Age determination and stable isotope ratios of sediment core RC11-83

The Southern Ocean is perhaps the only region where fluctuations in the global influence of North Atlantic Deep Water (NADW) can be monitored unambiguously in single deep-sea cores. A carbon isotope record from benthic foraminifera in a Southern Ocean core reveals large and rapid changes in the flux of NADW during the last deglaciation, and an abrupt increase in the NADW production rate which immediately preceded large-scale melting of the Northern Hemisphere ice sheets. This sudden strengthening of the NADW thermoha-line cell provides strong evidence for the importance of NADW in glacial-interglacial climate change.

The Global Plankton Database: an inventory and data from the Former Soviet Union expeditions

At present time, there is a lack of knowledge on the interannual climate-related variability of zooplankton communities of the tropical Atlantic, central Mediterranean Sea, Caspian Sea, and Aral Sea, due to the absence of appropriate databases. In the mid latitudes, the North Atlantic Oscillation (NAO) is the dominant mode of atmospheric fluctuations over eastern North America, the northern Atlantic Ocean and Europe. Therefore, one of the issues that need to be addressed through data synthesis is the evaluation of interannual patterns in species abundance and species diversity over these regions in regard to the NAO. The database has been used to investigate the ecological role of the NAO in interannual variations of mesozooplankton abundance and biomass along the zonal array of the NAO influence. Basic approach to the proposed research involved: (1) development of co-operation between experts and data holders in Ukraine, Russia, Kazakhstan, Azerbaijan, UK, and USA to rescue and compile the oceanographic data sets and release them on CD-ROM, (2) organization and compilation of a database based on FSU cruises to the above regions, (3) analysis of the basin-scale interannual variability of the zooplankton species abundance, biomass, and species diversity.

Stable carbon and oxygen isotope record of planktonic and benthic foraminifera at ODP Site 111-677 in the Panama Basin

Oxygen and carbon isotope ratio measurements are presented for Globigerinoides ruber and for benthic species (mainly Uvigerina spp.) in the Pleistocene and uppermost Pliocene section of ODP Hole 677A in the Panama Basin. This provides the best available continuous Pleistocene stable isotope records from any location, fully justifying the recoring of DSDP Site 504. Oxygen isotope stage 22 (age about 0.85 Ma) was of similar magnitude to the most extensive glacials of the Brunhes and constitutes a logical base for the middle Pleistocene. Oxygen isotope stages as defined by Ruddiman et al. (1986, doi:10.1016/0012-821X(86)90024-5) and by Raymo et al. (1989, doi:10.1029/PA004i004p00413) back to stage 104 are recognized. Although the internationally agreed base of the Quaternary at or near stage 62 (about 1.6 Ma) is not marked by a major isotopic event, it does approximate the base of a regime characterized by highly regular 41,000-yr climate cycles. The records at Site 677 are ideal for time-series analyses and will permit a new attempt to develop a chronology for the early Pleistocene based on tuning to the orbital frequencies. The carbon isotope records also appear to contain considerable variance at orbital frequencies throughout the sequence analyzed.

Permeability measurements on sheared and unsheared samples from different IODP Holes of Leg 316 and from IODP Hole 315-C0001E and ODP Hole 190-1174B

At subduction zones, the permeability of major fault zones influences pore pressure generation, controls fluid flow pathways and rates, and affects fault slip behavior and mechanical strength by mediating effective normal stress. Therefore, there is a need for detailed and systematic permeability measurements of natural materials from fault systems, particularly measurements that allow direct comparison between the permeability of sheared and unsheared samples from the same host rock or sediment. We conducted laboratory experiments to compare the permeability of sheared and uniaxially consolidated (unsheared) marine sediments sampled during IODP Expedition 316 and ODP Leg 190 to the Nankai Trough offshore Japan. These samples were retrieved from: (1) The décollement zone and incoming trench fill offshore Shikoku Island (the Muroto transect); (2) Slope sediments sampled offshore SW Honshu (the Kumano transect) ~ 25 km landward of the trench, including material overriden by a major out-of-sequence thrust fault, termed the "megasplay"; and (3) A region of diffuse thrust faulting near the toe of the accretionary prism along the Kumano transect. Our results show that shearing reduces fault-normal permeability by up to 1 order of magnitude, and this reduction is largest for shallow (< 500 mbsf) samples. Shearing-induced permeability reduction is smaller in samples from greater depth, where pre-existing fabric from compaction and lithification may be better developed. Our results indicate that localized shearing in fault zones should result in heterogeneous permeability in the uppermost few kilometers in accretionary prisms, which favors both the trapping of fluids beneath and within major faults, and the channeling of flow parallel to fault structure. These low permeabilities promote the development of elevated pore fluid pressures during accretion and underthrusting, and will also facilitate dynamic hydrologic processes within shear zones including dilatancy hardening and thermal pressurization.

