PhD DEFENSE | Ryo Dobashi | Air-sea gas exchange in coastal regions and inland seas

Title: Air-sea gas exchange in coastal regions and inland seas

Gases such as carbon dioxide (CO2) and dimethyl sulfide (DMS) play important roles in the climate system by acting as greenhouse gases and cloud condensation nuclei. Through air–sea gas exchange, the concentrations of these gases are continuously modified in both the atmosphere and the ocean. Accurate quantification of air–sea gas fluxes is therefore essential for understanding their roles in global biogeochemical cycles and climate change. Such robust calculation is particularly important in coastal regions, where human activities strongly influence these environments. Quantifying air–sea gas exchange requires determination of the gas transfer velocity (k), which is challenging to measure directly in the field. In the open ocean, k is commonly parameterized as a function of wind speed. On the other hand, in coastal regions, additional factors such as fetch limitation, turbulence from the bottom of the sea, and the presence of surfactants can also influence k. In this study, k were measured at four sites across three different coastal and inland sea environments to evaluate the validity of commonly used wind speed/k parameterizations and to examine factors controlling k. The results from the four experiments are introduced individually and synthesized to discuss the factors that contribute to a more accurate estimate of k in these ecosystems. Wind is the primary factor controlling k in coastal regions, which is similar to the open ocean. In addition, the fetch limitation can reduce k. Bottom-generated turbulence does not have a dominant effect when currents are weak, even in shallow environments.

Location: POST 723

Date & Time: Wednesday, March 11, 2026 at 9:30am or Zoom (Passcode: 390669)