Long-term Observational Program Research Articles

Dendrochemical indicators of tree rings reveal historical soil acidification in Swiss forest stands

The deposition of acidifying nitrogen and sulphur compounds from agriculture and fossil fuel combustion has drastically altered the chemical balance of forest soils in many regions of the world, leading to soil acidification with negative impacts on nutrient availability and thus also on tree vitality. The change of nutrient concentrations in the soil solution can be assessed by long-term investigations, however meaningful indicators, reflecting environmental changes, are needed to compare the current nutrient status with past values. We used dendrochemical indicators in stem wood of different tree species to access the impact of acidifying depositions on soil quality and tree nutrition. We selected 328 stem wood samples from 96 trees of Norway spruce (Picea abies), European beech (Fagus sylvatica), Sessile oak (Quercus petrea) and English oak (Quercus robur) from 22 forest sites, which are part of the long-term Intercantonal Forest Observation Program in Switzerland. Four time periods of 20 years were defined according to the emissions of air pollutants between 1910 and 2017. Our results showed a trend of increasing Al concentrations in tree rings of spruce peaking in the most recent time period (2000–2017). Mn and Ca concentrations in spruce and beech wood have decreased significantly throughout the time period 1910–2017. These dendrochemical indicators depended on the soil pH, with higher Al and lower Mn and Ca concentrations for soils with a low pH (pH<4.2). In oak trees the observed dendrochemical changes are confounded with dendrochemical differences between heartwood and sapwood. K and Mg showed inconsistent patterns in all three tree species, which are probably caused by translocation within the stem discs. With the use of piecewise structural equation models (SEM) we highlighted the direct and indirect influences of N deposition on element concentrations in stem wood. The data suggest a relation between increased N deposition and lower base saturation values in the forest soils for all three tree species, which were linked to higher Al concentrations in spruce and lower Mn concentrations in spruce and beech. The relation between Al concentrations in tree rings of Norway spruce and measured base saturation was used to reconstruct past soil base saturation values. It revealed a progressive soil acidification in the long-term forest observation sites. These reconstructed base saturation values were further used to validate modelled values from dynamic biogeochemical models such as SAFE/ForSAFE. This comparison pointed out possible shortcomings such as the lack of organic complexation in those models. Taken together, our analyses showed that element concentrations of Al, Mn, Ca in Norway spruce and European beech stem wood were suitable dendrochemical indicators of environmental change due to soil acidification, as they reflect both direct and indirect effects of air pollutants and chemical soil properties.

Velocity dispersion and dynamical masses for 388 galaxy clusters and groups

The second catalogue of Planck Sunyaev-Zeldovich (SZ) sources, hereafter PSZ2, represents the largest galaxy cluster sample selected by means of their SZ signature in a full-sky survey. Using telescopes at the Canary Island observatories, we conducted the long-term observational program 128- MULTIPLE-16/15B (hereafter LP15), a large and complete optical follow-up campaign of all the unidentified PSZ2 sources in the northern sky, with declinations above −15° and no correspondence in the first Planck catalogue PSZ1. This paper is the third and last in the series of LP15 results, after Streblyanska et al. (2019, A&amp;A, 628, A13) and Aguado-Barahona et al. (2019, A&amp;A, 631, A148), and presents all the spectroscopic observations of the full program. We complement these LP15 spectroscopic results with Sloan Digital Sky Survey archival data and other observations from a previous program (ITP13-08), and present a catalogue of 388 clusters and groups of galaxies including estimates of their velocity dispersion. The majority of them (356) are optical counterparts of PSZ2 sources. A subset of 297 of those clusters are used to construct the MSZ − Mdyn scaling relation based on the estimated SZ mass from Planck measurements and our dynamical mass estimates. We discuss and correct for different statistical and physical biases in the estimation of the masses, such as the Eddington bias when estimating MSZ and the aperture and the number of galaxies used to calculate Mdyn. The SZ-to-dynamical mass ratio for those 297 PSZ2 clusters is (1 − B) = 0.80 ± 0.04 (stat) ± 0.05 (sys), with only marginal evidence for a possible mass dependence for this factor. Our value is consistent with previous results in the literature, but is associated with a significantly smaller uncertainty due to the use of the largest sample size for this type of study.

