Plight of Pelagic Primary Producers in a Changing Marine Environment (P4)
An exciting location for the global climate system
In 2016, a team of international researchers led by chief scientists Ian Hall and Sidney Hemming, embarked on a two-month research expedition in the southern Indian Ocean onboard the JOIDES Resolution for the International Ocean Discovery Program (IODP) Expedition 361, Southern African Climates. The main aim of the expedition is to investigate past periods of major ocean and climate restructuring during the Pliocene and Pleistocene, to assess the role of the wider Agulhas Current system in shaping both regional- and global-scale ocean circulation and climate system development.
The Agulhas Current is an integral part of the global thermohaline circulation system because it acts as potential modulator of the Atlantic Meridional Overturning Circulation (AMOC) by transporting warm and saline water to the South Atlantic. As such, it has been suggested that the greater Agulhas Current system has major influence on the climate of the surrounding continents and the global climate system over at least the last 1.2 million years. However, the dynamics of this current system have not been explored past this timescale.
The sediment archives collected during Expedition 361 provides, for the first time, the potential to investigate the dynamics of this important current system during key time intervals beyond 1.2 million years, and explore its link to the regional and global climate evolution.
The P4 fellowship will combine biological, physical, and geochemical coccolithophore-derived datasets, focusing on the interval between 3.264 and 3.025 million years ago (the mid-Pliocene Warm Period), a time period considered to be the closest analogue for future warm climate. Through the generation of quantitative coccolithophore-based records, P4 offers multiple potential opportunities to address the role of the southern Indian Ocean in the Earth’s climate system and better assess the impacts of extreme climate events to the marine ecosystem.
Coccolithophores as paleoenvironmental tracers
Coccolithophores are marine, unicellular flagellate phytoplankton, belonging to phylum Haptophyta and division Prymnesiophyceae. Together with planktonic foraminifera and pteropods, they are considered the ocean’s most important suppliers of calcium carbonate in the water column and the seafloor. They are one of the most abundant phytoplankton groups, holding a vital position at the base of the food chain.
When the coccolithophore organism dies, its calcareous exoskeleton falls to the seafloor as aggregates (i.e., algal aggregates, faecal pellets, marine snow), and is preserved in sediments either as disaggregated coccoliths or as partially intact coccosphere. The fossil record of coccolithophores has been remarkably abundant and continuous since their first occurrence in the Late Triassic (230 million years ago) and constitutes a major part of deep-sea sediments since the Upper Jurassic.
The highly diverse morphology of coccoliths and coccospheres reflects the unique ecological strategies and environmental preferences of different coccolithophore groups. The particular environment is dominated by characteristic assemblages, which can be distinguished by their coccolith types and coccosphere morphology. For instance, placolith-bearing species (e.g., Emiliania huxleyi) are more often linked to eutrophic conditions in coastal and upwelling environments, while umbelliform taxa (e.g., Umbellosphaera tenuis) are more adapted to oligotrophic waters of the mid to low latitude. The floriform species Florisphaera profunda is typified to dominate assemblage of the deep photic layer whereas the motile group (e.g., Helicosphaera carteri) is found in mesotrophic environments.
Coccolithophores and the biogeochemical cycle
Coccolithophores are unique among other marine primary producers because they utilise carbon for both photosynthesis and calcification. As primary marine calcifiers, they play a crucial role in the global biogeochemical carbon cycle, because they can influence both the organic (photosynthesis) and inorganic (calcification) carbonate pumps.
Photosynthesis reduces aqueous carbon dioxide concentrations in the upper photic zone by converting carbon dioxide to organic compounds, whereas calcification increases atmospheric carbon dioxide concentrations of the surface waters and the atmosphere by the production and export of calcite plates (coccoliths).
The project team
This research was made possible through the support of the following organisations: European Union’s Horizon 2020 Research and Innovation Programme Marie Sklodowska-Curie Actions Individual Fellowship