Biogenic silica dissolution in diatom aggregates: insights from reactive transport modelling
KAUST Grant NumberKUK-C1-017-12
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Abstract© Inter-Research 2014. Diatom aggregates contribute significantly to the vertical sinking flux of particulate matter in the ocean. These fragile structures form a specific microhabitat for the aggregated cells, but their internal chemical and physical characteristics remain largely unknown. Studies on the impact of aggregation on the Si cycle led to apparent inconsistency. Despite a lower biogenic silica (bSiO2) dissolution rate and diffusion of the silicic acid (dSi) being similar in aggregates and in sea-water, dSi surprisingly accumulates in aggregates. A reaction-diffusion model helps to clarify this incoherence by reconstructing dSi accumulation measured during batch experiments with aggregated and non-aggregated Skeletonema marinoi and Chaetoceros decipiens. The model calculates the effective bSiO2 dissolution rate as opposed to the experimental apparent bSiO2 dissolution rate, which is the results of the effective dissolution of bSiO2 and transport of dSi out of the aggregate. In the model, dSi transport out of the aggregate is modulated by alternatively considering retention (decrease of the dSi diffusion constant) and adsorption (reversible chemical bonds between dSi and the aggregate matrix) processes. Modelled bSiO2 dissolution is modulated by the impact of dSi concentration inside aggregates and diatom viability, as enhanced persistence of metabolically active diatoms has been observed in aggregates. Adsorption better explains dSi accumulation within and outside aggregates, raising the possible importance of dSi travelling within aggregates to the deep sea (potentially representing 20% of the total silica flux). The model indicates that bSiO2 dissolution is effectively decreased in aggregates mainly due to higher diatom viability but also to other parameters discussed herein.
SponsorsWe thank S. Ni Longphuirt and M. Garvey, who kindly read earlier versions of this manuscript, and J. Thebault for his help with the figures. We are sincecerely grateful to the reviewers and the editor for their insightful comments that helped to considerably improve this manuscript. We acknowledge funding to B.M. from the EU, partly through the ORFOIS (EVK2-CT2001-00100) project and partly through the Si-WEBS (HPRN-CT-2002-00218) Research Training network of the Marie Curie programme, and funding to U.P. from the National Science Foundation (NSF). This research was also partly funded by King Abdullah University of Science and Technology (KAUST) Center-in-Development Award to Utrecht University (project No. KUK-C1-017-12).
PublisherInter-Research Science Center
JournalMarine Ecology Progress Series