About

Gregory Henkes is an Associate Professor in the Department of Geosciences at Stony Brook University. He holds a B.S. from Bates College (2008), a Ph.D. from The Johns Hopkins University (2014), and completed a postdoctoral fellowship at Harvard University (2014-2016). Since fall 2016, he has been a faculty member at Stony Brook. His research focuses on the stable isotope geochemistry of light elements such as hydrogen, carbon, nitrogen, oxygen, and sulfur, and their use as recorders of Earth's climatological, biogeochemical, and ecological evolution. His laboratory is dedicated to making novel stable isotope measurements from samples collected across a wide range of temporal and spatial scales. Currently, his research includes studying the temperature and isotopic evolution of seawater, the biogeochemistry of carbon and nitrogen in the ocean, the climate and environment of East Africa during the Cenozoic, carbonate clumped isotope geochemistry for understanding diagenetic, metamorphic, and igneous processes, and the use of isotopes as trophic level indicators in marine and terrestrial food webs. He is actively seeking talented undergraduates, graduate students, postdoctoral researchers, and visitors to join his research group and is affiliated with multiple departments and programs at Stony Brook, including the School of Marine and Atmospheric Sciences, the Interdepartmental Program in Anthropological Sciences, and the Turkana Basin Institute.

Research topics

• Geology
• Paleontology
• Ecology
• Geochemistry
• Chemistry
• Earth science
• Environmental science
• Biology
• Oceanography
• Physics
• Nuclear physics
• Mineralogy

Selected publications

• Cold low-latitude Ordovician paleotemperatures may be in hot water

  Proceedings of the National Academy of Sciences · 2025-03-06 · 6 citations

  letterOpen access
  PublisherOA PDFDOI

• Paleosol evidence for dynamic moisture regimes during the Middle Miocene in the Turkana Basin, northern Kenya

  Abstracts with programs - Geological Society of America · 2025-01-01

  article
  PublisherDOI

• Age and Temperature of Authigenic Carbonates Associated with Lithium-Bearing Illite Claystones, Thacker Pass, Nevada, USA

  SEPM (Society for Sedimentary Geology) eBooks · 2025-01-01

  book-chapter

  Key Messages: Calcite within the Li-bearing lens of the Thacker Pass Lithium clay deposit supports that the Li-illite alteration occurred in a hydrothermal system during caldera resurgence, rather than during burial diagenesis. (2) Synchrotron x-ray absorption spectroscopy reveals that the elevated REEs and Th within the calcite are sector zoned.

  PublisherDOI

• Age and Temperature of Authigenic Carbonates Associated with Lithium-Bearing Illite Claystones at Thacker Pass, Nevada, USA

  Abstracts with programs - Geological Society of America · 2025-01-01

  article
  PublisherDOI

• The Quaternary landscapes, chronostratigraphy, and paleoenvironments of the Chalbi Desert, Kenya

  Quaternary Research · 2025-11-12 · 1 citations

  article

  Abstract The Chalbi Desert, located in eastern Africa, is a significant but overlooked archive of the Pleistocene and Holocene periods that could add insight into investigations on human evolution. We revisited southeastern Chalbi Desert landforms between the towns of Kargi and Maikona to improve the chronostratigraphy and provide paleoenvironmental context. Direct U-series and electron spin resonance dating of various fossil teeth recovered from a deflated dune (Qzs) landform at the Farre locality return a mean age of ∼545 ka, which is compatible with biostratigraphic inferences. While this numerical age result should probably be regarded as mostly indicative given the existing uncertainty on the environmental dose rate evaluation, the data set available nevertheless strongly suggests a Middle Pleistocene age for at least some of the fauna. Sedimentology, luminescence, and 14 C dating further suggest that this Qzs landform and its contents were modified by alluvial fan development and weathering during denudation in a proximal fan setting through the late Pleistocene into the Holocene. The Qzs landform currently experiences aeolian additions, erosion, and salt-affected soil development in an arid climate. Pedogenic carbonate isotope geochemistry suggests that deflated sand dunes were covered by woody grasslands during Marine Isotope Stage (MIS) 4 and 3 pluvials, consistent with nearby fan progradation constrained at >35 ka. The desert experienced increased hydrologic activity during late Pleistocene and African humid period pluvials, as evidenced by additional optically stimulated luminescence and 14 C dating from fan, dune, and playa contexts. The last significant pluvial episode ended after 4.4 ± 0.3 cal ka BP, which coincides with the final regression of nearby Lake Turkana. This study extends the chronology of Quaternary sediments in the Chalbi Desert to the Middle Pleistocene and offers paleoenvironmental insights into the conditions experienced by Middle Stone Age tool users in the region.

