Lead and strontium isotope composition, mass accumulation rates and rare earth elements of selected samples from DSDP Sites 92-597 to 92-601

Most of the Pb isotope data for the Leg 92 metalliferous sediments (carbonate-free fraction) form approximately linear arrays in the conventional isotopic plots, extending from the middle of the field for mid-ocean ridge basalts (MORB) toward the field for Mn nodules. These arrays are directed closely to the average values of Mn nodules, the composition of which reflects the Pb isotope composition of seawater (Reynolds and Dasch, 1971). Since the Leg 92 samples are almost devoid of continentally derived detritus, it can be inferred that the more radiogenic end-member is seawater. The less radiogenic end-member lies in the very middle of the MORB field, and hence can be considered to reflect the Pb isotope composition of typical ocean-ridge basalt. The array of data lying between these two end-members is most readily interpreted in terms of simple linear mixing of Pb from the two different end-member sources. According to this model, eight samples from Sites 599 to 601 contain 50 to 100% basaltic Pb. Five of these samples have compositions that are identical within the uncertainty of the analyses. We use the average of these five values to define our unradiogenic end-member in the linear mixing model. The ratios used for this average are 206Pb/204Pb = 18.425 ± 0.010; 207Pb/204Pb = 15.495 ± 0.018; 208Pb/204Pb = 37.879 ± 0.068. These values should approximate the average Pb isotope composition of discharging hydrothermal solutions, and therefore also that of the basaltic crust, over the period of time represented by these samples ( 4 m.y., from 4 to 8 Ma). Sr isotope ratios show a significant range of values, from 0.7082 to 0.7091. The lower ratios are well outside the value of 0.70910 ± 6 for modern-day seawater (Burke et al., 1982). However, most values correspond very closely to the curve of 87Sr/86Sr versus age for seawater, with older samples having progressively lower 87Sr/86Sr ratios. The simplest explanation for this progressive reduction is that recrystallization of the abundant biogenic carbonate in the sediments released older seawater Sr which was incorporated into ferromanganiferous phases during diagenesis. Leg 92 metalliferous sediments have total rare earth element (REE) contents that range on a carbonate-free basis from 131 to 301 ppm, with a clustering between 167 and 222 ppm. The patterns have strong negative Ce anomalies. Samples from Sites 599 to 601 display a slight but distinct enrichment in the heavy REE relative to the light REE, whereas those from Sites 597 to 598 show almost no heavy REE enrichment. The former patterns (those for Sites 599 to 601) are interpreted as indicating moderate diagenetic alteration of metalliferous sediments originating at the EPR axis; the latter reflect more complete diagenetic modification.

Ogasawara winter Sr/Ca and U/Ca data of coral core OGA-02-1 and PDO reconstruction (coral-geoduck index)

The Pacific Decadal Oscillation (PDO), the leading mode of sea surface temperature (SST) anomalies in the extratropical North Pacific Ocean, has widespread impacts on precipitation in the Americas and marine fisheries in the North Pacific. However, marine proxy records with a temporal resolution that resolves interannual to interdecadal SST variability in the extratropical North Pacific are extremely rare. Here we demonstrate that the winter Sr/Ca and U/Ca records of an annually-banded reef coral from the Ogasawara Islands in the western subtropical North Pacific are significantly correlated with the instrumental winter PDO index over the last century. The reconstruction of the PDO is further improved by combining the coral data with an existing eastern mid-latitude North Pacific growth ring record of geoduck clams. The spatial correlations of this combined index with global climate fields suggest that SST proxy records from these locations provide potential for PDO reconstructions further back in time.

(Table 2) Varimax factor matrix of planktonic foraminifera at DSDP Hole 72-517

Quaternary sediments were recovered at all four Sites at Leg 72. Planktonic foraminifers were abundant and well preserved, especially in the holes shielded from Antarctic Bottom Water (AABW) influence. The fauna belonged to the subtropical province marked by Globigerinoides ruber and to a lesser extent by Globorotalia inflata. Thirty planktonic foraminiferal species were distinguished, and a detailed study of the Site 517 stratigraphy was made. The Quaternary sequence of the Rio Grande Rise was subdivided slightly differently from the Bolli and Premoli Suva (1973) pattern. Five subzones were identified but some difficulties arose when a precise correlation became necessary in the subzones of the tropical provinces. Correlations could nevertheless be made, particularly with respect to the earliest Quaternary. Quaternary faunal data have been dated by isotopic stratigraphy (Vergnaud Grazzini et al.,1983) and partially contradict results previously published for this part of the Atlantic (Williams and Ledbetter, 1979). By studying the occurrence of planktonic foraminifers, we obtained more information about hydrologic variations during the Quaternary sequence of Hole 517; two broad periods were recognized. Finally, we identified the interaction between the Brazil Current and the subtropical convergence

Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity

Aims. We carried out an investigation of the surface variegation of comet 67P/Churyumov-Gerasimenko, the detection of regions showing activity, the determination of active and inactive surface regions of the comet with spectral methods, and the detection of fallback material. Methods. We analyzed multispectral data generated with Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) narrow angle camera (NAC) observations via spectral techniques, reflectance ratios, and spectral slopes in order to study active regions. We applied clustering analysis to the results of the reflectance ratios, and introduced the new technique of activity thresholds to detect areas potentially enriched in volatiles. Results. Local color inhomogeneities are detected over the investigated surface regions. Active regions, such as Hapi, the active pits of Seth and Ma'at, the clustered and isolated bright features in Imhotep, the alcoves in Seth and Ma'at, and the large alcove in Anuket, have bluer spectra than the overall surface. The spectra generated with OSIRIS NAC observations are dominated by cometary emissions of around 700 nm to 750 nm as a result of the coma between the comet's surface and the camera. One of the two isolated bright features in the Imhotep region displays an absorption band of around 700 nm, which probably indicates the existence of hydrated silicates. An absorption band with a center between 800-900 nm is tentatively observed in some regions of the nucleus surface. This absorption band can be explained by the crystal field absorption of Fe2+, which is a common spectral feature seen in silicates.

(Table 1) Th and U concentrations and activity ratios in deep-sea sediments at ODP Hole 105-646B

The Labrador Sea is a particularly suitable high-latitude basin for investigating U and Th behavior in deep-sea sediments. During the late Quaternary, the cyclic development and decay of huge ice sheets on adjacent land masses resulted in large-amplitude changes in sedimentation rates and organic paleoproductivities. The resulting magnification of U and Th response is well illustrated by high-resolution studies on piston-cored sediments from the Greenland continental rise at Ocean Drilling Program Leg 105 Site 646 spanning isotopic stages 8 to 1. Our results show a clear positive correlation of 238U/232Th ratios with organic paleoproductivity indicators (e.g., dinocyst) due to U uptake in the water column and/or during the early early diagenesis of organic matter responding to carbon fluxes and to their climate forcing. 230Th excesses over 234U exceed the theoretical value of the 230Th rain from the overlying water column, indicating lateral input possibly from the Greenland slope and shelf. Because these horizontal fluxes of 230Th may be partly controlled by physical parameters, 230Th excesses cannot be unequivocally correlated with sedimentation rates and/or productivity as reported elsewhere. In this subarctic basin characterized by low overall organic carbon burial, the 238U/232Th ratio appears to be a sensible geochemical indicator of organic activity and paleoproductivity.

Tax differentials and inflow of foreign direct investments : evidence from foreign operations of U.S. multinational companies

This paper concerns the measurement of the impact of tax differentials across countries on inflow of Foreign Direct Investment (FDI) by using comprehensive data on the foreign operations of U.S. multinational corporations that has been collected by the Bureau of Economic Analysis (BEA), the U.S. Department of Commerce. In particular, this research focuses on examining: (1) how responsive FDI locations are to tax differentials across countries, (2) how different the tax effect on FDI inflow is between developed and developing countries, and (3) whether investment location decisions have become more or less sensitive to tax differences between countries over time ranging from the late 1990s to the early 2000s. Estimation results suggest that high rates of corporate income taxation are associated with reduced foreign assets of U.S. multinational firms in all industries by decreasing the return to foreign asset investment. Further, foreign assets of U.S. multinationals in all industries have become more responsive to non-income tax differentials across countries than to income tax differences from 1999 to 2004. Empirical estimates also indicate that foreign investment by American firms is associated with higher tax sensitivity more in developed countries than in those that are developing.

Why do oil importers diversify their import sources politically? : evidence from U.S. firm-level data

International politics affects oil trade. But why? We construct a firm-level dataset for all U.S. oil-importing companies over 1986-2008 to examine what kinds of firms are more responsive to change in "political distance" between the U.S. and her trading partners, measured by divergence in their UN General Assembly voting patterns. Consistent with previous macro evidence, we first show that individual firms diversify their oil imports politically, even after controlling for unobserved firm heterogeneity. We conjecture that the political pattern of oil imports from these individual firms is driven by hold-up risks, because oil trade is often associated with backward vertical FDI. To test this hold-up risk hypothesis, we investigate heterogeneity in responses by matching transaction-level import data with firm-level worldwide reserves. Our results show that long-run oil import decisions are indeed more elastic for firms with oil reserves overseas than those without, although the reverse is true in the short run. We interpret this empirical regularity as that while firms trade in the spot market can adjust their imports immediately, vertically-integrated firms with investment overseas tend to commit to term contracts in the short run even though they are more responsive to changes in international politics in the long run.