Monitoring ocean CO₂ relies on millions of measurements that require precision and traceability. With the update of the SOCAT and SnapO-CO₂ databases, the scientific community is refining its assessment of air-sea fluxes, an essential lever for quantifying the role of oceans in the global carbon cycle.
by Laurie Henry
Carbon dioxide emitted by human activities does not remain entirely in the atmosphere: nearly a quarter is absorbed each year by the oceans. While this absorption plays a central role in regulating the global climate, it also alters the chemistry of seawater, with direct consequences for marine ecosystems.
To monitor and understand these air-sea exchanges, scientific databases have been collecting measurements of dissolved CO₂ at the ocean surface for several decades. The 2025 version of the SOCAT atlas, accompanied by an update of the SnapO-CO₂ database, has just been published by the Institut Pierre-Simon Laplace (IPSL). This update, documented in a Cookbook led by Thanos Gkritzalis and published in 2024, provides a strict and transparent framework to ensure the quality of the data disseminated.
A reference atlas for climate monitoring
Since 2007, the SOCAT atlas – which stands for Surface Ocean CO₂ Atlas – has been an international database compiling millions of measurements of dissolved carbon dioxide at the ocean surface. It was launched on the initiative of the scientific community to meet a crucial need to gather, in a consistent and transparent manner, data collected by different programmes, ships and institutions around the world.
The aim is to make these measurements comparable, accessible and usable on a large scale. SOCAT now covers more than six decades of observations, with data dating back to 1957.
In 2025, it reached a milestone with 50 million data points from sea campaigns, commercial vessels and fixed stations, compared to 6.3 million data points in 2011 for the very first version. These data serve as a reference for global carbon assessments, climate models and IPCC assessments.