Abstract
The Siberian rivers supply large amounts of freshwater and terrestrial derived material to the Arctic Ocean. Although riverine freshwater and constituents have been identified in the central Arctic Ocean, the individual contributions of the Siberian rivers to and their spatiotemporal distributions in the Transpolar Drift (TPD), the major wind-driven current in the Eurasian sector of the Arctic Ocean, are unknown. Determining the influence of individual Siberian rivers downstream the TPD, however, is critical to forecast responses in polar and sub-polar hydrography and biogeochemistry to the anticipated individual changes in river discharge and freshwater composition. Here, we identify the contributions from the largest Siberian river systems, the Lena and Yenisei/Ob, in the TPD using dissolved neodymium isotopes and rare earth element concentrations. We further demonstrate their vertical and lateral separation that is likely due to distinct temporal emplacements of Lena and Yenisei/Ob waters in the TPD as well as prior mixing of Yenisei/Ob water with ambient waters.
Highlights
The Arctic Ocean is unique with respect to its high freshwater input from the Siberian and North American rivers (11% of global river discharge), which influences circulation, stratification and deep water formation in the high northern latitudes[1] and affects water column biogeochemistry and ecosystem functioning through addition of large amounts of river-borne macro- and micronutrients, as well as lithogenic elements to the open ocean[2,3,4,5,6,7,8,9,10,11]
Based on these tracer distributions we show that individual contributions of the major Siberian river systems, the Lena and Yenisei/Ob, are preserved along the Transpolar Drift (TPD) and largely do not mix during transport
Elevated [rare earth elements (REEs)], a relatively radiogenic εNd signal and a meteoric fraction of 2.5 to 7.1% suggest river influence from the surface down to 100 m water depth at station 69, which is in line with long-distance transport of Siberian river water via the TPD
Summary
The Arctic Ocean is unique with respect to its high freshwater input from the Siberian and North American rivers (11% of global river discharge), which influences circulation, stratification and deep water formation in the high northern latitudes[1] and affects water column biogeochemistry and ecosystem functioning through addition of large amounts of river-borne macro- and micronutrients, as well as lithogenic elements to the open ocean[2,3,4,5,6,7,8,9,10,11]. Alternative assessments based on dissolved lithogenic trace elements and their isotopes, such as rare earth elements (REEs) and neodymium isotope ratios (143Nd/144Nd, expressed as εNd, see ‘Methods’), can help to disentangle contributing water masses and provide a better understanding of recent and upcoming changes in water mass distribution and mixing Both REEs and εNd are essentially biologically inactive provenance tracers and are ideally suited to characterize the origin and transport pathways of waters contributing to the upper central Arctic Ocean and the TPD, given the highly varying REE concentrations ([REE]) and the distinct εNd signatures of Atlantic (εNd = − 11.76) and Pacific (εNd = − 5.524,25) inflows, as well as the major Siberian rivers including the Lena river (εNd = − 15.726), and the Yenisei and Ob rivers (εNd = − 5.2 and εNd = − 6.1, respectively[27]). Based on these tracer distributions we show that individual contributions of the major Siberian river systems, the Lena and Yenisei/Ob, are preserved along the TPD and largely do not mix during transport
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