Oceans of color

Faculty Lecture Series continues with deep-dive discussion of water’s signature blue hue

Xiaodong Zhang

Xiaodong Zhang, UND professor of Earth System Science & Policy, was chosen as the third speaker in the recently revived Faculty Lecture Series. He discussed his leading edge work in ocean optics, and how the color of water can help determine what is really contained in the oceans’ depths. Photo by Jackie Lorentz/UND Today

In the afternoon on a late November Thursday, it was Associate Professor Soizik Laguette’s duty to introduce a star faculty researcher from the UND Earth System Science & Policy department she chairs.

She chose an ideal way to do so, addressing a question floating among the dozens of faculty, staff, students and community members in the North Dakota Museum of Art.

“You may be thinking, what is an oceanographer doing in North Dakota? Is he lost?” she posed to a laughing crowd. “Xiaodong Zhang once said, ‘I’m at the geographical center of the continent, which is equidistant from all major oceans and the Gulf of Mexico – it is perfect. I can study any ocean I’d like.’”

Professor Zhang was chosen as the third speaker in UND’s recently revived Faculty Lecture Series, sponsored by the Offices of the President and Provost. The series was initially founded in 1954 as a way for campus researchers and scholars to share their work, and was reignited this year through the efforts of a committee of Chester Fritz Distinguished Professors.

On Nov. 29, Zhang discussed his wave-making work in examining the color of the ocean – why it appears blue, why the color shifts in different environments, and how that knowledge can be practically applied to larger scientific efforts.

“It is a great honor to be selected,” Zhang said. “I’m personally very proud of my research, and now the University’s acknowledgement has made it even better.”

Ocean of questions

Zhang laid the groundwork of his research with a quick history of the question, “Why is the ocean blue?” – an inquiry puzzling artists, philosophers and physicists for centuries. It was in the mid-19th century that true studies of how light interacts with matter – creating color through reflection, refraction, scattering and absorption – really started to evolve.

“We knew the ocean was blue, but at that time, we still didn’t know why,” Zhang said. “Many great minds have studied this, many who have been awarded Nobel Prizes in other fields.”

After busting the myth that the ocean’s blue color comes from the sky’s reflection on the surface of the water, scientists determined that the cause was more molecular.

“Water molecules tend to scatter more blue light than red light,” Zhang explained. “The absorption of water simply makes this blue more pure, so the blue color is caused by water molecules that scatter light back to the eye.”

Zhang found that different particles in the water – including bacteria, viruses, zooplankton, minerals, and even bubbles – interact with light in different ways, creating different colors. For example, in coastal areas with high concentrations of phytoplankton, the water appears greener because of the spectral absorption rates caused by photosynthesis.

“Phytoplankton a major player in the global carbon cycle, and this is why we’re so interested to know how much phytoplankton exists in the ocean,” he said.

The scientific field of ocean optics is a fairly new discipline, but Zhang says it’s becoming more heavily pursued because of its growing applications.

Right now, international scientists are using enhanced instruments both in the water and in space – including satellite sensors managed by NASA and NOAA – to observe the water’s particles from more angles, determining their size, composition, shape and structure. This constructs a more complete picture and reduces uncertainly in what is truly contained in the oceans’ depths.

In terms of varying particulates and the ways light is scattered by them, Zhang said, “We need to measure it, and we need to retrieve the information from the measurement.” That’s the ultimate goal of his research team, supported by funds from NASA, the National Science Foundation, and the U.S. Department of Agriculture.

Xiaodong Zhang & Hesham El-Rewini

UND Vice Provost and Dean of the College of Engineering & Mines Hesham El-Rewini presents Xiaodong Zhang with a token of appreciation from the Offices of the President and Provost. The two offices worked with a committee of Chester Fritz Distinguished Professors to reignite the Faculty Lecture Series this fall. Photo by Connor Murphy/UND Today.

Color us intrigued

At the conclusion of Zhang’s presentation, several hands shot up, ready with questions spanning rainbows, carbon capture and microplastics (small plastic particles found in the environment that come health and beauty products and some industrial processes).

Dustin Solberg, a visiting UND alum who now works as a conservation writer in Alaska, was especially interested in Zhang’s NASA-partnered research in measuring carbon levels in the ocean.

“That’s an issue that’s really relevant to people. The ocean seems like it’s a long way away, but it’s really not,” Solberg said. “The carbon we’re producing today, the carbon we’ve been producing since the Industrial Revolution, is continually being absorbed by our oceans. That’s helpful in ways, but it also has some detrimental effects on ocean life.”

Solberg believes the Faculty Lecture Series shows the potential of his alma mater to be a “real shining light” in North Dakota, tackling the science and social issues of a growing state and planet. “I’m interested in seeing knowledge and understanding from the University distilled so that the public at large can participate in those conversations,” he said.

“This is what a university is supposed to do – share its research results with the public and with friends and faculty from other discipline areas,” Zhang said. “It doesn’t matter where you are – it’s people that make a change and do the research. The location doesn’t matter.”

The lecture series will continue in the spring semester on Feb. 28, when Kit Johnson, associate professor of law, discusses Moguls, Models, Patients, and Princesses: Finding the Unexpected in Immigration Law.