The Roaring Forties and Furious Fifties are strong winds that encircle Antarctica. They are almost unimpeded by land except for the tip of South America and the southern end of New Zealand’s South Island.
These winds play a major role in Earth’s climate, helping to regulate the carbon dioxide exchange between the deep ocean and atmosphere, and influencing rainfall, temperature and sea ice extent in the Southern Hemisphere. Now scientists have uncovered a 17,000-year history of these shifting winds, sitting at the bottom of a New Zealand lake bed.
Last year, Gavin Dunbar and colleagues from Victoria University of Wellington in New Zealand drilled deep into the sediments underlying Lake Ohau – a lake that lies to the east of New Zealand’s Southern Alps, and underneath the path of the Roaring Forties.
In recent decades, growth of the ozone hole has forced the winds to shift southwards, resulting in summer rains decreasing by as much as 40% in southern New Zealand. This is reflected in the lake sediments, which accumulate when heavy rains wash them down the slopes of the nearby mountains.
The scientists extracted 80m of layered sediments, and radiocarbon dated twigs and leaves in the sediment to reveal 17,000 years of climate history.
Using data they had gathered over the last seven years, Dunbar and his colleagues were able to calibrate the sediment layers and recognise the difference between dry summers (millimetre scale couplets of fine silt) and flood events (centimetre thick silt layers). Their findings are published in Earth & Space Science News.
Now the scientists are working through the sediments layer by layer, listening to the howling of ancient winds.
