A 3000-year varved record of glacier activity and climate change from the proglacial lake Hvítárvatn, Iceland Darren J. Larsen a, b, * , Gifford H. Miller a, b , Áslaug Geirsdóttir b , Thorvaldur Thordarson c a INSTAAR, Department of Geological Sciences, University of Colorado, UCB 450, Boulder, CO 80309, USA b Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavík 101, Iceland c Earth and Planetary Science Group, School of Geosciences, University of Edinburgh, Grant Institute, The Kings Buildings, West Main Rd., Edinburgh EH9 3JW, United Kingdom article info Article history: Received 30 September 2010 Received in revised form 12 May 2011 Accepted 20 May 2011 Available online 6 July 2011 Keywords: Varves Iceland Lake sediment Glacier erosion Soil erosion Holocene paleoclimate Medieval warm period Little ice age abstract 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 Hví- tárvatn 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. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction An important goal of paleoclimate research is to understand the causes and scale of past climate variability, including the associated feedbacks that resulted in distinct system changes on local and regional scales (Jansen et al., 2007). Recently, attempts to synthe- size empirical data, multiproxy records, and computer simulations, have produced global and hemispheric temperature reconstruc- tions placing twentieth century warmth within the context of the last few millennia (Mann and Jones, 2003; Luterbacher et al., 2004; Moberg et al., 2005; Jones et al., 2009; Kaufman et al., 2009). The results from these efforts depict a highly variable late Holocene climate, characterized by nonlinear expressions of change that have been associated with internal modes of variability (i.e. El-Niño and the North Atlantic Oscillation) and external forcing agents, including changes in solar irradiance, aerosol concentrations, and explosive volcanism (Stuiver et al., 1997; Shindell et al., 2001; Ammann et al., 2007; Gao et al., 2008; Jones et al., 2009; Mann et al., 2009; Trouet et al., 2009). Such findings are compatible with increasing evidence for abrupt (Mayewski et al., 2004) and periodic (Denton and Karlén, 1973; Bond et al., 2001; Hodell et al., 2001) climate change occurring throughout the Holocene, illus- trating the dynamic nature of the climate system and the continued need for well-dated, high-resolution paleoclimate records. Iceland is the largest landmass in the central North Atlantic, with a total area above sea level of ca 103,000 km 2 . Paleoceanographic investigations performed around the Iceland shelf describe a vari- able late Holocene, with fluctuating sea-surface and bottom-water temperatures (Jiang et al., 2002, 2005; Bendle and Rosell-Melé, * Corresponding author. INSTAAR, Department of Geological Sciences, University of Colorado, UCB 450, Boulder, CO 80309, USA. Tel.: þ1 303 492 7808. E-mail address: darren.larsen@colorado.edu (D.J. Larsen). Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev 0277-3791/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2011.05.026 Quaternary Science Reviews 30 (2011) 2715e2731