Satellites reveal an increase in gross primary production in a greenlandic high arctic fen 1992 – 2008

Abstract

Arctic wetlands play a key role in the terrestrial carbon cycle. Recent studies have shown a greening trend and indicated an increase in CO2 uptake in boreal and sub- to low-arctic areas. Our aim was to combine satellite-based normalized difference veg- 5 etation index (NDVI) with ground-based flux measurements of CO2 to investigate a possible greening trend and potential changes in gross primary production (GPP) be- tween 1992 and 2008 in a high arctic fen area. The study took place in Rylekaerene in the Zackenberg Research Area (74◦28N 20◦34 W), located in the National park of North Eastern Greenland. We estimated the light use efficiency (ε) for the dominant 10 vegetation types from field measured fractions of photosynthetic active radiation (FA- PAR) and ground-based flux measurements of GPP. Measured FAPAR were correlated to satellite-based NDVI. The FAPAR-NDVI relationship in combination with ε was ap- plied to satellite data to model GPP 1992–2008. The model was evaluated against field measured GPP. The model was a useful tool for up-scaling GPP and all basic 15 requirements for the model were well met, e.g., FAPAR was well correlated to NDVI and modeled GPP was well correlated to field measurements. The studied high arctic fen area has experienced a strong increase in GPP between 1992 and 2008. The area has during this period also experienced a substantial increase in local air tempera- ture. Consequently, the observed greening trend is most likely due to ongoing climatic 20 change possibly in combination with CO2 fertilization, due to increasing atmospheric concentrations of CO2.