In the ocean, a little bit of metal can go a long way.
A new Cornell-led study shows that trace metals, deposited by aerosols like dust and other particles in the atmosphere, have a hefty impact on marine biota, affecting biological productivity and changing the ocean ecosystem.
The paper, “Aerosol Trace Metal Leaching and Impacts on Marine Microorganisms,” was published in Nature Communications in July.
“In the remote oceans, the atmospheric deposition of metals can be really important for the biota,” said lead author Natalie Mahowald, the Irving Porter Church Professor of Engineering and Atkinson Center for a Sustainable Future faculty director for the environment. “In a pollution event or a dust storm, and even in these faraway places, atmospheric deposition can be the most important source of new metals.”
The sources of such aerosol particles range from volcanoes, wildfires and desert dust to anthropogenic causes, like the burning of fossil fuels. After being spewed up and undergoing chemical reactions in the atmosphere, these particles often make their way to remote ocean regions, where they are deposited via precipitation or dry deposition.
Some metals prove to be insoluble and drop to the ocean floor, while others are taken up by various biota – “the little guys,” in Mahowald’s words – like phytoplankton and bacteria, which make up 80 percent of marine life and act as circulators of oxygen and nutrients throughout the ecosystem.
“If you change the ecosystem structure at this scale – this is where all the productivity occurs – it will cascade up and impact the fish and the animals we see more easily,” Mahowald said.
While previous research has focused on the pivotal role of iron in the oceans, Mahowald and her team examined the effects of other metals, as well, including aluminum, manganese, zinc, lead, copper, nickel, cobalt and cadmium. Many of these metals, such as copper, can be toxic pollutants, but the researchers found the metals sometimes function as nutrients, depending on how, where and with what they are mixed.
“One of the highlights of the paper is the heterogeneity,” Mahowald said. “Different sources of aerosols have different metals, different metals are taken up differently by different biota, and that impacts the phytoplankton. We can’t just talk about aerosol deposition into the oceans. We have to be very specific about where in the oceans and what kind of metals are going in, and what biota are there to receive them, because the response is specific to those issues.”
One example that illustrates the complexity and delicate interdependency of the ocean ecosystem is the necessity of iron, according to coauthor and postdoctoral fellow Douglas Hamilton.
“Even if you have all the main components people would think of for growth, like nitrogen and phosphorous, if you take away atmospheric iron deposition, productivity would basically shut down in the vast majority of the open oceans,” Hamilton said. “I thought there would be other ways the system would be able to cope, other sources for iron to get into the system, like rivers and hydrothermal vents. But the global oceans’ microorganism inhabitants are interesting. Without that atmospheric iron deposition, they’re like, ‘Nope, we’re not doing anything anymore.’”
Coauthors are Cornell postdoctoral fellow Rachel A. Scanza; Katherine R. M. Mackey and J. Keith Moore of the University of California, Irvine; Alex R. Baker of the University of East Anglia, U.K.; and Yan Zhang of Fudan University, China, previously a visiting scholar at Cornell.
The research was funded by grants from the Department of Energy and the National Science Foundation, as well as support from the Atkinson Center.
David Nutt is managing editor of the Atkinson Center.