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1

Hydrolysable amino acids in sediments from the Porcupine Abyssal Plain, northeast Atlantic Ocean  

Microsoft Academic Search

The distributions of hydrolysable amino acids have been examined in replicate sediment cores from the Porcupine Abyssal Plain in the northeastern Atlantic Ocean. The amino acid concentrations in surficial sediments ranged from 11.4 to 12.6 ?mol g?1 dry sediment, with a mean of 11.8 ?mol g?1 dry sediment, and decreased with increasing sediment depth, but showed a marked maximum between

Ian M. Horsfall; George A. Wolff

1997-01-01

2

Nitrogen cycling in deep-sea sediments of the Porcupine Abyssal Plain, NE Atlantic  

Microsoft Academic Search

Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH4) and nitrate (NO3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were

Jenny Brunnegård; Sibylle Grandel; Henrik Ståhl; Anders Tengberg; Per O. J. Hall

2004-01-01

3

The Argo Abyssal Plain  

Microsoft Academic Search

Eighteen geophysical transects were made in the Argo Abyssal Plain to study the magnetic anomalies, bathymetry and seismic structure. Magnetic anomalies were identified as being the Mesozoic anomalies M-10 to M-25, increasing in age from the Java Trench to the northwest continental shelf of Australia. A new bathymetric map shows that the Argo Abyssal Plain is bounded by the 5600-m

J. R. Heirtzler; P. Cameron; P. J. Cook; T. Powell; H. A. Roeser; S. Sukardi; J. J. Veevers

1978-01-01

4

Early diagenesis in North Atlantic abyssal plain sediments characterized by rock-magnetic and geochemical indices  

Microsoft Academic Search

Processes of early diagenesis are investigated in a sequence of late Quaternary turbiditic sediments from the Madeira Abyssal Plain (MAP), west of the NW African continental margin. In three sediment cores from this region, solid-phase geochemical indices of redox-sensitive ion mobilization are compared with rock-magnetic parameters as proxies for diagenesis characterization. The mud-dominated, distal turbidites are emplaced mainly as a

Simon G Robinson; John T. S Sahota; Frank Oldfield

2000-01-01

5

The Laurentian Fan: Sohm Abyssal Plain  

Microsoft Academic Search

The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust. Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to

David J. W. Piper; Dorrik A. V. Stow; William R. Normark

1984-01-01

6

The Laurentian Fan: Sohm Abyssal Plain  

Microsoft Academic Search

The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust.\\u000a Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern\\u000a Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to

David J. W. Piper; Dorrik A. V. Stow; William R. Normark

1984-01-01

7

The Laurentian Fan: Sohm Abyssal Plain  

NASA Astrophysics Data System (ADS)

The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust. Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to the fan is glacial in origin, and in part results from seismically triggered slumping on the upper continental slope. Sandy turbidity currents, such as the 1929 Grand Banks earthquake event, probably erode the fan-valley floors; but thick muddy turbidity currents build up the high levees.

Piper, David J. W.; Stow, Dorrik A. V.; Normark, William R.

1984-06-01

8

Provenance of distal Sohm Abyssal Plain sediments: history of supply from the Wisconsinan glaciation in eastern Canada  

Microsoft Academic Search

A 12-m-long core from the southern Sohm Abyssal Plain with 25 mud turbidites deposited during the past 40 ka is compared petrographically by X-ray diffraction analysis and spectrophotometry with possible source areas on the continental margin. Bathymetry and petrography show that no sediment is derived from the Northwest Atlantic Mid-Ocean Channel and most came across the Laurentian Fan. Resedimented Heinrich

David J. W. Piper; Thian Hundert

2002-01-01

9

Basement Structure and Sediment Architecture in the Southern Iberia Abyssal Plain  

Microsoft Academic Search

Deep-sea drilling and geophysical surveys at the Southern Iberia Abyssal Plain (SIAP) have revealed the existence of an up to 130 km wide Ocean-Continent-Transition (OCT). This OCT presents geophysical characteristics that match neither those of oceanic crust nor those of a thinned continental crust. This zone is characterized by weak and non-linear magnetic anomalies, variable topography, particular seismic velocities structures

G. Péron-Pinvidic; G. Manatschal

2005-01-01

10

The Laurentian Fan: Sohm Abyssal Plain  

USGS Publications Warehouse

The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust. Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to the fan is glacial in origin, and in part results from seismically triggered slumping on the upper continental slope. Sandy turbidity currents, such as the 1929 Grand Banks earthquake event, probably erode the fan-valley floors; but thick muddy turbidity currents build up the high levees. ?? 1984 Springer-Verlag New York Inc.

Piper, D. J. W.; Stow, D. A. V.; Normark, W. R.

1984-01-01

11

Observations of barophilic microbial activity in samples of sediment and intercepted particulates from the demerara abyssal plain.  

PubMed

To better understand the ecological significance of pressure effects on bacteria in the abyssobenthic boundary layer, experimental suspensions of sediments and sinking particulates were prepared from samples collected in boxcore and bottom-moored sediment traps at two stations (depth, 4,470 and 4,850m) in the Demerara abyssal plain off the coast of Brazil. Replicate samples were incubated shipboard at 3 degrees C and at both atmospheric and deep-sea pressures (440 or 480 atm [4.46 x 10 or 4.86 x 10 kPa]) following the addition of [C]glutamic acid (<10 mug liter) or yeast extract (0.025%) and the antibiotic nalidixic acid (0.002%). In seven of the eight samples supplemented with isotope, a barophilic microbial response was detected, i.e., substrate incorporation and respiration were greater under in situ pressure than at 1 atm (101.3 kPa). In the remaining sample, prepared from a sediment trap warmed to 24 degrees C before recovery, pressure was observed to inhibit substrate utilization. Total bacterial counts by epifluorescence microscopy decreased with depth in each sediment core, as did utilization of glutamic acid. Significant percentages of the total bacterial populations in cold sediment trap samples (but not the prewarmed one or any boxcore sample) were abnormally enlarged and orange fluorescing after incubation with yeast extract and nalidixic acid under deep-sea conditions. Results indicated that in the deep sea, barophilic bacteria play a predominant role in the turnover of naturally low levels of glutamic acid, and the potential for intense microbial activity upon nutrient enrichment is more likely to occur in association with recently settled particulates, especially fecal pellets, than in buried sediments. PMID:16346897

Deming, J W; Colwell, R R

1985-10-01

12

Acoustic environment of the Hatteras and Nares Abyssal Plains, western North Atlantic Ocean, determined from velocities and physical properties of sediment cores  

SciTech Connect

Seventeen piston cores up to 13 m long were recovered from representative acoustic and lithologic environments of the Hatteras and Nares Abyssal Plains in the western North Atlantic. Compressional-wave velocities (corrected to in situ conditions) and bulk physical properties measured on the cores are used to characterize the acoustic framework of these areas. For correlation with conventional seismic data, whole-core averages of properties are a better index to the acoustic nature of abyssal plain sediments than properties of the upper few centimeters of the seafloor because (1) strong changes in lithofacies (and acoustic properties) occur over depth scales of tens of centimeters to meters in the sediment column, and (2) conventional seismic frequencies of 3.5 kHz or less sample these variations to subbottom depths of tens of meters and more. Whole-core properties are a function of the thickness and distribution of high-velocity silt and sand layers in the core; they vary in a complex fashion with proximity to the source of turbidity currents, distance from axial paths of turbidity-current flows, local and regional basin geometry, and seafloor slope. Thus strongly reflective seabed regions with numerous high-velocity layers are not restricted simply to near-source areas nor are weakly reflective seabed regions (clay sediments only) limited to ''distal'' areas. Whole-core properties show a good qualitative correlation to variations in 3.5-kHz reflection profiles, and 3.5-kHz echo character therefore provides a useful means of mapping general acoustic properties over large regions of abyssal plains.

Tucholke, B.E.

1980-11-01

13

Uranium in pore waters from North Atlantic (GME and Southern Nares Abyssal Plain) sediments  

Microsoft Academic Search

A central question to be addressed by the international sub-seabed radioactive waste disposal program is the mobility of radionu-clides through sediments, which are the most important barrier to the transfer to the ocean and eventually to man. The major component of high-level radioactive waste is uranium. Here we report the measurement of low uranium concentrations in composite pore-water samples from

P. H. Santschi; C. Bajot; M. Mantovani; D. Orciuolot; R. E. Cranston; J. Bruno

1988-01-01

14

Acoustic environment of the Hatteras and Nares Abyssal Plains, western North Atlantic Ocean, determined from velocities and physical properties of sediment cores  

Microsoft Academic Search

Seventeen piston cores up to 13 m long were recovered from representative acoustic and lithologic environments of the Hatteras and Nares Abyssal Plains in the western North Atlantic. Compressional-wave velocities (corrected to in situ conditions) and bulk physical properties measured on the cores are used to characterize the acoustic framework of these areas. For correlation with conventional seismic data, whole-core

Brian E. Tucholke

1980-01-01

15

Late Quarternary Evolution of the Northern Hatteras Abyssal Plain.  

National Technical Information Service (NTIS)

The sedimentary history and seismic structure of a deep-water turbidite basin in the Western North Atlantic Ocean has been investigated to understand further the evolution of abyssal plains. This study integrates analyses of sedimentary and seismic facies...

E. P. Laine S. M. Dickson

1986-01-01

16

Ocean-Bottom Topography: The Divide between the Sohm and Hatteras Abyssal Plains.  

PubMed

A compilation of precision echo soundings has delineated the complex topography between the Sohm and Hatteras abyssal plains off the Atlantic coast of the United States. At present the divide between the two plains is a broad, flat area about 4950 meters deep; however, the configuration of channels and depressions suggests spillage of turbidity currents from the Sohm Plain into the Hatteras Plain and a shifting of the divide toward the northeast. Hudson Canyon terminates in the divide area and has probably fed sediment into both plains. PMID:17769918

Pratt, R M

1965-06-18

17

Abyssal plains heat exchange could explain global deficit  

NASA Astrophysics Data System (ADS)

When researchers measure the amount of heat flowing conductively from the seafloor to the ocean waters and then compare that value against a theoretical prediction of that heat loss, they observe that the global average measured heat flow is lower than expected. Researchers think that advection, a heat transfer mechanism that is difficult to measure, makes up this difference between predicted and observed heat exchange. They suggest that as seawater circulates through the permeable upper layers of the seafloor crust, driven by a thermal gradient, the water accumulates heat, drawing it into the ocean. Scientists have recently proposed that seafloor sediment plays an important role in controlling the geometry of such intraocean crust circulation. In the abyssal plains, the accumulation of millions of years' worth of low permeability sediment limits direct contact between the ocean and the crust. Where the sediment is thin or absent—for example, at outcrops—water is thought to be able to move between the ocean and the crust. Scientists propose that seawater can travel through the crust for tens of kilometers beneath the sediment, moving laterally from outcrop to outcrop.

Schultz, Colin

2012-07-01

18

RRS DISCOVERY Cruise 160, 30 June-25 July, 1986. Geochemical Sampling over the Madeira and Porcupine Abyssal Plains.  

National Technical Information Service (NTIS)

The main purpose of the cruise was to obtain samples of sediment and sediment pore waters for geochemical research. The primary objectives were: to sample the sediments in the 10 km x 10 km abyssal plain area centered on 31 deg 17 min N, 25 deg 24 min W (...

J. Thomson

1986-01-01

19

Late Quarternary evolution of the northern Hatteras Abyssal Plain. [LLW Ocean Disposal Program  

SciTech Connect

The sedimentary history and seismic structure of a deep-water turbidite basin in the Western North Atlantic Ocean has been investigated to understand further the evolution of abyssal plains. This study integrates analyses of sedimentary and seismic facies in order to examine the temporal and spatial patterns of sedimentation on the northern Hatteras Abyssal Plain during the Late Quaternary. Forty deep-sea sediment cores and 6000 km of high resolution (3.5 kHz) seismic reflection profiles from within 31-34/sup 0/N and 69-74/sup 0/W include portions of the Hatteras Outer Ridge, Lower Continental Rise and Bermuda Rise as well as the northern Hatteras Abyssal Plain. Seismic profiles (within 32-33/sup 0/N, 70-71.5/sup 0/W) define two acoustically-transparent seismic units beneath the Plain. The composition of these seismic units has been investigated with sediment cores. This study has found two notable features in the sedimentary framework of the Plain that appear to have resulted from temporal changes in sediment supply. The most recent change, a postglacial decline in turbidity current activity, produced a diagenetic iron enrichment at the Pleistocene-Holocene boundary. The stratigraphic thickness affected by diagenesis is related spatially to patterns of turbidite sedimentation. An earlier change, discovered in this research, occurred during the Wisconsinian glaciation and brought coarser-grained turbidity currents to the northern Plain. Deposition of sands from these flows appears to have been locally controlled by a broad topographic feature with less than ten meters relief. As a result of the topographic influence, there are abrupt boundaries, both verically and laterally, between an older mud facies and a younger sandy turbidite facies of the Plain.

Dickson, S.M.; Laine, E.P.

1986-05-01

20

Character, paleoenvironment, rate of accumulation, and evidence for seismic triggering of Holocene turbidites, Canada Abyssal Plain, Arctic Ocean  

Microsoft Academic Search

Four box cores and one piston core show that Holocene sedimentation on the southern Canada Abyssal Plain for the last 8010 ± 120 yr has consisted of a continuing rain of pelagic organic and ice-rafted clastic sediment with a net accumulation rate during the late Holocene of ?10 mm\\/1000 yr, and episodically emplaced turbidites 1–5 m thick deposited at intervals

Arthur Grantz; R. L. Phillips; M. W. Mullen; S. W. Starratt; G. A. Jones; A. Sathy Naidu; B. P. Finney

1996-01-01

21

The benthic response to the seasonal deposition of phytopigments at the Porcupine Abyssal Plain in the North East Atlantic  

Microsoft Academic Search

We have assessed the impact of seasonal pulses of phyto-detritus towards the bottom of the Porcupine Abyssal Plain (PAP) in the NE Atlantic. Phytopigments were determined (HPLC) in sediment, near-bottom suspended matter and sediment trap samples to obtain an impression of the quantity and quality of the organic material reaching the bottom. Its supposed effect on the benthic community was

R. Witbaard; G. C. A. Duineveld; J. A. Van der Weele; E. M. Berghuis; J. P. Reyss

2000-01-01

22

Geotechnical properties of fine-grained turbidite sequences: observations from the Nares Abyssal Plain  

SciTech Connect

Variations in the geotechnical properties of fine-grained turbidite sequences located in the Nares Abyssal Plain appear directly related to the dominant processes controlling sediment deposition. Changes in the index properties are gradational from the turbidite bases, often containing silt beds or laminae, upwards through the chemically laminated possibly turbiditic clays and into the nonturbiditic pelagic and hemipelagic clays. The depth at which consolidation processes begin to control the distribution of geotechnical properties is unclear; however, it is apparent that depositional processes predominate to depths of 3 to 4 meters. Consolidation test results indicate that abyssal plain sediments appear normally to overconsolidated using standard soil mechanics terminology and methods. Clay fabric analyses using transmission electron microscopy show significant variations in grain size, grain type, and orientation between the turbiditic and nonturbiditic clays.

Shephard, L.E.; Rutledge, A.K.; Bryant, W.R.; Moran, K.M.

1986-01-15

23

A case of post-depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the Madeira Abyssal Plain  

Microsoft Academic Search

A set of oxidized and unoxidized sediment intervals from the f-turbidite identified in two piston cores from the Madeira Abyssal Plain (MAP) was analyzed for calcium carbonate, total organic carbon (TOC), total nitrogen (TN), stable carbon composition of TOC (?13Ctoc), total hydrolyzable amino acids (THAA), total neutral sugars (TSUG), lignin phenols (LIG), two different lipid biomarkers of marine phytoplankton origin

Fredrick G. Prahl; Gert J. De Lange; Sven Scholten; Gregory L. Cowie

1997-01-01

24

Comparative Geoscience Studies of the Madeira and Southern Nares Abyssal Plains: NEA/SWG Preference Location Document.  

National Technical Information Service (NTIS)

This document summarizes the status of geoscience investigations in the two primary North Atlantic study locations Great Meteor East (GME) in the Madeira Abyssal Plain, and the Southern Nares Abyssal Plain (SNAP), and assesses the characteristics of these...

G. A. Auffret D. E. Buckley R. T. E. Schuttenhelm R. C. Searle L. E. Shephard

1986-01-01

25

Patterns in polychaete abundance and diversity from the Madeira Abyssal Plain, northeast Atlantic  

Microsoft Academic Search

Polychaete abundance and diversity patterns from the Madeira Abyssal Plain (MAP) were studied together with data from three other sites on the northeastern Atlantic abyssal plains. Polychaete abundance at MAP was significantly lower than at any of the other sites, including those lying under comparable productivity regimes. Analysis of diversity, using rarefaction and species counts per unit area, suggests that

Adrian Glover; Gordon Paterson; Brian Bett; John Gage; Myriam Sibuet; Martin Sheader; Lawrence Hawkins

2001-01-01

26

Morphogenesis of the SW Balearic continental slope and adjacent abyssal plain, Western Mediterranean Sea  

NASA Astrophysics Data System (ADS)

We present the seafloor morphology and shallow seismic structure of the continental slope south-east of the Balearic promontory and of the adjacent Algero-Balearic abyssal plain from multibeam and chirp sonar data. The main purpose of this research was to identify the sediment pathways from the Balearic promontory to the Algero-Balearic deep basin from the Early Pliocene to the Present. The morphology of the southern Balearic margin is controlled by a SW-NE structural trend, whose main expressions are the Emile Baudot Escarpment transform fault, and a newly discovered WSW-ENE trend that affects the SW end of the escarpment and the abyssal plain. We relate the two structural trends to right-lateral simple shear as a consequence of the Miocene westward migration of the Gibraltar Arc. Newly discovered steep and narrow volcanic ridges were probably enabled to grow by local transtension along the transform margin. Abyssal plain knolls and seahills relate to the subsurface deformation of early stage halokinetic structures such as salt rollers, salt anticlines, and salt pillows. The limited thickness of the overburden and the limited amount of deformation in the deep basin prevent the formation of more mature halokinetic structures such as diapirs, salt walls, bulbs, and salt extrusions. The uppermost sediment cover is affected by a dense pattern of sub-vertical small throw normal faults resulting from extensional stress induced in the overburden by subsurface salt deformation structures. Shallow gas seismic character and the possible presence of an active polygonal fault system suggest upward fluid migration and fluid and sediment expulsion at the seafloor through a probable mud volcano and other piercement structures. One large debris flow deposit, named Formentera Debris Flow, has been identified on the lower slope and rise of the south Formentera margin. Based on current observations, we hypothesize that the landslide originating the Formentera Debris Flow occurred in the Holocene, perhaps in historical times.

Camerlenghi, Angelo; Accettella, Daniela; Costa, Sergio; Lastras, Galderic; Acosta, Juan; Canals, Miquel; Wardell, Nigel

2009-06-01

27

New magnetic survey in the Tagus Abyssal Plain (TECTAP Project)  

NASA Astrophysics Data System (ADS)

The southern segment of the West Iberia Margin (WIM), the Tagus Abyssal Plain (TAP), and its conjugate margin, the southeast Grand Banks in Newfoundland, have not been drilled and geophysical data are sparse. On the contrary, the central and northern segments of the WIM are well-studied and the deep structure of the crust is well established. Nevertheless, a geological transect of the crust and upper mantle structure in the Tagus Abyssal Plain (TAP) was published in 2006, extending from the un-thinned continental crust in the East to the typical oceanic crust in the West (Afilhado, 2006; Afilhado et al., 2008). The results of the interpretation and modelling of seismic data, which includes refraction and wide-angle reflection and near vertical reflection, along IAM-5 multi-channel (MCS) profile are distinct to the one already available in the Iberia Abyssal Plain. These results on the deep structure indicate that nearly the entire TAP is underlain by oceanic crust. Both seismic, magnetic and free-air anomaly data modelling concur to the identification of a major rock property contrast at 10.5°W, which is interpreted as the eastern limit of the oceanic crust. A 40 km wide domain, to the east of 10.5°W, with high velocity gradient and seismic velocity in the range 6.0 km/s to 7.2 km/s (Afilhado, 2006; Afilhado et al., 2008) was recognized. Numerical modeling favours a serpentinized mantle composition in this domain, instead of continental crust affinity rocks (Neves et al., 2008), i.e. similar to the domain of exhumed serpentinized mantle recognized in the Iberia Abyssal Plain, to the north. However, this exhumed serpentinized mantle domain in the TAP is rather narrower than in the Iberia Abyssal Plain. This interpretation has important consequences to explain the nature of the crust in the transitional domain and for kinematics reconstructions. Moreover, the TAP is characterized, eastward of the J anomaly, by a set of low amplitude magnetic anomalies, suggesting a near N-S alignment. The origin of these anomalies and consequently the nature and age of the crust in the area, are matters of scientific dispute, unsolved till today. In order to confirm the interpretation of Afilhado et al., 2008 and to determine if low amplitude magnetic anomalies are really formed by seafloor spreading, we have acquired a new survey of the magnetic profiles in the TAP. These data and other available data on magnetics, geology and geophysics, from the TAP and its conjugate margin, will be used to update the plate kinematic evolution model for Iberia. The amount of stretching thus computed will put additional constrains on the model to explain the formation of this margin.

Moulin, M.

2009-04-01

28

Fate of corrosion products released from stainless steel in marine sediments and seawater. Part 4: Hatteras abyssal red clay  

Microsoft Academic Search

A study in which neutron-activated 347 stainless steel was exposed to surficial sediment from a site in the Hatteras Abyssal Plain of the Northwest Atlantic Ocean is described. This sediment consists of approx. 20% CaCO, which could lead to the formation of calcareous scale on the metal surface and reduce the corrosion rate. The distribution of indigenous metals among different

1982-01-01

29

The response of Oneirophanta mutabilis (Holothuroidea) to the seasonal deposition of phytopigments at the Porcupine Abyssal Plain in the Northeast Atlantic  

Microsoft Academic Search

The impact of seasonal pulses of phytodetritus on the grazing behaviour of Oneirophanta mutabilis was assessed on the Porcupine Abyssal Plain (PAP) in the NE Atlantic. Sediment and sediment trap samples were analysed by HPLC to estimate the quantity and quality of the organic material in terms of phytopigments and nucleic acids. Food selection by Oneirophanta was estimated by analysing

R. Witbaard; G. C. A. Duineveld; A. Kok; J. van der Weele; E. M. Berghuis

2001-01-01

30

Data Report for Current Meters on Mooring Nares-1, 1983-84; Nares Abyssal Plain.  

National Technical Information Service (NTIS)

The Nares Abyssal Plain has been selected as the study area at which the Subseabed Disposal Project (SDP) will carry out a risk assessment, validate the environmental models, and perform a site characterization for the 1989 concept assessment. Additionall...

R. D. Pillsbury D. Barstow B. Moore G. Pittock D. C. Root

1986-01-01

31

Major and trace element distributions in manganese nodules and micronodules as well as abyssal clay from the Clarion-Clipperton abyssal plain, Northeast Pacific  

NASA Astrophysics Data System (ADS)

The contents of seven major components (TiO2, Fe2O3, MgO, CaO, Na2O, K2O and P2O5) and 15 trace elements (Sc, V, Cr, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, Nd, Eu, Yb and Th) were determined by ICP-AE spectrometry in 27 samples of manganese nodules, micronodules as well as abyssal clay collected by dredging from an area of nearly 1,9802 nautical miles in the central Clarion-Clipperton abyssal plain at a depth of about 4,500 m. Statistical analyses were used to compare among individual as well as pooled datasets, in addition to different indicators such as La/Th, Ni/Cu and LREE/HREE ratios for the Clarion-Clipperton samples, as well as between these and corresponding values for the upper continental crust (UCC), North America Shale Composite (NASC), and igneous Indian and Pacific Mid-Ocean Ridge Basalts (MORBs). The results show significant correlations between major components in the Clarion-Clipperton samples and Pacific Ocean MORB, whereas trace elements (excepting Ni and Cu) correlate better with the UCC and NASC. There is also depletion in LREEs, together with a Ce negative anomaly for all Clarion-Clipperton samples. The nodule, micronodule and abyssal clay datasets each reveal typical clusters of components such as P2O5 and Y, La, Nd, Eu, Tb, or Ni and Cu. Compared to abyssal clay, the nodule as well as micronodules show significant enrichment in Ni and Cu; nevertheless, an essentially constant Ni/Cu ratio indicates that all samples come from the sediment surface. The distributions of major components as well as trace elements for the Clarion-Clipperton samples present, to different degrees, characteristics common to both the upper continental crust and Mid-Ocean Ridge Basalt, strongly implying a hydrothermal origin, most probably from East Pacific Rise material transported by the Pacific North Equatorial Current.

Duliu, O. G.; Alexe, V.; Moutte, J.; Szobotca, S. A.

2009-04-01

32

Microbial diversity and stratification of South Pacific abyssal marine sediments.  

PubMed

Abyssal marine sediments cover a large proportion of the ocean floor, but linkages between their microbial community structure and redox stratification have remained poorly constrained. This study compares the downcore gradients in microbial community composition to porewater oxygen and nitrate concentration profiles in an abyssal marine sediment column in the South Pacific Ocean. Archaeal 16S rRNA clone libraries showed a stratified archaeal community that changed from Marine Group I Archaea in the aerobic and nitrate-reducing upper sediment column towards deeply branching, uncultured crenarchaeotal and euryarchaeotal lineages in nitrate-depleted, anaerobic sediment horizons. Bacterial 16S rRNA clone libraries revealed a similar shift on the phylum and subphylum level within the bacteria, from a complex community of Alpha-, Gamma- and Deltaproteobacteria, Actinobacteria and Gemmatimonadetes in oxic surface sediments towards uncultured Chloroflexi and Planctomycetes in the anaerobic sediment column. The distinct stratification of largely uncultured bacterial and archaeal groups within the oxic and nitrate-reducing marine sediment column provides initial constraints for their microbial habitat preferences. PMID:21895908

Durbin, Alan M; Teske, Andreas

2011-09-06

33

Midwater biomass profiles over the Madeira Abyssal Plain and the contribution of copepods  

Microsoft Academic Search

Biomass profiles for plankton and micronekton throughout the water column at a site on the Madeira Abyssal Plain, position 31° 17' N 25° 24' W, depth 5 440 m, are described. Biomass declined exponentially with depth, > 80% of the plankton and > 95% of micronekton occured between 0–1000 m. The total biomass was low, ca 2 g dry weight

H. S. J. Roe

1988-01-01

34

Long-term change in the megabenthos of the Porcupine Abyssal Plain (NE Atlantic)  

Microsoft Academic Search

A radical change in the abundance of invertebrate megafauna on the Porcupine Abyssal Plain is reported over a period of 10 years (1989–1999). Actiniarians, annelids, pycnogonids, tunicates, ophiuroids and holothurians increased significantly in abundance. However, there was no significant change in wet weight biomass. Two holothurian species, Amperima rosea and Ellipinion molle, increased in abundance by more than two orders

D. S. M Billett; B. J Bett; A. L Rice; M. H Thurston; J Galéron; M Sibuet; G. A Wolff

2001-01-01

35

Heat flow evidence for hydrothermal convection in Cretaceous crust of the Madeira Abyssal Plain  

Microsoft Academic Search

36 measurements of heat flow have been made along two transects in an area to the east of Great Meteor Seamount, Madeira Abyssal Plain. Values ranging from 51 to 74 mW m-2 correlate partly with the basement topography. These data, together with results from a previous heat flow survey, have been compared to a numerical heat flux model which incorporates

Mark Noel; Mark W. Hounslow

1988-01-01

36

Interstitial water profiles and sites of diagenetic reactions, Leg 35, DSDP, Bellingshausen Abyssal Plain  

Microsoft Academic Search

Discrepancies between predicted and observed interstitial water profiles for sites 322 and 323, Leg 35, Bellingshausen Abyssal Plain, were used to identify sites of reaction for further mineralogical and chemical investigations. Two major reaction sites were identified at site 323: (1) In the silicification zone between 410 and 505 m depth, where dissolution of biogenic (opaline) silica, plagioclase and a

M. Kastner; J. M. Gieskes

1976-01-01

37

Tectonic evolution of the Perth Abyssal Plain's Quiet Zone, Southeast Indian Ocean  

NASA Astrophysics Data System (ADS)

During the Late Jurassic period, the Greater-Indian plate was torn away from Australia, dissociating East Gondwanaland. The Perth Abyssal Plain (PAP) is the southernmost rift segment along the western Australian margin, and has an onset age of ~136 Ma. New marine magnetic and swath bathymetry data, crossing the entire PAP, were acquired recently on geophysical cruise ss2011v06 aboard the R/V Southern Surveyor. These have lead to the outline of conjugate Indian and Australian M-series isochrons in the east and west PAP, respectively [1]. Yet, most of the PAP was created during the Cretaceous Normal Superchron (CNS, 121-83 Ma), a period of no geomagnetic field reversals, hence no comprehensive tectonic model for the PAP exists . Here we present preliminary findings of an analytic bathymetric and magnetic investigation aimed at elucidating the PAP's quiet zone. Recent discoveries regarding the evolution of the geomagnetic field during the CNS [2] provide new time markers that can be utilized to date the oceanic crust. The magnetic anomaly data exhibit the Q2 anomaly marker (~108 Ma), further constraining the spreading history of the PAP. Together with the ridgelet transform method [3] for automated abyssal hill delineation, we present new constraints on the development of crustal construction processes (spreading location, direction and rates) that took place along the PAP spreading center. References: [1] S.E. Williams, J.M. Whittaker, R. Granot, R.D. Muller (in preparation), New constraints on the seafloor spreading history in the Perth Abyssal Plain. [2] Granot, R., J. Dyment, and Y. Gallet (2012), Geomagnetic field variability during the Cretaceous Normal Superchron, Nature Geoscience, 5(3), 220-223. [3] Downey, N. J. and R. W. Clayton (2007), A ridgelet transform method for constraining tectonic models via abyssal-hill morphology, Geochemistry Geophysics Geosystems, 8, Q03004, doi: 10.1029/2006GC001440.

Ehrlich, Zohar Louis; Granot, Roi; Williams, Simon E.

2013-04-01

38

A new deep-sea pennatulacean (Anthozoa: Octocorallia: Chunellidae) from the Porcupine Abyssal Plain (NE Atlantic)  

NASA Astrophysics Data System (ADS)

During the BENGAL cruises, an important collection of deep-sea benthic organisms was sampled. Among the pennatulacean colonies, a previously undescribed species of chunellid was collected. That material is here described as the type species of a new genus, Porcupinella gen. nov. The new genus and species are described based on material collected in the Porcupine Abyssal Plain (NE Atlantic), 4,839-4,847 m in depth. This is the first time that a chunellid is reported from the Atlantic Ocean. The new genus is compared with the other genera in the family, and some phylogenetic remarks about the families Chunellidae and Umbellulidae are also provided.

López-González, Pablo J.; Williams, Gary C.

2011-09-01

39

The influence of oxic degradation on the sedimentary biomarker record I: evidence from Madeira Abyssal Plain turbidites  

Microsoft Academic Search

Free and ester-bound lipid biomarkers were analysed in oxidised and unoxidised parts of four distinct turbidites from the Madeira Abyssal Plain (MAP), which contained 1 to 2% organic carbon homogeneously distributed throughout the turbidites at the time they were deposited. These turbidites are well suited to study the effects of oxic degradation on lipid biomarkers without the complicating influence of

Marcel J. L. Hoefs; W. Irene C. Rijpstra; Jaap S. Sinninghe Damsté; J. W. de Leeuw

2002-01-01

40

Great Meteor East (Distal Maderia Abyssal Plain): Geological Studies of Its Suitability for Disposal of Heat-Emitting Radioactive Wastes.  

National Technical Information Service (NTIS)

The report summarizes geological and geophysical studies carried out by the Institute of Oceanographic Sciences up to December 1983 in an area of the Madeira Abyssal Plain in order to assess its suitability for the disposal of heat-emitting radioactive wa...

R. C. Searle P. J. Schultheiss P. P. E. Weaver M. Noel R. B. Kidd

1985-01-01

41

Export of organic carbon and biominerals derived from 234Th and 210Po at the Porcupine Abyssal Plain  

NASA Astrophysics Data System (ADS)

The simultaneous estimation of particulate organic carbon (POC), particulate inorganic carbon (PIC) and biogenic silica (BSi) export fluxes is key to the study of carbon export due to the hypothesized role of biominerals in the sinking of organic particles. This paper presents of the first attempts to measure downward fluxes of POC, PIC and BSi from the surface ocean using both the 234Th-238U and the 210Po-210Pb disequilibria and drifting sediments trap synchronously at the Porcupine Abyssal Plain in summer 2009. The combined use of the three techniques allowed us to analyze their suitability not only for POC flux estimates, but also as tracers of PIC and BSi fluxes. POC and biomineral/radionuclide ratios were measured in two size fractions to better understand differences between 234Th derived export and 210Po derived export. 210Po derived POC and biomineral fluxes were unexpectedly closer to POC and biomineral fluxes recorded by sediment traps than 234Th derived POC and biomineral fluxes which were higher than obtained from the other two approaches. We suggest that 210Po, because of its biogeochemical behavior, is a better proxy for POC and mineral fluxes than is 234Th in post bloom conditions. The contribution of smaller (1-53 ?m) particles to flux is also considered in order to explain the differences in derived fluxes.

Le Moigne, F. A. C.; Villa-Alfageme, M.; Sanders, R. J.; Marsay, C.; Henson, S.; García-Tenorio, R.

2013-02-01

42

Late Quaternary paleoenvironmental changes revealed by multi-proxy records from the Chukchi Abyssal Plain, western Arctic Ocean  

NASA Astrophysics Data System (ADS)

Late Quaternary paleoenvironmental changes in the western Arctic Ocean are revealed by multi-proxy records of core 03M03 from the Chukchi Abyssal Plain (CAP). Proxy parameters include lithology, grain size fractions, and mineralogy and petrology of ice-rafted detritus (IRD), element contents, biogenic components, ?18O, ?13C and Mg/Ca of planktonic foraminifera Neogloboquadrina pachyderma (sin.) (Nps). Seven IRD (> 250 ?m) peaks are interpreted as marking detrital input by rafting sea ice or icebergs during MIS 3 interstadials and early MIS 1. High MnO, CaO and MgO contents and high Ca/Al and Mg/Al ratios during MIS 3 and MIS 1 correspond to increases in ice-rafted detrital carbonates and the synchronous declines in siliciclastic elements (e.g., Al2O3, Fe2O3). Therefore, these warmer periods were characterized by a high detrital carbonate input entrained in icebergs from the Canadian Arctic Archipelago coeval with an increased input of Mn through rivers and/or coastal erosion. Relatively stable contents of siliciclastic elements and their ratios in the grayish sediment units are interpreted from turbid surface water plumes or nepheloid flows delivered by meltwater and/or brine rejection from ice-sheet margins at the Arctic Ocean periphery. Relatively stable clay- and silt-sized fractions were attributed mainly to sea ice entrainment over glacial–interglacial cycles. High foraminiferal abundances in the brown units during MIS 3 and 1 are related to enhanced calcareous plankton productivity under more open water conditions and/or the incremental input of Atlantic water masses. Relatively high TOC and opal contents in the grayish units of MIS 3 appear to have accumulated by lateral transport of organic matter from the Chukchi shelf to the deep abyssal plain. Lower contents of biogenic material in the brown units probably result from increased dilution by rapid IRD deposition, and from early diagenetic degradation. Depletions in Nps-?18O and -?13C concurrent with high foraminiferal abundances and IRD peaks within the brown units of MIS 3 and 1 are indicative of meltwater pulses, as previously documented across the Arctic Ocean. However, several Nps-?18O and -?13C depletions between the brown units B3 and B2 in MIS 3 could have resulted from enhanced sea ice formation. The Nps-Mg/Ca has the potential to record paleotemperature changes in the Arctic region, but still awaits a better calibration of the Nps-Mg/Ca–temperature relationship with results from core-tops, sediment traps, and plankton tows.

Wang, Rujian; Xiao, Wenshen; März, Christian; Li, Qianyu

2013-09-01

43

Tectonic implications of exposure of lower continental crust beneath the Iberia Abyssal Plain, Northeast Atlantic Ocean: Geophysical evidence  

NASA Astrophysics Data System (ADS)

We present new seismic data from a basement high beneath the southern Iberia Abyssal Plain that appears, from the latest Ocean Drilling Program (ODP) results and indirectly from various seismic observations, to consist of lower continental crustal material. This is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks. We infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting. Our results lead to the following new observations: low-angle detachment faults, previously reported along the east-west Lusigal-12 profile across the southern Iberia Abyssal Plain, penetrate both the 3-10 km thick continental crust and, unusually, the uppermost mantle. Processing of new multichannel seismic reflection profiles across the basement high on which ODP Sites 900, 1067, and 1068 are located reveals that the high is bounded by a previously unsuspected steep, landward dipping normal fault on its east flank. Basement cores from the above ODP sites also reveal that the high is not capped by the previously predicted early syn-rift sediment but by rocks from the lower continental crust. These unexpected observations are incorporated into a new tectonic model of the development of this part of the west Iberia margin which is also consistent with other geophysical observations. A novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3-6 km by a currently poorly understood process. The model implies three stages of deformation: (1) lithospheric extension, principally by symmetric pure shear, which leads to a ˜10 km thick crust in which the lower crust is largely absent over the axial zone and the crust-mantle boundary forms a shear zone, (2) further thinning and then dissection of the most distal continental crust by seaward dipping, low-angle normal faults, (3) inception of a high-angle, landward dipping normal fault that offsets the tectonized crust-mantle boundary and uplifts the lower crust to the crest of the basement high on which ODP Sites 900, 1067, and 1068 were drilled.

Whitmarsh, R. B.; Dean, S. M.; Minshull, T. A.; Tompkins, M.

2000-10-01

44

Hydrocarbon potential, organic matter diagenesis, sedimentology, and paleoenvironment of upper Mesozoic dark shales, northern Himalayas and Argo abyssal plain  

SciTech Connect

The Late Jurassic was a time favorable for the deposition of black shale-type sediments in shallow environments as known from circum-North Atlantic basins, North Sea, and Himalayan Tethys regions. Locally these shales have excellent hydrocarbon source potential. The site of the Spiti shales in the Thakkola region of north-central Nepal provides the opportunity to study a long-term (Oxfordian-Tithonian) stable, shallow, and oxygen-depleted environment. Strata with calcareous benthic communities show that the environment was not anoxic. Organic geochemical and sedimentological analyses on the Spiti shales (Oxfordian-Valanginian) were done to understand the hydrocarbon potential, organic matter diagenesis, sedimentology, and paleoenvironment of this sequence. The depositional environment changed, driven by tectono-eustatic and climatic events, from an open shelf (approximately 250 m) with low amounts of detrital input and rich macrofossil communities to an extremely shallow, partly continental environment with intercalations of quartzose channel fill, silty shales, rare lumachelle layers, and coal seams. Paleocurrents suggest a north-facing continental margin bordering the Tethys Sea. The organic matter changed from marine (Jurassic) to terrestrial in the Cretaceous. Analysis of coeval strata, deposited in the deep-marine environment off the northern Indian shelf (contiguous with the present-day Argo abyssal plain), demonstrates the changing shallow to deep-water hydrocarbon potential. It reflects the more advanced organic matter maturation of the onshore material due to Himalayan tectonics and allows tracing the transport of the organic matter.

Thurow, J.; Gibling, M.

1989-03-01

45

The Ionian Abyssal Plain - closure of a remnant Mesozoic oceanic domain: subbottom structures, deep deformation and the Calabrian subduction zone  

NASA Astrophysics Data System (ADS)

The Ionian Abyssal Plain (IAP), located in the Central Mediterranean area is a deep triangular shaped basin, surrounded by the Calabrian subduction zone to the NW, the Mediterranean Ridge to the NE and the Medina Ridges to the South. Available heat flow measurements show very low values under the Ionian Abyssal plain, suggesing a very old age of 180-200 Ma for the basin. The Bouguer gravity anomaly map shows only a strong positive anomaly in this region and the depth of the Moho is around 16 to 18 km corresponding to high refraction velocities of 8.1-8.2 km/s. The Ionian basin is interpreted as one of the oldest basins in the Mediterranean area, and is thought to represent a remnant part of the Mesozoic Tethyan ocean. Due to the complex relative motions of microplates and blocks, currently, the oceanic lithosphere of the Ionian basin is being simultaneously consumed by subduction to the NE beneath the Hellenic system and to the NW beneath Calabria. We present the most relevant lines of the Archimede multi-channel seismic cruise (1997, R/V Le Nadir) crossing the Ionian Abyssal Plain and the Calabrian subduction zone. Interpretation of this seismic dataset is based on correlation with published seismic data and with ESP results. Beneath the IAP, we identify a thick sedimentary cover (> 5km) from the Jurassic to the Plio-Quaternary in age, which overlies the oceanic basement. The Pre-Messinian sequences are affected by a set of NE/SW striking compressional faults with some syn-tectonic basins NW of these faults. These features are interpreted as a re-activated set of normal faults, possibly formed during rifting and/or subsequent accretion of oceanic crust. The orientation of the subbottom structures and the thickness of the Messinian deposits in the south-eastern part of the IAP may be linked with the presence of these faults and their activity through time. On the Calabrian side of the IAP, the Post-Messinian sequences are accreted to the Calabrian wedge. The weak rheology of the Messinian salts acts as the décollement level in the frontal part of the wedge. Repeated imbricate thrusting within in the Calabrian wedge allows the thickening of the Messinian sediments from 1200 m beneath the IAP to 2400 m 30 km away from the deformation front. A major tectonic structure is imaged east of the Malta Escarpment by the Archimede profiles, it offsets the top Pre-Messinian deposits by 0.5 - 1 sTWT increasing from S to N. This N150°E oriented lithospheric fault is interpreted as a tear fault (“STEP” fault) which has allowed the roll-back of the Ionian slab. The activity of these faults and the Calabrian and Mediterranean subduction zones have been reconstructed through time to reach the present-day physiology of the remnant Ionian basin. The analysis of their activity will allow a better understanding of the closure of the Ionian domain.

Gallais, F.; Gutscher, M.; Graindorge, D.; Klaeschen, D.

2010-12-01

46

Characteristics of sinking particles in the upper ocean at the Porcupine Abyssal Plain  

NASA Astrophysics Data System (ADS)

Sinking particles play an important role in the biological carbon pump, transferring carbon from the surface to the deep ocean. Data from deep ocean sediment traps suggest biominerals influence particle settling velocity, by increasing their density. However it is unclear whether this biomineral facilitated sinking applies to the upper ocean and if shape also plays a critical role on the rate at which particles sink. Measurements of particle settling velocity, density and drag were made in order to determine their influences on the particle sinking rate in the upper water column. Samples were taken during a cruise in summer 2009 from the Porcupine Abyssal Plain (PAP site) in the northwest Atlantic. Particles were collected from the base of the mixed layer (approximately 50m) using the Marine Snow Catcher. This instrument samples 100L of water and collects any settling particles in a 5L base chamber over 2 - 3 hours. After settling, the top 95L of water was drained off and any particles collected in the base chamber were transferred to the lab. Particles were individually picked using a Pasteur pipette and subdivided, into categories on the basis of appearance. Settling experiments were conducted in a 2L glass measuring cylinder filled with surface sea water, kept at a constant temperature of 15° C. After each experiment particles were preserved individually in buffered formalin for high quality image analysis back on land. Calculations of both excess density and drag were undertaken using data from microscopic measurements. Five main particle categories were identified; (1) diffuse fluff aggregates, (2) dense fluff aggregates, (3) centred particles (fluff aggregated around a central biomineral test), (4) organisms (biomineralising protists including foraminifera) and (5) calcareous tests. Statistical analysis suggested a significant difference in the rate at which the centred and calcareous particles sank (approximately 248 m day-1 and 1070 m day-1respectively) in relation to the other classes (142 - 184 m day-1). Excess densities and drag coefficients were respectively; 0.015 g cm-3 and 126, for organisms, 0.044 g cm-3 and 204 for centred particles and 1.68 g cm-3 and 1823 for calcareous tests. To determine whether particle density or drag, governs settling velocity, calculations were made of how typical (defined using averaged values from the observed data) sinking speeds vary with, (1) excess density and (2) drag coefficient. Comparison of the observed and typical particle characteristics suggested the differences observed in excess density were too small to account for the variation in measured sinking speed. However the change in calculated drag was larger than required to account for the observed variation in settling velocity. The results imply it is the process of aggregate formation and the resulting particle shape that has the greatest influence upon the rate at which particles sink in the upper ocean. This contrasts with the deep ocean ballast hypothesis, which suggests the incorporation of biominerals into aggregates influences particle sinking speeds.

Riley, Jennifer; Sanders, Richard; Achterberg, Eric

2010-05-01

47

Heat flow in the western abyssal plain of the Gulf of Mexico: Implications for thermal evolution of the old oceanic lithosphere  

NASA Astrophysics Data System (ADS)

The seafloor depth of an oceanic basin reflects the average temperature of the lithosphere. Thus the western abyssal plain of the Gulf of Mexico, which has tectonically subsided much (>1 km) deeper than other basins of comparable ages (late Jurassic), should be underlain by an anomalously cold lithosphere. In order to examine this hypothesis, we made suites of high-accuracy heat flow measurements at 10 sites along a line connecting Deep Sea Drilling Project (DSDP) sites 90 and 91 in the Sigsbee abyssal plain. The new heat flow sites were initially surveyed by 3.5-kHz echo sounding, 4-channel seismic reflection, seismic refraction with eight ocean bottom seismometers, and nine piston cores. We occupied a total of 48 heat flow stations along the seismic survey line (3 to 6 at each site), including 28 where we measured in situ thermal conductivities over the practical depth interval (4 m) of the new multioutrigger bow heat flow probe. We determined the heat flow associated with the lithosphere by correcting the values measured at the seafloor (41 to 45 mW/m2) for (1) the thermal effect of the sedimentation and (2) the additional heat from the radioactive elements within the sediments. The sedimentation history, required for the first, was reconstructed at each heat flow site based on ages and thicknesses of the major seismic stratigraphical sequences, age data from the DSDP cores, 3.5-kHz subbottom reflectors, and correlation of turbidite units found in the piston cores. Radiogenic heat production was measured for 55 sediment samples from four DSDP holes in the gulf, whose age ranged from present to Early Cretaceous (0.83 ?W/m3 on the average). This provided the correction for the second. The effects of these two secondary factors approximately cancel one another. The lithospheric heat flow under the abyssal plain thus estimated ranges from 40 to 47 mW/m2. These heat flow values are among the lowest in the Mesozoic ocean basins where highly reliable data (45 to 55 mW/m2) have been reported. Therefore the lithosphere under the gulf seems indeed colder than that under other old ocean basins. However, it is not as cold as expected from the large tectonic subsidence. The inconsistency between the depth and heat flow may imply an anomaly in the regional thermal isostasy.

Nagihara, S.; Sclater, J. G.; Phillips, J. D.; Behrens, E. W.; Lewis, T.; Lawver, L. A.; Nakamura, Y.; Garcia-Abdeslem, J.; Maxwell, A. E.

1996-02-01

48

Temporal variability of near-bottom particle resuspension and dynamics at the Porcupine Abyssal Plain, Northeast Atlantic  

Microsoft Academic Search

In order to study particle behaviour and its time-variability in the near-bottom layer on the Porcupine Abyssal Plain (48°50?N, 16°30?W, 4850 m), long-term measurements were made of currents, and nephelometry and particle samples were collected using an autonomous lander between mid-1996 and mid-1998. Water samples, collected in the Bottom Nepheloid Layer within 1000 m of the bottom, were filtered for

A. Vangriesheim; B Springer; P Crassous

2001-01-01

49

Seismic evidence of exhumed mantle rock basement at the Gorringe Bank and the adjacent Horseshoe and Tagus abyssal plains (SW Iberia)  

NASA Astrophysics Data System (ADS)

The Gorringe Bank is a gigantic seamount that separates the Horseshoe and Tagus abyssal plains offshore SW Iberia, in a zone that hosts the convergent boundary between the Africa and Eurasia plates. Although the region has been the focus of numerous investigations since the early 1970s, the lack of appropriate geophysical data makes the nature of the basement, and thus the origin of the structures, still debated. In this work, we present combined P-wave seismic velocity and gravity models along a transect that crosses the Gorringe Bank from the Tagus to the Horseshoe abyssal plains. The P-wave velocity structure of the basement is similar in the Tagus and Horseshoe plains. It shows a 2.5–3.0 km-thick top layer with a velocity gradient twice stronger than oceanic Layer 2 and an abrupt change to an underlying layer with a five-fold weaker gradient. Velocity and density is lower beneath the Gorringe Bank probably due to enhanced fracturing, that have led to rock disaggregation in the sediment-starved northern flank. In contrast to previous velocity models of this region, there is no evidence of a sharp crust–mantle boundary in any of the record sections. The modelling results indicate that the sediment overlays directly serpentinite rock, exhumed from the mantle with a degree of serpentinization decreasing from a maximum of 70–80% under the top of Gorringe Bank to less than 5% at a depth of ˜20 km. We propose that the three domains were originally part of a single serpentine rock band, of nature and possibly origin similar to the Iberia Abyssal Plain ocean–continent transition, which was probably generated during the earliest phase of the North Atlantic opening that followed continental crust breakup (Early Cretaceous). During the Miocene, the NW–SE trending Eurasia–Africa convergence resulted in thrusting of the southeastern segment of the exhumed serpentinite band over the northwestern one, forming the Gorringe Bank. The local deformation associated to plate convergence and uplift could have promoted pervasive rock fracturing of the overriding plate, leading eventually to rock disaggregation in the northern flank of the GB, which could be now a potential source of rock avalanches and tsunamis.

Sallarès, Valentí; Martínez-Loriente, Sara; Prada, Manel; Gràcia, Eulàlia; Ranero, César; Gutscher, Marc-André; Bartolome, Rafael; Gailler, Audrey; Dañobeitia, Juan José; Zitellini, Nevio

2013-03-01

50

Fate of corrosion products released from stainless steel in marine sediments and seawater. Part 4: Hatteras abyssal red clay  

SciTech Connect

A study in which neutron-activated 347 stainless steel was exposed to surficial sediment from a site in the Hatteras Abyssal Plain of the Northwest Atlantic Ocean is described. This sediment consists of approx. 20% CaCO/sub 3/, which could lead to the formation of calcareous scale on the metal surface and reduce the corrosion rate. The distribution of indigenous metals among different chemical fractions shows that extractable Cr, Mn, Fe, Co, and Zn were associated with amorphous Mn and Fe oxides. Most of the remaining extractable Cr, and about a third of the extractable Cu appear to have been weakly complexed. Major fractions (25 to 36%) of extractable Mn, Co and Ni were present as adsorbed cations. Organic complexation appears to account for a large amount of extractable Fe, Ni, Cu and Zn. Neutron-activated 347 stainless steel specimens were exposed to sediment slurry under aerobic and non-oxygenated conditions for a period of 94 days. The redox potential measurements for air-sparged and N/sub 2/, CO/sub 2/-sparged sediment slurries were +410 and +60 mv, respectively. The presence of 0/sub 2/ produced increased amounts of corrosion products. Chemical extraction showed that relatively labile substances constituted about 84% of the /sup 60/Co activity released in aerated sediment. Relatively labile substances constitute about 82% of the total /sup 60/Co activity released under non-oxygenated conditions. A large fraction of /sup 60/Co which was in the soluble or easily dissolved forms under non-oxygenated conditions appears to have been more strongly adsorbed to the sediment under aerated conditions.

Schmidt, R.L.

1982-07-01

51

Quantitative Estimates of Biological Mixing Rates in Abyssal Sediments  

Microsoft Academic Search

Biological mixing in deep-sea sediments is described in terms of a time-dependent eddy diffusion model where mixing takes place to a depth L at constant eddy diffusivity D. The differential equation that describes this model has been solved for an impulse source of tracer delivered to the plane surface that forms the top of the mixed layer. The solution then

D. R. Schink

1975-01-01

52

Connections between climate, food limitation, and carbon cycling in abyssal sediment communities  

PubMed Central

Diverse faunal groups inhabit deep-sea sediments over much of Earth's surface, but our understanding of how interannual-scale climate variation alters sediment community components and biogeochemical processes remains limited. The vast majority of deep-sea communities depend on a particulate organic carbon food supply that sinks from photosynthetically active surface waters. Variations in food supply depend, in part, on surface climate conditions. Proposed ocean iron fertilization efforts are also intended to alter surface production and carbon export from surface waters. Understanding the ecology of the abyssal sediment community and constituent metazoan macrofauna is important because they influence carbon and nutrient cycle processes at the seafloor through remineralization, bioturbation, and burial of the sunken material. Results from a 10-year study in the abyssal NE Pacific found that climate-driven variations in food availability were linked to total metazoan macrofauna abundance, phyla composition, rank-abundance distributions, and remineralization over seasonal and interannual scales. The long-term analysis suggests that broad biogeographic patterns in deep-sea macrofauna community structure can change over contemporary timescales with changes in surface ocean conditions and provides significant evidence that sediment community parameters can be estimated from atmospheric and upper-ocean conditions. These apparent links between climate, the upper ocean, and deep-sea biogeochemistry need to be considered in determining the long-term carbon storage capacity of the ocean.

Ruhl, Henry A.; Ellena, Jacob A.; Smith, Kenneth L.

2008-01-01

53

Seismic velocity structure across the Eastern Newfoundland (Grand Banks) and Iberia Abyssal Plain Continental Margin Conjugates  

NASA Astrophysics Data System (ADS)

We acquired coincident wide-angle and multi-channel seismic (MCS) data over three transects across the Eastern Grand Banks/Newfoundland Basin (NB) in July-August, 2000. This non-volcanic continental margin is conjugated to the Galicia Bank/Iberia Abyssal Plain (IAP) margins. The objective was to determine structures reaching from full thickness continental crust seaward to unequivocal oceanic crust, and to compare these with their conjugates in order to better constrain the nature of the extension. Reported here is the southernmost transect (Transect 3), which is conjugated to the southern IAP near profile IAM-9. Over this 565km-long profile, we recorded wide-angle reflection/refraction data on 23 ocean bottom seismometers. The seismic velocity structures from the beginning of the profile eastward to the landward limit of the Carson Basin can be interpreted as full thickness (35km) typical Newfoundland Appalachian continental crust. The crust thins abruptly beneath the Carson Basin to ~7km (extension factor = 5) over a distance of 50km and then gradually to < 3km thickness over the next 60km, beneath the NB. This thinning is dominated by the removal of the lower continental crust (extension factor = ~ 8.0). Crustal thinning of the IAP margin is relatively gentler (from 28km to 8km thickness over a distance of 90km). Similar to the IAP margin, a wide layer (~200km) of low velocity mantle (7.5-8.0km/s) is observed beneath the extremely thin (< 5km) crust of the NB up to 15km below sea level. These velocities are interpreted as of serpentinized mantle. A transition zone ~80km wide is found seaward of the extremely thin continental crust (beginning at ~150km from the shelf break) where the serpentinized mantle is observed very close to the basement. The thin 'crust' (~ 2km) over this zone is poorly resolved but is consistent with a high gradient layer similar to that of the IAP transition interpreted as exhumed mantle. The transition zone ends at ~230km from the shelf break without evidence of a ridge province similar to that observed at the seaward end of IAP transition zone. The presence of oceanic layer 2 (4.7-6.3km/s) and layer 3 (6.3-7.4km/s) seaward defines the oceanic crust, and the serpentinized-mantle layer pinches out. The MCS reflection data also show changes in reflection character of basement that match the changes in velocity structure outlined above. This velocity model, therefore, further supports observations in reflectivity to show that the conjugates are similar in gross scale but different within individual structural zones.

