Ice Sheets Research Papers - Academia.edu (original) (raw)

Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ18O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∽29.5 to 14.7 ka and from ∽12.9 to 11.0 ka. At the time... more

Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ18O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∽29.5 to 14.7 ka and from ∽12.9 to 11.0 ka. At the time of the last glacial maximum (LGM), the East Asian summer monsoon weakened and then strengthened in response to changes in Northern Hemisphere insolation. As the ice sheets retreated the East Asian summer monsoon weakened, especially during Heinrich event H1, when atmospheric and oceanic teleconnections transferred the climatic changes around the North Atlantic to the monsoonal regions of Eastern Asia. A depositional hiatus between ∽14.7 and 12.9 ka leaves the deglacial record incomplete, but an abrupt shift in δ18O values at ∽11.5 ka marks the end of the Younger Dryas and the transition into the Holocene. Comparisons of the J1 record to other Chinese speleothem records indicate synchronous climatic changes throughout monsoonal China. Further compar...

Reconstructions of the last (late Devensian) British ice sheet have hitherto been based on assumptions regarding its extent and form. Here we employ observational evidence for the maximum altitude of glacial erosion (trimlines) on... more

Reconstructions of the last (late Devensian) British ice sheet have hitherto been based on assumptions regarding its extent and form. Here we employ observational evidence for the maximum altitude of glacial erosion (trimlines) on mountains that protruded through the ice (palaeonunataks) to reconstruct the form of the ice sheet over ≈ 10 000 km2 of NW Scotland. Contrasts in the clay mineralogy of soils and exposure ages of rock surfaces above and below these trimlines confirm that they represent the upper limit of late Devensian glacial erosion. The reconstruction yields realistic values of basal shear stress and is consistent with independent evidence of ice movement directions. The ice sheet reached ≈ 950 m altitude over the present N–S watershed, descended northwards and north‐westwards, was deflected around an ice dome on Skye and an independent Outer Hebrides ice cap, and probably extended across the adjacent shelf on a bed of deforming sediments.

Degree of rock surface weathering was measured on sites in Oldedalen and Brigsdalen, where dates of deglaciation have been estimated. and on an altitudinal transect on the slopes of Skåla. representing one of the highest supra‐marine... more

Degree of rock surface weathering was measured on sites in Oldedalen and Brigsdalen, where dates of deglaciation have been estimated. and on an altitudinal transect on the slopes of Skåla. representing one of the highest supra‐marine reliefs in western Norway. The Schmidt hammer is useful only for distinguishing sites deglaciated during the Little Ice Age from those deglaciated during the Lateglacial and early Holocene. Degree of roughness of granitic augen gneiss bedrock surfaces was quantified from profiles measured in situ using a micro‐roughness‐meter and profile gauge. There is a significant increase in surface roughness above a clear trimline at c. 1350 m a.s.I. but no significant increase above a higher trimline previously proposed as the vertical limit of the last ice sheet in this area (c. 1560 m a.s.I.). The roughness of boulder surfaces on the summit blockfield does not direr significantly from the roughness of bedrock surfaces downslope as far as the lower trimline. Thes...

The National Space Science Data Center (NSSDC) has initiated an Intelligent Data Management (IDM) research effort which has, as one of its components, the development of an Intelligent User Interface (IUI). The intent of the IUI is to... more

The National Space Science Data Center (NSSDC) has initiated an Intelligent Data Management (IDM) research effort which has, as one of its components, the development of an Intelligent User Interface (IUI). The intent of the IUI is to develop a friendly and intelligent user interface service based on expert systems and natural language processing technologies. The purpose of such a service is to support the large number of potential scientific and engineering users that have need of space and land-related research and technical data, but have little or no experience in query languages or understanding of the information content or architecture of the databases of interest. This document presents the design concepts, development approach and evaluation of the performance of a prototype IUI system for the Crustal Dynamics Project Database, which was developed using a microcomputer-based expert system tool (M. 1), the natural language query processor THEMIS, and the graphics software s...

