Evidence for Holocene Event 3 and Little Ice Age in Taiwan: Constraints from Sediment Magnetic and Geochemical Paramete

1. PAGES-2ND-GMS-SHANGHAI Evidence for Holocene Event 3 and Little Ice Age in Taiwan: Constraints from Sediment Magnetic and Geochemical Parameters 13-15.09.2010 1. INTRODUCTION Previous studies have indicated the late Holocene (4000 14C or 4500 cal yr BP to the present) as a period of relatively dry climate (deMenocal, 2001, Science 292, 667-673; Weiss and Bradley, 2001, Science 291, 609-610), with three prominent climatic events: a (millennial-scale) long dry 4000 yr BP Event (Perry and Hsu, 2000, PNAS 97, 12433-12438) and two short but contrasting centennial-scale events, i.e. Little Ice Age (LIA) and Medieval Warm Period (MWP) (Keigwin, 1996, Science 274, 1504-1508). Importantly, the former event has been inferred as a root cause for widespread environmental modification and population redistribution in Asia and Africa. However, evidence for the presence of these events is scarce in the paleoclimate records of Taiwan where the East Asian monsoon (EAM; Fig. 1) and associated typhoon activity strongly influence the climate, forested mountain ecosystem and the society. This study presents the magnetic and geochemical parameters in a 168 cm long sediment core recovered from Emerald Peak Lake, the largest subalpine lake in Taiwan (Fig. 2) and provides evidences for monsoon and environmental changes during the last ca. 3750 cal yr BP, including the Holocene Event 3 and LIA. Kandasamy Selvaraj1, Shuh-Ji Kao1, Shih-Chieh Hsu1, Teh-Quei Lee2, Kuo-Yen Wei3, Kon-Kee Liu4 (ksraj@gate.sinica.edu.tw) 1Research Center for Environmental Changes and 2Institute of Earth Sciences, Academia Sinica, Taipei 115, Taiwan; 3Department of Geosciences, National Taiwan University, Taipei 106, Taiwan; 4Institute of Hydrological Sciences, National Central University, Jhongli 320, Taiwan 2. STUDY AREA 3. CHRONOLOGY Core location Fig. 1. The monsoon system in East Asia. Fig. 3. Core collection. Fig. 2. Emerald Peak Lake. Fig. 4. Age-depth model. 4. RESULTS Fig. 6. The relationship between N:C ratio and δ13C in sediments and other source materials depicting C3 vegetation and rock/soil-sourced organic carbon to Emerald Peak Lake. Fig. 5. LIA and Holocene Event 3 depicted from high-resolution (1 cm interval) magnetic parameters. 5. INTERPRETATIONS 6. CONCLUSIONS 1. Low MS value and S-ratio but high ARM/MS ratio with low C/N ratio, enriched δ13C and high δ15N in coarse-grained sediments between 3750 and 2050 cal yr BP, suggesting a low water level and influx of materials from the exposed lake shore likely due to a weak monsoon. 2. A prominent decrease of MS value and S-ratio but an increase of magnetic grain size between ~1300 AD and 1700 AD, attributed to increased hematite, providing an evidence for LIA in Taiwan. This is consistent with reduced solar activity observed between 13th and 18th century. Fig. 7. Down-core variations of size-fractionated TOC, TN, δ13C and δ15N. 3. The comparison of our proxy records with other land and marine records from China and adjoining marine realm suggests that the East Asian monsoon in NE Taiwan during the late Holocene was largely modulated by tropical Pacific forcing. Fig. 8. The proxy records of Emerald Peak Lake combined with the NH insolation, δ18O of Dongge Cave stalagmite, foraminifera % in marine sediment core from the Okinawa Trough and faunally-reconstructed SSTs from the WTP. ACKNOWLEDGEMENTS: This work was funded by the National Science Council (No.: NSC97-2628-M-001-025) of Taiwan.