Rapid tidewater glacier retreat: a comparison between Columbia Glacier, Alaska and Patagonian calving glaciers

Time-changes in the terminus positions of Patagonian grounded calving glaciers are studied. The framework for the study is a model of terminus retreat based on observations of Columbia Glacier, Alaska. The interpretation favored in this work is that rapid retreat is caused by the terminus thinning to near flotation and weakening of the ice by bottom crevasses. Both thinning and bottom crevasse formation are caused by the increase in near-terminus stretching during rapid retreat. The model is consistent with the behavior of calving Patagonian glaciers regardless of the salinity of the water body calved into. Continuity calculations on Glaciar San Rafael, Chile indicate internal voids, possibly in the form of bottom crevasses, as on Columbia Glacier.     

Landsat 8全色影像阴影的扁平冰山出水高度提取

冰山出水高度是测量冰山厚度进而估算冰山体积的一个重要几何参数,是定量评估冰山对海洋的淡水输入量的基础。冬季冰山在海冰上成影且阴影较长,本文提出利用阴影测高模型高精度测量冰山出水高度的方法。试验选择2016年8月29日、9月7日和9月16日中心太阳高度角分别为5.43°、7.49°和11.01°的3期Landsat 8全色15 m影像,以独立扁平冰山为例,自动提取冰山在海冰上的阴影长度计算冰山出水高度,并利用不同时相同名成影点进行交叉验证评估测量精度。结果显示：阴影长度测量误差优于1个像元,在太阳高度角低于11.01°时,全色15 m影像提取的冰山出水高度均方根误差（RMSE）低于2.0 m,平均绝对误差（MAE）低于1.5 m。由此表明：在冬季低太阳高度角下,Landsat 8全色15 m影像可用于高精度测量冰山出水高度,具有大范围测量南极冰山出水高度的潜力。     

Sea-floor scour at the mouth of Hudson Strait by deep-keeled icebergs from the Laurentide Ice Sheet

Physical evidence on the dimensions of icebergs released from the mouth of Hudson Strait into the northwest Atlantic during the last Heinrich event (H-0) is presented. Side-scan sonar imagery shows scour marks up to 700 m wide and longer than 28 km. These scour marks were carved by gigantic icebergs (megabergs) with keel drafts possibly as great as 660 m capable of scouring trenches 20 to 25 m deep into the seabed. These icebergs were likely calved from the grounding margin of a thick (possibly as thick as 640 m) rapidly-flowing glacial margin during the H-0 Heinrich event (11 ka BP). Along with the relatively few megabergs released were large numbers of smaller icebergs that calved from the ice margin at the same time and were also produced from break-up of the megabergs. Scouring of the seabed by the large and smaller icebergs happened at the same time, with megabergs scouring only in the deep waters of Hatton Basin, and the smaller bergs scouring only on the eastern, shallow margin of the Basin at the continental shelf break.     

The origin and flux of icebergs released into the Last Glacial Maximum Northern Hemisphere oceans: the impact of ice‐sheet topography

The precipitation fields of a palaeoatmospheric general circulation model are used to derive estimates of the geographical distribution, and flux, of icebergs from the Laurentide, Fennoscandinavian and eastern Siberian ice‐sheets at the Last Glacial Maximum (LGM). The atmospheric model fields from LGM simulations using CLIMAP or Peltier (ICE‐4G) ice orography were studied, to test the sensitivity of the predicted flux. The estimated Northern Hemispheric LGM iceberg flux is 3500–4000 km³ yr^?1, of which about 60% issued directly into the North Atlantic. The iceberg flux from the St Lawrence area is of similar significance to that issuing from Hudson Strait in all estimates. Both the North Pacific and the Arctic received substantial iceberg fluxes (ca. 700 km³ yr^?1), with relatively minor differences occurring between the two ice‐sheet reconstructions. Apparent discrepancies between Arctic deep‐sea core samples of ice‐rafted debris and our estimates of mean glacial iceberg flux may be ascribed to coastal trapping of bergs, the existence of floating ice tongues or a rapid exit of icebergs from the Arctic basin into the Greenland Sea through the Fram Strait. Copyright © 2001 John Wiley & Sons, Ltd.     

