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Where the Ice Age Caribou Ranged

Searching for prehistoric hunting grounds in an unlikely place

Monday, December 18, 2017

Caribou Hunters Herd


University of Michigan archaeologist John O’Shea was reading a book, some 10 years ago, about modern-day reindeer herders living in the Subarctic and some of the elaborate stone structures they use to manage their animals—usually called caribou in North America. O’Shea studies not only prehistoric cultures, but also nineteenth-century shipwrecks in the Great Lakes. That’s why at around the same time he was reading up on human interactions with reindeer, he was also examining new underwater topographical maps of Lake Huron. Those charts showed that a rocky underwater feature known as Six Mile Shoal was actually a continuous underwater ridge stretching 112 miles from northeastern Michigan to southern Ontario.


As O’Shea looked at the map and envisioned what this ridge might have looked like in the past, he realized that around the end of the last Ice Age, some 9,900 years ago, it would not have been submerged. Rather, it would have been a land bridge, with icy lakes on either side and the receding glacial ice sheet just a few hundred miles to the north. The ridge would probably have remained much colder than the mainland, offering a refuge in a slowly warming world for animals and vegetation adapted to very cold environments. Such isolated pockets of archaic ecosystems that endure after broad continent-wide climate shifts are known as refugia. O’Shea believed that during the end of the Ice Age, this land bridge could have been just such a refugium, preserving the frigid ecosystem that caribou thrive in even while the glacial ice sheet was in retreat. “It all came together for me—the fact that there was this geologic feature that would have been dry land 9,900 years ago that would still have had reindeer,” says O’Shea. And if herds of caribou had once migrated across this landscape, he reasoned, there were probably people hunting them. “I thought we could find signs of those hunters.”


Archaeologists have long suspected that since the Upper Midwest would have been an area attractive to these herds, the region’s prehistoric Ice Age inhabitants, known as Paleoindians, would have relied heavily on them. But evidence for this way of life has been scant.


Acidic soils around the Great Lakes break down bones quickly, making it difficult to find the remains of caribou—or of any ancient animal—in the region. Any stone hunting structures that may have existed were likely either knocked down by later settlers or are impossible to distinguish from walls and rock piles created by modern inhabitants. O’Shea thought that the ridge sitting beneath the waters of Lake Huron, now known as the Alpena-Amberley Ridge, could have acted as a time capsule. Though the lake is notoriously unpredictable and rough on the surface, its cold lower reaches are surprisingly calm, with gentle currents and 100 feet of visibility. O’Shea thought that some of the hunting structures that were destroyed in other parts of the Midwest might still persist on the submerged ridge, along with campsites, tools, and other remnants of the caribou hunters.


The idea, O’Shea admits, was a little bit wacky, but he thought his reasoning was sound even if locating the remains of that caribou hunting culture posed a daunting challenge. It would mean scanning hundreds of square miles of lake bed, 60 miles offshore. The chances of finding something as small as a campsite or hunting blind below the surface seemed remote. Furthermore, researching the ridge was a logistical nightmare, and meant signing up scuba-diving archaeologists, ROV operators, and boat pilots. It also meant sending researchers down 120 to 130 feet below the surface, the limit for divers using scuba gear, a depth at which they can only remain for short periods. Expectations for the project at the outset were kept low.