Around half of all carbon dioxide (CO₂) produced by humans since the Industrial Revolution has dissolved into the ocean. Therefore, understanding how the ocean exchanges CO₂ with the atmosphere is critical for the prediction of climate change. The global assessment of the air–sea CO₂ exchange is based on atmospheric and oceanic measurements. For the latter, ship data are generally collected at an approximate water depth of 3–5 m, e.g., the inlet depth of ship-based pipelines or the CTD depth closest to the water surface. The rationale behind this is the assumption that no gas gradient exists in the upper 0–5 m of the surface layer . However, ignoring this surface layer, including the sea surface microlayer (SML) directly at the air–water interface, can cause biases of 20–50% in estimating the exchange rate of CO₂.The primary objective of Carbon microcycle project, which is funded by the German Research Foundation (DFG) to measure this CO2 gradients in the top 2 meters of the ocean. Our earlier studies showed that pH in the sea surface microlayer differs from the underlying water.