Overview

I am a geochemist interested especially in the use of biominerals formed by marine invertebrates to understand palaeoenvironments. My work fits into the themes of analytical geochemistry, modern analogue studies and proxy development, diagenesis, and palaeoenvironmental reconstruction. The ultimate goal of my work is to create reliable geochemical datasets that allow us to accurately reconstruct temperature, ocean chemistry and carbon cycle through time, and to determine how animals co-evolved with the planet. My work is multidisciplinary and I particularly enjoy learning from experts in related fields, allowing to conduct research that is of broad relevance for the Earth Science community and beyond.

 

You can find my publications here:

https://scholar.google.co.uk/citations?hl=en&user=6aKjxc8AAAAJ&view_op=list_works

https://webofscience.clarivate.cn/wos/author/record/I-3227-2019

https://www.researchgate.net/profile/Clemens-Ullmann

 

Please feel free to reach out to me if you are interested in a research collaboration or in undertaking a research project under my guidance.

 

Analytical Geochemistry

My speciality is the use of quantitative analytical instrumentation to derive geochemical proxy information from biological calcite. This includes major and trace element concentrations, as well as traditional and non-traditional isotope systems. Over the years I have worked with various instruments, including ICP-OES, ICP-MS, TIMS, GS-IRMS and MC-ICP-MS and managed several analytical laboratories. At CUG (Wuhan) I am taking care of the Thermal Ionisation Mass Spectrometry (TIMS) facility housed at the State Key Laboratory of Geomicrobiology and Environmental Changes, Future City Campus.

 

Modern analogue studies and proxy development

Marine macrofossils are key to understanding Paleozoic and Mesozoic environments and are often used for geochemical analysis, but the understanding of isotopic and chemical composition of fossil shells is still comparatively limited. I am working on charting chemical fingerprints of shells of modern and extinct species and test which parameters control chemical and isotopic variability and broader chemical patterns in their calcite. This work has for instance looked into the chemistry of modern barnacles (https://www.sciencedirect.com/science/article/pii/S0016703718305271) and more recently the distribution of elements in brachiopod shells (https://www.sciencedirect.com/science/article/pii/S0016703726002565).

 

Diagenesis

No palaeoenvironmental study based on fossil geochemistry can be carried out without first assessing whether the analysed specimens are preserved well, but limited efforts have been undertaken in recent years to refine and update approaches to testing for fossil preservation. This is of particular relevance for novel geochemical tools which are often very vulnerable to shell alteration and contamination and thus require especially high confidence in the preservation of fossil material. I have been active in this field, summarising typical approaches to testing for preservation (https://gq.pgi.gov.pl/article/view/15932), giving recommendations for suitable sampling and analytical strategies for macrofossil calcite (https://vjs.pgi.gov.pl/article/view/34334), and proposing new tracers for alteration such as the variability of element/Ca ratios and co-variation of Mg/Ca with S/Ca ratios in brachiopod calcite (https://www.sciencedirect.com/science/article/pii/S0016703726002565).

 

Palaeoenvironmental reconstruction

An important benefit of macrofossil calcite is that its preservation can be tested with high confidence. However, animals that form this calcite are complex and geochemical indices encoded in fossils can therefore be complicated, for instance by so-called vital effects, but also by high-frequency changes in environmental conditions such as seasonality which can sometimes be resolved due to rapid secretion of the biological calcite. My contributions have led to a more refined understanding of the role of ecology in controlling geochemical signals in cephalopods (https://www.pnas.org/doi/abs/10.1073/pnas.1320156111) and brachiopods (https://www.nature.com/articles/s41598-020-63487-6) and I am working on improvements in the reconstruction of past seawater chemistry (https://pubs.geoscienceworld.org/gsa/geology/article/41/12/1211/131078/Tectonic-forcing-of-Early-to-Middle-Jurassic?guestAccessKey=).

 

In recent years I have been increasingly involved in supporting the creation of integrated stratigraphic schemes for the Early Jurassic, based on multiple stratigraphic techniques. This work has led to the creation of key datasets that can be used for global correlation of Early Jurassic strata, for instance for the Early Jurassic in the Cardigan Bay Basin, UK (https://pubs.geoscienceworld.org/jgs/article-abstract/doi/10.1144/jgs2021-018/600882) and Hettangian Stage in the Cheshire Basin, UK (https://link.springer.com/article/10.1007/s12583-025-0205-6).

Projects

01/2027-12/2030  Principal Investigator: Jurassic Reloaded - towards accurate temperature and carbon cycle reconstruction for a doubtful Greenhouse world. NSFC 4267030153.

10/2023-03/2025 Co-Investigator: Geotracer facility. British Government Shared Prosperity Fund BUS002c.

03/2023-02/2024 Co-Investigator: GW4 Micro-TIMS. GW4 Generator Grant.

04/2020-09/2020 Principal Investigator: Penryn Geo-Observatory as an interdisciplinary natural laboratory for Earth observations, research-led teaching, and practical skills development. Exeter Education Incubator.

10/2016-09/2021 Researcher Co-Investigator: Integrated Understanding of the Early Jurassic Earth System and Timescale (JET). NERC NE/N018508/1.

10/2014-09/2016 Leopldina Research Fellow: Fellowship of the Leopoldina - German National Academy of Sciences LDPS 2014-08.

 

Selected Publications

(PhD student / based on PhD work; MSc student / based on MSc work; BSc student / based on BSc work)

 

Zhao, K., Hesselbo, S.P., Huang, C., Ullmann, C.V., Damaschke, M., Hollaar, T.P., Jiang, M., Leng, M.J., 2026. Astronomical calibration of the Jurassic Hettangian Stage. Global and Planetary Change 267, 105690. https://doi.org/10.1016/j.gloplacha.2026.105690. T1

Jiang, M., Hesselbo, S.P., Pienkowski, G., Krzeminska, E., Riding, J.B., Uchman, A., Salata, A., Ullmann, C.V., 2026. Laurasian seaway history during the Early Jurassic from quantitative mineralogy and detrital zircon dating. Paleoceanography and Paleoclimatology 41(6), e2026PA005444. https://doi.org/10.1029/2026PA005444.  T2

Ullmann, C.V., Harper, E.M., Osbon, N., Peck, L.S., 2026. Chemical fingerprints of five modern brachiopod species and their application to support fossil geochemical studies. Geochimica et Cosmochimica Acta 423, 12-27. https://doi.org/10.1016/jgca.2026.040.31.  T1, 自然指数期刊

Ullmann, C.V., Damaschke, M., Hesselbo, S.P., Jiang, M., Lawrence, K., Leng, M.J., Mattioli, E., Bancalin, J., Page, K.N., Pudal, N., Ruhl, M., Silva, R.L., 2026. An integrated biostratigraphy and chemostratigraphy for the dawn of the Jurassic (the Hettangian Stage in the Cheshire Basin, UK). Journal of Earth Science 37(3), 945-967. https://doi.org/10.1007/s12583-025-0205-6. T1

Kasemann, S.A., Klein, T., Boyle, R.A., Ullmann, C.V., Aberhan, M., Meixner, A., Duarte, L.V., Lenton, T.M., Piazza, V., Wood, R.A., 2025. Ocean acidification at the Toarcian Anoxic Event captured by boron isotopes in the lime mud record. Communications Earth & Environment 6(1), 533. https://doi.org/10.1038/s43247-025-02510-y. T1

Reddin, C.J., Landwehrs, J.P., Mathes, G.H., Ullmann, C.V., Feulner, G., Aberhan, M., 2025. Marine species and assemblage change foreshadowed by their thermal bias over Early Jurassic warming. Nature Communications 16(1), 1370. https://doi.org/10.1038/s41467-025-56589-0. T1, 自然指数期刊

Ullmann, C.V., Szȕcs, D., Jiang, M., Hudson, A.J.L., Hesselbo, S.P., 2022. Geochemistry of macrofossil, bulk rock and secondary calcite in the Early Jurassic strata of the Llanbedr (Mochras Farm) drill core, Cardigan Bay Basin, Wales, UK. Journal of the Geological Society 179(1), jgs2021-018. https://doi.org/10.1144/jgs2021-018. 

Ullmann, C.V., Boyle, R., Duarte, L.V., Hesselbo, S.P., Kasemann, S.A., Klein, T., Lenton, T.M., Piazza, V., Aberhan, M., 2020. Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports 10(1), 6549. https://doi.org/10.1038/s41598-020-63487-6.

Ullmann, C.V., Gale, A.S., Huggett, J., Wary, D., Frei, R., Korte, C., Broom-Fendley, S., Littler, K., Hesselbo, S.P., 2018. The geochemistry of modern calcarous barnacle shells and applications for palaeoenvironmental studies. Geochimica et Cosmochimica Acta 243, 149-168. T1, 自然指数期刊

Ullmann, C.V., Frei, R., Korte, C., Lüter, C., 2017. Element/Ca, C and O isotope ratios in modern brachiopods: Species-specific signals of biomineralisation. Chemical Geology 460, 15-24. https://doi.org/10.1016/j.chemgeo.2017.03.034. T1

Ullmann, C.V., Campbell, H.J., Frei, R., Korte, C., 2016. Oxygen and carbon isotope and Sr/Ca signatures of high-latitude Permian to Jurassic calcite fossils from New Zealand and New Caledonia. Gondwana Research 38, 60-73. T2

Ullmann, C.V., Frei, R., Korte, C., Hesselbo, S.P., 2015. Chemical and isotopic architecture of the belemnite rostrum. Geochimica et Cosmochimica Acta 159, 231-243. https://doi.org/10.1016/j.gca.2015.03.034. T1, 自然指数期刊

Korte, C., Hesselbo, S.P., Ullmann, C.V., Dietl, G., Ruhl, M., Schweigert, G., Thibault, N., 2015. Jurassic climate mode governed by ocean gateway. Nature Communications 6(1), 10015. https://doi.org/10.1038/ncomms10015. T1, 自然指数期刊

Ullmann, C.V., Thibault, N., Ruhl, M., Hesselbo, S.P., Korte, C., 2014. Effect of a Jurassic oceanic anoxic event on belemnite ecology and evolution. Proceedings of the National Academy of Sciences 111(28), 10073-10076. https://doi.org/10.1073/pnas.1320156111. T1, 自然指数期刊

Ullmann, C.V., Hesselbo, S.P., Korte, C., 2013. Tectonic forcing of Early to Middle Jurassic seawater Sr/Ca. Geology 41(12), 1211-1214. https://doi.org/10.1130/G34817.1. T1, 自然指数期刊

Ullmann, C.V., Campbell, H.J., Frei, R., Hesselbo, S.P., Pogge von Strandmann, P.A.E., Korte, C., 2013. Partial diagenetic overprint of Late Jurassic belemnites from New Zealand: Implications for the preservation potential of δ⁷Li values in calcite fossils. Geochimica et Cosmochimica Acta 120, 80-96. https://doi.org/10.1016/j.gca.2013.06.029. T1, 自然指数期刊

Ullmann, C.V., Wiechert, U., Korte, C., 2010. Oxygen isotope fluctuations in a modern North Sea oyster (Crassostrea gigas) compared with annual variations in seawater temperature: Implications for palaeoclimate studies. Chemical Geology 277 (1-2), 160-166. https://doi.org/10.1016/j.chemgeo.2010.070.19. T1

Reviewer activity

• Nature Communications

• Proceedings of the National Academy of Sciences (PNAS)

• Science Advances

• Geology

• Geochimica et Cosmochimica Acta

• Earth and Planetary Science Letters

• Chemical Geology

• Scientific Reports

• Gondwana Research

• Proceedings of the Royal Society B

• Frontiers in Earth Science

• Geochemistry, Geophysics, Geosystems

• Global and Planetary Change

• Climate of the Past

• Palaeogeography, Palaeoclimatology, Palaeoecology

• Sedimentology

• Sedimentary Geology

• Palaios

• Lethaia

• Palaeontology

• Newsletters on Stratigraphy

• Journal of Paleolimnology

• Marine and Petroleum Geology

• Marine Biology

• Geological Magazine

• Royal Society Open Science

• International Journal of Earth Science

• International Geology Review

• The Depositional Record

• Cretaceous Research

• Journal of Paleolimnology

• Progress in Earth and Planetary Science

• Marine Science and Engineering

• Human and Ecological Risk Assessment

• Materials

• Minerals

• Geosciences

• Proceedings of the Yorkshire Geological Society

• Journal of African Earth Sciences

• New Zealand Journal of Marine and Freshwater Research