Christopher Siebert

Head of cleanroom and MCICPMS facilities in Paleo-Oceanography

Scientific interests

I develop and apply “heavy” stable isotope systems as proxies for biogeochemical processes and biomarkers in medicine.

My momentary focus is in the following areas:

• Development of isotope biomarkers for medical diagnosis
• Marine sedimentary processes, land/ocean interface
• Oxygen minimum zones and their temporal evolution
• Development of new methods in mass spectrometry; understanding of instrumental mass fractionation in mass spectrometry

A selection of ongoing projects:

• Investigation of the intensity and spatial distribution of the “oxygen minimum zone” (OMZ) off the coast of Peru since the Pliocene (molybdenum isotopes, iron speciation)
• Development and application of barium isotopes as (paleo) water mass proxy, in particular for the input of fresh water into the oceans; barium isotopes as process indicators in barite formation
• Transfer: Development of heavy stable isotopes as biomarkers for oxidative stress and cancer in human medical diagnostics
• Investigating the influence of plasma temperature on isotopic mass bias

Selected Publications

Yu, Y., Hathorne, E., Siebert, C., Gutjahr, M., Fietzke, J., Frank, M. (2024) Unravelling instrumental mass fractionation of MC-ICP-MS using neodymium isotopes, Chemical Geology, Vol. 662, 10.1016/j.chemgeo.2024.122220

Münker, C., Wombacher, F., Siebert, C. (2023) Cambrian ocean floor crust preserved in the Takaka Terrane, New Zealand, New Zealand Journal of Geology and Geophysics, Vol. 66, Issue 3, 405-427, 10.1080/00288306.2023.2197239

Scholz, F., Cheng, J., Zhang, Z.L,, Vosteen, P., Siebert, C., Frank, M. (2023) Benthic-pelagic coupling and isotopic fractionation of barium in Kiel Bight, SW Baltic Sea, Frontiers in Marine Science, Vol.10, 10.3389/fmars.2023.1101095

Yu, Y., Hathorne, E., Siebert, C., Felis, T., Rajendran, C.P., Frank, M. (2022) Monthly resolved coral barium isotopes record increased riverine inputs during the South Asian summer monsoon, Geochimica et Cosmochimica Act, Vol. 329, 152-167, 10.1016/j.gca.2022.05.001

Eroglu, S., Scholz, F., Salvatteci, R., Siebert, C., Schneider, R., Frank, M. (2021) The impact of postdepositional alteration on iron- and molybdenum-based redox proxies, Geology, Vol. 49, Issue 12, 1411-1415, 10.1130/G49291.1

Cao, Z.M., Rao, X.T., Yu, Y., Siebert, C., Hathorne, E.C., Liu, B., Wang, G.Z., Lian, E.G., Wang, Z.B., Zhang, R.F., Gao, L., Wei, G.J., Yang, S.Y., Dai, M.H., Frank, M. (2021) Stable Barium Isotope Dynamics During Estuarine Mixing, Geophysical Research Letters, Vol. 48, Issue 19, 10.1029/2021GL095680

Siebert, C., Scholz, F., Kuhnt, W. (2021) A new view on the evolution of seawater molybdenum inventories before and during the Cretaceous Oceanic Anoxic Event 2, Chemical Geology, Vol. 582, 10.1016/j.chemgeo.2021.120399

Yu, Y., Siebert, C., Fietzke, J., Goepfert, T., Hathorne, E., Cao, Z.M., Frank, M. (2020) The impact of MC-ICP-MS plasma conditions on the accuracy and precision of stable isotope measurements evaluated for barium isotopes, Chemical Geology, Vol. 549, 10.1016/j.chemgeo.2020.119697

Eroglu, S, Scholz, F, Frank, M, Siebert, C (2020) Influence of particulate versus diffusive molybdenum supply mechanisms on the molybdenum isotope composition of continental margin sediments, Geochimica et Cosmochimica Acta, Vol. 273, 51-69

Scholz, F., Baum, M., Siebert, C., Eroglu, S., Dale, A.W., Naumann, M., Sommer, S. (2018) Sedimentary molybdenum cycling in the aftermath of seawater inflow to the intermittendly euxinic Gotland Deep, Central Baltic Sea, Chemical Geology, 491, 27-38

Yang, J., Barling, J., Siebert, C., Fietzke, J., Stephens, E., Halliday, A. (2017) The molybdenum isotopic compositions of I-, S- and A-type granitic suites, Geochimica et Cosmochimica Acta, 205, 168-186

Scholz, F., Siebert, C., Dale, A.W., Frank, M., (2017) Intense molybdenum accumulation in sediments underneath a nitrogenous water column and implications for the reconstruction of paleo-redox conditions based on molybdenum isotopes, Geochimica et Cosmochimica Acta, 213, 400-417

Liang, H., Halliday, A.N., Siebert, C., Fitton, J.G., Burton, K.W., Wang, K-L., Harvey, J., (2017) Molybdenum isotope fractionation in the mantle, Geochimica et Cosmochimica Acta, 199, 91-111

Baronas, J.J., Hammond, D.E., McManus, J., Wheat, C.G., Siebert, C. (2017) A global Ge isotope budget, Geochimica et Cosmochimica Acta, 203, 265-283

Cao, Z., Siebert, C., Hathorne, E.C., Minhan, D., Frank, M. (2016) Constraining the oceanic barium cycle with stable barium isotopes, Earth and Planetary Science Letters, 434, 1-9

Abraham, K., Barling, J., Siebert, C., Belshaw, N., Gall, L., Halliday, A.N. (2015) Determination of mass-dependent variations in tungsten stable isotope compositions of geological reference materials by double-spike and MC-ICPMS, Journal of Analytical Atomic Mass Spectrometry, DOI: 10.1039/c5ja00210a

Ventura, G.T., Gall, L., Siebert, C., Prytulak, J., Szatmari, P., Hürlimann, M., Halliday, A.N. (2015) The stable isotope composition of vanadium, nickel, and molybdenum in crude oils, Applied Geochemistry, 59, 104-117

Dausmann, V., Frank, M., Siebert, C., Christl, M., Hein, J.R. (2015) The evolution of climatically driven weathering inputs into the western Arctic Ocean since the late Miocene: Radiogenic isotope evidence, Earth and Planetary Sciences Letters, 419, 111-124

Yang, J., Siebert, C., Barling, J., Savage, P., Liang, Y.-H., Halliday, A.N. (2015) Absence of molybdenum isotope fractionation during magmatic differentiation at Hekla volcano, Iceland, Geochimica et Cosmochimica Acta, 162, 126-136

Siebert, C., Pett-Ridge, J.C., Opfergelt, S., Guicharnaud, R.A., Halliday, A.N., Burton, K.W. (2015) Molybdenum isotope fractionation in soils: Influence of redox conditions, organic matter, and atmospheric inputs, Geochimica et Cosmochimica Acta, 162, 1-24

Gall, L., Williams, H.M., Siebert, C., Halliday, A.N., Herrington, R.J., Hein, J.R. (2013) Nickel isotopic compositions of ferromanganese crusts and the constancy of deep ocean inputs and continental weathering effects over the Cenozoic, Earth and Planetary Sciences Letters, 375, 148-155

Greber, N.D., Siebert, C., Naegler, T.F., Pettke, T. (2012) δ^98/95Mo values and Molybdenum Concentration Data for NIST SRM 610, 612 and 3134: Towards a       Common Protocol for Reporting Mo Data, Geostandards and Geoanalytical Research, 36 (3), 291

Gall, L., Williams, H.M., Siebert, C., Halliday, A.N. (2012) Determination of mass-dependent variations in nickel isotope compositions using double spiking and MC-ICPMS, Journal of Analytical Atomic Mass Spectrometry, 27,137 

Opfergelt S., Georg, R.B., Burton K.W., Guicharnaud, R., Siebert C., Gislason S.R., Halliday A.N. (2010) Silicon Isotopes in allophane as a proxy for mineral formation in volcanic soils, Applied Geochemistry, 26, S115

Siebert C., Ross A., McManus J. (2006), Germanium isotope measurements of high-temperature geothermal fluids using double-spike hydride generation MC-ICP-MS, Geochimica et Cosmochimica Acta 70 (15), 3986-3995

Poulson R.L., Siebert C., McManus J., Berelson W.M. (2006), Authigenic molybdenum isotope signatures in marine sediments, Geology, 34 (8), 617-620 

Siebert C., McManus J., Bice A., Poulson R., Berelson W.M. (2006), Molybdenum isotope signatures in continental margin marine sediments, Earth and Planetary Science Letters, 241 (3-4), 723-733 

Siebert C., Kramers J.D., Meisel T., Morel P., Nägler T.F. (2005), PGE, Re-Os, and Mo isotope systematics in Archean and early Proterozoic sedimentary systems as proxies for redox conditions of the early Earth,  Geochimica et Cosmochimica Acta,  69 (7), 1787-1801

Siebert, C., Nägler, T.F., von Blanckenburg, F., and Kramers, J.D. (2003), Molybdenum isotope records as potential new proxy for paleoceanography, Earth and Planetary Science Letters, 211 (3-4), 159-171

McManus, J., Nägler, T., Siebert, C., Wheat, C.G., and Hammond, D. (2002), Oceanic molybdenum isotope fractionation: Diagenesis and hydrothermal ridge flank alteration, Geochemistry Geophysics Geosytems, 3, Art. No. 1078, doi:10.1029/2002GC000356.

Siebert, C., Nägler, T.F., and Kramers, J.D. (2001), Determination of molybdenum isotope fractionation by double-spike multicollector inductively coupled plasma mass spectrometry, Geochemistry Geophysics Geosytems, 2, Art. No. 2000GC000124

CV:

2012-present: Senior Scientist, GEOMAR, Helmholtz Center for Ocean Research, Kiel, D

2010-2012: NERC Fellow, Department of Earth Sciences, University of Oxford, UK

2007-2010: Research Fellow, Department of Earth Sciences, University of Oxford, UK

2006: Research Associate, School of Earth and Space Exploration, Arizona State University, USA

2003-2005: SNF Fellow, College of Oceanic and Atmospheric Sciences, Oregon State University, USA

1999-2003: PhD, Institute of Geological Sciences, University of Berne, CH