Accuracy of Ocean CO2 Uptake Estimates at a Risk by a Reduction in the Data Collection

• Published in: Geophysical research letters Vol. 51; no. 9
• Main Authors: Dong, Yuanxu, Bakker, Dorothee C. E., Landschützer, Peter
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.05.2024; Wiley
• Subjects: Accuracy; Availability; Carbon budget; Carbon dioxide; Carbon dioxide flux; Carbon dioxide removal; Carbon sinks; Data collection; data decline; Datasets; Estimates; Fluctuations; flux trend; ocean CO2 sink; Oceans; SOCAT; Synthesis
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108502

Observation‐based quantification of ocean carbon dioxide (CO2) uptake relies on synthesis data sets such as the Surface Ocean CO2 ATlas (SOCAT). However, the data collection effort has dramatically declined and the number of annual data sets in SOCATv2023 decreased by ∼35% from 2017 to 2021. This decline has led to a 65% increase (from 0.15 to 0.25 Pg C yr−1) in the standard deviation of seven SOCAT‐based air‐sea CO2 flux estimates. Reducing the availability of the annual data to that in the year 2000 creates substantial bias (50%) in the long‐term flux trend. The annual mean CO2 flux is insensitive to the seasonal skew of the SOCAT data and to the addition of the lower accuracy data set available in SOCAT. Our study highlights the need for sustained data collection and synthesis, to inform the Global Carbon Budget assessment, the UN‐led climate negotiations, and measurement, reporting, and verification of ocean‐based CO2 removal projects. Plain Language Summary The Surface Ocean CO2 ATlas (SOCAT) data set plays a crucial role in estimating the ocean carbon sink component of the Global Carbon Budget. However, the number of data sets available in SOCAT each year has drastically decreased since 2017. This study shows that the uncertainty in the data‐based ocean CO2 flux estimate has increased by 65% due to this decline in data availability. The estimated fluxes, especially the long‐term flux trend, are remarkably affected by the data availability in SOCAT, reducing the reliability of ocean CO2 uptake estimates in years and regions with sparse observations. Key Points Lower surface ocean fCO2 data availability leads to higher uncertainty in data‐based estimates of ocean CO2 uptake The long‐term trend in the ocean CO2 flux increases by 1.5 times for subsequent years if the data availability is reduced to that in 2000 The annual mean CO2 flux is not sensitive to the seasonal skew in the data and to the addition of low accuracy data