| Date: |
10/12/2006 |
| Name: |
Dr. Craig McNeil |
| From: |
University of Rhode Island |
| Title: |
Observations of Air-Sea Gas Fluxes during a Hurricane |
Abstract
Uncertainty in the magnitude and wind speed dependence of the air-sea gas transfer rate (KT) at higher wind speeds leads to significant uncertainty in net global air-sea gas fluxes. Prior work has supported various wind speed dependencies for KT that range from linear to cubic. Prior work has also suggested that the efflux of CO2, a strongly soluble gas, from the ocean to the atmosphere during hurricanes is important globally. Prior measurements of KT have been limited to less than approximately 20 ms-1 and calculations of air-sea gas fluxes are based on extrapolation of KT to higher wind speeds. For our studies the air-sea fluxes of O2 and N2, two weakly soluble gases, were obtained
during Hurricane Frances in September 2004 using air-deployed neutrally buoyant floats (D'Asaro & McNeil, 2006). Budget derived O2 flux estimates were compared to O2 covariance flux estimates. The data reveal evidence of a new regime of air-sea gas transfer occurring at wind speeds in excess of 35 m s-1. In this regime, plumes of bubbles
of 1 mm and smaller in size are transported down from near the surface of the ocean to deep into the ocean mixed layer by strong vertical turbulent currents with speeds up to 20−30 cm s-1. The bubble plumes appear to completely dissolve, the majority before reaching depths of approximately 20 m. This process injects air directly into the ocean
and results in supersaturation of the least soluble gases. An O2 depleted layer of several meters in depth was observed at the sea surface and provides evidence that the gases were being simultaneously stripped from the supersaturated near surface ocean, presumably by wave breaking and other shallow aeration processes. Prior formulations of air-sea gas fluxes were modified to account for these processes. The new model was tested against
the data and estimates of KT at wind speeds up to 55 ms-1 were made (McNeil & D'Asaro, 2006). The key results of these studies will be presented and their implications for air-sea CO2 fluxes during hurricanes will be discussed.
Light refreshments are served in the Interaction Area (4th floor of the Oceanography/Physics Building) at 4:00 p.m.
All seminars begin at 3:00 p.m. and are held in room 200 of the Oceanography/Physics building.
