Mountain Ice Caps Research Articles

Recent advances in Quaternary paleoclimate research using Antarctic blue ice

<p indent="0mm">Remarkable scientific discoveries have been made from the studies of ice cores drilled in polar ice sheets and mountain ice caps. These samples serve as the most accurate archives of the past atmospheric composition thus far. Two milestone achievements of ice cores include a continuous record of atmospheric greenhouse gas concentrations over the past eight glacial cycles (800 ka) and the discovery of abrupt climate change events on millennial timescale, both made possible by deep drilling in polar ice sheets. Yet, this conventional approach of deep drilling is faced with challenges from prohibitive logistical and operational cost and limited sample supply, particularly with greater depth. To address these challenges, shallow coring in blue ice areas has emerged as an appealing alternative. Two significant advances have been recently achieved from blue ice studies. Ice older than <sc>800 ka</sc> from the Allan Hills Blue Ice Area was discovered and the trapped gases inside the ice allow, for the first time, for the direct observation of atmospheric carbon dioxide concentrations (pCO₂) before <sc>800 ka.</sc> The data show no long-term decline in atmospheric pCO₂, and consequently, the Mid-Pleistocene Transition is not the result of cooling resulting from a decreasing pCO₂. Moreover, large-volume samples retrieved by a large-diameter ice drill (“Blue Ice Drill”) in the Taylor Glacier Blue Ice Area allow for novel geochemical analyses such as the radiocarbon (¹⁴C) content of methane (CH₄). The ¹⁴C of CH₄ trapped in the Taylor Glacier ice suggests that old carbon reservoirs were not responsible for the deglacial rise of CH₄ in the last glacial cycle. Another example of new geochemical methods enabled by the unprecedented sample availability offered by the blue ice areas is the elemental ratios of xenon, krypton, and nitrogen which are sensitive to the mean ocean temperature (MOT). Taylor Glacier ice samples dating back to the penultimate glacial period record <sc>1.1±0.3°C</sc> warmer-than-modern MOT values at <sc>129 ka</sc>, near the end of the penultimate deglaciation. Despite these advances, several challenges and limits remain. First, to accurately establish a chronology for the blue ice samples requires methods of absolute dating, which have considerable uncertainties at present. A precise chronology can be established via timescale synchronization with existing deep ice cores only when the blue ice is younger than <sc>800 ka.</sc> Second, the original deposition site of the blue ice field is not always known, complicating the interpretations of climate proxies that are sensitive to depositional environments such as the stable water isotopes of the ice. Third, glacial flows disrupt the chronology of the ice and could lead to the incomplete and biased preservation of climate signals. In light of these issues and shortcomings, stratigraphically continuous ice cores cannot be fully replaced by temporally discrete samples from the blue ice areas, although blue ice records hold the potentials to provide snapshots of the critical intervals of the Quaternary climate. Future progress in blue ice research may be made in three directions: (1) The prospecting of new blue ice fields and identification of blue ice areas containing the climate records of key understudied intervals; (2) numerical simulations of glacial dynamics to better the interpretation of blue ice records; and (3) the development of novel analytical techniques that reveal new climate information.

Climate change impact on glacier lakes in Panjshir province of Afghanistan

The upper portion of the ‎Panjshir River watershed consists of steep mountain ‎valleys in the Hindu Kush mountain range, which reaches over 6,000 meters above sea ‎level and remains snow covered throughout the year. The Glacier Lakes there pose a potential flood risk to the Panjshir valley. As the weather is warming ‎globally, the increasing temperatures accelerate the melting rate of the ‎glacier, causing the mountain ice caps to melt and create numerous lakes. Over the last decade, two of these lakes ruptured, leaving dozens of deaths, many hectares of land farm washed out, and hundreds of houses destroyed. This study looks at the potential impact of climate change on villagers in the province.‎ Hydro-‎‎meteorological data ‎(wind, temperature, precipitation, and runoff) from five meteorological stations over the last decade were analyzed with satellite imagery. Discharge data at the outlet of this sub-basin over ten years were also analyzed with remote sensing data for higher accuracy and validity.‎ Rising regional climate temperatures have resulted in faster snow and glacier melting, causing more discharge, high evapotranspiration, and higher ‎water demand. Although precipitation decreased between 2008 and 2018, ‎discharge increased from melting glaciers.‎ Satellite imagery reveals 234 lakes in the valley; ‎‎66 lakes have potential or high-potential risk to the six districts of this province, and Paryan district is at most risk.

