C13A-0256 1340h
Arctic Coastal Dynamics (ACD)
The coastal zone is the interface through which land-ocean exchanges in the Arctic are mediated and it is the site of most of the human activity that occurs at high latitudes. The Arctic coastlines are highly variable and their dynamics are a function of environmental forcing and coastal geology, geocryology and morphodynamic behavior. Coastal processes in the Arctic are strongly controlled by Arctic-specific phenomena, i.e. the sea-ice cover and the existence of onshore and offshore permafrost. During the short ice-free period, the unlithified ice-rich, permafrost-dominated coastlines are rapidly eroded and the resulting coastal sediment, organic carbon, and nutrient fluxes play an important role in the material budget of the Arctic Ocean. Arctic Coastal Dynamics (ACD) is a multi-disciplinary, multi-national project of the International Arctic Science Committee (IASC) and the International Permafrost Association (IPA) which aims to: - establish the rates and magnitudes of erosion and accumulation of Arctic coasts and to estimate the amount of sediments and organic carbon derived from coastal erosion; - develop a network of long-term monitoring sites including local community-based observational sites; - refine and apply an Arctic coastal classification (includes ground-ice, permafrost, geology, etc.) in digital form (GIS format) and produce a series of thematic and derived maps (e.g. coastal classification, ground-ice, sensitivity etc.); - compile, analyze and apply existing information on relevant environmental forcing parameters (e.g. wind speed, sea-level, fetch, sea ice etc.); - identify and undertake focused research on critical processes; - develop empirical models to assess the sensitivity of Arctic coasts to environmental variability and human impacts. Currently, ca. 25 institutions from 9 countries are contributing to the ACD project. This presentation provides an overview of the research activities and the latest results of the ACD project.
C13A-0257 1340h
Electronic atlas of the Russian Arctic coastal zone: natural conditions and technogenic risk
The Arctic coast is characterized by a diversity of geological-geomorphological structures and geocryological conditions, which are expected to respond differently to changes in the natural environment and in anthropogenic impacts. At present, oil fields are prospected and developed and permanent and temporary ports are constructed in the Arctic regions of Russia. Thus, profound understanding of the processes involved and measures of nature conservation for the coastal zone of the Arctic Seas are required. One of the main field of Arctic coastal investigations and database formation of coastal conditions is the mapping of the coasts. This poster presents a set of digital maps including geology, quaternary sediments, landscapes, engineering-geology, vegetation, geocryology and a series of regional sources, which have been selected to characterize the Russian Arctic coast. The area covered in this work includes the 200-km-wide band along the entire Russian Arctic coast from the Norwegian boundary in the west to the Bering Strait in the east. Methods included the collection of the majority of available hard copies of cartographic material and their digital formats and the transformation of these sources into a uniform digital graphic format. The atlas consists of environmental maps and maps of engineering-geological zoning. The set of environmental maps includes geology, quaternary sediments, landscapes and vegetation of the Russian Arctic coast at a scale of 1:4000000. The set of engineering-geocryological maps includes a map of engineering-geocryological zoning of the Russian Arctic coast, a map of the intensity of destructive coastal process and a map of industrial impact risk assessment ( 1:8000000 scale). Detailed mapping has been performed for key sites (at a scale of 1:100000) in order to enable more precise estimates of the intensity of destructive coastal process and industrial impact. The engineering-geocryological map of the Russian Arctic coast was compiled based on the analysis of geotechnical and geocryological conditions in the areas adjacent to the coastal band. Industrial impact assessment has been estimated differently for each engineering-geocryological region distinguished on the coast, considering technological features of construction and engineering facilities: aerial construction, highways and airdromes, underground (with positive and negative pipe temperatures) and surface pipelines and quarries. The atlas is being used as a base for the circum-Arctic segmentation of the coastline and the analyses of coastal dynamics within the Arctic Coastal Dynamics (ACD) Project. The work has been supported by INTAS (project number 01-2332).
