Stratigraphic evidence for modern‐like glacier extents in south‐central Alaska within the last glacial period ( MIS 3)

The influence of the ‘Little Ice Age’ (LIA) on the glaciers of Svalbard has been well documented for a long time. This paper presents new data on the LIA maximum glacier extent and retreat by aerial photo interpretation and Geographic Information Systems (GIS) tools. We also make cartography where all results are shown in greater detail. During the LIA maximum, we find that the glacier area of Svalbard was 38,871 km2, and since then, the total glacier area loss in the archipelago has been 5096 km2 (13.1%). The total current glaciated area from the late 2000s is 33,775 km2. Since the LIA, the glaciers in the main islands of the archipelago have retreated by 12.8% in Spitsbergen, 13.4% in Nordaustlandet, and 16.7% in Barentsøya and Edgeøya. The analysis of the LIA maximum glacier extent in the different major drainage basins shows important differences; about 100 years ago, some glacier basins were more than 19% larger in the western and central regions of Spitsbergen, or even more than 23% larger in southern Nordaustlandet, while other small basins found in the northeast of this island were barely 1% larger. The greatest retreats are found in the tidewater glaciers, more variable and responsive to the water temperature changes, water dynamics, and bathymetry. In addition, the advances at some of these glaciers may correspond with surges, which means that the rapid retreats are caused by the post-surging phases as well as climate. The conclusions of this research point out an important ice loss in all of Svalbard since the LIA and the high vulnerability of this Arctic archipelago to global warming.

Evaluation of physical and chemical proxies used to interpret past glaciations with a focus on the late Paleozoic Ice Age

The Laurentide and Innuitian ice sheets during the Last Glacial Maximum

High-resolution stratigraphy of Central and Southern Adriatic Quaternary deposits of sub-Milankovian climate change on Mediterranean circulation

<p>Numerical modeling already demonstrated to be a powerful tool for investigating the role of surface processes, including glaciation, in landscape evolution. Ice model developments from 1-D simulations (Oerlemans, 1984; MacGregor et al., 2000) to more recent 2-/3D models (e.g. Egholm et al., 2011) allow investigating glacier dynamics and landscape erosion over various timescales by also incorporating the effects of rugged topography and feedbacks between erosion by glacial sliding and the extent of glaciation.</p><p>Precipitation and temperature are primary controls on glacier mass balance, driving basal sliding and erosion in response to changes in both ice thickness and extent. However, still little is known on how erosion patterns behave under temporally- and spatially-varying combinations of these two climatic parameters. Since ice basal sliding and fluctuations of water-pressure peak around the equilibrium-line altitude (ELA) (MacGregor et al., 2000; Herman et al., 2011), erosion would be expected to follow similar patterns due to their relationship with abrasion and quarrying. However, modeled glaciers with similar geographical extents may present significant differences in either ice thickness and/or ELA, depending on the simulated climate scenarios (i.e. combinations of precipitation/temperature). This will in turn affect ice dynamics and thus erosion patterns, especially differences between the accumulation and ablation areas.</p><p>In this study we aim to numerically explore how both ice dynamics and erosion patterns are influenced by specific climatic scenarios (i.e. precipitation and temperature conditions). Towards this, we used the Integrate Second Order Shallow Ice Approximation - iSOSIA (Egholm et al., 2011) model, which uses a positive degree-day (PDD) model for mass balance and a depth-integrated computation for ice flux with irregular Voronoi cell grids, allowing local mesh adjustments in selected topographic areas. In addition, this model is capable to couple ice, water and sediments which permits to explore erosion feedbacks onto ice dynamics.</p><p>Using a synthetic Alpine landscape, we performed a set of simulations with mass balance scenarios preserving similar ELAs and ice extents between runs. From these simulations, we generated glacial erosion patterns (e.g. steady-state erosion, total erosion integrated over a glacial cycle), testing different erosion laws (abrasion, quarrying) as well as the role of subglacial water and sediment entrainment. From the different scenarios, we also investigated how ice dynamics (i.e. ice flux and thickness) and erosion rates vary spatially and differ between the accumulation/ablation areas. Our ultimate goal is to understand how glacial erosion patterns, combined with classic paleo-glacial reconstructions and paleo-ELA estimates, can be used as proxies for paleoclimate reconstruction.</p><p> </p><p>

