Extensive Ice Cap Research Articles

Testing models of ice cap extent, South Georgia, sub-Antarctic

The extent of Last Glacial Maximum ice in South Georgia is contested, with two alternative hypotheses: an extensive (maximum) model of ice reaching the edge of the continental shelf, or a restricted (minimum) model with ice constrained within the inner fjords. We present a new relative sea-level dataset for South Georgia, summarising published and new geomorphological evidence for the marine limit and elevations of former sea levels on the island. Using a glacial isostatic adjustment model (ALMA) specifically suited to regional modelling and working at high spatial resolutions, combined with a series of simulated ice-load histories, we use the relative sea-level data to test between the restricted and extensive ice extent scenarios. The model results suggest that there was most likely an extensive Last Glacial Maximum glaciation of South Georgia, implying that the island was covered by thick (>1000 m) ice, probably to the edge of the continental shelf, with deglaciation occurring relatively early (ca. 15 ka BP, though independent data suggest this may have been as early as 18 ka). The presence of an extensive ice cap extending to the shelf edge would imply that if there were any biological refugia around South Georgia, they must have been relatively localised and restricted to the outermost shelf.

Quaternary glaciation in the Mediterranean mountains: a new synthesis

Abstract The Mediterranean mountains were repeatedly glaciated during the Pleistocene. Glaciers were present in most of the major mountains areas from Morocco in the west to the Black Sea coast of Turkey in the east. Some mountains supported extensive ice caps and ice fields with valley glaciers tens of kilometres long. Other massifs sustained only small-scale ice masses, although this was the exception rather than the norm. Glaciers still exist today and there is evidence that small glaciers were a common sight in many regions during the Little Ice Age. The Mediterranean mountains are important for palaeoclimate research because of their position in the mid-latitudes and sensitivity to changes in the climate regimes of adjacent areas including the North Atlantic. These mountains are also important areas of biodiversity and long-term biological change through the Quaternary ice age. All of this provided challenges and opportunities for Palaeolithic societies. This paper reviews the history of the study of glaciation in the Mediterranean mountains from pioneer nineteenth century observations through to the detailed geomorphological mapping and advanced geochronological datasets of recent times. We also review the current state of knowledge to frame the contributions presented in this volume. Lastly, this new synthesis then identifies outstanding research problems and assesses the prospects for new studies of glaciation in the Mediterranean mountains.

Terminal moraines in the fjord basins of sub-Antarctic South Georgia

Sub-Antarctic South Georgia (54° 17′ S, 36° 30′ W, 3755 km2) is a large heavily glacierized island that is 170 km long, 39 km wide and rises to elevations of 2934 m. The island has extensive evidence of past glacial expansion with moraines preserved on land (Bentley et al. 2007), in the fjords (Hodgson et al. 2014) and in glacial troughs that extend 60–100 km to the edge of the continental shelf where some terminate in trough-mouth fans (Graham et al. 2008). A paucity of chronological control means that, at present, it is not possible to identify which of these sets of features mark the limit of a more extensive ice cap from the Last Glacial Maximum (LGM). The glacial geomorphology of nine of the deep glacial fjords on South Georgia has been studied from ship-based geophysical surveys. Despite the different lengths, widths and orientations of the fjords, a relatively consistent pattern of large-scale (102–103 m) submarine geomorphological features is present (Hodgson et al. 2014). Most of the fjords have shallow (30–150 m) inner basins characterized by a range of seafloor sedimentary features including sediment gravity flows, debris fans and slope failures, all of which are associated with high glacigenic sediment supply. The inner …

Cosmogenic 36Cl exposure ages reveal a 9.3 ka BP glacier advance and the Late Weichselian-Early Holocene glacial history of the Drangajökull region, northwest Iceland