Lau, K. W. H.; Louden, K. E.; Funck, T.; Hall, J.; Deemer, S.; Tucholke, B.; Holbrook, W. S.; Larsen, H. C.; Hopper, J.

2003-04-01

54

Diversity of peracarid crustaceans (Malacostraca) from the abyssal plain of the Angola Basin  

Microsoft Academic Search

During the expedition DIVersity of the abyssal Atlantic benthos (DIVA-1) with RV “Meteor” in July 2000, samples were taken at seven stations by means of an epibenthic sledge north of the Walvis Ridge in the Angola Basin off Namibia in 5125–5415m depth. Two hundred and forty one species of Peracarida are identified from the material so far. Dominant elements of

Angelika Brandt; Nils Brenke; Hans-Georg Andres; Saskia Brix; Jürgen Guerrero-Kommritz; Ute Mühlenhardt-Siegel; Johann-Wolfgang Wägele

2005-01-01

55

Evidences of intraplate deformation in the West Madeira Abyssal Plain (eastern North Atlantic) from seismic reflection and multibeam swath bathymetry data  

Microsoft Academic Search

The West Madeira Abyssal Plain is located in the eastern North Atlantic off Madeira Islands, forming part of the Canary Basin and reaching a mean water depth of 5300 m. This region is also located within Africa plate at about 500 km southwards from the Açores-Gibraltar plate boundary, and for that reason lacks seismic activity. Although this region being located

C. Roque; M. Simões; N. Lourenço; M. Pinto de Abreu

2009-01-01

56

Heat flow in the western abyssal plain of the Gulf of Mexico: Implications for thermal evolution of the old oceanic lithosphere  

SciTech Connect

This report discusses the heat flow and constraints on the heat flux from the lithosphere under the thick sedimentary layer of the western abyssal plain of the Gulf of Mexico. This paper developes the best estimates for the lithospheric heat loss that is free from near-surface disturbance.

Nagihara, S. [Univ. of Houston, TX (United States); Sclater, J.G. [Univ. of California, San Diego, CA (United States); Phillips, J.D.; Behrens, E.W. [Univ. of Texas, Austin, TX (United States)] [and others

1996-02-10

57

Deep structure in the vicinity of the ocean-continent transition zone under the southern Iberia Abyssal Plain  

NASA Astrophysics Data System (ADS)

We present results from a seismic and magnetic study of acoustic basement beneath the southern Iberia Abyssal Plain. An ocean-continent transition zone (OCT), characterized by subdued basement relief and weak magnetization, lies seaward of thinned continental crust. Its western edge is a region with isochron-parallel ridges and generally higher basement magnetizations. The width of the OCT decreases to the north. The seaward change in basement morphology coincides with changes in seismic velocity structure, but in both regions, anomalously high velocities at shallow depths within acoustic basement suggest that the OCT consists largely of serpentinized peridotite. Our magnetic and seismic data support the hypothesis of exhumed upper mantle, more than that of ultraslow sea-floor spreading, for the origin of the OCT.

Discovery 215 Working Group; Minshull, T. A.; Dean, S. M.; Whitmarsh, R. B.; Russell, S. M.; Louden, K. E.; Chian, D.

1998-08-01

58

Epifaunal and shallow infaunal foraminiferal communities at three abyssal NE Atlantic sites subject to differing phytodetritus input regimes  

Microsoft Academic Search

Multiple corer samples (0–1 cm sediment layer and overlying phytodetritus) obtained at three northeast Atlantic sites were analysed for Rose Bengal stained benthic foraminifera ( > 63 ?m). Strong phytodetrital pulses have been documented at the northern site on the Porcupine Abyssal Plain (PAP; 48°50'N, 16°30'W) but not at the southern sites on the Madeira Abyssal Plain (MAP; 31°N, 20°W)

Andrew J. Gooday

1996-01-01

59

Depth-Imaging the Transfer Boundary Between the Galicia Bank and Iberia Abyssal Plain Rifted Margin Segments, Integrating MCS and OBS Data  

Microsoft Academic Search

We present multi-channel seismic reflection data and coincident wide-angle ocean-bottom seismometer (OBS) data from the non-volcanic rifted margin west of Iberia. Profile ISE-9 runs 270 km north-south, 200 km west of the Portuguese coast, imaging the physiographic transition between Galicia Bank in the north (500-3000 m water depths) and the Iberia Abyssal Plain in the south (4000-5500 m water depths).

S. A. Clark; D. S. Sawyer

2005-01-01

60

Seismic interpretation of pelagic sedimentation regimes in the 18-53 Ma eastern equatorial Pacific: Basin-scale sedimentation and infilling of abyssal valleys  

NASA Astrophysics Data System (ADS)

Understanding how pelagic sediment has been eroded, transported, and deposited is critical to evaluating pelagic sediment records for paleoceanography. We use digital seismic reflection data from an Integrated Ocean Drilling Program site survey (AMAT03) to investigate pelagic sedimentation across the eastern-central equatorial Pacific, which represents the first comprehensive record published covering the 18-53 Ma eastern equatorial Pacific. Our goals are to quantify (1) basin-hill-scale primary deposition regimes and (2) the extent to which seafloor topography has been subdued by abyssal valley-filling sediments. The eastern Pacific seafloor consists of a series of abyssal hills and basins, with minor late stage faulting in the basement. Ocean crust rarely outcrops at the seafloor away from the rise crest; both hills and basins are sediment covered. The carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data. Overall, we recognized three different sedimentation regimes: depositional (high sedimentation rate), transitional, and minimal sedimentation (low sedimentation rate) regimes. In all areas, the sedimented seafloor mimics the underlying basement topography, although the degree to which topography becomes subdued varies. Depositional regimes result in symmetric sedimentation within basins and subdued topography, whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief. Regardless of sedimentation regime, enhanced sediment deposition occurs within basins. However, we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills. If this variation is due to sediment focusing, the focusing factor in the basins, as measured by 230Th, is no more than a factor of ˜1.3 of the total vertical particulate rain.

Tominaga, Masako; Lyle, Mitchell; Mitchell, Neil C.

2011-03-01

61

Seismotectonics of the Gulf of Cadiz and Horseshoe Abyssal Plain - active faulting in continental and oceanic mantle  

NASA Astrophysics Data System (ADS)

In the area to the west of the Gibraltar Arc the plate boundary between Africa and Iberia is poorly defined. The deformation in the area is forced by the slow NW-SE convergence of 4 mm/yr between the oceanic domains of Iberia/Eurasia and Africa and is accommodated over a 200 km broad tectonically-active deformation zone. The region, however, is also characterized by large earthquakes and tsunamis, such as the 1969 Mw=7.9 Horseshoe Abyssal Plain earthquake and the November 1, 1755 Great Lisbon earthquake with an estimated magnitude of Mw~8.5. The exact location of the source of the 1755 Lisbon earthquake is still unknown. Recent work, however, may suggest that the event occurred in the vicinity of the Horseshoe fault, an oblique thrust fault. Further, the area is marked by the presence of compressive structures with a roughly NE-SW orientation and E-W trending, segmented, crustal-scale, strike slip faults that extend from the Gorringe Bank to the Gibraltar arc in the eastern Gulf of Cadiz, which were called "South West Iberian Margin" or SWIM faults. The fault system may mark a developing Eurasia-Africa plate boundary. Two local seismic networks were operated in the area. First, within the framework of TOPOE-EUROPE, a network of 24 ocean bottom seismometers (OBS) monitored the seismicity between January and July 2010 in the northern Gulf of Cadiz to the north of 36°N between 9°30'W and ~7 °W. The second network operated between April and October 2012 14OBS in the vicinity of the Horseshoe fault between 10°W to 11°W, and 35°50'N to 36°10'N. Recordings from the both deployments were supplemented by land stations operated in Portugal and the Gibraltar Arc. The networks provided in the order of 100 locale earthquakes occurring with the networks. In the Gulf of Cadiz, the two largest events of Mw~3.6 where thrust faulting events occurring in the vicinity of the Portimao Bank. With a depth of 40-50 km these events, among others, occurred within the continental mantle. Earthquakes in the Horseshoe occurred at even greater depth, at 40-60 km, either in oceanic or unroofed continental mantle. The large source depth observed in the Horseshoe Abyssal plain supports the interpretation that large catastrophic earthquakes, like the Great Lisbon earthquake of 1755, may indeed occur in the area.

Grevemeyer, Ingo; Matias, Luis

2013-04-01

62

Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies in the Perth Abyssal Plain  

NASA Astrophysics Data System (ADS)

seafloor within the Perth Abyssal Plain (PAP), offshore Western Australia, is the only section of crust that directly records the early spreading history between India and Australia during the Mesozoic breakup of Gondwana. However, this early spreading has been poorly constrained due to an absence of data, including marine magnetic anomalies and data constraining the crustal nature of key tectonic features. Here, we present new magnetic anomaly data from the PAP that shows that the crust in the western part of the basin was part of the Indian Plate—the conjugate flank to the oceanic crust immediately offshore the Perth margin, Australia. We identify a sequence of M2 and older anomalies in the west PAP within crust that initially moved with the Indian Plate, formed at intermediate half-spreading rates (35 mm/yr) consistent with the conjugate sequence on the Australian Plate. More speculatively, we reinterpret the youngest anomalies in the east PAP, finding that the M0-age crust initially formed on the Indian Plate was transferred to the Australian Plate by a westward jump or propagation of the spreading ridge shortly after M0 time. Samples dredged from the Gulden Draak and Batavia Knolls (at the western edge of the PAP) reveal that these bathymetric features are continental fragments rather than igneous plateaus related to Broken Ridge. These microcontinents rifted away from Australia with Greater India during initial breakup at ~130 Ma, then rifted from India following the cessation of spreading in the PAP (~101-103 Ma).

Williams, Simon E.; Whittaker, Joanne M.; Granot, Roi; Müller, Dietmar R.

2013-07-01

63

Seismic constraints on the three-dimensional geometry of low-angle intracrustal reflectors in the Southern Iberia Abyssal Plain  

NASA Astrophysics Data System (ADS)

Several lines of evidence suggest that simple shear rifting of the continental crust, in the form of low-angle detachment faulting, occurred during the final stages of continental breakup between West Iberia and the Grand Banks. The primary evidence for such faulting is the occurrence of low-angle, high amplitude reflectors within the basement adjacent to the ocean-continent transition zone. Here we present a series of intersecting, depth migrated seismic reflection profiles that image one such reflector, the H-reflector, located on the southern edge of Galicia Bank. `H' lies beneath several boreholes drilled during ODP Legs 149 and 173, in a region where the oceanward extent of extended continental crust steps at least 150 km westward from its location in the southern Iberia Abyssal Plain to its location off the relatively shallow Galicia Bank. In our profiles `H' appears to define a surface that extends over a region of at least 200 km2 and that dips down ~19° to the north, towards Galicia Bank. The profiles show that a close affinity exists between `H' and the most seaward continental crust. Based on geophysical data and ODP drilling results, we infer that the basement above `H' is composed of continental crust deformed by extensional faults into a series of wedge-shaped blocks and thin slivers. These basement wedges have a complex 3-D geometry. `H' rises to the basement surface on a number of the seismic profiles and appears to define locally the oceanward extent of continental fault blocks.

Dean, S. M.; Minshull, T. A.; Whitmarsh, R. B.

2008-11-01

64

South-directed mass wasting from the Galicia Bank: How might it affect interpretations of seismic and drilling results in the Iberia Abyssal Plain?  

NASA Astrophysics Data System (ADS)

Recently, we have interpreted seismic profiles ISE-1 and ISE-9 crossing the west and south sides of the Galicia Bank, west of Spain in the Atlantic Ocean, to show evidence of very large mass wasting events presumed to have occurred late in the process of continental breakup and the initiation of seafloor spreading. The events are driven by large topographic relief created at the boundary between the half-thickness, extended, continental crust of the Galicia Bank and crust composed of mantle rocks exhumed to the seafloor (Zone of exhumed continental mantle; ZECM) after the continental crust has separated and before normal seafloor spreading is established. The slide material is interpreted to consist of blocks of Galicia Bank extended continental crust and pre-sliding sediment. A portion of this slide material was emplaced over the ZECM. We examine possible consequences of this controversial hypothesis for the well-known and widely interpreted ODP Legs 149 and 173 drilling in the Iberia Abyssal Plain and nearby seismic profiles Lusigal 12 and IAM-9. We interpret that profile Lusigal 12 crosses the foot of the proposed south-directed landslide. We argue that the several low-angle faults (including H, HD, and HDD) observed in profile Lusigal 12 were formed within and at the base of the foot of the slide covering ZECM. We interpret that profile IAM-9 crosses the region of ZECM just to the south of the toe of the landslide. However, because the landslide moved continental crustal blocks to the south of their original position, we interpret that the pre-slide boundary between extended crust of the Galicia Bank and ZECM lies tens of km north of its presently mapped position. Specifically, we map this boundary north of both profile Lusigal 12 and the ODP drilling transect. This suggests that the eastern part of the drilling transect overlies mantle rocks that were exhumed at the seafloor and existed at the seafloor for some time before the continental rocks and pre-rift sediments were placed on top by southward sliding off the Galicia Bank. If true, this contrasts with the now commonly accepted model in which the eastern part of the drilling transect lies over mantle that was continuously covered by continental crust and pre-rift sediment, and where all movements of continental crust were to the west in detachment-bounded slivers.

Sawyer, D. S.; Clark, S. A.

2006-12-01

65

Characteristics of sinking particles in the upper ocean at the Porcupine Abyssal Plain  

Microsoft Academic Search

Sinking particles play an important role in the biological carbon pump, transferring carbon from the surface to the deep ocean. Data from deep ocean sediment traps suggest biominerals influence particle settling velocity, by increasing their density. However it is unclear whether this biomineral facilitated sinking applies to the upper ocean and if shape also plays a critical role on the

Jennifer Riley; Richard Sanders; Eric Achterberg

2010-01-01

66

Spatio-temporal changes in the distribution of phytopigments and phytoplanktonic groups at the Porcupine Abyssal Plain (PAP) site  

NASA Astrophysics Data System (ADS)

We have made a comprehensive study of pigment distributions and microscopically determined phytoplankton abundances within the Porcupine Abyssal Plain (PAP) location in the North Atlantic to better understand phytoplankton variability, and make some suggestions regarding the composition of the material falling to the sea bed and its impacts on benthic organisms such as Amperima rosea. The area has been the focus of many studies of ocean fluxes and benthic communities over recent years, but little attention has been given to the spatio-temporal variability in the surface waters. Dawn casts over a 12-day period at the PAP mooring site (48.83°N 16.5°W) revealed the presence of only one species, the diatom Actinocyclus exiguus, at bloom concentrations for just 5 days. Smaller populations of other diatoms and the dinoflagellates Gymnodinium and Gyrodinium were also present at this time. Following this 5-day interval, a mixed population of small-sized dinoflagellates, prymnesiophytes, prasinophytes, chrysophytes and cyanobacteria occurred. It is clear from concomitant CTD/bottle surveys that rapid changes in phytoplankton community structure at a fixed time series position do not necessarily reflect a degradation or manifestation of one particular species but rather represent the movement of eddies and other water masses within very short timescales. These cause substantial variability in the species class and size fraction that may explain the variability in carbon export that has been seen at the PAP site. We also make some suggestions on the variable composition of the material falling to the seabed and its impact on benthic organisms such as Amperima rosea.

Smythe-Wright, Denise; Boswell, Stephen; Kim, Young-Nam; Kemp, Alan

2010-08-01

67

Temporal and depth-related differences in prokaryotic communities in abyssal sediments associated with particulate organic carbon flux  

NASA Astrophysics Data System (ADS)

Particulate organic carbon (POC) flux is hypothesized to be the most important parameter influencing activity and biomass of prokaryotic and faunal communities in the abyssal seafloor, but there is little evidence of POC-related changes in community composition of prokaryotes. This hypothesis was tested by 16S rRNA-gene-based analysis of prokaryotic DNA and RNA extracted from abyssal seafloor sediments during periods of low and high POC flux. Fingerprint analysis of prokaryotic communities indicated that approximately 50% of the phylotypes were identical at each sediment horizon, regardless of the temporal variations in POC flux. However, phylotypes were also detected that represented a relatively dynamic component of these communities and were probably strongly influenced by the prevalent POC flux regime. These patterns were also detected in deeper sediment horizons. DNA- and RNA-based community profiles differed, although both approaches had similar community dynamics. Crenarchaeota showed the strongest shift in community composition in response to availability of labile POC, indicating that POC flux may have a more pronounced impact on crenarchaeal communities than on bacterial communities. The high number of phylotypes common to each sample time suggests that both standing stock and active prokaryotic communities are stable.

Moeseneder, M. M.; Smith, K. L., Jr.; Ruhl, H. A.; Jones, D. O. B.; Witte, U.; Prosser, J. I.

2012-12-01

68

Evidence for ocean-continent crust boundary beneath the abyssal plain of the East Central Atlantic  

NASA Astrophysics Data System (ADS)

A survey of geophysical results and basalt characteristics of the East Central Atlantic suggests that such data are at present unable to define the seaward limit of the thinned continental crust. The combined evidence from margin sedimentation, deep-sea diapirism, salinity concentration in DSDP-IPOD cores, and the distribution of deep-sea barite and palygorskite-sepiolite assemblages indicate that the Central Atlantic developed from a wide rift basin within a normal continental setting. The notion of an extensive pre-drift basin gains additional support from the occurrences of Lower Cretaceous black shales which are interpreted as resulting from a tectonomagmatic forerunner phase to the actual continental separation process. Seafloor spreading which appears to have commenced at around 90 Ma B.P. (Cenomanian-Turonian), following major phases of subsidence and crustal attenuation in Jurassic and Lower Cretaceous, is identified by an apparently sharp change-over from reducing to oxygenated deep-sea environment as well as by the 'onset' of a major sedimentary hiatus. The new development model of the East Central Atlantic is regarded as a representative example of a global pattern; commencement of seafloor spreading in the Upper Cretaceous probably explains the world wide 'Cenomanian' transgression as well as the formation of extensive Upper Cretaceous sedimentary basins in the interior of the major continental blocks. A consequence of this model is that vertical crustal dynamics seem to be as important as seafloor spreading in the development of the oceanic lithosphere. Thus, in the Central Atlantic spreading is probably confined only to the region of the elevated Mid-Atlantic Ridge.

Storetvedt, K. M.

1987-09-01

69

Weddell Fan and associated abyssal plain, Antarctica: Morphology, sediment processes, and factors influencing sediment supply  

Microsoft Academic Search

The newly discovered Weddell Fan, Antarctica, covers 0.75 million km2. The adjacent continental shelf is characterized by deep, rugged topography; the inner shelf is covered by a grounded polar ice sheet. The upper fan has numerous deep, V-shaped canyons that intersect a slope-base, leveed fan valley. Piston cores from the valley contain disorganized gravel grading upward into graded gravel and

John B. Anderson; Robyn Wright; Barbara Andrews

1986-01-01

70

Chemistry and mineralogy of pyrite-enriched sediments at a passive margin sulfide brine seep: abyssal Gulf of Mexico  

USGS Publications Warehouse

Pyrite is rapidly accumulating at the contact between the Cretaceous limestones of the Florida Platform and the hemipelagic sediments of the abyssal Gulf of Mexico. Sediments sampled with the submersible "Alvin" in 3266 m of water are associated with a dense community of organisms that depend on chemosynthetic primary production as a food source. Analysis of the chemistry, mineralogy, and textural composition of these sediments indicate that iron sulfide mineralization is occurring at the seafloor within an anoxic micro-habitat sustained by the advection of hydrogen sulfide-charged saline brines from the adjacent platform. The chemosynthetic bacteria that directly overlie the sediments oxidize hydrogen sulfide for energy and provide elemental sulfur that reacts with iron monosulfide to form some of the pyrite. The sediments are mixtures of pyrite (??? 30 wt.%), BaSr sulfates (??? 4 wt.%), clays, and locally derived biogenic carbonates and are progressively being cemented by iron sulfides. Oxidation of hydrogen sulfide produces locally acidic conditions that corrode the adjacent limestones. Potential sources of S, H2S, Fe, Ba, and Sr are discussed. ?? 1987.

Commeau, R. F.; Paull, C. K.; Commeau, J. A.; Poppe, L. J.

1987-01-01

71

Geochemical indicators of subsidence in sediment, Terrebonne coastal plain, Louisiana  

SciTech Connect

Sediments comprising the Terrebonne Coastal Plain consist primarily of clays, silts, and peats that fill the depressions between alluvial ridges created by former Mississippi River courses. These sediments are subsiding at variable rates. Depositional history, sedimentation rates, and environment of deposition affect both the types and abundances of diagenetic products found in deltaic sediments. Early diagenesis influences the geotechnical properties of these coastal plain deposits and their local subsidence rates. Diagenetic mineralogy and elemental geochemistry therefore offer clues to understanding some of the variability associated with subsidence in the lower deltaic plain. Results show that diagenetic minerals consist of carbonates (siderite, calcite, dolomite, and rhodochrosite), iron sulfides, vivianite, and iron oxides. In general, siderite and other carbonates as well as pyrite are higher in the fine-grained swamp and lacustrine clays of the upper/middle deltaic plain environments where sediment compaction and subsidence rates are considerably lower than rapidly deposited lower delta and marine deposits. Prodelta clays, for example, contain fewer varieties and lower abundances of diagenetic inclusions than their freshwater fine-grained counterparts. Oxidized sediments of well-drained swamp and natural levee deposits that contain goethite, iron oxides, manganese oxides, and carbonates are stabilized early in their depositional history and therefore do not lend themselves to rapid volume reduction associated with dewatering and compaction. Elemental concentrations can also be interpreted to reflect relative diagenetic activity in the sediments. These preliminary results indicate that close examination of diagenetic mineralogical and geochemical features can provide valuable information concerning the subsidence history of delta plain areas.

Bailey, A.M. (Univ. of Southwestern Louisiana, Lafayette (USA)); Roberts, H.H. (Louisiana State Univ., Baton Rouge (USA))

1990-09-01

72

Morphology and Late Quaternary sedimentation on the North Faeroes slope and abyssal plain, North Atlantic  

Microsoft Academic Search

Whilst the interplay between tectonics, glaciation and oceanography is reasonably well understood on some high-latitude margins, relatively little is known about the nature of Quaternary processes affecting the continental margin north of the Faeroe Islands. We therefore present side-scan sonar (GLORIA and TOBI) and 3.5kHz data in combination with a new regional bathymetry in order to characterise and analyse the

J Taylor; J. A Dowdeswell; N. H Kenyon; R. J Whittington; Tj. C. E van Weering; J Mienert

2000-01-01

73

Seismic Interpretation and Quantification of Abyssal-Hill-Scale Pelagic Sedimentation Regimes in the 0-53 Ma Eastern Equatorial Pacific  

NASA Astrophysics Data System (ADS)

To evaluate paleoceanographic conditions from chemical and physical records in pelagic sediments more accurately, it is imperative to understand how the sediment has been transported, deposited and eroded. To date, few researchers have studied how these processes have affected seafloor topography over time, and the works were limited to near surface data or to narrow geographic regions (e.g., Laguros and Shipley, 1989; Jordan and Webb, 1996; Malinverno, 1995; Mitchell, 1996). In this study, we have investigated pelagic sedimentation regimes across various parts of the 0-53 Ma eastern-central equatorial Pacific where changes in sedimentation rates are significant. Our goals are to quantify (1) abyssal-hill-scale primary deposition regimes with respect to the equatorial high productivity zone, and (2) the extent to which seafloor topography has been subdued by abyssal valley-filling. We used a recently collected seismic reflection data set (AMAT03 on R/V Revelle, 2006) aided by information from Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) holes where the seismic survey lines cross ODP Site 849, DSDP 572, and 80, and Integrated Ocean Drilling Program Site U1331-1338. The seismic data were collected using 4 and 48 channel streamers for underway and around-site surveys, respectively, and were processed by band-pass filtering, normal move-out, stacking, and F-K migration. The seafloor in this region is characterized by a series of abyssal hills and basins, with minor late stage faulting in the basement and some seamounts identifiable in multibeam sonar data also collected on the cruise. We focused on three long profiles that transect a series of abyssal hills and basins, and 10 and 8 selected study sites from underway and site-survey profiles, respectively. We revisited the seismic stratigraphy of Mayer et al. (1985, 1986) and Bloomer et al. (1995) to estimate ages of our interpreted seismic horizons. Overall, we recognized three different sedimentation regimes in our survey area: depositional (high sedimentation rate), transitional, and erosional or low sedimentation rate regimes. These regimes appear to persist with age in each location. In depositional regimes, sediment deposits are symmetric within basins, whereas in erosional regimes the deposits are more asymmetric and the sediment surface topography is a less subdued version of the basement topography. In all areas, the sediment topography mimics the underlying basement topography although the degree to which it becomes subdued varies. In the seismic data, the CCD is identified at 4500 m because top clay layer is observed below this depth. Regardless of sedimentation regime, enhanced sediment deposition occurs over basement valleys. However, the amount of this enhancement is not dependent on sedimentation regime and the basin infill is no more than twice thicker than above the abyssal hills. If this variation were solely due to sediment particle focusing, it limits the variation from hill to basin to be no more than 33% of the total vertical particulate rain.

Tominaga, M.; Lyle, M. W.; Mitchell, N.

2009-12-01

74

Latitudinal variation in invertebrate megafaunal abundance and biomass in the North Atlantic Ocean Abyss  

Microsoft Academic Search

Megafauna was collected by otter trawl at two widely separated abyssal sites in the eastern North Atlantic Ocean. The northern site, on the Porcupine Abyssal Plain (PAP, 4850m), is subject to strong seasonal pulses of phytodetritus deposition, whereas the southern site, on the Madeira Abyssal Plain (OLIGO, 4500–4650m), showed no indication of such deposition. Data from these two sites were

M. H. Thurston; A. L. Rice; B. J. Bett

1998-01-01

75

Amazonis Planitia: The role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on Mars  

Microsoft Academic Search

Amazonis Planitia, located between the two main volcanic provinces on Mars (Tharsis and Elysium), is characterized by extremely smooth topography at several scale lengths, as smooth as oceanic abyssal plains topography on Earth. We use Mars Global Surveyor (MGS) data (primarily very high resolution Mars Orbiter Laser Altimeter (MOLA) topography and derivative slope maps, gradient maps, and detrended maps) to

Elizabeth R. Fuller; James W. Head

2002-01-01

76

Amazonis Planitia: The role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on Mars  

Microsoft Academic Search

(1) Amazonis Planitia, located between the two main volcanic provinces on Mars (Tharsis and Elysium), is characterized by extremely smooth topography at several scale lengths, as smooth as oceanic abyssal plains topography on Earth. We use Mars Global Surveyor (MGS) data (primarily very high resolution Mars Orbiter Laser Altimeter (MOLA) topography and derivative slope maps, gradient maps, and detrended maps)

Elizabeth R. Fuller; James W. Head

2002-01-01

77

Paleoceanographic interpretations of late Pleistocene to Holocene sedimentological and geochemical proxy-data from SE-Atlantic abyssal plains (Cape, Angola and Guinea Basin)  

NASA Astrophysics Data System (ADS)

Sediments of the deep abyssal regions of the Southeast Atlantic (Cape Basin, Angola Basin and Guinea Basin) were studied to reconstruct changes in surface and deep water circulation, bioproductivity, and terrigenous sediment flux. To gain these results various sedimentological and geochemical proxies were imposed, including grain size data, foraminiferal fragmentation, carbonate and organic carbon content, as well as stable oxygen and carbon isotope contents of foraminiferal tests. Samples were gained with a multicorer device during Meteor cruise 63/2 (2005) in water depths between ~5,100 and ~5,600 m. The superficial 30 cm of sediment, sampled in 1/2, 1 and 5 cm steps, were processed for this study. The record covers parts of the Pleistocene and Holocene. Even if the sedimentation conditions seem to be similar in the deep-sea regions of the SE-Atlantic there are clear differences between the three sampled locations. This is caused by major changes in deep water corrosiveness leading to fluctuations in the sedimentation rate and carbonate preservation. Cape Basin localities show a pattern of enhanced carbonate preservation around 12 ka BP possibly indicating a delayed Last Glacial Maximum signal. This pattern, which is typical for Indo-Pacific records, clearly points to an influence of Antarctic Bottom Water (AABW) at water depths below 5000 m in the Northern Cape Basin. The non-correlation between carbonate content and grain size distribution is owing to a coccoliths' dominated carbonate production possibly caused by low nutrient availability in surface waters and the higher dissolution susceptibility of foraminiferal tests. Angola Basin samples delivered highest sand contents, a carbonate peak and low organic carbon values around 8.2 ka BP which indicate a reduced bioproduction and nutrient supply in superficial waters. A connection of the 8.2 ka cold event in the northern hemisphere and central African precipitation, equatorial East Atlantic (EEA) upwelling intensity and bioproduction is likely. Thus we expect the observed peak to be a response to the mentioned cold event at about 8.2 ka. The overall sedimentological record indicates that the Northern Angola Basin sedimentation may not be triggered by changes in the influence of North Atlantic Deep Water (NADW) and AABW as observed in the Northern Cape Basin. Therefore, the Walvis Ridge is expected to be an effective barrier for AABW. Studied Guinea Basin sediments (>5000 m) show quite uniform spatial bioproduction caused by the EEA divergence zone overlying the sample sites. Concerning the Holocene, temporal variations are mirrored in the grain size distribution which can possibly be correlated to changes in the thermocline depth. The trend to higher sand contents, especially in the uppermost sediment layers hints to increasing bioproductivity (foraminifers) and thus upwelling intensity during the Holocene. Dissolution, even in the deepest parts of the Guinea Basin, is minimal during the sampled timespan (low foraminferal fragmentation) owing to a predominant influence of NADW north of the Guinea Rise. Differences in the carbonate content are therefore expected to be caused by dilution by terrigenous material delivered by fluvial (Niger River) and eolian (Trade Winds) transport in combination with a change in bioproductivity.

Piller, W. E.; Müllegger, S.

2009-04-01

78

Sediment deformation and plate tectonics in the Gulf of Oman  

Microsoft Academic Search

The continental margin off the Makran coast of Iran and Pakistan is an excellent example of active deformation of sediments at a compressive plate boundary. Seismic reflection profiles across the margin suggest that relatively flat-lying sediments from the Oman abyssal plain are being scraped off the Arabian plate and accreted onto the Eurasian plate in a series of tightly folded

R. S. White; K. Klitgord

1976-01-01

79

Deep structure of the ocean-continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: The IAM-9 transect at 40°20?N  

NASA Astrophysics Data System (ADS)

We present a crust and mantle velocity structure for the West Iberia passive continental margin derived from a 320-km-long wide-angle seismic profile acquired in the southern Iberia Abyssal Plain. We observe a 170-km-wide ocean-continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault-bounded blocks of continental crust. The profile lies ˜40 km south of the transect sampled by Ocean Drilling Program (ODP) Legs 149 and 173. The transition zone structure can be divided into an upper layer, 2-4 km thick with velocities of between 4.5 and 7.0 km s-1 and generally a high-velocity-gradient (1 s-1), and a lower layer up to 4 km thick with a velocity of ˜7.6 km s-1 and a low-velocity-gradient. A weak Moho reflection in this zone was seen only on wide-angle profiles at an offset of ˜30 km. The upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope. Conversely, the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust. On the coincident seismic reflection profile, fault-bounded crustal blocks, identified in unequivocal extended continental crust, are not observed in the transition zone. The upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges, but no oceanic layer 3 velocity structure is present. While magnetic anomalies have been identified within the transition zone, they have not been modeled successfully as seafloor spreading magnetic anomalies, nor do they generally form long linear margin-parallel features. Finally, ODP boreholes, ˜40 km north of our profile and within the interpreted transition zone, have recovered up to 140-m-thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material. We conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust. Although current melting models predict a considerably thicker crust of decompression melt products, we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite.

Dean, S. M.; Minshull, T. A.; Whitmarsh, R. B.; Louden, K. E.

2000-03-01

80

Deep structure of the ocean-continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: Ocean Drilling Program (Legs 149 and 173) transect  

NASA Astrophysics Data System (ADS)

We present a wide-angle seismic refraction study of an 80×40 km region of the southern Iberia Abyssal Plain, south of Galicia Bank. An intersecting grid of two E-W and four N-S wide-angle reflection/refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean-continent transition (OCT). These structures can be systematically linked to variations in acoustic basement morphology and to results from Ocean Drilling Program (ODP) boreholes. Lateral changes in the velocity structure of the basement occur abruptly over distances of ˜20 km where complex variations may be found. Thinned upper continental crust, 2-5 km thick with velocities of 5.0-6.6 km/s, is limited to a series of N-S fault blocks immediately south of Galicia Bank. This crust is underlain by a high-velocity layer (7.3-7.9 km/s) of weakly serpentinized (i.e., 0-25%) peridotite, which exists throughout the eastern part of the survey area. Basement within the OCT appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally. In the southeast sector of our survey where basement topography deepens and becomes subdued, continental fault blocks are absent; instead, basement contains an upper layer of more pervasively serpentinized (i.e., 25-45%) peridotite that is ˜2 km thick. This layer is characterized by low velocity at the top of basement (4.2 km/s) that increases rapidly with depth, and it probably corresponds to a seismically unreflective layer, previously identified in reflection profiles to the south of our survey. In the western section of our survey, beneath a series of elevated basement ridges, velocities are reduced within both the upper basement layer (3.5-6.0 km/s) and lower layer (6.4-7.5 km/s). These changes suggest that both upper and lower layers have become more highly serpentinized (with values of 60-100% in the upper layer and 25-45% in the lower layer) probably during the last stages of rifting and immediately before formation of oceanic crust. A normal or slow spreading oceanic crustal structure is not found within the survey region. Thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at ODP Site 897 and east of the J magnetic anomaly.

Chian, Deping; Louden, Keith E.; Minshull, Tim A.; Whitmarsh, Robert B.

1999-04-01

81

Riverine sediment inflow to Louisiana Chenier Plain in the Northern Gulf of Mexico  

NASA Astrophysics Data System (ADS)

The Louisiana Chenier Plain is a geomorphologic extension of the Mississippi Deltaic Plain, highly influenced by sediments originating from the Mississippi River. With the Mississippi River unable to avulse closer to the Plain local riverine sediment resources are integral to maintaining the physical and ecological integrity of the estuaries and marshlands. To gain insight into the sediment resources, this study assessed two decades (1990-2009) of discharge and total suspended solids (TSS) of four rivers, Sabine River, Calcasieu River, Mermentau River, and Vermilion River that flow into the Chenier Plain. The study quantified long-term sediment delivery, analyzed seasonal and inter-annual trends of sediment transport, and investigated the effect of hydrometeorological conditions on sediment yields. Total sediment delivery from the rivers over the 20-year period was 6.86 × 106 tonnes, with the Sabine River contributing 62% of the sediment load. The Sabine River also showed a significant decreasing trend (p = 0.03) in annual sediment yield. Long-term trends of sediment loads in all the rivers were influenced by their discharge, not their TSS concentrations. Annual mean sediment load was 342,950 tonnes with higher sediment loading during the winter and spring months and lower during the summer and fall months. Annual sediment inflow has the capacity to create 2.3 × 107 m2 of land to the depth of 1 cm, but most of this sediment is unable to reach the coastline. The greatest asset that these rivers provide for the Chenier Plain is sediment and freshwater for restoration of marsh lost to salinization or inundation.

Rosen, Timothy; Xu, Y. Jun

2011-12-01

82

Spatial Distribution and Morphology of Sediments in Texas Southern High Plains Playa Wetlands  

Technology Transfer Automated Retrieval System (TEKTRAN)

Playas are depressional geomorphic features on the U.S. High Plains and about 20,000 Southern High Plains playa wetlands serve as runoff catchment basins, which are thought to be focal points of Ogallala aquifer recharge. Sediments in playas can alter biodiversity services, impede aquifer recharge,...

83

Spatial distribution and morphology of sediments in Texas Southern High Plains playa wetlands  

Technology Transfer Automated Retrieval System (TEKTRAN)

Playas are depressional geomorphic features on the U.S. High Plains. About 20,000 Southern High Plains playa wet¬lands serve as runoff catchment basins, which are thought to be focal points of Ogallala aquifer recharge. Sediments in playas can alter biodiversity services, impede aquifer recharge, an...

84

Exchanges of sediment between the flood plain and channel of the Amazon River in Brazil  

USGS Publications Warehouse

Sediment transport through the Brazilian sector of the Amazon River valley, a distance of 2010 km, involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at O??bidos (???1200 Mt yr-1). The exchanges occur through bank erosion, bar deposition, settling from diffuse overbank flow, and sedimentation in flood-plain channels. We estimated the magnitude of these exchanges for each of 10 reaches of the valley, and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach. Residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel. The annual supply of sediment entering the channel from bank erosion was estimated to average 1570 Mt yr-1 (1.3 ?? the O??bidos flux) and the amount transferred from channel transport to the bars (380 Mt yr-1) and the flood plain (460 Mt yr-1 in channelized flow; 1230 Mt yr-1 in diffuse overbank flow) totaled 2070 Mt yr-1 (1.7 ?? the O??bidos flux). Thus, deposition on the bars and flood plain exceeded bank erosion by 500 Mt yr-1 over a 10-16 yr period. Sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 Mt yr-1 over 16 yr, crudely validating the process-based calculations of the sediment budget, which in turn illuminate the physical controls on each exchange process. Another 300-400 Mt yr-1 are deposited in a delta plain downstream of O??bidos. The components of the sediment budget reflect hydrologie characteristics of the valley floor and geomorphic characteristics of the channel and flood plain, which in turn are influenced by tectonic features of the Amazon structural trough.

Dunne, T.; Mertes, L. A. K.; Meade, R. H.; Richey, J. E.; Forsberg, B. R.

1998-01-01

85

Composite refraction-reflection stack sections: Tracing faults in the Atlantic coastal plain sediments  

SciTech Connect

Seismic data from the Atlantic Coastal Plain are reprocessed and composite refraction-reflection stack sections produced to investigate basement faults that penetrate upward into Atlantic Coastal Plain sediments in South Carolina. Reprocessing recovered reflections from within the deep crust to the Moho as well as from within thin veneer (300) of the Atlantic Coastal Plain sediments. One of the major objectives of this paper is to discuss the use of shallow refracted arrivals to construct a composite refraction- reflection stack that allows better imaging of the subsurface at shallow depths.

Stephenson, D.E. [Westinghouse Savannah River Co., Aiken, SC (United States); Coruh, C.; Costain, J.K. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Geological Sciences

1993-05-01

86

Use of mining-contaminated sediment tracers to investigate the timing and rates of historical flood plain sedimentation  

Microsoft Academic Search

Changes in land use practices following European settlement in the 1830s produced accelerated sedimentation on virtually all valley floors in the Blue River Watershed, Wisconsin. The contamination of sediments by Pb and Zn mining allowed us to calculate cross-valley rates of flood plain sedimentation for three time periods: the pre-mining period (1830–1900), the mining period (1900–1920), and the post-mining period

Scott A. Lecce; Robert T. Pavlowsky

2001-01-01

87

Bacteria in deep coastal plain sediments of Maryland: A possible source of CO2 to groundwater  

Microsoft Academic Search

Nineteen cores of unconsolidated Coastal Plain sediments obtained from depths of 14 to 182 m below land surface near Waldorf, Maryland, were collected and examined for metabolically active bacteria. The age of the sediments cored range from Miocene to Early Cretaceous. Acridine orange direct counts of total (viable and nonviable) bacteria in core subsamples ranged from 108 to 104 bacteria\\/g

Francis H. Chapelle; Joseph L. Zelibor; D. Jay Grimes; LeRoy L. Knobel

1987-01-01

88

Geochemical signature of provenance, tectonics and chemical weathering in the Quaternary flood plain sediments of the Hindon River, Gangetic plain, India  

NASA Astrophysics Data System (ADS)

The Ganga basin in the Himalayan foreland is a part of the world's largest area of modern alluvial sedimentation. Flood plain sediments of the Hindon River of the Gangetic plain have been analyzed for sediment texture, major and trace elements including rare earth elements (REEs). The results have been used to characterize the source rock composition and to understand the intensity of chemical weathering, tectonics and their interplay in the Hindon flood plain. The sediments of the Hindon flood plain dominantly consist of sand sized particles with little silt and clay. The geochemistry of the Hindon sediments has been compared to the Siwalik mudstone of the Siwalik Group (Siwaliks). The Siwalik sedimentary rocks like sandstones, mudstones and conglomerates are the known source rocks for the Hindon flood plain sediments. Mudstone geochemistry has been considered best to represent the source rock characteristics. The UCC (Upper Continental Crust) normalized major and trace elements of the Hindon flood plain sediments are very similar to the Siwalik mudstone except for Th and Cr. Furthermore, the average chondrite normalized REE pattern of the Hindon flood plain sediments is similar to the Siwalik mudstone. Textural immaturity, K/Rb ratios and the average CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) values of the Hindon flood plain sediments indicate that the sediments have not been affected by chemical weathering. Our study suggests that the active tectonics of the Himalayas and monsoon climate enhances only physical erosion of the source rocks (Siwaliks) rather than the chemical alteration. These factors help the Hindon sediments to retain their parental and tectonic signature even after recycling.

Mondal, M. E. A.; Wani, H.; Mondal, Bulbul

2012-09-01

89

SEDIMENT PRODUCTION FROM SMALL, UNDISTURBED FORESTED BASINS fN THE UPPER COASTAL PLAIN  

Microsoft Academic Search

Forest lands in the Upper Coastal Plain (UCP) of the American South are widely recognized as producing water with relatrvely low amounts of sediment. Previous research has established that sediment concentrations from forest basins lacking well-defined channel networks averages 5.3 to 6.2 kg of sediment per hectare per centimeter of runoff (kg\\/ha-cm) in this physiographic region. Our results indicate that

Daniel A. Marion; Greg Malstaffz; Howard G. Halverson

90

Suspended sediment transport effectiveness of three large impounded rivers, U.S. Gulf Coastal Plain  

Microsoft Academic Search

Suspended sediment transport effectiveness was examined near the mouths of three large impounded rivers (Rio Grande, Brazos,\\u000a and Pearl Rivers) in differing precipitation regimes in the U.S. Gulf Coastal Plain. Magnitude and frequency analysis of suspended\\u000a sediment transport was performed by examining the effectiveness of both discharge and time in transporting suspended sediment.\\u000a Bivariate plots of discharge with infrequent values

Plain F. Hudson; Joann Mossa

1997-01-01

91

238U-234U-230Th disequilibria and the sediment transit time in alluvial plains: examples from the Gangetic plain rivers  

NASA Astrophysics Data System (ADS)

The mechanisms and timescales of processes controlling the sediment formation and their transfers from continent to ocean are a prerequisite for correctly quantifying the rates of continental erosion but also for precisely evaluating the response of the erosion and sedimentation processes to tectonic and climatic forcing. Here we propose to illustrate, in the case of the Gangetic plain river system, the interest of 238U-234U-230Th disequilibria in the bank-river sediments for estimating the transfer time of sediments in the alluvial plains. The studied rivers involve (1) mountain-fed rivers, i.e. river transferring a great quantity of sediments from their source of high relief and forming large depositional areas in the plain, and (2) a foothill-fed river, that derives its sediments from foothills and from within the plains, and for which a large proportion of this material is redeposited after local reworking. The main result displayed by the U-Th data is a regular evolution of the 238U-230Th-232Th systematics along the rivers with a systematic decrease of both (238U/232Th) and (230Th/232Th) ratios in river-bank sediments from upstream to downstream. The variations can be related to mineralogical and chemical sediment evolution during their transfer (and storage) in the alluvial plains and valleys. The choice of a realistic model for the U and Th evolution model during the transfer of alluvions in the valleys and plains allows us to estimate the transit time of sediments in the Gangetic plain : about 100 ka for rivers taking their source in the himalayan chain, and longer transit-time of about 160-250 ka for foothill-fed rivers. This difference is probably related to the difference in the sediment transport dynamics of these two types of rivers. These results highlight the potential of the 238U-234U-230Th disequilibria to constrain the dynamic of the sedimentary transfers in the alluvial plains.

Chabaux, F. J.; Granet, M.; Pelt, E.; Franc-Lanord, C.; Galy, V.

2005-12-01

92

Episodic sediment accumulation on Amazonian flood plains influenced by El Niño\\/Southern Oscillation  

Microsoft Academic Search

Continental-scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains. The spatial extent and depths of such deposits have been described, and flood-plain accumulation has been determined at decadal timescales, but it has not been possible to identify discrete events or to resolve deposition on near-annual timescales. Here we analyse 210Pb activity profiles

Rolf Aalto; Laurence Maurice-Bourgoin; Thomas Dunne; David R. Montgomery; Charles A. Nittrouer; Jean-Loup Guyot

2003-01-01

93

Monsoon sedimentation on the 'abandoned' tide-influenced Ganges-Brahmaputra delta plain  

NASA Astrophysics Data System (ADS)

Annual sediment delivery by the Ganges and Brahmaputra rivers to the Bengal margin has kept pace with sea level rise since the mid Holocene, sustaining subaerial growth of the delta. However, the Sundarbans region of the tidal delta is disconnected from major distributary sources of sediment and is often thought to be sediment starved, eroding, and susceptible to the meter of sea level rise predicted for the 21st century. Despite these assumptions, direct sedimentation measurements on the tidal delta plain reveal widespread mean annualized accretion rates of ˜1.1 cm yr-1, although heterogeneous depositional patterns indicate that topography and internal creek networks influence local sediment distribution. Short-lived radioisotope inventories (7Be: t1/2 = 53.3 days) measured on the freshly accumulated sediments indicate that about ½ of the mass deposited on the lower delta was sourced directly from the seasonal flood pulse of the river; the remaining ½ is derived from older (?1 yr) reworked sediments. Net sedimentation on this part of the delta traps ˜10% of annual Ganges-Brahmaputra sediment load, with accretion rates roughly equivalent to the mean regional rate of relative sea-level rise (RSLR) of ˜1.0 cm yr-1. If these sedimentation rates are representative of longer-term trends and subsidence rates remain stable over the next century, the lower delta plain may continue to maintain its elevation and stability despite documented mangrove retreat around its seaward edges.

Rogers, Kimberly G.; Goodbred, Steven L.; Mondal, Dhiman R.

2013-10-01

94

Episodic sediment accumulation on Amazonian flood plains influenced by El Niño/Southern Oscillation  

NASA Astrophysics Data System (ADS)

Continental-scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains. The spatial extent and depths of such deposits have been described, and flood-plain accumulation has been determined at decadal timescales, but it has not been possible to identify discrete events or to resolve deposition on near-annual timescales. Here we analyse 210Pb activity profiles from sediment cores taken in the pristine Beni and Mamore river basins, which together comprise 720,000km2 of the Amazon basin, to investigate sediment accumulation patterns in the Andean-Amazonian foreland. We find that in most locations, sediment stratigraphy is dominated by discrete packages of sediments of uniform age, which are typically 20-80cm thick, with system-wide recurrence intervals of about 8yr, indicating relatively rare episodic deposition events. Ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with La Niña events, which debouch extraordinary volumes of sediments from the Andes. We conclude that transient processes driven by the El Niño/Southern Oscillation cycle control the formation of the Bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon, nutrients and pollutants to the Amazon main stem.

Aalto, Rolf; Maurice-Bourgoin, Laurence; Dunne, Thomas; Montgomery, David R.; Nittrouer, Charles A.; Guyot, Jean-Loup

2003-10-01

95

Episodic sediment accumulation on Amazonian flood plains influenced by El Niño/Southern Oscillation.  

PubMed

Continental-scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains. The spatial extent and depths of such deposits have been described, and flood-plain accumulation has been determined at decadal timescales, but it has not been possible to identify discrete events or to resolve deposition on near-annual timescales. Here we analyse (210)Pb activity profiles from sediment cores taken in the pristine Beni and Mamore river basins, which together comprise 720,000 km2 of the Amazon basin, to investigate sediment accumulation patterns in the Andean-Amazonian foreland. We find that in most locations, sediment stratigraphy is dominated by discrete packages of sediments of uniform age, which are typically 20-80 cm thick, with system-wide recurrence intervals of about 8 yr, indicating relatively rare episodic deposition events. Ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with La Niña events, which debouch extraordinary volumes of sediments from the Andes. We conclude that transient processes driven by the El Niño/Southern Oscillation cycle control the formation of the Bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon, nutrients and pollutants to the Amazon main stem. PMID:14523442

Aalto, Rolf; Maurice-Bourgoin, Laurence; Dunne, Thomas; Montgomery, David R; Nittrouer, Charles A; Guyot, Jean-Loup

2003-10-01

96

The Role of Lateral Fluid Flow in Off-Axis, Oceanic Hydrothermal Systems Under Abyssal Sedimentation Conditions  

NASA Astrophysics Data System (ADS)

Off-axis hydrothermal circulation is significant to the thermal and chemical evolution of the oceanic crust, to the chemical evolution of the oceans, and potentially to a deep biosphere within the upper crust. These off-axis hydrothermal systems are impacted by the type and distribution of sediment because sufficiently thick and contiguous sediment cover will limit the exchange of fluid between the ocean and the crust. It has been suggested that in off-axis settings lateral transport between sediment-poor regions, through the high permeability lavas, is the dominant geometry of fluid convection in igneous crust underlying thick sediment. To aid in understanding the role of sediment cover on seafloor hydrothermal systems, a numerical model of pelagic supply, post-depositional down-slope sediment redistribution (following [1]), and crustal hydrogeology has been developed. Synthetic seafloor bathymetry representative of crust formed at different spreading rates [2] is used as the initial bathymetry and seamounts are added randomly with a size and frequency distribution representative of the global ocean [3]. Other sedimentation variables are the diffusivity of sediment, the pelagic sediment supply rate and the sediment hydrological properties. From this, the model predicts the changing distribution of potential hydrothermal fluid recharge and discharge sites in response to sedimentation. These results are coupled with a two-dimensional model of fluid and heat transport to evaluate the conditions under which lateral fluid flow in the igneous oceanic crust are consistent with the global data set of seafloor heat flow measurements. Preliminary results suggest that, of the parameters investigated, the spatial density of model-predicted outcrops is most sensitive to the rate of pelagic sediment supply. In areas with lower than average seamount abundances crustal spreading rate is also important to the distribution of outcrops, with more outcrops predicted on crust formed at slow-spreading ridges. The model-predicted separation distance between potential fluid recharge and discharge sites is generally lower than previously estimated [4] implying that pressure gradients driving lateral fluid flow may be higher than predicted and upper crustal permeability may be lower than previously predicted. Results of this modeling will be presented, and the influences of the rate and nature of sedimentation on off-axis hydrothermal circulation will be discussed. [1] Webb and Jordan, JGR 2001, v106, p 30,433; [2] Goff and Jordan, JGR 1988, v93, p 13,589; [3] Hillier and Watts, Geophysical Research Letters 2007, v34, doi:10.1029/2007GL029874; [4] Fisher and Becker, Nature 2000, v403 p 71.

Anderson, B. W.; Coogan, L. A.; Gillis, K. M.

2010-12-01

97

Amazonis Planitia: The role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on Mars  

NASA Astrophysics Data System (ADS)

Amazonis Planitia, located between the two main volcanic provinces on Mars (Tharsis and Elysium), is characterized by extremely smooth topography at several scale lengths, as smooth as oceanic abyssal plains topography on Earth. We use Mars Global Surveyor (MGS) data (primarily very high resolution Mars Orbiter Laser Altimeter (MOLA) topography and derivative slope maps, gradient maps, and detrended maps) to examine the surface morphology of Amazonis Planitia and the stratigraphic relationships among previously mapped and newly defined units. These new data reveal the presence of a 1300 km diameter Noachian impact basin in northwest Amazonis Planitia and an extensive Late Hesperian lava flow unit that appears to have originated from the Olympus Mons source area prior to aureole formation. The presence of this previously unrecognized flow unit strongly suggests that Olympus Mons activity dates back to at least the Hesperian, as did activity on the Tharsis Montes. Emplacement of this ~100 meter thick flow unit formed a barrier along the northern margin of Amazonis Planitia which had a profound influence on the subsequent geologic history of the region. Formation of Olympus Mons aureole deposits created an eastern topographic barrier, and subsequent Tharsis Montes lava flows entered the basin from the south, flowing around the aureole. These three barriers (degraded Noachian crater rim, proto-Olympus Mons flow unit, and Olympus Mons aureole) caused subsequent lava flows and outflow channel effluents, primarily from the Elysium region to the west, to pond on the floor of Amazonis Planitia, preferentially smoothing the terrain there. Mars Orbiter Camera (MOC) images substantiate that at least two very fluid lava flows alternated with fluvial episodes from Elysium Planitia, flowing through Marte Valles onto the floor of the Amazonis Planitia basin. Within Amazonis Planitia, MOC images show flow-like textures heavily mantled by sediments, and radar data reveal the presence of rough lava flow surfaces underlying the sedimentary debris. These data thus suggest that the unique smoothness of Amazonis Planitia is the result of deposition of thin fluid lava flows and fluvial sediments in an enclosed basin. Crater counts suggest that the most recent resurfacing may have occurred in the latest Amazonian Period, in the last 1% of the history of Mars. In light of its unique history, it is somewhat ironic to note that Amazonis Planitia was originally thought to be a typical young Martian surface and therefore used to name the Amazonian era.

Fuller, Elizabeth R.; Head, James W.

2002-10-01

98

Sedimentation Dynamics in Sweet Hall Marsh, a Tidal Freshwater Marsh of Coastal Plain Virginia  

NASA Astrophysics Data System (ADS)

Sedimentation rates were measured from May 1998 to March 1999 at Sweet Hall Marsh, a tidal freshwater marsh in the Coastal Plain of Virginia using various techniques (sediment catch plates, triangular survey method, Be-7 distribution). Rates of sedimentation vary spatially and temporally in the marsh. Sedimentation rates are generally greatest adjacent to a tidal creek and decrease progressively farther into the marsh. Differences in rates of sedimentation are greatest spatially during the summer and are least during the winter. Accuracy of rates calculated depend on the methods used to measure sedimentation. A combination of methods likely provides the most accurate trends of sedimentation change. The organic content of marsh sediment may influence marsh stability indirectly and also varies spatially and temporally. Organic content generally increases farther away from sediment sources in the marsh; increased organic content in interior parts of Sweet Hall Marsh may promote increased rates of respiration and thus greater loss of total sediment fraction. Organic content seems to correlate with decreased carbon/nitrogen ratios and increased respiration rates. The general evolution of Sweet Hall Marsh was described using evidence obtained from vibracoring and carbon-14 dating. Along with stratigraphic evidence, organic content of marsh sediment was analyzed with depth to depict the history of the marsh.

Constantine, J. A.; Neubauer, S. C.; Anderson, I. C.; Johnson, G. H.

