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Volcanoes Sheltered Life through Ice Ages

Mount Erebus is perhaps the most well-known volcano in Antarctica, and is one of the large volcanoes that may have sheltered life through past ice ages. Photo: Steven Chown

Mount Erebus is perhaps the most well-known volcano in Antarctica, and is one of the large volcanoes that may have sheltered life through past ice ages. Photo: Steven Chown

By Ceridwen Fraser

Researchers studying the diversity of life in Antarctica have found surprising evidence that many plants and animals survived past ice ages by huddling close to warm volcanoes.

As the Earth enters an ice age and the polar ice caps expand, many plants and animals move away from the poles towards the Equator. Then, as the world warms and the polar ice caps shrink, species move back towards the poles.

Increasingly, however, we’re seeing evidence from genetics and fossil pollen that many species must actually have survived within the ice-covered regions around the Arctic and Antarctic. How could species that need ice-free land to live manage to survive within regions covered by massive glaciers?

Do Hot Rocks Make Ice-Free Oases?

There are hundreds of volcanoes in the world, as well as “hot rocks” heated by radiogenic decay, which occurs when unstable isotopes of some elements change into other elements, emitting heat. Both volcanic and radiogenic heat are forms of geothermal energy.

If you climb into a car in the middle of a cold winter there’s a good chance you won’t be able to see through the windscreen because it will be covered with ice. One way to get rid of ice on a windscreen is to heat the glass by blowing hot air from the car engine across it. The warmth of the glass melts the ice, and a quick swipe with the wipers allows you to see the road again.

In much the same way, warm rocks on the surface of the planet might be able to keep some areas ice-free. Where glaciers tower hundreds of metres above the land, geothermal heat may even melt enough ice to make relatively warm, ice-free habitats – oases for plants and animals during ice ages.

Volcanoes and hot rocks may explain the persistence of diverse life in glaciated regions. Geothermal heat may even explain the survival of life at times when ice covered almost all of the planet.

Isolated Antarctica

Antarctica is a great place to study geothermal Ice Age refuges. Unlike the Northern Hemisphere, which has a lot of land at high

(sub-polar) latitudes, the southern polar region is surrounded by a large ocean that few species are able to cross. Species that can’t swim or fly long distances generally have not managed to get to Antarctica since the last Ice Age because their dispersal has been blocked by the Southern Ocean.

Antarctica is 99.7% covered in ice today. At the peak of the last Ice Age, about 20,000 years ago, Antarctica was even icier, with huge glaciers extending offshore, in some places right to the edge of the continental shelf.

Yet many species found in Antarctica – such as mosses, lichens and invertebrate animals like mites and worms – have been there for millions of years. We know this because, firstly, Antarctic populations of many species show striking genetic differences to populations elsewhere, indicating that they have evolved independently for millions of years. Secondly, some species are found in Antarctica and nowhere else, so they must have survived on the continent throughout past ice ages. For example, about 60% of Antarctic invertebrate species are not found anywhere else in the world.

Antarctic Terrestrial Life

When most people think of Antarctica they think of large, charismatic animals such as penguins, seals and albatrosses. These animals are all very good at long-distance travel – they have no trouble crossing oceans, so ice ages might not have been a big problem for them. As the Earth entered an ice age, they could travel north to find ice-free land to breed, and they could then come back to Antarctica in warmer times.

However, most of Antarctica’s terrestrial diversity is found in much smaller organisms. Mosses are very common in Antarctica as they don’t have the complex internal plumbing systems that vascular plants (such as flowering plants) have. Just as water pipes on a cold night can freeze and break, causing leaks in your house, vascular plants struggle in very cold areas.

Mosses are much better at weathering deep freezes than vascular plants. In fact, some Antarctic mosses can survive being frozen for more than 1000 years. Some lichens can also survive extremely cold temperatures (down to –196°C) and live for hundreds of years. There are many lichen species in Antarctica.

Hundreds of species of invertebrate animals thrive on the southern continent – mites, nematode worms, springtails and other insect-like animals, many of which are found in the tiny, lush “forests” of moss.

For most of these small plants and animals, crossing an ocean is an enormous challenge. So, as the Earth entered an ice age, heading north to other lands would not have been an option for many species. Without shelter on the continent they would face extinction.

Hot Spots in the Freezer

Antarctica has many active volcanoes, and at least 16 have been active since the coldest part of the last Ice Age. Some of these volcanoes have large magma chambers where molten lava roils for thousands – and even hundreds of thousands – of years. These large, long-lived volcanoes could have provided heat to the surface throughout many glacial/interglacial cycles.

