Lithostatigraphy of the CESAR cores

Sixteen piston cores and twelve gravity cores were successfully recovered from northern and southern crests of the eastern Alpha Ridge andfrom the Alpha Ridge graben. All but one core contain late Cenozoic muds with variable amounts of sand- to pebble-sized clastic material that probably reflects transport by ice during the past 4-5 Ma. Sixteen Cenozoic-Holocene lithostratigraphic units have been delimited on the basis of sediment texture, structure, colour, detrital carbonate and authigenicferromanganese content. The composition of the upper 13 units in the CESAR cores is similar to the Fletcher's Ice Island cores; hence most units can be broadly correlated over most of the Central Arctic Ocean. Three new lithostratigraphic units (A1-A3) occur at the base of CESAR cores from the northern Alpha Ridge crest. Paleomagnetic and palynological data indicate a Late Miocene-Early Pliocene age for unit A3, which confirms previous reports of a slow sedimentation rate during the Cenozoic. CESAR core 6 was obtained from an erosional surface on top of a fault block at the north edge of the Alpha Ridge graben. This core contains ca. 2m of laminated diatom ooze of Campanian-Maastrichtian age and two ?Paleogene volcanic ash units below a brown mud unit which probably corresponds to units A2 and A3. The biosiliceous ooze contains no foraminifera or silicoflagellates and only few dinoflagellates. There is little difference in biogenic or clastic sediment content between light and dark laminae and the rhythmites do not appear to be annual varves produced in an upwelling environment. The microstructure and fluctuating mineral composition of the laminae most closely resemble those of lami- nated chert beds in the Triassic forearc basins of Japan.

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.

Stable-isotope evidence for the origin of secondary carbonate veins at DSDP Leg 58 Holes

The stable-isotope composition of carbonate minerals is a function of the temperature and isotopic composition of the materials from which they were precipitated or recrystallized. Because carbonates are among the most abundant secondary phases in oceanic volcanic rocks, information derived from their isotopic composition is useful in determining the environment(s) of seafloor alteration. Isotopic analyses of secondary carbonates in basalt recovered from numerous DSDP sites have been reported previously (Anderson and Lawrence, 1976; Brenneke, 1977; Lawrence et al., 1977; Seyfried et al., 1976; among others). These results are consistent with the formation of most secondary carbonates with sea water at low temperatures. The good recovery of basalts during DSDP Leg 58 provided the opportunity to extend the isotopic study of low-temperature alteration and vein formation to the crust of marginal ocean basins. The evidence for complex off-ridge volcanism and intrusive emplacement encountered at Leg 58 sites (Klein et al., 1978) suggested that modes of alteration at these sites might differ from those previously observed and described.

Element and isotope composition of selected volcanics from the Bicol arc, Philippines

Pliocene to recent volcanic rocks from the Bulusan volcanic complex in the southern part of the Bicol arc (Philippines) exhibit a wide compositional range (medium- to high-K basaltic-andesites, andesites and a dacite/rhyolite suite), but are characterised by large ion lithophile element enrichments and HFS element depletions typical of subduction-related rocks. Field, petrographic and geochemical data indicate that the more silicic syn- and post-caldera magmas have been influenced by intracrustal processes such as magma mixing and fractional crystallisation. However, the available data indicate that the Bicol rocks as a group exhibit relatively lower and less variable 87Sr/86Sr ratios (0.7036-0.7039) compared with many of the other subduction-related volcanics from the Philippine archipelago. The Pb isotope ratios of the Bicol volcanics appear to be unlike those of other Philippine arc segments. They typically plot within and below the data field for the Philippine Sea Basin on 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, implying a pre-subduction mantle wedge similar to that sampled by the Palau Kyushu Ridge, east of the Philippine Trench. 143Nd/144Nd ratios are moderately variable (0.51285-0.51300). Low silica (<55 wt%) samples that have lower 143Nd/144Nd tend to have high Th/Nd, high Th/Nb, and moderately low Ce/Ce* ratios. Unlike some other arc segments in the Philippines (e.g. the Babuyan-Taiwan segment), there is little evidence for the involvement of subducted terrigenous sediment. Instead, the moderately low 143Nd/144Nd ratios in some of the Bicol volcanics may result from subduction of pelagic sediment (low Ce/Ce*, high Th/Nd, and high Th/Nb) and its incorporation into the mantle wedge via a slabderived partial melt.

Sedimentology and Nd isotope ratios of sediment core PS72/410-1

The freshwater budget of the Arctic Ocean is a key component governing the deep water formation in the North Atlantic and the global climate system. We analyzed the isotopic composition of neodymium (epsilon-Nd) in authigenic phases of marine sediments on the Mendeleev Ridge in the western Arctic Ocean spanning an estimated time interval from present to about 75 ka BP. This continuous record was used to reconstruct the epsilon-Nd of the polar deep water (PDW) and changes in freshwater sources to the PDW through time. Three deviations in epsilon-Nd from a long term average of -10.2 were identified at estimated 46-51, 35-39 and 13-21 ka BP. The estimated 46-51 ka BP event can be traced to bursting of ice-dammed lakes accompanying the collapse of the Barents-Kara Ice Sheet, which would have released radiogenic Nd to the eastern Arctic Ocean. The cyclonic surface circulation in the eastern Arctic Ocean must have been stronger than at present for the event to be recorded on the Mendeleev Ridge. For the 35-39 and 13-21 ka BP events, it is likely that the Laurentide Ice Sheet (LIS) supplied the unradiogenic freshwater. The configuration of the anticyclonic circulation in the western Arctic was probably similar to today or expanded eastward. Our simple mass balance calculations suggest that large amounts of freshwater were released but due to significant deep water formation within the Arctic Ocean, the effect on the formation of NADW was probably minor.

Radiocarbon dataing, stable oxygen isotopes, and Mg/Ca ratios in surface sediment samples of the tropical eastern Indian Ocean

Shell chemistry of planktic foraminifera and the alkenone unsaturation index in 69 surface sediment samples in the tropical eastern Indian Ocean off West and South Indonesia were studied. Results were compared to modern hydrographic data in order to assess how modern environmental conditions are preserved in sedimentary record, and to determine the best possible proxies to reconstruct seasonality, thermal gradient and upper water column characteristics in this part of the world ocean. Our results imply that alkenone-derived temperatures record annual mean temperatures in the study area. However, this finding might be an artifact due to the temperature limitation of this proxy above 28°C. Combined study of shell stable oxygen isotope and Mg/Ca ratio of planktic foraminifera suggests that Globigerinoides ruber sensu stricto (s.s.), G. ruber sensu lato (s.l.), and G. sacculifer calcify within the mixed-layer between 20 m and 50 m, whereas Globigerina bulloides records mixed-layer conditions at ~50 m depth during boreal summer. Mean calcifications of Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, and Globorotalia tumida occur at the top of the thermocline during boreal summer, at ~75 m, 75-100 m, and 100 m, respectively. Shell Mg/Ca ratios of all species show a significant correlation with temperature at their apparent calcification depths and validate the application of previously published temperature calibrations, except for G. tumida that requires a regional Mg/Ca-temperature calibration (Mg/Ca = 0.41 exp (0.068*T)). We show that the difference in Mg/Ca-temperatures of the mixed-layer species and the thermocline species, particularly between G. ruber s.s. (or s.l.) and P. obliquiloculata, can be applied to track changes in the upper water column stratification. Our results provide critical tools for reconstructing past changes in the hydrography of the study area and their relation to monsoon, El Niño-Southern Oscillation, and the Indian Ocean Dipole Mode.

Description, geochemistry, mineralogy and isotopes of sulfides from ODP Site 193-1189, PACMANUS field

Chemical and isotopic data for rare massive and semimassive sulfide samples cored at Site 1189 (Roman Ruins, PACMANUS) suggest their genetic relationship with sulfide chimneys at the seafloor. Sand collected from the hammer drill after commencement of Hole 1189B indicates that at least the lower section of the cased interval was occupied by material similar to the stockwork zone cored from 31 to ~100 meters below seafloor (mbsf) in this hole, but with increased content of barite, sphalerite, and lead-bearing minerals. Fractional crystallization of ascending hydrothermal fluid involving early precipitation of pyrite may explain vertical mineralogical and chemical zoning within the stockwork conduit and the high base and precious metal contents of Roman Ruins chimneys. A mineralized volcaniclastic unit cored deep in Hole 1189A possibly represents the lateral fringe of the conduit system. Lead isotope ratios in the sulfides differ slightly but significantly from those of fresh lavas from Pual Ridge, implying that at least some of the Pb within the Roman Ruins hydrothermal system derived from a deeper, more radiogenic source than the enclosing altered volcanic rocks.

Miocene foraminiferal, bolboformid, dinoflagellate and diatom age calibrations for the northeastern North Atlantic

This study presents a new Miocene biostratigraphic synthesis for the high-latitude northeastern North Atlantic region. Via correlations to the bio-magnetostratigraphy and oxygen isotope records of Ocean Drilling Program and Deep Sea Drilling Project Sites, the ages of shallower North Sea deposits have been better constrained. The result has been an improved precision and documentation of the age designations of the existing North Sea foraminiferal zonal boundaries of King (1989) and Gradstein and Bäckström (1996). All calibrations have been updated to the Astronomically Tuned Neogene Time Scale (ATNTS) of Lourens et al. (2004). This improved Miocene biozonation has been achieved through: the updating of age calibrations for key microfossil bioevents, identification of new events, and integration of new biostratigraphic data from a foraminiferal analysis of commercial wells in the North Sea and Norwegian Sea. The new zonation has been successfully applied to two commercial wells and an onshore research borehole. At these high latitudes, where standard zonal markers are often absent, integration of microfossil groups significantly improves temporal resolution. The new zonation comprises 11 Nordic Miocene (NM) Zones with an average duration of 1 to 2 million years. This multi-group combination of a total of 92 bioevents (70 foraminifers and bolboformids; 16 dinoflagellate cysts and acritarchs; 6 marine diatoms) facilitates zonal identification throughout the Nordic Atlantic region. With the highest proportion of events being of calcareous walled microfossils, this zonation is primarily suited to micropaleontologists. A correlation of this Miocene biostratigraphy with a re-calibrated oxygen isotope record for DSDP Site 608 suggests a strong correlation between Miocene planktonic microfossil turnover rates and the inferred paleoclimatic trends. Benthic foraminifera zonal boundaries appear to often coincide with Miocene global sequence boundaries. The biostratigraphic record is punctuated by four main stratigraphic hiati which show variation in their geographic and temporal extent. These are related to the following regional unconformities: basal Neogene, Lower/Middle Miocene ("mid-Miocene unconformity"), basal Upper Miocene and basal Messinian unconformities. Further coring of Neogene sections in the North Sea and Norwegian Sea may better constrain their extent and their effect on the biostratigraphic record.

Radiometric age determinations for basements of ODP Sites 123-765 and 123-766

The results of experiments in 40Ar/39Ar age dating using fresh basement material from Sites 765 and 766 of Leg 123 of the Ocean Drilling Program are inconsistent and cannot be used to constrain the basement age of the Argo Abyssal Plain in the Indian Ocean. However, a celadonite sample, which was precipitated during a low-temperature alteration event that affected the basement at Site 765, yielded a K-Ar age of 155.3 ±3.4 Ma. Celadonites, which have been dated using Rb-Sr methods for basement in the Atlantic Ocean (Staudigel et al., 1981, doi:10.1016/0012-821X(81)90186-2) and by K-Ar methods for the Troodos Ophiolite (Staudigel et al., 1986, doi:10.1130/0091-7613(1986)14<72:AASAOC>2.0.CO;2), and for sediments from the Pacific Ocean (Peterson et al., 1986, doi:10.2973/dsdp.proc.92.132.1986) yield ages that are up to 15 Ma younger than the age for the formation of basement. Thus, the celadonite age is retained as a reliable minimum age for basement at Site 765. This radiometric age is inconsistent with biostratigraphic ages, which indicate a maximum of late Berriasian (approximately 140 Ma) for Site 765, but is consistent with geophysical interpretations of marine magnetic anomalies and with the early north-south seafloor spreading history of the Argo Abyssal Plain region of the Indian Ocean.

Geochemical studies of the Cretaceous-Tertiary boundary in ODP Holes 113-689B and 113-690C

