14:45–15:00 | ABSTRACT 1217
TOWARDS OPTICAL CLOSURE IN A HIGHLY SCATTERING COCCOLITHOPHORE BLOOM
Coccolithophores are globally distributed calcifying haptophytes that, at high surface concentrations, strongly influence ocean optics through highly scattering calcium carbonate coccoliths. Quantifying their concentration from ocean colour signals requires accurate parameterisation of inherent optical properties (IOPs), particularly spectral absorption and backscattering coefficients. Here, we present a comprehensive set of in situ hyperspectral IOP and radiometric measurements, collected during an extensive coccolithophore bloom in the Icelandic Basin in June 2024. Total absorption was derived from a Point Source Integrating Cavity Absorption Meter (PSICAM), an instrument insensitive to scattering error. This was used to correct the absorption-attenuation (acs) instrument to obtain spectral scattering. Spectral backscattering (bb) was measured with the Hyper-bb instrument. Spectral remote sensing reflectance (Rrs) was modelled using the radiative transfer model HydroLight, parameterised with measured IOPs and observed boundary conditions. This was compared with in situ Rrs from TriOS instruments mounted on a floating frame to minimise ship-shadow effects. With absorption and Rrs well constrained, this measurement framework enabled targeted optimisation of backscattering coefficients. Initial optical closure assessments showed good agreement between in situ radiometry and modelled Rrs at lower particulate inorganic carbon (PIC) stations (i.e. lower coccolithophore abundance). In contrast, closure was not achieved at high PIC stations (indicative of bloom conditions). To account for potential signal loss due to pathlength attenuation in the Hyper-bb, a modified σ correction incorporating both absorption and a scaled scattering term (kscatt b) was applied. Iterative tuning of kscatt yielded an optimal value of 2.5, improving optical closure consistency across the observed PIC range.
Cait McCarry, University of Strathclyde, [email protected], https://orcid.org/0000-0001-9051-3907
Brynn Presler-Marshall, University of Strathclyde, [email protected]
Farley Miller, Bigelow Laboratory for Ocean Sciences, [email protected]
Catherine Mitchell, Bigelow Laboratory for Ocean Sciences, [email protected]
Alex Poulton, Heriot Watt University, [email protected]
David McKee, University of Strathclyde, [email protected]
