Brett D. Walker
Biography
Brett D. Walker, Ph.D., is Associate Professor in the Department of Earth System Science at the University of California, Irvine. Walker received a Ph.D. in Ocean Science from the University of California, Santa Cruz in 2011. From 2018 to 2024, he served as Canada Research Chair (Tier II) in Accelerator Mass Spectrometry and Marine Biogeochemistry at the University of Ottawa, where he also held the position of Interim Director of the André E. Lalonde Canadian Centre for AMS and Environmental Radionuclide Research and served as Principal Investigator for the Major Scientific Initiatives Fund supporting the national AMS laboratory.
Walker's research focuses on the sources, cycling, and transformation of marine dissolved and particulate organic carbon using radiocarbon and stable isotope approaches. His work has examined organic matter dynamics in diverse marine environments including the California Current upwelling system, the Gulf of Mexico, oxygen minimum zones, and the Canadian Arctic. Walker has participated in 16 field campaigns totaling over 150 days at sea, including expeditions aboard the CCGS Amundsen and multiple NOAA research vessels for CLIVAR/GO-SHIP programs. He has developed methodological advances in radiocarbon analysis, including improved sealed-tube zinc graphitization techniques for microgram carbon samples and small-volume ultrafiltration methods for size fractionation of dissolved organic matter.
Walker has authored or co-authored 47 peer-reviewed publications in journals including Nature Geoscience, Proceedings of the National Academy of Sciences, Geophysical Research Letters, and Global Biogeochemical Cycles. He has secured over $7.4 million CAD and $110,000 USD in research funding, including a $5.8 million CAD Canada Foundation for Innovation Major Scientific Initiatives award for the André E. Lalonde Accelerator Mass Spectrometry Facility. Walker serves on the Advisory and Planning Board for the National Ocean Sciences Accelerator Mass Spectrometry facility and has served as a reviewer for over 20 journals and multiple national funding agencies.
Return to topEducation
- Ph.D. in Ocean Science, University of California, Santa Cruz, 2011
- B.S. in Earth and Planetary Science, University of California, Santa Cruz, 2004
Distinctions
- Major Scientific Initiatives Principal Investigator: André E. Lalonde Canadian Centre for AMS and Environmental Radionuclide Research, University of Ottawa, 2022
- Canada Research Chair (Tier II) in Marine Biogeochemistry and Accelerator Mass Spectrometry, University of Ottawa, 2018-2024
- Outstanding Student Poster Award, ASLO Aquatic Sciences Meeting, 2005, 2007
- NSERC Discovery Grants Program - Accelerator Supplement, 2020-2023
- NSERC Discovery Launch Supplement (Early Career Award), 2020-2021
- Postdoctoral Scholarship, UCI Keck Carbon Cycle AMS Laboratory, 2012
- Doctoral Student Sabbatical Fellowship, UCSC Ocean Sciences, 2011
- Outstanding Student Achievement Award, UC Santa Cruz, Ocean Sciences, 2010
- Outstanding Teaching Assistant Award, UC Santa Cruz, Ocean Sciences, 2010
- Woods Hole Oceanographic Institute, National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Graduate Student Internship, 2009
Areas of Expertise
- Marine Biogeochemistry
- Dissolved Organic Carbon Cycling
- Accelerator Mass Spectrometry Applications
- Radiocarbon Isotope Tracing
- Arctic Ocean Carbon Dynamics
- Oxygen Minimum Zone Processes
- Molecular Size Fractionation
Recent Publications
- L. Jasperse, B.G.T. Else, L.A. Miller, G. Nickoloff, J. Walker, A.E. Fox, Brett D. Walker, “Tracing Pan-Canadian Arctic Water Masses and Dissolved Inorganic Carbon Cycling using Stable and Radiocarbon Isotopes” (opens in new tab), Global Biogeochemical Cycles, vol. 39, pp. e2024GB008179, 2025.
- Y. Shen, R. Benner, T.A.B. Broek, Brett D. Walker, M.D. McCarthy, “Special delivery of proteinaceous matter to deep-sea microbes” (opens in new tab), Science Advances, vol. 11, no. 12, 2025.
- K. McKee, H.A. Abdulla, L. O'Reilly, Brett D. Walker, “Cycling of bioavailable carboxyl-rich alicyclic molecules and carbohydrates in Baffin Bay” (opens in new tab), Nature Communications, vol. 15, pp. 8735, 2024.
- L. Baumser, L. Potts, Brett D. Walker, N. Mahmoudi, “Picky Eaters: Carbon isotopic evidence for the uniform bioavailability of riverine dissolved organic matter to a model marine microorganism” (opens in new tab), Geophysical Research Letters, vol. 51, no. 13, pp. e2024GL109326, 2024.
- C. Lewis, Brett D. Walker, E.R.M.D. Druffel, “Stable isotopic (δ¹³C) evidence for global microbial sequestration of refractory dissolved organic matter” (opens in new tab), Geophysical Research Letters, vol. 51, pp. e2023GL107684, 2024.
- A. Coppola, E.R.M. Druffel, T. Broek, N. Haghipour, T. Eglinton, M. McCarthy, Brett D. Walker, “Variable aging and storage of dissolved black carbon in the ocean” (opens in new tab), Proceedings of the National Academy of Sciences of the United States of America, vol. 121, no. 13, pp. e2305030121, 2024.
- E.R.M. Druffel, C. Lewis, S. Griffin, A. Flaherty, M. Rudresh, N. Hauksson, R. Key, A. McNichol, J. Hwang, Brett D. Walker, “Dissolved Organic Radiocarbon in the West Indian Ocean” (opens in new tab), Geophysical Research Letters, vol. 50, 2023.
