Pacific Ocean

Based on benthic foraminiferal delta18O from ODP Site 1143, a 5-Myr astronomical timescale for the West Pacific Plio-Pleistocene was established using an automatic orbital tuning method. The tuned Brunhes/Matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0.78 Ma. The tuned ages for several planktonic foraminifer bio-events also agree well with published dates, and new ages for some other bio-events in the South China Sea were also estimated.

Fine mineral grains of nonferrous and precious metals (Ag, Au, Cu, Ni, Pb, Sn, Zn, Sb, Ti, W, Mo, and Ce) were revealed for the first time by SEM and microprobe studies of polished sections of iron-manganese crusts from the Sea of Okhotsk. The metals form native and intermetallic compounds; less frequently they form mineral oxides or sulfides. A conclusion was drawn that the main part of the native minerals represents mechanical admixture in the ferromanganese crusts.

We present new last glacial maximum (LGM) sea-surface temperature (SST) maps for the oceans around Australia based on planktonic foraminifera assemblages. To provide the most reliable SST estimates we use the modern analog technique, the revised analog method, and artificial neural networks in conjunction with an expanded modern core top database. All three methods produce similar quality predictions and the root mean squared error of the consensus prediction (the average of the three) under cross-validation is only ?0.77 ?C.

The solution rate of biogenic opal in near-surface sediments in the Central Equatorial Pacific is three to eight orders of magnitude lower than similar acid-cleaned samples. Iron, magnesium and calcium aluminosilicates may be the minerals which are forming on the surface of the opal and reducing its solution rate. The scale height of the system studied suggests that diffusive and not advective processes are primarily responsible for the removal of dissolved silica in sediments.

Pelagic clay of the east-central Pacific province is shown to be a mixture of three primary detrital components, reflecting continental source areas in Asia, North America, and Central and South America. Relative contributions from each source area are a function of geography, and this distribution appears to have remained constant over the past five million years, despite changing flux rates. A Q-mode factor analysis of downcore records for Pb, Sr, and Nd isotopes identified three factors that account for 98% of the total variance.

Strontium isotopes are useful tracers of fluid-rock interaction in marine hydrothermal systems and provide a potential way to quantify the amount of seawater that passes through these systems. We have determined the whole-rock Sr-isotopic compositions of a section of upper oceanic crust that formed at the fast-spreading East Pacific Rise, now exposed at Hess Deep. This dataset provides the first detailed comparison for the much-studied Ocean Drilling Program (ODP) drill core from Site 504B.

A high-resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36?S off central-south Chile (GeoB 7165-1, 36?33'S, 73?40'W, 797 m water depth, core length 750 cm) indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka. Comparative analysis of several cores along the Chilean continental margin (30?-41?S) suggests that the onset and the pattern of deglacial warming was not uniform off central-south Chile due to the progressive southward migration of the Southern Westerlies and local variations in upwelling.

Differential dissolution affects the isotopic composition of different species of planktonic foraminifera in different ways. In the two species studied here in cores from Ontong Java Plateau, the less resistant species, Globigerinoides sacculifer, is more readily affected at a shallower depth than the more resistant species, Pulleniatina obliquiloculata (2.9 versus 3.4 km), but shows a smaller and less predictable response to partial dissolution (0.2 to 0.3 per mil versus 0.6 to 0.7 per mil).

Time-series sediment traps were deployed for five consecutive years in two distinctively different subarctic marine environments. The centrally located subarctic pelagic Station SA (49?N, 174?W; water depth 5406 m) was simultaneously studied along with the marginal sea Station AB (53.5?N, 177?W; water depth 3788 m) in the Aleutian Basin of the Bering Sea. A mooring system was tethered to the sea-floor with a PARFLUX type trap with 13 sample bottles, which was placed at 600 m above the sea-floor at each of the two stations.

We examined the flux of Al to sediment accumulating beneath the zone of elevated productivity in the central equatorial Pacific Ocean, along a surface sediment transect at 135?W as well as downcore for a 650 kyr record at 1.3?N, 133.6?W. Across the surface transect, a pronounced, broadly equatorially symmetric increase in Al accumulation is observed, relative to Ti, with Al/Ti ratios reaching values 3-4 times that of potential detrital sources.