Collaborative Research: Environmental changes alter the carbon cycle of high Arctic ecosystems: Shifts in the ages and sources of CO2 and DOC.

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The Arctic is undergoing structural and functional changes that appear to be the result of climate change, including shifts in vegetation distribution, increases in CO2 and CH4 efflux from ecosystems to the atmosphere, and the acceleration of dissolved organic carbon (DOC) export from land to oceans. Research in NW Greenland has produced four lines of evidence that climate change is affecting the High Arctic C cycle in ways we do not fully understand. First, soil organic C pools in polar semi-deserts, which occupy 1 x 106 km2 of the Arctic land surface, may be at least 6× greater than previous estimates, and ancient (30 ky BP) and young soil C pools are present in the active layer. Second, CO2 ecosystem exchange measurements have consistently shown net C losses during the growing season; these C losses are, however, reversed under warmer and wetter conditions and with modest snow depth increases during the previous winter. In situ ecosystem respiration has been found to increase by 25 and 35% with experimental summer warming of 1.3 and 2.4°C, respectively, but by 50% when the higher level of warming was combined with irrigation. Third, soil CO2 efflux measurements indicate that ancient soil C is being degraded by microbes before vegetation leaf-out. Losses are expected to continue throughout the growing season, but masked by high rates of plant respiration (recently-fixed C) during the mid-summer. Forth, interannual and temporal patterns of riverine DOC are not explained by simple differences in summer weather conditions. Articulating the magnitudes of CO2 and CH4 exchange and DOC export along with the ages of soil respired CO2 and DOC in soil solution and rivers, and determining the sensitivity of microbial degradation of different soil C pools to temperature and moisture will transform our understanding of environmental change, ecosystem function and C cycling in the Arctic. This study will address these questions: 1. How does the age (recently-fixed vs. older) of soil respired CO2 and DOC change over the course of a year, to what extent is this influenced by inter-annual variability in temperature and precipitation, and how does it correspond with the patterns of CO2 and CH4 fluxes? 2. To what extent do long-term experimental increases in temperature (+2 and + 4oC), and in water inputs (summer rain and winter snow) alter the ages, magnitudes, and patterns of C fluxes (CO2, CH4, and DOC)? 3. Are there differences in the extent of microbial degradation of young as opposed to older soil C pools and how sensitive are the degradation rates to changes in climate?