Metal binding capacity of selected maine surface waters

Concentrations of Ca, Cd, Cu, Fe, and Pb and binding capacities for Cd, Cu, and Pb were determined for water samples collected from 12 lakes in southwestern Maine using atomic absorption and ion-selective electrodes, respectively. Surface waters in this area are soft and characterized by low pH. Some lakes were highly colored with refractory organics, whereas others had very low organic carbon concentrations. Both Cu and Pb concentrations were positively correlated with organic carbon content. Copper and Pb binding capacities were significantly correlated with organic carbon content, whereas Cd binding capacity was positively correlated with pH, but not with organic carbon. Surface water binding capacity for Pb was greater than that for Cu or Cd. More than 99% of the Ca from all waters studied was removed onto cationic exchange resins. Less than 1% of the total Cu existed as cationic species in highly humic waters, whereas as much as 65% existed as cationic species in less huic waters. Conversely, more than 99% of the Cd present in humic waters existed as cationic species, whereas as little as 50% existed as cationic species in less humic, more alkaline waters. These correlative studies indicate that binding by organic carbon is important for both Cu and Pb in this area and must be considered in models of trace metal speciation. However, Cd binding in the same waters is not correlated with organic carbon, which does not need to be considered in speciation models for Cd.     

Basalts of unusual composition from the Chyulu Hills,Kenya

Five Ne-normative basalts are unusually rich in Cr, to a lesser degree in Co, and have very high La/Lu ratios and high contents of several excluded trace elements resembling kimberlites in these and other aspects. They seem to represent mantle-derived magmas, only slightly modified by shallow level crystal/liquid fractionation. Cr was apparently excluded from the crystalline phases in equilibrium with these magmas in the upper mantle.The Chyulu rocks differ in several respects from other Gregory Rift basalts, but closely resemble those from Jan Mayen Island near the Mid-Atlantic ridge. The generation of these unusual basalts is therefore not related simply to mantle composition or tectonic setting, but may reflect unusually high-T (1450°C), low-P (15–29 kbars) environments in the zones of last effective equilibration of these magmas with mantle rocks.     

Iceland and the North Atlantic: A review

Iceland is a special volcanic island in an anomalous ocean basin. A review of the unusual features shows that among others topography and gravity are broadly positive, spreading has been and still is complex, seismicity is slightly diffuse and the chemistry of the basalts is different from that at normal ridges. In summary we observe a tendency of lithospheric dispersal and spreading in the North Atlantic and its surroundings. These observations together with what is known about Icelandic crust, heat flow, tectonic history, etc., point to a hot mantle upwelling beneath Iceland. The shape of the upwelling currents is not known. Although at present much speculation is possible, the authors prefers to think of a broad rising region uplifting the lithospheric plates such that they tend to slide away from Iceland more forcefully than is the case from normal spreading ridges.     

Structure energies of the alkali feldspars

Structural energetics of the alkali feldspars have been studied using a “lattice” or structure energy model. Electrostatic energies, U _e,for 20 well-refined, non-intergrown alkali feldspars were calculated using Bertaut's (1952) summation procedure and average about ?13,400 kcal/mol; the repulsive energies of the alkali site in each structure (～15 kcal/mol) were calculated using repulsive parameters for K-O and Na-O interactions estimated from bulk modulus data for NaF and KF and the exponential form of the repulsive potential. Using a procedure in which the position of the alkali cation was varied while the oxygen cage was kept fixed, structure energy gradients for the alkali sites of high albite and a hypersolvus Ab₄₂Or₅₈ structure were computed. In both cases, a broad structure energy well, elongated approximately parallel to c and subparallel to the observed split Na positions, was found. In both structures there is a single energy minimum corresponding closely with the observed single alkali positions. Comparison of U _e values for the alkali feldspars with different K/Na ratios shows that intermediate compositions are predicted to be less “stable” than either endmember and that the potassic end-member is predicted to be less “stable” than the sodic one, assuming that all other factors contributiong to the free energies of each phase are approximately the same. Comparison of U _e values for the high albite and low sanidine structures with different Al/Si distributions and a fixed tetrahedral framework indicates that the ordered charge distributions are 63.0 and 54.8 kcal/mol, respectively, more “stable” than the disordered distributions. Smaller, more realistic energy differences were obtained by using U _evalues averaged from four separate calculations with a +3 charge on a different T site in each and with +4 charges on the other T sites. If, in addition, the charges on cations and oxygen are reduced to half their nominal formal charges, in agreement with Pauling's electroneutrality principle and the results of recent molecular orbital calculations on silicates, the predicted electrostatic energy differences are reduced to 3.6 and 1.6 kcal/mol, respectively. These calculations also indicate that the T₁O site in the high albite structure energetically favors Al and that the Al/Si distribution determines the Na position within the alkali site.     

