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1

Biogeochemical processes at the sediment water interface in a Northeastern Atlantic abyssal locality (Porcupine Abyssal Plain)  

NASA Astrophysics Data System (ADS)

Temporal and spatial variability in the composition of suspended particulate material (SPM) was found at a Northeastern Atlantic abyssal locality on the Porcupine Abyssal Plain at a depth of 4850 m. Total SPM was distinctly higher in July 1997 than in March-April 1997 and October 1996. The 20 m of water immediately overlying the seabed was strongly influenced by resuspension and the suspended particulate matter was enriched with iron and manganese. Two water distinct layers, which were characterized by being enriched with SPM, Fe p, Mn p and Al p, were encountered during all sampling periods at depths of 4000 m and 4800 m. The enrichment of SPM with biogenic elements such as Ba, Ca and Sr implies it has a high biogenic content. Increases were observed in the concentrations of these biogenic elements throughout the sampling period, which indicates that the biogenic content of the SPM was steadily increased. SPM content and element/aluminum ratios increased in the spring and summer of 1997 compared to autumn 1996, probably as a result of increases in primary productivity, coincidental increases in near-bottom current velocities and possibly other processes such as increases in bacterial activity and bioturbation. Authigenic formation of solid phases of Fe and Mn were also influencing the spatial variability. Chemical reactions involving organic carbon and oxygen, which lead to the incorporation of iron and manganese in various forms into sediments were deduced. It is proposed that there was formation of lepidocrocite (?-FeOOH) in the presence of organic carbon and oxygen, and also that iron may also have been transformed into Fe 2O 3. Re-precipitation of Fe and Mn is strongly enhanced by their enrichment in the SPM in the bottom waters. The sediments predominantly consist of biogenic carbonates and can be characterized as foraminiferal ooze. The proportion of these biogenic carbonates proved to be higher in the more recent sediments, either as result of recent increases in total primary productivity or because of carbonate dissolution within the subsurface sediments. Parallel increases of Mn, Fe and carbonates in the sediment layers supports the idea that the metallic ions are being adsorbed on to calcite surfaces, rather than being co-precipitated in the carbonate phases. Reprecipitation of iron and manganese in other solid phases with the involvement of organic carbon (C org) in the oxygen penetration zone is suggested.

Varnavas, S. P.; Panagiotaras, D.; Wolff, G. A.

2

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

3

Elemental Analysis of Sediments and Organisms from the Cape Verde Abyssal Plain (CV 1 and CV 2 Sites).  

National Technical Information Service (NTIS)

Some 20 stable elements were determined by neutron activation analysis in epibenthic organisms and sediments from the Cape Verde abyssal plain. The levels measured in two Plesiopenaeus sp. (shrimp) individuals and one Barathrites sp. (fish) individual are...

P. Germain D. Boust M. Sibuet J. C. Philippot G. Hemon

1984-01-01

4

Biogeochemical processes at the sediment–water interface in a Northeastern Atlantic abyssal locality (Porcupine Abyssal Plain)  

Microsoft Academic Search

Temporal and spatial variability in the composition of suspended particulate material (SPM) was found at a Northeastern Atlantic abyssal locality on the Porcupine Abyssal Plain at a depth of 4850 m. Total SPM was distinctly higher in July 1997 than in March–April 1997 and October 1996. The 20 m of water immediately overlying the seabed was strongly influenced by resuspension

S. P. Varnavas; D. Panagiotaras; G. A. Wolff

2001-01-01

5

Recycling and burial of organic carbon in sediments of the Porcupine Abyssal Plain, NE Atlantic  

NASA Astrophysics Data System (ADS)

Rates of degradation, recycling and burial of organic carbon (OC) and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP) in the Northeast Atlantic Ocean (depth 4800-4850 m) during six cruises in August 1996—April 1999. Benthic fluxes of total dissolved inorganic carbon ( CT) and alkalinity ( AT) were measured in situ using benthic chambers of a free-vehicle benthic lander on four of the cruises. To obtain the OC oxidation rate ( Cox), the CT flux in each chamber was corrected for CaCO 3 dissolution. Burial of OC was determined by using downcore profiles of OC ( n=20) in the solid phase of the sediment and sediment accumulation rates estimated from a model age based on 14C dating of foraminifera. Results obtained showed that during 1996-1999 Cox rates in PAP sediments varied between deployments from 0.21±0.04 to 0.86±0.23 mmol m -2 d -1 with a total mean of 0.46 mmol m -2 d -1 (SD±0.37, n=31). No statistically significant spatial (between stations) or temporal (seasonal as well as interannual) variation in the Cox rates could be detected during the sampling period. The mean burial rate was determined to be 0.03±0.01 mmol m -2 d -1. On average over the sampling period, ˜94% of the particulate organic carbon (POC) deposited was recycled as CT to the overlying water and ˜6% was buried. The calculated mean POC demand during 1996-1999 of 0.49±0.37 mmol m -2 d -1 (the sum of corrected CT and burial fluxes) was not significantly different from the annual integrated mean POC supply (1997-1999) of 0.24±0.06 mmol m -2 d -1 estimated from calibrated sediment traps 1800 mab at the same locality.

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

2004-06-01

6

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

NASA Astrophysics Data System (ADS)

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 (NH 4) and nitrate (NO 3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO 3, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with 14C-based sediment accumulation rates and dry bulk density. Average NH 4 and NO 3-effluxes were 7.4 ± 19 ?mol m -2 d -1 ( n = 7) and 52 ± 30 ?mol m -2 d -1 ( n = 14), respectively, during the period 1996-2000. During the same period, the DON-flux was 11 ± 5.6 ?mol m -2 d -1 ( n = 5) and the denitrification rate was 5.1 ± 3.0 ?mol m -2 d -1 ( n = 22). Temporal and spatial variations were only found in the benthic NO 3 fluxes. The average burial rate was 4.6 ± 0.9 ?mol m -2 d -1. On average over the sampling period, the recycling efficiency of the PON input to the sediment was ?94% and the burial efficiency hence ?6%. The DON flux constituted ?14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year -1, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3-12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean.

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

2004-12-01

7

Determination of sediment volumes, accumulation rates and turbidite emplacement frequencies on the Madeira Abyssal Plain (NE Atlantic): a correlation between seismic and borehole data  

Microsoft Academic Search

The sedimentary infill history of the Madeira Abyssal Plain (MAP) is established from correlation of ODP Leg 157 drillsites (Sites 950–952) with an almost regular grid of ?7000 km of intermediate-resolution seismic reflection profiles covering the central part of the abyssal plain. The most conspicuous seismic reflectors bounding the seismostratigraphic units have been identified and mapped. Correlation between seismic and

B. Alibés; R. G. Rothwell; M. Canals; P. P. E. Weaver; B. Alonso

1999-01-01

8

A Prediction of Sonic Properties of Deep-Sea Cores, Sohm Abyssal Plain and Environs.  

National Technical Information Service (NTIS)

Within the Sohm Abyssal Plain sand and coarse silt are major constituents of bottom deposits. These coarse layers are interstratified with clay. High impedence contrasts at the water-sediment interface and at textural breaks within the sediment section fa...

D. R. Horn M. Ewing M. N. Delach B. M. Horn

1969-01-01

9

Bioturbation, geochemistry and geotechnics of sediments affected by the oxygen minimum zone on the Oman continental slope and abyssal plain, Arabian Sea  

NASA Astrophysics Data System (ADS)

We investigate the way the oxygen minimum zone (OMZ) alters interactions between bioturbation and sediment geochemistry, and geotechnical properties. Sediments are compared within and below the OMZ on the Oman continental slope and adjacent abyssal plain during the post monsoonal autumn season. Quantitative measurements were made of Eh and pH, of total organic matter (TOM) and carbonate, of water content and shear strength, and of bioturbation structures in vertical profiles of subcores taken from spade-box core samples. The OMZ stations had distinctively low redox conditions and high carbonate content, and different geotechnical properties and different bioturbation structures than stations below the OMZ on the abyssal plain. These differences are related to the degree of anoxia and to water depth. Within the OMZ, Eh, pH and carbonate increased with water depth, and TOM and water content decreased. We also noted the presence of subsurface sediment heterogeneity on the continental slope within the OMZ. In the OMZ, Eh, water content and bioturbation decreased with increasing sediment depth. There was a slight decrease in pH in the top 5 cm at all stations. Shear strength nearly always increased with increasing sediment depth. At each water depth correlations show down-core trends in these parameters, while across all water depths correlations were significant at deeper sediment depths (20-30 cm). An Eh-pH diagram identified two water-depth groupings: 391-1008 and 1265-3396 m. Cluster analysis showed the upper and lower sediment depths form separate clusters, the break occurring at 4-7.5 cm; while there are also distinct clusters related to water depth. We relate our results to bottom-water oxygen concentrations reported by other investigators, and to regional-scale geochemical processes.

Meadows, Azra; Meadows, Peter S.; West, Fraser J. C.; Murray, John M. H.

2000-01-01

10

Aleutian Deep-Sea Channel on the Aleutian Abyssal Plain.  

National Technical Information Service (NTIS)

The Aleutian abyssal plain is a vast turbidite deposit south of the Aleutian trench. Another prominent channel trends south-westerly for more than 1,000 km across the abyssal plain. This feature consists of a series of deltaic structures extending along i...

F. P. Naugler

1970-01-01

11

Chemical Speciation Modelling of the South Terras and Madeira Abyssal Plain Natural Analogue Sites.  

National Technical Information Service (NTIS)

The chemical speciation of uranium has been modelled using field data from the South Terras and Madeira Abyssal Plain natural analogue sites. In general, validation is good, particularly for the Abyssal Plain model. Problems regarding uranium redox couple...

J. R. Duffield L. Xu D. R. Williams

1988-01-01

12

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

13

GLORIA side-scan imagery of Aleutian basin, Bering Sea slope and Abyssal plain  

SciTech Connect

During July-September 1986, about 700,000 km/sup 2/ of continental slope and abyssal plain of the Aleutian basin, Bering Sea, were insonified with GLORIA (Geological Long Range Inclined Asdic) side-scane sonar. A sonar mosaic displays prominent geomorphic features including the massive submarine canyons of the Beringian and the northern Aleutian Ridge slopes and shows well-defined sediment patterns including large deep-sea channels and fan systems on the Aleutian basin abyssal plain. Dominant erosional and sediment transport processes on both the Beringian and the Aleutian Ridge slopes include varieties of mass movement that range from small debris flows and slides to massive slides and slumps of blocks measuring kilometers in dimension. Sediment-flow patterns that appear to be formed by sheet flow rather than channelized flow extend basinward from the numerous canyons and gullies that incise the slopes of the Beringian margin and of Bowers Ridge and some places along the Aleutian Ridge. These Beringian and Bowers canyon sediment sources, however, appear to have contributed less modern sediment to the Aleutian basin than the large, well-defined channel systems that emanate from Bering, Umnak, and Amchitka submarine canyons and extend for several hundred kilometers across the abyssal plain. This GLORIA imagery emphasizes the important contribution of the Aleutian Ridge to modern sedimentation in the deep Bering Sea.

Carlson, P.R.; Cooper, A.K.; Gardner, J.V.; Karl, H.A.; Marlow, M.S.; Stevenson, A.J.; Huggett, Q.; Kenyon, N.; Parson, L.

1987-05-01

14

System requirements report for Abyssal Plains waste isolation project  

SciTech Connect

The Department of Defense`s Naval Research Laboratory (NRL) has been tasked by the Strategic Environmental Research and Development Program (SERDP) to study environmental viability of the storage of dredged materials, sewage sludge, and municipal incinerator fly ash in the abyssal plains of the ocean floor. Abyssal Plains Waste Isolation (APWI) is the term given by this project to the storage of waste in the abyssal plains. Oceaneering Technologies (OTECH) has been tasked by the NRL to assess waste handling technologies regarding engineering feasibility and reliability. The first step in assessing waste handling technologies as to engineering feasibility and reliability is to identify top level or system level requirements that will have to be met by any APWI technology considered. Sources of APWI system level requirements are environmental regulations, physical and chemical characteristics of the waste streams (dredged materials, sewage sludge, and municipal incinerator fly ash), weather/site conditions, and standard references for ocean going vessels. A literature search of each of these sources was performed. The information extracted from these various sources was placed into the categories of handling, transportation, and emplacement. System level requirements were then derived from the information contained in the sources mentioned above.

Marcy, A.L.; Richards, W.R.; Hightower, J.M.

1994-09-26

15

An Evaluation of Neogene Sedimentation on the Surveyor Fan, Gulf of Alaska: Geochemical, Mineralogical, and Rock Magnetic Provenance Variation in Alaskan Abyssal Plain Sediments  

NASA Astrophysics Data System (ADS)

Glaciated orogenic belts such as those of southeastern Alaska provide ideal environments in which to investigate climate-tectonic interactions because of significant glacigenic sediment production and transport along an active plate boundary. The sedimentary record of this interaction has a high potential for preservation in adjacent basins like the Gulf of Alaska because of a reduced transport distance from sediment source to deepwater sink. The Surveyor Fan in the northern Gulf of Alaska contains seismic stratigraphic evidence of a substantial shift in sedimentation type and source. Based on limited age control from DSDP Site 178 this shift occurs at ~1 Ma, which approximately correlates to increased glacial sediment input and accelerated exhumation of onshore terranes. This coincides with significantly increased global glaciation following the Mid-Pleistocene Transition (MPT). We hypothesize that the compositional changes in Surveyor Fan fine-grain sediments observed at Site 178 are related to intensified glaciation at 1 Ma, which resulted in focused erosion along the windward side of the St. Elias Range, as well as formation of cross-shelf sea valleys that isolated sediment transport pathways to the Surveyor Channel. Here, we address this hypothesis by developing preliminary source terrane signatures of fine-grained sediment and applying them to offshore sediments of the Surveyor Fan at DSDP Site 178. This is done by employing multiple analytical tools shown to be effective in previous provenance studies, including trace and major elemental geochemistry, quantitative mineralogy, and environmental magnetic properties. The results of these analyses indicate that the provenance of the likely source end-members (Orca and Valdez Groups of the Prince William Terrane, the Chugach Terrane, and the Kulthieth/Poul Creek Formations) along the windward side of the St. Elias Range can be differentiated using a combination of these techniques. Fine-grained sediments from the Orca and Valdez Groups (OVG) of the Prince William Terranes and the Kulthieth Formation of the Yakutat Terrane represent relatively more mafic and felsic compositional end members, respectively, with Chugach Terrane samples of intermediate composition, but with distinct environmental magnetic properties. Poul Creek Formation samples are most similar to the Kultieth, but with the addition from a more mafic source. Samples of the youngest onshore source, the Yakataga Formation, reflect a mixing of sources. DSDP 178 samples are of an intermediate composition between felsic and mafic end members, but with no apparent bulk fine-grain compositional difference between Upper and Mid-Lower Fan constituents. However, the variability in elemental composition is significantly decreased in Upper Fan sediments supporting the hypothesis that transport pathways to Site 178 were isolated following the MPT at ~ 1 Ma.

Jaeger, J. M.; Ullrich, A. D.

2011-12-01

16

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

17

Currents, Dispersion and Light Transmittance Measurements on the Madeira Abyssal Plain. Final Report March 1987,  

National Technical Information Service (NTIS)

Near bottom currents have been measured in the GME study area (near 31 30N 25W) over a 3 year period. The sites selected were on top of a small abyssal hill, on its flank and 30km distant from it on the abyssal plain. The magnitude of the mean currents 10...

P. M. Saunders

1987-01-01

18

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

USGS Publications Warehouse

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 elastic 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 of 830 to 3450 yr (average 2000 yr). The average net accumulation rate of the mixed sequence of turbidites and thin pelagite interbeds in the cores is about 1.2 m/1000 yr. Physiography suggests that the turbidites originated on the Mackenzie Delta or its clinoform, and ??13C values of -27 to - 25??? in the turbidites are compatible with a provenance on a delta. Extant displaced neritic and lower slope to basin plain calcareous benthic foraminifers coexist in the turbidite units. Their joint occurence indicates that the turbidites originated on the modern continental shelf and entrained sediment from the slope and rise enroute to their final resting place on the Canada Abyssal Plain. The presence of Middle Pleistocene diatoms in the turbidites suggests, in addition, that the turbidites may have originated in shallow submarine slides beneath the upper slope or outer shelf. Small but consistent differences in organic carbon content and ??13C values between the turbidite units suggest that they did not share an identical provenance, which is at least compatible with an origin in slope failures. The primary provenance of the ice-rafted component of the pelagic beds was the glaciated terrane of northwestern Canada; and the provenance of the turbidite units was Pleistocene and Holocene sedimentary deposits on the outer continental shelf and upper slope of the Mackenzie Delta. Largely local derivation of the sediment of the Canada Abyssal Plain indicates that sediment accumulation rates in the Arctic Ocean are valid only for regions with similar depositional sources and processes, and that these rates cannot be extrapolated regionally. The location of an elliptical zone of active seismicity over the inferred provenance of the turbidites suggests that they were triggered by large earthquakes. Distal turbidite sediment accumulation rates were more than two orders of magnitude greater than pelagic sediment accumulation rates on the Canada Abyssal Plain during the last 8000 years. This disparity reconciles the discrepancy between the high accumulation rates assumed by some for the Arctic Ocean because of the numerous major rivers and large ice sheets that discharge into this small mediterranean basin and the low pelagic sedimentation rates that have been reported from the Arctic Ocean.

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

1996-01-01

19

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

Microsoft Academic Search

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

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

2010-01-01

20

Variability in ultraplankton at the Porcupine Abyssal Plain study site  

NASA Astrophysics Data System (ADS)

Observations of the ultraplankton (<5 ?m) are presented from a 4 day mesoscale survey centred on the Porcupine Abyssal Plain (PAP) study site (49°00'N 16°30'W), in July 2006. The organisms enumerated include two groups of phytoplankton, Synechococcus cyanobacteria, heterotrophic bacteria, large viruses, and two size classes of heterotrophic protist. The dataset comprises over 400 samples from the mixed layer taken over a 100 × 100 km 2 area at a spatial resolution of typically 2-3 km. For phytoplankton and heterotrophic bacteria there is a clear bimodal structure to the histograms of abundance indicative of two distinct communities in the region. Using the strong bimodality of one of the phytoplankton groups' histogram as a basis, the dataset is split into two subsets, with roughly 200 points in each, corresponding to the two histogram peaks. Doing so provides evidence that Synechococcus and viruses may also have a bimodal structure. Correlations between all pairings of these five organisms (both phytoplankton groups, Synechococcus, heterotrophic bacteria and viruses) are positive and quite high (r>0.7). The two communities can therefore be characterised as high and low abundance. Although there is a coincidence of low abundances with high temperatures in the southwest corner of the region, where there was known to be an eddy present, the spatial distributions of these organisms over the whole region is poorly predicted by temperature (or salinity or density). Furthermore, the spatial distributions of heterotrophic protists are found to differ strongly from those of the other organisms, having a unimodal structure and no obvious large scale structure. The more random structure of the heterotrophs' spatial distribution compared to their prey is consistent with previous results from the continental shelf, but is demonstrated for the open ocean here for the first time. Spatial variability is a large potential source of error in point samples, such as those comprising time series or transect cruises, unless a sufficient number of samples are taken. This large dataset is further used to provide guidance on the number of samples that would be required to estimate the mean abundance for the organisms accurately in this spatially variable region. Even if the bimodal structure was known initially, many of the organisms would require 10 or more samples to estimate the mean with 25% accuracy.

Martin, Adrian P.; Zubkov, Mikhail V.; Holland, Ross J.; Tarran, Glen; Burkill, Peter

2010-08-01

21

Domains of occupation of abyssal scavengers inferred from baited cameras and traps on the Demerara Abyssal Plain  

NASA Astrophysics Data System (ADS)

Baited cameras and traps were deployed on the Demerara Abyssal Plain at a depth of 4850 m to assess the behavior, diversity, vertical zonation and abundance of motile near-bottom scavengers. The composition of the fauna that was attracted differed with type of bait and distance from bottom. While several fishes (primarily the ophidiid cf. Barathrites iris) and a penaeid crustacean (cf. Plesiopenaius edwardsi) were attracted to bait on the bottom, only a large mysid (cf. Gnathophausia ingens) gathered to a large tuna bait moored at 200 m off bottom. In no case was the bait utilized extensively. Rates of arrival over time were estimated for each species at each bait. These rates of recruitment were used in a model of "attractant dispersal" to define a "domain of occupation" for each of the common species. The possible ranges in animal abundances, given the uncertainties in the model, have been evaluated for each species.

Rowe, Gilbert T.; Sibuet, Myriam; Vangriesheim, Annick

1986-04-01

22

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

NASA Astrophysics Data System (ADS)

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 of magnitude. Samples from the Porcupine Abyssal Plain over a longer period (1977-1999) show that prior to 1996 these holothurian species were always a minor component of the megafauna. From 1996 to 1999 A. rosea was abundant over a wide area of the Porcupine Abyssal Plain indicating that the phenomenon was not a localised event. Several dominant holothurian species show a distinct trend in decreasing body size over the study period. The changes in megafauna abundance may be related to environmental forcing (food supply) rather than to localised stochastic population variations. Inter-annual variability and long-term trends in organic matter supply to the seabed may be responsible for the observed changes in abundance, species dominance and size distributions.

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

23

The Galicia Bank Influence on the Southern Iberia Abyssal Plain Drilling Transect  

NASA Astrophysics Data System (ADS)

The Iberia nonvolcanic rifted margin has been studied primarily within the context of two distinct segments: Galicia Bank (GB) and the Southern Iberia Abyssal Plain (SIAP). The bathymetric contrast between GB (2-4 km water depth) and the SIAP (~5 km water depth) differentiates the two segments, in addition to distinctions in the widths of extended continental crust (GB: ~260 km; SIAP: ~80 km) and the zone of exhumed continental mantle (ZECM; GB: 0-60 km; SIAP: ~170 km). We have speculated that crustal-scale mass wasting may have altered the original transform segment boundary between GB and the SIAP. Our interpretation proposes transport of extended continental crust and overlying pre-rift sediments southward from GB onto exhumed, serpentinized peridotite of the SIAP. We reexamine the ODP Legs 149/173 drilling transect in the context of this hypothesis. Shallow-water Tithonian-Berriasian sediments sampled at sites 901 and 1065 atop basement highs of interpreted 4-6 km-thick continental crust could have been originally deposited atop GB, slumping with upper crustal blocks to the south sometime during the Tithonian to Valanginian. In this interpretation, serpentinized peridotite sampled at site 1068 represents the pre-existing SIAP ZECM onto which the slump was deposited. We suggest that intra-crustal faulting caused by east-west extension may have weakened the upper crust of GB sufficiently to allow gravitational collapse. Our interpreted slump then represents the latest faulting of a polyphase rift evolution. Examination of the Iberia margin bathymetry hints at a concave fault-scarp at the crown of our proposed slump; we use the bathymetry to resolve other potential locations of slumping, as well as regions that appear unaffected by mass wasting.

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

2007-12-01

24

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

NASA Astrophysics Data System (ADS)

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 in an intraplate setting, the presence of faulted sediments was reported in several works published during the eighties of last century following a study conducted in late 1970s to evaluate the feasibility of disposal of high-level radioactive wastes in the ocean. According these works, the Madeira Abyssal Plain sediments are cut by many normal growth faults and this deformation is a result of compaction and dewatering of the sediments. Evidences of tectonic deformation of oceanic sediments in intraplate settings are uncommon, but folded sediments and reverse faults extending into the basement, were recognized in the equatorial Indian Ocean and in the West African continental margin. Recently, during 2006 multi-channel seismic reflection and multibeam swath bathymetry surveys were carried out in the West Madeira Abyssal Plain by EMEPC in order to prepare the Portuguese proposal for the extension of the continental shelf. The seismic lines were acquired onboard R/V Akademik Shatskiy using a source of 5720 cu in bolt gun array, cable length of 7950 m and shot interval of 50.00 m. The multibeam swath bathymetry was acquired onboard NRP Gago Coutinho, and allowed a high resolution mapping of the main geomorphological features. The multichannel seismic lines, oriented WNW-ESE, image the Madeira island lower slope located at about 4000 m water depth and the almost flat abyssal plain at about 5300 m water depth. These seismic lines show a thick sedimentary succession that reaches a maximum thickness of about 1.5 sec twt in the deepest parts of the West Madeira Abyssal Plain, overlying an irregular diffractive Late Cretaceous oceanic basement. This basement is outcropping in some places originating small highs, which top is placed at 4700-4800 m water depth, about 500 m above the surrounding flat abyssal plain. The acoustic facies shown by the sedimentary record suggests the presence of a great thickness of turbidites within the sedimentary succession. The sismostratigraphy interpretation allowed the identification of four distinctive seismic units named from bottom to top U1 to U4. A theoretical stratigraphic correlation model between these seismic units and the ODP 157 data (Sites 950, 951 and 952) is proposed in the present work. The oldest seismic units U1 and U2 rest above the oceanic basement and could be correlated with the Late Cretaceous to Early Miocene sediments drilled during ODP 157. The youngest seismic units U3 and U4 show a succession of very continuous and parallel reflections alternating between low and high amplitude. Such type of seismic facies could be correlated with alternating turbidites and pelagic sediments possibly of Middle-Upper Miocene to Pleistocene age considering the ODP 157 data. The Cenozoic sedimentary succession is cut by several normal faults, close spaced, possibly related to compaction and dewatering processes. The acoustic record suggests the occurrence of fluid circulation along these faults, which are rooted in the oceanic basement. In some places these faults cut though the entire sedimentary sequence, almost reaching the seafloor. Evidences of recent compressional deformation are shown by reverse faults that affected the sedimentary sequence and also deform the seafloor by buckling and high amplitude folding. A large pop-up structure is recognized, generating a seafloor high, suggesting the occurrence of recent compressional events in the West Madeira Abyssal Plain region.

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

2009-04-01

25

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

26

The Characterization of Organic Matter in Abyssal Sediments, Pore Waters and Sediment Traps  

Microsoft Academic Search

\\u000a Substantial information regarding the history, source and transfer of both carbon and nitrogen to and within the deep sea\\u000a lies in the chemical and isotopic signals of organic materials. Isotopic and chemical characterization of sediment trap samples\\u000a indicate that the captured particulate materials are an organic rich food source for abyssal organisms which become highly\\u000a altered at or just below

Stephen A. Macko

27

MODOO: A modular and mobile deep ocean observatory and its application to the Porcupine Abyssal Plain  

NASA Astrophysics Data System (ADS)

Many of todays scientific questions require to observe the various processes in the ocean in parallel and from the air/sea interface to the sea-floor interior. Moreover, socioeconomic as well as scientific requirements may even demand to excess data in real time - for example for marine safety or to adapt the instrumentation to episodic environmental conditions. Here we describe a muti-disciplinary deep ocean observatory that has been designed within the European FP6 ESONET Network of Excellence to meet todays scientific and socioeconomic requirements for ocean observatories. MODOO, the Modular and mObile Deep Ocean Observatory, combines underwater acoustic modules with a surface telecommunication module to access and combine a variety of instrumentation from the sea surface to below the sea floor. MODOO's first application will be at the Porcupine Abyssal Plain: here a BOBO deep sea lander will be connected to a full water depth (4800m) deep sea mooring with meteorological package that belongs to the European FP7 EuroSITES network. The main scientific mission of this MODOO configuration is to investigate physical and biogeochemical processes that control the propagation and impact of near surface events (e.g. chlorophyll bloom) to the deep sea. For this mission we make use of physical (T/S recorder, current meters/profilers) and biogeochemical sensors (nitrate, fluorescence, oxygen, turbidity, particle flux/composition) combined with deep sea photography. Scientific guest missions will be seismic records and passive acoustics to detect deep sea marine life. The first MODOO installation is planned to be installed by the end of May 2010 for a three month test. The MODOO instrumentation is not simply mounted together but part of the MODOO concept is to add a common time stamp to the individual instrumentations data set. All instrumentation that is directly connected to the acoustic modems - for the PAP application this will be T/S/turbidity, ADCP, seismometer, oxygen, sediment trap, photography - will receive a common time stamp generated by the modems electronics. This synchronization approach is expected to facilitate the joint interpretation of the diverse data sets. Further details of the MODOO data concept and possible future applications will be presented.

Karstensen, Johannes; Greinert, Jens; Lampitt, Richard; Grant, Fiona; Priede, Monty; Pagnani, Maureen

2010-05-01

28

STUDY OF ABYSSAL SEAFLOOR ISOLATION OF CONTAMINATED SEDIMENTS CONCLUDED  

EPA Science Inventory

Recognizing the rapidly decreasing availability of disposal sites on land, in 1993 Congress directed the Department of Defense to assess the technical and scientific feasibility of isolating contaminated dredged material on the abyssal seafloor. The Naval Research Laboratory (NRL...

29

High-resolution seismic stratigraphy of the Galicia Bank Region and neighbouring abyssal plains (NW Iberian continental margin)  

Microsoft Academic Search

The high-resolution seismic stratigraphy of the Galicia Bank Region and adjacent deposits of the neighbouring Iberian and Biscay Abyssal Plains was included as part of the geological studies conducted in the area where the oil-tanker Prestige wreck is located. This seismic stratigraphy is characterized by five seismic units (5 to 1, from oldest to youngest) lying above an irregular acoustic

G. Ercilla; S. García-Gil; F. Estrada; E. Gràcia; A. Vizcaino; J. T. Váquez; S. Díaz; F. Vilas; D. Casas; B. Alonso; J. Dañobeitia; M. Farran

2008-01-01

30

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

31

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

32

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

33

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

34

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

35

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

NASA Astrophysics Data System (ADS)

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 estimated on the basis of in situ Sediment Community Oxygen Consumption (SCOC) rates, deck oxygen micro profiles as well as chlorophyll mixing and degradation rates. There was considerable interannual variation in the deposition of fresh organic material. In September 1996 the mass flux at 10 m above the bottom was 0.25 g DW m -2 d -1. The material caught in the trap was relatively fresh with a chlorophyll-a : phaeophorbide ratio of 1.33. During the other seasons (March 1997, July 1997 and October 1997) such fresh material was absent and even in July, the period in which fresh material is supposed to have arrived on the bottom, the ratio remained low, viz. 0.23. Based on these findings we conclude that in 1997 only small amounts of already degraded material arrived at the sea floor. On the basis of the large quantities of fresh material found in September 1996, the existence and subsequent deposition of autumn blooms should be considered. With in situ respirometry no effect of the differential quality and quantity of the settling detritus could be detected, whereas model parameters based on oxygen microprofiles demonstrated changes associated with the supposed seasonal cycle. Also the downcore pigment distribution of chlorophyll-a and derived mixing and degradation coefficients showed variations which were linked to the observed seasonal changes in input of organic matter.

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

2000-02-01

36

36. ARGO ABYSSAL PLAIN MAGNETIC LINEATIONS REVISITED: IMPLICATIONS FOR THE ONSET OF SEAFLOOR SPREADING AND TECTONIC EVOLUTION OF THE EASTERN INDIAN OCEAN1  

Microsoft Academic Search

Linear magnetic anomalies in the Argo Abyssal Plain have been interpreted as having been recorded by seafloor spreading during Late Jurassic to Early Cretaceous Chrons M26 through M16. Ocean Drilling Program Leg 123 drilled at Site 765 in the southern Argo Abyssal Plain, near the base of the northwest Australia margin between anomalies thought to be M25A and M26. However,

William W. Sager; Lawrence G. Fullerton; Richard T. Buffler; David W. Handschumache

37

Study of abyssal seafloor isolation of contaminated sediments concluded  

SciTech Connect

Recognizing the rapidly decreasing availability of disposal sites on land, in 1993 Congress directed the Department of Defense to assess the technical and scientific feasibility of isolating contaminated dredged material on the abyssal seafloor. The Naval Research Laboratory (NRL) conducted and managed the assessment, which was funded during its first year by the Strategic Environmental Research and Development Program and in the following two years by the Defense Advanced Research Projects Agency. NRL carried out the projects in collaboration with participants from academic institutions and industrial organizations. The seafloor isolation concept is an attractive management option for contaminated dredged material because, if abyssal isolation is feasible and environmentally sound, air, land, or water supplies would not be contaminated. The participants concluded that it is technically and environmentally feasible. In ports where shipping costs are high, abyssal seafloor isolation is a cost-competitive strategy. They also outlined the architecture of a system to monitor conditions at the site and to detect and measure possible leaks of contaminated material.

Valent, P.

1998-12-31

38

Neotectonic morphotructures in the junction zone of the Cape Verde Rise and Cape Verde Abyssal Plain, Central Atlantic  

Microsoft Academic Search

Acoustic profiling carried out with an Edgetech 3300 prophilograph in the junction zone of the Cape Verde Rise, Cape Verde\\u000a Abyssal Plain, and Grimaldi and Bathymetrists seamounts in the Central Atlantic during Cruise 23 of the R\\/V Akademik Nikolaj Strakhov allowed us to obtain new data on neotectonic deformations in the ocean and to propose their interpretation. It has been

S. G. Skolotnev; S. Yu. Kolodyazhny; N. V. Tsukanov; N. P. Chamov; S. Yu. Sokolov

2009-01-01

39

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

40

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

41

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

NASA Astrophysics Data System (ADS)

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 suspended particles whose contents of organic carbon, nitrogen and pigments were determined. This study was co-ordinated with a water column flux study and a detailed programme of benthic studies to understand how the abyssal boundary layer responds to and modifies inputs of organic matter from the water column (MAST3/BENGAL programme). There were strong seasonal fluctuations in the near-bottom (2 m above the bottom, mab) particle flux, whose variation were correlated in time with the water column fluxes. During the periods of peak flux, the near-bottom flux was sometimes higher than that recorded higher up in the water column, but not always at other times. These excesses were attributed to the resuspension events, since we observed a correlation between current speed and nephelometry. However, in summer the peak in the particle resuspension flux could not be explained by the variations in the tidal amplitude. Instead we attribute it to the large quantities of fresh large particles (aggregations) that had just arrived on the bottom; it was probably linked to the feeding activity and sediment reworking by the rich and varied benthic and benthopelagic megafauna. In both 1997 and 1998, the nephelometry signal (directly related to fine particle concentration) and its variability increased after the peaks in large particle flux with a time-lag of 2-3 months. We assume that this time lag corresponds to the time it takes for the large fresh particles, once they have settled on the bottom, to be disaggregated into smaller particles, and hence become subject to resuspension in the quiet current conditions then prevailing in the BENGAL area. The suspended particle analyses confirm the vertical structure of the Bottom Nepheloid Layer, the lower part of which corresponds to the Bottom Mixed Layer (BML) where resuspension and mixing are higher.

Vangriesheim, A.; Springer, B.; Crassous, P.

42

Seismicity and seismotectonics of the diffusive Iberian/African plate boundary: Horseshoe Abyssal Plain and Gorringe Bank  

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 may suggest that the event occurred in the vicinity of the Horseshoe fault, an oblique thrust fault. However, estimates of tsunami arrival times suggested a source near the Gorringe Bank, a ~180 km-long and ~70 km-wide ridge that has a relieve of ~5000 m. Deep Sea Drilling (DSDP) and rock samples indicated that the bank is mainly composed of serpentinized peridotites with gabbroic intrusions, perhaps being created by overthrusting of the Horseshoe Abyssal Plain onto the Tagus Abyssal Plain in NW direction. Further, the Horseshoe Abyssal Plain 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, a network of 14 ocean-bottom seismometers (OBS) was operated between April and October 2012 in the vicinity of the Horseshoe fault between 10°W to 11°W, and 35°50'N to 36°10'N. From October 2013 to March 2014 a second network of 15 OBS monitored seismicity at the Gorringe Bank. Both networks benefitted from seismic stations operated in Portugal. The first network provided in the order of 100 locale earthquakes occurring with the network. Most earthquakes in the Horseshoe occurred at a depth of 40-60 km, either in oceanic or unroofed continental mantle. The large source depth of events observed in the Horseshoe Abyssal Plain supports the idea that large catastrophic earthquakes, like the Great Lisbon earthquake of 1755, may indeed occur in the area.

Grevemeyer, Ingo; Lange, Dietrich; Matias, Luis

2014-05-01

43

The peridotite ridge province in the southern Iberia Abyssal Plain: Seismic constraints revisited  

NASA Astrophysics Data System (ADS)

west Iberia margin has become the type example of a magma-starved margin in which extension during breakup led to the exhumation of mantle rocks apparently over a broad area. Much of our understanding of this process is based on geophysical and drilling data from the southern Iberia Abyssal Plain, where the seaward part of the region of exhumed mantle is composed of a series of margin-parallel basement ridges. Here we analyze wide-angle and normal-incidence seismic data from a series of intersecting profiles across this peridotite ridge province and develop a three-dimensional picture of its structure. Using these seismic data, we infer a location and age (magnetic anomaly M1; 125-127 Ma) of first-formed oceanic crust in this region that are consistent with Ocean Drilling Program data and data from the conjugate margin. We infer that the peridotite ridge province is about 70 km wide with strong serpentinization (>75%) at the top of the basement reducing to much lower degrees (< 25%) around 2 km below. We map the geometry of some prominent reflectors on the landward margin of the peridotite ridge province that likely represent detachment faults and show that one of these has a domal structure similar to that of detachment faults at slow to ultraslow spreading mid-ocean ridges.

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

2014-03-01

44

Decadal-scale changes in shallow-infaunal foraminiferal assemblages at the Porcupine Abyssal Plain, NE Atlantic  

NASA Astrophysics Data System (ADS)

Trends in the abundance, diversity and taxonomic composition of 'live' (rose Bengal stained) foraminiferal assemblages (0-1 cm layer, >63-?m fraction) were analysed in replicate multiple corer samples collected at the Porcupine Abyssal Plain (48° 50' N, 16° 30' W, 4850 m water depth) over a 13-yr period (1989-2002). Total densities were significantly higher in 1996-2002 compared to 1989-1994, a change coincident with a spectacular rise in the density of the holothurian Amperima. However, total densities exhibited no significant relation to seasons or any significant correlation with modelled organic matter flux, the North Atlantic Oscillation (NAO) index, Amperima densities, or megafaunal assemblage composition. Over the same period, species richness and diversity measures decreased and dominance increased, although not significantly. Multivariate analyses revealed three assemblages represented by samples collected in 1989-1994, 1996-July 1997 and October 1997-October 2002. These reflected temporal changes in the densities of higher taxa and species. Trochamminaceans, notably a small undescribed species, increased from 5-9% (1989-1994) to 29-40% (1996-2002) of the assemblage with a corresponding rise in absolute abundance. Species of Hormosinacea and Lagenammina also tended to increase in density from 1996/1997 onwards. Rotaliids, dominated by Alabaminella weddellensis and Epistominella exigua, showed a bimodal distribution over time with peak densities in May 1991 (32%) and September 1998 (28%) and lowest densities in 1996-1997. Responses by these species to seasonal phytodetritus inputs probably explain the relative abundance of E. exigua, and to a lesser extent A. weddellensis, in 1989 and 1991 when phytodetritus was present. A qualitative change in the phytodetrital food, repackaging of food by megafauna, increased megafaunal disturbance of the surficial sediment, or a combination of these factors, are possible explanations for the dominance of trochamminaceans from 1996 onwards. The miliolid Quinqueloculina sp. was virtually absent in multicore samples (0-1 cm, >63-?m fraction) from 1989-1994, peaked in September 1996 (22%) when degraded phytodetritus was present on core surfaces, was less common in March 1997, and thereafter was relatively uncommon. However, horizontally sliced box-core samples (0-5 cm, >250-?m fraction) revealed that large specimens were more abundant in March 1997, and also were concentrated in deeper sediment layers, than in September 1996. We suggest that Quinqueloculina sp. migrated to the sediment surface in response to a 1996 flux event, grew and reproduced, before migrating back into deeper layers as the phytodetrital food became exhausted. Overall, the abyssal time-series revealed decadal-scale changes among shallow-infaunal foraminifera, more or less coincident with changes in the megafauna, as well as indications of shorter-term events related to seasonally-pulsed phytodetrital inputs.

Gooday, A. J.; Malzone, M. G.; Bett, B. J.; Lamont, P. A.

2010-08-01

45

Temporal changes (1989-1999) in deep-sea metazoan meiofaunal assemblages on the Porcupine Abyssal Plain, NE Atlantic  

NASA Astrophysics Data System (ADS)

Trends among major metazoan meiofaunal taxa were investigated based on 56 deployments of a multicorer at 10 time points over a period of 11 years (1989-1999) at the Porcupine Abyssal Plain Sustained Observatory site (PAP-SO: 48°50'N 16°30'W, 4850 m depth). This area is characterised by a strong seasonality in the deposition of organic matter to the seafloor and by the massive increase in the density of holothurian species since 1996, the so-called ' Amperima event'. Total meiofaunal densities ranged from 346 to 1074 ind.×10 cm -2 and showed a significant increase with time when time was represented by cruises, years and the ' Amperima period' (1996-1999) vs. the pre- Amperima period (1989-1994). This pattern was driven mainly by the nematodes, which were the dominant taxon (˜90% of total abundance). The third most abundant group, the polychaetes, also increased significantly in abundance over the time series, while the ostracods showed a significant decrease. Most other taxa, including the second-ranked group, the copepods (harpacticoids and nauplii), did not exhibit significant temporal changes in abundance. Ordination of taxon composition showed a shift from the pre- Amperima to the Amperima periods, a trend supported by the significant correlation between the x-ordinate and time. The majority (52-75%) of meiofaunal animals inhabited the top 2 cm of the 5 cm sediment cores analysed. There were significant increases in the proportion of total meiofauna, nematodes and copepods (but not polychaetes) inhabiting the 0-1 cm layer over time (represented by cruises) and between the pre- Amperima and Amperima periods in the case of copepods and polychaetes. During the intensively sampled period (1996-1997), there were indications of seasonal changes in the vertical distribution patterns of total meiofauna and nematodes within the sediment. We discuss the potential link between temporal variations in organic matter flux to the seafloor and meiofaunal populations, considering both qualitative and quantitative changes in fluxes and how they may be linked to climate variations.

Kalogeropoulou, V.; Bett, B. J.; Gooday, A. J.; Lampadariou, N.; Martinez Arbizu, P.; Vanreusel, A.

2010-08-01

46

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

47

Diversity and large-scale biogeography of Paramesochridae (Copepoda, Harpacticoida) in South Atlantic Abyssal Plains and the deep Southern Ocean  

NASA Astrophysics Data System (ADS)

Multicorer samples for meiofaunal study were obtained within the framework of the international project CeDAMar, at 21 stations occupied during the DIVA and ANDEEP campaigns (2000, 2002 and 2005) to the southern Atlantic Ocean (Guinea, Angola and Cape Basins) and the Southern Ocean (Weddell and Scotia Seas), respectively. A total of 311 adult Paramesochridae Lang, 1944 (Copepoda, Harpacticoida) was extracted from 437 cores obtained during 83 deployments of the corer at depths between 1107 and 5655 m. All specimens were determined to species based on morphological characteristics. They belonged to 19 species and four genera ( Kliopsyllus Kunz, 1962, Leptopsyllus T. Scott, 1894, Paramesochra T. Scott, 1892 and Scottopsyllus Kunz, 1962). Eleven species were restricted to single regions, whereas the others showed a much wider distribution. For example, Kliopsyllus andeep Veit-Köhler, 2004 and Kliopsyllus diva Veit-Köhler, 2005, were both collected from Guinea, Angola and Weddell Abyssal Plains, and Kliopsyllus schminkei Veit-Köhler & Drewes, 2009 occurred in the three West-African basins. This study provides a first insight into the large-scale biogeography of deep-sea harpacticoids, represented by the Paramesochridae, and indicates that distribution ranges, at least in this family, may extend across South Atlantic and Southern Ocean Abyssal Plains.

