(Table 1) Radiocarbon ages and different calibrated ages for sediment core HLY0503-18TC obtained during the HOTRAX expedition

A short sediment core from a local depression forming an intra basin on the Lomonosov Ridge, was retrieved during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). It contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. The Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Calibration of the radiocarbon ages, using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core, results in marine reservoir ages of 1400 years or more, at least during the last deglaciation. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Lateglacial to the Holocene, suggesting circulation and ventilation changes.

Chemical and isotopic composition of carbonate veins from ODP Leg 209

Carbonate veins hosted in ultramafic basement drilled at two sites in the Mid Atlantic Ridge 15°N area record two different stages of fluid-basement interaction. A first generation of carbonate veins consists of calcite and dolomite that formed syn- to postkinematically in tremolite-chlorite schists and serpentine schists that represent gently dipping large-offset faults. These veins formed at temperatures between 90 and 170 °C (oxygen isotope thermometry) and from fluids that show intense exchange of Sr and Li with the basement (87Sr/86Sr = 0.70387 to 0.70641, d7Li L-SVEC = + 3.3 to + 8.6 per mil). Carbon isotopic compositions range to high d13C PDB values (+ 8.7 per mil), indicating that methanogenesis took place at depth. The Sr-Li-C isotopic composition suggests temperatures of fluid-rock interaction that are much higher (T > 350-400 °C) than the temperatures of vein mineral precipitation inferred from oxygen isotopes. A possible explanation for this discrepancy is that fluids cooled conductively during upflow within the presumed detachment fault. Aragonite veins were formed during the last 130 kyrs at low-temperatures within the uplifted serpentinized peridotites. Chemical and isotopic data suggest that the aragonites precipitated from cold seawater, which underwent overall little exchange with the basement. Oxygen isotope compositions indicate an increase in formation temperature of the veins by 8-12 °C within the uppermost ~ 80 m of the subseafloor. This increase corresponds to a high regional geothermal gradient of 100-150 °C/km, characteristic of young lithosphere undergoing rapid uplift.

Age determination of ODP Site 165-1002

An expanded Cariaco Basin 14C chronology is tied to 230Th-dated Hulu Cave speleothem records in order to provide detailed marine-based 14C calibration for the past 50,000 years. The revised, high-resolution Cariaco 14C calibration record agrees well with data from 230Th-dated fossil corals back to 33 ka, with continued agreement despite increased scatter back to 50 ka, suggesting that the record provides accurate calibration back to the limits of radiocarbon dating. The calibration data document highly elevated Delta14C during the Glacial period. Carbon cycle box model simulations show that the majority of observed Delta14C change can be explained by increased 14C production. However, from 45 to 15 ka, Delta14C remains anomalously high, indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today. Additional observations of the magnitude, spatial extent and timing of deep ocean Delta14C shifts are critical for a complete understanding of observed Glacial Delta14C variability.

Determination of Uranium, Thorium, and Ionium in sediment cores of the Caribbean and Ionian Sea

A rapid procedure for Io (Th230) dating of sediments with accumulation rates in the range of several cm/1000 years is described. Studying of large sample populations with very small Io-excess activity is possible as the counting time (around 1500 min/sample) are 2 to 5 times shorter than with the standard Io-excess method. Improved sensitivity of the Io-excess measurement is achieved by: 1) extraction ( ~90 %) of the authigenic Io-excess with EDTA, with minor leaching ( ~30 %) of the allogenic Th232 and Io-supported, 2) processing samples as large as 10 g or more. The procedure was applied to sediments from the Caribbean (V 12-122) and from the Ionian Sea (M22_48 and M17_17). In the case of the standard core V 12-122 our results are in good agreement with previous time-consuming Io determinations. The resulting average accumulation rates of 2.0 ± 0.3 cm/1000 years for the Ionian Sea cores are close to the average derived from magnetic reversal studies of a nearby core.

Reconstructions of eolian dust accumulation in northwest African margin sediments

Reconstructions of eolian dust accumulation in northwest African margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region. Existing records indicate dramatic changes in North African dust emissions over the last 20 ka, but the limited spatial extent of these records and the lack of high-resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 31°N to 19°N along the northwest African margin. By combining grain size endmember modeling with 230Th-normalized fluxes for the first time, we are able to document spatial and temporal changes in dust deposition under the North African dust plume throughout the last 20 ka. Our results provide quantitative estimates of the magnitude of dust flux changes associated with Heinrich Stadial 1, the Younger Dryas, and the African Humid Period (AHP; ~11.7-5 ka), offering robust targets for model-based estimates of the climatic and biogeochemical impacts of past changes in North African dust emissions. Our data suggest that dust fluxes between 8 and 6 ka were a factor of ~5 lower than average fluxes during the last 2 ka. Using a simple model to estimate the effects of bioturbation on dust input signals, we find that our data are consistent with abrupt, synchronous changes in dust fluxes in all cores at the beginning and end of the AHP. The mean ages of these transitions are 11.8±0.2 ka (1Sigma) and 4.9±0.2 ka, respectively.

Isotope analysis and heat flow measurements of Maria S. Merian cruise MSM21/4 on the western Svalbard margin

Methane hydrate is an ice-like substance that is stable at high-pressure and low temperature in continental margin sediments. Since the discovery of a large number of gas flares at the landward termination of the gas hydrate stability zone off Svalbard, there has been concern that warming bottom waters have started to dissociate large amounts of gas hydrate and that the resulting methane release may possibly accelerate global warming. Here, we can corroborate that hydrates play a role in the observed seepage of gas, but we present evidence that seepage off Svalbard has been ongoing for at least three thousand years and that seasonal fluctuations of 1-2°C in the bottom-water temperature cause periodic gas hydrate formation and dissociation, which focus seepage at the observed sites.

Grain size effects on excess Thorium-230 of sediment cores from the Southern Ocean and the South East Atlantic

Excess Thorium-230 (230Thxs) as a constant flux tracer is an essential tool for paleoceanographic studies, but its limitations for flux normalization are still a matter of debate. In regions of rapid sediment accumulation, it has been an open question if 230Thxs-normalized fluxes are biased by particle sorting effects during sediment redistribution. In order to study the sorting effect of sediment transport on 230Thxs, we analyzed the specific activity of 230Thxs in different particle size classes of carbonate-rich sediments from the South East Atlantic, and of opal-rich sediments from the Atlantic sector of the Southern Ocean. At both sites, we compare the 230Thxs distribution in neighboring high vs. low accumulation settings. Two grain-size fractionation methods are explored. We find that the 230Thxs distribution is strongly grain size dependent, and 50-90% of the total 230Thxs inventory is concentrated in fine material smaller than 10 µm, which is preferentially deposited at the high accumulation sites. This leads to an overestimation of the focusing factor Psi, and consequently to an underestimation of the vertical flux rate at such sites. The distribution of authigenic uranium indicates that fine organic-rich material has also been re-deposited from lateral sources. If the particle sorting effect is considered in the flux calculations, it reduces the estimated extent of sediment focusing. In order to assess the maximum effect of particle sorting on Psi, we present an extreme scenario, in which we assume a lateral sediment supply of only fine material (< 10 µm). In this case, the focusing factor of the opal-rich core would be reduced from Psi = 5.9 to Psi = 3.2. In a more likely scenario, allowing silt-sized material to be transported, Psi is reduced from 5.9 to 5.0 if particle sorting is taken into consideration. The bias introduced by particle sorting is most important for strongly focused sediments. Comparing 230Thxs-normalized mass fluxes biased by sorting effects with uncorrected mass fluxes, we suggest that 230Thxs-normalization is still a valid tool to correct for lateral sediment redistribution. However, differences in focusing factors between core locations have to be evaluated carefully, taking the grain size distributions into consideration.

(Table 1, page 119) 10Be and 9Be concentrations in manganese nodules of the Pacific Ocean

The usefulness of cosmogenic beryllium-10 (half life = 2.5 Ma) for studying the rates of accumulation of ferromanganese nodules is reported based on its measured depth distribution in the top 20 mm of these deposits. Accumulation rates have been obtained in the range of 1 to 4 mm/Ma, which are in good agreement with rates determined using the 230Th method on the same nodules. The use of 10Be offers promise in extending the dating to the outer few cm of the nodules. This contrasts with conventional methods using 230Th and 231Pa isotopes which, due to their comparatively short half lives, are limited to a few mm at the surface of the nodules. Detailed studies of 10Be in the manganese deposits coupled with other trace element analyses should prove valuable in understanding the processes of formation of these deposits and the chronology of events recorded by them.