Turbulence and Arctic marine ecosystems
Above: February in the Arctic Ocean as seen by Sentinel-1.

Research Topics

Bio-optical Argo floats

Remote sensing of the global ocean using satellites monitoring the state of marine ecosystems year-round. In the Arctic, the presence of sea ice and the long polar night are a showstopper for many of these approaches. Biogeochemical (BGC) Argo floats are autonomous robots that drift around with ocean currents, going up and down in the water column as they sample the world's oceans. The Takuvik laboratory that I am a part of has been deploying BGC Argo floats in Baffin Bay to study the year-round evolution of ecosystem dynamics, even during winter when satellites cannot look into the ocean.

Vertical turbulent nitrate fluxes

Without regular vertical mixing, most of the world ocean would be dead and deserted. The reason is that algae have a tendency to sink and hence take scarce plant nutrients with them to depth. These nutrients' only chance of getting back into the sunlight, where algae grow, is when the ocean is stirred by winds, the tides, upwelling of deeper water, or other currents. Because of the huge amounts of river and other fresh water sources in the Arctic Ocean, the Ocean is especially resistant to such mixing. Hence large parts of the Arctic Ocean are among the nutrient-poorest regions of the world's oceans which drastically limits its productivity. My Ph.D. thesis was one of the first systematic attempts to measure this 'vertical turbulent nitrate flux' with a large in-situ data set collected from drifting ice camps, research vessels, and moored instruments.

Ice-ocean interaction

One of the most distinctive features of Arctic marine ecosystems is the presence of sea ice. It alters how wind moves around the water and how those currents mix the upper ocean; it changes the flow of heat from the atmosphere into the water and back; it changes the supply of spent surface waters with deep, nutrient rich ones; it changes the density of the sea water and hence the turbulent mixing of the very environment in which plankton lives. It is the lack of sunlight in winter that makes the water freeze, but it is the heat stored in the ocean that makes the ice not grow forever. All of these phenomena are what oceanographers refer to when they use the rather prosaic expression 'flux of momentum, heat, salt, and other tracers'.

Given its relevance for the Arctic summer, when plankton grows, I have been especially interested in melting sea ice. Melting sea ice creates a layer that resists vertical mixing, often a drastic change from the more intense mixing that happens in winter, which I explored in two studies in 2014 and 2017.


From hypothetical reproducability to actual reusability

Code and ancillary data for publications

Have you ever read an article and thought "I wonder how their calculations would pan out if I used my own value for this one constant they could only guess", or "I would really like to use that figure, but I wish I could modify their color bar", or "Nice description, but how did they actually calculate that average"? Me too. And that is why we should not only share raw data, but also computer code, and other machine-readable information. In the section below you can find supporting material for my more recent publications. The first articles for which I published all necessary material are our 2020 analysis of how turbulent nitrate fluxes limit algae growth across the Arctic Ocean and a 2019 paper on ice edge phytoplankton blooms.

Open source software

Open source data science computer programs are more advanced than ever. I am an avid python user and contribute to the Holoviews package, part of the HoloViz ecosystem of visualisation and data handling tools. You can find some of my own material in this repository and in this toolbox.


Because the digital equivalent of flat paper is better with a journal logo on it

Code and Ancillary Data

  1. Randelhoff, Achim, Laurent Oziel, Philippe Massicotte, Guislain Bécu, Martí Galí, Léo Lacour, Dany Dumont, Anda Vladoiu, Claudie Marec, Flavienne Bruyant, Marie-Noëlle Houssais, Jean-Éric Tremblay, Gabrièle Deslongchamps, and Marcel Babin. 2019. “Code and Data for: The Evolution of Light and Vertical Mixing across a Phytoplankton Ice-Edge Bloom.” [repository] [archive]
  2. Randelhoff, Achim. 2020. “Software, Data, and Supplementary Material for: Pan-Arctic Ocean Primary Production Constrained by Turbulent Nitrate Fluxes.” [repository] [archive] [interactive paper]
  3. Randelhoff, Achim. 2020. “Code, Data, and Supplementary Information for: ‘Arctic Mid-Winter Phytoplankton Growth Revealed by Autonomous Profilers.’” [repository] [archive]


