Here is a list of my peer-reviewed publications and forthcoming papers along with a bit of a summary.
Peer-reviewed publications
Peer-reviewed publications
1. Krause, A.J., Mills, B.J.W., Merdith, A.S., Lenton, T.M. and Poulton, S.W. (2022) Extreme Variability in Atmospheric Oxygen Levels in the late Precambrian, Science Advances, 8, 41, 1-10. DOI: 10.1126/sciadv.abm8191
Significance: It is widely assumed that each broad rise in atmospheric O2 levels throughout Earth history has been a unidirectional increase. Here, using a biogeochemical model, we show that the second broad rise (the Neoproterozoic Oxygenation Event) was actually a chaotic event, with O2 levels fluctuating between very low (~1% of present day) and moderate (~50% of present day) levels. This means that animals likely evolved during a time of wild variability in the Earth system and could have consequences for understanding the evolution of life on exoplanets.
2. Shi, W., Li, C., Mills, B.J.W., Poulton, S.W., He, T., Shields, G.A., Krause, A.J., Zhou, Y. and Cheng, M. (2022) Decoupled oxygenation of the Ediacaran ocean and atmosphere during the rise of early animals, Earth and Planetary Science Letters, 591, 117619, 1-11. https://doi.org/10.1016/j.epsl.2022.117619
Significance: Evidence for the first animals can be found in Ediacaran aged rocks, but it is uncertain as to what atmospheric and oceanic conditions (i.e. O2 levels) were like at the time of their evolution, and the links between them. Here, using a biogeochemical model, we show that atmospheric and oceanic oxygenation were decoupled. While atmospheric O2 levels rose in the first half of the Ediacaran, it was not until the second half of the Ediacaran that oceanic O2 levels rose significantly, triggering the radiation of Ediacaran fauna in the process.
3. Pogge von Strandmann, P.A.E., Liu, X., Liu, C-Y., Wilson, D.J., Hammond, S.J., Tarbuck, G., Aristilde, L., Krause, A.J. and Fraser, W.T. (2022) Lithium isotope behaviour during basalt weathering experiments amended with organic acids, Geochimica et Cosmochimica Acta, 328, 37-57. https://doi.org/10.1016/j.gca.2022.04.032
Significance: Lithium isotopes are increasingly being used as a tracer of silicate weathering processes, both on the modern-day Earth, but also through deep time. Although plants do not cause isotopic fractionation when they uptake lithium, the effect of their organic acids on lithium isotope behaviour is unknown. Here we subject basalt to weathering by a number of different organic acids, as well as one inorganic acid, and water, to test their effect on lithium isotopes. We find that while the different acids alter the partitioning of lithium between different secondary phases, they do not significantly affect lithium isotopes compared to inorganic acids/water. This suggests that changes to the long-term lithium isotope record of seawater may reflect changes to weathering rates or congruence, rather than changes to the behaviour of lithium isotopes.
4. Alcott, L.J.+, Krause, A.J.+, Hammarlund, E.U., Bjerrum, C.J., Scholz, F., Xiong, Y., Hobson, A.J., Neve, L., Mills, B.J.W., März, C., Schnetger, B., Bekker, A. and Poulton, S.W. (2020) Development of iron speciation reference materials for paleoredox analysis, Geostandards and Geoanalytical Research, 44, 3, 581-591. DOI: 10.1111/ggr.12342
+ Indicates joint first author
Significance: Iron speciation is a widely utilised, laboratory-based method used to interrogate marine redox conditions in Earth’s past. However, each laboratory employing this technique uses a different reference material for comparison against their own data. Here we created a set of four reference materials that can now be used by all laboratories worldwide, helping to standardise this technique and provide greater certainty of results.
5. Mills, B.J.W., Krause, A.J., Scotese, C.R., Hill, D.J., Shields, G.A. and Lenton, T.M. (2019) Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day, Gondwana Research, 67, 172-186. DOI: 10.1016/j.gr.2018.12.001
Significance: In this paper we reviewed two well-known and widely used biogeochemical models of the Earth system, and explored their strengths and limitations when it comes to estimating atmospheric CO2 levels and temperature changes across the Phanerozoic. We made some updates to the models, which helped to improve results, and made suggestions for further improvements in the future which will help the community who use these models.
6. Krause, A.J., Mills, B.J.W., Zhang, S., Planavsky, N.J., Lenton, T.M. and Poulton, S.W. (2018) Stepwise oxygenation of the Paleozoic atmosphere, Nature Communications, 9:4081, 1-10. DOI: 10.1038/s41467-018-06383-y
Significance: Prior to this paper, it was generally considered that atmospheric O2 levels had risen in two broad steps across Earth history. Although one biogeochemical model had made the case for a third rise, the idea had failed to gain much traction. Here, using a different biogeochemical model based on the integration of carbon isotopes, we showed definitively that there was a third rise in atmospheric O2 to present day levels, which we named the, ‘Paleozoic Oxygenation Event’, and occurred in association with the evolution of plants on land. The timing and nature of this event may have contributed to the evolution of large animals, both in the seas and on land, and may also have implications for exoplanet habitability.
