between three cycles of different lengths, causing variations of more than 20 percent in the amount of sunshine reaching the northern latitudes. The site also notes that recent technical advances show variations that correlate with his figures.

137

A high glacier opens a view of the ice age tropics  

SciTech Connect

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

Mlot, C.

1995-07-07

138

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

139

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

NASA Astrophysics Data System (ADS)

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

Balco, Greg; Schaefer, Joerg M.; Larissa Group

2013-01-01

140

Paleoclimatology: Second clock supports orbital pacing of the ice ages  

SciTech Connect

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

Kerr, R.A.

1997-05-02

141

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

142

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

143

Guatemalan Glaciation: Tropical ice cap Reconstruction and Assessment.  

NASA Astrophysics Data System (ADS)

New geomorphological and Global Positioning System (GPS) data, utilizing field work, aerial photographs, and a digital elevation model (DEM), is the first of its kind to precisely constrain past glacial limits at the local last glacial maximum (LLGM) in the Guatemalan highlands. Prior glacial reconstruction work in this area (Anderson, 1969a, b; Hastenrath, 1974) was reconnaissance in nature, and describes the regions extensive glacial geomorphology in only basic terms. The Guatemalan highlands supported one small (~24 km2) and one large (~64 km2) ice cap during the LLGM and contain extensive geomorphological evidence of past glaciation such as recessional and end moraine sequences and glacially scoured bedrock surfaces. Evidence for cirque glaciation occurs on both the large and small ice cap, along with recessional moraine sequences that record a shrinking ice cap likely associated with deglaciation following the LGM. Equilibrium line altitudes (ELA) for the circum-Caribbean region (CCR) have shown that ELA depression was ~1100-1500m during the LLGM. Initial calculations based on THAR (0.2) reconstructions reveal an ELA depression estimate for Guatemala of ~1330m, suggesting significant highland temperature depression of 7.3 to 7.9°C. The LLGM moraines of the Guatemalan highlands were correlated to the LLGM moraines of the Mexican Trans-volcanic belt based on a similar morphology and weathering characteristics. This project will employ a physically based geographic information system (GIS) model (after Plummer and Phillips, 2003) to extrapolate the climate variables that correlate to the reconstructed ice extent and geomorphological evidence. By varying specific temperature and precipitation values as well as insolation, wind speed and direction, the modeled glacier extent will then be "matched" to the physical field evidence, and a paleo-temperature estimate calculated. Further study includes the potential to core dry moraine dammed lakes for 14C analysis, which will allow for minimum ages of deglaciation to be established.

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

2006-12-01

144

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

Microsoft Academic Search

Understanding the role of orbital forcing in the ice ages has now occupied paleoclimatologists and paleoceanographers for many decades, and still we don't really know how this works. Are ice ages directly forced by orbits, or are orbits a pacemaker that organize ice-age oscillations that would occur anyway (i.e., in the absence of orbital forcing)? Tuning of marine d18O (and

A. C. Mix

2010-01-01

145

Timing of the Little Ice Age in southern Greenland  

NASA Astrophysics Data System (ADS)

Northern hemisphere temperatures reached their Holocene minimum and most glaciers reached their maximum during The Little Ice Age (LIA), but the timing of specific cold intervals is site-specific. In southern Greenland, we have compiled data from organic matter incorporated in LIA sediments, used as a signal for ice-free terrain being overridden by LIA glacier advances, and data from threshold lakes showing the onset of glacier-fed lakes, thus revealing the advance-maximum phase initiating the LIA. Finally, we have compiled lichenometry results indicating the onset of bedrock vegetation succeeding ice retreat. Our results show that the advance of glaciers during the LIA occurs early after the Medieval Warm Period terminating soon after 1200 AD and culminates c. 1500-1600 AD. Historical maps also show that many glaciers on the western coast occupy a still-stand near the LIA maximum until 1900 AD before retreat commence. Thus in southern Greenland, we define LIA as the period between the first signs of Late Holocene glacier readvance and the latest onset of retreat - i.e. from ca. 1200 to c. 1900. During this period northern hemisphere annual mean temperatures, although fluctuating, were generally below the 1961-1990 average, with the coldest interval between c. 1600 and 1800. Even though winter temperatures may have dominated the cooling, also the summer temperatures which are most closely correlated with glacier mass balances, dropped, to c. 0.6° below the average in the northern hemisphere including the Arctic. Furthermore, the glacier response seems to be mirrored by a oceanic cooling between 500-1000 AD, followed by onset of the LIA at 1150-1250 AD as seen in the relative strength of warm subsurface water and the influence of the East Greenland Current.

Kjær, Kurt H.; Kjeldsen, Kristian K.; 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

146

Temperature differences between the hemispheres and ice age climate variability  

NASA Astrophysics Data System (ADS)

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 the Earth manage to warm and cool by so much? Here we argue that, for the big transitions at least, the Earth did not warm and cool as a single entity. Rather, the south warmed instead at the expense of a cooler north through massive redistributions of heat that were set off by the orbital forcing. Oceanic CO2 was vented up to the atmosphere by the same redistributions. The north then warmed later in response to higher CO2 and a reduced albedo from smaller ice sheets. This form of north-south displacement is actually very familiar, as it is readily observed during the Younger Dryas interval 13,000 years ago and in the various millennial-scale events over the last 90,000 years.

Toggweiler, J. R.; Lea, David W.

2010-06-01

147

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

148

Collapse of marine-based outlet glaciers from the Scandinavian Ice Sheet  

NASA Astrophysics Data System (ADS)

We present a reconstruction of the timing and retreat rates of more than 2000 m thick Younger Dryas (YD) fjord glaciers in western Norway using a detailed chronology of 10Be exposure ages from lateral moraines and 14C dated end moraines. A primary conclusion is that ice margins retreated up the 120-170 km long fjords at mean rates of 240-340 m yr-1 during the early Holocene. We further show that part of the south-western sector of the Scandinavian Ice Sheet collapsed in two distinct steps. The first step occurred between 19.5 and 18.5 ka BP as break up of the Norwegian Channel Ice Stream, which drained the ice sheet during the Last Glacial Maximum (LGM). The second step was the rapid retreat up the fjords mentioned above, dated to 11.6-11.1 ka BP. During the intervening ˜7000 years no net retreat occurred despite oscillations of the ice margin. This stepwise ice margin retreat strongly contrasts with the more monotonic decay of the ice sheet as a whole, indicating that water depths set the pace for climate-triggered ice margin retreat in this part of the ice sheet. Calving and melting of marine margins has dominated mass-loss from modern ice sheets in recent decades; however, the mechanisms and long-term (100-1000 yr) rate of ice-front retreat is less certain and empirical examples such as those given here may help in developing better numerical models.

Mangerud, Jan; Goehring, Brent M.; Lohne, Øystein S.; Svendsen, John Inge; Gyllencreutz, Richard

2013-05-01

149

Comments on Hamaker's hypothesis of a coming COâ-induced ice age  

Microsoft Academic Search

Over the past several years, John Hamaker and a number of followers have put forth a hypothesis that the imminent demise of the world's forests from lack of vital mineral nutrients will trigger an ice age. Their evidence in support of this hypothesis has recently appeared as a videotape entitled ''Stopping the Coming Ice Age.'' These comments were prepared in

MacCracken

1989-01-01

150

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

151

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

152

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

153

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

154

Global deep-sea extinctions during the Pleistocene ice ages  

NASA Astrophysics Data System (ADS)

The dark, near-freezing environment of the deep oceans is regarded as one of the most stable habitats on Earth, and this stability is generally reflected in the slow turnover rates (extinctions and appearances) of the organisms that live there. By far the best fossil record of deep-sea organisms is provided by the shells of benthic foraminifera (Protista). A little-known global extinction of deep-sea benthic foraminifera occurred during the Pleistocene ice ages. In the southwest Pacific, it caused the disappearance of at least two families, 15 genera, and 48 species (˜15% 25% of the fauna) of dominantly uniserial, elongate foraminifera with distinctive apertural modifications. These forms progressively died back and became extinct during glacial periods in the late Pliocene to middle Pleistocene (ca. 2.5 0.6 Ma); most extinctions occurred between 1.0 and 0.6 Ma, at the time of the middle Pleistocene climatic revolution. This first high-resolution study of this extinction event indicates that it was far more significant for deep-sea diversity loss than previously reported (10 species). The middle Pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms, a phase that began during cooling near the Eocene-Oligocene boundary and continued during the middle Miocene. Clearly these taxa declined when the world cooled, but the reason is yet to be resolved.

Hayward, Bruce W.

2001-07-01

155

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

156

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

157

New advance in research on the international little ice age climate change  

Microsoft Academic Search

The Little Ice Age (LIA) is a cold climatic event since Medieval Warm Period (MWP) and a previous period before global warming over the last 100 years. Recent years, the studies on LIA have achieved so many advances in the world by using the data such as ice core, tree-rings, stalagmite, lake sediment and historic documents, etc. The focuses of

Jinsong Wang; Fahu Chen; Bao Yang

2005-01-01

158

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

Microsoft Academic Search

The Greenland Ice Sheet's (GIS) largest and fastest outlet glacier, Jakobshavn Isbrae, is one of the most significant contributors to GIS mass loss, draining an estimated 6.5% of the GIS area (Rignot and Kanagaratnam, 2006). Jakobshavn Isbrae has retreated significantly since the Little Ice Age (LIA, ca. 1250- 1900; Csatho et al., 2008), and continues to exhibit rapid changes in

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

2009-01-01

159

Origin of Ice Ages: an Ice Shelf Theory for Pleistocene Glaciation  

Microsoft Academic Search

A RECENT paper by Wilson1 suggests that `thermal' surges of the Antarctic ice sheet led to the growth of large ice shelves in the Southern Ocean, and that these shelves cooled the Earth sufficiently to cause glaciations in the northern hemisphere. That the southern hemisphere may dominate the northern in this way is the antithesis of a suggestion in an

J. T. Hollin

1964-01-01

160

Neoproterozoic ice ages, boron isotopes, and ocean acidification  

NASA Astrophysics Data System (ADS)

The Neoproterozoic Earth underwent at least two severe glaciations, each extending to low palaeomagnetic latitudes and punctuating warmer climates. In concert with the environmental changes, the rocks display large amplitude fluctuations in their stable isotopic composition. These fluctuations are stratigraphically systematic, occur in many sections worldwide and are interpreted as being globally significant1. Thus, the Neoproterozoic carbonates provide a unique geological and isotopic archive to improve our understanding of major non-anthropogenically influenced changes in Earth System behaviour. The two widespread older and younger Cryogenian glacial deposits (commonly referred to as the Sturtian and Marinoan, respectively) in Namibia are directly overlain by cap carbonates deposited under inferred periods of high atmospheric carbon dioxide concentrations. Oceanic uptake of carbon dioxide decreases ocean pH and here we present a record of Cryogenian inter-glacial ocean pH, based on boron isotopes in marine carbonates. Our data document characteristically different B isotope profiles of the two Cryogenian carbonate transects that are consistent with the presence of two panglacial climate states, but indicate that each had its own distinct environmental conditions. The Marinoan interglacial ?11B profiles are systematic and remarkably consistent, and they vary by up to 11‰. This yields a relative pH variation of up to 1.5 pH units, and implies a pH of 8.5 at the onset of cap carbonate deposition, followed by a decrease in pH to ~7 and then a return to pH ~8 for the upper part of the section. The transient ocean acidification excursion and the alkaline pH condition near the start and termination of the inferred greenhouse state suggests a rapid draw-down of CO2 initiated at the start of the deglaciation and supports inferences of a thick, global sea-ice shield with minimal air-sea gas exchange during glaciation. In contrast, largely constant B isotope values for the Sturtian-aged glacial aftermath do not indicate extreme ocean pH (~8.3) conditions and do not support a contemporaneous major ocean acidification event and associated high pCO2 at the time of the older Cryogenian glaciation and deglaciation. That leads us to speculate that the ocean during the older glaciation was not totally frozen and that the hydrological cycle was functioning2. 1Hoffman, P.F., Kaufman, A.J., Halverson, G.P. and Schrag, D.P. (1998). A Neoproterozoic Snowball Earth. Science, 281, 1342-1346. 2Kasemann, S.A., Prave, A.R., Fallick, A.E., Hawkesworth, C.J. and Hoffmann, K.H. (2010). Neoproterozoic ice ages, boron isotopes, and ocean acidification: Implications for a snowball Earth. Geology, 38, 775-778.

