2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 210-65
Presentation Time: 9:00 AM-6:30 PM


YATES, Hayden R., Department of Geology, Washington and Lee University, 204 W. Washington St., Lexington, VA 24450, FALLS, Emily, Geology Department, Washington and Lee University, 204 W. Washington St., Lexington, VA 24450, GREER, Lisa, Department of Geology, Washington and Lee University, Lexington, VA 24450, DECORTE, Ilian, Geology Department, Macalester College, 1600 Grand Avenue, St. Paul, MN 55105, WIRTH, Karl R., Geology Department, Macalester College, Saint Paul, MN 55105, CURRAN, H. Allen, Department of Geosciences, Smith College, Northampton, MA NA, LEONARD-PINGEL, Jill, Geology Department, Washington and Lee University, Lexington, VA 24450 and GREENSTEIN, Benjamin J., Dept. of Geology, Cornell College, Mt Vernon, IA 52314, yatesh16@mail.wlu.edu

In this study, we used sclerochronology and stable oxygen isotopic records (δ18O) of both modern and Pleistocene corals from Rocky Point, Belize to compare seasonality at the last interglacial with that of today. The last interglacial interval is believed to have experienced stronger Northern Hemisphere solar insolation than today, which is thought to have resulted in a more northward and latitudinally extensive Intertropical Convergence Zone (ITCZ) over the Caribbean, presumably leading to higher amplitude seasonal temperature and/or precipitation cycles. We compared geochemical data from fossil and modern Orbicella sp. corals in northern Belize to explore changes in seasonality between the Pleistocene and present. The Pleistocene coral was dated at 124-128 ka using 230Th/234U dating methods and the modern coral was collected in 2014. Linear extension rates (LER) from the modern coral averaged 10.3±1.6 mm/year (n= 31) and showed higher normalized variability (stdev. = 1.4, n = 29) compared with the Pleistocene coral (mean LER of 2.5±0.9 mm/yr, stdev. = 0.9, n = 19). Both corals were sampled at a range of resolutions to examine the optimal method for reproducing seasonality. At the lowest sampling resolution (4 samples per year), the average δ18O values for the Pleistocene and modern coral were -4.19‰ and -3.96‰ respectively, but the Pleistocene coral had a seasonal δ18O range of 0.66‰ compared to the modern coral range of 0.40‰. At the highest sampling resolution (10 samples per year), the Pleistocene and modern δ18O indicated seasonal ranges of 2.47‰ and 0.99‰. Our data show that at the highest sampling resolutions, the Pleistocene seasonal δ18O ranges were greater than those of the modern coral by 1.48‰, representing a maximum potential temperature range of ~10°C. This exceeds the current seasonal temperature range of 7°C recorded from near-by in situ instrumental data. The larger seasonal range of the Pleistocene coral supports the hypothesis that the ITCZ was located at higher latitudes in the Northern Hemisphere and fluctuated within a greater latitudinal extent during the last interglacial, if δ18O is driven primarily by temperature in this coral.