We collected water samples from the river surface in the center of the Olenekskaya Channel near Samoylov Island using a pre-rinsed HDPE 1 L bottle. During the open water period (June to October), water was sampled from a small boat, and during ice-covered period (November to May), through a hole drilled through the river ice. Some samples during the river ice break-up (between May and June) as well as some samples during the ice freeze-up in October were taken from the shore due to the inaccessibility of a more centered location on the river channel. For DOC, the sample was filtered through a 0.45 μm cellulose acetate filter which had been rinsed with 20 mL sample water. DOC samples were filled into a pre-rinsed 20 mL glass vial and acidified with 25 μL HCl Suprapur (10 M) and stored in the dark at 4°C. After transport, DOC samples were analyzed at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research (AWI), Potsdam, Germany. DOC concentrations were analyzed using high temperature catalytic oxidation (TOC-VCPH, Shimadzu). Three replicate measurements of each sample were averaged. After every ten samples, a blank (Milli-Q water) and a standard was measured. Eight different commercially available certified standards covered a range between 0.49 mg/L (DWNSVW-15) and 100 mg/L (Std. US-QC). The results of standards provided an accuracy better than ± 5%.
