AN INVESTIGATION
OF ORGANIC-RICH SEDIMENT IN LAKE SHELBY, ALABAMA,
FOR MARKERS OF SEVERE STORM IMPACTS
FOR MARKERS OF SEVERE STORM IMPACTS
Abstract:
The historical record of severe storms that have impacted the Gulf Coast extends back only about 120 years. The brevity of the historical record does not allow for statistically significant predictions of future variations in severe storm frequency and intensity caused by either natural or anthropogenic induced global climate changes. Coasts may be most vulnerable to future climate change. A number of investigators have attempted to reconstruct millennia-long severe storm records based on proxy geologic records back to the time when global climate was different than today (e.g., Little Ice Age, Medieval Warm Period) to determine how storm frequencies and intensities have fluctuated in the past. One of the first pre-historical severe storm records was obtained from cores collected from Lake Shelby, Alabama, which is located only ~ 250 m from the Gulf of Mexico shoreline and is periodically inundated with marine water during coastal storms. The past 5,000-year record was derived from sand layers preserved in the muddy lake sediment, hypothesized to be the result of storm surges that transported beach/dune sand into the lake. New data sampled from Lake Shelby in this study suggest that a more complete understanding of the lake’s geologic setting is needed before deriving millennia-long sand-layer based storm records. Lithologic, radiocarbon, and geochemical data suggest that the current lacustrine environment has persisted over the past ~ 800 14C yrs BP. A clay unit occurring below the lacustrine sediment has been interpreted as lagoonal deposits, thus suggesting a different depositional environment prior to 800 14C yrs BP. A record of past severe coastal storm impacts on the Alabama Gulf Coast, based on a new geochemical-based model, is presented here and is limited to the lacustrine sediment. Shifts in stable isotope and percent organic material values for samples from the lake sediment are used as multiple proxies for detecting marine influxes into Lake Shelby. Correlation of proxy geochemical signals with lithologic data supports the proposed geochemical model. Geochemical data suggest an increase in storm frequency and/or intensity for the Alabama Coast during the Little Ice Age, which is consistent with other investigations that document increased Atlantic storm activity during global cooling events.
The Alabama coast has been
directly impacted by 10 hurricanes since 1871 resulting in
millions of dollars in damage and many deaths. The threat of such storms affects the
way thousands of people live their lives on the coast.
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Many scientists have attempted to reconstruct the record of past severe storms by studying evidence
preserved in the geologic record. Shown above is a stratigraphic model of a coastal lake
containing multiple sand layers representing overwash events caused by severe coastal storms.
_______________________________________________________________________
millions of dollars in damage and many deaths. The threat of such storms affects the
way thousands of people live their lives on the coast.
_______________________________________________________________________
Many scientists have attempted to reconstruct the record of past severe storms by studying evidence
preserved in the geologic record. Shown above is a stratigraphic model of a coastal lake
containing multiple sand layers representing overwash events caused by severe coastal storms.
_______________________________________________________________________
This map of Lake Shelby, Alabama
(along the northeastern Gulf of Mexico coast) shows the
locations of seismic lines, cores, and water profile casts collected for this study.
_______________________________________________________________________
Joe Lambert taking measurements of the lake water chemistry using a Hydrolab Scout II unit.
_______________________________________________________________________
Michael Rasbury collecting a 20-foot long vibracore aboard the RV Jenny.
_______________________________________________________________________
Three lithologies were sampled in Lake Shelby; a well sorted sand unit,
organic-rich fine-grained gyttja, and dark gray lagoonal clay.
_______________________________________________________________________
locations of seismic lines, cores, and water profile casts collected for this study.
_______________________________________________________________________
Joe Lambert taking measurements of the lake water chemistry using a Hydrolab Scout II unit.
_______________________________________________________________________
Michael Rasbury collecting a 20-foot long vibracore aboard the RV Jenny.
_______________________________________________________________________
Three lithologies were sampled in Lake Shelby; a well sorted sand unit,
organic-rich fine-grained gyttja, and dark gray lagoonal clay.
_______________________________________________________________________
Lithologic description of core 11
vs. depth (cm) and time (14C
yrs BP). The asterisk denotes age corrected using the standard
reservoir correction (400 yrs)
for marine shells (Stuiver and Braziunas, 1993). Ages in italics
are that of Liu
and Fearn (1993). Note the gross discrepancy between
reservoir-corrected radiocarbon ages of bulk
organics in this study (following the method of Stuiver, 1970) and the
uncorrected ages
reported by Liu and Fearn (1993). Plotted are weight percent
carbon (Corg) and d13C
(‰
PDB) values at 5 cm and 3
mm (inset) depth intervals. Representative error bars (1 sigma)
in the
lower figure are shown at the top of the curves.
For
additional information see:
Recent Publications
2008, Lambert, W.J., Aharon, P., and
Rodriguez, A.B., Catastrophic
Hurricane History Revealed by Organic Geochemical Proxies in Coastal
Lake Sediments: A Case Study of Lake Shelby, Alabama (USA). Journal
of Paleolimnology, v. 39, p. 117-131.
2003, Lambert, W. J., An Investigation of Organic-rich Sediment in Lake Shelby, Alabama, for Markers of Severe Storm Impacts. Master's thesis, University of Alabama.
2003, Lambert, W. J., An Investigation of Organic-rich Sediment in Lake Shelby, Alabama, for Markers of Severe Storm Impacts. Master's thesis, University of Alabama.
2003, Lambert, W. J., Aharon, P., and
Rodriguez, A.B., An
Assessment of the Late Holocene Record of Severe Storm Impacts
from Lake Shelby, Alabama. in
Gulf Coast Association of Geological Societies Transactions, v. 53, p.
443-452.
2003, Lambert, W. J., Aharon, P., and
Rodriguez, A.B., A
High-resolution Geochemical Record of Severe Storms from Lake Shelby,
Alabama, USA. Geol. Soc. Amer. Absts. with Progs. (in press).
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