HR: 1330h
AN: GC12A-0153    [PDF]
TI: Seasonal Variations of Precipitation $\delta^{18}$O in Eastern Asia
AU: * Posmentier, E S
EM: posmentier@liu.edu
AF: Long Island University, Departments of Physics and Mathematics, Brooklyn, NY 11201 United States
AU: Feng, X
EM: xiahong.feng@dartmouth.edu
AF: Dartmouth College, 6105 Fairchild Earth Sciences Department, Hanover, NH 03755 United States
AU: Zhao, M
EM: meixun.zhao@Dartmouth.edu
AF: Dartmouth College, 6105 Fairchild Earth Sciences Department, Hanover, NH 03755 United States
AB: Climate change often occurs through changes in seasonal influences, but paleoclimate records rarely have intra-annual resolution. The precipitation $\delta^{18}$O, either directly measured or indirectly inferred from other datable materials, is one of the most widely used proxies for paleoclimate studies. It is important, therefore, that we understand the seasonal distribution of meteoric $\delta^{18}$O in relation to climate dynamics. In most land areas, the precipitation $\delta^{18}$O is higher in the summer and lower in the winter. However, this isotopic seasonality is reversed in the coastal regions of East Asia, while moving further inland it becomes normal. The mechanisms causing this spatial distribution of the isotopic seasonality in East Asia have not been discussed. We have identified nine overlapping mechanisms responsible for isotopic seasonality, either normal or reversed. These mechanisms include, 1) temperature, 2) vertical atmospheric stability, 3) time span of moisture transport from coast to inland, 4) amount effect, 5) seasonal migration of the Intertropical Convergence, 6) seasonal migration of the Polar Front, 7) marine {\it versus} terrestrial evaporation ratio, 8) condensation to liquid {\it versus} ice and 9) seasonal difference in relative humidity. Using a simple $\delta^{18}$O model we show that the most important mechanism for the observed isotopic pattern in Asia may be the interseasonal variations in vertical atmospheric stability. The stability of air above land in the winter is greater relative to that above the ocean, and the opposite occurs in the summer. These variations are reflected in interseasonal variations of the horizontal and vertical advection of moisture by the large-scale Walker circulation, and of small-scale mixing by diffusion. Our results indicate that the complex causes of interseasonal, interannual, and interepochal variations of meteoric $\delta^{18}$O require considerable caution in the attribution of records of past $\delta^{18}$O variations to changes in specific climate variables.
DE: 1040 Isotopic composition/chemistry
DE: 1600 GLOBAL CHANGE (New category)
DE: 1620 Climate dynamics (3309)
DE: 1655 Water cycles (1836)
DE: 3319 General circulation
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting