Patterns and controls of erosion along the Barrow Environmental Observatory Coastline, Northern Alaska.

摘要

With pronounced arctic warming that is linked to loss of sea ice, sea level rise, and land cover change, over the coming decades arctic coastal regions are likely to undergo amongst the most dramatic changes of any ecosystem on Earth. This study used foot surveys and a Differential Global Positioning System (DGPS) to document at a high spatial (horizontal and vertical) resolution, the spatiotemporal dynamics of the eroding bluff along the coastline of the Barrow Environmental Observatory between 2003 and 2009. The coastline consists of an eroding bluff bordered by a shallow muddy lagoon. The coast is protected from strong waves by a series of barrier islands 7 km offshore. The barrier islands and lagoon are NW-SE elongate and the longest fetch in the lagoon in which winds can generate waves, is to the east and southeast. The shoreline is scalloped in shape, with North-South and East-west segments along the scallops. A bathymetric survey shows ridges of sediment that extend North across the lagoon from the western (North-south oriented) ends of the scallops in the coastline. Sediment is swept NW along the coast, to the point of the scallops and then North into the lagoon.;Erosion largely occurs through a combination of processes. Wave undercutting of the bluff can result in block failure and removal of sediment by wind driven currents. Thermal erosion and slumping of the bluff is also common in some areas of the coast. Surveys enabled the area and volumetric loss to be computed. Mean annual rates of coastal erosion are consistent with earlier reports (1-3m/yr) from the study area, that like this study, reported high rates of variability. Rates of erosion in summer between June and August were generally higher than those reported for August through the following June when normalized to the number of ice-free days. Unlike other studies in the region, a slight decrease in the rate of erosion was observed from year to year and could not be explained by the length of the ice-free period. Estimates of sediment input, particularly soil organic carbon to the marine system are substantially higher than reported by previous studies. Regression tree analysis suggests high rates of erosion are associated with water depths at a distance two kilometers offshore, strong winds perpendicular to the coast or from the south-southeast, and where wet and aquatic land cover types prevail. During survey periods with low windrun, the land cover type became a more important factor in the rate of erosion. Given the spatiotemporal variability in the rates of erosion documented and the complexity of the interacting factors controlling erosion, sustained observations of erosion will be essential to acquire the dataset required to develop process-level understanding and parameterization of models that could be used to develop forecast scenarios of future coastal states as this system responds to change.