A 12,000-Year-Old Loss Still Stings

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Elephants still play a pre-Ice-Age role of carrying nutrients around the landscape in Langoue Bai, Ivindo National forest, Gabon. Credit: Sam Moore

Most of us stopped grieving over the loss of giants sloths and armadillo-like glyptodonts and other megafauna of the last ice age a few days after we picked the last bits of their flesh from our teeth some 12,000 years ago. But the Earth is still recovering from the loss, according to a new study of soils in Amazonia, where many of the giant beasts lived.

When those big South American plant eaters died off, they appear to have taken with them a key method for spreading certain nutrients over Amazonia. Their disappearance could even account for why phosphorus, an important soil nutrient, is so scarce in the Amazon basin today, according to new paper in the August 11 edition of the journal Nature Geoscience.

Researchers at Oxford and Princeton universities used a new mathematical model to study how the dung and corpses of those large beasts spread laterally through the landscape and discovered that they play a disproportionately large role in carrying nutrients around.

“For example, we estimate that the extinction of the Amazonian megafauna decreased the lateral flux of the limiting nutrient phosphorus by more than 98 percent, with similar, though less extreme, decreases in all continents outside of Africa,” wrote Christopher Doughty and his colleagues.

This resulted in strong decreases in phosphorus in eastern Amazonia, away from the fertile floodplains.

What’s more, that decline may be continuing today. The low phosphorus levels in Amazon basin soils could be at least partially a relic of a past ecosystem.

“We argue that the Pleistocene megafauna extinctions resulted in large and ongoing disruptions to terrestrial biogeochemical cycling at continental scales,” they wrote. “To the extent humans contributed to the megafaunal extinctions, this suggests that major human impacts on global biogeochemical cycles stretch back to well before the dawn of agriculture.”

In other words, the patterns of soils we see today — usually considered to be created by geological forces — may have been partially created by our own ancestors. And so thickens the anthropogenic global change plot.