Controls on energy and carbon fluxes from select high-latitude terrestrialsurfaces

While the physical processes driving energy fluxes in the high latitudes ar e universal, some of the controlling factors such as permafrost, temperatur e, and vegetation play a special role. Annual net radiation at Arctic treel ine is larger over subarctic forest than over tundra as a result of smaller albedo during the snow-cover period. The absorbed solar radiation is notab ly larger in late winter. During the snow-free period, in well-watered area s, there is a hierarchy in potential evaporation from very high rates for s hallow tundra lakes and ponds to low rates for well-drained upland heath te rrain. With abundant moisture and warm conditions, open coniferous forests, dwarf deciduous forests, and sedge fens have similar energy and water bala nces. During the growing season when moisture is limiting, a sedge fen, mor e so than a coniferous forest, curtails its evaporation rate. Under cold co nditions, however, coniferous forest has the smaller evaporation. Soil heat fluxes in summer comprise from 10% to 15% of the net radiation and are fai rly uniform both temporally and spatially. The carbon budget of peatlands, which are major global repositories of carbon, responds strongly to air and soil temperatures and to the water balance. Warm and wet conditions suppor t strong photosynthesis and a substantial methane flux. Warm and dry condit ions favor strong respiration carbon losses from plants and soil. In a 2 x CO2 world, substantial changes in temperature, precipitation, and energy an d water balances are anticipated and these will drive substantial changes i n the high-latitude carbon budget.