A 3000-year varve-thickness record from Hvítárvatn, a glacier-dominated lake in central Iceland, preserves inter-annual variations in the delivery of glacially eroded sediment to the lake. The first-order low-frequency trend in varve thickness reflects increased glacial erosion through the Late Holocene, reaching a peak during the Little Ice Age (LIA). Superimposed on this trend are large inter-annual to decadal fluctuations in varve thickness that we suggest reflect variability in climate parameters that determine the efficiency of the fluvial transport system to deliver glacially eroded sediment to the lake each year. We use spectral analysis to test whether regular high-frequency cyclicity in varve thickness exists in the 3-ka record after removing the low-frequency variability. Spectral analyses from three sediment cores recovered from the lake show essentially the same periods of 2.8-3.4, 13, 35-40 and 85-93, for the overlapping ~900-year period. Additionally, cycles of 55, 130 and 290 years are found in the spectrum for the 3000-year record that do not show up in the spectra for the shorter cores. Some of these cycles show similar variability to those of the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO). This relationship is supported by a significant correlation between varve thickness and both the NAO (precipitation) and AMO (summer temperature) indices over the 180-year instrumental period. NAO cyclicities (2-15 years) are weakly expressed in the first half of the record, increase between 600 and 1000 AD, decrease in strength during medieval time, and are most strongly expressed between 1300 AD and the early 20th century. AMO cyclicities (50 to 130 years) are also relatively weak in the first half of the record, becoming quite strong between 600 and 1000 AD and again between 1100 and 1500 AD, but are essentially absent through the peak of the LIA, between 1500 and 1900 AD, a time when strong cyclicities of about 35 years appear.
Bibliographical noteFunding Information:
Financial support for this project was received from the Research Fund of the University of Iceland to Áslaug Geirsdóttir, the Environmental and Energy Research Fund from the Reykjavik Energy, the Icelandic Centre for Research – RANNÍS (Áslaug Geirsdóttir contract nr # 0070272011 ) in addition to a one year M.Sc. Grant to Ólafsdóttir from the Icelandic Research Fund for Graduate Students . Funding for the recovery of the sediment cores from Hvítárvatn was provided by the Icelandic Centre for Research – RANNÍS (Geirsdóttir) and the US National Science Foundation (ATM 0318479;Miller). We thank Trausti Jónsson at the Icelandic Meteorological Office, for contributing the extended temperature and precipitation records from Stykkishólmur. We are grateful for constructive comments from Maxime Debret and two anonymous reviewers.
Copyright 2013 Elsevier B.V., All rights reserved.
- Atlantic Multidecadal Oscillation
- Little Ice Age
- North Atlantic Oscillation
- Spectral Analysis