Age determination and stable isotope record of sediment cores at 9°S in the Indian Ocean

A continuous 10-m-long section consisting of roughly two thirds Ethmodiscus rex (a diatom) and one third mixed planktonic foraminifera was identified in a core from 3800 m depth at 9°S on the Indian Ocean's 90°E Ridge. Radiocarbon dates place the onset of deposition of this layer at >30,000 years B.P. and its termination at close to 11,000 years B.P. However, precise dating of the foraminifera from the Ethmodiscus layer itself proved to be impossible owing to the presence of secondary calcite presumably precipitated from the pore waters. During the Holocene, high calcium carbonate content ooze free of diatoms was deposited at this locale. As the site currently lies beneath the pathway taken by upper ocean waters entering the Indian Ocean from the Pacific (via the Indonesian Straits), it appears that during glacial time, thermocline waters moving along this same path provided the silica and other nutrients required by these diatoms.

Planktonic foraminifer assemblages and stable oxygen and carbon isotope record of sediment core MD07-3076Q

We report high-resolution planktonic foraminifer census counts and stable oxygen and carbon isotope measurements of the planktonic foraminifera G. bulloides and N. pachyderma s. from sediment core MD07-3076Q for the last deglaciation, the last glacial maximum and Marine Isotope Stage 3. These data provide insights into the marine cycling of carbon and frontal dynamics in the sub-Antarctic Atlantic during the last 68 ka.

Age model and stable isotope record of eastern equatorial Pacific sediment cores

Six deep sea cores from the eastern equatorial Pacific (EEP) were analyzed for planktonic foraminifera and stable isotopes in order to reconstruct sea surface temperatures (SST) for the last 40 ka. South of the Equatorial Front the abundance of Globorotalia inflata increased, and SST decreased by >5°C (core ODP846B), creating a stronger SST meridional gradient and advection of the Peru Current than present for the ~16-35 ka interval. A sharper SST meridional gradient forced stronger Choco jet events and a moisture increase in western Colombia, which supplied, through the San Juan River and the south-flowing equatorial and the Peru-Chile countercurrents, abundant hemipelagic quartz over the northern Peru basin (core TR163-31B). The Choco jet, and its associated mesoscale convective cells, provoked an increase in snow precipitation over the Central Cordillera of Colombia and the advance of the Murillo glacier. In synchrony with the intensified Choco jet events, the "dry island" effect over the Eastern Cordillera of Colombia intensified, and the level of Fuquene Lake dropped.

Stable carbon and oxygen isotope record of Cretaceous planktonic foraminifera from DSDP (Table 1)

The Cretaceous Heterohelix moremani (Cushman) was the only biserial planktonic foraminiferal species from its first appearance in the late Albian up to the Cenomanian/Turonian boundary. Within that time, it increased gradually in abundance relative to other planktonic foraminifera in five Circum-North Atlantic sections. It is generally rare in upper Albian sediments, common in most of the Cenomanian and very abundant in sediments representing the latest Cenomanian Oceanic Anoxic Event. Short-term variations on the overall abundance trend correlate with positive excursions in the bulk carbonate delta13C record. Maximum rain rates of H. moremani during OAE2 show that this species was an opportunist that did well in extreme conditions, but its overall distribution indicates that it is not necessarily a marker for very high palaeoproductivity environments. Stable oxygen and carbon isotope measurements on foraminiferal species indicate that H. moremani was a surface water dweller at least in part of its geographic range, but incorporated 13C out of equilibrium with ambient seawater. It is depleted in delta13C relative to other planktonic foraminifera, which is attributed to vital effects related to its opportunistic character.

Stable carbon and oxygen isotope ratios for different test sizes of live benthic foraminifera from the Arabian Sea

We determined the stable oxygen and carbon isotopic composition of live (Rose Bengal stained) tests belonging to different size classes of two benthic foraminiferal species from the Pakistan continental margin. Samples were taken at 2 sites, with water depth of about 135 and 275 m, corresponding to the upper boundary and upper part of the core region of the oxygen minimum zone (OMZ). For Uvigerina ex gr. U. semiornata and Bolivina aff. B. dilatata, delta13C and delta18O values increased significantly with increasing test size. In the case of U. ex gr. U. semiornata, delta13C increased linearly by about 0.105 per mil for each 100-µm increment in test size, whereas delta18O increased by 0.02 to 0.06 per mil per 100 µm increment. For B. aff. B. dilatata the relationship between test size and stable isotopic composition is better described by logarithmic equations. A strong positive linear correlation is observed between delta18O and delta13C values of both taxa, with a constant ratio of delta18O and delta13C values close to 2:1. This suggests that the strong ontogenetic effect is mainly caused by kinetic isotope fractionation during CO2 uptake. Our data underline the necessity to base longer delta18O and delta13C isotope records derived from benthic foraminifera on size windows of 100 µm or less. This is already common practice in down-core isotopic studies of planktonic foraminifera.

Stable carbon and oxygen isotope ratios of Planulina wuellerstorfi from sediments of the Sierra Leone Rise

Causes of change in deep water delta13C can be either global or local in extent. Global causes include (1) climatically-induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir (Shackleton, 1977), and (2) erosion and deposition of organic-rich, continental shelf sediments during sea level fluctuations which change the mean oceanic carbon: phosphorus ratio (Broecker, 1982 doi:10.1016/0079-6611(82)90007-6). Regional gradients of delta13C are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow. Changes in a single geological record of benthic foraminiferal delta13C can result from any combination of these global and abyssal circulation effects. By sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity. We can assume that each delta13C record was equally affected by global causes of delta13C variation. The differences seen between the delta13C records must, therefore, reflect changes in the distribution of delta13C in the deep ocean. We interpret these differences in distribution in terms of changes in the ocean's abyssal circulation. Benthic foraminiferal carbon isotopic evidence from a suite of Sierra Leone Rise cores indicates that the deeper parts of the eastern Atlantic basins underwent a reduction in [O2] during the maximum of the last glaciation. Reduced advection of O2-rich deep water through low-latitude fracture zones, associated with increased delivery of organic matter to the deep ocean, lowered the delta13C of deep water SumCO2 at all depths below the sill separating the eastern and western Atlantic basins (Metcalf et al., 1964 doi:10.1016/0011-7471(64)91078-2). This decreased advection into the eastern Atlantic Ocean coincides with the overall decrease in deep water production in the North Atlantic during the last glacial maximum (Curry and Lohmann, 1982 doi:10.1016/0033-5894(82)90071-0; Boyle and Keigwin, 1982 doi:10.1126/science.218.4574.784; Schnitker, 1979 doi:10.1016/0377-8398(79)90020-3; Streeter and Shackleton, 1979 doi:10.1126/science.203.4376.168).

Mineralogy, chemistry and stable isotope composition of hydrothermal altered sheeted dikes of ODP Hole 111-504B

During ODP Leg 111 Hole 504B was extended 212 m deeper into the sheeted dikes of oceanic Layer 2, for a total penetration of 1288 m within basement. Study of the mineralogy, chemistry, and stable isotopic compositions of the rocks recovered on Leg 111 has confirmed and extended the previous model for hydrothermal alteration at the site: axial greenschist hydrothermal metamorphism was followed by seawater recharge and subsequent off-axis alteration. The dikes are depleted in 18O (mean delta18O = +5.1 ? +/- 0.6 ?) relative to fresh mid-ocean ridge basalt. Oxygen isotopic data on whole rocks and isolated secondary minerals indicate temperatures during axial metamorphism of 250°-350°C and water/rock ratios about one. Increasing amounts of actinolite with depth in the dike section, however, suggest that temperatures increased downward in the dikes. Pyrite + pyrrhotite + chalcopyrite + magnetite was the stable sulfide + oxide mineral assemblage during axial alteration, but these minerals partly re-equilibrated later at temperatures less than 200°C. The dikes sampled on Leg 111 contain an average of 500 ppm sulfur, slightly lower than igneous values. The delta34S values of sulfide average 0?, which indicates the presence of basaltic sulfide and incorporation of little or no seawater-derived sulfide into the rocks. These data are consistent with models for the presence of rock-dominated sulfur in deep hydrothermal fluids. The presence of anhydrite at 1176 m within basement indicates that unaltered seawater can penetrate to significant depths in the crust during recharge.

(Table S3) Benthic foraminiferal Mg/Ca, Li/Ca and stable isotope ratios of ODP Site 122-761

The sensitivities of benthic foraminiferal Mg/Ca and Li/Ca to bottom water temperature and carbonate saturation state have recently been assessed. Here we present a new approach that uses paired Mg/Ca and Li/Ca records to calculate simultaneous changes in temperature and saturation state. Using previously published records, we first use this approach to document a cooling of deep ocean waters associated with the establishment of the Antarctic ice sheet at the Eocene-Oligocene climate transition. We then apply this approach to new records of the Middle Miocene Climate Transition from ODP Site 761 to estimate variations in bottom water temperature and the oxygen isotopic composition of seawater. We estimate that the oxygen isotopic composition of seawater varied by ~1 per mil between the deglacial extreme of the Miocene Climatic Optimum and the glacial maximum following the Middle Miocene Climate Transition, indicating large amplitude variations in ice volume. However, the longer-term change between 15.3 and 12.5 Ma is marked by a ~1°C cooling of deep waters, and an increase in the oxygen isotopic composition of seawater of ~0.6 per mil. We find that bottom water saturation state increased in the lead up to the Middle Miocene Climate Transition and decreased shortly after. This supports decreasing pCO2 as a driver for global cooling and ice sheet expansion, in agreement with existing boron isotope and leaf stomatal index CO2 records but in contrast to the published alkenone CO2 records.

Stable oxygen and carbon isotope record of foraminifera of ODP SIte 184-1146

Ocean Drilling Program Site 1146 was drilled within a small rift basin on the midcontinental slope of the northern South China Sea. It is located at 19°27.4'N, 116°16.37'E, in 2092 m water depth. This site was drilled to recover records of Asian monsoon variability into the middle Miocene with temporal resolution sufficient for orbital-scale analyses. Here we present oxygen and carbon isotopic measurements of planktonic foraminifers (Globigerinoides ruber) and benthic foraminifers (Uvigerina peregrina and Cibicides wuellerstorfi) as well as a preliminary age model for the top 185 meters composite depth (mcd).