Stable oxygen isotope distribution in the Huanghe (Yellow River) and the Changjiang (Yangtze River) estuarine systems

Water samples from the Huanghe (Yellow River) and Changjiang (Yangtze River) estuarine systems, and China Sea were analysed to determine their stable oxygen isotope composition (¹⁸O/¹⁶O). The riverine δ¹⁸O values range from -8.8 to -7.1‰ in these two rivers during the study periods. In the Changjiang estuary, the longitudinal profiles of δ¹⁸O show a linear distribution with chlorinity, reflecting the efficiency of mixing processes between river and seawaters, which corresponds to a short water residence time in the estuary, estimated at about 5 days. In the Huanghe estuary, the non-linear distribution of δ¹⁸O with chlorinity reveals the occurrence of "old water" masses in the Laizhou Bay, where the water residence time can reach 3-4 months. The difference of δ¹⁸O values between these two large Chinese rivers may reflect the "continental/altitude effect" on the isotope fractionation, during the transport of humid air mass from the Pacific and Indian Oceans to the Chinese continent. A rough estimation shows that source region water accounts for about 5-20% of the water discharge in the lower reaches of these two rivers.