• Persistent millennial-scale climate variability in Southern Europe during Marine Isotope Stage 6

      Exploring the mode and tempo of millennial-scale climate variability under evolving boundary conditions can provide insights into tipping points in different parts of the Earth system, and can facilitate a more detailed understanding of climate teleconnections and phase relationships between different Earth system components. Here we use fossil diatom and stable carbon and oxygen isotope analysis of lake sediment deposits (core I-284) from the Ioannina basin, NW Greece, to explore in further detail millennial-scale climate instability in southern Europe during Marine Isotope Stage 6 (MIS 6; ca. 185‒130 ka). This interval correlates with the Vlasian Stage in Greece and the Late Saalian Substage in northern Europe, which were both characterised by extensive glaciations. The new dataset resolves at least 18 discrete warmer / wetter intervals, many of which were associated with strong Asian Monsoon events and North Atlantic interstadials. A number of cooler / drier intervals are also identified in the I-284 record, which are typically associated with weaker Asian Monsoon events and North Atlantic stadials, consistent with a variable Atlantic Meridional Overturning Circulation. Unlike the subdued changes in tree populations that are observed at Ioannina during mid-to-late MIS 6, the diatom record contains frequent high-amplitude oscillations in species assemblages, pointing to its sensitivity at a time when the lake system must have been close to environmental thresholds. Millennial-scale variability in diatom species assemblages continues into late MIS 6 at Ioannina, contributing important evidence for an emerging picture of frequent and persistent climate instability even at times of high global ice volume.
    • Reconciling diverse lacustrine and terrestrial system response to penultimate deglacial warming in southern Europe

      Wilson, Graham P.; Reed, Jane M.; Frogley, Michael R.; Hughes, Philip D.; Tzedakis, Polychronis C.; University of Chester, University of Hull, University of Sussex, University of Manchester, University College London (The Geological Society of America, 2015-09-01)
      Unlike the most recent deglaciation, the regional expression of climate changes during the penultimate deglaciation remains understudied, even though it led into a period of excess warmth with estimates of global average temperature 1‒2 °C, and sea level ~6 m, above preindustrial values. We present the first complete high-resolution southern European diatom record capturing the penultimate glacial-interglacial transition, from Lake Ioannina (northwest Greece). It forms part of a suite of proxies selected to assess the character and phase relationships of terrestrial and aquatic ecosystem response to rapid climate warming, and to resolve apparent conflicts in proxy evidence for regional paleohydrology. The diatom data suggest a complex penultimate deglaciation driven primarily by multiple oscillations in lake level, and provide firm evidence for the regional influence of abrupt changes in North Atlantic conditions. There is diachroneity in lake and terrestrial ecosystem response to warming at the onset of the last interglacial, with an abrupt increase in lake level occurring ~2.7 k.y. prior to sustained forest expansion with peak precipitation. We identify the potentially important role of direct input of snow melt and glacial meltwater transfer to the subterranean karst system in response to warming, which would cause rising regional groundwater levels. This explanation, and the greater sensitivity of diatoms to subtle changes in temperature, reconciles the divergent lacustrine and terrestrial proxy evidence and highlights the sensitivity of lakes situated in mountainous karstic environments to past climate warming.