Early and Middle Pleistocene environments, landforms and sediments in Scotland

ABSTRACTThis paper reviews the changing environments, developing landforms and terrestrial stratigraphy during the Early and Middle Pleistocene stages in Scotland. Cold stages after 2.7 Ma brought mountain ice caps and lowland permafrost, but larger ice sheets were short-lived. The late Early and Middle Pleistocene sedimentary record found offshore indicates more than 10 advances of ice sheets from Scotland into the North Sea but only 4–5 advances have been identified from the terrestrial stratigraphy. Two primary modes of glaciation, mountain ice cap and full ice sheet modes, can be recognised. Different zones of glacial erosion in Scotland reflect this bimodal glaciation and the spatially and temporally variable dynamics at glacier beds. Depths of glacial erosion vary from almost zero in Buchan to hundreds of metres in glens in the western Highlands and in basins both onshore and offshore. The presence of tors and blockfields indicates repeated development of patches of cold-based, non-erosive glacier ice on summits and plateaux. In lowlands, chemical weathering continued to operate during interglacials, but gruss-type saprolites are mainly of Pliocene to Early Pleistocene age. The Middle Pleistocene terrestrial stratigraphic record in Scotland, whilst fragmentary and poorly dated, provides important and accessible evidence of changing glacial, periglacial and interglacial environments over at least three stadial–interstadial–interglacial cycles. The distributions of blockfields and tors and the erratic contents of glacial sediments indicate that the configuration, thermal regime and pattern of ice flow during MIS 6 were broadly comparable to those of the last ice sheet. Improved control over the ages of Early and Middle Pleistocene sediments, soils and saprolites and on long-term rates of weathering and erosion, combined with information on palaeoenvironments, ice extent and sea level, will in future allow development and testing of new models of Pleistocene tectonics, isostasy, sea-level change and ice sheet dynamics in Scotland.

The glacial history of the southern Svartenhuk Halvø, West Greenland

This paper presents a new, detailed geomorphological and sedimentological appraisal of the southern Svartenhuk Halvo, a remote area of West Greenland that has only been subjected to limited geomorphological and sedimentological research. Despite this, it is of importance as several studies have suggested it remained an ice-free enclave during the Last Glacial Maximum. This previous work, based on biostratigraphic and chronological evidence, has provided evidence for the ‘Svartenhuk Marine Event’, a period of ice free conditions and marine deposition into a higher than present relative sea-level during the previous interglacial (MIS 5a–e). This has been correlated to other interglacial deposits in West Greenland. New geomorphological and sedimentological investigations from this study present compelling arguments for the glaciation of southern Svartenhuk Halvo by valley glaciers and mountain ice caps, questioning the status of this peninsula as an ice-free enclave. Ice directional indicators and clast lithological results suggest ice covering Svartenhuk Halvo was sourced from the higher altitude interior of the peninsula and expanded to the present coastline. In a number of valleys, sedimentological evidence points to at least two glacial advances with subglacial till production through the reworking of glaciomarine sediments, and ice contact and glacier-fed delta deposition during phases of ice retreat. The geomorphological and sedimentological context of the sediments (Gilbert type deltas), coupled with evidence for eskers and kettled/pitted delta surfaces, suggests these features formed under glacial and not interglacial conditions. This is supported by new radiocarbon dates which suggest outlet glacier advance and retreat across the area towards the end of MIS 3 and possibly into the Early Holocene. Svartenhuk Halvo was not overrun by the main Greenland Ice Sheet during the last glacial cycle, but the development of an independent ice cap and local outlet glaciers across this region may have been instrumental in determining the dynamic evolution of the Uummannaq ice stream onset zone during the last glacial cycle.