Some volcanoes in Antarctica also have extensive cave systems around them, formed by warm steam hollowing out areas between the glacial ice and the rocky land. Inside these caves, the temperature can be tens of degrees warmer than outside, and light can flood in near the entrances. Such caves, as well as ice-free areas of land such as steam fields around volcanoes, might have been great places for species to hang out during ice ages.

To test the idea that hot rocks might have allowed species to survive in icy regions, Dr Aleks Terauds of the Australian Antarctic Division and I led a team of researchers from Australia and England that looked at biodiversity patterns in Antarctica. We analysed more than 30,000 records of more than 1300 species of plants, fungi and invertebrate animals collected by hundreds of researchers over decades of scientific work in Antarctica to see if patterns of diversity were related to the locations of volcanoes.

If volcanic and other geothermal areas really did shelter life through past ice ages, then these areas should still have the highest diversity of life. This is because dispersal to new regions depends on rare, chance events.

So, if one volcano had 100 species sheltering on it, and some new land became available nearby, some species might eventually be able to get to the new patch by being carried by birds or blown by strong winds. However, it would be very unlikely that all species would reach the new patch. If a third patch appeared even further away, the same process would occur, with some but not all species from the original and/or the second patch getting over to the third patch. The resulting pattern is a decline in diversity away from the refuges where species survived.

Similar diversity patterns have previously been used in studies of hundreds of different species in the Northern Hemisphere to work out in which regions they might have survived past ice ages, but nobody had yet used this method to test whether volcanoes might be ice age refuges.

Excitingly, we found a strong decrease in diversity (number of species) with distance from volcanoes in Antarctica – especially for plants – providing strong support for our hypothesis that volcanoes could have sheltered diverse life through ice ages.

Could Species Have Survived Some Other Way?

Volcanoes provide a neat solution to the mystery of how life could have survived in Antarctica through past ice ages, but some species might also have survived in other ways.

Nunataks are rocky outcrops sticking up through glaciers, where the rock is too steep or too high for the ice to cover it. Nunataks are often high up on mountains, harbouring species that are quite different to those found lower down and closer to the coast. However, they might help to explain the survival of some species – especially hardy organisms such as alpine lichens – through past ice ages.

Some parts of the McMurdo Dry Valleys in Antarctica are also thought to have been ice-free during the last ice age, and some local plants and animals may have survived there. These other sorts of refuges can only solve part of the puzzle, explaining the survival of some but not all species.

In contrast, volcanoes and other geothermal regions could explain the survival of a great many species across large parts of the continent. It seems these warm giants, despite their reputation for destruction, have nurtured life through some of its most challenging times.

Are Volcanoes Only Important in Antarctica?

We now have good evidence that volcanoes helped Antarctic species to survive ice ages, but does this apply to other regions and other times?

During the last ice age, glaciers covered huge parts of land in the Northern Hemisphere, as well as in southern South America (Patagonia), New Zealand and even central Tasmania. If geo­thermal heat melted patches of ice in Antarctica, and allowed species to survive among thick glaciers, similar refuges could have existed in other glaciated areas, allowing plants and animals that could not move away from the growing glaciers to survive. These warm oases might still be important for maintaining diverse life in cold places such as Greenland.

Hundreds of millions of years ago, before plants and animals moved out of the water onto the land, some extreme ice ages are thought to have completely frozen the surface of the planet, covering all land and sea with ice. These are known as the “Snowball Earth” periods. Life existed before Snowball Earth, and similar life existed afterwards.

But how could life have survived if thick ice covered the planet, stopping sunlight from reaching the photosynthetic organisms in the sea? Geothermal refuges could have been important during these times, melting patches of sea ice and allowing life to cling on.

What Next?

The next step in this research is to use genetic data to see if we observe the same sorts of diversity patterns within species as we do between species. I have now received funding for this genetic work, and hope to travel to Antarctica in 2015 to collect more samples, as well as using samples in existing collections in Australia and Britain. Future research can also start to assess the importance of these geothermal refuges in other parts of the world.

These findings are only the beginning of an exciting research program on geothermal refuges. Indeed, we may soon need to reconsider our image of volcanoes – they may be the guardians, not the destroyers, of life on Earth.

Ceridwen Fraser is a Lecturer in the Australian National University’s Fenner School of Environment and Society.