Synchrotron X-rays Illuminating Ocean Life

For the last 20 years, Senior Research Scientist Ben Twining has taken an unusual approach to studying the ocean. Several times a year, he takes phytoplankton collected from far-flung waters to a place distant from the ocean – a particle accelerator in Chicago.

Twining began making the trek to Argonne National Laboratory as a graduate student, drawn by an instrument under construction called the Advanced Photon Source synchrotron. A synchrotron is essentially an enormous electron accelerator ring that feeds a high-energy x-ray microscope. This synchrotron is nearly as wide as the Empire State Building is tall, making it a powerful tool useful for fields ranging from pharmaceuticals to planetary science.

Over the last two decades, Twining has used the synchrotron to analyze the elements inside thousands of individual phytoplankton cells from around the world. He is using that information to paint a picture of the diverse microbial life throughout the global ocean and elucidate the nutrient cycles that shape the ocean and atmosphere.

“This is a pretty unusual application of the synchrotron, and there’s no one else in the world doing this type of work,” said Twining, who is also the Henry L. and Grace Doherty Vice President for Education at Bigelow Laboratory. “My goal is to connect ocean biology to chemical cycles in order to show how these tiny little cells influence global climate.”

On his brief, intense trips to the synchrotron, Twining works around the clock using the instrument to bombard phytoplankton cells with high-energy x-rays. When the x-rays hit a cell, they cause the elements within to fluoresce, each glowing a different color. Twining can measure how much of each element is inside the cell as well as where the elements are located, collecting data that illuminates resource use and competition at the smallest scales – and sheds light on global cycles.

Phytoplankton act as a link between essential nutrients and complex ocean food webs. Individuals as small as a single cell can morph nitrogen between its several forms, transfer iron from inedible dust to edible biomass, and turn water into oxygen like alchemists. Collectively, phytoplankton support rich food webs, fuel ocean chemical cycles, and produce half the oxygen in the atmosphere.

Thanks to new molecular technologies, the amount that researchers know about phytoplankton is expanding rapidly. A recent explosion in “omics” techniques is allowing scientists to pinpoint how individual cells are acting within their ecosystems and whether they are chugging along smoothly or showing signs of stress. Twining can build off these observations by using the synchrotron to measure elements inside individual phytoplankton and determine how successfully they are competing for nutrients.

“Omics can give us this incredible view of how cells behave differently as they fight for limited resources, and the synchotron measurements show how successful they are in this fight,” Twining said. “Cells are very good sentinels of what is going on in the environment, and this information scales up to reveal how vital nutrient cycles work.”

Over the last two decades, Twining has used this approach to describe ocean nutrient cycles around the world and even disrupt a tenet of oceanography. Since 1934, the notion has persisted that the ratios of carbon, nitrogen, and phosphorus are basically constant in all phytoplankton, no matter where they grow. Work by Senior Research Scientist Mike Lomas and others has revealed that these nutrient ratios actually fluctuate around the world, shaping how nutrients cycle in different parts of the ocean.

Iron is also a critical nutrient for phytoplankton growth and ocean cycles. It is scarce in 40 percent of the ocean, where it confers a huge advantage on the cells who outcompete their neighbors for this limited resource. The amount of iron phytoplankton contain has also been long assumed to be constant, but Twining found that this concentration can vary by more than a factor of 100 between cells. This variation could have significant consequences for global climate change.

Cells in the Atlantic Ocean hold 50 times more iron than those in the South Pacific. Nutrient cycles are intricately linked, and the amount of iron available influences the amount of carbon that the ocean can store. This is particularly salient as researchers try to understand how climate will continue to change. A large part of Twining’s research today involves working with modelers to refine their global models and ensure that they match the unique real-world data he has collected.

“The amount of nutrients a cell in the ocean contains has a huge impact, and these small numbers really matter for our understanding of the ocean,” Twining said. “This is a really important piece of the puzzle and a satisfying place to arrive at in 20 years of work.”

The upper image is courtesy of Argonne National Laboratory.