Two high-sediment-accumulation-rate Icelandic lakes, the glacial lake Hvítárvatn and the non-glacial lake Haukadalsvatn, contain numerous tephra layers of known age, which together with high-resolution paleomagnetic secular variations allow synchronization with a well-dated marine core from the shelf north of Iceland. A composite standardized climate record from the two lakes provides a single time series that efficiently integrates multi-proxy data that reflect the evolution of summer temperatures through the Holocene. The first-order trends in biogenic silica (BSi), δ13C, and C:N rise relatively abruptly following deglaciation, reaching maximum values shortly after 8ka following a complex minimum between 8.7 and 8.0ka. The Holocene Thermal Maximum (HTM) in the lakes is marked by all proxies, with a sharp transition out of the 8ka cold event into peak summer warmth by 7.9ka, and continuing warm with some fluctuations until 5.5ka. Decreasing summer insolation after the HTM is reflected by incremental cooling, initially ~5.5ka, with subsequent cold perturbations recorded by all proxies 4.3 to 4.0ka and 3.1 to 2.8ka. The strongest disturbance occurred after 2ka with initial summer cooling occurring between 1.4 and 1.0ka, followed by a more severe drop in summer temperatures after 0.7ka culminating between 0.5 and 0.2ka. Following each late Holocene cold departure, BSi re-equilibrated at a lower value independent of the sediment accumulation rate. Some of the abrupt shifts may be related to Icelandic volcanism influencing catchment stability, but the lack of a full recovery to pre-existing values after the perturbation suggests increased periglacial activity, decreased vegetation cover, and glacier growth in the highlands of Iceland. The similarity in timing, direction and magnitude of our multi-proxy records from glacial and non-glacial lakes, and from the adjacent marine shelf, suggests that our composite record reflects large-scale shifts in ocean/atmosphere circulation throughout the northern North Atlantic.
Bibliographical noteFunding Information:
Our lacustrine sediment cores were obtained using the DOSECC GLAD-200 coring system with financial support from the US National Science Foundation ( OPP-0138010 ) and the Icelandic Centre of Research, RANNIS ( #040233021 ). Additional support was provided by the VAST (Volcanism in the Arctic System) Project, through NSF-ARC 0714074 and RANNIS #0070272011 and RANNIS project grant #100233021 . Thanks to DOSECC personnel, Thorsteinn Jónsson, Sveinbjörn Steinthórsson, and Doug Schnurrenberger for their assistance in the field, and to the people at the LRC, University of Minnesota and the Hu Laboratory at University of Illinois at Urbana-Champaign, for laboratory assistance and analyses. We thank Thor Thordarson for valuable discussions on the tephra chronology on both HAK and HVT, and Joe Stoner and Jim Channel for their input on the PSV measurements. Two anonymous reviewers are thanked for their critiques and suggestions that helped clarifying some issues in this manuscript.
Copyright 2013 Elsevier B.V., All rights reserved.
- 8.2 Event
- Abrupt climate transitions
- Holocene paleoclimate
- Holocene Thermal Maximum
- Lake sediment
- Little Ice Age
- Medieval warm period
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