ALBERT

Description: According to small subunit ribosomal RNA (ss rRNA) sequence comparisons all known Archaea belong to the phyla Crenarchaeota, Euryarchaeota, and—indicated only by environmental DNA sequences—to the 'Korarchaeota'1, 2. Here we report the cultivation of a new nanosized hyperthermophilic archaeon from a submarine hot vent. This archaeon cannot be attached to one of these groups and therefore must represent an unknown phylum which we name 'Nanoarchaeota' and species, which we name 'Nanoarchaeum equitans'. Cells of 'N. equitans' are spherical, and only about 400 nm in diameter. They grow attached to the surface of a specific archaeal host, a new member of the genus Ignicoccus3. The distribution of the 'Nanoarchaeota' is so far unknown. Owing to their unusual ss rRNA sequence, members remained undetectable by commonly used ecological studies based on the polymerase chain reaction4. 'N. equitans' harbours the smallest archaeal genome; it is only 0.5 megabases in size. This organism will provide insight into the evolution of thermophily, of tiny genomes and of interspecies communication.

Description: A key question in ecology is which factors control species diversity in a community1, 2, 3. Two largely separate groups of ecologists have emphasized the importance of productivity or resource supply, and consumers or physical disturbance, respectively. These variables show unimodal relationships with diversity when manipulated in isolation4, 5, 6, 7, 8. Recent multivariate models9, 10, however, predict that these factors interact, such that the disturbance–diversity relationship depends on productivity, and vice versa. We tested these models in marine food webs, using field manipulations of nutrient resources and consumer pressure on rocky shores of contrasting productivity. Here we show that the effects of consumers and nutrients on diversity consistently depend on each other, and that the direction of their effects and peak diversity shift between sites of low and high productivity. Factorial meta-analysis of published experiments confirms these results across widely varying aquatic communities. Furthermore, our experiments demonstrate that these patterns extend to important ecosystem functions such as carbon storage and nitrogen retention. This suggests that human impacts on nutrient supply11 and food-web structure12, 13 have strong and interdependent effects on species diversity and ecosystem functioning, and must therefore be managed together.

Description: BOOK REVIEWED: Plate Tectonics: An Insider's History of the Modern Theory of the Earth / edited by Naomi Oreskes Westview Press: 2001. 448 pp.

Description: The circulation of water masses in the northeastern North Atlantic Ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes1. But the ocean circulation at depths below the reach of satellite observations is difficult to measure, and only recently have comprehensive, direct observations of whole ocean basins been possible2, 3, 4. Here we present quantitative maps of the absolute velocities at two levels in the northeastern North Atlantic as obtained from acoustically tracked floats. We find that most of the mean flow transported northward by the Gulf Stream system at the thermocline level (about 600 m depth) remains within the subpolar region, and only relatively little enters the Rockall trough or the Nordic seas. Contrary to previous work5, 6, our data indicate that warm, saline water from the Mediterranean Sea reaches the high latitudes through a combination of narrow slope currents and mixing processes. At both depths under investigation, currents cross the Mid-Atlantic Ridge preferentially over deep gaps in the ridge, demonstrating that sea-floor topography can constrain even upper-ocean circulation patterns.

Description: Miocene Ignimbrite ‘A’ on Gran Canaria contains three compositional endmember fiamme types(two rhyolites and one trachyte) each of which crystallized distinct feldspar. Various textural and compositional criteria are interpreted as reflecting a complex scenario within the magma chamber in which the crystals formed. About 25–30% of the feldspar phenocrysts contain evidence for magma mixing in the form of (1) partial to severe dissolution–resorption rims, (2) distinct zones of drastically different compositions and (3) overgrowth textures on formerly resorbed crystals. Four major types of zoning in the oligoclase to anorthoclase feldspars of ignimbrite ‘A’ include a normal and a reversely zoned type and two complexly zoned types. The feldspars with normal and reverse zonation show only minor compositional amplitudes between individual zones (ΔAb, Or ∼4%), whereas the complexly zoned types show compositional differences between zones of up to 18 mol % Ab and 20 mol % Or and are commonly associated with an internal dissolution surface. Complex zoning with large compositional amplitudes and dissolution textures is taken as evidence of crystal movements within the magma and across compositional boundaries between magma batches. A multiple ‘step-cycle’ model, involving growth and transport of a crystal into another magma batch and its return to the original host magma, is suggested by the data. Moreover, feldspars from one rhyolite compositional group are found to be substantially elevated in δ18O, suggesting an input of a high δ18O component to this rhyolite. The other endmember rhyolite appears to be related to the endmember trachyte by mainly crystal fractionation of anorthoclase feldspar. This observation is consistent with trace element and rare earth element concentrations for the magma endmembers and their feldspars, where contamination led to a depletion in incompatible trace elements and light rare earth elements in the contaminated rhyolite and its feldspar phenocrysts. We suggest that the combination of textural and compositional variation in ternary feldspar of peralkaline rhyolitic systems is well suited to reconstruct dynamic processes such as magma mixing and contamination in evolving rhyolitic magma chambers.

Description: Incubation experiments with natural phytoplankton revealed a relationship between CO2 concentration and the production of transparent exopolymer particles (TEP), with TEP production being linearly related to theoretical CO2 uptake rates.

Description: normous amounts of potential energy lie buried in marine sediments in the form of reduced carbon compounds. The most familiar form of this vast energy reserve is petroleum, which drives the lion's share of today's energy economy. The next most obvious submarine energy reserve, even more abundant than petroleum, is methane. At deep-sea conditions of low temperature and high pressure, large amounts of this natural gas are found in sub-seafloor reservoirs of frozen methane hydrates [1]. Yet there is another abundant, but less obvious, marine energy reserve: sediment-associated organic carbon, which represents about 2% of the dry weight of marine sediments along continental margins. Is it possible to tap into this vast, dispersed form of submarine energy? If so, how? The answer, in part, is that microbes already have tapped into this large energy reserve. Now, in two papers, one in this issue [2] and the other in a previous issue of Science [3], researchers harness microbially generated power by constructing a fuel cell that can exploit the naturally occurring voltage gradient created by microbial activity in marine sediments.

Description: In many marine environments, a voltage gradient exists across the water sediment interface resulting from sedimentary microbial activity. Here we show that a fuel cell consisting of an anode embedded in marine sediment and a cathode in overlying seawater can use this voltage gradient to generate electrical power in situ. Fuel cells of this design generated sustained power in a boat basin carved into a salt marsh near Tuckerton, New Jersey, and in the Yaquina Bay Estuary near Newport, Oregon. Retrieval and analysis of the Tuckerton fuel cell indicates that power generation results from at least two anode reactions: oxidation of sediment sulfide (a by-product of microbial oxidation of sedimentary organic carbon) and oxidation of sedimentary organic carbon catalyzed by microorganisms colonizing the anode. These results demonstrate in real marine environments a new form of power generation that uses an immense, renewable energy reservoir (sedimentary organic carbon) and has near-immediate application.

Description: The oceanic carbon cycle is mainly determined by the combined activities of bacteria and phytoplankton, but the interdependence of climate, the carbon cycle and the microbes is not well understood. To elucidate this interdependence, we performed high-frequency sampling of sea water along a north-south transect of the Atlantic Ocean. Here we report that the interaction of bacteria and phytoplankton is closely related to the meridional profile of water temperature, a variable directly dependent on climate. Water temperature was positively correlated with the ratio of bacterial production to primary production, and, more strongly, with the ratio of bacterial carbon demand to primary production. In warm latitudes (25 degrees N to 30 degrees S), we observed alternating patches of predominantly heterotrophic and autotrophic community metabolism. The calculated regression lines (for data north and south of the Equator) between temperature and the ratio of bacterial production to primary production give a maximum value for this ratio of 40% in the oligotrophic equatorial regions. Taking into account a bacterial growth efficiency of 30%, the resulting area of net heterotrophy (where the bacterial carbon demand for growth plus respiration exceeds phytoplankton carbon fixation) expands from 8 degrees N (27 degrees C) to 20 degrees S (23 degrees C). This suggests an output of CO2 from parts of the ocean to the atmosphere.

Description: Population dynamics of major Baltic calanoid copepod species in the Gotland Basin during the last two decades were characterized by a decline of Pseudocalanus elongatus associated with declining salinities, and an increase of Temora longicornis and Acartia spp. potentially due to warmer conditions. Additionally this study investigated the effect of predation by the major planktivorous fish species herring (Clupea harengus) and sprat (Sprattus sprattus) for the period 1977–1996 in the Gotland Basin (Central Baltic Sea). Examination of consumption by these fish species in relation to copepod production estimates showed a switch by herring from consuming mainly CV/VI of P. elongatus and T. longicornis, to preying on CII of the latter copepod. This switch was potentially due to increased competition with the drastically increased sprat stock since the late 1980s. Further, an increased predation pressure by sprat on CV/CVI of both copepod species in spring resulted in higher copepod mortality rates. In consequence, based on these results we suggest that the increase in the sprat stock since the late 1980s contributed to a decline of P. elongatus, and additionally prevented an even more pronounced temperature-driven increase in the T. longicornis stock, as was observed for Acartia spp., which was not significantly consumed.