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NASA NTRS2018

Interpreting Precession-Driven δ O-18 Variability in the South Asian Monsoon Region

Speleothem records from the South Asian summer monsoon (SASM) region display variability in the ratio of O-18 and O-16 (δ O-18) in calcium carbonate at orbital frequencies. The dominant mode of variability in many of these records reflects cycles of precession. There are several potential explanations for why SASM speleothem records show a strong precession signal, including changes in temperature, precipitation, and circulation. Here we use an Earth system model with water isotope tracers and water-tagging capability to deconstruct the precession signal found in SASM speleothem records. Our results show that cycles of precession-eccentricity produce changes in SASM intensity that correlate with local temperature, precipitation, and δ O-18. However, neither the amount effect nor temperature differences are responsible for the majority of the SASM δ O-18 variability. Instead, changes in the relative moisture contributions from different source regions drive much of the SASM δ O-18 signal, with more nearby moisture sources during Northern Hemisphere summer at aphelion and more distant moisture sources during Northern Hemisphere summer at perihelion. Further, we find that evaporation amplifies the δ O-18 signal of soil water relative to that of precipitation, providing a better match with the SASM speleothem records. This work helps explain a significant portion of the long-term variability found in SASM speleothem records.

paleoclimate↗

NASA NTRS2000

Microscopic physical biomarkers in carbonate hot springs: implications in the search for life on Mars

Physical evidence of life (physical biomarkers) from the deposits of carbonate hot springs were documented at the scale of microorganisms--submillimeter to submicrometer. The four moderate-temperature (57 to 72 degrees C), neutral pH springs reported on in this study, support diverse communities of bacteria adapted to specific physical and chemical conditions. Some of the microbes coexist with travertine deposits in endolithic communities. In other cases, the microbes are rapidly coated and destroyed by precipitates but leave distinctive mineral fabrics. Some microbes adapted to carbonate hot springs produce an extracellular polymeric substance which forms a three-dimensional matrix with living cells and cell remains, known as a biofilm. Silicon and iron oxides often coat the biofilm, leading to long-term preservation. Submicrometer mineralized spheres composed of calcium fluoride or silica are common in carbonate hot spring deposits. Sphere formation is biologically mediated, but the spheres themselves are apparently not fossils or microbes. Additionally, some microbes selectively weather mineral surfaces in distinctive patterns. Hot spring deposits have been cited as prime locations for exobiological exploration of Mars. The presence of preserved microscopic physical biomarkers at all four sites supports a strategy of searching for evidence of life in hot spring deposits on Mars.

NASA Center JSC↗

NASA NTRS1993

New constraints on Precambrian ocean composition

The Precambrian record of carbonate and evaporite sedimentation is equivocal. In contrast to most previous interpretations, it is possible that Archean, Paleoproterozoic, and to a lesser extent, Meso to Neoproterozoic seawater favored surplus abiotic carbonate precipitation, as aragonite and (hi-Mg?) calcite, in comparison to younger times. Furthermore, gypsum/anhydrite may have been only rarely precipitated prior to halite precipitation during evaporation prior to about 1.8 Ga. Two effects may have contributed to these relationships. First, sulfate concentration of seawater may have been critically low prior to about 1.9 Ga so the product mCa++ x mSO4-- would not have produced gypsum before halite, as in the Mesoproterozoic to modern ocean. Second, the bicarbonate to calcium ratio was sufficiently high so that during progressive evaporation of seawater, calcium would have been exhausted before the gypsum field was reached. The pH of the Archean and Paleoproterozoic ocean need not have been significantly different from the modern value of 8.1, even at CO2 partial pressures of a tenth of an atmosphere. Higher CO2 partial pressures require somewhat lower pH values.

NASA Discipline Exobiology↗

NASA NTRS1985

Millimeter-scale variations of stable isotope abundances in carbonates from banded iron-formations in the Hamersley Group of Western Australia

