Dear all,
We are pleased to invite you to the next WISE Webinar on the topic of Breaking-driven air-sea gas exchange on Friday, 21/03/2025 at 11 AM (Eastern Standard Time), 5:00 PM (Central European Time).
Join us via https://tudelft.zoom.us/my/wisezoominars
First speaker: Alessandro Iafrati, Italian National Research Council
Title: Air entrainment and gas transfer processes in wave-breaking events
Abstract:
The contribution of the air entrainment during wave breaking events to the gas transfer process at the ocean surface is investigated numerically by a multiphase flow solver. Waves of different initial steepness leading to regular wave patterns, mild spilling and intense plunging breakers are examined and comparisons in terms of the gas flux across the interface and the gas concentration in the two fluids are established. It is shown that the amount of gas transferred increases remarkably when wave breaking occurs, in particular in presence of air entrainment. Starting from the distribution of the gas concentration in the two fluids, the gas transfer velocity can be computed. In this respect, the availability of the actual area of the air-water interface, which is generally unavailable in experiments, is fundamental. It is found that the increase in the gas transfer velocity is higher than the increase in the area of the interface across which the exchange takes place, meaning that there is an additional effect related to the enhanced turbulence associated with the gas fragmentation process. It is also observed that, provided the actual area of the air-water interface is accounted for, the gas transfer velocity scales approximately as the one-fourth power of the dissipation rate of the energy content in water, which is consistent with previous theoretical predictions.
Second speaker: Luc Deike, Department of Mechanical and Aerospace Engineering and High Meadows Environmental Institute. Princeton University
Title: The role of bubbles entrained by breaking waves in gas exchange between the atmosphere and the ocean.
Abstract:
Physical processes at the ocean-atmosphere interface have a large effect on climate and weather by controlling the transfer of momentum and mass. When waves are breaking, the surface experiences dramatic changes, with sea spray ejection in the atmosphere and air entrainment into the ocean water. In this talk I will discuss bubble mediated gas exchange and its importance on gas fluxes, highlighting the importance of asymmetric exchange due to small bubbles trapped in the water for low solubility gases. We combine detailed laboratory experiments and numerical simulations on wave breaking, air entrainment and bubble processes in turbulent flows exploring the very large range of scales, from wave statistics scales of order of km, O(1m-1km), to wave breaking dynamics, O(1-10m), air bubble entrainment, bubble dynamics in turbulence, O(microns to mm). We propose a universal formulation of gas exchange which we implement into a global ocean-biogeochemical model. We discuss the resulting oxygen fluxes and demonstrate that our wind-wave-bubble formulation better reproduces observed in-situ oxygen concentrations in water mass formation regions – where air-sea exchange is high - than a commonly used wind-only formulation.
Please note that WISE Webinars including the Q&A will be recorded and posted on the WISE YouTube Channel afterwards (https://www.youtube.com/@wisezoominars). By participating, you consent to any information you share to be included in the recording and shared.
Best wishes,
Alvise, Ton, Qingxiang, Bernard, Tripp, and Morteza
(The WISE Webinar organizing committee)