Alpena-Amberley land bridge reveals more evidence of prehistoric caribou hunting from 100 feet below the surface of Lake Huron

Dr. John O’Shea has a bottle of Scotch whiskey on the desk in his office, a gift from a colleague. The problem is, he’s not allowed to open it.

Not allowed, that is, until the colleague who gave it to him gives him the OK.

Since the summer of 2009, O’Shea, the curator of Great Lakes Archaeology in the Museum of Anthropology at the University of Michigan, has led a study of the Alpena-Amberley ridge, a 72-square mile post-Ice Age land bridge that once connected what is now Michigan’s northeastern Lower Peninsula near Alpena, with Point Clark in southwest Ontario about 9,000 years ago. Today, that ridge sits 100 feet below the water line at the bottom of Lake Huron.

In the 3-1/2 years his team has been studying the area, it has found compelling evidence that both caribou and mastodon used the ridge as a semi-annual migration path, and that humans, categorized as Paleoindian and Early Archaic hunters, devised ways to hunt and kill the animals on the ridge. But a skeptical colleague, that’s right, the one bearing the gift of Scotch, won’t be convinced until the group finds an arrowhead or a spearpoint, thereby in his mind confirming O’Shea’s theory.

“I want to be out there until I find that spearhead and I can open that bottle of Lagavulin,” O’Shea said with a laugh. “We’ve convinced a lot of skeptical critics that this probably is what was going on. The dates (carbon dating of wood poles found to be about 9,000 years old) are coming in, the simulation is working. Science is incremental, you’re always adding things together. But the pieces are falling together in a really nice way. So I’m very enthusiastic about this summer’s work that we will collect even more stuff.”

O’Shea has been a frequent visitor at the annual Great Lakes Shipwreck Festival, and once again spoke to a packed room, updating listeners on scientific findings in 2012.

On older nautical charts, the area including the ridge is labeled as the Six Fathom Shoal, and it once divided the Lake Huron basin into two distinct lakes, the largest of which is called Lake Stanley. Scientists believe the ridge exists because it is composed of limestones and dolomites, materials so hard that even the mighty glaciers that destroyed everything their path couldn’t cut into it.

While the ridge area includes the prehistoric Lake Stanley, Lake Chippewa, the forerunner to Lake Michigan sat to the west. Prior to the ice melt that eventually covered the Alpena-Amberly ridge, those two lakes did not connect at the Straits of Mackinac like they do today.

A computer rendering of the Alpena-Amberley land ridge, a 75-square mile ridge that once connected Michigan's Lower Peninsula to southwest Ontario. The green area represents the current water line of Lake Huron.

In years past, the team had found wooden poles, perhaps used to hang meat, that date to about 9,000 years ago. They found stone structures probably used as hunting blinds, caches or pits and “drive lanes” made by a linear path of rocks that would bring the animals close enough that hunters could attack them with spears and lances.

In 2012, the team discovered additional wood samples, potential fireplaces, charcoal, and in core samples flakeage or micro-debitage, stone microfragments made when chipping away at stone or rock to make tools, weapons or other implements. The microfragments are determined to be manmade since the way they are shaped couldn’t have happened naturally. The team is also transitioning from discovering artifacts to determining how the people of that time period lived.

Since it was during the post-Ice Age time period, the climate was milder than the Ice Age, but still bitterly cold with miserable conditions along the ridge. Those "warmer" conditions were comparably pleasant for the caribou and their thick hides. The subarctic tundra would have had developing grass areas, intermittent marshes and a scatter of coniferous trees, while the water’s edge would have provided various types of vegetation. The windy conditions would have given them relief from flies that bothered them during the warmer seasons. As for the hunters, the confined nature of the ridge would have provided a substantial element of predictability regarding herd movement which would have been of great value to them.

“These people probably lived in the Lower Peninsula, closer to the middle of the modern-day lake since the lakes were so much shallower then,” O’Shea said. “They probably only came out to the ridge to hunt. Maybe they would come out by sled in the winter to retrieve the meat that had been cached from the fall hunt.”

While many of the hunting blinds at the bottom of Lake Huron are set up to attack caribou moving in both migrational directions (southeast in the autumn to rut and northwest in the spring to calve) some are V-shaped, giving the impression that they would work for movement in only one direction. Based upon which direction they are facing, scientists can determine whether they were used for fall or spring migration. In addition, some blinds are minimal, suggesting their location didn’t work, while other blinds are more extensive and updated, indicating they are in better locations and fortified to allow for more hunters.

“A number of the structures are located on high ground at the break of the crest of a hill, so that the animals coming up the hill don’t really see (the hunters) until they are upon them,” O’Shea said. “They did things that make a lot of sense to a modern hunter’s eye.”

As for the final smoking guns, such as large pieces of bone or spear or arrowheads that would remove all doubt of hunting activity on the ridge, O’Shea said large or macro bone pieces almost certainly have dissolved over time. The microbone fragments that have been found were discovered in core drilling samples. Larger pieces of bone would only be found in holes or caches within the limestone.

The spear or arrowheads are still on the agenda and will hopefully be discovered, if only so O’Shea can uncork his whiskey. 

When asked if his team has made enough discoveries to certainly prove the existence of hunting on the ridge, his answer is one you may expect of a scientist.

“We’ve gone a long way towards ‘certainly,’ but I wouldn’t say absolutely … yet,” he said.

This summer, O’Shea’s team has plans to look for additional campsites, devise better means of collecting bulk sediment samples and search for cultural debris, expand the search to natural migration choke points and expand acoustic coverage.