In 2009 and 2010, there were several unexplained flooding events and unusually high tides along the east coast. This is where it gets weird. Researchers couldn’t explain it easily. There were no hurricanes. No major storm systems. Yet, the water kept rising along the shore from Cape Hatteras to Canada.

A new study has just been released and says changes in ocean circulation and winds are the culprit.

Co-author Jianjun Yin, an assistant professor of geosciences, said, “We are the first to establish the extreme sea level rise event and its connection with ocean circulation.”

First author Paul Goddard and his colleagues poured over decades of monthly tide-gauge records for the entire eastern coast. Only 2009 and 2010 showed such a massive increase in water levels.

“The thing that stands out is the time extent of this event as well as the spatial extent of the event,” said Goddard.

The team of researchers linked the jump in water levels to a change in the ocean’s Atlantic Meridional Overturning Circulation (AMOC) and changes in the North Atlantic Oscillation.

What kind of increase in water levels were seen? Sea levels between New York and Newfoundland saw a rise of four inches on average. Sea levels between Cape Hatteras and New York also saw increases, but not as much.

“The sea level rise of 2009-10 sticks out like a sore thumb for the Northeast,” said Goddard.

Ok, so what could cause just a portion of the east coast to see a rise in sea levels? I mentioned the Atlantic Meridional Overturning Circulation above. According to researchers, warmer temperatures in the North Atlantic’s Labrador Sea caused the strength of the AMOC to drop as much as 30%. This current brings warm water from the tropics to the North Atlantic. This water then cools and sinks before flowing back south in the deep ocean.

Goddard explained LiveScience what happens when the current weakens. “The anomalous heat made the surface waters less dense and less likely to sink, and it created a bottleneck.”

Winds also played a role in the higher water levels. A negative phase in the North Atlantic Oscillation caused winds to drive water into the northeast coast.

Imagine a hurricane’s storm surge, but a lot weaker and a broader scale.

According to Yin, further weakening of the AMOC is expected due to global warming.

Check out the full study here.

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