Steven D’Hondt


Life in the sediment beneath Earth’s ocean takes place at an extremely slow pace, under some unusual conditions and yet supplies a tremendous amount of information — enough to provide Dr. Steven D’Hondt with life-long research opportunities.

“My principal focus is studying the nature and consequences of life beneath the sea floor, including its activities, its diversity, and the organismal properties that allow life under these extraordinary conditions,” he says.

D’Hondt received a bachelor’s degree in geology from Stanford University and then worked at the U.S. Geological Survey in California studying ocean history. The work involved looking for evidence of ancient asteroid and comet impacts in marine sediment and put him in contact with other researchers who studied the fossil content of sediment. “I learned that we can use planktonic fossil history as a window to understand what the oceans used to be like — and to understand patterns and processes of evolution,” he explains.

Interested in Earth history, he obtained his doctorate in geological and geophysical sciences from Princeton. There were 4 or 5 micropaleontologist openings in the country at that time and the posted opening at GSO, he says, “was the plum job.” He applied and was accepted.

While researchers have studied ocean sediment since the middle of the 19th century, the field exploded in the 1960s when deep ocean drilling techniques were developed. These techniques made it possible to extract long cores from the sea floor.

Once the cores are extracted, a lot of their properties can be analyzed on board the drillship.

What is amazing about the microbes deep in ocean sediment, he says, is their slow rate of activity in contrast to microbes that are on the sea floor or in cultures. “The respiration rate of the average subseafloor microbe is a thousandth of the rate of the microbes on the seafloor, which in turn is one thousandth of the rate of microbes in bench-top cultures. They are breathing a million times more slowly than the things people study in the lab. It takes them hundreds to thousands of years just to replace the molecules in their bodies.” The energy fluxes that are available to the microbes are far below the theoretical level for cell division. “In other words they violate our understanding of the world. Or perhaps they are not dividing at all, in which case something in a 100-million year old sediment might be 100 million years old—so either they are immortal or they are capable of dividing on much less energy than we think is necessary to divide.”

Another “energy” project that D’Hondt and his students are working on is studying the possibility that microbes in very organic-poor sediments may be living off the natural radioactive splitting of water. “The jury is out on that—we don’t yet know the extent to which they are living off this process.”

“Our calculations suggest that there is as much or more energy available from radioactive splitting of water as from buried organic matter in some parts of the ocean,” he explains. This study is being done in the South Pacific and North Atlantic in abyssal clay where accumulation of sediment is extremely slow—as low as 10 centimeters in a million years.

Although life in deep ocean sediment is extremely slow, rapidly developing technology in gene sequencing has made D’Hondt’s life work a lot faster.

D’Hondt does a considerable amount of outreach. He was a principal in the URI Honors Colloquium in 2008 and all of his expeditions include an outreach component, typically led by a secondary school teacher who sails as a member of the shipboard science party.


I study life in marine sediment, deep beneath the seafloor. This deep subsurface world contains one of the very few ecosystems not yet pervasively altered by humans. With my students and collaborators, I study the abundance, activities and evolution of life in this remote microbial ecosystem. In doing so, we explore fundamental limits to life on Earth. Very little energy is available to support life in this ecosystem. We have demonstrated that these microbes respire orders of magnitude more slowly than microbes in the surface world. On average, they take hundreds of years to turn over the molecules in their bodies. Despite these very slow rates of activity, the total amount of life in marine sediment rivals the total amount in all the waters of the entire ocean. Some of my students are currently testing the possibility that many subseafloor microbes live on hydrogen produced by natural radioactive splitting of water. Other members of my group are documenting (i) microbial exchange between the ocean and this deep subsurface world, and (ii) the nature of taxonomic selection in this extraordinarily challenging environment.

My most recent major accomplishment is my discovery (through leadership of a large project) that oxygen penetrates through the entire sediment column in as much as 1/3 of the world ocean. Subsurface microbes use that oxygen to change the chemistry of the sediment and underlying volcanic rock. This activity may in turn affect the chemistry of Earth’s upper mantle and atmosphere on timescales of millions to billions of years.


Ph.D. Geological and Geophysical Sciences, Princeton University, 1990

B.S. Geology, Stanford University 1984

I regularly teach graduate courses in geobiology and marine stratigraphy. He and Chris Roman regularly co-teach an introductory undergraduate course on Ocean Exploration.

Selected Publications

D’Hondt, S., F. Inagaki, C. Alvarez Zarikian, L.J. Abrams, N. Dubois, T. Engelhardt, H. Evans, T. Ferdelman, B. Gribsholt, R. N. Harris, B.W. Hoppie, J.-H. Hyun, J. Kallmeyer, J. Kim, J.E. Lynch, C.C. McKinley, S. Mitsunobu, Y. Morono, R.W. Murray, R. Pockalny, J. Sauvage, T. Shimono, F. Shiraishi, D.C. Smith, C.E. Smith-Duque, A.J. Spivack, B.O. Steinsbu, Y. Suzuki, M. Szpak, L. Toffin, G. Uramoto, Y.T. Yamaguchi, G. Zhang, X.-H. Zhang and W. Ziebis, 2015. Presence of oxygen and aerobic communities from seafloor to basement in deep-sea sediment, Nature Geoscience 8, 299-304, DOI: 10.1038/NGEO2387.

Walsh, E.A., D.C. Smith, M.L. Sogin and S. D’Hondt, 2015. Bacterial and archaeal biogeography of the deep chlorophyll maximum in the South Pacific Gyre, Aquatic Microbial Ecology 75, 1-13, DOI: 10.3354/ame01746. Selected as a Feature Article by the Editors-in-Chief.

