HR: 0800h
AN: PP31A-1504    [Abstracts]
TI: Variability of North American Monsoon During the Past 20 Kyr Reflected by δ¹⁸O, δ¹³C, ⁸⁷Sr/⁸⁶Sr and Mg/Sr in Lacustrine Deposits in Salton Basin, California
AU: * Li, H
EM: hli@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AU: * Li, H
EM: hli@usc.edu
AF: Department of Earth Sciences, National Cheng-Kung University, No. 1 University Road, Tainan, 70101 Taiwan
AU: Ku, T
EM: rku@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AU: You, C
EM: cfy20@mail.ncku.edu.tw
AF: Department of Earth Sciences, National Cheng-Kung University, No. 1 University Road, Tainan, 70101 Taiwan
AU: Xu, X
EM: xxu@uci.edu
AF: Department of Earth System Science, University of California, 2103 Croul Hall, Irvine, CA 92697 United States
AU: Wan, N
EM: lnew1214@msn.com
AF: Department of Earth Sciences, National Cheng-Kung University, No. 1 University Road, Tainan, 70101 Taiwan
AB: Located in the arid southeastern California, Salton Basin is occupied by Salton Sea, a closed marine-like lake in the Colorado River drainage system. Shifts in the balance between the Colorado River inflow and evaporative loss resulted in multiple lake cycles in the Salton Basin -- the last cycle was called Lake Cahuilla which disappeared about 400 years ago. Modern precipitation patterns in the basin are controlled by winter Pacific storms and summer storms from the Gulf of Mexico and tropical Pacific. They are thus strongly affected by the summer monsoon strength and by the position and strength of the westerlies. We carried out a systematic study of paleohydrological changes recorded in sediment cores and shoreline tufas from modern and ancient lakes in the Salton Basin in an attempt to understand changes in the North American Monsoon. Below is a summary of the study: (1) Nineteen AMS ¹⁴C dates on modern barnacle shells, fossil gastropod shells, and shoreline tufa deposits indicate that the Salton basin was continuously occupied by a saline closed-basin lake between 1,300 and 20,000 years ago. (2) The lithology, δ¹⁸O and δ¹³C records of Core 64 from Salton Sea indicate: (a) a low but fluctuating lake level before 1905, (b) the formation of Salton Sea during the 1905-1907 flooding, (c) a decline of Salton Sea due to evaporation between 1908 and 1920, and its stabilization since 1920. (3) The ⁸⁷Sr/⁸⁶Sr ratios (0.709944 to 0.710137, n = 15) measured in tufa LC-1 from the shoreline of Lake Cahuilla show that the inflow water into Salton Basin between 1,300 and 20,000 yr BP was from the Colorado River, which has a ⁸⁷Sr/⁸⁶Sr ratio (0.710104) very different from that of the Whitewater River (0.715960). (4) Mg/Sr in carbonate deposits of Lake Cahuilla can be potentially used as a temperature proxy, with higher Mg/Sr ratios reflecting warmer water temperature. However, this proxy may be influenced by the process of tufa growth and lake salinity. (5) High-resolution δ¹⁸O, δ¹³C and Mg/Sr records of tufa LC-1 reveal past changes in the discharge and/or flood frequency of the Colorado River. The strong δ¹⁸O-δ¹³C covariance indicates that Lake Cahuilla was closed (or sometimes slowly overflowed) during the growth of LC-1. Between 1,300 and 20,000 yr BP, climatic shifts such as the last deglaciation, Heinrich-1 event, Trans-US wet period, Younger Dryas, Holocene Optimum, Medieval Warm Period, and variations in monsoon strength appear identifiable in the record. Wet climates in the Salton Basin during the LGM and Younger Dryas may be due to a southward shift of the polar jet stream. The transition from wet early Holocene to dry mid- and late Holocene in the Salton Basin could reflect the weakening of monsoons due to a progressive reduction of summer insolation throughout the Holocene.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1065 Major and trace element geochemistry
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1845 Limnology (0458, 4239, 4942)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005