Figure 1.
Interacting effects of Azolla, rain and wind on salinity stratification. A
) Salinity (mg L−1 ± standard error) in the top water layers (solid lines) and in the bottom water layers (dotted lines) of the beakers in the absence of Azolla (rounds), in the presence of Azolla (squares), with no influence of wind (closed figures) or with influence of wind (open figures) hours after the rain event. B) Salinity (mg L−1) profiles in the beakers 20 hours after the rain event.
Figure 2.
A) Development of the biomass density of Azolla filiculoides (g dry weight m−2 ± standard error) grown in freshwater or brackish water basins. 2B) Chloride concentrations and 2C) phosphate concentrations (µM ± standard error) in the top, middle and bottom water layers of the freshwater and brackish water basins during the mesocosm experiment. Significant differences between water layers are indicated by different letters. The cumulative amount of rainfall during the experiment (mm) is shown on the right axis in figure 2B.
Figure 3.
Conceptual model showing how Azolla arctica may have colonized the Eocene Arctic Ocean using phosphate sources from coastal areas for expansion to the open ocean where small-scale salinity stratification allows for efficient recycling of nutrients to sustain the standing biomass.