Improving ²¹⁰Po low level measurements in seawater

Area of Science:

• Oceanography
• Marine chemistry
• Radiochemistry

Background:

• The ocean plays a critical role in global carbon sequestration.
• Particulate organic carbon (POC) flux from surface to deep ocean is vital for carbon storage.
• Measuring POC flux relies on radioactive disequilibria, particularly 210Pb-210Po.

Purpose of the Study:

• To develop and validate a robust onboard method for measuring 210Po and 210Pb in seawater.
• To improve the accuracy of quantifying ocean carbon sequestration through better POC flux estimation.
• To address challenges in co-precipitating 210Po from complex seawater matrices.

Main Methods:

• Development of a novel co-precipitation technique using ferrous sulfate (FeSO4, Fe2+) for 210Po and 210Pb.
• Validation of the FeSO4 method with open-ocean samples from the PAP-Site Observatory.
• Comparison with a traditional co-precipitation method using ferric hydroxide (Fe(OH)3, Fe3+).

Main Results:

• The FeSO4 co-precipitation method provides accurate and consistent measurements of 210Po and 210Pb activities.
• The traditional Fe(OH)3 method significantly underestimates 210Po by an average of 40 ± 5%.
• The FeSO4 method correctly identified secular equilibrium in deep ocean waters, indicating no POC export, unlike the Fe(OH)3 method.

Conclusions:

• The FeSO4 co-precipitation method offers a more accurate and reliable approach for measuring 210Po and 210Pb in seawater.
• Accurate quantification of POC flux and ocean carbon sequestration is improved by this new method.
• This onboard-deployable technique enhances the study of ocean carbon cycling during research cruises.