Gheerardyn, Hendrik; Veit-Köhler, Gritta

2009-10-01

48

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

49

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

NASA Astrophysics Data System (ADS)

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 these constituents in the gut contents. The study area is characterised by large interannual variations in the deposition of fresh organic material. The mass fluxes at 10 m above bottom (mab) varied from 0.25 g DW m -2 d -1 in September 1996 to <0.1 g DW m -2 d -1 in March 1997. The material caught in the sediment trap in September 1996 had a relative fresh signature with a chlorophyll -a:phaeophorbide ratio of 1.33. During the other seasons (March 1997, July 1997 and October 1997) the chlorophyll -a:phaeophorbide ratio remained low. In sediment cores this ratio showed a similar seasonal and inter-annual pattern, and again September 1996 was the period of maximum abundance of fresh organic material in the surficial sediment. The analyses of the gut contents of Oneirophanta mirrored exactly the seasonal variation of the phytopigments in both the sediment and the sediment trap material. Concentrations of pigments in the fore-gut were 5 to 15 times higher than in the sediment and the nucleic acid concentrations were up to 80 times higher. This discrepancy between pigments and nucleic acids concentrations suggests that the latter are “indigenous” to the gut of Oneirophanta, either because the gut contains high numbers of actively-dividing bacteria or as a result of cell lysis of the gut epithelium. The seasonal differences in the pigment concentration factor suggest that Oneirophanta does not actively search for hotspots where pigment concentrations are enriched. By using the degradation rate of chlorophyll- a in the PAP sediments, the minimum residence time of chlorophyll in the sediment within the gut of Oneirophanta was calculated. In combination with gut volume and density data it was estimated that each year the Oneirophanta population skims a third of the sediment surface at the PAP site.

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

50

What does the 3D Sedimentary Architecture tell us about Continental Breakup: the Example of the Southern Iberia Abyssal Plain.  

NASA Astrophysics Data System (ADS)

Most of the conceptual ideas concerning the sedimentary architecture and tectonic evolution and models quantifying isostasy at rifted margins are based on either continental rifts or proximal margins both of which underwent only small amounts of crustal thinning. However, the increase number of higher-resolution seismic and drill-hole data from the more distal margins clearly show that: (1) concepts and models used in proximal margins are ineffective at predicting the deformation history as well as the subsidence history in more extended distal margins; and (2) deeper margins show a strong heterogeneity along strike. The aim of our study is to resolve the evolution of rift structures in time and space in the most distal parts of the margins by mapping the 3D architecture of dated sedimentary units in the Southern Iberia Abyssal Plain (SIAP). We defined 6 seismic formations based on own observations and descriptions given by Wilson et al. (1996). In order to have the best possible resolution and to be able to correlate these seismic formations with ODP drill sites, we used all available seismic lines (CAM, GP, IAM9, ISE, LG12, Sonne). Of particular interest for our study was the distribution of the lowermost formation overlying the basement, here referred to as Formation 6. This formation has been dated at DSDP Site 398 as Valanginian-Hauterivian to late Aptian (Wilson et al., 1996), considered as syn-rift to early post-rift. Our results show that: (1) growth structures in the northern SIAP show a progressive younging oceanwards; and (2) the sediment architecture of Formation 6 changes across the SIAP from north to south. Whilst the sediments of Formation 6 occur in the north in classical fault bounded basins overlying tilted blocks, to the south they overlie either exhumed basement or onlap against extensional allochthons. The changing sedimentary architecture reflects a major change in the basin architecture along strike in the OCT from low-strain basins to the north, characterized by steep bounding normal faults and sedimentary wedges overlying a tilted hanging wall, to high-strain basins soled by detachment faults to the south. In later case, accommodation space increases dominantly by horizontal movement, the detachment faults expose deep crustal and mantle rocks at the seafloor, and the syn-exhumation sedimentary strata are parallel or sub-parallel to the low-angle top basement detachment faults. Based on our detailed mapped sedimentary architecture, and on the characterization of the basement structure throughout the distal margin, we propose a 3D schematic model for the evolution of the SIAP. This model suggests a general migration of active faulting towards the future ocean, i.e. from the east to the west, and a change in the mode of extension along strike with upward concave faults in the north to downward concave faults in the south. The increase in strain from north to south may reflect an overall rotation of Iberia during the northward propagation of the spreading centre.

Peron-Pinvidic, G.; Manatschal, G.; Minshull, T.

2005-12-01

51

The Porcupine Abyssal Plain (pap) Time Series Site: Biological and Bigeochemical Changes During The Past 50 Years.  

NASA Astrophysics Data System (ADS)

The JGOFS "North Atlantic Bloom Experiment" took place in 1989 but this was not the first research into open ocean biology and biogeochemistry in the region. The Por- cupine Abyssal Plain (PAP) is the closest abyssal environment to Northwest Europe and hence has been extensively studied over many years and the NABE stimulated research that has continued since then. Trends in plankton abundance since 1950 are particularly well studied from the Continuous Plankton Recorder surveys (CPR) but since 1989 there have also been nearly continuous measurements of downward par- ticle flux. Benthic communities have frequently been examined over the past decade and it is suggested that these integrate the effects of upper ocean processes in both space and time. There is considerable interannual variability in the abundance of sev- eral planktonic groups in the region as determined by the CPR and more recently from satellite observations and here we examine links between these variations and basic environmental parameters such as the North Atlantic Oscillation index. We discuss links to processes occurring at greater depth such as organic carbon flux and the dra- matic change in benthic community structure which has taken place during this period. Research activity at the PAP site will increase very significantly over the next three years as it is one of the three ANIMATE sites (Atlantic Network of Interdisciplinary Moorings and Timeseries for Europe; an EU funded program). From Autumn 2002, real time data will be available on a variety of upper ocean properties such as PCO2, Nutrients, fluorescence and CTD and these will lead to a much better understand- ing of system function. We describe an upper ocean ecosystem model which gives a good description of deep water organic flux. This model will be developed further to accommodate the additional in situ data provided under ANIMATE.

Lampitt, R. S.; Billett, D. S. M.; Childs, R.; Popova, E. E.

52

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

53

Bannock Basin, Sirte Abyssal Plain and Conrad Spur: structural relationships between Mediterranean Ridge and its western foreland and implications on the character of the accretionary complex (eastern Mediterranean)  

Microsoft Academic Search

In previous publications, the relationship between the Sirte Abyssal Plain as foreland and the Mediterranean Ridge as accretionary\\u000a complex was considered to be simple: the foreland is undeformed, the accretionary complex consumes the foreland, the Messinian\\u000a evaporites control the internal structure of the growing complex. The compilation of our own and published data results in\\u000a a more complex tectonic pattern

W. Hieke; A. Camerlenghi; M. B. Cita; G. A. Dehghani; N. Fusi; H. B. Hirschleber; L. Mirabile; C. Müller; A. Polonia

2009-01-01

54

Material supply to the abyssal seafloor in the Northeast Atlantic  

Microsoft Academic Search

Downward particle flux was measured using sediment traps at various depths over the Porcupine Abyssal Plain (water depth ?4850 m) for prolonged periods from 1989 to 1999. A strong seasonal pattern of flux was evident reaching a maximum in mid-summer. The composition of the material changed with depth, reflecting the processes of remineralisation and dissolution as the material sank through

R. S Lampitt; B. J Bett; K Kiriakoulakis; E. E Popova; O Ragueneau; A Vangriesheim; G. A Wolff

2001-01-01

55

The Kefalonia Transform Zone (offshore Western Greece) with special emphasis to its prolongation towards the Ionian Abyssal Plain  

NASA Astrophysics Data System (ADS)

Information concerning two seismic lines, the first located northwest of the Lefkada Island and the second from the deep Ionian basin to the gulf of Patras, is used to trace the Kefalonia Transform Zone (KTZ) and to explore its relation with the sedimentary sequences and the deeper geologic structures in the study area. In addition, sea bottom topography and fault plane solutions are combined in order to explore the prolongation of the KTZ into the Ionian Abyssal Plain (IoAP) and to describe its properties. The boundary between the subduction of the eastern Mediterranean oceanic crust under the overriding continental crust and the KTZ is well constrained by the seismic data in association with seismicity and regional stress field. The southern prolongation of the KTZ is located in the IoAP towards the direction between Kefalonia and Zakynthos Islands at depth greater than 15 km. The southern part of the KTZ exhibits a strike slip motion with a thrust component according to fault plane solutions of moderate and strong earthquakes. The seismic section mostly confirms the existence of the thrust component and gives information about the tectonic status east and west of the KTZ.

Kokinou, E.; Papadimitriou, E.; Karakostas, V.; Kamberis, E.; Vallianatos, F.

2006-12-01

56

Do bottom mixed layers influence 234Th dynamics in the abyssal near-bottom water column?  

Microsoft Academic Search

Dynamics of the natural radioactive particle tracer 234Th (half-life: 24.1 days) within the abyssal water column up to 1000m above bottom and within surface sediments of the northeast Atlantic (Porcupine Abyssal Plain; depth: ?4845m) were investigated. Distributions of transmissometer voltages and potential temperature indicated a subdivision of the near-bottom water column into a benthic mixed layer (BML; thickness: ?10–65m) and

Robert Turnewitsch; Barbara M Springer

2001-01-01

57

Interelement relationship in abyssal Pacific ferromanganese nodules and associated pelagic sediments  

NASA Astrophysics Data System (ADS)

By R-mode factor analysis and enrichment factor calculations, most of the elements in abyssal ferromanganese nodules and associated pelagic sediments (excluding common authigenic minerals like apatite, barite, opal and carbonates) are found to be preferentially concentrated in one of the following three major phases: aluminosilicates ( e.g., Al, Si, Sc, Ga, Cr, Be, Na, K, Rb and Cs), Fe-oxides ( e.g., Fe, P, S, V, Se, Te, As, B, Sn, U, Hg, Pb, Ti, Ge, Y, Zr, Nb, Pd, In, rare-earths, Hf, Th, Pa, Pu, Am, Ru and Bi), and Mn-oxides ( e.g., Mn, Tl, Ag, Cd, Mg, Ca, Ba, Ra, Co, Ni, Cu, Zn, Mo, Sb and probably W). The specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties ( e.g., the pH of zero point of charge and dieletric constant) of these three phases.

Li, Yuan-Hui

1982-06-01

58

Controls on sediment delivery in coastal plain rivers.  

PubMed

Rivers crossing coastal plains are often inefficient conveyors of sediment, so that changes in upstream sediment dynamics are not evident at the river mouth. Extensive accommodation space and low stream power often result in extensive alluvial storage upstream of estuaries and correspondingly low sediment loads at the river mouth. However, gaging stations with sediment records are typically well upstream of the coast, and thus tend to overestimate sediment yields by under-representing the lower coastal plain and because there is often a net loss of sediment in lower coastal plain reaches. Studies of alluvial sediment storage have generally focused on accommodation space, but, using examples from Texas, we show that low transport capacity controlled largely by slope is a crucial factor. PMID:19892459

Slattery, Michael C; Phillips, Jonathan D

2011-02-01

59

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

60

Sediment storage, sea level, and sediment delivery to the ocean by coastal plain rivers  

Microsoft Academic Search

Coastal and marine sedimentary archives are sometimes used as indicators of changes in continental sediment production and fluvial sediment transport, but rivers crossing coastal plains may not be efficient conveyors of sediment to the coast. Where this is the case, changes in continental sediment dynamics are not evident at the river mouth. Stream power is typically low and accommodation space

Jonathan D. Phillips; Michael C. Slattery

2006-01-01

61

Benthic foraminifera living in Gulf of Mexico bathyal and abyssal sediments: Community analysis and comparison to metazoan meiofaunal biomass and density  

NASA Astrophysics Data System (ADS)

Benthic foraminiferal biomass, density, and species composition were determined at 10 sites in the Gulf of Mexico. During June 2001 and 2002, sediment samples were collected with a GoMex box corer. A 7.5-cm diameter subcore was taken from a box core collected at each site and sliced into 1-cm or 2-cm sections to a depth of 2 or 3 cm; the >63-?m fraction was examined shipboard for benthic foraminifera. Individual foraminifers were extracted for adenosine triphosphate (ATP) using a luciferin-luciferase assay, which indicated the total ATP content per specimen; that data was converted to organic carbon. Foraminiferal biomass and density varied substantially (˜2-53 mg C m -2; ˜3600-44,500 individuals m -2, respectively) and inconsistently with water depth: although two ˜1000-m deep sites were geographically separated by only ˜75 km, the foraminiferal biomass at one site was relatively low (˜9 mg C m -2) while the other site had the highest foraminiferal biomass (˜53 mg C m -2). Although most samples from Sigsbee Plain (>3000 m) had low biomass, one Sigsbee site had >20 mg foraminiferal C m -2. The foraminiferal community from all sites (i.e. bathyal and abyssal locales) was dominated by agglutinated, rather than calcareous or tectinous, species. Foraminiferal density never exceeded that of metazoan meiofauna at any site. Foraminiferal biomass, however, exceeded metazoan meiofaunal biomass at 5 of the 10 sites, indicating that foraminifera constitute a major component of the Gulf's deep-water meiofaunal biomass.

Bernhard, Joan M.; Sen Gupta, Barun K.; Baguley, Jeffrey G.

2008-12-01

62

Near-bottom particle flux in the abyssal northeast Atlantic  

Microsoft Academic Search

During a 17-month study at a site on the Porcupine Abyssal Plain of the northeast Atlantic (approx. 48°N20°W), the downward flux of particulate material within and above the benthic nepheloid layer (BNL) was measured using sediment traps 1455m above bottom (mab) (3100m depth) and 90mab (4465m depth). Flux at 90mab is usually higher than the primary flux at 3100m depth,

R. S. Lampitt; P. P. Newton; T. D. Jickells; J. Thomson; P. King

2000-01-01

63

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

64

Environmental Impacts in the Jianghan Plain: Evidence from Lake Sediments  

Microsoft Academic Search

There is growing concern about the environmental impact of rapid economic growth in China. The problem is compounded by the scarcity of baseline data on the state of China's natural environment. As a step towards solving this problem, palaeolimnological methods have been applied to seven lakes in the Jianghan Plain, China, to evaluate recent changes in human impact. Lake sediment

J. F. Boyle; N. L. Rose; H. Bennion; H. Yang; P. G. Appleby

1999-01-01

65

Late Pleistocene alluvial plain sedimentation in Lower Narmada Valley, Western India: Palaeoenvironmental implications  

Microsoft Academic Search

Late Pleistocene fluvial sediments that were deposited in a slowly sinking basin are now exposed as 30–50 m high incised vertical cliffs all along the Lower Narmada Valley in western India. The exposed fluvial deposits have been classified into two sediment packages, alluvial fan sediments overlain by alluvial plain sediments. The alluvial plain sequence has not been studied previously. It

S. Bhandari; D. M. Maurya; L. S. Chamyal

2005-01-01

66

The supply of nutrients due to vertical turbulent mixing: A study at the Porcupine Abyssal Plain study site in the northeast Atlantic  

NASA Astrophysics Data System (ADS)

As part of a multidisciplinary cruise to the Porcupine Abyssal Plain (PAP) study site (49°00'N 16°30'W), in June and July 2006, observations were made of the vertical nitrate flux due to turbulent mixing. Daily profiles of nitrate and turbulent mixing, at the central PAP site, give a mean nitrate flux into the euphotic zone of 0.09 (95% confidence intervals: 0.05-0.16) mmol N m -2 d -1. This is a factor of 50 lower than the mean observed rate of nitrate uptake within the euphotic zone (5.1±1.3 mmol N m -2 d -1). By using our direct observations to 'validate' a previously published parameterisation for turbulent mixing, we further quantify the variability in the vertical turbulent flux across a roughly 100×100 km region centred on the PAP site, using hydrographic data. The flux is uniformly low (0.08±0.26 mmol N m -2 d -1, the large standard deviation being due to a strongly non-Gaussian distribution) and is consistent with direct measurements at the central site. It is demonstrated that on an annual basis convective mixing supplies at least 40-fold more nitrate to the euphotic zone than turbulent mixing at this location. Other processes, such as those related with mesoscale phenomena, may also contribute significantly.

Martin, Adrian P.; Lucas, Michael I.; Painter, Stuart C.; Pidcock, Rosalind; Prandke, Hartmut; Prandke, Holger; Stinchcombe, Mark C.

2010-08-01

67

Hydrocarbons in the sediments of the Bermuda region lagoonal to abyssal depths  

Microsoft Academic Search

Gas chromatographic analyses of the pentane fraction derived from surface sediments collected from 20 stations (50 cores) around Bermuda from the subtidal zone to 40 m depth and one deep-water sediment sample from 1400 m depth showed that outside the protective boiler reef, the total aliphatic (pentane-extractable) hydrocarbon content was less than inside the reef (3-10 jg\\/g dry weight outside

T. D. Sletter; J. N. Butler; J. E. Barbash

1980-01-01

68

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

69

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

70

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

71

Seasonal and inter-annual biogeochemical variations in the Porcupine Abyssal Plain 2003-2005 associated with winter mixing and surface circulation  

NASA Astrophysics Data System (ADS)

We present a 3-year multidisciplinary biogeochemical data set taken in situ at the Porcupine Abyssal Plain (PAP) time-series observatory in the Northeast Atlantic (49°N, 16.5°W; water depth ˜4850 m) for the period 2003 to 2005. The high-resolution year-round autonomous measurements include temperature, salinity, chlorophyll-a (derived from in situ chlorophyll-fluorescence) and inorganic nitrate, all at a nominal depth of 30 m on an Eulerian observatory mooring. This study compares these in situ time-series data with satellite chlorophyll-a data, regional data from a ship of opportunity, mixed-layer depth measurements from profiling Argo floats and lateral advection estimates from altimetry. This combined and substantial data set is used to analyse seasonal and inter-annual variability in hydrography and nitrate concentrations in relation to convective mixing and lateral advection. The PAP observatory site is in the inter-gyre region of the North Atlantic where convective mixing ranges from 25 m in the summer to over 400 m in winter when nutrients are supplied to the surface. Small inter-annual changes in the winter mixed layer can result in large changes in nitrate supply and productivity. However the decrease in maximum winter nitrate over the three-year period, from 10 to 7 mmol m -3, cannot be fully explained by convective mixing. Trajectories leading to the PAP site, computed from altimetry-derived geostrophic velocities, confirm that lateral advection cannot be ignored at this site and may be an important process along with convective mixing. Over the three years, there is an associated decrease in new production calculated from nitrate assimilation from 85.4 to 40.3±4.3 gCm -2 a -1. This confirms year-to-year variability in primary production seen in model estimates for the region. The continuous in situ dataset also shows inter-annual variation in the timing of the spring bloom due to variations in heat flux; the 2005 bloom occurred earlier than in 2004.

Hartman, S. E.; Larkin, K. E.; Lampitt, R. S.; Lankhorst, M.; Hydes, D. J.

2010-08-01

72

Sediment deposition in the flood plain of Stemple Creek Watershed, northern California  

NASA Astrophysics Data System (ADS)

Over the past 150 years, major land use changes have occurred in the Stemple Creek Watershed in northern California that have caused erosion to move soils from the upland to the flood plain, stream channels, and the bay. The purpose of this study is to document the recent (1954 to present) sediment deposition patterns in the flood plain area adjacent to Stemple Creek using the 137Cesium technique. Sediment deposition ranged from 0.26 to 1.84 cm year -1 for the period from 1964 to 2002 with an average of 0.85±0.41 cm year -1. Sediment deposition rates were higher for the 1954 to 1964 period with a range of 0.31-3.50 cm year -1 and an average of 1.29±1.04 cm year -1. These data indicate that sediment deposition in the flood plain has decreased since the middle 1950s, probably related to reduction in row crop agriculture and an increase in pasturelands. This study shows that the flood plains in the Stemple Creek Watershed are a significant sink for the soils being eroded from the upland area. Given the significance of the flood plain for trapping eroded materials before they reach the stream channels or the bay, efforts need to be made to manage these flood plain areas to insure that they do not change and become a source rather than a sink for eroded materials as improved management practices on the upland areas reduce sediment input to the flood plain.

Ritchie, Jerry C.; Finney, Vernon L.; Oster, Kenneth J.; Ritchie, Carole A.

2004-08-01

73

Modern sediment supply to the lower delta plain of the Ganges-Brahmaputra River in Bangladesh  

Microsoft Academic Search

Vibracores and auger samples collected from the lower (tidal) delta plain of the Ganges-Brahmaputra River in Bangladesh were examined to determine whether the area is a significant sink for riverine sediments. Measurements of 137Cs activity and radiocarbon in the sediments indicate sediment accumulation is taking place on decadal and millennial time scales at rates reaching 1.1 cm\\/year. The sediment of

M. A. Allison; E. B. Kepple

2001-01-01

74

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

75

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

76

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

77

Late Quarternary Sedimentation in the Eastern Angola Basin.  

National Technical Information Service (NTIS)

Recent sedimentation in the eastern Angola Basin includes calcareous oozes in the north and south (Guinea Rise and Walvis Ridge) and hemipelagic lutites and terrigenous turbidites on the Congo Cone and on the Angola rise and abyssal plain. Slumped and pon...

B. D. Bornhold

1973-01-01

78

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

79

Direct observation of episodic growth in an abyssal xenophyophore (Protista)  

NASA Astrophysics Data System (ADS)

Three specimens of the xenophyophore Reticulammina labyrinthica were photographed on the Madeira Abyssal Plain (31°6.1'N, 21°10.9'W; 4944 m) using the Bathysnap time-lapse camera system. During the 8 month observation period, the specimens underwent an estimated 3-10 fold increase in volume. Growth occurred episodically in several distinct phases, each lasting 2-3 days, during which sediment was collected and incorporated into the test. These phases were separated by fairly regular periods of about 2 months when the organisms showed little obvious activity. The growth phases were approximately synchronous between specimens. However, it is not clear whether the periodicity and apparent synchronization of these events resulted from an external (environmental) cue or whether growth is internally controlled and the synchronization arose by chance. These unique observations, which represent the first direct measurement of growth in any abyssal organism living outside a hydrothermal vent field, suggest that xenophyophores combine test growth with deposit feeding. The tests appear to grow more quickly, and to be more active, dynamic structures, than previously believed.

Gooday, A. J.; Bett, B. J.; Pratt, D. N.

1993-11-01

80

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

81

Distributions, sources, and ecological risks of hexachlorocyclohexanes in the sediments from Haihe Plain, Northern China.  

PubMed

The levels of hexachlorocyclohexanes (HCHs) in the sediments from Haihe Plain, China, were measured by a gas chromatograph with a (63)Ni microelectron capture detector. The spatial distributions, possible sources, and potential ecological risks of these compounds were analyzed. The residual level of total HCHs was 33.84 ± 173.37 ng g(-1) dry weight (d.w.) with ranges of 0.13 ~ 1,107.41 ng g(-1) d.w. Much higher ?HCH contents were found in the lower reaches of some rivers and in the mouth of the main stream receiving tributaries. The predominance of ?-HCH (36%) in the sediments was similar to that in the soils from Haihe Plain. The high percentages of ?-HCH (23-41%) could be detected at 25% of the sampling sites in the seven river systems. There were statistically significant positive relationships between the contents of HCHs and total organic carbon. Lindane was identified as the primary source of HCHs in the sediments, and it seemed that recent illegal lindane inputs still existed in some areas in Haihe Plain, as indicated by the ?-/?-HCH and ?-/(? + ?)-HCH ratios. Severe potential ecological risks of ?-HCH to benthic organisms at some sampling sites were found based on the consensus-based sediment quality guidelines. PMID:23054791

Xu, Fu-Liu; Kong, Xiang-Zhen; He, Wei; Qin, Ning; Zhu, Ying; Tao, Shu

2013-04-01

82

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

83

North Atlantic Deep Water and Antarctic Bottom Water variability during the last 200 ka recorded in an abyssal sediment core off South Africa  

NASA Astrophysics Data System (ADS)

Benthic ? 13C values ( F. wuellerstorfi), kaolinite/chlorite ratios and sortable silt median grain sizes in sediments of a core from the abyssal Agulhas Basin record the varying impact of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) during the last 200 ka. The data indicate that NADW influence decreased during glacials and increased during interglacials, in concert with the global climatic changes of the late Quaternary. In contrast, AABW displays a much more complex behaviour. Two independent modes of deep-water formation contributed to the AABW production in the Weddell Sea: 1) brine rejection during sea ice formation in polynyas and in the sea ice zone (Polynya Mode) and 2) super-cooling of Ice Shelf Water (ISW) beneath the Antarctic ice shelves (Ice Shelf Mode). Varying contributions of the two modes lead to a high millennial-scale variability of AABW production and export to the Agulhas Basin. Highest rates of AABW production occur during early glacials when increased sea ice formation and an active ISW production formed substantial amounts of deep water. Once full glacial conditions were reached and the Antarctic ice sheet grounded on the shelf, ISW production shut down and only brine rejection generated moderate amounts of deep water. AABW production rates dropped to an absolute minimum during Terminations I and II and the Marine Isotope Transition (MIS) 4/3 transition. Reduced sea ice formation concurrent with an enhanced fresh water influx from melting ice lowered the density of the surface water in the Weddell Sea, thus further reducing deep water formation via brine rejection, while the ISW formation was not yet operating again. During interglacials and the moderate interglacial MIS 3 both brine formation and ISW production were operating, contributing various amounts to AABW formation in the Weddell Sea.

Krueger, S.; Leuschner, D. C.; Ehrmann, W.; Schmiedl, G.; Mackensen, A.

2012-01-01

84

Sediment compaction rates and subsidence in deltaic plains: Numerical constraints and stratigraphic influences  

USGS Publications Warehouse

Natural sediment compaction in deltaic plains influences subsidence rates and the evolution of deltaic morphology. Determining compaction rates requires detailed knowledge of subsurface geotechnical properties and depositional history, neither of which is often readily available. To overcome this lack of knowledge, we numerically forward model the incremental sedimentation and compaction of stochastically generated stratigraphies with geotechnical properties typical of modern depositional environments in the Mississippi River delta plain. Using a Monte Carlo approach, the range of probable compaction rates for stratigraphies with compacted thicknesses <150m and accumulation times <20kyr. varies, but maximum values rarely exceed a few mmyr-1 . The fastest compacting stratigraphies are composed primarily of peat and bar sand, whereas the slowest compacting stratigraphies are composed of prodelta mud and natural levee deposits. These results suggest that compaction rates can significantly influence vertical and lateral stratigraphic trends during deltaic evolution. ?? 2007 Blackwell Publishing Ltd.

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

2007-01-01

85

Grain size and depth constraints on microbial variability in coastal plain subsurface sediments  

Microsoft Academic Search

We have examined the effects of sediment grain size and depth on the abundance and activity of aerobic bacteria at two coastal plain sites in Virginia. Samples were collected at centimeter intervals as well as meter intervals because fine?scale sampling can be essential to assess microbial variability. At the Oyster site, grain size varied from 0.12 to 0.25 mm below

Chuanlun Zhang; Anthony V. Palumbo; Tommy J. Phelps; John J. Beauchamp; Fred J. Brockman; Chris J. Murray; Brian S. Parsons; Donald J. P. Swift

1998-01-01

86

A raised OIS 3 sea level recorded in coastal sediments, southern Changjiang delta plain, China  

NASA Astrophysics Data System (ADS)

The distribution of marine-influenced oxygen isotope stage (OIS) 5 to OIS 1 sediments was examined in several late Quaternary boreholes from the southern Changjiang (Yangtze) delta plain, China, using different dating methods including OSL, U-series, AMS 14C and paleomagnetism. Results demonstrate that coastal and estuarine deposition during OIS 5 and OIS 3 occurred throughout the study area. However, Holocene transgressive sediments were absent on the Taihu block. The burial depth of intertidal to subtidal sediment deposited during OIS 5e records 30-80 m subsidence caused by sediment compaction and tectonic movement since that time. However, coastal sediments formed during the late phase of OIS 3 were buried to a depth of ca. 6-15 m in the Taihu Lake area, while the burial depth increased eastward to ca. 45-60 m on the coastal plain. This phenomenon, combined with the distribution of Holocene marine strata, indicates at least 25-30 m uplift of the Taihu block since the end of OIS 3. We suggest that this uplift was mainly caused by the differential subsidence due to substantial amount of post-glacial deposition by the Changjiang and Huanghe Rivers on the continental shelf of east China marginal sea.

Wang, Zhanghua; Jones, Brian G.; Chen, Ting; Zhao, Baocheng; Zhan, Qing

2013-05-01

87

Aliphatic and polycyclic aromatic hydrocarbons in Black Sea sediments  

Microsoft Academic Search

Concentrations of aliphatic hydrocarbons (AHC) in sediments of the Black Sea ranged from 153,000 ng g?1 dw near the mouth of the Danube River to about 10,000 ng g?1 dw in abyssal plain sediments. Compound distributions were dominated by long-chain n-alkanes except at the Danube station where a significant petrogenic component with an unresolved complex mixture was also present. Polycyclic

Stuart G. Wakeham

1996-01-01

88

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

PubMed Central

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.

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

2009-01-01

89

Near-bottom particle flux in the abyssal northeast Atlantic  

NASA Astrophysics Data System (ADS)

During a 17-month study at a site on the Porcupine Abyssal Plain of the northeast Atlantic (approx. 48° N 20° W) , the downward flux of particulate material within and above the benthic nepheloid layer (BNL) was measured using sediment traps 1455 m above bottom (mab) (3100 m depth) and 90 mab (4465 m depth). Flux at 90 mab is usually higher than the primary flux at 3100 m depth, and this enhancement is especially pronounced during the winter. The additional material found in the near-bottom trap comprises recently deposited resuspended material (rebound flux), but with an admixture of refractory sediment. It is unlikely that scavenging of either BNL particles or dissolved material contributes greatly to the near-bottom flux. Fluxes of metal tracers ( 232Th and Al) and cyanobacteria into traps were used to examine the process of resuspension. The ratio of tracer flux at 90 mab to that at 3100 m depth was taken as a measure of the strength of the resuspension process (the resuspension factor RF) and reflects clearly the enhanced resuspension in winter. This seasonal variation appears to be related to both the magnitude of near-bottom currents and to the wave height at the surface 40 days before. It is also possible that recently deposited material forms a partly cohesive blanket on the sediment surface that restricts resuspension to the benthic boundary layer.

Lampitt, R. S.; Newton, P. P.; Jickells, T. D.; Thomson, J.; King, P.

90

Phytopigments as biomarkers of selectivity in abyssal holothurians; interspecific differences in response to a changing food supply  

NASA Astrophysics Data System (ADS)

Holothurians dominate the abyssal megabenthos. They are key consumers and bioturbators of surficial sediment. Compounds essential for holothurian reproduction, such as carotenoids, are in short supply in the deep ocean. Holothurians cannot synthesise carotenoids de novo; the compounds are supplied with the flux of phytodetritus. Therefore, the supply of these compounds may play an important role in regulating processes on the seafloor. This study examines the link between the diet of abyssal holothurians and their ovarian carotenoid biochemistry. Phytodetritus, surficial sediment, holothurian gut content and ovaries were sampled in June 2004 and in July 2005 at the Porcupine Abyssal Plain (PAP), NE Atlantic. Gut content chlorophyll a concentration showed that Amperima rosea, Peniagone diaphana and Oneirophanta mutabilis fed selectively on fresh organic matter, although when this was scarce, O. mutabilis was outcompeted and fed on more refractory material. All three species display consistent ovarian carotenoid profiles and have relatively high carotenoid concentrations in their ovaries. Psychropotes longicauda, Paroriza prouhoi, Pseudostichopus aemulatus, P. villosus and Molpadia blakei fed less selectively and exhibited low ovarian carotenoid concentrations with inconsistent profiles. The results suggest that abyssal holothurian ovarian biochemistry is a complex function of OM supply, holothurian feeding guild and reproductive adaptation. Changes in upper ocean biogeochemistry, altering the composition of organic matter reaching the deep-sea floor, may favour certain holothurian species, as suggested by the interspecific differences in holothurian ovarian biochemistry. This may lead to large community changes as seen at the PAP, which can alter the reworking rates of sediment, probably affecting carbon burial. The study also demonstrated that using the presence of biomarkers in gut contents to infer feeding selectivity should be used with caution. Only biomarkers in gut contents that are not present in the tissues of the holothurians (e.g., chlorophyll a) should be used to determine their feeding selectivity.

FitzGeorge-Balfour, Tania; Billett, David S. M.; Wolff, George A.; Thompson, Anu; Tyler, Paul A.

2010-08-01

91

Transparent layers in seismic reflection records from the central Ionian Sea (Mediterranean)—evidence for repeated catastrophic turbidite sedimentation during the Quaternary  

Microsoft Academic Search

Echosounding and SCS records from the Ionian and Sirte Abyssal Plains show, below the Holocene Augias megaturbidite, two additional thick transparent layers which by analogy are interpreted as turbidites. Estimated thicknesses are 10 and 35m (upper and lower) as a minimum (no consideration of presumable variations of acoustic velocities). The resulting sediment volumes are about 26 and about 200km3, respectively.

W. Hieke

2000-01-01

92

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

Microsoft Academic Search

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

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

2009-01-01

93

Occurrence of arsenic in sediment pore waters in the central Kanto Plain, Japan  

NASA Astrophysics Data System (ADS)

The Kanto Plain is known as the largest plain in Japan, where marine sediments are widely developed because of cyclic iteration of global sea-level changes even 50 km or more inland from the present shoreline. In this area, dependence on groundwater for water requirements is relatively high; in particular, around 40 % of the municipal water supply is dependent on groundwater. Arsenic levels greater than that permitted by the environmental standards of Japan have been detected in groundwater in this area. Therefore, to evaluate occurrences of arsenic and other related elements in pore waters contained in natural sediment layers, we measured the levels of various inorganic chemical substances such as arsenic (As), iron (Fe), and sulfur (S) and major dissolved ions such as sulfate (SO42-), calcium (Ca2+), and sodium (Na+). Pore waters were collected from sediment samples that were obtained by a drilling from the river bottom down to 44 m depth; pore water samples were obtained immediately after extraction of sediments. The sedimentary facies in the vertical profile are continental, transitional, and marine, including two aquifers. The upper aquifer (15-20 m) contains fine to medium sand, whereas the lower aquifer (37-44 m) contains medium to coarse and gravelly sand. Arsenic and other inorganic elements were measured by an inductively coupled plasma mass spectrometer (ICP/MS) and an inductively coupled plasma atomic emission spectrometer (ICP/AES), and major dissolved ions were measured by an ion chromatograph analyzer. The total content of chemical elements was measured by X-ray fluorescence analysis using solid sediment samples. We obtained the following results. The arsenic concentrations in pore waters in marine silt and clay sediments (approximately 0.04 mg/L) were about five times higher than that in continental sediments (approximately 0.008 mg/L). The highest concentration of arsenic (0.074 mg/L) was detected at a depth of 13 m, which is immediately above the upper aquifer. Visual observations confirmed that this level is under oxidizing conditions. Thus, it regards that arsenic was adsorbed to iron hydroxide in the sediments. On the other hand, in the top part of the section, from the river bottom to a depth of approximately 3 m, arsenic concentrations in the pore waters were clearly high and decreased gradually and continuously with depth. This is considered to be the result of anthropogenic impact on the river.

Hachinohe, Shoichi; Hamamoto, Hideki; Ishiyama, Takashi; Hossain, Sushmita; Oguchi, Chiaki T.

2014-05-01

94

Residence Time of Sediments in Alluvial Plains from U-Th Isotope Analyses: The Ganges River System. (Invited)  

NASA Astrophysics Data System (ADS)

As illustrated in recent studies (Granet et al., 2007 ; 2010), the analysis of U-Th disequilibria in sediments collected along rivers allows the estimation of sediment transfer time in alluvial plains. Such an approach requires understanding the secondary processes which modify the U and Th isotopes of the sediments during their transfer within the plain. It also assumes a negligible contribution of new and fresh sediments coming from the erosion of the plain substratum during the sedimentary transfer. In order to specify these first results on the Ganges Basin river system, the main Himalayan tributaries of the Ganges were sampled at the exit of the Himalayan range and at the outlet of their watershed just before their confluence with the Ganges. In addition, at several sampling locations, suspended sedimentary load was collected at different depths of the water column. Our new data along with previously published data in (Granet et al., 2007 ; 2010) show that a wide range of variation in Th activity ratios in bedload and suspended sediments for several of these rivers. Such differences probably point to contrasting (geographical, geological, lithological, pedological..) origins of these two types of sediments. Furthermore, bedload and suspended load exhibit very different covariations of U and Th isotope ratios from upstream to downstream. These different trends of variations highlight the occurrence of different transfer histories within the plain for the coarse-grained and fine-grained sediments: 100 ky or more for the bedload sediments from the Himalayan range to the confluence with the Ganges, but much less for the suspended sediments. Variations in the U-Th isotope ratios of suspended sediments recorded for the same sampling location but at different seasons suggest that their transfer time could be as fast as one year. These data therefore confirm the real potential of U and Th isotopes in river sediments to constrain their transfer time within alluvial plain but also their origin. M. Granet et al. (2007) time-scales of sedimentary transfer and weathering processes from U-series nuclides: Clues from the Himalayan rivers, Earth and Planet. Sc. Let., 261, 389-406. Granet M et al. (2010) U-series disequilibria in suspended river sediments and implication for sediment transfer time in alluvial plains : the case of the Himalayan rivers Geochim. Cosmochim. Acta, 74, 2851-2865

Chabaux, F. J.; Blaes, E.; Granet, M.; Dosseto, A.; Stille, P.; France-Lanord, C.; Lupker, M.

2010-12-01

95

Sedimentation along the Eastern Chenier Plain Coast: Down Drift Impact of a Delta Complex Shift  

NASA Technical Reports Server (NTRS)

The Mississippi River Chenier Plain is a shore parallel landform (down-drift from the Atchafalaya distributary of the Mississippi River) consisting of an alternating series of transgressive sand-shell ridges and regressive, progradational mudflats. The late 1940s shift of 1/3 of the flow of the Mississippi to the newly developing Atchafalaya delta complex to the west has resulted in injection of the river waters and suspended sediment into the westward flowing currents of the coastal current system. This has reactivated the dormant processes of mud accumulation along this coast. These environmental circumstances have provided the opportunity to: (1) investigate the depositional processes of the prograding, fine grained, mud flat facies of the open Chenier main coast and (2) to test the hypothesis that the impacts of the frequent cold front passages of fall, winter and spring exceed those of the occasional and more localized hurricane in shaping the coast and powering the dominant sedimentary processes. We conducted field investigations with the benefit of multi - scale, time series environmental surveillance by remote sensing systems, including airborne and satellite sensors. These systems provided invaluable new information on areal geomorphic patterns and the behavior of the coastal waters. This is a classic case of weather impacting inner shelf waters and sediments and causing the development of a new landform. It is clear that mud flats of the eastern chenier plain are prograding seaward, as well as progressively growing in a westerly direction.

Huh, Oscar K.; Walker, Nan D.; Moeller, Christopher

2001-01-01

96

Valley and interfluve sediments in the Southern Ganga plains, India: Exploring facies and magnetic signatures  

NASA Astrophysics Data System (ADS)

The western Ganga Plains of India show narrow, incised valleys that contain the major Himalayan-sourced rivers, separated by broad interfluves traversed by small plains-fed rivers. From analysis of four cores and outcrop sections to 50 m sub-surface, this geomorphic setting appears to be of Late Quaternary antiquity. A major river (paleo-Ganga) has been located near its present position since at least 26 ka BP, with indications of southward migration between 11 and 6 ka. Valley fill cores show repeated cycles of valley aggradation in response to Late Quaternary climatic oscillations, in accord with simulation models of drainage-basin response to climate change, and reflect interplay of discharge and sediment supply. Floodplain sediments within the valley fill show a generally weakly magnetic signature and only modest pedogenic activity. The valley margin records a major discontinuity that marks reduction of discharge in the Ganga River during the Last Glacial Maximum, when monsoonal precipitation was greatly reduced and lakes and eolian dunes occupied areas distant from the main channel. The lacustrine facies show marked magnetic enhancement, probably reflecting bacterial action and the availability of organic matter. The interfluve record yields no indication of major-river activity during the past 100 ka. Instead, the near-continuous activity of small plains-fed rivers generated cycles of alluviation and pedogenesis, the latter yielding strong magnetic signatures. Enhanced magnetic signatures are apparent in both valley and interfluve Holocene records, possibly linked to increased monsoonal strength, warmer conditions and enhanced rates of pedogenesis.

Sinha, R.; Bhattacharjee, P. S.; Sangode, S. J.; Gibling, M. R.; Tandon, S. K.; Jain, M.; Godfrey-Smith, D.

2007-10-01

97

Paleochannels and Sediment Characteristics of the Chenier Plain Inner Shelf, Louisiana  

NASA Astrophysics Data System (ADS)

In the last 3000 yrs, sediments from the Mississippi Delta have been transported to the western part of the Louisiana shelf, triggering beach progradation through a series of shell and sandy ridges (cheniers) separated by muddy hollows. Distinct events of chenier plain development have been explained as being the result of delta lobe switching in the Mississippi delta combined to local processes responsible for formation of beach ridges, recurved spits, eolian deposits, storm berms, and natural levees. In the present work we investigate the recent infill of the inner shelf off the Chenier Plain coast, just west of the recent deltaic deposits of the Mississippi River. We use shallow seismic analysis and the identification of paleochannels to understand their relationship with current rivers off the present coastline. We have been able to identify four seismic units U1 to U4 and their associated surfaces and discontinuities. A tentative reconstruction for the last 20 ky sedimentary infill is provided, correlating well with the datations available for the area. The identification and tracking of several buried channels across the shelf in units U1 and U3 let us track the position of the Mermentau-Calcasieu hydrological system in previous lowstands. It is interpreted that the Mermentau river was flowing more eastward during the Wisconsinan, occupying the location of our study and was then diverted to the west as a result of coastal processes and the development of the Chenier plains. Also, the Mermentau was re-occupying almost the same location at different lowstands, and only when the Chenier formed (due to reactivation of the west Mississippi lobe), the Mermentau was deviated westward due to sediment accumulation at the shoreline.

Garcia-Garcia, A.; Fagherazzi, S.; Orange, D.

2011-12-01

98

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

99

Do bottom mixed layers influence 234Th dynamics in the abyssal near-bottom water column?  

NASA Astrophysics Data System (ADS)

Dynamics of the natural radioactive particle tracer 234Th (half-life: 24.1 days) within the abyssal water column up to 1000 m above bottom and within surface sediments of the northeast Atlantic (Porcupine Abyssal Plain; depth: ?4845 m) were investigated. Distributions of transmissometer voltages and potential temperature indicated a subdivision of the near-bottom water column into a benthic mixed layer (BML; thickness: ?10-65 m) and the layer above the BML up to the upper boundary of the bottom nepheloid layer (BNL; thickness: ?1000 m). Comparison of 234Th fluxes (dpm m -2d -1) in sediment traps, vertical fluxes derived from 234Th/ 238U-disequilibrium in the near-bottom water column and excess 234Th inventories in the surface sediment provided evidence for lateral advection of 234Th-depleted water and a 'missing sink' for 234Th. A simple one-dimensional steady-state box-model approach was applied to investigate 234Th dynamics. Estimated residence times suggest the BML and the resuspension zone of the surface sediment to be highly dynamic systems with respect to particle cycling and sorptive reactions on a time scale of weeks. Model results indicate that, through the chemical forcing of changing particle concentration, a thickening BML results in (1) increasing residence times of particulate 234Th in the BML with respect to the net fluxes across the upper boundary of the BML and into the surface sediment; (2) declining adsorption rate constants in the BML; (3) increasing desorptive fluxes in the BML resulting in (4) enhanced 234Th decay in the BML; (5) decreasing net fluxes of particulate 234Th from the BML to the upper BNL above the BML and to the sediment. Potential consequences for carbon cycling in the water column of the deep ocean are discussed.

Turnewitsch, Robert; Springer, Barbara M.

2001-05-01

100

Geochemical Fractionations and Mobility of Arsenic, Lead and Cadmium in Sediments of the Kanto Plain, Japan.  

NASA Astrophysics Data System (ADS)

Lowland alluvial and floodplain sediment play a major role in transferring heavy metals and other elements to groundwater through sediment water interaction in changing environmental conditions. However identification of geochemical forms of toxic elements such as arsenic (As), lead (Pb) and cadmium (Cd) requires risk assessment of sediment and subsequent groundwater pollution. A four steps sequential extraction procedure was applied to characterize the geochemical fractionations of As, Pb and Cd for 44 sediment samples including one peat sample from middle basin area of the Nakagawa river in the central Kanto plain. The studied sediment profile extended from the bottom of the river to 44 m depth; sediment samples were collected at 1m intervals from a bored core. The existing sedimentary facies in vertical profile are continental, transitional and marine. There are two aquifers in vertical profile; the upper aquifer (15-20m) contains fine to medium sand whereas medium to coarse sand and gravelly sand contain in lower aquifer (37-44m). The total As and Pb contents were measured by the X-Ray Fluorescence analysis which ranged from 4 to 23 mg/kg of As and 10 to 27 mg/kg of Pb in sediment profile. The three trace elements and major heavy metals were determined by ICP/MS and ICP/AES, and major ions were measured by an ion chromatograph. The marine sediment is mainly Ca-SO4 type. The Geochemical analysis showed the order of mobility trends to be As > Pb > Cd for all the steps. The geochemical fractionations order was determined to be Fe-Mn oxide bound > carbonate bound > ion exchangeable > water soluble for As and Pb whereas the order for Cd is carbonate bound > Fe-Mn oxide bound > ion exchangeable > water soluble. The mobility tendency of Pb and Cd showed high in fine silty sediment of marine environment than for those from continental and transitional environments. In the case of As, the potential mobility is very high (>60%) in the riverbed sediments and clayey silt sediment at 13m depth which is just above the upper aquifer. This potential mobility may pose a threat to upper aquifer and riverbed aquatic system. The overall geochemical analysis revealed that the dissolution of Fe-Mn oxide is the most effective mechanism for As, Pb in groundwater however the mobility of Cd is mainly carbonate bound. In the present study, the pollution level is much below from leaching environmental standards (0.01 mg/L) for all three elements and the total content is within the natural abundance of As, Pb and Cd in sediment. The potential mobility of these elements in oxidized fine silty sediment and the possible further effect to the aquifer suggest that shallow groundwater abstraction should be restricted to protect seasonal groundwater fluctuation. Moreover marine sediment containing high total toxic element contents and mobility tendency at changing oxidation and reduction environments requires proper management when sediments are excavated for construction purpose.

Hossain, Sushmita; Oguchi, Chiaki T.; Hachinohe, Shoichi; Ishiyama, Takashi; Hamamoto, Hideki

2014-05-01

101

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

102

The IOSDL DEEPSEAS programme: introduction and photographic evidence for the presence and absence of a seasonal input of phytodetritus at contrasting abyssal sites in the northeastern atlantic  

NASA Astrophysics Data System (ADS)

This paper introduces the IOSDL DEEPSEAS programme. Two abyssal sites in the northeast Atlantic with presumed contrasting regimes of organic carbon supply have been studied. One of these sites, on the Porcupine Abyssal Plain (PAP), has an overlying water column with a winter mixed layer in excess of 500 m and was forecast to receive a highly seasonal organic input, a significant portion arriving in the form of rapidly sinking phytodetritus derived from the spring bloom. The winter mixed layer over the second site, on the Madeira Abyssal Plain (MAP), is much shallower, and the resulting flux to the benthos was expected to be quantitatively less and not in the form of aggregated phytodetritus. Recently published sediment-trap results from nearby localities indicate relatively similar total fluxes and widespread seasonality at depth, contrary to our expectations. However, benthic photographic data from the two stations seem to support the original hypothesis, at least in part. Transect photographs (and multiple-corer samples) at the PAP site in August 1989 and May 1991 revealed the presence of phytodetritus on the seafloor, relatively flocculent and evenly distributed in May and more granular and patchily distributed in August. Time-lapse photographs obtained between May 1991 and April 1992 recorded the sudden arrival of phytodetritus on 16 May and a further deposition at the beginning of June. In contrast, at the MAP site neither transect photographs in August 1990 nor time-lapse photographs obtained between August 1990 and July 1991 show evidence of the arrival of aggregated phytodetritus.

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

1994-09-01

103

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

104

Sulfur isotopic trends and pathways of iron sulfide formation in upper Holocene sediments of the anoxic Black Sea  

Microsoft Academic Search

Down-core trends for extents of iron sulfidation in upper Holocene microlaminated deposits of the Black Sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and\\/or very close to the sediment-water interface. Sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between

Timothy W. Lyons

1997-01-01

105

Cadmium and associated metals in soils and sediments of wetlands across the Northern Plains, USA.  

PubMed

Cadmium, present locally in naturally high concentrations in the Northern Plains of the United States, is of concern because of its toxicity, carcinogenic properties, and potential for trophic transfer. Reports of natural concentrations in soils are dominated by dryland soils with agricultural land uses, but much less is known about cadmium in wetlands. Four wetland categories - prairie potholes, shallow lakes, riparian wetlands, and river sediments - were sampled comprising more than 300 wetlands across four states, the majority in North Dakota. Cd, Zn, P, and other elements were analyzed by ICP-MS, in addition to pH and organic matter (as loss-on-ignition). The overall cadmium content was similar to the general concentrations in the area's soils, but distinct patterns occurred within categories. Cd in wetland soils is associated with underlying geology and hydrology, but also strongly with concentrations of P and Zn, suggesting a link with agricultural land use surrounding the wetlands. PMID:23583941

Jacob, Donna L; Yellick, Alex H; Kissoon, La Toya T; Asgary, Aida; Wijeyaratne, Dimuthu N; Saini-Eidukat, Bernhardt; Otte, Marinus L

2013-07-01

106

Volcanism and Sedimentation in Amazonis Planitia: The Origin of the Smoothest Plains on Mars  

NASA Astrophysics Data System (ADS)

Data from the Mars Orbiting Laser Altimeter (MOLA) are used to investigate Amazonis Planitia, the region with the smoothest plains on Mars. Amazonis Planitia, located just west of Olympus Mons, shows evidence for several volcanic episodes as well as geologically recent water-borne sedimentation. When normalized for regional slope ("detrended"), MOLA altimetry data clearly show small-scale relief variations that reveal previously masked elements of local topography. Using detrended MOLA data, we were able to map several new units and re-interpret previously identified units and relationships. The detrended data reveal that 1) Hesperian ridged plains underlie the current surface of Amazonis Planitia; 2) lava, presumably from Olympus Mons but possibly from Tharsis, flowed WNW across Amazonis prior to the creation of the Olympus Mons aureole; 3) post-aureole, lobate flows from southern Tharsis extend into southeastern Amazonis; 4) the very smooth central Amazonis unit appears to embay and abut the pre- and post-aureole flows; 5) the very smooth central Amazonis unit shows a variety of curving channel-like features that appear to originate at the mouth of Marte Vallis; 5) lava flow fronts from Marte Vallis extend a few km into these channels, supporting the theory [Plescia, Icarus, 88, 465, 1990; Keszthelyi et al., JGR, 105, 15027, 2000] that the Marte Vallis channels were carved by water and resurfaced by subsequent lava flow. On the basis of these observations, we propose the following geological history for Amazonis Planitia: 1) Hesperian volcanic resurfacing; 2) wrinkle ridge formation; 3) emplacement of pre-aureole flows; 4) emplacement of the Olympus Mons aureole; 5) emplacement of post-aureole flows from southern Tharsis; 6) basin flooding and sedimentation through Marte Vallis outflow channels; 7) emplacement of very young flows through Marte Vallis.

Fuller, E. R.; Head, J. W.; Kreslavsky, M. A.; Pratt, S.

2001-05-01

107

Into the Abyss  

NSDL National Science Digital Library

This website is part of NOVA online, which is produced for the Public Broadcasting System (PBS) by the Science Unit at WGBH in Boston. This site accompanies the television program and highlights exploration of the ocean floor. Topics include the Remotely Operated Platform for Ocean Science (ROPOS), deep sea machines, adaptation of life in the abyss, as well as the ROPOS team, and expeditions of the past, present, and future. The accompanying video is available through mail order.

108

U-series disequilibria in suspended river sediments and implication for sediment transfer time in alluvial plains: The case of the Himalayan rivers  

NASA Astrophysics Data System (ADS)

238U- 234U- 230Th radioactive disequilibria were analyzed in suspended sediments (collected at different depths) from the Ganges River and one of its main tributaries: the Narayani-Gandak River. Results associated with bedload sediment data suggest that uranium-series (U-series) disequilibria in river sediments of the Ganges basin vary with grain size and sampling location. The range of observed U-series disequilibria is explained by a mixing model between a coarse-grained sediment end-member, represented by bedload and bank sediments, and a fine-grained end-member that both originate from Himalaya but undergo different transfer histories within the plain. The coarse-grained sediment end-member transits slowly (i.e. >several 100's ky) in the plain whereas the fine-grained sediment end-member is transferred much faster (<20-25 ky), as indicated by the absence of significant variations in Th isotope composition of the fine-grained sediment end-members. These results show that U-series isotopes can be used to quantify the various transfer times of river sediments of different sizes and infer that there can be an order of magnitude of difference, or more, between the transfer time of suspended and bedload sediments. This underlines that a good knowledge of the proportion of suspended vs. bedload sediments transported in the river is required to accurately assess how fast erosion products are transferred in a catchment and how fast a catchment is likely to respond to external forcing factors.

Granet, M.; Chabaux, F.; Stille, P.; Dosseto, A.; France-Lanord, C.; Blaes, E.

2010-05-01

109

Source-To-Sink Perspectives On The Mississippi River System, Miocene To Present, Mountain To Abyss  

NASA Astrophysics Data System (ADS)

. The objective of this study is to present a synthesis of the Mississippi River source-to-sink system, from montane source to abyssal sink, to elucidate specific geomorphic components and boundaries in the system, controls on mass transfer, and resultant geomorphic and statigraphic development. The Mississippi River source-to-sink system constitutes one of the largest sources, conduits, and depocenters of sediment on Earth, extending from elevations of 3.7 km in the Rocky Mountains to the Gulf of Mexico abyssal plain. Despite being one of the most intensely studied fluvial-marine systems in the world, comprehensive understanding and management of the system's resources remain a challenge. The system is valuable in many ways: it provides navigation and water to the heart of North America, and sustains extensive marine fisheries. The river has built a delta that is home to millions of people and yet is subsiding rapidly. Ancestral Mississippi fluvial-marine deposits continue to yield high-value petroleum resources to exploration. To address the range of temporal and spatial scales over which the system has developed and continues to evolve, we will focus on three geological time spans that display contrasting geologic forcing and response: Miocene, Pleistocene, and late Holocene. The present configuration of source, conduit, and sink were established during the Miocene epoch, when tectonics (via the uplifting southern Rockies, and later the rejuvenated Appalachians) and climate (wet in the east and dry in the west) provided abundant water and sediment to prograde the shelf margin and initiate deep-sea fan growth. Pleistocene continental glaciation, eustasy, and catastrophic drainage events further sculpted the alluvial valley, and extended the shelf margin, and fan. Studies of Modern processes and Holocene delta development have provided keys to both the delta's past and future evolution, in terms of cyclic autogenic lobe-switching, mass-transport events, storm-driven sediment delivery to canyon heads, and allogenic/anthropogenic controls on sediment supply and subsidence.

Bentley, S. J.; Blum, M. D.

2013-12-01

110

Trends in nutrient and sediment retention in Great Plains reservoirs (USA).  

PubMed

Reservoirs are artificial ecosystems with physical, chemical, and biological transitional characteristics between rivers and lakes. Greater water retention time in reservoirs provides conditions for cycling materials inputs from upstream waters through sedimentation, biological assimilation and other biogeochemical processes. We investigated the effects of reservoirs on the water quantity and quality in the Great Plains (Kansas, USA), an area where little is known about these dominant hydrologic features. We analyzed a 30-year time-series of discharge, total phosphorus (TP), nitrate (NO3(-)), and total suspended solids (TSS) from six reservoirs and estimated overall removal efficiencies from upstream to downstream, testing correlations among retention, discharge, and time. In general, mean removal of TP (42-74%), TSS (0-93%), and NO3(-) (11-56%) from upstream to downstream did not change over 30 years. TP retention was associated with TSS removal, suggesting that nutrient substantial portion of P was adsorbed to solids. Our results indicated that reservoirs had the effect of lowering variance in the water quality parameters and that these reservoirs are not getting more or less nutrient-rich over time. We found no evidence of temporal changes in the yearly mean upstream and downstream discharges. The ratio upstream/downstream discharge was analyzed because it allowed us to assess how much contribution of additional unsampled tributaries may have biased our ability to calculate retention. Nutrient and sediment removal was less affected by hydraulic residence time than expected. Our study demonstrates that reservoirs can play a role in the removal and processing of nutrient and sediments, which has repercussions when valuing their ecological services and designing watershed management plans. PMID:24061791

Cunha, Davi Gasparini Fernandes; do Carmo Calijuri, Maria; Dodds, Walter Kennedy

2014-02-01

111

Sedimentation of lithogenic particles in the deep ocean  

USGS Publications Warehouse

Investigation of lithogenic particles collected by sediment traps in open-ocean stations revealed that the sediment flux increased linearly with depth in the water column. This rate of increase decreased with distance of the station from the continent; it was largest at the Panama Basin station and almost negligible at the E. Hawaii Abyssal Plain station. At the Panama Basin station, smectite flux increased with depth. We suggest that smectite resuspended from bottom sediments of the continental slope west of the sediment-trap station is advected by easterly deep currents, and the suspended particles are then possibly entrapped by large settling particles. On the other hand, the flux of hemipelagic clay particles, kaolinite and chlorite, was nearly constant at all depths; this can be explained by incorporation of these particles in fecal pellets which then settle from the surface water. At the Demerara Abyssal Basin Station, flux of illite and chlorite particles increased with depth and the flux of smectite was constant. A sudden increase of the flux of illite and chlorite was observed near the bottom traps at the So??hm Abyssal Plain station. The flux of quartz and feldspar was 10 to 15% of the clay flux. ?? 1982.

Honjo, S.; Manganini, S. J.; Poppe, L. J.

1982-01-01

112

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

113

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

114

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

115

Seismic evidence for pervasive deformation of oceanic sediments in the Eastern Equatorial Atlantic  

Microsoft Academic Search

Seismic reflection profiles from the equatorial Atlantic off Africa between 12°N and 1°N reveal remarkably widespread deformation of oceanic sediments in an area lacking teleseismic activity. Uplift of abyssal plain sequences has occurred along the eastern extensions of large-offset fracture zones on the Mid-Atlantic Ridge. Between the major transforms pervasive deformation is imaged in the sedimentary column. Diapirism and faulting

E. J. W. Jones

2003-01-01

116

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

SciTech Connect

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/sup 0/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 in the sediment. Fluid displacement due to convection is found to be less than 1 m. Laboratory studies of the geochemical effects induced by heating sediment/seawater mixtures indicate that the canister and waste form must be designed to resist a hot, acid (pH 3 to 4) oxidizing environment. Since the thermally altered sediment volume of about 5.5 m/sup 3/ is small relative to the sediment volume overlying the canister, the acid and oxidizing conditions are not anticipated to effect the properties of the far field. Using sorption coefficient correlations, the migration of four nuclides /sup 239/Pu, /sup 137/Cs, /sup 129/I, and /sup 99/Tc were computer for a canister buried 30 m deep in a 60 m thick red clay sediment layer. It was found that the /sup 239/Pu and /sup 137/Cs are essentially completely contained in the sediments, while /sup 129/I and /sup 99/Tc broke through the 30 m of sediment in about 5000 years. The resultant peak injection rates of 4.6 x 10/sup -5/ ..mu..Ci/year-m/sup 2/ for /sup 129/I and 1.6 x 10/sup -2/ ..mu..Ci/year-m/sup 2/ for /sup 99/Tc were less than the natural radioactive flux of /sup 226/Ra (3.5 to 8.8 x 10/sup -4/ ..mu..Ci/year-m/sup 2/) and /sup 222/Rn (0.26 to 0.88 ..mu..Ci/year-m/sup 2/).

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

1980-01-01

117

Transparent layers in seismic reflection records from the central Ionian Sea (Mediterranean)—evidence for repeated catastrophic turbidite sedimentation during the Quaternary  

NASA Astrophysics Data System (ADS)

Echosounding and SCS records from the Ionian and Sirte Abyssal Plains show, below the Holocene Augias megaturbidite, two additional thick transparent layers which by analogy are interpreted as turbidites. Estimated thicknesses are 10 and 35 m (upper and lower) as a minimum (no consideration of presumable variations of acoustic velocities). The resulting sediment volumes are about 26 and about 200 km 3, respectively. Both layers occupy the entire abyssal plain basins similar to the Holocene Augias megaturbidite. A provenance of mobilized sediments from the Gulf of Sirte into the basins is assumed. The ages of the two turbidites have been estimated at 235,000 and 650,000 years, respectively. It is speculated that mobilization was triggered by tsunamis related to volcanic events or earthquakes in the southern Aegean region.

Hieke, W.

2000-09-01

118

Invertebrate colonization of leaves and roots within sediments of intermittent coastal plain streams across hydrologic phases  

EPA Science Inventory

We compared benthic invertebrate assemblages colonizing three types of buried substrates (leaves, roots and plastic roots) among three intermittent Coastal Plain streams over a one year period. Invertebrate density was significantly lower in root litterbags than in plastic root l...

119

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

USGS Publications Warehouse

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. ?? 2010 Elsevier Inc.

Rodriguez, J. A. P.; Tanaka, K. L.; Berman, D. C.; Kargel, J. S.

2010-01-01

120

Influence of sediment provenance on background values of potentially toxic metals from near-surface sediments of Po coastal plain (Italy)  

NASA Astrophysics Data System (ADS)

Systematic variability in metal concentrations is recorded in near-surface (1 m deep) Late Quaternary sediments of Po coastal plain, across the boundary between alluvial deposits of Apenninic provenance and a formerly active, now abandoned, delta lobe of the Po River. In the latter area, high Cr and Ni concentrations, exceeding the national standard limits, are attributed to sediment provenance from ultramafic source rocks of Po catchment basin, and not to anthropogenic impact. Spatial distribution of carbonate-related elements, such as Ca and Sr, displays consistent differences between the two areas, confirming a primary control of provenance domains on sediment composition. Accurate facies characterization of near-surface sediments, coupled with detailed information on sediment dispersal patterns, enable a reliable interpretation of the spatial variability of major elements and trace metals in the study area. Particularly, detailed reconstructions of source area composition and changes in flow directions through historical times allow precise correlation of apparently anomalous geochemical patterns with distinctive depositional events, such as shifts in channel course, crevasse splay formation and beach-ridge evolution. The findings of unusually high, natural (provenance-controlled) heavy metal concentrations in pre-industrial near-surface levels highlight the contribution of a sedimentological approach to a reliable interpretation of geochemical data. This should be taken into account when determining background values versus anthropogenic impact.

Amorosi, Alessandro; Sammartino, Irene

2007-04-01

121

Use of U-series nuclides to constrain sediments transfer-times in the alluvial plains: example of the Ganges and Bramaputra river system.  

NASA Astrophysics Data System (ADS)

U-series nuclides have the potential to bring important information on the transfer time of sediments in the alluvial plains. This is a consequence of the dual property of these nuclides 1) to be fractionated during physical denudation and chemical weathering processes and 2) to have radioactive decay periods of the same order of magnitude as the time-scales of these processes (e.g. Chabaux et al., 2003b, 2008). We have illustrated such a potential with the analysis of U-series disequilibria in sediments collected in the Ganges and Bramaputra river basin. The approach relies on the analysis of U-series in river sediments collected along the streams. Indeed, as illustrated in Granet et al. (2007), in large alluvial plains where sediments are only transferred and not affected by additional inputs of new weathering products from fresh rocks, the intensity of 238U-234U-230Th disequilibria in river sediments will only depend on two parameters: (a) the duration of the transfer including the time spent in soils and in the river, and (b) the nature and the intensity of U-Th fractionations occurring in sediments during their transfer into alluvial plains. Recovering time information from the variation of U-Th disequilibria in such sediments requires therefore the use of realistic models accounting for the U-Th fractionation of sediments during their transfers into the plain. From the data, it is proposed for the Ganges and Bramaputra river sediments, that the main U-Th fractionation process is connected with the sediment weathering during their transit and storage in the plain. In this case the U-Th variation in sediments along the two main rivers lead to quite long sediment transfer time in the alluvial plains, of 100-150 ky for Bramaputra plain and of 400 or 500 ky for the Ganges river. Chabaux F., Riotte J., Dequincey O. (2003) U-Th-Ra fractionation during weathering and river transport, Rev Mineral. Geochem. 52, 533-576. Chabaux, F., Bourdon, B., Riotte, J., 2008. U-series Geochemistry in weathering profiles, river waters and lakes. In : S. Krishnaswami and J.K. Cochran (Eds.), U/Th Series Radionuclides in Aquatic Systems, Elsevier, Radioactivity in the Environment, 13, 49-104 M. Granet, F. Chabaux, C. France-Lanord, P. Stille, E. Pelt (2007). Time-scales of sedimentary transfer and weathering processes from U-series nuclides: Clues from the Himalayan rivers, Earth and Planetary Science Letters, 261, 389-406.

Chabaux, François; Granet, Mathieu; Blaes, Estelle; Stille, Peter; France-Lanord, Christian; Dosseto, Antony

2010-05-01

122

Pathways for arsenic from sediments to groundwater to streams: biogeochemical processes in the Inner Coastal Plain, New Jersey, USA.  

PubMed

The Cretaceous and Tertiary sediments that underlie the Inner Coastal Plain of New Jersey contain the arsenic-rich mineral glauconite. Streambed sediments in two Inner Coastal Plain streams (Crosswicks and Raccoon Creeks) that traverse these glauconitic deposits are enriched in arsenic (15-25mg/kg), and groundwater discharging to the streams contains elevated levels of arsenic (>80?g/L at a site on Crosswicks Creek) with arsenite generally the dominant species. Low dissolved oxygen, low or undetectable levels of nitrate and sulfate, detectable sulfide concentrations, and high concentrations of iron and dissolved organic carbon (DOC) in the groundwater indicate that reducing environments are present beneath the streambeds and that microbial activity, fueled by the DOC, is involved in releasing arsenic and iron from the geologic materials. In groundwater with the highest arsenic concentrations at Crosswicks Creek, arsenic respiratory reductase gene (arrA) indicated the presence of arsenic-reducing microbes. From extracted DNA, 16s rRNA gene sequences indicate the microbial community may include arsenic-reducing bacteria that have not yet been described. Once in the stream, iron is oxidized and precipitates as hydroxide coatings on the sediments. Arsenite also is oxidized and co-precipitates with or is sorbed to the iron hydroxides. Consequently, dissolved arsenic concentrations are lower in streamwater than in the groundwater, but the arsenic contributed by groundwater becomes part of the arsenic load in the stream when sediments are suspended during high flow. A strong positive relation between concentrations of arsenic and DOC in the groundwater samples indicates that any process-natural or anthropogenic-that increases the organic carbon concentration in the groundwater could stimulate microbial activity and thus increase the amount of arsenic that is released from the geologic materials. PMID:20580401

Barringer, Julia L; Mumford, Adam; Young, Lily Y; Reilly, Pamela A; Bonin, Jennifer L; Rosman, Robert

2010-11-01

123

Pathways for arsenic from sediments to groundwater to streams: Biogeochemical processes in the Inner Coastal Plain, New Jersey, USA  

USGS Publications Warehouse

The Cretaceous and Tertiary sediments that underlie the Inner Coastal Plain of New Jersey contain the arsenic-rich mineral glauconite. Streambed sediments in two Inner Coastal Plain streams (Crosswicks and Raccoon Creeks) that traverse these glauconitic deposits are enriched in arsenic (15–25 mg/kg), and groundwater discharging to the streams contains elevated levels of arsenic (>80 ?g/L at a site on Crosswicks Creek) with arsenite generally the dominant species. Low dissolved oxygen, low or undetectable levels of nitrate and sulfate, detectable sulfide concentrations, and high concentrations of iron and dissolved organic carbon (DOC) in the groundwater indicate that reducing environments are present beneath the streambeds and that microbial activity, fueled by the DOC, is involved in releasing arsenic and iron from the geologic materials. In groundwater with the highest arsenic concentrations at Crosswicks Creek, arsenic respiratory reductase gene (arrA) indicated the presence of arsenic-reducing microbes. From extracted DNA, 16s rRNA gene sequences indicate the microbial community may include arsenic-reducing bacteria that have not yet been described. Once in the stream, iron is oxidized and precipitates as hydroxide coatings on the sediments. Arsenite also is oxidized and co-precipitates with or is sorbed to the iron hydroxides. Consequently, dissolved arsenic concentrations are lower in streamwater than in the groundwater, but the arsenic contributed by groundwater becomes part of the arsenic load in the stream when sediments are suspended during high flow. A strong positive relation between concentrations of arsenic and DOC in the groundwater samples indicates that any process—natural or anthropogenic—that increases the organic carbon concentration in the groundwater could stimulate microbial activity and thus increase the amount of arsenic that is released from the geologic materials.

Barringer, Julia L.; Mumford, Adam; Young, Lily Y.; Reilly, Pamela A.; Bonin, Jennifer L.; Rosman, Robert

2010-01-01

124

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

125

Sediment sources and sedimentation processes of 2011 Tohoku-oki tsunami deposits on the Sendai Plain, Japan — Insights from diatoms, nannoliths and grain size distribution  

NASA Astrophysics Data System (ADS)

The 11th March 2011 Tohoku-oki tsunami inundated the low-lying Sendai Plain (Japan) more than 5 km inland leaving sand and mud deposits over most of the area. In order to establish the sources of the tsunami deposits and interpret processes of their sedimentation, samples were collected from the deposits, underlying soils and the beach along a shore-perpendicular transect and analysed for grain size, diatom assemblages and nannoliths. The fining-inland tsunami deposits consisted of poorly to moderately sorted medium to coarse sand within 2 km of the coastline and very poorly to poorly sorted mud farther inland. More specifically, there was a slight fining of the coarse to medium sand mode within the sandy deposits and an increased contribution of the coarse and very coarse silt fraction in the mud deposits. The tsunami deposits also exhibited vertical changes including fining upward and coupled coarsening-fining upward trends. Few diatoms were present in beach sediments, soils and tsunami deposits within 1 km of the coastline, while diatoms were more abundant farther inland. Diatom assemblages in the soil and tsunami deposits were similar and dominated by species typical of freshwater-brackish habitats, while no typically marine species were encountered. Nannoliths were generally absent in the studied sediments, except for few specimens. Our data indicate that there was probably no or only a very minor component of marine sediments transported onland by the tsunami. The sandy tsunami deposits within ~ 1 km of the coastline were mostly derived from beach and dune erosion. From 1 to 2 km landward the contribution of these sources decreased, while sources comprising local soil erosion and the entrainment of sediments from the Teizan-bori canal increased. Farther inland, local soil erosion was the major sediment source for the mud deposits. The tsunami deposits were most likely deposited during at least two inundations, mostly out from suspension resulting in an upward grain size fining trend. However, bed load deposition was also important in the sandy deposits as suggested by a common grain size upward coarsening, position on C-M diagrams and frequent horizontal lamination. The present study reveals that even very large tsunamis may not transport marine sediments onland and thus many commonly applied indicators of tsunami deposits based on the assumption of their offshore origin (marine diatoms, foraminifera, nannoliths, marine sediments) may be of limited use.

Szczuci?ski, Witold; Kokoci?ski, Miko?aj; Rzeszewski, Micha?; Chagué-Goff, Catherine; Cachão, Mario; Goto, Kazuhisa; Sugawara, Daisuke

2012-12-01

126

Use of U-series nuclides to constrain sediments transfer-times in the alluvial plains: example of the Ganges and Bramaputra river system  

Microsoft Academic Search

U-series nuclides have the potential to bring important information on the transfer time of sediments in the alluvial plains. This is a consequence of the dual property of these nuclides 1) to be fractionated during physical denudation and chemical weathering processes and 2) to have radioactive decay periods of the same order of magnitude as the time-scales of these processes

François Chabaux; Mathieu Granet; Estelle Blaes; Peter Stille; Christian France-Lanord; Antony Dosseto

2010-01-01

127

Sediment Sources, Sedimentation Processes and Post-Depositional Changes of the 2011 Tohoku-Oki Tsunami Deposits on the Sendai Plain, Japan  

NASA Astrophysics Data System (ADS)

The 11th March 2011 Tohoku-oki tsunami inundated the low-lying Sendai Plain (Japan) more than 5 km inland leaving sand and mud deposits over most of the area. In order to establish the sources of the tsunami deposits and interpret processes of their sedimentation, samples were collected from the deposits, underlying soils and the beach along a shore-perpendicular transect and analysed for grain size, heavy minerals, diatom assemblages and nannoliths. Surveys were undertaken 2, 5 and 7 months after the tsunami to assess the importance of post-depositional changes in tsunami deposits. The last survey took place shortly after a major typhoon. The fining-inland tsunami deposits consisted of poorly to moderately sorted medium to coarse sand within 2 km of the coastline and very poorly to poorly sorted mud farther inland. The tsunami deposits also exhibited vertical changes including fining upward and coupled coarsening-fining upward trends. Heavy minerals comprised on average 35% of the tsunami deposit in the 0.125 - 0.25 mm grain size fraction. Heavy mineral concentrations and assemblages were similar in the tsunami deposits, beach and underlying soils. Diatoms were rare in beach sediments, soils and tsunami deposits within 1 km of the coastline, while they were more abundant farther inland. Diatom assemblages in the soil and tsunami deposits were similar and dominated by species typical of freshwater-brackish habitats, while no typically marine species were encountered. Nannoliths were generally absent in the studied sediments, except for few specimens. Our data indicate that there was probably no or only a very minor component of marine sediments transported onland by the tsunami. The sandy tsunami deposits within ~1 km of the coastline were mostly derived from beach and dune erosion. From 1 to 2 km landward the contribution of these sources decreased, while sources comprising local soil and inland canal sediments increased. Farther inland, mud deposits were mostly derived from local soil erosion. The tsunami deposits were most likely deposited during at least two inundations, mostly from suspension resulting in an upward grain size fining trend. However, bed load deposition was also important in the sandy deposits. The tsunami deposits were generally well preserved after 2 months but sandy sediments in exposed areas were redeposited by wind action. After 7 months, preservation was still good. On the coastal dune slopes there was limited redeposition of sediment by flowing water. Plant recolonisation was slow. The surface of the tsunami deposits was commonly stabilised by an algal mat cover. In places where the deposits were thinner than 1 cm their visual discrimination from the underlying soil was problematic, however, the deposits were still relatively well preserved for about 80% of their original extent. The study reveals that even very large tsunamis may not transport marine sediments onland and thus many commonly applied indicators of tsunami deposits based on the assumption of their offshore origin may be of limited use. Preservation of tsunami deposits in a coastal plain setting primarily depends on their thickness and land topography. Most erosion and redeposition of the deposits take place shortly after tsunami inundation and depend on climate (wind, rain) and topography.

Szczucinski, W.; Chague-Goff, C.; Goto, K.; Sugawara, D.; Jagodzinski, R.; Kokocinski, M.; Cachao, M.; Sternal, B.; Rzeszewski, M.; Goff, J. R.; Jaffe, B. E.

2012-12-01

128

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

129

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

SciTech Connect

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 present in deep subsurface sediments. Although Fe(III) reduction in subsurface sediments is frequently regarded as an abiological reaction, the enzymatic reduction of Fe(III) by microorganisms reported here is the first mechanism of any kind actually shown to have the potential to couple the oxidation of organic matter to carbon dioxide with the reduction of Fe(III) under the environmental conditions typically found in deep aquifers. We propose that microbially catalyzed Fe(III) reduction is responsible for such late postdepositional phenomena as the formation of variegated red beds and the release of high concentrations of dissolved iron into anaerobic ground waters.

Lovley, D.R.; Phillips, E.J.P. (Geological Survey, Reston, VA (USA)); Chapelle, F.H. (Geological Survey, Columbia, SC (USA))

1990-10-01

130

Seismic deformation structures of the post-2300 a BP muddy sediments in Kawachi lowland plain, Osaka, Japan  

NASA Astrophysics Data System (ADS)

Deformed zones, consisting mainly of muddy sediments, deposited in palustrine environments, found during the excavations of archaeological sites, have been examined. The beds belong to the uppermost Holocene sequence, within 6 m depth from the present ground surface, in Kawachi alluvial lowland plain, Osaka Prefecture, Japan. Each deformation zone contained basically three deformation units related to fluidity and plasticity decreasing with depth beneath the fresh sedimentation surface. The units recognized were, from top to bottom: (1) a liquidized deformation unit expressed by a homogenized layer, in which the sediment and water have been mixed by turbulent flow; (2) a hydroplastic deformation unit characterized by a plumose pattern in the upper part of the unit and load structures in the lower part; and (3) a brittle deformation unit characterized by downward fissures and microfaults. The plumose pattern in the second unit may have formed where the more cohesive sediments in the lower part of the unit were dragged horizontally with repeated directional changes, and pulled upward by the movement of the sediments in the upper part. The load structures in the lower part of this unit are assumed to have been formed mainly by differential vertical and compressive forces applied to the sedimentary horizons. In the uppermost part of the liquidized deformation unit, load casts and pseudonodules with short horizontal tracks, suggesting movement while sinking, were seen locally. These features in the units are assumed to have been formed by the oscillatory and rotational force, irregular in intensity and direction, of an earthquake. The minor displacement of deformed sediments, such as mixing, truncation, intrusion, and injection, at the boundaries between the units and their internal layers suggests that the deformation process was initiated simultaneously in each unit, and was of short duration. The vertical occurrence order of the deformational features, similar to that of 'fault-graded bedding', especially of the plumose pattern and load structures, was recognizable in most deformation zones. By defining and separating superposed deformation zones according to the vertical order of the features, and by the relative dating of the zones based on the archaeological artifact chronology, a regional correlation of deformational event horizons may be proposed. Consequently, several synchronous seismic event horizons in prehistoric time have been recognized, and their lateral extents have been documented. Additionally, within one site, chronological correlation reveals that the ages of the post-13th century deformational event horizons are in accordance with the ages of historically recorded earthquakes.

Matsuda, J.-i.

2000-09-01

131

Evaluation of natural radioactivity in soil, sediment and water samples of Niger Delta (Biseni) flood plain lakes, Nigeria.  

PubMed

This paper presents the findings of a baseline study undertaken to evaluate the natural radioactivity levels in soil, sediment and water samples in four flood plain lakes of the Niger Delta using a hyper pure germanium (HPGe) detector. The activity profile of radionuclides shows low activity across the study area. The mean activity level of the natural radionuclides (226)Ra, (232)Th and (40)K is 20 ± 3, 20 ± 3 and 180 ± 50 Bq kg(-1), respectively. These values are well within values reported elsewhere in the country and in other countries with similar environments. The study also examined some radiation hazard indices. The mean values obtained are, 76 ± 14 Bq kg(-1), 30 ± 5.5 ?Gy h(-1), 37 ± 6.8 ?Sv y(-1), 0.17 and 0.23 for Radium Equivalent Activity (Ra(eq)), Absorbed Dose Rates (D), Annual Effective Dose Rates (E(ff) Dose), External Hazard Index (H(ex)) and Internal Hazard Index (H(in)) respectively. All the health hazard indices are well below their recommended limits. The soil and sediments from the study area provide no excessive exposures for inhabitants and can be used as construction materials without posing any significant radiological threat to the population. The water is radiologically safe for domestic and industrial use. The paper recommends further studies to estimate internal and external doses from other suspected radiological sources to the population of the Biseni kingdom. PMID:21514983

Agbalagba, E O; Onoja, R A

2011-07-01

132

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

1994-08-10

133

Chromium and nickel as indicators of source-to-sink sediment transfer in a Holocene alluvial and coastal system (Po Plain, Italy)  

NASA Astrophysics Data System (ADS)

A reliable quantitative estimate of changes in source-to-sink sediment transfer requires that high-resolution stratigraphic studies be coupled with accurate reconstructions of spatial and temporal variability of the sediment-routing system through time. Source-to-sink patterns from the contributing upland river catchments to the deltaic and coastal system are reconstructed from the Holocene succession of the Po Plain on the basis of selected geochemical indicators. Sediment supplied to the delta area by the major trunk river (the Po) exhibits naturally high Cr and Ni values, which invariably exceed the maximum permissible concentrations for unpolluted sites. This 'anomaly' reflects remarkable sediment contribution from ultramafic (ophiolitic) parent rocks cropping out in the Po drainage basin (Western Alps and NW Apennines). In contrast, alluvial and coastal plain deposits supplied by ophiolite-free, Apenninic catchments invariably display lower Cr and Ni contents. For constant sediment provenance domain, Cr and Ni distribution is observed to be controlled primarily by hydraulic sorting. Clay-silt deposits (floodplain, swamp and lagoon/bay facies associations) invariably show higher metal concentrations than their sandy counterparts (fluvial-channel, distributary-channel and beach-ridge facies associations). From a stratigraphic perspective, in sedimentary basins characterized by strong differences in sediment composition geochemical fingerprinting of individual facies associations framed by surfaces of chronostratigraphic significance is proposed as an invaluable approach towards an accurate quantitative assessment of sediment storage in alluvial and coastal depositional systems as opposed to volumetric reconstructions based on lithologic or geometric criteria alone.

Amorosi, Alessandro

2012-12-01

134

Saprolite formation beneath Coastal Plain sediments near Washington, D.C.  

USGS Publications Warehouse

Three lines of evidence indicate that this buried weathering profile (saprolite) has formed in the subsurface and is post-Miocene in age. The post-Miocene age for the subsurface saprolite profile shows that not all saprolite beneath Cretaceous sediment is pre-Cretaceous in age. These observations have important implications for the interpretation of age of the exposed Piedmont saprolite. -from Authors

Pavich, M. J.; Obermeier, S. F.

1985-01-01

135

Determination of transfer time for sediments in alluvial plains using 238U-234U-230Th disequilibria: The case of the Ganges river system  

NASA Astrophysics Data System (ADS)

An approach to deriving the transfer time of sediments within alluvial plains by using the variation of the U-series nuclides in sediments collected along rivers is presented in this article and discussed in the light of new data from samples from different locations within the Ganges watershed and its outlet. These data indicate that the upstream-downstream variation of 238U-234U-230Th disequilibria in the sediments, with different variation trends for suspended and coarse-grained sediments, is probably a general feature of all Himalayan rivers flowing across the Indo-Gangetic plain. The data therefore confirm the occurrence of very different transfer times within the plain, depending on the sediments granulometry, with much shorter transfer time for the fine-grained (a few ky or less) than for the coarse-grained sediments (100 ky or more). A new solving approach, using a parallel stochastic Quantum-behaved Particle Swarm Optimization (p-QPSO), has been developed for identifying the unknown parameters of the model necessary for the determination of the transfer time. The data of sediments collected at the Ganges outlet show significant variations of the 234U/230Th activity ratios for the fine-grained sediment end-member collected in 2004 and 2008. Such variations indicate that the fine-grained sediments transit quickly (a year or less) within the plain. The highly variable activity ratios might be the result of quickly changing weathering intensities. Conversely, the U-Th variations observed for the 2004 and 2008 bedload from the Ganges basin cannot result from a short sedimentary transfer time. They probably result from the dredge sampling procedure, which might be influenced by local placer effects controlling the abundance of U and Th carrying minerals. Dredging may not allow the sampling of a representative bedload, hence it may cause an artificial mineralogical and, therefore, an U-Th variability for bedload sediments collected at different periods. At this stage, the transfer time uncertainty induced by this variability is difficult to assess.

Chabaux, François; Blaes, Estelle; Granet, Mathieu; Roupert, Raphaël di Chiara; Stille, Peter

2012-11-01

136

Temporal variability in polychaete assemblages of the abyssal NE Atlantic Ocean  

NASA Astrophysics Data System (ADS)

Temporal variability in deep-sea polychaete assemblages was assessed at the Porcupine Abyssal Plain Sustained Observatory, NE Atlantic, over a 9-year period (eight cruises between August 1989 and September 1998). The polychaete communities were characterized by large number of individuals (abundance) and high family richness. The highest abundances occurred in the upper 1 cm sediment layer (53.2% of total abundance). The most abundant families were the Cirratulidae, Spionidae, Opheliidae and Paraonidae. Surface deposit feeders were the dominant trophic group (67.4% of total abundance). Significant temporal variability was evident in polychaete abundance with significant differences in polychaete abundance between sampling periods (cruises; p<0.01). Stepwise increases in abundance in September 1996 and March 1997 coincided with similar increases in abundance in large invertebrates (megafauna) in the same area (known as the ' Amperima Event' after a species of holothurian that increased in abundance by over three orders of magnitude). Similar patterns were observed for abundances across different layers of the sediment, main families and trophic groups showing significant differences between cruises ( p<0.05). A comparison of samples taken (1) before the ' Amperima Event' (1989-1994) and (2) during the ' Amperima Event' (1996-1998) showed significant differences in the polychaete abundance in the upper 3 cm of the sediment. There were significant differences in some trophic groups (predators, deposit feeders and burrowers) and the dominant families (Cirratulidae, Spionidae and Opheliidae). Not all elements of the polychaete community showed a response (e.g. the Paraonidae). Changes in surface deposit feeders were particularly evident. The temporal variability is likely to be related to seasonal and interannual variability in organic matter input. Greater food supply in some years may allow the growth and development of deposit-feeding polychaetes.

Soto, Eulogio H.; Paterson, Gordon L. J.; Billett, David S. M.; Hawkins, Lawrence E.; Galéron, Joelle; Sibuet, Myriam

2010-08-01

137

Long-term change in the abyssal NE Atlantic: The ‘Amperima Event’ revisited  

NASA Astrophysics Data System (ADS)

The results from a time series study (1989-2005) at a depth of 4850 m on the Porcupine Abyssal Plain, NE Atlantic, are presented, showing radical changes in the density of large invertebrates (megafauna) over time. Major changes occurred in a number of different taxa between 1996 and 1999 and then again in 2002. One species of holothurian, Amperima rosea, was particularly important, increasing in density by over three orders of magnitude. There were no significant changes in total megafaunal biomass during the same period. Peaks in density were correlated to reductions in mean body size, indicating that the increases were related to large-scale recruitment events. The changes occurred over a wide area of the Porcupine Abyssal Plain. Comparisons made with changes in the density of protozoan and metazoan meiofauna, and with macrofauna, showed that major changes in community structure occurred in all size fractions of the benthic community at the same time. This suggests that the faunal changes were driven by environmental factors rather than being stochastic population imbalances of one or two species. Large-scale changes in the flux of organic matter to the abyssal seafloor have been noted in the time series, particularly in 2001, and may be related to the sudden mass occurrence of A. rosea the following year. Time-varying environmental factors are important in influencing the occurrence of megafauna on the abyssal seafloor.

Billett, D. S. M.; Bett, B. J.; Reid, W. D. K.; Boorman, B.; Priede, I. G.

2010-08-01

138

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

139

Geophysical Evidence for Large Scale Fluid Vent Structure in the Abyssal Gulf of Mexico  

NASA Astrophysics Data System (ADS)

This talk examines geophysical evidence for the appearance of a large-scale fissure or fluid vent structure in the abyssal Gulf of Mexico, located in Lund Area. We notice a near vertical fissure 20,000 ft tall and about 100km long, which directly underlies the thickest portion of the Mississippi River Fan. Disruption of the sedimentary layers below the fan resembles fluid vent structures normally seen as localized chimneys on seismic from deep water. In this case, the feature has developed into a long, linear structure, the upper portion of which appears to contain hydrates. We expect a relationship between the formation of the fissure and the rapid deposition of the Mississippi Fan during Pleistocene and Holocene glacial lowstands. The expanding fan would have led to uneven loading of the pre-existing, layered sediments of the abyssal plain. This may have caused a zone of low effective stress to develop at the leading edge of the levee, reaching deep into the subsurface due to the large spatial wavelength of the load, and bringing pore pressures close to the fracture gradient in much the same manner as envisioned by Dugan & Flemings, 2000 for formation of the box canyons off the New Jersey coast. Geophysically, we can document: 1) A long, linear time structure appearing at all levels underlying the Mississippi Fan and above the known source rock section (i.e., Top K through Pliocene). 2) Isopachs show no thinning implying a late, catastrophic event. 3) Banded, high amplitude reflections crowded into the top of the vent may be hydrates or alternating layers of hydrates and free gas trapped under the fan sediments. 4) Low impedance, low frequency, chaotic seismic "halo" 20-25miles wide surrounds the vent. 5) Near and far offset stacks of seismic data resemble one another enough to prove the feature is not just a shallow velocity anomaly. Far offset raypaths would undershoot a near surface feature causing deep reflectors from a far offset record to differ from a near offset record if it were simply a shallow velocity anomaly. 6) Congruence of the subsurface feature with the bathymetric maximum thickness of the Mississippi Fan combined with the apparent late-stage deformation suggests a causal relationship. Understanding the formation of this vent feature may provide insight into large-scale petroleum migration routes, the origins of overpressure in the shallow sedimentary section, effects on the distribution of hydrates, and possibly rates of petroleum sourcing.

