The last surviving woolly mammoths were driven onto small islands by rising sea levels after the last ice age, where they eventually died out due to a lack of fresh water.

Glacier melt caused rising sea levels and corralled the remnant mammoths onto small islands, where they survived for thousands of years before going extinct. Now scientists have discovered evidence that a mammoth population on a Bering Sea island near Alaska died out due to a lack of clean fresh water.

Woolly Mammoths
Image source: Wikimedia Commons

Study explains how remnant woolly mammoths died off

The new study, which was published in the Proceedings of the National Academy of Sciences, used chemical analysis of lake sediment to recreate the conditions around the time that the remnant woolly mammoths went extinct. Samples were taken from a lake on St. Paul island, off Western Alaska, to be studied.

This particular woolly mammoth population survived until approximately 5,600 years ago, whereas most other populations in North America and Eurasia died off 5,000 years earlier. Despite sheltering on the isolated island, the woolly mammoths struggled as seawater levels rose and caused the climate to become warmer and drier.

The study, which was undertaken by a large team of scientists from around the world, reveals how the mammoths suffered as freshwater supplies dwindled.

“Freshwater resources look like the smoking gun for what pushed them into this untenable situation,” study co-author Matthew Wooller, director of the Alaska Stable Isotope Facility at the University of Alaska Fairbanks, said in a statement released by UAF.

Lake Hill provides sediment sample for analysis

The sediment core sample was taken from Lake Hill, on St. Paul island, in March 2013. Scientists were able to show that freshwater became scarce around 7,850 to 5,600 years ago by analyzing magnetic qualities, oxygen isotopes and remains of tiny aquatic creatures. The team also ran isotope analysis on mammoth bones and teeth to show that the creatures were suffering as conditions became drier.

According to study lead author and Penn State University paleontologist Russ Graham, dehydration and heat stress were likely responsible for killing off the remnant mammoths. He believes that the animals needed to consume large amounts of water in order to cool their bodies, and they were unable to move to areas with more water supplies as they were trapped on the island.

“This would have been particularly hard for woolly mammoths because they have evolved adaptations like specific hair types to keep them warm in the cold climates. This would have been a maladaptation for warmer climates,” he said.

Increasing mineral concentration

Falling water levels would have made for cloudier and dirtier water in the lakes. These are conditions that modern elephants avoid. Evaporation would also have meant that mineral concentrations rose in the remaining water.

“In essence the lake water was becoming more saline — although not as a result of mixing with ocean water but rather as a result of concentrating of minerals in the lake as lake levels dropped,” he said in an email.

According to the study the mammoths may have accelerated their extinction by digging mini lakeside wells. This would have stripped the edge of the lakes of plant cover and encouraged erosion that then led to decreased water quality.

Freshwater scarcity most likely reason for woolly mammoth extinction

Scientists say that it was unlikely that hunting led to the extinction of the St. Paul’s remnant woolly mammoth. Evidence suggests that the first human habitation of St. Paul Island came in the late 18th century, while predation from polar bears has also been ruled out as the oldest bear remains date from 1,000 years later than the last mammoth remains.

Another theory is that increased snowpack caused extinction, but that does not fit with the isotope analysis of sediments from the lakebed. Volcanic eruptions have also been discounted, as have changing vegetation types.

This means that scarcity of freshwater is the likeliest reason. The researchers claim that the St. Paul mammoths provide a cautionary tale about climate change today, with a focus on the vulnerability of island populations.

Graham said that the study “underscores the need to pay particular attention to islands in an environmentally changing world.” Some South Pacific islands are facing shortages of freshwater already.

Woolly mammoths found refuge on St. Paul island as well as other islands like Wrangel Island in Russia. Paleontological evidence shows that mammoths lived there until 3,700 years ago.

The extinction of the Wrangel mammoths is still under investigation, but recent research suggests that inbreeding due to isolation may have been a contributing factor.