We present twenty-four new cosmogenic isotope (36Cl) surface exposure ages from erratic boulders, moraine boulders and glacially eroded bedrock that constrain the late Weichselian to Holocene glacial history of the Drangajökull region, northwest Iceland. The results suggest a topographically controlled ice sheet over the Vestfirðir (Westfjords) peninsula during the last glaciation. Cold based non-erosive sectors of the ice sheet covered most of the mountains while fjords and valleys were occupied with erosive, warm-based ice.Old36Cl exposure ages from highlands and mountain plateaux (L8; 76.5 ka and H1; 41.6 ka) in combination with younger erratic boulders (L7; 26.2 and K1–K4; 15.0–13.8 ka) superimposed on such surfaces suggest the presence of non-erosive ice over uplands and plateaux in the Vestfirðir peninsula during the last glaciation. Glacially scoured terrain and erratic boulders yielding younger exposure ages (L1-L6; 11.3–9.1 ka and R1, R6-R7; 10.6–9.4 ka) in the lowland areas indicate that the valleys and fjords of the Vestfirðir peninsula were occupied by warm-based, dynamic ice during the last glaciation.The deglaciation of mountain Leirufjall by 26.2 ka BP suggests that ice thinning and deglaciation of some mountains and plateaux preceded any significant lateral retreat of the ice sheet. Subsequently this initial ice thinning was followed by break-up of the shelf based ice sheet off Vestfirðir about 15 ka BP. Hence, the new exposure ages suggest a stepwise asynchronous deglaciation on land, following the shelf break-up with some valleys and most of the highlands, ice free by 14–15 ka BP.The outermost moraine at the mouth of Leirufjörður is dated to 9.3 ka BP, and we suggest the moraine to be formed by a glacier re-advance in response to a cooler climate forced by the reduced Atlantic Meridional Overturning Circulation at around 9.3 ka BP. A system of moraines proximal to the 9.3 ka moraine in Leirufjörður as well as a 9.4 ka deglaciation age in the coastal area of Reykjarfjörður suggest that an extensive ice cap persisted over the eastern Vestfirðir peninsula at least until c. 9 ka BP.

Upper Pleistocene glacial valley-junction sediments at Pias, Trevinca Mountains, NW Spain

Abstract Sediments at Pias (Galicia) provide evidence of Upper Pleistocene glacial activities at a valley junction in the north-western mountains of Spain. The sedimentary sequence consists of lower, predominately fine-grained lacustrine deposits with few lonestones, overlain by poorly sorted, sandy gravels interstratified with massive diamicton deposited during mid-Weichselian times (MIS 3) (marine isotope stage 3). The lacustrine sediments were deposited in a glacial valley temporarily dammed by a confluent glacier. The presence of active ice is suggested by massive diamicton layers best interpreted as till, rafted sediments in lacustrine deposits and deformation structures indicative of loading and kettle formation. Frozen ground conditions are suggested by a few involution-like structures. The Pias area contains one of the few western-Spain sedimentary records of Upper Pleistocene glaciation at relatively low latitude (about 42°N) and low altitude (less than 1000 m a.s.l.). A southern dip of the Polar front to 40–45°N latitudes, as occurred during Last Glacial Maximum, could have cut moisture to the northern Fennoscandinavian ice sheets. At the same time, however, sufficient precipitations would have persisted in north-western Spain to sustain extensive ice caps and their outlets to elevations as low as c. 900 m a.s.l.

Groundwater flow, heat transport, and water table position within volcanic edifices: Implications for volcanic processes in the Cascade Range

