Strong potassium uptake in surface sediments of the Changjiang River Estuary and the East China Sea: Implications for authigenic processes and the marine potassium budget

Abstract

Potassium (K) is a major cation in seawater, but its budget remains not well understood mainly because of the poor constraint on the authigenic clay formation at the seafloor. Marine authigenic phases are assumed to have played a substantial role in balancing the long-term equilibrium of seawater chemistry and regulating Earth's climate. However, the global importance of K-rich authigenic clay minerals for the marine K budget remains poorly quantified. In this study, we report the K content and its spatial variation along the Changjiang (Yangtze) River-Estuary-East China Sea transect, aiming to reveal the influence of authigenic uptake processes on the marine K budget. By combining our new data on the K composition of various sediment and porewater samples with previously published data, we found that the K/Al ratio of the marine particulate matter is substantially higher than that of the riverine endmember, with the averages of 0.31 ± 0.04 and 0.25 ± 0.02, respectively. Based on the observation of decreasing K concentration with depth in porewater and an increasing abundance of green grains (mostly glauconite-like) towards the shelf, we propose that these geochemical changes are caused by the authigenic uptake of K from seawater. Our preliminary calculation suggests that when upscaled to all the river-dominated ocean margins, the global uptake flux of K is approximately 81 ± 62 Tg yr⁻¹, which is comparable in magnitude with the dissolved flux coming from global rivers. Our findings highlight the role of authigenic mineral formation in modifying the geochemistry of seawater and marine sediments.