OTTAWA (Reuters Life!) - A group of British explorers just back from a 60-day trip to the North Pole said Monday they had encountered unusual conditions, including ice sheets that drifted far faster than they had expected.

The three-member team walked across the frozen Arctic Ocean to study the impact of increased carbon dioxide absorption by the sea, which could make the water more acidic and put crucial food chains under pressure.

Expedition leader Ann Daniels said the ice drifted so much that they eventually covered 500 nautical miles (576 miles) rather than the 268 nautical miles initially envisaged.

One possible reason for the rapid drift was a lack of ice, she suggested. Satellite imagery reveals rapidly melting ice sheets in the Arctic, a region which is heating up three times more quickly than the rest of the Earth.

The first day the team was dropped off the ice moved so quickly to the south that it took the trio 10 days to make it back to their starting point.

“None of us had ever experienced that amount of southerly drift on our previous expeditions, and it continued for such a long period of time. We kept expecting it to stop, we began to pray it would stop,” Daniels said.

“At the end of the expedition we were losing three nautical miles a night ... it was quite a major factor,” she told a news conference in Ottawa.

Many scientists link the higher Arctic temperatures to the greenhouse gas emissions blamed for global warming.

Martin Hartley, a member of the team, said the condition of the ice was unpleasantly bad.

“We spent a couple of days walking on ice that was three or four inches thick with no other thicker ice around, which was a big surprise to us,” he told the news conference.

“On more than one occasion we came across enormous areas of very thin ice, which is quite stressful to travel on. We came across open water which we had to swim across.”

At one point an ice floe the team’s tent was moored on broke apart, although no one was injured.

Last month explorers at the team’s ice base some 680 miles further south reported a three-minute rain shower, which they described as a freak event.

The team is due to release preliminary results this September. The C$3 million ($2.9 million) expedition is sponsored by British insurer Catlin.

($1=$1.04 Canadian)