Climate evolution in the southeastern Indian Ocean d

image: Site location and geological setting off the southwest coast of Australia. The red dots are the locations of Site U1516 since the Miocene which is their research site.
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Credit: ©Science China Press

The Miocene, 23 to 5 million years ago, was an important period for the formation of the Antarctic Ice Sheets (AIS). The mid-latitudes of the southern hemisphere are the area where westerly winds predominate and the climate there is sensitive to changes in AIS volume. Recently, the research team led by Prof. Li Tiegang from the Institute of Oceanology, Chinese Academy of Sciences (IOCAS) reconstructed the Miocene climate evolution in the southeast Indian Ocean. This story builds an important bridge between the evolution of westerly winds and AIS. This study was published in Science Earth Sciences in China.

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 dramatically 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.

In 2017, the International Ocean Discovery Program (IODP) drilled deep-water sediment cores from the Mentelle Basin in the southeast Indian Ocean. Scientists from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) combined analysis of siliciclastic mass accumulation rate, grain size, clay minerals and elemental composition of sediments to reconstruct the paleoclimatic evolution at the middle 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 (eg AIS fluctuations), hydrosphere (eg Southern Ocean hydrography) and lithosphere ( for example, Australian plate drift and continental weathering) and the atmosphere (eg mid-latitude westerly winds).

The research results show that the amount of terrigenous material transported from southwest Australia to the ocean has increased significantly and that the contribution from the riverine component was greater than that of the wind dust component 13 years ago. millions of years. Scientists consider that it became wetter and that continental chemical weathering became stronger in southwestern Australia after the end of the Middle Miocene.

It was 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 towards lower latitudes.

Going forward, this research team will then combine Nd isotopes from seawater to study the impact of AIS expansion on ocean circulation in the Indian Ocean. This research will be of great importance for the study of the climatic effects of changes in the ice caps in the process of global warming.

This research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences and the National Natural Science Foundation of China.

Sun, T., Xu, Z., Chang, F., Li T. 2022. Miocene climate change in southwestern Australia and its main controlling factors. Science China Earth Sciences65(6): 1104-1115, https://doi.org/10.1007/s11430-021-9904-y


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