SCOPE-Gradients Project: Trace Metal Bioavailability and Recycling in the North Pacific
Many trace metals in seawater such as iron, nickel, copper and cobalt are important cofactors in several enzymes that are essential for processes such as primary production, nitrogen fixation and respiration. These metals are present in extremely low concentrations in seawater and are thus often a limiting or co-limiting nutrient for phytoplankton growth. In addition to being scarce nutrients, many trace metals are also bound by a heterogeneous pool of organic compounds that influence their biological uptake, residence times and recycling. These organic compounds range from biologically-produced metabolites to uncharacterized organic compounds present in seawater with a strong affinity for trace metals. The identities of many of these compounds are unknown, and yet can greatly influence the cycling of trace metals in the ocean.
The Bundy lab explores how the chemical speciation of trace metals shapes the biological community along the transition from the North Pacific subtropical gyre to the subpolar gyre. Specifically, we are interested in how organic compounds shape the bioavailability of trace metals, and how bacteria and phytoplankton actively mediate trace metal cycling by the production of novel metal-binding metabolites such as siderophores or other metal-binding ligands.
ECIMMEE Project: The Fundamental Role of Heterotrophic Bacteria in the Global Iron Cycle
Iron is an essential micronutrient in the ocean, controlling phytoplankton growth in many regions and impacting primary productivity and carbon dioxide (CO2) drawdown over long time scales. Extensive research has focused on the impacts of iron on phytoplankton growth, but very little is understood about the iron requirements of bacteria in the ocean. Heterotrophic bacteria convert organic carbon to carbon dioxide in the ocean, thus playing a major role in the carbon cycle. Heterotrophs are thought to use a significant amount of iron in order to respire carbon, and their iron requirements might even surpass those of eukaryotic phytoplankton in surface waters. Heterotrophic bacteria may therefore be significant competitors with phytoplankton for this scarce micronutrient, but very few studies have quantified the iron requirements of heterotrophic bacteria. Low iron conditions have also been shown to cause heterotrophs to respire organic carbon substrates less efficiently, causing them to produce more CO2 and incorporate less organic carbon into biomass. This suggests a potential connection between iron availability not only on surface ocean productivity but also on carbon export. This project aims to perform fundamental experimental studies to examine the role of heterotrophic bacteria in both the surface and mesopelagic oceanic iron cycle by identifying the iron demand of heterotrophic bacteria in surface waters, as well as quantifying the regeneration rates of iron in the ocean interior along with the impact of iron on the efficiency of carbon respiration. The results from laboratory studies will be incorporated into a one-dimensional model, with the goal of incorporating the results into larger biogeochemical models.
Randie Bundy is an assistant professor in the School of Oceanography at the University of Washington. Her research focuses on understanding the cycling of trace metals in the marine environment, with a focus on metals that are necessary for life. Specifically, she is interested in how the chemical speciation of trace elements impacts their uptake and recycling by phytoplankton and bacteria, and how microorganisms have adapted strategies for dealing with the insufficient concentrations of these essential nutrients present in the ocean. Many metals, such as iron, copper, cobalt and nickel, are essential components of key enzymes and proteins used for important metabolic processes in the ocean, such as carbon fixation and nitrogen assimilation. However, they are very scarce in the ocean and are often present in concentrations 10-100 times less than what is required for microbial growth. Bundy’s research
involves exploring microbial metal uptake and recycling in a variety of oceanic environments, ranging from the oligotrophic gyre of the North Pacific to the polar waters of the Arctic and Antarctic. Bundy received her B.S. in 2008 from the University of California at San Diego and her Ph.D. from Scripps Institution of Oceanography at UCSD in 2014. During her Ph.D. she worked on determining the sources and sinks of iron and copper-binding organic compounds in coastal waters, and elucidating their impact on trace metal bioavailability. Then, from 2014 to 2017, she worked as a postdoctoral research scholar at Woods Hole Oceanographic Institution studying the cycling of cobalt in the Arctic Ocean and isolating siderophores and other metal-binding organic compounds from seawater and determining their impact on phytoplankton growth.