Title = Thule_Biocomplexity_NMSDsf_NEE_archive Data Directory = Terrestrial Ecosystems PI = Dr. Jeff Welker Enivironment and Natural Resources Institute 707 A Street University of Alaska Anchorage Anchorage, AK, 99508 firstname.lastname@example.org 907-257-2701 Co PIs = Dr. Josh Schimel Department of Ecology, Evolution and Marine Biology Bren Hall, room 4304 University of California, Santa Barbara Santa Barbara, CA 93106 email@example.com 805-893-7688 Dr. Ron Sletten University of Washington Quaternary Reseach Center Johnson Hall 363 4000 15th Avenue NE Seattle,WA 98195-1310 firstname.lastname@example.org 206-543-0571 Funding Source = NSF Grant # 0221606 Data Set Overview = Ecosystem carbon dioxide flux measurements were taken at a High Arctic prostrate dwarf-shrub, herb tunda near Pituffik (Thule), Greenland (76° 29'N, 68° 26'W; elevation 245 m asl) northwest Greenland. Between 1978 and 2004, mean annual air temperature and precipitation for the site were -11.4°C and 12.5 cm respectively. Over the same period, growing season (June, July and August) air temperatures averaged 3.8°C and approximately 50% of precipitation fell between October and April as snow. The soil surface of the study site was approximately 40% covered by vascular plants and 60% unvegetated. Dominant vascular plants include the deciduous dwarf-shrub Salix arctica, the graminoid Carex rupestris and the wintergreen dwarf-shrub Dryas integrifolia. The dataset covers the growing seasons of 2006 and 2007. The treatments were three levels of winter snow accumulation; ambient snow (0.25 m), intermediate snow (0.55 m) and deep snow (1.1 m). The treatments were accomplished by the erection of a 1.2 m snow fence placed perpendicular to prevailing winds. Snow accumulated behind the fence in a continuously tapering drift and permanent experimental plots were located on the ground under the snow depths listed above. Instrument Descriptions = Midday carbon dioxide fluxes were measured in each plot (n = 6 per treatment) using a closed system clear acrylic chamber with an in-line LiCor 6200 infra-red gas analyzer (IRGA; Li-Cor Inc., Lincoln NE) which continuously monitors CO2 concentration (Vourlitis et al. 1993). Chamber air temperature and relative humidity were also measured. The clear-chamber flux measurement technique has previously been used successfully at the study site (Arens et al. 2008). The IRGA was calibrated using a gas of known CO2 concentration (500 ± 2 ppm) on a bi-weekly basis to avoid instrumental error. Instrumental drift did not exceed a 2 ppm departure from the calibrated value. Plot-level measurements of 5 and 10 cm soil temperature and volumetric soil moisture were taken with a VWR Traceable Temperature Probe (VWR Instruments, West Chester, PA) and a Hydrosense time-domain reflectometry (TDR) soil moisture probe (Campbell Scientific, Logan, UT), respectively, during each flux measurement. Data Collection and Processing = Carbon dioxide flux data were recorded using the LiCor 6200's internal memory and were later corrected for changes in chamber microclimate conditions using the method of Hooper et al. (2002). Net Ecosystem Exchange (NEE) and Ecosystem Respiration (ER) values were directly measured, while Gross Ecosystem Photosynthesis (GEP) values were calculated as the difference of NEE and ER (GEP = NEE - ER). All data were tested for normality and homogenous variance and were appropriately transformed when these criteria were not met. Data Format = The data are tab-delimited ASCII plain text formatted. References = Arens SJT, Sullivan PF, Welker JM (2008) Nonlinear responses to nitrogen and strong interactions with nitrogen and phosphorus additions drastically alter the structure and function of a high arctic ecosystem. Journal of Geophysical Research - Biogeosciences, 113, 1-10. Hooper DU, Cardon ZG, Chapin FS III, Durant M (2002) Corrected calculations for soil and ecosystem measurements of CO2 using the Li-Cor 6200 Portable Photosynthesis System. Oecologia, 132, 1-11. Vourlitis GL, Oechel WC, Hastings SJ, and Jenkins MA (1993) A system for measuring in situ CO2 and CH4 flux in unmanaged ecosystems: an Arctic example. Functional Ecology, 7, 36-379.