Sediment cores retrieved from the Arctic’s deep-sea floor by the Integrated Ocean Drilling Program’s Arctic Coring Expedition (ACEX) report that the Arctic Ocean changed from a landlocked body of water (a ‘lake stage’) through a poorly oxygenated ‘estuarine sea’ phase to a fully oxygenated ocean at 17.5 million years ago during the latter part of the early Miocene era.

The authors attribute the change in Arctic conditions to the evolution of the Fram Strait into a wider, deeper passageway that allowed an inflow of saline North Atlantic water into the Arctic Ocean. Scientists believe that the deep-water connection between the northern Atlantic and Arctic Oceans is a key driver of global ocean circulation patterns and global climate change.

Arctic Coring Expedition - ACEX

In 2004, the offshore ACEX research team cored a 428-meter thick sediment sequence from the crest of the Lomonosov ridge in the central Arctic Ocean, near the North Pole. These sediments provide the first geological validation of the Cenezoic paleoenvironmental history of the Arctic Ocean. Current evidence of the onset of the ventilated circulation system is preserved in the chemical and physical properties and the micropaleontology of the recovered seafloor sediments.

Co-chief scientist Jan Backman, Stockholm University, comments on the significance of the new findings, saying, “If we can learn what has happened in the geological past, we can begin to use that knowledge to look into the future. Scientists engaged in climate change studies are advancing an important area of knowledge about the planet we live on.”

Why drill arctic sediment cores?

Geological evidence from about 45-55 million years ago, such as alligator fossils from the Canadian Arctic suggests that the Arctic once was relatively warm and ice-free. Today, the Arctic Ocean is the only ocean that's always ice-covered. Scientists of the Arctic Coring Expedition (ACEX) intend to discover when this change from hothouse to icehouse occurred.

Interestingly, recent observations suggest a return to the warmer conditions of ancient times. Over the past 30 years, scientists have documented a thinning of the ice; from an average of roughly 3.1 to 1.8 metre. The area covered by ice has receded by 5 percent; roughly the size of France and Germany combined.

The Arctic plays a fundamental role in the global climate system. The sea ice and Greenland`s ice cap reflect part of the sun's energy back into space, influencing the temperature distribution and reducing the amount of absorbed heat. The Arctic is also a driving force in global ocean circulation.

A large-scale ocean circulation, know as the "global conveyor belt", redistributes heat over the planet. With continued global warming, and melting of Arctic ice, this heat conveyor may begin to falter, decreasing the flow of warm water to Europe and thereby cooling its climate.

The authors of the newly released study include Martin Jakobsson (Stockholm University), Jan Backman (Stockholm University), Bert Rudels (Finnish Institute of Marine Research), Jonas Nycander (Stockholm University), Martin Frank (Leibniz Institute of Marine Sciences, IFM-GEOMAR), Larry Mayer (University of New Hampshire), Wilfried Jokat (Alfred Wegener Institute for Polar and Marine Research), Francesca Sangiorgi (Utrecht University), Matther O’Regan (University of Rhode Island), Henk Brinkhuis (Utrecht Univesity), John King (University of Rhode Island) and Kathryn Moran (University of Rhode Island).

Source: ACEX