Geochemistry, minerals, color, rare earth elements and d18O at DSDP Hole 92-504B

Investigations of borehole waters sampled in Hole 504B during Leg 92 revealed changes in major-ion composition similar to changes observed previously (during Leg 83). The uniformity of chloride concentrations with increasing depth suggests efficient downhole mixing processes along density gradients caused by large temperature gradients. Chemical and mineralogical studies of suspended drilling mud (bentonite) suggest that this material has undergone substantial alteration and that CaSO4 (anhydrite/gypsum) has precipitated in the deeper parts of the hole. Rare earth element studies suggest contributions of both the bentonites and the basalts to the REE distributions. Studies of the isotopic composition (87Sr/86Sr) of dissolved strontium indicate a strong contribution of basaltic nonradiogenic strontium, although differences between the Leg 83 and Leg 92 data indicate an influence of bentonite during Leg 92. The oxygen isotope composition of the water does not change appreciably downhole. This uniformity can be understood in terms of high water-rock ratios and suggests that the chemical changes observed are due either to alteration processes involving bentonites and basaltic material from the walls of the hole or to exchange with formation fluids from the surrounding basement, which may have altered in composition at relatively high water-rock ratios.

(Table 1) Neodymium and Strontium measurements from sediment core MD01-2451

In the nineties, cold-water coral mounds were discovered in the Porcupine Seabight (NE Atlantic, west of Ireland). A decade later, this discovery led to the drilling of the entire Challenger cold-water coral mound (Eastern slope, Porcupine Seabight) during IODP Expedition 307. As more than 50% of the sediment within Challenger Mound consists of terrigenous material, the terrigenous component is equally important for the build-up of the mound as the framework-building corals. Moreover, the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development. In this study, the first in-depth investigation of the terrigenous sediment fraction of a cold-water coral mound is performed, combining clay mineralogy, sedimentology, petrography and Sr-Nd-isotopic analysis on a gravity core (MD01-2451G) collected at the top of Challenger Mound. Sr- and Nd-isotopic fingerprinting identifies Ireland as the main contributor of terrigenous material in Challenger Mound. Besides this, a variable input of volcanic material from the northern volcanic provinces (Iceland and/or the NW British Isles) is recognized in most of the samples. This volcanic material was most likely transported to Challenger Mound during cold climatic stages. In three samples, the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on Greenland, Scandinavia or Canada. The grain-size distributions of glacial sediments demonstrate that ice-rafted debris was deposited with little or no sorting, indicating a slow bottom-current regime. In contrast, interglacial intervals contain strongly current-sorted sediments, including reworked glacio-marine grains. The micro textures of the quartz-sand grains confirm the presence of grains transported by icebergs in interglacial intervals. These observations highlight the role of ice-rafting as an important transport mechanism of terrigenous material towards the mound during the Late Quaternary. Furthermore, elevated smectite content in the siliciclastic, glaciomarine sediment intervals is linked to the deglaciation history of the British-Irish Ice Sheet (BIIS). The increase of smectite is attributed to the initial stage of chemical weathering processes, which became activated following glacial retreat and the onset of warmer climatic conditions. During these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed. Therefore, we postulate that the deglaciation of the BIIS has an important effect on mound growth. It can seriously alter the hydrography, nutrient supply and sedimentation processes, thereby affecting both sediment input and coral growth and hence, coral mound development.

Neodymium isotopic record of planktonic foraminifera in sediment core MD81-LC21

A well developed sapropel (S5) was deposited in the eastern Mediterranean during the Last Interglacial (Eemian), 124-119 ka. Freshwater contributions to the basin at this time can be traced using the isotopic composition of Nd in planktonic foraminifera. This enables differentiation between radiogenic sources to the south, under the influence of the African monsoon, and unradiogenic sources to the north, relating to the mid-latitude westerlies. Here we compare new Nd data, from a core in the southeast Aegean Sea, with published data from the Ionian and Levantine Seas. Shifts towards more radiogenic Nd in the lower and middle parts of sapropel S5 are most pronounced in the Ionian Sea record, with epsioln-Nd and d18O G. ruber co-varying more closely here than in the Levantine and Aegean Seas. This is consistent with a freshwater source proximal to the Ionian Sea site, likely indicating a substantial reactivation of rivers flowing northward from the central Saharan watershed. The lack, during S5 deposition, of a noticeable shift towards more unradiogenic Nd in the Aegean record would exclude a large influx of water from the northern borders of the eastern Mediterranean during sapropel deposition. These findings support a scenario whereby the Last Interglacial eastern Mediterranean was influenced strongly by the remote effects of an intensified African monsoon, with more local precipitation in the northern borders contributing relatively little to the sea surface composition.

Control techniques for nitrogen oxides from stationary sources.

Includes bibliographies.

Reactions of uranium oxides and liquid nitrogen tetroxide /

Work performed at the Argonne National Laboratory.

Reactivity of certain uranium oxides with aluminum : terminal report /

"Contract No. AT-30-1 Gen-366."

The total and free energies of formation of the oxides of thirty-two metals,

Bibliographical foot-notes.