Oral Session 7

An Optical Sensor for Autonomous Detection of Particulate Inorganic Carbon (PIC) Concentration in Seawater

The ocean’s biological carbon pump (BCP) transports biogenic carbon from the surface to the deep ocean, exerting an important control over atmospheric CO2 levels and global climate. This pump is fueled by processes of photosynthesis and calcification in the surface ocean, generating particulate organic and inorganic carbon, POC, and PIC respectively. Distinguishing between POC and PIC is critical as their downward fluxes have opposing effects on air-sea CO2 flux. Recent technological advances have enabled observations of POC stocks and fluxes from robotic ocean profilers equipped with bio-optical sensors at unprecedented time and space scales. However, no autonomous sensor for PIC stocks and fluxes currently exists, which hampers our understanding of and ability to estimate the magnitude of the BCP accurately. Here, we present the first critical steps in developing an autonomous PIC sensor. We present a submersible sensor for PIC detection based on the depolarization of forward-scattered light induced by the birefringence of PIC. Laboratory calibrations with PIC from cultured calcifying phytoplankton reveal that the sensor can detect PIC in seawater across the oceanic concentration range, as low as 0.06 μg PIC/L. We show linearity in the relationship between PIC and depolarization over 3 orders of magnitude and discuss differences in this relationship between various PIC types. We also characterize the PIC sensor for realistic temperature and turbulence effects. Our PIC sensor prototype is suitable for laboratory use and ship-based underway flow-through mode. Further developments are ongoing to make the PIC sensor suitable for vertical profiling on autonomous platforms.

*Qiming Sun, Ghent University, Belgium, https://orcid.org/0000-0001-6132-5093

Georges Fournier, Defence Research and Development Canada, https://orcid.org/0000-0001-7981-4610

Filip Beunis, Ghent University, Belgium, https://orcid.org/0000-0002-3413-0829

Kristiaan Neyts, Ghent University, Belgium, https://orcid.org/0000-0001-5551-9772

Jordan Toullec, Ghent University, Belgium, https://orcid.org/0000-0002-2782-9607

Peter Chaerle, Ghent University, Belgium, https://orcid.org/0000-0002-8216-0299

Olga Chepurnova, Ghent University, Belgium

David Dana, Sequoia Scientific, Inc., USA

Chuck Pottsmith, Sequoia Scientific, Inc., USA

Wayne Slade, Florida Atlantic University, USA, https://orcid.org/0000-0003-1851-968X

Wim Vyverman, Ghent University, Belgium, https://orcid.org/0000-0003-0850-2569

Griet Neukermans, Ghent University, Belgium, https://orcid.org/0000-0002-8258-3590

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