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Solar radiation-driven photochemical modification of dissolved organic matter and its connections to the marine productivity


A large part of primary production in ocean is converted to dissolved organic matter (DOM). Rivers and upwelling waters import DOM to the surface waters of coastal and upwelling regions, respectively.

DOM provides nutrition to bacterioplankton and supports heterotrophic food webs. Prior to its biological utilization, the majority of DOM requires ectoenzymatic hydrolysis or photochemical cleavage.

We hypothesize that the nutrients and energy bound to DOM contribute to the productivity of upwelling and coastal regions, and that solar ultraviolet radiation alters significantly the bioavailability of DOM. The overall objective of the proposed study is to determine the importance of DOM and its photochemical alteration for overall marine productivity.

The proposed experiments will focus on DOM with different bioreactivity and functionalities in the coastal and upwelling regions. The proposed study quantifies the photochemical mineralization and the modification of the bioavailability of DOM, and relates these changes to the metabolic activities and community structure of bacterioplankton.

Experiments will assess the role of solar radiation-induced photochemical reactions in the remineralization of biologically recalcitrant DOM (the D-enantiomeric fraction of amino acids). The proposed study quantifies also the impact of solar radiation on the activity of extracellular enzymes (e.g. phosphomonoesterase present in <0.2-µm filtered water) and their diversity.

The photochemical rates will be related to the absorbed doses of radiation during the experiments to calculate apparent quantum yields for the photochemical reactions (AQY). These modeling parameters (AQYs) allow the determination of the photochemical rates in situ under the variable (or predicted future) environmental conditions.

We expect that DOM and photochemical reactions contribute significantly to overall systemÂ's productivity, and explain, in part, the high productivity of coastal and upwelling regions.

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