Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A molybdenum-isotope perspective on Phanerozoic deoxygenation events


The expansion and contraction of sulfidic depositional conditions in the oceans can be tracked with the isotopic composition of molybdenum in marine sediments. However, molybdenum-isotope data are often subject to multiple conflicting interpretations. Here I present a compilation of molybdenum-isotope data from three time intervals: the Toarcian Oceanic Anoxic Event about 183 million years ago, Oceanic Anoxic Event 2 about 94 million years ago, and two early Eocene hyperthermal events from 56 to 54 million years ago. A comparison of data from sites located in different hydrographic settings tightly constrains the molybdenum cycle for these intervals, allowing a direct comparison of the expanse of sulfidic conditions in each interval compared to today. Nonetheless, tracing rates of redox change over such rapid climatic events using molybdenum isotopes remains challenging. Future efforts to achieve this goal might be accomplished by analysing specific mineral phases, using complementary redox-sensitive geochemical techniques and by linking isotopic observations with Earth system modelling. Such improvements will make it possible to more fully assess the links between ocean deoxygenation, climatic and oceanographic changes, and biotic turnover.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Molybdenum-isotope fluxes in the modern marine environment.
Figure 2: Compilation of sediment Mo-isotope data.
Figure 3: Simplified mass-balance model of the fractional removal of molybdenum into sulfidic and oxic marine sediments as a function of the isotopic composition of seawater and riverine inputs.


  1. 1

    Jenkyns, H. C. Geochemistry of oceanic anoxic events. Geochem. Geophys. Geosyst. 11, Q03004 (2010).

    Article  Google Scholar 

  2. 2

    Ridgwell, A. & Schmidt, D. N. Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release. Nat. Geosci. 3, 196–200 (2010).

    Article  Google Scholar 

  3. 3

    Kendall, B., Dahl, T. W. & Anbar, A. D. Good golly, why moly? The stable isotope geochemistry of molybdenum. Rev. Mineral. Geochem. 82, 683–732 (2017).

    Article  Google Scholar 

  4. 4

    Arnold, G. L., Anbar, A. D., Barling, J. & Lyons, T. W. Molybdenum isotope evidence for widespread anoxia in mid-Proterozoic oceans. Science 304, 87–90 (2004).

    Article  Google Scholar 

  5. 5

    Pearce, C. R., Cohen, A. S., Coe, A. L. & Burton, K. W. Molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the Early Jurassic. Geology 36, 231–234 (2008).

    Article  Google Scholar 

  6. 6

    Dickson, A. J., Cohen, A. S. & Coe, A. L. Seawater oxygenation during the Paleocene–Eocene Thermal Maximum. Geology 40, 639–642 (2012).

    Article  Google Scholar 

  7. 7

    Dickson, A. J., Jenkyns, H. C., Porcelli, D., van den Boorn, S. & Idiz, E. Basin-scale controls on the molybdenum isotope composition of seawater during Oceanic Anoxic Event 2 (Late Cretaceous). Geochim. Cosmochim. Acta 178, 291–306 (2016).

    Article  Google Scholar 

  8. 8

    Westermann, S., Vance, D., Cameron, V., Archer, C. & Robinson, S. A. Heterogeneous oxygenation states in the Atlantic and Tethys oceans during Oceanic Anoxic Event 2. Earth Planet. Sci. Lett. 404, 178–189 (2014).

    Article  Google Scholar 

  9. 9

    Kendall, B. et al. Uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late Ediacaran Period. Geochim Cosmochim Acta 156, 173–193 (2015).

    Article  Google Scholar 

  10. 10

    Voegelin, A. R., Nägler, T. F., Samankassou, E. & Villa, I. M. Molybdenum isotopic composition of modern and Carboniferous carbonates. Chem. Geol. 265, 488–498 (2009).

    Article  Google Scholar 

  11. 11

    Nägler, T. F. et al. Proposal for an international molybdenum isotope measurement standard and data representation. Geostand. Geoanal. Res. 38, 149–151 (2014).

    Google Scholar 

  12. 12

    Siebert, C., Nägler, T. F., von Blanckenburg, F. & Kramers, J. D. Molybdenum isotope records as a potential new proxy for paleoceanography. Earth Planet. Sci. Lett. 211, 159–171 (2003).

    Article  Google Scholar 

  13. 13

    Neubert, N. et al. The molybdenum isotopic composition in river water: constraints from small catchments. Earth Planet. Sci. Lett. 304, 180–190 (2011).

    Article  Google Scholar 

  14. 14

    Pearce, C. R., Burton, K. W., Pogge van Strandmann, P. A. E., James, R. H. & Gíslason, S. R. Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain. Earth Planet. Sci. Lett. 295, 104–114 (2010).

    Article  Google Scholar 

  15. 15

    McManus, J., Nägler, T., Siebert, C., Wheat, C. G. & Hammond, D. E. Oceanic molybdenum isotope fractionation: diagenesis and hydrothermal ridge-flank alteration. Geochem. Geophys. Geosyst. 3, 1078 (2002).