Soil solution in Swiss forest stands: A 20 year's time series.

Soil solution chemistry is influenced by atmospheric deposition of air pollutants, exchange processes with the soil matrix and soil-rhizosphere-plant interactions. In this study we present the results of the long-term Intercantonal Forest Observation Program in Switzerland with soil solution measurements since 1998 on a current total of 47 plots. The forest sites comprise two major forest types of Switzerland including a wide range of ecological gradients such as different nitrogen (N) deposition and soil conditions. The long-term data set of 20 years of soil solution measurements revealed an ongoing, but site-specific soil acidification. In strongly acidified soils (soil pH below 4.2), acidification indicators changed only slowly over the measured period, possibly due to high buffering capacity of the aluminum buffer (pH 4.2-3.8). In contrast, in less acidified sites we observed an increasing acidification rate over time, reflected, for example, by the continuous decrease in the ratio of base cations to aluminum (BC/Al ratio). Nowadays, the main driver of soil acidification is the high rate of N deposition, causing cation losses and hampering sustainable nutrient balances for tree nutrition. Mean nitrate leaching rates for the years 2005-2017 were 9.4 kg N ha-1 yr-1, ranging from 0.04 to 53 kg N ha-1 yr-1. Three plots with high N input had a remarkable low nitrate leaching. Both N deposition and nitrate leaching have decreased since 2000. However, the latter trend may be partly explained due to increased drought in recent years. Nonetheless, those high N depositions are still affecting the majority of the forest sites. Taken together, this study gives evidence of anthropogenic soil acidification in Swiss forest stands. The underlying long-term measurements of soil solution provides important information on nutrient leaching losses and the impact climate change effects such as droughts. Furthermore, this study improves the understanding of forest management and tree mortality regarding varying nitrate leaching rates.

Future HAB science: Directions and challenges in a changing climate

There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends.

Diapause within the Context of Life-History Strategies in Calanid Copepods (Calanoida: Crustacea).

Post-embryonic diapause in copepods is an adaptation that allows species in the copepod family Calanidae to thrive in high-latitude environments by transforming a short spring phytoplankton bloom into large numbers of lipid-rich individuals capable of surviving a long period of starvation. The copepods, with their high-energy lipid reservoirs, are a critical food source for higher trophic levels, making the Calanidae a key component of high-latitude marine ecosystems. The physiological ecology of the developmental program remains poorly understood. However, new studies using high-throughput RNA sequencing approaches are giving detailed access to physiological status by generating gene expression profiles for both field-collected and laboratory-incubated individuals. These are beginning to characterize the diapause phenotype, elucidate the transcriptional and physiological progression through the diapause program, and illustrate the effects of organism-environment interactions. This paper reviews gene expression profiling studies on the life cycle and diapause program of Neocalanus flemingeri Miller (1988) that were conducted as part of a long-term observation program in the northern Gulf of Alaska. It summarizes recent findings and relates them to the ecology of this species and to that of other calanids.

Optical validation and characterization of Planck PSZ2 sources at the Canary Islands observatories

Aims. The second catalogue of Planck Sunyaev–Zeldovich (SZ) sources, hereafter PSZ2, is the largest sample of galaxy clusters selected through their SZ signature in the full sky. At the time of publication, 21% of these objects had no known counterpart at other wavelengths. Using telescopes at the Canary Island observatories, we conducted the long-term observational programme 128-MULTIPLE-16/15B (hereafter LP15), a large and complete optical follow-up campaign of all the unidentified PSZ2 sources in the northern sky, with declinations above −15° and no correspondence in the first Planck catalogue PSZ1. The main aim of LP15 is to validate all those SZ cluster candidates, and to contribute to the characterization of the actual purity and completeness of full Planck SZ sample. In this paper, we describe the full programme and present the results of the first year of observations. Methods. The LP15 programme was awarded 44 observing nights, spread over two years in three telescopes at the Roque de los Muchachos Observatory. The full LP15 sample comprises 190 previously unidentified PSZ2 sources. For each target, we performed deep optical imaging and spectroscopy. Our validation procedure combined this optical information with SZ emission as traced by the publicly available Planck Compton y-maps. The final classification of the new galaxy clusters as optical counterparts of the SZ signal is established according to several quantitative criteria based on the redshift, velocity dispersion, and richness of the clusters. Results. This paper presents the detailed study of 106 objects out of the LP15 sample, corresponding to all the observations carried out during the first year of the programme. We confirmed the optical counterpart for 41 new PSZ2 sources, 31 of them being validated using also velocity dispersion based on our spectroscopic information. This is the largest dataset of newly confirmed PSZ2 sources without any previous optical information. All the confirmed counterparts are rich structures (i.e. they show high velocity dispersion), and are well aligned with the nominal Planck coordinates (i.e. ∼70% of them are located at less than 3′ distance). In total, 65 SZ sources are classified as unconfirmed, 57 of them being due to the absence of an optical over-density, and eight of them due to a weak association with the observed SZ decrement. Most of the sources with no optical counterpart are located at low galactic latitudes and present strong galactic cirrus in the optical images, the dust contamination being the most probable explanation for their inclusion in the PSZ2 catalogue.

Characterization of a subsample of the Planck SZ source cluster catalogues using optical SDSS DR12 data

Aims. The Planck catalogues of Sunyaev –Zeldovich (SZ) sources, PSZ1 and PSZ2, are the largest catalogues of galaxy clusters selected through their SZ signature in the full sky. In 2013, we started a long-term observational programme at Canary Island observatories with the aim of validating ∼500 unconfirmed SZ sources. In this work we present results of the initial pre-screening of possible cluster counterparts using photometric and spectroscopic data of the Sloan Digital Sky Survey DR12. Our main aim is to identify previously unconfirmed PSZ2 cluster candidates and to contribute in the determination of the actual purity and completeness of Planck SZ source sample. Methods. Using the latest version of the PSZ2 catalogue, we selected all sources overlapping with the SDSS DR12 footprint and without redshift information. We validated these cluster fields following optical criteria (mainly distance with respect to the Planck pointing, magnitude of the brightest cluster galaxy, and cluster richness), and combined these criteria with the profiles of the Planck Compton y-maps. This combined procedure allows for a more robust identification of optical counterparts compared to simply cross-matching with existing SDSS cluster catalogues that have been constructed from earlier SDSS data releases. Results. The sample contains new redshifts for 37 Planck galaxy clusters that were not included in the original release of PSZ2 Planck catalogue. We detect three cases as possible multiple counterparts. We show that a combination of all available information (optical images and profile of SZ signal) can provide correct associations between the observed Planck SZ source and the optically identified cluster. We also show that Planck SZ detection is very sensitive even to high-z (z &gt; 0.5) clusters. In addition, we also present updated spectroscopic information for 34 Planck PSZ1 sources (33 previously photometrically confirmed and 1 new identification).

Interdecadal trends in ocean ambient sound at seven sites in the northern Pacific Ocean basin

A long-term observation program begun in approximately 1994 has amassed time-series of ambient sound short-time spectra from omni-directional hydrophones deployed on the ocean floor at seven locations in the northern Pacific Ocean. Each time-series consists of spectra estimated every 5 min over a useful band of 10–500 Hz, thereby encompassing the vocalizations of baleen whales, the anthropogenic contribution of ship traffic noise, and wind/wave noise due to sea surface processes. Simple linear trend lines show that traffic noise in the northern and northwestern reaches of the Pacific has increased by as much as 3 to 4 dB during this program. In the eastern North Pacific, however, the ambient sound shows a decrease of about 3 dB. The number of ships in the world merchant fleet increased by approximately 25% over this period. This change is insufficient to explain the increases in noise levels along northern and northwestern regions, and provides no explanation for the decreases observed in the north-east. The traffic noise field is evidently dependent on more complex temporal and geographical patterns of shipping traffic. [Work supported by ONR.]

The GAPS programme with HARPS-N at TNG

A long-term multi-purpose observational programme has started with HARPS-N@TNG aimed to characterise the global architectural properties of exoplanetary systems. In this first paper we fully characterise the transiting system Qatar-1. We exploit HARPS-N high-precision radial velocity measurements obtained during a transit to measure the Rossiter-McLaughlin effect in the Qatar-1 system, and out-of-transit measurements to redetermine the spectroscopic orbit. New photometric transit light-curves are analysed and a spectroscopic characterisation of the host star atmospheric parameters is performed based on various methods (line equivalent width ratios, spectral synthesis, spectral energy distribution). We achieved a significant improvement in the accuracy of the orbital parameters and derived the spin-orbit alignment of the system; this information, combined with the spectroscopic determination of the host star properties, allows us to derive the fundamental physical parameters for star and planet (masses and radii). The orbital solution for the Qatar-1 system is consistent with a circular orbit and the system presents a sky-projected obliquity of lambda = -8.4+-7.1 deg. The planet, with a mass of 1.33+-0.05 M_J, is found to be significantly more massive than previously reported. The host star is confirmed to be metal-rich ([Fe/H]= 0.20+-0.10) and slowly rotating (vsinI = 1.7+-0.3 km/s), though moderately active, as indicated by strong chromospheric emission in the Ca II H&K line cores (logR'_HK about -4.60). The system is well aligned and fits well within the general lambda vs Teff trend. We definitely rule out any significant orbital eccentricity. The evolutionary status of the system is inferred based on gyrochronology, and the present orbital configuration and timescale for orbital decay are discussed in terms of star-planet tidal interactions.

Detection of Laplace-resonant three-planet systems from transit timing variations

Transit timing variations (TTVs) are useful to constrain the existence of perturbing planets, especially in resonant systems where the variations are strongly enhanced. Here we focus on Laplace-resonant three-planet systems, and assume the inner planet transits the star. A dynamical study is performed for different masses of the three bodies, with a special attention to terrestrial planets. We consider a maximal time-span of ~ 100 years and discuss the shape of the inner planet TTVs curve. Using frequency analysis, we highlight the three periods related to the evolution of the system: two periods associated with the Laplace-resonant angle and the third one with the precession of the pericenters. These three periods are clearly detected in the TTVs of an inner giant planet perturbed by two terrestrial companions. Only two periods are detected for a Jupiter-Jupiter-Earth configuration (the ones associated with the giant interactions) or for three terrestrial planets (the Laplace periods). However, the latter system can be constrained from the inner planet TTVs. We finally remark that the TTVs of resonant three or two Jupiter systems mix up, when the period of the Laplace resonant angle matches the pericenter precession of the two-body configuration. This study highlights the importance of TTVs long-term observational programs for the detection of multiple-planet resonant systems.

The nucleus of Comet 67P/Churyumov-Gerasimenko

Context. Comet 67P/Churyumov-Gerasimenko is the target of the European Space Agency Rosetta spacecraft rendez-vous mission. Detailed physical characteristation of the comet before arrival is important for mission planning as well as providing a test bed for ground-based observing and data-analysis methods.Aims. To conduct a long-term observational programme to characterize the physical properties of the nucleus of the comet, via ground-based optical photometry, and to combine our new data with all available nucleus data from the literature.Methods. We applied aperture photometry techniques on our imaging data and combined the extracted rotational lightcurves with data from the literature. Optical lightcurve inversion techniques were applied to constrain the spin state of the nucleus and its broad shape. We performed a detailed surface thermal analysis with the shape model and optical photometry by incorporating both into the new Advanced Thermophysical Model (ATPM), along with all available Spitzer 8–24 μ m thermal-IR flux measurements from the literature.Results. A convex triangular-facet shape model was determined with axial ratios b /a = 1.239 and c /a = 0.819. These values can vary by as much as 7% in each axis and still result in a statistically significant fit to the observational data. Our best spin state solution has P sid = 12.76137 ± 0.00006 h, and a rotational pole orientated at Ecliptic coordinates λ = 78°(±10°), β = + 58°(±10°). The nucleus phase darkening behaviour was measured and best characterized using the IAU HG system. Best fit parameters are: G = 0.11 ± 0.12 and H R (1,1,0) = 15.31 ± 0.07. Our shape model combined with the ATPM can satisfactorily reconcile all optical and thermal-IR data, with the fit to the Spitzer 24 μ m data taken in February 2004 being exceptionally good. We derive a range of mutually-consistent physical parameters for each thermal-IR data set, including effective radius, geometric albedo, surface thermal inertia and roughness fraction. Conclusions. The overall nucleus dimensions are well constrained and strongly imply a broad nucleus shape more akin to comet 9P/Tempel 1, rather than the highly elongated or “bi-lobed” nuclei seen for comets 103P/Hartley 2 or 8P/Tuttle. The derived low thermal inertia of K-1 s−1/2 is comparable with that measured for other comets scaled to similar heliocentric distances, and implies a surface regolith finer than lunar surface material.