Dohmen, T. E.

2005-05-01

140

Hydrogeochemistry and adsorption behaviour of As-enriched sediment from Bengal Delta Plain, India  

NASA Astrophysics Data System (ADS)

Sixty-six groundwater samples were collected from an area of 16 sq. km in Chakdaha block, West Bengal. High arsenic (1 to 475 ?g/l) in anoxic groundwater is associated with relatively high Fe and pCO2. Groundwater redox potential is controlled by the Fe2+/Fe(OH)3 couple. X-ray fluorescence (XRF) analyses of 29 borehole sediments showed higher contents of As (8-14 mg/kg), Fe2O3 (5-9.6%) and MnO (0.07-0.15%) in silty clay whereas fine to medium sand have lower content of As (<5 mg/kg), Fe2O3 (1.15-3.9%) and MnO (0.02- 0.06%). Acid extractable As does not correlate with ascorbate extractable Fe oxyhydroxide. However, high Fe oxyhydroxide (10-12 g/kg) was obtained by ascorbate extraction in low As area. Organic carbon is low ~ 1% and groundwater temperature (26-31oC) may facilitate microbial process that leads to increase local reducing condition (redox traps). Speciation of Fe, Mn, HCO3- and As in groundwater samples was done by using MINTEQA2. Arsenate adsorption study performed on sandy riverbank sediment indicates very low affinity for As at pH ~7.5.

Nath, B.; Chakraborty, S.; Jean, J.; Charlet, L.; Chatterjeee, D.

2007-12-01

141

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

142

Comparison and correlation of physical properties from the plain and slope sediments in the Ulleung Basin, East Sea (Sea of Japan)  

Microsoft Academic Search

High-resolution profiles (chirp sonar, 2–7kHz) acquired from the Ulleung Basin, East Sea (Sea of Japan) revealed several discrete echo types, suggesting deposits formed mainly by mass flow processes. The Ulleung Basin plain sediments are characterized by turbidite\\/hemipelagic deposits, while slide, slump, and debrite deposits are mainly found in the slope area. Rock fall deposits also appear near the Ulleung Island.

G. Y Kim; D. C Kim

2001-01-01

143

Material supply to the abyssal seafloor in the Northeast Atlantic  

NASA Astrophysics Data System (ADS)

Downward particle flux was measured using sediment traps at various depths over the Porcupine Abyssal Plain (water depth ?4850 m) for prolonged periods from 1989 to 1999. A strong seasonal pattern of flux was evident reaching a maximum in mid-summer. The composition of the material changed with depth, reflecting the processes of remineralisation and dissolution as the material sank through the water column. However, there was surprisingly little seasonal variation in its composition to reflect changes in the biology of the euphotic zone. Currents at the site have a strong tidal component with speeds almost always less than 15 cm/sec. In the deeper part of the water column they tend to be northerly in direction, when averaged over periods of several months. A model of upper ocean biogeochemistry forced by meteorology was run for the decade in order to provide an estimate of flux at 3000 m depth. Agreement with measured organic carbon flux is good, both in terms of the timings of the annual peaks and in the integrated annual flux. Interannual variations in the integrated flux are of similar magnitude for both the model output and sediment trap measurements, but there is no significant relationship between these two sets of estimates. No long-term trend in flux is evident, either from the model, or from the measurements. During two spring/summer periods, the marine snow concentration in the water column was assessed by time-lapse photography and showed a strong peak at the start of the downward pulse of material at 3000 m. This emphasises the importance of large particles during periods of maximum flux and at the start of flux peaks. Time lapse photographs of the seabed show a seasonal cycle of coverage of phytodetrital material, in agreement with the model output both in terms of timing and magnitude of coverage prior to 1996. However, after a change in the structure of the benthic community in 1996 no phytodetritus was evident on the seabed. The model output shows only a single peak in flux each year, whereas the measured data usually indicated a double peak. It is concluded that the observed double peak may be a reflection of lowered sediment trap efficiency when flux is very high and is dominated by large marine snow particles. Resuspension into the trap 100 m above the seabed, when compared to the primary flux at 3000 m depth (1800 mab) was lower during periods of high primary flux probably because of a reduction in the height of resuspension when the material is fresh. At 2 mab, the picture is more complex with resuspension being enhanced during the periods of higher flux in 1997, which is consistent with this hypothesis. However there was rather little relationship to flux at 3000 m in 1998. At 3000 m depth, the Flux Stability Index (FSI), which provides a measure of the constancy of the seasonal cycle of flux, exhibited an inverse relationship with flux, such that the highest flux of organic carbon was recorded during the year with the greatest seasonal variation.

Lampitt, R. S.; Bett, B. J.; Kiriakoulakis, K.; Popova, E. E.; Ragueneau, O.; Vangriesheim, A.; Wolff, G. A.

144

An Abyssal Current in the Central Labrador Sea  

NASA Astrophysics Data System (ADS)

Lowered acoustic Doppler current profiler (LADCP) data collected along the repeat hydrographic section AR7W in the Labrador Sea has unveiled a new abyssal current, confined to a narrow trench extending from NW to SE over the entire abyssal basin and crossing AR7W in the center of the basin at about 57.8°N, 51.3°W. Maximum water depth in the trough is 75 - 100 m greater depth than the surrounding topography, and the current extends from about 160 m above the bottom to the bottom (3610 m), headed in a south to southeasterly direction. Maximum speeds of 10-20 cm s-1 occur in the deepest part of the current, implying a net transport of as much as 0.2 Sv of Denmark Strait Overflow Water (DSOW). Potential temperature and salinity in the bottom-intensified current tend to be well mixed below 3520 m, suggesting that the mixed bottom boundary layer is about 100 m thick. This V-shaped trench is part of the Northwest Atlantic Mid-Ocean Channel (NAMOC), which has been recognized as a turbidity current pathway by petrologists (Chough and Hesse, 1980; Chough et al., 1986). Another small trough intersects the main branch of the NAMOC where the abyssal current is observed, which may account for the varying direction of the current. This network of abyssal channels may provide a pathway for DSOW, entering the Labrador Sea around the southern tip of Greenland, to reach the central Labrador Sea with little delay. Indeed, Yashayaev and Dickson (2008) have noted the rapidity with which signals of hydrographic change in DSOW spread across the entire abyssal basin, reaching the central Labrador Sea within several months after their first appearance at the eastern boundary. Chough, S. K. and R. Hesse (1980). The Northwest Atlantic Mid-Ocean Channel of the Labrador Sea: III. Head spill vs. body spill deposits from turbidity currents on natural levees. J. of Sedimentary Petrology 50, 227-234. Chough, S. K., R. Hesse, and J. Muller (1987). The Northwest Atlantic Mid-Ocean Channel of the Labrador Sea. IV. Petrography and provenance of the sediments. Can. J. Earth Sci. 24, 731-740. Yashayaev, I., and R. R. Dickson (2008). Transformation and fate of overflows in the northern North Atlantic, in Arctic-Subarctic Ocean Fluxes: Defining the Role of the Northern Seas in Climate, edited by R. R. Dickson, J. Meincke, and P. Rhines, pp. 505- 526, Springer, New York.

Hall, M. M.; Yashayaev, I.; Torres, D. J.

2012-12-01

145

Chemistry of bottom sediments from the Cal-Sag channel and the Des Plaines and Illinois Rivers between Joliet and Havana, Illinois  

SciTech Connect

Cores were taken in 28 actual or proposed maintenance-dredging areas. Sixty-one core samples were analyzed to provide a data base for subsequent studies of the suitability of the potential dredged material for reclamation of abandoned surface-mined land bordering the Illinois Waterway. Samples were composited over 2-ft depth increments, up to a maximum 8-ft depth where possible. Parameters determined for each sample were: volatile solids, flash point, polyaromatic hydrocarbons (PAHs), base/neutral organic compounds, pH, total phosphorus, total phenols, oil and grease, polychlorinated biphenyls (PCBs), cyanide, arsenic, barium, cadmium, chromium, copper, lead, mercury, zinc, silver, nickel, selenium, and sulfide. Results showed PCBs to be higher in the Cal-Sag Channel sediments (..mu..=7.0 mg/kg) than in the Des Plaines River (..mu..=1.6 mg/kg), or Illinois River (..mu..=0.5 mg/kg) sediments. Concentrations of metals including arsenic, barium, cadmium, copper, lead, nickel, and silver were higher in the Des Plaines River samples than in the Cal-Sag Channel or Illinois River samples. Illinois River sediments were, generally, the least contaminated in terms of the measured parameters. Leach tests for arsenic, chromium, copper, lead, nickel, and zinc indicated low leachate-metal concentrations relative to total metal concentrations; thus, these metals exist in relatively insoluble solid states in the sediments.

Harrison, W.; Kucera, E.T.; Tome, C.; Van Loon, L.S.; Van Luik, A.

1981-02-01

146

Interaction of groundwater and shallow lakes on outwash sediments in the sub-humid Boreal Plains of Canada  

NASA Astrophysics Data System (ADS)

The hydrologic controls on the interaction between a shallow lake and a groundwater flow system have been determined for a coarse-textured landscape on the Boreal Plains of Canada. Lake-groundwater interactions were studied to provide an understanding of the near-surface hydrologic processes in a sub-humid climate, where annual precipitation is equal to, or less than potential evapotranspiration. This study was initiated to assess potential landscape impact from forestry and energy industrial activity, and future scenarios of climate change expected in the Western Boreal Forest. A 39 ha lake on outwash sediments was studied for two consecutive years. Hydrometric measurements and stable isotopic analyses indicated that evaporation was the dominant hydrologic flux during ice-free months, and was primarily responsible for a 0.2 m decline in lake level during this study. A combination of summer rain and consistent supply of groundwater discharge throughout each year were the dominant sources of water. The near equivalence of precipitation and evaporation, and relative dominance of each of these processes during the hydrologic year, resulted in the formation of a water table mound downgradient of the lake, and its disappearance each year. The presence of these humid (mound) and arid (complete disappearance) phenomena at one location within the same year, reveal the sensitivity of hydrologic systems in this sub-humid region to small variations in climate. The onset and duration of evaporation from the lake surface was a major controlling factor on groundwater exchange, to such a degree that the shallow lakes are thought to be evaporation windows in this landscape, creating sub-surface capture zones that depend on lake size and landscape position. These findings indicate a very dynamic relationship between atmospheric water fluxes and groundwater interaction, which could potentially conceal anthropogenic impacts within natural variability.

Smerdon, B. D.; Devito, K. J.; Mendoza, C. A.

2005-11-01

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

Relation of sediment load and flood-plain formation to climatic variability, Paria River drainage basin, Utah and Arizona  

USGS Publications Warehouse

Flood-plain alluviation began about 1940 at a time of decreasing magnitude and frequency of floods in winter, summer, and fall. No floods with stages high enough to inundate the flood plain have occurred since 1980, and thus no flood-plain alluviation has occurred since then. The decrease in magnitude and frequency of floods appears to have resulted from a decrease in frequency of large storms, particularly dissipating tropical cyclones, and not from a decrease in annual or seasonal precipitation. -from Authors

Graf, J. B.; Webb, R. H.; Hereford, R.

1991-01-01

149

Orogenic, Ophiolitic, and Abyssal Peridotites  

NASA Astrophysics Data System (ADS)

"Tectonically emplaced" mantle rocks include subcontinental, suboceanic, and subarc mantle rocks that were tectonically exhumed from the upper mantle and occur:(i) as dispersed ultramafic bodies, a few meters to kilometers in size, in suture zones and mountain belts (i.e., the "alpine," or "orogenic" peridotite massifs - De Roever (1957), Thayer (1960), Den Tex (1969));(ii) as the lower ultramafic section of large (tens of kilometers) ophiolite or island arc complexes, obducted on continental margins (e.g., the Oman Ophiolite and the Kohistan Arc Complex - Coleman (1971), Boudier and Coleman (1981), Burg et al. (1998));(iii) exhumed above the sea level in ocean basins (e.g., Zabargad Island in the Red Sea, St. Paul's islets in the Atlantic and Macquarie Island in the southwestern Pacific - Tilley (1947), Melson et al. (1967), Varne and Rubenach (1972), Bonatti et al. (1981)).The "abyssal peridotites" are samples from the oceanic mantle that were dredged on the ocean floor, or recovered from drill cores (e.g., Bonatti et al., 1974; Prinz et al., 1976; Hamlyn and Bonatti, 1980).Altogether, tectonically emplaced and abyssal mantle rocks provide insights into upper mantle compositions and processes that are complementary to the information conveyed by mantle xenoliths (See Chapter 2.05). They provide coverage to vast regions of the Earth's upper mantle that are sparsely sampled by mantle xenoliths, particularly in the ocean basins and beneath passive continental margins, back-arc basins, and oceanic island arcs.Compared with mantle xenoliths, a disadvantage of some tectonically emplaced mantle rocks for representing mantle compositions is that their original geodynamic setting is not exactly known and their significance is sometimes a subject of speculation. For instance, the provenance of orogenic lherzolite massifs (subcontinental lithosphere versus upwelling asthenosphere) is still debated (Menzies and Dupuy, 1991, and references herein), as is the original setting of ophiolites (mid-ocean ridges versus supra-subduction settings - e.g., Nicolas, 1989). In addition, the mantle structures and mineralogical compositions of tectonically emplaced mantle rocks may be obscured by deformation and metamorphic recrystallization during shallow upwelling, exhumation, and tectonic emplacement. Metamorphic processes range from high-temperature recrystallization in the stability field of plagioclase peridotites ( Rampone et al., 1993) to complete serpentinization (e.g., Burkhard and O'Neill, 1988). Some garnet peridotites record even more complex evolutions. They were first buried to, at least, the stability field of garnet peridotites, and, in some cases to greater than 150 km depths ( Dobrzhinetskaya et al., 1996; Green et al., 1997; Liou, 1999). Then, they were exhumed to the surface, dragged by buoyant crustal rocks ( Brueckner and Medaris, 2000).Alternatively, several peridotite massifs are sufficiently well preserved to allow the observation of structural relationships between mantle lithologies that are larger than the sampling scale of mantle xenoliths. It is possible in these massifs to evaluate the scale of mantle heterogeneities and the relative timing of mantle processes such as vein injection, melt-rock reaction, deformation, etc… Detailed studies of orogenic and ophiolitic peridotites on centimeter- to kilometer-scale provide invaluable insights into melt transfer mechanisms, such as melt flow in lithospheric vein conduits and wall-rock reactions (Bodinier et al., 1990), melt extraction from mantle sources via channeled porous flow ( Kelemen et al., 1995) or propagation of kilometer-scale melting fronts associated with thermalerosion of lithospheric mantle ( Lenoir et al., 2001). In contrast, mantle xenoliths may be used to infer either much smaller- or much larger-scale mantle heterogeneities, such as micro-inclusions in minerals ( Schiano and Clocchiatti, 1994) or lateral variations between lithospheric provinces ( O'Reilly et al., 2001).The abyssal peridotites are generally stro

Bodinier, J.-L.; Godard, M.

2003-12-01

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.

1990-01-01

151

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

152

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

153

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.

154

A 200,000-year record of late Quaternary Aeolian sedimentation on the Southern High Plains and nearby Pecos River Valley, USA  

NASA Astrophysics Data System (ADS)

Presently stabilized Southern High Plains (SHP) dune systems have been repeatedly re-activated during the past 200,000 years, providing an archive of environmental and related climatic change for the late Quaternary. Our data set of 38 optically dated samples from four different localities identifies eolian activity from late-middle Pleistocene to the historic period. Oldest eolian sediments are from the Blackwater Draw Formation and indicate accretion during late-middle to late Pleistocene. Younger sediments dating from the later Pleistocene through the Holocene are found in the Muleshoe, Lea-Yoakum, Mescalero, and Monahans dunes that overlie the Blackwater Draw Formation. Muleshoe dunes accreted during the Late Pleistocene between 31 ± 3 and 27 ± 2 ka, while Holocene deposition transpired 7.5 ± 0.4, 4.0 ± 0.7 ka through 3.6 ± 0.4 ka, and between 1.3 ± 0.2 and 1.1 ± 0.1 ka. A period of dune building for Lea-Yoakum dune sediments occurred during the late Pleistocene (48 ± 5 ka), and the later Holocene (3.6 ± 0.4 ka). Mescalero and Monahans dunes were accreting during the later Pleistocene between 29 ± 3 and 22 ± 2 ka followed by a sequence of eolian sand deposited ca. 15 ka. Holocene eolian sedimentation for the Mescalero and Monahans dunes occurred 7.5 ± 0.8, 5.1 ± 0.5, 4.3 ± 0.4, and 2.0 ± 0.3 ka. Historic eolian deposition is identifiable in the dune chronology with multiple optical age estimates overlapping established drought events recorded ca. 1890, 1910, 1920, and during the 1930's when the North American "Dust Bowl" transpired. These Quaternary eolian deposits mantling the Southern High Plains are an important component of the surficial material of the region and provide a rich archive of past climatic change.

Rich, J.; Stokes, S.

2011-03-01

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

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

157

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

Microsoft Academic Search

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 5655m on abyssal plains in the South and North Atlantic, Southern Ocean, southern Indian

Lena Menzel; Kai Horst George; Pedro Martínez Arbizu

2011-01-01

158

Abyssal Characteristics of the World Ocean Waters.  

National Technical Information Service (NTIS)

The abyssal characteristics of the World Ocean, including not only temperature but salinity, density, oxygen, and silica, are displayed on both maps and vertical sections to examine the origins of waters of some of the major basins. Although the coldest w...

A. W. Mantyla J. L. Reid

1983-01-01

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 ?gg-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

Results of analyses performed on soil adjacent to penetrators emplaced into sediments at McCook, Nebraska, January 1976. [simulated penetration into wind-deposited sediments on Martian plains  

NASA Technical Reports Server (NTRS)

During 1976 several penetrators (full and 0.58 scale) were dropped into a test site McCook, Nebraska. The McCook site was selected because it simulated penetration into wind-deposited sediments (silts and sands) on Martian plains. The physical and chemical modifications found in the sediment after the penetrators' impact are described. Laboratory analyses have shown mineralogical and elemental changes are produced in the sediment next to the penetrator. Optical microscopy studies of material next to the skin of the penetrator revealed a layer of glassy material about 75 microns thick. Elemental analysis of a 0-1-mm layer of sediment next to the penetrator revealed increased concentrations for Cr, Fe, Ni, Mo, and reduced concentrations for Mg, Al Si, P, K, and Ca. The Cr, Fe, Ni, and Mo were in fragments abraded from the penetrator. Mineralogical changes occurring in the sediment next to the penetrator included the introduction of micron-size grains of alpha iron and several hydrated iron oxide minerals. The newly formed silicate minerals include metastable phases of silica (cristobalite, lechatelierite, and opal). The glassy material was mostly opal which formed when the host minerals (mica, calcite, and clay) decomposed. In summary, contaminants introduced by the penetrator occur up to 2 mm away from the penetrator's skin. Although volatile elements do migrate and new minerals are formed during the destruction of host minerals in the sediment, no changes were observed beyond the 2-mm distance. The analyses indicate 0.58-scale penetrators do effectively simulate full-scale testing for soil modification effects.

Blanchard, M.; Bunch, T.; Davis, A.; Kyte, F.; Shade, H.; Erlichman, J.; Polkowski, G.

1977-01-01

161

Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Eastern Snake River Plain, Idaho.  

National Technical Information Service (NTIS)

The statistical stationarity of distributions of sedimentary interbed thicknesses within the southwestern part of the Idaho National Laboratory (INL) was evaluated within the stratigraphic framework of Quaternary sediments and basalts at the INL site, eas...

C. N. Stroup J. A. Wellhan L. C. Davis

2008-01-01

162

Surface Sediments in the Marsh-Sandy Land Transitional Area: Sandification in the Western Songnen Plain, China  

PubMed Central

The development of sandification process was studied, by monitoring the changes of sediment characteristics, at marsh-sandy land intersections in China's Songnen region. A series of sediment collection plates were deployed in the region; after one year, sediments in these plates were analyzed for changes of mass and chemical characteristics. The sediment flux and the sand content of the sediments decreased with the increasing longitudinal distance between the sampling site and the centre line of a sand dune. The mean sediment flux was 29±14 kg m?2 yr?1 and 0.6±0.3 kg m?2 yr?1 in the sandy land and marsh, respectively. Strong, positive correlations were found between the concentrations of organic matter, total nitrogen, P, Fe, Ti, V and Zr, all of which were also negatively correlated with the sand content. The concentrations of organic matter, total nitrogen, P, Fe, Ti, V and Zr in the marsh sediment samples were all significantly greater than the corresponding concentrations of the sandy land (p<0.001). Sand content and Ti, V and Zr concentrations all proved to be valid indicators of sandification intensity, and they showed that the marsh could be divided into three distinct zones. Sand expansion extended about 88 m into the marsh. The mean sand content in the sediments of the sandy land was 91% and then 64% in the marsh, which in turn was higher than that of marshes outside the influence of sandification, suggesting that the marsh in the marsh-sandy land transitional area has already undergone extensive sandification in the past. The study results provide information on the wetland's function of indicating and buffering the sandification process.

Yu, Xiaofei; Grace, Michael; Zou, Yuanchun; Yu, Xuefeng; Lu, Xianguo; Wang, Guoping

2014-01-01

163

Influences of climate, cattle density, and lake morphology on Sporormiella abundances in modern lake sediments in the US Great Plains  

Microsoft Academic Search

Sporormiella, a genus of coprophilous fungus, is increasingly used as a qualitative proxy for megafaunal density. Decreased spore abundances in Late-Pleistocene and Holocene sediments are thought to signal prehistoric megafaunal population declines and extinctions. However, much remains unknown regarding the dispersal, deposition, and preservation of Sporormiella, hindering interpretation. Here we collected lake-center and lake-margin surface-sediment samples from 24 lakes in

Nancy E Parker; John W Williams

2012-01-01

164

Surface sediments in the marsh-sandy land transitional area: sandification in the Western songnen plain, china.  

PubMed

The development of sandification process was studied, by monitoring the changes of sediment characteristics, at marsh-sandy land intersections in China's Songnen region. A series of sediment collection plates were deployed in the region; after one year, sediments in these plates were analyzed for changes of mass and chemical characteristics. The sediment flux and the sand content of the sediments decreased with the increasing longitudinal distance between the sampling site and the centre line of a sand dune. The mean sediment flux was 29±14 kg m-2 yr-1 and 0.6±0.3 kg m-2 yr-1 in the sandy land and marsh, respectively. Strong, positive correlations were found between the concentrations of organic matter, total nitrogen, P, Fe, Ti, V and Zr, all of which were also negatively correlated with the sand content. The concentrations of organic matter, total nitrogen, P, Fe, Ti, V and Zr in the marsh sediment samples were all significantly greater than the corresponding concentrations of the sandy land (p<0.001). Sand content and Ti, V and Zr concentrations all proved to be valid indicators of sandification intensity, and they showed that the marsh could be divided into three distinct zones. Sand expansion extended about 88 m into the marsh. The mean sand content in the sediments of the sandy land was 91% and then 64% in the marsh, which in turn was higher than that of marshes outside the influence of sandification, suggesting that the marsh in the marsh-sandy land transitional area has already undergone extensive sandification in the past. The study results provide information on the wetland's function of indicating and buffering the sandification process. PMID:24932717

Yu, Xiaofei; Grace, Michael; Zou, Yuanchun; Yu, Xuefeng; Lu, Xianguo; Wang, Guoping

2014-01-01

165

Distributions, sources, and ecological risks of DDT-related contaminants in water, suspended particulate matter, and sediments from Haihe Plain, Northern China.  

PubMed

The residual levels of dichlorodiphenyltrichloroethane (DDT) and its metabolites (DDXs, including p,p'-DDT, DDD, and DDE) in water, suspended particulate matter (SPM), and sediments from major rivers, lakes, and reservoirs in Haihe Plain were measured with a gas chromatograph equipped with a (63)Ni microelectron capture detector. In the fall of 2004, the contents of the total DDXs in the water and SPM were 0.29 ± 0.69 ng L(-1) and 423.13 ± 577.85 ng g(-1) dry wt., respectively. In the spring of 2005, the total DDXs were 0.36 ± 0.91 ng L(-1) for water and 35.93 ± 62.65 ng g(-1) dry wt. for SPM. The average concentration of DDXs for sediments was 7.10 ± 7.57 ng g(-1) dry wt. during the two seasons. The Eastern-Hebei-Province Coastland River System was the most polluted, which was mainly attributable to the extensive use of DDT pesticide and dicofol in that system. Recent DDT inputs still occur in some regions, as indicated by DDT/(DDD + DDE) > 1 at 29-36 % of the sites for water and 55-61 % of the sites for SPM. The potential ecological risks of DDT in the water were assessed using a species sensitivity distribution model. Only shrimp and crabs were found to have potentially affected fraction values of 1.63 × 10(-3) to 2.27 × 10(-4), with probabilities beyond the hazardous concentration for 5 % of species (HC5) values of 1.90-2.56 %, suggesting only slight risks. DDXs in the sediments of some sites were also of potential risk to benthic organism based on consensus-based sediment quality guidelines. PMID:22580748

Wang, Yan; He, Wei; Qin, Ning; He, Qi-Shuang; Kong, Xiang-Zhen; Tao, Shu; Xu, Fu-Liu

2013-02-01

166

Fresh Abyssal Peridotites -- not an Oxymoron!  

Microsoft Academic Search

The study of the Earths mantle and the generation of its crust has been hampered so far by the lack of unaltered mantle rocks from mid-ocean ridges. Whereas ophiolites, orogenic peridotites and xenoliths sometimes provide this freshness, their often unknown tectonic setting sets limits for a one-to-one transfer of the results to processes on mid-ocean ridges. Abyssal peridotites are usually

A. von der Handt; E. Hellebrand; J. E. Snow; S. T. Feig; Y. Gao; Z. Jovanovic; F. Nauret

2004-01-01

167

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

2010-09-01

168

Strath terraces on the western High Plains indicate climatically-driven variations in sediment supply from source basins in the Colorado Front Range  

NASA Astrophysics Data System (ADS)

Large strath terraces adjacent to the Colorado Front Range record the local history of fluvial planation and incision into the erodible rocks of the Denver basin over the last 2 million years. Terrace surfaces have been correlated into ~6 alluvial units using elevation and soil development; each alluvial unit was thought to represent a fairly consistent elevation of the Denver basin during various stages of exhumation, driven by base-level fall of the South Platte River. Here we show instead that (1) strath terraces in the western High Plains cannot be correlated based on elevation alone and (2) exhumation of the Denver basin is likely spatially and temporally variable due to climatically-driven variations in sediment supply from the source basins. We collected samples for cosmogenic radionuclide (CRN) profiles (10Be and 26Al) and a soil chronosequence from three strath terraces adjacent to Lefthand Creek near Boulder, CO. 10Be profile data on the upper- and middle-elevation terraces yield dates of 95 ka and 91 ka; these dates are much younger than the correlative alluvial units to the south of Boulder, which date to 1.5 Ma and 250 ka, respectively. Soils on the upper and middle terraces are similar in soil development and clast weathering, consistent with the narrow time window obtained from CRN dating of the two units. 10Be-derived rates for catchment-wide paleo-denudation are ~8.0 cm/ka from the flat and broad upper-terrace gravels and ~3.5 cm/ka from the steeper and narrower middle-terrace gravels. Young terraces at Lefthand Canyon are more consistent with a model of fluvial incision and aggradation driven by climate-controlled variations in sediment production from source basins in the Front Range. High catchment-wide denudation rates generate a high sediment supply, leading to aggradation and lateral planation. Terrace sediments are likely deposited and eroded multiple times during periods of lateral planation; the most recent occupation is preserved in the gravel caps on strath terraces. Lower catchment-wide denudation rates, and thus low sediment supply, lead to vertical bedrock incision and abandonment of terrace surfaces. Our data indicate that Front Range rivers experience a complex and basin-specific history where long periods of aggradation and lateral planation are punctuated by brief episodes of rapid incision through the soft Cretaceous shale underlying the Boulder area.

Foster, M. A.; Dühnforth, M.; Anderson, R. S.

2013-12-01

169

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

170

Modern alluvial fan and deltaic sedimentation in a foreland tectonic setting: the Lower Mesopotamian Plain and the Arabian Gulf  

NASA Astrophysics Data System (ADS)

The Arabo-Persian Gulf, generally considered as a classical carbonate basin, in fact also includes important terrigenous systems whose nature and geometry are related closely to the tectonic framework. The Gulf is bordered along its northeastern periphery by an active alpine system which constitutes a major source of both siliceous and calcareous detritus. There are four types of terrigenous discharge which are classified according to their structural relationships. Numerous alluvial fans terminate ephemeral consequent streams draining the flanks of anticlines forming the external parts of the Zagros Mountain belt. Alluvial-fan deltas studied in detail in southeastern Iran terminate semi-permanent streams which flow along major synclinal axis. They are composed mainly of fine carbonate detritus, part of which accumulates as spectacular marine mud banks. Two major types of delta occur. Relatively small marine deltas, associated with permanent antecedent streams which cross the Zagros fold system, are scattered along the Persian shoreline. The other is the a major deltaic complex which is associated with the Tigris-Euphrates Rivers. This system has prograded along the main axis of the Gulf, the resulting Mesopotamian Plain filling at least half of the original basin which, in early Quaternary times, extended from Hormuz to Syria.

Baltzer, Frédéric; Purser, Bruce H.

1990-05-01

171

Role of naturally occurring gas hydrates in sediment transport  

SciTech Connect

Naturally occurring gas hydrates have the potential to store enormous volumes of both gas and water in semi-solid form in ocean-bottom sediments and then to release that gas and water when the hydrate's equilibrium condition are disturbed. Therefore, hydrates provide a potential mechanism for transporting large volumes of sediments. Under the combined low bottom-water temperatures and moderate hydrostatic pressures that exist over most of the continental slopes and all of the continental rises and abyssal plains, hydrocarbon gases at or near saturation in the interstitial waters of the near-bottom sediments will form hydrates. The gas can either be autochthonous, microbially produced gas, or allochthonous, catagenic gas from deeper sediments. Equilibrium conditions that stabilize hydrated sediments may be disturbed, for example, by continued sedimentation or by lowering of sea level. In either case, some of the solid gas-water matrix decomposes. Released gas and water volume exceeds the volume occupied by the hydrate, so the internal pressure rises - drastically if large volumes of hydrate are decomposed. Part of the once rigid sediment is converted to a gas- and water-rich, relatively low density mud. When the internal pressure, due to the presence of the compressed gas or to buoyancy, is sufficiently high, the overlying sediment may be lifted and/or breached, and the less dense, gas-cut mud may break through. Such hydrate-related phenomena can cause mud diapirs, mud volcanos, mud slides, or turbidite flows, depending on sediment configuration and bottom topography. 4 figures.

McIver, R.D.

1982-06-01

172

Physical oceanographic characteristics of the Nares Plain region of the western North Atlantic  

Microsoft Academic Search

This document is a summary and synthesis of physical oceanographic observations available from the Nares Abyssal Plain region of the western North Atlantic Ocean. The observations mainly include historical Nansen bottle data obtained from the National Oceanographic Data Center (NODC); conductivity, temperature, and depth (CTD) data and bottom radon data both taken during the Transient Tracers in the Ocean (TTO)

Riser

1985-01-01

173

Survival Of Magnetic Paleoclimatic Signals From Shallow To Deep Water Marine Redoxomorphic Sediments Across The Northwest Iberian Continental Margin  

NASA Astrophysics Data System (ADS)

The magnetic properties of marine sediments on the North Atlantic Iberian continental Margin are strongly dependent on the organic matter input to the sediments and the onset of reductive diagenesis. An onshore-offshore gradient in the intensity of early diagenesis was recently described for the Ría de Vigo, matched by similar patterns in the adjacent rias of Pontevedra and Muros. In the ria environments of NW Iberia, early diagenetic dissolution of magnetic minerals can lead to magnetite half-lives of a few decades, and virtually obliterates any paleoenvironmental signal carried by magnetic minerals, rendering magnetic properties especially useful for the study of early diagenesis dynamics. Early diagenesis has also been identified in sediments of the adjacent continental shelf and deeper environments of the Galician Bank and Iberian Abyssal Plain. However, in these settings, slower dissolution of magnetic minerals allows the preservation of paleoclimatic signatures on different temporal scales. For instance, magnetic properties of continental shelf sediments reveal periods of enhanced rainfall and continental sediment input to the shelf, coincident with the Roman Warm Period and Medieval Climatic Optimum. On the contrary, cold periods are associated with less detrital input. Furthermore, levels of intensified diagenesis are also recorded during cold periods, which have been interpreted as periods of intensified coastal upwelling probably related to long-term North Atlantic Oscillation positive state. At the Galician Bank and Iberian Abyssal Plain sediments early diagenesis is also pervasive, although a paleoceanographic record of changes in the concentration of magnetic minerals transported by water masses flowing from the Portuguese Margin can still be identified. In addition to the progressive dissolution of magnetic minerals with depth, bulk magnetic properties in these deep marine settings show strong dependence on the pelagic carbonate sedimentation and low-magnetic turbiditic sediments that originate in the Galician Bank. Thin levels of highly magnetic sediments have been identified as Heinrich events, which provide an easily identifiable chronostratigraphic marker and a very fast and cost-effective tool for core correlation on a regional scale. These case-studies on the magnetic properties of sediments from the NW Iberian Margin provide examples of the range of applications of environmental magnetism in marine sediments with variable degrees of early diagenetic alteration of their magnetic mineral assemblage.

Mohamed Falcon, K. J.; Rey, D.; Rubio, B.

2013-05-01

174

Carbonate and siliciclastic deposits on slope and abyssal floor Adjacent to southwestern Florida platform  

SciTech Connect

Three distinct carbonate deposits have been identified on the slope and adjacent sea floor of the Southwestern Florida platform: (1) reef talus, recognized by shape and location, found on the upper slope of the Yucatan Channel and also east of the Marquesas Keys; (2) hemipelagic sediments, with complex sigmoidoblique bed forms, filling the intervening gap between the channel and Keys and forming two lobes on the floor of the northern Florida Straits; and (3) turbidite deposits, with chaotic internal bed forms, covering siliciclastic Mississippi fan sediments at the base of the canyons in the Florida escarpment. The source of the talus, eroded and transported during the many storms which frequent the region, is the reef complexes which have formed on the platform rim. The sediment of the other two deposits is of foraminiferal tests, produced in nutrient-rich waters at the shelf edge. Geophysical, geochemical, and sedimentological data suggest that the spatial relationships of these deposits are related to sea level variations. During extreme lowstands, with much of the shelf exposed, the dominant sedimentation is siliciclastic deposition on the abyssal floor, and slope talus development at the edge of the shelf. During a subsequent rise in sea level, after carbonate production on the shelf is initiated, sediment is transported southward to the head of the canyons and funneled to the abyssal floor. Subsequent rising sea level shifts the axis of transport farther on the shelf, bypassing the canyons and funneling the sediment through breaks in the carbonate reef-banks at the southern edge of the platform. At the sites of both the hemipelagic and the turbidite deposition, high-resolution seismic data indicate that at least three cycles of deposition have occurred.

Holmes, C.W.

1983-03-01

175

Analysis of the community structure of abyssal kinetoplastids revealed similar communities at larger spatial scales  

PubMed Central

Knowledge of the spatial scales of diversity is necessary to evaluate the mechanisms driving biodiversity and biogeography in the vast but poorly understood deep sea. The community structure of kinetoplastids, an important group of microbial eukaryotes belonging to the Euglenozoa, from all abyssal plains of the South Atlantic and two areas of the eastern Mediterranean was studied using partial small subunit ribosomal DNA gene clone libraries. A total of 1364 clones from 10 different regions were retrieved. The analysis revealed statistically not distinguishable communities from both the South-East Atlantic (Angola and Guinea Basin) and the South-West Atlantic (Angola and Brazil Basin) at spatial scales of 1000–3000?km, whereas all other communities were significantly differentiated from one another. It seems likely that multiple processes operate at the same time to shape communities of deep-sea kinetoplastids. Nevertheless, constant and homogenous environmental conditions over large spatial scales at abyssal depths, together with high dispersal capabilities of microbial eukaryotes, maintain best the results of statistically indistinguishable communities at larger spatial scales.

Salani, Faezeh Shah; Arndt, Hartmut; Hausmann, Klaus; Nitsche, Frank; Scheckenbach, Frank

2012-01-01

176

Luminescence chronology of river adjustment and incision of Quaternary sediments in the alluvial plain of the Sabarmati River, north Gujarat, India  

Microsoft Academic Search

River adjustment and incision in the Sabarmati basin, Gujarat, India have been examined at a site near Mahudi. Towards this, the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated. The upper fluvial sequence, along with the overlying aeolian sand and riverbed scroll plains, provide clues to the evolution of the present Sabarmati River. Sedimentological analyses of the

Pradeep Srivastava; Navin Juyal; Ashok K Singhvi; Robert J Wasson; Mark D Bateman

2001-01-01

177

Abyssal Sediment Waves in the Amirante Passage, Western Indian Ocean.  

National Technical Information Service (NTIS)

The deep western boundary current (DWBC) of the Indian Ocean flows northward along the western margin of the Mascarene Basin, and is funneled through a narrow passage (near 09 degrees S, 52 degrees E) prior to entering the Somali Basin to the north. Recen...

D. A. Johnson E. T. Bunce

1977-01-01

178

Internal tide generation by abyssal hills using analytical theory  

NASA Astrophysics Data System (ADS)

Internal tide driven mixing plays a key role in sustaining the deep ocean stratification and meridional overturning circulation. Internal tides can be generated by topographic horizontal scales ranging from hundreds of meters to tens of kilometers. State of the art topographic products barely resolve scales smaller than ˜10 km in the deep ocean. On these scales abyssal hills dominate ocean floor roughness. The impact of abyssal hill roughness on internal-tide generation is evaluated in this study. The conversion of M2 barotropic to baroclinic tidal energy is calculated based on linear wave theory both in real and spectral space using the Shuttle Radar Topography Mission SRTM30_PLUS bathymetric product at 1/120° resolution with and without the addition of synthetic abyssal hill roughness. Internal tide generation by abyssal hills integrates to 0.1 TW globally or 0.03 TW when the energy flux is empirically corrected for supercritical slope (i.e., ˜10% of the energy flux due to larger topographic scales resolved in standard products in both cases). The abyssal hill driven energy conversion is dominated by mid-ocean ridges, where abyssal hill roughness is large. Focusing on two regions located over the Mid-Atlantic Ridge and the East Pacific Rise, it is shown that regionally linear theory predicts an increase of the energy flux due to abyssal hills of up to 100% or 60% when an empirical correction for supercritical slopes is attempted. Therefore, abyssal hills, unresolved in state of the art topographic products, can have a strong impact on internal tide generation, especially over mid-ocean ridges.

Melet, Angélique; Nikurashin, Maxim; Muller, Caroline; Falahat, S.; Nycander, Jonas; Timko, Patrick G.; Arbic, Brian K.; Goff, John A.

2013-11-01

179

Feeding rates of abyssal scavenging amphipods ( Eurythenes gryllus) determined in situ by time-lapse photography  

NASA Astrophysics Data System (ADS)

Bait (100 g of mackerel), moored 20 m above bottom at 5830 m in the Nares Abyssal Plain, northwest Atlantic Ocean and photographed at 10 min intervals, was completely consumed by scavenging lysianassid amphipods ( Eurythenes gryllus) within 38 h. An average feeding rate of 1.8 g amphipod -1 h -1 was calculated from the total number of amphipods counted in photographs and the time required for complete consumption of bait. Amphipods were present as single individuals during 12 h after the first animal arrived with an average residence time of 30± 10 min. Weight loss, calculated from changes in bait volume observed in photographs during this period, indicated an average consumption rate of 2.9 g amphipod -1. Amphipods of different sizes ingested from 30 to 60% of their body equivalent weight and then departed from the bait. These are the first in situ observations that permit calculation of feeding rate for any deep-sea animal.

Hargrave, B. T.

1985-04-01

180

Variations in the invertebrate abyssal megafauna in the North Atlantic Ocean  

NASA Astrophysics Data System (ADS)

Epibenthic sledge and otter trawl samples of invertebrate megabenthos were collected from the abyss of the northeastern Atlantic Ocean. Stations were selected to have contrasting overlying water column structure. Strong seasonal pulses of phytodetritus on the sea floor have been recorded on the Porcupine Abyssal Plain (PAP) but not on the Madeira Abyssal Plain (MAP). Sledge-and trawl-derived abundances of 13.73 and 8.13 individuals 10 3 m -2 were found at PAP, with corresponding wet biomass values of 169.4 and 189.2 g 10 3 m -2. Data from sledge hauls taken at MAP gave an abundance of 7.48 individuals and 5.15g 10 3 m -2. Sledge and trawl abundances at Great Meteor East (GME) were 2.91 and 2.19 individuals 10 3 m -2 and 4.31 and 11.30 g 10 3 m -2. Holothurians dominated the invertebrate biomass at PAP while Astoroidea and Decapoda Natantia were important taxa at MAP and GME. Otter trawl samples demonstrated fish to be the major component of total megadaunal biomass and suggest that small fixed-frame trawls give gross underestimates of fish abundance and biomass. Size spectra based on abundance and biomass data indicated the megafauna to be a functional group at PAP stationl only. Here peak invertebrate biomass occurred in the 40-80 g wet wt size class. In contrast, no large invertebrates (>20 g wet wt) were found at MAP of GME. Concurrent photographic records indicate higher faunal densities than do net catches. Faunal differences between stations were examined, and a weak relationship between surface productivity and megafaunal abundance was established. Data are inadequate to detect a similar relationship with biomass. Biomass values at PAP of 16-39 times those of MAP and GME appear to be explained by the deposition of phytodetritus at PAP but not at MAP or, probably, at GME. Among invertebrates, detritivores form the dominant feeding guild at all localities, but carnivores are important at MAP and GME. Phytodetritus appears to support the abundant surface-grazing holothurians at PAP.

Thurston, M. H.; Bett, B. J.; Rice, A. L.; Jackson, P. A. B.

1994-09-01

181

Abyssal Hill Deflections at Pacific-Antarctic Ridge Transform Intersections  

NASA Astrophysics Data System (ADS)

Almost complete shipboard multibeam bathymetry coverage at the Menard and Pitman Fracture Zones allowed us to map abyssal hill deviations along their traces. We compared the mapped abyssal hill deflections to a detailed plate motion model for the Pacific-Antarctic Ridge to test how abyssal hill curvature correlates to changes in plate motion direction, which leads to periods of transtension or transpression. To better understand the range of curvatures, we compared our observations with a model for curved cracks [Pollard and Aydin, 1984]. Spreading centers can be considered as giant cracks. The propagation path of a crack under combined loading can be predicted as a function of the stress ratio between the relative stresses required for spreading at the spreading axis (Mode I loading) and stresses resisting sliding along the transform (Mode II loading). We mapped 124 abyssal hill deflections at Menard Fracture Zone and 113 at Pitman Fracture Zone, respectively. The observations show that the amount of curvature can change rapidly over short periods of time. A high abundance of deflected abyssal hills is expected when a significant adjustment in plate motion direction occurs, which puts stress on the transform fault. This is observed, in particular, at the Pitman Fracture Zone, which experienced significant transtension since chron C5y (9.8 Ma) in response to a 17° clockwise rotation of the spreading direction azimuth. In contrast to the abyssal hill tips, which were deflected in response to the changing stress field when approaching a ridge transform intersection, we also mapped several anomalously curved abyssal hill structures. Such anomalous deflections are expected in oceanic crust formed near ridge transform intersections during periods of transpression [Sonder and Pockalny, 1999]. We mapped 19 anomalous abyssal hill deflections at Menard Fracture Zone between chrons C15o and C7 (34.9 to 24.8 Ma) and 15 at Pitman Fracture Zone between chrons C11y and C6B (30.1 to 23.1 Ma), respectively. These anomalously curved abyssal hills are related to block rotation about a vertical axis, in response to the transpression, and typically occurs in seafloor less than 2 Ma old when the oceanic lithosphere is thin. References Pollard, D. D., and A. Aydin (1984), Propagation and Linkage of Oceanic Ridge Segments, Journal of Geophysical Research, 89(Nb12), 17-28. Sonder, L. J., and R. A. Pockalny (1999), Anomalously rotated abyssal hills along active transforms: Distributed deformation of oceanic lithosphere, Geology, 27(11), 1003- 1006.