Several diamond drill cores from formations within the Hamersley Group of Western Australia have been studied for evidence of short-range variations in the isotopic compositions of the carbonates. For a set of 32 adjacent microbands analyzed in a specimen from the Marra Mamba Iron Formation, carbon isotope compositions of individual microbands ranged from -2.8 to -19.8 per mil compared to PDB and oxygen isotope compositions ranged from 10.2 to 20.8 per mil compared to SMOW. A pattern of alternating abundances was present, with the average isotopic contrasts between adjacent microbands being 3.0 per mil for carbon and 3.1 per mil for oxygen. Similar results were obtained for a suite of 34 microbands (in four groups) from the Bruno's Band unit of the Mount Sylvia Formation. Difficulties were experienced in preparing samples of single microbands from the Dales Gorge Member of the Brockman Iron Formation, but overall isotopic compositions were in good agreement with values reported by previous authors. Chemical analyses showed that isotopically light carbon and oxygen were correlated with increased concentrations of iron. The preservation of these millimeter-scale variations in isotopic abundances is interpreted as inconsistent with a metamorphic origin for the isotopically light carbon in the BIF carbonates. A biological origin is favored for the correlated variations in 13C and Fe, and it is suggested that the 13C-depleted carbonates may derive either from fermentative metabolism or from anaerobic respiration. A model is presented in which these processes occur near the sediment-water interface and are coupled with an initial oxidative precipitation of the iron.

NASA Program Exobiology↗

NASA NTRS1993

Calcified microbes in Neoproterozoic carbonates: implications for our understanding of the Proterozoic/Cambrian transition

Tidal flat and lagoonal dolostones of the Neoproterozoic Draken Formation, Spitsbergen, exhibit excellent preservation of carbonate fabrics, including heavily calcified microfossils. The crust-forming cyanobacterium Polybessurus is preserved locally by carbonate precipitated on and within sheaths in mildly evaporitic upper intertidal to supratidal environments. In contrast, calcified filaments in columnar stromatolites reflect subtidal precipitation. Filament molds in dolomicrites independently document extremely early lithification. The presence of heavily calcified cyanobacteria in Draken and other Proterozoic carbonates constrains potential explanations for the widespread appearance of calcified microorganisms near the Proterozoic-Cambrian boundary. We propose that the rarity of Proterozoic examples principally reflects the abundance and wide distribution of carbonate crystals precipitated on the sea floor or in the water column. Cyanobacterial sheaths would have competed effectively as sites for carbonate nucleation and growth only where calcitic and/or aragonitic nuclei were absent. In this view, the Proterozoic-Cambrian expansion of calcified microfossils primarily reflects the emergence of skeletons as principal agents of carbonate deposition.

Non-NASA Center↗

NASA NTRS1994

Record of fluid-rock interactions on Mars from the meteorite ALH84001

Allan Hills (ALH) 84001 is the most recently recognized member of a suite of meteorites--the SNCs--that almost certainly originated on Mars. Several factors distinguish ALH84001 from the other SNC meteorites. Preliminary studies suggest that it may be older than other martian meteorites. Moreover, it contains abundant, zoned domains of calcium-iron-magnesium carbonate that are indigenous to the sample and thus may hold important clues regarding near-surface processes on Mars and the evolution of the martian atmosphere. We report here analyses of the carbon and oxygen stable-isotope compositions of the carbonates that place constraints on their formation conditions. Our results imply the presence of at least two chemically distinct carbonates--one Ca,Fe-rich, the other Mg-rich--that are enriched in 13C relative to terrestrial carbonates (delta 13C approximately +41/1000), consistent with martian atmospheric CO2 as the carbon source. The oxygen isotope compositions of the carbonates indicate that they precipitated from a low-temperature fluid in the martian crust. Combined with textural and bulk geochemical considerations, the isotope data suggest that carbonate deposition took place in an open-system environment in which the ambient temperature fluctuated.

Carbonates/analysis↗

NASA NTRS1995

Anomalous carbonate precipitates: is the Precambrian the key to the Permian?

Late Permian reefs of the Capitan complex, west Texas; the Magnesian Limestone, England; Chuenmuping reef, south China; and elsewhere contain anomalously large volumes of aragonite and calcite marine cements and sea-floor crusts, as well as abundant microbial precipitates. These components strongly influenced reef growth and may have been responsible for the construction of rigid, open reefal frames in which bryozoans and sponges became encrusted and structurally reinforced. In some cases, such as the upper biostrome of the Magnesian Limestone, precipitated microbialites and inorganic crusts were the primary constituents of the reef core. These microbial and inorganic reefs do not have modern marine counterparts; on the contrary, their textures and genesis are best understood through comparison with the older rock record, particularly that of the early Precambrian. Early Precambrian reefal facies are interpreted to have formed in a stratified ocean with anoxic deep waters enriched in carbonate alkalinity. Upwelling mixed deep and surface waters, resulting in massive seafloor precipitation of aragonite and calcite. During Mesoproterozoic and early Neoproterozoic time, the ocean became more fully oxidized, and seafloor carbonate precipitation was significantly reduced. However, during the late Neoproterozoic, sizeable volumes of deep ocean water once again became anoxic for protracted intervals; the distinctive "cap carbonates" found above Neoproterozoic tillites attest to renewed upwelling of anoxic bottom water enriched in carbonate alkalinity and 12C. Anomalous late Permian seafloor precipitates are interpreted as the product, at least in part, of similar processes. Massive carbonate precipitation was favored by: 1) reduced shelf space for carbonate precipitation, 2) increased flux of Ca to the oceans during increased continental erosion, 3) deep basinal anoxia that generated upwelling waters with elevated alkalinities, and 4) further evolution of ocean water in the restricted Delaware, Zechstein, and other basins. Temporal coincidence of these processes resulted in surface seawater that was greatly supersaturated by Phanerozoic standards and whose only precedents occurred in Precambrian oceans.

