Arctic warming leading to 'regime change' in North Atlantic ecosystems

The planet is experiencing some of the most dramatic climate changes in mankind's history, according to a new study.

Paul Eccleston, The Telegraph 10 Nov 08;

Arctic Ocean circulation patterns. Red arrows indicate inflow of Atlantic water into the Arctic Ocean. White arrows indicate surface flows of polar water. Yellow and orange arrows indicate inflow of Pacific water into the Arctic Ocean. Photo: CORNELL UNIVERISTY

Warming in the Arctic is leading to 'regime change' in North Atlantic ecosystems, the research claims.

Scientists from Cornell University looked at the effects fresh water – produced from melting ice in the Canadian Archipelago and Fram Strait - is having on ocean currents and marine life.

They say that while there have been many changes in the earth's climate over the past 65m years, changes in recent decades have been the most significant for 5,000 years.

"The rate of warming we are seeing is unprecedented in human history," said oceanographer Prof Charles Greene who led the study published in the journal Ecology.

The study looked at the climate record to gain a better understanding of melting Arctic ice sheets and glaciers and the impact on the North Atlantic. They found there had been periods of rapid cooling in the past when temperatures had dropped by as much as 10ºC in only a few years but they found nothing to match the current rate of warming.

The huge amounts – or 'pulses' – of fresh water melt over the past 10 years had led to clearly identifiable shifts in the distribution of plankton.

Microscopic algae previously found in the Pacific Ocean was now occurring in the North Atlantic for the first time in 800,000 years while a number of species of North Atlantic plankton were now being found much further south.

Both were indications that there had been a major change in the circulation patterns in the Arctic and Atlantic Oceans.

The increase in fresh water had extended the growing seasons of phytoplankton and microscopic drifting animals which were fundamental to the food chain of the Atlantic continental shelf.

"Such climate-driven changes can alter the structure of shelf ecosystems from the bottom of the food chain upwards," said Prof Greene.

While the collapse of cod populations had been blamed on overfishing it was also due in part to Arctic glacial melt adding more fresh and colder water to the ocean which had stifled cod reproduction and had hampered their recovery.

And in a knock-on effect less predatory cod and colder water had benefited shrimp and snow crab populations.

"As climate changes, there are going to be winners and losers, both in terms of biological species and different groups of people," added Prof Greene.

The study said the earth's climate system was changing so rapidly that it was difficult to predict future ecological changes but it was unlikely the deep North Atlantic will be heavily affected by the pulses of cold water this century.

However, the study concluded: "Continued exposure to such freshwater forcing, however, could disrupt global ocean circulation during the next century and lead to very abrupt changes in climate, similar to those that occurred at the onset of the last ice age."

Prof Greene added: "If the Earth's deep ocean circulation were to be shut down, many of the atmospheric, glacial and oceanic processes that have been stable in recent times would change, and the change would likely be abrupt."