MethodsSurveys of the coastal bluff were made with a survey-grade Differential Global Positioning System (DGPS). The first DGPS survey was completed in 2003 and repeat surveys have been made at least annually between 2006-2013. DGPS data are collected every second and typically have a horizontal and vertical accuracy of approximately 5 cm. After post processing (Trimble Business Center), x, y, z data were imported to ArcGIS (ESRI V9.3) to calculate annual erosion rates as areal and volumetric loss between surveys. Volumetric loss was then transformed to an estimate of soil organic carbon by normalizing volumetric loss with soil ice and carbon content reported for the top meter of soil in the study area by previous studies (Brown et al. 2003, Michaelson et al. 2008).To identify biophysical factors controlling erosion, survey sections were segmented into 20 meter sub-sections, using the Digital Analysis System (DSAS V3.2, Theiler et al. 2009). For each sub-section, dominant land cover type, elevation, orientation of the coastline, offshore water depth at multiple distances from the coastline, wind direction relative to the azimuth of the coastline for periods of ice-free days, and wind speed, were calculated using methods described in Aguirre (2011). Data were imported to the statistical software JMP (V8.0, SAS Institute, Inc. Cary NC) and a series of regression trees were developed for survey periods between 2006 and 2013.

Erosion and Inputs of Soil Carbon to Elson LagoonResults from the DGPS surveys are represented Figures 2 to 5. Spatiotemporal variability in erosion was high with mean annual erosion rates for all coastal sections combined ranging from 0.90 to 2.50 m/yr (Fig. 2) and volumetric losses ranging from 2.2 to 5 m3/m/yr (Fig. 3). Cumulative areal loss (m2/section length) has shown a sustained linear increase, with section D eroding the most followed By sections C, A, and B (Fig. 4). The cumulative area lost to erosion is given in Figures 4 and 5 respectively. Erosion rates for section D are almost triple rates documented for other sections. Rates of soil carbon input to Elson Lagoon are 35-100% greater than rates reported in previous studies (Table 1).

Controls of erosionThe top 10 nodes of the regression tree for areal loss between 2006 – 2013 explained 43% of the variability in the dataset. Areal loss was greatest where the bathymetric depth 2000m from the coast was greater than 2.5m (split 1) and windrun from the north was less than 3,150km (split 2). Where depth at 2000m from the coast was less than 2.5m (split 1), erosion was greatest where windrun perpendicular to the coast exceeded 6833km (split 3), depth 2000m from the coast was less than 2.3m (split 4) and a wet graminoid tundra landscape was present (split 5). Where tundra was not wet graminoid tundra (split 6), coastal segments with moist meadow landscapes had the next greatest rate of erosion (split 6) .Where moist meadow landscapes were not present (split 6), erosion was greatest where wind run from the south was less than 20,515km (split 7), and the azimuth of the coast was less than 156 degrees (split 8). Where depth 2000m from the coast was less than 2.3m (split 4), erosion was greatest where water depth 500m from the coast was greater than 1.2m (split 9). Where wind run perpendicular to the coast was less than 6,833km (split 3), erosion was greatest where water depth 1000m from the coast was greater than 2.1m (split 10).The regression tree describing controls of volumetric loss over 2006 – 2013 showed that volumetric loss was greatest where wet graminoid tundra was present (split 1) and wind run perpendicular to the coast was greater than 18,480 km (split 2). Where wind run perpendicular to the coast was less than 18,480km (split 2), loss was greatest when wind run from the south exceeded 31,812km (split 3). When a wet graminoid tundra landscape was not present (split 1), Bathymetric depth at 500 meters from the coast greater than 1.26m (split 4) and bathymetric depth at 300m from the coast less than 1.00m (split 5) explained the highest volumetric losses. Where depth at 300m was greater than 1.00m (split 5) erosion was greatest when wind run from the north less than 2,923 km (split 6). When wind run from the north was greater than 2923 km (split 6) but less than 5,375km (split 7) rates of erosion were next greatest. Rates of volumetric loss were next greatest when bathymetric depth at 500m was less than 1.26m (split 4), wind run from the south greater was greater than 18480 km (split 8), and when wind run perpendicular to the coast was greater than 16,037 km(split 9). When wind run from the south was less than 18,480 km (split 8), bathymetric depth at 100m from shore greater than 1.06m rates of volumetric loss were lowest.

