Growth rates of manganese nodules in Oneida Lake,New York

²²⁶Ra is used to document the growth histories of six manganese nodules from Oneida Lake, New York. Detailed sectioning and analysis reveal that there are discontinuous gradients in²²⁶Ra content in these samples. These gradients result from periods of rapid growth (>1 mm/100 years) separated by periods of no growth of erosion. Although the²²⁶Ra “age” of the nodules approximates the age of Oneida Lake, the nodules are not sediment-covered because they occur only in areas of the lake where fine-grained sediments are not accumulating.     

10Be dating of large manganese nodules from world oceans

The results of ¹⁰Be and ⁹Be measurements in several sections of ten large manganese nodules are presented along with U and Th isotope data on five of them.The ¹⁰Be and ¹⁰Be/⁹Be methods yield growth rates (covering a period of 5–10 Ma) which are in excellent agreement with each other. In three cases, these rates are also in very good agreement with those derived from the ²³⁰Th methods, whereas in the other two the ²³⁰Th-based rates are faster by over a factor of two.Based on the discrepancy between the inventory of ¹⁰Be (as well as ²³⁰Th) in nodules and the overhead seawater column, it is calculated that the former scavenge their Be and Th isotopes from 2–900 m of the overhead water column. The deduced ⁹Be concentrations of ocean water based on its ¹⁰Be contents and the ¹⁰Be/⁹Be ratios of nodule surfaces are found to be in good agreement with the direct ⁹Be measurements of seawater implying that ⁹Be in nodules (like¹⁰Be) is mostly authigenic.     

Post-depositional metal enrichment processes inside manganese nodules from the north equatorial Pacific

Interiors of manganese nodules from siliceous ooze beneath the Pacific equatorial high-productivity region, when examined by scanning electron microscopy (SEM) and electron microprobe, display post-depositional recrystallization textures and metalliferous oxide bands (diameter 1–10 μm, 30–40 wt.% Mn, 4–5% Ni, 3–4% Cu). SEM has revealed biogenic siliceous matter in all stages of degradation and dissolution within nodule interiors, creating cavities and voids. Often these miniature vugs contain authigenic phillipsite crystallites which are coated with delicate clusters of crystalline Mn-Fe oxides (todorokite) containing significant amounts of Ni and Cu. We postulate the following diagenetic processes and mechanism of uptake of transition metals inside manganese nodules: (1) palagonite + biogenic silica + pelagic clay → phillipsite + montmorillonite; (2) biogenic matter + amorphous FeOOH or δ-MnO₂ → Fe_aq²⁺ and/or Mn^IIMn^IV oxide (todorokite); (3) aerated seawater or δ-MnO₂ + Fe_aq²⁺ → FeOOH and/or todorokite (deposited on phillipsite); (4) (Ni^II and Cu^II) organic chelates (adsorbed on clays, etc.) + amorphous FeOOH or δ-MnO₂ → Ni-Cu-todorokite + phillipsite, etc.This mechanism explains the well-known positive Mn-Ni-Cu and negative Fe-Ni, Fe-Cu correlations in nodules. By analogy with terrestrial todorokites, which require about 8 wt.% Mn to be in the divalent state to stabilize the crystal structure, as much as 8 wt.% (Ni + Cu) could be accommodated in todorokite-bearing deep-sea manganese nodules. However, although such nodules beneficiate Ni and Cu with respect to marine sediments and seawater, they remain undersaturated in these divalent cations.     

Estimating limiting age for pleistocene erosional surfaces in central Montana by uranium-series dating of associated travertines

Travertine deposits overlie the highest Number 2 surfaces in central Montana and clasts of travertine occur in gravels on lower Number 2 surfaces. Dating these travertine deposits may provide limits on the ages of surfaces that record intervals of extensive erosion during Pleistocene time. Analysis of three travertine samples from the southeast side of The Park yield an average uranium-thorium age of 73 000 ±+M 7 000 years. Another sample from the west side of The Park is 320 000 (+ 160 000, ? 70 000) years old. These results indicate that travertine deposits may have formed at several intervals. The surface beneath The Park travertine is older than about 320 000 years. Number 2 pediment gravels that contain travertine downslope from the oldest dated sample may be younger than about 320 000 years.     

Ocean manganese nodules as stromatolite with a fractal like-signature

Deep-sea manganese (Mn) nodules are problematic in terms of factors such as their characteristic form and genesis. There are many reports of bacterial species from manganese nodules. However, the genesis of these nodules has not been fully confirmed. Samples, mainly from the Clarion Clipperton Fracture zone in the Pacific Ocean, were examined by mineralogical methods and X-ray CT. Thin sections of these samples showed columnar stromatolite structures with rhythmic bands. Mineralized bacteria were observed by SEM and TEM. Surface morphology could be described as having a fractal-like nature. The fractal characteristics of spherical to dome-like forms were fundamentally composed of at least four ranks. The 4th order form corresponds to the stromatolite dome top shapes. Similar granular domain units and porous characteristics in manganese nodules were clearly observed by X-ray CT sections. Mathematical simulation based on fractal models reproduced similar morphological characteristics to the natural samples. So, we arrived at the concluding hypothesis that manganese nodules are aggregated stromatolite with fractal-like characteristics. Furthermore, we discussed the possibility that the nature of the layer manganese oxide minerals as the major component of the nodule and associated Fe-oxyhydroxide minerals may become an absorber/scavenger of strategic heavy metals and also toxic metals in the environments.     

Constraining the age of rock art by dating a rockfall event using sediment and rock-surface luminescence dating techniques

Optically stimulated luminescence (OSL) is used to determine the age of a rockfall event that removed part of the pictograph figures at the Great Gallery rock art panel in Canyonlands National Park, Utah, USA. Analyses from the outer millimeter of the buried surface of a rockfall boulder and quartz grains from the underlying sediment both provide consistent ages that also agree with an AMS radiocarbon age of a cottonwood leaf found immediately between the clast and underlying sediment. Measurement of the OSL signals as a function of depth into the surface of the boulder clearly shows that there is no detectable increase in the OSL signal to a depth of at least 3 mm suggesting that the OSL signal was fully reset to this depth before burial. Consistent OSL and radiocarbon ages for this rockfall event provide a minimum age of ∼900 a for the Great Gallery, which is the type locality of Barrier Canyon Style rock art with a controversial and unknown origin.     

Os isotope dating and growth hiatuses of Co-rich crust from central Pacific

Up to now, accurate determination of the growth age and hiatuses of the Co-rich crust is still a difficult work, which constrains the researches on the genesis, growth process, controlling factors, regional tectonics, paleo-oceanographic background, etc. of the Co-rich crust. This paper describes our work in determining the initial growth age of the Co-rich crust to be of the late Cretaceous Campanian Stage (about 75-80 Ma), by selecting the Co-rich crust with clear multi-layer structures in a central Pacific seamount for layer-by-layer sample analysis and using a number of chronological methods, such as Co flux dating, dating by correlation with 187Os/188Os evolution curves of seawater, and stratigraphic divi- sion by calcareous nannofossils. We have also discovered growth hiatuses with different time intervals in the early Paleocene, middle Eocene, late Eocene and early-middle Miocene, respectively. These re- sults have provided an important age background for further researches on the Co-rich crust growth process and the paleo-oceanographic environment evolution thereby revealed in the said region.     

A record of changing redox conditions in the northern Peru Basin during the Late Quaternary deduced from Mn/Fe and growth rate variations in two diagenetic manganese nodules

Two diagenetic manganese nodules from the Peru Basin were investigated by thermal ionization mass spectrometry and high resolution alpha spectrometry for uranium and thorium. The TIMS concentrations for nodule 62KD (63KG) vary as follows: 0.12–1.01 ppb (0.06–0.59) ²³⁰Th, 0.51–1.98 ppm (0.43–1.40) ²³²Th, 0.13–0.80 ppb (0.09–0.49) ²³⁴U, and 1.95–13.47 ppm (1.66–8.24) ²³⁸U. Both nodules have average growth rates of 110 mm per million years. However, from the variations of excess ²³⁰Th with depth we estimate partial accumulation rates which range from 50 to 400 mm per million years. The δ²³⁴U dating method cannot be applied due to remobilization of U from the sediment and subsequent incorporation into the nodules' crystal lattice, reflected by decay corrected δ²³⁴U values far above the ocean water value. Sections of fast nodule growth are related to those layers having high Mn/Fe ratios (up to 200) and higher densities. As a possible explanation we develop a scenario that describes similar glacial/interglacial trends in both nodules as a record of regional changes of sediment and/or deep water chemistry.     

Fission track dating of zircon: Improved etching techniques

A simple new technique for the etching of fission tracks in zircon has been developed which overcomes the practical difficulties of previously described techniques. The etchant is a low melting-point binary eutectic of KOH and NaOH which is used at 200–220°C. As for previous etchants the etching time is strongly dependent on the spontaneous track density. The etched tracks have very similar characteristics to those produced by the earlier 100N NaOH etchant.     

