Location and associated carbon storage of erosional escarpments of seagrass Posidonia mats

Seagrasses of the genus Posidonia can form an irregular seascape due to erosional processes exposing thick walls of organic matter-rich soils. However, little is known about the location and characteristics of these particular formations. Here we provide comprehensive estimates of organic carbon (Corg) storage in Posidonia oceanica and Posidonia australis meadows, while providing insight into their location and mechanisms of formation, and highlighting future research directions. Erosional reef escarpments are restricted to shallow highly productive P. oceanica meadows from the Mediterranean Sea and P. australis meadows from the Indian Ocean, and sustain the existence of Corg-rich deposits in surrounding meadows. The thickness of the mat escarpments can reach up to 3 m and their length can vary from few to hundreds of meters. Mechanisms of formation appear to differ among sites, from naturally-induced escarpments by wave action and/or tidal flow to human-induced escarpments by dredging activities. The inter-twined remains of seagrass shoots within the sediment matrix consolidate the sandy substrate and hold the exposed Posidonia mat escarpments together, maintaining a semi-rigid structure. This phenomenon is unusual but of exceptional importance in marine biogeochemical cycles, revealing the largest Corg sinks among seagrasses worldwide (ranging from 15 to 176 kg Corg m−2 in 2 m-thick mats accumulated at 2–249 g Corg m−2 yr−1 over 300–3000 yr)

Efecto de la carga animal sobre la variación de peso en un potrero sometido a quema controlada en el área de pastizal natural

El objetivo de este trabajo fue detectar que carga animal es capaz de soportar el rebrote de un potrero de pastizal quemado, si el objetivo productivo es sostener vacas de cría en el periodo de gestación y principio de lactación. En la Estancia Bajo Verde, en el Departamento de Toay de la Provincia de La Pampa se realizó un ensayo de pastoreo, con diferentes cargas animales, del rebrote de pastizal natural quemado. Se usaron tres cargas de 0,86; 1,44 Y 2,3 EV/ha año. Los resultados de este ensayo demuestran que el rebrote del pastizal quemado permite al inicio de su pastoreo ganancias individuales superiores a los 0,700 Kg.ha-1 y que estas disminuyen más rápido cuando la carga es mayor. Se mantienen las ganancias de peso vivo por un periodo de 105 días con cargas de 1,44 EV/ha año y solamente la carga de 0,86 EV/ha año cubrió los requerimientos de mantenimiento los 150 días que duró el ensayo.Director: Dr. Edgardo Cerqueira. Cátedra de Producción Lecher

Analysis of colour-magnitude diagrams of rich LMC clusters: NGC 1831

We present the analysis of a deep colour-magnitude diagram (CMD) of NGC 1831, a rich star cluster in the LMC. The data were obtained with HST/WFPC2 in the F555W (~V) and F814W (~I) filters, reaching m_555 ~ 25. We discuss and apply a method of correcting the CMD for sampling incompleteness and field star contamination. Efficient use of the CMD data was made by means of direct comparisons of the observed to model CMDs. The model CMDs are built by an algorithm that generates artificial stars from a single stellar population, characterized by an age, a metallicity, a distance, a reddening value, a present day mass function and a fraction of unresolved binaries. Photometric uncertainties are empirically determined from the data and incorporated into the models as well. Statistical techniques are presented and applied as an objective method to assess the compatibility between the model and data CMDs. By modelling the CMD of the central region in NGC 1831 we infer a metallicity Z = 0.012, 8.75 < log(tau) < 8.80, 18.54 < (m-M)_0 < 18.68 and 0.00 < E(B-V) < 0.03. For the position dependent PDMF slope (alpha = -dlog(Phi(M))/dlog(M)), we clearly observe the effect of mass segregation in the system: for projected distances R < 30 arcsec, alpha ~ 1.7, whereas 2.2 < alpha < 2.5 in the outer regions of NGC 1831.Comment: 12 pages, 14 figure

Stars of extragalactic origin in the solar neighborhood

We computed the spatial velocities and the galactic orbital elements using Hipparcos data for 77 nearest main-sequence F-G-stars with published the iron, magnesium, and europium abundances determined from high dispersion spectra and with the ages estimated from theoretical isochrones. A comparison with the orbital elements of the globular clusters that are known was accreted by our Galaxy in the past reveals stars of extragalactic origin. We show that the relative elemental abundance ratios of r- and \alpha- elements in all the accreted stars differ sharply from those in the stars that are genetically associated with the Galaxy. According to current theoretical models, europium is produced mainly in low mass Type II supernovae (SNe II), while magnesium is synthesized in larger amounts in high mass SN II progenitors. Since all the old accreted stars of our sample exhibit a significant Eu overabundance relative to Mg, we conclude that the maximum masses of the SNII progenitors outside the Galaxy were much lower than those inside it are. On the other hand, only a small number of young accreted stars exhibit low negative ratios $[Eu/Mg] < 0$. The delay of primordial star formation burst and the explosions of high mass SNe II in a relatively small part of extragalactic space can explain this situation. We provide evidence that the interstellar medium was weakly mixed at the early evolutionary stages of the Galaxy formed from a single proto-galactic cloud and that the maximum mass of the SN II progenitors increased in it with time simultaneously with the increase in mean metallicity.Comment: Accepted for 2004, Astronomy Letters, Vol. 30, No. 3, P.148-158 15 pages, 3 figure

ps7 133 exposure response modelling and exposure safety modelling analyses in two phase ii studies of atacicept in sle

