An evaluation of the apparent dissociation constants of carbonic acid in seawater

The internal consistency of five sets of apparent dissociation constants of carbonic acid in seawater obtained by Buch (1951), Lyman (1956), Edmond and Gieskes (1970), Hansson (1973) and Mehrbach et al. (1973) have been tested using the GEOSECS Atlantic data for the total alkalinity, the total CO₂ concentration and the partial pressure of CO₂. As a measure of the consistency for each of the five sets of the dissociation constants with the data, the 77 measured values of the partial pressure of CO₂ have been compared with those calculated from the alkalinity and total CO₂ values determined for these samples. It has been found that: (1) the apparent dissociation constants of Lyman (1956), Hansson (1973) and Mehrbach et al. (1973) appear to be internally consistent with the data, whereas those of Buch (1951) and of Edmond and Gieskes (1970) appear to be markedly inconsistent with the GEOSECS data; and (2) on the basis of a statistical analysis of the data grouped in three temperature ranges, the dissociation constants of Lyman (1956) and of Mehrbach et al. (1973) appear to be most satisfactory.     

Stream function solutions for steady water waves

Two stream function solutions for steady two-dimensional water waves are reviewed. The algorithm developed by Dalrymple (1974, Proc. 6th Conf. Offshore Tech., pp. 843–856) and used by Hudspeth and Slotta (1978, Proceedings of the American Society of Civil Engineers,104, 319–334) is compared with the algorithm developed by Chaplin (1980, Coastal Engineering,3, 179–205). By examining more closely the near-breaking wave conditions, it is shown that celerity does not increase monotonically with increasing dimensionless wave steepness. Numerical comparisons between the two algorithms indicate that the Dalrymple algorithm is more accurate for near-breaking waves and requires less computer programming effort. Neither algorithm appears to be able to predict breaking wave conditions as accurately as the Cokelet (1977, Philosophical Transactions of the Royal Society of London,A286, 183–230) algorithm. Numerical comparisons of the Dalrymple free surface error convergence criteria with the Chaplin significant figures convergence criteria indicate that the free surface error convergence criterion is more consistent for stream function representations.     

Estimating the standard deviation for222Rn scintillation counting — a note concerning the paper by Sarmiento et al.

In a recent report Sarmiento et al. (1976) presented a method for estimating the statistical error associated with²²²Rn scintillation counting. Because of certain approximations, the method is less accurate than that of an earlier work by Lucas and Woodward (1964). We have compared the Sarmiento method and the Lucas method, and determined the magnitude of errors incurred using the approximations. For counting times greater than 300 minutes, the disadvantage of the slight inaccuracies of the Sarmiento method are outweighed by the advantage of easier calculation.     

Beryllium abundance of meteorites determined by “non-destructive” photon activation

The beryllium content of 73 stony and 4 iron meteorites has been determined “non-destructively” by a newly developed sensitive low-level counting device. A fairly widespread beryllium content of stones ranging from 13 to 386 ppb was found. As expected from the lithophilic character of Be the 4 siderites contained < 8 ppb only. The resulting average chondritic abundance of 74 ppb Be is more than one order of magnitude lower than the cosmic abundance value adopted earlier by H.E. Suess and H.C. Urey (1956), but still about a factor of 2 higher than the value chosen by A.G.W. Cameron (1968). 10–15-g samples were taken in order to guarantee a rather good “mean”. For comparison the Be content of the U.S. Geological Survey basalt BCR-1 was determined in the same way to be 1.390 ± 0.006 ppm Be.     

Ray tracing through models of the East African Rift

In this paper seismic rays are traced through proposed models of the East African Rift and the predicted travel-time residuals are compared to those observed at a number of African seismic stations. The velocity models are based on published gravity models of the East African Rift and empirical velocity-density relationships. Searle's (1970) revision of the models first proposed by Girdler et al. (1969), comprising a low-density, low-velocity asthenolith that partly replaces and thins the continental lithosphere beneath East Africa, is found to be compatible with most of the observed travel-time residuals. Results from the ray tracing suggest that the model may be improved by increasing the volume of normal mantle material between the two branches of the rift. Some of the interesting travel-time residuals associated with anomalous material away from the rift are also discussed.     