C13A-0258 1340h
The Dynamics of permafrost and the Gas Hydrate Stability Zone in Rift Structures on the Shelf of the Seas of Eastern Eurasia
The Eurasian Arctic shelf areas, especially those of the Kara, Laptev and East Siberian Seas, display submarine permafrost and gas hydrate occurrences as characteristic features. In some of the shelf areas oceanic rift zones stretch to the continent, as for example in the Laptev Sea area where the Lomonossov Ridge continues on land. Great differences in geothermal heat flow values (qgt) and rock's properties in undisturbed block of the lithosphere and in fault zones in this region have to been assumed just as in continental rifts (such as Momskii and Baikal rifts, etc.). As a result, differences in the thickness of permafrost and the gas hydrate stability zone (GHSZ) within these structures are expected. For the investigation of permafrost and GHSZ evolution, and their dynamic and interaction in rift structures a two - dimensional mathematical model has been elaborated. The paleogeographic scenario used in this calculation covers the time from middle - late Pleistocene to the Holocene (c. 400 kyr), i.e. the last four climatic and glacio-eustatic cycles. Model calculations for rift structures of different sizes, and different qgt values, which are typical for different geographic situation on the shelf and as the result have different paleogeographical history have been carried out. The modeling results show that the thickness of offshore permafrost in the stages of climatic warming and transgressions essentially decrease however, rather extremely irregularly. The permafrost thickness is more reduced in fault zones, than in the consolidated blocks with lower qgt values. Similar processes take place with the thickness variation of the GHSZ as well. According to the results of the simulations, a first estimation of the regularities of permafrost and GHSZ thickness variation has been carried out. The possibilities and the boundary conditions for the occurrence of open taliks, which may result in an emission of greenhouse gases from relict sub-permafrost layers, have been estimated.
C13A-0259 1340h
The use of Landsat-ETM Data, Digital Elevation Models and GIS Analyses for Quantification of Holocene Thermokarst: An Example From the Lena-Anabar Coastal Region (NE Siberia)
Ice super-saturated permafrost deposits, formed syn-genetically during the Late Pleistocene, are widely distributed in coastal lowland regions of Arctic NE Siberia. The ice content of the silty deposits (up to 160 weight-percent compared to dry mass) makes them very susceptible for large-area thawing and surface subsidence under warmer climate conditions. Hence, extensive thermokarst developed in this region during the Holocene. Generally, thermokarst is a significant factor in periglacial relief generation and landscape evolution. Additionally, the analysis of thermokarst-related transformation processes in periglacial landscapes is very important regarding the expected deep thawing of permafrost and the release of formerly frozen organic carbon in form of green house gases under a global warming scenario. To evaluate the Holocene thermokarst development and estimate possible future developments in the region, it is necessary to calculate and understand its actual extent. For this investigation, Landsat-ETM remote sensing data from the Lena-Anabar coastal lowland is used as an instrument for up-scaling local field data. Classes of different geomorphological units are discriminated with supervised classification algorithms based on various surface parameters like vegetation, relief, and soil moisture. These classes allow the characterization and quantification of periglacial landscape units with a focus on thermokarst features in the investigated area. The spatial distribution of identified thermokarst structures and their relationship to other geomorphological and hydrological features are analysed within a geographical information system using a digital elevation model and geomorphological parameters derived from the DEM. As result, quantitative and qualitative parameters for thermokarst structures in this Laptev Sea coastal region are derived.
C13A-0260 1340h
Numeric Apporach to the Thermal Evolution of Submarine Permafrost on the Laptev-Sea Shelf / Siberia
Almost 24 percent of the northern hemisphere are under permafrost influence. A special variety is the submarine or sub-sea permafrost proposed on the Laptev-Sea shelf in Siberia. However, temperatures far below the freezing point can establish in soils only under subaeric conditions without ice-cover. Submarine permafrost is considered to be a relic terrestrial permafrost formed on the shallow Laptev-Sea shelf during times of sealevel lowstand of the last galcioeustatic cycle. Vast areas of the shelf down to the present 120 meters isobath were exposed to acrtic mean annual temperatures of less than -15°C. At the end of the last glacial maximum, about 13.000 ky B.P., transgression of arctic sea-water started to drown the permafrost. Nowadays, the epicontinental Laptev-Sea provides water depth less than 40 meters throughout most of the shelf area. Rates of coastal retreat of approx. 5 m/y make the transition zone of land and sea a rapidly changing system that holds significant keys to the understanding of temporal and spatial development of the submarine permafrost. Due to the contact to relatively warm arctic saline water above (about -1.5 °C in average), the submarine permafrost assimilates heat energy from the seawater. This energy flux leads to a warming of the submarine permafrost close to the thaw temperature of fresh water in the pore space. The present state of permafrost degeneration is largely unknown. In order to learn more about the process of degeneration and to determine locations of special interest for fourthcoming expeditions, a numeric model based on finite-element method was developed. Assuming, that the process of heat diffusion strongly outweights convective mechanisms, a diffusion equation was used to compute the thermal development of the permafrost beginning from 50 ky B.P up to now. The model takes account of regional climate change, transgression of sea water/coastal retreat, basal heat flux, thermal rock-paramters for water saturated sediments and latent heat of fusion. Applying all this parameters to the numeric solution of the equation of heat diffusion, leads to spatial present-day temperature distribution across Laptev Sea. Results of numerical modelling show, that the submarine permafrost responds very sensitive to temperature changes applied to the upper boundary condition - in this case seawater (-1.5 °C). Already 1000 years after transgression, the model is close to a thermal equillibrium with sea water. All areas of Laptev-Sea that have been covered with sea water earlier than app. 3 ky B.P. show largely normal temperature gradients over depth. Much lower temperatures, probably retated with ice bonded permafrost, have been preserved only in less than 30 km distance from the coast. According to the model, the rate of transgression / coastal retreat strongly controls the distribution and conservation of submarine permafrost. This raises the question, whether the ice in the pore-space of submarine permafrost has been conserved further off the coast where temperature is close to its thawing temperature. At this crucial point probably other side effects and minor related paramter like depression of freezing point due to grain size, infiltration with salt water and variations in basal heat flux, become more important and could make a difference.
