Dr Darrell Kaufman

My group studies sediment cores from high-latitude lakes to reconstruct Holocene climate changes. We focus on physical and biological proxies of hydroclimate and temperature variability, including sedimentary (varve) properties, oxygen isotopes, and biogenic silica content. As part of our multi-proxy approach to understanding past climate changes, we combine the lake core data with geomorphic evidence for Holocene glacier fluctuations within the lake’s catchment. All of our lake cores from Alaska contain tephras, which provide key timelines for high-precision chronostratigraphy. I am currently leading two NSF projects: (1) Nonlinearities in the Arctic climate system during the Holocene--ARCSS 8 ka project This study focuses on the transition between the Holocene thermal maximum (HTM) and the onset of Neoglaciation, and on the step-like changes that occurred subsequently during the late Holocene. To understand how feedbacks and perturbations result in rapid changes, a geographically distributed network of proxy climate records is proposed to study the spatial and temporal patterns of change, and to quantify the magnitude of change during these transitions. The 12 PIs of this collaborative project will use lacustrine sediments to produce 13 new high-resolution proxy climate records of the past 8000 years. The proxy records generated in this project will use conventional and newly emerging techniques to document the spatio-temporal patterns of abrupt environmental changes, and to derive quantitative estimates of past summer temperature and hydroclimate variables. This project builds on on-going climate-modeling experiments that use NCAR’s Climate System Model (CCSM3) to study the sensitivities of the Arctic system to volcanism and solar variability. A new data-model comparison proposed for this study will test whether the most prominent changes in the Arctic system during the past 8 ka, as reconstructed from the proxy records, can be explained by a plausible combination of system-component conditions coincident with prolonged volcanism. (2) Coupled glacial and lacustrine evidence for decadal- to millennial-scale variability in the climatologic Aleutian Low, southern Alaska The overall goal of this project is to reconstruct the low-frequency behavior of the climatological Aleutian Low on decadal to millennial time scales, and to assess how its variability has related to past shifts in the mean state of climate during the Holocene. This project will continue on-going monitoring and lake-core-based investigations at nine lakes in southern Alaska with the dual aims of (1) understanding the primary controls on the sedimentary changes, and (2) applying this understanding to generate the highest quality time series of paleoclimate proxies that relate quantitatively to summer temperature and winter precipitation. The basic study design is to pair a glacial-fed lake (lamination record) with an organic-rich lake (chironomid record) in each of three study areas separated by 2100 km: Adak (middle Aleutian Islands) in the far west, Ahklun Mountains in the southwest, and Chugach Range in the Gulf of Alaska.