  1. Hudson, Stephen R., Mats A. Granskog, Arild Sundfjord, Achim Randelhoff, Angelika H. H. Renner, and Dmitry V. Divine. 2013. “Energy Budget of First-Year Arctic Sea Ice in Advanced Stages of Melt.” Geophysical Research Letters 40(11):2679–83. doi: 10.1002/grl.50517. [pdf] [webpage]
  2. Randelhoff, Achim, Arild Sundfjord, and Angelika H. H. Renner. 2014. “Effects of a Shallow Pycnocline and Surface Meltwater on Sea Ice-Ocean Drag and Turbulent Heat Flux.” J. Phys. Oceanogr. 44(8):2176–90. doi: 10.1175/jpo-d-13-0231.1. [pdf] [webpage]
  3. Randelhoff, Achim, Arild Sundfjord, and Marit Reigstad. 2015. “Seasonal Variability and Fluxes of Nitrate in the Surface Waters over the Arctic Shelf Slope.” Geophysical Research Letters 42(9):3442–49. doi: 10.1002/2015gl063655. [pdf] [webpage]
  4. Randelhoff, Achim, and John D. Guthrie. 2016. “Regional Patterns in Current and Future Export Production in the Central Arctic Ocean Quantified from Nitrate Fluxes.” Geophysical Research Letters. doi: 10.1002/2016gl070252. [pdf] [webpage]
  5. Randelhoff, Achim, Ilker Fer, Arild Sundfjord, Jean-Eric Tremblay, and Marit Reigstad. 2016. “Vertical Fluxes of Nitrate in the Seasonal Nitracline of the Atlantic Sector of the Arctic Ocean.” Journal of Geophysical Research-Oceans 121(7):5282–95. doi: 10.1002/2016JC011779. [pdf] [webpage]
  6. Peterson, Algot K., Ilker Fer, Miles G. McPhee, and Achim Randelhoff. 2017. “Turbulent Heat and Momentum Fluxes in the Upper Ocean under Arctic Sea Ice.” Journal of Geophysical Research: Oceans 122(2):1439–56. doi: 10.1002/2016JC012283. [pdf] [webpage]
  7. Randelhoff, Achim, Ilker Fer, and Arild Sundfjord. 2017. “Turbulent Upper-Ocean Mixing Affected by Meltwater Layers during Arctic Summer.” Journal of Physical Oceanography 47(4):835–53. doi: 10.1175/JPO-D-16-0200.1. [pdf] [webpage]
  8. Assmy, Philipp, Mar Fernández-Méndez, Pedro Duarte, Amelie Meyer, Achim Randelhoff, Christopher J. Mundy, Lasse M. Olsen, Hanna M. Kauko, Allison Bailey, Melissa Chierici, Lana Cohen, Anthony P. Doulgeris, Jens K. Ehn, Agneta Fransson, Sebastian Gerland, Haakon Hop, Stephen R. Hudson, Nick Hughes, Polona Itkin, Geir Johnsen, Jennifer A. King, Boris P. Koch, Zoe Koenig, Slawomir Kwasniewski, Samuel R. Laney, Marcel Nicolaus, Alexey K. Pavlov, Christopher M. Polashenski, Christine Provost, Anja Rösel, Marthe Sandbu, Gunnar Spreen, Lars H. Smedsrud, Arild Sundfjord, Torbjørn Taskjelle, Agnieszka Tatarek, Jozef Wiktor, Penelope M. Wagner, Anette Wold, Harald Steen, and Mats A. Granskog. 2017. “Leads in Arctic Pack Ice Enable Early Phytoplankton Blooms below Snow-Covered Sea Ice.” Scientific Reports 7:40850. doi: 10.1038/srep40850. [pdf] [webpage]
  9. Fer, Ilker, Algot K. Peterson, Achim Randelhoff, and Amelie Meyer. 2017. “One-Dimensional Evolution of the Upper Water Column in the Atlantic Sector of the Arctic Ocean in Winter.” Journal of Geophysical Research-Oceans 122(3):1665–82. doi: 10.1002/2016JC012431. [pdf] [webpage]
  10. Randelhoff, A., and A. Sundfjord. 2018. “Short Commentary on Marine Productivity at Arctic Shelf Breaks: Upwelling, Advection and Vertical Mixing.” Ocean Science 14(2):293–300. doi: 10.5194/os-14-293-2018. [pdf] [webpage]
  11. Randelhoff, Achim, Marit Reigstad, Melissa Chierici, Arild Sundfjord, Vladimir Ivanov, Mattias Cape, Maria Vernet, Jean-Éric Tremblay, Gunnar Bratbak, and Svein Kristiansen. 2018. “Seasonality of the Physical and Biogeochemical Hydrography in the Inflow to the Arctic Ocean Through Fram Strait.” Frontiers in Marine Science 5. doi: 10.3389/fmars.2018.00224. [pdf] [webpage]
