317 research outputs found
Burial and Origin of Permafrost Derived Carbon in the Nearshore Zone of the Southern Canadian Beaufort Sea
4-Bromo-N-phenylÂaniline
In the title compound, C12H10BrN, the dihedral angle between the benzene rings is 52.5â
(1)°, whereas the pitch angles, or the angles between the mean plane of each aryl group âpropeller bladeâ and the plane defined by the aryl bridging CâNâC angle, are 19.6â
(2) and 36.2â
(3)°. While the NâH group is not involved in hydrogen-bonding interÂactions, the structure exhibits a network of interÂmolecular CâHâŻÏ and NâHâŻÏ interÂactions
Variations in mid-latitude North Atlantic surface water properties during the mid-Brunhes (MIS 9â14) and their implications for the thermohaline circulation
© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Climate of the Past 6 (2010): 531-552, doi:10.5194/cp-6-531-2010.Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9â14 (300â540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north â south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.The
Fundacao para a Ciencia e a Tecnologia (FCT) through the
PORTO (PDCT/MAR/58282/2004) and SEDPORT projects (PDCTM/
40017/2003), and postdoctoral (SFRH/BPD/21691/2005)
and PhD (SFRH/BP/13749/2003) fellowships funded A. V. and
T. R. Additional funding to T. R. and J. G. was provided by the
Consolider-Ingenio 2100 Project CE-CSD2007-0067
Bathypelagic particle flux signatures from a suboxic eddy in the oligotrophic tropical North Atlantic: production, sedimentation and preservation
Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439âŻm water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2âŻÂ”molâŻkgâ1 at 40âŻm depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151âŻmgâŻmâ2âŻdâ1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of âŒâŻ15 and 13.3âŻmgâŻmâ2âŻdâ1, respectively, were observed in FebruaryâMarch 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic carbon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso-pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic carbon in the deep trap samples might be explained by particle focusing processes within the deeper part of the eddy. Molar CâŻ:âŻN ratios of organic matter during the ACME passage were around 18 and 25 for the upper and lower trap samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The ÎŽ15N record showed a decrease from 5.21 to 3.11âŻâ° from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in February/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid remineralisation of sinking organic-rich particles could have contributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from diatoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indicative of the presence of anammox (anaerobic ammonia oxidation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isorenieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detection thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below. Carbonate fluxes dropped from âŒâ52 to 21.4âŻmgâŻmâ2âŻdâ1 from January to February 2010, respectively, mainly due to reduced contribution of shallow-dwelling planktonic foraminifera and pteropods. The deep-dwelling foraminifera Globorotalia menardii, however, showed a major flux peak in February 2010, most probably due to the suboxia/hypoxia. The low oxygen conditions forced at least some zooplankton to reduce diel vertical migration. Reduced âflux feedingâ by zooplankton in the epipelagic could have contributed to the enhanced fluxes of organic materials to the bathypelagic traps during the eddy passage. Further studies are required on eddy-induced particle production and preservation processes and particle focusin
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Characterization of particulate organic matter in the Lena River delta and adjacent nearshore zone, NE Siberia â Part 2: Lignin-derived phenol compositions
The Lena River in central Siberia is one of the
major pathways translocating terrestrial organic matter (OM)
from its vast catchment area to the coastal zone of the Laptev
Sea and the Arctic Ocean. The permafrost soils of its far
south-stretching catchment, which store huge amounts of
OM, will most likely respond differently to climate warming
and remobilize previously frozen OM with distinct properties
specific for the source vegetation and soil. To characterize
the material discharged by the Lena River, we analyzed
the lignin phenol composition in total suspended matter
(TSM) from surface water collected in spring and summer,
surface sediments from Buor Khaya Bay along with
soils from the Lena Deltaâs first (Holocene) and third terraces
(Pleistocene ice complex), and plant samples. Our results
show that lignin-derived cinnamyl : vanillyl (C / V) and
syringyl : vanillyl (S / V) ratios are > 0.14 and 0.25, respectively,
in TSM and surface sediments, whereas in delta soils
they are > 0.16 and > 0.51, respectively. These lignin compositions
are consistent with significant inputs of organic matter
from non-woody angiosperm sources mixed with organic
matter derived from woody gymnosperm sources. We applied
a simple linear mixing model based on the C / V and
S / V ratios, and the results indicate the organic matter in
delta TSM samples and Buor Khaya Bay surface sediments
contain comparable contributions from gymnosperm material,
which is primarily derived from the taiga forests south
of the delta, and angiosperm material typical for tundra vegetation.
Considering the small catchment area covered by tundra
(~12 %), the input is substantial and tundra-derived OM
input is likely to increase in a warming Arctic. The similar
and high acid to aldehyde ratios of vanillyl and syringyl
(Ad / Al[subscript V, S]) in Lena Delta summer TSM (> 0.7 and > 0.5,
respectively) and Buor Khaya Bay surface sediments (> 1.0
and > 0.9, respectively) suggest that the OM is highly degraded
and Lena River summer TSM could be a possible
source of the surface sediments. The Ad / Al[subscript V, S] ratios of the
first and third delta terraces were generally lower (mean ratios
> 0.4 and > 0.4, respectively) than summer TSM and surface
sediments. This implies that TSM contains additional
contributions from a more degraded OM source (southern
catchment and/or finer more degraded particle size). Alternatively,
OM degradation on land after permafrost thawing
and subaqueously during transport and sedimentation could
be considerable. Despite the high natural heterogeneity of
OM stored in delta soils and exported by the Lena River, the
catchment-characteristic vegetation is reflected by the lignin
biomarker composition. Climate-warming-related changes in
the Lena River catchment may be detectable in changing
lignin biomarker composition and diagenetic alteration
Role of the cerebellum in visuomotor coordination
The initiation of coupled eye and arm movements was studied in six patients with mild cerebellar dysfunction and in six age-matched control subjects. The experimental paradigm consisted of 40 deg step-tracking elbow movements made under different feedback conditions. During tracking with the eyes only, saccadic latencies in patients were within normal limits. When patients were required to make coordinated eye and arm movements, however, eye movement onset was significantly delayed. In addition, removal of visual information about arm versus target position had a pronounced differential effect on movement latencies. When the target was extinguished for 3 s immediately following a step change in target position, both eye and arm onset times were further prolonged compared to movements made to continuously visible targets. When visual information concerning arm position was removed, onset times were reduced. Eye and arm latencies in control subjects were unaffected by changes in visual feedback. The results of this study clearly demonstrate that, in contrast to earlier reports of normal saccadic latencies associated with cerebellar dysfunction, initiation of both eye and arm movements is prolonged during coordinated visuomotor tracking thus supporting a coordinative role for the cerebellum during oculo-manual tracking tasks.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46565/1/221_2004_Article_BF00230206.pd
Expedition 306 summary
The overall aim of the North Atlantic paleoceanography study of Integrated Ocean Drilling Program Expedition 306 is to place late NeogeneâQuaternary climate proxies in the North Atlantic into a chronology based on a combination of geomagnetic paleointensity, stable isotope, and detrital layer stratigraphies, and in so doing generate integrated North Atlantic millennial-scale stratigraphies for the last few million years. To reach this aim, complete sedimentary sections were drilled by multiple advanced piston coring directly south of the central Atlantic âice-rafted debris beltâ and on the southern Gardar Drift. In addition to the North Atlantic paleoceanography study, a borehole observatory was successfully installed in a new ~180 m deep hole close to Ocean Drilling Program Site 642, consisting of a circulation obviation retrofit kit to seal the borehole from the overlying ocean, a thermistor string, and a data logger to document and monitor bottom water temperature variations through time
Reference materials for phase equilibrium studies. 1. Liquidâliquid equilibria (IUPAC Technical Report)
This article is the first of three projected IUPAC Technical Reports resulting from IUPAC Project 2011-037-2-100 (Reference Materials for Phase Equilibrium Studies). The goal of this project is to select reference systems with critically evaluated property values for the validation of instruments and techniques used in phase equilibrium studies of mixtures. This report proposes seven systems for liquidâliquid equilibrium studies, covering the four most common categories of binary mixtures: aqueous systems of moderate solubility, non-aqueous systems, systems with low solubility, and systems with ionic liquids. For each system, the available literature sources, accepted data, smoothing equations, and estimated uncertainties are given
Discrete peakons
We demonstrate for the first time the possibility for explicit construction
in a discrete Hamiltonian model of an exact solution of the form ,
i.e., a discrete peakon. These discrete analogs of the well-known, continuum
peakons of the Camassa-Holm equation [Phys. Rev. Lett. {\bf 71}, 1661 (1993)]
are found in a model different from their continuum siblings. Namely, we
observe discrete peakons in Klein-Gordon-type and nonlinear Schr\"odinger-type
chains with long-range interactions. The interesting linear stability
differences between these two chains are examined numerically and illustrated
analytically. Additionally, inter-site centered peakons are also obtained in
explicit form and their stability is studied. We also prove the global
well-posedness for the discrete Klein-Gordon equation, show the instability of
the peakon solution, and the possibility of a formation of a breathing peakon.Comment: Physica D, in pres
Chemical data evaluation: General considerations and approaches for IUPAC projects and the chemistry community (IUPAC Technical Report)
The International Union of Pure and Applied Chemistry has a long tradition of supporting the
compilation of chemical data and their evaluation through direct projects, nomenclature and terminology
work, and partnerships with international scientific bodies, government agencies, and other organizations.
The IUPAC Interdivisional Subcommittee on Critical Evaluation of Data has been established to provide
guidance on issues related to the evaluation of chemical data. In this first report, we define the general
principles of the evaluation of scientific data and describe best practices and approaches to data evaluation in
chemistryinfo:eu-repo/semantics/publishedVersio
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