4.3 Implication of typhoon precipitation isotopic composition
for paleoclimate and paleotempestology records
The paleoclimate proxies, such as
δ18O values of stalagmites and δD values of selected
plant-derived organic compounds (e.g., leaf wax) in lacustrine sediments
are often related to the δ18O or δD of local
precipitation during formation, and thus can be used to indicate
precipitation conditions in historical periods. The
δ18O value of stalagmite is mainly controlled by
drop-water and temperature in the cave, and also influenced by physical
processes such as evaporation and infiltration related to the
δ18O value of precipitation (Lachniet, 2009). Whereas
δD of leaf wax in sediments and δD and δ18O values of
tree ring cellulose are significantly controlled by ambient environment
water (e.g., precipitation and atmospheric moisture) during plant
growth, recording important information about regional precipitation
(Hou et al., 2008; McCarroll and Loader, 2004). Therefore, linking these
proxies to the δD and δ18O values of precipitation
during the atmospheric water cycle helps us to further reconstruct the
paleoclimatic conditions.
To date, a number of successful studies have been carried out to
reconstruct the evolution of the ancient monsoon in the corresponding
regions from paleoclimate proxies, such as the reconstruction of the
East Asian Summer Monsoon in a varied time scales using the
δ18O values of stalagmites (Zhang et al., 2013; Yang
et al., 2020). However, there is still a paucity of studies that use
these paleoclimate proxies to reconstruct extreme weather events (e.g.,
typhoons) from historical periods which is known as paleotempestology.
Studying the δD, δ18O of precipitation during typhoons
can provide a good scientific reference for paleotempestology
reconstruction of typhoon activity. The results of this study show that
the δD and δ18O values of typhoon-related
precipitation are significantly lower than those of normal precipitation
in the same period, which may associate with more negative
δ18O in speleothem and tree ring and more negative δD
in plant-derived compounds, indicating larger precipitation amount,
lower temperature, or most importantly, larger proportion of the
moisture being transported from tropical seas. At the same time, there
are significant decrease in temperature, water vapor pressure, and
atmospheric humidity and increases in precipitation amount in the study
area (Fig. 2), and these meteorological factors control the
δ18O of tree rings during tree growth period (from May
to September, consistent with the main period of typhoon occurrence)
(Anderson et al., 2002) and δD values of leaf waxes (Hou et al., 2008).
Thus, by using the δD and δ18O values in the
paleoclimate proxy we can reconstruct the precipitation events
(including typhoon-related precipitation), and then roughly invert the
frequency of typhoon events in the historical period. Unfortunately, the
stage changes of typhoon precipitation may be difficult to be recorded
in these paleoclimate proxies due to their small-time scales, leading to
great difficulties in the study of paleo-typhoon meteorological
processes. In addition, the intensity and migration route of typhoons
may have a significant effect on the D-excess values of precipitation
(Table 2). Therefore, it may be worthwhile to consider and further
investigate whether the D-excess values of paleoclimate proxies can be
used to reconstruct the intensity and approximate route of typhoons in
historical period.