My Acid Cruise

My Acid Cruise Nancy Lord (bio) I thought I'd grow up to be a scientist. As a child I was infatuated with pet mice and guppies and studying trees from the shapes of their leaves. And don't I remember, as a kindergartner, being ushered into the school basement to watch on TV the Russian satellite, Sputnik, soaring into outer space? We were lectured on the spot to start studying science and math, or the Russians would pound us all into the ground. There was no higher goal than to reach for the stars or dive to the bottom of the sea, to comprehend the universe. The Alan Shepards and Jacques Cousteaus who did these things were our heroes. King science and its applied technology informed our lives and the promise that was the future. Who knew, in that bright and shining time, that so much in our culture and politics would soon turn corrosive? But along the way, I found that science—the actual doing of it— is tedious, at least compared with watching guppies eat their young. The collection of data is a repetitive business, the same careful measurements over and over, across hours and days, years, decades. You gain small increments of understanding—or perhaps not. Your only understanding may be one of failure: an inability to find pattern or meaning, the need for more data, additional data sets, a new theory. We don't have time for this. We're an impatient people. I'm speaking of Americans now. We don't trust science, in any case. We don't understand it, which is reason enough not to trust it or the people in the white coats who, surely, can manipulate numbers any way they want as part of that vast scientific conspiracy to get rich off government funding. Why spend tax dollars for a bunch of wonky people to measure cow farts or fuss over some bit of whatever floating around in the ocean? We know what we know, anyway. We don't need those fancy-pants, with their heads in clouds and all those crazy charts and numbers, to tell us how to live. But wait. We don't understand irony either. [End Page 90] Instead of a scientist, I became a writer of the creative sort, but then— wouldn't you know?—the fish and the trees and the stars all kept calling to me and, increasingly, seemed to demand attention for more than their own sakes. In a crowded, warming world, I was drawn back both to the wonders of nature and to wanting to better understand the systems we all rely on. And so I find myself, the lone writer among scientists, aboard the research vessel Tiglax, on Alaska's Seward Line. September along the southern coast is often stormy—not an ideal time to boat on the open ocean. But here I am. The Seward Line: an imaginary straight line that extends from the mouth of Resurrection Bay south of Seward, Alaska, 150 miles into the Gulf of Alaska, to where the continental shelf falls off into very deep water. The Seward Line: also the name of a long-term observation program that studies changes in the marine system, especially in relationship to climate variability. There are twenty-two stations spaced along the Line, and we—a team from the University of Alaska Fairbanks, made up mostly of volunteer graduate students, with a couple of professors and me, a writer invited to help bring some public awareness to the work—stop at each station to collect basic oceanographic data. When we finish, we duck into Prince William Sound and do the same at stations there. We are enormously lucky on this week-long cruise. The sea has been so calm that the other day we drifted with a pair of fin whales and could see, looking down through the glassy blue surface, the entire body length of the whales as they passed by and under us. The larger one, when it lined up beside us, approached our own 120-foot length. Pale chevron markings descended its dark back. Its white right jaw, distinct from its dark left one, flashed...

