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School of Earth and Environmental Sciences
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Gillian Stewart

Marine Biogeochemistry

Science Building, Room E218
Phone: 718-997-3104

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Research Interests

Dr. Stewart is a biogeochemist with interest in the interactions between organisms and elemental cycling, particularly in the ocean. Currently she uses natural radionuclides to investigate the trophic transfer and bioaccumulation of metals by plankton, as well as to trace organic carbon cycling in the surface ocean. Her work sheds light on the mechanisms of contaminant accumulation in ecosystems as well as the ocean’s potential to sequester atmospheric carbon dioxide, a greenhouse gas. Further, her research into the behavior of present-day radioactive tracers may provide insight into the use of naturally-occurring paleotracers in the ocean. Primarily she has focused her research on the unique, short-lived, particle-reactive isotope polonium-210. At Queens College she has pursued regional environmental contaminant studies, done local research on the impacts of anthropogenic regional warming, and continues her work on large-scale oceanographic questions. She has been an active participant in the international GEOTRACES project.


Possible Future and Student Projects:

  • Metal accumulation and distribution in local coastal waterways
  • The influence of dust on carbon assimilation in plankton
  • Development of more specific environmental tracers for elemental cycling
  • The importance of food web structure in determining bioaccumulation
  • The effect of different particle types on radioisotope fractionation
  • Species-specific nutrient uptake and loss in the plankto


Teaching Philosophy

My teaching philosophy is very straight-forward: Tough but fair.

Courses Taught:


  • GEOL 08 Oceanography
  • GEOL 25 Natural Resources and the Environment
  • ENSCI 99 A Practical Guide to Environmental Choices
  • ENSCI 100 Our Planet in the 21st Century
  • GEO 356 Advanced Oceanography
  • GEO 373 Long Island Sound: Past and Present Climate
  • HNRS 228: Honors Seminar: Waterways and Climate in NYC
  • HMNS 102: Honors in Math and Na Sciences Directed Research


  • GEO 799.3 Special Topics: Environmental Biogeochemistry
  • GEO 799.3 Special Topics: Plankton Ecology
  • GEO 791.3 Special Topics: Tracers in the Sea
  • GEO 799.3 Special Topics: Environmental Science Course Design

Publications (selected, for full list see CV)

Hayes, C. T., Black, E. E., Andersen, R. A., Baskaran, M., Buesseler, K. O., Charette, M. A., Cheng, H., Cochran, J. K., Edwards, R. L., Fitzgerald, P., Lam, P. J., Lu, Y., Morris, S. O., Ohnemus, D. C., Pavia, F. J., Stewart, G., and Tang, Y. (2018) Flux of particulate elements in the North Atlantic Ocean constrained by multiple radionuclides. Global Biogeochemical Cycles,

Tang, Y., Castrillejo, M., Roca-Martí, M., Masqué, P., Lemaitre, N., and G. Stewart (2018) Distributions of 210Po and 210Pb activities along the North Atlantic GEOTRACES GA01 (GEOVIDE) cruise: partitioning between the particulate and dissolved phase. Biogeosciences, 15, 5437-5453,

Tang, Y., Stewart, G., Lam, P. J., Rigaud, S., & Church, T. (2017). The influence of particle concentration and composition on the fractionation of 210 Po and 210 Pb along the North Atlantic GEOTRACES transect GA03. Deep Sea Research Part I: Oceanographic Research Papers.

Schallenberg, C., Ross, A. R., Davidson, A. B., Stewart, G. M., & Cullen, J. T. (2017). Temporal variability of dissolved iron species in the mesopelagic zone at Ocean Station PAPA. Journal of Marine Systems, 172, 128-136.  

Rice E.J. and G. Stewart (2016) Decadal changes in zooplankton abundance and phenology of Long Island Sound reflect interacting changes in temperature and community composition. Marine Environmental Research, 120, 154-165.

Mackinson, B. L., Moran, S. B., Lomas, M. W., Stewart, G. M., & Kelly, R. P. (2015). Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific. Biogeosciences, 12(11), 3429-3446.

 Seebaugh DR, Wallace WG, L’Amoreaux WJ, Stewart GM (2012) Assimilation of elements and digestion in grass shrimp pre-exposed to dietary mercury.  Archives of Environmental Contamination and Toxicology, 63(2), 230-240.

Stewart, G., Moran, S.B., Lomas M., and Kelly, R.P. (2010) Direct comparison of 210Po, 234Th and POC particle-size distributions and export fluxes at the Bermuda Atlantic Time-series Study (BATS) site. Journal of Environmental Radioactivity, 102 (5), 479-489.

Buesseler K., Benitez-Nelson C., Moran S. B., Burd A., Charette M., Cochran J.K., Coppola L., Fisher N., Fowler S., Gardner W., Guo L., Gustafsson O., Lamborg C., Masque P., Miquel J-C., Passow U., Santschi P., Savoye N., Stewart G., Trull T., (2006) An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC proxy. Marine Chemistry, 100, 213-233.

Stewart G.M., S.W. Fowler, J.L. Tessyie, O. Cotret, and N.S. Fisher (2005) Contrasting the transfer of polonium-210 and lead-210 across three trophic levels in the marine plankton. Marine Ecology Progress Series, 290, 27-33.

Liu X.F., G.M. Stewart, J.K. Cochran, C. Lee, R.A. Armstrong, D. Hirschberg, J.C. Miquel, and B. Gasser (2005) Constraints on the differences between POC measured in samples from Niskin bottles and in-situ pumps. Deep Sea Research I, 52(7), 1324-1344.

Stewart G.M. and N.S. Fisher (2003) Bioaccumulation of polonium-210 in marine copepods. Limnology and Oceanography, 48(5), 2011-2019.



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