Corol Reefs And Rising Ocean Level

Research by French and American scientists, centred on a reef in Vanuatu that has a 23,000-year history, shows that a reef may no longer be able to keep up with the rising of the ocean's surface.

Work on a reef at the island of Urelapa, Vanuatu, produced the longest continuous record of growth‹17,000 years‹ever studied by scientists.

For the first time it gave researchers an uninterrupted record of environmental conditions in the Pacific Islands since the planet's glaciers last began retreating to the North and South poles about 20,000 years ago.

The most important finding is that the Urelapa reef's growth responded to environmental changes as the level of the ocean rose in response to the retreat of the glaciers.

The work by the French Development Research Institute in New Caledonia and universities of Minnesota, Arizona and Texas throws more light on how climate change affects the coral reefs of the Pacific, which are some of the ocean's most complex ecosystems.

The previous record of continuous reef growth, 14,000 years, came from a barrier reef in French Polynesia in 1999.

The growth of coral is affected by ocean temperatures, salinity, nutrient levels and input, the amount of light that penetrates the ocean, rough and calm sea conditions, earthquake activity and the kind of rock that coral grows on.

Ocean levels reached their lowest point, about 120 to 130 metres below the present level about 20,000 years ago and began to rise as glaciers melted.

Analysis of coral cores from five boreholes at Orelia showed that corals have a strong ability to adapt. They are affected to changes in environmental condition and in particular by ocean level changes.

From 23,000 to about 11,300 years before the present, the Urelapa reef grew continuously, keeping to shallow depths and following the rising ocean level very closely.

From 11,300 to 6000 years ago the reef grew more slowly in depths of 10 to 20 metres, where light penetration is poor. It did not keep pace with the acceleration of ocean level rise known to have happened from 11,300 years ago. The coral eventually changed the structure of its organisms to catch up.

This suggests that if atmospheric pollution is causing today's ocean level to rise as quickly as some scientists say that it is, present fringing reefs which are normally exposed at low tide, could eventually disappear for thousands of years with bad consequences for reef fish stocks and the protection of coastal regions from erosion

Meanwhile, you've heard of submarine volcanoes, submarines deserts and submarine landslides. Have you heard of submarine waves?
In March 2001, two scientists studied seawater temperatures off Palau recorded a 170-metre (560ft) wave which was entirely underwater and which quickly changed seawater temperatures, the Guam Pacific Daily News reported.

Patrick Colin, director of the Coral Reef Research Foundation in Palau, said the discovery had changed ideas about how coral reefs maintain themselves.

Coral needs nutrients yet in the tropics it lives in seas that lack them. While some scientists think that corals somehow recycle the few nutrients available, others suggest that waves carry nutrient-rich water to them from deep depths.

Palau's coral reefs are exceptionally diverse and prolific. Eric Wolanski, a physical oceanographer from the Australian Institute of Marine Science who worked at Palau, said that he had been struck by recording rapid temperatures at deep depths that could have been caused only by large up and down movements of water, or submarine waves. The waves are evident at levels at which layers of warm and cold water interfaced.

At a depth of 90 metres, the 170-metre wave changed the temperature from 82 degrees Fahrenheit to 47 degrees and back to 82 degrees in 90 minutes, allowing nutrient-rich cold water to rise and be carried to coral reefs. The two scientists say that submarine waves may be created by ocean currents.