In a study of ODP Hole 689B no iridium (Ir) anomaly was found in Sections 1 through 6 of Core 25X or in Core 26X from the top down to section 2, 3-12 cm. The background Ir abundance averaged 11 parts per trillion (ppt) and a clay-enriched region had nearly the same average, 26 ± 12 ppt. If the Cretaceous-Tertiary (K-T) contact is in the region studied, then sedimentation was not continuous, and the K-T boundary was probably either not deposited or it was eroded away. In a study of Cores 15X and 16X of ODP Hole 690C, an iridium peak with a maximum abundance of 1566 ± 222 ppt was found in Section 4 of Core 15X at 39-40 cm with a half-width of 6.6 cm. Background abundances were ~15 ppt and distinctly higher Ir abundances were observed from 119 cm below to 72 cm above the main peak. The Ir distribution below the main peak is attributed to bioturbation by organisms with burrows extending at least 0.4 m. The Ir distribution above the main peak may be due to the same cause but other explanations may be significant. There are variable enrichments of clay in the mainly CaCO3 sediment of Core 15X, and the stratigraphically lowest part of the most abundant clay deposits is found (within 2 cm) in the same position as the main Ir peak. The clay deposit, which is estimated to be about 50% of the sediment, extends upward ~19 cm and then slowly decreases to a background level of 10% over 1 m. The degree of homogeneity of the clay-rich interval suggests it was not due to episodic volcanism but may have been due to a decrease of the CaCO3 deposition rate which was possibly triggered by the impact of a large asteroid or comet on the Earth.

Stable oxygen isotope, UK'37, productivity, CaCO3 and XRF records from sediment core MD06-3075

Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking the terrestrial and marine realms. We present high-resolution stable isotope, UK'37 sea-surface temperature, X-ray fluorescence (XRF) core scanning and coccolithophore-derived paleoproductivity records covering the past 120 ka from International Marine Global Change (IMAGES) Program Core MD06-3075 (6°29' N, 125°50' E, water depth 1878 m), situated in the Davao Gulf on the southern side of Mindanao. XRF-derived log(Fe/Ca) records provide a robust proxy for runoff-driven sedimentary discharge from Mindanao, whilst past changes in local productivity are associated with variable freshwater runoff and stratification of the surface layer. Significant precessional-scale variability in sedimentary discharge occurred during Marine Isotope Stage (MIS) 5, with peaks in discharge contemporaneous with Northern Hemisphere summer insolation minima. We attribute these changes to the latitudinal migration of the Intertropical Convergence Zone (ITCZ) over the WPWP together with variability in the strength of the Walker circulation acting on precessional timescales. Between 60 and 15 ka sedimentary discharge at Mindanao was muted, displaying little orbital- or millennial-scale variability, likely in response to weakened precessional insolation forcing and lower sea level driving increased subsidence of air masses over the exposed Sunda Shelf. These results highlight the high degree of local variability in the precipitation response to past climate changes in the WPWP.

Magnetostratigraphic synthesis of ODP Leg 123 sites

During ODP Leg 123, Sites 765 and 766 were drilled to examine the tectonic evolution, sedimentary history, and paleoceanography of the Argo Abyssal Plain and lower Exmouth Plateau. At each site, the quality of magnetostratigraphic and biostratigraphic records varies because of complicating factors, such as the predominance of turbidites, the presence of condensed horizons, or deposition beneath the CCD. Based primarily on the presence of nannofossils, the base of the sedimentary section at Site 765 was dated as Tithonian. A complete Cretaceous sequence was recovered at this site, although the sedimentation rate varies markedly through the section. The Cretaceous/Tertiary boundary is represented by a condensed horizon. The condensed Cenozoic sequence at Site 765 extends from the upper Paleocene to the lower Miocene. A dramatic increase in sedimentation rate was observed in the lower Miocene, and a 480-m-thick Neogene section is present. The Neogene section is continuous, except for a minor hiatus in the lower Pliocene. The base of the sedimentary section at Site 766 is Valanginian, in agreement with the site's position on marine magnetic anomaly Mil. Valanginian to Barremian sediments are terrigenous, with variable preservation of microfossils, and younger sediments are pelagic, with abundant well-preserved microfossils. Sedimentation rate is highest in the Lower Cretaceous and decreases continually upsection. Upper Cenozoic sediments are condensed, with several hiatuses.

Ar and U-Th-Pb age determinations for minerals from ODP Holes of ODP Legs 173 and 210

We report U-Pb and 39Ar-40Ar measurements on plutonic rocks recovered from the Ocean Drilling Program (ODP) Legs 173 and 210. Drilling revealed continental crust (Sites 1067 and 1069) and exhumed mantle (Sites 1070 and 1068) along the Iberia margin and exhumed mantle (Site 1277) on the conjugate Newfoundland margin. Our data record a complex igneous and thermal history related to the transition from rifting to seafloor spreading. The results show that the rift-to-drift transition is marked by a stuttering start of MORB-type magmatic activity. Subsequent to initial alkaline magmatism, localized mid-oceanic ridge basalts (MORB) magmatism was again replaced by basin-wide alkaline events, caused by a low degree of decompression melting due to tectonic delocalization of deformation. Such "off-axis" magmatism might be a common process in (ultra-) slow oceanic spreading systems, where "magmatic" and "tectonic" spreading varies in both space and time.

