Progress in studying the modal transition of the Holocene precipitation season

The reconstruction of past precipitation evolution is based on the assumption that precipitation is seasonally stable and unchanged, but whether this assumption holds under large-scale climate change over long time scales has not been verified. If this hypothesis is held as expected, then there is only a change in magnitude in the past precipitation evolution, and the existing precipitation reconstruction is sufficient; If this assumption is not valid, the reconstruction of paleoprecipitation based on the stability assumption will be incomplete and will inevitably bias the understanding of past climate evolution.

In response to the above key scientific questions, Lanjianghu, researcher of the Institute of Earth Environment, Chinese Academy of Sciences, and Cheng Jun, professor of Nanjing University of Information Science and Technology, reconstructed the only high-resolution precipitation record in the early and middle Holocene of the modern winter rain area in the South China Sea based on the PKK lake sedimentation in southern Thailand. PKK records and TraCE-21ka simulations together reveal that the local precipitation season mode underwent a fundamental transition from summer to winter in the Holocene, and was realized in the form of abrupt changes around ~6ka. The results were recently published in Geophysical Research Letters, a geoscience journal.

Seasonal characteristics of precipitation in Southeast Asia and changes in early-middle Holocene precipitation recorded by PKK in southern Thailand.

The change of precipitation seasonal mode is the combined effect of the decrease of summer precipitation due to the weakening of summer winds and the increase of winter precipitation due to the westward migration of winter wind circulation in the South China Sea. Among them, the sharp increase of SST in the South China Sea due to the opening of the South China Sea through the current and the trend influence of orbital radiation is the leading factor for the westward movement of wind circulation and increased rainfall in winter.

Holocene precipitation changes and winter-summer rainy zone boundary changes simulated by TraCE-21ka.

Recording-simulations reveal changes in the Holocene winter summer wind system.

The change of precipitation seasonal patterns may occur in the boundary areas adjacent to different seasonal modes in the tropics and even in the world, and these boundary areas are often sensitive areas for the ecological environment to respond to climate change, and the amplitude of various environmental factors evolves with time, which is an ideal place for high-quality paleoclimatic records. Therefore, when reconstructing precipitation based on these regional paleoclimatic records, we should pay attention to the potential possibility of precipitation seasonal mode changes, and consider its impact in the attribution analysis of past ecological environment evolution.

This work clarifies for the first time that the seasonal mode of precipitation may undergo fundamental changes under long-term climate change, and the seasonal mode change of precipitation is another important feature in addition to the evolution of long-term climate change decline water value, which may be more important for shaping the ecological environment in the past. Therefore, the reconstruction of the evolution of past precipitation should pay attention to the evolution of quantitative values and the change of seasonal patterns. (Source: Yan Tao, China Science News)


Spatial distribution of global winter and summer rainfall areas, simulated precipitation seasonal modal changes since the last glacial maximum, and their impact on vegetation changes. (Courtesy of the Institute of Global Environment)

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