The position of the water table within a volcanic edifice has significant implications for volcano hazards, geothermal energy, and epithermal mineralization. We have modified the HYDROTHERM numerical simulator to allow for a free‐surface (water table) upper boundary condition and a wide range of recharge rates, heat input rates, and thermodynamic conditions representative of continental volcano‐hydrothermal systems. An extensive set of simulations was performed on a hypothetical stratovolcano system with unconfined groundwater flow. Simulation results suggest that the permeability structure of the volcanic edifice and underlying material is the dominant control on water table elevation and the distribution of pressures, temperatures, and fluid phases at depth. When permeabilities are isotropic, water table elevation decreases with increasing heat flux and increases with increasing recharge, but when permeabilities are anisotropic, these effects can be much less pronounced. Several conditions facilitate the ascent of a hydrothermal plume into a volcanic edifice: a sufficient source of heat and magmatic volatiles at depth, strong buoyancy forces, and a relatively weak topography‐driven flow system. Further, the plume must be connected to a deep heat source through a pathway with a time‐averaged effective permeability ≥1 × 10−16 m2, which may be maintained by frequent seismicity. Topography‐driven flow may be retarded by low permeability in the edifice and/or the lack of precipitation recharge; in the latter case, the water table may be relatively deep. Simulation results were compared with observations from the Quaternary stratovolcanoes along the Cascade Range of the western United States to infer hydrothermal processes within the edifices. Extensive ice caps on many Cascade Range stratovolcanoes may restrict recharge on the summits and uppermost flanks. Both the simulation results and limited observational data allow for the possibility that the water table beneath the stratovolcanoes is relatively deep.

Significance of Late Paleozoic Fission-track Ages in Volcanic Rocks from the Lavras Do Sul Region, Southernmost Brazil

This paper describes the application of apatite fission-track thermochronology to four outcrop samples of the basaltic to andesitic volcanic rocks of the Hilário Formation, located in the Precambrian Sul-rio-grandense Shield, in southernmost Brazil. The investigated unit was generated during the late stages of the Neoproterozoic Brasiliano/Pan-African Cycle (900-500 Ma), in a context of strike-slip motion along NE-trending structures and consequent basin inception. The apparent fission-track (FT) ages fall in the range 270.1 to 298.2 Ma, late Carboniferous to early Permian. The mean confined fission-track lengths range between 10.76 and 12.20 mm and the estimate for initial fission-track recording (below 110°C) is positioned around 359 and 344 Ma. Considering this, the Neoproterozoic volcanic rocks of the Hilário Formation were buried under at least 4 km of volcanic and sedimentary rocks, resulting in thermal fading of all the original fission-tracks, and remained so until the late Paleozoic. Then, the investigated rocks and the whole region acted as the southern margin and source area for the Paleozoic/Mesozoic intraplate Paraná Basin. A long-lived cooling trend, from the early Carboniferous (359-344 Ma) to the Permian/Triassic boundary (ca. 250 Ma) can be inferred from the analysis of the thermal history curves. This tendency can be associated to the conjunction of uplift and denudation of this region. During the Carboniferous, it probably reflects a response to the compressive events in the southwestern Gondwanan margin, in the context of the Eo-Hercynian (Chañic) Orogeny. This period, in the studied region, was also characterized by extensive ice caps related to the Gondwanan glaciation and by lack of sedimentation. With the collapse of the glaciers, alluvial fan and glaciogenic sedimentation took place during the late Carboniferous and early Permian. This cooling phase is probably recorded by the apparent FT ages. A subsequent uplifting event is revealed by the analysis of the thermal history curves, which show a strong inflection between 90 and 70 Ma. These data are here tentatively correlated with significant re-arrangements of the Brazilian southeastern coast, such as the Serra do Mar and Serra da Mantiqueira uplifts.

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.

Environmental conditions and physiological tolerances of intertidal fauna in relation to shore zonation at Husvik, South Georgia

