Authors: Grant L Harley*, University of Idaho, Kristine L DeLong, Louisiana State University, Samuel J Bentley Sr., Louisiana State University, Jeffrey B Obelcz, Louisiana State University, Carl A Reese, University of Southern Mississippi, Kehui Xu, Louisiana State University, Suyapa Gonzalez, Louisiana State University, Jonathan T Truong, Louisiana State University, Alicia Caporaso, Bureau of Ocean Energy Management
Topics: Paleoenvironmental Change, Biogeography, Physical Geography
Keywords: dendrochronology, pollen analysis, paleoclimatology, glacial refugium
Session Type: Paper
Start / End Time: 8:00 AM / 9:40 AM
Room: Grand Ballroom C, Astor, 2nd Floor
Presentation File: No File Uploaded
Shortly after Hurricane Ivan made landfall near Gulf Shores, Alabama in 2004, a fisherman discovered an ancient grove of previously buried logs and tree stumps rooted in growth position located in 18 meters of water about 13 kilometers off the coast in the northern Gulf of Mexico. Observations during diving expeditions found more than 50 well-preserved bald cypress (Taxodium distichum) tree stumps and logs. Dendrochronological analysis of stump samples produced a tree-ring chronology that spans 489 years “floating” in time, given that the stumps were found to be radiocarbon dead. The correlation between all measured series (n=10) demonstrates a high level of agreement (r=0.58, p<0.001). The chronology exhibits sharp cycles of growth variability and an interesting pattern of shared rapid growth decline toward the end of the chronology, indicating synchronous mortality. Radiocarbon dating of peat recovered in a vibracore (DF1) suggests that the sediment is likely Marine Isotope Stage 3, or earlier. Pollen results from the lowermost sections within the peat layer show an assemblage consistent with a bald cypress/tupelo gum (Nyssa aquatica) backwater. This is eventually replaced by a more open, possibly brackish, environment, dominated by grasses (Poaceae) and sedges (Cyperaceae). During this change however, there is a brief but very interesting period where the pollen assemblage may be analogous to the modern-day Atlantic Coastal Plain Blackwater Levee/Bar Forests of North and South Carolina. This rare find provides an opportunity to study in situ wood and fossil pollen from a glacial refugium in the northern Gulf of Mexico.