199 research outputs found
Autonomous and remotely operated vehicle technology for hydrothermal vent discovery, exploration, and sampling
Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 1 (2007): 152-161.Autonomous and remotely operated underwater vehicles play
complementary roles in the discovery, exploration, and detailed
study of hydrothermal vents. Beginning with clues provided
by towed or lowered instruments, autonomous underwater vehicles
(AUVs) can localize and make preliminary photographic
surveys of vent fields. In addition to finding and photographing
such sites, AUVs excel at providing regional context through
fine-scale bathymetric and magnetic field mapping. Remotely
operated vehicles (ROVs) enable close-up inspection, photomosaicking,
and tasks involving manipulation of samples and
instruments. Increasingly, ROVs are used to conduct in situ
seafloor experiments. ROVs can also be used for fine-scale
bathymetric mapping with excellent results, although AUVs are
usually more efficient in such tasks
Mid-ocean ridge exploration with an autonomous underwater vehicle
Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 4 (2007): 52-61.Human-occupied submersibles, towed
vehicles, and tethered remotely operated
vehicles (ROVs) have traditionally been
used to study the deep seafloor. In recent
years, however, autonomous underwater
vehicles (AUVs) have begun to replace
these other vehicles for mapping and
survey missions. AUVs complement the
capabilities of these pre-existing systems,
offering superior mapping capabilities,
improved logistics, and better utilization
of the surface support vessel by allowing
other tasks such as submersible operations,
ROV work, CTD stations, or multibeam
surveys to be performed while the
AUV does its work. AUVs are particularly
well suited to systematic preplanned surveys
using sonars, in situ chemical sensors,
and cameras in the rugged deep-sea
terrain that has been the focus of numerous
scientific expeditions (e.g., those to
mid-ocean ridges and ocean margin settings).
The Autonomous Benthic Explorer
(ABE) is an example of an AUV that has
been used for over 20 cruises sponsored
by the National Science Foundation
(NSF), the National Oceanic and
Atmospheric Administration (NOAA)
Office of Ocean Exploration (OE), and
international and private sources. This
paper summarizes NOAA OE-sponsored
cruises made to date using ABE
TU Tau B: The Peculiar 'Eclipse' of a possible proto-Barium Giant
TU Tau (= HD 38218 = HIP 27135) is a binary system consisting of a C-N carbon
star primary and an A-type secondary. We report on new photometry and
spectroscopy which tracked the recent disappearance of the A-star secondary.
The dimming of the A-star was gradual and irregular, with one or more brief
brightenings, implying the presence of nonhomogeneities in the carbon star
outflow. We also present evidence that the A-star is actively accreting
s-process enriched material from the carbon star and suggest that it will
therefore eventually evolve into a Barium giant. This is an important system as
well because the A-type star can serve as a probe of the outer atmosphere of
the carbon star.Comment: 9 pages, 9 figures, 4 tables, a number of amateur observatories made
significant contributions to this research. Paper accepted for publication in
The Astronomical Journa
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Virtual Schools in the U.S. 2017
In the five years since the first NEPC Annual Report on Virtual Education was released in 2013, virtual education continues to be a focal point for policymakers. Proponents argue that virtual education can expand student choices and improve the efficiency of public education. In particular, full-time virtual schools (also sometimes referred to as virtual charter schools, virtual academies, online schools or cyber schools) have attracted a great deal of attention. Many believe that online curriculum can be tailored to individual students more effectively than curriculum in traditional classrooms, giving it the potential to promote greater student achievement than can be realized in traditional brick-and-mortar schools. Further, the promise of lower costs—primarily for instructional personnel and facilities—makes virtual schools financially appealing to both policymakers and for-profit providers. The 2017 NEPC Annual Report contributes to the existing evidence related to virtual education, and so to debates surrounding it. It provides objective analysis of the characteristics and performance of full-time, publicly funded K-12 virtual schools; available research on virtual school practices and policy; and an overview of recent state efforts to craft new policy.</p
Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean
Author Posting. © Nature Publishing Group, 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 453 (2008): 1236-1238, doi:10.1038/nature07075.Roughly 60% of the Earthâs outer surface is comprised of oceanic crust formed by volcanic
processes at mid-ocean ridges (MORs). Although only a small fraction of this vast volcanic
terrain has been visually surveyed and/or sampled, the available evidence suggests that
explosive eruptions are rare on MORs, particularly at depths below the critical point for
steam (3000 m). A pyroclastic deposit has never been observed on the seafloor below 3000
m, presumably because the volatile content of mid-ocean ridge basalts is generally too low
to produce the gas fractions required to fragment a magma at such high hydrostatic
pressure. We employed new deep submergence technologies during an International Polar
Year expedition to the Gakkel Ridge in the Arctic Basin at 85°E, to acquire the first-ever
