Distribution Characteristics Of Silica In Bohai And Yellow Seas

Silicon is the second abundance element on earth, which is the necessarynutrition elements of marine siliceous organisms, and closely linked with the marinebiogeochemistry process. There is an increasing interesting of research of silicon allover the world in the past few years. Marginal sea covers8%area of the world’soceans,25%of global marine primary productivity and80%of organic carbon of theworld’s oceans. Bohai and Yellow seas are marginal sea of China, and closely relatedto human activities. Two cruises were carried out in spring and autumn in the Bohaiand Yellow Seas in2012, to analyze dissolved silicate (DSi) and biogenic silica (BSi)in water and sediment. The main conclusions are as follows:1) The average concentration of dissolved silicate Bohai was4.61μmol/L in Spring,and7.22μmol/L in Autumn, the average concentration of DSi Yellow was4.15μmol/L in Spring, and8.79μmol/L in Autumn. The average concentration of DSiBohai was higher than one of Yellow sea. The concentrations of DSi area near YellowRiver and the Yangtze River were higher than other areas, indicating river input’s ofYellow and Yangtze rivers were the important nutrients’ sources of the Yellow andthe Bohai Seas. Due to isolation of thermocline and decomposition of the underlyingmaterial, concentration of DSi was significantly higher in the bottom of Cold MassWater in the Yellow Sea than the surrounding areas.2) Potential limitations of phosphorus were existed in the Bohai and Yellow seas.Although the limitation of silicon was relatively weak, part of the sea was absolutelylimited by silicon due to their DSi below to1μmol/L.3) The average concentration of biogenic silica (BSi) was1.13μmol/L in the BohaiSea, and0.85μmol/L in the Yellow Sea in Spring. The average concentration of PBSiwas3.50μmol/L in the Bohai Sea, and2.08μmol/L in the Yellow Sea in Autumn.Mean concentration of BSi in Bohai was higher than the one in Yellow Sea. BSi, and particulate organic carbon and organic nitrogen showed a liner correlation relationship,indicating that they mostly came from marine phytoplankton.4) Contents of BSi in surface sediments in Bohai were between0.20%-0.69%,with an average of0.39%. The content of BSi in Bohai was lower than1%, with aquite low BSi level in the world. Meanwhile, BSi in Bohai was lower than other EastChina Seas. Terrestrial sediment input, to some extent, result in BSi dilution in thecostal sediment of East China seas.5) Concentration of DSi in core water was between24.5and334μmol/l.Concentration of DSi in core water had certain fluctuations in mobile sediment layers,and declined slowly in the accumulation sediment layers.6) Content of BSi in cylindrical sediment is low. The content of BSi were below1%except several samples in B02station. Distribution of every station was different.The ratios of OC/BSi (0.013~3.00) and ON/BSi (0.0011~0.39) in sediments weresignificantly lower than Redfield ratio, indicating that the decomposition rate oforganic matter is far higher than the dissolution rate of BSi under the sameenvironment conditions, which was benefit to BSi accumulation in the sediment.7) Budget calculation of silica indicated that river inputs were main net source forsilica in Bohai and Yellow seas, accounting for about5.3%load of silicon productiondemand, which was followed East China Sea input (2.2%) and atmospheric input(0.35%). Sediment-water silica flux was estimated to68.6×109mol/a, contributed to11.6%of primary production. Silicon regeneration and recycling were main source ofsilica required for primary production, which contributed to about80%of primaryproduction. The annual silica flux into the sediment was about56×109mol/a, whichindicated that9%of biogenic silica was trapped in sediment.