Geology topics

Research about Mono Lake

Source-linked reports with geographic coverage including Mono Lake.

25 records · Page 2Linked to original sources

USGS1993

Aspects of the biogeochemistry of methane in Mono Lake and the Mono Basin of California

Above-ambient levels of methane and higher hydrocarbons were detected in the atmosphere of the Mono Basin. These gases emanated from several different sources, including natural gas seeps (thermogenic and biogenic), and methanogenic activity in sediments. Seeps were distributed over nearly 33% of the lake bottom and were also present in the exposed former lakebed. They originated from one or more natural gas deposits that underlie the basin. Seeps associated with hot springs had a thermogenic character, whereas the others had the characteristics of bacterially formed gases. The radiocarbon content of methane in all seep gases was low (5-11% modern carbon), indicating an age of greater than about 20,000 years. Dissolved methane increased with depth in the sediments, ultimately reaching saturation levels (1-3 mM). The outward diffusive flux of methane into the anoxic bottom waters elevated concentrations to 60 µM during the 1984-1988 meromictic interval. The radiocarbon content of hypolimnion methane was equivalent to that of the dissolved inorganic carbon (~80% modern carbon), indicating derivation from current methanogenic activity. Oxidation by anaerobic bacteria was the major sink for this methane. Methane that escaped oxidation transited to the epilimnion where it attained supersaturation (0.1-3.0 µM) relative to the atmosphere. Measured outward fluxes over a 2-year period were highly variable, ranging from 0.01 to 4.82 mmoles CH 4 m -2 d -1 . Bacterial activity was detected in the sediments of the hypolimnion High rates of sulfate reduction (~200 µmoles L -1 d -1 ) were measured in the upper 5-cm interval but decreased > 10-fold with depth. The highest rate of methanogenic activity was ~1 µmole L -1 d -1 , as measured by reduction of 14 CO 2 . Bacteria metabolized dimethylsulfide, trimethylamine, acetate, and glucose to primarily CO 2 and some CH 4 . Turnovers of glucose (k = 0.16 d -1 ) and trimethylamine (k = 0.09 d -1 ) were highest in the upper 2.5-cm interval and decreased as much as 10-fold with depth. These results confirm that a low rate of methanogenic activity occurs in this extreme environment and is the source of methane to the hypolimnion.

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USGS1991

Gaylussite formation at Mono Lake, California

The salinity of Mono Lake has steadily increased since 1941 from 50%. to about 90%. due to diversion of tributary streams. This increase has resulted in the newly discovered precipitation of gaylussite (Na 2 Ca(CO 3 ) 2 · 5H 2 O). Chemical modeling of the lake water using Pitzer equations suggests that gaylussite has been forming year round since about 1970 when the salinity first exceeded 80%., and that it was earlier forming intermittently at lower salinities in the winter shortly after diversion began, breaking down incongruently to aragonite during summers. Lake water appears to remain at a constant 9-fold supersaturation with aragonite at all salinities, perhaps buffered by monohydrocalcite which appears to be just at saturation for all salinities. Other saline lakes also appear to be buffered by monohydrocalcite.

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USGS1990

Nitrogen fixation dynamics of two diazotrophic communities in Mono Lake, California

Two types of diazotrophic microbial communities were found in the littoral zone of alkaline hypersaline Mono Lake, California. One consisted of anaerobic bacteria inhabiting the flocculent surface layers of sediments. Nitrogen fixation (acetylene reduction) by flocculent surface layers occurred under anaerobic conditions, was not stimulated by light or by additions of organic substrates, and was inhibited by O 2 , nitrate, and ammonia. The second community consisted of a ball-shaped association of a filamentous chlorophyte ( Ctenocladus circinnatus ) with diazotrophic, nonheterocystous cyanobacteria, as well as anaerobic bacteria ( Ctenocladus balls). Nitrogen fixation by Ctenocladus balls was usually, but not always, stimulated by light. Rates of anaerobic dark fixation equaled those in the light under air. Fixation in the light was stimulated by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea and by propanil [ N -(3,4-dichlorophenyl)propanamide]. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea-elicited nitrogenase activity was inhibited by ammonia (96%) and nitrate (65%). Fixation was greatest when Ctenocladus balls were incubated anaerobically in the light with sulfide. Dark anaerobic fixation was not stimulated by organic substrates in short-term (4-h) incubations, but was in long-term (67-h) ones. Areal estimates of benthic N 2 fixation were measured seasonally, using chambers. Highest rates (∼29.3 μmol of C 2 H 4 m −2 h −1 ) occurred under normal diel regimens of light and dark. These estimates indicate that benthic N 2 fixation has the potential to be a significant nitrogen source in Mono Lake.

