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Unexpected Diversity of Small Eukaryotes in Deep-Sea Antarctic

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Unexpected Diversity of Small Eukaryotes in Deep-Sea Antarctic letters to nature and lower east sides of the volcano, and by the rapid transformation 9. Fiske, R. S., Hopson, C. A. & Waters, A. C. Geology of Mount Rainier National Park Washington. US of the collapsed material into a far-travelled lahar. The three large, Geol. Surv. Prof. Pap. 444, 93 (1963). 10. Sisson, T. W. & Lanphere, M. A. Geologic controls on the timing and location of ¯ank alteration at Mt. thick, nonmagnetic bodies that ring the edge of the Osceola Rainier, Washington. Eos 80, F1151±F1152 (1999). palaeocrater (below Russell cliff, east of Sunset amphitheater and 11. Crandell, D. R. Postglacial lahars from Mount Rainier Volcano, Washington. US Geol. Surv. Prof. Pap. near Gibraltar rock) (Fig. 2) are probably remnants of the old 677, 75 (1971). 12. Rystrom, V. L., Finn, Carol A. & Descsz-Pan, Maryla High resolution, low altitude aeromagnetic and altered core of the volcano. The absence of thick altered zones electromagnetic survey of Mt Rainier. US Geological Survey Open-File Report 00-027 [online], hhttp:// beneath the modern summit and the upper east slope suggests not greenwood.cr.usgs.gov/pub/open-®le-reports/ofr-00-0027/Rainierwebpage. htmli (2000). only that the Osceola collapse removed the altered core and upper 13. Deszcz-Pan, M., Fitterman, D. V. & Labson, V. F. Reduction of inversion errors in helicopter EM data eastern portion of the old dyke system (Fig. 1a) to substantial using auxiliary information. Explor. Geophys. 29, 142±146 (1998). 14. Woodward, D. J. & Mumme, T. C. Variation of magnetisation on White Island, New Zealand. N.Z. J. depths, but also that the vertical depth of incision of the Osceola Geol. Geophys. 36, 447±451 (1993). failure might have been limited by the base of highly altered 15. Fiske, R. S., Hopson, C. A. & Waters, A. C. Geologic Map and Section of Mount Rainier National Park rock. Washington (US Geological Survey Miscellaneous Investigations Series I-432, 1964). The absence of a large volume of alteration beneath the modern 16. Finn, C. & Williams, D. L. An aeromagnetic study of Mount St. Helens. J. Geophys. Res. 92, 10194± 110206 (1987). summit and east slope might restrict the collapse of altered material 17. Williams, D. L. & Finn, C. A. Evidence for a shallow pluton beneath the Goat Rocks Wilderness, to the west side of the volcano18, suggesting that a mud¯ow event as Washington, from gravity and magnetic data. J. Geophys. Res. 92, 4867±4880 (1987). large as the Osceola is no longer likely. If collapse retrogresses into 18. Reid, M. E., Christian, S. B., Brien, D. L. & Sisson, T. W. 3-D gravitational stability of stratovolcanoes. the core of the volcano, the relatively coherent core material might Eos 80, F1151 (1999). generate a debris avalanche that would be far less mobile than clay- rich lahars. As alteration is associated primarily with eruptive Acknowledgements periods at Mount Rainier10, the development of future weak, altered We thank D. Fitterman, V. J. S. Grauch and P. Lipman for helpful reviews. This work was supported by the Mineral Resource and Volcano Hazards Programs of the US Geological zones might depend on the frequency and volume of eruptions. The Survey. 25±50 m thickness of alteration at the modern summit has formed since ,2,000±5,000 yr ago. If magmatism and alteration were to Correspondence and requests for materials should be addressed to C.A.F. (e-mail: c®[email protected]). continue at these Holocene rates, it would take at least 20,000 yr to alter an appreciable thickness (.500 m) of the volcano's core. Signi®cant alteration associated with dyke injection also takes 50± 100 kyr10. This ®rst detailed assessment of the internal distribution of ................................................................. altered zones in an active volcano, using geophysical measurements, differs substantially from the distribution extrapolated from Unexpected diversity of small sur®cial exposures alone2±4. Lahars generated by the collapse of structurally incompetent hydrothermally altered rock are most eukaryotes in deep-sea probable on the west side of the volcano18. Strong shaking of the edi®ce during even small eruptive events could dislodge altered rock Antarctic plankton and generate a lahar capable of reaching densely populated areas. Although edi®ce collapse does not require weakened altered rocks, Puri®cacioÂnLoÂpez-GarcõÂa*, Francisco RodrõÂguez-Valera*, the widespread preservation of old (100±200 kyr) lava ¯ows at high Carlos PedroÂs-Alio² & David Moreira* elevations on Mount Rainier10, as well as the scarcity of debris avalanche deposits, as opposed to lahar deposits, suggests that * DivisioÂn de Microbiologia, Universidad Miguel HernaÂndez, unaltered ¯anks collapse infrequently. But Mount Rainier has 03550 San Juan de Alicante, Spain produced numerous far-travelled lahars that contain little or no ² Institut de CieÁnces del Mar, CSIC, 08039 Barcelona, Spain altered material. Some of these alteration-free lahars probably .............................................................................................................................................. formed as pyroclastic ¯ows or disaggregating active lava ¯ows Phylogenetic information from ribosomal RNA genes directly that swept across and incorporated glacial ice. Lahars originating ampli®ed from the environment changed our view of the bio- by this magma±ice interaction threaten all valleys draining the sphere, revealing an extraordinary diversity of previously unde- edi®ce. Nevertheless, the collapse of altered ¯anks, either during or tected prokaryotic lineages. Using ribosomal RNA genes from independently of eruptive activity, is a primary hazard at Mount marine picoplankton, several new groups of bacteria and archaea Rainier and elsewhere, and high-resolution geophysical surveys have been identi®ed, some of which are abundant2±4. Little is interpreted with the bene®t of detailed geological mapping is an known, however, about the diversity of the smallest planktonic effective tool for evaluating, substantiating and quantifying hazards eukaryotes, and available information in general concerns the from collapse-generated debris ¯ows. M phytoplankton of the euphotic region. Here we recover eukaryotes in the size fraction 0.2±5 mm from the aphotic zone (250±3,000 m Received 5 June; accepted 13 November 2000. deep) in the Antarctic polar front. The most diverse and relatively 1. Lopez, D. L. & Williams, S. N. Catastrophic volcanic collapse; relation to hydrothermal processes. abundant were two new groups of alveolate sequences, related to Science 260, 1794±1796 (1993). 2. Frank, D. Sur®cial extent and conceptual model of hydrothermal system at Mount Rainier, dino¯agellates that are found at all studied depths. These may be Washington. J. Volcanol. Geotherm. Res. 65, 51±80 (1995). important components of the microbial community in the deep 3. Zimbelman, D. R. Hydrothermal Alteration and its In¯uence on Volcanic Hazards; Mount Rainier, ocean. Their phylogenetic position suggests a radiation early in Washington, a Case History (Univ. Colorado, Boulder, Colorado, 1996). the evolution of alveolates. 4. Crowley, J. K. & Zimbelman, D. R. Mapping hydrothermally altered rocks on Mount Rainier, Washington, with Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data. Geology 25, 559± We ampli®ed 18S rRNA genes from samples taken at 250, 500, 562 (1997). 2,000 and 3,000 m deep at the Antarctic polar front limit in a 5. Crandell, D. R. & Waldron, H. H. A Recent volcanic mud¯ow of exceptional dimensions from Mount transect along the Drake passage (598 199 480 S, 558 459 110 W, sea Rainier, Washington. Am. J. Sci. 254, 349±362 (1956). ¯oor at 3,671 m). This sampling site interested us because it is a 6. Vallance, J. W. & Scott, K. M. The Osceola Mud¯ow from Mount Rainier: sedimentology and hazard implications of a huge clay-rich debris ¯ow. Geol. Soc. Am. Bull. 109, 143±163 (1997). region of water-mass mixing from the Atlantic and Southern 7. Scott, K. M., Vallance, J. W. & Pringle, P. T. Sedimentology, behavior, and hazards of debris ¯ows at oceans. It corresponds to cold and oligotrophic waters where Mount Rainier, Washington. US Geol. Surv. Prof. Pap. 1547, 1±56 (1995). microbial biomass, especially at 3,000 m deep, reached minimal 8. Moran, S. C., Zimbelman, D. R. & Malone, S. D. A model for the magmatic hydrothermal system at Mount Rainier, Washington, from seismic and geochemical observations. Bull. Volcanol. 61, 425±436 values in the area as deduced from DNA yields (see Methods). We (2000). constructed 18S rRNA environmental gene libraries from the 0.2± NATURE | VOL 409 | 1 FEBRUARY 2001 | www.nature.com © 2001 Macmillan Magazines Ltd 603 letters to nature 5 mm planktonic fraction and, for comparison, also from the a microbial fraction .5 mm at 3,000 m deep. After partial sequencing Microsporidia of the 39 region of the gene (700 base pairs, bp, on average), BLAST 5 Diplomonadida searches and phylogenetic reconstruction distance methods pro- Trichomonadida vided us with a ®rst survey of the type of eukaryotic sequences DH148-5-EKD18 Physarum polycephalum present in our samples. Twenty-four representative clones from all 80 DH148-EKB1 100 Diplonema papillatum 96 95 Euglena gracilis depths were subsequently chosen for complete sequencing. The DH145-EKD11 Phreatamoeba balamuthi complete sequences were aligned with 1,443 additional 18S rRNA Entamoeba histolytica gene sequences retrieved from databanks. A subset of 101 complete 50 Myxozoa Dictyostelium discoideum sequences was then selected for phylogenetic analysis, taking special 48 Ammonia beccarii care to include a taxonomically broad sample of eukaryotes (all and Haplosporidia closest relatives to our sequences) to minimize artefacts related to taxonomic sampling. We constructed distance (neighbour-joining, NJ), maximum-parsimony (MP) and maximum-likelihood (ML) 250 m trees, which produced similar congruent results. Figure 1 shows an 500 m 2,000 m Crown eukaryotes ML tree displaying the eukaryotic microbial diversity found. 3,000 m As was expected of cold, highly oxygenated waters, the majority of 3,000 m (> 5 µm) sequences af®liate with the eukaryotic ``crown'', the densely branched apical part of the eukaryotic tree6.
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