AUTHOR=Koestner Daniel , Stramski Dariusz , Reynolds Rick A. 

TITLE=A Multivariable Empirical Algorithm for Estimating Particulate Organic Carbon Concentration in Marine Environments From Optical Backscattering and Chlorophyll-a Measurements

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.941950

DOI=10.3389/fmars.2022.941950

ISSN=2296-7745

ABSTRACT=<p>Accurate estimates of the oceanic particulate organic carbon concentration (POC) from optical measurements have remained challenging because interactions between light and natural assemblages of marine particles are complex, depending on particle concentration, composition, and size distribution. In particular, the applicability of a single relationship between POC and the spectral particulate backscattering coefficient <italic>b<sub>bp</sub></italic>(λ) across diverse oceanic environments is subject to high uncertainties because of the variable nature of particulate assemblages. These relationships have nevertheless been widely used to estimate oceanic POC using, for example, <italic>in situ</italic> measurements of <italic>b<sub>bp</sub></italic> from Biogeochemical (BGC)-Argo floats. Despite these challenges, such an <italic>in situ</italic>based approach to estimate POC remains scientifically attractive in view of the expanding global-scale observations with the BGC-Argo array of profiling floats equipped with optical sensors. In the current study, we describe an improved empirical approach to estimate POC which takes advantage of simultaneous measurements of <italic>b<sub>bp</sub></italic> and chlorophyll-a fluorescence to better account for the effects of variable particle composition on the relationship between POC and <italic>b<sub>bp</sub></italic>. We formulated multivariable regression models using a dataset of field measurements of POC, <italic>b<sub>bp</sub></italic>, and chlorophyll-a concentration (Chla), including surface and subsurface water samples from the Atlantic, Pacific, Arctic, and Southern Oceans. The analysis of this dataset of diverse seawater samples demonstrates that the use of <italic>b<sub>bp</sub></italic> and an additional independent variable related to particle composition involving both <italic>b<sub>bp</sub></italic> and Chla leads to notable improvements in POC estimations compared with a typical univariate regression model based on <italic>b<sub>bp</sub></italic> alone. These multivariable algorithms are expected to be particularly useful for estimating POC with measurements from autonomous BGC-Argo floats operating in diverse oceanic environments. We demonstrate example results from the multivariable algorithm applied to depth-resolved vertical measurements from BGC-Argo floats surveying the Labrador Sea.</p>