东西伯利亚海岸侵蚀的速度加快

The high cliffs of Eastern Siberia -- which mainly consist of permafrost（永久冻土） -- continue to erode¹ at an ever quickening pace. This is the conclusion which scientists of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine² Research have reached after their evaluation³ of data and aerial（航空的） photographs of the coastal⁴ regions for the last 40 years. According to the researchers, the reasons for this increasing erosion are rising summer temperatures in the Russian permafrost regions as well the retreat of the Arctic sea ice. This coastal protection recedes⁵ more and more on an annual basis. As a result, waves undermine the shores. At the same time, the land surface begins to sink. The small island of Muostakh east of the Lena Delta⁶ is especially affected⁷ by these changes. Experts fear that it might even disappear altogether should the loss of land continue. The interconnectedness is clear and unambiguous: The warmer the east Siberian permafrost regions become, the quicker the coast erodes⁸. "If the average temperature rises by 1 degree Celsius⁹ in the summer, erosion accelerates by 1.2 metres annually," says AWI geographer¹⁰ Frank Günther, who investigates the causes of the coastal breakdown¹¹ in Eastern Siberia together with German and Russian colleagues, and who has published his findings in two scientific articles.   In these studies, he and his team evaluated high resolution air and satellite photos from 1951 to 2012 as well as measurements of the past four years. In addition, the researchers surveyed four coastal sections along the Laptev Sea (see map) and on the island of Muostakh.   One example of the changes documented in their research are the warming summers. While the temperatures during the period of investigation¹² exceeded zero degrees Celsius on an average of 110 days per year, the scientists counted a total of 127 days in the years 2010 and 2011. The following year, 2012, the number of days with temperatures above freezing increased to 134.   This increase in temperature is not without consequences. Whereas a thick layer of sea ice used to protect the frozen soil almost all year round, it now recedes in this part of the Arctic for increasing periods of time during the summer months. The number of summer days on which the sea ice in the southern Laptew Sea vanishes completely grows steadily¹³. "During the past two decades, there were, on average, fewer than 80 ice-free days in this region per year. During the past three years, however, we counted 96 ice-free days on average. Thus, the waves can nibble#p#分页标题#e#¹⁴ at the permafrost coasts for approximately two more weeks each year," explains AWI permafrost researcher Paul Overduin.