Nitrous oxide is a potent greenhouse gas that is accumulating in the troposphere at a rate of approximately 0.26% yr^-1. Relatively few studies have examined N₂O in nutrient impacted coastal zones, though high productivity, low dissolved oxygen conditions that promote denitrification, and large N pools typical of these systems indicate the potential for large emissions. We measured vertical profiles of dissolved nitrous oxide at multiple locations within the Gulf of Mexico Hypoxic Zone (GOMHZ) between August 3 and 7, 2008 from the R/V Pelican. Our survey was interrupted by Tropical Storm Edouard, which traveled northwest across the hypoxic zone on August 4 before making landfall along the Texas coast on August 6. Although TS Edouard disrupted our planned investigation, it provided a novel opportunity to estimate the release of N₂O associated with these episodic events.  We collected 15 CTD profiles prior to the passage of Edouard, in depths ranging from 4 to 32 m. 

Results/Conclusions

Except for the shallowest cast, all profiles showed a strong halocline starting at 2 – 4 m and one or more strongly hypoxic layers below 6 m.  Surface water was supersaturated with N₂O (103 – 127%) at all sampling points and corresponding surface emission estimates ranged from  12.0 to 341.0 nmol N₂O m^-2 hr^-1. Measurements immediately after the storm indicate that N₂O rich water in the middle and lower water column was mixed upward, increasing surface N₂O concentrations and emission rates by 23% and 61%, respectively. Comparison of pre- and post-storm vertical profiles suggests that 20% of the N₂O within the water column may have vented to the atmosphere during the storm.  The corresponding emission pulse is equivalent to 13% of the total seasonal (May – September) emission from the entire hypoxic zone using our pre-storm emission rate as the baseline.