Fossilisation in Extreme Environments: Deep-Sea Hydrothermal Vents

Principal Investigator: Dr C Little

Sponsor: NERC

Value: £30936.18

Dates: 1st March 2005 to 29th February 2008

Summary

Hydrothermal vents are extreme environments in the deep-sea where cold seawater seeps down through volcanic rocks, is heated by magma, reacts with the rocks and rises back to the surface of the ocean as hydrothermal vent fluid. Vent fluid is very hot, oxygen poor, acidic and full of metals (especially iron, zinc, copper and manganese) and hydrogen sulphide. When this fluid reacts with cold seawater there is a rapid precipitation of sulphate and sulphide minerals. Surprisingly, hydrothermal vents are home to large numbers of extraordinary animals, many of which are completely dependent on symbiotic bacteria to live. These bacteria use hydrogen sulphide in the vent fluid as their energy source. Vent communities are thus dependent on geochemical rather than solar energy sources and this buffers them from almost all major events (e.g. mass extinctions, global climate change) affecting all other photosynthesis-based marine and terrestrial ecosystems. Thus, the evolutionary history of vent animals and communities is likely to be very different to almost all other marine biotas. The only direct evidence for this evolutionary history comes from the fossil record of vent animals. Unfortunately this record is sparse and fundamental questions exist about why this is so. For example, why do some ancient vent deposits contain fossils which are absent from other vent deposits in the same state of preservation? These questions involve knowing much more about how animals living at modern vent sites become fossilized. In order to do so this project will use a manned submersible to place twelve specially designed identical sets of experimental materials (vent worm tubes, mollusc shells and controls) at vent sites with different chemistries and temperatures in an active hydrothermal vent field at 9 degrees N on the East Pacific Rise. After a year and a half these experimental materials will be retrieved from the seafloor and analysed in the laboratory to investigate the nature of the mineralization that has occurred on the biological and control material. The new data will allow us to make a model explaining how modern vent fauna become fossilized. Having a better understanding of this process will allow proper interpretation of the vent fossil record and substantially increase our understanding of evolutionary patterns in this extreme habitat. It will also enable us to find more ancient vent communities to increase the present poor record.