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  • Shell Center for Sustainability
  • Shell Center for Sustainability
 
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Mission

The Shell Center for Sustainability's mission is to foster an interdisciplinary program of research, outreach, and education to address actions that can be taken to ensure the sustainable development of communities' living standards, interpreted broadly, to encompass all factors affecting the overall quality of life.

Gulf Coast Issues

The Gulf Coastal Science Consortium addresses identified issues such as:

Sea Level Rise   

The historical acceleration of sea-level rise is real (Rahmstorf, 2007a; Nicholls and Cazenave, 2010; Fig. 1).  The most recent scientific results indicate that the rate of global sea level rise has increased from the long-term pre-historic rate of less than 0.6 mm/yr (the rate for the past ~3000 years) to the current rate of nearly 3.0 mm/yr.  The actual rate varies across the globe, and depends on local conditions. The increased rate of rise is attributed to expansion of the oceans as they are heated and from water released to the oceans when glacial ice is melted.  Both effects on sea-level are now well constrained (Rahmstorf, 2007a; 2007b, Vermeer and Rahmstorf 2009).   Scientists predict that the rate of rise will likely at least double by the end of this century (Bindoff et al., 2007).  Vermeer and Rahmstorf (2009) predict that sea-level rise will be a meter or more by 2100.  This does not account for potential contributions to sea-level rise from accelerated retreat of the Greenland and West Antarctic ice sheets (Zwally et al, 2005), which are currently exhibiting signs of instability. 

 

 INTERVIEW with Dr. Torbjorn Tornqvist 

gulf coast issue - sea level rise chart

Figure 1. Sea-level rise for the past few decades based on tide gauge records and satellite observations (from Rahmstorf, 2007a). 

 
Subsidence   

Tide gauge records from around the Gulf of Mexico show different rates of relative sea-level rise over historical time (Fig. 2).  The geographic variation in the rate of rise is due to subsidence due to compaction of younger sediments (Törnqvist et al., 2008; Yu et al., 2012) growth fault activity along the coast (Kreitler, 1976; Fisk, and McClelland, B., 1959) and to human impacts, in particular groundwater and oil and gas extraction (Morton et al., 2006; Kolker et al., 2011).   The thickness of younger, compactable sediments varies significantly and this contributes to geographic variability in subsidence. 

The highest rates of subsidence are in coastal Louisiana (Fig. 2).   There, the estimated rates can be as high as 23 mm/yr (Shinkle and Dokka, 2004). Differences in the magnitude of the rates are, in part, real and reflect regional variability due to growth fault activity and subsurface fluid extraction.  While there is some disagreement within the scientific community about the long-term subsidence rates (Shinkle and Dokka, 2004; Törnqvist et al., 2008; 2012), there is consensus that the current rate of subsidence in some areas must be unprecedented.  This implies human influence. 


 

INTERVIEW with Dr. Torbjorn Tornqvist 

gulf coast issue - subsidence 1
gulf coast issue - subsidence 2
gulf coast issue - subsidence 3

Figure 2. Historical sea-level changes from around the Gulf of Mexico (from NOAA, 2012). Note the long-term average historic rates of rise range from 2.10 to 9.24 mm/yr depending on the location along the Gulf of Mexico. The Pensacola, FL tide gauge is located in an area that is not subsideing so it more closely reflects the global rate of eustatic rise for the northern Gulf. 

 

 
Sediment Supply   

Prediction of coastal response to sea-level rise requires information about both the rate of sea-level rise and sediment supply.  Constraints on sediment supply and dispersal mechanisms are necessary for predicting coastal change and analyzing possible ways to combat change.   

By far the most serious case of coastal response to decreased sediment supply is that of south Louisiana.  Diversion of river sediment away from the Mississippi Delta plain and into the Gulf of Mexico has resulted in dramatic loss of wetlands and, according to some scientists, may be unrecoverable (Blum and Roberts, 2009). However, it could be possible to divert sediment from the Mississippi River in order to build back eroding land (Kim et al., 2009; Nittrouer et al., 2012). Similar problems occur in other areas, but they are just not as well known.  Several rivers that supply sediment to bayhead deltas have been dammed.  These include the Trinity and San Jacinto rivers (Galveston Bay), Sabine and Neches rivers (Sabine Lake),  Alabama River (Mobile Bay), and Appalachicola River (Appalachicola Bay).  The impacts of these dams have not been properly assessed, but it is known that the Sabine Lake and Trinity bayhead deltas have experienced significant loss of their delta plains over the past few centuries (Milliken et al., 2008; Anderson et al., 2008).   

