The world's oceans, we know, are constantly shaken and stirred by the winds and the tides and other physical forces of nature. But do fish and other swimming marine life stir the ocean, too?
The simple math: total the mechanical energy of all the estimated marine swimmers in all the world's oceans and you get a figure that suggests as much as a third of all the vertical mixing in the world's oceans is produced by marine life, according to a University of Wisconsin-Madison press release.
Since the question was first posed some rough “top down” calculations have emerged suggesting that marine swimmers — everything from whales to krill — could contribute a significant portion of the mechanical energy for all ocean mixing.
The problem assumes real importance in settings like fish farms and ocean aquaculture where large concentrations of confined fish can be at risk from bacterial infections caused by microbes that, in the open, mixed ocean, wouldn't be an issue.
Another and perhaps more precise way to approach the problem is to model the influence of a single swimmer on a fluid particle and multiply.
That is the approach described this week in the journal Physics Letters A by mathematicians Jean-Luc Thiffeault of the University of Wisconsin-Madison and Stephen Childress of New York University.
“Oceanographers want to know how things mix vertically in the ocean,” says Thiffeault, explaining that the ocean is like a layer cake, with tiers of water from top to bottom that have different temperatures and concentrations of nutrients, such as iron.
“Because of the ocean's stratification, water doesn't want to move vertically, but it eventually must, otherwise there would be no life on earth,” says Thiffeault. “This is called vertical transport. The question is where does it come from?”
