Stable carbon isotope compositions and concentrations of biphytanes from IODP Hole 311-U1327C and 311-U1328B

We have investigated the distributions and carbon isotopic compositions of archaeal membrane lipids in gas-hydrate-bearing sediments collected from the northern Cascadia Margin offshore from Vancouver Island (Sites U1327 and U1328) by the R/V JOIDES Resolution during IODP Expedition 311. Archaeal lipid biomarkers, including glycerol dialkyl glycerol tetraethers (GDGTs), tend to become abundant below 100 mbsf (meters below sea floor). Tricyclic biphytane (BP[3]; which is a robust biomarker derived from GDGT), crenarchaeol, and other BPs exhibit d13C values of ca. -20 per mil, and become abundant between 130 and 230 mbsf at Site U1328. In this depth range, concentrations of ammonium and phosphate in interstitial waters also increase, suggesting that a larger population and higher activity of heterotrophic community consisting of crenarchaeota and other archaea decompose the sedimentary organic matter, thereby liberating ammonium and phosphate. Such crenarchaeotic activity can produce other metabolic products such as molecular hydrogen by fermentation of organic matter during diagenesis. Furthermore, near the organic matter decomposition zone (130 to 230 mbsf), a probable methanogen biomarker (13C-depleted BP[1] with d13C values as low as -48.8 per mil) becomes abundant, indicating that methanogens utilize these diagenetic products. The molecular and isotopic distributions of archaeal lipid biomarkers indicate that the archaeal community plays an important role in the biogeochemical cycles of deep-sea sediments, including both methanogenesis and nutrient recycling.

(Table 3) Stable isotope record of Cretaceous foraminifera from DSDP Hole 44-392A

Mid-Cretaceous (Barremian-Turonian) plankton preserved in deep-sea marl, organic-rich shale, and pelagic carbonate hold an important record of how the marine biosphere responded to short- and long-term changes in the ocean-climate system. Oceanic anoxic events (OAEs) were short-lived episodes of organic carbon burial that are distinguished by their widespread distribution as discrete beds of black shale and/or pronounced carbon isotopic excursions. OAE1a in the early Aptian (~120.5 Ma) and OAE2 at the Cenomanian/Turonian boundary (~93.5 Ma) were global in their distribution and associated with heightened marine productivity. OAE1b spans the Aptian/Albian boundary (~113-109 Ma) and represents a protracted interval of dysoxia with multiple discrete black shales across parts of Tethys (including Mexico), while OAE1d developed across eastern and western Tethys and in other locales during the latest Albian (~99.5 Ma). Mineralized plankton experienced accelerated rates of speciation and extinction at or near the major Cretaceous OAEs, and strontium isotopic evidence suggests a possible link to times of rapid oceanic plateau formation and/or increased rates of ridge crest volcanism. Elevated levels of trace metals in OAE1a and OAE2 strata suggest that marine productivity may have been facilitated by increased availability of dissolved iron. The association of plankton turnover and carbon isotopic excursions with each of the major OAEs, despite the variable geographic distribution of black shale accumulation, points to widespread changes in the ocean-climate system. Ocean crust production and hydrothermal activity increased in the late Aptian. Faster spreading rates [and/or increased ridge length] drove a long-term (Albian-early Turonian) rise in sea level and CO2-induced global warming. Changes in ocean circulation, water column stratification, and nutrient partitioning lead to a reorganization of plankton community structure and widespread carbonate (chalk) deposition during the Late Cretaceous. We conclude that there were important linkages between submarine volcanism, plankton evolution, and the cycling of carbon through the marine biosphere.

Age models and stable isotope ratios of SO12 and SO35 sediment cores

Based on organic carbon accumulation rates, nine time slices of oceanic export paleoproductivity (Pnew) are presented which depict the variability of Pnew on a global scale through the last 30,000 years and document that the basic distribution patterns did not change through glacial and interglacial times. However, the glacial ocean shows an increased contrast of high- versus low-productivity zones. d13C values of near-surface-dwelling planktonic foraminifera Globigerinoides ruber suggest that the same contrast applies to the glacial nutrient inventories of the ambient surface waters, with a significant glacial transfer of PO4 from low- to high-productivity zones. In this way, glacial Pnew increased by a global average of about 2-4 Gt C/yr and led, via an enhanced CaCO3 dissolution and alkalinity in the deep ocean, to a significant extraction of CO2 from the surface water and the atrnosphere.

Sulphur isotope composition in the Gulf of California and the Eastern Pacific

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.

Distribution of foraminifera and other components in ODP Leg 188 sites

During Leg 188 of the Ocean Drilling Program (ODP), employing JOIDES Resolution, we drilled holes at three sites in the southern Indian Ocean in and near Prydz Bay, East Antarctica, between 28 January and 29 February 2000. The objectives of the voyage were to: - Core through sediments deposited when Antarctica underwent the transition from "greenhouse" to the modern "icehouse" state late in the Eocene or early in the Oligocene, at sites obtaining their sediment from the currently subglacial Gamburtsev Mountains that probably were the site of nucleation of the ice sheet (principally Site 1166); - Obtain a sediment record from times at which major changes in the ice sheet volume and characteristics took place as judged from oxygen isotope records, especially at ~23.7 Ma (Oligocene/Miocene boundary), 12-16 Ma (middle Miocene), and 2.7 Ma (late Pliocene) (mainly Site 1165); and - Sample through the upper Pliocene and Quaternary in an attempt to document fluctuations in the extent of the ice sheet over the continental shelf during the Quaternary (especially Site 1167). Paleogene foraminifer-bearing marine sections were not intersected, and thus discussion of marine sections is restricted to the Neogene. Foraminifers are not major contributors to Leg 188 chronostratigraphy but contribute to paleoenvironmental interpretation, to issues such as carbonate compensation depth (CCD) effects and source and history of sediment, and provide a basis for Sr and d18O studies. Chronostratigraphy for the various sections was compiled from diatoms, radiolarians, and paleomagnetism (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.188.101.2001). Foraminifers were sporadic rather than continuous except in short intervals; however, the Neogene foraminifers from the region are very poorly known and the new records proved to be of significant value in paleoenvironmental interpretation. Only at Site 1167 did drilling intersect a section that yielded foraminifers virtually throughout. Other than for the very young section at each site, there is virtually no continuity of assemblages between sites and thus each section is treated here as separate and unrelated.

Stable carbon and oxygen isotope record of planktonic foraminifera across the Paleocene-Eocene boundary

The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of 12C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic 'events' near the Paleocene-Eocene boundary provide strati-graphic information that can facilitate intersite correlations between marine and non-marine sequences. Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera bio-stratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean's carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO2. As a consequence of this exchange of 12C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.

Stable isotope record and sea surface reconstruction of sediment core MD88-770

Hydrographical changes of the southern Indian Ocean over the last 230 kyr, is reconstructed using a 17-m-long sediment core (MD 88 770; 46°01'S 96°28'E, 3290m). The oxygen and carbon isotopic composition of planktonic (N. pachyderma sinistra and G. bulloides) and benthic (Cibicidoides wuellerstorfi, Epistominella exigua, and Melonis barleeanum) foraminifera have been analysed. Changes in sea surface temperatures (SST) are calculated using diatom and foraminiferal transfer functions. A new core top calibration for the Southern Ocean allows an extension of the method developed in the North Atlantic to estimate paleosalinities (Duplessy et al., 1991). The age scale is built using accelerator mass spectrometry (AMS) 14C dating of N. pachyderma s. for the last 35 kyr, and an astronomical age scale beyond. Changes in surface temperature and salinity clearly lead (by 3 to 7 kyr) deep water variations. Thus changes in deep water circulation are not the cause of the early response of the surface Southern Ocean to climatic changes. We suggest that the early warming and cooling of the Southern Ocean result from at least two processes acting in different orbital bands and latitudes: (1) seasonality modulated by obliquity affects the high-latitude ocean surface albedo (sea ice coverage) and heat transfer to and from the atmosphere; (2) low-latitude insolation modulated by precession influences directly the atmosphere dynamic and related precipitation/ evaporation changes, which may significantly change heat transfer to the high southern latitudes, through their control on latitudinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation.

Diatom distribution in sediments of the Peruvian coastal upwelling

Two shelf and upper-slope sites (681 and 686) near present cores of active coastal upwelling on the Peruvian margin were sampled continuously at 7.5 cm intervals down to approximately 25 meters below the seafloor (mbsf). Sedimentary structures were subdivided into homogeneous/bioturbated, laminated, and laminated-varved intervals. Diatom analysis and statistical treatment of data revealed almost persistent upwelling over the last 400,000 yr, with slightly increased upwelling during oxygen-isotope Stages 3, 5, 7, and 8 that resulted in anoxic bottom-water conditions and deposition of laminated/undisturbed primary sedimentary structures.

Geochemistry and stable isotope record of carbonate oozes and chalks of ODP Hole 130-807B

Light greenish gray and pale purple color bands are common in the ooze and chalk of the Ontong Java Plateau. Analyses of Pleistocene and Pliocene ooze samples that contain abundant bands indicate that the purple bands are colored by finely disseminated iron sulfide, whereas the green bands are colored by finely disseminated Fe- and Al-bearing silicates (probably clays). No local contrasts in the total organic carbon contents, carbon and oxygen isotopic compositions, and grain sizes were found. Band abundances, counted from core photographs of all Leg 130 holes, can be correlated from hole to hole on the basis of age rather than depth. The temporal distribution of these color bands is also comparable with that of the green bands described from the Lord Howe Rise, which were previously interpreted as products of altered volcanic glass. This may indicate that the green and purple bands on the Ontong Java Plateau originate from the early alteration of volcanic ash. The crosscutting relationships between the green and purple bands and original structures in the host sediment indicate that the bands have been locally altered by redox conditions in the sediments after the bands were formed.

Chemical and isotope composition of poor fluid from gas-hydrate samples of ODP Site 146-892

Although the presence of extensive gas hydrate on the Cascadia margin, offshore from the western U.S. and Canada, has been inferred from marine seismic records and pore water chemistry, solid gas hydrate has only been found at one location. At Ocean Drilling Program (ODP) Site 892, offshore from central Oregon, gas hydrate was recovered close to the sediment-water interface at 2-19 m below the seafloor (mbsf) at 670 m water depth. The gas hydrate occurs as elongated platy crystals or crystal aggregates, mostly disseminated irregularly, with higher concentrations occurring in discrete zones, thin layers, and/or veinlets parallel or oblique to the bedding. A 2- to 3-cm thick massive gas hydrate layer, parallel to bedding, was recovered at ~17 mbsf. Gas from a sample of this layer was composed of both CH4 and H2S. This sample is the first mixed-gas hydrate of CH4-H2S documented in ODP; it also contains ethane and minor amounts of CO2. Measured temperatures of the recovered core ranged from 2 to -1.8°C and are 6 to 8 degrees lower than in-situ temperatures. These temperature anomalies were caused by the partial dissociation of the CH4-H2S hydrate during recovery without a pressure core sampler. During this dissociation, toxic levels of H2S (delta34S, +27.4?) were released. The delta13C values of the CH4 in the gas hydrate, -64.5 to -67.5? (PDB), together with deltaD values of -197 to -199? (SMOW) indicate a primarily microbial source for the CH4. The delta18O value of the hydrate H2O is +2.9? (SMOW), comparable with the experimental fractionation factor for sea-ice. The unusual composition (CH4-H2S) and depth distribution (2-19 mbsf) of this gas hydrate indicate mixing between a methane-rich fluid with a pore fluid enriched in sulfide; at this site the former is advecting along an inclined fault into the active sulfate reduction zone. The facts that the CH4-H2S hydrate is primarily confined to the present day active sulfate reduction zone (2-19 mbsf), and that from here down to the BSR depth (19-68 mbsf) the gas hydrate inferred to exist is a >=99% CH4 hydrate, suggest that the mixing of CH4 and H2S is a geologically young process. Because the existence of a mixed CH4-H2S hydrate is indicative of moderate to intense advection of a methane-rich fluid into a near surface active sulfate reduction zone, tectonically active (faulted) margins with organic-rich sediments and moderate to high sedimentation rates are the most likely regions of occurrence. The extension of such a mixed hydrate below the sulfate reduction zone should reflect the time-span of methane advection into the sulfate reduction zone.

Isotope ratios, IRD and planktonic foraminifera content during marine isotope stage 5 of sediment cores MD99-2303, MD99-2304 and MD95-2010

Variable climatic and oceanographic conditions characterized the last interglacial at high northern latitudes, probably related to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The magnitudes of these changes are comparable to the Holocene variability, and were thus significantly subdued compared to glacial climate changes. A thermal optimum occurred during the early part of the interglacial, followed by a period of reduced Atlantic inflow to the northernmost Nordic Seas. Subsequently, a new period with increased strength of the AMOC occurred. Significant amounts of Ice-Rafted Debris (IRD) were deposited in the northernmost Nordic Seas before any major change of the global ice volume. This implies an early onset of local ice sheet growth, probably the result of enhanced inflow of Atlantic water to the northernmost Nordic Seas contemporary with a Northern Hemisphere summer insolation minimum. Contrasting sea-land conditions provided large moisture fluxes towards land, giving rise to rapid, early glacial growth. Throughout the glacial part of Marine Isotope Stage (MIS) 5, millennial-scale cold events occurred along the axis of the warm water transport, from the subtropics all the way to the northernmost Nordic Seas. Correlation of IRD events from sites in the Fram Strait, on the Voring Plateau, and in the North Atlantic provides evidence that the major Northern Hemisphere ice sheets at times responded coherently to the same forcing. The widespread distribution of these events highlights the importance of the oceanic influence on the regional climate system.