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 EM-APEX 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.
The overall goal of this project was to improve our current understanding of the role of tropical cyclones (hurricanes and typhoons) in the global carbon cycle. It had previously been suggested that tropical cyclones over the ocean may play an important feedback role on climate if the rate at which they degas carbon-dioxide from the ocean back to the atmosphere is sufficiently large. Our approach was to develop novel instrumentation to directly measure the rate of exchange of gases between the atmosphere and ocean during hurricane force winds. The instruments were air-dropped into the ocean in front of the advancing storm and recovered by ship after the storm had passed. Rather than measuring carbon-dioxide directly, which is very difficult to do at the required accuracy and precision, we measured instead dissolved oxygen and nitrogen. Our first measurements were made in Hurricane Frances (2004) and showed air-sea gas transfer rates that were significantly smaller than those considered necessary for tropical cyclones to be an important feedback mechanism for climate change. An important aspect of the scientific method, however, is that measurements be repeated and verified. We performed our measurements in two other tropical cyclones: Hurricane Gustav (2008) and Typhoon Megi (2010). Our results from Hurricane Gustav are published and show significant similarity to those measurements made during Hurricane Frances. We have not yet published the results from Typhoon Megi, nor published a synthesis of results from all three storms. The preliminary interpretation is that measurements made during all three storms are sufficiently similar that they support the main conclusion drawn from the Hurricane Frances study, namely that tropical cyclones probably do not degas sufficient carbon-dioxide to be considered a significant feedback mechanism on climate change.
