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Remote Sens. 2019, 11(3), 318; https://doi.org/10.3390/rs11030318

Retrieval of Phytoplankton Pigments from Underway Spectrophotometry in the Fram Strait

1
Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, 27570 Bremerhaven, Germany
2
Faculty of Biology and Chemistry, University of Bremen, 28359 Bremen, Germany
3
School of Marine Sciences, University of Maine, Orono, ME 04469, USA
4
Division of Marine Science, University of Southern Mississippi, Stennis Space Center, MS 39529, USA
5
Department of Earth System Science and Policy, University of North Dakota, Grand Forks, ND 58202, USA
6
Helmholtz-Zentrum Geesthacht Center for Materials and Coastal Research, 21502 Geesthacht, Germany
7
Department of Biology, Chemistry and Geography, Université du Québec à Rimouski, Rimouski, QC G5L 3A1, Canada
8
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China
9
Institute of Environmental Physics, University of Bremen, 28359 Bremen, Germany
*
Author to whom correspondence should be addressed.
Received: 21 December 2018 / Revised: 24 January 2019 / Accepted: 30 January 2019 / Published: 6 February 2019
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Abstract

Phytoplankton in the ocean are extremely diverse. The abundance of various intracellular pigments are often used to study phytoplankton physiology and ecology, and identify and quantify different phytoplankton groups. In this study, phytoplankton absorption spectra ( a p h ( λ ) ) derived from underway flow-through AC-S measurements in the Fram Strait are combined with phytoplankton pigment measurements analyzed by high-performance liquid chromatography (HPLC) to evaluate the retrieval of various pigment concentrations at high spatial resolution. The performances of two approaches, Gaussian decomposition and the matrix inversion technique are investigated and compared. Our study is the first to apply the matrix inversion technique to underway spectrophotometry data. We find that Gaussian decomposition provides good estimates (median absolute percentage error, MPE 21–34%) of total chlorophyll-a (TChl-a), total chlorophyll-b (TChl-b), the combination of chlorophyll-c1 and -c2 (Chl-c1/2), photoprotective (PPC) and photosynthetic carotenoids (PSC). This method outperformed one of the matrix inversion algorithms, i.e., singular value decomposition combined with non-negative least squares (SVD-NNLS), in retrieving TChl-b, Chl-c1/2, PSC, and PPC. However, SVD-NNLS enables robust retrievals of specific carotenoids (MPE 37–65%), i.e., fucoxanthin, diadinoxanthin and 19 -hexanoyloxyfucoxanthin, which is currently not accomplished by Gaussian decomposition. More robust predictions are obtained using the Gaussian decomposition method when the observed a p h ( λ ) is normalized by the package effect index at 675 nm. The latter is determined as a function of “packaged” a p h ( 675 ) and TChl-a concentration, which shows potential for improving pigment retrieval accuracy by the combined use of a p h ( λ ) and TChl-a concentration data. To generate robust estimation statistics for the matrix inversion technique, we combine leave-one-out cross-validation with data perturbations. We find that both approaches provide useful information on pigment distributions, and hence, phytoplankton community composition indicators, at a spatial resolution much finer than that can be achieved with discrete samples. View Full-Text
Keywords: phytoplankton pigments; phytoplankton absorption; underway AC-S flow-through system; Gaussian decomposition; matrix inversion; singular value decomposition; non-negative least squares phytoplankton pigments; phytoplankton absorption; underway AC-S flow-through system; Gaussian decomposition; matrix inversion; singular value decomposition; non-negative least squares
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Liu, Y.; Boss, E.; Chase, A.; Xi, H.; Zhang, X.; Röttgers, R.; Pan, Y.; Bracher, A. Retrieval of Phytoplankton Pigments from Underway Spectrophotometry in the Fram Strait. Remote Sens. 2019, 11, 318.

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