Ocean bottom boundary layers (BBLs) occur very close to the seafloor
when currents flow over it, producing vertical mixing and motion
affected by the shape of the terrain. These dynamics affect large-scale
ocean circulation by extracting energy and momentum (movement of mass)
from the currents. They also affect stratification (layering of the
ocean by density) by mixing water with different temperatures and salt
content, causing them to rise and sink due to buoyancy. Currents flowing
over sloping terrain - such as along coasts - produce small but strong
movement very close to the surface that moves up and down the slope due
to Earth's rotation. This movement is produced because the seafloor does
not allow momentum or buoyancy to be transferred into it. This effect
is known as Ekman arrest, which changes how the density layers interact
with the slope, causing them to tilt perpendicular to the sloping
surface and reduce the amount of turbulence (mixing) that occurs in the
BBL. This study uses a numerical model called large eddy simulation to
characterize Ekman arrest and its effect on turbulence under different
conditions, which could prove useful for ocean circulation models.
Observations of ocean currents hugging the coast of the Antarctic
Peninsula provide evidence that BBL mixing can have significant effects
on the large-scale ocean circulation that is driven by buoyancy.
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