Reading 1b Edgar TB

Introduction to Tampa Bay Study

  • Objective: Analyze how Tampa Bay's environment has changed over time by evaluating prehistorical conditions and natural variations.

  • Importance of Sediment Study: Examines sediments accumulated around the bay.

  • Historical Context: The prehistorical record pre-dates European settlement around 1850, providing a baseline for comparison against sea-level rise, climate change, biological alterations, geochemical variations, and anthropogenic impacts.

  • Application of Data: Useful for wetland restoration and health improvement initiatives in the bay.

Approach to Research

Sediment Record

  • Core Sampling Technique:

    • Core barrels are inserted into the sea floor to collect sediments trapped within.

    • Collaborating institutions include U.S. Geological Survey (USGS), University of South Florida (USF), Eckerd College, and Florida Department of Environmental Protection (FDEP).

    • A total of 74 sediment cores have been collected; detailed examination on 6 cores has been prioritized.

  • Geochemical Analysis:

    • Evaluates chemical elements and isotopes to understand environmental conditions like salinity and temperature.

    • Pollen analysis from ancient vegetation assesses climate variations affecting bay-water components.

  • Sediment Layer Correlation:

    • Analyzing the six selected cores and correlating with data from the entire bay demonstrates sediment type variations over time.

Contaminants Study Using Clams

  • Research involves the analysis of southern quahog clams (Mercenaria campechiensis).

  • Shell Analysis:

    • Clams have a lifespan of up to 30 years, forming growth rings similar to trees, assisting in age determination.

    • Variations in trace metal concentrations in shells indicate historical contaminant levels seasonally.

Local Climate Change and Mangroves

  • Mangrove Sensitivity:

    • Mangroves are sensitive to freezing temperatures; their pollen found in sediment cores reflects environmental conditions.

  • Temperature Stability:

    • Initial results indicate that temperatures in the Tampa Bay area have not significantly changed over the last 2,000 years.

Sea-Level Change Overview

  • Ice Age Context:

    • The last ice age saw glaciers drawing water, resulting in a sea-level drop of about 125 m, placing the west coast of Florida approximately 200 km west of Tampa Bay.

    • Tampa Bay was primarily dry land during this period.

  • Post-Ice Age Sea Level Rise:

    • After the last glacial period (~21,000 years ago), rapid melting occurred, causing swift sea-level rise.

    • The past 5,000 years show minor fluctuations in sea level, with a significant rise of 76 cm recorded around 1,500 years ago based on Indian middens near ancient shorelines.

    • Midden Locations:

      • The presence of middens inland from current coastlines indicates historical sea-level changes and urbanization impact.

      • These middens serve as markers for ancient coastlines which are being mapped.

Research Implications

  • Health Evaluation:

    • Sediment cores provide both historic and ongoing assessments of Tampa Bay’s health, establishing baseline conditions predating human intervention.

  • Understanding Bay Formation:

    • Data assists in reconstructing how Tampa Bay transitioned from a freshwater environment to an estuarine system, revealing insights into the impacts of historical sea-level rise.

  • Porewater Salinity Variations:

    • Observations of porewater salinity in some sediment cores hint at fossil waters trapped during sedimentation, or variations due to fresh water seepage from aquifers.

Seismic Study and Data Correlation

  • Seismic Profiling:

    • Geologists create seismic profiles to identify sediment layers beneath the bay, informing core collection locations and sediment type correlation.

  • Identified Sediment Layers:

    • Distinction between marine sediment (blue), ancient lake sediment (green), and stream-derived sediment (yellow) is made for effective geological analysis.


  1. Historical Sea-Level Changes: The research reveals that Tampa Bay experienced significant sea-level changes over the last 21,000 years, particularly a notable rise of 76 cm around 1,500 years ago based on Indian middens. This highlights the area's dynamic geological history influenced by glacial melting and climate variations.

  2. Sediment Layer Variations: Analysis of sediment cores indicates distinct sediment types, including marine, ancient lake, and stream-derived sediments. This provides insight into the environmental conditions and processes that shaped Tampa Bay's formation and evolution over time.

  3. Porewater Salinity Insights: Observations of porewater salinity in sediment cores suggest trapped fossil waters or variations due to fresh water seepage, indicating complex hydrological interactions that have affected Tampa Bay’s ecosystem through geological history.