Influence of experimental climate changes and herbivores on C & N processes in arctic Alaska and western Greenland

Background/Question/Methods

The Arctic is a region with unprecedented changes that are becoming increasing complex. We have undertaken a series of long-term observational and experimental studies in northern Alaska, NW and WC Greenland addressing: “how do short and long-term increases in winter precipitation, summer warming (with and without added summer water) and herbivore grazing effect CO₂ exchange, N cycling and vegetation chemistry?” and “is there evidence that older, ancient C is being respired and exported from Arctic landscapes as active layers are expanding?”. Our studies are using snow fences to increases winter snow depth (Alaska and NW Greenland), ITEX chambers to induce simple warming (AK and WC Greenland), IR-lamps to induce multiple levels of warming with and without summer watering (NW Greenland) and exclosures to limit herbivory in WC Greenland.  CO₂ flux, N cycling and vegetation chemistry measurements were made since 1994 in some sites. Soil respired CO₂ and DOC was periodically collected and analyzed for ¹⁴C.

 Results/Conclusions

We have found: a) Arctic tundra winter CO₂ losses to the atmosphere are substantial and can account for up to 30% of annual C losses and winter lose are dramatically higher (100%) when snow depth is increased, b) deeper snow leads to warmer soils,  a deepening of the active layer (100% increase) and the loss of ancient C in northern Alaska, c) long-term warming stimulates shrub growth and net CO₂ sequestration, but shrub density and CO₂ flux are not linearly related, d) High Arctic gross ecosystem photosynthesis exhibits a linear response to increasing temperatures while the highest rates occur are when polar semi deserts are warm and wet, e) ancient C  is mixing with the modern atmosphere in the High Arctic via CO₂ efflux and into the rivers, streams and near shore marine in the form of DOC, and f) herbivores mediate the warming responses of WC Greenland landscapes by controlling vegetation composition and CO₂ exchange. We believe that tundra responses to climate tell us: 1) rapid changes are underway and feedback processes and responses will be locally, regionally and globally important, 2) tight linkages between the landscape and climate results in rapid changes that have long-lasting effects, 3) the ancient C cycle will become increasing active in the global C cycle as active layers deepen,  including driving changes along the terrestrial-aquatic-marine corridor, 4) biotic processes-herbivores-may be one of the most important unexplored regulators of tundra responses to warming and changes in precipitation.