Osmium isotope record of Late Pleistocene sediments

We report high temporal resolution osmium isotopes records of bulk sediment and sediment leachates from DSDP Site 480 (Gulf of California) over the last 30 ka; from ODP Site 849 (Eastern equatorial Pacific) from the last 200 ka and from ODP Site 1002C (Cariaco Basin) across the 9-17 ka time interval in order to critically evaluate claims of a global 10% shift in the 187Os/188Os of seawater from glacial to interglacial intervals. We use organic-rich continental margin sites and carbonate-rich pelagic sites to isolate the temporal variations of the osmium seawater isotopic composition. Our results reveal that variations in 187Os/188Os fail to correlate with global changes in temperature across glacials/interglacials cycles as previously claimed. Instead, these results indicate differences of a few percent in the measured 187Os/188Os between each oceanic basin. We argue that these differences strongly suggest that seawater is not well homogenized with respect to its Os isotope composition.

Mineralogic, elemental, and stable isotopic composition of bulk carbonate sediments from ODP Leg 166 sites

An intensive mineralogic and geochemical investigation was conducted on sediments recovered during Ocean Drilling Program Leg 166 from the western Great Bahama Bank at Sites 1006, 1008, and 1009. Pleistocene through middle Miocene sediments recovered from Site 1006, the distal location on the Leg 166 transect, are a mixture of bank-derived and pelagic carbonates with lesser and varying amounts of siliciclastic clays. A thick sequence of Pleistocene periplatform carbonates was recovered near the platform edge at Sites 1008 and 1009. Detailed bulk mineralogic, elemental (Ca, Mg, Sr, and Na), and stable isotopic (d18O and d13C) analyses of sediments are presented from a total of 317 samples from all three sites.

Evaluation of long chain 1,14-alkyl diols in marine sediments as indicators for upwelling and temperature

Long chain alkyl diols form a group of lipids occurring widely in marine environments. Recent studies have suggested several palaeoclimatological applications for proxies based on their distributions, but also revealed uncertainties about their applicability. Here we evaluate the use of long chain 1,14-alkyl diol indices for reconstruction of temperature and upwelling conditions by comparing index values, obtained from a comprehensive set of marine surface sediments, with environmental factors like sea surface temperature (SST), salinity and nutrient concentrations. Previous cultivation efforts indicated a strong effect of temperature on the degree of saturation and the chain length distribution of long chain 1,14-alkyl diols in Proboscia spp., quantified in the diol saturation index (DSI) and diol chain length index (DCI), respectively. However, values of these indices in surface sediments show no relationship with annual mean SST of the overlying water. It remains unknown what determines the DSI, although our data suggests that it may be affected by diagenesis, while the relationship between temperature and DCI may be different for different Proboscia species. In addition, contributions of algae other than Proboscia diatoms may affect both indices, although our data provide no direct evidence for additional long chain 1,14-alkyl diol sources. Two other indices using the abundance of 1,14-diols vs. 1,13-diols and C30 1,15-diols have previously been applied as indicators for upwelling intensity at different locations. The geographical distribution of their values supports the use of 1,14 diols vs. 1,13 diols [C28 + C30 1,14-diols]/[(C28 + C30 1,13-diols) + (C28 + C30 1,14-diols)] as a general indicator for high nutrient or upwelling conditions.

Stable isotope record and lithic fragments distribution in sediments of MIS9-14 of the North Atlantic

Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9-14 (300-540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north - south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.

