AN ULTRA-HIGH RESOLUTION HOLOCENE ISOTOPE ANALYSIS OF NEOGLOBOQUADRINA PACHYDERMA FORAMINIFERA IN THE ADéLIE BASIN, ANTARCTICA (IODP EXPEDITION 318)

High-resolution d18O and d13C records spanning the mid to late Holocene (6 kyr to present) from planktonic foraminiferal species Neogloboquadrina Pachyderma were obtained from the IODP Site 1357 located in the Adélie basin. These data provide a record of surface water conditions along the Adélie Coast of Antarctica. Site U1357 is located ~50 km off the coastline of East Antarctica (66°24.8′S, 140°25.7′E) in the Adélie Trough, which is a glacially scoured valley on the continental shelf, with water depths of ~1000m. IODP Site U1357 triple cored an exceptional sedimentary archive with Hole U1357A recovering a 186.6 m of sediment spanning the entire Holocene. Carbon-14 age dates provide a firm chronology, suggesting an average sedimentation rate of 1.7 cm/yr, with the base of the core dated, approximately, as 11,000 years old. In a collaborative effort with Stanford University, 1,800 samples were taken for foraminiferal studies on the ship at 10 cm spacing resulting in, approximately, a seven-year resolution. This study will focus on the upper half of the hole (1H to 9H), representing the last 6,000 years of deposition. Neogloboquadrina pachyderma contributes a major portion of the population of foraminifera in the samples examined and were used for developing stable isotopic records. The N. pachydermas that had grown to full maturity, or morphotype one (M1), were used for isotope analysis as their shells are the thickest of all the morphotypes identified. If there were insufficient numbers of M1 N. pachydermas for stable isotope measurements, large variants of M2 were used.

Preliminary results from the oxygen isotope records show two intervals of higher oxygen isotopes, interpreted to represent cooler surface waters; the first between 6kyr and 5kyr and the latter during the Antarctic Neoglacial, a previously identified cooling event that occurred after the Mid-Holocene warmth (3-0kyr). Oxygen isotopes were generally lower during the Mid-Holocene Climatic Optimum, which are interpreted as warmer surface waters,. In addition, the carbon and oxygen isotopes appear to correlate during the Neoglacial and anti-correlate during the first cooling event. An additional 125 stable isotopes measurements are currently being run on the mass spectrometer lab at Stanford University and will be integrated into this study.