Estuarine shorelines should be fringed with salt marsh, which can keep up with sea-level rise.  As development increases natural shorelines are being replaced with bulkheads and riprap.  These modifications can provide property some protection from flooding, but at the price of long-term loss of wetlands.  

Tidal inlets and deltas represent unique habitats where estuarine and Gulf of Mexico waters are mixed on a daily basis.  Most of the large tidal inlets of the Gulf Coast have been altered by dredging and jetty construction.  The likely impacts of these changes to tidal deltas has been significant reductions in sediment supply and retention, which has resulted in a reduction in their size; however, to our knowledge, documentation of this in the GOM is limited to only one study (Bolivar tidal delta; Siringan and Anderson, 1993). These changes have also impacted the salinity structure of the estuaries, which influences estuarine ecosytems.

 

INTERVIEW with Dr. David Mohrig 

INTERVIEW with Dr. John Day 

 
Hurricane Impact   

It is now increasingly certain that the frequency of strong hurricanes will increase in the 21st century.  Emanuel (2005) reported that sea surface temperatures in the tropics increased by about 1oC over the past half century.  During this same period, total hurricane intensity or power increased by about 80 percent. This increase in intensity was caused by an increased likelihood that storms would become more powerful and last longer, rather than occur in greater numbers. Similarly, Webster et al. (2005) reported an increase in the number of category 4 and 5 storms over the past several decades.  Hoyos et al. (2006) analyzed factors contributing to hurricane intensity and concluded that the increasing number of category 4 and 5 storms over the 34 years between 1970 and 2004 was directly linked to the increase in sea surface temperatures.  Some have argued, however, that these increases are not linked to climate change but to decadal cycles in tropical storm activity (Goldenberg 2001).  Whether the recent intensification of hurricanes is due to climate change or is part of a multi-decadal cycle, it appears likely that the future will bring stronger hurricanes. 

INTERVIEW with Dr. Davin Wallace 

 

References

Anderson, J., Milliken, K., Wallace, D., Rodriguez, A., and Simms, A., 2010, Coastal impact underestimated from rapid sea level rise, Eos Transactions American Geophysical Union, 91, 205–206. 

Anderson, J.B., and Rodriguez, A.B., 2008, Response of Upper Gulf Coast Estuaries to Holocene Climate Change and Sea-Level Rise, Geological Society of America Special Paper, 443, 146 pp. 

Anderson, J.B., Rodriguez, A.B., Milliken, K.T. and Taviani, M., 2008, The Holocene evolution of the Gavleston estuary complex, Texas: evidence for rapid change in estuarine environments, In: Response of Upper Gulf Coast Estuaries to Holocene Climate Change and Sea-Level Rise (Eds Anderson, J.B. and Rodriguez, A.B.), Geological Society of America Special Paper, 443, 89–104. 

Anderson, J.B. and Wallace, D.J., 2011, Science Behind the Plan, In: Atlas of Sustainable Strategies for Galveston Island (Eds Hight, C., Anderson, J., Robinson, M., and Biolsi, S.), Rice University, 7-23. 

Bindoff, N.L., J. Willebrand, V. Artale, A, Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. Le Quéré, S. Levitus, Y. Nojiri, C.K. Shum, L.D. Talley and A. Unnikrishnan, 2007, Observations: Oceanic Climate Change and Sea Level, In: Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Edited by Solomon, S. D., Qin, M., Manning, Z., Chen, M., Marquis, K.B., Averyt, M., Tignor and H.L. Miller), Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 

Blum, M.D. and Roberts H.H., 2009, Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise, Nature Geoscience, 2, 488–491. 

Fisk, H.N. and McFarlan, E., Jr., 1955, Late Quaternary deltaic deposits of the Mississippi River, Geological Society of America Special Paper, 62, 279-302. 

Fisk, H.N. and McClelland, B., 1959, Geology of the continental shelf off Louisiana: its influence on offshore foundation design, Geological Society of America Bulletin, 70, 1360–1394. 

