Fig. 4

Comparison of nutrient samples that were filtered and stored at −20 °C for 3 months, and natural seawater samples added chloroform and stored equally long at +4 °C. Each panel shows lower level of detection for Skalar-D (Table 4) used for these analyses (horizontal and vertical broken lines) and estimated analytical error (dotted lines) associated with nitrate (a), nitrite (b), phosphate (c) and silicate (d) measurements.