In the context of global warming with the increase in atmospheric carbon dioxide (CO2) and the melting of polar ice, the reconstruction of paleoclimatic and paleoenvironmental history during past periods when the Earth’s climate system changed drastically is important for understanding the climate mechanism and thus improving predictions of the future.
At present, deep-sea sediments offer scientists an ideal perspective for deciphering paleoclimatic and paleoenvironmental history.
The Miocene, 23 to 5 million years ago, was an important period for the formation of the Antarctic Ice Sheets (AIS). Recently, a research team led by Professor LI Tiegang from the Institute of Oceanology, Chinese Academy of Sciences (IOCAS) used deep-sea sediments off southwestern Australia to reconstruct the palaeoclimatic evolution at mid-latitudes of the southern hemisphere during this period.
This story builds an important bridge between the evolution of westerly winds and AIS. It also provides evidence of Antarctic signal transmission to lower latitudes when only unipolar ice sheets developed on Earth.
The study was published in Science China Earth Sciences April 22.
In 2017, the International Ocean Discovery Program (IODP) drilled deep-water sediment cores from the Mentelle Basin in the southeast Indian Ocean. IOCAS scientists combined analysis of siliciclastic mass accumulation rate, grain size, clay minerals and sediment elemental composition to reconstruct paleoclimatic evolution at mid-latitudes of the Southern Hemisphere .
Due to the northward drift of the Australian Plate since the Cenozoic, the Mentelle Basin and Australia were closer to Antarctica in the Miocene than today. At the same time, westerly winds prevailed in the mid-latitudes of the southern hemisphere and played a significant role in rainfall over southwestern Australia. This makes the Mentelle basin an ideal target area to study the interaction between the cryosphere, the hydrosphere, as well as the lithosphere and the atmosphere.
The results showed that the amount of terrigenous material transported from southwest Australia to the ocean increased significantly and that the contribution of the riverine component was greater than that of the wind dust component 13 years ago. millions of years. “It became wetter and continental chemical weathering became stronger in southwestern Australia after the end of the Middle Miocene,” Prof LI said.
The researchers also found that this significant climate transition of Australia occurred just after the permanent formation of the AIS with the dramatic drop in deep-sea temperatures and a remarkable expansion of zonal sea surface temperature gradients. and meridians. Meanwhile, the South Asian monsoon system suddenly strengthened. “These constant changes could indicate the transmission of Antarctic signals along the ocean and atmosphere to lower latitudes,” said SUN Tianqi, first author of the study.
“In the future, we will then combine Nd isotopes from seawater to study the impact of AIS expansion on ocean circulation in the Indian Ocean,” Prof LI said.
This research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences and the National Natural Science Foundation of China.