The possibility that a large ocean once occupied the northern plains of Mars has been proposed based on the interpretive identification of various landforms, including sedimentary deposits, outwash plains and shorelines - the latter based... more

The possibility that a large ocean once occupied the northern plains of Mars has been proposed based on the interpretive identification of various landforms, including sedimentary deposits, outwash plains and shorelines - the latter based largely on the work of Parker et al., who identified evidence of a series of nested levels, which they interpreted as shorelines, located along the highland/lowland boundary. The combination of high-resolution orbiter images with MOLA gridded topography has enabled the compilation of regional and global maps of the proposed shorelines. The highest and oldest of these was called the 'Arabian Level' and is believed to date back to the Late Noachian. In high-resolution MOC, HiRISE and HRSC images, the Arabian Level exhibits evidence of terracing (potentially indicative of wave-cut erosion); however, the topographically lower, younger 'shorelines' do not. The interior plains encompassed by these lower levels include vast expanses of col...

Full-thickness crevasses can transport water from the glacier surface to the bedrock where high water pressures can open kilometre-long cracks along the basal interface, which can accelerate glacier flow. We present a first computational... more

Full-thickness crevasses can transport water from the glacier surface to the bedrock where high water pressures can open kilometre-long cracks along the basal interface, which can accelerate glacier flow. We present a first computational modelling study that describes time-dependent fracture propagation in an idealised glacier causing rapid supraglacial lake drainage. A novel two-scale numerical method is developed to capture the elastic and viscoelastic deformations of ice along with crevasse propagation. The fluid-conserving thermo–hydro–mechanical model incorporates turbulent fluid flow and accounts for melting and refreezing in fractures. Applying this model to observational data from a 2008 rapid-lake-drainage event indicates that viscous deformation exerts a much stronger control on hydrofracture propagation compared to thermal effects. This finding contradicts the conventional assumption that elastic deformation is adequate to describe fracture propagation in glaciers over short timescales (minutes to several hours) and instead demonstrates that viscous deformation must be considered to reproduce observations of lake drainage rates and local ice surface elevation changes. As supraglacial lakes continue expanding inland and as Greenland Ice Sheet temperatures become warmer than −8 °C, our results suggest rapid lake drainage events are likely to occur without refreezing, which has implications for the rate of sea level rise.

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near... more

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5° to 7.0°C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level,...

Radar altimeters are one of the main tools for measuring elevation changes across the Antarctic and Greenland ice sheets and larger ice caps. A ground‐based radar was deployed in autumn 2004 and spring 2006 in the percolation zone of the... more

Radar altimeters are one of the main tools for measuring elevation changes across the Antarctic and Greenland ice sheets and larger ice caps. A ground‐based radar was deployed in autumn 2004 and spring 2006 in the percolation zone of the Greenland Ice Sheet. This radar is a high bandwidth system operating in the Ku band, the same frequency as several satellite altimeters. Measurements were made over an elevation range of 1795 to 2350 m, along with snow pit and shallow core studies. These measurements demonstrate the spatial and temporal variations in the backscatter. Relative strengths of surface and volume reflections change dramatically between spring and autumn and there is also high spatial variability across the percolation zone. The extent of percolation will affect elevation estimates made by radar altimeters.

The Western Antarctic Peninsula is warming. As a result, summertime salinity stratification may occur more frequently due to enhanced glacial melt water input. The resulting changes in environmental conditions could affect the seasonal... more

The Western Antarctic Peninsula is warming. As a result, summertime salinity stratification may occur more frequently due to enhanced glacial melt water input. The resulting changes in environmental conditions could affect the seasonal dynamics of phytoplankton and Bacteria. The aim of the present study was to examine the environmental characteristics that drive coastal Antarctic microbial community dynamics. Sampling was done at 15 m depth during the austral summer of 2010-2011 at the Rothera oceanographic and biological Time Series site (RaTS) in northern Marguerite bay, Antarctica. Environmental variables included salinity, temperature, density, irradiance, wind speed, major nutrients and δ18O, the latter indicative of fresh water origin. Phytoplankton biomass and group specific composition were followed using size fractionated Chl aand HPLC-CHEMTAX. Four different primer sets were used to study community changes using DGGE analysis: eukaryotes, diatoms, dinoflagellates and Bacte...

Landscape stability in the Dry Valleys sector of the Transantarctic Mountains provides evidence of extremely low rates of denudation and hence apparent climatic stability on Antarctica over the last 10 to 15 million years. This evidence... more

Landscape stability in the Dry Valleys sector of the Transantarctic Mountains provides evidence of extremely low rates of denudation and hence apparent climatic stability on Antarctica over the last 10 to 15 million years. This evidence has been widely used to support the ...