Travel back in time 56 million years, and you'd arrive during a period of heightened volcanic activity on Earth. The activity triggered significant shifts in the planet's climate, effectively turning some parts of the far north into a tropical paradise.
The outpouring of carbon dioxide is one cause for this warming, but it seems there's more to the story. According to a new study, the volcanism plugged up the seaway between the Arctic and Atlantic, changing how the oceans' waters mixed.
While the Paleocene-Eocene Thermal Maximum (PETM) is a well-known event in the geological history of Earth, the remote area of northeast Greenland studied here hasn't been the subject of much geological research – even though it lies at a crucial point for volcanic activity and the flow of water between the Arctic and the Atlantic.
Through a combination of sedimentary analysis across hundreds of kilometers, the study of microfossils, and the charting of geological boundaries through seismic imaging, a team of researchers led by the Geological Survey of Denmark and Greenland (GEUS) found that an uplifting of the geology in the area at this time caused a level of fragmentation that more or less cut two major oceans off from one another.
"We found that volcanic activity and the resulting uplift of the edge of the Greenland continent 56 million years ago led to the formation of a new tropical landscape and narrowing of the seaway connecting the Atlantic and Arctic oceans," says paleontologist Milo Barham from Curtin University in Australia.
"So not only did the spike in volcanic activity produce an increase in greenhouse gases, but the restriction of the seaway also reduced the flow of water between the oceans, disturbing heat distribution and the acidity of the deeper ocean."
The uplift, created through a combination of tectonic plate movements and rock made from cooling lava, would have narrowed the seaway separating Greenland and Norway (which is much bigger than it used to be). Deep waters would have been transformed into shallow estuaries, rivers, and swamps.
Then as now, these ocean connections play a major role in shaping the circulation of winds and weather around the globe. In this case, the waters of the Arctic would have been almost entirely isolated from the waters of the Atlantic, compounding the warming that was already happening.
There was another consequence, though: more land meant more migration options for the flora and fauna of the area. The researchers think many animals may have taken advantage of the extra space to move to cooler locations.
"The volcanic surge also changed the shape of Earth's continents, creating land bridges or narrowed straits, and enabling crucial migration responses for mammalian species such as early primates, to survive climate change," says geologist Jussi Hovikoski from GEUS.
Fast forward to today: While we don't have molten lava extending the size of the continents, the oceans and the air currents that move above them are just as important in terms of managing the climate of the planet.
The current climate crisis means some of the crucial weather patterns that we've come to rely on are now starting to collapse. As and when they do, that will mean severe consequences for how the planet continues to cool down or warm up in the future.
Our current condition has drawn many comparisons with the PETM – a time when there were palm trees in the Arctic – and through understanding how the climate has shifted in the past, we should be able to better prepare for the future.
"Recent studies have reported alarming signs of weakening ocean circulation, such as the Gulf Stream, which is an ocean current important to global climate and this slowing may lead to climatic tipping points or irreversible changes to weather systems," says Barham.
"As fires and floods increasingly ravage our ever-warming planet, the frozen north of eastern Greenland would seem an unlikely place to yield insights into a greenhouse world. However, the geological record there provides crucial understanding of environmental and ecological responses to complex climate disturbances."
The research has been published in Communications Earth & Environment.