6,687 research outputs found
Quantification of blue carbon in salt marshes of the Pacific coast of Canada
Tidal salt marshes are known to accumulate "blue carbon " at high rates relative to their surface area, which render these systems among the Earth's most efficient carbon (C) sinks. However, the potential for tidal salt marshes to mitigate global warming remains poorly constrained because of the lack of representative sampling of tidal marshes from around the globe, inadequate areal extent estimations, and inappropriate dating methods for accurately estimating C accumulation rates. Here we provide the first estimates of organic C storage and accumulation rates in salt marshes along the Pacific coast of Canada, within the United Nations Educational, Scientific and Cultural Organization (UNESCO) Clayoquot Sound Biosphere Reserve and Pacific Rim National Park Reserve, a region currently underrepresented in global compilations. Within the context of other sites from the Pacific coast of North America, these young Clayoquot Sound marshes have relatively low C stocks but are accumulating C at rates that are higher than the global average with pronounced differences between high and low marsh habitats. The average C stock calculated during the past 30 years is 54 +/- 5 Mg C ha(-1) (mean +/- standard error), which accounts for 81 % of the C accumulated to the base of the marsh peat layer (67 +/- 9 Mg C ha(-1)). The total C stock is just under one-third of previous global estimates of salt marsh C stocks, likely due to the shallow depth and young age of the marsh. In contrast, the average C accumulation rate (CAR) (184 +/- 50 g C m(-2) yr(-1) to the base of the peat layer) is higher than both CARs from salt marshes along the Pacific coast (112 +/- 12 g C m(-2) yr(-1)) and global estimates (91 +/- 7 g C m(-2) yr(-1)). This difference was even more pronounced when we considered individual marsh zones: CARs were significantly greater in high marsh (303 +/- 45 g C m(-2) yr(-1)) compared to the low marsh sediments (63 +/- 6 g C m(-2) yr(-1)), an observation unique to Clayoquot Sound among NE Pacific coast marsh studies. We attribute low CARs in the low marsh zones to shallow-rooting vegetation, reduced terrestrial sediment inputs, negative relative sea level rise in the region, and enhanced erosional processes. Per hectare, CARs in Clayoquot Sound marsh soils are approximately 2-7 times greater than C uptake rates based on net ecosystem productivity in Canadian boreal forests, which highlights their potential importance as C reservoirs and the need to consider their C accumulation capacity as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services
A 5,000-Year Fire History in the Strait of Georgia Lowlands, British Columbia, Canada
Improved knowledge of long-term fire regimes and climate-fire-human relationships are important for effective management of forested ecosystems. In this study, we use two, high-resolution sedimentary-charcoal records to provide new, mid to late Holocene fire histories for the driest forests in south coastal British Columbia, Canada: Somenos Lake in the Moist Maritime Coastal Douglas Fir (CDFmm) forests on southeastern Vancouver Island and Chadsey Lake in the Dry Maritime Coastal Western Hemlock (CWHdm) forests in the central Fraser Valley. Peak fire frequency at Somenos Lake in southeast Vancouver Island was highest prior to 3,500 cal yr BP at 9.5 fires per 1,000 years (at ~4,500 cal yr BP), with a mean fire return interval of 188 years (122–259) and 24 fire peaks for the 4,855 year record. Peak fire frequency at Chadsey Lake in the Fraser Valley of the Lower Mainland of BC was highest (5.9) at 2,736 cal yr BP but fairly uniform from ~4,300 to 2,500 cal yr BP. The mean fire return interval at Chadsey Lake was 214 years (150–285) with 15 fire peaks for the ~4,258 year record. The fire history for Chadsey Lake appears to be strongly tied to broad regional climate patterns for the region whereas the variability in the Somenos Lake fire record displays a more complex pattern likely the result of the interplay between climatic and anthropogenic factors. Our results show how different age models using long- vs. short-term temporal scales of analysis can affect fire history interpretation and highlight the importance of considering spatial variability when interpreting mechanisms driving fire activity in this region
Quantification of Blue Carbon in Salt Marshes of the Pacific Coast of Canada
Tidal salt marshes are known to accumulate “blue carbon” at high rates relative to their surface area, which render these systems among the Earth’s most efficient carbon (C) sinks. However, the potential for tidal salt marshes to mitigate global warming remains poorly constrained because of the lack of representative sampling of tidal marshes from around the globe, inadequate areal extent estimations, and inappropriate dating methods for accurately estimating C accumulation rates. Here we provide the first estimates of organic C storage and accumulation rates in salt marshes along the Pacific coast of Canada, within the United Nations Educational, Scientific and Cultural Organization (UNESCO) Clayoquot Sound Biosphere Reserve and Pacific Rim National Park Reserve, a region currently underrepresented in global compilations. Within the context of other sites from the Pacific coast of North America, these young Clayoquot Sound marshes have relatively low C stocks but are accumulating C at rates that are higher than the global average with pronounced differences between high and low marsh habitats. The average C stock calculated during the past 30 years is 54 5MgC ha-1 (mean standard error), which accounts for 81% of the C accumulated to the base of the marsh peat layer (67 9MgC ha-1/. The total C stock is just under one-third of previous global estimates of salt marsh C stocks, likely due to the shallow depth and young age of the marsh. In contrast, the average C accumulation rate (CAR) (184 50 gCm-2 yr-1 to the base of the peat layer) is higher than both CARs from salt marshes along the Pacific coast (112 12 gCm-2 yr-1/ and global estimates (91 7 gCm-2 yr-1/. This difference was even more pronounced when we considered individual marsh zones: CARs were significantly greater in high marsh (303 45 gCm-2 yr-1/ compared to the low marsh sediments (63 6 gCm-2 yr-1/, an observation unique to Clayoquot Sound among NE Pacific coast marsh studies. We attribute low CARs in the low marsh zones to shallow rooting vegetation, reduced terrestrial sediment inputs, negative relative sea level rise in the region, and enhanced erosional processes. Per hectare, CARs in Clayoquot Sound marsh soils are approximately 2–7 times greater than C uptake rates based on net ecosystem productivity in Canadian boreal forests, which highlights their potential importance as C reservoirs and the need to consider their C accumulation capacity as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services
Performance of a Low Noise Front-end ASIC for Si/CdTe Detectors in Compton Gamma-ray Telescope
Compton telescopes based on semiconductor technologies are being developed to
explore the gamma-ray universe in an energy band 0.1--20 MeV, which is not well
covered by the present or near-future gamma-ray telescopes. The key feature of
such Compton telescopes is the high energy resolution that is crucial for high
angular resolution and high background rejection capability. The energy
resolution around 1 keV is required to approach physical limit of the angular
resolution due to Doppler broadening. We have developed a low noise front-end
ASIC (Application-Specific Integrated Circuit), VA32TA, to realize this goal
for the readout of Double-sided Silicon Strip Detector (DSSD) and Cadmium
Telluride (CdTe) pixel detector which are essential elements of the
semiconductor Compton telescope. We report on the design and test results of
the VA32TA. We have reached an energy resolution of 1.3 keV (FWHM) for 60 keV
and 122 keV at 0 degree C with a DSSD and 1.7 keV (FWHM) with a CdTe detector.Comment: 6 pages, 7 figures, IEEE style file, to appear in IEEE Trans. Nucl.
Sc
Educational outcomes in extremely preterm children : neuropsychological correlates and predictors of attainment
This study assessed the impact of extremely preterm birth on academic attainment at 11 years of
age, investigated neuropsychological antecedents of attainment in reading and mathematics, and
examined early predictors of educational outcomes. Children born extremely preterm had significantly
poorer academic attainment and a higher prevalence of learning difficulties than their term
peers. General cognitive ability and specific deficits in visuospatial skills or phoneme deletion at 6
years were predictive of mathematics and reading attainment at 11 years in both extremely preterm
and term children. Phonological processing, attention, and executive functions at 6 years were also
associated with academic attainment in children born extremely preterm. Furthermore, social factors,
neonatal factors (necrotizing enterocolitis, breech delivery, abnormal cerebral ultrasound, early
breast milk provision), and developmental factors at 30 months (head circumference, cognitive development),
were independent predictors of educational outcomes at 11 years. Neonatal complications
combined with assessments of early cognitive function provide moderate prediction for educational
outcomes in children born extremely preterm
Measuring Cosmological Parameters with the JVAS and CLASS Gravitational Lens Surveys
The JVAS (Jodrell Bank-VLA Astrometric Survey) and CLASS (Cosmic Lens All-Sky
Survey) are well-defined surveys containing about ten thousand flat-spectrum
radio sources. For many reasons, flat-spectrum radio sources are particularly
well-suited as a population from which one can obtain unbiased samples of
gravitational lenses. These are by far the largest gravitational (macro)lens
surveys, and particular attention was paid to constructing a cleanly-defined
sample for the survey itself and for the underlying luminosity function. Here
we present the constraints on cosmological parameters, particularly the
cosmological constant, derived from JVAS and combine them with constraints from
optical gravitational lens surveys, `direct' measurements of ,
and the age of the universe, and constraints derived from CMB
anisotropies, before putting this final result into the context of the latest
results from other, independent cosmological tests.Comment: LaTeX, 9 pages, 6 PostScript figures, uses texas.sty. To appear in
the Proceedings of the 19th Texas Symposium on Relativistic Astrophysics and
Cosmology (CD-ROM). Paper version available on request. Actual poster (A0 and
A4 versions) available from
http://multivac.jb.man.ac.uk:8000/helbig/research/publications/info/
texas98.htm
CLASS B0827+525: `Dark lens' or binary radio-loud quasar?