  PublisherDOI

• CARBONATE CLUMPED ISOTOPES OF ARAGONITIC FOSSILS FROM THE LATE CRETACEOUS WESTERN INTERIOR SEAWAY AND THE ROLE OF BOND REORDERING IN SIGNAL PRESERVATION

  Abstracts with programs - Geological Society of America · 2024-01-01

  articleSenior author
  PublisherDOI

• Large, Negative Atmospheric Carbon Monoxide Clumped Isotope Values Result From Kinetic Isotope Fractionation, Tracing OH• Reactivity

  AGU Advances · 2024-09-23 · 1 citations

  articleOpen access1st author

  Abstract Because of its global abundance and reactivity with hydroxyl radicals (OH•), tropospheric carbon monoxide indirectly impacts the lifetimes of other OH•‐reactive gases, in particular methane and reactive hydrocarbons. The origin and chemistry of atmospheric CO have been studied using stable isotopes. Both 13 CO and C 18 O undergo isotopic fractionation during its main chemical loss reaction, CO + OH•. The kinetic isotope effect (KIE) for 13 CO is mass dependent, with a value of ∼5‰; 12 CO reacts faster than 13 CO with OH. Whereas C 18 O + OH• exhibits an inversely mass dependent KIE ∼−10‰. We hypothesize these KIEs result in a relative depletion of 13 C 18 O, a CO clumped isotope. To test this, we collected CO from air samples on Long Island, NY, and discovered a −3 to −8‰ difference in the clumped isotope ratio, Δ 31 , relative to a random distribution of 13 C and 18 O in CO. A clear negative trend between [CO] and Δ 31 is driven by two factors: (a) the atmospheric addition of CO from either a primary or secondary source with a Δ 31 of ∼0‰ and (b) the continuing reaction of CO with OH•, leaving the remaining CO pool relatively depleted in 13 C 18 O. This is analogous to the mechanism that determines CO Δ 17 O values. This study is among the first to show clumped isotope fractionation resulting from atmospheric chemistry and not thermal equilibration, which may inform the identification of clumped isotope KIEs in other atmospheric trace gases. These first Δ 31 observations motivate future experimental and observational studies targeted at characterizing the clumped isotopes of CO sources, background CO, and experimentally fractionated CO.

  PublisherOA PDFDOI

• Reconstructing paleoenvironments of the Late Cretaceous Western Interior Seaway, USA, using paired triple oxygen and carbonate clumped isotope measurements

  Geological Society of America Bulletin · 2024-07-12 · 6 citations

  article

  Abstract Fossiliferous carbonate concretions are commonly found in sediments deposited in the Late Cretaceous Western Interior Seaway. Although concretions are diagenetic features, well-preserved fossils from within them have been instrumental in reconstructing the temperature and δ18O value of Western Interior Seaway seawater, which is essential for accurate reconstruction of Late Cretaceous climate. Here, we constrain formation conditions of Late Campanian and early Maastrichtian carbonate concretions by combining triple oxygen isotope measurements with carbonate clumped isotope paleothermometry on different carbonate phases within the concretions. We measured both fossil skeletal aragonite and sparry calcite infill from cracks and within macrofossil voids to evaluate differences between “primary” and “altered” geochemical signals. Based on the two temperature-sensitive isotope systems of the primary fossil shell aragonite, the temperature of the Western Interior Seaway was between 20 °C and 40 °C and was likely thermally stratified during the Campanian. The reconstructed δ18Oseawater values of ~−1‰ for Campanian Western Interior Seaway waters are similar to those expected for the open ocean during greenhouse climates, while the Maastrichtian Western Interior Seaway may have been more restricted, with a δ18Oseawater value of ~2‰, which reflects more evaporative conditions. We reconstructed the diagenetic history of the sparry infill and altered fossils using a fluid-rock mixing model. Alteration temperature, alteration fluid δ18O value, and the initial formation temperature were calculated by applying the fluid-rock mixing model to a particle swarm optimization algorithm. We found a different range of initial formation temperatures between the Campanian (25–38 °C) and Maastrichtian (9–28 °C). We also found that alteration in the presence of light meteoric fluids (δ18O ≈ −10‰) is required to explain both the sparry infill and the altered fossil isotopic values. Based on our results, both lithification and alteration of the carbonates occurred soon after burial, and light meteoric fluids support prior findings that high-topographic relief existed on the western margin of the Western Interior Seaway during the Late Cretaceous. As one of the first studies to apply these techniques in concert and across multiple mineralogical phases within samples, our results provide important constraints on paleoenvironmental conditions in an enigmatic ocean system and will improve interpretations of the overall health of ecosystems leading into the end-Cretaceous mass extinction.

