Stable oxygen and carbon isotope record of Neogloboquadrina pachyderma of ODP Leg 178 holes

Oxygen and carbon isotopic ratios were measured on left-coiling Neogloboquadrina pachyderma separated from sediments recovered from Holes 1096B (3152 m water depth) and 1101A (3280 m water depth) during Ocean Drilling Program Leg 178. The sediment samples were widely spaced, extending over the past 2.1 m.y. The nature of the sediments from which they were separated and the measured oxygen isotopic ratios show that N. pachyderma (s) is preserved in both glacial and interglacial sediments over the entire period, pointing to the possibility of extracting a detailed isotopic record at these sites extending back to 2.1 Ma.

The Paleocene-Eocene boundary in ODP Leg 208 sites

The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of ~2000 * 10**9 metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowerd deep-sea pH, thereby triggering a rapid (<10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (<10,000 years) by more than 2 kilometers and recovered gradually (>100,000 years). These findings indicate that a large mass of carbon (>>2000 * 10**9 metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.

Strontium and neodymium isotope data for barite separates and pore waters, and isotope and concentration data for foraminifera and fish teeth from DSDP Leg 85 sediments

Strontium and neodymium isotopic data are reported for barite samples chemically separated from Late Miocene to Pliocene sediments from the eastern equatorial Pacific. At a site within a region of very high productivity close to the equator, 87Sr/86Sr ratios in the barite separates are indistinguishable from those of foraminifera and fish teeth from the same samples. However, at two sites north of the productivity maximum barite separates have slightly, but consistently lower (averaging 0.000062) ratios than the coexisting phases, although values still fall within the total range of published values for the contemporaneous seawater strontium isotope curve. We examine possible causes for this offset including recrystallization of the foraminifera, fish teeth or barite, the presence of non-barite contaminants, or incorporation of older, reworked deep-sea barite; the inclusion of a small amount of hydrothermal barite in the sediments seems most consistent with our data, although there are difficulties associated with adequate production and transportation of this phase. Barite is unlikely to replace calcite as a preferred tracer of seawater strontium isotopes in carbonate-rich sediments, but may prove a useful substitute in cases where calcite is rare or strongly affected by diagenesis. In contrast to the case for strontium, neodymium isotopic ratios in the barite separates are far from expected values for contemporary seawater, and appear to be dominated by an (unobserved) eolian component with high neodymium concentration and low 143Nd/144Nd. These results suggest that the true potential of barite as an indicator of paleocean neodymium isotopic ratios and REE patterns will be realized only when a more selective separation procedure is developed.

Characteristics of ice-rafted pebbles from ODP Leg 178 holes

Pebbles (>10 mm) sampled from three drill sites on the continental rise west of the Antarctic Peninsula during Ocean Drilling Program Leg 178 were classified by shape and roundness. In addition, pebble lithology and surface texture were visually identified. To increase the pebble sample number to 331, three sites that were drilled 94 to 213 km from the continental shelf edge were integrated into the data set using magnetostratigraphy for core correlation. Pebbles were compared in three groups defined by the same stratigraphic intervals at each site: 3.1-2.2 Ma (late Pliocene), 2.2-0.76 Ma (late Pliocene-late Pleistocene), and 0.76 Ma to the Holocene. Pebble lithologies originate from sources on the Antarctic Peninsula margin. Most pebbles are metamorphic and sedimentary pebbles are rare (<6%), whereas mafic volcanic and intrusive igneous lithologies increase in abundance upsection. Pebbles from 3.1 to 0.76 Ma, plotted on sphericity-roundness diagrams, indicate original transport as basal and supraglacial/englacial debris. Pebbles are abundant and of diverse lithology. From 0.76 Ma to the present, the number of pebbles is low and their shape characteristics indicate they originated as basal debris. Observed changes in ice-rafted pebbles can be explained by growth of an ice sheet and inundation of the Antarctic Peninsula topography by ice ~0.76 Ma. Prior to this, outlet and valley glaciers transported debris at high levels within and at the base of the ice. The mass accumulation rate of sand fluctuates and includes rounded quartz grains. Ice-sheet growth may have been accompanied by overall cooling from subpolar to polar glacial regimes, which halted meltwater production and enhanced the growth of ice shelves, which consequently reduced sediment supply to icebergs.

Spectral reflectance of ODP Leg 178 holes

The routine use of spectrophotometry on the sediment surfaces of archive halves of each section during the onboard sedimentological core description process is a great stride toward development of real-time noninvasive characterization of deep-sea sediments. Spectral reflectance data have been used so far for mineral composition studies as well as for lithostratigraphic correlation between sites (Balsam and Deaton, 1991; Balsam et al., 1997; Mix et al., 1995; Ortiz et al., 1999). Their results demonstrate that spectrophotometry can estimate CaCO3 content by using the 4.65-, 5.25-, and 5.55-µm wavelength spectrums. A detailed overview of various other noninvasive methods is given in Ortiz and Rack (1999). The purpose of this study is to test whether spectrophotometry in the visible band can be used as a tool to gather further information about grain-size variation, sorting, compaction, and porosity, which are directly linked to the sedimentation process. From remote sensing data analyses, it is known that diffuse spectral reflectance data in the visible band in the wavelength window of 7.0-6.5 µm are sensitive to grain-size variations. It appears that a relationship between grain size and signal absorption exists only in this wavelength window. (e.g., Clark, 1999; Gaffey, 1986; Gaffey et al., 1993). Variations in grain size during a sedimentation process are linked to depositional energy, which affects sorting, compaction, and porosity of sediment deposits. As an example, we study here the spectrophotometric data of the sedimentary sequence of Hole 1098C, which was deposited under widely varying environmental conditions. Alternating turbidite and finely laminated sediments were recovered from Hole 1098C. The turbidites are related to a high depositional energy environment; the finely laminated sediments are related to a low depositional energy environment. Data from Hole 1098C were therefore used to test whether the spectral reflectance data can provide a proxy for these different depositional environments.