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 June 2013
Description:
The physical environment in the oceans dictates not only how phytoplankton cells are dispersed
and their populations intermingled, but also mediates the supply of nutrients to the
surface mixed layer. In this thesis I explore both of these aspects of the interaction between
phytoplankton ecology and ocean physics, and have approached this topic in two distinct
but complementary ways, working with a global ocean ecosystem model, and collecting
data at sea.
In the first half of the thesis, I examine the role of mesoscale physical features in shaping
phytoplankton community structure and influencing rates of primary production. I
compare the output of a complex marine ecosystem model coupled to coarse resolution and
eddy-permitting physical models. Explicitly resolving eddies resulted in marked regional
variations in primary production, zooplankton and phytoplankton biomass. The same phytoplankton
phenotypes persisted in both cases, and were dominant in the same regions.
Global phytoplankton diversity was unchanged. However, levels of local phytoplankton
diversity were markedly different, with a large increase in local diversity in the higher
resolution model. Increased diversity could be attributed to a combination of enhanced
dispersal, environmental variability and nutrient supply in the higher resolution model. Diversity
”hotspots” associated with western boundary currents and coastal upwelling zones
are sustained through a combination of all of these factors.
In the second half of the thesis I describe the results of a fine scale ecological and
biogeochemical survey of the Kuroshio Extension Front. I found fine scale patterns in
physical, chemical and biological properties that can be linked back to both the large scale
horizontal and smaller scale vertical physical dynamics of the study region. A targeted
genomic analysis of samples focused on the ecology of the picoeukaryote Ostreococcus
clade distributions strongly supports the model derived hypotheses about the mechanisms
supporting diversity hotspots. Strikingly, two distinct clades of Ostreococcus co-occur in more than half of the samples. A ”hotspot” of Ostreococcus diversity appears to be supported
by a confluence of water masses containing either clade, as well as a local nutrient
supply at the front and the mesoscale variability of the region.
Description:
I gratefully acknowledge the financial support from the following
sources: MIT Presidential Fellowship, Gordon and Betty Moore Foundation Marine Microbiology
Initiative, NASA and NSF. Small grants for travel and equipment from the PAOC
Houghton Fund, EAPS Student Research Fund and MISTI Hayashi Fund allowed me to
pursue my research collaboration with Prof Takeyoshi Nagai at the Tokyo University of
Marine Science and Technology.
Keywords:
Phytoplankton populations
;
Marine biological diversity
;
Natsushima (Ship) Cruise
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
