COLLABORATIVE RESEARCH: A SYNTHESIS OF THE LAST 2000 YEARS OF CLIMATIC VARIABILITY FROM ARCTIC LAKES

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This project contributes to understanding the Arctic system by placing 20th century climatic change into a longer-term context of inter-decadal climatic variability spanning the last 2000 yr. The centerpiece of the project is a synthesis of standardized, high-resolution proxy climate records from lakes across the North American Arctic that will advance our understanding of the role of the Arctic within the Earth system.Recent results have demonstrated that proxy climate records from the Arctic preserve a signature of summer temperature that is related to both global mean warming and the Arctic Oscillation. This conclusion was based on a synthesis limited to just the last 600 yr. Available records that extend beyond the Little Ice Age to previous warm intervals are currently too few to capture modes of variability with adequate certainty. The longer-period evolution of these modes is identifiable in decadally resolved proxy records, and should be preserved in longer records of annual to multi-decadal resolution.This synthesis of annual to inter-decadal climatic variability will extend through the key warm interval of Medieval time. The certainty of the climate reconstruction will be significantly improved by nearly tripling the number of high-resolution, 2000-yr-long, proxy climate records currently available in the Arctic. The project facilitates integration of results by standardizing the methodologies and by holding workshops for vested collaborators and their students. This tightly focused synthetic study of the Arctic system will be integrated directly into a climate-modeling effort to explore the role of volcanism and solar irradiance fluctuations versus internal adjustments of the climate system and its inherent modes of variability to explain observed patterns in the proxy climate data.Across the Arctic, lacustrine archives contain the most accessible and widely distributed proxy records for the past 2000 yr. This work focuses on 30 of the PIs' highest-priority, most-promising lakes, nearly all of which have been cored previously. The network of sites includes two regional foci (Alaska and the NW North Atlantic) that generally encompass the nodes of the surface temperature expression for the Arctic Oscillation, thereby facilitating the reconstruction of this mode of variability. Half of the lakes contain laminated sediment with potential for annually resolved records; others have high sedimentation rates for sample resolution of 5 to 30 yr. The proxy data from most lakes can be compared with nearby tree-ring records or instrumental data, or can be applied to transfer functions to yield quantitative estimates of temperature or other climatic variables. Analyses at low-resolution have already begun on most of the cores as part of on-going research. Preliminary data from these lakes indicate their high potential for climate reconstructions.