C. Junge

Precambrian sedimentary carbonates: carbon and oxygen isotope geochemistry and implications for the terrestrial oxygen budget☆

Abstract Carbon isotope values of 260 Precambrian limestones and dolomites (most of them being substantially unaltered) have yielded an overall mean of δ 13 C = +0.4 ± 2.7‰ vs. PDB; the corresponding oxygen values average at δ 13 O = +20.0 ± 4.2‰ vs. SMOW. Like the overall mean, the δ 13C values furnished by individual carbonate occurrences are, as a rule, fairly “modern” and almost constant as from the very beginning of the sedimentary record. A remarkable exception are the “heavy” dolomites of the Middle Precambrian Lomagundi Group, Rhodesia, with δ 13 C = +9.4 ± 2.0‰ vs. PDB. As a result of our measurements, the sporadic occurrence in the geological past of anomalously heavy carbonates seems to be established. The approximate constancy around zero per mill of the δ 13C values of marine carbonates through geologic time would imply a corresponding constancy of the relative proportion of organic carbon in the total sedimentary carbon reservoir since about 3.3 · 109 y ago (with Corg/Ctotal ≅ 0.2). Utilizing this ratio and current models for the accumulation of the sedimentary mass as a function of time, we get a reasonable approximation for the absolute quantity of organic carbon buried in sediments and, accordingly, of photosynthetic oxygen released. Within the constraints of our model (based on a terrestrial degassing constant λ = 1.16 · 10−9 y−1) close to 80% of the amount of oxygen contained in the present oxygen budget should have been released prior to 3 · 109 y ago. Since geological evidence indicates an O2-deficient environment during the Early and most parts of the Middle Precambrian, there is reason to believe that the distribution of this oxygen between the “bound” and the “molecular” reservoir was different from that of today (with effective O2-consuming reactions bringing about an instantaneous transfer to the crust of any molecular oxygen released). Accordingly, the amount of Corg in the ancient sedimentary reservoir as derived from our isotope data is just a measure of the gross amount of photosynthetic oxygen produced, withholding any information as to how this oxygen was partitioned between the principal geochemical reservoirs. As a whole, the carbon isotope data accrued provide evidence of an extremely early origin of life on Earth since the impact of organic carbon on the geochemical carbon cycle can be traced back to almost 3.5 · 109y.

Carbon isotope geochemistry of the 3.7 × 109-yr-old Isua sediments, West Greenland: implications for the Archaean carbon and oxygen cycles

One hundred and twenty-four carbonate samples from the meta-sedimentary sequence of the 3.7 × 109 yr old Isua supracrustal belt (W-Greenland) have yielded a δ13Ccarb average of −2.5 ± 1.7%. vs PDB and a δ18Ocarb average of +13.0 ± 2.5%. vs SMOW. The oxygen mean comes fairly close to the averages of other early Precambrian carbonates. The carbon average, however, is some 2%. more negative than those of younger marine carbonates. In terms of a simple terrestrial 13C mass balance, if δ13Ccarb values are original sedimentary values, this more negative δ13C average would imply a considerably smaller CorgCcarb ratio in the sedimentary shell during Isua times, and would thus support the concept of a gradual buildup of a sedimentary reservoir of organic carbon during the early history of the Earth. Since, however, the Isua supracrustal rocks have experienced amphibolite-grade metamorphism, which in other areas has been shown to lower δ13Ccarb values, it is most likely that the original values of these rocks were approx 0%.. This indicates that Corx and Ccarb were present in the ancient carbon reservoir in about ‘modern’ proportions. Unless this early stabilization of the terrestrial carbon cycle in terms of a constant partitioning of carbon between the reduced and oxidized species is shown to have been caused by some inorganic geochemical process, a considerably earlier start of chemical evolution and spontaneous generation of life must be considered than is presently accepted.

Carbon isotope geochemistry of the Precambrian Lomagundi carbonate province, Rhodesia

Abstract Carbon isotope measurements carried out on 67 dolomite samples from the Middle Precambrian Lomagundi Group (Rhodesia) have yielded a δ 13 C mean of +8.2 ± 2.6%. vs PDB. With the outcrop of these dolomites extending over a distance of almost 300 km, the Lomagundi dolomite faces is likely to represent the largest isotopically anomalous sedimentary carbonate province ever recorded. It is concluded that the anomalous carbonates formed in a closed basin whose δ 13 C level had been substantially increased as a result of a preferential removal (within sedimentary organics) of the light carbon isotope.

The organic constituents of atmospheric particulate matter

Abstract The ether soluble fraction of atmospheric aerosol particles was separated into the following groups of compounds: organic acids and phenols, organic bases, aliphatic hydrocarbons, aromatic hydrocarbons and neutral compounds. These groups in turn were analyzed for individual constituents. Aerosol samples were collected from six different geographic regions: three over the European continent with different degrees of air pollution and three from Atlantic air masses. In all cases the organic fraction of atmospheric aerosol particles had a very complex composition. However, the relative composition with respect to the main groups of organic compounds remained fairly constant in all areas sampled. This indicates either a common origin or formative processes throughout the atmosphere resulting in a similar net product.

n-Alkane studies in the troposphere—I. Gas and particulate concentrations in north Atlantic air

Abstract Simultaneous measurements of gas phase and paniculate concentrations of C 9 –C 28 n -alkanes in clean air at the west coast of Ireland are reported. All n -alkanes were regularly present with gas phase concentrations between about 10 and 20 × 10 −9 g m −3 STP, showing no systematic decrease above C 13 . Continental air showed higher concentrations. The fraction of alkanes attached to aerosol particles increases from less than 1% at low C-numbers to several per cent at high C-numbers. The carbon preference index is generally close to 1.0; seawater samples from that area exhibit similar distributions of n -alkanes as the gas phase.

N-alkane studies in the troposphere—II: Gas and particulate concentrations in Indian Ocean air

Abstract Westerly winds arriving at the Australian Clean Air Baseline Station Cape Grim at the North Western tip of Tasmania have exceedingly long trajectories over the Indian Ocean. In these air masses we found the n-alkanes C 9 -C 28 to be always present in the gas phase and also in the aerosols. In aerosols we also measured total organic matter and its general composition. All these concentrations agree fairly well with our earlier data in marine air over the North Atlantic Ocean. Calculations of the life time of the gas phase n-alkanes due to reaction with OH radicals lead to the conclusion that these n-alkanes must be of oceanic origin in Indian Ocean air and — to a large extent — also in the North Atlantic air. The same conclusion is reached for the organic component in aerosols. Water Analyses show that the n-alkanes C 9 -C 28 seem to be normal constituents of the oceans.

Coupling among the terrestrial sulfur, carbon and oxygen cycles: numerical modeling based on revised Phanerozoic carbon isotope record

Abstract Numerical modeling of the terrestrial oxygen budget based on the revised δ13Ccarb record by Veizer et al. (1980) has shown that total photosynthetic oxygen has varied between ±7% and ±10% of its average reservoir size (∼3.2 × 1022 g) during the last 800 myr as a result of oscillations of the sedimentary reservoir of organic carbon. Calculated curves of oxygen evolution display a distinct minimum in the Early Paleozoic framed by two maxima in the Latest Proterozoic and the Mesozoic. The sympathetic relationship observed between the curves of total oxygen evolution and respective functions for the partial reservoir of sulfate-bound oxygen suggests that the O2 required for an additional conversion of sulfide to sulfate was most probably provided by excess burial of organic carbon, the results of the modeling thus adding credence to current interpretations proposed for the negative correlation between the secular 13 C 12 C and 34 S 32 S trends.

Studien zur bestimmung des Säuregehaltes von aerosolteilchen

Abstract The hydrogen ion concentration of aerosol samples dissolved in neutral water were determined by titration and also by measuring the pH-value. In parallel with these data, the concentration of sulfate and of soluble matter in aerosols, of sulfur dioxide, and of some other chemical constituents of the atmosphere, which may influence the formation of hydrogen ions in aerosols, were measured. Measurements in London, Goteborg, Gelsenkirchen, and Mainz gave the following characteristics: 1. (1) The titration method gave considerably higher hydrogen ion concentrations than the pH-method. This indicates that the hydrogen ion concentration of aerosol particles is either due to weak acids or to strong acids, e.g. H2SO4, which are buffered by weak bases. 2. (2) Most of the water soluble compounds of the aerosols and particularly the hydrogen ion content is associated with particles smaller than 0.1 μ radius in contrast to the total aerosol matter which is primarily associated with particles larger than 0–1 μ radius. 3. (3) The various locations showed differences in the hydrogen ion content with highest values in London. Correlations of the hydrogen ion concentration with the content of water soluble matter and of sulfate in aerosols or with the sulfur dioxide concentration were weak or nonexisting indicating that processes of acid formation on aerosols and its neutralisation are rather complex.

Kohlenmonoxid- und Wasserstoffproduktion mariner Mikroorganismen im Nhrmedium mit synthetischem Seewasser

