Extinction on the seafloor linked to past changes in productivity at the sea surface
(17 June 2016)
In a Natural Environment Research Council (NERC) project led by Dr Erin McClymont, a marine sediment core from the Tasman Sea was examined with two aims: (1) to better identify the timing of the extinction event by looking at samples closely spaced together in time, and (2) to provide the first reconstructions of the conditions at the seafloor across the same time window.
The results of the study have been published in Nature Communications, and show that the 'extinction group' (the Stilostomellids - see picture) disappeared abruptly around 800,000 years ago. The team found no changes in ocean temperatures to explain the extinction, rejecting one previously hypothesised cause of the event. However, there was a shift in the make-up of the plankton living at the sea surface (the 'coccolithophores') at the same time. The team interprets this shift to represent a change to the nature of the food supply to the seafloor which the extinction group were unable to adapt to. The results are important for demonstrating that even in the deep sea, evolution and extinction can occur in response to events at the ocean surface.
To create the data required for this study the team used a range of geochemistry techniques, which included characterising the type and quantity of organic matter in the sediments ('biomarkers'), and looking at the incorporation of metals into the carbonate shells; these were combined with microscope analyses of the fossils of both the benthic foraminifera and some of the sea surface algae. The sediment cores are part of the archive of the International Ocean Discovery Program.
For further details on the project see the project page.
Image from Hayward, B.W., Kawagata, S., Grenfell, H.R., Sabaa, A.T. and O'Neill, T. (2007), Last global extinction in the deep sea during the mid-Pleistocene climate transition, Paleoceanography, 22, PA3103, doi:10.1029/2007PA001424.