The geology of outer Nachvak Fiord provides an opportunity to differentiate lithologies originating in the Churchill Structural Province (central and inner fiord) from those in the sedimentary Ramah Group and the Nain Structural Province (outer fiord). As a result, the distribution of glacial erratics from the central and inner fiord depicts the former presence of regional Laurentide ice in the outer fiord, whereas the distribution of glacial deposits characterized by locally derived lithologies delimits the area of local glacier expansion.Based upon these criteria, the suggestion is made that regional ice at some time covered the deeply weathered mountain summits (900 m asl) in outer Nachvak Fiord. A later advance, confined to the fiord and valleys, deposited the highest moraines and till (180–115 m asl) recorded in the area. On the basis of geomorphic relationships, this advance is considered a discrete glacial event, separate from a later glaciation that was responsible for moraines and sediments at lower elevations (130–80 m asl). Two hypotheses are presented to explain the character of glacial features and sediments in the lower valleys.Hypothesis I requires that regional ice advanced through the study area and floated as ice shelves in the outer fiord and adjacent distributary valley. Sea level at this time was approximately 70 m higher than at present. Radiocarbon dates and amino-acid ratios from the shells in associated marine and glaciomarine sediments suggest a Middle Wisconsinan age for this event. During the Late Wisconsinan, regional Laurentide ice was restricted to the inner fiord while the sea (29–40 m above present) occupied the outer fiord area. The expansion of local cirque glaciers in upland areas may have occurred during both regional glaciations.In hypothesis II, the Middle Wisconsinan was characterized by extensive local glacier activity, depositing predominantly local material in the lower valleys, south of the fiord. Related fossiliferous sediments (same as above) provide the dating framework for this event. Late Wisconsinan regional ice advanced to the outer fiord and entered the distributary valley south of the fiord. Till deposited during this event is distinguished from the earlier local glaciation by the predominance of regional lithologies. Both Middle and Late Wisconsinan glaciations resulted in the formation of ice-shelf moraines at similar elevations. This implies similar relative sea-level responses to loading of the crust during both events, and consequently it is suggested that regional Laurentide ice had also advanced during the Middle Wisconsinan.Neither hypothesis conforms to a recently proposed Late Wisconsinan ice model for northern Labrador that requires extensive regional ice coverage in the outer fiord and on the Labrador Shelf.

Although much is known of the timing, geographical extent, and character of the late Paleozoic Gondwanan glaciation, its rec ord in eastern Australia is poorly resolved. Some previous investigations have asserted that large parts of Australia were covered by a cold-based continental ice sheet during the Pennsylvanian (late Carboniferous). New data from Queensland in northeast Australia reported herein, however, suggest that the glaciation there was restricted to discrete, short-lived periods, in the Namurian (315 Ma), Westphalian (311 Ma), and Sakmarian (289–293 Ma). Thick successions in three widely separated areas indicate that the glaciation was confined in each case to local (valley or mountain) glaciers and that the mainly proglacial sediments were enclosed in every case by substantial intervals of fluvial, lacustrine, and shallow-marine strata deposited under nonglacial conditions. Accordingly, we submit that the cessation of glacial sediment deposition elsewhere in Gondwana during the Pennsylvanian to earliest Permian was due to the decay of glaciers, rather than to a transition to a cold-based ice sheet or sheets, as has been previously suggested. The interpretations presented herein make a significant contribution toward constraining the size and extent of glaciation in Gondwana, which has major implications for late Paleozoic world climate and sea-level fluctuations.

This paper analyses the influence of topography on the extent of cirque glaciers for four different stages since the Little Ice Age (LIA). The study focuses on a Pyrenean massif affected by a marked glacial shrinkage. Modeled distributed probabilities of glacier development during each stage from terrain characteristics enabled us to: (1) quantify the percentage of variance of the glacier distribution explained by topography; (2) assess the influence of individual variables on ice extent at each stage; and (3) identify those areas most vulnerable to ice degradation during the subsequent stage. Results show that topography has a greater influence on ice extent during times of warmer climate. In addition, the relative role of the different topographic variables changed over time. The probabilities of ice existence predicted by the models for subsequent stages are in good agreement with the observed paths of glacier retreat. Thus, topography should be considered a key factor in further research into the impact of climate change on glacier evolution.

