Uranium and thorium isotopes and sedimentation rates in metalliferous sediments from the western flank of the East Pacific Rise at 21°-22°S

Isotopic compositions of uranium (234U and 238U) and thorium (230Th and 232Th) were measured in metalliferous sediments from the western flank of the East Pacific Rise at 21°-22°S, in the area of hydrothermal activity and massive sulfide accumulation at the axis of the EPR. Concentration of 232Th (on the carbonate-free base) is consistent with composition of mafic extrusive rocks; isotope ratios 232Th/238U and 234U/238U indicate that about 70% of uranium passes into sediments from sea water with hydrothermal iron hydroxide. Mean sedimentation rates are calculated for seven cores by the nonequilibrium 230Th method with use of the constant concentration model. Flux of 230Th to bottom sediments is calculated and its mean value is used to determine sedimentation rate in four other cores. The constant flux model is used to calculate change of sedimentation rate with depth for seven cores over time interval of 100-300 ky. Sedimentation rates varied not much (0.3-0.6 cm/ky). The greatest changes occurred in two cores: one located near massive sulfide structures, and another near the spreading axis. Determinations of mean rates by the radiocarbon method and the nonequilibrium thorium method are in good agreement.

Mineral content, major oxides and trace elements concentrations in clay from different IODP Holes of 331-C0013, 331-C0017, East China sea shelf and different Taiwan rivers

The Okinawa Trough (OT) in the East Asian continental margin is characterized by thick terrigenous sediment and ubiquitous volcanic-hydrothermal activities. In this study, the clays collected during IODP Expedition 331 to the middle OT (Iheya North Knoll) were analyzed for mineralogical and geochemical compositions. By comparing with the clays from the East China Sea shelf and surrounding rivers, we examine different clay origins. The hydrothermal field in the mid-OT is dominated by Mg-rich chlorite, while the recharge zone has clay mineral assemblages similar to the shelf and rivers, showing high content of illite, subordinate chlorite and kaolinite and scarce smectite. Compared to the terrigenous clays, the hydrothermal clays in the OT have high concentrations of Mg, Mn and Zr but low Fe, Na, K, Ca, Ba, Sr, P, Sc and Ti, while the hydrothermal clays in the mid-ocean ridge are relatively enriched in Fe and V and depleted in Al, Mg, Zr, Sc and Ti. Different fractionation patterns of rare earth elements also register in the terrigenous and hydrothermal clays, diagnostic of variable clay origins. We infer that the OT hydrothermal clay was primarily formed by the chemical alteration of detrital sediments subject to the hydrothermal fluids. The remarkably different compositions of hydrothermal clays between the sediment-rich back arc basin like OT and the sediment-starved ocean ridge suggest different physical and chemical processes of hydrothermal fluids and fluid-rock/sediment reactions under various geologic settings.

Abundance of microzooplankton in surface waters of the East Atlantic and Mediterranean in August-September 1970

Abundance of microzooplankton was studied from August to October 1970 in a ship laboratory using the method of concentration of water samples by filtration and then counting living organisms under a microscope. The main groups (in order of decreasing abundance) were as follows: infusorians, nauplii, copepodids, radiolarians, appendicularians, and some others (rotifers, worm and mollusk larvae). Concentration of infusorians rarely exceeded 100 #/l, possibly an underestimate. Nauplii often numbered 20 to 30 #/l. Study of vertical distribution of microzooplankton showed that peak concentrations in the Mediterranean Sea were at depth of 20-30 m regardless of day time. There were 2 peaks in the Atlantic Ocean, one in the 10- to 20-m layer, the other in the 50- to 75-m layer.

Occurrence of interlayers in sediment cores collected in the East Indian Ocean

In the East Indian Ocean direct contribution of land volcanism to sedimentation appears as interlayers of tephra and tuffaceous sediments, pumice fragments, and dispersed volcanoclastic materials of silty grain size. Similarity of distribution of tephra, tuffaceous sediments, Ethmodiscus ooze, and turbidites in the Pleistocene section results from deposition of all these materials under controll of a single factor, namely synchronous redistribution owing to seismic activity on the ocean floor and on the Sunda Islands. Burial of layers of oxidized deposits and formation of iron-manganese nodules is at least partly related to global climate cooling and to circulation of ocean waters.

Geochemical and palynological measurements from the ODP Leg 189 at Site 1172 on the East Tasman Plateau

A brief (~150 kyr) period of widespread global average surface warming marks the transition between the Paleocene and Eocene epochs, ~56 million years ago. This so-called "Paleocene-Eocene thermal maximum" (PETM) is associated with the massive injection of 13C-depleted carbon, reflected in a negative carbon isotope excursion (CIE). Biotic responses include a global abundance peak (acme) of the subtropical dinoflagellate Apectodinium. Here we identify the PETM in a marine sedimentary sequence deposited on the East Tasman Plateau at Ocean Drilling Program (ODP) Site 1172 and show, based on the organic paleothermometer TEX86, that southwest Pacific sea surface temperatures increased from ~26 °C to ~33°C during the PETM. Such temperatures before, during and after the PETM are >10 °C warmer than predicted by paleoclimate model simulations for this latitude. In part, this discrepancy may be explained by potential seasonal biases in the TEX86 proxy in polar oceans. Additionally, the data suggest that not only Arctic, but also Antarctic temperatures may be underestimated in simulations of ancient greenhouse climates by current generation fully coupled climate models. An early influx of abundant Apectodinium confirms that environmental change preceded the CIE on a global scale. Organic dinoflagellate cyst assemblages suggest a local decrease in the amount of river run off reaching the core site during the PETM, possibly in concert with eustatic rise. Moreover, the assemblages suggest changes in seasonality of the regional hydrological system and storm activity. Finally, significant variation in dinoflagellate cyst assemblages during the PETM indicates that southwest Pacific climates varied significantly over time scales of 103 - 104 years during this event, a finding comparable to similar studies of PETM successions from the New Jersey Shelf.