Study provides new look at ancient coastline, pathway for early Americans

August 27, 2014, Oregon State University

The first humans who ventured into North America crossed a land bridge from Asia that is now submerged beneath the Bering Sea, and then may have traveled down the West Coast to occupy sites in Oregon and elsewhere as long as 14,000 to 15,000 years ago.

Now a new study has found that the West Coast of North America may have looked vastly different than scientists previously thought, which has implications for understanding how these early Americans made this trek.

The key to this new look at the West Coast landscape is a fresh approach to the region's sea level history over the last several thousand years. Following the peak of the last ice age about 21,000 years ago, the large began to retreat, causing sea levels to rise by an average of about 430 feet. When the ice was prominent and sea levels were lower, large expanses of the continental shelf that today are submerged were then exposed.

As the melting progressed and sea levels rose, likely archaeological sites along the coast were submerged.

Most past models have assumed that as the massive North American ice sheets melted, rose in concert – a phenomenon known as "the bathtub model." But the authors of this new study, which was just published in the Journal of Archaeological Science, say does not happen uniformly.

"During the last deglaciation, sea level rise was significantly influenced by the weight of the large ice sheets, which depressed the land under and near the ice sheets," said Jorie Clark, a courtesy professor at Oregon State University and lead author on the study. "As the ice sheets melted, this land began to rise. At the same time, the weight of the water melting from the ice sheets and returning to the oceans also depressed the ocean basins.

"This exchange of mass between ice sheets and oceans led to significant differences in sea level at any given location from the assumption of a uniform change," she added.

The implications of this new approach are significant. The researchers ran models of what the sea level may have looked like over the last 20,000 years – based on knowledge of dimensions and the topography of the ocean floor – and concluded that parts of the West Coast looked radically different than previous reconstructions based on a model of uniform sea level rise.

The central Oregon shelf, for example, was thought to be characterized by a series of small islands some 14,000 years ago. However, the models run by Clark and her colleagues suggest that much of the continental shelf was exposed as a solid land mass, creating an extensive coastline. In some areas, the change in estimated sea level may have been as much as 100 feet.

"There has been new evidence that the peopling of the Americas happened earlier than was long thought to be the case, which has put a lot of focus on coastal paleogeography," said Clark, who is in OSU's College of Earth, Ocean, and Atmospheric Sciences. "This new look at changes helps explain how that earlier introduction into the Americas could be possible."

"It is also important for predicting where coastal villages that are now submerged on the may be located."

Explore further: Antarctica could raise sea level faster than previously thought

Related Stories

Flow of research on ice sheets helps answer climate questions

February 16, 2013

Just as ice sheets slide slowly and steadily into the ocean, researchers are returning from each trip to the Arctic and Antarctic with more data about climate change, including information that will help improve current models ...

Recommended for you

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...


Adjust slider to filter visible comments by rank

Display comments: newest first

2 / 5 (4) Aug 27, 2014
Huh. So global warming may not cause sea levels to rise as much as predicted?
4.2 / 5 (5) Aug 27, 2014
The very earliest of the many Bering Land Bridges expired at about 35Ky BP. There is good evidence of New World humans at Pedra Furada, Piauí, Brazil, 55Ky BP, here glossed and dismissed too easily.

Citations? Links?
4.3 / 5 (6) Aug 27, 2014
The very earliest of the many Bering Land Bridges expired at about 35Ky BP. There is good evidence of New World humans at Pedra Furada, Piauí, Brazil, 55Ky BP, here glossed and dismissed too easily.

I can only guess that you didn't include a link because the subject is controversial. If the findings can be verified I'll applaud the research but it's not there yet.
4.4 / 5 (7) Aug 27, 2014
Sorry, apparent brother in arms, that's not how science works, by validation/verification. Falsification is a much surer path to truth. I assert, you falsify.

You and I aren't doing science here, we are commenting on a science article. You made a statement followed by an opinion. The onus is on you.
4.2 / 5 (5) Aug 27, 2014
You provided no evidence to support your statement, you have to provide actual evidence (not opinion) before you can challenge anyone to disprove your statement.
You prove then others try to disprove.
5 / 5 (3) Aug 28, 2014
@Ghost - This doesn't change the estimate of the AVERAGE rise in sea level from a given amount of land-based ice melting.
What it does is to highlight that the rise might be quite uneven.

There are two major contributors to this - the weight of the ice depressing the land on which it rests, and the land surrounding that as well, and also the gravitational attraction from the mass of the ice (a surprisingly big factor). Both hold more water near the ice, lowering sea levels away from the ice more than the volume of water in the ice alone would, while correspondingly decreasing the change (relative to the coastline) near the ice.

Both factors are reversed when the ice melts, the gravitational factor as rapidly as the ice melts, and the rock rebounding over the course of thousands of years thereafter.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.