2020-2021 Changjiang Estuary dissolved oxygen isotopic and gas ratio data

Changjiang estuary and its adjacent sea is the typical coastal hypoxia area. When organic matter decomposition occurs in the ocean, water column respiration (WCR) and sedimentary oxygen consumption (SOC) lead to different change in dissolved oxygen concentration ([O₂]) and its δ¹⁸O, and these processes are also affected by physical mixing. The distribution and variation of δ¹⁸O and [O₂] in Changjiang estuary were investigated in July, August and October 2020 and in March 2021. δ¹⁸O and [O₂] showed significant opposite trends in both horizontally and vertically. In addition, through the incubation experiments we obtained the fractionation factor of water column respiration of 0.9791 and a series of apparent fractionation factor. Based on this, the contributions of WCR and SOC were calculated. The relationship of community oxygen isotope fractionation factors (Ɛ-c) for dissolved oxygen beneath the mixed layer and the productivity of mixed layer indicated that the oxygen consumption process in the northern region was more dynamic, and that in the southern region was more stable. These processes are related to the dynamic invasion of high salinity low oxygen water (HSLO) and the organic matter content of sediments.