Download or read book 10Be Chronology of Late Pleistocene and Holocene Glaciation of the Alapah Mountain and Arrigetch Peaks Areas Central Brooks Range Alaska written by Simon L. Pendleton and published by . This book was released on 2013 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: The amplification of climate change in the Arctic is due to several cyrosphere related feedback mechanisms, making it one of the most climate sensitive environments in the world. Due to this sensitivity, glaciers in this region are excellent recorders of past climate fluctuations. This high-resolution chronology left on the land by these glaciers is an important link in deciphering the dynamic relationship between glaciers and climate, leading to a better understanding of the extent and magnitude of past Arctic climate variability. Here we present new 10Be based glacier chronologies from the late Pleistocene through the Little Ice Age (LIA) for two valleys located in the north- and south-central Brooks range, Alaska. Moraine boulders from the Alapah Mountain moraines on the northern flank of the range indicate that the Itkillik III glaciation culminated by ~17 ka. This age is much older than previous estimates (~15-13 ka) and suggests a revision of the original late Pleistocene glacial chronology. This new Itkillik chronology requires substantial glacial retreat between ~27-23 ka, at the height of the northern hemisphere last glacial maximum (LGM). Due to their moisture sensitivity, expanded Arctic sea ice may have starved glaciers of precipitation during this time. Erratic boulders and scoured bedrock from several valleys in both the northern and southern Brooks Range show that deglaciation was underway by ~16 ka and glaciers retreated rapidly up valley to their Neoglacial limits, in some case by 14. 9 ℗ł 0. 8 ka. Sampled boulders from two Neoglacial moraines show that glaciers reached their maximum Holocene extent by 3. 2 ℗ł 0. 3 ka. In conjunction, these ages show that glaciers remained at or behind their Holocene maximum from ~14-3 ka. This means that Late Glacial (14-11 ka) or early to middle Holocene advances were either absent or less extensive than their Holocene maximum.

Download or read book Reconstructing Late Pleistocene Deglaciation and Holocene Glacial Advance Using Lacustrine Sediments and 10Be Exposure Dating Brooks Range Arctic Alaska written by Michael E. Badding and published by . This book was released on 2012 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Arctic is among the most sensitive locations to climate change, where feedback mechanisms involving the cryosphere result in climate amplification. Because of their sensitivity to summer temperature and winter precipitation, glaciers can be used as proxies for climate change and reconstructions of past glacier fluctuations provide details about paleoclimate. Here, a chronology of late Pleistocene deglaciation and Neoglacial growth is constructed for two valleys in the north-central Brooks Range, Arctic Alaska. Cosmogenic 10Be exposure dating was used on ice-sculpted valley-bottom bedrock outcrops and boulders from Holocene moraine crests. Both valleys show evidence of retreat from the range front ~16-15 ka, and retreat into individual cirques by ~14 ka. There is no evidence for a standstill or re-advance during Late Glacial (14-11 ka) time. Neoglaciation was underway during the middle Holocene, constrained by a moraine dated to 4. 6±0. 5 ka.^Using this moraine age, and another moraine dated at 2. 7±0. 2 ka, this project confirms the accuracy of the previously established lichen growth curve to estimate moraine ages. This project also confirms that glaciers during early Neoglaciation had equal or larger extents than during the Little Ice Age (1200-1900 AD). Sediments collected from a proglacial lake downvalley of modern cirque glaciers reveal episodic sediment deposition from which it is difficult to isolate a signal of glacier advance. Comparing the lake sediment data to the moraine chronology suggests that Upper Kurupa Lake, based on the measured proxies, does not record glacial advances. Several conditions within the lake's catchment likely obscures any glacial signal. Further, more detailed measurements on the lake sediment might reveal additional clues on glacier activity.^Despite the apparent lack of recording changes in glacial length, sediment characteristics suggest a period of stable deposition since 1300 AD, possibly attributed to cooling during the Little Ice Age.

