Ole Tumyr

Textural and chemical effects of bacterial activity on basaltic glass: an experimental approach

Abstract Naturally altered basaltic glass may show features such as pitted textures and variable degree of element mobilization relative to the fresh parent. The alteration process has generally been considered from only a chemical/physical point of view, but recent observations of bacteria in altered glass have, however, led to questions about the importance of microbial activity. In order to examine this, an experiment has been performed in which basaltic glass samples were immersed in growth media at room temperature for up to 394 days, inoculated with bacteria derived from a naturally altered pyroclastic deposit (Surtsey tuff). During the experiment it was observed that bacteria had a great affinity for attachment to the glass surface, which is in most cases connected to the production of extracellular polymers. Further, different species of bacteria were dominant at different time intervals. The bacteria activity caused a general decrease in pH from 8.0 to 5.8 during the time of the experiment. After 46 days of incubation, SEM studies of samples show rare examples of clear etching marks on the surface corresponding in size and shape of a minor group of bacteria. A local corrosion in a more irregular manner was observed after 181 days. Chemical analyses of the glass surface show no difference in composition compared to the fresh glass at this stage, i.e. any dissolution is congruent. Bacteria and biofilms attached to the glass surface show accumulation of elements, of which Al and Si could only have been derived by dissolution of the glass. However, the extent of accumulation of various elements may differ pronouncedly within and between the runs at 44, 77 and 181 days. This scatter probably reflects the diversity of the community and the ability of the different species of bacteria to accumulate elements. After 394 days the outermost glass rim, 1 μm in thickness, is highly depleted in all cations, except Si, which is relatively enriched. This incongruent dissolution of the glass, has only been active during the last 7 months of the experiment. The alteration rate is increased, at least, by a factor of 10 compared to that of the first 6 months. This is thought to be caused by the activity of a new, dominant bacterium group during this period. Microanalyses of the bacteria attached to the residual, leached glass rim, show more frequent accumulation of Si, and generally their chemistries are more homogenous than that observed in the other, shorter-termed runs. Bacterial activity may hence have a great influence on the textural and chemical developments commonly observed in naturally altered basaltic glass deposits.

Evidence for microbial activity at the glass-alteration interface in oceanic basalts

A detailed microbiological and geochemical study related to the alteration of basaltic glass of pillow lavas from the oceanic crust recovered from Hole 896A on the Costa Rica Rift (penetrating 290 m into the volcanic basement) has been carried out. A number of independent observations, pointing to the influence of microbes, may be summarized as follows: (1) Alteration textures are reminiscent of microbes in terms of form and shape. (2) Altered material contains appreciable amounts of C, N and K, and the N=C ratios are comparable to those of nitrogen-starved bacteria. (3) Samples stained with a dye (DAPI) that binds specifically to nucleic acids show the presence of DNA in the altered glass. Further, staining with fluorescent labeled oligonucleotide probes that hybridize specifically to 16S-ribosomal RNA of bacteria and archaea demonstrate their presence in the altered part of the glass. (4) Disseminated carbonate in the glassy margin of the majority of pillows shows d 13 C values, significantly lower than that of fresh basalt, also suggests biological activity. The majority of the samples have d 18 O values indicating temperatures of 20‐100oC, which is in the range of mesophilic and thermophilic micro-organisms.

A textural and chemical study of Icelandic palagonite of varied composition and its bearing on the mechanism of the glass-palagonite transformation

Palagonite of basalt and basaltic andesite parentages from hyaloclastite deposits in Iceland has been investigated. SEM studies indicate a sharp to diffuse alteration front which may propagate along microfractures in the glass, resulting in a progressive partial dissolution yielding palagonite of variable, but generally increasing porosity towards grain surfaces. The palagonite has a granular texture. Incipient alteration is indicated by the development of individual globules (ca. 0.01 μm in diameter), whereas at an advanced stage chains of globules, defining a sponge-like texture, characterize the palagonite. In the basaltic andesite, the precursor to brown Ti- and Fe-rich palagonite is a white variety, for which an evolutionary model is presented. EDS line-scans across the fresh glass-palagonite boundary show the existence of a 2–4 μm thick zone of glass-like material in which all elements have been depleted, except Si, and in some cases Al, which have been relatively enriched. The white palagonite is characterized by strong depletion of Ti, Fe, Na, Mg, and to lesser extent, Ca, Al (in order of decreasing loss). Regardless of the degree of porosity development (ca. 1–43 vol%), the extent of element depletion relative to SiO2 is constant. This gives evidence for selective element mobility prior to a variable degree of congruent network dissolution of the Si-rich residue, yielding zoned palagonite with a different porosity. In order for Fe, Ti, and Al to dissolve, a pH 3, Fe, Ti, and Al will precipitate in the pores of the white palagonite as oxides/hydroxides, thus creating the brown variety, which is characterized by highly variable contents of the above-mentioned elements. The applicability of this model to palagonite derived from basalt parentages at different pH conditions is discussed.

On the relation between dry matter and volume of bacteria.

Dry matter and volumes of 337 individual bacterial cells with volumes in the range 0.01–7μm3 from different origins were measured. An allometric relation was established between dry matter and volume, such that smaller bacteria tended to have a higher dry matter to volume ratio than larger bacteria. The results are compared to results from similar work on algae. The implications for the use of conversion factors are discussed.

Microbial fractionation of carbon isotopes in altered basaltic glass from the Atlantic Ocean, Lau Basin and Costa Rica Rift

Abstract Textural and DNA studies of pillow lavas in DSDP/ODP cores from the Atlantic Ocean, the Lau Basin and the Costa Rica Rift indicate that microbes had a significant role in the alteration of basaltic glasses. Carbon isotopes ( δ 13 C) in carbonates from glassy and crystalline basalts from these locations also show differences that may relate to microbial activity during alteration. The generally low δ 13 C values ( Bacteria and oxidation of organic matter. Positive δ 13 C values of some samples from the Atlantic suggest lithotrophic utilization of CO 2 , in which methanogenic Archaea produced CH 4 from H 2 and CO 2 . This may result from higher abiotic production of H 2 in the slow-spreading, fault-dominated Atlantic crust, due to more extensive serpentinization than at the intermediate-spreading Costa Rica Rift.

Evidence of ancient life at 207 m depth in a granitic aquife

The results of electron-microscopy investigations of calcite precipitated in a water-conducting fracture in a ca. 1800 Ma granitic rock from 207 m below sea level at the island of Aspo on the southeastern (Baltic) coast of Sweden are compared with measurements of carbon, oxygen, and sulfur isotope composition of the calcite and embedded pyrite. Parts of the calcite had extremely low delta 13C values, indicative of biological activity, and contained bacteria-like microfossils occurring in colonies and as typical biofllms. X-ray microanalysis demonstrated these fossils to be enriched in carbon. Our results provide evidence for ancient life in deep granitic rock aquifers and suggest that the modern microbial life found there is intrinsic. Modeling historical and present geochemical processes in deep granitic aquifers should, therefore, preferably include biologically catalyzed reactions. The results also suggest that the search for life on other planets, e.g., Mars, should include subsurface material.

Biogenic alteration of volcanic glass from the Troodos ophiolite, Cyprus

Alteration of basaltic glass through the entire volcanic sequence of the Troodos ophiolite is partly bio-mediated. The following observations support this conclusion: alteration textures resembling microbes in form and size; altered glass locally shows high carbon concentrations at the alteration front and organic remains. The absence of DNA suggests that the bio-alteration is a fossil process. Temperatures calculated from δ18O of carbonate, assumed to have been in equilibrium with seawater, yield 27–65°C, and δ18Osilicate versus H2O relationships indicate seawater alteration. These data are consistent with biogenic alteration during an early stage of ocean-floor alteration of the Troodos oceanic crust some 70–90 Ma ago.

Population density and zoning of olivine phenocrysts in tholeiites from Kauai, Hawaii

The population density of olivine phenocrysts of the tholeiites display an exponential variation, which is typical of igneous as well as contact metamorphic rocks. The exponential variation is explained by a new growth probability model, which is consistent with experimental work. The forsterite content of the olivine phenocrysts decreases with decreasing size. Various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber, after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place.

The Bjerkreim-Sokndal Layered Intrusion, Rogaland, SW Norway: Evidence from marginal rocks for a jotunite parent magma

Abstract The Late-Proterozoic Bjerkreim-Sokndal Layered Intrusion (BKSK) consists of andesine anorthosite, leuconorite, troctolite, norite, gabbronorite, jotunite, mangerite, quartz mangerite and charnockite. The sequence of appearance of cumulus minerals and their compositions suggest a parent magma that was evolved, had plagioclase (±olivine) on the liquidus, was sufficiently TiO2-rich for hemo-ilmenite to crystallise early, and low in CaO and CaO Al 2 O 3 compared to basalts as reflected by the sodic plagioclases and the delayed appearance of cumulus augite. Fine- to medium-grained jotunites found along the northern contact of the BKSK consist of plagioclase (An45–53), inverted pigeonite (Mg# = 55-50), sparse augite (Mg# = 69-59), Fe-Ti oxides, K-feldspar, quartz and apatite. They are basic to intermediate rocks with relatively high FeOtotal, high TiO2, low MgO/MgO + FeO, moderate Al2O3 and low CaO and normative diopside. The jotunites have compositions that are consistent with the parental magma for the lower part of the BKSK Layered Series, and are interpreted as being marginal chills. Similar, but slightly more differentiated, jotunite magmas were subsequently emplaced into the BKSK and the surrounding region as broad dykes and small plutons. Jotunite is a minor rock type in most massif-type anorthosite provinces but may have an important petrological significance.

Bio-signatures in metabasaltic glass of a Caledonian ophiolite, West Norway

Evidence of bioalteration of natural basaltic rocks, presently receiving much attention, has so far been restricted to in situ oceanic crust and ophiolites in which fresh glass is still present. Here we present evidence of preserved bio-signatures in the chilled margin of pillow lavas of an old (443 Ma) ophiolite that has suffered pervasive lower greenschist facies metamorphism and deformation. X-ray mapping of initial alteration zones shows the remains of organic carbon associated with highly-concentrated Fe and S. Bioproduction of CO 2 is further reflected in the low δ 13 C values of calcite extracted from pillow rims, compatible with microbe-induced fractionation during oxidation of organic matter. We attribute these effects to growth of sulphate-reducing bacteria at the early stage of ophiolite formation. During energy metabolism these bacteria reduce sulphate to H 2 S and oxidize organic matter to CO 2 . Hydrogen sulphide will eventually react with iron and form pyrite, and carbon dioxide is precipitated as calcium carbonate. The results of this study may thus trigger the search for bio-signatures in glassy volcanic rocks of any age.