Project Title: Arctic Bluff Retreat and Inundation of an Ecologically Sensitive Barrier Island System Due to a Changing Global Climate
Mendenhall Fellow: Li H. Erikson, (831) 427-4787, firstname.lastname@example.org
Duty Station: Pacific Science Center, Santa Cruz, CA
Start Date: March 2, 2009
Education: Ph.D. (2005), Coastal Engineering, Lund Institute of Technology, University of Lund, Sweden
Research Advisors: Bruce Richmond (831) 457-4731, email@example.com; Curt Storlazzi, (831) 427-4721, firstname.lastname@example.org; Patrick Barnard, (831) 427-4756, email@example.com; Carl Markon, (907) 786-7023, firstname.lastname@example.org; John (Lyle) Mars, (703) 648-6302, email@example.com
Through analysis of topographic maps, Landsat short-wave infrared images, and aerial photography, several recent studies have shown that bluff recession rates along the eastern section of Alaska’s North Slope are some of the world’s highest and that the rates are increasing (for example, Jones and others, 2009; Aquire, 2008; Mars and Houseknecht, 2007; Jorgenson and others, 2005). Global modeling studies consistently show the Arctic to be one of the most sensitive regions to global climate changes (Holland and others, 2006; ACIA, 2005) as evidenced by the increase of Arctic air temperatures, which are almost twice the global average rate over the past 50 to 100 years, of about 4°C (Chapman and Walsh, 2007; IPCC, 2007). This warming trend has been accompanied by an extension of the open water season, which typically extends from mid-June through early October, and a shrinking of the perennial ice sheet covering the North Pole and much of the Arctic. Satellite images show that the perennial ice sheet has shrunk by more than 30 per cent since 1979 and reached a historical minimum in 2007. Some of the changes, such as elevated sea surface and air temperatures, changes in the active layer depth and permafrost, later freeze-up and earlier break-up of the arctic ice sheet, and intensity and frequency of storm activity, are thought to be directly responsible for (1) the high and increased bluff recession rates and (2) an increase in the vulnerability of ecologically sensitive barrier island systems.
The overall objective of this study is to contribute to the development of a predictive model of Arctic bluff retreat and inundation of barrier islands due to a changing global climate. A process-based model, incorporating air and sea temperature changes, varying ice-coverage, and varying wind-climate will be developed to hindcast and predict the nearshore wave climate on an inter-annual and decadal time-scale. The model will also be used to determine the fate and transport of eroded bluff materials. Analytical and empirical models will be further developed to quantify bluff recession rates and ascertain the underlying mechanisms responsible for Arctic bluff erosion during a warming climate. Lastly, detailed nearshore and shoreline mapping data, along with oceanographic measurements will be collected and provide a baseline for future monitoring of coastline changes along Alaska’s North Slope.
The study site encompasses bluffs and a barrier island system facing the Chukchi Sea to the west of Point Barrow that is located at the terminus of the North Slope. Recession rates along a 75-km stretch from Barrow to Peard Bay were on the order of 0.3 ma-1 between 1948–49 and 1976 (Harper, 1978). Modern erosion rates, and how they compare to the 1948–49–1979 estimate, are at this time unknown but will be determined as part of this project and with airborne LiDAR planned for the summer of 2009 under the USGS National Shoreline Assessment Project.
The project consists of three major tasks as outlined below.
I. Numerical modeling of the wave climate and nearshore sediment transport
The state-of-the-art process-based numerical model Delft3D (WL Hydraulics, 2007) will be used to model the wave climate, currents, changing ice coverage, and sediment input from episodic bluff erosion events. A system of nested grids is being used to model the wave climate and changing ice coverage patterns (fig. 1). Wave boundary conditions will be obtained from global models such as WAVEWATCH III (Tollman, 1999; Tollman and others, 2002) but with boundary adjustments determined from (1) regional measurements of wind speed and direction, (2) hindcast wave data compared to past wave observations, overwash events, and historical shoreline retreat, and (3) comparison of measured and predicted wave conditions at temporary in situ monitoring sites.
Figure 1. Preliminary model grid and bathymetry (1-km resolution depth data in the offshore region (Alaska Ocean Observing System, http://ak.aoos.org/) and 200- to 500-m resolution soundings in the nearshore region (http://map.ngdc.noaa/); soundings are from 1945–47 and referenced to MLLW).
