Biogenic silica as an estimate of siliceous microfossil abundance in Great Lakes sediments

Oxygen isotope values of diatom silica ( δ 18 O diatom ) are increasingly used as paleoclimate proxies; however, the magnitude and timing of post‐mortem alteration of δ 18 O diatom values has been unclear. In freshwater diatom silica from a human‐made pond in northern New Mexico, post‐mortem alteration of δ 18 O diatom values occurs within one year of sediment burial. Diatom silica collected antemortem has an average δ 18 O diatom value of 21.5‰ (VSMOW, σ = 1.3, n = 23), whereas diatom silica from two sediment cores from the same freshwater environment records significantly higher δ 18 O diatom values (28.9‰, σ = 0.8, n = 13). The difference in ante‐ and post‐mortem δ 18 O diatom values indicate post‐mortem alteration of diatom silica oxygen that results in a >7‰ increase in δ 18 O values. This study demonstrates that δ 18 O diatom values reach mature values within 0.5 years of frustule death. Initial diatom δ 18 O values that record growing conditions are rapidly overwritten during silica maturation, and the mature diatom δ 18 O values approach isotopic equilibrium for quartz‐water. The rapid post‐mortem alteration of diatom δ 18 O values explains much of the disparate data regarding silica‐water fractionation for diatom silica and has a profound effect on the use of diatom silica δ 18 O values as a paleoclimate proxy in lacustrine and marine environments.

Frustule

Biogenic silica

Dissolved silica

10.1029/2011gc004019

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Citations (37)

Evaluating diatom succession: some pecularities of the Great Lakes case

Journal of Paleolimnology (1993)

EugeneF. Stoermer

Paleolimnology

Epilimnion

Dominance (genetics)