Evaluation and application of the ion microprobe in the strontium isotope geochemistry of carbonates

A modified AEI-IM20 ion microprobe has been used to measure⁸⁷Sr/⁸⁶Sr ratios in carbonates. A suite of carbonates with varying major elements (Ca, Mg, Fe, Mn) was studied at low and high (M/ΔM ? 3000) mass resolution to determine the types and intensities of molecular species isobaric with Sr peaks; Sr data collected at low mass resolution must be corrected for Ca₂ and CaMgO species. Rb/Sr ratios are extremely low, and correction for⁸⁷Rb is not required (< 0.1‰ of⁸⁷Sr).Usable Sr isotopic data may be obtained from calcite givenSr≥ 400ppm, and for Sr > 5000 ppm a precision of ～ ± 1‰ (± 0.0007) in⁸⁷Sr/⁸⁶Sr (2σ mean) can be achieved under optimum conditions. The corrections for Ca₂ and CaMgO are smaller than the within-run precision in calcite, but in dolomite the correction for CaMgO is + 1.5%. Mass fractionation corrections to⁸⁷Sr/⁸⁶Sr (based on⁸⁶Sr/⁸⁸Sr= 0.1194) are typically +8 to +10‰. Good agreement between ion probe and solid source mass spectrometer results was found for calcites of known Sr isotopic composition: ST4a (～ 400ppm Sr), average ion probe⁸⁷Sr/⁸⁶Sr= 0.7267 ± 0.0015, solid source⁸⁷Sr/⁸⁶Sr= 0.72680 ± 0.00008 [14]; JCG36 (～ 6000ppm Sr), average ion probe⁸⁷Sr/⁸⁶Sr= 0.7056 ± 0.0009, solid source⁸⁷Sr/⁸⁶Sr= 0.70588 ± 0.00009 [16]; JCG44 (～ 6000ppm Sr), average ion probe⁸⁷Sr/⁸⁶Sr= 0.7057 ± 0.0006, solid source⁸⁷Sr/⁸⁶Sr= 0.70540 ± 0.00008 [16]. The ability of the ion microprobe to measure⁸⁷Sr/⁸⁶Sr for 10-μm spots in calcite was used: (1) to measure variation in⁸⁷Sr/⁸⁶Sr of ～ 0.01 on a centimetre scale in a hydrothermally altered basalt from the Isle of Skye, northwestern Scotland; and (2) to determine the Sr isotopic composition of tiny (< 35 μm) calcite grains in a veined mantle lherzolite from Bultfontein, South Africa. Because of calcite's ubiquitous occurrence in many parageneses this technique may offer many opportunities for the measurement of fine scale heterogeneities in⁸⁷Sr/⁸⁶Sr.     

Geomagnetic secular variation in recent sediments from the Tyrrhenian Sea

Palaeomagnetic measurements on three cores from the Tyrrhenian Sea abyssal plain appear to provide evidence of short-period geomagnetic secular variation during historical times. Using these patterns of variation a method is proposed to determine the relative sedimentation rates between cores.Tentative correlation with dated secular variation curves from Lake Windermere, England (R. Thompson, 1973) gives absolute sedimentation rates for the Tyrrhenian cores in the range 65–130 cm/1000 years.     

