Increased precipitation during the Little Ice Age

Authors: LiangChi Wang Hermann Behling TehQuei Lee HongChun Li ChihAn Huh LiangJian Shiau SuHwa Chen JiunnTzong Wu

Publish Date: 2013/01/22

Volume: 49, Issue: 4, Pages: 619-631

PDF Link

Abstract

We studied diatoms in a 555cmlong sediment core from a subalpine lake in northern Taiwan Tsuifong Lake TFL to investigate environmental changes from AD 490 to present Diatom assemblages of the last century were dominated by acidophilous species whereas alkaliphilous taxa dominated the record between AD 1480 and 1910 Over the studied time frame four decadal periods with high precipitation were inferred from evidence of elevated soil input from the watershed supported by the stable isotope signatures δ15N δ13C of organic matter and magnetic susceptibility of the sediments We compared the inferred changes in pH of TFL to values obtained from three other Taiwanese subalpine lakes The present study revealed that elevated precipitation was associated with increased solar irradiance over the last five centuries with a stable dry period between AD 490 and 1450 Acidification of TFL in the last ~100 years was a consequence of deforestation and acid rainThe Little Ice Age LIA was a multicentury climate anomaly that occurred between the fifteenth and nineteenth centuries and is observed as having been cold and dry in most paleoclimate reconstructions from the Northern Hemisphere Grove 1988 Bradley and Jonest 1993 During that period there was global glacial expansion and enhanced polar atmospheric circulation The conventional view of a dry and cold climate during the LIA however is based largely on data from Western Europe and elsewhere in the North Atlantic region This view has been challenged by findings of increased rainfall during the LIA in southern Norway Nesje and Dahl 2003 Rasmussen et al 2010 northern Patagonia South America Villalba 1994 southwest China Chen et al 2005 southern tropical China Chu et al 2002 and northern Taiwan Chen et al 2009 Wang et al 2011 Such spatial variations in precipitation reflect the regional characteristics of climate such as the East Asia monsoon To improve understanding of the East Asia monsoon and global hydrology during the LIA data from numerous sites are requiredDiatoms are sensitive indicators of changes in aquatic environments and have been used widely for inferring paleoenvironmental characteristics such as past temperature pH salinity and nutrient concentrations Stoermer and Smol 1999 Smol et al 2001 Wu et al 2001 Even extreme events such as floods and earthquakes can be identified using diatoms Nelson et al 1996 Kashima 2003 Atwater et al 2004 Borromei et al 2010 Schütt et al 2010 Wiklund et al 2010 Saegusa et al 2011 Some environmental variables can be estimated quantitatively using diatombased transfer functions Shinneman et al 2009 2010Taiwan is located in a subtropical region close to the boundary between the Pacific Ocean and Eurasia and is strongly affected by monsoonal climate and summer typhoons There are few inferred rainfall records for the Taiwan area that cover the last millennium A few recent studies of lake sediments however provide some basic information on paleoclimate for this area Wu et al 1997 Lin et al 2003 2004 2007 Chen et al 2009 For this investigation we conducted a paleolimnological study of Tsuifong Lake TFL involving analysis of diatoms geochemistry and magnetic susceptibility MS The goal of this study was to obtain a highresolution record of paleoclimate change in the region during the late Holocene We focused on reconstructing paleoprecipitation in northeastern Taiwan during the last millenniumThe smaller NW basin of TFL is a seepage basin Fig 1 Its principal sources of water are direct precipitation and runoff supplemented by groundwater from the small drainage area Mao 2006 The maximum depth of TFL varies with the seasons being ~3 m in the dry season January to April and ~7 m in the wet season July to October The depth may increase to 15 m as a consequence of flooding during typhoon events when summer storms bring heavy rainfall within a short time periodLake surface waters are acidic pH 56–67 in the dry season and slightly alkaline pH 70–75 in the wet season Bottom waters are acidic yearround pH 58 at depth 47 m Mao 2006 Today TFL is oligotrophic to mesotrophic Lin 1996 documented deforestation for timber harvest between AD 1926 and 1982 There is no record of human disturbance in the watershed prior to that period

Keywords: