Droughts are recurrent features in sedimentary records at the prairie-forest ecotone of northern U.S.A. It is therefore important to understand the duration of such events, as well as their severity and consequences beyond the century-scale instrumental record. The existing drought records can be complemented with additional proxies that clearly document the interactions between external factors and the depositional environment. Here we attempt to reconstruct the last millennium drought history of Deming Lake, a small lake at Minnesota's prairie-forest ecotone, using sediment magnetism. In particular, this approach allowed us to explore the interactions between lake and catchment, and test the hypothesis that periods of moderate aridity result in decreased hydrologic sediment transport from the catchment to the lake, as a consequence of reduced erosion and overland flow. Concordantly, during dry episodes we find that the mass fractions of in-lake produced organic matter and biogenic magnetic particles increase relative to allochthonous component fractions. We identify several episodes of aridity at Deming Lake consistent with existing regional drought reconstructions. The most prolonged dry event occurred at the end of the Little Ice Age, suggesting that the second half of this cold interval was drier in the region than previously thought.
Bibliographical noteFunding Information:
We thank Kristina Brady and Colin Plank for help with fieldwork, Rachel Murray for preparing the piston core samples and performing some of the measurements, Vania Stefanova for palynological assistance with selecting the samples for radiocarbon dating, Dan Engstrom for analytical assistance with 210 Pb dating, and Bjoern Wissel for the carbon analyses. We thank the Minnesota Department of Natural Resources and the Itasca Biological Station for granting us permission to do research in Itasca State Park. Thoughtful reviews from Christoph Geiss and two anonymous referees greatly helped us improve the manuscript. IL benefited from the support of a University of Minnesota Doctoral Dissertation Fellowship. KKM was supported by NSF grant BCS-0955225 . The Institute for Rock Magnetism and LacCore greatly acknowledge the support of the Instruments and Facilities Program, Earth Sciences Division, National Science Foundation . This is IRM contribution 1104 and LRC contribution 12-01.
Copyright 2012 Elsevier B.V., All rights reserved.
- Biogenic magnetite
- Little ice age
- Prairie-forest ecotone
- Sediment magnetism