C13A-0261 1340h
Siberian Arctic coasts: sediment and organic carbon fluxes in connection with permafrost degradation
During the last decade detailed coastal studies along the Arctic Seas have been conducted within the frame of the Arctic Coastal Dynamics (ACD) Program. The results indicate that shore dynamics play an important role in the balance of sediment and organic carbon in the Arctic basin. Arctic coastal sediment flux exceeds river sediment discharge and other terrestrial sediment sources. Based on newly obtained data, this presentation evaluates average coastal erosion rates as well as sediment and organic fluxes within the Siberian Arctic coastal zone. The Siberian Arctic sector includes four seas: the Kara, Laptev, East Siberian and Chukchi Seas. The total length of the Siberian Arctic coastline, including the islands, is about 29,500 km. Most parts of this coast are characterized by very active coastal erosion processes. A considerable proportion of the Siberian Arctic coasts (especially for the Laptev and East Siberian Seas) consists of ice-rich permafrost deposits, which are rapidly reworked by sea erosion. It has been found that the coastal sediment flux into the seas listed above plays a dominant role in their sediment budget. Based on the amount of coastal sediment released to the sea and the average organic carbon contents of the key types of coastal deposits, the total organic carbon (TOC) supplied to the Siberian Arctic Seas (SAS) has been estimated. The assessment of these lithologic-dynamic parameters is based on unified methods, which involve detailed coastal segmentation and GIS-analyses. The calculated values of the sediment and TOC fluxes are considerably different from previously published data. Our results suggest that both coastal sediment flux (158 million tons per year) and coastal TOC flux (4.6 million tons per year) to the SAS significantly contribute to the Arctic Ocean sediment and carbon budget. This study was supported by the INTAS (grant 01 - 2329).
C13A-0262 1340h
Concentration of Natural Gas Hydrate Beneath the Permafrost Zone: Implications for Geochemical and Hydrologic Investigations
Gas hydrates are ice-like solids made of water molecules containing various gas molecules. The geological evaluations have suggested worldwide methane contents of gas hydrate beneath deep sea floors as well as permafrost-related zones to about twice the total reserves of conventional and unconventional hydrocarbon. Scientific and economic interests are increasing in gas hydrate as a new energy resource and a potential greenhouse gas. In 1998 and 2002 Mallik wells were drilled in the Canadian Arctic that clarified the characteristics of gas hydrate-dominant layers at depths from 890 to 1110 m beneath the permafrost zone. Continuous downhole well log data, anomalies of chloride contents in pore waters, core temperature depression as well as visible gas hydrates have confirmed the highly saturated pore-space hydrate as intergranular pore filling within sandy layers, whose saturations are higher than 70% in pore volume. Muddy sediments scarcely contain gas hydrate. The Nankai Trough runs along the Japanese Island, where forearc basins and accretionary prisms developed extensively and BSRs (bottom simulating reflectors) have been recognized widely. The METI Nankai Trough wells in 2000 also revealed the presence of pore-space hydrate filling intergranular pore of sandy layers. It is remarked that there are many similar features in appearance and characteristics between the Mallik and Nankai Trough areas with observations of well-interconnected and highly saturated pore-space hydrate. It is necessary for evaluating subsurface fluid flow behaviors to know both porosity and permeability of gas hydrate-bearing sandy sediments, and measurements of water permeability for them indicate that highly saturated sands may have permeability of a few millidarcies. Subsequent analyses in sedimentology and geochemistry performed on gas hydrate-bearing sands revealed important geologic and sedimentologic controls on the formation and concentration of gas hydrate. It is suggested that the distribution of a porous and coarser-grained sandy sediments is one of the most important factors to control the occurrence of gas hydrates, as well as physicochemical conditions.