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

2010-12-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

163

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

164

The last forests in Greenland, and the age of the ice sheet  

NASA Astrophysics Data System (ADS)

Recently ancient DNA (aDNA) studies of the basal ice in the Camp Century ice core, northern Greenland, have shown that mixed coniferous-deciduous forest grew here before the area was invaded and permanently covered by the ice sheet. The coring site is situated only 100 km from the present ice margin and more than 500 km from the ice divide, indicating that since this last inception the northern part of the ice sheet never receded more than 100 km from its present margin. Dating of the basal ice and obtaining an age for the forest and for the beginning of the ice sheet's permanency has been attempted by analyzing for optically stimulated luminescence (OSL), meteoric 10Be/36Cl cosmogenic nuclides, 234U/238U recoil. These methods all provide only minimum ages and show that the forest at Cap Century is older than 500 ka. Comparison with other Pleistocene "forest sites" in Greenland - the Kap København Formation in northernmost Greenland, the DYE-3 ice core in the south, the ODP boring 646 south of Greenland, as well as results from basal ice in the GRIP ice core - extends the minimum age to c. 1 ma. The maximum age is provided by the Kap København Formation, which must be older - or contemporaneous. The formation has recently been confirmed to date within the interval 2-2.5 ma, with a preferred age of 2.3-2.4 ma. Surprisingly, application of the molecular clock of insect COI sequences on the Camp Century aDNA now seem to push the minimum age just as far back - to 2.4 ma, suggesting that the timberline boreal forest at Kap København is contemporaneous with the mixed forest at Camp Century, 600 km to the south. From this we conclude that the northern ice sheet dome, which today contains 85% of the total ice sheet volume, has remained within 100 km of its present margin for at least 1 ma, and possibly may go back as far as 2.4 ma. The ice sheet has therefore survived both interglacials and "super interglacials" that were both warmer and longer than the present. This may give us some hope for the future.

Funder, Svend; Schmidt, Astrid M. Z.; Dahl-Jensen, Dorthe; Steffensen, Jørgen Peder; Willerslev, Eske

2014-05-01

165

Asynchronous Little Ice Age Megadroughts in Sub-Saharan Africa  

NASA Astrophysics Data System (ADS)

Lake Bosumtwi is a small (8 km-dia.), deep (78 m), hydrologically-closed lake located in the lowland forest zone of southern Ghana, West Africa. The steep-walled meteorite crater basin (10.5 km-dia.) is particularly sensitive to subtle changes in the regional precipitation-evaporation balance, and thus has long been cited as a benchmark paleoenvironmental site for West Africa. In an effort to enhance the value of the Bosumtwi sediments in reconstructing decade to century-scale monsoon variability, we collected a new suite of freeze-cores, and subsequently determined (e.g., with two independent radiometric systems) that the finely laminated sediments represented annual varves (Wheeler et al., AGU Fall Meeting 2002). In light of previous studies, we hypothesized that the ratio of carbon to nitrogen in the lake sediments provides a proxy for changing lake area, and hence regional hydrologic balance and monsoon strength. We confirmed the reliability of this proxy by comparing the sediment based ratio of carbon to nitrogen (C:N) against the age of well-dated dead trees submerged in water depths of 10 to 20m, and then created the first near-annually dated record of West African rainfall extending back eight centuries. The 20th century has been the wettest of the last eight centuries, with the 19th century close behind. Prior to ca. 1800, the Lake Bosumtwi region was generally characterized by drought, with the periods prior to 1300, and 1640 to 1720 AD the driest. This contrasts with comparable records from East Africa, and indicates that much of the Little Ice Age, including some hypothesized periods of reduced solar output, did not result in synchronous enhanced precipitation across North Africa. Instead, it appears that the solar Maunder Minimum resulted in a megadrought in subtropical West Africa coincident with increased rainfall in the Sahel. Thus, the out-of-phase relationship that characterizes interannual variability may extend to longer time scales of variation as well. In addition, anomalously strong Atlantic trade winds and cool SSTs appear to have been associated with the 80-year 17th to 18th century West Africa megadrought.

Overpeck, J.; Wheeler, W.; Beck, W.; Cole, J.; Scholz, C.; Arko, J.; Sharp, E.

2002-12-01

166

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

167

A preliminary 10Be chronology of Scandinavian Ice Sheet retreat from southwestern Norway  

NASA Astrophysics Data System (ADS)

Temporal and spatial patterns of Pleistocene ice sheet deglaciation provide targets for numerical ice sheet simulations, a basis for predicting contemporary ice sheet retreat, and insights into mechanisms that control the tempo of ice sheet retreat. To compliment existing chronologies for the Scandinavian Ice Sheet (SIS), we initiated a campaign to constrain the deglaciation of the SIS in southwestern Norway using 10Be dating. Our sample locations range from Utsira Island, off the southwestern Norwegian coast, to the central mountain plateaus of southern Norway. The samples include two Late Glacial moraine complexes, previously assigned to the Younger Dryas Period (YD) and the Preboreal Oscillation. Our chronology, which uses a 10Be production rate constrained nearby, currently consists of 20 10Be ages; an additional 33 ages are awaiting AMS analysis. The ages from Utsira (21.3±2.1 ka; n=5, more pending), the only site that lies within the Norwegian Channel Ice Stream, show an extremely fast break up of the ice stream. Additionally, we have thus far constrained the timing of deglaciation of coastal mainland Norway at Jæren (15.1±0.3 ka; n=3), the landscape beyond the mouth of Lysefjord (13.3±0.4 ka; n=3), which is immediately outboard the YD moraines, samples from up-fjord of the moraines (10.9±0.5 ka; n=3), and in the central uplands ~110 km from the coast (11.0±0.1 ka; n=2). When complete, we expect our final chronology to provide new constraints on several key episodes of the deglaciation of southern Norway. In particular, we will test the hypothesis that the maximum ice extent during the YD occurred at different times in different sectors of Scandinavia.

Briner, J. P.; Svendsen, J. I.; Mangerud, J.; Lohne, O. S.; Young, N. E.

2012-12-01

168

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

Microsoft Academic Search

The transient climate evolution of last Ice-Age termination (21,000 to 7,000 years ago) provides key observations for constraining climate sensitivity and understanding global carbon cycle. Here we present the first complete simulation of the last Ice-Age termination in a synchronously coupled atmosphere-ocean general circulation model. Our simulation reproduces many major features of the deglacial climate evolution in Greenland, Antarctic, tropical

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

2010-01-01

169

The coastal oasis: ice age springs on emerged continental shelves  

NASA Astrophysics Data System (ADS)

As ice caps expanded during each of the last five glaciations, sea level fell at least 120 m below current levels, exposing continental shelves worldwide to create vast areas of new land. As a result of this exposure, the ecology, climate, pedology, and geology of global shorelines were dramatically transformed, which in turn altered the carbon cycle and biodynamics of this new landmass. In this paper, we focus on a little-known hydrogeological phenomenon that may have had profound influences on biodiversity, human evolution, and carbon storage during periods of severe climatic stress of the Pleistocene Ice Ages. We propose that freshwater springs appeared on emerged continental shelves because falling sea level not only drew down and steepened the coastal water table gradient, thus increasing the hydrostatic head on inland groundwater aquifers, but also removed up to 120 m of hydrostatic pressure on the shelf, further enhancing groundwater flow. We call this phenomenon the "coastal oasis", a model based on three well-established facts. (1) In all coastal areas of the world, continental aquifers discharge a continuous flow of fresh water to the oceans. (2) Many submarine sedimentary and morphological features, as well as seepages and flow of fresh water, are known on and below the shelves from petroleum explorations, deep-sea drilling programs, and mariners' observations. (3) Hydraulic principles (Darcy's law) predict increased groundwater flow at the coast when sea level drops because the piezometric head increases by the equivalent depth of sea-level lowering. Sea level is presently in a relatively high interglacial position. Direct observation and verification of our model is difficult and must rely on explorations of terrain that are now deeply submerged on continental shelves. For this reason, we draw parallels between our predicted model and simple, well-exposed terrestrial hydrological systems, such as present-day springs that appear on the exposed shores of lakes whose free-air water levels fell during periods of aridity. Such modern examples are seen in the Caspian Sea and Dead Sea, the Afar Depression, and the Sahara Desert. These modern analogues demonstrate the likelihood that underground water will be more abundant on emerged shelves during sea-level fall, causing springs, oases, and wetlands to appear. Our model creates an apparent paradox: in tropical and subtropical arid lands, such as most of Africa, sea-level fall during hyperarid glacial phases would produce abundant fresh water flow onto emerged continental shelves as the continental interior desiccated. Thus, emergent shoreline springs provided new habitats for terrestrial vegetation and animals displaced from the interior by increasingly arid conditions, shrinking ecosystems, and dwindling water supplies. Such a scenario would have had a profound influence on the vegetation that spreads naturally to colonize the emerged shelves during glacio-eustatic sea-level lowstands, as well as creating new habitats for terrestrial mammals, including early humans.

Faure, Hugues; Walter, Robert C.; Grant, Douglas R.

2002-06-01

170

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

171

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

172

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

173

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

PubMed

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

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

2011-09-01

174

Moraine dam related to late Quaternary glaciation in the Yulong Mountains, southwest China, and impacts on the Jinsha River  

NASA Astrophysics Data System (ADS)

The Yulong Mountain massif is tectonically active during Quaternary and contains the southernmost glacierized mountains in China, and all of Eurasia. Past glacial remnants remain preserved on the east and west sides of the Yulong Mountains. A ridge of moraine protruded into the Jinsha River at the Daju Basin, damming the river, and forming a lake at the head of the Jinsha River. Cosmogenic 10Be and 26Al provide exposure age dates for the moraine-based fluvial terraces left behind after the dam breached, and for moraine boulders on both the eastern and western sides of the Yulong Mountains. Our results yield exposure ages for the terraces that range from 29 ka to 8 ka, and a downcutting rate of 7.6 m/ka. The preservation of the remaining dam for over 10,000 years suggests stability of the moraine dam and gradual erosion of the dam during drainage of the dammed lake. From the relationship between exposure ages and elevations of the fluvial terraces located in different walls of the Daju fault, we obtain a late Quaternary dip-slip rate of about 5.6 m/ka for the Daju fault. The exposure ages of 10.2 ka and 47 ka for moraine boulders located in the east and west sides of the Yulong Mountains, respectively, coincide with warm periods in the late Quaternary. This implies that precipitation provides the major control for glaciations on the Yulong Mountains, a domain of the southwest Asian monsoon.

Kong, Ping; Na, Chunguang; Fink, David; Zhao, Xitao; Xiao, Wei

2009-12-01

175

10Be chronology for the deglaciation of the western margin of the British-Irish Ice Sheet, Ireland  

NASA Astrophysics Data System (ADS)

AMS 14C dates of fossiliferous marine mud from sites along the Irish Sea Basin identify a major readvance of the ice sheet over the north and central lowlands of Ireland and the northern Irish Sea Basin during the Killard Point Stadial at approximately 14 14C ka BP (~17.5 cal ka). Well-dated records at Corvish, County Donegal, suggest a similar-age readvance of the northwestern sector of the Irish ice sheet, indicating ice-sheet wide response to climate forcing associated with Heinrich event 1. Ice readvance caused widespread transport of subglacial sediment to ice margins, particularly around bays where large moraines were formed. We sampled boulders for 10Be dating from moraines in the north and west of Ireland that may be coeval with the Killard Point Stadial. Samples were collected from quartz-bearing erratics from three distinct moraine sequences located in the northwest (Bloody Foreland, County Donegal) and west (Ox Mountains, County Sligo, and Clew Bay, County Mayo) of Ireland. Thus far, we have obtained the following 10Be ages from these moraine sequences: Bloody Foreland (15,500 ± 1400 yr, 18,900 ± 1400 yr, and 18,400 ± 1480 yr), Ox Mountains (13,590 ± 1200 yr, 14,210 ± 1150 yr, 14,450 ± 1370 yr, and 17,890 ± 1300 yr), and Furnace Lough (15,570 ± 2500 yr, 15,600 ± 1200 yr, and 13,500 ± 1000 yr). These data suggest an older deglaciation at Bloody Foreland at ~18.5 10Be ka following the last glacial maximum, and a younger deglaciation in the Ox Mountains and Furnace Lough areas at ~14.5 10Be ka following the Killard Point ice readvance.

Clark, J.; McCabe, M.; Schnabel, C.; Freeman, S.; Maden, C.; Xu, S.

2005-12-01

176

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

NASA Astrophysics Data System (ADS)

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

Reznichenko, Natalya; Davies, Tim; Winkler, Stefan

2013-04-01

177

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

SciTech Connect

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

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

1994-11-01

178

The coastal oasis: ice age springs on emerged continental shelves  

Microsoft Academic Search

As ice caps expanded during each of the last five glaciations, sea level fell at least 120 m below current levels, exposing continental shelves worldwide to create vast areas of new land. As a result of this exposure, the ecology, climate, pedology, and geology of global shorelines were dramatically transformed, which in turn altered the carbon cycle and biodynamics of

Hugues Faure; Robert C Walter; Douglas R Grant

2002-01-01

179

Variations in the earth's orbit: pacemaker of the ice ages  

Microsoft Academic Search

Among the explanations for fluctuations in the Pleistocene ice sheets, only the orbital hypothesis has been formulated so as to predict the frequencies of major Pleistocene fluctuations. It is also the only explanation which can be tested geologically by determining what the frequencies are. All versions of the orbital hypothesis predict that the obliquity of the earth's axis and the

J. D. Hays; J. Imbrie; N. J. Shackleton

1976-01-01

180

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

181

Extending Glacier Monitoring into the Little Ice Age and Beyond  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

182

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

183

Polyphase glacigenic deformation in the Waterloo Moraine, Kitchener, Ontario, Canada  

NASA Astrophysics Data System (ADS)

A sedimentological investigation of Quaternary sediments in the Waterloo Moraine was conducted to characterize the nature of deformation in stratified sediments in the Kieswetter Holdings Ltd. aggregate quarry, Kitchener, Ontario. Highly deformed interbedded clay, silt, fine- to very coarse-grained sand and granular to cobble gravel is exposed in two sets of contiguous panels. Analysis of the sediment revealed five recognizable stratigraphic units: 1) climbing ripple cross-laminated silt, 2) normally graded cobble gravel, 3) cross-bedded, fine- to coarse-grained sand, 4) interbedded clay, silt and fine- to very coarse-grained sand with granules and 5) crudely channelized interbedded medium- to very coarse-grained sand and granule to pebble gravel. These units suggest rapid deposition and fluctuating energy in a subaqueous environment prior to deformation. Deformation structures include normal faults with offsets ranging from 1 to 50 cm, widespread occurrences of density-driven ductile deformation ranging from 0.5 to 5 cm, open to closed folds (cm to m scale), as well as isolated occurrences of overturned folding ranging in size from 0.5 cm to approximately 1.2 m. Abundant reverse faulting with offsets ranging from 0.5 to 7 cm (average of 2 cm) and widespread occurrences of boudinage, bed attenuation and shear folds ranging in scale from 0.5 to 1.5 m were also observed. The nature and scale of deformation structures suggest complex polyphase deformation of heterogeneous sediments related to rapid sedimentation, sediment gravity flow, active ice deformation and melting of buried ice in a dynamic subaqueous environment.

