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Ocean Research


February 2011 Issue

Ocean Circulation Changes Made Europe Colder in the Past
Unusually cold weather across Europe this winter has been caused by a change in the winds: Instead of the typical westerly winds warmed by Atlantic surface ocean currents, cold northerly Arctic winds are influencing much of the continent. But scientists have long suspected that far more severe and longer-lasting cold intervals have been caused by changes to the circulation of the warm Atlantic ocean currents themselves. Now new research led by Cardiff University has revealed that these ocean circulation changes may have been more dramatic than previously thought.

The findings, published January 14 in Science, show that as the last ice age came to an end (10,000 to 20,000 years ago) the formation of deep water in the northeast Atlantic repeatedly switched on and off. This caused the climate to warm and cool for centuries at a time. Lead author Dr. David Thornalley of the Cardiff School of Earth and Ocean Sciences explained that the scientists used shells from small organisms found in North Atlantic ocean sediment cores to determine the distribution of radiocarbon at different times in the past. This method allowed the researchers to determine the rate of deep water formation in the North Atlantic at various periods.

Typically, cold, dense water sinks in the northeast Atlantic, drawing in warmer water from the tropics. The team of scientists found that each time deep water formation switched off, the northeast Atlantic did not fill with water that sank locally. Instead, it became inundated with water that had originally formed near Antarctica and then spread rapidly northwards.

These new results suggest that the Atlantic ocean is capable of radical changes in how it circulates, on timescales as short as a few decades.

"Whilst the circulation of the modern ocean is probably much more stable than it was at the end of the last ice age, and therefore much less likely to undergo such dramatic changes, it is important that we keep developing our understanding of the climate system and how it responds when given a push," Thornalley said. For more information, visit www.sciencemag.org.

Oxygen-Free Early Oceans Likely Delayed Rise of Life on Planet
Geologists at the University of California (UC), Riverside, have found chemical evidence in 2.6-billion-year-old rocks indicating that Earth's ancient oceans were oxygen-free and, surprisingly, contained abundant hydrogen sulfide in some areas.

"We are the first to show that ample hydrogen sulfide in the ocean was possible this early in Earth's history," said Timothy Lyons, a professor of biogeochemistry and the senior investigator for the study, which appeared in the February issue of Geology. "This surprising finding adds to growing evidence showing that ancient ocean chemistry was far more complex than previously imagined and likely influenced life's evolution on Earth in unexpected ways, such as by delaying the appearance and proliferation of some key groups of organisms."

Ordinarily, hydrogen sulfide in the ocean is tied to the presence of oxygen in the atmosphere. Even small amounts of oxygen favor continental weathering of rocks, resulting in sulfate, which in turn gets transported to the ocean by rivers. Bacteria then convert this sulfate into hydrogen sulfide.

How then did the ancient oceans contain hydrogen sulfide in the near absence of oxygen, as these findings indicate. The UC Riverside-led team explains that sulfate delivery in an oxygen-free environment can also occur in sufficient amounts via volcanic sources, with bacteria processing the sulfate into hydrogen sulfide.

Specifically, Lyons and his colleagues examined rocks rich in pyrite that date back to the Archean eon of geologic history (3.9 to 2.5 billion years ago) and typify very low-oxygen environments. Found in Western Australia, these rocks have preserved chemical signatures that constitute some of the best records of the very early evolutionary history of life.

The rocks formed 200 million years before oxygen amounts spiked during the so-called "Great Oxidation Event," an event 2.4 billion years ago that set the stage for life's proliferation.

"Our previous work showed evidence for hydrogen sulfide in the ocean more than 100 million years before the first appreciable accumulation of oxygen in the atmosphere at the Great Oxidation Event," Lyons said. "The data pointing to this 2.5 billion-year-old hydrogen sulfide are fingerprints of incipient atmospheric oxygenation. Now, in contrast, our evidence for abundant 2.6 billion-year-old hydrogen sulfide in the ocean ... shows that oxygen wasn't a prerequisite. The important implication is that hydrogen sulfide was potentially common for a billion or more years before the Great Oxidation Event, and that kind of ocean chemistry has key implications for the evolution of early life." For more information, visit http://geology.gsapubs.org.

Report Released on Geomorphic Evolution of Great Yarmouth Spit
Little has been known of the volume of sediment held within England's Great Yarmouth spit or its short-term fluctuations in sediment storage capacity. Such gaps in coastal sediment budgets mean that the effects of predicted increases in relative sea level and storminess are difficult to forecast.

A new report on historic changes in the Great Yarmouth spit and the related coastal system, produced by Hannah Evans of the British Geological Survey as a result of a Crown Estate-Caird Fellowship at the National Maritime Museum, has addressed this by examining the late-Holocene geomorphic evolution of the Great Yarmouth spit, providing a value for the volume of sediment stored within the feature and placing current morphological changes within a historical context.

The specific aims of this research were to investigate spit volume, spit morphological change, potential forcings for this change and likely future morphological trends.

Short-term fluctuations in the Great Yarmouth spit's sediment storage capacity were identified by investigating morphological changes within the feature's coastal zone from maps and aerial photographs. These fluctuations appear to be site-specific across the spit and adjacent areas. For more information, visit www.nmm.ac.uk.


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