GEOCHEMICAL ANALYSIS OF AN ANTARCTIC DEEP-WATER CORAL AS A CLIMATIC ARCHIVE AND SOURCE FOR RADIOCARBON AGE CORRECTION IN THE ROSS SEA

The results of radiocarbon analyses on inorganic and organic carbon from Antarctic marine fossils are notoriously difficult to interpret due to reworking and the prominent carbon reservoir effect in the Southern Ocean. Studies have shown significant geographic variability in the magnitude of the later effect depending on the depth, degree of vertical mixing, ocean-atmosphere interaction (regulated by sea ice cover), and location of the water mass relative to the Antarctic convergence (Gordon and Harkness, 1992). Because of this variability, region specific corrections for the carbon reservoir effect are essential for accurate dating of marine fossils.

During a series of dredges in the Adare Basin off the northwestern Ross Sea, the United States Antarctic Program (USAP) cruise NBP07-01 collected nearly a thousand fragments of the Stylasteridae coral species Errina aspera between the depths of 500 and 600 meters. This species is known to exist in relative abundance throughout the South Atlantic and Southern Ocean as well as in the Straight of Gibraltar (Álvarez-Pérez et al., 2005). Extensive efforts to piece the fragments together yielded a 9 cm long specimen with a modern growth tip as well as several shorter segments with modern growth tips. E. aspera is believed to grow at a rate of 1 to 7 mm per year, but in the environment where this specimen was collected, it is thought to grow 1 mm or less per year (Häussermann and Försterra, 2007), giving it a growth span of roughly 100 years that extends into the pre-bomb era (pre-1950).

This study aims to use one of the assembled coral specimens to calculate an accurate regional radiocarbon age correction for the Adare Basin. Preliminary radiocarbon analyses indicate that the age of the specimen is old enough to show a distinct bomb spike with finer sampling that will allow for accurate regional age correction. X-rays of the coral stems are used to analyze the growth pattern of the coral and determine what resolution sampling is necessary and, if distinct growth bands exist, they will be used to help calculate the reservoir correction. The macro-samples extracted from along the coral stem are analyzed for carbon and oxygen isotopes and correlated to seawater temperature using the correction presented by Smith et al. (2000) to account for the scale effects of isotope fractionation in corals.