Siliceous microfossils in middle Eocene sediments of ODP Holes 120-748B and 120-749B

The Middle Eocene Climatic Optimum (MECO) is a major transient warming event that occurred at ~ 40 Ma and reversed a long-term cooling trend through the early and middle Eocene. We report the results of a high-resolution, quantitative study of siliceous microfossils at Ocean Drilling Program Sites 748 and 749 (Southern Kerguelen Plateau, Southern Ocean, ~ 58°S) across a ~ 1.4 myr interval spanning the MECO event. At both sites, a significant increase in biosiliceous sedimentation is associated with the MECO event. Rich siliceous planktonic microfossil assemblages in this interval are unusual in that they are dominated by ebridians, with radiolarians as a secondary major component. Silicoflagellates and diatoms comprise only a minor fraction of the assemblage, in contrast to siliceous microfossil assemblages that characterize modern Southern Ocean sediments. Based on our new siliceous microfossil records, we interpret two ~ 300 kyr periods of elevated nutrient availability in Southern Ocean surface waters which span the peak warming interval of the MECO and the post-MECO cooling interval. A diverse assemblage of large silicoflagellates belonging to the Dictyocha grandis plexus is linked to the rapid rise in sea-surface temperatures immediately prior to peak warmth, and a pronounced turnover is observed in both ebridian and silicoflagellate assemblages at the onset of peak warming. The interval of peak warmth is also characterized by high abundance of cosmopolitan ebridians (e.g., Ammodochium spp.) and silicoflagellates (e.g., Naviculopsis spp.), and increased abundance of tropical and subtropical diatom genera (e.g., Asterolampra and Azpeitia). These observations confirm the relative pattern of temperature change interpreted from geochemical proxy data at multiple Southern Ocean sites. Furthermore, rapid assemblage changes in both autotrophic and heterotrophic siliceous microfossil groups indicate a reorganization of Southern Ocean plankton communities in response to greenhouse warming during the MECO event.

Chemical composition of ferromanganese micronodules and bulk sediments from ODP Hole 199-1216A

Distribution, size, mineral, and chemical compositions of ferromanganese micronodules (FMMNs) and chemical composition of host sediments were examined in a series of red clay samples with ages from Eocene to the present at Ocean Drilling Program Leg 199, Site 1216, south of the Molokai Fracture Zone in the Central Pacific Basin. The number of FMMNs changed drastically throughout the 40-m-long red clay intervals. FMMNs are abundant in the upper 9 m of core, decrease between 9 and 25 meters below seafloor (mbsf) with depth, and are very rare from 30 to 40 mbsf. Chemical composition of FMMNs showed high Mn/Fe ratios and Ni and Cu contents and a distinct positive Ce anomaly because of the existence of buserite. This suggests that FMMNs in the red clay from 25 mbsf to the top of the cored interval were deposited continuously in an oxic diagenetic bottom environment. The red clay below 30 mbsf with higher Mn contents contains few FMMNs but abundant tiny Mn particles within brown silicates coated by Fe (oxy-hydro)oxides. This indicates that the mode of manganese deposition changed between 25 and 30 mbsf.

Accumulation rates of bulk sediment and total organic carbon for Ontong Java Plateau sediments

Organic geochemical investigations were performed on sediments of Leg 130 to reconstruct the depositional environment of the Ontong Java Plateau. The Miocene to Quaternary sediments collected during the drilling campaign are characterized by extremely low organic carbon contents. As indicated by C/N ratios and Rock-Eval data, most of the organic matter is probably of marine origin. Based on mass-accumulation rates of organic carbon, the paleoproductivity for the Miocene-Pliocene and the late Pliocene-Pleistocene time intervals as well as the modern surface-water production were estimated. The productivity values of the surface sediments (25-59 gC/m2/yr) reflect the various influences of the equatorial upwelling cell on the different sites. The accumulation rates of organic carbon are generally low; however, they show a distinct increase at 8 Ma and a decrease at 2 Ma.

Manganese concentrations and flux data of sediments from Broken and Ninetyeast Ridge

Decomposition of organic matter combined with density stratification generate a pronounced intermediate water oxygen minimum zone (OMZ) in the northwest Indian Ocean. This zone currently lies between water depths of 200 and 2000 m and extends approximately 5000 km southeast from the Arabian coast. Based upon benthic foraminiferal assemblage changes, it has been suggested that this OMZ was even more extensive during the late Miocene-early Pliocene (6.5-3.0 Ma), with a maximum volume and/or intensity at approximately 5.0 Ma. While this inference may contribute to an understanding of the history of northwest Indian Ocean upwelling, corroborating geochemical evidence for this interpretation has heretofore been lacking. Ocean Drilling Program (ODP) sites 752, 754, and 757 on Broken and Ninetyeast ridges are located within central Indian Ocean intermediate water depths (1086-1650 m) but outside the present lateral dimensions of the Indian Ocean OMZ. High-resolution chemical analyses of sediment from these sites indicate significant reductions in the flux of Mn and normalized Mn concentrations between 6.5 and 3.0 Ma that are most pronounced at approximately 5.0 Ma. Because late Miocene-Pliocene paleodepths for these sites were essentially the same as at present and because extremely low sedimentation rates (0.3-1.3 cm/ky) most likely precluded sedimentary metal oxide diagenesis, we suggest that the observed Mn depletions reflect diminished deposition of reducible Mn oxyhydroxide phases within O2 deficient intermediate waters and that this effect was most intense at approximately 5.0 Ma. This interpretation implies that waters with less than 2.0 mL/L O2 extended at least 1500 km beyond their present limits and is consistent with changes in benthic foraminifera assemblages. We further suggest this expanded Indian Ocean OMZ is related to regionally and/or globally increased biological productivity.

(Table 1) Elemental composition, pyrite-Fe and degree of pyritisation in Upper Pliensbachian and Lower Toarcian sediments from the costal section of Yorkshire

Profiles of Mo/total organic carbon (TOC) through the Lower Toarcian black shales of the Cleveland Basin, Yorkshire, United Kingdom, and the Posidonia shale of Germany and Switzerland reveal water mass restriction during the interval from late tenuicostatum Zone times to early bifrons Zone times, times which include that of the putative Early Toarcian oceanic anoxic event. The degree of restriction is revealed by crossplots of Mo and TOC concentrations for the Cleveland Basin, which define two linear arrays with regression slopes (ppm/%) of 0.5 and 17. The slope of 0.5 applies to sediment from the upper semicelatum and exaratum Subzones. This value, which is one tenth of that for modern sediments from the Black Sea (Mo/TOC regression slope 4.5), reveals that water mass restriction during this interval was around 10 times more severe than in the modern Black Sea; the renewal frequency of the water mass was between 4 and 40 ka. The Mo/TOC regression slope of 17 applies to the overlying falciferum and commune subzones: the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years. The more restricted of the two intervals has been termed the Early Toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to NW Europe. Crossplots of Re, Os, and Mo against TOC show similar trends of increasing element concentration with increase in TOC but with differing slopes. Together with modeling of 187Os/188Os and d98Mo, the element/TOC trends show that drawdown of Re, Os, and Mo was essentially complete during upper semicelatum and exaratum Subzone times (Mo/TOC regression slope of 0.5). Drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of Re, Os, and Mo, via a low-salinity surface layer, created isotopic excursions of up to 1.3 per mil in d98Mo and up to 0.6 per mil for 187Os/188Os. Restriction thereby compromises attempts to date Toarcian black shales, and possibly all black shales, using Re-Os chronology and introduces a confounding influence in the attempts to use d98Mo and initial 187Os/188Os for palaeo-oceanographic interpretation.

Index properties, shear strenghts and consolidation characteristics of ODP Hole 164-995A sediments

Geotechnical properties of sediment from Ocean Drilling Program Leg 164 are presented as: (1) normalized shipboard strength ratios from the Cape Fear Diapir, the Blake Ridge Diapir, and the Blake Ridge; and (2) Atterberg limit, vane shear strength, pocket-penetrometer strength, and constant-rate-of-strain consolidation results from Hole 995A, located on the Blake Ridge. This study was conducted to understand the stress history in a region characterized by high sedimentation rates and the presence of gas hydrates. Collectively, the results indicate that sediment from the Blake Ridge exhibits significant underconsolidated behavior, except near the seafloor. At least 10 m of additional overburden was removed by erosion or mass wasting at Hole 993A on the Cape Fear Diapir, compared to nearby sites.

