Type
Text
Type
Thesis
Advisor
Lwiza, Kamazima | Wilson, Robert | Hameed, Sultan.
Date
2014-12-01
Keywords
Physical oceanography | Biennial signal, El Nino-Southern Oscillation, Indian Ocean Dipole, Madagascar, Ocean-atmosphere, Phytoplankton
Department
Department of Marine and Atmospheric Science.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76209
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Approximately every other year during the austral summer a larger phytoplankton bloom propagates off of the southeast tip of Madagascar. The cause of the interannual variability of this distinct oceanic feature remains unclear, so here we improve the analysis of the interannual variability of the bloom with a longer ocean color dataset, re-examine the existing mixed layer depth and iron fertilization hypotheses formerly used to explain bloom formation and analyze the variability in the larger ocean-atmosphere system in the region in relation to bloom formation. To resolve the forcings on the bloom, relevant satellite and reanalysis data were examined using principal component and wavelet analyses to tease out the dominant spatial and temporal patterns of variability. Composite maps were also created to examine how the physics evolves differently in bloom years compared to non-bloom years before and during bloom formation. The dominant periods of variability in chlorophyll concentration data are 2- and 4-years, which are also present in other oceanic and atmospheric variables in this region. Neither of the existing hypotheses of mixed layer depth and iron fertilization was supported by this research. The mixed layer depth hypothesis is discounted by the presence of a shallower mixed layer depth, Chl correlations with higher SSTs and weaker winds during the time of bloom formation and the iron fertilization hypothesis was also not supported because of the correlation between anomalously lower precipitation rates and Chl and lack of evidence in sea surface salinity data. Instead, an alternative hypothesis is presented based on the existence of a biennial ocean-atmosphere mechanism in the Indian Ocean controlled by the upper ocean heat content and zonal surface winds. The sea surface temperature anomalies in the greater Madagascar region indicate that temperatures are cooler going into austral summer, combined with weaker winds, which induces lower surface thermal fluxes. The lower cloud cover associated with lower thermal fluxes allows a larger amount of photosynthetically active radiation (PAR) to reach the upper ocean and encourage phytoplankton growth. The increase in eastward flow in surface currents supports the propagation of the bloom, and the phytoplankton follow the movement of the eddy field including both cyclonic and anti-cyclonic eddies. This mechanism is represented by anomalies in sea surface temperatures, zonal winds, precipitation rates, PAR, surface thermal radiation and, lastly, chlorophyll concentrations that act on an approximate 2-year timescale. However, this research does not explain the role of nutrients in the bloom, which were hypothesized to be regulated by the mixed layer depth. This conceptual framework based on statistical relationships and dominant variability in the oceanic and atmospheric fields over Madagascar sets the foundation of an alternative hypothesis to bloom development and an improved understanding of the ocean-atmosphere interactions in this region. | 58 pages
Recommended Citation
Roupe, Lindsay, "Oceanic and atmospheric influences on the interannual variability of the Madagascar phytoplankton bloom" (2014). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2146.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2146