Timing of terminal Pleistocene deglaciation at high elevations in southern and central British Columbia constrained by 10Be exposure dating

The Cordilleran Ice Sheet (CIS) covered most of British Columbia and southern Yukon Territory at the local Last Glacial Maximum (lLGM) during Marine Oxygen Isotope Stage 2. However, its subsequent demise is not well understood, particularly at high elevations east of its ocean-terminating margin. We present 10Be exposure ages from two high-elevation sites in southern and central British Columbia that help constrain the time of initial deglaciation at these sites. We sampled granodiorite erratics at elevations of 2126–2230 m a.s.l. in the Marble Range and 1608–1785 m a.s.l. in the Telkwa Range at the western margin of the Interior Plateau. The erratics at both sites are near ice-marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation. The locations of the erratics and their relations to meltwater channels ensure that the resulting 10Be ages date CIS deglaciation and not the retreat of local montane glaciers. Our sample sites emerged above the surface of the CIS as its divide migrated westward from the Interior Plateau to the axis of the Coast Mountains. Two of the four samples from the summit area of the Marble Range yielded apparent exposure ages of 14.0 ± 0.7 and 15.2 ± 0.8 ka. These ages are 1.8–3.0 ka younger than the well-established lLGM age of ca 17 ka for the Puget lobe of the CIS in Washington State; they are 1.7 ka younger than the lLGM age for the Puget lobe if a snow-shielding correction to their uncertainty-weighted mean age is applied. The other two samples yielded much older apparent exposure ages (20.6 ± 1.4 and 33.0 ± 1.5 ka), indicating the presence of inherited isotopes. Four samples collected from the summit area of the Telkwa Range in the Hazelton Mountains yielded well clustered apparent exposure ages of 10.1 ± 0.6, 10.2 ± 0.7, 10.4 ± 0.5, and 11.5 ± 1.1 ka. Significant present-day snow cover introduces a large uncertainty in the apparent exposure ages from this site. A snow-shielding correction based on present-day snow cover data increases the uncertainty-weighted mean exposure age of the Telkwa Range erratics to 12.4 ± 0.7 ka, consistent with deglacial 14C ages from areas near sea level to the west. Our exposure ages show a thinning of the southern portion of the CIS shortly after the lLGM and persistence of a remnant mountain ice cap in the central Coast Mountains into the Younger Dryas Chronozone. Our data also show that the summit area of the Marble Range was ice-covered during the lLGM. The presence of an ice body of considerable dimension in north-central British Columbia until, or possibly even after, the Younger Dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the Skeena Mountains in northwest British Columbia and the need for better understanding of the response of the CIS to Lateglacial climate fluctuations.

The Grand Thaw: Our Vanishing Cryosphere

Records reveal that beginning in the 1950s there has been an accelerated reduction in ice and snow across most mountain glaciers and ice caps. The glaciers of the Tibetan Plateau and the Himalayan Mountains are the main source of water for the Ganges and the Indus Rivers. During the summer higher temperatures are causing these glaciers to melt at an increasing rate while during the winter the warmer temperature are yielding a dearth of snowfall, which in turn leads to drought. Along the equator in Africa, glaciers are faced with a similar same situation. In Uganda, 80 percent of the glaciers have disappeared since 1850 and by 2050 they are expected to be completely gone. Only 20 percent of the glaciers on Mount Kenya still remain today as the neighboring rivers continue to dry up, and even the majestic Snows of Mount Kilimanjaro are projected to vanish completely by the middle of the 21st century. Since the 1900s, the glaciers that grace the European Alps have lost 50 percent of their mass, and during the 2003 heat wave in which 30,000 Europeans died, a staggering seven feet of ice melted from the Alpine glaciers. Again in 2005, considered by the National Aeronautics and Space Administration (NASA) to be the warmest year on record, glacial melt water runoff caused extensive flooding across Switzerland. Even in Glacier National Park most of the glaciers are vanishing and the park is expected to be ice free within the next few decades.