Frazier, D.E., 1967, Recent deltaic deposits of the Mississippi River, their development and chronology, Transactions Gulf Coast Association of Geological Societies, 17, 287-315. 

Kim, W., Mohrig, D., Twilley, R., Paola, C., Parker, G., 2009, Is it feasible to build new land in the Mississippi River delta? Eos, Transactions of the American Geophysical Union, 90, 373–374. 

Kreitler, C.W., 1976, Lineations and faults in the Texas Coastal zone, The University of Texas at Austin, Bureau of Economic Geology Report of Investigations, 85, 32 p. 

Milliken, K.T., Anderson, J.B. and Rodriguez, A.B. 2008, Record of dramatic Holocene environmental changes linked to eustasy and climate change in Calcasieu Lake, Louisiana, USA, In: Response of Upper Gulf Coast Estuaries to Holocene Climate Change and Sea-Level Rise (Edited by Anderson, J.B. and Rodriguez, A.B.), Geological Society of America Special Paper, 443, 43–64. 

Morton, R.A., Bernier, J.C., Barras, J.A., 2006, Evidence of regional subsidence and associated interior wetland loss induced by hydrocarbon production, Gulf Coast region, USA, Environmental Geology, 50, 261–274. 

National Oceanic and Atmospheric Administration, 2012, Tides and Currents, http://tidesandcurrents.noaa.gov/ (last accessed 2-5-12). 

Nicholls, R.J., and Cazenave, A., 2010, Sea-level rise and its impact on coastal zones, Science, 328, 1517-1520. 

Nittrouer, J., et al., 2012, Mitigating land loss in coastal Louisiana bycontrolled diversion of Mississippi River sand, Nature Geoscience, DOI: 10.1038/NGEO1525. 

Rahmstorf, S., Cazenave, A., Church, J.A., Hansen, J.E., Keeling, R.F., Parker, D.E., Somerville, R.C.J., 2007a, Recent climate observations compared to projections, Science, 316, 709. 

Rahmstorf, S., 2007b, A semi-empirical approach to projecting future sea-level rise, Science, 315, 368–370. 

Shinkle, K.D. and Dokka, R., 2004, Rates of vertical displacement at benchmarks in the lower Mississippi Valley and the northern Gulf Coast, NOAA Technical Report, NOS/NGS 50. 

Siringan, F. P. and Anderson, J.B., 1993, Seismic facies, architecture, and evolution of the Bolivar Roads tidal inlet/delta complex, east Texas Gulf Coast, Journal of Sedimentary Petrology, 63, 794–808. 

Törnqvist T. E., Kiddler, T. R., Autin ,W.J., Van Der Borg, K., Dejong, A.F.M., Klerks, C.J.W., Snijders, E.M.A, Storms, J.E.A., Van Dam R.L., and Wiemann, M.C., 1996, A revised chronology for Mississippi River subdeltas, Science, 273, 1693-1696. 

Törnqvist, T.E., Wallace, D.J., Storms, J.E.A., Wallinga, J., Van Dam, R.L., Blaauw, M., Derksen, M.S., Klerks, C.J.W., Meijneken, C., and Snijders, E.M.A., 2008, Mississippi Delta subsidence primarily caused by compaction of Holocene strata, Nature Geoscience, 1, 173-176. 

Wallace, D.J., 2010, Response of the Texas Coast to Global Change: Geologic Versus Historic Timescales, Ph.D. Dissertation, Rice University, 108 p. 

Wallace, D.J., and Anderson, J.B., in press, Unprecedented erosion of the upper Texas Coast: Response to accelerated sea-level rise and hurricane impacts, Geological Society of America Bulletin. 

Yu, S-Y, Tornqvist, T.E., and Hu, P., 2012, Qunatyfying Hoocene lithosphereic subsidence rates underneath the Mississippi Delta, Earth and Planetary Science Letters 3331-332, 21-30. 

Zwally, H. J., M. B. Giovinetto, J. Li, H. G. Cornejo, M. A. Beckley, A. C. Brenner, J. L. Saba, and D. Yi, 2005, Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea level rise: 1992–2002, Journal of Glaciology, 51, 509–527.