Magma genesis in the lesser Antilles island arc

¹⁴³Nd/¹⁴⁴Nd,⁸⁷Sr/⁸⁶Sr and REE results are reported on volcanic rocks from the islands of Dominica and St. Kitts in the Lesser Antilles. Particular attention is given to the lavas and xenoliths of the Foundland (basalt-andesite) and the Plat Pays (andesite-dacite) volcanic centres on Dominica. Combined major and trace element [2] and isotope results suggest that the bulk of the andesites and dacites on Dominica, and by analogy in the rest of the arc, are produced by fractional crystallisation of basaltic magma. The differences in the erupted products of the two volcanoes do not appear to be related to any significant differences in the source rocks of the magmas.Along the arc⁸⁷Sr/⁸⁶Sr ratios range from 0.7037 on St. Kitts, to 0.7041–0.7047 on Dominica, and 0.7039–0.7058 on Grenada [5], and these are accompanied by a parallel increase in K, Sr, Ba and the light REE's. Moreover, compared with LIL-element-enriched and -depleted rocks from MOR and intraplate environments, the basic rocks from the Lesser Antilles are preferentially enriched in alkaline elements (K, Ba, Rb, Sr) relative to less mobile elements such as the rare earths.¹⁴³Nd/¹⁴⁴Nd varies from 0.51308 on St. Kitts, to 0.51286 on Dominica, and 0.51264–0.51308 on Grenada [5], and all these samples have relatively high⁸⁷Sr/⁸⁶Sr ratios compared with the main trend of Nd and Sr isotopes for most mantle-derived volcanic rocks. Alkaline elements and⁸⁷Sr appear to have been introduced from the subducted ocean crust, but the results on other, less mobile elements are more ambiguous — island arc tholeiites (as on St. Kitts) do not appear to contain significant amounts of REE's, Zr, Y, etc., from the subducted oceanic crust, but such a contribution may be present in more LIL-element-enriched calc-alkaline rock types.     

Active faults in West Africa

Interpretation of offshore seismic surveys south of Accra, Ghana, has shown that Accra is situated near the intersection of the northeast-trending Akwapim fault zone and an east-trending coastal boundary fault. Seismic recordings from Kukurantumi Observatory and historical evidence of earthquakes indicate that both faults are currently active. This is also supported by geological evidence. The Akwapim fault is traced southwest across the continental shelf to link at the margin with the Romanche fracture zone on which there is evidence of tectonic activity beyond the confines of the offsets of the Mid-Atlantic Ridge. It is suggested that current tectonism along the Romanche fracture zone continues deep into the continent along the Akwapim fault zone and may represent an early stage in the development of a new plate boundary. Possibly the initiation of this boundary is through crustal fault propagation rather than rifting, perhaps by the mechanism of membrane tectonics proposed by Turcotte and Oxburgh (1973).     

Interdecadal change of the linkage between the North Atlantic Oscillation and the tropical cyclone frequency over the western North Pacific

The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linkage appears to have an interdecadal change from weak connection to strong connection. During the period of 1948–1977, the NAO was insignificantly correlated to the WNPTCF. However, during the period of 1980–2009, they were significantly correlated with stronger(weaker) NAO corresponding to more(fewer) tropical cyclones in the western North Pacific. The possible reason for such a different relationship between the NAO and the WNPTCF during the former and latter periods is further analyzed from the perspective of large-scale atmospheric circulations. When the NAO was stronger than normal in the latter period, an anomalous cyclonic circulation prevailed in the lower troposphere of the western North Pacific and the monsoon trough was intensified, concurrent with the eastward-shifting western Pacific subtropical high as well as anomalous low-level convergence and high-level divergence over the western North Pacific. These conditions favor the genesis and development of tropical cyclones, and thus more tropical cyclones appeared over the western North Pacific. In contrast, in the former period, the impact of the NAO on the aforementioned atmospheric circulations became insignificant, thereby weakening its linkage to the WNPTCF. Further study shows that the change of the wave activity flux associated with the NAO during the former and latter periods may account for such an interdecadal shift of the NAO–WNPTCF relationship.     

Ion microprobe analysis of a potassium self-diffusion experiment in biotite

Self-diffusion of potassium in biotite has been measured by inducing isotopic exchange between the potassium in the biotite and potassium enriched in ⁴¹K in a hydrothermal alkali chloride solution at 650°C and 2000 bars pressure, and then analyzing the resulting distribution of the K isotopes in the mica using an ion microprobe mass analyzer. The distribution of K isotopes in one mica flake was studied by three-dimensional mapping. The results show the diffusivity in the a or b directions to be greater than in the c direction by 2 to 4 orders of magnitude. In the c direction, the isotopic profile yields a diffusion coefficient of D = 1 × 10^?17cm²sec^?1 with an estimated error of a factor of ten. These results are in good agreement with bulk isotopic transport measurements on the same experiment reported by A.W. Hofmann and B.J. Giletti (1970). It is thus shown that diffusivities involving very slow net transport can be measured using an isotopic exchange technique and measuring the effect using an ion microprobe mass analyzer.     

