The Effects of Tides and Submesoscale Mixed Layer Eddies on Deep Convection in the Labrador Sea: Simulations at Resolutions Consistent with Coupled Climate Models

• Author / Creator

  Brown, Rowan

• The Intergovernmental Panel on Climate Change predicts that the large-scale overturning circulation will weaken over the 21st century. As with many other oceanic consequences of anthropogenic climate forcing, such as increased warming, acidification, glacial and sea ice melt, marine heatwaves, and coastal erosion, the high latitudes are predicted to be most strongly affected. A key tool in making these predictions is global coupled climate models, which in the most recent Coupled Model Intercomparison Project (phase 6) commonly utilized ocean components with resolutions of 1 to 1/4 degrees.

  The accurate representation of deep convection, a vertical mixing process connecting the surface and abyssal flows, is crucial for accurately predicting the future of the overturning circulation. Simultaneously, it is also a challenge due to the small scales of motion involved. In this monograph, we evaluate the effects of two processes on deep convection in the Labrador Sea, a key site of overturning in the western North Atlantic. We find that both processes, namely tidal forcing and the submesoscale mixed layer eddy parameterization (SMLEp), decrease deep mixed layer depth biases in a 1/4 degree regional atmospherically-forced model. The mechanisms by which they effect this change are less clear. Both tidal forcing and the SMLEp can alter the lateral boundary current-interior exchange of buoyancy, which can affect stratification. However, fluxes due to tidal forcing are characterized by a cooling and freshening whereas those from the SMLEp either become warmer and saltier or do not change (depending on the atmospheric forcing product). This is likely related to differences in how tidal forcing and the SMLEp affect boundary instabilities, especially baroclinic instabilities, through the water column. What is more clear, however, is that the principal behaviour of the SMLEp is not to alter the boundary fluxes but to slump isopycnals and accelerate post-convection restratification. To summarize, we find that both tidal forcing and the SMLEp could serve as valid tools for improving MLD biases in future medium-resolution (e.g., 1/4 degree) coupled climate models, which commonly experience unrealistically deep convection.

• Subjects / Keywords

  • Labrador Sea
  • climate
  • oceanography
  • Atlantic
  • marine
  • NEMO
  • convection
  • GCM

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-rw65-sp84

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.