Krister N. Jansson

Global sea-level contribution from the Patagonian Icefields since the Little Ice Age maximum

The melting of mountain glaciers and ice caps is expected to contribute significantly to sea-level rise in the twenty-first century(1-)3, although the magnitude of this contribution is not fully constrained. Glaciers in the Patagonian Icefields of South America are thought to have contributed about 10% of the total sea-level rise attributable to mountain glaciers in the past 50 years(3). However, it is unclear whether recent rates of glacier recession in Patagonia are unusual relative to the past few centuries. Here we reconstruct the recession of these glaciers using remote sensing and field determinations of trimline and terminal moraine location. We estimate that the North Patagonian Icefield has lost 103 +/- 20.7 km(3) of ice since its late Holocene peak extent in AD 1870 and that the South Patagonian Icefield has lost 503 +/- 101.1 km(3) since its peak in AD 1650. This equates to a sea-level contribution of 0.0018 +/- 0.0004 mm yr(-1) since 1870 from the north and 0.0034 +/- 0.0007 mm yr(-1) since 1650 from the south. The centennial rates of sea-level contribution we derive are one order of magnitude lower than estimates of melting over the past 50 years(3), even when we account for possible thinning above the trimline. We conclude that the melt rate and sea-level contribution of the Patagonian Icefields increased markedly in the twentieth century.

Palaeoglaciology of the Welsh sector of the British–Irish Ice Sheet

This palaeoglaciological reconstruction, based on the distribution of glacial lineations interpreted from satellite imagery, considers the extent, thickness and dynamics of the Welsh Ice Cap and its interaction with the British–Irish Ice Sheet. Two major ice-flow events were identified. The oldest phase of ice flow (Event I) is characterized by ice flowing from an ice dispersal centre situated over the higher terrain in north–central Wales and by ice thick enough to cover the mountain summits. At this time the interior of the ice cap is inferred to have been dominated by cold-based ice. During the growth of the Welsh Ice Cap it became confluent with the British–Irish Ice Sheet. The Welsh Ice Cap at this time was again sufficiently thick to submerge the highest mountain summits. The youngest detected phase of ice flow (Event II) was marked by an abrupt change in the dynamics of the Welsh Ice Cap. During Event II the Welsh Ice Cap was drained by at least four ice streams, which followed major troughs in northern and eastern Wales.

Using Landsat 7 ETM+ imagery and Digital Terrain Models for mapping glacial lineaments on former ice sheet beds

In this paper, we consider the application of Landsat 7 ETM+ imagery and Digital Terrain Models (DTM) for mapping glacial lineaments in a formerly glaciated area of Wales. A series of landform interpretation experiments were conducted using different false colour composites (FCC) and a DTM, both individually and in combination. The experiments indicate that the optimal FCC for detection of glacial lineaments at this scale includes the thermal‐infrared (TIR) band. However, by performing the interpretation both in the TIR composite and in a visible and near‐infrared (VNIR, bands 4, 3, and 2) draped over the DTM, we were able to substantially increase the number of lineaments identified. The glacial lineaments consist of fractured bedrock and are defined as rock drumlins. The landform system formed by these rock drumlins is characterized by convergent flow patterns at its head, attenuated lineaments, and abrupt lateral margins, which may indicate formation by fast‐flowing ice.

Early Holocene glacial lakes and ice marginal retreat pattern in Labrador/Ungava, Canada

Abstract The existence of glacial lakes Naskaupi, McLean, Minto, Melezes, and Wapussakatoo during the deglaciation of Labrador/Ungava, Canada, was recognized at the end of 1950s. However, glacial lakes have seldom been included in regional reconstructions to constrain the outline of successive ice margins during the glacial retreat in Labrador/Ungava. Reconstruction of the ice flow succession in Labrador/Ungava has often primarily focused on till lineation systems. These reconstructions often depict a late glacial ice dispersal center situated over central Labrador/Ungava. More recent studies on glacial geomorphology including meltwater features, however, suggest that north-central Labrador/Ungava exhibited cold-based conditions at least during the latest deglaciation. Cold-based conditions inhibit basal sliding and formation of landforms, except for meltwater traces such as meltwater channels, glacial lake shorelines and deltas. This situation implies that meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold-based deglaciation. Evidence presented in this study, such as glacial lake shorelines, fossil deltas, and spillway and drainage channels in north-central Labrador/Ungava, indicates the existence of numerous previously unmapped glacial lakes. The mapped glacial lake features are synthesized to a reconstruction of several glacial lake stages which, in turn, are used to constrain the late glacial ice margin retreat pattern over the inferred cold-based areas of north-central Labrador/Ungava. A total of 26 glacial lakes (65 sub-stages) existed during the deglaciation of Labrador/Ungava. These lakes were impounded along the southern margin of the shrinking ice sheet. The required damming ice margins indicate that the last ice remnant of the Laurentide Ice Sheet in Labrador/Ungava was situated over the southern Ungava Bay and the adjacent southern shore.

Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data

A major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

Glaciar Leon, Chilean Patagonia: late-Holocene chronology and geomorphology

Glaciar León is a temperate, grounded outlet of the eastern North Patagonian Icefield (NPI). It terminates at an active calving margin in Lago Leones, a 10 km long proglacial lake. We take a multidisciplinary approach to its description and use ASTER imagery and clast sedimentology to describe the geomorphology of the glacier and its associated moraines. We date periods of glacier retreat over the last 2500 years using a combination of lichenometric, dendrochronological, cosmogenic and optically stimulated luminescence techniques and show that the glacier receded from a large terminal moraine complex some 2500 years ago and underwent further significant recession from nineteenth-century moraine limits. The moraine dates indicate varying retreat rates, in conjunction with significant downwasting. The bathymetry of Lago Leones is characterized by distinct ridges interpreted as moraine ridges that dissect the lake into several basins, with water depths reaching 360 m. The fluctuations of Glaciar León appear to have been controlled by the interplay between climatic forcing and calving dynamics.

The Glacial Map of southern South America

Abstract Please click here to download the map associated with this article. This paper describes The Glacial Map of southern South America. This is a new map of the glacial geomorphology of southern South America between latitudes 38°S and 56°S, approximately the area covered by the former Patagonian Ice Sheets. The map was compiled from interpretation of remotely sensed images (Landsat 7 ETM+, pan-sharpened Landsat 7 and ASTER scenes). The mapped geomorphological features include terminal moraines, glacial lineations, ribbed moraine, glacier debris stripes, trimlines, empty cirques, plateau edge, volcanoes, meltwater channels, deltas, glacial lake shorelines, alluvial fans, sandar, and glacial lake outburst ood tracks. The map also indicates the current extent of major icefields and glaciers in the area, as well as other topographic features such as lakes, rivers, shorelines, deltas, plateau surfaces and volcanoes. We briey describe the most commonly occurring glacial landforms and provide an overview of their distribution within the mapped area.

Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia

In this article, we present a map of the glacial geomorphology of the Altai and Western Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 m resolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.

Glacial meltwater landforms of central British Columbia

Abstract Please click here to download the map associated with this article. The Cordilleran Ice Sheet (CIS), which grew and melted repeatedly across the mountain ranges of westernmost Canada during the late Cenozoic, has imprinted its legacy in the form of glacial landforms, such as meltwater landforms. However, despite their abundance, a coherent effort to map meltwater landforms has been lacking. Here, we present a first regional geomorphological map of glacial meltwater landforms of central British Columbia. Series of well-developed meltwater channels occur at higher elevations on the Interior Plateau, in marginal ranges east of the Coast Mountains, in the Skeena and Omineca mountains, and, in much lower abundances, in the Rocky Mountains. Single-ridged eskers, that in direction are consistent with the regional ice flow direction from glacial lineations, occur in elevated areas of the Interior Plateau. Multiple-ridged larger eskers and esker complexes are, on the other hand, confined to the main topographic lows. The geographical distribution of meltwater landforms is a new reliable dataset for use in palaeoglaciological reconstructions and inference of late glacial ice sheet dynamics in central British Columbia.

Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean

Large freshwater lakes formed in North America and Europe during deglaciation following the Last Glacial Maximum. Rapid drainage of these lakes into the Oceans resulted in abrupt perturbations in climate, including the Younger Dryas and 8.2 kyr cooling events. In the mid-latitudes of the Southern Hemisphere major glacial lakes also formed and drained during deglaciation but little is known about the magnitude, organization and timing of these drainage events and their effect on regional climate. We use 16 new single-grain optically stimulated luminescence (OSL) dates to define three stages of rapid glacial lake drainage in the Lago General Carrera/Lago Buenos Aires and Lago Cohrane/Pueyrredón basins of Patagonia and provide the first assessment of the effects of lake drainage on the Pacific Ocean. Lake drainage occurred between 13 and 8 kyr ago and was initially gradual eastward into the Atlantic, then subsequently reorganized westward into the Pacific as new drainage routes opened up during Patagonian Ice Sheet deglaciation. Coupled ocean-atmosphere model experiments using HadCM3 with an imposed freshwater surface “hosing” to simulate glacial lake drainage suggest that a negative salinity anomaly was advected south around Cape Horn, resulting in brief but significant impacts on coastal ocean vertical mixing and regional climate.