Publication Date

April 2018

Advisor(s)

Johan Varekamp

Major

Earth & Environmental Sciences

Language

English (United States)

Abstract

Paulina Lake, one of two small crater lakes in the Newberry Volcano caldera, Oregon, is fed by subaqueous hydrothermal springs that account for its carbonate-rich water composition. Its sediments consist predominantly of Fe and Si (up to 15 and 29%, respectively), with strong enrichments in P and As. All sediment analyses indicated the presence of some silicic volcanic ash, and a thick ash layer from the 720 A.D. Newberry eruption was identified in the main sediment core. An age model was calibrated around the ash layer, which suggested that the core represents 2800 years of lake history. Some of Paulina Lake?s hydrothermally-derived chemical constituents (e.g. Fe, As, Mn, P) precipitate immediately from the oxygenated, neutral waters (pH=~8) and settle into the sediments. Others (e.g. Ca, Na, K, Si) initially remain in the water as dissolved solids, although some hydrothermal silica may precipitate near the subaqueous hot springs. The dissolved species either leave the system through the Paulina Creek outflux or are sequestered by photosynthetic biota, and then accumulate into the sediment (~4% Corg). The lake releases CO2 from its surface, and the summation of the Paulina Creek outflow, organic sequestration, and CO2 release demand a weekly hydrothermal input of 40 tonnes of carbon. Taking all of the chemical sinks into account through the analysis of the sediment core and water chemistry data, a steady state mass balance equation was invoked to constrain the composition and fluxes of the subaqueous hot springs. The core analyses provided strong evidence for enhanced hydrothermal inputs between 0 and 500 B.C, and silica geothermometry indicated hydrothermal fluid temperatures of ~140 ?C. The Paulina Lake sediment shows strong similarities with Precambrian Iron Formations.

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