Spatial and temporal patterns in Arctic river ice breakup observed with MODIS and AVHRR time series

摘要

The timing of spring river-ice breakup, a major annual event for physical, biological, and human systems on Arctic rivers, has been used to infer regional climate variations over the past century or more. Most observations of ice breakup are recorded as point data taken from selected ground-based stations. It is unknown whether these point observations are fully representative of breakup patterns elsewhere along the course of a river, Here, daily time series of moderate resolution imaging spectroradiometer (MODIS) and advanced very high resolution radiometer (AVHRR) satellite images are used to remotely sense spatial and temporal patterns in ice breakup along 1600-3300 km lengths of the Lena, Ob', Yenisey, and Mackenzie Rivers. The first day of predominantly ice-free water is visually identified and mapped for ten years (1992-1993, 1995-1998, and 2000-2003), with a mean precision of ±1.75 days. The derived breakup dates show high correlation with ground-based observations, although a slight trend towards earlier satellite-derived dates can be traced to differences in the way ice breakup date is defined. Large ice jams are often observed, particularly at confluences, although smaller ice jams may not be visible due to the limited spatial resolution of the imagery used. At the watershed scale, spatial patterns in breakup seem to be primarily governed by latitude, timing of the spring flood wave, and location of confluences with major tributaries. Interestingly, channel-scale factors such as slope, width, and radius of curvature, which are known to influence ice breakup at the reach scale, do not appear to be major factors at the scale observed here. The degree of similarity between interannual trends in breakup date at distant points along a river is generally high, which supports the use of point-scale data to infer regional climate variations. This similarity does not hold true for the Mackenzie River, where substantial spatial differences in breakup trends are observed. A new variable, spatially integrated breakup date (d{sub}i), uses weighted spatial averaging to provide a more encompassing measure of breakup timing. The Ob' and Yenisey Rivers show similar trends in spatially integrated breakup date from year to year. In contrast, the Mackenzie and Lena show a remarkably consistent negative correlation, here attributed to sea surface temperature anomalies associated with the Pacific Decadal Oscillation Index.