C13A-0263 1340h
Synthetic Aperture Radar Remote Sensing of Bottom-Fast ice in the Mackenzie Delta Region, Northwest Territories, Canada
Bottom-fast ice (BFI) refers to sea- or lake-ice that freezes to the sea- or lake-bed during the course of the winter season. The timing and distribution of BFI controls the mean annual temperature of the upper sediment column and therefore the potential for development and maintenance of permafrost and the thickness of the sub-bottom active layer. Air- and satellite-borne Synthetic Aperture Radar (SAR) imagery has been used to identify and map the distribution of BFI in Alaskan lakes and more recently in the nearshore of the Laptev Sea. It has been demonstrated that relatively high backscatter of SAR signals in lacustrine environments is caused by a combination of a strong reflection from the ice-water interface and scattering by tubular bubble inclusions within the ice. Lower backscatter regions are found where ice is frozen to the bed and the SAR signal passes into and is absorbed by the soil beneath. Some estuarine environments (e.g. the Lena Delta-Laptev Sea) are characterised by sufficiently freshwater in the shallow nearshore that the SAR signal should behave in the same manner. This paper describes the application of these concepts to the lakes of the Mackenzie Delta and the adjacent uplands and along the Beaufort Sea coastline. Bathymetric data from lakes, ice thickness measurements, and interpretation of ground-penetrating radar (GPR) are used to validate the interpretations from SAR imagery. Regions of low SAR backscatter are associated with mapped shallow water in lakes and the nearshore regions of the Mackenzie Delta. Relatively higher backscatter is found in deeper areas. The maximum extent of low SAR backscatter occurs in April and is associated with regions of the sea and lake bed that are generally less than 1.5 m water depth. Interpretations of SAR imagery become problematic in May and June because of the presence of a wet snowpack and flood or meltwater on the surfaces of the ice. A time series of RADARSAT ScanSAR Narrow and fine mode images is used to monitor the growth of these low backscatter zones beginning with inception around subaerial shoals in November and culminating in extensive regions by April. Differences between interpretations of BFI extent based on RADARSAT and GPR suggests that the former may be more sensitive to areas that are either marginally bottom-fast or potentially subject to tidal influences (i.e. periodic lift-off from the seabed). Additional validation of the technique in the shallow coastal estuarine environment is presently underway.
C13A-0264 1340h
High Resolution Multichannel Seismic Images of Marine Permafrost - First Results from TRANSDRIFT X Cruise to the Laptev Sea
Large areas of the shallow shelf seas in the Siberian Arctic were exposed in glacial times and thereby subject to climatic conditions supporting the development and growth of permafrost. However, it is unclear, how the cyclic occurrence of transgressions and regressions have effected the presence and distribution of permafrost in the currently drowned shelf areas. As part of the Laptev Sea System' Project carried out in close partnership between German and Russian Research institutions, the TRANSDRIFT X cruise with R/V Smirnitsky was undertaken inSeptember 2004 to survey off-shore permafrost in the eastern Laptev Sea with a combination of acoustic and seismic systems, namely side scan sonar, chirp sonar and the new shallow marine multichannel seismic system FlaMMe of the University of Bremen. It was of particular interest to detect the top of the permafrost zone to analyze the stability of permafrost after the Holocene transgression to use the collected data for a drilling campaign planned for summer 2005. The MCS system consists of a 48-channel single hydrophone streamer of 50 m length with 5 cable levellers and additional 9 depth sensors built into the streamer to allow a superior geometry control and towing at very shallow depth of appx. 1 m. A SODERA Mini GI Gun and a SODERA S-15 Watergun were used to generate high frequency signals beyond the conventional seismic frequencies, which ranges between 100 and 500 and between 200 and 1600 Hz, respectively. Examples will be shown from areas near the coast, where the former thermokarst surface was nearly undestroyed by the transgression, as well as a region northeast of the Lena delta, where an unconformity indicated the transgressive reworking of the terrestrial landscape. Further targets are thermokarst structures like pingos or thermokarst lakes with associated taliks, the distribution of marine Holocene sediments and the permafrost degradation with respect to the location of the paleoriver valleys. Combined analyses of the acoustic data sets collected will allow detailed studies on the preservation state of permafrost in the southern Laptev Sea area.