South Georgia, an extremely isolated island within the Antarctic Convergence, was covered by an extensive icecap until ~10,000 years ago. In consequence the depauperate intertidal fauna is of recent origin and consists almost entirely of brooders or direct developers which probably arrived as a result of rafting. Environmental conditions between the tidemarks are comparable with northern Norway and Greenland, so the absence of mussels and barnacles is due to isolation from the nearest feasible sources of colonization (the Falkland Islands and Magellan), and not to a hostile environment. Intertidal animals (eight species studied) have median upper lethal temperatures that are positively and linearly related to maximum height of distribution on the shore. Thermal niche width (median upper lethal temperature minus median lower lethal temperature) is also positively correlated with maximum height of distribution on the shore with species below mid-tide level having narrow niches in contrast to species above mid-tide level that have wide niches. There is no relationship between freezing resistance and position on the shore. Salinity and desiccation tolerances were also greater in animal species from the upper shore than in those from the lower shore. In the case of those species also studied elsewhere (Lasaea rubra (Mollusca: Bivalvia); Nacella condnna (Mollusca: Gastropoda) and Tigriopus sp. (Crustacea: Copepoda)), evidence is presented to show that no special adaptation is exhibited by South Georgian animals, and that upper zonation limits are controlled primarily by physical tolerance. This is particularly marked in the case of N. condnna which has similar thermal tolerances on the Antarctic Peninsula, on Signy Island and at South Georgia; in consequence it can only inhabit the extreme lower shore at South Georgia, yet penetrates to mid-tide level at Signy Island.

Glacial history of the upper Derwent Valley, Tasmania

Part of an extensive ice cap that developed in the Tasmanian Central Highlands during the late Cenozoic discharged southwards via a major outlet glacier that occupied the valley of the Derwent River. At least three and probably five phases of glaciation took place. The first and most extensive glaciation may have been early Pleistocene in age, while the most recent and least extensive occurred during the late Last Glacial Stage. When the ice cover was most extensive, the Derwent Glacier was up to 500 m thick. It may have extended to as low as 230 m above sea level, 70 km downvalley. Diffluent lobes of this glacier spread eastwards to merge with other glaciers in the Nive Valley, southwards into the upper Gordon Valley, and westwards into the upper Franklin and Alma Valleys. The ice masses of west-central Tasmania were mainly of temperate maritime character.

Multiple Glaciation of the Upper Franklin Valley, Western Tasmania Wilderness World Heritage Area

Part of an extensive ice cap that developed in the Tasmanian Central Highlands during the late Cainozoic discharged southwards into the valley of the Franklin River and its upper tributaries where it merged with smaller glaciers that accumulated behind local snowfences. Glacial landforms and sediments in the now heavily forested valleys indicate that at least three and possibly as many as six glaciations took place. The earliest and most extensive glaciation occurred during the Pliocene or earliest Pleistocene. At this time ice extended at least 27km down the Franklin Valley and covered at least 326km2 of the study area. This ice was confluent with glaciers in the West Coast Range to the west and in the Derwent Valley to the east Such confluence offers the possibility of better correlation of glacial events between western Tasmania and the Central Highlands. The smallest and most recent glaciation occurred during the late Last Glacial Stage when the Franklin Glacier did not exceed 12km in length. The glaciers were characterised by high rates of mass throughput and were of temperate maritime type.

Zur letzten Eiszeit im alpinen und nordeuropäischen Raum

Abstract. On the last Glaciation of the Alps and Fennoscandia. During the Pleistocene the Alps and the Fennoscandian Shield were covered several times with extensive ice caps. During the last Ice Age. the Würm or Weichsel Glaciation, the maximum extent of the glaciers occurred at the end of the Ice Age, as late as 20.000 years ago. The main retreat phases during deglaciation were marked as distinct ice marginal zones and dated between 20,000 and 9,000 BP.