Pollen analysis was carried out on the Core MD982194 of 29.78 m retrieved from the Middle Okinawa Trough which was dated as old as ~200 ka BP. The results revealed that pollen assemblages mainly presented an alternation of coniferous and herb pollen. The coniferous saccate pollen, principally Pinus and Tsuga, predominated in most parts of the core, especially highlighted in the interstadial stages including MIS 1,3, 5 and MIS7, whereas the herb pollen significantly increased in the gla- cial periods. Thus the pollen flora and their percentages showed the sensitive changes under the influence of ice volume during the glacial and interglacial periods. Our record from this core has first documented that the percentage of Cyperaceae was ex- tremely high in the glacial stages with a notable increase in Artemisia, Gramineae, Asteraceae, Chenopodiaceae, and freshwa- ter algae, which can be used as a proxy for sea-level change at the study site because of their close negative correlation of the orbital-scale changes in sea level. The distance between the continental coastline and the Okinawa Trough has deeply short- ened due to the sea-level drop in the LGM. As a result, the sediment materials from Yangtze River were extensively deposited on the flat, exposed continental shelf owing to the rapid decline of river flow speed, leading to that pollen grains from Okinawa Trough are derived mainly from the flat coastal vegetation of exposed continental shelf at glacial stages. Changes of pollen as- semblage were consistent with the variation of temperature and humidity, which showed that the percentage of arboreal pollen was highly augmented at MIS 7, 5 and MIS 1, corresponding to the strengthening of the East Asian summer monsoon and in- creasing of rainfall. Moreover, the peak of Pinus percentage in MIS 5.3, 5.1 and MIS 3.3 may be closely linked by orbital and sub-orbital cycles of solar radiation and monsoonal variability. The present study of core MD981294 implied lower tempera- ture and precipitation during the lowest sea-level stage (LGM), and more visibly testified that the vegetation of the flat plain on the exposed continental shelf was dominated by intrazonal communities such as halophyte grasslands and freshwater wetlands instead of zonal steppe or semi-arid desert. All above evidence demonstrated that the fundamental changes of pollen assem- blage and their origins in Okinawa Trough since ~200 ka BP were affected by combine factors including the coastline position and climate fluctuation. Moreover, the substantial shortening of distance between shoreline and the Okinawa Trough driven by orbital insolation cycles was clearly indicated by the pollen spectra, whereas the source-area climate signal of the pollen record was largely weakened.

Holocene glacier behavior around the northern Antarctic Peninsula and possible causes

Local glaciers record delayed peak Holocene warmth in south Greenland

D URING the past quarter of a century most observations on the extent of land and sea ice have indicated a definite amelioration of climate. We may be witnessing the last stages of what the late Francois E. Matthes has called The Little Ice Age, which began about the end of the sixteenth century. Professor H. W. Ahlmann, the well-known Scandinavian glaciologist, has stated: It is proved by climatological, oceanographical, glaciological, and biological facts that a climatic fluctuation is now going on. In high northern latitudes it expresses itself in an improvement of the temperature, which in the last decades has been the greatest during the last 200 years. In some parts of the Tropics, e.g. East Africa, there is desiccation, probably belonging to the same climatic fluctuation. This climatic change is the first one in the endless series of climatic variations and fluctuations in the past and coming history of the Earth, which we can study, measure and possibly also explain.' Referring more specifically to the role ofglaciology, he continues: are very sensitive to climatic changes... They are natural climatic recorders even where no meteorological stations exist. They also tell us the history of the climate from times before any scientific investigations of climates had begun. In the summer of 1941 the American Geographical Society, motivated in part by the almost world-wide reports of enormous shrinkage of glaciers, sent a small field party into Southeastern Alaska, par excellence a region for glacier study.2 One of the areas visited was Taku Inlet, where an unusually interesting situation exists. Four large glaciers flow southward into the Taku River Valley and terminate at or near sea level; Norris Glacier and the Twin Glaciers have been receding, but, strangely, Taku Glacier and its distributary, Hole-in-the-Wall Glacier, have been advancing. Yet all four

