Ice-free summers in ancient Arctic may help predict future trends

Washington, July 10 (ANI): In a new research, scientists have obtained evidence for ice-free summers with intermittent winter sea ice in the Arctic Ocean during the Late Cretaceous period, which should help predict how the Arctic is likely to respond to future global warming.

The Late Cretaceous, the period between 100 and 65 million years ago leading up to the extinction of the dinosaurs, is crucial in this regard because levels of carbon dioxide (CO2) were high, driving greenhouse conditions.

In this regards, Dr Andrew Davies and Professor Alan Kemp of the University of Southampton's School of Ocean and Earth Science based at the National Oceanography Centre, Southampton, along with Dr Jennifer Pike of Cardiff University have presented the first seasonally resolved Cretaceous sedimentary record from the Alpha Ridge of the Arctic Ocean.

The scientists analyzed the remains of diatoms - tiny free-floating plant-like organisms - preserved in late Cretaceous marine sediments.

In modern oceans, diatoms play a dominant role in the 'biological carbon pump' by which CO2 is drawn down from the atmosphere through photosynthesis and a proportion of it exported to the deep ocean.

Unfortunately, the role of diatoms in the Cretaceous oceans has until now been unclear, in part because they are often poorly preserved in sediments.

But, the researchers struck lucky.

"With remarkable serendipity, successive US and Canadian expeditions that occupied floating ice islands above the Alpha Ridge of the Arctic Ocean, recovered cores containing shallow buried upper Cretaceous diatom ooze with superbly preserved diatoms," explained the researchers.

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.

According to the researchers, "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."

"With increasing CO2 levels and global warming giving rise to increased ocean stratification, this style of (marine biological) production may become of increasing importance," they added. (ANI)