Calcareous nannofossil stratigraphy, nannofossil events and carbon isotopic ratios of ODP Leg 183 sites

Cores from Sites 1135, 1136, and 1138 of Ocean Drilling Program Leg 183 to the Kerguelen Plateau (KP) provide the most complete Paleocene and Eocene sections yet recovered from the southern Indian Ocean. These nannofossil-foraminifer oozes and chalks provide an opportunity to study southern high-latitude biostratigraphic and paleoceanographic events, which is the primary subject of this paper. In addition, a stable isotope profile was established across the Cretaceous/Tertiary (K/T) boundary at Site 1138. An apparently complete K/T boundary was recovered at Site 1138 in terms of assemblage succession, isotopic signature, and reworking of older (Cretaceous) nannofossil taxa. There is a significant color change, a negative carbon isotope shift, and nannofossil turnover. The placement of the boundary based on these criteria, however, is not in agreement with the available shipboard paleomagnetic stratigraphy. We await shore-based paleomagnetic study to confirm or deny those preliminary results. The Paleocene nannofossil assemblage is, in general, characteristic of the high latitudes with abundant Chiasmolithus, Prinsius, and Toweius. Placed in context with other Southern Ocean sites, the biogeography of Hornibrookina indicates the presence of some type of water mass boundary over the KP during the earliest Paleocene. This boundary disappeared by the late Paleocene, however, when there was an influx of warm-water discoasters, sphenoliths, and fasciculiths. This not only indicates that during much of the late Paleocene water temperatures were relatively equable, but preliminary floral and stable isotope analyses also indicate that a relatively complete record of the late Paleocene Thermal Maximum event was recovered at Site 1135. It was only at the beginning of the middle Eocene that water temperatures began to decline and the nannofossil assemblage became dominated by cool-water species while discoaster and sphenolith abundances and diversity were dramatically reduced. One new taxonomic combination is proposed, Heliolithus robustus Arney, Ladner, and Wise.

Stable isotope ratios of foraminifera from the continental shelf off Troms, Northern Norway

A stable oxygen and carbon isotope stratigraphy is established for a Late Weichselian/Holocene glaciomarine/marine seguence in Andfjorden and Malangsdjupet on the continental shelf off Troms, Northern Norway. The stratigraphy demonstrates that the global signals, Termination I B and possibly also I A (upper parts), are present and radiocarbon date to 10.3-9.7 kyr B.P. and >14-13.5 kyr B.P., respectively. A temperature increase of 5°-6°C and possibly a small salinity increase occurred during Term. I. A near-glacial environment between 13 and 14 kyr B.P. was characterized by poorly ventilated bottom waters followed by a meltwater pulse at circa 13 kyr B.P. During the beginning intrusion of Atlantic Water between 13 and 10 kyr B.P., the bottom water was characterized by somewhat fluctuating temperatures and salinities. Temperatures close to those of the present were established around 9.7 kyr B.P. and seem to have been rather stable since.

Major element oxides, trace element content and isotopic ratios of dolerites from the Schirmacher Oasis

New results on the petrochemistry and geochemistry of dolerites from the Schirmacher Oasis shed light on the development of the Karoo-Maud plume in Antarctica. The basalts and dolerites are petrologically identical to the rocks of western Dronning Maud Land (DML), which were previously studied and interpreted as a manifestation of the Karoo-Maud plume in Antarctica. The spatial distribution of the dikes suggests eastward spreading of the plume material, up to the Schirmacher Oasis for at least 10 Ma. The geochemical characteristics of magmas from the Schirmacher Oasis reflect the influence of crustal contamination, which accompanied both the ascent and spreading of the plume. The magmas of the initial stage of plume activity (western DML) appeared to be the most contaminated in crustal components. It was found that the geochemical characteristics of Mesozoic magmas from the Schirmacher Oasis are identical to those of enriched tholeiites from the Afanasy Nikitin Rise and the central Kerguelen Plateau (Hole 749), which indicates that their enrichment was related to the ancient material of the Gondwana continent. This was caused by the opening of the Indian Ocean under the influence of the Karoo-Maud plume. This process was peculiar in that it occurred in the presence of nonspreading blocks of varying thickness, for instance, Elan Bank in the central Kerguelen Plateau, and was accompanied by the formation of intraplate volcanic rises, which are documented in the seafloor relief of basins around Antarctica. The geochemical characteristics of igneous rocks from the resulting rises (Afanasy Nikitin, Kerguelen, Naturaliste, and Ninetyeast Ridge) indicate the influence of processes related to crustal assimilation. The magmatism that occurred 40 Ma after the main phase of the Karoo-Maud volcanism at the margins of the adjacent continents of Australia (Bunbury basalts) and India (Rajmahal trapps) could be generated by the Karoo-Maud plume flowing along the developing spreading zone. The plume moved subsequently and was localized at the Kerguelen Plateau, where it occurs at present as an active hotspot.

