Influence of ambient water intrusion on the coral reef acidification in the coral-rich western Pacific Ocean

Abstract:

Ocean acidification in coral reef environments is controlled by the complex interactions of internal (i.e. net community calcification = calcification – dissolution; net community production = organic matter production – respiration) and external processes (intrusion of surrounding seawater and air-sea CO₂ exchange). The 7-year weekly records of the carbonate chemistry condition in the Chuuk lagoon, located in the coral-rich western Pacific Ocean, show that under the condition of weak intrusion of ambient seawater from the surrounding open ocean, two internal biological processes (calcification and respiration) were reinforced each other and collectively lowered the acidity of the reef water for extended periods, ranging from a few months to several months. Our study indicates that the acidification of reef water can be intensified by the enhancement of respiration under the weak intrusion of ambient water due to low winds (i.e. the longer residence time of reef water). Our finding is not an isolated phenomenon but may be widespread in the coral-rich western Pacific Ocean (the habitat of 50% of the global coral reefs), where the degree of ambient water intrusion was revealed to be closely associated with the El Niño Southern Oscillation-induced wind speed change.