17:15–17:30 | ABSTRACT 1118
BIO-OPTICAL INDICATORS OF DIATOMS IN THE OLIGOTROPHIC NORTH PACIFIC SUBTROPICAL GYRE: IMPLICATIONS FOR REMOTE SENSING
The North Pacific Subtropical Gyre (NPSG) is an oligotrophic ecosystem largely driven by the diversity and activity of picoplankton. The Hawai’i Ocean Time-series (HOT) is a sentinel time-series for this region, having sampled Station ALOHA (22.75°N, 158°W) since 1988. Although dominated by picoplankton, episodic diatom blooms, often containing endosymbiotic diazotrophs, generate an annual summer export pulse of biogenic silica that fuels deep-ocean carbon sequestration. Rare but impactful, these large cells disproportionately shape the ecosystem. The hyperspectral capabilities of NASA’s PACE mission provide an opportunity to resolve phytoplankton community composition in oligotrophic waters, where traditional algorithms often fail. Since May 2024, we have collected in situ measurements during PACE satellite overpasses at Station ALOHA, including hyperspectral phytoplankton absorption, HPLC pigment concentrations, and IFCB cell imaging. Results show that bulk absorption spectra exhibit statistically significant seasonal differences, with enhanced summer magnitudes corresponding to ~70× higher IFCB-derived diatom biovolume and elevated HPLC fucoxanthin concentrations, indicating a shift towards diatom-dominated communities. In contrast, winter conditions reflect picoplankton dominance. Spectral deconvolution of bulk phytoplankton absorption resolves pigment-specific contributions to diatoms with modeled fucoxanthin closely tracking independently measured HPLC concentrations. By applying these methods over multiple years, we will demonstrate that diatom-specific optical signatures can be quantitatively resolved from bulk hyperspectral absorption in oligotrophic waters. This provides a framework for linking ocean color observations to phytoplankton community structure, advancing the development of hyperspectral algorithms, and improving our ability to detect biologically driven carbon export processes from space in the planet’s bluest waters.
Paige Dillen*, University of Hawai’i at Manoa, [email protected], https://orcid.org/0009-0003-1595-072X
Angelicque White, University of Hawai’i at Manoa, [email protected], https://orcid.org/0000-0002-0938-7948
Fernanda Henderikx-Freitas, University of Hawai’i at Manoa, [email protected], https://orcid.org/0000-0002-4422-1396
