Silica and the silicon cycle

This ambitious objective requires identifying and quantifying silicon sources and sinks at the interfaces and describing the internal dynamics of the cycle in different ecosystems and on a global scale. At LEMAR we are particularly interested in the roles of different silicifiers not only for the silicon cycle, but also in other major biogeochemical cycles and in the functioning of ecosystems.

The silicon cycle is a historical theme of LEMAR. Our objective is to understand the oceanic cycle of silicon and the interactions with other biogeochemical cycles such as carbon, nitrogen, phosphorus and even iron and sulphur. This ambitious objective requires identifying and quantifying silicon sources and sinks at the interfaces and describing the internal dynamics of the cycle in different ecosystems and on a global scale. We have developed a transdisciplinary approach, including chemistry, biogeochemistry, biochemistry, physiology and biology, and use several experimental and modelling tools and multi-scale approaches from laboratory experiments to better understand the processes influencing the cycle to major natural environment observation campaigns. We have recently created an international “silicon school” bringing together a consortium of universities and organizations that offer higher-level teaching and research opportunities and an online learning course (under development) on the theme “Silica: from stellar dust to the living world”. The Silica School consortium currently includes 23 marine research institutes from 11 countries and continues to grow.

Silicifiers are living organisms that take advantage of the abundance of silicon (silicon is the second most abundant element in the earth’s crust) to build silicified architectures (in biogenic silica) from silica dissolved in water (orthosilicic acid or silicates). Their biogenic silica skeletons can help improve their physical strength, protect them from predators, improve their motility or help light and nutrients penetrate cells. In the marine domain, diatoms play a key role in the food webs of the most productive coastal or ocean ecosystems, as well as in the production of oxygen on which we depend and in the transfer of CO2 from the surface to the interior of the oceans (the biological carbon pump). The physiology and biochemistry of pelagic diatoms have been studied in depth, but there are still many gaps in the mechanisms by which they can biosynthesize biogenic silica under natural conditions far from those required for glass production in industry. Their role in the biological carbon pump and more generally the link between the Si and C cycles must also be reassessed.

In addition, recent meetings between international silicon specialists initiated by LEMAR (SILICAMICS and SILICAMICS 2) have shown that silicifiers other than pelagic diatoms can no longer be neglected. We have therefore expanded our research to include benthic diatoms, ice diatoms, sponges, picocyanobacteria, and some rhizaria that contribute to the dynamics of the silicon cycle and the functioning of many ecosystems more significantly than previously thought.