Journal Article

Global trends of ocean CO2 sink and ocean acidification: an observation-based reconstruction of surface ocean inorganic carbon variables

Iida, Yosuke, Kojima, Atsushi, Ishii, Masao, Takatani, Yusuke

2021

Overview

Ocean acidification is likely to impact marine ecosystems and human societies adversely and is a carbon cycle issue of great concern. Projecting the degree of ocean acidification and the carbon-climate feedback will require understanding the current status, variability, and trends of ocean inorganic carbon system variables and the ocean carbon sink. With this goal in mind, we reconstructed total alkalinity (TA), dissolved inorganic carbon (DIC), CO 2 partial pressure ( p CO 2 sea), sea–air CO 2 flux, pH, and aragonite saturation state (Ω arg ) for the global ocean based on measurements of p CO 2 sea and TA. We used a multiple linear regression approach to derive relationships to explain TA and DIC and obtained monthly 1° × 1° gridded values of TA and DIC for the period 1993–2018. These data were converted to p CO 2 sea, pH, and Ω arg , and monthly sea-air CO 2 fluxes were obtained in combination with atmospheric CO 2 . Mean annual sea–air CO 2 flux and its rate of change were estimated to be − 2.0 ± 0.5 PgC year −1 and − 0.3 (PgC year −1 ) decade −1 , respectively. Our analysis revealed that oceanic CO 2 uptake decreased during the 1990s and has been increasing since 2000. Our estimate of the globally averaged rate of pH change, − 0.0181 ± 0.0001 decade −1 , was consistent with that expected from the trend of atmospheric CO 2 growth. However, rates of decline of pH were relatively slow in the Southern Ocean (− 0.0165 ± 0.0001·decade −1 ) and in the western equatorial Pacific (− 0.0148 ± 0.0002·decade −1 ). Our estimate of the globally averaged rate of pH change can be used to verify Indicator 14.3.1 of Sustainable Development Goals.

• Publisher: Springer Singapore,Springer Nature B.V
• Subject: Acidification / Air / Alkalinity / Aragonite / Carbon / Carbon cycle / Carbon dioxide / Carbon sequestration / Carbon sinks / Chlorophyll / Data analysis / Datasets / Dissolved inorganic carbon / Earth and Environmental Science / Earth Sciences / Fluxes / Freshwater & Marine Ecology / Global warming / Marine ecosystems / Ocean acidification / Ocean circulation / Oceanic analysis / Oceanography / Original Article / Partial pressure / pH effects / Regression analysis / Salinity / Saturation / Sustainable development / Sustainable Development Goals / Temperature / Trends / Uptake / Variables