February 22, 2011

Ancient Antarctic Sea Creature Allows Climate Comparison

In the latest issue of 'Current Biology', researchers from the British Antarctic Survey (BAS) have published an analysis of growth rates of a tiny sea animal.

Samples of the bryozoan, (Cellarinella nutti) a sea-bed filter-feeding animal that looks like branching twigs, collected during Captain Scott's Antarctic trips, are yielding data that may prove valuable in projecting climate change, BBC News is reporting.

The samples were collected in the Ross Sea, where Capt. Robert Falcon Scott moored during both the Discovery expedition of 1901-04 and the Terra Nova expedition a decade later, where he lost his life attempting to return from the South Pole.

These early 20th century expeditions brought back many finds including samples of life from the sea floor. Comparing these samples with modern ones, scientists have now shown that the growth of the bryozoan has increased in recent years.

Growing during the period in the year when it can feed by drawing plankton from the water with its tentacles, the length of the feeding season is reflected in the size of the annual growth band, similar to tree rings.

Bryozoan samples, collected at the same site recently by the Census of Marine Life, have increased the flow of data over the past decade allowing researchers to show that the creatures grew roughly the same amount each year until about 1990.

Since then, there has been a steady increase, with the annual growth rate now being more than double the 20th century average. BAS scientists claim this means that the bryozoans are now eating longer, which means they are eating more phytoplankton - the tiny marine plants that draw dissolved CO2 from seawater.

"The 'branches' of the bryozoans break off and are easily buried, and we've seen that - so burial is taking carbon out of circulation," lead researcher David Barnes told BBC News. "This is important because it's locking away carbon," added Barnes.

This suggests that it is acting to increase the size of the carbon sink - the absorption and storage of CO2 - in the Southern Ocean. Other researchers, however, have concluded that the Southern Ocean is progressively absorbing less CO2.

Four years ago that the size of the global sink fell by 18 percent in the period 2000-06, with a large chunk of that decrease registered in the Southern Ocean, The Global Carbon Project, an international research network, concluded.

"Winds there have accelerated over the last 50 years, and it's thought this is speeding up the mixing in the Southern Ocean and bringing to the surface deep water that's rich in CO2," said Corinne Le Quere, a member of the Global Carbon Project and director of the Tyndall Centre for Climate Change Research.

"So we have observations of this physical process, but the biological activity we don't have much information about; if you're mixing the ocean more, how are organisms responding? Usually in my experience the biological response compensates a bit, but not enough [to counteract the physical change]; and the fact that you have this one organism with higher growth rates doesn't say how much this is going to affect the carbon balance, " Le Quere continued.

Both expeditions made the collection of scientific samples a top priority - including retrieving samples from the sea bed at a depth of half a kilometer using trawls. "Prior to this, I tended to associate success in the Antarctic with people like Amundsen and Shackleton - Scott, I thought, doesn't have the same attachment to success," said Dr. Barnes.

"But now I view things differently, and I think in 100 years' time people will still be using the collections he made - they're extensive and high quality, and in fact we struggled to find collections made after that that were as good. "He really should be given more credit for some of the scientific work they did."


Image Caption: Kymella polaris, a cheilostome bryozoan, at 32m depth. Credit: BAS


On the Net: