PHD PROJECTS

The impact of Antarctic sea ice on simulated Southern Ocean watermasses

Abstract

Despite being only 6% of the global ocean’s surface area, the Southern Ocean dominates the ocean’s absorption of anthropogenic heat and carbon (Frolicher et al., 2015), with critical implications for the planet’s response to increased greenhouse gas emissions. Absorbing this heat and carbon, and locking it away in the deep ocean, relies on a complex interplay of wind and buoyancy forcing that drives exchanges of sea water between the surface and deep ocean, that is poorly understood. There is strong evidence that Antarctic sea ice is an important factor in this process, by forcing surface salinity changes in the polar Southern Ocean (Abernathey et al., 2016, Haumann et al., 2016).

How well these processes are represented in coupled climate models, such as those used by the IPCC, and how that impacts global climate projections has not been explored. We do know, however, that climate models show a wide spread in how they represent Antarctic sea ice process (Schroeter et al., 2018) and Southern Ocean watermasses (Sallee et al., 2013).

In this project, the student will explore how Antarctic sea ice, and in particular its role in transporting fresh water from the Antarctic coastline to the open ocean, affects how well climate models in the latest Coupled Model Intercomparison Project (CMIP6) represent the major Southern Ocean water masses. Furthermore, the student will quantify how this relates to simulated ocean heat and carbon uptake under current and future climate conditions, and the resulting implications for global climate sensitivity.

Primary Supervisor

Will Hobbs

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Will.Hobbs@utas.edu.au 

Frontal variability of the Antarctic Circumpolar Current

Abstract

The Antarctic Circumpolar Current (ACC) plays a major role in regulating the transport of heat between the lower latitudes and Antarctica and in and out of the ocean depths. The ACC has multiple substructures and fronts. Over the last decades, several studies have investigated the variability and shifts of these fronts with variable answers. Some studies reported large southward shifts of the fronts by using reference dynamic topographic levels as proxy to frontal position other studies find no significant shifts.

This project will investigate the dynamics of the Antarctic Circumpolar Current variability and change circumpolar-wise over the last few decades. The objectives are to update and improve the monitoring of the ACC fronts to better characterize the changes and the drivers of these changes.

Primary Supervisor

Annie Foppert

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Annie.Foppert@utas.edu.au

Tidal melting of Antarctic ice shelves since Last Glacial Maxiumum

Abstract

During the Last Glacial Maximum (LGM) ice sheets were substantially increased in size compared to present day, resulting in sea levels lower by 120-130m globally. Modelling suggests this reduction in ocean volume resulted in dramatic increases in ocean tide amplitudes (Arbic et al., 2004; Egbert et al., 2004; Griffiths and Peltier, 2008; Griffiths and Peltier, 2009) with consequently increased tidal current speeds. Tidal currents are now known to play an important role in present-day basal melting of Antarctica’s ice shelves (Makinson et al., 2011; Mueller et al., 2012). The interaction between the Antarctic ice sheet and tidal currents during and after LGM has not yet been examined.

The project aims to develop our understanding of what caused the ice sheet retreat since the Last Glacial Maximum. It will test the hypothesis that large tidal currents resulted in enhanced tidal melting of the ice shelves and this varied over time.

Primary Supervisor

Chen Zhao

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Chen.Zhao@utas.edu.au 

Understanding the role of micronekton in the export of carbon in the Southern Ocean

Project 7: Krill & Ecosystems
Abstract

Carbon sequestration is the long-term storage of carbon on land and in the ocean. In the ocean, the biological gravitational pump was thought to be solely responsible for the transport of carbon from the surface waters to depth. However, it is now recognised that other processes are involved including particle injection via midwater biota. An important, yet understudied, component of this is the mesopelagic migrant pump which can lead to substantial amounts of carbon being actively transported to mesopelagic depths through the vertical migration of micronekton. Micronekton are free-swimming, taxonomically diverse, pelagic animals around 2-20 cm in size and comprise of some of the most abundant animals in the oceans. Micronekton contribute to the transport of carbon by feeding in the shallows and egesting C rich faeces in the deep. However, little is known about exactly how much carbon they transport.

This project aims to investigate the role micronekton play in sequestering carbon in the Southern Ocean. By linking ecosystem studies and biogeochemistry the successful student will use data and samples collected during the AAPP 2020/2021 SOLACE voyage to quantify carbon export by micronekton in the Southern Ocean. These data will be used as input into a carbon flux model for the Southern Ocean. Critically, this work will better link Southern Ocean midwater ecology and biogeochemistry.

Primary Supervisor

Philip Boyd

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Philip.Boyd@utas.edu.au

Modelling trends in atmospheric composition

Project 1: Atmosphere
Abstract

In this project, the candidate will use Australia’s state of the art chemistry-climate model to simulate multi-decadal trends in atmospheric composition. In particular, it is now possible to constrain the recent histories of a range of atmospheric constituents using ice core records of hydroxyl, dust, organic carbon, black carbon and methane-sulfonic acid to give new insight to a range of research questions around atmospheric composition.

Global climate models including the Australian Community Climate and Earth System Simulator (ACCESS) are being developed and improved at a rapid rate. A better understanding of how models simulate atmospheric composition over long time periods is needed to ensure we are producing realistic future projections exploring the state of the earth system. Complex climate models, commonly referred to as earth system models, increasingly include a complete representation of atmospheric chemistry in addition to detailed aerosol representation. Understanding how well we are simulating primary aerosol such as dust, black carbon or organic carbon, as well as secondary aerosol such as methane-sulfonic acid and the species that are required for its oxidation (eg. hydroxyl), is an important step towards ensuring that the next generation of earth system models appropriately represent these key species, and their role within the earth system.

Primary Supervisor

Sonya Fiddes

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Sonya.Fiddes@utas.edu.au 

Investigating Southern Ocean meridional fluxes from ARGO within the framework of a time-varying Gravest Empirical Mode climatology of watermass properties

Project 4: Oceans
Abstract

Changes in the Southern are substantial and widespread (Bindoff et al. 2019) and different to other regions (Meredith et al 2019). In order to quantify change, we generally calculate deviations of property values from a long-term average constructed on a latitude-longitude grid (e.g. World Ocean Atlas). In the Southern Ocean, the Antarctic Circumpolar Current fronts are constantly moving in response to instabilities that generate eddies along their path, and meanders due to interaction of the currents with the rough sea floor. Thus, any given location in the path of the ACC, could at one time be found north of a front, south of a front, or directly in its path. Constructing an average that combines all of these occurrences results in a climatology that does not resolve the rich frontal structure and instead smears the properties and adds noise to any analysis of variability.

An elegant solution to this problem is the Gravest Empirical Mode (GEM) climatology (Sun and Watts 2001, Watts et al. 2001, Meijers et al. 2011). As well as long-term time-evolving trends, the GEM can be combined with satellite sea surface height measurements (1992-present) to construct daily-varying maps of the Southern Ocean’s 3-D watermass property structure, known as SatGEM. The existing SatGEM of temperature and salinity (Meijers et al. 2011) has been used to trace transports, meridional heat fluxes, eddy mixing and stirring, eddy tracking and finally to document the changing state of the Southern Ocean (Meijers et al, 2012).  We now have vastly more data in the Southern Ocean thanks to the Argo profiling float array (Wijffels et al. 2016), the SOCCOM biogeochemical float array (SOCCOM) and instrumented seals  (Seal Data) in addition to recent field programs providing high-resolution observations at locations where current-topography interactions are strong (Kerguelen Plateau, Macquarie Ridge, Drake Passage). Interpreting these new data requires a new SatGEM that is updated and refined for new applications including biogeochemical cycling and circulation change.

Primary Supervisor

Nathan Bindoff

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email N.Bindoff@utas.edu.au 

Modelling downward carbon flux in the Southern Ocean: linking ocean midwater ecology and biogeochemistry

Project 7: Krill & Ecosystems
Abstract

The oceans act as major sinks of atmospheric carbon. The biological pump is the ocean’s biologically driven carbon sequestration system. It has several key pathways for sequestering carbon (e.g., gravitational pump and particle injection via diverse groups of midwater biota), however, understanding these pathways and their interactions is not easy and therefore has seldom been attempted. Often the models designed to quantify downward particulate carbon flux in the oceans lack information on key pathways and their parameterization may only focus on a limited number of these conduits. Development of a holistic model which links these ecological and biogeochemical pathways will provide a much more comprehensive and accurate picture of downward particulate carbon flux across the oceans. Such a model will enable researchers to track the oceans’ ongoing ability to sequester carbon in response to climate change.

As part of the the Joint Exploration of the Twilight Zone Ocean Network (JETZON, https://www.jetzon.org/) initiative the AAPP 2020/2021 SOLACE voyage aimed “to improve water column measurements of the downward export flux of carbon of the biological pump using an integrated suite of new technological advances from particle decomposition to mesopelagic vertical migration”.

Primary Supervisor

Philip Boyd

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Philip.Boyd@utas.edu.au

Understanding the ice-ocean interaction in Wilkes Land, Antarctica

Project 3: Ice Shelves
Abstract

In the past decade, the main mass loss in the East Antarctica was dominated by the Wilkes Land, which was attributable to the increases in ocean-induced basal melt. The two largest areas at risk of rapid retreat in the Wilkes Land are the Aurora and Wilkes marine subglacial basins, which together hold 6-8 m of potential global sea-level rise in regions grounded below sea level. Increases in ice‐ocean heat exchange have the potential to induce substantial ice shelf mass loss through the ice shelf thinning and consequently lead to the rapid changes in grounded-ice flux (Gudmundsson et al., 2019). However, this effect has not been quantified in the context of current ice mass loss in Wilkes Land. Lack of data and limitations in modelling has made it challenging to quantify the importance of ocean-induced changes in ice shelf thickness as a driver for ongoing mass loss. This PhD will focus on modelling the ice ocean interaction of the Wilkes Land system with a coupled ice sheet ocean model in an attempt to better understand the correlation between potential ocean thermal forcing and observed ice loss and retreat and find the evidence for ocean-induced melt being a driver for the ongoing mass loss. The candidate will choose one of the subglacial basins or the whole Wilkes Land system as the research region and construct a coupled ice sheet ocean model for it. Analysis of the model output will also be used to predict the behaviour of glaciers on Wilkes Land and estimate its potential contribution to sea level rise.

Primary Supervisor

Chen Zhao

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Chen.Zhao@utas.edu.au

Deriving accurate sea-ice (and snow) thickness near-real time estimates for the East Antarctic region

Project 6: Sea Ice
Abstract

The seasonal evolution of the ocean-atmosphere exchange at the surface of the Southern Ocean gives rise to the formation, advection, deformation and melt of Antarctic sea ice. While  observations are scarce, the existing measurements revealed substantial spatio-temporal variability in ice concentration and also ice thickness. Much of our information is based on passive-microwave derived two-dimensional measurements of the ice cover. More recently laser and radar altimetry have been supported on polar-orbiting satellites, opening possibilities to translate those into sea-ice freeboard and finally ice thickness.

This project will use remote sensing data from NASA’s ICESat-2 laser and ESA’s CryoSat-2 radar altimeter, and assess these together with in situ observations to derive the East Antarctic sea-ice thickness distribution. To do so, information on snow depth over the sea ice will also be quantified.

Primary Supervisor

Stuart Corney

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Stuart.Corney@utas.edu.au

Impacts of carbonate chemistry and trace metal perturbations related to ocean alkalinity enhancement on Southern Ocean plankton communities

Project 7: Krill & Ecosystems
Abstract

Keeping global warming below 2°C will require rapid carbon dioxide (CO2) emission reductions. Additionally, 100-900 gigatons of CO2 must be removed from the atmosphere by the end of the 21st century using a range of negative emission technologies (NETs). One of the most promising NETs is to accelerate natural rock weathering, whereby suitable rocks are extracted, pulverised, and dispersed over land and the oceans (known as “Enhanced Weathering” or “Ocean Alkalinity Enhancement”). CO2 is chemically absorbed in this process, and safely stored mainly as bicarbonate in the oceans for geological timescales. However, the desired consumption of atmospheric CO2 would inevitably be accompanied by release of mineral dissolution products. Gigatons of alkalinity, silicate, and dissolved metals would end up in the oceans, and these large-scale perturbations of seawater chemistry could substantially disrupt marine ecosystems – potentially more than climate change itself.

The Southern Ocean has recently been identified as a hot spot for Alkalinity Enhancement, due to its unique chemical and physical conditions that make increasing CO2 absorption at least twice as efficient as in the polar North Atlantic, for example. Furthermore, biological productivity in the Southern Ocean is limited by iron, and potentially other trace metals, so that large-scale trace metal perturbations associated with ocean alkalinity enhancement would likely affect productivity and ecosystem structure.

This project aims to identify the vulnerability of Southern Ocean plankton communities to perturbations associated with ocean alkalinity enhancement. These are mainly carbonate chemistry perturbations (increasing pH), trace metal enrichment and potentially silicate fertilization.

The overarching goal is to understand how these perturbations individually and/or combined will (i) change the physiological performance of key Southern Ocean phytoplankton species, (ii) affect higher trophic levels such as krill or copepods who feed on phytoplankton, and (iii) change the composition of Southern Ocean phytoplankton communities.