Erosion rates of alpine bedrock summit surfaces deduced from in situ Be and Al

We have measured the concentration of in situ produced cosmogenic ¹⁰Be and ²⁶Al from bare bedrock surfaces on summit flats in four western U.S. mountain ranges. The maximum mean bare-bedrock erosion rate from these alpine environments is 7.6 ± 3.9 m My⁻¹. Individual measurements vary between 2 and 19 m My⁻¹. These erosion rates are similar to previous cosmogenic radionuclide (CRN) erosion rates measured in other environments, except for those from extremely arid regions. This indicates that bare bedrock is not weathered into transportable material more rapidly in alpine environments than in other environments, even though frost weathering should be intense in these areas. Our CRN-deduced point measurements of bedrock erosion are slower than typical basin-averaged denudation rates ( 50 m My⁻¹). If our measured CRN erosion rates are accurate indicators of the rate at which summit flats are lowered by erosion, then relief in the mountain ranges examined here is probably increasing.

We develop a model of outcrop erosion to investigate the magnitude of errors associated with applying the steady-state erosion model to episodically eroding outcrops. Our simulations show that interpreting measurements with the steady-state erosion model can yield erosion rates which are either greater or less than the actual long-term mean erosion rate. While errors resulting from episodic erosion are potentially greater than both measurement and production rate errors for single samples, the mean value of many steady-state erosion rate measurements provides a much better estimate of the long-term erosion rate.     

Biogenesis and binary mineralization of organism and chemism of polymetallic nodules from Pacific Ocean

The biogenic structure and biominerals in the polymetallic nodules reveal their biogenic origin. The experiment of the cation substitution capacity of synthetic 1 nm manganate suggests that chemism participates in the mineralization of the polymetallic nodules. That means the mineralization of the polymetallic nodules is two-component. After discussing the mineralization mechanism, the authors pointed out that the formation of polymetallic modules in deep-sea must meet four prerequisites: oxidative environment, very low sedimentation rate and/or hiatuses, enough nuclei, and suitable for the ultra-microbes-nodule’s builder to live. Project supported by the Deep Sea Geologic Research Project of China Oceanic Mineral Resources Research and Development Association (COMRA)     

Floodplain sedimentation rates in an alpine watershed determined by radionuclide techniques

Vertical profiles of the activities of ¹³⁷Cs and ²¹⁰Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm^?2 yr^?1 and were in good agreement with sedimentation rates calculated from the inventories of ¹³⁷Cs and ²¹⁰Pb. Sedimentation rates calculated from the position of the ¹³⁷Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of ¹³⁷Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the ¹³⁷Cs and ²¹⁰Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.     

Helium-3 and manganese at the 21°N East Pacific Rise hydrothermal site

Water samples collected at the 21°N hydrothermal site on the East Pacific Rise crest, including Deep-Tow and hydrocast samples collected in 1977 and three hot vent water samples collected recently with the submersible “Alvin”, contain significant additions of³He,⁴He, and Mn. Although the vent water collections were at least 50-fold diluted with ambient seawater, they are up to 53 times enriched in³He and 7.4 times enriched in⁴He relative to saturated seawater, with concentrations of total dissolvable manganese (TDM) up to 310 μg/kg.³He and⁴He covary in the vent samples, with³He/⁴He about 8 times the atmospheric ratio, reflecting a mantle helium source. In contrast to the helium isotopes the Mn/³He ratio in the vent samples is variable, ranging from 4.3 × 10⁴ up to 1.0 × 10⁵ g/cm³. Profiles of³He/⁴He and TDM in the water column at 21°N show a sharp maximum ofδ(³He) = 47%and TDM= 0.69 μg/kg, much higher than the average values of 34% and 0.2 μg/kg for the deep water in this region. This spike in³He and Mn occurs at 2400 m depth, 200 m above the level of the 21°N vents, and 100 m higher than any local bathymetry, evidence for upward transport of the hydrothermal discharge via rising plumes of hot vent water. Two of the 21°N Deep-Tow samples associated with small (?0.010°C) temperature anomalies hadδ(³He) = 38%and TDM= 0.28 and 0.58 μg/kg, also slightly elevated relative to background. The Deep-Tow and hydrocast samples have lower Mn/³He ratios than average vent samples due to Mn removal by scavenging. Comparison of vent samples and water column measurements at 21°N indicate that the pure vent water could be detected using³He and Mn even when diluted ～10⁵ times with seawater, confirming that these two tracers are extremely sensitive indicators of submarine hydrothermal activity.     