7. Zhang, S., Planavsky, N.J., Krause, A.J., Bolton, E.W. and Mills, B.J.W. (2018) Model based Paleozoic atmospheric oxygen estimates: A revisit to GEOCARBSULF, American Journal of Science, 318(5), 557-589. DOI: 10.2475/05.2018.05
Significance: The GEOCARBSULF model and its results for atmospheric O2 are heavily cited across a wide range of disciplines: from environmental science to medicine. However, its results of high O2 levels in the early Paleozoic are in stark contrast to marine geochemical proxies which suggest prevalent low O2 in the oceans (and thus much lower than present day atmospheric O2 levels). Here we investigated what the key drivers of the anomalously high atmospheric O2 levels during this time might be, and found that the burial of organic carbon and reduced sulfur species – both sources of O2 – hold a dominant control.
Significance: It is widely assumed that each broad rise in atmospheric O2 levels throughout Earth history has been a unidirectional increase. Here, using a biogeochemical model, we show that the second broad rise (the Neoproterozoic Oxygenation Event) was actually a chaotic event, with O2 levels fluctuating between very low (~1% of present day) and moderate (~50% of present day) levels. This means that animals likely evolved during a time of wild variability in the Earth system and could have consequences for understanding the evolution of life on exoplanets.
2. Shi, W., Li, C., Mills, B.J.W., Poulton, S.W., He, T., Shields, G.A., Krause, A.J., Zhou, Y. and Cheng, M. (2022) Decoupled oxygenation of the Ediacaran ocean and atmosphere during the rise of early animals, Earth and Planetary Science Letters, 591, 117619, 1-11. https://doi.org/10.1016/j.epsl.2022.117619
Significance: Evidence for the first animals can be found in Ediacaran aged rocks, but it is uncertain as to what atmospheric and oceanic conditions (i.e. O2 levels) were like at the time of their evolution, and the links between them. Here, using a biogeochemical model, we show that atmospheric and oceanic oxygenation were decoupled. While atmospheric O2 levels rose in the first half of the Ediacaran, it was not until the second half of the Ediacaran that oceanic O2 levels rose significantly, triggering the radiation of Ediacaran fauna in the process.
3. Pogge von Strandmann, P.A.E., Liu, X., Liu, C-Y., Wilson, D.J., Hammond, S.J., Tarbuck, G., Aristilde, L., Krause, A.J. and Fraser, W.T. (2022) Lithium isotope behaviour during basalt weathering experiments amended with organic acids, Geochimica et Cosmochimica Acta, 328, 37-57. https://doi.org/10.1016/j.gca.2022.04.032
Significance: Lithium isotopes are increasingly being used as a tracer of silicate weathering processes, both on the modern-day Earth, but also through deep time. Although plants do not cause isotopic fractionation when they uptake lithium, the effect of their organic acids on lithium isotope behaviour is unknown. Here we subject basalt to weathering by a number of different organic acids, as well as one inorganic acid, and water, to test their effect on lithium isotopes. We find that while the different acids alter the partitioning of lithium between different secondary phases, they do not significantly affect lithium isotopes compared to inorganic acids/water. This suggests that changes to the long-term lithium isotope record of seawater may reflect changes to weathering rates or congruence, rather than changes to the behaviour of lithium isotopes.
4. Alcott, L.J.+, Krause, A.J.+, Hammarlund, E.U., Bjerrum, C.J., Scholz, F., Xiong, Y., Hobson, A.J., Neve, L., Mills, B.J.W., März, C., Schnetger, B., Bekker, A. and Poulton, S.W. (2020) Development of iron speciation reference materials for paleoredox analysis, Geostandards and Geoanalytical Research, 44, 3, 581-591. DOI: 10.1111/ggr.12342
+ Indicates joint first author
Significance: Iron speciation is a widely utilised, laboratory-based method used to interrogate marine redox conditions in Earth’s past. However, each laboratory employing this technique uses a different reference material for comparison against their own data. Here we created a set of four reference materials that can now be used by all laboratories worldwide, helping to standardise this technique and provide greater certainty of results.
5. Mills, B.J.W., Krause, A.J., Scotese, C.R., Hill, D.J., Shields, G.A. and Lenton, T.M. (2019) Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day, Gondwana Research, 67, 172-186. DOI: 10.1016/j.gr.2018.12.001
Significance: In this paper we reviewed two well-known and widely used biogeochemical models of the Earth system, and explored their strengths and limitations when it comes to estimating atmospheric CO2 levels and temperature changes across the Phanerozoic. We made some updates to the models, which helped to improve results, and made suggestions for further improvements in the future which will help the community who use these models.