Impact of Groins on Beach Morphology: A Case Study near Gopalpur Port, East Coast of India

Abstract MOHANTY, P.K.; PATRA, S.K.; BRAMHA, S.; SETH, B.; PRADHAN, U.; BEHERA, B.; MISHRA, P., and PANDA, U.S., 2012. Impact of groins on beach morphology: a case study near Gopalpur Port, east coast of India. Gopalpur Port is being developed as an all-weather open seaport from a fair-weather port which has existed since 1987. Two groins, a 530-m south groin and a 370-m north groin, were constructed during the periods from August 2007 to November 2009 and October 2007 to September 2008, respectively, on the north and south of the 500-m jetty which existed earlier. Port authorities are planning to construct a southern breakwater and a series of seven northern groins. Therefore, it is essential to assess the impacts of coastal structures on beach morphology and shoreline change in the present context and to predict future trends. To achieve this, a long-term observational programme has been conducted since May 2008. Observations include beach profile, shoreline change (berm position), littoral environment ...

The prevalence and impact of scoliosis in Pompe disease: Lessons learned from the Pompe Registry

Pompe disease is a rare, autosomal recessive, progressively debilitating, and often fatal neuromuscular disorder. While scoliosis is common in many other neuromuscular disorders, there is little information on its prevalence and impact in Pompe disease. To further our understanding, we performed a cross-sectional analysis of data from the Pompe Registry, a multinational, long-term observational program that contains the largest collection of data in the world of patients with Pompe disease. In this analysis, patients were categorized by age during the natural history period (defined as the time when patients never received enzyme replacement therapy) and by age at onset of symptoms as infants (≤0 to <2years of age); children (≥2 to <13years of age); juveniles (≥13 to <20years of age); and adults (≥20years of age). Scoliosis was defined by clinical assessment, X-ray of the spine, or both. Data on scoliosis were available in the majority of patients enrolled in the registry as of September 2010 (711/873, 81.4%). Scoliosis was present in a third of all patients with scoliosis data (235/711, 33%) in the Pompe Disease Registry. Scoliosis was found more frequently in patients with onset of Pompe symptoms as children (57.0%) and juveniles (52.9%) than in patients with onset of symptoms as adults (24.8%). Only 18.4% (38/206) of patients with onset of symptoms as infants were reported as having scoliosis. Scoliosis was reported in the majority (62.5%) of wheelchair users for all age groups. A larger percentage of patients with scoliosis required respiratory support than patients without scoliosis (44% vs 27.2%, respectively), and pulmonary function in those with scoliosis was consistently reduced in the 3 older age groups compared to those without scoliosis, with the largest differences demonstrated in juveniles. Patients with scoliosis had been diagnosed with Pompe disease for a mean of 1.2 (±14.34) years before the first reporting of scoliosis. As with other registry analyses, data were collected from multiple sites in different countries and assessments of scoliosis therefore may not be based on consistent criteria. However, the observed occurrence of scoliosis across all age groups of patients with Pompe disease and its association with increased clinical morbidity, underscores the need for clinical assessment of scoliosis in all patients with Pompe disease.

Patterns of asynchrony for phytoplankton fluctuations from reservoir mainstream to a tributary bay in a giant dendritic reservoir (Three Gorges Reservoir, China)

Seasonal fluctuations of phytoplankton have often been regarded as one of the important cyclic events in aquatic ecosystems, and have even been emphasized as an important sign of regional climatic variability in limnology. However, few attempts have been made to examine synchrony for phytoplankton fluctuations among different habitats in a single reservoir system. The present study employed Spearman rank correlation analysis and the Mantel test to assess levels of synchrony for phytoplankton abundance and taxonomic composition from reservoir mainstream to a tributary bay (Xiangxi Bay) in a giant dendritic reservoir, China (Three Gorges Reservoir, TGR). At the selected scale, asynchronous patterns of phytoplankton were found when looking at total abundance and taxonomic composition, suggesting that regional drivers were not strong enough to synchronize phytoplankton fluctuations, and local regulators were predominant. As a riverine system, the mainstream of TGR had high levels of algal synchrony, while asynchronous patterns of phytoplankton were detected within Xiangxi Bay, which is characterized as a lacustrine system. The present study further confirmed that external hydrological disturbances strongly homogenize habitat conditions and synchronize phytoplankton fluctuations within the mainstream, while spatial divergence of phytoplankton succession depend on local habitat conditions within Xiangxi Bay. Moreover, low synchrony of phytoplankton between the mainstream and Xiangxi Bay is probably caused by spatial divergence of phytoplankton succession within Xiangxi Bay and the lack of succession in the rapidly flushed mainstream. Independently of these mechanisms possibly explaining phytoplankton fluctuations, the present study has also an applied perspective to the improvement of a long-term observation program in which phytoplankton trends at the mainstream scale could be compiled from the data set in a single site, while a set of sampling sites should be required at the Xiangxi Bay scale.

Helioseismic Network Provides Valuable Data

[1] I read with interest the editorial in Space Weather entitled “The need for long-term solar-terrestrial data series” (7, S05006, doi:10.1029/2009SW000496). As discussed in the editorial, it can be difficult to convince funding agencies of the value of long-term observational programs with consistent instrumentation over decades. I would like to point out that one such program, the Global Oscillation Network Group (GONG), which operates a set of six sites around the world to obtain helioseismic data of the Sun's interior, has been providing solar data since 1995. GONG has achieved an average 24-hour observing fraction of 85–90% since its beginning. Continual solar magnetic field measurements are also being provided by GONG, and data on the hydrogen alpha emission line will be provided to the U.S. Air Force starting in summer of 2010.

The NOPP O-SCOPE and MOSEAN Projects: Advanced Sensing for Ocean Observing Systems

The National Oceanographic Partnership Program (NOPP) consecutively sponsored the Ocean-Systems for Chemical, Optical, and Physical Experiments (O-SCOPE) and Multi-disciplinary Ocean Sensors for Environmental Analyses and Networks (MOSEAN) projects from 1998 through 2008. The O-SCOPE and MOSEAN projects focused on developing and testing new sensors and systems for autonomous, concurrent measurements of biological, chemical, optical, and physical variables from a diverse suite of stationary and mobile ocean platforms. Design considerations encompassed extended open-ocean and coastal deployments, instrument durability, biofouling mitigation, data accuracy and precision, near-real-time data telemetry, and economy—the latter being critical for widespread sensor and system utilization. The complementary O-SCOPE and MOSEAN projects increased ocean sensing and data telemetry capabilities for addressing many societally relevant problems such as global climate change, ocean carbon cycling and sequestration, acidification, eutrophication, anoxia, and ecosystem dynamics, including harmful algal blooms. NOPP support enabled O-SCOPE and MOSEAN to accelerate progress in achieving multiscale, multidisciplinary, sustained observations of the ocean environment. Importantly, both programs produced value-added scientific results, which demonstrated the utility of these new technologies. The NOPP framework fostered strong collaborations among academic, commercial, and government entities, and facilitated technology transfers to the general research community and to long-term observational and observatory programs.

Disk and wind evolution of Achernar: the breaking of the fellowship

Aims. We use spectral energy distributions (SEDs), Hα line profiles, and visibilities available in the literature to study Achernar's envelope geometry and to propose a possible scenario for its circumstellar disk formation and dissipation.Methods. We use the SIMECA code to investigate possible geometries of the circumstellar environment by comparing our synthetic results with spectroscopic and high angular resolution data from the VLTI/VINCI instrument. We compute three different kinds of models: an equatorial disk, a polar wind, and a disk+wind model.Results. We develop a 2D axial symmetric kinematic model to study the variation of the observed Hα line profiles, which provides clear evidence of Achernar's equatorial disk formation and dissipation between 1991 and 2002. Our model can reproduce the polar-wind extension greater than 10 and a possible equatorial disk (≤ 5 ) but we were unable to estimate the wind opening angle. We reproduce the Hα line-profile variations using an outburst scenario, but the disk final contraction requieres an additional physical effect to be taken into account. The polar stellar wind does not appear to be linked to the presence of a disk or a ring around the star. We test the possibility of a binary companion to Achernar, as found by Kervella & Domiciano de Souza (2007, A&A, 474, L49), but conclude that the VLTI/VINCI visibilities cannot be explained by a rotationally-distorted Be star and a companion alone. The presence of a polar jet provides an important component to reproduce the observations even if it is not excluded that the companion could partially influence the observations. New interferometric observations at short baselines (5 ≤ B ≤ 20 m) are mandatory to constrain Achernar's circumstellar envelope, as well as spectroscopic long-term follow-up observational programs to link Achernar's mass-loss episodes with its circumstellar disk formation.