Trends and Variability in Sea Ice and Icebergs off the Canadian East Coast

ABSTRACT

Seasonal time series of sea-ice area or extent in several regions along the east coast of Canada were compiled from several sources for the period 1901 to 2013 and compared with an index of ice extent off southwest Greenland, iceberg season length south of 48°N, air temperature, and other climate indices. Trends in winter ice area and iceberg season length are significant over the past 100 years and 30 years. Variability of winter ice area and iceberg season length is associated with a combination of the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) indices superimposed on a negative trend. Thus, large declines in ice area and iceberg season length in the 1920s and 1990s can be attributed to a decreasing NAO index and a shift to the positive phase of the AMO at the end of these decades. Ice extent in southern areas such as the Scotian Shelf is more strongly correlated with the Western Atlantic index than with the NAO. Ice area trends (in percent per decade) are larger in magnitude and account for twice as much of the variance in ice area for summer than for winter, with summer trends significant over 30-, 60- and 100-year periods. Sea-ice variability is generally consistent with air temperature variability in the various regions; in the 1930s, during the early twentieth-century warming period, ice anomalies were higher and temperature anomalies were lower along the coast of eastern Canada than along the coast of southwestern Greenland.     

Long-range detection of hydroacoustic signals from large icebergs in the Ross Sea, Antarctica

Hydroacoustic signals detected in late 2000 by seismic stations in Polynesia are shown to originate from huge icebergs which at the time were drifting in the Ross Sea after calving off the Ross Ice Shelf. The signals present a broad variety of spectral characteristics, most of them featuring prominent eigenfrequencies in the 4-7 Hz range, often complemented by overtones. Most epicenters, obtained by combining observations of distant hydroacoustic and regional seismic records, follow the spatio-temporal evolution of the drift of iceberg B-15B. Most of the signals are generated during a 36-day time window when it is speculated that B-15B collided with smaller icebergs or was scraping the ocean floor on the shallow continental shelf. We speculate on the possible physical nature of the resonator generating the signals, which could correspond to an elastic mode of the iceberg, or to the oscillation of fluid-filled cracks in the ice.     

Symposium On Sediment Storage In Rivers And Estuaries

Book Reviewed in this article:

Geographical Aspects of Health and Disease in India. Rais Akhtarand A.T.A. Learmonth, eds.

Antarctic Treaty System: An Assessment. Proceedings of a Workshop at Beardmore South Field Camp, Antarctica.

American Electoral Mosaics. J. Clark Archerand Fred M. Shelley.

Kompas op Suidwes-Afrika/Namibie. W.S. Barnard, ed.

Jerusalem in the 19th Century: The Old City. Yehoshua Ben-Arieh.

The World as a Total System. Kenneth E. Boulding.

A Social History of Housing 1815–1985, Second Ed. John Burnett.

Human Migration. W.A.V. Clark.

Regional Population Projection Models. Andrei Rogers.

The State of Population Theory: Forward from Malthus. David Colemanand Roger Schofield, eds.

Imagining Tomorrow: History, Technology and the American Future. Joseph C. Corn, ed.

Swidden Agriculture in Indonesia: The Subsistence Strategies of the Kalimantan Kantú. Michael R. Dove.

Glacial Geologic Processes. David Drewry.

Physics of Desertification. Farouk El-Bazand M.H.A. Hassan, eds.

Housing the Homeless. Jon Ericksonand Charles Wilhelm, eds.

Settlement Patterns in Missouri: A Study of Population Origins, with a Wall Map. Russel L. Gerlach.

Desert Development: Man and Technology in Sparselands. Yehuda Gradus, ed.

Nuclear Winter. The Evidence and Risks. Owen Greene, Ian Percivaland Irene Ridge.

The Take-off of Suburbia and the Crisis of the Central City. Günter Heinritzand Elisabeth Lichtenberger, eds.

Regional Input-Output Analysis. Geoffrey J. D. Hewings.

Spatial Transportation Modeling. Christian Werner.

The Atlas of Georgia. Thomas W. Hodlerand Howard A. Schretter, eds.

Latin America. 5th ed. Preston E. Jamesand C.W. Minkel.

Applied Remote Sensing. C.P. Lo.

Localities, Class, and Gender. The Lancaster Regionalism Group.

Urban Social Movements: The City after Castells. Stuart Lowe.

Politics and Method. Doreen Masseyand Richard Meegan, eds.

Land Use. A. S. Mather.

The Kingdom of Coal. Donald L. Millerand Richard E. Sharpless.

The Presidio and Militia on the Northern Frontier of New Spain, A Documentary History, Vol. 1: 1570–1700. Thomas H. Naylorand Charles W. Polzer, S.J., comps. andeds.

Nuclear Power: Siting and Safety. Stan Openshaw.

The Central African Republic: The Continent's Hidden Heart. Thomas O'Toole.

Environmental and Dynamic Geomorphology. Márton Pécsi, ed.

Remote Sensing Principles and Interpretation. Floyd F. Sabins, Jr.

