WASHINGTON - Scientists have discovered that the ocean’s smallest swimming animals, such as jellyfish, can have a huge impact on large-scale ocean mixing.
John Dabiri, a Caltech bioengineer, along with Caltech graduate student Kakani Katija, discovered the new mechanism.
According to Dabiri, scientists have increasingly been thinking about how and whether the animals in the ocean might play a role in larger-scale ocean mixing, the process by which various layers of water interact with one another to distribute heat, nutrients and gasses throughout the oceans.
He said 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 explained. “In this mechanism, an individual organism literally drags the surrounding water with it as it goes,” he said.
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.
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. (ANI)
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