55 research outputs found
Seasonal dynamics of oceanographic conditions, phytoplankton, and zooplankton in the Malaspina Strait, Strait of Georgia
Plankton dynamics in the Salish Sea may directly impact resident and migratory fish populations that are of major economic importance in the region. The Malaspina Strait in the northern Salish Sea is of particular interest as it is an important migration route for juvenile salmon. Here, we present data collected at three stations in the Malaspina Strait as part of the Citizen Science initiative of the Salish Sea Marine Survival Project. Sampling was conducted at bi-monthly (or higher) frequency from February to October, 2015 to 2017. Relationships between the regional hydrography, environmental parameters (temperature, salinity, dissolved oxygen, etc.), nutrient concentrations, and phytoplankton and zooplankton community composition are considered. Preliminary results indicate that 2015 was an anomalous year with an earlier-than-average (mid-February) spring phytoplankton bloom. Phytoplankton community composition was dominated by centric, chain-forming diatoms in spring of all years, cell densities were higher in spring 2015 compared to 2016 and 2017. In both 2015 and 2016, copepods dominated the abundances of zooplankton at the deep locations in Malaspina Strait. However, the biomass was dominated by taxa known to be the preferred prey of juvenile salmonids (euphausiids, amphipods, crab larvae). At the nearshore station in both years, zooplankton biomass was dominated by âotherâ taxa, in particular gelatinous plankton. Biomass of large calanoid copepods and euphausiids was significantly positively correlated to the relative abundance of diatoms. Biomass of small calanoid copepods and non-calanoid copepods, on the other hand, was positively correlated with the relative abundance of dinoflagellates. Further analyses will relate environmental variables to the observed seasonal variations in phytoplankton and zooplankton. Results from this study will ultimately be extended to include other Citizen Science stations in order to gain a better understanding of how bottom-up processes vary in different regions of the Salish Sea, and the potential implications for higher trophic levels
High-Resolution Transmission Spectroscopy of the Terrestrial Exoplanet GJ 486b
Terrestrial exoplanets orbiting M-dwarf stars are promising targets for
transmission spectroscopy with existing or near-future instrumentation. The
atmospheric composition of such rocky planets remains an open question,
especially given the high X-ray and ultraviolet flux from their host M dwarfs
that can drive atmospheric escape. The 1.3 exoplanet GJ 486b
( 700 K), orbiting an M3.5 star, is expected to have one of
the strongest transmission spectroscopy signals among known terrestrial
exoplanets. We observed three transits of GJ 486b using three different
high-resolution spectrographs: IRD on Subaru, IGRINS on Gemini-South, and
SPIRou on the Canada-France-Hawai'i Telescope. We searched for atmospheric
absorption from a wide variety of molecular species via the cross-correlation
method, but did not detect any robust atmospheric signals. Nevertheless, our
observations are sufficiently sensitive to rule out several clear atmospheric
scenarios via injection and recovery tests, and extend comparative
exoplanetology into the terrestrial regime. Our results suggest that GJ 486b
does not possess a clear H/He-dominated atmosphere, nor a clear 100%
water-vapor atmosphere. Other secondary atmospheres with high mean molecular
weights or H/He-dominated atmospheres with clouds remain possible. Our
findings provide further evidence suggesting that terrestrial planets orbiting
M-dwarf stars may experience significant atmospheric loss.Comment: Accepted for publication in A
Climatological mean circulation at the New England shelf break
Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 1874â1893, doi:10.1175/2011JPO4604.1.A two-dimensional cross-shelf model of the New England continental shelf and slope is used to investigate the mean cross-shelf and vertical circulation at the shelf break and their seasonal variation. The model temperature and salinity fields are nudged toward climatology. Annual and seasonal mean wind stresses are applied on the surface in separate equilibrium simulations. The along-shelf pressure gradient force associated with the along-shelf sea level tilt is tuned to match the modeled and observed depth-averaged along-shelf velocity. Steady-state model solutions show strong seasonal variation in along-shelf and cross-shelf velocity, with the strongest along-shelf jet and interior onshore flow in winter, consistent with observations. Along-shelf sea level tilt associated with the tuned along-shelf pressure gradient increases shoreward because of decreasing water depth. The along-shelf sea level tilt varies seasonally with the wind and is the strongest in winter and weakest in summer. A persistent upwelling is generated at the shelf break with a maximum strength of 2 m dayâ1 at 50-m depth in winter. The modeled shelfbreak upwelling differs from the traditional view in that most of the upwelled water is from the upper continental slope instead of from the shelf in the form of a detached bottom boundary layer.WGZ was supported by the Woods Hole Oceanographic
Institution postdoctoral scholarship program.
GGGandDJMwere supported byONRGrant N-00014-
06-1-0739
Effects of warm water intrusions on populations of macrozooplankton on Georges Bank, Northwest Atlantic
Author Posting. © The Authors, 2004. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 25 (2005): 143-156, doi:10.1016/j.csr.2004.07.028.As part of the Georges Bank/North West Atlantic GLOBEC (Global Ocean Ecosystems Dynamics) Program, macrozooplankton and micronekton were collected on 30 Broad Scale Survey Cruises between January â June, 1995 â1999, using a 10 m2 MOCNESS (3mm mesh). The objective of this study is to examine the effects of warm water intrusions on populations of macrozooplankton, namely Salpa spp., Phronima spp., Neomysis americana, and Crangon septemspinosa, on Georges Bank. Salpa spp. and Phronima spp. showed a large degree of horizontal co-occurrence, being found predominantly in Upper Slope/Gulf Stream Water and Georges Bank/Gulf of Maine Water. Abundances of these taxa showed striking interannual variability, and were only abundant on the southern flank and in the Northeast Channel in late spring/early summer of 1995 and 1999, periods during which AVHRR imagery and hydrographic data showed the presence of warm water intrusions. These intrusions seemed to have little effect on the distribution of other macrozooplankton (e.g., Neomysis americana and Crangon septemspinosa). Warm water intrusions can directly affect Salpa spp. and Phronima spp. populations by advecting them onto Georges Bank, although other, more resident populations, especially those inside the 100m isobath, seem to be little affected by such intrusions.Additional thanks goes to Tom Niesen and Stan Williams for their advice on data analysis and interpretation. This work was supported by NSF award No. OCE96-17209 and NOAA award No. NA66GP0356 to S. M. Bollens provided from the US GLOBEC Northwest Atlantic/Georges Bank Program, a joint program of the National Science Foundation and the National Oceanic and Atmospheric Administration
Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra
TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky
exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth
atmospheric studies. Each TRAPPIST-1 planet has been observed in transmission
both from space and from the ground, confidently rejecting cloud-free,
hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with
JWST/MIRI are consistent with little to no atmosphere given the lack of heat
redistribution. Here we present the first transmission spectra of TRAPPIST-1 b
obtained with JWST/NIRISS over two visits. The two transmission spectra show
moderate to strong evidence of contamination from unocculted stellar
heterogeneities, which dominates the signal in both visits. The transmission
spectrum of the first visit is consistent with unocculted starspots and the
second visit exhibits signatures of unocculted faculae. Fitting the stellar
contamination and planetary atmosphere either sequentially or simultaneously,
we confirm the absence of cloud-free hydrogen-rich atmospheres, but cannot
assess the presence of secondary atmospheres. We find that the uncertainties
associated with the lack of stellar model fidelity are one order of magnitude
above the observation precision of 89 ppm (combining the two visits). Without
affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this
highlights an important caveat for future explorations, which calls for
additional observations to characterize stellar heterogeneities empirically
and/or theoretical works to improve model fidelity for such cool stars. This
need is all the more justified as stellar contamination can affect the search
for atmospheres around the outer, cooler TRAPPIST-1 planets for which
transmission spectroscopy is currently the most efficient technique.Comment: 26 pages, 11 figures, accepted for publication in The Astrophysical
Journal Letter
Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST
The JWST Early Release Observations (ERO) included a NIRISS/SOSS
(0.6-2.8m) transit of the 850K Saturn-mass exoplanet
HAT-P-18b. Initial analysis of these data reported detections of water,
escaping helium, and haze. However, active K dwarfs like HAT-P-18 possess
surface heterogeneities starspots and faculae that can complicate the
interpretation of transmission spectra, and indeed, a spot-crossing event is
present in HAT-P-18b's NIRISS/SOSS light curves. Here, we present an
extensive reanalysis and interpretation of the JWST ERO transmission spectrum
of HAT-P-18b, as well as HST/WFC3 and /IRAC transit
observations. We detect HO (12.5), CO (7.3), a
cloud deck (7.4), and unocculted starspots (5.8), alongside
hints of Na (2.7). We do not detect the previously reported CH
( CH -6 to 2). We obtain excellent agreement between
three independent retrieval codes, which find a sub-solar HO abundance
( HO ). However, the inferred CO abundance
( CO ) is significantly super-solar and
requires further investigation into its origin. We also introduce new stellar
heterogeneity considerations by fitting for the active regions' surface
gravities a proxy for the effects of magnetic pressure. Finally, we compare
our JWST inferences to those from HST/WFC3 and /IRAC. Our
results highlight the exceptional promise of simultaneous planetary atmosphere
and stellar heterogeneity constraints in the era of JWST and demonstrate that
JWST transmission spectra may warrant more complex treatments of the transit
light source effect
A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST
Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to
enable the atmospheric study of transiting terrestrial companions with JWST.
Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven
planets, which have been the favored targets of eight JWST Cycle 1 programs.
While Cycle 1 observations have started to yield preliminary insights into the
planets, they have also revealed that their atmospheric exploration requires a
better understanding of their host star. Here, we propose a roadmap to
characterize the TRAPPIST-1 system -- and others like it -- in an efficient and
robust manner. We notably recommend that -- although more challenging to
schedule -- multi-transit windows be prioritized to constrain stellar
heterogeneities and gather up to 2 more transits per JWST hour spent.
We conclude that in such systems planets cannot be studied in isolation by
small programs, thus large-scale community-supported programs should be
supported to enable the efficient and robust exploration of terrestrial
exoplanets in the JWST era
Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H
Measuring the abundances of carbon and oxygen in exoplanet atmospheres is
considered a crucial avenue for unlocking the formation and evolution of
exoplanetary systems. Access to an exoplanet's chemical inventory requires
high-precision observations, often inferred from individual molecular
detections with low-resolution space-based and high-resolution ground-based
facilities. Here we report the medium-resolution (R600) transmission
spectrum of an exoplanet atmosphere between 3-5 m covering multiple
absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST
NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an
average transit depth uncertainty of 221 ppm per spectroscopic bin, and present
minimal impacts from systematic effects. We detect significant absorption from
CO (28.5) and HO (21.5), and identify SO as the
source of absorption at 4.1 m (4.8). Best-fit atmospheric models
range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios.
These results, including the detection of SO, underscore the importance of
characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec
G395H as an excellent mode for time series observations over this critical
wavelength range.Comment: 44 pages, 11 figures, 3 tables. Resubmitted after revision to Natur
Early Release Science of the exoplanet WASP-39b with JWST NIRCam
Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet
atmospheres is a fundamental step towards constraining the dominant chemical
processes at work and, if in equilibrium, revealing planet formation histories.
Transmission spectroscopy provides the necessary means by constraining the
abundances of oxygen- and carbon-bearing species; however, this requires broad
wavelength coverage, moderate spectral resolution, and high precision that,
together, are not achievable with previous observatories. Now that JWST has
commenced science operations, we are able to observe exoplanets at previously
uncharted wavelengths and spectral resolutions. Here we report time-series
observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed
Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength
photometric light curves span 2.0 - 4.0 m, exhibit minimal systematics,
and reveal well-defined molecular absorption features in the planet's spectrum.
Specifically, we detect gaseous HO in the atmosphere and place an upper
limit on the abundance of CH. The otherwise prominent CO feature at 2.8
m is largely masked by HO. The best-fit chemical equilibrium models
favour an atmospheric metallicity of 1-100 solar (i.e., an enrichment
of elements heavier than helium relative to the Sun) and a sub-stellar
carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio
may indicate significant accretion of solid materials during planet formation
or disequilibrium processes in the upper atmosphere.Comment: 35 pages, 13 figures, 3 tables, Nature, accepte
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers âŒ99% of the euchromatic genome and is accurate to an error rate of âŒ1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
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