In partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ocean Science & Engineering

In the

School of Biological Sciences

ANH HUY PHAM

Will defend his dissertation

DELINEATING PLANKTONIC HABITATS IN DYNAMIC MARINE ENVIRONMENTS: FROM OCEANOGRAPHIC EXPEDITIONS TO AUTONOMOUS PLATFORM

28th, March 2024

10:00 AM

ES&T Building, Third Floor, Ocean Room

https://gatech.zoom.us/j/99771274347

Thesis Advisor:

Joseph Montoya, Ph.D. School of Biological Sciences

Georgia Institute of Technology

                                                                        Committee Members:

                                                            Joel Kostka, Ph.D. School of Biological Sciences

                                                                        Georgia Institute of Technology

                                                            Mark Hay, Ph.D. School of Biological Sciences

                                                                        Georgia Institute of Technology

Takamitsu Ito, Ph.D.

School of Earth & Atmospheric Science Georgia Institute of Technology

Kostas Konstantinidis, Ph.D. School of Civil Engineering Georgia Institute of Technology

ABSTRACT:

Phytoplankton are pivotal to marine ecosystems and biogeochemical cycles, serving as the foundation for oceanic food webs and playing a critical role in carbon sequestration.

Recognizing their significance, oceanographers and marine biologists have prioritized understanding phytoplankton biogeography through examination of environmental niches and species distribution patterns. Traditional efforts to characterize planktonic habitats have relied heavily on global-scale analyses, amalgamating extensive data compilations and literature reviews. However, it's become increasingly evident that mesoscale and sub-mesoscale processes can significantly influence phytoplankton growth and community structure. To resolve this multi-scale complexity, a novel method has been developed to dynamically define distinct planktonic habitats utilizing standard oceanographic measurements.

My work combined cutting-edge observational technologies, computational techniques, and advanced statistical analyses to provide a computational framework to enhance delineation of phytoplankton habitats. This framework facilitated a flexible and effective integration of diverse oceanographic data, leading to improved understanding of phytoplankton distributions and their environmental drivers.

I used this approach to investigate the spatial and temporal distribution of planktonic habitats over a span of ten years in waters of the Western Tropical North Atlantic influenced by the Amazon River Plume. This study unveiled consistent, distinct phytoplankton habitats associated with the Amazon River's two dominant seasonal flow regimes, underscoring the significant influence of freshwater inputs on marine biogeographical patterns.

Building on this foundation, I extended the habitat delineation framework to incorporate data from the BGC-Argo fleet of robotic profilers deployed in the Tropical North Atlantic. This extension yielded a higher-resolution and dynamic overview of phytoplankton biogeography relative to the widely used and static biogeochemical provinces of Longhurst. I was able to resolve a variety of meteorological and oceanic influences on phytoplankton distributions, including the seasonal displacement of the Intertropical Convergence Zone (ITCZ), the size of the North Atlantic Subtropical Gyre, and river discharges into the Tropical Atlantic and Eastern Caribbean Sea.