EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Dust and pyrogenic iron boost phytoplankton blooms in sub-Antarctic waters of the Tasman Sea

Joan Llort1,2, Richard J. Matear3, Pete G. Strutton2,4, Andrew R. Bowie2, and Zanna Chase2
Joan Llort et al.
  • 1Barcelona Supercomputing Centre, Climare Prediction Group - Ocean Biogeochemistry Team, Barcelona, Spain
  • 2Institute for Marine and Antarctic Studies - University of Tasmania, Hobart, Australia
  • 3CSIRO Oceans and Atmosphere, Hobart, Australia
  • 4Australian Research Council Centre of Excellence for Climate Extremes, Hobart, Australia

Although it is commonly accepted that atmospheric deposition of Fe particles can fertilise phytoplankton, there is yet no clear evidence on how such a fertilisation effect takes place. Several studies have attempted to link individual dust events with surface chlorophyll responses but generally, they do not find a clear correspondence between dust deposition and its impact on chlorophyll. In this work, we use a biogeochemical model to show that the atmospheric deposition of Fe in high-latitude seas, rather than creating instantaneous phytoplankton responses, replenish the upper mixed layer of the ocean during the pre-bloom period, from winter to early summer. The Fe accumulated at the surface boosts the phytoplankton bloom of the following summer, resulting in surface chlorophyll accumulations of up to 3 times larger than the years without atmospheric deposition. We used this mechanism to explain the strong inter-annual variability of the phytoplankton bloom in sub-Antarctic iron-limited waters east of Australia. Putting together more than a 15-years-long record of ocean colour observations and atmospheric aerosols reanalysis we uncovered a strong correlation (r2>0.6) between the dust that crossed the region during the pre-bloom period and the magnitude of the surface chlorophyll bloom. Interestingly, the correlation increased when taking into account pyrogenic aerosols in addition to dust. Our study presents the first observational link between Climate Change-enhanced droughts and wildfires, atmospheric aerosols and primary production of iron-limited waters.

How to cite: Llort, J., Matear, R. J., Strutton, P. G., Bowie, A. R., and Chase, Z.: Dust and pyrogenic iron boost phytoplankton blooms in sub-Antarctic waters of the Tasman Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7809,, 2020

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Presentation version 1 – uploaded on 07 May 2020
  • CC1: Comment on EGU2020-7809, Damien Cardinal, 08 May 2020

    Dear Joan

    Thanks for this nice and inspiring presentation. Do you have any data on the Fe content of dust vs. ash in the area and on the solubility change due to pH + ash as you hypothesize? Could also other micronutrients play a significant role in the fertilisation ?



    • CC2: Reply to CC1, Joan Llort, 08 May 2020

      Hi Damien,

      Thanks for comment.

      Regretfully, there is no atmospheric data above the Tasman Sea during this period. However, since early 2019 we do have aerosol composition data measured in Tasmania. We are currently analysing these data for the massive 2019-20 fire season. Regarding other nutrients, I think that Si could also play a role but only during summer, when it becomes limiting.

      Do not hesitate to contact me by mail you want to further discuss this work:



      • CC3: Reply to CC2, Damien Cardinal, 08 May 2020

        Thanks Joan, regarding Si and Fe please have a look at the impact on dust and volcanic ash deposit on phytoplankton Southern Ocean primary production & phytoplankton by C. Geisen et al. in this session.



        • CC4: Reply to CC3, Joan Llort, 08 May 2020

          Yes indeed. Looking forward to it. :)