Impact of Hurricanes on Coastal Biogeochemistry in the Gulf of Mexico

Abstract:

Hurricanes are episodic, extreme climate events that have a significant influence on life, property, and ecosystems. Using the Northern Gulf of Mexico as a test bed, we investigate the potential impacts of hurricanes on dissolved oxygen (DO) in the coast with a suite of in situ, remotely sensed and reanalysis data sets. Using sea surface salinity from model reanalysis and satellite data, we first demonstrate a time lag of approximately 5-7 days from the time a hurricane makes landfall near the Texas-Louisiana shelf to the time when the Mississippi River plume induced by the hurricane arrives at the mouth of the delta. This time lag allows the local impacts of hurricane-induced mixing on DO at the continental shelf to be isolated from the delayed response to the plume. Furthermore, we use satellite-derived observations of total suspended matter and particulate organic carbon, and spatially sub-sampled data from the eastern Gulf with less river plume influence and a western Gulf dominated by plume dynamics to estimate the local and delayed response of DO to hurricanes. In addition, our analysis agrees with literature estimates of the total resuspension of sediments by hurricanes in the region (~10 times the annual deposition by the Mississippi/Atchafalaya River system) Finally, using ship cruise measurements of DO before and after hurricanes, we analyze the two primary processes that occur during the hurricane and before the arrival of the plume: 1) vertical mixing that homogenizes the water column and decreases the hypoxic area, 2) sediment resuspension and subsequent remineralization that tends to increase the hypoxic area. We find that the consumption of DO from sediment resuspension partly compensates the effects of vertical mixing and is a significant sink of DO (about 10-15% of the effect of remineralization of terrestrial organic matter brought by the river plume). Furthermore, most shelf regions subjected to hurricanes are not influenced by large river plumes, while we can expect that sediment resuspension will be an ubiquitous process in mostly every continental shelf under extreme weather events. Therefore, our results point to the important role of sediment resuspension on hurricane-induced oxygen response in the Northern Gulf of Mexico and likely other regions, with potential implications for the carbon cycle.