Special Oceanography SeminarMay 14, 2:30pm - 3:30pm
Mānoa Campus, Marine Sciences Building, MSB 100
Dr. Kim Cobb*
Georgia Inst. of Technology
“Coral estimates of central tropical Pacific temperature over the last millennium: the good, the bad, and the ugly”
Abstract: Robust estimates of tropical Pacific sea-surface temperatures through the recent centuries are critical for the detection and attribution of anthropogenic climate change in this key region, yet have thus far proven elusive. Corals provide a wealth of environmental information over the past several centuries, in the case of living colonies, and many millennia, in the case of fossil corals. Specifically, coral Sr/Ca is a well-established proxy for sea-surface temperature, which when combined with coral oxygen isotopic composition (18O), can provide much-needed estimates of past seawater 18O variations (the latter closely related to salinity). Here we apply paired Sr/Ca and 18O analyses to a large, well-characterized collection of coral cores from Palmyra Island (6N, 162W) (e.g. Cobb et al., 2001; Cobb et al., 2003). We uncover a significant trend in 20th century seawater 18O indicative of regional freshening, consistent with model projections of increased P-E in this region in response to greenhouse forcing. In applying this approach to the fossil coral collection, we highlight a number of obstacles that must be overcome prior to obtaining robust coral Sr/Ca-based estimates of paleo-SST from fossil corals, and suggest strategies for reducing those sources of uncertainty. That said, our first estimates of SST from ~1000CE and 1600CE are consistent with regional cooling during both intervals, with more pronounced cooling inferred during the earlier “Medieval Climate Anomaly”.
*The speaker is a candidate for a faculty position in the Department of Oceanography.
Oceanography, Mānoa Campus