2001-05-01

99

Early organic diagenesis: The significance of progressive subsurface oxidation fronts in pelagic sediments  

Microsoft Academic Search

Porewater and solid phase geochemical data at two contrasting NE Atlantic stations are reported. Station 10552, on the Cape Verde abyssal plain, is a site of slow pelagic accumulation ( ca . 0.4 cm kyr -1 ). Molecular oxygen is present in the sediment column to at least 2 m, and probably much deeper, labile organic-carbon is almost totally consumed

T. R. S. Wilson; J. Thomson; S. Colley; D. J. Hydes; N. C. Higgs; J. Sørensen

1985-01-01

100

35. GEOCHEMICAL WELL LOGS FROM THE ARGO ABYSSAL PLAIN AND EXMOUTH PLATEAU, NORTHEAST INDIAN OCEAN, SITES 765 AND 766 OF LEG 1231  

Microsoft Academic Search

Geochemical well logs were obtained in sediments at Site 765 and in both sediments and basalts at Site 766 of Leg 123. Corrections have been applied to the logs to account for variations in hole size, drilling fluid interference, and casing or drill pipe attenuation. Weight fractions of the major oxides and of calcium carbonate have been calculated from the

Elizabeth Lewis Pratson; Cristina Broglia; David Castillo

101

Biogenic structures in modern slope to deep-sea sediments in the sulu sea basin (Philippines)  

Microsoft Academic Search

Wetzel, A., 1983. Biogenic structures in modern slope to deep~sea sediments in the Sulu Sea Basin (Philippines). Palaeogeogr., Palaeoclimatol., Palaeoecol., 42: 285--304. Slowly accumulated slope and rise sediments (5--20 cm\\/1000 yr) are totally biotur- bated as compared to only 10--30% in rapidly deposited abyssal plain sediments (100-- 200 cm\\/1000 yr). In contrast to a decrease in degree of bioturbation, biogenic

ANDREAS WETZEL

1983-01-01

102

Interpretive mineralogy: examples from Miocene coastal plain sediments  

SciTech Connect

Gulf Coast Miocene sediments are among the most lithologically complex in the entire nation. This varied lithology stems in part from multiple source areas that were active during this interval; but also if reflects major tectonic events that influenced depositional patterns throughout the Gulf Coast during the Miocene. Because fossils are scarce or lacking in many of the units, important questions relating to a number of geologic problems have been discussed illustrating how such analyses can be used to: (1) clarify stratigraphic relationships between units in contact, (2) define environmental conditions in the depositional basin, (3) reconstruct paleoclimate conditions, and (4) identify provenance area. A major anomaly in the mineralogy of central Gulf Coast Miocene sediments is explained by postulating a major ancestral Tennessee River originating in the southern Appalachians and flowing southwestward across Alabama and Mississippi to a terminus in the ancient Gulf of Mexico.

Isphording, W.C.

1983-09-01

103

Seismic interpretation of pelagic sedimentation regimes in the 18–53 Ma eastern equatorial Pacific: Basin-scale sedimentation and infilling of abyssal valleys  

Microsoft Academic Search

Understanding how pelagic sediment has been eroded, transported, and deposited is critical to evaluating pelagic sediment records for paleoceanography. We use digital seismic reflection data from an Integrated Ocean Drilling Program site survey (AMAT03) to investigate pelagic sedimentation across the eastern-central equatorial Pacific, which represents the first comprehensive record published covering the 18–53 Ma eastern equatorial Pacific. Our goals are

Masako Tominaga; Mitchell Lyle; Neil C. Mitchell

2011-01-01

104

Changes in the sorption capacity of Coastal Plain sediments due to redox alteration of mineral surfaces  

Microsoft Academic Search

Chemical characteristics of grain coatings in a Coastal Plain sandy aquifer on the Eastern Shore of Virginia were investigated where sediments have been exposed to distinct groundwater redox conditions. Dissolved O2 was 5.0 to 10.6 mg L?1 in the regionally extensive aerobic groundwater, whereas in a narrow leachate plume it was only <0.001 to 0.9 mg L?1. The amount of

Elizabeth P. Knapp; Janet S. Herman; Aaron L. Mills; George M. Hornberger

2002-01-01

105

Biomass and Decay Rates of Roots and Detritus in Sediments of Intermittent Coastal Plain Streams  

Microsoft Academic Search

Biomass and breakdown of tree roots within streambed sediments were compared with leaf and wood detritus in three Coastal\\u000a Plain headwater intermittent streams. Three separate riparian forest treatments were applied: thinned, clearcut, and reference.\\u000a Biomass of roots (live and dead) and leaf\\/wood was significantly higher in stream banks than in the channel and declined with\\u000a depth strata (0–10 > 10–20

Ken M. Fritz; Jack W. Feminella; Chris Colson; B. Graeme Lockaby; Robin Governo; Robert B. Rummer

2006-01-01

106

Low-energy Beach ridge sedimentation in the Mississippi River delta plain  

SciTech Connect

Regressive beach ridge plains, such as Cheniere Caminada, Cheniere Caillou, and Cheniere Ronquille, are common depositional features within the Mississippi River delta plain in southeastern Louisiana. Vibracored sequences indicate beach ridge formation is a 3 stage process: Stage 1: Distributary Progradation, followed by Stage 2: Longshore Transport Interception, and completed by Stage 3: Beach Ridge Progradation. Cheniere Caminada is the largest beach ridge plain and is associated with the Late Lafourche delta. Radiocarbon dates indicate beach ridge building began approximately 720 years BP, when the Bayou Lafourche distributaries built seaward of the older, retreating Bayou Blue shoreline and intercepted westward longshore sediment transport, resulting in the progradation of Cheniere Caminada. Near the fan apex, beach ridges are 7-8 m thick and thin westward 2-3 m thick against the levees of Bayou Moreau. A typical beach ridge vertical sequence coarsens upward, with shoreface silty sands overlain by a thin cap of beach, washover, and aeolian sands. Beach ridge progradation in this area ceased approximately 300 years BP with the abandonment of Bayou Lafourche. The documentation of multiple regressive beach ridge plains suggest these deposits are stratigraphically more significant in the Mississippi River delta plain than recognized previously. The regressive beach ridge sequence documented in this study both stratigraphically and genetically contrasts with the classic transgressive chenier ridges of southwestern Louisiana.

Gerdes, R.G.; Penland, S.

1985-01-01

107

Abyssal undular vortices in the Eastern Mediterranean basin  

NASA Astrophysics Data System (ADS)

Abyssal temperature and velocity observations performed within the framework of the Neutrino Mediterranean Observatory, a project devoted to constructing a km3-scale underwater telescope for the detection of high-energy cosmic neutrinos, demonstrate cross-fertilization between subnuclear physics and experimental oceanography. Here we use data collected south of Sicily in the Ionian abyssal plain of the Eastern Mediterranean (EM) basin to show for the first time that abyssal vortices exist in the EM, at depths exceeding 2,500m. The eddies consist of chains of near-inertially pulsating mesoscale cyclones/anticyclones. They are embedded in an abyssal current flowing towards North-Northwest. The paucity of existing data does not allow for an unambiguous determination of the vortex origin. A local generation mechanism seems probable, but a remote genesis cannot be excluded a priori. The presence of such eddies adds further complexity to the discussion of structure and evolution of water masses in the EM.

Rubino, A.; Falcini, F.; Zanchettin, D.; Bouche, V.; Salusti, E.; Bensi, M.; Riccobene, G.; de Bonis, G.; Masullo, R.; Simeone, F.; Piattelli, P.; Sapienza, P.; Russo, S.; Platania, G.; Sedita, M.; Reina, P.; Avolio, R.; Randazzo, N.; Hainbucher, D.; Capone, A.

2012-05-01

108

Large-scale patterns in biodiversity of microbial eukaryotes from the abyssal sea floor.  

PubMed

Eukaryotic microbial life at abyssal depths remains "uncharted territory" in eukaryotic microbiology. No phylogenetic surveys have focused on the largest benthic environment on this planet, the abyssal plains. Moreover, knowledge of the spatial patterns of deep-sea community structure is scanty, and what little is known originates primarily from morphology-based studies of foraminiferans. Here we report on the great phylogenetic diversity of microbial eukaryotic communities of all 3 abyssal plains of the southeastern Atlantic Ocean--the Angola, Cape, and Guinea Abyssal Plains--from depths of 5,000 m. A high percentage of retrieved clones had no close representatives in genetic databases. Many clones were affiliated with parasitic species. Furthermore, differences between the communities of the Cape Abyssal Plain and the other 2 abyssal plains point to environmental gradients apparently shaping community structure at the landscape level. On a regional scale, local species diversity showed much less variation. Our study provides insight into the community composition of microbial eukaryotes on larger scales from the wide abyssal sea floor realm and marks a direction for more detailed future studies aimed at improving our understanding of deep-sea microbes at the community and ecosystem levels, as well as the ecological principles at play. PMID:20007768

Scheckenbach, Frank; Hausmann, Klaus; Wylezich, Claudia; Weitere, Markus; Arndt, Hartmut

2009-12-10

109

22. MAGNETOSTRATIGRAPHY OF LOWER EOCENE TO LOWER MIOCENE SEDIMENTS IN CORES FROM THE NEW JERSEY COASTAL PLAIN 1  

Microsoft Academic Search

This paper describes the magnetostratigraphy of lower and middle Eocene, lower and upper Oligocene, and lower Miocene terrigenous sediments recovered in three on shore borecores on the New Jersey coastal plain (Island Beach, Atlantic City, Cape May Sites; Ocean Drilling Program Leg 150X). Near-shore, terrigenous sediments are quite often very weakly magnetized. Thus, to improve the practical measuring sensitivity of

Mickey C. Van Fossen

110

Crystallization of abyssal tholeiites  

Microsoft Academic Search

In some abyssal tholeiite magmas having a relatively high content of olivine component, olivine is the first mineral to crystallize. In others having a relatively high content of plagioclase component, plagioclase is the first mineral to crystallize. The rooks of these two groups are called OL- and PL-tholeiites respectively. Continued crystallization drives the residual liquids to the cotectic curve between

Fumiko Shido; Akiho Miyashiro; Maurice Ewing

1971-01-01

111

Abyssal circulation around New Zealand—a comparison between observations and a global circulation model  

Microsoft Academic Search

Observations of abyssal currents off eastern New Zealand are compared to results from the Los Alamos National Laboratory (LANL) global ocean circulation model. Physical oceanographic measurements are few along the 6000-km long path of the abyssal flow so they are supplemented by geological data including bottom photographs, nephelometer profiles, sediment analyses, and high resolution seismic profiles. While greatly increasing the

Lionel Carter; John Wilkin

1999-01-01

112

The Surface of Venus is Saturated With Ancient Impact Structures, and its Plains are Marine Sediments  

NASA Astrophysics Data System (ADS)

Conventional interpretations of Venus are forced to fit dubious pre-Magellan conjectures that the planet is as active internally as Earth and preserves no ancient surface features. Plate tectonics obviously does not operate, so it is commonly assumed that the surface must record other endogenic processes, mostly unique to Venus. Imaginative systems of hundreds of tiny to huge rising and sinking plumes and diapirs are invoked. That much of the surface in fact is saturated with overlapping large circular depressions with the morphology of impact structures is obscured by postulating plume origins for selected structures and disregarding the rest. Typical structures are rimmed circular depressions, often multiring, with lobate debris aprons; central peaks are common. Marine-sedimentation features are overlooked because dogma deems the plains to be basalt flows despite their lack of source volcanoes and fissures. The unearthly close correlation between geoid and topography at long to moderate wavelengths requires, in conventional terms, dynamic maintenance of topography by up and down plumes of long-sustained precise shapes and buoyancy. A venusian upper mantle much stronger than that of Earth, because it is cooler or poorer in volatiles, is not considered. (The unearthly large so-called volcanoes and tessera plateaus often are related to rimmed circular depressions and likely are products of impact fluidization and melting.) Plains-saturating impact structures (mostly more obvious in altimetry than backscatter) with diameters of hundreds of km are superimposed as cookie-cutter bites, are variably smoothed and smeared by apparent submarine impact and erosion, and are differentially buried by sediments compacted into them. Marine- sedimentation evidence includes this compaction; long sinuous channels and distributaries with turbidite- channel characteristics and turbidite-like lobate flows (Jones and Pickering, JGSL 2003); radar-smooth surfaces and laminated aspect in lander images; and widespread minor structures with neither terrestrial volcanic analogues nor plausible volcanic explanations. Broad tracts of polygonal reticulations 100 m to 5 km in diameter have dimensional and geometric terrestrial analogues in the polygonal faulting shown by 3-D reflection-seismic surveys of dewatered fine-grained sediments in marine basins. Impact-comminuted basaltic crust may dominate the fine sediment. Vast numbers of small low so-called shield volcanoes have geometric analogues in terrestrial mud volcanoes, not magmatic constructs. Less than half of the 1000 small misnamed pristine craters, the only venusian craters accepted by all as of impact origin, in fact are pristine. The rest are variably eroded, their craters partly filled by sediments that often display polygonal faulting, and their aprons partly covered by sediments of surrounding plains. All gradations are displayed between these structures and the more modified but otherwise similar structures from which they are arbitrarily and inconsistently separated. Lunar analogy dates the thousands of large venusian craters, 300-2000 km in rim diameter, as older than 3.8 Ga. Marine sedimentation began before late-stage accretion was complete. The nominally pristine craters are commonly assumed to be younger than 1 Ga but may go back to 3.8 Ga. Venusian oceans persisted long after that, without stillstands sufficient for development of global shorelines and shelves, before complete greenhouse evaporation, deep desiccation, and top-down metamorphism of sediments.

Hamilton, W. B.

2009-05-01

113

Spatial distribution and recent changes in carbon, nitrogen and phosphorus accumulation in sediments of the Black Sea  

Microsoft Academic Search

Sediment cores from the Black Sea were analyzed along two transects across the basin in West–East and North–South direction and ranging from the oxic and suboxic shelf to the anoxic slopes and abyssal plain. On the North-Western shelf, the average concentrations of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in recent sediments showed a decrease with

Cristian R. Teodoru; Gabriela Friedl; Jana Friedrich; Ursula Roehl; Michael Sturm; Bernhard Wehrli

2007-01-01

114

Sediment-Basalt Architecture, Pliocene and Pleistocene Eastern and Central Snake River Plain  

NASA Astrophysics Data System (ADS)

This presentation is a synthesis of known stratigraphic studies of the Pliocene, Pleistocene and Holocene basalts and interbedded sedimentary beds on the Eastern Snake River Plain (ESRP). This information is important for understanding the post-caldera tectonic evolution of the ESRP, especially for tracking patterns of volcanic eruption and changes in topography. Geophysical surveys and existing well logs indicate the depth of the basalt sequence is usually 2 km or less, even near the axis of the Plain. An alteration horizon, the product of high heat-flow in the wake of the Yellowstone hot spot, moderated by cold-water recharge in the thick and highly-transmissive Snake River Aquifer, has variable depth. The surface and near-surface of the lava fields are mainly basalts less than a half a million years old, from Island Park to Twin Falls/Shoshone. Near the junction of the Eastern and Western Snake River Plains, these youngest late Pleistocene basalts, many less than 100,000 years old, overlie early Pleistocene basalts more than a million and a half years old. Most basalt flows have been erupted from NW-trending volcanic rift zones like the Great Rift of Idaho or from the Axial Volcanic High (AVH). The AVH is a constructional axial ridge formed by multiple volcanic vents, small shield volcanoes and rhyolitic domes which run the length of the ESRP. A combination of previous and new stratigraphic and geochronology studies, including U-Pb detrital-zircon geochronology on sediments, reveals several lake sequences, formed by the damming of rivers. These tend to be thickest in upstream, valley-mouth, and Plain-marginal locations where the rivers were trapped. The lake beds generally pinch out toward the AVH. The most notable of these are the Mid-Pleistocene Raft Formation, the Late Pleistocene American Falls Lake Beds, at least two mid-Pleistocene sequences of ponded sediment from the Big Lost River at its egress onto the ESRP, and a 2.5 to 1.6 Ma sequence in the Big Lost Trough (BLT). Argon-argon dating of intercalated basalts demonstrates that the Big Lost River was trapped in the BLT starting about ~2Ma. Egress was blocked by the AVH to the southeast and by constructional volcanic rift zones to the southwest. Channel deposits of the ancestral Big Lost River are present in well logs, with one 20 m thick sequence traceable to the southwest under the Craters of the Moon National Monument (COM) between 1430 and 1380 m MSL. Other lake sequences in the ESRP subsurface include two mid-Pleistocene 30 to 50m thick sequences of clayey sediments in the BLT, near the southeast corner of the Idaho National Laboratory at ~250 to ~300 m depths. Two other fine-grained sediment sequences of unknown age are found at similar depths south of COM. Lake Terreton and its predecessors can be traced from Howe to Menan in the northeastern ESRP. Fluvial sediments here are coarse-grained gravels and sands of the Snake River, exposed near Blackfoot and logged in many well logs. Other notable fluvial sediments include the southwest-trending channel deposits and the two previously-mentioned clay sequences south of COM may prove to be parts of a paleo-Big Lost River that flowed to the southwest before 2 Ma.

Helm-Clark, C. M.; Link, P. K.

2006-12-01

115

Early diagenesis of lipid biomarker compounds in North Atlantic sediments  

NASA Astrophysics Data System (ADS)

Near-surface sediments (0-45 mm depth interval) from the Iceland Basin (59°N, 21°W, 3070-m water depth) and Biscay Abyssal Plain (48°N, 17°W, 4105-m water depth) were sectioned at millimeter-scale resolution to assess alterations in key lipid biomarkers during early diagenesis. Inventories (µg cm-2 in the topmost 45 mm) of biomarkers from presumed terrestrial sources (>C20 linear n-alkanes, n-alkanoic acids, n-alkanols) and from phytoplankton sources (phytosterols, long-chain alkenones and alkenoates) were 1.5-4 times more abundant in the Iceland Basin core than in the Biscay Abyssal Plain core, indicating greater sedimentary inputs and/or preservation at the Iceland Basin site. Biomarker concentrations varied significantly over millimeter-scale depth intervals. Pronounced subsurface concentration maxima were present at both sites. At the Biscay Abyssal Plain site, steep concentration gradients in the uppermost few mm of the sediment column indicate extensive diagenetic losses at or near the sediment/water interface. Strong covariance was seen in the concentrations of various compounds within each class (e.g., long-chain n-alkanes, n-alkanols, n-alkanoic acids and long-chain alkenones and alkyl alkenoates), indicating that individual compounds within each class are associated with the same organic matrix and have similar degradation and mixing rates. Thus biomarker indices for assessment of land-derived inputs (CPI, C29/C31, ACL) and sea surface temperature (IPT) remain largely unaltered by early diagenetic processes in oxic, abyssal sediments in spite of extensive bioturbation and degradative losses within the uppermost few centimeters of the sediment column.

Madureira, Luiz A. S.; Conte, Maureen H.; Eglinton, Geoffrey

1995-06-01

116

Sediment Transport and Channel Morphology of the Kosi River, North Bihar Plain (India)  

NASA Astrophysics Data System (ADS)

The Kosi River of the northern Bihar plain, India and Nepal, is well-known for the frequent lateral shift of its course. In the last two centuries, it migrated more than 150 km westward (Gole and Chitale, 1966; Wells and Dorr, 1987; Sinha.R, 2008). This westward shift produced a megafan of an area about 16,000 Km2. Today the river shows a braided networks of streams of various magnitude. The large dimension of the Kosi river, its sandy bed, and its avulsive nature makes it an ideal field site to understand sediment transport in large braided rivers. We report measurements of discharge, velocity, width and depth across channels of the Kosi river within its embankment. ADCP measurements were performed during the high flow period in late July to early August 2012. First-hand analysis of the ADCP data shows order-of-magnitude variations of channel aspect ratio, discharge and velocity. We use these measurements to evaluate wether individual threads are close to the threshold for the sediment movement, and to evaluate the relationship between channel shape and discharge. This represents a first step towards the establishment of sediment budgets in a large sandy braided river.

Gaurav, Kumar; Chauvet, Hugo; Metivier, Francois; Devauchelle, Olivier; Sinha, Rajiv

2013-04-01

117

Sedimentation model of gravel-dominated alluvial piedmont fan, Ganga Plain, India  

NASA Astrophysics Data System (ADS)

The Piedmont Zone of the Indo-Gangetic Plain contains numerous, laterally coalescing small alluvial fans. The Latest Pleistocene-Holocene 30 km long Gaula Fan can be divided into gravelly proximal fan (0-14 km down-stream), gravel-sand rich mid fan (14-22 km) and sand-mud dominated distal fan (22-30 km). The fan succession is composed of two fan expansion cycles A and B. Separated by an undulatory erosional contact of regional extent, cycle A is characterized by river borne clast-supported gravelly deposits, and the overlying fan expansion cycle B by matrix-supported gravely debris flows. The main process behind fan development has been lateral migration of channels over the fan surface probably due to rapid sedimentation caused by increased sediment supply, and the fluctuating water budget in response to changing climate. The water laid expansion cycle A represents a humid phase. The debris flow deposits of expansion cycle B suggest a dry phase. Approximately between 8 and 3 Ka, cycle B also indicates a phase of tectonic instability in the Siwalik Hills forming the mountain front. The tectonic activity caused incision of rivers into the fan surface, and in turn resulted in reduced fan-building activity. At present the fan surface is accreting by sheet flow processes.

Shukla, U. K.

2009-03-01

118

Age and correlation of tertiary sediments in the western South Carolina Coastal Plain  

SciTech Connect

Integration of coastal onlap stratigraphy, calcareous nannofossil, dinoflagellate, and megafossil biostratigraphy provide new data for interpretation of age and interregional correlation of Paleocene to Oligocene deposits of the western South Carolina Coastal Plain. Clastic and calcareous sediments examined in cores and outcrops in the vicinity of the Savannah River Plant record at least seven coastal onlap cycles. Basal Tertiary sediments of the Ellenton Formation represent cycles TA1.1 - 1.3 and contain dinoflagellates of Midwayan to Sabinian age. The overlying Williamsburg Formation probably represents deposits of cycle TA2.1. The superjacent siliciclastics of the Congaree Formation contain few fossils, but may preserve transgressive and highstand deposits of cycles TA2.4 - 3.3. The overlying unit is commonly calcareous, contains nannofossils indicative of zones NP16-17 (Upper Claibornian), and marks a significant change in depositional style subsequent to the 49.5 Ma eustatic fall. ''Marls'' of the overlying Griffins Landing Member of the Dry Branch Formation contain micro- and megafossils of Late Eocene (Jacksonian) age and represent transgressive deposits of cycle TA4.1. The discontinuous lateral distribution of these calcareous units and overlying clastics of the Dry Branch and Tobacco Road Formations results largely from erosion and deep incision during the mid-Oligocene eustatic fall (30 Ma). The ''Upland'' unit is interpreted as being deposited on this erosional surface.

Laws, R.A.; Harris, W.B.; Zullo, V.A.; Fallaw, W.C.; Price, V.

1987-01-01

119

Eolian sedimentation and soil development on a semiarid to subhumid grassland, Tertiary Ogallala and Quaternary Blackwater Draw Formations, Texas and New Mexico High Plains  

Microsoft Academic Search

Eolian sediments have accumulated as non-glacigenic loess and thin sand sheets on the Central and Southern High Plains grasslands of Texas and new mexico since the late Miocene. Locally as much as 110 m of eolian sediments with numerous paleosols are preserved in the Quaternary Blackwater Draw formation and the upper part of the Miocene-Pleiocene Ogallala formation. These sediments and

THOMAS C. GUSTAVSON; VANCE T. HOLLIDAY

1999-01-01

120

Thermal, chemical, and mass-transport processes induced in abyssal sediments by the emplacement of nuclear waste: experimental and modeling results  

Microsoft Academic Search

This paper discusses heat and mass transport studies of marine red clay sediments being considered as a nuclear waste isolation medium. Numerical models indicate that for a maximum allowable sediment\\/canister interface temperature of 200 to 250°C, the sediment can absorb about 1.5 kW initial power from waste in a 3 m long by 0.3 m dia canister buried 30 m

D. F. McVey; K. L. Erickson; W. Seyfried

1980-01-01

121

Heavy Metals in Freshly Deposited Stream Sediments of Rivers Associated with Urbanisation of the Ganga Plain, India  

Microsoft Academic Search

Freshly deposited stream sediments from six urban centres of the Ganga Plain were collected and analysed for heavy metals\\u000a to obtain a general scenery of sediment quality. The concentrations of heavy metals varied within a wide range for Cr (115–817),\\u000a Mn (440–1 750), Fe (28 700–61 100), Co (11.7–29.0), Ni (35–538), Cu (33–1 204), Zn (90–1 974), Pb (14–856) and

Munendra Singh; German Müller; I. B. Singh

2002-01-01

122

Extension controls Quaternary tectonics, geomorphology and sedimentation of the N-Appennies foothills and adjacent Po Plain (Italy)  

Microsoft Academic Search

In the middle Pleistocene, thrusting in the N-Apennine fold-and-thrust belt came to an end and foredeep sedimentation in the adjacent Po Plain basin ceased. A new tectono-sedimentary regime was installed. Extensional faults were activated in the foothills and are limited to the northeast by a major, SW-dipping normal fault, the Bologna fault for which a vertical displacement of >1000 m

G. V. Bertotti; R. Capozzi; V. Picotti

1997-01-01

123

Metasomatism of Abyssal Peridotite  

NASA Astrophysics Data System (ADS)

On Leg 153 of the Ocean Drilling Program, cores of typical serpentinized abyssal peridotite were recovered from the western wall of the median valley of the Mid-Atlantic Ridge south of the Kane F.Z. In a sample from this suite, we have found evidence for extensive metasomatism, resulting in large changes in mineral compositions, with only minor changes in modal mineralogy. Large enrichments in Ti and Na in CPX, Ti, Cr and Fe in spinel and Fe in olivine are observed. A thin, CPX-ilmenite bearing vein cuts the sample. It appears that interaction between invading, or trapped melt and peridotite resulted in substantial shifts in mineral compositions in the host peridotite. CPX compositions in this sample range from Mg# 74-90.5, with TiO2 contents varying from 1.1 to 0.1 wt. % and Na2O from 0.6 to 0.2 wt %. CPX in peridotite distal from the metasomatized zone has Mg# 90.5-93 and TiO2 of 0.08 to 0.10 wt. %. Some chromian spinel in this sample is substantially enriched in Ti (up to 5 wt. %), exsolving crystallographically oriented ulvospinel, and is adjacent to ilmenite grains. Cr# in these Ti-enriched grains is 50 to 58. Typical spinels in this suite have Cr# of 30-33. Olivine in this sample is Fo 82-84, but in the host peridotite is Fo 90-91. Rare plagioclase grains are found in the peridotite matrix of the metasomatized sample, with An 50-58 composition. Away from the CPX-ilmenite vein cutting this sample, modal changes in the host peridotite are minor. Less than 1 % ilmenite and plagioclase are the only modal sign that the peridotite is unusual. The large shift in Fo in olivine and the low An in plagioclase are clear signs of quite extensive interaction with evolved, invading melt. Less extensive melt-peridotite interactions could produce the subtle Ti and Na enrichments observed in typical abyssal peridotites.

Ross, K.; Elthon, D.

2001-12-01

124

Persistent Organic Pollutants (POPs) and Polycyclic Aromatic Hydrocarbons (PAHs) in surface sediments from selected fjords, tidal plains and lakes of the North Spitsbergen  

Microsoft Academic Search

The aim of this study was to examine the pollution level of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and selected chloroorganic pesti? cides (HCH isomers, DDT and its metabolites, aldrin, dieldrin, endrin, heptachlor, endo? sulfan I and II, and methoxychlor) in surface sediments from selected fjords, tidal plains and lakes from the North Svalbard area. The sediments were collected

Barbara WOJTASIK; Dorota BURSKA

125

Spatial Variability of Turbulent Mixing in the Abyssal Ocean  

PubMed

Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise. The diapycnal diffusivity there was estimated to be less than or approximately equal to 0.1 x 10(-4) meters squared per second. In contrast, mixing rates are large throughout the water column above the rough Mid-Atlantic Ridge, and the diffusivity deduced for the bottom-most 150 meters exceeds 5 x 10(-4) meters squared per second. Such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry. PMID:9082993

Polzin; Toole; Ledwell; Schmitt

1997-04-01

126

Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain, Bangladesh  

Microsoft Academic Search

The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate\\u000a the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved\\u000a oxygen (DO) of 0.8–1.8 mg\\/l, Ca contents of 5–50 mg\\/l, and Fe contents of 0.2–12.9 mg\\/l. Arsenic concentrations ranged from\\u000a 8 to 251 ?g\\/l, with an

Faruque Ahmed; M. Hawa Bibi; Hiroaki Ishiga; Takehiko Fukushima; Teruyuki Maruoka

2010-01-01

127

Late Hesperian plains formation and degradation in a low sedimentation zone of the northern lowlands of Mars  

NASA Astrophysics Data System (ADS)

The plains materials that form the martian northern lowlands suggest large-scale sedimentation in this part of the planet. The general view is that these sedimentary materials were transported from zones of highland erosion via outflow channels and other fluvial systems. The study region, the northern circum-polar plains south of Gemini Scopuli on Planum Boreum, comprises the only extensive zone in the martian northern lowlands that does not include sub-basin floors nor is downstream from outflow channel systems. Therefore, within this zone, the ponding of fluids and fluidized sediments associated with outflow channel discharges is less likely to have taken place relative to sub-basin areas that form the other northern circum-polar plains surrounding Planum Boreum. Our findings indicate that during the Late Hesperian sedimentary deposits produced by the erosion of an ancient cratered landscape, as well as via sedimentary volcanism, were regionally emplaced to form extensive plains materials within the study region. The distribution and magnitude of surface degradation suggest that groundwater emergence from an aquifer that extended from the Arabia Terra cratered highlands to the northern lowlands took place non-catastrophically and regionally within the study region through faulted upper crustal materials. In our model the margin of the Utopia basin adjacent to the study region may have acted as a boundary to this aquifer. Partial destruction and dehydration of these Late Hesperian plains, perhaps induced by high thermal anomalies resulting from the low thermal conductivity of these materials, led to the formation of extensive knobby fields and pedestal craters. During the Early Amazonian, the rates of regional resurfacing within the study region decreased significantly; perhaps because the knobby ridges forming the eroded impact crater rims and contractional ridges consisted of thermally conductive indurated materials, thereby inducing freezing of the tectonically controlled waterways associated with these features. This hypothesis would explain why these features were not completely destroyed. During the Late Amazonian, high-obliquity conditions may have led to the removal of large volumes of volatiles and sediments being eroded from Planum Boreum, which then may have been re-deposited as thick, circum-polar plains. Transition into low obliquity ˜5 myr ago may have led to progressive destabilization of these materials leading to collapse and pedestal crater formation. Our model does not contraindicate possible large-scale ponding of fluids in the northern lowlands, such as for example the formation of water and/or mud oceans. In fact, it provides a complementary mechanism involving large-scale groundwater discharges within the northern lowlands for the emplacement of fluids and sediments, which could have potentially contributed to the formation of these bodies. Nevertheless, our model would spatially restrict to surrounding parts of the northern plain either the distribution of the oceans or the zones within these where significant sedimentary accumulation would have taken place.

Rodríguez, José Alexis Palmero; Tanaka, Kenneth L.; Berman, Daniel C.; Kargel, Jeffrey S.

2010-11-01

128

Fe(III)-reducing bacteria in deeply buried sediments of the Atlantic Coastal Plain  

Microsoft Academic Search

The possibility that microorganisms are catalyzing the ongoing reduction of Fe(III) in the sediments of deep (20-250 m) aquifers was investigated. Acetate-oxidizing, Fe(III)-reducing bacteria were recovered from deep subsurface sediments, but only from sediments in which it appeared that Fe(III) reduction was the terminal electron-accepting process for oxidation of organic matter. The Fe(III)-reducing microorganisms were capable of reducing ferric oxides

Derek R. Lovley; E. J. P. Phillips; F. H. Chapelle

1990-01-01

129

Antecedent Water Content Effects on Runoff and Sediment Yields From Two Coastal Plain Utisols  

Technology Transfer Automated Retrieval System (TEKTRAN)

The highly-weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. Our objective was to quantify the effects of antecedent water content (AWC) on r...

130

Effects of sediment depositional environment and ground-water flow on the quality and geochemistry of water in aquifers in sediments of Cretaceous age in the coastal plain of South Carolina  

USGS Publications Warehouse

The quality and geochemistry of ground water are significantly affected by the depositional environment of aquifer sediments. Cretaceous sediments in the Coastal Plain of South Carolina have been deposited in fluvial, delta-plain, marginal-marine, and marine environments. Depositional environments of sediments within a single aquifer may grade from nonmarine, fluvial, or upper delta plain near the updip limit of the aquifer to transitional, lower delta plain and to marine toward the coast. In nonmarine sediments the major source of inorganic carbon in the water is the decomposition of organic material. The major aqueous geochemical processes are the dissolution and alteration of silicate minerals. Silica makes up a major part of the dissolved constituents in water from these sediments. In transitional and marine sediments the major aqueous geochemical processes are (1) the dissolution of calcium carbonate by hydrolysis and by carbonic acid derived from the decomposition of organic material and (2) the exchange of calcium in solution for sodium on the marine-clay minerals. The clay minerals may also serve as buffers by neutralizing the hydroxyl ion produced by hydrolysis. The effects of incompletely flushed dilute saltwater on water quality increase toward the coast and toward the northeast.

Speiran, Gary K.; Aucott, Walter R.

1994-01-01

131

Eolian sedimentation and soil development on a semiarid to subhumid grassland, Tertiary Ogallala and Quaternary Blackwater Draw Formations, Texas and New Mexico High Plains  

SciTech Connect

Eolian sediments have accumulated as non-glacigenic loess and thin sand sheets on the Central and Southern High Plains grasslands of Texas and new mexico since the late Miocene. Locally as much as 110 m of eolian sediments with numerous paleosols are preserved in the Quaternary Blackwater Draw formation and the upper part of the Miocene-Pleiocene Ogallala formation. These sediments and paleosols, which cover more than 130,000 km{sup 2}, are similar to recent surface sediments and soils and record a long period of episodic eolian transport and sedimentation, and pedogenesis on a stable low-relief grass-covered landscape. Eolian sections, which comprise the fine sand to coarse silt lithofacies of the Ogallala formation, and the very fine to fine sand and sandy mud lithofacies of the Blackwater Draw formation, generally lack primary sedimentary structures. Grain size of Ogallala sediments decreases from west to east and grain size of Blackwater Draw sediments decreases from southwest to northeast. Soil horizonation is well developed in most sections, and buried calcic and argillic horizons are common. Calcic horizons are characterized by sharply increased CaCO{sub 3} content in the form of filaments, nodules, and petrocalcic horizons (calcretes). Argillic horizons are characterized by increased illuvial clay, pedogenic structure, and darker reddish hues. Rhizocretions are common locally. Open root tubules, which are typically less than 1 mm in diameter and characteristic of small plants like grasses, are present in all Ogallala and Blackwater Draw eolian sediments. Paleosols preserved in eolian sediments of the High Plains reflect periods of sedimentation followed by episodes of landscape stability and pedogenesis, and negligible sedimentation. Episodes of sedimentation and soil development likely resulted from cyclic decreases and increases in available moisture and vegetative cover. Eolian sediments were eroded and transported eastward during dry periods when vegetation was sparse in source areas, such as the western High Plains and the Pecos Valley. During humid periods more abundant vegetation probably protected source areas from deflation, and resulted in landscape stability across the High Plains.

Gustavson, T.C. [Univ. of Texas, Austin, TX (United States). Texas Archeological Research Lab.; Holliday, V.T. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Geography

1999-05-01

132

Sedimentation model of gravel-dominated alluvial piedmont fan, Ganga Plain, India  

Microsoft Academic Search

The Piedmont Zone of the Indo-Gangetic Plain contains numerous, laterally coalescing small alluvial fans. The Latest Pleistocene–Holocene\\u000a 30 km long Gaula Fan can be divided into gravelly proximal fan (0–14 km down-stream), gravel-sand rich mid fan (14–22 km)\\u000a and sand–mud dominated distal fan (22–30 km). The fan succession is composed of two fan expansion cycles A and B. Separated\\u000a by an undulatory erosional contact

U. K. Shukla

2009-01-01

133

Assessing the accuracy of thermoluminescence for dating baked sediments beneath late Quaternary lava flows, Snake River Plain, Idaho  

SciTech Connect

Baked sediments beneath lava flows on the Snake River Plain, Idaho, with independent age control by either {sup 14}C or K/Ar dating were analyzed to evaluate the accuracy of the thermoluminescence (TL) technique. The age of flows ranges from {approximately}2 to 100 ka and multiple TL analyses by the total bleach method yielded ages that overlap at one sigma with independent chronologic control. The TL signal of one sample of baked sediment beneath a lava flow with an inferred age of at least 641 {plus_minus} 54 ka was near saturation, perhaps reflecting a relatively high environmental dose rate, and is not datable by TL. This study underscores several major limitations of luminescence geochronology, the natural spatial and temporal variability in environmental radioactivity and the susceptibility of silicate minerals to the growth and retention of a luminescence signal. Despite these limitations, the results demonstrate the utility of luminescence geochronology to date volcanic eruptive events during the Quaternary. 39 refs., 7 figs., 4 tabs.

Forman, S.L.; Pierson, J. [Ohio State Univ., Columbus, OH (United States); Valentine, G. [Los Alamos National Lab., NM (United States)] [and others

1994-08-10

134

Abyssal seafloor waste isolation: the concept  

Microsoft Academic Search

The Naval Research Laboratory (NRL), with industry and university participation, conducted an assessment of the concept of isolating certain wastes (i.e., sewage sludge, fly ash from municipal incinerators, and contaminated dredged material) on the oceans' abyssal seafloor. In this assessment the advantages, disadvantages, and economic and environmental viability of potential engineering methods for achieving abyssal waste isolation were identified and

Philip J Valent; David K Young; William B Sawyer; Thomas D Wright

1998-01-01

135

Infaunal density, biomass and bioturbation in the sediments of the Arctic Ocean  

Microsoft Academic Search

Little is known about the benthic communities of the Arctic Ocean's slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources

Lisa M. Clough; William G. Ambrose; J. Kirk Cochran; Christina Barnes; Paul E. Renaud; Robert C. Aller

1997-01-01

136

Sediment loading and controls in the grasslands of the Great Plains  

Technology Transfer Automated Retrieval System (TEKTRAN)

In this study, the effects of upstream conservation measures on sediment delivery to and half-life of the Fort Cobb Reservoir in West-Central Oklahoma are investigated. Few conservation practices were implemented on the Fort Cobb Reservoir watershed before the 1950s. In the second half of the 20th ...

137

Numerical constraints of current rates of subsidence due to compaction of shallow sediments in the Louisiana coastal plain  

NASA Astrophysics Data System (ADS)

The conversion of wetlands to open water occurs at alarming rates in coastal Louisiana, where relative sea level rise is ~1cm/yr. The value of wetlands for buffering storm surge and providing habitat has prompted efforts to identify and mitigate subsidence (and other) processes that cause wetland loss. Quantitative estimates of the relative contributions of geologic and anthropogenic processes to subsidence of coastal Louisiana are largely unknown. Such information is critical for ongoing regional wetland restoration. We use a stochastic methodology (see related abstract) to estimate the probable contribution of shallow (<200 m) natural compaction to present subsidence rates in the Louisiana coastal plain. Knowledge of present stratigraphic thickness and accumulation time at a location allows the cumulative distribution and probable maximum and minimum rates of surface elevation change due to compaction to be predicted. We then convert present thickness data above the late Wisconsin unconformity in coastal Louisiana to probable ranges of present rates of surface displacement due to compaction, assuming a constant accumulation rate. If regional average accumulation rates have been ~10 mm/yr, 90% of our calculated rates of land surface elevation change due to compaction of post late-Wisconsin sediments are <~2 mm/yr. If regional average accumulation rates have been closer to 40 mm/yr, 90% of compaction rates are likely <~4 mm/yr. We provide graphic solutions for assessing maximum probable surface-displacement rates due to compaction at any site of interest, provided fundamental stratigraphic characteristics are moderately well known. Our methods enable the identification of locations where observed subsidence rates are unlikely to result from post late-Wisconsin unconformity sediment compaction alone for further investigation. Observed subsidence rates greater than the 90th percentile of the calculated compaction rate distributions likely reflect processes in addition to compaction of post-late Wisconsin sediments.

Meckel, T. A.; ten Brink, U.; Williams, S. J.

2005-12-01

138

Temperature and humidity conditions of Macocha Abyss  

NASA Astrophysics Data System (ADS)

The paper deals with the evaluation of temperature and humidity measurements in the vertical profile of Macocha Abyss (Moravian Karst, South Moravia, Czech Republic). The measuring profile on a rock wall is made up of seven HOBO-PRO sensors. Two other meteorological stations are installed at the bottom and near the upper edge of the abyss. The evaluation was designed separately for warm season (June 1, 2008 to August 31, 2008) and cold season (November 1, 2008 to February 28, 2009). In the warm season, distribution of inverse temperatures dominated in the abyss. Temperature differences between the bottom of the abyss and its upper edge reached about 10 ° C. At the bottom of the abyss, the minimum temperatures proved to be higher than at its upper edge and in its vicinity. Thermal circulation is evident to the depth of about 60 m. The highest temperatures were observed in the deeper layers of the abyss in the warm period at around 10 a.m. of Central European Summer Time. Towards the upper edge of the abyss, the hour of daily maximum temperature shifts to 2 to 4 p.m. In the cold season, the minimum temperature was observed between 6 and 7 a.m. of Central European Time. A decrease in the accumulation of cold air (cold-air pool formation) was not found in the lower floors of the abyss. This phenomenon does not occur even during clear nights. The depth of 60 m from the upper edge of the area maintains a high relative humidity (above 95%) in the warm season. However, humidity decreases from this depth towards the top of the abyss. In the cold season, the whole abyss is filled with air with relative humidity of 90 to 95%.

Litschmann, Tomáš; Rožnovský, Jaroslav; St?eda, Tomáš; St?edová, Hana; Hebelka, Ji?í

2012-09-01

139

Effects of agricultural tillage and sediment accumulation on emergent plant communities in playa wetlands of the U.S. High Plains.  

PubMed

Identifying community assembly filters is a primary ecological aim. The High Plains, a 30 million ha short-grass eco-region, is intensely cultivated. Cultivation disturbance, including plowing and eroded soil deposition down-slope of plowing, influences plant composition in depressional wetlands, such as playas, within croplands. We evaluated influences of wetland cultivation and sediment deposition on plant composition in playas embedded within croplands (46 plowed and 32 unplowed) and native grasslands (79) across 6 High Plains' states. Sediment accumulation ranged from 7 to 78 cm in cropland and 1 to 35 cm in grassland playas. Deeper sediments and plowing each decreased wetland plant richness, 28% and 70% respectively in cropland wetlands. Sediment depth reduced richness 37% in small grasslands playas while it increased richness 22% in larger ones, suggesting moderate disturbance increased richness when there were nearby propagule sources. Sediment depth was unrelated to species richness in plowed wetlands, probably because plowing was a strong disturbance. Plowing removed perennial plants from vegetation communities. Sediment accumulation also influenced species composition in cropland playas, e.g., probability of Eleocharis atropurpurea increased with sediment depth, while probability of Panicum capillare decreased. In grassland playas, observed lighter sediment depths did not influence species composition after accounting for wetland area. Sediment accumulation and plowing shift wetland plant communities toward annual species and decrease habitat connectivity for wetland-dependent organisms in cropland playas over 39,000 and 23,400 ha respectively. Conservation practices lessening sediment accumulation include short-grass buffer strips surrounding wetlands. Further, wetland tillage, allowed under federal agricultural conservation programs, should be eliminated. PMID:23500104

O'Connell, Jessica L; Johnson, Lacrecia A; Daniel, Dale W; McMurry, Scott T; Smith, Loren M; Haukos, David A

2013-03-15

140

Aminostratigraphy of surface and subsurface Quaternary sediments, North Carolina coastal plain, USA  

USGS Publications Warehouse

The Quaternary stratigraphy and geochronology of the Albemarle Embayment of the North Carolina (NC) Coastal Plain is examined using amino acid racemization (AAR) in marine mollusks, in combination with geophysical, lithologic, and biostratigraphic analysis of 28 rotasonic cores drilled between 2002 and 2006. The Albemarle Embayment is bounded by structural highs to the north and south, and Quaternary strata thin westward toward the Suffolk paleoshoreline, frequently referred to as the Suffolk Scarp. The Quaternary section is up to ???90. m thick, consists of a variety of estuarine, shelf, back-barrier, and lagoonal deposits, and has been influenced by multiple sea-level cycles. The temporal resolution of the amino acid racemization method is tested statistically and with the stratigraphic control provided by this geologic framework, and it is then applied to the correlation and age estimation of subsurface units throughout the region. Over 500 specimens (primarily Mercenaria and Mulinia) from the subsurface section have been analyzed using either gas chromatographic (GC) or reverse-phase liquid chromatographic (RPLC) techniques. The subsurface stratigraphic data are compared with AAR results from numerous natural or excavated exposures from the surrounding region, as well as results from NC beach collections, to develop a comprehensive aminostratigraphic database for the entire Quaternary record within the NC coastal system. Age mixing, recognized in the beach collections, is also seen in subsurface sections, usually where major seismic reflections or core lithology indicate the presence of stratigraphic discontinuities. Kinetic models for racemization are tested within the regional stratigraphic framework, using either radiocarbon or U-series calibrations or comparison with regional biostratigraphy. Three major Pleistocene aminozones [AZ2, AZ3, and AZ4] are found throughout the region, all being found in superposition in several cores. Each can be subdivided, yielding a total of at least eight stratigraphically and statistically distinct aminozones. Kinetic modeling, supplemented with local calibration, indicates that these aminozones represent depositional events ranging from ???80. ka to nearly 2. Ma. Three prominent seismic reflections are interpreted to represent the base of the early, middle, and late Pleistocene, respectively, roughly 2. Ma, 800. ka, and 130. ka. The large number of samples and the available stratigraphic control provide new insights into the capabilities and limitations of aminostratigraphic methods in assessing relative and numerical ages of Atlantic Coastal Plain Quaternary deposits. ?? 2009 Elsevier B.V.

Wehmiller, J. F.; Thieler, E. R.; Miller, D.; Pellerito, V.; Bakeman, Keeney, V.; Riggs, S. R.; Culver, S.; Mallinson, D.; Farrell, K. M.; York, L. L.; Pierson, J.; Parham, P. R.

2010-01-01

141

Meiofauna communities along an abyssal depth gradient in the Drake Passage  

Microsoft Academic Search

Meiofauna standing stocks and community structure are reported for the first time for abyssal soft-sediment samples in Antarctic waters. At seven stations within a depth range of 2274–5194m a total of 128 sediment cores were retrieved with a multiple corer (MUC) on board of the R.V. Polarstern during the ANDEEP-1 cruise (ANT XIX\\/3). The metazoan meiofauna (defined by a lower

E. Gutzmann; P. Martínez Arbizu; A. Rose; G. Veit-Köhler

2004-01-01

142

Sediment community oxygen consumption in the deep Gulf of Mexico  

NASA Astrophysics Data System (ADS)

Sediment community oxygen consumption (SCOC) has been measured from the continental shelf out to the Sigsbee Abyssal Plain in the NE Gulf of Mexico (GoM). SCOC rates on the continental shelf were an order of magnitude higher than those on the adjacent continental slope (450-2750 m depth) and two orders of magnitude higher than those on the abyssal plain at depths of 3.4-3.65 km. Oxygen penetration depth into the sediment was inversely correlated with SCOC measured within incubation chambers, but rates of SCOC calculated from either the gradient of the [O 2] profiles or the total oxygen penetration depth were generally lower than those derived from chamber incubations. SCOC rates seaward of the continental shelf were lower than at equivalent depths on most continental margins where similar studies have been conducted, and this is presumed to be related to the relatively low rates of pelagic production in the GoM. The SCOC, however, was considerably higher than the input of organic detritus from the surface-water plankton estimated from surface-water pigment concentrations, suggesting that a significant fraction of the organic matter nourishing the deep GoM biota is imported laterally down slope from the continental margin.

Rowe, Gilbert T.; Morse, John; Nunnally, Clifton; Boland, Gregory S.

2008-12-01

143

Sediment Buffering and Transport in the Holocene Indus River System  

NASA Astrophysics Data System (ADS)

Submarine fans are the largest sediment bodies on Earth and potentially hold records of erosion that could be used to assess the response of continents to changing climate in terms of both physical erosion and chemical weathering. However, buffering between the mountain sources and the abyssal plain may make detailed correlation of climate and erosion records difficult. We investigated the nature of sediment transport in the Indus drainage in SW Asia. Through trenching in the flood plain, drilling in the delta and new seismic and coring data from the shelf and canyon we can now constrain sediment transport from source to sink since the Last Glacial Maximum (LGM). The Indus was affected by intensification of the summer monsoon during the Early Holocene and subsequent weakening since ca. 8 ka. Sediment delivery to the delta was very rapid at 12-8 ka, but slowed along with the weakening monsoon. At the LGM erosion in the Karakoram dominated the supply of sandy material, while the proportion of Lesser Himalayan flux increased with strengthening summer rainfall after 12 ka. Total load also increased at that time. Since 5 ka incision of rivers into the upper parts of the flood plain has reworked Lower Holocene sediments, although the total flux slowed. Coring in the Indus canyon shows that sediment has not reached the lower canyon since ca. 7 ka, but that sedimentation has recently been very rapid in the head of the canyon. We conclude that variations in sealevel and terrestrial climate have introduced a lag of at least 7 k.y. into the deep sea fan record and that monsoon strength is a primary control on whether sediment is stored or released in the flood plain.

Clift, P. D.; Giosan, L.; Henstock, T.; Tabrez, A. R.; Vanlaningham, S.; Alizai, A. H.; Limmer, D. R.; Danish, M.

2009-12-01

144

Tectonic and Sedimentation Interactions in the East Caribbean Subduction Zone: AN Overview from the Orinoco Delta to the Barbados Accretionary Prism  

NASA Astrophysics Data System (ADS)

Recent marine geophysical acquisitions and piston-coring allow to better understand the close interactions between the sand-rich Orinoco turbidite system and the compressional structures of the Barbados prism. Because of the morphologic and tectonic control in the east-Caribbean active margin, the Orinoco turbiditic pattern system does not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope of the South-American margin induces the convergence of the turbidite channels toward the abyssal plain, at the front of the accretionary prism. Also, whereas in most passive margins the turbidite systems are organized upstream to downstream as canyon, then channel-levee, then lobes, here, due to the tectonic control, the sedimentary system is organized as channel-levee, then canyons, then channelized lobes. At the edge of the Orinoco platform, the system has multiple sources with several distributaries and downward the channel courses are complex with frequent convergences or divergences that are emphasized by the effects of the undulating seafloor tectonic morphologies associated with active thrust tectonics and mud volcanism. On top of the accretionary prism, turbidite sediments are filling transported piggy-back basins whose timing of sedimentation vs. deformation is complex. Erosion processes are almost absent on the highly subsiding Orinoco platform and in the upper part of the turbidite system. Erosion processes develop mostly between 2000 and 4000 m of water depth, above the compressional structures of the Barbados prism (canyons up to 3 km wide and 300 m deep). In the abyssal plain, turbiditic channels develop on very long distance (> 1000 km) joining the mid-Atlantic channel (sourced mostly by the Amazon), filling several elongated basins corresponding to transform faults (notably the Barracuda Basin), and finally sourcing the Puerto-Rico trench, the deepest morphologic depression of this region. Piston-core surveys have demonstrated that turbidite sediments above the accretionary prism and in the abyssal plain are mostly coarse sandy deposits covered by recent pelagic planktonic-rich sediments, which indicate that sand deposition has slow down during the post-glacial sea level rise. Numerical stratigraphic modeling suggests that during the last glacial event, the main depocenters were located above the tectonic prism and in the abyssal plain, at the front of the prism and that, during the Holocene eustatic rise, a large accommodation space formed on the shelf confining sedimentation mostly on the Orinoco deltaic platform and producing a starvation downstream in the turbidite system. This is in good agreement with the piston coring results which show low deep turbidite sedimentation rates during recent times.

Deville, E.

2011-12-01

145

Submarine ridges do not prevent large-scale dispersal of abyssal fauna: A case study of Mesocletodes (Crustacea, Copepoda, Harpacticoida)  

NASA Astrophysics Data System (ADS)

We examined the large-scale distribution of deep-sea harpacticoid copepods at the species level, in order to clarify the underlying processes of copepod dispersal. The study was based on samples collected from 12 regions and a total of 113 stations: 57 stations at depths between 1107 and 5655 m on abyssal plains in the South and North Atlantic, Southern Ocean, southern Indian Ocean, and the Pacific Ocean, and 56 stations above 900 m in the North Atlantic and eastern Mediterranean Sea. We chose the genus Mesocletodes Sars, 1909 as an ideal group to study the large-scale distribution of harpacticoid copepods in the deep oceans. Clear apomorphies and a comparatively large body size of about 1 mm allow rapid recognition of allied species in meiofauna samples. In addition, Mesocletodes represents more than 50% of the family Argestidae Por, 1986, one of the most abundant harpacticoid families in the deep sea. The geographical distributions of 793 adult females of Mesocletodes belonging to 61 species throughout the South and North Atlantic, Southern Ocean, southern Indian Ocean, Pacific Ocean, and eastern Mediterranean Sea indicated that most species are cosmopolitan. Neither the topography of the sea bottom nor long distances seem to prevent species from dispersing. Passive transport by bottom currents after resuspension is likely the propulsive factor for the dispersal of Harpacticoida, while plate tectonics and movement of individuals in the sediment may play relatively minor roles.

Menzel, Lena; George, Kai Horst; Arbizu, Pedro Martínez

2011-08-01

146

Recent deformation of Quaternary sediments in the northwest Canterbury Plains, New Zealand, as inferred from GPR and seismic data  

Microsoft Academic Search

A high-resolution seismic reflection survey in the northwest Canterbury Plains, New Zealand, has revealed a network of interconnected faults and folds underneath the seemingly undisturbed flat surface. Known rates of background seismicity in the larger area suggest ongoing deformation in the Plains, despite a lack of convincing surface expression. Ongoing deformation would be seen as disturbance of the uppermost Quaternary

S. F. A. Carpentier; C. Dorn; J. A. Doetsch; F. M. Campbell; H. Horstmeyer; A. G. Green; A. E. Kaiser; J. Campbell; J. Pettinga; D. C. Nobes; M. Finnemore; R. Jongens

2010-01-01

147

Response of Late Cretaceous migrating deltaic facies systems to sea level, tectonics, and sediment supply changes, New Jersey Coastal Plain, U.S.A.  

USGS Publications Warehouse

Paleogeographic, isopach, and deltaic lithofacies mapping of thirteen depositional sequences establish a 35 myr high resolution (> 1 Myr) record of Late Cretaceous wave- and tide-influenced deltaic sedimentation. We integrate sequences defined on the basis of lithologic, biostratigraphic, and Sr-isotope stratigraphy from cores with geophysical log data from 28 wells to further develop and extend methods and calibrations of well-log recognition of sequences and facies variations. This study reveals the northeastward migration of depocenters from the Cenomanian (ca. 98 Ma) through the earliest Danian (ca. 64 Ma) and documents five primary phases of paleodeltaic evolution in response to long-term eustatic changes, variations in sediment supply, the location of two long-lived fluvial axes, and thermoflexural basement subsidence: (1) Cenomanian-early Turonian deltaic facies exhibit marine and nonmarine facies and are concentrated in the central coastal plain; (2) high sediment rates, low sea level, and high accommodation rates in the northern coastal plain resulted in thick, marginal to nonmarine mixed-influenced deltaic facies during the Turonign-Coniacian; (3) comparatively low sediment rates and high long-term sea level in the Santonian resulted in a sediment-starved margin with low deltaic influence; (4) well-developed Campanian deltaic sequences expand to the north and exhibit wave reworking and longshore transport of sands, and (5) low sedimentation rates and high long-term sea level during the Maastrichtian resulted in the deposition of a sediment-starved glauconitic shelf. Our study illustrates the widely known variability of mixed-influence deltaic systems, but also documents the relative stability of deltaic facies systems on the 106-107 yr scale, with long periods of cyclically repeating systems tracts controlled by eustasy. Results from the Late Cretaceous further show that although eustasy provides the template for sequences globally, regional tectonics (rates of subsidence and accommodation), changes in sediment supply, proximity to sediment input, and flexural subsidence from depocenter loading determines the regional to local preservation and facies expression of sequences. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Kulpecz, A. A.; Miller, K. G.; Sugarman, P. J.; Browning, J. V.

