Corg, CaCO3, bulk densities, accumulation rates and ages of ODP Leg 167 sites and three piston cores, California margin

Sediments from five Leg 167 drill sites and three piston cores were analyzed for Corg and CaCO3. Oxygen isotope stratigraphy on benthic foraminifers was used to assign age models to these sedimentary records. We find that the northern and central California margin is characterized by k.y.-scale events that can be found in both the CaCO3 and Corg time series. We show that the CaCO3 events are caused by changes in CaCO3 production by plankton, not by dissolution. We also show that these CaCO3 events occur in marine isotope Stages (MIS) 2, 3, and 4 during Dansgaard/Oeschger interstadials. They occur most strongly, however, on the MIS 5/4 glaciation and MIS 2/1 deglaciation. We believe that the link between the northeastern Pacific Ocean and North Atlantic is primarily transmitted by the atmosphere, not the ocean. Highest CaCO3 production and burial occurs when the surface ocean is somewhat cooler than the modern ocean, and the surface mixed layer is somewhat more stable.

XRF data, magnetic susceptibility, greyscale values and revised depths of sediments from ODP Leg 154 sites

The distinctly cyclic sediments recovered during ODP Leg 154 played an important role in constructing the astronomical time scale and associated astro(bio)chronology for the Miocene, and in deciphering ocean-climate history. The accuracy of the timescale critically depends on the reliability of the shipboard splice used for the tuning and on the tuning itself. New high-resolution colour- and magnetic susceptibility core scanning data supplemented with limited XRF-data allow improvement of the stratigraphy. The revised composite record results in an improved astronomical age model for ODP Site 926 between 5 and 14.4 Ma. The new age model is confirmed by results of complex amplitude demodulation of the precession and obliquity related cycle patterns. Different values for tidal dissipation are applied to improve the fit between the sedimentary cycle patterns and the astronomical solution. Due to the improved stratigraphy and tuning, supported by the results of amplitude demodulation, the revised time scale yields more reliable age estimates for planktic foraminiferal and calcareous nannofossil events. The results of this study highlight the importance of stratigraphy for timescale construction.

Pollen record and age determinations on four sites from Taymyr Peninsula, Russia

Pollen data from a Levinson-Lessing Lake sediment core (74°28'N, 98°38'E) and Cape Sabler, Taymyr Lake permafrost sequences (74°33'N, 100°32'E) reveal substantial environmental changes on the northern Taymyr Peninsula during the last c. 32 000 14C years. The continuous records confirm that a scarce steppe-like vegetation with Poaceae, Artemisia and Cyperaceae dominated c. 32 000-10 300 14C yr BP, while tundra-like vegetation with Oxyria, Ranunculaceae and Caryophyllaceae grew in wetter areas. The coldest interval occurred c. 18 000 yr BP. Lateglacial pollen data show several warming events followed by a climate deterioration c. 10 500 14C yr BP, which may correspond with the Younger Dryas. The Late Pleistocene/Holocene transition, c. 10 300-10 000 14C yr BP, is characterized by a change from the herb-dominated vegetation to shrubby tundra with Betula sect. Nanae and Salix. Alnus fruticosa arrived locally c. 9000-8500 14C yr BP and disappeared c. 4000-3500 14C yr BP. Communities of Betula sect. Nanae, broadly distributed at c. 10 000-3500 14C yr BP, almost disappeared when vegetation became similar to the modern herb tundra after 3500-3000 14C yr BP. Quantitative climate reconstructions show Last Glacial Maximum summer temperature about 4°C below the present and Preboreal (c. 10 000 14C yr BP) temperature 2-4°C above the present. Maximum summer temperature occurred between 10 000 and 5500 14C yr BP; later summers were similar to present or slightly warmer.

Eocene-Oligocene calcareous nannofossil events of ODP Sites from the Southern Ocean

The evolution of the Southern Ocean climate during the late Eocene-late Oligocene interval is examined through highresolution, quantitative calcareous nannofossil analyses on samples from the Southern Ocean sections on Maud Rise and Kerguelen Plateau. We determined the abundance patterns of the counted species to clarify the biostratigraphy, which we correlated with high-resolution magnetostratigraphy [Roberts, A.P., Bicknell, S.J., Byatt, J., Bohaty, S.M., Florindo, F., Harwood, D.M., 2003a. Magnetostratigraphic calibration of Southern Ocean diatom datums from the Eocene-Oligocene of Kerguelen Plateau (Ocean Drilling Program Sites 744 and 748). In: Florindo, F., Cooper, A.K., O'Brien, P.A. (Eds.), Antarctic Cenozoic Palaeoenvironments: Geologic Record and Models. Palaeogeogr., Palaeoclimatol., Palaeoecol. 198 145-168; Florindo, F., Roberts, A.P., in press. Eocene-Oligocene magnetobiochronology of ODP Sites 689 and 690, Maud Rise, Weddell Sea, Antarctica. Geol. Soc. Am. Bull.], and used this data to interpret paleoceanographic changes through the late Eocene to late Oligocene. Percentage plots of the individual species, compared with R-mode principal component and cluster analysis results, allowed us to divide the assemblages into three groups: temperate-water taxa, cool-water taxa, and no temperature-affinity taxa. We attempt correlations between these paleoecological groups and the major sea-surface temperature (SST) variations with tectonic and paleoceanographic changes in the Southern Ocean. During the late Eocene, the nannofossil assemblage data reveal that there were several minor SST decreases (coolings) from 36 to 34 Ma, before the Eocene/Oligocene (E/O) boundary. A sharp cooling event, dated at 33.54 Ma (earliest Oligocene), occurred about 160 kyr after the E/O boundary, which is dated at 33.7 Ma. Relatively stable, cool conditions are interpreted to persist until the latest Oligocene, when an increase in abundance of temperate-water taxa, which corresponds to an antithetical decrease in abundance of cool-water indicators, is recorded. On the basis of our dating, the opening of the Drake Passage, allowing shallow-water circulation, began by 33.54 Ma at the latest, while the establishment of deep-water connections through the Tasmanian Gateway occurred at 33 Ma, as suggested by Exon et al. [Proc. ODP, Init. Rep. 189 (2001) 1].

B, d11B, K and d18O data for altered oceanic crust at DSDP Sites 417/418

Samples of drilled oceanic crust, from DSDP Holes 417A, 417D and 418A and ODP Hole 735B, and oceanic crust from the Oman and Cyprus ophiolites, were analyzed for B contents and d11B. Composite samples from DSDP Holes 417A, 417D and 418A were used to represent the upper 550 m of altered oceanic crustal Layer 2A. Whole-rock samples from the Troodos ophiolite, Cyprus, and the Oman ophiolite were selected to represent crustal Layer 2B dikes. Composite samples from ODP Hole 735B were used to represent crustal Layer 3. The B content of the DSDP composites ranges from 7.2 ppm to 104 ppm and correlates with both d1818O and K, showing that it is a good indicator of the extent of low temperature alteration. The d11B of the DSDP composites varies between -2.5? and 5.4?. The B content of the samples from the Troodos ophiolite ranges from 2.4 ppm to 8.1 ppm; d11B varies from -0.9? to 7.8?. The B content of the Oman ophiolite samples ranges from 5.0 ppm to 11.1 ppm; d11B varies from -1.6? to 16.9?. The B content of the samples from ODP Hole 735B ranges from 1.1 ppm to 7.1 ppm; d11B varies from -4.3? to 24.9?. The general pattern displayed by these samples is one of greatest (and most variable) B enrichment at the top of the crust and least enrichment at the bottom of the section. All of these samples are enriched compared to unaltered MORB, which is believed to have a B content of approximately 0.5 ppm. The d11B values of deeper samples, from Layers 2B and 3, are more variable and generally higher than those from Layer 2A. Boron contents and d11B are not correlated. The data from the DSDP Site 417/418 composites indicate that the d11B of fluid circulating in the upper crust changes only slightly during alteration, increasing by an average of 5.1? with an accompanying decrease in B concentration of 7%. Low temperature alteration appears to be a water-dominated process resulting in minor modification of circulating seawater. A minimum water-rock ratio of 400 is calculated for these samples, implying a minimum low-temperature seawater flux through the upper oceanic crust of 3.4?10**14 l/y. The average B content of altered oceanic crust, as represented by these samples, is 5.2+/-1.7 ppm and the average d11B is 3.4+/-1.1?. This average isotopic composition is measurably different from the apparent average of oceanic sediments, supporting the idea that d11B could be useful for identifying the source(s) of B in island arcs.

Pliocene and Pleistocene abundance of siliceous microfossil assemblages in ODP Leg 127 sites

A close examination of the siliceous microfossil assemblages from the sediments of ODP Leg 127, Japan Sea Sites 794, 795, and 797, reveals that upper Pliocene and Pleistocene assemblages have been subjected to more dissolution than have lower Pliocene assemblages. This conclusion is based on semiquantitative observations of samples processed for diatoms and radiolarians. Although preservation of opaline microfossils in some upper Pliocene and Pleistocene samples is better than others, in general, the poorly preserved state of these assemblages supports the notion that opal dissolution, in response to lowered productivity, is responsible for the paucity of siliceous microfossils in upper Pliocene and Pleistocene sediments. The lithological transition from diatomaceous oozes to silts and clays corresponds to a change between dominantly well preserved to more poorly preserved siliceous assemblages, and is termed the late Pliocene Japan Sea opal dissolution transition zone (ODTZ). The base of the ODTZ is defined as the uppermost occurrence of high abundances of moderately to well preserved valves of the diatom Coscinodiscus marginatus. The dissolution transition zone is characterized by partially dissolved refractory assemblages of radiolarians, the presence of C. marginatus girdles, C. marginatus fragments, siliceous sponge spicules, and a general decrease in weakly silicified, less solution resistant diatoms upward in the section. The top of the dissolution transition zone marks the level where whole C. marginatus valves and C. marginatus fragments are no longer present in significant numbers. Dissolution of the late Pliocene and Pleistocene opaline assemblages is attributed mainly to changes in paleoceanographic circulation patterns and decreased nutrient (dissolved silicon) contents of the water column, and possibly dissolution at the sediment/water interface, rather than to post-depositional dissolution or diagenesis. We suggest that the transition from silica-rich to silica-poor conditions in the Japan Sea was due to fluctuations of deep-water exchange with the Pacific through the Tsugaru Strait between 2.9 and 2.3 Ma.

Biogenic opal content in bulk sediments of ODP Leg 181 sites, southwest Pacific

Biogenic opal concentrations were measured on bulk sediments recovered at Ocean Drilling Program Sites 1123, 1124, and 1125 off North Island of New Zealand in the southwest Pacific. Site 1124 showed opal contents ranging from approximately 2 to 8 wt%, which is relatively high compared to other sites. The subbottom maximum in biogenic opal content located between 1.0 and 1.5 m composite depth can be recognized at each site. Patterns of biogenic opal content in the uppermost parts of the cores appear to reflect the surface ocean settings relating to the migration of the Subtropical Convergence Zone.

Age models of ODP sites from the Barents Sea-Svalbard region

Based on a revised chronostratigraphy, and compilation of borehole data from the Barents Sea continental margin, a coherent glaciation model is proposed for the Barents Sea ice sheet over the past 3.5 million years (Ma). Three phases of ice growth are suggested: (1) The initial build-up phase, covering mountainous regions and reaching the coastline/shelf edge in the northern Barents Sea during short-term glacial intensification, is concomitant with the onset of the Northern Hemisphere Glaciation (3.6-2.4 Ma). (2) A transitional growth phase (2.4-1.0 Ma), during which the ice sheet expanded towards the southern Barents Sea and reached the northwestern Kara Sea. This is inferred from step-wise decrease of Siberian river-supplied smectite-rich sediments, likely caused by ice sheet blockade and possibly reduced sea ice formation in the Kara Sea as well as glacigenic wedge growth along the northwestern Barents Sea margin hampering entrainment and transport of sea ice sediments to the Arctic-Atlantic gateway. (3) Finally, large-scale glaciation in the Barents Sea occurred after 1 Ma with repeated advances to the shelf edge. The timing is inferred from ice grounding on the Yermak Plateau at about 0.95 Ma, and higher frequencies of gravity-driven mass movements along the western Barents Sea margin associated with expansive glacial growth.

Magnetostratigraphic age-depth tie points of ODP Leg 208 sites

We report the paleomagnetic and rock magnetic results from discrete sample analysis of sediments from Walvis Ridge, Leg 208 of the Ocean Drilling Program. In an effort to refine the shipboard magnetostratigraphy, alternating field and thermal demagnetization of discrete samples were carried out, predominantly on samples from Sites 1262 and 1267. Results are generally consistent with the shipboard pass-through cryomagnetometer data, though in some cases the discrete samples resolved ambiguities in the reversal record. Significantly, the C24r/C24n reversal boundary was identified at Sites 1262 and 1267, and most boundaries in the Paleocene and Upper Cretaceous sections are now identified to within 10-30 cm. Magnetic mineralogy results show that prior to the late Miocene, the predominant detrital magnetic component was coarse-grained magnetite and that after the late Miocene, titanomagnetite has also been present. This suggests a possible change in detrital source at that time.

Petrographic description and geochemistry of basalts and altered volcanic rocks from ODP Leg 183 sites

The basalts recovered during Legs 183 and 120 from the southern, central, and northernmost parts of the Kerguelen Plateau (Holes 1136A, 1138A, 1140A, and 747C, respectively), as well as those recovered from the eastern part of the crest of Elan Bank (Hole 1137A), represent derivates from tholeiitic melts. In the northern part of the Kerguelen Plateau (Hole 1140A), basalts may have formed from two sources located at different depths. This is reflected in the presence of both low- and high-titanium basalts. The basalts are variably altered by low-temperature hydrothermal processes (at temperatures up to 120°C), and some are affected by subaerial weathering. The hydrothermal alteration led mainly to the formation of smectites, chlorite minerals, mixed-layer hydromica-smectite and smectite-chlorite minerals, hydromica, serpentine(?), clinoptilolite, heulandite, stilbite, analcime, mordenite, thomsonite, natrolite(?), calcite, quartz, and dickite(?). Alteration of extrusive basalts is mainly related to horizontal fluid flow within permeable contact zones between lava flows. Under a nonoxidizing environment of alteration, the tendency to lose most of elements, including rare earth elements, from basalts dominates. Under on oxidizing environment, basalts accumulate many elements.

(Table T2) Sulfur isotopes of pore water from ODP Leg 201 sites

Fifty-seven interstitial water samples from six sites (Ocean Drilling Program Sites 1225-1229 and 1231) in the eastern equatorial Pacific Ocean and the Peru margin were analyzed for the stable sulfur isotopic composition (34S/32S) of dissolved sulfate along with major and minor ions. With the exception of Site 1231, sulfate from the interstitial fluids (d34S values as much as 89 per mil vs. the SF6-based Vienna-Canyon Diablo troilite standard) is found at depth to be enriched in 34S with respect to modern seawater sulfate (d34S = ~21 per mil), indicating that microbial sulfate reduction (MSR) took place to different extents at all investigated sites. Deeper sediments at Sites 1228 and 1229 are additionally influenced by diffusion of a sulfate-rich brine that has already undergone sulfate reduction. The intensity of MSR depends on the availability of substrate (organic matter), sedimentation conditions, and the active bacterial community structure. Formation of isotopically heavy diagenetic barite at the sulfate-methane transition zone is expected at Sites 1227 (one front), 1229 (two fronts), and probably Site 1228. At Site 1231, the constant sulfur isotopic composition of sulfate and concentrations of minor pore water ions indicate that suboxic (essentially iron and manganese oxide based) diagenesis dominates and no net MSR occurs.

(Supplement T1) Clay mineral compositions at the Aleutian Basin of the Bering Sea from IODP sites 323-U1343

The clay mineral composition at IODP Exp. 323 Site U1343 in the Bering Sea was analyzed so as to unravel their provenance over glacial-interglacial cycles for the last 2.4 Ma. Smectite was negatively correlated with the sum of illite and chlorite; therefore, their ratio [S/(I + C)] was used as an indicator of clay mineral composition changes. In general, the S/(I + C) ratio was rather similar for glacial and interglacial periods during most of the last 2.4 Ma. In addition, these results overlap with those of surface sediments in the modern East Aleutian Basin, which suggests that smectite-rich clay particles are delivered from the Aleutians by the northward Bering Slope Current (BSC) rather than from rivers in western Alaska. However, some clay mineral compositions of the glacial periods after the Mid-Pleistocene Transition (MPT: 1.25-0.7 Ma) were characterized by low illite and relatively high smectite. During this period, extensive ice-rafting might have transported the smectite-rich clay particles to Site U1343 from the glacial shelf off Alaska and/or from glacial rivers from that area.