Nav: Home

How deep-ocean vents fuel massive phytoplankton blooms

June 05, 2019

Researchers at Stanford University say they have found an aquatic highway that lets nutrients from Earth's belly sweep up to surface waters off the coast of Antarctica and stimulate explosive growth of microscopic ocean algae.

Their study, published June 5 in the journal Nature Communications, suggests that hydrothermal vents - openings in the seafloor that gush scorching hot streams of mineral-rich fluid - may affect life near the ocean's surface and the global carbon cycle more than previously thought.

Mathieu Ardyna, a postdoctoral scholar and the study's lead author, said the research provides the first observed evidence of iron from the Southern Ocean's depths turning normally anemic surface waters into hotspots for phytoplankton - the tiny algae that sustain the marine food web, pull heat-trapping carbon dioxide out of the air and produce a huge amount of the oxygen we breathe. "Our study shows that iron from hydrothermal vents can well up, travel across hundreds of miles of open ocean and allow phytoplankton to thrive in some very unexpected places," he said.

Kevin Arrigo, a professor of Earth system science and senior author of the paper, called the findings "important because they show how intimately linked the deep ocean and surface ocean can be."

Mysterious blooms

Phytoplankton need iron to thrive, and that limits their abundance in vast swaths of the ocean where concentrations of the nutrient are low. But when conditions are right, phytoplankton can also grow explosively, blooming across thousands of square miles in a matter of days.

That's what Ardyna noticed recently as he looked at data recorded in 2014 and 2015 by a fleet of floating robots outfitted with optical sensors in the Southern Ocean. More than 1,300 miles off the coast of Antarctica and 1,400 miles from the African continent, two unexpectedly large blooms cropped up in an area known for severe iron shortages and low concentrations of chlorophyll, an indicator of phytoplankton populations.

Massive blooms in this region could only be possible with an influx of iron. Ardyna and Arrigo quickly ruled out the ocean's most common sources, including continental shelves, melting sea ice and atmospheric dust, which were simply too far away to have much influence.

That led them to suspect that the nutrient must be welling up from below, possibly from a string of hydrothermal vents that dot a mid-ocean ridge 750 miles from where the massive blooms had inexplicably appeared. To help test their hypothesis, they recruited an international team of collaborators specialized in various aspects of oceanography and modeling.

"It has long been known that hydrothermal vents create unique and profound oases of life," Ardyna said. Until recently, scientists generally believed those nourishing effects remained fairly local. But a growing amount of evidence from computer simulations of ocean dynamics has hinted that iron and other life-sustaining elements spewed from hydrothermal vents may in fact fuel planktonic blooms over much wider areas.

However, direct measurements have been lacking.

In the Southern Ocean, that's partly due to the remote location, extreme cold and rough seas, which make it difficult to study up close or collect accurate data. "Your sensors have to be in the right place at the right time to see these blooms," Ardyna said. "Satellites can underestimate intensity or miss them altogether because of bad coverage or strong mixing of the water column, which pushes phytoplankton down too deep for satellites to see."

Clues from space, floating robots

To track the flow of particles from the vents on the mid-ocean ridge, the scientists analyzed data from satellites measuring chlorophyll and from autonomous, sensor-laden buoys known as Argo floats. As they dive and drift along ocean currents, some of these buoys detect chlorophyll and other proxies for phytoplankton biomass. "The floats give us precious and unique data, covering a large section of the water column down to 1,000 meters deep during an entire annual cycle," Ardyna said.

The scientists couldn't directly measure iron in the water, but instead analyzed measurements of helium collected by scientific cruises in the 1990s. The presence of helium signals waters influenced by hydrothermal vents, which funnel large amounts of primordial helium from beneath Earth's crust.

The chlorophyll, phytoplankton and helium data suggest that a powerful current circling Antarctica grabs nutrients rising up from vents. Two turbulent, fast-moving branches of the current then shuttle the nutrients eastward for a month or two before serving them like a banquet to undernourished phytoplankton. Together with the arrival of spring sunshine that phytoplankton need for photosynthesis, the delivery triggers a massive bloom that can likely absorb and store significant amounts of carbon from the atmosphere, said Arrigo, who is also the Donald and Donald M. Steel Professor in Earth Sciences.

Over time, the blooms drift eastward toward the current racing around Antarctica and fade as sea creatures devour them. "We suspect these hotspots are either consumed or exported to deep waters," Ardyna said.

Each bloom lasts little more than a month, but the mechanisms that trigger them are likely to be more common in the global ocean than scientists previously suspected.

"Hydrothermal vents are scattered all over the ocean floor," Ardyna said. Knowing about the pathways that bring their nutrients up to surface waters will help researchers make more accurate calculations about the flow of carbon in the world's oceans. "Much remains to be done to reveal other potential hotspots and quantify how this mechanism is altering the carbon cycle."
-end-


Stanford's School of Earth, Energy & Environmental Sciences

Related Phytoplankton Articles:

The foundation of aquatic life can rapidly adapt to global warming, new research suggests
Important microscopic creatures which produce half of the oxygen in the atmosphere can rapidly adapt to global warming, new research suggests.
NASA taking stock of phytoplankton populations in the Pacific
Among the most pressing questions scientists are investigating is how much of that carbon is being stored in the ocean over the long term.
From tiny phytoplankton to massive tuna
Phytoplankton are the foundation of ocean life, providing the energy that supports nearly all marine species.
Newly discovered phytoplankton groups appear to favor warmer oceans
An international research team has discovered two phytoplankton groups -- unlike any known species -- in climate-sensitive areas around the world.
Space-based lidar shines new light on plankton
A space-based sensor that can 'see' through fog, clouds and darkness has given scientists their first continuous look at the boom-bust cycles that drive polar plankton communities.
East Asian dust deposition impacts on marine biological productivity
Scientists find significant correlations between East Asian dust events and chlorophyll a concentration not only in the open ocean of North Pacific Ocean, but also in the Chinese marginal seas.
New 13-year study tracks effects of changing ocean temperature on phytoplankton
A new multiyear study has shown for the first time how changes in ocean temperature affect a key species of phytoplankton.
Temperature, not predatory pressures, drives plankton abundance
Plankton blooms in spring are largely driven by temperature-induced increases in cell division, a new study reveals.
The oceans are full of barriers for small organisms
Subtle and short-lived differences in ocean salinity or temperature function as physical barriers for phytoplankton, and result in a patchy distribution of the oceans' most important food resource.
Ocean warming and acidification impact on calcareous phytoplankton
Researchers from the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona, the University of Cambridge and the Marine Biological Association of the United Kingdom warn of the negative impacts of rapid ocean warming and ocean acidification on coccolithophores, and consequently in the regulatory processes of atmospheric and ocean concentrations of carbon dioxide (CO2).

Related Phytoplankton Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#529 Do You Really Want to Find Out Who's Your Daddy?
At least some of you by now have probably spit into a tube and mailed it off to find out who your closest relatives are, where you might be from, and what terrible diseases might await you. But what exactly did you find out? And what did you give away? In this live panel at Awesome Con we bring in science writer Tina Saey to talk about all her DNA testing, and bioethicist Debra Mathews, to determine whether Tina should have done it at all. Related links: What FamilyTreeDNA sharing genetic data with police means for you Crime solvers embraced...