Abstract
Mixed results have been reported on the evaluation of the coastal carbon cycle and its contribution to the global carbon cycle, mainly due to the shortage of observational data and the considerable spatiotemporal variability arising from complex biogeochemical factors. In this study, the partial pressure of carbon dioxide (pCO2) and related environmental factors were measured in the Jinhae–Geoje–Tongyeong bay region of the southeastern Korean Peninsula in February 2014, August 2014, April 2015, and October 2015. The mean pCO2 of surface seawater ranged from 215 to 471 μatm and exhibited a high correlation with the surface seawater temperature when data for August were excluded (R2 = 0.69), indicating that the seasonal variation in CO2 could be largely attributed to the variation in seawater temperature. However, a severe red tide event occurred in August 2014, when the lowest pCO2 value was observed despite a relatively high seawater temperature. It is considered that the active biological production of phytoplankton related to red tides counteracted the summer increase in pCO2. Based on the correlation between pCO2 and temperature, the estimated decrease in pCO2 caused by non-thermal factors was approximately 200 μatm. During the entire study period, the air–sea CO2 flux ranged from −14.2 to 3.7 mmol m–2 d–1, indicating that the study area served as an overall sink for atmospheric CO2, and only functioned as a weak source during October. The mean annual CO2 flux estimated from the correlation with temperature was −5.1 mmol m–2 d–1. However, because this estimate did not include reductions caused by sporadic events of biological production, such as red tides and phytoplankton blooms, the actual uptake flux is considered to be higher. The mean saturation state (ΩAr) value of carbonate aragonite was 2.61 for surface water and 2.04 for bottom water. However, the mean ΩAr of bottom water was <2 in August and October, and the ΩAr values measured at some of the bottom water stations in August were <1. Considering that the period from August to October corresponds to the reproduction and growth stages of shellfish, such low ΩAr values could be very damaging to shellfish production and the aquaculture industry.
Highlights
Climate change caused by the increase in greenhouse gases in Earth’s atmosphere raises the temperature of the ocean, and causes ocean acidification and deoxygenation, which are global concerns (IPCC, 2014)
The study area consists of Jinhae Bay (JB), Geoje-Hansan Bay (GHB), and Tongyeong-Goseong Bay (TGB) of Gyeongsangnam-do Province (Figure 1)
Water quality has improved since the late 1990s due to enforced onshore sewage treatment and increased environmental awareness, the area has still been affected by seasonal red tide events and hypoxia in its bottom water (Kwon et al, 2014; Lee et al, 2018; Lim et al, 2020)
Summary
Climate change caused by the increase in greenhouse gases in Earth’s atmosphere raises the temperature of the ocean, and causes ocean acidification and deoxygenation, which are global concerns (IPCC, 2014). Compared with pre-industrial times, the pH of the open ocean has already decreased by approximately 0.1 pH units (Bates et al, 2014; Le Quéré et al, 2018). The decrease in seawater pH due to ocean acidification affects the physiological activity, growth, and survival of aquatic organisms, as well as the saturation state of carbonate minerals, which could have a devastating impact on shellfish and coral reefs (Hoegh-Guldberg et al, 2007; Kroeker et al, 2013; Waldbusser et al, 2013; Pilcher et al, 2019). There is an urgent need to assess the status and mechanism of ocean acidification in coastal zones that are characterized by numerous marine organisms and active fishery activities (e.g., fishing grounds and aquaculture). It is necessary to predict the corresponding impact on the future fishery industry
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