Stable carbon and oxygen isotope records of Cibicidoides wuellerstorfi in DSDP and ODP sites in the Atlantic and Pacific Ocean

Carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago, the interval when significant northern hemisphere glaciation began. The delta18O and delta13C data from four Atlantic sites (552, 607, 610, and 704) and one Pacific site (677) show that global cooling over this interval was associated with increased suppression of North Atlantic Deep Water (NADW) formation. However, the relative strength of NADW production was always greater than is observed during late Pleistocene glaciations when extreme decreases in NADW are observed in the deep North Atlantic. Our data indicate that an increase in the equator-to-pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the North Atlantic but rather the opposite occurred. This is not unexpected as it is the "warm high-salinity" characteristic, rather than the "low temperature", of thermocline waters that is critical to the deepwater formation process in this region today.

(Table 1) Paleomagnetic of ODP Leg 126 sites

A paleomagnetic study was made on the deep-marine sediments and volcanic rocks drilled by Ocean Drilling Program Leg 126 in the Izu-Bonin forearc region (Sites 787, 792, and 793). This study evaluates the sense and amount of the tectonic drift and rotation associated with the evolution of the Philippine Sea Plate and the Izu-Bonin Arc. Alternating-field and thermal demagnetization experiments show that most of the samples have stable remanence and are suitable for paleomagnetic studies. Paleomagnetic declinations were recovered by two methods of core orientation, one of which uses a secondary viscous magnetization vector of each specimen as an orientation standard, and the other of which is based on the data of downhole microresistivity measurement obtained by using a formation microscanner. Oligocene to early Miocene samples show 10° to 14° shallower paleolatitudes than those of the present. Middle Miocene to early Oligocene samples show progressive clockwise deflections (up to ~80°) in declination with time. These results suggest large northward drift and clockwise rotation of the Izu-Bonin forearc region since early Oligocene time. Considering previous paleomagnetic results from the other regions in the Philippine Sea, this motion may reflect large clockwise rotation of the whole Philippine Sea Plate over the past 40 m.y.

(Table T1) Magnetic properties of MORB from ODP Leg 187 sites

The core samples of mid-ocean-ridge basalts (including Indian and Pacific type) recovered from the Southeast Indian Ridge (SEIR) area near the Australian Antarctic Discordance during Ocean Drilling Program Leg 187 were studied using rock magnetism, mineralogy, and petrography methods. On the basis of thermomagnetic analyses and low-temperature magnetometry, the dominant magnetic carrier in most of the basalt samples (pillow basalts) is characterized as titanomaghemite, which presumably formed by low-temperature oxidation of primary titanomagnetite. Some samples from unaltered massive basalts contain nearly unoxidized titanomagnetite as the main magnetic mineral. A metadiabase sample showing greenschist facies metamorphism contains magnetic minerals dominated by magnetite. The pillow basalts contain titanomaghemite ranging from stable single-domain to pseudosingle-domain (PSD) grains, and the majority are characterized by a single stable component of remanence. The massive basalts show hysteresis features of larger PSD grains and contain a very low coercivity remanence. The values of natural remanent magnetization (NRM) of the samples in this SEIR area are on the same order as those of other oceanic ridge basalts. They show a general decreasing trend of NRM with increasing crust age. However, the values of NRM show no correlation either with the tectonic zonations (Zone A vs. Zone B) or with the mantle provinces (Pacific vs. Indian types).

X-ray fluorescence (XRF) scannings and grain size analysis at sites in the Gulf of Cádiz

Contourites in the Gulf of Cádiz preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 5.3 Ma. In our study we investigate the potential of geochemical data obtained by XRF scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled through contourite deposits in the northern Gulf of Cadiz: Site U1387, which is bathed by the upper MOW core, and Site U1389, located more proximal to the Straits of Gibraltar. The lack of major downslope transport at both locations during the Pleistocene makes them ideal locations for the purpose of our study. The results indicate that the Zr/Al ratio, representing the relative enrichment of heavy minerals (zircon) over less dense alumosilicates under strong bottom current flow, is the most useful indicator for a semi-quantitative assessment of current strength. While most elements are biased by current-related processes, the bromine record, representing organic content, preserves the most pristine climate signal rather independent of grain size changes. Hence, Br can be used for chronostratigraphy and site-to-site correlation in addition to stable isotope stratigraphy. Based on these findings we reconstructed MOW variability for Marine Isotope Stages 1-5 using the Zr/Al ratio from Site U1387. The results reveal abrupt, millennial-scale variations of MOW strength during Greenland Stadials (GS) and Interstadials (GI) with strong MOW during GS and glacial Terminations and a complex behavior during Heinrich Stadials. Millennial-scale variability persisting during periods of poorly expressed GS/GI cyclicities implies a strong internal oscillation of the Mediterranean/North Atlantic climate system.

