Study On The Characteristics Of Organic Carbon Accumulation Rate In Marine Basin Sediments In Mountainous Area Of Western Pacific Ocean

Carbon sequestration is one of the most important ecosystem service of open oceans.Its significant impact was found on energy flow and material recycle.Based on the environmental survey of the typical seamount area in the northwest Pacific Ocean during the 48th scientific voyage of China,a study on the characteristics of the organic carbon accumulation rate of sediments was carried out.Sedimentary environment provides important conditions for orgaic carbon burial.The pH of sediments in the study area was weakly alkaline,ranging from 7.42 to 7.65,The overall level of redox potential in the sediments was high,ranging from 205³65mv,with an average value of 318±30 mv.The surface sediments were in a weakly oxidized environment.The dry density of sediments ranged from 1.76 to 2.32 g/cm³,with a mean value of 2.11±0.17 g/cm³.The porosity of sediments ranged from 71.93to 81.31%,with an average value of 74.83±3.28%.The type of sediment is clayey silt/Clayey fine silty sand,The mean grain size was between 6.3⁷.76?and the frequent curve was concentrated,indicating a stable and weak hydrodynamic setting with medium^poor sorting.The charatertistics of the organic carbon pool in sediments was illustrated as follows.The total organic carbon content?TOC?ranged from 0.22⁰.51%,with an average of 0.36±0.07%,decreasing with depths.?¹³C_orgrg was between-26.85 and-21.16‰,with an average value of-23.49±1.28‰and a decreasing trend with depths.The value of TN ranged from 0.07 to 0.08%,decreasing with depth.However,?¹⁵N is relatively constant in depths,with an average value of 8.50±0.56‰.TOC/TN ranged from 3.61 to 5.11,with a mean value of 4.66±0.40.The accumulation rate of organic nitrogen was estimated to be 0.36 gN/m²/ka in the surface sediments less than 11 cm in depth.The spatial distribution of accumulation rate of organic carbon in sediment and its potential impact factors were illustrated as follows.The accumulation rate of organic carbon in the basin was 1.60±0.11 gC/m²/ka in the mountainous region of the western Pacific Ocean,with the highest rate in the west-central region.From north to south,the TOC?%?value increased gradually.The average net primary productivity was 50.89±3.18 gC/m²/a with a decreasing trend from the north to the south.The average sediment mass accumulation rate was 0.49±0.09 kg/m²/ka,and the overall trend from north to south was gradually decreasing.Two sets of factors,the environmental factors from water column and sediments and topographic factors,was extracted by principle component analysis?PCA?that affected the organic carbon accumulation rate of sediement.The organic carbon accumulation rate was positively correlated with sediment mass accumulation rate and mean grain size,while negatively correlated with water depth,organic carbon content and Eh.In brief,the organic carbon accumulation rate and net primary productivity transfer efficiency in the western Pacific were lower than those in the eastern Pacific or the equatorial Pacific.On average,about 0.0031%of the region's net primary productivity was buried in sediments.