Atmospheric effects in the remote sensing of phytoplankton pigments

We investigate the accuracy with which relevant atmospheric parameters must be estimated to derive phytoplankton pigment concentrations (chlorophyll a plus phaeophytin a ) of a given accuracy from measurements of the ocean's apparent spectral radiance at satellite altitudes. The analysis is limited to an instrument having the characteristics of the Coastal Zone Color Scanner scheduled to orbit the Earth on NIMBUS-G. A phytoplankton pigment algorithm is developed which relates the pigment concentration (C) to the three ratios of upwelling radiance just beneath the sea surface which can be formed from the wavelengths () 440, 520 and 550 nm. The pigment algorithm explains from 94 to 98% of the variance in log₁₀ C over three orders of magnitude in pigment concentration. This is combined with solutions to the radiative transfer equation to simulate the ocean's apparent spectral radiance at satellite altitudes as a function of C and the optical properties of the aerosol, the optical depth of which is assumed to be proportioned to ^-n . A specific atmospheric correction algorithm, based on the assumption that the ocean is totally absorbing at 670 nm, is then applied to the simulated spectral radiance, from which the pigment concentration is derived. Comparison between the true and derived values of C show that: (1) n is considerably more important than the actual aerosol optical thickness; (2) for C 0299-1 0.2 g l^-1 acceptable concentrations can be determined as long as n is not overestimated; (3) as C increases, the accuracy with which n must be estimated, for a given relative accuracy in C, also increases; and (4) for C greater than about 0.5 g 1^-1, the radiance at 440 nm becomes essentially useless in determining C. The computations also suggest that if separate pigment algorithms are used for C 1gl^-1 and C 1 gl^-1, accuracies considerably better than ±± in log C can be obtained for C 1 g l^-1 with only a coarse estimate of n, while for C 10 gl^-1, this accuracy can be achieved only with very good estimates of n.Contribution No. 387 from the NOAA/ERL Pacific Environmental Laboratory.On leave from Department of Physics, University of Miami, Coral Gables, Florida.     

Polymerization of silicate and aluminate tetrahedra in glasses,melts, and aqueous solutions—I. Electronic structure of H6Si2O7, H6AlSiO71−, and H6Al2O72−

As part of a study of the effect of geologically common network modifiers on polymerization in silicate melts, glasses, and silica-rich aqueous solutions, we have studied the energies, electronic structures, and inferred chemical properties of ^IVT-O-^IVT linkages in the tetrahedral dimers H₆,Si₂O₇, H₆AlSiO₇^1?, and H₆Al₂O₇^2? using semi-empirical molecular orbital theory (CNDO/2). Our results indicate that the electron donating character of the bridging oxygen, O(br), linking two tetrahedra increases with increasing T-O(br) bond length but decreases with decreasing T-O(br)-T angles and increasing O-T-O(br) angles. This increase or decrease of the donor character of O(br) coincides with an increase or decrease of the affinity of O(br) for hard acceptors. The calculated electronic structure for the H₆Si₂O₇ molecule is compared with the observed X-ray emission, absorption, and photoelectron spectra of quartz and vitreous silica; the reasonable match between calculated and observed oxygen Kα emission spectra of vitreous silica supports our assertion that non-bonded O(br) electron density energetically at the top of the valence band controls the chemical reactivity of ^IVT-O-^IVT linkages in polymerized tetrahedral environments.     

Gulf of Alaska Atmosphere-Ocean Variability Over Recent Centuries Inferred from Coastal Tree-Ring Records

Eight tree-ring chronologies from coastal sites along the Gulf of Alaska (GOA) are used to develop a 227-year (1762–1988) reconstruction of spring/summer (March–September) coastal land temperatures for the region. This reconstruction explains 35% of the variance in the instrumental temperature data. The tree-ring records and reconstruction reflect the documented 1976 transition from cold to warm conditions in the North Pacific and are consistent with regional temperature compilations. Three of the eight ring-width series, from elevational timberline sites where trees are particularly stressed by temperature, extend back to A.D. 1600 and are used to identify additional occurrences of such transitions. The first principal component (PC) scores of these three longer records are positively correlated with spring (March–May) land and sea surface temperatures for the GOA region and are used to reconstruct land surface temperatures. Decadal-scale fluctuations in the reconstructions show agreement with decade-long changes in the intensity of the Aleutian Low pressure cell over the past century, suggesting that the tree-ring data may provide an index of past circulation changes for the northeast Pacific. Blackman-Tukey spectral analyses of both reconstructions indicate significant power at 7–11 years, with additional peaks at 3 years for the spring/summer reconstruction and 19 years for the longer spring temperature series. The modes of variation at about 3 and 7 years may correspond to those associated with the El Niño-Southern Oscillation bandwidth, whereas the 19-year term may relate to a proposed 20-year cycle of North Pacific circulation. The spring temperature series shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska over this interval. Comparison with the entire spring series suggests that the recent warming exceeds temperature levels of prior centuries, extending back to A.D. 1600.