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Ice Extent (ice + extent)
Selected AbstractsDistribution of minke whales in the Bellingshausen and Amundsen Seas (60°W,120°W), with special reference to environmental/physiographic variablesFISHERIES OCEANOGRAPHY, Issue 3 2000Fujio Kasamatsu The relationship between the distribution of minke whales (Balaenoptera acutorostrata) in the Bellingshausen and Amundsen Seas (longitude between 60°W and 120°W), and environmental and physiographic variables (sea-surface temperature, sea-ice extension, and sea-floor-slope type), was studied to determine whether these environmental and physical factors affect the distribution and density of minke whales. The analysis was based on sightings data obtained from the 1989/90 and 1982/83 IWC/IDCR cruises. The mean sea-surface temperatures for comparable areas were significantly higher in 1989/90 (2.04°C) than in 1982/83 (1.12°C), and the area where the sea-surface temperature was greater than 1°C in the 1989/90 study was approximately twice that of the 1982/83 study. Additionally, during the surveys, the extent of the sea ice in 1989/90 was less than that in 1982/83, with the mean ice edge about 92.6 km (50 nautical miles; 1 nautical mile ,1.852 km) farther south in 1989/90 than in 1982/83. This is consistent with the sea ice extent observed in winter, when the sea ice extent was less in 1989 than in 1982. The distribution of minke whales was substantially different between the two surveys, with the density and abundance of minke whales being greater in 1982/83 than in 1989/90. The warmer sea-surface temperatures, fewer cold-water intrusions, and the smaller extent of sea ice in 1989/90 may be related to the difference in distribution of minke whales from 1982/83, possibly owing to the shift in availability of prey. [source] Contrasting population changes in sympatric penguin species in association with climate warmingGLOBAL CHANGE BIOLOGY, Issue 3 2006JAUME FORCADA Abstract Climate warming and associated sea ice reductions in Antarctica have modified habitat conditions for some species. These include the congeneric Adélie, chinstrap and gentoo penguins, which now demonstrate remarkable population responses to regional warming. However, inconsistencies in the direction of population changes between species at different study sites complicate the understanding of causal processes. Here, we show that at the South Orkney Islands where the three species breed sympatrically, the less ice-adapted gentoo penguins increased significantly in numbers over the last 26 years, whereas chinstrap and Adélie penguins both declined. These trends occurred in parallel with regional long-term warming and significant reduction in sea ice extent. Periodical warm events, with teleconnections to the tropical Pacific, caused cycles in sea ice leading to reduced prey biomass, and simultaneous interannual population decreases in the three penguin species. With the loss of sea ice, Adélie penguins were less buffered against the environment, their numbers fluctuated greatly and their population response was strong and linear. Chinstrap penguins, considered to be better adapted to ice-free conditions, were affected by discrete events of locally increased ice cover, but showed less variable, nonlinear responses to sea ice loss. Gentoo penguins were temporarily affected by negative anomalies in regional sea ice, but persistent sea ice reductions were likely to increase their available niche, which is likely to be substantially segregated from that of their more abundant congeners. Thus, the regional consequences of global climate perturbations on the sea ice phenology affect the marine ecosystem, with repercussions for penguin food supply and competition for resources. Ultimately, variability in penguin populations with warming reflects the local balance between penguin adaptation to ice conditions and trophic-mediated changes cascading from global climate forcing. [source] Survey of Greenland instrumental temperature records: 1873,2001INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2002Jason E. Box Abstract Temporal and spatial variability are analysed in Greenland instrumental temperature records from 24 coastal and three ice sheet locations. Trends over the longest period available, 