Water samples were filtered through 0.7 µm GF/F filter, and acidified with 25 µL Suprapur HCl (10 M) on the same day of sampling. DOC samples were stored and kept at 4°C in the dark during transport until further analysis. Concentration of DOC was measured using high-temperature catalytic oxidation (TOC-VCPH, Shimadzu) at the Alfred-Wegener-Institute (AWI) Potsdam, Germany. Blanks (Milli-Q water) and certified reference standards (Battle-02, Mauri-09 or Super-05 from the National Laboratory for Environmental Testing, Canada) were measured for quality control.
Empty cells = NA