Non-NASA Center↗

NASA NTRS2000

Depositional facies and aqueous-solid geochemistry of travertine-depositing hot springs (Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, U.S.A.)

Petrographic and geochemical analyses of travertine-depositing hot springs at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, have been used to define five depositional facies along the spring drainage system. Spring waters are expelled in the vent facies at 71 to 73 degrees C and precipitate mounded travertine composed of aragonite needle botryoids. The apron and channel facies (43-72 degrees C) is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide-oxidizing Aquificales bacteria. The travertine of the pond facies (30-62 degrees C) varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures. Calcite "ice sheets", calcified bubbles, and aggregates of aragonite needles ("fuzzy dumbbells") precipitate at the air-water interface and settle to pond floors. The proximal-slope facies (28-54 degrees C), which forms the margins of terracette pools, is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face. Finally, the distal-slope facies (28-30 degrees C) is composed of calcite spherules and calcite "feather" crystals. Despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization, the compositions of spring-water and travertine predominantly reflect abiotic physical and chemical processes. Vigorous CO2 degassing causes a +2 unit increase in spring water pH, as well as Rayleigh-type covariations between the concentration of dissolved inorganic carbon and corresponding delta 13C. Travertine delta 13C and delta 18O are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher-temperature (approximately 50-73 degrees C) depositional facies. Conversely, travertine precipitating in the lower-temperature (< approximately 50 degrees C) depositional facies exhibits delta 13C and delta 18O values that are as much as 4% less than predicted equilibrium values. This isotopic shift may record microbial respiration as well as downstream transport of travertine crystals. Despite the production of H2S and the abundance of sulfide oxidizing microbes, preliminary delta 34S data do not uniquely define the microbial metabolic pathways present in the spring system. This suggests that the high extent of CO2 degassing and large open-system solute reservoir in these thermal systems overwhelm biological controls on travertine crystal chemistry.

Non-NASA Center↗

NASA NTRS1991

Coastal lithofacies and biofacies associated with syndepositional dolomitization and silicification (Draken Formation, Upper Riphean, Svalbard)

The Draken Formation (120-250 m) of northeast Spitsbergen (Svalbard) forms part of a thick Upper Proterozoic carbonate platform succession. It consists predominantly of intraformational dolomitic conglomerates, with excellent textural preservation. Six main lithofacies were recognized in the field: quartz sandstones, stromatolitic mats, conglomerates with silicified intraclasts, dolostone conglomerates with desiccated mudrocks, oolitic/pisolitic grainstones and fenestral dolostones. A series of five main gradational biofacies were recognized from silicified (and rare calcified) microfossils. Biofacies 1 represents low-energy subtidal benthos (erect filaments) and plankton (acritarchs and vase-shaped microfossils) whereas biofacies 2 to 5 are microbial mat assemblages (with filamentous mat-builders, and associated dwellers and washed-in plankton) ranging from basal intertidal to high intertidal/supratidal. Colour values (a measure of the lightness of the colour shade) of sawn rock samples were quantified using a Munsell chart, and exhibit a pronounced variation (means of major groups varying from 4.0 to 5.95) across the spectrum of subtidal to supratidal sediments as inferred from other criteria. The lightening in progressively more exposed sediments is related to lowering of organic carbon contents, probably mainly by oxidation. Six types of early cement have been recognized. Calcite microspar (type 1) is common as a subtidal cement in many Proterozoic formations, whereas types 2 (subtidal isopachous fringes), 3 (subtidal hardground dolomicrite) and 4 (intertidal meniscus dolomicrite) are very similar to Phanerozoic examples except for their dolomitic mineralogy. Types 5 and 6 are complex and variable dolomite growths associated with expansion and replacive phenomena. They characterize the fenestral lithofacies and compare with modern supratidal cements. Consideration of diagenetic fabrics and truncation textures of intraclasts indicates that leaching, dolomitization, silicification were all significant syndepositional processes altering the original metastable carbonates. The data set provides evidence for a spectrum of peritidal environments including ooid shoals, protected subtidal, tidal sandflats and protected carbonate mudflats. Different sections show a preponderance of particular facies. The coastal lithofacies continuum was completely dolomitized, unlike offshore to ooid shoal facies of adjacent formations. Dolomitization thus bears a relationship to depositional bathymetry. Although hydrodynamics clearly have a role, the potential importance of whiting precipitation in raising Mg/Ca in marginal marine environments is also stressed.