  PublisherDOI

• NEW EVIDENCE FROM THE PALEOPROTEROZOIC GUNFLINT IRON FORMATION FOR MICROBIALLY-DRIVEN, EARLY DIAGENETIC PRECIPITATION OF SIDERITE

  Abstracts with programs - Geological Society of America · 2024-01-01

  article
  PublisherDOI

• Preserved particulate organic carbon is likely derived from the subsurface sulfidic photic zone of the Proterozoic Ocean: evidence from a modern, oxygen‐deficient lake

  Geobiology · 2024-03-01

  articleOpen access

  Abstract Biological processes in the Proterozoic Ocean are often inferred from modern oxygen‐deficient environments (MODEs) or from stable isotopes in preserved sediment. To date, few MODE studies have simultaneously quantified carbon fixation genes and attendant stable isotopic signatures. Consequently, how carbon isotope patterns reflect these pathways has not been thoroughly vetted. Addressing this, we profiled planktonic productivity and quantified carbon fixation pathway genes and associated organic carbon isotope values (δ 13 C POC ) of size‐fractionated (0.2–2.7 and >2.7 μm) particulate matter from meromictic Fayetteville Green Lake, NY, USA. The high‐O 2 Calvin‐Benson‐Bassham (CBB) gene ( cbbL ) was most abundant in the <2.7 μm size fraction in shallow oxic and deep hypoxic waters, corresponding with cyanobacterial and eukaryote algal populations. The low‐O 2 CBB gene ( cbbM ) was most abundant near the lower oxycline boundary in the larger size fraction, coincident with purple sulfur bacteria populations. The reverse citric acid cycle gene ( aclB ) was equally abundant in both size fractions in the deepest photic zone, coinciding with green sulfur bacteria populations. Methane coenzyme reductase A ( mcrA ), of anaerobic methane cyclers, was most abundant at the lower oxycline boundary in both size fractions, coinciding with Methanoregula populations. δ 13 C POC values overlapped with the high‐O 2 CBB fixation range except for two negative excursions near the lower oxycline boundary, likely reflecting assimilation of isotopically‐depleted groundwater‐derived carbon by autotrophs and sulfate‐reducers. Throughout aphotic waters, δ 13 C POC values of the large size fraction became 13 C‐enriched, likely reflecting abundant purple sulfur bacterial aggregates. Eukaryote algae‐ or cyanobacteria‐like isotopic signatures corresponded with increases in cbbL , cbbM, and aclB , and enrichment of exopolymer‐rich prokaryotic photoautotrophs aggregates. Results suggest that δ 13 C POC values of preserved sediments from areas of the Proterozoic Ocean with sulfidic photic zones may reflect a mixture of alternate carbon‐fixing populations exported from the deep photic zone, challenging the paradigm that sedimentary stable carbon isotope values predominantly reflect oxygenic photosynthesis from surface waters.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: The influence of climate and tectonics on Miocene ecosystems and faunal evolution in the East African Rift, Kenya

  NSF · $670k · 2021–2025

Frequent coauthors

• E. Troy Rasbury

  Stony Brook University

  15 shared

• William G. Ambrose

  Conway School of Landscape Design

  13 shared

• Mae Saslaw

  13 shared

• Ethan L. Grossman

  11 shared

• Benjamin H. Passey

  University of Michigan–Ann Arbor

  11 shared

• Alberto Pérez‐Huerta

  University of Alabama

  10 shared

• Michael L. Carroll

  Centre for Arctic Gas Hydrate, Environment and Climate

  8 shared

• Torben C. Rick

  National Museum of Natural History

  8 shared

Labs

• Henkes LabPI

Education

• B.S.

  Bates College

  2008

• Ph.D.

  The Johns Hopkins University

  2014

• Other, 2014-2016

  Harvard University

  2014