POSTER Session 1

Emerging picture of bio-optical and ocean color characteristics of the Southern Ocean

Despite significant field activity over the past decades, bio-optical characteristics of the Southern Ocean (SO) waters are still insufficiently understood. This knowledge gap prevents an unambiguous interpretation of satellite ocean color observations in this critical region, with conflicting results as to whether the phytoplankton chlorophyll concentration (Chl) is properly estimated by satellite ocean color instruments. Here we synthesize results that our group has obtained on bio-optical properties of the SO, using data from the Antarctic Circumpolar Expedition (ACE; 2016/17) and the Southern Ocean Large Areal Carbon Export (SOLACE; 2020/21) voyage, combined with data from the BGC-Argo network. The main findings are: 1) lower Chl-specific phytoplankton absorption coefficients as compared to other oceans for the same Chl; 2) a larger contribution of non-algal particles to absorption for waters with Chl < ~0.2 mg/m3; 3) a larger contribution of colored dissolved organic matter to absorption as compared to what global models predict; 4) a particulate backscattering vs. Chl relationship consistent with global models except for Chl < ~0.2 mg/m3, where the relationship to Chl vanishes; 5) higher maximum photosynthetic rates per unit Chl south of the polar front as compared to lower latitudes of the SO; and 6) a general overestimation of satellite Chl for Chl <~0.2 mg/m3and conversely an underestimation above that threshold. In parallel, an analysis of 24 years of satellite ocean color observations was conducted to assess long-term Chl trends and to identify the main physical drivers of these changes.

David Antoine, Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Australia, and ARC Australian Centre for Excellence in Antarctic Sciences (ACEAS), University of Tasmania, Australia, https://orcid.org/0000-0002-9082-2395

Juan Li, Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Australia, and ARC Australian Centre for Excellence in Antarctic Sciences (ACEAS), University of Tasmania, Hobart, Australia

Md Rony Golder, Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Australia, and ARC Australian Centre for Excellence in Antarctic Sciences (ACEAS), University of Tasmania, Australia

Mingxing Cha, Chinese Antarctic Center of Surveying and Mapping, Wuhan University, China, and Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Australia

Yannick Huot, Centre d’Applications et de Recherches en Télédétection, Département de géomatique appliquée, Université de Sherbrooke, Canada,

Charlotte Robinson, Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Australia

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