It's hard to imagine, but about 55 million years ago, Antarctica was ice-free and full of lush forests. Now analysis of ancient pollen has revealed when the last Antarctic vegetation died out...and what's next for the continents's vast ice sheets.
The ice sheets that now completely engulf the frozen continent began forming about 38 million years ago, as Earth entered a long period of global cooling. It took 26 million years for the glaciers to cover the continent, as we now know that tundra vegetation survived on Antarctica's northern peninsula until 12 million years ago.
That peninsula is of interest to climate scientists today because it's one of the regions most severely affected by climate change. While global temperatures have generally been on the rise in recent decades, the northern peninsula has seen temperatures rise at six times the worldwide average. As such, it's useful to know just how that fits in with Antarctica's larger climatic history. Are such rapid changes common in the continent's past?
To find the answer, researchers from Rice and Louisiana State began drilling for pollen samples from frozen sediments, which allowed them to reconstruct the last 36 million years worth of Antarctica's climate history. It's taken them nearly a decade to plan the expeditions, find the samples, and analyze them, but now we have the results.
As LSU geologist Sophie Warny explains, it looks like the recent climate spike in the northern peninsula is far from normal:
"There's a longstanding debate about how rapidly glaciation progressed in Antarctica. We found that the fossil record was unambiguous; glacial expansion in the Antarctic Peninsula was a long, gradual process that was influenced by atmospheric, tectonic and oceanographic changes. The pollen record in the sedimentary layers was beautiful, both in its richness and depth. It allowed us to construct a detailed picture of the rapid decline of the forests during the late Eocene — about 35 million years ago — and the widespread glaciation that took place in the middle Miocene — about 13 million years ago."
The research has allowed us to fill in some vital blanks in the history of the continent - most notably when the last vegetation was swallowed up by glaciers - and it can also be useful moving forward as we try to contextualize the current warming ice sheets. Rice marine geologist John Anderson sums it up:
[This research] gave us the first reliable age constraints on the timing of ice sheet advance across the northern peninsula. The rich mosaic of organic and geologic material that we found in the sedimentary record has given us a much clearer picture of the climatic history of the Antarctic Peninsula. This type of record is invaluable as we struggle to place in context the rapid changes that we see taking place in the peninsula today."