Physical controls on copepod aggregations in the Gulf of Maine
Name
861506333-MIT.pdf
Description
Full printable version
Size
36.56 MB
Format
Adobe PDF
Checksum (MD5)
383c9123140d94399a6333e0cbdb044c
Author(s)
Woods, Nicholas W
Advisor(s)
David Fratantoni and Glenn Flierl.
Date Issued
2013
Publisher
Massachusetts Institute of Technology
Abstract
This thesis explores the role that the circulation in the Gulf of Maine (GOM) plays in determining the distribution of dense aggregations of copepods. These aggregations are an important part of the marine ecosystem, especially for endangered North Atlantic right whales. Certain ocean processes may generate dense copepod aggregations, while others may destroy them; this thesis looks at how different characteristics of the GOM circulation fit into these two categories. The first part of the thesis investigates a hypothetical aggregation mechanism in which frontal circulation interacts with copepod behavior to generate a dense patch of copepods. The first two chapters of this thesis address this mechanism in the context of coastal river plumes and salinity fronts. One chapter describes the characteristics and variability of coastal freshwater and salinity fronts using a historical dataset and a realistic numerical model. The seasonal variability of freshwater is tied in part to seasonality in river discharge, while variability on shorter time scales in the frontal position is related to wind stress. Another chapter applies the hypothetical mechanism to idealized river plumes using a suite of numerical models. The structure of the plume and plume-relative circulation change the resulting copepod aggregation from what is expected from the hypothetical mechanism. The second part of the thesis discusses the GOM circulation and how it may eliminate copepod patches. The summertime mean surface circulation and eddy kinetic energy are computed from a Lagrangian drifter dataset and an adaptive technique that allows for higher spatial resolution while also keeping uncertainty low. Eddy diffusivity is also computed over different regions of the GOM in an attempt to quantify the spreading of a patch of copepods, and is found to be lower near the coast where right whales are often found feeding on copepod patches. In the next chapter, a numerical drifter dataset is used to understand how the results of the previous chapter depend upon the quantity of observations. It is found that the uncertainty in estimating eddy diffusivity is tightly coupled to the number of drifters in the calculation.
Description
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 297-213).
Subjects
Joint Program in Physical Oceanography.
Earth, Atmospheric, and Planetary Sciences.
Woods Hole Oceanographic Institution.
MIT Department
Joint Program in Physical Oceanography
Woods Hole Oceanographic Institution
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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