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

The Changjiang estuary and its adjacent sea represent a typical coastal hypoxia area, with two major oxygen-depleted zones (ODZs) identified in the northern and southern regions. This study presents dissolved oxygen concentration ([O₂]) and oxygen isotopes (δ¹⁸O) data from four cruises conducted in 2020 and 2021 in the Changjiang Estuary and its adjacent sea. Through dark incubations using water samples from the mixed layer, we determined the specific oxygen isotopic fractionation factor for water column respiration (α_WCR) in the Changjiang Estuary. Spatial and temporal variations in oxygen depletion were analyzed by examining the [O₂] and δ¹⁸O datasets. The observed variations in the community oxygen consumption fractionation factor (αc) suggest that samples collected beneath the mixed layer may have been influenced by mixing, deviating from the expected pure water column respiratory oxygen consumption fractionation curve.To quantify the contributions of low-oxygen water mass mixing, water column respiration (WCR), and sum of contributions (SOC) to oxygen depletion, we employed a Monte Carlo mixing experiment. Our findings revealed that the formation of ODZs in the Changjiang Estuary is primarily triggered by the mixing of low-oxygen water masses. Low-oxygen water mixing accounted for 59% to 100% of the total oxygen deficit, while respiration contributed 0% to 41%. Notably, WCR was found to account for approximately 1.5 times more oxygen consumption than SOC.Finally, we discuss the influences of low-oxygen water mass mixing on the spatial and temporal differences observed in the two ODZs within the Changjiang Estuary. This study provides critical insights into the mechanisms driving hypoxia in this region and highlights the importance of considering both mixing and respiratory processes in understanding oxygen depletion dynamics.Sampling information, all isotopic and dissolved oxygen concentration data are listed in Table-2020-2021 Changjiang Estuary dissolved oxygen isotopic and gas ratio data.The code and results of Monte-Carlo mixing experiments show in the remaining two files