C11A-01 INVITED 08:00h
The Evolution of Coastal and Offshore Permafrost During the Last Climatic Cycle in the Laptev Sea Region, Russia
Coastal and offshore permafrost in the Laptev Sea region have been studied during the last years within the framework of the Russian-German programmes "Laptev Sea System" and "System Laptev Sea 2000." Mathematical simulations of permafrost evolution were carried out showing that ice-bearing and ice-bonded permafrost exists presently within coastal lowlands and under the shallow shelf. Open taliks, giving pathway to methane from unstable former gas hydrates, can develop from modern and palaeo-river taliks in active fault zones and from lake taliks over fault zones or lithospheric blocks with a higher geothermal heat flux. Ice-bearing and ice-bonded permafrost in the northern regions of lowlands and in the inner shelf zone, have been preserved during at least four Pleistocene climatic and glacial-eustatic cycles. Presently, they are subjected to degradation from the bottom under the impact of geothermal heat flux. In addition to the development of permafrost during the last glacial cycles the processes causing coastal erosion and changing the permafrost topography before and during the Holocene transgression of the shelf will be shown. About 13 kyr BP thermokarst started to destroy the so called Ice Complex (IC) both on the shelf and coastal lowlands. Thermokarst lakes and depressions were formed (11-11.5)-(9.5-8.5) kyr BP when the position of the shoreline was at the actual isobathes -60;-45 m. Thermokarst processes started before the submergence of the shelf by sea water with negative temperature. Due to the transgression, thermokarst lakes and alases with a bottom level below the actual sea level particulary on the shallow part of the shelf (between isobath - 20 m and the recent shoreline) were transformed into ,thermokarst lagoons". On the Bykovsky Peninsula and the vast areas eastward from the Yana river delta this process still occurs today and the resulting relief types can be found in the field. The formation of ,thermokarst lagoons" resulted in the formation of a irregular coastline, an increase of shores length subjected to thermoerosion, especially after 7.5 kyr BP.
C11A-02 INVITED 08:20h
Reassessment of the Genesis of "Thaw Lakes" on the Arctic Coastal Plain in Northern Alaska
Oriented lakes and drained lake basins on the Arctic Coastal Plain in northern Alaska have been the subject of numerous studies for more than 50 years. From the beginning, the waterbodies have been described as "thaw lakes" and since then a thermokarst genesis for the lakes has been accepted without any quantitative analysis of the initial permafrost conditions and thaw-susceptibility of the upper permafrost. We initially sought to quantify ground ice changes in support of this concept through detailed permafrost and terrain studies in the northeastern NPRA, an area with thick deposits of loamy sand and abundant lakes. During 2001-2004 we conducted detailed terrain analyses that included field surveys, permafrost investigations, and photogrammetry. A terrain-unit approach was used to relate soil and ground ice properties to surficial deposits related to lake development. Cryogenic structures, ice volumes, and properties of upper permafrost were described from borehole cores taken from every stage of lake-basin development and in surrounding areas. Ground ice also was described and sampled at 20 exposures at lake and riverbanks. We classified stages of drained basin development and quantified their permafrost characteristics. The primary stage of lake development is usually described as degradation of ice-wedges at their intersections. A thaw bulb then develops under the deep water and the thaw lakes expand laterally through both mechanical and thermal erosion. Although we observed numerous ponds at ice-wedge crossings we did not observe later sequential stages of thaw lake development. Instead, we observed that initial shallow ponds were soon colonized by vegetation, which halted thermokarst. In addition, ice volumes and thaw settlement properties of soils were insufficient to allow thaw lake development. Under the standard concept of lake development, the formation of ice wedges raises the surface and allows the development of new thermokarst, and thus creates a "thaw lake cycle." Although we found that the ice-content of soils increased with age of lake-basin deposits, the ice content of lake-basin margins was insufficient to substantially raise the surface. The genesis of surficial deposit varies throughout the Arctic Coastal Plain and is closely related to soil properties, ice content of permafrost, and geomorphic processes. Consequently, lake distribution should be closely associated with ground ice conditions, but lakes are abundant on all deposits. Although true thermokarst lakes occur in some regions, such as the Colville River Delta, lower Brooks Foothills with thick loess deposits, and the Beaufort Sea coast from Barrow to Cape Halkett where thick marine silts are present, the majority of lakes on sandy deposits common across the coastal plain are not due to thermokarst. Instead, our analysis shows that lakes that formed during Holocene could not have resulted from the degradation of ground ice. Rather, these lakes formed simply by the accumulation of water in depressions.
