| Marginal seas as potential area of biogenic silica burial play an essential role in the global marine Si cycle. Understanding the processes controlling biogenic silica (BSi) dissolution and burial is important for using BSi as an indice for ancient productivity and environmental changes. BSi dissolution and burial in sediment are important aspects of global marine Si cycle, closely link to the global carbon cycle. In the recent 50 years, ecological environment in the Yellow Sea (YS) and the East China Sea (ECS) has changed significantly including aggravation of eutrophication, silicic acid concentration reducing, decreasing proportion of diatom in phytoplankton community and the frequent occurences of the harmful algal blooms, therefore the regeneration of Si is significance in the YS and the ECS. It is useful to better understand BSi dissolution and burial in sediments of the YS and the ECS. Currently, the understanding of BSi dissolution in sediment of the YS and the ECS is very poor. In this study, sediment samples were collected in 2010 and 2011, the BSi, organic carbon (OC) and total nitrogen (TN) content, the solubility and dissolution constant of BSi in sediments, silicic acid contentration in pore water were analyzed and further research was carried out on factors affecting BSi dissolution and burial in sediments of the YS and the ECS. The major results areas follows:(1) The BSi contents (SiO2%) in surface sediments of the YS ranged from 0.40% to 3.7% with an average of 2.2±0.79%, and increased seawards. Areas with high values mainly located in the mud area of the central YS. The BSi contents in surface sediments of the ECS varied from 0.86% to 3.2% with an average of 2.0 ± 0.53%, and showed no obvious trend with high value in the Zhe-Min coastal area, the northeast of Taiwan and the mud area southwest of Cheju island. BSi distribution is influenced by the horizontal distribution of silicic acid, planktonic diatom, benthic diatom and sediment grain size. The correlation was significant between BSi% and OC%, TN%. The BSi/OC molar ratio in surface sediments of the YS ranged from 0.26 to 4.2 and BSi/TN molar ratio ranged from 2.1 to 20, the average of BSi/OC and BSi/TN were 1.1±0.55, and 7.9±0.44 respectively. The BSi/OC molar ratio in surface sediments of ECS ranged from 0.38 to 3.9 and BSi/TN molar ratio ranged from 2.7 to 23, the average of BSi/OC and BSi/TN were 1.2±0.42,8.4±0.34, respectively. BSi/OC and BSi/TN molar ratio in surface sediments of the YS and the ECS were higher than that in sediment traps and Redfield ratio. It showed that degradation rates of OC and TN were faster than BSi dissolution rate, BSi was well preserved in surface sediments. BSi burial flux in surface sediments of the YS varied from 0.12 to 2.3 mol m-2 yr-1 with an average of 0.85±0.65 mol m-2 yr-1. BSi burial flux in surface sediments of the ECS varied from 0.11 to 19 mol m-2 yr-1 with an average of 4.3±0.93 mol m-2 yr-1, slightly higher than that in the YS. Sediment accumulation rate was the major factor influencing BSi burial flux in surface sediments of the YS and the ECS.(2) BSi content in core sediments of the YS and the ECS had regional diversity, its vertical profile probably recorded century time scale of changes of diatoms quantity and the proportion of diatom in phytoplankton community. The silicic acid in pore water of the YS sediments ranged from 19.2 to 453 μmol L-1, and ranged from 51.6 to 542 μmol L-1 in the ECS sediments. The silicic acid in pore water of the YS and the ECS sediments had regional difference. BSi content, detrital/BSi ratio, sedimentary environment and the dissolution process of BSi were the main factors that affecting the distributions of silicic acid in pore water. The silicic acid flux in the sediment-water interface was calculated using diagenetic model, it was around 23.60-2299.2 mmol m-2 yr-1 in the YS and around 17.50-538.3 mmol m-2 yr-1 in the ECS. Releasing of silicic acid from sediments to the bottom water was one of the most important silicic acid sources, which provied 21.0%,15.5% silicic acid for primary production in the YS and the ECS.(3) BSi solubilities in surface sediments of the YS ranged from 124 μmol L-1 to 287 μmol L-1, BSi (specific) dissolution rate constants varied from 9.3 nmol g-1 h-1 (0.14 yr-1) to 18.5 nmol g-1 h-1 (1.70 yr-1). BSi solubilities in surface sediments of the ECS were 213-357 μ.mol L-1, BSi (specific) dissolution rate constants varied from 14.9 nmol g-1 h-1 (0.3 yr-1) to 56.6 nmol g-1 h-1 (1.9 yr-1). BSi solubility in core sediment of the YS ranged from 91 to 303 μmol L"1 and decreased downwards. BSi dissolution in the YS and the ECS sediment obeyed the non-linear dissolution kinetic progress. The detrital content in sediment, Al concentration in pore water and the specific surface area of diatom could influence BSi dissolution in the YS and the ECS. The detrital content in the YS and the ECS sediments was high in the world. However, BSi dissolution rate in the YS and the ECS sediments was about two or three orders lower than in the other oceans. The sedimentary environment in the YS and the ECS was suitable for the burial of BSi.(4) The Si budget in the YS and the ECS showed that regeneration of Si at sediment-water interface was higher than river input. Around 15% BSi produced in surface water of the YS was finaly preserved in sediment, while it was 19% for the ECS. BSi burial efficiency in the YS and the ECS were aaround 70% and 80%, respectively, which were higher than those of other marginal seas. BSi preserved in the YS and the ECS accounted for 5.1±3.5% and 9.4±7.8% of the total global BSi burial flux, respectively. The BSi burial in the YS and the ECS play an important role in the global marine BSi burial. |
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