1873,2001, at Ilulissat/Jakobshavn indicate statistically significant warming in all seasons: 5°C in winter. Trends over the 1901,2000 century in southern Greenland indicate statistically significant spring and summer cooling. General periods of warming occurred from 1885 to 1947 and 1984 to 2001, and cooling occurred from 1955 to 1984. The standard period 1961,90 was marked by 1,2°C statistically significant cooling. In contrast to Northern Hemisphere mean temperatures, the 1990s do not contain the warmest years on record in Greenland. The warmest years in Greenland were 1932, 1947, 1960, and 1941. The coldest years were 1918, 1984, 1993, and 1972, several of which coincide with major volcanic eruptions. Over 1991,2000, statistically significant 2,4°C warming was observed in western Greenland, 1.1°C warming at the ice sheet summit (3200 m), although this is statistically insignificant. Annual temperature trends are dominated by winter variability. Much of the observed variability is shown to be linked with the North Atlantic oscillation (NAO), sea ice extent, and volcanism. The correlation of coastal temperature anomalies with the NAO is statistically significant, in autumn and winter at western and southern sites. Warming from 1873 to 1930 and subsequent cooling persists after the removal of the NAO signal. Temperature trends are often opposite between west and east Greenland. This apparent teleconnection is spurious, however, given insignificant east,west correlation values. Frequency peaks correspond with periods of 3.7, 14.3, 9.1, 5.5,6.0, 11.1, and 7.1 years in both temperature and NAO. Copyright © 2002 Royal Meteorological Society. [source] A multi-dating approach applied to proglacial sediments attributed to the Most Extensive Glaciation of the Swiss AlpsBOREAS, Issue 3 2010ANDREAS DEHNERT Dehnert, A., Preusser, F., Kramers, J. D., Akçar, N., Kubik, P. W., Reber, R. & Schlüchter, C. 2010: A multi-dating approach applied to proglacial sediments attributed to the Most Extensive Glaciation of the Swiss Alps. Boreas, Vol. 39, pp. 620,632. 10.1111/j.1502-3885.2010.00146.x. ISSN 0300-9483. The number and the timing of Quaternary glaciations of the Alps are poorly constrained and, in particular, the age of the Most Extensive Glaciation (MEG) in Switzerland remains controversial. This ice advance has previously been tentatively correlated with the Riss Glaciation of the classical alpine stratigraphy and with Marine Isotope Stage (MIS) 6 (186,127 ka). An alternative interpretation, based on pollen analysis and stratigraphic correlations, places the MEG further back in the Quaternary, with an age equivalent to MIS 12 (474,427 ka), or even older. To re-evaluate this issue in the Swiss glaciation history, a multi-dating approach was applied to proglacial deltaic ,Höhenschotter' deposits in locations outside the ice extent of the Last Glacial Maximum. Results of U/Th and luminescence dating suggest a correlation of the investigated deposits with MIS 6 and hence with the Riss Glaciation. Cosmogenic burial dating suffered from large measurement uncertainties and unusually high 26Al/10Be ratios and did not provide robust age estimates. [source] Rethinking Late Weichselian ice-sheet dynamics in coastal NW SvalbardBOREAS, Issue 1 2005JON Y. LANDVIK New marine geological evidence provides a better understanding of ice-sheet dynamics along the western margin of the last Svalbard/Barents Sea Ice Sheet. A suite of glacial sediments in the Kongsfjordrenna cross-shelf trough can be traced southwards to the shelf west of Prins Karls Forland. A prominent moraine system on the shelf shows minimum Late Weichselian ice extent, indicating that glacial ice also covered the coastal lowlands of northwest Svalbard. Our results suggest that the cross-shelf trough was filled by a fast-flowing ice stream, with sharp boundaries to dynamically less active ice on the adjacent shelves and strandflats. The latter glacial mode favoured the preservation of older geological records adjacent to the main pathway of the Kongsfjorden glacial system. We suggest that the same model may apply to the Late Weichselian glacier drainage along other fjords of northwest Svalbard, as well as the western margin of the Barents Ice Sheet. Such differences in glacier regime may explain the apparent contradictions