Phase relationship between sea level and abrupt climate change

Direct traces of past sea levels are based on the elevation of old coral reefs at times of sea level highstands. However, these measurements are discontinuous and cannot be easily correlated with climate records from ice cores. In this study we show a new approach to recognizing the imprint of sea level changes in continuous sediment records taken from the continental slope at locations that were continuously submerged, even during periods of sea level lowstand. By using a sediment core precisely synchronized with Greenland ice cores, we were able to recognize major floods of the Mediterranean continental shelf over the past 270 kyr. During the last glacial period five flooding events were observed at the onset of the warmest Greenland interstadials. Consistent correspondence between warm climate episodes and eustatic sea level rises shows that these global flooding events were generated by pronounced melting of the Northern Hemisphere ice sheets, due to rapid intensification of Atlantic Meridional Overturning Circulation.The method described in this study opens a new perspective for inter-hemispheric synchronization of marine climate records if applied in other continental margins from the Southern Hemisphere or the equatorial regions.     

Experimental studies of sublimation of highly volatile ices in relevance to the ices of the solar system

Studies of sublimation of complex ices prepared by deposition of gaseous CO, CH₄, N₂, and NH₃ molecules on a cold plate have been performed. The low pressure and low temperature system was used: 10^?9–10^?5 mbar and the lowermost temperature 10 K. Diagnostic of composition of evaporates (at an actual temperature) was done by means of the mass spectrometer. The latter allowed following simultaneously the partial pressure of five different ions or radicals escaping from the substrate. It has been found that highly volatile molecules that were used simultaneously with the low volatile ones to form the complex ices (mixtures or clathrates) present a different sublimation pattern than the sublimation of pure high-volatile ices. In particular, the high-volatile component sublimes at two or even three different temperature regimes: At low temperature that is typical for sublimation of this component, as well as at much higher temperatures. This effect seems to be important when degassing and outbursts from cometary nuclei are considered. It can be also important for modeling of cryovolcanic processes on the icy satellites.     

Long-Term Amateur Ccd Monitoring Of Comet C/1999 S4 (Linear)

The results from the analysis of the extensive CCD photometry that we haveobtained during the long-term monitoring (from its discovery until its break-up)of comet C/1999 S4 (linear) are presented here. Our observations showthat the comet did not always behave as expected: it showed activity ahead oftime and in the end became fainter instead of brighter as it approached perihelion.A sequence of images and a lightcurve are shown.     

Improving Bayesian analysis for LISA Pathfinder using an efficient Markov Chain Monte Carlo method

We present a parameter estimation procedure based on a Bayesian framework by applying a Markov Chain Monte Carlo algorithm to the calibration of the dynamical parameters of the LISA Pathfinder satellite. The method is based on the Metropolis-Hastings algorithm and a two-stage annealing treatment in order to ensure an effective exploration of the parameter space at the beginning of the chain. We compare two versions of the algorithm with an application to a LISA Pathfinder data analysis problem. The two algorithms share the same heating strategy but with one moving in coordinate directions using proposals from a multivariate Gaussian distribution, while the other uses the natural logarithm of some parameters and proposes jumps in the eigen-space of the Fisher Information matrix. The algorithm proposing jumps in the eigen-space of the Fisher Information matrix demonstrates a higher acceptance rate and a slightly better convergence towards the equilibrium parameter distributions in the application to LISA Pathfinder data. For this experiment, we return parameter values that are all within ～1σ of the injected values. When we analyse the accuracy of our parameter estimation in terms of the effect they have on the force-per-unit of mass noise, we find that the induced errors are three orders of magnitude less than the expected experimental uncertainty in the power spectral density.     

Particulate organic carbon–Th relationships in particles separated by settling velocity in the northwest Mediterranean Sea

In order to better understand the relationship between the natural radionuclide ²³⁴Th and particulate organic carbon (POC), marine particles were collected in the northwestern Mediterranean Sea (spring/summer, 2003 and 2005) by sediment traps that separated them according to their in situ settling velocities. Particles also were collected in time-series sediment traps. Particles settling at rates of >100 m d⁻¹ carried 50% and 60% of the POC and ²³⁴Th fluxes, respectively, in both sampling years. The POC flux decreased with depth for all particle settling velocity intervals, with the greatest decrease (factor of 2.3) in the slowly settling intervals (0.68–49 m d⁻¹) over trap depths of 524–1918 m, likely due to dissolution and decomposition of material. In contrast the flux of ²³⁴Th associated with the slowly settling particles remained constant with depth, while ²³⁴Th fluxes on the rapidly settling particles increased. Taking into account decay of ²³⁴Th on the settling particles, the patterns of ²³⁴Th flux with depth suggest that either both slow and fast settling particles scavenge additional ²³⁴Th during their descent or there is significant exchange between the particle classes. The observed changes in POC and ²³⁴Th flux produce a general decrease in POC/²³⁴Th of the settling particles with depth. There is no consistent trend in POC/²³⁴Th with settling velocity, such as might be expected from surface area and volume considerations. Good correlations are observed between ²³⁴Th and POC, lithogenic material and CaCO₃ for all settling velocity intervals. Pseudo-K_ds calculated for ²³⁴Th in the shallow traps (2005) are ranked as lithogenic material opal <calcium carbonate <organic carbon. Organic carbon contributes 33% to the bulk K_d, and for lithogenic material, opal and CaCO₃, the fraction is 22% each. Decreases in POC/²³⁴Th with depth are accompanied by increases in the ratio of ²³⁴Th to lithogenic material and opal. No change in the relationship between ²³⁴Th and CaCO₃ was evident with depth. These patterns are consistent with loss of POC through decomposition, opal through dissolution and additional scavenging of ²³⁴Th onto lithogenic material as the particles sink.     

Particulate organic matter and ballast fluxes measured using time-series and settling velocity sediment traps in the northwestern Mediterranean Sea

Prompted by recent data analyses suggesting that the flux of particulate organic carbon sinking into deep waters is determined by fluxes of mineral ballasts, we undertook a study of the relationships among organic matter (OM), calcium carbonate, opal, lithogenic material, and excess aluminum fluxes as part of the MedFlux project. We measured fluxes of particulate components during Spring and Summer of 2003, and Spring of 2005, using a swimmer-excluding sediment trap design capable of measuring fluxes both in a time-series (TS) mode and in a configuration for obtaining particle settling velocity (SV) profiles. On the basis of these studies, we suggest that distinct OM–ballast associations observed in particles sinking at a depth of 200 m imply that the mechanistic basis of the organic matter–ballast association is set in the upper water column above the Twilight Zone, and that the importance of different ballast types follows the seasonal succession of phytoplankton. As in other studies, carbonate appears to enhance the flux of organic matter over opal. Particles must be at least half organic matter before their settling velocity is affected by ballast concentration. This lack of change in ballast composition with SV in particles with <40% OM content suggests that particle SV reaches a maximum because of the increasing importance of inertial drag. Relative amounts of OM and opal decrease with depth due to decomposition and dissolution; carbonates and lithogenic material contribute about the same amount to total mass, or increase slightly, throughout the water column. The high proportion of excess Al cannot be explained by its incorporation into diatom opal or reverse weathering, so Al is most likely adsorbed to particulate oxides. On shorter time scales, dust appears to increase particle flux through its role in aggregation rather than by nutrient inputs enhancing productivity. We suggest that the role of dust as a catalyst in particle formation may be a central mechanism in flux formation in this region, particularly when zooplankton fecal pellet production is low.     

Antenna phase center calibration for precise positioning of LEO satellites

Phase center variations of the receiver and transmitter antenna constitute a remaining uncertainty in the high precision orbit determination (POD) of low Earth orbit (LEO) satellites using GPS measurements. Triggered by the adoption of absolute phase patterns in the IGS processing standards, a calibration of the Sensor Systems S67-1575-14 antenna with GFZ choke ring has been conducted that serves as POD antenna on various geodetic satellites such as CHAMP, GRACE and TerraSAR-X. Nominal phase patterns have been obtained with a robotic measurement system in a field campaign and the results were used to assess the impact of receiver antenna phase patterns on the achievable positioning accuracy. Along with this, phase center distortions in the actual spacecraft environment were characterized based on POD carrier phase residuals for the GRACE and TerraSAR-X missions. It is shown that the combined ground and in-flight calibration can improve the carrier phase modeling accuracy to a level of 4 mm which is close to the pure receiver noise. A 3.5 cm (3D rms) consistency of kinematic and reduced dynamic orbit determination solutions is achieved for TerraSAR-X, which presumably reflects the limitations of presently available GPS ephemeris products. The reduced dynamic solutions themselves match the observations of high grade satellite laser ranging stations to 1.5 cm but are potentially affected by cross-track biases at the cm-level. With respect to the GPS based relative navigation of TerraSAR-X/TanDEM-X formation, the in-flight calibration of the antenna phase patterns is considered essential for an accurate modeling of differential carrier phase measurements and a mm level baseline reconstruction.

