期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：47
页码：13336-13341
DOI：10.1073/pnas.1613044113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceCliffed coasts erode when attacked by energetic waves. Cliff retreat threatens coastal assets and livelihoods. Understanding rates of past erosion is vital to quantifying these risks, particularly when confronted with expected increases in storminess and sea level, and given continued human occupation and engineering of coastal regions. Historical observations of cliff retreat span 150 y at most. We derived past cliff retreat rates over millennial time scales for chalk cliffs on the south coast of Great Britain by interpreting measured cosmogenic nuclides with numerical models. Our results provide evidence for accelerated erosion in recent centuries, which we suggest is driven by reduced sediment supply and thinning of beaches in the face of environmental and anthropogenic changes. Rising sea levels and increased storminess are expected to accelerate the erosion of soft-cliff coastlines, threatening coastal infrastructure and livelihoods. To develop predictive models of future coastal change we need fundamentally to know how rapidly coasts have been eroding in the past, and to understand the driving mechanisms of coastal change. Direct observations of cliff retreat rarely extend beyond 150 y, during which humans have significantly modified the coastal system. Cliff retreat rates are unknown in prior centuries and millennia. In this study, we derived retreat rates of chalk cliffs on the south coast of Great Britain over millennial time scales by coupling high-precision cosmogenic radionuclide geochronology and rigorous numerical modeling. Measured 10Be concentrations on rocky coastal platforms were compared with simulations of coastal evolution using a Monte Carlo approach to determine the most likely history of cliff retreat. The 10Be concentrations are consistent with retreat rates of chalk cliffs that were relatively slow (2-6 cm*y-1) until a few hundred years ago. Historical observations reveal that retreat rates have subsequently accelerated by an order of magnitude (22-32 cm*y-1). We suggest that acceleration is the result of thinning of cliff-front beaches, exacerbated by regional storminess and anthropogenic modification of the coast.
