Workshop on Pliocene Climate

The warm Pliocene epoch (5–3 million years ago) is often cited as a good analog for the near future climate because of its striking resemblance to the predictions of the “Intergovernmental Panel on Climate Change” for the next decades. Indeed, relative to today, during the Pliocene epoch, surface temperatures were 3–4°C warmer, sea level was about 5–40 meters higher, atmospheric CO2 concentrationswere relatively similar or slightly higher (~400 ± 50 ppmv), and ice sheets were restrained to Antarctica. However, since 3.0 Ma ago, the Earth’s climate has undergone a major transition from a warm and relatively stable state towards cold conditions marked by amplified glacial/interglacial cycles and widespread ice sheets in the Northern Hemisphere (NHG), and to a lesser extent over Antarctica. The causes and consequences of this global climate transition—driving warm periods to “icehouse” conditions marked by “Quaternary-style” glacial/interglacial cycles—are still uncertain. Yet, they may include the interaction of several mechanisms tied to oceanic and atmospheric circulations, tectonic-, greenhouse gases-, and biological activity, biogeochemical processes, and changes in Earth’s orbit

Net-zooplankton abundance and biomass from Annaba Bay (SW Mediterranean Sea) under estuarine influences

Zooplankton samples were collected in Annaba Bay (Algeria) from January 2009-March 2011 at three coastal sites differently affected by estuarine plumes and external currents. Aim of this survey was to analyze zooplankton composition, abundance and biomass and compare the results with previous studies to reveal possible populations and environmental changes. The mean zooplankton abundance varied between 1,200-6,000 ind. m-3 and biomass 6.70-25.70 mg DW m-3, according to the site. Copepods constituted the main fraction of zooplankton community, and Oithona similis and Paracalanus indicus successively dominated during autumn-winter and spring-summer. The dinoflagellate Noctiluca scintillans was one of the major zooplankton components, and developed high numbers during February-April, becoming common in neritic and coastal regions. The singularity of the zooplankton from Annaba Bay is the prevalence of P. indicus throughout the entire bay and the decrease in Acartia discaudata and A. clausi (with respect to previous years), possibly replaced by A. negligens. Additionally, Oithona nana abundance markedly decreased with the large development of O. similis. Annaba Bay also differs from other similar Mediterranean coastal areas by the large development of Centropages ponticus populations during the warm period. Among the identified copepod species, the alien species Pseudodiaptomus australiensis and P. arabicus are reported for the first time in the Mediterranean Sea. The occurrence of copepodid V stages of P. australiensis suggests that this species survives and reproduces in Annaba Bay, but so far without developing an abundant population.

Detection of very-high-energy gamma-ray emission from the vicinity of PSR B1706-44 with H.E.S.S

The energetic pulsar PSR B1706-44 and the adjacent supernova remnant (SNR) candidate G 343.1-2.3 were observed by H.E.S.S. during a dedicated observational campaign in 2007. A new source of very-high-energy (VHE; E > 100 GeV) gamma-ray emission, HESS J1708-443, was discovered with its centroid at RA(J2000) = 17h08m10s and Dec(J2000) = -44d21', with a statistical error of 3 arcmin on each axis. The VHE gamma-ray source is significantly more extended than the H.E.S.S. point-spread function, with an intrinsic Gaussian width of 0.29 +/- 0.04 deg. Its energy spectrum can be described by a power law with a photon index Gamma = 2.0 +/- 0.1 (stat) +/- 0.2 (sys). The integral flux measured between 1-10 TeV is ~17% of the Crab Nebula flux in the same energy range. The possible associations with PSR B1706-44 and SNR G343.1-2.3 are discussed.Comment: 4+ pages, 2 figures; v1 submitted to ICRC Proceedings on 15 May 2009; v2 has additional references and minor change

Vibration pumping of mdof structures using optimised multiple dynamic absorbers

International audienceThe concept of energy pumping is an innovative dynamic phenomenon; it gives rise to new generation of dynamic absorbers. Theoretical studies and feasibility tests are necessary for better understanding of their dynamic behaviour and to be applied on real structures or machines. In this paper, numerical evidence is firstly given for the passive and broadband targeted energy transfer in the case of a linear system under shock excitation with Multiple Dynamic Absorbers or Nonlinear Energy Sink (NES). Secondly, it is shown that many NES absorb shock energy in only way and dissipate this energy locally, without "spreading" it returns to the linear system. The numerical results of optimisation in the case of NES linked to a linear beam are compared to Tuned Mass Dampers (TMD) linked to the same beam

