Award: OCE-1760660

Hurricane Harvey impacts on coastal carbon and oxygen cycling The impacts of hurricanes Harvey in August and Nate in October 2017 on coastal carbon and oxygen (O2) concentrations and controlling processes on the Louisiana-Texas Shelf were investigated based on three research cruises conducted in July, September, and October. Prior to the cruises, we had hypothesized that the seasonal development of linked hypoxia and acidification would break down and reform differently following tropical storms because O2 can quickly respond to physical mixing and exchange with the atmosphere whereas CO2 is buffer by the dissolved inorganic carbon (DIC) system and would acidify the surface. Further, O2 and DIC would be impacted differently by the large amount of sediment resuspension that occurs during hurricanes. To test this hypothesis, we observed changes in water-column concentrations of O2, pCO2, pH, organic matter, and nutrients and changes in process rates for water-column primary production and respiration and sediment fluxes of dissolved O2, DIC, and alkalinity following hurricanes. Following Hurricane Harvey, average surface pCO2 was higher than that in normal summer season and net respiration prevailed in the water-column across the shelf. During the October cruise, Hurricane Nate crossed through our sampling area mid-cruise. Following Nate, the water-column was well-mixed and there was increased sediment resuspension and water-column and sediment respiration resulting in O2 uptake and DIC release. These processes led to higher pCO2 and lower pH in the surface and bottom water than the pre-storm conditions. The impacts of hurricanes temporarily turned the region from a CO2 sink to a source and transiently acidified the surface water. The results generally supported our hypothesis. Our group also found a massive remobilization of 4-8 cm of the surface sediment across much of the shelf as indicated by that 7Be activities in sediments. Total chlorophyll a concentrations during the Sep/Oct 2017 cruise period were highest around the Mississippi River birdfoot delta. Concentrations were also relatively higher for mid-shelf and offshore stations during Sep/Oct 2017 as compared to normal summers. As hurricanes are predicted to be more frequent or stronger by climate models, this study will shed light on larger carbon cycle issues on global coastal ocean scales and under future climate scenarios. The large amount of data obtained from this work will also benefit synthesis and modeling community as well as to the publics. Last Modified: 07/15/2019 Submitted by: Wei-Jun Cai