Iceberg Fleet Not to Blame for North Atlantic Cooling

A fleet of icebergs is probably not to blame for abrupt episodes of cooling in the North Atlantic over the past 440,000 years, according to new research.

Until now, it has long been suggested that these iceberg armadas may have caused cycles of abrupt climate change during the last glacial period by dumping loads of freshwater into the ocean and changing ocean currents.

But new findings by scientists at Cardiff University suggest the exact opposite: that icebergs were in fact the result of climate change, and not the cause of it.

Abrupt climate change, characterized by transitions between warm and cold conditions across the North Atlantic, is a universal feature of the Late Pleistocene - the most recent period of repeated glacial cycles. Scientists have long debated whether these extremely cold conditions were linked to the dispersal of icebergs that broke away from ice sheets bordering the North Atlantic.

But after retrieving a sediment core from the North East Atlantic, just south of Iceland, the Cardiff University team was able to construct records of changing surface ocean temperature and the movement of iceberg debris over the last 400,000 years, and has come up with an answer to this long-standing question.

"We found many examples of abrupt cooling events and many of these were paired with an increase in iceberg activity," Dr. Stephen Barker, who led the study, said in a news release. "However, crucially we found that in the majority of cases, icebergs appeared after cooling had occurred, meaning that icebergs arrived too late to have triggered cooling at this site - though [they] may have enhanced or prolonged these cold conditions."

"In fact," he added, "our findings imply that abrupt cooling events were preceded by intervals of more gradual cooling, suggesting that the descent into colder conditions should be considered as a non-linear response to a more gradual change across the North Atlantic."

These findings suggest that we still have much to learn about climate change, and that climate models should take into account these past changes if we are to better understand what the future may bring.

The results are described further in the journal Nature.

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