The north coast of Ellesmere Island is the location of the only known ice shelves in the northern hemisphere. Present Arctic ice shelves are as much as 40–50 m thick and occupy sheltered fiords and embayments. These thick floating ice masses are remnants of the once-extensive Ellesmere Ice Shelf that has disintegrated since 1876–1906, when Aldrich and Peary respectively travelled along the coast. Reasons for the disintegration are not clear, but it has created many ice islands that have been known to circulate in the Arctic Ocean for 35 years or more. Both ice islands and ice shelves are readily distinguished from their surroundings by an undulating surface topography of parallel ridges and troughs up to 300 m apart. The undulations probably owe their origin to the effects of wind and meltwater. Since 1952 these large ice masses have been the subject of considerable research. Ice shelf growth began about 4000 BP, when glaciers flowed off the land and remained afloat in fiords and inlets, and sea ice grew thick and remained fast to the coast. The glacier and sea ice acted as platforms for further thickening both by surface accumulation of snow and ice and by undersurface accretion of fresh, brackish and saline ice. Although much has been learned about the growth, structure and behaviour of arctic ice shelves, questions still remain concerning ice island calving mechanisms, bottom freezing, thick sea ice growth and origins of the ridges and troughs.
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