The Earth’s oceans absorb about 11 billion tonnes of carbon dioxide (CO2) each year, about 25% of all anthropogenic CO2. The oceans are huge reservoirs of CO2, and a better understanding on how the oceans absorb CO2 is critical for predicting climate change. The sea-surface microlayer (SML), the aqueous boundary layer between the ocean and atmosphere, plays an important role in the exchange of gases between the ocean and atmosphere. The effects of the SML on air-sea gas exchange have been widely ignored by past and current research efforts due to uncertainties to what extent the SML covers the oceans. However, we recently reported the ubiquitous coverage of the oceans with SML, which pushes the SML into a new and wider context that is relevant to many ocean and climate sciences.I propose experiments at multiple scales, i.e. in laboratory tanks, wind wave tunnel, mesocosm and during a long-term field study. I propose a systematic field study measuring air-sea CO2 fluxes and mapping chemical, biological and physical properties of the SML. With the experiments on smaller scales, such measurements will allow for the first time (i) to define new parameters controlling gas fluxes, (ii) to quantify short-time and seasonal variability, (iii) to define global proxies for the effects of the SML, and (iv) to develop and apply a new parameterization for the correction of global CO2 flux data. For the first time, biogeochemical processes relevant to carbon cycling are investigated on the ocean’s surface at an interfacial level. Furthermore, I aim to reconstruct the natural composition of the SML in a wind-wave tunnel to study its ability to modify the ocean’s surface at well-defined wind regimes.The results from the proposed studies can form the basis for an improvement of current assessments of CO2 fluxes, and oceanic uptake rates. A better understanding in the oceanic uptake of atmospheric CO2 is critical in predicting climate trends and establishing policies.