By Ainsley Lord

Faculty Mentor: Dr. Grothe

Abstract

The central tropical Pacific is a major driving force for global climate variability due to the El Niño Southern Oscillation (ENSO). However, it is unclear how this region is responding to human-induced climate change, which is critical to understand considering how this region may drive future impacts to the climate globally. Particularly, this region lacks instrumental temperature records before 1950, limiting our ability to investigate the human impact on the climate. To get a better understanding of this region’s climate history, proxies, like geochemical records from coral skeletons, are used to extend the instrumental sea surface temperature (SST) record, providing long term changes in SST beyond the industrial era. Traditionally, climate reconstructions from this region have solely relied on one species of coral, Porites, which is a reliable recorder of climate. However, relying on only one species of coral may potentially limit the temporal resolution of our SST reconstructions as it may not always be feasible to find enough samples through the past hundreds to thousands of years. This research proposes using two new species, Hydnophora sp. and Favia sp., to supplement the Porites records to extend the SST record back to 1800 C.E.. Specifically, we will measure the oxygen isotopes (d18O) and Sr/Ca in the coral skeleton to create a combined SST and sea surface salinity (SSS) time series from dozens of coral samples spanning this window. Working with numerous, smaller coral records is a challenge because the mean of each geochemical coral record can be offset from the other corals, adding large uncertainties in the conversion to SST. Additionally, corals are subject to weathering which can lead to diagenesis, or alterations in the geochemistry of the coral skeleton, that affect the geochemical/SST signal. I propose to analyze Hydnophora sp. corals that have been radiometrically dated to the last 200 years. Thus far, the samples have been screened for diagenesis and x-rayed to determine the major growth axis of the coral. My next steps are to complete monthly resolution d18O and Sr/Ca analyses that will be paired with a suite of Porites records back to 200 years ago. This work will help us better understand the timing and magnitude of SST and SSS since the industrial era, providing robust baseline data for climate models that are used to predict future climate change.