PEOPLE

Faculty

Staff

Associated Researchers

Jordan Hemingway

Jordan Hemingway

Post-doctoral Fellow
I’m interested in connections between the geologic and biospheric carbon cycles. Specifically, my work aims to understand how processes occurring in river basins transfer carbon between these two cycles in order to regulate atmospheric CO2 concentrations over geologic timescales. To do so, I combine a suite of isotope geochemistry techniques (including compound-specific isotope measurements and novel reaction monitoring methods) with inverse models, satellite products, and geospatial analysis. My current projects include analysis of multi-year time-series samples from the Ganges-Brahmaputra and Congo Rivers, high-frequency samples from mountainous rivers in Taiwan, isotope analysis of bacteriohopanepolyols in continental shelf sediments, and development of the Ramped PyrOx radiocarbon instrument. I'm additionally working on reconstructing the mechanisms that control Cenozoic CO2 variability using inverse modeling methods.

Graduate Students

Emma Bertran

Emma Bertran

Fourth year Ph.D student

Emma just moved to Boston from the land of the moose, the goose and the beaver. She received her undergraduate degree from McGill University, majoring in Biology and minoring in Geology, and recently submitted her Master’s thesis (also at McGill), which dealt with the fractionation of sulfur isotopes by a mutant strain of Desulfovibrio vulgaris incapable of reducing sulfate. Read more about Emma Bertran

Ana Gonzalez Valdes

Ana Gonzalez Valdes

First Year Ph.D Student

Ana Gonzalez Valdes received her B.A. in Earth Sciences from Columbia University in 2016. At Columbia and Caltech she worked to understand how microbes in unique environments cycle nutrients like phosphorus and sulfur. At Harvard Ana will be spanning the Johnston and Pearson labs and hopes to dig deeper into microbial nutrient cycling and how it can be measured isotopically.

Frasier Liljestrand

Frasier Liljestrand

Fourth year Ph.D student

Frasier got his BS in Earth Science from Rice University in 2013. While he was at Rice, he did research in biogeochemistry focusing broadly on trying to quantify global carbon fluxes and budgets. Here in the Johnston group Frasier hopes to expand his knowledge of global sulfur cycling and how the global cycles are expressed locally.

Anna Waldeck

Anna Waldeck

Second Year Graduate Student

Anna completed a BSc in Chemistry and in Geophysical Sciences at the University of Chicago in 2014. Since 2013 she has worked in a stable isotope ratio laboratory there, measuring oxygen isotope ratios in phosphates contained in small shelly fossils and tooth enamel. Anna’s interests pertain to reconstructing chemical cycling in ancient environments through a combination of field work and laboratory techniques.

Hoffman Lab, RM 305

Undergraduate Research Assistants

M_Miller

Matthew Miller

Undergraduate Research Assistant
My work mainly focuses on establishing novel mineral proxies to track sulfur cycle dynamics in deep time, notably carbonate-associated sulfate (CAS). This system, alongside the robust yet infrequent barite record, potentially represents a powerful way to track sulfur and oxygen isotope behavior in order to constrain marine chemistry in the past. Additionally, I have started some culture work with the sulfate-reducing bacterium Desulfovibrio vulgaris, and am currently investigating the evolution of its isotope-fractionating metabolism.

Gone, But Not Forgotten...

Alex Bradley

Alex Bradley

Former Postdoctoral Fellow

Now on the faculty at Washington University at St Louis.

Ben Cowie

Ben Cowie

Former Post-doctoral Fellow

Ben is an isotope geochemist with diverse interests in the Earth sciences. In the Johnston Group, he is currently exploring questions surrounding the

Read more about Ben Cowie
Renata Cummins

Renata Cummins

Former Undergraduate Thesis Student

Switched coasts and is working in the Bay Area, CA

Ben Gill

Ben Gill

Former Post-doctoral Fellow

Now on the faculty at Virginia Tech.

Alex Morgan

Alex Morgan

Former Thesis Student

Alex is now at Cambridge University working on her master's degree.

Tor O'brien

Former Thesis Students

Now a PhD candidate at Washington Univesrity in St. Louis working with Dave Fike

Joseph Shaffer

Joseph Shaffer

Former Undergraduate Thesis Student

Joe is an undergraduate concentrating in earth and planetary science with a secondary in chemistry. His thesis is a paleoenvironment study of the Utica

Read more about Joseph Shaffer
Scott Wankel

Scott Wankel

Former Postdoctoral Fellow

Now on the faculty at Woods Hole Oceanographic Institute.