Purpose Atacicept targets the B-cell stimulating factors BLyS and APRIL, and has been shown to reduce SLE disease activity. Methods APRIL-SLE (NCT00624338) and ADDRESS II (NCT01972568) were phase II, multicenter studies in patients (pts) with autoantibody-positive SLE randomised (1:1:1) to weekly SC injections of atacicept (75 or 150 mg) or placebo (PBO). In APRIL-SLE, pts had BILAG A/B flare at Screening that was reduced to BILAG C/D before randomization using corticosteroids; the primary endpoint was BILAG A/B flare over 52 weeks. In ADDRESS II, pts had SLEDAI-2K≥6 at Screening; the primary endpoint was SRI-4 response at Week 24. SLE responder index (SRI)−6 response was analysed post-hoc in high disease activity (HDA; SLEDAI-2K≥10) pts. Population pharmacokinetic (PK) model-derived exposure vs the probability of response (BILAG A/B flare, SRI-4, SRI-6), exploratory analysis of exposure vs safety, and population model simulations of serum IgG were analysed. Results Exposure-response modelling suggests a relationship between atacicept exposure and SLE clinical response [figure 1], including serum IgG changes from baseline. The optimal atacicept exposure was AUCtau,ss ≥~1 mg.hr/mL, which is more achievable with weekly SC doses of atacicept 150 mg than 75 mg across a range of body weights. Body weight-based dosing is unlikely to offer any value over a fixed 150 mg dose, based on comparable predicted clinical response. In HDA pts, greater reductions in serum IgG from baseline corresponded to a higher probability of SRI-6 response. Greater IgG reductions from baseline were associated with higher atacicept exposure; however, even at the highest exposure range, mean IgG reductions did not exceed ~40%. There was no association between serious/severe infections and exposure by PK quartile. Conclusions Exposure-response modelling indicated robust relationships between atacicept exposure and clinical response or IgG levels, supporting the proposed mechanism of action for atacicept. Atacicept 150 mg weekly SC is likely to provide an effective level of exposure with an acceptable safety profile. There was no evidence of an increased risk of severe or serious infections at higher exposures. Based on these results, the 150 mg dose merits further evaluation

Seagrass meadows as a globally significant carbonate reservoir

There has been growing interest in quantifying the capacity of seagrass ecosystems to act as carbon sinks as a natural way of offsetting anthropogenic carbon emissions to the atmosphere. However, most of the efforts have focused on the particulate organic carbon (POC) stocks and accumulation rates and ignored the particulate inorganic carbon (PIC) fraction, despite important carbonate pools associated with calcifying organisms inhabiting the meadows, such as epiphytes and benthic invertebrates, and despite the relevance that carbonate precipitation and dissolution processes have in the global carbon cycle. This study offers the first assessment of the global PIC stocks in seagrass sediments using a synthesis of published and unpublished data on sediment carbonate concentration from 403 vegetated and 34 adjacent un-vegetated sites. PIC stocks in the top 1 m of sediment ranged between 3 and 1660 Mg PIC ha(-1), with an average of 654 +/- 24 Mg PIC ha(-1), exceeding those of POC reported in previous studies by about a factor of 5. Sedimentary carbonate stocks varied across seagrass communities, with meadows dominated by Halodule, Thalassia or Cymodocea supporting the highest PIC stocks, and tended to decrease polewards at a rate of -8 +/- 2 Mg PIC ha(-1) per degree of latitude (general linear model, GLM; p \u3c 0.0003). Using PIC concentrations and estimates of sediment accretion in seagrass meadows, the mean PIC accumulation rate in seagrass sediments is found to be 126.3 +/- 31.05 g PIC m(-2) yr(-1). Based on the global extent of seagrass meadows (177 000 to 600 000 km(2)), these ecosystems globally store between 11 and 39 Pg of PIC in the top metre of sediment and accumulate between 22 and 75 Tg PIC yr(-1), representing a significant contribution to the carbonate dynamics of coastal areas. Despite the fact that these high rates of carbonate accumulation imply CO2 emissions from precipitation, seagrass meadows are still strong CO2 sinks as demonstrated by the comparison of carbon (PIC and POC) stocks between vegetated and adjacent un-vegetated sediments

Carbon enrichment of the evolved stars in the Sagittarius dwarf spheroidal

We present spectra of 1142 colour-selected stars in the direction of the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy, of which 1058 were taken with VLT/FLAMES multi-object spectrograph and 84 were taken with the SAAO Radcliffe 1.9-m telescope grating spectrograph. Spectroscopic membership is confirmed (at >99% confidence) for 592 stars on the basis of their radial velocity, and spectral types are given. Very slow rotation is marginally detected around the galaxy's major axis. We identify five S stars and 23 carbon stars, of which all but four carbon stars are newly-determined and all but one (PQ Sgr) are likely Sgr dSph members. We examine the onset of carbon-richness in this metal-poor galaxy in the context of stellar models. We compare the stellar death rate (one star per 1000-1700 years) to known planetary nebula dynamical ages and find that the bulk population produce the observed (carbon-rich) planetary nebulae. We compute average lifetimes of S and carbon stars as 60-250 and 130-500 kyr, compared to a total thermal-pulsing asymptotic giant branch lifetime of 530-1330 kyr. We conclude by discussing the return of carbon-rich material to the ISM.Comment: 14 pages, 10 figures, accepted MNRA

Field Blue Stragglers and Related Mass Transfer Issues

This chapter contains my impressions and perspectives about the current state of knowledge about field blue stragglers (FBS) stars, drawn from an extensive literature that I searched. I conclude my review of issues that attend FBS and mass transfer, by a brief enumeration of a few mildly disquieting observational facts.Comment: Chapter 4, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe