Modeling Carbon Dynamics in the Twin Newberry Volcanic Lakes, Oregon

Abstract

East Lake and Paulina Lake are twin crater lakes in the Newberry caldera, near Bend, Oregon. Despite their proximity, the lakes are chemically different: CO 2 and H 2 S inputs in East Lake, and hot carbonate-rich fluids in Paulina Lake. Paulina Lake has four times the concentration of dissolved species as East Lake. Dissolved carbon in East Lake is isotopically much heavier (up to +5.5‰) than in Paulina Lake (0‰). Both lakes have internal P CO2 > P CO2 (atm), leading to diffusive CO 2 loss from the lake surfaces. The carbon budgets are different for the two lakes, and this study focuses on the carbon cycling in East Lake, which involves geothermal CO 2 input, diffusive CO 2 losses from the lake surface, no CO 2 uptake from the atmosphere, photosynthesis, respiration, and organic carbon burial. The isotopic composition and C:N of East Lake sediment indicates that buried organic matter is ~45% phytoplankton, 35% subaqueous vegetation, 15% cyanobacteria, and 5% pine needles. East Lake has a strong vertical δ 13 C (DIC) gradient (up to 5‰), because volcanic and biological sources and sinks of carbon in East Lake cause identical trends in DIC concentration and isotopic composition with depth. Isotopically light geothermal CO 2 enters the bottom water and evades from the surface waters (-10.5‰ δ 13 C), while isotopically light organic carbon is removed from surface waters and falls to bottom waters through the photosynthetic-respiration loop. Field flux measurements, sequential Gaussian simulations, and models indicate that both Newberry lakes evade CO 2 at comparable rates for volcanic lakes with similar surface areas and that CO 2 flux rates are highest in the early summer. East Lake evaded an average of ~71 tonnes of CO 2 per day in early June 2016, compared to ~45 tonnes of

History of Hydrothermal Activity at Paulina Lake, Newberry Volcano, Oregon USA

“…Both PL1 and PL2 have low organic content and it has not been possible to find enough terrestrial organic matter in the lower sections of the cores for 14 C dating at this time. It is not possible to use lake derived carbon for 14 C dating as the carbon entering the lake through the hydrothermal system is depleted in 14 C (Brumberg, 2017).…”