C31A-01
Cold-Region Subsurface Hydro-thermal Sensitivity of Physical Land Scheme in Global Climate Model: Idealized Off-Line Evaluation
There have been a number of successful works and accumulation of experiences to understand the subterranean surface hydro-thermal processes in the cold regions, and to quantize by numerical physical models, targeted to specific plots to sub-catchments. However, for most of the land surface schemes in regional to global models improvement and optimizations seems necessary to realize required performance, in terms of the complexity of the resolved physical processes and properties, and the initial and boundary conditions. A series of 100-year sensitivity experiments were conducted with a land surface scheme (MATSIRO) in a coupled global climate model (GCM), CCSR/NIES/FRCGC MIROC v3.2, to provide information for the future refinement directions. To evaluate the model performance under climatological and warming conditions, two sets of idealized meteorological forcing were prepared, based on the observations taken at Barrow, AK for 1990 through 2003, for the 1990s climatology and the incremental warming condition with about 6 degree C per century. Quantitative impact of the following factors were investigated in the experiments: 1) total depth of the soil column, and the layer thickness in the top layers, 2) presence of organic layers close to the surface, 3) porosity profile of the soil column, 4) amount of precipitation, and 5) physical parameterization of the thermal and hydrological properties, namely consideration of co-existence of solid and liquid water under the freezing point. Major results and their implications include the following. Total depth of 20m or deeper would be necessary to provide appropriate thermal buffer and to justify the constant geothermal flux boundary conditions at the bottom, which also improved the seasonal cycle of simulated subsurface thermal regimes by eliminating numerical flaws resulted from a too shallow soil column. Inclusion of organic layers improved the thickness of maximum active layer, and suppressed its unrealistic increase under warming: more than doubled without organic layers, compared to 46% increase when included. Porosity profile showed little impact, although it could have affected total capacity and permeability of heat and water of the soil. Refined thermal parameterization improved the seasonal evolution of active layer thickness, and decelerated the change under warming conditions. With intensified precipitation, permanently unfrozen layers were formed above permafrost table in the warming experiments.
C31A-02
Permafrost in Iceland – Distribution, Ground Temperatures and Climate Change Impact
This paper gives an overview of distribution, thermal characteristics and geomorphological impact of mountain permafrost in Iceland. Borehole temperature monitoring since summer 2004 and simple distribution modelling implies widespread mountain permafrost in Iceland. The permafrost temperatures are close to 0 °C and some tens of meters thick in the elevation range of 800 to 1000 m a.s.l. Here snow coverage mainly governs the permafrost distribution, while above 1200 m a.s.l. smaller areas of continuous permafrost do exist. This presentation presents new borehole temperature data until the summer 2007 and associated numerical modelling of climate change impact. Further, the paper discusses possible impact of the maritime permafrost in Iceland on geomorphological and geotechnical processes and landform evolution.
C31A-03
Remote sensing of changes in near surface freeze and thaw timing from 1988 to 2006
We developed a technique to detect the date of near surface soil freeze and thaw using passive microwave satellite data from the SSM/I instrument. The difference between the 37 and 19 GHz channels is used as an indicator of soil freeze state. We generated a continuous record of freeze and thaw dates from 1988 to 2006 for all land areas north of 45 degrees north. Our analysis shows that the onset of fall freeze has moved progressively later (4 days/decade) in Boreal forests across the globe. Spring thaw is occurring earlier in tundra ecosystems (3 days/decade) and there has been a net increase in the growing season length in both Boreal (5 days/decade) and Tundra (4 days/decade) ecosystems globally. These results are compared to trends in surface air temperature and NDVI over the same period. Significant correlations between the annual anomalies in surface air temperature, average NDVI, and the freeze-thaw records exists for all biomes analyzed. This record is a new long-term metric of global climate change over the past 19 years.
C31A-04
Frozen Quaternary Deposits of the Laptev Sea Region as a Reservoir of Organic Carbon: Total Content and Composition.
