Mauritian ecosystems squeezed between climate extremes

This summer Henry Hooghiemstra, PhD student Erik de Boer and international 'Dodo-projectleader'  Kenneth Rijsdijk will set off for Mauritius. Their research expedition is seeking to explain how the island’s ecosystems survived climatologically unfavorable episodes in the past. Mauritian ecosystems experience wet conditions every 20,000 years, and dry conditions 10,000 years later. How have biomes survived these dramatic changes without being able to migrate from this small island? Lastly, the research will place the history of the dodo into a paleoclimatological context. What happened 4200 years ago in the coastal swamps of Mauritius, where mass graves containing dodos, turtles and other animals form a macabre testimony to an environmental accident?

2010 expedition

‘Following our expedition in 2008 we are returning to Mauritius this summer to drill new sediment cores. The last tiny remnants of original forest give important hints as to what this island must have looked like before the arrival of mankind. The natural vegetation left is degraded and is estimated to cover only 2% of the island. These last remnants are hidden between urban areas, tea plantations and endless fields of sugar cane. Once paleo-ecological studies have established what the original vegetation cover of Mauritius was like, restoration activities can begin and perhaps the Mauritian landscape can be upgraded and the country’s fragile economy boosted.’

Mauritian climate

The small Indian Ocean island of Mauritius has a special setting with respect to climate variability. Located at 20 degrees south the intertropical convergence zone (ITCZ) hits the island every 20,000 years, while the ITCZ is at more northern latitudes during the remaining part of this continuously repeating 20,000-year precession cycle. At low elevations in the tropics the precession cycle is a major driver of climate and environmental change. Consequently, Mauritian ecosystems experience their wettest conditions every 20,000 years, and their driest conditions 10,000 years later, when the ITCZ reaches its northernmost position.

Ecosystems squeezed between climate extremes every 10,000 years

Pollen records from the African and South American continents have shown that forests and savannas have migrated over distances of up to a thousand kilometers and more to keep in balance with migrating climate boundaries. But what happened on small oceanic islands, where biomes never had an opportunity to migrate? The surface area of Mauritius is about 40 x 60 km, and the 120-meter fall in sea levels during the last glacial maximum added only 20% to the land surface. How did wet biomes survive the dry millennia, and how did dry biomes survive the millennia with relatively high precipitation? Humidity is currently increasing, and the wettest phase in the precession cycle is only a few thousand years ahead. How can such islands keep their high levels of biodiversity when their ecosystems are squeezed between climate extremes every 10,000 years? Or does the warm Indian Ocean have a buffering effect on climate extremes?

History of the dodo

Lastly, the research will place the history of the dodo into a paleoclimatological context. What happened 4200 years ago in the Mauritian coastal swamps, where mass graves containing dodos, turtles and other animals form a macabre testimony to an environmental accident? The dodo’s distribution was limited to Mauritius and the bird seems to have escaped extinction 4200 years ago. However, the arrival of the Dutch on Mauritius in the 17^th century resulted in the endemic dodo becoming extinct within a very short period of time and the dodo is now the icon of extinction.

2008 expedition

‘In 2008 we conducted a pilot study and collected a 6 m-long sediment core in Tattos swamp. The lowermost part, which has been dated to 7000 years ago, shows the transition from a coastal palm forest into a possibly brackish environment, reflecting the effect of sea-level rise. We also collected a 10 m long core of peaty sediments in a volcano crater. Radiocarbon dating shows these sediments reflect the last 30,000 years of deposition history. For the first time we can now use a pollen diagram to get a glimpse of the dynamic history of the Mauritian ecosystems.’