15 Terrestrial records of hydroclimate variability from the Pleistocene through the Common Era

Landscapes respond to climatic variability, extreme hydrologic events, and long-term environmental change, informing water resource management. We invite terrestrial proxies of hydroclimate from perspectives in paleoclimatology, geomorphology, or hydrology. Submissions from early-career scientists are encouraged.

Monday, 9 March 2026
1:30 PM - 3:30 PM
RCC, 105

Floods and sea level history of the Alabama coast from Mobile Bay and Weeks Bay, Alabama

Paper number: 15-5
Program: Technical Sessions
Time: 2:35 PM – 2:50 PM

Authors

Abstract

For the northern Gulf Coast, accurate predictions of storms and sea level are essential to developing plans for adaptation and resiliency. To date, predictions of coastal response to intense storms and sea-level rise and are based on short-term records from instrumental data that do not capture the highest magnitude extreme events or their long-term frequency. To improve predictive capability and models, we extend the instrumental record of recent decades with long, decadal- to millennial-scale sedimentary archives of storms, floods, extreme sea-level rise events, and their associations with nutrients and ecosystem health. 

We collected long (9-m and 6-m) piston cores from the central setting of Mobile Bay and Weeks Bay, AL (a NOAA National Estuarine Research Reserve). Laser particle size, elemental concentrations from X-ray fluorescence, stable isotopes of carbon and nitrogen from bulk organic matter, foraminifera, and diatom assemblages were analyzed in each core, which together provide a complex story of environmental change and major floods over 9,000 years. 

Radiocarbon and short-lived isotopes are used to build high-resolution age models, allowing identification of modern storms and floods in the sediment records. Peaks in grain size indicate past flood and/or hurricane events that bring sand into the bay. Terrestrial run-off (during floods) is indicated by increase in concentration of titanium, potassium, and zirconium in the sediment. Stable carbon and nitrogen isotopes indicate nutrient sources, while diatom abundances indicate productivity in the water column. Foraminiferal assemblages indicate changing salinity conditions and oxygenation.

          Modern Mobile Bay formed during a period of extreme sea-level rise flooding starting ~9,000 years ago. A ca. 3,000-year period of reduced marine influence followed—until 5,000 years ago, when storm activity was prevalent. Modern Weeks Bay first formed ~7,800 years ago and finally became a freshwater estuary 2,000 years ago. Four gaged floods are recognized in the upper sediment record of Weeks Bay, and these are used to discriminate and document major floods over the last 7,000 years.  We also found that there are more prevalent diatom blooms in recent decades—even since Weeks Bay became a protected estuary—than in the last 3,000 years, suggesting that nutrient management upstream is a major concern. Ongoing analysis compares extreme events in the bays to other terrestrial records of hydroclimate variability of the region. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411832

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