- A. Fox, Brett D. Walker, “Sources and cycling of particulate organic matter in Baffin Bay: a multi-isotope δ¹³C, δ¹⁵N and Δ¹⁴C approach” (opens in new tab), Frontiers in Marine Science, vol. 9, pp. 846025, 2022.
- S. Zeidan, J. Walker, B.G.T. Else, L.A. Miller, K. Azetsu-Scott, Brett D. Walker, “Using radiocarbon measurements of dissolved inorganic carbon to determine a revised residence time for deep Baffin Bay” (opens in new tab), Frontiers in Marine Science, vol. 9, pp. 845536, 2022.
- Ellen R. M. Druffel, Steven R. Beaupré, Hendrik Grotheer, Christian B. Lewis, Ann P. McNichol, Gesine Mollenhauer, Brett D. Walker, “Marine Organic Carbon and Radiocarbon – Present and Future Challenges” (opens in new tab), Radiocarbon, vol. 64, pp. 1-17, 2022.
- C. Lewis, Brett D. Walker, E.R.M. Druffel, “New radiocarbon constraints on the global cycling of solid-phase extractable dissolved organic carbon” (opens in new tab), Geophysical Research Letters, vol. 48, pp. e2020GL090995, 2021.
- Walker B.D., T.P. Guilderson, K.M. Okimura, M.B. Peacock, M.D. McCarthy, “Corrigendum to "Radiocarbon signatures and size-age-composition relationships of major organic matter pools within a unique California upwelling system"” (opens in new tab), Geochimica et Cosmochimica Acta, vol. 312, pp. 392-395, 2021.
- Druffel E.R.M., Griffin S., Lewis C., Rudresh M., Garcia N., Key R., McNichol A., Hauksson H., Walker B.D., “Dissolved Organic Radiocarbon in the Eastern Pacific and Southern Oceans” (opens in new tab), Geophysical Research Letters, vol. 48, 2021.
- Walker B.D., Beaupré S.R., Griffin S., Walker J., Druffel E.R.M., Xu X., “A sealed-tube method for offline δ¹³C analysis of CO₂ via a Gas Bench II continuous-flow isotope ratio mass spectrometer” (opens in new tab), Rapid Communications in Mass Spectrometry, vol. 35, no. 7, 2021.
Most Cited Publications
- Christian A. Miller, Bernhard Peucker-Ehrenbrink, Brett D. Walker, Franco Marcantonio, “Re-assessing the surface cycling of molybdenum and rhenium” (opens in new tab), Geochimica et Cosmochimica Acta, vol. 75, pp. 7146-7179, 2011.
- Walker B.D., Beaupre, S.B., T.P. Guilderson, M.D. McCarthy, E.R.M. Druffel, “Pacific carbon cycling constrained by organic matter size, age, and composition relationships” (opens in new tab), Nature Geoscience, vol. 9, pp. 888-891, 2016.
- Druffel, E.R.M., Griffin, S., Coppola, A.I., Walker B.D., “Radiocarbon in dissolved organic carbon of the Atlantic Ocean” (opens in new tab), Geophysical Research Letters, vol. 43, no. 10, pp. 5279–5286, 2016.
- Walker B.D., S.R. Beaupre, T.P. Guilderson, E.R.M. Druffel, M.D. McCarthy, “Large-volume ultrafiltration for the study of marine dissolved organic matter radiocarbon signatures” (opens in new tab), Geochimica et Cosmochimica Acta, vol. 75, pp. 5187-5202, 2011.
- Broek, T.A.B., B.D. Walker, T.P. Guilderson, M.D. McCarthy, “Coupled ultrafiltration and solid phase extraction approach for the targeted study of semi-labile high molecular weight and refractory low molecular weight dissolved organic matter” (opens in new tab), Marine Chemistry, vol. 194, pp. 146-157, 2017.
- Walker B.D., McCarthy M.D., Fisher A.T., Guilderson T.P., “Dissolved inorganic carbon isotopic composition of low-temperature axial and ridge-flank hydrothermal fluids of the Juan de Fuca Ridge” (opens in new tab), Marine Chemistry, vol. 108, pp. 123-136, 2008.
- Broek T.A.B., Walker B.D., Guilderson T.P., Vaughn J.S., Mason H.E., McCarthy M.D., “Low Molecular Weight Dissolved Organic Carbon: Aging, Compositional Changes, and Selective Utilization During Global Ocean Circulation” (opens in new tab), Global Biogeochemical Cycles, vol. 34, 2020.
- Walker B.D., F.W. Primeau, S.R. Beaupre, T.P. Guilderson, E.R.M. Druffel, M.D. McCarthy, “Linked changes in marine dissolved organic carbon molecular size and radiocarbon age” (opens in new tab), Geophysical Research Letters, vol. 43, no. 19, pp. 10385–10393, 2016.
- Druffel E.R.M., Griffin S., Wang N., Garcia N., McNichol A.P., Key R.M., Walker B.D., “Dissolved Organic Radiocarbon in the Central Pacific Ocean” (opens in new tab), Geophysical Research Letters, vol. 46, pp. 5396-5403, 2019.
- Bour, A., Walker, B.D., Broek T.B., McCarthy M.D., “Radiocarbon analysis of individual amino acids: carbon blank quantification for a small-sample high pressure liquid chromatography purification method” (opens in new tab), Analytical Chemistry, vol. 88, no. 7, pp. 3521-3528, 2016.
Contact Information
Email: brett.walker@uci.edu
Phone: 949.824.1764
Address: 2212 Croul Hall, Irvine, CA 92697
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Last updated on 2/17/2026.