Download or read book Late Pleistocene Glacial Chronology of the Western Ahklun Mountains Southwestern Alaska written by Jason P. Briner and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: New glacial mapping and 35 cosmogenic 36Cl surface exposure ages, the first ever reported from Alaska , constrain the extent and timing of late Pleistocene glacial fluctuations in the western Ahklun Mountain s, southwe stern Alaska. Morphometric and soil relativeage data characterize two main drift units deposited during the Arolik Lake and Klak Creek glaciations , named herein. During the Arolik Lake glaciation (early Wisconsin), outlet glaciers emanated from an ice cap over the central portion of the Ahklun Mountains and deposited moraines at or beyond the modern coast. These moraines have slope angles averaging about 11℗ʻ and crests averaging about 35 m wide . Four moraine boulders deposited during this glaciation have a weighted mean surface exposure age of 53.6 ℗ł 2.0 36Cl ka. During the Klak Creek glaciation (late Wisconsin), ice-cap outlet glaciers deposited moraines 20-80 km up-valley from Arolik Lake moraines. Valley glaciers expanded from high massifs that fringe the major river valleys in the western Ahklun Mountains and terminated independently from the relatively restricted ice-cap outlet glaciers. Moraines deposited during the Klak Creek glaciation have steeper slopes (mean = -18℗ʻ) and sharper crests (mean= about 17 m) than do Arolik Lake moraines. Twenty-eight 36Cl ages were obtained from six Klak Creek moraines from three valleys and reveal two phases of glaciation during the late Wisconsin, one from about 25 to 23 36Cl ka, and another from 19 to 15 36Cl ka. An ice-cap outlet glacier moraine underlies a valley glacier terminal moraine, both of which have ages of 18-19 36Cl ka, and indicates that the ice-cap outlet glacier had retreated from its maximum position shortly before the valley glacier reached its maximum position. Equilibrium-line altitudes (ELAs) for reconstructed Klak Creek valley glaciers average about 400 m, which is only about 200 m below the estimated modem altitude. The restricted extent of Klak Creek glaciers might reflect a lack of available moisture as sea ice covered the Bering Sea during the peak of the last global glacial maximum. When compared to the marine oxygen-isotope record, the timing of glacier advances in the western Ahklun Mountains indicates that glaciers responded to both regional and global climate changes.

Download or read book Chronology and Paleoclimate of Late Pleistocene Glaciation in the Klamath Mountains CA written by Nathan W. Dickey and published by . This book was released on 2016 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: Glaciers are sensitive to local and global climate variations, especially to changes in precipitation and temperature over sub-millennial timescales. Therefore, glacial deposits are excellent tools for reconstructing past climates. The western United States exhibits an excellent record of glaciation, but ongoing work across the region shows complex and yetunexplained variation in timing and extent of deglaciation between different mountain ranges at the end of the Last Glacial Maximum (LGM). The Trinity Alps of the southern Klamath Mountains in Northern California contain an excellent record of Pleistocene glaciation which I use to fill a significant spatial gap in published glacial chronologies and to provide a bridge between the Sierra Nevada and the Cascades. The Trinity Alps Wilderness is a 2,130 sq. km. federally designated area located at 41.00° N, 123.00°W, approximately 60 km southwest of Mt. Shasta in Northern California. Glacial deposits in the Trinity Alps were located using Google Earth and previously published maps, and were confirmed in the field. Building on a series of previous expeditions, in the summer of 2015 twenty-four samples from five moraines were taken for 10Be exposure dating, as well as three samples from striated bedrock. Of these, six samples were selected for exposure age analysis: five from two early LGM moraines and one from an older moraine. These ages, in addition to twenty-four ages determined in a previous study, provide evidence for at least two stages of post-LGM glaciation of similar extent throughout the Trinity Alps: the first ending at 16.83 ± 1.85 ka, the second at 12.29 ± 1.23 ka. These ages correlate with the regional LGM (~17 ka) and the global Younger Dryas (~12 ka) cooling event, respectively. The moraine maps were then used to constrain results from a climate-driven 2D numerical model of glacier mass balance and flow. This model was used to determine the potential precipitation and temperature difference from modern climate that would generate the mapped glaciers. Comparison of the resulting paleoclimate curves with nearby proxies and global climate models suggest that an approximate 5.5°C decrease in temperature and 0 to 25% increase in precipitation drove LGM glaciation in the region. Additionally, these results suggest that a similarly wet but slightly warmer-than-LGM climate drove a regionally asynchronous re-advance in the Trinity Alps linked with the Younger Dryas cooling event.