Characterization of magnetic particles and magnetostratigraphic dating of shallow-water carbonates in the Ryukyu Islands, northwestern Pacific

Abstract   Characterization of magnetic particles, and magnetostratigraphic dating, of Holocene and Pleistocene shallow-water carbonates (the Ryukyu Group) in the Ryukyu Islands was carried out to infer the age of reef formation. Magnetic particles from these strata are dominated by fine-grained, single-domain magnetite/maghemite (40–140 nm in length). The magnetite crystals exhibit the size and morphologies characteristic of the magnetite formed by magnetotactic bacteria. No large multidomain grains were seen in transmission electron microscopy observations. The widespread presence of single-domain magnetite in the Ryukyu Islands suggests that bacterial magnetites carry depositional remanent magnetization, which is stable enough for magnetostratigraphic dating and thereby for elucidating the evolution of shallow-water carbonates. The polarity-reversal sequence seen in a core taken from the Ryukyu Group correlates with the timescale of the Matuyama chron, including the Jaramillo subchron, Kamikatsura or Santa Rosa Excursions, through the Brunhes chron. These magnetostratigraphic results imply that the time of reef initiation in the Ryukyu Islands of the northwestern Pacific was earlier than in the Great Barrier Reef of the southwestern Pacific, where it started after the Brunhes–Matuyama boundary.     

Long-term photographic,current, and nephelometer observations of manganese nodule environments in the Pacific

Long-term measurements on and near the seafloor were made at five locations in the Pacific as part of the Manganese Nodule Project (MANOP). Bottom Ocean Monitor (BOM) tripods deployed at each site contained a time-lapse camera, nephelometer, and current meter. From nearly three years of photographs of the seafloor, there was no evidence that benthic organisms turned over, rotated, or moved nodules. There were indications, however, that benthic organims cleaned sediment from the tops of nodules and in some cases deposited sediment underneath nodules. Currents never exceeded the expected threshold for sediment resuspension of nodule movement. Particle concentrations in the water remained uniformly low throughout the deployments. Degredation of fecal pellets and organic matter proceeded more rapidly than expected. All changes of the seafloor morphology were attributable to the activity of organisms as opposed to currents. The occurrence in one photo sequence of dark, fluffy globs may be related to phytoplankton blooms in the region of equatorial upwelling.     

Metal accumulation rates in the Southeast Pacific and the origin of metalliferous sediments

Metal accumulation rates over the East Pacific Rise and Bauer Deep rule out normal authigenic precipitation of iron and manganese as the major mechanism of enrichment to the metalliferous sediments. A hydrothermal source located along the East Pacific Rise is compatible with the transition metal and aluminum accumulation rates. For the Bauer Deep the accumulation rate data suggest either that metal-bearing phases are being transported from the rise to the protected basins of the deep or that a second hydrothermal source exists within the Bauer Deep. A major portion of the minor elements being deposited in the Bauer Deep could result from authigenic precipitation, thus accounting for their distinctive chemical composition.     

Fluctuations of total electron content in the ionosphere as deduced from measurements by single-frequency GPS receivers

Using an ionospheric diagnostic technique developed by the authors and single-frequency GPS receivers, we obtained the first results of these diagnostics. In particular, we show that the ionosphere is characterized by large-scale periodic processes with frequencies of 3–5 mHz.     

Depth distribution of stresses in the Hokkaido Wadati-Benioff zone as deduced by inversion of earthquake focal mechanisms

This study is based on the detailed geometry of the Hokkaido Wadati-Benioff zone and the paleosubduction zone as delineated by Hanus and Vanek (1984). The used data includes 217 CMT Harvard solutions for earthquakes, which belong to the Wadati-Benioff zone and 13 for the paleosubduction zone. The inverse technique by Gephart and Forsyth (1984) was incorporated for determining the best fit principal stress directions σ₁, σ₂, σ₃ and the ratio (R=σ₂−σ₁/σ₃−σ₁) for 20 km depth intervals in the Wadati-Benioff zone and for the paleosubduction zone considered as a single body. In almost all the considered depth layers, the maximum compressive stress σ₁ is normal to the strike of the slab and dips less than 25°, indicating the NW-SE convergence between the Pacific and Eurasian lithospheric plates. Exceptions are in the depth layer 81–120 km, the paleosubduction zone with steeply dipping along-strike σ₁, and the lower part of the subduction zone (161–220 km) where σ₁ is almost horizontal and of E trend. The minimum compressive stress σ₃ is mostly along-strike and of a different dip with the exception of the 21–60 km layer wher they are down-dipping. The results obtained for the depth ranges 0–20 km, 81–100 km, 121–160 km, and the paleosubduction zone indicate heterogeneous stress fields. These results show that the slab pull and the mantle resistance, acting on the slab edge, are not the main forces which control the contemporary plate tectonics in the Hokkaido region. Along-strike compression at depths 81–120 km and along-strike extension at 0–20 and 61–220 km are involved in the slab dynamics. These can be related to horizontal bending of the subducting Pacific plate.     

