Compositions of hydrogen and oxygen isotopes of precipitation in Xiamen,
Southeast China Coast: Seasonal variations, synoptic processes, and
typhoons impact
Abstract
In this study, the δD and δ18O values of 162 precipitation samples
(including 33 typhoon-related precipitation samples), collected in
Xiamen, Southeast China coast, during June 2018 to August 2019, were
investigated and analyzed. The results show that there are obvious
seasonal variations in the δD and δ18O, which are mainly controlled by
the East Asia Monsoon with significant influence of typhoon events in
summer. The influence of moisture sources on δ18O values overrides the
influence of precipitation fractionation process on δ18O values which
leads to an inverse temperature effect in the study area. In comparison
to the seasonal scale, the synoptic time-series variation of δD and δ18O
is much more complicated. In general, there are three types of isotopic
variations in the normal precipitation processes, which are obviously
affected by re-evaporation processes and continuing equilibrium
fractionation during condensation. The local meteorological parameters
during normal precipitation, which mainly control the re-evaporation
process, are the dominant factors for the variation patterns of δD and
δ18O, whereas moisture sources control the overall isotope values of
precipitation. The differences between the time-series of normal and
typhoon-related precipitation are mainly controlled by the changes of
physical processes and meteorologic parameters during the precipitation
process. However, due to the unique atmospheric structure and dynamic
processes of typhoons, the δD and δ18O of typhoon-related precipitation
changes in stages gradually as the distance between the typhoon’s center
and the study area changes. The uniformity of typhoon structure leads to
a similar staged changes in different typhoon-related precipitation. The
moisture source trajectory of typhoon-related precipitation shows a
clear spiral structure (except for typhoon Yutu), and the moisture
sources at different heights control the δD and δ18O values of
typhoon-related precipitation. This study is important for quantifying
the global changes of typhoon processes and paleotempestology studies.