Atmospheric deposition is increasingly being recognized as an important source of nutrients to the world ocean. Extensive studies have been done to show the impacts of atmospheric deposition on the dynamics of microbial food web, carbon cycling and climate change. The Northwest Pacific Ocean receives large quantities of mineral dusts and anthropogenic particles from the East Asia. The aim of my thesis is to investigate the effects of Asian aerosol on two main microbial groups, phytoplankton and prokaryotes. To achieve this goal, incubation bioassays with aerosol addition were conducted on-board during two cruises to the Northwest Pacific Ocean.

Firstly, we studied the responses of phytoplankton in terms of community composition, physiology and function. An overall negative...[ Read more ]

Atmospheric deposition is increasingly being recognized as an important source of nutrients to the world ocean. Extensive studies have been done to show the impacts of atmospheric deposition on the dynamics of microbial food web, carbon cycling and climate change. The Northwest Pacific Ocean receives large quantities of mineral dusts and anthropogenic particles from the East Asia. The aim of my thesis is to investigate the effects of Asian aerosol on two main microbial groups, phytoplankton and prokaryotes. To achieve this goal, incubation bioassays with aerosol addition were conducted on-board during two cruises to the Northwest Pacific Ocean.

Firstly, we studied the responses of phytoplankton in terms of community composition, physiology and function. An overall negative effect was observed. The abundance of phytoplankton decreased dramatically, particularly picophytoplankton such as Prochlorococcus and Synechococcus. This is accompanied by a shift in community composition, which changed from the dominance of picocyanobacteria to a dominance of prymnesiophytes, chlorophytes and chrysophytes. A parallel impairment was indicated by the decrease in photosynthetic efficiency and primary production. Secondly, prokaryotic transcriptional profile was analyzed to elucidate the functional response to atmospheric deposition. Corresponding to the decrease in the abundance of Prochlorococcus and Synechococcus, transcripts related with cyanobacteria, such as Prochlorococcus, Trichodesmium and Synechococcus, also decreased drastically. Positive effects included the overexpression of transcripts related with nutrient transporters and down-expression of P metabolism. Carbon metabolism appeared to be stimulated. Fe limitation appeared to be intensified. Other negative responses included a decline in N fixation, impaired sugar utilization, and the stimulation of oxidative stress, heavy metal toxicity and respiration.

This thesis provides new insights into the biogeochemical impacts of atmospheric deposition in the Western North Pacific Ocean and helps future global models to take into consideration of the spatial heterogeneity and multi-faceted effects of atmospheric deposition on the marine ecosystem.