Task 2: Holocene Evolution Northern Gulf Coast Climate, Geomorphology, and Sea Level

Task 2 Goals:

General locations of the Eastern Louisiana, Mississippi-Alabama, and Central Mississippi River Delta Plain study areas described in subtasks 2.1, 2.2, and 2.3 respectively [enlargement]

This task will implement a comprehensive geophysical survey and will collect geologic cores of the inner shelf and sounds from eastern Louisiana to western Florida. Together, these data will define the offshore geology within this region, and determine the climatological, geological, and physical processes that control the present geomorphic features and variations. 

Moreover, this task will provide a regional synthesis of the late Holocene geomorphic evolution of the submarine landscape of this coastal region.  By implication, this Task will determine the relative roles of broad spatial scale physical processes, including climate variability, sea-level rise, subsidence, and sediment supply, as drivers of recent seafloor modification across this region.  

The initial focus of this Task will be on surveying the eastern Louisiana inner continental shelf (Subtask 2.1), and reviewing, compiling, and synthesizing existing information from the Mississippi and Alabama shelf region (Subtask 2.2).  This initial synthesis will be used to identify gaps in knowledge and select locations and time-intervals for additional study.

Information on sediment distribution and geometry will be developed from seismic surveys on the continental shelf. Sediment coring will be done to “ground truth” and date the features identified in the seismic surveys.  Information on late Holocene climate and climate variability of the northern Gulf of Mexico region will be developed through analyses of faunal assemblages from core samples collected from the inner shelf, estuaries, and coastal ponds. 

Existing records and companion studies from areas adjacent to the NGOM coast will be used to place local records into regional and hemispheric context.  As the study progresses, onshore-offshore sampling transects will be established to fill in gaps, and to develop detailed information for selected regions and time periods.  Sediment coring to determine the distribution of storm deposits in time and space will be carried out in coordination with climate history work to determine any link between climate state and the variability, frequency, and magnitude of storms. 

The final stages of this effort will involve developing broad-scale landscape reconstructions for the northern Gulf Coast that depict distribution of major environments at selected time intervals. 

Analyses of planktic and benthic foraminifer assemblages will be used to develop information on climate and environmental conditions from marine sediments.  Light stable isotope and Mg/Ca measurements of foraminifer test will also be used to estimate past conditions in more open marine environments. Accelerator mass spectrometric (AMS) carbon dating of carbonate fossils and wood fragments will provide time control.  Much of the climate and environmental information will be obtained by evaluating existing records including analyses of pollen in continental sediments and isotope data from cave deposits.

Review and evaluation of the existing studies of the distribution of storm deposits in time and space and coring to obtain new records of storm deposits in the NGOM region will be carried out and compared with climate variability information in order to investigate the link between climate and the frequency and magnitude of major storms.  Time-series analyses of existing highly resolved climate records for the last few thousand years will be conducted to assess the existence and stability of climate oscillations that have potential for impacting climate and climate variability in the NGOM.