DIATOM RECONSTRUCTION OF TWO VOLCANIC CRATER LAKES WITHIN THE NEWBERRY VOLCANO, OREGON

Newberry Crater, located in central Oregon, is a low shield volcano that includes two meromictic volcanic lake systems within close proximity to each other. Paulina Lake and East Lake show significant chemical profile differences. Both lakes have subaqueous inputs of volcanic fluids, but fluids that enter East Lake are primarily hydrogen sulfide (H₂S) and carbon dioxide (CO₂) with minor amounts of mercury, while volcanic fluids that enter Paulina Lake are carbonate-rich and have abundant iron (Fe), arsenic (As), silicon (Si) and phosphorus (P). Multiple sediment cores were collected within each for diatom analysis. Changes in the fossil diatom assemblages from the lake sediments indicate long-term fluctuations in lake level, productivity, and other chemical and physical conditions. Benthic diatom communities thrive in shallow water where light can penetrate to the sediment-water interface. Planktic diatom communities are commonly found in open water away from shore. Changes in lake level are commonly identified using a planktic to benthic ratio. We created 3-D models of lakes’ morphometries to diagnose how changes in available diatom habitats are related to potential lake-level fluctuations. Diatom habitat area models can be used to predict relative changes in the available area for benthic and planktic diatom communities, and then can be compared against changes in planktic-benthic ratios in fossil assemblages from sediment cores to improve interpretations of past lake-level fluctuations. Research in these lakes is important because it offers a unique opportunity to analyze two lakes that are close geographically but are chemically distinct.