2008-01-01

148

Census of Marine Life: Census of the Diversity of Abyssal Marine Life  

NSDL National Science Digital Library

A field project of the multi-national Census of Marine Life, the Census of the Diversity of Abyssal Marine Life (CeDAMar) was created to document "actual species diversity of abyssal plains as a basis for global change research and for a better understanding of historical causes and actual ecological factors regulating biodiversity." This site provides Deep-Sea researchers with a forum for discussion and information-sharing. Specifically, this forum allows "researchers to exchange experiences and results from the Projects united under the umbrella of CeDAMar." Additionally, this site links to relevant Projects, Articles, News, FAQ, and Web links, and provides a search engine for locating specific information about CeDAMar.

149

Environmental factors affecting distribution and abundance of bacteria, fungi and protozoa in subsurface sediments of the Upper Atlantic Coastal Plain, USA  

SciTech Connect

Exploratory statistical analyses of microbiological, hydrological and geochemical data for samples from four boreholes drilled into Upper Atlantic Coastal Plain sediments near the Savannah River Site, SC, showed highly significant correlations between bacterial abundance (AODC and CFU) and hydraulic conductivity (K). Sediment texture variables (% sand (S), % silt, % clay (C), and S/C) were strongly interrelated with K and, therefore, also correlated with bacterial abundance. AODC did not correlate with the concentrations of dissolved inorganic nitrogen (DIN) or dissolved organic carbon (DOC) in pore water. CFU also did not correlate with DIN, but a negative relationship was found between the CFU and DOC for sandy sediments, suggesting that microbial activity may control pore water DOC concentration. In some, but not all boreholes, AODC and CFU correlated negatively with pore water concentrations of metals and positively with pH. Protozoan abundance correlated strongly with AODC and CFU in the two boreholes closest to the recharge areas for their major aquifers. It also correlated with sediment texture variables, but not with K. Fungal abundance did not correlate with the abundance of other microbial types when data from individual boreholes were considered; however it did correlate with both bacterial and protozoan abundance when data from all four boreholes were combined. There was no relationship between fungal abundance and either K or sediment texture.

Levine, S.N.; Ghiorse, W.C.

1990-01-01

150

Environmental factors affecting distribution and abundance of bacteria, fungi and protozoa in subsurface sediments of the Upper Atlantic Coastal Plain, USA  

SciTech Connect

Exploratory statistical analyses of microbiological, hydrological and geochemical data for samples from four boreholes drilled into Upper Atlantic Coastal Plain sediments near the Savannah River Site, SC, showed highly significant correlations between bacterial abundance (AODC and CFU) and hydraulic conductivity (K). Sediment texture variables (% sand (S), % silt, % clay (C), and S/C) were strongly interrelated with K and, therefore, also correlated with bacterial abundance. AODC did not correlate with the concentrations of dissolved inorganic nitrogen (DIN) or dissolved organic carbon (DOC) in pore water. CFU also did not correlate with DIN, but a negative relationship was found between the CFU and DOC for sandy sediments, suggesting that microbial activity may control pore water DOC concentration. In some, but not all boreholes, AODC and CFU correlated negatively with pore water concentrations of metals and positively with pH. Protozoan abundance correlated strongly with AODC and CFU in the two boreholes closest to the recharge areas for their major aquifers. It also correlated with sediment texture variables, but not with K. Fungal abundance did not correlate with the abundance of other microbial types when data from individual boreholes were considered; however it did correlate with both bacterial and protozoan abundance when data from all four boreholes were combined. There was no relationship between fungal abundance and either K or sediment texture.

Levine, S.N.; Ghiorse, W.C.

1990-12-31

151

Morphological and ecological parallels between sublittoral and abyssal foraminiferal species in the NE Atlantic: a comparison of Stainforthia fusiformis and Stainforthia sp  

Microsoft Academic Search

Dead specimens of a minute fusiform rotaliid foraminifer are common in the 28–63 ?m fraction of multiple corer samples from a 4850 m-deep site on the Porcupine Abyssal Plain (PAP). Their test morphology is remarkably similar to small specimens of Stainforthia fusiformis (Williamson, 1858), a species which is well known from coastal settings (intertidal to outer shelf) around NW Europe

Andrew J. Gooday; Elisabeth Alve

2001-01-01

152

Hydrodynamically Modified, Abyssal Isopod Fauna.  

National Technical Information Service (NTIS)

At the High Energy Boundary Layer Experiment (HEBBLE) site (4820 m depth in the western North Atlantic) periods of strong currents and sediment erosion alternate with periods of weak flow and massive deposition. We investigated the impact of this atypical...

D. Thistle G. D. Wilson

1987-01-01

153

Distribution of phthalate esters in alluvial sediment: A case study at JiangHan Plain, Central China  

Microsoft Academic Search

This study aimed to investigate the sources and distribution of phthalate esters (PAEs) in alluvial sediment of humid climate regions where water cycle is very active in order to reveal their behavior of transport from topsoil and\\/or surface water to deep sediment and groundwater. Topsoil and deeper sediment samples were collected from nine and seventeen sites in July 2007, and

Hui Liu; Hecheng Liang; Ying Liang; Dan Zhang; Cheng Wang; Hesheng Cai; Stepan. L. Shvartsev

2010-01-01

154

Isotope and trace element geochemistry of sediments from the Barbados Ridge-Demerara Plain region, Atlantic Ocean  

Microsoft Academic Search

Twenty-four piston core sediment samples and 13 sediments and 3 basalts from DSDP Leg 78 Site 543 were analyzed for Sr, Nd and Pb isotopic compositions. The results show sediment with highly radiogenic Pb 206 Pb \\/ 204 Pb up to 19.8) and rather radiogenic Sr and unradiogenic Nd has been deposited in the region since the Cretaceous. The source

William M. White; Bernard Dupré; Philippe Vidal

1985-01-01

155

Laboratory-Measured and Property-Transfer Modeled Saturated Hydraulic Conductivity of Snake River Plain Aquifer Sediments at the Idaho National Laboratory, Idaho  

USGS Publications Warehouse

Sediments are believed to comprise as much as 50 percent of the Snake River Plain aquifer thickness in some locations within the Idaho National Laboratory. However, the hydraulic properties of these deep sediments have not been well characterized and they are not represented explicitly in the current conceptual model of subregional scale ground-water flow. The purpose of this study is to evaluate the nature of the sedimentary material within the aquifer and to test the applicability of a site-specific property-transfer model developed for the sedimentary interbeds of the unsaturated zone. Saturated hydraulic conductivity (Ksat) was measured for 10 core samples from sedimentary interbeds within the Snake River Plain aquifer and also estimated using the property-transfer model. The property-transfer model for predicting Ksat was previously developed using a multiple linear-regression technique with bulk physical-property measurements (bulk density [pbulk], the median particle diameter, and the uniformity coefficient) as the explanatory variables. The model systematically underestimates Ksat,typically by about a factor of 10, which likely is due to higher bulk-density values for the aquifer samples compared to the samples from the unsaturated zone upon which the model was developed. Linear relations between the logarithm of Ksat and pbulk also were explored for comparison.

Perkins, Kim S.

2008-01-01

156

Abyssal Seafloor Waste Isolation: Environmental Report.  

National Technical Information Service (NTIS)

The Naval Research Laboratory (NRL) has completed a study of the concept of isolating industrial wastes (i.e., sewage sludge, fly ash from municipal incinerators, and dredged material) on the oceans' abyssal seafloor. In this study, the advantages and dis...

P. J. Valent D. K. Young

1995-01-01

157

Ewing Structure: A Possible Abyssal Impact Crater  

Microsoft Academic Search

We discovered a possible abyssal impact crater about 150 km in diameter that we call the Ewing structure. It lies between the Clarion and Clipperton fracture zones and is about the age of the late\\/middle Miocene boundary, a prominent mass extinction event. The Ewing structure has a weak topographic expression, but 6 cm to over 850-cm thick layers with high

D. H. Abbott; L. Burckle; T. Goldin; J. Hays

2001-01-01

158

Dredged material isolation on the abyssal seafloor: A feasibility study. Final report  

SciTech Connect

This report is the result of an examination of the feasibility of isolating contaminated dredged material on the abyssal seafloor. The focus is on the technical and environmental factors that constrain the considerations of feasibility. A thorough conceptual design of a dredging to abyssal deposition system is analyzed with regard to each subsystem and to the entire operational concept. These subsystems include: (1) a low leakage dredge, (2) equipment for material handling and loading into geosynthetic fabric containers (GFCs), (3) the barge for transport and navigation, and (4) the subsystem for releasing the GFCs to sink to the abyssal seafloor isolation site. Particular consideration is given to the exclusion of dredged material from the ocean`s productive zone in the upper 1000 m. New theoretical models and previous empirical results are used to predict GFC motion through the water column and response to impact on the abyssal seafloor, including the case of potential release of contaminated, turbid water at impact. A geochemical model of the temporal and spatial evolution of the post-deposition geochemistry of the water column, the GFC contents and the sediments below is developed and analyzed; the results show that release of metals into the ocean waters would be insignificant. A model of the biological impacts of the introduction of dredged material in the abyssal environment is used to infer that: (1) biological diversity in the vicinity of the deposition site will be diminished, (2) biomass will be increased by dominance of a few fast growing, opportunistic benthic species, and (3) concentrations of trace elements and organic contaminant.

Valent, P.J.; Young, D.K.

1997-12-01

159

Terrestrial plant biopolymers in marine sediments  

NASA Astrophysics Data System (ADS)

The vascular land plant biopolymers lignin and cutin were surveyed in the surface sediments of coastal and open ocean waters by controlled alkaline CuO oxidation/reaction. Two contrasting oceanic regimes were studied: the northwest Mediterranean (NWM) Sea, which receives significant particulate terrigenous debris through riverine discharge; and the northeast Atlantic (NEA) Ocean, with poorly characterised terrestrial carbon inputs. In the NWM products of lignin and cutin co-occurred at all stations, elevated levels (ca. 0.5-3.0 mg lignin phenols/100 mg organic carbon; ca. 0.01-0.09 mg cutin acids/100 mg organic carbon) were observed for near-shore deltaic and shelf sediments. The influence of terrestrial land plant inputs extended across the shelf and through the slope to the abyssal plain, providing molecular evidence for advective offshore transfer of terrestrial carbon. Mass balance estimates for the basin suggest riverine inputs account for the majority of surface sedimentary lignin/cutin, most of which (>90%) is deposited on the shelf. Products of CuO oxidation of lignin and cutin were also detected in NEA surface sediments, at levels comparable to those observed for the NWM continental slope, and were detectable at low concentrations ( ca . 0.5 g g -1 in the sediments of the abyssal plains (>4,000 m depth). While atmospheric deposition of lignin/cutin-derived material cannot be discounted in this open ocean system, lateral advective transfer of enriched shelf sediments is inferred as a possible transport process. A progressive enrichment in cutin-derived material relative to lignin was observed offshore, with evidence of an increase in the degree of oxidative alteration of lignin residues. To account for these observations, preferential offshore transport of finer and more degraded material is proposed. Nonspecific oxidation products dominated the gas chromatograms of NEA sediments, which appear to originate from marine sources of sedimentary organic carbon. Preliminary mass balance calculations applied to the global ocean margin suggest riverine sources of both particulate lignin and cutin are important and that most (>95%) deposition of recognisable land plant biopolymers occurs in shelf seas.

Gough, Mark A.; Fauzi, R.; Mantoura, C.; Preston, Martin

1993-03-01

160

27. CENOZOIC EVOLUTION OF THE NEW JERSEY COASTAL PLAIN: CHANGES IN SEA LEVEL, TECTONICS, AND SEDIMENT SUPPLY 1  

Microsoft Academic Search

The New Jersey Coastal Plain Drilling Project continuously cored three boreholes at Island Beach, Atlantic City, and Cape May, New Jersey. Sequence boundaries in the cores are expressed as physical surfaces, lithofacies breaks, and paraconformities (hiatuses) recognized using biostratigraphy and Sr-isotopic stratigraphy. By drilling along dip and strike profiles, we assembl ed a mosaic of 29 Paleocene to Miocene sequences

Kenneth G. Miller; James V. Browning; Stephen F. Pekar; Peter J. Sugarman

161

Characterization on arsenic sorption and mobility of the sediments of Chia-Nan Plain, where Blackfoot disease occurred  

Microsoft Academic Search

Higher levels of arsenic in the aquifers of Chia-Nan Plain in southwestern Taiwan were attributed to the cause of Blackfoot\\u000a disease in the area half a century ago. Although extensive studies were conducted on the occurrence, speciation, mobility,\\u000a and transport of arsenic in the region, the relationship between arsenic adsorption by different aquifer materials and the\\u000a concentration and speciation of

Zhaohui Li; Hanlie Hong; Jiin-Shuh Jean; Andria J. Koski; Chia-Chuan Liu; Selim Reza; Jeffrey J. Randolph; Stephan R. Kurdas; Jonathan H. Friend; Sarah J. Antinucci

162

Baroclinic characteristics of frictionally destabilized abyssal overflows  

Microsoft Academic Search

Observations show that the near-sill dynamics of dense abyssal overflows is variable and is governed, to a significant extent, by a balance between rotation, bottom friction and downslope acceleration due to gravity. Numerical simulations indicate that the near-sill downslope velocities are comparable to the phase\\/group velocities of long internal gravity waves. This suggests the possibility that overflows can become supercritical

GORDON E. S WATERS

2003-01-01

163

Abyssal food limitation, ecosystem structure and climate change.  

PubMed

The abyssal seafloor covers more than 50% of the Earth and is postulated to be both a reservoir of biodiversity and a source of important ecosystem services. We show that ecosystem structure and function in the abyss are strongly modulated by the quantity and quality of detrital food material sinking from the surface ocean. Climate change and human activities (e.g. successful ocean fertilization) will alter patterns of sinking food flux to the deep ocean, substantially impacting the structure, function and biodiversity of abyssal ecosystems. Abyssal ecosystem response thus must be considered in assessments of the environmental impacts of global warming and ocean fertilization. PMID:18584909

Smith, Craig R; De Leo, Fabio C; Bernardino, Angelo F; Sweetman, Andrew K; Arbizu, Pedro Martinez

2008-06-26

164

Recent deformation of Quaternary sediments as inferred from GPR images and shallow P-wave velocity tomograms: Northwest Canterbury Plains, New Zealand  

NASA Astrophysics Data System (ADS)

Prior to the recent highly damaging M 7.1 earthquake near the city of Christchurch on the South Island of New Zealand, we recorded coincident high-resolution seismic and ground-penetrating radar (GPR) data across parts of the northwest Canterbury Plains. The seismic reflection images reveal a vast network of interconnected faults and folds below a seemingly undisturbed flat surface. To complement the seismic images, which only provide limited information on the very shallow subsurface (i.e., < 20 m), we have now processed and analysed the GPR data. The migrated GPR images are dominated by complex reflection patterns characteristic of glaciofluvial sediments. Such sediments eroded from the Southern Alps are observed at the surface throughout our study site. Although it is difficult to distinguish between complexities associated with complicated sedimentation processes and disruptions and offsets of GPR reflections associated with recent movements on faults and folds, we identify a number of regions where the GPR data are consistent with tectonic deformation of Holocene sediments. Two of these regions straddle an interpolated connection between active faults mapped at the surface. In a third region, the development of river terraces imaged in the GPR data may have been affected by slip on newly discovered underlying faults. The most significant near-surface deformation, which is apparent on a coincident seismic reflection image, P-wave tomogram and GPR image, is observed on the flank of a major anticline that appears to have been thrust close to the surface along a reverse fault. Some of the faults and folds resolved in our seismic and GPR data may have been reactivated during the recent period of intense seismicity.

Carpentier, S. F. A.; Green, A. G.; Doetsch, J.; Dorn, C.; Kaiser, A. E.; Campbell, F.; Horstmeyer, H.; Finnemore, M.

2012-06-01

165

Oxidation fronts in pelagic sediments: diagenetic formation of metal-rich layers  

SciTech Connect

The periodic deposition of distal turbidites at a site on the Madeira Abyssal Plain causes the development of a nonsteady-state diagenetic system in which an oxidation front migrates downward into the sediment. Data presented here show that iron, manganese, and particulate organic carbon are oxidized at this front by oxidants (molecular oxygen and nitrate) diffusing from above. A numerical model of systems of this type predicts the formation of iron-rich layers under certain nonsteady-state conditions. The layers predicted by the model are closely comparable in thickness and general morphology to iron-rich layers found in certain ocean sediments, the origin of which has been until now unexplained. 23 references, 2 figures, 2 tables.

Wilson, T.R.S.; Thomson, J.; Hydes, D.J.; Colley, S.; Culkin, F.; Soerensen, J.

1986-05-23

166

Global sediment thickness data set updated for the Australian-Antarctic Southern Ocean  

NASA Astrophysics Data System (ADS)

We present a new, 5 min sediment thickness grid for the Australian-Antarctic region (60°E-155°E, 30°S-70°S). New seismic reflection and refraction data have been used to add detail to the conjugate Australian and Antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously. On the margins, sediment thickness estimates were computed from velocity-depth functions from sonobuoy/refraction velocity solutions ground-truthed against seismic reflection data. For the Southeast Indian Ridge abyssal plains, sediment thickness contours from Geli et al. (2007) were used. The new regional minimum sediment thickness grid was combined with the global National Geophysical Data Center (NGDC) sediment grid to create an updated global grid. Even using the minimum estimates, sediment accumulations on the extended Australian and Antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the Ceduna Basin compared to the global NGDC compilation of sediment thickness data.

Whittaker, Joanne M.; Goncharov, Alexey; Williams, Simon E.; Müller, R. Dietmar; Leitchenkov, German

2013-08-01

167

Early organic diagenesis: The significance of progressive subsurface oxidation fronts in pelagic sediments  

NASA Astrophysics Data System (ADS)

Porewater and solid phase geochemical data at two contrasting NE Atlantic stations are reported. Station 10552, on the Cape Verde abyssal plain, is a site of slow pelagic accumulation ( ca. 0.4 cm kyr -1). Molecular oxygen is present in the sediment column to at least 2 m, and probably much deeper, labile organic-carbon is almost totally consumed in the upper few centimetres of the sediment. By contrast, at station 10554 on the Madeira abyssal plain, the pelagic sequence has been interrupted by the occasional deposition of organic-rich turbidites. Porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic-carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column. This metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time. This phenomenon exerts a controlling influence on the present nutrient profile and redox succession. In a less extreme form, substrate distributions of this latter type are not uncommon in Atlantic sediments. A model has been developed which is controlled by both oxygen and nitrate data. This model permits a vertical profile of metabolic activity to be derived, and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations. About 30% of the total activity at station 10554 is located within the turbidite at the deepening reaction front; this is a non-steady-state condition. In fact, it is found that the integrated metabolic activity at the two stations is not dissimilar ( ca. 1-2 × 10 -13moles cm -2 sec -1). The striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column.

Wilson, T. R. S.; Thomson, J.; Colley, S.; Hydes, D. J.; Higgs, N. C.; Sørensen, J.

1985-03-01

168

The Gulf Stream pathway and the impacts of the eddy-driven abyssal circulation and the Deep Western Boundary Current  

NASA Astrophysics Data System (ADS)

A hydrodynamic model of the subtropical Atlantic basin and the Intra-Americas Sea (9-47°N) is used to investigate the dynamics of Gulf Stream separation from the western boundary at Cape Hatteras and its mean pathway to the Grand Banks. The model has five isopycnal Lagrangian layers in the vertical and allows realistic boundary geometry, bathymetry, wind forcing, and a meridional overturning circulation (MOC), the latter specified via ports in the northern and southern boundaries. The northward upper ocean branch of the MOC (14 Sv) was always included but the southward Deep Western Boundary Current (DWBC) was excluded in some simulations, allowing investigation of the impacts of the DWBC and the eddy-driven mean abyssal circulation on Gulf Stream separation from the western boundary. The result is resolution dependent with the DWBC playing a crucial role in Gulf Stream separation at 1/16° resolution but with the eddy-driven abyssal circulation alone sufficient to obtain accurate separation at 1/32° resolution and a realistic pathway from Cape Hatteras to the Grand Banks with minimal DWBC impact except southeast of the Grand Banks. The separation from the western boundary is particularly sensitive to the strength of the eddy-driven abyssal circulation. Farther to the east, between 68°W and the Grand Banks, all of the 1/16° and 1/32° simulations with realistic topography (with or without a DWBC) gave similar generally realistic mean pathways with clear impacts of the topographically constrained eddy-driven abyssal circulation versus very unrealistic Gulf Stream pathways between Cape Hatteras and the Grand Banks from otherwise identical simulations run with a flat bottom, in reduced-gravity mode, or with 1/8° resolution and realistic topography. The model is realistic enough to allow detailed model-data comparisons and a detailed investigation of Gulf Stream dynamics. The corresponding linear solution with a Sverdrup interior and Munk viscous western boundary layers, including one from the northward branch of the MOC, yielded two unrealistic Gulf Stream pathways, a broad eastward pathway centered at the latitude of Cape Hatteras and a second wind plus MOC-driven pathway hugging the western boundary to the north. Thus, a high resolution model capable of simulating an inertial jet is required to obtain a single nonlinear Gulf Stream pathway as it separates from the coast. None of the simulations were sufficiently inertial to overcome the linear solution need for a boundary current north of Cape Hatteras without assistance from pathway advection by the abyssal circulation, even though the core speeds of the simulated currents were consistent with observations near separation. In the 1/16° simulation with no DWBC and a 1/32° simulation with high bottom friction and no DWBC the model Gulf Stream overshot the observed separation latitude. With abyssal current assistance the simulated (and the observed) mean Gulf Stream pathway between separation from the western boundary and ˜70°W agreed closely with a constant absolute vorticity (CAV) trajectory influenced by the angle of the coastline prior to separation. The key abyssal current crosses under the Gulf Stream at 68.5-69°W and advects the Gulf Stream pathway southward to the terminus of an escarpment in the continental slope. There the abyssal current crosses to deeper depths to conserve potential vorticity while passing under the downward-sloping thermocline of the stream and then immediately retroflects eastward onto the abyssal plain, preventing further southward pathway advection. Thus specific topographic features and feedback from the impact of the Gulf Stream on the abyssal current pathway determined the latitude of the stream at 68.5-69°W, a latitude verified by observations. The associated abyssal current was also verified by observations.

Hurlburt, Harley E.; Hogan, Patrick J.

2008-08-01

169

Mercury in bottom sediments of the Amur River, its flood-plain lakes and estuary, Eastern Siberia.  

PubMed

Mercury (Hg) is an element of a special concern in the Amur River basin, where numerous cinnabar deposits and manifestations have been prospected. Moreover, the territory is under heavy anthropogenic pressure due to intensive economic development that includes activities accompanied by noticeable emissions of Hg to the environment through poor waste management practices and accidental emergency discharges. Yet, information on Hg distribution and behavior in this region is scarce and inadequate. In order to evaluate Hg levels and fate in this vast territory, surveys of river, lake, and estuarine bottom sediments, as integral indicators of environmental status, were carried out in 1990, 1991, 1997, and 2004. The results showed the following: (1) stagnation of the Russian economy in the 1990s has resulted in a noticeable decrease of the Hg content in the Amur River sediments to the basin pristine level of about 0.05 mg kg(-1); (2) Hg distribution in the sediment depth proves the element redox-dependent behavior; (3) in some cases, Hg enrichment may be related to the long-term anthropogenic emission; (4) Hg concentration in bottom sediments was found to increase in the following order-the Amur River mouth, the estuary, and the Sea of Okhotsk, showing the weakly non-conservative Hg behavior during estuarine water mixing. PMID:19629736

Kot, Fyodor S; Bakanov, Konstantin G; Goryachev, Nikolay A

2009-07-24

170

Results of rainfall simulation to estimate sediment-bound carbon and nitrogen loss from an Atlantic Coastal Plain (USDA) ultisol  

Technology Transfer Automated Retrieval System (TEKTRAN)

The impact of erosion on soil and carbon loss and redistribution within landscapes is an important component for developing estimates of carbon sequestration potential, management plans to maintain soil quality, and transport of sediment bound agrochemicals. Soils of the Southeastern U.S. Coastal Pl...

171

Paleogene Submarine Fan Depocenters of the Abyssal Gulf of Mexico: Paleogeography, Provenance, and Tectonic Implications  

NASA Astrophysics Data System (ADS)

In the abyssal Gulf of Mexico (AGOM) seven major Paleogene submarine fan depocenters are identified on regional 2D and local 3D seismic data tied to wells on adjacent structural belts. Source directions are inferred from (1) location of isopach maxima relative to paleo-margins; (2) seismic facies; (3) channel orientations on 3D seismic; and (4) sandstone composition, particularly that of lithic grains. Paleogene fan depocenters in the southwestern and southeastern AGOM are associated with relatively narrow and high-gradient (several degrees), high-bypass continental margins adjacent to orogenic belts. The (1) Chicontepec Fan (Paleocene, syn-Laramide) and (2) Post-Chicontepec Fan (Eocene-Oligocene) had westerly sources in east-central Mexico. Sandstone lithic modes are predominantly carbonate in the Chicontepec and mixed volcanic-carbonate in the Post-Chicontepec. The Laramide-age (3) Straits of Florida depocenter (Paleocene-Eocene?) was sourced from Cuba to the southeast; sandstone composition is unknown. In contrast, Paleogene fan depocenters in the northwestern AGOM are associated with large deltaic depocenters, low- to moderate-bypass margins, and very low-gradient (1 degree or less) continental slopes. The Wilcox fans (Upper Paleocene-Lower Eocene, syn-Laramide) had a dominant source direction to the northwest, but can be separated into (4) Lower Wilcox (northerly source), (5) Middle Wilcox (westerly source in NE Mexico), and (6) Upper Wilcox (westerly to northwesterly source). Like the Upper Wilcox, the (7) Frio fan depocenter (Middle Oligocene) had a westerly source associated with a large deltaic depocenter. Sandstone lithic modes of Wilcox fans range from metamorphic to mixed metamorphic-volcanic, clays are predominantly illite, and polygonal faulting is absent. Sandstones of the overlying Post-Chicontepec and Frio fans are mixed volcanic-carbonate, clays are smectite-rich, and polygonal faulting is abundant. Six of these depocenters attain maximum thicknesses of less than 1 km and can be related either to Laramide- age orogenesis (Chicontepec, Wilcox, Straits of Florida) or mid-Cenozoic arc volcanism (Frio). The Post- Chicontepec depocenter is anomalously thick, locally exceeding 3 km, and represents one of the major sediment influxes of AGOM history, attributed here to post-orogenic uplift of a large region extending possibly from the Mexican coastal plain to the Sierra Madre Occidental.

Winker, C. D.

2008-05-01

172

Abyssal food limitation, ecosystem structure and climate change  

Microsoft Academic Search

The abyssal seafloor covers more than 50% of the Earth and is postulated to be both a reservoir of biodiversity and a source of important ecosystem services. We show that ecosystem structure and function in the abyss are strongly modulated by the quantity and quality of detri- tal food material sinking from the surface ocean. Climate change and human activities

Craig R. Smith; Fabio C. De Leo; Angelo F. Bernardino; Andrew K. Sweetman; Pedro Martinez Arbizu

2008-01-01

173

Pb isotopes in surficial pelagic sediments from the North Atlantic  

SciTech Connect

The authors measured Pb isotopic composition and concentration in sediment samples close to the sea water interface in 6 box-cores from the NE Atlantic, 2 box-cores from the Sargasso Sea, and one from the US continental shelf. The anthropogenic Pb input to marine sediments due to the increase of Pb contamination over the ocean during the last century can be identified in all these cores. In the eastern part of the Atlantic, i.e., in regions under aeolian influence from Europe, Pb pollution can be recognized using its distinctive unradiogenic composition, clearly different from the upper-crustal values commonly found in pre-Holocene sediments. In contrast, Pb pollution in regions influenced by North American sources can be identified only in detailed concentration profiles because the American Pb pollution has an isotopic composition much closer to that of the natural detrital Pb input coming from weathering of the continental crust. Pb excess inventories are in good agreement with fluxes estimated from sediment-trap data and with the time record of Pb-contamination increase given by analyses in coral growth bands. Inventories of Pb contamination to the sediments of the Mud Patch (American shelf) are tenfold higher (84 {mu}g/cm{sup 2}) than those to Hatteras and Bermuda abyssal plains (4.3 and 2.8 {mu}g/cm{sup 2}).

Hamelin, B.; Grousset, F. (Lamont-Doherty Geological Observatory, Palisades, NY (USA)); Sholkovitz, E.R. (Woods Hole Oceanographic Institution, MA (USA))

1990-01-01

174

Extreme 2002: Mission to the Abyss  

NSDL National Science Digital Library

This is the expedition page of the 2002 Mission to the Abyss. Developed by the University of Delaware Graduate College of Marine Studies, the site highlights the mission and crew, seafloor geology, creature features, and high-tech tools used in the study. This interactive website allows students to explore the submersible Alvin, find out how hydrothermal vents form, define the deep ocean, study plate tectonics, and meet hydrothermal vent organisms. The site includes extreme experiments, including: compression of a fluid vs. a gas, rising under pressure, my cup shrinks, soda squeeze, and plant pressure.

2010-03-15

175

Eukaryotic Richness in the Abyss: Insights from Pyrotag Sequencing  

PubMed Central

Background The deep sea floor is considered one of the most diverse ecosystems on Earth. Recent environmental DNA surveys based on clone libraries of rRNA genes confirm this observation and reveal a high diversity of eukaryotes present in deep-sea sediment samples. However, environmental clone-library surveys yield only a modest number of sequences with which to evaluate the diversity of abyssal eukaryotes. Methodology/Principal Findings Here, we examined the richness of eukaryotic DNA in deep Arctic and Southern Ocean samples using massively parallel sequencing of the 18S ribosomal RNA (rRNA) V9 hypervariable region. In very small volumes of sediments, ranging from 0.35 to 0.7 g, we recovered up to 7,499 unique sequences per sample. By clustering sequences having up to 3 differences, we observed from 942 to 1756 Operational Taxonomic Units (OTUs) per sample. Taxonomic analyses of these OTUs showed that DNA of all major groups of eukaryotes is represented at the deep-sea floor. The dinoflagellates, cercozoans, ciliates, and euglenozoans predominate, contributing to 17%, 16%, 10%, and 8% of all assigned OTUs, respectively. Interestingly, many sequences represent photosynthetic taxa or are similar to those reported from the environmental surveys of surface waters. Moreover, each sample contained from 31 to 71 different metazoan OTUs despite the small sample volume collected. This indicates that a significant faction of the eukaryotic DNA sequences likely do not belong to living organisms, but represent either free, extracellular DNA or remains and resting stages of planktonic species. Conclusions/Significance In view of our study, the deep-sea floor appears as a global DNA repository, which preserves genetic information about organisms living in the sediment, as well as in the water column above it. This information can be used for future monitoring of past and present environmental changes.

Pawlowski, Jan; Christen, Richard; Lecroq, Beatrice; Bachar, Dipankar; Shahbazkia, Hamid Reza; Amaral-Zettler, Linda; Guillou, Laure

2011-01-01

176

Relationship between polymetallic nodule genesis and sediment distribution in the KODOS (Korea Deep Ocean Study) Area, Northeastern Pacific  

NASA Astrophysics Data System (ADS)

Polymetallic nodule and sediment characteristics were investigated for two blocks (KR2 and KR5) in the Korea Deep Ocean Study (KODOS) area in order to better understand nodule distribution and the potential effects of sediments on nodule genesis. The northern block (KR2) is dominated by hydrogenetic nodules, whereas the southern block (KR5) is dominated by diagenetic nodules. Sediments in the study area are assigned to three major lithologic units which are distinctive in color and texture. The northern block is characterized by a thick, metalpoor Unit 1 sediment, which is thin in the southern block, where metal-rich Units 2b and 3 occur close to the surface. The distribution of different nodule genetic types in the northern and southern blocks can be attributed to topographic variations (topographic high near seamounts in KR2 and abyssal plain in KR5) and different sedimentation rates (0.1 and 0.32 mm/kyr in blocks KR2 and KR5, respectively). The southern block has a geologic setting more conducive to diagenetic nodule formation, such as flat topography and sediment composition. Nodule distribution in the studied blocks might also be explained by the distribution of the sediment units of different metal contents. The northern block, in which Unit 1 is thicker, has more abundant hydrogenetic nodules, possibly because Unit 1 prevents metals that are remobilized from the underlying sediments from reaching the seabed where the nodules are forming.

Kim, Jonguk; Hyeong, Kiseong; Lee, Hyun-Bok; Ko, Young-Tak

2012-09-01

177

The Cainozoic geology of the Middle Shoalhaven Plain  

Microsoft Academic Search

The Middle Shoalhaven Plain is a large, tray?like depression bounded in the west by the Mulwaree fault and in the east by cliffed Permian sediments. The plain is probably Mesozoic in origin and was partially alluviated during the Early to mid?Eocene. Much of the plain and sediments were covered by basalts during the Late Eocene. This was followed by an

Bryan P. Ruxton; Graham Taylor

1982-01-01

178

Long-term change in benthopelagic fish abundance in the abyssal northeast Pacific Ocean.  

PubMed

Food web structure, particularly the relative importance of bottom-up and top-down control of animal abundances, is poorly known for the Earth's largest habitats: the abyssal plains. A unique 15-yr time series of climate, productivity, particulate flux, and abundance of primary consumers (primarily echinoderms) and secondary consumers (fish) was examined to elucidate the response of trophic levels to temporal variation in one another. Towed camera sled deployments in the abyssal northeast Pacific (4100 m water depth) showed that annual mean numbers of the dominant fish genus (Coryphaenoides spp.) more than doubled over the period 1989-2004. Coryphaenoides spp. abundance was significantly correlated with total abundance of mobile epibenthic megafauna (echinoderms), with changes in fish abundance lagging behind changes in the echinoderms. Direct correlations between surface climate and fish abundances, and particulate organic carbon (POC) flux and fish abundances, were insignificant, which may be related to the varied response of the potential prey taxa to climate and POC flux. This study provides a rare opportunity to study the long-term dynamics of an unexploited marine fish population and suggests a dominant role for bottom-up control in this system. PMID:16602284

Bailey, D M; Ruhl, H A; Smith, K L

2006-03-01

179

Influence of internal tides on Antarctic Bottom Water propagation through abyssal channels  

NASA Astrophysics Data System (ADS)

Antarctic Bottom Water (AABW) propagates in the Atlantic Ocean from the Weddell Sea to the north through narrow passages in submarine ridges. Submarine ridges are regions of strong internal tide generation in the ocean that causes mixing and eventually AABW loses its distinguishing properties such as low temperature and salinity. The Vema Fracture Zone (11? N) and Romanche Fracture Zone (equator) in the Mid-Atlantic Ridge (MAR) are pathways for AABW to the Northeast Atlantic. The deep basin of the Northeast Atlantic (Canary Basin and Gambia Abyssal Plain) are filled with the bottom water propagating through the Vema FZ rather than through the equatorial fracture zones because strong internal tides and mixing over the slopes of the MAR near the equator cause warming of AABW and decrease of its density. Further propagation of AABW through the Kane Gap is low. Recent field measurements in the fracture zones confirm this concept based on modeling results. Results of recent cruises are presented.

Morozov, Eugene

2010-05-01

180

A source-sink hypothesis for abyssal biodiversity.  

PubMed

Bathymetric gradients of biodiversity in the deep-sea benthos constitute a major class of large-scale biogeographic phenomena. They are typically portrayed and interpreted as variation in alpha diversity (the number of species recovered in individual samples) along depth transects. Here, we examine the depth ranges of deep-sea gastropods and bivalves in the eastern and western North Atlantic. This approach shows that the abyssal molluscan fauna largely represents deeper range extensions for a subset of bathyal species. Most abyssal species have larval dispersal, and adults live at densities that appear to be too low for successful reproduction. These patterns suggest a new explanation for abyssal biodiversity. For many species, bathyal and abyssal populations may form a source-sink system in which abyssal populations are regulated by a balance between chronic extinction arising from vulnerabilities to Allee effects and immigration from bathyal sources. An increased significance of source-sink dynamics with depth may be driven by the exponential decrease in organic carbon flux to the benthos with increasing depth and distance from productive coastal systems. The abyss, which is the largest marine benthic environment, may afford more limited ecological and evolutionary opportunity than the bathyal zone. PMID:15729648

Rex, Michael A; McClain, Craig R; Johnson, Nicholas A; Etter, Ron J; Allen, John A; Bouchet, Philippe; Warén, Anders

2004-12-22

181

A late Quaternary loess-paleosol pedosedimentary sequence at Monte Netto (northern Italy): loess sedimentation, soil formation and tectonics in the central Po Plain.  

NASA Astrophysics Data System (ADS)

In the area of the Po Plain south of Brescia several isolated hills are present (Castenedolo hill, Ciliverghe hill, and Monte Netto), corresponding to the top of Late Quaternary anticlines. The Castenedolo and Ciliverghe area was widely explored in the last decades and thick sequences of pedosediments furnished detailed archives for the evolution of this part of the Po Plain. A new thick and complex loess-paleosol sequence, resting upon fluvial and fluvioglacial deposits exposed in a clay pit at the top of the Monte Netto hill is being studied in great detail. The Monte Netto is a large flat hill, gently undulated at its top, and the clay pit was opened close to the centre of the anticline, where fluvial and fluvioglacial deposits are deformed. This succession, probably of middle Pleistocene age, is buried by a loess-paleosol sequence 2 to 7 m thick; the depth of the loess is related to its physiographic position, i.e. it becomes thicker going away from the top of the anticline. Furthermore, the upper pedosediments are faulted by bending-moment structures, developed during fold amplification and allow to date some of the latest movements of the anticline. A geopedological, sedimentological and micropedological investigation of the whole extension of the quarry shows a distinctive difference between the loess-paleosol sequence at the top of the anticline and the one placed at its southern fringe (150 m away). On the top of the anticline a deeply weathered red paleosols developed in loess underneath a weakly weathered loess. In this soil also a small lithic assemblage dating to the Middle Palaeolithic was found. The pedosedimentary sequence at the southern fringe of the anticline consists of several loess layers showing different degrees of weathering. According to OSL dating, the upper part of the sequence was formed in the Upper Pleistocene, when most of the loess at the margins of the Po Plain was deposited. A tentative model of the exposed profiles involves the burial of the anticline by loess layers since the Middle Pleistocene and their successive weathering (and probably truncation) during subsequent interglacials and interstadials. These events probably correspond to the number of loess-paleosol couplets identified in the outer part of the anticline. In this sense the light weathered horizons could represent buried paleosols. Furthermore, the highly rubfied paleosols at the top of the anticline should be regarded as a polygenetic soil or as a vetusol, developed near the surface for a long time since the Middle Pleistocene. The on-going geopedological, geoarchaeological and seismic analyses will permit to define the time and steps of development of the Monte Netto hill and help to clarify the climatic and tectonic context during which these sediments where deposited, deformed, and weathered.

Trombino, Luca; Zerboni, Andrea; Livio, Franz; Berlusconi, Andrea; Michetti, Alessandro M.; Spötl, Christoph; Rodnight, Helena

2013-04-01

182

Iodine diagenesis in non-pelagic deep-sea sediments  

SciTech Connect

Measurements of sediment geochemistry and pore water speciation have been made using eight cores containing turbidite sections from the Madeira and Nares Abyssal Plains. The results have been used to evaluate how the diagenetic chemistry of iodine in these sediments compares with that in sediments undergoing steady-state diagenesis. The behavior of iodine is related to the development of a redox front within the turbidite, between the organic-rich anoxic sediment and its oxic cap, and the downward migration of the front through the turbidite with time. In contrast to the steady-state case, sediment I contents and I/C ratios increase downwards through the oxidized section reaching a maximum at the redox front (Up to approx. 100 ..mu..g/g I; molar I/C approx. 20 x 10/sup -4/) below which values drop dramatically (I/C approx. 5 x 10/sup -4/). A strong iodate enrichment (up to approx. 3 ..mu..mol kg/sup -1/) is observed in the oxidized section of the sediment. At the front interconversion of I/sup -/ and IO/sub 3//sup -/ species occur and below the front pore water IO/sub 3//sup -/ is absent and I/sup -/ concentrations increase with depth up to approx. 10 ..mu..mol kg/sup -1/. In the oxidized section of the sediment the I enrichment has been supplied by upward transport of iodide with the increasing I content, with depth being accounted for by progressive diagenetic enrichment with time.

Kennedy, H.A.; Elderfield, H.

1987-09-01

183

Iodine diagenesis in pelagic deep-sea sediments  

SciTech Connect

Nineteen sediment cores from the Madeira, Seine, Tagus and Nares Abyssal Plains and the Alboran Sea have been used to evaluate the speciation, fluxes and diagenesis of iodine in the deep sea. The sediments have surficial molar I/C ratios of 10-30 x 10/sup -4/ in excess of previous reported values for planktonic material (approx. 1 x 10/sup -4/). Iodine species in the pore waters follow a vertical sequence of four zones: 1. a zone of I/sup -/ production where total dissolved iodine (..sigma..I) concentrations initially increase at the sea water-sediment interface; 2. a zone of I/sup -/ oxidation where interconversion of I/sup -/ to IO/sub 3//sup -/ occurs; 3. a zone of IO/sub 3//sup -/ reduction where interconversion of IO/sub 3//sup -/ back to I/sup -/ occurs which corresponds to the suboxic part of the sediment column; and 4. a further zone of I/sup -/ production which is confined to the lower anoxic part of the sediment column. In the surface sediment the observed I enrichment results from a quasi-closed cycle for iodine initially involving release of I/sup -/ from decomposing marine organic matter followed by rapid removal onto organic matter at the sediment-sea water interface where I/C regeneration ratios of up to 200 x 10/sup -4/ are found. Iodate reduction occurs during suboxic diagenesis, after denitrification and before MnO/sub 2/ reduction, consistent with the sequence of reactions predicted from the free energy yields for organic matter oxidation.

Kennedy, H.A.; Elderfield, H.

1987-09-01

184

Cross-equatorial flow through an abyssal channel under the complete Coriolis force: Two-dimensional solutions  

NASA Astrophysics Data System (ADS)

The component of the Coriolis force due to the locally horizontal component of the Earth's rotation vector is commonly neglected, under the so-called traditional approximation. We investigate the role of this "non-traditional" component of the Coriolis force in cross-equatorial flow of abyssal ocean currents. We focus on the Antarctic Bottom Water (AABW), which crosses from the southern to the northern hemisphere through the Ceara abyssal plain in the western Atlantic ocean. The bathymetry in this region resembles a northwestward channel, connecting the Brazil Basin in the south to the Guyana Basin in the north. South of the equator, the AABW leans against the western continental rise, consistent with a northward flow in approximate geostrophic balance. The AABW then crosses to the other side of the abyssal channel as it crosses the equator, and flows into the northern hemisphere leaning towards the east against the Mid-Atlantic Ridge.The non-traditional component of the Coriolis force is strongest close to the equator. The traditional component vanishes at the equator, being proportional to the locally vertical component of the Earth's rotation vector. The weak stratification of the abyssal ocean, and subsequent small internal deformation radius, defines a relatively short characteristic horizontal lengthscale that tends to make non-traditional effects more prominent. Additionally, the steep gradients of the channel bathymetry induce large vertical velocities, which are linked to zonal accelerations by the non-traditional components of the Coriolis force. We therefore expect non-traditional effects to play a substantial role in cross-equatorial transport of the AABW.We present asymptotic steady solutions for non-traditional shallow water flow through an idealised abyssal channel, oriented at an oblique angle to the equator. The current enters from the south, leaning up against the western side of the channel in approximate geostrophic balance, and crosses the channel as it crosses the equator. The "non-traditional" contribution to the planetary angular momentum must be balanced by stronger westward flow in the channel, which leads to an increased transport in a northwestward channel, and a reduced transport in a northeastward channel. Our results suggest that as much as 10-30% of the cross-equatorial flow of the AABW may be attributed to the non-traditional components of the Coriolis force.

Stewart, A. L.; Dellar, P. J.

185

Stratigraphy of the Martian Northern Plains.  

National Technical Information Service (NTIS)

The northern plains of Mars are roughly defined as the large continuous region of lowlands that lies below Martian datum, plus higher areas within the region that were built up by volcanism, sedimentation, tectonism, and impacts. These northern lowlands s...

K. L. Tanaka

1993-01-01

186

Brain areas in abyssal demersal fishes.  

PubMed

Four areas of the brain which receive primary projections from chemical senses ([1] olfactory bulb, [2] gustatory area including facial and vagal lobes), the eye ([3] optic tectum), and mechanosensory, and-hair-cell based systems i.e. the lateral line, vestibular and auditory systems ([4] trigeminal and octavolateral regions) have been studied and relative size differences used to make deductions on the sensory preferences of 35 fish species living on or near the bottom of the deep sea. Furthermore the relative volumes of the telencephalon and the corpus cerebelli were determined. Two evaluation modes were applied: (1) the relative mean of each system was calculated and species with above-average areas identified; (2) a cluster analysis established multivariate correlations among the sensory systems. The diversity of sensory brain areas in this population of fish suggests that the benthic and epibenthic environment of the abyss presents a rich sensory environment. Vision seems to be the single most important sense suggesting the presence of relevant bioluminescent stimuli. However, in combination the chemical senses, smell and taste, surpass the visual system; most prominent among them is olfaction. The trigeminal/octavolateral area indicating the role of lateral line input and possibly audition is also well represented, but only in association with other sensory modalities. A large volume telencephalon was often observed in combination with a prominent olfactory system, whereas cerebella of unusually large sizes occurred in species with above-average visual, hair-cell based, but also olfactory systems, confirming their role as multimodal sensorimotor coordination centers. In several species the predictions derived from the volumetric brain analyses were confirmed by earlier observations of stomach content and data obtained by baited cameras. PMID:11713385

Wagner, H J

2001-06-01

187

Mercury in waters, soils, and sediments of the New Jersey Coastal Plain: A comparison of regional distribution and mobility with the mercury contamination at the William J. Hughes Technical Center, Atlantic County, New Jersey  

USGS Publications Warehouse

Mercury in soils, surface water, and groundwater at the William J. Hughes Technical Center , Atlantic County, New Jersey, has been found at levels that exceed established background concentrations in Coastal Plain waters, and, in some cases, New Jersey State standards for mercury in various media. As of 2012, it is not known whether this mercury is part of regional mercury contamination or whether it is related to former military activities. Regionally, groundwater supplying about 700 domestic wells in the New Jersey Coastal Plain is contaminated with mercury that appears to be derived from anthropogenic inputs, such as agricultural pesticide use and atmospheric deposition. High levels of mercury occasionally are found in Coastal Plain soils, but disturbance during residential development on former agricultural land is thought to have mobilized any mercury applied during farming, a hypothesis borne out by experiments leaching mercury from soils. In the unsewered residential areas with mercury-contaminated groundwater, septic-system effluent is believed to create reducing conditions in which mercury sorbed to subsoils is mobilized to groundwater. In comparing the levels of mercury found in soils, sediments, streamwater, and groundwater at the William J. Hughes Technical Center site with those found regionally, mercury concentrations in groundwater in the region are, in some cases, substantially higher than those found in groundwater at the William J. Hughes Technical Center site. Nevertheless, concentrations of mercury in streamwater at the site are, in some instances, higher than most found regionally. The mercury contents in soils and sediment at the William J. Hughes Technical Center site are substantially higher than those found to date (2012) in the region, indicating that a source other than regional sources may be present at the site.

Barringer, Julia L.; Szabo, Zoltan; Reilly, Pamela A.

2012-01-01

188

Influence of sediment redox conditions on release/solubility of metals and nutrients in a Louisiana Mississippi River deltaic plain freshwater lake.  

PubMed

The influence of sediment redox conditions on solubility of selected metals and nutrients in sediment from a coastal Louisiana freshwater lake (Lake Cataouatche) receiving diverted Mississippi River water was quantified. Sediment redox was cycled step wise in 50 mV increments between oxidized (-200 to +500 mV) and reduced (+500 to -200 mV) conditions. Changes in sediment oxidation/reduction status and pH influenced solubility of both metals and nutrients. When redox potential (Eh) was increased from -200 to +500 mV, sediment pH decreased from 7.1 to 5.7. When the sediment Eh decreased from +500 to -200 mV, pH increased from 5.7 to 7.1. The increase in sediment acidity upon oxidation resulted in the release of the Pb, Ca, Mg, Al, and Zn into solution. The solution concentration of these elements was inversely proportional to Eh (Psediment suspension was strongly governed by changes in oxidation-reduction status of sediment. The oxidation of reduced sediment resulted in a decrease in amount of Fe and Mn in solution, a result of the conversion of soluble ferrous and manganous form to less soluble ferric and manganic form. Following reduction of oxidized sediment, Fe and Mn became more soluble because the ferric iron and manganic manganese form changed to ferrous and manganous form. Phosphorus behavior as influenced by oxidation/reduction status was closely related to Fe and Mn chemistry with an increase in phosphate following iron reduction. This study demonstrated that sediment redox potential is an important parameter affecting metal and nutrient solubility and mobility in Louisiana coastal freshwater lake sediment. Reduction or aeration status of sediment should be considered in predicting the release of these elements into the aquatic environment. PMID:16934856

Miao, Shenyu; DeLaune, R D; Jugsujinda, A

2006-08-24

189

Plain Facts About Plain Bearings.  

National Technical Information Service (NTIS)

This citation summarizes a one-page announcement of technology available for utilization. A special report has been prepared as a concise, practical, easy-to-read guide for anyone with an interest in or need for plain bearings. It begins with a brief hist...

1982-01-01

190

Recent deformation of Quaternary sediments as inferred from GPR images and shallow P-wave velocity tomograms: Northwest Canterbury Plains, New Zealand  

Microsoft Academic Search

Prior to the recent highly damaging M 7.1 earthquake near the city of Christchurch on the South Island of New Zealand, we recorded coincident high-resolution seismic and ground-penetrating radar (GPR) data across parts of the northwest Canterbury Plains. The seismic reflection images reveal a vast network of interconnected faults and folds below a seemingly undisturbed flat surface. To complement the

S. F. A. Carpentier; A. G. Green; J. Doetsch; C. Dorn; A. E. Kaiser; F. Campbell; H. Horstmeyer; M. Finnemore

191

Holocene Climate in the Northern Great Plains Inferred from Sediment Stratigraphy, Stable Isotopes, Carbonate Geochemistry, Diatoms, and Pollen at Moon Lake, North Dakota  

Microsoft Academic Search

Seismic stratigraphy, sedimentary facies, pollen stratigraphy, diatom-inferred salinity, stable isotope (?18O and ?13C), and chemical composition (Sr\\/Ca and Mg\\/Ca) of authigenic carbonates from Moon Lake cores provide a congruent Holocene record of effective moisture for the eastern Northern Great Plains. Between 11,700 and 950014C yr B.P., the climate was cool and moist. A gradual decrease in effective moisture occurred between

Blas L. Valero-Garcés; Kathleen R. Laird; Sherilyn C. Fritz; Kerry Kelts; Emi Ito; Eric C. Grimm

1997-01-01

192

Evaluation of Cross-Hole Seismic Tomography for Imaging Low Resistance Intervals and Associated Carbonate Sediments in Coastal Plain Sequences on the Savannah River Site, South Carolina  

SciTech Connect

The objectives of the pilot study were to investigate the limitations of the technique for imaging the presence, extent, and boundaries of the low-resistance intervals and associated carbonate sediments.

Cumbest, R. J.

1999-01-05

193

Priapulus abyssorum, New Species, the first Abyssal Priapulid  

Microsoft Academic Search

A SINGLE example of Priapulus was collected on November 27, 1958 by the R.V. Vema from a depth of 5680-5690 m. (corrected) at the southern end of the Mid-America Trench. Besides being a new species and the first abyssal record for the genus, this specimen represents the first priapulid collected from off the west coast of Central America. The specimen

Robert J. Menzies

1959-01-01

194

Abyssal recipes II: energetics of tidal and wind mixing  

Microsoft Academic Search

Without deep mixing, the ocean would turn, within a few thousand years, into a stagnant pool of cold salty water with equilibrium maintained locally by near-surface mixing and with very weak convectively driven surface-intensified circulation. (This result follows from Sandström’s theorem for a fluid heated and cooled at the surface.) In this context we revisit the 1966 “Abyssal Recipes”, which

Walter Munk; Carl Wunsch

1998-01-01

195

Northward abyssal transport through the Samoan passage and adjacent regions  

Microsoft Academic Search

A conductivity-temperature-depth\\/hydrographic survey in January-February 1994 and an 17-month deployment of current meter moorings from September 1992 to March 1994 were carried out to determine the volume transport, water mass characteristics, and diathermal fluxes of northward flowing abyssal waters in the Samoan Passage and adjacent regions of the South Pacific Ocean. Geostrophic calculations relative to 1.2°C potential temperature indicated northward

Dean Roemmich; Susan Hautala; Daniel Rudnick

1996-01-01

196

Mobility of authigenic rhenium, silver, and selenium during postdepositional oxidation in marine sediments  

NASA Astrophysics Data System (ADS)

Sedimentary records of redox-sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions. Records of Re can reveal the intensity of past reducing conditions in sediments at the time of deposition, whereas records of Ag may record the magnitude of past diatom fluxes to the seafloor. Confidence in paleoenvironmental reconstruction from records of either metal, however, requires it to have experienced negligible redistribution since deposition. This study examines diagenetic rearrangements of Re and Ag that occur in response to exposure to bottom-water O 2 in environments of low sedimentation rate, including Madeira Abyssal Plain turbidites and eastern Mediterranean basin sapropels. Authigenic Re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments. All records are consistent with previous work demonstrating that only a limited reimmobilization of Re occurs preferentially in C org-rich, reducing sediments. Silver was also mobilized quantitatively by oxidation, but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts, and these peaks remain immobile in anoxic conditions during long-term burial. Comparison of Ag, S, and Se records from various cores suggests that Ag is likely to have been immobilized as a selenide, a mechanism previously proposed for Hg in similar situations (Mercone et al., 1999). Coexisting narrow peaks of Ag and Hg with Se offer a means of assessing whether oxidative burndown has ever occurred at the top of C org- and sulfide-rich sedimentary units. Although these results suggest that caution must be used when inferring paleoenvironmental information from records of Ag and Re in cores with low sediment accumulation rates (<5 cm ka -1), they should not affect the promise that authigenic Ag and Re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously.

Crusius, John; Thomson, John

2003-01-01

197

A hydrodynamically modified, abyssal isopod fauna  

NASA Astrophysics Data System (ADS)

At the High Energy Benthic Boundary Layer Experiment (HEBBLE) site (4820 m depth in the western North Atlantic) periods of strong currents and sediment erosion alternate with periods of weak flow and massive deposition. We investigated the impact of this atypical hydrodynamic environment on the isopod fauna by testing for a difference in composition between the HEBBLE site and a tranquil location, the Deep Ocean Mining Environmental Study (DOMES) site A ( ca. 5000 m) in the equatorial Pacific. Epifaunal isopods were significantly less abundant at the HEBBLE site than at the comparison site despite significantly greater total isopod numbers at the HEBBLE site. We suggest that the hydrodynamic regime puts epifaunal isopods at risk, making them rare at the HEBBLE site.