Biogeographic History of Miocene Calcareous Nannoplankton and Paleoceanography of the Atlantic Ocean

Biogeographic patterns of Miocene calcareous nannoplankton in the North and South Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico are apparent from a Q-mode factor analysis of census data from 49 DSDP sites. In a total of 444 relatively well-preserved Miocene samples, 5 major and 1 minor (but relatively important) assemblages were recognized, most of which show distinct spatial and temporal distribution patterns. The major assemblages (identified by the dominant taxa) are the Dictyococcites minutus, Cyclicargolithus floridanus, Coccolithus pelagicus, Reticulofenestra pseudoumbilica-R. haqii, and Discoaster-Sphenolithus assemblages. Four of the major assemblages show distinct shifts through latitudes that are interpreted as a response to changing climate. Four warming and cooling cycles of 4 to 4.5 m.y. duration are identified in the Miocene. Both the paleobiogeographic and available isotopic data show the warming episode between 17 and 15.5 Ma and the cooling trend that followed, as well as the warming episode between 9 and 7 Ma, to have been particularly extreme in both Hemispheres, and probably of global extent. The sharp cooling centered at 1 5 Ma and the biogeographic changes at this time suggest this event to have been associated with the development of an extensive ice-cap on Antarctica. Biogeographic history of Miocene calcareous nannoplankton and paleoceanography of the Atlantic Ocean

Structural geology of central Peary Land, North Greenland

The region investigated in 1978 between Jørgen Brønlund Fjord - Øvre Midsommersø in the south and Frederick E. Hyde Fjord in the north consists of c. 1½ km thiekness of Lower Palaeozoic carbonates overlain by an up to 1 km thick series of Silurian flysch (Christie & Peel, 1977). In general the region is part of the Palaeozoic platform that ean be divided into three major E-W trending physiographic belts: a southern belt where the carbonates form plateaus incised by steep valleys, a central belt consisting of characteristic conical mountains marked by concentric terraces of resistant sandstone beds in the flyseh (Dawes, 1976, fig. 249), and in the fold belt to the north the mountains rise up to altitudes of 1000-1500 m and are covered by extensive ice caps (fig. 17). The southern border of the region, the Øvre Midsommersø - Jørgen Brønlund Fjord area, was mapped by Jepsen (1971) while the Lower Palaeozoic stratigraphy in the central part af the region has been established by Christie & Peel (1977) at Børglum Elv. Some structural aspects af the gealogy at Frederick E. Hyde Fjord are briefly described by Dawes (1971) and Dawes & Soper (1973). Prior to the field work a comprehensive photogeological interpretation was carried out on vertical aerial photographs (seale c. 1:60000) and compiled on six uneontoured l: 100000 photomosaic maps. The 1978 field work and laboratory studies using a Kern PG 2 photogrammetric instrument form the first detailed study of the fold belt margin. For descriptive purposes the region investigated in 1978 has been subdivided into seven areas (fig. 17), the main struetural features of which form the basis of this report.

The subglacial birth of Olympus Mons and its aureoles

The vast volcanic plains and shields of Mars, together with the thermal, spectrographic, and morphological evidence for water ice at the poles, for several percent water in Viking soil samples, for ground ice or permafrost over much of the planet, and for the existence of surface water at some time in the past, suggest that magma and water or ice may have interacted during evolution of the planet's landscape. Relatively small mesas and buttes, with and without summit craters, are remarkably similar to the table mountains of Iceland that formed by subglacial eruption during the late Quaternary period. Table mountains typically comprise foundations of pillow lava and palagonitized tuff breccias (móberg), overlain by subaerial lava flows that commonly culminated in a typical shield volcano; some table mountains, however, failed to reach the subaerial stage and thus lack the cap rock. Subglacial fissure eruptions produced ridges composed of pillow lava and móberg. Conical knobs on steep‐sided Martian plateaus are reminiscent of the small Icelandic shield volcanoes atop móberg pedestals. Candidate table mountains on Mars are especially numerous in the region between latitude 40°N and the margin of the north polar cap, and interaction of lava with a formerly more extensive ice cap may have occurred. More significant is the possibility that Olympus Mons and the broad lobate aureole deposits around its base may have had similar subglacial beginnings. This hypothesis requires an ice cap several kilometers thick in the vicinity of this enormous shield during its initial stages of eruption. The amounts of water ice required do not appear excessive, given the limits to present knowledge of the water budget throughout the planet's history. A mechanism for localizing such ice, however, is required.