Abstract
Seasonal and interannual variabilities in the partial pressure of CO2 (pCO2), pH, and calcium carbonate saturation state (Ω) were investigated in the highly eutrophicated Tokyo Bay, Japan, based on monthly observations that were conducted from 2011 to 2017. There were large variabilities in these parameters for surface and bottom waters due to photosynthesis and respiration, respectively. Warming/cooling and freshwater input also altered the surface Ω. During the observation period, calcium carbonate undersaturation was observed twice in the anoxic bottom waters in summer. The data indicate that anaerobic remineralization under anoxic conditions lowers the Ω, causing undersaturation. These findings suggest that de-eutrophication can decelerate ocean acidification in the bottom waters of Tokyo Bay. However, if atmospheric CO2 exceeds 650 ppm, aragonite undersaturation will be a common feature in the summer bottom water, even if hypoxia/anoxia are alleviated by de-eutrophication.
Highlights
Ocean acidification (OA) is defined as the progressive reduction in the pH of ocean over an extended period of time, typically decades or longer (Field et al, 2011)
The sporadic extreme freshening caused by river water input lowers the ar by ∼1.0. These physical processes do not cause large variations
pH when a CO2 equilibrium is achieved by an air-sea gas exchange
Summary
Ocean acidification (OA) is defined as the progressive reduction in the pH of ocean over an extended period of time, typically decades or longer (Field et al, 2011). Changes of seawater carbonate chemistry associated to OA, such as an increase in partial pressure of seawater CO2 (pCO2) concentration and a decrease in calcium carbonate (CaCO3) saturation state ( ) are included in the discussion of the effects of OA (Royal Society, 2005; IPCC, 2014). The increased CO2 concentration promotes the photosynthesis by primary producers such as phytoplankton and seagrass (Hinga, 2002; Palacios and Zimmerman, 2007; Hendriks et al, 2010), while the decreased adversely affects the calcification, as well as the growth and survival of calcifying organisms (e.g., Kroeker et al, 2010). The increased CO2 concentration affects the growth of otoliths (CaCO3 structures in ears), metabolic rate and behavior of some fishes (Heuer and Grosell, 2014 for review).
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