The effect of Hurricane Lili on the distribution of organic matter along the inner Louisiana shelf (Gulf of Mexico,USA) |
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| Institution: | 1. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Key Laboratory of Submarine Geosciences and Prospecting Technology, College of Marine Geosciences, Ocean University of China, Qingdao 266100, China;1. Key Laboratory of Coast and Island Development (Nanjing University), Ministry of Education, Nanjing 210093, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Collaborative Innovation Center of South China Sea Studies, Nanjing University, Nanjing 210093, China;4. Key Laboratory of Engineering Oceanography, Second Institute of Oceanography, SOA, Hangzhou 310012, China;1. Key Laboratory of Cities'' Mitigation and Adaptation to Climate Change in Shanghai, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China;2. Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China;3. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;4. Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, 264003, China;5. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;6. SKL-ESPC and BIC-EAST, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China;7. State Key Laboratory of Environmental Geochemistry, Guiyang Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;1. Key Laboratory of Submarine Geosciences and Technology, MOE, Ocean University of China, Qingdao 266100, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China |
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| Abstract: | On October 3, 2002 Hurricane Lili made landfall on a previously studied region of the inner Louisiana shelf as a Category 2 storm with winds over 160 km/h. A week after the hurricane, major impacts of the storm were not evident in the water column except for the lower than expected inshore salinities (～12 psu) for this time of year, which was characterized by low river discharge. Turbidity profiles were typical of those measured during previous investigations with suspended sediment concentrations >75 mg/L at inshore stations and <50 mg/L in surface waters and offshore. The implication is that the sediments resuspended during the hurricane settled soon after the storm passage. Water column particulate organic carbon (POC) concentrations ranged from 0.1 to over 2.0 mg/L, with the highest concentrations measured near the seabed and in the inshore portions of the study area. Suspended particles were characterized by low organic matter content (%POC of 0.5–2 wt%), low chlorophyll:POC ratios (Chl:POC<4 mg/g) and moderately elevated POC:particulate nitrogen ratios (POC:PN of 10–14 mol/mol), all suggesting their source was locally resuspended seabed sediment rather than from algal biomass or land-derived vascular plant detritus.Post hurricane sediment deposition throughout the study area resulted in a storm layer that ranged from <0.5 to 20 cm in thickness. In most locations sediment accumulation ranged from 3 to 10 cm. The storm deposits were generally composed of silty clays with a coarser, somewhat sandy 1–2 cm basal layer. Surface sediments from the storm layer were characterized by relatively high mineral surface areas (SA of 30–50 m2/g) and elevated OC contents (%OC of 1.0–2.0%). The dispersal of fine sediments following the hurricane resulted in marked changes in the SA and %OC values of surface sediments from offshore locations, which prior to the storm contained coarser, organic-poor particles (SA of 5–15 m2/g and %OC of 0.2–0.6%). The OC:SA and OC:N ratios of storm layer sediments ranged from 0.4 to 0.6 mg OC/m2 and from 10 to 12 mol/mol, respectively, and were comparable to those measured in surface sediments prior to the hurricane. Such similarities in the composition of the organic matter reinforce the idea that the source of the storm deposits was the finer fraction of resuspended seabed sediments, with little evidence for inputs from local land-derived sources or autochthonous algal production. Overall, the magnitude of sediment and organic matter deposition on the seabed after the storm greatly exceeded the annual inputs from the Atchafalaya River and coastal primary production. The combined effects of hurricane-driven erosion and post-storm deposition represent a major perturbation to the benthic community of the region, which is already subject to these types of disturbances due to the combined effects of peaks in river discharge and the passage of storm fronts. |
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