Download or read book Holocene Glaciation of the Central Brooks Range Alaska written by James M. Ellis and published by . This book was released on 1982 with total page 792 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late glacial Chronology written by Richard Jewett Lougee and published by . This book was released on 1976 with total page 610 pages. Available in PDF, EPUB and Kindle. Book excerpt: Compiled from Dr. Lougees's letters, articles, papers and lectures in support of his theory for glaciation classification.

Download or read book After the Ice Age written by E.C. Pielou and published by University of Chicago Press. This book was released on 2008-04-15 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt: The fascinating story of how a harsh terrain that resembled modern Antarctica has been transformed gradually into the forests, grasslands, and wetlands we know today.

Download or read book Regional Correlations of Late Pleistocene Climatic Changes Based on Cosmogenic Nuclide Exposure Dating of Moraines in Idaho written by Cody Sherard and published by . This book was released on 2006 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multiple post-last glacial maximum (LGM) moraines occur in the Sawtooth Range of the Rocky Mountains in central Idaho. Although relative ages of the moraines have been studied, few numerical ages exist for these moraine sequences. In this study, the ages of LGM and late glacial (Younger Dryas) moraines in the Redfish Lake drainage of Idaho are constrained with 23 new, cosmogenic, 10Be dates. Results of this study include developing a new chronology for the Redfish Lake late Pleistocene moraines that are consistent with regional morainal ages. New cosmogenic 10Be data from boulders on Bull Lake moraines at Redfish Lake are consistent with other dates obtained from Bull Lake moraines elsewhere in the Rocky Mountains. Ages of 107 to 206 ka and 238 to 323 ka suggest synchroniety with other Bull Lake glacial advances in the Wind River Range, Tetons, and Yellowstone. New cosmogenic 10Be data from boulders on terminal moraines in Redfish Lake valley, Idaho, show a LGM at 18.5 ± 0.9 ka to 15.6 ± 0.8 ka, recessional (or minor readvance) moraines deposited between 15.4 ± 0.7 ka and 14.2 ± 0.7 ka; and a Younger Dryas (YD) phase at 11.4-11.7 ± 0.5 ka. Boulders on an LGM moraine at Alturas Lake, Idaho were 10Be dated in order to supplement and test the existing concepts of glaciation there. Ages of 17.2 ± 1.0 ka and 16.8 ± 0.8 ka indicate that this moraine is late Pinedale, not mid-Pinedale as previously suggested by Thackray et al. (2004). The late Pleistocene ice chronology at Redfish Lake is consistent with the glacial chronology in the Wind River Range, WY (LGM 24 ka to l8 ka; recessional deposits 18 ka to 16 ka and YD 11.5 ka); Yellowstone, WY (LGM advances: 29.5-22.5 ka, and 19.5- 5.5 ka); Wallowa Mountains, OR (two 10Be dated LGM advances: 21.1 ± 0.4 ka and 17.0 ± 0.3 ka, and YD advance: 10.2 ± 0.6 ka); Crowfoot Lake, Canada (YD advance: 11,330 ± 220-10,100 ± 70 14C yrs B.P.); and many other places throughout western North America. This research provides chronological constraints on Pinedale LGM (~18.5 ka) moraines, Pinedale recessional (between 18.5 and 14.2 ka) moraines, and Younger Dryas (~11.4 ka) moraines in the Sawtooth Range of the Rocky Mountains, and assists in determining the areal extent of the late Pleistocene cold period in the Western United States.

