Sarah Clark

Estimating Sea Surface Temperature for the Earth's Past

Global average temperatures are  estimated to increase 2-5°C over the next century.  This rate of increase is alarming because it is happening 100 times faster than the natural global warming experienced since the Last Glacial Maximum (LGM—about  21,000 years ago) which was only ~6°C.  Ocean waters act as natural climate regulators over millennia.  It is debated as to whether the temperature of the tropical Pacific Ocean (TPO) has warmed 3-4°C or 1-1.5°C since the LGM.  The main cause of this debate is the disagreement between two independent sea surface temperature (SST) proxies.  These discrepancies must be resolved in order to better understand the ocean’s role in the regulation of global climate change. 


One of these SST proxies is based on proteins (alkenones) produced by planktonic algae which record the water temperatures in which the algae lived.  Upon death, the alkenones are preserved in deep sea sediments and used by paleo-oceanographers to estimate SST.  Likewise, Mg/Ca ratios in shells of planktonic foraminifera (zooplankton) are also sensitive to water temperatures.  However, the SST estimates from these two proxies rarely agree.


Investigating the cause of this disagreement requires comparing Mg/Ca ratios in the shells of the foraminifera Globigernoides ruber and alkenones from the same modern sediment samples.  Comparing both proxy estimates to satellite readings of seasonal and annual average SST in the TPO,  will likely  reveal any seasonal preferences of the respective organisms, potential presence of cryptic subspecies, variations in sea surface salinity, and/or errors in proxy calibration.

Faculty Mentor: Figen Mekik, Geology

Page last modified July 27, 2009