How did Antarctica come to be a barren, treeless land of ice? Once carpeted with flowers and forests, today it’s a frozen desert, good only for mosses, lichens and a few hardy species of grass. So what happened? Scientists drilling off the Antarctic Peninsula – the last refuge for plants as temperatures fell – have tracked its chilling story.
When Captain Scott and his team perished in 1912, they’d lost the race for the South Pole by five weeks, but their deaths were not entirely in vain. Because packed into their sledges were several pounds of rock collected by team doctor Edward Wilson. Among the samples were the fossilised remains of ancient leaves – the very first clues that Antarctica wasn’t always so harsh.
A century on, and scientists are still using fossil fragments to piece together Antarctica’s climate history, though the technology has come a long way from knocking off bits of rock with a hammer. Sixteen researchers, led by Dr John Anderson of Rice University, Houston, commissioned the RV Nathaniel B. Palmer – 94 metres of state-of-the-art research ship named after the first American to lay eyes on Antarctica.
During four cruises along the Antarctic Peninsula’s coast, the team drilled the sea floor for ancient sediments. The fossil pollen they found among the mud and grit has offered the clearest picture yet of which plant species were present and when they met their frosty demise.
Results published this week in Proceedings of the National Academy of Sciences, reveal that 37 million years ago, flowers, ferns and forests of southern beech enjoyed mean annual temperatures of 10.8°C – similar to Southern Patagonia today. But it wasn’t to last. Falling atmospheric carbon dioxide levels cooled the climate and mountain glaciers began to form.
By around 23 million years ago, conditions were getting tough. The flowers and ferns were gone and the southern beech was giving way to pine and low, shrubby tundra plants.
The final switch from Alpine-type conditions to the vast ice sheets we see today came at around 12 million years ago, killing off even the hardiest of tundra species.
While researchers blame falling atmospheric CO2 levels for the initial cooling, they believe Antarctica’s deep chill comes from being cut off from the rest of the world.
50 million years ago, Antarctica was joined to both South America and Australia, but since then tectonic processes have ripped the continents apart, allowing the frigid current that endlessly circles Antarctica to gain strength and block warmer currents from the Tropics.
However, the Antarctic Peninsula has warmed by 3°C since 1950, and with climate change predicted to raise temperatures further, could we see life returning to Antarctica’s frostbitten finger?