Methane seeps are discrete sites where fluids rich in methane flow onto the seafloor. Only discovered in 1984, they are now known in all the World’s oceans. Methane seeps support extraordinary biological communities, the workings of which have radically altered our view of the life in the deep sea. This is because the primary energy source for these ecosystems comes not directly from the sun, but instead from sub-surface chemical compounds, particularly methane and hydrogen sulphide. The animals that dominate modern seep communities are dependent nutritionally on symbiotic bacteria which directly use methane and hydrogen sulphide for their energy requirements. Much is still unknown about modern seep communities, in particular, how seep animals disperse between seep sites, which are patchily distributed. The few biogeographic studies show that while many seep species are restricted to individual seep sites, at higher taxonomic level the communities are largely similar throughout the World’s oceans.
This appears not to have been case in the Jurassic and Cretaceous eras. Preliminary evidence from high latitude methane seeps from East Greenland, Spitsbergen, Novaya Zemlya and Canadian Arctic suggests that there was a seep fauna in the Arctic area distinct from that of contemporary lower latitude seeps, and thus there was strong biogeographic control on seep communities for at least 90 million years in the Mesozoic.
Potential explanations may be related to the isolation of the Arctic area seeps in the Boreal Ocean (equivalent to today’s Arctic Ocean) in the Jurassic and Cretaceous, and/or contemporary differences in the environment, such as latitudinal seawater temperatures, or water depth. Latitudinal temperature controls were probably much weaker in the Jurassic and Cretaceous than today, because this was a greenhouse period in Earth History. However, it is also becoming apparent that during the Mesozoic there were also cold episodes, when limited polar ice may have been present. It is possible that during these periods relative sea levels would have been lower, so there may have been fewer connections between ocean basins, and thus less opportunity for exchange of animal larvae between contemporary high and low latitude seeps.
The project has two linked hypotheses:
1) There was a taxonomically distinct methane seep fauna in the high northern latitudes over 90 million years between the Upper Jurassic and the Upper Cretaceous, with a different evolutionary history to contemporary low latitude seep communities.
2) During periods of relative warmth and higher sea levels there was a greater interchange of the larvae of seep-restricted fauna through the shallow seaways linking the Boreal Ocean area and lower latitude seas than during cool time periods.
Dr Stephen Hunter is a PDRF on this project.