Programme website: http://inspire-dtp.ac.uk
The uptake and storage of heat and carbon by the ocean are crucial controls on the climate system and on future climate change, and are highly sensitive to the properties and distribution of deep waters upwelling in the Southern Ocean. These in turn depend on both the remote forcing of the Atlantic Meridional Overturning Circulation (AMOC) and localized subsurface processes driven by the unique dynamics of the Antarctic Circumpolar Current (ACC) . Numerical model predictions of these processes and their response to changing Southern Hemisphere winds differ, due largely to sensitivity to the representation of eddies .
The principal aim of this project is to understand what sets the properties of waters upwelling around Antarctica, by characterising the along-ACC evolution of deep water masses, inferring the sources of observed decadal variability, and diagnosing the role of mesoscale to submesoscale processes. Because the ACC is highly variable and subsurface observations are sparse , a comprehensive investigation drawing on both observations and numerical models is required.
Advances in our understanding of the variability and trends in Southern Ocean upwelling water masses provided by this study have the potential to improve climate-model predictions of global change.
The project will use both observations and numerical model output to investigate the variability and drivers of water masses upwelling in the ACC.
To estimate changes in Circumpolar Deep Waters due to 1) stirring and mixing along the upwelling path, and 2) variations in inflowing water properties, you will compute fluxes of temperature and salinity using data from repeat sections (http://www.go-ship.org/refsecs/goship_ref_secs.html
) crossing the ACC all around Antarctica. The open-access historical hydrography dataset permits evaluation of changes over the past three decades, spanning known variability in the AMOC. Whilst the historical dataset is sufficient to meet project objectives, you will also have opportunities to participate in annual Southern Ocean research cruises (http://projects.noc.ac.uk/drake-passage/
) and incorporate the new data.
You will repeat the analysis using three versions of the NEMO model (https://www.youtube.com/watch?v=I8ru1YvXU04
): coarse (1-degree), eddy-permitting (1/4-degree), and a new high-resolution (1/12-degree) run. You will compare the versions with the aim of determining how changing model resolution and eddy representation affects the structure of the deep water overturning circulation, including the strength and locations of upwelling and the magnitude of subsurface transformations. You will use the high-resolution model to identify processes responsible for accomplishing the alongstream transformations, and their sensitivity to wind forcing.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at National Oceanography Centre. Specific training will include:
Analysis of hydrographic observations in both spatial (flux) and thermohaline coordinates
Analysis of numerical model output, in both model spatial grid and thermohaline coordinates; techniques for linking modelled ocean perturbations and model forcing
Sea-going skills including collection and processing of oceanographic data
In addition to the exchanges associated with INSPIRE, the student will collaborate with investigators and postgraduate students involved in a multi-institution Southern Ocean programme (ORCHESTRA), and will be encouraged to travel to national and international scientific meetings to present results.
 Tamsitt et al., 2017, Spiraling pathways of global deep waters to the surface of the Southern Ocean, Nat. Comm., 8:172, doi:10.1038/s41457-017-00197-0.
 Bishop et al., 2016, Southern Ocean overturning compensation in an eddy-resolving climate simulation, J. Phys. Oceanogr., 46, 1575-1592, doi:10.1175/jpo-d-15-0177.1.
 Firing et al., 2017, Deep temperature variability in Drake Passage, J. Geophys. Res., 122, 713-725, doi:10.1002/2016jc012452.