(Table 2) Geochemistry of ore minerals and magnetization properties at the DSDP Leg 73 Holes

The samples investigated in this study come from DSDP Leg 73 Drill Holes 519A, 522B, and 524, all of which are in the South Atlantic. A general petrographic description of the basalts is given by Carman et al. (1984; doi:10.2973/dsdp.proc.73.120.1984).

Physical properties of 39 sediment cores from the Bengal Fan and northeast Indian Ocean

We obtained sediment physical properties and geochemical data from 47 piston and gravity cores located in the Bay of Bengal, to study the complex history of the Late Pleistocene run-off from the Ganges and Brahmaputra rivers and its imprint on the Bengal Fan. Grain-size parameters were predicted from core logs of density and velocity to infer sediment transport energy and to distinguish different environments along the 3000-km-long transport path from the delta platform to the lower fan. On the shelf, 27 cores indicate rapidly prograding delta foresets today that contain primarily mud, whereas outer shelf sediment has 25% higher silt contents, indicative of stronger and more stable transport regime, which prevent deposition and expose a Late Pleistocene relic surface. Deposition is currently directed towards the shelf canyon 'Swatch of No Ground', where turbidites are released to the only channel-levee system that is active on the fan during the Holocene. Active growth of the channel-levee system occurred throughout sea-level rise and highstand with a distinct growth phase at the end of the Younger Dryas. Coarse-grained material bypasses the upper fan and upper parts of the middle fan, where particle flow is enhanced as a result of flow-restriction in well-defined channels. Sandier material is deposited mainly as sheet-flow deposits on turbidite-dominated plains at the lower fan. The currently most active part of the fan with 10-40 cm thick turbidites is documented for the central channel including inner levees (e.g., site 40). Site 47 from the lower fan far to the east of the active channel-levee system indicates the end of turbidite sedimentation at 300 ka for that location. That time corresponds to the sea-level lowering during late isotopic stage 9 when sediment supply to the fan increased and led to channel avulsion farther upstream, probably indicating a close relation of climate variability and fan activity. Pelagic deep-sea sites 22 and 28 contain a 630-kyear record of climate response to orbital forcing with dominant 21- and 41-kyear cycles for carbonate and magnetic susceptibility, respectively, pointing to teleconnections of low-latitude monsoonal forcing on the precession band to high-latitude obliquity forcing. Upper slope sites 115, 124, and 126 contain a record of the response to high-frequency climate change in the Dansgaard-Oeschger bands during the last glacial cycle with shared frequencies between 0.75 and 2.5 kyear. Correlation of highs in Bengal Fan physical properties to lows in the d18O record of the GISP2 ice-core suggests that times of greater sediment transport energy in the Bay of Bengal are associated with cooler air temperatures over Greenland. Teleconnections were probably established through moisture and other greenhouse-gas forcing that could have been initiated by instabilities in the methane hydrate reservoir in the oceans.

Magnesium/Calcium ratios and sea surface temperature estimation for sediments of the Timor Sea

We use a multiproxy approach to monitor changes in the vertical profile of the Indonesian Throughflow as well as monsoonal wind and precipitation patterns in the Timor Sea on glacial-interglacial, precessional, and suborbital timescales. We focus on an interval of extreme climate change and sea level variation: marine isotope (MIS) 6 to MIS 5e. Paleoproductivity fluctuations in the Timor Sea follow a precessional beat related to the intensity of the Australian (NW) monsoon. Paired Mg/Ca and d18O measurements of surface- and thermocline-dwelling planktonic foraminifers (G. ruber and P. obliquiloculata) indicate an increase of >4°C in both surface and thermocline water temperatures during Termination II. Tropical sea surface temperature changed synchronously with ice volume (benthic d18O) during deglaciation, implying a direct coupling of high- and low-latitude climate via atmospheric and/or upper ocean circulation. Substantial cooling and freshening of thermocline waters occurred toward the end of Termination II and during MIS 5e, indicating a change in the vertical profile of the Indonesian Throughflow from surface- to thermocline-dominated flow.