Chemical, and Sr and Li isotopic composition of pore fluids and sediments from ODP Leg 170 and Leg 205 sites

Pore fluid and sediment chemical and isotopic data were obtained for samples from Ocean Drilling Program (ODP) Leg 205 Sites 1253, 1254, and 1255 in the Costa Rica subduction zone. The chemical and isotopic data reported here were generated in our shore-based laboratories to complement shipboard inorganic geochemical data. Li isotopic analyses were carried out by L.-H. Chan at Louisiana State University (USA). The data reported herein include fluoride, bromide, rubidium, cesium, and barium concentrations; Li and Sr isotopic compositions in pore fluids; and Rb, Cs, and Ba concentrations in representative bulk sediments. The data also include new pore fluid fluoride and bromide concentrations from corresponding ODP Leg 170 Sites 1039, 1040, and 1043. O.M. Saether's Site 1039 and 1040 fluoride concentration data are shown for comparison. Basal sediment fluoride concentrations and Li and Sr isotope ratios at both Sites 1253 and 1039 show reversals that approach modern seawater values. Br/Cl ratios are, however, conservative throughout the sediment section at Sites 1039 and 1253. The observed sharp F and Br concentration maxima, Rb and K concentration minima, the most radiogenic 87Sr/86Sr ratios, and highest 7Li values along the décollement and fracture zone (Sites 1040, 1043, 1254, and 1255) strengthen the evidence obtained during Leg 170 that a deeply sourced fluid, originating from fluid-rock reactions at ~150°C and corresponding to between 10 and 15 km depth, is transporting solutes to the ocean.

Organic compounds in sediments and pore waters of ODP Sites 117-723 and 117-724

Total organic carbon, amino compounds, and carbohydrates were measured in pore waters and sediments of Pliocene to Pleistocene age from Sites 723 and 724 (ODP Leg 117) to evaluate (1) relationships between organic matter in the sediment and in the pore water, (2) the imprint of lithological variations on the abundance and contribution of organic substances, (3) degradation of amino compounds and carbohydrates with time and/or depth, and (4) the dependence of the ammonia concentration in the pore water on the degradation of amino compounds in the sediment. Total organic carbon concentrations (TOC) of the investigated sediment samples range from 0.9% to 8.7%, and total nitrogen concentrations (TN) from 0.1% to 0.5%. Up to 4.9% of the TOC is contributed by hydrolyzable amino acids (THAA) which are present in amounts between 1.1 and 21.3 µmol/g dry sediment and decrease strongly downhole. Hydrolyzable carbohydrates (THCHO) were found in concentrations from 1.3 to 6.6 ?mol/g sediment constituting between 0.1% and 2.0% of the TOC. Differences between the distribution patterns of monomers in Sites 723 and 724 indicate higher terrigenous influence for Site 724 and, furthermore, enhanced input of organic matter that is relatively resistant to microbial degradation. Lithologically distinct facies close to the Pliocene/Pleistocene boundary yield different organic matter compositions. Laminated horizons seem to correspond with enhanced amounts of biogenic siliceous material and minor microbiological degradation. Total amounts of dissolved organic carbon (DOC) in pore waters vary between 11 and 131 mg/L. Concentrations of DOC as well as of dissolved amino compounds and carbohydrates appear to be related to microbial activity and/or associated redox zones and not so much to the abundance of organic matter in the sediments. Distributions of amino acids and monosaccharides in pore waters show a general enrichment in relatively stable components in comparison to those of the sediments. Nevertheless, the same trend appears between amino acids present in the sediments from Sites 723 and 724 as well as between amino acids in pore waters from these two sites, indicating a direct relation between the dissolved and the sedimentary organic fractions. Different ammonia concentrations in the pore waters of Sites 723 and 724 seem to be related to enhanced release of ammonia from degradation of amino compounds in Site 723.