Tropical Sea Surface Temperatures Over the Last 120,000 Years

April 27th, 2013

Sea surface temperature (SST) is one of the most important and fundamental components of Earth’s climate. Tropical SST determines the location of the Intertropical Convergence Zone where the northeast and southeast trade winds meet, and influences global moisture content, the strength of monsoons, and precipitation in the tropics. 

Therefore, the importance of understanding the changes in SST can help us grasp a better understanding of the effects of climate change. Several SST proxies have been developed including oxygen isotope, magnesium-calcium, and strontium-calcium ratios in foraminifera and corals, and alkenones in marine algae and foraminifera, all of which serve as important tools in palaeoceanography.

However, each method offers advantages and disadvantages. For example, an advantage for the magnesium-calcium method is that it can be measured along with oxygen isotope records found in the same shell of foraminifera.

A drawback to the magnesium-calcium method is that partial dissolution of foraminifera shells can occur after the shells reach the sea floor.  This dissolution can reduce the magnesium-calcium ratio, raising the apparent temperature.

Our understanding of SST variability decreases as we stretch deeper back in time; but over the last glacial cycle, fluctuations in SST occurred coincident with changes in glacial ice volume, atmospheric temperature, and changes in ocean circulation.  Reconstructed temperature estimates of up to 5°C warmer than present have been calculated for sea surface temperatures during this time period. The last time tropical SST was as high or higher than today was during Marine Isotope Stage 5e (120,000 years ago) which would imply similar climate conditions.

This study summarizes data that shows how the various proxies indicate fluctuations of SST over the last glacial cycle and how applying these results can give us a better understanding of the effects of climate change.

David Allen, ’13
Great Falls, MT
Major: Geology

Sponsor: Rhawn Denniston

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