Sediment resuspension as a driving force for organic carbon transference and rebalance in marginal seas.

The transfer of particulate organic carbon (POC) to dissolved organic carbon (DOC; OC transferP-D) is crucial for the marine carbon cycle. Sediment resuspension driven by hydrodynamic forcing can affect the burial of sedimentary POC and benthic biological processes in marginal sea. However, the role of sediment grain size fraction on OC transferP-D and the subsequent impact on OC cycling remain unknown. Here, we conduct sediment resuspension simulations by resuspending grain-size fractionated sediments (< 20, 20-63, and > 63 µm) into filtered seawater, combined with analyses of OC content, optical characteristics, 13C and 14C isotope compositions, and molecular dynamics simulations to investigate OC transferP-D and its regulations on OC bioavailability under sediment resuspension. Our results show that the relative intensities of terrestrial humic-like OC (refractory DOC) increase in resuspension experiments of < 20, 20-63, and > 63 µm sediments by 0.14, 0.01, and 0.03, respectively, likely suggesting that sediment resuspension drives refractory DOC transfer into seawater. The variations in the relative intensities of microbial protein-like DOC are linked to the change of terrestrial humic-like OC, accompanied by higher DOC content and reactivity in seawater, particularly in finer sediments resuspension experiments. This implies that transferred DOC likely fuels microbial growth, contributing to the subsequent enhancement of DOC bioavailability in seawater. Our results also show that the POC contents increase by 0.35 %, 0.66 %, and 0.93 % in < 20, 20-63, and > 63 µm resuspension experiments at the end of incubation, respectively. This suggests that the re-absorption of OC on particles may be a significant process, but previously unrecognized during sediment resuspension. Overall, our findings suggest that sediment resuspension promotes the OC transferP-D, and the magnitudes of OC transferP-D further influence the DOC and POC properties by inducing microbial production and respiration. These processes significantly affect the dynamics and recycling of biological carbon pump in shallow marginal seas.

Realization of parallel experiments in a diamond anvil cell and their application to water-mineral interactions at high-pressure and high-temperature conditions.

Parallel experiments are normally used to compare different chemical systems and conditions simultaneously. In the field of high-pressure experimental science, parallel experiments are hard to realize due to very limited reaction chamber size for the generation of high-pressure conditions, especially in diamond anvil cells (DACs). Multiple holes, instead of a single hole, can be drilled into a gasket (i.e., multihole gasket technique) to realize parallel experiments in a DAC. In this study, we conducted a series of systematic calibration experiments on multihole gasket techniques using statistical methods. Multiple (two or three or four) holes 100 µm in diameter were symmetrically drilled into a gasket by a laser drilling instrument with the help of a coded Python program. The pressure deviations among different holes in a gasket at average pressures below 10 GPa are constrained to less than 0.2 GPa in all calibration experiments at room temperature. We further checked the influences of the gasket material, hole number, pre-indented gasket thickness, and temperature on the pressure deviations among different holes in a gasket. Finally, we applied the multihole gasket technique in a DAC experiment and compared the solubility of calcite in different chemical environments at the same pressure and temperature conditions. The experimental results showed that the multihole gasket technique could be widely applied to study water-mineral interactions at high-P (<10 GPa) and high-T (<700 °C) conditions because multiple parallel experiments can be efficiently realized simultaneously.