Permafrost is a significant reservoir and potential source of ancient organic matter (OM) such as plant remains, humified organics, etc. and greenhouse gases. In according with different estimations 1 cubic meter of frozen deposits in this region consists up to 10 kg of Corg. Due to the degradation of permafrost under the both modern geological processes and global warming, this organic carbon is easily released into the present biogeochemical cycle Humus parameters, elementary and isotopic composition of OM, dissolved organic carbon content and some biomarkers in the following types of quaternary deposits were determined: Middle Pleistocene deposits contain 1-2% of TOC and characterised by the ratios of C/N 5-7,5 (syncryogenic) and 10-12 (epycryogenic). Late Pleistocene syncryogenic deposits composed by true syncryogenic deposits and buried soils. The former characterized by the 1-2% of TOC and C/N ratio 9-11 the later 4-16% of TOC and 12-16 C/N ratio. Late Pleistocene-Holocene taberal deposits. TOC – 1%, C/N - 10-12 Holocene alas deposits. TOC 4-6%, C/N - 10-12. Main part of total carbon is organic origin. Carbonates consist only 31 – 20 %. The following conclusions can be done: More transformed OM is in the buried soils and alas deposits. OM of syncryogenic deposits is a most labile. TOC and stage of organic matter transformation in the syncryogenic deposits depends on ratio of sedimentation and freezing rate. Decreasing of freezing rate leads to the more deposition and to deeper transformation of OM. Most transformed OM is in alas deposits and buried soils. About 20% of TOC presented by humus. Syncryogenic and taberal deposits are not so matured (humus content 15%). Content of organic matter potentially available to be dissolved in the water is low in the all investigated deposits. It consists approximately the 1-1,5% of TOC in Ice Complex deposits and 2-3% in alas and taberal deposits. Determination of biomarkers composition (n-alkanes, fatty acids and sterols) in alas and taberal deposits was carried out. Main part of organic matter in investigated deposits is presented by n-alkanes (37-74%, generally 55-60%). Fatty acids and sterols consist 13-22 and 2-7% correspondingly. On the base of the analyses conclusions about the main source of organic matter in the all investigated deposits can be done. Predomination of odd carbon-numbered long-chain n-alkanes (with 25-35 carbon atoms) and saturated fatty acids with long carbon chain (> C22) are character for terrestrial higher plants. There is a positive correlation of TOC and long-chain alkanes. All investigated deposits characterized by the low values of isotope C13 (from -24 to -24) what reflects the low decomposition of organic matter. Research was supported by RFBR (05-05-64062).
C31A-05
Exploring the Effectiveness of Alpine Permafrost Model Transfer Between Mountain Environments in Northwestern Canada
The BTS method developed by Haeberli (1973) has been used extensively to model mountain permafrost distribution in Europe, Asia and most recently in North America. The method involves recording the mid-winter temperature beneath a deep (>80 cm) snow pack in a variety of mountain locations as an indicator of the presence or absence of permafrost. The BTS results can then be related statistically to factors such as elevation and Potential Incoming Solar Radiation (PISR) which contribute to the existence of mountain permafrost. This empirical statistical methodology can be used to generate detailed permafrost predictions within a GIS using limited field information. When combined with binary permafrost ground-truthing undertaken in the late-summer months probability models can be generated using logistic regression. Although this methodology provides far more detailed information on permafrost occurrence than traditional permafrost maps one of the major drawbacks is that models are highly localized and thus require re-sampling from area to area. A potential reason for this is that mountain ranges in north-western Canada are often climatologically dissimilar with the development of permafrost occurring due to a variety of factors including elevation, regional climate, local snow depths, vegetation and substrate. This study explores how effectively a model created for one area can predict the occurrence of mountain permafrost in other locations both geographically and climatologically similar and dissimilar. Analyses demonstrate that similar patterns of mountain permafrost probability can be generated for areas with similar climate even if they are geographically distant. In climatologically dissimilar areas, however, the predicted spatial distribution of permafrost is not preserved as the weighting of the predictor variables differs significantly. Nevertheless, the total amount of permafrost predicted varies little and this appears to reflect the importance of the ground-truthing data. Trends between areas will be of great importance in future attempts to model discontinuous permafrost distribution in detail for the southern half of the Yukon Territory, Canada, an area of about 0.25 million square kilometers.