Trace elements in the aerosol at Neumayer Station, Antarctica

Atmospheric trace element concentrations were measured from March 1999 through December 2003 at the Air Chemistry Observatory of the German Antarctic station Neumayer by inductively coupled plasma - quadrupol mass spectrometry (ICP-QMS) and ion chromatogra-phy (IC). This continuous five year long record derived from weekly aerosol sampling re-vealed a distinct seasonal summer maximum for elements linked with mineral dust entry (Al, La, Ce, Nd) and a winter maximum for the mostly sea salt derived elements Li, Na, K, Mg, Ca, and Sr. The relative seasonal amplitude was around 1.7 and 1.4 for mineral dust (La) and sea salt aerosol (Na), respectively. On average a significant deviation regarding mean ocean water composition was apparent for Li, Mg, and Sr which could hardly be explained by mir-abilite precipitation on freshly formed sea ice. In addition we observed all over the year a not clarified high variability of element ratios Li/Na, K/Na, Mg/Na, Ca/Na, and Sr/Na. We found an intriguing co-variation of Se concentrations with biogenic sulfur aerosols (methane sul-fonate and non-sea salt sulfate), indicating a dominant marine biogenic source for this element linked with the marine biogenic sulfur source.

Barium concentrations und stable isotope ratios of late Paleocene deep-sea sediments

Deep-sea sediment Ba* (Ba/Al2O3(sample) * 15% - Ba(aluminosilicate) records show increasing values synchronous with the evolution of the late Paleocene global d13C maximum, reflecting an increase in marine surface primary production and biogenic barite formation at this time. At two oligotrophic locations, Deep Sea Drilling Project (DSDP) Sites 384 and 527 in the North and South Atlantic, respectively, Ba* increases from 160-360 ppm in the early Paleocene to 1100-3000 ppm during the d13C maximum. At equatorial DSDP Site 577, positioned within or near the high-productivity zone, Ba* increases from ~15,500 ppm in the early Paleocene to ~25,400 ppm in conjunction with late Paleocene maximum d13C values. Linear fitted correlation plots of sediment Ba* content versus surface water d13C in all three regions support barite originating in the euphotic zone. The early to late Paleocene relative increase in Ba* illustrates how burial rates of Corg (relative to Al2O3) accelerated by a factor of ~1.8 and ~6.0 in the eutrophic and oligotrophic areas, respectively. A tentative estimate, weighing our result for the entire ocean, suggests that accumulation rates of organic carbon increased by a factor of 2 during the late Paleocene d13C maximum.

Stable oxygen isotope ratios of pore waters from ODP Leg 166 sites

This study investigates the d18O of pore waters from Sites 1003 through 1007, drilled along the western margin of the Great Bahama Bank during Leg 166 of the Ocean Drilling Program. These pore waters generally show a positive correlation between d18O and the concentration of chloride. The exception to this trend is Site 1006, where the pore waters exhibit nonlinear behavior with respect to chloride. The correlation between the concentration of Cl- and d18O at most of the sites appears to be a coincidence because although the increase in Cl- is a result of diffusion from an underlying source, the increases in d18O result from the recrystallization of metastable carbonates in the presence of a geothermal gradient. The difference in behavior in the d18O of the pore water at Site 1006 is probably a result of the relative reduced rate of carbonate recrystallization at this site. The d18O of the pore waters in the upper portion of the cores shows a pattern similar to the concentration of chloride in that there is an interval of 30-50 m in which neither the d18O nor the concentration of Cl- changes. This interval is consistent with either an interval of very rapid deposition of sediment or the advection of fluid through the platform. Both the d18O and the concentration of Cl- increase toward the platform, suggesting an input of saline and isotopically heavy water from the platform surface.

Stable isotope and Magnesium/Calcium ratios of 4 profiles from the equatorial Pacific/Caribbean

This thesis examines the closure history of the Central American Seaway (CAS) and its effect on changes in ocean circulation and climate during the time interval from ~6 - 2.5 Ma. It was accomplished within the DFG Research Unit "Impact of Gateways on Ocean Circulation, Climate and Evolution" at the University of Kiel. Proxy records from Ocean Drilling Program (ODP) Sites 999 and 1000 (Caribbean), and from ODP Sites 1237, 1239 and 1241 (low-latitude east Pacific) are developed and examined. In addition, previously established proxy data from Atlantic Sites 925/926 (Ceara Rise) and 1006 (western Great Bahama Bank) and from two east Pacific sites (851, 1236) are included for interpretations. The main objectives of this study are (1) to acquire a consistent stratigraphic framework for all sites, (2) to reconstruct Pliocene changes in Caribbean and tropical east Pacific upper ocean water masses (i.e. temperature, salinity, thermocline depth), and (3) to identify potential underlying forcing mechanisms.

