Award: OCE-1760687

The overarching major scientific goal of this collaborative project was to discern impacts of a major storm event (Hurricane Harvey) on carbon cycling, community metabolism, and phytoplankton community composition. The effort comprised an examination of post-hurricane conditions in the northern Gulf of Mexico following Hurricane Harvey and comparison to available pre- and post-hurricane observations related to carbon and nutrient cycles, metabolic balance, ocean acidification and phytoplankton biomass and community composition. The specific goals of this PI?s portion of the project were the following: 1. To analyze water samples for inorganic nutrient and dissolved organic carbon (on a subset of samples) concentrations during two cruises in the northern Gulf of Mexico (nGOM) following the passage of Hurricane Harvey. 2. To examine and compare these new observations with data acquired on cruises prior to the storm (April and July 2017) and following the storm (January 2018) and during similar times of the year from past studies in the same region of the nGOM. 3. To combine our data with collaborators to examine the integrated impact of major storm events on carbon cycling, community metabolism, and phytoplankton community composition. The passage of Hurricane Harvey in late August and Hurricane Nate in October (during our cruise) resulted in the water column in the nGOM, particularly the western portions in the paths of both hurricanes, being largely mixed for extended periods. Overall across the sampling region of the broader shelf, concentrations of dissolved inorganic nutrients and organic carbon were greater during the pre-hurricane period (April and July) than immediately after (September and October) the passage of Hurricane Harvey. Overall, dissolved inorganic nitrogen (DIN) and dissolved organic carbon (DOC) concentrations were inversely correlated with site depth, with the lowest concentrations at the deepest sites furthest from the coasts. During the summer, DOC concentrations were always significantly higher at the surface than the bottom, while during the fall we typically observed no significant difference between surface and bottom DOC concentrations. DIN concentrations away from the river outlets were typically lower in the surface than bottom waters in the summer but the pattern was much weaker after the passage of Hurricane Harvey. The results from this effort demonstrated a significant impact of Hurricane Harvey nutrient and organic carbon dynamics as well as chlorophyll concentrations and phytoplankton community composition, a massive remobilization of surface sediments, and increased water column and sediment respiration resulting in dissolved oxygen uptake and dissolved inorganic carbon release. The net result of these impacts was the region temporarily turning from a CO2 sink to a source and the surface waters becoming transiently acidified. The large amount of data generated from this ongoing, multi-disciplinary collaborative effort will greatly improve our understanding of the impacts of hurricanes on nutrient and carbon cycling in coastal environments. Last Modified: 12/02/2020 Submitted by: Brian J Roberts