POSTER Session 2

ISLAND MASS EFFECT ON PHYTOPLANKTON PHYSIOLOGY USING IN-SITU VALIDATED REMOTE SENSING

Subtropical regions of the Pacific Ocean are among the most oligotrophic of the world’s oceans. The strong vertical stratification in these regions limits mixing and the associated nutrient enrichment of surface waters, resulting in low phytoplankton biomass year-round. In this context, interactions between island topography and prevailing wind and currents boost mixing in the vicinity and downstream of islands. This increased mixing, along with potential terrigenous inputs into the nearby ocean, often enriches the surface of the ocean in nutrient and trace metals, triggering spatial increases in phytoplankton biomass, a phenomenon known as the “island mass effects” (IME). Here we show a case study of a large IME detected around the Fiji archipelago using a combination of multiple satellite sensors data and in-situ continuous underway optical measurements. Beyond the biomass increase associated with the IME, the fluorescence quantum yield estimated from satellite data suggests an iron enrichment in the IME of Fiji consistent with an increase in iron concentration sampled in-situ. Metrics of physiological adaption of phytoplankton cells to light and nutrients limitation, as well as sea surface temperature measured underway and from remote sensing along a transect show evidence of an upwelling event close to the island’s shore, that likely contributed to this enrichment. These findings show the potential of remote sensing not only to detect the increase in chlorophyll concentration associated with IMEs, but also to identify some drivers of the nutrient enrichments that trigger phytoplankton blooms associated with IMEs.

*Guillaume Bourdin, University of Maine, School of Marine Sciences, USA, https://orcid.org/0000-0001-7608-5256

Emmanuel Boss, University of Maine, School of Marine Sciences, USA, https://orcid.org/0000-0002-8334-9595

Lee Karp-Boss, University of Maine, School of Marine Sciences, USA, https://orcid.org/0000-0003-2851-1921

Fabien Lombard, Sorbonne Université, Laboratoire d’Océanographie de Villefranche, France, https://orcid.org/0000-0002-8626-8782

Seth John, Department of Earth Science, University of Southern California, USA, https://orcid.org/0000-0002-8257-626X

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