Thistle, David; Wilson, George D. F.

1987-01-01

198

Hydrothermal Mineral Deposits From a Young (0.1Ma) Abyssal Hill on the Flank of the Fast-Spreading East Pacific Rise  

NASA Astrophysics Data System (ADS)

It has been estimated from heat flow measurements that at least 40% of the total hydrothermal heat lost from oceanic lithosphere is removed from 0.1-5 Ma abyssal hill terrain on mid-ocean ridge flanks. Despite the large magnitude of estimated hydrothermal heat loss from young abyssal hills, little is known about characteristics of hydrothermal vents and mineral deposits in this setting. This study describes the first abyssal hill hydrothermal samples to be collected on the flank of a fast-spreading ridge. The mineral deposits were discovered at "Tevnia Site" on the axis-facing fault scarp of an abyssal hill, located on ˜0.1 Ma lithosphere ˜5 km east of the East Pacific Rise (EPR) axis at 10\\deg 20'N. Observations of Galatheid crabs, "dandelion" siphonophores, and colonies of dead, yet still intact, Tevnia worm tubes at this site during Alvin dives in 1994 suggests relatively recent hydrothermal activity. The deposits are friable hydrothermal precipitates incorporating volcanic clasts brecciated at both the micro and macro scales. The petrographic sequence of brecciation, alteration, and cementation exhibited by the samples suggests that they formed from many pulses of hydrothermal venting interspersed with, and perhaps triggered by, repeated tectonic events as the abyssal hill was uplifted and moved off-axis (see also Haymon et al., this session). Observed minerals include x-ray amorphous opaline silica and Fe-oxide phases, crystalline Mn-oxides (birnessite and todorokite), an irregularly stratified mixed layer nontronite-celadonite, and residual calcite in sediment-derived microfossils incorporated into the breccia matrix. This mineral assemblage suggests that the deposits precipitated from moderately low-temperature (<140\\deg C) fluids, enriched in K, Fe, Si, and Mn, with a near-neutral pH. The presence of tubeworm casings at the site is evidence that the hydrothermal fluids carried H2S, however no metal sulfide phases were identified in the samples. Although the fluids were actively venting from an abyssal hill distal to the ridge crest, the presence of Fe- and K-rich nontronite-celadonite suggests an axial fluid source. However, the observed textures, minerals, and microfossils, combined with the absence of copper, zinc, and sulfur minerals, clearly distinguishes these near-axis samples from hydrothermal deposits formed at higher temperatures (>350\\deg C) on the mid-ocean ridge crest.

Benjamin, S. B.; Haymon, R. M.

2004-12-01

199

32. VERTICAL SEISMIC PROFILE AT SITE 765 AND SEISMIC REFLECTORS IN THE ARGO ABYSSAL PLAIN1  

Microsoft Academic Search

The first Ocean Drilling Program (ODP) vertical seismic profile (VSP) experiment in a thick sedimentary section was conducted at Site 765 to measure compressional wave velocities and to correlate drilling results with seismic data. Measurements were performed through the cased portion of the hole between 186 and 915 mbsf using both air-gun and water-gun sources. Average velocities for the air-gun

S. T. Bolmer; R. T. Buffler; H. Hoskins; R. A. Stephen; S. A. Swift

200

Revisiting Plain Language.  

ERIC Educational Resources Information Center

Discusses the plain language movement and its origins. Reviews past and current resources related to plain language writing. Examines criticism of the movement while examining past and current plain language literature, with particular attention to the information design field. (SR)

Mazur, Beth

2000-01-01

201

Glacial-interglacial sedimentation rates and turbidite frequency in the Bahamas: a clear case of carbonate shedding during high sea level stands  

SciTech Connect

Vail's sea level curve is built on a basic principle that siliciclastic continental shelves and implicitly carbonate platforms mainly export sediment toward the surrounding basins during sea level low stands. The authors late Quaternary Bahamian data demonstrate however, that sediment export from carbonate banks is just the opposite. Five, 8-13 m long, piston cores were studied from the southern Tongue of the Ocean, a 1300 m deep flat-floored basin in the Bahamas, surrounded on its three sides by wide shallow carbonate banks. Turbidite layers were visually distinguished from intervening periplatform ooze. Glacial cyclic variations of aragonite content in the periplatform ooze, along with nannoplankton stratigraphy were used to identified the last two glacial and interglacial intervals, low and high stand situations respectively. On average, turbidite frequency and accumulation rates were much higher, 14 times and 45 to 22 times respectively, during interglacial than glacial stages. The Bahamian carbonate banks export therefore more material during sea level high stands when the platform tops are flooded and produce sediment. This is in direct opposition with siliciclastic ocean margins, where sediment is stored on the inner shelf during high stands and passed on to continental rises and abyssal plains during low stands. In addition, aragonite dissolution as postulated by Droxler et al. (Geology April 1983) is working in phase with the input signal by removing material during glacial intervals.

Droxler, A.W.; Schlager, W.

1985-01-01

202

The Ocean's Abyssal Mass Flux Sustained Primarily By the Wind: Vector Correlation of Time Series in Upper and Abyssal Layers  

NASA Astrophysics Data System (ADS)

As Wunsch has recently noted (2002), use of the term "thermohaline circulation" is muddled. The term is used with at least seven inconsistent meanings, among them abyssal circulation, the circulation driven by density and pressure differences in the deep ocean, the global conveyor, and at least four others. The use of a single term for all these concepts can create an impression that an understanding exists whereby in various combinations the seven meanings have been demonstrated to mean the same thing. But that is not the case. A particularly important consequence of the muddle is the way in which abyssal circulation is sometimes taken to be driven mostly or entirely by temperature and density differences, and equivalent to the global conveyor. But in fact the distinction between abyssal and upper-layer circulation has not been measured. To find out whether available data justifies a distinction between the upper-layer and abyssal circulations, this study surveyed velocity time series obtained by deep current meter moorings. Altogether, 114 moorings were identified, drawn from about three dozen experiments worldwide over the period 1973-1996, each of which deployed current meters in both the upper (200abyssal (z>3750) layers. For each pair of current meters, the Kundu and Crosby measures of vector correlation were estimated, as well as coherences for periods from 10 to 60 days. In the North Atlantic, for example, Kundu vector correlation (50-day window): 0.48 +/- .03 Crosby vector correlation (absolute value, 50 day window): 0.46 +/- .07 Coherence at 60 days: .36 +/- .07 - at 30 days: 0.40 +/- .06 - at 10 days: 0.22 +/- .05 Most figures for the South Atlantic, Pacific and Southern Oceans are similar. Those obtained in the Indian Ocean or near the Equator are somewhat different. The statistics obtained here are consistent with the work of Wunsch (1997), and tend to confirm Wunsch's result that current velocities at depth are linked with those in the upper layers. Energetics of the circulation that do not take this into account are making an unjustifiable approximation of the physics. These results do not tell us whether time averaged flow on longer time scales might permit distinction of upper layer and abyssal flow components. Some intriguing corollaries do follow. First, the abyssal circulation is not identically the same thing as a global conveyor belt driven by temperature and density differences. Rather, as Wunsch noted (2002), the ocean's mass flux is sustained primarily by the wind. We may add that these wind patterns are about as robust as the temperature differences between equator and pole; this major driver of circulation is not a frail phenomenon. Second, the classical notion of a level of no motion that is also a constant-density surface, an LNM, is inconsistent with the results presented here. Such an LNM would wall off the upper layer circulation from the lower, and as they are not walled off, there can be no such LNM. Third, wind stress is being transmitted down column, presumably to the sea floor.

Hancock, L. O.

2003-12-01

203

Mercury net methylation in five tropical flood plain regions of Brazil: high in the root zone of floating macrophyte mats but low in surface sediments and flooded soils.  

PubMed

In aquatic systems, bottom sediments have often been considered as the main methylmercury (MeHg) production site. In tropical floodplain areas, however, floating meadows and flooded forests extend over large areas and can be important Hg methylating sites. We present here a cross-system comparison of the Hg net methylation capacity in surface sediments, flooded soils and roots of floating aquatic macrophytes, assayed by in situ incubation with 203Hg and extraction of formed Me203 Hg by acid leaching and toluene. The presence of mono-MeHg was confirmed by thin layer chromatography and other techniques. Study areas included floodplain lakes in the Amazon basin (Tapajós, Negro and Amazon rivers), the Pantanal floodplain (Paraguay river basin), freshwater coastal lagoons in Rio de Janeiro and oxbow lakes in the Mogi-Guaçú river, São Paulo state. Different Hg levels were added in assays performed in 1994-1998, but great care was taken to standardise all other test parameters, to allow data comparisons. Net MeHg production was one order of magnitude higher (mean 13.8%, range 0.28-35) in the living or decomposing roots of floating or rooted macrophyte mats (Eichhornia azurea, E. crassipes, Paspalum sp., Eleocharis sellowiana, Salvinia sp., S. rotundifolia and Scirpus cubensis) than in the surface layer of underlying lake sediments (mean 0.6%, range 0.022-2.5). Methylation in flooded soils presented a wide range and was in some cases similar to the one found in macrophyte roots but usually much lower. In a Tapajós floodplain lake, natural concentrations of MeHg in soil and sediment cores taken along a lake-forest transect agreed well with data on net methylation potentials in the same samples. E. azurea, E. crassipes and Salvinia presented the highest methylation potentials, up to 113 times higher than in sediments. Methylation in E. azurea from six lakes of the Paraguay and Cuiabá rivers, high Pantanal, was determined in the 1998 dry and wet seasons and ranged from 1.8 to 35%. Methylation was lower in washed roots than in untreated roots of E. azurea and methylation in solids isolated from the roots, was higher than in sediments but lower than in untreated roots. This indicates that the methylation in roots zones occurs mainly in the root-associated solids. Floating meadows are sites of intense production of biomass and of highly bioavailable MeHg and appear to be an essential link of the MeHg cycle in tropical aquatic systems. PMID:11036981

Guimarães, J R; Meili, M; Hylander, L D; de Castro e Silva, E; Roulet, M; Mauro, J B; de Lemos, R

2000-10-16

204

Late-Holocene flooding and drought in the Northern Great Plains, USA, reconstructed from tree rings, lake sediments and ancient shorelines  

Microsoft Academic Search

During the AD 1990s the Waubay Lakes complex in eastern South Dakota experienced historically unprecedented high water levels. Property damage from this flooding led to an examination of the occurrence of past pluvial episodes and their relation to climate. A 1000-year hydroclimate reconstruction was developed from local bur oak (Quercus macrocarpa) tree-ring records and lake-sediment cores. Analysis of lake shoreline

M. D. Shapley; W. C. Johnson; D. R. Engstrom; W. R. Osterkamp

2005-01-01

205

The use of environmental radionuclides in investigations of sediment sources and overbank sedimentation rates in the Himalaya Foreland, India  

Microsoft Academic Search

This paper presents some preliminary results from an investigation of overbank sedimentation rates on the flood plains of the Teesta and Brahmaputra Rivers in the Himalaya Foreland, India. The 210Pbex, 226 Ra and 137 Cs depth distributions in sediment cores have been used to derive estimates of overbank sedimentation rates. The estimated sedimentation rates for the flood plains of the

W. FROEHLICH; D. E. WALLING

206

Abyssal peridotite Hf isotopes identify extreme mantle depletion  

NASA Astrophysics Data System (ADS)

The isotopic composition of radiogenic systems is a powerful tool to investigate Earth's evolution through time. Most of our understanding of the processes that affect the isotopic composition of the oceanic mantle comes from the study of basalts. Far fewer isotope analyses of actual oceanic mantle rocks (i.e. abyssal peridotites) exist, owing to their scarcity and often altered state. Here we present new Hf and Nd isotope analyses of clinopyroxene (cpx) from abyssal peridotites from the Gakkel Ridge in the Arctic Ocean, the Southwest Indian ridge and the South Atlantic. The Hf and Nd isotope ratios in the Indian Ocean and the South Atlantic peridotite cpx mostly overlap those of MORB, whereas coupled depletions in Nd and Hf isotope ratios in the Gakkel Ridge samples (?Hf and ?Nd values of 60.4 and 20.5, respectively) extend the MORB and ocean island basalt (OIB) Hf-Nd isotope array to considerably more depleted values. Some samples from the Gakkel Ridge range to extreme Hf isotope values up to ?Hf of 104, but lack the corresponding depletion in Nd isotopes (?Nd of about 8). The Hf, rather than the Nd isotope ratios of the Gakkel Ridge peridotites correlate with major and trace element indices of depletion (e.g. Al2O3 and Yb content, spinel Cr#) and their previously determined Os isotope ratios. Hence the Hf and Os isotope compositions of these samples preserve a record of ancient mantle depletion, whereas their Nd isotope signatures often do not. The example of the Gakkel Ridge peridotites suggests that the Sm/Nd and Nd isotope ratios in abyssal peridotites in general are very susceptible to resetting by melt-rock interaction, and that Nd isotope ratios in abyssal peridotites rarely preserve ancient mantle depletion to a similar extent as the Os and Hf isotope ratios. The oceanic mantle could thus range to more depleted Hf isotope signatures, and is thus isotopically more variable than inferred from oceanic basalts alone. MORB may therefore underestimate the average Hf and Nd isotope composition of the depleted mantle (DM), which may present an, as of yet, unrecognized obstacle for global mass balance models of Earth's differentiation. If the average DM is more depleted than MORB suggest, these models generally overestimate its mass fraction and would permit prolonged timescales for early Earth differentiation (> 30 Ma).

Stracke, A.; Snow, J. E.; Hellebrand, E.; von der Handt, A.; Bourdon, B.; Birbaum, K.; Günther, D.

2011-08-01

207

Metal accumulation rates in northwest Atlantic pelagic sediments  

NASA Astrophysics Data System (ADS)

Measurements of 230Th, 87Sr /86Sr and twenty-four metals were made on cores from the Nares Abyssal Plain. The sediment is characterized by slowly-accumulating (0.3-0.7 g/cm 2 10 3 yr) pelagic red clays and rapidly deposited grey clays transported by turbidity currents. Despite their colour differences and the enrichment of Mn, Fe, Cu, Co, Ni, Zn, V and, to a lesser degree, the rare earths in the red clays, Sr isotope evidence demonstrates that the clays have the same terrigenous origin. The excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated. The fluxes obtained are in the ranges 20-50 ?mol/cm 2 10 3 yr for Mn and Fe, 0.1-0.4 ?mol/cm 2 10 3 yr for Cu, Co, Ni, Zn, V, Sr and Ce, 10-20 nmol/cm 2 10 3 yr for La and Nd, and 0.5-3 nmol/cm 2 10 3 yr for Sm, Eu, Gd, Dy, Er and Yb. Authigenic fluxes of Y, Nb, Cr, Zr, Rb, U and Th were not resolvable. Fluxes appear to be near constant on the Plain but comparison with other areas shows that they are quite variable both between and within ocean basins. The chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter-element comparisons and from differences in fluxes between Atlantic and Pacific red clays corresponding to the oceanic reactivities of the elements.

Thomson, J.; Carpenter, M. S. N.; Colley, S.; Wilson, T. R. S.; Elderfield, H.; Kennedy, H.

1984-10-01

208

Another Nail in the Coffin of the Glacial-Age Isolated Abyssal Reservoir Scenario  

NASA Astrophysics Data System (ADS)

Radiocarbon-age differences were determined for coexisting G. sacculifer-mixed benthic-foraminifera pairs from six glacial-age samples from an equatorial Pacific core at 4.4 km water depth. The results range from 1.6 to 2.8 kyrs and average 2.2 kyrs. Age differences based on P. obliquiloculata, N. dutertrei and G. tumida range from 0.1 to 1.5 kyrs and average 0.8 kyrs. Although the data set is certainly imperfect, as the sedimentation rate for this core averages only 2 cm kyr-1, biases resulting from bioturbation are to be expected. Despite these inadequacies, the results appear to eliminate the possibility that the demise of a salt-stabilized glacial-age isolated abyssal reservoir can be called upon to explain the 15 percent drop in surface ocean and atmospheric 14C to C ratio during the Mystery Interval (17.5 to 14.5 kyr). If the 14C to C decline were to be explained in this way, the expected benthic-planktic age difference would have to be at least 5 kyrs.

Broecker, W. S.; Clark, E. H.

2009-12-01

209

Effect of abyssal circulation changes on Oligocene to Miocene benthic foraminifera in the North Atlantic  

SciTech Connect

Benthic foraminiferal ranges at western North Atlantic Sites 563 and 558 show: 1) gradual Oligocene last occurrences in response to subsidence from the upper to lower abyssal zones; 2) a preponderance of extinctions in the early middle Miocene (about 15.5-13.5 Ma). Comparison of relative and absolute abundance changes at Site 563 sows that percentages of some taxa (e.g. Nuttallides umbonifera) reliably reflect their accumulations while percentages of others vary independently. Regional abundance changes include: 1) maxima N. umbonifera in the middle Oligocene of the deepest sites (10 and 119); 2) increased Planulina wuellerstorfi in the early middle Miocene; 3) increased N. umbonifera in the late middle Miocene. Seismic stratigraphic and delta/sup 13/C evidence indicates a northern bottom-water source for the North Atlantic throughout much of the Oligocene and Miocene. Benthic foraminifera apparently responded to bottom-water changes inferred from carbon isotopic comparisons. The extinction of relict Paleogene taxa and the ascendancy of P. wuellerstorfi in the middle Miocene apparently correlate with increased advection into the eastern Atlantic, subsidence of the Iceland-Faeroe Ridge and increased North Atlantic carbonate sedimentation. The authors speculate that this faunal reorganization was in response to global ocean chemistry changes resulting from increased ventilation of the North Atlantic.

Katz, M.E.; Miller, K.G.

1985-01-01

210

Soils and landscape evolution of eolian plains: the Southern High Plains of Texas and New Mexico  

Microsoft Academic Search

Holliday, V.T., 1990. Soils and landscape evolution of eolian plains: the Southern High Plains of Texas and New Mexico. In: P.L.K. Knuepfer and L.D. McFadden (Editors), Soils and Landscape Evolution. Geomorphology, 3:489-515. Sheets of eolian sediment cover many areas of the earth's surface, sand seas, dune fields, and loess sheets being the best known examples of such features. Less well

Vance T. Holliday

1990-01-01

211

Organic geochemistry of lipids in marine sediments in the Canary Basin: Implications for origin and accumulation of organic matter  

Microsoft Academic Search

The Canary basin consists of the continental margin off the coast of Northwest Africa, the deep basin, the Madeira Abyssal Plain (MAP) and the volcanic Canary Islands.The continental margin has an area of upwelling marine productivity with special characteristics: (a) a wide shelf area, (b) a wide irregular zone of upwelling, and (c) proximity to a large dust source—the Saharan

Sten Lindblom; Ulf Järnberg

2004-01-01

212

Organic-Carbon Sequestration in Soil/Sediment of the Mississippi River Deltaic Plain - Data; Landscape Distribution, Storage, and Inventory; Accumulation Rates; and Recent Loss, Including a Post-Katrina Preliminary Analysis (Chapter B)  

USGS Publications Warehouse

Soil/sediment of the Mississippi River deltaic plain (MRDP) in southeastern Louisiana is rich in organic carbon (OC). The MRDP contains about 2 percent of all OC in the surface meter of soil/sediment in the Mississippi River Basin (MRB). Environments within the MRDP differ in soil/sediment organic carbon (SOC) accumulation rate, storage, and inventory. The focus of this study was twofold: (1) develop a database for OC and bulk density for MRDP soil/sediment; and (2) estimate SOC storage, inventory, and accumulation rates for the dominant environments (brackish, intermediate, and fresh marsh; natural levee; distributary; backswamp; and swamp) in the MRDP. Comparative studies were conducted to determine which field and laboratory methods result in the most accurate and reproducible bulk-density values for each marsh environment. Sampling methods included push-core, vibracore, peat borer, and Hargis1 sampler. Bulk-density data for cores taken by the 'short push-core method' proved to be more internally consistent than data for samples collected by other methods. Laboratory methods to estimate OC concentration and inorganic-constituent concentration included mass spectrometry, coulometry, and loss-on-ignition. For the sampled MRDP environments, these methods were comparable. SOC storage was calculated for each core with adequate OC and bulk-density data. SOC inventory was calculated using core-specific data from this study and available published and unpublished pedon data linked to SSURGO2 map units. Sample age was estimated using isotopic cesium (137Cs), lead (210Pb), and carbon (14C), elemental Pb, palynomorphs, other stratigraphic markers, and written history. SOC accumulation rates were estimated for each core with adequate age data. Cesium-137 profiles for marsh soil/sediment are the least ambiguous. Levee and distributary 137Cs profiles show the effects of intermittent allochthonous input and/or sediment resuspension. Cesium-137 and 210Pb data gave the most consistent and interpretable information for age estimations of soil/sediment deposited during the 1900s. For several cores, isotopic 14C and 137Cs data allowed the 1963-64 nuclear weapons testing (NWT) peak-activity datum to be placed within a few-centimeter depth interval. In some cores, a too old 14C age (when compared to 137Cs and microstratigraphic-marker data) is the probable result of old carbon bound to clay minerals incorporated into the organic soil/sediment. Elemental Pb coupled with Pb source-function data allowed age estimation for soil/sediment that accumulated during the late 1920s through the 1980s. Exotic pollen (for example, Vigna unguiculata and Alternanthera philoxeroides) and other microstratigraphic indicators (for example, carbon spherules) allowed age estimations for marsh soil/sediment deposited during the settlement of New Orleans (1717-20) through the early 1900s. For this study, MRDP distributary and swamp environments were each represented by only one core, backswamp environment by two cores, all other environments by three or more cores. MRDP core data for the surface meter soil/sediment indicate that (1) coastal marshes, abandoned distributaries, and swamps have regional SOC-storage values >16 kg m-2; (2) swamps and abandoned distributaries have the highest SOC storage values (swamp, 44.8 kg m-2; abandoned distributary, 50.9 kg m-2); (3) fresh-to-brackish marsh environments have the second highest site-specific SOC-storage values; and (4) site-specific marsh SOC storage values decrease as the salinity of the environment increases (fresh-marsh, 36.2 kg m-2; intermediate marsh, 26.2 kg m-2; brackish marsh, 21.5 kg m-2). This inverse relation between salinity and SOC storage is opposite the regional systematic increase in SOC storage with increasing salinity that is evident when SOC storage is mapped by linking pedon data to SSURGO map units (fresh marsh, 47 kg m-2; intermediate marsh, 67 kg m-2; brackish marsh, 75 kg m-2; and salt marsh, 80 kg m-2). MRDP core data for this study also indicate that levees and backswamp have regional SOC-

Markewich, Helaine W.; Buell, Gary R.; Britsch, Louis D.; McGeehin, John P.; Robbins, John A.; Wrenn, John H.; Dillon, Douglas L.; Fries, Terry L.; Morehead, Nancy R.

2007-01-01

213

Stratigraphy of the Martian northern plains  

NASA Astrophysics Data System (ADS)

The northern plains of Mars are roughly defined as the large continuous region of lowlands that lies below Martian datum, plus higher areas within the region that were built up by volcanism, sedimentation, tectonism, and impacts. These northern lowlands span about 50 x 106 km2 or 35 percent of the planet's surface. The age and origin of the lowlands continue to be debated by proponents of impact and tectonic explanations. Geologic mapping and topical studies indicate that volcanic, fluvial, and eolian deposition have played major roles in the infilling of this vast depression. Periglacial, glacial, fluvial, eolian, tectonic, and impact processes have locally modified the surface. Because of the northern plains' complex history of sedimentation and modification, much of their stratigraphy was obscured. Thus the stratigraphy developed is necessarily vague and provisional: it is based on various clues from within the lowlands as well as from highland areas within and bordering the plains. The results are summarized.

Tanaka, K. L.

214

Stratigraphy of the Martian northern plains  

Microsoft Academic Search

The northern plains of Mars are roughly defined as the large continuous region of lowlands that lies below Martian datum, plus higher areas within the region that were built up by volcanism, sedimentation, tectonism, and impacts. These northern lowlands span about 50 x 106 km2 or 35 percent of the planet's surface. The age and origin of the lowlands continue

K. L. Tanaka

1993-01-01

215

Strontium, neodymium, and lead isotopic and trace-element signatures of the East indonesian sediments: provenance and implications for banda arc magma genesis  

NASA Astrophysics Data System (ADS)

We present new trace-element and Sr-Nd-Pb isotope data for 127 surface sediments and five sediments from DSDP Site 262, distributed along and across the arc-continent collision region of the Banda Arc, East Indonesia. The results are used to evaluate the role of subducted continental material (SCM) in the genesis of the Banda Arc magmas and to assess the extent to which geochemical and isotopic signatures of SCM are controlled by sediment provenance. In the surface sediments lead and neodymium isotope ratios are variable: 206Pb/ 204Pb = 18.65-19.57; 143Nd/ 144Nd = 0.51230-0.51190, with an increase in lead isotope ratios and a decrease in the 143Nd/ 144Nd ratio from northeast to southwest along the Banda Arc. DSDP Site 262 sediments, farthest to the west in the Timor Trough, overlap with the surface sediments and have 206Pb/ 204Pb = 18.89-19.23 and 143Nd/ 144Nd = 0.51200-0.51220. In contrast, the trace-element ratios and REE patterns of the sediments do not show systematic along-arc variations and largely overlap with estimated values for Upper Continental Crust, Post Archean Australian Shale (PAAS), and ODP Site 765 sediments from the Argo Abyssal Plain. From the combined isotopic and trace-element ratios in the terrigenous fraction of the sediments four major provenance areas can be distinguished: North New Guinea + Seram, South New Guinea, Timor, and northern Australia. The lead isotopic variations in the shelf and wedge sediments along the Banda Arc are parallel to similar variations in the volcanics; this is considered to be strong evidence for the incorporation of subducted continental material in the arc magmas. The trace-element characteristics of both the volcanics and the sediments are also consistent with the involvement of sediments in the Banda Arc magma genesis. The hinterland of the sediments is responsible for isotopic signatures created in the Banda Arc mantle through recent subduction. This suggests that some of the mantle heterogeneities that are inferred from oceanic basalts can be explained by differences in the provenance of (ancient) subducted sediment.

Vroon, P. Z.; van Bergen, M. J.; Klaver, G. J.; White, W. M.

1995-06-01

216

Morphology and Late Quaternary sedimentation in the Gulf of Oman Basin  

NASA Astrophysics Data System (ADS)

The morphology of the Gulf of Oman Basin, a 3,400 m deep oceanic basin between Oman and southern Pakistan and southern Iran, ranges from a convergent margin (Makran margin) along the north side, a passive type (Oman margin) along the south side, translation types along the basin's west (Zendan Fault-Oman Line) and east (Murray Ridge) sides and a narrow continental rise and a wide abyssal plain in the centre of the basin. Sediment input into the basin during the Late Quaternary has been mainly from the north as a result of the uplift of the Coast Makran Mountains in the Late Miocene-Pliocene. Today most of this detritrus is deposited on the shelf and upper continental slope and perched basins behind the fold/fault ridges on the lower slope. The presence of fans and channels on the continental rise on the north side of the basin indicate, however, that continental derived debris was, and possibly is, being transported to the deep-sea by turbidity currents via gaps in the ridges on the lower slope. In addition to land derived terrigenous sediments, the basin deposits also contain biogenic (organic matter and calcium carbonate), eolian detritus and hydrates and authigenic carbonates from the tectonic dewatering of the Makran accretionary wedge. The eolian sediment is carried into the Gulf of Oman Basin from Arabia and the Mesopotamia Valley by the northwesterly Shamal winds. This type of detritus was particularly abundant during the glacial arid periods 21,000-20,000 and 11,000 (Younger Dryas) years ago when exposure of the Persian (Arabian) Gulf increased the area of dust entrainment and shifted the position of the source of the eolian sediments closer to the basin.

Uchupi, Elazar; Swift, S. A.; Ross, D. A.

217

Use of OSL dating to establish the stratigraphic framework of Quaternary eolian sediments, Anton scarp upper trench, Northeastern Colorado High Plains, USA  

USGS Publications Warehouse

This paper contains the results of the optically stimulated luminescence (OSL) dating used to establish stratigraphic ages and relationships of eolian sediments in a trench in northeastern Colorado, USA. This trench was located in the upper face of the Anton scarp, a major topographic lineament trending NW-SE for a distance of 135 km, in anticipation of intersecting near-surface faulting. The trench was 180 m long, 4.5-6.0 m deep, and exposed 22 m of stratigraphic section, most of which dipped gently west and was truncated by gulley channeling at the face of the scarp. No direct evidence of faulting was found in the upper trench. The stratigraphy from the trench was described, mapped and dated using OSL on quartz and potassium feldspar, and 14C obtained from woody material. OSL dating identified two upper loess units as Peoria Loess and Gilman Canyon Loess, deposited between 16 and 30 ka ago. The bottom layers of the trench were substantially older, giving OSL ages in excess of 100 ka. These older ages are interpreted as underestimates, owing to saturation of the fast component of OSL. Using OSL and 14C dating, we can constrain the erosion and down cutting of the scarp face as occurring between 16 and 5.7 ka. As the trenching investigation continues in other parts of the scarp face, the results of this preliminary study will be of importance in relating the ages of the strata that underlie different parts of the scarp, and in determining whether Quaternary faulting was a mechanism that contributed to the formation of this regional geomorphic feature.

Mahan, S. A.; Noe, D. C.; McCalpin, J. P.

2009-01-01

218

[The role of antarctica in formation of the cenozoic climate and contemporary open sea abyssal fauna].  

PubMed

The key role of the Antarctic continent in the formation of the contemporary (Cenozoic) zonal-contrast climate and related geologically "young" (Postmesozoic) contemporary abyssal fauna of the World Ocean is discussed on the basis of the current concepts of pleitectonics, history of planetary climates, paleobiooceanology, and bioevolution. It has been shown that the flows of cold aerated near-Antarctic waters that started to descend in the open sea abyssal in the middle of Cenozoic were capable of substituting for previously (in Mesozoic) heated (up to 15-20 degrees C) abyssal waters within only 1500-2000 years. Following the descending near-Antarctic waters, the shallow and cold water oxyphilic fauna assimilated the abyssal zone that had been warm water and weakly populated. PMID:15926327

Kuznetsov, A P

219

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea.  

PubMed

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth >2000 m) and analysed for (239,240)Pu and (137)Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity - depth profiles of (210)Pb, together with (14)C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess (210)Pb inventory was used to normalize (239,240)Pu and (137)Cs inventories for variable sediment fluxes. The (239,240)Pu/(210)Pb(xs) ratio was uniform across the entire sea, with a mean value of 1.24x10(-3), indicating homogeneous fallout of (239,240)Pu. The (137)Cs/(210)Pb(xs) ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of (239,240)Pu/(137)Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of (239,240)Pu in the water column and major sedimentation of (137)Cs in the eastern basin. Although areas with water depths of >2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the (239,240)Pu and 0.95% of the (137)Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments. PMID:18986686

Garcia-Orellana, J; Pates, J M; Masqué, P; Bruach, J M; Sanchez-Cabeza, J A

2008-11-04

220

Abyssal hill deflections at Pacific-Antarctic ridge-transform intersections  

Microsoft Academic Search

Nearly complete coverage of shipboard multibeam bathymetry data at the right-stepping Menard and Pitman Fracture Zones allowed us to map abyssal hill deviations along their traces. In this study we distinguish between (1) J-shaped curvatures at their origin, where modeling is addressing primary volcanism and faulting following a curved zone, and (2) straight abyssal hills getting bent in anti-J-shaped curvatures,

Marcel B. Croon; Steven C. Cande; Joann M. Stock

2010-01-01

221

Benthic foraminiferal response to trophic changes across the last glacial-Holocene transition in the abyssal eastern Mediterranean Sea  

NASA Astrophysics Data System (ADS)

Benthic foraminifers have been studied in high temporal resolution in a well-dated abyssal sediment record from the Levantine Basin of the eastern Mediterranean Sea. Major target was to document the exact temporal sequence of changes in quantity and quality of organic matter fluxes and reconstruction of nutrient cycling during the last glacial, glacial termination and Holocene intervals and to evaluate its role in the formation of sapropel S1 during the early Holocene. The low-diverse modern benthic foraminiferal faunas of the abyssal eastern Mediterranean Sea are dominated by miliolids, and a few epifaunal arenaceous and hyaline taxa reflecting low food availability and ultra-oligotrophic conditions in the open-marine surface waters of this region. Specifically, the presence of the small opportunistic species Eponides pusillus and Anomalinoides minimus are associated with seasonal phytoplankton blooms and related phytodetritus pulses to the deep-sea. During the last glacial period, elevated proportions of shallow infaunal taxa indicate relatively higher organic matter fluxes than at present. The inferred glacial increase in surface water productivity can be attributed to intensified wind-induced vertical mixing of surface waters and related nutrient cycling. With the transition to Holocene boundary conditions, surface water productivity decreased and the abyssal faunas lack evidence for eutrophication with onset of sapropel S1 formation. This finding corroborates results from recent studies on the stable nitrogen isotope signature of organic matter but is in contrast to previous geochemical evidence. Comparison with faunal records from marginal areas of the eastern Mediterranean basins suggests that increased productivity in surface waters during the early Holocene was restricted to areas in the vicinity of riverine nutrient fluxes. Enhanced productivity in surface waters and related organic matter fluxes did obviously not contribute to the formation of sapropel S1 in the deeper basins. In addition, the record of the small opportunistic taxa allowed a detailed reconstruction of changes in the seasonality of surface water production and phytodetritus pulses that will aid to map the spatial and temporal variability of trophic changes in the eastern Mediterranean Sea during the transition from the last glacial to the Holocene.

Müller-Navarra, K.; Lochte, A.; Schmiedl, G.

2012-04-01

222

Holocene fluvial processes in Troy plain  

NASA Astrophysics Data System (ADS)

The Troy plain is the lower part of Scamander (Karamenderes) River basin before its mouth in the Dardanelle straits. The fluvial processes of the deltaic progradation and floodplain aggradation have changed the landscape of the plain during the past 10,000 years. They transformed a sheltered gulf reaching the Ancient Troy into an extensive plain. Ancient Troy is today 7 km inland while Simois (Dumrek) River is a tributary of Scamander (Karamenderes) River. A detailed geomorphological survey with high resolution topographical measurements was carried out using of a TOPCON FC100 differential GPS. This survey took place not only along the Troy plain but further southwards in Araplar gorge and Ezine basin. The morphological analysis of the data showed that the graded channel profile of the Scamander River is lower than its alluvial plain. The channel incision ranging from 2 to 5 meters is responsible for the formation of a pair of alluvial terraces along the channel. These aggradational terraces formed into the resent alluvial sandy deposits of the basin. The channel morphology of an alluvial river like Scamander is highly sensitive in changes concerning the discharge and the sediment load at downstream points. Active tectonics, climate change and sea level rise are the main causes of changes in the channel equilibrium. Ten sediment samples, from the alluvial terraces in Araplar gorge, were dated with OSL technique. The sample ages allowed the time estimation of the channel changes.

Vouvalidis, Konstantinos; Ates, Ozkan; Syrides, George; Pavlides, Spyros; Tutkun, Zeki; Chatzipetros, Alexandros; Ozden, Suha; Mavroudis, Petros; Sboras, Sotirios; Kurcer, Akin; Valkaniotis, S.

2010-05-01

223

Methane in water columns and sediments of the north western Sea of Japan  

NASA Astrophysics Data System (ADS)

This paper presents the results of methane measurements in water and sediments, first performed along the north western continental slope and abyssal plain of the Sea of Japan. Methane concentrations in the study area were very low. However, some features of its distribution are revealed. The highest dissolved methane concentrations (10-14 nmol kg-1) are characteristic of the pycnocline layer at a depth of 30-50 m in the northern shallow stations. With increasing depth, the methane is reduced to minimum values (0.5-1.0 nmol kg-1). The greatest variability in methane concentrations was observed in the layers at 0-500 m, which can be explained by the hydrodynamic conditions of the environment on the slope. Methane plumes (1.7 and 1.3 nmol kg-1) on the northern section were recorded at the depth of 1250 and 1495 m, respectively. Plumes (1.2 nmol kg-1) are also observed on near bottom layers at the deepest (more than 3000 m) stations. CH4 concentration in bottom sediments is also low (from 1 nmol kg-1 at 7 cm level to 752 nmol kg-1 at the 53 cm level of the core sediment in the northern part). Reduced sediments in the southern part of the study region have maximal methane concentration for sediment (2549 nmol kg-1) at the horizon 44 cm bsf (below sea floor) with a smell of H2S. These results assume a close relation of CH4 with sediment properties. A few stations with maximum methane (86-101 nmol kg-1) in the surface sediment layer are at the foot of a steep slope. Herewith, the highest abundance of some pericarid species was observed at the points with the highest values of methane concentrations in the surface sediment layer. Weak methane seepage can cause anoxic marine waters. Methane emission from water to the atmosphere is low because its concentration is close to equilibrium in surface water. An improved formula for calculating the methane flux of water into the atmosphere, taking into account high wind speeds, is presented in the paper.

Vereshchagina, Olga F.; Korovitskaya, Elena V.; Mishukova, Galina I.

2013-02-01

224

The response of abyssal organisms to low pH conditions during a series of CO2-release experiments simulating deep-sea carbon sequestration  

NASA Astrophysics Data System (ADS)

The effects of low-pH, high-pCO2 conditions on deep-sea organisms were examined during four deep-sea CO2 release experiments simulating deep-ocean C sequestration by the direct injection of CO2 into the deep sea. We examined the survival of common deep-sea, benthic organisms (microbes; macrofauna, dominated by Polychaeta, Nematoda, Crustacea, Mollusca; megafauna, Echinodermata, Mollusca, Pisces) exposed to low-pH waters emanating as a dissolution plume from pools of liquid carbon dioxide released on the seabed during four abyssal CO2-release experiments. Microbial abundance in deep-sea sediments was unchanged in one experiment, but increased under environmental hypercapnia during another, where the microbial assemblage may have benefited indirectly from the negative impact of low-pH conditions on other taxa. Lower abyssal metazoans exhibited low survival rates near CO2 pools. No urchins or holothurians survived during 30-42 days of exposure to episodic, but severe environmental hypercapnia during one experiment (E1; pH reduced by as much as ca. 1.4 units). These large pH reductions also caused 75% mortality for the deep-sea amphipod, Haploops lodo, near CO2 pools. Survival under smaller pH reductions (?pH<0.4 units) in other experiments (E2, E3, E5) was higher for all taxa, including echinoderms. Gastropods, cephalopods, and fish were more tolerant than most other taxa. The gastropod Retimohnia sp. and octopus Benthoctopus sp. survived exposure to pH reductions that episodically reached -0.3 pH units. Ninety percent of abyssal zoarcids (Pachycara bulbiceps) survived exposure to pH changes reaching ca. -0.3 pH units during 30-42 day-long experiments.

Barry, J. P.; Buck, K. R.; Lovera, C.; Brewer, P. G.; Seibel, B. A.; Drazen, J. C.; Tamburri, M. N.; Whaling, P. J.; Kuhnz, L.; Pane, E. F.

2013-08-01

225

Elemental and major biochemical changes across oxidation fronts in N. E. Atlantic sediments  

SciTech Connect

Fine-grained turbidites from the Madeira Abyssal Plain often contain surficial oxidation fronts in which molecular oxygen has burned down through sediments containing organic substances that previously coexisted with porewater sulfate for thousands of years. These deposits provide an opportunity to establish the extent and selectivity of slow oxic degradation without the need for conditions of long-term steady state deposition without mixing. The authors analyzed the elemental and major biochemical compositions of oxidized and unreacted sediments from f-turbidite sequences recovered at depths of 7--9 m from two separate MAP cores. In both turbidites, one sample from the reddish upper layer was compared to two deeper unreacted sediments. The unoxidized deeper sequences of both turbidites contained 0.93--1.02 wt% organic carbon and 0.05--0.07 wt% total nitrogen, with C/N ratios near 20. The oxidized upper horizons of both sequences contained approximately 1/5th the organic carbon and total nitrogen with C/N ratios of about 10. All samples gave extremely low yields of lignin phenols and comparable yields of total aldoses and total amino acids, indicated little land-derived organic matter and nonselective oxic degradation of these major biochemical classes. Reactivity differences among individual aldoses and protein amino acids were also relatively subtle and in non instance clearly indicated in situ formation. The most outstanding compositional differences were that the oxidized horizons yielded decreased percentages of total aldose and amino acid carbon, decreased percentages of amino acid nitrogen and elevated percentages of nonprotein amino acids. Comparison of these compositional trends to those observed in other marine environments suggests that the three previous parameters broadly reflect the diagenetic state of sedimentary organic mixtures.

Cowie, G.L. (Univ. de Nantes (France). Lab. Biologie Marine); Hedges, J.I. (Univ. of Washington, Seattle, WA (United States). School of Oceanography); Prahl, F.G. (Oregon State Univ., Corvallis, OR (United States). Coll. of Oceanography); Lange, G.J. de (Univ. of Utrecht (Netherlands). Dept. of Geochemistry)

1992-01-01

226

Ekman destabilization of inertially stable baroclinic abyssal flow on a sloping bottom  

NASA Astrophysics Data System (ADS)

Baroclinic abyssal currents on a sloping bottom, which are nonlinearly stable in the sense of Liapunov in the absence of dissipation, are shown to be destabilized by the presence of a bottom Ekman boundary layer for any positive value of the Ekman number. When the abyssal flow is baroclinically unstable, the dissipation acts to reduce the inviscid growth rates except near the marginal stability boundary where it acts to increase the inviscid growth rates. It is shown that when the abyssal flow is baroclinically stable, the Ekman destabilization corresponds to the kinematic wave phase velocity lying outside the range of the inertial topographic Rossby phase velocities. The transition mechanism described here might provide a dynamical bridge between the nonrotational roll-wave instability that can occur in supercritical abyssal overflows and frictionally induced destabilization in subinertial geostrophically balanced baroclinic abyssal currents. In addition, the theory presented here suggests a dissipation-induced destabilization mechanism for coastal downwelling fronts whose cross-slope potential vorticity gradient does not satisfy the necessary condition for baroclinic instability.

Swaters, Gordon E.

2009-08-01

227

Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography  

Microsoft Academic Search

Surface samples, mostly from abyssal sediments of the South Atlantic, from parts of the equatorial Atlantic, and of the Antarctic Ocean, were investigated for clay content and clay mineral composition. Maps of relative clay mineral content were compiled, which improve previous maps by showing more details, especially at high latitudes. Large-scale relations regarding the origin and transport paths of detrital

Rainer Petschick; Gerhard Kuhn; Franz Gingele

1996-01-01

228

Edwardsia sojabio sp. n. (Cnidaria: Anthozoa: Actiniaria: Edwardsiidae), a new abyssal sea anemone from the Sea ofJapan  

NASA Astrophysics Data System (ADS)

The paper describes new deep-water edwardsiid sea anemone Edwardsia sojabio sp. n. which is very common on soft muddy bottoms at lower bathyal and upper abyssal depths in the Sea of Japan. It was recorded in high quantity in depths between 2545 and 3550 m and is the second abyssal species of the genus Edwardsia.

Sanamyan, Nadya; Sanamyan, Karen

2013-02-01

229

The Plains City Story  

ERIC Educational Resources Information Center

|This case study portrays a contemporary phenomenon that affects many U.S. school districts. Specifically, the authors address the challenges that the superintendent of the Plains City school district faced as a result of a change in the demographic distribution of his district. The gradual development of the pig farming industry in Plains City…

van Olphen, Marcela; Rios, Francisco; Berube, William; Dexter, Robin; McCarthy, Robert

2006-01-01

230

SEDIMENT SAMPLING GUIDELINES  

EPA Science Inventory

The guidance document will detail the measures needed to collect and analyze soils/sediments from flood plains, wetlands, bogs, rivers, and streams that are impacted by high moisture content. High moisture in the above matrices can manifest itself as increased detection limits a...

231

Geology, geochemistry, and tectonostratigraphic relations of the crystalline basement beneath the coastal plain of New Jersey and contiguous areas  

USGS Publications Warehouse

Coastal plain sediments are underlain by pre-Mesozoic crystalline rocks. The inner coastal plain is underlain by schist that is correlated with the Potomac Terrane, as well as by mafic rocks probably equivalent to the Wilmington or Bel Air-Rising Sun terranes. The northern and central outer coastal plain is underlain by metasedimentary rocks similar to the Brompton-Cameron Terrane. Rocks beneath the southern coastal plain probably correlate with those of the Chopawamsic and Roanoke Rapids terranes.

Volkert, Richard A.; Drake, Avery Ala, Jr.; Sugarman, Peter J.

1996-01-01

232

Marine geology of the hess rise, 1, bathymetry, surface sediment distribution, and environment of deposition  

SciTech Connect

New charts of bathymetry, acoustic character, and sediment distribution describe the Hess Rise, a large oceanic plateau in the central north Pacific. Discrete physiographic provinces on the Hess Rise are the High Plateau, shallower than 3900 m, trending N30/sup 0/W; the Northeastern Flank, a smooth, gentle slope gradually increasing in depth to the northeast; the Woollard Abyssal Plain, extending farther to the northeast; the Volcanic Province with its high peaks and ridges along the southern margin of the Hess Rise; the Mendocino Fracture Zone to the south, expressed by broad, planar seafloor regions bordered by ridges and scarps; the Western Steps, formed by structural benches on the western side of the Rise; and the Emperor Deep, between the rise and the Emperor Seamounts. Five types of acoustic units have been mapped and interpreted: a transparent layer, predominantly of biosiliceous pelagic clay; a stratified layer, predominantly of nannofossil ooze; a diffuse layer of debris flows that seem to have originated mostly in the Volcanic Province; an opaque horizon commonly formed of volcaniclastic sediments that are usually found on the seafloor of the Mendocino Fracture Zone; and a hyperbolic horizon, indicating outcrops of igneous rock. The pronounced effect of bottom currents on the present-day environment of deposition in the Hess Rise is evidenced by the presence of the opaque horizon, which is interpreted as an erosion surface, and by current moating, abrupt thinning of surface layers and truncation of subbottom reflectors. The widespread erosion on the seafloor of the Mendocino Fracture Zone is attributed to the flow of Antarctic bottom water.

Nemoto, K.; Kroenke, L.W.

1981-11-10

233

Fractionation of Abyssal Tholeiites: Samples from the Oceanographer Fracture Zone (35 deg n, 35 deg W).  

National Technical Information Service (NTIS)

Chemical analyses of 48 fresh abyssal tholeiite specimens sampled from two dredge localities clearly define systematic chemical differences which indicate a moderate iron-enrichment trend of fraction oblique to the FeO-MgO side of the AFM diagram. This ma...

T. Shibata P. J. Fox

1975-01-01

234

Monologue or Dialogue? Stepping Away from the Abyss in Higher Education  

ERIC Educational Resources Information Center

|This paper investigates the possibilities of the use of dialogue, and the dangers of the use of monologue, in higher education in the early twenty-first century, in a period facing a number of smaller- and larger-scale crises--each interpreted as an "abyss" of some kind. How does higher education contribute, positively or negatively, to personal…

Stern, Julian

2009-01-01

235

Engineering concepts for the placement of wastes on the abyssal seafloor  

Microsoft Academic Search

The Naval Research Laboratory (NRL), with industry and academic participation, has completed a study of the concept of isolating industrial wastes (i.e., sewage sludge, fly ash from municipal incinerators, and dredged material) on the abyssal seafloor. This paper presents results of the technical and economic assessment of this waste management concept. The results of the environmental impacts portion of the

Philip J Valent; Andrew W. Palowitch; David K Young

1998-01-01

236

Adaptation to the rarefied air of abysses and caves.A laboratory study  

Microsoft Academic Search

Introduction and aims: The atmosphere in the abysses of the mountains of Garraf (Barcelona) have lower oxygen levels and higher CO2 concentrations with respect to normality. To evaluate the risk of speleological exploration in this area, we studied 19 cavers (14 men and 5 women) while performing controlled exercise in a hypercapnic, hypoxic and normobaric atmosphere (15.2 ± 0.8% of

Ignasi De Yzaguirre i Maura; Jaume Escoda i Mora; Joan Bosch Cornet; Jose Antonio Gutiérrez Rincón; Diego Dulanto Zabala; Ramón Segura Cardona

2008-01-01

237

Salt Plains Microbial Observatory  

NSDL National Science Digital Library

This site is home of the Salt Plains Microbial Observatory, located in the Salt Plains National Wildlife Refuge in northern Oklahoma. This area has permitted the first extensive study of a non-marine, terrestrial, hypersaline environment. The web site offers information about the extreme environment, images and video clips of its microbial inhabitants, an image-rich summary of research activities, information about summer courses and research opportunities, a list of publications, and links to other informative resources pertaining to hypersaline environments.

Buchheim, Mark; University Of Tulsa, Biological S.

238

Rapid Subsidence and Historical Wetland Loss in the Mississippi Delta Plain: Likely Causes and Future Implications.  

National Technical Information Service (NTIS)

Five representative areas of the Mississippi River delta plain were investigated using remote images, marsh elevations, water depths, sediment cores, and radiocarbon dates to estimate the timing, magnitudes, and relative rates of marsh erosion and land su...

R. A. Morton J. C. Bernier J. A. Barras N. F. Ferina

2005-01-01

239

River sediments.  

PubMed

River history is reflected in the nature of the sediments carried and deposited over time. Using examples drawn from around the world, this account illustrates how river sediments have been used to reconstruct past environmental changes at a variety of scales in time and space. Problems arising from a patchy alluvial record and from influences external to the river basin can make interpretation difficult. The Nile is treated in some detail because its history is further complicated by tectonic, volcanic and climatic events in its headwaters and by enduring human impacts. It arose soon after 30 Ma. Since that time approximately 100,000 km(3) of rock have been eroded from its Ethiopian sources and deposited in the eastern Mediterranean, with minor amounts of sediment laid down along its former flood plains in Egypt and Sudan. From these fragmentary alluvial remains, a detailed history of Nile floods and droughts has been reconstructed for the last 15 kyr, and, with less detail, for the past 150 kyr, which shows strong accordance with global fluctuations in the strength of the summer monsoon, which are in turn perhaps modulated by changes in solar insolation caused by changes in the Earth's orbit and by variations in solar irradiance. PMID:22474677

Williams, Martin

2012-05-13

240

Holocene evolution of the deltaic plain: a perspective — from Fisk to present  

Microsoft Academic Search

Before publication of Fisk's classic scientific papers dealing with the Mississippi River alluvial valley and deltaic plain, geological knowledge of the Holocene deltaic plain was the product of surficial geomorphological studies with a temporal framework provided by archaeology. Fisk and his co-workers provided the third and fourth dimensions, the three-dimensional characteristics of sediment bodies, by numerous deep borings and better

Harry H. Roberts; James M. Coleman

1996-01-01

241

Meiobenthos distribution pattern in the tropical East Atlantic: indication for fractionated sedimentation of organic matter to the sea floor?  

Microsoft Academic Search

To test the extent to which sea surface productivity governs the distribution pattern of benthic organisms, meiobenthic standing\\u000a stocks were investigated on the shelf, continental margin and the adjacent abyssal plains off the western African coast between\\u000a Guinea (10°N) and Angola (18°S). The area of investigation is characterized by gradients in surface productivity due to spatially\\u000a and seasonally varying coastal

T. Soltwedel

1997-01-01

242

Hydrologic impacts of strip tillage for a Coastal Plain soil  

Technology Transfer Automated Retrieval System (TEKTRAN)

Strip till is a growing practice among many Coastal Plain cotton growers which can lead to reduced surface runoff and reduced transport of sediment and agrichemicals. This research examines nine years of rainfall-runoff data from a paired conventional till / strip till research site. Annual water ...

243

Sedimentary deposits in the northern lowland plains, Mars  

Microsoft Academic Search

The lowland plains on Mars have surfaces marked by large polygonal fracture patterns. It was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels. The authors support this hypothesis because of the following observations. (1) Polygonal fracture patterns tend to occur in low areas on Mars that apparently received influx of sediments; the area of

B. K. Lucchitta; H. M. Ferguson; C. Summers

1986-01-01

244

Sedimentary deposits in the northern lowland plains, Mars  

Microsoft Academic Search

The lowland plains on Mars have surfaces marked by large polygonal fracture patterns. It was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels. We support this hypothesis because of the following observations. (1) Polygonal fracture patterns tend to occur in low areas on Mars that apparently received influx of sediments; the area of northern

B. K. Lucchitta; H. M. Ferguson; C. Summers

1986-01-01

245

A global and regional stochastic analysis of near-ridge Abyssal Hill morphology  

NASA Astrophysics Data System (ADS)

This paper presents the results of a global and regional stochastic analysis of near-ridge abyssal hill morphology. The analysis includes the use of Sea Beam data for the estimation of stochastic parameters up to order 4. These parameters provide important quantitative physical information regarding abyssal hills, including their rms height, azimuthal orientation, characteristic width, aspect ratio, Hausdorff dimension, skewness, tilt, and peakiness. The global data set consists of 64 Sea Beam swaths near the Rivera, Cocos, and Nazca spreading sections of the East Pacific Rise, the Mid-Atlantic Ridge, and the Central Indian Ridge. In one form of analysis, the parameters are averaged among spreading rate bins. Each of the spreading rate subsets can be identified as unique from the others in at least one aspect The slowest spreading rate subset (Mid-Atlantic data) exhibit the largest scales (rms height and characteristic width and length) of abyssal hills. These parameters generally decrease as spreading rate increases up to the fast spreading rate data (Pacific-Cocos) but increase going from fast to very fast (Pacific-Nazca) spreading rate data. This indicates some complexity in the relationship between spreading rate and abyssal hill morphology. The plan view aspect ratio is nearly twice as large for the fast spreading rate data than for any of the other subsets and is smallest for the very fast spreading rate data. The fractal dimension is nearly identical for all spreading rate subsets. The vertical skewness is positive for the slow and medium spreading rate data, indicating larger peaks than troughs, and negative for the fast spreading rate data, indicating larger troughs than peaks. The kurtosis, or peakiness is everywhere larger than the Gaussian value of 3 and tends to be larger in the Atlantic than the Pacific. The tilting parameter provides substantial evidence indicating steeper inward facing slopes in the medium and fast spreading rate data, but only marginal evidence for it in the slow spreading rate data. From an analysis of correlations among parameters it is found that subsets sometimes behave differently from the entire data set. In particular, while over the global data set the characteristic width exhibits a well-resolved positive trend when plotted versus rms height, these parameters exhibit a more gradual positive trend in the Mid-Atlantic data and a negative trend in the Pacific-Cocos data. In addition, the plan view aspect ratio, while generally uncorrelated with rms height for the global data set, is positively correlated with rms height for the Pacific-Cocos data set. These results emphasize a strong uniqueness of the Pacific-Cocos data relative to the rest of the data global set The Pacific-Cocos data consist of 27 swaths concentrated between the Siquieros and Orozco fracture zones. These data provide very good abyssal hill coverage of this well-mapped and well-studied region and form the basis of a regional analysis of the correlation between ridge morphology and stochastic abyssal hill parameters. In this analysis, it is found that abyssal hill parameters are correlated with the depth of the adjacent ridge axis, indicating that the relative abundance in magma supply, which likely controls the ridge axis depth, may also be an important influence on the formation of abyssal hills.

Goff, John A.

1991-12-01

246

Flood Plain Management Information Report, Ohio.  

