Coccolith mass variability and contribution to carbonate production of coccolithophores in the Southern Ocean: modern versus fossil assemblages

The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities.

Coccolithophores, unicellular algae that secrete calcite plates (coccoliths), develop extensive blooms associated to the major Southern Ocean fronts during summer. Changes in coccolithophore abundance, composition and degree of calcification may potentially impact the entire marine ecosystem and ocean chemistry, ultimately affecting the climate. 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.

We present here early results from the recently launched SONAR-CO₂ project. Cutting-edge and traditional microscopy techniques combined with biogeochemical analyses are being applied to Southern Ocean time-series records and sediment samples to characterize and quantify coccolithophore assemblages and evaluate their response to increasing CO₂ levels during the industrial era.