210 research outputs found
Calcareous nannofossils from the Eocene North Atlantic Ocean (IODP Expedition 342 Sites U1403-1411)
Integrated Ocean Drilling Program Expedition 342 (June-July 2012) cored nine sites and 18
holes (Sites U1403-U1411) on the J-Anomaly and the Southeast Newfoundland ridges in the
NW Atlantic Ocean. These sites recovered sections ranging from Pleistocene to upper Albian,
but the expedition particularly focussed on the recovery of expanded Paleogene successions
with high quality microfossil preservation. This was achieved by choosing sites with thick
packages of drift-type sediments on topographic highs that would maximise the preservation of
carbonate. The expedition suceeded in recovering middle Eocene to lower Oligocene and upper
Oligocene to lower Miocene high sedimentation rate sediment sequences with very well
preserved microfossils. Highlights of the expedition include the recovery of continuous
Eocene/Oligocene and Oligocene/Miocene boundaries, a Cretaceous-Paleogene boundary
section with intact spherule layer, and Cenomanian/Turonian section with a 44 cm black shale.
Here, we describe notable aspects of the Eocene nannofossil record, including the exceptional
preservation and the evolution of several important Eocene groups: Nannotetrina, the
Sphenolithus furcatolithoides group, the Reticulofenestra bisecta group and the Coccolithus
gigas group. We also present a taxonomic overview of the Eocene nannofossil assemblages
from Sites U1403-1411, illustrating 164 taxa and describing 25 new species (Blackites
friedrichii, Blackites sextonii, Blackites subtilis, Calcidiscus scullyae, Clausicoccus norrisii,
Coccolithus hulliae, Coccolithus opdykei, Cruciplacolithus nishii, Helicosphaera prolixa,
Holodiscolithus agniniae, Holodiscolithus lippertii, Holodiscolithus liuii, Holodiscolithus
whitesideae, Nannotetrina plana, Nannotetrina ruda, Neococcolithes purus, Neococcolithes
radiatus, Pontosphaera brinkhuisii, Pontosphaera hollisii, Pontosphaera romansii,
Pontosphaera wilsonii, Reticulofenestra magniscutum, Scyphosphaera interstincta,
Semihololithus pseudobiskayae, Syracosphaera octiforma) and five new combinations
(Blackites inversus, Pontosphaera zigzag, Reticulofenestra erbae, Reticulofenestra isabellae,
Umbilicosphaera elliptica)
Muted calcareous nannoplankton response at the Middle/Late Eocene Turnover event in the western North Atlantic
Key extinctions in two major planktonic foraminiferal groups and high taxic turnover in radiolarians have led to the identification of the Middle/Late Eocene Turnover (MLET) and point towards significant palaeoclimatic and/or palaeoceanographic changes at around 38 million years ago. Here we present quantitative calcareous nannofossil data from Ocean Drilling Program Site 1052 (Blake Nose, western North Atlantic) in order to investigate the response of phytoplankton during the MLET. Our data show only minor shifts in taxon abundance, with no strong trends identified through the interval and no nannofossil origination or extinction events associated with the MLET. The assemblages are characterised by the dominance of neritic braarudosphaerids and eurytopic reticulofenestrids. The increased abundance of warm to temperate and mesotrophic nannofossils (Reticulofenestra reticulata, Reticulofenestra bisecta and Coccolithus pelagicus) in and around the MLET occur against a backdrop of cooling, as indicated by oxygen isotopes, suggesting that changing nutrient conditions was the principle driver of these shifts in the nannoplankton assemblage. This is further supported by an increase in radiolarian accumulation rates at this time. The lack of response in the calcareous nannoplankton relative to the zooplanktonic planktonic foraminifera and radiolaria demonstrates the contrasting sensitivity to environmental change in these different plankton groups, with radiolarians showing the highest degree of change at the MLET and the nannoplankton showing little or none
Rapid GRB Follow-up with the 2-m Robotic Liverpool Telescope
We present the capabilities of the 2-m robotic Liverpool Telescope (LT),
owned and operated by Liverpool John Moores University and situated at ORM, La
