A modeling study of the physical processes affecting the development of seasonal hypoxia over the inner Louisiana-Texas shelf: Circulation and stratification |
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| Authors: | Lixia Wang Dubravko Justi? |
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| Institution: | 1. CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China;3. Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China;4. University of Chinese Academy of Sciences, Beijing 100049, China;1. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, No. 3663 North Zhongshan Road, Shanghai 200062, PR China;2. Key Laboratory of Marine Chemistry Theory and Technology Ministry of Education, Ocean University of China, No. 238 Songling Road, Qingdao, Shandong 266100, PR China |
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| Abstract: | The physical processes affecting the development of seasonal hypoxia over the Louisiana-Texas shelf were examined using a high-resolution, three-dimensional, unstructured-grid, Finite Volume Coastal Ocean Model (FVCOM). The model was forced with the observed freshwater fluxes from the Mississippi and Atchafalaya Rivers, surface winds, heat fluxes, tides and offshore conditions. The simulations were carried out over a six-month period, from April to September 2002, and the model performance was evaluated against several independent series of observations that included tidal gauge data, Acoustic Doppler Current Profiler (ADCP) data, shipboard measurements of temperature and salinity, vertical salinity and sigma-t profiles, and satellite imagery. The model accurately described the offshore circulation mode generated over the Louisiana-Texas shelf by the westerly winds during summer months, as well as the prevalent westward flow along the coast caused by the easterly winds during the rest of the study period. The seasonal cycle of stratification also was well represented by the model. During 2002, the stratification was initiated in early spring and subsequently enhanced by the intensity and phasing of riverine freshwater discharges. Strong stratification persisted throughout the summer and was finally broken down in September by tropical storms. The model simulations also revealed a quasi-permanent anticyclonic gyre in the Louisiana Bight region formed by the rotational transformation of the Mississippi River plume, whose existence during 2002 was supported by the satellite imagery and ADCP current measurements. Model simulations support the conclusion that local wind forcing and buoyancy flux resulting from riverine freshwater discharges were the dominant mechanisms affecting the circulation and stratification over the inner Louisiana-Texas shelf. |
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