Studies On The Distribution And Related Characteristics Of Particulate Organic Carbon In The South China Sea

Particulate organic carbon(POC)is an important component of the ocean biogeochemical process.In order to make more complete carbon budgets it is necessary to know the magnitude and distribution of POC.With the improvement of optical methodology and the increase of in situ observation,a major breakthrough has been made on the study of POC in the South China Sea.Based on in situ data sets collected using biogeochemical profiling floats(BGC-Argo floats),in this work,we present POC concentration and distribution and POC export flux in the upper layer in the South China Sea,and its spatio-temporal changes were also analyzed.Moreover the standing stock of POC was studied preliminarily from the euphotic zone.First of all,in this work,the Zeu from ocean color measurement was verified by the Zeu produced from the PAR data.With the comparison of results using different algorithms of remote sensing,the Zeu produce from the algorithm of Shang had the best correction with the measured data which was based on PAR data from BGC-Argo float.So,we use this algorithm to calculate the Zeu using three BGC-Argo floats in the SCS.Our results show that:Zeu have obvious seasonal variation characteristics in the north SCS,which is in turn induced by the strong northeast wind and the change of net heat flux,Zeu was the shallowest in winter and the average depth was about 30.6 m.An decreases wind speed and the change of net heat flux were leading to the maximum value of Zeu,the average depth was about 71.3 m.The center of sea basin was oligotrophic.With only minor changes,the value of Zeu ranged from 60 m to 85 m.When the BGC-Argo float met the Vietnamese cold eddy,Zeu is shallower.Then,bbp and POC were highly correlated in previous studies,this work showed that POC was estimated from bbp and its spatio-temporal changes were obvious.POC concentration had a significant difference.Sea surface POC concentration reached their extreme value(maximum?104.5 mg.m-3)during the algal bloom in winter in the northern SCS,and Sea surface POC concentration was reduced to 35 mg.m-3 in the summer.Sea surface POC concentration was smaller(about 20?40 mg.m-3)in the SCS basin,and it was showed that phytoplankton growth in the subsurface layer,there is a trend of increase in POC concentration.With increasing depth,light rapidly fell and POC concentration decreased(about 15?25 mg.m-3).When the BGC-Argo float met the Vietnamese cold eddy,we found that the high value of POC concentration(?70 mg.m-3).Furthermore,carbon sequestration capacity of SCS was closely related to POC export flux.In this work,we first got the standing stock of POC with the trapezoidal integration,and for sought POC export flux in the upper 100 m layer using their correlation relationships.This work found that POC export flux had a significant seasonal variation.POC export flux reached higher value during the algal bloom in winter,and the maximum value was 88.08 mg.m-2.d-1,the minimum value was 38.80 mg.m-2.d-1.The POC export flux kept a relatively stable,there was no obvious seasonal change,ranged from 41.16 to 64.97 mg.m-2.d-1 and from 36.07 to 78.57 mg.m-2.d-1,respectively.Finally,this work found out the relationship between the standing stock of chlorophyll a and the standing stock of POC from the euphotic zone in the SCS,so that the standing stock of POC data could be fetched from the remote sensing data.This work showed the standing stock of POC in the euphotic zone was controlled by the changes of the standing stock of chlorophyll a,at different depths there existed different linear correlation.Within 0.75 times of euphotic zone depth,the IChla accounted for about 1.68%,0.69%and 1.1%of the Ipoc,and 1.25 times of euphotic zone depth,the IChla accounted for about 1.68%,2.07%,2.44%of the Ipoc.