A suite of environmental proxies in annually laminated sediments from Hvítárvatn, a proglacial lake in the central highlands of Iceland, are used to reconstruct regional climate variability and glacial activity for the past 3000 years. Sedimentological analysis is supported by tephrostratigraphy to confirm the continuous, annual nature of the laminae, and a master varve chronology places proxies from multiple lake cores in a secure geochronology. Varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent Langjökull ice cap. The continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record. Varve thickness, varve thickness variance, ice-rafted debris, total organic carbon (mass flux and bulk concentration), and C:N of sedimentary organic matter, reveal a dynamic late Holocene climate with abrupt and large-scale changes in ice-cap size and landscape stability. A first-order trend toward cooler summers and ice-cap expansion is punctuated by notable periods of rapid ice cap growth and/or landscape instability at ca 1000 BC, 600 BC, 550 AD and 1250 AD. The largest perturbation began ca 1250 AD, signaling the onset of the Little Ice Age and the termination of three centuries of relative warmth during Medieval times. Consistent deposition of ice-rafted debris in Hvítárvatn is restricted to the last 250 years, demonstrating that Langjökull only advanced into Hvítárvatn during the coldest centuries of the Little Ice Age, beginning in the mid eighteenth century. This advance represents the glacial maximum for at least the last 3 ka, and likely since regional deglaciation 10 ka. The multi-centennial response of biological proxies to the Hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments, and catchment sensitivity to perturbations.
Bibliographical noteFunding Information:
The Hvítárvatn sediment cores were recovered in 2003 using the DOSECC GLAD 200 coring rig with the financial support of the US National Science Foundation ( OPP-0138010 ) and the Icelandic Centre of Research, RANNIS (# 040233021 ). Core analyses were supported by the VAST (Volcanism in the Arctic System) Project, through NSF-OPP- ARC 0714074 and RANNIS # 0070272011 , We would like to sincerely thank Thorsteinn Jónsson, Sveinbjörn Steinthórsson, and Doug Schnurrenberger for their tireless and skillful work in the field. Thanks also to the great folks at the LRC, University of Minnesota, Caroline Alden, Anna Jagan, Clayton Roehner, Chris Florian, Benjamin Schupack, and Kate Zalzal for laboratory and field assistance. Anna Wagner and Kristbjörg María Guðmundsdóttir are acknowledged for their work in confirming the annual nature of the laminae. Grain size analysis was performed by Anna Wagner as part of a B.A. thesis at the University of Colorado. The cores were sampled for thin sections by Jessica Black at the LRC and thin sections were prepared by Paul Boni at the University of Colorado. TOC and TN were analyzed at the University of California at Davis Stable Isotope Facility. We would like to acknowledge Jessica Black for assistance during early stages of the research project, and thank Helgi Björnsson and Gwenn Flowers for valuable discussions. We thank P. Francus and an anonymous reviewer for strengthening the manuscript.
Copyright 2011 Elsevier B.V., All rights reserved.
- Glacier erosion
- Holocene paleoclimate
- Lake sediment
- Little ice age
- Medieval warm period
- Soil erosion
Continental Scientific Drilling Facility tags