The rate of air-sea exchange of O2 and N2 will be measured at high to extreme wind speeds (20-60 m/s). A physical understanding of the gas exchange processes and parameterizations of the flux rates will be developed from this data. Custom-built water-following Lagrangian floats will be air-deployed into hurricanes during 2008 and 2009. Fluxes will be measured from the mixed layer budgets of O2 and N2 and from the eddy-covariance of vertical velocity and gas concentration using a combination of two different commercial oxygen sensors and custom-built total gas tension sensors. The floats will also measure temperature and salinity, surface wave spectra, surface wave breaking rates and bubble properties. Additional profiling floats will provide the depth-time profiles of temperature, salinity and velocity necessary to model the mixing component of the gas budgets. Wind and pressure data will be provided by operational aircraft remote sensing and drop sonde data. The flux measurement techniques will be compared with other methods during two North Atlantic cruises of the SOLAS-DOGEE program during 2006 and 2007. Modeling and data analysis will focus on understanding the physics of bubble-mediated gas transfer and will use this understanding to formulate new parameterizations of gas transfer rates at high wind speeds.
Broader Impacts. Gas exchange across the air-sea interface is a key component of the global carbon budget. Uncertainties in the parameterizations for gas exchange rate at high wind speeds lead to uncertainties of up to 70% in the directly computed net global CO2 uptake by the ocean. This work aims to reduce these uncertainties by improving the parameterizations. The gas sensors developed by this project will be commercially available. They will be specifically designed for use on autonomous platforms such as floats, gliders, surface drifters and autonomous underwater vehicles. One currently enrolled graduate student will be supported through the completion of his Ph.D thesis. Undergraduates will participate during the summers at both the University of Rhode island and the University of Washington.
Gas exchange between the atmosphere and the oceans removes carbon dioxide and sequesters some of it for long periods of time in the deep sea. Approximately half of all carbon dioxide emitted due to the burning of fossil fuels has ended up in the oceans. This is changing the basic chemistry of the oceans. Although most of this carbon enters the ocean from the atmosphere through the air-sea surface, the rates at which this occurs at not very well known, particularly at high wind speeds. The goal of this project was to measure air-sea gas fluxes at the very highest wind speeds, those found in tropical cyclones (Hurricanes and Typhoons), and thereby help constrain our estimates of overall gas fluxes. Measurements were made in one hurricane (Gustav) and one typhoon (Megi) by air-deploying specialized oceanographic instruments (Lagrangian floats) ahead of the storm using C130 'Hurricane Hunter' aircraft which routinely penetrate these storms. The bottom image shows an air-launch. These instruments are build at APL/UW. They measure oxygen and nitrogen levels in the water and from these, and their fluctuations and the float's motion, measure the gas fluxes. Wind was measured by the C130's as part of their storm surveillance. After the storm, the floats surface relay their data by satellite and are recovered by ship. We found dramatic increases in gas levels in both storms, despite very high existing gas levels. We find that these gasses are injected into the ocean in clouds of bubbles (sea foam) generated by waves at the surface. The bubbles are carried 10-20m into the ocean interior and dissolve, releasing their gases and leading to the large increase in gas levels. The largest gas influx does not occur at the strongest winds, but on the rising winds, when the waves and bubble formation are the largest. The gas rates agree with a model formulated from our previous observations in Hurricane Frances.
