Seminar
Sponsored by Bolin Centre for Climate Research Research Area 6
Drilling into a Modern Archaean Ocean:
the ICDP Lake Towuti Drilling Project

When? 19 February, 13h00 | Where? Rum U26 , Geovetenskapens hus

 

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. Due to the extreme clarity of the water, the upper part of the anoxic water column lies in the photic zone. Here, and in those areas where the lake floor lies in the photic zone, the iron oxides are reduced, leading to liberation of phosphorus and secondary productivity. The extreme scarcity of sulphate (low µmolar levels) and the virtual absence of other electron acceptors like nitrate and nitrite makes the anoxic bottom waters of Lake Towuti a prime analogue for the Archaean Ocean.

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 have the analytical procedures tested 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-reducing bacteria were present at all sites, but more active at the shallow site. Fingerprinting of bacterial intracellular DNA emphasized a decrease of Shannon diversity from the shallow to the deep site that correlated with the presence and level of activity of sulphate reducing bacteria in the microbial assemblage. The quick loss of extracellular DNA indicated that microbial remineralization of organic matter was strongest in the uppermost sediment layers.

The 150 m site of the pilot study was the site of the ICDP drilling campaign, which took place from May to July 2015. For the first time in the history of ICDP a dedicated geomicrobiology/geochemistry core was recovered. We tested a new particulate tracer with good results. The first on-site data reveal a geologic record that shows strong diagenetic overprint.

 

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