14-37. Application of organic geochemical proxies to characterize modern- and paleo-storm deposits
The natural catastrophes observed along the Atlantic and Gulf of Mexico coastal zone caused by Hurricanes Sandy, Katrina and Isaac serve to highlight 1) the significance of tropical and extratropical storms as geologic agents driving coastal change and 2) the cumulative effects of storms and sea-level rise on extreme coastal inundation. Storm surge, the most pervasive mechanism associated with these tropical cyclone events, results from a setup of the coastal ocean due to prevailing winds and associated ocean currents as well as pressure gradients, waves, and tides. The effects of storm surge are well documented for recent storms where scientific data (imagery, high-resolution global positioning systems and elevation data, cores, etc.) allow for critical and analytical assessment of net change before and after storm events. Some have argued that there has been an increase in the frequency and/or magnitude of hurricane events during the last 100 years (see discussion in Mann and Emanuel, 2006). However, this hypothesis is far from certain due to the short period for which GPS, satellite imagery and tide gauge observations have been available. For a more comprehensive assessment of storm frequency the geologic record provides long-term baseline information on event deposition over the last few millennia. The same is true for modern and paleo-storm frequencies, as well as sea-level rise. Extending the record of storms to include prehistorical events over the last ~7000 years of the Holocene provides multiple benefits to assessments of coastal storm surge hazard and rising sea level during a changing climate. Specific advantages of paleo-reconstructions include:
As such, geologic records of coastal systems provide context for modern trends and assessments of coastal change as well as improve predictive capabilities.
Storm deposits often contain sediment characteristics (i.e., grain size, sand or mud content, organic matter content, shell content, etc.) or biological characteristics that are distinct from autochthonous sediment deposited in coastal environments (e.g. organic marsh sediment, lacustrine sediment, etc.) (Liu and Fearn, 1993). Recently, inorganic and organic geochemical signatures of sediment have been identified as potential storm-proxies that may be used in conjunction with traditional stratigraphic techniques to delineate of paleo-storm layers (e.g., Lambert et al., 2008; Dezileau et al., 2011). Unfortunately, only a few studies have been published such that the applicability of these techniques has not been fully explored. In contrast and specifically, organic geochemical proxies (OGPs)-- which include bulk organic parameters, bulk organic isotopic signature, molecular biomarkers, compound specific isotopic signatures, among others -- have been used extensively for paleoclimate reconstructions (Richey et al., 2010) as well as precipitation, hydrologic, and sediment-provenance variations (Bianchi et al., 2002; Sampre et al., 2011). Similar applications seem feasible and logical for coastal event deposition. Applicants are invited to propose research projects that explore the applicability of OGPs. This may include the following topics as well as others -- geolipid content and variability, ligin-phenol ratios, compound specific isotopic signatures. A primary goal should be to help refine the identification of event layers / storm deposits as well as their origin (marine overwash, estuarine inundation, riverine flooding). The development of OGP for event deposits is expected to be done in conjunction with more traditional microfossil (benthic foraminifer, diatoms, ostracodes) and plant fossil (pollen, roots, and charcoal) proxies.
Research under this Mendenhall Opportunity is expected to focus both on short-term (coastal storm surge) and long-term (sea level) processes responsible for the evolution of coastal systems. There is an opportunity to expand and augment ongoing USGS work through the development of a model of modern to recent storm deposition using a combination of traditional stratigraphic techniques and specific organic geochemical proxies. Such work may serve as a basis for understanding modern environmental conditions in the Gulf of Mexico and Atlantic coastal zone but also is expected to help characterize (pre)historical natural and anthropogenic impacts to the coastal system. Ultimately, we expect this research to improve our understanding of coastal responses to sea-level rise, extreme storm events, pollution, and climate change (droughts/ floods). The ideal candidate would have background in organic geochemistry or organic chemistry with an interest in integrating organic geochemical proxies with microfossils and geochronologic information to develop paleo-environmental proxies to help resolve the frequency of paleo-storm activity along the Gulf of Mexico and/or Atlantic coast.
Bianchi, T.S., Mitra, S., and McKee, B.A., 2002, Sources of terrestrially-derived organic carbon in lower Mississippi River and Louisiana shelf sediments: implications for differential sedimentation and transport at the coastal margin: Marine Chemistry, 77, 211-223.
Dezileau, L., Sabatier, P., Blanchemanche, P., Joly, B., Swingedouw, D., Cassou, C., Castaings, J., Martinez, P., and Von Grafenstein, U., 2011. Intense storm activity during the Little Ice Age on the French Mediterranean coast. Palaeogeography, Palaeoclimatology, Palaeoecology 299, 289-297.
Lambert, W., Aharon, P., and Rodriguez, A., 2008. Catastrophic hurricane history revealed by organic geochemical proxies in coastal lake sediments: a case study of Lake Shelby, Alabama (USA). Journal of Paleolimnology 39, 117-131.
Liu, K. B. and Fearn, M. L., 1993. Lake-Sediment Record of Late Holocene Hurricane Activities from Coastal Alabama. Geology 21, 793-796.
Mann, M.E., and Emanuel, K.A., 2006, Atlantic hurricane trends linked to climate change: EOS, Transactions American Geophysical Union 87, 233-241.
Richey, J.N., Hollander, D.J., Flower, B.P., and Eglinton, T.I., 2011, Merging late Holocene molecular organic and foraminiferal-based geochemical records of sea surface temperature in the Gulf of Mexico: Paleoceanography, 26.
Sampere, T.P., Bianchi, T.S., and Allison, M.A., 2011, Historical changes in terrestrially derived organic carbon inputs to Louisiana continental margin sediments over the past 150 years: J. Geophys. Res., 116, G01016.
Proposed Duty Station: St. Petersburg, Florida
Areas of Ph.D.: Organic geochemistry, coastal geology, chemical engineering, paleoceanography, or related fields (candidates holding a PhD. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Chemist, Research Oceanographer.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant’s background, education, and research proposal. The final classification of theposition will be made by the Human Resources specialist).
Research Advisors: Christopher Smith (727) 803-8747 x3035, firstname.lastname@example.org.; Thomas Cronin (703) 648-6363, email@example.com.; Julie Richey (727) 803-8747 x3123, firstname.lastname@example.org; Lisa Osterman (727) 803-8747 x3084, email@example.com.
Human Resources Office Contact: Junell Norris, (303) 236-9557, firstname.lastname@example.org.
|Summary of Opportunities|