Croon, M. B.; Cande, S. C.; Stock, J. M.

2009-05-01

182

Punctuated Sediment Input into Small Subpolar Ocean Basins During Heinrich Events and Preservation in the Stratigraphic Record  

NASA Astrophysics Data System (ADS)

Small subpolar ocean basins such as the Labrador Sea received a major portion (25%) of their sediment fill during the Pleistocene glaciations (less than 5% of the basin's lifetime), but the timing of sediment supply to the basin remained essentially unknown until recently. Discovery of the hitherto little known depositional facies of fine-grained lofted sediment suggests that the main sediment input into the basin was not coupled to major glacial cycles and associated sea-level changes but was related to Heinrich events. Heinrich events are known as Late Pleistocene ice-rafting episodes of unparalleled intensity in the North Atlantic that were associated with major melt-water discharge pulses and, as it appears now, also were the times of the main sediment delivery to the basin. The facies of lofted sediment consists of stacked layers of graded muds that contain ice-rafted debris (IRD) which impart a bimodal grain-size distribution to the graded muds. The texturally incompatible grain populations of the muds (median size between 4 and 8 micrometers) and the coarse silt and sand-sized IRD require the combination of two transport processes that delivered the populations independently and allowed mixing at the depositional site: (i) sediment rafting by icebergs and (ii) the rise of turbid freshwater plumes out of fresh-water generated turbidity currents. Fresh-water generated turbidity currents have built a huge sand and gravel abyssal plain in the Labrador Sea (700 by 120 km underlain by 150 m of coarse-grained sediment on average) which is one of the largest sand accumulations (104 km3) on Earth. The hyperpycnal portion of individual discharge events that generated these currents would have had an estimated volume on the order of 103 km3 (1012 m3) which would have flowed for 10-15 days or less, assuming estimated discharge ranges for subglacial outburst floods of up to 106 m3/s. Sediment lofting from turbidity currents is a process that occurs in density currents generated from fresh-water discharges into the sea that can produce reversed buoyancy, as is well known from experiments. When the flows have traveled long enough, their tops will have lost enough sediment by settling such that their density decreases below that of the ambient seawater causing the current tops to lift up. The turbid fresh-water clouds buoyantly rise out of the turbidity current to a level of equal density, presumably the pycnocline, where they spread out laterally, even up-current, and generate interflows that deposit graded layers. The process is slow enough to allow incorporation into the graded layers of debris melting out of drifting icebergs. The observed lofted depositional facies is exclusively found in Heinrich layers. The most likely candidates for the parent currents from which lofting occurred were the sandy flows that formed the sand abyssal plain. Through this stratigraphic relationship the lofted facies ties the main pulses of Late Pleistocene sediment supply in the Labrador Basin to Heinrich events. Dating of pelagic interlayers during future ocean drilling may provide the proof that packages of sand turbidites underlying the abyssal plain are correlated to individual Heinrich events. The correlation may thus be documented in the stratigraphic record. Similar situations may exist in the Bering Sea or along the Maury Channel System in North Atlantic.

Hesse, R.

2006-12-01

183

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

2006-12-01

184

Internal wave structures in abyssal cataract flows  

NASA Astrophysics Data System (ADS)

We discuss some theoretical approaches, experimental results and field data concerning wave phenomena in ocean near-bottom stratified flows. Such strong flows of cold water form everywhere in the Atlantic abyssal channels, and these currents play significant role in the global water exchange. Most interesting wave structures arise in a powerful cataract flows near orographic obstacles which disturb gravity currents by forced lee waves, attached hydraulic jumps, mixing layers etc. All these effects were observed by the authors in the Romanche and Chain fracture zones of Atlantic Ocean during recent cruises of the R/V Akademik Ioffe and R/V Akademik Sergei Vavilov (Morozov et al., Dokl. Earth Sci., 2012, 446(2)). In a general way, deep-water cataract flows down the slope are similar to the stratified flows examined in laboratory experiments. Strong mixing in the sill region leads to the splitting of the gravity current into the layers having the fluids with different densities. Another peculiarity is the presence of critical layers in shear flows sustained over the sill. In the case under consideration, this critical level separates the flow of near-bottom cold water from opposite overflow. In accordance with known theoretical models and laboratory measurements, the critical layer can absorb and reflect internal waves generated by the topography, so the upward propagation of these perturbations is blocked from above. High velocity gradients were registered downstream in the vicinity of cataract and it indicates the existence of developed wave structures beyond the sill formed by intense internal waves. This work was supported by RFBR (grants No 12-01-00671-a, 12-08-10001-k and 13-08-10001-k).

Makarenko, Nikolay; Liapidevskii, Valery; Morozov, Eugene; Tarakanov, Roman

2014-05-01

185

Sediment structures and sediment ages of the Chukchi region, Amerasia Basin  

NASA Astrophysics Data System (ADS)

In 2008, the Alfred Wegener Institute (AWI) of Germany, using the RV Polarstern, collected multichannel seismic reflection data in the eastern Arctic Ocean (73-79°N and 170°E-165°W), namely the East Siberian Shelf, the Chukchi Shelf, - Plateau, and - Abyssal Plain, and the southern part of the Mendeleev Ridge. For the seismic data acquisition an air gun array with up to six air guns (48 ltr. total volume fired at 200 bar) was used. With a 3000 m long streamer including 240 active channels and a 600 m long streamer including 96 active channels the seismic signals were recorded. Obtaining the ages of the sediments, the information of five exploration wells near the coast of Alaska were correlated into the new seismic lines. For this correlation an existing network of more than 200 seismic reflection lines on the East Siberian Shelf and Chukchi Shelf from the USGS, TGS-NOPEC and ION-GX Technology were used. The research area is dominated by two different sediment packages ranging from the Paleocene to the Jurassic. The upper part is an undisturbed unit with low amplitudes and flat-lying reflections. In contrast, the lower package is dominated by an undulated stratification with many fractures and faults. Moreover, the lower unit consists of higher amplitudes with strong reflection bands. The sedimentary thickness varied from the East Siberian Shelf to the Chukchi Plateau from more than 8 km to 4 km. In the basin between the Chukchi Plateau and the Mendeleev Ridge the sedimentary thickness is about 2 km. Furthermore, a series of prograding sequences at the continental margin of the Chukchi Shelf with ages of 65 Ma and younger were analysed. These sequences are the result of an enormous sediment influx from Siberia and Alaska and can be explained by variations in the sedimentation rate over time.

Hegewald, A.; Jokat, W.

2011-12-01

186

Pelagic-Benthic Coupling of Nucleic Acids in an Abyssal Location of the Northeastern Atlantic Ocean  

PubMed Central

Spatial and temporal changes in sedimentary nucleic acid concentrations in an abyssal locality of the northeastern Atlantic Ocean were investigated in relation to fluxes of nucleic acids produced in the photic layer. Sediment trap material, collected between 1996 and 1998 at depths of 1,000, 3,000, and 4,700 m, and sediment samples were analyzed for DNA and RNA content. Nucleic acid concentrations in the sediments were very high and displayed significant temporal changes, whereas mesoscale variability was low. DNA and RNA concentrations generally displayed opposite temporal patterns, which are likely to be dependent on the nature and characteristics of DNA and RNA molecules. Nucleic acid fluxes were high and displayed clear seasonal changes apparently coupled with seasonal pulses of primary production. However, while median values of DNA fluxes were relatively similar in all sediment traps, median values of RNA fluxes almost doubled from the 1,000- to the 4,700-m depth, suggesting differences in the metabolic activity of microbes associated with sinking particles. Significant relationships between DNA concentrations in the sediments and DNA fluxes and between RNA concentrations and RNA fluxes, indicating the presence of a clear pelagic-benthic coupling of particulate nucleic acids, were observed. The benthic system investigated was not steady state since we estimated that, from September 1996 to October 1998, nucleic acid concentration in the sediments decreased by about 165 mg of DNA m?2. Vertical profiles revealed a significant decrease in DNA concentration with depth in the sediments, reaching an asymptotic value of about 5 ?g g?1. This DNA fraction constitutes a pool of potentially refractory DNA (accounting for 16 to 40% of the total DNA pool) that might be buried in the sediments.

Dell'Anno, A.; Fabiano, M.; Mei, M. L.; Danovaro, R.

1999-01-01

187

Plain Language  

Cancer.gov

The Plain Writing Act of 2010 requires federal agencies to write "clear Government communication that the public can understand and use." President Obama also emphasized the importance of establishing "a system of transparency, public participation, and collaboration" in his January 21, 2009, Memorandum on Transparency and Open Government.

188

Evidence for episodic recruitment in a small opheliid polychaete species from the abyssal NE Atlantic  

NASA Astrophysics Data System (ADS)

The abundance and size spectra of an infaunal opheliid polychaete species was followed over a two year period (September 1996-October 1998) in meiofaunal-(32 ?m-1 mm) and macrofaunal -(>250 ?m) samples collected at an abyssal site (4850 m depth) in the NE Atlantic. The site, situated on the Porcupine Abyssal Plain (PAP), is characterised by the episodic deposition of aggregated phytodetritus. The response of the fauna to this seasonal food supply was addressed by time-series sampling within the MAST-III BENGAL programme. In autumn 1996, small opheliid juveniles (mean length: 281 ?m in September and 254 ?m in October) were sampled only in the meiofauna samples. In March 1997, juvenile specimens of the opheliid, which were on average nearly twice as large (mean length: 480 ?m) as those collected in 1996 were sampled in both both meio- and macrofaunal samples. The occurrence of only small juvenile individuals in 1996 suggests that a synchronous recruitment event had taken place earlier during that year. Small juveniles (mean length: 252 ?m) were also abundant in a sample collected at the PAP site in May 1991, immediately following the deposition of a pulse of phytodetritus. The opheliid population structure in 1997 and 1998 indicates the slow progression of the settled cohort, possibly supplemented by a further, but relatively minor recruitment event in March 1998. Size spectra analysis implies that either growth was slow or that immigration of larger juveniles had augmented the population. The PAP opheliid may be an opportunist, which waits for optimal conditions before converting its slowly accumulated energy into reproduction. In addition, this species can apparently maintain a stable pool of developing juveniles if the organic pulse fails to materialise. The present study also shows that a more holistic approach is necessary to investigate the life cycles of some organisms, which lie close to the boundary between the meiofauna and macrofauna.

Vanreusel, A.; Cosson-Sarradin, N.; Gooday, A. J.; Paterson, G. L. J.; Galéron, J.; Sibuet, M.; Vincx, M.

189

Abyssal ostracods from the South and Equatorial Atlantic Ocean: Biological and paleoceanographic implications  

USGS Publications Warehouse

We report the distribution of ostracods from ???5000 m depth from the Southeast and Equatorial Atlantic Ocean recovered from the uppermost 10 cm of minimally disturbed sediments taken by multiple-corer during the R/V Meteor DIVA2 expedition M63.2. Five cores yielded the following major deep-sea genera: Krithe, Henryhowella, Poseidonamicus, Legitimocythere, Pseudobosquetina, and Pennyella. All genera are widely distributed in abyssal depths in the world's oceans and common in Cenozoic deep-sea sediments. The total number of ostracod specimens is higher and ostracod shell preservation is better near the sediment-water interface, especially at the 0-1 cm core depths. Core slices from ???5 to 10 cm were barren or yielded a few poorly preserved specimens. The DIVA2 cores show that deep-sea ostracod species inhabit corrosive bottom water near the carbonate compensation depth (CCD) even though their calcareous valves are rarely preserved as fossils in sediment cores due to postmortem dissolution. Their occurrence at great water depths may partially explain the well-known global distributions of major deep-sea taxa in the world's oceans, although further expeditions using minimal-disturbance sampling devices are needed to fill geographic gaps. ?? 2008 Elsevier Ltd. All rights reserved.

Yasuhara, M.; Cronin, T. M.; Martinez, Arbizu, P.

2008-01-01

190

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

191

Abyssal circulation of the southeastern Pacific and some geological implications  

Microsoft Academic Search

The abyssal circulation of the Pacific Ocean east of the East Pacific Rise is deduced from hydrographic data, supported by a few direct current measurements. Two main flow paths are recognized: across the Chile Rise into the Chile Basin, and thence northward into the Peru Basin and Panama Basin: and eastward across the East Pacific Rise into the Guatemala Basin

Peter Lonsdale

1976-01-01

192

Seasonal dynamics of nitrogen and phosphorus in water and sediment of a multi-level ditch system in Sanjiang Plain, Northeast China  

Microsoft Academic Search

The multi-level ditch system developed in the Sanjiang Plain, Northeast China has sped up water drainage process hence transferred\\u000a more pollutants from farmlands into the rivers of this region. Understanding the seasonal dynamics of nitrogen (N) and phosphorus\\u000a (P) transportation in the ditch system and the role of different ditch size is thus crucial for water pollution control of\\u000a the

Lei Guo; Keming Ma

2011-01-01

193

Ferromanganese oxide deposits from the Central Pacific Ocean, II. Nodules and associated sediments  

Microsoft Academic Search

Bulk chemical, mineralogical and selective leach analyses have been made on a suite of abyssal ferromanganese nodules and associated sediments from the S.W. equatorial Pacific Ocean. Compositional relations between nodules, sediment oxyhydroxides and nearby ferromanganese encrustations are drawn assuming that the crusts represent purely hydrogenetic ferromanganese material. Crusts, MnO 2 -rich nodules and sediment oxyhydroxides are compositionally similar and distinct

Andrew C. Aplin; David S. Cronan

1985-01-01

194

Suspended sediment sources and tributary effects in the lower reaches of a coastal plain stream as indicated by radionuclides, Loco Bayou, Texas  

Microsoft Academic Search

Characterizing the dynamics of fluvial sediment sources over space and time is often critical in identifying human impacts on fluvial systems. Upland interfluve and subsoil sources of suspended sediment at Loco Bayou, Texas, were distinguished using 226Ra\\/ 232Th, 226Ra\\/ 230Th and, 228Ra\\/ 232Th. Source contributions were apportioned at three stations during within-bank and flood flows. 137Cs and 210Pb xs (excess

K. M. Yeager; P. H. Santschi; J. D. Phillips; B. E. Herbert

2005-01-01

195

Estimated post-Messinian sediment supply and sedimentation rates on the Ebro continental margin, Spain  

USGS Publications Warehouse

Because of the extensive data base of seismic profiles, radiometric ages, and stratigraphic time markers such as the subaerial Messinian surface, sedimentation rates and Ebro River sediment discharge can be estimated for different periods and environments of the Ebro continental margin. New values for sediment discharge (i.e., 6.2 versus previous estimates of 2-3.5 million t/yr) for the Holocene highstand are more reliable but remain minimum estimates because a small proportion of Ebro sediment advected to the Balearic Rise and Abyssal Plain cannot be accounted for, especially during lowstands. The general highstand conditions of the Pliocene, which were similar to those of the Holocene, resulted in a low discharge of Ebro River sediment (ca. 6.5 million t/yr) and an even thickness of sediment across the margin that deposited at rates of about 24-40 cm/ky. In contrast, sediment supply increased two-three times during the Pleistocene, the margin prograded rapidly and deposition occurred at rates of 101-165 cm/ky on the outer shelf and slope, but basin floor rates remained anomalously low (21-26 cm/ky) because sediment was drained and broadly dispersed eastward in Valencia Trough. During the late Pleistocene rise of sea level, the main depocenters progressively shifted shoreward and sedimentation rates greatly decreased from 175 cm/ky on the upper slope during the early transgression to 106 cm/ky on the outer shelf and then to 63 cm/ky on the mid-shelf during the late transgression as the river sediment discharge dropped to half by Holocene time. Maximal sedimentation rates occurred in active depocenters of sediment dispersal such as the Holocene delta (370 cm/ky) or the youngest Pleistocene Oropesa channel-levee complex (705 cm/ky) where deposition rates increased by an order of magnitude or more compared to average Ebro shelf (38 cm/ky) or base-of-slope rates in the Pleistocene (21 cm/ky). The sedimentation rates verify the importance of sea-level control on the progressive change in location of depocenters and amount of sediment supply, but Pleistocene climatic change and deforestation alone can be observed to double river sediment discharge. The latter observation helps explain the anomalously high deposition rates in Pleistocene turbidite systems compared with older systems that may be controlled more by tectonic and sea-level changes alone. During the past 2000 years, in contrast, man has controlled deposition in the Ebro margin system, first by deforestation that more than doubled river sediment discharge and shelf deposition rates to equal those of Pleistocene time; and second by dam contruction that reduced sediment discharge to less than 5% of the normal Holocene discharge. Similar recent discharge reductions from the Nile and Rhone Rivers suggest that loss of the majority of the river sediment supply in the Mediterranean Sea may result in significant erosion of biologically and agriculturally important lobate delta areas. ?? 1990.

Nelson, C. H.

1990-01-01

196

Utopia Plain  

NASA Technical Reports Server (NTRS)

5 March 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a dark-toned, cratered plain in southwest Utopia Planitia. Large, light-toned, windblown ripples reside on the floors of many of the depressions in the scene, including a long, linear, trough.

Location near: 30.3oN, 255.3oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

2006-01-01

197

Reconstructing past plate motions with abyssal hill topography  

NASA Astrophysics Data System (ADS)

The seafloor spreading history of oceanic plates is primarily reconstructed by using a combination of dated seafloor magnetic anomalies and fracture zone trends to locate Euler poles and determine rotation rates. In some regions, these conventional measures of determining spreading history do not exist and alternative methods are required. Abyssal hills are elongate, topographic highs that are created at and form parallel to the ridge axis of spreading centers. Once formed, the abyssal hills are transported onto the ridge flank and provide a record of ridge axis orientation. We propose using the orientation of abyssal hill topography to supplement existing plate motion reconstruction methods and to serve as a stand-alone method for regions where conventional methods will not apply. Our new method uses high-resolution bathymetry grids created with multibeam data with grid-node spacing of 100-200 m, determined by regional water depths. The bathymetric grids are detrended to remove depth-age relationships and spatially filtered to remove anomalous regions where seafloor age is unknown. The detrended grids are then clipped to remove anomalously deep (e.g., fracture zones) or anomalously shallow topography (e.g., seamounts). Abyssal hill orientations are determined by calculating the modal frequencies of slope azimuth for pre-defined sub-regions (e.g., 50 km x 50 km) of these modified grids. The Euler Pole is then found by an iterative least-squares method from a grid of potential Euler Poles; first a coarse grid and then a fine grid are utilized to avoid local minima. At each potential Euler Pole, the sum of the differences between predicted and observed abyssal hill trends is squared and the minimum value identifies the location of the best-fit Euler Pole. Our method was applied to the well-mapped Cocos-Pacific plate boundary along the northern East Pacific Rise for the past 3 Ma and the poorly constrained Mid-Cretaceous seafloor (84 - 120 Ma) in the southwest Pacific Ocean. The results for the northern East Pacific Rise are very encouraging and our calculated Euler Poles are within 4 degrees of the NUVEL 1a and 2 degrees of the MORVEL global relative motion models. We also applied our method to the EMAG2 magnetic anomaly intensity grids with similar encouraging results; 17 degrees NUVEL 1a & 11 degrees MORVEL. The results for the southwest Pacific are still preliminary, but the method effectively identifies regions with similar abyssal hill trends and may be useful for more detailed tectonic reconstructions of the enigmatic region.

Dahn, M. R.; Pockalny, R. A.; King, C.

2013-12-01

198

Depth Transects of Sediment Age, Reflectance, and Aquifer Arsenic in the Bac Bo Plain, Vietnam: Implications for Groundwater Arsenic Heterogeneity in the Red River Delta  

NASA Astrophysics Data System (ADS)

Shallow aquifer groundwater arsenic heterogeneity is well documented in many of the fluvial regions of Asia. To this day, the cause for the heterogeneity remains poorly understood in part because of the heterogeneity of sediment properties inherent to a young floodplain depositional environment. In April 2006, a needle-sampler device was used to obtain depth transects of both sediment and porewater samples as the first step towards understanding the heterogeneous subsurface environment. Depth transects were taken between sites with opposing trends in tube-well arsenic, e.g. low As cluster to high As cluster, in a stable, fault controlled river bend in Van Phuc, Vietnam, to determine how sediment properties such as grainsize and reflectance relate to dissolved arsenic. Luminescence dating of aquifer sands and He3/H3 dating of the groundwater was conducted to investigate how aquifer redox conditions and groundwater arsenic evolve in Van Phuc's river-bend over time. Results indicate that localized zones of sediments enriched in leachable arsenic exist at depth within the aquifer and provide a mostly local source of arsenic. It also appears that groundwater flow encountering sediments of different ages can account for some of the observed spatial patterns of groundwater heterogeneity. Compiled with observations that reducing groundwaters with both low dissolved and extractable arsenic exist in the upper deltaic region, it appears that heterogeneities in shallow floodplain arsenic can be driven by magnitude differences in sediment-labile arsenic. Finally, given that these localized packages of arsenic enrichment correspond to a particular in-filling type of facies, it appears that fluvial cycling along the delta is the underlying cause of arsenic heterogeneity in the shallow floodplain.

Weinman, B.; Goodbred, S. L.; Radloff, K.; Aziz, Z.; Jung, H.; Frei, F.; Berg, M.; Trang, P. K.; Singhvi, A.; van Geen, A.

2007-12-01

199

Feeding Preferences of Abyssal Macrofauna Inferred from In Situ Pulse Chase Experiments  

PubMed Central

Climatic fluctuations may significantly alter the taxonomic and biochemical composition of phytoplankton blooms and subsequently phytodetritus, the food source for the majority of deep-sea communities. To examine the response of abyssal benthic communities to different food resources we simulated a food sedimentation event containing diatoms and coccolithophorids at Station M in the NE Pacific. In one set of experiments we measured incorporation of diatomC and coccoN into the macrofauna using isotopically enriched 13C-diatoms and 15N-coccolithophores. In a second experiment we measured incorporation of C and N from dual-labelled (13C and 15N) diatoms. The second experiment was repeated 2 months later to assess the effect of seasonality. The simulated food pulses represented additions of 650 – 800 mg C m?2 and 120 mg N m?2 to the seafloor. In all cases rapid incorporation of tracer was observed within 4 days, with between 20% and 52% of the macrofauna displaying evidence of enrichment. However, incorporation levels of both diatomC and coccoN were low (<0.05% and 0.005% of the added C and N). Incorporation of labelled diatoms was similar during both June and September suggesting that the community was not food limited during either period. We found no evidence for selective ingestion of the different food types in the metazoan fauna suggesting that macrofauna do not have strong preferences for diatom vs. coccolithophore dominated phytodetrital pulses. C?N ratios from both experiments suggest that the metazoan macrofauna community appear to have higher C demands and/or assimilation efficiencies compared to N. Concomitantly, the foraminifera preferentially selected for diatomN over coccoN, and we suggest that this may be related to foraminiferal requirements for intracellular nitrate. These experiments provide evidence that abyssal faunal feeding strategies are in part driven by an organism's internal stoichiometric budgets and biochemical requirements.

Jeffreys, Rachel M.; Burke, Ciara; Jamieson, Alan J.; Narayanaswamy, Bhavani E.; Ruhl, Henry A.; Smith, Kenneth L.; Witte, Ursula

2013-01-01

200

Feeding preferences of abyssal macrofauna inferred from in situ pulse chase experiments.  

PubMed

Climatic fluctuations may significantly alter the taxonomic and biochemical composition of phytoplankton blooms and subsequently phytodetritus, the food source for the majority of deep-sea communities. To examine the response of abyssal benthic communities to different food resources we simulated a food sedimentation event containing diatoms and coccolithophorids at Station M in the NE Pacific. In one set of experiments we measured incorporation of diatomC and coccoN into the macrofauna using isotopically enriched (13)C-diatoms and (15)N-coccolithophores. In a second experiment we measured incorporation of C and N from dual-labelled ((13)C and (15)N) diatoms. The second experiment was repeated 2 months later to assess the effect of seasonality. The simulated food pulses represented additions of 650 - 800 mg C m(-2) and 120 mg N m(-2) to the seafloor. In all cases rapid incorporation of tracer was observed within 4 days, with between 20% and 52% of the macrofauna displaying evidence of enrichment. However, incorporation levels of both diatomC and coccoN were low (<0.05% and 0.005% of the added C and N). Incorporation of labelled diatoms was similar during both June and September suggesting that the community was not food limited during either period. We found no evidence for selective ingestion of the different food types in the metazoan fauna suggesting that macrofauna do not have strong preferences for diatom vs. coccolithophore dominated phytodetrital pulses. C?N ratios from both experiments suggest that the metazoan macrofauna community appear to have higher C demands and/or assimilation efficiencies compared to N. Concomitantly, the foraminifera preferentially selected for diatomN over coccoN, and we suggest that this may be related to foraminiferal requirements for intracellular nitrate. These experiments provide evidence that abyssal faunal feeding strategies are in part driven by an organism's internal stoichiometric budgets and biochemical requirements. PMID:24303022

Jeffreys, Rachel M; Burke, Ciara; Jamieson, Alan J; Narayanaswamy, Bhavani E; Ruhl, Henry A; Smith, Kenneth L; Witte, Ursula

2013-01-01

201

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

202

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

203

Cross-Equatorial Flow of Grounded Abyssal Ocean Currents  

NASA Astrophysics Data System (ADS)

An idealized process study is presented describing the cross-equatorial flow of grounded abyssal ocean currents in a differentially-rotating meridional channel with parabolic bottom topography. In particular we fully examine the dependence of the cross-equatorial volume flux on the underlying flow parameters including slope of the channel's walls (s), half-width of the channel (l), width and height of the abyssal current (a and H), magnitude of the rotation vector (O), Earth's radius (R) and reduced gravity (g'). We determined that the ratio between the width of the channel and the zonal wavelength of a narrow wave structure that is formed by the current in the equatorial region plays a crucial role in determining into which hemisphere the current flows after its interaction with the equator. It is found that some parameters (a and H) do not have any significant effect on the zonal wavelength, while variations in other parameters (s, O, R and g') change the zonal wavelength and, consequently, the behaviour of the abyssal current. After examining an auxiliary model of a particle in a rotating channel, we derived a combination of these parameters LRh = 12g' sy01/2 RW called the Rhines scale and the zonal wavelength is found to be linearly proportional to this scale.

Kim, Alexander

204

Examination of abyssal sea floor and near-bottom water mixing processes using Ra-226 and Rn-222  

SciTech Connect

Since Broecker's (1965) original work, extensive studies have been made on abyssal near-bottom water-mixing processes using the radioactive parent-daughter pair radium-226 (Ra) - radon-222 (Rn). One assumption critical to all of these studies is that sediments immediately under a given water column are the source of excess radon (=Rn concentration - Ra concentration) found in bottom waters. Since 1965 theoretical works of increasing complexity have tried to explain areal variations of excess radon and radium. However, Key et al. (1979b) have reported the only extensive measurements of radium and radon in bottom water and sediments at the same location. This dissertation is an expansion of that work both in theory and in scope. A diagenetic sediment model based on the work of Schink and Guinasso (1978), Cochran (1979), and Key et al. (1979b) was developed to model Ra-Rn in near-surface abyssal sediments. In order to maximize model application information, the degrees of freedom were minimized by measuring as many of the model parameters as possible. The most glaring discrepancy found was that measured near-surface total radium profiles could not be fit using plutonium-derived bioturbation rates. There is an implication that plutonium profiles modeled with currently accepted bioturbation models do not give a true indication of the real biologically induced mixing process. After adjusting for this problem in the source function, diagenetic theory explains near-surface radon-distributions adequately. Using both the adjusted diagenetic model and the empirical model developed by Key et al. (1979b), reasonable agreement was found between the sedimentary radon deficit and near-bottom water surplus. Inadequacy of present diagenetic theory makes any attempt to differentiate sedimentary radium sources academic.

Key, R.M.

1981-01-01

205

Reproductive patterns of the abyssal asteroid Styracaster elongatus from the N.E. Atlantic Ocean  

NASA Astrophysics Data System (ADS)

We analysed the reproductive biology of the asteroid species Styracaster elongatus based on time-series samples from a 5000-m-deep site on the Porcupine Abyssal Plain (N.E. Atlantic). The ratio of males to females, the gonadosomatic index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads. Fecundity and oocyte-size distribution were determined by histological and image analyses. Styracaster elongatus is a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Oogenesis was asynchronous. The previtellogenic oocytes grew to a size of ˜230 ?m before undergoing vitellogenesis. Maximum oocyte size was ˜620 ?m. The ovary volume was mainly occupied by small previtellogenic oocytes (100-150 ?m) at any one time. Mean GI was 6.38±3.30 for females and 9.04±4.1 for males. Mean PCI was 7.44±1.66 for females and 7.66±1.46 for males. Mean fecundity was 16,373±5988 oocites per female. There were no seasonal variations in GI and fecundity. There was evidence of a pyiloric caecum seasonal development for females and males. For S. elongatus there is no direct relationship among seasonal primary production at the surface and production of vitellogenic oocytes. Nevertheless, this species takes advantage of the pulse of phytodetritus to the seabed by increasing the storage of nutrients in the pyloric caecum in order to maintain a constant production of eggs and sperm.

Benítez-Villalobos, Francisco; Díaz-Martínez, Julia P.

2010-01-01

206

Summertime trends in pelagic biogeochemistry at the Porcupine Abyssal Plain study site in the northeast Atlantic  

NASA Astrophysics Data System (ADS)

Measurements of nitrate and carbon uptake made in July 2006 in the Northeast Atlantic Ocean are evaluated with reference to the photophysiology of the attendant phytoplankton population. Over the 11-day observation period integrated chlorophyll concentrations and carbon fixation rates decreased by 76% and 60%, respectively. Integrated nitrate uptake decreased by 50% from initial to final rates but was generally less variable than carbon fixation and chlorophyll in the intervening period. Satellite derived estimates of surface chlorophyll concentrations reveal the uptake observations to be coincident with, and subsequent to, a peak in summer time production. Large reductions in diatom and dinoflagellate abundance were also seen at this time, with indications that increased grazing, due to an increase in ciliate abundance, was an important mechanism terminating summertime production in the NE Atlantic. Meanwhile, the presence of consistently low values of Fv/Fm (<0.3), particularly in surface waters, suggests that production occurs, or is inhibited, with suboptimal photochemical efficiency widespread amongst the phytoplankton population. Furthermore, the low values of Fv/Fm were not alleviated by day-to-day variability in macronutrient concentration. The timing of our observations places them within the seasonal period recognised for the widespread phenomena of carbon overconsumption, and we estimate C:N uptake ratios at this time could be as high as 13:1.

Painter, Stuart C.; Lucas, Michael I.; Stinchcombe, Mark C.; Bibby, Thomas S.; Poulton, Alex J.

2010-08-01

207

MODOO: A modular and mobile deep ocean observatory and its application to the Porcupine Abyssal Plain  

Microsoft Academic Search

Many of todays scientific questions require to observe the various processes in the ocean in parallel and from the air\\/sea interface to the sea-floor interior. Moreover, socioeconomic as well as scientific requirements may even demand to excess data in real time - for example for marine safety or to adapt the instrumentation to episodic environmental conditions. Here we describe a

Johannes Karstensen; Jens Greinert; Richard Lampitt; Fiona Grant; Monty Priede; Maureen Pagnani

2010-01-01

208

CTD Data from the Madeira Abyssal Plain CHARLES DARWIN Cruise 1/85.  

National Technical Information Service (NTIS)

The report presents lists and graphs of CTD data taken aboard RRS Charles Darwin during February 1985. The majority of the lowerings were made in support of two experiments; the deployment of deep SOFAR floats near 32 degrees N 24 degrees W and of mooring...

P. M. Saunders

1985-01-01

209

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

210

Relation of Mercury to Other Chemical Constituents in Ground Water in the Kirkwood-Cohansey Aquifer System, New Jersey Coastal Plain, and Mechanisms for Mobilization of Mercury from Sediments to Ground Water  

USGS Publications Warehouse

Water from 265 domestic wells that tap the unconfined Kirkwood-Cohansey aquifer system in the Coastal Plain of New Jersey contained concentrations of mercury that are equal to or exceed the U.S. Environmental Protection Agency maximum contaminant level (MCL) of 2 ug/L (micrograms per liter). The wells range in depth from 50 to 200 feet, and are located in 32 discrete, mostly residential, areas that were developed primarily on former agricultural land during the 1950?s through the 1970?s. Concentrations in two other areas exceeded 1 ug/L. Naturally occurring mercury concentrations in ground water from the Kirkwood-Cohansey aquifer system typically are less than 0.01 ug/L, but concentrations in water from some wells were as much as 42 ug/L. No evidence currently exists that conclusively links known point sources such as landfills, industrial operations, or commercial enterprises to most of the elevated concentrations of mercury in ground water in the residential areas. Possible sources of the mercury include pesticides and atmospheric deposition. Analysis of water from wells in 6 of the 34 areas for other constituents indicates that nitrate concentrations also commonly are elevated above background levels (which typically are undetectable at 0.01 milligrams per liter), and exceed the MCL of 10 milligrams per liter in some samples. Several volatile organic compounds (VOCs), including chloroform, also have been measured in water from wells at many of the 34 sites. Analytical results for water samples collected at several depths from boreholes at 2 of the 34 sites indicate elevated concentrations of calcium, magnesium, barium, strontium, nitrate, and chloride, which may be related to both agricultural chemical applications and septic-system effluent. Determinations of tritium and helium concentrations indicate that water containing elevated concentrations of mercury recharged the aquifer between 9.4 and 79 years ago, which includes the period during which many of the 34 sites were undergoing a change from agricultural or undeveloped to residential land use. Batch equilibrium experiments were used to measure adsorption of dissolved mercury, mercuric chloride, and phenylmercuric acetate by aquifer sediments at pH 3.5-4.0, 4.5-5.0, and 5.5-6.0. In nearly all cases, 55 to 95 percent of the mercury added to the sediments was adsorbed. Mercury mobilization from aquifer sediments inoculated with mercury was investigated by leaching the sediments with two concentrations of nitric acid (a component of acid rain), a sodium chloride solution (simulating road salt), and three fertilizer solutions. A solution of 20-20-20 (nitrogenphosphorous-potassium) fertilizer removed virtually all of the mercury with which the sediments had been inoculated. The sodium chloride solution was moderately effective in removing applied mercury from the sediments, as was a solution of nitric acid. A more dilute nitric acid solution and two sodium nitrate fertilizer solutions were less effective. Results of these experiments indicate that mercury adsorbs to aquifer sediments, but that varying amounts can be removed by infiltrating solutions, some of which can be related to specific land uses. Land-use history at the 34 sites generally indicates a change from agricultural or undeveloped settings to residential settings. Whatever the source of mercury to these sites, a change in the geochemical environment of the soil and aquifer brought about by land-use change probably provides mechanisms for mobilizing the mercury from soils and sediments to ground water.

Barringer, Julia L.; MacLeod, Cecilia L.

2001-01-01

211

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

212

Morphological disparity as a biodiversity metric in lower bathyal and abyssal gastropod assemblages.  

PubMed

Studies of deep-sea biodiversity focus almost exclusively on geographic patterns of alpha-diversity. Few include the morphological or ecological properties of species that indicate their actual roles in community assembly. Here, we explore morphological disparity of shell architecture in gastropods from lower bathyal and abyssal environments of the western North Atlantic as a new dimension of deep-sea biodiversity. The lower bathyal-abyssal transition parallels a gradient of decreasing species diversity with depth and distance from land. Morphological disparity measures how the variety of body plans in a taxon fills a morphospace. We examine disparity in shell form by constructing both empirical (eigenshape analysis) and theoretical (Schindel's modification of Raup's model) morphospaces. The two approaches provide very consistent results. The centroids of lower bathyal and abyssal morphospaces are statistically indistinguishable. The absolute volumes of lower bathyal morphospaces exceed those of the abyss; however, when the volumes are standardized to a common number of species they are not significantly different. The abyssal morphospaces are simply more sparsely occupied. In terms of the variety of basic shell types, abyssal species show the same disparity values as random subsets of the lower bathyal fauna. Abyssal species possess no evident evolutionary innovation. There are, however, conspicuous changes in the relative abundance of shell forms between the two assemblages. The lower bathyal fauna contains a fairly equable mix of species abundances, trophic modes, and shell types. The abyssal group is numerically dominated by species that are deposit feeders with compact unsculptured shells. PMID:15068350

McClain, Craig R; Johnson, Nicholas A; Rex, Michael A

2004-02-01

213

The benthic silica cycle in the Northeast Atlantic: annual mass balance, seasonality, and importance of non-steady-state processes for the early diagenesis of biogenic opal in deep-sea sediments  

NASA Astrophysics Data System (ADS)

Within the framework of the EU-funded BENGAL programme, the effects of seasonality on biogenic silica early diagenesis have been studied at the Porcupine Abyssal Plain (PAP), an abyssal locality located in the northeast Atlantic Ocean. Nine cruises were carried out between August 1996 and August 1998. Silicic acid (DSi) increased downward from 46.2 to 213 ?M (mean of 27 profiles). Biogenic silica (BSi) decreased from ca. 2% near the sediment-water interface to <1% at depth. Benthic silicic acid fluxes as measured from benthic chambers were close to those estimated from non-linear DSi porewater gradients. Some 90% of the dissolution occurred within the top 5.5 cm of the sediment column, rather than at the sediment-water interface and the annual DSi efflux was close to 0.057 mol Si m -2 yr -1. Biogenic silica accumulation was close to 0.008 mol Si m -2 yr -1 and the annual opal delivery reconstructed from sedimentary fluxes, assuming steady state, was 0.065 mol Si m -2 yr -1. This is in good agreement with the mean annual opal flux determined from sediment trap samples, averaged over the last decade (0.062 mol Si m -2 yr -1). Thus ca. 12% of the opal flux delivered to the seafloor get preserved in the sediments. A simple comparison between the sedimentation rate and the dissolution rate in the uppermost 5.5 cm of the sediment column suggests that there should be no accumulation of opal in PAP sediments. However, by combining the BENGAL high sampling frequency with our experimental results on BSi dissolution, we conclude that non-steady state processes associated with the seasonal deposition of fresh biogenic particles may well play a fundamental role in the preservation of BSi in these sediments. This comes about though the way seasonal variability affects the quality of the biogenic matter reaching the seafloor. Hence it influences the intrinsic dissolution properties of the opal at the seafloor and also the part played by non-local mixing events by ensuring the rapid transport of BSi particles deep into the sediment to where saturation is reached.

Ragueneau, O.; Gallinari, M.; Corrin, L.; Grandel, S.; Hall, P.; Hauvespre, A.; Lampitt, R. S.; Rickert, D.; Stahl, H.; Tengberg, A.; Witbaard, R.

214

Aged black carbon in marine sediments and sinking particles  

NASA Astrophysics Data System (ADS)

report measurements of oceanic black carbon (BC) to determine the sources of BC to abyssal marine sediments in the northeast Pacific Ocean. We find that the average 14C age of BC is older (by 6200 ± 2200 14C years) than that of the concurrently deposited non-BC sedimentary organic carbon. We investigate sources of aged BC to sediments by measuring a sample of sinking particulate organic carbon (POC) and find that POC may provide the main transport mechanism of BC to sediments. We suggest that aged BC is incorporated into POC from a combination of resuspended sediments and sorption of ancient dissolved organic carbon BC onto POC. Our BC flux estimate represents ~8-16% of the global burial flux of organic carbon to abyssal sediments and constitutes a minimum long-term removal estimate of 6-32% of biomass-derived BC using the present day emission flux.

Coppola, Alysha I.; Ziolkowski, Lori A.; Masiello, Caroline A.; Druffel, Ellen R. M.

2014-04-01

215

Taphonomy and paleoecology of nonmarine mollusca: indicators of alluvial plain lacustrine sedimentation, upper part of the Tongue River Member, Fort Union Formation ( Paleocene), Northern Powder River Basin, Wyoming and Montana ( USA).  

USGS Publications Warehouse

The composition, species abundances, and spatial and temporal distributions of mollusc assemblages were controlled by the environments in which they lived and the depositional processes that affected the molluscs after death and before final burial. Post-mortem transport, reworking and concentration of shells, and mixing of faunal elements from discrete habitats produced a taphonomic 'overprint' on assemblage characteristics that directly reflects the processes of alluvial plain and floodbasin lacustrine sedimentation. The 'overprint' can be interpreted from outcrop analysis of molluscan biofabric, which consists of: 1) orientation, fragmentation, size-sorting, abrasion, density, and dispersion of shells, 2) the nature and extent of shell-infilling, and 3) ratio of articulated to disarticulated bivalves. Taphonomic characteristics were used with sedimentological properties to differentiate in-place, reworked, transported, and ecologically mixed mollusc assemblages. This study also defines the paleoecology of habitat preferences of mollusc species as a basis for recognition of the environments in which these assemblages were deposited: 1) large floodbasin lakes, 2) small floodbasin lakes, and 3) crevasse deltas and splays. Integration of sedimentology and paleoecology provides an interdisciplinary approach to the interpretation of alluvial environments through time in the Tongue River Member. -Authors

Hanley, J. H.; Flores, R. M.

1987-01-01

216

Peculiarities of Environment Pollution as a Special Type of Radioactive Waste: Field Means for Comprehensive Characterization of Soil and Bottom Sediments and their Application in the Survey at the Flood plain of Techa River - 13172  

SciTech Connect

Contamination of natural objects - zone alarm fallout, zones and flood plains near production sites (the result of technological accidents and resource extraction) occupy large areas. Large area and volume of contaminated matter, moderate specific activity (as low - medium-level wastes) make such objects specific types of radioactive waste. These objects exist for a long time, now they are characterized by a bound state of nuclides with the matrix. There is no cost-effective ways to remove these waste, the only solution for the rehabilitation of such areas is their isolation and regular monitoring through direct and indirect measurements. The complex of instruments was developed to field mapping of contamination. It consists of a portable spectrometric collimated detector, collimated spectrometric borehole detector, underwater spectrometer detector, spectrometer for field measurements of the specific activity of Sr-90, connected to a portable MCA 'Colibry (Hummingbird)'. The complex was used in settlements of Bryansk region, rivers Techa and Yenisei. The effectiveness of the developed complex considered by the example of characterization of the reservoir 10 (artificial lake) in Techinsky cascade containing a huge amount of radioactive waste. The developed field means for comprehensive characterization of soil and bottom sediments contamination are very effective for mapping and monitoring of environment contamination after accidents. Especially in case of high non-uniformity of fallout and may be very actual in Fukushima area. (authors)

Ivanov, Oleg; Danilovich, Alexey; Potapov, Victor; Stepanov, Vyacheslav; Smirnov, Sergey; Volkovich, Anatoly [National Research Centre - Kurchatov Institute, 1 Kurchatov Sq. (Russian Federation)] [National Research Centre - Kurchatov Institute, 1 Kurchatov Sq. (Russian Federation)

2013-07-01

217

Sedimentation in Canada Basin, Western Arctic  

NASA Astrophysics Data System (ADS)

The Canada Basin of the western Arctic Ocean is the least studied ocean basin on Earth. Marine seismic field programs were conducted during the past 5 years in order to study the geology, sedimentary history and geomorphology of the region. As part of this program, five annual icebreaker expeditions acquired bathymetric, seismic reflection and seismic refraction data on a regional scale. More than 12,000 km of multi-channel seismic reflection data and 120 sonobuoy seismic refraction records over abyssal plain and continental rise regions of Canada Basin, Northwind Ridge and Alpha Ridge were acquired. The success of these programs was achieved through novel technical modifications to equipment to permit towing in heavy ice conditions and through collaboration between multiple Canadian and US agencies and institutions, enabling utilization of two ice breakers during seismic and multibeam data acquisition in heavy ice. The seafloor of the Canada Basin is remarkably flat-lying in its central region, with little bathymetric change over most of its extent. The sedimentary succession is generally flat lying with reflections extending over hundreds of km. These reflections onlap bathymetric highs, such as Alpha and Northwind ridges. The sedimentary succession is thickest in the Beaufort Sea region, reaching more than 6.5 km, and generally thins to the north and west. Reflection characteristics suggest that sediment volume input to the Arctic Ocean has been high and dominated by turbidity current deposition, similar to Amundsen and Nansen Basins of the eastern Arctic. These turbidites originate from the eastern and southern continental margins. There is no evidence of contemporaneous or post-depositional reworking by bottom currents. Additionally, there is little evidence of tectonic deformation after primary basin-forming events except in the NE quadrant, nearer Alpha Ridge. In this area, there is significant normal faulting propagating from basement through much of the sedimentary succession. Basement graben stuctures in combination with these faults imply possible crustal extension contemporaneous with deposition.