[Davy et al., 2010a] reported on pockmark observations along the Chatham Rise, offshore New Zealand’s South Island. The observed structures fall into three categories: features of approx. 150 m diameter are found in water depths of 500 m – 700 m, depressions with diameters of up to 5 km and the largest structures with diameters of up to 11 km were observed in water depth of 800 - 1100 m. Seismic sections across the pockmarks were available at only a few locations and mainly consisted of Parasound data. Multiple layers of small pockmarks could be correlated with sediment interfaces of increased amplitudes that correspond to the transitions between glacial maxima and minima. Consequently [Davy et al., 2010a] assumed that sealevel lowstands during glacial maxima caused the dissolution of gas hydrates and hence triggered the formation of pockmarks. Project SO226 CHRIMP aimed to test this hypothesis with an extended data base. Additional bathymetric coverage revealed multiple occurrences of large and medium size structures. Three working areas were selected along the Chatham Rise each representing one of the three types / sizes of seafloor depression. Area one was chosen to be centred around 178°40’E with the largest pockmark structure of up to 15 km diameter. From the extended bathymetric coverage a south-west to north-east oriented alignment of three similar structures was observed. Seismic sections show a highly variable sedimentation. Inside the structures all sediments had been fully eroded to a surface that can be mapped throughout the entire region. All observed pockmarks show a radial eroded rim to the South-West with a base that corresponds to the above mentioned erosional surface. Near vertical faults and blanking patterns are found underneath the eroded rim of the structures. Shallow bright spots with negative polarity are interpreted as indicators for free gas. Nevertheless no signs were found for active fluid venting above the structure or in the surrounding. The second area centred around 177°05’E hosts medium-size pockmarks. Five depressions were mapped, but some of them might be formed by overlapping pockmarks. Partly resedimented the structures show an eroded southern part with a sharp radial rim. Indifferent from area one a roughly 250 m wide blanking zone was found underneath one of the pockmarks. The area is imaged right above a conical shaped upward extension of a deeper sediment interface. From the 3D data the interface shows a rough topography. The conical structure and the blanking area are interpreted as an ancient feeder channel. This chimney terminates at an erosional interface, which forms the base of the seafloor depression. Multiple events of erosion, sedimentation and slumping have been identified above the erosional surface. Again water column imaging and geochemical analyses do not show indications for active methane venting within this area. The third working area was chosen to be centred 174°35’E where a large zone of small pockmarks was known from earlier mapping. A 2D seismic profile confirms the existence of stacked pockmark layers. The wide funnel shaped opening of the buried pockmarks terminates at distinguished sediment interfaces that show an increased reflection amplitude. This corresponds to the interpretation of [Davy et al., 2010a]. At greater depth the horizontal layering of the sediments is not interrupted. As with the previous two working areas there is no sign of a BSR and active methane venting could not be confirmed by water column imaging or geochemical analyses. In summary all three areas do show images of gas migration pathways of various sizes within the deeper sediments. Nevertheless active venting of fluids could not be confirmed. Therefore other models need to be developed to explain todays still sharp defined rims of the pockmark-like seafloor depressions.

Tree-ring studies at 13 glacier forefields in western Prince William Sound show‘Little Ice Age’ glacial fluctuations were strongly synchronous on decadal timescales. Cross-dated glacially overrun trees at eight sites indicate ice margins advanced in the early (late twelfth through thirteenth centuries) and middle (seventeenth to early eighteenth centuries)‘Little Ice Age’. Tree-ring dates of 22 moraines at 13 glaciers show two main periods of stabilization. The earlier of these, in the first decades of the eighteenth century, overlaps with the second period of glaciers overrunning trees and marks culmination of this middle‘Little Ice Age’ expansion. Stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of‘Little Ice Age’ glacial advance. The detailed‘Little Ice Age’ record from land-terminating glaciers in western Prince William Sound is consistent on a timescale of decades with four other tree-ring-dated glacial histories from across the northern Gulf of Alaska. This coastal northeastern Pacific glacial record reveals the structure of the‘Little Ice Age’ in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years.

Geomorphological and geological evidence for former Quaternary glaciation has been mapped in the Pindus Mountains of northwest Greece. The dynamics and chronology of glaciation in this area has been established through sedimentological analysis, soil analysis and Uranium-series dating. Four glacial events are recorded in the sedimentological and geomorphological records. The most extensive recorded glaciation pre-dates 350,000 years BP and was characterised by extensive valley glaciers and ice-fields. A second glaciation occurred prior to the last interglacial, before ca. 127,000 years BP, and was characterised by glaciers that reached mid-valley positions. The height of the last glacial stage in Greece (30-20,000 14C years BP) is recorded by small cirque glacier moraines and relict periglacial rock glaciers. Evidence for a fourth glacial phase is recorded only in the highest cirques of Mount Smolikas (2637 m a.s.l.), the highest peak in the Pindus Mountains. This phase of glaciation is likely to have occurred during the Late-glacial Substage (14-10,000 14C years BP). All of the glaciers during the different glacial stages were reconstructed and used alongside periglacial rock glaciers to determine palaeoclimate. During the glacial maximum of the last glacial stage, mean annual temperatures were ca. 8-9 degrees C lower than at present and mean annual precipitation greater than 2000 mm - similar to modern values. Earlier glacial maxima are likely to have been colder but with mean annual precipitation still greater than 2000 mm. Maximum glacier extent in the Pindus Mountains is likely to have preceded the most severe arid phase of glacial cycles indicated in the pollen record and also global glacial maxima. This was because of the small size of the former Pindus glaciers and their rapid response to climate change, as well as the increased prevalence of aridity around the global glacial maxima. The glacial sequence in the Pindus Mountains represents the best-dated and longest recognised record of glaciation in the Mediterranean region and provides a stratigraphical framework for Quaternary cold-stage climates in Greece.