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Dynamics of silicon metabolism and silicon isotopic discrimination in a marine diatomas a function of pCO 2
Author(s) -
Milligan Allen J.,
Varela Diana E.,
Brzezinski Mark A.,
Morel François M. M.
Publication year - 2004
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2004.49.2.0322
Subject(s) - diatom , frustule , biogenic silica , silicon , dissolution , environmental chemistry , isotopes of silicon , isotope , flux (metallurgy) , chemistry , stable isotope ratio , fractionation , analytical chemistry (journal) , oceanography , geology , chromatography , physics , organic chemistry , quantum mechanics
Opal accumulation rates in sediments have been used as a proxy for carbon flux, but there is poor understanding of the factors that regulate the Si quota of diatoms. Natural variation in silicon isotopes (δ 30 Si) in diatom frustules recovered from sediment cores are an alternative to opal mass for reconstructing diatom Si use and potential C export over geological timescales. Understanding the physiological factors that may influence the Si quota and the δ 30 Si isotopic signal is vital for interpreting biogenic silica as a paleoproxy. We investigated the influence of p CO 2 on the Si quota, fluxes across the cell membrane, and frustule dissolution in the marine diatom Thalassiosira weissflogii and determined the effect that p CO 2 has on the isotopic fractionation of Si. We found that our Si flux estimates mass balance and, for the first time, describe the Si budget of a diatom. The Si quota rose in cells grown with low p CO 2 (100 ppm) compared with controls (370 ppm), and the increased quota was the result of greater retention of Si (i.e., lower losses of Si through efflux and dissolution). The ratio of efflux : influx decreased twofold as p CO 2 decreased from 750 to 100 ppm. The efflux of silicon is shown to significantly bias measurements of silica dissolution rates determined by isotope dilution, but no effect on the Si isotopic enrichment factor (ε) was observed. The latter effect suggests that silicon isotopic discrimination in diatoms is set by the Si transport step rather than by the polymerization step. This observation supports the use of the v signal of biogenic silica as an indicator of the percentage utilization of silicic acid.