  12. Randelhoff, Achim, Laurent Oziel, Philippe Massicotte, Guislain Bécu, Martí Galí, Léo Lacour, Dany Dumont, Anda Vladoiu, Claudie Marec, Flavienne Bruyant, Marie-Noëlle Houssais, Jean-Éric Tremblay, Gabrièle Deslongchamps, and Marcel Babin. 2019. “The Evolution of Light and Vertical Mixing across a Phytoplankton Ice-Edge Bloom.” Elem Sci Anth 7(1):20. doi: 10.1525/elementa.357. [pdf] [webpage]
  13. Graham, Robert M., Polona Itkin, Amelie Meyer, Arild Sundfjord, Gunnar Spreen, Lars H. Smedsrud, Glen E. Liston, Bin Cheng, Lana Cohen, Dmitry Divine, Ilker Fer, Agneta Fransson, Sebastian Gerland, Jari Haapala, Stephen R. Hudson, A. Malin Johansson, Jennifer King, Ioanna Merkouriadi, Algot K. Peterson, Christine Provost, Achim Randelhoff, Annette Rinke, Anja Rösel, Nathalie Sennéchael, Von P. Walden, Pedro Duarte, Philipp Assmy, Harald Steen, and Mats A. Granskog. 2019. “Winter Storms Accelerate the Demise of Sea Ice in the Atlantic Sector of the Arctic Ocean.” Scientific Reports 9(1):1–16. doi: 10.1038/s41598-019-45574-5. [pdf] [webpage]
  14. Oziel, L., P. Massicotte, A. Randelhoff, J. Ferland, A. Vladoiu, L. Lacour, V. Galindo, S. Lambert-Girard, D. Dumont, Y. Cuypers, P. Bouruet-Aubertot, C.-J. Mundy, J. Ehn, G. Bécu, C. Marec, M.-H. Forget, N. Garcia, P. Coupel, P. Raimbault, M.-N. Houssais, and M. Babin. 2019. “Environmental Factors Influencing the Seasonal Dynamics of Spring Algal Blooms in and beneath Sea Ice in Western Baffin Bay.” Elem Sci Anth 7(1):34. doi: 10.1525/elementa.372. [pdf] [webpage]
  15. Randelhoff, Achim, Johnna Holding, Markus Janout, Mikael Kristian Sejr, Marcel Babin, Jean-Éric Tremblay, and Matthew B. Alkire. 2020. “Pan-Arctic Ocean Primary Production Constrained by Turbulent Nitrate Fluxes.” Frontiers in Marine Science 7. doi: 10.3389/fmars.2020.00150. [pdf] [webpage] [interactive paper]
  16. Oziel, L., A. Baudena, M. Ardyna, P. Massicotte, A. Randelhoff, J.-B. Sallée, R. B. Ingvaldsen, E. Devred, and M. Babin. 2020. “Faster Atlantic Currents Drive Poleward Expansion of Temperate Phytoplankton in the Arctic Ocean.” Nature Communications 11(1):1–8. doi: 10.1038/s41467-020-15485-5. [pdf] [webpage]
  17. Randelhoff, Achim, Léo Lacour, Claudie Marec, Edouard Leymarie, José Lagunas, Xiaogang Xing, Gérald Darnis, Christophe Penkerc’h, Makoto Sampei, Louis Fortier, Fabrizio D’Ortenzio, Hervé Claustre, and Marcel Babin. 2020. “Arctic Mid-Winter Phytoplankton Growth Revealed by Autonomous Profilers.” Science Advances 6(39):eabc2678. doi: 10.1126/sciadv.abc2678. [pdf] [webpage]
  18. Le Traon, Pierre-Yves, Fabrizio D’Ortenzio, Marcel Babin, Edouard Leymarie, Claudie Marec, Sylvie Pouliquen, Virginie Thierry, Cecile Cabanes, Hervé Claustre, Damien Desbruyères, Leo Lacour, Jose-Luis Lagunas, Guillaume Maze, Herle Mercier, Christophe Penkerc’h, Noe Poffa, Antoine Poteau, Louis Prieur, Virginie Racapé, Achim Randelhoff, Eric Rehm, Catherine Marie Schmechtig, Vincent Taillandier, Thibaut Wagener, and Xiaogang Xing. 2020. “Preparing the New Phase of Argo: Scientific Achievements of the NAOS Project.” Frontiers in Marine Science 7. doi: 10.3389/fmars.2020.577408. [pdf] [webpage]
  19. Dybwad, Christine, Philipp Assmy, Lasse M. Olsen, Ilka Peeken, Anna Nikolopoulos, Thomas Krumpen, Achim Randelhoff, Agnieszka Tatarek, Józef M. Wiktor, and Marit Reigstad. 2021. “Carbon Export in the Seasonal Sea Ice Zone North of Svalbard From Winter to Late Summer.” Frontiers in Marine Science 7. doi: 10.3389/fmars.2020.525800. [pdf] [webpage]