Lake Towuti, Revealing Ancient Climate History
BANDUNG, itb.ac.id – Located in South Sulawesi, Towuti is the second-largest freshwater lake in Indonesia. Spanning widely over 561.1 km2, Lake Towuti has a maximum water depth of 203m. Other than that, Lake Towuti, which is located at an altitude of 293m above sea level, has five islands as well.
Settling in the Malili Lake system, Lake Towuti connects South Sulawesi Province and Southeast Sulawesi Province. Its water sources come from some water springs in the surrounding area, connected by 26 rivers.
A research project on Lake Towuti was published in the scientific journal Nature Communications. This study involved institutions from various countries, such as Germany, Canada, Switzerland, Denmark, Indonesia, and the USA.
As one of the co-authors of this study, Prof. Satria Bijaksana, professor of rock magnetism at Institut Teknologi Bandung (ITB), discussed this topic at The Exhibition of the Institute for Research and Community Services (LPPM ITB) on December 20th, 2022. "In my expertise, I see the closest thing to us. I am involved in a global geophysics group," Prof. Satria said.
"We tried to look for a topic closest to us. Therefore, it is quite easy for me to explain the research. One mountain, one Ph.D. One lake, one Ph.D. One river, one Ph.D. We have a Ph.D. about Lake Singkarak in West Sumatra. We have a Ph.D. in biology. We have 4 to 5 Ph.D.s about Lake Towuti," he added. There were also some doctoral students who were interested in studying Lake Towuti because it is one of the most ancient lakes in the world.
"The location in central Indonesia is also giving the important opportunity to reconstruct long-term terrestrial paleoclimatology changes in very crucial regions but rarely studied: the Western Pacific warm pool, the heart of El Nio-Southern Oscillation," said the other co-authors, Henrik Vogel, a Professor of Sedimentary Biochemistry at the Institute of Geological Sciences and the Oeschger Centre for Climate Change Research, University of Bern, Switzerland.
The Western Pacific Warm Pool is the biggest water body in the world, with the warmest seawater surface temperature of over 28 oC.Due to the water's being warm enough to toss heat and water vapor into the atmosphere, this warm pool has massive effects on the climate in its surroundings. This aspect also plays a significant role in the regulation of the rainy season system in most countries in Asia and Africa. Therefore, research about Lake Towuti has its own unique interests.
"Lake Towuti also has a high biodiversity of endemic flora and fauna, surrounded by tropical rainforest with the highest biodiversity in the world, making it one of Southeast Asia’s centers of biodiversity. The geologic arrangement in its surrounding area, which contains ultrabasic rocks and laterite soil, provides rich mineral substrates. These minerals support an ecosystem full of biodiversity for exotic microbe species that live in the waters and sediments of Lake Towuti. The ecosystem might be made as an analogy of microbe ecosystems in the Archaeal Sea or on Mars," Vogel added.
A map of Indonesia (A), an illustration of the geological formation of the Malili Lake system in Sulawesi Island, with Lake Towuti being the largest (B), and a bathymetric map of Lake Towuti (C)
As an ancient lake, the climate in the ancient geological age (paleoclimate) of Lake Towuti can be learned through its sediment contents. "As a part of the Towuti Drilling Project (TDP) incorporated with the International Scientific Drilling Program (ICDP), we collect sediment samples at a depth of 156m, well below the oxycline depth at the drilling time," said André Friese, the primary author of this research.
Lake Towuti has oxygenated water to 70m in depth, and after 130 m, dissolved oxygen cannot be found at all. The condition of this drastic oxygen level change is called oxycline. Interestingly, at a depth of 130m, the water of this lake is rich in dissolved iron.
"The deposit of iron-containing sediment (ferruginous sediment) is often found in Archaean and Proterozoic eons; this aspect plays a significant role in the world’s biochemistry cycle," said Friese, who gained his Ph.D. from the GFZ German Research Center for Geosciences.
Analytical results show that the sediment forms with a thickness of 19cm every few thousand years. It implies that the upper 12 m of sediment stores climate information from around 60 thousand years ago.
Geochemistry analysis shows that the sediment of Lake Towuti is rich in organic carbon. The research, involving 17 researchers, had succeeded in revealing the organic matter mineralization process of Lake Towuti’s ferruginous sediment. Within the upper 12m of sediment, reduction of iron and sulfate occurs, as does the methanogenesis process, or methane production. The processes are the key to the organic matter mineralization, with methanogenesis being the most dominant process (90%).
Although it has a high amount of iron, the iron itself only contributes about 8% to the organic matter mineralization process. Friese said, "At the same time, it also reveals that the iron found in sediment samples is stable only for a few tens of thousands of years."
"Similar to the iron reduction process, sulfate reduction plays an insignificant role in the organic matter mineralization process as well. However, it has to be highlighted that the observation result that shows sulfate reduction is retained in the sediment core confirms microbes reactivity towards organic matter in these sediments," Friese said.
Microbes in the sediments of Lake Towuti produce methane (methanogenesis), which is the primary component of greenhouse gases. The high amount of greenhouse gases is presumably related to the climate condition of the earth about 3 billion years ago. The ancient greenhouse gas effect causes additional heating to the planet (aside from the greenhouse gas effect these days), which is enough to match the dim sunlight at that time (known as the faint young sun paradox).
Further studies of Lake Towuti can reveal lots of valuable information. Hopefully, the climate change study saved in the sediments of Lake Towuti can be used not only for looking to the past but also for predicting the future.
Reporter: Favian Aldilla (Teknik Sipil, 2019)
Source: https://www.nature.com/articles/s41467-021-22453-0
Translator: Hanifa Juliana (Perencanaan Wilayah dan Kota, 2020)
Editor: Anggi Nurdiani (Manajemen, 2021)
scan for download
