Submesoscale Biogeochemistry in the EAC

Supervisors

Pete Strutton, UTas

Christina Schallenberg, CSIRO

Tamara Schlosser, UTas

Quantifying the submesoscale biogeochemical variability across fronts associated with East Australian Current eddies

Project description

The East Australian Current (EAC) is one of Australia’s strongest and most important ocean currents, flowing south along the densely populated east coast to ~32°S where it forms large (~150 km diameter) mesoscale eddies. Eddy interactions can cause sharp temperature and velocity fronts to form between eddies that drive small-scale processes with horizontal scales of ~1-10 km. These submesoscale processes strongly impact the 3D dispersion of biogeochemical (BGC) tracers, and frontal instability can lead to subduction of surface waters (Levy et al., 2018).

The goal of this project is to quantify the biogeochemical fluxes and processes associated with fronts in the EAC eddy system, and to characterize the distribution of biogeochemical tracers across fronts. Using data from a research voyage aboard RV Investigator in October 2023, the student will examine biogeochemical variability across and within fronts, including the prevalence of subduction events. BGC tracers will help constrain subduction velocities, and underway measurements will allow characterization of biogeochemical properties across fronts (Archer et al., 2020; Freilich & Mahadevan, 2021). The student will constrain nutrient fluxes associated with fronts, which will put chlorophyll concentrations and estimates of primary productivity into context. The influence of horizontal advection on chlorophyll concentrations will also be considered. Ultimately, the project will determine the extent to which frontal processes drive phytoplankton productivity in the EAC system. This PhD project is a contribution to a multi-institutional ARC Discovery Project with collaborators at UNSW and BoM.

Key research topics/chapters

1. Evaluation of biogeochemical variability across fronts associated with EAC eddies, including phytoplankton community composition
2. Fronts as hot spots of primary productivity: quantify the relative contribution of in situ (vertical) processes compared to horizontal processes (advection)
3. How common are subduction events at fronts, and what are the conditions that cause them? What is the fate of the subducted organic material?

Suggested reading:

Archer et al. (2020); doi 10.1175/JPO-D-19-0131.1

Malan et al. (2020); doi 10.1029/2019JC015613

Freilich & Mahadevan (2021); doi 10.1029/2020JC017042