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VARIABILITY IN SUMMER ARCTIC TEMPERATURE AND ARCTIC OSCILLATION OVER THE PAST 600 YEARS.
HUGHEN, KONRAD WHOI.
Huybers, Peter MIT.
High Resolution Working Group, PARCS www.ncdc.noaa.gov/paleo/parcs.
Spatial arrays of high-resolution (annual-decadal) paleoclimate records from throughout the Arctic were used to distinguish different modes of variability and trace their behavior back in time. A previous compilation of primarily annual-resolution records provided a view of average Arctic summer temperature during the past 400 years, documenting dramatic 20th-century warming that ended the Little Ice Age in the Arctic and caused dramatic retreats of glaciers, melting of permafrost and sea-ice, and alteration of terrestrial ecosystems. Some evidence suggests that these recent changes may be linked to an increasing positive phase of the Arctic Oscillation (AO), and that this trend in the AO itself may theoretically be due to greenhouse warming. Multi-century records of temperature and AO behavior are needed to identify natural background variability and evaluate potential linkages. A new international collaboration has created a spatial array of high-resolution Arctic paleotemperature records for the past ~600 years. Annually resolved archives were used wherever possible (e.g., tree rings, varved lake sediments, and annual ice layers), but sub-decadal resolution records from ice cores and high deposition-rate lake and marine sediments were included as well. Empirical Orthogonal Function (EOF) analysis was used to characterize the spatial and temporal modes of variability contained in the proxy array. The three leading modes of proxy variability all have highly significant correlations to the three leading modes identified in NCEP-NCAR reanalysis data, and are associated with dynamically significant processes, including: 1) a circum-Arctic average temperature trend with rapid 20th-century warming; 2) the Arctic Oscillation; and 3) a Urals Trough wave number three circulation pattern. Our analyses demonstrate the ability to identify the major modern observed modes of Arctic SAT variability within an array of proxy data, and reconstruct these modes back in time. These results provide insight into the long-term natural background variability of the AO and its relation to average Arctic temperature, and place their recent positve co-variation into a pre-anthropogenic context.
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