Pyroxenes in the system Mg2Si2O6-CaMgSi2O6 at high pressure

The enstatite-diopside solvus in the system Mg₂Si₂O₆-CaMgSi₂O₆ has been experimentally determined within the pressure range 5–40 kbars and the temperature range 900–1500°C. Experiments involving reversal of the phase boundaries by unmixing from glass starting material and by reaction of pure clinoenstatite and diopside showed difficulty in achieving equilibration due to persistence of metastable, subcalcic clinopyroxene and to the sluggishness of reaction rate. The experimental data showed that the temperature dependence of the diopside limb is less than previously accepted. At 1500°C and 30 kbars subcalcic diopside found by Davis and Boyd (1966) is shown to be metastable with respect to enstatite and more calcic diopside of composition En_42.3Di_57.7. The solvus widens with increasing pressure between 5 and 40 kbars at 1200°C, but at 900°C the pressure effect on the solvus is very small. The stability relationships of the four pyroxenes, protoenstatite, enstatite, iron-free pigeonite and diopside are summarized, based on data from the literature and the present study.     

Rifting of a tethyan continent — Rare earth evidence of an accreting plate margin

Rifting of a continent in the Tethys ocean was associated with two forms of volcanism initially identified by Hynes (1972). An early light rare earth element (LREE)-enriched magma accompanied rifting of the continental crust and subsidence of a marginal carbonate platform. The early basalts are high K₂O, nepheline-normative basalts, associated with silic igneous rocks, and carrying olivine pseudomorphs. A later or contemporaneous LREE-depleted magma is associated with the active formation of sea floor in a marginal embryo ocean basin. The ophiolite basalts are low K₂O, hypersthene-normative basalts containing feldspar laths and pyroxene subhedra. Similar transitions or changes in extrusives are evident in present-day embryo oceans and at the edges of rifted continental margins which surrounded larger ocean basins. Genesis of the tholeiites can be related to 10–30% partial fusion of foliated mantle lherzolites a sample of which adheres to the base of the Othris ophiolite. The alkalic basalts require either a fractionation model, or a more LREE-enriched source perhaps similar to the Ataq lherzolites, since the “tholeiite source lherzolite” can only produce alkalic basalts at low degrees of melting.     

Studies in diffusion,IV. Pressure dependence of Ar diffusion in phlogopite mica

Radiogenic Ar diffusion from phlogopite mica has been measured at 900° and 1080°C at 15 kbars pressure, using a Griggs-type hot creep tester operated at hydrostatic pressure, and followed by standard mass spectrometric analysis. The diffusion coefficients fall within the uncertainty of the diffusion results reported by Giletti (1974) at 1 kbar at 900° and on extrapolation of that Arrhenius plot to 1080°C. That linear plot is given by D₀ = 0.75 and Q = 57.9kcal/g-atom Ar. In the observed temperature range, the effect of pressure up to 15 kbars is not significant. A second Ar diffusion, which employed Ca(OH)₂-CaO as a water buffer, was run at 1 atm H₂O pressure and 550°C for 781 days. The resulting diffusion coefficient agrees, within the uncertainty, with the extrapolation of the earlier curve. This result, and both earlier ones at 600°, are similar in that they fall below the curve. Consequently, despite the agreement within the uncertainty, it is possible that diffusion of Ar from phlogopite below 650°C is somewhat slower than given by the above equation parameters.     

