Timing of deglaciation and postglacial environmental dynamics in NW Iberia: the Sanabria Lake record

72 páginasThe multiproxy study (sedimentology, geochemistry and diatoms) of sediment cores from Sanabria Lake (42°07′30″ N, 06°43′00″ W, 1000 m a.s.l.) together with a robust 14C chronology provides the first high-resolution and continuous sedimentary record in the region, extending back the last 26 ka. The development of a proglacial lake before 26 cal ka BP demonstrates the onset of deglaciation before the global Last Glacial Maximum, similarly to other alpine glaciers in southern European mountains. Rapid deglaciation occurred at the beginning of the Greenland Interstadial GI-1e (Bølling, 14.6 cal ka BP). Following a short-lived episode of glacier re-advance (14.4–14.2 cal ka BP, GI-1d), a climatic improvement at 13.9 cal ka BP suggests the glaciers retreated from the lake basin during the GI-1c. Another glacier reactivation phase occurred between ca 13.0–12.4 ka, starting earlier than the onset of GS-1 (Younger Dryas). Rapid deglaciation during the Early Holocene (11.7–10.1 cal ka BP) was followed by a period of higher river discharge (10.1–8.2 cal ka BP). After 8.2 ka, the Holocene is characterized by a general decreasing trend in humidity, punctuated by the driest phase during the Mid Holocene (ca 6.8–4.8), a wetter interval between 4.8 and 3.3 cal ka BP, and a relatively decline of rainfall since then till present, with a minor increase in humidity during some phases (ca 1670–1760) of the Little Ice Age. Discrete silt layers intercalated in the organic-rich Holocene deposits reflect large flooding events of the Tera River (ca 10.1, 8.4, 7.5, 6.2, 5.7–5.6, 4.6, 4.2, 3.7, 3.3, 3.1, 2.7, 2.5 and 2.0 cal ka BP). Their synchronicity with a number of cold and humid events described in the Atlantic demonstrates a strong control of NW Iberian climate by North Atlantic dynamics at centennial–millennial scale. Comparison with Western Mediterranean records points to similar regional dynamics during the Holocene, although modulated in the NW Iberian Peninsula by the stronger Atlantic influence.Funding for this research has been provided by the Spanish Ministry of Economy and Competitiveness through the CALIBRE CGL2006-13327-C04-01/CLI and CONSOLIDER-GRACCIE CSD2007-00067 projects and by the Fundación Patrimonio Natural Castilla y León. M. Jambrina-Enríquez is supported by a PhD fellowship from Salamanca University (Spain). A. Moreno acknowledges the funding from the “Ramón y Cajal” postdoctoral program. We are grateful to Doug Schnurrenberger, Anders Noren and Mark Shapley (LRC, University of Minnesota) for the 2004 coring expedition.We thank Parque Natural Lago de Sanabria and Laboratorio Limnológico de Sanabria (Junta de Castilla y León) for logistic support. We are also grateful to the detailed criticisms and suggestions by two reviewers that greatly improved the manuscript.Peer reviewe