Washington, Nov 14: A new DNA-based research by biologists would help to determine the vulnerability of cods to future global warming by finding out their location during the Ice Age.

The researchers, from the University of Sheffield, have used a computer model and DNA techniques to estimate where cod could be found in the Ice Age, when colder temperatures and lower sea-levels caused the extinction of some populations and the isolation of others.

On land, plants and animals, including humans, are known to have moved further south when the northern ice sheets reached their maximum extent around 20,000 years ago.

Biologists estimate that similar migrations must have happened for plankton and fish in the sea.

But this theory has two complications.

Firstly, greatly reduced sea levels meant that many shallow and highly productive marine habitats around Europe and North America ceased to exist.

The second complication would be that the ice-age circulation patterns in the North Atlantic caused the temperature change between tropical and polar conditions to occur over a much shorter north-south distance, reducing the area suitable for temperate species, such as cod.

The new analyses included these effects, together with other environmental and ecological information, in order to estimate where it was possible for Atlantic cod to reproduce and survive.

The results indicated that though the ice-age range of Atlantic cod extended as far south as northern Spain, the total area of suitable habitat was much more restricted. Nevertheless, populations of cod continued to exist on both sides of the North Atlantic.

These findings were confirmed by genetic data, based on over a thousand DNA analyses of present-day cod populations, from Canada, Greenland, Iceland and around Europe.

"This research shows that cod populations have been able to survive in periods of extreme climatic change, demonstrating a considerable resilience, " said Professor Grant Bigg, Head of the University of Sheffield's Department of Geography.

"However, this does not necessarily mean that cod will show the same resilience to the effects of future climatic changes due to global warming, " he added.

New findings have shown that though natural climate change has previously reduced the range of cod to around a fifth of what it is today, they continue to populate both sides of the North Atlantic. (ANI)