Non-NASA Center↗

NASA NTRS1990

Carbonate deposition during the late Proterozoic Era: an example from Spitsbergen

Carbonate sediments reflect the physico-chemical and biological circumstances of their formation; thus, features of limestones and dolomites may provide insights into both environmental and evolutionary change through geological time. The Upper Proterozoic (approx 800-700 Ma) Akademikerbreen Group, Spitsbergen, comprises 2000 m of carbonates, with only minor intercalations of quartz arenite and shale. Although Proterozoic carbonates are often seen as predominantly dolomitic, the Akademikerbreen Group is about 45 percent limestone. Stromatolites are conspicuous in outcrop but constitute only 25 percent of the total section. Micrites and coarser intraclastic carbonates derived mainly from micritric precursors comprise 60 percent of the group, while oolites make up the remaining 15 percent. Distinctive sedimentary features of the group include giant (up to 16 mm) ooids, very early diagenetic calcite nodules and cements, micrites containing subaqueous shrinkage cracks filled with equant microspar cement, and strong 13C enrichment in both carbonates and co-occurring organic matter. The principal features of Akademikerbreen carbonates are widely distributed in coeval successions. However, these rocks appear to differ from older limestones and dolomites in their relative abundance of grainstones and, perhaps, micrites, as well as their paucity of tufa-like laminates and columnar or coniform stromatolites that preserve petrographic evidence of in situ precipitation as a dominant means of carbonate accretion. Upper Proterozoic carbonates also differ from Paleozoic accumulations, but the transition is not abrupt. Most changes accompanying the Proterozoic/Phanerozoic transition can be interpreted in terms of the consequences rather than the causes of metazoan and metaphyte evolution, including the evolution of biomineralization. Carbonate sedimentology reinforces data from other sources which indicate the last 200 to 300 Ma of the Proterozoic Eon was a distinctive interval of Earth history.

NASA Discipline Number 52-30↗

NASA NTRS1990

Carbonate petrography, kerogen distribution, and carbon and oxygen isotope variations in an early Proterozoic transition from limestone to iron-formation deposition, Transvaal Supergroup, South Africa

The transition zone comprises Campbellrand microbialaminated (replacing "cryptalgalaminate") limestone and shale, with minor dolomite, conformably overlain by the Kuruman Iron Formation of which the basal part is characterized by siderite-rich microbanded iron-formation with minor magnetite and some hematite-containing units. The iron-formation contains subordinate intraclastic and microbialaminated siderite mesobands and was deposited in deeper water than the limestones. The sequence is virtually unaltered with diagenetic mineral assemblages reflecting a temperature interval of about 110 degrees to 170 degrees C and pressures of 2 kbars. Carbonate minerals in the different rock types are represented by primary micritic precipitates (now recrystallized to microsparite), early precompactional sparry cements and concretions, deep burial limpid euhedral sparites, and spar cements precipitated from metamorphic fluids in close contact with diabase sills. Paragenetic pathways of the carbonate minerals are broadly similar in all lithofacies with kerogen intimately associated with them. Kerogen occurs as pigmentation in carbonate crystals, as reworked organic detritus in clastic-textured carbonate units, and as segregations of kerogen pigment around late diagenetic carbonate crystals. Locally kerogen may also be replaced by carbonate spar. Carbon isotope compositions of the carbonate minerals and kerogen are dependent on their mode of occurrence and on the composition of the dominant carbonate species in a specific lithofacies. Integration of sedimentary, petrographic, geochemical, and isotopic results makes it possible to distinguish between depositional, early diagenetic, deep burial, and metamorphic effects on the isotopic compositions of the carbonate minerals and the kerogen in the sequence. Major conclusions are that deep burial thermal decarboxylation led to 13C depletion in euhedral ferroan sparites and 13C enrichment in kerogen (organic carbon). Metamorphic sparites are most depleted in 13C. Carbonates in oxide-rich iron-formations are more depleted in 13C than those in siderite-rich iron-formation whereas the kerogens in oxide banded iron-formations (BIF) are more enriched. This implies that the siderite-rich iron-formations were not derived from oxide-rich iron-formation through reduction of ferric iron by organic matter. Organic matter oxidation by ferric iron did, however, decrease the abundance of kerogen in oxide-rich iron-formation and led to the formation of isotopically very light sparry carbonates. Siderite and calcmicrosparite both represent recrystallized primary micritic precipitates but differ in their 13C composition, with the siderites depleted in 13C by 4.6 per mil on average relative to calcmicrosparite. This means that the siderites were precipitated from water with dissolved inorganic carbon depleted in 13C by about 9 per mil relative to that from which the limestones precipitated. This implies an ocean system stratified with regard to total carbonate, with the deeper water, from which siderite-rich iron-formation formed, depleted in 13C. Iron-formations were deposited in areas of very low organic matter supply. Depletion of 13C may, therefore, derive not from degradation of organic matter but from hydrothermal activity, a conclusion which is supported by 18O composition of the carbonate minerals and trace element and rare earth element (REE) compositions of the iron-formations.

