Postdoc Spotlight: Particles Return to Sea

Particles and decomposed algae at the bottom of the coastal ocean could be an unexpected source of global climate change, according to Veronica Ruiz-Xomchuk, Ph.D., a postdoctoral fellow at the FAU Harbor Branch Oceanographic Institute.

Ruiz-Xomchuk is co-leading a research project to study the role of organic matter trapped in the sediments of the bottom of the Gulf of Mexico in the Earth’s carbon budget. For this work, the team was recently awarded a $736,000 grant from the National Aeronautics and Space Administration (NASA).

The carbon budget tells researchers how much carbon dioxide is released into the Earth to drive global warming and other negative effects like the creation of harmful algal blooms, and how much of it is captured by the oceans to slow this process.

“Scientists think about the ocean as a carbon sink, and often only consider what is coming from the environment that lands into the ocean as a part of the carbon budget, but they fail to include what’s coming back up from the sediments in their discussion about budgets or the increase in blooms,” she said.

The work that Ruiz-Xomchuk studies brings awareness to what is trapped in the sediments and the lower water column at the bottom of the coastal ocean. Decomposed animals, debris, algae, nutrients, low oxygen water and organic carbon, all is contained within the sediments on the ocean’s floor.

But when hurricanes or strong winds disrupt the ocean’s currents, that sediment has the potential to lift back up and mix into the ocean.

“All that organic matter that re-circulates, that was buried and apparently lost, becomes part of the biogeochemical cycle again, and when there’s a high amount of nutrients in the water from the matter, it can cause ecological problems like algal blooms,” Ruiz-Xomchuk said.

Ruiz-Xomchuk grew up in Ecuador, watching famous ocean explorations and oceanographers like Jacques Cousteau on TV. She said Cousteau’s work inspired her to earn her bachelor’s degree in chemical and physical oceanography in 2002 from the School of Escuela Superior Politécnica del Litoral in Ecuador.

In 2003, she earned a master’s degree in marine sciences from Ghent University in Belgium, where she studied the tiny organisms in the zone where the ocean meets sandy beaches.

In 2012 she took a job in Ecuador with the Navy as an oceanographer studying the continental shelf. The job required her to create forecast modeling systems, but Ruiz-Xomchuk said her knowledge was limited in that area, so she needed help. The additional researcher they hired turned out to be her future doctoral advisor who encouraged her to attend graduate school and work at his lab in Texas.

“I was nervous because I had been out of school for so long when he asked me to apply, but I thought this is a once-in-a-lifetime opportunity that I couldn’t let walk away from me,” Ruiz-Xomchuk said. “I also wanted to understand more about ocean modeling and how physical processes in the ocean could affect biological and chemical processes.”

In 2014, Ruiz-Xomchuk applied to Texas A&M University and completed her doctorate degree in physical oceanography in 2020.

For her dissertation, she looked at the physical processes that contributed to hypoxia, low oxygen conditions, at the bottom of the Texas-Louisiana shelf. “I studied small scale variability, or the patchiness of bottom hypoxia, to determine what physical processes could affect the layering that is created by hypoxia, and to understand how large, widespread or even how patchy is the dead zone,” Ruiz-Xomchuk said.

When freshwater, like from the Mississippi River, spills into the ocean it sits on top of saltwater and prevents oxygen from entering the ocean’s floor. When certain areas of the bottom of the ocean become hypoxic it turns into a dead zone, where all life is depleted and fish even race to the ocean’s surface to find oxygen, she said.

Now working in the lab of Jordan Beckler, Ph.D., assistant research professor, Harbor Branch, and fellow of FAU’s Institute for Sensing and Embedded Networks Systems Engineering, Ruiz-Xomchuk said she is using her knowledge of hypoxia and of physical processes that create ventilation of the bottom water to understand how these same circulation features affect the carbon budget by potentially resuspending sediments.

“Working with Jordan is a great mix because we both care about bottom processes. He as a chemist, cares about the sediments and the nutrient rich pore waters in them, and I care about the processes and physical interactions at the bottom of the ocean that can bring those back up,” she said. “They matter more than we consider.”