My research involved using a new technique, Mg/Ca paleothermometry, to determine past ocean temperatures from foraminiferal shell calcite. This technique takes advantage of the observation that as the temperature of calcification increases, Mg is incorporated into the foraminiferal shell in greater proportions. Several other techniques exist for estimating past ocean temperatures, including oxygen isotopes, faunal transfer functions and alkenones. However, all have their limitations and complications. Professor David Lea's lab is working to refine the Mg/Ca paleotemperature technique in foraminifera by conducting calibration experiments with foraminifera from cultures, sediment traps and plankton tows, and by applying the technique to fossil foraminifera from marine sediment cores. We hope that Mg/Ca of foraminiferal calcite, in conjunction with oxygen isotopes, can provide a more accurate estimate of past ocean temperatures than has previously been available.

In 1996, the Ocean Drilling Program recovered a long sediment core from the Santa Lucia Slope off of Point Conception. This core, known as Site 1017E, has an unusually high accumulation rate (23 cm of sediment per thousand years) which makes it ideal for studying the record of millennial scale climate events over the past 500,000 yrs. Oxygen isotopic analyses have been completed on 2 species of foraminifera: G. bulloides which is a near surface dweller, and N. pachyderma which is a thermocline dweller. Temperature estimates based on the oxygen isotopic data suggest that during the Holocene there was a 4 to 8 degree temperature difference between the surface waters and the thermocline (similar to the modern scenario), that disappeared to almost 0 degrees during the glacial. One of the possible interpretations is that an increase in coastal upwelling during the glacial led to a decrease in the thermal stratification of the waters off Pt. Conception.

We looked at Mg/Ca in both G. bulloides and N. pachyderma from the past 60 kyr at Site 1017E to determine 1) if the millennial scale oxygen isotopic events are recorded in Mg/Ca, 2) if the magnitude of the events are similar in O18 and Mg/Ca, 3) if the phasing is similar, and 4) if glacial/interglacial changes in the structure of the water column inferred from oxygen isotopes are confirmed by Mg/Ca. In addition, we will be working to refine the Mg/temperature calibration curves with analyses of modern G. bulloides and N. pachyderma collected from the Santa Barbara Channel in 1995-1999.