First results from a VLBA proper motion survey of H$_\mathsf{2}$O masers in low-mass YSOs: the Serpens core and RNO 15-FIR

This article reports first results of a long-term observational program aimed to study the earliest evolution of jet/disk systems in low-mass YSOs by means of VLBI observations of the 22.2 GHz water masers. We report here data for the cluster of low-mass YSOs in the Serpens molecular core and for the single object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the Serpens cluster, the water maser emission comes from two small (< 5 AU in size) clusters of features separated by ~25 AU, having line of sight velocities strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of the molecular cloud. The two maser clusters are oriented on the sky along a direction that is approximately perpendicular to the axis of the radio continuum jet observed with the VLA towards SMM1. The spatial and velocity distribution of the maser features lead us to favor the interpretation that the maser emission is excited by interaction of the receding lobe of the jet with dense gas in the accretion disk surrounding the YSO in SMM1. Towards RNO~15-FIR, the few detected maser features have both positions and (absolute) velocities aligned along a direction that is parallel to the axis of the molecular outflow observed on much larger angular scales. In this case the maser emission likely emerges from dense, shocked molecular clumps displaced along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1 is more massive than the one in RNO~15-FIR. We discuss the case where a high mass ejection rate can generate jets sufficiently powerful to sweep away from their course the densest portions of circumstellar gas. In this case, the excitation conditions for water masers might preferably occur at the interface between the jet and the accretion disk, rather than along the jet axis.

MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. I. First-Epoch 15 GHz Linear Polarization Images

We present first-epoch, milliarcsecond-scale linear polarization images at 15 GHz of 133 jets associated with active galactic nuclei (AGNs) from the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) survey. MOJAVE is a long-term observational program to study the structure and evolution of relativistic outflows in AGNs. The sample consists of all known AGNs with Galactic latitude |b| > 25, J2000.0 declination greater than -20°, and correlated 15 GHz Very Long Baseline Array (VLBA) flux density exceeding 1.5 Jy (2 Jy for sources below the celestial equator) at any epoch during the period 1994–2003. Of the 133 AGNs that satisfy these criteria, 96 are also part of the VLBA 2 cm Survey. Because of strong selection effects, the sample is dominated by blazars with parsec-scale morphologies consisting of a bright core component at the extreme end of a one-sided jet. At least one-third of the cores are completely unresolved on the longest VLBA baselines, indicating brightness temperatures above 1011 K. These cores tend to have electric vectors that are better aligned with the inner jet direction, possibly indicating the presence of a stationary shock near the base of the jet. The linear polarization levels of the cores are generally low ( 50%) and electric vectors aligned with the jet ridge line, consistent with optically thin emission from transverse shocks. The cores and jets of the radio galaxies show very little or no linear polarization. Both the weak- and strong-lined blazar classes (BL Lac objects and high-polarization radio quasars) show a general increase in fractional polarization with distance down the jet, but the BL Lac jets are generally more polarized and have electric vectors preferentially aligned with the local jet direction. We show that these differences are intrinsic to the jets and not the result of observational biases. We find that distinct features in the jets of gamma-ray-loud (EGRET) blazars are typically twice as luminous as those in non-EGRET blazars and are more highly linearly polarized. These differences can be adequately explained if gamma-ray blazars have higher Doppler-boosting factors, as the result of better alignment with the line of sight and/or higher bulk Lorentz factors.