On the Horizontal Advection and Biogeochemical Impacts of North Atlantic Mode Waters and Boundary Currents
Abstract
Using a combination of hydrographic data and the trajectories and profiles of isobaric
floats, this dissertation evaluates the connections between remote regions in the
North Atlantic. First, I establish that the production and advection of the North
Atlantic Subtropical Mode Water (STMW) introduces spatial and temporal variability
in the subsurface nutrient reservoir of the subtropical gyre. As the mode water is
formed, its nutrients are depleted by biological utilization. When the depleted water
mass is exported to the gyre, it injects a wedge of low-nutrient water into the upper
layers of the ocean. Contrary to intuition, cold winters that promote deep convective
mixing and vigorous mode water formation may diminish downstream primary productivity
by altering the subsurface delivery of nutrients. Next, the source of elevated nutrient
concentrations in the Gulf Stream is assessed. The historical hydrographic data suggest
that imported water advected into the Gulf Stream via the tropics supplies an important
source of nutrients to the Gulf Stream. Because the high nutrients are likely imported
from the tropics, diapycnal mixing need not be invoked to explain the Gulf Stream's
high nutrient concentrations, as had been previously hypothesized. Furthermore, nutrients
do not increase along the length of the Stream, as would be expected with strong diapycnal
mixing.Finally, profiling float data are used to investigate how the Labrador Sea
Water enters the Deep Western Boundary Current, one of the primary pathways by which
it exits the subpolar gyre. With the trajectories and profiles of an extensive array
of P-ALACE floats I evaluate three processes for their role in the entry of Labrador
Sea Water in the Deep Western Boundary Current (DWBC): 1) LSW is formed directly in
the DWBC, 2) Eddies flux LSW laterally from the interior Labrador Sea to the DWBC,
and 3) A horizontally divergent mean flow advects LSW from the interior to the DWBC.
Each of the three processes has the potential to remove heat from the boundary current,
and both the formation of LSW directly in the boundary current and the eddy heat flux
are possible sources of interannual variability in the exported LSW product.
Type
DissertationDepartment
Earth and Ocean SciencesSubject
Physical OceanographyBiology, Oceanography
North Atlantic
nutrients
ocean color
Gulf Stream
Labrador Sea Water
Meridional Overturning Circulation
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https://hdl.handle.net/10161/386Citation
Palter, Jaime Beth (2007). On the Horizontal Advection and Biogeochemical Impacts of North Atlantic Mode Waters
and Boundary Currents. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/386.Collections
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