Mineralogy of sediments from the Exmouth Plateau and Argo Basin

Correlation of mineral associations from sediment recovered on the northwestern Australian continental margin document the juvenile-to-mature evolution of a segment of the Indian Ocean. Lower Cretaceous sediments contain sandy-to-silty radiolarian claystone that consists of highly smectitic mixed-layered illite/smectite (I/S) in addition to minor amounts of diagenetic pyrite, barite, and rhodochrosite. These immature, poorly sorted sediments were derived from nearby continental margin sources. Discrete bentonite layers and abundant smectite are the alteration products of volcanic material deposited during early basin formation. Abundant quartz-replaced radiolarian tests suggest high surface-water productivity, and calcareous fossils indicate water depths were above the calcite compensation depth (CCD) in the juvenile Indian Ocean. The increase in pelagic carbonate from the mid- to Late Cretaceous signals the transition to mature, open-ocean conditions. Similar to other slowly deposited contemporaneous deep-sea sediments, mid- to Upper Cretaceous sediments of the northwestern margin of Australia contain palygorskite. This palygorskite is associated with calcareous sediment across the ooze-to-chalk transition, detrital mixed-layered I/S, and zeolite minerals in places. This palygorskite occurs above the transformation from opal-A to opal-CT. The underlying opal-CT sediment contains abundant smectite and zeolite minerals. Calcareous sediment dominates the Cenozoic, except at abyssal sites that were not inundated by calcareous turbidites. Paleocene and Eocene sediments contain abundant smectite and zeolite minerals derived from the alteration of volcanic material. Palygorskite was found to be associated with sepiolite and dolomite in Miocene sediments from Site 765 in the Argo Basin. Pliocene and Quaternary sediments contain detrital kaolinite and mixed-layered I/S, abundant opal-A radiolarian tests, and minor amounts of pyrite

Biology community and bottom sediments in the West Bay of the Furugelm Island, Sea of Japan

An experiment was carried out on the soft bottom in the sublitoral zone of the Furugelm Island (Peter the Great Bay, Sea of Japan) to study formation of benthic communities. Boxes with defauned sediments were placed on depths of 4, 6 and 13 m and exposed during 60 days in the summer period. Half of them were covered with a net with mesh size 2 cm to prevent effect of large predators. It was found that spatial pattern of invertebrates' sinking in the bay conforms to distribution of benthic communities. Larvae of benthic invertebrates sinks in general in places inhabited by their adult species. The main factors responsible for recolonzation are: sediment type and local hydrodynamic conditions. Heart-shaped sea urchin Echinocardium cordatum is numerically dominated in the bay on depth 3-4.5 m, but its larvae sinks in the deeper area. Community structure is supported by mature specimen migration to places inhabited by species. Predators affect largely on the species.

Major and minor elements in hydrothermal and pelagic sediments at DSDP Leg 70 Holes

Interaction between young basaltic crust and seawater near the oceanic speading centers is one of the important processes affecting the chemical composition of the oceanic layer. The formation of metalliferous hydrothermal sediments results from this interaction. The importance of the interaction between seawater and basalt in determining the chemical composition of pore waters from sediments is well known. The influence of mineral solutions derived from this interaction on ocean water composition and the significant flux of some elements (e.g., Mn) are reported by Lyle (1976), Bogdanov et al. (1979), and others. Metal-rich sediments found in active zones of the ocean basins illustrate the influence of seawater-basalt interaction and its effect on the sedimentary cover in such areas. The role of hydrothermal activity and seawater circulation in basalts with regard to global geochemistry cycles has recently been demonstrated by Edmond, Measures, McDuff, McDuff et al. (1979), and Edmond, Measures, Mangum (1979). In the area of the Galapagos Spreading Center the interaction of sediments and solutions derived from interaction of seawater and basalt has resulted in the formation of hydrothermal mounds. The mounds are composed of manganese crusts and green clay interbedded and mixed with pelagic nannofossil ooze. These mounds are observed only in areas characterized by high heat flow (Honnorez, et al., 1981) and high hydrothermal activity.