Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Intense deep-ocean turbulence in equatorial Pacific could help drive global circulation

23.02.2016

Waves crashing on the equatorial seafloor generate centimeter-scale turbulence that is crucial for driving ocean circulation on a global scale, Stanford scientists say.

The findings, presented this week at the annual American Geophysical Union Ocean Sciences conference and recently published online in the journal Geophysical Research Letters, could eventually be incorporated into global climate simulations to improve future climate forecasts.


Simulations of internal waves propagating near the equator. The north-south velocity of the water is plotted in the left two panels while a measure of the strength of the turbulence generated by the waves is shown in the panels on the right. The 'traditional' simulations (first and third panel) do not include the horizontal component of Earth's rotation while the 'non-traditional' simulations (second and fourth panel) include it. The shape of the two vertical bands, or mirror surfaces, are altered near the seafloor by the horizontal component of Earth's rotation, causing the waves to be trapped and drive mixing there.

Credit: Ryan Holmes

"Climate models don't do a great job of simulating global ocean circulation because they can't simulate the small scales that are important for deep ocean mixing," said Ryan Holmes, a graduate student at Stanford's School of Earth, Energy & Environmental Sciences.

The meridional overturning circulation, or MOC, is a global ocean conveyor belt wherein surface waters cooled in the high latitudes flow along deep currents toward the equatorial regions, where they mix with warmer, less dense water and rise to the surface. This upwelled water eventually flows towards the higher latitudes to complete the cycle. One circuit takes hundreds to thousands of years to complete.

The MOC is important for transporting heat, salt and carbon around the globe and influences the rate at which carbon stored in the deep ocean is exchanged with the atmosphere. But until now, scientists only had a rough sense of where in the tropical oceans this mixing-driven upwelling occurs.

To better understand mixing in the tropical oceans, James Moum, a professor of physical oceanography at Oregon State University, organized a five-week research cruise in the equatorial Pacific and invited Holmes, who had been investigating equatorial mixing in ocean models for his PhD dissertation. The group brought along an experimental sensor called a ?-pod (pronounced "kai-pod") that is designed to measure turbulence all the way to the seafloor - 4000 meters, or nearly 2.5 miles, below the surface.

"Upwelling requires mixing of waters with different temperatures and therefore different densities. What we measured using the ?-pod is the turbulence that generates this mixing," Holmes said. "This marked the first time that anyone had ever measured mixing to these depths on the equator."

Two weeks into the cruise, the team encountered a patch of strong turbulence occurring along a 2,300-foot (700-meter) vertical stretch of water near the ocean bottom. This was surprising because the seafloor in that part of the ocean was relatively flat, and for many years, scientists had assumed that intense deep ocean mixing required water to flow over rugged bottom features such as seamounts or ridges.

"This was the first time that anyone had observed turbulence over smooth topography that was as strong as that found over rough topography," Holmes said.

To understand what was happening, Moum enlisted the help of Leif Thomas, an expert in the physics of ocean circulation at Stanford and Holmes' graduate advisor.

Using computer models, Thomas and Holmes were able to simulate how winds blowing across the ocean surface can generate "internal waves" that propagate vertically down through the ocean depths and transport the energy required to mix waters at the seafloor. However, their model was not able to reproduce the observed abyssal mixing: Instead of generating turbulence, the internal waves ping-ponged between two vertical bands of water on either side of the equator and the smooth seafloor without breaking.

"These waves in the model were trapped to the equator between two vertical bands that act like funhouse mirrors bouncing light rays back and forth," said Thomas, an associate professor in the department of Earth System Science.

The Stanford scientists were stumped-until Thomas had the idea to incorporate the horizontal component of the Earth's spin, conventionally disregarded in ocean models, into their simulation. Thomas recalled from his previous studies that the horizontal spin of strong currents, such as the Gulf Stream, could cause internal waves in the mid-latitudes to amplify and break when they reflect off the bottom of the ocean. "It occurred to me that internal waves at the equator, where the effects of the horizontal component of the Earth's spin are most pronounced, could experience an analogous behavior when the waves reflect off the seafloor," Thomas said. "With this in mind, I suggested to Ryan to explore this idea."

Thomas' hunch proved correct. The Stanford scientists found that in the equatorial waters they were modeling, the Earth's rotation imparts a subtle vertical motion to moving objects. This nudge is enough to disrupt the reflection of internal waves, trapping them near the ocean bottom and focusing their energy to generate turbulence.

"We included this horizontal component and found that it changed the physics of waves in the deep equatorial oceans, potentially causing them to break and drive turbulence and mixing," Holmes said.

The new findings highlight the critical importance of deep equatorial waters for Earth's climate system, Thomas said. "Scientists have long known that the equatorial upper ocean is critical for the physics of interannual variations in climate such as El Niño," he said. "Our new study suggests the abyssal ocean at the equator could impact the climate system on much longer timescales."

Ker Than | EurekAlert!

Further reports about: Earth Environmental Sciences deep ocean deep-ocean seafloor waves

More articles from Earth Sciences:

nachricht Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Predicting unpredictability: Information theory offers new way to read ice cores

07.12.2016 | Earth Sciences

Sea ice hit record lows in November

07.12.2016 | Earth Sciences

New material could lead to erasable and rewriteable optical chips

07.12.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>