Skip to content

Study finds new deep sea waves affecting mixing of warm and cool water, turbulence affects climate models-Geophysical Research Letters

September 11, 2013

9/11/13, “800 feet tall deep sea waves discovered in Pacific Ocean, UK Telegraph, Richard Gray

Researchers found the waves, which are also known as internal waves, form at the boundary between two layers of water with different densities in a deep ocean trench in the South Pacific Ocean. The waves rise up due to ridges on the ocean floor of a narrow channel to the north west of Samoa that forces cold, saltier water to rise up into the warmer water above.

These form 800 foot waves that rear up and then plunge hundreds of feet down into the dense water on the other side of the sill. However, each wave takes around an hour to break.

So while it might never be possible for surfers to ride these enormous waves, the

Professor Matthew Alford, an oceanographer at the University of Washington who led an expedition to the channel, known as the Samoan Passage, said:

Oceanographers used to talk about the so-called ‘dark mixing’ problem, where they knew that there should be a certain amount of turbulence in the deep ocean, and yet every time they made a measurement they observed a tenth of that.

“We found there are loads and loads of turbulence in the Samoan Passage, and detailed measurements show it’s due to breaking waves.” The findings are published in the journal Geophysical Research Letters.

The layers of water form because dense cold water in Antarctica sinks into the deep Pacific Ocean and is forced through a 25 mile gap north east of Samoa.

Around six million cubic metres of water pass through the gap every second – around the same as 35 Amazon Rivers.

Dr Alford and his team lowered specially designed “wave chaser” instruments three miles to the seabed and took measurements over thirty hour periods

  • of the turbulence at the boundary between the cold dense water and warmer water above.

They found that as the dense bottom layer of water flows over two consecutive ridges in the Samoan Passage, it causes them to form lee waves, like air rising over a mountain.

These become unstable and break,

Professor Alford said this helps to explain why dense cold water does not permanently pool at the bottom of the ocean.

The waves may also play a role in stimulating global currents. They believe waves like this form at other locations in the Samoan Passage and elsewhere in the ocean.

At their most powerful, some internal waves can sweep submarines off course or cause them to surface.

“In addition to the primary sill, other locations along the multiple interconnected channels through the Samoan Passage also have an effect on the mixing of the dense water.

In fact, quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometres, suggesting that abyssal mixing depends sensitively on bathymetric details on small scales.

Climate models are really sensitive not only to how much turbulence there is in the deep ocean, but to where it is.

The primary importance of understanding deep-ocean turbulence is to get the climate models right on long timescales,” Alford said.”…

==================================

9/3/13, “Turbulent mixing and hydraulic control of abyssal water in the Samoan Passage,” GRL

From → Uncategorized

Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: