(Table 1) n-alkane distribution, and stable carbon and deuterium isotope ratios of DSDP Hole 10-94

Hydrology, source region, and timing of precipitation are important controls on the climate of the Great Plains of North America and the composition of terrestrial ecosystems. Moisture delivered to the Great Plains varies seasonally and predominately derives from the Gulf of Mexico/Atlantic Ocean with minor contributions from the Pacific Ocean and Arctic region. For this work, we evaluate long-term relationships for the past ~ 35 million years between North American hydrology, climate, and floral change, using isotopic records and average carbon chain lengths of higher plant n-alkanes from Gulf of Mexico sediments (DSDP Site 94). We find that carbon isotope values (d13C) of n-alkanes, corrected for variations in the d13C value of atmospheric CO2, provide minor evidence for contributions of C4 plants prior to the Middle Miocene. A sharp spike in C4 input is identified during the Middle Miocene Climatic Optimum, and the influence of C4 plants steadily increased during the Late Miocene into the Pleistocene - consistent with other North American records. Chain-length distributions of n-alkanes, indicative of the composition of higher plant communities, remained remarkably constant from 33 to 4 Ma. However, a trend toward longer chain lengths occurred during the past 4 million years, concurrent with an increase in d13C values, indicating increased C4 plant influence and potentially aridity. The hydrogen isotope values (dD) of n-alkanes are relatively invariant between 33 and 9 Ma, and then become substantially more negative (75 per mil) from 9 to 2 Ma. Changes in the plant community and temperature of precipitation can solely account for the observed variations in dD from 33 to 5 Ma, but cannot account for Plio-Pleistocene dD variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery. We posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the Panamanian Seaway, amplification of North Atlantic Deep Water Production and an associated increase of meridional winds. The southerly movement of the Intertropical Convergence Zone near 4 Ma allowed for the development of a near-modern pressure/storm track system, driving increased aridity and changes in seasonality within the North American interior.

Stable carbon and oxygen isotope ratios of Paleogene planktonic foraminifera from the Maud Rise

The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic foraminifer species from Maud Rise, Weddell Sea (ODP Sites 689 and 690), the first such results from the Antarctic. The results provide information about large-scale changes in the evolution of temperatures, seasonally, and structure of the upper water column prior to the development of a significant Antarctic cryosphere. The early Paleocene was marked by cooler surface-water conditions compared to the Cretaceous and possibly a less well developed thermocline. The late Paleocene and early Eocene saw the expansion of the thermocline as Antarctic surface waters became warm-temperate to subtropical. The late Paleocene to early Eocene thermal maximum was punctuated by two brief excursions during which time the entire Antarctic water column warmed and the meridional temperature gradient was reduced. The first of these excursions occurred at the Paleocene/Eocene boundary, in association with a major extinction in deep sea benthic foraminifers. The second excursion occurred within the early Eocene at ~54.0 Ma. These excursions are of global importance and represent the warmest intervals of the entire Cenozoic. The excursions were associated with fundamental changes in deep-water circulation and global heat transport. The thermal maximum of the early Eocene ended with the initiation of a long-term cooling trend at 52.0 Ma. This cooling trend was associated with reduced seasonality, and diminished structure and/or duration of the seasonal thermocline. The cooling trend was punctuated by three major cooling steps at 43.0, 40.0, and -36.0 Ma.

Element concentrations, and Sr and Os isotope ratios of DSDP Leg 92 metalliferous carbonates

The Os concentration and isotopic composition of metalliferous carbonates deposited on the East Pacific Rise over the past 28 Ma are reported with complimentary Sr isotope data. Variations in the Os isotopic composition of these samples are interpreted as a record of past changes in the Os isotopic composition of seawater. These results are consistent with isotopic analyses of leachable Os in pelagic clays which have also been interpreted as a record of the 187Os/186Os ratio of seawater through time (Pegram et al., 1992, doi:10.1016/0012-821X(92)90132-F). The metalliferous carbonate record clearly shows that seawater Os and Sr isotope systems are partially decoupled from one another over the past 28 Ma. Accelerated weathering of ancient organic-rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the 187Os//186Os ratio of seawater over the past 15 Ma. This rapid increase suggests that the seawater Os record can potentially be used as a stratigraphic tool in some Neogene marine deposits.

Stable oxygen and carbon isotope ratios and paleotemperature reconstructions from Inoceramus in Cretaceous sediments of DSDP Sites

Inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths. A survey of all Cretaceous sediments from Deep Sea Drilling Project legs 1-69 and 75 revealed over 500 Inoceramus specimens at twenty sites. Of these, 47 well-preserved Late Cretaceous specimens from the South Atlantic, Pacific and Indian Oceans were analyzed for oxygen and carbon isotopes. The specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep-sea habitat. Paleotemperatures ranging from 5 to 16°C show that Late Cretaceous oceans were significantly warmer than the present oceans. The data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics.

Stable carbon and oxygen isotope ratios and age model of ODP Hole 182-1127B

The aim of this study was to evaluate the potential of constructing an oxygen and carbon isotope stratigraphy for the late Pleistocene succession from Hole 1127B drilled on the Great Australian Bight. Stable isotope analyses were performed on bulk- and fine-fraction (<38 µm) sediment samples. The oxygen isotope variations are generally smaller in magnitude than expected from global pelagic records. This is most likely due to the neriticly dominated sediment composition. Correlation of the oxygen isotope data with carbonate mineralogy and downhole logging data shows simultaneous variations and trends, which are particularly evident in the mid-Pleistocene sediments. Correlation of the oxygen isotope data with the classic SPECMAP curve is used to evaluate the stratigraphic potential of the Site 1127 sediments. This study indicates that an isotope stratigraphy based on planktonic and benthic foraminifers is needed to fully evaluate the response of cool-water carbonates deposited in a margin setting to global ice-volume fluctuations and, hence, the associated sea level variations.

Comparison of accumulation rates and stable isotope ratios

Since 1979/80, glaciological studies have been carried out at Ekströmisen, Antarctica, including accumulation-stake measurements, snow-pit and shallow-firn-core studies. Snowstratigraphy, chemical properties and stable-isotope ratios (d18O) were investigated. This study focuses on three cores taken between 1982 and 1998. The 1998 core was dated using dielectric profiling, d18O profiles and stake measurements. Accumulation rates showhigh interannual and spatial variability due to the extreme wind influence. No significant trend was found for the last 50 years; during the first half of the 20th century, accumulation decreased. The high spatial and interannual variability, however, means that trends must be interpreted with care. In spite of the highly irregular accumulation distribution, stable-isotope ratios show little spatial variability. The mean annual d18O values of cores B04 and FB0198 agree fairly well for the time period 1955-82 covered by both cores. d18O values have increased during most of the 20th century; since the late 1980s a decrease is observed. This change is not related to air temperature, since mean annual air temperatures at Neumayer show no significant trend over the last two decades.

Stable oxygen and carbon isotope ratios of foraminifera and test results after different sample cleaning procedures from ODP Leg 207 sediments

We report oxygen and carbon stable isotope analyses of foraminifers, primarily planktonic, sampled at low resolution in the Cretaceous and Paleogene sections from Sites 1257, 1258, and 1260. Data from two samples from Site 1259 are also reported. The very low resolution of the data only allows us to detect climate-driven isotopic events on the timescale of more than 500 k.y. A several million-year-long interval of overall increase in planktonic 18O is seen in the Cenomanian at Site 1260. Before and after this interval, foraminifers from Cenomanian and Turonian black shales have d18O values in the range -4.2 per mil to -5.0 per mil, suggestive of upper ocean temperatures higher than modern tropical values. The d18O values of upper ocean dwelling Paleogene planktonics exhibit a long-term increase from the early Eocene to the middle Eocene. During shipboard and postcruise processing, it proved difficult to extract well-preserved foraminifer tests from black shales by conventional techniques. Here, we report results of a test of procedures for cleaning foraminifers in Cretaceous organic-rich mudstone sediments using various combinations of soaking in bleach, Calgon/hydrogen peroxide, or Cascade, accompanied by drying, repeat soaking, or sonication. A procedure that used 100% bleach, no detergent, and no sonication yielded the largest number of clean, whole individual foraminifers with the shortest preparation time. We found no significant difference in d18O or d13C values among sets of multiple samples of the planktonic foraminifer Whiteinella baltica extracted following each cleaning procedure.

Element concentrations and Osmium, Platinum and Rhenium isotope ratios of ODP Site 153-920 abyssal peridotites

Abyssal peridotites are normally thought to be residues of melting of the mid-ocean ridge basalt (MORB) source and are presumably a record of processes affecting the upper mantle. Samples from a single section of abyssal peridotite from the Kane Transform area in the Atlantic Ocean were examined for 190Pt-186Os and 187Re-187Os systematics. They have uniform 186Os/188Os ratios with a mean of 0.1198353 +/- 7, identical to the mean of 0.1198340 +/-12 for Os-Ir alloys and chromitites believed to be representative of the upper mantle. While the Pt/Os ratios of the upper mantle may be affected locally by magmatic processes, these data show that the Pt/Os ratio for the bulk upper mantle has not deviated by more than about +/- 30% from a chondritic Pt/Os ratio over 4.5 billion years. These observations are consistent with the addition of a chondritic late veneer after core separation as the primary control on the highly siderophile element budget of the terrestrial upper mantle. The 187Os/188Os of the samples range from 0.12267 to 0.12760 and correlate well with Pt and Pt/Os, but not Re/Os. These relationships may be explained by variable amounts of partial melting with changing D(Re), reflecting in part garnet in the residue, with a model-dependent melting age between about 600 and 1700 Ma. A model where the correlation between Pt/Os and 187Os/188Os results from multiple ancient melting events, in mantle peridotites that were later juxtaposed by convection, is also consistent with these data. This melting event or events are evidently unrelated to recent melting under mid-ocean ridges, because recent melting would have disturbed the relationship between Pt/Os and 187Os/188Os. Instead, this section of abyssal peridotite may be a block of refractory mantle that remained isolated from the convecting portions of the upper mantle for 600 Ma to >1 Ga. Alternatively, Pt and Os may have been sequestered during more recent melting and possibly melt/rock reaction processes, thereby preserving an ancient melting history. If representative of other abyssal peridotites, then the rocks from this suite with subchondritic 187Os/188Os are not simple residues of recent MORB source melting at ridges, but instead have a more complex history. This suite of variably depleted samples projects to an undepleted present-day Pt/Os of about 2.2 and 187Os/188Os of about 0.128-0.129, consistent with estimates for the primitive upper mantle.

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).

Re-OS and Pb isotope ratios of sediments from Saanich Inlet, Western Canada

Re-Os and Pb-Pb isotopic analysis of reduced varved sediments cored in the deeper basin of Saanich Inlet (B.C.) are presented. From core top to 61 cm down-core, spanning approximately the last 100 yrs of sedimentation, 187Os/188Os ratio and Os concentration respectively increase from ~0.8 to ~0.9 and from 55 to 60 ppt, whereas Re concentration decreases from 3600 to 2600 ppt. Re correlates with Corg (R2=0.6) throughout the entire section, whereas Os follows Re and Corg trends deeper down-core, suggesting a decoupling of a Re- and Os-geochemistry during burial and/or very early diagenesis. No systematic compositional differences are observed between seasonal laminae. 204Pb-normalized lead isotope ratios increase from sediment surface down to 7 cm down-core, then decrease steadily to pre-industrial levels at ~50 cm down-core. This pattern illustrates the contamination from leaded gasoline until the recent past. The measured Pb isotopic ratios point primarily toward gasoline related atmospheric lead from the USA. The osmium isotopic values measured are significantly lower than those of modern seawater-Os. In comparison with other anoxic environments, the osmium content of Saanich Inlet sediments is low, and its Os isotopic composition suggests significant inputs from unradiogenic sources (detrital and/or dissolved). Ultramafic lithologies in the watershed of the Fraser River are suspected to contribute to sedimentary inputs as well as to the input of dissolved unradiogenic osmium in the water of Saanich Inlet. The presence of some unradiogenic Os from anthropogenic contamination cannot be discounted near the core top, but since deeper, pre-anthropogenic levels also yielded unradiogenic Os results, one is led to conclude that the overall low 187Os/188Os ratios result from natural geochemical processes. Thus, the bulk sediment of Saanich Inlet does not appear to record 187Os/188Os composition of the marine end-member of the only slightly below normal salinity, fjord water. The low seawater-derived Os content of the sediment, coupled with unradiogenic Os inputs from local sources, explains the overall low isotopic values observed. As a consequence, such near-shore anoxic sediments are unlikely to record changes in the past ocean Os isotopic composition.