A Scientist's Life: Kathy Barbeau

Marine chemist studies how the presence of trace metals such as iron and copper affect marine life and even the climate

Kathy Barbeau is a marine chemist and a professor at Scripps Institution of Oceanography at the University of California San Diego. She joined Scripps in 2001 after a stint as a postdoctoral researcher at UC Santa Barbara. She received her PhD in 1998 from the MIT-WHOI Joint Program.

explorations now: What do you do for a living?

Kathy Barbeau: I study the biogeochemical cycling of trace elements in the marine environment. These are trace metals that interact strongly with marine life – primarily things like iron, which could be an important micronutrient for phytoplankton in the open ocean in many areas. There’s also copper, which is both a micronutrient in the open ocean but can also be toxic to phytoplankton at higher concentrations in harbors and other impacted areas.

We need to know about things like trace metals – iron, for example – because these trace elements, although they’re needed by organisms in very minute concentrations, they’re present in the ocean in vanishingly small concentrations. And as such, they can have really important impacts on phytoplankton productivity and the larger overall global cycling of carbon and nitrogen. Iron has been implicated as an important factor in glacial-interglacial cycles and changing the CO2 concentration of the atmosphere. Changes in iron supply to the oceans can thus enhance climate warming or cause cooling.

The ocean is overall a really extreme environment in terms of iron supply. And it's ironic, no pun intended, because iron is one of the most abundant elements in the earth as a whole. It's very abundant in the rocks and minerals of the earth, but because of its chemistry in the ocean, iron is extremely insoluble and it never accumulates in the dissolved phase above very, very trace concentrations. Iron can be limiting in a lot of different areas of the ocean for biological productivity because of its chemistry.

en: Describe some of your current projects.

KB: We're prepping right now to leave in the next week on a [August 2019] process cruise as part of our participation in the CCE LTER program. That's the California Current Ecosystem Long-Term Ecological Research program. We're looking at the impact of long-term climate shifts on the ecosystem of the southern California Current. My group's role in CCE is to look at the impact of iron as a limiting or co-limiting nutrient in the coastal upwelling ecosystem that we're studying off the coast of California and in the larger California Current area. Iron supply is crucial in upwelling regions just as it is in the open ocean for generating and sustaining phytoplankton.

Usually our main area of focus is the Point Conception upwelling region just north of Santa Barbara. In a coastal upwelling system, the winds in our area are blowing towards the equator and that forces surface waters offshore. But that allows cooler nutrient-rich waters to come up from below. And that fuels phytoplankton blooms in the coastal region. Those blooms are important for productivity, and hence for fisheries. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) time series was founded in this region to study the upwelling system because it supports the large anchovy and sardine fisheries that are historically part of this area.

Our region is just one example of an eastern boundary upwelling system. These are found all over the world's oceans, both in the Atlantic and Pacific. And these are very key regions for phytoplankton production, for carbon uptake from the atmosphere, and carbon sequestration in the sediments and deep water. We're studying our region to gain information about these very important regions in general.

en: What are some of the main questions in your field?

KB: One of my main interests is to try and look at how iron is cycling and how it connects to the larger global cycle of carbon. How are microbes taking up iron, remineralizing iron, and turning it over in the ocean? How do those mechanisms actually work on a really detailed microbial and mechanistic level? That's something that interests me very much, but it's also significant to our ability to understand and model the carbon cycle overall.

We need to be able to describe the framework of connections between the major nutrients and the micronutrients in order to effectively model the global carbon cycle so that we can understand what's happening now, what's happened in the past, and what's going to happen going forward. In terms of CCE LTER, our goals are to understand the climate change impacts on the California Current ecosystem, how that system is responding to a warming event or changes in atmospheric forcing and what we can expect going forward in that system as well. That's a very interdisciplinary study. I'm just one small part of it, but it's really exciting for me to be able to interact with a whole range of biologists, ecologists, physicists, other chemists to try to figure out what's going on in this system.

The idea of seeding the ocean with iron became a high-impact story in the 1990s, when [Moss Landing Marine Laboratories oceanographer] John Martin said "give me a tanker of iron and I'll give you an ice age." And that really stimulated a lot of subsequent research in the field. The idea is that we can fertilize certain areas of the ocean by adding iron and stimulate algal growth and thereby draw down atmospheric carbon dioxide concentrations. A lot of subsequent research has gone into looking at just what areas of the open ocean are iron-limited and what kinds of iron fertilization, what kind of scales that operation would have to be conducted on to really have an impact on atmospheric CO2 concentrations.

Although it's still something that's mentioned in a geoengineering context, I think there's a growing consensus that iron fertilization would be extremely costly to implement on the kind of scale that would be required to really draw down atmospheric CO2 and the potential impacts on the ocean ecosystem, if we were to implement it on those scales, are not well known. It could disturb other cycles, like the nitrogen cycle for example. It could result in the production of other greenhouse gases that are damaging as well. So although iron fertilization is still of interest in that context, also in the context of smaller-scale operations that might be used for carbon sequestration, carbon credit-type operations, my own research is more focused on looking at how natural iron fertilization, how iron naturally gets into the ocean and interacts with microbes, how that impacts global biogeochemical cycles.

There are a lot of fundamental aspects of the iron cycle that we still don't really understand. Things like what forms of iron are most biologically available and to which organisms are these forms available? How does iron cycle and how quickly is it removed from surface waters? How far does iron move from a source of input, like a hydrothermal vent, for example. These are basic processes that we still don't understand. And in order to effectively model what's happening with iron in the ocean and how it interacts with the global carbon cycle, we need a lot more of this basic information.

en: What tools do you use in your research?

KB: It's challenging to study the concentration of iron in the ocean because the amount of it is vanishingly small. If you think of an Olympic size swimming pool, the amount of iron would equate to just a drop of water in that entire pool. So it's really an extremely tiny diffuse amount of iron that's present in open ocean seawater. This is why it can be such a struggle for marine life to get the iron that they need to support their biological processes. And it's a struggle for trace metal chemists who study trace elements in the ocean to get clean samples of ocean water when they're based on a ship that's literally made out of mostly iron and other metals.

It's a constant challenge to go out on this large metal object, sample the surrounding seawater where metals are present at low concentrations and not contaminate your samples. I have specialized sampling gear: a rosette with special bottles and special cables that I use. I can't just use the ship's main rosette to collect my samples. When I go to sea, I also bring a clean laboratory with me. That’s a special van that we set up with a positive pressure so no outside air can get in. Everything inside is non-metallic materials and that's where we process our samples, filter them, set up incubations to study the impact of metals on the ecosystem.

In the laboratory, I use a variety of instrumentation to measure trace metal concentrations and the chemical form of trace metals in seawater. But I work on the interface between chemistry and biology so I also use genomic tools to look at how trace elements like iron cycle in seawater. That can tell us both about trace metal chemistry in seawater and about the mechanisms that marine organisms are using to interact with and acquire these very scarce micronutrients in their environment.

en: Why did you come to Scripps?

KB: For me, coming to Scripps was obviously a great opportunity because of its reputation as one of the best places in the world for oceanography. I was trained as an oceanographer at Woods Hole Oceanographic Institution. Coming to Scripps as a faculty member was a dream come true. And here it's especially been great because I do such interdisciplinary research. Scripps is such a large center that we have a lot of expertise in any area of oceanography and earth science in general. The ability to get great students and interact with great faculty that have a variety of expertise has really been an advantage.

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