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Abstracts Water samples from nine vertical profiles down to 110 m water depth and 19 samples from the sea-surface were studied for coccolithophore abundance and distribution across oceanic frontal regions of the Indian sector of the Southern Ocean. Sampling was performed along a north-south transect (between 39°S and 65.49°S, ~ 57.3°E) during the 4th Indian Southern Ocean Expedition (between 31st January and 18th February 2010). Coccospheres and coccoliths were counted separately using a Scanning Electron Microscope (SEM). A total of 39 taxa (including morphotypes, types and subspecies) were recorded as intact coccospheres with abundances reaching up to 750 × 10 3 coccospheres/l. In addition, 85 taxa (including varieties, morphotypes) were counted as coccoliths reaching up to 900 × 10 5 coccoliths/l. Emiliania huxleyi was recognized as the most abundant species, accounting for > 86% of the total coccolithophore assemblage at each station. Elevated coccolithophore diversity was observed in the subtropical zone whereas high coccolithophore abundance was observed in the Subantarctic zone. A monospecific Emiliania huxleyi assemblage was recorded within and south of the Polar frontal zone. Three assemblages were recognized based on coccolithophore abundance and diversity. The assemblage of the Agulhas Retroflection frontal zone and Subtropical zone is highly diverse (39 taxa) and can be linked to relatively warm, high saline and oligotrophic waters. The Subantarctic zone assemblage is characterized by a reduced number (thirteen) of coccolithophore taxa, whereas the Polar Frontal zone comprises a monospecific E. huxleyi assemblage (preferentially morphotypes C and B/C). Multivariate statistics indicated that regions with elevated temperature and low nutrient concentration show high coccolithophore diversity whereas regions with high nutrient concentrations and low temperature show a strongly reduced coccolithophore diversity with abundant monospecific E. huxleyi (morphotypes B/C and C) assemblages. [ABSTRACT FROM AUTHOR]

We documented scanning electron micrographs of Emiliania huxleyi morphotypes from 9 vertical profile samples collected between 39°S and 65.49°S (57.3°E) during the Fourth Indian Southern Ocean expedition (January–February, 2010). Water samples were obtained from 6 different depths (between 0 and 110m) to study the distribution and abundance of E. huxleyi morphotypes with respect to associated environmental factors in the oceanic frontal regions of the Southern Indian Ocean. Five E. huxleyi morphotypes were identified, quantified and the preference of each morphotype with regard to physico-chemical parameters assessed by Canonical Correspondence Analysis (CCA). Morphotypes A and B comprised 6.2% and 0.7% of the total E. huxleyi abundance, respectively, and dominated at stations located north of the Southern Subtropical Front (SSTF) associated with warmer, highly saline and nutrient-poor surface waters. Morphotypes C and B/C are cold water forms representing 23.2% and 68.5% of the total E. huxleyi abundance, respectively, and dominated in the Subantarctic (SAF2) and Polar Frontal (PF1) regions of the Southern Indian Ocean. Morphotypes C and B/C dominated in the SAF2 and PF1 regions, which were identified as the most productive areas due to the elevated nutrient concentrations. Salinity, nitrate, phosphate and probably light intensity were the most important parameters for the proliferation of E. huxleyi in these frontal regions. Towards the south, a consistent decrease in the E. huxleyi abundance was observed and their lowest abundance recorded at the southernmost station located in the Antarctic coastal region (65.49°S). [ABSTRACT FROM AUTHOR]