Thin section from Blue Lake

Blue Lake, July 2006

Brooks Range from Lake Galbrath

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A Synthesis of the last 2000 Years of Climatic Variability from Arctic Lakes

A National Science Foundation funded multi-investigator collaborative research project

Grant #ARC0454941

Project Web Site

www.arcus.org/synthesis2k/

Principal Investigators

Darrell Kaufman (N Arizona U), Glen MacDonald (UCLA), Mark Abbott (Pitt), Raymond Bradley (UMass), Jason Briner (SUNY Buffalo), Donna Francis (UMass), Feng Sheng Hu (U Illinois), Konrad Hughen (Woods Hole), Gifford Miller (U Colorado), Bette Otto-Bliesner (NCAR), Jonathan Overpeck (U Arizona), David Porinchu (Ohio State U), Mike Retelle (Bates College), Al Werner (Mt Holyoke College)

Project Summary

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.

Without this campaign, our understanding of inter-decadal Arctic climatic variability and its causes will remain scattered and inconclusive. A few additional proxy records will emerge as part of ongoing NSF-ESH research, but the goal of synthesizing a coherent reconstruction over the past 2000 yr will remain largely unfulfilled. Recent results of the PARCS High-Resolution Working Group 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.

With this campaign, our 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 will facilitate 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 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 proposal focuses on 30 of the PI’s 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 30 yr or better. 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. This proposal requests funds to cover the cost of high-resolution analysis of multiple proxies and closely spaced 14C and 210Pb dating.

Blue Lake: Brooks Range, Alaska

As part of the 2000-year arctic climate synthesis initiative I am studying Blue Lake, a small glacial-fed lake along the continental divide in the central Brooks Range. The sediments in Blue Lake are annually deposited laminations (varves), whose thickness is positively related to average summer (June-July-August) temperatures from the Atigun Pass weather station (41 km east of Blue Lake). Using down core varve thickness measurements from a network of sediment cores, I have developed an annually-resolved climate record for the central Brooks Range that spans the past 2000 years. The 20^th century is the warmest period in the last 1250 years. The temperature record does not encompass the entire 2000 years because wet conditions in the Brooks Range prior to 730 AD obscured the temperature varve relationship, thus precluding our ability to estimate temperatures during this period. The Little Ice Age (1620-1880 AD) and an event from 980-1030 AD are the coldest episodes in the record with temperature 1.6 and 1.1°C below the 1950-2005 AD average, respectively. Though not as warm as the 20^th century, two warm periods are noted between 1350-500 AD and 1550-1620 AD that were 0.5 and 0.4°C colder, respectively. These trends coincide with changes in the Pacific ocean-atmosphere system as manifested by variations in the strength and position of the Aleutian low, which are inferred from proxy records.