Physical and chemical factors controlling the distribution of the major phytoplankton classes at the Antarctic Polar Front, 170 W̊. Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rj430881j

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  • This study was part of the Antarctic Environment and Southern Ocean Study (AESOPS) program, whose main goal was to investigate the role of the biota in the carbon flux from the atmosphere to the interior of the ocean. We quantified the abundance of the major phytoplankton classes and examined the physical and chemical controls of their distribution during a cruise in January/February 1998 near the Antarctic Polar Front (APF). In order to extrapolate our knowledge of the phytoplankton class distribution over the entire season we explored possible physical and optical proxies that allow us to map the class distribution for the entire growing season using mooring or drifter data. Chlorophyll a in the APF region had declined since the bloom in early summer, but was high at the location of the Southern Antarctic Circumpolar Current Front (SACCF), and coinciding with the location of the meridional silicic acid gradient. The APF separated the diatom-dominated phytoplankton south of the front from the nanoflagellate-dominated phytoplankton (mostly prymnesiophytes) to the north. The absence of diatoms north of the front is most likely due to silicic acid limitation. Their dominance south of the front is likely a consequence of increased silicic acid and iron flux from below the surface mixed layer south of the front, where nutrient concentrations below the mixed layer are significantly higher. The dominance of diatoms over flagellates is negatively correlated with temperature (r = -0.83), particularly within the PF region. Therefore sea surface temperature could be used to estimate diatom dominance in this particular region. The optical data from the drifter released during the January/February cruise indicate a higher ratio of upwelling radiance at 555 nm to downwellng irradiance at 490 nm (Lu555/Ed490) associated with increased diatom dominance. This ratio normalized to chlorophyll is an indicator for backscattering properties of the algal community. The community with the higher diatom dominance has a significantly higher Lu555/Ed49O/chl a ratio and it appears that the backscattering properties could be used to distinguish between the diatoms and prymnesiophytes in the Southern Ocean.
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