Fingerprinting the high seas: A&M-led expedition is studying how trace metals support life in the southwestern Pacific

A 55-day expedition led by two Texas A&M University oceanographers is collecting tens of thousands of liters of water in the southwestern Pacific Ocean to discover if and how trace metals—such as iron, copper, zinc, nickel, manganese, cadmium and lead—contribute to sea life in that region.

Jessica Fitzsimmons, associate professor of chemical oceanography, and Chrissy Wiederwohl, instructional associate professor in oceanography, are spearheading the cruise, which left Tahiti on December 1, bound for Chile by January 25.

The project is part of the the National Science Foundation’s GEOTRACES program, a globally funded, multi-million dollar initiative involving scientists from more than 35 countries. Its mission is to map and understand the processes controlling the distribution of trace elements. The data is collected through research cruises around the world. 

“This is a massive global-scale study,” Fitzsimmons said. “This will be the fifth ocean section that the U.S. has studied as part of GEOTRACES, and it’s exciting for a lot of reasons. Some highlights of what we’re going to be sampling are waters with some of the lowest photosynthesis rates anywhere in the global ocean. In these areas, you can see very clear water with nearly nothing growing in it, so we are studying how nutrients contribute to such low production.”

The team will also cross an area of the ocean that is severely understudied due to strong currents and poor operational conditions.

“But there are several bands of nutrients with different organisms growing as a result, and when these organisms are exported to the sea floor, they influence seafloor sediment geochemistry as well,” Fitzsimmons said. “Studying the interface between that modern ocean chemistry and the sediment record over the geologic past is another goal of the expedition.”

Studying the surface ocean on this cruise transect is also special because it is the birthplace of subsurface water masses that move throughout the rest of the ocean. Water masses are identifiable bodies of ocean water with a distinctive and narrow range of temperature and salinity and a particular density resulting from these two parameters.

“We hope to get the chemical fingerprints of various water masses, which is really important to us in this mapping quest as well,” Fitzsimmons said.

The researchers will also collect samples from a large unexplored area of hydrothermal vents along the Pacific-Antarctic Ridge. According to Fitzsimmons, a common theory in chemical oceanography is that these vents in the southern ocean are producing a disproportionately large supply of metals to certain parts of the surface ocean, allowing deep ocean sources to fertilize phytoplankton — microscopic organisms that photosynthesize and serve as the base of the aquatic food chain.

“These vents haven’t been studied very much because they’re difficult to get to, so we’re going to be one of the first cruises to capture the signatures of those fluxes,” Fitzsimmons said. “That’s a really big deal for my lab, because we specialize in hydrothermal vents. Additionally, as we come around the other side of South America, there’s a water mass called the Pacific Deep Water that carries iron from hydrothermal sources that we are going to map right before it’s going to upwell to the surface. That’s an important goal: to map how much iron is in the current before it reaches the surface and potentially fuels photosynthesis.”

“They’re basically going from the oldest water in the ocean to the newest water, in the sense of when the water was last in contact with the atmosphere,” Wiederwohl added.