It is known that rivers are among the main sources of inorganic and organic carbon in the Arctic shelf and control, to a large extent, the character of the carbon cycle in the Arctic basin. Of special interest are the influence of river runoff on exchange processes in the ocean–atmosphere system and the formation of the planetary maximum of greenhouse gases in the high latitude atmosphere. The role of continental runoff in the hydrological and hydrochemical regime of the Arc tic basin has been addressed in numerous studies; how ever, the character of and reasons for its variations are not adequately understood.

The Lena is one of the largest Siberian rivers, second only to the Yenisei in the magnitude of discharge. Milli man et al.[1] assigned it to the category of excess rivers: a tendency of an increase in its annual discharge into the Arctic Ocean was established in 1951–2000, despite a decrease in total precipitation, which was previously noted in [2]. The reasons for the observed discrepancy and the redistribution of contributions from various sources of water recharge are still disputable. Although several international expeditions have recently explored the basin of the Lena River, only limited information was acquired on the interannual variability and transformation of carbon delivered by the Lena water into the Laptev Sea. Combined geochemical investiga tions were carried out on a high analytical level [3–6], but observations directly in the river were performed sporadi cally and in different months. The middle and lower reaches of the river were the main targets, whereas the dynamics of the carbonate system (CS) along the whole main channel was not studied. The problem of the char acter of changes in the CS parameters of the water of Arc tic rivers en route to the collecting basin and controlling processes remains poorly explored.