DiscussionAnthropogenically induced climate warming will continue to affect the Arctic coastal system in the future (IPCC 2014). Considering the many impacts that can arise from increased erosion rates in the Arctic, there is a need to monitor and assess spatiotemporal trends and the biophysical controls of eroding permafrost coastlines. Through the a series of DGPS surveys spanning the last decade, this study documents substantial small-scale spatiotemporal variability in erosion rates along the BEO coast, which appear to be under-appreciated by studies employing multi-temporal image analysis that typically have decade-long gaps in their assessments. Interestingly, erosion rates observed in this study are almost double the erosion rates calculated by Brown et al, 2003 (1979 to 2000), suggesting recent erosional loss is markedly higher than in the past. Significant input of soil carbon and other nutrients to the ocean can drastically alter near shore biophysical processes. This study suggests that carbon input to Elson Lagoon from coastal erosion is substantially higher than previous estimates (Michaelson et al. 2008 and Brown et al. 2003 ). Regression tree analyses suggest that characteristics of the marine, terrestrial, and prevailing climatological environment are important controls of erosion. Factors that are particularly important include land cover type, wind run, and water depth. Similar drivers of erosion were identified by Jorgenson and Brown (2005).

Future Directions Ongoing studies are examining erosion rates along a ~140 km km of coast near Barrow, including ~53 km along the Chukchi Sea coast, which opposes the featured coastline relative to prevailing winds. Improved bathymetry and near-shore habitat mapping is underway and characterization of soil carbon along eroding bluff lines is planned for 2014-15. Improved methods for monitoring wave impacts using microseismometers, and slumping and thermokarst along coastal landscapes using terrestrial LiDAR and stereographic analysis from kite aerial photography and unmanned aerial vehicles are also under development.

AcknowledgementsWe are grateful to UMIAQ, CH2M Hill Polar Field Services, UNAVCO and BASC for providing logistic support. NSF awards 0454996, 0454997, 0732885, 0856628, 1023654 and a BOEM-CIAP grant through the USFWS have funded this study. We also thank more than a dozen undergraduate and graduate students who have conducted DGPS surveys and processed data in GIS while undergoing internships in the Systems Ecology Lab at UTEP. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of NSF, BOEM, or USFWS.

Introduction Approximately 34% (~101,447 km) of the world’s coastlines are found in the Arctic (Lantuit et al. 2012). During periods of ice-free seas, these coastlines are prone to erosion. With climate warming, there has been a dramatic loss of arctic sea ice (Polyak et al. 2010), and several studies have noted increased rates of erosion in recent decades (Mars and Houseknecht 2012). Arctic coastlines have become recognized as one of the most threatened ecosystems on Earth (Lantuit et al. 2011). Over the past decade, a gamut of research has documented decade-time scale erosion trends for large sections of arctic coastlines using mostly multi-temporal aerial and satellite image time series (e.g. Jones et al. 2009; Lantuit and Pollard 2008). Few studies have examined erosion dynamics at high spatiotemporal scales using ground based surveys (sensu Tweedie et al. 2012), which have been shown to be more accurate than remotely sensed surveys for relatively short sections of coastline (Jones et al. 2008). Elsewhere in the world, studies of this type have been useful in identifying processes and controls that regulate erosion dynamics (Quinn et al. 2010). Such knowledge has the potential to advance many facets of arctic science including (but not limited to) enhanced parameterization of models, assessment of sensitivity to erosion, and the fate and transport of the significant arctic soil organic carbon store. This study presents an update to records derived from high-spatial and high-temporal resolution, ground-based surveys of the northernmost Elson Lagoon coastline near Barrow, Alaska. The following questions have been addressed in this study:

How have erosion rates varied over time and space? What biophysical factors appear to be important controls of erosion?

Study AreaThe Elson Lagoon and Beaufort Sea coastlines are situated east-northeast of the village of Barrow,

Alaska. Elson Lagoon is a shallow expanse of water that is ~30km long, ~10km wide, and bordered by the mainland coast to the south and west and by barrier Islands to the north and east. These barrier islands separate Elson Lagoon from the Beaufort Sea. Coastal bluffs span the length of the Elson Lagoon coastline and are typically less than 4.5 meters in height. The terrestrial landscape adjacent to Elson Lagoon is characterized by low-gradient polygonized tundra, and graminoid-dominated land cover typical of the Arctic Coastal Plane. Water depths within Elson Lagoon rarely exceed 3.5 meters and shallow submerged sand bars are relatively common along the coastal margin (Aguirre 2011). The Elson Lagoon coastline is particularly exposed to prevailing wind and wave action from the North through East. This study was conducted along the Elson Lagoon coastline of the Barrow Environmental Observatory (BEO), a 3021 hectares parcel of land set aside by the Ukpeaġvik Iñupiat Corporation for Science. To align with historic coastal erosion studies in the area, the BEO coast was dived into four sections labeled A, B, C, & D (Fig. 1).