C11A-03 INVITED 08:40h
Modeling Block Failure in Vertical Cliffs of Arctic Coasts Underlain by Permafrost
Arctic coasts lie at the interface between terrestrial systems dominated by permafrost, and marine systems that are characterized by long periods of ice cover and short periods of open water when wave action and storm activity are important. Permafrost, sea ice and wind-wave conditions are driven by regional and local climate forcing and interact in such a way that a change in one produces feedbacks affecting the other two. However, under predicted climate change scenarios of warming, increased storm activity and sea level rise will profoundly affect all three leading to potentially devastating rates of coastal erosion and permafrost degradation. Permafrost coasts are subject to complex erosional processes, however one of the most poorly understood but probably most important is block failure. Thermo-abrasional falls or block collapses provide the most spectacular form of coastal recession in permafrost areas. This study provides computational models for block failure mechanisms and investigates the relative contribution of horizontal thermo-erosional niches and ice wedges to block failure of permafrost cliffs fronted by a beach.
C11A-04 INVITED 09:00h
Ocean Wave Energy Regimes of the Circumpolar Coastal Zones
Ocean wave activity is a major enviromental forcing agent of the ice-rich sediments that comprise large sections of the arctic coastal margins. While it is instructive to possess information about the wind regimes in these regions, direct application to geomorphological and engineering needs requires knowledge of the resultant wave-energy regimes. Wave energy information has been calculated at the regional scale using adjusted reanalysis model windfield data. Calculations at this scale are not designed to account for local-scale coastline/bathymetric irregularities and variability. Results will be presented for the circumpolar zones specified by the Arctic Coastal Dynamics Project.
C11A-05 09:20h
Spatial Analysis of Coastal Erosion over Five Decades near Barrow, Alaska
There has been increasing interest in processes affecting Arctic coastlines, including shoreline erosion. The prospect of continued -- and possibly accelerated -- coastal erosion is a major concern for many Arctic communities. Documenting and understanding spatial variability in erosion rates are increasingly attainable as high-resolution imagery becomes available, and as GIS and remote-sensing tools are more widely accepted. This study presents such an analysis for a broad area near Barrow, Alaska. Shoreline erosion and accretion were quantified by comparison of coregistered datasets and imagery. Orthorectified Radar Imagery (ORRI) was acquired in July, 2002 at 1.25 m resolution. Twenty frames of aerial photos from August, 1955 were scanned and georectified to the ORRI using a polynomial transformation in ArcGIS, with resulting resolution of about 1.4 m and RMS error of 2.6 m. The 2002 and 1955 shorelines were digitized with points spaced every 20 m along the 250 km of mainland coastline. For barrier islands and the Barrow Spit, the 1955 coastline was digitized from DRG files depicting the USGS 15-minute maps. Using a variety of vector ArcInfo commands, horizontal displacement of the mainland shoreline was converted to erosion and accretion rates for the intervening 47 years. (Note that time-averaged rates will underrepresent episodically high rates during storm events). Overall error considering georectification, digitizing, and transient waterline shifts due to microtidal fluctuation and wave-set up is approx. 