NASA Discipline Number 52-30↗

NASA NTRS1997

Whiting events: biogenic origin due to the photosynthetic activity of cyanobacterial picoplankton

An annual whiting event occurs each year in late May to early June in Fayetteville Green Lake, New York. The initiation of this event correlates with exponential growth of the Synechococcus population within the lake. Synechococcus is the dominant (by approximately 4 orders of magnitude) autotrophic organism owing to the oligotrophic condition of the lake. The delta 13C values of the dissolved inorganic C range seasonally from -9.5% in winter to -6.2% in summer due to photosynthetic activity. Calcite precipitates principally in the microenvironment surrounding Synechococcus because of a photosynthetically driven alkalization process and the availability of the cells as nucleation sites. This calcite has a heavier delta 13C value (>4%) than does the dissolved inorganic C of the lake water owing to the cells' preferential uptake of 12C. A conceptual model suggests that photosynthetic activity and cell surface chemistry, together with the substantial surface area that arises from the great abundance of micron-sized cells, allow Synechococcus to dominate the annual whiting events in Fayetteville Green Lake.

NASA Center ARC↗

NASA NTRS2014

Nutritional Status Assessment (SMO 016E)

The Nutritional Status Assessment Supplemental Medical Objective was initiated to expand nominal clinical nutrition testing of ISS astronauts, and to gain a better understanding of the time course of changes in nutritional status during flight. The primary activity of this effort was collecting blood and urine samples during flight for analysis after return to Earth. Samples were subjected to a battery of tests. The resulting data provide a comprehensive survey of how nutritional status and related systems are affected by 4-6 months of space flight. Analysis of these data has yielded many findings to date, including: Vision. Documented evidence that biochemical markers involved in one-carbon metabolism were altered in crewmembers who experienced vision-related issues during and after flight (1). Iron, Oxidative Stress, and Bone. In-flight data document a clear association of increased iron stores, markers of oxidative damage to DNA, and bone loss (2). Exercise. Documented that well-nourished crewmembers performing heavy resistance exercise returned from ISS with bone mineral densities unchanged from preflight (3). Furthermore, the response of bone to space flight and exercise countermeasures was the same in men and women (4). Body Mass. Crewmembers lose 2-5% of their body mass in the first month of flight, and maintain the lower body mass during flight (5). Additionally, the two devices to measure body mass on orbit, the SLAMMD and BMMD, provide similar results (5). Cytokines. Findings indicated that a pattern of persistent physiological adaptations occurs during space flight that includes shifts in immune and hormonal regulation (6). Fish/Bone. Documented a relationship between fish intake and bone loss in astronauts (that is, those who ate more fish lost less bone) (7). Vitamin K. Documented that in generally well-fed and otherwise healthy individuals, vitamin K status and bone vitamin K-dependent proteins are unaffected by space flight (and bed rest) (8). Testosterone. Documented that blood concentrations of testosterone were unchanged during flight, but a transient decline occurred after landing (9). Calcium. Nutrition SMO data contributed to the ISS Program by helping understand how and why the Urine Processor Assembly clogged with calcium sulfate precipitate (10). Sample Processing. Ground-based analytical testing results have also been published (11).

Smith, S. M.↗