Abstract
Drained thermokarst lake basins accumulate significant amounts of soil organic carbon in the form of peat, which is of interest to understanding carbon cycling and climate change feedbacks associated with thermokarst in the Arctic. Remote sensing is a tool useful for understanding temporal and spatial dynamics of drained basins. In this study, we tested the application of high-resolution X-band Synthetic Aperture Radar (SAR) data of the German TerraSAR-X satellite from the 2009 growing season (July–September) for characterizing drained thermokarst lake basins of various age in the ice-rich permafrost region of the northern Seward Peninsula, Alaska. To enhance interpretation of patterns identified in X-band SAR for these basins, we also analyzed the Normalized Difference Vegetation Index (NDVI) calculated from a Landsat-5 Thematic Mapper image acquired on July 2009 and compared both X-band SAR and NDVI data with observations of basin age. We found significant logarithmic relationships between (a) TerraSAR-X backscatter and basin age from 0 to 10,000 years, (b) Landat-5 TM NDVI and basin age from 0 to 10,000 years, and (c) TerraSAR-X backscatter and basin age from 50 to 10,000 years. NDVI was a better indicator of basin age over a period of 0–10,000 years. However, TerraSAR-X data performed much better for discriminating radiocarbon-dated basins (50–10,000 years old). No clear relationships were found for either backscatter or NDVI and basin age from 0 to 50 years. We attribute the decreasing trend of backscatter and NDVI with increasing basin age to post-drainage changes in the basin surface. Such changes include succession in vegetation, soils, hydrology, and renewed permafrost aggradation, ground ice accumulation and localized frost heave. Results of this study show the potential application of X-band SAR data in combination with NDVI data to map long-term succession dynamics of drained thermokarst lake basins.
Highlights
Thermokarst lakes and drained thermokarst lake basins (DTLBs) are important indicators of permafrost and thermokarst dynamics in arctic and subarctic lowlands with ice-rich permafrost [1,2,3,4,5].In Alaska, they occupy a large portion of the Arctic Coastal Plain, the Arctic Foothills and the SewardPeninsula [6,7,8], forming a complex and dynamic landscape with repeated cycles of lake formation and drainage due to permafrost degradation and aggradation [9,10,11]
Results of this study show the potential application of X-band Synthetic Aperture Radar (SAR) data in combination with Normalized Difference Vegetation Index (NDVI) data to map long-term succession dynamics of drained thermokarst lake basins
The amount of carbon sequestered in DTLBs and its role for the carbon budget in permafrost regions in a warming scenario is yet to be quantified for the Arctic
Summary
Thermokarst lakes and drained thermokarst lake basins (DTLBs) are important indicators of permafrost and thermokarst dynamics in arctic and subarctic lowlands with ice-rich permafrost [1,2,3,4,5].In Alaska, they occupy a large portion of the Arctic Coastal Plain, the Arctic Foothills and the SewardPeninsula [6,7,8], forming a complex and dynamic landscape with repeated cycles of lake formation and drainage due to permafrost degradation and aggradation [9,10,11]. DTLBs accumulate soil organic carbon (SOC) in the form of peat, which has important implications for northern SOC pool distribution and high-latitude carbon cycling [10,12,13]. Recent attention has focused on the effect of projected climate warming on the rate of microbial decomposition of SOC stored in northern permafrost and peatland regions that will have an impact on greenhouse gas release to the atmosphere [14,15,16,17]. Northern SOC pools have the potential for large emissions of methane (CH4) or carbon dioxide (CO2), depending on the soil aerobic regime, due to an enhanced rate of microbial decomposition of organic matter that will serve as a positive feedback to climate warming [17,18].
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