PhD Thesis

In the North Atlantic Ocean, warm and salty surface waters are transported northward and are responsible for a relatively mild climate in Europe. In the deep sea cold and fresh waters flow southward. This circulation is also known as overturning. Due to climate change this overturning is predicted to weaken with a potential impact on European climate. For better predictions of those future changes long-term ocean observations are needed that monitor the currents contributing to this overturning process. The aim of this thesis was to better understand the mechanisms driving one of those currents in the Irminger Sea, southeast of Greenland: the Irminger Current (IC). The IC brings warm and salty waters from the subtropics northward. With the use of instruments that record current velocity, temperature and salinity I showed that the strength of the IC on long time scales is driven by changes in the ocean’s density over the whole Irminger Sea. I further showed that in response to very low salinity waters that arrive in the IC in 2016, the current brings more lighter waters northward with a potential impact on overturning. I also studied where the waters feeding the IC come from. One part originates from further east, in the Iceland Basin, but some waters also originate from the Irminger Sea itself. As the IC contributes to the overturning, mechanisms and changes described in this thesis are important to better understand potential future changes in overturning.

Field campaigns

• Expedition to the Irminger Sea and Iceland Basin 2022, AR69-02, RV Neil Armstrong
  Responsibilities: mooring work, mooring instrument data recovery, CTD watch, salinometer measurements
  
• Expedition to the Irminger Sea 2020, PE473, RV Pelagia
  Responsibilities: CTD watch, mooring work
  Blog
• Expedition to the Labrador Sea 2018, MSM74, RV Maria S. Merian
  Responsibilities: salinometer measurements, CTD watch, mooring work
• Expedition to Northern Greenland 2018, PAMARCMIP, Station North/Villum Research Station
  Responsibilities: black carbon measurements on snow, snow pit work
  National Geographic Article, New York Times Article
• Expedition to the Labrador Sea 2016, MSM54, RV Maria S. Merian
  Responsibilities: CTD calibration, CTD watch, mooring work
• Expedition to Tropical Atlantic, 2015 M119, RV Meteor
  Responsibilities: salinometer measurements, CTD watch, mooring work

Publications

• Fried, N., Gelderloos, R., Tooth, O. J., Katsman, C. A., and de Jong, M. F.: On the fate of the Irminger Current water and its impact on the convection region in the Irminger Sea – a Lagrangian model study. (2026). Ocean Sci., 22, 1763–1780, https://doi.org/10.5194/os-22-1763-2026.
• Fu, Y., Lozier, M. S., Bower, A., Burmeister, K., Carrilho Biló, T., Cyr, F., Cunningham, S. A., deYoung, B., Dilmahamod, A. F., de Jong, M.F., Fried, N. et al. (2025). Characterizing the interannual variability of North Atlantic subpolar overturning. Geophysical Research Letters, 52, e2025GL114672. https://doi.org/10.1029/2025GL114672
• Fried, N., Biló, T. C., Johns, W., Katsman, C. A., Fogaren, K. E., Yoder, M. F., ... & de Jong, M. F. (2024), Recent Freshening of the Subpolar North Atlantic Increased the Transport of Lighter Waters of the Irminger Current From 2014 to 2022, Journal of Geophysical Research: Oceans, 129(11). https://doi.org/10.1029/2024JC021184
• Fried, N. , Katsman, C. A., & de Jong, M. F. (2024). Where do the two cores of the Irminger Current come from? A Lagrangian study using a 1/10 ocean model simulation. Journal of Geophysical Research: Oceans, 129(10),https://doi.org/10.1029/2023JC020713
• Sanchez-Franks, A., Holliday, N. P., Evans, D. G., Fried, N., Tooth, O. J., Chafik, L., ... & Johnson, H. L. (2024). The Irminger Gyre as a key driver of the Subpolar North Atlantic overturning. Geophysical Research Letters, 51(8), https://doi.org/10.1029/2024GL108457. https://doi.org/10.1029/2024GL108457
• Fu, Y., Lozier, M. S., Biló, T. C., Bower, A. S., Cunningham, S. A., Cyr, F., Fried,N. ... & Yashayaev, I. (2023). Seasonality of the Meridional Overturning Circulation in the subpolar North Atlantic. Communications earth & environment, 4(1), 181., https://doi.org/10.1038/s43247-023-00848-9
• Desbruyères, D. G., Bravo, E. P., Thierry, V., Mercier, H., Lherminier, P., Cabanes, C., Biló, T.C., Fried, N., De Jong, M. F. (2022). Warming‐to‐cooling reversal of overflow‐derived water masses in the Irminger Sea during 2002‐2021. Geophysical Research Letters, e2022GL098057. https://doi.org/10.1029/2022GL098057
• Fried, N., & Femke de Jong, M. (2022). The role of the Irminger Current in the Irminger Sea northward transport variability. Journal of Geophysical Research: Oceans, 127, e2021JC018188. https://doi.org/10.1029/2021JC018188
• Li, F.; Lozier, M. S.; Bacon, S.; Bower, A. S.; Cunningham, S. A.; de Jong, M. F.; deYoung, B.; Fraser, N.; Fried, N.; Han, G.; Holliday, N. P.; Holte, J.; Houpert, L.; Inall, M. E.; Johns, W. E.; Jones, S.; Johnson, C.; Karstensen, J.; Le Bras, I. A.; Lherminier, P.; Lin, X.; Mercier, H.; Oltmanns, M.; Pacini, A.; Petit, T.; Pickart, R. S.; Rayner, D.; Straneo, F.; Thierry, V.; Visbeck, M.; Yashayaev, I.; Zhou, C. (2021). Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation. Nature Comm. 12: 3002. https://hdl.handle.net/10.1038/s41467-021-23350-2
• de Jong, M.F.; de Steur, L.; Fried, N.; Bol, R.; Kritsotalakis, S. (2020). Year‐round measurements of the Irminger Current: Variability of a two‐core current system observed in 2014–2016. JGR: Oceans 125(10). https://doi.org/10.1029/2020jc016193

Recent Conferences

Teaching at the University of Münster

• Lecture Climatology (winter semester 24/25, 25/26)
• Practical Climatology (winter semester 24/25, 25/26; summer semester 2025, 2026)
• Seminar Climate Geography (summer semester 2025, 2026)

• Zwischen Effizienz und Emission - Die Rolle Künstlicher Intelligenz im Klimakontext und ihre gesellschaftliche Wahrnehmung unter Studierenden (Jana Schwark, BSc Geography and English, University of Münster, 2026)
• Entwicklung und Ausgestaltung des arktischen Kreuzfahrttourismus am Beispiel Grönlands (Lynn Steffen, BSc Geography, University of Münster, 2026)
• Klimaangst im Klassenzimmer: Wie Jugendliche den Klimawandel emotional erleben und wie Schule darauf reagieren kann (Inga-Carola Koßmann, BSc Geography and Mathematics, University of Münster, 2026)
• The Effect of Lamb Weather Types on Storm Surges on the Irish Coast (Emma Hermes, BSc in Geography and English, University of Münster, 2025)
• Polare Meere im Stress: Über die Auswirkungen des Klimawandels auf marine Ökosysteme und die Darstellung der Problematik in Schulbüchern (Finn Wehmeyer, BSc in Geography and Biology, University of Münster, 2025)
• Mehr Plastik als Muscheln? Eine Literaturbasierte Analyse von Clean-up-Daten zur Zusammensetzung und Verbreitung von Plastikmüll an Europas Küsten (Fiona Uhlenbrock, BSc in Geography and Physics, Univeristy of Münster, 2025)