Trends and persistence in ocean acidification as measured by Station Aloha

Abstract

This paper applies fractional integration to obtain evidence on ocean acidification using the long-term Station ALOHA observational record. The modelling framework sheds light on the persistence properties as well as on the presence of trends in ocean surface pH dynamics based on the Station ALOHA series. The results indicate that the series exhibit a significant negative time trend; however, whether or not the hypothesis of a unit root is rejected depends on the assumption made about the errors. The key finding (when the errors are not incorrectly specified as I(0) processes) is the presence of long memory, which implies that the effects of shocks are long-lived, regardless of whether or not mean reversion occurs. The recursive analysis indicates that both the degree of persistence and the downward trend in the pH level have increased over time. This evidence points to the need for decisive policies to address the issue of ocean acidification and protect marine life and biodiversity.