Biogenic Silica Cycling in Marine Environments

Biogenic silica (BSi) cycling encompasses the production, transformation and burial of opaline material derived mainly from diatom frustules and other siliceous organisms. In the surface ocean, silicic acid is taken up by diatoms to construct their silica‐based shells, fuelling a significant fraction of marine primary production and driving the efficiency of the biological pump. Upon cell death or grazing, frustules sink and undergo partial dissolution in the water column; the balance between dissolution kinetics and transport determines the delivery of reactive silica to deeper waters and sediments. Riverine inputs of dissolved and particulate silicon supply coastal and shelf systems, while margin processes such as sediment resuspension and sponge‐mediated benthic production further modulate the local silica budget. Globally, the ocean Si cycle is closely linked to the biogeochemical cycles of carbon, nitrogen and phosphorus, with stoichiometric imbalances influencing phytoplankton community structure and the sequestration of atmospheric CO₂. Changes in ocean temperature, acidification, land use and river damming are altering silica fluxes at multiple scales, with consequences for diatom populations, nutrient limitation patterns and the long‐term storage of both silica and organic carbon in marine sediments.

Research from Nature Portfolio

Recent experimental mesocosm work has revealed that ocean acidification slows the chemical dissolution of sinking silica, increasing the silicon to nitrogen ratio of exported biogenic matter by around 17 per cent under future pCO₂ scenarios. Earth system simulations leveraging these findings project that decreased silica dissolution will lower surface silicic acid availability and trigger a global decline of diatom abundance by up to a quarter by 2200, illustrating an unexpected feedback on primary production. Complementary laboratory studies on model diatom species have demonstrated that temperature exerts control over silicification patterns: under silicon‐limited conditions, cooler growth temperatures induce a more tree‐like valve structure, whereas warmer conditions and ample silicon produce a denser mesh‐like morphology. These temperature‐dependent changes in frustule architecture have implications for sinking rates and dissolution behaviour in a warming ocean.

Biogenic Silica Cycling in Marine Environments publication trend

The graph below shows the total number of articles in biogenic silica cycling in marine environments across all publications each year (not limited to Nature Index journals).

Technical terms

Biogenic silica (BSi): Opaline silica material produced by organisms such as diatoms and sponges, forming frustules or spicules.

Silicic acid: The dissolved form of silicon (Si(OH)₄) available for uptake by siliceous organisms.

Diatom frustule: The two‐part silica shell of a diatom cell, providing protection and influencing sinking dynamics.

Dissolution kinetics: The rate at which biogenic silica dissolves back into silicic acid under varying chemical and physical conditions.

Biological pump: The process by which organic matter and associated minerals are transferred from the surface ocean to depth, sequestering carbon.

Stoichiometry: The elemental ratios (e.g. Si : N : P) that govern nutrient limitation and phytoplankton community composition.

References

1. Enhanced silica export in a future ocean triggers global diatom decline. Nature (2022).
2. Temperature affects the silicate morphology in a diatom. Scientific Reports (2015).
3. Riverine concentrations and export of dissolved silicon, and potential controls on nutrient stoichiometry, across the land–ocean continuum in Great Britain. Journal of Hydrology (2024).
4. Spatial and seasonal dynamics of biogenic silica in a eutrophic marginal sea, the East China Sea. Fundamental Research (2023).
5. Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean. Biogeosciences (2021).