A GEOCHEMICAL INVESTIGATION OF LATE HOLOCENE LAKE SEDIMENT CORES FROM PYRAMID LAKE, FIORDLAND, NEW ZEALAND

Pyramid Lake is a small (c. 500 meters in diameter), semi-closed lake thought to have formed 12000 – 13000 years ago, following the Green Lake Landslide at the end of the last ice age. Recent records of watershed change indicate regional climate variability from natural and anthropogenic sources. Biogenic silica, stable isotopes (δ¹³C and δ¹⁵N) and carbon and nitrogen elemental ratios of bulk sediment were examined in two sediment cores, 28 and 34 cm respectively, collected from Pyramid Lake to shed light on nutrient dynamics and primary production within the watershed. Carbon isotopes ranged from -27.7‰ to -29.0‰, showing an overall depletion from the bottom to top of core while nitrogen isotopes ranged from 0.9‰ to 1.9‰, showing a slight enrichment up core. Biogenic silica ranged from 0.97% to 23.8% and increased towards to the top of the cores. These results suggest an increase in primary productivity near the surface of the cores. ²⁴⁰Pu dates are pending as is compound-specific lipid biomarker analysis. By learning how the lake’s primary productivity has changed in response to its environment, we can gain an understanding of the extent of human impact and predict how it could change in the future in the face of human-induced climate change.