Exploring Paleoclimatology in the Classroom Using Coral Radioisotope Data from Rarotonga Island in the South Pacific

Coral Radioisotope Data from the Homepage for the World Data Center for Paleoclimatology provides users with access to atomic ratio data (Sr/Ca) and Sea Surface Temperature (SST) data for coral samples near Rarotonga Island in the South Specific gyre. The dataset covers a 271 year period and is presented in graphical and raw text formats.

Reconstructing past climate histories is vital for understanding and predicting global climate change. Paleoclimatology provides data that can be used to determine climatic variations including historical changes in temperature. In the case of coral reefs, carbon dating of samples can be used to estimate sample age while the ratio of strontium and calcium can be used as a record of SST changes. The Coral Radioisotope Data demonstrate how isotopic data and atomic ratios can be used to obtain an accurate picture of oceanic temperature oscillations.

This dataset can be used to teach the following skills and topics Paleoclimatology, Physical Oceanography, and Biogeochemistry:

• Methods for reconstructing temperature records
• South Pacific gyre
• El Niño Southern Oscillation
• Relevance of decadal variations in sea surface temperature

• Using data to generate graphs comparing Sr/Ca ratios to historical temperature data
• Calculating statistical relationship between Sr/Ca ratios and empirical temperature data
• Using linear regression analyses to compare and evaluate methods for reconstructing climate history
• Interpreting chemical data from coral samples

Data for Sr/Ca ratios and SST are provided for the period from 1726-1997. Data are available in raw format (as a text file) and in graphical form (as a JPEG image).

Raw data can be accessed via ftp. A description of the data, including graphical representations, is archived at the Paleoclimatology branch of the NOAA website.

One way that students can process the data is to create graphs from raw data (provided text files) using a spreadsheet application such as Excel.

Raw data can be downloaded and imported into a spreadsheet application such as Excel for further processing. The Starting Point site provides a tutorial for using Excel. Linear regression analysis can be performed to examine the robustness of the relationship between Sr/Ca ratios and SST.

The Story Behind the Data

A non-technical narrative describing the data collection and scientific process is provided in a 'data story' from CIRES.

A hydraulic drill was used to extract a core sample from coral growing 18.3 m off of Rarotonga Island (21°14'11"S, 159°49'59"W). Sr/Ca ratios for a 271 year period were determined by performing atomic emission spectroscopy on 1 mm intervals of a 3.5 m core sample extracted from Porites lutea coral colonies in 1997. Measured SST data was obtained from Integrated Global Ocean Service System Products (IGOSS).

Limitations to climate reconstruction depend on the methodology used. Sr/Ca ratios as well as oxygen isotope data can be used to calculate SST with an accuracy near 0.5°C.

For More Detail

More complete information about the data is available in question/answer format from CORIS.

• Decadal sea surface variability in the subtropical South Pacific from 1726 to 1997 A.D.: Research article describing data collection and its significance for understanding the role of tropical forcing in SST oscillations (from Science ).

• Sea-Surface Temperature from Coral Skeletal Strontium/Calcium Ratios: A research article describing the relationship between Sr/Ca ratios in coral to SST (from Science ).
• Biological Controls on Coral Sr/Ca and Δ¹⁸O Reconstructions of Sea Surface Temperatures: This research article discusses the impact of biological factors on strontium and calcium uptake in coral and the robustness of using Sr/Ca ratios as a proxy for SST.

• Air-sea Interactions: Activities in Oceanography: An example from Teaching Quantitative Skills in the Geosciences site that includes a module on the El Nino Southern Oscillation.
• An activity related to Coral Bleaching is described in a data tip from Bridge, the Ocean Sciences Education Resource Teacher Center archive.

• Data are archived at the NOAA Satellite and Information Service (more info)
• ReefBase ( This site may be offline. ) provides information and data on coral, including a section on coral bleaching, which may be related to changes in SST.
• The National Climatic Data Center provides numerous links to websites on paleoclimatology and coral reefs.