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Oceanic distribution of inorganic germanium relative to silicon: Germanium discrimination by diatoms
Author(s) -
Sutton Jill,
Ellwood Michael J.,
Maher William A.,
Croot Peter L.
Publication year - 2010
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2009gb003689
Subject(s) - germanium , silicon , fractionation , analytical chemistry (journal) , seawater , materials science , mineralogy , geology , chemistry , environmental chemistry , oceanography , chromatography , optoelectronics
Seventeen inorganic germanium and silicon concentration profiles collected from the Atlantic, southwest Pacific, and Southern oceans are presented. A plot of germanium concentration versus silicon concentration produced a near‐linear line with a slope of 0.760 × 10 −6 (±0.004) and an intercept of 1.27 (±0.24) pmol L −1 ( r 2 = 0.993, p < 0.001). When the germanium‐to‐silicon ratios (Ge/Si) were plotted versus depth and/or silicon concentrations, higher values are observed in surface waters (low in silicon) and decreased with depth (high in silicon). Germanium‐to‐silicon ratios in diatoms (0.608–1.03 × 10 −6 ) and coupled seawater samples (0.471–7.46 × 10 −6 ) collected from the Southern Ocean are also presented and show clear evidence for Ge/Si fractionation between the water and opal phases. Using a 10 box model (based on PANDORA), Ge/Si fractionation was modeled using three assumptions: (1) no fractionation, (2) fractionation using a constant distribution coefficient (K D ) between the water and solid phase, and (3) fractionation simulated using Michaelis‐Menten uptake kinetics for germanium and silicon via the silicon uptake system. Model runs indicated that only Ge/Si fractionation based on differences in the Michaelis‐Menten uptake kinetics for germanium and silicon can adequately describe the data. The model output using this fractionation process produced a near linear line with a slope of 0.76 × 10 −6 and an intercept of 0.92 (±0.28) pmol L −1 , thus reflecting the oceanic data set. This result indicates that Ge/Si fractionation in the global ocean occurs as a result of subtle differences in the uptake of germanium and silicon via diatoms in surface waters.