Design of light concentrators for Cherenkov telescope observatories

The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray detector ever built in the world. It will be installed at two different sites in the North and South hemispheres and should be operational for about 30 years. In order to cover the desired energy range, the CTA is composed of typically 50-100 collecting telescopes of various sizes (from 6 to 24-m diameters). Most of them are equipped with a focal plane camera consisting of 1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics, whose double function is to maximize the amount of Cherenkov light detected by the photo-sensors, and to block any stray light originating from the terrestrial environment. Two different optical solutions have been designed, respectively based on a Compound Parabolic Concentrator (CPC), and on a purely dioptric concentrating lens. In this communication are described the technical specifications, optical designs and performance of the different solutions envisioned for all these light concentrators. The current status of their prototyping activities is also given

Variations in Mediterranean Outflow Water and its salt discharge versus Pliocene changes in North Atlantic thermohaline circulation prior and during the onset of major Northern Hemisphere Glaciation, 3.7 – 2.6 Ma

Pliocene changes in Mediterranean Outflow Water (MOW) and its potential influence on northern North Atlantic thermohaline circulation prior and during the onset of Northern Hemisphere Glaciation (NHG; 3.7 – 2.6 Ma) were investigated at westernmost Mediterranean Site ODP 978 (1930 m w.d.) and along the northeast Atlantic continental margin, at Sites DSDP 548 (1250 m w.d.) and ODP 982 (1135 m w.d.). Foraminiferal δ18O records (and geomagnetic events) formed the base for stable isotope stratigraphy which led to a major revision of age control at Site 982. The Nd isotopic composition (εNd) of bottom seawater served to trace back the origin of water masses. Sea surface temperatures (SST) were reconstructed from the alkenone unsaturation index (Uk'37) and Mg/Ca estimates on planktic shells. Bottom water temperatures (BWT) were estimated from Mg/Ca measured on epibenthic foraminifera. Epibenthic δ13C records were used as tracer of bottom water ventilation. This investigation consists of four interrelated studies. Study 1 provides new insights from proxy intercomparison. Uk'37-based vs Mg/Ca-based SST estimates at Site 982 show that SST values derived from alkenones are ~1°C higher than those based on Mg/Ca in planktic foraminifera. However, both proxies report similar climate trends. Over the period of fairly global stable climate between 3.7 and 3.3 Ma both proxies record a large orbital-scale variability that may be linked to changes in the strength and position of the North Atlantic atmospheric pressure systems and the position of the North Atlantic Current (NAC). From ~3.3 to 3.0 Ma northeast Atlantic SST underwent a major drop, a result that may contradict the PRISM concept assuming a time slice of largely constant climate conditions. Study 2 documents a major and long-term Upper Pliocene intensification of the Mediterranean outflow, 3.5 – 3.3 Ma. εNd values higher than -11 to -9 show that MOW spread continuously over the northeast Atlantic throughout the Upper Pliocene and reached up to the Rockall Plateau from 3.4 until 2.7 Ma and after 2.55 Ma. From 3.5 – 3.3 Ma, northeast Atlantic Sites 548 and 982 showed a singular and persistent increase in bottom water salinities (BWS) by ~2 psu and in densities (BWD) by 1 kg m-3, which was matched by a ~1 to 3°C increase in BWT at Sites 548 and 982. This event of increased MOW flow was coeval with a unique and long-term rise in BWS by ~1 psu and in BWD by ~1 kg m-3 of WMDW at West Mediterranean Site 978 which partly forms the source of MOW by turbulent entrainment. These changes were most likely linked to a major aridification in the Mediterranean region following a key change in the African monsoon system. Precisely at the same interval, surface waters of the Alboran Sea showed an increase of nutrient contents (decreasing planktic δ13C). The increase was most likely linked to an enhanced Atlantic inflow of nutrient-enriched surface waters that had to compensate for the enhanced outflow of MOW. Study 3 concerned the onset of major NHG from ~3.0 to 2.7 Ma, when the long-term average BWT and BWS at S. 548 decreased by 3°–4°C and 2 psu, respectively, until 2.82 Ma (MIS G10). However, BWT and BWS at the shallower (and most distal) S. 982 continued to oscillate at a level that was 3°C and 1.5-psu higher than today. Generally, BWD then was slightly higher at S. 982 than at S. 548. Accordingly, it appears that the coeval enhanced production of upper North Atlantic Deep Water (NADW) may have diluted and/or rather displaced the core of the MOW tongue upward in the region off Brittany up to a level shallower than 1250 m w.d. (S. 548), although BWD still was about 0.5-kg m-3 higher than today. Study 4 concerned potential links between the strength of MOW salt discharge and upper NADW formation. The increased advection of salt with MOW from 3.5 – 3.3 Ma did not translate into any trends of better ventilation (δ13C) of Lower NADW and Upper NADW, except for a single potential response of (distal) Upper NADW at Caribbean Sea S. 999. Likewise, the distinct change in MOW advection and salt injection after 2.9 Ma was not linked to any coeval change in the ventilation of NADW. In total, the influence of MOW salt injections into the North Atlantic Meridional Overturning Circulation (MOC) may be too small to produce any significant effects

