Temperature and salinity controls on the release of manganese from continental margin sediments

Continental margin sediments serve as important sources and sink for trace metals in marine environments, with manganese (Mn) playing a critical role in oceanic biogeochemical processes. However, the quantitative effects of temperature and salinity on the release kinetics of Mn from continental margin sediments remain poorly understood under marine conditions. Here, we conducted static incubation experiments on continental margin sediments to investigate Mn release under temperature conditions of 10-30 °C and salinity ranges of 32-38 to mimic typical marine environments. Our results demonstrated that Mn release from the sediments was greatly enhanced at elevated temperatures. The release kinetics were best described by first-order or pseudo-second-order models, indicating that the temperature-dependent Mn mobilization was controlled by diffusion. Salinity exhibited a non-linear impact on the Mn release, with maximum Mn mobilization occurred at salinities of 34-36, potentially due to ion exchange processes. Salinities of >36 inhibited the long-term Mn release through re-oxidization and/or re-adsorption. Based on our experimental results, we estimated that Mn release from global continental sediments is 4.41 × 10⁹-1.13 × 10¹⁰ mol yr^-1. Under a scenario of global warming by 2 °C, we predicted the Mn release could be increased by approximately 20%, potentially altering marine biogeochemical cycles and hence the functioning of marine ecosystems. Our findings provide critical parameters for predicting Mn cycling in response to climate change and highlight the sensitivity of trace metal mobilization from continental margin sediments to environmental perturbations.