Hotspots of small swimming marine organisms may contribute to mixing

January 15, 2016 by Emil Venere
New research using high-fidelity numerical simulations is revealing details about how “hotspots” of small swimming organisms might contribute to the mixing of ocean waters. The research is depicted in this animated GIF. Credit: Shiyan Wang and Arezoo Ardekani

New research findings suggest small marine organisms swimming in concentrated "hotspots" likely contribute to the mixing of water needed to distribute nutrients for ocean species.

The ocean consists of a top nutrient-depleted layer that is well mixed by turbulence created primarily by wind, tides and other mechanisms, and a bottom unmixed nutrient-rich layer. In between is a layer called the pycnocline marked by a sharp change in density, said Arezoo Ardekani, an assistant professor of mechanical engineering at Purdue University.

"We are trying to learn about the potential contribution of marine organisms to the processes that transport water from this nutrient-rich bottom region through the pycnoline layer and to the nutrient-depleted region," she said.

Ocean mixing is critical for distributing nutrients to the nutrient-depleted layer.

"Some move vertically between the top and bottom layers during the day and night through a process called diel vertical migration," she said.

While it is known that wind and waves are the primary cause of ocean mixing, one unknown factor is whether organisms contribute to this vital mixing. Previous research has suggested the organisms transport volumes of fluid and nutrients with them, a concept known as Darwinian drift. However, some scientists argue that the drifted fluid can re-stratify in marine environments and may not cause mixing.

The Purdue researchers used high-fidelity numerical simulation (animated gif available) of a "simplified swimming model" to determine whether the small ocean organisms such as zooplankton swimming in concentrated hotspots contribute to the mixing.

"So there are local hotspots where this mixing can be comparable to the turbulent mixing in the mid-ocean," Ardekani said. "The mixing induced by horizontally swimming organisms is one hundred times weaker than the contribution of vertically swimming organisms."

The hotspots may be especially important in the mid-ocean, where the majority of energy from waves and wind is dissipated prior to contributing to mixing.

Findings were detailed in a paper published in December in the journal Scientific Reports published by the Nature Publishing Group. The paper was authored by doctoral student Shiyan Wang and Ardekani.

Explore further: Aquatic creatures mix ocean water

More information: Shiyan Wang et al. Biogenic mixing induced by intermediate Reynolds number swimming in stratified fluids, Scientific Reports (2015). DOI: 10.1038/srep17448

Related Stories

Aquatic creatures mix ocean water

November 22, 2009

Understanding mixing in the ocean is of fundamental importance to modeling climate change or predicting the effects of an El Niño on our weather. Modern ocean models primarily incorporate the effects of winds and tides. ...

Tides stir up deep Atlantic heat in the Arctic Ocean

February 17, 2015

Researchers have identified how warm Atlantic water that is flowing deep into the Arctic Ocean is mixing with colder waters above to contribute to sea-ice loss in the Arctic. The results, published this week in the journal ...

Image: The North Sea abloom

July 7, 2015

Despite its cold waters and harsh winds, the North Sea is a fertile basin for phytoplankton blooms. The drifting, plantlike organisms tend to be most abundant in late spring and early summer due to high levels of nutrients ...

Recommended for you

New Amazon threat? Deforestation from mining

October 18, 2017

Sprawling mining operations in Brazil are destroying much more of the iconic Amazon forest than previously thought, says the first comprehensive study of mining deforestation in the world's largest tropical rainforest.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.