Palma. Robotic control and scheduling of the LT make it especially powerful for
observations in time domain astrophysics including: (i) rapid response to
Targets of Opportunity: Gamma Ray Bursts, novae, supernovae, comets; (ii)
monitoring of variable objects on timescales from seconds to years, and (iii)
observations simultaneous or coordinated with other facilities, both
ground-based and from space. Following a GRB alert from the Gamma Ray
Observatories HETE-2, INTEGRAL and Swift we implement a special over-ride mode
which enables observations to commence in about a minute after the alert,
including optical and near infrared imaging and spectroscopy. In particular,
the combination of aperture, site, instrumentation and rapid response (aided by
its rapid slew and fully-opening enclosure) makes the LT excellently suited to
help solving the mystery of the origin of optically dark GRBs, for the
investigation of short bursts (which currently do not have any confirmed
optical counterparts) and for early optical spectroscopy of the GRB phenomenon
in general. We briefly describe the LT's key position in the RoboNet-1.0
network of robotic telescopes.Comment: 6 pages, 2 figures, to appear in the proceedings of Interacting
Binaries: Accretion, Evolution and Outcomes, 4-10 July 2004, Cefalu, Sicily,
Italy, eds. Antonelli et a
Coccolithophore calcification response to past ocean acidification and climate change
Anthropogenic carbon dioxide emissions are forcing rapid ocean chemistry changes and causing ocean acidification (OA), which is of particular significance for calcifying organisms, including planktonic coccolithophores. Detailed analysis of coccolithophore skeletons enables comparison of calcite production in modern and fossil cells in order to investigate biomineralization response of ancient coccolithophores to climate change. Here we show that the two dominant coccolithophore taxa across the PaleoceneâEocene Thermal Maximum (PETM) OA global warming event (~56 million years ago) exhibited morphological response to environmental change and both showed reduced calcification rates. However, only Coccolithus pelagicus exhibits a transient thinning of coccoliths, immediately before the PETM, that may have been OA-induced. Changing coccolith thickness may affect calcite production more significantly in the dominant modern species Emiliania huxleyi, but, overall, these PETM records indicate that the environmental factors that govern taxonomic composition and growth rate will most strongly influence coccolithophore calcification response to anthropogenic change
Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene-Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean
The EoceneâOligocene transition (EOT; âŒ34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continentalâscale iceâsheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of longâterm surface ocean cooling and trophic conditions, suggesting causeâeffect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (ÎŽ18O, ÎŽ13C and %CaCO3) over a âŒ5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warmâoligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warmâoligotrophic phase, precursor diversityâdecrease phase, early Oligocene coldâeutrophic phase, and a steadyâstate cosmopolitan phase. The most prominent shift in the assemblages occurred during the âŒ550 kyrâlong precursor diversityâdecrease phase, which has relatively high bulk ÎŽ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial MaximumâEOGM)
Difference image photometry with bright variable backgrounds
Over the last two decades the Andromeda Galaxy (M31) has been something of a
test-bed for methods aimed at obtaining accurate time-domain relative
photometry within highly crowded fields. Difference imaging methods, originally
pioneered towards M31, have evolved into sophisticated methods, such as the
Optimal Image Subtraction (OIS) method of Alard & Lupton (1998), that today are
most widely used to survey variable stars, transients and microlensing events
in our own Galaxy. We show that modern difference image (DIA) algorithms such
as OIS, whilst spectacularly successful towards the Milky Way bulge, may
perform badly towards high surface brightness targets such as the M31 bulge.
