POSTER Session 1

Absorption spectra of phytoplankton in the UV: A simple parametrization to include variations caused by Mycosporine-like Amino Acids (MAAs)

Observations by the Plankton, Aerosol, cloud Ecosystem (PACE) mission provide unprecedented opportunities to improve satellite-based ocean products retrievals. The main objective of PACE measurements in the Ultra-Violet (UV) is to retrieve properties of Colored Dissolved Organic Matter (CDOM). An important assumption made for these retrievals is that oceanic absorption in the UV is dominated by variations in CDOM. However, phytoplankton absorption (aph) spectra also vary substantially in the UV, and these variations cannot be modeled in terms of Chlorophyll-a concentration [Chla] like in the visible (VIS). It is therefore critically important for CDOM retrievals from PACE to also understand and model coinciding variations of aph in the UV. We analyzed hundreds of UV-VIS aph spectra from the 2006 IOCCG dataset and from four cruises that cover polar, subtropical, and tropical ocean waters. Our analyzes show that (1) the UV variations of aph spectra cluster around three distinct UV wavelength bands; (2) the UV bands correlate with absorption spectra of Mycosporine-like Amino Acids (MAAs); (3) the UV variations can be modeled using the Kramers-Kronig relationships. We used these results to construct a three-parameter model for absorption by MAAs in the UV-VIS. We also extended the VIS heritage [Chla]-based model for aph (Bricaud et al., 1998) down to 350 nm. Combining our MAA and [Chla]-based models, we show that UV-VIS aph spectra can be reproduced with root-mean-square error (RMSE) values that match the RMSE values obtained by the heritage model for VIS aph spectra.

Jacek Chowdhary, Columbia University and NASA Goddard Institute for Space Studies, USA, https://orcid.org/0000-0002-5824-2163

Toshiro Tokunaga, Santa Monica College, USA

Kendra Herweck, Cleveland State University, USA

Anna Wadhwa, Massachusetts Institute of Technology, USA

Dariusz Stramski, Scripps Institution of Oceanography, USA

Rick A. Reynolds, Scripps Institution of Oceanography, USA

Matteo Ottaviani, Terra Research Inc, USA

Snorre Stamnes, NASA Langley Research Center, USA

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