Angela StahlFollow


Marine Biology


Robinson, Rebecca S

Advisor Department

Oceanography, Graduate School of


Kelly, Roger

Advisor Department

Oceanography, Graduate School of




Iodine/Calcium ratios; oxygen levels; past climate

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Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


ANGELA STAHL (Marine Biology)

Iodine to Calcium Ratios in Marine Carbonates as an Indicator of Oxygen Levels

Sponsor: Rebecca Robinson (Graduate School of Oceanography)

The Earth goes through natural cycles of warm and cool periods. In the past,

warmer oceans during interglacial periods have been shown to hold less oxygen

in their waters compared to cooler, glacial oceans. For this research, we are

studying an area in the Eastern Tropical Pacific where it is known to have

variable concentrations of dissolved oxygen in the waters due to the influence of

the climate. Oxygen is a vital component for most organisms to function, even

in the ocean. Organisms take up dissolved oxygen from the water and use it for

respiration, which produces energy for the organisms.

The organisms focused on for this research are marine microorganisms called

foraminifera, which form calcium carbonate shells. These organisms take up

carbonate ions (CO32-) and calcium ions (Ca2+) and combine the two to make

hard calcium carbonate (CaCO3) shells. These foraminifera have been shown

to use iodate in an ionic substitution for the carbonate ion in their shells when

iodate is present in seawater. Iodate concentration directly varies with oxygen

concentration in seawater. By measuring the iodine to calcium ratio in the

fossilized shells of these marine microorganisms, scientists can estimate how

much oxygen was in the ocean during these glacial-interglacial cycles of the past.

To measure the iodine to calcium ratio of the shells, the microfossils are crushed,

stripped from any surface contamination, dissolved in acid, and measured using

an inductively coupled plasma mass spectrometer, ICP-MS. I am measuring the

iodine to calcium ratios in microfossils that range in age from 1,000 to 120,000


With climate change raising global temperatures of the atmosphere and the

ocean, measuring the oxygen levels of a warmer past could possibly give us an

idea of what to expect in the future. Learning how organisms function during

these warmer, lower oxygen periods could show us what could happen in the

near future if we do not actively try to reduce our carbon emissions and slow

human-induced climate change.

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