Oral Session 11

Unique bio-optical properties and community composition of west Antarctic Peninsula phytoplankton: optical distinctiveness in a polar environment

In the west Antarctic Peninsula, where terrestrial sources of sediments or CDOM are largely absent, extreme cold-adapted phytoplankton (psychrophiles) with relatively low species diversity represent a distinctive particle population with unique bio-optical properties differing from relationships found in the global ocean. Phytoplankton in this region show a seasonal succession from large diatoms in spring to cryptophytes in summer to smaller diatoms in fall, with additional episodic blooms of haptophyte Phaeocystis antarctica and a smaller background population of mixed flagellates. Unique absorption and backscattering features are associated with the relative abundance of these different groups. This work evaluates the success of satellite-derived Chl-a algorithms and our understanding of why traditional algorithms underestimate in situ Chl-a by a factor of two in coastal Antarctic waters. Mechanisms include pigment packaging, phytoplankton physiology in extreme cold temperatures, less non-plankton particulate backscattering (e.g., less sediments, detritus, and bacteria), and low concentrations of CDOM. This work identifies major phytoplankton groups’ relative abundances and explores the bio-optical properties contributing to the factor of two difference using an in situ optical dataset collected in 2021-2024, with concurrent IFCB imaging, HPLC pigments, QFT-ICAM filter pad hyperspectral absorption spectra, and above-water hyperspectral reflectance spectra (handheld at point locations and automated/robotic underway). These results will improve our understanding of the bio-optical characteristics that make Antarctic phytoplankton unique in the global ocean and enhance satellite detection of phytoplankton community composition in Antarctic coastal ecosystems.

Jessica Turner, University of Connecticut, USA, https://orcid.org/0000-0003-3392-0316

Michael Cappola, University of Delaware, USA

Hilde Oliver, Woods Hole Oceanographic Institution, USA, https://orcid.org/0000-0002-5507-3333

Oscar Schofield, Rutgers University, USA, https://orcid.org/0000-0003-2359-4131

Heidi Dierssen, University of Connecticut, USA, https://orcid.org/0000-0003-4276-5530

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