Subtask 2.3: Hindcast of NGOM Holocene Climate and Climate Variability

Subtask Leader: Richard Poore - USGS Florida Integrated Science Center, St. Petersburg

Subtask 2.3 Aim:

Information on climate, climate variability, and sea-level change during the Holocene are needed to help establish the forces controlling the evolution of northern Gulf of Mexico coastal systems. Evaluation and synthesis of existing data are needed to identify gaps in knowledge and to identify the areas and types of new information that are needed. Accordingly, Subtask 2.3 will characterize and synthesize climatic changes in the coastal region of the northern Gulf of Mexico over the last ~10,000 years. Climatic variables that will be studied using stable isotopic, geochemical tracers, and faunal records will include storm frequency-severity, sea surface temperature, and aridity - humidity. Emphasis will be on the last 6,000 years, with a particular focus on selected intervals representing end-member variations in climate, and on climate variability such as that represented by the Little Ice Age, the Medieval Warm Period, and the mid-Holocene warm interval. The objective of this subtask is to reconstruct climate and climate variability of the NGOM coast, including changes in the magnitude and frequency of severe storms; sea-level history will be included in this effort.

The initial focus will be on reviewing, compiling and synthesizing existing field observations relevant to NGOM Holocene climate and sea-level history, in part to identify gaps in knowledge, and to select locations and time-intervals for additional study. Information on sediment distribution and geometry will be developed from seismic surveys on the continental shelf to be conducted within Subtasks 2.1 and 2.2. Sediment coring will be done to a "ground truth" and date the features identified in the seismic surveys.

Information on climate and climate variability will be developed through analyses of marine and continental sediments. 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, a series of onshore-offshore sampling transects will be established and surveyed, in order to fill in gaps and develop detailed information for selected regions and time periods. Sediment coring to determine the distribution of storm deposits in time and space will be conducted in coordination with climate history work to investigate links between climate state and variability and the frequency and magnitude of storms. The final stages of the effort will involve developing broad-scale landscape reconstructions for the NGOM that depict distribution of major environments at selected time intervals.

Seismic surveys will be used to guide sediment coring to"ground truth" and date subsurface units. Sites that appear to have potential for preserving detailed climate records will also be cored and analyzed to develop detailed local climate information.

Information on local climate and environmental conditions developed from cores taken during this study will be integrated with existing information and new studies in offshore areas to develop a regional climate and environmental history of the NGOM region. Review and evaluation of the published 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 to investigate the link between climate and the frequency and magnitude of major storms. The final stages of this subtask will be to participate in the development of broad-scale landscape reconstructions for the NGOM that depict distribution of major environments at selected time intervals.

Subtask 2.3 Activities:

The goal of subtask 2.3 is to reconstruct sea-level history, climate, and climate variability of the NGOM, including changes in magnitude and frequency of severe storms.

The specific objectives are to:

• Document climate and sea-level histories from NGOM marine and continental sediments at specific localities, and

• Synthesize these results into a regional summary of conditions during the Holocene as they impact the evolution of the NGOM coast.