Climate, Tectonics or...?: Speculations on the Recent Paleolimnology of Yellowstone Lake

The sediments of Yellowstone Lake may reveal the paleoecological history of this lake over the last few centuries. These sediments contain up to 60% biogenic silica derived from diatom frustules settling out from the overlying water. The sediment record reveals large variations in the diatom deposition over the last ~350 years. Some of these variations appear to correlate extremely well with independent climate records, particularly mean annual winter temperature and precipitation, derived from tree ring data extrapolations. A strong correlation occurs, for example, during an extended period of below-normal winter temperatures and above-normal precipitation seen during the late 1800s. Below-normal winter temperatures can significantly extend winter ice cover and shorten the icefree, isothermal period during which the spring diatom bloom occurs. Rapid thermal stratification following prolonged ice cover may reduce annual diatom production and the subsequent silica deposition. Yet the forcing factors in this system may not be so straightforward. Sublacustrine hydrothermal springs found in the lake are a potential source of nutrients that may vary in strength and in time. These inputs may have the potential to alter the nutrient biogeochemistry of the lake. A pronounced chloride enrichment observed within the lake may be explained by input of a source of undiluted geothermal water equivalent to >0.06% of the riverine input. Calculations based upon silica removal indicate that such hydrothermal inputs would have to contribute up to ~107 moles of nitrogen annually, for example, in order to significantly shift the nutrient status of the lake. Observations to date, which are limited in space and time, do not appear to support such a flux for the whole lake. However, the existence of high-activity vents in past eras (as indicated by numerous relict features) or in unexplored regions of the lake cannot be ruled out. Introduction The integrity and value of the paleoecological history recorded in lake sediments is dependent upon a number of factors. For example, a good record contains: a relatively undisturbed sediment accumulation rate regime, a coherent and quantifiable sediment chronology, and minimal or quantifiable post-depositional alteration of biological or geochemical indicators as a consequence of diagenesis, mixing, migration, or other physical disturbances. The time scale of interest Climate, Tectonics or ...?: Speculations on the Recent Paleolimnology of Yellowstone Lake