Comparison of accumulation rates and stable isotope ratios

Since 1979/80, glaciological studies have been carried out at Ekströmisen, Antarctica, including accumulation-stake measurements, snow-pit and shallow-firn-core studies. Snowstratigraphy, chemical properties and stable-isotope ratios (d18O) were investigated. This study focuses on three cores taken between 1982 and 1998. The 1998 core was dated using dielectric profiling, d18O profiles and stake measurements. Accumulation rates showhigh interannual and spatial variability due to the extreme wind influence. No significant trend was found for the last 50 years; during the first half of the 20th century, accumulation decreased. The high spatial and interannual variability, however, means that trends must be interpreted with care. In spite of the highly irregular accumulation distribution, stable-isotope ratios show little spatial variability. The mean annual d18O values of cores B04 and FB0198 agree fairly well for the time period 1955-82 covered by both cores. d18O values have increased during most of the 20th century; since the late 1980s a decrease is observed. This change is not related to air temperature, since mean annual air temperatures at Neumayer show no significant trend over the last two decades.

Isotopic ratios of methane, ethane, carbon dioxide, inorganic carbon and organic matter from ODP Leg 164 sites

The isotopic characteristics of CH4 (d13C values range from -101.3 per mil to -61.1 per mil PDB, and dD values range from -256 per mil to -136 per mil SMOW) collected during Ocean Drilling Program (ODP) Leg 164 indicate that the CH4 was produced by microbial CO2 reduction and that there is not a significant contribution of thermogenic CH4 to the sampled sediment gas from the Blake Ridge. The isotopic values of CO2 (d13C range -20.6 per mil to +1.24 per mil PDB) and dissolved inorganic carbon (DIC; d13C range -37.7 per mil to +10.8 per mil PDB) have parallel profiles with depth, but with an offset of 12.5 per mil. Distinct downhole variations in the carbon isotopic composition of CH4 and CO2 cannot be explained by closed-system fractionation where the CO2 is solely derived from the locally available sedimentary organic matter (d13C -2.0 per mil ± 1.4 per mil PDB) and the CH4 is derived from CO2 reduction. The observed isotopic profiles reflect the combined effects of upwards gas migration and decreased microbial activity with depth.

Isotopic composition and Strontium/Calcium ratios of foraminifera of ODP Holes 113-689B and 113-690C

Oxygen and carbon isotopic ratios were measured from Maestrichtian benthic and planktonic foraminifer species and bulk carbonate samples from ODP Sites 689 and 690, drilled on the Maud Rise during Leg 113. Careful scanning electron microscope observations reveal that test calcite in some intervals was diagenetically altered, although Sr/Ca and isotopic ratios of these tests do not appear to have been modified significantly. Foraminifer d18O values at both sites document a cooling trend during early Maestrichtian time, a rapid drop in water temperatures at the time of the first appearance of Abathomphalus mayaroensis in the high southern latitude regions (about 69.9 Ma), and lower water temperatures during late Maestrichtian time. d13C values record a depletion in 13C in the latest early Maestrichtian time beginning at about 72.2 Ma, just prior to the sharp late Maestrichtian increase in d18O values. These trends are similar to those previously reported for well-preserved benthic foraminifer species from Seymour Island, in the Antarctic Peninsula. Paleotemperature estimates are also comparable to those at Seymour Island and suggest temperate climatic conditions in Antarctica and that bottom waters in the southern South Atlantic region were of Antarctic origin. Benthic and planktonic foraminifer 613C values fluctuate sympathetically and are higher in upper Maestrichtian sediments than in the lower Maestrichtian sequence.

Isotope ratios, trace elements and ultrastructure results of Mytilus galloprovincialis shells and experimental site data off Ischia (Italy)

Bivalve shells can provide excellent archives of past environmental change but have not been used to interpret ocean acidification events. We investigated carbon, oxygen and trace element records from different shell layers in the mussels Mytilus galloprovincialis combined with detailed investigations of the shell ultrastructure. Mussels from the harbour of Ischia (Mediterranean, Italy) were transplanted and grown in water with mean pHT 7.3 and mean pHT 8.1 near CO2 vents on the east coast of the island. Most prominently, the shells recorded the shock of transplantation, both in their shell ultrastructure, textural and geochemical record. Shell calcite, precipitated subsequently under acidified seawater responded to the pH gradient by an in part disturbed ultrastructure. Geochemical data from all test sites show a strong metabolic effect that exceeds the influence of the low-pH environment. These field experiments showed that care is needed when interpreting potential ocean acidification signals because various parameters affect shell chemistry and ultrastructure. Besides metabolic processes, seawater pH, factors such as salinity, water temperature, food availability and population density all affect the biogenic carbonate shell archive.