Acid Rain and Friendly Neighbors: The Policy Dispute between Canada and the United States. Jurgen Schmandtand Hilliard Roderick, eds.

Earth's Changing Surface: An Introduction to Geomorphology. M.J. Selby.

International Migration: The Female Experience. Rita J. Simonand Caroline B. Brettell, eds.

On Geography and Its History. D.R. Stoddart.

Transportation Networks: A Quantitative Approach. D. Teodorovic.

Processes in Physical Geography. R.D. Thompson, A.M. Mannion, C.W. Mitchell, M. Parry, J.R.G. Townshend.

Imaging Radar for Resources Surveys. J.W. Trevett.

Dominance and Affection: The Making of Pets. Yi-Fu Tuan.

Capturing the Horizon. The Historical Geography of Transportation since the Transportation Revolution of the Sixteenth Century. James E. Vance, Jr.

Nations at Risk: The Impact of the Computer Revolution. Edward Yourdon.     

BOOK REVIEWS

Book Reviewed in this article: Geographical Aspects of Health and Disease in India . Rais Akhtar and A.T.A. Learmonth , eds . Antarctic Treaty System: An Assessment . Proceedings of a Workshop at Beardmore South Field Camp, Antarctica. American Electoral Mosaics . J. Clark Archer and Fred M. Shelley . Kompas op Suidwes-Afrika/Namibie . W.S. Barnard , ed . Jerusalem in the 19th Century: The Old City . Yehoshua Ben -Arieh . The World as a Total System . Kenneth E. Boulding . A Social History of Housing 1815–1985, Second Ed . John Burnett . Human Migration . W.A.V. Clark . Regional Population Projection Models . Andrei Rogers . The State of Population Theory: Forward from Malthus . David Coleman and Roger Schofield , eds . Imagining Tomorrow: History, Technology and the American Future . Joseph C. Corn , ed. Swidden Agriculture in Indonesia: The Subsistence Strategies of the Kalimantan Kantú . Michael R. Dove . Glacial Geologic Processes . David Drewry . Physics of Desertification . Farouk El -Baz and M.H.A. Hassan , eds . Housing the Homeless . Jon Erickson and Charles Wilhelm , eds . Settlement Patterns in Missouri: A Study of Population Origins, with a Wall Map . Russel L. Gerlach . Desert Development: Man and Technology in Sparselands . Yehuda Gradus , ed . Nuclear Winter. The Evidence and Risks . Owen Greene , Ian Percival and Irene Ridge . The Take-off of Suburbia and the Crisis of the Central City . Günter Heinritz and Elisabeth Lichtenberger , eds . Regional Input-Output Analysis . Geoffrey J. D. Hewings . Spatial Transportation Modeling . Christian Werner . The Atlas of Georgia . Thomas W. Hodler and Howard A. Schretter , eds . Latin America. 5th ed . Preston E. James and C.W. Minkel . Applied Remote Sensing . C.P. Lo . Localities, Class, and Gender . The Lancaster Regionalism Group . Urban Social Movements: The City after Castells . Stuart Lowe . Politics and Method . Doreen Massey and Richard Meegan , eds . Land Use . A. S. Mather . The Kingdom of Coal . Donald L. Miller and Richard E. Sharpless . The Presidio and Militia on the Northern Frontier of New Spain, A Documentary History, Vol. 1: 1570–1700 . Thomas H. Naylor and Charles W. Polzer , S.J., comps . and eds . Nuclear Power: Siting and Safety . Stan Openshaw . The Central African Republic: The Continent's Hidden Heart . Thomas O'Toole . Environmental and Dynamic Geomorphology . Márton Pécsi , ed . Remote Sensing Principles and Interpretation . Floyd F. Sabins , Jr . Acid Rain and Friendly Neighbors: The Policy Dispute between Canada and the United States . Jurgen Schmandt and Hilliard Roderick , eds . Earth's Changing Surface: An Introduction to Geomorphology . M.J. Selby . International Migration: The Female Experience . Rita J. Simon and Caroline B. Brettell , eds . On Geography and Its History . D.R. Stoddart . Transportation Networks: A Quantitative Approach . D. Teodorovic . Processes in Physical Geography . R.D. Thompson , A.M. Mannion , C.W. Mitchell , M. Parry , J.R.G. Townshend . Imaging Radar for Resources Surveys . J.W. Trevett . Dominance and Affection: The Making of Pets . Yi -Fu Tuan . Capturing the Horizon. The Historical Geography of Transportation since the Transportation Revolution of the Sixteenth Century . James E. Vance , Jr . Nations at Risk: The Impact of the Computer Revolution . Edward Yourdon .