Study reveals currents can push plankton to anywhere in the world in less than a decade

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Plankton can move around the world's oceans drifting in currents far faster than previously believed. Researchers have found that anywhere on the planet can be reached in less than a decade by tiny singled-celled phytoplankton - the first link in our ocean's food chain.

The study by Princeton University is good news in the sense that it means the oceans have a strong mechanism to repopulate any part of the world hit by a catastrophe and maintain biodiversity. But is also means that man-made pollutants such as plastics can spread equally effectively.

'Our study shows that the ocean is quite efficient in moving things around,' said Bror Fredrik Jönsson, an associate research scholar in Princeton's Department of Geosciences, who conducted the study with co-author James R Watson, a former Princeton postdoctoral researcher who is now a researcher at Stockholm University.

'This comes as a surprise to a lot of people, and in fact, we spent about two years confirming this work to make sure we got it right,' Jönsson said. 

Animation by Bror Jönsson, Department of Geosciences

The model above shows how phytoplankton travelling on ocean currents would spread over a three-year period. The researchers 'released' thousands of particles representing phytoplankton and garbage from a starting point (green) stretching north to south from Greenland to the Antarctic Peninsula. The colours to the left indicate low (blue) or high (red) concentration of particles. Over time, the particles spiral out to reach the North and South Pacific, Europe, Africa and the Indian Ocean. 

One of the strengths of the model is its approach of following phytoplankton wherever they go throughout the world rather than focusing on their behaviour in one region, Jönsson said. Because most marine organisms are mobile, this particle-tracking approach can yield new insights compared to the approach of studying one area of ocean.

The world's ocean currents

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The resulting model works for objects that have no ability to control their movement such as phytoplankton, bacteria and man-made debris. Organisms that can control their movement even a small amount — such as zooplankton, which can control their vertical position in water — are not accounted for in the model. Nor does the model apply to objects such as boats that protrude above the water and can be pushed by surface winds.

The team applied a computer algorithm to calculate the fastest route an object can travel via ocean currents between various points on the globe. Most previous studies looked only at movement of phytoplankton within regions. 

The researchers confirmed that the travel times calculated by their model were similar to the time it took real objects accidentally dumped into the ocean to be carried by currents. For instance, 29,000 rubber ducks and other plastic bath toys toppled off a Chinese freighter in 1992 and have since been tracked as a method of understanding ocean currents. A similar utility has stemmed from the Great Shoe Spill of 1990 when more than 60,000 Nike athletic shoes plunged into the ocean near Alaska and have been riding the currents off the Pacific Northwest ever since.

 rubber ducks jason ahrnsRubber ducks dumped by a Chinese freighter have been used to study ocean currents/ Jason Ahrns

The researchers' model also matched the amount of time it took radioactive particles to reach the West Coast of the United States from Japan's Fukushima I Nuclear Power Plant, which released large amounts of radioactive materials into the Pacific Ocean following heavy damage from a tsunami in March 2011. The actual travel time of the materials was 3.6 years; the model calculated it would take 3.5 years.

To create the model, Jönsson and Watson obtained surface current data from a database of modelled global surface currents developed at the Massachusetts Institute of Technology and housed at NASA's Jet Propulsion Laboratory in California. Into this virtual world, they released thousands of particles that represented phytoplankton and then ran simulations multiple times, comparing past and present runs for accuracy and making tweaks to improve the model. They eventually tracked more than 50 billion positions of particles, which is just a fraction of the actual number of phytoplankton in the ocean.

Because phytoplankton mainly reproduce asexually — meaning that one organism alone can produce offspring — only one individual needs to reach a new area to colonise it. This fact led the team to look at the shortest time it takes to get around the world rather than the average time.  

 

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