Dr Emma Kast: Research Fellow in Geography, Geology and Geophysics

Emma joined Trinity Hall in 2020 to study the marine nitrogen cycle of the early Cenozoic period and how that can inform our understanding of today’s climate.

Where did you grow up and live before coming to Cambridge?

I grew up in Phoenix, Arizona in the southwest US. I moved to New York for university, and then New Jersey for my PhD.

What made you want to specialise in the marine nitrogen cycle?

My university degree is in physics and chemistry, and I took a paleoclimate course my last year which I really loved. The Earth sciences appealed to me because it includes chemistry and physics in a way that is applied to the natural world! I applied to a variety of PhD programs, and ultimately decided to work with my advisor, Danny Sigman, who is an expert on the marine nitrogen cycle. Biogeochemical cycles, including the nitrogen cycle, are like this intricate web where pulling one strand can affect all the others. Understanding those connections is a fascinating puzzle, particularly when you add in the fact that we are looking into the past using the chemistry and isotope composition of fossils that are millions of years old!

What does it mean to you to be the recipient of a research fellowship at Trinity Hall?

I am very thankful and proud to be the recipient of a research fellowship at Trinity Hall. The independence and the stability of a three-year position have certainly allowed me the freedom to direct my own research path and the space to be creative. While I haven’t been able to fully engage with the College community yet, I am also excited to have the chance to be here in Cambridge and to be part of the College.

Dr Emma Kast
Dr Emma Kast

Talking of engaging with the College community, how has Lockdown affected your ability to interact with the College community? What do you miss the most?

Lockdown has certainly limited my ability to interact with the College community. Having arrived in October, I have so far missed out on experiencing normal College events and just the chats over lunch and coffee that helps in getting to know people. While there are certainly light-hearted things I miss (for example, playing volleyball!) I think most of all I look forward to worrying less about the health of my family and friends.

What can the global changes during the early Cenozoic period teach us about Earth’s environment today? Are there any parallels you can draw between the environmental changes we’re experiencing now and those in the Cenozoic period?

There are absolutely ways in which the Cenozoic (the last 65 million years) (and more broadly, studying paleoclimate and paleoceanography in general!) can teach us about Earth’s environment today. While not my own work, for one example there has been some really interesting research done on temperature reconstructions along with climate modeling of the Cenozoic, which has given us insights into the long-term “climate sensitivity” or how strongly Earth’s temperature responds to CO2 concentrations, particularly at higher CO2 concentrations which existed in the early Cenozoic. Looking toward the past is one way we can have access to very different environmental conditions, like a natural experiment. More specifically to my research, examining the nitrogen cycle over the early Cenozoic by constructing new isotope records from marine fossils we found some results that were really surprising to us given what we thought should happen to nitrogen during the long-term cooling from the early Cenozoic to present day. To summarize, the nitrogen cycle is sensitive to how much oxygen is in the ocean. Oxygen is more soluble under warmer temperatures, leading to greater ocean oxygen concentrations. From this, we expected that the nitrogen cycle changes we saw from our isotope records should be related to temperature. However, this was not the case at all! We found that oxygen and nitrogen changes may have been driven more by ocean circulation rather than temperature. This has implications for our understanding of the controls on the marine nitrogen cycle in the past, present, and future.

You work with the nitrogen isotope composition of fossils to reconstruct the nitrogen cycle. What types of organisms are best for this purpose?

The fossils we have been using to reconstruct the nitrogen cycle are a group of animals called foraminifera. They are small single-celled heterotrophs and form a carbonate shell. Those that live in the surface ocean are called planktonic (or planktic) foraminifera, and tend to be good recorders of oceanographic conditions at the surface. And importantly, they can be abundant in marine sediments! Because they are small, we actually measure 100s of individual fossil shells at once. The chemistry and isotopic composition of foraminifera have been used to understand all sorts of things about paleoclimate and paleoceanography.

Sample of foraminifera (fossil shells)
Sample of foraminifera (fossil shells)

You work in a related field to Graduate Tutor Dr Sasha Turchyn. How does your research relate to hers?

My research is closely related to Dr Sasha Turchyn’s, and much of my research here will take place in her lab. Dr Turchyn has a wide range of research interests, one of which is the biogeochemical cycling of sulfur and carbon over Earth History. Interestingly, there are some signs that profound shifts in the cycling of sulfur and nitrogen (as revealed from isotopes in foraminifera!) happened at a similar time in the early Cenozoic (specifically from 57 to 50 million years ago). However, there are a lot of unresolved questions – did these changes actually happen at the same time? What are the underlying mechanisms that could link these cycles? What are the implications for ocean biogeochemistry and productivity?  My research here will use my PhD expertise working on the marine nitrogen cycle and Dr Turchyn’s expertise in the sulfur and carbon cycles to try to answer some of these questions.

What is the biggest ‘unknown’ in your research area that you would like to be able to explain/solve?

This is such a tough question! In thinking about biogeochemical cycles and Earth history, each one of us researchers does a small bit – but together we slowly build up a much more clear and robust understanding of what happened in the past and why. That being said there are certainly lots of outstanding questions about the Cenozoic! As one major example, there is a long-term cooling that happens over most of the Cenozoic that is due to changing CO2 concentrations. However, the underlying reason or mechanism for the changes in CO2 is still a matter of great interest. Understanding how nitrogen, sulfur, and carbon change over these intervals may play a part in unraveling that story.

Finally, and importantly, how do you relax?

While I am still building up my art supply stash after an international move, I have been doing some watercolors and printmaking. I really enjoy reading, particularly science fiction. And during lockdown I have started playing some videogames, my favorite recently has been Ori and the Blind Forest. Plus plenty of lovely walks around Cambridge with my boyfriend. In non-COVID times I usually play volleyball regularly, looking forward to when that is possible again!

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