National Technical Information Service (NTIS)

Contents: Development of Flood Plains; Why Flood Plain Management, What is Good Flood Plain Management; Sample Flood Plain Regulations; Responsibility of State, County, and Local Governments; What Information is Available; What Local Action can be Taken b...

1973-01-01

247

Mountain-Plains Curriculum.  

ERIC Educational Resources Information Center

|The document lists the Mountain-Plains curriculum by job title (where applicable), including support courses. The curriculum areas covered are mathematics skills, communication skills, office education, lodging services, food services, marketing and distribution, welding support, automotive, small engines, career guidance, World of Work, health…

Mountain-Plains Education and Economic Development Program, Inc., Glasgow AFB, MT.

248

Turbulent mixing and hydraulic control of abyssal water in the Samoan Passage  

NASA Astrophysics Data System (ADS)

We report the first direct turbulence observations in the Samoan Passage (SP), a 40 km wide notch in the South Pacific bathymetry through which flows most of the water supplying the North Pacific abyssal circulation. The observed turbulence is 1000 to 10,000 times typical abyssal levels —strong enough to completely mix away the densest water entering the passage—confirming inferences from previous coarser temperature and salinity sections. Accompanying towed measurements of velocity and temperature with horizontal resolution of about 250 m indicate the dominant processes responsible for the turbulence. Specifically, the flow accelerates substantially at the primary sill within the passage, reaching speeds as great as 0.55 m s-1. A strong hydraulic response is seen, with layers first rising to clear the sill and then plunging hundreds of meters downward. Turbulence results from high shear at the interface above the densest fluid as it descends and from hydraulic jumps that form downstream of the sill. In addition to the primary sill, other locations along the multiple interconnected channels through the Samoan Passage also have an effect on the mixing of the dense water. In fact, quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometers, suggesting that abyssal mixing depends sensitively on bathymetric details on small scales.

Alford, Matthew H.; Girton, James B.; Voet, Gunnar; Carter, Glenn S.; Mickett, John B.; Klymak, Jody M.

2013-09-01

249

Abyssal Scavenging Communities attracted to Sargassum and fish in the Sargasso Sea  

NASA Astrophysics Data System (ADS)

Deep-sea communities rely on epipelagic surface production as a primary source of energy and food. The flux of phytodetritus drives many abyssal ecological processes but the flux of large particles such as nekton carcasses, macroalgae, and wood may also be important. Recent baited camera experiments noted that some abyssal fish consumed spinach and phytoplankton placed on the seafloor. To evaluate if fish or other scavengers would consume natural plant or macroalgal material falling to the deep-sea floor we conducted camera experiments using Sargassum or mackerel bait in the Sargasso Sea. A benthic community of invertebrates was attracted to Sargassum, which naturally falls to the seafloor in this area. In five instances it was observed that an isopod Bathyopsurus sp. removed a piece of Sargassum from the main clump and left the field of view with it. An ophiuroid is also observed handling a piece of Sargassum. The group of scavengers attracted to mackerel bait was very different and was dominated by large ophidiid fish. In contrast to studies elsewhere in the abyssal North Atlantic, only a small number of rattails are observed, which could be related to water depth or an ichthyofaunal zonal change between oligotrophic and eutrophic regions.

Fleury, Aharon G.; Drazen, Jeffrey C.

2013-02-01

250

Early diagenesis in deep sea turbidites: The imprint of paleo-oxidation zones  

Microsoft Academic Search

Sediment cores up to 35 m long have been removed from turbidite sequences in the Madiera Abyssal Plain and the Southern Nares Abyssal Plain. Detailed geochemical analyses of these sediments (Si, Al, Fe, Mn, Ca, organic and inorganic carbon) and associate pore waters (nitrate, ammonia, silicate, Fe{sup 2+}, Mn{sup 2+} and alkalinity) provide representative profiles of both steady-state and nonsteady-state

D. E. Buckley; R. E. Cranston

1988-01-01

251

The geomorphology of the Mississippi River chenier plain  

USGS Publications Warehouse

The chenier plain of the Mississippi River is a shore-parallel zone of alternating transgressive clastic ridges separated by progradational mudflats. The term chenier is derived from the cajun term chene for oak, the tree species that colonizes the crests of the higher ridges. The Mississippi River chenier plain stretches 200 km from Sabine Pass, Texas, to Southwest Point, Louisiana and ranges between 20 and 30 km wide, with elevations of 2-6 m. The timing and the process of formation could be re-evaluated in the light of new chronostratigraphic findings in the Mississippi River delta plain. The stratigraphic relationship between the Teche and Lafourche delta complexes and Ship Shoal offshore indicates that these delta complexes belong to different delta plains that developed at different sealevels. It appears that the Teche delta complex is associated with the late Holocene delta plain which developed 7000 to 3000 yrs B.P. when sealevel stood 5-6 m lower than present. A regional transgression occurred between approximately 3000 BP and 2500 yrs B.P., leading to the transgressive submergence of the late Holocene delta plain, producing the regional Teche shoreline. The timing of this transgression conforms to the age of the most landward ridge in the chenier plain, the Little Chenier-Little Pecan Island trend, which dates at about 2500 yrs B.P. This ridge trend was originally interpreted as representing the Teche delta complex switching event with the landward Holocene/Pleistocene contact representing the high stand shoreline. The implication of this new interpretation is that the Little Chenier-Little Pecan Island trend represents the high stand shoreline, a continuation of the Teche shoreline separating the late Holocene and Recent delta plains, and that the Holocene/Pleistocene contact represents the leading edge of the marshes transgressing onto the Prairie Terrace. Significant mudflat progradation seems to require a westerly position of the Mississippi River, but the numerous different forms and ages of cheniers do not correspond well to the timing of major delta complex switching. Progradation of the chenier plain appears to be associated with building of the Recent delta plain and not the Teche complex of the late Holocene delta plain. The occurrence of individual ridges appears to be primarily tied to delta lobe switching within the Lafourche complex and variations in sediment supply from local rivers. The recent development of the Atchafalaya delta complex to the west is the closest position of an active distributary to the chenier plain since sealevel stabilization; a new episode of rapid mudflat progradation is thus taking place. ?? 1989.

Penland, S.; Suter, J. R.

1989-01-01

252

Proximal storage and controls on sediment flux in large Himalayan river systems  

Microsoft Academic Search

The central and eastern Himalaya are drained by the Ganga River and its tributaries, which flow southeastward across the Gangetic Plain in the northern Indian . Rivers in the eastern Gangetic Plain are generally characterized by high sediment fluxes and frequent avulsions in the foreland, leading to the deposition of very large, low-gradient alluvial fans. Rivers in the western Plain,

Alexander Densmore; Rajiv Sinha; Jason Barnes; Vikrant Jain; S. K. Tandon

2010-01-01

253

Time Domain Finite Difference Modeling of Abyssal T-Phases  

NASA Astrophysics Data System (ADS)

A long standing problem in T-phase research is the disconnect between i) the steep grazing angles of sound propagation in the ocean from a source in the crust or upper mantle and ii) the shallow grazing angles required for sound traveling in the ocean sound channel. The characteristics of earthquakes, as revealed by T-phase observations, have the potential to provide important constraints on physical models of crustal processes under the oceans. We do not know, however, how to infer earthquake source mechanisms, magnitudes, or depth from T-phase observations because we do not know the physical mechanisms responsible for getting T-phase energy from the earthquake epicenter into the ocean sound channel. Scattering, "wave tunneling", interface waves (Stoneley, Scholte and Rayleigh waves), and shear wave resonances (modes) in the sediments have been proposed as possible mechanisms to convert the compressional and shear body waves from earthquakes into the low grazing angle paths necessary for propagation in the ocean sound channel. In order to quantitatively compare the various mechanisms we have constructed a numerical model of the ocean crust, seafloor and ocean sound channel that can be used to study full elastic wave propagation at 10Hz out to 30km in two dimensions.

Stephen, R. A.; Smith, D. K.; Williams, C. M.

2004-12-01

254

Infuence of Underground Water on Hidromorphic Soils in a Protected Area of Aluvial Plain in Middle Part of Danube Basin  

Microsoft Academic Search

The soil genesis in the inundations of big rivers is closely associated with fluvial sedimentation. According to quantity and origin of deposite, the aluvial plain is consisted of folowing morphological forms: costal, central and near the terrace part. The objects of this work are hidromorphic soils of aluvial plains un the area of midle Danube basin. The pedological and hidrological

Ljiljana Nesi; Sasa Pekec; Petar Ivanisevic; Milivoj Beli

2010-01-01

255

Orientation study of central Arkansas. National Uranium Resource Evaluation program. Hydrogeochemical and stream-sediment reconnaissance  

Microsoft Academic Search

Samples of ground water, stream water, and sediment were Collected at 335 sites for an orientation study that included parts of the Ouachita Mountain and Gulf Coastal Plain regions in central Arkansas. Black shales, tuffs, and intrusive rocks, and the sediments of the Gulf Coastal Plain provide an environment that could be favorable to the formation of uranium deposits. The

Steele

1982-01-01

256

A correspondence of altimetric gravity texture to abyssal hill morphology along the flanks of the Southeast Indian Ridge  

NASA Astrophysics Data System (ADS)

We examine the relationship between altimetric gravity and abyssal hill textures along the flanks of Southeast Indian Ridge, where previous studies observed a progressive west-to-east increase in abyssal hill roughness and scales. Such a relationship is often considered unlikely because abyssal hills are typically smaller than upward continuation filter scales. However, our results, which exclude ridges, fracture zones and large pseudofaults, show that altimetric gravity roughness and characteristic scales in this region also increase from west to east and, at the largest scales, gravity texture exhibits ridge-parallel lineaments. Synthetic profiles also demonstrate how the texture parameters of a filtered field are related to those of the unfiltered field, particularly where the characteristic scale of the latter is smaller than the filter length.

Goff, John A.; Smith, Walter H. F.

2003-12-01

257

High Plains Regional Climate Center  

NSDL National Science Digital Library

The mission of the High Plains Regional Climate Center is to increase the use and availability of climate data in the High Plains region. This site contains a variety of climatic and hydrologic data from High Plains research projects. Data types include automated weather data, interactive climate summary maps, historical weather data, and an interactive climate atlas. Research projects include Nebraska soil moisture, crop phenology, and wind energy on the High Plains. This website also features relevant publications and a variety of weather and climate links.

Resources, School O.; Lincoln, University O.

258

Influence of carbonate complexes on uranium migration through abyssal red clays  

SciTech Connect

Diffusion experiments have been conducted to study the interactions between uranyl carbonate complexes and abyssal red clays. Experimental results indicate that in pH 8.8 solutions containing high concentrations of bicarbonate, uranyl carbonate complexes migrate rapidly through the clay samples. At lower pH values and bicarbonate concentrations, the uranyl carbonate complexes are converted to uranyl hydroxide complexes which are strongly sorbed by the clays and do not migrate. A competitive equilibrium model has been developed which explains these results, and which can be used to define the chemical environments in which uranium migration through the red clays should be rapid. 10 references.

Bunker, B.C.; Erickson, K.L.

1983-09-01

259

Plenty on the Plains  

NSDL National Science Digital Library

In this activity, learners compare the ways of life of Plains Native Americans who hunted and moved frequently to follow the buffalo herds, and Native Americans who farmed and lived in more permanent villages along the river valleys. As they learn about different ways of life, learners also explore the benefits of trading. Learners act out a trading scenario, in which they make and trade goods including wristbands and popcorn snacks. This activity is featured on pp.24-25 of the "One With the Earth: Native Americans and the Natural World" multidisciplinary unit of study for kindergarten through third grade.

Indianapolis, The C.

2012-06-26

260

Wet coastal plain tundra  

SciTech Connect

This years's census data for the wet coastal plain tundra in Alaska; North Slope Borough, 3 km SSW of Naval Arctic Research Laboratory, Barrow; 71/sup 0/ 18'N, 156/sup 0/ 43'W; Barrow Quadrangle, USGS, reflect an increase in breeding species of 31% over the 5-year average, while breeding density was up 22%. Ten species increased and only 4 decreased. There was a total of 17 species; 61.5 territorial males or females (171/km/sup 2/, 69/100 acres).

Myers, J.P.; McCaffery, B.J.; Pitelka, F.A.

1980-01-01

261

Sediment Removal.  

National Technical Information Service (NTIS)

When properly conducted, sediment removal is an effective lake management technique. This chapter describes: (1) purposes of sediment removal, (2) environmental concerns, (3) appropriate depth of sediment removal, (4) sediment removal techniques, (5) suit...

S. A. Peterson

1984-01-01

262

Metalliferous sediments from DSDP Leg 92: The East Pacific Rise transect  

NASA Astrophysics Data System (ADS)

The carbonate-free metalliferous fraction of thirty-nine sediment samples from four DSDP Leg 92 sites has been analyzed for 12 elements, and a subset of 16 samples analyzed for Pb isotopic composition. The main geochemical features of this component are as follows: i) very high concentrations of Fe and Mn, typically 25-39% and 5-14%, respectively; ii) Al and Ca contents generally less than 2% and 5%, respectively; iii) high Cu (1000-2000 ppm), and Zn and Ni (500-1000 ppm) values; and iv) Co and Pb concentrations of 100-250 ppm. In terms of element partitioning within the metalliferous fraction, amorphous to poorly crystallized oxide-oxyhydroxides removed by the second leach carry virtually all of the Mn, and about 90% of the Ca, Sr and Ni. The well-crystallized goethite-rich material removed by the third leach carries the majority of Fe, Cu, and Pb. These relations hold for sediments as young as ~ 1-2 Ma, indicating early partitioning of hydrothermal Fe and Mn into separate phases. Calculated mass accumulation rates (MAR) for Fe, Mn, Cu, Pb, Zn and Ni in the bulk sediment show the same overall trends at three of the sites, with greatest MAR values near the basement, and a general decrease in MAR values towards the tops of the holes (for sediments deposited above the lysocline). These relations strongly support the concept of a declining hydrothermal contribution of these elements away from a ridge axis. Nevertheless, MAR values for these metals up to ~200 km from the ridge axis are orders of magnitude higher than on abyssal seafloor plains where there is no hydrothermal influence. Mn/Fe ratios throughout the sediment column at two sites indicate that the composition of the hydrothermal precipitates changed during transport through seawater, becoming significantly depleted in Mn beyond 2˜00-300 km from the axis, but maintaining roughly the same proportion of Fe. Most of the Pb isotope data for the Leg 92 metalliferous sediments form approximately linear arrays in the conventional isotopic plots, extending from the middle of the field for mid-ocean ridge basalts toward the field for Mn nodules. The array of data lying between these two end-members is most readily interpreted in terms of simple linear mixing of Pb derived from basaltic and seawater end-member sources. The least radiogenic sediments reflect the average Pb isotope composition of discharging hydrothermal solutions and ocean-ridge basalt at the EPR over the ?4-8 Ma B.P. interval. Pb in sediments deposited up to 250 km from the axis can be almost entirely of basaltic-hydrothermal origin. Lateral transport of some basaltic Pb by ocean currents appears to extend to distances of at least 1000 km west of the East Pacific Rise.

Barrett, T. J.; Taylor, P. N.; Lugoqski, J.

1987-09-01

263

Particle export from the euphotic zone: Estimates using a novel drifting sediment trap, 234Th and new production  

NASA Astrophysics Data System (ADS)

We describe the first results obtained using a novel free-drifting neutrally buoyant sediment trap called PELAGRA (Particle Export measurement using a LAGRAngian trap). The trap uses an APEX float (Autonomous Profiling EXplorer) to maintain its location at a predetermined depth or density horizon and is designed to be deployed in the depth range 100-600 m for periods of up to a week. PELAGRA was deployed into a well characterised region of the Northeast (NE) Atlantic over the Porcupine Abyssal Plain (PAP) during the summers of 2003, 2004, 2005 and 2006 in post-bloom conditions. In parallel, measurements were made of total and new primary production and estimates of particle export based on 234Th deficits in the upper water column. Samples of sinking material from PELAGRA were recovered almost uncontaminated by "swimmers". The material collected differed from that obtained using water bottles and an in situ filtration system and this indicated selective export of centric diatoms. Fluxes of 234Th into the traps were less than that calculated from the deficit of this isotope in the upper water column. It is concluded that this reflects export events that had occurred prior to these deployments. Fluxes of organic carbon into the PELAGRA traps were similar to those expected from measurements of new production in the upper mixed layer. During 2006, simultaneous PELAGRA deployments at depths of 150 and 250 m provided a direct measurement of the decrease in flux with depth. This decrease was substantially more than that predicted by the often-used "Martin equation" and yielded a " b value" of 1.7. Using this value in the NE Atlantic about 14% of the total production reaches a depth of 150 m during the post-bloom period under nutrient limitation.

Lampitt, R. S.; Boorman, B.; Brown, L.; Lucas, M.; Salter, I.; Sanders, R.; Saw, K.; Seeyave, S.; Thomalla, S. J.; Turnewitsch, R.

2008-11-01

264

Organic matter budget in the Southeast Atlantic continental margin close to the Congo Canyon: In situ measurements of sediment oxygen consumption  

NASA Astrophysics Data System (ADS)

A study of organic carbon mineralization from the Congo continental shelf to the abyssal plain through the Congo submarine channel and Angola Margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling. Two measurement techniques were coupled on a single autonomous platform: in situ benthic chambers and microelectrodes, which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters. In addition, sediment trap fluxes, sediment composition (Org-C, Tot-N, CaCO 3, porosity) and radionuclide profiles provided measurements of, respectively input fluxes and burial rate of organic and inorganic compounds. The in situ results show that the oxygen consumption on this margin close to the Congo River is high with values of total oxygen uptake (TOU) of 4±0.6, 3.6±0.5 mmol m -2 d -1 at 1300 and 3100 m depth, respectively, and between 1.9±0.3 and 2.4±0.2 mmol m -2 d -1 at 4000 m depth. Diffusive oxygen uptakes (DOU) were 2.8±1.1, 2.3±0.8, 0.8±0.3 and 1.2±0.1 mmol m -2 d -1, respectively at the same depths. The magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel-levee system, which indicates that cross-slope transport processes are active over the entire margin. Comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5-8 times larger than the vertical flux recorded in traps. Transfer of material from the Congo River occurs through turbidity currents channelled in the Congo valley, which are subsequently deposited in the Lobe zone in the Congo fan below 4800 m. Ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone, which agrees with the high organic carbon content (3%) and the large sedimentation rate (19 mm y -1) found on this site. The Lobe region could receive as high as 19 mol C m -2 y -1, 1/3 being mineralized and 2/3 being buried and could constitute the largest depocenter of organic carbon in the South Atlantic.

Rabouille, C.; Caprais, J.-C.; Lansard, B.; Crassous, P.; Dedieu, K.; Reyss, J. L.; Khripounoff, A.

2009-12-01

265

The absence of sharks from abyssal regions of the world's oceans  

PubMed Central

The oceanic abyss (depths greater than 3000?m), one of the largest environments on the planet, is characterized by absence of solar light, high pressures and remoteness from surface food supply necessitating special molecular, physiological, behavioural and ecological adaptations of organisms that live there. Sampling by trawl, baited hooks and cameras we show that the Chondrichthyes (sharks, rays and chimaeras) are absent from, or very rare in this region. Analysis of a global data set shows a trend of rapid disappearance of chondrichthyan species with depth when compared with bony fishes. Sharks, apparently well adapted to life at high pressures are conspicuous on slopes down to 2000?m including scavenging at food falls such as dead whales. We propose that they are excluded from the abyss by high-energy demand, including an oil-rich liver for buoyancy, which cannot be sustained in extreme oligotrophic conditions. Sharks are apparently confined to ca 30% of the total ocean and distribution of many species is fragmented around sea mounts, ocean ridges and ocean margins. All populations are therefore within reach of human fisheries, and there is no hidden reserve of chondrichthyan biomass or biodiversity in the deep sea. Sharks may be more vulnerable to over-exploitation than previously thought.

Priede, Imants G; Froese, Rainer; Bailey, David M; Bergstad, Odd Aksel; Collins, Martin A; Dyb, Jan Erik; Henriques, Camila; Jones, Emma G; King, Nicola

2006-01-01

266

Two depositional models for Pliocene coastal plain fluvial systems, Goliad Formation, south Texas Gulf Coastal plain  

SciTech Connect

The Goliad Formation consists of four depositional systems-the Realitos and Mathis bed-load fluvial systems in the southwest and the Cuero and Eagle Lake mixed-load fluvial systems in the northeast. Five facies are recognized in the Realitos and Mathis bed-load fluvial systems: (1) primary channel-fill facies, (2) chaotic flood channel-fill facies, (3) complex splay facies, (4) flood plain facies, and (5) playa facies. A model for Realitos-Mathis depositional environments shows arid-climate braided stream complexes with extremely coarse sediment load, highly variable discharge, and marked channel instability. Broad, shallow, straight to slightly sinuous primary channels were flanked by wide flood channels. Flood channels passed laterally into broad, low-relief flood plains. Small playas occupied topographic lows near large channel axes. Three facies are recognized in the Cuero and Eagle Lake mixed-load fluvial systems: (1) channel-fill facies, (2) crevasse splay facies, and (3) flood plain facies. A model for Cuero-Eagle Lake depositional environments shows coarse-grained meander belts in a semi-arid climate. Slightly to moderately sinuous meandering streams were flanked by low, poorly developed natural levees. Crevasse splays were common, but tended to be broad and ill-defined. Extensive, low-relief flood plains occupied interaxial areas. The model proposed for the Realitos and Mathis fluvial systems may aid in recognition of analogous ancient depositional systems. In addition, since facies characteristics exercise broad controls on Goliad uranium mineralization, the proposed depositional models aid in defining target zones for Goliad uranium exploration.

Hoel, H.D.; Galloway, W.E.

1983-03-01

267

Chenier Plain Coast, Louisiana: Seasonal to Decadal-Scale Shoreline Evolution and Response to Episodic Storm Events  

Microsoft Academic Search

Multiple aerial photographic surveys conducted above the chenier plain coast, Louisiana, between 1987 and 2001 reveal rapid morphologic evolution along this mud-dominated shoreline west of the Atchafalaya River. Mudflat progradation is apparent on sub-seasonal time scales, as sediment derived from the Atchafalaya River plume and shallow inner shelf accretes on to the coast. Much of this accreted sediment is subsequently

A. E. Draut; O. K. Huh; C. C. Moeller; J. M. Grymes; G. C. Kineke

2002-01-01

268

Microbial respiration and diffusive oxygen uptake of deep-sea sediments in the Southern Ocean (ANTARES-I cruise)  

Microsoft Academic Search

Benthic microbial respiration and diffusive oxygen uptake were measured, and used to calculate rates of aerobic mineralisation of organic matter and concomitant CO2 production at the sediment water interface in the abyssal region of the Crozet Basin. This study was part of the ANTARES-I cruise on the R.V. Marion Dufresne, in the Permanent Open Ocean Zone of the Southern Ocean

Rutger De Wit; Jean-Claude Relexans; Thierry Bouvier; David J. W. Moriarty

1997-01-01

269

Flood plain and channel dynamics of the Quinault and Queets Rivers, Washington, USA  

USGS Publications Warehouse

Comparison of historic channel migration rates, modern planform conditions, and overall sediment, wood, and flow conditions and interactions for the Quinault River and Queets River in the western Olympic Peninsula, Washington, reveals decadal- to century-scale interactions between gravel-bed channels and forested flood plains in temperate maritime environments. The downstream alluvial portions of these two rivers can be divided into three reaches of different slope, flow, sediment, and wood regimes: (i) the upper Quinault River is aggrading behind Lake Quinault, a natural lake that traps most sediment and wood transported from the Olympic Mountain headwaters. (ii) The lower Quinault River, downstream of Lake Quinault, transports only sediment and wood derived from reworking of flood-plain deposits and contributed from valley margins. (iii) The Queets River has unimpeded movement of sediment and water from the mountainous headwaters to the Pacific Ocean. Measurements of channel planform characteristics and historic migration rates and patterns show that these three reaches have correspondingly distinct channel and flood-plain morphologies and dynamics. The aggrading and sediment-rich upper Quinault River has the widest flood plain, widest active channel, greatest number of low-flow channels and flanking gravel bars, and an average channel migration rate of 12.7??3.3 m/year between 1900 and 1994. The comparatively sediment-poor lower Quinault River has the narrowest flood plain, narrowest active channel, and lowest channel migration rate (4.0??1.2 m/year); and most flow is through a single channel with few adjacent gravel bars. The Queets River has attributes intermediate between the lower and upper Quinault Rivers, including an average channel migration rate of 7.5??2.9 m/year. Flood-plain turnover rates are similar for all three reaches, with channels eroding the flood plain at the rate of about 0.2% of the flood-plain area per year, and with corresponding flood-plain half-lives of 300 to 500 years. Observations from this study and previous studies on the Queets River show that channel and flood-plain dynamics and morphology are affected by interactions between flow, sediment, and standing and entrained wood, some of which likely involve time frames similar to 200-500-year flood-plain half-lives. On the upper Quinault River and Queets River, log jams promote bar growth and consequent channel shifting, short-distance avulsions, and meander cutoffs, resulting in mobile and wide active channels. On the lower Quinault River, large portions of the channel are stable and flow within vegetated flood plains. However, locally, channel-spanning log jams have caused channel avulsions within reaches that have been subsequently mobile for several decades. In all three reaches, log jams appear to be areas of conifer germination and growth that may later further influence channel and flood-plain conditions on long time scales by forming flood-plain areas resistant to channel migration and by providing key members of future log jams. Appreciation of these processes and dynamics and associated temporal and spatial scales is necessary to formulate effective long-term approaches to managing fluvial ecosystems in forested environments. Published by Elsevier Science B.V.

O'Connor, J. E.; Jones, M. A.; Haluska, T. L.

2003-01-01

270

Contemporary changes in sediment yield in an alpine mountain basin due to afforestation (the upper Drôme in France)  

Microsoft Academic Search

The Baurières plain within the upper Drôme River basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment. A considerable body of archival information is available. Furthermore, the plain acts as a natural sediment trap and the reach–basin interaction has not been disrupted by human activity. Based on archival

Hervé Piégay; Desmond E. Walling; Norbert Landon; Qinping He; Fred Liébault; Robert Petiot

2004-01-01

271

Modeling Tsunami Sedimentation  

NASA Astrophysics Data System (ADS)

The inundation of a tsunami, whether generated from a submarine landslide or an underwater earthquake, often results in beach erosion, landward sediment transport, and deposition of a tsunami deposit. If the deposit is preserved, then it becomes a record of the tsunami, and may be useful in interpreting a region's tsunami hazard. In addition to the knowledge that a tsunami had previously inundated an area, is there more that can be learned from paleo-tsunami deposits? To address this question we are developing models of tsunami inundation and sediment transport and using them to relate sedimentological characteristics of the deposit, such as grain size and thickness, to hydrodynamic characteristics of the tsunami, such as maximum velocity and flow depth. Model results are tested and verified using field data from the 2004 Indian Ocean tsunami. Data on tsunami flow depth, inundation distance, nearshore bathymetry, topography, tsunami deposit thickness, and sediment samples for grain size analysis were collected along several cross shore transects in Sumatra. These data are compared to predictions of erosion and deposition from a high resolution tsunami inundation and sediment transport model constructed over a 4-km cross shore section of coast. The Delft3D model, which solves the non-linear shallow water equations and calculates sediment transport with van Rijn (1993), is implemented with a flooding algorithm proven accurate for dam-break scenarios with rapid flooding. Forced with an offshore water level boundary condition taken from an Indian Ocean propagation model, the high-resolution inundation model predicts tsunami shoaling at the coast, with the wave-form steepening, wavelength decreasing, and wave height increasing. Maximum flow at the shoreline is directed offshore during the drawdown phase and is enhanced by the draining of water off the coastal plain. This offshore flow erodes the beach, transporting a substantial volume of sediment to a depth of approximately 12 m (msl), precisely the location of an offshore bar observed in the bathymetric data. Onshore flow, reaching a maximum velocity of approximately 8 m/s, also erodes the beach and carries sand onto the coastal plain. The tsunami deposit on land varies in thickness, with thinner deposits on topographic highs and thicker deposits in topographic lows. Model results suggest that variations in thickness results from divergences and convergences in the sediment flux as the flow slows over the topographic lows and speeds up over the topographic highs. Model results also indicate that the deposit thickness is sensitive to sediment grain size. Since the grain size of the deposit is poly-modal, multiple grain sizes should be included in future simulations.

Gelfenbaum, G.; Jaffe, B.; Elias, E.; Moore, A.; Ruggiero, P.; Morton, R.

2006-12-01

272

Ages of Lunar Light Plains  

NASA Astrophysics Data System (ADS)

Light plains are characterized by their relative smoothness and lower crater densities (compared to the highlands), and their occurrence as crater fills. They also exhibit highland-like characteristics, such as high albedos (in comparison to mare basalts) and their geological and stratigraphic setting. Despite the long history of investigating light plains, there are still numerous open questions concerning their mode of emplacement, their mineralogical composition, their ages, and their origin. We dated 16 light plains with crater size-frequency distribution (CSFD) measurements. All dated regions were previously identified as light plains in the geologic maps [1-5] and either mapped as smooth light plains (Ip) or light plains with undulatory surfaces (INp). The studied light plains occur both inside and outside the South Pole-Aitken (SPA) basin within a latitudinal band between ~-36° and ~-75°. In particular, we investigated the following smooth light plains: Janssen (40.82°E, -44.96°; Ip [1]), Nishina (-170.8°E, -44.57°; Ip [2]), South of Nishina (Ip [2]), Obruchev (162.43°E, -38.67°; Ip [2]), Oresme (169.22°E, -42.61°, Ip [2]), Schrödinger (132.93°E, -74.73°; Ip [3]), Nearch (39.01°E, -58.58°; Ip [3]), Nasmyth (-56.39°E, -50.49°; Ip [3]), Manzinus (26.37°E, -67.51°; Ip [3]), Klaproth (-26.26°E, -69.85°; Ip [3]), Phocylides (-57.31°E, -52.79°, Ip [3]), Buffon (-133.53°E, -40.64°; Ip [4]), Roche (136.54°E, -42.37°; Ip [5]). We also dated the following light plains with undulatory surfaces: Koch (150.33°E, -42.13°; INp [2]), Garavito (156.78°E, -47.21°; INp [2]), Eötvös (134.43°E, -35.61°; INp [5]). Our CSFD measurements resulted in absolute model ages of 3.71 to 4.02 Ga for all investigated light plains, thus confirming the Imbrian and/or Nectarian ages of the geologic maps [1-5]. We only dated three INp light plains, but they appear to have ages that are close to the upper limit, i.e., 3.96-4.02 Ga. However, further CSFDs of INp light plains are necessary to corroborate this preliminary observation. In general, our new absolute model ages are similar to model ages derived for light plains north of Mare Frigoris (3.65-4.0 Ga) [6], light plains within the SPA basin (3.43-3.81 Ga) [7], and light plains in the surroundings of the Orientale and Imbrium basins (3.8-4.3 Ga) [8]. The ages are not only similar, but also show similar ranges. While our model ages vary by about 300 Ma, model ages of [6,7] exhibit ranges of ~350 Ma and ~380 Ma, respectively. Ages of [8] show a somewhat wider range of ~500 Ma. From this wide range in ages it has been concluded that a formation of the light plains by a single event (i.e., Orientale or Imbrium) is unlikely [6-8]. References: [1] Wilhelms and McCauley (1971), USGS I-703; [2] Stuart-Alexander (1978), USGS I-1047; [3] Wilhelms et al. (1979), USGS I-1162; [4] Scott et al. (1977), USGS I-1034; [5] Wilhelms and El-Baz (1977), USGS I-948; [6] Köhler et al. (2000), LPSC 31, #1822; [7] Thiessen et al. (2012), LPSC 43, #2060; [8] Neukum (1977b), Moon 17, 383-393.

Hiesinger, Harald; Howes van der Bogert, Carolyn; Thiessen, Fiona; Robinson, Mark

2013-04-01

273

In favor of (plain) phenomenology  

Microsoft Academic Search

Plain phenomenology explains theoretically salient mental or psychological distinctions with an appeal to their first-person\\u000a applications. But it does not assume (as does heterophenomenology) that warrant for such first-person judgment is derived\\u000a from an explanatory theory constructed from the third-person perspective. Discussions in historical phenomenology can be treated\\u000a as plain phenomenology. This is illustrated by a critical consideration of Brentano’s

Charles Siewert

2007-01-01

274

Quantifying variable rainfall intensity events on runoff and sediment losses  

Technology Transfer Automated Retrieval System (TEKTRAN)

Coastal Plain soils in Georgia are susceptible to runoff, sediment, and chemical losses from short duration-high intensity, runoff producing storms at critical times during the growing season. We quantified runoff and sediment losses from a Tifton loamy sand managed under conventional- (CT) and stri...

275

Sediment flux and the Anthropocene.  

PubMed

Data and computer simulations are reviewed to help better define the timing and magnitude of human influence on sediment flux--the Anthropocene epoch. Impacts on the Earth surface processes are not spatially or temporally homogeneous. Human influences on this sediment flux have a secondary effect on floodplain and delta-plain functions and sediment dispersal into the coastal ocean. Human impact on sediment production began 3000 years ago but accelerated more widely 1000 years ago. By the sixteenth century, societies were already engineering their environment. Early twentieth century mechanization has led to global signals of increased sediment flux in most large rivers. By the 1950s, this sediment disturbance signal reversed for many rivers owing to the proliferation of dams, and sediment load reduction below pristine conditions is the dominant signal today. A delta subsidence signal began in the 1930s and is now a dominant signal in terms of sea level for many coastal environments, overwhelming even the global warming imprint on sea level. Humans have engineered how most water and sediment are discharged into the coastal ocean. Hyperpycnal flow events have become more common for some rivers, and less common for other rivers. Bottom trawling is now widespread, suggesting that even continental shelves have received a significant but as yet quantified Anthropocene impact. The Anthropocene attains the level of a geological climate event, such as that seen in the transition between the Pleistocene and the Holocene. PMID:21282156

Syvitski, James P M; Kettner, Albert

2011-03-13

276

Seismic character of the BSR in the Ulleung Basin plain, East Sea (Japan Sea)  

Microsoft Academic Search

A bottom simulating reflector (BSR) was identified in multichannel seismic reflection profiles collected in the Ulleung Basin\\u000a plain, East Sea (Japan Sea). The BSR, occurring in densely stratified sediments, is observed very close to the boundary between\\u000a two sequences interpreted as low-energy turbidites\\/hemipelagic sediments and mass-transport deposits. The essential characteristics\\u000a of the BSR include its cross-cutting relationship to strata at

Han-Joon Kim; Gwang Hoon Lee; Hyeong-Tae Jou; Sang Hoon Lee; Dong-Geun Yoo; Nam-Hyung Koo; Gap-Sik Jeong; Bong-Chool Suk

2010-01-01

277

Bait-attending fauna of the Kermadec Trench, SW Pacific Ocean: Evidence for an ecotone across the abyssal–hadal transition zone  

Microsoft Academic Search

The bait-attending fauna of the abyssal–hadal transition zone of the Kermadec Trench, SW Pacific Ocean (4329–7966m), was investigated using a baited camera and a trap lander. The abyssal stations (4329–6007m) revealed a typical scavenging fish community comprising macrourids and synaphobranchid eels, as well as natantian decapods. At the hadal depths of 7199 and 7561m, the endemic liparid Notoliparis kermadecensis was

A. J. Jamieson; N. M. Kilgallen; A. A. Rowden; T. Fujii; T. Horton; A.-N. Lörz; K. Kitazawa; I. G. Priede

2011-01-01

278

Geology and Wine 11. Terroir of the Western Snake River Plain, Idaho, USA  

Technology Transfer Automated Retrieval System (TEKTRAN)

This article explores unique factors that shape the terroir of Idaho’s principal wine grape-growing district. Most Idaho wine grape vineyards are located in the Western Snake River Plain (WSRP) rift basin (~43°N, ~114°W) on soils derived from lake, river, or wind-blown sediments, volcanic events, a...

279

Receiver function study of the rifted margin of the Gulf Coast Plain: A Pilot Project  

Microsoft Academic Search

The Gulf Coast Plain (GCP) is one of the deepest sedimentary basins in the world; as a result little is known about the basement structure beneath this region. The few refraction seismic investigations of the GCP found sediment depths of 15 to 20 km, underlain by severely attenuated continental or transitional crust. A 2-D refraction investigation along the Texas-Louisiana Border,

M. Brundrett; H. Gurrola; J. Pulliam; R. J. Stern; E. Y. Anthony; G. R. Keller; S. S. Gao; K. L. Mickus

2009-01-01

280

Freshwater and marine coupling in estuaries of the Mississippi River deltaic plain  

Microsoft Academic Search

The estuaries of Louisiana's Mississippi River deltaic plain (MRDP) exhibit sharp physical and biological contrasts due to their different successional stages in delta development. The Atchafalaya- Fourleague Bay complex is a young deltaic system with high freshwater and sediment inputs. The area has been undergoing rapid land building since 1973. The Barataria Basin estuary occupies a deltaic land mass which

CHRISTOPHER J. MADDEN; JOHN W. DAY; JOHN M. RANDALL

1988-01-01

281

Hydrogeochemical processes and facies in confining units of the Atlantic Coastal Plain in New Jersey  

Microsoft Academic Search

Pore water solutes and sediments in the New Jersey Coastal Plain were studied to assess processes that control pore water chemistry in confining units and interactions with aquifer water chemistry. Solute chemistry and variations with depth are reported for 19 samples collected from a continuously cored borehole in the lower Miocene Kirkwood Formation at Atlantic City, New Jersey. In 14

Amleto A. Pucci; A. A. Jr

1998-01-01

282

Nutrient yield of the Apalachicola River flood plain, Florida; water-quality assessment plan  

USGS Publications Warehouse

The Apalachicola River in northwestern Florida is the location of one of four current U.S. Geological Survey National River Quality Assessments. The investigation of the Apalachicola River and flood plain is designed to quantify the organic detritus and nutrient yield to the productive, estuarine Apalachicola Bay. The extensive riverine flood plain is subject to seasonal flooding which transports large quantities of accumulated, decaying leaf litter from the flood plain into the river and ultimately into Apalachicola Bay. The Apalachicola River Quality Assessment has four major objectives; (1) Determine the accumulation of organic substances and trace elements in benthic organisms and fine-grained sediments; (2) Define the distribution of the major tree communities on the flood plain; (3) Assess the role of leaf fall and decomposition on nutrient yield; and (4) Identify and quantify major sources and pathways of nutrients to the river. Extensive emphasis is given to investigation approaches and techniques to facilitate technology transfer to similar wetland ecosystems. (USGS)

Mattraw, H. C., Jr.; Elder, John F.

1980-01-01

283

Tracing abyssal food supply back to upper-ocean processes over a 17-year time series in the northeast Pacific  

Microsoft Academic Search

Detrital aggregates episodically deposited on the seafloor represent an underestimated food source to deep-sea communities. A 17-yr time-series study was conducted from 1990 to 2006 in the abyssal northeast Pacific (Sta. M, 4100 m in depth) to evaluate the importance of this food source and its temporal relationship to water column and surface ocean processes. Detrital aggregates appeared on the

K. L. Smith; H. A. Ruhl; R. S. Kaufmann; M. Kahru

2008-01-01

284

Trace Element Systematics in Bulk-Rock Abyssal Peridotites and Constituent Minerals: Evidence for Porous Melt Migration Beneath Ocean Ridges  

Microsoft Academic Search

Trace element studies of residual clinopyroxene (cpx) in abyssal peridotites (AP) [1,2] confirmed the earlier notion that AP are mantle melting residues for MORB [3-5], and also argued that near-perfect fractional melting best explains the cpx trace element data, e.g., progressively more depleted in the lighter rare earth elements (REEs). However, a recent study [6] showed that light REEs in

Y. Niu

2006-01-01

285

Late Pleistocene marine transgression of North Slope coastal plain  

SciTech Connect

Two late Pleistocene marine transgressions of contrasting character are recorded by deposits of the Arctic coastal plain. Deposits of the oldest trangression extend from Harrison Bay west to near Barrow and contain a fauna that documents interglacial conditions. Five thermoluminescence (TL) dates on the marine deposits average 127 Ka and indicate a correlation with oxygen isotope stage 5e. Sedimentary structures characteristic of the swash zone occur at altitudes within the commonly accepted range (6 not equal 4m) for eustatic high sea level at that time, showing that this part of the coastal plain has been tectonically stable for the past 125,000 years. Deposits of the youngest transgression are glaciomarine sediments that contain ice-rafted erratics of Canadian provenance. They compose the flaxman member of the Gubik Formation and occur locally along the Beaufort Sea coast and inland to altitudes of about 7 m. TL dates on these sediments suggest that the Flaxman transgression occurred between 70 and 80 ka and is correlative with deposits dated to this interval that are exposed near sea level on the North Carolina coastal plain. However, the deep-sea oxygen-isotope record is commonly interpreted to indicate that sea level was below its modern position at that time. The present altitude of the Flaxman deposits cannot be attributed to tectonism because their distribution includes the part of the coastal plain determined to be tectonically stable for the past 125 ka. Isostatic depression and subsequent elevation are unlikely considering the correlative deposits of North Carolina. This paradox could be explained if enormous volumes of floating glacial ice were produced by the rapid breakup of a large part of the Laurentide ice sheet, and recent work indeed suggests that the Hudson Bay lowlands were ice free at this time.

Carter, L.D.

1985-04-01

286

Suspended particulate loads and transports in the nepheloid layer of the abyssal Atlantic Ocean  

USGS Publications Warehouse

Vertical profiles of light scattering from over 1000 L-DGO nephelometer stations in the Atlantic Ocean have been used to calculate mass concentrations of suspended particles based on a calibration from the western North American Basin. From these data are plotted the distributions of particulate concentrations at clear water and in the more turbid near-bottom water. Clear water is the broad minimum in concentration and light scattering that occurs at varying mid-depths in the water column. Concentrations at clear water are as much as one-to-two orders of magnitude lower than those in surface water but still reflect a similar geographic distribution: relatively higher concentrations at ocean margins, especially underneath upwelling areas, and the lowest concentrations underneath central gyre areas. These distributions within the clear water reflect surface-water biogenic productivity, lateral injection of particles from shelf areas and surface circulation patterns and require that the combination of downward vertical and horizontal transport processes of particles retain this pattern throughout the upper water column. Below clear water, the distribution of standing crops of suspended particulate concentrations in the lower water column are presented. The integration of mass of all particles per unit area (gross particulate standing crop) reflects a relative distribution similar to that at the surface and at clear water levels, superimposed on which is the strong imprint of boundary currents along the western margins of the Atlantic. Reducing the gross particulate standing crop by the integral of the concentration of clear water yields a net particulate standing crop. The distribution of this reflects primarily the interaction of circulating abyssal waters with the ocean bottom, i.e. a strong nepheloid layer which is coincident with western boundary currents and which diminishes in intensity equatorward. The resuspended particulate loads in the nepheloid layer of the basins west of the Mid-Atlantic Ridge, resulting from interaction of abyssal currents with the bottom, range from ??? 2 ?? 106 tons in the equatorial Guyana Basin to ??? 50 ?? 106 tons in the North American Basin. The total resuspended particulate load in the western basins (111 ?? 106 tons) is almost an order of magnitude greater than that in the basins east of the Mid-Atlantic Ridge (13 ?? 106 tons). The net northward flux of resuspended particles carried in the AABW drops from ??? 8 ?? 106 tons/year between the southern and northern ends of the Brazil Basin and remains ??? 1 ?? 106 tons/year across the Guyana Basin. ?? 1977.

Biscaye, P. E.; Eittreim, S. L.

1977-01-01

287

Structure and evolution of the abyssal jet in the Vema Channel of the South Atlantic  

NASA Astrophysics Data System (ADS)

The Vema Channel represents the only major conduit through which the deepest and coldest (<0.2 °C potential temperature) Antarctic Bottom Water (AABW) flows from the Argentine into the Brazil Basin. From 2003 to 2007 two current meter moorings were present on each side of the Vema Sill, close to the narrowest spot of the Vema Channel. The data from the moorings are compared with earlier current and temperature observations. On average the maximum current core lies ˜100 m above the bottom of the sill with a mean northward speed of 0.3 m s-1. Farther up in the water column where Lower Circumpolar Deep Water and North Atlantic Deep Water prevail, one finds a level of sluggish currents with a southward tendency in the sub-centimeter-per-second range. The lower boundary of a layer of 'no' motion was observed at ˜3700 m depth where the mean potential temperature amounts to 1.5 °C. The evolution of the abyssal warming phenomenon over the last decades with notable fluctuations at the choke point between the Argentine and the Brazil Basin differs from the more stable attitude of deep horizontal currents. Starting with CTD observations in 1972 we find a steady increase of temperatures of the coldest AABW in the Vema Channel. This general trend of rising abyssal potential temperatures of almost 2 mKelvin per year is based on mostly annual CTD observations. The overall warming trend is fully compatible with our three-year moored temperature series in agreement with earlier records with high temporal resolution. Distinct frequently fluctuating horizontal current shear between the western and eastern sides of the Vema Sill may be explained by two different catchment areas for AABW at the mouth of the Vema Channel. One pathway originates at the American continental rise and advects bottom water in form of the deep western boundary current. A second pathway is supplied by an eastern boundary current along the Mid Atlantic Ridge in the Argentine Basin. Both source waters merge at the channel entrance, mix, and their respective strengths can alternate within the sill area.

Zenk, Walter; Visbeck, Martin

2013-01-01

288

The Horoman Peridotite Massif: an Example of Ancient Ultraslow-Spreading Ridge Abyssal Peridotites?  

NASA Astrophysics Data System (ADS)

Ultraslow-spreading ridges (full spreading rate less than 20 mm per year) comprise about one third (lengthwise) of the global ridge system today, and might also have been important in the geologic past, particularly after breakup of large continents. Geochemical studies of abyssal peridotites show that large local- scale (single-dredge to hand specimen scales) variations in isotopic composition, modal abundance of clinopyroxene (CPX), and trace element abundance in CPX are distinct characteristics of ultraslow-spreading ridge peridotites. It is suggested that these local-scale variabilities are produced by melt-rock reaction during melt migration in the mantle (e.g., Warren et al., 2006). We explored using these geochemical characteristics to identify ancient ultraslow-spreading ridge peridotites among "orogenic lherzolite massifs". The Horoman peridotite massif in Hokkaido, Japan, possesses DMM-like initial Nd and Sr isotopic characteristics at the time of melt extraction, and displays large variations in modal CPX (13.2 - 5.2%, only for lherzolites and plagioclase lherzolites) and in trace elements in CPX (e.g., Nd ranges from 0.3 to 10 times C1 chondrite) over a sampling scale length of 150 m. Additionally, there is ample evidence for chromatographic melt-rock reaction in the presence of garnet (Takazawa et al., 1996; Yoshikawa and Nakamura, 2000). These geochemical characteristics are very similar to those observed for the present-day ultraslow-spreading ridge peridotites such as those from the SWIR and Gakkel ridge. A whole-rock Sm-Nd isochron age for the plagioclase lherzolites of 830+/-78 Ma (Yoshikawa and Nakamura, 2000) and a suggestion by Saal et al. (2001) that refertilization of depleted peridotites by a MORB-like magma occurred around 900 Ma, based on the Re-Os systematics, indicate that melt extraction and melt-rock reaction formed the Horoman peridotite massif at 800 to 900 Ma. This time is similar to that, 750 Ma, estimated for formation of the Paleopacific ocean by rifting of the Rodinia supercontinent (e.g., Torsvik, 2003). We suggeset that the Horoman massif could represent abyssal peridotite beneath the Paleopacific ridge when its spreading rate was ultraslow. Saal et al. (2001) J. Petrol., 42, 25-37; Takazawa et al. (1996) Chem. Geol., 134, 3-26; Torsvik (2003) Science, 300, 1379-1381; Yoshikawa and Nakamura (2000) JGR, 105, 2879-2901; Warren et al. (2006) Goldschmidt Conf. Abstract.

Shimizu, N.; Warren, J. M.; Frey, F. A.; Takazawa, E.

2006-12-01

289

Genetic and Morphological Divergences in the Cosmopolitan Deep-Sea Amphipod Eurythenes gryllus Reveal a Diverse Abyss and a Bipolar Species.  

PubMed

Eurythenes gryllus is one of the most widespread amphipod species, occurring in every ocean with a depth range covering the bathyal, abyssal and hadal zones. Previous studies, however, indicated the existence of several genetically and morphologically divergent lineages, questioning the assumption of its cosmopolitan and eurybathic distribution. For the first time, its genetic diversity was explored at the global scale (Arctic, Atlantic, Pacific and Southern oceans) by analyzing nuclear (28S rDNA) and mitochondrial (COI, 16S rDNA) sequence data using various species delimitation methods in a phylogeographic context. Nine putative species-level clades were identified within E. gryllus. A clear distinction was observed between samples collected at bathyal versus abyssal depths, with a genetic break occurring around 3,000 m. Two bathyal and two abyssal lineages showed a widespread distribution, while five other abyssal lineages each seemed to be restricted to a single ocean basin. The observed higher diversity in the abyss compared to the bathyal zone stands in contrast to the depth-differentiation hypothesis. Our results indicate that, despite the more uniform environment of the abyss and its presumed lack of obvious isolating barriers, abyssal populations might be more likely to show population differentiation and undergo speciation events than previously assumed. Potential factors influencing species' origins and distributions, such as hydrostatic pressure, are discussed. In addition, morphological findings coincided with the molecular clades. Of all specimens available for examination, those of the bipolar bathyal clade seemed the most similar to the 'true' E. gryllus. We present the first molecular evidence for a bipolar distribution in a macro-benthic deep-sea organism. PMID:24086322

Havermans, Charlotte; Sonet, Gontran; d'Udekem d'Acoz, Cédric; Nagy, Zoltán T; Martin, Patrick; Brix, Saskia; Riehl, Torben; Agrawal, Shobhit; Held, Christoph

2013-09-25

290

Genetic and Morphological Divergences in the Cosmopolitan Deep-Sea Amphipod Eurythenes gryllus Reveal a Diverse Abyss and a Bipolar Species  

PubMed Central

Eurythenes gryllus is one of the most widespread amphipod species, occurring in every ocean with a depth range covering the bathyal, abyssal and hadal zones. Previous studies, however, indicated the existence of several genetically and morphologically divergent lineages, questioning the assumption of its cosmopolitan and eurybathic distribution. For the first time, its genetic diversity was explored at the global scale (Arctic, Atlantic, Pacific and Southern oceans) by analyzing nuclear (28S rDNA) and mitochondrial (COI, 16S rDNA) sequence data using various species delimitation methods in a phylogeographic context. Nine putative species-level clades were identified within E. gryllus. A clear distinction was observed between samples collected at bathyal versus abyssal depths, with a genetic break occurring around 3,000 m. Two bathyal and two abyssal lineages showed a widespread distribution, while five other abyssal lineages each seemed to be restricted to a single ocean basin. The observed higher diversity in the abyss compared to the bathyal zone stands in contrast to the depth-differentiation hypothesis. Our results indicate that, despite the more uniform environment of the abyss and its presumed lack of obvious isolating barriers, abyssal populations might be more likely to show population differentiation and undergo speciation events than previously assumed. Potential factors influencing species’ origins and distributions, such as hydrostatic pressure, are discussed. In addition, morphological findings coincided with the molecular clades. Of all specimens available for examination, those of the bipolar bathyal clade seemed the most similar to the ‘true’ E. gryllus. We present the first molecular evidence for a bipolar distribution in a macro-benthic deep-sea organism.

Havermans, Charlotte; Sonet, Gontran; d'Udekem d'Acoz, Cedric; Nagy, Zoltan T.; Martin, Patrick; Brix, Saskia; Riehl, Torben; Agrawal, Shobhit; Held, Christoph

2013-01-01

291

Chenier Plain Coast, Louisiana: Seasonal to Decadal-Scale Shoreline Evolution and Response to Episodic Storm Events  

NASA Astrophysics Data System (ADS)

Multiple aerial photographic surveys conducted above the chenier plain coast, Louisiana, between 1987 and 2001 reveal rapid morphologic evolution along this mud-dominated shoreline west of the Atchafalaya River. Mudflat progradation is apparent on sub-seasonal time scales, as sediment derived from the Atchafalaya River plume and shallow inner shelf accretes on to the coast. Much of this accreted sediment is subsequently transported to the west by prevailing longshore currents. On a decadal scale, erosion dominates the central and eastern chenier plain, with the exception of a 13-km strip of shoreline where pronounced accretion has formed an increasingly stable mudflat, the result of both natural processes and reworking of dredged sediment. Aerial still photography, aerial video surveys, synoptic weather-type classifications, and the historical hurricane record have been employed to generate an overview of the chenier plain's response to episodic storm events. Chenier plain accretion is shown to correlate with storm activity during winter cold fronts, associated with southerly winds that force resuspension and onshore transport of sediment. It is estimated that annual onshore mud deposition on the eastern chenier plain is equivalent to approximately 8 to 16% of the mass of sediment leaving Atchafalaya Bay each year. This study provides additional insight into the recently recognized phenomenon of fine-grained sediment deposition under highly energetic conditions. Abundant suspended sediment near shore leads to rapid attenuation of wave energy, encouraging deposition, in stark contrast to erosion of sandy beaches under similar conditions. These results attest to the ability of cold front storms, hurricanes, and tropical storms to cause aggradation, progradation, and increased lateral continuity of mudflats in the presence of abundant fine-grained sediment. Such powerful storms have not previously been appropriately recognized as such potentially important agents of coastal accretion.

Draut, A. E.; Huh, O. K.; Moeller, C. C.; Grymes, J. M.; Kineke, G. C.

2002-12-01

292

Direct connectivity between upstream and downstream promotes rapid response of lower coastal-plain rivers to land-use change  

NASA Astrophysics Data System (ADS)

Low-relief fluvial systems that originate in the lower coastal plain and discharge into estuaries are common along passive margins. These watersheds are thought to be disconnected from their termini by floodplains, which buffer the sediment-routing system by sequestration. Here, we present a detailed study of the Newport River, a typical lower coastal-plain system, which reveals high connectivity between watershed and delta. Connectivity is measured as the time lag between initiation of a silviculture operation, which increased landscape erosion, and when the sediment appeared at the bay-head delta. The time lag, measured from aerial photographs and sedimentation rates calculated from 210Pb- and 137Cs-activities in cores from the watershed and delta, is <3 years. Most lower coastal-plain rivers are steeper and have less floodplain accommodation available for storage than their larger counterparts that originate landward of the fall line, which promotes higher connectivity between upstream and downstream.

Mattheus, Christopher R.; Rodriguez, Antonio B.; McKee, Brent A.

2009-10-01

293

Lava Flows on Coastal Plain  

USGS Multimedia Gallery

The lava flows on the coastal plain, which show up as the light colored flows in the foreground, are erupted into the TEB tube system from the D fissure which first opened up in July 2007. This vent is faintly visible as a fuming source in the background near the upper left corner of the photo. Smal...

2010-06-18

294

49 CFR 229.64 - Plain bearings.  

Code of Federal Regulations, 2012 CFR

... 2012-10-01 2012-10-01 false Plain bearings. 229.64 Section 229.64 Transportation...Requirements Suspension System § 229.64 Plain bearings. A plain bearing box shall contain visible free oil and may not...

2012-10-01

295

49 CFR 229.64 - Plain bearings.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 2011-10-01 false Plain bearings. 229.64 Section 229.64 Transportation...Requirements Suspension System § 229.64 Plain bearings. A plain bearing box shall contain visible free oil and may not...