Weaver, Laura; Arnaud, Emmanuelle

2011-04-01

184

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

185

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

186

Ice age at the Middle-Late Jurassic transition?  

NASA Astrophysics Data System (ADS)

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (?18O values of shark tooth enamel) indicates a severe cooling at the Middle-Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1-3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle-Late Callovian widespread deposition of organic-rich marine sediments (e.g. northwestern Europe, Central Atlantic, and Arabian Peninsula). This thermal deterioration can thus be ascribed to a downdraw in atmospheric CO2 via enhanced organic carbon burial which acted as a negative feedback effect (i.e. the inverse greenhouse effect). The glacial episode of the MLJT climaxed in the Late Callovian, lasted about 2.6 Myr, and had a pronounced asymmetrical pattern composed of an abrupt (˜0.8 Myr) temperature fall opposed to a long-term (˜1.8 Myr), stepwise recovery. The glacial conditions at the MLJT reveal that atmospheric CO2 levels could have dropped temporarily to values lower than 500 ppmv during Mesozoic times.

Dromart, G.; Garcia, J.-P.; Picard, S.; Atrops, F.; Lécuyer, C.; Sheppard, S. M. F.

2003-08-01

187

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

188

Ice  

NSDL National Science Digital Library

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

Harris, Kathryn L.

189

Glacial age precipitation and temperature estimates for the tropical Guatemalan highlands  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

190

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

191

On the interpretation of paleomagnetic data on moraines  

NASA Astrophysics Data System (ADS)

Some methods of the interpretation and application of paleomagnetic data for the stratigraphic separation and correlation of Neopleistocene moraines, as well as the factors affecting the degree of ordering of magnetic moments of ferromagnetic particles in a moraine, are considered. A refined interpretation of the well-known Ryabushkin-Pevzner model of moraine magnetization is proposed. It is shown that the way of using an occasional coincidence of the direction of long axes of fragments with the direction of magnetization vectors, which is stated in some publications, has no grounds for its application for the stratigraphic separation of moraines related to the Dnieper and Moscow glaciations. However, it cannot be ruled out that this phenomenon may be used for the investigation of processes of glacial lithogenesis.

Bol'Shakov, V. A.

2011-09-01

192

Evaluation of Pollution Abatement Procedures, Moraine State Park.  

National Technical Information Service (NTIS)

Various mine drainage pollution abatement techniques completed during the construction phase of the Moraine State Park, Pennsylvania are evaluated. The remedial methods employed included strip mine reclamation, underground mine sealing, grouting, surface ...

J. W. Foreman D. C. McLean

1973-01-01

193

Varve and radiocarbon dating support the rapid advance of Jakobshavn Isbræ during the Little Ice Age  

NASA Astrophysics Data System (ADS)

Large outlet glaciers draining the Greenland Ice Sheet significantly influence overall ice sheet mass balance. Considerable short term (years to decades) retreat and fluctuations in velocity of Jakobshavn Isbræ, western Greenland, illustrate the complex nature by which large outlet glaciers respond to climate change, making predictions of future ice sheet change challenging. To provide a longer-term view (centuries), we investigate the geological record of Jakobshavn Isbræ change. We use continuous sediment records from lakes that were influenced by the recent advance of Jakobshavn Isbræ, which took place during the Little Ice Age. In particular, we explore the use of annually laminated lake sediments (varves) to precisely constrain the advance of the ice margin as it approached its late Holocene maximum extent. We find that the ice margin advanced recently, at least after ˜1650 to ˜1700 AD, and more likely ˜1800 AD. We suggest that during this period Jakobshavn Isbræ advanced at a rate that was similar to its historically documented average retreat since ˜1850 AD. Our results indicate that Jakobshavn Isbræ, and presumably other large marine calving glaciers, have the ability to advance quickly in response to climate forcing.

Briner, J. P.; Young, N. E.; Thomas, E. K.; Stewart, H. A. M.; Losee, S.; Truex, S.

2011-09-01

194

Continental atmospheric circulation over Europe during the Little Ice Age inferred from grape harvest dates  

Microsoft Academic Search

Estimates of climate conditions before the 19th century are based on proxy data reconstructions or sparse meteorological measurements. The reconstruction of the atmospheric circulation that prevailed during the European Little Ice Age (~1500-1850) has fostered many efforts. This study illustrates a methodology combining historical proxies and modern data sets to obtain detailed information on the atmospheric circulation that prevailed over

P. Yiou; I. García de Cortázar-Atauri; I. Chuine; V. Daux; E. Garnier; N. Viovy; C. van Leeuwen; A. K. Parker; J.-M. Boursiquot

2011-01-01

195

Continental atmospheric circulation over Europe during the Little Ice Age inferred from harvest dates  

Microsoft Academic Search

Estimates of climate conditions before the 19th century are based on proxy data reconstructions or sparse meteorological measurements. In particular, the reconstruction of the atmospheric circulation that prevailed during the Little Ice Age (~1500-1850) has fostered many efforts. It is generally assumed that the North Atlantic Oscillation played an important role in this variability. In this study, we use proxy

Pascal Yiou; Isabelle Chuine; Valérie Daux; Iñaki García de Cortázar-Atauri; Emmanuel Garnier; Nicolas Viovy

2010-01-01

196

A Comparison of Competing Theories of The 100,000-yr Ice Age Cycle  

Microsoft Academic Search

A plethora of theories have been proposed as to what the physical mechanisms are that give rise to the quasiperiodic ice ages of the Pleistocene. Many of these theories have been expressed as mathematical models with only a few free parameters. However, there has been little effort to compare the relative ability of rival theories to explain the record of

Gerard H. Roe; Myles R. Allen

2002-01-01

197

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

Microsoft Academic Search

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

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

2004-01-01

198

Earth's orbital eccentricity and the rhythm of the Pleistocene ice ages: the concealed pacemaker  

Microsoft Academic Search

Most paleoclimate researchers would probably agree that variations in Earth's axial tilt and precession parameters have influenced past climate change. However, claims of connections between orbital eccentricity and ice age climate are more difficult to demonstrate or accept, especially since the amplitude of the strongest component of eccentricity-induced insolation, the 413-ky signal, is conspicuously small or absent from the power

J. A. Rial

2004-01-01

199

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

Microsoft Academic Search

The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for ‘present’ climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Since no external forcing was permitted during the model run all such fluctuations

B. G. Hunt

2006-01-01

200

A comparison of competing explanations for the 100,000-yr ice age cycle  

Microsoft Academic Search

There currently exists no consensus as to the cause of the ice ages of the late Pleistocene. Many of the competing hypotheses have been formulated into mathematical models which enables a rigorous comparison to be made. Spectral analysis fails to distinguish rival models. Using regression analysis, we examine the relative performance of several models, each representative of a different type

Gerard H. Roe; Myles R. Allen

1999-01-01

201

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

Microsoft Academic Search

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

Gary Shaffer

2009-01-01

202

Little Ice Age glacial activity in the Mt. Waddington area, British Columbia Coast Mountains, Canada  

Microsoft Academic Search

The establishment of fourteen Little Ice Age (LIA) glacier chronologies in the Mt. Waddington area led to the development of an extended history of glacial activity in this portion of the southern British Columbia Coast Mountains, Canada. The glaciers were located within four different mountain ranges, and were of varying size and aspect. Dendrochronological and lichenometric techniques were used to

S. J. Larocque; D. J. Smith

2003-01-01

203

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

204

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

SciTech Connect

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

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

1994-10-01

205

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

NASA Astrophysics Data System (ADS)

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

Mix, A. C.

2010-12-01

206

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

National Technical Information Service (NTIS)

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 bef...

P. J. Wetzel P. Chylek G. Lesins

2002-01-01

207

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

208

Pre-Little Ice Age advance and retreat of Linnébreen on Svalbard  

NASA Astrophysics Data System (ADS)

Arctic glaciers are often assumed to have reached their late-Holocene maximum extent during the Little Ice Age (LIA) of the last several centuries. Using 10Be exposure ages we show that following an ice-free period between 12.6×0.4 ka and the early to middle Holocene, Linnébreen (glacier) in west Svalbard reached a pre-LIA maximum from which it retreated at 1.6×0.2 ka. Comparison with calibrated 14C dates from other glaciers suggests that this period of retracted ice at ~1.6 ka could be regional in extent. This interval of glacier retreat is concurrent with the northward incursion of warm Atlantic waters and consequent sea-ice retreat. The current retreat of Linnébreen has a pre-historic precedent in the late Holocene. We suggest that increased glacier ablation from ocean warming overwhelmed increased glacier accumulation from reduced sea ice and drove the retreat of Linnébreen. This pattern will likely be repeated, which has implications for the future response of Svalbard glaciers to human-induced climate change.

Reusche, M.; Winsor, K.; Carlson, A. E.; Marcott, S. A.; Rood, D.; Novak, A.; Roof, S.; Retelle, M.; Werner, A.; Caffee, M. W.; Clark, P. U.

2013-12-01

209

Exposure history of the lunar meteorite, Elephant Moraine 87521  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

210

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

212

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

213

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

SciTech Connect

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

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

1996-11-29

214

Continental atmospheric circulation over Europe during the Little Ice Age inferred from grape harvest dates  

NASA Astrophysics Data System (ADS)

Estimates of climate conditions before the 19th century are based on proxy data reconstructions or sparse meteorological measurements. The reconstruction of the atmospheric circulation that prevailed during the European Little Ice Age (~1500-1850) has fostered many efforts. This study illustrates a methodology combining historical proxies and modern data sets to obtain detailed information on the atmospheric circulation that prevailed over the North Atlantic region during the Little Ice Age. We use reconstructions of temperature gradients over France based on grape harvest dates to infer the atmospheric circulation. We find that blocking situations were more likely in summer, inducing a continental atmospheric flow. This study advocates that the reconstructions of the past atmospheric circulation should take this regime into account.

Yiou, P.; García de Cortázar-Atauri, I.; Chuine, I.; Daux, V.; Garnier, E.; Viovy, N.; van Leeuwen, C.; Parker, A. K.; Boursiquot, J.-M.

2011-09-01

215

Continental atmospheric circulation over Europe during the Little Ice Age inferred from grape harvest dates  

NASA Astrophysics Data System (ADS)

Estimates of climate conditions before the 19th century are based on proxy data reconstructions or sparse meteorological measurements. The reconstruction of the atmospheric circulation that prevailed during the European Little Ice Age (∼1500-1850) has fostered many efforts. This study illustrates a methodology, combining historical proxies and modern datasets to obtain detailed information on the atmospheric circulation that prevailed over the North Atlantic region during the Little Ice Age. We used reconstructions of temperature gradients over France based on grape harvest dates to infer the atmospheric circulation. We found that blocking situations were more likely in summer, inducing a continental atmospheric flow. This study advocates that the reconstructions of the past atmospheric circulation should take this regime into account.

Yiou, P.; García de Cortázar-Atauri, I.; Chuine, I.; Daux, V.; Garnier, E.; Viovy, N.; van Leeuwen, C.; Parker, A. K.; Boursiquot, J.-M.