3.1 m for the mainland coast, equating with 0.07 m/yr. For barrier features, where the DRG's are less accurate, error is about 28 m (0.6 m/yr). Nearly all of the mainland coast (91%) has experienced erosion. Highly variable, rates average -0.91 m/yr, with an average horizontal shoreline displacement of -42.5 m. (Rates and displacements are negative for erosion). Relatively low rates of about -0.3 m/yr occur along the Chukchi coast, where sand- and gravel-dominated beaches are backed by bluffs up to 15 m high. Rates are higher along the low coastal plain facing Elson Lagoon, exceeding -5 m/yr near Scott, Ross, and Christie Points, before decreasing again in the sheltered waters of inner Admiralty Bay. Rates also decrease within small bays and inlets. Lateral accretion from 1955 to 2002 is uncommon, limited to short stretches of widening beach along the Chukchi coast, and isolated progradation or shifting of small nearshore spits and bars. Immediately adjacent to Barrow, the shoreline has eroded -0.2 to -0.8 m/yr, in agreement with a higher-resolution, related study, whereas the beach near the NARL/UIC complex has prograded on average +0.3 m/yr. The narrow offshore barrier islands have migrated considerably, with an average horizontal shift of 205 m. Although erosion over five decades has been locally variable, a few patterns emerge. High bluffs and coarse beach sediment help protect the Chukchi shoreline, whereas low coastal bluffs exposing ice-rich, peaty soils are susceptible along the Beaufort coast. Beyond bluff height and shoreface lithologies, fetch plays an important role, with the inner portions of bays and inlets protected at a variety of scales. Erosion appears to be more pronounced where ice-wedge polygons are strongly developed within mature thaw-lake basins. Near Barrow, human activities in the nearshore zone have played a role, and erosion is a concern -- even though it occurs there more slowly than the region as a whole. The importance of extreme weather events, and the possibility of accelerated change due to warming and decreasing summer sea ice, will be examined as other imagery improves the temporal resolution for analysis.
C11A-06 09:35h
Do Physical Oceanographers Care About Coastal Processes in Water Less Than 20-m Deep?
The resounding yes may surprise Arctic researchers and old-style oceanographers, but the physics of coastal waters less than 20-m deep has been the subject of intense experimental and theoretical study over the last decade by physical oceanographers. For example, discoveries on the dynamics of (often sediment ladden) freshwater discharges into the coastal ocean relate to many Arctic systems that receive freshwater from rivers and ice melt. Boundary layer processes due to bottom and surface friction, too, often dominate coastal dynamics. Material transport and fluxes both along and across the coastal zone are strongly affected by stress- and buoyancy induced physical processes that mid-latitude physical oceanographers have explored extensively. Much of this progress has yet to migrate into the Arctic research community where oceanographers appear to focus on steady-state and deep-basin problems with little interest to processes impacted by the presence of a coastline and/or flow phenomena at the internal Rossby radius of deformation. This situation has left geological and biological scientists working on pressing Arctic coastal zone problems isolated from new advances, understanding, and technologies of exchange processes at the land-ocean interface that generally is less than 20-m deep. More specifically, I discuss published and unpublished observational and theoretical model results from both Arctic and mid-latitude inner shelf systems. The inner shelf is here defined as the region where surface and bottom boundary layers overlap. I will contrast data from the Canadian Mackenzie and Russian East Siberian shelf seas with similar data (and models to explain them) from North- and South-American inner shelves. I will demonstrate conceptionally how frictional and buoyancy forces interact in waters less than 20-m deep to cause circulations, vertical stratification, and depth-dependent material transport that differs substantially from steady and linear perceptions of a bygone era. I will also demonstrate how observational techniques in physical oceanography have advanced far beyond the conventional water sampling and analyses to include direct velocity observations in space and time. The inner shelf of the coastal ocean emerges as a dynamically rich, complex, and unsteady environment that varies in space and time at predictable scales. Failure to properly resolve these scales in experimental design cause unanticipated aliasing and mis-interpretation of environmentally sensitive biogeochemical fields and underlying processes.
http://newark.cms.udel.edu/~muenchow