Pacific Southern Ocean coccolithophore-derived particulate inorganic carbon (PIC): A novel comparative analysis of in-situ and satellite-derived measurements
Abstract. Polar plankton communities are already experiencing the impact of ocean acidification and global warming. Coccolithophores are the main type of calcifying phytoplankton in the Southern Ocean (SO) and they play a key role in the carbon cycle through the production of particulate organic, and inorganic carbon (PIC). Coccolithophores account for most of the optical PIC backscattering in the sea, so remote sensing is potentially an excellent monitoring tool. However, in situ measurements in the SO are sparse in space and time due to the harsh weather conditions.
Here, we combine micropalaeontology and remote-sensing to evaluate critical discrepancies between coccolithophore and satellite-derived PIC in the Pacific SO in non-bloom conditions. Plankton samples were collected from two latitudinal transects: from New Zealand to Antarctica (December 2004–January 2005) and across the Drake Passage (February–March 2016). Coccolithophore species specific PIC estimates were compared, based on 1) Scanning Electron Microscope cocolith morphometric analyses and 2) remote sensing PIC values acquired from NASA’s Ocean Color Web service. Considering that the SO is the cloudiest region on Earth (which limits the amount of satellite data available), in-situ and satellite-derived PIC datasets show very good agreement in both transects, particularly in the Subantarctic and Polar Front zones. Emiliania huxleyi morphogroup B substantially contributes to the sea-surface PIC content south of the Subantarctic Front in both transects, whereas E. huxleyi types A, A overcalcified, and other taxa (e.g. Calcidiscus leptoporus), only contribute to coccolithophore PIC in the northernmost stations.
Of particular interest are strong peaks in satellite-derived PIC south of the Polar Front, which do not show up in the coccolithophore data. We suggest that the high reflectance signal from this southernmost region (which could have been initially attributed to coccolithophores) may be due to the prevalence of small opal particles or unknown highly reflective particles (such as Phaeocystis aggregations or suspended sediment). Our observations highlight the importance of satellite products for estimating global PIC levels, while emphasizing the critical need for validation through field samples. This work contributes to our understanding of coccolithophore PIC dynamics in the “data desert” Pacific SO, offering valuable insights for both remote sensing applications and the broader field of marine science.
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