Download or read book Late Pleistocene Glacial Chronology Northeastern St Elias Mountains Canada written by George H. Denton and published by . This book was released on 1965 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Pleistocene and Holocene Aged Glacial and Climate Reconstructions in the Goat Rocks Wilderness Washington United States written by Joshua Andrews Heard and published by . This book was released on 2012 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Eight glaciers, covering an area of 1.63 km2, reside on the northern and northeastern slopes of the Goat Rocks tallest peaks in the Cascades of central Washington. At least three glacial stands occurred downstream from these glaciers. Closest to modern glacier termini are Little Ice Age (LIA) moraines that were deposited between 1870 and 1899 AD, according to the lichenometric analysis. They are characterized by sharp, minimally eroded crests, little to no soil cover, and minimal vegetation cover. Glacier reconstructions indicate that LIA glaciers covered 8.29 km2, 76% more area than modern ice coverage. The average LIA equilibrium line altitude (ELA) of 1995 ± 70 m is ~150 m below the average modern ELA of 2149 ± 76 m. To satisfy climate conditions at the LIA ELA, the winter snow accumulation must have been 8 to 43 cm greater and mean summer temperatures 0.2 to 1.3 oC cooler than they are now. Late Pleistocene to early Holocene (LPEH) aged moraines are located between 100 and 400 m below the LIA deposits. They have degraded moraine crests, few surface boulders, and considerable vegetation and soil cover. Volcanic ashes indicate LPEH moraines were deposited before 1480 AD while morphometric data suggest deposition during the late Pleistocene or early Holocene. The average LPEH ELA of 1904 ± 110 m is ~ 240 m and ~90 m below the modern and LIA ELAs, respectively. The climate change necessary to maintain a glacier with an ELA at that elevation for LPEH conditions requires the winter accumulation to increase by 47 to 48 cm weq and the mean summer temperature to cool by 1.4 to 1.5 oC. Last glacial maximum (LGM) moraines are located more than 30 km downstream from modern glacial termini. They are characterized by hummocky topography, rounded moraine crests, complete vegetation cover, and well developed soil cover. Moraine morphometry, soil characteristics, and distance from modern glacial termini indicate that deposition occurred at least 15 ka BP during an expansive cooling event, the last being the LGM. The LGM ELA of 1230 m is ~920 m below the modern ELA. The climate change necessary to maintain a glacier with an ELA at that elevation for LGM conditions requires the mean summer temperature to cool by 5.6 oC with no change in precipitation.

Download or read book The Ice Age in North America and Its Bearings Upon the Antiquity of Man written by George Frederick Wright and published by . This book was released on 1889 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Pleistocene and Holocene Glacier and Climate Change written by Shaun Andrew Marcott and published by . This book was released on 2011 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents results from three studies that address major scientific questions in glacial geology and paleoclimatology for the late Pleistocene and Holocene using relatively new geochemical and statistical techniques. Each of the studies attempts to answer a longstanding question in the respective field using geochemical or statistical methods that have not been applied to the problem thus far. A longstanding question in glaciology is the nature and mechanism of the so- called "Heinrich events" of the last ~60 ka. These massive iceberg discharge events into the North Atlantic from the partial breakup of the Laurentide Ice Sheet are identified from distinct ice rafted debris and detrital carbonate layers in marine sediment cores. The mechanism associated with the initiation of these events is commonly thought to be related to internal ice sheet instabilities. However, Heinrich events consistently occur following a long cooling trend that culminates in an extreme cold event, thus suggesting a possible triggering mechanism by climate. Recent modeling work has proposed an oceanic mechanism associated with ocean warming, but no physical evidence has been made available to date. To test this ocean-warming hypothesis, we measured temperature sensitive trace metals and stable isotopes in benthic foraminifera from a sediment core collected in the western North Atlantic that spans the last six Heinrich events and compared our results to climate model simulations using CCSM3. Our results show subsurface warming occurred prior to or coeval with nearly all of the Heinrich events of the last ~60 ka, thus implicating subsurface ocean warming as the main trigger of these rapid breakups of the Laurentide Ice Sheet. In the field of glacial geology a longstanding question has been the timing of alpine glacial advances during the Holocene. A number of studies have interpreted several Holocene glacial advances in western North America, but age control is based largely on relative dating techniques, which have been shown to be in error by up to 10,000 yrs in some cases. Based on 124 10Be surface exposure ages from twenty cirque moraines in ten mountain ranges across western North America, glacier were retreating from moraine positions during the latest Pleistocene or earliest Holocene and not throughout the Holocene epoch as previously assumed, thus requiring a refined interpretation of Holocene glacial activity in western North America and the associated climate forcing. In the field of paleoclimatology a question regarding how global temperature varied over the entirety of the Holocene epoch has remained to be answered for some time. While many temperature reconstructions exist for the last 2000 years, a full Holocene temperature stack does not exist, despite its potential utility of putting modern climate change into a full interglacial perspective. Based on a global composite of 73 proxy based temperature record, a Holocene temperature stack was constructed and used to demonstrate that a general cooling of ~1°C has occurred from the early to mid Holocene and that centennial and millennial scale variability is modest. We account for both temperature calibration and chronologic uncertainties using a Monte Carlo based approach. Our results are consistent with prior reconstructions of the last 2000 years and now allow for a full Holocene temperature perspective for evaluation with present and future climate change.

