Causes of the Regional Variability in Observed Sea Level,Sea Surface Temperature and Ocean Colour Over the Period 1993–2011

We analyse the regional variability in observed sea surface height (SSH), sea surface temperature (SST) and ocean colour (OC) from the ESA Climate Change Initiative datasets over the period 1993–2011. The analysis focuses on the signature of the ocean large-scale climate fluctuations driven by the atmospheric forcing and do not address the mesoscale variability. We use the ECCO version 4 ocean reanalysis to unravel the role of ocean transport and surface buoyancy fluxes in the observed SSH, SST and OC variability. We show that the SSH regional variability is dominated by the steric effect (except at high latitude) and is mainly shaped by ocean heat transport divergences with some contributions from the surface heat fluxes forcing that can be significant regionally (confirming earlier results). This is in contrast with the SST regional variability, which is the result of the compensation of surface heat fluxes by ocean heat transport in the mixed layer and arises from small departures around this background balance. Bringing together the results of SSH and SST analyses, we show that SSH and SST bear some common variability. This is because both SSH and SST variability show significant contributions from the surface heat fluxes forcing. It is evidenced by the high correlation between SST and buoyancy-forced SSH almost everywhere in the ocean except at high latitude. OC, which is determined by phytoplankton biomass, is governed by the availability of light and nutrients that essentially depend on climate fluctuations. For this reason, OC shows significant correlation with SST and SSH. We show that the correlation with SST displays the same pattern as the correlation with SSH with a negative correlation in the tropics and subtropics and a positive correlation at high latitude. We discuss the reasons for this pattern.     

Low dispersive modeling of Rayleigh waves on partly staggered grids

In elastic media, finite-difference (FD) implementations of free-surface (FS) boundary conditions on partly staggered grid (PSG) use the highly dispersive vacuum formulation (VPSG). The FS boundary is embedded into a “vacuum” grid layer (null Lame’s constants and negligible density values) where the discretized equations of motion allow computing surface displacements. We place a new set of compound (stress-displacement) nodes along a planar FS and use unilateral mimetic FD discretization of the zero-traction conditions for displacement computation (MPSG). At interior nodes, MPSG reduces to standard VPSG methods and applies fourth-order centered FD along cell diagonals for staggered differentiation combined with nodal second-order FD in time. We perform a dispersion analysis of these methods on a Lamb’s problem and estimate dispersion curves from the phase difference of windowed numerical Rayleigh pulses at two FS receivers. For a given grid sampling criterion (e.g., six or ten nodes per reference S wavelength λ ^S), MPSG dispersion errors are only a quarter of the VPSG method. We also quantify root-mean-square (RMS) misfits of numerical time series relative to analytical waveforms. MPSG RMS misfits barely exceed 10 % when nine nodes sample the minimum S wavelength $\lambda _{\text {MIN}}^{\mathrm {S}}$ in transit (along distances $\sim $ 145 $\lambda _{\text {MIN}}^{\mathrm {S}}$ ). In same tests, VPSG RMS misfits exceed 70 %. We additionally compare MPSG to a consistently fourth-order mimetic method designed on a standard staggered grid. The latter equates the former’s dispersion errors on grids twice denser and shows higher RMS precision only on grids with six or less nodes per $\lambda _{\text {MIN}}^{\mathrm {S}}$ .     

Nd and Sr isotope study of hydrothermal scheelite and host rocks at Omai, Guiana Shield: implications for ore fluid source and flow path during the formation of orogenic gold deposits

Omai is a high tonnage, low-grade, world-class gold deposit located in the Paleoproterozoic Guiana Shield. It is the second most important gold deposit in the Guiana Shield (after Las Cristinas, Venezuela), and one of the largest in South America (4.0 million oz.). Sm-Nd and Sr isotope data are presented for host rocks and for scheelite from auriferous quartz-carbonate-scheelite-sulfide-telluride veins from the Omai deposit. Gold-bearing veins are hosted by the Paleoproterozoic Barama-Mazaruni Supergroup, a greenstone belt sequence consisting of mafic volcanic rocks interbedded with sedimentary rocks that are intruded by quartz-feldspar porphyry and rhyolite dikes. This lithologic sequence was folded and metamorphosed to lower greenschist facies during the Paleoproterozoic Trans-Amazonian orogeny. The volcano-sedimentary unit was intruded by a post-tectonic quartz monzodiorite-diorite-hornblendite stock. Initial Nd isotope ratios for the Omai volcanic rocks range from ɛ_Nd=+2.1 to +4.2. These values suggest that this part of the Guiana Shield was a site of new crust formation during the Paleoproterozoic and was not contaminated by older (Archean), reworked continental crust. Initial Nd isotope ratios for the Omai stock range between +0.5 and +2.3, which suggest limited contamination with previously formed continental crust. Although the Nd isotopic ratios of gold-related scheelites overlap with those of the host rocks, particularly the tholeiitic basalts at the interpreted time of vein emplacement, the lack of both isotopic mixing and significant Nd movement during the hydrothermal process suggest that the Nd isotope composition can be used to determine the isotopic characteristics of the ore fluid source area. At Omai, the ore fluid is largely derived from a radiogenic Nd source, represented by mantle or lower crustal reservoirs. Strontium isotope ratios for the scheelites cluster tightly between 0.7019 and 0.7021. The Sr isotope data suggest that unlike Nd, Sr was significantly mobile during the hydrothermal process. The fluids responsible for the Omai deposit may have picked up Sr along the flow path. The constant low Sr isotope values of scheelites probably reflect the key role that the local tholeiitic basalts played as the main source of Sr in the fluids. Whereas Nd isotopes identify the fluid source area, the Sr isotopes map the fluid flow paths. Received: 11 February 1999 / Accepted: 1 November 1999     

Quick Detection System for Planck satellite

Q uick D etection S ystem or qds is a software package that has been developed for detecting point sources in the Planck satellite data as soon as the data become available, a few days after transmission to the Earth. Point sources are detected by filtering the data with a filter defined by the Mexican hat wavelet. An alert is generated on those detections that are found to be interesting, such as prominent flaring, according to the criteria specified to the software. The goal is to detect spectral or flux variability in active galactic nuclei so that instant multifrequency follow-up observations with other instruments could be arranged to study the interesting behaviour.     

The structure of clusters with bimodal distributions of galaxy radial velocities. II: A1775

We analyze the structure of the cluster of galaxies Abell 1775 (α = 13 ^h 42 ^m , δ = +26°22′, cz ≈ 21000 km/s), which exhibits a bimodal distribution of radial velocities of the containing galaxies. The difference of the subcluster radial velocities is ΔV ≈ 2900 km/s. We use the results of our photometric observations made with the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the spectroscopic and photometric data from the SDSS DR6 catalog to determine independent distances to the subclusters via three different methods: the Kormendy relation, photometric plane, and fundamental plane. We find that the A1775 cluster consists of two independent clusters, A1775A (cz = 19664 km/s) and A1775B (cz = 22576 km/s), each located at its own Hubble distance and having small peculiar velocities. Given the velocity dispersions of 324 km/s and 581 km/s and the dynamic masses within the R ₂₀₀ radius equal to 0.6 × 10¹⁴ and 3.3 × 1014 M _⊙, the A1775A and A1775B clusters have the K-band luminosity-to-mass ratios of 29 and 61, respectively. A radio galaxy with an extended tail belongs to the A1775B cluster.     

Collisional modification of the acapulcoite/lodranite parent body revealed by the iodine‐xenon system in lodranites

Abstract— The I‐Xe system of three lodranites has been investigated. Samples of Gibson yielded no isochrons, and late model ages are attributed to late addition of iodine. Two metal and one silicate separate from the transitional lodranite Graves Nunataks (GRA) 95209 gave ages that are consistent with each other and with the literature I‐Xe age of Acapulco feldspar. These yield a mean closure age 4.19 ± 0.53 Ma after the Shallowater enstatite reference age (4562.3 ± 0.4 Ma). Such identical I‐Xe ages from distinct phases imply that the parent material underwent a period of rapid cooling, the absolute age of this event being 4558.1 ± 0.7 Ma. Such rapid cooling indicates an increase in the rate at which heat could be conducted away, requiring a significant modification of the parent body. We suggest the parent body was modified by an impact at or close to the time recorded by the I‐Xe system. An age of 10.4 ± 2.3 Ma after Shallowater has been determined for one whole‐rock sample of Lewis Cliff (LEW) 88280. Since the release pattern is similar to that of GRA 95209 this hints that the larger grain size of this sample may reflect slower cooling due to deeper post impact burial.     

Low-temperature thermodynamic properties of disordered zeolites of the natrolite group

 The heat capacity of paranatrolite and tetranatrolite with a disordered distribution of Al and Si atoms has been measured in the temperature range of 6–309 K using the adiabatic calorimetry technique. The composition of the samples is represented with the formula (Na_1.90K_0.22Ca_0.06)[Al_2.24Si_2.76O₁₀]·nH₂O, where n=3.10 for paranatrolite and n=2.31 for tetranatrolite. For both zeolites, thermodynamic functions (vibrational entropy, enthalpy, and free energy function) have been calculated. At T=298.15 K, the values of the heat capacity and entropy are 425.1 ± 0.8 and 419.1 ±0.8 J K⁻¹ mol⁻¹ for paranatrolite and 381.0 ± 0.7 and 383.2 ± 0.7 J K⁻¹ mol⁻¹ for tetranatrolite. Thermodynamic functions for tetranatrolite and paranatrolite with compositions corrected for the amount of extraframework cations and water molecules have also been calculated. The calculation for tetranatrolite with two water molecules and two extraframework cations per formula yields: C _p (298.15)=359.1 J K⁻¹ mol⁻¹, S(298.15) −S(0)=362.8 J K⁻¹ mol⁻¹. Comparing these values with the literature data for the (Al,Si)-ordered natrolite, we can conclude that the order in tetrahedral atoms does not affect the heat capacity. The analysis of derivatives dC/dT for natrolite, paranatrolite, and tetranatrolite has indicated that the water- cations subsystem within the highly hydrated zeolite may become unstable at temperatures above 200 K. Received: 30 July 2001 / Accepted: 15 November 2001