Various factors, from cyclones to the Crown of Thorns starfish,

are being blamed for the loss of the reef.

Australia's Great Barrier Reef has lost more than half its coral cover in the past 27 years, a new study shows.

Researchers analysed data on the condition of 217 individual reefs that make

up the World Heritage Site.

The results show that coral cover declined from 28.0% to 13.8% between 1985

and 2012.

They attribute the decline to storms, a coral-feeding starfish and bleaching

linked to climate change.

The research is published in the Proceedings of the National Academy of

Sciences journal.

Glen De'ath from the Australian Institute of Marine Science (AIMS) and

colleagues determined that tropical cyclones - 34 in total since 1985 - were

responsible for 48% of the damage, while outbreaks of the coral-feeding

crown-of-thorns starfish accounted for 42%.

Two severe coral bleaching events in 1998 and 2002 due to ocean warming also

had "major detrimental impacts" on the central and northern parts of the reef,

the study found, putting the impact at 10%.

"This loss of over half of initial cover is of great concern, signifying

habitat loss for the tens of thousands of species associated with tropical coral

Antarctic may host methane stores

[[{"type":"media","view_mode":"media_crop","fid":"127","attributes":{"alt":"","class":"media-image","id":"media_crop_6810678576135","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"17","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","typeof":"foaf:Image"}}]]

 
Ancient organic matter could be converted to methane by microbes.
 

Large volumes of methane - a potent

greenhouse gas - could be locked beneath the ice-covered regions of Antarctica,

according to a new study.

It says this methane could be released into the atmosphere as ice retreats,

contributing to climate warming.

The findings indicate that ancient deposits of organic matter may have been

converted to methane by microbes under the ice.

An international team reported the results in Nature journal.

Study leader Jemima Wadham, from Bristol University, said: "This is an

immense amount of organic carbon, more than ten times the size of carbon stocks

in northern permafrost regions.

"Our laboratory experiments tell us that these sub-ice environments are also

biologically active, meaning that this organic carbon is probably being

metabolised to carbon dioxide and methane gas by microbes."

They estimate that there could be hundreds of billions of tonnes of carbon

Scientists have identified thousands of sites in the Arctic where methane that has been stored for many millennia is bubbling into the atmosphere. The methane has been trapped by ice, but is able to escape as the ice melts. Writing in the journal Nature Geoscience, the researchers say this ancient gas could have a significant impact on climate change. Methane is the second most important greenhouse gas after CO2 and levels are rising after a few years of stability. There are many sources of the gas around the world, some natural and some man-made, such as landfill waste disposal sites and farm animals. Tracking methane to these various sources is not easy. But the researchers on the new Arctic project, led by Katey Walter Anthony from the University of Alaska at Fairbanks (UAF), were able to identify long-stored gas by the ratio of different isotopes of carbon in the methane molecules. Using aerial and ground-based surveys, the team identified about 150,000 methane seeps in Alaska and Greenland in lakes along the margins of ice cover. Local sampling showed that some of these are releasing the ancient methane, perhaps from natural gas or coal deposits underneath the lakes, whereas others are emitting much younger gas, presumably formed through decay of plant material in the lakes. "We observed most of these cryosphere-cap seeps in lakes along the boundaries of permafrost thaw and in moraines and fjords of retreating glaciers," they write, emphasising the point that warming in the Arctic is releasing this long-stored carbon.