Upper Triassic nannofossils from Wombat Plateau, Northwest Australia

A taxonomic and biostratigraphic investigation has been carried out on Upper Triassic (Carnian-Rhaetian) nannofossils from Sites 759, 760, 761 and 764 drilled on the Wombat Plateau during ODP Leg 122. The recovery of continuous sequences containing well preserved nannofossils has enabled us to refine the previous taxonomy and biostratigraphy of this interval. Fossil assemblages are of two major types: (1) previously described calcareous taxa were recovered at Sites 761 and 764; and (2) sideritic forms, which may represent diagenetic replacement of calcareous nannofossils, were observed in material from Sites 759 and 760. The sideritic forms proved difficult to study taxonomically due to inadequate optical properties. Calcareous nannofossil assemblages in the Upper Triassic are dominated by Prinsiosphaera triassica. We show that the multitude of identities of this species in the light microscope are the result of selective etching on a layered structure. We propose an evolutionary lineage for the earliest known coccoliths, with Crucirhabdus primulus as the ancestor. This species gave rise to C. minutus and Archaeozygodiscus koessenensis. The Upper Triassic can be subdivided based on the sequential first occurrences of C. primulus and Eoconusphaera zlambachensis in the upper Norian. The late Norian and Rhaetian were times of slow evolution of calcareous nannofossils. However, we noted three morphometric changes in this time-interval which possess biostratigraphic utility: (1) P. triassica increases in diameter from an average of 6 µm to over 9 µm; (2) E. zlambachensis evolves from a stubby to an elongated shape; and (3) C. primulus increases in size. Upper Triassic assemblages from the Wombat Plateau are similar in composition and diversity to those which have been described in detail from the Alps. In both areas, nannofossiliferous sediments interfinger with massive limestones deposited in reef and peri-platform environments. Stable isotopic analyses of Wombat Plateau nannofossil assemblages indicate that they thrived in open ocean conditions. Biostratigraphy allows sequence chronostratigraphic interpretation of ODP Site 761 and supports the chronostratigraphic cycle charts of Haq et al. (1987).

Pigment data set from the SeaWiFS Bio-optical Archive and Storage System (1961-1996)

The oceans play a critical role in the Earth's climate, but unfortunately, the extent of this role is only partially understood. One major obstacle is the difficulty associated with making high-quality, globally distributed observations, a feat that is nearly impossible using only ships and other ocean-based platforms. The data collected by satellite-borne ocean color instruments, however, provide environmental scientists a synoptic look at the productivity and variability of the Earth's oceans and atmosphere, respectively, on high-resolution temporal and spatial scales. Three such instruments, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard ORBIMAGE's OrbView-2 satellite, and two Moderate Resolution Imaging Spectroradiometers (MODIS) onboard the National Aeronautic and Space Administration's (NASA) Terra and Aqua satellites, have been in continuous operation since September 1997, February 2000, and June 2002, respectively. To facilitate the assembly of a suitably accurate data set for climate research, members of the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project and SeaWiFS Project Offices devote significant attention to the calibration and validation of these and other ocean color instruments. This article briefly presents results from the SIMBIOS and SeaWiFS Project Office's (SSPO) satellite ocean color validation activities and describes the SeaWiFS Bio-optical Archive and Storage System (SeaBASS), a state-of-the-art system for archiving, cataloging, and distributing the in situ data used in these activities.

Stable oxygen isotope record of epibenthic foraminifera and water samples of the Arctic Ocean