Influence of Continental Ice Retreat on Future Global Climate

Abstract Evidence from observations indicates a net loss of global land-based ice and a rise of global sea level. Other than sea level rise, it is not clear how this loss of land-based ice could affect other aspects of global climate in the future. Here, the authors use the Community Climate System Model version 3 (CCSM3) to evaluate the potential influence of shrinking land-based ice on the Atlantic meridional overturning circulation (AMOC) and surface climate in the next two centuries under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario with prescribed rates of melting for the Greenland Ice Sheet, West Antarctic Ice Sheet, and mountain glaciers and ice caps. Results show that the AMOC, in general, is only sensitive to the freshwater discharge directly into the North Atlantic over the next two centuries. If the loss of the West Antarctic Ice Sheet would not significantly increase from its current rate, it would not have much effect on the AMOC. The AMOC slows down further only when the surface freshwater input due to runoff from land-based ice melt becomes large enough to generate a net freshwater gain in the upper North Atlantic. This further-weakened AMOC does not cool the global mean climate, but it does cause less warming, especially in the northern high latitudes and, in particular, in Europe. The projected precipitation increase in North America in the standard run becomes a net reduction in the simulation that includes land ice runoff, but there are precipitation increases in west Australia in the simulations where the AMOC slows down because of the inclusion of land-based ice runoff.

A multi-proxy record of the Last Glacial Maximum and last 14,500 years of paleoenvironmental change at Lone Spruce Pond, southwestern Alaska

Sediment cores from Lone Spruce Pond (60.007°N, 159.143°W), southwestern Alaska, record paleoenvironmental changes during the global Last Glacial Maximum (LGM), and during the last 14,500 calendar years BP (14.5 cal ka). We analyzed the abundance of organic matter, biogenic silica, carbon, and nitrogen, and the isotope ratios of C and N, magnetic susceptibility, and grain-size distribution of bulk sediment, abundance of alder shrub (Alnus) pollen, and midge (Chironomidae and Chaoboridae) assemblages in a 4.7-m-long sediment sequence from the depocenter at 22 m water depth. The basal unit contains macrofossils dating to 25–21 cal ka (the global LGM), and is interpreted as glacial-lacustrine sediment. The open water requires that the outlet of the Ahklun Mountain ice cap had retreated to within 6 km of the range crest. In addition to cladocerans and diatoms, the glacial-lacustrine mud contains chironomids consistent with deep, oligotrophic conditions; several taxa associated with relatively warm conditions are present, suggestive of relative warmth during the global LGM. The glacial-lacustrine unit is separated from the overlying non-glacial lake sediment by a possible disconformity, which might record a readvance of glacier ice. Non-glacial sediment began accumulating around 14.5 cal ka, with high flux of mineral matter and fluctuating physical and biological properties through the global deglacial period, including a reversal in biogenic-silica (BSi) content during the Younger Dryas (YD). During the global deglacial interval, the δ13C values of lake sediment were higher relative to other periods, consistent with low C:N ratios (8), and suggesting a dominant atmospheric CO2 source of C for phytoplankton. Concentrations of aquatic faunal remains (chironomids and Cladocera) were low throughout the deglacial interval, diversity was low and warm-indicator taxa were absent. Higher production and air temperatures are inferred following the YD, when bulk organic-matter (OM) content (LOI 550 °C) increased substantially and permanently, from 10 to 30 %, a trend paralleled by an increase in C and N abundance, an increase in C:N ratio (to about 12), and a decrease in δ13C of sediment. Post-YD warming is marked by a rapid shift in the midge assemblage. Between 8.9 and 8.5 cal ka, Alnus pollen tripled (25–75 %), followed by the near-tripling of BSi (7–19 %) by 8.2 cal ka, and δ15N began a steady rise, reflecting the buildup of N and an increase in denitrification in soils. Several chironomid taxa indicative of relatively warm conditions were present throughout the Holocene. Quantitative chironomid-based temperature inferences are complicated by the expansion of Alnus and resulting changes in lake nutrient status and production; these changes were associated with an abrupt increase in cladoceran abundance and persistent shift in the chironomid assemblage. During the last 2,000 years, chironomid-assemblage changes suggest cooler temperatures, and BSi and OM values were generally lower than their maximum Holocene values, with minima during the seventh and eighth centuries, and again during the eighteenth century.

