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E3.04 - Structural Properties of Southern Ocean Pteropods 
December 2, 2014   9:30am - 9:45am

This study aims to determine the impact of ocean acidification on Southern Ocean pteropods via a detailed understanding of the structural and mechanical properties of their shells.

Many marine organisms build their external skeletons and shells from biogenic calcium carbonate (CaCO3­). As both the ocean pH and the availability of dissolved CO32- decreases, it is likely that these calcifying organisms will find it increasingly difficult to form and maintain their shells.

Pteropods, also known as sea butterflies, are small planktonic free-swimming marine molluscs that are common in polar waters. They produce shells of aragonite, a form of calcium carbonate, and are expected to be adversely affected by ocean acidification. Pteropods are an integral part of the marine food chain of the Southern Ocean with many organisms, from zooplankton to whales, relying on them as a food source [2]. Consequently, changes in their abundance or distribution could have a substantial flow-on effect for the whole Southern Ocean ecosystem.

In this work, two sets of Southern Ocean pteropod shells collected in 1998 and 2007 were analyzed. Shells were mounted in epoxy resin and polished to reveal a cross-section. Nanoindentation was used to measure the mechanical properties (hardness and modulus), and Raman microspectroscopy identified the material of the shells. Focused Ion Beam (FIB) methods were used to prepare sections for transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was used to examine both the surfaces of the shells (prior to mounting in epoxy resin) and cross-sections (after polishing).

The average hardness from each shell ranged between 0.5 GPa to 4.5 GPa and the modulus ranged between 12 GPa to 64 GPa. The mechanical properties were not position sensitive with respect to the region of the shell indented. There was no statistically significant difference in the average modulus between the two sets of shells, but some weak evidence of a difference in average hardness. TEM revealed information on the multi-layered structure of the shells and with Raman microspectroscopy, identified the shell material as aragonite.


[1] J. Orr et al, “Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms”, Nature, vol. 437, pp. 681-686, September 2005.
[2] Hunt et al, “Pteropods in Southern Ocean ecosystems”, Progress in Oceanography, vol 78, pp. 193-221, 2008.

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