PP21A-1671

1. PP21A-1671 Detailed Tropical Sea Level Record Spanning the Younger Dryas Chronozone N. A. Abdul1; R. A. Mortlock1; J. D. Wright1; R. G. Fairbanks2, 11. Earth and Planetary Sciences, Rutgers University, Piscataway, NJ; 2. Columbia University, Palisades, NY. Introduction The Younger Dryas climate event (~12,900 to 11,600 calendar years BP) is the “poster child” example of rapid climate change. It is popularly described as "A RAPID RETURN TO GLACIAL CONDITIONS" and is treated as an unsolved mystery with multiple suspects. The frightening consequences conjured of its sequel brought on by anthropogenic causes have been implanted in the popular media and into the dialog of international politics. The Younger Dryas is most clearly defined in the climate proxies of Greenland ice cores, circum-North Atlantic terrestrial records, and North Atlantic marine sediments. Climate proxies measured in the annual layers in ice cores preserve a remarkable record of change.  We note however, conditions on Greenland may change rapidly due to the fact that this region is a mixing zone of extremely divergent air masses that converge from great distances.   The most popular explanations for the cause(s) of the Younger Dryas climate event are catastrophic in nature, developed in an attempt to pinpoint a physical cause for a climate catastrophe. These range from “THE GREAT FLOOD” caused by the instantaneous drainage of proglacial Lake Agassiz that in turn “SHUT DOWN” North Atlantic Deep Water to “Earth’s collision with carbonaceous chrondrites or comets....producing multiple airbursts and possible surface impacts”in,,,,,n Furthermore, numerous publications suggest that the Younger Dryas climate event is a “GLOBAL CLIMATE EVENT” and thus elevates its importance to new heights because this implies shifts in the global energy budget and implicates many more parts of the climate system. A less sensational scenario for the “cause” of the Younger Dryas climate event, and the one that we continue to favor, is the simple shifting of air masses and surface ocean mixing zones due to the rapidly changing topography of the Laurentide and Fennoscandian Ice Sheets during the deglaciation of the Northern Hemisphere.  Our detailed sea level record shows that global ice melting rate was not markedly changed during the Younger Dryas Chronozone compared to the bracketing time intervals. Scientists & crew drilling & collecting cores aboard the RV Knorr offshore Barbados. Results We generated a detailed sea level record spanning the interval 14,000 to 11,200 years BP from the coral offshore drilling expedition (KNORR 189-2) and combined them with previously published data (Fairbanks, 1990; Peltier and Fairbanks, 2006). 17 of these dates fall within the Younger Dryas Chronozone. All sea level estimates were based on samples of fossil coral of the single species Acropora palmata. We used 4 overlapping and contemporaneous offshore drill cores (RGF 12 & 16 and BBDS 9 & 10) and corrected for minor tectonic uplift (0.34 mm per year). Depth uncertainty is +6 meters (+5 for habitat range of Acropora palmata and ±1 m for drilling depth corrections). 2 sigma age uncertainty ranges from 38 to 70 years. Study area Bathymetric map of the south coast of Barbados showing the drilling locations. All drilling was conducted on submerged reef ridges. Red arrows show sights drilled in 1988 while blue arrows represent sights drilled in 2007. B) B) A) • The reef crest coral species Acropora palmata is restricted to 5 meter water depth and is considered to be the best coral fossil indicator of sea level when sampled from the Acropora palmata facies. Although isolated Acropora palmata corals have been found in deeper waters, the interlocking reef framework diagnostic of shallow water varieties is absent (Lighty et al., 1982). Our drill cores contain thick sequences of the reef crest coral Acropora palmata, strongly suggesting that core samples were recovered from the reef crest facies and are very unlikely to represent isolated specimens. • Methods • Coral sample and data quality control: • X-ray diffraction (XRD) on each sample indicated no detectable calcite (<0.2 %) • d234U initial of the coral sample was between 138 and 150 per mil • U-series age determinations were measured by Multi-collector ICP-MS (PLASMA 54) with a precision of better than ±6 per mil (two sigma). A) A. palmata from drill cores - Barbados 1988 cruise (Fairbanks, 1990). A. palmata from drill cores – Barbados 1988 cruise (Peltier and Fairbanks 2006) combined with A. palmata samples from 2007 cruise. • Conclusions • During the Younger Dryas (12,900 to 11,600 years BP) sea level rose from ~68 to 60 m below present sea level with an initial rate of about 10 meters/kyr. Sea level decreased smoothly to a rate of <5 meters/kyr towards the end of the Younger Dryas. • In the context of the Barbados sea level record, the Younger Dryas interval recorded only a minor slowing of sea level rise and is a continuation of the trend that began at the top of Meltwater Pulse 1A (14,000 years BP) and ended with Meltwater Pulse 1B (11,200 years BP). B) • The Younger Dryas Chronozone is highlighted in both the Northern (A) and Southern (B) hemisphere ice records: • Greenland ice cores record a shift towards more depleted d18O values indicative of cooler temperatures. • DomeC ice cores in contrast record a steady shift to more “Greenhouse-like conditions” in Antarctica (increase in atmospheric CO2) which peaked towards the end of the YD. The RV Knoor Acknowledgements Captain and Crew RV Knorr 189-2 L. Cao (Pacific Northwest National Labs), J. Mey (Lamont-Doherty Earth Observatory), K. Ellins (Univ. Texas, Austin), L. Teneva (Stanford University). National Science Foundation School of Arts and Sciences, Rutgers University, New Brunswick NJ. A. Cotet (Rutgers University) References: Fairbanks, R.G., 1990, The Age and Origin of the "Younger Dryas Climate Event" in Greenland Ice Cores: Paleoceanography, v. 5. Lighty, R.G., Macintyre, I.G., and Stuckenrath, R., 1982, Acropora palmata Reef Framework: A Reliable Indicator of Sea Level in the Western Atlantic for the Past 10,000 Years: Coral Reefs, v. 1, p. 125-130. Monnin, E., Indermühle, A., Dällenbach, A., Flückiger, J., Stauffer, B., Stocker, T.F., Raynaud, D., and Barnola, J.-M., 2001, Atmospheric CO2 Concentrations over the Last Glacial Termination: Science, v. 291, p. 112-114. Peltier, W.R., and Fairbanks, R.G., 2006, Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record: Quaternary Science Reviews, v. 25, p. 3322-3337. Rasmussen, S.O., Andersen, K.K., Svensson, A.M., Steffensen, J.P., Vinther, B.M., Clausen, H.B., Siggaard-Andersen, M.L., Johnsen, S.J., Larsen, L.B., Dahl-Jensen, D., Bigler, M., Röthlisberger, R., Fischer, H., Goto-Azuma, K., Hansson, M.E., and Ruth, U., 2006, A new Greenland ice core chronology for the last glacial termination: J. Geophys. Res., v. 111, p. D06102.