Satellite Observations of Spatial Patterns and Interannual Variability in Spring Thaw and Terrestrial Net Primary Production for the Pan-Arctic

Spatial and temporal variability in the timing of spring thaw is a major driver of regional vegetation activity and net carbon exchange with the atmosphere at high northern latitudes. We conducted a temporal classification of the primary spring thaw event from 1988 to 2001 across the pan-arctic basin and Alaska using passive and active microwave remote sensing measurements from the Special Sensor Microwave Imager (SSM/I) and SeaWinds scatterometer. Spatial patterns and interannual variability in the timing of spring thaw are examined in relation to regional biospheric activity indicated by atmospheric CO₂ measurements and terrestrial annual net primary production (NPP) derived from AVHRR Pathfinder and MODIS satellite data. The timing of the primary terrestrial seasonal thaw event in spring spans a 1.8 month period across the region with interannual variability on the order of 1 week (+/-46%), while spatial and interannual variability in NPP is found to be on the order of 3 Mg C ha^-1 yr^-1 (+/-79-94%). Satellite observations of the timing of spring thaw correspond significantly to seasonal patterns and interannual variability in the timing of carbon uptake and associated vegetation activity as indicated by atmospheric CO₂ measurements and spatial patterns of annual NPP derived from global satellite observations. The timing of satellite based spring thaw measurements corresponds directly to the timing of regional net carbon uptake in spring as indicated by atmospheric CO₂ measurements, though interannual variability in spring thaw does not necessarily correspond to similar changes in NPP. These differences are attributed to the coarse spatial scale of GCM meteorological inputs used to derive satellite based NPP results and the influence of seasonal temperature, radiation and precipitation patterns on NPP. Satellite observations of seasonal thaw appear to provide a consistent, indirect measure of regional biospheric activity at high northern latitudes. This work was performed at the University of Montana, and at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.