The nature of the sea surface as deduced from composite temperature analysis

Summary A technique is described for preparing detailed sea surface temperature analyses for large ocean areas utilizing injection temperature observations from commercial ships. The inadequacies of analyses based on averaged data are discussed, as well as some of the difficulties inherent in contouring scalar fields.Sea surface temperatures are interpreted according to some concepts derived from cross sectional profiles and surface current data. Isotach analyses of mean current drift are considered as flow patterns to aid temperature analysis in areas where data are sparse.

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Die Schwankungen der Oberflächentemperatur des Meeres nach der zusammengesetzten Temperaturanalyse

Zusammenfassung Es wird eine Methode beschrieben, die geeignet ist, mittels Temperaturbeobachtungen von Handelsschiffen aus die Vorarbeiten zu detaillierten Analysen von Oberflächentemperaturen in großräumigen Meeresgebieten durchzuführen. Die Unzulänglichkeit von Analysen gemittelter Werte sowie einige Schwierigkeiten bei der graphischen Darstellung von Skalarfeldern werden besprochen.Gemäß den Vorstellungen, die von Querschnittsprofilen und Oberflächenstromwerten abgeleitet wurden, werden Oberflächentemperaturen gedeutet. Um die Temperaturanalyse in Gebieten mit geringen Beobachtungen zu erleichtern, werden Isotachen-Analysen mittlerer Strömungswerte als Strömungsvorbilder benutzt.

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La nature de la température superficielle de la mer suivant l'analyse composée de la température

Résumé L'article actuel décrit une méthode propre à préparer, au moyen des observations de la température faites au bord des navires marchands, des analyses détaillées de la température superficielle dans de grandes étendues océaniques. L'impropriété de l'analyse des valeurs moyennes ainsi que plusieurs difficultés que l'on rencontre en représentant des champs scalaires sont exposées.Suivant les conceptions déduites des coupes transversales et des courants de surface, on interprète les températures superficielles des courants de l'océan. Dans le but de faciliter l'analyse des températures dans de grandes zones océaniques où des observations sont rares, on se serve comme modèle de courant des analyses des isotaches des valeurs moyennes de courants.

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Submitted October 1961 for publication in Deutsche Hydrographische Zeitschrift.     

U–Th dating of carbonate nodules from methane seeps off Joetsu, Eastern Margin of Japan Sea

We performed U–Th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off Joetsu, of the eastern margin of Japan Sea, to decipher the active period of the methane seep. The carbonates contain ²³⁰Th, part of which is located in detritus such as silicate and organics, at the time of precipitation. The initial ²³⁰Th renders accurate dating with U–Th radioactive disequilibrium method difficult. We assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty. A (²³⁰Th/²³²Th)–(²³⁴U/²³²Th) isochron drawn by three chips divided from a carbonate nodule (PC05-04-50) passed through data points of local sediments. We conclude that the problem of initial ²³⁰Th can be resolved by measurements of local sediments. Results show that carbonate nodules include local sediment as impurities. Furthermore, the results of trace element analyses such as Rb, Zr, Nb, REE, Pb, and Th also support the idea.In all, 18 carbonate samples were dated with correction of initial ²³⁰Th using the mean value of local sediment in this study. The U–Th correction ages show 12–35ka with an isochron age of 26 ± 3ka. Results indicate that during the time interval of U–Th ages, from 12ka to 35ka, environmental conditions must have been favorable for enhanced methane flux through sediment. The extensive methane flow period at 20ka accords with the lowest-stand sea level during the last glacial age. Results of this study also suggest that U–Th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation. In order to acquire U–Th ages of carbonate at methane seep sites, however, it is important to evaluate the amount of initial ²³⁰Th accurately using the value of sediment.