2011-10-01

296

Aquatic sediments  

SciTech Connect

A literature review of pollution in aquatic sediments is presented. Studies on analytical and sampling methods are discussed, along with heavy metals, organic compounds, and modeling and sediment transport. (JM)

DePinto, J.V.; Young, T.C.; Martin, S.C.

1983-06-01

297

Development of abyssal circulation in the eastern North Atlantic: benthic foraminiferal carbon isotopic evidence  

SciTech Connect

The eastern basin of the northern North Atlantic at present is ventilated by overflow of the Iceland-Faeroe Ridge, Faeroe Bank Channel, and Wyville-Thompson Ridge. The evolution of Cenozic abyssal circulation of this region was related to tectonic opening and subsidence of these sills. The authors used delta/sup 13/C records of the benthic foraminifera Cibicidoides to decipher the timing of tectonically-controlled changes in bottom-water circulation in the eastern North Atlantic. Records from Site 608 show that from about 24 to 15 Ma delta/sup 13/C values in Kings Trough were depleted compared to western North Atlantic values and were, in fact, more similar to Pacific values. This reflects lower ventilation of the Kings Trough region compared to the well-oxygenated western North Atlantic. Oligocene delta/sup 13/C comparisons of Site 119 (Bay of Biscay) with western North Atlantic records suggests that the eastern basin was also relatively isolated prior to 24 Ma. At about 15 Ma, delta/sup 13/C values at Site 608 attained values similar to the western North Atlantic, indicating increased eastern basin ventilation in the middle Miocene. This increased advection into the eastern basin pre-dated a major delta/sup 18/O increase which occurred at about 14.6 Ma. Subsidence estimates of the Greenland-Scotland Ridge indicate that the deepening of the Iceland-Faeroe Ridge was coincident with the marked change in eastern basin deep-water ventilation.

Miller, K.G.; Fairbanks, R.G.; Thomas, E.

1985-01-01

298

Strong Flows of Bottom Water in Abyssal Channels of the Atlantic  

NASA Astrophysics Data System (ADS)

Analysis of bottom water transport through the abyssal channels of the Atlantic Ocean is presented. The study is based on recent observations in the Russian expeditions and historical data. A strong flow of Antarctic Bottom Water from the Argentine Basin to the Brazil Basin through the Vema Channel is observed on the basis of lowered profilers and anchored buoys with current meters. The further flow of bottom water in the Brazil Basin splits in the northern part of the basin. Part of the bottom water flows to the East Atlantic through the Romanche and Chain fracture zones. The other part follows the bottom topography and flows to the northwester into the North American Basin. Part of the northwesterly flow propagates through the Vema Fracture Zone into the Northeastern Atlantic. This flow generally fills the bottom layer in the Northeastern Atlantic basins. The flows of bottom waters through the Romanche and Chain fracture zones do not spread to the Northeast Atlantic due to strong mixing in the equatorial zone and enhanced transformation of bottom water properties.

Morozov, E. G.

299

Tillage effects on rainfall partitioning and sediment yield from an ultisol in central Alabama  

Microsoft Academic Search

Coastal Plain soils in the Southeast have been intensively cropped, traditionally managed under conventional tillage practices, and are susceptible to erosion. Conservation tillage systems have significant potential as a management tool for row crop production, especially on sandy surface soils of the Coastal Plain because they reduce soil loss and conserve water. We quantified rainfall partitioning and sediment delivery from

C. C. Truman; J. N. Shaw; D. W. Reeves

300

Tectonic control of Eocene arkosic sediment deposition, Oregon and Washington  

Microsoft Academic Search

Chronostratigraphic and geographic studies of Eocene arkosic sandstones suggest deposition during a volcanically quiet interval resulting from the westward jump of the Farallon-Kula plate subduction zone in Oregon and Washington. The Eocene arkosic sandstones were deposited as part of a broad fluvial plain-coastal plain-shelf margin basin complex extending throughout Oregon and Washington between uplands of Mesozoic rocks. Feldspathic-quartzose sediments were

J. M. Armentrout; A. R. Ulrich

1983-01-01

301

Early Holocene Landscape evolution of Thessaloniki Plain, Northern Greece  

NASA Astrophysics Data System (ADS)

Seven cores from the western part of the Thessaloniki plain have been drilled and analysed for palaeoenvironmental studies. This paper aims to detail the links between the landscape changes and the human occupation of the actual largest deltaic plain of Greece during Neolithic Times. During the maximum of the last post glacial marine transgression, this large alluvial plain was occupied by a wide bay, subsequently affected by a marine regression running from the west to the east. Facies identification, geochemical analyses, radiocarbon dating and magnetic susceptibility measurements revealed different sediment environments and helped to redefine the precise position of the different Neolithic settlements from 6000 BC and 3000 BC. The results highlight the presence of large marine bay at 6000 years cal.BC and gradually a lagoon stage and an important peat stage developped in context of deceleration of the sea level rise. Archaeological studies (Bintliff, 1976; Rodden & Wardle, 1996) were incorporated into the work and the interpretation must be reconsidered with the help of the new data presented here. Moreover, the previous geoarchaeological studies (Ghilardi, 2007) must be completed for the early holocene.

Ghilardi, Matthieu

2010-05-01

302

Suspended-sediment and fresh-water discharges in the Ob and Yenisey rivers, 1960-1988  

Microsoft Academic Search

Of the world's great rivers, the Ob and Yenisey rank among the largest suppliers of fresh water and among the smallest suppliers of suspended sediment to the coastal ocean. Sediment in the middle reaches of the rivers is mobilized from bordering terraces and exchanged between channels and flood plains. Sediment in the lower reaches of these great rivers is deposited

R. H. Meade; N. N. Bobrovitskaya; V. I. Babkin

2000-01-01

303

CTD (Conductivity-Temperature-Depth) Data from the Madeira and Iberian Abyssal Plains. Charles Darwin Cruises 3/85 and 9A/85.  

National Technical Information Service (NTIS)

Conductivity-temperature-depth (CTD) data from areas of the Atlantic considered for radioactive waste disposal were obtained to support the deployment of deep SOFAR floats and of deep moored current meters, the latter near the Great Meteor East site. All ...

P. M. Saunders

1986-01-01

304

A fossil, serpentinization-related hydrothermal vent, Ocean Drilling Program Leg 173, Site 1068 (Iberia Abyssal Plain): Some aspects of mineral and fluid chemistry  

NASA Astrophysics Data System (ADS)

The basement at Site 1068, Ocean Drilling Program (ODP) Leg 173 (serpentinized peridotite in fault contact with overlying amphibolite-clast-dominated sedimentary and tectonic breccias) is host to a hydrothermal system rooted in serpentinization reactions occurring at depth. The serpentinite grades downward from cataclasites at the fault, through brecciated, recrystallized, tochilinite-bearing serpentinite, to awaruite-bearing massive, mesh-textured serpentinite. Andradite is common throughout and is a major sink for iron. The breccias are similarly zoned, from tectonized rocks near the fault upward into sedimentary breccias. Mg-silicate vein assemblages and rodingitized amphibolite clasts near the fault give way to calcite veins and nonpervasive albite-chlorite alteration upsection. Marcasite (± pyrrhotite at the fault) is the sulfide phase and occurs only in the tectonic breccias. Fe oxides are magnetite near the fault and hematite and ferric oxyhydroxides upsection. The zonation reflects mixing of seawater with a fluid whose composition (low fO2, fS2 Si, CO2, high Ca, Fe, Ca/Mg, pH) is controlled by serpentinization reactions. The deepest serpentinites have strongly reduced mineral assemblages that are unusual in a totally serpentinized peridotite. This probably reflects equilibration with a fluid derived from ongoing serpentinization at depth. The upper serpentinites, on through the mineral sequences seen in the breccias reflect increasing input from seawater upsection. Increased fO2 and fS2 stabilizes increasingly S- and O-rich assemblages. Calcite (and ferric oxide) precipitation decreases pH, stabilizing marcasite. Relative to mid-ocean ridge hydrothermal systems, fluids in serpentinite-hosted hydrothermal systems are poor in S and rich in Mg and are unlikely to host large sulfide ore deposits.

Beard, James S.; Hopkinson, Laurence

2000-07-01

305

South-directed mass wasting from the Galicia Bank: How might it affect interpretations of seismic and drilling results in the Iberia Abyssal Plain?  

Microsoft Academic Search

Recently, we have interpreted seismic profiles ISE-1 and ISE-9 crossing the west and south sides of the Galicia Bank, west of Spain in the Atlantic Ocean, to show evidence of very large mass wasting events presumed to have occurred late in the process of continental breakup and the initiation of seafloor spreading. The events are driven by large topographic relief

D. S. Sawyer; S. A. Clark

2006-01-01

306

High Plains Aquifer Hydrologic Observatory  

NASA Astrophysics Data System (ADS)

The High Plains Aquifer encompasses 174,000 square miles in eight states and provides the primary source of potable water to the region. The hydrologic cycle exhibits great diversity across this geological basin, with significant expanses experiencing sustained declines in groundwater elevation (e.g., portions of the southern and central basins in Kansas, New Mexico, Oklahoma, and Texas) while other areas are experiencing rises (e.g., portions of the northern basin in central Nebraska). The proposed High Plains Aquifer Hydrologic Observatory would promote significant scientific advancement in hydrology related to: (1) Recharge and evapotranspiration, (2) Surface water-groundwater exchange in dynamic riparian corridors, (3) Ecological role of vegetation in the hydrologic cycle, (4) Human systems and the hydrologic cycle, (5) Multi-scale monitoring, modeling & analysis, (6) Climate change studies, and (7) Utilization of remote sensing technology

Steward, D. R.

2004-12-01

307

Plain Polynomial Arithmetic on GPU  

NASA Astrophysics Data System (ADS)

As for serial code on CPUs, parallel code on GPUs for dense polynomial arithmetic relies on a combination of asymptotically fast and plain algorithms. Those are employed for data of large and small size, respectively. Parallelizing both types of algorithms is required in order to achieve peak performances. In this paper, we show that the plain dense polynomial multiplication can be efficiently parallelized on GPUs. Remarkably, it outperforms (highly optimized) FFT-based multiplication up to degree 212 while on CPU the same threshold is usually at 26. We also report on a GPU implementation of the Euclidean Algorithm which is both work-efficient and runs in linear time for input polynomials up to degree 218 thus showing the performance of the GCD algorithm based on systolic arrays.

Anisul Haque, Sardar; Moreno Maza, Marc

2012-10-01

308

The Arctic Coastal Plain, Alaska  

NSDL National Science Digital Library

This tutorial is about the Arctic tundra biome; the plants and animals found there; and the amount of sunlight, temperatures, seasons and permafrost. Examples of Arctic ecosystem interactions, food chains, and biological adaptations to the Arctic Coastal Plain are given. There are photographs of wolves, caribou, arctic hares, minks, lemmings, arctic foxes, polar bears, seals, walruses, ptarmigans, hawks, and owls. Definitions of ecosystem terms can be found by clicking on the term within the tutorial.

309

Serratotantulus chertoprudae gen. et sp. n. (Crustacea, Tantulocarida, Basipodellidae): A new tantulocaridan from the abyssal depths of the Indian Ocean.  

PubMed

A single tantulus larva was found at the abyssal depth of the Indian Ocean attached to a harpacticoid host of the family Cletodidae. It represents a new genus and species of Tantulocarida, family Basipodellidae. Its ultrastructure was studied with SEM. This genus can be easily distinguished from the other genera of Basipodellidae by the pore pattern, bilobed oral disk with strong longitudinal ridges and the posterior projection of the cephalic shield. A morphological analysis of two related families Basipodellidae and Deothertridae shows that they represent polyphyletic taxa and need further revision. PMID:21669851

Savchenko, Alexandra S; Kolbasov, Gregory A

2009-05-22

310

Deep-water sedimentary environments of the northwestern Weddell Sea and South Sandwich Islands, Antarctica  

Microsoft Academic Search

Two transects have been sampled using short cores (multi and box), seabed photography, video sequences, and sediment profile images across the northwestern Weddell Sea and South Sandwich Forearc, Antarctica. A total of 12 core stations were examined for sediment structure, texture and composition to determine their depositional history. Four of the core stations from the Weddell Continental Slope, Abyssal Plain

John A. Howe; Tracy M. Shimmield; Robert Diaz

2004-01-01

311

Middle and upper jurassic depositional environments at outer shelf and slope of Baltimore Canyon Trough  

Microsoft Academic Search

New CDP data acquired in the Baltimore Canyon Trough during project LASE made it possible to map a continuous Jurassic sedimentary sequence from the continental margin to the abyssal plain without interruption by basement structures. Intense carbonate sedimentation is inferred at the outer shelf during the Middle and Late Jurassic. Carbonate sedimentation probably started during the Middle Jurassic with a

L. A. Gamboa; P. L. Stoffa; M. Truchan

1985-01-01

312

Yellowstone-Snake River Plain seismic profilling experiment: Crustal structure of the eastern Snake River Plain  

SciTech Connect

Seismic refraction profiles recorded along the eastern Snake River Plain (ESRP) in southeastern Idaho during the 1978 Yellowstone-Snake River Plain cooperative seismic profiling experiment are interpreted to infer the crustal velocity and attenuation (Q-1) structure of the ESRP. Travel-time and synthetic seismogram modeling of a 250 km reversed refraction profile as well as a 100 km detailed profile indicate that the crust of the ESRP is highly anomalous. Approximately 3 to 6 km of volcanic rocks (with some interbedded sediments) overlie an upper-crustal layer (compressional velocity approx. =6.1 km/s) which thins southwestward along the ESRP from a thickness of 10 km near Island Park Caldera to 2 to 3 km beneath the central and southwestern portions of the ESRP. An intermediate-velocity (approx. =6.5 km/s) layer extends from approx. =10 to approx. =20 km depth. a thick (approx. =22 km) lower crust of compressional velocity 6.8 km/s, a total crustall thickness of approx. =42 km, and a P/sub n/ velocity of approx. =7.9 km/s is observed in the ESRP, similar to the western Snake River Plain and the Rocky Mountains Provinces. High attenuation is evident on the amplitude corrected seismic data due to low-Q values in the volcanic rocks (Q/sub p/ = 20 to 200) and throughout the crust (Q/sub p/ = 160 to 300). Based on these characteristics of the crustal structure and volcanic-age progression data, it is suggested that the ESRP has resulted from an intensitive period of intrusion of mantle-derived basaltic magma into the upper crust generating explosive silicic volcanism and associated regional uplift and caldera collapse. This activity began about 15 m.y. ago in southwestern Idaho and has migrated northeast to its present position at Yellowstone. Subsequent cooling of the intruded upper crust results in the 6.5 km/s velocity intermediate layer. Crustal subsidence and periodic basaltic volcanism as represented by the ESRP complete the sequence of crustal evolution.

Braile, L.W.; Smith, R.B.; Ansorge, J.; Baker, M.R.; Sparlin, M.A.; Prodehl, C.; Schilly, M.M.; Healy, J.H.; Mueller, S.; Olsen, K.H.

1982-04-10

313

A qualitative assessment of the influence of bioturbation in Lake Baikal sediments  

NASA Astrophysics Data System (ADS)

The impact of bioturbation in Lake Baikal sediments, particularly on rhythmic layering and mixing, was assessed by studying the actual vertical distribution of benthic animals in continuous accumulation zones selected by seismic survey (Vydrino Shoulder, Posolskoe Bank, Continent Ridge). To assess the influence of the bioturbation, animals were extracted from short cores and identified at the relevant taxonomic level. The faunal distribution is examined in parallel with the bioturbation tracks observed in thin section. Oligochaeta, Nematoda, Ostracoda, Copepoda, Gammaridae, Chironomidae and Hydrachnidia were found inhabiting the sediment. Among them, only oligochaete worms were assumed to have a significant impact on sediment mixing because of their “conveyor belt” feeding. The other two most abundantly sampled groups, nematods and copepods, belong to the interstitial fauna that has no significant impact on the vertical displacement of sediment particles and do not ingest the sediment. The presence of a benthic fauna as deep as 15 cm in the sediment indicates that the possibility of sediment disturbance by invertebrate activity cannot be dismissed in Lake Baikal. The effect of biological mixing is more limited in the deepest stations because the number of potential bioturbators is reduced, qualitatively as well as quantitatively. Located in the abyssal zone, Continent and Vydrino (but outside turbidites) deep stations appear to be most promising sediment records for tracking climate signal at high resolution.

Martin, Patrick; Boes, Xavier; Goddeeris, Boudewijn; Fagel, Nathalie

2005-04-01

314

Coastal morphodynamics and Chenier-Plain evolution in southwestern Louisiana, USA: A geomorphic model  

NASA Astrophysics Data System (ADS)

Using 28 topographic profiles, air-photo interpretation, and historical shoreline-change data, coastal processes were evaluated along the Chenier Plain to explain the occurrence, distribution, and geomorphic hierarchy of primary landforms, and existing hypotheses regarding Chenier-Plain evolution were reconsidered. The Chenier Plain of SW Louisiana, classified as a low-profile, microtidal, storm-dominated coast, is located west and downdrift of the Mississippi River deltaic plain. This Late-Holocene, marginal-deltaic environment is 200 km long and up to 30 km wide, and is composed primarily of mud deposits capped by marsh interspersed with thin sand- and shell-rich ridges (“cheniers”) that have elevations of up to 4 m. In this study, the term “ridge” is used as a morphologic term for a narrow, linear or curvilinear topographic high that consists of sand and shelly material accumulated by waves and other physical coastal processes. Thus, most ridges in the Chenier Plain represent relict open-Gulf shorelines. On the basis of past movement trends of individual shorelines, ridges may be further classified as transgressive, regressive, or laterally accreted. Geomorphic zones that contain two or more regressive, transgressive, or laterally accreted ridges are termed complexes. Consequently, we further refine the Chenier-Plain definition by Otvos and Price [Otvos, E.G. and Price, W.A., 1979. Problems of chenier genesis and terminology—an overview. Marine Geology, 31: 251 263] and define Chenier Plain as containing at least two or more chenier complexes. Based on these definitions, a geomorphic hierarchy of landforms was refined relative to dominant process for the Louisiana Chenier Plain. The Chenier Plain is defined as a first-order feature (5000 km2) composed of three second-order features (30 to 300 km2): chenier complex, beach-ridge complex, and spit complex. Individual ridges of each complex type were further separated into third-order features: chenier, beach ridge, and spit. To understand the long-term evolution of a coastal depositional system, primary process response mechanisms and patterns found along the modern Chenier-Plain coast were first identified, especially tidal-inlet processes associated with the Sabine, Calcasieu, and Mermentau Rivers. Tidal prism (?) and quantity of littoral transport (Mtotal) are the most important factors controlling inlet stability. Greater discharge and/or tidal prism increase the ability of river and estuarine systems to interrupt longshore sediment transport, maintain and naturally stabilize tidal entrances, and promote updrift deposition. Thus, prior to human modification and stabilization efforts, the Mermentau River entrance would be classified as wave-dominated, Sabine Pass as tide-dominated, and Calcasieu Pass as tide-dominated to occasionally mixed. Hoyt [Hoyt, J.H., 1969. Chenier versus barrier, genetic and stratigraphic distinction. Am. Assoc. Petrol. Geol. Bull., 53: 299 306] presented the first detailed depositional model for chenier genesis and mudflat progradation, which he attributed to changes in Mississippi River flow direction (i.e., delta switching) caused by upstream channel avulsion. However, Hoyt's model oversimplifies Chenier-Plain evolution because it omits ridges created by other means. Thus, the geologic evolution of the Chenier Plain is more complicated than channel avulsions of the Mississippi River, and it involved not only chenier ridges (i.e., transgressive), but also ridges that are genetically tied to regression (beach ridges) and lateral accretion (recurved spits). A six-stage geomorphic process-response model was developed to describe Chenier-Plain evolution primarily as a function of: (i) the balance between sediment supply and energy dissipation associated with Mississippi River channel avulsions, (ii) local sediment reworking and lateral transport, (iii) tidal-entrance dynamics, and (iv) possibly higher-than-present stands of Holocene sea level. Consequently, the geneses of three different ridge types (transgressive, regressive, and lat

McBride, Randolph A.; Taylor, Matthew J.; Byrnes, Mark R.

2007-08-01

315

Water Isotopic and Hydrochemical Evolution of a Lake Chain in the Northern Great Plains and its Paleoclimatic Implications  

Microsoft Academic Search

Oxygen isotopes and geochemistry from lake sediments are commonly used as proxies of past hydrologic and climatic conditions, but the importance of present -day hydrologic processes in controlling these proxies are sometimes not well established and understood. Here we use present-day hydrochemical data from 13 lakes in a hydrologically connected lake chain in the northern Great Plains (NGP) to investigate

Zicheng Yu; Emi Ito; Daniel R. Engstrom

2001-01-01

316

Water isotopic and hydrochemical evolution of a lake chain in the northern Great Plains and its paleoclimatic implications  

Microsoft Academic Search

Oxygen isotopes and geochemistry from lake sediments are commonly used as proxies of past hydrologic and climatic conditions, but the importance of present-day hydrologic processes in controlling these proxies are sometimes not well established and understood. Here we use present-day hydrochemical data from 13 lakes in a hydrologically connected lake chain in the northern Great Plains (NGP) to investigate isotopic

Zicheng Yu; Emi Ito; Daniel R. Engstrom

2002-01-01

317

Disequilibria in the uranium decay series in sedimentary deposits at Allen's cave, nullarbor plain, Australia: Implications for dose rate determinations  

Microsoft Academic Search

Disequilibrium in the uranium decay series can cause a time-dependent variation in the radiation dose received by deposited sediments. In luminescence and ESR dating studies, the observation of disequilibrium usually requires modelling of the variation in dose rate as a function of burial time. In this paper, we report on radionuclide data collected from Allen's Cave on the Nullarbor Plain,

Jon M. Olley; Richard G. Roberts; Andrew S. Murray

1997-01-01

318

First seismic imaging results of tectonically complex structures at shallow depths beneath the northwest Canterbury Plains, New Zealand  

Microsoft Academic Search

Seismogenic structures underlie many regions of the vast Canterbury Plains on the South Island of New Zealand. Most of these structures are hidden beneath a layer of rapidly deposited Late Pleistocene sediments, the youth and thickness of which make the general application of conventional paleoseismological studies impractical. In an attempt to improve our understanding of potentially active structures in this

C. Dorn; S. Carpentier; A. E. Kaiser; A. G. Green; H. Horstmeyer; F. Campbell; J. Campbell; R. Jongens; M. Finnemore; D. C. Nobes

2010-01-01

319

Prolonged carbonate diagenesis under an evolving late cenozoic climate; Nullarbor Plain, southern Australia  

NASA Astrophysics Data System (ADS)

The Nullarbor Plain in southern Australia, the largest areal karst on the globe, is a ~ 240,000 km2 uplifted succession of Cenozoic marine carbonates whose surface has been exposed for 14 to 15 m.y. The middle Miocene Nullarbor Limestone forms the upper surface of the plain and hosts a complex and prolonged record of meteoric diagenesis. Such a complete record offers unique insights into the effects of climate, tectonics, sea level, topography, and hydrology on the style and placement of numerous diagenetic events in flat low lying carbonate plains. Alteration took place during three broad phases comprising eight stages that are interpreted to have formed against a background of dramatic climate change. Middle Miocene phase one diagenesis took place under a humid climate and resulted in rapid mineral equilibration, calcite cementation, extensive karst development, and finally widespread lacustrine and palustrine sedimentation. Resultant palustrine sediments, especially terrestrial ooids, are now preserved at the surface and in underlying karst cavities. Latest middle Miocene to middle Pliocene phase two diagenesis occurred during a prolonged period (~ 8 m.y.) of temperate climate and resulted in initial deep cave dissolution during low sea levels and later shallow cave development in the course of a high sea level. Onset of a somewhat more arid climate in the latest Pliocene led to the development of the modern desolate landscape of the Plain. This final phase of diagenesis involved creation of solution pits filled with black limestone pebbles, open and closed dolines with associated colluvium fill, and pervasive pedogenic calcrete. The Nullarbor Plain demonstrates that low lying carbonate plains can have low surficial erosion rates, precisely record relative sea level positions, be able to have extensive caves with extended periods of arrested calcite precipitation, and finally host extensive terrestrial ooid deposits. The importance of this comprehensive paragenetic record is its applicability to not only recognize unconformities in the rock record but to better appreciate the climate in which they formed.

Miller, Cody R.; James, Noel P.; Bone, Yvonne

2012-06-01

320

Wet coastal plain tundra III  

SciTech Connect

This year's census data for the wet coastal plain tundra in Alaska; North Slope Borough, 3 km SSE of Naval Arctic Research Laboratory, Barrow; 71/sup 0/ 18'N, 156/sup 0/ 38'W; Barrow Quadrangle, USGS reflect a decrease in the total number of species breeding. However, total breeding density rose by 82%. Lapland Longspurs (up 105%) accounted for half of this increase while the rest was spread among many species. There was a total of 8 species; 40.5 territorial males or females (162/km/sup 2/, 66/100 acres).

Myers, J.P.; Gellman, S.T.; Pitelka, F.A.

1980-01-01

321

Quaternary sedimentation in a tide-dominated estuary, northern New England  

Microsoft Academic Search

Northern New England is characterized by rocky shorelines frequently interrupted by linear embayments or estuaries. In contrast to more commonly studied coastal plain estuaries further south, these embayments often have relatively limited fluvial sediment supply, are affected by ice, and are strongly influenced by bedrock geology. High resolution subbottom seismics, sidescan sonar, surficial sediment sampling and gravity coring were conducted

1993-01-01

322

Holocene delta evolution and sediment discharge of the Mekong River southern Vietnam  

Microsoft Academic Search

Evolutionary changes, delta progradation, and sediment discharge of the Mekong River Delta, southern Vietnam, during the late Holocene are presented based on detailed analyses of samples from six boreholes on the lower delta plain. Sedimentological and chronostratigraphic analyses indicate clearly that the last 3 kyr were characterized by delta progradation under increasing wave influence, southeastward sediment dispersal, decreasing progradation rates,

Thi Kim Oanh Ta; Van Lap Nguyen; Masaaki Tateishi; Iwao Kobayashi; Susumu Tanabe; Yoshiki Saito

2002-01-01

323

Rates of Microbial Metabolism in Deep Coastal Plain Aquifers  

PubMed Central

Rates of microbial metabolism in deep anaerobic aquifers of the Atlantic coastal plain of South Carolina were investigated by both microbiological and geochemical techniques. Rates of [2-14C]acetate and [U-14C]glucose oxidation as well as geochemical evidence indicated that metabolic rates were faster in the sandy sediments composing the aquifers than in the clayey sediments of the confining layers. In the sandy aquifer sediments, estimates of the rates of CO2 production (millimoles of CO2 per liter per year) based on the oxidation of [2-14C] acetate were 9.4 × 10?3 to 2.4 × 10?1 for the Black Creek aquifer, 1.1 × 10?2 for the Middendorf aquifer, and <7 × 10?5 for the Cape Fear aquifer. These estimates were at least 2 orders of magnitude lower than previously published estimates that were based on the accumulation of CO2 in laboratory incubations of similar deep subsurface sediments. In contrast, geochemical modeling of groundwater chemistry changes along aquifer flowpaths gave rate estimates that ranged from 10?4 to 10?6 mmol of CO2 per liter per year. The age of these sediments (ca. 80 million years) and their organic carbon content suggest that average rates of CO2 production could have been no more than 10?4 mmol per liter per year. Thus, laboratory incubations may greatly overestimate the in situ rates of microbial metabolism in deep subsurface environments. This has important implications for the use of laboratory incubations in attempts to estimate biorestoration capacities of deep aquifers. The rate estimates from geochemical modeling indicate that deep aquifers are among the most oligotrophic aquatic environments in which there is ongoing microbial metabolism.

Chapelle, Francis H.; Lovley, Derek R.

1990-01-01

324

Rates of microbial metabolism in deep coastal plain aquifers  

USGS Publications Warehouse

Rates of microbial metabolism in deep anaerobic aquifers of the Atlantic coastal plain of South Carolina were investigated by both microbiological and geochemical techniques. Rates of [2-14C]acetate and [U-14C]glucose oxidation as well as geochemical evidence indicated that metabolic rates were faster in the sandy sediments composing the aquifers than in the clayey sediments of the confining layers. In the sandy aquifer sediments, estimates of the rates of CO2 production (millimoles of CO2 per liter per year) based on the oxidation of [2-14C]acetate were 9.4 x 10-3 to 2.4 x 10-1 for the Black Creek aquifer, 1.1 x 10-2 for the Middendorf aquifer, and <7 x 10-5 for the Cape Fear aquifer. These estimates were at least 2 orders of magnitude lower than previously published estimates that were based on the accumulation of CO2 in laboratory incubations of similar deep subsurface sediments. In contrast, geochemical modeling of groundwater chemistry changes along aquifer flowpaths gave rate estimates that ranged from 10-4 to 10-6 mmol of CO2 per liter per year. The age of these sediments (ca. 80 million years) and their organic carbon content suggest that average rates of CO2 production could have been no more than 10-4 mmol per liter per year. Thus, laboratory incubations may greatly overestimate the in situ rates of microbial metabolism in deep subsurface environments. This has important implications for the use of laboratory incubations in attempts to estimate biorestoration capacities of deep aquifers. The rate estimates from geochemical modeling indicate that deep aquifers are among the most oligotrophic aquatic environments in which there is ongoing microbial metabolism.

Chapelle, F. H.; Lovley, D. R.

1990-01-01

325

Electrophoretic and biometric variability in the abyssal grenadier Coryphaenoides armatus of the western North Atlantic, eastern South Pacific and eastern North Pacific Oceans  

Microsoft Academic Search

Specimens of the abyssal grenadier Coryphaenoides armatus (Hector, 1875), from the western North Atlantic and eastern North Pacific Oceans were compared electrophoretically at 27 presumptive gene loci. At 6 of the 7 polymorphic loci there were only minor differences in allelic frequencies but a nearly fixed difference was found at one locus, phosphogluconate dehydrogenase. Eastern North Pacific grenadiers typically have

R. R. Wilson; R. S. Waples

1984-01-01

326

Mineralogical and chemical records of melt-rock and fluid-rock interaction in abyssal peridotites from the Mid-Atlantic Ridge (ODP Leg 209)  

Microsoft Academic Search

At slow- and ultraslow-spreading mid-ocean ridges, abyssal peridotites are commonly exposed at the seafloor. They are chemically influenced by interaction with both gabbroic\\/plagiogranitic melts and seawater-derived fluids. Shear zones crosscutting the peridotites are marked by talc- and\\/or chlorite-bearing lithologies, which are often referred to as \\

N. Jöns; W. Bach; T. Schroeder; F. Klein

2009-01-01

327

Hydrogeologic Framework of the New Jersey Coastal Plain  

USGS Publications Warehouse

This report presents the results of a water-resources, oriented subsurface mapping program within the Coastal Plain of New Jersey. The occurrence and configuration of 15 regional hydrogeologic units have been defined, primarily on the basis of an interpretation of borehole geophysical data. The nine aquifers and six confining beds are composed of unconsolidated clay, silt, sand, and gravel and range in age from Cretaceous to Quaternary. Electric and gamma-ray logs from more than 1,000 Coastal Plain wells were examined. Of these, interpretive data for 302 sites were selected, on the basis of logged depth, quality of data, and data distribution, to prepare structure contour and thickness maps for each aquifer and a thickness map for each confining bed. These maps, together with 14 hydrogeologic sections, show the geometry, lateral extent, and vertical and horizontal relationships among the 15 hydrogeologic units. The hydrogeologic maps and sections show that distinct lower, middle, and upper aquifers are present within the Potomac, Raritan-Magothy aquifer system near the Delaware River from Burlington County to Salem County. Although the lower aquifer is recognized only in this area, the middle aquifer extends into the northeastern Coastal Plain of New Jersey, where it is stratigraphically equivalent to the Farrington aquifer. The upper aquifer extends throughout most of the New Jersey Coastal Plain and is stratigraphically equivalent to the Old Bridge aquifer in the northeastern Coastal Plain. The overlying Merchantville-Woodbury confining bed is the most regionally extensive confining bed within the New Jersey Coastal Plain. Its thickness ranges from less than 100 feet near the outcrop to more than 450 feet along the coast. The Englishtown aquifer system acts as a single aquifer throughout most of its subsurface extent, but it contains two water-bearing sands in pars of Monmouth and Ocean Counties. The overlying Marshalltown-Wenonah confining bed is a thin, leaky unit ranging in thickness from approximately 20 to 80 feet. The Wenonah-Mount Laurel aquifer is identified in the subsurface throughout the New Jersey Coastal Plain southeast of its outcrop area. Sediments that overlie the Wenonah-Mount Lauren aquifer and that are subjacent to the major aquifers within the Kirkwood Formation and the Cohansey Sand are described hydrologically as a composite confining bed. These include the Navesink Formation, Red Bank Sand, Tinton Sand, Hornerstown Sand, Vincentown Formation, Manasquan Formation, Shark River Formation, and Piney Point Formation and the basal clay of the Kirkwood Formation.. The Vincentown Formation functions as n aquifer within 3 to 10 miles downdip of its outcrop area. In areas farther downdip the Vincentown Formation functions as a confining bed. The Piney Point aquifer is laterally persistent from the southern New Jersey Coastal Plain northward into parts of Burlington and Ocean Counties. The Atlantic City 800-foot sand of the Kirkwood Formation can be recognized in the subsurface along coastal areas of Cape May, Atlantic, and southern Ocean Counties, but inland only as far west as the extent of the overlying confining bed. In areas west of the extent of the overlying confining bed, the Kirkwood Formation is in hydraulic connection with the overlying Cohansey Sand and younger surficial deposits and functions as an unconfined aquifer.

Zapecza, Otto S.

1989-01-01

328

Early chromite mining and agricultural clearance: Opportunities for the investigation of agricultural sediment dynamics in the Eastern Piedmont (USA)  

USGS Publications Warehouse

Many flood plains in the Eastern Piedmont (USA) are buried under deposits of sediment resulting from European agricultural clearance. Classic radioisotopic dating techniques cover temporal periods too short (137Cs, 210Pb) or too long (14C) to reliably date sediments deposited during periods of local European activity (1660-1900). Moreover, many potential biomarkers, such as pollen, degrade in oxic flood plain sediments. In the Baltimore, Maryland (USA) region, early chromite mining (1820 - 1880) occurred during periods of rapid agricultural clearance. Use of chromium (Cr) chemostratigraphic profiles in flood plain sediments tied to historical mining activity can provide improved precision in overbank accumulation rates and timing. Sediment cores were collected from the Red Run basin, which is part of the Baltimore Ecosystem Study, an urban Long-Term Ecological Research site. Trace metal chemostratigraphic profiles were measured and peaks in Cr concentration tied to historic mining activity. Dates from Cr chemostratigraphic profiles were combined with 137Cs dating to reconstruct flood plain sedimentation rates. Red Run early sedimentation rates (1820 - 1880) were higher (0.45 - 1.19 cm/yr) than more recent (1880 - 1963) rates (0.08 - 0.46 cm/yr). This indicates that Piedmont flood plain vertical sediment accumulation might have peaked before the peak in agricultural clearance, earlier than assumed by regional models. The Cr chemostratigraphy is applicable to a wider region including much of the Maryland and Pennsylvania (USA) Piedmont.

Bain, D. J.; Brush, G. S.

2005-01-01

329

Contributions of 1990s - 2000s Abyssal Global Ocean and Deep Southern Ocean Warming to Local and Global Sea Level Budgets. (Invited)  

NASA Astrophysics Data System (ADS)

We present abyssal global ocean and deep Southern Ocean temperature trends from the 1990s through the 2000s and assess their role in local and global sea level budgets. We estimate warming rates along twenty-eight full-depth, high-quality hydrographic sections that have been occupied two or more times between 1980 and 2010: usually first by the World Ocean Circulation Experiment (WOCE) Hydrographic Program (mostly after 1990) and more recently by the Global Ship-Based Hydrographic Investigations Program (GO-SHIP). We divide the ocean into 32 deep basins and estimate a vertical profile of warming rate and its uncertainty for each sampled basin. We use a volume-integrated warming rate below 4000 m to calculate a sea level rise rate due to thermal expansion in the abyss for each basin. In addition, we similarly estimate a sea level rise rate owing to ocean warming from 1000-4000 m south of the Sub-Antarctic Front. We find the largest local sea level rise rates due to abyssal warming in the Southern Ocean, with magnitudes ranging from 0.20 (±0.14) to 0.44 (±0.36) mm yr-1 (with 95% confidence intervals). Deep Southern Ocean (1000-4000 m south of the SAF) warming adds an additional 0.87 (±0.76) mm yr-1 to the abyssal contributions, meaning recent local decadal sea level rise rates in the Southern Ocean due to thermal expansion below 1000 m exceed 1 mm yr-1. The abyssal (below 4000 m) warming signal weakens northward in the central Pacific, western Atlantic, and eastern Indian Oceans with local contributions to sea level rise rates an order of magnitude smaller than in the Southern Ocean. Basins in the eastern Atlantic and western Indian Oceans show small abyssal cooling trends (mostly statistically insignificant) and thus decreases in sea level from this contribution. Using all the observed changes we estimate an average global contribution to sea level rise from warming below 4000 m of 0.05 (±0.02) mm yr-1. The deep warming south of the Sub-Antarctic Front adds another 0.09 (±0.08) mm yr-1 globally. Global abyssal and deep Southern Ocean warming from the 1990s to 2000s accounts for statistically significant fractions of both local and global sea level rise rates.

Purkey, S. G.; Johnson, G. C.

2010-12-01

330

Titan’s “blandlands”: nature, distribution, and possible origin of Titan’s plains  

NASA Astrophysics Data System (ADS)

Titan’s diverse and Earth-like geologic features have been mapped and interpreted based on their morphological characteristics (e.g. Lopes et al., 2010, Icarus 205; Aharonson et al., 2012, Titan: Surface, Atmosphere, Magnetosphere, Cambridge University Press). While the interpretation for the origin of some units, such as dunes and well-preserved impact craters, has been relatively straightforward, others have been more challenging. In particular, the undifferentiated plains first mapped by Lopes et al. (2010) remain mysterious. These vast expanses, often referred to as “blandlands” (also “undifferentiated plains unit”, Lopes et al., 2010) are mostly found at mid-latitudes and appear relatively featureless at radar wavelengths, with no significant topography. Their gradational boundaries and paucity of features in SAR data make geologic interpretation particularly challenging. We examine and evaluate different formation mechanisms. Plains may be sedimentary in origin, resulting from fluvial or lacustrine deposition or accumulation of photolysis products created in the upper atmosphere. Alternatively, the plains may be cryovolcanic, consisting of overlapping flows of low relief, obscured by accumulation of sediments. In this paper, we use SAR, radiometry, scatterometry, and SARTopo data to examine the characteristics of the plains and compare them with other geologic units. We also compare their global distribution with that of other units and examine the implications.

Lopes, Rosaly M.; Malaska, M. J.; Le Gall, A.; Hayes, A.; Mitchell, K. L.; Kirk, R.; Radebaugh, J.; Neish, C.; Stofan, E.; Janssen, M.; Wall, S. D.; Lucas, A.; Lorenz, R. D.; Cassini RADAR Team

2013-10-01

331

49 CFR 230.102 - Tender plain bearing journal boxes.  

Code of Federal Regulations, 2010 CFR

... 2009-10-01 false Tender plain bearing journal boxes. 230.102 Section 230.102 Transportation...Running Gear § 230.102 Tender plain bearing journal boxes. Plain bearing journal boxes with the following defects shall be...

2009-10-01

332

49 CFR 230.102 - Tender plain bearing journal boxes.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false Tender plain bearing journal boxes. 230.102 Section 230.102 Transportation...Running Gear § 230.102 Tender plain bearing journal boxes. Plain bearing journal boxes with the following defects shall be...

2010-10-01

333

12 CFR 611.1217 - Plain language requirements.  

Code of Federal Regulations, 2013 CFR

... 7 2013-01-01 2013-01-01 false Plain language requirements. 611.1217 Section...Termination of System Institution Status § 611.1217 Plain language requirements. (a) Plain language presentation. All...

2013-01-01

334

Saltwater intrusion in the Muravera plain (Italy)  

Microsoft Academic Search

The Muravera plain is located in the South-Eastern part of Sardinia, Italy's second largest island, at the mouth of the Flumendosa river, and covers an extension of about 130 km2. The three main centers of the plain (Muravera, Villaputzu and San Vito) comprise a population of circa 13000. The main economic activities in this area are farming, citrus fruit growing,

E. Lorrai; G. Lecca; M. R. Lai; A. Cadeddu; A. Giacomelli

335

Ohio Conservation Plan: Plains gartersnake, Thamnophis radix  

Microsoft Academic Search

This plan outlines strategies and methods used in an ongoing study initiated in 1999 to restore a selfsustaining population of the Plains gartersnake (Thamnophis radix) in Ohio. Restoring a self-sustaining population would require increases in the current population to where the ratios of T. radix to T. sirtalis are approximately 1:1 in multiple locations in Killdeer Plains Wildlife Area (KPWA).

Norman Reichenbach; M. Barrie; K. Becka; G. Burghardt; S. Butterworth; C. Caldwell; F. Dierkes; P. Johantgen; K. Stanford; D. Wynn

2010-01-01

336

Second chance for the plains bison  

Microsoft Academic Search

Before European settlement the plains bison (Bison bison bison) numbered in the tens of millions across most of the temperate region of North America. Within the span of a few decades during the mid- to late-1800s its numbers were reduced by hunting and other factors to a few hundred. The plight of the plains bison led to one of the

Curtis H. Freese; Keith E. Aune; Delaney P. Boyd; James N. Derr; Steve C. Forrest; C. Cormack Gates; Peter J. P. Gogan; Shaun M. Grassel; Natalie D. Halbert; Kyran Kunkel; Kent H. Redford

2007-01-01

337

The data management facilities of PLAIN  

Microsoft Academic Search

The programming language PLAIN has been designed to support the construction of interactive information systems within the framework of a systematic programming methodology. One of the key goals of PLAIN has been to achieve an effective integration of programming language and database management concepts, rather than either the functional interface to database operations or the low-level database navigation operations present

Anthony I. Wasserman

1979-01-01

338

Great Plains Wind Energy Transmission Development Project  

Microsoft Academic Search

In fiscal year 2005, the Energy & Environmental Research Center (EERC) received funding from the U.S. Department of Energy (DOE) to undertake a broad array of tasks to either directly or indirectly address the barriers that faced much of the Great Plains states and their efforts to produce and transmit wind energy at the time. This program, entitled Great Plains

P. E. Brad G. Stevens; Troy K. Simonsen; Kerryanne M. Leroux

2012-01-01

339

Hydrologic influence on sediment transport of low-gradient, forested ...  

Treesearch

... stream systems, such as those existing in much of the southeastern Coastal Plain. ... and determine their effect on the transport of suspended and dissolved sediment. ... seasonal variation, and loading was mainly controlled by discharge levels. ... the low runoff decreases erosion susceptibility from harvesting activities.

340

Sediment Tubes  

NSDL National Science Digital Library

In this activity, students will observe how different density soils and rocks behave in wind and in water. They will make predictions and careful observations as they learn about sediment transport and sediment rates in streams and rivers. Upper junior high and high school science classes can extend the activity to include environmental discussions of agricultural runoff, turbidity measurements, and/or colloids in solutions that never settle out.

Huffman, Louise

341

Sediment Transport  

NSDL National Science Digital Library

Each student reviews a recent USGS publication detailing sediment transport data collection and reduction on the Yellowstone River. Using that report, they answer a series of questions about sediment transport and make some basic hydrologic and hydraulic calculations using data in the report. They also use USGS software to analyze cross-sections on the Yellowstone in a real world application. Designed for a geomorphology course

Williams, Karen

342

PLAINS CO2 REDUCTION PARTNERSHIP  

SciTech Connect

The Plains CO{sub 2} Reduction (PCOR) Partnership continues to make great progress. Task 2 (Technology Deployment) focused on developing information regarding deployment issues to support Task 5 (Modeling and Phase II Action Plans) by providing information to be used to assess CO{sub 2} sequestration opportunities in the PCOR Partnership region. Task 3 (Public Outreach) focused on developing an informational video about CO{sub 2} sequestration. Progress in Task 4 (Sources, Sinks, and Infrastructure) included the continued collection of data regarding CO{sub 2} sources and sinks and data on the performance and costs for CO{sub 2} separation, capture, treatment, and compression for pipeline transportation. Task 5 focused on screening and qualitatively assessing sequestration options. Task 5 activities also continue to be useful in structuring data collection and other activities in Tasks 2, 3, and 5.

Edward N. Steadman; John A. Harju; Erin M. O'Leary; James A. Sorensen; Daniel J. Daly; Melanie D. Jensen; Thea E. Reikoff

2004-10-01

343

PLAINS CO2 REDUCTION PARTNERSHIP  

SciTech Connect

The Plains Co{sub 2} Reduction (PCOR) Partnership continues to make great progress. Task 2 (Technology Deployment) activities have focused on developing information on deployment issues to support Task 5 activities by providing information to be used to assess CO{sub 2} sequestration opportunities in the PCOR Partnership region. Task 3 (Public Outreach) activities have focused on developing an informational video about CO{sub 2} sequestration. Progress in Task 4 (Sources, Sinks, and Infrastructure) has included the continued collection of data regarding CO{sub 2} sources and sinks and data on the performance and costs for CO{sub 2} separation, capture, treatment, and compression for pipeline transportation. Task 5 (Modeling and Phase II Action Plans) activities have focused on screening and qualitatively assessing sequestration options. Task 5 activities also continue to be useful in structuring data collection and other activities in Tasks 2, 3, and 5.

Edward N. Steadman

2004-07-01

344

PLAINS CO2 REDUCTION PARTNERSHIP  

SciTech Connect

The Plains CO{sub 2} Reduction (PCOR) Partnership continues to make great progress. Task 2 (Technology Deployment) focused on developing information regarding deployment issues to support Task 5 (Modeling and Phase II Action Plans) by providing information to be used to assess CO{sub 2} sequestration opportunities in the PCOR Partnership region. Task 3 (Public Outreach) focused on developing an informational video about CO{sub 2} sequestration. Progress in Task 4 (Sources, Sinks, and Infrastructure) included the continued collection of data regarding CO{sub 2} sources and sinks and data on the performance and costs for CO{sub 2} separation, capture, treatment, and compression for pipeline transportation. Task 5 focused on screening and qualitatively assessing sequestration options. Task 5 activities also continue to be useful in structuring data collection and other activities in Tasks 2, 3, and 5.

Edward N. Steadman; John A. Harju; Erin M. O'Leary; James A. Sorensen; Daniel J. Daly; Melanie D. Jensen; Thea E. Reikoff

2005-01-01

345

Planetary plains: subsidence and warping  

NASA Astrophysics Data System (ADS)

A common feature of all celestial bodies is their tectonic dichotomy best studied, naturally, at Earth [1]. Here there is an opposition of the eastern continental hemisphere and the western oceanic one. The first one is uplifted and cracked, the second one subsided, squeezed and warped. The next excellent example of dichotomy is at Mars where the subsided northern hemisphere is opposed by the highly uplifted southern one. The enigmatic two-face Iapetus now with help of Cassini SC presents a more clear picture: the leading dark hemisphere is opposed by the trailing light one. The light hemisphere is built mainly of water ice, the dark one of some more dense material. Bean-shaped asteroids with one convex and another concave hemispheres are best exemplified by Ida. Examples of dichotomic asteroids, satellites, planets and stars could be extended. Ubiquity of this phenomenon was expressed as the 1st theorem of the planetary wave tectonics [2 & others]: "Celestial bodies are dichotomic". A reason of this phenomenon is in action of inertia-gravity waves occurring in any celestial body because of its movement in non-round but elliptical (parabolic) orbit with periodically changing accelerations. The inertia-gravity standing waves warp rotating bodies (but all bodies rotate !) in 4 ortho- and diagonal interfering directions and in several harmonic wave-lengths. The fundamental wave1 produces ubiquitous tectonic dichotomy (2?R-structure): an opposition of two hemispheres with different planetary radii. To keep angular momenta of two hemispheres equal (otherwise a body will fall apart) the lower subsiding one is constructed of denser material than the higher one. Normally in terrestrial planets lowlands are filled with dense basalts, highlands are built by lighter lithologies. A subsidence means diminishing radius, otherwise, the larger surface must be fit into a smaller space. It is possible only if an original infilling is warped. At Earth cosmic altimetry shows complex fabric of oceanic floors. Short, medium wave undulations of Pacific's floor (A. Cazenave et al., 1992; D. McAdoo & K. Marks, 1992) present lineations underlining its whole shape. NE lineations predominate on its northern sub-basin, NW lineations on its southern one. They cross at the equatorial zone and together with some other directions give a pattern resembling that observed on the venusian surface. The venusian regional plains typically deformed by wrinkle ridges show interesting similarities to volcanic plains on the Moon and Mars [3]. A subsidence along with warpings can squeeze out some "superfluous" material to surface through planetary scale fissures. This material builds mid-oceanic ridges and huge Hawaii volcano. The Cassini Regio on Iapetus is crossed in the equatorial plain by the dark ridge in some places high 20 km. References: [1] Kochemasov G. G. (2004) Mars and Earth: two dichotomies - one cause. In Workshop on "Hemispheres 1 apart: the origin and modification of the martian crustal dichotomy", LPI Contribution # 1203, Lunar and Planetary Institute, Houston, p. 37. [2] Kochemasov G.G.(1999) Theorems of wave planetary tectonics // Geophys. Res. Abstr. v.1, #3, p.700 . [3] Basilevsky A.T., Head J.W. (2006) Impact craters on regional plains in Venus: Age relations with wrinkle ridges and implications for the geological evolution of Venus // JGR, v.111, EO3006, doi: 10.1029/2005JE002473, 2006. 2

Kochemasov, G.

346

Structure of plain and complex flagellar hooks of Pseudomonas rhodos.  

PubMed Central

The proximal hooks of plain and complex flagella produced by a strain of Pseudomonas rhodos have been analyzed by electron microscopy and optical diffraction and filtering. Plain flagellar hooks are cone-shaped, 70 nm long, and 13 to 21.5 nm wide, and consist of helically arranged subunits. Complex flagellar hooks are cylinders, 180 to 190 nm long, and 15 to 16 nm wide, and are composed of globular subunits. The structure comprises four small-scale helical rows of subunits intersecting bewteen 10 and 11 large-scale helices of pitch angle 80 degrees. The axial and lateral dimensions of the unit cell, which define the surface lattice, are 4.9 and 4.7 nm, respectively. In addition, a core structure, approximately 5 nm wide, has been demonstrated inside the hook cylinder. Complex flagellar hooks were isolated and purified by gradient centrifugation after acid degradation of the attached filaments. Isolated hook particles have an average sedimentation constant of 130S and consist of a protein of molecular weight 43,000. A model of the complex flagellar hook is presented, and its possible role in flagellar assembly and rotation is discussed. Images

Raska, I; Mayer, F; Edelbluth, C; Schmitt, R

1976-01-01

347

Structure of plain and complex flagellar hooks of Pseudomonas rhodos.  

PubMed

The proximal hooks of plain and complex flagella produced by a strain of Pseudomonas rhodos have been analyzed by electron microscopy and optical diffraction and filtering. Plain flagellar hooks are cone-shaped, 70 nm long, and 13 to 21.5 nm wide, and consist of helically arranged subunits. Complex flagellar hooks are cylinders, 180 to 190 nm long, and 15 to 16 nm wide, and are composed of globular subunits. The structure comprises four small-scale helical rows of subunits intersecting bewteen 10 and 11 large-scale helices of pitch angle 80 degrees. The axial and lateral dimensions of the unit cell, which define the surface lattice, are 4.9 and 4.7 nm, respectively. In addition, a core structure, approximately 5 nm wide, has been demonstrated inside the hook cylinder. Complex flagellar hooks were isolated and purified by gradient centrifugation after acid degradation of the attached filaments. Isolated hook particles have an average sedimentation constant of 130S and consist of a protein of molecular weight 43,000. A model of the complex flagellar hook is presented, and its possible role in flagellar assembly and rotation is discussed. PMID:1245467

Raska, I; Mayer, F; Edelbluth, C; Schmitt, R

1976-02-01

348

Variability of the sediment phosphate composition of a temporary pond (Doñana National Park, SW Spain)  

Microsoft Academic Search

This study reports on the spatial and temporal variability of the phosphate composition in the sediment of a temporary pond over a period of 3 years using the EDTA-method for P-fractionation. Sediment samples were collected at three different sites (open-water, littoral and flood plain) to compare the effect of the length of the wet\\/dry phase on the sediment phosphate composition,

L. Serrano; I. Calzada-Bujak; J. Toja

2003-01-01

349

Salt marsh vegetation response to edaphic and topographic changes from upland sedimentation in a Pacific estuary  

Microsoft Academic Search

This study investigated how changes in salt marsh soil properties and topography on sediment fans related to shifts in salt\\u000a marsh plant community composition in the Elkhorn Slough Watershed, California, USA. Several sediment fans have formed in this\\u000a watershed as soil eroding from farms moved downslope, filling marshes, mudflats, and channels. Sandy sediment deposition increased\\u000a marsh plain elevation and altered

Kristin B. Byrd; Maggi Kelly

2006-01-01

350

Petrological, magnetic and chemical properties of basalt dredged from an abyssal hill in the North-east pacific  

USGS Publications Warehouse

OVER the years, samples of basalt from the oceanic crust have been taken mainly from seamounts, fracture zones and ridge and rise crests1-6, and rarely from the vast fields of abyssal hills which cover a large part of the deep-sea floor. The basalt sampled from the deeper regions of the oceanic crust (for example, on fault scarps) is a distinct variety of tholeiitic basalt, while alkali basalt is restricted to the volcanic edifices4. Oceanic tholeiitic basalt differs from alkali basalt and continental tholeiite chiefly in having a relatively low percentage of K2O (0.2 weight per cent)4. Some authors have speculated that this type of tholeiitic basalt is the major extrusion from the upper mantle and constitutes the predominant rock type in the upper oceanic crust. ?? 1969 Nature Publishing Group.

Luyendyk, B. P.; Engel, C. G.

1969-01-01

351

Descending into the abyss: Bathymetric patterns of diversity in decapod crustaceans shift with taxonomic level and life strategies  

NASA Astrophysics Data System (ADS)

The aim of this study was to examine the depth-related changes in the diversity of decapod crustaceans from the intertidal to abyssal zones off Madeira Archipelago, a chain of islands in the subtropical North East Atlantic Ocean. The bathymetric gradient in species richness was evaluated using the reported ranges of 175 out of approximately 186 decapod species known in this archipelago. The depth-related changes at different taxonomic (order, sub-orders and families) and life strategy (pelagic, benthopelagic and benthic) levels were investigated and different ecological hypotheses (species-energy, mid-domain and Rapoport's effects) were tested to explain the observed patterns. No unimodal trend of Decapoda diversity was revealed and, instead, a monotonic decrease towards the abyss was observed, mainly as a consequence of the depth-related changes in the benthic diversity of the suborder Pleocyemata. Nonetheless, all bathymetric gradients of pelagic diversity (at order and suborder levels) displayed parabolic trends. There was also a general increase in bathymetric range towards greater depth, and the major faunal break was identified within the continental shelf area. All species richness-depth patterns were significantly nested, but there was a clear increasing trend in randomness from the benthic to the pelagic realm. The present study shows for the first time that even within the same taxonomic group and geographic region different bathymetric patterns of diversity can be observed, depending on the taxonomic level and, more importantly, on the group's life strategies. Moreover, our analysis supports the species-energy hypothesis, implicating a combination of temperature and food availability as the main causal predictors explaining diversity variation.