between the marine and land geological record, and may also serve as a model for glaciation dynamics in other fjord regions. [source] Modeling the deglaciation of the Green Bay Lobe of the southern Laurentide Ice SheetBOREAS, Issue 1 2004CORNELIA WINGUTH We use a time-dependent two-dimensional ice-flow model to explore the development of the Green Bay Lobe, an outlet glacier of the southern Laurentide Ice Sheet, leading up to the time of maximum ice extent and during subsequent deglaciation (c. 30 to 8 cal. ka BP). We focus on conditions at the ice-bed interface in order to evaluate their possible impact on glacial landscape evolution. Air temperatures for model input have been reconstructed using the GRIP ,8O record calibrated to speleothem records from Missouri that cover the time periods of c. 65 to 30 cal. ka BP and 13.25 to 12.4 cal. ka BP. Using that input, the known ice extents during maximum glaciation and early deglaciation can be reproduced reasonably well. The model fails, however, to reproduce short-term ice margin retreat and readvance events during later stages of deglaciation. Model results indicate that the area exposed after the retreat of the Green Bay Lobe was characterized by permafrost until at least 14 cal. ka BP. The extensive drumlin zones that formed behind the ice margins of the outermost Johnstown phase and the later Green Lake phase are associated with modeled ice margins that were stable for at least 1000 years, high basal shear stresses (c. 100 kPa) and permafrost depths of 80,200 m. During deglaciation, basal meltwater and sliding became more important. [source] Chronology of deglaciation based on 10Be dates of glacial erosional features in the Grimsel Pass region, central Swiss AlpsBOREAS, Issue 4 2006MEREDITH A. KELLY Surface exposure dating, using in situ produced cosmogenic 10Be, is applied to determine the time since deglaciation of bedrock surfaces in the Grimsel Pass region. Nine 10Be dates from bedrock surfaces corrected for cover by snow are minimum ages for deglaciation of the pass. Four 10Be dates from surfaces below 2500 meters above sea level (m a.s.l.) on Nägelisgrätli, east of Grimsel Pass, yield ages that range from about 14 000 to 11 300 years. Three 10Be dates from locations above 2600 m a.s.l. on Nägelisgrätli are between about 11 700 and 10 400 years. Two 10Be dates from locations at 2560 m a.s.l. below Juchlistock are about 12 100 and 11 000 years. The geographical distribution of 10Be dates on Nägelisgrätli either may show the timing of progressive deglaciation of Grimsel Pass or may reflect differences in subglacial erosion of bedrock in the pass region. All dates are discussed in the context of deglaciation of the late Würmian Alpine ice cap and deglaciation from Last Glacial Maximum (LGM) ice extents in other regions. [source] Modeling the deglaciation of the Green Bay Lobe of the southern Laurentide Ice SheetBOREAS, Issue 1 2004CORNELIA WINGUTH We use a time-dependent two-dimensional ice-flow model to explore the development of the Green Bay Lobe, an outlet glacier of the southern Laurentide Ice Sheet, leading up to the time of maximum ice extent and during subsequent deglaciation (c. 30 to 8 cal. ka BP). We focus on conditions at the ice-bed interface in order to evaluate their possible impact on glacial landscape evolution. Air temperatures for model input have been reconstructed using the GRIP ,8O record calibrated to speleothem records from Missouri that cover the time periods of c. 65 to 30 cal. ka BP and 13.25 to 12.4 cal. ka BP. Using that input, the known ice extents during maximum glaciation and early deglaciation can be reproduced reasonably well. The model fails, however, to reproduce short-term ice margin retreat and readvance events during later stages of deglaciation. Model results indicate that the area exposed after the retreat of the Green Bay Lobe was characterized by permafrost until at least 14 cal. ka BP. The extensive drumlin zones that formed behind the ice margins of the outermost Johnstown phase and the later Green Lake phase are associated with modeled ice margins that were stable for at least 1000 years, high basal shear stresses (c. 100 kPa) and permafrost depths of 80,200 m. During deglaciation, basal meltwater and sliding became more important. [source] | ||||||||||