Mosher, D. C.; Shimeld, J.; Jackson, R.; Hutchinson, D. R.; Chapman, B.; Chian, D.; Childs, J. R.; Mayer, L. A.; Edwards, B. D.; Verhoef, J.

2010-12-01

218

Abyssal ocean warming around Antarctica strengthens the Atlantic overturning circulation  

NASA Astrophysics Data System (ADS)

abyssal warming around Antarctica is one of the most prominent multidecadal signals of change in the global ocean. Here we investigate its dynamical impacts on the Atlantic Meridional Overturning Circulation (AMOC) by performing a set of experiments with the ocean-sea ice model NEMO-LIM2 at ½° horizontal resolution. The simulations suggest that the ongoing warming of Antarctic Bottom Water (AABW), already affecting much of the Southern Hemisphere with a rate of up to 0.05°C decade-1, has important implications for the large-scale meridional overturning circulation in the Atlantic Ocean. While the abyssal northward flow of AABW is weakening, we find the upper AMOC cell to progressively strengthen by 5-10% in response to deep density changes in the South Atlantic. The simulations suggest that the AABW-induced strengthening of the AMOC is already extending into the subtropical North Atlantic, implying that the process may counteract the projected decrease of the AMOC in the next decades.

Patara, Lavinia; Böning, Claus W.

2014-06-01

219

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

220

Inter-annual dynamics of abyssal polychaete communities in the North East Pacific and North East Atlantic—A family-level study  

NASA Astrophysics Data System (ADS)

Characterising how deep-sea communities change on contemporary time-scales and understanding underlying ecosystem processes has become important under changing climate and the rise in the exploitation of deep-sea resources. However, little is known about these dynamics and processes. Long-term observations from which inter-annual variations can be detected are scarce in the deep sea. This study examines inter-annual changes in density, family richness and evenness, family and functional group rank abundance distributions of infaunal polychaetes at two abyssal stations in the North East Pacific (Station M, 1991 to 2005) and in the North East Atlantic (Porcupine Abyssal Plain, 1991 to 1999). The two long-term data sets were used to investigate not only if polychaete community structure and composition varied at inter-annual scales in terms of diversity and rank abundance distributions but also if any changes were related to previous observations in megafauna and environmental factors at each locality. The polychaete community structure at each locality was analysed using univariate statistics as well as multivariate ordination techniques based on Bray-Curtis similarity of the yearly family density. Sub-surface deposit feeders, such as Paraonidae, dominated the North East Pacific, whereas surface deposit feeders, such as Cirratulidae, dominated the North East Atlantic. Both stations showed inter-annual variations in density, family evenness and rank abundance distributions. The greatest changes occurred in 1998 in both time series when polychaete densities peaked, and switches in the rank abundance of the most abundant families and functional groups took place. Inter-annual variations in the polychaete community were correlated with a limited number of holothurian species changes, but no correlation was found with particulate organic matter flux or climate indices. Ecological and environmental factors behind the family-level changes remain elusive. Overall, changes in the dominance of functional groups imply changes in abyssal ecosystem functioning with potential consequences on carbon cycling at the seabed.

Laguionie-Marchais, C.; Billett, D. S. M.; Paterson, G. L. D.; Ruhl, H. A.; Soto, E. H.; Smith, K. L., Jr.; Thatje, S.

2013-05-01

221

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

222

Abyssal Boundary Current Studies Current Measurements North of the Falkland Plateau January 1986-1987.  

National Technical Information Service (NTIS)

The data described in this report were collected in support of the program, Abyssal Boundary Current Studies. This program was designed to improve our understanding of the structure and variability of the deep western boundary currents and to estimate the...

R. D. Pillsbury D. Barstow J. M. Bottero G. Pittock D. C. Root

1989-01-01

223

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

NASA Astrophysics Data System (ADS)

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 and North America. A detailed comparison of the PAP form with typical individuals of S. fusiformis from Norwegian waters (55-203 m depth), however, reveals slight but consistent morphological differences. The PAP specimens are smaller (test length 40-140 ?m) than those from Norway (test length 80-380 ?m), the chambers tend to be rather less elongate, the density of pores in the test wall is much lower, and there are differences in apertural features. We therefore conclude that the diminutive abyssal form is a distinct species, here referred to as Stainforthia sp. This interpretation is consistent with increasing evidence for genetic differentiation in deep-sea organisms, particularly along bathymetric gradients. Stainforthia sp. was previously illustrated by Pawlowski as Fursenkoina sp. and appears to be widespread and abundant in the abyssal North Atlantic (>4000 m depth). Stainforthia fusiformis, on the other hand, is most abundant in continental shelf and coastal settings. It extends onto the continental slope in the North Atlantic but has not been reported reliably from depths greater than about 2500 m. We suggest that the striking morphological convergence between these two species reflects the adoption of similar ecological strategies in widely separated habitats. Both are enrichment opportunists, a life-style which may explain the rather broad bathymetric range of Stainforthia fusiformis. This is a dominant species in organically-enriched and sometimes extremely oxygen-depleted environments on the continental shelf, and is a rapid coloniser of formerly azoic habitats. Live specimens of the abyssal form are typically found embedded within phytodetrital aggregates (organic material derived from primary production in the euphotic zone). It is presumably the availability of these organic-rich microhabitats, which enables this species to survive in the otherwise oligotrophic deep sea.

Gooday, Andrew J.; Alve, Elisabeth

224

Meiofauna and macrofauna community structure in relation to sediment composition at the Iberian margin compared to the Goban Spur (NE Atlantic)  

NASA Astrophysics Data System (ADS)

Meiofauna and macrofauna communities and several sediment characteristics were compared between a slope situated far from the coast (Goban Spur) and two transects across the Iberian Margin with steep slopes and close to the shore. The northern Galician transect (off La Coruña) was situated in an area subjected to wind-induced upwelling events. The western Galician transect was also subjected to upwelling, was additionally influenced by outflows of water rich in organic matter from the Rías Bajas. This transect also included the Galicia Bank. Macrofauna density decreased exponentially from the shelf edge (154 m) to the abyssal plain (4951 m) and different communities occurred on the shelf, the upper- and lower slope and on the abyssal plain. Apart from two extremely low-density stations on the Iberian Margin, there were no significant differences in the meiofauna between the Goban Spur and the Iberian Margin. Along the La Coruña-transect a station where meiofaunal densities were low occurred at a depth of 1522 m, where the sediment was characterised by having a high median-grain size, ripple structures, a low C org and total N content. There were relatively high numbers of macrofaunal filter-feeders but low numbers of crustaceans, indicating a high current velocity regime. On top of the Galicia Bank (~770 m) the sediment consisted mainly of shells of pelagic foraminifers, and had low contents of C org and N. The macrofauna was dominated by filter-feeding and carnivorous taxa. At both these stations meiofauna densities were low. Meiofauna densities and community structure differed between the Goban Spur and the Iberian Margin. Meiofauna densities on the Galician shelf were more than double those on the Goban Spur shelf. The two deep stations on the La Coruña transect and the deepest station on the Galicia Bank transect all contained meiofaunal densities that were higher than found at similar depths off the Goban Spur. The meiofaunal densities were inversely correlated with %CaCO 3 content and, excluding the shelf stations, were positively correlated with both %C org and total N at the Iberian Margin. Neither upwelling nor the enriched outflows from the rias affected the macrofauna, but meiofaunal densities were greatly enhanced.

Flach, Els; Muthumbi, Agnes; Heip, Carlo

225

Abyssal Sequestration of Nuclear Waste in Earth's Crust  

NASA Astrophysics Data System (ADS)

This work outlines a new method for disposing of hazardous (e.g., nuclear) waste. The technique is called Abyssal Sequestration, and it involves placing the waste at extreme depths in Earth's crust where it could achieve the geologically-long period of isolation. Abyssal Sequestration involves storing the waste in hydraulic fractures driven by gravity, a process we term gravity fracturing. In short, we suggest creating a dense fluid (slurry) containing waste, introducing the fluid into a fracture, and extending the fracture downward until it becomes long enough to propagate independently. The fracture will continue to propagate downward to great depth, permanently isolating the waste. Storing solid wastes by mixing them with fluids and injecting them into hydraulic fractures is a well-known technology. The essence of our idea differs from conventional hydraulic fracturing techniques only slightly in that it uses fracturing fluid heavier than the surrounding rock. This difference is fundamental, however, because it allows hydraulic fractures to propagate downward and carry wastes by gravity instead of or in addition to being injected by pumping. An example of similar gravity-driven fractures with positive buoyancy is given by magmatic dikes that may serve as an analog of Abyssal Sequestration occurring in nature. Mechanics of fracture propagation in conditions of positive (diking) and negative (heavy waste slurry) buoyancy is similar and considered in this work for both cases. Analog experiments in gelatin show that fracture breadth (horizontal dimension) remains nearly stationary when fracturing process in the fracture 'head' (where breadth is 'created') is dominated by solid toughness, as opposed to the viscous fluid dissipation dominant in the fracture tail. We model propagation of the resulting 'buoyant' or 'sinking' finger-like fracture of stationary breadth with slowly varying opening along the crack length. The elastic response of the crack to fluid loading in a horizontal cross-section is local and can be treated similar to the classical Perkins-Kern-Nordgren (PKN) model of hydraulic fracturing. The propagation condition for a finger-like crack is based on balancing the global energy release rate due to unit crack extension and the rock fracture toughness. It allows to relate the net fluid pressure at the tip to the fracture breadth and rock toughness. Unlike the PKN fracture, which breadth is known a priori, the final breadth of a finger-like fracture is a result of the fracturing process in the fracture head. To resolve the breadth, we relax the local elasticity assumption in the fracture head by neglecting viscous pressure drop there. The resulting fracture head model is a 3D analog of the Weertman's hydrostatic pulse, and yields expressions for the terminal breadth, b = 0.34 (K / Delta rho g))^(2/3), and for the head volume, V = 10.4 K b^(5/2) / E'. We then combine the finger crack solution for the viscous tail with the 3-D pulse solution for the fracture head. The obtained closed-form solution is compared to numerical simulations. Based on this solution, we analyzed the gravity fracture propagation in conditions of either continuous injection or finite volume release for sets of parameters representative of the heavy waste injection technique and low viscosity magma diking.

Germanovich, L. N.; Garagash, D.; Murdoch, L. C.; Robinowitz, M.

2013-12-01

226

Sediment recycling at convergent plate margins (Indo-Burman Ranges and Andaman-Nicobar Ridge)  

NASA Astrophysics Data System (ADS)

Subduction complexes large enough to be exposed subaerially and become significant sources of terrigenous detritus are formed by tectonic accretion above trenches choked with thick sections of remnant-ocean turbidites. They thus need to be connected along strike to a major collision zone, where huge volumes of orogenic detritus are produced and conveyed via a major fluvio-deltaic system to the deep sea. In this article we investigate sediment generation and recycling in the archetype of such settings, the eastern prolongation of the Himalayan collisional system. We illustrate the petrographic and heavy-mineral suites of modern sands produced all along the Indo-Burman-Andaman-Nicobar subduction complex, which includes accreted abyssal-plain sediments overthrust by ophiolites and unconformably overlain by volcaniclastic forearc strata. "Subduction Complex Provenance" is thus composite, and overwhelmingly consists of detritus recycled from largely turbiditic parent rocks (Recycled Clastic Provenance), with local supply from obducted ultramafic and mafic rocks of forearc lithosphere (Ophiolite Provenance) or recycled paleovolcanic to neovolcanic sources (Volcanic Arc Provenance). In order to specifically investigate the effect of recycling, we characterize the diverse detrital signatures of Cenozoic sandstones originally deposited during subsequent stages of "soft" and "hard" Himalayan collision and presently exposed from Bangladesh to the Andaman Islands, and discuss the reasons for compositional discrepancies between parent sandstones and their recycled daughter sands. Long-distance, multistep and multicyclic sediment transfer along and across convergent plate boundaries follows complex trajectories in space and time, which must be resolved whenever we want to obtain a reasonably faithful paleogeographic reconstruction for the recent and less recent geological past.

Garzanti, Eduardo; Limonta, Mara; Resentini, Alberto; Bandopadhyay, Pinaki C.; Najman, Yani; Andò, Sergio; Vezzoli, Giovanni

2013-08-01

227

Open ocean pelago-benthic coupling: cyanobacteria as tracers of sedimenting salp faeces  

NASA Astrophysics Data System (ADS)

Coupling between surface water plankton and abyssal benthos was investigated during a mass development of salps ( Salpa fusiformis) in the Northeast Atlantic. Cyanobacteria numbers and composition of photosynthetic pigments were determined in faeces of captured salps from surface waters, sediment trap material, detritus from plankton hauls, surface sediments from 4500-4800 m depth and Holothurian gut contents. Cyanobacteria were found in all samples containing salp faeces and also in the guts of deep-sea Holothuria. The ratio between zeaxanthin (typical of cyanobacteria) and sum of chlorophyll a pigments was higher in samples from the deep sea when compared to fresh salp faeces, indicating that this carotenoid persisted longer in the sedimenting material than total chlorophyll a pigments. The microscopic and chemical observations allowed us to trace sedimenting salp faeces from the epipelagial to the abyssal benthos, and demonstrated their role as a fast and direct link between both systems. Cyanobacteria may provide a simple tracer for sedimenting phytodetritus.

Pfannkuche, Olaf; Lochte, Karin

1993-04-01

228

Alluvial Pollen on the North China Plain  

NASA Astrophysics Data System (ADS)

Mordern alluvial pollen varies with geomorphic setting and depositional facies in sediments of the Yellow, Hutuo, and Luan rivers and in Baiyangdian and Hengshuihu lakes. Most of the arboreal pollen is derived from the mountains, whereas most of the nonarboreal pollen is derived from the plain itself. Alluvium dominated by Pinuspollen and Selaginellaspores was deposited during a flood. Hydrodynamic sorting of alluvial pollen exists in the sediments of floodplain, central bar, natural levees, and point bar. In reconstructing the ancient vegetation and past climate based on pollen in alluvium, it is important to consider sedimentary facies and geomorphologic setting.

Qinghai, Xu; Xiaolan, Yang; Chen, Wu; Lingyao, Meng; Zihui, Wang

1996-11-01

229

Agriculture on the Chaco Plain, Paraguay, South America  

NASA Technical Reports Server (NTRS)

This view of extensive agriculture on the Chaco Plain, Paraguay, (22.5S, 60.5W) depicts the fertility of the soils between the Andes Mountains and the Paraguay - Parana Rivers in the northwestern Paraguay. The Gran Chaco Plain is flat landscape built up by sediments. Frontier settlements like Marsical Estigarribia, seen in the image, are dominated by agriculture along the stream courses that abound in the area.

1990-01-01

230

Managing contaminated sediments  

Microsoft Academic Search

While remediation and storage of contaminated dredged materials is a key issue at harbour sites, there is another type of\\u000a sediment pollution problem, which mainly originates from large-scale dispersion of contaminants in flood-plains, dike foreshores\\u000a and polder areas. In recent years, catastrophic cases of sediment contaminations have occurred in connection with the failure\\u000a of tailing dams from mines. Unlike problems

Ulrich Förstner; Joachim Gerth; Martina Lindemann; Uwe Wittmann

2001-01-01

231

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

232

Using Breccia-Hosted Spinels of Abyssal Peridotites to Obtain a Representative Local Mantle Composition  

NASA Astrophysics Data System (ADS)

Surprisingly little is known about the extent, scale, and causes of local (outcrop/dredge) heterogeneity in the oceanic mantle. Our primary sources of information are abyssal peridotites, which are fragments of the residual MORB mantle tectonically exposed on the ocean floor at mid-ocean ridges. On a ridge scale it is impossible to objectively pick representative samples for detailed petrological and geochemical analyses, due to analytical limitations and financial restrictions, as well as operator-biased sample selection. This is particularly important for the ultraslow spreading Gakkel Ridge (Arctic Ocean), where thousands of individual peridotite specimens from nearly forty sampling locations are available. Preliminary conventional (i.e. major and trace element mineral analyses in-situ) petrological investigations at Gakkel Ridge have revealed variable dredge-scale heterogeneities, which are related to regional changes in the extent and relative proportion of melting/melt-migration. In order to better assess the extent and distribution of dredge-scale chemical variations, we have separated spinel grains out of carbonate-cemented peridotite breccias that were collected along with normal serpentinized peridotites (and which are common on the ocean floor). The rationale for this is that the spinel clasts may provide a more representative composition of the local outcrop, or slope from which the serpentinite fragments were sedimented by mass wasting. In a pilot study, we selected 29 breccia samples from 7 dredge hauls. For each of these dredge hauls major and trace element mineral data of more than 8 normal residual abyssal peridotite (RAP) samples are available. The major element spinel compositions of the RAP hand specimens (n=95) were then compared with those obtained on breccia-hosted (BH) spinels (n=1300) from the same dredge haul. The agreement between BH spinels and those from the RAP is very good. As expected, BH-spinels cover a larger range than RAP-spinels, although each individual breccia only covers a part of the entire spectrum within a single dredge. This may mean that the spinels are derived quite locally and not mixed much. The Cr#-Ti systematics of the spinels can be used to infer degrees of melting, extent of reaction with percolating melts, and spatial distribution and abundance of dunites channels. Besides spinels from residual peridotites, the breccias host spinels from peridotites affected by high-level melt percolation, such as plagioclase-bearing peridotites or ones affected by crosscutting dykelets. In most cases, it possible to distinguish the non-residual from the residual ones (e.g. dredge D34: 40% residual, 50% dunitic, 10% vein-influenced; n=162). Despite some limitations (higher spinel mode in dunite, possible preferential weathering of dunite), this may prove a useful tool to estimate the local proportions of residual mantle, melt transport channels, and the volume of mantle affected by late-stage crosscutting dykelets.

Hellebrand, E.; Snow, J. E.; Emami, M.; Dick, H. J.

2003-12-01

233

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

234

Northern Great Plains  

USGS Publications Warehouse

We describe waterfowl populations and habitats in the Northern Great Plains; relate habitats and habitat managemnet pratices to annual cycle requirements of migrating and wintering ducks and geese; and suggest management approaches for wintering and migrating waterfowl.

Pederson, R.L.; Jorde, D.G.; Simpson, S.G.

1989-01-01

235

The Plains of Venus  

NASA Astrophysics Data System (ADS)

Volcanic plains units of various types comprise at least 80% of the surface of Venus. Though devoid of topographic splendor and, therefore often overlooked, these plains units house a spectacular array of volcanic, tectonic, and impact features. Here I propose that the plains hold the keys to understanding the resurfacing history of Venus and resolving the global stratigraphy debate. The quasi-random distribution of impact craters and the small number that have been conspicuously modified from the outside by plains-forming volcanism have led some to propose that Venus was catastrophically resurfaced around 725×375 Ma with little volcanism since. Challenges, however, hinge on interpretations of certain morphological characteristics of impact craters: For instance, Venusian impact craters exhibit either radar dark (smooth) floor deposits or bright, blocky floors. Bright floor craters (BFC) are typically 100-400 m deeper than dark floor craters (DFC). Furthermore, all 58 impact craters with ephemeral bright ejecta rays and/or distal parabolic ejecta patterns have bright floor deposits. This suggests that BFCs are younger, on average, than DFCs. These observations suggest that DFCs could be partially filled with lava during plains emplacement and, therefore, are not strictly younger than the plains units as widely held. Because the DFC group comprises ~80% of the total crater population on Venus the recalculated emplacement age of the plains would be ~145 Ma if DFCs are indeed volcanically modified during plains formation. Improved image and topographic data are required to measure stratigraphic and morphometric relationships and resolve this issue. Plains units are also home to an abundant and diverse set of volcanic features including steep-sided domes, shield fields, isolated volcanoes, collapse features and lava channels, some of which extend for 1000s of kilometers. The inferred viscosity range of plains-forming lavas, therefore, is immense, ranging from the extremely fluid flows (i.e., channel formers), to viscous, possibly felsic lavas of steep-sided domes. Wrinkle ridges deform many plains units and this has been taken to indicate that these ridges essentially form an early stratigraphic marker that limits subsequent volcanism to a minimum. However, subtle backscatter variations within many ridged plains units suggest (but do not prove) that some plains volcanism continued well after local ridge deformation ended. Furthermore, many of volcanic sources show little, if any, indications of tectonic modification and detailed analyses have concluded that resurfacing rates could be similar to those on Earth. Improving constraints on the rates and styles of volcanism within the plains could lend valuable insights into the evolution of Venus's internal heat budget and the transition from thin-lid to thick-lid tectonic regimes. Improved spatial and radiometric resolution of radar images would greatly improve abilities to construct the complex local stratigraphy of ridged plains. Constraining the resurfacing history of Venus is central to understanding how Earth-sized planets evolve and whether or not their evolutionary pathways lead to habitability. This goal can only be adequately addressed if broad coverage is added to the implementation strategies of any future mapping missions to Venus.

Sharpton, V. L.

2013-12-01

236

Titan's Plains: Global Distribution and Possible Origin  

NASA Astrophysics Data System (ADS)

Titan's diverse and Earth-like geologic features have been mapped and interpreted based on their morphological characteristics (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, mostly found at mid-latitudes are relatively featureless and appear to have low relief. Their gradational boundaries and paucity of features in SAR data make geologic interpretation particularly difficult using only this dataset. 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 of a possible cryovolcanic origin.

Lopes, R. M.; Le Gall, A.; Kirk, R. L.; Kargel, J. S.; Stofan, E. R.; Mitchell, K. L.; Lucas, A.; Janssen, M. A.; Wall, S. D.; Malaska, M. J.

2012-12-01

237

Holocene lahar deposits in the Whakapapa catchment, northwestern ring plain, Ruapehu volcano (North Island, New Zealand)  

Microsoft Academic Search

The Holocene sedimentary record on the northwestern ring plain of Mount Ruapehu records intermittent volcanic activity over the past 9500 years that is not preserved by primary pyroclastic deposits. The sedimentary record of eruptive activity comprises packages of lahar deposits, representing rapid aggradation of the ring plain in response to increased sediment influx. During these times, large debris flows (calculated

Beth A. Palmer

1991-01-01

238

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

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

Using Eulerian and Lagrangian Approaches to Investigate Wind-Driven Changes in the Southern Ocean Abyssal Circulation  

NASA Astrophysics Data System (ADS)

This study uses a global ocean eddy-permitting climate model to explore the export of abyssal water from the Southern Ocean and its sensitivity to projected twenty-first-century poleward-intensifying Southern Ocean wind stress. The authors investigate the abyssal flow pathways and transport using a combination of Lagrangian and Eulerian techniques. In an Eulerian format, the equator- and poleward flows within similar abyssal density classes are increased by the wind stress changes, making it difficult to explicitly diagnose changes in the abyssal export in a meridional overturning circulation framework. Lagrangian particle analyses are used to identify the major export pathways of Southern Ocean abyssal waters and reveal an increase in the number of particles exported to the subtropics from source regions around Antarctica in response to the wind forcing. Both the Lagrangian particle and Eulerian analyses identify transients as playing a key role in the abyssal export of water from the Southern Ocean. Wind-driven modifications to the potential energy component of the vorticity balance in the abyss are also found to impact the Southern Ocean barotropic circulation.

Spence, Paul; van Sebille, Erik; Saenko, Oleg; England, Matthew

2014-05-01

241

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

242

West Atlantic abyssal circulation during the past 120,000 years  

Microsoft Academic Search

Three faunal assemblages of benthic foraminifera are associated with the three abyssal water masses of the West Atlantic. Faunal distribution 15,000 yr ago indicates cessation of Arctic bottom water flow and a modified supply of Antarctic Water during the last full glacial period, resulting in an apparent warming of the bottom water. Faunal distribution and thus the deep sea circulation

Detmar Schnitker

1974-01-01

243

Recent Decadal Warming and Freshening of Antarctic-Derived Abyssal Waters  

Microsoft Academic Search

Waters of Antarctic origin ventilate much of the abyssal global ocean and a significant fraction of the entire global ocean. WOCE hydrographic sections occupied mostly in the 1990's provide a high-accuracy survey of global water properties. A subset of these sections has been reoccupied in the current decade. Comparison of these repeat sections reveals statistically significant warming in relatively vertically

G. C. Johnson; S. G. Purkey; J. L. Bullister; A. H. Orsi; C. S. Wiederwohl; M. J. Warner; S. Mecking; B. M. Sloyan; S. E. Wijffels; S. C. Doney

2008-01-01

244

Temporal variability in currents and the benthic boundary layer at an abyssal station off central California  

NASA Astrophysics Data System (ADS)

Current meter records from seven sequential moorings were collected during 1993-1996 at an abyssal station off central California (Sta. M; 4100 m depth). The entire 2 1/4-yr time series of the flow at 600, 50, and 2.5 m above bottom (above, near the top of, and within the benthic boundary layer) were analyzed for mean flow statistics and subtidal and tidal variability. The mean current vectors at each altitude were southward at <1 cm s -1, although not significantly different from zero. Spectral analysis revealed energetic mesoscale and seasonal oscillations in the flow, indicated by peaks in principal axis magnitudes at periods of 50-175 days. Tidal (mainly semidiurnal) and inertial forcing contributed to flow variability and influenced the mean principal axis orientation calculated for each record. The highest flow speeds were recorded at 50 m above bottom (with an average of 3.8 cm s -1; maximum 18.2 cm s -1). An examination of monthly-averaged current vectors at this altitude revealed that flow was to the south during the months of highest flow speed (April 1994 and 1995 and October 1994) and to the north and west during the months of lowest flow speed (July 1994 and August 1995). Profiles of light transmission and potential temperature, collected intermittently during the 2 1/4-yr period, showed that the benthic mixed layer at Sta. M extended on average 40 m above bottom (range 15-80 mab). Evidence for local resuspension of recently deposited detritus came from time-lapse photographs of the sea floor that showed a period of near-bottom turbidity that corresponded to a period of high near-bottom flow. However, rough estimates of friction velocity indicated that the bed stress usually was too low at Sta. M to cause local resuspension of sediments. We hypothesize that the observed benthic mixed layers contained suspended particles advected from more energetic areas to the north of Sta. M.

Beaulieu, Stace; Baldwin, Roberta

245

Biostratigraphy Beneath the CCD: Using Agglutinated Foraminifera to correlate abyssal sediments  

NASA Astrophysics Data System (ADS)

The sub-CCD areas of the ocean constitute the world's largest biotope, populated by diverse faunas of agglutinated foraminifera. A reasonable estimate for the diversity of modern agglutinated foraminifera in the deep ocean is a thousand species. Therefore the potential must exist to use their fossils for the purposes of stratigraphic correlation. In spite of over a hundred years of study on this fossil group, the Mesozoic to Cenozoic foraminiferal biostratigraphy of the sub-CCD areas are still only sparsely studied. One of the main focuses of Felix Gradstein's micropalaeontological reseach has been to improve our understanding of agglutinated foraminifera and their applications for biostratigraphy, especially in the northern hemisphere petroleum-producing basins. Over the past 20 years, quantitative biostratigraphical schemes based on agglutinated foraminifera have now been constructed for the Upper Cretaceous to Cenozoic sequences of the Labrador Margin, North Sea, Norwegian Sea, and Barents Sea. These zonal schemes have been correlated to the standard chronostratigraphy by means of planktonic microfossils, and can be compared to the benthic foraminiferal records obtained from North Atlantic DSDP/ODP sites to establish better correlations to the Geological Timescale, and to assess the utility of agglutinated foraminifera ranges and acmes for stratigraphic correlation. In addition to coining the term "flysch-type" agglutinated foraminifera, Felix Gradstein has pioneered the efforts to establish both local and supra-regional zonations using probabilitic methods to and incorporate these microfossils into standard zonal schemes. Although the stratigraphic ranges of agglutinated foraminifera are long in comparison to planktonic foraminifera and in many cases their total ranges are unknown, their high diversity in the North Atlantic offshore basins and the presence of distinctive acmes improves their value for local (basin-wide) biostratigraphical schemes. Both geographical and palaeobathymetrical differences in the ranges of taxa are observed, for example the ranges of some taxa extend to younger levels in the northern part of the Norwegian Sea. Nevertheless, by examining elements in common between the local zonation schemes, we are now much closer to the ultimate goal of defining a "standard" zonal scheme for sub-CCD biostratigraphy using agglutinated foraminifera.

Kaminski, Michael A.

2010-05-01

246

CTD Data from the Madeira and Iberian Abyssal Plains CHARLES DARWIN Cruises 3/85 and 9A/85.  

National Technical Information Service (NTIS)

The report presents lists and graphs of CTD data taken aboard RRS Charles Darwin on cruises 3 (May 1985) and 9A (November 1985). All CTD data is compared with reversing thermometer observations, and with determinations of salinity and dissolved oxygen der...

P. M. Saunders

1986-01-01

247

CTD (Conductivity-Temperature-Depth) Data from the Madeira Abyssal Plain. Charles Darwin Cruise 1/85.  

National Technical Information Service (NTIS)

Lists and graphs of conductivity-temperature-depth (CTD) data taken aboard RRS Charles Darwin during February 1985 for sites considered for high level radioactive waste disposal are presented. The majority of the lowerings were made in support of the deve...

P. M. Saunders

1985-01-01

248

Evaluation of Holocene pollen records from the Romanian Plain  

Microsoft Academic Search

This study is a critical review of pollen analyses carried out on Holocene sequences from 15 sites in and near the Romanian Plain. Three sites come from natural sediments, 10 sites are from anthropogenic deposits and two are from both anthropogenic and natural settings. The general reconstruction is of a steppe-forest-steppe vegetation through the Holocene. The nature of the deposits,

Alexandru Mihail; Florian Tomescu

249

Evaluation of Holocene pollen records from the Romanian Plain  

Microsoft Academic Search

This study is a critical review of pollen analyses carried out on Holocene sequences from 15 sites in and near the Romanian Plain. Three sites come from natural sediments, 10 sites are from anthropogenic deposits and two are from both anthropogenic and natural settings. The general reconstruction is of a steppe–forest–steppe vegetation through the Holocene. The nature of the deposits,

Alexandru Mihail Florian Tomescu

2000-01-01

250

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

251

Formation of Mercury's smooth plains  

Microsoft Academic Search

Indirect evidence is presented for a volcanic origin in the case of two smooth plains on Mercury, the Borealis Planitia and the Hilly and Lineated Terrain. These results, in conjunction with those previously obtained for the circum-Caloris plains and the Tolstoj basin, indicate that smooth plains volcanism was a global process on Mercury. It is further suggested that the smooth

W. S. Kiefer; B. C. Murray

1987-01-01

252

Abyssal peridotite mylonites: implications for grain-size sensitive flow and strain localization in the oceanic lithosphere  

Microsoft Academic Search

Microstructures preserved in abyssal peridotites dredged from the oceans record several different physical regimes of deformation. Fabrics associated with deformation processes at slow-spreading mid-ocean ridges form two major classes of abyssal peridotites based on detailed microstructural observations. The most abundant class are medium- to coarse-grained tectonites with microstructures that reflect deformation processes during mantle upwelling and emplacement to the base

G. E. Jaroslow; G. Hirth; H. J. B. Dick

1996-01-01

253

Flood hydrology and methylmercury availability in Coastal Plain rivers  

USGS Publications Warehouse

Mercury (Hg) burdens in top-predator fish differ substantially between adjacent South Carolina Coastal Plain river basins with similar wetlands coverage. In the Congaree River, floodwaters frequently originate in the Blue Ridge and Piedmont regions, where wetlands coverage and surface water dissolved methylmercury (MeHg) concentrations are low. Piedmont-driven flood events can lead to downward hydraulic gradients in the Coastal Plain riparian wetland margins, inhibiting MeHg transport from wetland sediments, and decreasing MeHg availability in the Congaree River habitat. In the adjacent Edisto River basin, floodwaters originate only within Coastal Plain sediments, maintaining upward hydraulic gradients even during flood events, promoting MeHg transport to the water column, and enhancing MeHg availability in the Edisto River habitat. These results indicate that flood hydrodynamics contribute to the variability in Hg vulnerability between Coastal Plain rivers and that comprehensive regional assessment of the relationship between flood hydrodynamics and Hg risk in Coastal Plain streams is warranted.

Bradley, Paul M.; Journey, Celeste A.; Chapelle, Francis H.; Lowery, Mark A.; Conrads, Paul A.

2010-01-01

254

Flood hydrology and methylmercury availability in coastal plain rivers.  

PubMed

Mercury (Hg) burdens in top-predator fish differ substantially between adjacent South Carolina Coastal Plain river basins with similar wetlands coverage. In the Congaree River, floodwaters frequently originate in the Blue Ridge and Piedmont regions, where wetlands coverage and surface water dissolved methylmercury (MeHg) concentrations are low. Piedmont-driven flood events can lead to downward hydraulic gradients in the Coastal Plain riparian wetland margins, inhibiting MeHg transport from wetland sediments, and decreasing MeHg availability in the Congaree River habitat. In the adjacent Edisto River basin, floodwaters originate only within Coastal Plain sediments, maintaining upward hydraulic gradients even during flood events, promoting MeHg transport to the water column, and enhancing MeHg availability in the Edisto River habitat. These results indicate that flood hydrodynamics contribute to the variability in Hg vulnerability between Coastal Plain rivers and that comprehensive regional assessment of the relationship between flood hydrodynamics and Hg risk in Coastal Plain streams is warranted. PMID:21080644

Bradley, Paul M; Journey, Celeste A; Chapelle, Francis H; Lowery, Mark A; Conrads, Paul A

2010-12-15

255

Formation of Mercury's smooth plains  

SciTech Connect

Indirect evidence is presented for a volcanic origin in the case of two smooth plains on Mercury, the Borealis Planitia and the Hilly and Lineated Terrain. These results, in conjunction with those previously obtained for the circum-Caloris plains and the Tolstoj basin, indicate that smooth plains volcanism was a global process on Mercury. It is further suggested that the smooth and intercrater plains may have resulted from two separate volcanic episodes, with smooth plains volcanism being a consequence of Caloris impact-triggering. 45 references.

Kiefer, W.S.; Murray, B.C.

1987-12-01

256

ROLE OF LAND USE AND BMPS IN REDUCING THE EFFECT OF EXTREME MAGNITUDE EVENTS ON SEDIMENT AND POLLUTANT TRANSPORT IN THE SE US COASTAL PLAIN AND MISSISSIPPI ALLUVIAL VALLEY  

EPA Science Inventory

Suspended sediment is a major non-point source pollutant of surface waters. Best management practices (BMPs) and current landuse decisions may not be sufficient to protect water quality in a changing climate, as a result of a loss of efficiency at reducing suspended sedimen...

257

Species composition and distribution of bivalves in bathyal and abyssal depths of the Sea of Japan  

NASA Astrophysics Data System (ADS)

Twenty-six bivalve species collected by four Russian (1972, 1976, 1985, 2005) and Russian-German (2010) expeditions in the bathyal and abyssal depths of the Sea of Japan (465-3435 m) are listed with the material examined and illustrated. Taxonomic decisions herein: Robaia habei Scarlato, 1981 is synonymized with Nuculana (Robaia) robai (Kuroda, 1929); following Scarlato (1981) and Coan et al. (2000)Dacrydium nipponicum Okutani, 1975 and Dacrydium minimum Okutani and Izumidate, 1992 are synonymized with Dacrydium vitreum (Möller, 1842); Maorithyas yamatotaensis Okutani and Izumidate, 1992 is synonymized with Adontorhina cyclia Berry, 1947; Axinopsida rubiginosa Okutani and Izumidate, 1992 is synonymized with Mendicula ferruginosa (Forbes, 1844); Cardiomya lindbergi batialis Scarlato, 1972 is synonymized with Cardiomya tosaensis (Kuroda, 1948); Cuspidaria sadoensis Okutani and Ito, 1983 is synonymized with Cuspidaria ascoldica Scarlato, 1972; Cyclocardia rjabininae (Scarlato, 1955) recognized as valid and distinct from Cyclocardia ovata (Rjabinina, 1952). The deep-water bivalve fauna of the Sea of Japan is characterized by an impoverished shelf fauna and consists of eurybathic species that extend from the shelf to the bathyal and abyssal zones. Most of them have a wide geographic distribution and inhabit cold water regions of the Northern Atlantic, Northern Pacific, and Arctic Ocean. Only five species are endemic to the Sea of Japan. With increase in depth, the species richness of bivalves decreases. In the depth range from 200 to 1600 m, all species (26) found in the deep Sea of Japan were recorded, while only 10 species were recorded in the lower bathyal slope (1700-3000 m). At depths below 3000 m, only D. vitreum, Delectopecten vancouverensis (Whiteaves, 1893), and Thyasira (Parathyasira) sp. were found. The lack of typical abyssal species of bivalves in the deep Sea of Japan is probably connected with the isolation of this body of water from the Pacific abyssal depths.

Kamenev, Gennady M.

2013-02-01

258

Spatially heterogeneous diapycnal mixing in the abyssal ocean: A comparison of two parameterizations to observations  

NASA Astrophysics Data System (ADS)

The spatial distributions of the diapycnal diffusivity predicted by two abyssal mixing schemes are compared to each other and to observational estimates based on microstructure surveys and large-scale hydrographic inversions. The parameterizations considered are the tidal mixing scheme by Jayne, St. Laurent and co-authors (JSL01) and the Roughness Diffusivity Model (RDM) by Decloedt and Luther. Comparison to microstructure surveys shows that both parameterizations are conservative in estimating the vertical extent to which bottom-intensified mixing penetrates into the stratified water column. In particular, the JSL01 exponential vertical structure function with fixed scale height decays to background values much nearer topography than observed. JSL01 and RDM yield dramatically different horizontal spatial distributions of diapycnal diffusivity, which would lead to quite different circulations in OGCMs, yet they produce similar basin-averaged diffusivity profiles. Both parameterizations are shown to yield smaller basin-mean diffusivity profiles than hydrographic inverse estimates for the major ocean basins, by factors ranging from 3 up to over an order of magnitude. The canonical 10-4 m2 s-1abyssal diffusivity is reached by the parameterizations only at depths below 3 km. Power consumption by diapycnal mixing below 1 km of depth, between roughly 32°S and 48°N, for the RDM and JSL01 parameterizations is 0.40 TW & 0.28 TW, respectively. The results presented here suggest that present-day mixing parameterizations significantly underestimate abyssal mixing. In conjunction with other recently published studies, a plausible interpretation is that parameterizing the dissipation of bottom-generated internal waves is not sufficient to approximate the global spatial distribution of diapycnal mixing in the abyssal ocean.

Decloedt, Thomas; Luther, Douglas S.

2012-11-01

259

Temporal variability in currents and the benthic boundary layer at an abyssal station off central California  

Microsoft Academic Search

Current meter records from seven sequential moorings were collected during 1993–1996 at an abyssal station off central California (Sta. M; 4100m depth). The entire 214-yr time series of the flow at 600, 50, and 2.5m above bottom (above, near the top of, and within the benthic boundary layer) were analyzed for mean flow statistics and subtidal and tidal variability. The

Stace Beaulieu; Roberta Baldwin

1998-01-01

260

Determination of Fault Friction from Reactivation of Abyssal-Hill Faults in Subduction Zones  

Microsoft Academic Search

Abyssal-hill faults accommodate extension of newly formed crust near spreading centers, but become inactive within 50 km of the ridge axis. These faults remain inactive as they are transported across the ocean basin until they reach the outer-slope of trenches, where they are reactivated when they strike within 25° (transition angle) from trench-parallel; otherwise, new faults form parallel to the

M. I. Billen; E. Cowgill

2006-01-01

261

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

262

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

263

Polygon-Cracked Plain  

NASA Technical Reports Server (NTRS)

21 July 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a polygon-cracked plain in the south polar region of Mars. When this picture was acquired in April 2005, the surface was covered with seasonal carbon dioxide frost. Dark spots and streaks indicate areas where the frost had begun to change and sublime away.

Location near: 86.8oS, 300.5oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

2005-01-01

264

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.23-24 of the "One With the Earth: Native Americans and the Natural World" multidisciplinary unit of study for kindergarten through third grade.

Indianapolis, The C.

2014-04-30

265

Uranium and thorium series isotopes as indicators of geochemical processes in recent Venezuela Basin sediments  

SciTech Connect

Several uranium and thorium series isotopes are important indicators of abyssal geochemical and physical processes: sedimentation, bioturbation, compaction, dissolution and precipitation. This research was designed to investigate the relative importance of each of these on early sediment diagenesis in different abyssal environments. Sediment samples were collected from three different sedimentary environments from the Venezuela Basin. Samples were designated as pelagic carbonate, hemipelagic and turbidite-rich, based on bulk sediment characteristics. Selected members of the U and Th radioisotope series ({sup 238}U, {sup 234}U, {sup 230}Th, {sup 226}Ra, {sup 210}Pb, and {sup 232}Th), {sup 14}C, and anthropogenic {sup 239,240}Pu were determined on selected intervals. Other sedimentary parameters, including porosity, calcium carbonate content, stable isotopes, macrofaunal abundances, organic carbon and grain size, were measured or available from the literature. A model, based on the constancy of {sup 230}Th production in sea water, was developed to determine fine-scale sedimentation rates for the last 14 ky, 6 ky, and 2 ky for sediments from pelagic carbonate, hemipelagic and turbidite-rich environments, respectively. Nannofossil {delta}{sup 13}C values correlated well with carbonate accumulation rates. {sup 226}Ra fluxes across the sediment/sea water interface were estimated from losses in the expected {sup 226}Ra activities. {sup 226}Ra fluxes across the interface were low due to low {sup 230}Th activities. A multi-layer explicit finite difference model was developed to simulate the effects of diffusive and advective bioturbation on the distributions of {sup 210}Pb and {sup 239,240}Pu in abyssal sediments.

Cole, K.P.H.

1988-01-01

266

Trophic transition in a lake on the Virginia coastal plain.  

PubMed

To examine possible connections between lake trophic status and runoff from surrounding subwatersheds, we determined patterns of sediment and nutrient deposition in a hypereutrophic, 16-ha impoundment on the Virginia coastal plain. Spatial survey of nutrients in surface sediments documented a strong correlation between total P and extractable Fe (r2 = 0.53). Elevated biogenic silica concentrations up to 0.25% by weight were measured in sections of the lake receiving perennial stream discharge. Sediment C to N ratios were > 20 in those same sections, suggesting a large allochthonous contribution to organic matter deposition. Sediment cores 0.9 to 2.3 m in length, representing 70 years of deposition, were analyzed to develop vertical profiles of changes in sediment and nutrient deposition in deltas downstream from two more-developed and three less-developed subwatersheds (with 49 and 9% commercial and residential development, respectively). The average sediment weight percent +/- standard deviation of biogenic silica (0.027 +/- 0.037 vs. 0.009 +/- 0.006%) and total P (0.040 +/- 0.025 vs. 0.024 +/- 0.019%) was significantly higher downstream of more-developed subwatersheds. Using elevated P loadings and biogenic silica deposition as proxies for algal production, transition of the lake to its current hypereutrophic state appears to have occurred in the last 70 yr. Changes in trophic status as revealed by sediment analysis of this small lake on the Virginia coastal plain reflect a common pattern of eutrophication observed for the entire Chesapeake Bay drainage basin. Analysis of sediments from stream deltas appears to be a reasonable strategy for identifying and targeting subwatershed areas needing better management of nutrient runoff that otherwise would lead to eutrophication of downstream waters. PMID:15074809

Pensa, Mellisa A; Chambers, Randolph M

2004-01-01

267

Hidden in Plain Sight  

NSDL National Science Digital Library

Steganography is the science and art of hiding messages in plain sight so only the sender and intended recipient know the existence of a message. Steganography can be characterized as security through obscurity. Through this lesson, students experience a portion of the engineering design process as they research steganography and steganographic methods; identify problems, criteria and constraints; brainstorm possible solutions; and generate ideas. These are the critical first steps in the engineering design process, often overlooked by students who want to get to the "doing" phasesâdesigning, building and testing. In computer science, a thorough design phase makes program implementation much easier and more effective. Students obtain practice with a portion of the design process that may be less exciting, but is just as important as the other steps in the process.

