Residual overturning circulation and its connection to Southern Ocean dynamics

dc.contributer.editor Southern Ocean
dc.contributer.editor overturning
dc.contributer.editor eddies Youngs, Madeleine K. 2020-08-27T14:34:14Z 2020-08-27T14:34:14Z 2020-09
dc.description Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2020. en_US
dc.description.abstract Over the last 20 years, our understanding of the meridional overturning circulation has improved, but primarily in a two-dimensional, zonally-averaged framework. In this thesis, I have pushed beyond this simplification and shown that the additional complexity of meanders, storm tracks, and other zonal asymmetries is necessary to reproduce the lowest-order behavior of the overturning circulation. First I examined the role of basin width for determining whether the Atlantic or Pacific oceans experience deep convection. I used a two layered model and a rectangular single-basin model to show that the basin width, in combination with scalings for the overturning circulation make the overturning relatively weaker in the wider basin, priming it for a convection shut down. In addition to this large-scale work, I have examined Southern Ocean-like meanders using a hierarchy of idealized models to understand the role of bottom topography in determining how the large-scale circulation responds to climate change scenarios. These are useful because they preserve the lowest-order behavior, while remaining simple enough to understand. I tested the response of the stratification and transport in the Southern Ocean to changes in wind using a highly-idealized two-layer quasi-geostrophic model. In addition to showing that meanders are necessary to reproduce the behavior of the Southern Ocean, I found that strong winds concentrate the baroclinic and barotropic instabilities downstream of the bottom topography and weaken the instabilities elsewhere due to a form-drag process. With weak winds, however, the system is essentially symmetric in longitude, like a flat-bottomed ocean. This result is consistent with observations of elevated turbulence downstream of major topography in the Southern Ocean. My next study investigated a more realistic Southern Ocean-like channel, with and without bottom topography, and examined the three-dimensional circulation in order to understand where vertical transport occurs and develop a picture of the pathways taken by each individual water parcel. I found that the vertical transport happens in very isolated locations, just downstream of topography. Finally, I added a biogeochemical model to my simulations and found that carbon fluxes are enhanced near topography, again highlighting the role of zonal asymmetries. en_US
dc.description.sponsorship I have been funded by the American Meteorological Society’s Graduate Fellowship, as well as the National Defense Science and Engineering Graduate Fellowship. I have also been supported by NSF OCE-1536515 and NCAR Large Scale Computing Award UMIT0025. en_US
dc.identifier.citation Youngs, M. K. (2020). Residual overturning circulation and its connection to Southern Ocean dynamics [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server.
dc.identifier.doi 10.1575/1912/26126
dc.language.iso en_US en_US
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en_US
dc.relation.ispartofseries WHOI Theses en_US
dc.title Residual overturning circulation and its connection to Southern Ocean dynamics en_US
dc.type Thesis en_US
dspace.entity.type Publication
relation.isAuthorOfPublication 13d83126-0552-4f54-bc87-7ca61fb7706e
relation.isAuthorOfPublication.latestForDiscovery 13d83126-0552-4f54-bc87-7ca61fb7706e
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
12.79 MB
Adobe Portable Document Format
License bundle
Now showing 1 - 1 of 1
No Thumbnail Available
1.88 KB
Item-specific license agreed upon to submission