C13A-0265 1340h
Organic Carbon Contents of Permafrost Soils Along the Yukon Coastal Plain, Canada
The response of Arctic coasts to climate change can effect changes to the global carbon cycle. This is because degrading permafrost and eroding shorelines have the potential to release not only carbon dioxide and methane directly to the atmosphere, but soil organic carbon into the nearshore zone as well. This feedback has implications for carbon system dynamics and future climate change. In this regard shorelines containing ice-rich permafrost and backshore areas with extensive wetlands are the most sensitive. The Yukon Coastal Plain along Canada's Beaufort Sea represents potentially one of the most sensitive coastal climate systems. This study details the methodology for quantifying the amount of soil organic carbon along the Yukon coast. A morphological method developed to estimate the relative percentages of sediment and ground ice is applied to various terrain units in different geomorphic settings, with the resulting values being calibrated by field data. Published values for soil carbon are then used to calculate the organic carbon contents of the coastal soils. The potential contribution of organic carbon to the nearshore zone caused by climate change-induced thawing of permafrost and increased wave erosion along the Beaufort Sea coast is discussed.
C13A-0266 1340h
Trends in Arctic and Antarctic Melt Season Parameters From Reanalysis
Melt season is an important period in the cryoshpere. Its timing, duration, and intensity guide the response of many natural processes and system states, including ecological, hydrological, ground-thermal, glaciological, sea-ice, and snow cover. Capturing an overview of spatial-temporal patterns in melt-season parameters contributes to understanding process and state response. Trends for several melt-season parameters have been calculated from NCEP/NCAR reanalysis data for both hemispheres, including: melt season start and end dates, melt season length, and annual melting degree-day (MDD) totals. Results from the Arctic indicate simple linear trends in MDD as large as +/- 20 days/year, however it is unlikely that such rates of change have been uniformly maintained over a 50-year period. This suggests more complex temporal dynamics, similar to that exhibited by northern hemisphere temperature trends, such that trend periods should be further broken down and greater analysis performed. In terms of specific years, in certain regions of the Arctic the difference between two years can be very large, on the order of hundreds of MDD. This level of interannual variation can be of the same magnitude as MDD seasonal totals, and suggests large interannual cryospheric response to thermal forcing that should be taken into consideration when studying physical response of a cryospheric system. A subset of these results are presented.
C13A-0267 1340h
Ice-Bonded Sediments and Massive Ground Ice in a Transgressive Barrier-Lagoon and Delta Complex, Yukon Coast of Beaufort Sea, Western Arctic Canada
The barrier-lagoon estuary of the Babbage River is predominantly less than 1.5 m deep (the approximate thickness of winter ice). It is partially enclosed by a spit 4 km long averaging 60 m wide. There is a 2 km wide baymouth opening at the end of the spit opposite the delta front. The system receives runoff and sediment from Deep Creek and Babbage River, which drain part of the coastal plain and mountains to the south. The rate of relative sea-level rise exceeds the rate of delta-plain sedimentation, resulting in slow inundation and landward migration of the delta front. A number of shallow boreholes drilled in winter to depths between 10 and 36 m showed ice-bonded sediments beneath the surrounding high ground, delta plain, tidal flats, and bottomfast ice in the lagoon. In about 2 m water depth seaward of the spit, the seabed sand and gravel and upper part of underlying mud were unfrozen to a depth of 10 m and underlain by ice-bonded silt and clay with thin lenses of massive ice. Farther seaward in 8 m water depth, the sediments were unbonded to at least 22 m below seabed. Barrier-beach sand and underlying silt beneath the spit were ice-bonded to 9 m at one site (11 m at another), below which a 4 m thick talik of unfrozen silt was found above the contact with underlying ice-bonded silt and clay. The unbonded layer at depth beneath the spit and thicker units of unbonded sediments beneath the backbarrier lagoon suggest downward refreezing of shallow estuarine sediments as the washover-dominated spit migrates landward into the lagoon. The delta plain is a low-relief surface with numerous shallow ponds and very subtle levees along channel margins. We hypothesize that anomalous higher surfaces of chaotic microtopography may be elevated in part by massive ice growth fed from taliks beneath adjacent deep channels. A borehole through one such surface near the delta front, adjacent to an 8 m deep thalweg scour depression in the main distributary channel, was underlain by 3.5 m of massive ice over ice-bonded gravel with 20% ice by volume. Salt water under pressure was encountered at 23 m. Salinities as high as 60 psu or higher have been measured in water confined below winter ice in the delta. These results confirm preservation in shallow coastal waters of massive ice and ice bonding developed below formerly subaerial surfaces which have subsequently been transgressed. Observations of ice-wedge polygon terrain below shallow lagoon margins elsewhere along the Beaufort Sea coast support similar conclusions. Downward thaw of seabed sediments is initiated in the nearshore seaward of the spit as it migrates landward.