The sources and seasonal fluxes of particulate organic carbon in the Yellow River

Abstract The Yellow River transports a large amount of sediment and particulate organic carbon (POC), which is thought to mainly derive from erosion of the Chinese Loess Plateau (CLP). However, the compositions, sources and erosional fluxes of POC in the Yellow River remain poorly constrained. Here we combined measurements of mineralogy, total organic carbon content (OC total ), stable organic carbon isotopes (δ 13 C org ), radiocarbon ( 14 C) activity of organic matter in bulk suspended sediments collected seasonally from the upper and middle Yellow River, to quantify the compositions and fluxes of the POC and to assess its sources (biospheric and petrogenic POC, i.e. POC bio and POC petro , respectively). The results showed that the POC loading of sediments was controlled by mineralogy, grain size and specific surface area of loess particles. The F mod of POC (0.71 to 0.31) can be explained by mixing of POC petro with modern and aged POC bio . A binary mixing model based on the hyperbolic relationship of the F mod and OC total revealed a wide range of ages of POC bio from 1300 to 11100 14 C years. Relative to the upstream station, the annual POC bio and POC petro fluxes in the Yellow River are more than doubled after it flows crossing the CLP within 35% drainage area gain, resulting in POC bio and POC petro yields of the CLP at 3.50 ± 0.59 and 0.48 ± 0.49 tC/km 2 /yr, respectively. POC flux seasonal variation revealed that monsoon rainfall exerts a first‐order control on the export of both POC bio and POC petro from the CLP to the Yellow River, resulting in more than 90% of the annual POC exported during the monsoon season. Around one third of annual POC erosional flux was transported during a storm event period, highlighting the important role of extreme events in POC export in this large river. © 2020 John Wiley & Sons, Ltd.