A review of Si particle fluxes in the modern ocean

• Main Authors: Ragueneau, Olivier, Tréguer, Paul, Leynaert, Aude, Anderson, Robert F, Brzezinski, Mark A, DeMaster, David J, Dugdale, Richard, Dymond, Jack R, Fischer, Gerhard, Francois, Roger, Heinze, Christoph, Maier-Reimer, Ernst, Martin-Jézéquel, Véronique, Nelson, David M, Quéguiner, Bernard
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 2000
• Subjects: Barcelona Coast; ORFOIS; Origin and Fate of Biogenic Particle Fluxes in the Ocean; Pertuis Charentais; Silicon Cycling in the World Ocean; SINOPS; Taranto Mare Piccolo; Southern Ocean
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.787476; https://doi.org/10.1594/PANGAEA.787476

Due to the major role played by diatoms in the biological pump of CO2, and to the presence of silica-rich sediments in areas that play a major role in air-sea CO2 exchange (e.g. the Southern Ocean and the Equatorial Pacific), opal has a strong potential as a proxy for paleoproductivity reconstructions. However, because of spatial variations in the biogenic silica preservation, and in the degree of coupling between the marine Si and C biogeochemical cycles, paleoreconstructions are not straitghtforward. A better calibration of this proxy in the modern ocean is required, which needs a good understanding of the mechanisms that control the Si cycle, in close relation to the carbon cycle. This review of the Si cycle in the modern ocean starts with the mechanisms that control the uptake of silicic acid (Si(OH)4) by diatoms and the subsequent silicification processes, the regulatory mechanisms of which are uncoupled. This has strong implications for the direct measurement in the field of the kinetics of Si(OH)4 uptake and diatom growth. It also strongly influences the Si:C ratio within diatoms, clearly linked to environmental conditions. Diatoms tend to dominate new production at marine ergoclines. At depth, they also succeed to form mats, which sedimentation is at the origin of laminated sediments and marine sapropels. The concentration of Si(OH)4 with respect to other macronutrients exerts a major influence on diatom dominance and on the rain ratio between siliceous and calcareous material, which severely impacts surface waters pCO2. A compilation of biogenic fluxes collected at about 40 sites by means of sediment traps also shows a remarkable pattern of increasing BSi:Corg ratio along the path of the "conveyor belt", accompanying the relative enrichment of waters in Si compared to N and P. This observation suggests an extension of the Si pump model described by Dugdale and Wilkerson (1989, doi:10.1038/34630), giving to Si(OH)4 a major role in the control of the rain ratio, which is of major importance in the global ...