(Table 1) Sr isotopes and chemical composition of DSDP Hole 61-462A basalts

Sixteen elemental abundances and 87Sr/86Sr ratio of the Nauru Basin basalt (Cores 75 to 90: sub-bottom depths 950 m to 1050 m) from Hole 462A have been determined by inductively coupled plasma-optical emission spectroscopy and mass spectrometry. The result indicates that the basalt is a new type of oceanic tholeiite, elementally similar to normal mid-oceanic ridge basalts and isotopically similar to oceanic island-type basalts.

(Table 1) Concentrations and isotopic ratio of Argon in Cretaceous deep-sea basaltic glass of DSDP Hole 51-417D

The abundance and isotopic composition of rare gas in the mantle provides an important constraint on the origin and evolution of the Earth's atmosphere. One of sources of such information is basalts which erupted from ocean ridges. Ozima (1975, doi:10.1016/0016-7037(75)90054-X) stated that a high 40Ar/36Ar ratio in the mantle suggests sudden degassing at an early stage of the Earth's evolution. Several authors (Funkhouser et al., 1968, doi:10.1016/S0012-821X(68)80021-4; Darlymple and Moor, 1968, doi:10.1126/science.161.3846.1132) have reported excess 40Ar and high 40Ar/36Ar ratios in rapidly quenched rims of young deep-sea basalts. However, the Ar composition in old ridge basalts was not known. We report here a measurement of the isotopic composition of Ar in old deep-sea basalts. The Glomar Challenger drilled a Cretaceous ocean floor near the southern end of the Bermuda Rise in Deep Sea Drilling Project. The drilled site (Site 417) is on the magnetic anomaly MO which has been estimated to be 108 Myr old.

(Table 1) Characteristics of silicified sediments at DSDP Site 61-462 according to host-rock lithology, opal-CT-to-quartz ratio, and the origin of the quartz phase

This study deals with the mineralogical variability of siliceous and zeolitic sediments, porcellanites, and cherts at small intervals in the continuously cored sequence of Deep Sea Drilling Project Site 462. Skeletal opal is preserved down to a maximum burial depth of 390 meters (middle Eocene). Below this level, the tests are totally dissolved or replaced and filled by opal-CT, quartz, clinoptilolite, and calcite. Etching of opaline tests does not increase continously with deeper burial. Opal solution accompanied by a conspicuous formation of authigenic clinoptilolite has a local maximum in Core 16 (150 m). A causal relationship with the lower Miocene hiatus at this level is highly probable. Oligocene to Cenomanian sediments represent an intermediate stage of silica diagenesis: the opal-CT/quartz ratios of the silicified rocks are frequently greater than 1, and quartz filling pores or replacing foraminifer tests is more widespread than quartz which converted from an opal-CT precursor. As at other sites, there is a marked discontinuity of the transitions from biogenic opal via opal-CT to quartz with increasing depth of burial. Layers with unaltered opal-A alternate with porcellanite beds; the intensity of the opal-CT-to-quartz transformation changes very rapidly from horizon to horizon and obviously is not correlated with lithologic parameters. The silica for authigenic clinoptilolite was derived from biogenic opal and decaying volcanic components.

Cadmium/Calcium and stable isotope ratios of benthic foraminifera from the northeast Atlantic Ocean

The delta13C and Cd measurements from benthic foraminifera from Biogeochemical Ocean Flux Study (BOFS) northeast Atlantic Ocean sediment cores are presented. The delta13C values in glacial foraminifera are consistent with those from elsewhere in the North Atlantic Ocean. For intermediate water (1000 - 2000 m water depth), delta13C values were higher at the last glacial maximum than in present North Atlantic Deep Water (NADW), whereas for deep water (>2000 m) they were lower during the glacial maximum. The Cd concentrations of glacial northeast Atlantic intermediate water were lower than those of present NADW. However, deepwater Cd concentrations increased to values between NADW and present Pacific Deep Water (PDW). The delta13C and Cd data are consistent and show that the northeast Atlantic Ocean was strongly stratified with 13C enriched, low Cd intermediate water overlying 13C depleted, high Cd deep water. The glacial water column comprised two different water masses: deep water, similar in character to present Antarctic Bottom Water (AABW), and intermediate water, different in character from both AABW and NADW, and any present intermediate-depth North Atlantic water. The characteristics of glacial intermediate water were, however, similar to present near-surface waters in the North Atlantic, which suggests rapid ventilation of the glacial ocean to depths of up to 2000 m by cold, nutrient-depleted young surface waters.

Geochemistry of Late Paleocene thermal maximum sediments

The late Paleocene thermal maximum (LPTM) was a dramatic, short-term global warming event that occurred ~55 Ma. Warming of high-latitude surface waters and global deep waters during the LPTM has been well documented; however, current data suggest that subtropical and tropical sea surface temperatures (SSTs) did not change during the event. Conventional paradigms of global climate change, such as CO2-induced greenhouse warming, predict greater warming in the high latitudes than in the tropics or subtropics but, nonetheless, cannot account for the stable tropical/subtropical SSTs. We measured the stable isotope values of well-preserved late Paleocene to early Eocene planktonic foraminifera from South Atlantic Deep Sea Drilling Project (DSDP) Site 527 to evaluate the subtropical response to the climatic and environmental changes of the LPTM. Planktonic foraminiferal d18O values at Site 527 decrease by ~0.94 per mil from pre-LPTM to excursion values, providing the first evidence for subtropical warming during the LPTM. We estimate that subtropical South Atlantic SSTs warmed by at least ~1°-4°C, on the basis of possible changes in evaporation and precipitation. The new evidence for subtropical SST warming supports a greenhouse mechanism for global warming involving elevated atmospheric CO2 levels.