Using Driftwood to Retrace 10,000 Years of Arctic Sea Ice History
10.08.2011 - Water & Oceans, Ice & Snow, Arctic
Scientists from the Centre for Geogenetics at the University of Copenhagen have recently designed a method to measure the variations in the ice ten millennia back in time using carbon-14 dating of driftwood. Published in the journal Science, the findings of their research indicate that over the past 10,000 years, summer sea ice in the Arctic has known many variations; at times it was less than half of its current extent.
To draw their conclusions, twhich were published in the journal Science, the team of scientists mostly based themselves on driftwood they gathered along the coast of northern Greenland, the last place where summer ice is expected to survive as temperatures increase in the Arctic. The driftwood they dated had been embedded in the sea ice when it originally froze, eventually reaching Greenland as the ice floe moved it. The amount of driftwood in the ice determines the amount of multilayer sea ice there was at the time it was frozen in the ice.
The team found differing varieties of driftwood. The two dominant varieties they found were spruce, which is widespread in the boreal forests of North America, and larch, which dominates the Siberian taiga. The discovery of driftwood form different types of trees from different regions of the Arctic indicate that travel routes, currents, and wind conditions in the ocean have varied over time.
The team also examined the beach ridges along the Greenland coast. It is impossible for such beach ridges cannot be formed today due to perennial ice cover; however they could in the past when sea ice cover was lower. The scientists mapped the long rows of beach ridges over 500 km of the current shoreline. Using carbon-14 dating, the team was able to determine that during the Holocene Maximum, a warm period which lasted from about 8,000 until 5,000 years ago, there was more open water and less coastal ice than today.
The study clearly shows that there are great natural variations in the amount of Arctic sea ice; it also shows the clear connection between temperature and the amount of sea ice. The changes in sea ice are most often caused by the impact changing temperatures have on the prevailing wind system.
The team’s findings also indicated that even if current sea ice cover drops to less than 50% of the current sea ice extent, which reached a record minimum in September 2007, sea ice is not likely to reach a “point of no return” beyond which sea ice will not be able to grow back once cooler temperatures return.
The study is also useful for studying how polar bears were able to survive during the warmer Holocene Maximum.