We present radio, optical, near-infrared and spectroscopic observations of
the source B0827+525. We consider this source as the best candidate from the
Cosmic Lens All-Sky Survey (CLASS) for a `dark lens' system or binary
radio-loud quasar. The system consists of two radio components with somewhat
different spectral indices, separated by 2.815 arcsec. VLBA observations show
that each component has substructure on a scale of a few mas. A deep K-band
exposure with the W.M.Keck-II Telescope reveals emission near both radio
components. The K-band emission of the weaker radio component appears extended,
whereas the emission from the brighter radio component is consistent with a
point source. Hubble Space Telescope F160W-band observations with the NICMOS
instrument confirms this. A redshift of 2.064 is found for the brighter
component, using the LRIS instrument on the W.M.Keck-II Telescope. The
probability that B0827+525 consists of two unrelated compact flat-spectrum
radio sources is ~3%, although the presence of similar substructure in both
component might reduce this.
We discuss two scenarios to explain this system: (i) CLASS B0827+525 is a
`dark lens' system or (ii) B0827+525 is a binary radio-loud quasar. B0827+525
has met all criteria that thus far have in 100% of the cases confirmed a source
as an indisputable gravitational lens system. Despite this, no lens galaxy has
been detected with m_F160W<=23 mag. Hence, we might have found the first binary
radio-loud quasar. At this moment, however, we feel that the `dark lens'
hypothesis cannot yet be fully excluded.Comment: 9 pages, 6 figures; Accepted for publication in Astronomy &
Astrophysics; Full-res. images 1 and 3 can be obtained from L.V.E.
Paleoecological Investigation of Vegetation, Climate and Fire History in, and Adjacent to, Kootenay National Park, Southeastern British Columbia, Canada
Paleoecological investigation of two montane lakes in the Kootenay region of southeast British Columbia, Canada, reveal changes in vegetation in response to climate and fire throughout the Holocene. Pollen, charcoal, and lake sediment carbon accumulation rate analyses show seven distinct zones at Marion Lake, presently in the subalpine Engelmann Spruce-Subalpine Fir (ESSF) biogeoclimatic (BEC) zone of Kootenay Valley, British Columbia. Comparison of these records to nearby Dog Lake of Kootenay National Park of Canada in the Montane Spruce (MS) BEC zone of Kootenay Valley, British Columbia reveals unique responses of ecosystems in topographically complex regions. The two most dramatic shifts in vegetation at Marion Lake occur firstly in the early Holocene/late Pleistocene in ML Zone 3 (11,010–10,180 cal. yr. B.P.) possibly reflecting Younger Dryas Chronozone cooling followed by early Holocene xerothermic warming noted by the increased presence of the dry adapted conifer, Douglas-fir (Pseudotsuga menziesii) and increasing fire frequency. The second most prominent change occurred at the transition from ML Zone 5 through 6a (∼2,500 cal. yr. B.P.). This zone transitions from a warmer to a cooler/wetter climate as indicated by the increase in western hemlock (Tsuga heterophylla) and subsequent drop in fire frequency. The overall cooling trend and reduction in fire frequency appears to have occurred ∼700 years later than at Dog Lake (∼43 km to the south and 80 m lower in elevation), resulting in a closed montane spruce forest, whereas Marion Lake developed into a subalpine ecosystem. The temporal and ecological differences between the two study sites likely reflects the particular climate threshold needed to move these ecosystems from developed forests to subalpine conditions, as well as local site climate and fire conditions. These paleoecological records indicate future warming may result in the MS transitioning into an Interior Douglas Fir (IDF) dominated landscape, while the ESSF may become more forested, similar to the modern MS, or develop into a grassland-like landscape dependent on fire frequency. These results indicate that climate and disturbance over a regional area can dictate very different localized vegetative states. Local management implications of these dynamic landscapes will need to understand how ecosystems respond to climate and disturbance at the local or ecosystem/habitat scale
The new two-image gravitational lens system CLASS B2319+051
We report the discovery of a new two-image gravitational lens system from the
Cosmic Lens All-Sky Survey, CLASS B2319+051. Radio imaging with the Very Large
Array (VLA) and Multi-Element Radio-Linked Interferometer Network (MERLIN)
shows two compact components with a flux density ratio of 5:1, separated by
1.36 arcsec. Observations with the Very Long Baseline Array (VLBA) resolve each
of the radio components into a pair of parity-reversed subcomponents. Hubble
Space Telescope (HST) observations with the Near-Infrared Camera and
Multi-Object Spectrometer (NICMOS) show a bright elliptical galaxy (G1)
coincident with the radio position, and a second irregular galaxy (G2) 3.4
arcsec to the northwest. Previous spectroscopic studies have indicated that
these galaxies are at different redshifts: z(G1) = 0.624, z(G2) = 0.588.
Infrared counterparts to the lensed radio components are not detected in the
NICMOS image, and the source redshift has not yet been determined. Preliminary
mass modeling based on the VLBA subcomponent data indicates that the lensing
potential includes a strong external shear contribution. A VLA monitoring
program is currently being undertaken to measure the differential time delay.Comment: 16 pages, 7 figs, several typos corrected, AJ in press (August 2001
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