We determined d18OCib values of live (Rose Bengal stained) and dead epibenthic foraminifera Cibicidoides wuellerstorfi, Cibicides lobatulus, and Cibicides refulgens in surface sediment samples from the Arctic Ocean and the Greenland, Iceland, and Norwegian seas (Nordic Sea). This is the first time that a comprehensive d18OCib data set is generated and compiled from the Arctic Ocean. For comparison, we defined Atlantic Water (AW), upper Arctic Bottom Water (uABW), and Arctic Bottom Water (ABW) by their temperature/salinity characteristics and calculated mean equilibrium calcite d18Oequ from summer sea-water d18Ow and in situ temperatures. As a result, in the Arctic environment we compensate for Cibicidoides- and Cibicides-specific offsets from equilibrium calcite of -0.35 and -0.55 per mil, respectively. After this taxon-specific adjustment, mean d18OCib values plausibly reflect the density stratification of principle water masses in the Nordic Sea and Arctic Ocean. In addition, mean d18OCib from AW not only significantly differs from mean d18OCib from ABW, but also d18OCib from within AW differentiates in function of provenience and water mass age. Furthermore, in shallow waters brine-derived low d18Ow can significantly lower the d18OCib of Cibicides spp. and thus d18OCib may serve as a paleobrine indicator. There is no statistically significant difference, however, between deeper water masses mean d18OCib of the Nordic Sea, and of the Eurasian and Amerasian basins, and no influence of low-d18Ow brines is recorded in Recent uABW and ABW d18OCib of C. wuellerstorfi. This may be due to dilution of a low-d18Ow brine signal in the deep sea, and/or to preferential incorporation of relatively high-d18Ow brines from high-salinity shelves. Although our data encompass environments with seasonal sea-ice and brine formation supposed to ultimately ventilate the deep Arctic Ocean, d18OCib from uABW and ABW do not indicate negative excursions. This may challenge hypotheses that call for enhanced Arctic brine release to explain negative benthic d18O spikes in deep-sea sediments from the late Pleistocene North Atlantic Ocean.

Oxygen- and carbon-isotopes at DSDP Leg 73 Holes

We established a composite oxygen- and carbon-isotope stratigraphy for the Pliocene in the central South Atlantic. Monospecific samples of benthic and planktonic foraminifers from pelagic sediments from DSDP Sites 519, 521, 522, and 523 were analyzed isotopically. The resulting benthic oxygen-isotope stratigraphy allowed three paleoclimatic periods in the Pliocene to be distinguished. During the early Pliocene (5.2-3.3 Ma), low-amplitude climatic changes prevailed in a world that was less glaciated than during the Pleistocene. A net increase in global ice volume is documented in a 0.5 permil positive shift in the average 18O composition of the benthic foraminifers at 3.2 Ma. The middle Pliocene (3.3-2.5 Ma) is not only characterized by a more widespread glaciation of the Southern and Northern hemispheres but also by more drastic isotopic differences between glacial and interglacial times. A minor shift in the average 18O composition of the benthic foraminifers marks the beginning of the late Pliocene-early Pleistocene climatic period (2.5-1.1 Ma). Alternating cold and warm climate is documented in both the oxygen-isotope record and in the pelagic sediments. During cold periods, sediments with a lower CaCO3 content indicate more corrosive bottom-water conditions. More negative 13C signals in the benthic foraminifers from these sediments suggest that the Antarctic Bottom Water current was intensified in glacial times. The oxygen-isotope composition of the measured planktonic foraminifers suggests that the surface water in this part of the South Atlantic remained relatively warm during the growth of the Pliocene glaciers.

Nannofossil bioevents and biozones of ODP Holes 197-1203A and 197-1204A on Detroit Seamount

Calcareous nannofossils were studied in sedimentary successions recovered from two holes on the Detroit Seamount in the northwestern Pacific Ocean. Preservation of calcareous nannoflora assemblages varies from poor to good throughout the sediments recovered from both Holes 1203A and 1204A. Biostratigraphic investigation allowed the identification of 19 nannofossil zones in Hole 1203A and 7 in Hole 1204A. The sedimentary cover in Hole 1203A ranges from lower Eocene (Zone NP12) to upper Miocene (Zone NN9). The sedimentary interval investigated directly overlying the basalt recovered at Hole 1204A is late Campanian in age (Zones CC22-CC23), and the top of the section is middle Eocene (Zone NP15) in age. Major unconformities were observed in Hole 1204A between upper Campanian (Zones CC22-CC23) and lower Thanetian (Zone NP7) sediments and between upper Thanetian (Zone NP8) and upper Ypresian (Zone NP12) sediments.

Minerals and geochemistry at DSDP Hole 62-466

Alkali-basalt clasts in Upper Cretaceous sediments from Site 466 on southern Hess Rise suggest that parts of Hess Rise were constructed by off-ridge volcanic activity. Apparently, tectonic adjustments at Hess Rise occurred during the Late Cretaceous (Campanian-Maastrichtian), when parts of the original volcanic pedestal were uplifted and provided source rocks for the clasts. Synchronous volcanism may have occurred. Causes for the Late Cretaceous tectonic adjustments (and volcanism?) are not known, but they may be related to intraplate movement along the Mendocino Fracture Zone.

