Pacific Ocean

Oxygen isotope data are compared with relative abundances of selected planktic foraminifera through a ca. 15 m interval at DSDP Site 593 (Tasman Sea, southwest Pacific, 40?S) in which there are prominent changes in population sizes, as well as several evolutionary events. We focus on the relation between faunal and climatic histories. The base of early Miocene oxygen isotope Zone Mi1b (uppermost planktic foraminiferal Zone N.6) is identified from closesampled (c. 14 kyr) isotope records of Globigerina woodi and Cibicides kullenbergi.

Metamorphosed oceanic gabbros provide a record of the cooling history of the lower crust near mid-ocean ridges, but the temperature range, rate, and location of subsolidus events are poorly known. We combine hornblende-plagioclase thermometry, statistical analysis, and thermal models to estimate precisely the temperature, time, distance from axis, and duration of metamorphism in East Pacific Rise gabbros from Hess Deep, ODP Hole 894G.

Seafloor recycling of organic materials in Santa Monica Basin, California was examined through in situ benthic chamber experiments, shipboard whole-core incubations and pore water studies. Mass balance calculations indicate that the data are internally consistent and that the estimated benthic exchange rates compare well with those derived from deep, moored conical sediment traps and hydrographic modeling. Pore water and benthic flux observations indicate that the metabolizable organic matter at the seafloor must be composed of at least two fractions of very different reactivities.

Four boreholes, drilled a few tens of meters into igneous basement on the eastern flank of the Juan de Fuca Ridge during ODP Leg 168, were sealed and instrumented for long-term monitoring to observe the hydrologic state of young sediment-sealed oceanic crust. The thermal regime is dominated by the effects of rapid fluid circulation in uppermost igneous basement driven by very small non-hydrostatic pressure gradients. Upper basement temperatures are uniform laterally between pairs of holes over distances of hundreds of meters to kilometers.

The age of the Brunhes-Matuyama boundary, until recently taken as 730 k.y. in standard time scales for the Quaternary (e.g., Imbrie et al., 1984; Prell et al., 1986, doi:10.1029/PA001i002p00137) and in Ocean Drilling Program results (Kroenke et al., 1991, doi:10.2973/odp.proc.ir.130.1991; Shackleton et al., 1992 doi:10.2973/odp.proc.ir.138.1992) has been revised to between 780 k.y. and 790 k.y., based on both orbital tuning of oxygen isotope data (e.g., Shackleton et al., 1990) and on new 40Ar-39Ar dates on volcanic rocks (e.g., Baksi et al., 1992, doi:10.1126/science.256.5055.356).

Compressional (Vp) and shear (Vs) wave velocities have been measured to 10 kb in 32 cores of basalt from 14 Pacific sites of the Deep Sea Drilling Project. Both Vp and V s show wide ranges (3.70 to 6.38 km/sec for Vp and 1.77 to 3.40 km/sec for V s at 0.5 kb) which are linearly related to density and sea floor age, confirming earlier findings by Christensen and Salisbury of decreasing velocity with progressive submarine weathering based on studies of basalts from five sites in the Atlantic.

Surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep-sea floor. As a rule of thumb, for each 1 mg of organic carbon arriving at the sea floor, one benthic foram shell >150 ?m is deposited. The correlation can be used to reconstruct organic flux to the sea floor in the past, and hence the productivity of past oceans.

A north-south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33? to 42?N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, Corg, and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time-space maps reveal a complex pattern of changes that do not follow a simple glacial-interglacial two-mode model.

The accumulation of extraterrestrial 3He, a tracer for interplanetary dust particles (IDPs), in sediments from the Ontong Java Plateau (OJP; western equatorial Pacific Ocean) has been shown previously to exhibit a regular cyclicity during the late Pleistocene, with a period of ~100 ka. Those results have been interpreted to reflect periodic variability in the global accretion of IDPs that, in turn, has been linked to changes in the inclination of Earth's orbit with respect to the invariable plane of the solar system.

Little is known about the fluxes to and from the ocean during the Cenozoic of phosphorus (P), a limiting nutrient for oceanic primary productivity and organic carbon burial on geologic timescales. Previous studies have concluded that dissolved river fluxes increased worldwide during the Cenozoic and that organic carbon burial decreased relative to calcium carbonate burial and perhaps in absolute terms as well.