D’Hondt, S., G. Wang and A.J. Spivack, 2014. The underground economy (Energetic Constraints of Subseafloor Life), Chapter 2.3 in Earth and Life Processes Discovered from Subseafloor Environment – A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP), R. Stein, D. Blackman, F. Inagaki, and H.-C. Larsen (Eds.), Series Developments in Marine Geology, Elsevier Amsterdam/New York, p 127-148 of 804 pp.

Gallagher, S.J., N. Exon, M. Seton, M. Ikehara, C.J. Hollis, R. Arculus, S. D’Hondt, C. Foster, M. Gurnis, J.P. Kennett, R. McKay, A. Malakoff, J. Mori, K. Takai, and L. Wallace, 2014. Exploring new drilling prospects in the Southwest Pacific, Scientific Drilling 17, 45–50, DOI:10.5194/sd-17-45-2014.

Lado Insua, T., A.J. Spivack, D. Graham, S. D’Hondt and K. Moran, 2014. econstruction of Pacific Ocean bottom water salinity during the Last Glacial Maximum, Geophys. Res. Lett. 41, 2914–2920, doi:10.1002/2014GL059575..

Miller, J.H., L. Kloepper, G.R. Potty, A.J. Spivack, S.L. D’Hondt, C. Turner and A.M. Simmons, The effects of pH on acoustic transmission loss in an estuary, 2014. Proceedings of Meetings on Acoustics 22, 005001, DOI: 10.1121/2.0000007.

Sauvage, J., A.J. Spivack, R.W. Murray and S. D’Hondt, 2014. Determination of in situ dissolved inorganic carbon concentration and alkalinity for marine sedimentary porewater, Chemical Geology 387, 66-73.

D’Hondt, S., 2013. Subsurface sustenance, News and Views, Nature Geoscience 6, 426–427, doi:10.1038/ngeo1843.

D’Hondt, S., F. Inagaki, C Alvarez Zarikian and the IODP Expedition 329 Scientists, 2013. IODP Expedition 329: Life and habitability beneath the seafloor of the South Pacific Gyre, Scientific Drilling 15, 4-10.

Dunlea, A.G., R.W. Murray, R.N. Harris, M.A. Vasiliev, H. Evans, A.J. Spivack, and S. D’Hondt, 2013. Assessment and Use of NGR Instrumentation on the JOIDES Resolution to Quantify U, Th, and K Concentrations in Marine Sediment, Scientific Drilling 15, 57-63.

Colwell, F.S., and S. D’Hondt, 2013. Nature and extent of the deep biosphere, in Carbon in the Earth, Reviews in Mineralogy and Geochemistry 75, ed. by R.M. Hazen, R.J. Hemley, A. Jones and J. Baross, 547-574.

D’Hondt, S., 2012. Introduction to Zachos, J. C., Arthur, M. A., and Dean, W. E., 1989, Geochemical Evidence for Suppression of Pelagic Marine Productivity at the Cretaceous/Tertiary Boundary. Nature, v. 337, p. 61-64, for Foundations of Paleoecology.

Kallmeyer, J., R. Pockalny, R. Adhikari, D.C. Smith and S. D’Hondt, 2012. Global distribution of subseafloor sedimentary biomass, Proceedings of the National Academy of Sciences 109(40), 16213-16216.

Røy, H., J. Kallmeyer, R.R. Adhikari, R. Pockalny, B.B Jørgensen and S. D’Hondt, 2012. Aerobic microbial respiration in 86-million-year-old deep-sea red clay, Science 336 (6083), 922-925, DOI: 10.1126/science.1219424. Erratum (figure correction) in Science 336 (6088), 1506, DOI: 10.1126/science.336.6088.1506.

Lomstein, B.A., A.T. Langerhuus, S. D’Hondt, B.B. Jørgensen and A.J. Spivack, 2012. Spore abundance, microbial growth and necromass turnover in deep subseafloor sediment, Nature 484, 101–104, doi:10.1038/nature10905.

Zhang, G., C. Smith-Duque, S. Tang, H. Li, C. Zarikian, S. D’Hondt, 2012. F. Inagaki and IODP Expedition 329 Scientists, Geochemistry of basalts from IODP site U1365: Implications for magmatism and mantle source signatures of the mid-Cretaceous Osbourn Trough, Lithos 144-145, 73-87.


D’Hondt, S., F. Inagaki, C. Alvarez Zarikian, Y. Morono, R. Pockalny, J. Sauvage, A.J. Spivack and the IODP Expedition 329 Shipboard Science Party, 2014. Microbial Cells and Aerobic Respiration from Seafloor to Basement in the South Pacific Gyre, Abstract B21L-08 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.

D’Hondt, S., G Wang and A.J. Spivack, 2014. Energetic Constraints of Subseafloor Life, Abstract B11F-0102 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.

Dunlea, A.G., R.W. Murray, J. Sauvage, A.J. Spivack, R.N. Harris, and S. D’Hondt, 2014. Paleoceanography in Pelagic Clay of the South Pacific Gyre, Abstract PP21A-1297 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.

Sauvage, J., D. Graham, A.J. Spivack, A.G. Dunlea, R.W. Murray and S. D’Hondt, 2014. Boosting subsurface life: is subseafloor sediment a natural catalyst for radiolytic hydrogen production? Abstract B11H-0147 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.

Walsh, E.A., J. Kirkpatrick, R. Pockalny, J. Sauvage, M.L. Sogin and S. D’Hondt, 2014. Bacterial diversity, sediment age and organic respiration in the marine sedimentary biosphere, Abstract B11H-0134 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.