@article {200,
	title = {Controls on dissolved inorganic carbon and δ13C in cave waters from DeSoto Caverns: Implications for speleothem δ13C assessments},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {75},
	year = {2011},
	note = {id: 2195},
	pages = {753-768},
	abstract = {Unraveling the factors controlling the carbon chemistry and transport of carbon within extant karst systems has important implications concerning the assessment of time-series δ13C records of speleothems. Here we report the results of a 3-year study of total dissolved inorganic carbon [DIC] and δ13CDIC from cave waters at DeSoto Caverns (Southeastern USA) that offer valuable insight on carbon transport and the accompanied isotope fractionations from end-member sources to speleothems. [DIC] and δ13CDIC values of cave waters range from 0.2 to 6.0 mM and 2.7 to -12.9 ({\textperthousand} VPDB), respectively. [DIC] and δ13CDIC of {\textquotedblleft}seasonal drips{\textquotedblright} show seasonal, albeit noisy, variability and are inversely related (δ13CDIC = -2.49[DIC] + 0.64, r2 = 0.84). A shallow pool fed by multiple drips shows a bimodal δ13CDIC distribution with an isotopically heavier mode during winter (-4{\textperthousand} to -5{\textperthousand} VPDB) relative to summer months (-9{\textperthousand} to -10{\textperthousand} VPDB). A multi-year trend of decreasing water availability during the study period is not reflected in a response of cave water carbon chemistry suggesting that rainfall amount may not be a significant controlling factor of the carbon chemistry. Coupled cave air winter ventilation/summer stagnation and varying CO2 fluxes through the soil horizon and epikarst exert the strongest influence on seasonal [DIC] and δ13CDIC variability. Measured values of high [DIC] and low δ13CDIC from cave waters collected during the summer/early fall closely approximate isotopic equilibrium conditions. Conversely, low [DIC] and high δ13CDIC values during winter/early months indicate kinetically enhanced isotopic fractionations within the cave waters. The kinetically enhanced isotopic fractionation of HCO 3 - partitioned between degassed CO2 and precipitated CaCO3 ( 1000 ln α [ ( CO 2 - HCO 3 ) + ( CaCO 3 (AR) - HCO 3 ) ] / 2 ) is greater by about a factor of two (-6.7 {\textpm} 0.3{\textperthousand}) relative to the same isotopic fractionation under equilibrium conditions (-3.1{\textperthousand}).},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2010.11.006},
	url = {http://www.sciencedirect.com/science/article/pii/S0016703710006319},
	author = {Lambert, W. Joe and Aharon, Paul}
}
@article {526,
	title = {Catastrophic hurricane history revealed by organic geochemical proxies in coastal lake sediments: a case study of Lake Shelby, Alabama (USA)},
	journal = {Journal of Paleolimnology},
	volume = {39},
	year = {2008},
	note = {id: 2037; PT: J; UT: WOS:000251730600010},
	pages = {117-131},
	abstract = {We developed a new method for reconstructing millennia-long hurricane records from coastal environments that uses Organic Geochemical Proxies (OGPs) of organic carbon and nitrogen concentrations and their delta C-13 and delta N-15 compositions. The new method is independent of presence/absence of sand layers and improves significantly the severe-storm history resolution. The subject of this investigation is a 1.5 m long sediment core raised at 2.8 m water depth from the center of Lake Shelby, Alabama, a freshwater lake located approximately 250 m from the Gulf of Mexico, from which an overwash sand-layer based record was previously derived. The core contains two distinct sediment units; an upper 62 cm thick, fine-grained, organic-rich lacustrine sapropel (gyttja) that shows no visible structures except one sand lamina at 23.7 cm depth, and an underlying 90 cm thick, organic-poor lagoon/estuary clay unit. The sapropel unit was deposited over a 682 +/- 30 cal year time interval (1320-2002 A.D.) with a mean sedimentation rate of 0.79 +/- 0.04 mm/year. Lake Shelby{\textquoteright}s water column exhibits two contrasting states based on water chemistry surveys (i) an "isolated", stratified, mode under calm weather conditions with a relatively low trophic state, and (ii) a "flooded" mode occurring during storm surges when nutrient-rich seawater floods the lake. Statistically significant delta C-13 and delta N-15 positive excursions in organic matter, up to maximum values of -25 (parts per thousand PDB) and 4 (parts per thousand Air N-2), respectively, are interpreted as geochemical responses to the marine intrusions that fertilize the lake, increase light availability, and cause eutrophication spikes. Detailed OGPs analyses crossing a sand layer that offers visual evidence of a catastrophic hurricane overwash event at 1717 A.D. exhibit large delta C-13 and delta N-15 positive shifts bounded by rapid returns to base values, thus confirming the validity of the hurricane identification by the OGPs model. Our data indicate that 11 catastrophic hurricanes hit the Alabama coast over the past 682 years with a rough recurrence interval of one in 62 years.},
	issn = {0921-2728},
	doi = {10.1007/s10933-007-9101-6},
	author = {Lambert, W. Joe and Aharon, Paul and Rodriguez, Antonio B.}
}
@article {938,
	title = {An assessment of the Late Holocene record of severe storm impacts from Lake Shelby, Alabama},
	journal = {Gulf Coast Association of Geological Societies Transactions},
	volume = {53},
	year = {2003},
	note = {id: 1111},
	pages = {443-452},
	abstract = {The historical record of severe storms on the Gulf Coast extends back only about 100 years. To better predict how the Gulf Coast will be impacted by future climate change and associated changes in storm frequency it is necessary to extend the severe storm record back to the time when global climate was different than today. A 3200-year record of severe storm impacts was reported from Lake Shelby, AL, using sand layers as proxies of storm intensity and frequency (Liu and Fearn, 1993). To enhance the understanding of the Lake Shelby environment and changes that may occur during severe storms seismic data, water chemistry profiles, sediment cores, radiocarbon dates, and geochemical measurements were obtained. The results indicate that Lake Shelby is a stratified lake in terms of salinity and dissolved oxygen. The lake floor is composed of two general lithologies, gyttja located below about 2 m water depth, and sand located along the entire perimeter of the lake. Radiocarbon dates and stable isotope data indicate that the lake was a brackish water lagoon prior to 80014C yrs BP when it became isolated and transformed into a lacustrine environment. Interpretation of sand layers recognized in sediment cores from Lake Shelby as indicators of severe storms may be ambiguous. New data suggest that severe-storm records based on geochemical stratigraphy may provide higher resolution and confidence than conventional overwash techniques.},
	author = {Lambert, W. Joe and Aharon, Paul and Rodriguez, Antonio B.}
}
