Julio Sepúlveda

  • Associate Professor
  • Associate Director of Community and Belonging, INSTAAR
  • GEOLOGICAL SCIENCES
Address

Office: SEEC S256

Biogeochemistry • Geobiology • Biomarker research • Paleoclimate & paleoceanography

Organic and stable isotope biogeochemistry, geobiology, biomarker research, paleoceanography, paleoclimate, extreme climates, mass extinction events

I joined CU in August 2014 as an Assistant Professor in Geological Sciences and Fellow at INSTAAR. I came to CU after having worked as a postdoctoral associate and research scientist in the Geobiology and Astrobiology Group of Prof. Roger Summons in the Department of Earth, Atmospheric and Planetary Sciences at MIT. Originally from Chile, I began my career as a marine biologist (BSc) and chemical oceanographer (MSc) at the University of Concepción, Chile under the supervision of Prof. Silvio Pantoja (Marine Organic Geochemistry Group), where the field of organic biogeochemistry fascinated me. After feeling the desire to explore the world and expand my expertise, I moved to Germany and obtained a PhD in Marine Geosciences from the University of Bremen under the supervision of Prof. Kai-Uwe Hinrichs (Organic Geochemistry Group).

Organic Geochemistry Lab  News about Julio 

 

Research

My research group studies the interplay between microorganisms, biogeochemical processes, and climate in contemporary settings (e.g., continental margins, marine oxygen minimum zones, extreme environments), and paleo-ecosystems across major climatic/biotic transitions in Earth history (e.g., mass extinction events, greenhouse climates, glacial-interglacial transitions). We approach these systems with a focus on the structures, distributions, and stable isotope composition of cell membrane lipids (biomarkers) that can be identified in water bodies, sediments, soils, and their fossilized remains preserved in the rock record. See more at the Organic Geochemistry Lab

Periods of extreme climates in the geological record are associated with changes in ocean geochemistry and varying degrees of extinction, and can serve as partial analogues to study ecosystem resilience to projected scenarios of ocean deoxygenation and acidification. However, our current understanding of ecosystem’s resilience derives almost exclusively from the body fossil record, thus disregarding important microbial biota lacking hard, fossilizable skeletons, which exert strong control on ocean geochemistry and climate.

My current efforts aim to unravel the role of photoautotrophic eukaryotes and prokaryotes, and chemosynthetic prokaryotes in sustaining carbon fixation across periods of extreme climate change and extinction, as well as to unravel the environmental responses (e.g., water column stratification, oxygenation, nutrient budgets) to CO2 forcing. I currently study five major climatic events associated with varying degrees of extinction during the Mesozoic and Cenozoic: (a) end–Triassic mass extinction; (b) end-Cretaceous mass extinction; (c) early Jurassic OAE; (d) mid-late Cretaceous OAEs; (e) Paleocene-Eocene Thermal Maximum (PETM).

Marine oxygen minimum zones (OMZs) are key areas of the world’s ocean for the recycling of carbon, nutrients and the release of greenhouse gases through microbial processes, therefore influencing the global climate system.  OMZs have expanded over the last five decades, and this expansion is expected to continue, in parallel with ocean acidification, in response to current and projected trends of climate change. Therefore, reliable proxies for oxygenation and microbial processes in the past are required to constrain the response of OMZs to future warming scenarios.

My current research efforts aim to illuminate microbially–driven processes in modern oxygen–depleted environments through the tandem analysis of lipid biomarkers and gene-based techniques, as well as the validation of biomarkers as proxies for paleoxygenation and ocean biogeochemistry in sedimentary records.  I presently study the provenance and diversity of microbial biomarkers across five distinctive oxygen-depleted marine environments. Results from this study are expected to improve our understanding of biomarkers for microbial metabolism involved in nitrogen and sulfur cycling under different degrees of anoxia/euxinia.  Also, I currently study the biogeochemical evolution of the Chilean OMZ over past warm climatic transitions (i.e., Marine Isotope Stages 5 and 11, mid-Holocene warm period). A particular interest is to elucidate the relative role of different denitrifying processes (denitrification vs. anaerobic ammonium oxidation) on controlling nutrient budgets and climate variability. These results should greatly facilitate our interpretation of present and past responses of OMZs to natural and anthropogenic forcing, thus assisting our understanding of potential future scenarios.

Continental margins are important components of the global carbon cycle as they support high levels of primary productivity and increased carbon burial rates.  I am interested in the cycling of marine and terrestrial organic mater along continental margins subject to increasingly human pressure. My work also focuses on the validation of organic geochemical proxies for paleoclimate reconstructions.  Current areas of study include the fjord system of Patagonia and the upwelling area of central and northern Chile.

Education

  • PhD (Marine Geosciences): University of Bremen, Germany, 2008
  • MS (Oceanography): University of Concepción, Chile, 2005
  • BS (Marine Biology and Oceanography): University of Concepción, Chile, 2001

Awards

  • School of Science Infinitive Kilometer Award, MIT, USA, 2012
  • MARUM Research Prize – Best PhD thesis in Marine Geosciences, University of Bremen, Germany, 2010
  • Best undergraduate thesis in Marine Biology, University of Concepción, Chile, 2000
  • Best student presentation in Biological Oceanography, Chilean Society of Marine Sciences, 1999

Current students and postdocs

Join us

Interested in joining the Organic Geochemistry Lab as a student or postdoc? Contact Prof. Julio Sepúlveda directly for current opportunities.

Courses taught

  • GEOL 4700/5700-008: Organic Geochemistry
    • This course explores the “biomarker concept” as a tool to elucidate biogeochemical and climatic processes in natural systems through four fundamental questions: How can we characterize and classify organic molecules in complex, natural mixtures? What processes control the synthesis, preservation and destruction of organic matter in nature? How can we use lipid biomarkers to study biogeochemical processes in modern and ancient systems? How can biomarkers inform us about Earth’s past climate and biota.
  • GEOL 5700-030: Geological Topics Seminar: Lipid Biomarkers in the Geosciences
    • Recent analytical advances in organic and stable isotope geochemistry have revolutionized the Earth Sciences by providing an ever-growing number of tools to study the complex interplay between biology, biogeochemistry, geology and climate at different time scales. This course for graduate students explores hot topics in lipid biomarker and compound-specific stable isotope research. Compared to the regular Organic Geochemistry class (GEOL 4700-003/5700-0044), this course will be conducted in seminar format with interspersed small background lectures, and with a stronger focus on specific applications in the Earth Sciences. We will read and discuss seminal and recent research papers that are expanding our understanding of how our planet works, and how it has changed since the emergence of life.
  • GEOL 3040: Global Change: The recent geological record
    • This course for undergraduate students explores the science of global change with a focus on how the geological record can inform the study of future climate change. We discuss the basics of the global climate system, how the climate of our planet has changed over geological time scales due to natural processes, and how it has changed and will continue to change due to human impact. Students will learn: (a) How the climate system works; (b) What factors cause climate to change across different time scales; (c) How scientists use different archives (records) and tools (proxy or proxies) to study climate change in the past (paleo-climate); (d) How scientists use observations, models, and theory to make predictions about future climate change and its consequences for our planet.

Outreach

In a TED-style talk, Julio shares how he came to investigate the tiny microbes that fill our oceans. He describes what they can tell us about climate through time, the impact of climate change on the ecosystems that depend on these microbes, and how we can all contribute to protecting our oceans and planet. Julio’s talk was part of CU Boulder's annual Research & Innovation Week, where the 2022 Faculty Fellows gave short talks at the Dairy Arts Center in Boulder.

 

Publications