The former takes place during blooms, while the latter in both th

The former takes place during blooms, while the latter in both the growing and non-growing periods. Slope coefficients of linear dependences (Figure 6, Figure 7 and Figure 8) were used (Table 5) to characterise further the relations

between the individual environmental factors (Chl a, Feo, pH, Temp) and the DOC and POC concentrations. Each slope coefficient indicates a change in DOC/POC concentration [mg dm− 3] when the given property changes by one unit (1 °C, 1 mg m− 3 Chl a, 1 mg m− 3 Feo, 1 pH). The results, also given as the percentage increase of DOC and POC, show that each of the environmental factors influences DOC and POC concentrations to a different extent ( Table 5). Thus, when Chl a, Feo, pH and Temp change by one unit, the DOC concentration increase is equal to 18% (Chl a), 27% (Feo), 22% and (pH), 5% (Temp). In the case of the POC concentration, the increase of Chl a, Feo, pH and Temp by one unit causes POC to increase by 6% (Chl a), 18% (Feo), 37% (pH), 22% (Temp, growing season) and 12.5% (Temp, non-growing season). The highest increase ion DOC concentration was due to a 1 mg dm− 3 increase in POC concentration (59%). The largest increase in POC was related to pH increase (37% per unit). The Baltic is still a poorly investigated sea with respect to DOC and POC concentrations. A comparison of DOC and POC concentrations from this study (separately for the growing

and non-growing oxyclozanide seasons) with literature data is given in Table 6. The low concentrations of DOC (2.4–3.8 mg dm− 3) reported in this study are characteristic of the sub-halocline water layer for the non-growing period. The high concentrations (6.0–8.2 mg dm− 3) are characteristic

of the short periods associated with the late spring algal blooms. Apart from this, the DOC concentrations in the surface water layer range from 3.6 mg dm− 3 (non-growing season) to 5.0 mg dm− 3 (growing season). As far as POC is concerned, the extreme concentrations are 0.05 mg dm− 3 (sub-halocline/non-growing season), and 1.4 mg dm− 3 (surface/late spring), while typical concentrations range from 0.2 to 0.6 mg dm− 3. The concentrations reported in this study differ considerably from those reported in the literature. For one thing, concentrations < 3.2 mg dm− 3 (DOC) and 0.1 mg dm− 3 (POC) have not been reported so far, most likely because the sub-halocline water layer in the non-growing season has never yet been sampled. Moreover, the average concentrations are substantially lower than those reported in the literature, except for the concentrations measured by Kuliński & Pempkowiak (2008). This can be attributed to incidental sampling during the course of individual, one-two week long cruises that most often took place in spring or summer. Thus the DOC and POC concentrations typical of offshore Baltic water and the dynamics of the concentrations are better characterised thanks to the data presented here.

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