Assessment: Baltic Proper (Alg@line observations)

Dissolved inorganic Phosphate (PO4)

In 2006 the range of annual surface water DIP concentration varied between 0.00–0.95 µmol l-1 (in Fig 4). The highest winter nutrient concentrations were measured at the Bornholm Basin and in the Gulf of Finland. In the Arkona Basin and the Bornholm Basin the concentrations were higher than the Alg@line reference from beginning of the year to the end of May. The DIP concentration was above the Alg@line-reference in all regions in the beginning of the year.  

Dissolved inorganic nitrogen (NO3 + NO2  + NH4)

In 2006 the annual surface water concentration of DIN varied between 0.0-11.1 µmol l-1 (in Fig. 5). The highest early spring levels of DIN concentrations were found at the entrance to and with in the Gulf of Finland, where the concentrations were like the Alg@line-reference concentrations. In Arkona and Bornholm Basin the winter concentrations were lower than in the Alg@line-reference conditions.                                                                                                                      

Chlorophyll a

In 2006 the annual concentrations of chlorophyll a varied between 0.5-29.5 mg m-3 (in Fig. 6). The concentrations were highest at the entrance and within the Gulf of Finland and weakest at the Arkona and Bornholm Basin. The chlorophyll a concentrations during 2006 followed closely the Alg@line-reference conditions.

Silicate (SiO4)

In 2006 the annual surface water concentration of silicate varied between 0.6-16.2 µmol l-1 (in Fig. 7). The highest spring and winter levels of silicate concentrations were in the Arkona Basin. In the Arkona and Bornholm Basin the concentrations were higher than on the Alg@line-reference. In the Gotland basin the concentration was lower than the Alg@line-reference. However the concentrations of the year 2006 followed the Alg@line-reference fairly well throughout the year.   

Ratio of dissolved inorganic nitrogen and dissolved inorganic phosphor (DIN:DIP)

In 2006 the DIN:DIP ratio exceeded the HELCOM-reference value (16 µmol l-1) three times, but in summertime (in Fig. 8). In the Arkona and Bornholm Basin the 2006 ratio were lower than in the Alg@line-reference. Otherwise the DIN:DIP ratio behaved close to the Alg@line-reference conditions. 

Ratio of dissolved inorganic nitrogen and silicate (DIN:SiO4)

In 2006 the DIN:silicate ratio did not exceed the HELCOM-reference value (1 µmol l-1) once during the whole year (in Fig. 9). During the spring 2006 the ratio was higher than the Alg@line-reference in the Gulf of Finland and lower than the Alg@line-reference in the Arkona and Bornholm Basin. Thus the DIN:silicate ratio in 2006 behaved much like the Alg@line reference.   

Figure 4.  The annual variation of dissolved inorganic phosphate (PO4 µmol l-1) as a function of position and time along the ship route (see Figure 22). On the left is the year 2006 and on the right is the Alg@line-reference  (average of the years 1993-2004) with 10 days interval. Cumulative day number is used as a temporal scale. The figures are based on red dots or triangles in case of west route of the Gotland. Click images to enlarge!   

Figure 5. Idem, but dissolved inorganic nitrogen (NO3+NO2 +NH4  µmol l-1).  Click images to enlarge!

Figure 6.  Idem, but chlorophyll a (mg m-3). Click images to enlarge!   

Figure 7. Idem, silicate  (µmol l-1). Click images to enlarge!    

Figure 8.  Idem, but ratio of dissolved inorganic nitrogen and -phosphate  ((NO3+NO2 +NH4)/PO4). Click images to enlarge!  

Figure 9.  Idem, but ratio of dissolved inorganic nitrogen and silicate ((NO3+NO2 +NH4)/SiO4). Click images to enlarge!

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