On the processes that influence the transport and fate of Mississippi waters under flooding outflow conditions
The Mississippi River (MR) freshwater outflow is a major circulation forcing mechanism for the Northern Gulf of Mexico. We investigate the transport and fate of the brackish waters under flood conditions. The largest outflow in history (45,000 m3/s in 2011) is compared with the second largest outflow in the last 8 years (41,000 m3/s in 2008). Realistically forced simulations reveal the synergistic effect of enhanced discharge, winds, stratification of ambient shelf waters, and offshore circulation over the transport of plume waters. The strongest impact is attributed to the evolution of the Loop Current (LC) and associated frontal cyclonic eddies and anticyclonic rings, which exhibited distinctly different influence during the two study periods. The northward LC intrusion in the summer of 2011 weakened and blocked the buoyancy-driven downstream (westward) transport of brackish waters. The 2011 flood was thus characterized by upstream (eastward) flow and an extensive coverage of the Mississippi–Alabama–Florida shelf. An immediate response between the LC and the brackish offshore eastward spreading is computed during and after this historic event. The absence of a LC northward intrusion during the 2008 flood, in combination with wind effects, promotes downstream advection of MR waters towards the Louisiana–Texas shelf; large amounts of buoyant waters are also retained near the Delta, subject to local offshore advection under the synergistic action of LC-associated counter-rotating eddies.
KeywordsMississippi River Buoyant plume River flood Northern Gulf of Mexico Numerical modeling HYCOM
This research was made possible in part by a grant from BP/The Gulf of Mexico Research Initiative and in part by the National Science Foundation (NSF OCE-0929651). The MODIS/Aqua satellite images were provided by the Optical Oceanography Lab of USF/CMS (University of South Florida/College of Marine Science). We are grateful to HeeSook Kang (University of Miami) for performing the majority of the NGoM-HYCOM simulations and to P. Hogan and O.M. Smedstad (Naval Research Lab/SSC) for providing the regional GoM-HYCOM model fields. The manuscript greatly benefited from discussions with Rafael Schiller (MARINTEK do Brasil). We thank Nicolas Lopez (Florida State University) for providing us with in situ data for the NGoM domain from the Shipboard Automated Meteorological and Oceanographic System (SAMOS) and Richard Patchen (NOAA/NOS) for providing the compilation of the river outflow data set, which is based on daily flow measurements by the US Geological Survey (USGS).
- Allison MA, Demas CR, Ebersole BA, Kleiss BA, Little CD, Meselhe EA, Powell NJ, Pratt TC, Vosburg BM (2012) A water and sediment budget for the Lower Mississippi-Atchafalaya River in flood years 2008–2010: implications for sediment discharge to the oceans and coastal restoration in Louisiana. J Hydrol 432–433:84–97CrossRefGoogle Scholar
- Barry JM (1997) Rising tide: the Great Mississippi flood of 1927 and HOW IT changed America. Simon & Schuster, New YorkGoogle Scholar
- Briggs K, Smith SR, Rolph JJ (2012) 2011 SAMOS data quality report. COAPS, Tallahassee, p 140Google Scholar
- Cummings JA (2005) Operational multivariate ocean data assimilation. J R Meteorol Soc 131:3583–3604Google Scholar
- Fabre JB (2012) Sediment flux and fate for a large-scale diversion: the 2011 Mississippi River flood, the Bonnet Carré Spillway, and the implications for coastal restoration in South Louisiana. Master Thesis, Louisiana State University, USA, 51 ppGoogle Scholar
- Hickey BM, Kudela RM, Nash JD, Bruland KW, Peterson WT, MacCready P, Lessard EJ, Jay DA, Banas NS, Baptista AM, Dever EP, Kosro PM, Kilcher LK, Horner-Devine AR, Zaron ED, McCabe RM, Peterson JO, Orton PM, Pan J, Lohan MC (2010) River influences on shelf ecosystems: introduction and synthesis. J Geophys Res 115(C00B17). doi: 10.1029/2009JC005452
- Lutken C, D'Emidio M, Falcini F, Horton BP, Jerolmack DJ, Khan NS, Li C, Macelloni L, McKee KL (2011) Connecting the historic 2011 Mississippi River flood to marsh sedimentation on the Delta. American Geophysical Union, Fall Meeting 2011Google Scholar
- Rabalais NN, Turner RE, Wiseman WJ Jr, Boesch DF (1991) A brief summary of hypoxia on the northern Gulf of Mexico continental shelf: 1985–1988. In: Tyson RV, Pearson TH (eds) Modern and ancient continental shelf anoxia. Geological Society, Special Publication no. 58, London, pp 35–46Google Scholar
- Trotter PS, Johnson A, Ricks R, Smith DR, Woods D (1998) Floods on the lower Mississippi: an historical economic overview. U.S. Department of Commerce, U.S. National Weather Service Tech. Attachment SR/SSD 98-9. [Available online at http://www.srh.noaa.gov/topics/attach/html/ssd98-9.htm]
- Walker ND, Huh OK, Rouse LJ Jr, Murray SP (1996) Evolution and structure of a costal squirt off the Mississippi River delta: Northern Gulf of Mexico. J Geophys Res 101:20,643–20,655Google Scholar
- Walker ND, Pilley CT, Raghunathan VV, D’Sa EJ, Leben RR, Hoffmann NG, Brickley PJ, Coholan PD, Sharma N, Graber HC, Turner E (2011) Impacts of a loop current frontal eddy cyclone and wind forcing on the 2010 Gulf of Mexico oil spill. In: Liu Y, MacFadyen A, Ji Z, Weisberg R (eds) Monitoring and modeling the deepwater horizon oil spill: a record-breaking enterprise. Geophys. Monogr. Ser, Washington, pp 103–116CrossRefGoogle Scholar