Climatedriven changes in water level a decadal s

Authors: Rikke Bjerring Jesper Olsen Erik Jeppesen Bjørn Buchardt Jan Heinemeier Suzanne McGowan Peter R Leavitt Renée Enevold Bent V Odgaard

Publish Date: 2012/12/28

Volume: 49, Issue: 2, Pages: 267-285

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Abstract

A twostage change in lake level during the 82ka event was identified in Lake Sarup Denmark 55°N using a multiproxy approach on precise radiocarbon wigglematched annually laminated sediments deposited 8740–8060 cal yr BP Changes in δ13C and δ18O indicated closed lake hydrology driven by precipitation The isotopic sedimentary and plant macrofossil records suggested that the lake level started to decrease around 8400 cal yr BP the decrease accelerating during 8350–8260 before an abrupt increase during 8260–8210 This pattern shows that the climate anomaly started ~150 years before the onset of the 82ka cooling event registered in Greenland ice cores but was synchronous with hydrologic change in the North American Lake Agassiz drainage The lake level decrease was accompanied by a higher accumulation rate of inorganic matter and lower accumulation rates of cladoceran subfossils and algal pigments possibly due to increased turbidity and reduced nutrient input during this drier period Pigment analysis also showed added importance of diatoms and cryptophytes during this climate anomaly while cyanobacteria became more important when the water level rose Moreover Nymphaeaceae trichosclereids were abundant during the period of algal enrichment Cladoceran taxa associated with floating leaved plants or benthic habitats responded in a complex way to changes in water level but the cladoceran assemblages generally reflected deep lake conditions throughout the period The lake did not return to its pre82ka event status during the period of analysis but remained more productive for centuries after the climatic anomaly as judged from the pigment accumulation and assemblage composition The change to more eutrophic conditions may have been triggered by erosion of marginal deposits Together these data confirm the chronology of hydrologic changes and suggest for the first time that lake levels exhibited both a decline and an increase in rapid succession in response to the 82ka event in southern ScandinaviaWe thank the Sarupteam Emily Bradshaw Peer Hansen Peter Rasmussen Kirsten Rosendahl David Ryves Lucia Wick for help with sediment coring and Teresa Buchaca Estany for inspiring discussions on isotopic and pigment aspects Thanks also to Anne Mette Poulsen and Tinna Christensen for manuscript editing and figure layout This project was funded by the research project “Holocene and interglacial varved sediments” Danish Natural Science Research Council 21020532 CLEAR a Villum Kann Rasmussen Centre of Excellence project CRES CIRCE the EUP7 project REFRESH No 244121 NSERC Canada and the International School of Aquatic Sciences SOAS Aarhus University Denmark

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