Arctic climate under greenhouse conditions in the Late ...(ceous diatom ooze with superbly preserve...)

Date:7/9/2009

ceous diatom ooze with superbly preserved diatoms." This has allowed them to conduct a detailed study of the diatom fossils using sophisticated electron microscopy techniques. In the modern ocean, scientists use floating sediment traps to collect and study settling material. These electron microscope techniques that have been pioneered by Professor Kemp's group at Southampton have unlocked a 'palaeo-sediment trap' to reveal information about Late Cretaceous environmental conditions.

They find that the most informative sediment core samples display a regular alternation of microscopically thin layers composed of two distinctly different diatom assemblages, reflecting seasonal changes. Their analysis clearly demonstrates that seasonal blooming of diatoms was not related to the upwelling of nutrients, as has been previously suggested. Rather, production occurred within a stratified water column, indicative of ice-free summers. These summer blooms comprised specially adapted species resembling those of the modern North Pacific Subtropical Gyre, or preserved in relatively recent organically rich Mediterranean sediments called 'sapropels'.

The sheer number of diatoms found in the Late Cretaceous sediment cores indicates exceptional abundances equalling modern values for the most productive areas of the Southern Ocean. "This Cretaceous production, dominated by diatoms adapted to stratified conditions of the polar summer may also be a pointer to future trends in the modern ocean," say the researchers: "With increasing CO2 levels and global warming giving rise to increased ocean stratification, this style of (marine biological) production may become of increasing importance."

However, thin accumulations of earthborn sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, a finding that supports "a wide body of evidence for low Arctic late Cretaceous winter temperatures rather than recent suggestions
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Contact: Rory Howlett r.howlett@noc.soton.ac.uk 44-023-805-98490 National Oceanography Centre, Southampton (UK) Source:Eurekalert

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