Discovery of a highly energetic pulsar associated with IGR J14003-6326 in a young uncataloged Galactic supernova remnant G310.6-1.6

We report the discovery of 31.18 ms pulsations from the INTEGRAL source IGR J14003-6326 using the Rossi X-ray Timing Explorer (RXTE). This pulsar is most likely associated with the bright Chandra X-ray point source lying at the center of G310.6-1.6, a previously unrecognised Galactic composite supernova remnant with a bright central non-thermal radio and X-ray nebula, taken to be the pulsar wind nebula (PWN). PSR J1400-6325 is amongst the most energetic rotation-powered pulsars in the Galaxy, with a spin-down luminosity of Edot = 5.1E+37 erg.s-1. In the rotating dipole model, the surface dipole magnetic field strength is B_s = 1.1E+12 G and the characteristic age tau_c = P/2Pdot = 12.7 kyr. The high spin-down power is consistent with the hard spectral indices of the pulsar and the nebula of 1.22 +/- 0.15 and 1.83 +/- 0.08, respectively, and a 2-10 keV flux ratio F_PWN/F_PSR ~ 8. Follow-up Parkes observations resulted in the detection of radio emission at 10 and 20 cm from PSR J1400-6325 at a dispersion measure of ~ 560 cm-3 pc, which implies a relatively large distance of 10 +/- 3 kpc. However, the resulting location off the Galactic Plane of ~ 280 pc would be much larger than the typical thickness of the molecular disk, and we argue that G310.6-1.6 lies at a distance of ~ 7 kpc. There is no gamma-ray counterpart to the nebula or pulsar in the Fermi data published so far. A multi-wavelength study of this new composite supernova remnant, from radio to very-high energy gamma-rays, suggests a young (< 1000 yr) system, formed by a sub-energetic (~ 1E+50 ergs), low ejecta mass (M_ej ~ 3 Msun) SN explosion that occurred in a low-density environment (n_0 ~ 0.01 cm-3).Comment: 9 pages, 6 figures, 2 tables. Accepted for publication in ApJ (after responding to referee's comments, expanded version after the radio detection of the pulsar

Changes in Indian Summer Monsoon Using Neodymium (Nd) Isotopes in the Andaman Sea During the Last 24,000 years

Dramatic changes from a cold and dry last glacial to a warm and wet Holocene period intensified the Indian summer monsoon (ISM), resulting in vigorous hydrology and increased terrestrial erosion. Here we present seawater neodymium (Nd) data (expressed in εNd) from Andaman Sea sediments to assess past changes in the ISM and the related impact of Irrawaddy–Salween and Sittoung (ISS) river discharge into the Andaman Sea in the northeastern Indian Ocean. Four major isotopic changes were identified: (1) a gradual increase in εNd toward a more radiogenic signature during the Last Glacial Maximum (22–18 ka), suggesting a gradual decrease in the ISS discharge; (2) a relatively stable radiogenic seawater εNd between 17.2 and 8.8 ka, perhaps related to a stable reduced outflow; (3) a rapid transition to less radiogenic εNd signature after 8.8 ka, reflecting a very wet early–mid-Holocene with the highest discharge; and (4) a decrease in εNd signal stability in the mid–late Holocene. Taking into account the contribution of the ISS rivers to the Andaman Sea εNd signature that changes proportionally with the strengthening (less radiogenic εNd) or weakening (more radiogenic εNd) of the ISM, we propose a binary model mixing between the Salween and Irrawaddy rivers to explain the εNd variability in Andaman Sea sediments. We hypothesize that the Irrawaddy river mainly contributed detrital sediment to the northeastern Andaman Sea for the past 24 ka. Our εNd data shed new light on the regional changes in Indo-Asian monsoon systems when compared with the existing Indian and Chinese paleo-proxy records

Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in very-high-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as sub-sets) and smaller-scale simulations dedicated to individual aspects were carried out and are on-going. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the on-going new round of MC simulations.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at arXiv:1307.223