New Evidence of an Ancient Bald Cypress Forest on the Inner Shelf of Northern Gulf of Mexico

Junghyung (Johnny) Ryu1, Kristine L DeLong2, Samuel J Bentley3, Kehui Xu1, Grant L. Harley4, Andy Reese4, Jeffrey Obelcz5, Thomas P Guilderson6 and Suyapa Michell Gonzalez Rodriguez7, (1)Louisiana State University, Oceanography and Coastal Sciences, Baton Rouge, LA, United States, (2)Louisiana State University, Department of Geography and Anthropology, Baton Rouge, LA, United States, (3)Louisiana State University, Baton Rouge, LA, United States, (4)University of Southern Mississippi, Geography and Geology, Stennis Space Center, MS, United States, (5)Coastal Studies Institute, Baton Rouge, LA, United States, (6)Lawrence Livermore National Laboratory, Livermore, CA, United States, (7)Louisiana State University (LSU), Department of Geology and Geophysics, Baton Rouge, LA, United States
Abstract:
Climate models suggest cold-adapted trees grew in the southeastern United States (SE US) during glacial intervals yet there is a scarcity of paleoclimate records for marine isotope stages 3 to 5 in this region, limiting our understanding of early glacial oceanic-climatic conditions. Here we describe an offshore site with well-preserved in situ bald cypress stumps (Taxodium distichum) and woody remnants exposed in an eroding swale located 13.5 km from Orange Beach, Alabama in 18 m of seawater. T. distichum grows in warm and humid climates with low elevations (>0–50 m) preferring freshwater riparian environments with frequent flooding. Wood samples from exposed stumps and sediments have good preservation with cellular structure intact and smell like freshly cut cypress indicating preservation in anoxic conditions that suppressed biodegradation. Radiocarbon dating of eight wood subsamples, including an in situ stump, was inconclusive due to detection limits indicating the wood is older than 50,000 years. We conducted high-resolution geophysical surveys and coring operations in August 2015 recovering a total of 17.075 m of sediment cores. The base of these cores contain wood-bearing muddy peat sediments of the Pleistocene terrestrial wetlands. The geophysical surveys reveal the stumps are located around the eroding swale with possible river landforms visible in the side-scan sonar suggesting a paleochannel surrounded by bald cypress trees similar to modern swamps and bayous. Preliminary pollen analysis reveals an abundance of bald cypress (T. distichum), tupelo (Nyssa aquatic), and pine (Pinus spp.) similar to modern SE US wetlands. Ongoing sediment core analysis includes microfossil, palynology, and sedimentology analysis. Our preliminary results from this submerged glacial landscape suggest that coastal T. distichum wetlands were present in the early glacial interval along the northern Gulf Coast.
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