Non-linear Holocene climate evolution in the North Atlantic: a high-resolution, multi-proxy record of glacier activity and environmental change from Hvítárvatn, central Iceland

Iceland is well situated to monitor North Atlantic Holocene climate variability. Terrestrial sites there offer the potential for well-dated, high-resolution, continuous records of environmental change and/or glacier activity. Laminated sediments from the proglacial lake Hvítárvatn provide a continuous record of environmental change and the development of the adjacent Langjökull ice cap for the past 10.2 ka. Replicate lake sediment cores, collected from multiple locations in the basin, are placed in a secure geochronology by splicing a varve chronology for the past 3 ka with a tephra-constrained, paleomagnetic secular variation derived chronology for older sediments. Multiple proxies, including sedimentation rate, bulk density, ice-rafted debris, sediment organic matter, biogenic silica, and diatom abundance, allow annual to multi-decadal resolution and reveal a dynamic Holocene terrestrial climate. Following regional deglaciation of the main Iceland Ice Sheet, summer temperatures were high enough that mountain ice caps had already melted, or were contributing insignificant sediment to the lake. Pronounced increases in sedimentation rate, sediment density, and the influx of terrestrial organic matter, between 8.7 and 7.9 ka suggest early Holocene warmth was interrupted by two distinct pulses of cold summers leading to widespread landscape destabilization and possibly glacier growth. The Holocene thermal maximum (HTM; 7.9 to 5.5 ka) was characterized by high within-lake productivity and ice-free conditions in the watershed. Neoglaciation is recorded as a non-linear transition toward cooler summers, landscape destabilization, and the inception and expansion of Langjökull beginning ca 5.5 ka, with notable increases in ice cap size and landscape instability at 4.2 and 3.0 ka. The past two millennia are characterized by the abrupt onset of sustained cold periods at ca 550 and 1250 AD, separated by an interval of relative warmth from ca 950 to 1150 AD. The greatest Holocene extent of Langjökull occurred in the nineteenth century and is coincident with peak landscape instability, followed by ice recession throughout the twentieth century.

Glacial landsystems of Satujökull, Iceland: A modern analogue for glacial landsystem overprinting by mountain icecaps

Mapping of the surficial geology and geomorphology of the Satujökull foreland of the northern Hofsjökull ice cap in central Iceland provides a clear signature of glacial landsystem overprinting as a result of complex glacier behaviour during the historical period. Landsystem 1 comprises a wide arc of ice-cored moraine and controlled ridges lying outside fluted and drumlinized terrain, and is indicative of polythermal conditions. This landform assemblage commonly marks the historical Little Ice Age maximum limit on the forelands of upland icefields in the arid interior of Iceland and is therefore a record of climatically driven glacier advance. Landsystem 2 contains most of the diagnostic criteria for the surging glacier landsystem and records two separate surges by the western margin of Satujökull in the period since the attainment of the Little Ice Age maximum advance. The occurrence of Landsystem 2 is significant because Satujökull has not been previously regarded as a surging glacier, even though other outlets of Hofsjökull are prone to surging. Landsystem overprinting, especially in response to changing thermal regimes and/or glacier dynamics, and particularly by different flow units in the same glacier, is rarely reported but is crucial to the critical application of modern landsystem analogues to Quaternary palaeoglaciological reconstruction.

