Retrieval of Phytoplankton Pigments from Underway Spectrophotometry in the Fram Strait

• Published in: Remote Sensing
• Main Authors: Yangyang Liu, Emmanuel Boss, Alison Chase, Hongyan Xi, Xiaodong Zhang, Rüdiger Röttgers, Yanqun Pan, Astrid Bracher
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2019
• Subjects: phytoplankton pigments; phytoplankton absorption; underway AC-S flow-through system; Gaussian decomposition; matrix inversion; singular value decomposition; non-negative least squares; Science; Q; Fram Strait
• Online Access: https://doi.org/10.3390/rs11030318; https://doaj.org/article/f9b9e4186c624af8a8c80065fb1e0836

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 ( <math display="inline"> <semantics> <mrow> <msub> <mi>a</mi> <mrow> <mi>p</mi> <mi>h</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>λ</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> ) 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 <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>′</mo> </msup> </semantics> </math> -hexanoyloxyfucoxanthin, which is currently not accomplished by Gaussian decomposition. More robust predictions are obtained using the Gaussian decomposition method when the observed <math ...