POSTER Session 2

RELATIONSHIP BETWEEN PHYTOPLANKTON CARBON AND OPTICAL PROPERTIES IN OLIGOTROPHIC WATERS OF EASTERN INDIAN OCEAN

Particulate backscattering (bbp) and beam attenuation (cp) coefficients co-vary with the concentration of particles in oceanic waters. The correlation between these optical parameters and particulate organic carbon (POC) offers a basis to estimate phytoplankton carbon (Cphyto) across spatial and temporal scales that are beyond the reach of conventional sampling techniques. However, variable relationships between optical proxies and Cphyto have been reported in previous studies. During a 2019 research voyage revisiting the 110° E meridian as part of the second International Indian Ocean Expedition, we collected POC samples and simultaneously measured bbp and cp at 20 stations in mostly oligotrophic waters. The POC ranges from about 6 mg/l at the surface within the Indian subtropical gyre to 124 mg/l in the deep chlorophyll maxima. We examined several existing approaches for estimating Cphyto using optical measurements or Chl. This included refining the correlation between POC and bbp and between bbp and cp. Additionally, we investigated how the relationship between POC and cp varies with the phytoplankton community composition and its impact on the bbp variability. We also conducted a validation exercise comparing satellite-derived POC (MODIS-Aqua instrument) with in situ POC at the surface along the track. The result shows a good correlation (R2 = 0.72) with an overestimate of satellite POC values by up to 10%.

Chandanlal Parida, Curtin University, Australia, https://orcid.org/0000-0003-4258-1440

David Antoine, Curtin University, Australia

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