A detailed paleomagnetic survey of the type location for the Gilsa geomagnetic polarity event

A total of 163 cores have been taken from a maximum of 40 separate lavas in three separate sections of the Jökuldalur, southwest of Egilsstadir, Iceland, and subjected to paleomagnetic analysis and some K-Ar dating. Previous work on the sections by McDougall and Wensink (1966) led to the establishment of the Gilságeomagnetic polarity event, with an age of about 1.60 m.y., during the reversed polarity Matuyama epoch. This earlier study described a possible reversely magnetized lava separating the Gilsáevent from a second normal polarity lava, perhaps representing the Olduvai event. Such a possibility was subsequently a source of speculation from diverse sources concerning the polarity history for the lower Matuyama. The present study indicates clearly that there is no second normal polarity event represented in the sections. Only one normal polarity event is therefore represented in the lower Matuyama of the Jökuldalur, and the age of the lavas involved is confirmed to be approximately 1.58 ± 0.08 m.y. Because of uncertainties in the interpretation of the original K-Ar results from Olduvai Gorge, it is still not possible to be certain that the Olduvai and Gilsáevents are separated in time. An incidental result of the survey is evidence to show that, contrary to recent suggestions by Einarsson (1972), there is no substantial hiatus between the major lower parts of the section and lavas believed to represent extrusions after a regional tilting and peneplanation.     

The influence of pressure,temperature and bulk composition on the appearance of garnet in orthogneisses — an example from South Harris,Scotland

Granulite facies metamorphism of the igneous complex of South Harris has produced garnet-clinopyroxene-plagioclase assemblages from olivine-normative rocks and 2 pyroxene-plagioclase-quartz assemblages from quartz-normative rocks. The appearance of garnet can be considered in terms of two complex reactions:Olivine + plagioclase₁ → (Ca, Mg, Fe) garnet + plagioclase₂(olivine-normative) (A)Orthopyroxene + plagioclase₁ → (Ca, Mg, Fe) garnet + plagioclase₂ + quartz (quartz-normative) (B)For bulk compositions of the South Harris rocks the equilibrium pressure for reaction (A) has been exceeded whereas that for reaction (B) was not reached. Estimated physical conditions of metamorphism bracketed by these and other reactions are: 800–860°C and 10–13 kbar. These estimates, based on experimental data on simple systems combined with thermodynamic models of the solid solutions involved are in good agreement with extrapolated pressures for the experimentally determined appearance of garnet in basaltic compositions (Green and Ringwood, 1967). The latter give 9–12 kbar in the temperature range of interest. The calculations are also consistent with the occurrence of kyanite in associated metapelites and with the stability of spinel-lherzolite during the granulite metamorphism.     

Geochemistry of Archaean spinifex-textured peridotites and magnesian and low-magnesian tholeiites

Major and trace element (Rb, Sr, Ba, Zr, Y, Nb, Ni, Co, V, Cr) data are presented for 11 spinifex-textured peridotites (STP) and a number of high-magnesian and low-magnesian tholeiitic basalts. The STP, representing high-magnesian liquids, come from the Yilgarn Block of Western Australia, Munro Township in the Abitibi Belt of Canada and one sample from the Barberton area of South Africa. All of the basaltic samples come from the Yilgarn Block.The STP and high-magnesian rocks are considered to belong to the komatiite suite (1, 2) despite their low CaO/Al₂O₃ ratios. It is argued that the high values (about 1.5) reported for this ratio from the Barberton area can be explained by a combination of factors, viz. garnet separation, Al loss or Ca addition during metamorphism. The processes can be evaluated using CaO/TiO₂, Al₂O₃/TiO₂ ratios, the REE group and trace elements (e.g. Y, Sc). It would appear that most STP from other Archaean belts do not have abnormal CaO/Al₂O₃ ratios.The STP display close to chondritic ratios for Ti/Zr, Zr/Nb, Zr/Y, and TiO₂/Al₂O₃ and are considered to represent liquids produced by large amounts of partial melting of the Archaean mantle. The data suggest that virtually all phases other than olivine were removed by melting during the production of STP liquids. In the STP, Ti/V, Ti/P ratios are non-chondritic, suggesting original depletion and/or incorporation into the core.For lower levels of partial melting, including mid-ocean ridge basalts (MORB) non-chondritic ratios are exhibited by Zr/Y, TiO₂/Al₂O₃, TiO₂/CaO, suggesting controlling phases in the residue for Y, Ca, Al. It is apparent that for STP, Cr is not being controlled, indicating the absence of chromite in the residual. However, at about 15% MgO the data suggest that chromite becomes a residual phase.The transition metals, with the exception of Mn, have higher abundances in Archaean basaltic rocks than in MORB. This is interpreted as being mainly due to more extensive partial melting of the mantle in the Archaean, as a result of higher temperatures.It is suggested that the generation of STP liquids with about 32% MgO is due to upwelling mantle diapirs which probably originated at depths greater than 400 km and at temperatures in excess of 1900°C.Modern equivalents to Archaean greenstone sequences are lacking. The closest tectonic analogue would be the development of oceanic crust within a rifted continental block.     