IMPART RET Program, College of Information Science & Technology,

268

Determination of Fault Friction from Reactivation of Abyssal-Hill Faults in Subduction Zones  

NASA Astrophysics Data System (ADS)

Abyssal-hill faults accommodate extension of newly formed crust near spreading centers, but become inactive within 50 km of the ridge axis. These faults remain inactive as they are transported across the ocean basin until they reach the outer-slope of trenches, where they are reactivated when they strike within 25° (transition angle) from trench-parallel; otherwise, new faults form parallel to the trench. Preferential reactivation of appropriately-oriented abyssal-hill faults suggests that although these faults may heal and re-strengthen as they cross the ocean basin they remain zones of weakness, but how weak? The coefficient of sliding friction and coefficient of internal friction are similar in laboratory experiments (0.6--1.0), in which failure obeys Byerlee's Law. However, pre-existing faults with significant displacement appear to be weaker than surrounding rock, although the degree of weakening is difficult to constrain. In addition, formation of clays (or serpentinites at slow spreading ridges) due to hydrothermal activity at the ridge may reduce the coefficient of friction to values 0.2--0.5. We use a 3D Mohr Circle failure analysis and the observed transition angle to constrain the coefficient friction on reactivated abyssal-hill faults. The analysis assumes that the maximum principal stress, which is vertical, is due to the lithostatic stress (overburden), the intermediate stress, which is trench-parallel, is due to Poisson expansion (elastic restoring force), and that faulting occurs due to bending-induced extension perpendicular to the trench. If we assume that new faults, which form parallel to the trench, obey Byerlee's Law, then determination of the coefficient of sliding friction on reactivated faults is independent of the absolute value of the principal stresses and depends only on the Poisson ratio of the crust and the coefficient of friction on new faults. We find that reactivated faults, dipping at 45°, are 30% weaker than surrounding crust and have a coefficient of friction of 0.6. These results suggest that while abyssal-hill faults represent a pre-existing weakness, the strength anisotropy in the oceanic crust is small, and the coefficient of sliding friction on crustal-scale oceanic faults is consistent with that observed in the laboratory.

Billen, M. I.; Cowgill, E.

2006-12-01

269

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

270

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

271

Determination of fault friction from reactivation of abyssal-hill faults in subduction zones  

NASA Astrophysics Data System (ADS)

Abyssal-hill faults are reactivated on the outer slope of trenches when they strike within 25° from trench parallel; otherwise, new faults form parallel to the trench. We use the observed transition angle (25°) and a three-dimensional failure analysis to determine the coefficient of friction on reactivated abyssal-hill faults. The stress state in the outer slope is modeled as the superposition of the overburden stress and bending-induced plane strain deformation. If new trench-parallel faults fail according to a linear failure relationship with no cohesion, then determination of the coefficient of sliding friction (?s) on reactivated faults is independent of the absolute value of the principal stresses and depends only on the Poisson ratio of the crust and the slope of the failure law for new faults (?f). We find that reactivated faults, dipping at 45°, are ˜30% weaker than surrounding crust (e.g., ?s = 0.6 for ?f = 0.85). These results suggest that the variation in the strength of oceanic crust due to the seafloor spreading fabric is small, and that the coefficient of sliding friction on oceanic faults is consistent with that observed in the laboratory.

Billen, M.; Cowgill, E.; Buer, E.

2007-09-01

272

On the frictional destabilization of abyssal overflows dynamically coupled to internal gravity waves  

NASA Astrophysics Data System (ADS)

In the immediate vicinity of a sill, abyssal overflows can possess current speeds greater the local long internal gravity wave speed with bottom friction and downslope gravitational acceleration playing a dominant role in the dynamics. The transition to instability is described of supercritical frictional abyssal overflows on a super-inertial time scale (where rotation, and hence along slope motion, is secondary), but where there is dynamic coupling between the overflow and gravest-mode internal gravity waves in the overlying water column. It is shown that dynamical coupling with ambient internal gravity waves leads to a significant ‘up or blue spectrum’ shift in the frequencies, wavelengths and growth rates as compared to an instability theory without dynamical coupling. For oceanographically relevant parameter values, the most unstable mode has been found to have a wavelength of about 484 ?m, an e-folding amplification time of about 13 min, a geostationary period of about 17 min and propagates in a retrograde manner with a co-moving period of about 19 min.

Swaters, Gordon E.

2006-02-01

273

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

274

Major Elements Budget Between Abyssal Peridotite And Seawater During The Serpentinization  

NASA Astrophysics Data System (ADS)

Water-Rock Interaction is one of the most hot-debated issues among geologists, geophysicists, as well as geochemists. Abyssal peridotites recovered from the seafloor are often greatly affected or alterated by seawater in the form of serpentinization. The alteration to the peridotites makes it difficult to do the straightforward analysis for its primary composition as it was settled in the upper mantle, which confine the usage of these rare direct samples from the mantle in the scientific study, such as mantle dynamics, mantle composition and crust-mantle interaction. Besides, It was revealed recently that the serpentinization of abyssal peridotites may give birth to the hydrothermal activity. The elements migration during the serpentinization may perform a great role on the chemical composition of the hydrothermal fluid, which can support a hidden chemosynthetic ecosystem in the abyssal seabed. The research work focused on the major elements behavior during the serpentinization by studying the partially serpentinized samples of abyssal peridotite from Southwest Indian Ridge. The primary mineral assemblage of peridotite is olivine (Mg2SiO4), orthopyroxene (Mg2Si2O6), clinopyroxene (CaMgSi2O6) and spinel ((Mg,Fe)(Al,Cr)2O4). The major chemical composition are usually as SiO2 (30~45wt.%), MgO (20~45 wt.%), FeO and Fe2O3 (total 5~15 wt.%). Besides there are very few MnO, CaO, Al2O3, Cr2O3, NiO, Na2O, K2O and H2O. While on the other hand the serpentinized peridotite shows a more complicated mineral assemblage, besides the primary minerals there are more alteration minerals, such as serpentine (Mg3[Si2O5](OH)4), magnetite (Fe3O4), talc (Mg3[Si4O10](OH)2), brucite (Mg(OH)2), tremolite (Ca2Mg5[Si8O22](OH)2), chromite (FeCr2O4), chlorite ((Mg,Fe)6[(Si,Al)4O10](OH)8), and other accessary minerals like native metals, sulfides, clay minerals and hornblende. According to the EMPA analysis, the serpentinized sample shows the chemical composition as SiO2(~40 wt.%), MgO(~30 wt.%), total FeO(~7 wt.%), Al2O3(~1 wt.%), MnO(~0.4 wt.%), Cr2O3(~0.3 wt.%), NiO(~0.2 wt.%), CaO(~0.2 wt.%), and very few TiO2, Na2O and K2O. The overall percentages for all the elements mentioned above are usually around 80wt.%, about 20% less than full percent, which indicates the volatile matters in the altered samples. Based on the preliminary study, we get the general picture for the major elements behavior during the alteration. Taking the abyssal peridotite for example, it gains large quantities of H and O in the form of H2O, and other volatile elements like F, Cl, B from the seawater during serpentinization. It may also get additional Na, K, Mg from the seawater as shown from the standardized concentration in primary minerals as well as altered minerals. It loses Fe, Al, Ca, Si during the serpentinization seen from the EMPA mapping results. The element Mn, Cr and Ni are relatively immobile during the alteration. To get more precise deduction as to the element budget during the alteration process, much more sensitive analytical instruments like LA-ICP-MS are needed. And more work need to be done to get the quantitive estimation for transferring rate of each element.

Yu, X.; Dong, Y.; Li, X.; Chu, F.

2012-12-01

275

The Interior Lowland Plains Unit of Mars: Evidence for a Possible Mud Ocean and Induced Tectonic Deformation  

NASA Technical Reports Server (NTRS)

We conclude from MOC and MOLA data that the northern plains of Mars were infilled by a sediment-rich, mud ocean. Evidence for subsidence within the north polar basin and reversed channel-floor gradients are consistent with tectonic deformation due to the sediment load.

Tanaka, K. L.; Banerdt, W. B.

2000-01-01

276

Bathymetric patterns of deep-sea benthic communities from bathyal to abyssal depths in the western South Pacific (Solomon and Coral Seas)  

NASA Astrophysics Data System (ADS)

Ten stations were sampled from bathyal to abyssal depths (695-4350 m) in the Solomon and Coral Seas to determine variations in densities of Protozoa, meiofauna and macroinfauna in relation to environmental conditions and bacterial densities and productivity. Densities of large flagellates and amoebae did not change with water depth, whereas the abundance of other microbenthic groups either decreased (Foraminifera, ciliates) or increased (yeasts) significantly with increasing ocean depth. Numerically, the microbenthos was dominated by Foraminifera, followed in decreasing order of abundance by yeasts, large flagellates, amoebae and ciliates. Densities of total metazoan meiofauna and macroinfauna were low at most stations compared to communities of other regions at equivalent depths, and declined significantly with ocean depth, although many taxa and total macroinfaunal biomass did not. Differences in the rate of decline between total metazoan meiofaunal and macroinfaunal densities with depth were not significant. When the effect of water depth was held constant, only a few protozoan, meiofaunal and macroinfaunal taxa correlated with bacteria and sediment characteristics. Depth-related variables (e.g. low temperatures) appear to be the dominant factors regulating bathymetric patterns. However, there is some evidence that rapid transport of turbidites and other shallow-water materials (wood, vascular plant and fresh algal detritus) lead to episodes of erosion and deposition that may influence the distribution and standing crop of these deep-sea benthic communities. These events may be influential in other tectonically active basins within tropical oceans bordered by steep continental margins and dominated by extensive reefs and large rivers.

Alongi, Daniel M.

1992-04-01

277

Distribution of Particulate Organic Carbon and Radiocarbon in the Water Column from the Upper Slope to the abyssal NE Pacific Ocean  

NASA Astrophysics Data System (ADS)

We report profiles of concentrations and radiocarbon contents of suspended particulate organic carbon (POC susp) and sedimentary organic carbon from an abyssal site (Stn M) in the northeast (NE) Pacific collected in September 1994 (a period of very high flux of particulate carbon in the deep sea) and June 1995, as well as from stations on the continental rise and slope off the coast of California in June 1995. We show that during a period of anomalously high sinking POC flux to the deep sea (September 1994), ? 14C of suspended POC did not decrease detectably between 85 and 1600 m depth. This is in contrast to depth profiles during low and moderate fluxes of sinking POC at this station where ? 14C-POC susp decreased 50-60‰ in this depth range. One explanation for the constant ? 14C values of POC susp between 85 and 1600 m is that large quantities of sinking POC could continuously release labile, 14C-enriched POC susp during biological and chemical alteration of the sinking POC. The radiocarbon evidence further suggests that resuspension of organic carbon from the sediment surface, either locally or laterally transported from the slope to the deep sea, is likely, but is probably limited to depths within a few hundred meters of the bottom. Sorption of 'old' DOC by suspended particulate matter in the water column is also possible, especially at shallower depths (<3500 m), though proof of this mechanism cannot be demonstrated at this time.

Druffel, E. R. M.; Griffin, S.; Bauer, J. E.; Wolgast, D. M.; Wang, X.-C.

278

Petrological, Magnetic and Chemical Properties of Basalt Dredged from an Abyssal Hill in the North-East Pacific.  

National Technical Information Service (NTIS)

A sample of basalt was retrieved from a low-relief (100 m) fault scarp on the side of an abyssal hill in the north-east Pacific (32 degrees 25 minutes N, 125 degrees 45 minutes W). Thin section examination shows the basalt to be a fine grained labradorite...

B. P. Luyendyk C. G. Engel

1969-01-01

279

Os Isotopic Signature of Backarc Abyssal Peridotites from the Godzilla Megamullion  

NASA Astrophysics Data System (ADS)

Backarc seafloor spreading is a unique form of extension intimately tied to subduction zone dynamics. Unlike volcanism at mid-ocean ridges, backarc volcanism evolves from arc-like to MORB-like compositions over the short lifespan (~15 Ma) of the backarc. Our understanding of the evolution of oceanic mantle during backarc extension is limited to exposures of abyssal peridotite and ophiolites. While some ophiolites are thought to have formed in a backarc environment, few direct comparisons of ophiolite and backarc peridotite have been made due to the dearth of documented exposures and limited in situ samples from backarc settings. As a consequence, isotopic investigations have thus far been limited to ophiolite and mid-ocean ridge settings, limiting our understanding of the backarc oceanic mantle. Here we report preliminary Os isotopic data for backarc abyssal peridotites from the Godzilla Megamullion, a massive ~9000 km2 oceanic core complex located in the Parece Vela Basin (Philippine Sea). In this region, Izu-Bonin-Mariana subduction zone is responsible for creating the Parece Vella and Shikoku backarc basins as well as the Mariana Trough. In the last decade, five expeditions have collectively sampled the length of the Godzilla Megamullion. The distal end records early, magmatically productive extension marked by moderately depleted spinel peridotites. This transitions into a less melt-productive medial region characterized by more fertile peridotite. The proximal region represents the most recently exhumed portion of the megamullion and was the focus of the latest (October 2011) mapping and sampling expedition. Ultramafic samples from the proximal region are dominantly spinel lherzolite +/- plagioclase. Spinel grains record high TiO2 and Cr# produced by melt stagnating and interacting with the mantle. Whole rock 187Os/188Os (0.1245-0.1295) ranges from mildly subchondritic to PUM values, consistent with abyssal peridotites from mid-ocean ridge settings. The isotopic data suggest that the backarc oceanic mantle in this region did not experience significant ancient melt depletion. The Os isotopic values close to PUM (0.1296; Meisel et al., 2001) may be the result of seawater interaction. However, we argue these data are the product of melts mingling with the peridotite, thus generating a slightly more radiogenic isotopic signature over time.

Nelson, W. R.; Snow, J. E.; Ohara, Y.; Brandon, A. D.

2012-12-01

280

Aerosols Over Yellow Sea Sediments  

NASA Technical Reports Server (NTRS)

This SeaWiFS image shows complex phytoplankton distribution patterns in the Bohai and Yellow seas. A wide band of brownish water along the coast north and south of the mouth of the Yangtze River indicates a heavy load of suspended sediment. The air over eastern central China and the Yellow Sea is thick with aerosols. Farther north over the Manchurian Plain and Greater Khingan Range, the air is much clearer.

2002-01-01

281

Abyssal recipes  

Microsoft Academic Search

Vertical distributions in the interior Pacific (excluding tbe top and bottom kilometer) are not inzonsistent with a simple model involving a constant upward vertical velozity w ~ 1-2 cm clu y-t and eddy diffusivity ,¢ ~ 1.3 cm ~- sec -1. Thus temperature and salinity can be fitted by exponential- like solutions to (,¢- d\\

WALTER H. MUNK

1966-01-01

282

Northern Plains Of Mars  

NASA Technical Reports Server (NTRS)

This rocky panoramic scene is the second picture of the Martian surface that was taken by Viking Lander 2 shortly after touchdown on September 3 at 3:58 PM PDT (Earth received time). The site is on a northern plain of Mars, at about 48 N. Lat., 226 W. Long., known as Utopia Planitia. The picture sweeps around 330 degrees in azimuth, starting from northwest at the left through north (above the sampler arm housing) past east, where the sky is bright at the center, and southeast toward the right above the radioisotope thermoelectric generator cover. The surface is strewn with rocks out to the horizon, ranging in size up to several meters across. Some pitted rocks resemble fragments of porous volcanic lava. Other rocks have grooves that may have been eroded by windblown sand and dust. Although fine-grained material is seen between the boulders, no sand dunes are evident. The dip in the eastern horizon at the center is an illusion caused by an 8-degree tilt of the Lander toward the west. Actually, the terrain is more level than that at the Viking 1 site. The horizon toward the left of the panorama (northwest) appears featureless, indicating that it may be several kilometers distant. The sky at the center (east) is bright because the sun was above but out of the picture at 10 AM Mars time. Toward the right (southeast), the rocks that are silhouetted against the skyline indicate that the horizon is much nearer, probably because of a slight rise in that area of the terrain. The circular high-gain antenna at the right has clots of fine-grained material adhering to the lower half, some of which appeared to have been sliding downward while the camera was scanning the area. At the extreme right, the banded appearance resulted because the camera continued to scan while it was no longer moving in azimuth. Any motion or other variation in the scene would show up as a change in successive lines.

1976-01-01

283

Paleoenvironmental interpretation of an ancient Arctic coastal plain: Integrated paleopedology and palynology from the Late Cretaceous (Maastrichtian) Prince Creek Formation, North Slope, Alaska, USA  

Microsoft Academic Search

The Cretaceous (Early Maastrichtian), dinosaur-bearing Prince Creek Formation, North Slope, Alaska, records high-latitude, alluvial sedimentation and soil formation on a low-lying, coastal plain during a greenhouse phase in Earth history. This study combines outcrop observations, micromorphology, geochemistry, and palynological analyses of paleosols in order to reconstruct local paleoenvironments of weakly developed, high-latitude coastal plain soils. Sediments of the Prince Creek

P. J. McCarthy; P. P. Flaig; A. R. Fiorillo

2010-01-01

284

Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean  

PubMed Central

The deep ocean, covering a vast expanse of the globe, relies almost exclusively on a food supply originating from primary production in surface waters. With well-documented warming of oceanic surface waters and conflicting reports of increasing and decreasing primary production trends, questions persist about how such changes impact deep ocean communities. A 24-y time-series study of sinking particulate organic carbon (food) supply and its utilization by the benthic community was conducted in the abyssal northeast Pacific (?4,000-m depth). Here we show that previous findings of food deficits are now punctuated by large episodic surpluses of particulate organic carbon reaching the sea floor, which meet utilization. Changing surface ocean conditions are translated to the deep ocean, where decadal peaks in supply, remineralization, and sequestration of organic carbon have broad implications for global carbon budget projections.

Smith, Kenneth L.; Ruhl, Henry A.; Kahru, Mati; Huffard, Christine L.; Sherman, Alana D.

2013-01-01

285

Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean.  

PubMed

The deep ocean, covering a vast expanse of the globe, relies almost exclusively on a food supply originating from primary production in surface waters. With well-documented warming of oceanic surface waters and conflicting reports of increasing and decreasing primary production trends, questions persist about how such changes impact deep ocean communities. A 24-y time-series study of sinking particulate organic carbon (food) supply and its utilization by the benthic community was conducted in the abyssal northeast Pacific (~4,000-m depth). Here we show that previous findings of food deficits are now punctuated by large episodic surpluses of particulate organic carbon reaching the sea floor, which meet utilization. Changing surface ocean conditions are translated to the deep ocean, where decadal peaks in supply, remineralization, and sequestration of organic carbon have broad implications for global carbon budget projections. PMID:24218565

Smith, Kenneth L; Ruhl, Henry A; Kahru, Mati; Huffard, Christine L; Sherman, Alana D

2013-12-01

286

The crustacean scavenger guild in Antarctic shelf, bathyal and abyssal communities  

NASA Astrophysics Data System (ADS)

Peracarid crustaceans form a significant part of the macrobenthic community that is responsible for scavenging on large food falls onto the sea floor. Although several studies are available about scavengers from tropical and temperate seas, very little information has been published about such species living in Antarctic waters, particularly at greater depths. The present paper is based on a collection of 31 baited trap sets deployed in the Weddell Sea, Scotia Sea, and off the South Shetland Islands, and presents results on the geographical and bathymetric distribution of the different taxa and on the eco-functional role of scavengers. Some 68,000 peracarid crustaceans from 62 species were collected. About 98% of individuals belonged to the amphipod superfamily Lysianassoidea, and 2% to the isopod family Cirolanidae. Of these species, 31, including 26 lysianassoids (1400 individuals), were collected deeper than 1000 m. High species richness was discerned for the eastern Weddell Sea shelf compared with other Antarctic areas. The Antarctic slope also seems to be richer in species than other areas investigated in the world, while in the abyss, scavenger species richness appears to be lower in Antarctica. A richness gradient was thus observed from the shelf to the deep. For amphipods, a number of species extend their distribution from the shelf to the slope and only one to the abyssal zone. Amphipod species showed degrees of adaptation to necrophagy. The functional adaptations of the mandible and the storage function of the gut are discussed. Feeding experiments conducted on lysianassoid species collected at great depths and maintained in aquaria showed a mean feeding rate of about 1.4-4.1% dry body weight day -1, which is consistent with data obtained from other species.

De Broyer, Claude; Nyssen, Fabienne; Dauby, Patrick

2004-07-01

287

Establishment of Rio Grande Cottonwood Seedlings Using Micro-irrigation of Xeric Flood Plain Sites  

Microsoft Academic Search

Flood control, irrigation structures, and flow control practices on the Middle Rio Grande have prevented the deposition of sediments and hydrologic conditions conducive to the germina- tion and establishment of Rio Grande cottonwood (Populus fremontii S. Wats.). The Los Lunas Plant Materials Center has been investi- gating the use of micro-irrigation systems on xeric flood plain sites to promote regeneration

David R. Dreesen; Gregory A. Fenchel; Joseph G. Fraser

288

Sedimentological and morphological characteristics of some nabkha deposits in the northern coastal plain of Kuwait, Arabia  

Microsoft Academic Search

Nabkhas in the sabkha flat of the northern coastal plain of Kuwait are generallylocated in areas slightly higher than the evaporitic sabkha pans, and facing the alluvium fans descending from the bordering cliffs and slopes. They are developed by the deposition of wind-driven sediments around Nitraria retusa shrubs. The nabkhas vary in shape and size. However, they mostly have an

F. I. Khalaf; R. Misak; A. Al-Dousari

1995-01-01

289

Seismic Images of the Southwestern Tip of the Okinawa Trough - the Ilan Plain, Taiwan  

NASA Astrophysics Data System (ADS)

The Ilan Plain is situated at the southwestern tip of the Okinawa trough. The triangle-shaped Ilan Plain is bounded by the Shiehshan range in the northwest and the Central range in the south. Although there were many studies conducted, subsurface structure of the Ilan Plain was still not clear. In this paper, we use 19 shallow seismic reflection profiles to reveal the subsurface structure beneath the Ilan Plain. Results of the study should be able to provide a preliminary three dimensional image for understanding the sediments deposited and the active structures beneath the plain. Integrating seismic images with the interval velocities and results from core borings, we may find that the Ilan Plain is situated on top of a graben. The structure was mainly formed by subsidence of two normal faults; one is located in the south and dipping to the north, and the other is in the north and dipping to the south. In addition to the two main faults, many minor high angle normal faults can be traced in the seismic images as well. On top of the Tertiary basement, we may divide the sediments into two zones by a significant interface, which could be correlated to the age of early Holocene. The depth of the deepest part of the basement was around 880 m, which is located in the center of the Ilan Plain at north of the Lanyang River. From the deepest part of the basement, we may see the depths of the basement were fast reduced to around 550 m toward the south and the north first, and then the variations were become smaller. Subsidence of the graben was gradually reduced along the two normal faults after the early Holocene; therefore, thicknesses of the Holocene sediment from south to northward have only minor variation.

Chen, T.; Shih, R.; Chen, W.

2012-12-01

290

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

291

Genetic Variation in Great Plains Juniperus.  

National Technical Information Service (NTIS)

Fifth-year analyses of Great Plains Juniperus seed sources indicate eastern redcedar should be collected in east-central Nebraska for use throughout the Great Plains; Rocky Mountain juniper seed should be collected from Northwest Nebraska, or central Mont...

D. F. Van Haverbeke R. M. King

1990-01-01

292

PLAINS CO2 REDUCTION PARTNERSHIP  

Microsoft Academic Search

The Plains COâ 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 COâ sequestration opportunities in the PCOR Partnership region. Task 3 (Public Outreach) focused on developing an informational video about COâ

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

2004-01-01

293

PLAINS CO2 REDUCTION PARTNERSHIP  

Microsoft Academic Search

The Plains COâ 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 COâ sequestration opportunities in the PCOR Partnership region. Task 2 efforts also included preparation of a draft topical report entitled

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

2005-01-01

294

PLAINS CO2 REDUCTION PARTNERSHIP  

Microsoft Academic Search

The Plains COâ 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 COâ Sequestration in the PCOR Partnership Region''. Task 3 (Public Outreach) has developed an informational Public Television program entitled ''Nature in the Balance'', about

Edward N. Steadman; John A. Harju; Erin M. OLeary; James A. Sorensen; Daniel J. Daly; Melanie D. Jensen; Lisa S. Botnen

2005-01-01

295

PLAINS CO2 REDUCTION PARTNERSHIP  

Microsoft Academic Search

The Plains Coâ 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 COâ sequestration opportunities in the PCOR Partnership region. Task 3 (Public Outreach) activities have focused on developing an informational video about COâ sequestration.

Edward N. Steadman

2004-01-01

296

PLAINS CO2 REDUCTION PARTNERSHIP  

Microsoft Academic Search

The Plains COâ 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 COâ sequestration opportunities in the PCOR Partnership region. Task 3 (Public Outreach) focused on developing an informational video about COâ

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

2005-01-01

297

'Endurance' Goal Across the Plains  

NASA Technical Reports Server (NTRS)

This mosaic image from the Mars Exploration Rover Opportunity's panoramic camera provides an overview of the rover's drive direction toward 'Endurance Crater,' which is in the upper right corner of image.

The plains appear to be uniform in character from the rovers current position all the way to Endurance Crater. Granules of various sizes blanket the plains. Spherical granules fancifully called blueberries are present some intact and some broken. Larger granules pave the surface, while smaller grains, including broken blueberries, form small dunes. Randomly distributed 1-centimeter (0.4 inch) sized pebbles (as seen just left of center in the foreground of the image) make up a third type of feature on the plains. The pebbles' composition remains to be determined. Scientists plan to examine these in the coming sols.

Examination of this part of Mars by NASA's Mars Global Surveyor orbiter revealed the presence of hematite, which led NASA to choose Meridiani Planum as Opportunity's landing site. The rover science conducted on the plains of Meridiani Planum serves to integrate what the rovers are seeing on the ground with what orbital data have shown.

Opportunity will make stop at a small crater called 'Fram' (seen in the upper left, with relatively large rocks nearby) before heading to the rim of Endurance Crater.

2004-01-01

298

White Plains MetARs  

NSDL National Science Digital Library

In this activity, students use METeorological Aerodome Reports (METARs) to view changes in temperature, dew point, air pressure, sky condition, wind, and visibility at White Plains, New York. After studying the reports, they answer a series of questions related to radiation and insolation, radiative balance, and meteorological processes.

Kluge, Steve

299

Geochemistry of the northern Atlantic Coastal Plain aquifer system  

USGS Publications Warehouse

Sediments of the northern Atlantic Coastal Plain comprise a complex multiaquifer flow system. On a large scale (greater than 500 square miles) ground water in this system evolves from predominantly calcium magnesium bicarbonate water with a low dissolved-solids content and low pH, near outcrop-recharge areas, to predominantly sodium bicarbonate water with a high-dissolved solids content and high pH, downgradient. This sodium bicarbonate water then grades into a sodium chloride water. This large-scale predictable progression of hydrochemical facies results from the summation of many smaller scale geochemical processes that chiefly depend on the sedimentary depositional environments of the aquifers.

Knobel, L. L.; Chapelle, F. H.; Meisler, Harold

1998-01-01

300

The formation of Mercury's smooth plains  

Microsoft Academic Search

There has been extensive debate about whether Mercury's smooth plains are volcanic features or impact ejecta deposits. The authors present new indirect evidence which supports a volcanic origin for two different smooth plains units. In Borealis Planitia, stratigraphic relations indicate at least two distinct stages of smooth plains formation. At least one of these stages must have had a volcanic

W. S. Kiefer; B. C. Murray

1987-01-01

301

49 CFR 229.64 - Plain bearings.  

Code of Federal Regulations, 2013 CFR

...Transportation 4 2013-10-01 2013-10-01 false Plain bearings. 229.64 Section 229.64 Transportation...Safety Requirements Suspension System § 229.64 Plain bearings. A plain bearing box shall contain visible free oil and may...

2013-10-01

302

Investigating the effects of abyssal peridotite alteration on Si, Mg and Zn isotopes  

NASA Astrophysics Data System (ADS)

Around 1/3 of Earth's divergent ridge system is now classified as "slow" spreading [1], exposing ultramafic rocks (abyssal peridotites) at the seafloor. Such material is often highly altered by serpentinisation and steatisation (talc formation). It is crucial to understand such processes in order to access the original composition of the mantle, and to quantify any impact on ocean composition. Here we examine the effect of both serpentinisation and steatisation on Si, Mg and Zn isotopes. Hydrothermal alteration and seafloor weathering are both sources of oceanic Si [2] and weathering of abyssal peridotites is a source of oceanic Mg [3]; hence isotopic fractionation as a result of seafloor alteration could affect oceanic Si and Mg isotope composition. Zinc isotopes can provide complimentary information; the magnitude and direction of fractionation is highly dependent on complexing ligand [4] and can provide compositional information on the fluids driving metasomatism. For this study, two cores from the well-characterised abyssal peridotites recovered on ODP Leg 209 were examined [5]. Hole 1274a peridotites exhibit variable serpentinisation at ~200°C, whereas samples from Hole 1268a have been comprehensively serpentinised and then subsequently steatised to talc facies at ~350°C, by a low Mg/Si, low pH fluid. The Si, Mg and Zn isotope compositions of 1274a samples are extremely homogeneous, identical to that of pristine mantle rocks (BSE) i.e., serpentinisation at this locality was predominantly isochemical [5]. In contrast, samples from 1268a show greater isotopic variability. In all samples, Mg is enriched in the heavier isotopes relative to BSE, consistent with formation of isotopically heavy secondary phases [6]. For Si, serpentinised samples are slightly enriched in the lighter isotopes compared to BSE, again consistent with the behaviour of Si during formation of secondary phases [7]. Within the steatised samples, some exhibit enrichments in the lighter Si isotopes (similar to the serpentinites), however, some are isotopically heavy, relative to BSE. Such samples were found to have abundant chlorite, whose formation requires fluid with high Al activity, likely sourced from late-emplaced gabbroic dykes. The Zn of all 1268a samples are enriched in the lighter isotopes, implying the involvement of isotopically light sulfide precipitation during metasomatism [4]. The consistently heavy Mg isotope data suggest that seafloor alteration of peridotites can input an isotopically light Mg-bearing fluid to the ocean. Fluid composition is less easy to determine from the more complex behaviour observed in Si isotopes, although it is unlikely to substantially deviate from BSE, consistent with previous observations [8]. Finally, the strong enrichment in the lighter isotopes of Zn confirms that this isotope system could be used as a tracer of recycled serpentinised material at arc settings, as suggested in [4]. [1] Dick et al. (2003) Nature 426, 405-412; [2] Treguer and De La Rocha (2013) Ann. Rev. Mar. Sci. 5, 477-501; [3] Snow & Dick (1995) GCA, 59, 4219-4235; [4] Pons et al. (2011) PNAS 108(43) 17639-17643; [5] Bach et al., (2004) G3 5; [6] Tipper et al. (2006) EPSL 247, 267-279; [7] Opfergelt et al. (2012) Chem. Geol. 326, 113-122; [8] De La Rocha et al. (2000) GCA 64, 2467-2477.

Savage, P. S.; Wimpenny, J.; Harvey, J.; Yin, Q.; Moynier, F.

2013-12-01

303

The formation of Mercury's smooth plains  

NASA Technical Reports Server (NTRS)

Indirect evidence is presented for a volcanic origin in the case of two smooth plains on Mercury, the Borealis Planitia and the Hilly and Lineated Terrain. These results, in conjunction with those previously obtained for the circum-Caloris plains and the Tolstoj basin, indicate that smooth plains volcanism was a global process on Mercury. It is further suggested that the smooth and intercrater plains may have resulted from two separate volcanic episodes, with smooth plains volcanism being a consequence of Caloris impact-triggering.

Kiefer, Walter S.; Murray, Bruce C.

1987-01-01

304

Southern Ocean abyssal heat uptake in fine and coarse resolution climate model simulations  

NASA Astrophysics Data System (ADS)

The recently observed warming of Antarctic Bottom Water (AABW) represents an important component of accumulated sea level rise and global ocean heat uptake. Yet in simulations of greenhouse warming with coarse resolution climate models (which parameterize ocean eddies), Southern Ocean heat uptake dominantly occurs within near-surface waters, which are subsequently transported northward and subducted at mid-latitudes. Here, we examine the response of the abyssal Southern Ocean to greenhouse forcing within a global climate model run with a fine resolution (eddy-resolving) ocean component, which more faithfully simulates AABW formation than its coarse resolution counterparts. We argue that AABW warming may play a more important role in Southern Ocean heat uptake than is suggested by the CMIP5 ensemble of coarse resolution models. We examine the heat uptake in the Southern Ocean using the Community Climate System Model version 3.5 (CCSM 3.5). The model was run at two resolutions in the ocean and sea ice components: coarse (1 degree), which is a standard resolution of many CMIP5 models, and fine (.1 degree), in which sea ice and AABW is formed more realistically. The atmosphere and land components were fixed throughout at .5 degrees resolution. Each version was forced identically with a 1% ramping of CO2 for 150 years. The fine resolution simulation produces more dense water in the control climate, which sinks to a more realistic depth. We attribute this to the improved simulation of sea ice formation regions granted by increasing the ocean model resolution. The reduction of AABW formation as the climate warms leads to a larger response at depth at fine resolution; below 2000 meters, the fine resolution simulation takes up two orders of magnitude more heat than at coarse resolution. We further propose a framework to weigh the amount of heat taken up at depth in the Southern Ocean by the timescale at which it is sequestered, giving more value to heating of regions with long ventilation timescales. Using this framework, the degree of deep ocean heating emerges as a key difference between fine and course resolution, and an important component of the total heat sequestered in the Southern Ocean. Our work suggests that realistic abyssal ocean heat uptake may be an important component missing from many standard resolution models, and may play an important role in the observed decrease in sea surface temperatures around Antarctica in recent decades.

Newsom, E. R.; Singh, H.; Bitz, C. M.

2013-12-01

305

Can Geothermal Abyssal Heating be a Trigger of Abrupt Climate Change?  

NASA Astrophysics Data System (ADS)

There are observational data and numerical models suggesting that geothermal heating of ocean bottom waters may play an important role in the large-scale oceanic circulation. However, the role of abyssal geothermal heating in abrupt climate change has not been evaluated. Energy is continuously escaping the interior of Earth at a rate of 47 TW (1012 W), mostly through the ocean floors. Geothermal heat flow density varies from about 40 mWm-2 over the oldest oceanic crust to greater than 200 mWm-2 over the young mid-ocean ridges, with a mean of around 100 mWm-2. In general, this geothermal energy flux is capable of warming a 1000 m thick water layer by 0.0008 °C a year, or around 1.5 °C in two thousand years. Deep ocean waters are layered and rich in minerals and greenhouse gases. When the temperature of a static abyssal water parcel increases, it becomes more buoyant. There must be a buoyancy threshold when deep water starts upwelling due to geothermal heating. Small scale upwelling may not have a significant climate impact. But a basin-wide eruption of upwelling could perhaps interrupt global thermohaline and meridional overturning circulation. Most existing hypotheses on abrupt climate change rely on climate-dependent processes such as albedo feedback, fresh water influx, and wind-driven circulation. However, paleoclimate records indicate that abrupt changes in climate occurred during both glacial and interglacial periods. Geothermal-driven deep ocean water upwelling is a climate-independent hypothesis given that geothermal heat flow is a persistent energy source from below the ocean floor. This conceptual model is consistent with the recent report that the rise in atmospheric CO2 during the last deglaciation was preceded by deep water warming [Stott, et al., 2007, Nature, 466, 1093-1097] and the evidence that the abrupt ending of the last ice age was associated with the release of very old (14C-depleted) CO2 from the deep ocean to the atmosphere on a cross ocean scale [Rose, et al., 2010, Nature, 466, 1093-1097]. We are searching more paleoclimate records to identify abrupt changes that might carry evidence of a geothermal trigger.

Huang, S.

2010-12-01

306

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

307

The Oceanic Lithosphere as Reactive Filter: Implications for MORB and Abyssal Peridotite Compositions  

NASA Astrophysics Data System (ADS)

Melt-rock reaction in the lithosphere is, as suggested by textural observations and compositional data, a ubiquitous phenomenon capable of generating locally diverse peridotite series, such as those observed at oceanic spreading centers and transform faults, and may represent an important mechanism of creating compositional diversity in MORBs [1]. Whereas our understanding of the principles governing reactive melt transport is supported by basic theories and models, studies that attempt to quantify the physical conditions and mechanisms creating heterogeneities in the oceanic lithosphere are still limited in number [e.g. 2]. Using Adiabat_1ph 3.0 [3] in combination with the pMELTS algorithm [4], we have previously shown that reactive percolation of basaltic melts through depleted harzburgites can generate the dunite-(wehrlite)-harzburgite-lherzolite spectrum observed in the abyssal mantle and ophiolites, and that the amplitude of transformations is a function of thermal boundary layer thickness and amount of available melt [5]. To gain further insight into how melt-rock reactions shape the oceanic lithosphere, here we extend our study to show that the major and trace element variability in the oceanic mantle and rising melts are also significantly influenced by the mechanism of melt transport. If associated with cooling, distributed porous melt percolation (simulated by incremental addition of the same amount of melt) more efficiently converts harzburgites into fertile lherzolites and creates more pronounced compositional gradients in the abyssal mantle than imparted during channelized melt influx (simulated as batch addition of large amounts of melt) under otherwise identical circumstances. To remain within the tholeiitic trend observed in MORB, reacted melts must be released before clinopyroxene precipitation peaks. Further reaction with harzburgite causes liquids to evolve toward boninite-like compositions. As reaction progresses with decreasing temperature, the chance of such liquids to erupt diminishes rapidly, because reactive melt productivity declines rapidly after the point of clinopyroxene precipitation maximum. We speculate that decreasing melt productivity associated with decreasing temperature, which promotes crystallization, are major factors that prevent such boninite-like liquids to become globally important MORB components. [1] Collier & Kelemen (2010) J Pet. 51/1913; [2] Kelemen (1990), J Pet. 31/51; [3] Antoshechkina et al. ED11-AGU Fall 2010; [4] Ghiorso et al. (2002), G-cubed 3/1030; [5] Luffi & Lee (2009), V33A-2025 AGU Fall 2009.

Luffi, P. I.; Lee, C.; Antoshechkina, P. M.

2010-12-01

308

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

309

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

310

Observations of intercrater plains on Mercury  

NASA Technical Reports Server (NTRS)

Analysis of Mariner 10 stereoscopic images of the surface of Mercury suggest that ancient, intercrater plains consist in part of visually indistinct but topographically defined circular depressions inferred to be highly degraded craters and basins. Embayment of some craters within the heavily cratered terrain and transection of basins and craters by intercrater plains suggest that formation of at least some intercrater plains postdates the later portions of the bombardment of Mercury by large objects. On the other hand, superposition of crater ejecta onto portions of intercrater plains in other areas indicates that some large craters formed into a pre-existing, intercrater plains unit. A single episode of obliteration (to form intercrater plains) or bombardment (to produce the large craters) cannot be reconciled with available observations. A more complex history of contemporaneous crater and plains formation is suggested.

Malin, M. C.

1976-01-01

311

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

312

Aquatic Sediments.  

ERIC Educational Resources Information Center

Presents a literature review of aquatic sediments and its effect upon water quality, covering publications of 1976-77. This review includes: (1) sediment water interchange; (2) chemical and physical characterization; and (3) heavy water in sediments. A list of 129 references is also presented. (HM)

Sanville, W. D.; And Others

1978-01-01

313

Moraine Sediments  

NSDL National Science Digital Library

In this assignment students look at the provenance of glacial sediments and the size and shape of clasts to investigate the sources of moraine material and what happens as glaciers transport sediment. Students visit the field site to see sediment in place, collect a sample to sort in the lab, and compile and review a geologic map in ArcGIS.

Tranel, Lisa

314

AQUATIC SEDIMENTS  

EPA Science Inventory

One hundred seventeen literature references in the area of freshwater sediments were abstracted and synthesized to produce a review of sediment-related research for the period November, 1975 through October, 1976. Research areas covered included sediment-water interchange, sampli...

315

Plio-Pleistocene sequence stratigraphic architecture of the eastern Niger Delta: A record of eustasy and aridification of Africa  

Microsoft Academic Search

This study synthesizes the stratigraphic behavior of the whole eastern Niger Delta during the Plio-Pleistocene and discusses controls on deposition by eustasy, subsidence and sediment supply at various scales. The sequence stratigraphic architecture is determined by integrating the whole sedimentary system from the coastal plain down to the abyssal plain. We combined structural geology, sedimentology biostratigraphy, and seismic stratigraphy. Data

P. Jermannaud; D. Rouby; C. Robin; Thierry Nalpas; François Guillocheau; Stéphane Raillard

2010-01-01

316

Deep-sea fluid and sediment dynamics—Influence of hill- to seamount-scale seafloor topography  

NASA Astrophysics Data System (ADS)

Deep-sea sediments play a central role in a wide range of subject areas. A number of important controls on the formation of sedimentary deposits have been studied. However, to date, the impact of submarine landscape geometry as a possible control has received comparatively little attention. This seems to be particularly true for intermediate-scale topographic features such as abyssal hills, knolls and seamounts that can be found in many regions of the global seafloor: recent estimates suggest that in the deep open oceans, away from continental margins, there might be as many as ~ 25 × 106 abyssal hills, knolls and seamounts. Despite this large number very little is known about how they influence environmental complexity and patchiness, biogeochemical fluxes and the formation of sedimentary records.

Turnewitsch, Robert; Falahat, Saeed; Nycander, Jonas; Dale, Andrew; Scott, Robert B.; Furnival, Darran

2013-12-01

317

Diversity and distribution of Porifera in the bathyal and abyssal Weddell Sea and adjacent areas  

NASA Astrophysics Data System (ADS)

During the ANDEEP I-III expeditions, we obtained a rich and highly diverse sponge collection from the deep Weddell Sea. All the three Poriferan classes, Calcarea, Demospongiae and Hexactinellida, were well represented. Among this material, we have identified a total of 76 species from 47 genera and 30 families. Of these, 17 species (22%) are new to science and 37 (49%) new for the Southern Ocean. Particularly remarkable is the considerable depth of the boundary between bathyal and abyssal sponge faunas. Both Demospongiae and Hexactinellida show a strong shift in their taxonomic composition from a typical shelf assemblage to a more cosmopolitan deep-sea fauna at around 2500 m. Within the Demospongiae, the families Polymastiidae and Cladorhizidae (carnivorous sponges) are particularly abundant and very diverse. The Calcarea are recorded for the first time from the Antarctic deep sea. The type of sampling gear used, especially the epibenthic sledge, was an important factor for the successful collection of deep-sea sponges during the ANDEEP campaigns.

Janussen, Dorte; Tendal, Ole Secher

2007-08-01

318

Simulated strengthening of the Atlantic Meridional Overturning Circulation in response to abyssal ocean warming around Antarctica  

NASA Astrophysics Data System (ADS)

Studies of repeat hydrographic observations have revealed a conspicuous multi-decadal warming, and partly, freshening, of the frigid abyssal ocean waters originating from the fringes of the Antarctic continent. The warming and contraction of Antarctic Bottom Water (AABW) represents one of the most prominent signals of change in Earth's climate and accounts for a substantial fraction of the present global energy and sea level budgets. Here we present a set of ocean model experiments demonstrating that the ongoing loss of AABW also has important dynamical consequences for the large-scale meridional overturning circulation in the Atlantic Ocean. In conjunction with a slowdown of the bottom cell, we find that the upper cell of the Atlantic Meridional Overturning Circulation (AMOC) progressively strengthens in response to changes in density gradients in the deep South Atlantic. Changes in the AMOC are tightly connected to increased meridional heat transport and therefore have a strong influence on global and regional climate patterns in the North Atlantic. The simulations suggest that the AABW-induced strengthening of the AMOC is already extending into the North Atlantic, progressing at a rate of about 0.2 Sv per decade, implying that the process may need to be taken into account in projections of future North Atlantic climate.

Patara, L.; Boning, C. W.

