Stable phase field approximations of anisotropic solidification

We introduce unconditionally stable finite element approximations for a phase field model for solidification, which take highly anisotropic surface energy and kinetic effects into account. We hence approximate Stefan problems with anisotropic Gibbs{Thomson law with kinetic undercooling, and quasi-static variants thereof. The phase field model is given by #wt + � %(') 't = r: (b(')rw) ; c a � %(')w = " � � �(r') '

Present day Nd isotopic composition of seawater and sediment leaches from the Pacific sector of the Southern Ocean

ABSTRACT FINAL ID: PP11B-1785 The Southern Ocean plays a key role in the climate evolution of Earth’s history, nevertheless its biggest region, the Pacific sector, has been poorly investigated in comparison to other regions in many paleoceanographic aspects. Some of them will try to be explained by the SOPATRA Project (SOuth PAcific TRAnsects). One of those aspects is radiogenic isotope compositions. Hereby we present the first εNd data extracted from Fe-Mn hydroxide coatings of bulk sediments from the Pacific sector of the Southern Ocean. These surface sediments results, scattered along a longitudinal transect of about 10,000 miles, collected from cruise SO213 from middle Chile to New Zealand (between 36°S and 45°S), represent a reliable overview of the present day Nd isotopic composition of the ambient water masses in this region, and will provide useful information for the interpretation of later downcore studies of this water mass tracer. Multiple analysis were carried out to confirm the reliability of the data as well as the validity of the applied leaching method: 1) Measurements of the present day radiogenic Nd bottom water signatures were compared to the Nd isotope compositions of the leachates in order to verify their seawater origin. 2) The leachates’ 87Sr/86Sr isotope ratios were monitored to confirm the holocenic origin of the samples. 3) Radiogenic Nd and Sr compositions of the detrital fraction of the sediment were measured after total dissolution of the same set of samples in order to exclude detrital contamination of leachates. 4) Two different leaching procedures were tested. Preliminary results show εNd values between -4 and -6, corresponding the lowest values to central south Pacific, which could represent the imprint of the circumpolar deep water moving northward. These findings are in agreement with other authors who extracted bottom water Nd isotope compositions from manganese nodules

A functional CLT for the occupation time of a state-dependent branching random walk

We show that the centred occupation time process of the origin of a system of critical binary branching random walks in dimension $d\ge 3$, started off either from a Poisson field or in equilibrium, when suitably normalized, converges to a Brownian motion in $d\ge4$. In $d=3$, the limit process is a fractional Brownian motion with Hurst parameter 3/4 when starting in equilibrium, and a related Gaussian process when starting from a Poisson field. For (dependent) branching random walks with state dependent branching rate we obtain convergence in f.d.d. to the same limit process, and for $d=3$ also a functional limit theorem.Comment: Published in at http://dx.doi.org/10.1214/009117907000000150 the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

Reconstructing the South Pacific upper water conditions during the Late Quaternary

PP11B-1780: The Antarctic Circumpolar Current system (ACCs) is the most important current system in the Southern Ocean, characterized by strong zonal variations in specific surface water properties, variations used to classify regions whose edges are defined by fronts. The past changes in the strength and latitudinal position of the ACC frontal system are supposed to play a major role on the global oceanic circulation and thus the Earth’s climate through their impact on atmospheric CO2 contents by changes in water stratification conditions, Therefore the study of variability in the surface characteristics of the ACCs provides crucial information to understand and to reconstruct the global climate evolution. The dynamics of the upper-ocean vertical structure, primarily defined by vertical changes in salinity and temperature from the mixed layer down to the seasonal and permanent thermocline, can be tracked using the differences in stable oxygen isotopes (__18O) and Mg/Ca-based temperatures (_T) recorded in the test of planktic foraminifera. Only Mg/Ca thermometry coupled with _18O can guarantee a common source of signal, averaging the same environmental conditions (season and spatial habitat), where, the combined measurements of Mg/Ca and _18O allow to extract the _18O record of past upper ocean water, and accordingly salinity variations In this study we present paired measurements of Mg/Ca and stable oxygen isotopes of shallow-living and deeper-living planktic foraminifera preserved in core top and downcore samples from the South Pacific (36° to 45° S) retrieved during the SOPATRA cruise (South Pacific Paleoceanographic Transect) Chile-New Zealand. The total Mg/Ca values preserved in the foraminiferal calcite from 31 core top samples ranged from ~2 to 1.3 mmol/mol, allowing estimate SSTs between 16° and 12° C. Additionally, to evaluate the reliability of the Mg/Ca signal paleothermometry for long term reconstruction we determined the effect of calcite saturation state (_CO32-) into on foraminiferal Mg/Ca concentration in the different selected species. In order to track the upper water column dynamics and strength of the ACC during the last ~200 kyr, we will test our calibration on downcore records gravity cores SO213-59-2 and SO213-60-2 retrieved from the northern border of the Subantarctic Zone (SAZ) of the East Pacific Rise