A Scientist's Life: Sarah Aarons

Earth scientist studies the role dust plays in shaping ecosystems

Sarah Aarons is an earth scientist at Scripps Institution of Oceanography at UC San Diego. She received her bachelor's degree in geological and environmental science at Stanford University in 2009 and PhD in geology from the University of Michigan in 2016.

explorations now: What do you do for a living?

Sarah Aarons: I describe myself as an isotope geochemist, so I'm primarily interested in understanding the geochemistry of natural earth surface materials. I'm using a variety of geochemical techniques ranging from wet chemistry to mass spectrometry. I'm interested in understanding the geochemical evolution of Earth’s surface through time and I primarily focus on sediments and dust both in the modern and paleoclimate records.

An isotope is a variation of an element with a different number of neutrons. Rocks, for example, are chemically distinct from one another so they vary based on the magma that they initially came from and their age. If you scoop up some rock or sediment from Australia and you compare it to rock or sediment from South America, both will have very distinct geochemical and isotopic compositions. We use these variations in isotope compositions as a way to fingerprint from where dust or sediment originated.

For example, if you are interested in probing the ecological significance of dust in a mountain ecosystem, you can measure the isotope composition of the bedrock, the soil, the dust transported to that site, and the vegetation. You can differentiate between nutrients supplied by atmospherically transported dust versus nutrients produced from the weathering of bedrock.

en: What got you into this field?

SA: I never was exposed to a geology class in high school. It wasn't until I took a geology class as an undergrad when I instantly fell in love with it.  I took two classes that resonated with me. The first one was an isotope geochemistry class and I just thought it was so cool that you could use isotopes as a way to trace what happened to a material. It's like being a detective and using science as a way to figure out where did this stuff come from? What happened to it during transport? How hot was it when this material was formed? The other class was paleoclimate and paleoclimate records. Marine sediment cores and ice cores extracted from the earth are like time machines that tell us information about the Earth’s surface thousands or millions of years ago.

en: What are some of your current projects?

SA: The projects that I'm currently working on are all dust- or sediment-related. One I'm involved in is looking at ice from Antarctica. Recently there was a study that came out that found over two million-year-old ice in the Allan Hills of Antarctica. I had an incoming graduate student travel to Antarctica this past winter where he helped with ice collection led by a team from Princeton University and he's going to be focusing on the geochemistry of dust in that record. We’re really interested in trying to understand how dust composition and flux vary over really significant climate transitions, and how this may be related to atmospheric CO2 concentrations.

We've also been focusing on the ecological significance of dust in mountain ecosystems. We focus on places that are underlain by bare rock. The rocks beneath the Sierra Nevada and San Jacinto Peak are primarily granite, which can have low amounts of phosphorus, a critical nutrient needed to sustain life. When you don't have enough nutrients that are generated by the weathering of bedrock beneath plants, the transport and deposition of dust from other areas can actually be a more important driver of landscape evolution than we previously thought.

Our field site at San Jacinto Peak is right outside of Palm Springs, Calif. This is a really unique place because the elevation change from the valley floor in Palm Springs to the top of the peak is over 10,000 feet. This results in significantly different climate conditions as you move up the mountain profile.

We are probing how dust flux and compositions change over the course of a year and monitoring how they change from the summer to winter. Some specific questions we are hoping to answer are whether there are time or spatial variations in dust from Asia, from nearby agricultural activity, or originating from the Salton Sea, which is currently drying out. A lot of this research is building on previous work in an effort to understand whether dust from long-range sources like Asia is actually fertilizing the plants that are growing in ecosystems that are nutrient limited.

en: What are some of the tools you use in your research?

SA: A lot of my research involves fieldwork. I measure the geochemistry of dust and sediments from samples I have collected. My work involves going to places like Antarctica, California, and some of my work brings me to Alaska. Once I have my samples in hand, I do my processing in a clean lab environment. The clean lab is a lab that's designed to keep out any sort of outside contamination because the isotopes I’m measuring in dust and sediment are trace elements. And then when you're thinking about dust that's coming from ice cores, it is in itself a trace amount in ice. It's as low as 15 parts per billion, which is like 15 drops in an Olympic swimming pool.

I limit the amount of metal that's in my lab and then we always suit up when we do our processing and chemistry. We use a lot of strong acids to dissolve our sediment and dust samples to extract the element that we are interested in measuring.

en: Why did you come to Scripps?

SA: One of the reasons I was really excited to come to Scripps is that it's really a multidisciplinary institution. There are people here who are working on topics ranging from isotope geochemistry to atmospheric dynamics to understanding how the mantle and the lithosphere are interacting with each other.

Scripps has this really strong history of isotope geochemistry and polar research, specifically ice core research, here already. So I felt like I would be really well supported in terms of intellectual stimulation and would have a great set of colleagues to collaborate with.

I measure isotopes of the element neodymium and one of the standards that we use for measuring this isotope is called the La Jolla neodymium reference standard because it was made here. So it's cool to be able to come here and be at the place where these standards were made initially many years ago.

I also think it's a really great place to get inspired. The series of lectures that takes place here, for example, provides a natural opportunity to interact with colleagues, where you are exposed to the research and projects they are involved in. Common themes throughout different fields can lead to exciting multidisciplinary collaborations. Another reason I was really excited to come to the University of California was because of the strong institutional commitment to addressing inequities in science such as the number of underrepresented minorities and women in STEM fields and in faculty positions. I think that the strong commitment to equity, diversity, and inclusion is something that was really attractive to me. You can't find that at a lot of other institutions. That's one of the primary reasons why I wanted to come here.

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