Speakers Club: Dr. Kathleen Johnson

Event Date: 

Thursday, October 30, 2014 - 2:00pm

Event Location: 

  • Webb Hall 1100

Dr. Kathleen Johnson of UC Irvine will give a talk at Speakers Club entitled "A multi-proxy record of ocean-atmosphere dynamics and local water balance since 854 AD from a Southern California speleothem."




Reconstructions of Southwestern North America (SWNA) hydroclimate reveal substantial interannual-to-centennial scale variability in moisture transport and precipitation amount over the last millennium. Understanding the underlying dynamics and spatial and temporal characteristics of this variability, which has been linked to Pacific and Atlantic sea surface temperature (SST) regimes, is critical for improving projections of future change.  A recently published speleothem d18O record (CRC-3)  from Crystal Cave, CA, was shown to record variations in moisture source region and storm track from 854 to 2007 AD, with lower values reflecting transport from the North Pacific and higher values reflecting transport from the tropical Pacific (McCabe-Glynn, 2013).  As CRC-3 ?18O values are more strongly influenced by atmospheric circulation patterns than by local precipitation amount, we investigated the potential of  additional proxies that may be more sensitive to local water balance.  I will present the results of 1,028 d13C and trace element (Mg, Sr, Ba) measurements conducted on CRC-3, assess their utility as proxies of local water balance at Crystal Cave, and compare them with other high-resolution paleoclimate records from the region to investigate the relationship between North Pacific SST patterns and SWNA hydroclimate.    We find that speleothem d13C, Mg/Ca, Sr/Ca, and Ba/Ca are only weakly correlated throughout the record, indicating that prior calcite precipitation is not the primary control on speleothem trace elements and carbon isotopes and that trace element proxies have limited utility at this site.  Multiple regression analysis of speleothem d13C against instrumental temperature and precipitation data, however,  indicates that both factors are significant (R2 = 0.44, p<0.0001).  This suggests that d13C may be a useful proxy for local water balance at this site, possibly reflecting the sensitivity of soil respiration to soil moisture.  Finally, the CRC-3 d13C record agrees well with tree ring based PDSI reconstructions from Southern California, confirming the existence of arid conditions during the Medieval Climate Anomaly. Through this multi-proxy approach, we demonstrate how records of large-scale ocean-atmosphere dynamics and local hydroclimate may be obtained from individual speleothem samples.