Talk by Andrea Spolaor, University of Siena – Niels Bohr Institute - University of Copenhagen

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Talk by Andrea Spolaor, University of Siena

Importance of element speciation in ice core studies

Since Willi Dansgaard's demonstration that oxygen and hydrogen isotope ratios in ice are related to the temperatures of water condensation and evaporation, many elements and gases have been studied to understand climate variations in the past. For example, in Antarctica dust size is used to understand transport pathways while 10Be is used to reconstruct the solar irradiance in the upper troposphere, sodium is commonly used to evaluate the influence of sea spray while CO2 and CH4 have been used to reconstruct the composition of the ancient atmosphere from the air bubbles trapped in ice.

Analysis of total element concentrations is common however there is a lack of data regarding element speciation - which is the chemical oxidation state of the element. The chemical form of an element is as important as its concentration since the behavior of some elements changes dramatically with oxidation state. For example distinguishing between the two species of iron is important since the Fe(II) form is more soluble and bio-available than the Fe(III) form - an important key to evaluating potential iron fertilization and CO2 drawdown in the Southern Ocean and other nutrient limited oceanic zones.

Moreover the chemical speciation could be driven by a particular atmospheric process and for this reason determining the species of a particular element could be important to understanding atmospheric processes.

Studying Antarctic (Talos Dome) ice, we find speciation changes for iodine and iron between glacial and interglacial while for bromine only the bromide species is present. We suggest that other elements might present similar variations in their chemical speciation between cold and warm periods.