St. Petersburg Coastal and Marine Science Center
Foraminifers and sediments document that over the last century channel dredging and spoil disposal have altered circulation, reduced estuarine mixing, changed sedimentation patterns, and caused a faunal turnover within Mobile Bay. Since the completion of the current shipping channel in the 1950s has further restricted tidal flushing and increased terrestrial organic matter accumulation in the bay. In deeper areas of the bay, hypoxic water has negatively impacted the marine microfauna. Comparisons of the present-day microfossil assemblage with those from the 1970s indicate that the continued biologic loss of calcareous foraminifers in the bay has allowed the introduction of a new foraminiferal species into the bay.
In this project we have documented that a specific faunal proxy, termed the PEB index (= % Protononion atlanticum + % Epistominella vitrea + % Buliminella morgani), is statistically representative of the modern seasonal Louisiana hypoxia zone. The PEB index can be used as a low-oxygen proxy to detect past hypoxic (dissolved oxygen <2 mg L-1) conditions in the Holocene-aged sediments from the Louisiana and Texas continental shelves. Records of past changes in bottom water oxygen content allow an understanding of the roles of natural variability versus human activities in the development of seasonal hypoxic conditions in the Gulf of Mexico.
Our research demonstrates that the development of low-oxygen bottom water on the Louisiana shelf is a natural process that has occurred periodically for at least the last 1,000 years in response to natural climate variations. However hypoxia became a chronic problem about 50 years ago as anthropogenic influences increased in the Mississippi Basin (Fig. 5). Our findings suggest that future population growth, and land use/ land cover changes combined with climate variability and potential climate change may cause chronic hypoxia to spread to other regions of the northern Gulf Coast.
Smith, C.G., Osterman, L E., and Poore, R.Z., 2013, An examination of historical inorganic sedimentation and organic matter accumulation in several marsh types within the Mobile Bay and Mobile - Tensaw River delta region: Jounal of Coastal Research, Special Issue 63, p. 68-83. [http://dx.doi.org/10.2112/SI63-011.1]
Richwine, K.A., and Osterman, L.E., 2012, Benthic foraminiferal Census data from Mobile Bay, Alabama: Counts of surface samples and boxcores. USGS data series D-740. [http://pubs.usgs.gov/ds/704/]
Osterman, L.E., and Smith, C.G., 2012, Over 100 years of environmental change recorded by foraminifers and sediments in a large Gulf of Mexico estuary, Mobile Bay, AL, USA: Estuarine, Coastal and Shelf Science, v. 115, p. 345-358. [http://dx.doi.org/10.1016/j.ecss.2012.10.001]
Umberger, D.K., Osterman, L.E., Smith, C.G., Frazier, J., Richwine, K.A, 2012, Seasonal Variability in the Surface Sediments of Mobile Bay, AL, Recorded by Geochemistry and Living/Dead Foraminifera (2009-2010): USGS Data Series 733. [http://pubs.er.usgs.gov/publication/ds733]
Bianchi, T.S., Li, X., Yang Z., Osterman, L.E., Allison M.A., Di Marco, S.F. and Yang, G., 2011, Historical Trends of Hypoxia in Changjiang River Estuary: Applications of Chemical Biomarkers and Microfossils: Journal of Marine Systems, v. 86, p. 57-68. [http://dx.doi.org/10.1016/j.jmarsys.2011.02.003]
Osterman, L.E., Poore, R.Z., Swarzenski, P.W., Hollander, D. J, and Turner, R.E., 2011, Over 300 years of anthropogenic and naturally induced Low-oxygen bottom-water events on the Louisiana continental shelf, in Buster, N.A. and Holmes, C.W., (eds.), Gulf of Mexico, origins, waters, and biota, Volume 3, Geology: Chapter 23, pp. 381-390.
Osterman, L.E., and Twichell, D.C., 2011, Holocene evolution of Apalachicola Bay, Florida: U.S. Geological Survey Fact Sheet 2011–3028, 2 p. [http://pubs.usgs.gov/fs/2011/3028/]
Twichell, D., Edmiston, L., Andrews, B., Stevenson, W., Donoghue, J., Poore, R., and Osterman, L., 2010, Geologic controls on the recent evolution of oyster reefs in Apalachicola Bay and St. George Sound, Florida: Estuarine, Coastal and Shelf Science, v. 88, p. 385-394. [http://dx.doi.org/10.1016/j.ecss.2010.04.019]
Osterman, L.E., Poore, R.Z., Swarzenski, P.W., Senn, D.B., and DiMarco, S.F., 2009, The 20th-century development and expansion of Louisiana shelf hypoxia, Gulf of Mexico: Geo-Marine Letters, v. 29, p. 405-414, doi:10.1007/s00367-009-0158-2. [http://dx.doi.org/10.1007/s00367-009-0158-2]
Osterman, L.E., Twichell, D.C., and Poore, R.Z., 2009, Holocene evolution of Apalachicola Bay, Florida: Geo-marine letters. Available online doi: 10.1007/s00367-009-0159-1. [http://dx.doi.org/10.1007/s00367-009-0159-1]
Twichell, D.C., Pendelton, E.A., Poore, R.Z., Osterman, L.E., and Kelso, K., 2009, Vibracore, radiocarbon, microfossil, and grain-size data from Apalachicola Bay, Florida: U.S. Geological Survey Open File Report 2009-1031. [http://pubs.usgs.gov/of/2009/1031/]
Osterman, L.E., Poore, R.Z., and Swarzenski, P.W., 2008, The last 1000 years of natural and anthropogenic low-oxygen bottom-water on the Louisiana shelf, Gulf of Mexico: Marine Micropaleontology, v. 66, p. 291-303. [http://dx.doi.org/10.1016/j.marmicro.2007.10.005]
Osterman, L.E., Campbell, P.L., Swarzenski, P.W., and Ricardo, J.P., 2007, Biological, Physical, and Chemical Data From Gulf of Mexico Gravity and Box Core MRD05-04: U.S. Geological Survey Open File Report 2007-1024. [http://pubs.usgs.gov/of/2007/1024/]
Osterman, L.E., Poore, R.Z., and Swarzenski, P.W., 2006, Gulf of Mexico dead zone-the last 150 years: U.S. Geological Survey Fact Sheet 2006-3005, 2 p. [http://pubs.usgs.gov/fs/2006/3005/]
Osterman, L.E., Pavich, K., and Caplan, J., 2004, Benthic Foraminiferal Census Data from Gulf of Mexico Cores (Texas and Louisiana Continental Shelf): U.S. Geological Survey Open File Report 2004-1209. [http://pubs.usgs.gov/of/2004/1209/]
Osterman, L.E., Erlandsen, M., and Castenson, E.D. 2001, Benthic foraminiferal census data from surface sediment samples, western Gulf of Mexico (Louisiana and Texas continental shelf and slope): U.S. Geological Survey Open File Report. [http://pubs.er.usgs.gov/usgspubs/ofr/ofr01182]