Arctic climate under greenhouse conditions in the Late ...( New evidence for ice-free summers wi...)

New evidence for ice-free summers with intermittent winter sea ice in the Arctic Ocean during the Late Cretaceous a period of greenhouse conditions - gives a glimpse of how the Arctic is likely to respond to future global warming.

Records of past environmental change in the Arctic should help predict its future behaviour. 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. But scientists have disagreed about the climate at this time, with some arguing for low Arctic late Cretaceous winter temperatures (when sunlight is absent during the Polar night) as against more recent suggestions of a somewhat milder 15°C mean annual temperature.

Writing in Nature, 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 take this debate a step forward by presenting the first seasonally resolved Cretaceous sedimentary record from the Alpha Ridge of the Arctic Ocean.

The scientists analysed 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 carbon dioxide 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," they explain, " successive US and Canadian expeditions that occupied floating ice islands above the Alpha Ridge of the Arctic Ocean, recovered cores containing shallow buried upper Creta
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