2012-03-01

216

Response of Jakobshavn Isbræ, west Greenland, to Little Ice Age climate change  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet (GIS) plays a critical role in the cryosphere’s link with climate change. The recent fluctuations of thickness and velocity of Jakobshavn Isbræ, one of the largest outlet glaciers draining the GIS, indicates that Greenland’s outlet glaciers have the potential to make faster contributions to sea-level rise than previously believed. To evaluate whether ongoing changes in ice flow are climatically significant, ice stream histories must be determined over longer timescales. Although the 35 km retreat of Jakobshavn Isbræ’s calving front since the Little Ice Age (LIA) maximum extent (1850 AD) is well documented, it is does not represent the history of the broader ice margin because the terminus was periodically floating and thus susceptible to subtle perturbations in climate and ocean conditions. Here, we combine a 3D reconstruction of margin retreat from the LIA extent, measured from stereo imagery, with a geologic reconstruction of the timing and magnitude of the advance phase of the ice margin during LIA, to quantify the response of broader Jakobshavn Isbræ ice margin to LIA climate change. We measured the ice sheet margin in 3D from vegetation trimlines marking the LIA ice extent (1850 AD), aerial photographs acquired in 1985, and SPOT satellite images acquired in 2007. The calving front of Jakobshavn Isbræ retreated at an average rate of 0.178 km/yr between the LIA and 1985 (over which time mean annual temperature increased by 2.76°C). The average retreat rate increased to 0.545 km/yr between 1985 and 2007 (mean annual temperature increased 0.23°C). Land based margins north of Jakobshavn Isbræ retreated at an average rate of 0.007 km/yr between 1850 and 1985, and increased to 0.030 km/yr between 1985 and 2007. Alanngorliup Sermia, an outlet glacier ~30 km south of Jakobshavn Isbræ, experienced negligible change between 1850 and 1985, and retreated at an average rate of 0.017 km/yr between 1985 and 2007. We place these post-1850 AD ice margin changes into a longer-term context using sedimentary signatures stored in proglacial threshold lakes. Radiocarbon-dated sediment sequences from three lakes reveal that the land-based ice margin north of Jakobshavn Isbræ has resided near its 1850 extent since 1400-1640 AD. Data from one lake south of Jakobshavn Isbræ suggest that the ice margin has been near its 1850 margin for ~2000 years. Together, these data reveal that the Jakobshavn ice margin responds to climate change on centennial timescales, but varying rates of retreat since 1850 AD highlight the modulation of retreat by dynamic controls. Furthermore, on centennial timescales, the marine terminus of Jakobshavn Isbræ seems to have a significantly larger response than adjacent land-based margins to equal climate forcing.

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

2009-12-01

217

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

Microsoft Academic Search

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

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

2001-01-01

218

Little Ice Age glacial activity in Strathcona Provincial Park, Vancouver Island, British Columbia, Canada  

Microsoft Academic Search

Dendroglaciological and lichenometric techniques are used to establish the Little Ice Age (LIA) history of two glaciers (Colonel Foster and Septimus) in Strathcona Provincial Park, Vancouver Island, British Columbia. Our lichenometric investigations were preceded by the development of a locally calibrated Rhizocarpon geographicum growth curve (1708-1998 A.D.). Documentation of a 3-4-year ecesis interval for both trees and lichen greatly reduces

Dave H. Lewis; Dan J. Smith

2004-01-01

219

Medieval Warm Period, Little Ice Age, and 20th Century Climate Variability From Chesapeake Bay  

Microsoft Academic Search

We investigated late Holocene climate variability during the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century in the Mid-Atlantic region of the U. S. using Marion-Dufresne core MD99-2209 from Chesapeake Bay. Mg\\/Ca ratios in the ostracode Loxoconcha and oxygen and carbon isotopes in the benthic foraminifer Elphidium were used to reconstruct spring\\/early summer temperature (influenced by oceanic

T. M. Cronin; G. S. Dwyer; R. C. Thunell; H. J. Dowsett; E. J. Tappa; C. D. Vann

2001-01-01

220

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

Microsoft Academic Search

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

Peter Molnar; Mark A. Cane

2002-01-01

221

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

Microsoft Academic Search

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

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

2007-01-01

222

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

Microsoft Academic Search

A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan\\u000a formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was\\u000a built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed

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

1999-01-01

223

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

Microsoft Academic Search

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

B. F. Molnia

2001-01-01

224

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

225

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

226

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

227

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

PubMed

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

Prell, W L; Hutson, W H

1979-10-26

228

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

229

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

230

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

231

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

Microsoft Academic Search

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

I. P. Montanez

2007-01-01

232

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

NASA Astrophysics Data System (ADS)

This paper offers three interdependent contributions to studies of climate variation: (1) the recognition and analysis of an intrinsic millennial oceanic oscillation that affects both Northern and Southern high latitude climates, (2) The recognition of an oceanographic switch to ice-free seas west of Greenland that explains the initiation of the Last Ice Age, and (3) an analysis of the effect of increasing salinity in the seas east of Greenland that suggests the possibility of the initiation of an ice age threshold climate in the near future. In the first contribution the millennial oscillation in the flow of the North Atlantic Drift reported by Bond et al. (1997) is proposed to be part of a 1500 yr intrinsic deep ocean oscillation. This oscillation involves the exchange of North Atlantic intermediate-level deep water (NADW) formed in the seas east of Greenland with Antarctic Bottom Water formed in a shallow-water zone at the edge of the Antarctic continent. The concept of NADW formation is already well known, with details of the sinking water flowing out of the Greenland Sea observed by Smethie et al. (2000) using chlorofluorocarbon tracers. The concept of Antarctic Bottom Water formation is also already well established. However, its modulation by the changing fraction of NADW in the Southern Ocean, which I infer from the analysis of Weyl (1968), has not been previously discussed. The modulated lower-salinity Antarctic Bottom Water that reaches the northern North Atlantic then provides negative feedback for the cyclic variation of NADW formation as proposed here. This causes the 1500 yr bipolar oscillation. The feedback suggests the possible sinusoidal character of the proposed oscillation model. The model is consistent with the cooling of the Little Ice Age (Lamb, 1972, 1995), and it also correctly predicts NASA's observation of today's record maximum area of winter sea ice on the Southern Ocean and the present observed record low rate of Antarctic Bottom Water production cited by Broecker (2000). The sinusoidal form of this conceptual model is therefore reinforced by both old and new data, and provides insights into world-wide climate change. The second contribution of this paper is a hypothesis for the initiation of Pleistocene ice ages, typified by the Last Ice Age that began 120 000 yr BP. Instead of the classical Northern high-latitude summer cooling caused by orbital precession and changes in Earth's axis inclination, this hypothesis proposes the sudden onset of year-round ice-free seas west of Greenland, with greatly increased precipitation in the ice sheet nucleation regions of Baffin Island, northern Quebec, and Labrador. Devon Island ice-core studies by Koerner at al. (1988) and deep-sea sediment data reported by Fillon (1985) support the concept of ice-free seas west of Greenland and imply the initial meteorological conditions that are proposed here. These conditions are consistent with the heavy precipitation inferred by Adkins et al. (1997) from deep-sea sediment data. The changes in northeastern Canada were accompanied by quite cold conditions in northern Europe, inferred by Field et al. (1994) from tree pollen data. The European cooling was probably caused by loss of the recurring Iceland low-pressure system due to the dominant effect of a frequent stronger low-pressure system over the Labrador Sea, as postulated in this paper. The key to ice-free seas west of Greenland is the loss of the near-surface stratification that normally enables sea ice to freeze. Using the high-resolution European Space Agency's ENVISAT system, I have monitored the flows through the Nares Strait and found that the dominant southward flow of lower density polar water into Baffin Bay correlated with the growing area of seasonal sea ice forming early in the winter in the Bay near the southern end of the Strait. This implies that low-salinity polar water was the cause of the stratification. A search for the cause of the stratification loss then became a search for the cause of the loss of the southward flow of polar water. The los

Johnson, R. G.

2014-05-01

233

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

234

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

235

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

236

Polyphase glacigenic deformation in the Waterloo Moraine, Kitchener, Ontario, Canada  

Microsoft Academic Search

A sedimentological investigation of Quaternary sediments in the Waterloo Moraine was conducted to characterize the nature of deformation in stratified sediments in the Kieswetter Holdings Ltd. aggregate quarry, Kitchener, Ontario. Highly deformed interbedded clay, silt, fine- to very coarse-grained sand and granular to cobble gravel is exposed in two sets of contiguous panels. Analysis of the sediment revealed five recognizable

Laura Weaver; Emmanuelle Arnaud

2011-01-01

237

Bibliographic Instruction at Moraine Valley Community College: A Position Paper.  

ERIC Educational Resources Information Center

This paper presents a plan for implementing bibliographic instruction at Moraine Valley Community College in Palos Hills, Illinois. The definition and purpose of bibliographic instruction are reviewed, educational strategies in bibliographic instruction are discussed, and an implementation proposal is presented. The proposal describes three phases…

Miller, Larry A.; And Others

238

Deep Ocean Circulation Changes During the Transition to the Last Ice Age  

NASA Astrophysics Data System (ADS)

The transition between marine isotope stages (MIS) 5a and 4 appears in the stacked benthic foraminferal ? 18O SPECMAP record as a gradual increase in ice volume. In contrast, the transition occurs in the Greenland ice core ? 18O records with two well-developed interstadial events (I19 and I20), which are the first Dansgaard-Oescheger events of the last ice age. The MIS 5b/5a transition appears as a much more rapid warming in both the Greenland ice and benthic ? 18O records. Recent work (Lehmann et al. 2002, Chapman et al. 1999) indicates that climate variability in MIS 5 as indicated in the Greenland ice record was closely interconnected with iceberg discharges, surface temperature changes, and deep ocean circulation in the North Atlantic. In order to determine the response of deep ocean circulation to climate changes from late in MIS 5 to full glacial MIS 4, we have measured Nd isotope ratios from the Fe-Mn portion of core TNO57-21 from the Cape Basin in the South Atlantic. Nd isotopes, unlike nutrient water mass proxies, are not affected by biological fractionation, and reflect the strength of the North Atlantic Deep Water (NADW) signal in the seawater above the core site. Results from cores TNO57-21 and RC11-83 (also from the Cape Basin) indicate that the NADW export to the Southern Ocean has varied on time scales reflecting glacial-interglacial cycles through MIS 4 (Rutberg et al. 2000) and during interstadial events through MIS 3 (Piotrowski et al. Fall AGU), and was stronger and weaker during warmer and colder Northern Hemisphere climate intervals, respectively. The extension of the Nd isotope record to MIS 5a and 5b indicates an increased NADW signal during MIS 5, therefore the long-term pattern of strong and weak NADW export during warm and cold periods persists beyond the last ice age. The Nd isotope pattern during MIS 4 through 5b generally corresponds to the benthic foraminferal ? 13C record from Cape Basin cores (Ninnemann et al. 1999), indicating that the pattern of the carbon isotope record also generally reflects ocean circulation changes. Over the transition to the last ice age (MIS 5a to 4) the NADW signal rapidly decreases toward LGM levels, and displays a smaller decrease between the MIS 5b and 5a peaks. However, during MIS 4 the NADW signal is stronger than during the LGM, and during the MIS 5a and 5b peaks it is weaker than during the Holocene. There is a larger degree of millennial-scale variability in THC intensity during MIS 5a than MIS 4, a pattern that is also observed in MIS 3 and 2, respectively (Piotrowski et al. Fall AGU). The sharp decrease in NADW intensity over the MIS 5a/4 transition appears to correspond to the end of interstadial 19 at ˜70 ka, in contrast with the gradual increase in ice volume, which approached its maximum at that time. This may indicate that the system reached a threshold that forced a rapid change to a different ocean circulation mode.

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

2003-12-01

239

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.

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

2013-01-01

240

10Be Dating of the Last Retreat of the Southern Margin of the Scandinavian Ice Sheet: Preliminary Results  

Microsoft Academic Search

Prominent moraines crossing the Baltic region mark the late Pleistocene maximum extent and recessional phases of the southern margin of the Late Pleistocene Scandinavian Ice Sheet (SIS). The presence of five main moraines between the advance during the Last Glacial Maximum (LGM) and the Younger-Dryas Salpausselkä Moraines in southern Finland dated at 11.6 \\\\pm 0.5 10Be ka suggest a strong

V. R. Rinterknecht; P. U. Clark; G. M. Raisbeck; F. Yiou; A. Bitinas; L. Marks; V. Zelcs

2001-01-01

241

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

242

Influence of the Little Ice Age on the biological structure of lakes in South West Greenland  

NASA Astrophysics Data System (ADS)

Arctic lakes are considered to be particularly sensitive to environmental change, with biological remains in lake sediment records being interpreted as reflecting climate forcing. However the influence that differences in catchment properties and lake morphometries have on the sedimentary record is rarely considered. We investigated sediment cores from three lakes located close to the inland ice sheet margin in the Kangerlussuaq area of South West Greenland but within a few kilometres of one another. This regional replication allowed for direct comparisons of biological change in lakes exposed to identical environmental pressures (cooling, increased wind speeds) over the past c.2000 years. Sedimentary pigments were used as a proxy for whole-lake production and to investigate differences in phytoplankton community structure whilst fossil diatom assemblages were studied to determine differences in ecological responses during this time. We noted several major effects of the Little Ice Age cooling (LIA, c. 1400-1850AD). The organic content of sediments in all three lakes declined, and this effect was most pronounced in lakes closest to the inland ice sheet margin, which suggests that aeolian inputs derived from the glacial outwash plains (sandurs), and wind-scouring of the thin catchment soils by strong katabatic winds associated with the regional cooling might have both contributed to this sedimentary change. During the LIA total algal production (as indicated by chlorophyll and carotenoid pigments) was lower in all three lakes, most likely because of extended ice-cover and shorter growing seasons, and the ratio of planktonic: benthic diatom taxa increased, possibly because of lower light availability or fertilization from loess material. Despite this coherence in lake response to the LIA, diatom community composition changes in individual lakes differed, reflecting individual lake morphometry and catchment characteristics. These findings highlight the importance of regionally-replicated palaeo-studies when interpreting ecological impacts of long-term climate variability, and in assessing likely future response to climate change.

McGowan, S.; Hogan, E. J.; Jones, V.; Anderson, N. J.; Simpson, G.

