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OceansScience

Ancient Tides Are Sometimes Dramatically Different Than Today

Often thought to be one of the more stable processes on Earth, the rise and fall of the tides, have turned out to be as unpredictable as anything else, when considered over a longer time frame. This, from new research which suggests that shows how tides have changed dramatically over thousands of years.

“Scientists study past sea levels for a range of things, to learn about climate changes, geology, marine biology,” said David Hill, an associate professor in the School of Civil and Construction Engineering at Oregon State University. “In most of this research it was assumed that prehistoric tidal patterns were about the same as they are today. But they weren’t, and we need to do a better job of accounting for this.”

The research was published in the Journal of Geophysical Research, and was conducted by scientists from Oregon State University, the University of Leeds, University of Pennsylvania, University of Toronto, and Tulane University.

Phenomena such as ice ages, plate tectonics, land uplift, erosion, and sedimentation have all played their own part in changing how the tides react and work over a large period of time. Tides along the east coast of the United States of America have, at times, been drastically higher than they are today; a difference between low and high tide of 10 to 20 feet, compared to the current range of 3 to 6 feet.

According to Hill, one of the more interesting finds in their research was that, approximately 9,000 years ago, as Earth emerged from the most recent ice age, there was a massive increase amplification in tides of the western Atlantic Ocean, ranging up to three times more extreme that currently exist today.

One could imagine that, given the massive amounts of water that were locked in ice sheets in the northern and southern poles, a change in the tides would not be unexpected, but Hill says it’s not that easy.

“Part of what we found was that there are certain places on Earth where tidal energy gets dissipated at a disproportionately high rate, real hot spots of tidal action,” Hill said. “One of these today is Hudson Bay, and it’s helping to reduce tidal energies all over the rest of the Atlantic Ocean. But during the last ice age Hudson Bay was closed down and buried in ice, and that caused more extreme tides elsewhere.”

The researchers pointed to many other features which could affect tides, and noted that in understanding these factors and their impacts on the tides will allow a better understanding of past sea levels and ocean dynamics, which will continue to help in predicting the effects of sea level rise in the future.

“Understanding the past will help us better predict tidal changes in the future,” Hill said. “And there will be changes, even with modest sea level changes like one meter. In shallow waters like the Chesapeake Bay, that could cause significant shifts in tides, currents, salinity and even temperature.”

Source: Oregon State University
Image Source: NASA




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