Primary Supervisor

Lennart Bach

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Lennart.Bach@utas.edu.au

Use of biomarkers to trace how changing sea-ice affects the ecological roles of krill and zooplankton in the Southern Ocean

Project 7: Krill & Ecosystems
Abstract

Studies have estimated rapid decline in sea-ice coverage over many regions of Antarctica as well as increasing variability in the timing and duration across all seasons. These changes have implications for ecosystem structure and function, particularly due to freshening and warming that is also occurring. There is a sense of increasing urgency to identify and quantify how species utilise and depend on this this habitat given these patterns of rapid change. Sea-ice is a critical habitat to several polar organisms, including zooplankton grazers and Antarctic krill (Euphausia superba) that form direct energy links between primary producers and higher order predators. Sea-ice algae has been shown to be an essential food source for spawning and early developmental stages of copepod species. Given the prospect of more ice-free days in summer, identifying how krill and zooplankton grazers use sea-ice habitat is crucial to understanding responses to changes in sea-ice seasonality and coverage. While krill are widely known to use sea-ice for refuge there remains considerable debate about the suitability and importance of the habitat as a feeding ground.

Newly emerging and novel biotracers, called highly-branched isoprenoids (HBIs), are showing promising results in attempts distinguish between ice algae and phytoplankton, as a reliable means to characterise primary food sources for grazers. While this method has been applied to Antarctic grazers the results are preliminary and there has been no attempt to undertake a systematic appraisal of its utility as a monitoring tool for krill and zooplankton grazers over seasonal and annual cycles. Use of stable isotopes (SIA) as biomarkers will be encouraged to supplement HBI analyses to characterise grazing activity and trophic relationships among different grazing species. Using multiple biomarkers, this project will seek ways of developing rapid and reproducible methods for describing krill and zooplankton feeding over extended spatial and temporal scales. This research aims to contribute ecological data towards a sustainable long-term monitoring plan being developed for the spatial management of the krill fishery throughout the marginal ice zone of East Antarctica.

Primary Supervisor

Christine Weldrick

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Christine.Weldrick@utas.edu.au

Robust estimates of Antarctic ice sheet melt

Project 3: Ice Shelves
Abstract

Ocean-driven Antarctic mass loss is a large source of uncertainty in future sea level rise. To date, there has been no broad-scale comparison and evaluation of mass loss predictions from ocean-ice sheet interaction models. This project will analyse data from a range of circum-Antarctic ocean models, assessing their performance in matching observed ice-shelf melt rates over a range of spatial and temporal scales, with a first focus on the Amery Ice Shelf that has been substantial Australian-based focus of research over the last two decades. This project will contribute to the WCRP-supported Realistic Ice-sheet/Ocean State Estimates (RISE) project.

This PhD project will build on initial data collation and analysis undertaken under RISE by an AAPP postdoc. Beyond simply examining where models agree and disagree, this project will:

  • Incorporate a broader dataset to assess the impact of oceanographic context on model performance
  • Assess whether the models agree in trend and variability of melt and develop new understanding of the sensitivity of melt to ocean forcing.
  • Provide robust evaluation against observational data from both satellite and in situ methods (e.g. autonomous radar)

The candidate will develop skills in data handling, spatial and statistical analysis. A successful completion will improve our ability to assess the models used to predict future sea level rise.

Primary Supervisor

Sue Cook

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Sue.Cook@utas.edu.au

Modelling climate change impacts on Antarctic ecosystems using an end-to-end ecosystem model

Project 7: Krill & Ecosystems
Abstract

Antarctic marine ecosystems provide ecosystem services that are important on a global scale, and there is a strong imperative to understand and predict the responses of these systems and services to current and future climate change. Atlantis is a 3D, spatially explicit trophodynamic ecosystem model that integrates biology, physics, chemistry, and human impacts (e.g., the effects of fishing on ecosystem structure) to provide a synoptic view of marine ecosystems. An implementation of the Atlantis end-to-end ecosystem model has been developed through collaboration by partner-agencies AAD and CSIRO (though the previous ACE CRC) led by Dr Melbourne-Thomas. This East Antarctic model focuses on the Australian Antarctic Territory and adjacent East Antarctic sector of the Southern Ocean. The model inputs are assembled, and the model is running but requires calibration and deployment for scenario evaluation and validation. This model represents a powerful tool to look at across-food web responses to simulation of altered Southern Ocean conditions. This project is closely aligned with the Antarctic Science Strategic Plan, addressing key research areas that aim to understand sea ice – ecosystems interactions and to determine impacts of physical and chemical change on primary and secondary producers.

Primary Supervisor

Sophie Bestley

Closing Date

29th October 2021*

Applicants should contact the primary supervisor, and submit their Expression of Interest (EOI) and Application as soon as possible.

*unless filled earlier

For information on eligibility and the application process please visit the University of Tasmania Graduate Research page or email Sophie.Bestley@utas.edu.au