Publication Date:
2022-05-25
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 February 2013
Description:
Physical oceanographers have known for several decades the total amount of abyssal mixing
and upwelling required to balance the deep-water formation, but are still working to
understand the mechanisms and locations—how and where it happens. From observational
studies, we know that areas of rough topography are important and the hundreds of
Grand-Canyon sized canyons that line mid-ocean ridges have particularly energetic mixing.
To better understand the mechanisms by which rough topography translates into energetic
currents and mixing, I studied diffusive boundary layers over varying topography using
theoretical approaches and idealized numerical simulations using the ROMS model. In this
dissertation, I show a variety of previously unidentified characteristics of diffusive boundary
layers that are likely relevant for understanding the circulation of the abyssal ocean.
These boundary layers share many important properties with observed flows in abyssal
canyons, like increased kinetic energy near topographic sills and strong currents running
from the abyssal plains up the slopes of the mid-ocean ridges toward their crests. They also
have a previously unknown capacity to accelerate into overflows for a variety of oceanographically
relevant shapes and sizes of topography. This acceleration happens without
external forcing, meaning such overflows may be ubiquitous in the deep ocean. These
boundary layers also can force exchange of large volumes of fluid between the relatively
unstratified boundary layer and the stratified far-field fluid, altering the stratification far
from the boundary. We see these effects in boundary layers in two– and three–dimensions,
with and without rotation.
In conclusion, these boundary layer processes, though previously neglected, may be
a source of a dynamically important amount of abyssal upwelling, profoundly affecting
predictions of the basin-scale circulation. This type of mechanism cannot be captured by
the kind of mixing parameterizations used in current global climate models, based on a
bottom roughness. Therefore, there is much work still to do to better understand how
these boundary layers behave in more realistic contexts and how we might incorporate that
understanding into climate models.
Description:
I gratefully acknowledge the financial support of the NSF Graduate Research Fellowship
Program and WHOI Academic Programs.
Keywords:
Oceanic mixing
;
Upwelling
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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