Bacterioplankton dynamics in surface waters of the north-eastern (sub-)tropical Atlantic Ocean affected by Aeolian dust

• Main Author: Hill, Polly Georgiana
• Format: Thesis
• Language: English
• Published: 2010
• Subjects: North Atlantic
• Online Access: https://eprints.soton.ac.uk/168937/; https://eprints.soton.ac.uk/168937/1/Polly_Hill_2010.pdf

The microbial community dominates biogeochemical cycling of the ocean, affecting global climate. The impact of physical disturbance of near surface microbial populations was studied in the northeastern tropical and subtropical Atlantic Ocean. This region lies beneath easterly trade winds, resulting in strong perturbations in terms of wind driven mixing and Aeolian dust deposition. Firstly, the region’s surface water bacterioplankton community was compared with adjacent regions in terms of metabolic activity, by measuring the uptake rates of radioactively labelled amino acids (3H-leucine and 35S-methionine) as a proxy for bacterial production. Remarkably, there was little variation in uptake rates between the two Atlantic (sub-)tropical gyres. Rates reflected regional photosynthetic biomass, except in the study region. The bacterioplankton community of this region was less metabolically active than that of the oligotrophic north Atlantic gyre, despite ocean colour data identifying the region as productive. The region’s uniqueness is probably related to the episodic Saharan dust inputs experienced. To test whether dust deposition controls microbial community structure, surface communities were compared, using flow cytometry and fluorescence in situ hybridisation, between two winter periods when either wind-driven mixing or dust deposition occurred. Wind-driven mixing was associated with domination by the ubiquitous SAR11 clade of Alphaproteobacteria, whereas key primary producers, Prochlorococcus cyanobacteria, numerically dominated during calmer conditions. Phytoplankton-associated Bacteroidetes and Synechococcus cyanobacteria were most abundant during turbulent conditions. Gammaproteobacteria, encompassing opportunistic species, were the only group to benefit from dust inputs; thus dust deposition seems to have a minor influence on the region’s bacterioplankton community compared to wind mixing, suggesting community change following dust storm events may be linked to nutrients delivered by wind mixing, as much ...