C31A-06
Snow and Ground Temperature
A numerical model of snow-ground thermal interactions has been developed to investigate the effect of seasonal snow cover on the mean annual ground temperature. The model is parameterized in terms of three snow event parameters: onset time of the annual snow event, duration of the event, and maximum depth of snow during the event. These parameters are commonly available from meteorological and remotely sensed data making the model broadly applicable. The model is validated using surface air temperature (SAT), surface ground temperature (SGT), and snow depth data from observations at Emigrant Pass climate observatory (EPO) in northwestern Utah and National Weather Service data from sites across North America. Measured subsurface temperature-time series compare well with changes predicted by the model. We define a "snow effect" as the difference in mean annual ground temperatures with and without a snow event and explore how the snow effect might change with a warming climate. During the period 1950-2002, the mean North American snow event onset (December 15) and duration (81 days) has remained relatively constant although interannual variation as much as 18 days (onset) and 15 days (duration) are present. Across all North American stations with snow cover during this period, the trend in mean annual SGT-SAT offset is about \- 0.02 K/decade. One unanticipated finding is that snow can either raise or lower the mean annual ground temperature depending principally on the timing of the snow event.
C31A-07
An Increase in Rates of Retrogressive Thaw Slumping and Implications to Lake Water Quality, Western Arctic, Canada.
The growth rates of retrogressive thaw slumps in the Mackenzie Delta region Northwest Territories, Canada have increased significantly since 1973 in concert with accelerated climate warming. To evaluate change over time, we analyzed historical temperature records and mapped all slumps on 23, 49 km2 study plots using 1950, 1973 and 2004 aerial photographs. The aerial extent of slumping since 1950 had increased 15 percent by 1973 and 36 percent by 2004. The mean rate of slump expansion from 1973 to 2004 was about 1.5 times greater than that estimated from 1950 to 1973, whereas the mean maximum rates of headwall retreat from the lakeshore more than doubled. Degrading permafrost releases soluble materials, which are transported by surface runoff from ion-rich slump soils into adjacent aquatic systems, elevating ionic concentrations in the water of small tundra lakes. A positive association between lake water ionic concentrations and the proportion of catchment area influenced by thaw slumping suggests that degradation of ice-rich permafrost will be an important factor influencing chemistry of thousands of lakes in a warming western Arctic.
C31A-08
Why could Permafrost be sometimes so persistent?
Recent changes in climate make permafrost warmer and less stable in many locations throughout the Arctic and sub-Arctic. At some of these locations, permafrost already started to thaw. However, most of the permafrost in the Northern Hemisphere is still generally stable and the threshold of the widespread permafrost thawing is not crossed yet. Moreover, from paleo-environmental studies, it is known that permafrost survived much warmer- than-now climatic conditions that existed during the early and middle Holocene in the areas where permafrost now is just one degree Centigrade or less from the melting point of ice. This paradox has not been explained yet, though it is very important to do so, especially in the view of better understanding the future trajectories of permafrost evolution under conditions of possible further climate warming. One of the possible explanations of this phenomenon is related to the fact that some amount of ice in fine- grained material, such as frozen silt or clay, starts to melt long before the soil temperature reaches the 0 C threshold. During a warming period, a zone of distributed heat sinks appears in the upper permafrost layer. As permafrost temperature moves closer to 0 C, this zone starts to spread to the deeper permafrost, eventually occupying the entire permafrost layer. As a result, a significant part of the heat flux entering thawing permafrost from its top boundary (permafrost table) penetrates through the phase boundary between the permafrost and the bottom of the growing talik and dissipates within the entire permafrost body. This heat is spent on partial melting of the constituent ice within the permafrost. Portioning of the amount of heat consumed by the thawing permafrost at the permafrost table and within the entire permafrost body depends on the thermal conditions at the ground surface and on the soil characteristics. The percentage of the heat flux that dissipates inside the permafrost layer is especially significant when long-term heat flux into the upper permafrost is small and when the temperature interval where distributed phase change occurs is large. Because this percentage could be as large as 80% or more, "formal" thawing of permafrost (downward movement of the permafrost table) could be delayed and/or slowed down very significantly. Large amount of excess ice in the upper permafrost would make the permafrost system even more inertial. All these effects together can delay and/or slow down the complete permafrost disappearance for centuries. In this presentation I will show measured permafrost temperature data that can support this hypothesis. Results of some relevant numerical experiments will be also presented.