II. Investigation of bluff recession due to notching and subsequent mass failure
The primary process by which Arctic bluff erosion occurs appears to be by notching near the base of the bluff followed by block failure (fig. 2).
Figure 2. Active bluff erosion near Point Barrow (photograph taken in July 2008).
Development of the notch typically occurs either from (1) direct wave impact at the base of the bluff or (2) thermal niching whereby the relatively warm seawater and higher than normal air temperatures melt the permafrost at the base of the bluff. Block failure or overtopping then occurs either as a result of exceeded tensile strength, or more commonly, the presence of an ice wedge back some distance from the bluff face. A model for notch development by wave impact and subsequent overtopping by tensile strength failure was previously developed for compacted dunes and berms (Erikson and others, 2007; figs. 3A, B). This model, together with a similar model for arctic bluffs backed by ice wedges (fig. 3C), will be modified to predict erosion and recession of the bluffs. It is anticipated that wave impact as well as thermal niching are responsible for the observed bluff erosion. It is hypothesized that the former process is the dominant mechanism in the study area along the Chukchi Sea, while temperature changes are the driving force of bluff recession on the Beaufort coast along the eastern section of the North Slope.
Figure 3. Schematic of (A) notching at the base of the bluff by incident bores (Erikson and others, 2007), (B) resisting and overturning forces associated with tensile failure of a bluff overhang (Erikson and others, 2007), and (C) overturning moments associated with the presence of an ice wedge (Hoque and Pollard, 2008).
III. Data collection, post-processing, and analysis
Hydrodynamic, bathymetric, and bluff and seabed property data is rather scarce on the North Slope, and, as such, a field campaign is planned for data collection within the study area. Spectral wave conditions and currents will be collected at two select locations within the study area in addition to nearshore bathymetry, sediment grain size, bluff material properties, and cliff topography. The data are anticipated to provide insight into the processes controlling coastal erosion, to serve as calibration and validation data for hydro- and morpho-dynamic modeling, and to provide a baseline for future studies. The data will be freely available to help build up a comprehensive picture of Arctic shoreline erosion and its causes.
ACIA, 2005, Arctic climate impact assessment: Cambridge University Press, 1042 p.
Aguire, A., Tweedie, C. E., Brown, J., and Gaylord, A., 2008, Erosion of the Barrow Environmental Observatory coastline 2003–2007, northern Alaska, in Proceedings of the Ninth International Conference on Permafrost.
Chapman, W., and Walsh, J., 2007, Observed climate change: Arctic Climate Research at the University of Illinois [ http://arctic.atmos.uiuc.edu/]
Erikson, L.H., Larson, M.P., and Hanson, H., 2007, Laboratory investigation of beach scarp and dune recession due to notching and subsequent failure: Marine Geology, v. 245. no. 1–4, p. 1–19.
Harper, J.R., 1978, Coastal erosion rates along the Chukchi Sea coast near Barrow, Alaska: Arctic, v. 31, no. 4, p. 428–433.
Holland, M. M., Bitz, C. M., and Tremblay, B., 2006, Future abrupt reductions in the summer Arctic sea ice: Geophysical Research Letters, v. 33.
Hoque, Md. A., and Pollard, W.H., 2008, Thermal and mechanical erosion along ice-rich Arctic coasts, in Proceedings of the Ninth International Conference on Permafrost.
IPCC (Intergovernmental Panel on Climate Change, 2007, Summary for policymakers, contribution of working group I to the 4th assessement report.
Jones, B.M., Arp, C.D., Jorgenson, M.T., Hinkel, K.M., Schmutz, J.A., and Flint, P.L., 2009, Increase in the rate and uniformity of coastline erosion in Arctic Alaska: Geophysical Research Letters, v. 36.
Jorgenson, M.T., and Brown, J., 2005. Classification of the Alaskan Beaufort Sea coast and estimation of carbon and sediment inputs from coastal erosion: Geomarine Letters, v. 25, p. 69–80.
Mars, J.C., and Houseknecht, D.W., 2007, Quantitative remote sensing study indicates doubling of coastal erosion rate in past 50 yr along a segment of the Arctic coast Alaska. Geology, v. 35, no. 7, p. 583–586.
Tolman, H. L., 1999. User manual and system documentation of WAVEWATCH-III version 1.18: NOAA/NWS/NCEP/OMB Technical Note 166, 110 p.
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