Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-30
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
12 Apr 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Causes of simulated, longterm changes in chlorophyll concentrations in the Baltic Sea
Jenny Hieronymus1, Kari Eilola1, Magnus Hieronymus1, H. E. Markus Meier2,1, and Sofia Saraiva1 1Research and Development Department, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden
2Department of Physical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany
Abstract. The co-variation of key variables with modelled phytoplankton concentrations in the Baltic proper has been examined using wavelet analysis and results of a long-term simulation for 1850–2008 with a high-resolution, coupled physical-biogeochemical circulation model for the Baltic Sea. By focusing on interannual variations it is possible to track effects acting on decadal time scales such as temperature increase due to climate change as well as changes in nutrient input. The results indicate the largest inter-annual coherence of phytoplankton with the limiting nutrient. However, after 1950 the coherence is reduced due to high mixed layer nutrient concentrations diminishing the effect of smaller long-term variations. Furthermore, the inter-annual coherence of mixed layer nitrate with riverine input of nitrate is much larger than the coherence between mixed layer phosphate and phosphate loads. This indicates a greater relative importance of internal loads i.e. mixing of phosphate from deeper layers. In addition, shifts in nutrient patterns give rise to changes in phytoplankton nutrient limitation. The modelled pattern shifts from purely phosphate limited to a seasonally varying regime. The results further indicate some effect of inter-annual temperature increase on cyanobacteria and flagellates. Changes in mixed layer depth affect mainly diatoms due to a high sinking velocity while inter-annual coherence between irradiance and phytoplankton is not observed.

Citation: Hieronymus, J., Eilola, K., Hieronymus, M., Meier, H. E. M., and Saraiva, S.: Causes of simulated, longterm changes in chlorophyll concentrations in the Baltic Sea, Biogeosciences Discuss., doi:10.5194/bg-2017-30, in review, 2017.
Jenny Hieronymus et al.
Jenny Hieronymus et al.
Jenny Hieronymus et al.

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This paper investigates how phytoplankton concentrations in the Baltic Sea covary with nutrient concentrations and other key variables on inter annual time scales in a model integration over the years 1850–2008. The study area is not only affected by climate change, it has also been subjected to greatly increased nutrient loads due to extensive use of agricultural fertilizers. The results indicate the largest inter-annual coherence of phytoplankton with the limiting nutrient.
This paper investigates how phytoplankton concentrations in the Baltic Sea covary with nutrient...
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