Modeling erosion of ice-rich permafrost bluffs along the Alaskan Beaufort Sea coast
Modeling erosion of ice-rich permafrost bluffs along the Alaskan Beaufort Sea coast
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DOI：
10.1002/2013jf002845
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发表时间：
2014-05-01
影响因子：
3.9
通讯作者：
Urban, Frank E.
中科院分区：
文献类型：
--
作者：
Barnhart, Katherine R.;Anderson, Robert S.;Urban, Frank E.
北极气候正在发生变化，导致富含冰的永久冻土海岸悬崖加速退缩。自1955年以来，阿拉斯加波弗特海岸的侵蚀率增加了大约三倍，从每年6.8米增加到每年19米，而自1979年以来，无冰季节从45天增加到100天，增加了大约两倍。我们开发了一个断崖退缩的数值模型，以评估在这种情况下，海洋无冰季节长度、海平面、水温、近岸波场和永久冻土温度在控制侵蚀速率方面的相对作用。该模型捕捉了在波弗特海岸的短期监测实验中观察到的侵蚀过程，包括融化缺口的演变、冰楔块的倾覆以及这些块的退化。模型结果与断裂带演化时移图像和海洋仪器时间序列相吻合。侵蚀是高度偶发的，40%的侵蚀是在不到5%的无冰季节完成的。在我们评估的海底侵蚀速率公式中，我们提倡同时考虑水温和近岸波场的公式。由于高水位是侵蚀的先决条件，未来任何增加水位超过悬崖底部频率的变化都将增加海岸侵蚀的速度。海平面的一定上升和暴风雨的潜在变化都将促成这种影响。由于水温也会影响侵蚀率，任何将无冰季节进一步延长至日照最多的仲夏期的情况都可能导致海岸退缩率的进一步增加。
The Arctic climate is changing, inducing accelerating retreat of ice-rich permafrost coastal bluffs. Along Alaska's Beaufort Sea coast, erosion rates have increased roughly threefold from 6.8 to 19 m yr-1 since 1955 while the sea ice-free season has increased roughly twofold from 45 to 100 days since 1979. We develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice-free season, sea level, water temperature, nearshore wavefield, and permafrost temperature in controlling erosion rates in this setting. The model captures the processes of erosion observed in short-term monitoring experiments along the Beaufort Sea coast, including evolution of melt notches, topple of ice wedge-bounded blocks, and degradation of these blocks. Model results agree with time-lapse imagery of bluff evolution and time series of ocean-based instrumentation. Erosion is highly episodic with 40% of erosion is accomplished during less than 5% of the sea ice-free season. Among the formulations of the submarine erosion rate we assessed, we advocate those that employ both water temperature and nearshore wavefield. As high water levels are a prerequisite for erosion, any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion. The certain increases in sea level and potential changes in storminess will both contribute to this effect. As water temperature also influences erosion rates, any further expansion of the sea ice-free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates.