Jannik Martens

I am an earth and environmental scientist with interests in climate change and carbon cycling. My experience and area of expertise include marine geology, paleoclimate research, isotope geochemistry and molecular analysis of organic matter. Some of my key interests and contributions are summarized below.

Arctic Ocean acidification during past and present climate change

The increasing uptake of CO2 by the Arctic Ocean leads to ocean acidification and may cause ecosystem and socio-economic stress within and beyond the Arctic region. Ocean acidification in the Arctic is commonly attributed to the rise in atmospheric CO2. However, Arctic warming is expected to trigger massive release of terrestrial organic carbon from rivers and collapsing permafrost, which may exacerbate ocean acidification by additional supply of CO2 from mineralized terrestrial carbon. In this project we investigate Arctic Ocean acidification during past climate change, e.g. during the last deglaciation or over past glacial-interglacial cycles. Past changes in ocean pH and pCO2 are studied using the boron isotope proxy (11B) in foraminifera, as well as through microbial biomarkers. With this work we hope to expand our understanding of the natural variability of the Arctic Ocean carbonate system during changing climate, and study the contribution of terrestrial processes to Arctic Ocean acidification.

Permafrost carbon release during past warming events

Center to my work as a PhD student was to study past changes in carbon release from terrestrial systems, to learn about its potential for carbon cycle perturbations in the near-future. As part of this work, I studied sediment archives to reconstruct the climate sensitivity of Arctic permafrost and OC release to the Arctic Ocean during past warming events, such as the last glacial termination. This work resulted in two studies published in Global Biogeochemical Cycles (Martens et al., 2019) and Science Advances (Martens et al., 2020) in which we studied carbon isotopes (13C, 14C) and terrestrial biomarkers (plant lipids, e.g. n-alkanes and n-alkanoic acids; as well as lignin phenols) in marine sediment cores from the Arctic Ocean. The results reveal massive permafrost carbon release during three warming events documented in Greenland ice cores, which suggests that climate warming by a few °C might be sufficient to trigger large-scale permafrost thaw. This work provides a paleo-reference for the potential of future carbon release from permafrost in response to anthropogenic climate change.

Circum-Arctic carbon cycling today

Arctic warming causes destabilization of high-latitude soils and permafrost deposits, yet large uncertainties exist regarding the dynamics and processes of carbon release from these systems. Over the past years, I was part of an international team of scientists that created a new database of biogeochemical observations in Arctic Ocean sediments, the Circum-Arctic Sediment Carbon DatabasE (CASCADE; incl. a paper in Earth System Science Data; Martens et al., 2021). For this work, we collected and investigated data of carbon isotopes (13C, 14C) and terrestrial biomarkers (plant lipids, e.g. n-alkanes and n-alkanoic acids; as well as lignin phenols) in sediments to deduce carbon release and re-mineralization through the perspective of the shelf receptor.

Based on the creation of the CASCADE and a number of application studies, we also study the spatial patterns and differences of carbon release and re-mineralization in the vast circum-Arctic drainage basin. For this work, we use spatial data analysis tools and statistical dual-isotope (13C, 14C) source apportionment to estimate terrestrial carbon accumulation in the circum-Arctic shelf seas and study the lateral carbon mobilization from different Arctic carbon reservoirs (e.g. permafrost and peatlands). This work was recently published in Nature Communications (Martens et al. 2022)

Fields of Interest

My scientific interests are in the field of global carbon cycling, climate-carbon couplings and paleoceanography, with specific focus on the Arctic region. 

Please have a look at my Google Scholar and Researchgate accounts, and find out more about my upcoming participation in Expedition 400 of the International Ocean Discovery Program (IODP) to NW Greenland, or about my participation in the ISSS-2020 Arctic Ocean Expedition.


  • 2021 Ph.D. (Environmental Science) Stockholm University, Sweden
  • 2016 M.Sc. (Quaternary Science) University of Cologne, Germany
  • 2014 B.Sc. (Physical Geography) University of Cologne, Germany

Martens, J., Wild, B., Semiletov, I., Dudarev, O. and Gustafsson, Ö. (2022), Circum-Arctic release of terrestrial carbon varies between regions and sources. Nature Communications 13, 5858. https://doi.org/10.1038/s41467-022-33541-0

Matsubara, F., Wild, B., Martens, J., Andersson, A., Wennström, R., Bröder, L., Dudarev, O., Semiletov, I., and Gustafsson, Ö. (2022). Molecular-multiproxy assessment of land-derived organic matter degradation over extensive scales of the East Siberian Arctic Shelf Seas. Global Biogeochemical Cycles, 36, e2022GB007428. https://doi.org/10.1029/2022GB007428

Dudarev, O., Charkin, A., Shakhova, N., Ruban, A., Chernykh, D., Vonk, J., Тesi, T., Martens, J., Pipko, I., Pugach, S., Leusov, A., Grinko, A., Gustafsson, Ö., and Semiletov, I. (2022), East Siberian Sea: interannual heterogeneity of the suspended particulate matter and its biogeochemical signature. Progress in Oceanography
102903. https://doi.org/10.1016/j.pocean.2022.102903

Chuvilin, E., Bukhanov, B., Yurchenko, A., Davletshina, D., Shakhova, N., Spivak, E., Rusakov, V., Dudarev, O., Khaustova, N., Tikhonova, A., Gustafsson, O., Tesi, T., Martens, J., Jakobsson, M., Spasennykh, M. and Semiletov, I. (2022). In-situ temperatures and thermal properties of the East Siberian Arctic shelf sediments: Key input for understanding the dynamics of subsea permafrost. Marine and Petroleum Geology, 138, 105550. https://doi.org/10.1016/j.marpetgeo.2022.105550

Martens, J., Romankevich, E., Semiletov, I., Wild, B., van Dongen, B., Tesi, T., Shakhova, N., Dudarev, O. V, Kosmach, D., Vetrov, A., Lobkovsky, L., Belyaev, N., Macdonald, R., Pieńkowski, A. J., Haghipour, N., Dahle, S., Carroll, M. L., Åström, E. K., Grebmeier, M., Cooper, L. W., Possnert, G. and Gustafsson, Ö. (2021). CASCADE - The Circum-Arctic Sediment CArbon DatabasE. Earth System Science Data, 13, 2561–2572. https://doi.org/10.5194/essd-13-2561-2021

Nybom, I., Horlitz, G., Gilbert, D., Berrojalbiz, N., Martens, J., Arp, H.P., and Sobek, A. (2021), Effects of Organic Carbon Origin on Hydrophobic Organic Contaminant Fate in the Baltic Sea. Environmental Science & Technology, 55, 19, 13061-13071. https://doi.org/10.1021/acs.est.1c04601

Martens, J., Wild, B., Muschitiello, F., O’Regan, M., Jakobsson, M., Semiletov, I., Dudarev, O. V. and Gustafsson, Ö. (2020). Remobilization of dormant carbon from Siberian-Arctic permafrost during three past warming events. Science Advances, 6 (42). https://doi.org/10.1126/sciadv.abb6546

Muschitiello, F., O'Regan, M., Martens, J., West, G., Gustafsson, Ö., and Jakobsson, M. (2020). A new 30 000-year chronology for rapidly deposited sediments on the Lomonosov Ridge using bulk radiocarbon dating and probabilistic stratigraphic alignment. Geochronology, 2, 81–91. https://doi.org/10.5194/gchron-2-81-2020

Martens, J., Wild, B., Pearce, C., Tesi, T., Andersson, A., Bröder, L., O’Regan, M., Jakobsson, M., Sköld, M., Gemery, L., Cronin, T. M., Semiletov, I., Dudarev, O. V. and Gustafsson, Ö. (2019). Remobilization of old permafrost carbon to Chukchi Sea sediments during the end of the last deglaciation. Global Biogeochemical Cycles, 33. https://doi.org/10.1029/2018GB005969

Tanski, G., et al. incl. Martens, J. (2019). The Permafrost Young Researchers Network (PYRN) is getting older: The past, present, and future of our evolving community. Polar Record, 55 (4), 216-219. https://doi.org/10.1017/S0032247418000645