Brane World Cosmologies and Statistical Properties of Gravitational Lenses

Brane world cosmologies seem to provide an alternative explanation for the present accelerated stage of the Universe with no need to invoke either a cosmological constant or an exotic \emph{quintessence} component. In this paper we investigate statistical properties of gravitational lenses for some particular scenarios based on this large scale modification of gravity. We show that a large class of such models are compatible with the current lensing data for values of the matter density parameter $\Omega_{\rm{m}} \leq 0.94$ ($1\sigma$). If one fixes $\Omega_{\rm{m}}$ to be $\simeq 0.3$, as suggested by most of the dynamical estimates of the quantity of matter in the Universe, the predicted number of lensed quasars requires a slightly open universe with a crossover distance between the 4 and 5-dimensional gravities of the order of $1.76 H_o^{-1}$.Comment: 6 pages, 3 figures, revte

Spatial and temporal variation of fish assemblage associated with aquatic macrophyte patches in the littoral zone of the Ayapel Swamp Complex, Colombia

ABSTRACT: Aim: The purpose of the present study was to examine spatial and temporal variation in fish assemblage structure associated with aquatic macrophytes in the littoral zone of the ASC. Methods: Specimens were caught between January 2008 and February 2009, over four limnimetric moments, using both cast net and seine net. Data on the temperature, electrical conductivity, pH and dissolved oxygen was recorded for the characterization of the water mass in the sites. Results: A total of 34,151 specimens from 44 species were collected. The most abundant species were Eigenmannia virescens, Astyanax caucanus, Astyanax fasciatus, Roeboides dayi and Cyphocharax magdalenae, which together accounted for more than 75% of the sample. Temporal and spatial comparisons showed variation in the environmental conditions and highlighted the existence of heterogeneous abiotic conditions (p0.05) regarding the fish assemblage structure. The multivariate analysis showed no significant relationship between existing environmental conditions and the fish assemblage (p=0.04). The analysis also showed the absence of a relationship between the fish assemblage and environmental variables with respect to the flood pulse and sampling sites (p>0.05). Conclusion: The uniformity of the fish communities that inhabit aquatic macrophyte patches in the littoral region of the ASC may be related to the availability of suitable habitat in structural terms, that probably supports a more abundant and varied wildlife

Using tetraether lipids archived in North Sea Basin sediments to extract North Western European Pliocene continental air temperatures

The Pliocene is often regarded as a suitable analogue for future climate, due to an overall warmer climate (2–3 °C) coupled with atmospheric CO2 concentrations largely similar to present values (∼400 ppmv). Numerous Pliocene sea surface temperature (SST) records are available, however, little is known about climate in the terrestrial realm. Here we generated a Pliocene continental temperature record for Northwestern Europe based on branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids stored in a marine sedimentary record from the western Netherlands. The total organic carbon (TOC) content of the sediments and its stable carbon isotopic composition () indicate a strong transition from primarily marine derived organic matter (OM) during the Pliocene, to predominantly terrestrially derived OM after the transition into the Pleistocene. This trend is supported by the ratio of branched and isoprenoid tetraethers (BIT index). The marine–terrestrial transition indicates a likely change in brGDGT sources in the core, which may complicate the applicability of the brGDGT paleotemperature proxy in this setting. Currently, the application of the brGDGT-based paleothermometer on coastal marine sediments has been hampered by a marine overprint. Here, we propose a method to disentangle terrestrial and marine sources based on the degree of cyclization of tetramethylated brGDGTs (#rings) using a linear mixing model based on the global soil calibration set and a newly developed coastal marine temperature transfer function. Application of this method on our brGDGT record resulted in a ‘corrected’ terrestrial temperature record (MATterr). This latter record indicates that continental temperatures were ∼12–14 °C during the Early Pliocene, and 10.5–12 °C during the Mid Pliocene, confirming other Pliocene pollen based terrestrial temperature estimates from Northern and Central Europe. Furthermore, two colder (Δ 5–7 °C) periods in the Pliocene MATterr record show that the influence of Pliocene glacials reached well into NW Europe

A new species of electric knifefish, genus Compsaraia

A new species of the neotropical electric fish genus Compsaraia is described from the western Amazon of Peru and Brazil. Compsaraia samueli is distinguishable from all other apteronotids by sexual dimorphism in which mature males exhibit extreme elongation and slenderness of the snout and jaws. Compsaraia samueli is readily distinguishable from its only congener, C. compsa, by more caudal-fin rays (1718 vs. 1316), a shorter caudal peduncle (mean length 9% vs. 34% body length to end of anal fin), a less tapering body shape in lateral profile (mean ratio of body depth at origins of anal fin and dorsal organ 93% vs. 75%), and a smaller maximum adult body size (230 vs. 305 mm). The genus Compsaraia is readily separated from other apteronotids by a pale antorbital stripe and a pale L-shaped patch over the supratemporal canal. The phylogenetic position of C. samueli is estimated by inclusion in a previously published data matrix of osteological and other morphological characters. Comparisons of the cranial bones in apteronotids shows the derived morphology of C. samueli to be a composite of three developmentally and phylogenetically discrete characters: (1) positive allometric growth before sexual maturity in both sexes of the pre-orbital region of the neurocranium, (2) positive allometric growth of the (oral) jaws, and (3) secondary sexual dimorphism of snout and jaw morphology. The genus Compsaraia represents one of at least three phylogenetically independent cases of snout elongation and one of at least four cases of jaw elongation within the Apteronotidae. Compsaraia samueli also represents one of at least four cases of secondary sexual dimorphism in snout and jaw length within the Apteronotidae. The phylogenetic distribution of snout and jaw characters within the Apteronotidae suggests the influence of both sexual and trophic functional influences on the evolution of head morphology. © 2009 Copyright The Natural History Museum

Early-middle Eocene chronology of the Southern Ocean: magnetostratigraphic data from the South Island of New Zealand

During the Paleogene the Earth experienced a pronounced warming trend culminating with the early Eocene climatic optimum (EECO, ~52-50 Ma), which was followed by a long-term cooling trend over the middle-late Eocene. This long-term climate evolution was punctuated by several transient (~10^3-5 yr) hyperthermal events (e.g. Paleocene Eocene thermal maximum). Even though great advances have been made in the last few years in understanding the paleoclimate history of the southwestern Pacific Ocean and the implications on the sedimentation patterns, a precise correlation between sites and global events is still missing. This is mainly because of the poor preservation of calcareous nannofossils, diachronous ranges of index species, and a lack of a good magnetic polarity reversals record. We present preliminary early-middle Eocene magnetostratigraphy from the Mid Waipara and the Mead Stream marine sections, cropping out in the South Island of New Zealand. These sections provide the best-known record of oceanic changes in the southern Pacific high-latitude (50-60\ub0S) for this time period. Magnetostratigraphic data, integrated with new and published biostratigraphy, indicates that the sampled ~45 m of the Mid Waipara section straddles polarity Chrons from C23n to C21n (~51.5-47 Ma), with an average sediment accumulation rate of ~9 m/Myr, calculated by means of correlation with the GPTS2004 time scale. This robust chronological framework allow to constrain in time the paleotemperature dataset of Hollis et al. (EPSL 349-350, pp. 53-56, 2012), confirming that the Ashley Mudstone formation of Mid Waipara includes at least the upper part of the EECO and the early-middle Eocene transition. The sampled ~320 m of the Mead Stream section, which comprises the three upper member of the Amuri Limestone (Lower Marl, Upper Limestone and Upper Marl), encompass polarity Chrons from C24r to C18r (~55-40 Ma), with an average sedimentation rate of ~17 m/Myr. We confirm evidence from carbon isotopes (Slotnick et al., J. Geol. 120, 2012) and biostratigraphy that the upper marl-dominated parts of Lower Marl and Upper Marl may be correlated with the EECO and MECO (middle Eocene climatic optimum), respectively. This is a major contribution to the knowledge about the early Paleogene Earth's climate and environmental dynamics

Using tetraether lipids archived in North Sea Basin sediments to extract North Western European Pliocene continental air temperatures

The Pliocene is often regarded as a suitable analogue for future climate, due to an overall warmer climate (2–3 °C) coupled with atmospheric CO2 concentrations largely similar to present values (∼400 ppmv). Numerous Pliocene sea surface temperature (SST) records are available, however, little is known about climate in the terrestrial realm. Here we generated a Pliocene continental temperature record for Northwestern Europe based on branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids stored in a marine sedimentary record from the western Netherlands. The total organic carbon (TOC) content of the sediments and its stable carbon isotopic composition () indicate a strong transition from primarily marine derived organic matter (OM) during the Pliocene, to predominantly terrestrially derived OM after the transition into the Pleistocene. This trend is supported by the ratio of branched and isoprenoid tetraethers (BIT index). The marine–terrestrial transition indicates a likely change in brGDGT sources in the core, which may complicate the applicability of the brGDGT paleotemperature proxy in this setting. Currently, the application of the brGDGT-based paleothermometer on coastal marine sediments has been hampered by a marine overprint. Here, we propose a method to disentangle terrestrial and marine sources based on the degree of cyclization of tetramethylated brGDGTs (#rings) using a linear mixing model based on the global soil calibration set and a newly developed coastal marine temperature transfer function. Application of this method on our brGDGT record resulted in a ‘corrected’ terrestrial temperature record (MATterr). This latter record indicates that continental temperatures were ∼12–14 °C during the Early Pliocene, and 10.5–12 °C during the Mid Pliocene, confirming other Pliocene pollen based terrestrial temperature estimates from Northern and Central Europe. Furthermore, two colder (Δ 5–7 °C) periods in the Pliocene MATterr record show that the influence of Pliocene glacials reached well into NW Europe

