Date of Award

5-2014

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Mary Jane Perry

Second Committee Member

Collin S. Roesler

Third Committee Member

Joaquim I. Goes

Abstract

Increases in near-surface algal concentrations in the northern Arabian Sea from 1997 to 2004 have been linked to the appearance of the mixotrophic dinoflagellate Noctiluca miliaris (also known as Noctiluca sscintillans). This emerging presence of N. miliaris is ultimately expected to alter predator-prey relationships of higher trophic levels and, thus, carbon export to the deep ocean. The origination of and mechanism driving the emergence of N. miliaris is currently unknown, although recent studies suggest it correlates with a shallowing of the permanent oxygen minimum zone. Unfortunately, records of in situ counts of N. miliaris only first appear in the late 1990s.

The daily, synoptic images provided by satellite ocean color instruments, such as the NASA Moderate Resolution Imaging Spectroradiometer onboard Aqua (MODISA), provide viable data streams for observing changes in the biogeochemistry of marine ecosystems. These sensors provide consistent and high-density data on temporal and spatial scales that far exceed current field and aircraft sampling strategies, often with time-series of sufficient length to allow retrospective analysis of decadal oceanographic trends. The ocean color time-series of MODISA, launched in 2002, has potential for identifying the dynamics of N. miliaris blooms during the Northeast Monsoon. This dissertation explores the use an ocean reflectance inversion model (ORM) to generate estimates of chlorophyll-a concentrations and absorption coefficients for N. milaris from a decade of MODISA data records. The ORM discriminates between N. miliaris and other phytoplankton by producing estimates of spectral absorption for these algal groups.

The Arabian Sea challenges our collective abilities to generate remote-sensing time-series that consistently provide glimpses of phytoplankton dynamics on temporal and spatial scales that accommodate seeing ephemeral features. High spatial resolution (<1 km) satellite data records that predate the first in situ observations of N. milaris (pre mid-1990s) do not exist. That said, the MODISA imagery provided substantial insight into phytoplankton dynamics that cannot be achieved by conventional in situ sampling alone and, futhermore, pointed to specific places and times for targeted future studies. The combination of ORM-derived optical backscattering and chlorophyll-a provided valuable data records that supported our ultimate conclusion that N. miliaris now appears as a dominant grazer at the fringes of diatom blooms.

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