2013-12-01

243

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

SciTech Connect

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

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

1994-05-01

244

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

245

On the effects of anisotropic rheology on ice flow, internal structure, and the age-depth relationship at ice divides  

Microsoft Academic Search

We use numerical modeling with a full-system Stokes solver to elucidate the effects of nonlinear rheology and strain-induced anisotropy on ice flow at ice divides. We find that anisotropic rheology profoundly affects the shape of both isochrone layering and surface topography. Anisotropic effects cause the formation of a downward curving fold, i.e., a syncline, in isochrones in the lower central

Carlos Martín; G. Hilmar Gudmundsson; Hamish D. Pritchard; Olivier Gagliardini

2009-01-01

246

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

247

Geomorphic relations among glacial Lake Algonquin and the Munising and Grand Marais moraines in eastern Upper Michigan, USA  

NASA Astrophysics Data System (ADS)

Data obtained from ground-penetrating radar (GPR), optically stimulated luminescence (OSL) dating, and geostatistical reconstructions of Lake Algonquin water planes indicate that high-standing outwash aprons flanking the Munising moraine's southern margin in eastern Upper Michigan terminate as large, coalescing Gilbert-type ice-contact deltas graded to the Main level of Lake Algonquin. Nearly 30 km of GPR imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition. Landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation. In time, these deltas aggraded to the Main Lake Algonquin level as the ice margin stabilized. An OSL date of 12.5 ± 1.1 ka on a nearby beach ridge associated with the Main Algonquin shoreline is consistent with this interpretation. These new data, coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta, indicate that Lake Algonquin was falling as delta deposition waned, eventually reaching a level concordant with the Lower Orillia level before final abandonment. Large, regionally extensive heads of outwash marking the crest of the Munising moraine are graded to the upper margins of these deltas and, by inference, must also correlate with Main Lake Algonquin and the associated Two Rivers deglaciation ca. 13-12.5 ka. The deltas, in turn, are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group Lake Algonquin shoreline. Because these aforementioned heads of outwash, part of Drexler and others' Grand Marais moraine, correlate with the Marquette moraine farther west, they likely date to the Marquette advance ca. 11.5 ka. Thus, landforms related to Two Rivers and to Marquette glaciations appear to comingle across the study area. In the absence of extensive exposures and datable materials, our work highlights the fact that crosscutting relationships and distinct differences in base level can provide an important first step for untangling the complicated landform relationships in this part of Michigan.

Blewett, William L.; Drzyzga, Scott A.; Sherrod, Laura; Wang, Hong

2014-08-01

248

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

249

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 uppermost valley areas is sub-arctic oceanic and the lithology consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. The Little Ice Age glacier advance affected parts of the valleys with the maximum glacier extent around AD 1750. In this study five sites on moraine and colluvium materials were selected to examine the main soil properties to assess if soil profile characteristics and pattern of fallout radionuclides (FRNs) and environmental radionuclides (ERNs) are affected by different stages of ice retreat. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. The sampled soils on the colluviums outside the LIA glacier limit became ice-free during the Preboral. The Regosols present better-developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Significant lower mass activities of FRNs are found in soils on the moraines than on colluviums. Variations of ERNs activities in the valleys are related to characteristics soil mineralogical composition. These results indicate differences in soil development that are consistent with the age of ice retreat. In addition, the pattern distribution of 137Cs and 210Pbex activities differs in the soils related to the LIA glacier limits in the drainage basins.

Navas, A.; Laute, K.; Beylich, A. A.; Gaspar, L.

2014-01-01

250

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 were formed after deglaciation. The climate in the uppermost valley areas is sub-arctic oceanic, and the lithology consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. The Little Ice Age glacier advance affected parts of the valleys with the maximum glacier extent around AD 1750. In this study five sites on moraine and colluvium materials were selected to examine main soil properties, grain size distribution, soil organic carbon and pH to assess if soil profile characteristics and patterns of fallout radionuclides (FRNs) and environmental radionuclides (ERNs) are affected by different stages of ice retreat. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. The sampled soils on the colluviums outside the LIA glacier limit became ice-free during the Preboral. The Regosols present better-developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Significantly lower mass activities of FRNs were found in soils on the moraines than on colluviums. Variations of ERN activities in the valleys were related to characteristics of soil mineralogical composition. These results indicate differences in soil development that are consistent with the age of ice retreat. In addition, the pattern distribution of 137Cs and 210Pbex activities differs in the soils related to the LIA glacier limits in the drainage basins.

Navas, A.; Laute, K.; Beylich, A. A.; Gaspar, L.

2014-06-01

251

Revised Deglacial Chronology of the Laurentide Ice Sheet and Implications for Catastrophic Meltwater Discharge as Triggers for Abrupt Climate Change  

NASA Astrophysics Data System (ADS)

A current hypothesis suggests that the Younger Dryas climate change involves the sudden release of stored meltwater from glacial Lake Agassiz. However, such a trigger requires a specific flood chronology and volume. Because the retreat patterns of the Laurentide Ice Sheet control meltwater routing, timing, and volume, it is useful to assess whether the current retreat chronologies support meltwater release from Lake Agassiz immediately preceding the Younger Dryas. Specifically, we reexamine ice margin retreat from proposed outlet areas on the sub-continental divide through which Agassiz meltwater flowed. These outlet areas are the first gates any meltwater must have flowed through before reaching the ocean. In these two gate areas: Fort McMurray, Alberta (proposed northwest outlet), and Thunder Bay, Ontario (proposed eastern outlet), our geomorphic analysis of glacial landforms suggest a more complex deglaciation pattern than previously reconstructed. New radiocarbon analyses indicate that ice recession occurred up to 1000 14C yr later than previously thought. At least four distinct moraine sets around Fort McMurray record downslope ice margin recession that prevented ice-dammed meltwater from draining northward to the Arctic Ocean. These moraines are provisionally assigned ages of 10,460; 9,850; 9,660; and 9,510 14C yr, and the large Clearwater-lower Athabasca spillway cross-cuts the three oldest moraines. This relationship implies that the ice dam held until at least 9,660 14C yr, after which dam failure, lake drainage and any northwest drainage from Lake Agassiz across this divide occurred. Many long linear moraines southwest of Thunder Bay record deglaciation across the uplands of the Gunflint range from 12,000 until 10,550 14C yr. West of Thunder Bay in the lowlands north of the Gunflint range, along which the oldest eastern outlet into the Lake Superior basin is proposed, was not deglaciated until about 10,400 14C yr. Moreover, with continued ice recession, glaciolacustrine sediment records a widespread, ponded water body over the divide region until 10,100 14C yr. These new, younger deglacial chronologies from the proposed northwestern and eastern outlet regions do not support the hypothesis that meltwater from glacial Lake Agassiz triggered the Younger Dryas. Therefore as the evidence for a younger Lake Agassiz concomitant with a younger deglacial chronology continues to mount, it may be prudent to search elsewhere for a cause for the Younger Dryas.

Lowell, T. V.; Fisher, T. G.; Hajdas, I.

2005-12-01

252

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

253

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

254

Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record  

NASA Astrophysics Data System (ADS)

The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one 'flowsets' comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset cross-cutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative 'age-stack' of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset - its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, 'smudged' landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories. The flowsets and their palaeo-glaciological significance that we derive for Ireland provide a regional framework and context for interpreting results from local scale fieldwork, provide major flow events for testing numerical ice sheet models, and underpin a data-driven reconstruction of the Irish Ice Sheet that we present in an accompanying paper - Part 2.

Greenwood, Sarah L.; Clark, Chris D.

2009-12-01

255

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

256

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

257

A new Little Ice Age chronology of the Franz Josef Glacier, New Zealand  

NASA Astrophysics Data System (ADS)

The Little Ice Age (LIA) chronology of the Franz Josef Glacier (FJG), New Zealand, was reassessed due to previous uncertainty surrounding the timing of its maximum extent, eg. 1450 (Burrows 1990), 1600 (Wardle 1973) or 1750 AD (Lawrence and Lawrence 1965). Tree age-size relationships based on data from 75 ring counts and diameters collected from southern rata (Metrosideros umbellata) and kamahi (Weinmannia racemosa) allowed the ages of 1340 trees measured within fifty, 150 m2 quadrats in the Waiho Valley to be predicted. Ages of the oldest trees were then used to determine the time elapsed since deglaciation, or alternatively, the culmination of the preceding advance. The revised chronology showed that the LIA maximum of the FJG culminated by c. 1470-1530 AD, when the terminus was located approximately 4.5 km down-valley of its position in 2001. Subsequent, but smaller magnitude, re-advances culminated by c. 1580-1610 and c. 1790-1840 AD. Average terminus retreat rates after the LIA maximum varied between 7-9 m a-1 and reached 23 m a-1 by the early to mid-1800's, which suggests that climatic amelioration signalling the end of the LIA occurred in New Zealand by the early 19th Century.

McKinzey, K. M.; Lawson, W.; Kelly, D.

2003-04-01

258

Surface changes in the eastern Labrador Sea around the onset of the Little Ice Age  

NASA Astrophysics Data System (ADS)

the relative climate stability of the present interglacial, it has been punctuated by several centennial-scale climatic oscillations; the latest of which are often colloquially referred to as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA). The most favored explanation for the cause of these anomalies is that they were triggered by variability in solar irradiance and/or volcanic activity and amplified by ocean-atmosphere-sea ice feedbacks. As such, changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) are widely believed to have been involved in the amplification of such climatic oscillations. The Labrador Sea is a key area of deep water formation. The waters produced here contribute approximately one third of the volume transport of the deep limb of the AMOC and drive changes in the North Atlantic surface hydrography and subpolar gyre circulation. In this study, we present multiproxy reconstructions from a high-resolution marine sediment core located south of Greenland that suggest an increase in the influence of polar waters reaching the Labrador Sea close to MCA-LIA transition. Changes in freshwater forcing may have reduced the formation of Labrador Sea Water and contributed toward the onset of the LIA cooling.

Moffa-Sánchez, Paola; Hall, Ian R.; Barker, Stephen; Thornalley, David J. R.; Yashayaev, Igor

2014-03-01

259

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

USGS Publications Warehouse

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

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

2008-01-01

260

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

261

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

262

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.

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

2014-01-01

263

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

264

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

265

Deglaciation ages and meltwater routing in the Fort McMurray region, northeastern Alberta and northwestern Saskatchewan, Canada  

NASA Astrophysics Data System (ADS)

A field-based reconstruction of the deglacial paleogeography in the Fort McMurray area permits: 1) constraining the timing of meltwater routing to the Arctic from the present Hudson Bay drainage basin; and 2) minimum-age estimates for ice-margin positions that can be used to constrain ice-sheet modeling results. A downslope recession of the Laurentide Ice Sheet resulted in a series of proglacial lakes forming between the ice margin and higher land to the southwest. The paleogeography of these lakes is poorly constrained in part from the masking effect of boreal forest vegetation and map-scale issues. However, recent space-shuttle based DEMs increase the number and spatial extent of moraines identified within the study area resulting in a coherent pattern of ice margin retreat focused on the Athabasca River valley. An intensive lake-coring program resulted in a minimum ten-fold increase in the radiocarbon database used to limit moraine ages. Results indicate that deglaciation in this region was younger than previously reported, and it is likely that the meltwater could not drain northward to the Arctic Ocean from any source southeast of the Fort McMurray area until approximately 9850-9660 14C BP.

Fisher, Timothy G.; Waterson, Nickolas; Lowell, Thomas V.; Hajdas, Irka

2009-08-01

266

Organic Remains from the Istorvet Ice Cap, Liverpool Land, East Greenland: A Record of Late Holocene Climate Change  

NASA Astrophysics Data System (ADS)

Radiocarbon dates of emergent organic remains along the western margin of Istorvet ice cap (70.8°N, 22.2°W) indicate a time when the ice cap was smaller than at present. This ice cap, similar to others in east Greenland, exhibits "historic" moraines ~1-2 km in front of the presently retreating ice margins. At Istorvet, ice margin retreat has exposed a thin (~8 cm) organic horizon and in situ plant remains in bedrock cracks lie less than 10 m away from the present ice margin (453 m asl in 2006). Clusters of multi-species vegetation also were found on two nuntaks (to 719 m asl) located ~3 km from the historic drift limit. All organic remains were located in protected bedrock lees. On the west side of the ice-cap, vegetation is sparse but present at elevations near the ice margin. Both the ice cap geometry and the presence of overrun organic remains indicate past temperatures at least as warm as those at present. At Istorvet plant remains yielded 12 number of radiocarbon dates. These ages, when converted to calendar years, range from A.D. 400 to 1014, with the largest concentration from A.D. 800 to 1014. This work hones the conclusion of Funder (1978) who reported general climate deterioration since 800 BC. Moreover, it indicates warm conditons at this latitude at the time of Norse colonization of Greenland.

Lowell, T. V.; Kelly, M. A.; Hall, B.; Smith, C. A.; Garhart, K.; Travis, S.; Denton, G. H.

