What controls the Global Overturning Circulation?
Detta är ett förslag på examensarbete för kandidat- eller masternivå vid Institutionen för marina vetenskaper. Examensarbeten vid Institutionen för marina vetenskaper görs självständigt och bedöms individuellt.
Subject: Oceanography
Level: Bachelor’s (15hp) or Master’s (45-60 hp) thesis project
Location: Gothenburg
Supervisor: Fabien Roquet, Professor
Project background
The Global Overturning Circulation (GOC) is a slow global-scale circulation generated by deep-reaching horizontal gradients of temperature and salinity in the ocean (Cessi 2019). The GOC has a two cell structure, with an upper cell connecting the North Atlantic convective regions to the Southern Ocean, while the lower cell originates from the Antarctic shelf and fills a large fraction of the abyss.
The GOC is important for the climate as it is responsible for large transports of heat, salt and dissolved carbon (among other tracers) between the surface and the ocean interior and can be associated with decadal to millennial climate variability.
An outstanding question concerning the Global Overturning Circulation has long been how its structure and variability depends on the geometry of ocean basins, and what is the role of high latitude convection in controlling them (Klocker et al 2023).
In particular, the presence of a reentrant channel in the Southern Ocean is thought to drive a far deeper and vigorous overturning transport than there would be otherwise (Shakespeare et al 2012).
Project description
In this project, the student will study basic concepts about the Global Overturning Circulation, implementing analytical models of the GOC available in the literature and exploring their basic predictions (e.g. Ferrari et al. 2018). Conceptual models will be implemented in Python and used to gain insights on the GOC. For a Bachelor project, the student will focus on a simpler conceptual model (Gnanadesikan 1999).
Skills
- Explore fundamental notions of Fluid Dynamics applied to the ocean
- Learn how simplified analytical models are built and used to test theories
- Learn how to solve simple equations with a scientific programming tool
Contact
Fabien Roquet
Professor
E-mail: fabien.roquet@gu.se
References / Links:
Cessi, P., 2019. The Global Overturning Circulation. Annual Review of Marine Science 11, 249–270. https://doi.org/10.1146/annurev-marine-010318-095241
Ferrari, R., Nadeau, L.-P., Marshall, D.P., Allison, L.C., Johnson, H.L., 2018. A Model of the Ocean Overturning Circulation with Two Closed Basins and a Reentrant Channel. Journal of Physical Oceanography 47, 2887–2906. https://doi.org/10.1175/JPO-D-16-0223.1
Gnanadesikan, A., 1999. A Simple Predictive Model for the Structure of the Oceanic Pycnocline. Science 283, 2077–2079.
Klocker, A., Munday, D., Gayen, B., Roquet, F., LaCasce, J.H., 2023. Deep-Reaching Global Ocean Overturning Circulation Generated by Surface Buoyancy Forcing 75, 392–409. https://doi.org/10.16993/tellusa.3231
Shakespeare, C.J., Hogg, A.McC., 2012. An Analytical Model of the Response of the Meridional Overturning Circulation to Changes in Wind and Buoyancy Forcing. Journal of Physical Oceanography 42, 1270–1287. https://doi.org/10.1175/JPO-D-11-0198.