PhD opportunity on Southern Ocean biological pump, University of Tasmania, Hobart, Australia

Project: Southern Ocean biological pump, application of Thorium-230 to quantify the biological pump in the Southern Ocean

The ocean’s biological carbon pump is a key component of the earth’s carbon cycle and climate. Changes in the operation of the biological carbon pump impact atmospheric carbon dioxide concentrations and therefore climate. One major uncertainty is the depth to which organic carbon is exported before being degraded, or remineralised, back to dissolved inorganic carbon, and how this varies spatially and is regulated by factors such as temperature, oxygen and community composition. Observational constraints on how much sinking carbon reaches different ocean depths are needed to resolve this uncertainty, particularly in the poorly sampled Southern Ocean.

The biological pump in the Southern Ocean is inefficient due primarily to iron limitation. Despite this poor efficiency, the amount of carbon exported in the Southern Ocean is high, representing ~25% of carbon exported via the biological carbon pump. Large zonal gradients in phytoplankton community composition across the Southern Ocean, coupled with its importance on the global scale, make the Southern Ocean a key focus for studies of the biological carbon pump.

This PhD project will quantify carbon export as a function of depth in the Southern Ocean using a relatively new method based on the radioisotope Thorium-230. Samples collected along a zonal transect in the Indian Ocean, from Perth to Antarctica, will be the primary focus, supplemented by samples collected in the Subantarctic zone and the Antarctic slope. There may be opportunities for the student to participate in research voyages to collect new samples. Note that there is some flexibility in the direction of this project. For example, depending on student interest and aptitude this project could include a component of modelling or model-data comparison. Alternatively, a slight variation of the same Th-based approach can be used to estimate dust fluxes, and estimates of dust flux could be compared to estimates of carbon export.

Deadline for applications: 1 February 2024

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