The ocean's smallest swimming animals, such as jellyfish, can have a huge impact on large-scale ocean mixing, researchers have discovered.
"The perspective we usually take is how the ocean--by its currents, temperature, and chemistry--is affecting animals," says John Dabiri, a Caltech bioengineer who, along with Caltech graduate student Kakani Katija, discovered the new mechanism. "But there have been increasing suggestions that the inverse is also important, how the animals themselves, via swimming, might impact the ocean environment."
Dabiri's and Katija's findings show this inverse to be true, and are published in the July 30 issue of the journal Nature.
"Results from this study will change some of our long-held conceptions about mixing processes in the oceans," says David Garrison, director of NSF's biological oceanography program, which funded the research.
Scientists have increasingly been thinking about how and whether the animals in the ocean might play a role in larger-scale ocean mixing, says Dabiri, the process by which various layers of water interact with one another to distribute heat, nutrients and gasses throughout the oceans.
He says that oceanographers had previously dismissed the idea that animals might have a significant effect on ocean mixing, believing that the viscosity of water would cancel out any turbulence created, especially by small planktonic, or drifting, animals.
But Dabiri and Katija thought there might be a mechanism that had been overlooked, a mechanism they call Darwinian mixing, because it was first discovered and described by Darwin's grandson.
"Darwin's grandson discovered a mechanism for mixing similar in principle to the idea of drafting in aerodynamics," Dabiri explains. "In this mechanism, an individual organism literally drags the surrounding water with it as it goes."
Using this idea as their basis, Dabiri and Katija performed mathematical simulations of what might happen if many small animals all moved at the same time, in the same direction.
Each day, for example, billions of tiny krill and copepods migrate hundreds of meters from the depths of the ocean toward the surface.
Darwin's mechanism would suggest that they drag some of the colder, heavier bottom water up with them toward warmer, lighter water at the top. This would create instability, and eventually, the water would flip, mixing itself as it went.
The researchers found that the water's viscosity enhances Darwin's mechanism, and that the effects are magnified with very small animals like krill and copepods.
"It's like a human swimming through honey," Dabiri explains. "What happens is that even more fluid ends up being carried by a copepod, relatively speaking, than would be carried by a whale."
To verify the findings from their simulations, the scientists traveled to the island of Palau, where they studied animal-led transport of water--otherwise known as induced drift--among jellyfish.
Their jellyfish experiments involved putting fluorescent dye in the water in front of the jellies, then watching what happened to that dye and to the water that took up the dye as the jellyfish swam.
Rather than being left behind the jellyfish, or dissipated in turbulent eddies, the dye travelled right along with them, following for long distances.
The findings verified that swimming animals are capable of carrying bottom water with them as they migrate upward, and that the movement indeed creates an inversion that results in ocean mixing.
After a series of calculations, Dabiri and Katija were able to estimate the impact of this biogenic ocean mixing.
"There are enough of these animals in the ocean," Dabiri says, "that the global power input from this process is as much as a trillion watts of energy, comparable to that of wind forcing and tidal forcing."
While these numbers are estimates, they are likely to be conservative estimates, Dabiri says. "They were based on the fluid transport induced by individual animals swimming in isolation."
In the ocean, these individual contributions to fluid transport may interact with one another, and amplify how far ocean waters can be pulled upward.
In addition, says Dabiri, scientists have yet to consider the effects of such factors as fecal pellets and marine snow (falling organic debris), which pull surface water along as they drift downward.
"This may have an impact on carbon sequestration on the ocean floor," says Dabiri. "It's something we need to look at."
Dabiri says the next major question is how these effects can be incorporated into computer models of global ocean circulation. Such models are important for simulations of global climate change scenarios.
The research was also supported by the Office of Naval Research, the Department of Defense's National Science and Engineering Graduate Fellowship, and the Charles Lee Powell Foundation.
Cheryl Dybas | EurekAlert!
Joint research project on wastewater for reuse examines pond system in Namibia
19.12.2016 | Technische Universität Darmstadt
Scientists produce a new roadmap for guiding development & conservation in the Amazon
09.12.2016 | Wildlife Conservation Society
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction