SONAR-CO2 · Southern Ocean Nanoplankton Response to CO2

Southern Ocean Nanoplankton Response to CO2

The impact of anthropogenic ocean acidification on calcifying organisms is expected to be imminent, particularly in high latitude ecosystems. The Southern Ocean is responsible for about 40% of the global oceanic uptake of anthropogenic CO2 with much of the drawdown occurring in the Sub-Antarctic Zone or SAZ. This large inventory of anthropogenic CO2 makes this region an ideal setting to assess the response of marine calcifying plankton to increasing anthropogenic CO2 levels in their natural habitat. Indeed, there is evidence that the ongoing ocean acidification in the SAZ is already affecting the calcification of key calcifying plankton, such as planktonic foraminifera and pteropods. Coccolithophores, unicellular eukaryotic algae that secrete calcite plates (coccoliths; Figure 1), are the most abundant marine calcareous phytoplankton and play an important role in the marine carbon cycle by contributing to the oceanic pumps of organic matter and carbonate (Figure 2). The cosmopolitan coccolithophore Emiliania huxleyi is known to develop large-scale blooms in high latitudes systems where the production and shedding of coccoliths give the surface waters a milky-turquoise appearance allowing their detection from satellites. The Marie Skłodowska-Curie funded project Southern Ocean Nanoplankton Response to CO2 (SONaR-CO2) aims to shed light on the ongoing debate whether or not ocean acidification will lead to a replacement of heavily-calcified coccolithophores by lightly-calcified ones in subpolar ecosystems. SONaR-CO2 aims to answer the call by the European Project on OCean Acidification (EPOCA) and Southern Ocean Observing System (SOOS) for urgent and increased effort in research initiatives that address the impacts of ocean acidification on marine and coastal ecosystems and resources. Project Description Australian and New Zealand sediment trap programs were launched in the late ‘90s along two latitudinal transects (140°E and 178°E meridians). These collections represent the longest deep Southern Ocean time-series and provide an exceptional opportunity to examine the response of marine calcifying organisms to ocean acidification. In this project, cutting-edge and traditional microscopy techniques combined with biogeochemical analyses will be applied to the longest existing subantarctic time-series records and sediment samples from two sectors of the Southern Ocean in order to achieve the following objectives: 1. Detect changes in the calcification response of the dominant coccolithophore species Emiliania huxleyi in relation to changes in the CO2 concentration in the surface waters of the SAZ at different time scales. 2. Determine the diversity, abundance and temporal community changes of coccolithophores. 3. Estimate, for the first time, the partial contribution of coccolithophores to total carbonate export in the Subantarctic Zone. 4. Explore the potential impacts of environmental stressors on the biomarker signature of coccolithophores.

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