Modelling Siberian river runoff — implications for contaminant transport in the Arctic Ocean

Abstract This model study investigates the role of Siberian river runoff for the transport of possible river contaminants in the Arctic Ocean. Three-dimensional coupled ice-ocean-models of different horizontal resolution are applied to simulate the dispersion of river water from Ob, Yenisei and Lena. These Siberian rivers are supposed to be important sources for various contaminants. The relevant processes which are considered in this study include the dispersion of dissolved or suspended contaminants in the water column and the transport of contaminated particles, incorporated into drifting sea ice. Circulation model results from both spatial scales explain the main pathways and transit times of Siberian river water in the Arctic Ocean. Kara Sea river water clearly dominates in the Siberian branch of the Transpolar Drift, while the Lena water dominates in the Canadian branch. River water concentrations in Nares Strait, Canadian Archipelago, are similar to those in the northern Fram Strait. Special emphasis is given to the seasonal variability of the river plume in the Kara Sea. Particle tracking simulations on the regional scale illustrate that Ob and Yenisei tracers behave differently. Yenisei tracers leave the Kara Sea quite fast towards the Arctic Ocean or the Laptev Sea, but Ob tracers spread also in the southern Kara Sea, in particular at lower levels. A comparison of simulated freezing rates and particle concentrations in Siberian coastal waters suggests that during autumn, the incorporation of particles into freezing sea ice near the estuaries of Ob and Yenisei is very likely. Simulated ice trajectories, started close to the Lena river delta easily reach the multi-year Transpolar Drift within one winter. Ice trajectories from Ob and Yenisei estuaries, however, mostly drift towards the Barents Sea where the ice melts close to Svalbard. The model study confirms that contaminant transport through sediment-laden sea ice offers a short and effective pathway for pollutant transport from Siberian rivers to the Barents and Nordic Seas.

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