Collaborative studies of High Arctic ecosystem responses to long-term simulated changes in climate was initiated in late July through mid-August by Jeff Welker (University of Wyoming) and Greg Henry (University of British Columbia) and their research groups at Alexandra Fiord, Ellesmere Island, Canada (79^oN, 75^oE). Jeff Welker and Bob Piper installed chamber CO₂ flux bases in three ecosystems where ITEX open-top chambers have been used for the past eight years to warm the tundra. The ecosystems spanned a moisture gradient ranging from wet sedge (Carex dominated), mesic tundra (Dryas, Cassiope and Salix dominated) and dry tundra (Salix and Oxyria dominated). All three ecosystems are within 2 km of each other in the lowland and our studies were carried out during peak growth.

Comparative measures of net ecosystem CO₂ flux, ecosystem respiration and gross photosynthesis were made between the three communities (10 am to 6 pm) under clear skies and relatively warm conditions (5^oC) to compare ITEX warming effects on CO₂ exchange. In addition, diurnal measure of total daily CO₂ exchange was carried out in the mesic tundra. Soil and plant samples were collected from all ecosystems (ambient and warmed conditions) for quantification of total soil C & N. Winter CO₂ flux measures were also initiated using chemical absorption (NaOH traps) techniques which will be collected in late May-early June. In addition, winter N mineralization studies were also initiated using PVC cores and resin bags. These too will be collected in early summer 2000.

Initial estimates of the spatial variation in CO₂ dynamics across Eastern Ellesmere Island were undertaken with ecosystem respiration measures at Princess Maria Bay, 70 km north of Alexandra Fiord. This area too, is a High Arctic lowland with two dominant ecosystems, wet sedge and dry tundra. At this site, ecosystem respiration measures were carried out during a single day between the hours of 1-4 pm and soil & plant samples were collected for total C & N analysis.

We will be analyzing our CO₂ flux, soil and vegetation data for comparisons with Alaskan and other High Arcitc carbon and nitrogen information and will make the data available for use by ATLAS investigators and others modeling the circumarctic C budget. We anticipate a winter trip to Alexandra Fiord for measurements of winter carbon flux using the CO₂ gradient through snow to cross-calibrate our chemical absorption techniques and to make more extensive measures of winter carbon loss across the entire lowland and in other nearby lowlands. We will begin our growing season chamber CO₂ flux measures in late May and anticipate quantifying diurnal patterns of carbon exchange in all three ecosystems (ambient and experimentally warmed) throughout the summer and into the fall. In addition, we anticipate quantifying growing season N mineralization to complement the over-winter mineralization studies initiated this year. We also plan bi-weekly sampling of vegetation for C & N content. These High Arctic studies are designed to complement similar measures of ITEX carbon dynamics being carried out at Toolik Lake in moist tussock and dry tundra under ambient and experimentally warmed conditions (Welker and Oberbauer groups) and studies at Barrow and Atqasuk (Oberbauer & Webber) in wet sedge and dry tundra. (This report is being filed from Resolute, Cornwallis Island, NWT).