Mineralogy, geochemistry and selected chemical formulas of sediments from ODP Holes 161-986B and 161-977A

Upper Miocene to Pleistocene hemipelagites and resedimented facies recovered at Holes 976B and 977A (Leg 161) in the Alboran Basin consist mainly of biogenic and detrital components, with a minor contribution of neoformed mineral phases. Diagenetic processes have not obliterated the primary deposition signal, and therefore detrital components (quartz, feldspar, detrital dolomite, rock fragments, and clays) provide information about source rocks and provenances. No major bulk or clay mineralogy differences were recognized between resedimented and hemipelagic facies; in fact, similar mineral assemblages in both types of facies suggest common source rocks. However, mineral abundance fluctuations can be related to climate variations and tectonic factors, as the main controls of sediment fill of this basin. A marked increase in smectites in Messinian sediments suggests an extensive development of soils during that time, probably favored by the alternation of wet and dry climate episodes and the relative aridification of the Mediterranean borderlands. A notable increase in detrital components suggests a sea-level fall and/or tectonic uplift during the late Pliocene. The significant increase in detrital dolomite in the uppermost Pliocene deposits suggests the uplift of dolomite-rich rocks as source areas. Mineral components in Pleistocene sediments indicate increasing tectonic stability, and clay-mineral fluctuations during the Pleistocene can be related not only to tectonic events, but also to alternating cooling and warming periods.

Lead 210 and silicate profiles from sediments of the equatorial Pacific and South Atlantic

Particle mixing rates have been determined for 5 South Atlantic/Antarctic and 3 equatorial Pacific deep-sea cores using excess 210Pb and 32Si measurements. Radionuclide profiles from these siliceous, calcareous, and clay-rich sediments have been evaluated using a steady state vertical advection diffusion model. In Antarctic siliceous sediments210Pb mixing coefficients (0.04-0.16 cm**2/y) are in reasonable agreement with the 32Si mixing coefficient (0.2 or 0.4 cm**2/y, depending on 32Si half-life). In an equatorial Pacific sediment core, however, the 210Pb mixing coefficient (0.22 cm**2/y) is 3-7 times greater than the 32Si mixing coefficient (0.03 or 0.07 cm**2/y). The difference in 210Pb and 32Si mixing rates in the Pacific sediments results from: (1) non-steady state mixing and differences in characteristic time and depth scales of the two radionuclides, (2) preferential mixing of fine-grained clay particles containing most of the 210Pb activity relative to coarser particles (large radiolaria) containing the 32Si activity, or (3) the supply of 222Rn from the bottom of manganese nodules which increases the measured excess 210Pb activity (relative to 226Ra) at depth and artificially increases the 210Pb mixing coefficient. Based on 32Si data and pore water silica profiles, dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32Si profile in the mixed layer. Deep-sea particle mixing rates reported in this study and the literature do not correlate with sediment type, sediment accumulation rate, or surface productivity. Based on differences in mixing rate among three Antarctic cores collected within 50 km of each other, local variability in the intensity of deep-sea mixing appears to be as important as regional differences in sediment properties.

Primary composition, alteration, and origin of Cretaceous volcaniclastic rocks at DSDP Site 89-585

