Measuring and Estimating Fluxes of Carbon, Major and Trace Elements to the Arctic Ocean

Abstract

This chapter describes the methods and case studies of element flux measurements in the Arctic and subarctic rivers, in the Russian boreal and subarctic zone, along the gradient of permafrost-free terrain to continuous permafrost settings, developed on various lithology and vegetation coverage. The majority of existing flux measurements is based on a combination of daily discharges from Russian Hydrological Survey gauging stations with grab samples or year-round sampling of dissolved and particulate load following the chemical analysis. In this chapter, a new, geochemical-based perspective on the functioning of aquatic boreal systems is described which takes into account the role of the following factors on riverine element fluxes: (1) the specificity of lithological substrate; (2) the importance of organic and organo-mineral colloidal forms, notably during the spring flood; (3) the role of permafrost presence within the small and large watersheds; and (4) the governing role of terrestrial vegetation in element mobilization from rock substrate to the rivers. This kind of multiple approach allows a first-order prediction of element fluxes in a scenario of progressive warming in high latitudes. Two novel dimensions added to the existing knowledge on element transport from the land to the Arctic Ocean by the Russian boreal and subarctic rivers are (i) evaluation of colloidal flux of dissolved substances and low molecular weight (LMW) fraction and (ii) assessing, for the first time, the isotopic signatures of Ca, Mg, Si, and Fe in several case watersheds of various lithology and permafrost coverage. The results of this study and available data from the literature demonstrate that, while climate warming will certainly affect the wintertime element fluxes and speciation, it is unlikely to change the nature and magnitude of the main fraction of trace elements TE flux to the ocean. This fraction of the flux occurs in colloidal form during several weeks of the spring flood. At the present time, it is not strongly affected by climate change, or this influence is within the uncertainty of the flux measurements. Overall, the major changes in the chemical and isotopic nature of riverine fluxes to the Arctic Ocean from Northern Eurasia in a climate warming scenario are likely to be linked to the change in the vegetation (species, biomass and geographical extension), rather than temperature and hydrology. The increase in the depth of the active layer has an influence of second-order importance on the riverine fluxes given that the majority of continental flux to the Arctic Ocean is formed on permafrost soils, highly homogeneously over the depth profile.