Northern Ellesmere Island ice shelf and ice tongue extents

The ice shelves along the northern coast of Ellesmere Island have been in a state of decline since at least the early 20th century. Available data derived from explorers' journals, aerial photographs and satellite imagery have been compiled into a single geospatial database of ice shelf and glacier ice tongue extent over 13 observation periods between 1906 to 2015. During this time there was a loss of 8,061 km² (94%) in ice shelf area. The vast majority of this loss occurred via episodic calving, in particular during the first six decades of the 20th century. More recently, between 1998 and 2015, 515 km² of shelf ice calved. Some ice shelves also thinned in situ, transitioning to thinner and weaker ice types that can no longer be considered ice shelf, although the timing of this shift is difficult to constrain with the methods used here. Some ice shelves composed partly of ice tongues (glacier or composite ice shelves) also disintegrated to the point where the ice tongues were isolated, representing a loss of ice shelf extent. Our digitization methods were typically repeatable to within 3%, and generally agreed with past determinations of extent. This research highlights the fact that the break-up of these massive features is an ongoing phenomenon. It is hoped that this comprehensive dataset will provide a basis for comparison of future changes in this region. [Abstract from Mueller DR, Copland L, Jeffries MO (2017) Changes in Canadian Arctic ice shelf extent since 1906. In: Copland L, Mueller DR (eds) Arctic Ice Shelves and Ice Islands, Springer, Dordrecht]埃尔斯米尔岛（Ellesmere Island）北海岸的冰架自至少20世纪初以来便持续处于衰退状态。研究人员将探险家日志、航空摄影照片与卫星影像所获取的可用数据整合为一套统一的地理空间数据库，记录了1906年至2015年间13个观测周期内的冰架与冰川冰舌范围。在此期间，冰架总面积减少了8061平方千米，占原总面积的94%。其中绝大多数面积损失源于间歇性冰架崩解，尤以20世纪前六十年最为突出。而在近年的1998年至2015年间，又有515平方千米的架冰发生崩解。部分冰架还发生了原位变薄，转变为更薄、强度更低的冰体类型，已不再能被归类为冰架，但利用本研究采用的方法难以确定这一转变的具体时间节点。部分由冰舌构成的冰架（冰川冰架或复合冰架）也发生解体，最终导致冰舌与主体分离，进一步造成冰架范围的损失。本研究采用的数字化方法重复性误差通常控制在3%以内，且与过往的冰架范围测定结果基本吻合。本研究凸显了一个事实：这类巨型冰体的崩解是一个持续发生的过程。本套全面的数据集有望为该区域未来的冰况变化对比研究提供基础支撑。[本文摘要源自Mueller DR、Copland L、Jeffries MO（2017）《1906年以来加拿大北极冰架范围变化》，收录于Copland L、Mueller DR主编的《北极冰架与冰岛》，施普林格（Springer）多德雷赫特分社出版]