6. Krause, A.J., Mills, B.J.W., Zhang, S., Planavsky, N.J., Lenton, T.M. and Poulton, S.W. (2018) Stepwise oxygenation of the Paleozoic atmosphere, Nature Communications, 9:4081, 1-10. DOI: 10.1038/s41467-018-06383-y
Significance: Prior to this paper, it was generally considered that atmospheric O2 levels had risen in two broad steps across Earth history. Although one biogeochemical model had made the case for a third rise, the idea had failed to gain much traction. Here, using a different biogeochemical model based on the integration of carbon isotopes, we showed definitively that there was a third rise in atmospheric O2 to present day levels, which we named the, ‘Paleozoic Oxygenation Event’, and occurred in association with the evolution of plants on land. The timing and nature of this event may have contributed to the evolution of large animals, both in the seas and on land, and may also have implications for exoplanet habitability.
7. Zhang, S., Planavsky, N.J., Krause, A.J., Bolton, E.W. and Mills, B.J.W. (2018) Model based Paleozoic atmospheric oxygen estimates: A revisit to GEOCARBSULF, American Journal of Science, 318(5), 557-589. DOI: 10.2475/05.2018.05
Significance: The GEOCARBSULF model and its results for atmospheric O2 are heavily cited across a wide range of disciplines: from environmental science to medicine. However, its results of high O2 levels in the early Paleozoic are in stark contrast to marine geochemical proxies which suggest prevalent low O2 in the oceans (and thus much lower than present day atmospheric O2 levels). Here we investigated what the key drivers of the anomalously high atmospheric O2 levels during this time might be, and found that the burial of organic carbon and reduced sulfur species – both sources of O2 – hold a dominant control.
Forthcoming publications
1. Mills, B.J.W., Krause, A.J., Jarvis, I. and Cramer, B.D. (In press, estimated October publication) Evolution of Atmospheric O2 through the Phanerozoic, Revisited. Annual Review of Earth and Planetary Sciences
Significance: Here we present a comprehensive and critical review on how atmospheric O2 levels are thought to have changed throughout the last ~540 million years, as inferred by both geochemical proxies in the marine and terrestrial realm, and by biogeochemical models. Using the latest data, including a new compilation of carbon isotopes, we generate new biogeochemical model estimates of atmospheric O2. We then combine this with approximate levels suggested by the most robust geochemical proxy data to produce a well-defined insight into how atmospheric O2 levels may have changed over the Phanerozoic.
2. Krause, A.J., Sluijs, A., van der Ploeg, R., Lenton, T.M. and Pogge Von Strandmann, P.A.E. (In review at Nature Geoscience) The middle Eocene climatic conundrum resolved by enhanced clay formation.
Significance: The Middle Eocene Climatic Optimum (~40 million years ago) was a ~500,000 year period of warm temperatures on Earth. Despite being the focus of widespread attention, the cause of this warming and subsequent return to lower temperatures is not well understood. Over such a long timescale, silicate weathering, which draws down CO2 from the atmosphere, and acts as Earth’s thermostat, should have been able to keep pace with CO2 release from volcanism, but did not. Here, using lithium isotopes and a geochemical model, we show that volcanism triggered initial warming but also provided fresh materials for extensive clay formation, which can short circuit the silicate weathering feedback mechanism, allowing CO2 levels, and thus temperature to rise. This has implications for modern day climate change and potential CO2 sequestration methods using enhanced silicate weathering.
Significance: Here we present a comprehensive and critical review on how atmospheric O2 levels are thought to have changed throughout the last ~540 million years, as inferred by both geochemical proxies in the marine and terrestrial realm, and by biogeochemical models. Using the latest data, including a new compilation of carbon isotopes, we generate new biogeochemical model estimates of atmospheric O2. We then combine this with approximate levels suggested by the most robust geochemical proxy data to produce a well-defined insight into how atmospheric O2 levels may have changed over the Phanerozoic.
2. Krause, A.J., Sluijs, A., van der Ploeg, R., Lenton, T.M. and Pogge Von Strandmann, P.A.E. (In review at Nature Geoscience) The middle Eocene climatic conundrum resolved by enhanced clay formation.
Significance: The Middle Eocene Climatic Optimum (~40 million years ago) was a ~500,000 year period of warm temperatures on Earth. Despite being the focus of widespread attention, the cause of this warming and subsequent return to lower temperatures is not well understood. Over such a long timescale, silicate weathering, which draws down CO2 from the atmosphere, and acts as Earth’s thermostat, should have been able to keep pace with CO2 release from volcanism, but did not. Here, using lithium isotopes and a geochemical model, we show that volcanism triggered initial warming but also provided fresh materials for extensive clay formation, which can short circuit the silicate weathering feedback mechanism, allowing CO2 levels, and thus temperature to rise. This has implications for modern day climate change and potential CO2 sequestration methods using enhanced silicate weathering.