2007-12-01

267

Varve and radiocarbon dating support the rapid advance of Jakobshavn Isbræ during the Little Ice Age  

Microsoft Academic Search

Large outlet glaciers draining the Greenland Ice Sheet significantly influence overall ice sheet mass balance. Considerable short term (years to decades) retreat and fluctuations in velocity of Jakobshavn Isbræ, western Greenland, illustrate the complex nature by which large outlet glaciers respond to climate change, making predictions of future ice sheet change challenging. To provide a longer-term view (centuries), we investigate

J. P. Briner; N. E. Young; E. K. Thomas; H. A. M. Stewart; S. Losee; S. Truex

2011-01-01

268

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

269

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

Microsoft Academic Search

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

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

2010-01-01

270

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

Microsoft Academic Search

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

Barry Saltzman; Kirk A. Maasch

1988-01-01

271

Fluctuations in Tree Ring Cellulose d18O during the Little Ice Age Correlate with Solar Activity  

Microsoft Academic Search

The Maunder Minimum (AD1645-1715), when sunspots became exceedingly rare, is known to coincide with the coldest period during the Little Ice Age. This is a useful period to investigate possible linkage between solar activity and climate because variation in solar activity was different from that of today. The solar cycle length was longer (14 and 28 years) than that of

Y. T. Yamaguchi; Y. Yokoyama; H. Miyahara; T. Nakatsuka

2008-01-01

272

Stable isotope and sea-level data from New Guinea supports Antarctic ice-surge theory of ice ages  

Microsoft Academic Search

Two theories of glaciation have received considerable attention, the Milankovitch orbital theory1,2 in which climatic change is ascribed to latitude-dependent variations in solar radiation that accompany changes in the Earth's orbital parameters, and the Antarctic surge hypothesis3-6, in which a large Antarctic ice sheet `surges' into the Southern Ocean thereby increasing the Earth's albedo, and the resultant cooling triggers the

Paul Aharon; John Chappell; William Compston

1980-01-01

273

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

274

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

275

Glacier changes since Local Last Glacial Maximum in the South-West slope of Nevado Hualcán, Cordillera Blanca, Peru, deduced from moraine mapping and GIS-based analysis  

NASA Astrophysics Data System (ADS)

Anticipating and assessing hazards and risks associated with the shrinking of surface and subsurface ice in cold mountain chains is facilitated by empirical-quantitative data on present and past rates of change, as well as by a general understanding of related landforms and landscape evolution through time. Rock/ice avalanches and devastating outburst floods from glacial lakes indeed constitute a major cause of severe damage in populated mountain areas such as the Cordillera Blanca whose combination of tectonic, topographic and glaciological characteristics make it a threatened region. This study focuses on the Río Chucchún catchment above the city of Carhuaz, which was recently affected by a flood/debris flow from a rock/ice avalanche impacting a recently grown lake (Laguna 513). Traces left by past glaciations strongly affect the current geomorphodinamic behaviour of the catchment. For instance, a prominent sediment-filled glacial overdeepening behind Younger Dryas (YD) moraines (Pampa de Shonquil) with its retention function strongly influenced the chain of processes initiated by the outburst of Laguna 513. The aim of this study is to reconstruct earlier glacial phases in the SW slope of Nevado Hualcán (Río Chucchún catchment), in order to compile quantitative information on surface areas and Equilibrium Line Altitudes (ELAs). To do so, glacier stages were assigned to five different glacial phases, through photointerpretation and moraine cartography: 2003; 1962; Hualcán-I-LIA (15th to 18th centuries); Hualcán-II-YD (~12,5 ka BP); and Hualcán-III-LLGM (~34 to 21 ka BP). Glacial stages Hualcán-I-LIA, Hualcán-II-YD and Hualcán-III-LLGM present relative dating based on previous studies from different authors in the Peruvian Andes. Once glaciers were delimited, their surface areas and Equilibrium Line Altitudes (ELAs) were calculated. For ELA estimation three different methods were used: the mid-range elevation, the Accumulation Area Ratio (AAR), and the Area x Altitude Balance Ratio (AABR). The results show a decrease in surface area with respect to Hualcán-III-LLGM of 16% for Hualcán-II-YD; 50% for Hualcán-I-LIA; and 74% for 2003. With respect to 2003, ELAs shifted ~520 m since the Local Last Glacial Maximum (LLGM), ~470 m since a marked late-glacial stage (YD?), ~130 m since the Little Ice Age (LIA) and about ~100 m since 1962. If the changes are exclusively attributed to temperature effects, warming since LLGM can be estimated at some 3°C and since the maximum glacier extent of LIA at about 0.8°C. Such values are rather close to mean global temperature change during the corresponding intervals. Most of the ELA shift since LIA appears to have taken place during recent decades characterized by very rapid glacier shrinkage, although air temperature does not seem to have risen considerably during the last 30 years. These results along with other environmental and social approaches will contribute to a better understanding of impacts from climate change and glacier shrinkage in order to develop adaptation, mitigation and disaster risk reduction strategies in the Peruvian Andes.

Giráldez, Claudia; Palacios, David; Haeberli, Wilfried; Úbeda, Jose; Schauwecker, Simone; Torres, Judith

2014-05-01

276

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

277

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

278

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

279

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

280

Simple energy balance model resolving the seasons and the continents - Application to the astronomical theory of the ice ages  

NASA Technical Reports Server (NTRS)

An analysis is undertaken of the properties of a one-level seasonal energy balance climate model having explicit, two-dimensional land-sea geography, where land and sea surfaces are strictly distinguished by the local thermal inertia employed and transport is governed by a smooth, latitude-dependent diffusion mechanism. Solutions of the seasonal cycle for the cases of both ice feedback exclusion and inclusion yield good agreements with real data, using minimal turning of the adjustable parameters. Discontinuous icecap growth is noted for both a solar constant that is lower by a few percent and a change of orbital elements to favor cool Northern Hemisphere summers. This discontinuous sensitivity is discussed in the context of the Milankovitch theory of the ice ages, and the associated branch structure is shown to be analogous to the 'small ice cap' instability of simpler models.

North, G. R.; Short, D. A.; Mengel, J. G.

1983-01-01

281

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

282

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

283

Late Weichselian local ice dome configuration and chronology in Northwestern Svalbard: early thinning, late retreat  

NASA Astrophysics Data System (ADS)

The chronology and configuration of the Svalbard Barents Sea Ice Sheet (SBSIS) during the Late Weichselian (LW) are based on few and geographically scattered data. Thus, the timing and configuration of the SBSIS has been a subject of extensive debate. We present provenance data of erratic boulders and cosmogenic 10Be ages of bedrock and boulders from Northwest Spitsbergen (NWS), Svalbard to determine the thickness, configuration and chronology during the LW. We sampled bedrock and boulders of mountain summits and summit slopes, along with erratic boulders from coastal locations around NWS. We suggest that a local ice dome over central NWS during LW drained radially in all directions. Provenance data from erratic boulders from northern coastal lowland Reinsdyrflya suggest northeastward ice flow through Liefdefjorden. 10Be ages of high-elevation erratic boulders in central NWS (687-836 m above sea level) ranging from 18.3 ± 1.3 ka to 21.7 ± 1.4 ka, indicate that the centre of a local ice dome was at least 300 m thicker than at present. 10Be ages of all high-elevation erratics (>400 m above sea level, central and coastal locations) indicate the onset of ice dome thinning at 25-20 ka. 10Be ages from erratic boulders on Reinsdyrflya ranging from 11.1 ± 0.8 ka to 21.4 ± 1.7 ka, indicate an ice cover over the entire Reinsdyrflya during LW and a complete deglaciation prior to the Holocene, but apparently later than the thinning in the mountains. Lack of moraine deposits, but the preservation of beach terraces, suggest that the ice covering this peninsula possibly was cold-based and that Reinsdyrflya was part of an inter ice-stream area covered by slow-flowing ice, as opposed to the adjacent fjord, which possibly was filled by a fast-flowing ice stream. Despite the early thinning of the ice sheet (25-20 ka) we find a later timing of deglaciation of the fjords and the distal lowlands. Several bedrock samples (10Be) from vertical transects in the central mountains of NWS pre-date the LW, and suggest either ice free or pervasive cold-based ice conditions. Our reconstruction is aligned with the previously suggested hypothesis that a complex multi-dome ice-sheet-configuration occupied Svalbard and the Barents Sea during LW, with numerous drainage basins feeding fast ice streams, separated by slow flowing, possibly cold-based, inter ice-stream areas.

Gjermundsen, Endre F.; Briner, Jason P.; Akçar, Naki; Salvigsen, Otto; Kubik, Peter; Gantert, Niklas; Hormes, Anne

2013-07-01

284

Tracing the effects of the Little Ice Age in the tropical lowlands of eastern Mesoamerica  

PubMed Central

The causes of late-Holocene centennial to millennial scale climatic variability and the impact that such variability had on tropical ecosystems are still poorly understood. Here, we present a high-resolution, multiproxy record from lowland eastern Mesoamerica, studied to reconstruct climate and vegetation history during the last 2,000 years, in particular to evaluate the response of tropical vegetation to the cooling event of the Little Ice Age (LIA). Our data provide evidence that the densest tropical forest cover and the deepest lake of the last two millennia were coeval with the LIA, with two deep lake phases that follow the Spörer and Maunder minima in solar activity. The high tropical pollen accumulation rates limit LIA's winter cooling to a maximum of 2°C. Tropical vegetation expansion during the LIA is best explained by a reduction in the extent of the dry season as a consequence of increased meridional flow leading to higher winter precipitation. These results highlight the importance of seasonal responses to climatic variability, a factor that could be of relevance when evaluating the impact of recent climate change.

del Socorro Lozano-Garcia, Ma.; Caballero, Margarita; Ortega, Beatriz; Rodriguez, Alejandro; Sosa, Susana

2007-01-01

285

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.

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

2007-01-01

286

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

287

From Shakespeare to Defoe: malaria in England in the Little Ice Age.  

PubMed Central

Present global temperatures are in a warming phase that began 200 to 300 years ago. Some climate models suggest that human activities may have exacerbated this phase by raising the atmospheric concentration of carbon dioxide and other greenhouse gases. Discussions of the potential effects of the weather include predictions that malaria will emerge from the tropics and become established in Europe and North America. The complex ecology and transmission dynamics of the disease, as well as accounts of its early history, refute such predictions. Until the second half of the 20th century, malaria was endemic and widespread in many temperate regions, with major epidemics as far north as the Arctic Circle. From 1564 to the 1730s the coldest period of the Little Ice Age malaria was an important cause of illness and death in several parts of England. Transmission began to decline only in the 19th century, when the present warming trend was well under way. The history of the disease in England underscores the role of factors other than temperature in malaria transmission.

Reiter, P.

2000-01-01

288

Banded corals: changes in oceanic carbon-14 during the little ice age.  

PubMed

Radiocarbon analyses and stable isotope measurements are presented foro recent cores of banded corals from the Florida Straits. These values provide a record of variations in the ratio of carbon-14 to carbon-12 in the dissolved inorganic carbon in the surface waters of the Gulf Stream from A.D. 1642 to 1800. An increase in the carbon-14/carbon-12 ratio of 7 per mil for coral growth during the early 1700's was most likely induced by an increase in the carbon-14/carbon-12 ratio of 20 per mil in the atmospheric carbon dioxide that occurred at about 1700. The ratios of oxygen 18 to oxygen-16 in these coral bands show a small decrease of a water temperature ( approximately 1 degrees C) during the latter part of the Little Ice Age (1700 to 1725). These results support the hypothesis that the increase in atmospheric carbon-14 at about 1700, and possibly the temperature change as well, was caused by a decrease in solar activity (Maunder sunspot minimum). PMID:17776697

Druffel, E M

1982-10-01

289

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.

Hooghiemstra, Henry; Van der Hammen, Thomas

2004-01-01

290

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

291

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

292

Response of Jakobshavn Isbræ, west Greenland, to Little Ice Age climate change  

Microsoft Academic Search

The Greenland Ice Sheet (GIS) plays a critical role in the cryosphere's link with climate change. The recent fluctuations of thickness and velocity of Jakobshavn Isbræ, one of the largest outlet glaciers draining the GIS, indicates that Greenland's outlet glaciers have the potential to make faster contributions to sea-level rise than previously believed. To evaluate whether ongoing changes in ice

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

2009-01-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

294

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

295

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

Microsoft Academic Search

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

Jan Sedlácek; Lawrence A. Mysak

2009-01-01

296

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

NASA Astrophysics Data System (ADS)

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

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

2005-10-01

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  

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

298

A comparison of age-depth scales derived from shallow ice cores and an FMCW radar in West Antarctica  

NASA Astrophysics Data System (ADS)

The Satellite Era Accumulation Traverse (SEAT) collected near-surface firn cores and Ultra High Frequency (UHF) Frequency Modulated Continuous Wave (FMCW) radar data across the West Antarctic Ice Sheet (WAIS) divide in 2010. Five firn cores were collected with average accumulation rates ranging from approximately 200 to 275 mm of water equivalent per year. Age-depth scales for each core were developed using the seasonal signals of the ?18O and ?D records. ECM and density profiles were used to refine sections of the age-depth scale where the isotopic seasonal cycles were noisy or unclear. Age-depth scales were determined from the radar data by picking spatially continuous (approximately 1 km) layers in the radar echograms at the core sites. The continuous radar layers were assumed annual and dated. This study used data from the Ku-band Radar developed by the University of Kansas' Center for Remote Sensing of Ice Sheets operating between the frequencies of 12.5 GHz to 15.132 GHz, giving a vertical resolution of approximately 4.5 cm in the firn. Radar travel time was converted to depth using 2 cm density data from the ice core. A comparison of the core and radar derived age-depth scales shows that at higher accumulation sites the independent age-depth scales agree relatively well with maximum errors of up to +/-3 years in a given year. At lower accumulation sites dating errors from the radar age-depth scale are larger which is attributed to the difficulty in distinguishing annual layers from sub-annual peaks in density in the radar echogram.

Koenig, L.; Onana, V.; Forster, R. R.; Miege, C.; Rupper, S.; Burgener, L. K.; Patel, A. E.; MacGregor, J. A.

2012-12-01

299

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

300

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

301

Coupled climate modelling of ocean circulation changes during ice age inception  

Microsoft Academic Search

Freshening of high latitude surface waters can change the large-scale oceanic transport of heat and salt. Consequently, atmospheric and sea ice perturbations over the deep water production sites excite a large-scale response establishing an oceanic \\

K. J. Meissner; R. Gerdes

2002-01-01

302

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

303

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

304

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

305

Terrestrial Kr-81-Kr ages of Antarctic meteorites  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

306

Internal oscillations of the thermohaline circulation and the Dansgaard-Oeschger events of the last ice age  

NASA Astrophysics Data System (ADS)

The Dansgaard-Oeschger (DO) climatic oscillations of the last ice age are a prime example of abrupt climate change in the paleoclimate record, clearly evidencing that large and extremely rapid climate fluctuations have repeatedly happened in the recent past. In spite of their obvious relevance to the assessment of plausible ranges of present and future natural climate variability, the cause(s) of abrupt climate change are not completely understood, although there is wide agreement that a likely driver may involve changes in the strength of the Atlantic thermohaline circulation (THC). Here we use a 3D coupled global atmosphere-ocean- sea-ice model of intermediate complexity (ECBilt-Clio) to study the natural variability of the THC and associated climate changes in the North Atlantic. Under boundary conditions appropriate for the ice age the model simulations produce a large amplitude, DO-like oscillation that switches chaotically (i.e., at random times), between two quasi-stationary states of the THC. Without varying external forcing, the DO-like oscillation, we argue, is an internally driven, self-sustained, nonlinear free oscillation of the THC caused by energy imbalance between the advection of cold water and the diffusion of heat by vertical turbulent mixing in the high latitude deep ocean. The transition between the two states is a rapid, threshold-dependent process involving convective instability Sea ice advances and retreats correlate with the THC fluctuations and plausibly contribute to intensifying the abruptness and regional influence of the simulated DO oscillations. These simulation results are robust over a wide range of boundary conditions, and thus the chance that the actual DO oscillations are powered by a similar mechanism to that driving the modeled DO may be significant.

Yang, M.; Rial, J. A.

2006-12-01

307

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

308

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.

2014-05-01

309

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

310

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

311

Ice velocities near the terminus of the Matanuska Glacier, Alaska, during an unseasonably warm melt season  

Microsoft Academic Search

Horizontal ice motion in the western terminus region of the Matanuska Glacier, AK, was tracked over an 18-day period during June-July 2004. The movement of 23 stakes anchored into the ice was monitored using total station surveying equipment, which was set up over a temporary benchmark on an end moraine. The summer of 2004 was unique in that there was

Monica Z. Bruckner

312

Modeling the ice age: the finite-element method in glaciology  

Microsoft Academic Search

To comprehend the Earth's climatic system we develop more and more complex models of its atmosphere, hydrosphere, cryosphere (the icy regions), and even biosphere to understand the interactions that control climate. Ice sheet modeling is tied intrinsically to the understanding of past and future climatic change. Many climate models behave well in recreating present conditions, but we must test them

J. L. Fastook

1994-01-01

313

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

Microsoft Academic Search

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

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

2010-01-01

314

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

Microsoft Academic Search

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

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

2008-01-01

315

A volcanically triggered regime shift in the subpolar North Atlantic ocean as a possible origin of the Little Ice Age  

NASA Astrophysics Data System (ADS)

Among the climatological events of the last millennium, the Northern Hemisphere Medieval Climate Anomaly (MCA), succeeded by the Little Ice Age (LIA) are of exceptional importance. The origin of these regional climate anomalies remains however a subject of debate and besides external influences like solar and volcanic activity, internal dynamics of the climate system might have also played a dominant role. Here, we present transient last millennium simulations of the fully-coupled model Climber 3? forced with stochastically reconstructed wind fields. Our results indicate that short-lived volcanic eruptions might have triggered a cascade of sea-ice - ocean feedbacks in the North Atlantic, ultimately leading to a persistent regime shift in the ocean circulation. We find that an increase in the Nordic Sea sea-ice extent on decadal timescales as a consequence of major volcanic eruptions leads to a spin-up of the subpolar gyre (SPG) and a weakened Atlantic Meridional Overturning Circulation, eventually causing a persistent, basin-wide cooling. These results highlight the importance of regional climate feedbacks such as a regime shift in the subpolar gyre circulation for past and future climate.

Schleussner, C. F.; Feulner, G.

2012-12-01

316

Barents Sea Inflow as control of the North Atlantic Oscillation during the onset of the Little Ice Age  

NASA Astrophysics Data System (ADS)

The transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA) is believed to have been driven by an interplay of external forcing and internal variability. While the hemispheric cooling signal was clearly dominated by decreasing solar irradiance, the understanding of mechanisms shaping the climate on continental scale is less robust. A recent reconstruction proposes that a shift from a persistent positive North Atlantic Oscillation (NAO), orchestrated by tropical sea surface temperatures and atmospheric teleconnection, dominated the North Atlantic-European area during the transition phase. We test this hypothesis in an ensemble of transient simulations with a comprehensive climate model, covering the transition phase of 1150-1500 AD. Preliminary results from this ensemble suggest an alternative mechanism, in which the atmosphere is not the leading component: a decrease in the Barents Sea Inflow, favored by a weak Atlantic Overturning and decreasing solar irradiation, leads to local sea ice growth and consequently the alteration of the atmospheric pressure pattern above the Barents Sea. This in turn further favors the growth of sea ice, representing a positive feedback. The increased pressure at high latitude is then reflected in a decreasing NAO index, however, the simulated amplitude of this NAO drop is much smaller than in the reconstruction.

Lehner, F.; Born, A.; Raible, C. C.; Stocker, T. F.

2012-04-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

318

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

319

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  

NASA Astrophysics Data System (ADS)

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, and sea ice cover) within bounds set by observations decreases CO2 by no more than 36 ppm, a drawdown that could be caused by any one of these mechanisms in isolation. However, these Antarctic changes reverse the CO2 effect of the observed ice age shoaling of North Atlantic overturning: in isolation, the shoaling raises CO2 by 16 ppm, but alongside the Antarctic changes, it lowers CO2 by an additional 13 ppm, a 29 ppm synergy. The total CO2 decrease does not reach 80 ppm, partly because Antarctic stratification, Antarctic sea ice cover, and the shoaling of North Atlantic overturning all strengthen the sequestration of alkalinity in the deepest ocean, which increases CO2 both by itself and by decreasing whole ocean alkalinity. Increased nutrient consumption in the sub-Antarctic causes as much as an additional 35 ppm CO2 decrease, interacting minimally with the other changes. With its inclusion, the lowest ice age CO2 levels are within reach. These findings may bear on the two-stepped CO2 decrease of the last ice age.

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

2010-12-01

320

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

321

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

322

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

323

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

324

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

Microsoft Academic Search

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

Peter Molnar; Mark A. Cane

2007-01-01

325

Valley-fill alluviation during the Little Ice Age (ca. A.D. 1400–1880), Paria River basin and southern Colorado Plateau, United States  

Microsoft Academic Search

Valley-fill alluvium deposited from ca. A.D. 1400 to 1880 is widespread in tribu- taries of the Paria River and is largely co- incident with the Little Ice Age epoch of global climate variability. Previous work showed that alluvium of this age is a map- pable stratigraphic unit in many of the larger alluvial valleys of the southern Col- orado Plateau.

Richard Hereford

2002-01-01

326

Rates of Holocene chemical weathering, `Little Ice Age' glacial erosion and implications for Schmidt-hammer dating at a glacier—foreland boundary, Fåbergstølsbreen, southern Norway  

Microsoft Academic Search

Average rates of Holocene chemical weathering and `Little Ice Age' glacial erosion of bedrock are estimated across the glacier—foreland boundary of an outlet glacier of the Jostedalsbreen ice-cap, southern Norway. Estimates are derived from two types of evidence: (1) the heights of quartz veins above adjacent surfaces of granitic or granodioritic gneiss; and (2) Schmidt-hammer R-values of rock hardness. Average

Geraint Owen; John A. Matthews; Paul G. Albert

2007-01-01

327

Interpretation of the past glacial landforms from the present processes: the hypothesis of the secondary moraine  

NASA Astrophysics Data System (ADS)

The new glacial dating techniques do not always solve the problems regarding the interpretation of the paleoclimatic significance of the glacial forms, due to the complexity of the geomorphologic processes involved. A traditional geomorphologic observation, frequently forgotten, suggests carrying out the interpretation of ancient landforms through the study of current processes. In Peñalara glacial cirque (40°51'N, 3°57'O; 2.428 m asl), located in Sierra de Guadarrama, 70 km to the north of Madrid, two small and consecutive moraine arches can be found, which preserve a very clear glacial form except for a sector affected by a torrent. Up valley from these small arches several large moraine ridges arise. The traditional interpretation given to these separated units was that the large moraines had overtopped the small ones and, therefore, the former were subsequent to the latter. Even it was considered that both units could belong to different glaciations. It was difficult to admit that a first advance created small arches, whereas a later advance swept an important part of the crystalline weathered mantle, forming moraine accumulations much bigger than the former ones. We have carried out absolute dating techniques on five moraine boulders from each moraine system, analysing the production of the cosmogenic isotope Cl36 (Palacios et al., 2012). The results show that both units belong to the same period (21-17 ka BP). In order to explain this fact, we analyzed current glaciers which show similar characteristics to the former ones in Peñalara. We found similar glaciers in Kebnekaise massif (Northern Sweden) and in Tröllaskagi massif (Northern Island). In these glaciers, the ablation surface acts as a snow catchment basin. The snow swept by the wind accumulates on the leeward side of the moraines creating a small glacier which moves the boulders of this moraine and forms its own small moraine arches. This example confirms that the interpretation of ancient landforms can be deduced by the observation of current processes. Palacios, D., Andrés, N., Marcos, J. Vázquez-Selem, L. (2012): Glacial landforms and their paleoclimatic significance in Sierra de Guadarrama, Central Iberian Peninsula, Geomorphology doi:10.1016/j.geomorph.2011.10.003 Research funded by CGL2009-7343 project, Government of Spain.

Andrés, N.; Palacios, D.

2012-04-01

328

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

329

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

330

Seasonally asymmetric transition of the Asian monsoon in response to ice age boundary conditions  

NASA Astrophysics Data System (ADS)

Modulation of a monsoon under glacial forcing is examined using an atmosphere-ocean coupled general circulation model (AOGCM) following the specifications established by Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) to understand the air-sea-land interaction under different climate forcing. Several sensitivity experiments are performed in response to individual changes in the continental ice sheet, orbital parameters, and sea surface temperature (SST) in the Last Glacial Maximum (LGM: 21 ka) to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon. Comparison of the model results in the LGM with the pre-industrial (PI) simulation shows that the Arabian Sea and Bay of Bengal are characterized by enhancement of pre-monsoon convection despite a drop in the SST encompassing the globe, while the rainfall is considerably suppressed in the subsequent monsoon period. In the LGM winter relative to the PI, anomalies in the meridional temperature gradient (MTG) between the Asian continents minus the tropical oceans become positive and are consistent with the intensified pre-monsoon circulation. The enhanced MTG anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude, showing an opposing view to a warmer future climate. It is also evident that a latitudinal gradient in the SST across the equator plays an important role in the enhancement of pre-monsoon rainfall. As for the summer, the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the Asian continent, which is consistent with the reduction of MTG involved in the attenuated monsoon. The surplus pre-monsoon convection causes a decrease in the SST through increased heat loss from the ocean surface; in other words, negative ocean feedback is also responsible for the subsequent weakening of summer convection.

Ueda, Hiroaki; Kuroki, Harumitsu; Ohba, Masamichi; Kamae, Youichi

2011-12-01

331

The 1890 surge end moraine at Eyjabakkajökull, Iceland: a re-assessment of a classic glaciotectonic locality  

NASA Astrophysics Data System (ADS)

The glaciotectonic architecture and sequential evolution of the Eyjabakkajökull 1890 surge end moraines in Iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics. Based on morphological, geological and geophysical data from terrain cross-profiles, cross-sections and ground penetrating radar profiles, we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the Eyjabakkajökull moraines. Firstly, a narrow, single-crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport. Secondly, large lobate end moraine ridges with multiple, closely spaced, narrow asymmetric crests formed by proglacial piggy-back thrusting. Thirdly, a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum. This is true for the eastern and western parts of the Eyjabakkajökull moraines as they show similar morphological and structural styles which developed to different degrees. The former represents an intermediate member with décollement at 4-5 m depth and 27-33% shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface. The latter represents an end member with décollement at about 27 m depth and 39% horizontal shortening through multiple high amplitude, overturned and overthrusted anticlines, appearing as broadly spaced symmetric crests. We propose that the opposite end member would be a moraine of multiple symmetric, wide open anticlinal crests of low amplitude. Our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70-190 m of its terminal position. This indicates a time frame of 2-6 days for the formation of the end moraines.

Benediktsson, Í. Ö.; Schomacker, A.; Lokrantz, H.; Ingólfsson, Ó.

2010-02-01

332

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

333

An investigation into the use of color as a device to convey memes during the Little Ice Age  

NASA Astrophysics Data System (ADS)

Color is used as a tool in visual communication to express ideas in a symbolic fashion. It can also be used as a guide to assist the viewer in the visual narrative. Artwork created in the period of time between 1300 to 1850 in northern and central Europe provides a comprehensive perspective in the use of color as symbol and color as an elucidative devise. This period of time is known as the Little Ice Age, the duration of which spans European history between the Medieval period and the Romantic era. The extreme climatic conditions of this era caused profound changes in society on many levels and influenced the use of color in paintings throughout this chapter in history. The new paradigm of the science of ideas, called memetics, provides a framework to analyze the expression of ideas through the use of color within this span of time.

White, Peter A.

334

Lake carbonate-??18O records from the Yukon Territory, Canada: Little Ice Age moisture variability and patterns  

USGS Publications Warehouse

A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water ??18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake's hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to tHe lake increase, lake-water ??18O values decrease. Past lake-water ??18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate ??18O, supplemented by those in carbonate and organic ??13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ???AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ???AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake ??18O, a similarly small, stratified, alkaline lake located ???250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances. ?? 2011.

Anderson, L.; Finney, B. P.; Shapley, M. D.

2011-01-01

335

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

336

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

337

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

338

Little Ice Age fluctuations of small glaciers in the Monte Fitz Roy and Lago del Desierto areas, south Patagonian Andes, Argentina  

Microsoft Academic Search

Current knowledge about late Holocene glacier fluctuations in the south Patagonian Andes is mainly based on evidence from large outlet glaciers of the North and South Patagonian Icefields, and few data exist for the smaller glaciers elsewhere in the region. Here we provide dendrogeomorphological evidence for Little Ice Age (LIA) and post-LIA activity for five small glaciers near the northeast

M. H. Masiokas; B. H. Luckman; R. Villalba; S. Delgado; P. Skvarca; A. Ripalta

2009-01-01

339

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

340

Plio-Pleistocene history of Ferrar Glacier, Antarctica: Implications for climate and ice sheet stability  

Microsoft Academic Search

The areal distribution and elevation of glacial drifts in Vernier Valley, southern Victoria Land, are used to reconstruct the Plio-Pleistocene history of upper Ferrar Glacier. 21Ne cosmogenic-nuclide analyses of surface cobbles on four moraines, Ferrar 1, 2, 3, and 4, provide age control. A minimum-age estimate for Ferrar Drifts calculated by assuming zero surface erosion indicates that the oldest moraine,

J. W. Staiger; D. R. Marchant; J. M. Schaefer; P. Oberholzer; J. V. Johnson; A. R. Lewis; K. M. Swanger

2006-01-01

341

THE 1890 SURGE END MORAINE AT EYJABAKKAJÖKULL, ICELAND: A RE-ASSESSMENT OF A CLASSIC GLACIOTECTONIC LOCALITY  

NASA Astrophysics Data System (ADS)

This study reveals the glaciotectonic architecture and sequential evolution of the Eyjabakkajökull 1890 surge end moraines in Iceland. Based on morphological, geological and geophysical data from terrain cross-profiles, cross-sections and ground penetrating radar profiles, we demonstrate that three different models are required to explain the genesis of the Eyjabakkajökull moraines. Firstly, a narrow, single crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport. Secondly, large lobate end-moraine ridges with multiple, closely spaced, narrow asymmetric crests formed by proglacial piggy-back thrusting. Thirdly, a new model shows that moraine ridges with different morphologies may reflect different members of an end-moraine continuum. This is true for the eastern and western parts of the Eyjabakkajökull moraines as they show similar morphological and structural styles which developed to different degrees. The former represents an intermediate member with décollement at 4-5 m depth and 27-33% shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface. The latter represents an end member with décollement at about 27 m depth and 39% horizontal shortening through multiple high amplitude, overturned and overthrusted anticlines, appearing as broadly spaced symmetric crests. We propose that the opposite end member would be a moraine of multiple symmetric, wide open anticlinal crests of low amplitude. Our data suggest that the glacier coupled to the foreland to initiate the end-moraine formation when it had surged to within 70-190 m of its terminal position. This indicates a time frame of 2-6 days for the formation of the end moraines.

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

2009-12-01

342

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

343

The subglacial characteristics of the Tweed Palaeo Ice Stream, British Ice Sheet  

NASA Astrophysics Data System (ADS)

The landforms and sediments of palaeo ice stream beds can provide important data on the basal characteristics and flow mechanisms pertaining to rapid flow. The Tweed Ice Stream drained a substantial sector of the last (LGM) British Ice Sheet, flowing eastwards from the Southern Uplands to the present day coastline where it was deflected and became confluent with the southerly-flowing North Sea ice. This study applies a range of techniques to present a comprehensive depiction of the Tweed Ice Stream subglacial environment at multiple scales. Subglacial bedforms were mapped from a high resolution (5 m) digital elevation model and variations in their morphometry were analysed both along and across the ice stream bed. Sedimentological studies were conducted at sites within the ice stream bed and directly outside the ice stream bed and include lithofacies analysis, clast fabric, particle size distribution, clast morphology analysis, geotechnical measurements and micromorphological sampling and analysis. This analysis shows that the ice stream bed is characterised by an isochronous swarm of elongated drumlins and subglacial meltwater channels. A lack of landforms related to slow or punctuated ice retreat (e.g. major moraine systems or glaciofluvial outwash) implies rapid retreat of the ice stream. Sub ice stream sediments are highly consolidated and deformed whilst the sediments outside the ice stream are less consolidated and very different in character. These differences appear to reflect the broad contrast in strain. Clast fabrics are highly variable over short distances and reasons for this are considered.

Channon, H. A.; Carr, S. J.; Stokes, C. R.

2009-04-01

344

Decreased Variability in Shallow Water Ventilation in the North Atlantic during the End of the Little Ice Age  

NASA Astrophysics Data System (ADS)

Previous work examining corals from the North Atlantic employed the ratio of 14C/12C to document that large decadal pulses in North Atlantic ventilation occurred from 1890 to 1950 (Druffel 1997 and 1989). The results of these studies revealed variable reservoir age corrections for the North Atlantic surface ocean and drew connections between deep ocean circulation and the North Atlantic Oscillation (NAO). Being able to extend this record further back in time can provide insight into whether this behavior occurred during the end of the Little Ice Age (1800-1850) and the Dalton solar minimum (1800-1830). In this study, we measured radiocarbon from a brain coral (Diploria labyrinthiformis) collected along the south shore of Bermuda. This colony lived from 1780-1999, capturing both recent and historical periods of interest. Biennial Delta 14C measurements from 1893-1921 show approximately 70 percent less variability than results previously reported from the same species collected along the north shore (p=0.01, n=15). Low variability along the south shore is also seen during the end of the Little Ice Age (LIA), implying that pulses of rapid ventilation seen on the north shore of Bermuda are not as clearly defined to the south. The absence of a significant correlation between del18O and Delta14C (r=0.31, p=0.22, n=17), which was previously found in the corals to the north of Bermuda, indicate less of an influence of deep water mixing. These results raise questions about circulation of ocean waters around the island of Bermuda and the Sargasso Sea. Delta 14C values from the south shore, however, do not show a difference in the mean value during the end of the LIA relative to the beginning of the 20th century. Samples measured from 1800-1840 (n=6) have an average of approximately 2 permil higher than samples taken after 1840 (n=21), a difference that is within the range of error (±2.5-4.0 permil). During the Dalton solar minimum we would expect higher Delta 14C values in atmospheric CO2 due to increased stratospheric production of 14C. The lack of a change in surface water 14C may indicate increased vertical mixing at this time, consistent with colder and less saline sea surface water (Goodkin et al. 2008) at this site and an extended positive NAO (Luterbacher et al. 2001).

Goodkin, N. F.; Druffel, E. R.; Hughen, K. A.

2008-12-01

345

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

346

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

347

The Evolution of Credit-By-Examination at Moraine Valley Community College.  

ERIC Educational Resources Information Center

Two programs were introduced at Moraine Valley Community College (Illinois) in an effort to assess, evaluate, and assign hour equivalency credit for the non-traditional learning experiences of mature vocational and technical students. Equivalency credit was granted for performance on the College-Level Examination Program (CLEP), military service,…

Allan, Henry C., Jr.

348

Moraine Area Career System (MACS). Technology Preparation Final Report for 1992.  

ERIC Educational Resources Information Center

The Moraine Area Career System (MACS) Tech Prep Applied Academics Core project was undertaken to develop a written replicable model core of applied academics for selected vocational-technical programs that would emphasize Illinois goals for learning and technical content (including critical and computer literacy). A tech prep advisory council…

Moraine Valley Community Coll., Palos Hills, IL.

349

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

350

Palæomagnetism in Some Norwegian Sparagmites and the Late PreCambrian Ice Age  

Microsoft Academic Search

PRE-PLEISTOCENE glacial deposits have been claimed from many ages and latitudes. Palæomagnetic studies of the Permian tillites in Australia1 suggest that they were near the geomagnetic, and probably also the geographical pole. The late Pre-Cambrian (`Eo-Cambrian', Varangian, Sinian, etc.) tillites are of special interest for several reasons: (1) Widespread occurrences have been claimed2 and many are well established, for example,

W. B. Harland; D. E. T. Bidgood

1959-01-01

351

The Sea of Okhotsk; a Window on the Ice Age Ocean  

Microsoft Academic Search

Radiolarian faunas of glacial age high-latitude deep-sea sediments are dominated by Cycladophora davisiana. In Recent sediments, only those of the Sea of Okhotsk have comparable relative abundances. The sea of Okhotsk supports an unusually abundant deep-water fauna (>200meters. A sediment trap array in the central Sea of Okhotsk, had annual daily mean radiolarian flux to the deep trap (1061 meters),

J. D. Hays

2001-01-01

352

Little Ice Age and recent treeline fluctuations at the Columbia Icefield, Alberta  

Microsoft Academic Search

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

T. A. Kavanagh; B. H. Luckman

1995-01-01

353

Post-Little Ice Age (1891-2011 AD) volume loss of Kotárjökull glacier, southeastern Iceland, as established from historical photography  

NASA Astrophysics Data System (ADS)

Kotárjökull is one of several outlet glaciers draining the ice-covered central volcano Öræfajökull in SE-Iceland. We estimate the average annual specific mass loss of the glacier, to be 0.22 m (water equivalent)over the post Little Ice Age period 1891-2011. The glacial recession corresponds to an areal decrease of 2.7 km2 (20%) and a volume loss of 0.4 km3 (30%). A surface lowering of 180 m is observed near the snout decreasing to negligible amounts above 1700 m elevation. This minimal surface lowering at high altitudes is supported by a comparison of the elevation of trigonometrical points on Öræfajökull's plateau from the Danish General Staff map of 1904 and a recent LiDAR-based digital elevation model. Our estimates are derived from a) three pairs of photographs from 1891 and 2011, b) geomorphological field evidence delineating the maximum glacier extent at the end of the Little Ice Age, and c) the high-resolution digital elevation model from 2010- 2011. The historical photographs of Frederick W.W. Howell from 1891 were taken at the end of the Little Ice Age in Iceland, thus providing a reference of the maximum glacier extent.

Gudmundsson, Snaevarr; Hannesdóttir, Hrafnhildur; Björnsson, Helgi

2013-04-01

354

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

355

Dynamic ancient ice caps in the sub-Antarctic suggested by new mapping of submarine ice-formed landscapes  

NASA Astrophysics Data System (ADS)

Recent bathymetric investigations have provided hints of significant past glaciations on several Southern Ocean sub-polar islands. The extent and behaviour of ice cover in these regions is important because it provides critical limits on the evolution of refugia and marine benthic organisms, as well as unique far-field constraints for improving polar ice-sheet model sensitivity. However, despite improvements in regional mapping, sea-floor acoustic data from key shelf areas have still not been of sufficient quality, or broad enough in their coverage, to resolve the number, form or flow of past glacial episodes. Hence the history and style of sub-Antarctic glaciation remains poorly known. Here we use a compilation of multibeam bathymetry and fisheries echo-sounding data to provide evidence for dynamic, widespread ice caps on sub-Antarctic South Georgia during past glacial periods. We present a hitherto unmapped record of sea-bed glacigenic structures, including end moraines and subglacial landforms, from which the flow and form of at least three major, entirely marine-terminating configurations is resolved. The largest glaciation covered the majority of the continental shelf, and included fast-flowing outlets, possible switching of internal flow, meltwater activity, warm-based ice erosion, and substantial marginal deposition during retreat: all features of dynamic ice-cap behaviour. Existing biological evidence suggests the largest glaciation likely pre-dated the Last Glacial Maximum, which may have been restricted in extent reaching to the island's fjord mouths, while a third mid-shelf limit appears partially recorded. Work on dating the relict landscape of ancient ice cap advance and retreat is ongoing, but our preliminary age model suggests that South Georgia's history is unique from the