24 Jun 2021

24 Jun 2021

Review status: this preprint is currently under review for the journal BG.

Modeling cyanobacteria life cycle dynamics and historical nitrogen fixation in the Baltic Sea

Jenny Hieronymus1, Kari Eilola1, Malin Olofsson2, Inga Hense3, H. E. Markus Meier4, and Elin Almroth-Rosell1 Jenny Hieronymus et al.
  • 1Department of research and development, Swedish Meteorological and Hydrological Institute, 60175 Norrköping, Sweden
  • 2Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden
  • 3Institute of Marine Ecosystem and Fishery Science, Universität Hamburg, 22767 Hamburg, Germany
  • 4Department of Physical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research Warnemünde, 18119 Rostock, Germany

Abstract. Dense blooms of filamentous diazotrophic cyanobacteria are formed every summer in the Baltic Sea. These autotrophic organisms may bypass nitrogen limitation by performing nitrogen fixation, which also governs surrounding organisms by releasing bioavailable nitrogen. The magnitude of the nitrogen fixation is important to estimate from a management perspective since this might counteract eutrophication reduction measures. Here, a cyanobacteria life cycle model has been implemented for the first time in a high-resolution 3D coupled physical and biogeochemical model of the Baltic Sea spanning the years 1850–2008. The explicit consideration of life cycle dynamics and transitions significantly improves the representation of the cyanobacterial phenological patterns. Compared to earlier 3D-modelling efforts, the rapid increase and decrease of cyanobacteria in the Baltic Sea is well captured by our developed model and is now in concert with observations. The current improvement in timing of cyanobacteria blooms had a large effect on the estimated nitrogen fixation load and is in agreement with in situ measurements. By performing four phosphorus sensitivity runs we demonstrate the importance of both organic and inorganic phosphorus availability for historical cyanobacterial biomass estimates. The used model combination can be used to continuously estimate internal nitrogen loads via nitrogen fixation in Baltic Sea ecosystem management, which is of extra importance in a future ocean with changed conditions for the filamentous cyanobacteria.

Jenny Hieronymus et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-156', Anonymous Referee #1, 06 Jul 2021
    • AC1: 'Reply on RC1', Jenny Hieronymus, 26 Aug 2021
  • RC2: 'Comment on bg-2021-156', Anonymous Referee #2, 19 Jul 2021
    • AC2: 'Reply on RC2', Jenny Hieronymus, 26 Aug 2021
  • RC3: 'Comment on bg-2021-156', Anonymous Referee #3, 25 Jul 2021
    • AC3: 'Reply on RC3', Jenny Hieronymus, 26 Aug 2021

Jenny Hieronymus et al.

Data sets

Modeling cyanobacteria life cycle dynamics and historical nitrogen fixation in the Baltic Sea - Datasets Jenny Hieronymus, Kari Eilola, Malin Olofsson, Inga Hense, H. E. Markus Meier, Elin Almroth-Rosell

Jenny Hieronymus et al.


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Short summary
Dense blooms of cyanobacteria occurs every summer in the Baltic Sea and can add to eutrophication by their ability to turn nitrogen gas into dissolved inorganic nitrogen. Being able to correctly estimate the size of this nitrogen fixation is important for management purposes. In this work, we find that the life cycle of cyanobacteria plays an important roll in capturing the seasonality of the blooms as well as the size of nitrogen fixation in our ocean model.