Biometry, and fatty acid and fatty alcohol composition of the Arctic ctenophore Mertensia ovum from Kongsfjorden

Lipids of the Arctic ctenophore Mertensia ovum, collected from Kongsfjorden (Svalbard) in 2001, were analysed to investigate seasonal variability and fate of dietary lipids. Total lipids, lipid classes and fatty acid and alcohol compositions were determined in animals, which were selected according to age-group and season. Changes in lipids of age-group 0 animals were followed during growth from spring to autumn. Total lipids increased from May to September. Lipids as percentage of dry mass were lowest in August indicating their use for reproduction. Higher values occurred in September, which may be due to lipid storage for overwintering. Wax esters were the major lipid class accounting for about 50% of total lipids in age-group 0 animals from July and August. Phospholipids were the second largest lipid fraction with up to 46% in this age-group. The principal fatty acids of M. ovum from all age-groups were 22:6(n-3), 20:5(n-3) and 16:0. Wax ester fatty alcohols were dominated by 22:1(n-11) and 20:1(n-9) followed by moderate proportions of 16:0. The unique feature of M. ovum lipids was the high amount of free fatty alcohols originating probably from the dietary wax esters. In May, free alcohols exhibited the highest mean proportion with 14.6% in age-group 0 animals. We present the first data describing a detailed free fatty alcohol composition in zooplankton. This composition was very different from the alcohol composition of M. ovum wax esters because of the predominance of the long-chain monounsaturated 22:1 (n-11) alcohol accounting for almost 100% of total free alcohols in some samples. The detailed lipid composition clearly reflected feeding of M. ovum on the herbivorous calanoid species, Calanus glacialis and C. finmarchicus, the abundant members of the zooplankton community in Kongsfjorden. Other copepod species or prey items seem to be less important for M. ovum.

Paleomagnetic and rock magnetic characterization of ODP Leg 210 cores

We conducted an integrated paleomagnetic and rock magnetic study on cores recovered from Ocean Drilling Program Sites 1276 and 1277 of the Newfoundland Basin. Stable components of magnetization are determined from Cretaceous-aged sedimentary and basement cores after detailed thermal and alternating-field demagnetization. Results from a series of rock magnetic measurements corroborate the demagnetization behavior and show that titanomagnetites are the main magnetic carrier. In view of the normal polarity of magnetization and radiometric dates for the sills at Site 1276 (~98 and ~105 Ma, both within the Cretaceous Normal Superchron) and for a gabbro intrusion in peridotite at Site 1277 (~126 Ma, Chron M1), our results suggest that the primary magnetization of the Cretaceous rocks is likely retained in these rocks. The overall magnetic inclination of lithologic Unit 2 in Hole 1277A between 143 and 180 meters below seafloor is 38°, implying significant (~35° counterclockwise, viewed to the north) rotation of the basement around a horizontal axis parallel to the rift axis (010°). The paleomagnetic rotational estimates should help refine models for the tectonic evolution of the basement. The mean inclinations for Sites 1276 and 1277 rocks imply paleolatitudes of 30.3° ± 5.1° and 22.9° ± 12.0°, respectively, with the latter presumably influenced by tectonic rotation. These values are consistent with those inferred from the mid-Cretaceous reference poles for North America, suggesting that the inclination determinations are reliable and consistent with a drill site on a location in the North America plate since at least the mid-Cretaceous. The combined paleolatitude results from Leg 210 sites indicate that the Newfoundland Basin was some 1800 km south of its current position in the mid-Cretaceous. Assuming a constant rate of motion, the paleolatitude data would suggest a rate of 12.1 mm/yr for the interval from ~130 Ma (Site 1276 age) to present, and 19.6 mm/yr for the interval from 126 Ma (Site 1277 age) to recent. The paleolatitude and rotational data from this study are consistent with the possibility that Site 1276 may have passed over the Canary and Madeira hotspots that formed the Newfoundland Seamounts in the mid-Cretaceous.