Poor results can occur in the presence of common systematics which add spurious
flux contributions to images, such as internal reflections, scattered light or
fringing. Using data from the Angstrom Project microlensing survey of the M31
bulge, we show that very good results are usually obtainable by first
performing careful photometric alignment prior to using OIS to perform
point-spread function (PSF) matching. This separation of background matching
and PSF matching, a common feature of earlier M31 photometry techniques, allows
us to take full advantage of the powerful PSF matching flexibility offered by
OIS towards high surface brightness targets. We find that difference images
produced this way have noise distributions close to Gaussian, showing
significant improvement upon results achieved using OIS alone. We show that
with this correction light-curves of variable stars and transients can be
recovered to within ~10 arcseconds of the M31 nucleus. Our method is simple to
implement and is quick enough to be incorporated within real-time DIA
pipelines. (Abridged)Comment: 12 pages. Accepted for publication in MNRAS. Includes an expanded
discussion of DIA testing and results, including additional lightcurve
example
The Angstrom Project Alert System: real-time detection of extragalactic microlensing
The Angstrom Project is undertaking an optical survey of stellar microlensing
events across the bulge region of the Andromeda Galaxy (M31) using a
distributed network of two-meter class telescopes. The Angstrom Project Alert
System (APAS) has been developed to identify in real time candidate
microlensing and transient events using data from the Liverpool and Faulkes
North robotic telescopes. This is the first time that real-time microlensing
discovery has been attempted outside of the Milky Way and its satellite
galaxies. The APAS is designed to enable follow-up studies of M31 microlensing
systems, including searches for gas giant planets in M31. Here we describe the
APAS and we present a few example light curves obtained during its
commissioning phase which clearly demonstrate its real-time capability to
identify microlensing candidates as well as other transient sources.Comment: 4 pages, submitted to ApJ Letter
The Automatic Real-Time GRB Pipeline of the 2-m Liverpool Telescope
The 2-m Liverpool Telescope (LT), owned by Liverpool John Moores University,
is located in La Palma (Canary Islands) and operates in fully robotic mode. In
2005, the LT began conducting an automatic GRB follow-up program. On receiving
an automatic GRB alert from a Gamma-Ray Observatory (Swift, INTEGRAL, HETE-II,
IPN) the LT initiates a special override mode that conducts follow-up
observations within 2-3 min of the GRB onset. This follow-up procedure begins
with an initial sequence of short (10-s) exposures acquired through an r' band
filter. These images are reduced, analyzed and interpreted automatically using
pipeline software developed by our team called "LT-TRAP" (Liverpool Telescope
Transient Rapid Analysis Pipeline); the automatic detection and successful
identification of an unknown and potentially fading optical transient triggers
a subsequent multi-color imaging sequence. In the case of a candidate brighter
than r'=15, either a polarimetric (from 2006) or a spectroscopic observation
(from 2007) will be triggered on the LT. If no candidate is identified, the
telescope continues to obtain z', r' and i' band imaging with increasingly
longer exposure times. Here we present a detailed description of the LT-TRAP
and briefly discuss the illustrative case of the afterglow of GRB 050502a,
whose automatic identification by the LT just 3 min after the GRB, led to the
acquisition of the first early-time (< 1 hr) multi-color light curve of a GRB
afterglow.Comment: PASP, accepted (8 pages, 3 figures
Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope
We present the first optical observations of a Gamma Ray Burst (GRB)
afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and
operated by Liverpool John Moores University and situated on La Palma. We
briefly discuss the capabilities of LT and its suitability for rapid follow-up
observations of early optical and infrared GRB light curves. In particular, the
combination of aperture, site, instrumentation and rapid response (robotic
over-ride mode aided by telescope's rapid slew and fully-opening enclosure)
makes the LT ideal for investigating the nature of short bursts, optically-dark
bursts, and GRB blast-wave physics in general. We briefly describe the LT's key
position in the RoboNet-1.0 network of robotic telescopes. We present the LT
observations of GRB041006 and use its gamma-ray properties to predict the time
of the break in optical light curve, a prediction consistent with the
observations.Comment: 4 pages, 1 figure, accepted for publication in Il nuovo cimento (4th
Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004
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