Inter-annual Variability of the Carbonate System in the Hypoxic Upper Pearl River Estuary in Winter

Abstract

Hypoxia has become a universal environmental and ecological problem in recent decades. The Pearl River estuary (PRE), the largest estuary in Southern China, is hypoxic year-round in the upper estuary. This study reports the inter-annual variation between 2005 and 2019 in the carbonate system of the hypoxic upper PRE in winter. In January 2005, both dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations were >3000 µmol kg −1 at the upstream-most station and decreased sharply downstream. However, DIC and TA were lower, with concentrations of 2300 and 1950 µmol kg −1 , respectively, at the upstream-most in January 2019. At salinities >15, both DIC and TA were conservative and reached steady values at the downstream seawater endmember. The upstream-most station was taken as an example to quantify the influences of biogeochemical processes on DIC and TA, including CO 2 degassing, organic carbon oxidation, pelagic nitrification, CaCO 3 dissolution and benthic release. Among the biogeochemical process, a decrease in CaCO 3 dissolution (from 734.4 µmol kg −1 in 2005 to 168.9 µmol kg −1 in 2019) was the major factor driving the decreases of DIC and TA in 2019. In the context of global change, inter-annual variability in biogeochemical process should receive more attention.

Drivers of Phytoplankton Variability in and Near the Pearl River Estuary, South China Sea During Typhoon Hato (2017): A Numerical Study

“…The PRE is located in the central area of the Guangdong‐Hong Kong‐Marco Greater Bay Area of China. In recent years, with a rapidly growing population and socioeconomic development, input of nutrients and diverse contaminants increased rapidly, which led to a wide range of environmental problems, such as eutrophication, hypoxia, and ocean acidification (Guo et al., 2020; Hu et al., 2021; Ke et al., 2022; Y. Zhao et al., 2021). Furthermore, during the past decade, the activity of typhoons (also referred to as tropical cyclones [TCs] or hurricanes) has increased because of global warming (Balaguru et al., 2012, 2016; Da et al., 2021; Elsner et al., 2008; Goldenberg et al., 2001; Mei et al., 2015; Webster et al., 2005; Wu et al., 2005).…”

“…However, the offshore bloom did not occur due to the high grazing impact from the zooplankton. and ocean acidification (Guo et al, 2020;Hu et al, 2021;Ke et al, 2022;Y. Zhao et al, 2021).…”