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. Water samples for dissolved elemental and dissolved ion concentrations were filtered using a syringe-mounted 0.45 μm CA filter and kept cool and dark until analysis. Concentrations of major anions were determined using ion chromatography (Thermo-Fischer ICS 2100; Weiss, 2001). Total dissolved elemental concentrations were measured with inductively coupled plasma optical emission spectroscopy (ICP-OES; Perkin Elmer Optima 8300DV; Boss and Fredeen, 1997). Both analyses were performed at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research (AWI), Potsdam, Germany.

0 = below detection limit