SPECTRAL SIGNATURES OF HYPERTHERMOPHILE MATS AND ASSOCIATED SINTER IN YELLOWSTONE NATIONAL PARK

Visible-near infrared (350-2500 nm) reflectance spectra have been collected at high temperature springs and associated hyperthermophile mats and sinter deposits in Yellowstone National Park. Springs spanning a range of temperatures (ambient to ~95° C) and chemistries (acidic-alkaline) were examined. Each major hyperthermophile community (e.g., Synechococcus, Chloroflexus, Phormidium, Cyanidium) has a distinct spectrum resulting from the unique combination and concentration of chlorophylls and carotenoids. Typical absorptions occur near 675-680, 735, 800, 885, and 980 nm (the exact wavelength of maximum absorption depends upon how the coloring compound is bound in the cell). Using the “albedo” at various wavelengths and relative absorption strength, the major communities can be quickly defined at a given spring. The primary mineralogy of these deposits is amorphous silica although calcium carbonate dominates in the Mammoth area. If the outflow from a spring changes location or ceases, the mats become exposed and die; sinter deposition also ceases on the spring margin and across the mat-covered apron. Once dead, a significant fraction of the mat’s organic component decays, but some remains trapped in the sinter. Spectra of the inactive mat, although dominated by silica, show distinct absorptions characteristic of chlorophylls and carotenoids. In the Mammoth area, these same organic absorptions are observed; however in that area absorptions due to calcium carbonate are observed. Absorptions characteristic of the hyperthermophile organism are often observed in the sinter around the spring edge, in association with active sinter deposition, even when such biota are not visible, suggesting that organics occur at some level. Inactive sinter (including sinter-sand and -fragments and solid sinter) often display the same characteristic absorptions as observed in active mats, despite the fact that they are dry, at ambient temperature, and display no visible biota. These results indicate that the hyperthermophile organisms are being trapped in the sinter and that some of their associated organic compounds are preserved, such that they are recognizable at a later time.