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USGS1987

Sources and flux of natural gases from Mono Lake, California

The ability to identify a formation mechanism for natural gas in a particular environment requires consideration of several geochemical factors when there are multiple sources present. Four primary sources of methane have been identified in Mono Lake. Two of these sources were associated with numerous natural gas seeps which occur at various locations in the lake and extend beyond its present boundary; the two other gas sources result from current microbiological processes. In the natural gas seeps, we observed flow rates as high as 160 moles CH 4 day −1 , and estimate total lakewide annual seep flux to be 2.1 × 10 6 moles CH 4 . Geochemical parameters ( δ 13 CH 4 , δDCH 4 , CH 4 /[ C 2 H 6 + C 3 H 8 ]) and δ 14 CH 4 measurements revealed that most of the seeps originate from a paleo-biogenic ( δ 13 CH 4 = about −70%.). natural gas deposit of Pleistocene age which underlies the current and former lakebed. Gas seeps in the vicinity of hot springs had, in combination with the biogenic gas, a prominent thermogenic gas component resulting from hydrothermal alteration of buried organic matter.

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USGS1983

Plutonium speciation in water from Mono Lake, California

The solubility of plutonium in Mono Lake water is enhanced by the presence of large concentrations of indigenous carbonate ions and moderate concentrations of fluoride ions. In spite of the complex chemical composition of this water, only a few ions govern the behavior of plutonium, as demonstrated by the fact that it was possible to duplicate plutonium speciation in a synthetic water containing only the principal components of Mono Lake water.

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USGS1980

Calcite-impregnated defluidization structures in littoral sands of Mono Lake, California

Associated locally with well-known tufa mounds and towers of Mono Lake, California, are subvertical, concretionary sand structures through which fresh calcium-containing artesian waters moved up to sites of calcium carbonate precipitation beneath and adjacent to the lake. The structures include closely spaced calcite-impregnated columns, tubes, and other configurations with subcylindrical to bizarre cross sections and predominantly vertical orientation in coarse, barely coherent pumice sands along the south shore of the lake. Many structures terminate upward in extensive calcareous layers of caliche and tufa. Locally they enter the bases of tufa mounds and towers. A common form superficially resembles root casts and animal burrows except that branching is mostly up instead of down. Similar defluidization structures in ancient sedimentary rocks have been mistakenly interpreted as fossil burrows.

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USGS1960

Geophysical investigation of Mono Basin, California

Gravity and seismic studies in Mono Basin , Mono County, California , completed during the summer of 1957 revealed a large, roughly triangular block that had subsided about 18,000 ± 5000 feet and received an accumulation of about 300 ± 100 cubic miles of light clastic sediments and volcanic material of Cenozoic age. The seemingly near-vertical faults that bound this great block are displaced toward the center of the basin from the surrounding mountain masses, but in general they are parallel to well-defined Basin and Range trends. The gravity minimum anomaly associated with the Mono Basin structure has a residual gravity relief of about 50 mgals, and the lowest gravity readings (on Paoha Island) yield a complete Bouguer gravity value of about - 260 mgals with respect to the International Ellipsoid. The computed depth of subsidence is based on a density of 2.3 gms/ cm 3 for the basin fill and 2.7 gms/cm 3 for the basement rocks. Seismic-refraction profiles at several places in the basin demonstrate that the Cenozoic deposits are thick where the gravity is low and relatively thin where the gravity is higher. Along common seismic and gravity profiles steep seismic dips coincide with steep gravity gradients. Numerous seismic reflections are present within the basin fill. Anomalies on four aeromagnetic profiles are related in part to volcanic material within the Cenozoic section. It is concluded that Mono Basin may be a volcano-tectonic depression caused by subsidence along faults, following extrusion of magma from a magma chamber at depth. Volcanic rocks of Pliocene(?) and Pleistocene ages are exceptionally abundant in this area.

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