1. INTRODUCTION
The isotopes of hydrogen (H, 2H or D,3H) and oxygen (16O,17O, 18O) are distributed in
different phases by different ratios during the water cycle due to
isotope fractionation (Sun et al., 2020).
Atmospheric precipitation is one
of the most crucial parts of the global water cycle. When the water
vapor condenses, the heavier isotopes (D and 18O)
preferentially enter into the liquid water, resulting in a positive
hydrogen and oxygen isotopic composition (δD and δ18O)
of rainwater at the beginning of the rainfall, and then the δD and
δ18O value of precipitation gradually decreases with
the condensation of D and 18O (Gedzelman et al.,
2001). As climate changes, the δD and δ18O in
atmospheric precipitation also show spatial and temporal variations (Cai
et al., 2018; Ansari et al., 2020). Therefore, the δD and
δ18O of atmospheric precipitation can either be used
as tracers of moisture sources or to invert atmospheric processes
(Lawrence et al., 1982; Lawrence et al., 2004; Liu et al., 2009; Wolf et
al., 2020), which reflect seasonal and synoptic-related climatic
features to some extent (Gedzelman et al., 2001).
Seasonal variations in the isotopic composition of precipitation are
mostly controlled by the regional climate, including the source of
moisture controlled by the monsoon (Cai et al., 2018; Guo et al., 2021),
whereas variations in synoptic scales are mainly influenced by
meteorological factors, including local temperature, humidity, etc. (Xie
et al., 2011; Salamalikis et al.,
2016). In addition, extreme
weather events such as typhoons are also known to have significant
effects on precipitation isotope values (Ohsawa and Yusa, 2000).
Although typhoons have a wide range of effects, their short lifetime and
complex impact processes have led to a lack of understanding of
typhoon-related precipitation isotopic composition compared to normal
precipitation. Previous studies have shown that the
δ18O of typhoon-related precipitation is significantly
depleted than that of other tropical and subtropical summer
precipitation (Lawrence and Gedzelman, 1996; Lawrence et al., 2002),
with the δ18O decreasing gradually from the periphery
of the typhoon toward the center (Gedzelman et al., 2001). The depleted
isotopic composition of typhoon-related precipitation may be attributed
to the high and deep clouds, the large precipitation amount, the high
stratiform precipitation fractions, and the deep convection system
(Lawrence et al., 1998; Fudeyasu et al., 2008; Han et al., 2021). In
addition, the inward decrease of isotopic composition was proposed to be
due to the isotopic exchange between precipitation and lossy water vapor
in the atmospheric boundary layer (Lawrence et al., 1998; Xu et al.,
2019). The isotopes of typhoon-related precipitation are also affected
by the physical processes at different stages of the typhoon, with
significantly higher isotope values in the early and late stages of
precipitation than in the middle stage (Xu et al., 2019). There are both
similarities and differences in the effects of different typhoons on
precipitation isotopes, which may be related to the intensity, lifetime,
and migration route of the typhoons as well as the source of moisture
for typhoon-related precipitation (Gedzelman et al., 2001; Lawrence et
al., 2004; Xu et al., 2019). Therefore, it is important
to explore the differences between
typhoon and normal precipitation processes and their mechanisms, to
further clarify the role of moisture sources in the typhoon
precipitation process, and to analyze the differences in the effects of
various typhoon processes on precipitation isotopes as an important
basis to understand and investigate the isotopic fractionation effects
of typhoon-related precipitation.
The southeastern coast of China is
in the prevalent East Asian monsoon region, and thus the seasonal
variation of precipitation isotopes is significantly controlled by the
monsoon climate. In addition, it has been experiencing a large number of
typhoons every year that have caused risks for the safety of people’s
lives and properties, as well as social and economic impacts on the
region. In recent years, under the influence of global climate change,
the frequency of typhoon events in the western Pacific region has
decreased, whereas their intensity has increased significantly (Zhang et
al., 2015a; Walsh et al., 2019), and thus their destructive power has
intensified too. Because of these enhanced risks, it is even more
essential to further understand the past and present typhoon dynamics
and their evolutionary trends under the effect of persistent global
climate change. Heavy rainfall caused by typhoons is one of the most
dramatic processes that can affect the natural environment, thus the
study of typhoon-related precipitation is helpful to understand the
typhoon meteorological processes (Zhang et al., 2018). Studying the
hydrogen and oxygen isotopes of typhoon-related precipitation can
provide a reference for typhoon meteorological processes, typhoon
geological records, and paleotempestology studies, which is crucial for
quantifying global changes and for assessing natural disaster risks in
typhoon-affected regions.
In this study, we analyzed the δD and δ18O values of
atmospheric precipitation in Xiamen, Southeast China Coast, based on the
measured data of 162 atmospheric precipitation samples (including 35
typhoon-related precipitation samples) collected from June 2018 to
August 2019. The objectives of this study were to investigate the
seasonal variations, synoptic processes, and typhoon impact on isotopic
composition of atmospheric precipitation. We analyzed the influential
factors responsible of the seasonal variation of precipitation isotopic
compositions, explored the differences between typhoon and normal
precipitation processes, and clarified the role of a typhoon on the
isotopic composition of atmospheric precipitation. This study is
important for understanding and investigation of the effects of typhoon
processes on the isotopic fractionation of precipitation.