Evolution of a Lateglacial mountain icecap in northern Scotland

Detailed geomorphological mapping of the Beinn Dearg massif, northern Scotland, was conducted to examine the maximum (Younger Dryas) extent, and earlier interstadial evolution, of an icecap that existed during the Lateglacial period (14.7–11.7 cal. ka BP). Landform evidence indicates a plateau icecap configuration during the Younger Dryas. The interpreted age is supported by new cosmogenic exposure ages and previously reported interstadial sediments beyond the icecap margin. The reconstructed Younger Dryas Beinn Dearg icecap covered 176 km2. Equilibrium line altitudes (ELAs) of ∼570–580 m were calculated for the icecap as a whole. The empirically reconstructed icecap is compared with recent numerical model simulations. The two methods produce an icecap with a similar configuration; however, differences are apparent in the extent of eastern and western outlets (±1–5 km), and in the spatial variation of ELAs. Results suggest that the numerical simulation overestimates the western and underestimates the eastern icecap extent. We attempt to quantify these differences in terms of icecap mass balance and assess their possible causes. Geomorphological evidence for the pre-Younger Dryas icecap configuration indicates that the Beinn Dearg massif remained an important source during earlier deglaciation. In contrast, the neighbouring Fannich mountains acted as an ‘unzipping’ zone, and were ice-free on their northern side by the Allerod (Greenland Interstadial 1c to 1a). Deglaciation continued over the western Beinn Dearg plateau, with the possibility that glaciers remained in some central and eastern catchments prior to (Younger Dryas) icecap (re)growth.

Extremely low long‐term erosion rates around the Gamburtsev Mountains in interior East Antarctica

The high elevation and rugged relief (&gt;3 km) of the Gamburtsev Subglacial Mountains (GSM) have long been considered enigmatic. Orogenesis normally occurs near plate boundaries, not cratonic interiors, and large‐scale tectonic activity last occurred in East Antarctica during the Pan‐African (480–600 Ma). We sampled detrital apatite from Eocene sands in Prydz Bay at the terminus of the Lambert Graben, which drained a large pre‐glacial basin including the northern Gamburtsev Mountains. Apatite fission‐track and (U‐Th)/He cooling ages constrain bedrock erosion rates throughout the catchment. We double‐dated apatites to resolve individual cooling histories. Erosion was very slow, averaging 0.01–0.02 km/Myr for &gt;250 Myr, supporting the preservation of high elevation in interior East Antarctica since at least the cessation of Permian rifting. Long‐term topographic preservation lends credence to postulated high‐elevation mountain ice caps in East Antarctica since at least the Cretaceous and to the idea that cold‐based glaciation can preserve tectonically inactive topography.

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

During the Last Glacial Maximum (LGM), a 5000 km 2 ice cap covered the San Juan Mountains of southwest Colorado. The largest valley glacier draining this ice cap occupied the Animas Valley and flowed 91 km to the south. To characterize the post-LGM demise of the Animas Valley glacier, we employ cosmogenic 10 Be to date the LGM terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples. The 10 Be depth profile within the terrace sediments suggests abandonment at 19.4 ± 1.5 ka. As deglaciation began, the ponding of Glacial Lake Durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment. The age of the terrace therefore records the initiation of LGM retreat. Negligible 10 Be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory. Glacial polish exposure ages monotonically decrease up-valley from 17.1 to 12.3 ka, with the single exception of a sample collected from a quartzite rib, yielding an average retreat rate of 15.4 m/yr. This trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history. Retreat of the Animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes. Deglaciation lasted for ∼7.2 k.y., and was complete by 12.3 ± 1.0 ka. The retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying.

Responses of mountain ice caps in central Iceland to Holocene climate change

A chronology of Holocene fluctuations of small outlet glaciers from the Regnabuðajökull ice cap on Hrútfell, central Iceland, allows comparison of their sensitivity with the margin of the nearby Langjökull icefield, to ascertain which frequencies of climatic variability are recorded by adjacent glaciers of different size. Dating utilised tephra layers in aeolian soils lying on, between and beneath moraine ridges. Key marker isochrones dating from the Hekla 4 tephra ( c. 3.8 ka BP) to Katla A.D. 1918 provide unequivocal bracketing ages. The stratigraphy and geochemical fingerprinting of tephras on younger moraines allows subdivision of “Little Ice Age” moraines. Five groups of moraines are identified, at c. 4.5–5.0, c. 3.0–3.5 ka BP, c. 2.0–2.5 ka BP, and from the “Little Ice Age” at c. A.D. 1700 and in the late 19th/early 20th century. These represent a Neoglacial sequence in which steep, small glaciers readvanced to similar positions during what are here termed “Little Ice Age”-type periods (LIATPs). In contrast, the nearby margins of Langjökull show evidence of a late nineteenth-century advance only, suggesting that this was the Holocene maximum for this glacier. The contrasting responses of local glaciers and the large icefield are explained by their different sizes and response times, so that the preserved moraine record is largely pre-conditioned by the glacier type. In general, the forefields of steep, fast-responding glaciers contain more complete archives of Holocene climatic changes than do the margins of the large icefields.

New Zealand maritime glaciation: millennial-scale southern climate change since 3.9 Ma.

Ocean Drilling Program Site 1119 is ideally located to intercept discharges of sediment from the mid-latitude glaciers of the New Zealand Southern Alps. The natural gamma ray signal from the site's sediment core contains a history of the South Island mountain ice cap since 3.9 million years ago (Ma). The younger record, to 0.37 Ma, resembles the climatic history of Antarctica as manifested by the Vostok ice core. Beyond, and back to the late Pliocene, the record may serve as a proxy for both mid-latitude and Antarctic polar plateau air temperature. The gamma ray signal, which is atmospheric, also resembles the ocean climate history represented by oxygen isotope time series.

A ~33,000 year record of environmental change from Arolik Lake, Ahklun Mountains, Alaska, USA

A continuous record of lacustrine sedimentation capturing the entire full-glacial period was obtained from Arolik Lake in the Ahklun Mountains, southwestern Alaska. Fluctuations in magnetic susceptibility (MS), grain size, organic-matter (OM) content, C/N ratios, 13 C, and biogenic silica (BSi) record marked environmental changes within the lake and its watershed during the last 33 cal ka. Age control is provided by 31 14 C ages on plant macrofossils in four cores between 5.2 and 8.6 m long. Major stratigraphic units are traceable throughout the lake subbottom in acoustical profiles, and provisional ages are derived for six prominent tephra beds, which are correlated among the cores. During the interstadial interval between 33 and 30 cal ka, OM and BSi contents are relatively high with values similar to those of the Pleistocene‐Holocene transition, suggesting a similar level of aquatic productivity. During the glacial interval that followed (30‐15 cal ka), OM and BSi decrease in parallel with declining summer insolation. OM and BSi values remain relatively uniform compared with the higher variability before and after this interval, and they show no major shifts that might correlate with climate fluctuations evidenced by the local moraine record, nor with other global climate changes. The glacial interval includes a clay-rich unit with a depauperate diatom assemblage that records the meltwater spillover of an icedammed lake. The meltwater pulse, and therefore the maximum extent of ice attained by a major outlet glacier of the Ahklun Mountain ice cap, lasted from 24 to 22 cal ka. The Pleistocene‐Holocene transition (15‐11 cal ka) exhibits the most prominent shifts in OM and BSi, but rapid and dramatic fluctuations in OM and BSi continue throughout the Holocene, indicating pronounced paleoenvrionmental changes.

Dynamics of mountain ice caps during glacial cycles: the case of Patagonia

We use a time-dependent ice-cap model to predict the pattern of growth and decay of the Patagonian ice cap during a simulated glacial cycle. The purpose is to illuminate the internal system dynamics and identity thresholds of stability related to the underlying topography. This is a necessary step if former ice-cap behaviour is to be linked to climatic change. The model, which is fully described elsewhere, portrays ice extent and surface altitude at intervals of 1000–5000 years. The modelling suggests that there are two stable ice-cap states largely influenced by topography, namely, the present distribution of upland ice fields and the long, linear ice cap along the Andes as represented by the Last Glacial Maximum. Both states can coexist in equilibrium with a climate similar to that of the present day. There is a third, larger variable state in which a more extensive ice cap extends into the adjacent plains, as occurred during early Quaternary glaciations. Warmer and/or drier conditions are required to remove all these ice caps. There are five ice centres during ice-cap growth.

