Drilling into a ferruginous tropical lake: The ICDP Lake Towuti Project
Lake Towuti is a deep tectonic basin in Sulawesi, Indonesia. Its geographic position and relatively great age (estimated >600 ky) makes the lake a prime location to record paleoclimatic changes in the tropical Western Pacific warm pool in its sedimentary sequence. It was therefore chosen as a drilling target by the International Continental Drilling Program (ICDP). The catchment is characterized by ultramafic rocks and lateritic weathering. As a result of phosphorus adsorption onto the iron oxides derived from lateritic soils, the lake is oligotrophic and among the least productive tropical lakes on Earth. The lake is stratified, with anoxic conditions below 130 m. At the oxycline the iron oxides are reduced, leading to liberation of phosphorus and secondary productivity. Two pilot studies were carried out in 2013 and 2014 in order to obtain not just a better understanding of the biogeochemical processes in Lake Towuti, but also to test the analytical procedures prior to the ICDP drilling campaign in May/June 2015. For the pilot study three sites were selected in water depths of 60, 150 and 200 m water depth, representing different bottom water oxygenation levels. Microbial cell densities were highest at the shallow site and reflected greater availability of labile organic matter and electron acceptors. Despite the low sulphate concentrations, sulphate reduction rates were surprisingly high, indicating rapid reoxidation of reduced sulphur compounds. The quick loss of extracellular DNA indicates that microbial remineralization of organic matter is strongest in the uppermost sediment layers. The 150 m site of the pilot study was chosen for the ICDP drilling campaign, which took place from May to July 2015. For the first time in the history of ICDP a dedicated core for geomicrobiology and geochemistry was recovered. We tested a new particulate contamination tracer with good results. The first on-site data reveal a geologic record that shows strong diagenetic overprint. Additional to high-resolution pore water chemistry, different iron minerals were extracted from the sediment and analysed for their isotopic composition and morphology. Initial results reveal a highly complex interplay between erosion as well as water-column and sedimentary processes.
https://www.munich-geocenter.org/events/seminars/frontiers-in-earth-sciences-18/drilling-into-a-ferruginous-tropical-lake-the-icdp
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Drilling into a ferruginous tropical lake: The ICDP Lake Towuti Project
Abstract
Lake Towuti is a deep tectonic basin in Sulawesi, Indonesia. Its geographic position and relatively great age (estimated >600 ky) makes the lake a prime location to record paleoclimatic changes in the tropical Western Pacific warm pool in its sedimentary sequence. It was therefore chosen as a drilling target by the International Continental Drilling Program (ICDP).
The catchment is characterized by ultramafic rocks and lateritic weathering. As a result of phosphorus adsorption onto the iron oxides derived from lateritic soils, the lake is oligotrophic and among the least productive tropical lakes on Earth. The lake is stratified, with anoxic conditions below 130 m. At the oxycline the iron oxides are reduced, leading to liberation of phosphorus and secondary productivity.
Two pilot studies were carried out in 2013 and 2014 in order to obtain not just a better understanding of the biogeochemical processes in Lake Towuti, but also to test the analytical procedures prior to the ICDP drilling campaign in May/June 2015.
For the pilot study three sites were selected in water depths of 60, 150 and 200 m water depth, representing different bottom water oxygenation levels. Microbial cell densities were highest at the shallow site and reflected greater availability of labile organic matter and electron acceptors. Despite the low sulphate concentrations, sulphate reduction rates were surprisingly high, indicating rapid reoxidation of reduced sulphur compounds. The quick loss of extracellular DNA indicates that microbial remineralization of organic matter is strongest in the uppermost sediment layers.
The 150 m site of the pilot study was chosen for the ICDP drilling campaign, which took place from May to July 2015. For the first time in the history of ICDP a dedicated core for geomicrobiology and geochemistry was recovered. We tested a new particulate contamination tracer with good results. The first on-site data reveal a geologic record that shows strong diagenetic overprint. Additional to high-resolution pore water chemistry, different iron minerals were extracted from the sediment and analysed for their isotopic composition and morphology. Initial results reveal a highly complex interplay between erosion as well as water-column and sedimentary processes.