Intra-clinothem variability in sedimentary texture and process regime recorded down slope profiles

Shelf-margin clinothem successions can archive process interactions at the shelf to slope transition, and their architecture provides constraints on the interplay of factors that control basin-margin evolution. However, detailed textural analysis and facies distributions from shelf to slope transitions remain poorly documented. This study uses quantitative grain-size and sorting data from coeval shelf and slope deposits of a single clinothem that crops out along a 5 km long, dip-parallel transect of the Eocene Sobrarbe Deltaic Complex (Ainsa Basin, south-central Pyrenees, Spain). Systematic sampling of sandstone beds tied to measured sections has captured vertical and basinward changes in sedimentary texture and facies distributions at an intra-clinothem scale. Two types of hyperpycnal flow-related slope deposits, both rich in mica and terrestrial organic matter, are differentiated according to grain size, sorting and bed geometry: (i) sustained hyperpycnal flow deposits, which are physically linked to coarse channelized sediments in the shelf setting and which deposit sand down the complete slope profile; (ii) episodic hyperpycnal flow deposits, which are disconnected from, and incise into, shelf sands and which are associated with sediment bypass of the proximal slope and coarse-grained sand deposition on the medial and distal slope. Both types of hyperpycnites are interbedded with relatively homogenous, organic-free and mica-free, well-sorted, very fine-grained sandstones, which are interpreted to be remobilized from wave-dominated shelf environments; these wave-dominated deposits are found only on the proximal and medial slope. Coarse-grained sediment bypass into the deeper-water slope settings is therefore dominated by episodic hyperpycnal flows, whilst sustained hyperpycnal flows and turbidity currents remobilizing wave-dominated shelf deposits are responsible for the full range of grain sizes in the proximal and medial slope, thus facilitating clinoform progradation. This novel dataset highlights previously undocumented intra-clinothem variability related to updip changes in the shelf process-regime, which is therefore a key factor controlling downdip architecture and resulting sedimentary texture.     

A single vs. double spike approach to improve the accuracy of Th measurements in small-volume seawater samples

²³⁴Th is a particle-reactive radionuclide widely used to trace biogeochemical oceanic processes occurring over short timescales. During the last few years, small-volume techniques based on the co-precipitation of ²³⁴Th with MnO₂ coupled with beta-counting have been developed as an alternative to large volume gamma-spectrometric techniques. Here a procedure has been developed to enhance quantitative measurement of ²³⁴Th in MnO₂ precipitates. The main objectives were to obtain a purified Th fraction for beta-counting and to determine the chemical recovery of ²³⁴Th using Th spikes and alpha-spectrometry as an alternative to ICP-MS based methods. Two variations of the procedure are presented. In the first “1 spike” method a ²³⁰Th tracer is added to the sample prior to precipitation of MnO₂, and UTEVA® extraction chromatography is used to obtain a NdF₃(Th) purified source that can be used for both beta-counting of ²³⁴Th and alpha-spectrometry of ²³⁰Th. In the “2 spike” method a ²³⁰Th spike is added and the MnO₂(Th) precipitate is directly beta-counted for ²³⁴Th and subsequently spiked with ²²⁸Th or ²²⁹Th prior to UTEVA® purification and alpha-spectrometry. The results confirm the need to process small-volume seawater samples for ²³⁴Th measurement in presence of a yield tracer, and show that both the 1 spike and 2 spike methods allow an accurate and precise determination of ²³⁴Th (relative percent difference, RPD, between expected and mean measured value < 1%; CV between replicate samples < 3%). Our work also suggests that, although the combined analytical uncertainty on total ²³⁴Th measurements accomplished with both versions of the NdF₃ procedure is promising (6% for 2-L samples), the precision of the ²³⁴Th flux estimation will ultimately depend on the degree of disequilibrium between ²³⁴Th and ²³⁸U.