2013-12-01

319

Abyssal water mass exchange between the Japan and Yamato Basins in the Japan Sea  

NASA Astrophysics Data System (ADS)

Bottom water exchange between the Japan and Yamato Basins in the abyssal Japan Sea is investigated based on data from two research cruises in June 2010 and June 2011. Distributions of water properties and velocity profiles from CTD/LADCP observations revealed a two-layer water mass exchange in a rotating system. The cold Japan Basin Bottom Water (JBBW) with high dissolved oxygen (DO) concentrations flowed into the Yamato Basin along the northern boundary of the channel connecting the basins, while the warmer, lower-DO Yamato Basin Bottom Water (YBBW) extended over the JBBW along the southern periphery of the channel. A benthic front between the JBBW and YBBW was observed in both cruises, though the front shifted to the northeast in 2011 compared with its 2010 location. Further, the bottom flows in the channel were not unidirectional in 2011, though consistent southwestward flows were observed in 2010. The JBBW transport into the Yamato Basin was also larger in 2010 than in 2011. Analysis of historical hydrographic data showed that the benthic front exists mostly in the narrowest region of the channel, though it fluctuates temporarily to the northeast or southwest. The fluctuation of the benthic front appears to be associated with the JBBW transport because the observations in June 2010 and June 2011 were carried out during periods of southwestward extension of cold water and northeast protrusion of warm water, respectively. A relationship between benthic front displacements and mesoscale warm eddy migrations is suggested.

Senjyu, Tomoharu; Aramaki, Takafumi; Tanaka, Shinichi S.; Zhang, Jin; Isoda, Yutaka; Kumamoto, Yuichiro; Hibino, Sho; Nakano, Toshiya

2013-10-01

320

Evaluation of abyssal meiobenthos in the eastern central Pacific (Clarion-Clipperton fracture zone)  

NASA Astrophysics Data System (ADS)

Meiobenthos were sampled from 17 stations in the abyssal deep-sea system of the central Pacific centered around 14°N, 130°W at depths 4960-5154m, during the Nixo 47 R/V Jean Charcot cruise. Meiofaunal density range from 45-89 ind. 10cm 2. Predominant taxa are nematodes (84-100%) and copepods (0-10%). Rotifera, Polychaeta, and Acarina also occur. Nematodes are uniformly distributed spatially with 45 species or so; Monhysteridae is the dominant taxon, and Syringolaimus sp. (Ironidae) co-occurs faithfully. Low biomass (0.4-70.6?g 10cm 2) are attributed to supposed dwarfism of metazoan meiofauna and very high proportion (60-80%) of juveniles and pre-adult forms. The majority of protozoans and metazoans are detritus- or deposit-feeders; in addition symbiotic associations, coprophagy and gardening activities are frequent. In such an oligotrophic environment, low food supply may limit meiofaunal abundance, biomass and maturation, and to a lesser extent species richness.

Renaud-Mornant, Jeanne; Gourbault, Nicole

321

Evidence for enhanced mixing over rough topography in the abyssal ocean  

PubMed

The overturning circulation of the ocean plays an important role in modulating the Earth's climate. But whereas the mechanisms for the vertical transport of water into the deep ocean--deep water formation at high latitudes--and horizontal transport in ocean currents have been largely identified, it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished. Turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise. However, measurements of the internal wave field, the main source of energy for mixing, and of turbulent dissipation rates, have typically implied diffusivities across surfaces of equal density of only approximately 0.1 cm2 s(-1), too small to account for the return flow. Here we report measurements of tracer dispersion and turbulent energy dissipation in the Brazil basin that reveal diffusivities of 2-4 cm2 s(-1) at a depth of 500 m above abyssal hills on the flank of the Mid-Atlantic Ridge, and approximately 10 cm2 s(-1) nearer the bottom. This amount of mixing, probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry, may be large enough to close the buoyancy budget for the Brazil basin and suggests a mechanism for closing the global overturning circulation. PMID:10646599

Ledwell; Montgomery; Polzin; St. Laurent LC; Schmitt; Toole

2000-01-13

322

The use of caesium-137 measurements to establish a sediment budget for the Start catchment, Devon, UK  

Microsoft Academic Search

Caesium-137 (Cs) measurements have been used to investigate the delivery of sediment from the hillslopes to a lake which marks the downstream limit of the small agricultural Start basin in Devon, UK. Total Cs inventories and Cs depth distributions in sediment cores were used to estimate that the eroded sediment stored within the fields and on the flood plain of

PHILIP N. OWENS; DESMOND E. WALLING; QINGPING HE; JO SHANAHAN; IAN D. L. FOSTER

1997-01-01

323

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

324

History of plains resurfacing in the Scandia region of Mars  

NASA Astrophysics Data System (ADS)

We present a preliminary photogeologic map of the Scandia region of Mars with the objective of reconstructing its resurfacing history. The Scandia region includes the lower section of the regional lowland slope of Vastitas Borealis extending about 500-1800 km away from Alba Mons into the Scandia sub-basin below -4800 m elevation. Twenty mapped geologic units express the diverse stratigraphy of the region. We particularly focus on the materials making up the Vastitas Borealis plains and its Scandia sub-region, where erosional processes have obscured stratigraphic relations and made the reconstruction of the resurfacing history particularly challenging. Geologic mapping implicates the deposition, erosion, and deformation/degradation of geologic units predominantly during Late Hesperian and Early Amazonian time (˜3.6-3.3 Ga). During this time, Alba Mons was active, outflow channels were debouching sediments into the northern plains, and basal ice layers of the north polar plateau were accumulating. We identify zones of regional tectonic contraction and extension as well as gradation and mantling. Depressions and scarps within these zones indicate collapse and gradation of Scandia outcrops and surfaces at scales of meters to hundreds of meters. We find that Scandia Tholi display concentric ridges, rugged peaks, irregular depressions, and moats that suggest uplift and tilting of layered plains material by diapirs and extrusion, erosion, and deflation of viscous, sedimentary slurries as previously suggested. These appear to be long-lived features that both pre-date and post-date impact craters. Mesa-forming features may have similar origins and occur along the southern margin of the Scandia region, including near the Phoenix Mars Lander site. Distinctive lobate materials associated with local impact craters suggest impact-induced mobilization of surface materials. We suggest that the formation of the Scandia region features potentially resulted from crustal heating related to Alba Mons volcanism, which acted upon a sequence of lavas, outflow channel sediments, and polar ice deposits centered within the Scandia region. These volatile-enriched sediments may have been in a state of partial volatile melt, resulting in the mobilization of deeply buried ancient materials and their ascent and emergence as sediment and mud breccia diapirs to form tholi features. Similar subsurface instabilities proximal to Alba Mons may have led to surface disruption, as suggested by local and regional scarps, mesas, moats, and knob fields.

Tanaka, Kenneth L.; Fortezzo, Corey M.; Hayward, Rosalyn K.; Rodriguez, J. Alexis P.; Skinner, James A.

2011-09-01

325

Origin and Classification of Coastal Plain Kaolins, Southeastern USA, and the Role of Groundwater and Microbial Action  

Microsoft Academic Search

Along the inner Coastal Plain, kaolinite-metahalloysite-rich, neritic muds of Cretaceous-Eo- cene age have undergone intense postdepositional alteration in the recharge area of the regional ground- water system. Weathering processes have had the following profound effects on the original sediments: 1) strong compositional and textural modification of both clay and non-clay minerals; 2) whitening of the originally darker sediments by partial

Vernon J. Hurst; SAM M. PICKERING

1997-01-01

326

Influence of the Atchafalaya River on recent evolution of the chenier-plain inner continental shelf, northern Gulf of Mexico  

USGS Publications Warehouse

This study examines the influence of the Atchafalaya River, a major distributary of the Mississippi River, on stratigraphic evolution of the inner continental shelf in the northern Gulf of Mexico. Sedimentary, geochemical, and shallow acoustic data are used to identify the western limit of the distal Atchafalaya subaqueous delta, and to estimate the proportion of the Atchafalaya River's sediment load that accumulates on the inner shelf seaward of Louisiana's chenier-plain coast. The results demonstrate a link between sedimentary facies distribution on the inner shelf and patterns of shoreline accretion and retreat on the chenier plain. Mudflat progradation on the eastern chenier-plain coast corresponds to the location of deltaic mud accumulation on the inner shelf. On the central chenier-plain shelf, west of the subaqueous delta, relict sediment is exposed that was originally deposited between ???1200 and 600 years BP during activity of the Lafourche lobe of the Mississippi Delta complex. Mass-balance calculations indicate that the eastern chenier-plain inner shelf and coastal zone form a sink for 7??2% of the sediment load carried by the Atchafalaya River. ?? 2004 Elsevier Ltd. All rights reserved.

Draut, A. E.; Kineke, G. C.; Velasco, D. W.; Allison, M. A.; Prime, R. J.

2005-01-01

327

Martian Plain in Late Summer  

NASA Technical Reports Server (NTRS)

The Surface Stereo Imager on NASA's Mars Phoenix Lander acquired this view of the textured plain near the lander at about 11 a.m. local Mars solar time during the mission's 124th Martian day, or sol (Sept. 29, 2008).

The image was taken through an infrared filter. The brighter patches are dustier than darker areas of the surface.

The last signal from the lander came on Nov. 2, 2008.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

2008-01-01

328

Lunar Smooth Plains Identification and Classification  

NASA Astrophysics Data System (ADS)

Smooth plains are widespread on the Moon and have diverse origins. The maria comprise the majority of the smooth plains and are volcanic in origin. Highland smooth plains are patchy, and tend to fill large craters and basins; their origins have eluded unambiguous classification. Prior to the Apollo 16 mission, many workers thought that highland plains were volcanic, possibly more silicic than the maria. However, as the Apollo 16 samples are mostly impact breccias, the highland smooth plains were re-interpreted basin impact ejecta, most likely from the Imbrium and possibly Orientale basins. Conversely, some known non-mare volcanic units, such as the Apennine Bench Formation, contain light plains. These interpretations do not rule out alternate origins for a subset of highland smooth plains, including impact melt or volcanic origins (effusive or pyroclastic). We developed an algorithm to identify smooth plains using topographic parameters from the WAC Global Lunar Digital Terrain Model (DTM) (GLD100), sampled at 333 m/pixel. We classify the smooth plains using the Clementine UVVIS FeO map and photometrically corrected Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) images. Terrain with slopes less than 2° (1 km baseline) and standard deviation of slope less than 0.75° (1 km x 1 km box, n=9) are defined as smooth plains. Highland smooth plains are distinguished from basaltic smooth plains using the following criteria: LROC WAC 643 nm normalized reflectance > 0.056, LROC WAC 321 nm / 415 nm ratio < 0.74, and Clementine FeO < 12 wt.% (excluding Clementine non-coverage areas). The remaining smooth plains are classified as maria and are subdivided into two classes: LROC WAC 321 nm / 415 nm ratio > 0.77 is termed blue maria and a ratio ? 0.77 is termed red maria. The automatic classification was limited to the 87% of the Moon covered by photometrically normalized WAC data (60°S to 60°N). The differences between the maria and highland smooth plains deposits were more ambiguous in regions where the Clementine data had gores and albedo of the maria was elevated (i.e. Mare Frigoris and eastern Imbrium basin). For example, Schickard crater hosts a mare deposit that was covered by Orientale basin ejecta. However the cryptomare in Schickard crater were successfully classified and cratering after basin ejecta emplacement can be seen to have excavated the mare material. Known impact melt deposits, such as the melt pool adjacent to King crater, are resolved as highlands smooth plains. Classified Smooth Plains Distribution;

Boyd, A. K.; Robinson, M. S.; Mahanti, P.; Lawrence, S. J.; Spudis, P.; Jolliff, B. L.

2012-12-01

329

Aquatic sediments  

SciTech Connect

This literature review includes conference proceedings on the interactions of PCBs. Papers range from the adsorption/desorption behavior of PCBs to the influence of suspended and benthic sediments on fate and transport modeling of PCBs in the Great Lakes. Other papers are included in the review which involve analytical and sampling methods, paleolimnology, and modeling and sediment transport. Two papers presented the results of using radionuclides (Pb-210, Ru-106, Cs-137) in the study of lake-sediment dynamics. 111 references.

DePinto, J.V.; Young, T.C.; Booty, W.G.

1984-06-01

330

A conceptual model to facilitate amphibian conservation in the northern Great Plains  

USGS Publications Warehouse

As pressures on agricultural landscapes to meet worldwide resource needs increase, amphibian populations face numerous threats including habitat destruction, chemical contaminants, disease outbreaks, wetland sedimentation, and synergistic effects of these perturbations. To facilitate conservation planning, we developed a conceptual model depicting elements critical for amphibian conservation in the northern Great Plains. First, we linked upland, wetland, and landscape features to specific ecological attributes. Ecological attributes included adult survival; reproduction and survival to metamorphosis; and successful dispersal and recolonization. Second, we linked ecosystem drivers, ecosystem stressors, and ecological effects of the region to each ecological attribute. Lastly, we summarized information on these ecological attributes and the drivers, stressors, and effects that work in concert to influence the maintenance of viable and genetically diverse amphibian populations in the northern Great Plains. While our focus was on the northern Great Plains, our conceptual model can be tailored to other geographic regions and taxa.

Mushnet, David M.; Euliss, Ned H., Jr.; Stockwell, Craig A.

2012-01-01

331

Noble gas behavior during deformation and serpentinization of abyssal peridotites: St. Peter-St. Paul massif  

NASA Astrophysics Data System (ADS)

We present new noble gas (He, Ne, Ar), Sr and Pb isotopic analyses of St. Peter-St. Paul (SPSP) abyssal peridotites sampled in 1998-1999 using the Nautile submersible (IFREMER). The goals of the study were to geochemically characterize both granular and mylonitized peridotites, and to evaluate the effects of mylonitization and serpentinization on rare gas concentrations and isotopic compositions. Samples included whole rocks for mylonitic peridotites, and mineral separates (serpentine and olivine+pyroxene) from massive peridotites. The abyssal peridotites exhibit strong enrichment in light rare earths and other incompatible elements, and positive Ce anomalies are found in several non-mylonitic samples. Mylonitic samples are characterized by lower loss on ignition, and higher SiO2 and MgO, and unradiogenic 87Sr/86Sr isotopic composition (~0.7034) and extremely radiogenic 206Pb/204Pb (up to 20), which is more radiogenic than previous measurements from SPSP. Rare gas analyses were made by paired in vacuo crushing and melting of whole rocks and mineral separates. Most SPSP peridotites contain high concentrations of He, Ne, and Ar that are air-like demonstrating atmospheric contamination. The group of samples plots along a He-Ne mixing line between air and typical mantle values, where the mylonitic samples are characterized by higher fractions of mantle Ne (20Ne/22Ne>10) and 3He/4He (R/Ra~7). The binary mixing behavior is also supported by Ar-Ne isotopes. For the mylonites, melting released high concentrations of He (1.4x10-5ccSTP/g) and the most radiogenic argon (40Ar/36Ar = 2810), demonstrating that noble gases are stored in the crystal structure of the minerals. In contrast, the undeformed peridotites had much lower total helium concentrations for both serpentine (2x10-8ccSTP/g) and olivine+pyroxene (6.9x10-8ccSTP/g) separates. The serpentine mineral separate showed low 3He/4He (R/Ra~1) that was similar in both crushed and melting methods and low air-like 40Ar/36Ar (~355), although they released the highest argon concentration (3.2x10-5cc/g). The low He concentrations suggest that serpentine is not a determining mineral phase in He fractionation. The olivine+pyroxene mineral separates yield lower 3He/4He through the melting method and similar to whole rock values and lower 40Ar/36Ar (~383). Because melt inclusions are not found in the mylonites, the large fraction of 4He released during melting suggests that a significant mantle component may be retained in the recrystallized neoblasts during the deformation processes. It is hypothesized that recrystallization and grain growth in the mylonitization process may have favored gas retention (i.e. supporting a relationship between deformation and gas contents), or is related to metasomatism in a gas-rich (CO2 and rare gas) environment.

Angel Amaya, J.; Kurz, M. D.; Sichel, S. E.; Blusztajn, J.

2010-12-01

332

Population genetic structure of the abyssal grenadier (Coryphaenoides armatus) around the mid-Atlantic ridge  

NASA Astrophysics Data System (ADS)

Understanding the factors that affect the levels and distribution of genetic diversity in oceanic and deep sea environments is a central focus in marine population genetics. Whilst it has been considered that the oceans represent a homogenous environment that would facilitate dispersal and minimise population structure, it is now clear that topographical features and current patterns can influence the extent of spatial gene flow and promote significant population genetic divergence even at local scales. Here we examine patterns of population genetic structure among N. Atlantic populations of the cosmopolitan abyssal grenadier Coryphaenoides armatus in relation to two hypothesised barriers to gene flow—the mid-Atlantic Ridge and the Charlie-Gibbs Fracture Zone/Sub-Polar Front. A suite of microsatellite markers were developed to examine the spatial pattern of allelic variation among 210 individuals from ten sampling locations encompassing sites east and west of the MAR and north and south of the CGFZ, plus a geographically distinct sample of individuals from the Crozet Islands in the Indian Ocean. Considerable genetic diversity was detected among individuals (na=5-13 and HO=0.46-0.69 across populations) but with an overall lack of genetic divergence between populations. Pairwise estimates of divergence among NE Atlantic samples were small and non-significant (max FST=0.04) and Structure-based Bayesian analysis of genetic clusters returned no distinct population structure. The only indication of genetic structure was between the Atlantic and Indian Oceans, with FST estimates of ca. 0.05. Patterns of genetic diversity and divergence are discussed in relation to what has been resolved in Coryphaenoides congeners, and what is known about the life history and ecology of C. armatus.

Ritchie, H.; Cousins, N. J.; Cregeen, S. J.; Piertney, S. B.

2013-12-01

333

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

2009-08-01

334

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

335

Coastal Mudflat Accretion under Energetic Conditions, Louisiana Chenier-Plain Coast, USA  

NASA Technical Reports Server (NTRS)

Mudflat accretion on the chenier-plain coast of Louisiana, northern Gulf of Mexico, is anomalous in an area that otherwise experiences widespread land loss due to rapid relative sea level rise. Accretion is shown to be related to energetic events (Winta cold fronts and occasional tropical-dcprrssion srmms) using a 17-year record of meteorological conditions and aerial surveys The results indicate substantial differences between the behavior of sand- and mud-dominated coastal systems under energetic conditions. Comparison of the Louisiana chenier plain to other mud-rich coasts indicates that certain conditions are necessary for mudflat accretion to occur during energetic atmospheric activity. These include an abundant supply of fine-grained fluvial sediment and resuspension events that maintain an unconsolidated sea floor, dominant onshore wind direction during energetic conditions, particularly when onshore winds coincide with high fluvial sediment input to the coastal ocean, and a low tidal range.

Draut, Amy E.; Kineke, Gail C.; Huh, Oscar K.; Grymes, John M., III; Westphal, Karen A.; Moeller, Christopher C.

2005-01-01

336

Aquatic sediments  

SciTech Connect

The authors present a literature review concerning sediment properties, interactions, and conditions. Topics of discussion include the following: biological activity and toxicity; nutrients; metals; organic compounds; dredging; radionuclides; oxygen demand and organic carbon; mathematical modeling; sediment transport and suspension; and paleolimnology.

Bonner, J.S.; Autenrieth, R.L.; Schreiber, L. (Texas A and M Univ., College Station (United States))

1990-06-01

337

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

338

Progressive deformation of an evaporite-bearing accretionary complex: SeaMARC I, SeaBeam and piston-core observations from the Mediterranean Ridge  

Microsoft Academic Search

The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge.

Kim A. Kastens; Nancy A. Breen; Maria B. Cita

1992-01-01

339

Natural oil and gas seeps on the Black Sea floor  

Microsoft Academic Search

Migration of hydrocarbons to the seafloor in the Black Sea occurs via direct seepages, mud volcanoes, and development of fluidized sediment flows (e.g., diapers). Gas migration occurs on the shelf, continental slope, and abyssal plain. Gas hydrates are spatially related to gas accumulations and are present in shallow subsurface sediment layers. Their distribution is controlled by the activity of mud

R. P. Kruglyakova; Y. A. Byakov; M. V. Kruglyakova; L. A. Chalenko; N. T. Shevtsova

2004-01-01

340

Vertical and temporal variations of particle fluxes in the deep tropical atlantic  

Microsoft Academic Search

Results from the study of particle samples collected during two years of sediment trapping experiments at three depths (2000, 200, 10m above the bottom) in the oligotrophic Cape Verde abyssal plain (4600m depth) are reported in this paper. Hydrodynamical and sediment data are assessed in order to ascertain their influence on the carbon budget in the deep-sea. The currents affected

Alexis Khripounoff; Annick Vangriesheim; Philippe Crassous

1998-01-01

341

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

342

Second chance for the plains bison  

Microsoft Academic Search

Before European settlement the plains bison (Bison bison bison) numbered in the tens of mil- lions across most of the temperate region of North America. Within the span of a few dec- ades 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

Curtis H. Freesea; Keith E. Auneb; Delaney P. Boydc; James N. Derrd; Steve C. Forresta; C. Cormack Gatese; Peter J. P. Goganf; Shaun M. Grasselg; Natalie D. Halbertd; Kyran Kunkelh; Kent H. Redfordi

343

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

344

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

345

Clear It Up: Plain Language in Government Health Information  

MedlinePLUS

... Clear It Up: Plain Language in Government Health Information What is plain language? It is communication that ... you've done to clear it up! More Information Federal Plain Language Health Literacy Contact CDC's Office ...

346

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

347

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

348

49 CFR 230.102 - Tender plain bearing journal boxes.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Tender plain bearing journal boxes. 230.102 Section 230...and Tenders Running Gear § 230.102 Tender plain bearing journal boxes. Plain bearing journal boxes with the following...

2013-10-01

349

MOVEMENT OF TRACTIVE SEDIMENT FROM DISTURBED LANDS.  

USGS Publications Warehouse

The Smoky Creek basin of the coal area of northeastern Tennessee shows extensive evidence of tractive movement of coarse sediment from mined tributary basins into the main channel. Coal-rich gravel bars and flood-plain debris are common below tributaries. Using a combination of techniques including channel-geometry and bar measurements, sediment sampling for rock-debris and coal size distributions, and botanical dating of flood events and geomorphic features, an average annual yield of 65 metric tons per square kilometer (187 tons per square mile) for tractively moved sediment has been calculated for the period 1977 to 1982. This value, 8 percent of the total sediment load, is probably an underestimate owing to the method of calculation. Slightly more than half of the traction load is coal, which moves through the basin within a few years. Rock debris, however, appears to require years to decades to move similar distances.

Osterkamp, W. R.; Carey, W. P.; Hupp, C. R.; Bryan, B. A.

1984-01-01

350

Geomorphic evidence for an eolian contribution to the formation of the Martian northern plains  

NASA Technical Reports Server (NTRS)

The northern plains of Mars have many morphologic characteristics that are uncommon or absent on the rest of the planet. Mariner 9 and Viking images obtained north of latitude 30 deg N revealed 'smooth' and 'mottled' plains of an uncertain origin. Some or all of the northern plains were interpreted to consist of lava plains intermixed with eolian and volcanic materials thick eolian mantles that buried portions of the mid latitudes periglacial deposits resulting from the presence of ground ice and as water-transported sediments derived from fluvial runoff, lacustrine deposition in standing bodies of water, or glacial runoff. The highest-resolution Viking images show many intriguing details that may provide clues to the origin of this complex and distinctive terrain. Some of the informative features present in the best Viking images, comparing the observations to what may be expected from various hypotheses of formation, are reviewed. While the results are not conclusive for any single hypothesis, eolian processes have played a major role in the erosion (and possibly deposition) of the materials that make up the surface exposures in the Martian northern plains.

Zimbelman, J. R.

1993-01-01

351

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

352

Shift in detrital sedimentation in the eastern Bay of Bengal during the late Quaternary  

NASA Astrophysics Data System (ADS)

Down-core variations of granulometric, geochemical and mineral magnetism of a 70-cm long sediment core retrieved from the eastern Bay of Bengal abyssal region were studied to understand sedimentation pattern and sediment provenance during the last ˜12 kyr BP. Based on down-core physical and elemental variations, three units were identified: unit 3 (70-43 cm) is a ˜30 cm thick clayey silt organic carbon-rich (0.5-0.92%) turbidite probably delivered by the Brahmaputra River during the late Quaternary period. Units 2 (43-24 cm) and 1 (24-0 cm) represent enhanced and reduced supply of coarse-grained detrital sediments from the Ganges River during early and late Holocene period, respectively. Increased terrigenous supply dilutes calcium carbonate (CaCO3) and biogenic elements (P, Ba and Cu) in units 3 and 2. On the contrary, a reduction in detrital input enhances CaCO3 and biogenic elements in unit 1. Lithogenic elements (Ti, Al, K and Rb) and shale-normalized REE patterns in all three units suggest terrigenous source. The shift in provenance from the Brahmaputra to the Ganges derived sediments is evident by a sharp increase in sediment grain size, increased concentration and grain size assemblages of magnetic minerals, lithogenic elements concentration and Lan/Ybn ratio. This study highlights terrigenous dilution on biogenic sedimentation in the eastern Bay of Bengal sediments.

Prakash Babu, C.; Pattan, J. N.; Dutta, K.; Basavaiah, N.; Ravi Prasad, G. V.; Ray, D. K.; Govil, P.

2010-06-01

353

Lead isotope signatures of Holocene fluvial sediments from the Loire River valley  

Microsoft Academic Search

The distribution of Mn, V, Th, Pb and isotopes of Pb in the labile fraction of sediments from a channel infill in the Middle Loire alluvial plain are used to highlight some aspects of the basin evolution over the period from 0 to 10 ka BP. The acid extractable matter (AEM) in the sediment samples is variable in amount and

Philippe Négrel; Wolfram Kloppmann; Manuel Garcin; Denis Giot

2004-01-01

354

Strontium isotopic record of signatures of Holocene fluvial sediments in the Loire valley, France  

Microsoft Academic Search

The distribution of Sr contents and isotopes of strontium Sr in the labile fraction of sediments from a channel fillings infill in the Middle Loire alluvial plain is used to highlight aspects of the evolution of the basin over the period from 10 000 yr. BP to the present. The acid extractable matter (AEM) in the sediment samples is variable

Philippe Négrel; Wolfram Kloppman; Manuel Garcin; Denis Giot

2002-01-01

355

75 FR 69157 - Notice of Intent To Rule on Request To Release Airport Property at the Plains Airport, Plains, MT.  

Federal Register 2010, 2011, 2012, 2013

...Rule on Request To Release Airport Property at the Plains Airport, Plains, MT. AGENCY: Federal Aviation Administration...and invite public comment on the release of land at Plains Airport under the provisions of 49 U.S.C....

2010-11-10

356

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

357

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

358

Distribution of particulate organic carbon and radiocarbon in the water column from the upper slope to the abyssal NE Pacific Ocean  

Microsoft Academic Search

We report profiles of concentrations and radiocarbon contents of suspended particulate organic carbon (POCsusp) and sedimentary organic carbon from an abyssal site (Stn M) in the northeast (NE) Pacific collected in September 1994 (a period of very high flux of particulate carbon in the deep sea) and June 1995, as well as from stations on the continental rise and slope

E. R. M Druffel; S. Griffin; J. E Bauer; D. M Wolgast; X.-C Wang

1998-01-01

359

A revision of the bathyal and abyssal necrophage genus Cyclocaris Stebbing, 1888 (Crustacea: Amphipoda: Cyclocaridae) with the addition of two new species from the Atlantic Ocean.  

PubMed

Two new species of the deep-sea scavenging genus Cyclocaris (Crustacea: Amphipoda) are described from bathyal and abyssal depths in the North and tropical Atlantic Ocean, bringing the total number of species in the genus to four. An account of all four species is given and an updated key to the genus Cyclocaris is provided. PMID:24870690

Horton, Tammy; Thurston, Michael H

2014-01-01

360

Geobotanical assessment in the Great Plains, Rocky Mountains and Himalaya  

NASA Astrophysics Data System (ADS)

Vegetation patterns and dendrochronology were used to study landforms and processes in three unique geographic areas. Specifically, we report on geobotanical associations related to forest fires, slope failures, rivers, and glaciers. The work was conducted in the Niobrara valley of the Great Plains of Nebraska, Tensleep Canyon of the Bighorn Mountains, Yellowstone Teton fire areas of the Snake River drainage in Wyoming, and the Nanga Parbat and Batura areas of the western Himalaya. Results indicate that geobotanical associations can be used to provide additional information to study landforms, natural hazards, and sediment yields. In addition, geobotany can be used to detect processes responsible for environmental change. Remote sensing technology can play an important role in detecting vegetation distributions and green biomass variations.

Shroder, John F.; Bishop, Michael P.

1995-09-01

361

Different ages of lunar light plains  

NASA Technical Reports Server (NTRS)

The crater populations of 18 lunar light plains (Cayley plains) show a variation in relative ages by a factor of about 4 in crater frequency in regions in the surroundings of the Orientale and Imbrium basin, and by a factor of greater than 25 for more distant sites. Thus the idea of a moon-wide synchronism in the emplacement of the lunar light plains with the formation of the basins Imbrium or Orientale cannot be supported. Some light plains are younger than the youngest basin Orientale. Since these plains cannot have been emplaced by any other basin-forming event and local impact-derived origin can certainly be excluded, an endogenic (magmatic) origin is proposed for these plains. Age determination data (D sub L values) by Soderblom and Lebofsky (1972) and Soderblom and Boyce (1972) are shown to be correlated with own cumulative crater frequency data (N) for surfaces younger than about 3.8 b.y. It is found that D sub L is proportional to the 0.6 power of N. For ages greater than 3.8 b.y., the D sub L data by those authors, especially their light plains data, are incompatible with the present crater frequency data.

Neukum, G.

1977-01-01

362

Flood Plain Lakes Along the Elbe River - a Forgotten Risk  

NASA Astrophysics Data System (ADS)

Flood Plain Lakes Along the Elbe River - a Forgotten Risk Introduction: Along the German part of the Elbe River, more than 1000 "side structures" form potential sinks of contaminated sediment. They are mostly remains of previous river courses which have been cut off by natural causes or anthropogenic alterations of the river (oxbow lakes), or are floodplain lakes that were formed during high water conditions. These water bodies sometimes have a small opening towards the Elbe, or are hydrodynamically connected only in situations of high discharges. High discharges in the Elbe River, however, are mainly responsible for transporting historic contaminants along with suspended matter from former historic sources in the middle Elbe downstream. As these may settle when the current dies down at the end of a high discharge period, side structures have been under suspicion to have accumulated contaminated material over the last decades. Until this study was conducted, nothing was known about erodibility and contamination of sediment in these lakes even though they could have a large impact on the Elbe River itself: A preliminary investigation showed that the total surface of side structures in the Elbe floodplain adds up to about 50 km2. In case that deposited sediment is contaminated and only the upper 20 cm are prone to resuspension and transport during flooding, 10 Mio m3 of contaminated sediment could potentially be added to the contaminant load during a high water event. This study was carried out to evaluate the risk from these side structures for the environmental quality of the Elbe River. Methods: 15 side structures were investigated. Sediment cores were taken on 1 to 3 locations per water body in order to obtain the following information: • Depth of sediment layer • Erodibility of surface sediment, measured immediately after sampling - using the "Gust Microcosm", • Eroded mass at over-critical shear stress, measured in the lab by eroding a sediment core for one hour and collecting the suspended sediment matter. • Chemical contamination • Ecotoxicological effects Results and Discussion All side structures that were sampled exceeded the national quality guidelines for sediments which have been set by the International Commission for the Protection of the Elbe. In some cases very high concentrations were reached such as 1300 µg/kg dw for p,p-DDD, up to 61 mg/kg for Hg and 39 mg/kg for Cd. Erodibility varied a lot with critical shear stresses of less than 1 cm/s to more than 2 cm/s. Ecotoxicological data were also very different between side structures and sampling locations, but partly indicating very high inhibitions. Methanol extracts of sediments on all locations were screened using the luminescence bacteria test with Vibrio fischeri. Selected sediemt samples were tested applying the sediment contact test with Arthrobacter globiformes and the algae growth inhibition test with Pseudokirchneriella subcapitata. An integrated evaluation of all information led to a classification of 7 sites out of 15 to be of high risk, 7 to be of medium risk and only one site to be of low risk for the environmental quality of the Elbe River.

Heise, Susanne

2014-05-01

363

What can we learn about the history of oceanic shield volcanoes from deep marine sediments? Example from La Reunion volcanoes.  

NASA Astrophysics Data System (ADS)

The discovery in 2006, during the oceanographic survey FOREVER, of large volcaniclastic sedimentary systems off La Réunion Island (western Indian ocean) revealed a new image of the evolution of oceanic shield volcanoes and their dismantling. Marine data obtained from 2006 to 2011 during the oceanographic surveys ERODER 1 to ERODER 4 included bathymetry, acoustic imagery, echosounding profiles, dredging and coring. Six major turbidite systems were mapped and described on the submarine flanks of La Reunion volcanic edifice and the surrounding oceanic plate. The interpretation of sediment cores enable us to characterise the processes of gravity-driven sediment transfer from land to deep sea and also to revisit the history of the volcanoes of La Réunion Island. Turbidite systems constitute a major component of the transfer of volcanic materials to the abyssal plain (Saint-Ange et al., 2011; 2013; Sisavath et al., 2011; 2012; Babonneau et al., 2013). These systems are superimposed on other dismantling processes (slow deformation such as gravity sliding or spreading, and huge landslides causing debris avalanches). Turbidite systems mainly develop in connection with the hydrographic network of the island, and especially at the mouths of large rivers. They show varying degrees of maturity, with canyons incising the submarine slope of the island and feeding depositional areas, channels and lobes extending over 150 km from the coast. The cores collected in turbidite systems show successions of thin and thick turbidites alternating with hemipelagic sedimentation. Sedimentological and stratigraphic analysis of sediment cores yielded a chronology of submarine gravity events. First-order information was obtained on the explosive activity of these volcanoes by identifying tephra layers in the cores (glass shards and pumice). In addition, major events of the volcanic and tectonic history of the island can be identified and dated. In this contribution, we focus most attention on the southernmost turbidite system (St-Joseph system). Sedimentary records allow us to establish a link between two major landslides affecting the flanks of Piton de la Fournaise volcano and the triggering of major turbidity currents. Thus, the age of these events could be obtained; their chronology being far too difficult to establish otherwise. In short: a beautiful example of the contribution of sedimentology to the study of the structural evolution of the volcanoes. References Babonneau N., Delacourt C., Cancouet R., Sisavath E., Bachelery P., Deschamps A., Mazuel A., Ammann J., Jorry S.J., Villeneuve N., 2013, Marine Geology, 346, 47-57. Saint-Ange F., Bachèlery P., Babonneau N., Michon, L., Jorry S.J., 2013, Marine Geology. 337, 35-52. Saint-Ange, F., Savoye, B., Michon, L., Bachelery, P., Deplus, C., De Voogd, B., Dyment, J., Le Drezen, E., Voisset, M., Le Friant, A., and Boudon, G., 2011. Geology, 39, 271-274, doi: 10.1130/G31478.1. Sisavath, E., Mazuel, A., Jorry, S., Babonneau, N., Bachèlery P., De Voogd, B., Salpin, M., Emmanuel, L., Beaufort, L., Toucanne, S., 2012, Sedimentary Geology, 281, p. 180-193, doi :10.1016/j.sedgeo.2012.09.010. Sisavath, E., Babonneau N., Saint-Ange F., Bachèlery P., Jorry S., Deplus C., De Voogd B., Savoye B., 2011, Marine Geology, v. 288, p. 1-17, doi:10.1016/j.margeo.2011.06.011.

Bachelery, Patrick; Babonneau, Nathalie; Jorry, Stephan; Mazuel, Aude

2014-05-01

364

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

365

On the Abyssal Circulation in the Atlantic Basin at the Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

Our understanding of oceanic variability on time scales longer than the time span of direct oceanographic measurements (about a century at best) relies on our capability to interpret the marine sediment record. Sediment observations have reached the point where some general hypotheses about ocean circulation during the Last Glacial Maximum (LGM, near ca. 20 kyr B.P.) can be tested. Among the most common observations are ?18O and ?13C on benthic foraminifera. A recent compilation of ?13C data has been taken to imply the existence in the glacial Atlantic of a southern source water near 1000 m water depth, a northern source water near 1500 m, and a southern source water below ca. 2000 m (Curry and Oppo, 2005). Here an inverse method is used to provide a rigorous test of the null hypothesis that ?18O and ?13C data for glacial sediments are consistent with the modern circulation. Particular emphasis is put on the minimal uncertainties in the sediment data and in our current understanding of the behavior of the oxygen and carbon isotopes in the ocean, which must be assumed in order to rule out the hypothesis with confidence.

Marchal, O.; Curry, W.

2008-12-01

366

Targeting the Plains of Venus from Orbit  

NASA Astrophysics Data System (ADS)

Lowland plains house a spectacular array of poorly understood volcanic, tectonic, and impact features that are key to settling the continuing global stratigraphy debate and resolving how the only other accessible Earth-sized planet has evolved.

Sharpton, V. L.

2014-05-01

367

Plain Language Thesauruses | accrualnet.cancer.gov  

Cancer.gov

These resources offer plain language equivalents to medical terms, phrases, and references frequently used in clinical trials. They are helpful when developing informed consent forms and other patient information text.

368

Flood information for flood-plain planning  

USGS Publications Warehouse

Floods are natural and normal phenomena. They are catastrophic simply because man occupies the flood plain, the highwater channel of a river. Man occupies flood plains because it is convenient and profitable to do so, but he must purchase his occupancy at a price-either sustain flood damage, or provide flood-control facilities. Although large sums of money have been, and are being, spent for flood control, flood damage continues to mount. However, neither complete flood control nor abandonment of the flood plain is practicable. Flood plains are a valuable resource and will continue to be occupied, but the nature and degree of occupancy should be compatible with the risk involved and with the degree of protection that is practicable to provide. It is primarily to meet the needs for defining the risk that the flood-inundation maps of the U.S. Geological Survey are prepared.

Bue, Conrad D.

1967-01-01

369

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

370

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

371

Does Reactivation of Louisiana's Chenier Plain Lead to the Development of Interior Coastal Wetlands? Assessing the Relative Roles of Storm Impacts and Riverine Deposits  

NASA Astrophysics Data System (ADS)

At the beginning of the 20th century, increased flow into the Atchafalaya River from the Mississippi River reactivated sediment dynamics along the Chenier Plain. The Chenier Plain is a microtidal, storm-dominated coastal environment situated west and downdrift of the Mississippi River Delta. Composed of alternating mudflats, marsh, and elevated “chenier” (oak) ridges, this coastal system provides an ideal case study to both investigate the success of the Atchafalaya River diversion in building wetlands, and to construct a chronology of storm impacts on the Louisiana Gulf coast. To examine whether and how the reactivation of the Chenier Plain has impacted sediment dynamics in coastal wetlands, sediment cores from Miller Lake in the Chenier Plain were analyzed. Historic photos and maps of Miller Lake show open water in an area now dominated by marsh. The recent filling in of Miller Lake suggests new deposition by a possible combination of storm impacts and riverine deposits. In this study, carbonate deposition is used as a proxy for marine-dominated sedimentation, which reflects the shelly marine-dominated coastal environment of the Chenier Plain. Grain size analysis data was collected to distinguish sand layers from possible overwash deposits of storm impacts. Rates of sediment accretion and mineral deposition were determined using the naturally occurring radioisotope 210Pb. The collected sediment cores indicate new marsh developing over muddy sediments. In contrast to SE Louisiana’s high rates of wetland loss, this study points to evidence of wetland accretion in SW Louisiana as a result of the Atchafalaya River diversion.

Ramatchandirane, C. G.; Kolker, A.; Ameen, A. D.; Williams, K.; Donnelly, J. P.; Giosan, L.

2010-12-01

372

Ice-walled-lake plains: Implications for the origin of hummocky glacial topography in middle North America  

USGS Publications Warehouse

Ice-walled-lake plains are prominent in many areas of hummocky-till topography left behind as the Laurentide Ice Sheet melted from middle North America. The formation of the hummocky-till topography has been explained by: (1) erosion by subglacial floods; (2) squeezing of subglacial till up into holes in stagnant glacial ice; or (3) slumping of supraglacial till. The geomorphology and stratigraphy of ice-walled-lake plains provide evidence that neither the lake plains nor the adjacent hummocks are of subglacial origin. These flat lake plains, up to a few kilometers in diameter, are perched as much as a few tens of meters above surrounding depressions. They typically are underlain by laminated, fine-grained suspended-load lake sediment. Many ice-walled-lake plains are surrounded by a low rim ridge of coarser-grained shore sediment or by a steeper rim ridge of debris that slumped off the surrounding ice slopes. The ice-walled lakes persisted for hundreds to thousands of years following glacial stagnation. Shells of aquatic molluscs from several deposits of ice-walled-lake sediment in south-central North Dakota have been dated from about 13 500 to 10 500??B.P. (calibrated radiocarbon ages), indicating a climate only slightly cooler than present. This is confirmed by recent palaeoecological studies in nearby non-glacial sites. To survive so long, the stagnant glacial ice had to be well-insulated by a thick cover of supraglacial sediment, and the associated till hummocks must be composed primarily of collapsed supraglacial till. ?? 2007 Elsevier B.V. All rights reserved.

Clayton, L.; Attig, J. W.; Ham, N. R.; Johnson, M. D.; Jennings, C. E.; Syverson, K. M.

2008-01-01

373

Ages of plains volcanism on Mars  

Microsoft Academic Search

Plain-style volcanism [1] is widespread in the Tharsis and Elysium volcanic provinces on Mars, [2,3]. Detailed images and topographic data reveal the morphology and topography of clusters of low shields and associated lava flows. The landforms of plains volcanism on Mars have all well-known terrestrial analogues in basaltic volcanic regions, such as Hawaii, Iceland, and in particular the Snake River

Ernst Hauber; Felix Jagert; Petr Broz

2010-01-01

374

Planetary stations and Abyssal Benthic Laboratories: An overview of parallel approaches for long-term investigation in extreme environments  

NASA Technical Reports Server (NTRS)

In spite of the apparent great differences between deep ocean and space environment, significant similarities can be recognized when considering the possible solutions and technologies enabling the development of remote automatic stations supporting the execution of scientific activities. In this sense it is believed that mutual benefits shall be derived from the exchange of experiences and results between people and organizations involved in research and engineering activities for hostile environments, such as space, deep sea, and polar areas. A significant example of possible technology transfer and common systematic approach is given, which describes in some detail how the solutions and the enabling technologies identified for an Abyssal Benthic Laboratory can be applied for the case of a lunar or planetary station.

Dipippo, S.; Prendin, W.; Gasparoni, F.

1994-01-01

375

A reconnaissance study of the effect of irrigated agriculture on water quality in the Ogallala Formation, Central High Plains Aquifer  

USGS Publications Warehouse

In 1998, the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program began a regional study of water quality in the High Plains aquifer. The High Plains aquifer underlies an area of about 174,000 square miles in parts of eight States. Because of its large size, the High Plains aquifer has been divided into three regions: the Southern High Plains, Central High Plains, and Northern High Plains (fig. 1A). Although an assessment of water quality in each of the three regions is planned, the initial focus will be the Central High Plains aquifer. Anyone who has flown over the Central High Plains in the summer and has seen the large green circles associated with center pivot sprinklers (fig. 2) knows that irrigated agriculture is a widespread land use. Pesticides and fertilizers applied on those irrigated fields will not degrade ground-water quality if they remain in or above the root zone (fig. 3). However, if those chemicals move downward through the unsaturated zone to the water table, they may degrade the quality of the ground water. Water is the principal agent for transporting chemicals from land surface to the water table, and in the semiarid Central High Plains, irrigation often represents the most abundant source of water during the growing season. One objective of NAWQA's High Plains Regional Ground-Water study is to evaluate the effect of irrigated agriculture on the quality of recently recharged water in the Ogallala Formation of the Central High Plains aquifer (figs. 1A and 1B). The Ogallala Formation is the principal geologic unit in the Central High Plains aquifer, and it consists of poorly sorted clay, silt, sand, and gravel that generally is unconsolidated (Gutentag and others, 1984). Approximately 23 percent of the cropland overlying the Ogallala Formation is irrigated (U.S. Department of Agriculture, 1999). The NAWQA Program generally defines recently recharged ground water to be water recharged in the last 50 years. The water table in the Ogallala Formation is separated from overlying land-use practices by as much as 400 feet of unsaturated sediments. Consequently, one may hypothesize that recently recharged water is not present in the formation. The U.S. Geological Survey conducted a reconnaissance study in 1999 to establish (a) if recently recharged water was present in the Ogallala Formation underlying irrigated cropland and (b) if agricultural land-use practices affect water quality. Results from the reconnaissance study will be used to determine whether a full-scale land-use study is warranted.

McMahon, Peter B.

2000-01-01