An upper Aptian to middle Albian series of volcaniclastic rocks more than 300 m thick was drilled at Site 585 in the East Mariana Basin. On the basis of textural and compositional (bulk-rock chemistry, primary and secondary mineral phases) evidence, the volcaniclastic unit is subdivided into a lower (below 830 m sub-bottom) and an upper (about 670-760 m) sequence; the boundary in the interval between is uncertain owing to lack of samples. The rocks are dominantly former vitric basaltic tuffs and minor lapillistones with lesser amounts of crystals and basaltic lithic clasts. They are mixed with shallow-water carbonate debris (ooids, skeletal debris), and were transported by mass flows to their site of deposition. The lower sequence is mostly plagioclase- and olivine-phyric with lesser amounts of Ti-poor clinopyroxene. Mineralogical and bulk-rock chemical data indicate a tholeiitic composition slightly more enriched than N-MORB (normal mid-ocean ridge basalt). Transport was by debris flows from shallow-water sites, as indicated by admixed ooids. Volcanogenic particles are chiefly moderately vesicular to nonvesicular blocky shards (former sideromelane) and less angular tachylite with quench plagioclase and pyroxene, indicating generation of volcanic clasts predominantly by spalling and breakage of submarine pillow and/or sheet-flow lavas. The upper sequence is mainly clinopyroxene- and olivine-phyric with minor plagioclase. The more Ti-rich clinopyroxene and the bulk-rock analyses show that the moderately alkali basaltic composition throughout is more mafic than the basal tholeiitic sequence. Transport was by turbidity currents. Rounded epiclasts of crystalline basalts are more common than in the lower sequence, and, together with the occurrence of oxidized olivine pseudomorphs and vesicular tachylite, are taken as evidence of derivation from eroded subaerially exposed volcanics. Former sideromelane shards are more vesicular than in the lower sequence; vesicularity exceeds 60 vol.% in some clasts. The dominant clastic process is interpreted to be by shallow-water explosive eruptions. All rocks have undergone low-temperature alteration; the dominant secondary phases are "palagonite," chlorite/smectite mixed minerals, analcite, and chabazite. Smectite, chlorite, and natrolite occur in minor amounts. Phillipsite is recognized as an early alteration product, now replaced by other zeolites. During alteration, the rocks have lost up to 50% of their Ca, compared with a fresh shard and fresh glass inclusions in primary minerals, but have gained much less K, Rb, and Ba than expected, indicating rapid deposition prior to significant seafloor weathering.

Foraminifer, coarse fraction and carbonate characteristics of sediments from ODP Leg 198 sites on Shatsky Rise

Holes 1209A and 1211A on Southern High, Shatsky Rise contain expanded, nearly continuous records of carbonate-rich sediment deposited in deep water of the equatorial Pacific Ocean during the Paleocene and Eocene. In this study, we document intervals of carbonate dissolution in these records by examining temporal changes in four parameters: carbonate content, coarse size fraction (>38 µm), benthic foraminiferal abundance, and planktonic foraminiferal fragmentation ratio. Carbonate content is not a sensitive indicator of carbonate dissolution in the studied sections, although rare intervals of low carbonate may reflect times of relatively high dissolution. The proportion of coarse size fraction does not accurately record carbonate dissolution either because the relative abundance of nannofossils largely determines the grain-size distribution. Benthic abundance and fragmentation covary (r**2 = 0.77) and are probably the best indicators for carbonate dissolution. For both holes, records of these parameters indicate two episodes of prominent dissolution. The first of these occurs in the upper Paleocene (~59-58 Ma) and the second in the middle to upper Eocene (~45-33.7 Ma). Other intervals of enhanced carbonate dissolution are located in the upper Paleocene (~56 Ma) and in the upper lower Eocene (~51 Ma). Enhanced preservation of planktonic foraminiferal assemblages marks the start of both the Paleocene and Eocene epochs.

Oxygen, carbon and strontium isotope data for DSDP Hole 35-323

A downhole decrease in 18O, Mg(2+) and K+, an increase in Ca(2+) and a low 87Sr/86Sr ratio of 0.7067 in the pore fluids of DSDP site 323 were caused principally by the alteration of volcanic material. These chemical and isotopic patterns were produced by the alteration, in order of decreasing importance of: a 60-m thick basal layer of volcanic ash; the underlying basalts; and igneous components in the 640-m thick upper sequence composed largely of terrigenous material. A significant portion of the alteration of the ash in the basal sequence must have occurred before the deposition of the upper sediments, perhaps under the influence of advecting solutions. The rest of the alteration occurred during the deposition of the thick upper sediments. Mass balance considerations and the low d18O values of most of the alteration products suggest that much of the later alteration occurred progressively over the last 13 Myr. The principal alteration products were smectite, potassium feldspar, clinoptilolite and calcite.