Early to middle Eocene magneto-biochronology of the southwest Pacific Ocean and climate influence on sedimentation: new data from the Mead Stream section (Marlborough, New Zealand)

The Mead Stream section (South Island, New Zealand) consists of a 650-m-thick series of continuous and well-exposed strata deposited on a South Pacific continental slope from the Late Cretaceous to the middle Eocene. We examined the uppermost Paleocene-middle Eocene part of the Mead Stream section, which consists of ~360 m of limestone and marl, for detailed magnetic polarity stratigraphy, calcareous nannofossil, and foraminifera biostratigraphy. Magneto-biostratigraphic data indicate that the section straddles magnetic polarity Chrons from C24r to C18n, calcareous nannofossil Zone from NP9a to NP17 (CNP11-CNE15 following a recently revised Paleogene zonation), and from the Waipawan to the Bortonian New Zealand stages (i.e., from the base of the Ypresian to the Bartonian international stages), encompassing 17 Myr (56-39 Ma) of Southwest Pacific Ocean history. The ages of calcareous nannofossil biohorizons are consistent with low to mid-latitude data from the literature, indicating that during the early-middle Eocene the low-mid latitude calcareous nannofossil domain extended at least to ~50-55\ub0S in the South Pacific. Correlation of the magnetic polarity stratigraphy from the Mead Stream section with the geomagnetic polarity time scale allows us to derive the sediment accumulation rates (SAR), which range between 8 and 44 m/Myr. Comparing the SAR with paleotemperature proxy records, we found that two intervals of increased SAR occurred during the early Eocene climatic optimum (EECO; 52-50 Ma) and during the transient climate warming culminating with the middle Eocene climatic optimum (MECO; 40.5 Ma). This correlation indicates that the climate evolution of the early-middle Eocene is recorded in the sedimentation patterns whereby times of warmer climate promote continental weathering, transportation, and accumulation of terrigenous sediments

Large amplitude variations in carbon cycling and terrestrial weathering during the latest Paleocene and earliest Eocene

Global temperatures rose ~6°C from the late Paleocene ca. 58 Ma to the Early Eocene Climatic Optimum (EECO) ca. 52–50 Ma. Superimposed, were certainly two geologically brief (< 200 kyr) intervals of extreme warming, the Paleocene-Eocene thermal maximum (PETM) and Eocene thermal maximum 2 (ETM-2 or H-1); at least four more events, H-2, I-1, I-2 and K/X, probably occurred. Both the longterm rise and short-term “hyperthermals” have been linked to massive injections of 13C-depleted carbon into the ocean-atmosphere system and greater continental weathering. However, relationships remain uncertain, principally because detailed and coupled proxy records do not extend across the entire interval of interest. Mead Stream, New Zealand, exposes a ~650 m-thick sequence of limestone originally deposited on an upper continental slope from the late Cretaceous to the middle Eocene. Previous work has provided accurate ages for this expanded section, and has shown that the PETM, ETM-2, H-2, I-1 and I-2 hyperthermals are marked by pronounced negative carbon isotope excursions (CIEs) and clay-rich horizons (marls), the latter caused by excess terrigenous dilution. 283 new samples were collected, mostly above the I-2 event; these were analyzed for carbonate content, lithology, and bulk carbonate carbon isotopes. A greatly expanded (100 m-thick) unit represented by a series of marl beds lies above I-2 and correlates to the EECO. Carbonate contents are generally 60–90% throughout the studied interval, with lows being marls. The δ13C is generally low but, in detail, represents a series of negative CIEs with magnitudes ranging between 0.2–0.6‰. Of these, the K/X/ETM-3 event is the most pronounced (0.6‰). The late Paleocene-early Eocene δ13C record at Mead Stream is remarkably similar to that generated at Site 1262 at Walvis Ridge (south Atlantic), except that lows in δ13C span intervals of relatively high sedimentation (terrigenous dilution) rather than intervals of relatively low sedimentation (carbonate dissolution). We suggest that over ~6 million years, there was a series of short-term climate perturbations, each characterized by massive carbon input and greater continental weathering. The suspected link involves global warming and enhanced seasonality in precipitation. We are evaluating this model further by identifying hyperthermal events in DSDP sites from the Indian Ocean, and assessing whether they are related to carbonate dissolution or siliciclastic dilutio