Petrology of basalts from DSDP Hole 83-504B

Basalts from Hole 504B, Leg 83, exhibit remarkable uniformity in major and trace element composition throughout the 1075.5 m of basement drilled. The majority of the basalts, Group D', have unusual compositions relative to normal (Type I) mid-ocean ridge basalts (MORB). These basalts have relatively high mg values (0.60-0.70) and CaO abundances (11.7-13.7%; Ca/Al = 0.78-0.89), but exhibit a marked depletion in compatible trace elements (Cr and Ni); moderately incompatible trace elements (Zr, Y, Ti, etc.); and highly incompatible trace elements (Nb, LREE, etc.). Petrographic and compositional data indicate that most of these basalts are evolved, having fractionated significant amounts of plagioclase, olivine, and clinopyroxene. Melting experiments on similar basalt compositions from the upper portion of Hole 504B (Leg 70; Autio and Rhodes, 1983) indicate that the basalts are co-saturated with olivine and plagioclase and often clinopyroxene on the 1-atm. liquidus. Two rarely occurring groups, M' and T, are compositionally distinct from Group D' basalts. Group T is strongly depleted in all magmaphile elements except the highly incompatible ones (Nb, La, etc.), while Group M' has moderate concentrations of both moderately and highly incompatible trace elements and is similar to Type I MORB. Groups M' and T cannot be related to Group D' nor to each other by crystal fractionation, crystal accumulation, or magma mixing. The large differences in magmaphile element ratios (Zr/Nb, La/Yb) among these three chemical groups may be accounted for by complex melting models and/or local heterogeneity of the mantle beneath the Costa Rica Ridge. Xenocrysts and xenoliths of plagioclase and clinopyroxene similar in texture and mineral composition to crystals in coarse-grained basalts from the lower portion of the hole are common in Hole 504B basalts. These suggest that addition of solid components either from conduit or magma chamber walls has occurred and may be a common source of disequilibrium crystals in these basalts. However, mixing of plagioclase-laden depleted melts (similar to the Costa Rica Ridge Zone basalts) with normal MORB magmas could provide an alternate source for some refractory plagioclase crystals found out of equilibrium in many phyric MORB. The uniformity of major element compositions in Hole 504B basalts affords an ideal situation for investigating the effects of alteration on some major and trace elements in oceanic basalts. Alteration observed in whole-rock samples records primarily two events - a high-temperature and a low-temperature phase. High-temperature phases include: chlorite, talc, albite, actinolite, sphene, quartz, and pyrite. The low-temperature phases include smectite (saponite), epistilbite or laumontite, and minor calcite. Laumontite may actually straddle the gap between the low- and high-temperature mineral assemblages. Alteration is restricted primarily to partial replacement of primary phases. Metamorphic grade, in general, increases from the top to the bottom of Hole 504B (Legs 69, 70, and 83) as seen in the change from a smectiteto- chlorite-dominated secondary mineral assemblage. However, a systematic progression for the interval recovered during Leg 83 is not apparent. Rather, the extent of alteration appears to be a function of the initial texture and fracture density. Variations in whole-rock major and trace element concentrations cannot be attributed convincingly to any differences in alteration observed. Compositional characteristics of the secondary minerals indicated that extensive remobilization of elements has not occurred; local redistribution is suggested in most cases. Thus, the major and trace element signature of these basalts remains effectively the same as the original composition prior to alteration.