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Refractory "dark biogenic silica" and its effects on the connection between the marine cycles of carbon and silicon

AuthorsMaldonado, Manuel ; García-Puig, Marta ; López-Acosta, María ; Sitjà, Cèlia ; Ercilla, Gemma
Issue Date14-Feb-2018
PublisherAmerican Geophysical Union
Association for the Sciences of Limnology and Oceanography
Citation2018 Ocean Sciences Meeting (2018)
AbstractQuantifying in detail the role of the oceans as net sink of atmospheric CO2 is a major international objective. The marine phytoplankton is responsible for the bulk of the CO2 consumption. It is used as an inorganic carbon (C) source, which through the photosynthesis, is converted into organic C to sustain cell growth. Within the phytoplankton, the most important CO2 consumers are diatoms. Unlike other phytoplankton groups, the consumption of CO2 by diatoms is intimately and stoichiometrically associated to the consumption of silicic acid (DSi), because diatoms need DSi to elaborate their silica shell for cell growth. Upon death, the siliceous shell of diatoms is preserved in sediments better than the organic C cell remains. Consequently, the C:Si ratios in sediments are seen as a valuable proxy to estimate net C export to depths and subsequent burial in sediments during both present and past ocean conditions. Here we show that, contrary to the current understanding, a large part of the biogenic silica (BSi) in the marine sediments is not in the form of frustules, but in the form of sponge spicules. The sponge silica may contribute to total BSi with similar even higher values than diatoms do, depending on the depositional environment. More importantly, we show that the sponge silica is highly resistant to dissolution and that it has about 6 times more potential for preservation in the sediments. This refractory sponge silica is also herein defined as “dark silica” because it has been produced without connection to photoautotrophic consumption of CO2. Therefore, the traditional neglect of large amounts of sponge silica occurring in many marine sediments is disrupting our understanding of the connections between the C and Si cycles. According to our set of quantifications, the current inference of C:Si ratios may be affected by errors larger than 50% in some ocean areas, particularly on continental margins and around seamount systems
Description2018 Ocean Sciences Meeting, 11-16 February, in Portland, Oregon
Publisher version (URL)https://agu.confex.com/agu/os18/meetingapp.cgi/Paper/306650
Appears in Collections:(CEAB) Comunicaciones congresos
(ICM) Comunicaciones congresos
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