HOLOCENE TRENDS IN BIOGENIC SILICA REVEALED BY FTIR SPECTROSCOPY APPLIED TO A LAKE SEDIMENT RECORD FROM NORTHERN NORWAY

Reconstructing Holocene climate of the North Atlantic provides valuable context for evaluating broader Northern Hemisphere changes because of the region’s significant ocean and atmosphere circulation systems. One approach to reconstructing past climate change is by assessing lake productivity, which can be linked to atmospheric temperatures or landscape dynamics. In this project, we measured fluctuations in biogenic silica (BSi) in an 11,000-year old lake sediment core from the Lofoten Islands, Norway by Fourier-Transform Infrared Spectroscopy (FTIRS). Dried and ground samples mixed with KBr were scanned on a Thermo Scientific Nicolet iS10 FTIRS with a Praying Mantis diffuse reflectivity accessory over wavelengths 650-1300 cm^-1. The area under the absorbance curve was integrated over wavelengths 1000-1250 cm^-1_, which are associated with vibrational energy of Si-O bonds. Absorbance values were calibrated to biogenic silica using select samples processed via conventional chemical digestion techniques. Reproducibility of FTIRS-BSi was evaluated by measuring six samples ranging in BSi biweekly, which show an average standard deviation of 1-3 in %BSi. FTIRS-BSi data show a strong relationship to data acquired using conventional methods and display significant Holocene variation. The record shows a general increasing trend of BSi abundance, ranging from 9.5% to 26.9%. Low BSi trends in the early Holocene, 11-10 ka, likely reflect low lake productivity in response to cooler conditions and early landscape development following deglaciation. Increasing values from 10-6 ka correspond with an increase in lake productivity that reflect higher insolation and warmer summer temperatures during the Holocene Thermal Optimum. The late Holocene is characterized by a steady, gradual increase in BSi, deviating from regional temperature records that show cooling. This likely indicates that late Holocene BSi-inferred lake productivity at this site is not controlled by temperatures but may be more influenced by catchment-derived nutrient inputs. We also compared trends in BSi to other temperature proxies and regional records and demonstrate how this site provides important context for evaluating climate change effects in the North Atlantic.