Fig. 4. Cumulative areal loss to erosion for each section (A-D) and all sections combined 2003 - 2012.

Fig. 2. Mean aerial loss per annual survey period for each section and all sections combined (Avg).

Fig. 5. Cumulative aerial loss at the coastal bluff for each coastal section and the mean of all sections combined 2003 - 2012.

Fig. 3. Mean volumetric loss per annual survey period for each section and all sections combined. Note volumetric loss for 2003-06 could not be calculated due to an error in processing elevation in 2003.

Fig. 1. (Left) Map of the study site along the 10.7 km coastline of the Barrow Environmental Observatory (BEO) including the four survey sections (A, B, C, D) and the 14 historic Arctic Coastal Dynamics transects (triangles, Tweedie et al. 2012), within the BEO east of Barrow Alaska. (Right) Aerial Photograph of survey sections adjacent to Elson Lagoon.

Author C kg/C/m2 Elevation (m) Erosion (m/yr) Meters Length km kg C/km Ton C/yr Ton C/yr /kmBrown et al. 2003 50 1 1.3 1000 10.6 63500 673.1 63.5Michaelson et al. 2008 70 1.4 1 1000 11.7 98000 1150.1 98This study 63 1 2.2 1000 10.6 135450 1435.8 135.5

Table 1. Estimates of Soil Organic Carbon Input to Elson Lagoon

Trends and Controls of Coastal Erosion along the Barrow Evironmental Observatory, Northern Alaska (2003- 2013)Craig E. Tweedie1, A. Lopez1, R. Cody1, S. Vargas1, A. Aguirre1, K. Kofoed1, A. Gaylord2, J. Brown3, W. Manley4, L. Lestak4, Q. Aiken5, L. Nelson5

1.Systems Ecology Laboratory, The University of Texas at El Paso. El Paso, TX; 2. Nuna Technologies, Homer AK;3. International Permafrost Association, Woods Hole, MA; 4. University of Colorado, Boulder, CO; 5. UMIAQ, Barrow, AK

In A Nutshell:•With the loss of wave-buffeting sea ice in the Arctic, the expanse and duration of open water adjacent to coastlines is increasing. Wind-wave induced and thermal erosion of arctic ice-rich permafrost coastlines appears to have increased at some locations as a result. •Increased coastal erosion in the Arctic can result in numerous impacts - most human settlements are situated near coastlines; coastline retreat drains arctic wetlands and modifies the surface hydrology of low-gradient coastal landscapes; and transfer and remobilization of the substantial arctic soil organic carbon pool to the marine environment can alter near-shore biophysical processes. •Fine-scale spatiotemporal dynamics of coastal erosion and the relative importance of terrestrial, marine, and climatic controls of erosion along permafrost coastlines have been poorly explored. Nonetheless, these study topics have the potential to guide future scenarios of change relevant to policy and management, guide monitoring activities, and bridge ongoing and planned research efforts. •This study updates reporting for a 10-year time series of differential global positioning System (DGPS) surveys of the ~ 1-4 m high coastal bluffs along the 10.7 km Barrow Environmental Observatory adjacent to Elson Lagoon in northern Alaska. •Erosion was spatiotemporally variable and averaged 1-4 meters per year from 2003-2013, which is lower than other areas of the Beaufort Sea coast that lack protective barrier islands, but higher than historic rates calculated for the period 1948-2003. Since 2003, more than 19 ha of land has eroded from the study site. There is no evidence of erosion rates increasing over time. Estimates of sediment input to the marine environment calculated in this study are substantially higher than reported by previous studies. •Regression tree analysis suggests high rates of erosion are positively 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 wind-run, the importance of land cover type had a greater relative importance. •Ongoing studies are examining erosion rates along a ~140 km km of coast near Barrow, including ~53 km along the Chukchi Sea coast. Improved bathymetry and near-shore habitat mapping is underway and characterization of soil carbon along eroding bluff lines is planned for 2014-15. Improved methods for monitoring wave impacts using microseismometers, and slumping and thermokarst along coastal landscapes using terrestrial LiDAR and stereographic analysis from kite aerial photography and unmanned aerial vehicles are also under development.