photographic images of âzero-ageâ volcanic terrain on this remote, ice-covered MOR. Our
imagery reveals that the axial valley at 4000 m water depth is blanketed with
unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele),
covering a large area greater than 10 km2. At least 13.5 wt% CO2 is required to fragment
magma at these depths, which is ~10x greater than the highest values measured to-date in
a MOR basalt. These observations raise important questions regarding the accumulation
and discharge of magmatic volatiles at ultra-slow spreading rates on the Gakkel Ridge (6-
14 mm yr-1, full-rate), and demonstrate that large-scale pyroclastic activity is possible
along even the deepest portions of the global MOR volcanic system.This research was
funded by the National Aeronautics and Space Administration, the National Science Foundation,
and the Woods Hole Oceanographic Institution
Effusive and explosive volcanism on the ultraslow-spreading Gakkel Ridge, 85°E
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q10005, doi:10.1029/2012GC004187.We use high-definition seafloor digital imagery and multibeam bathymetric data acquired during the 2007 Arctic Gakkel Vents Expedition (AGAVE) to evaluate the volcanic characteristics of the 85°E segment of the ultraslow spreading Gakkel Ridge (9 mm yrâ1 full rate). Our seafloor imagery reveals that the axial valley is covered by numerous, small-volume (order ~1000 m3) lava flows displaying a range of ages and morphologies as well as unconsolidated volcaniclastic deposits with thicknesses up to 10 cm. The valley floor contains two prominent volcanic lineaments made up of axis-parallel ridges and small, cratered volcanic cones. The lava flows appear to have erupted from a number of distinct source vents within the ~12â15 km-wide axial valley. Only a few of these flows are fresh enough to have potentially erupted during the 1999 seismic swarm at this site, and these are associated with the Oden and Loke volcanic cones. We model the widespread volcaniclastic deposits we observed on the seafloor as having been generated by the explosive discharge of CO2 that accumulated in (possibly deep) crustal melt reservoirs. The energy released during explosive discharge, combined with the buoyant rise of hot fluid, lofted fragmented clasts of rapidly cooling magma into the water column, and they subsequently settled onto the seafloor as fall deposits surrounding the source vent.We gratefully acknowledge
the financial support of the National Aeronautics and Space
Administration, the National Science Foundation (N.S.F.), the
International Polar Year 2007â2008, and Woods Hole Oceanographic
Institution; and the graduate support provided by N.S.F.,
the NDSEG Fellowship, and WHOI Deep Ocean Exploration
Institute.2013-04-0
Geochemistry of lavas from the 2005â2006 eruption at the East Pacific Rise, 9°46âČNâ9°56âČN : implications for ridge crest plumbing and decadal changes in magma chamber compositions
Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 11 (2010): Q05T09, doi:10.1029/2009GC002977.Detailed mapping, sampling, and geochemical analyses of lava flows erupted from an âŒ18 km long section of the northern East Pacific Rise (EPR) from 9°46âČN to 9°56âČN during 2005â2006 provide unique data pertaining to the short-term thermochemical changes in a mid-ocean ridge magmatic system. The 2005â2006 lavas are typical normal mid-oceanic ridge basalt with strongly depleted incompatible trace element patterns with marked negative Sr and Eu/Eu* anomalies and are slightly more evolved than lavas erupted in 1991â1992 at the same location on the EPR. Spatial geochemical differences show that lavas from the northern and southern limits of the 2005â2006 eruption are more evolved than those erupted in the central portion of the fissure system. Similar spatial patterns observed in 1991â1992 lavas suggest geochemical gradients are preserved over decadal time scales. Products of northern axial and off-axis fissure eruptions are consistent with the eruption of cooler, more fractionated lavas that also record a parental melt component not observed in the main suite of 2005â2006 lavas. Radiogenic isotopic ratios for 2005â2006 lavas fall within larger isotopic fields defined for young axial lavas from 9°N to 10°N EPR, including those from the 1991â1992 eruption. Geochemical data from the 2005â2006 eruption are consistent with an invariable mantle source over the spatial extent of the eruption and petrogenetic processes (e.g., fractional crystallization and magma mixing) operating within the crystal mush zone and axial magma chamber (AMC) before and during the 13 year repose period. Geochemical modeling suggests that the 2005â2006 lavas represent differentiated residual liquids from the 1991â1992 eruption that were modified by melts added from deeper within the crust and that the eruption was not initiated by the injection of hotter, more primitive basalt directly into the AMC. Rather, the eruption was driven by AMC pressurization from persistent or episodic addition of more evolved magma from the crystal mush zone into the overlying subridge AMC during the period between the two eruptions. Heat balance calculations of a hydrothermally cooled AMC support this model and show that continual addition of melt from the mush zone was required to maintain a sizable AMC over this time interval.This work has been supported by
NSF grants OCEâ0525863 and OCEâ0732366 (D. J. Fornari
and S. A. Soule), OCEâ0636469 (K. H. Rubin), and OCEâ
0138088 (M. R. Perfit), as well as postdoctoral fellowship funds
from the University of Florida
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