    Article  Google Scholar 

  16. 16

    Archer, C. & Vance, D. The isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans. Nat. Geosci. 1, 597–600 (2008).

    Article  Google Scholar 

  17. 17

    Siebert, C. et al. Molybdenum isotope fractionation in soils: influence of redox conditions, organic matter and atmospheric inputs. Geochim. Cosmochim. Acta 62, 1–24 (2015).

    Article  Google Scholar 

  18. 18

    Barling, J., Arnold, G. L. & Anbar, A. D. Natural mass-dependent variations in the isotopic composition of molybdenum. Earth Planet. Sci. Lett. 193, 447–457 (2001).

    Article  Google Scholar 

  19. 19

    Barling, J. & Anbar, A. D. Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet. Sci. Lett. 217, 315–329 (2004).

    Article  Google Scholar 

  20. 20

    Wasylenki, L. E., Rolfe, B. A., Weeks, C. L., Spiro, T. G. & Anbar, A. D. Experimental investigation of the effects of temperature and ionic strength on Mo isotope fractionation during adsorption to manganese oxides. Geochim. Cosmochim. Acta 72, 5997–6005 (2008).

    Article  Google Scholar 

  21. 21

    Goldberg, T., Archer, C., Vance, D. & Poulton, S. W. Mo isotope fractionation during adsorption to Fe (oxyhydr)oxides. Geochim. Cosmochim. Acta 73, 6502–6516 (2009).

    Article  Google Scholar 

  22. 22

    Poulson, R. L., Siebert, C., McManus, J. & Berelson, W. M. Authigenic molybdenum isotope signatures in marine sediments. Geology 34, 617–620 (2006).

    Article  Google Scholar 

  23. 23

    Poulson-Brucker, R. L., McManus, J., Severmann, S. & Berelson, W. M. Molybdenum behavior during early diagenesis: insights from Mo isotopes. Geochem. Geophys. Geosyst. 10, Q06010 (2009).

    Article  Google Scholar 

  24. 24

    Helz, G. R. et al. Mechanism of molybdenum removal from the sea and its concentration in black shales: EXAFS evidence. Geochim. Cosmochim. Acta 60, 3631–3642 (1996).

    Article  Google Scholar 

  25. 25

    Eriksson, B. E. & Helz, G. R. Molybdenum(IV) speciation in sulphidic waters: stability and lability of thiomolybdates. Geochim. Cosmochim. Acta 64, 1149–1158 (2000).

    Article  Google Scholar 

  26. 26

    Neubert, N., Nägler, T. F. & Böttcher, M. E. Sulphidity controls molybdenum isotope fractionation into euxinic sediments: evidence from the modern Black Sea. Geology 36, 775–778 (2008).

    Article  Google Scholar 

  27. 27

    Nägler, T. F., Neubert, N., Böttcher, M. E., Dellwig, O. & Schnetger, B. Molybdenum isotope fractionation in pelagic euxinia: evidence from the modern Black and Baltic Seas. Chem. Geol. 289, 1–11 (2011).

    Article  Google Scholar 

  28. 28

    Azrieli-Tal, I. et al. Evidence from molybdenum and iron isotopes and molybdenum–uranium covariation for sulphidic bottom waters during Eastern Mediterranean sapropel S1 formation. Earth Planet. Sci. Lett. 393, 231–242 (2014).

    Article  Google Scholar 

  29. 29

    Miller, C. A., Peucker-Ehrenbrink, B., Walker, B. D. & Marcantonio, F. Re-assessing the surface cycling of molybdenum and rhenium. Geochim. Cosmochim. Acta 75, 7146–7179 (2011).

    Article  Google Scholar 

  30. 30

    Nakagawa, Y. The molybdenum isotopic composition of the modern ocean. Geochem. J. 46, 131–141 (2012).

    Article  Google Scholar 

  31. 31

    Dickson, A. J., Cohen, A. S. & Coe, A. L. Continental margin molybdenum isotope signatures from the early Eocene. Earth. Planet. Sci. Lett. 405, 389–395 (2014).

    Article  Google Scholar 

  32. 32

    Helz, G. R., Bura-Nakić, E. Mikac, N. & Ciglenečki, I. New model for molybdenum behavior in euxinic waters. Chem. Geol. 284, 323–332 (2011).

    Article  Google Scholar 

  33. 33

    Dahl, T. W., Chappaz, A., Fitt, J. P. & Lyons, T. W. Molybdenum reduction in a sulphidic lake: evidence from X-ray adsorption fine-structure spectroscopy and implications for the Mo paleoproxy. Geochim. Cosmochim. Acta 103, 213–231 (2013).

    Article  Google Scholar 

  34. 34

    Chappaz, A. et al. Does pyrite act as an important host for molybdenum in modern and ancient euxinic sediments? Geochim. Cosmochim. Acta 126, 112–122 (2014).

    Article  Google Scholar 

  35. 35

    Algeo, T. J. & Lyons, T. W. Mo–total organic carbon covariation in modern anoxic marine environments: implications for analysis of paleoredox and paleohydrologic conditions. Paleoceanography 21, PA1016 (2006).

    Article  Google Scholar 

  36. 36

    Gordon, G. W. et al. When do black shales tell molybdenum isotope tales? Geology 37, 535–538 (2009).

    Article  Google Scholar 

  37. 37

    Ruebsam, W., Dickson, A. J., Hoyer, E.-M. & Schwark, L. Multiproxy reconstruction of oceanographic conditions in the southern epeiric Kupferschiefer Sea (Late Permian) based on redox-sensitive trace elements, molybdenum isotopes and biomarkers. Gondwana Res. 44, 205–218 (2017).

    Article  Google Scholar 

  38. 38

    Chen, X. et al. Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals. Nat. Commun. 6, 7142 (2015).

    Article  Google Scholar 

  39. 39

    Schlanger, S. O. & Jenkyns, H. C., Cretaceous oceanic anoxic events: causes and consequences. Geol. Mijnbouw 55, 179–184 (1976).

    Google Scholar 

  40. 40

    Goldberg, T., Poulton, S. W., Wagner, T., Kolonic, S. F. & Rehkämper, M. Molybdenum drawdown during Cretaceous Oceanic Anoxic Event 2. Earth Planet. Sci. Lett. 440, 81–91 (2016).

    Article  Google Scholar 

  41. 41

    Dickson, A. J. & Cohen, A. S., A molybdenum isotope record of Eocene Thermal Maximum 2: implications for global ocean redox during the early Eocene. Paleoceanography 27, PA3230 (2012).

    Article  Google Scholar 

  42. 42

    Dickson, A. J. et al. Molybdenum isotope chemostratigraphy and paleoceanography of the Toarcian Oceanic Anoxic Event (Early Jurassic). Paleoceanography 32, PA003048 (2017).

    Article  Google Scholar 

  43. 43

    Dickson, A. J. et al. A Southern Hemisphere record of global trace-metal drawdown and orbital modulation of organic-matter burial across the Cenomanian–Turonian boundary (ODP Site 1138, Kerguelen Plateau). Sedimentology 64, 186–203 (2017).

    Article  Google Scholar 

  44. 44

    Algeo, T. J. & Tribovillard, N. Environmental analysis of paleoceanographic systems based on molybdenum–uranium covariation. Chem. Geol. 268, 211–225 (2009).

    Article  Google Scholar 

  45. 45

    Ling, H.-F., Gao, J.-F., Zhao, K.-D., Jiang, S.-Y. & Ma, D.-S. Comment on “Molybdenum isotope evidence for widespread anoxia in Mid-Proterozoic oceans.” Science 309, 1017 (2005).

    Article  Google Scholar 

  46. 46

    Reinhard, C. T. et al. Proterozoic ocean redox and biogeochemical stasis. Proc. Natl Acad. Sci USA 110, 5357–5362 (2013).

    Article  Google Scholar 

  47. 47

    Owens, J. D. et al. Sulfur isotopes track the global extent and dynamics of euxinia during Cretaceous Oceanic Anoxic Event 2. Proc. Natl Acad. Sci USA 110, 18407–18412 (2013).

    Article  Google Scholar 

  48. 48

    Monterio, F. M., Pancost, R. D., Ridgwell, A. & Donnadieu, Y. Nutrients as the dominant control on the spread of anoxia and euxinia across the Cenomanian–Turonian oceanic anoxic event [OAE2]: model-data comparison. Paleoceanography 27, PA002351 (2012).

    Google Scholar 

  49. 49

    Hetzel, A., Böttcher, M. E., Wortmann, U. G. & Brumsack, H.-J. Paleo-redox conditions during OAE 2 reflected in Demerara Rise sediment geochemistry (ODP Leg 207). Palaeogeogr. Palaeoclimatol. Palaeoecol. 273, 302–328 (2009).

    Article  Google Scholar 

  50. 50

    Romaniello, S. J., Herrmann, A. D. & Anbar, A. D. Syndepositional diagenetic control of molybdenum isotope variations in carbonate sediments from the Bahamas. Chem. Geol. 438, 84–90 (2016).

    Article  Google Scholar 

Download references


The ideas in this paper benefitted from discussions with H. Jenkyns, A.S. Cohen, M.-L. Bagard, J. Barling, D. Porcelli and E. Idiz.

Author information



Corresponding author

Correspondence to Alexander J. Dickson.

Ethics declarations

Competing interests

The author declares no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 670 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Dickson, A. A molybdenum-isotope perspective on Phanerozoic deoxygenation events. Nature Geosci 10, 721–726 (2017).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing