CONFIRMATION OF THE USE OF FTIR SPECTROSCOPY TO DETERMINE BIOGENIC SILICA CONTENT OF ARCTIC LAKE SEDIMENTS: A POWERFUL TOOL FOR HIGH-RESOLUTION PALEOCLIMATE RECONSTRUCTIONS

The biogenic silica (opal) content of sediments from Arctic lakes were determined using Fourier Transform Infrared Spectroscopy (FTIRS). Biogenic silica has been shown to record siliceous microfossil abundances in lakes and has been interpreted as a paleo-producitivity/paleoclimate proxy. Traditional wet chemistry extraction measurements are time-consuming and expensive, prohibiting high-resolution analysis. A new method of determining biogenic silica using infrared spectroscopy allows for large numbers of samples to be run quickly and cheaply, greatly increasing the usefulness of this proxy for paleoclimate studies.

FTIRS analysis requires only a small amount of sediment (~0.01g) and minimal pretreatment (mixing with non-toxic potassium bromide). When a sample is exposed to infrared (IR) radiation, molecules containing polar bonds vibrate at wavelengths specific to their structural and atomic composition and absorb the IR radiation. By measuring the absorption spectra of a sample and integrating the peak area of certain molecules, relative amounts can be determined. To quantify the actual percentage of biogenic silica in a given sample, absorbance peak areas characteristic of amorphous SiO₄ were regressed against traditional measurements. A linear regression shows a significant correlation, with an r² of 0.88 (n=21).

This calibration was then applied to all downcore samples from Nanerersarpik Lake in SE Greenland to produce a high-resolution paleo-productivity record for the Holocene. Preliminary analysis suggests some resemblance between the highly variable biogenic silica concentrations and reconstructed temperatures from the GISP2 Renland/Agassiz ice core compilations over the past ~2000yr. While the absolute agreement of these records is debatable, it nevertheless demonstrates the potential advantage of this type of analysis. The use of FTIR spectroscopy allows for many more samples to be analyzed than traditional methods would permit with the same application of resources and can provide high-resolution measurements of an informative paleoclimate proxy.