Carbonate Counter Pump in the Southern Ocean: who is driving carbonate production and export?

Overview

The production of calcium carbonate (CaCO3) by marine calcifying plankton causes CO2 to be released and generates an export of Particulate Inorganic Carbon (PIC) to the deep ocean. This mechanism, known as the Calcium Carbonate Counter Pump because, it is opposite to the process driving the Biological Carbon Pump (where CO2 is consumed by phytoplankton, leading to a drawdown of CO2 and export of Particulate Organic Carbon (POC)). Thus, to determine the capacity for the ocean to store CO2 and how this mechanism can change within a changing climate, it is crucial to understand the dynamics of PIC vs. POC. The extent of carbonate precipitation depends on the composition of calcifying plankton within the plankton community. In the Southern Ocean (SO), calcifying plankton are often very abundant and can dominate carbonate fluxes. The sensitivity of the SO to the intensification of Ocean Acidification has recently highlighted the importance of understanding the process regulating the carbonate production and export in this region.

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Image Captions

Calcifying plankton (pteropods) collected with a sediment trap in the Southern Ocean deployed at 2000m depth. Image curtesy of C. Manno

Methodology

The goal of the project is to assess the contribution of each part of the plankton calcifying community (pteropods, foraminifera, coccolithphores, ostracods) to the strength of the carbonate pump in the SO at different oceanic sites (i.e. naturally iron-fertilised region, polynya, iron-limited region). The student will use a combination of BAS archived samples collected from ship activities (e.g. plankton net) and moored platforms (e.g. sediment traps, water collectors, phytoplankton collector, pCO2 sensors) to determine the seasonal cycle in carbonate production and export. The assemblage and abundance of calcifying plankton will be investigated by plankton nets and collectors (Year 1) and their contribution to carbon export by sediment traps deployed on floating and mooring stations at the sites (Year 2). The strength of the carbonate counter pump (expressed as reduction of the CO2 drawdown by the biological pump) will be estimated by combining carbonate chemistry and biogeochemical analysis (Year 3) with results from (Year 1-2).

Project Timeline

Year 1

The student will analyse samples from the BAS archives (plankton collectors deployed on mooring platforms over the year and plankton nets). The student will measure the concentration of the plankton calcifies (pteropods, ostracods, foraminifera, coccolithophores). The organisms will be characterised in term of species abundance, size and life stage using different microscope techniques (Light microscope, Scanning Electron Microscope (SEM), Zooscan)

Year 2

The student will use floating and moored sediment trap samples, from the BAS archives, to measure the biogeochemical components of the flux (PIC, Particulate Inorganic Carbon; POC, particulate Organic Carbon) using a CHN auto-analyser. The carbonate contribution of calcifying plankton will be assessed in term of biomass and sinking rates. Sinking rates of shells will be performed under different hydrological and chemical water condition to simulate the influence of seasonal environmental variability. First results will be presented at a national conference.

Year 3

The student will determine the seasonal variability in the carbonate chemistry. She/he will analyse water samples collected from devices deployed on the mooring platforms (Aquamonitor and pCO2 sensors). The trend of total alkalinity (TA) and dissolved inorganic carbon (DIC), over the year will be determined using potentiometric titration and a coulometer technique. The student will participate to an international conference to present thesis results.

Year 3.5

The last 6 months will focus on finalising the writing up of thesis chapters.

Training
& Skills

This project will be linked to the NERC-funded PICCOLO project, allowing the student to interact with the UK Antarctic research community. At BAS, the student will learn to use a range of mooring devices/collectors. She/he will get skills in plankton identification and on high resolution imaging techniques (SEM and Zooscan). At St. Andrews the student will learn foraminiferal taxonomy, calcification and morphometrics characterization. The student will develop skills in carbonate chemistry (UEA) and POC, PIC (BAS) analysis. The student will work on BAS archived samples and she/he will develop ability to manage long data set and data interpretation. There could be an opportunity to participate in an Antarctic cruises (via PICCOLO project or BAS survey) for which the student will receive training in sea-survival and field-laboratory health and safety.

References & further reading

• Manno et al. (2018) Threatened species drive the strength of the carbonate pump in the northern Scotia Sea. Nature Communications, 9. 7 pp. 10.1038/s41467-018-07088-y
• Buitenhuis et al. (2019), Large Contribution of Pteropods to Shallow CaCO3 Export , Global Biogeoc hemical Cycles, 33, 458-468, https://doi.org/10.1029/2018GB006110

• Manno et al. (2015) The contribution of zooplankton faecal pellets to deep carbon transport in the Scotia Sea (Southern Ocean). Biogeosciences, 12. 1955-1965. 10.5194/bg-12-1955-2015
• Salter et al., (2014) Carbonate counter pump stimulated by natural iron fertilization in the Polar Frontal Zone, Nature Geoscience, https://doi.org/10.1038/ngeo2285

• Treguer et al. (2018) Influence of diatom diversity on the ocean biological carbon pump, Nature Geoscience, https://doi.org/10.1038/s41561-017-0028-x

Further Information

Clara Manno, clanno@bas.ac.uk, 01223 221400

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