Download or read book Cosmogenic Exposure age Chronologies of Pinedale and Bull Lake Glaciations in Greater Yellowstone and the Teton Range US written by Joseph M. Licciardi and published by . This book was released on 2008 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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±1310Be ka and oldest ages of ~151-15710Be 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±1.410Be ka, and possibly as young as 14.6±70.710Be 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 signi?cant 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±1.110Be 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.

Download or read book The Ice Age in North America written by George Frederick Wright and published by . This book was released on 1911 with total page 848 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Ice Age in North America and Its Bearings Upon the Antiquity of Man written by George Frederick Wright and published by . This book was released on 1889 with total page 662 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Late Pleistocene and Holocene High resolution Glacial and Paleoclimate Record from the Southern Sangre de Cristo Mountains Northern New Mexico written by Jake Armour and published by . This book was released on 2002 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Reconstruction of Late Pleistocene Paleoclimatic Characteristics in the Great Basin and Adjacent Areas written by Kenneth A. Bevis and published by . This book was released on 1995 with total page 556 pages. Available in PDF, EPUB and Kindle. Book excerpt: A sequence of glaciation based on relative dating parameters was established in each of nine mountain ranges located along a northwest to southeast transect through the northern Great Basin. Each sequence consists of two or three drift units. Degree of weathering suggests that the younger drift unit in a two-fold sequence and the intermediate drift unit in a three-fold sequence represents deposition during the late Pleistocene. The late Pleistocene equilibrium-line altitude (ELA) in each range was determined by reconstructing the maximum ice extent associated with these drift units and using the accumulation area ratio technique. Paleo-ELAs increase from about 2100 m in northeastern Oregon to approximately 3200 m in central Utah. Paleoclimatic conditions along the study transect were estimated by comparing modern climatic conditions at the reconstructed late Pleistocene ELAs with climatic conditions occurring at the ELAs of modem mid-latitude glaciers. Assuming no change in winter accumulation or in the seasonal distribution of precipitation from the present, a mean summer temperature depression ranging from about 9.0 °C at the northern end of the transect to about 4.0 °C at the southern end would have been necessary to sustain glaciers in these ranges during the late Pleistocene. To simulate possible changes in late Pleistocene precipitation patterns, a change in winter accumulation between 0.5 and 2.0 times the modem value resulted in a respective increase or decrease in temperature depression by approximately 2.0 °C. These results suggest that increases in precipitation during the late Pleistocene alone could not have sustained glaciers in the mountain ranges of the study transect, except possibly at its southern end, in the central Great Basin. An increase in precipitation in this area during the late Pleistocene agrees with the interpretation of other paleoclimatic records and paleoclimatic model simulations for the Great Basin.