Rosa, Rui; Boavida-Portugal, Joana; Trübenbach, Katja; Baptista, Miguel; Araújo, Ricardo; Calado, Ricardo

2012-06-01

352

Rates of microbial metabolism in deep coastal plain aquifers  

SciTech Connect

Rates of microbial metabolism in deep anaerobic aquifers of the Atlantic coastal plain of South Carolina were investigated by both microbiological and geochemical techniques. Rates of (2-{sup 14}C)acetate and (U-{sup 14}C)glucose oxidation as well as geochemical evidence indicated that metabolic rates were faster in the sandy sediments composing the aquifers than in the clayey sediments of the confirming layers. In the many aquifer sediments, estimates of the rates of CO{sub 2} production (millimoles of CO{sub 2} per liter per year) based on the oxidation of (2-{sup 14}C) acetate were 9.4 {times} 10{sup {minus}3} to 2.4 {times} 10{sup {minus}1} for the Black Creek aquifer, 1.1 {times} 10{sup {minus}2} for the Middendorf aquifer, and < 7 {times} 10{sup {minus}5} for the Cape Fear aquifer. These estimates were at least 2 orders of magnitude lower than previously published estimates that were based on the accumulation of CO{sub 2} in laboratory incubations of similar deep subsurface sediments. In contrast, geochemical modeling of groundwater chemistry changes along aquifer flowpaths gave rate estimates that ranged from 10{sup {minus}4} to 10{sup {minus}6} mmol of CO{sub 2} production could have been no more than 10{sup {minus}4} mmol per liter per year. Thus, laboratory incubations may greatly overestimate the in situ rates of microbial metabolism in deep subsurface environments. This has important implications for the use of laboratory incubations in attempts to estimate biorestoration capacities of deep aquifers. The rate estimates from geochemical modeling indicate that deep aquifers are among the most oligotrophic aquatic environments in which there is ongoing microbial metabolism.

Chapelle, F.H. (Geological Survey, Columbia, SC (USA)); Lovley, D.R. (Geological Survey, Reston, VA (USA))

1990-06-01

353

CORN BELT PLAIN RIVER AND STREAMS PROJECT - 3 BIOCRITERIA PRODUCTS  

EPA Science Inventory

This effort resulted in eight products, as follows: 1) Development of Index of Biotic Integrity Expectations for the Ecoregions of Indiana I. Central Corn Belt Plain; 2) Ibid. II. Huron-Erie Lake Plain; 3) Ibid III. Northern Indiana Till Plain; 4) Ibid .IV.Eastern Corn Belt Plain...

354

The High Plains: Land of Extremes.  

ERIC Educational Resources Information Center

|Provides rich background information about unique High Plains ecosystems. Focuses on water, plant, animal, and energy resources. Describes hands-on activities related to ground water movement and energy resources. Contains 18 references. (DDR)|

Capron, Ranel Stephenson; And Others

1996-01-01

355

High Plains Regional Technology in Education Consortium  

NSDL National Science Digital Library

The High Plains Regional Technology in Education Consortium site contains information on creating class web pages, lesson oriented sites, and educational resources such as instructional software, lab activities and lesson plans.

1996-01-01

356

Tyrrhena Terra: Hydrated Lobate Ejecta and Plains  

NASA Astrophysics Data System (ADS)

Hydrated minerals as phyllosilicates have been identified with OMEGA/Mars Express in Tyrrhena Terra, both on crater ejecta blankets and alluvial plains. Hypothesis are formulated about their origin and link.

Loizeau, D.; Bouley, S.; Mangold, N.; Meresse, S.; Costard, F.; Poulet, F.; Ansan, V.; Le Mouelic, S.; Bibring, J.-P.; Gondet, B.; Langevin, Y.

2009-03-01

357

Tyrrhena Terra: Hydrated Lobate Ejecta and Plains  

Microsoft Academic Search

Hydrated minerals as phyllosilicates have been identified with OMEGA\\/Mars Express in Tyrrhena Terra, both on crater ejecta blankets and alluvial plains. Hypothesis are formulated about their origin and link.

D. Loizeau; S. Bouley; N. Mangold; S. Meresse; F. Costard; F. Poulet; V. Ansan; S. Le Mouelic; J.-P. Bibring; B. Gondet; Y. Langevin

2009-01-01

358

High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth  

NASA Astrophysics Data System (ADS)

Microbes control the decomposition of organic matter inmarine sediments. Decomposition, in turn, contributes to oceanic nutrient regeneration and influences the preservation of organic carbon. Generally, rates of benthic decomposition decline with increasing water depth, although given the vast extent of the abyss, deep-sea sediments are quantitatively important for the global carbon cycle. However, the deepest regions of the ocean have remained virtually unexplored. Here, we present observations of microbial activity in sediments at Challenger Deep in the Mariana Trench in the central west Pacific, which at almost 11,000m depth represents the deepest oceanic site on Earth. We used an autonomous micro-profiling system to assess benthic oxygen consumption rates. We show that although the presence of macrofauna is restricted at Challenger Deep, rates of biological consumption of oxygen are high, exceeding rates at a nearby 6,000-m-deep site by a factor of two. Consistently, analyses of sediments collected from the two sites reveal higher concentrations of microbial cells at Challenger Deep. Furthermore, analyses of sediment 210Pb profiles reveal relatively high sediment deposition in the trench. We conclude that the elevated deposition of organic matter at Challenger Deep maintains intensified microbial activity at the extreme pressures that characterize this environment.

Glud, Ronnie N.; Wenzhöfer, Frank; Middelboe, Mathias; Oguri, Kazumasa; Turnewitsch, Robert; Canfield, Donald E.; Kitazato, Hiroshi

2013-04-01

359

PLAINS CO2 REDUCTION PARTNERSHIP  

SciTech Connect

The Plains CO{sub 2} Reduction (PCOR) Partnership continues to make great progress. Task 2 (Technology Deployment) focused on developing information regarding deployment issues to support Task 5 (Modeling and Phase II Action Plans) and provided information to be used to assess CO{sub 2} sequestration opportunities in the PCOR Partnership region. Task 2 efforts also included preparation of a draft topical report entitled ''Deployment Issues Related to Geologic CO{sub 2} Sequestration in the PCOR Partnership Region'', which is nearing completion. Task 3 (Public Outreach) focused on developing an informational video about CO{sub 2} sequestration. The video will be completed and aired on Prairie Public Television in the next quarter. Progress in Task 4 (Sources, Sinks, and Infrastructure) included the continued collection of data regarding CO{sub 2} sources and sinks and data on the performance and costs for CO{sub 2} separation, capture, treatment, and compression for pipeline transportation. The addition of the Canadian province of Alberta to the PCOR Partnership region expanded the decision support system (DSS) geographic information system database. Task 5 screened and qualitatively assessed sequestration options. Task 5 activities also continue to be useful in structuring data collection and other activities in Tasks 2, 3, and 5.

Edward N. Steadman; John A. Harju; Erin M. O'Leary; James A. Sorensen; Daniel J. Daly; Melanie D. Jensen; Thea E. Reikoff

2005-04-01

360

PLAINS CO2 REDUCTION PARTNERSHIP  

SciTech Connect

The Plains CO{sub 2} Reduction (PCOR) Partnership characterization work is nearing completion, and most remaining efforts are related to finalizing work products. Task 2 (Technology Deployment) has developed a Topical Report entitled ''Deployment Issues Related to Geologic CO{sub 2} Sequestration in the PCOR Partnership Region''. Task 3 (Public Outreach) has developed an informational Public Television program entitled ''Nature in the Balance'', about CO{sub 2} sequestration. The program was completed and aired on Prairie Public Television in this quarter. Task 4 (Sources, Sinks, and Infrastructure) efforts are nearing completion, and data regarding CO{sub 2} sources and sinks and data on the performance and costs for CO{sub 2} separation, capture, treatment, and compression for pipeline transportation are being incorporated into a series of topical reports. The expansion of the Decision Support System Geographic Information System database has continued with the development of a ''save bookmark'' feature that allows users to save a map from the system easily. A feature that allows users to develop a report that summarizes CO{sub 2} sequestration parameters was also developed. Task 5 (Modeling and Phase II Action Plans) focused on screening and qualitatively assessing sequestration options and developing economic estimates for important regional CO{sub 2} sequestration strategies.

Edward N. Steadman; John A. Harju; Erin M. O'Leary; James A. Sorensen; Daniel J. Daly; Melanie D. Jensen; Lisa S. Botnen

2005-07-01

361

Plain papers for color hard copy technologies  

NASA Astrophysics Data System (ADS)

The expression 'Plain' paper was coined in the early days of electrophotography to distinguish the capabilities of the new dry toner based photocopying process which did not require a sensitized or special coated paper to produce an image. Currently 'Plain' paper is considered in the electronic printing industry, to be any uncoated paper, usually of the type used in office photocopying applications. It is assumed that all 'Plain' papers are identical or at least equivalent in their properties such that all papers will give equivalent print quality performance. Due to the wide availability and low price of 'Plain' papers, it is also considered desirable by vendors of electronic marking processes, that their technology be capable of producing good image quality on 'Plain' paper. The chemical and physical differences which can occur among 'Plain' papers are discussed with respect to the specific image quality and engine reliability requirements of the major nonimpact electronic marking technologies, including electrophotography and laser printing, electrographic and ionographic processes, thermal transfer and ink jet. Paper properties of interest include, smoothness, surface energy, electrical resistivity, porosity and aqueous and nonaqueous liquid adsorption. Color printing has added additional requirements to paper quality, if good image quality is to be achieved and maintained. Given the apparently conflicting requirements for some of the electronic marking technologies, it will be a challenge to define a single grade of paper which will produce optimum print quality for all electronic printing processes.

Rutland, David F.

1995-04-01

362

The Distribution of Young Plains on Mercury  

NASA Astrophysics Data System (ADS)

Large portions of Mercury's surface are covered by contiguous plains having densities of impact craters consistent with ages younger than the cessation of the period of late heavy bombardment [1-3]. The youngest subsets of these include smooth plains and intermediate plains [e.g., 4], the latter of which have slightly higher crater densities and often slightly more gradational boundaries. A third category, the intercrater plains, is still more heavily cratered and has a large abundance of superposed secondary craters <10 km in diameter. Many of these units have been interpreted to be volcanic in origin [e.g., 1,5], although formation through impact melting or fluidization of basin ejecta remain possible interpretations in some regions [6]. Earlier analyses from images acquired during flybys by the Mariner 10 and MESSENGER spacecraft yielded estimates of total smooth plains area ranging from 15 to 40% of the planet [2,7,8]. Here, we use images from the Mercury Dual Imaging System (MDIS) acquired from orbit to produce a global map of the distribution of smooth and intermediate plains, with implications for the temporal and spatial distribution of volcanism on Mercury.

Denevi, B. W.; Robinson, M. S.; Murchie, S. L.; Ernst, C. M.; Byrne, P. K.; Solomon, S. C.; Peplowski, P. N.

2012-09-01

363

Geogenic arsenic in groundwaters from Terai Alluvial Plain of Nepal  

NASA Astrophysics Data System (ADS)

The origin and mobility of arsenic (As) in the groundwater environment has received serious attention in recent years. Recent studies have reported naturally occurring As in groundwaters of the Terai Alluvial Plains (TAP) in southern Nepal, where groundwater exploitation has increased since the 1960s. The source of As in TAP is geogenic and leached primarily due to weathering of As bearing rocks and sediments in the Himalayas. In our present study, we have investigated the groundwater chemistry in the central part of the TAP in Nawalparasi district. TAP groundwaters are near-neutral to alkaline, with predominantly reducing character and high HCO3^- low SO^{2-}_4 and NO3^- concentrations. Elevated HCO3 levels possibly result due to the oxidation of organic matter, low SO4^{2-} levels reflect sulfate reduction. Elevated NH4^+ concentrations in these groundwaters suggest dissimilatory nitrate reduction in the aquifers. Total arsenic (Astot) levels in groundwater varied from 1.7 ?g/L to as high as 404 ?g/L with dominance of As (III) species and elevated levels of dissolved Fe and Mn. Arsenic is mobilized in groundwaters as a result of desorption of As-oxyanions adsorbed onto Fe-and Mnoxides as well as reductive dissolution of these surface reactive phases from the sediments along with release ouf as in anoxie groundwaters.

Bhattacharya, P.; Tandukar, N.; Nekul, A.; Valero, A. A.; Mukherjee, A. B.; Jacks, G.

2003-05-01

364

A snapshot of suspended sediment and fluid mud occurrence in a mixed-energy embayment, Tijucas Bay, Brazil  

Microsoft Academic Search

Along the southern Brazilian coast, Tijucas Bay is known for its unique muddy tidal flats associated with chenier plains. Previous field observations pointed to very high suspended sediment concentrations (SSCs) in the inner parts of the bay, and in the estuary of the Tijucas River, suggesting the presence of fluid mud. In this study, the occurrences of suspended sediments and

Carlos Augusto Fran Ça Schettini; Dermeval Costa de Almeida; Eduardo Siegle; Ant Ônio Carlos Brand Ão de Alencar

2010-01-01

365

Assessment of the effects of farming and conservation programs on pesticide deposition in high plains wetlands.  

PubMed

We examined pesticide contamination in sediments from depressional playa wetlands embedded in the three dominant land-use types in the western High Plains and Rainwater Basin of the United States including cropland, perennial grassland enrolled in conservation programs (e.g., Conservation Reserve Program [CRP]), and native grassland or reference condition. Two hundred and sixty four playas, selected from the three land-use types, were sampled from Nebraska and Colorado in the north to Texas and New Mexico in the south. Sediments were examined for most of the commonly used agricultural pesticides. Atrazine, acetochlor, metolachlor, and trifluralin were the most commonly detected pesticides in the northern High Plains and Rainwater Basin. Atrazine, metolachlor, trifluralin, and pendimethalin were the most commonly detected pesticides in the southern High Plains. The top 5-10% of playas contained herbicide concentrations that are high enough to pose a hazard for plants. However, insecticides and fungicides were rarely detected. Pesticide occurrence and concentrations were higher in wetlands surrounded by cropland as compared to native grassland and CRP perennial grasses. The CRP, which is the largest conservation program in the U.S., was protective and had lower pesticide concentrations compared to cropland. PMID:22356096

Belden, Jason B; Hanson, Brittany Rae; McMurry, Scott T; Smith, Loren M; Haukos, David A

2012-03-08

366

Excess Olivine and Positive FeO-MgO Trend in Bulk-rock Abyssal Peridotites as a Consequence of Porous Melt Migration Beneath Ocean Ridges  

Microsoft Academic Search

Abyssal peridotites (AP) are mantle melting residues for mid-ocean ridge basalts (MORB) [1-4]. Recent studies [5-8] have confirmed the complementary relationship between MORB and AP, but also revealed the hidden complexities in these peridotites such as olivine addition [5-7] and melt refertilization [7,9,10]. These same studies [5,6] have immediately excited serious debates on AP petrogenesis [11-15]. These debates are stimulating

Y. Niu

2003-01-01

367

Ancient melt extraction from the oceanic upper mantle revealed by Re–Os isotopes in abyssal peridotites from the Mid-Atlantic ridge  

Microsoft Academic Search

Comprehensive major-, trace-element and rhenium–osmium (Re–Os) isotope data are presented for abyssal peridotites from Ocean Drilling Program (ODP) Leg 209, in the North Atlantic. The samples are from a single core (Site 1274A) located on the western wall of the axial rift valley of the Mid-Atlantic ridge, and their study allows elemental and isotope information to be precisely related to

Jason Harvey; Abdelmouhcine Gannoun; Kevin W. Burton; Nick W. Rogers; Olivier Alard; Ian J. Parkinson

2006-01-01

368

Light Plains in the South-Pole Aitken Basin: Surface Ages and Mineralogical Composition  

NASA Astrophysics Data System (ADS)

We studied light plains in the north-eastern South-Pole Aitken basin to investigate their origin, ages, and mineralogical composition. Light plains, also known as the Cayley Formation, occur on the near- and farside of the Moon. Due to their smooth texture, lower crater densities, and occurrence as crater fills, they were thought to be of volcanic origin [e.g., 1]. However, Apollo 16 samples of light plains deposits were in fact highly brecciated rocks [2]. Therefore, the Imbrium and Orientale impacts were thought to have formed light plains because they reshaped the surface thousands of kilometers from their impact sites. Subsequent studies revealed varying surface ages of light plains [e.g., 3] and different mineralogical compositions, which are in some cases more highland-like and in others more mare-like. Hence, an origin solely from the Imbrium and/or Orientale impacts is unlikely. Thus, the question whether light plains formed due to large impacts or regional cratering, or through endogenic processes remains open. We performed crater size-frequency measurements [e.g., 4] on Lunar Reconnaissance Orbiter Wide Angle Camera images and obtained absolute model ages between 3.43 and 3.81 Ga. We observed neither a distinctive peak of light plains ages nor clustering of similar ages in any specific regions of the studied area. Due to the fact that the derived ages vary as much as 380 Ma, an origin by a single event seems unlikely. Moreover, some ages even post-date the Imbrium and Orientale impacts, and thus an origin related to those impacts is not likely. Examination of multispectral data from Clementine [5] shows that the Ti abundances vary between 0.2 and 3 wt % and Fe abundances between 12.5 and 19 wt %. We observed a regional difference in distribution: light plains units within the Apollo basin have lower Fe and Ti values and are more highland-like, whereas light plains outside the Apollo basin show higher Fe and Ti values and are more mare-like. Furthermore, M3 spectra from small impact craters on light plains show characteristic absorption bands for pyroxene. We conclude that light plains are unlikely to have formed by the Imbrium and Orientale impacts due to the range of surface ages and the compositional differences. Nevertheless, these impacts together with secondary cratering and sedimentation from regional and local impacts may have played an important role in forming these plains. An endogenic origin can still not be excluded due to the mare-like composition of some light plains. [1] Wilhelms D.E. (1970) Astrogeol. Stud. Ann. Prog. Report, 13-28. [2] Young J.W. (1972) NASA Apollo 16 Prelim. Sci. Rep., 5-1-5-6. [3] Neukum, G. (1977) The Moon 17, 383-393. [4] Neukum G. et al. (1975) The Moon 12, 201-229. [5] Lucey P.G. et al. (2000) J. Geophys. Res. 105, 20,297-20,305.

Thiessen, F.; Hiesinger, H.; van der Bogert, C. H.; Pasckert, J. H.; Robinson, M. S.

2012-04-01

369

Effects of Late Cretaceous and Cenozoic faulting on the geology and hydrology of the coastal plain near the Savannah River, Georgia and South Carolina  

USGS Publications Warehouse

Geologic and hydrologic investigations by the U.S. Geological Survey have defined stratigraphic and hydraulic anomalies suggestive of faulting within Coastal Plain sediments between the Ogeechee River in east-central Georgia and the Edisto River in west-central South Carolina. Examination of borehole cuttings, cores, and geophysical logs from test wells indicate that Triassic rocks and Upper Cretaceous and lower Tertiary Coastal Plain sediments near the Barnwell-Allendale County line near Millett, South Carolina, are offset by a northeast-trending fault downthrown to the northwest. The location of this suspected Coastal Plain fault generally coincides with the location of an inferred fault in basement rocks as interpreted from aeromagnetic surveys. Apparent vertical offsets range from about 700 feet at the base of Upper Cretaceous sediments to about 20 feet in strata of Late Eocene age. As a result, the Upper Cretaceous Middendorf Formation which directly overlies crystalline and Triassic rocks updip (northwest) of this fault, is absent immediately downdip of the fault. The thickness of Tipper Cretaceous sediments is also sharply reduced from about 700 feet to about 180 feet across the fault. Sediments of the basal Coastal Plain aquifer are largely truncated by uplifted Triassic rocks at the fault near Millett, South Carolina. Lateral ground-water flow near the Savannah River Is consequently disrupted updip of the fault and ground water is transferred vertically into overlying sediments and possibly into the Savannah River. At several locations, abrupt changes in potentiometric head occur across this fault. Computed transmissivity of the basal Coastal Plain aquifer is also radically reduced downdip of the fault, sharply reversing a downdip trend of rapidly increasing aquifer transmissivity. Other anomalous potentiometric data along a northeast-trending line between Statesboro, Georgia, and Fairfax, South Carolina, suggest the possibility of similar faulting in correlative geologic units. The location of the suspected fault near Statesboro, Georgia, generally coincides with the eastward extension of the Gulf Trough, a regional potentiometric anomaly in central Georgia.

Faye, R. E.; Prowell, D. C.

1982-01-01

370

Behaviour of fluid mobile elements during subduction and exhumation of abyssal peridotites: Example of serpentinites from Cuba and Dominican Republic  

NASA Astrophysics Data System (ADS)

Seawater interaction with abyssal peridotites at the sea floor is an important process for chemical exchange between lithosperic mantle and ocean at slow-spreading ridge. Serpentinites from oceanic lithosphere are known to represent an important sink for fluid mobile element, notably boron. In parallel we know extreme enrichment in fluid mobile element (As, Sb, B, U, Li) in high-pressure serpentine minerals (antigorite) coming from part of mantle wedge hydrated by slab's fluids released (Himalaya, Deschamps et al., in prep.). In order to constrain geochemical behaviour of fluid mobile element hosted by serpentine during subduction processes, we examined abyssal serpentinites coming from the accretionary wedge of Greater Carribean (Cuba and Dominican Republic). They represent subducted Atlantic oceanic lithosphere, which have experienced low to high- metamorphism (greenschist to eclogite facies), before being exhumed. These rocks are an opportunity to understand the chemical mobility of fluid mobile element during prograde metamorphism occurring along subduction surface. Here we present bulk-rock and in-situ composition of serpentinites and their primary and alteration-related phase obtained on (LA-)HR-ICP-MS. Except for a few cumulates, serpentinites have depleted compositions in agreement with a refractory mantle, but also strong enrichment in U, Pb, Th, Sr, and other fluid mobile element (e.g., U up to 10xPM) indicating extensive fluid-rock intercation. In-situ composition allows the distinction of two groups of serpentine. Group 1 is characterized by relatively flat and depleted REE patterns (Yb ? 0.5xChondrite) reflecting formation after olivine, while group 2 formed after pyroxene is characterized by slightly higher HREE content (Yb ? 1xChondrite) but light LREE depleted patterns and displays higher content in Sc, V, Ti and Co. Both groups are strongly enriched in B (up to 120 ppm), and reach values already observed in serpentinites from mantle wedge (Himalaya, Deschamps et al., in prep.). Other fluid mobile elements such As (up to 6.85 ppm), Sb (up to 0.84 ppm), Li (up to 2 ppm) or U (up to 0.62 ppm) present strong enrichment in serpentine from both groups (0.1 up to 50 times primitive mantle values). The occurrence of amphibole having REE signature close to oceanic amphiboles, in cumulates, are in favour of an hydration event, leading to the observed strong mobile element enrichment, at the ridge. Compositions of the oceanic derived samples - especially in fluid mobile elements - are relatively close to the abyssal peridotites from MARK Zone (Andreani et al., 2008), without evidence of mobility for trace element during prograde and retrograde metamorphism. It confirms that the observed enrichment result from sea-water/peridotites interactions at the ridge. Also it suggests that mobile element stored into serpentine minerals become immobile during subduction processes. Major consequence of this observation is that serpentine minerals (chrysotile and lizardite) are a good sink for mobile element (As, Sb and B) into subduction zones, until their dehydration.

Deschamps, F.; Guillot, S.; Godard, M.; Chauvel, C.; Andreani, M.

2009-04-01

371

Suspended-sediment and fresh-water discharges in the Ob and Yenisey rivers, 1960-1988  

USGS Publications Warehouse

Of the world's great rivers, the Ob and Yenisey rank among the largest suppliers of fresh water and among the smallest suppliers of suspended sediment to the coastal ocean. Sediment in the middle reaches of the rivers is mobilized from bordering terraces and exchanged between channels and flood plains. Sediment in the lower reaches of these great rivers is deposited and stored (permanently, on a millennial time scale) in flood plains. Sediment discharges, already small under natural conditions, are diminished further by large manmade reservoirs that trap significant proportions of the moving solids. The long winter freeze and sudden spring breakup impose a peakedness in seasonal water runoff and sediment discharge that contrasts markedly with that in rivers of the tropics and more temperate climates. Very little sediment from the Ob and Yenisey rivers is being transported to the open waters of the Arctic Ocean under present conditions.

Meade, R. H.; Bobrovitskaya, N. N.; Babkin, V. I.

2000-01-01

372

Sediment Sources and Storage in the Chesapeake Bay Watershed  

NASA Astrophysics Data System (ADS)

Physically and chemically, sediment is a pollutant of concern in many waterbodies. In the Chesapeake Bay, sediment is having an adverse effect on the living resources and habitat of the Chesapeake Bay and its watershed. Identifying significant sources of watershed sediment is important in reducing sediment loads. In the Chesapeake Bay, several approaches were used to understand the sources, transport, and storage of watershed-derived sediment. From 1985 through 2001, the U.S. Geological Survey collected suspended sediment at 35 stations draining portions of the 103,000 km2 Chesapeake Bay. Of the 35 sites, 4 of the 6 highest sediment yields were in the Conestoga River Basin, Pennsylvania, which drains to the Susquehanna River. In the Susquehanna River Basin (43,600 km2), erosion rates were determined using atmospheric 10Be at 92 river outlets and confirmed that the highest rates of erosion were in the Conestoga River Basin. In three small watersheds draining to the Chesapeake Bay -- the Pocomoke River (157 km2), Little Conestoga Creek (68.1 km2), and Mattawoman Creek (92.8 km2) -- sediment sources were identified using a sediment-source identification approach. In this approach, the sources of fine-grained suspended sediment in transport can be established by comparing physical and chemical properties of the suspended sediment to potential sources. In this study, suspended sediment (< 0.062 mm) collected during storm runoff was compared to upland sediment sources (cropland, construction sites, and forest) and channel corridor sources (channel banks and bed) using radionuclides (210Pb, 137Cs), stable isotopes (13C, 15N), and total C, N, and P. Preliminary results are available for two of the three watersheds. In the Pocomoke River watershed, which drains the Coastal Plain physiographic province, ditch beds which were dug to drain cropland were a significant source of sediment. In the Little Conestoga Creek watershed, which drains the Piedmont physiographic province, river banks and cropland were significant sources.

Gellis, A. C.; Landwehr, J. M.; Pavich, M.; Hupp, C. R.; Ritchie, J. C.

2006-05-01

373

Influences of depositional environment and diagenesis on geophysical log response in the South Carolina Coastal Plain: effects of sedimentary fabric and mineralogy  

Microsoft Academic Search

Interpretations of depositional environments and hydrologic units are made routinely from the study of geophysical well logs. Spontaneous potential (SP) and resistivity logs can be used as indicators of textural parameters. Gamma-ray logs denote lithologic zones based on the presence of radioactive material, particularly in fine-grained sediments. On the South Carolina Coastal Plain, surficial fluvially derived cobbles, sands and clays

Donald L. Siron; Marylin P. Segall

1997-01-01

374

The influence of barometric pressure fluctuations, earth tides and rainfall loading on fluid pressures in coastal plain aquifers, Burke County, Georgia  

Microsoft Academic Search

High precision pressure measurements from several aquifers in the top 225 m of coastal plain sediments reveal that barometric pressure fluctuations, earth tides and rainfall loading create pressure fluctuations on the order of tens of centimeters. If not correctly identified, erroneous conclusions regarding the magnitude of pressure communication within and across aquifers during pumping tests may be inferred. Aquifer pressure

S. M. Benson; J. Moore; J. Daggett; D. S. Snipes

1993-01-01

375

Angiosperm pollen zonation of the continental cretaceous of the Atlantic coastal plain and its application to deep wells in the Salisbury embayment  

Microsoft Academic Search

This paper presents and illustrates an informal palynological zonation of the pre?Magothy continental Cretaceous sediments of the Atlantic Coastal Plain (Potomac Group, Raritan Formation), based primarily on new and previously published studies of angiosperm pollen from two wells near Delaware City, Delaware, and from outcrop samples from Virginia through New Jersey, following lines established by Brenner (1963). Monosulcate angiosperm pollen

James A. Doyle; Eleanora I. Robbins

1977-01-01

376

The Geologic Story of the Great Plains  

USGS Publications Warehouse

The Great Plains! The words alone create a sense of space and a feeling of destiny - a challenge. But what exactly is this special part of Western America that contains so much of our history? How did it come to be? Why is it different? Geographically, the Great Plains is an immense sweep of country; it reaches from Mexico far north into Canada and spreads out east of the Rocky Mountains like a huge welcome mat. So often maligned as a drab, featureless area, the Great Plains is in fact a land of marked contrasts and limitless variety: canyons carved into solid rock of an arid land by the waters of the Pecos and the Rio Grande; the seemingly endless grainfields of Kansas; the desolation of the Badlands; the beauty of the Black Hills. Before it was broken by the plow, most of the Great Plains from the Texas panhandle northward was treeless grassland. Trees grew only along the floodplains of streams and on the few mountain masses of the northern Great Plains. These lush prairies once were the grazing ground for immense herds of bison, and the land provided a bountiful life for those Indians who followed the herds. South of the grasslands, in Texas, shrubs mixed with the grasses: creosote bush along the valley of the Pecos River; mesquite, oak, and juniper to the east. The general lack of trees suggests that this is a land of little moisture, as indeed it is. Nearly all of the Great Plains receives less than 24 inches of rainfall a year, and most of it receives less than 16 inches. This dryness and the strength of sunshine in this area, which lies mostly between 2,000 and 6,000 feet above sea level, create the semiarid environment that typifies the Great Plains. But it was not always so. When the last continental glacier stood near its maximum extent, some 12,000-14,000 years ago, spruce forest reached southward as far as Kansas, and the Great Plains farther south was covered by deciduous forest. The trees retreated northward as the ice front receded, and the Great Plains has been a treeless grassland for the last 8,000-10,000 years. For more than half a century after Lewis and Clark crossed the country in 1805-6, the Great Plains was the testing ground of frontier America - here America grew to maturity (fig. 1). In 1805-7, explorer Zebulon Pike crossed the southcentral Great Plains, following the Arkansas River from near Great Bend, Kans., to the Rocky Mountains. In later years, Santa Fe traders, lured by the wealth of New Mexican trade, followed Pike's path as far as Bents Fort, Colo., where they turned southwestward away from the river route. Those pioneers who later crossed the plains on the Oregon Trail reached the Platte River near the place that would become Kearney, Nebr., by a nearly direct route from Independence, Mo., and followed the Platte across the central part of the Great Plains.

Trimble, Donald E.

1980-01-01

377

Visual sedimentation.  

PubMed

We introduce Visual Sedimentation, a novel design metaphor for visualizing data streams directly inspired by the physical process of sedimentation. Visualizing data streams (e. g., Tweets, RSS, Emails) is challenging as incoming data arrive at unpredictable rates and have to remain readable. For data streams, clearly expressing chronological order while avoiding clutter, and keeping aging data visible, are important. The metaphor is drawn from the real-world sedimentation processes: objects fall due to gravity, and aggregate into strata over time. Inspired by this metaphor, data is visually depicted as falling objects using a force model to land on a surface, aggregating into strata over time. In this paper, we discuss how this metaphor addresses the specific challenge of smoothing the transition between incoming and aging data. We describe the metaphor's design space, a toolkit developed to facilitate its implementation, and example applications to a range of case studies. We then explore the generative capabilities of the design space through our toolkit. We finally illustrate creative extensions of the metaphor when applied to real streams of data. PMID:24051811

Huron, Samuel; Vuillemot, Romain; Fekete, Jean-Daniel

2013-12-01

378

Towards a holistic sediment budget in a glacier forefield (Gepatschferner/Austria) - The contribution of fluvial sediment transport  

NASA Astrophysics Data System (ADS)

Glaciers in the European Alps have been retreating since the end of the Little Ice Age around 1850. Where the glaciers shrink, they leave unconsolidated sediment stores (moraines, till, glacifluvial deposits). These deposits are highly vulnerable to subsequent erosion. But knowledge of sediment fluxes and the interrelated geomorphological processes in proglacial areas, based on field-data, is lacking. Therefore, a new joint research project PROSA (High resolution measurements of the morphodynamic in rapidly changing PROglacial Systems of the Alps), is set up in the Kaunertal valley, Austrian Alps. It is focussed on the quantification of recent and subrecent sediment transport processes in the entire catchment in order to construct a holistic sediment budget. The fluvial system (main river) in proglacial areas is more or less continuously fed with (fine) sediment by glacial melt water (glacial milk) and infrequently (e.g. during rainstorm events) supplied with sediment by landslides, debris flows, rock fall from the slopes. A part of the sediment input is temporary stored in intermitted sinks, such as the river bed, bars or braid plains. These stores can be reworked and become a source for fluvial sediment transport mainly during floods. These sediment transporting processes are highly variable in both time and space. So the main aim of this project is the investigation of the interrelations of the sediment transport rates in the proglacial river below the Gepatschferner in the Kaunertal valley and the connected sediment sources and how these interrelations influence the sediment budget of the river. Suspended sediment load, solute load and bed load will be measured at several locations in the river on different time scales (event-based, daily, weekly etc.). Additionally the surface changes of important sediment sources (moraines, bars), which are directly connected to the river system, will be quantified by a comparison of multitemporal terrestrial and airborne laserscanning data.

Morche, D.; Baewert, H.; Schmidt, K.-H.

2012-04-01

379

Fire Cycles on the Northern Great Plains and Their Relation to Prairie Drought  

NASA Astrophysics Data System (ADS)

Drought is a naturally occurring, recurrent phenomenon that has historically gripped large regions of the United States, often with catastrophic consequences. Human insight into the duration, frequency, and dynamics of drought is largely limited to short-term observation. For example, the "Dust Bowl" of the 1930's in the central plains is one of the most vivid cases of prolonged drought in the USA and yet it persisted for less than a decade. To circumnavigate this limited perspective, we employed a paleoenvironmental approach to better characterize landscape response to prairie droughts and specifically document fire response to droughts. Two long sediment cores were collected from Kettle and Brush lakes in the Northern Great Plains (NGP) and age-depth models were developed for the cores by fitting locally weighted loess curves to AMS radiocarbon dates. The cores were continuously sub-sampled at high resolution (1 cm) for particulate charcoal, pollen, sediment mineralogy, and loss-on-ignition. In contrast to recent human observation, spectral and wavelet analyses reveal that multi-decadal to centennial drought cycles have persisted on the northern plains for much of the last ca. 10,000 years, though there were intervals where the cycles were muted, further compounding the dynamics of climate on the plains. In the latest Holocene interval, 160-year fire and drought cycles are clearly denoted. Fires are more common during the wet phases of the drought cycles because moist conditions foster increased grass productivity, resulting in greater fuel loads. In contrast, forbs expanded during the drier periods, limiting fuel loads which resulted in less fire. The charcoal data reveal three general Holocene fire intervals on the NGP associated with millennial-scale changes in climate. In general, the incidence of fire was greater in the early- and late-Holocene with less fire during the warm dry mid-Holocene.

Brown, K. J.; Clark, J. S.; Grimm, E. C.; Donovan, J. J.; Mueller, P.

2004-12-01

380

Holocene flood plain soil formation in the lower Mississippi River Valley: Implications for the interpretation of alluvial paleosols  

SciTech Connect

Holocene Mississippi River flood soils representing different depositional environments and ages were sampled along three east-west transects between Vicksburg, MS and Baton Rouge, LA. Flood plain soil development is primarily controlled by episodic flood plain sedimentation and ground water table fluctuations as evidenced by relatively thick cumulative soil profiles with abundant mottles, nodules, and slickensides. Within flood plain deposits of similar age, profile, development is best expressed in moderately-drained silty and sandy soils in natural levee and point bar ridge environmental that occur within and adjacent to meander belts. Soils in natural levee and point bar ridge environments greater than 3 ka generally are acidic and have better-developed Bt horizons and brighter mottles than their younger counterparts. In addition to being acidic and brightly mottled, older back swamp soils have larger and more abundant slickensides and iron nodules. This study suggests that alluvial paleosols formed in aggradational settings may be better suited for interpreting flood plain depositional histories and paleohydrology than climate. Parameters such as solum thickness and clay and carbonate accumulations, routinely used to estimate relative time and climatic effects on soil development in Quaternary studies of stable geomorphic surfaces, may not be applicable to ancient alluvial deposits that reflect continuous sediment aggradation.

Aslan, A. (Univ. of Colorado, Boulder, CO (United States). Dept. of Geological Sciences); Autin, W.J. (Louisiana Geological Survey, Baton Rouge, LA (United States))

1992-01-01

381

Glaciation of the Coastal Plain of Northern Alaska  

NASA Astrophysics Data System (ADS)

Our 15 years of studies of permafrost soils on the coastal plain of northern Alaska show that it was affected by a continental ice sheet during the last glacial maximum. Evidence for this includes: occurrence of buried glacial basal ice at Barter Island; widespread sandy diamicton from Demarcation Bay to Barrow of late Pleistocene age; orientation of surficial deposits; poorly integrated drainage and gentle ridge and swale topography; the continuity of glacial-related deposits from the coast to the Brooks Foothills; and perennially frozen sediments unlike those of unglaciated Arctic regions. We documented a 10-m-high exposure ~1 km long at Barter Island that had abundant basal glacier ice with large-scale deformation structures, complex ice-contact deposits, and highly deformed bedded silt, sand, and gravel inclusions within the basal ice. Similar ice structures were observed at Prudhoe Bay and Cape Halkett. The glacial till is highly unusual in that it is comprised of massive, non-fossiliferous, brackish, slightly pebbly loamy sand with occasional gravel to cobble-sized clasts. In most areas the till is only 2-5 m thick, although at Barter Island the till was up to 10- m thick. Gravel particles, which comprise 1-5% of the deposits, usually are 0.5-2 cm long, mostly durable chert, highly polished, and frequently cracked off at one end, with the broken face faceted and polished. We believe the material mostly originated from marine deposits on the continental shelf, although rocks of Canadian provenance also occur. Prevalent, large (1-5 m) deformation features of discontinuous yellow oxidized and gray reduced sediment suggest deformation of sediment during collapse of the ice sheet. The sandy till is found along most of the Beaufort coast with the exception of deltas and lagoons and is found inland as much as 80 km. The sandy till is easily eroded, causing the morainal margin to be indistinct and the topography subdued. Previous thermoluminescence dating by Rawlinson (1993) of the sediment indicates it was deposited 20-30 ka BP, and our radiocarbon dating of organic matter at the surface of the sediment indicates that deglaciation and surface stabilization occurred 10-17 ka BP. The glacial deposit is synchronous with the extensive late Pleistocene sand sea in the western Beaufort coastal plain that dates to 9.6-11.4 ka BP (Carter 1981) and the large loess belt along the lower Brooks Foothills that was deposited 20-30 ka BP. The sand sea and loess belt probably were deposited in unglaciated areas by catabatic winds associated with the ice sheet. The presence of an ice sheet that covered the Beaufort Sea and adjacent coast helps explain the lack of typical ice-rich Pleistocene permafrost (yedoma) along the Beaufort coast, the reported lack of permafrost on the outer continental shelf of the Beaufort Sea, and the lack of thaw-lake depressions on the continental shelf. In contrast, these features are abundant on unglaciated portions of the continental shelf in the Russian Arctic and northern Seward Peninsula and adjacent Chukchi Sea. This evidence from terrestrial deposits is consistent with recent evidence of glacial scouring at depths up to 700 m along the continental margin of the Beaufort Sea documented by Engels et al. (2007). We name this glaciation the Kuukpik Glaciation and the deposit the Kuukpik member of the Gubik Formation.

Jorgenson, M. T.; Shur, Y.

2008-12-01

382

Reaction-induced porosity and onset of carbonation in abyssal peridotites: insights from 3D high-resolution microtomography  

NASA Astrophysics Data System (ADS)

Serpentinites are products of hydrous alteration of ultramafic rocks and they are particularly common at slow-spreading mid-oceanic ridges, where tectonic faulting causes exposure of abyssal peridotites at the seafloor. Upon interaction with seawater, the chemical composition as well as the physical properties of peridotites change, and both hydration and carbonation are common. To understand the underlying processes, we performed a detailed study on harzburgite samples from ODP Leg 209 Site 1270D, located at the Mid-Atlantic ridge near 14°45'N. The study focused on one sample taken just 0.75 metres below seafloor. Detailed thin section microscopy revealed a high degree of serpentinization, but relict orthopyroxene (Mg/[Mg+Fe] = 0.91-0.92) and spinel are present. Locally, minor amounts of secondary talc and amphibole were found. Former olivine is completely replaced by serpentine (Mg/[Mg+Fe] = 0.95-0.97) and magnetite in mesh textures. Mesh centers commonly consist either of empty space (

Jöns, Niels; Kahl, Wolf-Achim; Bach, Wolfgang

2013-04-01

383

Isotopic signatures and nutrient relations of plants inhabiting brackish wetlands in the northeastern coastal plain of Venezuela  

Microsoft Academic Search

The semi-diurnal tidal regime (?2 m) in the Paria Gulf on the Atlantic coast of Venezuela, and the flat landscape of the region,\\u000a allow the penetration for tens of km of marine waters into the rivers draining the northeastern coastal plain of the country.\\u000a The levels of salinity, tidal flooding, and sedimentation decrease perpendicularly from the river channel toward the back

Ernesto Medina; Marta Francisco; Antonio Quilice

2008-01-01

384

Influence of lignite mining and utilization on organic matter budget in the Alfeios River Plain, Peloponnese (South Greece)  

SciTech Connect

The Megalopolis Lignite Centre (MLC) is a lignite mining and power generation complex located in Southern Greece. In the present study, we investigate the influence of mining and combustion activities on the organic matter (OM) budget of the adjacent Alfeios River plain sediments. A total of 28 plain-sediment samples along with 13 lignite and ash samples from the MLC were collected. The sediment samples were collected from sites upstream and downstream, as well as from the vicinity of the MLC. Their OM and total organic carbon contents range from 0.9 to 43.4 and 0.2 to 24.0 wt %, respectively. The particulate OM was classified in coal-derived, carbonized particles and fresh tissues according to its origin. The different OM phases were quantified using maceral analysis on the sediments' light fraction obtained after heavy media separations. Approximately 75 vol % of the OM was of anthropogenic origin (coal and char particles) related to mining, transport, and combustion processes at the MLC, revealing a high contamination degree. The most contaminated sites were those in the vicinity of the MLC, but upstream and downstream sites also proved to contain high concentrations of anthropogenic OM. The polycyclic aromatic hydrocarbons content of the same sediments was very low, similar to pristine areas indicating that there is no contamination from such compounds in the area. 82 refs., 7 figs., 6 tabs.

G. Siavalas; S. Kalaitzidis; G. Cornelissen; A. Chatziapostolou; K. Christanis [University of Patras, Rio-Patras (Greece). Department of Geology

2007-09-15

385

Hydrogeochemical analysis for Tasuj plain aquifer, Iran  

NASA Astrophysics Data System (ADS)

This study investigated the hydrogeochemical processes of groundwater in the Tasuj plain, Iran. The Tasuj plain is one of the 12 marginal plains around Urmia Lake which is currently under a critical ecological condition. In the last decades, the Tasuj plain aquifer suffered from severe groundwater level declination and caused degradation of groundwater quality. To better understand hydrogeochemical processes in the Tasuj plain, this study adopted graphical methods and multivariate statistical techniques to analyze groundwater samples. A total of 504 groundwater samples was obtained from 34 different locations (qanats, wells, and springs) over 12 years (1997-2009) and analyzed for 15 water quality parameters. From the results, the Piper diagram indicated four groundwater types and the Stiff diagram showed eight different sources of groundwater samples. The Durov diagram identified five major hydrogeochemical processes in the aquifer. However, hierarchical cluster analysis (HCA) identified five water types in the groundwater samples because HCA was able to analyze more chemical and physical data than graphical methods. The HCA result was checked by discriminant analysis and found consistency in all samples that were classified into correct groups. Using factor analysis, we identified three factors that accounted for 81.6% of the total variance of the dataset. Based on the high factor loadings of the variables, factors 1 and 2 reflected the natural hydrogeochemical processes and factor 3 explained the effect of agricultural fertilizers and human activities in the Tasuj plain. Dendrograms from 2000 to 2009 were studied to understand the temporal variation of groundwater quality. Comparing the distributions of groundwater types in 2000 and 2009, we found that the mixing zone was expanded. This may be due to artificial groundwater recharge in the recharge area and the effect of inverse ion exchange in the discharge area.

Nadiri, Ata Allah; Moghaddam, Asghar Asghari; Tsai, Frank T.-C.; Fijani, Elham

2013-08-01

386

Late Middle Pleistocene deposits at Norton Farm on the West Sussex coastal plain, southern England  

NASA Astrophysics Data System (ADS)

The coastal plain of West Sussex, southern England, is internationally important because of the sequence of discrete high-sea-level events preserved at various elevations across it. New evidence is presented from a site at Norton Farm, near Chichester, on the Lower Coastal Plain, where Pleistocene marine sands, fining upwards into silts, occur between 5.3 m and 9.1 m OD. The sequence reflects a regressive tendency at the transition from an interglacial to a cold stage. The marine sands have yielded foraminifera, ostracods and molluscs that indicate a declining marine influence through the sequence, culminating in a tidal mudflat, strongly weathered in places. Cool-climate foraminifera (including Elphidium clavatum, Cassidulina reniformis and Elphidium albiumbilicatum) and ostracods have been recovered from the marine sands. Some species with an apparent preference for warmer water conditions, however, are also present. Freshwater taxa washed into the terminal marine sediments include some cold climate indicators, such as Pisidium stewarti and P. obtusale lapponicum. Additional evidence for cool climatic conditions during the deposition of the upper part of the marine sequence is provided by the lack of tree taxa in the pollen record and by features of the micromorphology. The marine sediments probably began accumulating during OIS 7, a conclusion based on their elevation, on amino acid ratios from shells, but especially on vertebrate evidence, particularly the presence of a small form of horse, together with a large, distinctive, form of northern vole (Microtus oeconomus). The occurrence of cool climate indicators in these marine sediments may demonstrate a lag between the climatic deterioration and the expected glacio-eustatic fall in relative sea-level. This evidence appears to support the conclusions drawn from the study of coral terraces in Barbados. Such a scenario would provide the conditions necessary for the emplacement of the large erratic boulders reported from the Lower Coastal Plain of West Sussex.

Bates, Martin R.; Bates, C. Richard; Gibbard, Philip L.; MacPhail, Richard I.; Owen, Frederick J.; Parfitt, Simon A.; Preece, Richard C.; Roberts, Mark B.; Robinson, J. Eric; Whittaker, John E.; Wilkinson, Keith N.

2000-01-01

387

Iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids  

NASA Astrophysics Data System (ADS)

Volcanogenic sediments are typically rich in Fe and Mn-bearing minerals that undergo substantial alteration during early marine diagenesis, however their impact on the global biogeochemical cycling of Fe and Mn has not been widely addressed. This study compares the near surface (0-20 cm below sea floor [cmbsf]) aqueous (<0.02 ?m) and aqueous + colloidal here in after 'dissolved' (<0.2 ?m) pore water Fe and Mn distributions, and ancillary O2(aq), NO3- and solid-phase reactive Fe distributions, between two volcanogenic sediment settings: [1] a deep sea tephra-rich deposit neighbouring the volcanically active island of Montserrat and [2] mixed biosiliceous-volcanogenic sediments from abyssal depths near the volcanically inactive Crozet Islands archipelago. Shallow penetration of O2(aq) into Montserrat sediments was observed (<1 cmbsf), and inferred to partially reflect oxidation of fine grained Fe(II) minerals, whereas penetration of O2(aq) into abyssal Crozet sediments was >5 cmbsf and largely controlled by the oxidation of organic matter. Dissolved Fe and Mn distributions in Montserrat pore waters were lowest in the surface oxic-layer (0.3 ?M Fe; 32 ?M Mn), with maxima (20 ?M Fe; 200 ?M Mn) in the upper 1-15 cmbsf. Unlike Montserrat, Fe and Mn in Crozet pore waters were ubiquitously partitioned between 0.2 ?m and 0.02 ?m filtrations, indicating that the pore water distributions of Fe and Mn in the (traditionally termed) 'dissolved' size fraction are dominated by colloids, with respective mean abundances of 80% and 61%. Plausible mechanisms for the origin and composition of pore water colloids are discussed, and include prolonged exposure of Crozet surface sediments to early diagenesis compared to Montserrat, favouring nano-particulate goethite formation, and the elevated dissolved Si concentrations, which are shown to encourage fine-grained smectite formation. In addition, organic matter may stabilise authigenic Fe and Mn in the Crozet pore waters. We conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water, which may impact significantly on deep ocean biogeochemistry. Diffusive flux estimates from Montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved Mn to the bottom waters, and therefore a source for the widespread hydrogenous MnOx deposits found in the Caribbean region.

Homoky, W. B.; Hembury, D. J.; Hepburn, L. E.; Mills, R. A.; Statham, P. J.; Fones, G. R.; Palmer, M. R.

2011-09-01

388

Data and Administrative Considerations for Two District Flood Plain Zoning.  

National Technical Information Service (NTIS)

National flood plain management policy has shifted from placing the primary emphasis on structural controls to a balance between structural and regulatory type controls. Two district flood plain zoning, in which the flood hazard area is divided into flood...

S. J. Burges J. S. Hillmer

1974-01-01

389

18 CFR 801.8 - Flood plain management and protection.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2012-04-01 true Flood plain management and protection. 801...COMMISSION GENERAL POLICIES § 801.8 Flood plain management and protection. ...waterways has not discouraged development of flood hazards areas. Major floods cause...

2013-04-01

390

Evolution of radioactive dose rates in fresh sediment deposits along coastal rivers draining Fukushima contamination plume  

PubMed Central

Measurement of radioactive dose rates in fine sediment that has recently deposited on channel bed-sand provides a solution to address the lack of continuous river monitoring in Fukushima Prefecture after Fukushima Dai-ichi nuclear power plant (FDNPP) accident. We show that coastal rivers of Eastern Fukushima Prefecture were rapidly supplied with sediment contaminated by radionuclides originating from inland mountain ranges, and that this contaminated material was partly exported by typhoons to the coastal plains as soon as by November 2011. This export was amplified during snowmelt and typhoons in 2012. In 2013, contamination levels measured in sediment found in the upper parts of the catchments were almost systematically lower than the ones measured in nearby soils, whereas their contamination was higher in the coastal plains. We thereby suggest that storage of contaminated sediment in reservoirs and in coastal sections of the river channels now represents the most crucial issue.

Evrard, Olivier; Chartin, Caroline; Onda, Yuichi; Patin, Jeremy; Lepage, Hugo; Lefevre, Irene; Ayrault, Sophie; Ottle, Catherine; Bonte, Philippe

2013-01-01

391

Evolution of radioactive dose rates in fresh sediment deposits along coastal rivers draining Fukushima contamination plume.  

PubMed

Measurement of radioactive dose rates in fine sediment that has recently deposited on channel bed-sand provides a solution to address the lack of continuous river monitoring in Fukushima Prefecture after Fukushima Dai-ichi nuclear power plant (FDNPP) accident. We show that coastal rivers of Eastern Fukushima Prefecture were rapidly supplied with sediment contaminated by radionuclides originating from inland mountain ranges, and that this contaminated material was partly exported by typhoons to the coastal plains as soon as by November 2011. This export was amplified during snowmelt and typhoons in 2012. In 2013, contamination levels measured in sediment found in the upper parts of the catchments were almost systematically lower than the ones measured in nearby soils, whereas their contamination was higher in the coastal plains. We thereby suggest that storage of contaminated sediment in reservoirs and in coastal sections of the river channels now represents the most crucial issue. PMID:24165695

Evrard, Olivier; Chartin, Caroline; Onda, Yuichi; Patin, Jeremy; Lepage, Hugo; Lefèvre, Irène; Ayrault, Sophie; Ottlé, Catherine; Bonté, Philippe

2013-10-29

392

Sediment Risk Assessment Workshop.  

National Technical Information Service (NTIS)

Sediments are both a source and a sink for persistent contaminants which enter the aquatic environment. Sediment quality assessments involving sediment bioassays began at about the same time as environmental risk assessment (ERA) procedures (the early 198...

G. Schiefer

1995-01-01

393

CONTAMINATED SEDIMENTS SCIENCE PRIORITIES  

EPA Science Inventory

The Contaminated Sediment Science Priorities (CSSP) document isa mechanism for the U.S. EPA to develop and coordinate Agency-wide science activities that affect contaminated sediments. It analyzes current Agency contaminated sediments science activities, identifies and evaluates...

394

Karst evolution of the Nullarbor Plain, Australia  

Microsoft Academic Search

The Nullarbor Plain of southeastern Australia, ~200,000 km2 in area, is flat and mostly treeless. It contains widely scattered collapse dolines and a few hundred caves, some of which are large and extensive. Initial karst development probably occurred during the warm, seasonally wet climatic conditions of the Oligocene, when the with- drawal of the sea exposed the recently deposited Eocene

John A. Webb; Julia M. James

395

The plain abdominal radiograph in acute appendicitis.  

PubMed Central

Although the radiological features of acute appendicitis have been well documented, the value of the plain abdominal radiograph has not been fully appreciated. This article summarises the role of radiology in acute appendicitis, especially in atypical cases and extremes of age, where there is often delay in diagnosis. Images FIG. 1 FIG. 2

Thorpe, J. A.

1979-01-01

396

Great plains regional climate assessment technical report  

Technology Transfer Automated Retrieval System (TEKTRAN)

The Great Plains region (GP) plays important role in providing food and energy to the economy of the United States. Multiple climatic and non-climatic stressors put multiple sectors, livelihoods and communities at risk, including agriculture, water, ecosystems and rural and tribal communities. The G...

397

Agricultural Change Among Great Plains Russian Germans  

Microsoft Academic Search

Russian German farmers who concentrated on the Great Plains in the late nineteenth century brought with them agricultural experience in a subhumid environment. Their diversified operations and use of small grains contrasted sharply with the humid-land agricultural system, emphasizing corn and livestock, dominant among settlers from the Midwest. The need to adopt strategies appropriate to the climate of the Great

Bradley H. Baltensperger

1983-01-01

398

Geothermal features of Snake River plain, Idaho  

SciTech Connect

The Snake River plain is the track of a hot spot beneath the continental lithosphere. The track has passed through southern Idaho as the continental plate has moved over the hot spot at a rate of about 3.5 cm/yr. The present site of the hot spot is Yellowstone Park. As a consequence of the passage, a systematic sequence of geologic and tectonic events illustrates the response of the continental lithosphere to this hotspot event. The three areas that represent various time slices in the evolution are the Yellowstone Plateau, the Eastern Snake River plain downwarp, and the Western Snake River plain basin/Owhyee Plateau. In addition to the age of silicic volcanic activity, the topographic profile of the Snake River plain shows a systematic variation from the high elevations in the east to lowest elevations on the west. The change in elevation follows the form of an oceanic lithosphere cooling curve, suggesting that temperature change is the dominant effect on the elevation.

Blackwell, D.D.

1987-08-01

399

Reading for Young People: The Great Plains.  

ERIC Educational Resources Information Center

One of five annotated bibliographies that describe books about certain regions of the United States, this compilation focuses on books about the Great Plains. The stated purposes of these regional bibliographies are: (1) to introduce young people living in the subject region to books dealing with their cultural heritage, (2) to help young people…

Laughlin, Mildred

400

Dynamics of Urban Development on Flood Plains.  

National Technical Information Service (NTIS)

This study presents a descriptive analysis of urban land use development on flood plain areas within Wichita, Kansas. The principal data source is building permits and tax records which identify the number of square feet of floor space constructed, year o...

R. F. Wiseman

1977-01-01