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Title of Journal: J Paleolimnol

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Abbravation: Journal of Paleolimnology

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Springer Netherlands

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10.1007/bf01834177

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1573-0417

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Increased precipitation during the Little Ice Age in northern Taiwan inferred from diatoms and geochemistry in a sediment core from a subalpine lake

Authors: Liang-Chi Wang, Hermann Behling, Teh-Quei Lee, Hong-Chun Li, Chih-An Huh, Liang-Jian Shiau, Su-Hwa Chen, Jiunn-Tzong Wu,

Publish Date: 2013/01/22
Volume: 49, Issue:4, Pages: 619-631
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Abstract

We studied diatoms in a 55.5-cm-long 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 rain.The Little Ice Age (LIA) was a multi-century 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 required.Diatoms 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 diatom-based transfer functions (Shinneman et al. 2009, 2010).Taiwan 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 high-resolution record of paleoclimate change in the region during the late Holocene. We focused on reconstructing paleoprecipitation in northeastern Taiwan during the last millennium.The 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 period.Lake surface waters are acidic (pH 5.6–6.7) in the dry season and slightly alkaline (pH 7.0–7.5) in the wet season. Bottom waters are acidic year-round (pH 5.8 at depth 4.7 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.


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