High-pressure reconnaissance investigation in the system Mg3Al2Si3O12-Fe3Al2Si3O12

Two synthetic end-members and two natural solid solutions of the system Mg₃Al₂Si₃O₁₂-Fe₃Al₂Si₃O₁₂ have been found to display successive phase transformations at increasingly high pressures when they were compressed in a diamond-anvil cell and heated with a YAG laser to temperatures of approximately 1400–1800°C. X-ray diffraction studies of the quenched samples show that the iron-rich garnets apparently first transform to a garnet-related high-pressure phase, then disproportionate into a mixture of magnesiowüstite plus an unknown phase(s). The latter phase(s) may further transform to a still denser unknown phase(s). The ultimate high-pressure phase may be a perovskite-like structure as was previously found for the magnesium-rich garnets. One of the unknown phases may be the high-pressure phase of Al₂O₃ · nSiO₂ compounds. Magnesium-rich garnets display similar phase transformations as do the iron-rich garnets with the exception of the garnet-related high-pressure phase. These results disagree with a previous interpretation for the high-pressure phase of iron-silicate garnets recovered in shock-wave experiments reported by Ahrens and Graham (1972).     

Application of a sigma coordinate sea model to the calculation of wind-induced currents

A three-dimensional numerical sea model is formulated in terms of sigma coordinates in the vertical. The vertical grid spacing in the model is arbitrary and can be refined to give enhanced resolution in high shear regions (e.g., close to the sea surface in wind-driven flows, and/or across the thermocline in stratified flows). A method of accurately determining surface currents and indicating how fine a grid is required in the surface layer is described.The problem of determining a suitable formulation of vertical eddy viscosity to use in a model of wind-induced flow in a tidal sea is considered in detail. A formulation in which surface eddy viscosity depends upon the roughness of the sea surface and the transfer of momentum to depth by surface waves appears reasonable. Below the surface layer turbulence is related to the current at depth.Idealized calculations are performed to demonstrate the accuracy and stability of the sigma coordinate model. Results of these calculations indicate that the formulation of eddy viscosity developed in this paper can explain the high surface shears reported in lake measurements of wind-induced surface currents, and the lack of shear under strong wind conditions in the open sea (GORDON, 1982, Journal of Geophysical Research, 87, 1939–1951).Surface current to surface wind ratio are also computed.     

Contrasting18O enrichment and origins of High Himalayan and Transhimalayan intrusives

Twelve analysed leucogranites of the High Himalaya in Bhutan (Chung La, Mönlakarchung) and Garhwal (Badrinath) are among the most¹⁸O-enriched granites known (11.5–12.4‰ δ¹⁸O_SMOW with two exceptions) and separate minerals show good isotopic concordance. The data strongly support an origin of the granites by anatexis of continental basement such as the Indian crystalline basement sheet or slab, undercut by the Main Central Thrust, of which five samples were analysed. In contrast, the pre-collision Transhimalayan (Gangdese) batholiths to the north of the Indus-Tsangpo suture, as exemplified by the Ladakh intrusives, show an initially oceanic trend of δ¹⁸O vs. SiO₂ that becomes gradually somewhat enriched with respect to Hachijo-Jima. While not completely outside the range of enrichment that seems possible by fractional crystallisation, this could tie in with the⁸⁷Sr inhomogeneities reported by Honegger et al. [9], which may be due to assimilation of variably radiogenic Eurasian continental basement. For both the leucogranites and Ladakh intrusives the¹⁸O levels and the concordance between minerals rule out significant cumulative water/rock ratios in syn- or post-magmatic interaction with subsurface waters.