The origin of a p o g a m o u s spo rophy te s f rom t he s econda ry p r o t o n e m a in mosses was observed by Baue r [1,2] in t he d ip lophase and later by Lal [3] in t he hap lophase . We became in te res ted in s t u d y i n g t he d e v e l o p m e n t of a p o g a m o u s sporop h y t e s f rom a haplo id s econda ry p r o t o n e m a ar is ing f rom the g a m e t o p h y t e s and t he exogenous factors involved in th i s u n u s u a l d i f ferent ia t ion unde r asept ic cu l tura l condi t ions . G a m e t o p h y t e s ob ta ined f rom t he spores of tile moss Physcomitrium pyri/orme Brid. were repea ted ly s u b c u l t u r e d in Moore s minera l n u t r i e n t m e d i u m jelled wi th 0.8% Difcobac to-agar . The haploid s econda ry p r o t o n e m a t a ar is ing in th is sugar-f ree m e d i u m produced exc lus ive ly g a m e t o p h y t i c buds in t he usua l way. However , when t he m e d i u m was s u p p l e m e n t e d wi th 2 % sucrose, d i f fe ren t ia t ion of a p o g a m o u s sporophytes , ill add i t ion to tile g a m e t o p h y t e s , was observed af te r a b o u t two weeks in 25 to 30 per cen t of t he cu l tures (Fig. 1 A). I t was fu r the r es tab l i shed t h a t t he supp ly of exogenous sucrose a t a low concen t ra t ion (0.5 %) and t he presence of low l ight i n t ens i t y (50--100 Lux) were m o s t effect ive in t he p roduc t ion of a p o g a m o u s sporophy tes . I n h i gh concen t r a t ions of sucrose (6%) and a t h igh l igh t i n t e n s i t y (5000 to 6000 Lux) a p o g a m o u s spo rophy te s were no t fo rmed; only t he game to p h y t i c buds were produced . I n the absence of sucrose in the med ium, t he aux i n s (indole-acetic acid, n a p h t h a l e n e acetic acid) and cy tok in in (kinetin) were ineffect ive in i nduc ing a p o g a m o u s sporophytes , t h o u g h p re l imina ry resu l t s of exper i m e n t s now in progress sugges t t he possibi l i ty of an in te rac t ion of sucrose wi th exogenous ly suppl ied gTowth subs t ances . A t t e m p t s were made to replace sucrose wi th o the r suga r s in equ imola r concen t ra t ions but , except for glucose which was m u c h less effective t h a n sucrose, no o ther suga r gave posi t ive resul ts . I n t he deve lopmen ta l sequence of a p o g a m o u s spo rophy te s on the l inear ly growing p ro tonema , it was observed t h a t the re was first t he d i f ferent ia t ion of a special, smal l in te rca la ry cell (Fig. I B) a m o n g the o rd ina ry long, cyl indrical ceils. This specialized cell d iv ided ant ic l ina l ly (Fig. t C) and organized an apical cell w i th two cu t t i ng faces. The la t te r gave rise to all organized sporophyte , or some t imes d ivided i r regular ly to form a callus on which sporophy t i c o rgan iza t ion took place a t a la ter s tage. Some of t he smal l cells failed to divide fur ther . A t t imes a n u m b e r of smal l cells were produced near the apex of t he p ro tonema , and of these only some were mer i s t emat i c , o the r s being senescent . The callus fo rmed f rom special ized cells of the p r o t o n e m a did no t Mways fo rm sporophy tes in t h e pa ren ta l m e d i u m ; in some cul tures it t u r n e d b rown and lay quiescent . I t was fu r the r observed t h a t a spo rophy t e or a callus could also arise f rom a seemingly unmodi f i ed cell f rom which a g a m e t o p h y t e would no rma l ly arise (Fig. t D). Our f indings sugges t for the first t ime t h a t exogenously supplied sucrose can influence lhe linearly growing secondary protonemal [ilament to modi/y its devdopmental sequence and give rise to a callus or a spo rophy te ins t ead of a g a m e t o p h y t e . I n the n o r m a l sequence of g a m e t o p h y t i c di f ferent ia t ion, an apical cell w i th three cu t t i ng faces is es tab l i shed t h r o u g h a t r an s i t o ry s tage of two-faced apical cell. I n our exper iments , the two-faced apical cell was s tabi l ized and d iver ted to grow into a sporophy te . Of special in te res t is t he se t t ing apa r t on t he p r o t o n e m a of special smal l cells wh ich are endowed wi th zygotel ike potent ia l i t ies of growing di rect ly in to a sporophyte . A co m p ara t ive s t u d y of t he histological and u l t r a s t r u c t u r a l peculiarit ies of the zygote as well as the specialized smal l ceils is u n d e r way.

Die Entwicklung der Erdatmosphäre und ihre Wechselbeziehung zur Entwicklung der Sedimente und des Lebens

The formation of the atmosphere-together with that of the oceans and sediments-was determined by three important processes: the loss of noble gases and volatiles in the solar nebula, the enrichment of these substances at the Earths surface by exhalation from the Earths mantle, and finally the formation of the hydrosphere, enabled by-in contrast to our neighboring planets-a suitable distance from the sun. In this way the development of the atmospheric gases N2, H2O and CO2 was largely fixed. Oxygen, on the other hand, appeared late in the atmosphere. It originated from biological photosynthesis which apparently developed rather early in the Earths history but lead at first only to oxidation of iron and sulfur. The subsequently occurring accumulation of free oxygen in the atmosphere resulted in interesting interrelations with the development of life.