Dynamics of mountain ice caps during glacial cycles: the case of Patagonia

We use a time-dependent ice-cap model to predict the pattern of growth and decay of the Patagonian ice cap during a simulated glacial cycle. The purpose is to illuminate the internal system dynamics and identity thresholds of stability related to the underlying topography. This is a necessary step if former ice-cap behaviour is to be linked to climatic change. The model, which is fully described elsewhere, portrays ice extent and surface altitude at intervals of 1000–5000 years. The modelling suggests that there are two stable ice-cap states largely influenced by topography, namely, the present distribution of upland ice fields and the long, linear ice cap along the Andes as represented by the Last Glacial Maximum. Both states can coexist in equilibrium with a climate similar to that of the present day. There is a third, larger variable state in which a more extensive ice cap extends into the adjacent plains, as occurred during early Quaternary glaciations. Warmer and/or drier conditions are required to remove all these ice caps. There are five ice centres during ice-cap growth.

Quaternary glaciation of tibet: The geological evidence

The question of the number and extent of Pleistocene glaciations on the Qinghai-Xizang (Tibet) Plateau remains contentious. There has been considerable research activity in Tibet by Chinese scientists since the late 1950s and their principal findings, including data on glacial and periglacial geomorphology, sedimentology, tectonics, stratigraphy and lake history, have been used to reconstruct ice margins and palaeosnowlines. Three, and in places, four distinct glaciations have been recognised, the most extensive occurring in the later Middle Pleistocene. Valley and piedmont glacial systems, with some mountain ice caps and a small ice sheet on the upper reaches of the Huang He, have been recognised but there is no evidence of a single Tibetan ice sheet. As the Plateau and the Himalaya-Karakoram underwent accelerating uplift through the Quaternary, there occurred progressive desiccation in the interior as the influx of Indian Ocean moisture was constrained. Equilibrium line elevations in the last glacial maximum were 4000 m in the south, east and northeast Plateau margins, rising to 5500 m in the northwest interior. The heat island provided by the Plateau, the progressive reduction in precipitation most marked during the glacials, and the strong southeast to northwest precipitation gradients, produced a glacier distribution pattern dominated by the trans-Tibetan mountain ranges. Tectonics and periglacial (including aeolian) processes have played an equal role with glaciation in generating the Plateau's Quaternary sedimentary succession.

Quaternary glaciations of New Guinea

Weathered glacial deposits outside limits of the last glaciation show that the New Guinea mountains were covered by glacier systems before Oxygen Isotope Stage 5. KAr dates from interbedded volcanic materials suggest that earlier glaciations may have occurred at ca. 300 ka BP and at ca. 700 ka BP. This implies that the still tectonically active island was high enough in the Early and Mid Quaternary to support mountain ice caps. Glacial deposits older than a radiocarbon age of 30 ka BP suggest that New Guinea developed glaciers in the early part of the last glaciation, most probably during Isotope Stage 4. Following interstadial conditions radiocarbon dated to >31 ka BP and >41 ka BP, the last glaciation is said to have culminated during the interval 18-15 ka BP, but the moraines of this stage are not closely bracketed with radiocarbon dating. Estimates of Equilibrium Line Altitude (ELA) depression are 1000–1100 m, implying a lowering of mean annual temperature by at least 6–7°C (possibly more, as precipitation also decreased). Radiocarbon dates from basal peat within the moraine limits show that glaciers receded by 13 ka BP and that New Guinea may have been wholly ice free by 7 ka BP. A small-scale advance at 121 ka BP was a response to either increased precipitation as global sea level rose and covered dry shelf areas around New Guinea, or to late-glacial global cooling. Glaciers developed again during an interval of Neoglacial cooling beginning at ca. 5 ka BP. At least four significant readvances occurred during the last 3.5 ka, radiocarbon dated to the intervals 3.5-2.9 ka BP, 2.5-1.5 ka BP (two advances) and within the last 1.5 ka BP. The Little Ice Age ended ca. 120–150 years ago and continuous glacier retreat has occurred to the present day.