Climatic variability during the last interglacial inferred from geochemical proxies in the Lake El'gygytgyn sediment record
Introduction
Rapid warming observed within the latter part of the 20th century raised many questions regarding the rate at which global climate can change (Kelts, 1992). In answer to this, palaeoclimatic data from a variety of proxies have demonstrated multiple, rapid shifts from full glacial conditions to milder interglacial conditions (e.g. Petit et al., 1999). For example, the isotopic composition of ice-cores from Greenland suggests a 10 °C increase in temperature occurred within a decade (Alley, 2000, Steffensen et al., 2008). Furthermore, episodes of abrupt climatic change occur repeatedly within the past 100 thousand years (kyr), as evidenced by both terrestrial and marine palaeoclimate records (Dansgaard et al., 1993, Genty et al., 2003). Since polar regions have been glaciated for most of this time, it is often argued that large, abrupt changes in climate could not occur without high volumes of ice present in the northern and southern hemispheres (Denton, 2000). Abrupt, large scale, climatic changes have been reported during the Holocene (the present interglacial period) from many different geographical regions (Rohling et al., 2002, Moros et al., 2004), however, there is still limited evidence for abrupt climate changes during the Last Interglacial Period (LIP) when ice volumes were even lower than today (Chapman and Shackleton, 1999, Karabanov et al., 2000).
The higher number of palaeoclimate records available for the LIP, relative to earlier interglacials, means that the LIP is often used as an analogue for the Holocene and to infer potential impacts of continued global warming under reduced ice conditions (Rioual et al., 2001, McManus et al., 2002, Tzedakis, 2003). These research efforts have, however, increased uncertainty as to the temporal and spatial extent of climatic changes during this period, partly due to contradictory results produced by different proxy records. To help address this issue, and to understand the rate, extent, and mechanisms of climate change, several palaeoclimate records covering the last glacial–interglacial cycle have been generated, with the highest density of records for the North Atlantic and adjacent continental regions (e.g., Tzedakis et al., 2003, Martrat et al., 2004, Oppo et al., 2006, Brauer et al., 2007). Within the Arctic, recent low-resolution records indicate a significant climatic shift during the LIP (e.g. Chapligin et al., 2012, Snyder et al., 2012). Despite this, high-resolution records extending beyond the last interglacial are extremely scarce from the Arctic. To study the rate and extent of climate change, as well as the role of complex feedback mechanisms as contributors to past climate change (Holland and Bitz, 2003, Serreze and Francis, 2006), it is essential to investigate long and continuous palaeoclimate records from this key region of global climate change, in high resolution.
El'gygytgyn Crater Lake hosts the longest terrestrial record of climate change from the Arctic (Brigham-Grette et al., 2007) with a continuous sediment record spanning the last 3.6 Ma (Melles et al., 2012). Variations in the composition of these sediments reflect climate-induced changes in the catchment and water column of Lake El'gygytgyn (Nowaczyk et al., 2002, Nowaczyk et al., 2007, Asikainen et al., 2007, Lozhkin et al., 2007, Melles et al., 2007, Melles et al., 2012, Minyuk et al., 2007). Geochemical proxies such as biogenic silica (BSi), total organic carbon (TOC), magnetic susceptibility (MS) and the elemental ratios of silica to titanium (Si/Ti) and iron to manganese (Mn/Fe) can provide valuable information about past climatic and environmental conditions at this site (Melles et al., 2012, Cunningham et al., 2013). For example, BSi reflects the productivity of silica producing organisms, which are predominantly diatoms in Lake El'gygytgyn (Cremer and Wagner, 2003, Cherapanova et al., 2007). At this location, the productivity of diatom communities is strongly affected by climate. Warmer climates lead to reduced ice and snow cover both on the lake and within the catchment, thus increasing light availability and nutrient supply, respectively and thus stimulating productivity (Melles et al., 2012, Cunningham et al., 2013). Thus diatoms are not responding solely to increased air temperatures or precipitation, but also to environmental changes driven by these climatic variables. The same is true of the geochemical proxies incorporated within this study thus the inclusion of multiple proxies enables a more complete interpretation. The selected geochemical parameters are ideal for high resolution studies as they can be rapidly and cost-effectively quantified using methods such as FTIRS or XRF core-scanning. Consequently a high-resolution study was undertaken using these geochemical proxies to assess both the amplitude and rapidity of climatic changes during the LIP and thus contribute to our understanding of climate change during interglacial periods.
Section snippets
Site description
Lake El'gygytgyn (67°30′N, 172°05′E) is situated in a 3.6 Ma old, 18 km wide meteorite impact crater located in the Far East Russian Arctic (Fig. 1). The 12 km wide lake is bowl shaped with steep slopes, a flat and extensive bottom, and a maximum water depth of 170 m (Melles et al., 2012). Lake El'gygytgyn is a monomicitic, oligotrophic lake (Nolan and Brigham-Grette, 2007), with a water residence time of ~ 100 years (Fedorov et al., 2012).
The region surrounding Lake El'gygytgyn has a cold Arctic
Methods
In May 2003 a 16.6 m composite core (Lz1024) was recovered from the central part of Lake El'gygytgyn, where a seismic survey indicated horizontal bedding and parallel reflectors (Niessen et al., 2007). The surface sediments and deeper sediments of core Lz1024 were collected using a 0.6 m gravity corer and a 3 m long percussion piston corer, respectively (both UWITEC Co.). Prior to subsampling, the cores were split lengthwise into halves. One of the core halves was used for high-resolution X-ray
The proxy records
Distinct changes are observed in the proxy records during the LIP (Fig. 2). The MSSI data shows the most abrupt changes, possibly indicating thresholds within the oxygenation state of the lake (i.e. sudden changes from anoxic to oxic). For example, a change from a permanently ice covered lake to seasonally open lake could result from a gradual warming; however, the disruption of stratified layers might be expressed more abruptly. The Mn/Fecps shows a relatively similar profile as the MSSI,
Conclusions
The climatic reconstruction presented here shows a good general agreement with palaeoclimate reconstructions from Lake Baikal, although there is some suggestion that climatic changes may have occurred slightly earlier at Lake El'gygytgyn. This paper demonstrates the occurrence of several important climatic features within the Arctic immediately prior to, during, and after the LIP including:
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a ‘Younger Dryas’ like cold reversal during Termination II;
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high frequency climatic variability during the
Acknowledgements
The authors would like to thank the participants on the spring campaign of the Lake El'gygytgyn expedition 2003 for the recovery of the sediment core Lz1024 used in this study. They also gratefully acknowledge the expertise and leadership provided by Martin Melles and Julie Brigham-Grette, without which this project wouldn't have been possible. We would also like to thank Annika Holmgren, Jan Åberg, Carin Olofsson and Thomas Westin for laboratory assistance. Funding was provided by the German
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